Oil-based ballpoint pen

Abstract

To provide an oil-based ink composition for writing instruments that has improved lubricity, suppresses the wear of a ball seat and improves its writing feel, and allows easy start of writing, and a writing instrument including the same.SOLUTION: An oil-based ink composition for writing instruments contains a colorant, an organic solvent, and a methyl branched fatty acid .SELECTED DRAWING: Figure 3

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] When writing with a writing instrument, the writing feel of a ballpoint pen or marking pen can be easily affected by the writing resistance between the writing tip and the surface being written on. Ballpoint pens in particular have a configuration in which a ballpoint pen tip is attached to an ink reservoir tube and comprises a metal tip made of stainless steel or the like at the tip and a transfer ball made of metal such as carbide that is held in a ball receiving seat of the metal tip. When writing, the rotation of the ball causes wear to the ball seat, resulting in problems such as skipped lines and smudges in the handwriting and a poor writing feel, leaving room for improvement.

[0003] In order to solve these problems, many oil-based ink compositions for writing instruments have been proposed that use various lubricants to improve lubricity and reduce writing resistance between the writing tip and the surface being written on during writing.

[0004] Oil-based ink compositions using such lubricants are disclosed in JP 5-331403 A, entitled "Oil-based Ballpoint Pen Ink," which uses alkyl β-D-glucosides; JP 2007-176995 A, entitled "Oil-based Ballpoint Pen Ink," which uses N-acylamino acids, N-acylmethyl tauric acid, and N-acylmethyl alanine; JP 2013-151594 A, entitled "Oil-based Ballpoint Pen Ink," which uses polycyclic aromatic compounds; and JP 2014-88486 A, entitled "Oil-based Ballpoint Pen Ink," which uses dialkyl polysulfides as a lubricant. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] "Unexamined Japanese Patent Publication No. 5-331403" [Patent Document 2] "JP 2007-176995 A" [Patent Document 3] "JP 2013-151594 A" [Patent Document 4] "JP 2014-88486 A" Summary of the Invention [Problem to be solved by the invention]

[0006] However, when various lubricants such as those described in Patent Documents 1 to 4 are used, the writing resistance between the writing tip and the surface being written on can be reduced to some extent, but this is not sufficient, and there is room for further improvement. Furthermore, in the case of a ballpoint pen, when a small diameter ball with a ball diameter of 0.5 mm or less is used, the smaller the ball diameter is, the more the ball will rotate when writing the same distance, and with a small diameter ball, a load is applied to the ball seat, which causes severe wear on the ball seat and leads to poor writing, and using a small diameter ball is likely to cause new problems. There is also a need for an oil-based ink composition for a writing instrument that improves the writing performance when the writing tip (tip tip) is left exposed to the atmosphere and the writing tip (tip tip) dries. This is particularly important when using a retractable oil-based writing instrument such as a knock-type oil-based ballpoint pen or a twist-and-pull type oil-based ballpoint pen, as the writing performance is likely to be affected.

[0007] The object of the present invention is to provide an oil-based ink composition for a writing instrument that improves the lubricity of the writing tip, thereby suppressing wear of the ball seat and improving the writing feel, and that has good writing performance, and a writing instrument using the same. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention "1. An oil-based ink composition for a writing instrument, comprising a colorant, an organic solvent, and a methyl-branched fatty acid. 2. The ink composition according to item 1, wherein the content of the methyl-branched fatty acid is 0.1 to 10% by mass based on the total amount of the ink composition. 3. 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 a phosphoric acid ester. 4. An oil-based ink composition for a writing instrument according to any one of items 1 to 3, characterized in that the oil-based ink composition for a writing instrument contains a ketone resin or a polyvinyl butyral resin. 5. The oil-based ink composition for a writing instrument according to any one of items 1 to 4, wherein, when the content of the ketone resin relative to the total amount of the ink composition is C and the content of the polyvinyl butyral resin relative to the total amount of the ink composition is D, the relationship C / D satisfies 0.1≦C / D≦10. 6. The oil-based ink composition for a writing instrument according to any one of items 1 to 5, characterized in that the oil-based ink composition for a writing instrument contains a fatty acid ester. 7. A writing instrument containing the oil-based ink composition for a writing instrument according to any one of items 1 to 6. 8. An oil-based ballpoint pen, characterized in that it has a ballpoint pen tip that rotatably holds a ball at the tip of an ink reservoir, and the oil-based ink composition for a writing instrument described in any one of items 1 to 7 is contained in the ink reservoir. [Effects of the Invention]

[0009] The present invention has made it possible to obtain an oil-based ink composition for a writing instrument, which has good initial writing performance, and a writing instrument using the same, which improves the lubricity of the writing tip, thereby reducing friction and suppressing the writing resistance of the writing tip, maintaining the lubricity of the writing tip (between the ball and the tip body), and suppressing wear of the ball seat, thereby preventing smearing of handwriting and improving the writing feel. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a vertical cross-sectional view showing a ballpoint pen according to a first embodiment. [Figure 2] 1 is a partially omitted longitudinal cross-sectional view of a main part of a ballpoint pen refill according to a first embodiment. [Figure 3] 1 is a partially omitted longitudinal cross-sectional view of a main part showing a ballpoint pen tip of a first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] In this specification, "parts," "%," "ratio," and the like indicating the composition are based on mass unless otherwise specified.

[0012] A feature of the present invention is an oil-based ink composition for a writing instrument that contains a methyl-branched fatty acid. The inclusion of the methyl-branched fatty acid improves lubricity through a lubricating layer formed by the methyl-branched fatty acid, maintains lubricity between the ball and the tip body, suppresses wear of the ball seat, prevents smearing of handwriting, and improves writing feel. Furthermore, when the writing tip (tip tip) is left in the air, it is possible to improve writing performance when the writing tip (tip tip) dries.

[0013] (Methyl-branched fatty acids) The methyl-branched fatty acids used in the present invention improve lubricity, thereby maintaining the lubricity of the writing tip (between the ball and the tip body), suppressing wear of the ball seat, suppressing handwriting smearing, and improving the writing feel. This is because the methyl-branched fatty acids are adsorbed to the metal surface of the writing tip (the ball and tip body of a ballpoint pen tip), suppressing metal contact at the writing tip (between the ball and the tip body), and the friction-reducing effect can suppress the writing resistance of the writing tip. In particular, the presence of methyl-branched fatty acids allows for a bulky structure, increasing the area covering the metal surface and suppressing metal contact between the writing tip (the ball and the tip body). This suppresses wear of the ball seat, suppresses handwriting smearing, and improves the writing feel. Furthermore, it is possible to improve writing performance, which is effective when used in oil-based ballpoint pens. In particular, in the case of ballpoint pens, even when a small diameter ball with a ball diameter of 0.5 mm or less is used, wear on the ball seat is suppressed, blurred handwriting is suppressed, and a good writing feel is maintained. Even when a load is applied locally between the ball and seat as with a small diameter ball, lubrication is easily maintained, which is effective and preferable. It is also effective when the ball diameter is 0.4 mm or less, which is preferable, and it is further effective and preferable when the ball diameter is 0.3 mm or less.

[0014] Regarding methyl-branched fatty acids, in consideration of lubricity, the carbon number of the methyl-branched fatty acid is preferably 10 to 20. This is because a carbon number of 10 or more is an alkyl group length suitable for improving the desired lubricity, and the fatty acid is easily adsorbed to the metal surface of the writing tip (ballpoint pen tip). On the other hand, if the alkyl group has a carbon number of more than 20, the molecules repel each other, which inhibits adsorption to the metal surface and tends to inhibit improvement in lubricity. Furthermore, in consideration of better lubricity, the carbon number of the methyl-branched fatty acid is preferably 16 to 20, and in consideration of further improving wear suppression of the ball seat, the carbon number of the methyl-branched fatty acid is preferably 18 to 20.

[0015] Methyl-branched fatty acids have a chemical structure in which a methyl group branches from the main chain of a methyl-branched fatty acid, and examples thereof include methyl-branched saturated fatty acids and methyl-branched unsaturated fatty acids. However, in consideration of lubricity, methyl-branched saturated fatty acids are preferred. Specific examples of methyl-branched saturated fatty acids include methyl-branched undecanoic acid, methyl-branched dodecanoic acid, methyl-branched tridecanoic acid, methyl-branched tetradecanoic acid, methyl-branched pentadecanoic acid, methyl-branched heptadecanoic acid, methyl-branched octadecanoic acid (methyl-branched stearic acid), methyl-branched nonadecanoic acid, and methyl-branched docosanoic acid. Among these, methyl-branched octadecanoic acid (methyl-branched stearic acid) is preferred in consideration of suppressing wear of the ball seat, preventing blurred handwriting, and improving writing feel, and 16-methyloctadecanoic acid (16-methylstearic acid) is even more preferred. In particular, when the ball diameter is 0.5 mm or less, it is preferable because lubrication is easily maintained even when a load is applied locally between the ball seats, and this is effective. It is also preferable when the ball diameter is 0.4 mm or less, and it is also effective and preferable when the ball diameter is 0.3 mm or less.

[0016] Examples of methyl-branched fatty acids include 10-methylundecanoic acid, 10-methyldodecanoic acid, 12-methyltridecanoic acid, 12-methyltetradecanoic acid, 14-methylpentadecane, 14-methylhexadecane, 16-methylheptadecanoic acid, 16-methyloctadecanoic acid (16-methylstearic acid), 10-methylnonadecanoic acid, 10-methylheptadecanoic acid, 10-methylhexadecanoic acid, and 10-methylpentadecanoic acid.

[0017] If the content of the methyl-branched fatty acid is less than 0.1% by mass, relative to the total amount of the ink composition, the desired lubricating effect may not be obtained, whereas if it exceeds 10% by mass, the ink stability over time may be affected. Therefore, the content is preferably 0.1 to 10% by mass, relative to the total amount of the ink composition, and from the perspective of better lubricity, 0.5 to 10% by mass is preferred, and from the perspective of ink stability over time, 1 to 5% by mass is preferred.

[0018] (phosphate ester) In the present invention, it is preferable to use a phosphate ester in order to improve the lubricity of the writing tip and thereby reduce the writing resistance of the writing tip. Furthermore, in order to further reduce the wear of the ball seat and improve the writing feel, it is preferable to use a phosphate ester. l H 2l+1 O-C2H4O or C m H 2m+1 It is preferable to use a phosphate ester having C (l, m = 1 to 30). This is different from conventional phosphate esters in that l H 2l+1 O-C2H4O (alkoxyethyl group) or C m H 2m+1 By forming a lubricating layer using a phosphoric acid ester having an O (alkoxyl group), it is easy to improve the lubricity of the writing tip, suppress wear on the ball seat, suppress smearing of handwriting, and improve the writing feel, so it is effective when used in oil-based ballpoint pens. Therefore, by using methyl-branched fatty acids and phosphate esters in combination, the lubricating effect of the two lubricating layers formed through their interaction can provide high lubricity that was previously unattainable. l H 2l+1 O-C2H4O or C m H 2m+1 It is preferable to use a phosphate ester having O (l, m = 1 to 30) in combination. Furthermore, when the ball diameter is 0.5 mm or less, even when a load is applied locally between the ball seats, it is effective and preferable because it maintains higher lubrication, and it is also effective and preferable when the ball diameter is 0.4 mm or less, and it is further effective and preferable when the ball diameter is 0.3 mm or less. Furthermore, it is possible to improve the writing performance.

[0019] Regarding the phosphate ester, those represented by the general formulas (Chemical Formula 1) and (Chemical Formula 2) are preferred in view of their stability in ink and their tendency to improve the lubricity of the writing tip. This is because the phosphate esters of the general formulas (Chemical Formula 1) and (Chemical Formula 2) are stable in ink, and the O adjacent to the P in the structures of the general formulas (Chemical Formula 1) and (Chemical Formula 2) is adsorbed to the metallic ballpoint pen tip body or ball, forming C l H 2l+1 O-C2H4O (alkoxyethyl group) and C m H 2m+1 O (alkoxyl group) forms a lubricating layer, improving lubricity and suppressing wear of the ball seat, which helps prevent blurred writing and improves the writing feel. In particular, considering the suppression of wear of the ball seat, C l H 2l+1 It is preferable to use the general formula (Chemical Formula 1) having O-C2H4O (alkoxyethyl group). [ka] [ka]

[0020] In addition, among the phosphate esters such as those represented by the general formulas (Chemical Formula 1) and (Chemical Formula 2), C l H 2l+1 O-C2H4O (alkoxyethyl group), C m H 2m+1 It is preferable that the carbon chain (l, m) of the terminal alkyl group of O (alkoxyl group) is a specific carbon chain (l, m), and the effect of this is presumed as follows. C l H 2l+1 O-C2H4O, C m H 2m+1 The carbon chain (l, m) of the terminal alkyl group of O is preferably 1 to 15. l H 2l+1 O-C2H4O or C m H 2m+1If the carbon chain of the terminal alkyl group of O becomes too long, the writing feel and initial writing performance are good, but wear of the ball seat is difficult to suppress. This is because when the carbon chain (l, m) of the terminal alkyl group exceeds 15, the carbon chains tend to entangle with each other, the carbon chain arrangement becomes random, and the carbon chains are not aligned. This prevents a lubricating layer with sufficient lubrication and makes it difficult to suppress wear of the ball seat. Furthermore, when the carbon chain (l, m) of the terminal alkyl group exceeds 15, the polarity of the terminal alkyl group shifts to the low polarity side, resulting in poor affinity for polar organic solvents, which can easily affect the dissolution stability, especially in glycol ether solvents, and can easily cause problems with dissolution stability in the ink. As a result, metal salt precipitates are easily formed due to the influence of metal ions in the metal tip during long-term storage, which can lead to poor ink stability over time and make it difficult to achieve the lubricating effect of the present invention. Therefore, the carbon chain (l, m) of the terminal alkyl group is preferably 1 to 15, and from a more particular consideration, the carbon chain (l, m) of the terminal alkyl group is preferably 1 to 10, and from a more particular consideration, from the viewpoint of suppressing wear of the ball seat and suppressing blurred writing, the carbon chain (l, m) of the terminal alkyl group is preferably 1 to 5. On the other hand, when the carbon chain length (l, m) of the terminal alkyl group is 3 or less, ball seat wear is effectively suppressed, but the alkyl group does not form a sufficiently thick lubricating layer in the ink, resulting in a lubricating layer that does not provide sufficient cushioning between the ball and the ball seat, which is likely to affect the writing feel, initial writing performance, and ball seat wear suppression. Therefore, using butoxyethyl acid phosphate (l = 4) or butyl acid phosphate (m = 4) in which the terminal alkyl group has a butyl group (terminal alkyl group carbon chain: 4) is preferred, as this tends to suppress ball seat wear and improve writing feel and initial writing performance, and butyl acid phosphate with a butoxyethyl group (C4H9OCH2CHO, terminal alkyl group carbon chain: 4) is particularly preferred. In particular, when the ball diameter is 0.5 mm or less, lubrication is easily maintained even when a load is applied locally between the ball seats, making it effective in suppressing wear of the ball seats and therefore preferable.A ball diameter of 0.4 mm or less is also effective and therefore preferable, and a ball diameter of 0.3 mm or less is also effective and therefore preferable.

[0021] Furthermore, with respect to the phosphate esters of the general formulas (Chemical Formula 1) and (Chemical Formula 2), examples include monoesters of phosphate esters (n=1 in Chemical Formula 1 and Chemical Formula 2), diesters of phosphate esters (n=2 in Chemical Formula 1 and Chemical Formula 2), triesters of phosphate esters (n=3 in Chemical Formula 1 and Chemical Formula 2), and mixtures thereof. Among these, in consideration of suppressing wear of the ball seat and the writing feel, it is preferable to use a mixture of monoesters of phosphate esters (n=1 in Chemical Formula 1 and Chemical Formula 2) and diesters of phosphate esters (n=2 in Chemical Formula 1 and Chemical Formula 2). This is because, in the case of triesters of phosphate esters (n=3 in Chemical Formula 1 and Chemical Formula 2), C l H 2l+1 O-C2H4O (alkoxyethyl group), C m H 2m+1 This is because too much O (alkoxyl group) can easily affect the ink's stability over time. Furthermore, in consideration of suppressing wear of the ball seat, it is preferable to mix a monoester of phosphate ester with a diester of phosphate ester. In this case, the mixing ratio of the diester of phosphate ester (n=2 in Chemical Formula 1 and Chemical Formula 2) is C l H 2l+1 O-C2H4O (alkoxyethyl group) and C m H 2m+1 The higher the O (alkoxyl group), the better the lubricity and the longer the ink will last, so the more phosphate diesters there are. Therefore, the ratio is preferably in the range of 1:1 to 1:5, and furthermore, the ratio is preferably in the range of 1:1 to 1:3.

[0022] Specific examples of phosphate esters such as those represented by general formulas (Chemical Formula 1) and (Chemical Formula 2) include butoxyethyl acid phosphate (l=4) for general formula (Chemical Formula 1), and methyl acid phosphate (m=1), ethyl acid phosphate (m=2), butyl acid phosphate (m=4), 2-ethylhexyl acid phosphate (m=8), isodecyl acid phosphate (m=10), lauryl acid phosphate (m=12), alkyl (m=12, 14, 16, 18) acid phosphate, isotridecyl acid phosphate (m=13), oleyl acid phosphate (m=18), and tetracosyl acid phosphate (m=24) for general formula (Chemical Formula 2).

[0023] The content of the phosphate ester is more preferably 0.1 to 10% by mass relative to 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 10% by mass, the ink tends to become unstable over time. Taking these tendencies into consideration, the content is preferably 0.1 to 5% by mass, and even more preferably 0.3 to 3% by mass.

[0024] When the total content of the methyl-branched fatty acid relative to the total amount of the ink composition is X and the content of the phosphate ester relative to the total amount of the ink composition is Y, taking into consideration the prevention of wear of the ball seat and the improvement of the writing feel, it is preferable that the relationship be 0.1≦X / Y≦5, and more particularly, 0.3≦X / Y≦3 is preferable, and furthermore, it is preferable that the relationship be 0.5≦X / Y≦2.

[0025] (organic amine) Furthermore, when using the methyl-branched fatty acid and the phosphate ester as in the present invention, it is preferable to use an organic amine. This is because neutralizing the methyl-branched fatty acid and the phosphate ester with an organic amine stabilizes their dissolution in the ink, making it easier to obtain the effects of the methyl-branched fatty acid and the phosphate ester and also improving the stability over time of other ink components such as colorants. Considering the stability of the organic amine with the methyl-branched fatty acid, the phosphate ester, and the colorant, 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 most reactive, followed by secondary amines and tertiary amines, which tend to react easily with the phosphate ester, methyl-branched fatty acid, colorant, and other components, thereby affecting the stability over time of the ink. Therefore, it is preferable to use a secondary amine or a tertiary amine, and from further considerations, it is preferable to use a tertiary amine.

[0026] Specific examples of organic amines include aliphatic amines such as amines containing ethylene oxide, such as oxyethylene alkylamines and polyoxyethylene alkylamines; alkyl amines, such as laurylamine and stearylamine; and dimethyl alkyl amines, such as distearylamine, dimethyl laurylamine, dimethyl stearylamine and dimethyl octylamine. Of these, taking stability in the ink into consideration, amines containing ethylene oxide and dimethyl alkyl amines are preferred, and from this perspective, amines containing ethylene oxide are more preferred.

[0027] Furthermore, the total amine value of the organic amine is preferably 100 to 300 (mgKOH / g) in consideration of the stability with the phosphate ester, the methyl-branched fatty acid, the colorant, and other components. If the total amine value exceeds 300 (mgKOH / g), the organic amine is highly reactive and easily reacts with the above-mentioned components, which tends to deteriorate the ink stability over time. On the other hand, if the total amine value is less than 100 (mgKOH / g), the methyl-branched fatty acid, C l H 2l+1 O-C2H4O or C m H 2m+1 This tends to affect the stability of the phosphate ester having O (l, m = 1 to 30), and when used in an oil-based ballpoint pen, the adsorption of metals such as the ball and tip body tends to be poor, making it difficult to obtain lubricating performance. In consideration of the stability and lubricity with the above components, a range of 150 to 300 (mgKOH / g) is preferred, in consideration of stability more particularly, 200 to 300 (mgKOH / g) is preferred, and in consideration of stability most particularly, 230 to 270 (mgKOH / g) is preferred.

[0028] Specific examples of organic amines include oxyethylene alkylamines and polyoxyethylene alkylamines, such as Nymeen L-201 (total amine value: 232 to 246, secondary amines), Nymeen L-202 (total amine value: 192 to 212, tertiary amines), Nymeen L-207 (total amine value: 107 to 119, tertiary amines), Nymeen S-202 (total amine value: 152 to 166, tertiary amines), Nymeen S-204 (total amine value: 120 to 134, tertiary amines), Nymeen S-210 (total amine value: 75 to 85, tertiary amines), Nymeen DT-203 (total amine value: 227 to 247, tertiary amines), and Nymeen DT-208 (total amine value: 146 to 180, tertiary amines) (manufactured by NOF Corporation). Specific examples of alkylamines include Farmin 80 (total amine value: 204 to 210, primary amine), Farmin D86 (total amine value: 110 to 119, secondary amine), Farmin DM2098 (total amine value: 254 to 265, tertiary amine), Farmin DM8680 (total amine value: 186 to 197, tertiary amine) (Kao Corporation), Nissan Tertiary Amine BB (total amine value: 243 to 263, tertiary amine), Nissan Tertiary Amine FB (total amine value: 230 to 250, tertiary amine) (manufactured by NOF Corporation). These may be used alone or in combination of two or more.

[0029] 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 stability with the methyl-branched fatty acid, the phosphate ester, the colorant, and other components, and furthermore, taking into consideration the neutralization with the surfactant described below, it is preferably 0.5 to 5 mass%.

[0030] When the total content of the phosphate ester and the methyl-branched fatty acid relative to the total amount of the ink composition is A, and the content of the organic amine relative to the total amount of the ink composition is B, taking into consideration the stability of the ink over time due to neutralization, it is preferable that the relationship be 0.01≦A / B≦5, and more preferably 0.1≦A / B≦3.

[0031] (coloring agent) ​The colorant used in the present invention is not particularly limited and may be a dye, a pigment, or the like, and may be appropriately selected and used, and dyes and pigments 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 an acid dye and a basic dye, salt-forming dyes formed from a basic dye and an organic acid, 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. Specific examples of dyes include Balifast Black 1802, Balifast Black 1805, Balifast Black 1807, Balifast Violet 1701, Balifast Violet 1704, Balifast Violet 1705, Balifast Blue 1601, Balifast Blue 1605, Balifast Blue 1613, Balifast Blue 1621, Balifast Blue 1631, Balifast Red 1320, Balifast Red 1355, Balifast Red 1360, Balifast Yellow 1101, Balifast Yellow 1151, Nigrosine Base EXBP, Nigrosine Base EX, BASE OF BASIC DYES ROB-B, BASE OF BASIC DYES RO6G-B, BASE OF BASIC DYES VPB-B, BASE OF BASIC DYES VB-B, and BASE OF BASIC DYES MVB-3 (all manufactured by Orient Chemical Industry Co., Ltd.), Aizen Spiron Black GMH-Special, and Aizen Spiron Violet C-RH, Aizenspiron Blue GNH, Aizenspiron Blue 2BNH, Aizenspiron Blue C-RH, Aizenspiron Red C-GH, Aizenspiron Red C-BH, Aizenspiron Yellow C-GNH, Aizenspiron Yellow C-2GH, SPT Blue 111, SPT Blue GLSH-Special, SPT Red 533, SPT Orange 6, SBN Yellow 510, SBN Yellow 530, SRC-BH (all manufactured by Hodogaya Chemical Co., Ltd.).

[0032] Furthermore, as the colorant, it is preferable to use at least a salt-forming dye in consideration of the stability over time due to the compatibility with the methyl-branched fatty acid and the phosphate ester. Furthermore, in consideration of maintaining stability over time due to the stability of the salt-forming bond, it is preferable to use a salt-forming dye formed between a basic dye and an organic acid, a salt-forming dye formed between an acid dye and a basic dye, or a salt-forming dye formed between an acid dye and an organic amine. From a more specific perspective, it is preferable to use a salt-forming dye formed between a basic dye and an organic acid, or a salt-forming dye formed between an acidic dye and an organic amine, and from a more specific perspective, it is preferable to use a salt-forming dye having an azo skeleton dye, a salt-forming dye having a xanthene skeleton dye, or a salt-forming dye having an aromatic amine, and among these, it is preferable to use a salt-forming dye formed between an azo basic dye and an organic acid, or a salt-forming dye formed between an acidic dye and an aromatic amine, because the bond is stable and methyl-branched fatty acid and phosphate esters are less likely to be affected.

[0033] Regarding the organic acid of the salt-forming dye of a basic dye and an organic acid, an organic acid having a phenyl sulfone group is preferred because it is likely to form a lubricating film that is easily adsorbed to the metal of the writing tip, improving the lubricity of the writing tip and improving the writing feel and wear prevention of the ball seat.Furthermore, in consideration of long-term stability in the ink, it is preferred to use alkylbenzene sulfonic acid as the organic acid. Regarding the acid dye and organic amine, in order to improve the lubricity and the lightfastness, an acid metal complex dye containing Cu, Cr, Fe, or Co is preferred, and therefore it is preferable to use a salt-forming dye of the acid metal complex dye and organic amine. In order to stabilize the acid metal complex dye in oil-based ink, it is preferable to neutralize it with an amine having an aromatic ring, among organic amines, to form a salt-forming dye. Regarding the acidic metal-containing dye, in order to improve stability over time in the ink, it is preferable to use an acidic metal-containing dye containing Cu. Furthermore, there are phthalocyanine-based and azo-based dyes, among which copper phthalocyanine-based acidic dyes are preferred. Furthermore, the acidic metal-containing dye may have a sulfo group (-SO3H) or a carboxyl group (-COOH) in its structure, but in order to further improve lubricity, an acidic metal-containing dye having a sulfo group (-SO3H) is preferred. This is because the sulfo group (-SO3H) easily forms a strong lubricating layer between the ball and the ball seat, which is thought to improve lubricity, and when used in combination with an amine having an aromatic ring, a synergistic lubricating effect can be obtained.

[0034] Furthermore, 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.

[0035] Considering lubricity, it is preferable to use a pigment as the colorant. This is because the pigment particles penetrate into the gap between the ball at the writing tip and the tip body, which acts like a bearing, and suppresses metal contact at the writing tip, improving lubricity, improving writing feel, and suppressing wear of the ball seat. In particular, it is preferable to use a pigment, such as methyl branched fatty acid, C l H 2l+1 O-C2H4O or C m H 2m+1The lubricating layer made of a phosphate ester having O (l, m = 1 to 30) and the synergistic effect of the pigment particles and bearing action facilitates lubrication, suppresses ball seat wear, and improves writing comfort. Furthermore, taking into consideration the gaps inside the ballpoint pen tip, the average particle diameter is preferably 1 to 500 nm. It is more preferably 30 to 350 nm, and even more preferably 50 to 300 nm. Here, the average particle diameter can be determined by laser diffraction, specifically, by measuring the particle diameter at 50% cumulative volume (D50) of the particle size distribution measured using a laser diffraction particle size distribution analyzer (product name "MicrotracHRA9320-X100", Nikkiso Co., Ltd.) based on values ​​calibrated using standard samples or other measurement methods. In addition, since the pigment exhibits the above-mentioned effects depending on the dispersed state of the pigment in the oil-based ink composition for a writing instrument, it is preferable to determine the particle size in the dispersed state. Furthermore, pigments are preferable because they have excellent water resistance and light resistance and can produce good color development.

[0036] As for the type of pigment, in consideration of lubrication due to compatibility with methyl-branched fatty acids and phosphate esters, it is preferable to use carbon black, quinacridone-based, threne-based, and diketopyrrolopyrrole-based pigments. Furthermore, in consideration of compatibility over time and the ink stability over time, it is preferable to use diketopyrrolopyrrole-based pigments.

[0037] The content of the colorant is preferably 5 to 30% by mass of 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 30% by mass, it tends to affect the solubility in the ink. Taking these tendencies into consideration, the content is preferably 7 to 25% by mass, and even more preferably 10 to 20% by mass.

[0038] (organic solvent) Examples of organic solvents that can be used in the present invention include organic solvents that are commonly used in inks for writing instruments, such as glycol ether solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol monophenyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol dimethyl ether, 3-methoxybutanol, and 3-methoxy-3-methylbutanol; 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.

[0039] Among these organic solvents, it is preferable to use a water-insoluble organic solvent to stabilize the dissolution of the ink composition for an oil-based ballpoint pen, since the effect of improving lubricity is likely to be obtained when the solubility of the methyl-branched fatty acid and the phosphate ester is taken into consideration. Among these, glycol ether solvents are preferred. This is because glycol ether solvents tend to have good affinity with methyl-branched fatty acids and phosphate esters, resulting in stable dissolution and therefore ink stability over time even when stored for long periods of time. Furthermore, glycol ether solvents are prone to moisture absorption, which softens the strength of the coating formed when the tip tip dries and tends to improve writing performance. This is even more effective when used in combination with a surfactant, as described below. Considering stability in the ink, aromatic glycol ether solvents are preferred. Furthermore, for organic solvents other than glycol ether solvents, alcohol solvents are preferred. This is because alcohol solvents volatilize and dry easily at the tip tip, which more quickly thickens the writing tip (within the tip tip), thereby suppressing ink leakage from the gaps in the writing tip and improving ink leakage suppression performance. Furthermore, aromatic alcohols such as benzyl alcohol are preferred because they also have the effect of improving lubricity. Therefore, it is preferable to use glycol ether solvents in combination with alcohol solvents.

[0040] The content of the organic solvent is preferably 10 to 70% by mass of the total amount of the ink composition, taking into consideration improvements in solubility, handwriting drying properties, bleeding, etc. The content of the alcohol solvent is preferably 30 to 90% by mass, more preferably 50 to 90% by mass, of the total amount of organic solvent, taking into consideration drying properties at the tip end. (resin)

[0041] In the present invention, a resin may be used as a viscosity modifier, and specific examples thereof include polyvinyl butyral resin, polyacetal resin, polyvinyl alcohol resin, cellulose resin, polyvinylpyrrolidone resin, ketone resin, terpene resin, alkyd resin, phenoxy resin, and polyvinyl acetate resin. Among these, ketone resins are preferred because they improve the lubricity of the writing tip, suppress wear of the ball seat, and make it easier to prevent smearing of handwriting. In particular, they are preferred because they are compatible with the methyl-branched fatty acid and the phosphate ester, and synergistically improve lubricity without impairing the lubricity that is a feature of the present invention, thereby making it easier to further suppress wear of the ball seat.

[0042] Among ketone resins, it is preferable to use ketone resins having a cyclic structure such as an aromatic ring skeleton (having a benzene ring such as a phenyl group, an acetophenone group, or a naphthalene group) or a cyclohexane skeleton (having a cyclohexane ring such as a cyclohexane group or a cyclohexanone group). This is because the cushioning effect of the ketone resin with a cyclic structure is obtained, improving lubricity, suppressing wear of the ball seat, and making it easier to suppress blurring of handwriting. More preferably, ketone resins having aromatic rings have many double bond structures, making it easier to obtain a stronger cushioning effect, which is effective for lubrication and is therefore preferable. Furthermore, the ketone resin preferably has a hydroxyl value of 100 mgKOH / g or more. This is because a hydroxyl value of 100 mgKOH / g or more makes it more soluble in organic solvents such as alcohol solvents and glycol solvents, and the interaction between the methyl-branched fatty acid and the phosphate ester when used in combination makes it easier to achieve the effect of inhibiting ball seat wear. To further consider ball seat wear inhibition, a hydroxyl value of 200 mgKOH / g or more is preferred, and even more particularly, a hydroxyl value of 300 mgKOH / g or more is preferred. In particular, when the ball diameter is 0.5 mm or less, lubrication is easily maintained even when a load is applied locally between the ball seats, making this effective in inhibiting ball seat wear. This is also preferable when the ball diameter is 0.4 mm or less, as this is effective, and is further preferable when the ball diameter is 0.3 mm or less, as this is effective.

[0043] Ketone resins can improve the lubricity of the writing tip and help reduce wear on the ball seat, but they do not sufficiently improve the writing feel, so it is preferable to use them in combination with polyvinyl butyral resins. Polyvinyl butyral resins, when used in combination with methyl-branched fatty acids, and even more so with the phosphate esters, can easily form a lubricating layer that provides a higher lubrication effect. Therefore, a constantly elastic ink layer is formed at the writing tip (between the ball and the ball seat), reducing direct contact and improving the writing feel. Furthermore, the use of polyvinyl butyral resins is preferred because the coating formed can more easily reduce ink leakage. Furthermore, when a pigment is used as a colorant, polyvinyl butyral resins are also preferred because they provide a pigment dispersion effect, making them effective when used in oil-based ballpoint pens. 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.

[0044] 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 organic solvents and are therefore unlikely to provide sufficient improvements in writing feel or ink leakage suppression. Furthermore, considering the writing performance due to hygroscopicity, it is preferable to use polyvinyl butyral resins with a hydroxyl group content of 25 mol% or more. Furthermore, polyvinyl butyral resins with a hydroxyl group content of 30 mol% or more are preferred because they tend to improve writing feel. This is because, during writing, frictional heat is generated by the rotation of the ball, warming the ink at the tip of the tip and increasing the ink temperature. However, unlike other resins, polyvinyl butyral resins have the property of preventing ink viscosity from decreasing even when the ink temperature increases, and they form a constantly elastic ink layer at the writing tip (between the ball and the ball seat), reducing direct contact and thus improving writing feel. 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, so polyvinyl butyral resins with a hydroxyl group content of 40 mol% or less are preferred. Therefore, polyvinyl butyral resins with a hydroxyl group content of 30 to 40 mol%, and more preferably those with a hydroxyl group content of 30 to 36 mol%, are 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 %).

[0045] Furthermore, with regard to the average degree of polymerization of the polyvinyl butyral resin, if the average degree of polymerization is 200 or higher, the ink leakage suppression performance is likely to be improved, and if the average degree of polymerization exceeds 2500, the ink viscosity tends to become too high, affecting the writing feel, so the average degree of polymerization is preferably 200 to 2500. Furthermore, in consideration of the writing feel and the suppression of ink leakage, the average degree of polymerization is preferably 1500 or less, and more preferably 1000 or less. Here, the average degree of polymerization refers to the number of basic units constituting one molecule of the polyvinyl butyral resin, and a value measured based on the method specified in JIS K6728 (2001 edition) can be used.

[0046] Furthermore, when a ketone resin and a polyvinyl butyral resin are used in combination, assuming that the content of the ketone resin relative to the total amount of the ink composition is C and the content of the polyvinyl butyral resin relative to the total amount of the ink composition is D, in order to suppress wear of the ball seat and easily achieve a balanced improvement in suppression of handwriting smearing, writing feel, suppression of ink leakage, and ink aging, it is preferable that the relationship be 0.1≦C / D≦10, and more particularly, 0.5≦C / D≦7 is more preferable, and a relationship of 1.5≦C / D≦5 is even more preferable.

[0047] If the total content of the resins is less than 1% by mass relative to the total amount of the ink composition, the desired writing feel, ball seat wear prevention, and ink leakage prevention performance tend to be inferior, while if it exceeds 40% by mass, the solubility in the ink tends to be inferior, so it is preferably 1 to 40% by mass relative to the total amount of the ink composition. Further considerations mean that a content of 5% 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 5 to 30% by mass is preferable.

[0048] Resins other than ketone resins and polyvinyl butyral resins may be used with a stringiness imparting agent as appropriate. In particular, polyvinylpyrrolidone resin is preferably included, as its incorporation improves ink binding properties and helps prevent excess ink from forming at the tip. If the content of the polyvinylpyrrolidone resin is less than 0.01% by mass relative to the total ink composition, it tends to be difficult to prevent excess ink from forming. If it exceeds 3.0% by mass, its solubility in the ink tends to be poor. Therefore, a content of 0.01 to 3.0% by mass relative to the total ink composition is preferred. Considering the above reasons, a content of 0.1 to 2.0% by mass is preferred. Specific examples include PVP K-15, PVP K-30, PVP K-90, and PVP K-120, both of which are products of ISP Japan Co., Ltd. These may be used alone or in combination.

[0049] (surfactant) In the present invention, it is preferable to use a surfactant as the lubrication agent, considering that it suppresses wear of the ball seat, prevents blurring of handwriting, improves the writing feel, and improves the writing performance when the writing tip (tip tip) is left in the air and dries. This is because the use of a surfactant tends to soften the coating that is formed, improving the writing performance and also improving the lubricity. Examples of surfactants include unsaturated fatty acids, silicone surfactants, fluorine surfactants, and phosphate ester surfactants (C l H 2l+1 O-C2H4O or C m H 2m+1 O (excluding phosphate esters having l, m=1 to 30). Among them, taking the above effects into consideration, unsaturated fatty acids, silicone surfactants, phosphate ester surfactants (C l H 2l+1 O-C2H4O or C m H 2m+1 It is preferable to use one or more of the above phosphate esters (excluding phosphate esters having l, m=1 to 30), and more preferably two or more of them. In particular, phosphate ester surfactants (C l H 2l+1 O-C2H4O or C m H 2m+1 When using a phosphate ester surfactant (excluding phosphate esters having 1, m=1 to 30), it is preferable to use a phosphate ester surfactant because the phosphate ester has a similar structure, which makes it easier to obtain a synergistic lubricating effect. This is because the phosphate ester surfactant (C l H 2l+1 O-C2H4O or C m H 2m+1 O (excluding phosphate esters having l, m=1 to 30)), the lubricating layer of the phosphate ester and the phosphate ester surfactant (C l H 2l+1 O-C2H4O or C m H 2m+1 O (excluding phosphate esters having l, m = 1 to 30)) interacts with the lubricating layer, forming a lubricating layer with higher lubricity, which is presumed to maintain the lubricity of the writing tip, suppress wear of the ball seat, suppress blurring of handwriting, and facilitate improvement of the writing feel. Furthermore, the use of phosphate ester surfactants (C l H 2l+1 O-C2H4O or C m H 2m+1 When using a surfactant containing phosphate ester (excluding phosphate esters having l, m=1 to 30), the acid value is preferably 160 or less (mgKOH / g). This is to facilitate the improvement of lubricity due to the phosphate ester surfactant. Furthermore, taking into consideration stability and lubricity in the ink, the acid value is preferably 30 to 160, and more preferably 70 to 120 (mgKOH / g). The acid value is expressed as the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of sample. Furthermore, the use of the above-mentioned methyl-branched fatty acid, ketone resin, and polyvinyl butyral resin is more preferable because it is easier to improve lubricity.

[0050] The surfactant preferably has an HLB value of 6 to 14 in order to further improve both lubricity and writing performance. This is because an HLB value of more than 14 tends to result in strong hydrophilicity, which tends to result in poor solubility in oil-based inks, making it difficult to obtain the effects of the surfactant and lubrication. Furthermore, an HLB value of less than 6 tends to result in excessively strong lipophilicity, which tends to affect compatibility with organic solvents, making it difficult for the ink to stabilize over time and further improving writing performance. Furthermore, in consideration of lubricity, the HLB value is preferably 12 or less, and an HLB value of 6 to 12 is preferable. In consideration of better writing performance, an HLB value of 7 to 12 is preferable. The HLB can be determined by the Griffin method, the Kawakami method, or the like, and as an example, it can be determined from the general formula HLB=7+11.7log(Mw / Mo), where Mw is the molecular weight of the hydrophilic group and Mo is the molecular weight of the lipophilic group. In particular, in retractable writing instruments such as knock-type writing instruments and rotary-type writing instruments, unlike cap-type writing instruments, the pen tip is always exposed to the outside, which is likely to affect the writing performance when the writing tip dries, so it is more preferable to use a surfactant with the above HLB value.

[0051] Specific examples of the surfactant include unsaturated fatty acids such as oleic acid and linoleic acid, silicone surfactants such as dimethyl silicone, methylphenyl silicone, polyether-modified silicone, and higher fatty acid ester-modified silicone, and fluorine-based surfactants such as perfluorobutyl sulfonate, perfluorocarboxylate, perfluorophosphate, perfluorophosphate-containing compound, perfluoroalkyl betaine, and perfluoroalkylamine oxide compound. l H 2l+1 O-C2H4O or C m H 2m+1O (excluding phosphate esters having l, m=1 to 30)), examples thereof include polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate monoesters, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate diesters, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate triesters, alkyl phosphate esters, alkyl ether phosphate esters, and derivatives thereof.

[0052] 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.

[0053] (fatty acid esters) In the present invention, fatty acid esters are preferably used in consideration of the above-mentioned lubricity and the improved writing performance when the writing tip (tip tip) is left in the atmosphere and dries. Fatty acid esters facilitate softening of the coating strength formed on the writing tip (tip tip) when the ink dries, thereby facilitating improved writing performance. Furthermore, by facilitating improved lubricity, wear of the ball seat is suppressed, suppressing blurring of handwriting, and improving both writing feel and writing performance. Therefore, the combined use of a methyl-branched fatty acid, a phosphate ester, and a fatty acid ester facilitates the lubrication effect due to the interaction with the formed lubricating layer, thereby achieving a high level of lubricity not previously attainable. This facilitates a balanced improvement in wear suppression of the ball seat, writing feel, writing performance, and ink aging, and is therefore preferred, especially when used in oil-based ballpoint pens.

[0054] Fatty acid esters are those obtained by esterifying fatty acids with alcohols such as monohydric alcohols and polyhydric alcohols, and among these fatty acid esters, it is preferable to use fatty acid esters having a branched alkyl group in order to further improve writing performance. This is because fatty acid esters having a branched alkyl group have a bulkier structure than linear structures, and the bulkiness of the branched alkyl group makes it possible to form a thick lubricating film when adsorbed onto the surface of a metal ball or the ball seat of the tip body, thereby improving lubrication. At the same time, the bulkiness of the branched alkyl group softens the strength of the film formed at the tip end when the ink dries, thereby improving writing performance.

[0055] Furthermore, the fatty acid ester preferably has an acid value of 0.01 to 5 (mgKOH / g), because it has good compatibility with the methyl-branched fatty acid, the phosphate ester, and other components in the oil-based ink and is stable in the ink for a long period of time, thereby improving writing performance and lubricity over a long period of time and making it easier to improve the writing feel. From this perspective, the acid value is preferably 0.01 to 2.5 (mgKOH / g), and more preferably 0.05 to 1.0 (mgKOH / g). The acid value is expressed as the number of mg of potassium hydroxide required to neutralize the acidic components (free fatty acids) contained in 1 g of sample.

[0056] The alcohol used in the esterification reaction of the fatty acid ester is preferably a polyhydric alcohol. While the reason for this is unclear, it is presumed that the more hydroxyl groups in the alcohol used in the esterification reaction of the fatty acid ester, the more moisturizing the alcohol is, which softens the strength of the coating formed when the tip end dries and smooths the ball's rotation, resulting in improved writing performance without blurred writing. Considering further improvement in writing performance and lubricity, polyhydric alcohols with trivalent or greater hydroxyl groups are preferred, and more preferably with pentavalent or greater hydroxyl groups. Furthermore, since too many hydroxyl groups can easily affect stability in oil-based inks, it is preferred that the hydroxyl groups be octavalent or less, and more preferably with hexavalent or less hydroxyl groups.

[0057] Specific examples of alcohols used in the esterification reaction of the fatty acid esters include monohydric alcohols such as pentanol, cyclohexanol, hexanol, heptanol, octanol, 2-ethylhexanol, nonanol, isononanol, decanol, lauryl alcohol, myristyl alcohol, stearyl alcohol, and docosanol, and polyhydric alcohols such as ethylene glycol, propylene glycol, polyalkylene glycol, 1,3-propanediol, diethylene glycol, glycerin, 2-methylpropanetriol, neopentyl glycol, trimethylolethane, triethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, and tripentaerythritol. Among these, in order to further improve the writing performance and take into consideration the ink stability over time, it is preferable to contain a fatty acid ester esterified with a pentaerythritol such as pentaerythritol, dipentaerythritol, or tripentaerythritol, and from further consideration, it is preferable to contain a fatty acid ester esterified with dipentaerythritol.

[0058] The content of the fatty acid ester is more preferably 0.1 to 10% 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 writing performance, and if it exceeds 10% by mass, the ink tends to become unstable over time. Taking these tendencies into consideration, the content is preferably 0.1 to 5% by mass, and even more preferably 0.1 to 3% by mass, and most preferably 0.3 to 2% by mass.

[0059] 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.

[0060] If the ink viscosity exceeds 15,000 mPa·s, the ball rotation resistance during writing increases, making writing feel heavy, affecting the wear of the ball seat, and affecting writing performance and ink tracking performance. -1 The ink viscosity (when writing) is preferably 15,000 mPa·s or less. In consideration of improved writing feel and reduced wear of the ball seat, 10,000 mPa·s or less is preferable, and in consideration of improved writing feel and reduced wear of the ball seat, 8,000 mPa·s or less is preferable, and in consideration of improved writing feel, 6,000 mPa·s or less is preferable. Also, at 20°C and a shear rate of 500 sec -1 If the ink viscosity (when writing) is less than 10 mPa·s, it is likely to cause wear on the ball seat, bleeding in the writing, or ink dripping. -1 The ink viscosity (when writing) is preferably 10 mPa·s or more, and even more preferably 100 mPa·s or more. Furthermore, taking into consideration the prevention of wear of the ball seat, the ink viscosity is preferably 500 mPa·s or more, and even more preferably 1000 mPa·s or more, and more preferably 2000 mPa·s or more.

[0061] (ballpoint pen) Furthermore, the ink consumption of a ballpoint pen per 100 m is preferably 20 to 70 mg. This is because if the ink consumption per 100 m is less than 20 mg, it is difficult to obtain thick handwriting or a good writing feel, and if the ink consumption per 100 m exceeds 70 mg, the gap between the ball and the tip end is likely to affect ink leakage prevention, and further, writing performance and blobbing are likely to occur. From these considerations, a value of 20 to 60 mg is preferable. In particular, when the ball diameter is relatively small, such as 0.5 mm or less, the ink consumption tends to be small, which can affect the writing feel and writing performance such as blurring, so 20 to 50 mg is preferable, and more particularly, 20 to 45 mg is more preferable. Furthermore, when the ball diameter is 0.5 mm or less, it is effective to not only set the ink consumption amount but also consider the relationship with the ball diameter in order to achieve darker handwriting, improved writing feel, and ink leakage prevention. Specifically, the ratio of the ball diameter (mm) to the ink consumption (mg) per 100 m of an oil-based ballpoint pen (ball diameter:ink consumption) is preferably 1:40 to 1:140, a different relationship from the conventional one, because it is easier to achieve darker handwriting, improved writing feel, and ink leakage prevention. Taking further consideration, a ratio of 1:50 to 1:130 is preferable, and a ratio of 1:60 to 1:120 is even more preferable. Regarding ink consumption, a spiral writing test was conducted using five test samples at a writing speed of 4 m / min on JIS P3201 writing paper at a writing angle of 70° and a writing load of 200 g at 20°C, and the average ink consumption per 100 m was defined as the ink consumption per 100 m.

[0062] The use of an ink composition for an oil-based ballpoint pen containing a methyl-branched fatty acid and a phosphate ester as in the present invention can suppress ball seat wear and stabilize ink consumption from the beginning to the end of writing, thereby favorably achieving a smooth writing experience, less smearing of handwriting, and stable, dark writing performance. Specifically, when the ink consumption E mg from the initial 0 to 100 m is expressed as the ink consumption F mg at the 100 m before the end of the ink run, a ratio (E:F) of 1:0.7 to 1:1.3 is preferred because it improves the writing experience, reduces smearing of handwriting, and promotes stable, strong writing performance. From a more specific perspective, a ratio of 1:0.8 to 1:1.2 is preferred, with a ratio of 1:0.9 to 1:1.1 being more preferred. A ball diameter of 0.5 mm or less is particularly effective and preferred.

[0063] (ballpoint pen tip) For ballpoint pen tips, it is preferable to maintain lubricity between the ball and the tip body, suppress wear on the ball seat, suppress blurring of handwriting, and improve the writing feel, and to provide a ball seat 19a with an approximately arc-shaped surface on the bottom wall 19 of the ball holding chamber.

[0064] Furthermore, it is preferable that a sealing surface 14c having a substantially arcuate shape is formed on the inner wall of the tip end portion, a sealing surface having a substantially arcuate shape is formed on the inner wall of the tip end portion, a sealing surface having a substantially arcuate shape is formed on the inner wall of the tip end portion, and a ball seat having a substantially arcuate shape is provided on the bottom wall of the ball holding chamber, and that the tip end portion has a first crimped portion 14a with an inclination angle of 70 to 110°, and that a second crimped portion 14b with an inclination angle of 100 to 140° is provided forward of the first crimped portion. This is because by ensuring space for ink to accumulate between the ball and the tip edge, it is easier to ensure ink consumption, which reduces ink stagnation, improves dark handwriting, writing feel, and reduces wear on the ball seat, and also increases the ball retention force.Taking this into consideration further, it is preferable that the inclination angle (α) of the first crimping portion be 80 to 100°, and the inclination angle (β) of the second crimping portion be 110 to 130°. The inclination angle of the first crimped portion 14a may be referred to as a first inclination angle α. The inclination angle of the second crimped portion 14b may be referred to as a second inclination angle β. These inclination angles may be referred to as crimping angles.

[0065] The inclination angle (γ) of the bottom wall 19 of the ball holding chamber is preferably 100 to 140°, and more preferably 110 to 130°. It is also preferable that the angle be close to the inclination angle (β) of the second crimping portion, and in particular, the difference between the inclination angle (γ) of the bottom wall of the ball holding chamber and the inclination angle (β) of the second crimping portion is preferably ±10°, and more preferably ±5°. This has the effect of smoothing the rotation of the ball by providing ball seat 19a and seal surface 14c, and also making it less likely that wear changes will occur due to differences in the angles of the bottom wall of the ball holding chamber and the inner wall of the second crimping portion, even if the ball seat or seal surface wears. In addition, it is thought that the ink flowing into the ball holding chamber from the ink flow hole and the ink that flows from the tip of the tip into the ball holding chamber without being transferred to the paper surface (ink return) will stabilize the flow of ink within the ball holding chamber, which also has the effect of allowing a stable ink flow rate to be obtained even if the ball seat or sealing surface wears, making it easier to achieve the effects of the present invention. The inclination angle (γ) of the bottom wall 19 is the angle of the bottom wall 19 along the outer periphery of the ball tip in a cross section along the tip direction of the ballpoint pen tip 11, as shown in FIG.

[0066] Furthermore, when forming the ball seat 19a and the seal surface 14c, the ball is transferred to the wall surface at an approximate angle between the bottom wall of the ball holding chamber and the inner wall of the second crimping portion. Therefore, even if the curvature changes due to spring back after transfer, the curvature of the resulting transferred surface is approximate, which prevents the ball from becoming biased. It also prevents uneven wear on the ball seat and the seal surface at the tip of the tip due to ball rotation, ensuring stable ball rotation and stable ink flow.

[0067] The arithmetic mean roughness (Ra) of the ball surface of the ballpoint pen tip used in the present invention is preferably 0.1 to 12 nm. This is because if the arithmetic mean roughness (Ra) is less than 0.1 nm, it is difficult for ink to adhere sufficiently to the ball surface, making it difficult to obtain thick handwriting, and line skipping and smearing are likely to occur in the handwriting. If the arithmetic mean roughness (Ra) is more than 12 nm, the ball surface is too rough, increasing the rotational resistance between the ball and the ball seat, which tends to deteriorate the writing feel. Furthermore, it is likely to affect writing performance, such as smearing, line skipping, and line unevenness in the handwriting. Considering these factors, the arithmetic mean roughness (Ra) is preferably 0.1 to 10 nm, and more preferably 0.5 to 5 nm. Surface roughness can be measured using a Seiko Epson SPI3800N.

[0068] 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.

[0069] 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 and stability over time, it is preferable to use a tip body made of stainless steel.

[0070] Furthermore, the amount of movement of the ball in the ballpoint pen tip used in the present invention along its vertical axis is preferably 3 to 30 μm. This is because if it is less than 3 μm, it becomes difficult to obtain thick handwriting or a good writing feel, and if it exceeds 30 μm, ink dripping performance is likely to be affected. Taking this into consideration, a value of 10 to 25 μm is preferable. In particular, a relatively small ball diameter of 0.5 mm or less tends to reduce ink consumption and affect writing feel, so the amount of movement of the ball in the ballpoint pen tip along its vertical axis is preferably 12 to 25 μm, and more preferably 14 to 25 μm. A ball diameter of 0.4 mm or less is also effective and preferable, and a ball diameter of 0.3 mm or less is also effective and preferable.

[0071] To prevent ink leakage, a valve mechanism is provided in which the ball rotatably held at the tip of the ballpoint pen tip is pressed against the inner wall of the tip edge by a resilient member such as a coil spring, either directly or via a pressing body, to create a gap between the inner wall of the tip edge and the ball using the pressure during writing, allowing ink to flow out. The minute gap at the tip tip is also preferably closed when not in use. To facilitate maintaining a good writing experience, the resilient member's pressing load is preferably set to 30 gf or less. In particular, when the ball diameter is 0.5 mm or less, a pressing load of 20 gf is preferred, with 15 gf or less being even more preferred, in order to maintain high lubricity and facilitate a good writing experience even when a load is applied locally between the ball and the seat. Furthermore, considering the ease of preventing ink leakage and improving ink tracking, a pressing load of 3 gf or more is preferred, with 5 gf or more being more preferred.

[0072] The present invention will now be described with reference to examples. The ink composition for an oil-based ballpoint pen in Example 1 was prepared by adding a pigment and a pigment dispersant to an organic solvent and dispersing them in a disperser, and then using the pigment dispersion, dye, organic solvent, methyl-branched fatty acid, polyvinyl butyral resin, ketone resin, phosphate ester, organic amine, surfactant, fatty acid ester, and spinnability-imparting resin, weighing out predetermined amounts, heating to 60°C, and completely dissolving them in a disper stirrer to obtain an ink composition for an oil-based ballpoint pen. The specific blending amounts are as follows:

[0073] Example 1 Colorant (salt-forming dye of acid dye and basic dye) 10.0% by mass Colorant (salt-forming dye of basic dye and organic acid) 5.0% by mass Pigment dispersion (pigment content 20%, diketopyrrolopyrrole pigment) 15.0% by mass Methyl-branched fatty acid (methyl-branched octadecanoic acid (carbon number: 18)) 2.0% by mass C l H 2l+1 O-C2H4O or C m H 2m+1 Phosphate ester having O (Chemical formula 1: l=4, mixture of n=1 and n=2) 2.0% by mass Alcohol solvent (benzyl alcohol) 25.0% by mass Glycol ether solvent (ethylene glycol monophenyl ether) 19.5% by mass Surfactant (phosphate ester surfactant) 2.0% by mass Organic amine 2.0% by mass Fatty acid ester (acid value: 0.1 mg KOH / g, hydroxyl group hexavalent) 2.0 mass% Polyvinyl butyryl resin (hydroxyl group content: 36 mol%) 5.0 mass% Ketone resin (ketone resin with aromatic ring) 10.0% by mass Spinnability-imparting resin (polyvinylpyrrolidone resin) 0.5% by mass

[0074] Examples 2 to 26 As shown in the table, except for changing the components and tip specifications, inks were formulated in the same manner as in Example 1 to obtain ink compositions for oil-based ballpoint pens of Examples 2 to 26. The measurement and evaluation results are shown in the table. In addition, under an environment of 20°C, shear rate of 500 sec -1 The ink viscosities of Examples 1, 2, 9, 14, 18, 25, and 26 were measured using a Brookfield Viscometer RVDVII+Pro CP-52 spindle, and the results were as follows: Example 1 and Example 2: Ink viscosity = 4500 mPa·s Example 9: Ink viscosity = 3700 mPa·s Example 14: Ink viscosity = 2800 mPa·s Example 18: Ink viscosity = 3500 mPa·s Example 24: Ink viscosity = 5900 mPa·s Example 25: Ink viscosity = 7100 mPa·s Example 26: Ink viscosity = 1500 mPa·s

[0075] Comparative Examples 1 to 3 As shown in the table, except that the components and tip specifications were changed, ink compositions for oil-based ballpoint pens of Comparative Examples 1 to 3 were obtained in the same manner as in Example 1. The measurement and evaluation results are shown in the table. [Table 1] [Table 2] [Table 3]

[0076] Testing and Evaluation The oil-based ink compositions for writing instruments prepared in Examples 1 to 26 and Comparative Examples 1 to 3 were used in an oil-based ballpoint pen manufactured by Pilot Corporation. The oil-based ink compositions for writing instruments prepared in Examples 1 to 26 and Comparative Examples 1 to 3 were used in an oil-based ballpoint pen manufactured by Pilot Corporation. The oil-based ink compositions for writing instruments were used in an oil-based ballpoint pen manufactured by Pilot Corporation. The oil-based ink compositions for writing instruments were used in an oil-based ballpoint pen manufactured by Pilot Corporation. The oil-based ink compositions for writing instruments were used in an oil-based ballpoint pen manufactured by Pilot Corporation. The oil-based ink compositions for writing instruments were used in an oil-based ballpoint pen manufactured by Pilot Corporation. The oil-based ink compositions for writing instruments manufactured by Pilot Corporation ... The following tests and evaluations were carried out using P3201. When a spiral writing test was conducted using an oil-based ballpoint pen, the ink consumption per initial 100 m of Examples 1, 2, 9, and 14 was 30 mg / 100 m, 27 mg / 100 m, 25 mg / 100 m, and 40 mg / 100 m, respectively. The ratio of the ball diameter (mm) to the ink consumption (mg) per initial 100 m of the oil-based ballpoint pens of Examples 1, 2, 9, and 14 (ball diameter: ink consumption) is: The ratios were 1:100 for Example 1, 1:90 for Example 2, 1:83 for Example 9, and 1:80 for Example 14, respectively. In addition, when the ink consumption amount E mg at the initial 0-100 m point in Examples 1, 2, 9, and 14 is set to be the ink consumption amount F mg at 100 m before the ink runs out, the E:F ratio is as follows: The ratios were 30:33=1:1.1 in Example 1, 27:25=1:0.93 in Example 2, 25:27=1:1.08 in Example 9, and 40:42=1:1.05 in Example 14, respectively.

[0077] Next, the present invention will be described with reference to an embodiment of a writing instrument (ballpoint pen) shown in the drawings. Example 1 to 3, ballpoint pen 1 of the first embodiment (Example 1) has a barrel body formed by detachably threading a front barrel 2 and a rear barrel 3, and stores ballpoint pen refill 4 biased rearward by coil spring 5. A retractable ballpoint pen 1 is configured such that a retractable mechanism using a rotating cam 6 provided in rear barrel 3 presses a knock member 7, thereby allowing the front end of ballpoint pen tip 11, which serves as the pen tip of ballpoint pen refill 4, to protrude and retract from front end opening 2a of front barrel 2. A clip 8 is provided on rear barrel 3, and a grip 9 made of an olefin-based thermoplastic elastomer is attached to hold front barrel 2.

[0078] As a retraction mechanism for extending and retracting the ballpoint pen refill 4, the rear barrel 3 is provided with a cam mechanism having a rotating cam 6 for switching the extension and retraction of the ballpoint pen tip 11 of the ballpoint pen refill 4 and a cam groove (not shown) that engages with the rotating cam 6. When the knock member 7 is pressed (knocked) with the ballpoint pen tip 11 of the ballpoint pen refill 4 retracted in the front barrel 2, the rotating cam 6 slides along the cam groove, causing the ballpoint pen tip 11 of the ballpoint pen refill 4 to protrude forward from the opening 2c of the front barrel 2. Furthermore, the action of the cam mechanism rotates the rotating cam 6, restricting the relative movement of the ballpoint pen refill 4 rearward in the axial direction, and maintaining this protruding state even after the pressing operation is terminated. Furthermore, when the knock member 7 is pressed (knocked) again in this protruding state, the action of the cam mechanism allows the ballpoint pen refill 4 to move rearward in the axial direction, and the biasing force of the coil spring 5 pushes the ballpoint pen refill 4 and the knock member 7 back axially, returning them to their initial states.

[0079] To explain the ballpoint pen refill 4 in more detail, the ballpoint pen refill 4 has a ballpoint pen tip 11 made of stainless steel wire attached to the tip end of the ink reservoir 22 via a tip holder 23, and a tail plug 24 attached to the rear end of the ink reservoir 22.

[0080] The ballpoint pen tip 11 has a tip body 12, a ball holding chamber 15, an ink flow hole 16 in the center of the ball holding chamber 15, and ink flow grooves 17 that extend radially and communicate with the ink flow hole 16 but do not reach the tip rear hole 18. A 0.3 mm diameter tungsten carbide ball 20 is placed on the bottom wall 19 of the ball holding chamber 15, and the tip tip end 13 is crimped inward to rotatably hold the ball 20 so that a portion of the ball protrudes from the tip tip 13. The tip tip 13 is formed with a two-stage crimped portion 14 consisting of a first crimped portion 14a and a second crimped portion 14b.

[0081] The ballpoint pen tip 11 is made by cutting a stainless steel wire rod having a diameter of 2.3 mm and a hardness of 230Hv to 280Hv to a desired length, and after forming the ball holding chamber 15, ink flow groove 17, ink flow hole 16, and tip rear hole 18, a ball 20 is placed on the bottom wall 19 of the ball holding chamber 14, and a ball seat 19a is formed on the bottom wall 19 of the ball holding chamber 14, and a sealing surface 14c having approximately the same shape as the ball 20 is formed on the inner wall of the tip tip portion 13 (the inner wall of the second crimping portion 14b).

[0082] Furthermore, the ball projection H protruding from the tip end of the tip when the ball 20 is placed on the bottom wall 19 is 30% of the ball diameter, the first inclination angle (crimping angle) α is 90 degrees, the second inclination angle (crimping angle) β is 120 degrees, the inclination angle γ of the bottom wall 19 is 120 degrees, the rear angle δ from the tip tip 13 is 30 degrees, and the vertical clearance of the ball is 18 μm. Although not shown, a coil spring 21 is disposed behind the ball 20, and the pressing force of this spring presses the ball 20 against the seal surface 14 c of the inner wall of the tip tip 13. The pressing force of the coil spring 21 pressing the ball 20 is 8 gf, and the ball retention force is 300 gf.

[0083] When writing with this ballpoint pen 1, the rotation of the ball 20 and the writing pressure cause the ball 20 to move toward the bottom wall 19 by the amount of the vertical clearance described above, creating a gap between the inner wall of the tip end 13 and the ball 20, allowing ink to be ejected and writing to be performed.

[0084] Abrasion resistance test (ball seat abrasion test): The abrasion of the ball seat after the writing test was measured using a running test machine with a load of 100 gf, a writing angle of 70°, and a speed of 4 m / min. Ball seat wear of less than 5 μm Ball seat wear is 5 μm or more and less than 10 μm... Wear of the ball seat is 10 μm or more but less than 20 μm, but writing is possible... △ The ball seat is badly worn, causing poor writing.

[0085] Writing feel: Evaluation was carried out by a sensory test using handwriting. Very smooth... Smooth ○ Smooth enough for practical use △ Heavy items ×

[0086] Writing performance test: After handwriting, the tip was left exposed in an environment of 20 or 65% RH for 30 minutes, and then writing was performed under the following writing conditions in a running test, and the length of the smeared handwriting at the start of writing was measured. <Writing conditions> A straight line was written on a running test machine under the following conditions: writing load 70 gf, writing angle 70°, writing speed 4 m / min, and evaluation was performed. The length of the smudged handwriting is less than 10 mm. The length of the smudged handwriting is 10mm or more but less than 20mm. The length of the smudged handwriting is 20mm or more but less than 40mm...△ The length of the blurred handwriting is 40mm or more... ×

[0087] Ink aging test: The ink inside the chip 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. ×

[0088] In Examples 1 to 26, good performance was obtained in the abrasion resistance test (abrasion test of the ball seat), writing feel, writing start performance test, and ink aging test.

[0089] In Comparative Examples 1 to 3, because no methyl-branched fatty acid was used, the wear of the ball seat was severe in the abrasion resistance test (ball seat abrasion test), causing smearing of handwriting, resulting in poor writing quality. Furthermore, in Comparative Examples 1 to 3, the writing performance and ink aging test were also poor.

[0090] Furthermore, when using a retractable writing instrument such as a knock-type writing instrument or a rotary-type writing instrument, writing performance is one of the important performance characteristics, so it is effective to use at least an ink composition such as that of the present invention.

[0091] Furthermore, in this example, an oil-based ballpoint pen in which a ballpoint pen refill containing an oil-based ink composition for a writing instrument in an ink storage tube is disposed within the barrel has been exemplified, but the writing instrument of the present invention may be a writing instrument in which the barrel itself serves as the ink storage tube and the oil-based ink composition for a writing instrument is directly stored within the barrel, such as a direct-fill type ballpoint pen, marking pen, or felt-tip pen, or may have a structure in which an ink storage tube containing an oil-based ink composition for a writing instrument (ballpoint pen refill) is used as a ballpoint pen as is. [Industrial Applicability]

[0092] The present invention can be used as an oil-based ink composition for a writing instrument, and more specifically, can be widely used as a cap-type or knock-type oil-based ballpoint pen, a marking pen, or a felt-tip pen filled with the oil-based ink composition for a writing instrument. [Explanation of symbols]

[0093] 1...ballpoint pen 2...front shaft, 2a...opening 3...Rear shaft (shaft cylinder body) 4...Ballpoint pen refill 5...Coil spring 6...Rotating cam 7...Knock section 8...Clip 9...Grip 11...Ballpoint pen tip 12...Chip body 13...Tip tip 14... crimped portion, 14a... first crimped portion, 14b... second crimped portion, 14c... sealing surface 15...Ball holding room 16...Ink flow hole 17...Ink flow groove 18...Tip rear hole 19...Bottom wall, 19a...Ball seat 20...ball 21...Coil spring 22...Ink storage tube 23...Chip holder 24...Tail plug

Claims

1. An oil-based ballpoint pen having a ballpoint pen tip rotatably holding a ball at the tip of an ink reservoir, and an oil-based ink composition for a writing instrument containing a colorant, an organic solvent, a methyl-branched fatty acid, and a phosphate ester, the oil-based ballpoint pen comprising: The phosphate ester has at least one of the general formulas (Chemical Formula 1) and (Chemical Formula 2), When the total content of the methyl-branched fatty acid relative to the total amount of the ink composition is X and the content of the phosphate ester relative to the total amount of the ink composition is Y, the relationship of 0.3≦X / Y≦3 is satisfied, When the ink consumption amount E mg of the oil-based ballpoint pen at the initial 0-100 m point is defined as E mg, and the ink consumption amount F mg at 100 m before the ink runs out, the ratio of the ink consumption amount E mg at the initial 0-100 m point to the ink consumption amount F mg at 100 m before the ink runs out (E:F) is 1:0.8 to 1:1.

2. An oil-based ballpoint pen characterized by: 【Chemistry 1】 【Chemistry 2】

2. The oil-based ink composition for a writing instrument comprises an organic amine, Furthermore, when the total content of the phosphate ester and the methyl-branched fatty acid relative to the total amount of the ink composition is A, and the content of the organic amine relative to the total amount of the ink composition is B, the relationship is 0.01≦A / B≦5.

2. The oil-based ballpoint pen according to claim 1.

3. 3. The oil-based ballpoint pen according to claim 1, wherein the oil-based ink composition for a writing instrument contains a ketone resin and a polyvinyl butyral resin.

4. 4. The oil-based ballpoint pen according to claim 3, wherein the relationship between the content of the ketone resin relative to the total amount of the ink composition is C and the content of the polyvinyl butyral resin relative to the total amount of the ink composition is D, and the relationship between the content of the ketone resin relative to the total amount of the ink composition is 0.1≦C / D≦10.

5. 5. The oil-based ballpoint pen according to claim 1, wherein the oil-based ink composition for a writing instrument contains a fatty acid ester.

6. 6. The oil-based ballpoint pen according to claim 1, wherein the ink consumption per 100 m of the oil-based ballpoint pen is 20 to 70 mg.

7. 7. The oil-based ballpoint pen according to claim 1, wherein the ball diameter of the oil-based ballpoint pen is 0.5 mm or less.

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