JP5912823B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for tires and a pneumatic tire using the same.

In recent years, due to increasing interest in environmental issues, there has been a strong demand for low fuel consumption for automobiles, and even for rubber compositions (tire rubber compositions) used for automobile tires, low fuel consumption has been achieved. There is a demand for excellence. As rubber compositions for tires, rubber compositions containing natural rubber, conjugated diene polymers such as polybutadiene and butadiene-styrene copolymers, and fillers such as carbon black and silica are used. .

As a method for improving fuel economy, for example, Patent Document 1 proposes a method using a diene rubber (modified rubber) modified with an organosilicon compound containing an amino group and an alkoxy group. However, when modified rubber is used, the reaction efficiency between silica and rubber (polymer) is improved and fuel efficiency is improved. On the other hand, the bond between silica and rubber becomes too dense, resulting in rubber strength and resistance. Abrasion may be reduced.

In addition, since the rubber composition for tires, especially the rubber composition for cap treads in contact with the road surface, is required to have excellent wet grip performance in terms of safety, it has low fuel consumption, rubber strength, and wear resistance. Therefore, there is a demand for a method for improving these performances at a high level in a balanced manner. However, in particular, low fuel consumption and wet grip performance are also contradictory performances, and the present situation is that a rubber composition for tires that has improved the above-described performance in a high-order and well-balanced manner has not yet been obtained.

JP 2000-344955 A

The present invention solves the above-mentioned problems, and provides a rubber composition for a tire that can improve fuel economy, wet grip performance, wear resistance, and rubber strength in a balanced manner, and a pneumatic tire using the rubber composition. With the goal.

The present invention relates to a rubber component containing 10 to 80% by mass of 100% by mass of an epoxidized natural rubber having an epoxidation rate of 7 to 15 mol%, and silica having a nitrogen adsorption specific surface area of 150 m ² / g or more (1). And a silica (2) having a nitrogen adsorption specific surface area of 100 m ² / g or less, and a total content of the silica (1) and (2) with respect to 100 parts by mass of the rubber component is 30 to 120 parts by mass. The present invention relates to a rubber composition.

In the tire rubber composition, the contents of the silicas (1) and (2) preferably satisfy the following formula.
(Content of silica (2)) × 0.2 ≦ (content of silica (1)) ≦ (content of silica (2)) × 6.5

The tire rubber composition preferably contains butadiene rubber and / or styrene butadiene rubber.

The tire rubber composition is preferably used as a cap tread rubber composition.

The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, a rubber component containing 10 to 80% by mass of 100% by mass of an epoxidized natural rubber having an epoxidation rate of 7 to 15% by mol, and silica having a nitrogen adsorption specific surface area of 150 m ² / g or more ( 1) and silica (2) having a nitrogen adsorption specific surface area of 100 m ² / g or less, and the total content of silica (1) and (2) relative to 100 parts by mass of the rubber component is 30 to 120 parts by mass. Since it is a rubber composition for a tire, fuel economy, wet grip performance, wear resistance, and rubber strength can be improved in a well-balanced manner.

The tire rubber composition of the present invention includes a rubber component containing 10 to 80% by mass of an epoxidized natural rubber having an epoxidation rate of 7 to 15 mol% in 100% by mass of a rubber component, and a nitrogen adsorption specific surface area of 150 m ² / g. Including the silica (1) and silica (2) having a nitrogen adsorption specific surface area of 100 m ² / g or less, the total content of the silica (1) and (2) is 100 to 100 parts by mass of the rubber component. 120 parts by mass.

By blending silica with epoxidized natural rubber with a specific epoxidation rate, fuel economy and wet grip performance can be improved in a better balance than when natural rubber or butadiene rubber is used with silica. The fuel economy, rubber strength (destructive property), and wear resistance can be improved in a more balanced manner than when butadiene rubber is used together with silica.

On the other hand, blending silica (1) can improve wet grip performance and wear resistance, but lowers fuel efficiency and rubber strength. Further, by blending silica (2), the fuel economy and wear resistance can be improved, but wet grip performance and rubber strength are lowered. On the other hand, in the present invention, by using silica (1) and (2) together with epoxidized natural rubber having a specific epoxidation rate, it is possible to synergistically improve fuel economy, wet grip performance, and wear resistance, Further, the rubber strength that was not improved by silica (1) and (2) alone can be improved, and the fuel economy, wet grip performance, wear resistance, and rubber strength can be improved in a well-balanced manner.

In the present invention, epoxidized natural rubber (ENR) having an epoxidation rate of 7 to 15 mol% is used as the rubber component. Thereby, low fuel consumption, wet grip performance, wear resistance, and rubber strength can be improved in a well-balanced manner. In addition, you may use it in combination with ENR whose epoxidation rate is outside the above range.

The ENR is not particularly limited as long as the epoxidation rate is an ENR within the above range, and may be a commercially available epoxidized natural rubber or an epoxidized natural rubber (NR). The method for epoxidizing natural rubber is not particularly limited, and examples thereof include a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, a peracid method, and the like (Japanese Patent Publication No. 4-26617, Japanese Patent Application Laid-Open No. 2). No. 110182, British Patent No. 2113692, etc.). Examples of the peracid method include a method of reacting natural rubber with an organic peracid such as peracetic acid or performic acid. In addition, epoxidized natural rubber having various epoxidation rates can be prepared by adjusting the amount of organic peracid and the reaction time.
In the present invention, the epoxidation rate is the ratio (mol%) of the number of epoxidized double bonds to the total number of double bonds in the rubber before being epoxidized. Moreover, in this invention, an epoxidation rate is a value obtained by the measuring method as described in the Example mentioned later.

The natural rubber to be epoxidized is not particularly limited. For example, SIR20, RSS # 3, TSR20, deproteinized natural rubber (DPNR), high-purity natural rubber (HPNR), and the like used in the tire industry are used. it can.

The epoxidation rate of ENR is 7 mol% or more, preferably 8 mol% or more, more preferably 9 mol% or more. If the epoxidation rate is less than 7 mol%, the modification effect on the rubber composition is not sufficient, and there is a tendency that low fuel consumption, wet grip performance, wear resistance, and rubber strength cannot be improved in a balanced manner. The epoxidation rate is 15 mol% or less, preferably 14 mol% or less, more preferably 12 mol% or less. When the epoxidation rate exceeds 15 mol%, fuel economy and rubber strength tend to deteriorate. When the epoxidation rate is within the above range, low fuel consumption, wet grip performance, wear resistance, and rubber strength can be obtained in a well-balanced manner.

The content of ENR in 100% by mass of the rubber component is 10% by mass or more, preferably 15% by mass or more, more preferably 25% by mass or more, and further preferably 40% by mass or more. If it is less than 10% by mass, fuel economy and rubber strength tend to decrease. The content of ENR is 80% by mass or less, preferably 75% by mass or less. When it exceeds 80% by mass, wet grip performance and wear resistance tend to be lowered.

Examples of rubber components other than ENR used in the rubber composition include diene rubbers. For example, NR, butadiene rubber (BR), styrene butadiene rubber (SBR), epoxidized styrene butadiene rubber (ESBR), isoprene rubber ( IR), butyl rubber (IIR), halogenated butyl rubber (X-IIR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), styrene-isoprene-butadiene copolymer rubber (SIBR) and the like can be used. In addition to diene rubbers, ethylene-propylene copolymers, ethylene-octene copolymers, and the like can be used. These rubber components may be used alone or in combination of two or more. Among these, those containing 50% by mass or more of structural units derived from conjugated diene compounds can be suitably used from the viewpoint that fuel economy, cut resistance, rubber strength and processability can be improved in a balanced manner. For this reason, BR and SBR are more preferable, and BR is more preferable because of its good wear resistance.

It is not particularly limited as BR, for example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B having high cis content such as BR150B, VCR412, VCR617 manufactured by Ube Industries, Ltd. Commonly used in the tire industry, such as BR containing syndiotactic polybutadiene crystals, can be used. Of these, the BR cis content is preferably 90% by mass or more because of its good wear resistance.

When the rubber composition of the present invention contains BR, the content of BR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 15% by mass or more. If it is less than 10% by mass, the cut resistance, wear resistance, and low fuel consumption tend to decrease. The BR content is preferably 50% by mass or less, more preferably 40% by mass or less, and still more preferably 35% by mass or less. When it exceeds 50% by mass, wet grip performance and rubber strength tend to decrease.

The SBR is not particularly limited, and those generally used in the tire industry such as emulsion polymerization styrene butadiene rubber (E-SBR) and solution polymerization styrene butadiene rubber (S-SBR) can be used.

When the rubber composition of the present invention contains SBR, the content of SBR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 25% by mass or more. If it is less than 10% by mass, the wet grip performance tends to decrease. The content of the SBR is preferably 60% by mass or less, more preferably 50% by mass or less. If it exceeds 60% by mass, the wear resistance, fuel efficiency and rubber strength tend to decrease.

The rubber composition of the present invention comprises a silica (1) having a nitrogen adsorption specific surface area (N ₂ SA) of 150 m ² / g or more and a silica (2) having a nitrogen adsorption specific surface area (N ₂ SA) of 100 m ² / g or less. Including.

Examples of silicas (1) and (2) include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and wet process silica is preferred because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica (1) is 150 m ² / g or more, preferably 160 m ² / g or more, more preferably 165 m ² / g or more. If it is less than 150 m < ² > / g, coexistence with reduction of rolling resistance (improvement of fuel-consumption property) and improvement of wet grip performance by using together with silica (2) cannot be performed. The N ₂ SA is preferably 400 m ² / g or less, more preferably 360 m ² / g or less, still more preferably 250 m ² / g or less, and particularly preferably 200 m ² / g or less. When it exceeds 400 m ² / g, not only the workability is deteriorated, but also the rolling resistance tends not to be sufficiently reduced.

As silica (1), for example, Zeosyl 1205MP manufactured by Rhodia, Ultrasil VN3-G manufactured by Evonik Degussa, or the like can be used. In addition, as silica (1), only 1 type may be used, but you may use in combination of 2 or more type.

The nitrogen adsorption specific surface area (N ₂ SA) of silica (2) is 100 m ² / g or less, preferably 80 m ² / g or less, more preferably 70 m ² / g or less. If it exceeds 100 m ² / g, it is impossible to achieve both reduction of rolling resistance (improvement of fuel efficiency) and improvement of wet grip performance by using together with silica (1). The N ₂ SA is preferably 20 m ² / g or more, more preferably 30 m ² / g or more. If it is less than 20 m ² / g, the rubber strength (breaking strength) of the resulting rubber composition tends to decrease.

As silica (2), for example, Ultrasil 360 manufactured by Evonik Degussa, Z40, RP80 manufactured by Rhodia, etc. can be used. As silica (2), only 1 type may be used, but you may use in combination of 2 or more type.

In the present invention, N ₂ SA of silica is a value measured by the BET method according to ASTM D3037-81. In addition, when each of silica (1) or (2) is composed of two or more types of silica, each N ₂ SA of silica (1) or (2) is all silica corresponding to silica (1) or (2) Is a value obtained by measuring a sample consisting of

The content of silica (1) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and further preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 5 parts by mass, sufficient rubber strength, abrasion resistance and wet grip performance may not be obtained. The content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and still more preferably 60 parts by mass or less. If the amount exceeds 100 parts by mass, the processability and fuel efficiency tend to deteriorate even if the rubber strength can be improved.

The content of silica (2) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and further preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, sufficient fuel economy may not be obtained. The content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 50 parts by mass or less, and particularly preferably 25 parts by mass or less. If it exceeds 100 parts by mass, the rubber strength, wear resistance, and wet grip performance tend to deteriorate even if the fuel efficiency can be improved.

The contents of silica (1) and (2) preferably satisfy the following formula.
(Content of silica (2)) × 0.2 ≦ (content of silica (1)) ≦ (content of silica (2)) × 6.5
The blending amount of silica (1) is 0.2 times or more, preferably 0.5 times or more, more preferably 1.2 times or more of the blending amount of silica (2). If the blending amount of silica (1) is less than 0.2 times the blending amount of silica (2), the rubber strength may be lowered. Moreover, the compounding quantity of silica (1) is 6.5 times or less of the compounding quantity of silica (2), Preferably it is 4 times or less, More preferably, it is 3 times or less, More preferably, it is 2.2 times or less. If the blending amount of silica (1) exceeds 6.5 times the blending amount of silica (2), wet grip performance, rubber strength, and wear resistance may be reduced.

The total content of silica (1) and (2) is 30 parts by mass or more, preferably 35 parts by mass or more, more preferably 40 parts by mass or more, and still more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. It is. If it is less than 30 parts by mass, the effects of the blending of silica (1) and (2) cannot be sufficiently obtained, and wet grip performance, wear resistance, and rubber strength cannot be sufficiently obtained. The content is 120 parts by mass or less, preferably 80 parts by mass or less. If it exceeds 120 parts by mass, it will be difficult for silica to be uniformly dispersed in the rubber composition, and the fuel efficiency will deteriorate.

The rubber composition of the present invention may contain silica other than silica (1) and (2).

The rubber composition of the present invention preferably contains a silane coupling agent together with silica. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, sulfide type, mercapto type, vinyl type, amino type, glycidoxy type, nitro type And chloro-based silane coupling agents. Among these, a sulfide system is preferable because the effects of the present invention can be obtained satisfactorily.

As the sulfide-based silane coupling agent, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3- Triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, and 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide are preferable, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferable.

The content of the silane coupling agent is preferably 2 parts by mass or more, more preferably 3 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, the silica cannot be sufficiently dispersed, and there is a risk that the fuel efficiency, wear resistance, and rubber strength will deteriorate. Further, the content of the silane coupling agent is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and still more preferably 7 parts by mass or less. When the amount exceeds 20 parts by mass, a coupling effect commensurate with the increase in the amount of the silane coupling agent cannot be obtained sufficiently, and the reinforcing property and wear resistance are lowered, and the cost tends to increase. In addition, in this invention, the compounding quantity of a silane coupling agent means the quantity with respect to the total compounding quantity of a silica.

The rubber composition of the present invention preferably contains carbon black. Thereby, wet grip performance, abrasion resistance, and rubber strength can be further improved. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. Carbon black may be used independently and may use 2 or more types together.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² / g or more, and more preferably 90 m ² / g or more. If it is less than 50 m ² / g, sufficient reinforcing properties cannot be obtained, and sufficient wet grip performance, wear resistance, and rubber strength may not be obtained. The _N 2 SA is preferably 150 meters ² / g or less, more preferably 130m ² / g. When it exceeds 150 m ² / g, heat generation increases, and fuel economy tends to deteriorate.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

The dibutyl phthalate oil absorption (DBP) of carbon black is preferably 50 ml / 100 g or more, more preferably 90 ml / 100 g or more. If it is less than 50 ml / 100 g, sufficient reinforcement cannot be obtained, and sufficient wet grip performance, wear resistance, and rubber strength may not be obtained. The DBP of carbon black is preferably 200 ml / 100 g or less, and more preferably 125 ml / 100 g or less. When it exceeds 200 ml / 100 g, the heat generation becomes large and the fuel efficiency tends to deteriorate.
The DBP of carbon black is measured according to JIS K 6217-4: 2001.

The content of carbon black is preferably 3 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 3 parts by mass, sufficient wet grip performance, wear resistance, and rubber strength may not be obtained. The content is preferably 80 parts by mass or less, more preferably 50 parts by mass or less, and still more preferably 20 parts by mass or less. If it exceeds 80 parts by mass, heat generation will increase and fuel economy tends to deteriorate.

When carbon black is contained, the total content of silica (preferably silica (1), (2)) in 100% by mass of silica (preferably silica (1), (2)) and carbon black is preferably Is 50% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. By setting the content to 50% by mass or more, the effect of the present invention can be obtained more suitably. On the other hand, the total content is preferably 95% by mass or less.

The rubber composition of the present invention preferably contains an alkaline fatty acid metal salt. Since the alkaline fatty acid metal salt neutralizes the acid used during the ENR synthesis, it can prevent deterioration due to heat during ENR kneading and vulcanization. It can also prevent reversion. Further, by adding an alkaline fatty acid metal salt to the rubber composition of the present invention, the wear resistance and the like obtained by combining ENR having a specific epoxidation rate and silica (1) and (2) are improved. The effect can be increased.

Examples of the metal in the alkaline fatty acid metal salt include sodium, potassium, calcium, barium, magnesium, zinc and the like. Among them, there are many in nature, the environmental load is small, and the heat resistance effect is large. From the viewpoint of compatibility with the epoxidized natural rubber, calcium, zinc and barium are preferable, and calcium is more preferable. Specific examples of alkaline fatty acid metal salts include sodium stearate, magnesium stearate, calcium stearate, barium stearate and other metal stearates, sodium oleate, magnesium oleate, calcium oleate, barium oleate and other oleic acids Examples thereof include metal salts. Of these, calcium stearate and calcium oleate are preferred because they are excellent in aging resistance and heat resistance, have high compatibility with epoxidized natural rubber, and are relatively inexpensive.

The content of the alkaline fatty acid metal salt is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of ENR. If it is less than 0.5 parts by mass, the wear resistance and heat resistance tend not to be sufficiently improved. The content of the alkaline fatty acid metal salt is preferably 12 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 7 parts by mass or less. When it exceeds 12 parts by mass, the wear resistance, rubber strength, and low fuel consumption tend to deteriorate.

In addition to the above-mentioned components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, for example, reinforcing fillers such as calcium carbonate, aluminum hydroxide, alumina, clay and talc, oxidation Zinc, stearic acid, processing aids, various anti-aging agents, softening agents such as oil, aromatic petroleum resins, vulcanizing agents such as wax and sulfur, vulcanization accelerators and the like can be appropriately blended.

Although it does not specifically limit as a softener which can be used by this invention, For example, mineral oils, such as aromatic oil, a process oil, paraffin oil, will be mentioned if it is oil. These softeners may be used alone or in combination of two or more.

In the present invention, the amount of oil is preferably 1 to 15 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the rubber component, because the effects of the present invention can be suitably obtained. . Here, the amount of oil contained in the oil-extended rubber is also included in the amount of oil blended.

Examples of the vulcanization accelerator include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Etc. These vulcanization accelerators may be used alone or in combination of two or more. Of these, sulfenamide vulcanization accelerators are preferred.

Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N -Dicyclohexyl-2-benzothiazolylsulfenamide (DCBS) and the like.

The content of the vulcanization accelerator is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts per 100 parts by mass of the rubber component. It is below mass parts. By adjusting within the above range, the effect of the present invention can be obtained more suitably.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, the above components are kneaded using a rubber kneader such as an open roll, a Banbury mixer, a closed kneader, and then added. It can be manufactured by a method of sulfurating.

The rubber composition of the present invention can be suitably used for each member of a tire, and in particular, can be suitably applied to a cap tread of a pneumatic tire.

A cap tread is a surface layer portion of a tread having a multilayer structure. In the case of a tread having a two-layer structure, the tread includes a surface layer (cap tread) and an inner surface layer (base tread).

A tread having a multilayer structure is produced by pasting a sheet into a predetermined shape, or by inserting it into two or more extruders and forming it into two or more layers at the head outlet of the extruder. Can do.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as necessary is extruded in accordance with the shape of a cap tread or the like at an unvulcanized stage, molded by a normal method on a tire molding machine, etc. After being bonded together with the tire member to form an unvulcanized tire, the tire can be manufactured by heating and pressing in a vulcanizer.

The pneumatic tire of the present invention is preferably used as a tire for passenger cars, a tire for trucks and buses, a tire for motorcycles, a tire for competition, and the like, and more preferably used as a tire for passenger cars.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in the production examples will be described together.
High ammonia type natural rubber latex: Hytex made by Nomura Trading Co., Ltd.
Nonionic emulsifier: Emulgen 106 manufactured by Kao Corporation
Hydrogen peroxide: Hydrogen peroxide manufactured by Wako Pure Chemical Industries, Ltd. (reagent grade 1, active ingredient 35%)
Acetic anhydride: Acetic anhydride manufactured by Wako Pure Chemical Industries, Ltd. (Reagent grade 1, active ingredient 93%)
Ammonia: Ammonia water manufactured by Wako Pure Chemical Industries, Ltd. (Reagent grade 1, active ingredient 25%)

The following evaluation was performed on the ENR obtained by the following production example.
(Epoxidation rate)
The epoxidation rate was determined by dissolving the obtained dry rubber (ENR) in deuterated chloroform and analyzing it by nuclear magnetic resonance (NMR (JNM-ECA series manufactured by JEOL Ltd.)) spectroscopic analysis. It calculated using the following calculation formulas from the ratio of the integral value h (ppm) of a bond part and an aliphatic part.
(Epoxidation rate E%) = 3 × h (2.69) / (3 × h (2.69) + 3 × h (5.14) + h (0.87)) × 100

Production Example 1 (Preparation of ENR (1) (10 mol%))
1750 g of high ammonia type natural rubber latex (solid content 60%) was placed in a 5 L glass container, stirred with a stirring blade, and diluted with 1500 g of distilled water so that the solid content would be 30%. To this, 21 g of a nonionic emulsifier was added with stirring. Next, 215 g of hydrogen peroxide and 230 g of acetic anhydride were reacted in another container to prepare peracetic acid, and the prepared peracetic acid was slowly added to the 5 L glass container. After the addition, the mixture was reacted at room temperature for 30 minutes, neutralized with ammonia, only the rubber component was coagulated with methanol, washed with tap water, and dried to prepare ENR (1). The epoxidation rate of the obtained ENR (1) was 10 mol%.

Production Example 2 (Preparation of ENR (2) (3 mol%))
1750 g of high ammonia type natural rubber latex (solid content 60%) was placed in a 5 L glass container, stirred with a stirring blade, and diluted with 1500 g of distilled water so that the solid content would be 30%. To this, 21 g of a nonionic emulsifier was added with stirring. Next, 65 g of hydrogen peroxide and 70 g of acetic anhydride were reacted in another container to prepare peracetic acid, and the prepared peracetic acid was slowly added to the 5 L glass container. After the addition, the mixture was reacted at room temperature for 30 minutes, neutralized with ammonia, only the rubber component was coagulated with methanol, washed with tap water, and dried to prepare ENR (2). The epoxidation rate of the obtained ENR (2) was 3 mol%.

Production Example 3 (Preparation of ENR (3) (8 mol%))
1750 g of high ammonia type natural rubber latex (solid content 60%) was placed in a 5 L glass container, stirred with a stirring blade, and diluted with 1500 g of distilled water so that the solid content would be 30%. To this, 21 g of a nonionic emulsifier was added with stirring. Next, 172 g of hydrogen peroxide and 185 g of acetic anhydride were reacted in another container to prepare peracetic acid, and the prepared peracetic acid was slowly added to the 5 L glass container. After the addition, the mixture was reacted at room temperature for 30 minutes, neutralized with ammonia, only the rubber component was coagulated with methanol, washed with tap water, and dried to prepare ENR (3). The epoxidation rate of the obtained ENR (3) was 8 mol%.

Production Example 4 (Preparation of ENR (4) (13 mol%))
1750 g of high ammonia type natural rubber latex (solid content 60%) was placed in a 5 L glass container, stirred with a stirring blade, and diluted with 1500 g of distilled water so that the solid content would be 30%. To this, 21 g of a nonionic emulsifier was added with stirring. Next, 280 g of hydrogen peroxide and 300 g of acetic anhydride were reacted in another container to prepare peracetic acid, and the prepared peracetic acid was slowly added to the 5 L glass container. After the addition, the mixture was reacted at room temperature for 30 minutes, neutralized with ammonia, only the rubber component was coagulated with methanol, washed with tap water, and dried to prepare ENR (4). The epoxidation rate of the obtained ENR (4) was 13 mol%.

Production Example 5 (Preparation of ENR (5) (25 mol%))
1750 g of high ammonia type natural rubber latex (solid content 60%) was placed in a 5 L glass container, stirred with a stirring blade, and diluted with 1500 g of distilled water so that the solid content would be 30%. To this, 21 g of a nonionic emulsifier was added with stirring. Next, 538 g of hydrogen peroxide and 575 g of acetic anhydride were reacted in another container to prepare peracetic acid, and the prepared peracetic acid was slowly added to the 5 L glass container. After the addition, the mixture was reacted at room temperature for 30 minutes, neutralized with ammonia, only the rubber component was coagulated with methanol, washed with tap water, and dried to prepare ENR (5). The epoxidation rate of the obtained ENR (5) was 25 mol%.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
ENR (1): ENR (1) produced in Production Example 1 and having an epoxidation rate of 10 mol%
ENR (2): ENR (2) produced in Production Example 2 and having an epoxidation rate of 3 mol%
ENR (3): ENR (3) produced in Production Example 3 and having an epoxidation rate of 8 mol%
ENR (4): ENR (4) produced in Production Example 4 and having an epoxidation rate of 13 mol%
ENR (5): ENR (5) produced in Production Example 5 and having an epoxidation rate of 25 mol%
BR: Ubepol BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass)
SBR: SBR1502 manufactured by Sumitomo Chemical Co., Ltd.
Silica (1): Ultrasil VN3-G (N ₂ SA: 175 m ² / g) manufactured by Evonik Degussa
Silica (2): Ultrasil 360 manufactured by Evonik Degussa (N ₂ SA: 50 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Evonik Degussa
Carbon Black: Show Black N220 (N ₂ SA: 111 m ² / g, DBP: 115 ml / 100 g) manufactured by Cabot Japan
Oil: X-140 manufactured by Japan Energy Co., Ltd.
Anti-aging agent: Antigen 3C manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: Beads manufactured by NOF Co., Ltd. Beads of calcium stearate Calcium stearate: Calcium stearate manufactured by NOF Co., Ltd. Zinc oxide: Zinc Hua No. 1 manufactured by Mitsui Kinzoku Mining Co., Ltd. ) Sannok N made
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. (1): Soxinol CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Sumitomo Chemical Co., Ltd.
Vulcanization accelerator (2): Soxinol D (1,3-diphenylguanidine) manufactured by Sumitomo Chemical Co., Ltd.

(Examples and Comparative Examples)
According to the formulation shown in Tables 1 and 2, materials other than sulfur and a vulcanization accelerator were kneaded for 3 minutes at 150 ° C. using a Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 3 minutes at 80 ° C. using a biaxial open roll to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was press vulcanized with a 0.5 mm thick mold at 170 ° C. for 20 minutes to obtain a vulcanized rubber composition.
Further, the obtained unvulcanized rubber composition was molded into a cap tread shape, bonded together with other tire members on a tire molding machine, press vulcanized at 160 ° C. for 20 minutes, and a test tire ( Tire size: 195 / 65R15) was obtained.

The following evaluation was performed about the obtained vulcanized rubber composition and the tire for a test. The results are shown in Tables 1 and 2. In Tables 1 and 2, the reference comparative example is Comparative Example 1.

(Low fuel consumption)
Rolling resistance when the manufactured test tire was run at a speed (80 km / h) under the conditions of a rim (15 × 6JJ), internal pressure (230 kPa) and load (3.43 kN) using a rolling resistance tester. The rolling resistance index of the reference comparative example was taken as 100, and the rolling resistance of each formulation was displayed as an index according to the following calculation formula. In addition, it shows that rolling resistance can be reduced and a fuel-consumption property is excellent, so that a rolling resistance index | exponent is large.
(Rolling resistance index) = (Rolling resistance of the reference comparative example) / (Rolling resistance of each formulation) × 100

(Wet grip performance)
The manufactured test tire was mounted on all wheels of a test vehicle (domestic FF2000cc), and the brake was stepped on the wet asphalt road surface while traveling at an initial speed of 100 km / h to measure the braking distance. And the wet grip performance index | exponent of the reference | standard comparative example was set to 100, and the braking distance of each mixing | blending was displayed as an index | exponent with the following formula. In addition, it shows that wet grip performance is so favorable that a wet grip performance index | exponent is large.
(Wet grip performance index) = (braking distance of reference comparative example) / (braking distance of each formulation) × 100

(Abrasion resistance)
The manufactured test tire was mounted on all wheels of a test vehicle (domestic FF2000cc) and traveled on an actual vehicle, and the change in the groove depth of the tread pattern before and after traveling 30000 km was calculated. Then, the wear resistance index of the reference comparative example was set to 100, and the change in groove depth of each formulation was displayed as an index by the following calculation formula. In addition, it shows that it is excellent in abrasion resistance, so that an abrasion resistance index | exponent is large.
(Abrasion resistance index) = (Change in groove depth of reference comparative example) / (Change in groove depth of each composition) × 100

(Rubber strength)
A tensile test was performed in accordance with JIS K6251 to measure elongation at break. The measurement results are shown as an index with the reference comparative example as 100. The larger the index, the better the rubber strength (breaking strength).
(Rubber strength index) = (breaking elongation of each compound) / (breaking elongation of reference comparative example) × 100

From the results of Tables 1 and 2, epoxidized natural rubber having a specific epoxidation rate, silica (1) having a nitrogen adsorption specific surface area of 150 m ² / g or more, silica having a nitrogen adsorption specific surface area of 100 m ² / g or less ( 2) can improve fuel economy, wet grip performance, wear resistance, and rubber strength in a well-balanced manner.

Claims (6)

A rubber component containing 10-80% by mass of 100% by mass of epoxidized natural rubber having an epoxidation rate of 7-15 mol%, silica (1) having a nitrogen adsorption specific surface area of 150 m ² / g or more, and nitrogen adsorption Including silica (2) having a specific surface area of 100 m ² / g or less, and oil ;
A rubber composition for a tire , wherein the total content of the silica (1) and (2) is 30 to 120 parts by mass and the amount of the oil is 1 to 15 parts by mass with respect to 100 parts by mass of the rubber component. The tire rubber composition according to claim 1, wherein the contents of the silica (1) and (2) satisfy the following formula.
(Content of silica (2)) × 0.2 ≦ (content of silica (1)) ≦ (content of silica (2)) × 6.5 The rubber composition for tires according to claim 1 or 2 containing butadiene rubber and / or styrene butadiene rubber. The tire rubber composition according to any one of claims 1 to 3, comprising 0.5 to 12 parts by mass of an alkaline fatty acid metal salt with respect to 100 parts by mass of the epoxidized natural rubber. The tire rubber composition according to any one of claims 1 to 4 , which is used as a rubber composition for a cap tread. The pneumatic tire produced using the rubber composition in any one of Claims 1-5 .