Aqueous ink composition and writing instrument

Abstract

Provided are: an aqueous ink composition capable of suppressing an increase and a decrease in the pH of the aqueous ink composition due to a change over time and suppressing an increase in bubbles in the aqueous ink composition, thereby capable of maintaining good writing properties stably over a long period of time; and a writing instrument equipped with the aqueous ink composition. The aqueous ink composition is blended with a specific phenol compound. Specifically, the present invention provides an aqueous ink composition which contains a coloring material, water and a phenol compound represented by formula (1) and containing at least one chlorine atom as a substituent. (In the formula (1), R1, R2, R3, R4, and R5 are each independently a hydrogen atom, a chlorine atom, or a C1-C4 alkyl group, and at least one among R1, R2, R3, R4, and R5 is a chlorine atom.)

Description

Water-based ink composition and writing instrument

[0001] The present invention relates to an aqueous ink composition and a writing instrument equipped with the aqueous ink composition.

[0002] Traditionally, water-based ballpoint pens containing water-based ink compositions have a lifespan of several months to several years between the manufacture of the ink composition and its complete consumption by the user. Under these circumstances, if the physical properties of the ink composition change during this period, the quality of the writing instrument, particularly its writing characteristics, may not be maintained over the long term.

[0003] The writing performance of writing instruments containing water-based ink compositions may deteriorate due to various factors. For example, if the pH of the water-based ink composition increases over time, the metal components of the pen tip may corrode, causing skipping or streaking. On the other hand, if the pH of the water-based ink composition decreases, the dyes and other components contained in the water-based ink composition may become unable to dissolve, crystallize, and clog the pen tip, reducing writing performance.

[0004] Under these circumstances, in order to maintain the stability of pH over time, Patent Document 1 proposes incorporating a specific compound into the ink composition along with amines as pH adjusters. Patent Document 1 proposes an aqueous ink composition for writing instruments containing at least one of phosphonobutanetricarboxylic acid and its salts, and amines.

[0005] Another factor that reduces the writing performance of writing instruments equipped with water-based ink compositions is the generation of air bubbles in the water-based ink composition over time. When the number of air bubbles in the water-based ink composition increases, the generated air bubbles obstruct the flow of ink, hindering the supply of ink to the pen tip, and when the air bubbles move to the pen tip, they cause skipping during writing.

[0006] In response to this, it has been proposed to add a bubble inhibitor to the ink composition in order to suppress the generation of bubbles within the ink composition. For example, Patent Document 2 proposes a technique of adding ascorbic acid as a bubble inhibitor to an aqueous ink composition.

[0007] JP 2014-43481 A JP 3-275778 A

[0008] According to Patent Document 1, the decrease in pH of the ink composition over time can be suppressed. However, the increase in pH of the ink composition over time has not yet been sufficiently suppressed.

[0009] Furthermore, while the aqueous ink composition containing ascorbic acid described in Patent Document 2 achieves a degassing effect, the high reactivity of ascorbic acid itself may affect the dispersibility of pigments and other components in the composition. Specifically, the ascorbic acid may cause aggregation or sedimentation of pigments and other components in the ink composition.

[0010] The present invention has been made in view of the above, and aims to provide an aqueous ink composition and a writing instrument equipped with the aqueous ink composition that can suppress the rise and fall of the pH of the aqueous ink composition due to changes over time, and suppress the increase of air bubbles in the aqueous ink composition, thereby maintaining good writing performance stably over a long period of time.

[0011] The inventors diligently conducted research to achieve the above objective. They discovered that by incorporating a specific phenolic compound into an aqueous ink composition, good writing performance can be stably maintained over a long period of time, thus completing the present invention.

[0012] In other words, the present invention includes the following embodiments.

[0013] The present invention relates to an aqueous ink composition comprising a colorant, water, and a phenol compound represented by the following formula (1) which contains at least one chlorine atom as a substituent.

[0014] In formula (1), R １ , R ２ , R ３ , R ４ , and R 5 Each of these is independently a hydrogen atom, a chlorine atom, or an alkyl group having 1 to 4 carbon atoms, and R １ , R ２ , R ３ , R４ and R 5 At least one of them is a chlorine atom.

[0015] The phenol compound is preferably represented by the following formula (2).

[0016] In formula (2), R ６ and R ７ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X １ , X ２ , and X ３ are each independently a hydrogen atom or a chlorine atom, and at least one of X １ , X ２ , and X ３ is a chlorine atom.

[0017] The phenol compound is preferably represented by the following formula (3).

[0018] In formula (3), X ４ and X ５ are each independently a hydrogen atom or a chlorine atom.

[0019] The phenol compound is preferably at least one selected from the group consisting of 4-chloro-3-methylphenol, 4-chloro-3,5-dimethylphenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol.

[0020] The content of the phenol compound is preferably 0.01% by mass or more and 7.0% by mass or less based on the total amount of the aqueous ink composition.

[0021] The content of the water is preferably 10% by mass or more based on the total amount of the aqueous ink composition.

[0022] The aqueous ink composition preferably has a dissolved oxygen concentration (%O ２ ) of 1.5 mg / L or less after storage at 25°C for 3 months.

[0023] The aqueous ink composition preferably has a change in pH over time from the initial value after storage at 50°C for 3 months of 0.5 or less.

[0024] Another aspect of the present invention is a writing instrument equipped with the aqueous ink composition of the present invention.

[0025] The aqueous ink composition of the present invention can suppress increases and decreases in pH over time, and can also suppress the increase of air bubbles in the aqueous ink composition. As a result, writing instruments equipped with the aqueous ink composition of the present invention can maintain good writing performance stably over a long period of time.

[0026] <Aqueous Ink Composition> The aqueous ink composition of this disclosure is intended for use in writing instruments and the like, and comprises at least a colorant, water, and a phenol compound having at least one chlorine atom as a substituent represented by the following formula (1).

[0027] In formula (1), R １ , R ２ , R ３ , R ４ , and R ５ Each of these is independently a hydrogen atom, a chlorine atom, or an alkyl group having 1 to 4 carbon atoms, and R １ , R ２ , R ３ , R ４ , and R 5 At least one of them is a chlorine atom.

[0028] <Dissolved oxygen concentration after storage at 25°C for 3 months> Dissolved oxygen concentration (%O) of the aqueous ink composition of this disclosure after storage at 25°C for 3 months ２ The dissolved oxygen concentration (%O) after storage at 25°C for 3 months is preferably 1.5 mg / L or less. ２ If the concentration is 1.5 mg / L or less, the amount of dissolved air in the ink composition is sufficiently small, which can suppress the generation of bubbles and reduce smudging during writing.

[0029] In this specification, the dissolved oxygen concentration (%O) in the aqueous ink composition is defined as follows: ２ The dissolved oxygen concentration (%O) was measured using a needle-type oxygen concentration meter MicroxTX3 (PreSense). ２ This value indicates the oxygen concentration among the air (bubbles) dissolved in the aqueous ink composition.

[0030] Dissolved oxygen concentration (%O) of aqueous ink composition after storage at 25°C for 3 months ２ The amount is more preferably 1.4 mg / L or less, even more preferably 1.3 mg / L or less, even more preferably 1.2 g / L or less, particularly preferably 1.1 mg / L or less, and most preferably 1.0 mg / L or less.

[0031] <Changes in pH over time> The aqueous ink composition of this disclosure preferably has a pH change of 0.5 or less from the initial level after being stored at 50°C for three months. If the pH change after being stored at 50°C for three months is 0.5 or less, it is possible to suppress corrosion of the metal constituting the pen tip, etc., due to an increase in pH. Furthermore, a decrease in pH can prevent components such as dyes contained in the aqueous ink composition from dissolving, and the phenomenon of dyes etc. crystallizing and clogging the pen tip can be suppressed. As a result, writing instruments equipped with the aqueous ink composition of this disclosure can maintain good writing performance stably over a long period of time.

[0032] In this specification, the change in pH from the initial state after storage at 50°C for three months (hereinafter also referred to as "pH change over time") is determined by the following method. First, the pH of the prepared aqueous ink composition at 25°C is measured and set as the initial pH. Next, the aqueous ink composition is filled into a glass bottle with a lid and stored at 50°C for three months, after which the pH at 25°C is measured and set as the pH after time has passed. Then, the absolute value obtained by subtracting the pH after time has passed from the initial pH is defined as the "pH change".

[0033] Furthermore, in this specification, pH was measured using a HORIBA pH / ION METER F-23 (HORIBA Corporation).

[0034] The change in pH over time after storage of the aqueous ink composition at 50°C for 3 months is more preferably 0.45 or less, even more preferably 0.40 or less, particularly preferably 0.35 or less, and most preferably 0.30 or less.

[0035] <Phenol Compound> [Structure of Phenol Compound] The phenol compound represented by formula (1) above, which is an essential component of the aqueous ink composition of this disclosure, contains at least one chlorine atom as a substituent. The position of the substituted chlorine atom is not particularly limited and may be, for example, the ortho, meta, or para position.

[0036] In formula (1), R １ , R ２ , R ３ , R ４ , and R 5 Examples of alkyl groups having 1 to 4 carbon atoms include methyl, ethyl, propyl, butyl, isopropyl, isobutyl, and tert-butyl groups. Among these, alkyl groups having 1 or 2 carbon atoms are preferred, and methyl groups are particularly preferred.

[0037] The phenol compound represented by formula (1) above, which is an essential component of the aqueous ink composition of this disclosure, may be a single compound or two or more compounds may be used in combination.

[0038] The aqueous ink composition of this disclosure contains a phenol compound represented by formula (1) above, which suppresses the rise and fall of pH over time and suppresses the generation of bubbles in the aqueous ink composition. As a result, a writing instrument equipped with the aqueous ink composition of this disclosure can maintain good writing performance stably over a long period of time.

[0039] The phenol compound represented by formula (1) above is more preferably represented by the following formula (2).

[0040] In formula (2), R ６ , and R ７ Each is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X １ , X ２ , and X ３ Each of these is independently a hydrogen atom or a chlorine atom, and X １ , X ２ , and X ３ At least one of them is a chlorine atom.

[0041] In formula (2), R ６ and R ７ Examples of alkyl groups having 1 to 4 carbon atoms include methyl, ethyl, propyl, butyl, isopropyl, isobutyl, and tert-butyl groups. Among these, alkyl groups having 1 or 2 carbon atoms are preferred, and methyl groups are particularly preferred.

[0042] Among the phenol compounds represented by the above formula (2), it is preferable that at least one is selected from the group consisting of 4-chloro-3-methylphenol and 4-chloro-3,5-dimethylphenol, from the viewpoint of being readily available and exhibiting stable effects.

[0043] The phenol compound represented by formula (1) above is more preferably represented by the following formula (3).

[0044] In formula (3), X ４ and X ５ These are, independently, a hydrogen atom or a chlorine atom.

[0045] Among the phenol compounds represented by the above formula (3), it is preferable that at least one is selected from the group consisting of 2,4-dichlorophenol and 2,4,6-trichlorophenol, from the viewpoint of being readily available and exhibiting stable effects.

[0046] Therefore, the phenol compound represented by formula (1) above, which is an essential component of the aqueous ink composition of this disclosure, is preferably at least one selected from the group consisting of 4-chloro-3-methylphenol, 4-chloro-3,5-dimethylphenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol.

[0047] [Phenol compound content] The content of the phenol compound represented by formula (1) above, which is an essential component of the aqueous ink composition of this disclosure, is preferably 0.01% by mass or more and 7.0% by mass or less of the total aqueous ink composition.

[0048] The effects of the present invention can be achieved at a higher level by having a phenol compound content of 0.01% by mass or more and 7.0% by mass or less relative to the entire aqueous ink composition.

[0049] The content of the phenol compound represented by formula (1) above may be 0.05% by mass or more, 0.1% by mass or more, 0.5% by mass or more, 0.8% by mass or more, 1.0% by mass or more, 1.2% by mass or more, 1.5% by mass or more, 1.8% by mass or more, 2.0% by mass or more, 2.3% by mass or more, or 2.5% by mass or more, relative to the entire aqueous ink composition.

[0050] On the other hand, the content of the phenol compound represented by formula (1) above may be 6.5% by mass or less, 6.0% by mass or less, 5.5% by mass or less, 5.0% by mass or less, 4.5% by mass or less, or 4.0% by mass or less, relative to the entire aqueous ink composition. Furthermore, if the content of the phenol compound represented by formula (1) above is 6.0% by mass or less, relative to the entire aqueous ink composition, a writing instrument equipped with the aqueous ink composition of this disclosure can maintain good writing performance stably over a long period of time at a higher level.

[0051] <Colorants> The aqueous ink composition of this disclosure contains a colorant as an essential component. By including a colorant in the aqueous ink composition, the aqueous ink composition can be colored to any desired color.

[0052] The colorants contained in the aqueous ink compositions of this disclosure are not particularly limited, and known colorants used in writing instruments can be applied. Examples of colorants incorporated into the aqueous ink compositions of this disclosure include dyes, pigments, colored resin particles, and particles containing at least one of a dye and a pigment.

[0053] Here, the dyes and pigments may be organic or inorganic. Furthermore, multiple types of colorants may be used in the aqueous ink composition of this disclosure, and two or more types may be used in combination from among dyes, pigments, colored resin particles, and particles containing at least one of the dyes and pigments.

[0054] [Dyes] The dyes applicable to the aqueous ink compositions of this disclosure are not particularly limited and may be any dyes that dissolve or disperse in water. Among these, dyes that dissolve in water are preferred because they allow for greater enjoyment of the effects of the present invention. Specifically, according to the present invention, the phenomenon in which dissolved dyes precipitate and crystallize due to an increase in the pH of the aqueous ink composition over time, causing the pen tip to clog and reducing writing performance, can be suppressed.

[0055] [Pigments] The pigments applicable to the aqueous ink compositions of this disclosure are not particularly limited, and pigments known in the field of writing instruments can be used. Furthermore, the pigments may be organic pigments or inorganic pigments.

[0056] Examples of inorganic pigments include carbon black, lead sulfate, lead yellow, zinc yellow, red iron oxide, cadmium red, Prussian blue, ultramarine blue, Prussian blue, chromium oxide green, cobalt green, amber, titanium black, and synthetic iron black.

[0057] Examples of organic pigments include azo, phthalocyanine, quinacridone, isoindolinone, imidazolon, diketopyrrolopyrrole, dioxazine, and perinone.

[0058] [Colored Resin Particles] The colored resin particles applicable to the aqueous ink composition of this disclosure are not particularly limited, and particles known in the field of writing instruments can be used. Examples of colored resin particles applicable to the aqueous ink composition of this disclosure include particles obtained by granulating a resin in which at least one of a dye and a pigment is mixed, and particles obtained by impregnating resin particles with a dye or the like.

[0059] [Particles containing at least one of a dye and a pigment] The particles containing at least one of a dye and a pigment that can be applied to the aqueous ink compositions of this disclosure are not particularly limited, and particles known in the field of writing instruments can be applied. Examples of particles containing at least one of a dye and a pigment that can be applied to the aqueous ink compositions of this disclosure include thermochromic particles, photochromic particles, and composite particles thereof.

[0060] Examples of thermochromic particles include particles produced by microencapsulating a thermochromic composition that contains at least a leuco dye that functions as a color developer, a color developer that is a component capable of causing the leuco dye to develop color, and a color change temperature regulator that can control the color change temperature in the color development of the leuco dye and the color developer.

[0061] Examples of photochromic particles include particles composed of at least one selected from photochromic dyes and fluorescent dyes and a resin such as a terpene phenol resin, and particles produced by microencapsulating a photochromic composition containing at least one selected from photochromic dyes and fluorescent dyes, an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers.

[0062] <Water> The aqueous ink compositions of this disclosure contain water as an essential component. The water applicable to the aqueous ink compositions of this disclosure is not limited to any particular dissolved oxygen concentration, but can be any water that is used in the field of writing instruments.

[0063] Examples of water included as an essential component in the aqueous ink composition of this disclosure include tap water, purified water, distilled water, ion-exchanged water, and pure water.

[0064] In the aqueous ink composition of this disclosure, the water content, which is an essential component, is preferably 10% by mass or more of the total aqueous ink composition. If the water content is 10% by mass or more of the total aqueous ink composition, the effects of the present invention can be enjoyed to the fullest extent. Specifically, it is possible to suppress the rise and fall of the pH of the aqueous ink composition due to changes over time, and to suppress the increase of air bubbles in the aqueous ink composition, thereby realizing a writing instrument that can stably maintain good writing performance over a long period of time.

[0065] Furthermore, there is no particular upper limit to the water content in an aqueous ink composition. It can be set as appropriate depending on the amount of the necessary components blended into the aqueous ink composition.

[0066] <Other Components> In addition to the essential components described above, the aqueous ink composition of this disclosure may contain other components necessary for writing instruments. Examples of other components include water-soluble solvents, and, to the extent that they do not impair the effects of the present invention, dispersants, lubricants, surfactants, solubilizers, thickeners, pH adjusters, rust inhibitors, preservatives, antibacterial agents, etc.

[0067] In particular, the aqueous ink composition of this disclosure may contain various alcohols such as ethanol, or solubilizers such as ether, for the purpose of increasing the solubility of the phenol compound represented by formula (1) in water.

[0068] Furthermore, the aqueous ink composition of this disclosure has a shear rate of 383 sec. －１ If the viscosity (at 25°C) is 80 mPa·s or less, and the surface tension is between 15 mN / m (25°C) and 60 mN / m (25°C), then the writing properties on paper will be good. The viscosity was measured using an EMD viscometer (Tokyo Keiki Co., Ltd.) at a shear rate of 383 sec. －１ The ink viscosity (mPa·s) was measured at a temperature of 25°C, and the surface tension (25°C) was measured using a surface tension measuring device: CBVP-Z (Kyowa Interface Science Co., Ltd.).

[0069] ≪Writing Instruments≫ Another disclosure is a writing instrument equipped with the aqueous ink composition of this disclosure. The writing instrument is not particularly limited and includes, for example, ballpoint pens, marking pens, etc., which have a pen tip such as a ballpoint pen tip, fiber tip, felt tip, plastic tip, fiber core, porous core, etc.

[0070] <Ballpoint pen> A ballpoint pen equipped with the aqueous ink composition of this disclosure means a pen having a mechanism that causes ink stored in an ink reservoir to seep out by the rotation of a ball provided in the writing section.

[0071] For example, a ballpoint pen equipped with the aqueous ink composition of this disclosure comprises an ink reservoir (refill) having a ball with a diameter of 0.18 mm or more and 2.0 mm or less, an ink follower, a joint, and a pen tip. The aqueous ink composition of this disclosure is used when contained in the ink reservoir (refill).

[0072] The ink follower is a liquid that is incompatible with the aqueous ink composition of this disclosure contained in the ink container and has a lower specific gravity than the aqueous ink composition, such as polybutene, silicone oil, mineral oil, or synthetic hydrocarbon oil.

[0073] <Marking Pen> A marking pen equipped with the aqueous ink composition of this disclosure means a pen having a mechanism that supplies ink stored in an ink reservoir to a resin writing section by capillary action, and also includes pens referred to as felt-tip pens.

[0074] The structure of a writing instrument equipped with the aqueous ink composition of this disclosure is not particularly limited. For example, it may be a direct-ink type ballpoint pen, marking pen, or other writing instrument equipped with a collector structure (ink holding mechanism) in which the barrel itself serves as the ink reservoir and the aqueous ink composition of this disclosure is filled into the barrel.

[0075] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0076] <Materials for the aqueous ink composition> The materials for the aqueous ink composition used in the examples and comparative examples are shown below.

[0077] [Phenol compounds] 4-chloro-3-methylphenol, 4-chloro-3,5-dimethylphenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, phenol

[0078] [Colorants] ・Carbon black: MCF88 (Mitsubishi Chemical Corporation) ・Water-soluble dye: Water Black 191L ​​(Orient Chemical Industry Co., Ltd.) ・Colored resin particles: Pink, NKW3207E (Nippon Fluorescent Co., Ltd.) ・Leuco dye-encapsulated particles: Black, thermochromic microcapsule pigment (3 μm)

[0079] [Solvents] ・Ion-exchanged water ・Glycerin ・Propylene glycol

[0080] [Dispersant] ・Joncryl 60J

[0081] [Solubilizer] ・Ethanol

[0082] [Bubble inhibitor] • N-vinyl-2-pyrrolidone oligomer

[0083] [Rust inhibitor] ・Benzotriazole

[0084] [pH adjuster] Triethanolamine

[0085] [Thickening agent] Xanthan gum: KELZNS (Sansho Co., Ltd.)

[0086] [Lubricant] • Phosphate ester: Phosphanol RB-410 (Toho Chemical Co., Ltd.)

[0087] <Examples 1 to 17, Comparative Examples 1 to 2> [Preparation of Aqueous Ink Compositions] An aqueous solvent consisting of deionized water and a mixture of glycerin and / or propylene glycol was mixed with a colorant, a phenol compound, a pH adjuster, a bubble inhibitor, a rust inhibitor, a thickener, and a lubricant in the combinations and mass ratios shown in Table 1 (100% by mass in total, for emulsions etc., the mass percentage of solids). The mixtures were thoroughly mixed using a homomixer to prepare an aqueous ink composition.

[0088] [Evaluation of Aqueous Ink Compositions] The physical properties of the prepared aqueous ink compositions were evaluated using the following method. The results are shown in Tables 1 and 2.

[0089] (Dissolved oxygen concentration after 3 months of storage) Each prepared aqueous ink composition was filled into a glass bottle with a lid and stored at 25°C for 3 months. The dissolved oxygen concentration (%O) was then measured at a temperature of 25°C. ２ The dissolved oxygen concentration (%) was measured using a needle-type oxygen meter MicroxTX3 (PreSense). ２ This value indicates the oxygen concentration among the air (bubbles) dissolved in the aqueous ink composition.

[0090] The evaluation criteria are as follows: A: Dissolved oxygen concentration is 1.5 mg / L or less B: Dissolved oxygen concentration is greater than 1.5 mg / L and less than 3.5 mg / L C: Dissolved oxygen concentration is 3.5 mg / L or more

[0091] (Change in pH over time) The pH of each prepared aqueous ink composition was measured at 25°C and recorded as the initial pH. Then, each aqueous ink composition was filled into a glass bottle with a lid and stored at 50°C for 3 months. After storage, the pH at 25°C was measured and recorded as the pH after time. The absolute value obtained by subtracting the pH after time from the initial pH was calculated and recorded as the change in pH over time. The pH was measured using a HORIBA pH / ION METER F-23 (HORIBA Corporation).

[0092] The evaluation criteria are as follows: A: The change in pH over time from the initial state after 3 months of storage is 0.5 or less. B: The change in pH over time from the initial state after 3 months of storage is greater than 0.5 and less than 1.2. C: The change in pH over time from the initial state after 3 months of storage is 1.2 or more.

[0093] [Manufacturing of Writing Instruments] Water-based ballpoint pens were manufactured using each of the prepared water-based ink compositions. Specifically, the barrel of a ballpoint pen (Mitsubishi Pencil Co., Ltd., product name: Signo UM-100) was used, and a polypropylene ink reservoir tube with an inner diameter of 4.0 mm and a length of 113 mm, a stainless steel tip (carbide ball, ball diameter 0.7 mm), and a connector were prepared. An empty refill was made by connecting the ink reservoir tube and the tip with the connector. Subsequently, each of the prepared water-based ink compositions was filled into the prepared empty refill, and an ink-following body was loaded into the rear end of the ink to manufacture a water-based ballpoint pen.

[0094] [Evaluation of Writing Instruments] The following evaluations were conducted on the manufactured writing instruments. The results are shown in Tables 1 and 2.

[0095] (Writability after 3 months at 50°C) The water-based ballpoint pens prepared as described above were stored upside down for 3 months in an environment with a temperature of 50°C and a relative humidity of 65%. After storage, the writability was evaluated by freehand drawing 50 spiral circles of approximately 2 cm in diameter on writing paper conforming to ISO standards at a writing speed of approximately 3 m / min.

[0096] The evaluation criteria are as follows: A: Only one or fewer smudges occurred. B: Two to four smudges occurred. C: Five or more smudges occurred.

[0097]

[0098]

[0099] The aqueous ink composition of the present invention can suppress increases and decreases in pH over time, and can also suppress the increase of air bubbles in the aqueous ink composition. As a result, writing instruments equipped with the aqueous ink composition of the present invention can maintain good writing performance stably over a long period of time.

Claims

1. An aqueous ink composition comprising a coloring material, water, and a phenolic compound containing at least one chlorine atom represented by the following formula (1) as a substituent. (In formula (1), R １ , R ２ , R ３ , R ４ , and R ５ are each independently a hydrogen atom, a chlorine atom, or an alkyl group having 1 to 4 carbon atoms, and at least one of R １ , R ２ , R ３ , R ４ , and R 5 is a chlorine atom.) 2. The aqueous ink composition according to claim 1, wherein the phenol compound is represented by the following formula (2). (In formula (2), R ６ , and R ７ Each is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X １ , X ２ , and X ３ Each of these is independently a hydrogen atom or a chlorine atom, and X １ , X ２ , and X ３ At least one of them is a chlorine atom.

3. The aqueous ink composition according to claim 1, wherein the phenol compound is represented by the following formula (3). (In formula (3), X ４ , and X ５ These are, independently, a hydrogen atom or a chlorine atom.

4. The aqueous ink composition according to claim 1, wherein the phenol compound is at least one selected from the group consisting of 4-chloro-3-methylphenol, 4-chloro-3,5-dimethylphenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol.

5. The aqueous ink composition according to claim 1, wherein the content of the phenol compound is 0.01% by mass or more and 7.0% by mass or less of the total aqueous ink composition.

6. The aqueous ink composition according to claim 1, wherein the water content is 10% by mass or more relative to the entire aqueous ink composition.

7. Dissolved oxygen concentration (%O) after storage at 25°C for 3 months ２ The aqueous ink composition according to claim 1, wherein the concentration of ) is 1.5 mg / L or less.

8. The aqueous ink composition according to claim 1, wherein the change in pH from the initial state after storage at 50°C for 3 months is 0.5 or less.

9. A writing instrument equipped with the aqueous ink composition described in any one of claims 1 to 8.

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