JP6312247B2 - Oil-based ballpoint pen ink composition - Google Patents

Description

  The present invention relates to an oil-based ballpoint pen ink composition. More specifically, the present invention relates to an oil-based ballpoint pen ink composition that does not leak even after long-term storage and can provide a smooth and light writing feeling.

  Conventionally, oil-based ballpoint pens have a drawback that the writing feeling is heavy because the viscosity of the ink is high, and the tendency is particularly remarkable when the ink viscosity at 25 ° C. is around 8,000 to 10,000 mPa · s. . Although the writing feeling can be improved by setting the ink viscosity at 25 ° C. to around 1,000 to 5,000 mPa · s, by reducing the viscosity, the tip leaks when the pen nib is stored downward for a long time ( Leakage of ink from the nib) was a problem.

  In order to solve this problem, by adding 0.05 to 1.0% by weight of hydrophilic or hydrophobic silica fine particles having a specific surface area in a specific range and 0.01 to 10% by weight of polyvinylpyrrolidone, the viscosity is reduced. There has been proposed a method for eliminating the leakage at the time of long-term storage while having a light writing feeling (see, for example, Patent Documents 1 to 4). This is because the silica fine particles are linked to each other by the hydrogen bond of the silanol group (SiOH) that the silica fine particle has on the surface, the viscosity increases due to this bond and the network structure is formed, thereby leaking the ink from the pen tip. At the same time, polyvinyl pyrrolidone expected to form the above network structure more effectively and to make the structure very easy to break by applying a shearing force by writing. Is.

  However, the oil-based ballpoint pen ink proposed in Patent Document 1 and the like absorbs moisture by mixing the polar organic solvent, polyvinylpyrrolidone, colorant and the like into the ink. Because of this water mixing, it interacts with water and solvates, so the silanol bond between silica is inhibited and the polyvinyl pyrrolidone that should effectively form a network structure is However, in order to show compatibility, there is a problem in that the original enhancement effect is lost and leakage occurs. In addition, the silica fine particles aggregate and settle due to long-term storage, so that a network structure cannot be formed, and there is a problem that tip leakage occurs.

  In order to eliminate ink leakage, it has been conventionally done to add thixotropy to the ink, but this causes poor ink ejection, and it tends to cause blurring of writing lines at the beginning of writing. . As countermeasures for reducing the blur, Patent Documents 5 to 6 propose inks to which a modified silicone compound is added. The ink disclosed in Patent Document 6 is obtained by adding fine particle silica (Aerosil) as a thixotropic agent to the filtrate of an organic solvent, a resin, a colorant and a reactive amino-modified silicone dissolved by heating and stirring. The ink is obtained by sufficiently dispersing with three rolls. However, the ink thus obtained has poor long-term stability because the amino-modified silicone is highly reactive and gels with time.

JP-A-10-204368 Japanese Patent Laid-Open No. 11-286642 Japanese Patent Laid-Open No. 10-195365 JP-A-10-204368 JP 61-012773 A JP 2001-096991 A

  The object of the present invention is to improve the disadvantages of these conventional oil-based ballpoint pen inks. That is, it is an object of the present invention to provide an oil-based ballpoint pen ink that does not cause leakage even after long-term storage and can obtain a smooth and light writing feeling.

  As a result of intensive studies, the present inventors dispersed hydrophobic silica fine particles in a polar organic solvent, and dispersed water or a silicone compound having a low affinity for the polar organic solvent in an emulsion state in the solvent. As a result, it was found that silica fine particles are adsorbed on the silicone compound, and as a result, the silica fine particles play a role as an emulsifier and become a stable dispersion (so-called Pickering emulsion). Pickering emulsion is known as an emulsion in which fine particles are adsorbed on the surface (liquid-liquid interface) of emulsion particles, and the fine particles function like an emulsifier and maintain a stable dispersion state. It is speculated that the irreversible adsorption that is easy to adsorb and does not desorb when adsorbed is the stabilization mechanism.

  And by maintaining the above stable dispersion state, the network structure by the silanol bond of the silica fine particles is more stable and effective in suppressing the leakage before the silica fine particles and the solvent are dispersed in the solid-liquid state. It was found that it can be expressed in

  In addition, a silicone compound with a low affinity for water and polar organic solvents is liquid-dispersed as an emulsion, and hydrophobic silica fine particles are adsorbed on the liquid-liquid interface, so that the silica fine particles have a network structure even in polar organic solvents. Even when water is mixed due to moisture absorption, silanol bonds between silica particles are not inhibited and the effect of suppressing leakage is remarkable. The present invention has been reached.

  That is, the present invention is an emulsion containing hydrophobic silica fine particles, a non-reactive silicone compound and a polar organic solvent, wherein the polar organic solvent is used as a dispersion medium, the silicone compound is used as a dispersoid, and the hydrophobic silica is used. An oil-based ballpoint pen ink composition comprising an emulsion formed by adsorbing fine particles on an interface.

  According to the present invention, it is possible to provide an oil-based ballpoint pen ink composition that does not cause leakage even after long-term storage and can obtain a smooth and light writing feeling.

Hereinafter, embodiments of the present invention will be described in detail.
The oil-based ballpoint pen ink composition of the present invention is an emulsion containing hydrophobic silica fine particles, a silicone compound and a polar organic solvent, wherein the polar organic solvent is used as a dispersion medium, the silicone compound is used as a dispersoid, and the silica fine particles are used. Contains an emulsion formed by adsorbing to the interface.

  In the emulsion of the present invention, in order for silica fine particles to function effectively as an emulsifier, it is important that the silica fine particles exhibit amphipathic properties with respect to a low polarity silicone compound and a high polarity organic solvent. Such silica fine particles are preferably hydrophobic silica fine particles. This enhances the adsorptive power by interacting with the hydrophobic silicone compound, makes it easy for silica fine particles to form a network structure in a polar organic solvent, and solvates the moisture due to moisture absorption. Since it can be prevented, it has a remarkable effect of suppressing leakage.

  Among the hydrophobic silica fine particles, the hydrophobic silica fine particles obtained by partially chemically treating the surface of the hydrophilic silica fine particles with silane or siloxane are optimal. Such hydrophobic silica fine particles function effectively as an emulsifier because they have an affinity with a silicone compound due to the affinity between silicon and the like, and also with a polar organic solvent due to a silanol group. Examples of commercially available products of hydrophobic silica fine particles include Aerosil R974, R972, R972CF manufactured by Nippon Aerosil Co., Ltd.

  The hydrophobic silica fine particles preferably have a primary average particle diameter of 10 to 20 nm. If the primary average particle diameter is 10 nm or more, the effect of suppressing the increase in the viscosity of the ink due to the aggregation of particles is high, and if it is 20 nm or less, clogging at the tip of the pen and writing line blurring at the beginning of writing are generated. High suppression effect. The primary average particle diameter can be measured by an image analysis method using a transmission electron microscope (TEM) or the like.

  The content of the hydrophobic silica fine particles is preferably 0.01 to 3.0% by mass, more preferably 0.05 to 2.0% by mass, and still more preferably 0.1% with respect to the total amount of the oil-based ballpoint pen ink composition. It is -1.0 mass%. If the amount is less than 0.01% by mass, it is difficult to obtain a remarkable effect, and if it exceeds 3.0% by mass, the ink viscosity may increase or the particles may aggregate to cause inability to write.

  The silicone compound used in the emulsion of the present invention is not particularly limited as long as it is a non-reactive silicone compound capable of forming a pickering emulsion. Side chain type, both terminal types, one terminal type, both side chains A terminal type or the like can be used. These silicone compounds are desirably silicone compounds that are not compatible with polar organic solvents. Among non-reactive silicone compounds, non-reactive side-chain modified silicone compounds are partially chemically treated compared to double-ended and single-ended types because the modified portion is not localized. There is an advantage that it has a certain affinity for both the hydrophobic silica fine particles and the polar organic solvent, and it is easy to form a stable emulsion.

As a non-reactive side chain type modified silicone compound,
In the following [Chemical Formula 1], the organic group is an aralkyl group (for example, C ₆ H ₅ —CH (CH ₃ ) —CH ₂ —), an alkyl group (for example, —C _a H _{2a + 1} ), an alkyl group, and an aralkyl group (for example, , C ₆ H ₅ —CH (CH ₃ ) —CH ₂ —, —C _a H _{2a + 1} ), a fluoroalkyl group (eg, —CH ₂ CH ₂ CF ₃ ), an aralkyl-modified silicone, an alkyl-modified silicone, an alkyl. Non-reactive side chain type modified silicone selected from aralkyl modified silicone, fluoroalkyl modified silicone, phenyl modified silicone,
In the following [Chemical Formula 2], a non-reactive side chain type modified silicone selected from alkyl-modified silicone and alkyl-aralkyl-modified silicone, wherein R and R ′ are alkyl groups, or alkyl groups and aralkyl groups, is a preferred compound. As mentioned.
Of these, an alkyl-aralkyl-modified silicone compound in which R is an alkyl group and R ′ is an aralkyl group in [Chemical Formula 2] is more preferable.
All of these silicone compounds have low affinity for water and polar organic solvents, and in these solvents, they do not dissolve and can exist as emulsions. Further, it does not gel or thicken over time unlike reactive modified silicone, and does not inhibit the solubility of other components such as dyes in the ink.
Examples of commercially available non-reactive side chain-modified silicones include TSF4420, XF42-334, XF42-B3629, and alkyl-modified silicones TSF4421, XF42- A3161 etc. are mentioned.

  Further, as a silicone compound used in the emulsion of the present invention, a surfactant selected from low-HLB polyglycerin-modified silicone, polyether-modified silicone, polyether-alkyl-aralkyl-modified silicone, which is incompatible with polar organic solvents, and non-reactive These side chain type modified silicones are mentioned as preferred compounds. These silicone compounds have polar groups, but those with low HLB that are not compatible with polar organic solvents have low affinity for water and polar organic solvents, and are not soluble in these solvents. It can exist as an emulsion.

Examples of the polyglycerin-modified silicone include a surfactant having a polyglycerin chain branched from a silicone chain and a surfactant obtained by co-modifying a polyglycerin chain and an alkyl chain from a silicone chain. Examples of commercially available modified silicones include polyglycerin-modified silicones KF6104 and KF6105 manufactured by Shin-Etsu Silicone Co., Ltd.
Examples of the polyether-modified silicone include a polyether-modified silicone compound in which the organic group has a polyether group (—R (C _x H _2x O) _y R ′, x = 2 to 3) in the above [Chemical Formula 1]. Among these, a polyether-modified silicone compound having a polyoxyethylene group or a polyoxyethylene group / polyoxypropylene group is preferable. As the low HLB silicone compound, a commercially available one can be used, but one having HLB adjusted by modification may be used. Examples of the modifying group effective to increase the HLB include ether modification, and the modifying group effective to decrease the HLB includes alkyl modification and fluoroalkyl modification. Examples of such commercially available modified silicone include KF945, KF6020, and X22-4515 manufactured by Shin-Etsu Silicone Co., Ltd.

  The content of the silicone compound is preferably 0.05 to 3.0 mass%, more preferably 0.1 to 1.0 mass%, based on the total amount of the ink composition for oil-based ballpoint pens. If the amount is less than 0.05% by mass, it may be difficult to obtain a remarkable effect. If the amount exceeds 3.0% by mass, the ink viscosity becomes high, or causes problems such as separation in the ink due to aggregation or coalescence. It may become. Silicone compounds may be used alone or in combination of two or more.

As the polar organic solvent used in the emulsion of the present invention, the solubility required of the ink composition for oil-based ballpoint pens for the colorants, resins and additives described later, such as alcohols, glycols, glycol ethers, cellosolves And known solvents that exhibit dispersibility can be used.
Specifically, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, t-butanol, benzyl alcohol, phenoxyethanol, glycerin; ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol Glycols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monoisobutyl ether, diethylene glycol Monoethyl ether , Diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol dimethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monophenyl ether, propylene glycol monopropyl ether, tripropylene glycol And glycol ethers such as monomethyl ether and tripropylene glycol monobutyl ether; cellosolves such as ethylene glycol monomethyl ether acetate and phenyl cellosolve; and the like. Among these polar organic solvents, benzyl alcohol, phenoxyethanol, propylene glycol monobutyl ether, propylene glycol monomethyl ether and the like are preferable. A polar organic solvent can be used individually or in combination of 2 or more types.

  The content of the polar organic solvent is preferably in the range of 30.0 to 90.0% by mass, more preferably, based on the total amount of the ink composition for oil-based ballpoint pens, in consideration of ink viscosity, silica dispersibility, and the like. It is in the range of 50.0-70.0% by mass. The polar organic solvent is necessary for ensuring basic performance as an ink for oil-based ballpoint pens, and in addition to dispersing or dissolving silica fine particles, colorants, and resins, in order to obtain an appropriate writing line drying property. It is necessary for

  Various methods can be adopted as a method for producing the oil-based ballpoint pen ink composition containing the emulsion of the present invention. For example, hydrophobic silica fine particles are dispersed in an appropriate amount of a polar organic solvent to an average particle size of about 0.1 μm in dynamic light scattering particle size distribution measurement, and then a silicone compound is added to the dispersion and stirred. Pickering emulsion can be obtained by emulsifying and dispersing. As a dispersion means of hydrophobic silica fine particles, a mixing device such as a disperser, a sand mill, a bead mill, a high-pressure homogenizer, a homomixer, or the like can be used. There is no particular limitation as long as it is a uniform mixing method such as a paddle blade, a disper, or a homomixer. The dispersion temperature is preferably 15 to 30 ° C, more preferably 20 to 25 ° C. When dispersing, a surfactant for stabilizing the emulsion may be added or not added as long as it does not inhibit the formation of the pickering emulsion. In the present invention, it is stable and effective to disperse the emulsion particle diameter of the silicone compound in the range of 0.3 μm to 5.0 μm as a guide. The emulsion formation state and the formed emulsion particle size can be observed and measured with a dynamic light scattering particle size distribution analyzer, a laser diffraction particle size distribution analyzer, an optical microscope, or the like.

  Subsequently, the obtained emulsion and a colorant, resin, polar organic solvent, and other additives are uniformly stirred and mixed to obtain an oil-based ballpoint pen ink composition. For the stirring, a method using a stirrer such as a mixer, a homogenizer, a disper, a roll, or a disperser can be used.

  Alternatively, polar organic solvent, hydrophobic silica fine particles and silicone compound are dispersed in high concentration in advance, diluted to a constant concentration with polar organic solvent, and then added with colorant, resin and other additives, stirred and mixed The method to do is also good.

  When forming an emulsion, the content of the silicone compound and the hydrophobic silica fine particles is preferably an amount that does not greatly deviate. When the proportion of the hydrophobic silica fine particles is increased, blurring at the time of writing tends to occur, and on the contrary, when the proportion of the silicone compound is increased, leaking easily occurs. The content ratio (mass ratio) of the silicone compound and the hydrophobic silica fine particles is preferably in the range of 1: 0.2 to 1: 7, more preferably 1: 0.5 to 1: 5.

  In the ink composition for oil-based ballpoint pens of the present invention, it is preferable to blend an emulsion so that the content of the silica fine particles and the silicone compound is 0.05 to 8% by mass with respect to the total amount of the ink composition. If it is less than 0.05% by mass, the effect of preventing leaking may be insufficient, and if it exceeds 8% by mass, writing property after storage may be deteriorated or the writing line at the beginning of writing may be blurred. A more preferable content is 0.15 to 5% by mass with respect to the total amount of the ink composition.

As the colorant used in the present invention, it is possible to use known dyes and pigments that are usually used for writing instruments and paint inks. A coloring agent can be used individually or in combination of 2 or more types.
As the dye, alcohol-soluble dyes, oil-soluble dyes, metal-containing dyes, basic dyes, acid dyes, direct dyes, and various salt-forming dyes can be used. For example, nigrosine base, spiron black GMH special, spiron blue # 111, spiron violet C-RH, # 510, spiron red # 530, CB C-GH, C-BH, spirone orange # 6, GH Spiron Yellow 2GH, C-GH, # 510, # 530, Bali Black # 1802, # 1805, # 3820, Bali Blue # 1601, Bali Violet # 1701, Bali Yellow YUM # 3104, Bali Fast Red # 2320, # 1320, Auramin, Rhodamine, Methyl Bio Red Base, Victoria Blue Base and the like.
As the pigment, an inorganic pigment or an organic pigment can be used as it is, and a processed pigment or a dispersed toner whose surface has been modified with a resin or a surfactant can also be used. For example, titanium oxide, carbon black, metal powder, phthalocyanine pigment, azo pigment, anthraquinone pigment, cymnadrine pigment, nitro pigment, nitroso pigment and the like can be mentioned. When a pigment is blended as a colorant, a dispersant such as a surfactant can be added in addition to polyvinyl butyral, polyvinyl pyrrolidone, polyvinyl alcohol, and an acrylic resin.

  There is no restriction | limiting in particular in content of a coloring agent, What is necessary is just the quantity according to the solubility or dispersion power of a coloring agent, or the quantity suitable for a desired hue and density | concentration. A preferable content of the colorant is 5 to 40% by mass with respect to the total amount of the ink.

  Examples of the resin used in the present invention include ketone resin, rosin resin, sulfoamide resin, maleic acid resin, ester gum, xylene resin, alkyd resin, phenol resin, acrylic resin, polyvinyl pyrrolidone, polyvinyl butyral, and the like. These may be used alone or in combination of two or more. The resin is preferably a resin that can be dissolved in the polar organic solvent to be blended from the viewpoint of the storage stability of the ink. The preferable content of the resin is 0.1 to 30.0% by mass with respect to the total amount of the ink.

  The ink composition for oil-based ballpoint pens of the present invention, if necessary, for oil-based ballpoint pens, such as surfactants, preservatives, rust preventives, lubricants, and pH adjusters, as long as the effects of the present invention are not impaired. Various additives used in the ink can be used.

  The viscosity of the oil-based ballpoint pen ink composition is not particularly limited, but in order to obtain a light writing feeling, a range of 500 to 4,000 mPa · s is preferable at 25 ° C. In this viscosity range, the above pickering emulsion is used. Due to the action, there is no leakage from long-term storage.

  The ballpoint pen of the present invention is composed of an ink containing tube, a ball, a chip holder, a spring for pressing the ball, a joint for assembling them and joining the ink containing tube, a pen shaft, etc. However, the configuration of the ballpoint pen is not limited to this. The ink storage tube may be a refill.

  Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. In addition, this invention is not limited only to a following example.

(Examples 1 to 10)
According to the composition shown in Table 1, an oil-based ballpoint pen ink composition was prepared. Phenyl glycol and hydrophobic silica fine particles (the following (* 1)) were placed in a bead mill and operated at 20 to 25 ° C. and 5,000 rpm for 2 hours to obtain a dispersion of hydrophobic silica fine particles. Further, a silicone compound was added to the above dispersion, and the mixture was operated with a homomixer at 8,000 rpm × 15 minutes to obtain a pickering emulsion dispersion of the silicone compound and hydrophobic silica fine particles. Thereafter, benzyl alcohol, a dye, a resin, polyvinyl pyrrolidone, and a phosphate ester surfactant were added, dissolved, and mixed to obtain an oil-based ballpoint pen ink.

  In addition, the preparation method of the pickering emulsion is preliminarily dispersed in a high concentration of phenyl glycol, hydrophobic silica fine particles and silicone compound, diluted to a constant concentration with phenyl glycol and benzyl alcohol, dye, ketone resin, polyvinylpyrrolidone. Alternatively, a method of adding a surfactant may be used.

(Examples 11 to 13)
According to the composition shown in Table 1, an oil-based ballpoint pen ink composition was prepared. Phenyl glycol, benzyl alcohol, carbon black, and polyvinyl butyral as a dispersing agent were run in a bead mill at 5,000 rpm for 2 hours to obtain a colorant dispersion. At this time, this color material dispersion was prepared at a high concentration. On the other hand, phenyl glycol and hydrophobic silica fine particles are placed in a bead mill and run at 5,000 rpm for 2 hours to prepare a dispersion of hydrophobic silica fine particles. Further, a silicone compound is added to the dispersion, and a homomixer is used. It was operated at 8,000 rpm × 15 minutes to obtain a pickering emulsion dispersion of a silicone compound and hydrophobic silica fine particles. At this time, this pickering emulsion was prepared at a high concentration. After mixing the above high-concentration colorant dispersion, the above-mentioned high-concentration pickering emulsion, phenyl glycol, and benzyl alcohol, add a dye, a ketone resin, polyvinyl pyrrolidone, and a phosphate ester surfactant, and dissolve and mix them. An oil-based ballpoint pen ink was obtained.

(Comparative Example 1)
In Example 1, oil-based ballpoint pen ink was obtained in the same manner as in Example 1 except that hydrophilic silica fine particles (Aerosil # 200; Nippon Aerosil Co., Ltd.) were used instead of the hydrophobic silica fine particles.

(Comparative Example 2)
In Example 1, an oil-based ballpoint pen ink was obtained in the same manner as in Example 1 except that the entire amount of the silicone compound was replaced with hydrophobic silica fine particles.

(Comparative Example 3)
In Example 1, an oil-based ballpoint pen ink was obtained in the same manner as in Example 1 except that the amount of the hydrophobic silica fine particles was entirely replaced with the silicone compound.

(* 1) Aerosil R974 (Nippon Aerosil Co., Ltd.) primary average particle size 16nm

(* 2)

(* 3) Polyglyceryl-3 polydimethylsiloxyethyl dimethicone

(*Four)

(*Five)

  The test methods for the oil-based ballpoint pen inks obtained in the examples and comparative examples are as follows. The evaluation results are shown in Table 1.

[Viscosity] The viscosity of the ink composition for oil-based ballpoint pens was measured using a TV-22 viscometer manufactured by Toki Sangyo Co., Ltd. Measurement temperature: 25 ° C., rotor no. 01, rotational speed 10 rpm.

[Writing test]: Using writing paper A defined in JIS P 3201, a hand-written sensory test was performed, and the weight and lightness of writing at that time were evaluated.

[Leak test]: In the form of a knock-type ballpoint pen with a tip with a spring inserted inside, the ink tip leaks after standing for 2 weeks in an 80% 80% environment with the pen tip facing downward We evaluated whether there was any outage.

[Writing property after storage]: The oil-based ink composition for ballpoint pens was allowed to stand at 50 ° C., Dry for 4 weeks, and then evaluated for the occurrence of blurring when writing on the writing paper A defined in JIS P 3201.

  From the results of Table 1, the ink compositions of the examples using the emulsified hydrophobic silica fine particles and the silicone compound are low in viscosity and light in writing feeling, have no leakage, and have excellent writing properties after storage. I understand that. It was confirmed that by increasing the amount of the hydrophobic silica fine particles and the silicone compound in the ink composition, the writing feeling becomes very light at a low viscosity.

  On the other hand, although hydrophilic silica fine particles have the characteristics of low viscosity and light writing feeling, the adsorption force of hydrophilic silica to silicone compounds is weak, and in addition to the phenomenon that silica fine particles and silicone compounds are separated and aggregated. As a result of moisture absorption due to moisture absorption, a phenomenon in which silanol bonds between silica fine particles decreased was observed, leading to leakage.

  By using the ink composition for oil-based ballpoint pens of the present invention, it is possible to provide an oil-based ballpoint pen that does not leak even after long-term storage and has a light writing feeling like an aqueous ballpoint pen.

Claims (9)

Hydrophobic silica fine particles 0.01 to 3.0 % by mass , non-reactive silicone compound 0.05 to 3.0% by mass and an emulsion containing a polar organic solvent, the polar organic solvent as a dispersion medium, An oil-based ballpoint pen ink composition comprising an emulsion formed by using the silicone compound as a dispersoid and adsorbing the hydrophobic silica fine particles to an interface.
  The ink composition for oil-based ballpoint pens according to claim 1, wherein the silicone compound is a silicone compound that is incompatible with the polar organic solvent.   The ink composition for oil-based ballpoint pens according to claim 1 or 2, wherein the silicone compound is a non-reactive side chain type modified silicone compound.   The silicone compound is one or a mixture of two or more selected from non-reactive side chain modified silicone compounds having an alkyl group, an aralkyl group, an alkyl-aralkyl group, a phenyl group, or a fluoroalkyl group. The ink composition for oil-based ball-point pens in any one of 1-3.   The silicone compound is one or a mixture of two or more selected from polyglycerin-modified silicone compounds, polyether-modified silicone compounds, polyether-alkyl-aralkyl-modified silicones that are incompatible with the polar organic solvent. 4. The ink composition for oil-based ballpoint pens according to any one of 3 above. The content of the silica fine particles and the silicone compound is 0.15 to 5 % by mass with respect to the total amount of the ink composition, and the content ratio of the silica fine particles and the silicone compound is 1: 0.2 to 1: 7. The ink composition for oil-based ballpoint pens according to any one of claims 1 to 5.
  Furthermore, the ink composition for oil-based ball-point pens in any one of Claims 1-6 containing a coloring agent and resin which can be melt | dissolved in the said polar organic solvent.   The ink composition for oil-based ballpoint pens according to claim 7, which has a viscosity at 25 ° C of 500 to 4,000 mPa · s.   An oil-based ballpoint pen comprising an ink containing tube filled with the ink composition for an oil-based ballpoint pen according to claim 1.