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

Abstract

To provide an oil-based ink composition for writing instruments that contains a colorant, an alkylene glycol alkyl ether solvent, and a nonionic surfactant, having excellent initial writing performance, ink stability over time, and writing feels, and a writing instrument including the same.SOLUTION: An oil-based ink composition for writing instruments contains a colorant, an alkylene glycol alkyl ether solvent, and a nonionic surfactant.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] In an oil-based ink composition for a writing instrument, if the tip end is left in the atmosphere, the solvent in the ink evaporates, and when the colorant, resin, etc. dry and solidify, there is a drawback in that the handwriting becomes smudged when starting to write when the ink dries up.

[0003] In order to improve the writing performance during this drying-up period, the use of various solvents and additives has been investigated. For example, JP-A-6-247093 (1994) discloses an "oil-based ballpoint pen" as a main solvent containing a non-volatile organic solvent with a vapor pressure of 0.005 to 0.5 mmHg (20°C), JP-A-7-196971 (1995) discloses an "ink composition for an oil-based ballpoint pen" as a main solvent containing polyethylene glycol with a specific molecular weight of 200 to 4,000,000, and JP-A-2008-88264 (1998) discloses an "oil-based ink composition for a ballpoint pen" as a main solvent containing at least deca-macadamia nut oil fatty acid decaglyceryl and a polyoxyethylene alkyl ether whose alkyl group has 16 or more carbon atoms and is solid at room temperature.

[0004] However, in Patent Document 1, when a non-volatile organic solvent with a vapor pressure of 0.005 to 0.5 mmHg (20°C) is used as the organic solvent, it is effective in preventing the ink from drying out completely, but the ink does not dry out easily, and the ink is not able to satisfy the writing performance when it dries up.

[0005] Furthermore, Patent Document 2 discloses that when polyethylene glycol of a specific molecular weight is added as an additive, a resin film is formed at the tip of the tip, which prevents further drying of the tip and prevents the ink inside the tip from thickening, thereby improving writing performance to a certain extent; however, because the resin film is hard, smearing of handwriting occurs when writing after drying up, and sufficient writing performance cannot be achieved.

[0006] In addition, in Patent Document 3, by using a combination of deca-macadamia nut oil fatty acid decaglyceryl and polyoxyethylene alkyl ether, it is possible to improve writing performance to a certain extent, but the lubricity is insufficient and the writing feel is inferior. Furthermore, because a special surfactant is used, depending on the selection of colorants, organic solvents, other surfactants, etc., the stability of the ink over time can be affected, and if the ink is incompatible with dyes or other surfactants, precipitates will occur, causing poor writing, and there is room for improvement. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] "Unexamined Japanese Patent Publication No. 6-247093" [Patent Document 2] "Unexamined Japanese Patent Publication No. 7-196971" [Patent Document 3] "JP 2008-88264 A" [Patent Document 4] "JP 2007-176995 A" Summary of the Invention [Problem to be solved by the invention]

[0008] There is a need for an oil-based ink composition for a writing instrument that satisfies the initial writing performance upon drying up, the ink stability over time, and the writing feel, which were not satisfied by the above Patent Documents 1 to 4. This is particularly important when using a retractable writing instrument (oil-based ballpoint pen) such as a knock-type writing instrument (oil-based ballpoint pen) or a rotary-type writing instrument (oil-based ballpoint pen), as the initial writing performance is likely to be affected.

[0009] An object of the present invention is to provide an oil-based ink composition for a writing instrument which has good writing performance, ink stability over time, and writing feel, and a writing instrument using the same. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention "1. An oil-based ink composition for a writing instrument, comprising a colorant, an alkylene glycol alkyl ether solvent, and a nonionic surfactant. 2. The oil-based ink composition for a writing instrument according to item 1, wherein the alkylene glycol moiety of the alkylene glycol alkyl ether solvent has 2 to 8 carbon atoms. 3. The oil-based ink composition for a writing instrument according to item 1 or 2, wherein the alkyl ether moiety of the alkylene glycol alkyl ether solvent has 1 to 8 carbon atoms. 4. An oil-based ink composition for a writing instrument according to any one of items 1 to 3, characterized in that the content of the alkylene glycol alkyl ether solvent is 50% or more of the total solvent content in the oil-based ink composition for a writing instrument. 5. The oil-based ink composition for a writing instrument according to any one of items 1 to 4, wherein the HLB value of the nonionic surfactant is 14 or less. 6. An oil-based ink composition for a writing instrument according to any one of items 1 to 5, characterized in that the nonionic surfactant is one or more selected from fatty acid esters, polyalkylene alkyl ethers, polyoxyethylene alkylamines, alkyl alkanolamides, and alkyl imidazolines. 7. The oil-based ink composition for a writing instrument according to any one of items 1 to 6, wherein the colorant is a salt-forming dye. 8. A writing instrument containing the oil-based ink composition for a writing instrument according to any one of items 1 to 7. 9. An oil-based ballpoint pen having a ballpoint pen tip that rotatably holds a ball at the tip of an ink reservoir, and containing the oil-based ink composition for a writing instrument described in any one of items 1 to 8 inside the ink reservoir. " [Effects of the Invention]

[0011] The present invention has made it possible to obtain an oil-based ink composition for a writing instrument, which contains an alkylene glycol alkyl ether solvent and a nonionic surfactant, and thereby improves writing performance by forming a coating that is easy to peel off, and which is less likely to exhibit ionic properties, thereby providing excellent ink stability over time.At the same time, the writing resistance (ball rotation resistance) at the writing tip during writing (when the ball is rotating) is reduced, thereby providing a good writing feel, and a writing instrument using the same. 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 feature of the present invention is an oil-based ink composition for a writing instrument, which comprises an alkylene glycol alkyl ether solvent and a nonionic surfactant. This is because, when the tip end dries, the coating formed at the tip end by the alkylene glycol alkyl ether solvent and the nonionic surfactant contained in the ink is a stable, uniform, and soft coating, which peels off easily, improving writing performance. At the same time, since the coating is soft during writing (when the ball rotates), the writing resistance (ball rotation resistance) at the writing tip can be reduced, resulting in a good writing feel. In particular, in the case of a ballpoint pen, this is effective because it easily adheres to the metal surface in a ballpoint pen tip made of metal, facilitating the formation of a lubricating layer and improving the writing feel. Furthermore, nonionic surfactants are less likely to exhibit ionic properties, are less likely to cause precipitation due to other components in the ink, and can improve the ink stability over time. Therefore, as described above, it is possible to improve the initial writing performance, ink stability over time, and writing feel.

[0014] (nonionic surfactant) With nonionic surfactants, the coating formed on the writing tip by the components (colorants, resins, etc.) contained in the ink composition is a uniform, soft coating that peels off easily, improving writing performance, maintaining lubricity and improving the writing feel, allowing the ink to be ejected smoothly, and increasing ink consumption tends to favorably improve the robustness of the handwriting (water resistance, alcohol resistance, light resistance). Furthermore, because nonionic surfactants are nonionic, they are less likely to produce precipitates due to the components (colorants, resins, etc.) contained in the ink composition, which improves the ink's stability over time.

[0015] With regard to nonionic surfactants, in consideration of ink stability over time, the HLB value is preferably 16 or less, more preferably 1 to 14, and particularly preferably 4 to 10. In consideration of improving initial writing performance and writing feel, the HLB value is preferably 10 or less, more preferably 6 or less. In consideration of achieving a good balance between ink stability over time and initial writing performance, the HLB value is preferably 1 to 10, and more preferably 4 to 10. The HLB value can be determined by the Griffin method or the like.

[0016] Unlike cap-type writing instruments, retractable writing instruments, such as knock-type writing instruments and rotary-type writing instruments, have a pen tip that is always exposed to the outside. In such cases, the writing tip is prone to drying out. Surfactants with the above HLB values ​​can also alleviate this problem, so their use is more preferable.

[0017] Nonionic surfactants include fatty acid esters, polyalkylene alkyl ethers, polyoxyethylene alkylamines, alkylimidazolines, alkylalkanolamides, oxyethyleneoxypropylene block copolymers, and surfactants with acetylene bonds. Among these, considering compatibility with alkylene glycol alkyl ether solvents and the above-mentioned initial writing performance, writing feel, and stability over time, it is preferable to select one or more from fatty acid esters, polyalkylene alkyl ethers, polyoxyethylene alkylamines, alkylimidazolines, and alkylalkanolamides. In particular, considering improving initial writing performance, it is preferable to use fatty acid esters. These surfactants may be used alone or in combination of two or more. Considering the solubility in alkylene glycol alkyl ether solvents described below, the above-mentioned nonionic surfactants have a solubility parameter (SP value) of 9 to 15 (cal / cm 3 ) 1 / 2It is preferable because it is easy to dissolve and stabilize in the alkylene glycol alkyl ether solvent, and it is easy to improve the writing performance and writing feel. 3 ) 1 / 2 Further, if considered, the solubility parameter (SP value) is preferably 9 to 12 (cal / cm 3 ) 1 / 2 It is preferable that the temperature is 10 to 12 (cal / cm 3 ) 1 / 2 It is preferable that:

[0018] Examples of fatty acid esters include sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid esters, sucrose fatty acid esters, glycerin fatty acid esters, polyglycerin fatty acid esters, polyoxyethylene fatty acid esters, etc. Among these, considering that writing performance can be easily improved, it is preferable to select one or more from sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, glycerin fatty acid esters, and sucrose fatty acid esters, and furthermore, it is preferable to use sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and sucrose fatty acid esters, which have a structure with a cyclic skeleton.Furthermore, fatty acid esters having multiple hydroxyl groups can appropriately retain moisture in the coating formed on the writing tip, so it is preferable to select one or more from sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and sucrose fatty acid esters.

[0019] Furthermore, taking into consideration the writing performance, it is preferable that the alkyl group of fatty acid esters such as sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and sucrose fatty acid esters contain 1 to 20 carbon atoms, and more particularly, it is preferable that the alkyl group of sorbitan fatty acid esters contain 10 to 20 carbon atoms, and more preferably 12 to 18 carbon atoms.

[0020] Specific examples of sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters include sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan monococoate, sorbitan dilaurate, sorbitan distearate, sorbitan dioleate, sorbitan trioleate, sorbitan tristearate, and composites thereof; and polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tristearate, and composites thereof. Specific examples of sucrose fatty acid esters include sucrose laurate, sucrose myristate, sucrose palmitate, sucrose stearate, sucrose oleate, sucrose linoleate, sucrose linolenate, sucrose behenate, sucrose erucate, etc. Polyglycerol fatty acid esters are esters of polyglycerol and fatty acids, and specific examples of the fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, eicosanoic acid, oleic acid, etc.

[0021] The content of the nonionic surfactant is more preferably 0.1 to 15% by mass of 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 writing performance and writing feel, and if it exceeds 15% by mass, the ink tends to become unstable over time. In consideration of this tendency, the content is preferably 0.5 to 10% by mass, and most preferably 0.5 to 5% by mass, of the total amount of the ink composition.

[0022] (Alkylene glycol alkyl ether solvent) The alkylene glycol alkyl ether solvent has good dissolution stability with the nonionic surfactant, and the coating formed is a stable, uniform, soft coating that peels off easily, improving writing performance. Furthermore, the softness of the coating makes it possible to improve the writing feel.

[0023] Regarding the number of carbon atoms in the alkylene glycol moiety of the alkylene glycol alkyl ether solvent, in consideration of easy dissolution stability with nonionic surfactants and colorants and ink stability over time, the number of carbon atoms is preferably 2 to 10, more preferably 2 to 8, and more preferably 2 to 6. Furthermore, in consideration of good compatibility with nonionic surfactants and easy improvement in writing performance and writing feel, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, and even more preferably 4 to 6. Among these, in consideration of solubility in alkylene glycol alkyl ether solvents, ink stability over time, initial writing performance, and writing feel, it is preferable to select from among triethylene glycol monoalkyl ether solvents, solvents having a butylene glycol monoalkyl ether structure, and dipropylene glycol monoalkyl ether, and from further consideration, triethylene glycol monoalkyl ether solvents and solvents having a butylene glycol monoalkyl ether structure are preferred, with triethylene glycol monoalkyl ether solvents being even more preferred.

[0024] Regarding the number of carbon atoms in the alkyl ether moiety of the alkylene glycol alkyl ether solvent, in consideration of the ease of dissolution stability with nonionic surfactants and colorants and the ink stability over time, the number of carbon atoms is preferably 1 to 8, more preferably 3 to 6, and more preferably 1 to 3. Furthermore, in consideration of the ease of compatibility with surfactants described below and the ease of improving the writing performance and writing feel, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, and even more preferably 1 to 3. Among these, taking into consideration the solubility in alkylene glycol alkyl ether solvents, and the ink stability over time, writing performance, and writing feel, alkylene glycol monomethyl ether solvents and alkylene glycol monobutyl ether solvents are preferred, and from these considerations, alkylene glycol monomethyl ether solvents are more preferred.

[0025] In addition, the solubility parameter (SP value) of alkylene glycol alkyl ether solvents is 9 to 15 (cal / cm 3 ) 1 / 2 This is to improve the dissolution stability with the nonionic surfactant and colorant and to obtain the effects of the present invention, and from further consideration, the solubility parameter (SP value) is preferably 9 to 13 (cal / cm 3 ) 1 / 2 Further, if considered, the solubility parameter (SP value) is preferably 9 to 12 (cal / cm 3 ) 1 / 2 It is preferable that the temperature is 10 to 12 (cal / cm 3 ) 1 / 2 It is preferable that: The solubility parameter (SP value) of a solvent in the present 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), and this value was used. The unit is (cal / cm 3 ) 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).

[0026] Furthermore, the boiling point of the alkylene glycol alkyl ether solvent is preferably 170°C or higher. This is because if the boiling point is lower than 170°C, the solvent will easily evaporate, which will likely affect the ink's stability over time and increase the ink's viscosity, so from a more careful consideration, a boiling point of 220°C or higher is preferable. On the other hand, if the boiling point is higher than 300°C, it will likely affect the drying properties of the handwriting, so a boiling point of 300°C or lower is preferable, and from a more careful consideration, a boiling point of 280°C or lower is more preferable.

[0027] Examples of alkylene glycol monoalkyl ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, those having a butylene glycol monomethyl ether structure, those having a butylene glycol monoethyl ether structure, etc. These may be used alone or in combination of two or more. Examples of alkylene glycol dialkyl ethers include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, those having a dibutylene glycol dimethyl ether structure, those having a dibutylene glycol diethyl ether structure, etc. These may be used alone or in combination of two or more.

[0028] The content of the alkylene glycol alkyl ether solvent is preferably 50% or more of the total solvent content in the oil-based ink composition for writing instruments, and is used as the main solvent. This is because it is more likely to be dissolved stably with the nonionic surfactant and colorant, and the effects of the present invention are more easily exhibited. Taking the above into consideration, the content of the alkylene glycol alkyl ethers is preferably 70% or more, and more preferably 90% or more of the total solvent content.

[0029] Furthermore, in consideration of improving solubility, handwriting drying properties, bleeding, etc., the content of the alkylene glycol alkyl ether solvent is preferably 10 to 70 mass % and more preferably 20 to 60 mass % relative to the total amount of the ink composition.

[0030] (coloring agent) In the present invention, the colorant may be appropriately selected from dyes, pigments, etc., and may 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 from a direct dye and an amine, salt-forming dyes formed from an acid dye and a basic dye, salt-forming dyes formed from an organic acid and a basic dye, and salt-forming dyes formed from an acid dye and an organic amine. These dyes may be used alone or in combination of two or more. As the dye, it is preferable to use a salt-forming dye, which is likely to have solubility stability in alkylene glycol alkyl ether solvents and nonionic surfactants and which makes it easier to obtain the effects of the present invention. Furthermore, in consideration of maintaining stability over time due to the stable salt-forming bond, it is preferable to select one or more from salt-forming dyes of direct dyes and amines, salt-forming dyes of basic dyes and organic acids, salt-forming dyes of acid dyes and basic dyes, and salt-forming dyes of acid dyes and organic amines. In consideration of the ink stability over time, it is preferable to use a salt-forming dye of direct dyes and amines. From this perspective, it is preferable to use a salt-forming bond of Direct Black and amines, or a salt-forming dye of Direct Blue and amines, with a salt-forming bond of Direct Black and amines being more preferable. Furthermore, the salt-forming dye contains a compound having an aromatic ring, which provides a lubricating effect at the writing tip, allowing the ink to be ejected smoothly. This increases the amount of ink consumed, which is advantageous for the fastness of the handwriting, and also prevents the handwriting from fading, making it easy to improve the writing performance, which is particularly effective when used in a ballpoint pen.

[0031] As for salt-forming dyes formed from direct dyes and amines, examples of Direct Black include Direct Black 17, 19, 22, 32, 38, 51, 71, 154, 168, and 195, and Direct Blue 86, 87, and 199. However, in consideration of dissolution stability with alkylene glycol alkyl ether solvents and nonionic surfactants, water resistance, alcohol resistance, and light fastness (fastness), it is preferable to use an azo dye (-N=N-) or a metal-containing dye, and Direct Black 19, Direct Black 154, Direct Blue 86, and Direct Blue 87 are preferred. Furthermore, in consideration of salt-forming stability with amines and maintaining stable water resistance, alcohol resistance, and light fastness (fastness), Direct Black 19 and Direct Blue 86, which contain a large amount of (-N=N-), are preferred.

[0032] As the amine of the salt-forming dye, organic amines such as aromatic amines, aliphatic amines, alicyclic amines, alkoxyalkylamines, and amines of guanidine derivatives are preferred in consideration of the stability of the salt-forming bond. The above-mentioned salt-forming dyes have a solubility parameter (SP value) of 9 to 15 (cal / cm 3 ) 1 / 2 It is preferable because it is easy to dissolve and stabilize in the alkylene glycol alkyl ether solvent, and it is easy to improve the writing performance and writing feel. 3 ) 1 / 2 Further, if considered, the solubility parameter (SP value) is preferably 9 to 12 (cal / cm 3 ) 1 / 2 It is preferable that the temperature is 10 to 12 (cal / cm 3 ) 1 / 2 It is preferable that:

[0033] 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.

[0034] It is preferable to use a pigment as the colorant. In the case of a ballpoint pen, the use of a pigment allows the pigment particles to enter the gap between the ball and the tip body, making it easier for the pigment to act like a bearing, and by suppressing metal contact, it is possible to improve lubricity, improve the writing feel, and suppress wear on the ball seat.

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

[0036] (resin) In order to further improve ink leakage suppression, it is preferable to use a resin as an ink viscosity modifier. Examples of resins include polyvinyl butyral resin, ketone resin, polyacetal resin, polyvinyl alcohol resin, cellulose resin, terpene resin, alkyd resin, phenoxy resin, and polyvinyl acetate resin. Among these, polyvinyl butyral resin or ketone resin is preferable, considering stability with colorants, alkylene glycol alkyl ether solvents, and nonionic surfactants. Furthermore, the resin film formed in the handwriting is preferable because it easily imparts fastness (water resistance, alcohol resistance, and light resistance), easily blocks ultraviolet light, and is particularly easy to impart light resistance.

[0037] Polyvinyl butyral resins are easy to form a lubricating layer that provides a higher lubricating effect. This is because the use of polyvinyl butyral resins allows a constantly elastic ink layer to be formed between the ball and the ball seat, reducing direct contact and improving the writing experience. This allows for smooth ink ejection, and by increasing ink consumption, the durability of handwriting tends to be advantageous. Furthermore, the use of polyvinyl butyral resins is preferable because the coating formed can more easily improve ink leakage. Furthermore, when a pigment is used as a colorant, polyvinyl butyral resins are also preferable because they provide a pigment dispersion effect. Here, the polyvinyl butyral resin is obtained by reacting polyvinyl alcohol (PVA) with butyraldehyde (BA), and has a structure having butyral groups, acetyl groups, and hydroxyl groups.

[0038] Furthermore, it is preferable that the polyvinyl butyral resin has a hydroxyl group content of 25 mol% or more. This is because polyvinyl butyral resins with a hydroxyl group content of less than 25 mol% are insufficient in solubility in alkylene glycol alkyl ether solvents, making it difficult to achieve the effects of the present invention. Furthermore, considering the influence of moisture absorption on writing performance, it is preferable to use a polyvinyl butyral resin with a hydroxyl group content of 25 mol% or more. From a more specific perspective, polyvinyl butyral resins with a hydroxyl group content of 30 mol% or more are preferred, as they tend to improve the writing feel, allow smooth ink ejection, and increase ink consumption, which is advantageous for the robustness of handwriting. Furthermore, polyvinyl butyral resins with a hydroxyl group content of more than 40 mol% tend to absorb a large amount of moisture, which can affect the stability over time of the ink components. Therefore, polyvinyl butyral resins with a hydroxyl group content of 40 mol% or less are preferred. Therefore, a polyvinyl butyral resin having a hydroxyl group content of 30 to 40 mol % is preferred, and a hydroxyl group content of 30 to 36 mol % is more preferred. The amount of hydroxyl groups (mol %) of the polyvinyl butyral resin refers to the content of hydroxyl groups (mol %) relative to the total molar amount of butyral groups (mol %), acetyl groups (mol %), and hydroxyl groups (mol %).

[0039] Furthermore, a stringiness imparting agent may be used as the resin as appropriate. In particular, when polyvinylpyrrolidone resin is contained, it is compatible with alkylene glycol alkyl ether solvents, nonionic surfactants, and salt-forming dyes, and is therefore preferred because it enhances ink binding and helps to prevent excess ink from being generated at the tip end.

[0040] If the content of the resin is less than 1% by mass of the total ink composition, the desired lubricity and ink leakage prevention performance tend to be inferior, and if it exceeds 40% by mass, the solubility in the ink tends to be inferior, so it is preferably 1 to 40% by mass of the total ink composition. Furthermore, from consideration, 3% by mass or more is preferable, and if it exceeds 30% by mass, the ink viscosity tends to become too high, affecting the writing feel, so 3 to 30% by mass is preferable, and from consideration more, 5 to 25% by mass is preferable.

[0041] In the present invention, considering the stability of the ink components in the ink, it is preferable to use an organic amine (excluding the amine of the salt-forming dye). Considering the stability of the organic amine with the alkylene glycol alkyl ether solvent, nonionic surfactant, and salt-forming dye, it is preferable to use a secondary amine or a tertiary amine. This is because, in terms of reactivity in oil-based inks, primary amines are the most reactive, followed by secondary amines and tertiary amines, which tend to react more easily with nonionic surfactants, salt-forming dyes, and other components, and thus affect the ink's stability over time. Therefore, it is preferable to use a secondary amine or a tertiary amine, and from further consideration, it is preferable to use a tertiary amine.

[0042] Examples of organic amines include amines having 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. Of these, amines having ethylene oxide, dimethyl alkylamines and alkanolamines are preferred, taking stability in the ink into consideration.

[0043] Furthermore, considering the stability with the alkylene glycol alkyl ether solvent, nonionic surfactant, salt-forming dye, and other components, the total amine value of the organic amine is preferably 70 to 300 (mgKOH / g). This is because if it exceeds 300 (mgKOH / g), the organic amine is highly reactive and easily reacts with the above components, resulting in poor ink stability over time. Furthermore, if the total amine value is less than 70 (mgKOH / g), the stability of the nonionic surfactant is likely to be affected. Considering the stability with the above components, a range of 100 to 300 (mgKOH / g) is preferred, and considering stability even more, a range of 150 to 300 (mgKOH / g) is preferred. The total amine value indicates the total amount of primary, secondary, and tertiary amines, and is expressed as the number of milligrams of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize 1 g of sample.

[0044] In addition, examples of organic solvents other than alkylene glycol alkyl ether solvents include polyhydric alcohol solvents such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, and glycerin; aromatic alcohols such as benzyl alcohol; and aliphatic alcohol solvents such as methanol, ethanol, 1-propanol, 2-propanol, isobutanol, and t-butanol.

[0045] Furthermore, in consideration of improving solubility, handwriting drying properties, bleeding, etc., the content of the organic solvent is preferably 10 to 80 mass %, more preferably 30 to 80 mass %, based on the total amount of the ink composition.

[0046] In addition, surfactants other than nonionic surfactants may be used in combination with fatty acids, silicone surfactants, fluorine surfactants, phosphate ester surfactants, surfactants having an acetylene bond, and the like.

[0047] In addition, as viscosity modifiers, pseudoplasticity imparting agents such as fatty acid amides and hydrogenated castor oil, colorant stabilizers, plasticizers, chelating agents, water, etc. may be used as appropriate. These may be used alone or in combination of two or more.

[0048] The viscosity of the oil-based ink composition for writing implements of the present invention is not particularly limited, but if the viscosity is too high, the writing performance, writing feel, and ink followability tend to deteriorate. -1 The ink viscosity (at rest) is preferably 30,000 mPa·s or less. Furthermore, since an excessively low viscosity makes it difficult to prevent ink leakage, the viscosity is preferably 500 mPa·s or more, and more preferably 1,000 mPa·s or more. Considering further improvements in ink leakage prevention, writing feel, ink tracking performance, and initial writing performance, the viscosity of the ink composition is preferably 500 to 25,000 mPa·s, more preferably 1,000 to 25,000 mPa·s, and even more preferably 800 to 25,000 mPa·s. Furthermore, from the viewpoints of initial writing performance and initial writing feel, the viscosity is more preferably 1,000 to 20,000 mPa·s, and even more preferably 2,000 to 20,000 mPa·s.

[0049] (ballpoint pen) Furthermore, for ballpoint pen tips, the amount of movement of the ball in the vertical axis direction of the ballpoint pen tip is preferably 3 to 25 μm. This is because, within the above range, it is easy to maintain good writing performance, such as writing start performance and the prevention of blurring and smearing of handwriting, while producing thick handwriting. Furthermore, by ensuring the ink discharge volume and increasing the ink consumption, thick handwriting can be obtained, which tends to favorably work on the robustness of handwriting. From further consideration, the amount of movement in the vertical axis direction is preferably 5 to 20 μm, and more preferably 7 to 18 μm. In the present invention, the amount of movement of the ball of the ballpoint pen tip in the vertical axis direction is the shape of the ballpoint pen tip of the ballpoint pen in its initial state before writing begins.

[0050] The arithmetic mean roughness (Ra) of the ball surface of a ballpoint pen tip is preferably 0.1 to 12 nm. This is because within this range, writing performance, writing feel, and writing smearing and blobbing can be maintained while producing thick handwriting. Furthermore, ink can be easily spread on the ball surface, allowing for smooth ink ejection. By increasing ink consumption, thick handwriting can be obtained, which favorably contributes to the robustness of the handwriting. An arithmetic mean roughness (Ra) of 0.1 to 10 nm is preferred because it allows ink to be easily spread on the ball surface, and from further considerations, a value of 2 to 8 nm is preferable. Surface roughness can be measured using a Seiko Epson SPI38, 00N model.

[0051] The material used for the balls is not particularly limited, but examples include cemented carbide balls mainly composed of tungsten carbide, metal balls such as stainless steel, ceramic balls such as silicon carbide, silicon nitride, alumina, silica, and zirconia, and ruby ​​balls.

[0052] In addition, materials for ballpoint pen tips include metals such as stainless steel, nickel silver, brass, aluminum bronze, and aluminum, and resins such as polycarbonate, polyacetal, and ABS, but considering wear of the ball seat, stability over time, and cost, it is preferable to use a tip body made of stainless steel.

[0053] (Example) The present invention will now be described with reference to examples. The ink composition for an oil-based ballpoint pen in Example 1 uses a salt-forming dye, an alkylene glycol alkyl ether solvent, a nonionic surfactant, a polyvinyl butyral resin, and a polyvinylpyrrolidone resin, and these are weighed out in predetermined amounts, heated to 60°C, and then completely dissolved using a Disper stirrer to obtain an ink composition for an oil-based ballpoint pen. The specific blending amounts are as follows: The viscosity of the ink in Example 1 was measured using a Brookfield Viscometer RVDVII+Pro CP-52 spindle at a shear rate of 5 seconds at a temperature of 20°C. -1 The ink viscosity was 3300 mPa·s.

[0054] Example 1 (ink formulation) Colorant (Direct Black 19 and amine salt-forming dye) 30.0% by mass Alkylene glycol alkyl ether solvent (solubility parameter (SP value): 10.5 (cal / cm 3 ) 1 / 2 , boiling point: 249℃) 65.2% by mass Nonionic surfactant (sorbitan fatty acid ester) 2.0% by mass Polyvinyl butyral resin 2.5% by mass Polyvinylpyrrolidone resin 0.3% by mass

[0055] Examples 2 to 24 As shown in Table 1, oil-based ink compositions for writing instruments of Examples 2 to 24 were obtained in the same manner as in Example 1, except that the ink components were changed. The table shows the measurement and evaluation results.

[0056] Comparative Examples 1 to 5 As shown in the table, oil-based ink compositions for writing instruments of Comparative Examples 1 to 5 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] [Table 3]

[0057] Testing and Evaluation The oil-based ink compositions (0.4 g) for writing instruments prepared in Examples 1 to 24 and Comparative Examples 1 to 5 were filled into oil-based ballpoint pen refills equipped with ballpoint pen tips (having a coil spring inside the tip that presses the ball directly against the inner wall of the tip end edge, ball longitudinal movement: 10 μm, arithmetic mean roughness (Ra): 3 nm) that rotatably hold 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.

[0058] In addition, in the same manner as in Example 1, in Examples 23 and 24, the temperature was 20°C, the shear rate was 5 sec -1 The ink viscosity was measured at a rotation speed of 2.5 rpm, and was found to be 5000 mPa·s in Example 23 and 10000 mPa·s in Example 24.

[0059] Writing performance test: After handwriting, the pen was left in an environment of 20°C and 65% RH for 24 hours with the tip of the pen protruding. Then, writing was performed under the following conditions in a running test, and the length of the smeared handwriting at the beginning of writing was measured. <Writing conditions> A straight line was written on a running test machine under the following conditions: writing load 200 gf, writing angle 70°, writing speed 4 m / min, and evaluation was performed. The length of the smudged handwriting is less than 1mm. The length of the smudged handwriting is 1mm or more but less than 5mm. The length of the smudged handwriting is 5mm or more but less than 15mm. The length of the smudged handwriting is 15mm or more but less than 30mm...△ The length of the blurred handwriting is 30mm or more... ×

[0060] Ink aging test: After one month in a 50°C environment, the ink inside the tip body was observed under a microscope. No deposits, good condition... A small amount of precipitates occurred... Precipitation occurred, but no practical problems occurred. Deposits may occur, causing blurring or poor writing results.

[0061] Writing feel: Evaluation was carried out by a sensory test using handwriting. Very smooth... Smooth Slightly heavy...△ Heavy items ×

[0062] Water resistance test: After spiral writing on writing paper and drying, the paper was immersed in water for 24 hours and the condition of the writing was observed. The handwriting is good. The handwriting has faded, but is still legible... Handwriting not visible ×

[0063] Alcohol resistance test: After spiral writing on writing paper was allowed to dry, the paper was immersed in ethanol (50% aqueous solution) for 10 minutes and the condition of the writing was observed. The handwriting is good. The handwriting has faded, but is still legible... Handwriting not visible ×

[0064] In Examples 1 to 24, good performance was obtained in the writing performance test, ink stability over time, writing feel, and water resistance and alcohol resistance tests. An oil-based ballpoint pen was created using the oil-based ink of Example 1 in the same manner as in Example 1, except that the ballpoint pen tip specifications were changed to a ball movement distance of 15 μm in the longitudinal direction and an arithmetic mean roughness (Ra) of the ball surface of 6 nm. The same tests and evaluations were carried out, and the results were equivalent to those of Example 1, with good results in all tests.

[0065] In Comparative Examples 1 to 5, the absence of an alkylene glycol alkyl ether solvent and a nonionic surfactant resulted in poor writing performance and poor writing feel. Furthermore, in Comparative Examples 4 and 5, the ink stability over time was poor, and therefore other tests could not be evaluated.

[0066] Furthermore, when using a retractable writing instrument (retractable ballpoint pen) such as a knock-type writing instrument or a rotary-type writing instrument, the writing performance is easily affected by blurred handwriting, so it is effective to use an oil-based ink composition for a writing instrument such as that of the present invention.

[0067] In order to improve writing performance (handwriting smearing) and suppress ink leakage, it is preferable to provide a valve mechanism in which the ball, which is rotatably held at the tip of the ballpoint pen tip, is pressed against the inner wall of the tip edge by a coil spring directly or via a pressing body, creating a gap between the inner wall of the tip edge and the ball due to the pressing force during writing, allowing ink to flow out, and also to close the minute gap at the tip when not in use.

[0068] 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 ink composition for a writing instrument is directly contained in the barrel is stored, 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]

[0069] 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. 1. An oil-based ink composition for a writing instrument, comprising a colorant, an alkylene glycol alkyl ether solvent, and a nonionic surfactant, wherein the colorant is a salt-forming dye formed from a direct dye and an amine, and the alkylene glycol alkyl ether solvent is a triethylene glycol monoalkyl ether solvent.

2. An oil-based ink composition for a writing instrument as described in Claim 1, characterized in that the number of carbon atoms in the alkyl ether portion of the triethylene glycol monoalkyl ether solvent is 1 to 6.

3. 3. The oil-based ink composition for a writing instrument according to claim 1, wherein the content of the triethylene glycol monoalkyl ether solvent is 50% or more of the total solvent content in the oil-based ink composition for a writing instrument.

4. 4. The oil-based ink composition for a writing instrument according to claim 1, wherein the colorant is a salt-forming dye formed by a salt-forming bond between Direct Black and an amine, or a salt-forming dye formed by a salt-forming bond between Direct Blue and an amine.

5. 5. The oil-based ink composition for a writing instrument according to claim 1, wherein the HLB value of the nonionic surfactant is 14 or less.

6. The oil-based ink composition for a writing instrument according to any one of claims 1 to 5, characterized in that the nonionic surfactant is selected from one or more of fatty acid esters, polyalkylene alkyl ethers, polyoxyethylene alkylamines, alkyl alkanolamides, and alkyl imidazolines.

7. A writing instrument containing the oil-based ink composition for a writing instrument according to any one of claims 1 to 6.

8. 8. An oil-based ballpoint pen comprising an ink reservoir having a tip at the tip end thereof, the tip holding a ball in a freely rotatable manner, and the ink reservoir containing the oil-based ink composition for a writing instrument according to claim 1.

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