JP7783136B2 - Ink composition for writing implements and writing implements using the same - Google Patents

Description

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

Ink-based writing instruments have long been known and are used by people of all ages due to their ease of use. These writing instruments contain colorants, solvents, surfactants, and other ingredients, allowing them to write smoothly on paper. (Patent Document 1)

During normal use, it is possible to write well on paper, but when writing on prints made with toner or other printing ink, the handwriting becomes blurred and smudged, making it difficult to write well. This is because, in the case of ballpoint pens, the ball slides over the print when writing, preventing the ball from rotating sufficiently, resulting in blurred lines and smudged handwriting. This leaves room for improvement. (Patent Document 1)

Furthermore, writing instruments are prone to affecting the writing feel of ballpoint pens, marking pens, and the like due to the writing resistance that occurs between the writing tip and the surface being written on when writing. Ballpoint pens in particular have a configuration in which a ballpoint pen tip is attached to an ink reservoir, and the ball tip consists of 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.
Furthermore, when writing for a long period of time, since the ink storage tube is made of a material such as polyolefin resin, it has a strong affinity with the writing instrument ink, and as the ink moves inside the ink storage tube, the ink tends to adhere to the inner wall, making it difficult to see the remaining ink (visibility of remaining ink), which leaves room for improvement.

To address these issues, numerous 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. (Patent Documents 2 to 5)

JP 8-41406 Japanese Patent Application Publication No. 5-331403 Japanese Patent Application Laid-Open No. 2007-176995 JP 2013-151594 A JP 2014-88486 A

However, while the use of various new lubricants can reduce the writing resistance between the writing tip and the surface being written on to some extent, this is not sufficient, and the load on the ball seat can cause wear on the ball seat, resulting in poor writing, so there is room for improvement (Patent Documents 2 to 5).

The object of the present invention is to provide an ink composition for a writing instrument, which improves the lubricity of the writing tip, thereby enabling good writing on marks formed with printing ink such as toner, suppressing wear on the ball seat, improving writing feel, and allowing the remaining ink to be visually confirmed, as well as a writing instrument using the same.

In order to solve the above problems, the present invention provides: "1. An ink composition for a writing instrument, comprising a colorant, an organic solvent, and a (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer.
2. The ink composition for a writing instrument according to item 1, wherein the content of the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer is 0.1 to 10% by mass based on the total amount of the ink composition.
3. The ink composition for a writing instrument according to any one of items 1 and 2, characterized in that the ink composition for a writing instrument contains a surfactant.
4. The ink composition for a writing instrument according to item 3, wherein the HLB value of the surfactant is 6 or more and 14 or less.
5. A writing instrument containing the ink composition for a writing instrument according to any one of items 1 to 4.
6. 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 ink composition for a writing instrument described in any one of items 1 to 4 is contained in the ink reservoir.

The present invention has made it possible to obtain an ink composition for a writing instrument, and a writing instrument using the same, which improves the lubricity of the writing tip on prints made with printing inks such as toner, thereby suppressing line skipping and smearing of handwriting and providing good writing performance. It also reduces wear on the ball seat, improves writing feel, and prevents ink from adhering to the inner wall as it moves through the ink reservoir, allowing the remaining ink to be visually confirmed (visible remaining ink).

In this specification, "parts," "%," "ratio," and other terms used to indicate composition are based on mass unless otherwise specified.

A feature of the present invention is an ink composition for a writing instrument comprising a (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer. The inclusion of the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer improves the lubricity of the writing tip, thereby suppressing line skipping and smearing of handwriting even on prints made with printing inks such as toner, resulting in good writing performance and an improved writing feel. In the case of a ballpoint pen, the copolymer improves the lubricity between the ball and the ball seat of the tip body, reducing friction between the ball seat and thereby suppressing wear of the ball seat and further improving the writing feel. Furthermore, the copolymer can be effectively used in ballpoint pens, and considering the suppression of line skipping and smearing of handwriting even on prints made with printing inks such as toner, it is preferable to use the copolymer as an oil-based ink composition for a writing instrument, and preferably as an oil-based ballpoint pen.
Furthermore, by preventing ink from adhering to the inner wall as it moves through the ink reservoir, the remaining ink amount can be visually checked, improving visibility. This eliminates the need to apply a surfactant or other coating to the inner surface of the ink reservoir, reducing the number of production steps and achieving cost savings.

(Diglycerin/Dilinoleic Acid/Hydroxystearic Acid Copolymer)
The (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer used in the present invention is a copolymer of diglycerin, dilinoleic acid, and hydroxystearic acid, which improves the lubricity of the writing tip and suppresses line skipping and blurring of handwriting even on prints made with printing inks such as toner, resulting in good writing properties and an improved writing feel.In the case of a ballpoint pen, it improves the lubricity between the ball and ball seat and reduces friction between the ball seat, thereby suppressing wear on the ball seat, further improving the writing feel, and making it possible to improve the visibility of the remaining ink.
The (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer is a copolymer of diglycerin, dilinoleic acid, and hydroxystearic acid.
Specifically, there is Lithocasta HSDA manufactured by Higher Alcohols.

The content of the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer is preferably 0.1% by mass or more of the total amount of ink composition. This is because a content of 0.1% by mass or more makes it easier to achieve the effects of the present invention, and from a more specific perspective, 0.5% by mass or more is preferable, and 1% by mass or more is even more preferable. Furthermore, because this is less likely to affect the ink stability over time and makes it easier to achieve the effects of the present invention, it is preferably 10% by mass or less, and from a more specific perspective, 5% by mass or less is preferable, and 4% by mass or less is even more preferable.

(solvent)
The solvent used in the ink composition for a writing instrument used in the present invention may be water, an organic solvent, or a mixed solvent of water and an organic solvent.

Organic solvents include 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, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, 3-methoxybutanol, 3-methoxy-3-methylbutanol, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide. Examples of organic solvents commonly used in writing instrument inks include amide solvents of β-alkoxypropionamides such as 3-ethoxy-N,N-dimethylpropanamide, 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.

Among these organic solvents, glycol ether solvents or amide solvents are preferred, considering their compatibility with diglycerin/dilinoleic acid/hydroxystearic acid copolymers, which facilitates the realization of the effects of the present invention. This improves the lubricity of the writing tip, suppresses line skipping and smearing even on prints made with printing inks such as toner, and facilitates a smooth writing experience. In the case of ballpoint pens, this improves the lubricity between the ball and ball seat, reduces friction between the ball and seat, and inhibits wear on the ball seat, further improving the writing experience. Furthermore, alkylene glycol monoalkyl ethers and amide solvents of β-alkoxypropionamides are preferred, considering that they stabilize the ink over time even when stored for long periods of time, thereby facilitating the realization of the effects of the present invention. Furthermore, they can be effectively used in ballpoint pens, and are particularly effective in suppressing line skipping and smearing even on prints made with printing inks such as toner. Therefore, they are preferred for use in oil-based ink compositions for writing instruments, and are preferably used in oil-based ballpoint pens.

Furthermore, in consideration of the ease with which the alkylene glycol moiety of the alkylene glycol monoalkyl ether can stably exhibit its effect together with the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer, the number of carbon atoms is preferably 2 or more and 10 or less. In consideration of the ease with which the effect can be more stably obtained, the number of carbon atoms is preferably 3 or more and 8 or less, and more preferably 5 or more and 6 or less.
Furthermore, the number of carbon atoms in the alkyl ether moiety of the alkylene glycol monoalkyl ether is preferably shorter in order to ensure stable and effective use with the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer. Therefore, the number of carbon atoms is preferably 1 to 6, and from the viewpoint of stability and ease of obtaining the effect, it is preferably 1 to 4, and more preferably 1 to 2.

Furthermore, the alkylene glycol monoalkyl ether preferably has a solubility parameter (SP value) of 8 to 13 (cal/cm ³ ) ^1/2 . This is because the effects of the present invention are more easily exhibited due to its compatibility with the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer, and from further consideration, the solubility parameter (SP value) is preferably 9 to 12 (cal/cm ³ ) ^1/2 , and from further consideration, the solubility parameter (SP value) is more preferably 10 to 11 (cal/cm ³ ) ^1/2 .
The solubility parameter (SP value) of a solvent used 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). The SP value is used here. The unit is (cal/cm ³ ) ^1/2 , and the value is at 25°C.
For those for which no data is given, the values can be calculated by the method described in R. F. Fedors, Polymer Engineering Science, 14, p. 147 (1967).

Furthermore, the boiling point of the alkylene glycol monoalkyl ether is preferably 170°C or higher. This is because if it is below 170°C, the alkylene glycol monoalkyl ether is likely to evaporate, the ink viscosity is likely to increase, and it is difficult to suppress line skipping and blurring of handwriting on prints made with printing inks such as toner, which is likely to affect the writing feel. From a more considered perspective, a boiling point of 220°C or higher is preferable. On the other hand, if the boiling point exceeds 300°C, it is likely to affect the drying speed of handwriting, so a boiling point of 300°C or lower is preferable, and from a more considered perspective, a boiling point of 280°C or lower is preferable.

In addition, taking into consideration improvements in solubility, writing drying properties, and bleeding, the organic solvent content is preferably 10% by mass or more and 70% by mass or less of the total amount of ink composition. In addition, taking into consideration drying properties at the tip end, the alcohol solvent content is preferably 30% by mass or more and 90% by mass or less of the total organic solvent, and more preferably 50% by mass or more and 90% by mass or less.

As the water, conventional water such as ion-exchanged water, distilled water, and tap water can be used.
In the present invention, the ink composition for a writing instrument preferably contains water. This is because the use of water reduces the ink viscosity, improves the ball's slipperiness, improves ink dischargeability, suppresses line skipping and blurred handwriting even on prints formed with printing inks such as toner, improves the writing feel, suppresses dot unevenness and bleeding, and easily improves writing performance. Water can be used effectively, particularly when used with a ballpoint pen.

The water content is preferably 0.1% by mass or more and 20% by mass or less, based on the total amount of the ink composition. This is because within this range, ink ejection properties are improved, line skipping and smearing are suppressed even on prints made with printing inks such as toner, and writing feel is improved. Furthermore, uneven dots and bleeding are suppressed, improving writing performance. Taking this into consideration, the water content of the total amount of the ink composition is preferably 1% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 10% by mass or less.

(Coloring agent)
The colorant used in the water-based ink composition for a writing instrument and the oil-based ink composition for a writing instrument 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. Dyes and pigments may also be used in combination.

Dyes that can be used in oil-based ink compositions 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 an organic acid and a basic dye, salt-forming dyes formed from an acid dye and an organic amine, etc. Among these, salt-forming dyes are preferred in view of their stability with the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer.
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, and BASE OF BASIC DYES VB-B, BASE OF BASIC DYES MVB-3 (all manufactured by Orient Chemical Industries Co., Ltd.), Aizenspiron Black GMH-Special, Aizenspiron 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, S.P.T. Blue 111, S.P.T. Blue GLSH-Special, S.P.T. Red 533, S.P.T. Orange 6, S.B.N. Yellow 510, S.B.N. Yellow 530, S.R. C-BH (all manufactured by Hodogaya Chemical Co., Ltd.).
Examples of pigments include inorganic, organic, and processed pigments. Specific examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, metallic pigments, pearl pigments, fluorescent pigments, and phosphorescent pigments.
These dyes and pigments may be used alone or in combination of two or more.

As the dyes used in the aqueous ink composition, direct dyes, acid dyes, basic dyes, metal-containing dyes, various salt-forming dyes, etc. can be used.
(a) Direct dyes include Direct Yellow 4, 26, 44, 50, and 85; Direct Red 1, 2, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, and 227; Direct Blue 1, 3, 15, 41, 71, 86, 106, and 119; and Direct Orange 6. (b) Acid dyes include Acid Black 1, 2, 24, 26, 31, and 5. 2, 107, Acid Orange 56, Acid Yellow 3, 7, 17, 19, 23, 42, 49, 61, 92, Acid Red 8, 9, 14, 18, 51, 52, 73, 87, 92, 94, Acid Blue 1, 7, 9, 22, 62, 90, 103, Acid Green 3, 9, 16, 25, 27, Acid Violet 15, 17, etc., (c) basic dyes include C.I. Basic Yellow -1, 2, 21, 7, 40, C.I. Basic Orange 2, 14, 32, C.I. Basic Red 1, 1:1, 2, 9, 14, C.I. Basic Violet 1, 3, 7, 10, 11:1, C.I. Basic Blue 3, 7, 26, Basic Green 4, C.I. Basic Brown 12, C.I. Basic Black 2, methyl violet, Victoria Blue FB, malachite green, rhodamine series, etc. (d) Other dyes include disperse dyes such as Disperse Yellow 82, 121, and Disperse Blue 7.

It is also preferable to use a pigment as the colorant, because in the case of a ballpoint pen, the pigment particles create a physical obstacle in the gap between the ball and the inner wall of the tip, which makes it easy to suppress ink leakage. Pigments are also preferred because they provide excellent handwriting durability, especially excellent light resistance.
Furthermore, in the case of a ballpoint pen, the use of a pigment allows the pigment particles to penetrate into the gap between the ball and the tip body, acting like a bearing, and by suppressing metal contact, it is possible to improve lubricity, improve the writing feel, and reduce wear of the ball seat, making it preferable to use a pigment. When using a (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer to improve lubricity, as in the present invention, the use of a pigment is more effective. Furthermore, the synergistic effect of the bearing action between the lubricating layer formed by the surfactant (described below) and the pigment particles makes it easier to maintain lubricity and improve the writing feel, making it preferable.

The colorant content is preferably 5% by mass or more and 30% by mass or less of the total amount of 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, a content of 7% by mass or more and 25% by mass or less is preferable, and even more considering, a content of 10% by mass or more and 20% by mass or less is preferable.

(Surfactant)
In the present invention, it is preferable to use a surfactant, because it improves the lubricity of the writing tip, suppresses line skipping and blurring of handwriting even on prints made with printing ink such as toner, and is likely to improve the writing feel, and in the case of a ballpoint pen, it improves the lubricity between the ball and ball seat, reduces friction between the ball seat, and suppresses wear of the ball seat, which is likely to further improve the writing feel.
Furthermore, the use of a surfactant is preferred because it facilitates improved writing performance when the writing tip (tip tip) dries when the writing tip (tip tip) is left in the air. This is because the use of a surfactant tends to soften the coating formed, improving writing performance and lubricity. Examples of surfactants include silicone surfactants, fluorine-based surfactants, phosphate ester surfactants, polyoxyalkylene alkyl ethers, fatty acids, and fatty acid esters. Considering the above effects, it is preferable to use one or more surfactants selected from phosphate ester surfactants, polyoxyalkylene alkyl ethers, fatty acids, and fatty acid esters. Considering these, it is more preferable to use two or more surfactants. Considering the need for good writing even on prints made with printing inks such as toner, it is preferable to use a phosphate ester surfactant and a polyoxyalkylene alkyl ether in combination.
In particular, when used in a ballpoint pen, it can be used effectively, and further, considering that it suppresses line skipping and blurring of handwriting even on prints formed with printing ink such as toner, it is preferably used as an oil-based ink composition for a writing instrument, and preferably in an oil-based ballpoint pen.

Furthermore, when a phosphate ester surfactant is used, the acid value is preferably 160 or less (mgKOH/g). This is because the improved lubricity provided by the phosphate ester surfactant is easily exhibited, and good writing is facilitated even on characters printed with printing ink such as toner. Furthermore, taking into consideration stability in the ink and lubricity, the acid value is preferably 30 or more and 160 or less, and more preferably 70 or more and 120 or less (mgKOH/g). The acid value is expressed in mg of potassium hydroxide required to neutralize the acidic components contained in 1 g of sample.
When a polyoxyalkylene alkyl ether is used, the alkyl group preferably has 10 to 20 carbon atoms. This is because the alkyl group chain of the polyoxyalkylene alkyl ether has a length suitable for maintaining stable performance of the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer in a solvent and allows for good writing even on prints formed with printing inks such as toner. In consideration of the length of the alkyl group chain, the alkyl group preferably has 12 to 18 carbon atoms. Furthermore, in consideration of maintaining stable performance in a solvent, the alkyl group is preferably a lauryl group, an oleyl group, a stearyl group, or a cetyl group, and more preferably a lauryl group.

The surfactant preferably has an HLB value of 6 or more and 14 or less. This is because an HLB value exceeding 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 to maintain stable performance in solvents, which is likely to affect the effects of the present invention. Furthermore, an HLB value of less than 6 tends to result in excessively strong lipophilicity, which tends to affect compatibility with organic solvents and makes it difficult for the ink to stabilize over time. Furthermore, in consideration of the effects of the surfactant, the HLB value is preferably 12 or less, and an HLB value of 6 or more and 12 or less is preferable. In consideration of better ink performance over time, an HLB value of 7 or more and 12 or less 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 + 11.7 log (Mw/Mo), (Mw: molecular weight of the hydrophilic group, Mo: 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.

Specific examples of surfactants include fatty acids such as oleic acid and linoleic acid; fatty acid esters include fatty acid esters obtained by esterifying fatty acids with monohydric alcohols and fatty acid esters obtained by esterifying fatty acids with alcohols such as polyhydric alcohols; silicone surfactants include dimethyl silicone, methylphenyl silicone, polyether-modified silicone, and higher fatty acid ester-modified silicone; fluorine-based surfactants include perfluoro-group-containing butyl sulfonates, perfluoro-group-containing carboxylates, perfluoro-group-containing phosphate esters, perfluoro-group-containing phosphate ester-type compounds, perfluoroalkyl betaines, and perfluoroalkylamine oxide compounds; phosphate ester surfactants 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; and polyoxyalkylene alkyl ethers include polyoxyethylene alkyl ethers and polyoxypropylene alkyl ethers.

The surfactant content is preferably 0.1% by mass or more and 5.0% by mass or less, based on the total amount of the ink composition. This is because if it is less than 0.1% by mass, it is difficult to achieve the desired lubricity, and if it exceeds 5.0% by mass, the ink is likely to become unstable over time. Taking this into consideration, a content of 0.3% by mass or more and 3.0% by mass or less is preferred, and even more preferably a content of 0.5% by mass or more and 3.0% by mass or less is preferred.

(organic amine)
In the present invention, when a surfactant such as a phosphate ester surfactant is used, neutralization is preferred because it stabilizes the solution in the ink, further improves the lubricity of the writing tip, and helps prevent line skipping and blurring of handwriting even on prints made with printing inks such as toner. It also helps prevent wear on the ball seat, thereby improving the writing feel and writing performance. Examples of organic amines include amines containing ethylene oxide, such as oxyethylene alkylamines and polyoxyethylene alkylamines; alkylamines, such as laurylamine and stearylamine; aliphatic amines, such as dimethyl alkylamines, distearylamine, dimethyl laurylamine, dimethyl stearylamine, and dimethyl octylamine; and alkanolamines, such as diethanolamine and triethanolamine. Among these, amines containing ethylene oxide or dimethyl alkylamines are preferred, considering their solubility in the ink. These may be used alone or in combination.

Furthermore, in consideration of the stability with the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer, colorant, surfactant, and other components, the total amine value of the organic amine is preferably 300 (mgKOH/g) or less. This is because if it exceeds 300 (mgKOH/g), the reactivity is strong and it is likely to affect the above-mentioned components, which is likely to affect the ink stability over time. From this perspective, the total amine value is preferably 200 (mgKOH/g) or less, and even more preferably 150 (mgKOH/g) or less. On the other hand, in consideration of the above effects, the lower limit of the total amine value is preferably 30 (mgKOH/g) or more.
The total amine value indicates the total amount of primary, secondary and tertiary amines, and is expressed as the number of mg of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize 1 g of sample.

The HLB value of the organic amine is preferably 5 to 17. This is because the organic amine is more likely to be stable with the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer, colorant, surfactant, resin, and other components, and the effects of the present invention are more likely to be obtained. From further consideration, the HLB value is more preferably 7 to 17, and even more preferably 9 to 16.
In particular, when a polyacrylic acid resin is used, it is preferable to neutralize it and stabilize its swelling dispersion with the solvent, since this will provide a stable thickening effect.

Taking into consideration stability with the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer, colorant, surfactant, and other components, the content of the organic amine is preferably 0.1% by mass or more and 10% by mass or less of the total amount of the ink composition; and further taking into consideration neutralization of the surfactant mentioned above, it is preferably 0.5% by mass or more and 5% by mass or less.

In the present invention, a resin may also be used 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, polyvinyl acetate resin, polyvinylpyrrolidone resin, ethylene oxide polymer, etc., as well as resin particles such as acrylic ester resin particles and amino resin particles. These may be used alone or in combination of two or more types.

In the present invention, it is preferable to use a shear thinning agent. Examples of shear thinning agents include polyacrylic acid resin, xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, oxidized cellulose, and diutan gum. The inclusion of these agents is preferable because they form a three-dimensional network structure in the ink, which easily imparts pseudoplasticity and is effective in improving the writing feel and writing performance (suppression of handwriting smearing). Among these, polyacrylic acid resins are preferred because they easily form a three-dimensional network structure and a denser crosslinked structure, and from this perspective, crosslinked polyacrylic acid resins are preferred. Polyacrylic acid resins are used as thickeners. Polyacrylic acid resins have affinity with alkylene glycol alkyl ethers, and by swelling and dispersing, they provide pseudoplasticity and a stable thickening effect. Furthermore, from the perspective of writing feel and writing performance (suppression of handwriting smearing and blobbing), crosslinked polyacrylic acid resins are preferred. Furthermore, carboxyvinyl polymers are preferred because they form a denser crosslinked structure, which makes it easier to impart pseudoplasticity, thereby reducing the ink viscosity during writing and improving the writing feel and writing performance (suppressing smearing and bleeding).
In particular, it is effective and preferable to use an amide solvent such as alkylene glycol monoalkyl ether or β-alkoxypropionamide as the organic solvent, since it is easy to form a more three-dimensional network structure.
In particular, when used in a ballpoint pen, it can be used effectively, and further, considering that it suppresses line skipping and blurring of handwriting even on prints formed with printing ink such as toner, it is preferably used as an oil-based ink composition for a writing instrument, and preferably in an oil-based ballpoint pen.

Furthermore, with regard to polyacrylic acid resins, the carboxyl group content in the polyacrylic acid resin is preferably 40% by mass or more and 80% by mass or less, considering that a stable thickening effect can be obtained together with alkylene glycol alkyl ethers. Even more preferably, it is 50% by mass or more and 70% by mass or less. In particular, when alkylene glycol monoalkyl ethers are used as the alkylene glycol alkyl ethers, polyacrylic acid resins with a carboxyl group content of 55% by mass or more and 65% by mass or less are preferred, as they have excellent swelling and dispersibility, and by imparting pseudoplasticity, they tend to lower the ink viscosity during writing and improve the writing feel. Furthermore, alkylene glycol monomethyl ethers are even more preferred.

If the content of the polyacrylic acid resin is less than 0.1% by mass relative to the total amount of the ink composition, the swelling is insufficient and pseudoplasticity is not achieved, making it difficult to improve the writing feel. If it exceeds 5.0% by mass, the swelling and dispersibility in the ink is likely to deteriorate, so the content is preferably 0.1% to 5.0% by mass relative to the total amount of the ink composition. Furthermore, taking into consideration the writing feel, etc., a content of 0.3% to 3.0% by mass is more preferable, and from further consideration, a content of 0.6% to 1.8% by mass is more preferable.

Other additives that may be used include viscosity adjusters, pseudoplasticity-imparting agents such as fatty acid amides and hydrogenated castor oil, as well as colorants, stabilizers, plasticizers, chelating agents, etc. These may be used alone or in combination of two or more.

The ink viscosity of the ink composition for a writing instrument of the present invention is not particularly limited, but in consideration of reducing the ink viscosity during writing, increasing ink consumption, suppressing line skipping and blurring of handwriting even on prints formed with printing inks such as toner, and facilitating an improved writing feel, the ink viscosity at 20°C and a shear rate of 24 sec ^-1 (during writing) is preferably 7000 mPa·s or less, and more preferably 6000 mPa·s or less, and even more preferably 5000 mPa·s or less. On the other hand, in consideration of writing properties such as bleeding, smearing, strike-through, and drying properties of handwriting, the ink viscosity is preferably 100 mPa·s or more, and even more preferably 200 mPa·s or more, and even more preferably 400 mPa·s or more.

Furthermore, when a polyacrylic acid resin is used, imparting pseudoplasticity reduces the ink viscosity during writing, increases ink consumption, and suppresses line skipping and blurring of handwriting even on prints formed with printing inks such as toner, thereby improving the writing feel. In this regard, the ink viscosity at 20°C and a shear rate of 200 sec ^-1 (during writing) is preferably 1500 mPa·s or less, and more preferably 1000 mPa·s or less. Further considerations make the ink viscosity 900 mPa·s or less preferable. On the other hand, in consideration of writing properties such as bleeding, smearing, strike-through, and drying of handwriting, the ink viscosity is preferably 100 mPa·s or more, and more preferably 200 mPa·s or more, and more preferably 400 mPa·s or more.

Furthermore, in consideration of ink followability, the ink viscosity at 20°C and a shear rate of 0.18 sec ^-1 (at rest) is preferably 50,000 mPa·s or less, and more preferably 30,000 mPa·s or less. On the other hand, in consideration of ink leakage suppression, the ink viscosity is preferably 1,000 mPa·s or more, and more preferably 2,000 mPa·s or more, and more preferably 3,000 mPa·s or more.
This is also effective for retractable writing instruments such as knock-type writing instruments and rotary-propelling writing instruments, in which it is necessary to give greater consideration to preventing ink leakage.

When a shear thinning agent is used as in the present invention, the viscosity index n refers to n in the viscosity formula expressed as S = αD ⁿ , where S is the shear stress (dyn/cm ² = 0.1 Pa), D is the shear rate (s ^-1 ), and α is the viscosity coefficient. The viscosity index n can be calculated by measuring the ink viscosity at 20°C using a TA Instruments AR-G2 rheometer (cone plate 40 mm, angle 2°).
The viscosity index n is preferably 0.3 or more and 0.8 or less, in order to suppress line skipping and blurring of handwriting even on prints formed with printing ink such as toner, and in consideration of writing performance such as smooth writing, smearing, and blurring. Considering the balance of writing performance such as smooth writing, smearing, and blurring, the viscosity index n is preferably 0.35 or more and 0.7 or less, and more preferably 0.4 or more and 0.7 or less. It can be used particularly effectively when used in a ballpoint pen.

(ballpoint pen)
Furthermore, the ink consumption per 100 m of a ballpoint pen is preferably 20 mg or more and 100 mg or less. This is because, when the ink consumption per 100 m is within the above range, line skipping and blurring of handwriting are suppressed even on prints formed with printing inks such as toner, improving the writing feel and making it easier to produce thick handwriting. From further consideration, the ink consumption is preferably 25 mg or more and 90 mg or less, and more preferably 40 mg or more and 80 mg or less.
The ink consumption is measured by conducting a spiral writing test 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 is defined as the ink consumption per 100 m.

(ballpoint pen tip)
For ballpoint pen tips, it is preferable to maintain lubricity between the ball and the tip body, prevent blurred handwriting, and reduce wear on the ball seat, improving the writing feel, and to provide a ball seat with an approximately arc-shaped surface on the bottom wall of the ball holding chamber.

The arithmetic mean roughness (Ra) of the ball surface of the ballpoint pen tip used in the present invention is preferably 0.1 nm or more and 12 nm or less. This is because an arithmetic mean roughness (Ra) within this range suppresses line skipping and blurred handwriting even on prints made with printing ink such as toner, improving the writing feel and making it easier to produce thick handwriting. Taking further considerations into account, the arithmetic mean roughness (Ra) is preferably 0.1 nm or more and 10 nm or less, and more preferably 1 nm or more and 8 nm or less. Surface roughness can be measured using a Seiko Epson SPI3800N instrument.

The material used for the balls is not particularly limited, but examples include cemented carbide balls primarily 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.

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 on the ball seat and stability over time, it is preferable to use a stainless steel tip body.

Furthermore, the amount of movement of the ball in the ballpoint pen tip used in the present invention along the vertical axis is preferably 3 μm or more and 25 μm or less. This is because, within this range, ink consumption is increased, preventing line skipping and blurring of handwriting even on prints made with printing ink such as toner, improving the writing feel and making it easier to produce thick handwriting. From a more specific perspective, the amount of movement of the ball in the ballpoint pen tip along the vertical axis is preferably 3 μm or more and 22 μm or less, more preferably 5 μm or more and 20 μm or less, and even more preferably 7 μm or more and 18 μm or less.
(Example)

The present invention will now be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

The present invention will now be described with reference to examples.
The oil-based ink composition for a writing instrument 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 a pigment dispersion, dye, organic solvent, ketone resin, organic amine, surfactant, and resin, weighing out predetermined amounts of these, heating them to 60°C, and then completely dissolving them in a disper stirrer to obtain an oil-based ink composition for a writing instrument. The specific blending amounts are as follows:

Example 1
Colorant (dye, salt-forming dye of acid dye and basic dye) 10.0% by mass
Colorant (dye, salt-forming dye of basic dye and organic acid) 5.0% by mass
Pigment dispersion (pigment content 20%) 15.0% by mass
Alcohol solvent (benzyl alcohol) 28.5% by mass
Glycol ether solvent (ethylene glycol monophenyl ether) 20.0% by mass
(Diglycerin/Dilinoleic Acid/Hydroxystearic Acid) Copolymer 1.0% by mass
Surfactant (phosphate ester surfactant) 2.0% by mass
Surfactant (polyoxyalkylene alkyl ether) 2.0% by mass
Organic amine (HLB value: 15.4) 1.0% by mass
Polyvinyl butyral resin (hydroxyl group amount: 36 mol%) 5.0 mass%
Ketone resin (ketone resin having an aromatic ring) 10.0% by mass
Spinnability-imparting resin (polyvinylpyrrolidone resin) 0.5% by mass

Examples 2 to 4
As shown in the table, except for changing each component, inks were formulated in the same manner as in Example 1 to obtain oil-based ink compositions for writing instruments of Examples 2 to 4. The table shows the measurement and evaluation results.

Example 5
The oil-based ink composition for a writing instrument of Example 5 was prepared by adding a pigment and a pigment dispersant to an organic solvent and dispersing them using a disperser, and then using a colorant, organic solvent, surfactant, and organic amine, weighing out predetermined amounts of these, heating them to 60°C, and dissolving them using a disper stirrer to prepare a base ink. Thereafter, while heating the base ink prepared above, a polyacrylic acid resin was added and the mixture was thoroughly mixed and stirred using a homogenizer stirrer until a uniform state was achieved, thereby obtaining the oil-based ink composition for a writing instrument of Example 5.

Examples 6 to 18
As shown in the table, except for changing the components and tip specifications, inks were formulated in the same manner as in Example 5 to obtain oil-based ink compositions for writing instruments of Examples 6 to 18. The table shows the measurement and evaluation results.

The ink viscosities of Examples 1 and 2 were measured at a shear rate of 500 sec ^-1 in an environment of 20°C using a viscometer, Viscometer RVDVII+Pro CP-52 spindle, manufactured by Brookfield Co., Ltd., and the ink viscosity was 4,500 mPa s in both cases.
Similarly, the ink viscosity of Example 5 was 10,000 mPa·s at a shear rate of 0.18 sec ⁻¹ in an environment of 20° C., and 700 mPa·s at a shear rate of 200 sec ⁻¹ in an environment of 20° C., with a viscosity index n of 0.58.
Similarly, the ink viscosity of Example 8 was 4500 mPa·s at a shear rate of 0.18 sec ⁻¹ in an environment of 20° C., and 550 mPa·s at a shear rate of 200 sec ⁻¹ in an environment of 20° C., with a viscosity index n of 0.67.

Comparative Examples 1 and 2
As shown in the table, except that the components and tip specifications were changed, an oil-based ink composition for a writing instrument of Comparative Example 1 was obtained in the same manner as in Example 1. Also, an oil-based ink composition for a writing instrument of Comparative Example 2 was obtained in the same manner as in Example 5. The measurement and evaluation results are shown in the table.

Tests and Evaluations A ballpoint pen tip was attached to the tip of an ink reservoir (made of polypropylene), which rotatably held a ball (φ0.7 mm) of the ballpoint pen tip, with the ball pressed against the inner wall of the tip end edge by a resilient member, and 0.3 g of the oil-based ink compositions for writing instruments prepared in Examples 1 to 18 and Comparative Examples 1 and 2 was directly placed in the ink reservoir, and the ballpoint pen refill was placed in an oil-based ballpoint pen manufactured by Pilot Corporation, to prepare an oil-based ballpoint pen. The following tests and evaluations were carried out using writing paper JIS P3201 as the writing test paper.
When a spiral writing test was carried out using an oil-based ballpoint pen, the ink consumption per initial 100 m of Examples 1, 2, 5, and 15 was 44 mg/100 m, 40 mg/100 m, 70 mg/100 m, and 80 mg/100 m, respectively.

Writability test 1 (test of writing on toner-printed paper): Handwriting was performed on the toner-printed paper, and the handwriting was observed.
◎: No broken lines or smudged handwriting ○: Some broken lines or smudged handwriting △: Some broken lines or smudged handwriting, but no practical problems ×: Severe broken lines or smudged handwriting

Abrasion resistance test (abrasion test of ball seat): The abrasion of the ball seat after the writing test was measured using a running tester with a load of 350 gf, a writing angle of 70°, and a speed of 4 m/min.
◎: Wear of the ball seat is less than 5 μm. ○: Wear of the ball seat is 5 μm or more but less than 10 μm. △: Wear of the ball seat is 10 μm or more but less than 20 μm, but writing is still possible. ×: Wear of the ball seat is so severe that writing becomes difficult.

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

Writability test 2 (crying and blobbing test): The handwriting was observed after a 100 m writing test using a running tester with a load of 200 gf, a writing angle of 70°, and a speed of 4 m/min.
◎・・・Handwriting has little or no bleeding or blobbing
○: There is some blurring or blobbing in the handwriting, but it is not a problem for practical use.
△: There are tears or smudges in the writing, which affect its practical use.
×...Have a lot of blurred or smudged handwriting

In Examples 1 to 18, good performance was obtained in all of the writability test 1 (writing test on toner-printed paper), abrasion resistance test (ball seat abrasion test), writing feel, and writability test 2 (test for weeping and smearing). When Example 1 and Example 12 were compared in writability test 1 (writing test on toner-printed paper), Example 5, which contained a phosphate ester surfactant, produced significantly better handwriting.
Furthermore, in Examples 1 to 18, a writing test was conducted using a running tester with a load of 200 gf, a writing angle of 70°, and a speed of 4 m/min until the ink ran out. As a result, the remaining ink amount in the ink reservoir could be confirmed throughout the test, and the visibility of the remaining ink amount was good.

In Comparative Examples 1 and 2, the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer was not used, and therefore in Writability Test 1 (writing test on toner-printed paper), when handwritten writing was performed on the toner-printed paper, there was severe line skipping and smearing of the handwriting. Furthermore, in the abrasion resistance test (ball seat abrasion test), the abrasion of the ball seat was also poor.

In addition, in this example, an oil-based ballpoint pen was exemplified in which a ballpoint pen refill containing an oil-based ink composition for a writing instrument was disposed within the barrel. However, the writing instrument of the present invention may also be a direct-fill type ballpoint pen, marking pen, or felt-tip pen in which the barrel itself serves as the ink reservoir and the oil-based ink composition for a writing instrument is directly contained within the barrel, or may have a structure in which an ink reservoir containing an oil-based ink composition for a writing instrument (ballpoint pen refill) is used as a ballpoint pen as is.

The present invention can be used as an ink composition for writing instruments, and more specifically, can be widely used as a cap-type, knock-type, or other oil-based ballpoint pen, marking pen, or felt-tip pen filled with the ink composition for writing instruments.

Claims (6)

An ink composition for a writing instrument, comprising a colorant, a solvent, and a (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer. The ink composition for a writing instrument according to claim 1, characterized in that the content of the (diglycerin/dilinoleic acid/hydroxystearic acid) copolymer is 0.1 to 10% by mass based on the total amount of the ink composition. The writing instrument ink composition according to claim 1 or 2, further comprising a surfactant. The ink composition for a writing instrument according to claim 3, characterized in that the HLB value of the surfactant is 6 or more and 14 or less. A writing instrument containing the writing instrument ink composition described in claim 1. A ballpoint pen having a ballpoint pen tip that rotatably holds a ball at the tip of an ink reservoir, and containing the writing instrument ink composition described in claim 1 within the ink reservoir.