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

Abstract

The present invention relates to an ink composition for a writing instrument, comprising at least a pigment comprising a uric acid pigment and a solvent.

Description

Technical Field

[0001] This invention relates to an ink composition for writing instruments and a writing instrument comprising an ink composition for writing instruments. More specifically, it relates to an ink composition for writing instruments that exhibits excellent pigment dispersion stability and is capable of forming clear, subtle handwriting, and a writing instrument comprising an ink composition for writing instruments. Background Technology

[0002] In the past, writing instrument ink compositions using white pigments such as titanium dioxide have been known to produce inks with concealed writing quality. Furthermore, writing instrument ink compositions that can form pastel-toned writing by mixing with other colorants are also preferred among such ink compositions with high concealed quality.

[0003] However, since titanium dioxide is a pigment with a high specific gravity, it presents the following problems: the pigment tends to settle over time, and if lumps form, redispersibility becomes difficult. Furthermore, for writing instruments using ink compositions containing titanium dioxide, the ink density tends to decrease when stored with the writing tip facing upwards, and ink flowability tends to decrease when stored with the writing tip facing downwards. Therefore, research has been conducted on using thickeners to increase the ink viscosity and suppress titanium dioxide settling. However, writing instruments that can utilize such high-viscosity ink compositions are limited. Additionally, in ink compositions combining titanium dioxide with other colorants, color separation occurs in the ink due to the difference in specific gravity between titanium dioxide and the colorant. Therefore, research has been conducted on suppressing titanium dioxide settling and inhibiting the formation of lumps (see, for example, Patent Documents 1-4).

[0004] Patent document 1 discloses an aqueous pigment composition containing titanium dioxide, aluminum silicate pigments, and a specific resin.

[0005] In addition, Patent Document 2 discloses an aqueous ink composition comprising at least titanium dioxide, succinopolysaccharide, and water.

[0006] In addition, Patent Document 3 discloses a water-based ink for ballpoint pens, which contains titanium dioxide and oleic acid.

[0007] In addition, Patent Document 4 discloses a writing instrument containing water-based pigment ink, which contains titanium dioxide, colored pigment, silica powder and / or aluminosilicate, water-soluble resin, specific dispersant, surfactant, and water.

[0008] In the above-mentioned composition (ink composition), although the sedimentation rate of titanium oxide can be reduced by using specific compounds, titanium oxide settles over time and forms hard lumps, or it is prone to color separation in the ink, making it difficult to disperse titanium oxide stably in the ink composition.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 59-217776

[0012] Patent Document 2: Japanese Patent Application Publication No. 8-113752

[0013] Patent Document 3: Japanese Patent Application Publication No. 10-251588

[0014] Patent Document 4: Japanese Patent Application Publication No. 11-217532 Summary of the Invention

[0015] The problem that the invention aims to solve

[0016] The present invention aims to provide an ink composition for writing instruments and a writing instrument comprising an ink composition for writing instruments, wherein the ink composition has excellent dispersion stability of pigments and can be easily redispersed, and can form clear handwriting with good concealment.

[0017] Methods for solving problems

[0018] The key point of this invention is that it comprises a writing instrument ink composition containing at least a pigment containing uric acid pigment and a solvent.

[0019] Furthermore, a key feature of the aforementioned ink composition for writing instruments is that it further comprises a dispersant, which includes a polymeric dispersant. Another key feature is that the average particle size of the uric acid pigment is 0.05 μm to 1 μm, and the content of the uric acid pigment relative to the total mass of the ink composition is 1% to 50% by mass. Furthermore, a key feature of the aforementioned ink composition for writing instruments is that it further comprises a colorant.

[0020] A further key point is that the writing instrument is made by containing the ink composition of the aforementioned writing instrument.

[0021] The effects of the invention

[0022] This invention relates to an ink composition for writing instruments using pigments containing uric acid pigments, which exhibit excellent pigment dispersion stability. Consequently, it is possible to provide an ink composition for writing instruments and a writing instrument containing the ink composition for writing instruments, where the pigment does not form hard clumps even if it settles over time, thus allowing for easy redispersibility and the formation of clear, subtle handwriting. Detailed Implementation

[0023] The ink composition for writing instruments of the present invention (hereinafter sometimes referred to as "ink composition" or "ink") comprises at least a pigment containing uric acid pigment and a solvent. The components constituting the ink composition of the present invention are described below.

[0024] The ink composition of the present invention contains uric acid pigment. Uric acid pigment is a pigment containing uric acid. Uric acid is a component produced in the human body through metabolism. Therefore, uric acid is a biologically derived organic compound, and the compound itself has high safety.

[0025] Uric acid pigment exists in a dispersed state in ink compositions. Due to its high refractive index, uric acid is white, providing an indistinct effect on handwriting. Titanium oxide, commonly used as a white pigment, is dense and tends to settle in ink compositions, easily forming lumps and thus difficult to redisperse. In contrast, uric acid pigment is less dense than titanium oxide, therefore it does not easily settle in ink compositions, and even if it does settle over time, it does not form lumps. Therefore, uric acid pigment can be easily redispersed.

[0026] Therefore, in the ink composition of the present invention, by using a pigment containing uric acid pigment, the pigment exhibits excellent dispersion stability, and even if the pigment settles over time, it does not form hard lumps and is easily redispersed. Thus, the ink composition of the present invention can form clear, concealed writing at a uniform concentration. Furthermore, even when containing the colorant described later, the ink composition of the present invention can suppress the separation of the uric acid pigment and the colorant in the ink composition. Therefore, the ink composition of the present invention can form concealed, colored writing at a uniform concentration.

[0027] The content of uric acid pigment relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 1% to 50% by mass, more preferably 5% to 30% by mass. If the content of uric acid pigment is higher than 50% by mass, the ink dispensing stability of the writing instrument containing the ink composition is easily reduced, and writing defects such as smudges and streaks are easily produced. On the other hand, when the content is less than 1% by mass, it is difficult to obtain a suitable penmanship concentration for a writing instrument, and the concealment of the penmanship is easily compromised.

[0028] There are no particular limitations on uric acid pigments, as long as they can be dispersed in the ink composition. For example, uric acid pigments can be manufactured by mechanically pulverizing crystalline uric acid into granules using various dispersers such as jet mills, ultrafine mills, and bead mills. Alternatively, pigments that are colored by uric acid pigments themselves can also be used.

[0029] 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 in the range of 0.1 μm to 0.5 μm. By keeping the average particle size within the above range, the dispersion stability of the uric acid pigment in the ink composition can be improved.

[0030] It should be noted that the average particle size is a volume-based average particle size value measured using a dynamic light scattering particle size distribution measuring device [manufactured by Microtrac BEL Co., Ltd., product name: NANOTRAC FLEX].

[0031] A dispersant can be further incorporated into the ink composition of the present invention. For example, when the solvent of the present invention is water, the dispersant can be adsorbed onto the surface of the uric acid pigment, thus separating the uric acid pigment from each other and maintaining a certain distance between them to prevent aggregation, thereby improving the dispersion stability of the uric acid pigment in the ink. In addition, even if the uric acid pigment aggregates to form aggregates, low-density aggregates will be formed, thus suppressing the hardening of the uric acid pigment after sedimentation.

[0032] Examples of dispersants include surfactants, polymeric dispersants, and inorganic compounds.

[0033] Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants.

[0034] Specifically, regarding surfactants used as dispersants, examples include polyoxyalkylene alkylamines represented by the following general formula (1) [in general formula (1), the sum of m and n (m+n) is 29 or less].

[0035] [Chemistry 1]

[0036]

[0037] In general formula (1), R1, R2, m and n are shown below.

[0038] R1: Alkyl or alkenyl groups with 10 to 20 carbon atoms

[0039] R2: Alkylene with 2 or 3 carbon atoms

[0040] m+n: a number greater than 1 and less than 29

[0041] Examples of R1 include octyl, lauryl, myristyl, palmityl, stearyl, eicosyl, palmitoleyl, oleyl, transoleyl, coconut oil alkyl, tallow alkyl, etc., with lauryl and stearyl being preferred. Examples of R2 include ethylene or propylene, with ethylene being preferred. m+n is preferably a number of 1 to 15, more preferably a number of 2 to 10.

[0042] There is no limitation on the commercially available surfactant represented by the above general formula (1) used in this invention. Examples include Blanon L-205 [manufactured by Aoki Yushi Kogyo Co., Ltd., m+n=5 in general formula (1)], Blanon S-202 [manufactured by Aoki Yushi Kogyo Co., Ltd., m+n=2 in general formula (1)], Blanon S-207 [manufactured by Aoki Yushi Kogyo Co., Ltd., m+n=7 in general formula (1)], Blanon S-210 [manufactured by Aoki Yushi Kogyo Co., Ltd., m+n=10 in general formula (1)], Blanon S-215 [manufactured by Aoki Yushi Kogyo Co., Ltd., m+n=15 in general formula (1)], and Viscofine E2C [manufactured by Kawaken Fine Chemical Co., Ltd., m+n=2 in general formula (1)].

[0043] Furthermore, regarding surfactants used as dispersants, examples include surfactants having -CO-NH- or -CO-N(CH3)- as linking groups. Specifically, examples include surfactants represented by the following general formula (2), the following general formula (3), or the following general formula (4).

[0044] [Chemistry 2]

[0045]

[0046] In general formulas (2), (3) and (4), R1, R2, R3, R4 and n are respectively shown below.

[0047] R1: Alkyl group with 9 to 19 carbon atoms

[0048] R2: Hydrogen atom or serine amino acid residue

[0049] R3: COOX (X is a hydrogen atom, sodium atom, or potassium atom)

[0050] R4: Alkyl group with 1 to 3 carbon atoms

[0051] n: an integer between 1 and 3

[0052] Examples of R1 include nonyl, undecyl, tridecyl, pentadecyl, heptadecanyl, nonadecanyl, coconut oil fatty acid residues, and tallow fatty acid residues, with undecyl or coconut oil fatty acid residues being preferred. Examples of R4 include methyl, ethyl, and n-propyl, with both R4s preferably being methyl.

[0053] It should be noted that when R2 is a serine amino acid residue, X is preferably a potassium atom.

[0054] It should be noted that when X is a hydrogen atom (H), R3 can be a salt obtained by neutralization with triethanolamine.

[0055] Commercially available surfactants represented by the above-described general formulas (2), (3), or (4) used in this invention are not limited to any particular type. Examples of surfactants used as dispersants include Kawasilk S (manufactured by Kawaken Fine Chemical Co., Ltd.), Soypon SLTA (manufactured by Kawaken Fine Chemical Co., Ltd.), Soypon M-30 (manufactured by Kawaken Fine Chemical Co., Ltd.), Alanon ALTA (manufactured by Kawaken Fine Chemical Co., Ltd.), Softazoline LAO (manufactured by Kawaken Fine Chemical Co., Ltd.), Sarcosinate PN (manufactured by Kawaken Fine Chemical Co., Ltd.), and Sarcosinate CN-30 (manufactured by Nikkol Chemicals Co., Ltd.).

[0056] In addition, examples of surfactants used as dispersants include polyoxyethylene ethynyl glycol, phytosterols, and amine salts of anionic surfactants. Commercially available examples of these surfactants include Acetylenol E40 (manufactured by Kawaken Fine Chemical Co., Ltd.), Acetylenol E60 (manufactured by Kawaken Fine Chemical Co., Ltd.), Acetylenol E100 (manufactured by Kawaken Fine Chemical Co., Ltd.), NIKKOL BPS-10 (manufactured by Nikkol Chemicals Co., Ltd.), NIKKOL BPS-20 (manufactured by Nikkol Chemicals Co., Ltd.), and Disparlon AQ-360 (manufactured by Kusunoki Chemical Co., Ltd.).

[0057] Examples of polymeric dispersants used as dispersants include polyvinylpyrrolidone, polyvinyl butyral, polyvinyl ether, styrene-maleic acid copolymer, ketone resin, hydroxyethyl cellulose and its derivatives, synthetic resins such as styrene-acrylic acid copolymer, acrylic polymers, PO·EO adducts, and amine oligomers of polyesters.

[0058] Specifically, regarding polymeric dispersants used as dispersants, examples include polymeric dispersants with at least one of an acid value and an amine value greater than 0 mg KOH / g. Among these, polymeric dispersants with an amine value greater than 0 mg KOH / g, or polymeric dispersants with both an acid value and an amine value greater than 0 mg KOH / g, are preferred.

[0059] The amine value represents the mass (mg) of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize 1g of solid component. The amine value can be determined by the method described in JIS K7237:1995.

[0060] In addition, acid value indicates the mass (mg) of potassium hydroxide required to neutralize 1g of solid component. Acid value can be determined by the method described in JIS K 0070:1992.

[0061] As a polymeric dispersant with an acid value greater than 0 mg KOH / g, it is preferable to use a polymeric dispersant with an acid value less than 10 mg KOH / g, and even more preferably, a polymeric dispersant with an acid value of 5 mg KOH / g or less. Commercially available polymeric dispersants that meet these conditions include, for example, DISPER BYK-199 [manufactured by BYK Chemical Co., Ltd. (Japan)] and BYK-2060 [manufactured by BYK Chemical Co., Ltd. (Japan)].

[0062] As a polymeric dispersant with an amine value greater than 0 mg KOH / g, it is preferable to use a polymeric dispersant with an amine value of 5 mg KOH / g or more and 50 mg KOH / g or less, and even more preferably a polymeric dispersant with an amine value of 15 mg KOH / g or more and 40 mg KOH / g or less. Commercially available polymeric dispersants that meet these conditions include, for example, DISPER BYK-184 [manufactured by BYK Chemical Co., Ltd. (Japan)], DISPER BYK-2055 [manufactured by BYK Chemical Co., Ltd. (Japan)], Hinoact NB [manufactured by Kawaken Fine Chemical Co., Ltd.], and Solsperse 20000 [manufactured by Lubrizol Corporation, Japan].

[0063] As a polymeric dispersant with an acid value and amine value greater than 0 mg KOH / g, it is preferable to use a polymeric dispersant with an acid value of 5 mg KOH / g or more and 50 mg KOH / g or less, and an amine value of 10 mg KOH / g or more and 45 mg KOH / g or less. Furthermore, it is more preferable to use a polymeric dispersant with an acid value of 5 mg KOH / g or more and 50 mg KOH / g or less, an amine value of 10 mg KOH / g or more and 45 mg KOH / g or less, and an acid value greater than the amine value, i.e., an acid value / amine value ratio greater than 1. Commercially available examples of such polymeric dispersants include DISPER BYK-191 (manufactured by BYK Chemicals (Japan) Co., Ltd.), DISPER BYK-2010 (manufactured by BYK Chemicals (Japan) Co., Ltd.), DISPER BYK-2013 (manufactured by BYK Chemicals (Japan) Co., Ltd.), ANTI TERRA-250 (manufactured by BYK Chemicals (Japan) Co., Ltd.), Disparlon AQ-380 (manufactured by Kusumoto Chemical Co., Ltd.), and Flowlen G-700AMP (manufactured by Kyoei Chemicals Co., Ltd.).

[0064] In addition, oligomers containing fluorine groups can be cited as examples of polymeric dispersants. Commercially available examples of such polymeric dispersants include MEGAFACE F-477 [manufactured by DIC Corporation], MEGAFACE F-553 [manufactured by DIC Corporation], and MEGAFACE F-554 [manufactured by DIC Corporation].

[0065] In addition, inorganic compounds used as dispersants include, for example, pyrophosphate and hexametaphosphate.

[0066] When the ink composition of 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 in the range of 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 maintained more stably.

[0067] The ink composition of the present invention comprises a solvent. Examples of solvents include water and organic solvents.

[0068] There are no particular restrictions on what constitutes water; examples include tap water, ion-exchanged water, ultrafiltered water, and distilled water.

[0069] There are no particular limitations on organic solvents, for example, glycol ether solvents, glycol solvents, alcohol solvents, ketone solvents, ester solvents, hydrocarbon solvents, etc.

[0070] 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.

[0071] Examples of diol-based solvents include diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butanediol, and ethylene glycol.

[0072] Examples of alcohol 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.

[0073] Examples of ketone solvents include acetone, dimethyl ketone, diethyl ketone, methyl ethyl ketone, and methyl isobutyl ketone.

[0074] Examples of ester-based 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.

[0075] Examples of hydrocarbon solvents include n-hexane, n-heptane, n-octane, isooctane, cyclohexane, methylcyclohexane, ethylcyclohexane, toluene, xylene, ethylbenzene, etc.

[0076] Solvents may be used in combination or one or more.

[0077] The content of solvent relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 10% to 90% by mass, more preferably 30% to 80% by mass.

[0078] Colorants can be further mixed into the ink composition of the present invention. By combining uric acid pigments with colorants, it is possible to produce ink compositions that exhibit a concealing colored (pastel-toned) appearance.

[0079] As a coloring agent, there are no particular limitations on any dye or pigment that can be dissolved or dispersed in a solvent.

[0080] Examples of dyes include acid dyes, basic dyes, direct dyes, oil-soluble dyes, and disperse dyes.

[0081] As acid dyes, examples include neocarmine (CI16255), tartrazine (CI19140), acid blue black 10B (CI20470), guinea green (CI42085), brilliant blue FCF (CI42090), acid violet 6B (CI42640), soluble blue (CI42755), naphthalene green (CI44025), eosin (CI45380), flame red (CI45410), erythrosine (CI45430), aniline black (CI50420), and acid flavin (CI56205).

[0082] As basic dyes, examples include Basic Orange (CI11270), Methyl Violet FN (CI42535), Crystal Violet (CI42555), Malachite Green (CI42000), Victoria Blue FB (CI44045), Rhodamine B (CI45170), Acridine Orange NS (CI46005), and Methylene Blue B (CI52015).

[0083] As direct dyes, examples include Congo Red (CI22120), Direct Sky Blue 5B (CI24400), Violet BB (CI27905), Direct Deep Black EX (CI30235), Direct Fast Black G Concentrate (KayarusBlack GConc) (CI35225), Direct Fast Black G (CI35255), and Phthalocyanine Blue (CI74180).

[0084] 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.

[0085] 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, CI Disperse Violet 57, etc.

[0086] As pigments, examples include inorganic pigments, organic pigments, luminescent pigments, fluorescent pigments, and phosphorescent pigments.

[0087] Examples of inorganic pigments include carbon black, iron black, iron oxide yellow, iron oxide red, and ultramarine.

[0088] Examples of organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, violet ketone pigments, isoindolineone pigments, isoindoline pigments, dioxazine pigments, indigo pigments, anthraquinone pigments, quinoline ketone pigments, diketopyrrolopyrrole pigments, vat pigments, indigo pigments, phthaloline ketone pigments, methylene-azomethyl base pigments, and metal complex pigments.

[0089] Alternatively, water-dispersible pigments can be used, which are prepared by pre-dispersing pigments in an aqueous medium using surfactants or resins in a fine and stable manner.

[0090] Specifically, examples of water-dispersible pigments include CI Pigment Blue 15:3B [manufactured by Sanyo Pigment Co., Ltd., product name: Sandye Super Blue GLL-E (solid content: 24%)], CI Pigment Red 146 [manufactured by Sanyo Pigment Co., Ltd., product name: Sandye Super Pink FBL (solid content: 21.5%)], CI Pigment Yellow 81 [manufactured by Dainippon Seika Co., Ltd., product name: TC Yellow FG (solid content: approx. 30%)], and CI Pigment Red 220 / 166 [manufactured by Dainippon Seika Co., Ltd., product name: TC Red FG (solid content: approx. 35%)].

[0091] It should be noted that examples of resins used to disperse 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 resins, maleic acid resins, gum arabic, cellulose, dextran, casein, and their derivatives, as well as copolymers of the above resins.

[0092] Examples of luminescent pigments include metallic pigments formed by coating the surface of core materials such as glass sheets with gold, silver, etc.; natural mica; synthetic mica; pearlescent pigments formed by coating the surface of core materials such as flake alumina with metal oxides such as titanium oxide; cholesteric liquid crystal pigments; metallic powder pigments; metallic pigments obtained by peeling off metal vapor-deposited films such as aluminum formed on substrates such as films; and metallic pigments formed by forming metal vapor-deposited films such as aluminum on colorless transparent or colored transparent films and then processing them into powder.

[0093] As a metallic luster pigment formed by coating the surface of core materials such as glass sheets with gold, silver, etc., examples include products manufactured by Nippon Sheet Glass Co., Ltd. such as Metashine 5480PS, Metashine 5230PS, Metashine 5150PS, Metashine 5090PS, Metashine 2080PS, Metashine 1030PS, Metashine2025PS, Metashine 1030GP, and Metashine 2080GP.

[0094] Pearlescent pigments, which are made by coating the surface of natural mica with titanium dioxide, include, specifically, products manufactured by Merck Co., Ltd., such as Iriodin 100, Iriodin 111, Iriodin 120, Iriodin 153, Iriodin 201, Iriodin 211, Iriodin 223, Iriodin 231, Iriodin 302, Iriodin 323, Iriodin 520, Iriodin 522, and Iriodin 524.

[0095] In addition, as pearlescent pigments made by coating the surface of synthetic mica with titanium dioxide, examples include the following products manufactured by Nippon Koken Kogyo Co., Ltd.: Twincle Pearl SXB, Twincle Pearl YXB, Twincle Pearl RXB, Twincle Pearl BXB, Twincle Pearl SXD, Twincle Pearl YXD, Twincle Pearl RXD, Twincle Pearl BXD, Twincle Pearl SX, Twincle Pearl YX, Twincle Pearl RX, Twincle Pearl BX; and the following products manufactured by Nippon Koken Kogyo Co., Ltd.: Ultimica SB-100, Ultimica SD-100, Ultimica SE-100, Ultimica SF-100, Ultimica SH-100, Ultimica YB-100, Ultimica YE-100, Ultimica YF-100, etc.

[0096] In addition, as pearlescent pigments made by coating the surface of thin-film alumina with titanium dioxide, examples include products manufactured by Merck Co., Ltd., such as Xirallic T60-10 WNT Crystal Silver, Xirallic T60-20 WNT Sunbeam Gold, Xirallic T60-21 WNT Solaris Red, Xirallic T60-23 WNT Galaxy Blue, Xirallic T60-24 WNT Stellar Green, and Xirallic T60-25 WNT Cosmic Turquoise.

[0097] As cholesteric liquid crystal pigments, examples include Helicone HC Sapphire, Helicone HC Scarabeus, Helicone HC Jade, and Helicone HC Maple manufactured by Wacker Chemie.

[0098] Examples of metallic pigments include aluminum powder, brass powder, stainless steel powder, bronze powder, and other metallic pigments with a metallic luster, as well as metallic pigments made by adsorbing colorants such as dyes or pigments onto these metallic pigments. Alternatively, the aforementioned metallic pigments can be pre-processed using surfactants, resins, solvents, etc., to disperse them, thus creating paste-like or liquid metallic pigment dispersions.

[0099] As fluorescent pigments, examples include synthetic resin microparticle fluorescent pigments formed by solidifying various fluorescent dyes in a resin matrix.

[0100] As a phosphorescent pigment, any pigment that can absorb and store light from the sun or electric lamps and slowly release it in the dark to emit light (this is called residual light) can be used. Examples of phosphorescent pigments include CaS / Bi series, CaSrS / Bi series, ZnS / Cu series, ZnCdS / Cu series, and SrAl2O4 / rare earth metal series.

[0101] The above-mentioned colorants may be used in combination, either one or more.

[0102] When the ink composition of 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 content of the colorant is higher than 50% by mass, the ink dispensing stability of the writing instrument containing the ink composition is easily reduced, and writing defects such as smudges and streaks are easily produced. On the other hand, if the content is less than 0.01% by mass, it is difficult to obtain a suitable pen ink concentration for a writing instrument.

[0103] In addition, when using the above-mentioned pigments as colorants, pigment dispersants 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.

[0104] The aforementioned dyes or pigments are effective even when used directly, but microencapsulated pigments or resin particles containing dyes or pigments can also be used as colorants suitable for this invention. In particular, by encapsulating dyes or pigments in microcapsules, they can be isolated from and protected from the external environment, improving the water resistance and lightfastness of the encapsulated material.

[0105] As microcapsule pigments containing dyes or pigments, examples include microcapsule pigments containing colorants formed by dispersing or dissolving dyes or pigments in an oily medium.

[0106] As pigments, the aforementioned inorganic pigments, organic pigments, luminescent pigments, fluorescent pigments, and phosphorescent pigments can be used; as dyes, the aforementioned oil-soluble dyes and disperse dyes can be used.

[0107] Examples of oily media include monocarboxylic acid esters, dicarboxylic acid monoesters, dicarboxylic acid diesters, polyols (partial to full esters), aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes, higher alcohols, ketones, and ethers.

[0108] The aforementioned oily media can be used in combination, either one or more.

[0109] Microencapsulation of pigments can be achieved through well-known methods such as interfacial polymerization of isocyanate-based materials, in-situ polymerization of melamine-formaldehyde materials, liquid-curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion cooling, air-suspension coating, and spray drying, with the appropriate method selected based on the application. Examples of capsule materials include epoxy resins, urea resins, urethane resins, and isocyanate resins.

[0110] Furthermore, a secondary resin coating can be further applied to the surface of the microcapsules to impart durability or modify the surface properties for practical use, depending on the purpose.

[0111] Examples of resin particles containing dyes include resin particles formed by uniformly dissolving or dispersing the dye in the resin particles, and resin particles formed by dyeing the resin particles with dye.

[0112] As a dye, there are no particular limitations as long as it can dissolve, disperse, or dye the resin that constitutes the resin particles. The above-mentioned acid dyes, basic dyes, direct dyes, oil-soluble dyes, disperse dyes, etc. can be used.

[0113] When the resin particles contain dye, examples of resins constituting the resin particles include polystyrene, acrylic resins, epoxy resins, melamine resins, polyesters, polyvinyl chloride, polybutadiene, benzoguanamine resins, polyamides, urethane resins, polymethyl methacrylate, acrylic-urethane copolymer resins, phenolic resins, polyethylene, polypropylene, polyacrylonitrile, polyacetal, ethylene-propylene copolymer resins, ethylene-vinyl acetate copolymer resins, styrene-acrylic acid copolymer resins, styrene-butadiene copolymer resins, styrene-acrylonitrile copolymer resins, and acrylonitrile-butadiene copolymer resins, among which thermosetting resins are preferred.

[0114] Compared with thermoplastic resins, thermosetting resins have superior solvent resistance and heat resistance, and the dyes they contain also have excellent migration resistance, which can inhibit the dissolution of dyes from the resin, making them suitable.

[0115] Examples of thermosetting resins include epoxy resins, epoxy acrylate resins, xylene resins, toluene resins, guanidine resins, benzoguanidine resins, melamine resins, urethane resins, phenolic resins, alkyd resins, polyamides, polyimides, polyamide esters, urea resins, silicone resins, and unsaturated polyesters. Among these, guanidine resins or melamine resins are preferred for further suppressing dye leaching.

[0116] Examples of resin particles containing pigments include resin particles in which the pigment is uniformly dispersed in the resin particles, and resin particles in which the surface of the resin particles is coated with pigment.

[0117] As a pigment, there are no particular limitations as long as it can be dispersed in or adsorbed onto the resin constituting the resin particles; the aforementioned inorganic pigments, organic pigments, luminescent pigments, fluorescent pigments, phosphorescent pigments, etc., can be used. It should be noted that, for the purpose of improving the dispersibility or adsorption to the resin constituting the resin particles, the aforementioned pigments can be surface-treated using various methods known in the art.

[0118] The same substance as the resin used to form the resin particles can be used as described above for forming the dye-containing resin particles.

[0119] The aforementioned resin particles can be manufactured by pulverization, spray drying, or polymerization in an aqueous or oil-based medium in the presence of dyes or pigments. Examples of polymerization methods include suspension polymerization, suspension condensation polymerization, dispersion polymerization, and emulsion polymerization.

[0120] Furthermore, there are no particular limitations on the shape of the resin particles. Spherical, polygonal, or flat resin particles, such as perfectly spherical, ellipsoidal, or approximately spherical, can be used. Spherical resin particles are preferred.

[0121] As a colorant, when the ink contains microcapsule pigments or resin particles encapsulated with dyes or pigments, 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% to 50% by mass, more preferably 0.1% to 30% by mass. If the content of the colorant is higher than 50% by mass, the ink flowability of the writing instrument containing the ink composition is easily reduced, and writing defects such as smudges and streaks are easily produced. On the other hand, if the content is less than 0.01% by mass, it is difficult to obtain a suitable pen ink density for a writing instrument.

[0122] In addition, functional materials such as thermochromic materials or photochromic materials can also be used as colorants.

[0123] Examples of thermochromic materials include: (a) electron-donating chromogenic organic compounds; (b) electron-accepting compounds; and (c) reversible thermochromic compositions formed by a reaction medium that determines the temperature at which the chromogenic reaction of the components (a) and (b) occurs.

[0124] As a reversible thermochromic composition, a heat-decolorizing type reversible thermochromic composition with a relatively small hysteresis width (ΔH) (ΔH = 1-7°C) as described in Japanese Patent Publication Nos. 51-44706, 51-44707, and 1-29398 can be used. Heat-decolorizing type refers to a composition that decolorizes upon heating and develops color upon cooling. This reversible thermochromic composition changes color around a predetermined temperature, specifically the color change point. It exhibits a decolorized state in the temperature range above the high-temperature side color change point and a colored state in the temperature range below the low-temperature side color change point. Furthermore, this reversible thermochromic composition exists in only one of these two states in the room temperature range. Moreover, the other state of this reversible thermochromic composition is maintained during the application of heat or cold required to exhibit that state, and returns to the state exhibited in the room temperature range if heat or cold is not applied.

[0125] In addition, reversible thermochromic compositions exhibiting a large hysteresis width (ΔH = 8–50°C) that are heat-induced decolorizing can be used, as described in Japanese Patent Application Publications Nos. 4-17154, 7-179777, 7-33997, and 8-39936. Furthermore, reversible thermochromic compositions exhibiting a large hysteresis characteristic that are heat-induced decolorizing can be used, as described in Japanese Patent Application Publications Nos. 2006-137886, 2006-188660, 2008-45062, and 2008-280523. In these reversible thermochromic compositions, the shape of the curve obtained by plotting the change in color concentration caused by temperature changes shows significantly different color change paths when the temperature rises from a lower temperature range compared to the color change temperature region, and conversely, when it falls from a higher temperature range compared to the color change temperature region. Furthermore, in these reversible thermochromic compositions, the color state in the temperature region below the complete color development temperature t1, or the color-decolorizing state in the high-temperature region above the complete color-decolorizing temperature t4, exhibits color memory within a specific temperature region. This specific temperature region refers to the temperature range between the color development onset temperature t2 and the color-decolorizing onset temperature t3, i.e., the substantial two-phase retention temperature region.

[0126] It should be noted that, when the above-described reversible thermochromic composition with color memory is applied in this invention, specifically, the complete color development temperature t1 is limited to a temperature obtainable only in a freezer, cold place, etc., and the complete color decolorization temperature t4 is limited to a range of temperatures obtainable from frictional heat based on a friction body, a nearby heating body such as a hair dryer, etc. Furthermore, by limiting the ΔH value to 40°C to 100°C, the function of maintaining the color presented under normal conditions (daily life temperature range) can be effectively achieved.

[0127] Temperatures obtainable only in freezers, cold environments, etc., are -50°C to 0°C, preferably -40°C to -5°C, and more preferably -30°C to -10°C. Temperatures obtained from heating elements such as hair dryers are 50°C to 95°C, preferably 50°C to 90°C, and more preferably 60°C to 80°C.

[0128] Alternatively, as a reversible thermochromic composition, a heat-developing type reversible thermochromic composition using gallic acid esters, as described in Japanese Patent Publication No. 51-44706 and Japanese Patent Application Publication No. 2003-253149, may also be used. Heat-developing type refers to a composition that develops color upon heating and decolorizes upon cooling.

[0129] The reversible thermochromic composition is a mixture of components (a), (b), and (c) as essential components, and the proportions of each component are affected by concentration, color-changing temperature, color-changing morphology, and type of each component. Generally, the component ratios for obtaining the desired properties are, relative to component (a) being 1, component (b) being 0.1 to 100 parts, preferably 0.1 to 50 parts, more preferably 0.5 to 20 parts, and component (c) being 1 to 800 parts, preferably 5 to 200 parts, more preferably 10 to 100 parts. It should be noted that all these proportions are parts by mass.

[0130] As photochromic materials, examples include known photochromic compounds such as spiroxazine derivatives, spiropyran derivatives, and naphthopyran derivatives, which show color when exposed to sunlight, ultraviolet light, or blue light with a peak emission wavelength in the range of 400-495 nm, and decolorize when the irradiation is stopped.

[0131] Examples of spirooxazine derivatives include, for example, existing well-known indoline spirobenzoxazine compounds, indoline spironaphthazine compounds, indoline spirophenanthrenexazine compounds, and indoline spiroquinolinexazine compounds.

[0132] In addition, examples of photochromic compounds with light memory (color memory photochromic properties) include, for example, well-known ursolic anhydride derivatives and diarylethylene derivatives.

[0133] Alternatively, as a photochromic material, a reversible photochromic composition prepared by dissolving the aforementioned photochromic compound in various oligomers can also be used.

[0134] Examples of oligomers include styrene-based oligomers, acrylic-based oligomers, terpene-based oligomers, and terpene-phenol-based oligomers.

[0135] Examples of styrene-based oligomers include low molecular weight polystyrene, styrene-α-methylstyrene copolymers, α-methylstyrene polymers, and copolymers of α-methylstyrene and vinyltoluene.

[0136] Examples of acrylic oligomers include, for example, acrylate copolymers.

[0137] Examples of terpene oligomers include α-pinene polymers, β-pinene polymers, and d-limonene polymers.

[0138] Examples of terpene phenolic oligomers include, for example, α-pinene-phenol copolymers.

[0139] By dissolving photochromic compounds in various oligomers, the lightfastness of the photochromic compounds can be improved, and the color development concentration can be increased, thereby adjusting the color change sensitivity.

[0140] In addition, one or more of the above-mentioned oligomers may be used.

[0141] The above-mentioned reversible thermochromic composition or reversible photochromic composition is effective when used directly, or it can be encapsulated in microcapsules to form reversible thermochromic microcapsule pigments or reversible photochromic microcapsule pigments, or dispersed in thermoplastic resins or thermosetting resins to form reversible thermochromic resin particles or reversible photochromic resin particles, and used as colorants in this invention.

[0142] It should be noted that, in the following text, reversible thermochromic microcapsule pigments and reversible photochromic microcapsule pigments are sometimes referred to as "microcapsule pigments", and reversible thermochromic resin particles and reversible photochromic resin particles are sometimes referred to as "resin particles".

[0143] Reversible thermochromic compositions or reversible photochromic compositions are preferably encapsulated in microcapsules to form reversible thermochromic microcapsule pigments or reversible photochromic microcapsule pigments. This is because encapsulation in microcapsules allows for the formation of chemically and physically stable pigments. Consequently, under various usage conditions, the reversible thermochromic composition or reversible photochromic composition can maintain the same composition and exert the same effects.

[0144] Microencapsulation can be achieved through various methods, including isocyanate-based interfacial polymerization, melamine-formaldehyde in-situ polymerization, liquid-based curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion cooling, air-suspension coating, and spray drying, among others, with the appropriate method chosen depending on the application. Examples of capsule materials include epoxy resin, urea resin, urethane resin, and isocyanate resin.

[0145] Furthermore, a secondary resin coating can be further applied to the surface of the microcapsules to impart durability or modify the surface properties for practical use, depending on the purpose.

[0146] In the aforementioned microcapsule pigments, the mass ratio of the encapsulated material to the wall film is preferably 7:1 to 1:1. By keeping the mass ratio of the encapsulated material to the wall film within this range, it is possible to prevent a decrease in color concentration and clarity during color development. More preferably, the mass ratio of the encapsulated material to the wall film is 6:1 to 1:1.

[0147] Alternatively, color-changing behavior from colored (1) to colored (2) can be achieved by mixing common dyes or pigments with microcapsule pigments.

[0148] Examples of reversible thermochromic resin particles or reversible photochromic resin particles include resin particles formed by uniformly dispersing the aforementioned reversible thermochromic composition or reversible photochromic composition in resin particles.

[0149] There are no particular limitations on the type of resin that constitutes the resin particles, as long as it is a thermoplastic resin or a thermosetting resin.

[0150] Examples of thermoplastic resins include polystyrene, acrylic resins, polyesters, polyvinyl chloride, polybutadiene, polymethyl methacrylate, acrylate-urethane copolymers, polyethylene, polypropylene, polyacrylonitrile, polyacetal, ethylene-propylene copolymers, ethylene-vinyl acetate copolymers, styrene-acrylic acid copolymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, and acrylonitrile-butadiene copolymers.

[0151] Examples of thermosetting resins include epoxy resins, epoxy acrylate resins, xylene resins, toluene resins, guanidine resins, benzoguanidine resins, melamine resins, urethane resins, phenolic resins, alkyd resins, polyamides, polyimides, polyamide esters, urea resins, silicone resins, and unsaturated polyesters.

[0152] The aforementioned resin particles can be manufactured by pulverization, spray drying, or polymerization in an aqueous or oily medium in the presence of a reversible thermochromic composition or a reversible photochromic composition. Examples of polymerization methods include suspension polymerization, suspension condensation polymerization, dispersion polymerization, and emulsion polymerization.

[0153] Furthermore, there are no particular limitations on the shape of the resin particles. Spherical, polygonal, or flat resin particles, such as perfectly spherical, ellipsoidal, or approximately spherical, can be used. Spherical resin particles are preferred.

[0154] Alternatively, color-changing behavior from colored (1) to colored (2) can be achieved by mixing common non-color-changing colorants such as dyes or pigments into the resin particles.

[0155] When the colorant comprises the aforementioned reversible thermochromic composition, reversible photochromic composition, microcapsule pigments containing these compositions, or resin particles containing these compositions, 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 5% to 40% by mass, more preferably 10% to 40% by mass, and even more preferably 15% to 35% by mass. If the content of the colorant is greater than 40% by mass, the ink flowability of the writing instrument containing the ink composition decreases, and writing defects such as smudges and streaks are easily produced. On the other hand, when the content is less than 5% by mass, it is difficult to obtain suitable color-changing properties and ink density as a writing instrument, and it is difficult to fully satisfy the color-changing function.

[0156] The average particle size of the reversible thermochromic microcapsule pigments or resin particles, or the reversible photochromic microcapsule pigments 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 aforementioned microcapsule pigments or resin particles exceeds 5 μm, it is difficult to obtain good ink flow properties when used in writing instruments. On the other hand, if the average particle size is less than 0.01 μm, it is difficult to exhibit high concentrations of color development.

[0157] It should be noted that the average particle size is determined using image-analytical particle size distribution measurement software [manufactured by Mountech Co., Ltd., product name: Mac View]. The particle region is identified, and the diameter of the projected area equivalent circle (Heywood diameter) is calculated based on the area of ​​the particle region. The average particle size of particles equivalent to an equal-volume sphere is then determined based on this value, and the obtained value is taken as the average particle size.

[0158] In addition, when the particle size of all or most of the particles is greater than 0.2 μm, the particle size distribution measuring device [manufactured by Beckman Coulter Co., Ltd., product name: Multisizer 4e] can be used to measure the average particle size of particles equivalent to spheres of equal volume using the Coulter method.

[0159] Alternatively, the aforementioned software or a measuring device based on the Coulter method can be used, and based on the measured values, a calibrated laser diffraction / scattering particle size distribution measuring device [manufactured by Horiba Corporation, product name: LA-300] can be used to measure the particle size and average particle size on a volume basis.

[0160] In addition to the essential components described above, optional components may be mixed into the ink composition of the present invention within a range that does not impair the effects of the present invention.

[0161] The ink composition of the present invention may be mixed with a thickener to inhibit pigment aggregation or sedimentation, thereby producing an ink composition with good stability over time.

[0162] As a thickener, conventionally known substances can be used, but substances capable of imparting shear-thinning properties to the ink composition (shear-thinning agents) are preferred.

[0163] Ink compositions using shear-thinning agents exhibit high viscosity and are difficult to flow when at rest or under low stress, but readily decrease in viscosity when external stress is applied. Therefore, they prevent ink leakage, separation, or backflow when not writing, and ensure good stability of ink flow from the pen tip during writing.

[0164] Especially when using such an ink composition in a writing instrument (ballpoint pen) with a ballpoint tip, the ink composition has a high viscosity when at rest without applied shear stress, thus the ink composition remains stably within the ballpoint pen. Therefore, when writing, the rotation of the ball applies a strong shear stress to the ink composition, making it easier for the ink composition near the ball to decrease in viscosity, thus ensuring good ink dispensing stability.

[0165] When the ink composition of 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% by mass to 20% by mass.

[0166] Examples of shear-thinning agents include water-soluble polysaccharides, polymers with a molecular weight of 100,000 to 150,000 with alkyl esters of methacrylic acid as the main component, crosslinked poly-N-vinyl amides, benzyl sorbitol and its derivatives, benzyl xylitol and its derivatives, basic tackifying acrylic resins, crosslinked acrylic polymers, inorganic microparticles, nonionic surfactants with an HLB value of 8 to 12, metal salts of dialkyl sulfonated succinic acid, and amine salts.

[0167] Shear-thinning agents can be used in one or more combinations.

[0168] Examples of water-soluble polysaccharides include xanthan gum, zetashi gum, zetashi gum, zetashi gum, zetashi gum, succinyl polysaccharides with organic acid-modified monosaccharides of glucose and galactose (average molecular weight of about 1 million to 8 million), guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alginate alkyl esters, glucomannan, agar or carrageenan, and other carbohydrates with gelling ability extracted from seaweed.

[0169] Furthermore, a coagulant can be incorporated into the ink composition of the present invention. The pigment forms loose aggregates through the coagulant, which inhibits direct aggregation of pigments and improves the dispersion stability of the pigment. Alternatively, the coagulant can be used in combination with the aforementioned dispersant. When both the coagulant and dispersant are used together, the dispersibility of the loose aggregates formed by the coagulant is improved, further enhancing the dispersion stability of the pigment in the ink.

[0170] When the ink composition of the present invention contains a coagulant, the content of the coagulant relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.05% by mass to 1% by mass.

[0171] Examples of coagulants include polyvinylpyrrolidone, polyethylene oxide, and water-soluble polysaccharides.

[0172] Examples of water-soluble polysaccharides include tragacanth gum, guar gum, pullulan, cyclodextrin, and water-soluble cellulose derivatives.

[0173] In addition, examples of water-soluble cellulose derivatives include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose.

[0174] The ink composition of the present invention can be mixed with surfactants, which can adjust the surface tension of the ink composition to an appropriate range.

[0175] Surfactants used in adjusting surface tension include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants, all of which can be used appropriately.

[0176] Surfactants used to adjust surface tension include, for example, phosphate ester surfactants, silicone surfactants, surfactants with acetylene bonds in their structure, fluorinated surfactants, etc., which can be appropriately selected according to the composition or purpose of the ink composition.

[0177] It should be noted that surfactants used as dispersants can also be used to improve pigment dispersibility and adjust surface tension.

[0178] When the ink composition of the present invention contains a surfactant for adjusting surface tension, the content of the surfactant for adjusting surface tension relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.01% to 2% by mass, more preferably 0.05% to 1% by mass.

[0179] A pH adjuster can be added to the ink composition of the present invention to adjust the pH of the ink composition to an appropriate range. Various acidic and alkaline substances can be used as the pH adjuster.

[0180] 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.

[0181] Examples of alkaline substances include ammonia, sodium carbonate, sodium hydrogen phosphate, potassium hydrogen phosphate, sodium hydroxide, potassium hydroxide, and sodium acetate. Alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine can also be used.

[0182] When the ink composition of 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 0.1% to 5% by mass, more preferably 0.5% to 2% by mass.

[0183] When water is used as the solvent in this invention, a water-soluble organic solvent that is compatible with water can be mixed in to suppress the evaporation of water from the pen tip of the writing instrument.

[0184] Examples of water-soluble organic solvents include ethanol, propanol, butanol, glycerol, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thioethylene glycol, polyethylene glycol, propylene glycol, butanediol, 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.

[0185] Water-soluble organic solvents may be used in combination or in one or more ways.

[0186] When the ink composition of 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% to 40% by mass, more preferably 5% to 30% by mass, and even more preferably 10% to 25% by mass. If the content of the water-soluble organic solvent is higher than 40% by mass, the ink viscosity tends to increase, the ink flowability of the writing instrument containing the ink composition decreases, and writing defects such as smudges and streaks are easily produced. On the other hand, if the content is less than 1% by mass, it lacks the effect of inhibiting water evaporation.

[0187] Water-soluble resins such as alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin can be blended into the ink composition of the present invention, which can also impart adhesion and tack to the paper surface.

[0188] Water-soluble resins can be used in combination, either one or two or more.

[0189] When the ink composition of 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% to 30% by mass, more preferably 1% to 10% by mass.

[0190] The ink composition of the present invention can also be mixed with various additives as needed.

[0191] Examples of additives include rust inhibitors, corrosion inhibitors or mildew inhibitors, bubble absorbers, wetting agents, defoamers, and specific gravity adjusters.

[0192] Examples of rust inhibitors include dicyclohexylammonium nitrite, diisopropylammonium nitrite, and saponins.

[0193] Examples of preservatives or fungicides include phenol, sodium salt of 1,2-benzothiazoline-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl p-hydroxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine.

[0194] Examples of bubble absorbers include ascorbic acid, isoascorbic acid, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkyl hydroxylamine, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, hypophosphonates, sulfites, hyposulfites, dithionites, thiosulfates, and thiourea dioxide.

[0195] Examples of humectants include reduced or non-reduced starch hydrolysates, disaccharides such as trehalose, oligosaccharides, sucrose, cyclodextrin, glucose, dextrin, sorbitol, mannitol, sodium pyrophosphate, etc.

[0196] When the ink composition of the present invention is contained in a writing instrument (ballpoint pen) with a ballpoint pen tip, a lubricant may also be mixed into the ink composition.

[0197] Lubricant can improve the lubrication of the ball bearing holder inside the pen tip body and the ball bearing at the front of the pen tip body, easily preventing wear of the ball bearing holder and improving the writing feel.

[0198] Examples of lubricants include, for example, higher fatty acids such as oleic acid, nonionic surfactants having long-chain alkyl groups, polyether-modified silicone oils, trithiophosphites such as trithiophosphites (alkoxycarbonylmethyl ester) or trithiophosphites (alkoxycarbonylethyl ester), polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether phosphate monoesters, polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether phosphate diesters, and their metal salts, ammonium salts, amine salts and alkanoylamine salts, etc., of phosphate ester type surfactants.

[0199] When the ink composition of the present invention is applied to a ballpoint pen having a ballpoint pen tip (which includes a pen tip body having a ball bearing holder made of metal and a ball bearing made of metal), a phosphate ester-based surfactant is preferably used as a lubricant.

[0200] Phosphate ester surfactants have the property of readily adsorbing phosphate groups onto metals. Therefore, when an ink composition containing a phosphate ester surfactant is applied to the aforementioned ballpoint pen, the surfactant is adsorbed onto the ball and ball holder, forming a lubricating layer on both surfaces. This improves the lubrication between the ball and ball holder, allowing the ball to rotate smoothly. Furthermore, it inhibits wear on the ball holder, resulting in a superior writing experience.

[0201] The method for manufacturing the ink composition of the present invention is not particularly limited, and any method known in the prior art can be used.

[0202] Specifically, the mixture containing the above-mentioned components is stirred using various mixers such as propeller mixers, homogenizers, or homogeneous mixers, or dispersed using various dispersers such as bead mills, thereby producing an ink composition.

[0203] The viscosity characteristics of the ink composition of the present invention are not particularly limited. For example, ink compositions with viscosity characteristics such as high shear thinning (gel ink), low viscosity and low shear thinning ink compositions, and low viscosity and non-shear thinning ink compositions (Newtonian ink) can be used. The uric acid pigment used in the present invention exhibits excellent dispersion stability, and the pigment does not easily settle even when the ink composition is low viscosity; therefore, low viscosity ink compositions can be appropriately used.

[0204] When the ink composition of the present invention is used in a ballpoint pen, regarding its viscosity, at 20°C and a rotational speed of 1 rpm (shear rate 3.84 sec), -1When the conditions are measured, the following range is preferred for the purpose of making the dispersion stability of the pigment more stable. Specifically, the viscosity of the ink composition under these conditions is preferably 1 mPa·s to 2000 mPa·s or less, more preferably 10 mPa·s to 1500 mPa·s or less, and even more preferably 100 mPa·s to 1000 mPa·s or less.

[0205] Additionally, at 20°C and a rotation speed of 100 rpm (shearing rate 384 sec), -1 When measured under the conditions described above, the viscosity is preferably within the following range for the purpose of ensuring good ink flow from the ballpoint pen tip. Specifically, the viscosity of the ink composition under these conditions is preferably 1 mPa·s to 200 mPa·s, more preferably 10 mPa·s to 100 mPa·s, and even more preferably 20 mPa·s to 50 mPa·s.

[0206] By keeping the viscosity of the ink composition within the above-mentioned range, it is possible to maintain the dispersion stability of the pigment and the easy flowability of the ink within the ballpoint pen structure at a high level.

[0207] It should be noted that the viscosity of the ink composition was determined using a rheometer [TA Instruments, Discovery HR-2, cone plate (40mm diameter, 1° angle)], with the ink placed at 20°C and rotated at 1 rpm (shear rate 3.84 sec). -1 Or a rotational speed of 100 rpm (shearing speed 384 sec) -1 The value is obtained by measuring under the conditions of ).

[0208] When the ink composition of the present invention is used in a marker pen, its viscosity, when measured at 20°C and 50 rpm, is preferably within the following range for the purpose of maintaining a high level of ink flowability and pigment dispersion stability. Specifically, the viscosity of the ink composition in this case is preferably 1 mPa·s to 30 mPa·s, more preferably 1 mPa·s to 20 mPa·s, and even more preferably 1 mPa·s to 10 mPa·s.

[0209] It should be noted that the viscosity of the ink composition was measured using an E-type rotational viscometer [manufactured by Toki Sangyo Co., Ltd., product name: RE-85L, conical rotor: standard type (1°34′×R24)], with the ink composition placed at 20°C.

[0210] When the ink composition of the present invention is used in ballpoint pens or markers, its pH is preferably in the range of 6 to 10, more preferably 7 to 9. By keeping the pH within the above range, excessive viscosity or deterioration of the ink composition can be suppressed.

[0211] It should be noted that the pH of the ink composition was measured using a pH meter [manufactured by Toa DKK Corporation, product name: IM-40S], with the ink placed at 20°C.

[0212] When the ink composition of the present invention is used in a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited. For example, it can be used by filling a ballpoint pen refill or a ballpoint pen that has a ballpoint pen tip and an ink filling mechanism.

[0213] A ballpoint pen tip includes a pen tip body and a ball bearing located at the front end of the pen tip body. Examples of ballpoint pen tips include those formed by holding the ball bearing in a ball bearing holding part (which is formed by extruding and deforming the front end of the pen tip body, which is made of a metal tube, from the outside in), those formed by holding the ball bearing in a ball bearing holding part (which is formed by cutting the pen tip body, which is made of metal material, using a drill bit or the like), those with a resin ball bearing holder inside a metal or plastic pen tip body, and those formed by applying forward force to the ball bearing held in the above-mentioned pen tips using a spring body.

[0214] There are no particular limitations on the materials used for the pen tip and the ball bearing; examples include superhard alloys (superhard), stainless steel, ruby, ceramic, resin, and rubber. Furthermore, the ball bearing can be surface-treated with materials such as DLC coating.

[0215] The diameter of the beads can be typically 0.2mm to 3mm, preferably 0.2mm to 2mm, more preferably 0.2mm to 1.5mm, and even more preferably 0.2mm to 1mm.

[0216] As an ink filling mechanism, an ink container that can be directly filled with ink can be exemplified, for example.

[0217] As ink containment bodies, molded bodies or metal tubular bodies made of thermoplastic resins such as polyethylene, polypropylene, polyethylene terephthalate, and nylon are used, for example.

[0218] By connecting the ballpoint pen tip directly or via a connecting component to the ink reservoir and filling the ink reservoir directly, a ballpoint pen refill (sometimes referred to as "refill" below) can be formed. A ballpoint pen can be formed by housing the refill inside the cylinder.

[0219] An ink backflow preventer is provided at the rear end of the ink filling the ink container. Examples of ink backflow preventers include liquid plugs and solid plugs.

[0220] Liquid plugs are made of non-volatile liquids and / or low-volatility liquids, such as petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefins, oligomers or co-oligomers of α-olefins, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, and fatty acid-modified silicone oil.

[0221] Non-volatile liquids and / or low-volatility liquids may be used in combination, either one or more.

[0222] It is preferable to add a thickener to a non-volatile liquid and / or a non-volatile liquid to thicken it to a suitable viscosity.

[0223] Examples of tackifiers include, for example, hydrophobically treated silica, methylated microcrystalline silica, aluminum silicate, swollen mica, clay-based tackifiers such as hydrophobically treated bentonite or montmorillonite, fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate, tribenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax, hydrogenated castor oil, fatty acid dextrins and other dextrin compounds, and cellulose compounds.

[0224] Examples of solid plugs include those made of polyethylene, polypropylene, and polymethylpentene.

[0225] As an ink backflow prevention device, the above-mentioned liquid plug can also be used in combination with the solid plug.

[0226] Alternatively, the cylinder itself can be used as an ink filling mechanism, directly filling the cylinder with ink, and a ballpoint pen tip can be installed at the front end of the cylinder, thus forming a ballpoint pen with a ballpoint pen tip and an ink filling mechanism.

[0227] When the ink filled into the ink filling mechanism is of low viscosity, a ballpoint pen having a ballpoint pen tip and an ink filling mechanism can further have an ink supply mechanism for supplying the ink filled into the ink filling mechanism to the pen tip.

[0228] There are no particular limitations on the ink supply mechanism. For example, the following can be cited: (1) a mechanism that provides ink flow regulation by using an ink guide core made of fiber bundles as an ink flow regulator and supplies ink to the pen tip while holding the ink flow regulator; (2) a mechanism that provides ink flow regulation by using a comb-shaped ink flow regulator and supplies ink to the pen tip while holding the ink flow regulator; (3) a mechanism that arranges multiple discs with comb-shaped gaps in between, provides a slit-shaped ink guide groove that runs longitudinally through the discs along the axis and a ventilation groove that is wider than the groove, and provides an ink guide core for guiding ink from the ink filling mechanism to the pen tip along the axis, and supplies ink to the pen tip by means of the pen core formed therefrom; etc.

[0229] There are no particular restrictions on the material used for the pen refill, as long as it is a synthetic resin that can be injection molded into a comb-like structure of multiple discs. Examples of synthetic resins include common polycarbonate, polypropylene, polyethylene, and acrylonitrile-butadiene-styrene copolymer resin (ABS resin). Acrylonitrile-butadiene-styrene copolymer resin (ABS resin) is particularly suitable for use due to its high moldability and ease of obtaining the pen refill properties.

[0230] When a ballpoint pen has the aforementioned ink supply mechanism, in addition to the aforementioned ink container and cylinder, an ink absorber capable of filling ink can also be used as the ink filling mechanism.

[0231] Ink absorbent is a fiber bundle formed by bundling curled fibers along its length. It is constructed by being embedded in a plastic cylinder, membrane, or other coating, and is adjusted to achieve a porosity of approximately 40% to 90%.

[0232] Alternatively, an ink-impregnating element containing ink can be housed within an ink container. An ink supply mechanism is positioned at the front end of the ink container and connected to the ink-impregnating element. The ballpoint pen tip is then connected to the ink supply mechanism directly or via a connecting component, thereby forming a ballpoint pen refill comprising a ballpoint pen tip, an ink filling mechanism, and an ink supply mechanism. Alternatively, an ink-impregnating element containing ink can be housed within an ink container. An ink supply mechanism is positioned inside the ink container and connected to the ink-impregnating element. The ballpoint pen tip is then connected to the ink container directly or via a connecting component, thereby forming a ballpoint pen refill.

[0233] Specifically, examples of ballpoint pens that contain the ink composition of the present invention include: (1) a ballpoint pen having an ink container filled with ink inside a barrel, with the pen tip directly or by means of a connecting member connected to the ink container, and an ink backflow prevention body filled on the end face of the ink; (2) a ballpoint pen having a mechanism that directly fills the barrel with ink, and supplies ink to the pen tip by clamping a comb-shaped ink flow regulator or a guide core made of fiber bundles, etc., as an ink flow regulator; (3) a ballpoint pen having a mechanism that directly fills the barrel with ink, and supplies ink to the pen tip by means of the aforementioned pen core; (4) a ballpoint pen having a mechanism that houses an ink absorbent body made of fiber bundles impregnated with ink inside a barrel, and supplies ink to the pen tip by clamping an ink guide core made of fiber bundles, etc., as an ink flow regulator; and so on.

[0234] Furthermore, when the ink composition of the present invention is used in a marker, the structure and shape of the marker itself are not particularly limited. For example, it can be used in a marker refill or marker that has a marker tip and an ink filling mechanism.

[0235] As a marker tip, examples include porous components with interconnected pores that have been commonly used, such as resin-processed bodies of fibers, welded bodies of thermoplastic fibers, and felt bodies, or extruded bodies of synthetic resins with a porosity of approximately 30% to 70%, or multiple ink outlet holes extending along the axial direction. One end is processed into a shape corresponding to the purpose, such as a cannonball, a rectangle, or a wedge, for practical use.

[0236] As an ink filling mechanism, an ink absorber capable of filling ink can be exemplified, for example.

[0237] Ink absorbent is a fiber bundle formed by bundling curled fibers along its length. It is constructed as a coating material inside a plastic cylinder, membrane, etc., and the porosity is adjusted to approximately 40% to 90%.

[0238] An ink absorber containing ink can be housed inside the barrel. The marker tip is connected to the barrel directly or via a connecting component according to the connection method with the ink absorber, thus forming a marker.

[0239] Alternatively, an ink absorber containing ink can be housed in an ink reservoir. The marker tip can be connected to the ink reservoir directly or via a connecting component, thereby forming a marker refill (sometimes referred to as "refill" below). A marker pen can be formed by housing this refill in a cylinder.

[0240] As ink containment bodies, molded bodies or metal tubular bodies made of thermoplastic resins such as polyethylene, polypropylene, polyethylene terephthalate, and nylon are used, for example.

[0241] A marker pen having a pen tip and an ink filling mechanism can further have an ink supply mechanism for supplying the ink composition filled in the ink filling mechanism to the pen tip.

[0242] There are no particular limitations on the ink supply mechanism. For example, the following can be cited: (1) a mechanism that provides ink to the pen tip by having an ink guide core made of fiber bundles or the like as an ink flow regulator; (2) a mechanism that provides ink to the pen tip by having a comb-shaped ink flow regulator; (3) a mechanism that arranges multiple discs with comb-shaped gaps in between, provides a slit-shaped ink guide groove that runs longitudinally through the discs along the axis and a venting groove that is wider than the groove, and provides an ink guide core that guides ink from the ink filling mechanism to the pen tip along the axis, and provides ink to the pen tip by means of the pen core formed therein; (4) a mechanism that provides ink to the pen tip by opening a valve-based ink flow regulator; and so on.

[0243] There are no particular restrictions on the material used for the pen refill, as long as it is a synthetic resin that can be injection molded into a comb-like structure of multiple discs. Examples of synthetic resins include common polycarbonate, polypropylene, polyethylene, and acrylonitrile-butadiene-styrene copolymer resin (ABS resin). Acrylonitrile-butadiene-styrene copolymer resin (ABS resin) is particularly suitable for use due to its high moldability and ease of obtaining the pen refill properties.

[0244] As a valve mechanism, a traditionally common suction type that opens by pressing the pen tip can be used, and it is appropriate to set the spring pressure so that it can be opened by pen pressure.

[0245] When a marker pen has an ink supply mechanism, in addition to the ink absorber mentioned above, an ink container that can directly fill with ink can also be used as the ink filling mechanism. Alternatively, the barrel itself can be used as the ink filling mechanism to directly fill with ink.

[0246] Alternatively, an ink reservoir can be used to house an ink absorber impregnated with ink. An ink supply mechanism is positioned at the front end of the ink reservoir and connected to the ink absorber. The marker tip is then connected to the ink supply mechanism directly or via a connecting component, thus creating a marker refill comprising a marker tip, an ink filling mechanism, and an ink supply mechanism. Alternatively, an ink reservoir can be used to house an ink absorber impregnated with ink. An ink supply mechanism is positioned inside the ink reservoir and connected to the ink absorber. The marker tip is then connected to the ink reservoir directly or via a connecting component, thus creating a marker refill.

[0247] Specifically, examples of a marker pen that incorporates the ink composition of the present invention include: (1) a marker pen in which an ink-absorbing body composed of a fiber bundle impregnated with ink is housed in a barrel, and a marker pen tip formed of a fiber processed body or resin molded body with capillary gaps is directly or by means of a connecting member connected to the barrel; (2) a marker pen having the following mechanism: a mechanism that directly fills the barrel with ink, and uses a comb-shaped ink flow regulator or an ink guide core composed of fiber bundles as an ink flow regulator to supply ink to the pen tip; (3) a marker pen having A marker pen with the following mechanisms: (4) a mechanism that directly fills the barrel with ink and supplies ink to the pen tip by means of the aforementioned pen core; (5) a marker pen that has a pen tip and an ink reservoir by means of a valve mechanism that opens the valve by pressing the pen tip, and the ink reservoir is directly filled with ink; (6) a marker pen that has an ink reservoir in the barrel, which contains an ink absorber made of a fiber bundle impregnated with ink; a marker pen in which a pen tip with capillary gaps, made of a fiber processed body or a resin molded body, is directly or by means of a connecting component connected to the ink reservoir; etc.

[0248] In addition, when ballpoint pens or markers are directly filled with writing ink, a stirring element, such as a stirring ball, can be built into the ink container or cylinder to facilitate the redispersibility of the ink. Examples of the stirring element's shape include spheres and rods. The material of the stirring element is not particularly limited; examples include metal, ceramic, resin, and glass.

[0249] Furthermore, the aforementioned writing instruments, such as ballpoint pens or markers, can also be made into a detachable structure, thus taking the form of an ink cartridge. In this case, it can be used by replacing the ink cartridge in the writing instrument with a new one after the ink in the cartridge is used up.

[0250] As an ink cartridge, it can be a component that also serves as a shaft sleeve (which, when connected to the main body of the writing instrument, constitutes the writing instrument), or a component that, after being connected to the main body of the writing instrument, is protected by a shaft sleeve (rear shaft). It should be noted that, in the latter case, besides being used as a standalone ink cartridge, it can also be any of the following: a component formed by connecting the main body of the writing instrument and the ink cartridge in the writing instrument before use; or a component housed in a non-connected state within a shaft sleeve, in a manner that allows the user to begin using the writing instrument by connecting the ink cartridge within the shaft sleeve.

[0251] Furthermore, in the writing instrument described above, a cap-type writing instrument is made by providing a cap that is installed in a manner that covers the pen tip (writing tip), thereby preventing the pen tip from drying out and becoming unusable for writing or preventing the writing tip from being contaminated or damaged.

[0252] In addition, in ballpoint pens or markers that house refills inside the barrel, a telescopic writing instrument can be made by incorporating a telescopic mechanism inside the barrel that allows the writing tip to extend and retract from the barrel, thus preventing the writing tip from being contaminated or damaged.

[0253] All telescopic writing instruments are usable as long as the writing tip is exposed to the outside air while being housed in a cylinder, and the writing tip protrudes from the opening of the cylinder through the operation of a telescopic mechanism.

[0254] Examples of telescopic mechanisms include: (1) a side-sliding telescopic mechanism in which an operating part (pen clip) that can move forward and backward from the rear side wall of the cylinder protrudes radially outward, and the operating part is slid forward, thereby extending or retracting the writing tip from the front opening of the cylinder; (2) a rear-end pressing telescopic mechanism in which the operating part located at the rear end of the cylinder is pressed forward, thereby extending or retracting the writing tip from the front opening of the cylinder; (3) a side-pressing telescopic mechanism in which the operating part protruding from the outside of the side wall of the cylinder is pressed radially inward, thereby extending or retracting the writing tip from the front opening of the cylinder; (4) a rotary telescopic mechanism in which the operating part at the rear of the cylinder is rotated, thereby extending or retracting the writing tip from the front opening of the cylinder; and so on.

[0255] Furthermore, the form of ballpoint pens and markers is not limited to the above-mentioned configurations. In addition to installing nibs of different shapes or nibs that dispense ink of different shades, they can also be composite writing instruments (double-ended, pen tip extended, etc.) with nibs of different shapes and ink of different shades dispensed from each nib.

[0256] Alternatively, it can be made into a composite telescopic writing instrument that houses multiple refills inside the shaft and allows the writing tip of any refill to extend or retract from the opening of the shaft through the operation of a telescopic mechanism.

[0257] When reversible thermochromic compositions, reversible thermochromic microcapsule pigments, or reversible thermochromic resin particles are used as colorants, the ink marks formed on the writing surface using a writing instrument containing the ink of the present invention can change color by rubbing with a finger, heating or cooling with a tool.

[0258] Examples of heating tools include electric heating color-changing tools equipped with resistive heat-dissipating elements such as PTC elements, heating color-changing tools filled with media such as warm water, heating color-changing tools using steam or lasers, and applications of hair dryers. From the perspective of being able to change color through simple methods, friction parts and friction bodies are preferred.

[0259] As a cooling tool, examples include electric temperature-changing color-changing tools using Peltier elements, temperature-changing color-changing tools filled with refrigerants such as cold water or ice flakes, cold storage agents, refrigerators, and freezers.

[0260] As friction components and friction bodies, elastic materials such as elastic bodies and plastic foams that are elastic and can generate frictional heat through moderate friction during rubbing are preferred, but plastic molded bodies, stone, wood, metal, and cloth can also be used.

[0261] It should be noted that while common erasers used for removing pencil-based marks can be used, since they produce shavings during erasure, it is preferable to use the aforementioned friction components and friction bodies that produce almost no shavings.

[0262] Materials used for friction components and friction bodies include, for example, silicone resin and SEBS resin (styrene-ethylene-butadiene-styrene block copolymer). Since silicone resin tends to adhere to areas that can be easily removed by rubbing and the ink is repelled upon repeated writing, SEBS resin is more suitable.

[0263] The aforementioned friction component or friction body can be any shape and separate from the writing instrument, but it can also be incorporated into the writing instrument to achieve excellent portability. Alternatively, the writing instrument and the friction component or friction body of any shape and separate from the writing instrument can be combined to obtain a writing instrument kit.

[0264] When the writing instrument is a cap-type writing instrument, there is no particular limitation on the location where the friction component or friction body is set. For example, the cap itself can be formed by the friction component, or the cylinder itself can be formed by the friction component, or the clip itself can be formed by the friction component when a clip is provided, or the friction component or friction body can be set at the front end (top) of the cap or the rear end (part without a writing front end).

[0265] When the writing instrument is a telescopic writing instrument, there is no particular limitation on the location where the friction component or friction body is set. For example, the friction component can form the cylinder itself, or the friction component can form the pen clip itself when a pen clip is further provided, or the friction component or friction body can be set near the opening of the cylinder, at the rear end of the cylinder (the part without the writing front end) or at the pressing part.

[0266] Example

[0267] The following examples are shown, but the present invention is not limited thereto. It should be noted that, unless otherwise stated, "parts" in the examples refer to "parts by mass".

[0268] Example 1

[0269] Preparation of pigment dispersions

[0270] Ten parts of uric acid, one part of dispersant [manufactured by BYK Chemical Co., Ltd. (Japan), product name: DISPER BYK-191], and 89 parts of water were mixed. Then, 100 parts of 2.0 mm diameter glass beads were added as a medium, and the mixture was pulverized and dispersed using a bead mill for 12 hours to prepare a pigment dispersion (uric acid pigment dispersion). It should be noted that the average particle size of the uric acid pigment dispersed in the pigment dispersion is 0.3 μm.

[0271] Comparative Example 1

[0272] Preparation of pigment dispersions

[0273] Ten parts of titanium dioxide [manufactured by TAYCA Corporation, product name: JR-301], one part of dispersant [manufactured by BYK Chemical Co., Ltd. (Japan), product name: DISPER BYK-191], and 89 parts of water were mixed. Then, 100 parts of 2.0 mm diameter glass beads were added as a medium, and the mixture was pulverized and dispersed using a bead mill for 12 hours to prepare a pigment dispersion (titanium dioxide dispersion). It should be noted that the average particle size of the titanium dioxide dispersed in the pigment dispersion is 0.3 μm.

[0274] Dispersion stability evaluation

[0275] 40 g of each pigment dispersion from Example 1 and Comparative Example 1 was added to a screw-top bottle (No. 7) and allowed to stand at room temperature (25°C) for 1 day. After 1 day, the dispersions were visually inspected, and their dispersion stability was evaluated according to the following criteria. The evaluation results are shown in Table 1 below.

[0276] A: The pigment remains dispersed, and the pigment dispersion is a uniform white color.

[0277] B: Most of the pigments settled, and the supernatant (water layer) was identified in the pigment dispersion, separating into two layers.

[0278] Redispersibility assessment

[0279] The pigment dispersions of Example 1 and Comparative Example 1 were placed in sealed glass test tubes with a diameter of 15 mm and left to stand at room temperature (25°C) for 7 days. After 7 days, each glass test tube was vibrated up and down, and the redispersibility of each pigment dispersion was visually confirmed. The redispersibility was evaluated according to the following criteria. The evaluation results are shown in Table 1 below.

[0280] A: Through vibration, the pigment is easily redispersed.

[0281] B: Even with vibration, the pigment was not redispersed.

[0282] [Table 1]

[0283]

[0284] Example 2

[0285] Preparation of pigment dispersions

[0286] Ten parts of uric acid, one part of surfactant [Blaunon L-205 manufactured by Aoki Oils & Fats Co., Ltd., product name: Blaunon L-205] as a dispersant, and 89 parts of water were mixed. Then, 200 parts of zirconia beads with a diameter of 1.0 mm were added as a medium, and the mixture was pulverized and dispersed using a bead mill for 1 hour to prepare a pigment dispersion (uric acid pigment dispersion).

[0287] Dispersion stability evaluation

[0288] The pigment dispersion of Example 2 was examined using an optical microscope [Olympus Corporation, product name: System Biological Microscope BX53, 100x], and the dispersion stability was evaluated according to the following criteria. The evaluation results are shown in Table 2 below.

[0289] A: Visually confirm that the pigment is evenly dispersed.

[0290] B: A quick visual inspection confirms that the pigment particles have agglomerated.

[0291] C: Visual inspection confirmed that the pigments had significantly agglomerated.

[0292] Redispersibility assessment

[0293] The pigment dispersion of Example 2 was placed in a sealed glass test tube with a diameter of 15 mm and left to stand at room temperature (25°C) for 7 days. After 7 days, the glass test tube was vibrated up and down, and the redispersibility of the pigment dispersion was visually confirmed. The redispersibility was evaluated according to the following criteria. The evaluation results are shown in Table 2 below.

[0294] A: Through vibration, the pigment is easily redispersed.

[0295] B: Even with vibration, the pigment was not redispersed.

[0296] Examples 3 to 12

[0297] As dispersants, the surfactants shown in Table 2 were used instead of the surfactants used as dispersants in Example 2, and the pigment dispersions were prepared in the same manner as in Example 2. Furthermore, 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.

[0298]

[0299] Example 13

[0300] Preparation of pigment dispersions

[0301] Ten parts of uric acid, one part of a polymeric dispersant [manufactured by BYK Chemical Co., Ltd. (Japan), product name: DISPER BYK-191], and 89 parts of water were mixed. Then, 200 parts of 1.0 mm diameter zirconia beads were added as a medium, and the mixture was pulverized and dispersed using a bead mill for one hour to prepare a pigment dispersion (uric acid pigment dispersion, 1% dispersant, pulverized and dispersed for 1 hour). The average particle size of the uric acid pigment dispersed in the pigment dispersion was 0.34 μm.

[0302] In addition, except that the duration of the pulverization and dispersion treatment was 6 hours, the pigment dispersion (uric acid pigment dispersion, 1% dispersant, pulverized and dispersed for 6 hours) was prepared in the same manner as in Example 13. The average particle size of the uric acid pigment dispersed in the pigment dispersion was 0.30 μm.

[0303] 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.

[0304] Examples 14 to 26

[0305] As a dispersant, the polymeric dispersants shown in Tables 3 and 4 were used instead of the polymeric dispersants used in Example 13. Except for this, the pigment dispersion (uric acid pigment dispersion, 1% dispersant, pulverized and dispersed for 1 hour) was prepared in the same manner as in Example 13.

[0306] Examples 27 to 30

[0307] As a dispersant, the polymeric dispersants shown in Table 5 were used instead of the polymeric dispersants used in Example 13; and the polymeric dispersant was 2 parts and the water was 88 parts. Except as described above, the pigment dispersion (uric acid pigment dispersion, 2% dispersant, 1 hour of pulverization and dispersion) was performed in the same manner as in Example 13 to prepare a pigment dispersion (uric acid pigment dispersion, 2% dispersant, 1 hour of pulverization and dispersion).

[0308] In addition, 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.

[0309]

[0310]

[0311]

[0312] Example 31

[0313] Preparation of ink composition

[0314] 25 parts of uric acid, 2.5 parts of dispersant [manufactured by BYK Chemical Co., Ltd. (Japan), product name: DISPER BYK-191], and 72.5 parts of water were mixed. Then, 100 parts of 2.0 mm diameter glass beads were added as a medium, and the mixture was pulverized and dispersed using a bead mill for 12 hours to prepare a pigment dispersion (uric acid pigment dispersion). It should be noted that the average particle size of the uric acid pigment dispersed in the pigment dispersion is 0.3 μm.

[0315] Next, 88 parts of the above-mentioned pigment dispersion, 0.2 parts of shear-thinning agent (succinopolysaccharide) [manufactured by Sansho Co., Ltd., product name: Rheozan], 1 part of phosphate ester surfactant [manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., product name: Plysurf AL], 1 part of pH adjuster (triethanolamine), 0.1 parts of 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.

[0316] Making ballpoint pens

[0317] After the above-mentioned ink composition is drawn and filled into an ink container made of polypropylene tubing, it is connected to the ballpoint pen tip, which holds a 0.5mm diameter ultra-hard ball, via a resin retainer. Next, a viscoelastic ink backflow preventer (liquid plug) with polybutene as the main component is filled from the rear end of the ink container, and the tail plug is further fitted into the rear of the tube. After degassing by centrifugation, a ballpoint pen refill is obtained.

[0318] Next, the aforementioned replacement core is assembled into the shaft cylinder to produce a ballpoint pen (retractable ballpoint pen).

[0319] The ballpoint pen described above is equipped with a rear-end press-type telescopic structure. The pen tip, which is located in the ballpoint pen refill, is housed in the cylinder in a state of being exposed to external gas. By pressing the operating part located at the rear end of the cylinder forward, the pen tip protrudes from the opening at the front end of the cylinder.

[0320] Using the ballpoint pen described above, handwriting was performed on A4-sized black paper at room temperature (20°C). [Manufactured by Nagatoya Shoten Co., Ltd., Product Name: Colored Paper A4 Medium Thickness (Thickness: 0.09mm, Density: 80g / m³)] 2 Writing on the surface resulted in no writing defects such as scribbling or streaking, producing clear white ink marks. Furthermore, the ink marks effectively concealed the writing surface, making them excellent and discreet handwriting.

[0321] Example 32

[0322] Preparation of ink composition

[0323] An ink composition was prepared by mixing 88 parts of the pigment dispersion from Example 31, 7 parts of acrylic resin [manufactured by BASF Japan Co., Ltd., product name: JONCRYL PDX-7600], 0.3 parts of acetylene glycol surfactant [manufactured by Nissin Chemical Industry Co., Ltd., product name: Dynol 604], 0.2 parts of preservative [manufactured by Lonza Japan Co., Ltd., product name: PROXEL XL-2(S)], and 4.5 parts of water.

[0324] Marker pen making

[0325] The above ink composition is filled into an ink container (which is made of a resin-processed pen body (ball-shaped) with polyester fiber at the front end and a metal ball-shaped stirring body inside), so that the ink composition is absorbed into the pen body, and a cap is installed to make a marker pen.

[0326] Using the marker described above, write by hand on A4-sized black paper at room temperature (20°C). [Manufactured by Nagatoya Shoten Co., Ltd., Product Name: Colored Paper A4 Medium Thickness (Thickness: 0.09mm, Density: 80g / m³)] 2 Writing on the surface resulted in no writing defects such as scribbling or streaking, producing clear white ink marks. Furthermore, the ink marks effectively concealed the writing surface, making them excellent and discreet handwriting.

[0327] Example 33

[0328] An ink composition was prepared by mixing 80 parts of the pigment dispersion from Example 31, 2 parts of red dye [manufactured by Hodogaya Chemical Industry Co., Ltd., product name: Phloxine], 1 part of phosphate ester surfactant [manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., product name: PlysurfAL], 1.5 parts of resin emulsion [manufactured by Dow Chemical Japan Co., Ltd., product name: Primal ASE-60], 10 parts of diethylene glycol, 4 parts of glycerol, 1 part of pH adjuster (triethanolamine), and 0.5 parts of phenol.

[0329] Making ballpoint pens

[0330] After the above-mentioned ink composition is drawn and filled into an ink container made of polypropylene tubing, it is connected to the ballpoint pen tip, which holds a 0.7mm diameter ultra-hard ball at the front end, via a resin retainer. Next, a viscoelastic ink backflow preventer (liquid plug) with polybutene as the main component is filled from the rear end of the ink container, and the tail plug is further fitted into the rear of the tube. After degassing by centrifugation, a ballpoint pen refill is obtained.

[0331] Next, assemble the aforementioned core into the shaft cylinder, install the cap, and manufacture a ballpoint pen (cap-type ballpoint pen).

[0332] Using the ballpoint pen described above, handwriting was performed on A4-sized black paper at room temperature (20°C). [Manufactured by Nagatoya Shoten Co., Ltd., Product Name: Colored Paper A4 Medium Thickness (Thickness: 0.09mm, Density: 80g / m³)] 2 When writing on the surface, no writing defects such as scribbling or streaking occurred, resulting in clear, pastel-toned red ink marks. Furthermore, the ink marks effectively obscure the writing surface, making them excellent and discreet handwriting.

Claims

1. An ink composition for a concealable writing instrument, comprising at least a pigment containing granular uric acid pigment and a solvent, wherein the average particle size of the uric acid pigment is 0.05 μm or more and 1 μm or less, and the content of the uric acid pigment is 5% by mass or more and 30% by mass relative to the total mass of the ink composition.

2. The ink composition for a concealed writing instrument as claimed in claim 1, further comprising a dispersant.

3. The ink composition for a writing instrument with concealment as described in claim 2, wherein, The dispersant comprises a polymeric dispersant.

4. The ink composition for a writing instrument with concealment as described in claim 1 or claim 2, further comprising a colorant.

5. A writing instrument comprising an ink composition for a concealed writing instrument as described in claim 1 or claim 2.

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