JP7299827B2 - Oil-based ink composition for writing instrument and writing instrument using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oil-based ink composition for writing instruments and writing instruments using the same.

When the tip of an oil-based ink composition for writing instruments is left in the atmosphere, the solvent, etc. in the ink evaporates, and when the coloring agent, resin, etc., dries and solidifies, blurring of handwriting occurs when writing during dry-up. There was a drawback.

In order to improve the writing performance during such dry-up, the use of various solvents and additives has been investigated. For example, Japanese Patent Application Laid-Open No. 6-247093 "oil-based ballpoint pen" discloses a non-volatile organic solvent having a vapor pressure of 0.005 to 0.5 mmHg (20°C) as a main solvent. JP-A-7-196971 "Ink composition for oil-based ballpoint pen" discloses a composition containing polyethylene glycol having a molecular weight of 200 to 4,000,000. has 16 or more carbon atoms and contains at least a polyoxyethylene alkyl ether which is solid at room temperature is disclosed in Japanese Unexamined Patent Application Publication No. 2008-88264 "Oil-based ink composition for ballpoint pens".

However, in Patent Document 1, if a non-volatile organic solvent having a vapor pressure of 0.005 to 0.5 mmHg (20° C.) is contained as the organic solvent, it has the effect of preventing the ink from drying completely, but the handwriting The drying property of the ink was poor, and this alone was not enough to satisfy the writing performance during dry-up.

Further, in Patent Document 2, when polyethylene glycol having a specific molecular weight is contained as an additive, a resin film is formed on the tip end portion, thereby suppressing further drying of the tip end portion and increasing the amount of ink in the tip. Although it is possible to improve the writing performance to some extent by suppressing the stickiness, the resin film is hard, so when writing during dry-up, the handwriting is blurred, and sufficient writing performance was not obtained. .

Further, in Patent Document 3, by using deca macadamia nut oil fatty acid decaglyceryl together with polyoxyethylene alkyl ether, it is possible to improve the writing performance to some extent, but the lubricity is insufficient and the writing feeling is poor. In addition, since special surfactants are used, depending on the selection of colorants, organic solvents, other surfactants, etc., the ink stability over time will be affected, and dyes and other surfactants If the ink is not compatible with the ink, precipitates are formed, which tends to cause problems in writing.

In addition, in Patent Document 4, in order to improve lubricity and writing comfort, Japanese Patent Application Laid-Open No. 2007-176995 "Ink for oil-based ballpoint pen" discloses N-acylamino acid, N- Although acylmethyltaurate and N-acylmethylalanine were used, the writing resistance between the writing tip and the surface to be written can be reduced to some extent, but they are not sufficiently satisfactory, and the writing performance is also unsatisfactory. Performance was not obtained, and there was room for improvement.

"Japanese Unexamined Patent Publication No. 6-247093" "JP-A-7-196971" "Japanese Unexamined Patent Publication No. 2008-88264" "Japanese Unexamined Patent Publication No. 2007-176995"

There is a need for an oil-based ink composition for writing instruments that satisfies both the writing performance during dry-up and the writing feel, which were not satisfied by the above Patent Documents 1 to 4. This is particularly important when using retractable writing instruments (oil-based ballpoint pens) such as knock-type writing instruments (oil-based ballpoint pens) and rotary feed-type writing instruments (oil-based ballpoint pens), as writing performance is likely to be affected.
Furthermore, in recent years, with oil-based ballpoint pen ink, in order to improve the writing feel, the ink viscosity has been reduced, and when writing with high writing pressure (high writing pressure resistance, writing load 300 to 500 gf) , The lubricity is likely to be affected, and the wear of the ball seat is likely to affect the writing performance. Therefore, in order to further reduce the writing resistance between the writing tip and the surface to be written, it is desired to improve the lubricity and the resistance to high writing pressure.

An object of the present invention is to provide an oil-based ink composition for writing instruments which improves writing performance and writing feel, and has good ink stability over time, and writing instruments using the same.

In order to solve the above problems, the present invention provides: "1. An oil-based ink composition for writing instruments, comprising a colorant, an organic solvent, and a polyglycerin condensed fatty acid ester.
2. 2. The oil-based ink composition for writing instruments according to item 1, wherein the content of the polyglycerin condensed fatty acid ester is 0.1 to 10% by mass with respect to the total amount of the ink composition.
3. Item 3. The oil-based ink composition for writing instruments according to item 1 or 2, wherein the organic solvent is an aromatic alcohol.
4. The oil-based ink composition for writing instruments according to any one of items 1 to 3, wherein the ink viscosity at 20° C. and a shear rate of 5 sec ⁻¹ is 30000 mPa·s or less.
5. A writing instrument containing the oil-based ink composition for writing instruments according to any one of items 1 to 4.
6. The oil-based ink composition for writing utensils according to any one of items 1 to 4 is placed in the ink storage tube, and the tip of the ink storage tube has a ballpoint pen tip that rotatably holds a ball. An oil-based ballpoint pen characterized by being housed. ”.

In the present invention, the film formed by the resin contained in the ink and the polyglycerol condensed fatty acid ester is easy to peel off, so that the writing performance is improved, and at the same time, during writing (when the ball rotates), the conventional An oil-based ink composition for writing instruments that improves the writing feel by reducing the writing resistance (rotational resistance of the ball) at the writing tip than the oil-based ink composition, and is less likely to exhibit ionicity, and has good ink stability over time. I was able to obtain a writing instrument using it.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In this specification, "parts", "%", "ratios", etc. indicating formulations are based on mass unless otherwise specified, and the content refers to the constituent components based on the mass of the ink composition. is the mass % of

A feature of the present invention is to provide an oil-based ink composition for writing instruments comprising a polyglycerin condensed fatty acid ester. This is because when the tip of the tip dries, the coating formed by the resin contained in the ink and the polyglycerol condensed fatty acid ester at the tip of the tip is a stable, uniform, and brittle coating, which is easily peeled off. , While improving the writing performance, at the same time, since the coating is fragile during writing (when the ball rotates), writing resistance at the tip of the writing (ball rotation resistance) is reduced more than before. can be improved.
Furthermore, the polyglycerin condensed fatty acid forms a lubricating layer to maintain the lubricity between the writing tip and the writing surface (including the lubricity between the ball and the tip body). , the writing resistance (rotational resistance of the ball) at the writing tip can be suppressed, and the feeling of writing can be improved. Therefore, in addition to reducing the writing resistance at the writing tip (ball rotation resistance) due to the fragility of the coating formed as described above, the writing resistance at the writing tip (ball rotation resistance) is reduced by forming a lubricating layer. It is effective because the synergistic effect of reducing the rotational resistance of the roller can improve the writing feel. In particular, in the case of a ballpoint pen, the ballpoint pen tip made of a metal material is effective because it easily adsorbs to the metal surface, easily forms a lubricating layer, and can improve the writing feel.
Furthermore, the polyglycerol condensed fatty acid is less likely to exhibit ionicity, less likely to generate precipitates due to other components in the ink, and it is possible to improve the ink stability over time.
Therefore, as described above, it is possible to improve all of the writing performance, writing feel, and ink stability over time.

(Polyglycerin condensed fatty acid ester)
In the present invention, the polyglycerin condensed fatty acid ester is obtained by further ester-bonding an ester obtained by condensing the fatty acids with a fatty acid having one hydroxyl group and polyglycerin obtained by polymerizing glycerin.

The polyglycerin constituting the polyglycerin condensed fatty acid ester used in the present invention includes those having an average degree of polymerization of 2 to 15. Specifically, diglycerin (average degree of polymerization: 2), triglycerin (average degree of polymerization: 3 ), tetraglycerin (average degree of polymerization 4), hexaglycerin (average degree of polymerization 6), octaglycerin (average degree of polymerization 8), decaglycerin (average degree of polymerization 10), etc. can be exemplified. It works well for hygroscopicity and at the same time, it is easy to suppress ink thickening at the tip tip, so it tends to be advantageous for writing performance. Therefore, it is preferable that the average degree of polymerization is 3 to 12. Considering the writing performance, the average degree of polymerization is preferably 4 to 10, more preferably 4 to 8.

The polyglycerol condensed fatty acid ester preferably has an HLB value of 10 or less in consideration of further improving both writing performance and lubricity. This is because when the HLB value is 10 or less, the lipophilicity tends to be strong, which is effective in the present invention. Furthermore, if the HLB value is 5 or less, when the tip tip dries, the coating formed tends to be a stable, uniform, and brittle coating, which is easily peeled off. The HLB value is preferably from 0.3 to 5, since writing resistance (rolling resistance of the ball) can be suppressed and writing comfort can be easily improved. Note that HLB can be determined by the Griffin method or the like.
In particular, in retractable ballpoint pens such as retractable ballpoint pens and rotating ballpoint pens, unlike cap-type ballpoint pens, the tip of the pen is always exposed to the outside, which affects the writing performance when the writing tip is dry. It is more preferable to use the polyglycerin condensed fatty acid ester with the above HLB value because it is easy to use.

In addition, considering that the fatty acid constituting the polyglycerin condensed fatty acid ester improves the writing performance and writing feel, the length of the carbon number of the fatty acid constituting the polyglycerin is set to an appropriate length in order to exhibit the above effects. Specifically, it is preferable to use a fatty acid having 12 to 20 carbon atoms, more preferably a fatty acid having 16 to 20 carbon atoms. Specifically, polyglycerin-condensed ricinoleate and polyglycerin-condensed stearate are preferable. It is preferred to use acid esters.
Specific examples of polyglycerol condensed ricinoleate include Poem PR-100, Poem PR-300 (manufactured by Riken Vitamin), SY Glister CR-310, CR-500, CR-ED (Sakamoto Yakuhin Kogyo Co., Ltd.). (manufactured by Taiyo Kagaku), and Sunsoft 818SK (manufactured by Taiyo Kagaku Co., Ltd.).

The content of the polyglycerin condensed fatty acid 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 is difficult to obtain the desired writing performance and writing feel, and if it exceeds 10% by mass, the ink tends to become unstable over time. Then, it is preferably 0.3 to 5% by mass, more preferably 0.5 to 3% by mass, based on the total amount of the ink composition.

(Organic solvent)
Organic solvents used in the present invention include 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 -glycol ether solvents such as methoxybutanol and 3-methoxy-3-methylbutanol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, glycol solvents such as ethylene glycol, 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. Organic solvents generally used as inks for writing instruments, such as alcohol solvents, can be exemplified.

Among these organic solvents, aromatic alcohols improve lubricity by having an aromatic ring, and easily dissolve with polyglycerin condensed fatty acid esters and polyoxyalkylene glyceryl ethers described later, so they are aromatic. Group alcohol solvents are preferably used.
In addition, when a glycol ether solvent is used, since it easily absorbs moisture, it softens the strength of the coating formed when the tip end part dries, and it is easy to improve writing performance. It is more effective when using a polyoxyalkylene glyceryl ether, which will be described later. Considering stability in the ink, it is preferable to use an aromatic glycol ether solvent.

Further, the content of the organic solvent is preferably 10 to 90% by mass, more preferably 20 to 90%, based on the total amount of the ink composition, in consideration of improving solubility, lubricity, drying property of handwriting, etc. % by mass is preferred, more preferably 40 to 70% by mass.

(coloring agent)
The coloring agent used in the present invention is not particularly limited and may be selected appropriately from dyes, pigments and the like, and dyes and pigments may be used in combination. Dyes include oil-soluble dyes, acid dyes, basic dyes, metal-containing dyes, and various salt-forming type dyes thereof. and salt-forming dyes with acid dyes and organic amine salt-forming dyes. These dyes may be used alone or in combination of two or more.

In addition, it is preferable to use a pigment as the coloring agent in consideration of lubricity. This is because the pigment particles enter the gap between the ball and the tip body, which makes it easier to act like a bearing and prevent metal contact. It is preferable to use a pigment because the effect of suppressing it is likely to improve lubricity, improve writing feel, and suppress abrasion of the ball seat. Furthermore, pigments are preferable because they are excellent in water resistance and light resistance, and good color development can be obtained.

Examples of pigments include inorganic, organic, and processed pigments. Specifically, carbon black, aniline black, ultramarine blue, yellow lead, titanium oxide, iron oxide, phthalocyanine, azo, quinacridone, diketo Examples include pyrrolopyrrole-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, metallic pigments, pearl pigments, fluorescent pigments, and phosphorescent pigments.

In addition, it is preferable to use a pigment as the coloring agent in consideration of lubricity. This is because the pigment particles enter the gap between the ball and the tip body, which makes it easier to act like a bearing and prevent metal contact. It is preferable to use a pigment because the effect of suppressing it is likely to improve lubricity, improve writing feel, and suppress abrasion of the ball seat. Furthermore, pigments are preferable because they are excellent in water resistance and light resistance, and good color development can be obtained.

When a dye is used, it is preferable to use a salt-forming dye in consideration of stability over time due to compatibility with polyoxyalkylene glyceryl ether. Considering this, it is preferable to use a salt-forming dye from a basic dye and an organic acid, a salt-forming dye from an acid dye and a basic dye, or a salt-forming dye from an acid dye and an organic amine. Considering the stability with the components in the ink, a salt forming dye of a basic dye and an organic acid is preferable.

The content of the colorant is preferably 5 to 30% by mass based on the total amount of the ink composition. If it is less than 5% by mass, it tends to be difficult to obtain a dark handwriting. 7 to 25% by mass is preferable, and 10 to 20% by mass is more preferable if further consideration is taken into consideration.

When the polyglycerin condensed fatty acid ester is contained as in the present invention, it is preferable to further contain an organic solvent having a solubility parameter (SP value) of 16 to 30 in addition to the organic solvent. This makes it easier to obtain a surfactant effect in which the condensed polyglycerin fatty acid ester gathers at the interface between the highly polar organic solvent and the less polar polyglycerin condensed fatty acid ester, which is the effect of the present invention. This is because it is easy to suppress the wear of the ball seat under writing pressure and to improve the writing performance.
In particular, when the HLB value is set low, specifically, when using a polyglycerin condensed fatty acid ester with an HLB value of 10 or less, an organic solvent having a solubility parameter (SP value) as described above, It becomes easier to obtain the surfactant effect as described above, and it is effective and preferable because it is easy to improve the writing performance and suppress wear of the ball seat under high writing pressure, which are the effects of the present invention. A polyglycerin condensed fatty acid ester having an HLB value of 5 or less is preferred. Furthermore, in the case of a ball-point pen, the organic solvent within the range of the solubility parameter (SP value) as described above is likely to adsorb to the metal surface and form a lubricating layer on the ball-point pen tip made of a metal material, making it easier to write. It is effective because it can improve taste,
The SP value in the present invention means the solubility parameter (SP value) of an organic solvent, and is a value represented by the square root of molecular cohesive energy. The SP value is described in Polymer Handbook (Second Edition) Chapter IV Solubility Parameter Values, and the value is the SP value in the present invention. Also, the unit is (MPa) ^1/2 and indicates the value at 25°C.

Examples of organic solvents with a solubility parameter (SP value) of 16 to 30 include polyoxyalkylene glyceryl ether, alkylene glycol alkyl ether, alkylene glycol, etc. Considering to further improve both writing performance and lubricity. If so, it is preferable to use polyoxyalkylene glyceryl ether. The polyoxyalkylene glyceryl ether is obtained by addition polymerization of alkylene oxide to glycerin or polyglycerin, and examples thereof include polyoxyalkylene glyceryl ether, polyoxyalkylene diglyceryl ether and polyoxyalkylene triglyceryl ether.
Polyoxyalkylene glyceryl ether is a compound having alkylene oxide in its structure and having hydrophilicity and lipophilicity. By having a hydrophilic group with high polarity in the structure, in the case of a ballpoint pen, it becomes easier to adsorb to the metal material of the ballpoint pen tip, and by creating a lubricating layer, lubricity can be further improved. It is possible to suppress the wear of the ball seats and improve the writing feel even under rolling (writing load of 300 to 500 gf). In addition, by using the polyglycerin condensed fatty acid ester and polyoxyalkylene glyceryl ether used in the present invention together, they have glycerin skeletons in their structures and form a more effective lubricating layer, which further improves lubricity. preferred because it is easy to
Furthermore, since polyoxyalkylene glyceryl ether is difficult to evaporate, it is easy to improve the writing performance even when the writing tip is left in the atmosphere. By using them together, it is possible to improve the hygroscopicity, and at the same time, it is easy to suppress thickening due to ink evaporation at the tip end, and it is easy to obtain a synergistic effect in terms of writing performance, which is preferable.
Furthermore, the polyoxyalkylene glyceryl ether, like the polyglycerin condensed fatty acid ester used in the present invention, has a glycerin skeleton, and thus is stable in the ink, and the ink tends to be stable over time, which is preferable. .

As described above, polyoxyalkylene glyceryl ether is preferable because it is easy to suppress evaporation and can improve ink followability by suppressing ink thickening of the oil-based ink composition for writing instruments as much as possible. In addition, when a pigment is used as a colorant, the viscosity of the ink generally increases due to aggregation of the pigment over time, and the ink followability decreases. and stably disperse the pigment in the oil-based ink, it is possible to improve ink followability by suppressing an increase in ink viscosity due to aggregation of the pigment.
In addition, the polyoxyalkylene glyceryl ether includes polyoxyethylene glyceryl ether, polyoxypropylene glyceryl ether, and the like. By having a propylene group, it has excellent lipophilicity and suppresses moisture absorption of the ink, so that the ink can be used over time. It is preferred to use polyoxypropylene glyceryl ether because it is stable to

Considering that polyoxyalkylene glyceryl ether suppresses abrasion of the ball seat under high writing pressure (writing load of 300 to 500 gf), improves writing feel, and improves writing performance and ink stability over time due to ink absorption. , The average number of added moles of alkylene oxide ((m + n + o + p), (w + x + y + z)) is preferably 1 to 50, and considering the stability of the ink over time due to moisture absorption, the average number of added moles of alkylene oxide is 1 to 30. Furthermore, considering the suppression of wear of the ball seat under high writing pressure, the improvement of the writing feel, the writing performance, and the ink stability over time, the average number of alkylene addition moles is 5 to 20. is preferred.
In particular, considering the suppression of wear of the ball seat under high writing pressure, the average added mole number of propylene oxide (m+n+o+p) is preferably 1 to 30, and more preferably, the average added mole number of propylene oxide is 5 to 30. 20 is preferred, and 8-16 is preferred. Further, considering that the effect of the present invention is likely to be exhibited, the structure of the polyoxyalkylene glyceryl ether is preferably a structure represented by (Chem. 1) or (Chem. 2), and the ink aging due to moisture absorption of the ink is preferable. Considering stability, the structure of (Chem. 1) is preferred.

In addition, the average weight molecular weight of the polyoxyalkylene glyceryl ether is preferably 5000 or less. This is because if the average weight molecular weight is too large, the hygroscopicity tends to increase, which affects the ink stability over time in the oil-based ink. This is because it tends to come out easily, and the viscosity of the ink tends to increase, which tends to affect the ink followability. Considering the stability of the ink over time and the followability of the ink, the average weight molecular weight is preferably 3,000 or less, more preferably 1,500 or less, and more preferably 1,200 or less. On the other hand, if the average weight molecular weight is too small, it is likely to affect the wear suppression of the ball seat, the writing property, and the pigment dispersibility under high writing pressure, so the average weight molecular weight is preferably 300 or more. Considering wear suppression of the ball seat, the average weight molecular weight is preferably 500 or more.
The weight average molecular weight is a value obtained in terms of polystyrene using GPC (gel permeation chromatography).

In addition, when the content of the polyoxyalkylene glyceryl ether is less than 0.1% by mass with respect to the total amount of the ink composition, abrasion of the ball seat under high writing pressure as described above can be suppressed, writing quality, writing performance, There is a risk that the effect of ink followability will not be obtained, and if it exceeds 40% by mass, there is a risk of affecting ink stability over time and ink leakage. It is preferably 3 to 30% by mass in consideration of the above effects, and more preferably 5 to 25% by mass in consideration of the balance between wear suppression of the ball seat and ink stability over time, most preferably 8 to 25% by mass.

In the present invention, the compounding ratio of polyoxyalkylene glyceryl ether to polyglycerin condensed fatty acid ester (polyoxyalkylene glyceryl ether/polyglycerin condensed fatty acid ester) is preferably 1 to 25 times by mass, preferably 3 to 20. More preferably, it is doubled, and most preferably 5 to 12 times. This is because within the above range, it is possible to suppress the wear of the ball seat and improve the writing feel, writing performance, and ink followability in a well-balanced manner.

(resin)
In addition, in order to further improve the suppression of ink leakage, it is preferable to use a resin as an ink viscosity modifier. Examples include alkyd resins, phenoxy resins, polyvinyl acetate resins, etc. Among them, polyvinyl butyral resins and ketone resins are preferred.

Polyvinyl butyral resin also tends to form a lubricating layer that provides a higher lubricating effect. This is because, when the polyvinyl butyral resin is used, an ink layer that is always elastic is formed between the ball and the ball seat, making it difficult to make direct contact with the ball. A higher lubricating effect is likely to be obtained due to the synergistic effect of the lubricating layer formed by using together with polyoxyalkylene glyceryl ether. Furthermore, the use of the polyvinyl butyral resin is preferable because the film formed makes it easier to prevent ink leakage.In addition, when a pigment is used as a coloring agent, a pigment dispersion effect is also obtained, so the use of the polyvinyl butyral resin is preferable. It is preferable to use
Here, the polyvinyl butyral resin is obtained by reacting polyvinyl alcohol (PVA) with butyraldehyde (BA), and has a structure having a butyral group, an acetyl group and a hydroxyl group.

Further, the polyvinyl butyral resin preferably has a hydroxyl group content of 25 mol % or more. This is because polyvinyl butyral resin with a hydroxyl group content of less than 25 mol% does not have sufficient solubility in organic solvents, and it is difficult to obtain sufficient lubricating effect and ink leakage suppression effect. This is because it is preferable to use a polyvinyl butyral resin having a hydroxyl group content of 25 mol % or more. In addition, the polyvinyl butyral resin having a hydroxyl group content of 30 mol % or more is preferable because writing feel is easily improved. This is because frictional heat is generated by the rotation of the ball during writing, which warms the ink at the tip of the tip and raises the temperature of the ink. Unlike other resins, the polyvinyl butyral resin Even if the ink temperature rises, the ink viscosity does not easily decrease, and an elastic ink layer is always formed between the ball and the ball seat, making direct contact difficult and improving the writing feel. tends to be easy. In particular, it is effective for an oil-based ballpoint pen, since writing is often performed with a high writing pressure. Further, if a polyvinyl butyral resin having a hydroxyl group content exceeding 40 mol % is used, the amount of moisture absorption tends to increase, and the stability over time of the ink component is likely to be affected. Therefore, a polyvinyl butyral resin having a hydroxyl group content of 30 to 40 mol % is preferable, and a hydroxyl group content of 30 to 36 mol % is more preferable.
The amount of hydroxyl groups (mol%) of the polyvinyl butyral resin refers to the total molar amount of butyral groups (mol%), acetyl groups (mol%), and hydroxyl groups (mol%). rate.

Regarding the average degree of polymerization of the polyvinyl butyral resin, when the average degree of polymerization is 200 or more, the ink leakage suppressing performance tends to be improved. The average degree of polymerization is preferably 200 to 2,500 because it tends to affect writing feel. Furthermore, in consideration of the above, the average degree of polymerization is preferably 1500 or less, and considering the mutual lubricating effect with polyglycerin condensed fatty acid ester and polyoxyalkylene glyceryl ether, the average degree of polymerization is 200 to 1000. is preferred. Here, the average degree of polymerization refers to the number of basic units constituting one molecule of the polyvinyl butyral resin, and the value measured based on the method specified in JISK6728 (2001 edition) can be adopted. .

The content of the polyvinyl butyral resin is preferably 50% or more of the total resin content in the oil-based composition for oil-based ballpoint pens, and is preferably used as the main resin. This is because when the content of the polyvinyl butyral resin is less than 50% of the total resin content, the other resins tend to hinder the formation of an elastic ink layer, resulting in poor writing quality. In addition, it tends to inhibit the formation of a resin film on the tip tip, the ink dripping cannot be suppressed, and the formation of an elastic ink layer is inhibited, resulting in the effect of improving the writing feel. This is because it will be difficult for Considering the tendency to improve writing quality and ink dripping performance, the polyvinyl butyral resin content is preferably 70% or more, preferably 90% or more, of the total resin content.

If the content of the resin is less than 1% by mass of the total amount of the ink composition, the desired lubricity and ink leakage control performance tend to be poor, and if it exceeds 40% by mass, the solubility in the ink tends to be poor. , preferably 1 to 40% by mass based on the total amount of the ink composition. Furthermore, taking into consideration, it is preferably 5% by mass or more, and if it exceeds 30% by mass, the viscosity of the ink becomes too high and tends to affect the writing feel. ~25 wt% is preferred.

In the present invention, the lubricity of the writing tip (ball and ball seat of the ballpoint pen) is improved, the writing feeling is improved, and the writing tip is left in the air for a longer time to write when the writing tip is dry. Considering that the performance (long-time writing performance) is improved, and that the ballpoint pen tip and the ink container are made of metal, the rust prevention effect can be easily obtained, the phosphate ester surfactant is further included. It is preferable to be
This is because the phosphate ester surfactant has a phosphoric acid group, so in the case of a ballpoint pen, it easily adsorbs to the metal surface of the ballpoint pen tip, and in particular, forms a lubricating layer between the ball and the ball seat. Therefore, the phosphoric acid ester-based surfactant can improve the long-time writing performance more than the polyglycerin condensed fatty acid ester while improving the lubricity and writing comfort. Therefore, the combined use of a phosphoric acid ester surfactant and a polyglycerin condensed fatty acid ester or polyoxyalkylene glyceryl ether works synergistically to further enhance the lubricity between the ball and the ball seat. It can improve the smoothness of writing. Furthermore, the phosphate ester surfactant also has the effect of improving the writing performance, and by using it in combination with polyglycerin condensed fatty acid esters and polyoxyalkylene glyceryl ethers, the writing performance can be further improved. A rust-preventing effect is also obtained.
Therefore, in the present invention, it is effective to use a phosphoric acid ester-based surfactant in combination with polyglycerin condensed fatty acid ester or polyoxyalkylene glyceryl ether.
Furthermore, in the present invention, when polyvinyl butyral is used, the use of a phosphate ester surfactant further improves lubricity due to a lubricating layer of polyvinyl butyral and a lubricating layer of a phosphate ester surfactant. easy, effective and preferred.

In the phosphate ester-based surfactant, the HLB value is preferably 6 to 14 in consideration of further improving both lubricity and writing performance. This is because if the HLB value exceeds 14, the hydrophilicity tends to be strong, and the solubility in the ink tends to be poor, so it is difficult to obtain the effect of the phosphate ester surfactant, and in particular, it is difficult to obtain the lubricating effect. It's for. On the other hand, if the HLB value is less than 6, the lipophilicity becomes too strong, which tends to affect compatibility with organic solvents, makes it difficult to obtain ink stability over time, and makes it difficult to improve writing performance. In consideration of lubricity, the HLB value is preferably 12 or less, preferably 6 to 12, and more preferably 7 to 12 in consideration of writing performance. In particular, in retractable ballpoint pens such as retractable ballpoint pens and rotating ballpoint pens, unlike cap-type ballpoint pens, the tip of the pen is always exposed to the outside, which affects the writing performance when the writing tip is dry. It is more preferable to use a phosphate surfactant with the above HLB value because it is easy to use. The HLB can be determined by Griffin's method, Kawakami's method, or the like.

Phosphate ester-based surfactants include phosphate esters having an alkoxy group (C _a H _2a+1 O), monoester phosphates of polyoxyethylene alkyl ethers or polyoxyethylene alkylaryl ethers, polyoxyethylene alkyl ethers or poly Phosphate diesters of oxyethylene alkyl aryl ethers, phosphate triesters of polyoxyethylene alkyl ethers or polyoxyethylene alkyl aryl ethers, alkyl phosphates, alkyl ether phosphates or derivatives thereof, and the like.

In addition, when a phosphate ester surfactant is used, the acid value is preferably 150 or less. Considering stability in ink and lubricity, the acid value is preferably 30 to 120, more preferably 70 to 120. The acid value is included in 1 g of the sample. It is expressed in milligrams of potassium hydroxide required to neutralize acidic components.

In the present invention, considering the stability of the ink components in the ink, it is preferable to use an organic amine. Amines containing ethylene oxide such as oxyethylenealkylamine and polyoxyethylenealkylamine; alkylamines such as laurylamine and stearylamine; and dimethylalkylamines such as distearylamine, dimethyllaurylamine, dimethylstearylamine and dimethyloctylamine. Of these, ethylene oxide-containing amines and dimethylalkylamines are preferred in terms of stability in ink, and dimethylalkylamines are more preferred.

Regarding the reactivity between the organic amine and other components in the ink, the primary amine has the highest reactivity, followed by the secondary amine and the tertiary amine, which have the lowest reactivity. Preference is given to using secondary or tertiary amines. You may use these individually or in mixture of 2 or more types.

In addition, as viscosity modifiers, pseudoplasticity imparting agents such as fatty acid amides and hydrogenated castor oil, colorant stabilizers, plasticizers, chelating agents, and the like may be used as appropriate. These may be used singly or in combination of two or more.

The ink viscosity ^of the oil-based ink composition for writing instruments of the present invention is not particularly limited. The ink viscosity at 20° C. and a shear rate of 5 sec ⁻¹ (at rest) is preferably 30000 mPa·s or less because the taste and ink followability tend to be poor. In addition, if the ink viscosity is less than 1000 mPa·s at 20° C. and a shear rate of 5 sec ⁻¹ (at rest), it is difficult to suppress ink leakage. Considering the improvement of ink leakage suppression, writing feel, ink followability, and writing performance, the ink viscosity is more preferably 1000 to 25000 mPa s. 20000 mPa·s is preferred.

(writing implements)
The oil-based ink composition for writing instruments according to the present invention can be applied to various writing instruments, including oil-based ballpoint pens and oil-based marking pens. It is preferably used for retractable type ballpoint pens such as knock type and rotating feed type. Such a ball-point pen comprises a storage cylinder containing the oil-based ink composition according to the present invention, and a ball-point pen tip having a ball rotatably held in a ball-holding chamber disposed at the tip of the storage cylinder. is. The ball-point pen tip can be projected and retracted from the front end opening of the barrel, and has a structure generally called a retractable ball-point pen. In general, when the ink composition is used in a retractable ballpoint pen whose pen tip is not sealed, the tip tip is constantly left in the atmosphere, so the tip tip dries and tends to cause blurring at the time of writing. , the use of the composition according to the present invention is preferred because such problems are ameliorated.

(ballpoint pen tip)
Further, the arithmetic average roughness (Ra) of the ball surface of the ball-point 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 to sufficiently apply ink to the ball surface, it is difficult to obtain dark handwriting when writing, line skipping and blurring are likely to occur in handwriting, and arithmetic average roughness If the roughness (Ra) exceeds 12 nm, the surface of the ball is too rough and the rotational resistance between the ball and the ball seat is large, so the ball seat is likely to wear and the writing quality is poor. This is because writing performance such as unevenness is likely to be affected. Further, when the arithmetic mean roughness (Ra) is 0.1 to 10 nm, when the ink composition of the present invention is used, it is more preferable because it improves the writing feel and the ink easily spreads on the ball surface. Considering the writing comfort, the thickness is preferably 2 to 8 nm. The surface roughness can be measured by (model name SPI3800N manufactured by Seiko Epson Corporation).

The material used for the balls is not particularly limited, but includes cemented carbide balls containing tungsten carbide as a main component, metal balls such as stainless steel, and ceramics such as silicon carbide, silicon nitride, alumina, silica, and zirconia. A ball, a ruby ball, etc. are mentioned.

Ballpoint pen tip materials include metal materials such as stainless steel, nickel silver, brass (brass), aluminum bronze, and aluminum, and resin materials such as polycarbonate, polyacetal, and ABS. Considering the durability, it is preferable to use a tip body made of stainless steel.

(Example)
The present invention will now be described with reference to examples.
To the oil-based ink composition for writing instruments of Example 1, an organic solvent, a pigment, and a pigment dispersant were added in advance and dispersed with a three-roll disperser to prepare a pigment dispersion. After that, a pigment dispersion, an organic solvent, polyglycerin condensed fatty acid ester, polyvinylpyrrolidone, and polyvinyl butyral resin are adopted, and a predetermined amount of them are weighed, heated to 60° C., and completely dissolved using a disper stirrer. An oil-based ink composition for writing instruments was obtained. Specific compounding amounts are as follows.
The ink viscosity of Example 1 was measured at a shear rate of 5 sec ⁻¹ (rotation speed of 2.5 rpm) in an environment of 20° C. using a Viscometer RVDVII + Pro CP-52 spindle manufactured by Brookfield Co., Ltd. , the ink viscosity was 3000 mPa·s.

Example 1
Pigment dispersion (20% pigment content, 20% polyvinyl butyral content) 20.0% by mass
Alcohol solvent (benzyl alcohol) 76.5% by mass
Polyglycerin condensed fatty acid ester (hexaglycerin ester: average degree of polymerization 6, constituent fatty acid: ricinol (carbon number 18)) 2.0% by mass
Polyvinylpyrrolidone 0.5% by mass
Polyvinyl butyral resin 1.0% by mass

Examples 2-19
As shown in the table, except that each component was changed, the ink was blended in the same procedure as in Example 1 to obtain oil-based ink compositions for writing instruments of Examples 2 to 19. The evaluation results are shown in the table.

Comparative Examples 1-2
As shown in the table, oil-based ink compositions for writing instruments of Comparative Examples 1 and 2 were obtained in the same procedure as in Example 1, except that each component was changed. The evaluation results are shown in the table.

Test and Evaluation The oil-based ink compositions for writing instruments prepared in Examples 1 to 19 and Comparative Examples 1 and 2 were applied to the tip of an ink container (made of polypropylene) with a ball (φ0.7 mm, the arithmetic mean roughness of the ball surface ( Ra): 7 nm))) was rotatably held, and the oil-based ballpoint pen ink (0.2 g) of Example 1 was directly accommodated in the ink container cylinder, and a ballpoint pen refill was supplied. ) It was placed in an oil-based ballpoint pen (trade name: Supergrip (registered trademark)) manufactured by Pilot Corporation to prepare an oil-based ballpoint pen, and the following tests and evaluations were performed using writing paper JIS P3201 as a writing test paper.

Abrasion resistance test (abrasion test of ball seat): Abrasion of the ball seat after the writing test was measured using a running tester with a load of 400 gf, a writing angle of 70°, and a speed of 4 m/min.
Abrasion of the ball seat is less than 5μm・・・◎
Abrasion of the ball seat is 5 μm or more and less than 10 μm ・・・○
Wear of the ball seat is 10 μm or more and less than 20 μm, but writable ・・・△
The wear of the ball seat is severe, resulting in poor writing ・・・×

Writing feel: Evaluation was made by performing a sensory test by handwriting.
Very smooth...◎
Smooth ・・・○
Practical level of smoothness ・・・△
heavy thing ...×

Writing performance test: After writing by handwriting, leave it in an environment of 20 ° C. and 65% RH for 24 hours with the tip tip exposed, and then write under the following writing conditions in a running test. was measured.
<Writing conditions> Under the conditions of a writing load of 200 gf, a writing angle of 70°, and a writing speed of 4 m/min, linear writing was performed using a running tester and evaluated.
The length of handwriting blur is less than 5 mm ◎
The length of handwriting blurring is 5 mm or more and less than 10 mm ・・・○
△
The length of handwriting blur is 20 mm or more ・・・×

Ink aging test: After one month in an environment of 50° C., the ink inside the chip body was observed under a microscope.
Good with no deposits ・・・◎
Minor deposits ・・・○
Precipitates are generated, but there is no practical problem ・・・△
Deposits that cause blurred or poor writing, etc. ・・・×

Ink followability test: After one month in an environment of 50°C, continuous rapid handwriting was performed for 10 seconds.
No blurry handwriting, no skipped lines ・・・◎
There were some handwriting faintness and line skipping, but it was at a level that was not a problem for practical use ・・・○
Wrong handwriting, missing lines ・・・△
Scratches in handwriting and severe line skipping ・・・×

In Examples 1 to 19, good performance was obtained in the abrasion resistance test (ball seat wear test), writing quality, writing performance test, ink aging test, and ink follow-up performance test.
In Examples 1 to 17 and 19, pigments were used as colorants, and the pigment dispersibility was good and stable.

In Comparative Examples 1 and 2, since no polyoxyalkylene glyceryl ether was used, the wear resistance test (ball seat wear test) was poor. was inferior.

In addition, when using retractable oil-based writing instruments (ball-point pens, marking pens) such as knock-type oil-based writing instruments (ball-point pens, marking pens) and rotary feeding-type oil-based writing instruments (ball-point pens, marking pens), writing performance is one of the important performances. Therefore, it is effective to use the ink composition of the present invention.

Further, in the present embodiment, an oil-based ball-point pen in which a ball-point pen refill containing an oil-based ink composition for a writing instrument is disposed in the barrel is exemplified in the ink reservoir cylinder. It may be a direct filling type ballpoint pen in which the oil-based ink composition for writing instruments is directly stored in the cylinder, an oil-based ballpoint pen as a marking pen, or an oil-based marking pen, and the oil-based ink for writing instruments is stored in the ink storage cylinder. A structure in which a ballpoint pen or a marking pen is used as it is may be used as a refill containing the composition.

INDUSTRIAL APPLICABILITY The present invention can be used as an oil-based ink composition for writing instruments, and more specifically, it can be widely used as cap-type, knock-type, etc. oil-based ballpoint pens and oil-based marking pens filled with the ink composition for oil-based writing instruments.

Claims (6)

An oil-based ink composition for writing instruments, comprising a coloring agent, an organic solvent, and a polyglycerin condensed fatty acid ester. 2. The oil-based ink composition for writing instruments according to claim 1, wherein the content of said polyglycerol condensed fatty acid ester is 0.1 to 10% by mass with respect to the total amount of the ink composition. 3. The oil-based ink composition for writing instruments according to claim 1, wherein the organic solvent is an aromatic alcohol. 4. The oil-based ink composition for writing instruments according to claim 1, wherein the ink viscosity at 20° C. and a shear rate of 5 sec ⁻¹ is 30000 mPa·s or less. A writing instrument containing the oil-based ink composition for writing instruments according to any one of claims 1 to 4. A ball-point pen tip rotatably holding a ball is provided at the tip of the ink containing cylinder, and the oil-based ink composition for writing instruments according to any one of claims 1 to 4 is contained in the ink containing cylinder. An oil-based ballpoint pen characterized by: