Oil-based ink composition for writing instrument and writing instrument containing the same

Abstract

To provide an oil-based ink composition for writing instrument which, while being the oil-based ink containing a dye, can form highly water-resistant writing that remains smear-free even upon water contact on writing surfaces made of various materials, and a writing instrument containing the oil-based ink composition.SOLUTION: The present invention provides an oil-based ink composition for writing instrument, comprising a dye, an organic solvent, and a phenol compound represented by the general formula (1), and a writing instrument incorporating the oil-based ink composition. In the formula, R1 represents a hydrogen atom, a straight-chain, branched, or cyclic aliphatic alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms; R2 represents a hydrogen atom or a straight-chain, branched, or cyclic aliphatic alkyl group having 1 to 8 carbon atoms; s is a numerical value of 0 to 2, the total number of hydroxyl groups in the compound (i.e., the sum of s) being 2 or more; and a is a numerical value of 0 to 2.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an oil-based ink composition for writing instruments. More specifically, the present invention relates to an oil-based ink composition for writing instruments that can form a handwriting with excellent water resistance, and a writing instrument incorporating the same.

Background Art

[0002] Conventionally, in oil-based ink compositions, dyes have been widely used as colorants because of their excellent color development properties. However, oil-based ink compositions containing dyes tend to have reduced water resistance, and when water adheres, bleeding of the ink composition from the handwriting occurs and spreads around, resulting in bleeding of the handwriting. In view of this problem, methods such as incorporating gold-containing dyes into the ink composition or increasing the amount of the resin contained have been carried out. However, ink compositions containing gold-containing dyes do not have sufficient color development properties, and ink compositions with an increased amount of resin have a high viscosity, and there is room for improvement in their writing performance.

[0003] In order to solve the above problems, the addition of various compounds has been studied. For example, it has been proposed to incorporate sucrose fatty acid esters with an HLB value of 8 or less or sucrose fatty acid esters with an HLB value of 9 to 11 into the ink composition (see, for example, Patent Documents 1 and 2). However, even for sucrose fatty acid esters with a specified HLB value, sufficient effects were not exhibited depending on the type of dye used, the material of the writing surface, etc., and the water resistance of the handwriting could not be improved. In particular, when the material of the writing surface is paper, the handwriting oozes and spreads easily around the handwriting when water adheres, and the appearance of the handwriting becomes extremely poor. Therefore, there has been a demand for an oil-based ink composition that can form a handwriting with high water resistance capable of preventing the occurrence of bleeding even when the material of the writing surface is paper.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, the problem to be solved by the present invention is to provide an oil-based ink composition for writing instruments that can form a handwriting with high water resistance, even with an oil-based ink containing a dye, and that does not bleed even when water adheres to writing surfaces made of various materials.

Means for Solving the Problems

[0006] The present invention requires an oil-based ink composition for writing instruments comprising a dye, an organic solvent, and a phenolic compound represented by the following general formula (1).

Chemical Formula

Effects of the Invention

[0007] According to the present invention, while maintaining excellent color development using a dye, it has high water resistance against writing surfaces of various materials and can form a handwriting without bleeding. In particular, even when the material of the writing surface is paper that is prone to bleeding of the handwriting, it is possible to form a handwriting having high water resistance without bleeding. Furthermore, according to the oil-based ink composition for writing instruments of the present invention, it is possible to provide a writing instrument incorporating an oil-based ink composition for writing instruments that is excellent in convenience and rich in practicality.

Embodiments for Carrying Out the Invention

[0008] (Oil-based ink composition for writing instruments) The oil-based ink composition for writing instruments of the present invention (hereinafter simply referred to as "ink composition") is characterized by containing at least a dye, an organic solvent, and a phenolic compound represented by the following general formula (1). In addition, the dye, organic solvent, and phenolic compound are not encapsulated in microcapsules and are discharged during writing as an oil-based ink using the organic solvent as a solvent, and are an oil-based ink composition incorporated in a normal writing instrument.

[0009] (Phenolic compound) The phenolic compound contained in the ink composition of the present invention is a compound having two or more phenolic hydroxyl groups as represented by the following general formula (1), and its solubility in water is low. When the phenolic hydroxyl group is ionized to become an anion by proton dissociation in the ink, it is presumed that the cation derived from the dye forms an ionic bond, thereby hydrophobizing the highly water-soluble dye. Thereby, it is presumed that the dissolution of the dye in water can be suppressed. That is, the water resistance of the handwriting can be improved, and the occurrence of bleeding caused by the adhesion of water or the like can be suppressed. This effect acts effectively on solvent dyes (also called oil-soluble dyes) using basic dyes with particularly weak water resistance as raw materials, so that clear handwriting that is difficult to bleed in water can be formed regardless of the type of dye.

Chemical formula

[0010] In the general formula (1) above, R 1 is a substituent selected from a hydrogen atom or a linear, branched or cyclic aliphatic alkyl group having 1 to 8 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, and R 2 is a substituent selected from a hydrogen atom or a linear, branched or cyclic aliphatic alkyl group having 1 to 8 carbon atoms, and each R 1 , R 2 can be a substituent with an independent structure. Further, s represents a numerical value from 0 to 2, and each s is an independent value, but it is essential that the total number of hydroxyl groups (the total value of s) in the compound is 2 or more. Furthermore, a represents a numerical value from 0 to 2, and each a is an independent value.

[0011] Among the general formula (1) above, R 2 can each independently select a substituent with an independent structure from the above examples, but those with the same four substituents are preferred from the viewpoint of high compound stability. In addition, tris-phenol structures in which s of each hydroxyl group is 1 or more are particularly suitable from the viewpoint of a structure in which the water resistance improvement of the handwriting due to the phenol structure is particularly likely to be exhibited.

[0012] The content of the phenol compound in the ink composition of the present invention is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass based on the total mass of the ink composition. By setting the content of the phenol compound within the above numerical range, the water resistance of the handwriting formed using the ink composition of the present invention can be further improved.

[0013] (Dye) Examples of the dye contained in the ink composition of the present invention include organic solvent-soluble dyes, basic dyes, acidic dyes, direct dyes, and food dyes classified as solvent dyes in the Color Index. The ink composition may contain two or more of these dyes. Generally, basic dyes have high solubility in water, and handwriting formed using an ink composition containing a solvent dye or the like having a basic dye as a constituent component is likely to bleed due to the adhesion of water. However, according to the oil-based ink composition of the present invention, the water resistance of the handwriting is improved, so the occurrence of bleeding is suppressed.

[0014] Specific examples of the solvent dye include Valifast Black 3806 (C.I. Solvent Black 29), Valifast Black 3807 (trimethylbenzylammonium salt of C.I. Solvent Black 29), Spirit Black SB (C.I. Solvent Black 5), Spiron Black GMH (C.I. Solvent Black 43), Nigrosine Base EX (C.I. Solvent Black 7), Spiron Pink BH (C.I. Solvent Red 82), Neozapon Blue 808 (C.I. Solvent Blue 70), Spiron Violet CRH (C.I. Solvent Violet 8-1), Valifast Red 1308 (salting compound of C.I. Basic Red 1 and C.I. Acid Yellow 23), Valifast Red 1320, Spirit Red 102 (salting compound of C.I. Basic Red 1 and C.I. Acid Yellow 42), Valifast Violet 1701 (salting compound of C.I. Basic Violet 1 and C.I. Acid Yellow 42), Valifast Violet 1702 (salting compound of C.I. Basic Violet 3 and C.I. Acid Yellow 36), Spiron Red CGH (salting compound of C.I. Basic Red 1 and dodecyl(sulfophenoxy)-benzenesulfonic acid), Spiron Yellow C-GNH, and Oil Blue 613 (mixture of C.I. Solvent Blue 5 and resin), etc. Specific examples of the basic dye include C.I. Basic Red 1, C.I. Basic Orange 2, C.I. Basic Orange 14, C.I. Basic Green 4, C.I. Basic Blue 9, C.I. Basic Blue 26, C.I. Basic Violet 1, C.I. Basic Violet 3, and C.I. Basic Violet 10, etc. Specific examples of the acid dyes include C.I. Acid Red 18, C.I. Acid Red 51, C.I. Acid Red 52, C.I. Acid Red 87, C.I. Acid Red 92, C.I. Acid Red 289, C.I. Acid Orange 10, C.I. Acid Yellow 3, C.I. Acid Yellow 7, C.I. Acid Yellow 23, C.I. Acid Yellow 42, C.I. Acid Green 3, C.I. Acid Green 16, C.I. Acid Blue 1, C.I. Acid Blue 9, C.I. Acid Blue 22, C.I. Acid Blue 90, C.I. Acid Blue 239, C.I. Acid Blue 248, C.I. Acid Violet 15, C.I. Acid Violet 49, C.I. Acid Black 1, C.I. Acid Black 2, and the like. Specific examples of the direct dyes include C.I. Direct Red 28, C.I. Direct Yellow 44, C.I. Direct Blue 86, C.I. Direct Blue 87, C.I. Direct Violet 51, C.I. Direct Black 19, and the like. Specific examples of the food dyes include C.I. Food Yellow 3, C.I. Food Black 2, and the like.

[0015] The content of the dye in the ink composition of the present invention is preferably 3 to 40% by mass based on the total mass of the ink composition.

[0016] (Organic solvent) As the organic solvent contained in the ink composition of the present invention, conventionally widely used solvents can be used. Further, the ink composition may contain two or more organic solvents. Specifically, benzyl alcohol, ethylene glycol, diethylene glycol, propylene glycol, benzyl glycol, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monoethyl ether, diethylene glycol monophenyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monophenyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monophenyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monophenyl ether, methyl lactate, ethyl lactate, γ-butyrolactone, etc. can be mentioned.

[0017] In one embodiment, it is particularly preferable to use an organic solvent having a vapor pressure of 5.0 to 50 mmHg, more preferably 10 to 50 mmHg, at 20°C, which is easily volatile. Such an organic solvent is particularly preferable when the writing instrument containing the ink composition is a marking pen. By using an organic solvent having such a vapor pressure, the drying property of the handwriting can be improved. Therefore, when touching the handwriting, good handwriting can be formed without causing problems such as undried ink adhering to the hand or contaminating the blank portion on the writing surface where the handwriting is not formed. Examples of the organic solvent having a vapor pressure of 5.0 to 50 mmHg at 20°C include alcohol-based organic solvents such as ethyl alcohol (45), n-propyl alcohol (14.5), isopropyl alcohol (32.4), n-butyl alcohol (5.5), isobutyl alcohol (8.9), sec-butyl alcohol (12.7), tert-butyl alcohol (30.6), tert-amyl alcohol (13.0), ethylene glycol monomethyl ether Glycol ether-based organic solvents such as ethylene glycol diethyl ether (9.7), ethylene glycol monoisopropyl ether (6.0), propylene glycol monomethyl ether (7.6), propylene glycol monoethyl ether (10.6), etc., n-heptane (35.0), n-octane (11.0), isooctane (41.0), methylcyclohexane (37.0), ethylcyclohexane (10.0), tolu Hydrocarbon-based organic solvents such as benzene (24.0), xylene (5.0 - 6.0), ethylbenzene (7.1), etc., ketone-based organic solvents such as methyl isobutyl ketone (16.0), methyl n-propyl ketone (12.0), methyl n-butyl ketone (12.0), di-n-propyl ketone (5.2), etc., ester-based organic solvents such as n-butyl formate (22.0), isobutyl formate (33.0), n-propyl acetate (25.0), isopropyl acetate (48.0), n-butyl acetate (8.4), isobutyl acetate (13.0), ethyl propionate (28.0), n-butyl propionate (45.0), methyl butyrate (25.0), ethyl butyrate (11.0), etc. can be mentioned. In addition, the numbers in parentheses indicate the vapor pressure of each organic solvent at 20°C.

[0018] Among the above-mentioned organic solvents, from the viewpoints of quick-drying property of handwriting and solubility of resins and additives that can be used, alcohols having 4 or less carbon atoms and / or glycol ethers having 4 or less carbon atoms are more preferable, and ethyl alcohol, n-propyl alcohol, isopropyl alcohol, ethylene glycol monomethyl ether, ethylene glycol diethyl ether, ethylene glycol monoisopropyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether are even more preferable.

[0019] Furthermore, it is preferable that the ink composition of the present invention contains an organic solvent having a boiling point of 160 to 250°C. Such a relatively high-boiling organic solvent is preferable when the writing instrument containing the ink composition is a ballpoint pen. In addition, by incorporating such a relatively high-boiling organic solvent into an ink composition that is contained in a marking pen or the like and used, and adjusting the drying rate of the handwriting, it is possible to suppress the whitening of the handwriting that is likely to occur in a humid environment. In particular, when using an organic solvent having a vapor pressure of 5.0 to 50 mmHg at 20 °C, such as an alcohol having 3 or fewer carbon atoms and / or a glycol ether having 4 or fewer carbon atoms, it is preferable to use such a high-boiling organic solvent in combination to adjust the drying rate.

[0020] Examples of the high-boiling organic solvent include benzyl alcohol (205), ethylene glycol monophenyl ether (245), propylene glycol - n - butyl ether (170), dipropylene glycol methyl ether (190), propylene glycol diacetate (190), dipropylene glycol dimethyl ether (175), dipropylene glycol - n - propyl ether (212), dipropylene glycol methyl ether acetate (209), propylene glycol phenyl ether (243), tripropylene glycol methyl ether (242), dipropylene glycol - n - butyl ether (229), tripropylene glycol - n - butyl ether (274), p - xylene glycol dimethyl ether (235), benzyl formate (201), benzyl acetate (212), benzyl propionate (222), benzyl butyrate (240), and benzyl isobutyrate (230), etc. Note that the numbers in parentheses indicate the boiling points (°C) of the respective organic solvents.

[0021] The content of the organic solvent in the ink composition of the present invention is preferably 40 to 80% by mass based on the total mass of the ink composition. In addition, in the case of a marking pen application, the content of the organic solvent having a vapor pressure of 5.0 to 50 mmHg at 20 °C described above is preferably 50% by mass or more, more preferably 70% by mass or more, based on the total mass of the organic solvent. Furthermore, the content of the above-described high-boiling organic solvent is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, based on the total mass of the organic solvent.

[0022] (Any component) The ink composition of the present invention may contain any components as listed below.

[0023] (Resin) The ink composition of the present invention may contain a resin. Thereby, the fixing property of the handwriting can be improved, and the fastness and the like can be imparted. The ink composition of the present invention may contain two or more kinds of resins. The resin that can be used is not particularly limited as long as it is soluble in the organic solvent contained in the ink composition. For example, ketone resin, amide resin, alkyd resin, rosin-modified resin, rosin-modified phenol resin, phenol resin, xylene resin, polyvinyl butyral resin, terpene resin, coumarone-indene resin, polyethylene oxide, polymethacrylate, ketone-formaldehyde resin, α- and β-pinene·phenol polycondensation resin, polyvinyl butyral resin, maleic acid resin, acrylic resin, and polyacrylic acid-polymethacrylic acid copolymer, etc. may be mentioned.

[0024] The content of the resin in the ink composition of the present invention is preferably 0.5 to 40% by mass, more preferably 1 to 35% by mass based on the total mass of the ink composition.

[0025] (Pigment) The ink composition of the present invention may contain a pigment. Examples of the pigment include inorganic pigments such as carbon black, ultramarine blue, and titanium dioxide pigment; organic pigments such as azo pigments, phthalocyanine pigments, indigo pigments, thioindigo pigments, perylene pigments, quinacridone pigments, anthraquinone pigments, perinone pigments, and isoindolinone pigments; metal pigments such as aluminum powder and metal pigments obtained by treating the surface of aluminum powder with a colored resin; metallic luster pigments obtained by forming a metal vapor deposition film on a transparent or colored transparent film; fluorescent pigments, phosphorescent pigments; and pearl pigments obtained by coating the surface of a core material such as natural mica, synthetic mica, glass flakes, alumina, and transparent film flakes with a metal oxide such as titanium dioxide.

[0026] (Lightfastness improver) The ink composition of the present invention may contain a lightfastness improver. Thereby, the lightfastness of the handwriting can be improved, and even when a mixed dye or a salt-forming dye of a basic dye and an acidic component is used as the dye, fading of the dye can be preferably prevented, and handwriting of various desired color tones excellent in lightfastness can be formed. As the lightfastness improver, for example, benzotriazole derivatives such as 2-(3-t-butyl-5-octyloxycarbonylethyl-2-hydroxyphenyl)benzotriazole can be used.

[0027] (Shear-thinning viscosity improver) The ink composition of the present invention may contain a shear-thinning viscosity improver. Thereby, the occurrence of bleeding in the handwriting can be further suppressed, so that even when the material of the writing surface is a fiber material such as paper or a highly permeable fabric, the occurrence of bleeding in the handwriting can be suppressed. When the writing instrument containing the ink composition is a ballpoint pen, it is particularly preferable to use a shear-thinning viscosity improver. Thereby, it is possible to prevent ink leakage from the gap between the ball and the tip when not in use, and to prevent backflow of the ink when the writing tip is left upward (in an upright state). Examples of the shear-thinning viscosity-imparting agent include crosslinked acrylic resins, emulsion types of crosslinked acrylic resins, non-crosslinked acrylic resins, crosslinked N-vinyl carboxylic acid amide polymers or copolymers, non-crosslinked N-vinyl carboxylic acid amide polymers or copolymers, hydrogenated castor oil, fatty acid amide waxes, waxes such as oxidized polyethylene waxes, fatty acid metal salts such as aluminum salts of stearic acid, palmitic acid, octylic acid, and lauric acid, dibenzylidene sorbitol, N-acyl amino acid-based compounds, smectite-based inorganic compounds, montmorillonite-based inorganic compounds, bentonite-based inorganic compounds, and hectorite-based inorganic compounds. In addition, the ink composition of the present invention may contain two or more shear-thinning viscosity-imparting agents.

[0028] (Lubricant) The ink composition of the present invention may contain a lubricant. When the writing instrument containing the ink composition is a ballpoint pen, by including a lubricant in the ink composition, wear at the contact portion between the ball seat and the ball can be prevented, and the durability of the ballpoint pen can be improved. Examples of the lubricant include higher fatty acids such as oleic acid, nonionic surfactants having a long-chain alkyl group, polyether-modified silicone oil, phosphate ester-based surfactants, fluorine-based surfactants, silicone-based surfactants, fatty acid alkanolamides, anionic surfactants, cationic surfactants, amphoteric surfactants, or metal salts, ammonium salts, amine salts, alkanolamine salts, etc. thereof. Among the above-mentioned lubricants, phosphate ester-based surfactants are particularly preferable because wear of the ball seat and the ball can be more effectively prevented. Examples of phosphate ester surfactants include triester thiophosphites such as tris(alkoxycarbonylmethyl ester) thiophosphite and tris(alkoxycarbonylethyl ester) thiophosphite, monophosphate esters such as polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether, diphosphate esters such as polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether, triphosphate esters such as polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether, alkyl phosphate esters, alkyl ether phosphate esters, or derivatives thereof.

[0029] (Resin for imparting drawability) In addition to the above resins, the ink composition of the present invention may contain a resin for imparting drawability. When the writing instrument containing the ink composition is a ballpoint pen, the ink composition can improve the binding property of the ink composition and suppress the generation of excess ink at the tip of the nib by containing a resin for imparting drawability. Examples of the resin for imparting drawability include polyvinylpyrrolidone resin.

[0030] In addition, the ink composition of the present invention may contain other components such as a viscosity modifier, a coloring stabilizer, a plasticizer, a chelating agent, and a co-solvent such as water.

[0031] (Writing instrument) The writing instrument of the present invention incorporates the above ink composition. The type of the writing instrument is not particularly limited, and examples include a marking pen or a ballpoint pen having a tip attached to the writing tip portion.

[0032] The marking pen according to the present invention is not particularly limited in terms of the structure and shape of the marking pen itself. For example, it has a tip such as a fiber tip, a felt tip, or a plastic tip at the writing tip, and the ink storage body made of a fiber bundle housed inside the shaft cylinder is impregnated with ink, and the ink is supplied to the writing tip. There is a marking pen with a structure, a marking pen with a similar tip that directly stores ink inside the shaft cylinder and supplies ink to the writing tip through a comb-shaped ink flow rate adjusting member or an ink flow rate adjusting member made of a fiber bundle. Incidentally, as the shaft cylinder, a resin molded product or a metal processed body such as an aluminum can is used.

[0033] The ballpoint pen according to the present invention is not particularly limited in terms of the structure and shape of the ballpoint pen itself. For example, an ink storage body made of a fiber bundle housed inside the shaft cylinder is impregnated with ink, and the ink is supplied to a ballpoint pen tip with a ball attached to the tip. There is a ballpoint pen with a structure, a ballpoint pen with a structure that directly stores ink inside the shaft cylinder and supplies ink to the ballpoint pen tip through a comb-shaped ink flow rate adjusting member or an ink flow rate adjusting member made of a fiber bundle, and an ink storage tube that stores an ink composition inside the shaft cylinder. The ink storage tube communicates with the ballpoint pen tip, and further, there is a ballpoint pen with a structure in which a liquid plug for preventing backflow and, if necessary, a solid ink backflow prevention body are in close contact with the end face of the ink in the ink storage tube. Incidentally, as the shaft cylinder and the ink storage tube, a resin molded product or a metal processed body is used.

Example

[0034] [Evaluation of water resistance] The ink compositions of the examples and comparative examples are shown in the following table. Incidentally, the numerical values of the compositions in the table indicate parts by mass.

[0035]

Table 1

[0036] The contents of the raw materials in the table are explained according to the reference numbers. (1) Manufactured by Orient Chemical Industry Co., Ltd., product name: Nigrosine Base EX (2) Manufactured by Orient Chemical Industries Co., Ltd., Product Name: Valifast Red 1308 (3) Manufactured by Orient Chemical Industries Co., Ltd., Product Name: Oil Blue 613 (4) Manufactured by Hodogaya Chemical Co., Ltd., Product Name: Spiron Yellow C-GNH (5) Manufactured by Arakawa Chemical Industries, Ltd., Product Name: Keton Resin K-90 (6) Manufactured by Arakawa Chemical Industries, Ltd., Product Name: Rosin WW (7) Manufactured by Hitachi Chemical Co., Ltd., Product Name: Hylac 110H (8) 4,6-Bis〔1-(4-hydroxyphenyl)-1-methylethyl〕resorcinol (9) 1,3-Bis〔2-(4-hydroxyphenyl)-2-propyl〕benzene (10) 2,6-Bis〔(2-hydroxy-5-methylphenyl)methyl〕-4-methylphenol (11) 1,3-Bis(phenylmethyl)benzene (12) 1,3-Bis(hydroxyphenylmethyl)benzene (13) Manufactured by Toho Chemical Industry Co., Ltd., Product Name: Phosphanol RA-600 (14) Manufactured by Ashland Japan Co., Ltd., Product Name: Polyvinylpyrrolidone K-90 (15) Oleic acid

[0037] Preparation of Ink Composition for Marking Pen The respective raw materials were mixed in the blending amounts described in Examples 1 to 5 and Comparative Examples 1 to 4 of Table 1 above, and stirred and dissolved at 20 °C for 3 hours to obtain an ink composition.

[0038] Production of Marking Pen 5 g of the ink compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were placed in a commercially available marking pen exterior (manufactured by Pilot Corporation; WMBM-12L, equipped with a polyester tip) to obtain an oil-based marking pen.

[0039] Preparation of Ink Composition for Ballpoint Pen The respective raw materials were mixed in the blending amounts described in Examples 6 to 7 and Comparative Examples 5 to 6 of Table 1 above, heated to 60°C, and then completely dissolved using a dispersing stirrer. After cooling to room temperature, an ink composition was obtained.

[0040] Production of ballpoint pen 0.2 g of the ink compositions obtained in Examples 6 to 7 and Comparative Examples 5 to 6 was accommodated in a commercially available ballpoint pen exterior (manufactured by Pilot Corporation: BPS-GPN-F) equipped with a ball having a ball diameter of φ0.7 mm to obtain a ballpoint pen.

[0041] Water resistance test (marking pen) Using the marking pen prepared as described above, in accordance with the water resistance test specified in JIS S6037, except that only the immersion time was changed, the water resistance test was conducted according to the following procedure. Using each marking pen confirmed to be capable of writing, in an environment of 20°C, it was handwritten spirally on JISP3201 writing paper A. Next, the writing paper was immersed in water for 30 minutes so that the handwriting would soak, then taken out and dried. After drying, the state of the handwriting was visually confirmed and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2 below.

[0042] Water resistance test (ballpoint pen) Using the ballpoint pen prepared as described above, in accordance with the water resistance test specified in JIS S6039, the water resistance test was conducted according to the following procedure. Using each ballpoint pen confirmed to be capable of writing, in an environment of 20°C, it was handwritten spirally on JIS P3201 writing paper A. Next, the writing paper was immersed in water for 60 minutes so that the handwriting would soak, then taken out and dried. After drying, the state of the handwriting was visually confirmed and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2 below.

[0043] Evaluation criteria A: No bleeding of handwriting occurs. B: The handwriting dye slightly oozed out, or the entire paper and the immersion liquid were slightly colored. C: The dye oozed out around the handwriting, or the entire paper and the immersion liquid were colored.

[0044]

Table 2

Claims

1. An oil-based ink composition for writing instruments comprising a dye, an organic solvent, and a phenol compound represented by the following general formula (1). 【Chemistry 1】 [In the formula, R １ R represents a hydrogen atom, or a linear, branched, or cyclic aliphatic alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms. ２ R represents a hydrogen atom or a linear, branched, or cyclic aliphatic alkyl group having 1 to 8 carbon atoms, and each R represents a hydrogen atom or a linear, branched, or cyclic aliphatic alkyl group. １ , R ２ The elements do not have to be identical. s represents a numerical value between 0 and 2, and each s does not have to be identical, but the number of hydroxyl groups in the compound (total value of s) is 2 or more. a represents a numerical value between 0 and 2, and each a does not have to be identical.

2. The ink composition according to claim 1, wherein the dye is a solvent dye.

3. The ink composition according to claim 2, wherein the solvent dye is a salt-making dye.

4. The ink composition according to claim 1, wherein the vapor pressure of the organic solvent at 20°C is 5 to 50 mmHg.

5. A writing instrument containing an oil-based ink composition for writing instruments according to any one of claims 1 to 4.

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