JP2001081389A - Aqueous ink composition for writing tool and writing tool including the same in the interior - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous ink composition for a writing tool capable of providing a good handwriting by preventing bubbles from being generated in the ink. SOLUTION: This aqueous ink composition for a writing tool contains a coloring matter, water, a water-soluble organic solvent, an agent for imparting viscosity-reducing properties caused by shear, and a synthetic polyphenol. Preferably, the ink composition contains 0.001-5 wt.% synthetic polyphenol or derivative thereof based on the ink composition, and has pH>=7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based ink composition for a writing implement and a writing implement incorporating the same. More specifically, the present invention relates to a water-based ink composition for a writing instrument exhibiting a shear thinning property, and a writing instrument filled with the ink and an ink backflow preventive that follows with the consumption of the ink.

[0002]

2. Description of the Related Art An aqueous ballpoint pen ink composition containing a shear-thinning agent such as a high molecular weight polysaccharide has been disclosed as a water-based ink having a shear-thinning property (Japanese Patent Application Laid-Open No. HEI 4 (1999)).
-2144782). This type of ink has a high viscosity at rest when no shear stress is applied, and is stably held in the mechanism.In writing, the high shearing force of the high-speed rotating ball reduces the ink near the ball. As a result, the ink is ejected from the gap between the ball and the ball container and transferred to the paper. Since the ink transferred to the paper surface is released from the shearing force, it becomes a high-viscosity state again, and does not cause blur of the handwriting, which is a drawback of the conventional aqueous ink composition. Further, ink leakage does not occur depending on the above-mentioned shear thinning, and a flow rate adjusting member (pen core) for adjusting the ink flow rate is not required.
A writing instrument with a simple structure can be obtained. The above-described writing implement using the water-based ink exhibiting shear thinning has a simple structure, and since the air does not enter into the inside with the consumption of the ink as in the writing implement using the flow rate adjusting member, the internal pressure is reduced. While it has the advantage of little change and not causing ink dropping, special considerations are required when preparing and filling the ink. This prevents the solvent in the ink from evaporating on the rear end face of the ink, or prevents the ink from flowing backward when the writing tip is in an upright state (upright state). This is because the backflow preventer (liquid stopper) is filled, and the ink exists in an airtight space that is shut off from the outside air. If gas is mixed in the ink, the gas collects over time and bubbles are generated. This is because it is generated and adversely affects ink ejection during writing, and writing may not be possible if bubbles are present at the tip of the writing. In order to solve the above-mentioned problem, defoaming treatment for mechanically removing gas in the ink is mainly performed, but it is difficult to perform sufficient defoaming by this method alone, and gas remains in the ink. There is. Further, when a colorant insoluble in a solvent such as pigment, metal powder, titanium oxide, or the like is used, if a treatment such as centrifugal defoaming is performed, the colorant is unevenly distributed in the ink container. Therefore, a method of chemically removing gas in the ink is considered. For example, an ascorbic acid derivative is added (Japanese Patent Publication No. 7-113101),
α-tocopherol may be added (Japanese Unexamined Patent Publication No.
No. 672) and further attempts to add catechins (Japanese Patent Laid-Open No. 10-298483).

[0003]

However, among the compounds that chemically remove the gas in the ink, ascorbic acid derivatives are liable to cause the aggregation of the pigment in a system using a pigment as a coloring agent, so that practical use is not possible. Limited.
In addition, α-tocopherol is insoluble in water and is separated over time, making it difficult to permanently remove gas. Also,
The catechins are not limited to a coloring agent to be applied, and the gas removing function does not cause problems such as disappearing in a short period of time. For this reason, the purity is low, and the number of functional groups that exhibit gas reducibility and remove gas is small, so that a large amount must be added to obtain a desired effect. The present invention provides a water-based ink composition for a writing implement that has a wide practicality and can obtain good writing performance by using a specific compound that chemically removes the gas in the ink described above, and a built-in ink composition. It is to provide a writing implement that has been developed.

[0004]

SUMMARY OF THE INVENTION The present invention provides a colorant, water,
A water-based ink composition for a writing implement comprising a water-soluble organic solvent, a shear thinning agent, and a synthetic polyphenol or a derivative thereof is required. Further, it is required that the above-mentioned synthetic polyphenol or its derivative be contained in the ink composition in an amount of 0.001 to 5% by weight, and that the pH of the ink composition be 7 or more. Further, a writing tool in which the ink composition is filled in a writing tool of a type in which an ink backflow preventing body that follows the ink consumption is arranged is required.

The inventor of the present invention has shown that among the above-mentioned compounds for chemically removing gas in ink, there is little effect on various additives, and the compound has a sufficient gas removing function with a small amount of addition. As a result of intensive studies on compounds to be permanently expressed, it has been found that synthetic polyphenols or derivatives thereof exhibit a long-term remarkable gas removal function while maintaining good writing performance.

The above-mentioned synthetic polyphenol is mainly used as a reducing agent, and exhibits good oxygen absorbing ability when added to an ink composition. Therefore, it is presumed that gas containing oxygen in the ink is prevented from collecting and forming bubbles. Examples of the synthetic polyphenol include hydroquinone, catechol, pyrogallol, phloroglucin, resorcin, 2,3,4-hydroxybenzophenone,
2,3,5-trimethylhydroquinone or a derivative thereof can be exemplified. Further, the synthetic polyphenol may be a derivative in which a hydroxyl group is partially substituted with an alkyl group, an alkenyl group, or the like, and 4-hydroxy-3-t may be used.
tert-butylanisole and the like can be exemplified. In addition, since the synthetic polyphenol or its derivative exhibits a strong reducing property under an alkaline atmosphere, the P
By adjusting H to 7 or more, the compound functions well as a compound having excellent oxygen absorbing ability.

[0007] The synthetic polyphenol or its derivative is present in an ink composition in an amount of 0.001 to 5% by weight, preferably
0.01 to 0.5% by weight can be added. 0.0
If the content is less than 01% by weight, it is difficult to obtain the desired effect of suppressing the generation of bubbles. If the content is less than about 5% by weight, the desired effect is sufficiently obtained, so that further addition is not required.

As the colorant, all dyes and pigments that can be dissolved or dispersed in an aqueous medium can be used, and specific examples thereof are shown below. As the dye, an acid dye, a basic dye, a direct dye, or the like can be used. As the acid dye, neucoccin (C.I.
I. 16255), tartrazine (CI. 1914)
0), Acid Blue Black 10B (CI.204
70), Guinea Green (CI. 42085), Brilliant Blue FCF (CI. 42090), Acid Violet 6B (CI. 42640), Soluble Blue (CI. 42755), Naphthalene Green (C. .I.44025), eosin (CI.4538)
0), Phloxine (CI. 45410), Erythrosin (CI. 45430), Nigrosine (CI. 50)
420), acid flavin (CI. 56205) and the like.

As the basic dye, chrysoidin (C.I.
I. 11270), methyl violet FN (CI.
42535), crystal violet (C.I.42)
555), malachite green (CI. 4200)
0), Victoria Blue FB (CI.44045),
Rhodamine B (CI. 45170), Acridine Orange NS (CI. 46005), Methylene Blue B
(C.I. 52015) and the like are used.

As a direct dye, Congo Red (C.I.
I. 22120), Direct Sky Blue 5B (C.I.
I. 24400), Violet BB (CI. 279)
05), direct deep black EX (CI.3
0235), Kayalas Black G Conch (CI.35
225), Direct Fast Black G (CI.3)
5255), phthalocyanine blue (CI. 7418)
0) etc. are used.

As the pigment, in addition to inorganic pigments such as carbon black and ultramarine blue, and organic pigments such as copper phthalocyanine blue and benzidine yellow, finely and stably dispersed in an aqueous medium using a surfactant or a resin in advance. Water-dispersed pigment products and the like. I. Pigment Blue 15: 3B [Product name: Sandy Super Blue GLL, pigment content 24%, manufactured by Sanyo Dyeing Co., Ltd.] C.I. I. Pigment Red 146 [Product name: S
andy Super Pink FBL, pigment content 2
1.5%, manufactured by Sanyo Dyeing Co., Ltd.] C.I. I. Pigment Yellow 81 [Product name:
TC YellowFG, pigment content: about 30%, manufactured by Dainichi Seika Kogyo Co., Ltd.] I. Pigment Red 220/166 [product name: TC Red FG, pigment content: about 35%, manufactured by Dainichi Seika Kogyo Co., Ltd.] and the like. In addition, as the resin for dispersing the pigment, polyamide resin, polyurethane resin, polyester resin, epoxy resin, melamine resin, phenol resin, silicone resin, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, Examples include polystyrene, acrylic resin, maleic resin, gum arabic, cellulose, dextran, casein, and the like, and derivatives thereof, and copolymers of the above resins. As the fluorescent pigment, a fluorescent pigment in the form of fine particles of a synthetic resin in which various fluorescent dyes are made into a solid solution in a resin matrix can be used.
Also, white pigments such as titanium dioxide, metal powders such as aluminum, pearl pigments, gold and silver metallic pigments, luminous pigments, fragrances and fragrance capsule pigments can be used. The pigments may be used alone or in combination of two or more, and 1 to 25% by weight in the ink composition.
Preferably, it is used in the range of 2 to 15% by weight.

As the water-soluble organic solvent, a conventional general-purpose solvent compatible with water is used. 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, N-methyl-2-pyrrolidone and the like. The water-soluble organic solvent may be used alone or in combination of two or more, and is used in an amount of 2 to 60% by weight, preferably 5 to 35% by weight.

In addition, if necessary, a pH adjuster, a preservative or a fungicide can be added. Examples of the pH adjuster include inorganic salts such as ammonia, sodium carbonate, sodium phosphate, sodium hydroxide, and sodium acetate; and organic basic compounds such as water-soluble amine compounds such as triethanolamine and diethanolamine. Examples of the preservative or fungicide include sodium salt of carboxylate, 1,2-benzisothiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6 −
Tetrachloro-4- (methylsulfonyl) pyridine and the like. In addition, it is also possible to add a fluorine surfactant for improving the permeability of the solvent, a nonionic, anionic or cationic surfactant, and an antifoaming agent such as dimethylpolysiloxane.

One or more water-soluble resins such as an alkyd resin, an acrylic resin, a styrene-maleic acid copolymer, a cellulose derivative, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin are added in a range that does not hinder the drying resistance. Alternatively, one or more humectants such as urea, nonionic surfactant, sorbite, mannitol, sucrose, glucose, reduced starch hydrolyzate, sodium pyrophosphate and the like can be added.

As the shear-thinning agent, water-soluble or dispersible substances are effective, and xanthan gum, welan gum, and succinoglycan whose constituent monosaccharide is an organic acid-modified heteropolysaccharide of glucose and galactose are used. (Average molecular weight of about 1 to 8 million), guar gum, locust bean gum and derivatives thereof, hydroxyethylcellulose, alginic acid alkyl esters, polymers having a molecular weight of 100,000 to 150,000, and glycomannan, which are mainly composed of alkyl esters of methacrylic acid; Thickening polysaccharides having gelling ability extracted from seaweeds such as agar and carrageenin, benzylidene sorbitol and benzylidene xylitol or derivatives thereof, a crosslinkable acrylic acid polymer, inorganic fine particles,
Polyglycerin fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyethylene glycol fatty acid ester, polyoxyethylene castor oil, polyoxyethylene lanolin, lanolin alcohol, beeswax derivative, polyoxyethylene alkyl ether, polyoxypropylene alkyl ether, polyoxyethylene alkyl HLB value of phenyl ether, fatty acid amide, etc. is 8
To 12 nonionic surfactants, salts of dialkyl or dialkenyl sulfosuccinic acid, and the like, and these can be used alone or in combination. Further, N-alkyl-
A mixture of 2-pyrrolidone and an anionic surfactant, and a mixture of polyvinyl alcohol and an acrylic resin can also be used. The shear thinning agent can be used in an amount of 0.1 to 20% by weight in the ink composition.

Examples of the rust preventive include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, ethylenediaminetetraacetate, saponin, dialkylthiourea and the like. Examples of the lubricant include metal soap, polyalkylene glycol fatty acid ester, ethylene oxide addition type cationic activator, phosphate ester activator, thiocarbamate, dimethyldithiocarbamate and the like.

[0017] The lubricants preferably used include:
Phosphate ester surfactants described in the following general formula (1) or Japanese Patent Publication No. 1-1508 are exemplified.

[0018]

Embedded image (Wherein, R ₁ represents an alkyl group or alkenyl group of 8 to 18,
Alternatively, a phenyl group, an alkylphenyl group, R ₂
It is OH, OM, R-O- ( CH 2 CH 2 O) shows the _n,
M represents an alkali metal, an amine, or an alkanolamine, and n represents 1 to 30. )

The aqueous ink composition for a writing instrument of the present invention is filled in a marking pen or a ball-point pen having a fiber tip, a felt tip, a plastic tip, and a ball-point tip attached to a writing tip.

The structure and shape of the ball-point pen itself are not particularly limited, and conventional ball-point pens can be used. For example, a ball-point pen has an ink container filled with an ink composition in a shaft cylinder. Is a ball-point pen that communicates with a chip having a ball attached to the tip, and a liquid stopper for preventing backflow is in close contact with the end surface of the ink.

The ball-point pen tip will be described in more detail. A tip formed by holding a ball in a ball holding portion formed by pressing and deforming the vicinity of the tip of a metal pipe inward from the outer surface, or a metal material such as a drill A chip holding a ball in a ball holding portion formed by cutting by the above or a ball held by a chip formed by cutting a metal pipe or a metal material is urged forward by a spring body. Can be applied. Also, the ball is
0.1% of cemented carbide, stainless steel, ruby, ceramic, etc.
Those having a diameter of about 3 to 1.2 mm can be applied.

As the ink containing tube for containing the ink composition, for example, a molded article made of a thermoplastic resin such as polyethylene, polypropylene, and polyethylene terephthalate is suitably used in terms of low ink evaporation and productivity. The ink container preferably has an inner diameter of 2.5 to 10 mm. Further, by using a transparent, colored transparent or translucent molded body as the ink storage tube, it is possible to confirm the ink color, the remaining amount of the ink, and the like. In addition to directly connecting the chip to the ink storage tube, the ink storage tube and the chip may be connected via a connecting member. In addition, the ink storage tube has a form of refill,
The refill may be housed in the barrel, or the barrel itself with the tip attached to the tip as an ink container.
The shaft cylinder may be directly filled with ink.

The back end of the ink composition contained in the ink containing tube is filled with an ink backflow preventer. As the ink backflow preventive, any liquid or solid can be used.Examples of the liquid ink backflow preventive include non-volatile media such as polybutene and silicone oil.
If desired, silica, aluminum silicate and the like can be added to the medium. In addition, examples of the solid ink backflow preventer include a resin molded product. Further, the liquid and solid ink backflow preventers may be used in combination.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous ink composition for a writing instrument of the present invention is used when a dye or pigment (pigment dispersion), a synthetic polyphenol, and additives are mixed in a medium comprising water and a water-soluble organic solvent. Is prepared by adding an appropriate additive, heating and stirring as needed, dissolving and dispersing, and filling and using a writing implement such as a ball-point pen, a felt-tip pen, a felt-tip pen, and a brush pen.

[0025]

EXAMPLES The ink compositions of the present invention and the ink compositions of comparative examples and the preparation method are described below. The numbers in the composition indicate parts by weight. Example 1 Red acid dye 5.0 [manufactured by Eisen Co., Ltd., C.I. I. Acid Red 92, C.I. I. 45410] Ethylene glycol 15.0 Xanthan gum 0.5 Hydroquinone [manufactured by Seiko Chemical Co., Ltd.] 0.2 Sodium carbonate 0.5 Carbonic acid 0.5 Water 78.5 Total 100.0

The above composition is mixed, heated at 60 ° C., stirred for 1 hour with a mixer, cooled, and filtered to obtain a water-based ink composition for writing implements. In addition,
The pH of the ink composition was 9.61.

Example 2 Fluorescent pigment [manufactured by Nippon Fluorescent Chemical Co., Ltd., trade name: Lumicol 2117] 35.0 glycerin 15.0 succinoglycan 0.3 (constituent monosaccharide is an organic acid-modified heteropolysaccharide of glucose and galactose) Body) Catechol [produced by Ube Industries, Ltd.] 0.2 Triethanolamine 1.0 Carbonate 0.3 Water 48.2 Total 100.0

The above composition is mixed, stirred at a mixer for 1 hour while heating at 60 ° C., cooled, and filtered to obtain a water-based ink composition for a writing instrument. In addition,
The pH of the ink composition was 8.22.

Example 3 Blue pigment 20.0 [SS BLUE GLL, C.I. I. Pigment Blue 15: 3B, pigment content 24%] diethylene glycol 15.0 hexaglyceryl monooleate 13.0 [Hexaglyn 1-0, manufactured by Nippon Surfactant Co., Ltd.] pyrogallol 0.05 1,2-benzisothiazolin-3-one 0.1 [manufactured by Zeneca Corporation, trade name: Proxel XL-2] Water 51.85 Total 100.0

The above composition is mixed, stirred at a temperature of 40 ° C. for 30 minutes with a three-one motor, cooled, and filtered to obtain a water-based ink composition for writing implements. The pH of the ink composition was 7.43.

Example 4 Aluminum paste [96-2104, manufactured by Toyo Aluminum Co., Ltd.] 7.0 Amine salt of EDTA [Cyrest M-50, manufactured by Kyrest Co., Ltd.] 1.0 α-cyclodextrin 3.0 [ Glycerin 8.0 Ethylene glycol 8.0 Succinoglycan 0.3 (organic acid-modified heteropolysaccharide of glucose and galactose as constituent monosaccharide) Phloroglucin 0.5 Sodium oma Gin (trade name: Topside 280) 0.3 Phosphate ester surfactant 0.5 [Daiichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf M208B] Water 71.4 Total 100.0

The above-mentioned composition is mixed, stirred with a disper for 2 hours, and then filtered to obtain a water-based ink composition for writing implements. The pH of the ink composition was 7.70.

Comparative Example 1 Red Acid Dye 5.0 [manufactured by Eisen Co., Ltd., C.I. I. Acid Red 92, C.I. I. 45410] Ethylene glycol 15.0 Xanthan gum 0.5 Sodium carbonate 0.5 Carbonate 0.5 Water 78.7 Total 100.0

The above composition is mixed, stirred at a mixer for 1 hour while heating at 60 ° C., cooled, and filtered to obtain a water-based ink composition for writing implements. In addition,
The pH of the ink composition was 9.52.

Comparative Example 2 Fluorescent pigment [manufactured by Nippon Fluorescent Chemical Co., Ltd., trade name: Lumicoll 2117] 35.0 glycerin 15.0 succinoglycan 0.3 (constituent monosaccharide is an organic acid-modified heteropolysaccharide of glucose and galactose) Body) Triethanolamine 1.0 Carbonate 0.3 Water 48.4 Total 100.0

The above composition is mixed, stirred at a mixer for 1 hour while heating at 60 ° C., cooled, and filtered to obtain a water-based ink composition for writing implements. In addition,
The pH of the ink composition was 8.10.

Comparative Example 3 Blue pigment 20.0 [SS BLUE GLL, C.I. I. Pigment Blue 15: 3B, pigment content 24%] diethylene glycol 15.0 hexaglyceryl monooleate 13.0 [Nippon Surfactant Co., Ltd., Hexaglyn 1-0] 1,2-benzisothiazolin-3-one 0.1 [ Made by Zeneca Corporation, trade name: Proxel XL-2] Water 51.9 Total 100.0

The above composition is mixed, stirred at a temperature of 40 ° C. for 30 minutes with a three-one motor, cooled, and filtered to obtain a water-based ink composition for writing implements. The pH of the ink composition was 7.36.

Comparative Example 4 Blue Pigment 20.0 [SS BLUE GLL, C.I. I. Pigment Blue 15: 3B, pigment content 24%] diethylene glycol 15.0 pyrogallol 0.05 hexaglyceryl monooleate 13.0 [Nippon Surfactant Co., Ltd., Hexaglyn 1-0] 1,2-benzisothiazolin-3-one 0.1 [trade name: Proxel XL-2, manufactured by Zeneca Corporation] Phosphate ester surfactant 0.5 [trade name: Plysurf A212C, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.] Polyoxyethylene tridecyl ether Mixture of monoester and diester of phosphoric acid] Water 51.35 Total 100.0

The above composition is mixed, stirred at a mixer for 1 hour while heating at 40 ° C., cooled, and filtered to obtain a water-based ink composition for a writing instrument. In addition,
The pH of the ink composition was 3.42.

Comparative Example 5 Aluminum paste [96-2104, manufactured by Toyo Aluminum Co., Ltd.] 7.0 Amine salt of EDTA [Cylest M-50, manufactured by Kyresto Co., Ltd.] 1.0 α-cyclodextrin 3.0 [ Glycerin 8.0 Ethylene glycol 8.0 Succinoglycan 0.3 (Constituent monosaccharide is an organic acid-modified heteropolysaccharide of glucose and galactose) Sodium Omazine (trade name) : Topside 280) 0.3 Phosphate ester-based surfactant 0.5 [manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf M208B] Water 71.9 Total 100.0

According to the above-mentioned ink preparation method, inks of Examples and Comparative Examples were prepared. A stainless steel tip holding a ball having a diameter of 0.4 mm was filled in a ballpoint pen refill fitted to one end of a polypropylene pipe. Further, after filling the ink backflow preventive body in close contact with the rear end face of the ink, the ballpoint pen refill was incorporated into a shaft cylinder to obtain a ballpoint pen.

After the ballpoint pen obtained as described above was allowed to stand at 50 ° C. for 30 days, the presence or absence of air bubbles in the ink container and the state of the handwriting were visually observed by a writing test as compared with the initial stage. The results are shown below.

[0044]

[Table 1]

The criteria in the above table are as follows. Handwriting state ：: Good handwriting is obtained. ×: Scatter is seen in the handwriting.

[0046]

The aqueous ink for a writing instrument of the present invention contains no synthetic polyphenol or a derivative thereof, so that no bubbles are generated. Therefore, a writing instrument using the ink does not generate bubbles with the passage of time. The ink can be smoothly led out to the tip of writing, stable writing performance can be maintained, and good handwriting can be obtained continuously.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C350 GA01 GA02 GA03 GA04 GA06 KF03 NA10 NC06 4J039 AB01 AB02 AB04 AB07 AB12 AD06 AD09 AD10 AE07 BA04 BA23 BC07 BC09 BC12 BC13 BC16 BC19 BC20 BC29 BC31 BC35 BC36 BC50 BC54 BC60 BE03 BE04 BE05 BE12 BE22 BE23 BE24 BE33 EA15 EA16 EA17 EA19 EA20 EA42 EA44 EA48 GA26 GA27

Claims (4)

[Claims] An aqueous ink composition for a writing implement comprising a colorant, water, a water-soluble organic solvent, a shear-thinning agent, and a synthetic polyphenol or a derivative thereof. 2. The aqueous ink composition for a writing instrument according to claim 1, wherein the synthetic polyphenol or a derivative thereof is contained in an amount of 0.001 to 5% by weight in the ink composition. 3. The aqueous ink composition for a writing instrument according to claim 1, wherein the pH of the ink composition is 7 or more. 4. A writing implement of the type in which an ink backflow preventive that follows the ink consumption is arranged, wherein the writing implement is filled with the ink composition according to any one of claims 1 to 3.