JP4902166B2 - Rubber composition for sidewall, method for producing the same, and pneumatic tire using the rubber composition - Google Patents

Description

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

  Conventionally, as a rubber composition for tire sidewalls, in order to improve the flex crack resistance characteristics, along with rubber exhibiting excellent tensile strength and tear strength (crack resistance) such as natural rubber (NR), Carbon black has been used as a reinforcing filler in order to mix butadiene rubber (BR) and the like, and to further improve the reinforcement and strength of the rubber composition.

However, in recent years, there has been a demand for lower fuel consumption of automobiles, and tires are also required to have improved rolling resistance characteristics. For example, an attempt has been made to improve the rolling resistance characteristics of the entire tire by using a white filler such as silica or calcium carbonate instead of a part of carbon black. Among the pneumatic tires, when manufacturing a high-performance tire, it is particularly required to reduce the rolling resistance of the entire tire. In recent years, environmental issues have become more important, regulations on reducing CO ₂ emissions have been tightened, and oil resources are limited and the supply volume has been decreasing year by year. The use of blends consisting of petroleum resources such as carbon black is limited.

  As described above, it is necessary to actively use silica, calcium carbonate, and the like obtained from non-petroleum resources from carbon black obtained from petroleum resources. Patent Literature 1 discloses a pneumatic tire in which carbon black and calcium carbonate are blended as fillers and rolling resistance characteristics are improved without reducing discoloration resistance and ozone resistance. However, in rolling resistance characteristics, a sufficient improvement effect cannot be obtained, and since a large amount of carbon black derived from petroleum resources is blended as a filler, it is not environmentally friendly.

JP 2003-113270 A

  The present invention provides a rubber composition for a sidewall used for a tire exhibiting excellent bending crack resistance, crack resistance and rolling resistance characteristics, a method for producing the rubber composition, and a pneumatic tire using the rubber composition. With the goal.

  The present invention is a rubber composition for a sidewall containing a rubber component and a white filler, wherein one or more discontinuous phases and continuous phases have a sea-island structure, and at least one of the continuous phases is The present invention relates to a rubber composition for sidewalls in which the white filler is unevenly distributed.

  As a method for producing the rubber composition, (a) a step of kneading a rubber component constituting a continuous phase and a white filler, and (b) a discontinuous phase in the kneaded product obtained in step (a). It preferably comprises a step of kneading the constituent rubber components.

  When the rubber component constituting the discontinuous phase has a higher affinity with the white filler than the rubber component constituting the continuous phase, the rubber component constituting the discontinuous phase in step (b) contains a plasticizer in advance. A rubber component is preferred.

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

  Moreover, this invention relates to the pneumatic tire which has a side wall using the rubber composition for side walls obtained by the said manufacturing method.

  According to the present invention, by using a white filler as a filler and unevenly distributing it in a continuous phase, the rubber composition for a sidewall which has improved the bending crack resistance, crack resistance and rolling resistance characteristics of the tire, and A production method thereof and a pneumatic tire using the rubber composition can be provided.

  The rubber composition for a side wall of the present invention contains a rubber component and a white filler as a filler, wherein one or more discontinuous phases and continuous phases exhibit a sea-island structure, and the white filler Are unevenly distributed in at least one of the continuous phases.

  As shown in FIG. 1, the sea-island structure means that the continuous phase 1 in which the white filler is unevenly distributed is the sea and the discontinuous phase 2 is the island.

  The rubber component in the present invention includes a rubber component constituting a continuous phase in which white filler is unevenly distributed (hereinafter referred to as rubber (1)) and a rubber component constituting a discontinuous phase (hereinafter referred to as rubber (2)). ).

  In order for the white filler to be unevenly distributed in the continuous phase, it is necessary that the rubber (1) and (2) have different affinity with the white filler, melt viscosity, and blending amount.

  The rubber (1) has a high affinity with the white filler because the white filler is unevenly distributed and sufficient strength can be obtained. Further, the rubber (2) has an affinity with the white filler. Is preferably low.

  The rubber (1) is selected from the group consisting of ethylene oxide-propylene oxide-allyl glycidyl ether copolymer, acrylonitrile butadiene rubber (NBR), epichlorohydrin rubber, natural rubber (NR), and diene rubber having a polar group. One or more rubbers are preferred. The rubber (1) is preferably a diene rubber having NR or a polar group, and particularly preferably a diene rubber having a polar group.

  When the rubber (1) is a diene rubber having a polar group, examples of the polar group include halogen groups such as a bromo group and a chloro group, an epoxy group, and an amino group. Examples of the diene rubber include NR, butadiene rubber (BR), and styrene butadiene rubber (SBR).

  As the rubber (1), epoxidized diene rubber is particularly preferable, and epoxidized natural rubber (ENR) is more preferable.

  When epoxidized diene rubber, especially ENR is used, stronger reinforcement, bending crack fatigue resistance and good whiteness are obtained due to the interaction between the epoxy group and the polar group such as hydroxyl group of silica, aluminum hydroxide, alumina, etc. The uneven distribution state of the filler can be easily obtained.

  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. Examples of the peracid method include a method of reacting NR with an organic peracid such as peracetic acid or performic acid.

  The SP value of rubber (1) is preferably 7.9 or more, and more preferably 8.5 or more. If the SP value is less than 7.9, the polarity is too low and the affinity with a white filler such as silica tends to be low, and it tends to be difficult to unevenly distribute the white filler therein. Further, the SP value of the rubber (1) is preferably 11 or less, more preferably 10 or less, and further preferably 9.5 or less. If the SP value exceeds 11, the polarity is too high, the compatibility with the rubber (2) becomes too bad, and the mechanical strength of the entire compound and the adhesive strength with other members tend to be reduced. is there.

The Mooney viscosity (ML _{1 + 4} ) of the rubber (1) at a measurement temperature of 100 ° C. is preferably 25 or more, and more preferably 30 or more. When the Mooney viscosity is less than 25, the tackiness increases, and it tends to be difficult to mix the white filler therein using a normal rubber kneader. The Mooney viscosity (ML _{1 + 4} ) of the rubber (1) at a measurement temperature of 100 ° C. is preferably 115 or less, more preferably 100 or less, and even more preferably 85 or less. When the Mooney viscosity exceeds 115, the processability is deteriorated, and further, it tends to be difficult to mix the white filler therein.

  When the rubber (1) is an epoxidized diene rubber, the epoxidation rate of the epoxidized diene rubber is preferably 10 mol% or more, more preferably 15 mol% or more, and 20 mol% or more. More preferably it is. When the epoxidation rate is less than 10 mol%, it tends to be difficult to make the white filler unevenly distributed in the rubber (1) as the continuous phase. The epoxidation rate of the epoxidized diene rubber is preferably 80 mol% or less, more preferably 60 mol% or less, and further preferably 55 mol% or less. When the epoxidation rate exceeds 80 mol%, the SP value increases, the mechanical strength of the entire compound as described above and the adhesive strength with other members tend to decrease, and the hardness becomes too high. There is also a trend.

  The content of the rubber (1) in the total rubber component is preferably 25% by weight or more, more preferably 30% by weight or more, further preferably 40% by weight or more, and 50% by weight or more. Is particularly preferred. If the content of the rubber (1) is less than 25% by weight, the white filler cannot be blended into the continuous phase to obtain sufficient reinforcement, and even if a technique such as dynamic vulcanization is used, it is required. There is a tendency that the obtained rubber composition is not obtained. The content of rubber (1) in all rubber components is preferably 85% by weight or less, more preferably 80% by weight or less, further preferably 75% by weight or less, and 65% by weight. % Or less is particularly preferable. When the content of the rubber (1) exceeds 85% by weight, it tends to be difficult to improve the bending crack fatigue resistance.

  As rubber (2), NR, hydrogenated natural rubber, BR, NBR with low nitrile content (5-24%), hydrogenated nitrile rubber with low nitrile content (5-24%), ethylene propylene diene copolymer Rubber (EPDM), ethylene propylene rubber (EPM), butyl rubber (IIR), halogenated butyl rubber (X-IIR), SBR, hydrogenated SBR, hydrogenated BR, ENR with an epoxidation rate of 30 mol% or less, epoxidation rate Is at least one rubber selected from the group consisting of epoxidized styrene butadiene rubber (ESBR) with an epoxidation rate of 30% or less, epoxidized butadiene rubber (EBR) with an epoxidation rate of 30% or less, and modified products thereof. Is preferred. Among them, the rubber (2) is preferably NR, hydrogenated natural rubber or BR, and particularly preferably NR or hydrogenated natural rubber. Since NR and hydrogenated natural rubber are obtained from non-petroleum resources, they are also preferable from an environmental point of view.

  The SP value of the rubber (2) is preferably 10 or less, more preferably 9.5 or less, and further preferably 9 or less. When the SP value exceeds 10, the white filler tends to be distributed in the rubber (2), and the white filler tends to be unevenly distributed in the rubber (1).

  When an epoxidized diene rubber such as ENR is used as the rubber (2), the epoxidation rate of the epoxidized diene rubber is preferably 1 mol% or more, more preferably 3 mol% or more. More preferably, it is at least mol%. If the epoxidation rate is less than 1 mol%, the modification effect by epoxidation tends to be insufficient. The epoxidation rate of the epoxidized diene rubber is preferably 30 mol% or less, more preferably 25 mol% or less, further preferably 20 mol% or less, and 15 mol% or less. Particularly preferred. When the epoxidation rate exceeds 30 mol%, the white filler tends to be unevenly distributed in the rubber (2) which is a discontinuous phase.

The Mooney viscosity (ML _{1 + 4} ) of the rubber (2) at a measurement temperature of 100 ° C. is preferably 5 or more, more preferably 10 or more, and further preferably 25 or more. If the Mooney viscosity is less than 5, the tackiness tends to increase and a problem in terms of workability tends to occur. The Mooney viscosity (ML _{1 + 4} ) of the rubber (2) at a measurement temperature of 100 ° C. is preferably 115 or less, more preferably 100 or less, and even more preferably 85 or less. If the Mooney viscosity exceeds 115, the processability tends to be poor, and it tends to be difficult to use for tire sidewalls.

  The content of rubber (2) in the total rubber component is preferably 15% by weight or more, more preferably 20% by weight or more, further preferably 25% by weight or more, and 35% by weight or more. Is particularly preferred. If the content of the rubber (2) is less than 15% by weight, it tends to be difficult to improve the bending crack fatigue resistance. The content of rubber (2) in the total rubber component is preferably 75% by weight or less, more preferably 70% by weight or less, still more preferably 60% by weight or less, and 50% by weight. % Or less is particularly preferable. If the content of rubber (2) exceeds 75% by weight, white filler cannot be blended into the continuous phase to obtain sufficient reinforcement, and even if a technique such as dynamic vulcanization is used, There is a tendency that the rubber composition required in the invention cannot be obtained.

  The rubber composition for a sidewall of the present invention can further contain a plasticizer such as aroma oil, naphthenic oil, paraffin oil, vegetable oil. These may be used alone or in combination of two or more. However, vegetable oil is preferred as the plasticizer because it is obtained from non-petroleum resources and is environmentally friendly.

  The SP value of the plasticizer is preferably 7.4 or more, and more preferably 8.0 or more. When the SP value of the plasticizer is less than 7.4, the polarity is low, the compatibility with the rubber is poor, and there is a tendency to separate. Moreover, it is preferable that SP value of a plasticizer is 11.5 or less, and it is more preferable that it is 10.5 or less. When the SP value exceeds 11.5, the polarity of the plasticizer is high, the compatibility with the rubber is poor, and there is a tendency to separate.

  When the plasticizer is blended, the blending amount of the plasticizer is preferably 2 parts by weight or more and more preferably 5 parts by weight or more with respect to 100 parts by weight of the rubber (2). When the blending amount of the plasticizer is less than 2 parts by weight, there is a tendency that a sufficient plasticizing effect by blending the plasticizer cannot be obtained. Further, the blending amount of the plasticizer is preferably 50 parts by weight or less, and more preferably 30 parts by weight or less. When the blending amount of the plasticizer exceeds 50 parts by weight, the viscosity is remarkably lowered, and further, the workability tends to be lowered.

  The difference in SP value between the rubber (2) and the plasticizer is preferably 3 or less, and more preferably 2 or less. When the difference in the SP value of the plasticizer exceeds 3, the plasticizer is not compatible with the rubber (2) and tends not to exhibit the softening effect of the discontinuous phase.

  Examples of the white filler used as the filler include silica, calcium carbonate, aluminum hydroxide, clay, mica, alumina, talc and the like. These may be used alone or in combination of two or more. Also good. Especially, it is preferable that it is 1 or more types chosen from a silica, a calcium carbonate, and aluminum hydroxide from the point which can improve cost reduction, reinforcement property, and fuel-consumption property, and should be silica and / or calcium carbonate. Is more preferable.

The BET specific surface area of the white filler is preferably 5 m ² / g or more, more preferably 20 m ² / g or more, and further preferably 50 m ² / g or more. When the BET specific surface area of the white filler is less than 5 m ² / g, the particle size tends to be large, and sufficient reinforcement and mechanical strength tend to be difficult to obtain. Further, the BET specific surface area of the white filler is preferably 600 m ² / g or less, more preferably 500 m ² / g or less, and further preferably 450 m ² / g or less. When the BET specific surface area of the white filler exceeds 600 m ² / g, it is difficult to uniformly disperse and the raw material cost tends to increase.

  Silica is preferably used in combination with a silane coupling agent. There is no restriction | limiting in particular as a silane coupling agent, What is generally used in the tire industry like Si69 can be used.

  Calcium carbonate is preferably subjected to surface treatment such as fatty acid treatment. In particular, calcium carbonate surface-treated with a fatty acid is preferably used together with a derivative / modified product of NR as a rubber component because good reinforcing properties can be obtained.

  The content of the white filler is preferably 5 parts by weight or more, more preferably 15 parts by weight or more, and further preferably 25 parts by weight or more with respect to 100 parts by weight of the rubber component. When the content of the white filler is less than 5 parts by weight, sufficient reinforcement to the rubber composition cannot be obtained, and crack resistance and bending crack resistance tend to be insufficient. The content of the white filler is preferably 80 parts by weight or less, more preferably 65 parts by weight or less, and further preferably 50 parts by weight or less. When the content of the white filler exceeds 80 parts by weight, the hardness of the rubber composition becomes excessively high, so that a problem tends to occur when used for tires. By setting the content of the white filler within the range of 5 to 80 parts by weight, it is possible to achieve both the reinforcing property and low fuel consumption of the tire and reduce the cost.

  In the rubber composition for a sidewall of the present invention, examples of the filler include carbon black and graphite in addition to the white filler.

  The white filler content relative to the total filler content is preferably 50% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and 90% by weight or more. Particularly preferred is 100% by weight.

  The rubber composition for a sidewall of the present invention includes, in addition to the rubber component, filler, silane coupling agent and plasticizer, wax, anti-aging agent, stearic acid, zinc white, vulcanizing agent and vulcanization accelerator. Additives can be blended.

  The rubber composition for a sidewall of the present invention is obtained by a production method comprising the kneading steps (a) and (b).

  In the kneading step (a), it is preferable to knead the rubber (1) and the white filler.

  In the kneading step (a), the blending ratio of the rubber (1) in the kneading step (a) with respect to the total blending amount of the rubber component is preferably 50 to 100% by weight, more preferably 75 to 100% by weight. . If the blending ratio is less than 50% by weight, the ratio of the filler to the rubber (1) becomes high, so the viscosity of the kneaded product tends to be very high and difficult to process. The blending ratio is most preferably 100% by weight.

  The white filler content in the kneading step (a) is preferably 50 to 100% by weight of the white filler content used in the entire kneading step. When the blending amount is less than 50% by weight, in the step (b), a large amount of white filler is blended in the rubber (2) to form a hard layer, so that the flex crack resistance tends to be inferior. The blending amount is most preferably 100% by weight.

  In the kneading step (a), it is preferable to add other additives such as a silane coupling agent, an anti-aging agent, stearic acid, and zinc oxide.

  In the kneading step (b), it is preferable to knead the rubber (2).

  When rubber (2) has higher affinity with the white filler than rubber (1), rubber (2) in step (b) is preferably a rubber component containing a plasticizer in advance. The rubber (2) has a higher affinity with the white filler than the rubber (1). For example, the rubber (1) has a lower affinity with the white filler such as NR and hydrogenated natural rubber. And a rubber having high affinity with a white filler such as ENR is used as the rubber (2). In this case, before the step (b), the rubber (2) is pre-blended with a plasticizer to be plasticized, and the obtained rubber is mixed with the kneaded product obtained in the step (a) in the step (b). Knead.

  The blending ratio of the rubber (2) in the kneading step (b) is preferably 50 to 100% by weight with respect to the total blending amount of the rubber component in this step. When the blending ratio is less than 50% by weight, it is difficult to blend the necessary amount of rubber (2) to form a discontinuous phase.

  After preferably using the production method comprising the kneading steps (a) and (b), it is extruded in accordance with the shape of the sidewall of the tire at an unvulcanized stage, and molded by a normal method on a tire molding machine. Thus, a pneumatic tire can be obtained by forming an unvulcanized tire and heating and pressurizing the unvulcanized tire in a vulcanizer.

  The pneumatic tire of the present invention is preferably a high-performance tire that exhibits excellent rolling resistance performance, such as a sports tire and a fuel-efficient vehicle tire.

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

Next, various chemicals used in Examples and Comparative Examples will be described in detail.
Natural rubber (NR): RSS # 3 (Mooney viscosity at a measurement temperature of 100 ° C .: 100, SP value: 8.2)
Butadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd. (Mooney viscosity at a measurement temperature of 100 ° C .: 43, SP value: 8.2)
Epoxidized natural rubber (ENR): ENR25 manufactured by Guthrie Polymer sdn. Bhd (epoxidation rate 25 mol%, Mooney viscosity at measurement temperature 100 ° C .: 75, SP value: 9)
ENR1: Pre-blend in which 10 parts by weight of epoxidized soybean oil is added to 100 parts by weight of ENR (Mooney viscosity at a measurement temperature of 100 ° C .: 47, SP value: 9.1)
Ethylene propylene diene copolymer rubber (EPDM): Esprene 586 manufactured by Sumitomo Chemical Co., Ltd. (Mooney viscosity at a measurement temperature of 100 ° C .: 85, SP value: 7.9)
Silica: Ultrasil VN3 manufactured by Degussa (BET specific surface area: 175 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Carbon Black: Show Black N330 (HAF) manufactured by Showa Cabot Corporation
Aroma oil: Process X140 made by Japan Energy Co., Ltd.
Resin: SP1068 resin stearic acid manufactured by Nippon Shokubai Co., Ltd .: Stearic acid “paulownia” manufactured by Nippon Oil & Fats Co., Ltd.
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-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd. )
Wax: Ozoace 0355 manufactured by Nippon Seiki Co., Ltd.
Sulfur: Tsurumi Chemical Co., Ltd. vulcanization accelerator BBS: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfanamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator CBS: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfanamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-5 and Comparative Examples 1-4
According to the blending amount shown in step (a) of Table 1, the rubber component, filler, softener, resin, wax, anti-aging agent, stearic acid, and zinc oxide are filled so that the filling rate is 58%. A 1.7 L Banbury mixer manufactured by Steel Works was filled and kneaded at 80 rpm until the rubber temperature reached 140 ° C.

  Next, with respect to Examples 1 to 5, the kneaded product obtained in the step (a) is blended with a rubber component according to the blending amount shown in the step (b) of Table 1, and at 70 rpm using a Banbury mixer. Kneaded for 3 minutes. On the other hand, the kneaded product obtained in Comparative Examples 1 to 4 was not subjected to step (b).

  To the kneaded product obtained in step (a) or (b), sulfur and vulcanization accelerators BBS and CBS were blended according to the blending amount shown in step (c) of Table 1, and the resulting unadded By vulcanizing the vulcanized rubber composition at 160 ° C. for 20 minutes, a vulcanized rubber brass sheet (for viscoelasticity test) of approximately 2 mm × 130 mm × 130 mm and a rubber sample (for tearing test and demach flexural crack growth test) are obtained. Each was produced.

  The following tests were conducted using the obtained rubber composition.

(Viscoelasticity test)
Vulcanization of Examples 1 to 5 and Comparative Examples 1 to 4 under the conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz, using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd. The tan δ of the rubber brass sheet was measured. Then, the rolling resistance index was calculated from the measured tan δ by the following formula. The larger the rolling resistance index, the lower the rolling resistance and the better the rolling resistance characteristics.

    (Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Tear test)
In accordance with JIS K 6252 “Vulcanized Rubber and Thermoplastic Rubber—How to Obtain Tear Strength”, the tear strength (N / mm) was measured by using an angle-shaped test piece without cutting. Then, from the measured tear strength, a tear strength index was calculated by the following formula. It shows that tear strength is so large that a tear strength index | exponent is large.

    (Tear Strength Index) = (Tear Strength of Each Formulation) / (Tear Strength of Comparative Example 1) × 100

(Demach flex crack growth test)
According to JIS K 6260 “Demach bending crack growth test method for vulcanized rubber and thermoplastic rubber”, cracks after 1 million tests were performed on a rubber composition sample under conditions of a temperature of 23 ° C. and a relative humidity of 55%. The length or the number of bends until growing into a 1 mm crack was measured. And based on the obtained crack length and the number of times of bending, the number of times of bending until the crack grew to a length of 1 mm in the rubber test piece sample was expressed logarithmically. A larger value indicates that cracks are less likely to grow and that the resistance to flex crack growth is superior. Here, 70% and 110% indicate the elongation percentage with respect to the length of the original rubber composition sample.

  The test results are shown in Table 1.

(Evaluation of polymer dispersion)
The morphology of the test samples of Example 4 and Comparative Example 2 was observed by the phase mode of an atomic force microscope (AFM) scanning probe microscope (SPM). The evaluation results of the polymer dispersion are shown in FIGS.

  In the rubber compositions of Examples 1 to 3, silica that is a white filler can be preferentially dispersed in ENR that is a continuous phase.

  In addition, in the rubber composition of Example 4, epoxidized natural rubber (ENR1) containing epoxidized soybean oil in advance is added in the step (b) and kneaded, so that it is generally epoxidized instead of ENR1. Silica can be positively dispersed in NR having a lower interaction with silica than natural rubber. This is clear from the fact that the rubber composition of Example 4 contains a filler in the continuous phase as shown in FIG.

  Furthermore, in the rubber composition of Example 5, silica can be more actively dispersed in the NR forming the continuous phase by adding and kneading EPDM together with BR in the step (b).

  The rubber compositions of Examples 1 to 5 are all inferior in tear strength and roll as compared with the rubber composition of Comparative Example 1 (a rubber composition containing BR and carbon black used in the past). Excellent resistance characteristics and resistance to flex crack growth.

  On the other hand, the rubber composition of Comparative Example 1 is greatly inferior in rolling resistance characteristics as compared with the Examples.

  In the rubber composition of Comparative Example 2, as shown in FIG. 3, silica is dispersed in the discontinuous phase mainly composed of ENR, and compared with the rubber compositions of Examples 1 to 5 and Comparative Example 1. In particular, the resistance to flex crack growth is inferior.

  The rubber composition of Comparative Example 3 is composed of only one phase whose rubber component is NR. The rolling resistance characteristics were extremely good, but the resistance to flex crack growth was inferior because there was no island phase preventing crack growth.

  The rubber composition of Comparative Example 4 does not contain a filler, has insufficient reinforcement, and is inferior in tear strength and flex crack growth resistance.

From the results of Examples 1 to 5 and Comparative Examples 1 to 4, it is considered that the silica is easily distributed as follows.
EPDM ≦ BR <NR <ENR

It is a figure which shows the sea-island structure of the rubber composition which consists of a continuous phase and one type of discontinuous phase. 4 is a scanning probe microscope (SPM) photograph of a test sample obtained in Example 4. FIG. 4 is a scanning probe microscope (SPM) photograph of a test sample obtained in Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Continuous phase 2 Non-continuous phase 3 Natural rubber 4 Epoxidized natural rubber 5 Filler mainly containing white filler

Claims (6)

A rubber composition for a sidewall containing a rubber component and a white filler,
(A) a step of kneading the rubber component constituting the continuous phase and the white filler, and (b) a step of kneading the rubber component constituting the discontinuous phase in the kneaded product obtained in the step (a). One or more discontinuous and continuous phases have a sea-island structure,
The white filler is unevenly distributed in at least one of the continuous phases;
The solubility parameter ( SP value ) of the rubber component constituting the discontinuous phase is 10 or less,
The content of the rubber component constituting the continuous phase in all rubber components is 25 to 85% by weight,
The rubber component constituting the continuous phase is natural rubber, butadiene rubber or epoxidized natural rubber,
The content of the rubber component constituting the discontinuous phase in the total rubber component is 15 to 75% by weight,
The rubber component constituting the discontinuous phase is natural rubber, butadiene rubber, epoxidized natural rubber or ethylene propylene diene copolymer rubber,
The content of the white filler is 5 to 80 parts by weight with respect to 100 parts by weight of the rubber component,
A rubber composition for a sidewall, wherein the white filler is at least one selected from the group consisting of silica, calcium carbonate, aluminum hydroxide, clay, mica, alumina, and talc. The rubber composition for a sidewall according to claim 1, wherein the SP value of the rubber component constituting the continuous phase is 7.9 or more. (A) a step of kneading the rubber component constituting the continuous phase and the white filler, and (b) a step of kneading the rubber component constituting the discontinuous phase in the kneaded product obtained in the step (a). The manufacturing method of the rubber composition for sidewalls of Claim 1 or 2. When the rubber component constituting the discontinuous phase has a higher affinity with the white filler than the rubber component constituting the continuous phase,
The method for producing a rubber composition for a sidewall according to claim 3, wherein the rubber component constituting the discontinuous phase in step (b) is a rubber component containing a plasticizer in advance. A pneumatic tire having a sidewall using the rubber composition for a sidewall according to claim 1. A pneumatic tire having a sidewall using the rubber composition for a sidewall obtained by the production method according to claim 3 or 4.

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