JP2010065086A - Ink composition for writing utensil and writing utensil having the same built-in - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink composition for a writing utensil using a novel optical interference color pigment that can form a handwriting producing an excellent optical interference color even when writing on a writable medium having a color tone which reflects light such as white paper or the like and can write stably over a long period of time and to provide a writing utensil having the ink composition built-in. <P>SOLUTION: The ink composition for a writing utensil contains an optical interference color pigment produced by coating the surface of aluminum flake with silicon dioxide in a solvent. The optical interference color pigment has an average particle size in a range of 3-50 μm. The writing utensil has the ink composition for a writing utensil built-in. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ink composition for writing instruments. Furthermore, the present invention relates to an ink composition for a writing instrument using an interference color pigment and a writing instrument incorporating the ink composition.

Conventionally, pearl pigments coated with titanium dioxide on the surface of mica and glass flakes, or aluminum surfaces to impart light-interference colors with visual-dependent polychromaticity (effects that look different depending on the viewing angle) to the handwriting Ink compositions using interference color pigments coated with titanium dioxide have been provided (see, for example, Patent Documents 1 to 3).
JP-A-9-78019 Japanese Patent Laid-Open No. 2001-262036 JP 2002-338866 A

The pearl pigment is sufficient when writing on a writing material such as white paper (underlying color reflecting light) because the mica or glass flake as a base material has poor light shielding properties and transmits incident light. The light interference color cannot be visually recognized, and in order to obtain the light interference color in the handwriting, it is necessary to write on a dark colored object such as black paper, which lacks versatility.
On the other hand, in the interference color pigment, since aluminum serving as a base material has light shielding properties, the handwriting written on a general-purpose paper exhibits a light interference color without being limited to the color tone of the paper.
However, since the specific gravity of titanium dioxide serving as the coating is large, the interference color pigment is liable to precipitate and aggregate, and there is a risk of inconveniences such as being unable to write over time.

  The present invention is capable of forming a handwriting that expresses an excellent light interference color even when writing on a writing object of a color tone that reflects light, such as white paper, and is capable of stable writing over a long period of time. The present invention provides an ink composition for a writing instrument using various interference color pigments and a writing instrument incorporating the ink composition.

The present invention requires an ink composition for a writing instrument containing an interference color pigment having a surface of aluminum flake coated with silicon dioxide in a solvent.
Furthermore, the average particle diameter of the interference color pigment is in the range of 3 to 50 μm, the interference color pigment is contained in the range of 0.1 to 30% by weight in the total amount of the ink composition, and the ink composition Using water as a solvent and containing a shear thinning agent, the viscosity of the ink composition is in the range of 100 to 2000 mPa · s measured by a rotational viscometer at 20 ° C. and 1 rpm, and shear thinning The requirement is that the index is in the range of 0.2 to 0.8.
Furthermore, a writing instrument incorporating any of the ink compositions for writing instruments is required.

  The ink composition for writing instruments of the present invention can form a handwriting that exhibits an excellent light interference color even when written on a writing body that reflects light, such as white paper, so that it has decorative and versatile properties. Will be expensive. In addition, since the interference color pigment does not easily precipitate or aggregate, it is possible to perform stable writing over a long period of time without causing poor writing over time.

The interference color pigment used in the present invention is a pigment having viewing angle dependent polychromaticity obtained by coating silicon dioxide on the surface of aluminum flakes which are flaky fine substrates.
The interference color pigment is a phase difference due to an optical path difference between reflected light reflected from the surface of silicon dioxide and reflected light reflected from the aluminum surface after passing through the medium (silicon dioxide coating) among light incident from the outside. As a result, visual-dependent polychromaticity (effect that looks different tones depending on the viewing angle) is developed. Furthermore, since aluminum is used as the base material, it exhibits high reflectivity with respect to incident light without causing light transmission to the back side of the base material. Therefore, an excellent light interference color is exhibited even when writing on a writing body having a color tone (white or the like) that reflects light.

  As the interference color pigment, those having an average particle diameter of 3 to 50 μm, preferably 5 to 40 μm are used. When the particle diameter is smaller than 3 μm, it is difficult to give high luminance, and when it is larger than 50 μm, it is difficult to move in a thin tube such as a fiber bundle.

Specific examples of the interference color pigment include trade names “Chromashine” manufactured by Toyo Aluminum Co., Ltd .: CRS GD 20-R (golden interference color), CRS BL 20-X (blue interference color), CRS BL 20-R. (Blue interference color), CRS BL 10-R (blue interference color), CRS GR 20-R (green interference color) and the like can be exemplified.
The interference color pigments can be used singly or in combination of two or more, and are used in the range of 0.1 to 30% by weight, preferably 1 to 20% by weight, based on the total amount of the ink composition. In that case, besides being used as a powder, it can be used after being processed into a paste or dispersion.

As the ink composition using the interference color pigment, general-purpose water-based ink and oil-based ink are used.
The water-based ink composition includes a colorant (including an interference color pigment), water, a water-soluble organic solvent, and an additive such as a resin.

As the colorant, a general-purpose dye or general pigment can be used together with the above-described interference color pigment to adjust the color tone of the handwriting (ink).
As the general-purpose 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 blue, and organic pigments such as copper phthalocyanine blue and benzidine yellow, as well as water-dispersed pigments that are finely and stably dispersed in an aqueous medium in advance using a surfactant or the like. Products are used, for example
C. I. Pigment Blue 15: 3B [Product Name: S.P. S. Blue GLL, pigment content 22%, manufactured by Sanyo Dye Co., Ltd.]
C. I. Pigment Red 146 [Product Name: S.P. S. Pink FBL, pigment content 21.5%, manufactured by Sanyo Color Co., Ltd.]
C. I. Pigment Yellow 81 [Product name: TC Yellow FG, pigment content about 30%, manufactured by Dainichi Seika Kogyo Co., Ltd.]
C. I. Pigment Red220 / 166 [Product name: TC Red FG, pigment content: about 35%, manufactured by Dainichi Seika Kogyo Co., Ltd.].
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.
Other examples include pearl pigments, gold and silver metallic pigments, luminous pigments, white pigments such as titanium dioxide used in correction pens, metal powders such as aluminum, fragrances, and fragrance capsule pigments.

  The general-purpose 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.

Specific examples of water-soluble organic solvents include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, and ethylene glycol monomethyl. Examples include ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, sulfolane, 2-pyrrolidone, and N-methyl-2-pyrrolidone.
In addition, the said water-soluble organic solvent can be used 1 type or in combination of 2 or more types, and is used in 2 to 60 weight%, Preferably it is 5 to 35 weight%.

  Furthermore, a water-soluble resin can be added in order to impart adhesion to the paper surface or viscosity. Examples of the water-soluble resin include alkyd resins, acrylic resins, styrene maleic acid copolymers, cellulose derivatives, polyvinyl pyrrolidone, polyvinyl alcohol, and dextrin. The water-soluble resin can be used alone or in combination of two or more, and is used in the range of 1 to 30% by weight in the ink composition.

  Other additives include pH adjusters such as inorganic salts such as sodium carbonate, sodium phosphate and sodium acetate, organic basic compounds such as water-soluble amine compounds, metal soap, polyalkylene glycol, and phosphoric acid as necessary. Lubricants such as esters, ethylene oxide addition type cationic activators, phosphoric acid activators, rust preventives such as benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, saponin, carboxylic acid, 1,2-benzthiazoline Preservatives or antifungal agents such as 3-one sodium salt, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6-tetrachloro-4- (methylsulfonyl) pyridine , Urea, nonionic surface activity Sorbents such as sorbitol, mannitol, sucrose, glucose, reduced starch hydrolyzate, sodium pyrophosphate, fluorine surfactants and silicone surfactants that improve ink permeability, ascorbic acid, erythorbic acid, It is also possible to add antifoaming agents and antioxidants such as α-tocopherol, catechin, synthetic polyphenol, kojic acid, alkylhydroxylamine, oxime derivatives, α-glucosyl rutin, phosphonate, phosphinate, thiourea dioxide, etc. it can.

A shear thinning agent can also be added to the 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), molecular weight 10 based on guar gum, locust bean gum and derivatives thereof, diutane gum, zeta sea gum, poly N-vinylcarboxylic acid amide, hydroxyethyl cellulose, alkyl alginate, alkyl ester of methacrylic acid 10 10,000 to 150,000 polymers, glucomannan, carbohydrates having gelling ability extracted from seaweed such as agar and carrageenin, benzylidene sorbitol and benzylidene xylitol or their derivatives, crosslinkable acrylic acid polymer, inorganic fine particles, HLB value 8 ~ 2 nonionic surfactants, metal salts and amine salts of dialkylsulfosuccinic acid, and the like. Furthermore, N-alkyl-2-pyrrolidone and an anionic surfactant are added to the ink composition. Can provide stable shear thinning.

As the viscosity of the water-based ink, a value measured at 20 ° C. in the range of 100 to 2000 mPa · s at 1 rpm is preferable because the interference color pigment can be maintained more stably in a dispersed state.
Further, as a viscous properties of the ink, a shear stress value by shear thinning index [viscometer (T) and guided by rheological measurements shear rate (j) values, the empirical formula (T = Kj ^n: where, K is The value obtained by adjusting the n value calculated by applying (the calculated constant) to a range of 0.2 to 0.8 is more preferable because the interference color pigment can be maintained in a stable state in a non-writing state. is there.

Furthermore, when the water-based ink composition is filled in the shaft cylinder, an ink backflow prevention body (liquid stopper) can be disposed at the rear end of the ink composition.
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 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.

The oil-based ink composition includes a colorant (including an interference color pigment), an organic solvent, and an additive such as a resin.
As the colorant, a general-purpose dye or general pigment can be used together with the above-described interference color pigment to adjust the color tone of the handwriting (ink).
As the general-purpose colorant, all dyes and pigments that can be dissolved or dispersed in an organic solvent can be used, and specific examples thereof are illustrated below.

  As the dye, conventionally known oil-soluble dyes can be used. Specifically, rhodamine B base (CI 45170B, Taoka Dye Manufacturing Co., Ltd.), Soldan Red 3R (CI 21260, Chugai) Kasei Co., Ltd.), methyl violet 2B base (C.I. 42535B, USA, National Aniline Div.), Victoria Blue F4R (C.I. 42563B), nigrosine base LK (C.I. 50415) (above) Germany, manufactured by BASF), Bali First Yellow # 3104 (C.I. 13900A), Bali First Yellow # 3105 (C.I. 18690A), Orient Spirit Black AB (C.I. 50415), Bali First Black # 3804 (C.I. 12195), Bali First Yellow -# 1109, Bali First Orange # 2210, Bali First Red # 1320, Bali First Blue # 1605, Bali First Violet # 1701 (manufactured by Orient Chemical Co., Ltd.), Spiron Black GMH Special, Spiron Yellow C -2GH, Spiro Yellow C-GNH, Spiro Red C-GH, Spiro Red C-BH, Spiro Blue C-RH, Spiro Violet C-RH, S. P. T.A. Orange 6, S. P. T.A. Examples include Blue 111 (manufactured by Hodogaya Chemical Co., Ltd.). Furthermore, C.I. I. Basic Blue 1, 7, 7, 8, C.I. I. Basic violet 1, 3 and C.I. I. Basic dyes such as Basic Red 1 and C.I. I. Examples thereof include salt-forming dyes with acid dyes selected from Acid Yellow 23, 36 and the like.

As the pigment, a conventionally known pigment can be used. I. PIGMENT RED2, 3, 5, 8, 17, 17, 22, 31, 38, 41, C.I. I. PIGMENT ORANGE 5, 10, 13, 16, 36, 40, 43, 61, 64, 71, 73, C.I. I. PIGMENT VIOLET 19, 23, 31, 33, 36, 37, 38, 50, C.I. I. PIGMENT BLUE 2, 9, 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, 17, 17, 22, 25, 28, 29, 36 60, 68, 76, C.I. I. PIGMENT BROWN 23, 25, 26, C.I. I. PIGMENT YELLOW 1, 3, 12, 13, 24, 83, 93, 94, 95, 97, 99, 128, 139, 153, 173, C.I. I. PIGMENT GREEN 7, 10, 36, C.I. I. Organic pigments such as PIGMENT BLACK 7, carbon black such as black iron oxide, furnace black, channel black, thermal black, acetylene black, yellow iron oxide, red iron oxide, ultramarine, bitumen, cobalt blue, titanium yellow, turquoise, Examples thereof include inorganic pigments such as molybdate orange and titanium oxide.
Further, as other pigments, fluorescent pigments, pearl pigments, phosphorescent pigments, metal pigments, composite metal pigments, metal oxide pigments, and the like can be used.

  The general colorants can be used alone or in combination of two or more, and are used in the range of 1 to 45% by weight in the ink composition.

As the organic solvent, conventionally known oil-based ink solvents can be used. For example, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol Monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl glycol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mononormal butyl ether, propylene glycol mononormal butyl ether, propylene Glycol monophenyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mononormal propyl ether, dipropylene glycol monophenyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol mono Glycol ether solvents such as butyl ether and tripropylene glycol monophenyl ether, glycol solvents such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, hexylene glycol, glycerin and polyethylene glycol, dimethyl carbonate, diethyl carbonate, acetic acid 2-ethylhexyl, isobutyl isobutyrate, lactic acid Ester solvents such as chill, butyl lactate, etc., ethanol, normal propanol, normal butanol, isopropanol, benzyl alcohol, β-phenylethyl alcohol, α-methylbenzyl alcohol, lauryl alcohol, tridecyl alcohol, isododecyl alcohol, isotridodecyl Alcohol solvents such as alcohol, n-pentane, n-hexane, n-octane, n-decane, n-heptane, isohexane, isoheptane, isooctane, isodecane and other aliphatic hydrocarbons, methylcyclohexane, ethylcyclohexane, decalin, etc. Examples thereof include alicyclic hydrocarbons, aromatic hydrocarbons such as toluene and xylene.
In addition, the said organic solvent can be used 1 type or in combination of 2 or more types, can be used in 20 to 90 weight%, Preferably it is used in 35 to 75 weight%.

  As the resin, a resin used as a fixing agent or a dispersant is appropriately used. For example, a ketone resin, a sulfoamide resin, an acrylic resin, a maleic acid resin, a copolymer of styrene and maleic ester, styrene and acrylic Copolymer with acid or ester thereof, ester gum, xylene resin, urea resin, polyamide resin, alkyd resin, phenol resin, alkylphenol resin, terpene phenol resin, rosin resin and its hydrogenated compound, polyvinyl butyral, polyvinyl acetal, Examples thereof include polyvinyl alkyl ether, polyvinyl pyrrolidone, and polyethylene oxide. The resins can be used singly or in combination of two or more, and are used in the range of 0.1 to 30% by weight in the total amount of the ink composition.

  Furthermore, viscosity modifiers such as bentonite, synthetic fine powder silica, hydrogenated castor oil, fatty acid amide wax, antiseptics, rust preventives, antifoaming agents, lubricants, dispersants, anti-scratch agents, leak-proofing agents, surfactants Etc. can also be added to oil-based ink.

The ink composition for writing instruments prepared in the form of the water-based ink or oil-based ink is practically used by filling a marking pen or a ball-point pen with a tip attached to the writing tip.
When filling the marking pen, the structure and shape of the marking pen itself are not particularly limited. For example, a fiber tip, felt tip, plastic tip is attached to the writing tip, and the fiber bundle contained in the shaft cylinder is used. The ink occlusion body is impregnated with ink, the ink is supplied to the tip of the writing, the ink is directly stored inside the shaft cylinder, and the ink flow rate adjustment member consisting of a comb groove-like ink flow rate adjustment member or fiber bundle is interposed Examples include a marking pen having a structure in which ink is directly stored in the shaft cylinder and a predetermined amount of ink is supplied to the writing tip portion by a valve mechanism.

  When filling the ball-point pen, the structure and shape of the ball-point pen itself are not particularly limited. For example, an ink occlusion body composed of a fiber bundle housed in the shaft tube is impregnated with ink and supplied to the writing tip. Structure, ink is stored directly inside the shaft cylinder, and there is an ink storage tube filled with the ink composition in the shaft cylinder, with a comb groove-shaped ink flow control member and an ink flow control member consisting of fiber bundles interposed The ink storage tube communicates with a tip having a ball attached to the tip, and a ballpoint pen having a structure in which an ink follower such as a liquid stopper or a solid stopper is in close contact with the end face of the ink to prevent backflow it can.

The ball-point pen tip will be described in more detail. A tip formed by holding a ball in a ball holding portion in which the vicinity of the tip of a metal pipe is pressed and deformed 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.
The ball may be cemented carbide, stainless steel, ruby, ceramic, or the like.

Examples will be described below, but the present invention is not limited to these examples.
The composition of the water-based inks of Examples and Comparative Examples, viscosity, and shear thinning index are shown in the following table. In addition, the numerical value of a composition in a table | surface shows a weight part.
The ink viscosity of each Example and Comparative Example was measured at 1 rpm using an EM rotational viscometer (manufactured by Tokyo Keiki Co., Ltd.) at 20 ° C. Further, the shear thinning index is a value calculated from the measured value of each ink viscosity.

The contents of the raw materials in the table will be described along the note numbers.
(1) Toyo Aluminum Co., Ltd., trade name: Chromashine CRS GD 20-R (solid content 60%)
(2) Toyo Aluminum Co., Ltd., trade name: Chromashine CRS GR 20-R (solid content 60%)
(3) Toyo Aluminum Co., Ltd., trade name: Chromashine CRS BL 10-R (solid content 60%)
(4) Eisen Hodogaya Co., Ltd., trade name: Eosin (5) Interference color pigment with aluminum dioxide coated on titanium dioxide, Asahi Kasei Kogyo Co., Ltd., trade name: Color flop aluminum (6) Mica dioxide on the surface of mica Pearl pigment coated with titanium, manufactured by Merck & Co., Ltd., trade name: Iriodin 201
(7) Pearl pigment with titanium dioxide coated on the surface of glass flake, manufactured by Nippon Sheet Glass Co., Ltd., trade name: Metashine RCFSX-1040RC
(8) Product name: Alcon P-100, manufactured by Arakawa Chemical Industries, Ltd.
(9) Product name: YS Polystar S145, manufactured by Yasuhara Chemical Co., Ltd.
(10) Product name: John Crill 61J, manufactured by Johnson Polymer Co., Ltd.
(11) Nippon Pure Chemical Industries, Ltd., trade name: Junron PW-110
(12) Product name: KELZAN, manufactured by Sanki Co., Ltd.
(13) Product name: Prisurf A212C, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

Preparation of ink Each raw material was mixed in the blending amounts of the Examples and Comparative Examples, and stirred and dissolved (dispersed) to obtain an ink composition for writing instruments.

Production of Writing Instruments A sample marking pen was produced by filling the inks of Examples 1 and 3 and Comparative Examples 1 and 3 into a commercially available marking pen (manufactured by Pilot Corporation, M-20PM).
After the inks of Examples 2 and 4 and Comparative Examples 2 and 4 were filled in a commercially available ballpoint pen (PH Corp., LH-20C7), an ink backflow preventer was disposed at the rear end of the ink so that a sample ballpoint pen was used. Produced.

Handwriting test Using the sample marking pen and the sample ballpoint pen, the handwriting was continuously written by hand on a black paper and a white paper, and was observed by changing the viewing angle.
At that time, the handwriting of Examples 1 to 4 and Comparative Example 1 developed a light interference color regardless of the color tone of the paper, but the handwriting of Comparative Examples 2 to 4 developed a light interference color on black paper. However, the light interference color was not visible on the white paper.

Ink Stability Test 3 g of the ink of Example 1 and Comparative Example 1 was placed in a sample bottle and the state of the ink when allowed to stand at room temperature for 24 hours was observed.
At that time, although the ink of Example 1 maintained a uniform dispersion state, the ink of Comparative Example 1 showed sedimentation of the pigment, and layer separation with the transparent supernatant was confirmed.

Claims (6)

  An ink composition for a writing instrument comprising an interference color pigment having a surface of aluminum flakes coated with silicon dioxide in a solvent.   The ink composition for a writing instrument according to claim 1, wherein an average particle diameter of the interference color pigment is in the range of 3 to 50 µm.   The ink composition for a writing instrument according to claim 1 or 2, wherein the interference color pigment is contained in the range of 0.1 to 30% by weight in the total amount of the ink composition.   The ink composition for a writing instrument according to any one of claims 1 to 3, wherein the ink composition contains water as a solvent and contains a shear thinning agent.   The viscosity of the ink composition is a value measured by a rotational viscometer at 20 ° C. and 1 rpm in the range of 100 to 2000 mPa · s, and the shear thinning index is in the range of 0.2 to 0.8. Item 5. The ink composition for a writing instrument according to Item 4.   A writing instrument incorporating the ink composition for a writing instrument according to any one of claims 1 to 5.