Water-based ink composition for writing instruments and writing instruments containing the same

Abstract

The objective is to provide an aqueous ink composition for writing instruments and a writing instrument containing it, which provides a preservative effect and prevents writing defects such as smudging of the ink by incorporating a hydroxamic acid derivative of a specific structure into the aqueous ink. Furthermore, the preservative effect obtained by the hydroxamic acid derivative is improved by further including an amine compound having a hydroxyl group. [Solution] An aqueous ink composition for writing instruments comprising a colorant, water, and a hydroxamic acid derivative of a specific structure, and a writing instrument containing the same.

Description

Technical Field

[0001] The present disclosure relates to an aqueous ink composition for writing instruments.

Background Art

[0002] Since an aqueous ink composition mainly contains water, microorganisms (for example, fungi such as mold and yeast, bacteria) are likely to propagate. When microorganisms propagate in the aqueous ink, the aqueous ink deteriorates, deposits and aggregates occur in the ink composition, discoloration of the aqueous ink occurs, a putrid odor occurs from the ink composition, and changes occur in physical properties such as a decrease or increase in the viscosity of the aqueous ink, and the function as an aqueous ink may be impaired. Therefore, it has been widely practiced to add preservatives and fungicides such as potassium sorbate and 1,2-benzisothiazolin-3-one to the aqueous ink to suppress the propagation of microorganisms (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, some conventional preservatives and fungicides need to be added in a large amount to obtain a sufficient antiseptic effect. In recent years, the safety of preservatives and fungicides in the human body and the environment has been emphasized. Some preservatives and fungicides have strong skin irritation and skin sensitization, and there are problems with safety. Therefore, it is necessary to reduce the content of preservatives and fungicides in the aqueous ink, and as a result, a sufficient antiseptic effect may not be obtained.

[0005] This disclosure was made in view of the above-mentioned problems, and aims to provide an aqueous ink composition for writing instruments and a writing instrument containing the same, which provides a preservative effect by containing a hydroxamic acid derivative of a specific structure in an aqueous ink, and prevents writing defects such as smudging of the writing line. [Means for solving the problem]

[0006] [1] A water-based ink composition for writing instruments comprising a colorant, water, and a hydroxamic acid derivative represented by the following general formula (1). [ka] (In the formula, R 1 (This represents a hydrocarbon group with 1 to 15 carbon atoms.)

[0007] [2] The aqueous ink composition for writing instruments according to [1], wherein the content of the hydroxamic acid derivative is 0.01 to 1% by mass with respect to the total amount of the aqueous ink composition.

[0008] [3] The aqueous ink composition for writing instruments according to [1] or [2], further comprising an amine compound having a hydroxyl group.

[0009] [4] A writing instrument containing the aqueous ink composition for writing instruments described in [1] to [3]. [Effects of the Invention]

[0010] According to this disclosure, an aqueous ink composition for writing instruments and a writing instrument containing the same are provided, which have excellent preservative effects and do not cause writing defects such as smudging of the writing line, by containing a hydroxamic acid derivative represented by general formula (1) in the aqueous ink. [Modes for carrying out the invention]

[0011] The specific embodiments described in this disclosure are described in detail below. However, the embodiments described below are not the only ones.

[0012] "Parts", "%", "ratio", etc. indicating the formulation in this specification are based on mass unless otherwise specified.

[0013] "Antiseptic" in this specification includes "mildew prevention" which is used particularly against mildew among microorganisms such as bacteria and fungi.

[0014] The aqueous ink composition for writing instruments of the present disclosure (hereinafter, sometimes referred to as "ink composition", "aqueous ink", or "ink") is characterized by comprising a colorant, water, and a hydroxamic acid derivative represented by the general formula (1).

[0015] <Colorant> As the colorant, dyes, pigments, and resin particles that are soluble or dispersible in an aqueous medium can all be used. That is, the colorant may contain any one or more selected from the group consisting of dyes, pigments, and resin particles.

[0016] <Dye> Examples of the dye include acid dyes, basic dyes, direct dyes, reactive dyes, vat dyes, sulfur dyes, mordant dyes, cationic dyes, disperse dyes, etc.

[0017] <Pigment> Examples of the pigment include inorganic pigments, organic pigments, metallic pigments, fluorescent pigments, phosphorescent pigments, etc. Further, a water-dispersed pigment in which the pigment is finely and stably dispersed in an aqueous medium using at least one of a surfactant and a resin in advance can also be used.

[0018] Also, a pigment dispersant can be used as needed. Examples of the pigment dispersant include surfactants such as anionic and nonionic types; anionic polymers such as polyacrylic acid and styrene-acrylic acid; nonionic polymers such as PVP and PVA.

[0019] Also, the pigment may be a self-dispersing pigment. A self-dispersible pigment is a pigment that can be dispersed in an aqueous medium without using a dispersant such as a resin or a surfactant. By subjecting the pigment to physical or chemical treatment to form hydrophilic functional groups on the surface of the pigment, it becomes possible to disperse the pigment in an aqueous medium without using a dispersant. Examples of applicable pigments include carbon black, benzimidazoline-based pigments, condensed azo-based pigments, isoindolinone-based pigments, quinophthalone-based pigments, quinacridone-based pigments, phthalocyanine-based pigments, aluminum, and the like.

[0020] Further, the pigment may be a microcapsule pigment. A microcapsule pigment is one in which a core substance is encapsulated in a wall film formed by a wall film-forming material. Since the core substance is isolated and protected from the external environment by being encapsulated in the microcapsule, the water resistance and light resistance of the core substance can be improved.

[0021] Examples of the core substance include a coloring composition composed of a coloring material and a medium. Examples of the coloring composition include those in which a dye or a pigment as a coloring material is dissolved or dispersed in an aqueous medium or an oily medium. The dyes or pigments described above can be used.

[0022] Examples of the aqueous medium include water such as tap water, ion-exchanged water, ultrafiltration water, and distilled water. Examples of the oily medium include esters such as monobasic acid esters, dibasic acid monoesters, dibasic acid diesters, partial esters or complete esters of polyhydric alcohols, aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes, higher alcohols, ketones, ethers, and the like. The aqueous medium or the oily medium may be used alone or in combination of two or more.

[0023] As the coloring composition, a photochromic material that changes color depending on the presence or absence of light irradiation may be used. This color change may be reversible or irreversible, but a reversible photochromic material is preferred because it can repeatedly exhibit color changes depending on the presence or absence of light irradiation. Examples of photochromic materials used in colored compositions include colored compositions in which a photochromic compound as a coloring material is dissolved in an oligomer as a medium, i.e., reversible photochromic compositions consisting of at least a photochromic compound and an oligomer. By encapsulating the reversible photochromic composition in microcapsules, reversible photochromic microcapsule pigments can be formed.

[0024] Examples of photochromic compounds include conventionally known spirooxazine derivatives, spiropyran derivatives, naphthopyran derivatives, etc., which develop color when irradiated with sunlight or light containing ultraviolet light such as ultraviolet light, or with purple or blue light having a peak emission wavelength in the range of 400 to 495 nm, and lose their color when irradiation is stopped. Examples include the compounds described in Japanese Patent Publication No. 2021-120493 and International Publication No. 2020 / 137469. Furthermore, photochromic compounds having optical memory properties (color memory photochromic properties) can also be used. Examples of such photochromic compounds include diarylethene derivatives, and for example, the compound described in Japanese Patent Application Publication No. 2021-120493 can be cited.

[0025] Examples of oligomers include styrene-based oligomers, acrylic-based oligomers, terpene-based oligomers, and terpene-phenol-based oligomers. By dissolving photochromic compounds in various oligomers, both lightfastness and color intensity can be improved, and the sensitivity to color change can also be adjusted. Oligomers can be used individually or in combination of two or more types.

[0026] Furthermore, a thermochromic material that changes color with temperature changes may be used as the coloring composition. This color change may be reversible or irreversible, but a reversible thermochromic material is preferred because it can repeatedly exhibit color changes due to temperature changes. Examples of thermochromic materials used in colored compositions include colored compositions comprising at least (a) an electron-donating chromogenic organic compound as a coloring material and (b) an electron-accepting compound as a medium. Furthermore, examples of colored compositions comprising at least a homogeneous compatible solution of component (a) as a coloring material and component (b) as a medium, and a reaction medium that determines the temperature at which the color reaction of components (a) and (b) occurs, i.e., a reversible thermochromic composition comprising at least (a) an electron-donating chromogenic organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of components (a) and (b) occurs. Reversible thermochromic microcapsule pigments can be formed by encapsulating the reversible thermochromic composition in microcapsules.

[0027] As the reversible thermochromic composition, a heat-decolorizing type reversible thermochromic composition having a relatively small hysteresis width (ΔH) (ΔH = 1 to 7°C), as described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc., can be used. This reversible thermochromic composition changes color before and after a predetermined temperature (color change point), exhibiting a decolorized state in the temperature range above the high-temperature color change point and a colored state in the temperature range below the low-temperature color change point. Of the two states, only one specific state exists in the room temperature range, and the other state is maintained as long as the heat or cold required to bring about that state is applied, but returns to the state exhibited in the room temperature range when the application of heat or cold is stopped. Furthermore, as a reversible thermochromic composition, a heat-decolorizing type reversible thermochromic composition having a large hysteresis width (ΔH = 8 to 80°C) as described in Japanese Patent Publication No. 4-17154, Japanese Patent Application Publication No. 7-179777, Japanese Patent Application Publication No. 7-33997, Japanese Patent Application Publication No. 8-39936, Japanese Patent Application Publication No. 2005-1369 can also be used. In this reversible thermochromic composition, the shape of the curve plotted for the change in color intensity due to temperature change follows a significantly different path depending on whether the temperature is raised from a temperature lower than the color change temperature range or lowered from a temperature higher than the color change temperature range. The colored state at temperatures below the complete color development temperature t1, or the decolorized state at high temperatures above the complete decolorization temperature t4, exhibits color memory in a specific temperature range [the temperature range between the color development start temperature t2 and the decolorization start temperature t3 (essentially a two-phase retention temperature range)]. Furthermore, "heat-decolorizing type" means that it decolorizes when heated and develops color when cooled.

[0028] When applying the above-described reversible thermochromic composition with color memory properties, the reversible thermochromic composition can be specifically configured such that the complete color development temperature t1 is a temperature that can only be obtained in a freezer or cold region, and the complete decolorization temperature t4 is a temperature that can be obtained from frictional heat from a friction body or a familiar heating element such as a hair dryer, and the ΔH value is specified to be 40 to 100°C, thereby effectively maintaining the color exhibited under normal conditions (daily living temperature range). Temperatures that can only be obtained in a freezer or cold region are in the range of -50 to 0°C, preferably -40 to -5°C, and more preferably -30 to -10°C. The temperature obtained from readily available heating elements such as hair dryers is 50 to 95°C, preferably in the range of 50 to 90°C, and more preferably in the range of 60 to 80°C.

[0029] As a reversible thermochromic composition, a heat-activated, reversible thermochromic composition using gallic acid ester, as described in Japanese Patent Publication No. 51-44706, Japanese Patent Application Publication No. 2003-253149, etc., can also be used. Furthermore, "heat-activated coloring type" means that the color develops when heated and disappears when cooled.

[0030] The reversible thermochromic composition is a compatible mixture containing the above-mentioned components (a), (b), and (c) as essential components. The proportion of each component depends on the concentration, discoloration temperature, discoloration form, and type of each component, but generally, the component ratios that yield the desired properties are in the range of 1 part (a) to 0.1 to 100 parts (b), preferably 0.1 to 50, more preferably 0.5 to 20 parts (c), and 1 to 800 parts (c), preferably 5 to 200, more preferably 5 to 100, and even more preferably 10 to 100 parts (c).

[0031] Examples of wall-forming materials, i.e., resins that constitute the wall film, include urea resins, urethane resins, urea-urethane resins, epoxy resins, melamine resins, benzoguanamine resins, isocyanate resins, and the like.

[0032] Microcapsule pigments may contain various additives, such as antioxidants, ultraviolet absorbers, infrared absorbers, solubilizers, preservatives, and fungicides, to the extent that they do not affect their function.

[0033] Microencapsulated pigments can be manufactured by microencapsulation methods. Examples of conventional microencapsulation methods include isocyanate-based interfacial polymerization, melamine-formaldehyde-based in situ polymerization, liquid curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion-cooling, air suspension coating, and spray drying. These methods are selected appropriately depending on the application. Furthermore, depending on the purpose, a secondary resin coating can be applied to the surface of the microcapsule pigment to provide durability or modify its surface properties for practical use.

[0034] The reversible thermochromic microcapsule pigment or the reversible photochromic microcapsule pigment preferably has a core material:wall film mass ratio of 7:1 to 1:1. By having the core material to wall film mass ratio within the above range, a decrease in color density and vividness during color development can be prevented. More preferably, the core material:wall film mass ratio is 6:1 to 1:1.

[0035] Reversible thermochromic microcapsule pigments or reversible photochromic microcapsule pigments can also be made into microcapsule pigments that exhibit a color change behavior from a first color to a second color by incorporating a non-color-changing coloring agent such as a general dye or pigment into the microcapsule.

[0036] <Resin particles> Examples of resin particles include resin particles containing at least one of the above-mentioned dyes, pigments, thermochromic materials, and photochromic materials.

[0037] Examples of resin particles containing dyes include colored resin particles in which the dye is homogeneously dissolved or dispersed within the resin particles, and colored resin particles in which the dye is deposited onto the resin particles.

[0038] Examples of resin particles containing pigments include colored resin particles in which the pigment is homogeneously dispersed within the resin particles, and colored resin particles in which the surface of the resin particles is coated with pigment. Here, the pigment may be surface-treated by various conventionally known methods for the purpose of improving its dispersibility and adsorption to the resin constituting the resin particles.

[0039] Examples of resin particles containing a thermochromic material or a photochromic material include colored resin particles in which a reversible thermochromic composition is homogeneously dispersed (hereinafter, sometimes referred to as "reversible thermochromic resin particles") and colored resin particles in which a reversible photochromic composition is homogeneously dispersed (hereinafter, sometimes referred to as "reversible photochromic resin particles").

[0040] The resin constituting the resin particles can be any thermoplastic resin or thermosetting resin without any particular limitations. Examples of thermoplastic resins include polystyrene, acrylic resin, polyester, polyvinyl chloride, polybutadiene, polymethyl methacrylate, acrylic-urethane copolymer resin, polyethylene, polypropylene, polyacrylonitrile, polyacetal, ethylene-propylene copolymer resin, ethylene-vinyl acetate copolymer resin, styrene-acrylic copolymer resin, styrene-butadiene copolymer resin, styrene-acrylonitrile copolymer resin, and acrylonitrile-butadiene copolymer resin. Examples of thermosetting resins include epoxy resin, epoxy acrylate resin, xylene resin, toluene resin, guanamine resin, benzoguanamine resin, melamine resin, urethane resin, phenolic resin, alkyd resin, polyamide, polyimide, polyamide ester, urea resin, silicone resin, and unsaturated polyester.

[0041] The resin particles may be solid resin particles with no voids inside, or hollow resin particles with voids inside.

[0042] Resin particles can be produced by pulverization, spray drying, or polymerization in which a dye, pigment, thermochromic material, and photochromic material are polymerized in an aqueous or oily medium. Examples of polymerization methods include suspension polymerization, suspension polycondensation, dispersion polymerization, and emulsion polymerization.

[0043] The shape of the resin particles is not particularly limited and can include spherical, ellipsoidal, or nearly spherical shapes, as well as polygonal and flattened shapes, with spherical resin particles being preferred.

[0044] Reversible thermochromic resin particles or reversible photochromic resin particles can also be made into resin particles that exhibit a color change behavior from a first color to a second color by incorporating non-color-changing colorants such as general dyes or pigments into the resin particles.

[0045] It is preferable to use a reversible thermochromic composition or a reversible photochromic composition as a microcapsule pigment by encapsulating it in microcapsules. This is because encapsulating it in microcapsules allows for the formation of a chemically or physically stable pigment, and furthermore, under various usage conditions, the reversible thermochromic composition or reversible photochromic composition maintains the same composition and can exert the same effects.

[0046] The colorants disclosed herein may be used individually or in combination of two or more.

[0047] When the coloring agent is a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, the average particle size of these coloring agents is not particularly limited, but is preferably in the range of 0.01 to 5 μm, more preferably 0.1 to 3 μm, and even more preferably 0.5 to 3 μm. When the average particle size of the colorant is 5 μm or less, good ink ejection is easily obtained when used in a ballpoint pen, and when the average particle size is 0.01 μm or more, it is easier to obtain high-density color development in the handwriting.

[0048] The average particle diameter was measured using image analysis-based particle size distribution measurement software [Mountec Co., Ltd., product name: MacView] to determine the particle area, calculate the projected area circle equivalent diameter (Heywood diameter) from the area of ​​the particle area, and then measure the average particle diameter of particles equivalent to an equivolute sphere based on that value.

[0049] Furthermore, if the particle size of all or most of the particles exceeds 0.2 μm, it is also possible to measure the average particle size of particles equivalent to equivolute spheres using the Coulter method with a particle size distribution analyzer [Beckman Coulter, Ltd., product name: Multisizer 4e].

[0050] Furthermore, volume-based particle diameter and average particle diameter may be measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name: LA-960V2) that has been calibrated based on the values ​​measured using the above-mentioned software or measuring device using the Coulter method.

[0051] The colorant content is not particularly limited, but is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 3 to 10% by mass, relative to the total amount of water-based ink. By limiting the content to 20% by mass or less, stable ink discharge performance of the writing instrument containing the ink composition can be obtained, and by limiting the content to 0.5% by mass or more, excellent color development of the handwriting can be obtained.

[0052] When the colorant is a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, the content of the colorant relative to the total mass of the ink composition is preferably in the range of 5 to 40% by mass, more preferably 10 to 40% by mass, and even more preferably 10 to 30% by mass. By setting the content to 40% by mass or less, stable ink discharge performance of the writing instrument containing the ink composition can be obtained, and by setting the content to 5% by mass or more, excellent color development of the writing can be obtained, and the color-changing function can also be fully satisfied.

[0053] <Water> There are no particular restrictions on the type of water that can be used; for example, tap water, deionized water, purified water, distilled water, ultrafiltered water, pure water, deep-sea water, groundwater, etc. The water content is not particularly limited, but is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and even more preferably 20 to 85% by mass, relative to the total amount of water-based ink.

[0054] <Hydroxamic acid derivatives> The aqueous ink composition of this disclosure is characterized by comprising a hydroxamic acid derivative represented by the following general formula (1).

[0055] [ka]

[0056] In general formula (1), R 1 It is a hydrocarbon group having 1 to 15 carbon atoms.

[0057] From the standpoint of obtaining a long-term preservative effect, a carbon number of 4 to 12 is preferred, and a carbon number of 6 to 9 is more preferred.

[0058] R 1 The hydrocarbon group may be linear, branched, or cyclic, or a combination of these. Also, R 1 The hydrocarbon group may have an unsaturated bond at its terminal or non-terminal end.

[0059] Examples of hydrocarbon groups include aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, aromatic hydrocarbon groups, and hydrocarbon groups formed by combining these.

[0060] Examples of aliphatic hydrocarbon groups include chain-like hydrocarbon groups such as alkyl groups, alkenyl groups, and alkynyl groups. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, octyl, nonyl, and decyl groups. Examples of alkenyl groups include, but are not limited to, vinyl, propenyl, isopropenyl, butenyl, isobutenyl, tert-butenyl, pentenyl, hexenyl, heptenyl, octinyl, isooctinyl, nonenyl, and decenyl groups.

[0061] The alicyclic hydrocarbon group may be monocyclic or polycyclic. Furthermore, the polycyclic group may be a spirocyclic, fused, or bridging cyclic group. Examples of alicyclic hydrocarbon groups include, but are not limited to, cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl, cyclononyl, cyclodecyl, cyclododecyl, norbornyl, and adamantyl groups, as well as cyclopentenyl, cyclohexenyl, and cycloalkenyl groups.

[0062] Examples of aromatic hydrocarbon groups include aryl groups, and specifically, phenyl, naphthyl, biphenyl, anthrasyl, tolyl, mesityl, benzyl, and phenethyl groups.

[0063] Examples of hydroxamic acid derivatives represented by general formula (1) include, but are not limited to, acetohydroxamic acid, heptanohydroxamic acid, caprylhydroxamic acid, benzohydroxamic acid, naphthohydroxamic acid, biphenylhydroxamic acid, and sorbohydroxamic acid.

[0064] These hydroxamic acid derivatives may be used individually or in combination of two or more.

[0065] The content of the hydroxamic acid derivative is not particularly limited, but is preferably 0.001 to 5% by mass, more preferably 0.01 to 1% by mass, and even more preferably 0.05 to 0.5% by mass, relative to the total amount of aqueous ink.

[0066] <Amine compounds containing a hydroxyl group> The aqueous ink composition for writing instruments of this disclosure may further contain an amine compound having a hydroxyl group (hereinafter optionally referred to as "amine compound" or "amine"). By further including an amine compound having a hydroxyl group in the aqueous ink, the hydroxamic acid derivative represented by general formula (1) can be solubilized, thereby improving the preservative effect in the aqueous ink.

[0067] The amine compounds having a hydroxyl group of this disclosure also include amine compounds having a carboxyl group, and may also be amine compounds having both a carboxyl group and a hydroxyl group other than a carboxyl group.

[0068] The amine compounds of this disclosure may be monoamines, diamines, or triamines. Furthermore, the amine compound may be a salt or a hydrate.

[0069] The amine compound having a hydroxyl group is not particularly limited as long as it solubilizes the hydroxamic acid derivative represented by general formula (1). Examples include monoethanolamine, diethanolamine, triethanolamine, N-methylethanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine, monopropanolamine, isopropanolamine, alaninol, N,N-diisopropanolamine, butanolamine, isobutanolamine, tetrasodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate tetrahydrate, tetrapotassium ethylenediaminetetraacetate, trisodium nitrilotriacetate, trisodium nitrilotriacetate monohydrate, pentasodium diethylenetriaminepentaacetate, hexasodium triethylenetetraaminehexaacetate, tetrasodium L-glutamic acid diacetate, trisodium hydroxyethylethylenediaminetriacetate dihydrate, trisodium hydroxyethylethylenediaminetriacetate, disodium hydroxyethyliminodiacetate, and sodium dihydroxyethylglycine.

[0070] These amine compounds may be used individually or in combination of two or more.

[0071] The content of the amine compound having a hydroxyl group is not particularly limited, but is preferably in the range of 0.01 to 5% by mass, and more preferably in the range of 0.1 to 3% by mass, relative to the total amount of the aqueous ink composition.

[0072] <Other additives> The aqueous ink composition for writing instruments of this disclosure may further contain various additives in the aqueous ink as needed. Examples of additives include shear viscosity reducing agents, water-soluble organic solvents, water-soluble resins, specific gravity adjusters, surfactants, pH adjusters, resin particles, rust inhibitors, wetting agents, viscosity modifiers, bubble absorbers or oxygen absorbers, defoamers, antioxidants, UV absorbers, lubricants, and the like. These additives can be selected from those conventionally used in water-based inks and used as appropriate.

[0073] Furthermore, it may further contain a shear viscosity reducing agent. Examples of shear-thickening agents include xanthan gum, gellan gum, zeta-C gum, dieutan gum, macrophopsis gum, succinoglycans (for example, succinoglycans whose constituent monosaccharides are organic acid-modified heteropolysaccharides of glucose and galactose (average molecular weight of approximately 1 million to 8 million)), guar gum, locust bean gum and its derivatives, alkyl alginates, glucomannan, agar and carrageenan, and other water-soluble polysaccharides such as gelling carbohydrates extracted from seaweed, polymers with a molecular weight of 100,000 to 150,000 mainly composed of alkyl esters of methacrylic acid, poly-N-vinyl carboxylic acid amide crosslinks, benzylidene sorbitol and its derivatives, benzylidene xylitol and its derivatives, alkali-thickening acrylic resins, crosslinkable acrylic acid polymers, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, and metal salts or amine salts of dialkyl sulfosuccinate. These shear-reducing viscosity-imparting agents may be used individually or in combination of two or more types. The content of the shear viscosity reducing agent is not particularly limited, but is preferably 0.01 to 1% by mass, more preferably 0.05 to 0.5% by mass, and even more preferably 0.1 to 0.5% by mass, relative to the total amount of aqueous ink.

[0074] Furthermore, it may also contain conventional, commonly used, water-soluble organic solvents that are compatible with water. Examples of water-soluble organic solvents include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, hexylene glycol, 1,3-butanediol, neoprene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, 2-pyrrolidone, and N-methyl-2-pyrrolidone. The water-soluble organic solvent may be used alone or in combination of two or more types, and its content is not particularly limited, but it is preferably 2 to 60% by mass, and more preferably 5 to 35% by mass, relative to the total amount of water-based ink.

[0075] Furthermore, a pH adjusting agent may be included to adjust the pH to a desired level in accordance with the characteristics of the ink composition. Conventional known acidic and basic substances can be used as pH adjusters. 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. Examples of basic substances include strong alkalis such as sodium hydroxide and potassium hydroxide, and weak alkalis such as sodium carbonate, ammonia, sodium hydrogen phosphate, and potassium hydrogen phosphate.

[0076] Furthermore, it may further contain a bubble absorbent or an oxygen absorbent. Examples of oxygen absorbers include ascorbic acid, ascorbic acid derivatives, natural or synthetic polyphenols, N-vinylpyrrolidone oligomers, kojic acid, hydroxylamines, oxime derivatives, α-glucosylrutin, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, thiourea dioxide, formamidine sulfinate, glutathione, and reaction products of n-butyraldehyde and aniline.

[0077] It may also contain a rust inhibitor. Examples of rust inhibitors include benzotriazole and its derivatives, triazole derivatives, tetrazole derivatives, pyrazole derivatives, pyrazolone derivatives, thiazole derivatives, dicyclohexylammonium nitride, diisopropylammonium nitride, and saponins.

[0078] In addition, water-soluble resins such as alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin may be used as needed; wetting agents such as urea, sorbitol, mannitol, sucrose, glucose, hydrolyzed reduced starch, and sodium pyrophosphate; defoaming agents such as silicone emulsions; and fluorine-based or nonionic surfactants to improve ink penetration may be used. Furthermore, lubricants can be added, and examples include metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-additive cationic surfactants, phosphate ester surfactants, N-acyl amino acid surfactants, dicarboxylic acid-type surfactants, β-alanine-type surfactants, 2,5-dimercapto-1,3,4-thiadiazole and its salts or oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine and their salts. Furthermore, the function in the retractable form can be enhanced by adding thickening inhibitors such as N-vinyl-2-pyrrolidone oligomer, N-vinyl-2-piperidone oligomer, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, and N-vinyl-ε-caprolactam oligomer.

[0079] In addition, general-purpose preservatives or fungicides may be used in combination. Examples of preservatives or fungicides include 2-n-octyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, 4-chloro-3-methylphenol, phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, and sodium 2-pyridinethiol-1-oxide.

[0080] <Writing implements> Examples of writing instruments that can contain the aqueous ink composition of this disclosure include various writing instruments such as ballpoint pens, marking pens, fountain pens, brush pens, and calligraphy pens.

[0081] <Ballpoint pen> When the aqueous ink of this disclosure is applied to a ballpoint pen, the structure and shape of the ballpoint pen are not particularly limited, and it can be used, for example, by filling it into a ballpoint pen refill or ballpoint pen equipped with a ballpoint pen tip and an ink filling mechanism.

[0082] A ballpoint pen tip consists of a tip body and a ball located at the front end of the tip body. Examples of ballpoint pen tips include a tip in which a ball is held in a ball-holding portion formed by pressing the tip area of ​​a metal pipe inward from the outer surface near the tip; a tip in which a ball is held in a ball-holding portion formed by cutting a metal tip body with a drill or the like; a tip in which a resin ball seat is provided inside a metal or plastic tip body; or a tip in which the ball held in the tip is biased forward by a spring.

[0083] The material of the tip body and ball is not particularly limited, and examples include cemented carbide, stainless steel, ruby, ceramic, resin, rubber, etc. Furthermore, the ball may be surface-treated with DLC coating or the like.

[0084] The diameter of the ball is generally in the range of 0.1 to 3.0 mm, preferably 0.2 to 2.0 mm, more preferably 0.2 to 1.5 mm, and even more preferably 0.2 to 1 mm. Ballpoint pens containing the water-based ink of this disclosure provide excellent writing performance without ink smudging, even in ballpoint pens equipped with small diameters such as 0.5mm, 0.4mm, 0.38mm, 0.35mm, 0.3mm, 0.28mm, 0.25mm, and 0.18mm.

[0085] An example of an ink filling mechanism is an ink container that can be directly filled with ink. The ink container can be a molded body made of thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a tubular metal body.

[0086] A ballpoint pen refill can be formed by directly connecting a ballpoint pen tip to an ink reservoir, either via a connecting member, and directly filling the ink reservoir with ink. A ballpoint pen can then be formed by housing this ballpoint pen refill inside the barrel.

[0087] An ink backflow prevention element is filled at the trailing end of the ink that is to be filled into the ink container. Examples of ink backflow prevention devices include liquid stoppers and solid stoppers, and solid stoppers and liquid stoppers may be used in combination.

[0088] The stopper is made of a non-volatile or low-volatility liquid, and examples include petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or co-oligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc. Non-volatile or low-volatility liquids may be used individually or in combination of two or more types.

[0089] For non-volatile or low-volatile liquids, it is preferable to add a thickening agent to increase the viscosity to a suitable level. Examples of thickening agents include, for example, clay-based thickeners such as silica with a hydrophobic surface treatment, fine silica particles with a methylated surface treatment, aluminum silicate, swollen mica, and hydrophobic treated bentonite or montmorillonite; fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate; dextrin compounds such as tripenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax, hydrogenated castor oil, and fatty acid dextrins; and cellulose compounds.

[0090] Examples of solid stoppers include those made of polyethylene, polypropylene, polymethylpentene, and the like.

[0091] Furthermore, the barrel itself can be designed as an ink-filling mechanism. By directly filling the barrel with ink and attaching a ballpoint pen tip to the front end of the barrel, a ballpoint pen equipped with both a ballpoint pen tip and an ink-filling mechanism can be formed.

[0092] If the ink to be filled into the ink filling mechanism is of low viscosity, a ballpoint pen comprising a ballpoint pen tip and an ink filling mechanism may further include an ink supply mechanism. The ink supply mechanism is for supplying the ink to be filled into the ink filling mechanism to the pen tip.

[0093] The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that provides an ink guide core made of a fiber bundle or the like as an ink flow rate regulator and supplies ink to the pen tip via this interposed element; (2) a mechanism that provides a comb-shaped ink flow rate regulator and supplies ink to the pen tip via this interposed element; and (3) a mechanism that provides ink to the pen tip via a pen core in which a number of discs are arranged in parallel with comb-shaped spacing, a slit-shaped ink guide groove that penetrates the discs axially, and a ventilation groove wider than the groove, and an ink guide core that guides ink from the ink filling mechanism to the pen tip is arranged at the axis.

[0094] Specific examples of the configuration of a ballpoint pen containing the aqueous ink of this disclosure include: (1) a ballpoint pen having an ink reservoir filled with ink inside the barrel, to which a ballpoint pen tip is connected directly or via a connecting member, and to which an ink backflow prevention body is filled at the end face of the ink; (2) a ballpoint pen in which ink is directly filled inside the barrel and a mechanism is provided to supply ink to the pen tip by interposing an ink flow control body such as a comb-shaped ink flow control body or an ink guide core made of a fiber bundle as an ink flow control body; and (3) a ballpoint pen in which ink is directly filled inside the barrel and a mechanism is provided to supply ink to the pen tip via the pen core mentioned above.

[0095] <Marking pen> When the aqueous ink of this disclosure is applied to a marking pen, the structure and shape of the marking pen are not particularly limited, and it can be used, for example, by filling a marking pen refill or marking pen that includes a marking pen tip and an ink filling mechanism.

[0096] Examples of marking pen tips include conventional porous materials with interconnected pores selected from a range of approximately 30-70% porosity, such as resin processed fiber bodies, heat-meltable fiber fused bodies, and felt bodies, or extruded synthetic resin bodies having multiple ink outlets extending in the axial direction. One end is processed into a shape according to the purpose, such as a bullet shape, rectangular shape, chisel shape, or pen shape, for practical use.

[0097] An example of an ink filling mechanism is an ink-absorbing body that can be filled with ink. The ink-absorbing material is a fiber bundle formed by gathering crimped fibers in the longitudinal direction, and is constructed by embedding it in a covering such as a plastic cylinder or film, and adjusting the porosity to be in the range of approximately 40-90%.

[0098] A marking pen can be formed by housing an ink-impregnated ink-absorbing body inside the barrel, and connecting a marking pen tip to the barrel, either directly or via a connecting member, so as to connect to the ink-absorbing body.

[0099] Furthermore, a marking pen refill can be formed by housing an ink-impregnated ink reservoir in an ink container, and connecting a marking pen tip to the ink reservoir, either directly or via a connecting member. A marking pen can then be formed by housing this marking pen refill in a barrel.

[0100] For the ink container, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body can be used.

[0101] A marking pen comprising a marking pen tip and an ink filling mechanism may further include an ink supply mechanism. The ink supply mechanism supplies the ink composition to be filled into the ink filling mechanism to the pen tip.

[0102] The ink supply mechanism is not particularly limited, and examples include, in addition to the ink supply mechanism provided in the ballpoint pen described above, (4) a mechanism that provides an ink flow rate regulator by a valve mechanism and supplies ink to the pen tip when the valve is opened. The valve mechanism can use a conventional pumping type that opens when pressed by the tip, and it is preferable that the spring pressure is set to allow it to be opened by the pressure of a pen.

[0103] If the marking pen is equipped with an ink supply mechanism, in addition to the ink absorbent described above, an ink container that can be directly filled with ink may be used as the ink filling mechanism. Alternatively, the barrel itself may be used as the ink filling mechanism to directly fill the ink.

[0104] Specific examples of the configuration of a marking pen containing the aqueous ink of this disclosure include: (1) a marking pen in which a marking pen tip made of a fiber processed body or resin molded body, in which ink is impregnated into an ink absorbent body made of a fiber bundle and housed in a barrel, and in which capillary gaps are formed, is connected to the barrel directly or via a connecting member so as to connect the ink absorbent body and the tip; (2) a marking pen in which ink is directly filled into the barrel and a mechanism is provided to supply ink to the pen tip by interposing an ink guide core made of a comb-groove-shaped ink flow regulator or a fiber bundle as an ink flow regulator; (3) a marking pen in which ink is directly filled into the barrel and a mechanism is provided to supply ink to the pen tip via the pen core described above; and (4) a marking pen in which the tip and an ink absorbent body are provided via a valve mechanism that opens when the tip is pressed, and ink is directly filled into the ink absorbent body.

[0105] If the ballpoint pen or marking pen of this disclosure is directly filled with ink, an agitator or stirring element, such as an agitating ball or agitating bar, may be incorporated into the ink container or barrel in which the ink is filled, in order to facilitate the redispersion of the colorant. The shape of the stirring body or stirring bar is not particularly limited and can be changed; for example, a spherical body, a rod-shaped body, etc. The material of the stirring body is not particularly limited, and examples include metal, ceramic, resin, glass, etc.

[0106] The writing instrument described herein, such as a ballpoint pen or marking pen, may also be provided with a removable ink cartridge. In this case, after the ink contained in the ink cartridge of the writing instrument is used up, the writing instrument can be used again by replacing it with a new ink cartridge. Ink cartridges can be either those that connect to the writing instrument body and also serve as the barrel of the writing instrument, or those that cover and protect the barrel (rear barrel) after being connected to the writing instrument body. In the latter case, the ink cartridge may be used alone, or the writing instrument body and ink cartridge may be connected before use, or the ink cartridge may be housed in the barrel in an unconnected state so that the user can connect it when using the writing instrument to begin use.

[0107] The ballpoint pen or marking pen or other writing instrument described herein may be equipped with a cap to make it a capped writing instrument. By attaching a cap so as to cover the pen tip (writing tip), it is possible to prevent the writing tip from becoming contaminated or damaged.

[0108] Furthermore, writing instruments such as ballpoint pens or marking pens in which the refill is housed inside the barrel may be equipped with a retractable mechanism to create a retractable writing instrument. The retractable mechanism is provided inside the barrel and allows the writing tip to extend and retract from the barrel, preventing contamination and damage to the writing tip.

[0109] Any retractable writing instrument can be used if its tip is housed inside the barrel and exposed to the outside air, and the tip protrudes from the barrel opening when the retraction mechanism is activated. Furthermore, it can also be a composite type of retractable writing instrument that houses multiple refills within the barrel, and the writing tip of any of the refills is extended or retracted from the barrel opening by the operation of a retractable mechanism.

[0110] Examples of retractable / retractable mechanisms include: (1) a side-slide type retractable / retractable mechanism in which an operating part (clip) that can move in the front-rear direction is provided protruding radially outward from the rear side wall of the barrel, and the writing tip is extended and retracted from the front end opening of the barrel by sliding the operating part forward; (2) a rear-end knock type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by pressing an operating part provided at the rear end of the barrel forward; (3) a side-knock type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by pressing an operating part that protrudes from the outer surface of the barrel side wall radially inward; and (4) a rotary type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by rotating an operating part at the rear of the barrel.

[0111] The form of ballpoint pens and marking pens is not limited to the configuration described above, and may also be multi-function writing instruments (double-ended or retractable tip type, etc.). Examples of multi-function writing instruments include (1) writing instruments equipped with tips of different shapes, (2) writing instruments equipped with tips that dispense ink of different tones or hues, and (3) writing instruments equipped with tips of different shapes, in addition to the fact that the ink dispensed from each tip is of different tones or hues.

[0112] When the coloring agent includes reversible thermochromic microcapsule pigments or reversible thermochromic resin particles, the writing formed on the writing surface using a writing instrument containing the ink composition of this disclosure can be discolored by rubbing with a finger or by using a heating or cooling device.

[0113] Examples of heating devices include electrically heated color change devices equipped with resistance heating elements such as PTC elements, heated color change devices filled with a medium such as hot water, heated color change devices using steam or laser light, and the application of a hair dryer. However, friction members or friction bodies are preferred because they can change color by a simple method.

[0114] Cooling devices include electrically charged cooling devices using Peltier elements, cooling devices filled with refrigerants such as cold water or ice chips, cold storage agents, and applications of refrigerators and freezers.

[0115] As the friction member or friction body, an elastic material such as an elastomer or plastic foam is preferred, which is highly elastic and can generate appropriate friction and frictional heat when rubbed. However, plastic molded bodies, stone, wood, metal, cloth, etc., can also be used. Although it is also possible to rub off the pencil marks using a general eraser, eraser residue is generated when rubbing, so the above-mentioned friction members and friction bodies that generate almost no eraser residue are preferably used.

[0116] Examples of materials for friction members and friction bodies include silicone resin, styrene-ethylene-butylene-styrene block copolymer (SEBS resin), and the like.

[0117] The friction member or friction body described above may be a separate component of any shape from the writing instrument, but by attaching it to the writing instrument, portability can be improved. Furthermore, a writing instrument set can be obtained by combining a writing instrument with a separate friction member or friction body of any shape.

[0118] In the case of writing instruments equipped with a cap, the location where a friction member or friction body is provided is not particularly limited. For example, the cap itself may be formed from a friction member, the barrel itself from a friction member, or, if a clip is provided, the clip itself may be formed from a friction member, or a friction member or friction body may be provided at the tip (top) of the cap or the rear end of the barrel (the part without a writing tip).

[0119] In the case of writing instruments equipped with a retractable mechanism, the location where a friction member or friction body is provided is not particularly limited. For example, the barrel itself may be formed from a friction member, or if a clip is provided, the clip itself may be formed from a friction member, or a friction member or friction body may be provided near the barrel opening, at the rear end of the barrel (the part without a writing tip), or at the knock mechanism. [Examples]

[0120] Examples are described below, but the present invention is not limited to these examples. Table 1 shows the compositions of the water-based inks for writing instruments in the examples and comparative examples. Note that the composition values ​​in the table represent parts by mass.

[0121] [Table 1]

[0122] The contents of the raw materials listed in the table are explained according to the footnote numbers. (1) Red dye [CI Acid Red 92, manufactured by Hodogaya Chemical Industry Co., Ltd., product name: Phloxine] (2) A microcapsule pigment containing a reversible thermochromic composition consisting of (a) 4.5 parts of 2-(2-chloroanilino)-6-di-n-butylaminofluorane, (b) 4.5 parts of 1,1-bis(4′-hydroxyphenyl)n-decane and 7.5 parts of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane, and (c) 50.0 parts of 4-benzyloxyphenylethyl caprate (T1: -20℃, T2: -9℃, T3: 40℃, T4: 57℃, ΔH: 63℃, average particle size: 2.5 μm, changes color from black to colorless). (3) Triethanolamine (4) Ethylenediaminetetraacetate tetrasodium salt tetrahydrate (5) Diethanolamine (6) Phosphate ester surfactant [Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Prysurf A219B]

[0123] <Preparation of Pigment Dispersion> A blue pigment dispersion was prepared by mixing 22 parts of pigment [PigmentBlue15:3B], 5 parts of dispersant [BIC Chemie Japan Co., Ltd., product name: DISPERBYK-167], and 73 parts of water, and stirring the mixture at 20°C for 1 hour using a bead mill.

[0124] <Ink preparation> A writing instrument aqueous ink composition was obtained by mixing the raw materials in the proportions specified in the examples and comparative examples, and stirring at 20°C for 3 hours.

[0125] <Preservative efficacy test> The preservative efficacy test was conducted and evaluated in accordance with the preservative efficacy test described in the reference information of the "18th Revised Japanese Pharmacopoeia". Specifically, test samples were obtained by inoculating various test bacterial solutions into a prepared aqueous ink composition for writing instruments and mixing them uniformly. Each test sample was stored for 7 days in a light-shielded environment at 25°C, and the number of viable bacteria in the test sample was measured. The preservative efficacy was evaluated based on the increase or decrease in the number of viable bacteria. The test organisms used were two types of bacteria, Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), and two types of fungi, Candida albicans (C. albicans) and Aspergillus brasiliensis (A. braziliensis). The evaluation results are shown in Table 1. A: A significant decrease in the number of viable bacteria was observed after 7 days. B: A decrease in the number of viable bacteria was observed after 7 days. C: No change was observed in the number of viable bacteria after 7 days. D: An increase in the number of viable bacteria was observed after 7 days.

[0126] <Preparation of the ink backflow prevention device> An ink backflow prevention body was obtained by adding 1.5 parts of fatty acid amide as a thickening agent to 98.5 parts of polybutene as a base oil, and then kneading the mixture using a three-roll machine.

[0127] <Making a ballpoint pen> A ballpoint pen refill was prepared by filling a ballpoint pen refill, in which a stainless steel tip holding a 0.4 mm diameter cemented carbide ball was fitted to one end of a polypropylene pipe, with the aqueous ink compositions for writing instruments of Examples 1-8 and Comparative Examples 1-3, which had been inoculated with the test bacterial solution used in the preservative efficacy test. After placing the ink backflow prevention body at the rear end, the ballpoint pen refill was assembled into the barrel to create a sample ballpoint pen.

[0128] <Written Exam 1> Using each sample ballpoint pen that had been left at 25°C for 7 days, the condition of the handwriting was visually examined when 12 spiral circles were continuously written in a single line on report paper (writing paper A conforming to JIS P3201). The test results are shown in Table 1. A: Good handwriting can be obtained. B: There was some slight smudging at the beginning of writing, but it was not a problem for practical use. C: The handwriting shows smudging and skipped lines.

[0129] The results of written test 1 confirmed that including a hydroxamic acid derivative in the water-based ink provides a preservative effect, preventing smudging and skipping of lines.

[0130] <Making a marking pen> The aqueous ink compositions for writing instruments of Example 9 and Comparative Example 4, which were inoculated with the test bacterial solution used in the preservative efficacy test, were impregnated into an ink-absorbing body made of polyester sliver coated with a synthetic resin film, respectively. These bodies were then housed in a polypropylene barrel, and a resin-processed pen body (chisel type) made of polyester fiber was attached to the tip of the barrel via a resin holder to connect it to the ink-absorbing body. A cap was then attached to create a sample marking pen.

[0131] <Written Exam 2> The condition of the handwriting was visually inspected when each sample was marked with a marking pen that had been left at 25°C for 7 days, and then handwritten in a straight line on report paper (writing paper A conforming to JIS P3201). The test results are shown in Table 1. A: Good handwriting can be obtained. B: There was some slight smudging at the beginning of writing, but it was not a problem for practical use. C: The handwriting shows smudging and gaps.

[0132] These results confirm that the product can be applied to all types of water-based inks, regardless of the writing instrument (such as ballpoint pens or markers), and that it provides a preservative effect.

Claims

1. A water-based ink composition for writing instruments comprising a coloring agent, water, and a hydroxamic acid derivative represented by general formula (1). 【Chemistry 1】 (In the formula, R １ (This represents a hydrocarbon group with 1 to 15 carbon atoms.)

2. The aqueous ink composition for writing instruments according to claim 1, wherein the content of the hydroxamic acid derivative is 0.01 to 1% by mass with respect to the total amount of the aqueous ink composition.

3. The aqueous ink composition for writing instruments according to claim 1 or 2, further comprising an amine compound having a hydroxyl group.

4. A writing instrument containing the aqueous ink composition for writing instruments described in any one of claims 1 to 3.

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