Ink composition for writing instrument and writing instrument containing the ink composition

Abstract

This ink composition for a writing instrument contains at least a solvent and a pigment including a uric acid pigment.

Description

[Technical Field]

[0001] The present invention relates to an ink composition for a writing instrument and a writing instrument containing the ink composition. More specifically, the present invention relates to an ink composition for a writing instrument that has excellent pigment dispersion stability and is capable of forming clear handwriting with excellent hiding power, and a writing instrument containing the ink composition for a writing instrument. [Background technology]

[0002] Ink compositions for writing instruments that use white pigments such as titanium oxide to obtain handwriting with hiding properties have been known. Furthermore, ink compositions for writing instruments that can form pastel-colored handwriting by blending colorants of other colors into such ink compositions with high hiding properties are also preferably used.

[0003] However, because titanium oxide is a pigment with a high specific gravity, it tends to settle over time, and once a hard cake forms, it becomes difficult to redisperse the pigment. Furthermore, writing instruments using ink compositions containing titanium oxide tend to experience a decrease in writing density when stored with the writing tip facing up, and a decrease in ink dischargeability when stored with the writing tip facing down. For this reason, efforts have been made to suppress the settling of titanium oxide by increasing the viscosity of the ink using a thickener or the like. However, there are limitations on the writing instruments to which such high-viscosity ink compositions can be applied. Furthermore, in ink compositions using titanium oxide in combination with colorants of other colors, the difference in specific gravity between the titanium oxide and the colorant can cause color separation in the ink. Therefore, efforts have been made to suppress the settling of titanium oxide and the formation of hard cakes (see, for example, Patent Documents 1 to 4).

[0004] Patent Document 1 discloses an aqueous pigment composition comprising titanium oxide, an aluminum silicate pigment, and a specific resin.

[0005] Furthermore, Patent Document 2 discloses an aqueous ink composition comprising at least titanium oxide, succinoglycan, and water.

[0006] Furthermore, Patent Document 3 discloses a water-based ink for ballpoint pens that is composed of titanium oxide and oleic acid.

[0007] Furthermore, Patent Document 4 discloses an aqueous pigment ink for a writing instrument, which comprises titanium oxide, a chromatic pigment, silica powder and / or an aluminosilicate, a water-soluble resin, a specific dispersant, a surfactant, and water.

[0008] Although the settling rate of titanium oxide in the above-mentioned composition (ink composition) can be slowed by using a specific compound, titanium oxide tends to settle over time to form a hard cake or to cause color separation in the ink, making it difficult to stably disperse titanium oxide in the ink composition. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 59-217776 [Patent Document 2] Japanese Patent Application Publication No. 8-113752 [Patent Document 3] Japanese Patent Application Publication No. 10-251588 [Patent Document 4] Japanese Patent Application Publication No. 11-217532 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide an ink composition for a writing instrument, in which the pigment has excellent dispersion stability and is easily redispersible, and which can form clear handwriting with excellent hiding power, and a writing instrument containing the ink composition for a writing instrument. [Means for solving the problem]

[0011] The present invention provides an ink composition for a writing instrument, which comprises at least a pigment containing a uric acid pigment and a solvent.

[0012] The writing instrument ink composition further comprises a dispersant, the dispersant comprising a polymer dispersant. The writing instrument ink composition further comprises a uric acid pigment having an average particle size of 0.05 μm or more and 1 μm or less, and a content of the uric acid pigment relative to the total mass of the ink composition of 1% by mass or more and 50% by mass or less. The writing instrument ink composition further comprises a colorant.

[0013] Furthermore, the present invention is directed to a writing instrument containing the ink composition for a writing instrument. [Effects of the Invention]

[0014] The present invention provides a writing instrument ink composition using a pigment containing a uric acid pigment, which exhibits excellent dispersion stability of the pigment. Furthermore, even if the pigment settles over time, the pigment does not form a hard cake, making it easy to redisperse the pigment, and can produce clear handwriting with excellent hiding power. The present invention also provides a writing instrument ink composition and a writing instrument containing the writing instrument ink composition. DETAILED DESCRIPTION OF THE INVENTION

[0015] The ink composition for a writing instrument according to the present invention (hereinafter sometimes referred to as "ink composition" or "ink") contains at least a pigment containing a uric acid pigment and a solvent. Each component constituting the ink composition according to the present invention will be described below.

[0016] The ink composition according to the present invention contains a uric acid pigment. The uric acid pigment is a pigment made of uric acid. Uric acid is produced by metabolism in the human body. Therefore, uric acid is an organic substance of biological origin, and the compound itself is highly safe.

[0017] The uric acid pigment is present in a dispersed state in the ink composition, and exhibits a white color due to the high refractive index of uric acid, thereby providing the effect of imparting hiding power to handwriting. Titanium oxide, which is commonly used as a white pigment, has a high specific gravity and therefore tends to settle in the ink composition, and further tends to form a hard cake, which can make redispersion difficult. In contrast, the uric acid pigment has a smaller specific gravity than titanium oxide and therefore does not settle in the ink composition, and even if the uric acid pigment settles over time, it does not form a hard cake. Therefore, the uric acid pigment can be easily redispersed.

[0018] Therefore, by using a pigment containing a uric acid pigment, the ink composition of the present invention has excellent pigment dispersion stability and is easy to redisperse without forming a hard cake even if the pigment settles over time. Therefore, the ink composition of the present invention can form clear handwriting with excellent hiding power at a uniform density. Furthermore, even when the ink composition of the present invention contains a colorant described below, separation of the uric acid pigment and the colorant in the ink composition is suppressed. Therefore, the ink composition of the present invention can form colored handwriting with excellent hiding power at a uniform density.

[0019] The content of the uric acid pigment relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 1% by mass to 50% by mass, more preferably 5% by mass to 30% by mass. If the content of the uric acid pigment exceeds 50% by mass, the ink ejection stability of the writing instrument containing the ink composition is likely to decrease, and writing defects such as smearing and skipped lines are likely to occur. On the other hand, if the content is less than 1% by mass, it becomes difficult to obtain a suitable writing density for the writing instrument, and the hiding power of the writing is likely to be impaired.

[0020] The uric acid pigment is not particularly limited as long as it can be dispersed in the ink composition. For example, the uric acid pigment can be produced by mechanically pulverizing crystalline uric acid into granules using various dispersing machines such as a jet mill, an attritor, or a bead mill. As the uric acid pigment, a uric acid pigment itself that is colored can also be used.

[0021] The average particle size of the uric acid pigment is not particularly limited, but is preferably in the range of 0.05 μm to 1 μm, more preferably 0.1 μm to 0.5 μm. By having the average particle size within the above range, the dispersion stability of the uric acid pigment in the ink composition can be improved.

[0022] The average particle size is a volume-based average particle size value measured using a dynamic light scattering particle size distribution analyzer (manufactured by Microtrac-Bell Corporation, product name: NANOTRAC FLEX).

[0023] The ink composition according to the present invention can further contain a dispersant. For example, when the solvent used in the present invention is water, the dispersant adsorbs to the surface of the uric acid pigment, separating the uric acid pigments from one another while maintaining a certain distance between the uric acid pigments and preventing aggregation, thereby improving the dispersion stability of the uric acid pigment in the ink. Furthermore, even when the uric acid pigments aggregate to form aggregates, the aggregates formed are low-density, and therefore hard caking after settling of the uric acid pigment can be suppressed.

[0024] Examples of the dispersant include a surfactant, a polymer dispersant, and an inorganic compound.

[0025] Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants.

[0026] Specifically, surfactants used as dispersants include polyoxyalkylene alkylamines represented by the following general formula (1) (in which the sum of m and n (m+n) is 29 or less):

[0027] [ka]

[0028] In the general formula (1), R1, R2, m, and n each represent the following.

[0029] R1: an alkyl or alkenyl group having 10 to 20 carbon atoms R2: an alkylene group having 2 or 3 carbon atoms m+n: a number between 1 and 29

[0030] Examples of R1 include capryl, lauryl, myristyl, palmityl, stearyl, arachidyl, palmitoleyl, oleyl, elaidyl, coconut oil alkyl, and beef tallow alkyl, with lauryl and stearyl being preferred. Examples of R2 include ethylene and propylene, with ethylene being preferred. m+n is preferably a number between 1 and 15, more preferably between 2 and 10.

[0031] Commercially available surfactants represented by the general formula (1) used in the present invention include, but are not limited to, Braunon L-205 (manufactured by Aoki Oil & Fat Industries Co., Ltd.; in general formula (1), m+n=5), Braunon S-202 (manufactured by Aoki Oil & Fat Industries Co., Ltd.; in general formula (1), m+n=2), Braunon S-207 (manufactured by Aoki Oil & Fat Industries Co., Ltd.; in general formula (1), m+n=7), Braunon S-210 (manufactured by Aoki Oil & Fat Industries Co., Ltd.; in general formula (1), m+n=10), and Braunon S-215 (manufactured by Aoki Oil & Fat Industries Co., Ltd.; in general formula (1), m+n=15), and Biscofine E2C (manufactured by Kawaken Fine Chemicals Co., Ltd.; in general formula (1), m+n=2).

[0032] Furthermore, surfactants used as dispersants include surfactants having -CO-NH- or -CO-N(CH3)- as linking groups. Specific examples of such surfactants include surfactants represented by the following general formula (2), (3), or (4): [ka]

[0033] In general formula (2), general formula (3), and general formula (4), R1, R2, R3, R4, and n each represent the following.

[0034] R1: an alkyl group having 9 to 19 carbon atoms R2: hydrogen atom or silk amino acid residue R3: COOX (X is a hydrogen atom, sodium atom, or potassium atom) R4: an alkyl group having 1 to 3 carbon atoms n: an integer between 1 and 3

[0035] Examples of R1 include nonyl, undecyl, tridecyl, pentadecyl, heptadecyl, nonadecyl, coconut oil fatty acid residue, and beef tallow fatty acid residue, and are preferably undecyl or coconut oil fatty acid residue. Examples of R4 include methyl, ethyl, and n-propyl groups, and are preferably both methyl groups.

[0036] When R2 is a silk amino acid residue, X is preferably a potassium atom.

[0037] When X is a hydrogen atom (H), R3 may be a salt neutralized with triethanolamine.

[0038] The commercially available surfactants represented by the general formula (2), (3), or (4) used in the present invention are not limited. Examples of surfactants used as dispersants include Kawasilk S (manufactured by Kawaken Fine Chemicals Co., Ltd.), Soypon SLTA (manufactured by Kawaken Fine Chemicals Co., Ltd.), Soypon M-30 (manufactured by Kawaken Fine Chemicals Co., Ltd.), Alanon ALTA (manufactured by Kawaken Fine Chemicals Co., Ltd.), Softazoline LAO (manufactured by Kawaken Fine Chemicals Co., Ltd.), Sarcosinate PN (manufactured by Kawaken Fine Chemicals Co., Ltd.), and Sarcosinate CN-30 (manufactured by Nikko Chemicals Co., Ltd.).

[0039] Examples of surfactants used as dispersants include polyoxyethylene acetylene glycol, phytosterol, and amine salts of anionic surfactants. Commercially available surfactants include Acetylenol E40 (manufactured by Kawaken Fine Chemicals Co., Ltd.), Acetylenol E60 (manufactured by Kawaken Fine Chemicals Co., Ltd.), Acetylenol E100 (manufactured by Kawaken Fine Chemicals Co., Ltd.), NIKKOL BPS-10 (manufactured by Nikko Chemicals Co., Ltd.), NIKKOL BPS-20 (manufactured by Nikko Chemicals Co., Ltd.), and Disparlon AQ-360 (manufactured by Kusumoto Chemicals Co., Ltd.).

[0040] Examples of polymeric dispersants used as dispersants include synthetic resins such as polyvinylpyrrolidone, polyvinyl butyral, polyvinyl ether, styrene-maleic acid copolymer, ketone resin, hydroxyethyl cellulose and its derivatives, and styrene-acrylic acid copolymer, acrylic polymers, PO·EO adducts, and polyester amine oligomers.

[0041] Specifically, examples of polymer dispersants used as dispersants include those having an acid value or an amine value of at least 0 mgKOH / g. Among these, it is preferable to use a polymer dispersant having an amine value of 0 mgKOH / g or a polymer dispersant having both an acid value and an amine value of 0 mgKOH / g.

[0042] The amine value represents the mass (mg) of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize 1 g of solid content. The amine value can be measured by the method described in JIS K7237:1995.

[0043] The acid value represents the mass (mg) of potassium hydroxide required to neutralize 1 g of solid content and can be measured by the method described in JIS K0070:1992.

[0044] As a polymer dispersant with an acid value of more than 0 mgKOH / g, it is preferable to use a polymer dispersant with an acid value of less than 10 mgKOH / g, and it is preferable to use a polymer dispersant with an acid value of 5 mgKOH / g or less. Commercially available polymer dispersants that satisfy these conditions include DISPER BYK-199 (manufactured by BYK Japan Co., Ltd.) and BYK-2060 (manufactured by BYK Japan Co., Ltd.).

[0045] As a polymer dispersant having an amine value of more than 0 mgKOH / g, it is preferable to use a polymer dispersant having an amine value of 5 mgKOH / g to 50 mgKOH / g, and more preferably a polymer dispersant having an amine value of 15 mgKOH / g to 40 mgKOH / g. Commercially available polymer dispersants that satisfy these conditions include DISPER BYK-184 (manufactured by BYK Japan Co., Ltd.), DISPER BYK-2055 (manufactured by BYK Japan Co., Ltd.), Hinoact NB (manufactured by Kawaken Fine Chemical Co., Ltd.), and Solsperse 20000 (manufactured by Lubrizol Japan Co., Ltd.).

[0046] As a polymeric dispersant having an acid value and an amine value exceeding 0 mgKOH / g, it is preferable to use a polymeric dispersant having an acid value of 5 mgKOH / g to 50 mgKOH / g and an amine value of 10 mgKOH / g to 45 mgKOH / g.More preferably, it is more preferable to use a polymeric dispersant having an acid value of 5 mgKOH / g to 50 mgKOH / g and an amine value of 10 mgKOH / g to 45 mgKOH / g, and having a high acid value relative to the amine value, i.e., an acid value / amine value ratio of more than 1. Commercially available examples of such polymer dispersants include DISPER BYK-191 (manufactured by BYK Japan Co., Ltd.), DISPER BYK-2010 (manufactured by BYK Japan Co., Ltd.), DISPER BYK-2013 (manufactured by BYK Japan Co., Ltd.), ANTI TERA-250 (manufactured by BYK Japan Co., Ltd.), Disparlon AQ-380 (manufactured by Kusumoto Chemical Co., Ltd.), and FLORENE G-700AMP (manufactured by Kyoeisha Chemical Co., Ltd.).

[0047] The polymer dispersant may also be a fluorine-containing oligomer. Commercially available polymer dispersants include Megafac F-477 (manufactured by DIC Corporation), Megafac F-553 (manufactured by DIC Corporation), and Megafac F-554 (manufactured by DIC Corporation).

[0048] Examples of inorganic compounds used as dispersants include pyrophosphates and hexametaphosphates.

[0049] When the ink composition according to the present invention contains a dispersant, the content of the dispersant relative to the uric acid pigment is not particularly limited, but is preferably in the range of 0.1% by mass to 100% by mass, more preferably 1% by mass to 50% by mass. By keeping the content of the dispersant within the above range, the dispersion stability of the uric acid pigment in the ink composition can be more stably maintained.

[0050] The ink composition according to the present invention contains a solvent, such as water or an organic solvent.

[0051] The water is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water.

[0052] The organic solvent is not particularly limited, and examples thereof include glycol ether solvents, glycol solvents, alcohol solvents, ketone solvents, ester solvents, and hydrocarbon solvents.

[0053] Examples of glycol ether solvents include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol monophenyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol dimethyl ether, 3-methoxybutanol, and 3-methoxy-3-methylbutanol.

[0054] Examples of glycol solvents include diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, and ethylene glycol.

[0055] Examples of alcohol-based solvents include benzyl alcohol, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, isobutanol, 2-butanol, tert-butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, ethylene glycol monomethyl ether acetate, and other higher alcohols.

[0056] Examples of ketone solvents include acetone, dimethyl ketone, diethyl ketone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of ester solvents include n-butyl formate, isobutyl formate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, ethyl propionate, n-butyl propionate, methyl butyrate, ethyl butyrate, methyl lactate, and ethyl lactate.

[0057] Examples of hydrocarbon solvents include n-hexane, n-heptane, n-octane, isooctane, cyclohexane, methylcyclohexane, ethylcyclohexane, toluene, xylene, and ethylbenzene.

[0058] The solvents can be used alone or in combination of two or more.

[0059] The content of the solvent relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 10% by mass to 90% by mass, more preferably 30% by mass to 80% by mass.

[0060] The ink composition of the present invention can further contain a colorant. By using a uric acid pigment in combination with a colorant, it is possible to obtain an ink composition that exhibits a color (pastel color) with hiding power.

[0061] The colorant is not particularly limited as long as it is a dye or pigment that can be dissolved or dispersed in a solvent.

[0062] Examples of dyes include acid dyes, basic dyes, direct dyes, oil-soluble dyes, and disperse dyes.

[0063] Specific examples of acid dyes include New Coccine (CI 16255), Tartrazine (CI 19140), Acid Blue Black 10B (CI 20470), Guinea Green (CI 42085), Brilliant Blue FCF (CI 42090), Acid Violet 6B (CI 42640), Soluble Blue (CI 42755), Naphthalene Green (CI 44025), Eosin (CI 45380), Phloxine (CI 45410), Erythrosine (CI 45430), Nigrosine (CI 50420), and Acid Flavin (CI 56205).

[0064] Specific examples of basic dyes include chrysoidine (CI 11270), methyl violet FN (CI 42535), crystal violet (CI 42555), malachite green (CI 42000), Victoria blue FB (CI 44045), rhodamine B (CI 45170), acridine orange NS (CI 46005), and methylene blue B (CI 52015).

[0065] Specific examples of direct dyes include Congo Red (CI 22120), Direct Sky Blue 5B (CI 24400), Violet BB (CI 27905), Direct Deep Black EX (CI 30235), Kayalas Black G Conc (CI 35225), Direct Fast Black G (CI 35255), and Phthalocyanine Blue (CI 74180).

[0066] Examples of oil-soluble dyes include CI Solvent Black 7, CI Solvent Black 123, CI Solvent Blue 2, CI Solvent Blue 25, CI Solvent Blue 55, CI Solvent Blue 70, CI Solvent Red 8, CI Solvent Red 49, CI Solvent Red 100, CI Solvent Violet 8, CI Solvent Violet 21, CI Solvent Green 3, CI Solvent Yellow 21, CI Solvent Yellow 44, CI Solvent Yellow 61, and CI Solvent Orange 37.

[0067] Examples of disperse dyes include CI Disperse Yellow 82, CI Disperse Yellow 3, CI Disperse Yellow 54, CI Disperse Red 191, CI Disperse Red 60, and CI Disperse Violet 57.

[0068] Examples of pigments include inorganic pigments, organic pigments, glitter pigments, fluorescent pigments, and phosphorescent pigments.

[0069] Examples of inorganic pigments include carbon black, iron black, yellow iron oxide, red iron oxide, and ultramarine.

[0070] Examples of organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, perinone pigments, isoindolinone pigments, isoindoline pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, threne pigments, indigo pigments, phthalone pigments, methine azomethine pigments, and metal complex pigments.

[0071] It is also possible to use water-dispersed pigments, which are pigments that have been finely and stably dispersed in an aqueous medium in advance using a surfactant or resin.

[0072] Specific examples of water-dispersible pigments include CI Pigment Blue 15:3B (manufactured by Sanyo Dye Co., Ltd., product name: Sandye Super Blue GLL-E (solid content: 24%)), CI Pigment Red 146 (manufactured by Sanyo Dye Co., Ltd., product name: Sandye Super Pink FBL (solid content: 21.5%)), CI Pigment Yellow 81 (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name: TC Yellow FG (solid content: approximately 30%)), and CI Pigment Red 220 / 166 (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name: TC Red FG (solid content: approximately 35%)).

[0073] Examples of resins for dispersing pigments include polyamides, urethane resins, polyesters, epoxy resins, melamine resins, phenolic resins, silicone resins, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polystyrene, acrylic acid resins, maleic acid resins, gum arabic, cellulose, dextran, casein, and derivatives thereof, and copolymers of the above resins.

[0074] Examples of luster pigments include metallic luster pigments in which the surface of a core substance such as glass flakes is coated with gold, silver, or the like; pearl pigments in which the surface of a core substance such as natural mica, synthetic mica, or flaky aluminum oxide is coated with a metal oxide such as titanium oxide; cholesteric liquid crystal pigments; metal powder pigments; metal pigments obtained by peeling off a metal vapor-deposited film of aluminum or the like formed on a substrate such as a film; and metal pigments in which a metal vapor-deposited film of aluminum or the like is formed on a colorless, transparent, or colored transparent film and then powdered.

[0075] Specific examples of metallic luster pigments in which the surface of a core material such as a piece of glass is coated with gold, silver, or the like include those manufactured by Nippon Sheet Glass Co., Ltd., under the product names Metashine 5480PS, 5230PS, 5150PS, 5090PS, 2080PS, 1030PS, 2025PS, 1030GP, and 2080GP.

[0076] Specific examples of pearl pigments in which the surface of natural mica is coated with titanium oxide include those manufactured by Merck Ltd., under the product names Iriodin 100, 111, 120, 153, 201, 211, 223, 231, 302, 323, 520, 522, and 524.

[0077] Specific examples of pearl pigments in which the surface of synthetic mica is coated with titanium oxide include those manufactured by Nihon Koken Kogyo Co., Ltd., product names: TWINCLE PEARL SXB, YXB, RXB, BXB, SXD, YXD, RXD, BXD, SX, YX, RX, and BX; and those manufactured by Nihon Koken Kogyo Co., Ltd., product names: ULTIMICA SB-100, SD-100, SE-100, SF-100, SH-100, YB-100, YE-100, and YF-100.

[0078] Specific examples of pearl pigments in which the surface of flaky aluminum oxide is coated with titanium oxide include Xirallic T60-10 WNT Crystal Silver, T60-20 WNT Sunbeam Gold, T60-21 WNT Solaris Red, T60-23 WNT Galaxy Blue, T60-24 WNT Stellar Green, and T60-25 WNT Cosmic Turquoise, all manufactured by Merck Ltd.

[0079] Specific examples of cholesteric liquid crystal pigments include those manufactured by Wacker Chemie under the product names HELICONE HC Sapphire, HELICONE HC Scarabeus, HELICONE HC Jade, and HELICONE HC Maple.

[0080] Examples of metal powder pigments include metal powder pigments with metallic luster such as aluminum powder, brass powder, stainless steel powder, and bronze powder, as well as metal powder pigments in which a colorant such as a dye or pigment is adsorbed onto these metal powder pigments. Also usable are pigment dispersions in which the above metal powder pigments are previously processed and dispersed with a surfactant, resin, solvent, etc. to form a paste, and liquid metal powder pigment dispersions.

[0081] Examples of fluorescent pigments include fine particle fluorescent pigments of synthetic resins in which various fluorescent dyes are solid-dissolved in a resin matrix.

[0082] Any general-purpose phosphorescent pigment can be used as long as it has the property of absorbing and storing light from the sun or an electric lamp, and gradually releasing and emitting light in the dark (this is called afterglow). Examples of phosphorescent pigments include CaS / Bi-based, CaSrS / Bi-based, ZnS / Cu-based, ZnCdS / Cu-based, and SrAl2O4 / rare earth metal-based pigments.

[0083] The above colorants can be used alone or in combination of two or more.

[0084] When the ink composition according to the present invention contains a colorant, the content of the colorant relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.01% by mass to 50% by mass, more preferably 0.1% by mass to 30% by mass. If the colorant content exceeds 50% by mass, the ink ejection stability of a writing instrument containing the ink composition is likely to decrease, and writing defects such as smearing and skipped lines are likely to occur. On the other hand, if the content is less than 0.01% by mass, it becomes difficult to obtain a writing density suitable for the writing instrument.

[0085] When the above pigments are used as colorants, a pigment dispersant can be used as needed. Examples of pigment dispersants include anionic and nonionic surfactants, anionic polymers such as polyacrylic acid and styrene acrylic acid, and nonionic polymers such as PVP and PVA.

[0086] The dyes or pigments described above are effective when used as they are, but microencapsulated pigments in which the dyes or pigments are encapsulated in microcapsules, or resin particles containing the dyes or pigments, can also be used as colorants in the present invention. In particular, by encapsulating the dyes or pigments in microcapsules, they are isolated and protected from the external environment, and the water resistance and light resistance of the encapsulated material can be improved.

[0087] Examples of microcapsule pigments encapsulating dyes or pigments include microcapsule pigments encapsulating colored bodies obtained by dispersing or dissolving dyes or pigments in an oily medium.

[0088] As the pigment, the above-mentioned inorganic pigments, organic pigments, luster pigments, fluorescent pigments, phosphorescent pigments, etc. can be used, and as the dye, the above-mentioned oil-soluble dyes, disperse dyes, etc. can be used.

[0089] Examples of oily media include esters such as monobasic acid esters, dibasic acid monoesters, dibasic acid diesters, partial esters and complete esters of polyhydric alcohols, aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes, higher alcohols, ketones, ethers, and the like.

[0090] The above oily media can be used alone or in combination of two or more.

[0091] Microencapsulation of microcapsule pigments can be performed by conventionally known methods such as an isocyanate-based interfacial polymerization method, an in situ polymerization method such as a melamine-formalin-based method, a liquid curing coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melt-dispersion cooling method, an air suspension coating method, and a spray drying method, and is appropriately selected depending on the application. Examples of capsule materials include epoxy resins, urea resins, urethane resins, and isocyanate resins.

[0092] Furthermore, depending on the purpose, a secondary resin film may be provided on the surface of the microcapsules to impart durability or modify the surface properties for practical use.

[0093] Examples of resin particles containing a dye include resin particles in which a dye is homogeneously dissolved or dispersed in the resin particles, and resin particles in which a dye is dyed.

[0094] The dye is not particularly limited as long as it can be dissolved, dispersed, or dyed in the resin that constitutes the resin particles, and the above-mentioned acid dyes, basic dyes, direct dyes, oil-soluble dyes, disperse dyes, etc. can be used.

[0095] When the resin particles contain a dye, examples of the resin that constitutes the resin particles include polystyrene, acrylic resin, epoxy resin, melamine resin, polyester, polyvinyl chloride, polybutadiene, benzoguanamine resin, polyamide, urethane resin, polymethyl methacrylate, acrylic-urethane copolymer resin, phenolic resin, polyethylene, polypropylene, polyacrylonitrile, polyacetal, ethylene-propylene copolymer resin, ethylene-vinyl acetate copolymer resin, styrene-acrylic copolymer resin, styrene-butadiene copolymer resin, styrene-acrylonitrile copolymer resin, and acrylonitrile-butadiene copolymer resin, and among these, thermosetting resins are preferred.

[0096] Thermosetting resins are preferable because they have superior solvent resistance and heat resistance compared to thermoplastic resins, and also have excellent resistance to migration of the dye contained therein, making it possible to prevent the dye from eluting from the resin.

[0097] Examples of thermosetting resins include epoxy resins, epoxy acrylate resins, xylene resins, toluene resins, guanamine resins, benzoguanamine resins, melamine resins, urethane resins, phenolic resins, alkyd resins, polyamides, polyimides, polyamide esters, urea resins, silicone resins, and unsaturated polyesters. Among these, guanamine resins and melamine resins are preferred because they can further suppress the elution of dyes.

[0098] Examples of resin particles containing a pigment include resin particles in which the pigment is uniformly dispersed, and resin particles whose surfaces are coated with a pigment.

[0099] The pigment is not particularly limited as long as it can be dispersed in or adsorbed to the resin that constitutes the resin particles, and the above-mentioned inorganic pigments, organic pigments, luster pigments, fluorescent pigments, phosphorescent pigments, etc. The above-mentioned pigments may be surface-treated by various conventionally known methods in order to improve their dispersibility or adsorption to the resin that constitutes the resin particles.

[0100] The resin constituting the resin particles may be the same as the resin constituting the dye-containing resin particles described above.

[0101] The resin particles can be produced by a pulverization method, a spray drying method, or a polymerization method in which polymerization is carried out in an aqueous or oily medium in the presence of a dye or pigment, such as a suspension polymerization method, a suspension polycondensation method, a dispersion polymerization method, or an emulsion polymerization method.

[0102] The shape of the resin particles is not particularly limited, and resin particles having a spherical shape such as a perfect sphere, an oval sphere, or an approximately spherical shape, a polygonal shape, or a flat shape can be used, but it is preferable to use spherical resin particles.

[0103] When the colorant contains microencapsulated pigments or resin particles encapsulating dyes or pigments, the colorant content relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.01% to 50% by mass, more preferably 0.1% to 30% by mass. If the colorant content exceeds 50% by mass, the ink discharge performance of the writing instrument containing the ink composition is likely to deteriorate, and writing defects such as smearing and skipped lines are likely to occur. On the other hand, if the content is less than 0.01% by mass, it becomes difficult to obtain a writing density suitable for the writing instrument.

[0104] Furthermore, functional materials such as thermochromic materials and photochromic materials can also be used as colorants.

[0105] Examples of thermochromic materials include reversible thermochromic compositions comprising (i) an electron-donating color-forming organic compound, (ii) an electron-accepting compound, and (iii) a reaction medium that determines the temperature at which the color-forming reaction of the above components (i) and (ii) occurs.

[0106] Examples of reversible thermochromic compositions include heat-discolorable reversible thermochromic compositions having a relatively small hysteresis width (ΔH) (ΔH = 1 to 7°C), as described in Japanese Patent Publication Nos. 51-44706, 51-44707, and 1-29398. "Heat-discolorable" refers to a composition that discolors upon heating and develops color upon cooling. These reversible thermochromic compositions undergo color changes around a predetermined temperature, a color change point, exhibiting a discolored state above the high-temperature color change point and a colored state below the low-temperature color change point. Furthermore, these reversible thermochromic compositions only exist in one of two specific states at room temperature. The other state of the reversible thermochromic composition is maintained while the heat or cold required to achieve that state is applied, but returns to the state it exhibits at room temperature once the application of heat or cold is removed.

[0107] Furthermore, reversible thermochromic compositions of the heat-discoloring type having a relatively large hysteresis width (ΔH=8 to 50°C) can be used, as described in JP-B-4-17154, JP-A-7-179777, JP-A-7-33997, JP-A-8-39936, etc. Also usable are reversible thermochromic compositions of the heat-discoloring type exhibiting large hysteresis characteristics, as described in JP-A-2006-137886, JP-A-2006-188660, JP-A-2008-45062, JP-A-2008-280523, etc. These reversibly thermochromic compositions exhibit color change along significantly different paths when the temperature is increased from a lower temperature than the color-change temperature range, as compared to when the temperature is decreased from a higher temperature than the color-change temperature range. These reversibly thermochromic compositions exhibit color memory in a specific temperature range, either in a colored state at or below the complete color-developing temperature t1 or in a decolorized state at or above the complete decolorization temperature t4. The specific temperature range refers to the temperature range between the color-developing onset temperature t2 and the decolorization onset temperature t3, i.e., the temperature range in which two phases are essentially maintained.

[0108] When the reversible thermochromic composition having the above-mentioned color memory property is applied to the present invention, the reversible thermochromic composition specifically specifies the complete color development temperature t1 to a temperature that can only be obtained in a freezer or cold region, and the complete decolorization temperature t4 to a temperature range that can be obtained from frictional heat generated by a friction body or a familiar heating body such as a hair dryer. By specifying the ΔH value to be between 40°C and 100°C, the composition can effectively maintain the color it exhibits under normal conditions (the temperature range in everyday life).

[0109] The temperatures that can only be obtained in freezers, cold regions, etc. are −50° C. or higher and 0° C. or lower, preferably −40° C. or higher and −5° C. or lower, and more preferably −30° C. or higher and −10° C. The temperatures that can be obtained from familiar heating devices such as hair dryers are 50° C. or higher and 95° C. or lower, preferably 50° C. or higher and 90° C. or lower, and more preferably 60° C. or higher and 80° C. or lower.

[0110] Furthermore, as the reversible thermochromic composition, a heat-coloring type reversible thermochromic composition using a gallic acid ester, as described in JP-B No. 51-44706, JP-A No. 2003-253149, etc., can also be used. "Heat-coloring type" means that the color develops when heated and disappears when cooled.

[0111] The reversible thermochromic composition is a compatible solution containing the above components (A), (B), and (C) as essential components, and the ratio of each component depends on the concentration, color change temperature, color change form, and type of each component. Generally, the component ratio that achieves the desired properties is 1 part of component (A) to 0.1 to 100, preferably 0.1 to 50, more preferably 0.5 to 20, of component (B), and 1 to 800, preferably 5 to 200, more preferably 10 to 100, of component (C). All of the above ratios are in parts by mass.

[0112] Examples of photochromic materials include conventionally known photochromic compounds such as spirooxazine derivatives, spiropyran derivatives, and naphthopyran derivatives, which develop color when irradiated with sunlight, ultraviolet light, or blue light having a peak emission wavelength in the range of 400 to 495 nm, and lose color when the irradiation is stopped.

[0113] Examples of spirooxazine derivatives include conventionally known indolinospirobenzoxazine compounds, indolinospironaphthoxazine compounds, indolinospirophenanthrooxazine compounds, and indolinospiroquinolinoxazine compounds.

[0114] Furthermore, examples of photochromic compounds having a photomemory property (color memory and photochromic property) include conventionally known fulgide derivatives and diarylethene derivatives.

[0115] Furthermore, as the photochromic material, a reversible photochromic composition in which the above photochromic compound is dissolved in various oligomers can also be used.

[0116] Examples of the oligomer include styrene-based oligomers, acrylic-based oligomers, terpene-based oligomers, and terpene-phenol-based oligomers.

[0117] Examples of styrene oligomers include low molecular weight polystyrene, styrene-α-methylstyrene copolymer, α-methylstyrene polymer, and copolymer of α-methylstyrene and vinyltoluene.

[0118] Examples of the acrylic oligomer include acrylic acid ester copolymers.

[0119] Examples of the terpene oligomer include α-pinene polymer, β-pinene polymer, d-limonene polymer, and the like.

[0120] An example of the terpene phenol oligomer is an α-pinene-phenol copolymer.

[0121] By dissolving the photochromic compound in various oligomers, it is possible to improve the light resistance of the photochromic compound, as well as to improve the color density and adjust the color change sensitivity.

[0122] The above oligomers can be used alone or in combination of two or more.

[0123] The above-mentioned reversible thermochromic composition or reversible photochromic composition is effective when used as it is, but it can also be encapsulated in microcapsules to form a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule pigment, or dispersed in a thermoplastic resin or a thermosetting resin to form reversible thermochromic resin particles or reversible photochromic resin particles, and used as a colorant to be applied to the present invention.

[0124] In the following, the reversible thermochromic microcapsule pigment and the reversible photochromic microcapsule pigment may be referred to as "microcapsule pigment", and the reversible thermochromic resin particles and the reversible photochromic resin particles may be referred to as "resin particles".

[0125] The reversible thermochromic composition or reversible photochromic composition is preferably encapsulated in microcapsules to form a reversible thermochromic microencapsulated pigment or reversible photochromic microencapsulated pigment, because encapsulation in microcapsules makes it possible to form a chemically and physically stable pigment, and furthermore, the reversible thermochromic composition or reversible photochromic composition can maintain the same composition under various use conditions and exhibit the same effects.

[0126] Microencapsulation can be performed by conventionally known methods such as isocyanate-based interfacial polymerization, melamine-formalin-based in situ polymerization, liquid curing coating, phase separation from an aqueous solution, phase separation from an organic solvent, melt-dispersion cooling, air suspension coating, and spray drying, and is appropriately selected depending on the application. Examples of capsule materials include epoxy resins, urea resins, urethane resins, and isocyanate resins.

[0127] Furthermore, depending on the purpose, a secondary resin film may be provided on the surface of the microcapsules to impart durability or modify the surface properties for practical use.

[0128] The above-mentioned microcapsule pigment preferably has a mass ratio of inclusions to wall film of 7:1 to 1:1, and by having the mass ratio of inclusions to wall film within the above range, it is possible to prevent a decrease in color density and vividness during color development. More preferably, the mass ratio of inclusions to wall film is 6:1 to 1:1.

[0129] Furthermore, by blending a non-color-changing colorant such as a general dye or pigment into the microcapsule pigment, it is possible to exhibit color change behavior from color (1) to color (2).

[0130] Examples of reversibly thermochromic resin particles or reversibly photochromic resin particles include resin particles in which the above-mentioned reversibly thermochromic composition or reversibly photochromic composition is uniformly dispersed in the resin particles.

[0131] The resin constituting the resin particles is not particularly limited as long as it is a thermoplastic resin or a thermosetting resin.

[0132] Examples of thermoplastic resins include polystyrene, acrylic resin, polyester, polyvinyl chloride, polybutadiene, polymethyl methacrylate, acrylic-urethane copolymer resin, polyethylene, polypropylene, polyacrylonitrile, polyacetal, ethylene-propylene copolymer resin, ethylene-vinyl acetate copolymer resin, styrene-acrylic copolymer resin, styrene-butadiene copolymer resin, styrene-acrylonitrile copolymer resin, and acrylonitrile-butadiene copolymer resin.

[0133] Examples of thermosetting resins include epoxy resins, epoxy acrylate resins, xylene resins, toluene resins, guanamine resins, benzoguanamine resins, melamine resins, urethane resins, phenolic resins, alkyd resins, polyamides, polyimides, polyamide esters, urea resins, silicone resins, and unsaturated polyesters.

[0134] The resin particles can be produced by a pulverization method, a spray drying method, or a polymerization method in which polymerization is carried out in an aqueous or oily medium in the presence of a reversible thermochromic composition or a reversible photochromic composition, such as suspension polymerization, suspension polycondensation, dispersion polymerization, or emulsion polymerization.

[0135] The shape of the resin particles is not particularly limited, and resin particles having a spherical shape such as a perfect sphere, an oval sphere, or an approximately spherical shape, a polygonal shape, or a flat shape can be used, but it is preferable to use spherical resin particles.

[0136] Furthermore, by blending a non-discoloring colorant such as a general dye or pigment into the resin particles, it is possible to cause the particles to exhibit a discoloration behavior from color (1) to color (2).

[0137] When the colorant in the ink composition includes the reversible thermochromic composition, the reversible photochromic composition, the microencapsulated pigment containing the reversible thermochromic composition, or the resin particles containing the reversible photochromic composition, the colorant content relative to the total mass of the ink composition is not particularly limited, but is preferably 5% to 40% by mass, more preferably 10% to 40% by mass, and even more preferably 15% to 35% by mass. If the colorant content exceeds 40% by mass, the ink discharge performance of a writing instrument containing the ink composition decreases, and writing defects such as blurring and skipped lines are likely to occur. On the other hand, if the content is less than 5% by mass, it is difficult to achieve the color change and writing density suitable for a writing instrument, and the color change function is not fully achieved.

[0138] The average particle size of the reversible thermochromic microencapsulated pigment or resin particles, or the reversible photochromic microencapsulated pigment or resin particles, is preferably 0.01 μm to 5 μm, more preferably 0.1 μm to 3 μm, and even more preferably 0.5 μm to 3 μm. If the average particle size of the microencapsulated pigment or resin particles exceeds 5 μm, it becomes difficult to obtain good ink ejection properties when used in a writing instrument. On the other hand, if the average particle size is less than 0.01 μm, it becomes difficult to achieve high-density color development.

[0139] The average particle diameter was measured by determining the particle region using image analysis particle size distribution measurement software (manufactured by Mountec Co., Ltd., product name: MacView), calculating the diameter equivalent to a circle with a projected area (Heywood diameter) from the area of ​​the particle region, and measuring the average particle diameter of particles equivalent to a sphere with the same volume using this value.

[0140] Furthermore, if the particle size of all or the majority of particles exceeds 0.2 μm, it is also possible to measure the average particle size of particles equivalent to an equal volume sphere by the Coulter method using a particle size distribution analyzer (product name: Multisizer 4e, manufactured by Beckman Coulter, Inc.).

[0141] Furthermore, the volumetric particle size and average particle size may be measured using a calibrated laser diffraction / scattering particle size distribution analyzer (manufactured by HORIBA, Ltd., product name: LA-300) based on values ​​measured using the above-mentioned software or a measuring device using the Coulter method.

[0142] In addition to the essential components described above, the ink composition of the present invention may contain optional components within a range that does not impair the effects of the present invention.

[0143] The ink composition of the present invention can be blended with a thickener to inhibit aggregation and sedimentation of the pigment, thereby providing an ink composition with good stability over time.

[0144] As the thickener, any known substance can be used, but it is preferable to use a substance that can impart shear thinning properties to the ink composition (shear thinning agent).

[0145] An ink composition using a shear thinning agent has high viscosity and is difficult to flow when left at rest or under low stress, but easily reduces viscosity when external stress is applied. As a result, ink leakage, separation, and backflow can be prevented when not writing, and ink ejection stability from the pen tip can be easily improved when writing.

[0146] In particular, when such an ink composition is used in a writing instrument (ballpoint pen) equipped with a ballpoint tip as the pen tip, the ink composition is stably retained in the ballpoint pen because it has a high viscosity when left standing without shear stress. Therefore, during writing, a strong shear stress is applied to the ink composition due to the rotation of the ball, which makes it easier for the viscosity of the ink composition in the vicinity of the ball to decrease, thereby improving the ink ejection stability.

[0147] When the ink composition according to the present invention contains a thickener, the content of the thickener relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.1 mass % to 20 mass %.

[0148] Examples of shear thinning agents include water-soluble polysaccharides, polymers having a molecular weight of 100,000 or more and 150,000 or less, mainly composed of alkyl esters of methacrylic acid, crosslinked poly-N-vinylcarboxylic acid amides, benzylidene sorbitol and its derivatives, benzylidene xylitol and its derivatives, alkali-thickening acrylic resins, crosslinkable acrylic acid polymers, inorganic fine particles, nonionic surfactants having an HLB value of 8 or more and 12 or less, and metal salts and amine salts of dialkyl sulfosuccinic acid.

[0149] The shear thinning agents may be used alone or in combination of two or more.

[0150] Examples of water-soluble polysaccharides include xanthan gum, welan gum, zeta sea gum, diutan gum, macrophomopsis gum, succinoglycan (average molecular weight of approximately 1 million to 8 million), which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alkyl alginate esters, glucomannan, and carbohydrates with gelling ability extracted from seaweed such as agar and carrageenan.

[0151]

[0033] Furthermore, the ink composition according to the present invention can be blended with a flocculant, which allows the pigment to form loose aggregates via the flocculant, thereby preventing direct aggregation of the pigments themselves and improving the dispersion stability of the pigment. The flocculant can also be used in combination with the above-mentioned dispersant. When both the flocculant and the dispersant are used in combination, the dispersibility of the loose aggregates formed via the flocculant can be improved, and the dispersion stability of the pigment in the ink can be further improved.

[0152] When the ink composition according to the present invention contains a flocculant, the content of the flocculant relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.05 mass % or more and 1 mass % or less.

[0153] Examples of the flocculant include polyvinylpyrrolidone, polyethylene oxide, and water-soluble polysaccharides.

[0154] Examples of water-soluble polysaccharides include tragacanth gum, guar gum, pullulan, cyclodextrin, and water-soluble cellulose derivatives.

[0155] Furthermore, examples of water-soluble cellulose derivatives include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose.

[0156] The ink composition of the present invention may contain a surfactant, which allows the surface tension of the ink composition to be adjusted within an appropriate range.

[0157] The surfactants used to adjust the surface tension include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, etc., and any of them can be suitably used.

[0158] Examples of surfactants used to adjust the surface tension include phosphate ester surfactants, silicone surfactants, surfactants having an acetylene bond in their structure, and fluorine-based surfactants. These surfactants are appropriately selected depending on the components and application of the ink composition.

[0159] The surfactant used as the dispersant may be used both to improve the dispersibility of the pigment and to adjust the surface tension.

[0160] When the ink composition according to the present invention contains a surfactant used to adjust the surface tension, the content of the surfactant used to adjust the surface tension relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.01% by mass or more and 2% by mass or less, and more preferably 0.05% by mass or more and 1% by mass or less.

[0161] The ink composition of the present invention can be blended with a pH adjuster to adjust the pH of the ink composition to an appropriate range. Various acidic and basic substances can be used as the pH adjuster.

[0162] Examples of acidic substances include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, lactic acid, citric acid, tartaric acid, and malic acid.

[0163] Examples of basic substances include ammonia, sodium carbonate, sodium hydrogen phosphate, potassium hydrogen phosphate, sodium hydroxide, potassium hydroxide, and sodium acetate. In addition, alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine can also be used.

[0164] When the ink composition according to the present invention contains a pH adjuster, the content of the pH adjuster relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.1 mass % or more and 5 mass % or less, and more preferably 0.5 mass % or more and 2 mass % or less.

[0165] When the solvent used in the present invention is water, a water-soluble organic solvent that is compatible with water can be blended to prevent water from evaporating from the pen tip of the writing implement.

[0166] Examples of water-soluble organic solvents include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thioethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, sulfolane, 2-pyrrolidone, and N-methyl-2-pyrrolidone.

[0167] The water-soluble organic solvents can be used alone or in combination of two or more.

[0168] When the ink composition according to the present invention contains a water-soluble organic solvent, the content of the water-soluble organic solvent relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 1% by mass to 40% by mass, more preferably 5% by mass to 30% by mass, and even more preferably 10% by mass to 25% by mass. If the content of the water-soluble organic solvent exceeds 40% by mass, the ink viscosity tends to increase, the ink dischargeability of a writing instrument containing the ink composition decreases, and writing defects such as smearing and skipped lines tend to occur. On the other hand, if the content is less than 1% by mass, the effect of suppressing water evaporation is poor.

[0169] The ink composition according to the present invention can be blended with water-soluble resins such as alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin, and can also be used to impart adhesion and viscosity to the paper surface.

[0170] The water-soluble resins can be used alone or in combination of two or more.

[0171] When the ink composition according to the present invention contains a water-soluble resin, the content of the water-soluble resin relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 1 mass % or more and 30 mass % or less, and more preferably 1 mass % or more and 10 mass % or less.

[0172] The ink composition of the present invention may also contain various other additives as required.

[0173] Examples of the additives include rust inhibitors, antiseptics or antifungal agents, air bubble absorbers, wetting agents, antifoaming agents, specific gravity adjusters, and the like.

[0174] Examples of the rust inhibitor include dicyclohexylammonium nitrite, diisopropylammonium nitrite, and saponin.

[0175] Examples of antiseptics or antifungal agents include carbolic acid, sodium salt of 1,2-benzothiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine.

[0176] Examples of air bubble absorbers include ascorbic acids, erythorbic acids, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkylhydroxylamines, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, and thiourea dioxide.

[0177] Examples of wetting agents include reduced or non-reduced starch hydrolysates, disaccharides such as trehalose, oligosaccharides, sucrose, cyclodextrin, glucose, dextrin, sorbitol, mannitol, sodium pyrophosphate, and the like.

[0178] When the ink composition according to the present invention is contained in a writing instrument (ballpoint pen) equipped with a ballpoint pen tip, a lubricant may also be blended into the ink composition.

[0179] The lubricant improves the lubricity between the ball receiving seat provided inside the tip body and the ball provided at the front end of the tip body, making it possible to easily prevent wear of the ball receiving seat and improve the writing feel.

[0180] Examples of lubricants include higher fatty acids such as oleic acid, nonionic surfactants having a long-chain alkyl group, polyether-modified silicone oil, thiophosphite triesters such as thiophosphite tri(alkoxycarbonylmethyl ester) and thiophosphite tri(alkoxycarbonylethyl ester), phosphate ester surfactants such as polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate monoesters, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate diesters, and metal salts, ammonium salts, amine salts, and alkanolamine salts thereof.

[0181] When the ink composition according to the present invention is applied to a ballpoint pen having a ballpoint pen tip comprising a tip body provided with a metal ball receiving seat and a metal ball, it is preferable to use a phosphate ester surfactant as the lubricant.

[0182] The phosphate group of a phosphate ester surfactant has the property of easily adsorbing to metals. Therefore, when an ink composition containing a phosphate ester surfactant is applied to the above-mentioned ballpoint pen, the phosphate ester surfactant is adsorbed to the ball and ball seat, forming a lubricating layer made of the phosphate ester surfactant on the surface of the ball and the surface of the ball seat, improving the lubrication between the ball and the ball seat and allowing the ball to rotate smoothly. This also reduces wear on the ball seat and improves the writing feel, such as the writing experience.

[0183] The method for producing the ink composition of the present invention is not particularly limited, and any conventionally known method can be used.

[0184] Specifically, the ink composition can be produced by stirring a mixture of the above components with various stirrers such as a propeller stirrer, a homodisper, or a homomixer, or by dispersing the mixture with various dispersers such as a bead mill.

[0185] The viscosity characteristics of the ink composition according to the present invention are not particularly limited. For example, ink compositions having viscosity characteristics such as a high shear thinning ink composition (gel ink), a low viscosity, low shear thinning ink composition, or a low viscosity, non-shear thinning ink composition (Newtonian ink) can be used. The uric acid pigment used in the present invention has excellent dispersion stability, and the pigment is unlikely to settle even in a low viscosity ink composition, so a low viscosity ink composition is preferably used.

[0186] When the ink composition of the present invention is used in a ballpoint pen, its viscosity is measured at a rotation speed of 1 rpm (shear rate of 3.84 sec) in an environment of 20°C. -1 ), the following range is preferred because it can further stabilize the dispersion stability of the pigment. Specifically, the viscosity of the ink composition in this case is preferably in the range of 1 mPa·s or more and 2000 mPa·s or less, more preferably 10 mPa·s or more and 1500 mPa·s or less, and even more preferably 100 mPa·s or more and 1000 mPa·s or less.

[0187] In addition, in an environment of 20°C, the rotation speed was 100 rpm (shear rate 384 sec -1 When measured under the conditions of (1), the viscosity is preferably in the following range, since this allows for good ink discharge from the pen tip of a ballpoint pen. Specifically, the viscosity of the ink composition in this case is preferably in the range of 1 mPa·s or more and 200 mPa·s or less, more preferably 10 mPa·s or more and 100 mPa·s or less, and even more preferably 20 mPa·s or more and 50 mPa·s or less.

[0188] By ensuring that the viscosity of the ink composition is within the above range, it is possible to maintain high levels of pigment dispersion stability and ink flowability within the ballpoint pen mechanism.

[0189] The viscosity of the ink composition was measured using a rheometer (manufactured by TA Instruments, product name: Discovery HR-2, cone plate (diameter 40 mm, angle 1°)) at a rotation speed of 1 rpm (shear rate 3.84 sec) while placing the ink in an environment of 20°C. -1 ), or rotation speed 100 rpm (shear rate 384 sec -1 ) are values ​​measured under the conditions.

[0190] When the ink composition according to the present invention is used in a marking pen, the viscosity thereof, measured at a rotation speed of 50 rpm in an environment of 20°C, is preferably in the following range, since this allows the ink fluidity and pigment dispersion stability to be maintained at a high level. Specifically, the viscosity of the ink composition in this case is preferably in the range of 1 mPa·s or more and 30 mPa·s or less, more preferably 1 mPa·s or more and 20 mPa·s or less, and even more preferably 1 mPa·s or more and 10 mPa·s or less.

[0191] The viscosity of the ink composition was measured using an E-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd., product name: RE-85L, cone-type rotor: standard type (1°34' x R24)) by placing the ink composition in an environment of 20°C.

[0192] When the ink composition according to the present invention is used in a ballpoint pen or a marking pen, the pH thereof is preferably in the range of from 6 to 10, more preferably from 7 to 9. When the pH is within the above range, excessive viscosity increase and deterioration of the ink composition can be suppressed.

[0193] The pH of the ink composition was measured by placing the ink in an environment of 20°C using a pH meter (manufactured by DKK-TOA Corporation, product name: IM-40S).

[0194] When the ink composition according to the present invention is used in a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited, and the ink composition may be used by being filled into, for example, a ballpoint pen refill or ballpoint pen equipped with a ballpoint pen tip and an ink filling mechanism.

[0195] A ballpoint pen tip consists of a tip body and a ball attached to the front end of the tip body. Examples of ballpoint pen tips include a tip formed by deforming a metal pipe tip body near the tip end by pressing the ball inward from the outer surface in a ball-holding portion, a tip formed by cutting a metal tip body with a drill or the like to hold the ball, a tip with a resin ball receiving seat provided inside a metal or plastic tip body, and a tip in which the ball held by the tip is biased forward by a spring.

[0196] The material of the tip body and the ball is not particularly limited, and examples thereof include cemented carbide (super hard), stainless steel, ruby, ceramic, resin, rubber, etc. Furthermore, the ball can be subjected to a surface treatment such as a DLC coating.

[0197] The diameter of the ball is generally 0.2 mm or more and 3 mm or less, preferably 0.2 mm or more and 2 mm or less, more preferably 0.2 mm or more and 1.5 mm or less, and even more preferably 0.2 mm or more and 1 mm or less.

[0198] An example of the ink filling mechanism is an ink reservoir that can be directly filled with ink.

[0199] The ink reservoir may be, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a tubular body made of metal.

[0200] A ballpoint pen refill (hereinafter sometimes referred to as "refill") can be formed by connecting a ballpoint pen tip directly or via a connecting member to an ink reservoir and directly filling the ink reservoir with ink. A ballpoint pen can be formed by storing this refill in a barrel.

[0201] The ink reservoir is filled with an ink backflow preventer at the rear end thereof, which may be a liquid stopper or a solid stopper.

[0202] The liquid plug is made of a non-volatile liquid and / or a hardly-volatile liquid, examples of which include petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or co-oligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, and fatty acid-modified silicone oil.

[0203] The non-volatile liquid and / or the hardly-volatile liquid can be used alone or in combination of two or more kinds.

[0204] It is preferable to add a thickener to the non-volatile liquid and / or the hardly-volatile liquid to thicken it to a suitable viscosity.

[0205] Examples of thickeners include clay-based thickeners such as silica with a hydrophobic surface treatment, fine particle silica with a methylated surface, aluminum silicate, swellable mica, hydrophobically treated bentonite or montmorillonite, fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate, dextrin-based compounds such as tribenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax, hydrogenated castor oil, and fatty acid dextrins, and cellulose-based compounds.

[0206] Examples of solid stoppers include solid stoppers made of polyethylene, polypropylene, polymethylpentene, and the like.

[0207] As the ink backflow preventer, the above-mentioned liquid stopper and solid stopper can be used in combination.

[0208] In addition, by using the barrel itself as the ink filling mechanism, filling ink directly into the barrel, and attaching a ballpoint pen tip to the front end of the barrel, it is possible to form a ballpoint pen equipped with a ballpoint pen tip and an ink filling mechanism.

[0209] If the ink filled in the ink filling mechanism has a low viscosity, a ballpoint pen equipped with a ballpoint pen tip and an ink filling mechanism may further include an ink supply mechanism for supplying the ink filled in the ink filling mechanism to the pen tip.

[0210] The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that has an ink guide core made of a fiber bundle or the like as an ink flow rate regulator and supplies ink to the pen tip through this; (2) a mechanism that has a comb-shaped ink flow rate regulator and supplies ink to the pen tip through this; and (3) a mechanism that supplies ink to the pen tip through a pen core consisting of multiple disks arranged in parallel with comb-shaped intervals, with slit-shaped ink guide grooves running vertically through the disks in the axial direction and wider ventilation grooves than the grooves, and an ink guide core arranged in the axial center to guide ink from the ink filling mechanism to the pen tip.

[0211] The material for the pen core is not particularly limited as long as it is a synthetic resin that can be injection molded into a structure in which multiple discs are arranged in a comb-like groove pattern. Examples of synthetic resins include general-purpose polycarbonate, polypropylene, polyethylene, and acrylonitrile-butadiene-styrene copolymer resin (ABS resin). In particular, acrylonitrile-butadiene-styrene copolymer resin (ABS resin) is preferably used because it has high moldability and is easy to obtain pen core performance.

[0212] When a ballpoint pen is provided with the ink supply mechanism, the ink filling mechanism may be an ink reservoir that can be filled with ink, in addition to the ink reservoir and barrel.

[0213] The ink occlusion body is a fiber bundle formed by bundling crimped fibers in the longitudinal direction, and is placed inside a covering such as a plastic cylinder or film, and is configured so that the porosity is adjusted to be in the range of approximately 40% to 90%.

[0214] A ballpoint pen refill including a ballpoint pen tip, an ink filling mechanism, and an ink supply mechanism can also be formed by accommodating an ink occluder impregnated with ink in an ink reservoir, providing an ink supply mechanism at the front end of the ink reservoir so as to connect to the ink occluder, and connecting a ballpoint pen tip to the ink supply mechanism directly or via a connecting member. Alternatively, a ballpoint pen refill can also be formed by accommodating an ink occluder impregnated with ink in an ink reservoir, providing an ink supply mechanism inside the ink reservoir so as to connect to the ink occluder, and connecting a ballpoint pen tip to the ink reservoir directly or via a connecting member.

[0215] Specific examples of the configuration of a ballpoint pen containing the ink composition according to the present invention include: (1) a ballpoint pen having an ink reservoir filled with ink in a barrel, to which a ballpoint pen tip is connected either directly or via a connecting member, and in which an ink backflow preventer is filled at the end face of the ink reservoir; (2) a ballpoint pen in which ink is directly filled in the barrel and which is provided with a mechanism for supplying ink to the pen tip by using a comb-shaped ink flow regulator or an ink guide core made of a fiber bundle or the like as an ink flow regulator; (3) a ballpoint pen in which ink is directly filled in the barrel and which is provided with a mechanism for supplying ink to the pen tip via the above-mentioned pen core; and (4) a ballpoint pen in which an ink occlusion body made of a fiber bundle impregnated with ink is contained in the barrel and which is provided with a mechanism for supplying ink to the pen tip by using an ink guide core made of a fiber bundle or the like as an ink flow regulator.

[0216] Furthermore, when the ink composition according to the present invention is used in a marking pen, the structure and shape of the marking pen itself are not particularly limited, and it may be used by being filled into, for example, a marking pen refill or a marking pen equipped with a marking pen tip and an ink filling mechanism.

[0217] Examples of marking pen tips include conventional, general-purpose porous members with interconnected pores, such as resin-processed fibers, fused heat-fusible fibers, and felt, with a porosity selected from the range of approximately 30% to 70%, or extrusion-molded synthetic resins with multiple ink outlet holes extending in the axial direction, and one end of the tip can be processed into a bullet-like, rectangular, chisel-like, or other shape appropriate for the purpose for practical use.

[0218] An example of the ink filling mechanism is an ink occlusion body that can be filled with ink. The ink occlusion body is a fiber bundle formed by bundling crimped fibers in the longitudinal direction, and is contained within a covering such as a plastic cylinder or film, with the porosity adjusted to a range of approximately 40% to 90%.

[0219] A marking pen can be formed by housing an ink-impregnated ink reservoir inside the barrel and connecting the marking pen tip to the barrel directly or via a connecting member so that it is connected to the ink reservoir.

[0220] Furthermore, a marking pen refill (hereinafter sometimes referred to as a "refill") can be formed by storing an ink occlusion body impregnated with ink in an ink reservoir and connecting a marking pen tip to the ink reservoir directly or via a connecting member. A marking pen can be formed by storing this refill in a barrel.

[0221] The ink reservoir may be, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a tubular body made of metal.

[0222] A marking pen equipped with a marking pen tip and an ink filling mechanism may further include an ink supply mechanism for supplying the ink composition filled in the ink filling mechanism to the pen tip.

[0223] The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that has an ink guide core made of a fiber bundle or the like as an ink flow regulator and supplies ink to the pen tip through this; (2) a mechanism that has a comb-shaped ink flow regulator and supplies ink to the pen tip through this; (3) a mechanism that supplies ink to the pen tip through a pen core consisting of a number of disks arranged in parallel with comb-shaped intervals, with slit-shaped ink guide grooves running axially through the disks and wider ventilation grooves than the grooves, and an ink guide core arranged in the axial center to guide ink from the ink filling mechanism to the pen tip; and (4) a mechanism that has an ink flow regulator with a valve mechanism and supplies ink to the pen tip by opening the valve.

[0224] The material for the pen core is not particularly limited as long as it is a synthetic resin that can be injection molded into a structure in which multiple discs are arranged in a comb-like groove pattern. Examples of synthetic resins include general-purpose polycarbonate, polypropylene, polyethylene, and acrylonitrile-butadiene-styrene copolymer resin (ABS resin). In particular, acrylonitrile-butadiene-styrene copolymer resin (ABS resin) is preferably used because it has high moldability and is easy to obtain pen core performance.

[0225] The valve mechanism can be a conventional, general-purpose pumping type that opens when the tip is pressed, and is preferably set to a spring pressure that can be pressed and released by the pressure of the writing pen.

[0226] When the marking pen is provided with an ink supply mechanism, the ink filling mechanism may be an ink reservoir that can be directly filled with ink, in addition to the ink occlusion body described above. Also, the barrel itself may serve as the ink filling mechanism, allowing ink to be directly filled.

[0227] Alternatively, a marking pen refill including a marking pen tip, an ink filling mechanism, and an ink supply mechanism can be formed by accommodating an ink occluder impregnated with ink in an ink reservoir, providing an ink supply mechanism at the front end of the ink reservoir so as to connect to the ink occluder, and connecting a marking pen tip to the ink supply mechanism directly or via a connecting member. Alternatively, a marking pen refill can be formed by accommodating an ink occluder impregnated with ink in an ink reservoir, providing an ink supply mechanism inside the ink reservoir so as to connect to the ink occluder, and connecting a marking pen tip to the ink reservoir so as to connect to the ink supply mechanism directly or via a connecting member.

[0228] Specific configurations of marking pens containing the ink composition of the present invention include: (1) a marking pen in which an ink occlusion body made of a fiber bundle impregnated with ink is contained in a barrel, and a marking pen tip made of a fiber processed body or a resin molded body with capillary gaps formed therein is connected to the barrel directly or via a connecting member so that the ink occlusion body and the tip are connected; (2) a marking pen in which ink is directly filled in the barrel, and which is provided with a mechanism for supplying ink to the pen tip by using an ink flow regulator such as a comb-shaped ink flow regulator or an ink guide core made of a fiber bundle or the like as an ink flow regulator; and (3) a marking pen in which ink is directly filled in the barrel, and a marking pen tip made of a fiber bundle or the like as an ink flow regulator. Examples include: (4) a marking pen that is filled with ink and is equipped with a mechanism that supplies ink to the pen tip via the pen core; (5) a marking pen that is equipped with an ink reservoir that is connected to a tip and an ink container via a valve mechanism that opens when the tip is pressed, and in which ink is directly filled into the ink container; and (6) a marking pen that has an ink reservoir that contains an ink absorbing body made of a fiber bundle impregnated with ink within its barrel, and in which a marking pen tip made of a fiber processed body or a resin molded body with a capillary gap formed therein is connected to the ink reservoir directly or via a connecting member so that the ink absorbing body and the tip are connected.

[0229] Furthermore, when a ballpoint pen or a marking pen is directly filled with writing instrument ink, an agitator such as an agitating ball for agitating the ink can be built into the ink reservoir or barrel into which the ink is filled in order to facilitate re-dispersion of the pigment. Examples of the shape of the agitator include a spherical body and a rod-like body. The material of the agitator is not particularly limited, and examples thereof include metal, ceramic, resin, and glass.

[0230] Furthermore, the writing implements such as the ballpoint pens and marking pens described above may be in the form of a detachable ink cartridge. In this case, after the ink contained in the ink cartridge of the writing implement is used up, it can be replaced with a new ink cartridge and used again.

[0231] As ink cartridges, those that double as the barrel that constitutes the writing instrument when connected to the writing instrument body, and those that cover and protect the barrel (rear barrel) after being connected to the writing instrument body are used. Note that the latter may be used as an ink cartridge alone, or may be one in which the writing instrument body and ink cartridge are connected in the writing instrument before use, or one that is stored in the barrel in a disconnected state so that the user of the writing instrument can connect the ink cartridge in the barrel when using it to start use.

[0232] Furthermore, by providing a cap that is attached to cover the pen tip (writing tip) of the writing instrument having the above-described configuration to make it a cap-type writing instrument, it is possible to prevent the pen tip from drying out and becoming unable to write, and to prevent the writing tip from becoming contaminated or damaged.

[0233] In addition, a ballpoint pen or marking pen that contains a refill inside the barrel can be made into a retractable writing instrument by providing a retraction mechanism inside the barrel that allows the writing tip to protrude and retract from the barrel, thereby preventing the writing tip from being contaminated or damaged.

[0234] Any retractable writing instrument can be used as long as the writing tip is housed within a barrel and exposed to the outside air, and the writing tip protrudes from the barrel opening when the retractable mechanism is activated.

[0235] Examples of retraction mechanisms include: (1) a side-slide retraction mechanism in which an operating part (clip) that can move back and forth in the radial direction protrudes radially outward from the rear side wall of the barrel, and the writing tip is retracted from the front end opening of the barrel by sliding the operating part forward; (2) a rear-end knock retraction mechanism in which the operating part at the rear end of the barrel is pressed forward to cause the writing tip to retract from the front end opening of the barrel; (3) a side-knock retraction mechanism in which the operating part that protrudes from the outer surface of the barrel side wall is pressed radially inward to cause the writing tip to retract from the front end opening of the barrel; and (4) a rotary retraction mechanism in which the operating part at the rear of the barrel is rotated to cause the writing tip to retract from the front end opening of the barrel.

[0236] Furthermore, the shape of ballpoint pens and marking pens is not limited to the configurations described above, and they may be equipped with tips of different shapes, or with tips that dispense ink of different colors, or they may be composite writing instruments (double-headed, retractable tip, etc.) that are equipped with tips of different shapes and dispense ink of different colors from each tip.

[0237] It may also be a composite type retractable writing instrument in which a plurality of refills are housed in the barrel, and the writing tip of one of the refills is caused to protrude and retract from the barrel opening by the operation of the retraction mechanism.

[0238] When a reversible thermochromic composition, a reversible thermochromic microcapsule pigment, or a reversible thermochromic resin particle is used as a colorant, handwriting formed on a surface using a writing instrument containing the writing instrument ink of the present invention can be discolored by rubbing with a finger or by using a heating or cooling tool.

[0239] Examples of the heating tool include an electrically heated discoloring tool equipped with a resistance heating element such as a PTC element, a heat discoloring tool filled with a medium such as hot water, a heat discoloring tool using steam or laser light, and the application of a hair dryer. However, friction members and friction bodies are preferred because they can change color in a simple manner.

[0240] Examples of cooling devices include electrically operated thermochromic devices using a Peltier element, thermochromic devices filled with a refrigerant such as cold water or ice chips, refrigerants, refrigerators, freezers, and the like.

[0241] As the friction member and friction body, an elastic body such as an elastomer or a plastic foam, which has a high elastic feel and can generate appropriate friction and frictional heat when rubbed, is preferred, but plastic molded bodies, stone, wood, metal, cloth, etc. can also be used.

[0242] Although a general eraser used for erasing pencil marks may be used to rub the marks, eraser dust is generated during the rubbing, and therefore the above-mentioned friction member and friction body which hardly generate eraser dust are preferably used.

[0243] Examples of materials for the friction member and friction body include silicone resin, SEBS resin (styrene-ethylene-butadiene-styrene block copolymer), etc. Silicone resin tends to adhere to areas that have been erased by rubbing, and handwriting tends to be repelled when writing is repeated, so SEBS resin is more preferably used.

[0244] The friction member or friction body may be a separate component of any shape from the writing instrument, but by providing it in the writing instrument, the writing instrument can be made highly portable. Also, a writing instrument set can be obtained by combining a writing instrument with a friction member or friction body of any shape that is separate from the writing instrument.

[0245] When the writing instrument is a cap-type writing instrument, the location where the friction member or friction body is provided is not particularly limited. For example, the cap itself may be formed from a friction member, the barrel itself may be formed from a friction member, or if a clip is provided, the clip itself may be formed from a friction member, or the friction member or friction body may be provided at the tip (top) of the cap or the rear end of the barrel (the part where the writing tip is not provided), etc.

[0246] When the writing implement is a retractable writing implement, the location where the friction member or friction body is provided is not particularly limited. For example, the barrel itself may be formed from a friction member, and if a clip is further provided, the clip itself may be formed from a friction member, or the friction member or friction body may be provided near the barrel opening, at the rear end of the barrel (the part where the writing tip is not provided), or at the knock portion. [Example]

[0247] Examples are shown below, but the present invention is not limited thereto. Unless otherwise specified, "parts" in the examples refer to "parts by mass."

[0248] Example 1 Preparation of pigment dispersions 10 parts of uric acid, 1 part of a dispersant (manufactured by BYK Japan, product name: DISPER BYK-191), and 89 parts of water were mixed. 100 parts of 2.0 mm diameter glass beads were added as media, and the mixture was ground and dispersed in a bead mill for 12 hours to prepare a pigment dispersion (uric acid pigment dispersion). The average particle size of the uric acid pigment dispersed in the pigment dispersion was 0.3 μm.

[0249] Comparative Example 1 Preparation of pigment dispersions 10 parts of titanium dioxide (manufactured by Teika Corporation, product name: JR-301), 1 part of dispersant (manufactured by BYK Japan, product name: DISPER BYK-191), and 89 parts of water were mixed. 100 parts of 2.0 mm diameter glass beads were added as media, and the mixture was milled and dispersed in a bead mill for 12 hours to prepare a pigment dispersion (titanium dioxide dispersion). The average particle size of the titanium dioxide dispersed in the pigment dispersion was 0.3 μm.

[0250] Dispersion stability evaluation 40 g of each pigment dispersion from Example 1 and Comparative Example 1 was placed in a screw cap bottle (No. 7) and allowed to stand at room temperature (25°C) for one day. After one day had passed, each pigment dispersion was visually inspected and its dispersion stability was evaluated according to the following criteria. The evaluation results are shown in Table 1 below.

[0251] A: The pigment remained dispersed, and the pigment dispersion was a uniform white color. B: Most of the pigment had settled, and a supernatant (aqueous layer) was visible in the pigment dispersion, showing separation into two layers.

[0252] Redispersibility evaluation Each pigment dispersion from Example 1 and Comparative Example 1 was placed in a sealed glass test tube with a diameter of 15 mm and allowed to stand at room temperature (25°C) for 7 days. After 7 days had passed, each glass test tube was shaken up and down, and the redispersion state of each pigment dispersion was visually confirmed, and the redispersibility was evaluated according to the following criteria. The evaluation results are shown in Table 1 below. A: The pigment was easily redispersed by shaking. B: The pigment did not redisperse even after shaking.

[0253] [Table 1]

[0254] Example 2 Preparation of pigment dispersions 10 parts of uric acid, 1 part of a surfactant (product name: Brownon L-205, manufactured by Aoki Oil & Fat Industries Co., Ltd.) acting as a dispersant, and 89 parts of water were mixed together. 200 parts of zirconia beads with a diameter of 1.0 mm were then added as media, and the mixture was ground and dispersed in a bead mill for 1 hour to prepare a pigment dispersion (uric acid pigment dispersion).

[0255] Dispersion stability evaluation The pigment dispersion of Example 2 was observed under an optical microscope (manufactured by Olympus Corporation, product name: System Biological Microscope BX53, 100x magnification) and the dispersion stability was evaluated according to the following criteria. The evaluation results are shown in Table 2 below.

[0256] A: The pigment appears to be uniformly dispersed. B: A slight aggregation of primary pigment particles was visually observed. C: Significant pigment aggregation was observed.

[0257] Redispersibility evaluation The pigment dispersion of Example 2 was placed in a sealed glass test tube with a diameter of 15 mm and allowed to stand at room temperature (25°C) for 7 days. After 7 days had passed, the glass test tube was shaken up and down, and the redispersion state of the pigment dispersion was visually confirmed, and the redispersibility was evaluated according to the following criteria. The evaluation results are shown in Table 2 below.

[0258] A: The pigment was easily redispersed by shaking. B: The pigment did not redisperse even after shaking.

[0259] Examples 3 to 12 Pigment dispersions were prepared in the same manner as in Example 2, except that the surfactants shown in Table 2 were used as dispersants instead of the surfactant used as the dispersant in Example 2. The dispersion stability and redispersibility of the pigment dispersions of Examples 3 to 12 were evaluated in the same manner as in Example 2. The evaluation results are shown in Table 2 below.

[0260] [Table 2]

[0261] Example 13 Preparation of pigment dispersions 10 parts of uric acid were mixed with 1 part of a polymer dispersant (manufactured by BYK Japan, product name: DISPER BYK-191) and 89 parts of water. 200 parts of 1.0 mm diameter zirconia beads were added as media, and the mixture was milled and dispersed for 1 hour in a bead mill to prepare a pigment dispersion (uric acid pigment dispersion, 1% dispersant, milled and dispersed for 1 hour). The average particle size of the uric acid pigment dispersed in the pigment dispersion was 0.34 μm.

[0262] In addition, a pigment dispersion (uric acid pigment dispersion, 1% dispersant, pulverized and dispersed for 6 hours) was prepared in the same manner as in Example 13, except that the duration of the pulverization and dispersion treatment was set to 6 hours. The average particle size of the uric acid pigment dispersed in the pigment dispersion was 0.30 μm.

[0263] The dispersion stability and redispersibility of the pigment dispersion of Example 13 were evaluated in the same manner as in Example 2. The evaluation results are shown in Table 3 below.

[0264] Examples 14 to 26 Pigment dispersions (uric acid pigment dispersion, 1% dispersant, pulverized and dispersed for 1 hour) were prepared in the same manner as in Example 13, except that the polymer dispersants shown in Tables 3 and 4 were used as dispersants instead of the polymer dispersant used in Example 13.

[0265] Examples 27 to 30 A pigment dispersion (uric acid pigment dispersion, 2% dispersant, 1-hour grinding and dispersion) was prepared in the same manner as in Example 13, except that the polymer dispersant shown in Table 5 was used as the dispersant instead of the polymer dispersant used in Example 13, and that the amount of polymer dispersant used as the dispersant was 2 parts and the amount of water was 88 parts.

[0266] Furthermore, the dispersion stability and redispersibility of the pigment dispersions of Examples 13 to 30 were evaluated in the same manner as in Example 2. The evaluation results are shown in Tables 3 to 5 below.

[0267] [Table 3]

[0268] [Table 4]

[0269] [Table 5]

[0270] Example 31 Preparation of ink composition 25 parts of uric acid, 2.5 parts of a dispersant (manufactured by BYK Japan, product name: DISPER BYK-191), and 72.5 parts of water were mixed. 100 parts of 2.0 mm diameter glass beads were added as media, and the mixture was milled and dispersed in a bead mill for 12 hours to prepare a pigment dispersion (uric acid pigment dispersion). The average particle size of the uric acid pigment dispersed in the pigment dispersion was 0.3 μm.

[0271] Next, 88 parts of the above pigment dispersion, 0.2 parts of a shear thinning agent (succinoglycan) [manufactured by Sansho Co., Ltd., product name: LEOSAN], 1 part of a phosphate ester surfactant [manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Plysurf AL], 1 part of a pH adjuster (triethanolamine), 0.1 parts of a preservative [manufactured by Lonza Japan Co., Ltd., product name: Proxel XL-2(S)], and 9.7 parts of water were mixed to prepare an ink composition.

[0272] Making a ballpoint pen The ink composition was filled by suction into an ink reservoir made of a polypropylene pipe, and then connected to a ballpoint pen tip having a 0.5 mm diameter carbide ball at its tip via a resin holder. Next, a viscoelastic ink backflow preventive material (liquid stopper) mainly composed of polybutene was filled into the rear end of the ink reservoir, and a tail plug was fitted to the rear of the pipe. The ink was then degassed by centrifugation to obtain a ballpoint pen refill.

[0273] Next, the refill was incorporated into a barrel to prepare a ballpoint pen (retractable ballpoint pen).

[0274] The above-mentioned ballpoint pen has a tip provided in a ballpoint pen refill stored in a barrel while being exposed to the outside air, and is provided with a rear-end knock-type protruding / retracting structure in which the tip protrudes from the front end opening of the barrel by pressing forward an operating part provided at the rear end of the barrel.

[0275] Using the above ballpoint pen, a mark was written on A4 size black paper (manufactured by Nagatoya Shoten Co., Ltd., product name: Color Paper A4 Medium Weight (thickness: 0.09 mm, density: 80 g / m)) at room temperature (20°C). 2 When handwritten on the ink, clear white handwriting was formed without any writing defects such as smearing or skipped lines. Furthermore, this handwriting concealed the written surface, resulting in good handwriting with excellent concealing properties.

[0276] Example 32 Preparation of ink composition An ink composition was prepared by mixing 88 parts of the pigment dispersion of Example 31, 7 parts of an acrylic resin (manufactured by BASF Japan Ltd., product name: JONCRYL PDX-7600), 0.3 parts of an acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., product name: DYNOL 604), 0.2 parts of a preservative (manufactured by Lonza Japan Ltd., product name: PROXEL XL-2(S)), and 4.5 parts of water.

[0277] Making a marking pen The above-mentioned ink composition was filled into an ink reservoir having a resin-processed pen body (bullet-shaped) made of polyester fiber at the tip and a spherical metal agitator built in, and the ink composition was allowed to soak into the pen body, and a cap was attached to prepare a marking pen.

[0278] Using the above marking pen, marking was performed on A4 size black paper (manufactured by Nagatoya Shoten Co., Ltd., product name: Color Paper A4 Medium Weight (thickness: 0.09 mm, density: 80 g / m)) at room temperature (20°C). 2 When handwritten on the ink, clear white handwriting was formed without any writing defects such as smearing or skipped lines. Furthermore, this handwriting concealed the written surface, resulting in good handwriting with excellent concealing properties.

[0279] Example 33 An ink composition was prepared by mixing 80 parts of the pigment dispersion of Example 31, 2 parts of a red dye (manufactured by Hodogaya Chemical Co., Ltd., product name: Phloxine), 1 part of a phosphate ester surfactant (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Plysurf AL), 1.5 parts of a resin emulsion (manufactured by Dow Chemical Japan Co., Ltd., product name: Primal ASE-60), 10 parts of diethylene glycol, 4 parts of glycerin, 1 part of a pH adjuster (triethanolamine), and 0.5 parts of carbolic acid.

[0280] Making a ballpoint pen The ink composition was filled by suction into an ink reservoir made of a polypropylene pipe, and then connected to a ballpoint pen tip having a 0.7 mm diameter carbide ball at its tip via a resin holder. Next, a viscoelastic ink backflow preventive material (liquid stopper) mainly composed of polybutene was filled into the rear end of the ink reservoir, and a tail plug was fitted to the rear of the pipe. The ink was then degassed by centrifugation to obtain a ballpoint pen refill.

[0281] Next, the refill was incorporated into the barrel, and a cap was attached to prepare a ballpoint pen (cap-type ballpoint pen).

[0282] Using the above ballpoint pen, a mark was written on A4 size black paper (manufactured by Nagatoya Shoten Co., Ltd., product name: Color Paper A4 Medium Weight (thickness: 0.09 mm, density: 80 g / m)) at room temperature (20°C). 2 When handwritten on the ink, a clear, pastel-colored red handwriting was formed without any writing defects such as smearing or skipped lines. Furthermore, the handwriting concealed the written surface, resulting in a good handwriting with excellent concealing properties.

Claims

1. An ink composition for a writing instrument comprising at least a pigment containing a uric acid pigment and a solvent.

2. 2. The ink composition for a writing instrument according to claim 1, further comprising a dispersant.

3. The ink composition for a writing instrument according to claim 2 , wherein the dispersant comprises a polymeric dispersant.

4. 3. The ink composition for a writing instrument according to claim 1, wherein the average particle size of the uric acid pigment is 0.05 μm or more and 1 μm or less.

5. 3. The ink composition for a writing instrument according to claim 1, wherein the content of the uric acid pigment relative to the total mass of the ink composition is 1% by mass or more and 50% by mass or less.

6. 3. The ink composition for a writing instrument according to claim 1 or claim 2, further comprising a colorant.

7. A writing instrument containing the ink composition for a writing instrument according to claim 1 or 2.

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