JP2010242045A - Water-based ink composition for writing utensil, and writing utensil containing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based ink composition for a writing utensil, the ink composition exhibiting excellent functions of removing foams and effects of suppressing generation of foams even when using a specific compound which chemically removes a gas in the ink without corroding metallic utensil components such as a pen tip; and to provide a writing utensil containing the same. <P>SOLUTION: The water-based ink composition for the writing utensil comprises at least a colorant, water and one or more disulfide compound selected from dithiothreitol, dithioerythritol and their salts. The writing utensil comprises an ink storage tube into which the ink composition is directly filled, and an ink back-flow inhibitor is closely placed at the rear end of the ink, moving with consumption of the ink. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a water-based ink composition for a writing instrument and a writing instrument filled with the water-based ink composition for a writing instrument and an ink backflow preventive body that follows the ink consumption.

  Conventionally, an aqueous ballpoint pen ink composition containing a shear thinning agent such as a polymer polysaccharide has been disclosed as an ink having shear thinning among aqueous inks (see, for example, Patent Document 1).

This type of ink has a high viscosity when it is left to stand without shear stress, and is stably held in the mechanism. When writing, the ink in the vicinity of the ball is low due to the high shear force of the ball rotating at high speed. As a result, the ink is discharged from the gap between the ball and the ball container and transferred onto the paper surface. Since the ink transferred onto the paper surface is released from the shearing force, it becomes a high viscosity state again, and does not cause the blotting of the handwriting, which is a defect of the conventional aqueous ink composition.
In addition, ink leakage does not occur depending on the above-described shear thinning, and a flow rate adjusting member (temporary ink storage member such as a comb-like member) for adjusting the ink flow rate is not required. A writing instrument with a structure is obtained.

  The conventional writing instrument using water-based ink exhibiting shear thinning has a simple structure, and the air pressure does not enter the interior as the ink is consumed as in the writing instrument using the flow rate adjusting member. While there is little change and there is an advantage that the ink does not fall off, special preparations such as preventing gas from being mixed in the ink are necessary when preparing and filling the ink. This prevents the solvent in the ink from evaporating on the rear end surface of the ink, or prevents the ink from flowing backward when the writing tip portion is in the upward state (upright state), and follows the ink consumption. This is because the ink backflow prevention body (liquid stopper) is filled, and since the ink exists in an airtight space that is blocked from the outside air, if the gas is mixed in the ink, the gas gathers over time and bubbles are generated. Since it may occur or may be mixed from the pen tip by a knock impact in a knock type ballpoint pen, it may adversely affect ink ejection such as handwriting at the time of writing, and writing may be impossible if bubbles exist at the tip of the writing Because.

  Apart from this, as a writing instrument of the type filled with the ink backflow preventive body, by providing a valve mechanism in the vicinity of the writing tip, it can be filled with an aqueous ink composition that does not exhibit shear thinning, As with, the presence of bubbles will adversely affect writing performance.

In order to solve the problems described above, defoaming treatment is mainly performed to remove the gas in the ink mechanically. However, it is difficult to perform sufficient defoaming by this method alone, and the gas remains in the ink. There is. In addition, when using a colorant that is insoluble in a solvent such as pigment, metal powder, titanium oxide, etc., if the specific gravity difference from the vehicle is large, the colorant will be contained in the ink container when processing such as centrifugal defoaming is performed. The problem of uneven distribution occurs.
Therefore, a method of chemically removing the gas in the ink is conceivable. For example, attempts to add an ascorbic acid derivative or α-tocopherol have been disclosed (see, for example, Patent Documents 2 to 3).

When a compound that chemically removes the gas in the ink is added, a peroxide radical that is a corrosive component is generated by acting on oxygen in the ink, so metal members such as stainless steel, brass, and carbide are used. When incorporated in a writing instrument, the metal member may be corroded over time.
Therefore, as a method for preventing the above-described corrosion over time, a method of adding a sulfide compound or thiourea into an ink using an ascorbic acid derivative or the like is disclosed (for example, see Patent Document 4).

Japanese Patent Laid-Open No. 4-214782 Japanese Patent Publication No.7-113101 Japanese Patent Laid-Open No. 10-330672 JP 2004-115684 A

  However, when the sulfide compound or thiourea is added, it may cause problems such as generating an odor depending on the structure of the compound, or precipitation due to long-term aging, making it difficult to obtain a sufficient corrosion inhibiting effect. Therefore, as a result, the writing quality is deteriorated or the handwriting is faint, which is insufficient to prevent problems during writing.

  Even if a specific compound that chemically removes gas in the ink is used, the present invention does not corrode metal writing instrument members such as a nib, and has an excellent bubble removal function and bubble suppression effect. Therefore, the present invention provides a water-based ink composition for a writing instrument that is highly practical and capable of obtaining good writing performance, and a writing instrument incorporating the same.

The water-based ink composition for writing instruments of the present invention is required to contain at least one colorant, water, one or two or more disulfide compounds selected from dithiothreitol, dithioerythritol, and salts thereof.
Furthermore, it is a requirement that the ink composition contains 0.05 to 5% by weight of the disulfide compound and that the pH of the water-based ink composition is 7 to 12.
Furthermore, it is a writing instrument formed by directly filling the ink containing tube with the water-based ink composition for a writing instrument according to any one of the above, and closely arranging an ink backflow prevention body that follows as the ink is consumed at the rear end of the ink. As a requirement, the writing instrument contains one or a plurality of ballpoint pen refills containing a water-based ink composition in the refill, and the writing tip of the ballpoint pen refill appears and disappears from the front end opening of the shaft cylinder by the operation of the retracting mechanism It is required to be a ballpoint pen type.

  The water-based ink composition for a writing instrument of the present invention is blended with dithiothreitol, dithioerythritol, or a salt thereof, and has excellent bubble removal function and bubble suppression effect without corroding a metal writing instrument member such as a nib. Therefore, the writing instrument using the ink is capable of smoothly guiding the ink to the tip of the writing without causing bubbles over time, and can maintain stable writing performance for a long time. And a writing instrument with it built in.

The dithiothreitol and dithioerythritol have high solubility in water and express a strong reducing power in an aqueous medium, and exhibit a bubble removing effect and a bubble suppressing effect in aqueous ink for a long period of time. be able to. Furthermore, since it has the effect of suppressing metal corrosion together with the above effect, it is suitable for addition to water-based ink applied to a writing instrument using a metal member.
Moreover, it is also possible to apply the salt of dithiothreitol or dithioerythritol, and examples of the salt include alkali metal salts such as lithium, sodium and potassium, and amine salts such as alkanolamine and ammonia.

One or more disulfide compounds selected from dithiothreitol, dithioerythritol and salts thereof may be added in an amount of 0.05 to 5% by weight, preferably 0.1 to 3% by weight, in the ink composition.
If it is less than 0.05% by weight, it is difficult to obtain the desired bubble generation inhibiting effect, and even if it exceeds 5% by weight, no further bubble inhibiting effect can be obtained. I don't need it.

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 illustrated below.
As the dye, an acid dye, a basic dye, a direct dye, or the like can be used.
Examples of the acid dye include New Coxin (CI. 16255), Tartrazine (CI. 19140), Acid Blue Black 10B (CI. 20470), Guinea Green (CI. 42085), Brilliant Blue FCF. (CI.42090), Acid Violet 6B (C.I.42640), Soluble Blue (C.I.42755), Naphthalene Green (C.I.44025), Eosin (C.I.45380), Phloxin (C.I. 45410), erythrosine (C.I. 45430), nigrosine (C.I. 50420), acid flavin (C.I. 56205) and the like are used.

  Examples of basic dyes include chrysoidine (C.I. 11270), methyl violet FN (C.I. 42535), crystal violet (C.I. 42555), malachite green (C.I. 42000), Victoria Blue FB ( CI 44045), rhodamine B (C.I. 45170), acridine orange NS (C.I. 46005), methylene blue B (C.I. 52015) and the like are used.

  As direct dyes, Congo Red (C.I. 22120), Direct Sky Blue 5B (C.I. 24400), Violet BB (C.I. 27905), Direct Deep Black EX (C.I. 30235), Kaya Las Black G Conch (C.I. 35225), Direct Fast Black G (C.I. 35255), Phthalocyanine Blue (C.I. 74180) and the like are used.

Examples of the pigment include inorganic pigments such as carbon black and ultramarine, and organic pigments such as copper phthalocyanine blue and benzidine yellow, as well as water dispersion finely and stably dispersed in an aqueous medium in advance using a surfactant or resin. Pigment products and the like are used. I. Pigment Blue 15: 3B [Product name: Sandy Super Blue GLL, pigment content 24%, manufactured by Sanyo Dye Co., Ltd.], C.I. I. Pigment Red 146 [Product name: Sandy Super Pink FBL, pigment content 21.5%, manufactured by Sanyo Dye Co., Ltd.], C.I. I. Pigment Yellow 81 [Product name: TC Yellow FG, pigment content about 30%, manufactured by Dainichi Seika Kogyo Co., Ltd.], C.I. I. Pigment Red 220/166 [Product name: TC Red FG, pigment content of about 35%, manufactured by Dainichi Seika Kogyo Co., Ltd.].
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 thereof include polystyrene, acrylic acid resin, maleic acid resin, gum arabic, cellulose, dextran, casein, and derivatives thereof, and copolymers of the above-described resins.
As the fluorescent pigment, a fluorescent pigment in the form of fine particles of a synthetic resin in which various fluorescent dyes are formed into a solid solution in a resin matrix can be used.
In addition, white pigments such as titanium dioxide, metal powders such as aluminum, natural mica, synthetic mica, alumina, pearl pigments in which the surface of the core material is coated with a metal oxide such as titanium dioxide, cholesteric liquid crystal type glitter A functional pigment or the like can also be used.
Furthermore, a thermochromic composition, a photochromic composition, a fragrance and the like, capsule pigments in which these are encapsulated, and the like can be exemplified.

The thermochromic composition includes (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reversible thermochromic composition comprising a reaction medium that determines the temperature at which the color reaction occurs. The composition is suitable and is encapsulated in microcapsules and applied as a reversible thermochromic microcapsule pigment.
Examples of the reversible thermochromic composition include those described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc., at a predetermined temperature (discoloration point). Discolored before and after, decolored state in the temperature range above the high temperature side discoloration point, color development state in the temperature range below the low temperature side discoloration point, only one specific state exists in the normal temperature range among the two states, The other state is maintained as long as the heat or cold required to develop the state is applied, but when the heat or cold is no longer applied, the hysteresis width returns to the state exhibited in the normal temperature range. A heat decolorable microcapsule pigment in which a reversible thermochromic composition having relatively small characteristics (ΔH = 1 to 7 ° C.) is encapsulated in a microcapsule can be applied.

Furthermore, large hysteresis characteristics (ΔH _B = 8 to 50 ° C.) described in JP- _B -4-17154, JP-A-7-179777, JP-A-7-33997, JP-A-8-39936, and the like. ), That is, when the shape of the curve plotting the change in the color density due to the temperature change is lowering the temperature from the lower temperature side than the color changing temperature range, as opposed to increasing the temperature from the lower temperature side. Reversible heat with color memory in a specific temperature range when the color changes in a low temperature range below the complete color development temperature or in a high temperature range above the complete color erase temperature. A heat-decolorable microcapsule pigment in which the color-changing composition is encapsulated in microcapsules is also applicable.
Specifically, as the reversible thermochromic composition having color memory, a complete color development temperature can be obtained only in a freezing room, a cold district, etc., that is, −50 to 0 ° C., preferably −40 to − 5 ° C., more preferably −30 to −10 ° C., and complete decoloring temperature obtained from a frictional heat generated by a friction body, a heating body such as a hair dryer, ie 50 to 95 ° C., preferably 50 to 90 ° C. More preferably, by specifying the range of 60 to 80 ° C. and specifying the ΔH value of 40 to 100 ° C., it is possible to effectively function to maintain the color exhibited in the normal state (daily life temperature range).
The colorant may be used alone or in combination of two or more, and is used in the range of 1 to 25% by weight, preferably 2 to 15% by weight in the ink composition.

Further, as the water-soluble organic solvent, conventional general-purpose solvents compatible with water are used, and ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiol Diethylene 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.
In addition, the said water-soluble organic solvent can also use 1 type, or 2 or more types together, It is 2-60 weight% in an ink composition, Preferably it is used in 5-35 weight%.

In addition, a pH adjuster, an antiseptic, or an antifungal agent can be added as necessary.
Examples of the pH adjuster include inorganic salts such as ammonia, sodium carbonate, sodium phosphate, sodium hydroxide and sodium acetate, organic basic compounds such as water-soluble amine compounds such as triethanolamine and diethanolamine, lactic acid and citric acid. Etc.
Examples of the preservative or antifungal agent include carboxylic acid, sodium salt of 1,2-benzisothiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6 -Tetrachloro-4- (methylsulfonyl) pyridine and the like.
Furthermore, an antifoaming agent such as a fluorine-based surfactant that improves the permeability of the solvent, a nonion, an anion, a cationic surfactant, or dimethylpolysiloxane may be added.

  Also, one or more water-soluble resins such as alkyd resin, acrylic resin, styrene maleic acid copolymer, cellulose derivative, polyvinyl pyrrolidone, polyvinyl alcohol, and dextrin may be added in a category that does not impair drought resistance, urea, One or more wetting agents such as nonionic surfactants, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolyzate and sodium pyrophosphate can be added.

A shear thinning agent can be added to the water-based ink composition.
As the shear thinning agent, a water-soluble or dispersible substance is effective, and xanthan gum, welan gum, and succinoglycan whose constituent monosaccharide is an organic acid-modified heteropolysaccharide of glucose and galactose (average molecular weight) About 1,000 to 8 million), guar gum, locust bean gum and derivatives thereof, zeta sea gum, diutane gum, hydroxyethyl cellulose, alkyl esters of alginic acid, alkyl ester of methacrylic acid, and a polymer having a molecular weight of 100,000 to 150,000, Gelatinizable thickening polysaccharides extracted from seaweed such as glucomannan, agar and carrageenin, benzylidene sorbitol and benzylidene xylitol or their derivatives, 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 alkylphenyl ether, fatty acid amide, etc. Nonionic surfactants having an HLB value of 8 to 12, salts of dialkyl or dialkenylsulfosuccinic acid and the like can be exemplified, and these can be used alone or in combination.
Furthermore, a mixture of N-alkyl-2-pyrrolidone and an anionic surfactant, a mixture of polyvinyl alcohol and an acrylic resin can also be used.
The shear thinning agent can be used in the range of 0.1 to 20% by weight in the ink composition.

In addition, a rust preventive agent, a lubricant, etc. can be added as needed.
Examples of the rust inhibitor include benzotriazole and derivatives thereof, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, ethylenediaminetetraacetate, saponin, and dialkylthiourea.
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.
In addition, examples of the lubricant that is particularly preferably used include phosphate ester surfactants described in JP-B-1-13508.

The water-based ink composition is conventionally used by adjusting to a pH applied to a writing instrument, and in particular, adjusting to a neutral to alkaline region of pH 7 to 12, preferably a weak alkaline region of pH 7.1 to 11. Is preferred.
By adjusting to the pH, the dithiothreitol and dithioerythritol are present in a more stable state in the ink, and a high effect can be expressed. Furthermore, when a dye is used as the colorant, the color developability of the dye is improved.

  The water-based ink composition for a writing instrument of the present invention is filled in a marking pen or a ballpoint pen having a fiber tip, a felt tip, a plastic tip or a ballpoint tip attached to the tip of the writing.

  The structure and shape of the ballpoint pen itself are not particularly limited, and a conventional one can be applied. For example, the ballpoint pen has an ink containing tube filled with an ink composition, and the ink containing tube has a ball. An example is a ballpoint pen that communicates with a tip attached to the tip, and further has an ink backflow prevention body in close contact with the ink end face.

The ballpoint pen tip will be described in more detail. A tip formed by holding a ball in a ball holding portion obtained by pressing and deforming the vicinity of the tip of a metal pipe inward from the outer surface, or a metal material is cut by a drill or the like A chip formed by holding the ball in the ball holding part formed by the above, or a ball held in a chip formed by cutting a metal pipe or metal material, and the like that is urged forward by a spring body, etc. Can be applied.
Moreover, a cemented carbide, stainless steel, a ruby, a ceramic, etc. can be applied to the said ball | bowl, and the thing of the range of diameter 0.1mm-2.0mm is used suitably.
Of these balls, those made of cemented carbide are preferably used because of their high hardness and resistance to wear. In particular, cemented carbide balls mainly composed of tungsten carbide contain a metal binder such as cobalt or nickel. Since the amount is large and these metal binders are easily eluted in the water-based ink, they have a drawback of being easily corroded with time.
Therefore, when the water-based ink composition of the present application is incorporated, the elution of the metal material into the ink can be suppressed and the ball corrosion over time is less likely to occur, so that the configuration becomes more useful.

For example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, or polyethylene terephthalate is preferably used as the ink storage tube for storing the water-based ink composition in terms of low ink evaporation and productivity. Further, by using a transparent, colored transparent, or translucent molded body as the ink containing tube, the ink color, the remaining amount of ink, and the like can be confirmed.
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.
The ink storage tube may be a refill type in which the refill is stored in a shaft tube, or the shaft tube itself having a tip attached to a tip is used as an ink container, and ink is directly applied to the shaft tube. It may be filled.

Further, an ink backflow preventer (liquid stopper) is filled in the rear end portion of the ink composition filled in the ink containing tube.
As the ink backflow preventer, either liquid or solid can be used, and examples of the liquid ink backflow preventer include non-volatile media such as polybutene, α-olefin co-oligomer, silicone oil, and refined mineral oil. If desired, silica, aluminum silicate, swellable mica, fatty acid amide and the like can be added to the medium. Moreover, a resin molding is mentioned as a solid ink backflow prevention body. The liquid and solid ink backflow preventers can be used in combination.

When the ball-point pen form is used as the writing instrument, it may be either a cap-type or a retractable form, and the retractable ball-point pen is a barrel (with a writing tip provided on the ball-point pen refill exposed to the outside air ( Any structure can be used as long as it is housed in the outer shaft) and the writing tip protrudes from the shaft tube opening by the operation of the retracting mechanism.
Examples of the operation method of the retracting mechanism include a knock type, a rotary type, and a slide type.
The knock type has a knock portion on the rear end portion of the shaft tube and the side surface of the shaft tube, and by pressing the knock portion, the writing tip portion of the ballpoint pen refill is projected and retracted from the front end opening portion of the shaft tube, or on the shaft tube. The structure which makes the writing tip part of a ball-point pen refill appear and disappear from the axial cylinder front-end opening part by pressing the provided clip part can be illustrated.
The rotary type has a rotating part at the rear part of the shaft cylinder, and can be exemplified by a configuration in which the writing tip part of the ballpoint pen refill is projected and retracted from the front end part of the shaft cylinder by turning the rotating part.
The slide type has a slide part on the side surface of the shaft cylinder, and the sliding tip of the writing point of the ballpoint pen refill is projected and retracted from the front end opening of the shaft cylinder by operating the slide, or the clip part provided on the shaft cylinder is slid. By doing so, it is possible to exemplify a configuration in which the writing tip of the ballpoint pen refill is projected and retracted from the opening at the front end of the shaft cylinder.
The retractable ballpoint pen may be a composite retractable ballpoint pen (refill exchange type) in which a plurality of ballpoint pen refills are accommodated in a shaft cylinder.

Examples will be described below, but the present invention is not limited to these examples.
Table 1 shows the compositions of the water-based inks of Examples and Comparative Examples. In addition, the numerical value of a composition in a table | surface shows a weight part.

The contents of the raw materials in the table will be described along the note numbers.
(1) Product name: Acid Blue PG (Acid Blue 90), manufactured by Sumitomo Chemical Co., Ltd.
(2) Eisen Co., Ltd., trade name: Erythrosin (Acid Red 51)
(3) Phosphate ester surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Prisurf AL

Preparation of ink Each raw material was mixed in the blending amounts of the above-mentioned Examples and Comparative Examples, stirred and dissolved at 20 ° C. for 1 hour, and then filtered to obtain a writing instrument water-based ink composition.

Preparation of Ink Backflow Preventing Body After adding 1.5 parts of fatty acid amide as a thickener to 98.5 parts of polybutene as a base oil, an ink backflow preventing body was obtained by kneading with 3 rolls.

Production of ballpoint pens Each ink composition is filled in a ballpoint pen refill in which a stainless steel chip holding a WC-Co cemented carbide ball having a diameter of 0.3 mm is fitted to one end of a polypropylene pipe, After the ink backflow prevention body was disposed at the rear end, the ballpoint pen refill was assembled in a shaft tube and a cap was fitted to prepare a sample ballpoint pen.

The following tests were conducted using the ink composition and the sample ballpoint pen.
Written test Each sample ballpoint pen that was confirmed to be writable was allowed to stand for 60 days in a horizontally placed environment at 50 ° C., then the presence or absence of bubbles in the ink containing tube, and the old JIS P3201 writing paper A The writing feeling and the state of the handwriting when the hand-drawn spiral circle was continuously written were visually confirmed.
Ball Corrosion Test 5 g of each ink prepared was transferred to a sample bottle, covered with a WC-Co cemented carbide ball used for the previous sample ballpoint pen, and then left standing in an environment of 70 ° C. for 30 days. Then, the state of each ball | bowl surface was confirmed with the optical microscope (1000-times multiplication factor) at room temperature.
The results of the test are shown in the following table.

The evaluation of the test results is as follows.
Writing test ○: Writing was smooth and good handwriting was shown.
(Triangle | delta): There exists a feeling of being caught at the time of writing, and a slight blur and a line jump are seen in a handwriting.
X: Written feeling is poor and many blurs and line jumps are seen in the handwriting, or writing is impossible.
Ball corrosion test ○: No change from the initial stage.
(Triangle | delta): The glossiness was lost compared with the initial stage.
X: The surface is rough compared with the initial stage, or there is precipitation or deposits.

Claims (5)

  A water-based ink composition for a writing instrument comprising at least one colorant, water, one or more disulfide compounds selected from dithiothreitol, dithioerythritol, and salts thereof.   The water-based ink composition for a writing instrument according to claim 1, comprising 0.05 to 5% by weight of the disulfide compound in the ink composition.   The aqueous ink composition for a writing instrument according to claim 1 or 2, wherein the aqueous ink composition has a pH of 7 to 12.   4. A writing instrument comprising a water-based ink composition for a writing instrument according to any one of claims 1 to 3, which is directly filled in an ink containing tube, and an ink backflow preventive body which follows as the ink is consumed is closely arranged at the rear end of the ink.   A retractable ballpoint pen configuration in which the writing instrument contains one or more ballpoint pen refills containing a water-based ink composition in the refill, and the writing tip portion of the ballpoint pen refill appears and disappears from the front end opening of the barrel by the operation of the retracting mechanism. The writing instrument according to claim 4.