JP2023177364A - Oil-based ballpoint ink composition and oil-based ballpoint including the same - Google Patents

Abstract

To provide an oil-based ballpoint ink composition that improves writing feel, produces handwriting without fading or blotting, and ensures a satisfactory writing experience.SOLUTION: An oil-based ballpoint ink composition contains a colorant, β-alkoxypropionamide, water, and polyacrylic acid resin. The ink viscosity at 20°C and a shear rate of 20 sec-1 is 5000 mPa s or less.SELECTED DRAWING: None

Description

The present invention relates to an ink composition for an oil-based ballpoint pen and an oil-based ballpoint pen using the same.

When writing with oil-based ballpoint pens, the writing resistance between the ball and the tip body tends to affect the writing quality of the ballpoint pen.In particular, unlike other types of writing instruments, ballpoint pens have a metal tip made of stainless steel or the like at the tip. It has a structure in which a transfer ball made of metal such as ultra-steel is held in a ball receiving seat of the metal tip, and a ballpoint pen tip is attached to an ink storage cylinder, but when writing, due to the rotation of the ball, handwriting may become blurred or It had the disadvantages of uneven dots, poor writing quality, and smudges due to ink remaining at the tip of the tip.

To solve these problems, many ink compositions for oil-based ballpoint pens using various lubricants have been proposed for the purpose of improving lubricity in order to suppress the writing resistance between the ball and the tip body.

Ink compositions for oil-based ballpoint pens using such additives include those using alkyl β-D-glucosides, such as ``Oil-based Ballpoint Pen Ink'' published in JP-A-5-331403 and having an average molecular weight of 200 to 4,000,000. An example using a certain polyethylene glycol is JP-A-7-196971 "Ink composition for oil-based ballpoint pen", an example using N-acyl amino acid, N-acylmethyl tauric acid, N-acylmethylalanine is as follows. JP-A-2007-176995 ``Oil-based ballpoint pen ink'' containing at least a big macadamia nut oil fatty acid decaglyceryl and a polyoxyethylene alkyl ether whose alkyl group has 16 or more carbon atoms and is solid at room temperature, It is disclosed in JP-A No. 2008-88264 "Oil-based ink composition for ballpoint pen" and the like.

"Unexamined Japanese Patent Publication No. 5-331403" "Unexamined Japanese Patent Publication No. 7-196971" "Unexamined Japanese Patent Publication No. 2007-176995" "Unexamined Japanese Patent Publication No. 2008-88264"

However, when various additives such as those disclosed in Patent Documents 1 to 4 are used, it is possible to reduce the writing resistance between the ball and the chip body to some extent, but the writing quality is not satisfactory, and the handwriting It was not possible to improve the writing quality, such as smudges and tears, and there was room for improvement. Furthermore, when a new lubricant is used, it may be compatible with other ink components, which tends to affect the stability over time in the ink.

An object of the present invention is to obtain an ink composition for an oil-based ballpoint pen that improves the writing feel and has good writing properties without blurring or blotchy handwriting, and an oil-based ballpoint pen using the same.

The present invention aims to solve the above problems.
1. An ink composition for an oil-based ballpoint pen, comprising a colorant, an amide solvent, and a polyacrylic acid resin.
2. 2. The ink composition for an oil-based ballpoint pen according to item 1, wherein the amide solvent is β-alkoxypropionamide.
3. The oil-based ballpoint pen ink composition according to item 1 or 2, wherein the content of the amide solvent is 50% or more with respect to the total solvent content in the oil-based ballpoint pen ink composition. thing.
4. The ink composition for an oil-based ball-point pen according to any one of Items 1 to 3, wherein the ink composition for an oil-based ball-point pen contains a surfactant.
5. An ink composition for an oil-based ball-point pen, characterized in that the ink composition for an oil-based ball-point pen according to any one of items 1 to 4 has a viscosity index n of 0.2 to 0.6 at 20°C. .
6. The tip of the ink storage cylinder has a ballpoint pen tip rotatably holding a ball, and the ink composition for an oil-based ballpoint pen according to any one of items 1 to 5 is placed in the ink storage cylinder. An oil-based ballpoint pen characterized by a housing. ”.

By containing an amide solvent and a polyacrylic acid resin, the present invention can obtain a stable thickening effect and impart pseudoplasticity to lower the viscosity of the ink during writing and improve the writing feel. It was possible to obtain an ink composition for an oil-based ballpoint pen that had good results, had no blurring or blotches in the handwriting, and did not affect ink tracking performance or ink leakage control, and an oil-based ballpoint pen using the same.

Embodiments of the present invention will be described in detail below. In this specification, "parts", "%", "ratio", etc. indicating formulations are based on mass unless otherwise specified, and content refers to the constituent components based on the mass of the ink composition. mass%.

In this specification, "parts", "%", "ratio", etc. indicating compositions are based on mass unless otherwise specified.

The present invention is characterized by an ink composition for an oil-based ballpoint pen comprising a colorant, β-alkoxypropionamide, water, and a polyacrylic acid resin, the ink composition having an ink viscosity of 5000 mPa·s at 20°C and a shear rate of 20 sec ^-1 . This is an ink composition for an oil-based ballpoint pen characterized by the following.

By containing an amide solvent and a polyacrylic acid resin in the ink composition for an oil-based ballpoint pen, it is possible to impart pseudoplasticity and lower the viscosity of the ink during writing, thereby maintaining a good writing feel. I understand that. This is because by including the amide solvent and the polyacrylic acid resin, pseudoplasticity can be imparted by swelling and dispersing the resin. Furthermore, it has been found that the handwriting is free from smudges and smudges and the writing quality can be improved.

(amide solvent)
The amide solvent used in the present invention is a compound that contains one carboxylic acid amide structure in its molecular structure and has an ether bond in its linear alkyl structure. It is a solvent that has the ability to impart pseudoplasticity, and it has been found that by having pseudoplasticity, it is possible to lower the viscosity of the ink during writing and maintain a good writing feel. . In particular, when a cross-linked polyacrylic acid resin is used, it is easy to form a three-dimensional network structure and a denser cross-linked structure with an amide solvent, which makes it easy to impart pseudoplasticity and is effective. . Furthermore, since the amide solvent itself can improve the lubricity more easily than before, it is possible to further improve the writing quality and to suppress blurring of the handwriting. In addition, since it is difficult to wet the metal ballpoint pen tip, ink does not creep up from the tip of the tip, no ink remains, and by suppressing smeared handwriting, it is possible to improve writing performance. be.
In particular, when using a ballpoint pen, strong shear is easily applied when writing, and the pseudoplastic structure is temporarily dissolved due to the impact of shearing the ball when writing, lowering the ink viscosity and maintaining a good writing feel. Therefore, it can be suitably used in a ballpoint pen.

Regarding amide solvents, specifically, 3-methoxy-N,N-dimethylpropanamide (boiling point 215°C), 3-butoxy-N,N-dimethylpropanamide (boiling point 252°C), 3-ethoxy-N , N-dimethylpropanamide and other β-alkoxypropionamides, formamide (boiling point 210°C), N,N-dimethylformamide (boiling point 153°C), N,N-dimethylacetamide (boiling point 165°C), N,N- Examples include formaldehydes such as diethylformamide (boiling point 177°C) and N,N-diethylacetamide (boiling point 185°C). It is preferable to use β-alkoxypropionamide because it is easier to swell and disperse the polyacrylic acid resin, give it pseudoplasticity, and improve the writing feel. Furthermore, it is more stable with the polyacrylic resin and is more effective. Considering that 3-methoxy-N,N-dimethylpropanamide and 3-butoxy-N,N-dimethylpropanamide are used, most preferably 3-methoxy-N,N-dimethyl It is propanamide.
Furthermore, in order to improve the drying properties of handwriting, it is preferable to use an amide solvent with a boiling point of 300° C. or lower, and more preferably an amide solvent with a boiling point of 270° C. or lower.

The content of the amide solvent is preferably 50% or more of the total solvent content in the oil-based ballpoint pen ink composition, and it is preferably used as the main solvent. This is because when used as the main solvent, it tends to inhibit the swelling and dispersion of polyacrylic acid resin by other solvents, which has an effect on imparting pseudoplasticity and tends to affect the writing feel. . Considering the writing feel, the content of the amide solvent is preferably 70% or more, preferably 90% or more, and more preferably, only the amide solvent is used as the solvent. preferable.

The content of the amide solvent is preferably 0.1 to 80% by mass based on the total amount of the ink composition. If it is less than 0.1% by mass, it is difficult to obtain the swelling and dispersion effect of the polyacrylic acid resin, the ink viscosity at rest is difficult to increase, and it is difficult to suppress ink leakage, and if it exceeds 80% by mass, the ink This is because stability over time tends to be poor. Further, taking the above effects into consideration, it is preferably 20 to 80% by mass, and more preferably 40 to 80% by mass.

(Polyacrylic acid resin)
The polyacrylic acid resin used in the present invention is used as a thickener and has an affinity for amide solvents, and by swelling and dispersing it, a stable thickening effect with pseudoplasticity can be obtained. Furthermore, in consideration of the writing feel, it is preferable to use a crosslinked polyacrylic acid resin. This cross-linked polyacrylic acid resin itself has a cross-linked structure, and with amide solvents, it is easy to form a three-dimensional three-dimensional network structure, and it is easy to form a denser cross-linked structure, which reduces pseudoplasticity. This is because it is easy to apply, the ink viscosity during writing tends to be low, and the writing quality is easily improved. Particularly preferred is carboxyvinyl polymer.

Further, regarding the polyacrylic acid resin, the carboxyl group content in the polyacrylic acid resin is preferably 40 to 80% by mass, considering that a stable thickening effect can be obtained with an amide solvent. Taking more consideration into consideration, it is preferably 50 to 70% by mass, and particularly when β-alkoxypropionamide is used as the amide solvent, polyacrylic acid having a carboxyl group content of 55 to 65% by mass It is preferable to use a resin because it has excellent swelling and dispersion properties and easily improves the writing feel.

If the content of the polyacrylic acid resin is less than 0.1% by mass based on the total amount of the ink composition, the swelling property will not be sufficient and pseudoplasticity will not be obtained, making it difficult to improve the writing feel. If it exceeds 0.0% by mass, the swelling and dispersibility in the ink tends to be poor, so it is preferably 0.1 to 5.0% by mass based on the total amount of the ink composition. Furthermore, if writing quality is taken into consideration, 0.3 to 3.0% by mass is preferable, and if more consideration is given, 0.6 to 2.0% by weight is preferable.

In the present invention, the blending ratio of the amide solvent to the polyacrylic acid resin (amide solvent/polyacrylic acid resin) is preferably 5 to 150 times, more preferably 25 to 120 times, on a mass basis. Preferably, it is most preferably 35 to 80 times. If this is within the above range, it is possible to improve the writing quality, writing properties such as tearing, blurring, etc. in a well-balanced manner.

(colorant)
The coloring agent used in the present invention is not particularly limited, and can be appropriately selected and used, such as dyes and pigments. Dyes and pigments may be used in combination.
Dyes include oil-soluble dyes, acidic dyes, basic dyes, metal-containing dyes, and their various salt-forming dyes, such as salt-forming dyes of acidic dyes and basic dyes, organic acid and basic dyes, etc. Examples include salt-forming dyes with acid dyes and organic amines, and salt-forming dyes with acid dyes and organic amines. These dyes may be used alone or in combination of two or more. As the dye, it is preferable to use at least a salt-forming dye, considering stability over time due to compatibility with amide solvents, and further considering that stability over time can be maintained due to stable salt-forming bonds. It is preferable to use salt-forming dyes with a basic dye and an organic acid, salt-forming dyes with an acidic dye and a basic dye, and salt-forming dyes with an acidic dye and an organic amine. A salt-forming dye made of organic acid and organic acid is preferred. Furthermore, regarding the organic acids constituting the salt-forming dyes, organic acids with phenylsulfonic groups tend to form a lubricating film that is easily adsorbed to metals, improving lubricity, improving writing quality, and suppressing ball seat wear. Specific examples include alkylbenzenesulfonic acid, naphthalenesulfonic acid, naphthalenesulfonic acid-formaldehyde condensate, alkyldiphenyl ether disulfonic acid, and polyoxyethylene alkylphenyl ether phosphoric acid, which are stable in the ink for a long time. Considering this, it is preferable to use alkylbenzenesulfonic acid as the organic acid.

Regarding the dyes, specifically, Varifast Black 1802, Varifast Black 1805, Varifast Black 1807, Varifast Violet 1701, Varifast Violet 1704, Varifast Violet 1705, Varifast Blue 1601, Varifast Blue 1605, Varifast Blue 1613, Varifast Blue 1621, Varifast Blue 1631, Varifast Red 1320, Varifast Red 1355, Varifast Red 1360, Varifast Yellow 1101, Varifast Yellow 1151, Nigrosine Base EXBP, Nigrosine Base EX, BASE OF BASIC DYES ROB-B, BASE OF BASIC DYES RO6G-B, BASE OF BASIC DYES VPB-B, BASE OF BASIC DYES VB-B, BASE OF BASIC DYES MVB-3 (manufactured by Orient Chemical Industry Co., Ltd.), Eisenspi Ron Black GMH-Special, Eisenspiron Violet C-RH, Eisenspiron Blue GNH, Eisenspiron Blue 2BNH, Eisenspiron Blue C-RH, Eisenspiron Red C-GH, Eisenspiron Red C-BH, Eisenspiron Yellow C-GNH, Eizenspiron 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. Violet 510, S. B. N. Yellow 530, S. R. Examples include C-BH (manufactured by Hodogaya Chemical Industry Co., Ltd.).

Pigments include inorganic, organic, and processed pigments, but specific examples include carbon black, aniline black, ultramarine blue, yellow lead, titanium oxide, iron oxide, phthalocyanine, azo, quinacridone, and diketotin. 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.

It is preferable to use pigments as the coloring agent.In the case of ballpoint pens, the pigment particles enter the gap between the ball and the tip body, making it easier to act like a bearing. It is preferable to use pigments because by suppressing contact, the effects of improving lubricity, improving writing quality, and suppressing wear of the ball seat can be easily obtained. As in the present invention, it is preferable to use pigments because the writing quality can be improved by lowering the viscosity of the ink during writing using an amide solvent or polyacrylic acid resin.

The total content of the colorant is preferably 5 to 45% by mass based on the total amount of the ink composition. This is because if it is less than 5% by mass, it is difficult to obtain dark handwriting, and if it exceeds 45% by mass, it tends to affect the solubility in the ink. 7 to 35% by weight is preferred, and with further consideration 10 to 30% by weight.

Moreover, in the present invention, it is preferable that water is included. The reason for this is not clear, but water has an excellent affinity for amide solvents and polyacrylic acid resin, and the amide solvent and polyacrylic resin make the swelling dispersion more stable. This is because it is easy to obtain a thickening effect, and it also improves the slipperiness of the ball, improves ink ejection performance, suppresses dot unevenness, blotches, and smudges, and improves writing performance.

When the content of water is less than 0.1% by mass based on the total amount of the ink composition, it tends to affect the slipperiness of the ball and the ink dischargeability, and when it exceeds 30% by mass, the solubility in the ink is poor. Since it is easy to use, it is preferably 0.1 to 30% by mass based on the total amount of the ink composition. Furthermore, in consideration of suppressing spot unevenness, blotches, smudges, etc., it is preferably 2 to 20% by mass, and more preferably 3 to 15% by mass.

(surfactant)
In the present invention, it is possible to easily improve the writing quality by improving lubricity, and it is also important to take into consideration that the writing performance when the tip end dries after being left in the air is improved. For example, it is preferable to use a surfactant. This is because the lubricating layer formed by the surfactant can easily improve the lubricity, and further soften the film formed by the surfactant, making it easier to improve the writing performance. Examples of the surfactant include fatty acids, silicone surfactants, fluorine surfactants, phosphate ester surfactants, and the like. Among these, in view of the above effects, it is preferable to use one or more of fatty acids, silicone surfactants, and phosphate ester surfactants.
In particular, when used in ballpoint pens, phosphate ester surfactants have a phosphoric acid group that easily adsorbs to ballpoint pen tips and balls made of metals and other materials, making it easy to obtain a lubricating effect. It is preferable to use an activator, and by containing the amide solvent and polyacrylic acid resin used in the present invention, it is easy to obtain an extreme pressure effect between the metal ball and the ball seat, thereby improving lubricity. It is preferable because it is easier to improve.

Regarding the HLB value of the surfactant, considering its compatibility with the amide solvent and polyacrylic acid resin, the HLB value is 5 because it does not easily inhibit swelling and dispersion with the amide solvent and polyacrylic acid resin. ˜17 is preferable. In consideration of further improving swelling dispersibility, lubricity, and writing performance, it is preferable that the HLB value is 6 to 14. Furthermore, in consideration of lubricity, it is preferable that the HLB value is 12 or less, and it is preferable that the HLB value is 6 to 12.
Note that the HLB value used in the present invention can be determined by Griffin's method, Kawakami's method, or the like. In particular, in retractable writing instruments such as knock-type writing instruments and rotary-feeding writing instruments, unlike cap-type writing instruments, the nib is always exposed to the outside, which affects the writing performance when the writing tip is dry. Since it is easy to use, it is more preferable to use a surfactant having the above HLB value.

Specifically, examples of the surfactant include fatty acids such as oleic acid, stearic acid, and linoleic acid, and examples of silicone surfactants include dimethyl silicone, methylphenyl silicone, polyether-modified silicone, and high-grade silicone. Examples include fatty acid ester-modified silicones, and examples of fluorosurfactants include perfluoro group butyl sulfonate, perfluoro group-containing carboxylate, perfluoro group-containing phosphate ester, and perfluoro group-containing phosphate ester type compound. Examples of phosphate surfactants include phosphoric acid monoesters of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether, polyoxyethylene alkyl Examples include phosphoric acid diesters of ethers or polyoxyethylene alkylaryl ethers, phosphoric triesters of polyoxyethylene alkyl ethers or polyoxyethylene alkylaryl ethers, alkyl phosphoric esters, alkyl ether phosphoric esters, or derivatives thereof. In addition, when using a phosphate ester surfactant, the acid value is preferably 150 or less. This makes it easier to obtain a stable thickening effect of the polyacrylic acid resin, and also This is to facilitate the improvement of lubricity by the activator. Considering more stable thickening effect and lubricity, the acid value is preferably 30 to 130. More preferably, the acid value is 50 to 120. Preferable Note that the acid value is expressed in mg of potassium hydroxide required to neutralize the acidic component contained in 1 g of the sample.

The content of the surfactant is more preferably 0.1 to 5.0% by mass 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 obtain the desired lubricity, and if it exceeds 5.0% by mass, the ink tends to become unstable over time. Considering this, the amount is preferably 0.3 to 3.0% by mass based on the total amount of the ink composition, and more preferably 0.5 to 3.0% by mass is most preferred.

(organic amine)
In the present invention, it is preferable to use an organic amine because by neutralizing and stabilizing the polyacrylic acid resin with an organic amine, it is possible to sufficiently swell and disperse the resin and obtain a stable thickening effect. Furthermore, even when using a phosphoric acid ester surfactant, it is preferable because it is neutralized and stabilized so that it is stable in the ink, and the effect of improving writing taste and writing performance can be easily obtained. Examples of organic amines include amines containing ethylene oxide such as oxyethylene alkylamine and polyoxyethylene alkylamine, alkyl amines such as laurylamine and stearylamine, distearylamine, dimethyllaurylamine, dimethylstearylamine, dimethyloctylamine, etc. Examples include aliphatic amines such as dimethylalkylamine, alkanolamines such as diethanolamine and triethanolamine, and among these, amines having ethylene oxide are preferred in consideration of stability with polyacrylic acid resin.

Regarding the reactivity between the organic amine and other components in the ink, primary amines are the strongest, followed by secondary amines and tertiary amines, which have the lowest reactivity, so taking into consideration the stability of the ink over time, It is preferable to use a secondary amine or a tertiary amine, and in consideration of neutralizing and stabilizing the polyacrylic acid resin, a tertiary amine is most preferable. These may be used alone or in combination of two or more.

The HLB value of the organic amine is preferably 5 to 17. This is because a stable thickening effect can be obtained by neutralizing and stabilizing the polyacrylic acid resin and stabilizing the swelling and dispersion with the amide solvent. In consideration of stabilizing neutralization and improving swelling and dispersion properties, it is preferable that the HLB value is 6 to 17, and further, that the HLB value is 7 to 16.

In the present invention, the blending ratio of organic amine to polyacrylic acid resin (organic amine/polyacrylic acid resin) is preferably 0.1 to 10 times, and preferably 0.3 to 5 times, based on mass. is more preferable, and most preferably 0.5 to 3 times. This is because a stable thickening effect can be obtained by neutralizing and stabilizing the polyacrylic acid resin and stabilizing the swelling and dispersion with the amide solvent.

Further, it is preferable that the blending ratio of organic amine (organic amine/(polyacrylic acid resin + surfactant)) to (polyacrylic acid resin + surfactant) is 0.01 to 5 times on a mass basis, It is more preferably 0.1 to 3 times, and most preferably 0.3 to 2 times. This is because within the above range, it is easy to neutralize and stabilize the polyacrylic acid resin and stabilize the swelling and dispersion with the amide solvent, and even when using a surfactant, the neutralization is stabilized and the writing quality and writing performance are improved. This is because it is easy to obtain the effect of improving.

The content of the organic amine is preferably 0.1 to 10% by mass based on the total amount of the ink composition, considering the neutralization stability with the polyacrylic acid resin and phosphate ester surfactant. Considering neutralization of the phosphate ester surfactant, the amount is preferably 0.1 to 5% by weight, and more preferably 0.5 to 3% by weight.

In the present invention, organic solvents other than amide solvents may be used, and specifically, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol monophenyl ether, propylene glycol Glycol ether solvents such as monomethyl ether, propylene glycol monoethyl ether, diethylene glycol dimethyl ether, 3-methoxybutanol, 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, Examples include organic solvents commonly used in oil-based inks, such as alcohol solvents such as ethylene glycol monomethyl ether acetate and other higher alcohols.

In addition, the content of the organic solvent is preferably 10 to 90% by mass based on the total amount of the ink composition, considering the improvement of solubility, handwriting drying properties, bleeding, etc., and considering the drying property at the tip of the tip. For example, it is preferably 20 to 90% by weight, more preferably 40 to 70% by weight.

(resin)
Further, in the present invention, a resin may be used as an ink viscosity modifier to improve ink leakage control. Examples of the resin include polyvinyl butyral resin, ketone resin, polyacetal resin, polyvinyl alcohol resin, cellulose resin, terpene resin, alkyd resin, phenoxy resin, polyvinyl acetate resin, polyvinylpyrrolidone resin, and ethylene oxide polymer.
Here, polyvinyl butyral resin is made by reacting polyvinyl alcohol (PVA) with butyraldehyde (BA), and has a structure having a butyral group, an acetyl group, and a hydroxyl group.

If the total resin content is less than 0.1% by mass based on the total amount of the ink composition, it is difficult to suppress ink leakage, and if it exceeds 30% by mass, the solubility in the ink tends to be poor, so the ink composition The amount is preferably 0.1 to 30% by mass based on the total amount of the substance. Furthermore, in consideration of further suppressing ink leakage, it is preferably 3 to 20% by mass.

The ink viscosity of the ink composition for oil-based ballpoint pens of the present invention is not particularly limited, but when using an amide solvent or polyacrylic acid resin, the ink viscosity can be lowered by imparting pseudoplasticity. The ink viscosity at 20°C and a shear rate of 20 sec ^-1 (during writing) is preferably 7000 mPa・s or less, since it is easy to improve the writing quality and writing properties such as blotches and smudges. For example, the ink viscosity is preferably 5000 mPa·s or less, and more preferably the ink viscosity is 3000 mPa·s or less. In addition, in consideration of ink leakage control and ink followability, the ink viscosity at 20°C and shear rate of 0.18 sec ^-1 (at rest) is preferably 10,000 to 60,000 mPa・s, and more preferably 15,000 to 50,000 mPa・s. is preferred.
In addition, it is effective in retractable writing instruments such as knock-type writing instruments and rotary-feeding writing instruments, since it is necessary to take into account ink leakage suppression.

When an amide solvent and a polyacrylic acid resin are used as in the present invention, the viscosity index n refers to n in the viscosity formula represented by S=αD ⁿ . Note that S represents shear stress (dyn/cm ² =0.1 Pa), D represents shear rate (s ⁻¹ ), and α represents viscosity coefficient. The viscosity index n can be calculated by measuring the ink viscosity at 20° C. using a Viscometer RVDVII+Pro CP-52 spindle manufactured by Brookfield Corporation.
Regarding the viscosity index n, it is preferable to set the viscosity index n = 0.2 to 0.6, considering the writing quality, writing properties such as tearing smudges, and smearing. Considering the balance, it is preferable that the viscosity index n=0.3 to 0.55, and more preferably 0.35 to 0.50.

(ballpoint pen tip)
Further, it is preferable that the amount of movement of the ball of the ballpoint pen tip in the vertical axis direction is 3 to 25 μm. If it is less than 3 μm, it tends to affect the writing quality and feel such as blurred handwriting, blotches, and uneven dots, and if it exceeds 25 μm, it tends to affect blotches, ink tracking performance, and ink leakage control. Therefore, if more consideration is given, it is preferable that the amount of movement in the vertical axis direction is 3 to 20 μm, and if more considered, it is preferable that the amount of movement in the vertical axis direction is 5 to 16 μm.

The arithmetic mean roughness (Ra) of the ball surface of the ballpoint pen tip is preferably 0.1 to 12 nm. This is because if the arithmetic mean roughness (Ra) is less than 0.1 nm, it will be difficult for the ink to be sufficiently applied to the ball surface, and handwriting will likely become blurry or uneven. If this is exceeded, the ball surface will be too rough and the rotational resistance between the ball and the ball seat will be large, which will likely result in poor writing quality, and will also affect the writing quality, such as scratches, smudges, and uneven dots. be. Further, it is preferable that the arithmetic mean roughness (Ra) is 0.1 to 10 nm because ink can easily be deposited on the ball surface, and more preferably 2 to 8 nm. Note that the surface roughness can be measured using (model name SPI38, 00N manufactured by Seiko Epson Corporation).

The materials used for the balls are not particularly limited, but include cemented carbide balls whose main component is tungsten carbide, metal balls such as stainless steel, and ceramics such as silicon carbide, silicon nitride, alumina, silica, and zirconia. Balls, ruby balls, etc.

In addition, the ballpoint pen tip is made of metal materials such as stainless steel, nickel silver, brass, aluminum bronze, and aluminum, and resin materials such as polycarbonate, polyacetal, and ABS. In consideration of performance and cost, it is preferable to use a tip body made of stainless steel.

Example 1
The oil-based ballpoint pen ink composition of Example 1 was prepared by collecting and stirring the amide solvent and polyacrylic acid at 60°C using a disper stirrer, and then adding the colorant, phosphate ester surfactant, and organic The amine was collected, stirred and dissolved, and then cooled to room temperature to obtain an ink composition for an oil-based ballpoint pen.
The blending ratio of organic amine to polyacrylic acid resin (organic amine/polyacrylic acid resin) was 1.6 times. The blending ratio of organic amine (organic amine/(polyacrylic acid resin + surfactant)) to (polyacrylic acid resin + surfactant) was 0.58 times.
The specific blending amounts are as follows. In addition, when the ink viscosity of Example 1 was measured using a Viscometer RVDVII + Pro CP-52 spindle manufactured by Brookfield Co., Ltd., in an environment of 20°C, shear rate was 0.18 sec ^-1 , and ink viscosity = 48500 mPa. Ink viscosity was 2500 mPa·s at a shear rate of 20 sec ⁻¹ in an environment of 20°C. Further, the viscosity index n was 0.37.

Example 1 (ink formulation)
Coloring agent (dye, salt-forming dye of basic dye and organic acid) 10.0% by mass
Coloring agent (dye, salt forming dye with acid dye and amine) 10.0% by mass
Amide solvent (β-alkoxypropionamides: 3-methoxy-N,N-dimethylpropanamide) 74.8% by mass
Crosslinked polyacrylic acid resin 1.25% by mass
Surfactant (phosphate ester surfactant) 2.0% by mass
Organic amine (HLB value: 15) 2.0% by mass

Examples 2-18
As shown in Table 1, ink compositions for oil-based ballpoint pens of Examples 2 to 18 were obtained in the same manner as in Example 1 except that the ink components were changed. The measurement and evaluation results are shown in the table.

Comparative examples 1 to 4
As shown in the table, ink compositions for oil-based ballpoint pens of Comparative Examples 1 to 4 were obtained in the same manner as in Example 1 except that the ink components were changed. The measurement and evaluation results are shown in the table.

Test and Evaluation The oil-based ballpoint pen ink compositions (0.27 g) prepared in Examples 1 to 18 and Comparative Examples 1 to 4 were placed in an ink storage cylinder (polypropylene), and a ball with a ball diameter of φ0.7 mm was rotatably placed. A held ballpoint pen tip (with a coil spring inside the tip that presses the ball directly against the inner wall of the tip edge, axial movement of the ball: 8 μm, arithmetic mean roughness (Ra) of the ball surface: 5 nm). The installed oil-based ballpoint pen refill was filled with the oil-based ballpoint pen to produce an oil-based ballpoint pen. The following tests and evaluations were conducted using writing paper JIS P3201 as a written test paper.

Writing taste: A handwritten sensory test was conducted and evaluated.
Something very smooth...◎
Something smooth...○
Slightly less smooth...△
Heavy things...×

Weakness/Bottle Test (Writability Test 1): The handwriting after the 100m writing test was observed using a running test machine with a load of 200gf, a writing angle of 70°, and a speed of 4m/min.
There are no tears or smudges in the handwriting, or there are few...◎
There are some tears and smudges in the handwriting, but there is no problem for practical use...○
Handwriting has tears or smudges that affect practical use...△
Handwriting with a lot of tears and smudges...×

Scratch test (Writability test 2): The handwriting after the 100 m writing test was observed using a running test machine with a load of 200 gf, a writing angle of 70°, and a speed of 4 m/min.
There are no or few scratches or uneven dots in the handwriting...◎
There are some scratches and uneven dots in the handwriting, but it is at a level that does not pose any practical problems...○
There are scratches or uneven dots in the handwriting, which affects practical use...△
Handwriting with many scratches or uneven dots...×

In Examples 1 to 18, good performance was obtained in both the writing taste, the tear/blemish test (writability test 1), and the smudge test (writability test 2).
The ink viscosities of Examples 2, 3, and 9 were measured using a Viscometer RVDVII+Pro CP-52 spindle manufactured by Brookfield Co., Ltd., and the viscosity index n was calculated.
In Example 2, in an environment of 20 °C, shear rate 0.18 sec ^-1 , ink viscosity = 43100 mPa s, in an environment of 20 °C, shear rate 20 sec ^-1 , ink viscosity = 2000 mPa s, viscosity index n is: It was 0.35.
In Example 3, in an environment of 20 °C, shear rate 0.18 sec ^-1 , ink viscosity = 23100 mPa s, in an environment of 20 °C, shear rate 20 sec ^-1 , ink viscosity = 1500 mPa s, viscosity index n is: It was 0.42.
In Example 9, in an environment of 20 °C, shear rate 0.18 sec ^-1 , ink viscosity = 45200 mPa s, in an environment of 20 °C, shear rate 20 sec ^-1 , ink viscosity = 2250 mPa s, viscosity index n is: It was 0.36.

In Comparative Examples 1 and 2, since no amide solvent was used, the polyacrylic acid resin could not be swelled and dispersed, and the writing quality, tearing/blurring test (writability test 1), and staining test (writability test 2) were insufficient. No effect was obtained.

In Comparative Example 3, polyacrylic acid resin was not used, and in Comparative Example 4, fatty acid amide wax was used as a shear thinning agent, but the writing quality, tearing/blemishing test (writing property test 1), and smearing test ( In writing test 2), sufficient effects were not obtained.

In addition, when using a retractable writing instrument (retractable ballpoint pen) such as a knock-type writing instrument or a rotary-feeding writing instrument, the influence of blurred handwriting is likely to occur, so the above-mentioned amide solvent and polyacrylic acid resin as in the present invention are used. It is effective to use an oil-based ballpoint pen ink composition containing the above.

In addition, in order to suppress ink leakage and improve writing performance (fading of handwriting), the ball, which is rotatably held at the tip of the ballpoint pen tip, is pressed against the inner wall of the edge of the tip by a coil spring, either directly or via a pressing body. It is preferable to include a valve mechanism that allows ink to flow out by creating a gap between the inner wall of the edge of the tip and the ball by the pressing force during writing, and closes the minute gap at the tip when not in use.

In addition, in this example, for convenience, an oil-based ballpoint pen is exemplified in which a refill for an oil-based ballpoint pen containing an ink composition for a writing instrument is directly stored in the barrel, but the writing instrument of the present invention does not have an ink composition in the barrel. The writing instrument may be a ballpoint pen, a marking pen, or a felt-tip pen, which is a direct filling type in which the ink composition for a writing instrument is directly stored in the barrel as a storage cylinder.
Further, in this embodiment, for convenience, a ballpoint pen tip formed by cutting a wire rod is exemplified, but a ballpoint pen tip formed by pressing a pipe material may also be used.

INDUSTRIAL APPLICABILITY The present invention can be used as a writing instrument, and more specifically, it can be widely used as a ballpoint pen as a writing instrument such as a cap type or a retractable type.

Claims (6)

An ink composition for an oil-based ballpoint pen comprising a colorant, β-alkoxypropionamide, water, and a polyacrylic acid resin, characterized in that the ink viscosity at 20° C. and a shear rate of 20 sec ^-1 is 5000 mPa·s or less. An ink composition for an oil-based ballpoint pen. The ink composition for an oil-based ballpoint pen according to claim 1, wherein the water content is 0.1 to 30% by mass based on the total amount of the ink composition. The ink composition for an oil-based ballpoint pen according to claim 1 or 2, wherein the polyacrylic acid resin has a carboxyl group content of 40 to 80% by mass. The oil-based ballpoint pen according to any one of claims 1 to 3, wherein the content of the amide solvent is 50% or more based on the content of all solvents in the oil-based ballpoint pen ink composition. Ink composition for use. Any one of claims 1 to 4, wherein the ink composition for an oil-based ballpoint pen contains one or more surfactants selected from fatty acids, silicone surfactants, and phosphate ester surfactants. The ink composition for an oil-based ballpoint pen according to item 1. The tip of the ink storage cylinder has a ballpoint pen tip rotatably holding a ball, and the ink composition for an oil-based ballpoint pen according to any one of claims 1 to 5 is stored in the ink storage cylinder. An oil-based ballpoint pen that is characterized by the ability to