Oil-based ink composition for writing instruments and writing instrument including the same

Abstract

To provide an oil-based ink composition for writing instruments that exhibits superior water resistance and offers superior writing performance without excessive penetration of ink traces into the paper and without bleed-through on paper, and a writing instrument including the same.SOLUTION: An oil-based ink composition for writing instruments contains a colorant, a water-soluble organic solvent, and a polycarbonate resin.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an oil-based ink composition for a writing instrument and a writing instrument using the same. [Background technology]

[0002] Conventionally, oil-based ink compositions for writing instruments have contained dyes as colorants because of their excellent color development properties, and many oil-based ink compositions for writing instruments have been proposed that use various dyes as colorants, such as basic dyes, acid dyes, and direct dyes, or dyes that are processed from these dyes.

[0003] Various dyes are used in such oil-based ink compositions for writing instruments. Examples of ink compositions using a salt-forming dye consisting of a triarylmethane-based basic dye and an azo-based yellow acid dye are disclosed in JP-A-9-165542 ("Oil-based black ink") and JP-A-9-71745 ("Oil-based black ink"), and examples of ink compositions using a salt-forming dye based on a basic dye are disclosed in JP-A-8-134393 ("Black ink composition for oil-based ballpoint pens"). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] "Unexamined Japanese Patent Publication No. 9-165542" [Patent Document 2] "Unexamined Japanese Patent Publication No. 9-71745" [Patent Document 3] "Unexamined Japanese Patent Publication No. 8-134393" Summary of the Invention [Problem to be solved by the invention]

[0005] However, unlike pigments, the inks in Patent Documents 1 to 3 redissolve when the handwriting is wetted with water or alcohol, causing the dye to bleed out, which can cause problems such as making the written characters difficult to read and causing the dye to transfer onto unused writing media. Furthermore, the ink stability over time is easily affected by factors such as precipitation of the dye, and in particular, when a surfactant is contained, the surfactant may react with the dye to cause precipitation, raising concerns about the ink stability over time.

[0006] An object of the present invention is to provide an oil-based ink composition for a writing instrument which has excellent water resistance and writing properties without bleed-through, and a writing instrument using the same. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention "1. An oil-based ink composition for a writing instrument, comprising a colorant, a water-soluble organic solvent, and a polycarbonate resin. 2. The oil-based ink composition for writing instruments according to item 1, wherein the content of the polycarbonate resin is 0.1 to 35% by mass based on the total amount of the ink composition. 3. The oil-based ink composition for a writing instrument according to item 1 or 2, wherein the viscosity average molecular weight of the polycarbonate resin is 10,000 to 50,000. 4. The oil-based ink composition for writing instruments described in item 1 or 2, characterized in that the water-soluble organic solvent is selected from the group consisting of alkylene glycol alkyl ethers, alkylene oxide derivatives of glycerin, amide solvents, and alkylene oxide derivatives of glycerin. 5. The solubility parameter (SP value) of the organic solvent that dissolves in water is 9 to 15 (cal / cm 3 ) 1 / 2 3. The oil-based ink composition for a writing instrument according to claim 1 or 2, characterized in that 6. The oil-based ink composition for a writing instrument according to item 1 or 2, characterized in that the oil-based ink composition for a writing instrument contains a surfactant. 7. A writing instrument, characterized in that it contains the oil-based ink composition for a writing instrument described in item 1 or 2. Effect of the Invention

[0008] The present invention provides an oil-based ink composition for a writing instrument that contains a colorant, a water-soluble organic solvent, and a polycarbonate resin, and thus has excellent water resistance and writing properties without excessive penetration into paper and without strike-through, and a writing instrument using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments of the present invention will be described in detail. In this specification, unless otherwise specified, "parts", "%", "ratio" and the like indicating the composition are based on mass, and the content is the mass% of the constituent components based on the mass of the ink composition.

[0010] The present invention is characterized in that it comprises a colorant, a water-soluble organic solvent, and a polycarbonate resin, and thereby dissolves stably in the water-soluble organic solvent, has excellent water resistance, and provides writing properties without bleed-through, and provides an oil-based ink composition for a writing instrument and a writing instrument using the same.

[0011] By including a polycarbonate resin in the oil-based ink composition for writing instruments, water resistance is obtained that allows the handwriting to be visible even if the handwriting is wetted with water or alcohol, and further, the handwriting does not penetrate too much into the paper surface, making it possible to achieve excellent writing properties without bleed-through.

[0012] (Polycarbonate resin) In the present invention, by containing a polycarbonate resin, even if the handwriting is wetted with water or alcohol, it is difficult for the handwriting to redissolve, has excellent water resistance, and can be stably dissolved in water-soluble organic solvents. As the polycarbonate resin, it is preferable to use the following general formula (Chemical Formula 1), and specific examples include Mitsubishi Gas Chemical's Iupizeta series. JPEG2025012761000001.jpg27125

[0013] The lower limit of the viscosity average molecular weight (Mv) of the polycarbonate resin is preferably 10000 or more, more preferably 15000 or more, and particularly preferably 20000 or more. The upper limit of the viscosity average molecular weight (Mv) is preferably 50000 or less, more preferably 40000 or less, and even more preferably 35000 or less. By setting the viscosity average molecular weight to be equal to or more than the above lower limit, the ink can be stably dissolved in a water-soluble organic solvent, and even if the handwriting is wetted with water or alcohol, the handwriting can be visually recognized. Furthermore, the handwriting does not penetrate too much into the paper surface, and excellent writing properties can be achieved without bleed-through. The viscosity average molecular weight (Mv) is measured according to the following method. <Measurement of viscosity average molecular weight (Mv)> The viscosity average molecular weight (Mv) of the polycarbonate resin was calculated from the intrinsic viscosity (η) (unit: dL / g) at 20°C using an Ubbelohde viscometer with methylene chloride as a solvent, and the viscosity average molecular weight (Mv) was calculated from the following Schnell viscosity formula. η=1.23×10-4×Mv0.83

[0014] Moreover, the polycarbonate resin preferably has a glass transition temperature of 100° C. or higher, more preferably 110° C. or higher, and even more preferably 120° C. or higher. The upper limit of the glass transition temperature is preferably 180° C. or lower, and even more preferably 160° C. or lower. The glass transition temperature is measured according to the method described in the examples below (hereinafter the same applies to the glass transition temperature). By setting the glass transition temperature to be equal to or higher than the above lower limit, the ink can be stably dissolved in a water-soluble organic solvent, and even if the handwriting is wetted with water or alcohol, water resistance is obtained that allows the handwriting to be visible, and further, the handwriting does not penetrate too much into the paper surface, resulting in excellent writability without bleed-through. The glass transition point is a temperature calculated by the midpoint method using a differential scanning calorimeter, measuring 10 mg of a sample at a heating rate of 10° C. / min.

[0015] The content of the polycarbonate resin is preferably 0.1 to 35% 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 desired water resistance and writing performance without strike-through, and if it exceeds 35% by mass, it is likely to affect the solubility with water-soluble organic solvents. From a more detailed consideration, the content is preferably 1 to 20% by mass, and from a further consideration, the content is preferably 1 to 15% by mass, and more preferably 3 to 15% by mass.

[0016] (Water-soluble organic solvent) The water-soluble organic solvent is an organic solvent that dissolves at 0.1 g or more in 100 g of water at 20° C., and specifically includes alkylene glycol alkyl ethers such as alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers, amide solvents of β-alkoxypropionamides such as 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, and 3-ethoxy-N,N-dimethylpropanamide, polyoxyalkylene glyceryl ethers, polyoxyalkylene alkyl glucosides, polyoxypropylene alkyl ethers, and the like. Examples of organic solvents include alkylene oxide derivatives of glycerin such as glycerol, 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 water-soluble organic solvents, taking into consideration the solubility with polycarbonate resin, organic solvents that dissolve 3 g or more in 100 g of water at 20° C. are preferred, more preferably organic solvents that dissolve 10 g or more, and more preferably organic solvents that dissolve 20 g or more.

[0017] Among these water-soluble organic solvents, in consideration of solubility in polycarbonate resin and ease of exhibiting better water resistance and writing performance without strike-through, it is preferable to select from alkylene glycol alkyl ethers, amide solvents, alkylene oxide derivatives of glycerin, and aromatic alcohols, and from this viewpoint, alkylene glycol alkyl ethers, β-alkoxypropionamide amide solvents, and alkylene oxide derivatives of glycerin are more preferable, and in consideration of further improving water resistance and writing performance without strike-through, alkylene glycol alkyl ethers and β-alkoxypropionamide amide solvents are more preferable.

[0018] In addition, for organic solvents that are soluble in water, the solubility parameter (SP value) is 9 to 15 (cal / cm 3 ) 1 / 2 This is to improve the solubility with the polycarbonate resin and obtain the effects of the present invention, and from further consideration, the solubility parameter (SP value) is preferably 9 to 13 (cal / cm 3 ) 1 / 2 Further, if considered, the solubility parameter (SP value) is preferably 9 to 12 (cal / cm 3 ) 1 / 2 It is preferable that the density is 10 to 12 (cal / cm 3 ) 1 / 2 It is preferable that: The solubility parameter (SP value) of the solvent in the present invention is a value expressed by the square root of the molecular cohesive energy, and is described in Chapter IV, Solubility Parameter Values, of the Polymer Handbook (Second Edition), and this value was used. The unit is (cal / cm 3 ) 1 / 2 and refers to the value at 25°C. For those cases where no data is given, the values ​​can be calculated according to the method described in RF Edors, Polymer Engineering Science, 14, p. 147 (1967).

[0019] In addition, the boiling point of the water-soluble organic solvent is preferably 170° C. or higher. If the boiling point is lower than 170° C., the organic solvent is likely to evaporate, which may affect the ink stability over time and increase the ink viscosity, so from further consideration, it is preferable to set the boiling point to 200° C. or higher. On the other hand, if the boiling point exceeds 300° C., it is likely to affect the drying property of the handwriting, so it is preferable to set the boiling point to 300° C. or lower, and from further consideration, it is preferable to set the boiling point to 280° C. or lower.

[0020] In addition, in consideration of improving solubility, handwriting drying properties, bleeding, etc., the content of the water-soluble organic solvent is preferably 10 to 80 mass %, more preferably 20 to 70 mass %, based on the total amount of the ink composition.

[0021] Regarding alkylene glycol alkyl ethers, in consideration of the ease of dissolving stably in polycarbonate resin and ink stability over time, the number of carbon atoms in the alkylene glycol moiety of the alkylene glycol alkyl ether is preferably 2 to 10, more preferably 2 to 8, and more preferably 2 to 6. Furthermore, in consideration of good compatibility with polycarbonate resin and surfactants described below and ease of improving writing performance and writing feel, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, and more preferably 4 to 6. Among these, in consideration of the solubility of the salt-forming dye in the polycarbonate resin and the ink stability over time, it is preferable to select from among triethylene glycol monoalkyl ether solvents, ethylene glycol monoalkyl ether solvents, and dipropylene glycol monoalkyl ether solvents, and from further consideration, it is preferable to select from among triethylene glycol monoalkyl ether solvents and ethylene glycol monoalkyl ether solvents, with triethylene glycol monoalkyl ether solvents being more preferable.

[0022] Regarding the number of carbon atoms in the alkyl ether moiety of the alkylene glycol alkyl ethers, in consideration of the ease of dissolving stably in polycarbonate resin and the ink stability over time, the number of carbon atoms is preferably 1 to 8, and more preferably 3 to 6, and more preferably 1 to 3. Furthermore, in consideration of good compatibility with polycarbonate resin and surfactants described below and the ease of improving the writing performance and writing feel, the number of carbon atoms is preferably 1 to 8, and more preferably 1 to 6, and more preferably 1 to 3. Among these, taking into consideration the solubility with polycarbonate resin, the ink stability over time, and the start-up performance, it is preferable to select from among alkylene glycol monomethyl ether solvents, alkylene glycol monobutyl ether solvents, and alkylene glycol monophenyl ether solvents, and from these considerations, alkylene glycol monomethyl ether solvents and alkylene glycol monophenyl ether solvents are preferred, with alkylene glycol monomethyl ether solvents being more preferred.

[0023] Examples of alkylene glycol monoalkyl ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, butylene glycol monomethyl ether structure, butylene glycol monoethyl ether structure, etc. These may be used alone or in combination of two or more. Examples of alkylene glycol dialkyl ethers include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, those having a dibutylene glycol dimethyl ether structure, those having a dibutylene glycol diethyl ether structure, etc. These may be used alone or in combination of two or more.

[0024] In the present invention, the colorant may be appropriately selected from dyes, pigments, etc., and may be used in combination. Examples of dyes include oil-soluble dyes, acid dyes, basic dyes, metal-containing dyes, and various salt-forming dyes thereof, such as salt-forming dyes of acid dyes and basic dyes, salt-forming dyes of organic acids and basic dyes, and salt-forming dyes of acid dyes and organic amines. These dyes may be used alone or in combination of two or more. As dyes, salt-forming dyes are preferably used in consideration of stability over time due to compatibility with water-soluble organic solvents and polycarbonate resins, and salt-forming dyes are preferably used in consideration of stability over time due to stable salt-forming bonds, such as salt-forming dyes of basic dyes and organic acids, salt-forming dyes of acid dyes and basic dyes, and salt-forming dyes of acid dyes and organic amines.

[0025] Examples of pigments include inorganic, organic, and processed pigments, and specific examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, metallic pigments, pearl pigments, fluorescent pigments, and phosphorescent pigments. These may be used alone or in combination of two or more.

[0026] As the colorant, it is preferable to use a pigment, since the use of a pigment can improve water resistance.

[0027] The total content of the colorants 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 tends to be difficult to obtain thick handwriting, and if it exceeds 45% by mass, it tends to affect the solubility in the ink. Taking this tendency into consideration, the content is preferably 7 to 35% by mass, and more preferably 10 to 30% by mass.

[0028] (resin) It is also preferable to use a resin as an ink viscosity adjuster. 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, and the like. Among these, it is preferable to use a polyvinyl butyral resin or a ketone resin because of its stability with water-soluble organic solvents and the ease with which water resistance can be imparted by the resin film formed on the handwriting. If water resistance is taken into consideration, a ketone resin is preferable.

[0029] Polyvinyl butyral resin is easy to form a lubricating layer that can provide a higher lubricating effect. This is because, when the polyvinyl butyral resin is used, a resilient ink layer is always formed between the ball and the ball seat, making direct contact difficult, and therefore the writing feel is easily improved, so that the ink can be discharged smoothly, and by increasing the ink consumption, the robustness (water resistance, alcohol resistance, light resistance) of the handwriting is easily improved. Furthermore, when the polyvinyl butyral resin is used, the coating formed makes it easier to improve ink leakage, which is preferable, and when a pigment is used as a colorant, a pigment dispersion effect is also obtained, so that the polyvinyl butyral resin is preferably used. Here, the polyvinyl butyral resin is obtained by reacting polyvinyl alcohol (PVA) with butyraldehyde (BA), and has a structure having butyral groups, acetyl groups, and hydroxyl groups.

[0030] In addition, the polyvinyl butyral resin preferably has a hydroxyl group content of 25 mol% or more. This is because polyvinyl butyral resins with a hydroxyl group content of less than 25 mol% are not sufficiently soluble in the water-soluble organic solvent, making it difficult to obtain the effects of the present invention, and furthermore, considering the writing performance due to hygroscopicity, it is preferable to use polyvinyl butyral resins with a hydroxyl group content of 25 mol% or more. From a more detailed consideration, polyvinyl butyral resins with a hydroxyl group content of 30 mol% or more are preferable, and furthermore, since it is easy to improve the writing feel, the ink can be discharged smoothly, and by increasing the ink consumption, it is easy to work advantageously on the robustness (water resistance) of the handwriting. In addition, when a polyvinyl butyral resin with a hydroxyl group content of more than 40 mol% is used, the amount of moisture absorption is likely to increase, which is likely to affect the stability over time with the ink components, so polyvinyl butyral resins with a hydroxyl group content of 40 mol% or less are preferable. Therefore, a polyvinyl butyral resin having a hydroxyl group amount of 30 to 40 mol % is preferable, and a hydroxyl group amount of 30 to 36 mol % is more preferable. The amount (mol %) of hydroxyl groups in the polyvinyl butyral resin refers to the content of hydroxyl groups (mol %) relative to the total molar amount of butyral groups (mol %), acetyl groups (mol %), and hydroxyl groups (mol %).

[0031] If the content of the resin is less than 1% by mass relative to the total amount of the ink composition, the desired lubricity, ink leakage suppression performance, and water resistance are likely to be inferior, and if it exceeds 40% by mass, the solubility in the ink is likely to be inferior, so the content is preferably 1 to 40% by mass relative to the total amount of the ink composition.Furthermore, if the content is more than 3% by mass, the ink viscosity tends to become too high and affect the writing feel, so the content is preferably 3 to 30% by mass, and more preferably 5 to 25% by mass.

[0032] (Surfactant) The ink composition according to the present invention preferably contains a surfactant, because the surfactant softens the coating formed on the writing tip by the components (colorant, resin, etc.) contained in the ink composition, and is likely to improve the writing performance and lubricity, thereby improving the writing feel, allowing the ink to be discharged smoothly, and increasing the ink consumption, which tends to favor the fastness (water resistance, alcohol resistance, light resistance) of the handwriting. Examples of the surfactant include silicone surfactants, fluorine surfactants, phosphate surfactants, polyoxyalkylene alkyl ethers, fatty acids, fatty acid esters, etc. Among them, in consideration of the above effects, it is preferable to use one or more selected from phosphate surfactants, polyoxyalkylene alkyl ethers, fatty acids, and fatty acid esters, and since it is easier to improve the writing feel, eject the ink smoothly, and increase the ink consumption to improve the fastness of the handwriting, it is preferable to use phosphate surfactants and polyoxyalkylene alkyl ethers, and in consideration of the above, phosphate surfactants are preferable.

[0033] 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 by increasing the amount of ink consumed, the fastness of the handwriting (water resistance, alcohol resistance, light resistance) is more likely to be advantageous. Furthermore, taking into consideration the stability and lubricity in the ink, 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 as the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of sample. When a polyoxyalkylene alkyl ether is used, the number of carbon atoms in the alkyl group is preferably 10 or more and 20 or less. This is because the alkyl group chain of the polyoxyalkylene alkyl ether has a length suitable for maintaining stable performance in the organic solvent, and the effects of the present invention are easily exhibited, and in consideration of the length of the alkyl group chain, the number of carbon atoms in the alkyl group is preferably 12 or more and 18 or less. Furthermore, in consideration of maintaining stable performance in the organic solvent, the alkyl group is preferably a lauryl group, an oleyl group, a stearyl group, or a cetyl group, and in consideration of this, a lauryl group is more preferable.

[0034] The surfactant preferably has an HLB value of 6 or more and 14 or less. This is because when the HLB value exceeds 14, the surfactant is likely to have strong hydrophilicity, and therefore is likely to have poor solubility in oil-based ink, making it difficult to obtain the effects of the surfactant and difficult to maintain stable performance in the solvent, which is likely to affect the effects of the present invention. In addition, when the HLB value is less than 6, the surfactant is too lipophilic, which is likely to affect compatibility with the organic solvent, making it difficult for the ink to become stable over time. Furthermore, in consideration of the effects of the surfactant, the HLB value is preferably 12 or less, and more preferably 6 or more and 12 or less, and more preferably 7 or more and 12 or less in consideration of ink performance over time. The HLB can be determined by the Griffin method, the Kawakami method, etc., and as an example, it can be determined from the general formula HLB=7+11.7log(Mw / Mo), (Mw: molecular weight of hydrophilic group, Mo: molecular weight of lipophilic group), etc. 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.

[0035] Specific examples of the surfactant include fatty acids such as oleic acid and linoleic acid, fatty acid esters obtained by esterification reaction of fatty acids with monohydric alcohols, and fatty acid esters obtained by esterification reaction of alcohols such as polyhydric alcohols, silicone surfactants such as dimethyl silicone, methylphenyl silicone, polyether-modified silicone, and higher fatty acid ester-modified silicone, fluorine-based surfactants such as perfluoro group-containing butyl sulfonate, perfluoro group-containing carboxylate, perfluoro group-containing phosphate, perfluoro group-containing phosphate type compound, perfluoroalkyl betaine, and perfluoroalkylamine oxide compound, phosphate ester surfactants such as polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate monoester, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate diester, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate triester, alkyl phosphate ester, alkyl ether phosphate ester, and derivatives thereof, and polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ether and polyoxypropylene alkyl ether.

[0036] The content of the surfactant 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 obtain the desired lubricity, and if it exceeds 5.0% by mass, the ink tends to become unstable over time. From a more specific perspective, the content is preferably 0.3% by mass or more and 3.0% by mass or less based on the total amount of the ink composition, and even more preferably 0.5% by mass or more and 3.0% by mass or less.

[0037] (Organic amine) In the present invention, when a surfactant such as a phosphate surfactant is used, neutralization is preferred because it is easy to obtain the effect of dissolving and stabilizing the surfactant in the ink, further improving the lubricity of the writing tip, and improving the writing feel and writing performance. Examples of organic amines include amines having ethylene oxide such as oxyethylene alkylamines and polyoxyethylene alkylamines, alkyl amines such as laurylamine and stearylamine, aliphatic amines such as dimethyl alkyl amines such as distearylamine, dimethyl lauryl amine, dimethyl stearyl amine, and dimethyl octyl amine, and alkanol amines such as diethanol amine and triethanol amine. Among these, amines having ethylene oxide or dimethyl alkyl amines are preferred in consideration of dissolving stability in the ink. These may be used alone or in combination of two or more.

[0038] Furthermore, the total amine value of the organic amine is preferably 300 (mgKOH / g) or less, taking into consideration the stability with water-soluble organic solvents, polycarbonate resins, colorants, and other components. If it exceeds 300 (mgKOH / g), the reactivity is strong, and it is likely to affect the above-mentioned components, which in turn 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, taking into consideration 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 milligrams of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize 1 g of sample.

[0039] The HLB value of the organic amine is preferably 5 to 17. This is because the organic amine is easily stable with a water-soluble organic solvent, a polycarbonate resin, a colorant, and other components, and the effects of the present invention are easily obtained. From further consideration, the HLB value is preferably 7 to 17, and from further consideration, the HLB value is preferably 9 to 16.

[0040] Taking into consideration the stability with the water-soluble organic solvent, the polycarbonate resin, the colorant, and other components, the content of the organic amine is preferably 0.1 mass % or more and 10 mass % or less of the total amount of the ink composition, and further taking into consideration neutralization with the above-mentioned surfactant, the content is preferably 0.5 mass % or more and 5 mass % or less.

[0041] In addition, as viscosity adjusters, pseudoplasticity imparting agents such as fatty acid amides and hydrogenated castor oil, colorant stabilizers, spinnability imparting agents, plasticizers, chelating agents, water, etc. may be appropriately used. These may be used alone or in combination of two or more.

[0042] Also, at 20°C and a shear rate of 1.9 sec -1 The ink viscosity at is not particularly limited, but considering that it is easy to improve the writing feel, the ink can be discharged smoothly, and the fastness of the handwriting (water resistance, alcohol resistance, light resistance) is favorably improved by increasing the ink consumption, it is recommended to use a shear rate of 1.9 sec at 20°C. -1 In this case, the ink viscosity is preferably 6000 mPa·s or less, more preferably 5000 mPa·s or less, and more preferably 4500 mPa·s or less. On the other hand, having a suitable ink viscosity suppresses the promotion of wear between the ball and the ball seat of the tip body, and taking into consideration writing properties such as bleed-through, bleeding, bleeding, and drying of handwriting, and pigment dispersibility, the ink viscosity is preferably 150 mPa·s or more, and more preferably 250 mPa·s or more. This is also effective for retractable writing instruments such as knock-type writing instruments and rotary-type writing instruments, in which it is necessary to give special consideration to preventing ink leakage.

[0043] (Ballpoint pen) In addition, the ink consumption of the ballpoint pen per 100 m is preferably 20 mg or more and 100 mg or less. This is because when the ink consumption per 100 m is in the above range, the writing feel is improved and it is easy to produce thick handwriting. From further consideration, it is preferable that the ink consumption is 25 mg or more and 90 mg or less, and more preferably 40 mg or more and 80 mg or less. Regarding ink consumption, a spiral writing test is conducted using five test samples at a writing speed of 4 m / min on JIS P3201 writing paper at a writing angle of 70° and a writing load of 200 g at 20°C. The average ink consumption per 100 m is defined as the ink consumption per 100 m.

[0044] (Ballpoint pen tip) As for the ballpoint pen tip, it is preferable to maintain lubricity between the ball and the tip body to improve the writing feel, and to provide a ball seat having a substantially arcuate surface on the bottom wall of the ball holding chamber.

[0045] In addition, 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 when the arithmetic mean roughness (Ra) is in the above range, the writing feel is easily improved, the ink can be discharged smoothly, and the fastness (water resistance, alcohol resistance, light resistance) of the handwriting is easily improved by increasing the ink consumption. From further consideration, the arithmetic mean roughness (Ra) is preferably 0.1 nm or more and 10 nm or less, more preferably 1 nm or more and 8 nm or less. The surface roughness can be measured using a model named SPI3800N manufactured by Seiko Epson Corporation.

[0046] The material used for the balls is not particularly limited, but examples include cemented carbide balls mainly composed of tungsten carbide, metal balls such as stainless steel, ceramic balls such as silicon carbide, silicon nitride, alumina, silica, and zirconia, and ruby ​​balls.

[0047] In addition, materials for ballpoint pen tips include metal materials such as stainless steel, nickel silver, brass, aluminum bronze, and aluminum, and resin materials such as polycarbonate, polyacetal, and ABS, but considering wear of the ball seat and stability over time, it is preferable to use a stainless steel tip body.

[0048] In addition, the movement amount of the ball in the ballpoint pen tip used in the present invention in the vertical direction is preferably 3 μm or more and 25 μm or less. This is because, within the above range, the ink consumption is increased, the writing feel is improved, and thick handwriting is easily obtained, and from further consideration, the movement amount of the ball in the ballpoint pen tip in the vertical direction 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.

[0049] (Example) The present invention will now be described with reference to examples. The ink composition for oil-based ballpoint pens in Example 1 was prepared by weighing out a predetermined amount of a colorant, a water-soluble organic solvent, a polycarbonate resin, a phosphoric acid ester surfactant, an organic amine, and a ketone resin, and then completely dissolving the ingredients using a disper stirrer to obtain an ink composition for oil-based ballpoint pens. The specific blending amounts are as follows: The ink viscosity of Example 1 was measured using a Brookfield Viscometer RVDVII+Pro CP-42 spindle at a shear rate of 1.9 sec at a temperature of 20°C. -1 , the ink viscosity was 4500 mPa·s.

[0050] Example 1 (ink formulation) Colorant (salt-forming dye of acid dye and basic dye) 10.0% by mass Colorant (basic dye and organic acid salt-forming dye) 5.0% by mass Colorant (pigment dispersion) 15.0% by mass Water-soluble organic solvent (β-alkoxypropionamides) (solubility parameter (SP value): 10.5 (cal / cm 3 )1 / 2 , boiling point: 215℃)) 47.0% by mass Polycarbonate resin 15.0% by mass Phosphate ester surfactant 2.0% by mass Organic amine (polyoxyethylene alkylamine (HLB: 15.4) 1.0% by mass Ketone resin 5.0% by mass

[0051] Examples 2 to 15 As shown in Table 1, oil-based ink compositions for writing instruments of Examples 2 to 15 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.

[0052] Comparative Examples 1 to 4 As shown in the table, except that the ink components were changed, oil-based ink compositions for writing instruments of Comparative Examples 1 to 1 were obtained in the same manner as in Example 1. The evaluation results are shown in the table. [Table 1] [Table 2]

[0053] Testing and Evaluation The oil-based ink compositions (0.4 g) for writing instruments prepared in Examples 1 to 15 and Comparative Examples 1 to 4 were filled into oil-based ballpoint pen refills equipped with a ballpoint pen tip (having a coil spring in the tip that presses the ball directly against the inner wall of the tip end edge, the ball's movement in the vertical axis direction: 10 μm, the arithmetic mean roughness (Ra): 3 nm) that rotatably holds a ball with a ball diameter of φ0.7 mm in an ink storage tube, to prepare oil-based ballpoint pens. The following tests and evaluations were carried out using JIS P3201 writing paper as the writing test paper.

[0054] In the same manner as in Example 1, Examples 2, 3, and 5 were subjected to a shear rate of 1.9 sec in an environment of 20°C. -1The ink viscosity was measured at a rotation speed of 0.5 rpm and was found to be 1200 mPa·s in Example 2, 250 mPa·s in Example 3, and 710 mPa·s in Example 5.

[0055] Water resistance test: Handwriting was written in a spiral on writing paper, and after drying, it was immersed in water for 24 hours and the condition of the handwriting was observed. ◎ The handwriting is good. ○ The handwriting has faded but is still legible △: The handwriting is faint and causes problems in practical use. × Handwriting is not visible

[0056] Writability test (penetration test): The handwriting was observed after a 30m writing test using a running test machine with a load of 200gf, a writing angle of 70°, and a writing speed of 4m / min. ◎ No bleed-through of handwriting ○: There is some bleeding through of the writing, but it is not a problem for practical use. △: Writing shows through to the other side, affecting practical use ×: There is a lot of bleed-through in the writing

[0057] Writing feel: Evaluation was performed by a sensory test using handwriting. ◎ Very smooth ○ Smooth △ Slightly inferior smoothness ×Heavy items

[0058] Solubility test: The ink was left at room temperature for one month and then observed under a microscope. ◎ Stable and good dissolution ○ A small amount of insoluble matter has occurred △: Insoluble matter was generated, but no practical problems were observed. × Insoluble matter may occur, causing blurring or poor writing results.

[0059] In Examples 1 to 15, good performance was obtained in the water resistance test, the writability test (writing bleed-through test), the writing feel, and the solubility test.

[0060] In Comparative Examples 1 and 2, since no polycarbonate resin was used, the water resistance and the writability test (writing bleed-through test) were poor. In Comparative Examples 3 and 4, since a water-soluble organic solvent was not used, the polycarbonate resin did not dissolve, and the water resistance and writability test (writing bleed-through test) were poor.

[0061] In addition, in this embodiment, for convenience, an oil-based ballpoint pen is exemplified in which an oil-based ballpoint pen refill in which an oil-based ink composition for a writing instrument is directly contained within the barrel. However, the writing instrument of the present invention may also be a directly-filled ballpoint pen, marking pen, or felt-tip pen in which the barrel serves as an ink-containing barrel and the ink composition for a writing instrument is directly contained within the barrel. Further, in this embodiment, for convenience, a ballpoint pen tip formed by cutting a wire material is exemplified, but a ballpoint pen tip formed by pressing a pipe material may also be used. [Industrial Applicability]

[0062] INDUSTRIAL APPLICABILITY The present invention can be used as a writing instrument, and more specifically, can be widely used as a ballpoint pen, such as a cap type or a retractable type writing instrument.

Claims

1. An oil-based ink composition for a writing instrument, comprising a colorant, a water-soluble organic solvent, and a polycarbonate resin.

2. 2. The oil-based ink composition for writing instruments according to claim 1, wherein the content of the polycarbonate resin is 0.1 to 35% by mass based on the total amount of the ink composition.

3. 3. The oil-based ink composition for writing instruments according to claim 1, wherein the viscosity average molecular weight of the polycarbonate resin is 10,000 to 50,000.

4. 3. The oil-based ink composition for writing instruments according to claim 1, wherein the water-soluble organic solvent is selected from the group consisting of alkylene glycol alkyl ethers, alkylene oxide derivatives of glycerin, amide solvents, and alkylene oxide derivatives of glycerin.

5. The solubility parameter (SP value) of the water-soluble organic solvent is 9 to 15 (cal / cm ３ ) １／２ 3. The oil-based ink composition for a writing instrument according to claim 1, wherein

6. 3. The oil-based ink composition for a writing instrument according to claim 1, further comprising a surfactant.

7. A writing instrument, comprising the oil-based ink composition for writing instruments according to claim 1 or 2 contained therein.

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