JP2011032302A - Rubber composition for tread and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tread capable of compatibilizing advantageous rolling resistance properties and advantageous durability performance (such as cracking resistance and wear resistance) at a higher order and capable of obtaining excellent wet grip performance and excellent driving stability, and a pneumatic tire using the same. <P>SOLUTION: This rubber composition for tread includes a rubber component containing an epoxidized natural rubber and a butadiene rubber, a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, and a white filler, in which the content of the epoxidized natural rubber is 35 mass% or more, relative to 100 mass% of the rubber component. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

In recent years, rubber compositions for tire treads composed mainly of natural rubber or the like have been proposed from the viewpoints of depletion of petroleum resources, reduction of rolling resistance, consideration for the environment, and the like (see, for example, Patent Document 1). However, when natural rubber is used as the main component of the rubber component, there is a problem that it is inferior to a tread using conventional styrene butadiene rubber (SBR) in terms of wet grip performance. For this reason, epoxidized natural rubber (ENR) is used in tire treads to improve wet grip performance, and is actively working to cope with the depletion of petroleum resources and to reduce CO ₂ emissions (for example, patent documents) 2-3).

In this way, although good wet grip performance can be obtained by using ENR, it is particularly high-performance (high flat) tire compared to the conventional SBR type tread, and when used for tires for heavy-duty vehicles even in passenger cars Further improvements are demanded in terms of crack resistance and wear resistance. As crack resistance here, suppression of the crack along the groove direction in the tread groove bottom especially produced by ozone or repeated deformation is calculated | required.

Moreover, epoxidized natural rubber, natural rubber, butadiene rubber, and the like undergo reversion after sulfur vulcanization. This phenomenon is that the rubber is deteriorated or the cross-linked state is deteriorated, and it has become clear as a result of the study by the present inventors that the wear resistance and the rolling resistance characteristic deteriorate at this time. In addition, the rigidity feeling may be reduced, and steering stability may be deteriorated. Further, in order to increase the productivity of the tire, vulcanization may be performed at a higher temperature. In such a case, the above phenomenon becomes particularly remarkable.

Conventionally, as a method of suppressing the reversion of vulcanizable rubber compositions used in rubber products such as tires and improving the heat resistance, the amount of the vulcanization accelerator is increased with respect to sulfur as a vulcanizing agent. A method and a method of blending a thiuram vulcanization accelerator as a vulcanization accelerator are known. In addition, as a crosslinking agent that can form a long-chain crosslinked structure represented by — (CH ₂ ) ₆ —S— or the like, PERKALINK 900 manufactured by Flexis, Duralink HTS, Vulcuren KA9188 manufactured by Bayer, and the like are known. It is known that the reversion of the rubber composition can be suppressed by blending these crosslinking agents into the rubber composition. However, these methods are effective in suppressing reversion of natural rubber and isoprene rubber, but there is also a problem that butadiene rubber has no effect or little effect.

Patent Document 4 discloses a tire rubber composition in which a mixture of an aliphatic carboxylic acid and an aromatic carboxylic acid zinc salt is blended, but the blend containing epoxidized natural rubber and butadiene rubber has been studied in detail. Not. In addition, there remains room for improvement in terms of obtaining a good balance of rolling resistance characteristics, crack resistance, wear resistance, wet grip performance, and steering stability.

JP 2003-64222 A JP 2004-359773 A JP 2007-169317 A JP 2007-321041 A

The present invention solves the above-mentioned problems, and can achieve both excellent rolling resistance characteristics and durability performance (crack resistance, wear resistance, etc.) at a high level, as well as excellent wet grip performance and steering stability. An object of the present invention is to provide a rubber composition and a pneumatic tire using the same.

The present invention contains a rubber component containing an epoxidized natural rubber and a butadiene rubber, a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, and a white filler, and 100% by mass of the rubber component. It is related with the rubber composition for tread whose content of epoxidized natural rubber is 35 mass% or more.

The tread rubber composition preferably further contains an alkaline fatty acid metal salt.
The cis rubber content of the butadiene rubber is preferably 80 mol% or more.
As said white filler, it is preferable to contain 30-150 mass parts of silica of nitrogen adsorption specific surface area 40-450 m < ² > / g with respect to 100 mass parts of rubber components.

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

According to the present invention, the rubber component 100 contains a rubber component containing epoxidized natural rubber and butadiene rubber, a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, and a white filler. Since the rubber composition has a content of epoxidized natural rubber in 35% by mass of 35% by mass or more, by using the rubber composition in a tread, good rolling resistance characteristics and durability performance (crack resistance, It is possible to provide a pneumatic tire in which all of these performances are exhibited in a well-balanced manner.

The rubber composition for a tread of the present invention includes a rubber component containing an epoxidized natural rubber (ENR) and a butadiene rubber (BR), a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, and white Containing a filler. The content of the epoxidized natural rubber in 100% by mass of the rubber component is 35% by mass or more.

By blending the mixture with specific amounts of ENR and BR, reversion (reversion) can be suppressed, and deterioration of rubber and cross-linked state can be suppressed. Deterioration of rolling resistance characteristics and steering stability (rigidity) can be prevented. These components not only provide excellent wet grip performance, but also improve crack resistance (particularly, suppression of cracks along the groove direction at the bottom of the tread groove) and wear resistance.

Therefore, in a tire using the rubber composition in a tread, both excellent rolling resistance (low tan δ) and durability performance (crack resistance, wear resistance, etc.) can be achieved, which is desirable from the viewpoint of environmental considerations. It also has excellent wet grip performance and handling stability. Furthermore, since reversion can be suppressed even by vulcanization at a high temperature for a short time, productivity can be improved and good processability can be obtained in an unvulcanized rubber composition.

In the present invention, ENR is used. As a result, good wet grip characteristics can be obtained while depleting petroleum resources, reducing rolling resistance, and considering the environment. As ENR, commercially available ENR may be used, or NR may be epoxidized. The method for epoxidizing NR is not particularly limited, and can be carried out using a method such as a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, or a peracid method (Japanese Patent Publication No. 4). No. -26617, JP-A-2-110182, UK Patent GB2113692, etc.). Examples of the peracid method include a method of reacting NR with an organic peracid such as peracetic acid or performic acid.

The epoxidation rate of ENR is preferably 10 mol% or more, more preferably 15 mol% or more, and further preferably 20 mol% or more. When the epoxidation ratio of ENR is less than 10 mol%, it tends to be difficult to sufficiently improve wet grip performance. The epoxidation rate of ENR is preferably 60 mol% or less, more preferably 50 mol% or less, and still more preferably 40 mol% or less. When the epoxidation rate of ENR exceeds 60 mol%, the polymer tends to gel, and ozone resistance and vulcanization resistance tend to deteriorate.
The epoxidation rate means the ratio of the number of epoxidized out of the total number of carbon-carbon double bonds in the natural rubber component before epoxidation. For example, titration analysis, nuclear magnetic resonance (NMR) analysis, etc. Is required.

As the NR to be epoxidized, those generally used in the rubber industry such as RSS # 3 and TSR20 and their latexes can be used. Examples of the ENR include ENR25, ENR50 (manufactured by Kumpoul Langley), and the like. ENRs may be used alone or in combination of two or more.

The content of ENR in 100% by mass of the rubber component is 35% by mass or more, preferably 45% by mass or more, and more preferably 55% by mass or more. If it is less than 35% by mass, it tends to be difficult to sufficiently improve the wet grip performance. The content of ENR is preferably 95% by mass or less, more preferably 85% by mass or less, and still more preferably 75% by mass or less. If it exceeds 95% by mass, the amount of BR tends to be relatively small, and it tends to be difficult to improve crack resistance and wear resistance.

In the present invention, BR is used. As a result, good wear resistance and crack resistance can be realized. Moreover, rolling resistance characteristics can be further improved. With regard to wear resistance and crack resistance, particularly when used in high-performance (high flatness) tires and tires for heavy-duty vehicles even in passenger cars, better performance is exhibited.

As BR, it is preferable to use a cis content of 80 mol% or more. Thereby, abrasion resistance can be made more favorable. The cis content is more preferably 85 mol% or more, still more preferably 90 mol% or more, and most preferably 95 mol% or more.

BR preferably has a 5% toluene solution viscosity at 25 ° C. of 80 cps or more. Thereby, the workability improvement effect and the wear resistance improvement effect can be enhanced. The toluene solution viscosity is preferably 200 cps or less. If it exceeds 200 cps, the viscosity tends to be too high, and the processability tends to be reduced, or it tends to be difficult to mix with other rubber components. The lower limit of the viscosity of the toluene solution is more preferably 110 cps, and the upper limit is more preferably 150 cps.

From the viewpoint of improving the wear resistance, a BR molecular weight distribution (Mw / Mn) of 3.0 or less may be used. Moreover, you may use BR with Mw / Mn of 3.0-3.4 from the point which can improve workability and wear-resistant improvement.

The BR content in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 15% by mass or more. If it is less than 5% by mass, it tends to be difficult to improve crack resistance and wear resistance. The BR content is preferably 60% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less. When it exceeds 60% by mass, the content of ENR becomes relatively small, and it tends to be difficult to sufficiently improve wet grip performance.

From the viewpoint of reducing the burden on the environment, it is preferable to use a butadiene rubber synthesized from a biomass-derived material. Such a butadiene rubber can be obtained, for example, by a method in which a catalyst is allowed to act on bioethanol to obtain butadiene, which is synthesized as a raw material. Although butadiene rubber synthesized from a biomass-derived material may be blended, it is particularly preferable that 100 mass% of biomass-derived butadiene rubber is contained as BR in the rubber composition. The biomass material means “renewable biological organic resources excluding fossil resources”. Moreover, whether it originates in biomass can be confirmed by a method (ASTM-D6866) for identifying the amount of C14.

As rubber components, in addition to ENR and BR, natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber ( CR), acrylonitrile butadiene rubber (NBR) or the like may be blended.

In the present invention, a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid is used. Thereby, reversion of both ENR and BR can be suppressed, and a rubber composition for tread having low rolling resistance and good wear resistance can be produced. Moreover, high rigidity is obtained and excellent steering stability is obtained. In particular, the deterioration of these characteristics when vulcanized at a high temperature can be suppressed. The above mixture is very suitable as an anti-reversion agent that works well on both ENR and BR, and other anti-reversion agents are effective in NR and ENR, but the vulcanization of BR Often there is little or no effect on the return.

As the aliphatic carboxylic acid in the zinc salt of aliphatic carboxylic acid, palm oil, palm kernel oil, camellia oil, olive oil, almond oil, canola oil, peanut oil, rice sugar oil, cocoa butter, palm oil, soybean oil, Examples include aliphatic carboxylic acids derived from vegetable oils such as cottonseed oil, sesame oil, linseed oil, castor oil and rapeseed oil, aliphatic carboxylic acids derived from animal oils such as beef tallow, and aliphatic carboxylic acids chemically synthesized from petroleum. It is also possible to prepare for future reductions in the supply of petroleum, and furthermore, since vulcanization reversion can be sufficiently suppressed, aliphatic carboxylic acids derived from vegetable oils are preferred, and palm oil, palm kernel oil or palm Oil-derived aliphatic carboxylic acids are more preferred.

The aliphatic carboxylic acid preferably has 4 or more carbon atoms, more preferably 6 or more carbon atoms. If the aliphatic carboxylic acid has less than 4 carbon atoms, the dispersibility tends to deteriorate. The carbon number of the aliphatic carboxylic acid is preferably 16 or less, more preferably 14 or less, and still more preferably 12 or less. When the carbon number of the aliphatic carboxylic acid exceeds 16, there is a tendency that the vulcanization return cannot be sufficiently suppressed.

The aliphatic group in the aliphatic carboxylic acid may be a chain structure such as an alkyl group or a cyclic structure such as a cycloalkyl group.

Examples of the aromatic carboxylic acid in the zinc salt of the aromatic carboxylic acid include benzoic acid, phthalic acid, melittic acid, hemimellitic acid, trimellitic acid, diphenic acid, toluic acid, and naphthoic acid. Of these, benzoic acid, phthalic acid, or naphthoic acid is preferable because reversion can be sufficiently suppressed.

The content ratio of the zinc salt of aliphatic carboxylic acid and the zinc salt of aromatic carboxylic acid in the mixture (molar ratio, zinc salt of aliphatic carboxylic acid / zinc salt of aromatic carboxylic acid, hereinafter referred to as the content ratio) is 1/20 or more is preferable, 1/15 or more is more preferable, and 1/10 or more is still more preferable. If the content ratio is less than 1/20, it is not possible to consider the environment or prepare for a future reduction in the amount of oil supplied, and the dispersibility and stability of the mixture tend to deteriorate. The content ratio is preferably 20/1 or less, more preferably 15/1 or less, and still more preferably 10/1 or less. When the content ratio exceeds 20/1, there is a tendency that the vulcanization return cannot be sufficiently suppressed.

The zinc content in the mixture is preferably 3% by mass or more, and more preferably 5% by mass or more. If the zinc content in the mixture is less than 3% by mass, there is a tendency that the vulcanization return cannot be sufficiently suppressed. Moreover, 30 mass% or less is preferable and, as for the zinc content rate in a mixture, 25 mass% or less is more preferable. When the zinc content in the mixture exceeds 30% by mass, the workability tends to decrease and the cost increases unnecessarily.

The content of the mixture is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, most preferably 1.4 parts by mass with respect to 100 parts by mass of the rubber component. That's it. If the amount is less than 0.2 parts by mass, sufficient vulcanization resistance cannot be ensured, and the durability maintenance effect of the tire tends to be difficult to obtain. The content of the mixture is 10 parts by mass or less, preferably 7 parts by mass or less, more preferably 5 parts by mass or less. When the amount exceeds 10 parts by mass, the tendency to bloom increases, and the improvement of the effect on the added amount decreases, and the cost tends to increase unnecessarily.

The rubber composition of the present invention contains a white filler. The white filler means a white and inorganic filler, and more specifically, silica, calcium carbonate, aluminum hydroxide and the like are exemplified. Among these, it is preferable to use silica in terms of a reinforcing effect, a rolling resistance reducing effect, and a grip performance improving effect.

Examples of the silica include, but are not limited to, dry method silica (anhydrous silicic acid), wet method silica (anhydrous silicic acid), and the like, and wet method silica is preferable because it has many silanol groups. Silica may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 40 m ² / g or more, more preferably 50 m ² / g or more, still more preferably 80 m ² / g or more, and most preferably 100 m ² / g or more. If it is less than 40 m ² / g, the reinforcing property is insufficient, and the wear resistance, mechanical strength, tensile strength, elongation at break, and fracture energy tend to deteriorate. Further, N ₂ SA of silica is preferably 450 m ² / g or less, more preferably 200 m ² / g or less, and still more preferably 180 m ² / g or less. When it exceeds 450 m ² / g, the dispersibility decreases, the exothermic property of the rubber composition increases, and the rolling resistance characteristic tends to deteriorate.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The amount of silica is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and still more preferably 45 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 30 parts by mass, the reinforcing effect tends to be insufficient. The amount of silica is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and still more preferably 100 parts by mass or less. When it exceeds 150 parts by mass, the rolling resistance reduction effect tends to be insufficient.

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, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-tri Ethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilyl) Butyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) Trisulfi Bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4 -Triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropylbenzothiazoli And sulfide systems such as tetratetrasulfide and 3-triethoxysilylpropylbenzothiazole tetrasulfide. Moreover, mercapto type, vinyl type, glycidoxy type, nitro type, chloro type and the like can also be mentioned. Of these, bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide are preferably used from the viewpoint of the reinforcing effect and processability of the silane coupling agent.

The content of the silane coupling agent is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and most preferably 7 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 1 mass part, there exists a tendency for fracture strength to fall large. Moreover, 15 mass parts or less are preferable with respect to 100 mass parts of silica, and, as for content of this silane coupling agent, 10 mass parts or less are more preferable. If it exceeds 15 parts by mass, effects such as an increase in fracture strength and a reduction in rolling resistance due to the further addition of the silane coupling agent cannot be obtained, and the cost tends to increase unnecessarily.

You may mix | blend alkaline fatty acid metal salt with the rubber composition of this invention. 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.

Examples of the metal in the alkaline fatty acid metal salt include sodium, potassium, calcium, barium and the like. Among these, calcium and barium are preferable from the viewpoint of increasing the heat resistance effect and compatibility with the epoxidized natural rubber. Specific examples of alkaline fatty acid metal salts include sodium stearate, magnesium stearate, calcium stearate, barium stearate and other stearic acid metal salts, sodium oleate, magnesium oleate, calcium oleate, barium oleate and other oleic acid Examples thereof include metal salts. Of these, calcium stearate and calcium oleate are preferable because they have a large heat resistance effect, high compatibility with epoxidized natural rubber, and relatively low cost.

The content of the alkaline fatty acid metal salt is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and further preferably 3 parts by mass or more with respect to 100 parts by mass of ENR. If it is less than 1 part by mass, it tends to be difficult to obtain sufficient effects with respect to heat resistance and reversion resistance. The content of the alkaline fatty acid metal salt is preferably 10 parts by mass or less, more preferably 8 parts by mass or less. If it exceeds 10 parts by mass, the fracture strength and wear resistance tend to deteriorate.

The rubber composition of the present invention may be blended with fatty acids such as stearic acid, palmitic acid, myristic acid, lauric acid, caprylic acid, oleic acid, linoleic acid, and stearic acid because of its low cost. Is preferred.

In the rubber composition of the present invention, the total content of the alkaline fatty acid metal salt, the zinc salt of the aliphatic carboxylic acid and the zinc salt of the aromatic carboxylic acid, and the fatty acid is based on 100 parts by mass of the rubber component. Preferably it is 2.5 mass parts or more, More preferably, it is 4 mass parts or more, More preferably, it is 6 mass parts or more. When the amount is less than 2.5 parts by mass, there is a tendency that ENR deterioration and reversion cannot be sufficiently prevented, and the efficiency of effectively crosslinking the added sulfur cannot be improved. The total content is preferably 20 parts by mass or less, more preferably 17 parts by mass or less, and still more preferably 12 parts by mass or less. When the amount exceeds 20 parts by mass, the wear resistance and mechanical strength tend to decrease.

In the rubber composition, in addition to the above components, compounding agents conventionally used in the rubber industry, for example, fillers such as carbon black, oils or plasticizers, antioxidants, anti-aging agents, zinc oxide, sulfur, You may contain vulcanizing agents, such as a sulfur-containing compound, a vulcanization accelerator, etc.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing. The rubber composition is used for tire treads.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, the rubber composition containing the above components is extruded in accordance with the tread shape at an unvulcanized stage and molded together with other tire members on a tire molding machine by a normal method. Form a sulfur tire. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The use of a pneumatic tire having a tread produced using the rubber composition of the present invention is not particularly limited, but it can be suitably used particularly as a high performance tire (high flat tire) and a tire for a passenger car high load vehicle.

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 Examples and Comparative Examples will be described together.
BR1: BR150B manufactured by Ube Industries, Ltd. (cis 1,4 bond amount: 97 mol%, ML _{1 + 4} (100 ° C.): 40, 5% toluene solution viscosity at 25 ° C .: 48 cps, Mw / Mn: 3.3)
BR2: BR360L manufactured by Ube Industries, Ltd. (cis 1,4 bond amount: 98 mol%, ML _{1 + 4} (100 ° C.): 51, 5% toluene solution viscosity at 25 ° C .: 124 cps, Mw / Mn: 2.4)
BR3: BR A prototype manufactured by Ube Industries, Ltd. (cis 1,4 bond amount: 98 mol%, ML _{1 + 4} (100 ° C.): 51, 5% toluene solution viscosity at 25 ° C .: 122 cps, Mw / Mn: 3. 3)
Epoxidized natural rubber 1 (ENR-25): manufactured by MRB (Malaysia) (epoxidation rate: 25 mol%, Tg: -47 ° C.)
Epoxidized natural rubber 2 (ENR-37.5): prototype manufactured by MRB (Malaysia) (epoxidation rate: 37.5 mol%, Tg: -35 ° C)
NR: RSS # 3
Silica: Ultrasil VN2 (N ₂ SA: 125 m ² / g) manufactured by Degussa Co., Ltd.
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Tegussa Co., Ltd.
Vegetable oil: Soybean white oil (S) manufactured by Nissin Oil Co., Ltd. (iodine value: 131, fatty acid component 84.9% having 18 or more carbon atoms)
Alkaline fatty acid metal salt: calcium stearate manufactured by NOF Corporation stearic acid: tung reversion inhibitor 1 manufactured by NOF Corporation (mixture of zinc salt of aliphatic carboxylic acid and zinc salt of aromatic carboxylic acid): Activator 73A ((i) Aliphatic carboxylic acid zinc salt: Zinc salt of fatty acid (carbon number: 8 to 12) derived from palm oil, (ii) Aromatic carboxylic acid zinc salt: Zinc benzoate , Content molar ratio: 1/1, zinc content: 17% by mass)
Reversion inhibitor 2: Parkerlink 900 (1,3-bis (citraconimidomethyl) benzene) manufactured by Flexis
Zinc oxide: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N'-phenyl-p- manufactured by Ouchi Shinsei Chemical Co., Ltd.) Phenylenediamine)
Wax: Sunnock wax manufactured by Ouchi Shinsei Chemical Co., Ltd. Sulfur: Sulfur powder vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. TBBS: Noxeller NS (N-tert- manufactured by Ouchi Shinsei Chemical Co., Ltd.) Butyl-2-benzothiazolylsulfenamide)

Examples 1-11 and Comparative Examples 1-8
According to the blending contents shown in Table 1, using a 1.7 L Banbury mixer, materials other than sulfur and vulcanization accelerator among the blended materials are kneaded for 5 minutes so that the discharge temperature is 150 ° C. Obtained. 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 at 170 ° C. for 15 minutes to obtain a vulcanized rubber sheet.
Moreover, the tire for a test was produced by shape | molding the obtained unvulcanized rubber composition in a tread shape, bonding with another tire member, and vulcanizing for 15 minutes at 170 degreeC.

The following evaluation was performed using the obtained unvulcanized rubber composition, vulcanized rubber sheet, and test tire. Each test result is shown in Table 1.

(1) Wet grip performance Wet grip performance was evaluated based on the braking performance obtained by the anti-lock brake system (ABS) evaluation test. That is, the test tire is mounted on a passenger car equipped with 1800 cc class ABS, and the asphalt road surface (wet road surface state, skid number of about 50) is actually driven, and braking is applied at a speed of 100 km / h. The deceleration until the passenger car stopped was calculated. Here, the deceleration is a distance until the passenger car stops. And the wet grip performance index of the comparative example 1 was set to 100, and the deceleration of each formulation was shown as the wet grip performance index by the following formula. The larger the grip performance index, the better the braking performance and the better the wet grip performance.
(Wet grip performance index) = (Deceleration of Comparative Example 1) / (Deceleration of each formulation) × 100

(2) Dry grip performance The test tire was mounted on a passenger car and traveled on a dry asphalt road test course, and characteristics relating to handle response, rigidity, grip and the like were evaluated by sensory evaluation of the driver. The results are displayed as an index with Comparative Example 1 as 100. The larger the value, the better, and the better dry grip performance and steering stability.

(3) Rolling resistance test A vulcanized rubber sheet having a size of 2 mm x 130 mm x 130 mm was prepared in the same manner as described above, a test piece for measurement was cut out therefrom, and a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) was used. The tan δ of each test piece was measured under the conditions of a temperature of 50 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. The rolling resistance index of Comparative Example 1 was set to 100, and the rolling resistance characteristics were each indicated by an index according to the following formula. The larger the index, the lower the rolling resistance and the better.
(Rolling resistance index) = (tan δ of Comparative Example 1 / tan δ of each formulation) × 100

(4) Wear resistance test (wear test)
The manufactured test tire was mounted on a car, and the amount of decrease in the groove depth after traveling 8000 km in an urban area was measured, and the travel distance when the groove depth decreased by 1 mm was calculated. Furthermore, the abrasion resistance index of Comparative Example 1 was set to 100, and the amount of decrease in the groove depth of each formulation was displayed as an index according to the following formula. In addition, it shows that it is excellent in abrasion resistance, so that an abrasion resistance index | exponent is large.
(Abrasion resistance index) = (travel distance when the groove depth of 1 mm decreases in each composition) / (travel distance when the groove of the tire of Comparative Example 1 decreases by 1 mm) × 100

(5) Fracture energy index The tensile strength and elongation at break of each vulcanized rubber sheet were measured according to JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber—How to Obtain Tensile Properties”. Furthermore, the fracture energy was calculated by tensile strength × break elongation / 2, and the fracture energy index was calculated by the following formula.
(Fracture energy index) = (Fracture energy of each formulation) / (Fracture energy of Comparative Example 1) × 100

(6) Ozone resistance test Based on JIS K 6259 "Vulcanized rubber and thermoplastic rubber-Determination of ozone resistance", a dynamic ozone deterioration test of each vulcanized rubber sheet was conducted, and the frequency of reciprocating motion was 0.5. The ozone resistance was evaluated by observing the state of cracks after testing for 48 hours under the conditions of ± 0.025 Hz, ozone concentration 50 ± 5 pphm, test temperature 40 ° C., and tensile strain 20 ± 2%. The evaluation method represented the number and size of cracks according to the method described in JIS. Note that the alphabet (A, B, and C) indicates that A is a small number of cracks and C is a large number of cracks, and that the larger the number, the larger the size of the crack. Indicates that no cracks occurred. The better the ozone resistance, the better the crack resistance as a tire.

(7) The vulcanization curve of the unvulcanized rubber composition at 170 ° C. was measured using a vulcanization resistance reversion vulcanization tester (for example, a Clastometer manufactured by JSR Trading). The maximum torque (MH) value, the minimum torque (ML) value, and the torque value M20 20 minutes after the start of vulcanization were measured, and the vulcanization return of each formulation was evaluated by the following formula. In addition, it shows that a vulcanization return can be suppressed and it is excellent, so that a vulcanization return rate (reversion rate) is small.
(Reversion rate (%)) = (MH−M20) / (MH−ML) × 100

In Comparative Examples 1 to 4 and Comparative Example 7, ozone resistance was poor, whereas in Examples, both were improved. In particular, the greater the amount of BR, the better the ozone resistance. In Example 11 using the epoxidized natural rubber 2 (ENR-37.5), it was slightly improved compared to Comparative Examples 1 to 4 and Comparative Example 7. In Example 11, the epoxidized natural rubber 2 (ENR-37.5) can greatly improve the wet grip performance, and even the wear resistance can be greatly improved as compared with each comparative example.

In other examples, wear resistance and crack resistance were good. In particular, the abrasion resistance was good in the Examples having a high BR blend ratio. Also, the rolling resistance characteristics were very good in the examples, which were inferior to those in Comparative Example 1.

Since Comparative Examples 1-4 did not blend BR, ozone resistance and abrasion resistance were bad. Although Comparative Example 5 is blended with BR, it does not contain a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid or an alkaline fatty acid metal salt. It was inferior. Although Comparative Example 6 was blended with BR, the anti-reversion agent 2 other than a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid or an alkaline fatty acid metal salt was used. It was bad and the rolling resistance characteristic was also slightly bad. In Comparative Example 7, since epoxidized natural rubber 2 (ENR-37.5) was used, the wet grip performance was very good, but a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, Since an alkaline fatty acid metal salt was not blended, the wear resistance was poor, the rolling resistance index was also deteriorated, and the fracture energy was also reduced. Since Comparative Example 8 did not blend ENR, the wet grip performance was very poor. Moreover, since the reversion resistance was also poor compared to Examples 1 to 4 and 6 to 11, the improvement rate of rolling resistance characteristics and wear resistance was low even though ENR was not blended.

On the other hand, the examples have good performance, in particular, the amount of the mixture of zinc salt of aliphatic carboxylic acid and zinc salt of aromatic carboxylic acid (part by mass) + the amount of alkaline fatty acid metal salt (part by mass) + the amount of stearic acid ( In Examples 1 to 6 and 9 to 11 in which the total amount of (parts by mass) was 6.7 to 11 parts by mass, the balance of the physical properties was good.

Claims (5)

A rubber component including epoxidized natural rubber and butadiene rubber, a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, and a white filler;
A rubber composition for a tread, wherein the content of epoxidized natural rubber in 100% by mass of the rubber component is 35% by mass or more. The rubber composition for a tread according to claim 1, further comprising an alkaline fatty acid metal salt. The rubber composition for a tread according to claim 1 or 2, wherein the cis content of the butadiene rubber is 80 mol% or more. The rubber composition for treads in any one of Claims 1-3 which contains 30-150 mass parts of silica of nitrogen adsorption specific surface area 40-450 m < ² > / g as a white filler with respect to 100 mass parts of rubber components. The pneumatic tire which has a tread produced using the rubber composition in any one of Claims 1-4.