JP2012021083A - Method for producing rubber composition for sidewall, rubber composition for sidewall, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a sidewall, which is earth-friendly by improving the content ratio of resources other than petroleum, can be prepared for the decrease of the quantity of oil supplied in the future and exhibits excellent resistance against flexure and crack and excellent tear strength.SOLUTION: Provided is the method for producing the rubber composition for the sidewall, which includes: a step 1 for kneading a natural rubber, silica, and a silane coupling agent; a step 2 for kneading a kneaded product 1 obtained by step 1, stearic acid, and zinc oxide; and a step 3 for kneading a kneaded product 2 obtained by step 2 and an epoxidated natural rubber.

Description

The present invention relates to a method for producing a rubber composition for a sidewall, a rubber composition for a sidewall, and a pneumatic tire using the same.

Conventionally, as rubber compositions used for tire sidewalls, in addition to natural rubber exhibiting excellent tear strength, butadiene rubber has been blended to improve flex cracking resistance, and weather resistance and reinforcing properties have been further improved. In order to improve, carbon black was widely used.

However, in recent years, become environmental issues are important, CO ₂ emission regulation has been enhanced Further, since petroleum resources are finite, are expected future oil prices, butadiene rubber, carbon black, etc. There are limits to the use of raw materials made from other petroleum resources. Therefore, it is desirable to use non-petroleum resources such as natural rubber, silica, white fillers such as calcium carbonate, and even in that case, performance equal to or better than the rubber composition using petroleum resources (bending crack resistance, It is necessary to provide reinforcement.

Patent Document 1 discloses a method for producing a rubber composition in which natural rubber and silica are kneaded, and then epoxidized natural rubber is kneaded. Patent Document 2 discloses a raw rubber, silica, and silane coupling agent in a sealed rubber mixer. A kneading method is disclosed in which kneading and then kneading with a twin-screw kneader taking a predetermined temperature and time. However, there has been a demand for a method for producing a rubber composition having better bending crack resistance and tear strength.

JP 2006-70093 A JP 2010-84057 A

The present invention solves the above problems and increases the content ratio of non-petroleum resources, which is gentle to the earth and can prepare for a reduction in the future supply of oil, and also exhibits excellent flex crack resistance and tear strength. It aims at providing the manufacturing method of the rubber composition for sidewalls.

The present invention is obtained in Step 1 for kneading natural rubber, silica and silane coupling agent, Step 2 for kneading the kneaded product 1 obtained in Step 1 above, stearic acid and zinc oxide, and Step 2 above. And a kneaded product 2 and a process 3 for kneading epoxidized natural rubber.

Step 1 is preferably a step of kneading natural rubber and surface-treated silica obtained by treating silica with a silane coupling agent.
Step 2 is preferably a step of further kneading an antioxidant and a wax.

The present invention also provides a rubber for a sidewall obtained by the above production method, wherein the content of natural rubber in 100% by mass of rubber component is 30 to 90% by mass and the content of epoxidized natural rubber is 10 to 70% by mass Relates to the composition.
The nitrogen adsorption specific surface area of silica is preferably 30 to 500 m ² / g, and the silica content is preferably 15 to 60 parts by mass with respect to 100 parts by mass of the rubber component.

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

According to the present invention, since it is a method for producing a rubber composition for a sidewall including specific steps 1 to 3, it is kind to the earth by increasing the content ratio of non-oil resources, and in the future, the supply amount of oil is reduced. A rubber composition for a sidewall is obtained which is provided and exhibits excellent bending crack resistance and tear strength.

The method for producing a rubber composition for a sidewall of the present invention comprises a step 1 for kneading natural rubber, silica and a silane coupling agent, and a kneaded product 1, stearic acid and zinc oxide obtained in step 1 above. Step 2 to be performed, and Step 3 to knead the kneaded product 2 obtained in Step 2 and the epoxidized natural rubber. By sequentially performing these steps, a rubber composition with improved resistance to bending cracking and tear strength can be produced.

The reason for such an effect is not clear, but is presumed to be due to the following functions.
First, if Step 1 of kneading natural rubber (NR), silica and a silane coupling agent is performed in advance before kneading stearic acid and zinc oxide, the reaction of the silane coupling agent is inhibited by stearic acid or the like. There is nothing. Therefore, compared with the method of kneading these components in the same step, the reaction rate is increased and the reaction (bonding) between the silica and NR via the silane coupling agent can be promoted. Moreover, since NR is kneaded prior to the epoxidized natural rubber (ENR), uneven distribution of silica and silane coupling agent on the ENR side can be suppressed. Subsequently, by kneading the obtained kneaded material 1, stearic acid, and zinc oxide and then kneading ENR (steps 2 to 3), the reaction of the silane coupling agent with respect to NR is promoted more than ENR. . Therefore, the reaction rate is increased as compared with the method of kneading kneaded material 1 and ENR and then kneading stearic acid or the like. As described above, the reaction rate promoting effect is exhibited, and the dispersibility of silica is increased, so that it is presumed that the resistance to bending cracking and the tearing strength are improved.

(Process 1)
In step 1, NR, silica, and a silane coupling agent are kneaded.
The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used.

The blending amount of NR in Step 1 is preferably 40 to 100% by mass of the blending amount of all NRs used in all steps. If the blending amount is less than 40% by mass, the ratio of the amount of silica to NR increases, so the viscosity of the kneaded product tends to be very high and difficult to process. The blending amount is most preferably 100% by mass.

Although there is no restriction | limiting in particular as a silica, A dry process silica (anhydrous silicic acid), a wet process silica (hydrous silicic acid), etc. are mentioned, The wet process silica is preferable from the reason that there are 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 by the BET method is preferably 30 m ² / g or more, more preferably 50 m ² / g or more, and still more preferably 80 m ² / g or more. If it is less than 30 m ² / g, the reinforcing effect tends to be small. The _N 2 SA is preferably 500 meters ² / g or less, more preferably ^{400m 2 / g, 200m 2 /} g or less is more preferable. If it exceeds 500 m ² / g, the dispersibility of silica may be lowered.
The _N 2 SA of silica can be measured by the BET method in conformity with ASTM-D-4820-93.

It is preferable that the compounding quantity of the silica in process 1 is 80-100 mass% of the compounding quantity of all the silica used in all the processes. When the blending amount is less than 80% by mass, since a large amount of silica is blended in ENR in Step 3 to form a hard layer, the flex crack resistance tends to be inferior. The blending amount is most preferably 100% by mass.

The silane coupling agent is not particularly limited, and those conventionally used in the tire field can be used. For example, sulfide type, mercapto type vinyl type, amino type, glycidoxy type, nitro type, chloro type silane coupling agent Etc. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. A sulfide system can be preferably used.

It is preferable that the compounding quantity of the silane coupling agent in the process 1 is 80-100 mass% of the compounding quantity of all the silane coupling agents used in all the processes. If the blending amount is less than 80% by mass, a large amount of the silane coupling agent is blended in the ENR in Step 3 to form a hard layer, so that the flex crack resistance tends to be inferior. The blending amount is most preferably 100% by mass.

Step 1 is a step of kneading natural rubber and surface-treated silica obtained by treating silica with a silane coupling agent, that is, surface treatment in which silica is treated with a silane coupling agent as silica and silane coupling agent. It is preferable to use silica. Thereby, the reaction rate of a silane coupling agent can be improved, the resistance to bending cracks can be further improved, and deterioration of tear strength due to thermal aging can also be prevented.

The method for producing the surface-treated silica is not particularly limited as long as it can coat all or part of the surface of the silica. For example, a method of mixing silica and a silane coupling agent in the absence of a solvent, a solvent And a method of removing the solvent after mixing the silica and the silane coupling agent in the presence of.
A preferable N ₂ SA of the surface-treated silica is the same as the foregoing silica.

When the silica is treated with a silane coupling agent, the amount of the silane coupling agent is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 1 part by mass, the silica may not be sufficiently treated. The amount is preferably 20 parts by mass or less, more preferably 15 parts by mass or less. When the amount exceeds 20 parts by mass, not only the performance improvement effect is small, but the unreacted silane coupling agent remains on the silica surface, and the workability tends to decrease.

When performing the said process, process temperature becomes like this. Preferably it is 120 degreeC or more, More preferably, it is 125 degreeC or more. If it is less than 120 degreeC, a silica and a silane coupling agent cannot fully react, and it may have a bad influence on workability and performance. The treatment temperature is preferably 180 ° C. or lower, more preferably 175 ° C. or lower. When the temperature exceeds 180 ° C., the stability of the sulfur moiety in the silane coupling agent is lost, which may adversely affect the performance.

In the step 1, it is preferable to knead only NR, silica, and the silane coupling agent because the reaction rate of the silane coupling agent is high.

The kneading method in step 1 is not particularly limited as long as each component can be kneaded while controlling the temperature. For example, a closed kneader such as a Banbury mixer can be suitably used.

The kneading temperature in Step 1 is preferably 135 to 145 ° C., and the kneading time is preferably 3 to 4 minutes. If it is less than the lower limit, the dispersion of silica and the reaction of the silane coupling agent may be insufficient. If the upper limit is exceeded, the NR tends to be damaged during kneading, and the flex crack resistance and tear strength tend to deteriorate.

(Process 2)
In the step 2, the kneaded product 1, stearic acid and zinc oxide are kneaded. By kneading stearic acid and zinc oxide after kneading NR in step 1 and before kneading ENR in step 3, the reaction rate of the silane coupling agent can be improved.

The blending amount of stearic acid and zinc oxide in Step 2 is preferably 80% by mass or more, and most preferably 100% by mass, based on the blending amount of total stearic acid and zinc oxide used in all steps.

In the step 2, it is preferable to knead an anti-aging agent and a wax together with stearic acid and zinc oxide. By kneading these components in step 2, a good reaction rate improvement effect can be obtained.

Antiaging agents include diphenylamine (p- (p-toluenesulfonylamide) -diphenylamine, octylated diphenylamine, etc.), p-phenylenediamine (N- (1,3-dimethylbutyl) -N′-phenyl-p -Phenylenediamine (6PPD), N-phenyl-N'-isopropyl-p-phenylenediamine (IPPD), N, N'-di-2-naphthyl-p-phenylenediamine, etc.). A conventionally well-known thing can be used as a wax, For example, a conventionally well-known natural wax, petroleum wax, etc. can be used.

In the step 2, in addition to the kneaded material 1 and the components (stearic acid, zinc oxide, anti-aging agent, wax), other components may be appropriately blended, or only these components may be blended.

Examples of the kneading method in step 2 include the same method as in step 1.
The kneading temperature in step 2 is preferably 125 to 135 ° C., and the kneading time is preferably 2 to 4 minutes. If it is less than the lower limit, the dispersion of silica and the reaction of the silane coupling agent may be insufficient. If the upper limit is exceeded, the NR tends to be damaged during kneading, and the flex crack resistance and tear strength tend to deteriorate.

(Process 3)
In the step 3, the kneaded product 2 and ENR obtained in the step 2 are kneaded. Since step 3 is performed after step 2, the flex crack resistance can be significantly improved.

As the ENR, a commercially available ENR (ENR25, ENR50 (manufactured by Kunpu Langursley, 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. 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 performs epoxidation, what is common in the rubber industry can be used. Moreover, ENR may be used independently or may be used in combination of 2 or more type.

The epoxidation rate of ENR is preferably 12 mol% or more. If it is less than 12 mol%, the effect of the present invention tends to be reduced because ENR is compatible with NR. The epoxidation rate of ENR is preferably 50 mol% or less. When it exceeds 50 mol%, the rubber strength of the obtained rubber composition tends to be insufficient. 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 blending amount of ENR in step 3 is preferably 50 to 100% by mass of the blending amount of all ENRs used in all steps. If it is less than 50% by mass, since a large amount of silica is blended in ENR to form a hard layer, the flex crack resistance tends to be inferior. The amount of ENR is most preferably 100% by mass.

In Step 3, other components other than ENR can be appropriately blended within a range that does not impair the effects of the present invention. However, it is preferable to blend only ENR because the reaction rate of the silane coupling agent is high.

Examples of the kneading method in step 3 include the same method as in step 1.
The kneading temperature in Step 3 is preferably 125 to 135 ° C., and the kneading time is preferably 2 to 4 minutes. If it is less than the lower limit, the dispersion of silica and the reaction of the silane coupling agent may be insufficient. If the upper limit is exceeded, the NR tends to be damaged during kneading, and the flex crack resistance and tear strength tend to deteriorate.

(Process 4)
In the present invention, after performing the base kneading in the above steps 1 to 3, usually the finishing kneading step, for example, the kneaded product 3 obtained in step 3, the vulcanizing agent such as sulfur, the vulcanization accelerator, etc. is 75 to 85. A kneading step is performed under the conditions of 2 ° C. and 2 to 4 minutes, and then a vulcanized rubber composition is obtained by performing a vulcanization step.

In the rubber composition for a sidewall obtained by the above-described production method, the content of NR in 100% by mass of the rubber component is preferably 30% by mass or more, more preferably 40% by mass or more. If it is less than 30% by mass, sufficient rubber strength tends to be not obtained. The content is 90% by mass or less, preferably 80% by mass or less. When it exceeds 90 mass%, the bending crack resistance tends to deteriorate.

In the rubber composition, the content of ENR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more. If it is less than 10% by mass, the flex crack resistance tends to deteriorate. The content is preferably 70% by mass or less, more preferably 60% by mass or less, and still more preferably 50% by mass or less. When it exceeds 70 mass%, there is a tendency that sufficient rubber strength cannot be obtained.

In addition to NR and ENR, rubber such as polybutadiene rubber, styrene butadiene rubber, butyl rubber, halogenated butyl rubber, halide of copolymer of isobutylene and p-methylstyrene can be used as the rubber component. From the point of use of external resources, it is preferable to use only NR and ENR.

In the rubber composition, the content of silica is preferably 15 parts by mass or more, more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 15 parts by mass, the tear strength is low, and cutting may occur when the projections come into contact with the projections during traveling. The content is 60 parts by mass or less, preferably 50 parts by mass or less. When it exceeds 60 parts by mass, the bending crack resistance tends to be inferior.

4 mass parts or more are preferable with respect to 100 mass parts of silica, and, as for content of a silane coupling agent, 6 mass parts or more are preferable. The content is preferably 20 parts by mass or less, and more preferably 10 parts by mass or less. By setting the content within the above range, good bending crack resistance can be obtained.

The stearic acid content is preferably 1 to 5 parts by mass, and the zinc oxide content is preferably 1 to 5 parts by mass with respect to 100 parts by mass of the rubber component.

In the rubber composition, the content of the fatty acid metal salt is preferably 0.5 parts by mass or less, more preferably 0.1 parts by mass or less, particularly preferably 0 parts by mass with respect to 100 parts by mass of the rubber component. . By not using a fatty acid metal salt, a heat aging effect due to an improvement in the reaction rate of the silane coupling agent is obtained, and an excellent heat aging property is exhibited. In addition, the initial bending crack resistance can be improved.

The fatty acid metal salt includes 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 metal salts. Etc.

The pneumatic tire of the present invention is produced by a normal method using the rubber composition for sidewalls. That is, the rubber composition obtained by the above production method is extruded according to the shape of the sidewall of the tire at an unvulcanized stage, molded by a normal method on a tire molding machine, Bonding together with the tire member forms an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

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.
NR: TSR20
BR: BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass)
ENR25: ENR25 (epoxidation rate: 25 mol%) manufactured by Kumpulan Guthrie Berhad (Malaysia)
ENR50: ENR50 (epoxidation rate: 50 mol%) manufactured by Kumpulan Guthrie Berhad (Malaysia)
Carbon black: Dia Black E (FEF, N ₂ SA: 41 m ² / g) manufactured by Mitsubishi Chemical Corporation
Silica: Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Surface-treated silica (1): COUPSIL 8113 (silica: Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA, silane coupling agent: Si69, silane coupling agent with respect to 100 parts by mass of silica 12. 7 mass parts reacted)
Surface-treated silica (2): COUPSIL 6109 (silica: Ultrasil VN2 (N ₂ SA: 125 m ² / g) manufactured by EVONIK-DEGUSSA, silane coupling agent: Si69, silane coupling agent 9 mass relative to 100 mass parts of silica Part reacted)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: Anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: Antigen 6C (6PPD) (N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Calcium stearate: GF200 manufactured by NOF Corporation
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

(Manufacture of rubber composition)
Step 1: In accordance with the formulation of Tables 1 and 2, a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd. was charged so that the filling rate was 58%, and kneaded until reaching 140 ° C. at 80 rpm. Got.
Step 2: The components shown in Step 2 were blended into the kneaded product obtained in Step 1, and kneaded at 70 rpm for 3 minutes using a Banbury mixer. In Comparative Examples 1 to 7 and 10, Step 2 was not performed.
Step 3: The components shown in Step 3 were blended into the kneaded product obtained in Step 1 or Step 2, and kneaded under the same conditions as in Step 2. In Comparative Examples 5 to 10, step 3 was not performed.
Step 4: The components shown in Step 4 were blended into the kneaded product obtained in Step 3, and kneaded under the same conditions as in Step 2. Step 4 was not performed except for Comparative Examples 3 and 4.
Finish kneading step: Add sulfur and vulcanization accelerator shown in the finishing kneading step to the kneaded product obtained in step 1, step 3 or step 4, and knead for 3 minutes at 80 ° C. A vulcanized rubber composition was obtained. Furthermore, the obtained unvulcanized rubber composition was press vulcanized for 20 minutes under the condition of 160 ° C. to prepare a vulcanized rubber composition.

The following evaluation was performed using the obtained vulcanized rubber composition. The results are shown in Tables 1-2. The evaluation after heat aging in Table 2 was performed after the sample was held at 80 ° C. for 3 days in an air atmosphere.

(hardness)
The rubber hardness was measured with a type A durometer according to JIS-K6253 “Testing method for hardness of vulcanized rubber and thermoplastic rubber”.

(Tear test)
In accordance with JIS-K6252, “Vulcanized rubber and thermoplastic rubber-Determination of tear strength”, an angle-shaped test piece (vulcanized rubber composition) without cutting was used to determine the tear strength (N / mm). It was measured. It shows that it is excellent in crack resistance, so that tear strength is large.

(Crack growth resistance evaluation)
A rubber slab sheet of 1 mm x 50 mm x 20 mm is produced using the vulcanized rubber composition, cut with a razor to a sample width of 2 mm, and an initial crack is formed, in the long side direction (direction perpendicular to the cutting direction). Repeated distortion was added. The distortion rate was 5%, the frequency was 5 Hz, and the sample temperature was 70 ° C.
The initial crack growth rate dc / dn (m / cycle) from the time when repeated strain was applied until the crack growth length reached about 1 mm was measured. The data was an average of N = 4. It shows that it is excellent in crack growth resistance, so that crack growth rate dc / dn is small.

From Tables 1 and 2, in Comparative Examples 7 and 10, the crack growth resistance is good, but butadiene rubber, which is a synthetic rubber, is used as the rubber, and carbon black derived from fossil resources is used as the filler. This is not preferable from the viewpoint of consideration for the environment.

In Examples 1-2, the tear strength was equivalent to Comparative Examples 1-2, 5-6, but the dc / dn value was small in the crack growth resistance evaluation results, and the results were improved. .

In Example 7, the tear strength was larger than those in Comparative Examples 8 and 9, and the dc / dn value was also small in the crack growth evaluation result, which was a favorable result. Moreover, the tear strength after heat aging and the heat aging resistance in evaluation of crack growth resistance were also improved.

Claims (6)

Step 1 of kneading natural rubber, silica and silane coupling agent;
The kneaded product 1 obtained in the step 1, the step 2 of kneading stearic acid and zinc oxide, and
The manufacturing method of the rubber composition for sidewalls including the kneaded material 2 obtained at the said process 2, and the process 3 which knead | mixes the epoxidized natural rubber. The method for producing a rubber composition for a sidewall according to claim 1, wherein step 1 is a step of kneading natural rubber and surface-treated silica obtained by treating silica with a silane coupling agent. The process for producing a rubber composition for a sidewall according to claim 1 or 2, wherein the step 2 is a step of further kneading an antioxidant and a wax. The content of natural rubber in 30% by mass of rubber component is 30 to 90% by mass, and the content of epoxidized natural rubber is 10 to 70% by mass. Rubber composition for side walls. The nitrogen adsorption specific surface area of silica is 30 to 500 m ² / g,
The rubber composition for a sidewall according to claim 4, wherein the content of silica is 15 to 60 parts by mass with respect to 100 parts by mass of the rubber component. A pneumatic tire having a sidewall produced using the rubber composition according to claim 4.