Oil-based ink composition for writing instruments and writing instruments using the same

Abstract

To provide an ink composition for a writing instrument, exhibiting thickening action effect, suppressing ink leakage, making writing feel excellent, suppressing blurred writing, and excellent in writing property due to containing a thixotropy-imparting agent enabling stable thickening action without being inhibited in thickening by an ionic material (metallic ion or the like), unlike a conventional a thixotropy-imparting agent, and to provide a writing instrument using the same.SOLUTION: An ink composition for a writing instrument contains a coloring agent, a solvent, and an (acrylic acid / acrylic acid perfluoroalkyl) copolymer. A writing instrument using the same is also provided.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an ink composition for writing instruments and a writing instrument using the same.

Background Art

[0002] Conventionally, aqueous ink compositions and oil-based ink compositions have been used for ink compositions for writing instruments. In particular, for ballpoint pens, there are aqueous ballpoint pens filled with an aqueous ink composition and oil-based ballpoint pen compositions filled with an oil-based ink composition. Among them, a gel ink composition having shear-thinning viscosity imparted to the ink composition is known, and various proposals have been made regarding the shear-thinning viscosity imparting agent.

[0003] As the shear-thinning viscosity imparting agent, in the aqueous ink composition, polysaccharides such as xanthan gum, welan gum, and diutan gum have been proposed. In the oil-based ink composition, fatty acid amide wax, hydrogenated castor oil, etc. have been proposed.

[0004] As such a writing instrument ink composition, for the technology using xanthan gum, welan gum, and diutan gum, there are Japanese Patent Publication No. 64-8673 "Oil-based ink composition for writing instruments", Japanese Unexamined Patent Application Publication No. 4-214782 "Ink composition for aqueous ballpoint pens", Japanese Unexamined Patent Application Publication No. 2005-068363 "Aqueous ink composition and aqueous ballpoint pen using the same", and for the technology using fatty acid amide wax and hydrogenated castor oil, they are disclosed in Japanese Unexamined Patent Application Publication No. 7-196972 and Japanese Unexamined Patent Application Publication No. 7-268268.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] In Patent Documents 1 to 3, shear thinning viscosity can be imparted, and a certain degree of thickening effect can be obtained. However, depending on the type of coloring agent, the type of surfactant, other ink components, and the metal material of the ballpoint pen tip, thickening inhibition is likely to occur due to ionic substances (such as metal ions) present in the ink, and the desired thickening effect may not be obtained. In addition, in Patent Documents 4 and 5, although a certain degree of thickening effect can be obtained with hydrogenated castor oil or fatty acid amide wax, the ink viscosity at rest becomes high, which may affect the writing feel, the ink followability is likely to be poor, and streaks may occur in the handwriting, leaving room for improvement.

[0007] The object of the present invention is to provide a shear thinning viscosity-imparting agent that, unlike conventional shear thinning viscosity-imparting agents, can exhibit a stable thickening action without being inhibited by ionic substances (such as metal ions), thereby achieving a thickening effect, suppressing ink leakage, improving the writing feel, suppressing handwriting streaks, and obtaining a writing instrument ink composition with excellent writing properties and a writing instrument using the same.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention "1. A writing instrument ink composition comprising a coloring agent, a solvent, and an (acrylic acid / perfluoroalkyl acrylate) copolymer. 2. The writing instrument ink composition 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 writing instruments according to claim 1 or 2, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer comprises an acrylate ester represented by the general formula (Chemical Formula 1).

Chemical Formula

Chemical Formula

Advantages of the Invention

[0009] The present invention includes a colorant, a solvent, and a (acrylic acid / perfluoroalkyl acrylate) copolymer. Even when ionic substances (such as metal ions) are present in the ink, it has a stable gel structure, imparts shear thinning viscosity, increases the ink viscosity at rest, suppresses ink leakage from the gap at the tip of the writing instrument (ink leakage from the gap between the ball and the tip of the ballpoint pen in the case of a ballpoint pen), reduces the ink viscosity during writing, improves the writing feel, suppresses writing streaks, and provides an ink composition for writing instruments with excellent writing performance and a writing instrument using the same.

Embodiments for Carrying Out the Invention

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

[0011] By including a colorant, a solvent, and an (acrylic acid / perfluoroalkyl acrylate) copolymer in the ink composition for writing instruments, it has been found that in the ink, a stable gel structure is formed, shear-thinning viscosity is imparted, ink leakage from the gap at the writing tip is suppressed, the writing feel is improved, writing smear is suppressed, and the writing performance is excellent.

[0012] ((acrylic acid / perfluoroalkyl acrylate) copolymer) The (acrylic acid / perfluoroalkyl acrylate) copolymer used in the present invention is at least a copolymer having a structural unit derived from an acrylate ester and a structural unit derived from acrylic acid (methacrylic acid), which are constituent components of an acrylate ester and acrylic acid (methacrylic acid). Different from conventional shear-thinning viscosity imparting agents, the (acrylic acid / perfluoroalkyl acrylate) copolymer contains perfluoroalkyl acrylate (acrylate ester having a fluorine atom) as a constituent component. Therefore, it is presumed that it can form a stable network structure and a gel structure without being inhibited from thickening by ionic substances (metal ions) in the ink, and can increase the ink viscosity. 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 tip of the writing part (ink leakage from the gap between the ball and the tip of the nib in the case of a ballpoint pen) can be suppressed. Furthermore, since it has a weak network structure, the gel structure can be temporarily broken by impacts such as shearing during writing, resulting in a decrease in ink viscosity and enabling good writing feel. In particular, when used in a ballpoint pen, it is presumed that an effect of easily improving the writing feel can be obtained by impacts such as shearing of the ball during writing, and it is effective and thus preferable when used as an ink composition for a ballpoint pen. Also, as the (acrylic acid / perfluoroalkyl acrylate) copolymer, the (acrylic acid / perfluoroalkyl acrylate) cross-polymer is preferred. This is effective and preferable because by using the cross-polymer, it is easier to form a three-dimensional network structure, and by forming a denser three-dimensional network structure, it is easier to form a more stable gel structure. In particular, when used as an ink composition for a ballpoint pen, it is effective and thus preferable. Furthermore, when a pigment is used as the colorant, it can be more preferably used because the gel structure easily maintains pigment dispersibility, which is preferable.

[0013] In addition, for the (acrylic acid / perfluoroalkyl acrylate) copolymer, as a constituent component of perfluoroalkyl acrylate (acrylate having a fluorine atom), it is preferable to contain an acrylate represented by the general formula (Chemical Formula 1). This is because, even if ionic substances (such as metal ions) such as a colorant and a surfactant are present in the ink component, unlike conventional shear-thinning viscosity-imparting agents, since an acrylate having a fluorine atom is used as a constituent component, a stable network structure can be formed without being inhibited from thickening, and by forming a gel structure, the ink viscosity can be increased. By setting the ink viscosity at rest high, the effect of suppressing ink leakage from the gap at the tip of the writing part (ink leakage from the gap between the ball and the tip of the chip) can be achieved. Moreover, since it has a weak network structure, the gel structure can be temporarily broken by an impact such as shearing during writing, so that the ink viscosity becomes low and the writing feel can be kept good.

Chemical Formula

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

[0015] Specific examples of such an acrylate represented by the general formula (Chemical Formula 1) include 2-perfluorohexylethyl (meth)acrylate, 3-perfluorohexylpropyl (meth)acrylate, 4-perfluorohexylbutyl (meth)acrylate, and the like. In the above specific examples, (meth)acrylate means acrylate and / or methacrylate. Furthermore, among the acrylic esters represented by the general formula (Formula 1), those that form a more stable network structure are preferred because they can suppress ink leakage from the gaps at the tip of the writing utensil and easily maintain good writing feel. 2-Perfluorohexylethyl (meth)acrylate is preferred, and more preferably, 2-perfluorohexylethyl acrylate is considered.

[0016] Also, for the (acrylic acid / perfluoroalkyl acrylate) copolymer, as a constituent component of acrylic acid, it is preferably composed of acrylic acid represented by the general formula (Formula 2). This is because it is easier to form a more stable network structure and a weak network structure, which can suppress ink leakage from the gaps at the tip of the writing utensil and easily maintain good writing feel. In particular, when used as an ink composition for a ballpoint pen, it is preferred because it is effective. Furthermore, considering the above effects, R in the general formula (Formula 2) B is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Further considering, R in the general formula (Formula 2) B is preferably a hydrogen atom or an alkyl group having 1 carbon atom. Considering that it is easier to form a more stable network structure, R in the general formula (Formula 2) B is preferably a hydrogen atom. Specific examples of the acrylic ester represented by the general formula (Formula 2) include acrylic acid, methacrylic acid, etc. Considering the above effects, acrylic acid and methacrylic acid are preferred, and more preferably, acrylic acid is preferred.

Chemical formula

[0017] Regarding the (acrylic acid / perfluoroalkyl acrylate) copolymer used in the present invention, since the above-described effects are easily obtained, it is preferably a copolymer containing at least an acrylate ester represented by the general formula (Chemical Formula 1) and acrylic acid represented by the general formula (Chemical Formula 2) as constituent components. To more easily obtain the effects, it is preferably a cross-polymer containing at least an acrylate ester represented by the general formula (Chemical Formula 1) and acrylic acid represented by the general formula (Chemical Formula 2) as constituent components. This is because it is easy to form a three-dimensional network structure and a denser three-dimensional network structure, making it easier to form a more stable gel structure. In particular, when used as an ink composition for a ballpoint pen, it is effective and thus preferable. Also, considering the ink thickening property (ink viscosity expressibility) and stability in the ink, the ratio (weight ratio) of the acrylate ester (Chemical Formula 1) to 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.

[0018] As a constituent component of the (acrylic acid / perfluoroalkyl acrylate) copolymer used in the present invention, in addition to the above-described acrylic acid and perfluoroalkyl acrylate, it is preferably composed of a crosslinking agent as a constituent component. This is because by including a crosslinking agent, it is easy to crosslink acrylic acid and perfluoroalkyl acrylate, making it easy to thicken the ink (express the ink viscosity), and by more easily forming a stable network structure, the effects of the present invention can be easily obtained. In particular, it is preferably a copolymer containing an acrylate ester (Chemical Formula 1), acrylic acid (Chemical Formula 2), and a crosslinking agent as constituent components, and more preferably a cross-polymer containing an acrylate ester (Chemical Formula 1), acrylic acid (Chemical Formula 2), and a crosslinking agent as constituent components. This is because it is easy to form a three-dimensional network structure and a denser three-dimensional network structure, making it easier to form a more stable gel structure. In particular, when used as an ink composition for a ballpoint pen, it is effective and thus preferable.

[0019] Examples of the crosslinking agent include 1,10-decanediol diacrylate, pentaerythritol triallyl ether, diethylene glycol diallyl ether, N,N'-methylenebisacrylamide, diethylene glycol diallyl ether, dipropylene glycol diallyl ether, dibutylene glycol diallyl ether and other dialkylene glycol diallyl ethers, polyethylene glycol diallyl ether, polypropylene glycol diallyl ether, polybutylene glycol diallyl ether and other polyalkylene glycol diallyl ethers. Among these crosslinking agents, considering that the effect of the present invention can be easily obtained by making it easy to thicken the ink (develop ink viscosity) and further easily form a stable network structure, 1,10-decanediol diacrylate, pentaerythritol triallyl ether, diethylene glycol diallyl ether, and N,N'-methylenebisacrylamide are preferred. More preferably, diethylene glycol diallyl ether is preferred. Therefore, in the present invention, it is preferable to use a cross-polymer containing acrylate (Chemical Formula 1), acrylic acid (Chemical Formula 2), and diethylene glycol diallyl ether as constituent components. Specifically, (acrylic acid / perfluorohexylethyl acrylate) cross-polymer is preferred, and 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: Saltrellar, manufactured by Fujifilm Wako Pure Chemical Corporation) is most preferred.

[0020] Considering that it is easy to thicken the ink (develop ink viscosity) and form a stable network structure, the ratio (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, still more preferably 0.1 to 1 part by weight, and even more preferably 0.15 to 0.5 parts by weight with respect to a total of 100 parts by weight of acrylate and acrylic acid.

[0021] As components of the (acrylic acid / perfluoroalkyl acrylate) copolymer of the present invention, in addition to the above-mentioned acrylate ester, acrylic acid, and crosslinking agent, (meth)acrylate 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 based on the total amount of the ink composition. If it is less than 0.01% by mass, it is difficult to obtain the desired ink thickening, and it is difficult to suppress ink leakage. If it exceeds 10% by mass, the ink viscosity becomes high, and the writing feel and ink followability are likely to be inferior. Therefore, more preferably, it is 0.01 to 5% by mass. Furthermore, considering the above effects, in the case of an aqueous ink composition, 0.01 to 5% by mass is preferable, more preferably 0.1 to 3% by mass, and most preferably 0.5 to 2% by mass. In the case of an oily ink composition, 0.5 to 5% by mass is preferable, more preferably 0.5 to 4% by mass, and most preferably 0.8 to 3.5% by mass.

[0023] (Solvent) As the solvent used in the ink composition for writing instruments used in the present invention, water, an organic solvent, or a mixed solvent of water and an organic solvent may be used. By using a solvent, it is presumed that the (acrylic acid / perfluoroalkyl acrylate) copolymer can form a stable network structure and a gel structure, so that it is possible to increase the ink viscosity.

[0024] Also, as the water, conventional water such as ion-exchanged water, distilled water, and tap water can be used. Examples of the organic solvent 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 ether and alkylene glycol dialkyl ether; aromatic alcohols such as benzyl alcohol; and aliphatic alcohol solvents such as methanol, ethanol, 1-propanol, 2-propanol, isobutanol, and t-butanol.

[0025] In the case of an aqueous ink composition, considering the stability with water and the formation of a stable network structure of the (acrylic acid / perfluoroalkyl acrylate) copolymer, polyhydric alcohol solvents are preferred. Further considering this, polyhydric alcohols having a divalent or trivalent hydroxyl group are more preferred. In the case of an oil-based ink composition, considering the formation of a stable network structure with the (acrylic acid / perfluoroalkyl acrylate) copolymer, alkylene glycol alkyl ether solvents are preferred, and alkylene glycol monoalkyl ethers are more preferred. Further, regarding the number of carbon atoms in the alkylene glycol moiety of the alkylene glycol monoalkyl ether, considering the ease of ink thickening (ink viscosity development) with the (acrylic acid / perfluoroalkyl acrylate) copolymer, the number of carbon atoms is preferably 2 to 10, more preferably 3 to 8, and even more preferably 5 to 6. Regarding the number of carbon atoms in the alkyl ether moiety of the alkylene glycol monoalkyl ether, considering the swelling dispersibility, writing feel, and writing properties (suppression of feathering and bleeding) with the (acrylic acid / perfluoroalkyl acrylate) copolymer, a shorter alkyl ether moiety is preferred. For this reason, the number of carbon atoms is preferably 1 to 6, more preferably 1 to 4 considering the ease of stabilization with the (acrylic acid / perfluoroalkyl acrylate) copolymer and the ease of obtaining the effects, and even more preferably 1 to 2. Furthermore, alkylene glycol monoalkyl ethers having a solubility parameter (SP value) of 8 to 13 are preferred.

[0026] Also, in the case of an oil-based ink composition, the solvent preferably contains a small amount of water. Although the reason is not clear, water has excellent affinity with the (acrylic acid / perfluoroalkyl acrylate) copolymer, and can impart a higher thickening effect and stable swelling property to the swelling dispersion by the (acrylic acid / perfluoroalkyl acrylate) copolymer. Furthermore, it can improve the slipperiness of the pen tip (ball), improve the ink ejection property, suppress dot unevenness, bleeding, streaking, etc., and is likely to improve the writing property. In particular, it is preferable to use an alkylene glycol alkyl ether solvent and water together as the solvent because it is easier to impart a higher thickening effect and stable swelling property.

[0027] If the water content is less than 0.1% by mass based on the total amount of the ink composition, it is likely to affect the slipperiness of the pen tip (ball) and the ink ejection property. If it exceeds 20% by mass, the solubility in the ink is likely to be poor. Therefore, 0.1 to 20% by mass is preferable based on the total amount of the ink composition. Furthermore, considering the solubility in the ink and the writing property (suppression of streaking and bleeding), 1 to 10% by mass is preferable, and more preferably 2 to 10% by mass.

[0028] The content of the solvent in the ink composition for writing instruments is preferably 20 to 90% by mass, and more preferably 30 to 80% by mass based on the total amount of the ink composition. If the content of the solvent is within the above numerical range, the (acrylic acid / perfluoroalkyl acrylate) copolymer can form a stable network structure and a gel structure, making it possible to increase the ink viscosity, suppress ink leakage from the gap at the pen tip, and when writing, the ink viscosity becomes low, so it can suppress handwriting streaking, has excellent writing properties, and is likely to improve the writing feel.

[0029] Also, regarding the blending ratio of the solvent to the (acrylic acid / perfluoroalkyl acrylate) copolymer (solvent / perfluoroalkyl acrylate), it is preferably 10 to 1000 times, more preferably 20 to 200 times, and even more preferably 30 to 100 times on a mass basis. This is because when it is within the above range, a stable network structure is formed, and it becomes easier to form a gel structure, so that the effects of suppressing ink leakage, excellent writing properties, and improved writing feel can be easily obtained.

[0030] (Colorant) The colorants used in the aqueous ink composition and the oily ink composition of the present invention are not particularly limited, such as dyes and pigments, and can 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, and various salt-forming type dyes can be adopted. (a) As direct dyes, Direct Yellow 4, 26, 44, 50, 85, Direct Red 1, 2, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, 227, Direct Blue 1, 3, 15, 41, 71, 86, 106, 119, Direct Orange 6, etc.; (b) As acid dyes, 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) As basic dyes, C.I. Basic Yellow-1, 2, 21, 7, 40, C.I. Basic Orange 2, 14, 32, C.I. Basic Red 1, 1:1, 2, 9, 14, C.I. Basic Violet 1, 3, 7, 10, 11:1, C.I. Basic Blue-3, 7, 26, Basic Green 4, C.I. Basic Brown 12, C.I. Basic Black 2, methyl violet, Victoria Blue FB, malachite green, rhodamine series, etc.; (d) As other dyes, disperse dyes such as Disperse Yellow 82, 121, Disperse Blue 7, etc.

[0032] As dyes used in the oil-based ink composition, there are oil-soluble dyes, acid dyes, basic dyes, metal-containing dyes, etc., and as various salt-forming type dyes thereof, there are types such as salt-forming dyes of acid dyes and basic dyes, salt-forming dyes of organic acids and basic dyes, salt-forming dyes of acid dyes and organic amines, etc. Considering not inhibiting the network structure of the (acrylic acid / perfluoroalkyl acrylate) copolymer used in the present invention and stably thickening the ink viscosity, it is preferable to use salt-forming dyes. Examples of dyes include Vat Fast Black 1802, Vat Fast Black 1805, Vat Fast Black 1807, Vat Fast Violet 1701, Vat Fast Violet 1704, Vat Fast Violet 1705, Vat Fast Blue 1601, Vat Fast Blue 1605, Vat Fast Blue 1613, Vat Fast Blue 1621, Vat Fast Blue 1631, Vat Fast Red 1320, Vat Fast Red 1355, Vat Fast Red 1360, Vat Fast Yellow 1101, Vat Fast 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 (manufactured by Orient Chemical Industries, Ltd. as above), Isenspirone Black GMH-Special, Isenspirone Violet C-RH, Isenspirone Blue GNH, Isenspirone Blue 2BNH, Isenspirone Blue C-RH, Isenspirone Red C-GH, Isenspirone Red C-BH, Isenspirone Yellow C-GNH, Isenspirone Yellow C-2GH, S.P.T. Blue 111, S.P.T. Blue GLSH-Special, S.P.T. Red 533, S.P.T. Orange 6, S.B.N. Yellow 510, S.B.N. Yellow 530, S.R.C-BH (manufactured by Hodogaya Chemical Co., Ltd. as above), etc. Examples of pigments include inorganic, organic, and processed pigments, etc. Specifically, carbon black, aniline black, ultramarine, lead yellow, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, quinophthalone-based, perylene-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, metallic pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, etc. These dyes and pigments may be used alone or in combination of two or more.

[0033] As the colorant, it is preferable to use a pigment. This is because the pigment particles cause a physical obstruction in the gap between the ball and the inner wall of the tip in the case of a ballpoint pen, making it easy to suppress ink leakage. Also, the pigment is excellent in the fastness of the handwriting, especially in light resistance, so it is preferable. Furthermore, by using a pigment, in the case of a ballpoint pen, when the pigment particles enter the gap between the ball and the tip body, an action like that of a bearing easily works. By suppressing metal contact, lubricity is improved, the writing feel is improved, and the effect of suppressing wear of the ball seat is easily obtained. Therefore, it is preferable to use a pigment. As in the present invention, by using a (acrylic acid / perfluoroalkyl acrylate) copolymer, the ink has a gel structure and the ink viscosity during writing becomes low viscosity, so metal contact between the ball and the tip body easily occurs. Therefore, improving lubricity and suppressing wear of the ball seat, it is preferable to use a pigment. Furthermore, due to the synergistic effect of the lubricating layer formed by the surfactant described later and the pigment particles and the bearing action, it is easy to maintain lubricity and improve the writing feel, so it is preferable.

[0034] The content of the colorant is preferably 1 to 30% by mass based on the total amount of the ink composition. If it is less than 1% by mass, there is a tendency that it is difficult to obtain a dark handwriting. If it exceeds 30% by mass, it is likely to affect solubility and dispersibility in the ink. More preferably, it is 3 to 25% by mass, and even more preferably, it is 5 to 25% by mass.

[0035] (Stabilizer) In the present invention, in order to stably swell and disperse the (acrylic acid / perfluoroalkyl acrylate) copolymer in the ink and easily obtain a stable thickening effect, it is preferable to use a stabilizer. Further, even when a surfactant such as a phosphate ester surfactant is used, neutralization makes it easy to obtain the effect of stabilizing dissolution in the ink and improving the writing feel and writing performance, so it is preferable. Examples of the stabilizer include basic inorganic compounds such as ammonia, sodium carbonate, sodium phosphate, and sodium hydroxide, alkanolamines such as diethanolamine and triethanolamine, amines having ethylene oxide such as oxyethylene alkylamine and polyoxyethylene alkylamine, alkylamines such as laurylamine and stearylamine, and dimethylalkylamines such as distearylamine, dimethyllaurylamine, dimethylstearylamine, and dimethyloctylamine, basic organic compounds such as sodium acetate, lactic acid, and citric acid. Among them, considering the stability with the (acrylic acid / perfluoroalkyl acrylate) copolymer, basic inorganic compounds are preferable, and more preferably, alkanolamines are preferable. In particular, in the case of an aqueous ink composition, alkanolamines are preferable, and it is preferable to use triethanolamine which is weakly basic. In the case of an oil-based ink composition, amines having ethylene oxide are preferable. These may be used alone or in combination of two or more.

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

[0037] Furthermore, considering the 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. If it exceeds 300 (mgKOH / g), due to its strong reactivity, it is likely to react with the above components, resulting in poor ink stability over time. Further, considering the stability with the solvent and (acrylic acid / perfluoroalkyl acrylate) copolymer, the total amine value is preferably 200 (mgKOH / g) or less, and more preferably 150 (mgKOH / g) or less. On the other hand, considering the above effects, the lower limit of the total amine value is preferably 30 (mgKOH / g) or more. Note that the total amine value indicates the total amount of primary, secondary, and tertiary amines, and is represented by the number of milligrams of potassium hydroxide equivalent to the hydrochloric acid required to neutralize 1 g of the sample.

[0038] Regarding the HLB value of the organic amine, the HLB value 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 dispersion with the solvent. Further considering neutralization stability and improvement of swelling dispersibility, the HLB value is preferably 7 to 17, and 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 preferably 0.5 to 8 times. This is because it is easy to stably swell and disperse the (acrylic acid / perfluoroalkyl acrylate) copolymer in the ink to obtain a stable thickening effect.

[0040] Considering the neutralization stability with the (acrylic acid / perfluoroalkyl acrylate) copolymer and the phosphate ester surfactant, the content of the stabilizer is preferably 0.1 to 10% by mass based on the total amount of the ink composition. Further, considering the neutralization with the phosphate ester surfactant, it is preferably 0.1 to 8% by mass, and more preferably 0.5 to 6% by mass.

[0041] (Surfactant) In the present invention, considering that improving lubricity makes it easier to improve writing feel and further improving the writing performance when the tip of the writing instrument is left in the air and dries, it is preferable to use a surfactant. This is because the lubricating layer formed by the surfactant makes it easier to improve lubricity, and further, the surfactant can soften the film formed by the drying of the tip of the writing instrument, making it easier to improve the writing performance. Examples of the surfactant include fatty acids, silicone-based surfactants, fluorine-based surfactants, phosphate ester-based surfactants, surfactants having an acetylene bond, fatty acid esters, polyalkylene alkyl ethers, alkyl alkanolamides, and the like. Among them, 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, the phosphate ester-based surfactant has a phosphate group, so it is likely to adsorb to the ballpoint pen tip or ball made of metals, etc., and it is easy to obtain a lubricating effect. Therefore, it is preferable to use a phosphate ester-based surfactant. Since it is easy to obtain an extreme pressure effect between the ball made of a metal material and the ball seat, it is preferable because it is easier to improve lubricity. In the case of an aqueous ink composition, among the phosphate ester-based surfactants, there are mentioned phosphate ester-based surfactants such as linear alcohol-based, styrenated phenol-based, nonylphenol-based, octylphenol-based, etc. Among them, it is preferable to use linear alcohol-based and styrenated phenol-based phosphate ester-based surfactants. Considering that it is easier to improve the writing feel, it is more preferable to use a linear alcohol-based phosphate ester-based surfactant. In the case of an oil-based ink composition, among phosphate ester surfactants, considering the ease of improving the writing feel, it is preferable to use a phosphate ester surfactant with an acid value of 180 (mgKOH / g) or less. Further considering, it is more preferable to use a phosphate ester surfactant with an acid value of 70 to 160 (mgKOH / g). Note that the acid value is represented by the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of the sample.

[0042] Regarding the HLB value of the surfactant, considering the compatibility with the (acrylic acid / perfluoroalkyl acrylate) copolymer, it is preferably 5 to 17. Further considering the improvement of swelling dispersibility, lubricity, and writing performance, it is preferably 6 to 14. Furthermore, considering lubricity, it is preferably 12 or less, and preferably 6 to 12. In addition, the HLB value used in the present invention can be determined by the Griffin method, Kawakami method, etc. In particular, in retractable writing instruments such as knock-type writing instruments and rotary feed writing instruments, unlike cap-type writing instruments, the writing tip is always exposed to the outside, so it is more likely to affect the writing performance when the writing tip is dry. Therefore, it is more preferable to use the surfactant with the above HLB value.

[0043] Specific examples of the surfactant include, as fatty acids, oleic acid, stearic acid, linoleic acid, etc.; as silicone surfactants, dimethyl silicone, methylphenyl silicone, polyether-modified silicone, higher fatty acid ester-modified silicone, etc.; as fluorine surfactants, perfluoro group-containing butyl sulfonate, perfluoro group-containing carboxylate, perfluoro group-containing phosphate ester, perfluoro group-containing phosphate ester type compound, perfluoroalkyl betaine, perfluoroalkylamine oxide compound, etc.; and as phosphate ester surfactants, phosphoric acid monoesters of polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether, phosphoric acid diesters of polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether, phosphoric acid triesters of polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether, alkyl phosphate esters, alkyl ether phosphate esters or their derivatives, etc. Among these, considering lubricity and thickening effect, it is preferable to use phosphate ester surfactants.

[0044] The content of the surfactant is more preferably 0.1 to 5.0% by mass based on 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. More preferably, it is 0.3 to 3.0% by mass based on the total amount of the ink composition, and even more preferably, it is 0.5 to 3.0% by mass.

[0045] (Resin) In the present invention, a resin may also be used as an ink viscosity adjuster, an ink leakage inhibitor, a pigment dispersant, or a fixing agent. Examples of the resin include polyvinyl butyral resin, ketone resin, polyacetal resin, polyvinyl alcohol resin, cellulose resin, terpene resin, alkyd resin, phenoxy resin, polyvinyl acetate resin, polyvinyl pyrrolidone resin, ethylene oxide polymer, acrylic resin, styrene-acrylic resin, styrene-maleic acid resin, etc., and resin particles such as olefin-based resin particles, acrylate resin particles, amino resin particles, acrylic resin particles, styrene-butadiene resin particles, etc. These may be used alone or in combination of two or more.

[0046] Among these resins, in consideration of suppressing ink leakage, it is preferably composed of resin particles. Further considering, it is preferably to use organic resin particles. More preferably, it is composed of particles selected from acrylate resin particles, olefin-based resin particles, and amino resin particles. This can cause a physical obstacle by the resin particles from the gap at the tip of the writing instrument (in the case of a ballpoint pen, the gap between the ball and the tip of the nib), thereby suppressing ink leakage. Furthermore, when the particles are partially deformed and adhere to each other, a structure formed by weak aggregation is generated, and a structure with a high resistance to ink leakage during standing is formed in the ink, enabling high ink leakage suppression. On the other hand, due to the structure formed by weak aggregation, the aggregation structure is crushed by physical actions such as the rotation of the ball during writing, so it is possible to obtain good writing feel and writing performance with suppressed scratching without inhibiting the ink fluidity during writing. Furthermore, it is preferable because a higher ink leakage suppression effect is easily obtained by the interaction between the ink leakage suppression effect due to the stable network structure of the (acrylic acid / perfluoroalkyl acrylate) copolymer and the physical obstacle by the resin particles. In particular, it is preferably used as an ink composition for a ballpoint pen because it is effective.

[0047] Regarding the average particle diameter of the resin particles, the smaller the average particle diameter, the easier it is for the particles to adhere to each other and form a weak aggregation structure, and the easier it is to suppress ink leakage. Therefore, it is preferably 7 μm or less, more preferably 5 μm or less. Further, considering the dispersion stability (ink stability over time) of the resin particles in the ink, it is preferably 3 μm or less, and more preferably less than 1 μm. On the other hand, if the average particle diameter is too small, the ink leakage suppression effect is likely to be inferior. Therefore, the average particle diameter is preferably 0.1 μm or more, and more preferably 0.3 μm or more. The average particle diameter can be determined by measuring the particle diameter (D50) at 50% volume cumulative of the particle size distribution measured based on the numerical values calibrated using a Coulter counter method, a Coulter MultisizerTM3 (a measuring device manufactured by Beckman Coulter), and standard samples or other measuring methods.

[0048] Among these resin particles, considering the stability in the ink, the stability with respect to the solvent, and the suppression of ink leakage, it is preferably selected and used from among olefin resin particles, acrylate resin particles, and amino resin particles. Considering that it is easier to improve the ink leakage suppression due to being more stable in the ink, it is preferably selected and used from among polyethylene resin particles, methacrylate resin particles, melamine resin particles, and benzoguanamine resin particles. Further considering, polyethylene resin particles and methacrylate resin particles are preferred. Particularly, in the case of an aqueous ink composition, olefin resin particles are preferred considering the compatibility with the solvent and the ink leakage suppression effect, and polyethylene resin particles are more preferred. In the case of an oil-based ink composition, acrylate resin particles are preferred considering the compatibility with the solvent and the ink leakage suppression effect, and methacrylate resin particles are more preferred. These resin particles may be used alone or in combination of two or more, and may be a mixture or a copolymer.

[0049] Regarding the shape of the resin particles, spherical or irregular-shaped particles can be used. However, considering the effect of suppressing ink leakage due to the adhesion between resin particles, spherical resin particles are preferred. The spherical resin particles referred to here are not limited to perfect spheres, and may also be substantially spherical resin particles or substantially ellipsoidal resin particles.

[0050] Among resins, considering improving writing feel, suppressing pen mark blur and dot unevenness, and facilitating improvement of pigment dispersibility, it is preferable to use ketone resin and polyvinyl butyral resin. Considering improving writing feel, suppressing pen mark blur (writing property), it is preferable to use ketone resin.

[0051] Regarding the content of the resin particles, 0.01 to 10% by mass is more preferable based on the total amount of the ink composition. This is because when the content of the resin particles is less than 0.01% by mass, it is difficult to suppress ink leakage, and when it exceeds 10% by mass, the aggregation structure tends to become strong, which easily affects the ink stability over time, writing feel, and writing performance. Further considering, 0.1 to 5% by mass is preferable, 0.3 to 3% by mass is particularly preferable, and most preferably, 0.5 to 3% by mass is preferable.

[0052] In addition, a shear-thinning viscosity-imparting agent other than the (acrylic acid / perfluoroalkyl acrylate) copolymer may be used in combination. It can adjust the viscosity of the ink composition and improve the dispersion stability of the pigment. Specifically, examples include polysaccharides such as fatty acid amide, hydrogenated castor oil, polyacrylic acid, xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, and diutan gum.

[0053] In the case of an aqueous ink composition, it is preferable to use dextrin in order to suppress ink leakage and improve writing performance. By using dextrin, when the ink at the writing tip dries, a film is formed, thereby obtaining an effect of suppressing ink leakage (in the case of a ballpoint pen, ink leakage from the gap between the ball and the tip of the nib), and further, by suppressing the drying and solidification of the writing tip, an effect of improving the writing performance due to drying up is exerted.

[0054] Regarding the weight average molecular weight of dextrin, 5000 to 120000 is more preferable. When the weight average molecular weight exceeds 120000, the film formed at the writing tip is hard, and in writing during drying up, the handwriting is likely to smear. On the other hand, when the weight average molecular weight is less than 5000, the hygroscopicity tends to be high, the film at the writing tip tends to be soft, and it is difficult to sufficiently obtain the ink leakage suppressing effect. Furthermore, when the weight average molecular weight is less than 20000, the film tends to be thin, so the weight average molecular weight of 20000 to 120000 is most preferable.

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

[0056] The ink viscosity of the ink composition for writing instruments of the present invention is not particularly limited, but by imparting shear thinning viscosity with a (acrylic acid / perfluoroalkyl acrylate) copolymer, the ink viscosity at rest is increased to facilitate suppression of ink leakage, and the ink viscosity during writing is decreased to easily improve writing properties such as writing feel and smearing. In the case of an aqueous ink composition, at 20°C, shear rate 192 sec -1During writing, the ink viscosity is preferably 300 mPa·s or less because it is easier to improve writing quality and writing properties such as scratching. Considering writing quality and writing properties more, it is preferably 200 mPa·s or less. Also, considering ink leakage suppression and ink followability, at 20 °C and a shear rate of 1.92 sec -1 During rest, the ink viscosity is preferably 100 to 5000 mPa·s. Considering more, it is preferably 200 to 3500 mPa·s. Considering further, it is more preferably 300 to 3000 mPa·s. Here, the ink viscosity of the aqueous ink composition is measured using a Brookfield DV-II viscometer (CPE-42 rotor). In the case of an oil-based ink composition, at 20 °C and a shear rate of 20 sec -1 During writing, the ink viscosity is preferably 7000 mPa·s or less. Considering writing quality and writing properties more, an ink viscosity of 4000 mPa·s or less is preferable. Considering more, an ink viscosity of 3000 mPa·s or less is preferable. Also, considering writing properties such as bleeding, smudging, bleeding through, and drying of the handwriting, an ink viscosity of 100 mPa·s or more is preferable. Considering more, 200 mPa·s or more is preferable, and 500 mPa·s or more is preferable. Also, considering ink followability, at 20 °C and a shear rate of 0.18 sec -1 During rest, the ink viscosity is preferably 50000 mPa·s or less. Considering more, it is preferably 30000 mPa·s or less. Considering more, it is preferably 20000 mPa·s or less. Also, considering ink leakage suppression, at 20 °C and a shear rate of 0.18 sec -1 During rest, the ink viscosity is preferably 1000 mPa·s or more. Considering more, it is preferably 2000 mPa·s or more. Considering more, it is preferably 3000 mPa·s or more. Here, the ink viscosity of the oil-based ink composition is measured using a Brookfield viscometer RVDVII+Pro CP-52 spindle at 20 °C. In addition, in retractable writing instruments such as click-type writing instruments and rotary feed writing instruments, it is necessary to consider ink leakage prevention more, so it is effective.

[0057] In the present invention, the viscosity index n refers to n in the viscosity formula represented by S = αD n Note that 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 measured and calculated at 20°C using the above viscometer to measure the ink viscosity. Regarding the viscosity index n, considering writing properties such as ink leakage prevention, writing feel, and scratching, it is preferably 0.4 to 0.9. Considering the balance of writing properties such as ink leakage prevention, writing feel, and scratching, it is preferably 0.5 to 0.85, and more preferably 0.55 to 0.8.

[0058] (Writing instrument) The 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, etc. as pen tips or ballpoint pen tips. The writing instrument of the present invention may be configured to directly fill the ink composition for writing instruments, or may be provided with an ink container or an ink reservoir that can hold the ink composition for writing instruments.

[0059] The retractable mechanism of the writing instrument of the present invention is not particularly limited, and examples include a cap type, a click type, a rotary type, and a slide type provided with a cap that covers the pen tip. Further, it may be a retractable type in which the pen tip can be accommodated in the shaft cylinder.

[0060] Also, the ink supply mechanism in the writing instrument is not particularly limited. For example, (1) a mechanism that includes an ink guiding 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 includes a comb-shaped ink flow rate adjusting member and supplies the ink composition to the pen tip through this member; (3) a mechanism that includes an ink flow rate adjusting member by a valve mechanism and supplies the ink composition to the pen tip; and (4) a mechanism that directly supplies the ink composition from an ink container or a shaft cylinder equipped with a pen tip to the pen tip, etc. can be mentioned.

[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, etc. Further, its shape may be a bullet shape, a chisel shape, or a fountain pen shape, etc. In one embodiment, the writing instrument is a ballpoint pen, and it is preferably a ballpoint pen equipped with an ink backflow prevention body.

[0062] (Ballpoint pen tip) Also, in the case of a ballpoint pen, the movement amount of the ball in the longitudinal axis direction of the ballpoint pen tip 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 is difficult to obtain good writing feel and suppression of blurred handwriting, and if it exceeds 50 μm, it is likely to affect ink leakage suppression, bleeding, and ink follow-up performance. More preferably, it is 20 to 50 μm, and more preferably, the movement amount in the longitudinal 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 is difficult to obtain good writing feel and suppression of blurred handwriting, and if it exceeds 25 μm, it is likely to affect ink leakage suppression, bleeding, and ink follow-up performance. More preferably, it is 3 to 20 μm, and more preferably, the movement amount in the longitudinal axis direction is 5 to 16 μm. The movement amount (clearance) of the ball of the ballpoint pen tip in the axial direction indicates the distance that the ball can move in the longitudinal axis direction of the ballpoint pen tip body.

[0063] Also, in order to suppress wear of the ball seat and improve writing quality, it is preferable that the arithmetic mean roughness (Ra) of the ball surface be 0.1 to 10 nm. This is because if the arithmetic mean roughness (Ra) exceeds this range, the ball surface is too rough, and the rotational resistance between the ball and the ball seat tends to increase, so it is likely to affect the writing quality and wear of the ball seat. Also, if it is below this range, the ink does not sufficiently adhere to the surface of the ball, so it is likely to affect the writing performance such as streaks in the handwriting. Therefore, in order to suppress wear of the ball seat, improve writing quality, and obtain sufficient writing performance, it is preferable that the arithmetic mean roughness (Ra) of the ball surface be 0.1 to 10 nm, more preferably 0.1 to 8 nm, and particularly preferably 0.1 to 6 nm. Regarding the arithmetic mean roughness of the ball surface, from the roughness curve measured by a surface roughness measuring instrument (model name SPI3800N manufactured by Seiko Epson Corporation), a reference length is extracted in the direction of the mean line, and the sum of the absolute values of the deviations from the mean line of this extracted portion to the measurement curve is averaged.

[0064] Also, the material used for the ball is not particularly limited, and 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, zirconia, and ruby balls.

[0065] Also, the materials for the ball pen tip include metal materials such as stainless steel, nickel silver, brass, aluminum bronze, and aluminum, and resin materials such as polycarbonate, polyacetal, and ABS. However, considering the wear of the ball seat, stability over time, and cost, it is preferable to use a stainless steel tip body.

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

[0067] <Example 1> <Water-based ballpoint pen ink composition> A pigment dispersion, water, polyhydric alcohol, stabilizer, organic resin particles, surfactant, and rust inhibitor were used as colorants. These were weighed in predetermined amounts, heated to 60 °C, and then completely dissolved using a dispersing stirrer to prepare a base ink. Thereafter, while heating the prepared base ink, a (acrylic acid / perfluorohexylethyl acrylate) copolymer was added and thoroughly mixed and stirred using a homogenizer stirrer until a uniform state was achieved, thereby obtaining the water-based 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 times. Incidentally, the ink viscosity of Example 1 was measured at 20 °C using a Brookfield DV-II viscometer (CPE-42 rotor) under the condition of a shear rate of 1.92 sec -1 (rotation speed 0.5 rpm), and the ink viscosity was measured to be 1027 mPa·s. Under the environment of 20 °C and a shear rate of 192 sec -1 (rotation speed 50 rpm), it was 152 mPa·s. Also, the viscosity index n was 0.59.

[0068] Pigment dispersion (colored resin particles, solid content 34%) 20.0 mass% Water 64.0 mass% Polyhydric alcohol (glycerin) 10.0 mass% (Acrylic acid / perfluorohexylethyl acrylate) cross-polymer 1.5 mass% "Constituent components: Acrylic ester (chemical modification 1), Acrylic acid (chemical modification 2), Diethylene glycol diallyl ether (chemical modification 1) / (chemical modification 2)=0.3 Ratio of diethylene glycol diallyl ether to the total of 100 parts by weight of acrylic ester and acrylic acid: 0.29 part by weight" Organic resin particles (polyethylene resin, average particle diameter: 6 μm) 1.0 mass% Stabilizer (triethanolamine) 2.0 mass% Phosphate surfactant (HLB value: 11.5) 1.0% by mass Rust inhibitor (benzotriazole) 0.5% by mass

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

[0070] The ink compositions for aqueous ballpoint pens (1.0 g) prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were filled into an ink storage cylinder (polypropylene) with a ballpoint pen tip that rotatably held a ball with a ball diameter of φ0.7 mm (the ball was directly pressed against the inner wall at the tip edge of the tip by a coil spring having a vertical movement amount of the ball: 30 μm, arithmetic mean roughness of the ball surface (Ra): 1 nm) to produce a ballpoint pen. The following tests and evaluations were conducted using writing paper JIS P3201 as the writing test paper.

[0071] <Example 11> <Ink composition for oil-based ballpoint pen> A colorant, a solvent, a surfactant, and organic resin particles were employed, weighed in predetermined amounts, heated to 60°C, and then completely dissolved using a dispersing stirrer to prepare a base ink. Then, while heating the base ink prepared above, (acrylic acid / perfluorohexylethyl acrylate) cross-polymer was added and sufficiently mixed and stirred using a homogenizer stirrer until a uniform state was achieved to obtain the oiliness of Example 11. The specific blending amounts are as follows. Incidentally, when the ink viscosity of Example 11 was measured using a viscometer RVDVII+Pro CP-52 spindle manufactured by Brookfield Co., Ltd., in an environment of 20°C and a shear rate of 0.18 sec -1 at 15000 mPa·s, and in an environment of 20°C and a shear rate of 20 sec -1It was 2700 mPa·s. Also, the viscosity index n was 0.64.

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

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

[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 an ink storage cylinder (polypropylene) with a ballpoint pen tip that rotatably held a ball with a diameter of φ0.7 mm (the ball had a coil spring that directly pressed the ball against the inner wall at the tip edge of the tip, the amount of movement of the ball in the longitudinal axis direction: 8 μm, arithmetic mean roughness (Ra) of the ball surface: 5 nm) to prepare a ballpoint pen. The following tests and evaluations were conducted using writing paper JIS P3201 as the writing test paper.

[0075]

Table 1

[0076]

Table 2

[0077]

Table 3

[0078] Writing feel: Conducted a sensory test by handwritten and evaluated it. Very smooth ··· ◎ Smooth ··· ○ Smoothness at a practical problem-free level ··· △ Heavy ··· ×

[0079] (Water-based ballpoint pen) Ink leakage test: Attached a 40 g weight to the gel ink ballpoint pen, protruded the ballpoint pen tip downward, kept the ball of the ballpoint pen tip in contact with the bottom of the ballpoint pen display case, left it in an environment of 20 °C and 65% RH for 1 day, and measured the ink leakage amount from the tip of the ballpoint pen tip. Ink leakage amount less than 5 mg ··· ◎ Ink leakage amount between 5 and 15 mg ··· ○ Ink leakage amount exceeding 15 mg and less than 30 mg ··· △ Ink leakage amount of 30 mg or more ··· × (Oil-based ballpoint pen) Ink leakage suppression test: Left the pen tip downward in an environment of 30 °C and 85% RH for 7 days, and checked for ink leakage from the tip of the chip. No ink drops at the tip of the chip ··· ◎ Ink drops at the tip of the chip within 1 / 4 of the tapered part ··· ○ Ink drops at the tip of the chip exceeding 1 / 4 of the tapered part and less than 1 / 2 ··· △ Ink drops at the tip of the chip 1 / 2 or more of the tapered part ··· ×

[0080] (Water-based ballpoint pen) Writing performance test: After a 100 m writing test using a running tester with a load of 100 gf, a writing angle of 70°, and a speed of 4 m / min, the writing trace was observed. (Oil-based ballpoint pen) Writing performance test: After a 100 m writing test using a running tester with a load of 200 gf, a writing angle of 70°, and a speed of 4 m / min, the writing trace was observed. Those with no or few streaks in the writing trace ··· ◎ Those with some streaks in the writing trace but at a level with no practical problems ··· ○ Those with streaks in the writing trace and having an impact in practical use ··· △ Those with many streaks in the writing trace ··· ×

[0081] In Examples 1 to 27, good performance was obtained in terms of writing feel, ink leakage suppression test, and writing performance. Also, in Examples 1 to 9 and Examples 23 to 27, for the pigment ink, when observed under a microscope, the pigment dispersibility was good and there were no precipitates, which was good. In addition, as described above, using the viscometer manufactured by Brookfield Co., Ltd., the ink viscosities of Examples 4 and 12 were measured, and the viscosity imparting index n was calculated. In Example 4, in an environment of 20 °C, shear rate 1.92 sec -1 (Rotation speed 0.5 rpm), ink viscosity = 345 mPa·s, in an environment of 20 °C, shear rate 192 sec -1 (Rotation speed 50 rpm), ink viscosity = 73 mPa·s, and the viscosity imparting index n was 0.66. In Example 12, in an environment of 20 °C, shear rate 0.18 sec -1 , ink viscosity = 10000 mPa·s, in an environment of 20 °C, shear rate 20 sec -1 and the ink viscosity was 2000 mPa·s, and the viscosity imparting index n was 0.66. In Example 23, in an environment of 20 °C, shear rate 0.18 sec -1 , ink viscosity = 11000 mPa·s, in an environment of 20 °C, shear rate 20 sec -1 and the ink viscosity was 2400 mPa·s, and the viscosity imparting index n was 0.71. In Example 24, in an environment of 20°C and a shear rate of 0.18 sec -1 , the ink viscosity = 6600 mPa·s, in an environment of 20°C and a shear rate of 20 sec -1 , the ink viscosity = 2200 mPa·s, and the viscosity imparting index n was 0.79.

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

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

[0084] Also, when using retractable writing instruments (retractable ball pens) such as knock-type writing instruments and rotary feed writing instruments, since ink leakage suppression performance is one of the most important performances, ink leakage (ink leakage from the gap between the ball and the tip of the nib) from the gap at the writing tip can be suppressed as in the present invention, and it is effective to use the ink composition for writing instruments containing the (acrylic acid / perfluoroalkyl acrylate) copolymer as in the present invention to achieve good ink leakage suppression performance.

[0085] As in the present invention, in order to suppress ink leakage and improve writing performance, a ball rotatably held at the tip of a ball pen nib is pressed against the inner wall of the tip edge of the nib directly or through a pressing body by a coil spring, and a valve mechanism is provided to give a gap between the inner wall of the tip edge of the nib and the ball by the pressing force during writing to allow the ink to flow out, and it is preferable to close even the minute gap at the tip of the nib when not in use.

[0086] In addition, in this embodiment, for the sake of convenience, a ballpoint pen containing a refill for a ballpoint pen directly containing a writing instrument ink composition in a shaft cylinder is exemplified. However, the writing instrument of the present invention may be a writing instrument having a shaft cylinder as an ink storage cylinder and directly containing a writing instrument ink composition in the shaft cylinder, such as a direct-fill type ballpoint pen, a marking pen, or a signature pen. Further, when it is a marking pen or a signature pen directly containing a writing instrument ink composition in the shaft cylinder, since the effects of suppressing ink leakage and ink bottle dropping can be obtained, it can be preferably used. In addition, in this embodiment, for the sake of convenience, a ballpoint pen tip formed by cutting a wire rod is exemplified. However, it may be a ballpoint pen tip formed by pressing a pipe material.

Industrial Applicability

[0087] The present invention can be used as a writing instrument. More specifically, it can be widely used as a ballpoint pen, a marking pen, or a signature pen as a writing instrument such as a cap type or a retractable type.

Claims

1. An oil-based ink composition for writing instruments, comprising a colorant, an organic solvent, and an (acrylic acid / perfluoroalkyl acrylate) copolymer, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer comprises an acrylate ester represented by the general formula (Chemical Formula 1) as a constituent component, and the content thereof is 0.01 to 5% by mass based on the total amount of the ink composition. 【Chemical 1】

2. The oil-based ink composition for writing instruments according to Claim 1, wherein the organic solvent is an alkylene glycol alkyl ether solvent.

3. The oil-based ink composition for writing instruments according to Claim 1 or 2, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer comprises acrylic acid represented by the general formula (Chemical Formula 2) as a constituent component. [Chemical 2]

4. The oil-based ink composition for writing instruments according to any one of Claims 1 to 3, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer comprises a crosslinking agent as a constituent component.

5. The oil-based ink composition for writing instruments according to any one of Claims 1 to 4, wherein the viscosity index n of the oil-based ink composition for writing instruments is 0.5 to 0.

85.

6. The oil-based ink composition for writing instruments according to any one of Claims 1 to 5, further comprising a surfactant.

7. The oil-based ink composition for writing instruments according to any one of Claims 1 to 6, further comprising resin particles.

8. A writing instrument, comprising the oil-based ink composition for writing instruments according to any one of Claims 1 to 7.

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