JP5551904B2 - Rubber composition for tread and pneumatic tire - Google Patents

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 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. 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) or the like in terms of wet grip characteristics. As a method for solving this problem, for example, Patent Document 1 discloses a rubber composition for a tread containing epoxidized natural rubber (ENR).

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.

JP 2009-19210 A

The present invention solves the above-mentioned problems, and provides good environmental performance (rolling resistance characteristics, response to petroleum resource depletion, consideration for CO ₂ emissions) and durability performance (crack resistance, wear resistance, mechanical strength, etc.) An object of the present invention is to provide a rubber composition for a tread that can achieve a high level of compatibility with the above and a superior grip performance (wet grip performance, dry grip performance), and a pneumatic tire using the same.

The present invention comprises an epoxidized natural rubber, a rubber component containing a first rubber having a lower polarity (lower glass transition temperature) than the epoxidized natural rubber, and silica, and 100% by mass of the rubber component Further, the present invention relates to a rubber composition for a tread in which the content of the epoxidized natural rubber is 35% by mass or more and the silica dispersion is 90% or more.

The first rubber is preferably butadiene rubber and / or natural rubber.

The cis rubber content of the butadiene rubber is preferably 80% by mass or more.

In 100% by mass of the rubber component, the content of the natural rubber is preferably 0.1 to 35% by mass.

The nitrogen adsorption specific surface area of the silica is preferably 40 to 600 m ² / g, and the blending amount of the silica with respect to 100 parts by mass of the rubber component is preferably 30 to 150 parts by mass.

The rubber composition is preferably obtained by a first kneading step of kneading a part of the silica to obtain a kneaded product, and a second kneading step of kneading the remainder of the silica together with the kneaded product.

Alternatively, the first kneading step is a step of kneading a part of the rubber component and a part of the silica to obtain a kneaded product, and the second kneading step is a remaining part of the rubber component and a remaining part of the silica. It is preferable to be a step of kneading together with the kneaded product.

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

According to the present invention, the epoxidized natural rubber contains a rubber component including a epoxidized natural rubber and a first rubber having a polarity lower than that of the epoxidized natural rubber, and silica. Since the rubber composition has a rubber content of 35% by mass or more and the silica dispersion is 90% or more, good environmental performance (rolling resistance characteristics) can be obtained by using the rubber composition in a tread. , To cope with oil resource depletion, consideration for CO ₂ emissions) and durability performance (crack resistance, wear resistance, mechanical strength, etc.) at a high level and excellent grip performance (wet grip performance, Dry grip performance) can also be obtained, and it is possible to provide a pneumatic tire that exhibits all these performances in a well-balanced manner.

The rubber composition for a tread of the present invention contains an epoxidized natural rubber (ENR), a rubber component containing a first rubber having a lower polarity (lower glass transition temperature) than the epoxidized natural rubber, and silica. To do. The content of the epoxidized natural rubber in 100% by mass of the rubber component is 35% by mass or more. Furthermore, the dispersion rate of the silica is 90% or more.

Rolling resistance characteristics can be improved by blending the first rubber with a specific amount of ENR and having a specific silica dispersion rate. ENR not only provides excellent grip performance (wet grip performance, dry grip performance), but also crack resistance (especially suppression of cracks along the groove direction at the tread groove bottom), wear resistance, machine Strength can also be improved.

Therefore, a tire using the rubber composition in the tread can achieve both excellent rolling resistance (low tan δ) and durability performance (crack resistance, wear resistance, mechanical strength, etc.) and environmental considerations (depletion of petroleum resources) , And consideration of CO ₂ emissions). In addition, grip performance (wet grip performance, dry grip performance) is also excellent.

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 (ENR25, ENR50 (manufactured by MRB (Malaysia)), etc.) may be used, or natural rubber (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, British Patent Application No. 2113692, etc.). Examples of the peracid method include a method of reacting NR with an organic peracid such as peracetic acid or performic acid. In addition, as NR which epoxidizes, what is common in rubber industries, such as RSS # 3, TSR20, and those latex can be used. Moreover, ENR may be used independently or may be used in combination of 2 or more type. That is, ENRs having different epoxidation rates may be used in combination.

The epoxidation rate of ENR is preferably 5 mol% or more, more preferably 10 mol% or more, still more preferably 15 mol% or more, and most preferably 20 mol% or more. If the epoxidation rate of ENR is less than 5 mol%, it may 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. If the epoxidation rate of ENR exceeds 60 mol%, the polymer may gel, and ozone resistance and reversion resistance may 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.

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 may 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 mass%, the amount of the first rubber is relatively small, and it may be difficult to sufficiently improve crack resistance and wear resistance.

The rubber composition of the present invention contains a rubber (first rubber) having a lower polarity than ENR. Thereby, ozone resistance, crack resistance, wear resistance, and mechanical strength are improved.
A highly polar rubber also has a high glass transition temperature (Tg). Therefore, the polarity of ENR and the first rubber can be determined by comparing the glass transition temperatures (Tg). Tg in the present invention is a value measured according to JIS-K7121, using a differential scanning calorimeter (Q200) manufactured by T.A.

The difference in Tg between ENR and the first rubber is preferably 10 ° C. or higher, more preferably 20 ° C. or higher, and further preferably 30 ° C. or higher. If it is less than 10 ° C., it may be difficult to sufficiently improve crack resistance, wear resistance and the like. Further, the difference in Tg between the ENR and the first rubber is preferably 150 ° C. or less, and more preferably 120 ° C. or less. If the temperature exceeds 150 ° C., the polarities are too different, and the ENR and the first rubber tend to be difficult to mix.

As the first rubber, butadiene rubber (BR), natural rubber (NR) (non-epoxidized natural rubber), isoprene rubber (IR), ethylene propylene rubber (EPDM), butyl rubber (IIR), or the like can be used. . Of these, BR, NR, and IR are preferably used, and BR and NR are more preferably used in combination. By using BR, good wear resistance and crack resistance can be realized in a high dimension. 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. Further, by using NR, it is possible to improve the dispersion rate of silica and improve wear resistance and rolling resistance characteristics. Furthermore, when BR and NR are used in combination, NR improves the kneading processability of BR, thereby improving the dispersion rate of silica and the like.
In this specification, when it is described as natural rubber (NR), ENR is not included.

The NR is not particularly limited, and the same NR as that for the epoxidation described above can be used.

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.

From the viewpoint that the dispersibility of silica can be further improved, BR having a terminal modified (modified BR) may be used.
Examples of the functional group introduced into the modified BR include an amino group, a hydroxyl group, an epoxy group, an alkylsilyl group, an alkoxysilyl group, a carboxyl group, and a lactam group. From the viewpoint that the properties can be further improved, an amino group, an epoxy group, an alkylsilyl group, and an alkoxysilyl group are preferable, and it is more preferable to use two or more of them in combination. The functional group introduced into the modified BR may be one type or two or more types, but preferably two or more types. Moreover, in this specification, when describing as BR, modified | denatured BR shall be included.

The cis content of BR is preferably 80% by mass or more. Thereby, abrasion resistance can be made more favorable. The cis content is more preferably 85% by mass or more, still more preferably 90% by mass or more, and most preferably 95% by mass or more.
The cis content can be measured by infrared absorption spectrum analysis, nuclear magnetic resonance (NMR) analysis, or the like.

BR preferably has a 5% toluene solution viscosity at 25 ° C. of 40 cps or more. Thereby, 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 toluene solution viscosity is more preferably 80 cps, still 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 content of the first rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more, and most preferably 30% by mass or more. If it is less than 5% by mass, it may be difficult to sufficiently improve crack resistance and wear resistance. The content of the first rubber is preferably 60% by mass or less, more preferably 50% by mass or less. If it exceeds 60% by mass, the ENR content is relatively small, and it may be difficult to sufficiently improve the wet grip performance.

When the rubber composition of the present invention contains NR, the content of NR in 100% by mass of the rubber component is preferably 0.1% by mass or more, more preferably 1% by mass or more, and further preferably 3% by mass or more. is there. If it is less than 0.1% by mass, it may be difficult to sufficiently improve the kneadability of other first rubber such as BR. The NR content is preferably 35% by mass or less, more preferably 20% by mass or less, still more preferably 10% by mass or less, and most preferably 7% by mass or less. If it exceeds 35% by mass, the content of other first rubbers such as BR and ENR becomes relatively small, so that the crack resistance and wear resistance can be sufficiently improved while maintaining the wet grip performance. May be difficult.

When the rubber composition of the present invention contains BR, the content of BR in 100% by mass of the rubber component is preferably 5% by mass, more preferably 10% by mass or more, and further preferably 15% by mass or more. If it is less than 5% by mass, it may be difficult to effectively 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. If it exceeds 60% by mass, the ENR content is relatively small, and it may be difficult to sufficiently improve the wet grip performance.

In addition to ENR and first rubber, styrene butadiene rubber (especially high styrene content), acrylonitrile butadiene rubber, chlorinated natural rubber, highly polar modified natural rubber, etc. may be blended as the rubber component. Good.

The rubber composition of the present invention contains silica as a filler. Thereby, reinforcement of a rubber composition, reduction of rolling resistance, and improvement of wet grip performance can be performed.

The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferable because of its large number of 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 becomes insufficient, and the wear resistance and mechanical strength (tensile strength, breaking elongation, breaking energy) tend to deteriorate. Further, N ₂ SA of silica is preferably 600 m ² / g or less, more preferably 450 m ² / g or less, still more preferably 200 m ² / g or less, and most preferably 180 m ² / g or less. If it exceeds 600 m ² / g, the silica dispersion rate decreases, so the exothermic property of the rubber composition increases and the rolling resistance characteristics tend 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 dispersion rate of silica in the rubber composition of the present invention is 90% or more, preferably 93% or more, more preferably 95% or more. Thereby, good wear resistance and mechanical strength can be obtained.

The dispersion rate of silica can be measured by the following procedure. First, the vulcanized rubber composition was cut using a microtome at a temperature not higher than the glass transition point in a nitrogen atmosphere to obtain a fresh smooth surface. Next, the proportion of foreign matter presumed to be silica agglomerates on the smooth surface in the measurement area was corrected by the silica content in the vulcanized rubber composition, and the silica dispersion was calculated. In addition, the area of the foreign matter was measured by summing up the areas corresponding to circles with an equivalent circle diameter of 4 μm or more using an optical microscope and an image analysis device. The calculation formula of the dispersion rate of silica is shown below. In this case, the closer the silica dispersion is to 100%, the better the silica dispersion. In addition, when a fresh smooth surface is obtained by cutting with a sharp blade etc., without cooling especially a vulcanized rubber composition, such a method may be used.
Silica dispersion (%) = [1- (A × B) / (C × D)] × 100
(In the above formula, A represents the area occupied by the aggregate of silica having an equivalent circle diameter of 4 μm or more, B represents the measurement area, C represents the volume of the blended silica, and D represents the volume of the vulcanized rubber composition. .)

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 a fracture strength to fall large with respect to 100 mass parts of silica. Moreover, 15 mass parts or less are preferable, 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. Also, reversion can be prevented.

Examples of the metal in the alkaline fatty acid metal salt include sodium, potassium, calcium, barium, and the like. Among them, calcium has a high effect of improving the heat resistance of ENR, and is highly compatible with ENR. Barium is preferred. Specific examples of alkaline fatty acid metal salts include stearic acid metal salts such as sodium stearate, magnesium stearate, calcium stearate, and barium stearate, and olein such as sodium oleate, magnesium oleate, calcium oleate, and barium oleate. Examples include acid metal salts. Of these, calcium stearate and calcium oleate are preferred in that the effect of improving the heat resistance of ENR is great, the compatibility with ENR is high, and the cost is relatively low.

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 may be difficult to sufficiently improve 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, 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.

As a method for producing the rubber composition of the present invention, a known method can be used. For example, the above components are kneaded using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanized. Can be manufactured. In addition, the following manufacturing methods are specifically mentioned as a method of making the dispersion rate of a silica 90% or more.

(Method I)
The step of kneading the rubber component and silica from the viewpoint that the dispersion rate of silica can be easily improved (90% or more) is the first step of kneading part of the rubber component and part of silica to obtain a kneaded product. It is preferable to include a kneading step and a second kneading step of kneading the remaining rubber component and the remaining silica together with the kneaded product. In addition, ENR is preferably not kneaded in the first kneading step but only kneaded in the second kneading step from the viewpoint that the dispersion rate of silica can be improved more easily and the fracture energy and wear resistance can be improved. . Furthermore, the first rubber such as BR and NR is preferably kneaded in the first kneading step.

“Mass of silica kneaded in first kneading step / mass of silica kneaded in second kneading step” is “mass of rubber component kneaded in first kneading step / rubber kneaded in second kneading step”. A value obtained by multiplying the “mass of the component” by 0.5 to 1.5 is preferable, and a value obtained by multiplying 0.8 to 1.2 is more preferable. Thus, by adjusting the amount of silica added in each step, better dispersibility of silica can be obtained.

(Method II)
In Method II, all of the rubber component and part of the silica are kneaded in the first kneading step, and the remaining silica is kneaded in the second kneading step. Thus, by kneading silica in two stages, the silica dispersion can be easily improved (90% or more).

The “mass of silica kneaded in the first kneading step / mass of silica kneaded in the second kneading step” is preferably as large as possible, specifically, preferably 2 or more, more preferably 3 More preferably, it is 5 or more, and most preferably 6 or more. Moreover, the mass of the silica kneaded in the first kneading step is preferably 75 parts by mass or less, more preferably 70 parts by mass or less with respect to 100 parts by mass of the rubber component.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, if necessary, a rubber composition containing various additives is extruded into a tread shape at an unvulcanized stage, molded by a normal method on a tire molding machine, and other tire members The tires can be produced by pasting together to form an unvulcanized tire and then heating and pressing in a vulcanizer.

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 content: 97% by mass, ML _{1 + 4} (100 ° C.): 40, 5% toluene solution viscosity at 25 ° C .: 48 cps, Mw / Mn: 3.3, Tg: −90 ℃)
BR2: BR360L manufactured by Ube Industries, Ltd. (cis content: 98% by mass, ML _{1 + 4} (100 ° C.): 51, 5% toluene solution viscosity at 25 ° C .: 124 cps, Mw / Mn: 2.4, Tg: −90 ℃)
BR3: BR A prototype manufactured by Ube Industries, Ltd. (cis content: 98 mass%, ML _{1 + 4} (100 ° C.): 47, 5% toluene solution viscosity at 25 ° C .: 122 cps, Mw / Mn: 3.3, Tg : -90 ° C)
Epoxidized natural rubber 1 (ENR-25): manufactured by MRB (Malaysia) (epoxidation rate: 25 mol%, Tg: -47 ° C.)
Epoxidized natural rubber 2 (ENR-37.5): a prototype manufactured by MRB (Malaysia) (epoxidation rate: 37.5 mol%, Tg: -35 ° C)
NR: RSS # 3 (Tg: -70 ° C)
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
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: paulownia zinc oxide manufactured by NOF Corporation: two types of zinc oxide manufactured by Mitsui Kinzoku Mining Co., Ltd. Nocrack 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-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 1-8
Using a 1.7 L Banbury mixer, the chemicals in the blending amount shown in Step 1 of Table 1 were added and kneaded for 5 minutes so that the discharge temperature was about 150 ° C. Next, with respect to the kneaded material obtained in the step 1, the amount of chemicals shown in the step 2 was added and kneaded for 5 minutes so that the discharge temperature was about 150 ° C. to obtain a kneaded material. Next, after cooling the kneaded material obtained in the step 2, the sulfur and the vulcanization accelerator of the blending amounts shown in the step 3 are added, and using a biaxial open roll for 3 minutes under the condition of about 80 ° C. By kneading, an unvulcanized rubber composition was obtained. Then, the vulcanized rubber sheet of Examples 1-8 was produced by carrying out press vulcanization for 30 minutes at 150 ° C.

Comparative Examples 1-5
Except not performing process 2, it carried out similarly to Examples 1-8, and produced the vulcanized rubber sheet of Comparative Examples 1-5.

In addition, the unvulcanized rubber composition obtained in Step 3 was formed into a tread shape, bonded to another tire member, and vulcanized at 150 ° C. for 30 minutes, so that Examples 1 to 8 and Comparative Example 1 were used. ~ 5 test tires were prepared.

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

(1) Wet grip performance The 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 wet 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 test piece for measurement was cut out from a vulcanized rubber sheet having a size of 2 mm × 130 mm × 130 mm, and using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), a temperature of 50 ° C., an initial strain of 10%, Under the conditions of dynamic strain of 2% and frequency of 10 Hz, the tan δ of each test rubber composition was measured, and the rolling resistance index of Comparative Example 1 was set to 100, and the rolling resistance characteristics were expressed as an index by 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. The larger the fracture energy index, the better the mechanical strength.
(Fracture energy index) = (Fracture energy of each formulation) / (Fracture energy of Comparative Example 1) × 100

(6) A test specimen for measurement was cut out from each vulcanized rubber sheet having a silica dispersion rate of 2 mm × 130 mm × 130 mm and measured by the following method. First, the test specimen for measurement was cut using a microtome at a temperature not higher than the glass transition point in a nitrogen atmosphere to obtain a fresh smooth surface. Next, the proportion of foreign matter presumed to be silica agglomerates on the smooth surface in the measurement area was corrected with the silica content in the test specimen, and the silica dispersion was calculated. In addition, the area of the foreign matter was measured by summing up the areas corresponding to circles with an equivalent circle diameter of 4 μm or more using an optical microscope and an image analysis device. The calculation formula of the dispersion rate of silica is shown below. In this case, the closer the silica dispersion is to 100%, the better the silica dispersion. Silica dispersion (%) = [1- (A × B) / (C × D)] × 100
(In the above formula, A represents the area occupied by the aggregate of silica having an equivalent circle diameter of 4 μm or more, B represents the measurement area, C represents the volume of the blended silica, and D represents the volume of the test specimen for measurement. )

(7) Ozone resistance test Each vulcanized rubber sheet was subjected to a dynamic ozone deterioration test based on JIS K 6259 "Vulcanized rubber and thermoplastic rubber-Determination of ozone resistance", 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 indicates that the number of cracks is small and C indicates that the number of cracks is large. The larger the number, the larger the size of the crack. The better the ozone resistance, the better the crack resistance as a tire.

In Comparative Examples 1 to 3 and Comparative Example 5, ozone resistance was poor, whereas in Examples, all were improved. In particular, in Examples 1 to 3 and 5 to 7 using epoxidized natural rubber 1 (ENR-25), the effect of improving ozone resistance was great.

In the examples, NR was blended and the kneading method was further improved to improve the silica dispersion, thereby improving the fracture energy index. Therefore, the wear resistance index was also good.

In Examples 1 to 3 and 5 to 7 using the epoxidized natural rubber 1 (ENR-25), the rolling resistance index was also better than the comparative examples having the same BR ratio. Also, the wear resistance was good.

On the other hand, in Examples 4 and 8 using epoxidized natural rubber 2 (ENR-37.5), the wet grip performance was greatly improved and even the wear resistance was greatly improved as compared with each comparative example. .

In particular, in Steps 1 to 4 in which only BR and NR and silica were kneaded among the rubber components in Step 1 (ENR was not kneaded in Step 1 (first kneading step)), in Examples 1-4, the silica dispersion rate and destruction The energy was further improved, so that the wear resistance was even better.

The rolling resistance characteristics were very good in Examples 1 to 3 and 5 to 7. In addition, Examples 4 and 8 were inferior levels compared to Comparative Example 1.

Since Comparative Examples 1-3 did not blend BR, ozone resistance was bad, and abrasion resistance was also bad compared with the Example. Although Comparative Examples 4 and 5 were blended with BR, since the silica dispersion was low, the wear resistance and fracture energy were low compared to the Examples. In Comparative Example 5, since epoxidized natural rubber 2 (ENR-37.5) was used, wet grip performance was good, but since there was no improvement in the kneading method, the silica dispersion was low. As a result, the fracture energy, wear resistance, and rolling resistance characteristics also deteriorated.

Claims (7)

Containing rubber components including epoxidized natural rubber, natural rubber and butadiene rubber, and silica;
In 100% by mass of the rubber component, the content of the epoxidized natural rubber is 35% by mass or more,
A rubber composition for a tread having a silica dispersion ratio of 90% or more,
Obtained by a production method comprising a first kneading step of kneading a part of the silica, the natural rubber and the butadiene rubber to obtain a kneaded product, and a second kneading step of kneading the remainder of the silica together with the kneaded product. Tread rubber composition. The rubber composition for treads according to claim 1 whose cis content of said butadiene rubber is 80 mass% or more. The rubber composition for a tread according to claim 1 or 2, wherein a content of the natural rubber is 0.1 to 35% by mass in 100% by mass of the rubber component. The silica has a nitrogen adsorption specific surface area of 40 to 600 m ² / g,
The rubber composition for a tread according to any one of claims 1 to 3, wherein a compounding amount of the silica is 30 to 150 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition for a tread according to any one of claims 1 to 4, wherein the epoxidized natural rubber is kneaded only in the second kneading step. The pneumatic tire which has a tread produced using the rubber composition for treads in any one of Claims 1-5. A method for producing a rubber composition for a tread, comprising a rubber component including epoxidized natural rubber, natural rubber and butadiene rubber, and silica,
A first kneading step of kneading a part of the silica, the natural rubber and the butadiene rubber to obtain a kneaded product, and a second kneading step of kneading the remainder of the silica together with the kneaded product. The manufacturing method of the rubber composition for treads in any one of.