JP2010059270A - Hydrophobic inorganic oxide and rubber composition using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition excellent in low heat generation and wear resistance. <P>SOLUTION: A hydrophobic inorganic oxide is obtained by subjecting hydrophilic inorganic oxide particles such as silica to a surface treatment with a sulfide silane coupling agent, an organic silane compound (for example, an aminosilane compound) and a hydrophobizing agent (for example, a carboxylic acid compound, an alkylketene dimer and a diisocyanate compound), wherein the hydrophobic inorganic oxide has: the sulfide silane coupling agent coupled to hydroxy groups on the particle surface; and the hydrophobizing agent coupled via the organic silane compound to hydroxy groups on the particle surface. A rubber composition is prepared by mixing the hydrophobic inorganic oxide with rubber. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydrophobic inorganic oxide and a rubber composition containing the hydrophobic inorganic oxide.

  Inorganic oxides such as silica are used in various applications including fillers for rubber compositions and resin compositions. The inorganic oxide includes a hydrophilic inorganic oxide having a hydroxyl group on the particle surface. For example, in the case of silica, the particle surface has a silanol group (Si—OH). Thus, when a hydroxyl group exists on the particle surface, there is a problem that the particles of the inorganic oxide are easily aggregated due to the influence thereof and the dispersibility is poor. Therefore, a hydrophobic inorganic oxide obtained by hydrophobizing a hydrophilic inorganic oxide by surface treatment with a hydrophobizing agent is known.

  By the way, in general, a pneumatic tire has required performance such as low fuel consumption, good wear resistance, and high grip force. Of these, in order to improve fuel efficiency, it is effective to reduce the hysteresis loss of the rubber composition constituting the tire so as to reduce heat generation. Therefore, in a tire rubber composition, carbon black as a filler is replaced with silica, and a silane coupling agent is further blended.

  However, the demand for reducing the fuel consumption of pneumatic tires has recently increased, and it is required to reduce the hysteresis loss of the rubber composition more than before. On the other hand, in order to ensure good wear resistance as a tire, the rubber composition is also required to have excellent reinforcing properties. From such a viewpoint, the further improvement of the said inorganic oxide used as a filler is desired.

  Patent Document 1 below proposes a hydrophobic silica obtained by treating silica with an aminoalkylsilane compound and then reacting with at least one hydrophobizing agent selected from carboxylic acid, alkyl ketene dimer and diisocyanate compound. Yes. However, this document is merely an improvement in the hydrophobicity of silica for the purpose of improving the photoaging prevention performance of general paints, etc., and improving the abrasion resistance of rubber and resin and improving the reinforcement of mechanical strength. However, when actually blended with a rubber composition, it is inferior in wear resistance and is insufficient in terms of low heat build-up.

  Patent Document 2 listed below discloses a rubber composition obtained by blending and kneading silica, which has been surface-treated with an organic silicon compound to a predetermined degree of hydrophobicity, in a diene rubber. In this document, it is disclosed that a silane coupling agent is blended together with the partially hydrophobized silica, but the silane coupling agent is added when the rubber is mixed. Therefore, the dispersibility of silica is insufficient, the effect of improving the low heat build-up is small, and the reinforcement is not sufficient.

  Patent Document 3 below proposes a method for producing an anhydrous oxide surface-treated with an alkoxysilane compound having a thiocyanate group or a sulfide bond, and its blending into a rubber composition. However, this document discloses that the silica is surface-treated by a predetermined modification method using an organosilicon compound such as a sulfide silane coupling agent in order to improve the storage stability of the silica itself. Such silica has insufficient dispersibility in the rubber composition, and the effect of improving fuel economy is small.

  Patent Document 4 below discloses a tire using a rubber composition in which silica that has been hydrophobized in advance to diene rubber, and organomercaptosilane and alkoxyalkylsilane are used as silica that has been hydrophobized in advance. Silicas treated with are disclosed. Thus, although the silica surface-treated using the mercaptosilane coupling agent and the hydrophobizing agent has been disclosed, further improvement is required in terms of low heat buildup and reinforcement.

In Patent Document 5 below, in a rubber composition constituting a tire, together with silica as a filler, bis- (3-triethoxysilylpropyl) tetrasulfide as a silica coupler and n-octadecyl as a hydrophobizing agent. The incorporation of trimethoxysilane is disclosed. However, in this document, the silica coupler and the hydrophobizing agent are blended together with silica at the time of rubber mixing, and silica is not surface-treated in advance.
JP 2006-117445 A Japanese Patent Laid-Open No. 08-176345 Japanese Patent Laid-Open No. 05-017705 JP 2001-354805 A Japanese Patent Laid-Open No. 10-001565

  Conventionally, it is known to surface-treat inorganic oxides such as silica as in Patent Documents 1 to 4, and such surface-treated silica is blended in a rubber composition as in Patent Documents 2 to 4. It is also known. However, it has not been known that the inorganic oxide is previously surface-treated with a sulfide silane coupling agent, an organic silane compound, and a hydrophobizing agent, and blended with the rubber composition.

  In view of the above, the present invention provides a hydrophobic inorganic oxide capable of imparting excellent low heat buildup and wear resistance when blended in a rubber composition, and a rubber composition using the same. The purpose is to do.

  The hydrophobic inorganic oxide according to the present invention is obtained by subjecting hydrophilic inorganic oxide particles to a surface treatment with a sulfide silane coupling agent, an organic silane compound, and a hydrophobizing agent. It has a bonded sulfide silane coupling agent and a hydrophobizing agent bonded to the hydroxyl group on the particle surface via an organosilane compound.

  The rubber composition according to the present invention is a mixture of the hydrophobic inorganic oxide and rubber.

  The hydrophobic inorganic oxide of the present invention has a hydrophobizing agent bonded to the particle surface via an organic silane compound together with a sulfide silane coupling agent, so that it has excellent dispersibility when blended in a rubber composition. In addition to being excellent in low heat generation, it is excellent in wear resistance due to improved reinforcement.

  More specifically, a hydrophobic inorganic oxide that is only surface-treated to an inorganic oxide with a sulfide silane coupling agent has poor dispersibility in rubber. Further, a hydrophobic inorganic oxide surface-treated with only an organic silane compound and a hydrophobizing agent has poor reinforcement with rubber. Hydrophobic inorganic oxidation that combines reinforcing properties with rubber and dispersibility into rubber by providing a hydrophobizing agent bonded via an organic silane compound and a sulfide silane coupling agent in a state where they are bonded to the particle surface. A remarkable synergistic effect in low heat buildup and wear resistance. In addition, when mixing the rubber, adding and mixing the inorganic oxide and the sulfide silane coupling agent, the organic silane compound and the hydrophobizing agent, such an excellent effect cannot be obtained. An effect is obtained.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  The hydrophilic inorganic oxide to be surface-treated in the present invention has a hydroxyl group on the particle surface and is not particularly limited. Examples of the inorganic oxide include silica, alumina, zinc oxide, titanium oxide, clay, talc, diatomaceous earth, and the like, and these can be used alone or in combination of two or more. Silica is particularly preferable as the inorganic oxide, and examples of the silica include wet precipitation silica, wet gelation silica, and dry silica.

  The organosilane compound used in the present invention is preferably an aminosilane compound having an amino group as a binding site with a hydrophobizing agent, and the hydrophobizing agent has a functional group capable of reacting with an amino group. Is preferred. Further, the hydrophobizing agent is preferably a compound having 5 or more carbon atoms, more preferably a compound having 10 or more carbon atoms, in order to impart high hydrophobicity to the inorganic oxide. Here, the hydrophobization means that the polarity of the surface of the inorganic oxide is reduced by the surface treatment. Therefore, the hydrophobic inorganic oxide of the present invention is a surface-treated hydrophilic inorganic oxide before the treatment. In contrast, it means that the surface has a small polarity.

Specific examples of the hydrophobizing agent include the following general formula (1) (wherein R ¹ is a linear or branched alkyl group having 3 to 22 carbon atoms, an alkenyl group, and X is a hydroxyl group or a chlorine atom. And a carboxylic acid compound represented by the following general formula (2) (wherein R ² and R ³ are both a linear or branched alkyl group having ^{3 to} 22 carbon atoms, an alkenyl group, An alkyl ketene dimer represented by the following general formula (3) (wherein R ⁴ is an alkylene group having 6 to 24 carbon atoms and an alkyl phenylene group): It is preferable to use at least one of these.

  The carboxylic acid compound represented by the general formula (1) is a carboxylic acid or a carboxylic acid halide. Specifically, as carboxylic acid, propionic acid, butanoic acid, hexanoic acid, decanoic acid, dodecanoic acid, myristic acid, isomyristic acid, palmitic acid, isopalmitic acid, stearic acid, isostearic acid, oleic acid, behenic acid, etc. Is mentioned. The carboxylic acid halide is an acid chloride or acid bromide of the above carboxylic acid. Specifically, propion acid chloride, propion acid bromide, butanoic acid chloride, hexanoic acid chloride, decanoic acid chloride , Dodecanoic acid chloride, myristic acid chloride, isomyristic acid chloride, palmitic acid chloride, isopalmitic acid chloride, stearic acid chloride, stearic acid bromide, isostearic acid chloride, isostearic acid bromide, oleic acid chloride , Behenyl acid chloride and the like. These can be used alone or in combination of two or more.

In the alkyl ketene dimer represented by the general formula (2), specific examples of R ² and R ³ include propyl group, butyl group, octyl group, 2-ethylhexyl group, decyl group, dodecyl group, coconut alkyl (carbon number: 10 -12) group, tetradodecyl group, stearyl group, isostearyl group, hardened beef tallow alkyl (carbon number 14-18) group, tallow alkyl (carbon number 14-18) group, oleyl group, behenyl group, ethylphenyl group, isopropyl Examples thereof include a phenyl group, a butylphenyl group, an octylphenyl group, a nonylphenyl group, a decylphenyl group, and a dodecylphenyl group. R ² and R ³ preferably have 10 to 22 carbon atoms.

  Specific examples of the alkyl ketene dimer include butylene ketene dimer, octyl ketene dimer, 2-ethylhexyl ketene dimer, decyl ketene dimer, dodecyl ketene dimer, palm alkyl (10 to 12 carbon atoms) ketene dimer, tetradecyl ketene dimer, hexadecyl Examples include ketene dimer, stearyl ketene dimer, isostearyl ketene dimer, behenyl ketene dimer, hardened beef tallow alkyl (carbon number 14 to 18) ketene dimer, oleyl ketene dimer, octylphenyl ketene dimer, dodecyl phenyl ketene dimer, and the like. These can be used alone or in combination of two or more. As such an alkyl ketene dimer, an alkyl ketene dimer (AKD) for papermaking which is used as a sizing agent in the paper industry can be used. For example, Size Pine K series manufactured by Arakawa Chemical Industries, Ltd. is commercially available. And its use is recommended.

Examples of the diisocyanate compound represented by the general formula (3) include 1,6-hexamethylene diisocyanate, 2,2,4-trimethyltetramethylene diisocyanate, methylene bis- (1,4-cyclohexylene) diisocyanate, isophorone diisocyanate, norbornane diisocyanate. And alkyl phenylene diisocyanates such as 4,4′-diphenylmethane diisocyanate, xylylene diisocyanate, and tolylene diisocyanate. These can be used alone or in combination of two or more. More preferably, R ⁴ has 6 to 14 carbon atoms.

  Among the above-mentioned hydrophobizing agents, particularly preferred are decanoic acid, dodecanoic acid, palmitic acid, stearic acid, decanoic acid chloride, dodecanoic acid chloride, stearic acid chloride, hardened tallow alkyl (carbon number 14-18) ketene. Examples include dimer, stearyl ketene dimer, behenyl ketene dimer, 1,6-hexamethylene diisocyanate, 4,4′-diphenylmethane diisocyanate, xylylene diisocyanate, and tolylene diisocyanate. More preferred are dodecanoic acid, palmitic acid, and stearic acid.

  As the aminosilane compound suitable as the organic silane compound, those represented by the following general formula (4) are suitable.

_{^{H 2 N- (R 5 -NH)}} n -R 6 -Si (R 7) (R 8) (R 9) ... (4)
In the formula, R ⁵ is an alkylene group having 1 to 4 carbon atoms, and specific examples include a methylene group, an ethylene group, a propylene group, and an isopropylene group. R ⁶ is an alkylene group having 1 to 4 carbon atoms, and examples thereof include a methylene group, an ethylene group, a propylene group, an isopropylene group, a butylene group, and an isobutylene group. R ⁷ , R ⁸ , and R ⁹ are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or an alkoxy group, such as a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a methoxy group, or an ethoxy group. It is a group. n is an integer of 0-5.

  Specific examples of the aminosilane compound include 2-aminoethyltrimethoxysilane, 2-aminoethyltriethoxysilane, 2-aminoethylethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropylmethyldimethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) Examples thereof include aminopropylethyldiethoxysilane, preferably 2-aminoethyltriethoxysilane, 3-aminopropyltriethoxysilane, and 3- (2-aminoethyl) aminopropyltrimethoxysilane. These can be used alone or in combination of two or more.

  The sulfide silane coupling agent used in the present invention binds silica and rubber, and includes a sulfide portion as a functional group capable of reacting with a rubber polymer, and a hydroxyl group of an inorganic oxide (in the case of silica, silanol). A silane compound having a functional group such as an alkoxy group or halogen which can react with the group). Preferably, what is represented by the following general formula (5) is used.

(R ¹⁰ O) ₃ Si—R ¹¹ —S _x —R ¹¹ — (OR ¹⁰ ) ₃ (5)
In the formula, R ¹⁰ is a methyl group or an ethyl group, and R ¹¹ is an alkylene group having 1 to 4 carbon atoms. x is 2 to 8, more preferably 2 to 4. In addition, x has a normal distribution, that is, it is generally marketed as a mixture having different numbers of sulfur chain bonds, and x represents an average value thereof. Specific examples of the sulfide silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide and the like.

  The hydrophobic inorganic oxide according to the present invention comprises a sulfide silane coupling agent bonded to a hydroxyl group on the particle surface of the hydrophilic inorganic oxide, and a hydrophobized bonded to the hydroxyl group on the particle surface via an organosilane compound. It has an agent. Such a hydrophobic inorganic oxide is obtained by subjecting the hydrophilic inorganic oxide particles to a surface treatment with a sulfide silane coupling agent and an organic silane compound in advance, and a hydrophobic group having a functional group capable of reacting with an amino group of the organic silane compound. It can be produced by reacting an agent.

  Each treatment method is not particularly limited, and can be performed according to a normal hydrophobized surface treatment method. For example, while stirring the hydrophilic inorganic oxide in a mixer or blender, a sulfide silane coupling agent and an organic silane compound can be added and reacted, and then a hydrophobizing agent can be added and reacted. Any one of the sulfide silane coupling agent and the organic silane compound may be reacted first, or may be reacted simultaneously. Each reaction can be performed in a state where silica is dispersed in a solvent such as water or isopropyl alcohol. By producing in this way, the sulfide silane coupling agent and the organic silane compound are bonded to the hydroxyl group on the surface of the hydrophilic inorganic oxide particles, respectively, and the hydrophobizing agent is bonded to the organic silane compound. .

  It is preferable that the usage-amount of a sulfide silane coupling agent is 2-20 weight part with respect to 100 weight part of hydrophilic inorganic oxides, More preferably, it is 4-15 weight part. When there is too little usage-amount of a sulfide silane coupling agent, it is inferior to the reinforcement improvement effect when it mix | blends with a rubber composition. If the amount used is too large, the cost is high and uneconomical, and the amount of the organic silane compound for introducing the hydrophobic agent to the inorganic oxide surface decreases.

  It is preferable that the usage-amount of an organosilane compound is 0.5-10 weight part with respect to 100 weight part of hydrophilic inorganic oxides, More preferably, it is 0.8-4 weight part. When there is too little usage-amount of an organosilane compound, it is inferior to the dispersibility improvement effect with respect to a rubber composition. Moreover, when there are too many the usage-amounts, while it is expensive and uneconomical, the coupling | bonding amount with respect to the inorganic oxide surface of a sulfide silane coupling agent will decrease.

  The molar ratio of the sulfide silane coupling agent to the organosilane compound is preferably 10: 1 to 1: 3, more preferably 5: 1 to 1: 1. If the ratio of the sulfide silane coupling agent is too large, the effect of improving the dispersibility with respect to the rubber composition becomes low. Conversely, if the ratio of the organic silane compound is too large, the effect of improving the reinforcing property when blended in the rubber composition. Inferior to

  The rubber composition according to the present invention is a mixture of a hydrophobic inorganic oxide surface-treated in advance as described above and rubber. The dispersibility in the rubber composition can be mainly improved by the hydrophobizing agent fixed to the particle surface by the binding reaction with the organosilane compound. Apart from this, the sulfide silane coupling agent bonded to the particle surface is bonded to the rubber polymer by the sulfide portion, whereby the reinforcement can be mainly improved. Therefore, the rubber composition containing the hydrophobic inorganic oxide is excellent in low heat build-up due to the excellent dispersibility of the inorganic oxide, and is excellent in wear resistance due to improved reinforcement. On the other hand, when the rubber is mixed, an inorganic oxide, a sulfide silane coupling agent, an organic silane compound, and a hydrophobizing agent are added and mixed. Since the fixing structure is not obtained and a synergistic effect with the sulfide silane coupling agent is not obtained, the rubber composition is completely different, and the above-described excellent effect is not obtained.

  As the rubber, a diene rubber having an unsaturated bond capable of reacting with the sulfide portion of the sulfide silane coupling agent is suitable. Examples of the diene rubber include, but are not limited to, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, styrene-isoprene rubber, butadiene-isoprene rubber, nitrile rubber, ethylene-propylene-diene terpolymer, and the like. These can be used alone or in admixture of two or more.

  The compounding quantity of the hydrophobic inorganic oxide with respect to the said rubber | gum is not specifically limited, According to the use etc. of a rubber composition, it can set suitably. Generally, it can be used at 5 to 200 parts by weight with respect to 100 parts by weight of rubber. Further, for example, in the case of a tire rubber composition, it can be used in an amount of 10 to 150 parts by weight, more preferably 20 to 100 parts by weight, with respect to 100 parts by weight of a diene rubber.

  In addition to the above, the rubber composition according to the present invention may contain various additives such as a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, zinc white, a softening agent, a plasticizer, an activator, and a lubricant as necessary. Can be added. The hydrophobic inorganic oxide according to the present invention can be used in combination with a known inorganic oxide such as untreated silica or a known silane coupling agent. The rubber composition can be prepared by kneading using a commonly used mixer such as a Banbury mixer or a kneader. The use of the rubber composition is not particularly limited, but it can be used for various rubber compositions such as tires such as treads and sidewalls, conveyor belts, and vibration-proof rubbers.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Preparation of hydrophobic silica 1 (Example))
Using a 500 mL three-necked flask equipped with a stirrer and a thermometer, 20 g of hydrophilic silica (“Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.) was added to 100 mL of isopropyl alcohol and stirred. While stirring, 1.6 g of sulfide silane coupling agent A (Degussa “Si75”, bis (3-triethoxysilylpropyl) disulfide) was added. After stirring for 20 minutes, 0.8 g of aminosilane compound A (“SH6020” manufactured by Toray Dow Corning Co., Ltd., 3- (2-aminoethyl) aminopropyltrimethoxysilane) was added, and stirring was further continued for 20 minutes.

  The obtained slurry was transferred to a 500 mL eggplant flask, and the solvent was removed under reduced pressure by an evaporator until the solvent became about 1/3. Then, 1 g of stearic acid (“Lunac S-20” manufactured by Kao Corporation) was melted at 50 ° C. in 50 mL of toluene, mixed with the slurry in the eggplant flask, and stirred for 120 minutes using a magnetic stirrer. Then, it dried under reduced pressure with the evaporator and the hydrophobic silica 1 was obtained.

(Preparation of hydrophobic silica 2 (Example))
Using a 500 mL three-necked flask equipped with a stirrer and a thermometer, 20 g of hydrophilic silica (“Nip Seal AQ” manufactured by Tosoh Silica Corporation) was added to 100 mL of isopropyl alcohol and stirred. While stirring, 1.6 g of sulfide silane coupling agent B (Degussa “Si69”, bis (3-triethoxysilylpropyl) tetrasulfide) was added. After stirring for 20 minutes, 0.8 g of aminosilane compound B (“SH6011” manufactured by Toray Dow Corning Co., Ltd., 3-aminopropyltriethoxysilane) was added, and stirring was further continued for 20 minutes.

  The obtained slurry was transferred to a 500 mL eggplant flask, and the solvent was removed under reduced pressure by an evaporator until the solvent became about 1/3. Thereafter, 3.33 g of alkyl ketene dimer (“Size Pine K-931” manufactured by Arakawa Chemical Industries, Ltd., solid content concentration: 30% by weight) was mixed with the slurry in the eggplant flask and stirred for 120 minutes using a magnetic stirrer. . Then, it dried under reduced pressure with the evaporator and the hydrophobic silica 2 was obtained.

(Preparation of hydrophobic silica 3 (Example))
Using a 500 mL three-necked flask equipped with a stirrer and a thermometer, 20 g of hydrophilic silica (“Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.) was added to 100 mL of isopropyl alcohol and stirred. While stirring, 1.6 g of the above sulfide silane coupling agent B was added. After stirring for 20 minutes, 0.8 g of the aminosilane compound B was added, and stirring was further continued for 20 minutes.

  The obtained slurry was transferred to a 500 mL eggplant flask, and the solvent was removed under reduced pressure by an evaporator until the solvent became about 1/3. Thereafter, a mixture of 50 mL of toluene and 1 g of diphenylmethane diisocyanate (manufactured by Tomen Chemical Co., Ltd.) was mixed with the slurry in the eggplant flask and stirred for 120 minutes using a magnetic stirrer. Then, it dried under reduced pressure with the evaporator and the hydrophobic silica 3 was obtained.

(Preparation of Hydrophobic Silica 4 (Example))
Using a 500 mL three-necked flask equipped with a stirrer and a thermometer, 20 g of hydrophilic silica (“Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.) was added to 100 mL of isopropyl alcohol and stirred. While stirring, 1.6 g of the above sulfide silane coupling agent B was added. After stirring for 20 minutes, 0.8 g of the aminosilane compound B was added, and stirring was further continued for 20 minutes.

  The obtained slurry was transferred to a 500 mL eggplant flask, and the solvent was removed under reduced pressure by an evaporator until the solvent became about 1/3. Then, what mixed 1 g of lauric acid (made by Nacalai Tesque Co., Ltd.) with 50 mL of toluene at 50 ° C. was mixed with the slurry in the eggplant flask, and stirred for 120 minutes using a magnetic stirrer. Then, it dried under reduced pressure with the evaporator and the hydrophobic silica 4 was obtained.

(Preparation of hydrophobic silica 5 (comparative example))
Using a 500 mL three-necked flask equipped with a stirrer and a thermometer, 20 g of hydrophilic silica (“Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.) was added to 100 mL of isopropyl alcohol and stirred. While stirring, 1.6 g of the above sulfide silane coupling agent A was added, and stirring was continued for 20 minutes. The obtained slurry was transferred to a 500 mL eggplant flask and dried under reduced pressure with an evaporator to obtain hydrophobic silica 5.

(Preparation of hydrophobic silica 6 (comparative example))
Using a 500 mL three-necked flask equipped with a stirrer and a thermometer, 20 g of hydrophilic silica (“Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.) was added to 100 mL of isopropyl alcohol and stirred. While stirring, 0.8 g of the aminosilane compound A was added and stirring was continued for 20 minutes.

  The obtained slurry was transferred to a 500 mL eggplant flask, and the solvent was removed under reduced pressure by an evaporator until the solvent became about 1/3. Then, 1 g of stearic acid (“Lunac S-20” manufactured by Kao Corporation) was melted at 50 ° C. in 50 mL of toluene, mixed with the slurry in the eggplant flask, and stirred for 120 minutes using a magnetic stirrer. Then, it dried under reduced pressure with the evaporator and the hydrophobic silica 6 was obtained.

(Preparation of hydrophobic silica 7 (comparative example))
Using a 500 mL three-necked flask equipped with a stirrer and a thermometer, 20 g of hydrophilic silica (“Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.) was added to 100 mL of isopropyl alcohol and stirred. While stirring, 1.6 g of the above sulfide silane coupling agent A was added. After stirring for 20 minutes, 1 g of an alkylsilane compound (“Z6341” manufactured by Toray Dow Corning Co., Ltd., triethoxyoctylsilane) was added, and stirring was further continued for 20 minutes. The obtained slurry was transferred to a 500 mL eggplant flask and dried under reduced pressure with an evaporator to obtain hydrophobic silica 7.

(Evaluation of rubber composition)
Using a Banbury mixer, according to the formulation shown in Table 1 below, each component was added and mixed to prepare a rubber composition. The detail of each component of Table 1 is as follows.

SSBR: styrene-butadiene rubber, “VSL5025-OHM” manufactured by Bayer,
-BR: butadiene rubber, "BR150B" manufactured by Ube Industries,
・ Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.
・ Sulphide silane coupling agent: “Si75” manufactured by Degussa,
Aminosilane compound: “SH6020” manufactured by Toray Dow Corning Co., Ltd.
Stearic acid: “Lunac S-20” manufactured by Kao Corporation.

  In each rubber composition, 3 parts by weight of zinc white (“Zinc Hana 1” manufactured by Mitsui Mining & Mining) and an anti-aging agent (“Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.) per 100 parts by weight of diene rubber ) 2 parts by weight, 40 parts by weight of process oil (“Process Oil X-140” manufactured by JOMO), 2 parts by weight of wax (“OZOACE0355” manufactured by Nippon Seiki), sulfur (“5% oil-filled fine powder sulfur” manufactured by Tsurumi Chemical Industries) ) 1.5 parts by weight, 1.8 parts by weight of a vulcanization accelerator (“Soxinol CZ” manufactured by Sumitomo Chemical) and 2.0 parts by weight of a vulcanization accelerator (“Noxeller D” manufactured by Ouchi Shinsei Chemical) were blended.

  About each obtained rubber composition, the sample vulcanized | cured on the conditions of 160 degreeC x 30 minutes was produced, and low heat build-up and abrasion resistance were evaluated. Moreover, the balance (abrasion resistance / low heat generation property) of both was evaluated. The evaluation method is as follows.

Low exothermic property (low hysteresis loss): Loss tangent tan δ was measured using a rheology manufactured by Rheology under the conditions of 60 ° C. and shear strain of 5%. The value of tan δ is shown as an index with the value of Comparative Example 1 as 100. The smaller the value, the smaller the hysteresis loss and the better the low heat buildup.

-Abrasion resistance: Using an Lambourn abrasion tester, the amount of wear loss was measured at a temperature of 23 ° C and a slip rate of 50%, and the result was shown as an index with Comparative Example 1 taken as 100. It shows that it is excellent in abrasion resistance, so that a numerical value is large.

Abrasion resistance / low heat buildup: An index of the balance between low heat buildup and wear resistance, calculated by (wear resistance / low heat buildup) × 100. The higher this value, the better.

  The results are as shown in Table 1. In the rubber compositions of Examples 1 to 6 according to the present invention, silica treated with a sulfide silane coupling agent and an aminosilane compound was further treated with a hydrophobizing agent such as stearic acid. By using the hydrophobic silica obtained by reacting with the above, the loss of hysteresis was remarkably reduced by the improvement of the dispersibility of the silica, and the exothermic property was excellent. Moreover, it was excellent in abrasion resistance by improving the reinforcement.

  On the other hand, as in Comparative Example 2, when the rubber was mixed and mixed with silica, a sulfide silane coupling agent, an aminosilane compound and stearic acid, the effect of improving low heat build-up was small and the wear resistance was reduced. Was worse than Comparative Example 1.

  Moreover, although the silica was surface-treated in advance, Comparative Example 3 using the hydrophobic silica 5 surface-treated only with the sulfide silane coupling agent was poor in dispersibility in rubber, and the effect of improving low heat build-up was achieved in the examples. It was clearly inferior. Further, in Comparative Example 5 in which an aminosilane compound and stearic acid were added to the rubber during mixing, there was no further improvement effect of low exothermicity, and the wear resistance was deteriorated.

  On the other hand, in Comparative Example 4 using hydrophobic silica 6 that was previously surface-treated with an aminosilane compound and stearic acid, the reinforcement with rubber was inferior, and the wear resistance was remarkably deteriorated. Further, in Comparative Example 6 in which the sulfide silane coupling agent was added to the rubber during mixing, the low heat build-up deteriorated on the contrary, and the wear resistance was insufficient.

  Furthermore, even in Comparative Example 7 using hydrophobic silica 7 surface-treated in advance with a sulfide silane coupling agent and an alkylsilane compound, the heat generation resistance and the abrasion resistance were inferior to Examples 1-6.

  As described above, in Examples 1 to 6, together with the sulfide silane coupling agent, hydrophobic silica having a hydrophobizing agent such as stearic acid bonded to the particle surface via an aminosilane compound was used. An excellent effect of improving the low heat build-up and wear resistance exceeding the prediction of those skilled in the art, which cannot be said to be a simple combination of these surface treatments, was obtained.

Claims (6)

  A sulfide silane coupling agent bonded to a hydroxyl group on the particle surface obtained by surface-treating hydrophilic inorganic oxide particles with a sulfide silane coupling agent, an organic silane compound and a hydrophobizing agent, and a hydroxyl group on the particle surface A hydrophobic inorganic oxide having a hydrophobizing agent bonded to a group via an organosilane compound. The hydrophobizing agent of the general formula (1) (wherein, R ¹ represents straight-chain or branched-chain alkyl group having 3 to 22 carbon atoms, an alkenyl group, X is a hydroxyl group, a chlorine atom, a bromine atom.) A carboxylic acid compound represented by general formula (2) (wherein R ² and R ³ are both a linear or branched alkyl group, an alkenyl group, and an alkylphenyl group having ^{3 to} 22 carbon atoms). At least one hydrophobic compound selected from diisocyanate compounds represented by an alkyl ketene dimer represented by the general formula (3) (wherein R ⁴ is an alkylene group having 6 to 24 carbon atoms or an alkylphenylene group): The hydrophobic inorganic oxide according to claim 1, wherein the hydrophobic inorganic oxide is an agent.

  The hydrophobic inorganic oxide according to claim 2, wherein the hydrophobizing agent has 10 or more carbon atoms.   The hydrophobic inorganic oxide according to any one of claims 1 to 3, wherein the organosilane compound is an organosilane compound having an amino group as a bonding site with the hydrophobizing agent.   A rubber composition obtained by mixing rubber and the hydrophobic inorganic oxide according to any one of claims 1 to 4.   The rubber composition according to claim 5, wherein the rubber is a diene rubber.