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

Abstract

To provide an oil-based ink composition for a writing instrument which improves writing performance by suppressing color development, blurring of handwriting and excessive ink adhesion while obtaining dissolution stability of a dye in an ink and to provide a writing instrument using the same.SOLUTION: There is provided an oil-based ink composition for a writing instrument comprising a salt-forming dye including a polymethine basic dye and an organic solvent.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] BACKGROUND ART A large number of oil-based ink compositions for writing instruments have been proposed to date, which use, as colorants, various dyes such as nigrosine dyes, basic dyes, and acid dyes, or dyes obtained by processing these dyes.

[0003] Various colorants are used as oil-based ink compositions for such writing instruments. Examples of those using nigrosine dyes include JP-A-5-320558 "Oil-based black ink", and those using salt-forming dyes of triarylmethane-based basic dyes and azo-based yellow acid dyes include JP-A-9-165542 "Oil-based black ink", JP-A-9-71745 "Oil-based black ink", and those using salt-forming dyes based on basic dyes include JP-A-8-134393 "Black ink composition for oil-based ballpoint pens", JP-A-2009-155401 "Oil-based ink composition", and JP-A-2019-1991 "Salt-forming dye". [Prior art documents] [Patent documents]

[0004] [Patent Document 1] "Unexamined Japanese Patent Publication No. 5-320558" [Patent Document 2] "Unexamined Japanese Patent Publication No. 9-165542" [Patent Document 3] "Unexamined Japanese Patent Publication No. 9-71745" [Patent Document 4] "Unexamined Japanese Patent Publication No. 8-134393" [Patent Document 5] "Unexamined Japanese Patent Publication No. 2009-155401" [Patent Document 6] "Patent Publication No. 2019-1991" Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, when nigrosine dyes are used as colorants, they are highly concentrated, inexpensive, and have been used conventionally, but it is necessary to take into consideration the solubility stability with ink components such as organic solvents, resins, and surfactants, as well as the stability of the ink over time.

[0006] Furthermore, in Patent Documents 2 and 3, when a salt-forming dye consisting of a triarylmethane-based basic dye and an azo-based yellow acid dye is used as a colorant, a part of the salt-forming dye breaks down over a long period of time, resulting in the generation of precipitates and poor color development.

[0007] Furthermore, in Patent Document 4, when a salt-forming dye based on a basic dye is used as a colorant, the ink has good stability over time. However, in order to improve writing performance such as the writing feel, a surfactant or the like may be newly added to improve the writing performance. However, the surfactant may react with the dye to produce precipitates, and there is therefore room for consideration of the balance between the compatibility with the ink components and the writing performance.

[0008] Therefore, in inks using dyes as colorants as in Patent Documents 1 to 6, there is an increasing demand for better solubility of the dye, organic solvent, and other ink components, color development, and writing performance.

[0009] An object of the present invention is to provide an ink composition for a writing instrument which has good ink solubility, color development and writing performance, and a writing instrument using the same.

[0010] In order to solve the above problems, the present invention "1. An oil-based ink composition for a writing instrument, comprising a salt-forming dye including a polymethine basic dye and an organic solvent. 2. The oil-based ink composition for a writing instrument according to item 1, wherein the organic solvent is selected from the group consisting of alkylene glycol alkyl ethers, amide solvents, and alkylene oxide derivatives of glycerin. 3. The oil-based ink composition for a writing instrument according to item 1 or 2, wherein the salt-forming dye is a salt-forming dye of a polymethine basic dye and an acidic compound. 4. The oil-based ink composition for a writing instrument according to claim 1, wherein the acidic compound is an organic acid. 5. The oil-based ink composition for a writing instrument according to item 1 or 2, characterized in that the oil-based ink composition for a writing instrument contains an acrylic acid resin. 6. A writing instrument characterized by containing the oil-based ink composition for a writing instrument according to item 1 or 2. [Effects of the Invention]

[0011] The present invention can achieve good color development, suppression of smearing and bleeding of handwriting, and good writing performance while obtaining solubility stability of the dye in the ink. DETAILED DESCRIPTION OF THE INVENTION

[0012]

[0023] In the present specification, the terms "parts," "%," "ratio," and the like, which indicate the composition, are based on mass unless otherwise specified, and the content is the mass % of the constituent components based on the mass of the ink composition.

[0013] The present invention is characterized by providing an oil-based ink composition for a writing instrument, which comprises a salt-forming dye including a polymethine basic dye and an organic solvent.

[0014] (Salt-forming dyes including polymethine basic dyes) In the present invention, when a salt-forming dye containing a polymethine basic dye and an organic solvent are contained, they are dissolved stably in the ink, and good color development can be achieved.

[0015] The salt-forming dye containing a polymethine basic dye may be any salt-forming dye having a structure containing a polymethine basic dye having a structure (-CH=CH-)n in which double bonds and single bonds are repeated, and has good solubility in organic solvents, good compatibility with other ink components, and good color development. Furthermore, even when other colorants are used, the color development is good without separation of the colorants while maintaining the solubility stability of each other.

[0016] Furthermore, the salt-forming dye containing a polymethine basic dye is preferably a salt-forming dye formed from a polymethine basic dye and an acidic compound. This is presumably because the salt-forming dye formed by reacting a polymethine basic dye with an acidic compound improves the affinity with the organic solvent in the oil-based ink, enabling the dye to be dissolved stably in the oil-based ink.

[0017] The acidic compound may be an organic acid, an acid dye, or the like, but it is preferable to use an organic acid. This is presumably because the organic acid neutralizes the polymethine basic dye to form a salt-forming dye, which brings the polarity of the organic solvent in the oil-based ink closer to the polarity of the salt-forming dye, thereby enabling the dye to maintain stable dissolution with the organic solvent in the oil-based ink.

[0018] Furthermore, examples of acidic compounds include those with sulfo groups (-SO3H) and carboxyl groups (-COOH), but in order to further improve lubricity, acidic compounds with sulfo groups (-SO3H) are preferred. This is because the presence of sulfo groups (-SO3H) makes it easier to form a strong lubricating layer between the ball and ball seat, which improves lubricity and reduces smearing, improving writing performance.

[0019] Furthermore, as the organic acid, alkylbenzenesulfonic acid is preferred, considering that it has a strong ionic bonding force with the polymethine basic dye, resulting in a more stable salt-forming dye, and that it maintains dissolution stability by improving its affinity with the organic solvent in the oil-based ink. Furthermore, in consideration of stability over time in oil-based inks, alkylbenzenesulfonic acids having an alkyl group with 8 to 18 carbon atoms are preferred, and even more preferably 8 to 14 carbon atoms, with dodecyldiphenyloxidedisulfonic acid or dodecylbenzenesulfonic acid being preferred.

[0020] Furthermore, examples of acidic compounds include those with sulfo groups (-SO3H) and carboxyl groups (-COOH), but in order to further improve lubricity, acidic compounds with sulfo groups (-SO3H) are preferred. This is because the presence of a sulfo group (-SO3H) makes it easier to form a strong lubricating layer between the ball and ball seat, which improves lubricity, prevents smearing, and improves writing performance.

[0021] Furthermore, as the organic acid, alkylbenzene sulfonic acid is preferred, taking into consideration that it has a strong ionic bonding force and maintains solubility stability with the organic solvent in the oil-based ink. Furthermore, taking into consideration the organic solvent and dissolution stability, the alkyl group of the alkyl benzene sulfonic acid is preferably one having 8 to 18 carbon atoms, and more preferably one having 8 to 14 carbon atoms, and dodecyldiphenyloxide disulfonic acid or dodecylbenzene sulfonic acid is preferred.

[0022] In addition, as for the polymethine basic dye, it is preferable to use the following general formula (Chemical Formula 1) or (Chemical Formula 2) in consideration of good solubility in organic solvents and good color development. TIFF2025142512000001.tif83126 TIFF2025142512000002.tif62165

[0023] Furthermore, if the content of the salt-forming dye containing the polymethine basic dye is less than 0.1% by mass relative to the total amount of the ink composition, it is difficult to obtain the desired color development, and if it exceeds 40% by mass, the dissolution stability in the ink is likely to be affected, so the content is preferably 0.1 to 40% by mass relative to the total amount of the ink composition, more preferably 3 to 35% by mass, and even more preferably 7 to 30% by mass relative to the total amount of the ink composition.

[0024] (organic solvent) The organic solvent can improve the color development while providing the dissolution stability of the dye, and can improve the writing performance by suppressing the smearing and bleeding of handwriting. Specific examples of the organic solvent include alkylene glycol alkyl ethers such as alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers, amide solvents such as β-alkoxypropionamides such as 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, and 3-ethoxy-N,N-dimethylpropanamide, alkylene oxide derivatives of glycerin such as polyoxyalkylene glyceryl ethers, polyoxyalkylene alkyl glucosides, and polyoxypropylene alkyl ethers, glycol solvents such as diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, and ethylene glycol, and alcohol solvents such as benzyl alcohol, methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, ethylene glycol monomethyl ether acetate, and other higher alcohols.

[0025] Among these organic solvents, in order to stably dissolve salt-forming dyes including polymethine basic dyes and to obtain good color development, it is preferable to select from alkylene glycol alkyl ethers, amide solvents, and alkylene oxide derivatives of glycerin. In order to obtain good color development and to suppress blurring and smearing of handwriting and to maintain good writing performance, alkylene glycol alkyl ethers or amide solvents are preferred. Furthermore, alkylene glycol alkyl ethers and β-alkoxypropionamides are preferred because, even when other colorants are used, they maintain dissolution stability, do not separate the colorant, provide good color development, and can suppress smearing and bleeding of handwriting (writing performance). From this perspective, alkylene glycol monoalkyl ethers and 3-methoxy-N,N-dimethylpropanamide are preferred.

[0026] Regarding alkylene glycol alkyl ethers, the number of carbon atoms in the alkylene glycol moiety of the alkylene glycol monoalkyl ether is preferably 3 or more and 8 or less, and more preferably 4 or more and 6 or less, in order to dissolve and stabilize salt-forming dyes including polymethine basic dyes, improve color development, and improve writing performance. Regarding the number of carbon atoms in the alkyl ether moiety of alkylene glycol alkyl ethers, in consideration of dissolving and stabilizing salt-forming dyes including polymethine basic dyes, improving color development, and suppressing blurring and blobbing of handwriting (writing performance), the shorter the alkyl ether moiety, the better. Therefore, the number of carbon atoms is preferably 1 to 4, and in consideration of easier stability and easier effect, it is preferably 1 to 2.

[0027] Furthermore, among the alkylene glycol alkyl ethers described above, those having a triethylene glycol alkyl ether or butylene glycol alkyl ether structure are preferred, taking into consideration that when a salt-forming dye including a polymethine basic dye or an organic solvent is contained, the ink is dissolved stably, the color develops well, and the writing performance is suppressed, resulting in smearing and bleeding. From this perspective, those having a triethylene glycol monomethyl ether or butylene glycol monomethyl ether structure are more preferred.

[0028] Furthermore, with regard to the amide solvent, in order to improve color development and maintain good writing performance by suppressing smearing and bleeding of handwriting, it is preferable to use β-alkoxypropionamides such as 3-methoxy-N,N-dimethylpropanamide (boiling point 215°C), 3-butoxy-N,N-dimethylpropanamide (boiling point 252°C), and 3-ethoxy-N,N-dimethylpropanamide, and from further consideration, it is preferable to use 3-methoxy-N,N-dimethylpropanamide or 3-butoxy-N,N-dimethylpropanamide, with 3-methoxy-N,N-dimethylpropanamide being even more preferable.

[0029] Furthermore, with regard to alkylene oxide derivatives of glycerin, polyoxyalkylene glyceryl ethers are preferred in view of the fact that they can further improve lubricity and thereby suppress line blurring and smearing of handwriting, and from this perspective, it is even more preferable to use polyoxyalkylene diglyceryl ethers. Furthermore, polyoxyalkylene glyceryl ethers include polyoxyethylene glyceryl ether, polyoxypropylene glyceryl ether, and the like. Of these, polyoxypropylene glyceryl ether has a propyl group, which makes it easy to form a strong lubricating layer between the ball and the ball seat, improving lubricity and suppressing line skipping and blurred handwriting, making it easier to achieve the effects of the present invention, and therefore it is preferable to use polyoxypropylene glyceryl ether.

[0030] In addition, the solubility parameter (SP value) of organic solvents is between 8 and 13 (cal / cm 3 ) 1 / 2 This is because the effect of the present invention is easily exhibited due to the affinity with the salt-forming dye including the polymethine basic dye, and from a more specific perspective, the solubility parameter (SP value) is preferably 9 or more and 12 or less (cal / cm 3 ) 1 / 2 Further, if considered, the solubility parameter (SP value) is preferably 10 or more and 11 or less (cal / cm 3 ) 1 / 2 It is preferable that: The solubility parameter (SP value) of a solvent used in this invention is a value expressed as the square root of the molecular cohesive energy, and is described in Chapter IV, Solubility Parameter Values, of the Polymer Handbook (Second Edition). The SP value is expressed in units of (cal / cm3)1 / 2 and refers to the value at 25°C. For those for which no data is given, the values ​​can be calculated by the method described in RF Fedors, Polymer Engineering Science, 14, p. 147 (1967).

[0031] Furthermore, it is preferable that the boiling point of the organic solvent is 170°C or higher. This is because if the boiling point is lower than 170°C, the organic solvent is likely to evaporate, the ink viscosity is likely to increase, it is difficult to suppress line skipping and handwriting smearing, and the writing feel is likely to be affected, so from further consideration, it is preferable that the boiling point is 200°C or higher. On the other hand, if the boiling point is higher than 300°C, it is likely to affect the drying properties of the handwriting, so it is preferable that the boiling point is 300°C or lower, and from further consideration, it is preferable that the boiling point is 280°C or lower.

[0032] Furthermore, in consideration of improving solubility, strike-through, handwriting drying properties, bleeding, etc., the content of the organic solvent is preferably 10% by mass or more and 90% by mass or less, and more preferably 25% by mass or more and 80% by mass or less, of the total amount of the ink composition.

[0033] In the present invention, dyes, pigments, etc. may be appropriately selected and used as colorants other than the salt-forming dyes including polymethine basic dyes, and dyes and pigments may also be used in combination. Examples of dyes include oil-soluble dyes, acid dyes, basic dyes, metal-containing dyes, and various salt-forming dyes thereof, such as salt-forming dyes formed between an acid dye and a basic dye, salt-forming dyes formed between an organic acid and a basic dye, and salt-forming dyes formed between an acid dye and an organic amine. These dyes may be used alone or in combination of two or more. Considering compatibility with organic solvents and polymethine basic dyes, salt-forming dyes are preferred. Furthermore, considering that the stable salt-forming bond maintains stability over time, it is preferred to use salt-forming dyes formed between a basic dye and an organic acid, salt-forming dyes formed between an acid dye and a basic dye, and salt-forming dyes formed between an acid dye and an organic amine.

[0034] Examples of pigments include inorganic, organic, and processed pigments, and 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 may be used alone or in combination of two or more.

[0035] The total content of the colorants is preferably 5 to 45% by mass relative to the total amount of the ink composition, because if it is less than 5% by mass, it is difficult to obtain thick handwriting, and if it exceeds 45% by mass, it is likely to affect the solubility in the ink. Taking this into consideration, a content of 7 to 35% by mass is more preferable, and even more preferably 10 to 30% by mass.

[0036] (pseudoplasticity imparting agent) In the present invention, it is also preferable that the composition contains a pseudoplasticity-imparting agent. Examples of pseudoplasticity-imparting agents include acrylic acid resins (polyacrylic acid resins), polysaccharides such as xanthan gum, welan gum, succinoglycan, cellulose derivatives, and diutan gum, as well as fatty acid amides and hydrogenated castor oil. Among these, in consideration of stability with salt-forming dyes including polymethine basic dyes and organic solvents, it is preferable that the composition contains an acrylic acid resin, and more preferably a polyacrylic acid resin.

[0037] Acrylic acid resins (polyacrylic acid resins) are preferred because they have affinity with alkylene glycol alkyl ethers and amide solvents, among other organic solvents, and swell and disperse to provide pseudoplasticity and stable thickening properties. Considering the writing feel and writing performance (reduction of smearing and blobbing), crosslinked polyacrylic acid resins are preferred. This is because crosslinked polyacrylic acid resins themselves have a crosslinked structure, which facilitates the formation of a more three-dimensional network structure with alkylene glycol alkyl ethers and amide solvents. Therefore, the formation of a denser crosslinked structure facilitates the impartation of pseudoplasticity, which reduces the ink viscosity during writing and improves the writing feel and writing performance (reduction of smearing and blobbing). Carboxyvinyl polymers are particularly preferred.

[0038] Furthermore, for acrylic acid resins (polyacrylic acid resins), the carboxyl group content in the acrylic acid resin (polyacrylic acid resin) is preferably 40% by mass or more and 80% by mass or less, in order to obtain a stable thickening effect together with organic solvents. Even more preferably, it is 50% by mass or more and 70% by mass or less. In particular, when alkylene glycol alkyl ethers or amide solvents are used, polyacrylic acid resins with a carboxyl group content of 55% by mass or more and 65% by mass or less are preferred, as they have excellent swelling and dispersibility and impart pseudoplasticity, thereby lowering the ink viscosity during writing and improving the writing feel. Furthermore, alkylene glycol monoalkyl ethers and β-alkoxypropionamides are even more preferred.

[0039] Furthermore, the bulk density (g / ml) of the acrylic acid resin (polyacrylic acid resin) is preferably 0.5 (g / ml) or less. This is because the effects of the present invention are more readily exhibited by having excellent swelling and dispersibility in organic solvents and water, and from a more particular perspective, it is preferably 0.3 (g / ml) or less. On the other hand, if the bulk density (g / ml) of the acrylic acid resin (polyacrylic acid resin) is less than 0.01 (g / ml), swelling and dispersion are difficult, and the acrylic acid resin (polyacrylic acid resin) is more likely to aggregate. For this reason, it is preferably 0.01 (g / ml) or more, and from a more particular perspective, it is preferably 0.1 (g / ml) or more. The bulk density can be measured, for example, by a bulk density measuring device (Scott volume meter, manufactured by Tsutsui Scientific Instruments Co., Ltd.).

[0040] If the content of the acrylic acid resin (polyacrylic acid resin) is less than 0.1% by mass relative to the total amount of the ink composition, the swelling property is insufficient and pseudoplasticity is difficult to obtain, and if it exceeds 5.0% by mass, the swelling and dispersibility in the ink tends to deteriorate, so the content is preferably 0.1% by mass or more and 5.0% by mass or less relative to the total amount of the ink composition. Even more particularly, the content is preferably 0.3% by mass or more and 3.0% by mass or less, and even more particularly, the content is preferably 0.6% by mass or more and 1.8% by mass or less.

[0041] In the present invention, the blending ratio of the organic solvent to the acrylic acid resin (polyacrylic acid resin) (organic solvent / acrylic acid resin (polyacrylic acid resin)) is preferably 5 to 150 times by mass in consideration of swelling and dispersibility. In consideration of more stable swelling and dispersibility, it is more preferably 10 to 120 times, and from further consideration, it is more preferably 20 to 100 times.

[0042] In the present invention, it is also preferable for the ink to contain water. Although the reason for this is unclear, water has excellent affinity with acrylic acid resins (polyacrylic acid resins), and by further stabilizing the swelling and dispersion with the acrylic acid resins (polyacrylic acid resins), a stable thickening effect is easily obtained. Furthermore, water improves the slipperiness of the ball while improving ink ejection, and is likely to improve writing performance by suppressing bleeding and smearing. Furthermore, water is also preferred because it has excellent affinity with alkylene glycol alkyl ethers or amide solvents and is stable.

[0043] If the water content is less than 0.1% by mass of the total ink composition, it is likely to affect the ball's sliding properties and writing performance, and if it exceeds 30% by mass, it is likely to deteriorate the solubility in the ink, so the water content is preferably 0.1 to 30% by mass of the total ink composition. Furthermore, in consideration of suppressing uneven dots, bleeding, smearing, etc., it is preferably 2 to 20% by mass, and even more preferably 3 to 15% by mass.

[0044] (resin) It is also preferable to use a resin as an ink viscosity modifier or a pigment dispersant. Examples of the resin include polyvinyl butyral resin, ketone resin, polyacetal resin, polyvinyl alcohol resin, terpene resin, alkyd resin, phenoxy resin, and polyvinyl acetate resin.

[0045] If the resin content is less than 0.1% by mass relative to the total amount of the ink composition, it is difficult to obtain the desired effect, and if it exceeds 30% by mass, the solubility in the ink is likely to be poor. Therefore, the resin content is preferably 0.1 to 30% by mass relative to the total amount of the ink composition, and more particularly, 0.1 to 20% by mass is more preferable.

[0046] (surfactant) In the present invention, it is preferable to use a surfactant because improving lubricity improves the writing feel, and furthermore, when the tip end is left in the air and the tip end dries, it suppresses smearing, improving writing performance. This is because the lubricating layer formed by the surfactant facilitates improving lubricity, and further, the surfactant softens the coating formed when the tip end dries, suppressing smearing, and improving writing performance. Examples of surfactants include fatty acids, silicone-based surfactants, fluorine-based surfactants, and phosphate ester-based surfactants. Among these, considering the above effects, it is preferable to use one or more of fatty acids, silicone-based surfactants, and phosphate ester-based surfactants. 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, such as metal, and therefore makes it easy to obtain a lubricating effect.

[0047] Regarding the HLB value of the surfactant, in consideration of the dissolution stability of the salt-forming dye including the polymethine basic dye, the suppression of smearing, and good writing performance (initial writing performance), the HLB value is preferably 5 to 17. In consideration of further dissolution stability, the suppression of smearing, and improved writing performance (initial writing performance), the HLB value is preferably 6 to 14. Furthermore, in consideration of lubricity, the HLB value is preferably 12 or less, and an HLB value of 6 to 12 is preferable. The HLB value used in the present invention can be determined by the Griffin method, Kawakami method, etc. In particular, in retractable writing implements such as knock-type writing implements and rotary-extending writing implements, unlike cap-type writing implements, the pen tip is always exposed to the outside, so it is easy to affect the writing performance when the writing tip is dry, so it is more preferable to use a surfactant with the above HLB value.In particular, when used in a ballpoint pen, it is easy to affect the writing performance when the ballpoint pen tip is dry, so it is effective and preferable.

[0048] (surfactant) In the present invention, it is preferable to use a surfactant because improving lubricity improves the writing feel and also suppresses smearing when the tip of the tip is left in the air and dries, thereby improving writing performance. This is because the lubricating layer formed by the surfactant facilitates improving lubricity, and furthermore, it can soften the coating formed by the surfactant, suppressing smearing and improving writing performance. Examples of surfactants include fatty acids, silicone surfactants, fluorine surfactants, and phosphate ester surfactants. Among these, considering the above effects, it is preferable to use one or more of fatty acids, silicone surfactants, and phosphate ester surfactants. 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, such as metal, and therefore makes it easy to obtain a lubricating effect.

[0049] Regarding the HLB value of the surfactant, in order to improve the dissolution stability of the salt-forming dye containing the polymethine basic dye and the writing performance (initial writing performance) that suppresses smearing, the HLB value is preferably 5 to 17. In order to further improve the lubricity and the writing performance (initial writing performance) that suppresses smearing, the HLB value is preferably 6 to 14. Furthermore, in order to consider lubricity, the HLB value is preferably 12 or less, and an HLB value of 6 to 12 is preferable. 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-type writing instruments, the pen tip is always exposed to the outside, unlike cap-type writing instruments, and therefore the writing performance is easily affected when the writing tip dries, so it is more preferable to use a surfactant with the above HLB value.

[0050] 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-based surfactants such as perfluorobutyl sulfonate, perfluorogroup-containing carboxylate, perfluorogroup-containing phosphate, perfluorogroup-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.

[0051] The content of the surfactant is more preferably 0.1 to 5.0% by mass of the total amount of the ink composition. This is because if it is less than 0.1% by mass, it tends to be difficult to obtain the desired lubricity, and if it exceeds 5.0% by mass, the ink tends to become unstable over time. Taking these tendencies into consideration, the content is preferably 0.3 to 3.0% by mass of the total amount of the ink composition, and even more preferably 0.5 to 3.0% by mass.

[0052] (organic amine) In the present invention, the use of an organic amine is preferred because neutralizing and stabilizing the acrylic acid resin with the organic amine allows for sufficient swelling and dispersion, making it easier to achieve a stable thickening effect. Furthermore, even when a phosphate ester surfactant is used, neutralizing and stabilizing the ink makes it easier to improve the writing feel and writing performance, making it more preferable. Examples of organic amines include amines containing ethylene oxide, such as oxyethylene alkylamines and polyoxyethylene alkylamines; alkylamines, such as laurylamine and stearylamine; aliphatic amines, such as dimethyl alkylamines, distearylamine, dimethyl laurylamine, dimethyl stearylamine, and dimethyl octylamine; and alkanolamines, such as diethanolamine and triethanolamine. Among these, amines containing ethylene oxide are preferred in terms of stability with the acrylic acid resin.

[0053] 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 resin and stabilizing the swelling and dispersion with the organic solvent. In consideration of further stabilizing the neutralization and improving the swelling and dispersion properties, the HLB value is preferably 6 to 17, and further considering this, the HLB value is preferably 7 to 16.

[0054] The content of the organic amine 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 resin and the surfactant, and further taking into consideration the neutralization with the surfactant, it is preferably 0.1 to 5 mass%, and more preferably 0.5 to 3 mass%.

[0055] The content of the organic amine 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 resin and the surfactant, and further taking into consideration the neutralization with the surfactant, it is preferably 0.1 to 5 mass%, and more preferably 0.5 to 3 mass%.

[0056] In addition, as viscosity adjusters, pseudoplasticity imparting agents such as fatty acid amides and hydrogenated castor oil, colorant stabilizers, spinnability imparting agents, plasticizers, chelating agents, etc. may be used as appropriate. These may be used alone or in combination of two or more.

[0057] (Example) The present invention will now be described with reference to examples. The oil-based ink composition for writing instruments of Example 1 uses a colorant, an organic solvent, acrylic acid, a phosphate ester surfactant, and an organic amine, which are weighed out in predetermined amounts, heated to 60°C, and then completely dissolved using a Disper stirrer to obtain an oil-based ink composition for writing instruments. The specific blending amounts are as follows:

[0058] Example 1 (ink formulation) Colorant (salt-forming dye of polymethine basic dye and acidic compound) 10.0% by mass Colorant (salt-forming dye of acid dye and basic dye) 10.0% by mass Alkylene glycol alkyl ethers (solubility parameter (SP value): 10.5 (cal / cm3) 1 / 2 , boiling point: 249℃) 73.0% by mass Water 3.0% by mass Acrylic acid (crosslinked polyacrylic acid resin) 1.0% by mass Phosphate ester surfactant (HLB value: 10.5) 2.0% by mass Organic amine (HLB value: 15.4) 1.0% by mass

[0059] Examples 2 to 15 As shown in Table 1, oil-based ink compositions for writing instruments of Examples 2 to 15 were obtained in the same manner as in Example 1, except that the ink components were changed. The evaluation results are shown in the table.

[0060] Comparative Examples 1-2 As shown in the table, oil-based ink compositions for writing instruments of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the ink components were changed. The evaluation results are shown in the table. [Table 1] [Table 2]

[0061] Testing and Evaluation The oil-based ink compositions (0.4 g) for writing instruments prepared in Examples 1 to 15 and Comparative Examples 1 and 2 were filled into oil-based ballpoint pen refills equipped with a stainless steel ballpoint pen tip (having a coil spring inside the tip that presses the ball directly against the inner wall of the tip edge) that rotatably holds a ball with a ball diameter of φ0.7 mm in an ink reservoir, to prepare oil-based ballpoint pens. The following tests and evaluations were carried out using JIS P3201 writing paper as the test paper.

[0062] Ink solubility test: After one week at 30°C and 85% humidity, the ink was observed under a microscope and handwritten on, and the handwriting was observed. ◎ The dye is soluble and stable, and no color separation is observed in the writing. ×: Color separation is evident throughout the handwriting, causing practical problems

[0063] Color development test: Handwriting was carried out and the handwriting was observed. ◎ Vivid handwriting and good color development △: The color development of the handwriting is slightly inferior, but there is no problem in practical use. ×: Poor color development of handwriting, causing practical problems

[0064] Writability test (smudges, smudges): The handwriting was observed after a 100m writing test using a running test machine with a load of 200gf, a writing angle of 70°, and a speed of 4m / min. ◎ No or minimal smudges or blemishes in the handwriting ○: There are some smudges and blemishes in the handwriting, but it is not a problem for practical use. △: The handwriting is smudged or blurred, affecting its practical use. ×...Handwriting is smudged and has many blemishes

[0065] In Examples 1 to 15, good performance was obtained in the ink solubility test, color development test, and writing test (fading and smearing).

[0066] In Comparative Examples 1 and 2, since no salt-forming dye containing a polymethine basic dye was used, the solubility stability of the dye was poor, the color of the handwriting separated, and the color development was poor.

[0067] In addition, in this example, for convenience, an oil-based ballpoint pen is exemplified in which an oil-based ballpoint pen refill in which an oil-based ink composition for a writing instrument is directly contained in the barrel, but the writing instrument of the present invention may also be a writing instrument in the form of a direct-fill type ballpoint pen, marking pen, or felt-tip pen in which the barrel serves as an ink storage tube and the ink composition for a writing instrument is directly contained in the barrel. 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]

[0068] The present invention can be used as a writing instrument, and more specifically, can be widely used as a ballpoint pen, such as a cap-type or retractable writing instrument.

Claims

1. An oil-based ink composition for a writing instrument, comprising a salt-forming dye including a polymethine basic dye and an organic solvent.

2. 2. The oil-based ink composition for a writing instrument according to claim 1, wherein the organic solvent is selected from the group consisting of alkylene glycol alkyl ethers, amide solvents, and alkylene oxide derivatives of glycerin.

3. 3. The oil-based ink composition for a writing instrument according to claim 1, wherein the salt-forming dye is a salt-forming dye of a polymethine basic dye and an acidic compound.

4. 2. The oil-based ink composition for a writing instrument according to claim 1, wherein the acidic compound is an organic acid.

5. 3. The oil-based ink composition for a writing instrument according to claim 1, wherein the oil-based ink composition for a writing instrument contains an acrylic acid resin.

6. A writing instrument containing the oil-based ink composition for writing instruments according to claim 1 or 2.

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