Oil-based ink composition for writing instruments

Abstract

To provide a novel oil-based ink composition for writing instruments that prevents paper fibers from being caught therein and exhibits superior writing quality and color development.SOLUTION: An oil-based ink composition for writing instruments is used for writing instruments for black, red, and blue ink. The oil-based ink composition includes at least a colorant, a white or colorless fluorescent dye, a resin, and an organic solvent. The content of the fluorescent dye is 0.05-12.0 mass% relative to the mass of the oil-based ink composition for writing instruments.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an oil-based ink composition for a writing instrument, and more particularly to an oil-based ink composition for a ballpoint pen. [Background technology]

[0002] The oil-based ink composition for ballpoint pens is composed of a colorant, an organic solvent, a resin, etc. In addition, in an oil-based ballpoint pen using such an oil-based ink composition for ballpoint pens, problems such as adhesion of ink to the outer surface of the ballpoint pen tip, spreading of ink onto the pen tip, dripping (blotting), etc., arise from the mechanism in which the ink is transferred to the paper surface via the ball to obtain a drawn line. In order to solve such problems, various proposals have been made regarding the oil-based ink composition for ballpoint pens.

[0003] Patent Document 1 discloses an oil-based ink composition for ballpoint pens, which is characterized by containing at least a colorant, a resin, and 0.01 to 1.5% by weight of a high-polymerization polybutylvinylal having a degree of polymerization of 900 or more (calculated molecular weight 60,000), and containing a solvent selected from alcohols, polyhydric alcohols, and glycol ethers, each of which has a vapor pressure of 0.001 mmHg or more at 25°C, as a main solvent accounting for 50% or more of the total solvent.

[0004] In Patent Document 2, the first normal stress at 25°C is -1 More than 3000s -1 Ballpoint pen inks having a viscosity of 5000 Pa or more within the following ranges are disclosed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-263612 A [Patent Document 2] JP 2004-107596 A Summary of the Invention [Problem to be solved by the invention]

[0006] With conventional ballpoint pen inks, the rotation of the pen tip during writing can cause paper fibers to become caught in the ball house, resulting in poor writing results such as smudged lines.

[0007] Therefore, the present invention provides a novel oil-based ink composition for writing instruments which is suppressed from wrapping around paper fibers and has good writing properties and color development properties. [Means for solving the problem]

[0008] As a result of intensive research, the present inventors have found that the above problems can be solved by the following means, and have completed the present invention. That is, the present invention is as follows: <Aspect 1> An oil-based ink composition for a writing instrument for black characters, red characters, and blue characters, The composition contains at least a coloring material, a white or colorless fluorescent dye, a resin, and an organic solvent, The content of the fluorescent dye is 0.05 to 12.0% by mass relative to the mass of the oil-based ink composition for a writing instrument. Oil-based ink composition for writing instruments. <Aspect 2> Shear rate 300 to 1000 s -1 2. The oil-based ink composition for a writing instrument according to claim 1, wherein the first normal stress difference measured under the conditions above is 4000 Pa or less. Aspect 3: The oil-based ink composition for a writing instrument according to Aspect 1 or 2, which has a viscosity of 300 to 5000 mPa·s. Aspect 4: The oil-based ink composition for a writing instrument according to any one of Aspects 1 to 3, wherein the resin is polyvinyl butyral. Aspect 5: A writing instrument filled with the oil-based ink composition for a writing instrument according to any one of Aspects 1 to 4. Effect of the Invention

[0009] According to the present invention, it is possible to provide a novel oil-based ink composition for writing instruments which is suppressed from wrapping around paper fibers and has good writing properties and color development properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 《Oil-based ink composition for writing instruments》 The oil-based ink composition for a writing instrument of the present invention comprises: An oil-based ink composition for a writing instrument for black, red, and blue characters, The composition contains at least a coloring material, a white or colorless fluorescent dye, a resin, and an organic solvent, The content of the fluorescent dye is 0.05 to 12.0% by mass relative to the mass of the oil-based ink composition for a writing instrument. An oil-based ink composition for a writing instrument.

[0011] The present inventors have unexpectedly discovered that, according to the above configuration, by incorporating a white or colorless fluorescent dye, it is possible to obtain a low first normal stress difference (the force that tends to gather at the center of rotation) while moderately increasing the viscosity, and as a result, it is possible to provide a novel oil-based ink composition for writing instruments that provides good writing performance due to the moderate viscosity while suppressing the entrainment of paper fibers due to the low first normal stress difference.

[0012] Although not wishing to be bound by theory, this is believed to be due to the unique structure of the fluorescent dye, particularly the presence of conjugated double bonds and planar structure, which moderately increases viscosity while suppressing the increase in the first normal stress difference.In addition, by using a white or colorless fluorescent dye, it is possible to adjust the viscosity and the first normal stress while providing good color development without giving undesirable coloring in the oil-based ink composition for black, red, and blue writing instruments.

[0013] Incidentally, in the past, white or colorless fluorescent dyes have not generally been used in oil-based ink compositions for dark-colored writing instruments, particularly in oil-based ink compositions for writing instruments for black, red, and blue characters.

[0014] Here, the first normal stress difference refers to the stress that acts perpendicular to the shear direction of the object to be measured when shear is applied to the object to be measured. Specifically, the entangled polymer compounds in the ink composition tend to wrap around the center of rotation due to rotation and gather at the center of rotation, increasing the pressure at the center of rotation and generating a force that tends to expand the surface of rotation. This force that tends to expand is called the first normal stress difference. In other words, an ink with a large first normal stress difference is an ink in which the polymer compounds in the composition are strongly entangled.

[0015] The oil-based ink composition for a writing instrument having the above-mentioned composition has a shear rate of 300 to 1000 s -1 The first normal stress difference measured under the above conditions can be 4000 Pa or less, 3500 Pa or less, 3200 Pa or less, 3000 Pa or less, 2800 Pa or less, 2700 Pa or less, or 2600 Pa or less. Specifically, the first normal stress difference can be measured under the following conditions using a measuring device (MCR 102, Anton Paar). Temperature: 25℃ Corn plate: CP-25-1 Measurement position: 0.052 mm above the measurement plate Measurement time: 2 minutes Measurement interval: Every 0.5 seconds Shear rate measurement range: 0.01 to 10,000 s -1 (logarithmic change)

[0016] The viscosity of the oil-based ink composition for a writing instrument having the above configuration can be 300 mPa·s or more, 400 Pa·s or more, 500 mPa·s or more, 600 mPa·s or more, 700 mPa·s or more, 800 mPa·s or more, 900 mPa·s or more, or 1000 mPa·s or more, and can be 5000 mPa·s or less, 4000 mPa·s or less, 3000 mPa·s or less, 2800 mPa·s or less, 2500 mPa·s or less, 2300 mPa·s or less, 2100 mPa·s or less, 2000 mPa·s or less, 1800 mPa·s or less, 1500 mPa·s or less, or 1300 mPa·s or less.

[0017] This viscosity is measured at a temperature of 25° C. and a shear rate of 5 rpm, and can be measured with a known viscosity measuring device, such as TVE-20H (Toki Sangyo), using a regular cone equivalent to the R range.

[0018] Each component of the present invention will now be described.

[0019] <Coloring material> The coloring material may be black, red, or blue. In addition to these coloring materials, auxiliary coloring materials that exhibit other colors may be used. These coloring materials may be used alone or in combination.

[0020] As the black colorant, black dyes such as Direct Black 154 and Nigrosine NB, and black pigments such as carbon black, titanium black, iron black, and talc can be used.

[0021] Examples of red colorants that can be used include red dyes such as acid red, eosin, and phloxine; inorganic red pigments such as red iron oxide, vermilion, and cadmium red; and organic red pigments such as CI Pigment Red 5, CI Pigment Red 22, CI Pigment Red 38, CI Pigment Red 48, CI Pigment Red 49, CI Pigment Red 53, CI Pigment Red 57, CI Pigment Red 81, CI Pigment Red 104, CI Pigment Red 146, and CI Pigment Red 245.

[0022] Examples of blue colorants that can be used include blue dyes such as Water Blue #105, Brilliant Blue FCF, and Direct Sky Blue 5B; inorganic blue pigments such as cobalt blue, ultramarine, and Prussian blue; and organic blue pigments such as CI Pigment Blue 17, CI Pigment Blue 15, CI Pigment Blue 17, and CI Pigment Blue 27.

[0023] As the colorant, in addition to the above colorants, auxiliary dyes or pigments can be used.

[0024] As the auxiliary coloring dye, any dye that dissolves or disperses in water can be used, for example, acid dyes such as Water Yellow #6-C; direct dyes such as Violet BB; basic dyes such as rhodamine and methyl violet.

[0025] As the auxiliary color pigment, pigments other than the pigments mentioned above can be used.

[0026] Examples of such inorganic pigments that can be used include chromium oxide, yellow iron oxide, viridian, cadmium yellow, yellow lead, molybdate orange, zinc chromate, strontium chromate, baryte powder, manganese violet, and brass powder.

[0027] Examples of such organic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, nitroso pigments, etc. Examples of such organic pigments include CI Pigment Yellow 1, CI Pigment Yellow 3, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 17, CI Pigment Yellow 34, CI Pigment Yellow 55, CI Pigment Yellow 74, CI Pigment Yellow 95, CI Pigment Yellow 166, CI Pigment Yellow 167, CI Pigment Orange 5, CI Pigment Orange 13, CI Pigment Orange 16, CI Pigment Violet 1, CI Pigment Violet 3, CI Pigment Violet 19, CI Pigment Violet 23, CI Pigment Violet 50, CI Pigment Green 7, etc.

[0028] These colorants can be used alone or in a mixture of two or more. Among these colorants, the average particle diameter of water-dispersible pigments, resin particle pigments, pseudopigments, white plastic pigments, multi-coated pigments, thermochromic pigments, photochromic particles, etc. varies depending on the ball diameter, ink composition, viscosity, etc., but it is desirable to have an average particle diameter of 0.02 to 6 μm. This average particle diameter may be, for example, 0.02 μm or more, 0.05 μm or more, 0.07 μm or more, 0.10 μm or more, 0.20 μm or more, 0.30 μm or more, 0.50 μm or more, 0.70 μm or more, or 0.90 μm or more, and may be 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less.

[0029] The content of these colorants can be increased or decreased as appropriate depending on the line density of the ink, but may be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, 0.9% by mass or more, or 1.0% by mass or more, and is preferably 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less, based on the total amount of the oil-based ink composition for writing instruments.

[0030] Among the colorants, the content of black, red, and blue colorants may be 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 100% by mass or more, relative to the total mass of the colorants.

[0031] <Fluorescent dye> The fluorescent dye is a colorless or white fluorescent dye. Generally, the fluorescent dye is a dye having a conjugated double bond and a planar structure, and the colorless or white fluorescent dye is a dye having an electron donating group and not having a strong electron withdrawing group such as NO2, -N=N-. As such a fluorescent dye, a commercially available fluorescent dye can be used as an indicator of the colorless or white fluorescent dye.

[0032] From the viewpoint of obtaining the above-mentioned first normal stress, it is preferable that the content of the fluorescent dye is 0.05% by mass or more, 0.10% by mass or more, 0.20% by mass or more, 0.30% by mass or more, 0.40% by mass or more, 0.50% by mass or more, 0.60% by mass or more, 0.70% by mass or more, 0.80% by mass or more, or 0.90% by mass or more, and is 12.0% by mass or less, 10.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, or 5.0% by mass or less, relative to the mass of the oil-based ink composition for writing instruments.

[0033] <resin> As the resin, any resin that can be used for fixing a coating film can be used, such as sulfonamide resin, maleic acid resin, terpene resin, terpene phenol resin, ester gum, xylene resin, alkyd resin, phenol resin, rosin, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl alcohol, acrylic resin, melamine resin, nitrocellulose resin, urea resin, and derivatives thereof.

[0034] The resin content in the oil-based ink composition for writing instruments of the present invention is preferably 1% by mass or more, 2% by mass or more, or 3% by mass or more, from the viewpoint of obtaining sufficient adhesion, and is preferably 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 7% by mass or less, or 5% by mass or less, from the viewpoint of preventing the viscosity of the ink from becoming excessively high.

[0035] <Resin: Polyvinyl butyral> Polyvinyl butyral is a (co)polymer produced by reacting polyvinyl alcohol with butyraldehyde. Specifically, this resin is a copolymer represented by the following formula: [ka]

[0036] The mass average molecular weight of the polyvinyl butyral may be 10,000 or more, 20,000 or more, 30,000 or more, or 35,000 or more, and is preferably 150,000 or less, 140,000 or less, 130,000 or less, 120,000 or less, 110,000 or less, 100,000 or less, 90,000 or less, 80,000 or less, 70,000 or less, or 60,000 or less, from the viewpoint of the balance between viscosity and adhesion as an oil-based ink composition for a writing instrument.

[0037] The mass average molecular weight herein is a value calculated as a standard polystyrene equivalent based on a measurement value obtained by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

[0038] The hydroxyl content of polyvinyl butyral may be 37 mol% or less, 35 mol% or less, 30 mol% or less, 29 mol% or less, 28 mol% or less, 27 mol% or less, or 26 mol% or less, and is particularly preferably 26 mol% or less from the viewpoint of improving the scratch resistance of the resulting coating film. The acetalization degree may be 20 mol% or more, or 22 mol% or more.

[0039] The hydroxyl content is a molar fraction obtained by dividing the amount of ethylene groups to which hydroxyl groups are bonded by the total amount of ethylene groups in the main chain, expressed as a percentage (mol%).The hydroxyl content is a molar fraction obtained by dividing the amount of ethylene groups to which acetal groups are bonded by the total amount of ethylene groups in the main chain, expressed as a percentage (mol%).

[0040] The amount of ethylene groups to which the hydroxyl groups are bonded can be determined, for example, by measuring the amount of ethylene groups to which the hydroxyl groups of the polyvinyl acetal resin are bonded, using a method in accordance with JIS K6728 "Testing methods for polyvinyl butyral."

[0041] <Organic Solvent> As the organic solvent, for example, aromatics, alcohols, polyhydric alcohols, glycol ethers, hydrocarbons, esters, etc. These solvents may be used alone or in combination.

[0042] At least a part of the organic solvent is preferably aromatic from the viewpoint of dissolving a white or colorless fluorescent dye. From this viewpoint, the organic solvent is preferably a mixed solvent of glycol ethers and aromatics. The content of aromatics may be 0.1 mass% or more, 0.3 mass% or more, 0.5 mass% or more, 0.7 mass% or more, 0.9 mass% or more, or 1.0 mass% or more, and may be 5.0 mass% or less, 4.0 mass% or less, 3.0 mass% or less, 2.0 mass% or less, or 1.5 mass% or less, based on the mass of the organic solvent.

[0043] Examples of aromatic compounds that can be used include benzyl alcohol, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, propylene glycol monophenyl ether, diethylene glycol monophenyl ether, alkylsulfonic acid phenyl ester, butyl phthalate, ethylhexyl phthalate, tridecyl phthalate, ethylhexyl trimellitate, diethylene glycol dibenzoate, and dipropylene glycol dibenzoate.

[0044] Examples of alcohols that can be used include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, 1-pentanol, isoamyl alcohol, sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, n-hexanol, methylamyl alcohol, 2-ethylbutanol, n-heptanol, 2-heptanol, 3-heptanol, n-octanol, 2-octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, n-decanol, undecanol, n-decanol, trimethylnonyl alcohol, tetradecanol, heptadecanol, cyclohexanol, and 2-methylcyclohexanol.

[0045] Examples of polyhydric alcohols that can be used include ethylene glycol, diethylene glycol, 3-methyl-1,3 butanediol, triethylene glycol, dipropylene glycol, 1,3 propanediol, 1,3 butanediol, 1,5 pentanediol, hexylene glycol, and octylene glycol.

[0046] Examples of glycol ethers that can be used include methyl isopropyl ether, ethyl ether, ethyl propyl ether, ethyl butyl ether, isopropyl ether, butyl ether, hexyl ether, 2-ethylhexyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylbutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol tertiary butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and tetrapropylene glycol monobutyl ether.

[0047] As the hydrocarbons, for example, straight chain hydrocarbons such as hexane, isohexane, heptane, octane, nonane, decane, etc., and cyclic hydrocarbons such as cyclohexane, methylcyclohexane, ethylcyclohexane, etc. can be used.

[0048] Examples of esters include propylene glycol methyl ether acetate, propylene glycol diacetate, 3-methyl-3-methoxybutyl acetate, propylene glycol ethyl ether acetate, ethylene glycol ethyl ether acetate, butyl formate, isobutyl formate, isoamyl formate, propyl acetate, butyl acetate, isopropyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, isobutyl propionate, isoamyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, propyl isobutyrate, Methyl valerate, ethyl valerate, propyl valerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate, methyl trimethylacetate, ethyl trimethylacetate, propyl trimethylacetate, methyl caproate, ethyl caproate, propyl caproate, methyl caprylate, ethyl caprylate, propyl caprylate, methyl laurate, ethyl laurate, methyl oleate, ethyl oleate, caprylic acid triglyceride, tributyl acetate citrate, octyl oxystearate, propylene glycol monoricinoleate, methyl 2-hydroxyisobutyrate, 3-methoxybutyl acetate, and the like can be used.

[0049] Other Ingredients Examples of other components include dispersants, leveling agents, rust inhibitors, preservatives, lubricants, and surface conditioners. Examples of leveling agents that can be used include fluorine-based surfactants, silicone oils, and phosphate ester surfactants. Examples of surface conditioners that can be used include silicon-based surface conditioners.

[0050] 《Writing implements》 The writing instrument contains the oil-based ink composition for a writing instrument. The writing instrument may have an ink storage section, a writing section, and a holding section, and in this case, the ink storage section may store an oil-based ink. The writing instrument may be a ballpoint pen.

[0051] Ink storage section The ink reservoir contains the oil-based ink composition for a writing instrument.

[0052] The ink storage section can be any type that is capable of storing ink and supplying ink to the writing section, and may be a direct ink type with a collector structure (ink retention mechanism) or a padded ballpoint pen.

[0053] <Writing Department> The writing part can be a writing part having a ballpoint pen tip at its tip.

[0054] The ballpoint pen tip may be composed of a ball and a holder that rotatably holds the ball. The ball may be composed of any material used for ballpoint pen balls, such as stainless steel, cemented carbide, ceramics, etc. The shape of the ballpoint pen tip is not particularly limited, and may be, for example, a bullet shape, a needle shape, etc.

[0055] <Holding part> The holder may be a portion that allows the writing instrument of the present invention to be held by hand, and may have a hollow structure capable of housing the ink storage part. The holder may have a shape such as a cylindrical shape or a polygonal cylindrical shape. EXAMPLES

[0056] The present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these.

[0057] <<Preparation of Oil-Based Ink Composition for Writing Instruments>> The materials shown in Table 1 were mixed in the parts by mass shown in Table 1 to prepare oil-based ink compositions for writing instruments of Examples 1 to 11 and Comparative Examples 1 and 2.

[0058] Details of the materials mentioned in Table 1 are as follows: Black pigment: Printex #35, Degussa Corporation Red pigment: Pigment Red 254, Degussa Corporation Blue pigment: Pigmet Blue 60, Degussa Corporation Black dye A: Varifast Black #3830, Orient Chemical Industry Co., Ltd. Black dye B: Spin Black GMH Special, Hodogaya Chemical Co., Ltd. Yellow dye: Spiron Yellow C-GNH, Hodogaya Chemical Co., Ltd. Blue-purple dye A: Varifast Violet #1701, Orient Chemical Industry Co., Ltd. Blue-purple dye B: Spiron Violet C-RH, Hodogaya Chemical Industry White fluorescent dye A: MPI-609, Nippon Fluorescent Co., Ltd. White fluorescent dye B: AIZEN MP-1, Hodogaya Chemical Co., Ltd. White fluorescent dye C: FM-109, Shinroihi Co., Ltd. PVB-A: S-LEC B BH-3, Sekisui Chemical Co., Ltd., hydroxyl group approx. 34 mol%, molecular weight approx. 110,000 PVB-B: S-LEC B BL-1, Sekisui Chemical Co., Ltd., hydroxyl group approx. 36 mol%, molecular weight approx. 19,000 Fumed silica: AEROSIL R972, Nippon Aero Co., Ltd. Phosphorus surfactant: Phosphanol LB-400, Toho Chemical Industry Co., Ltd.

[0059] Evaluation of ink properties <viscosity> The viscosity of the prepared ink was measured at a temperature of 25° C. using a TVE-20H R range equivalent regular cone at 5 rpm.

[0060] <First normal stress difference> The first normal stress difference of the prepared ink was measured using a measuring device (MCR 102, Anton Paar). The measurement conditions were as follows: Temperature: 25℃ Corn plate: CP-25-1 Measurement position: 0.052 mm above the measurement plate Measurement time: 2 minutes Measurement interval: Every 0.5 seconds Shear rate measurement range: 0.01 to 10,000 s -1 (logarithmic change)

[0061] <Evaluation as a ballpoint pen> Each of the ink compositions prepared above was filled into a ballpoint pen, and the following evaluations were carried out.

[0062] <Paper fiber entrapment> Using a writing tester (Minitec writing tester, Mitsubishi Pencil Co., Ltd.) conforming to JIS S6039, paper fibers were forcibly entrained by spiral writing on straw paper under the following writing conditions: writing speed 4 m / min, writing angle 40°, writing load 2.35 N, and writing distance 25 m. Then, a writing test was conducted again under the same conditions as the above test, and the paper fiber entrainment property was confirmed by visually checking the state of blurred lines. Furthermore, a writing test was conducted under the same conditions as the above test, and the discharge property of the entrained paper fibers was confirmed.

[0063] The evaluation criteria are as follows: A: There was no paper fiber entrapment, and the drawn lines were in good condition. B: Some paper fibers were caught and some lines were blurred. C: Paper fibers were caught in the ink, but they were mostly expelled. There was some smearing in the lines, but the ink was still usable. D: Paper fibers were caught in the paper and could not be expelled, making it impossible to write.

[0064] <Writability> The writing feel when handwriting in a spiral on PPC paper was evaluated sensorily according to the following criteria. A: The writing experience was smooth and gliding, without any feeling of gripping the paper. B: There was no feeling of gripping the paper and the writing was smooth. C: There was a slight feeling of grip on the paper, but the writing experience was generally smooth. D: There is a feeling that the writing surface catches on the paper and the writing experience is not smooth.

[0065] Color development The color was hand-painted onto a sheet of PPC paper to form a 1 cm x 1 cm square, and the color development was evaluated sensorily according to the following criteria. A: Vivid, clear and highly pigmented. B: Slight dullness and somewhat low color development. C: Significant dullness is observed, and color development is extremely poor.

[0066] Table 1 shows the configurations and evaluation results of the examples and comparative examples.

[0067] [Table 1]

[0068] From Table 1, it can be seen that the oil-based ink compositions for writing instruments of the examples, which contain 0.05 to 12.0 mass % of a white or colorless fluorescent dye relative to the mass of the oil-based ink composition for writing instruments, are oil-based ink compositions for writing instruments that suppress the entrapment of paper fibers and have good writing properties and color development properties.

[0069] The first normal stress difference of the oil-based ink composition for writing instruments in the examples was measured at a shear rate of 300 to 1000 s -1 It can be seen that in all cases, the pressure is below 4000 Pa.

Claims

1. An oil-based ink composition for writing instruments in black, red, and blue, comprising at least a colorant, a white or colorless fluorescent dye, a resin, and an organic solvent, wherein the content of the fluorescent dye is 0.05 to 12.0% by mass based on the mass of the oil-based ink composition, an oil-based ink composition for writing instruments.

2. Cutting speed: 300 to 1000 s －１ The oil-based ink composition for writing instruments according to claim 1, wherein the first normal stress difference measured under the conditions of －１ is 4000 Pa or less.

3. The oil-based ink composition for writing instruments according to claim 1 or 2, having a viscosity of 300 to 5000 mPa·s.

4. The oil-based ink composition for writing instruments according to claim 1 or 2, wherein the resin is polyvinyl butyral.

5. A writing instrument filled with the oil-based ink composition for writing instruments according to claim 1 or 2.

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