JP5748368B2 - Oil-based ink composition for writing instruments - Google Patents

Description

  The present invention relates to an oil-based ink composition for writing instruments, and in particular, there is no repelling on various writing surfaces including not only a normal writing surface such as a paper surface but also a smooth and poor wettability writing surface. The present invention relates to an oil-based ink composition for a writing instrument capable of forming a handwriting with excellent adhesion.

  Conventionally, oil-based inks used for writing instruments include a colorant, an organic solvent, a resin, and, if necessary, a surfactant, and are required to adhere to handwriting formed on writing surfaces of various materials. Smooth, hard and poorly wettable materials, such as synthetic resin film, glass, metal, surface coated with resin or silicone, etc. will cause repellency, adhesion may be insufficient, A good handwriting could not be formed.

  In order to solve the above problem, a coating film when writing on a non-absorbing surface of a metal, plastic, silicone-coated craft tape or the like containing a colorant, an organic solvent, a terpene phenol resin, and a silicone-modified acrylic resin An ink for an oil-based marking pen having excellent fixability is disclosed (for example, see Patent Document 1). However, the silicone-modified acrylic resin used in this oil-based ink composition is poor in the ability to fix the coating film to the writing surface, and requires a separate use of 5 to 10% by mass of the fixing resin.

  Patent Document 2 discloses an oil-based ink composition for a writing instrument comprising a colorant, an organic solvent comprising an isoparaffin hydrocarbon having 6 to 10 carbon atoms, and an acrylic-silicone graft copolymer. Although it is said that good writing can be performed even on a wet writing surface, the organic solvent has a problem that a usable material is limited due to low solubility. Further, as in Patent Document 1, a separate use of 25% by mass of the fixing resin is recommended.

  Further, Patent Document 3 discloses an oil-based ink composition for writing instruments using a silicone acrylic resin composed of a colorant, an organic solvent, a resin, and a silicone macromonomer having a dendrimer structure. Since the resin is bulky in the dendrimer part, the contact area of the acrylic resin with respect to the writing surface in one molecule of the resin is low, and the fixing performance of the acrylic resin is difficult to be exhibited. Further, since the orientation density of the resin itself on the writing surface is lowered, as a result, the fixing force is poor as in the above example, and a separate fixing resin is required.

  In order to improve the adhesion of the writing line, when a separate fixing resin is used, the viscosity of the ink generally tends to increase, and it may be difficult to mount the ink on various writing instruments. Even in a ballpoint pen or the like, there is a case where the ink is torred or blurred. In particular, in a writing instrument that ejects ink through a felt tip in a batting type marking pen, it is extremely difficult to ensure the fluidity of the ink.

JP 2007-070544 A JP 2010-168438 A JP 2010-106136 A

  The present invention is intended to solve the problems of this type of ink composition, that is, it repels handwriting formed on the writing surface against various writing surfaces including a smooth and poorly wet writing surface. It is an object to provide an oil-based ink composition for a writing instrument that is excellent in adhesion after writing while being able to form good writing.

  As a result of intensive research to achieve the above object, the present inventor has achieved that an oil-based ink composition containing a specific polar group-containing siloxane polymer, a colorant and an organic solvent has good adhesion to various writing surfaces. An excellent handwriting was formed, and it was found that a separate fixing resin such as a terpene phenol resin or a ketone resin was not necessary, and the present invention was completed.

  That is, the present invention provides (A) (a) a siloxane macromonomer represented by the following formula (1), (b) a hydroxyl group-containing vinyl monomer, (c) a carboxyl group-containing vinyl monomer, and (d) (meth) acrylic acid. A polar group-containing siloxane polymer having a hydroxyl value of 60 to 200 mgKOH / g and an acid value of 10 to 100 mgKOH / g obtained by copolymerization of an alkyl ester, (B) a colorant, and (C) an organic solvent. Provided is an oil-based ink composition for a writing instrument.

（式中、Ｒ^１は炭素数１〜１０のアルキル基を表し、Ｒ^２は炭素数１〜６の２価の炭化水素基を表し、Ｒ^３は水素またはメチル基を表し、ｎは６〜３００である。）

(In the formula, R ¹ represents an alkyl group having 1 to 10 carbon atoms, R ² represents a divalent hydrocarbon group having 1 to 6 carbon atoms, R ³ represents hydrogen or a methyl group, and n represents 6 to 6). 300.)

  In the oil-based ink composition of the present invention, it is not clear why the fixing resin is not required, but the polar group (hydroxyl group and carboxyl group) contained in the polar group-containing siloxane polymer is the adhesion and toughness of the coating film. It is presumed that the use of the fixing resin is unnecessary in order to increase the resistance.

  As described above, according to the present invention, an oil-based ink composition for a writing instrument that is free of repellency on a writing surface formed of various materials, can form a good writing, and has excellent adhesion after writing. Can be provided.

  In the present invention, (A) a polar group-containing siloxane polymer is composed of (a) a siloxane macromonomer, (b) a hydroxyl group-containing vinyl monomer, (c) a carboxyl group-containing vinyl monomer, and (d) a (meth) acrylic acid alkyl ester. It is obtained by polymerization. (A) The polar group-containing siloxane polymer contains a hydroxyl group and a carboxyl group at the same time in the molecular structure, and has a hydroxyl value of 60 to 200 mgKOH / g and an acid value of 10 to 100 mgKOH / g. Used to form clear handwriting that does not repel when written on materials with poor wettability. In the present invention, mgKOH / g which is a unit of hydroxyl value and acid value means 1 g of mgKOH / polar group-containing siloxane polymer.

  The (a) siloxane macromonomer is represented by the following formula (1), and various writing surfaces with low polarity, for example, the surface, for example, the surface are treated with silicone due to the effect of the silicone part contained in the molecular structure. Also improves wettability to craft tape and separators. (A) A siloxane macromonomer can use 1 type (s) or 2 or more types.

Here, R ¹ represents an alkyl group having 1 to 10 carbon atoms, R ² represents a divalent hydrocarbon group having 1 to 6 carbon atoms, R ³ represents hydrogen or a methyl group, and n represents a dimethylsiloxane unit. The average degree of polymerization is 6 to 300, preferably 6 to 100.

  The (a) siloxane macromonomer generally has a number average molecular weight of 300 to 30,000, preferably 500 to 20,000, and more preferably 600 to 20,000.

The (b) hydroxyl group-containing vinyl monomer imparts polarity to the (A) polar group-containing siloxane polymer and improves the adhesion to the writing surface, and one or more types can be used.
Specifically, for example, the number of carbon atoms of acrylic acid or methacrylic acid such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, hydroxypropyl (meth) acrylate, etc. 2-4 hydroxyalkyl esters; monoesters of polyether polyols such as polyethylene glycol, polypropylene glycol and polybutylene glycol and unsaturated carboxylic acids such as (meth) acrylic acid; glycidyl (meth) acrylate . Among these monomers, acrylic acid or methacrylic acid hydroxyalkyl ester having 2 to 4 carbon atoms is preferable.

(C) The carboxyl group-containing vinyl monomer imparts polarity to the (A) polar group-containing siloxane polymer to improve the adhesion to the writing surface, and one or more types can be used.
Specific examples include α, β-unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid. Among these monomers, acrylic acid and methacrylic acid are preferable.

(D) The (meth) acrylic acid alkyl ester imparts film-forming properties to the (A) polar group-containing siloxane polymer and enhances the adhesion to the writing surface, and one or more of them may be used. it can.
Specifically, for example, an alkyl ester having 1 to 4 carbon atoms of acrylic acid such as methyl acrylate, ethyl acrylate, and butyl acrylate, an alkyl ester having 1 to 4 carbon atoms of methacrylic acid such as methyl methacrylate, ethyl methacrylate, and the like can be given. be able to.

  The use ratio of each of the above monomers constituting the (A) polar group-containing siloxane polymer of the present invention is 2 to 40% by mass of (a) siloxane macromonomer, and (b) hydroxyl group, based on the total amount of the monomer mixture. The content vinyl monomer is 12 to 50% by mass, (c) the carboxyl group-containing vinyl monomer is 1 to 15% by mass, and the balance is (d) (meth) acrylic acid alkyl ester, which can be synthesized by solution polymerization or emulsion polymerization. it can.

  In the case of solution polymerization, it can be synthesized by heating and copolymerizing the monomer mixture in the presence of a polymerization initiator in an organic solvent according to a known method. The organic solvent to be used is not particularly limited as long as it dissolves the monomer mixture and the polar group-containing siloxane polymer, and the same solvent as the organic solvent (C) used in the oil-based ink composition for writing instruments of the present invention is used. It can also be used. As such an organic solvent, ethylene glycol diethyl ether, ethylene glycol monoisopropyl ether, propylene glycol monomethyl ether is preferable.

  In the case of emulsion polymerization, it can be synthesized by adding a monomer mixture to water in which a surfactant and a polymerization initiator are dissolved and emulsifying it, followed by heating and copolymerization according to a known method. .

  By copolymerizing each monomer at the above use ratio, the polar group-containing siloxane polymer (A) having a hydroxyl value in the range of 60 to 200 mgKOH / g and an acid value in the range of 10 to 100 mgKOH / g is obtained. Can be obtained. When the hydroxyl value is less than 60 mgKOH / g, or when the acid value is less than 10 mgKOH / g, the adhesiveness and toughness of the coating film are lowered, so that a separate fixing resin is required. On the other hand, when the hydroxyl value exceeds 200 mgKOH / g, or when the acid value exceeds 100 mgKOH / g, the water resistance of the coating film decreases.

  (A) The carboxyl group-containing vinyl monomer constituting the polar group-containing siloxane polymer may be used in an unneutralized state, or may be used in a partially neutralized state. Neutralization may be carried out after neutralizing the carboxyl group-containing vinyl monomer, or after the copolymerization.

  As the neutralizing agent, ethanolamine such as monoethanolamine, diethanolamine, and triethanolamine, sodium hydroxide, potassium hydroxide, and the like can be used. (A) The polar group-containing siloxane polymer coating film is flexible, Ethanolamine is preferred because of its good solubility in organic solvents.

  The neutralization rate is preferably 50 mol% or less, more preferably 25 mol% or less. When the neutralization rate increases, the water resistance of the coating film of the polar group-containing siloxane polymer (A) may decrease.

  (A) The polar group-containing siloxane polymer has a number average molecular weight of 1,000 to 100,000, preferably 3,000 to 50,000.

  A preferred (A) polar group-containing siloxane polymer is a silicone-grafted acrylic polymer, and a commercially available product is also available. For example, Cymac US-450, 480, Reseda GS-1015 (made by Toagosei Co., Ltd.), etc. are mentioned.

  In the present invention, since the (A) polar group-containing siloxane polymer contains a large amount of polar groups such as hydroxyl groups and carboxyl groups in the molecular structure, the polarity of the whole polymer is high and the adhesive strength as an acrylic resin is excellent. As a result, the writing line coating film can be sufficiently fixed to the writing surface without newly adding a fixing resin.

  (A) The polar group-containing siloxane polymer is used in the range of 1 to 30% by mass, preferably 5 to 20% by mass, based on the total amount of the ink composition, as a solid content. By using 1% by mass or more, good handwriting can be formed, and by using 30% by mass or less, there is no problem that the handwriting is faded or cannot be written.

  In the present invention, a pigment or a dye is used as the colorant (B). The colorant may be used singly or in combination of two or more, and is used in the range of 3 to 40% by mass, preferably 5 to 30% by mass in the total amount of the ink composition. When the colorant is 3% by mass or more, a clear writing line can be obtained even on a transparent material such as glass, and when it is 40% by mass or less, problems such as a decrease in storage stability of the ink may occur. There is no.

  Examples of pigments include carbon black, ocher, barium yellow, bitumen, cadmium red, titanium oxide, zinc white, bengara, chromium oxide, iron black, cobalt blue, alumina white, iron oxide yellow, iron oxide red, ultramarine blue, and chrome green. Inorganic pigments, azo pigments, phthalocyanine pigments, nitroso pigments, nitro pigments, basic dye pigments, acid dye pigments, vat dye pigments, mordant dye pigments, natural dye pigments, quinacridone pigments And organic pigments such as pigments, anthraquinone pigments and dioxazine pigments.

  As dyes, organic solvent-soluble dyes such as Balifast Black 1807, 3806, 3807, Bali Fast Violet 1701, Bali Fast Red 1360, 2320, 1320, Bali Fast Blue 1601, 1605, 1621, Nigrosine Base EX (manufactured by Orient Chemical Industries), SP-Black GMH, Methyl Violet Base, SP-Violet C-RH, Violet 521, SP-Red 533, SP-Red C-GH, SP-Red C-BH, SP .T-orange 6, S.B.N-yellow 510, S.P.T-blue 111, blue 121, SP-blue C-RH (manufactured by Hodogaya Chemical Co., Ltd.), C.I. I. Solvent Black 46, C.I. I. Solvent Black 5 etc. are mentioned.

  In the present invention, a general-purpose solvent can be used as the organic solvent (C), and it is used in the range of 40 to 85% by mass, preferably 50 to 85% by mass in the total amount of the ink composition. If the blending ratio of the organic solvent is too small, the viscosity of the oil-based ink composition becomes too high, resulting in a problem that the handwriting is faded and the long-term stability of the ink is lowered. Moreover, when there are too many compounding ratios of an organic solvent, it will become easy to produce malfunctions, such as an ink back-through and a blur of a writing line. The organic solvent includes a solvent for synthesizing the polar group-containing siloxane polymer (A) or a solvent for dissolving the polymer.

As the organic solvent,
Alcoholic organic solvents such as ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, tert-amyl alcohol, benzyl alcohol;
Ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, ethylene glycol diethyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propylene glycol mono Ethyl ether, propylene glycol monobutyl ether, propylene glycol monophenyl ether, diethylene glycol monoethyl ether, diethylene glycol monophenyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, tripropylene glycol Bruno ether, 3-methoxybutanol, 3-methoxy-3-glycol ethers such as methyl butanol organic solvents;
hydrocarbon organic solvents such as n-heptane, n-octane, methylcyclohexane, ethylcyclohexane;
Ketone organic solvents such as methyl n-propyl ketone, methyl n-butyl ketone and di-n-propyl ketone;
Ester organic solvents such as n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, ethyl propionate, n-butyl propionate, methyl lactate, ethyl lactate, and γ-butyrolactone;
Etc. Two or more organic solvents may be used in combination.

  (C) The main solvent of the organic solvent is preferably an organic solvent having a vapor pressure of 5.0 to 50 mmHg at 20 ° C., and the organic solvent having a vapor pressure of 5.0 to 50 mmHg at 20 ° C. is the total amount of the organic solvent. The content is preferably 50% by mass or more. Since these organic solvents are relatively easy to volatilize and have excellent dryness of handwriting, when the handwriting is touched, undried ink adheres to the hand or a blank that does not form handwriting on the writing surface. Good handwriting can be formed without causing problems such as contamination of parts.

As an organic solvent having a vapor pressure of 5.0 to 50 mmHg (20 ° C.),
Ethyl alcohol (44), n-propyl alcohol (14.5), isopropyl alcohol (32.4), isobutyl alcohol (8.9), sec-butyl alcohol (12.7), tert-butyl alcohol (30.6) ), Alcohol-based organic solvents such as tert-amyl alcohol (13.0);
Glycol ether organic solvents such as ethylene glycol diethyl ether (9.7), ethylene glycol monoisopropyl ether (6.0), propylene glycol monomethyl ether (7.6);
hydrocarbon organic solvents such as n-heptane (35.0), n-octane (11.0), methylcyclohexane (37.0), ethylcyclohexane (10.0);
Ketone organic solvents such as methyl n-propyl ketone (12.0) and di-n-propyl ketone (5.2);
Ester organic solvents such as n-propyl acetate (25.0), isopropyl acetate (43.2), n-butyl acetate (8.4), isobutyl acetate (13.0), ethyl propionate (28.0) ;
Can be mentioned.
Here, the numbers in parentheses indicate the vapor pressure of each organic solvent at 20 ° C.

The organic solvent having a vapor pressure of 5.0 to 50 mmHg at 20 ° C. includes a solvent (C ₁ ) having a vapor pressure of 5.0 to 20 mmHg at 20 ° C., and an organic solvent (C ₂ having a vapor pressure of 21 to 50 mmHg at 20 ° C. ) In combination.

As the organic solvent (C ₁ ) having a vapor pressure of 5.0 to 20 mmHg at 20 ° C., a glycol ether organic solvent is preferable. Specifically, ethylene glycol diethyl ether, ethylene glycol monoisopropyl ether, propylene glycol monomethyl ether is used. preferable. This is because these solvents are excellent in quick-drying of handwriting and excellent in solubility of various additives.

As the organic solvent (C ₂ ) having a vapor pressure of 21 to 50 mmHg at 20 ° C., an alcohol-based organic solvent is preferable, and specifically, ethyl alcohol and isopropyl alcohol are preferable.

The organic solvent (C ₂ ) having a vapor pressure of 21 to 50 mmHg at 20 ° C. is preferably contained in an amount of 5 to 15% by mass in the total amount of the ink composition. By containing this organic solvent in the above-mentioned amount range, the drying property of the writing line is greatly improved, and the repelling on the writing surface with poor wettability is also suppressed. In addition, the drying property of the entire oil-based ink composition is improved, and the phenomenon that the strength of the coating film decreases due to the low-vapor pressure organic solvent remaining in the coating film during film formation is suppressed, and a tough coating film is produced. It becomes possible to do.

  The oil-based ink composition for a writing instrument according to the present invention includes a viscosity modifier, a dye solubilizer, a pigment dispersant, and a component other than the components (A) polar group-containing siloxane polymer, (B) colorant, and (C) organic solvent. An appropriate amount of various additives such as a dispersion aid, a rust inhibitor, a shear thinning agent, and a surfactant may be contained. Further, an appropriate amount of another fixing resin may be contained as long as the effects of the present invention are not impaired.

  The oil-based ink composition for writing instruments of the present invention can be prepared by mixing the above-mentioned components. The method for preparing the ink composition is not particularly limited. For example, first, (B) a colorant is dispersed or dissolved in (C) an organic solvent using an appropriate technique, and then (A) a polar group-containing siloxane polymer, Examples of the method include adding other additives as necessary and mixing by stirring.

  The oil-based ink composition for a writing instrument of the present invention is used by filling a marking pen or a ballpoint pen having a tip attached to a writing tip.

  As long as the marking pen is provided with the oil-based ink composition for a writing instrument of the present invention, the marking pen is not limited to a method such as a batting type or a direct liquid type.

  As long as the ballpoint pen is provided with the oil-based ink composition for writing instruments of the present invention, the structure and shape of the ink cylinder itself are not particularly limited. For example, the ink is directly contained in the shaft cylinder, and the comb groove Having an ink flow rate adjusting member made of a fiber bundle and an ink flow rate adjusting member made of a fiber bundle, and an ink storage tube filled with an ink composition in a shaft tube, and the ink storage tube has a ball attached to the tip portion Examples include a simple structure communicating with the chip, and a ballpoint pen having a structure in which a liquid stopper for backflow prevention is in close contact with the end face of the ink. As the ball, a cemented carbide ball made of tungsten carbide or the like, a ceramic ball such as silica, alumina, zirconia, silicon carbide, or the like is used. The holder material of the chip is stainless steel, white or white, brass, nickel-plated brass, or the like.

  For the shaft cylinder and the ink storage tube, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, nylon, or a metal is used.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only the following Examples. In each example, unless otherwise specified, parts and% are based on mass.

(Examples 1-5, Comparative Examples 1-6)
Inks shown in Table 3 were prepared using various silicone-grafted acrylic polymers, colorants and organic solvents shown in Tables 1 and 2. In addition, the numerical value in a table | surface shows the mass%.

(Production of ballpoint pen)
Each of the ink compositions prepared in Examples and Comparative Examples was filled into a polypropylene pipe, and a stainless steel spring tip (ball surface roughness (arithmetic average roughness: Ra) of 0.06 μm) was attached thereto. Thereafter, grease for preventing ink drying and outflow was filled from the end, and a test ballpoint pen core and a ballpoint pen were produced.

  Using the above test ballpoint pen, a writing test, a scratch test and a storage test were carried out by the following methods. The results are shown in Tables 4-6.

(written examination)
Using each test ballpoint pen, writing was made on craft tape, polypropylene, and glass, and the repelling and blurring of the writing lines were visually determined according to the following criteria.
○: No repelling or blurring is observed in the handwriting △: Some repelling is recognized in the handwriting ×: Repelling is recognized in the handwriting ▲: Scratching is recognized in the handwriting

  “Repel” indicates that ink discharge is good, but the ink does not spread out on the writing surface, and there is a portion where no handwriting remains on the writing surface. This represents a state in which there is a portion where no handwriting remains on the writing surface.

(Abrasion test)
Using each test ballpoint pen, write on kraft tape, polypropylene, and glass, and visually check the state of the handwriting after 10 rounds of rubbing with a 500 g load on the written line using a cotton swab. The determination was made according to the following criteria.
○: There was no change in the state of the handwriting before and after rubbing △: The handwriting was peeled off to about half before rubbing ×: All the handwriting was peeled off

(Preservation test)
Each test ballpoint pen was stored for 2 weeks in a thermostatic bath at 50 ° C. and then written on craft tape, polypropylene, and glass, and the state of the handwriting was visually determined according to the following criteria.
A: Ink ejection is normal and no repelling is seen in the handwriting.
○: The ink is ejected normally, but the handwriting is slightly repelled.
X: The ink is ejected normally, but the handwriting is repelled.
(Triangle | delta): The discharge of ink is bad and a blur is seen in a handwriting.
▲: Ink is not ejected and writing is not possible.

  Table 4 shows the results of the written test.

  The results of the abrasion test are shown in Table 5.

  Table 6 shows the results of the storage test.

  From Tables 4 to 6, it was found that the oil-based ink composition for a writing instrument of the present invention showed good results in a writing test, a scratch test and a storage test.

  The siloxane polymer containing only the hydroxyl group (Comparative Example 1) and the siloxane polymer containing only the carboxyl group (Comparative Example 2) exhibited insufficient ink fixing properties because the handwriting was peeled off in the scratch test. I found out. The acrylic siloxane copolymer (Comparative Example 3) containing neither a hydroxyl group nor a carboxyl group was inferior to Comparative Examples 1 and 2 in all the test results described above. Similarly, the acrylic dimethicone copolymer (Comparative Example 4) containing neither hydroxyl group nor carboxyl group was inferior to Comparative Example 3 in all the test results.

  In addition, when a ketone resin is blended as a fixing resin in the comparative polymer 4, writing can be performed if the blending amount is small, but the sticking property is poor (Comparative Example 5), and the sticking property is improved by increasing the blending amount. Has come to be accepted. This tendency is particularly remarkable during the storage test (Comparative Example 6).

(Examples 6 to 8)
The ink composition prepared in Example 1 was filled into a polypropylene pipe, and a stainless steel spring tip (ball surface roughness (Ra) 0.04 to 0.08 μm) was attached to each of the pipes. Filled with grease for preventing ink drying and spilling, the ballpoint pen was made as the core of the test ballpoint pen.

  Using the above test ballpoint pen, writing was made on craft tape, polypropylene, and glass, and whether or not writing was possible was visually determined according to the following criteria. Table 7 shows the results of a writing test on the ball surface roughness (Ra).

○: Writing is possible without slipping △: Writing is possible but slight slipping occurs: ×: Slipping is not possible and writing is not possible

  From the results of Table 7, the oil-based ink composition for a writing instrument of the present invention is mounted on an oil-based ballpoint pen having a ballpoint pen tip having a ball surface roughness (arithmetic average roughness: Ra) of 0.06 μm or more. It can be seen that a ballpoint pen that can be written without slipping is obtained.

Claims (10)

(A) (a) by copolymerization of a siloxane macromonomer represented by the following formula (1), (b) hydroxyl group-containing vinyl monomer, (c) carboxyl group-containing vinyl monomer, and (d) (meth) acrylic acid alkyl ester A polar group-containing siloxane polymer having a hydroxyl value of 60 to 200 mgKOH / g and an acid value of 10 to 100 mgKOH / g,

(In the formula, R ¹ represents an alkyl group having 1 to 10 carbon atoms, R ² represents a divalent hydrocarbon group having 1 to 6 carbon atoms, R ³ represents hydrogen or a methyl group, and n represents 6 to 6). 300.)
An oil-based ink composition for a writing instrument, comprising (B) a colorant and (C) an organic solvent.   (B) the hydroxyl group-containing vinyl monomer constituting the polar group-containing siloxane polymer (A) is a C2-C4 hydroxyalkyl ester of acrylic acid or methacrylic acid, and (c) the carboxyl group-containing vinyl monomer is acrylic. The oil-based ink composition for a writing instrument according to claim 1, which is an acid or methacrylic acid.   The oil-based ink composition for a writing instrument according to claim 2, wherein the polar group-containing siloxane polymer (A) is a silicone-grafted acrylic polymer.   The oil-based ink composition for writing implements in any one of Claims 1-3 which contain 1-30 mass% of said polar group containing siloxane polymers (A) in the ink composition whole quantity.   The oil-based ink composition for writing implements in any one of Claims 1-4 which contain 40-85 mass% of said organic solvents (C) in the ink composition whole quantity.   The oil-based ink composition for a writing instrument according to any one of claims 1 to 5, wherein the main solvent of the organic solvent (C) is an organic solvent having a vapor pressure of 5.0 to 50 mmHg at 20 ° C. The organic solvent having a vapor pressure of 5.0 to 50 mmHg at 20 ° C, the organic solvent (C ₁ ) having a vapor pressure of 5.0 to 20 mmHg at 20 ° C, and the organic solvent having a vapor pressure of 21 to 50 mmHg at 20 ° C ( It becomes because C ₂₎ and the organic solvent (C ₂₎ a writing instrument oil-based ink composition according to claim 6 containing 5 to 15 mass% in the total amount of the ink composition. The oil-based ink composition for a writing instrument according to claim 7, wherein the organic solvent (C ₁ ) is a glycol ether organic solvent. The organic solvent (C ₂₎ is, writing instrument oil-based ink composition according to claim 7 is an alcohol-based organic solvent.   2 to 30% by mass of the polar group-containing siloxane polymer (A), 3 to 40% by mass of the colorant (B), and 40 to 85% by mass of the organic solvent (C) in the total amount of the ink composition. The oil-based ink composition for writing instruments in any one of -9.