Rubber composition with improved electrical insulation properties for reducing galvanic corrosion

Description

BACKGROUND OF THE DISCLOSURE1. Technical Field

[0001] The present disclosure relates to a rubber composition having improved electrical insulation properties for reducing galvanic corrosion, a method of preparing the same and a rubber hose for vehicles using the same.2. Description of the Related Art

[0002] Currently, rubber hoses are mainly used to transfer various fluids to cooling systems, fuel systems, braking systems, and the like in vehicles.

[0003] It is common to use metal clamps to fix hoses in such systems. However, there is a corrosion problem due to galvanic corrosion owing to the potential difference between the metal and the rubber material, which may lead to the deterioration of merchantability and performance due to loss of hose. FIG. 1 is a photograph showing a rusting phenomenon of a development vehicle for testing durability. FIG. 2 shows a field rusting phenomenon of a mass-produced vehicle.

[0004] When two different metals are in contact with each other in an electrolyte, a potential difference is created. The potential difference causes current to flow between the metals, thereby suppressing corrosion of the metal (cathode) having high corrosion resistance and promoting corrosion of the metal (anode) having high activity. This corrosion is called galvanic corrosion.

[0005] In order to reduce such corrosion, attempts are currently made to subject the clamp to zinc galvanizing. However, the addition of a plating layer to reduce corrosion increases manufacturing costs and also fails to solve the problem due to plating cracks caused by tools during clamp assembly.

[0006] Therefore, there is a need for a technique for solving the above problems.

[0007] US 2018 / 231152 A1 discloses a non-conductive rubber hose.

[0008] WO 2012 / 147386 A1 discloses a rubber composition for a water hose and a water hose using the same.SUMMARY OF THE DISCLOSURE

[0009] Accordingly, the present disclosure has been made keeping in mind the problems encountered in the related art. An objective of the present invention is to provide a rubber composition for a hose, which has improved electrical insulation properties so as to prevent galvanic corrosion. Specifically, an objective of the present invention is to provide a rubber composition for a hose, in which the electrical resistance of the hose is drastically improved.

[0010] In order to accomplish the above objective, the invention provides a rubber composition according to claim 1, a rubber hose for a vehicle according to claim 8 and a method for preparing a rubber composition according to claim 9. Further embodiments are described in the dependent claims.

[0011] According to the present invention, the rubber composition has high electrical insulation resistance. Specifically, the electrical insulation resistance (10 7< Ω·cm) can be 50 or more, and the electrical insulation resistance can be 50 to 500.

[0012] According to the present invention, the rubber composition has high hardness. Specifically, the hardness (Hs) can be 60 to 70.

[0013] According to the present invention, the rubber composition has high tensile strength. Specifically, the tensile strength (kgf / cm 2< ) can be 100 to 130.

[0014] According to the present invention, the rubber composition has high elongation. Specifically, the elongation (%) can be 300 to 500.

[0015] According to the present invention, the rubber composition has high product-bursting strength. Specifically, the product-bursting strength (kgf / cm 2< ) can be 15 to 25.

[0016] According to the present invention, the rubber composition has superior product formability.BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 is a photograph showing a rusting phenomenon of a development vehicle for testing durability; FIG. 2 shows a field rusting phenomenon of a mass-produced vehicle; FIGS. 3aand 3b show the components of Examples 1-7 and Comparative Examples 1-7 and the results of evaluation of properties thereof; and FIG. 4 shows the test results of Test Example 3.

[0018] In an aspect of the present disclosure, the plasticizer may be paraffin oil.

[0019] In an aspect of the present disclosure, an amount of the crosslinking agent may be 0.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer.

[0020] In an aspect of the present disclosure, the crosslinking agent may be sulfur.

[0021] Another aspect of the present disclosure provides a rubber hose for a vehicle, including the above rubber composition.

[0022] Still another aspect of the present disclosure provides a method of preparing the above rubber composition. The method includes mixing a base polymer with a reinforcing agent, an anti-aging agent, an activating agent, and a plasticizer and mixing the mixed polymer with a crosslinking agent.

[0023] In still another aspect of the present disclosure, the base polymer may include a first EPDM rubber and a second EPDM rubber. The first EPDM rubber may be EPDM including 8% to 10% of ENB. The second EPDM rubber may be EPDM including 70% to 75% of ethylene. A weight ratio of the first EPDM rubber and the second EPDM rubber may be 30 to 50 : 50 to 70.

[0024] In still another aspect of the present disclosure, the reinforcing agent may include carbon black and an inorganic filler. Based on 100 parts by weight of the base polymer, an amount of the carbon black may be 30 to 50 parts by weight and an amount of the inorganic filler may be 25 to 45 parts by weight.

[0025] In still another aspect of the present disclosure, an amount of the anti-aging agent may be 0.5 to 1.5 parts by weight based on 100 parts by weight of the base polymer. An amount of the activating agent may be 1.5 to 6 parts by weight based on 100 parts by weight of the base polymer.

[0026] In still another aspect of the present disclosure, an amount of the plasticizer may be 1.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer.

[0027] According to an aspect of the present disclosure, the rubber composition has high electrical insulation resistance. Specifically, the electrical insulation resistance (10 7< Ω·cm) can be50 or more, and the electrical insulation resistance can be 50 to 500.

[0028] According to an aspect of the present disclosure, the rubber composition has high hardness. Specifically, the hardness (Hs) can be 60 to 70.

[0029] According to an aspect of the present disclosure, the rubber composition has high tensile strength. Specifically, the tensile strength (kgf / cm 2< ) can be 100 to 130.

[0030] According to an aspect of the present disclosure, the rubber composition has high elongation. Specifically, the elongation (%) can be 300 to 500.

[0031] According to an aspect of the present disclosure, the rubber composition has high product-bursting strength. Specifically, the product-bursting strength (kgf / cm 2< ) can be 15 to 25.

[0032] According to an aspect of the present disclosure, the rubber composition has superior product formability.BRIEF DESCRIPTION OF DRAWINGS

[0033] FIG. 1 is a photograph showing a rusting phenomenon of a development vehicle for testing durability; FIG. 2 shows a field rusting phenomenon of a mass-produced vehicle; FIGS. 3aand 3b show the components of Examples 1-7 and Comparative Examples 1-7 and the results of evaluation of properties thereof; and FIG. 4 shows the test results of Test Example 3. DESCRIPTION OF SPECIFIC EMBODIMENTS

[0034] Repeated descriptions and detailed descriptions of known functions and configurations that may obscure the gist of the present disclosure have been omitted. As used herein, the term "comprising" or "including" means that other elements may be further included unless otherwise specified.

[0035] In the present specification, when a range is described for a variable, it should be understood that the variable includes all values including the end points described within the stated range. For example, the range of "5 to 10" should be understood to include any subranges, such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like, as well as individual values of 5, 6, 7, 8, 9 and 10, and should also be understood to include any value between valid integers within the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, and the like. Also, for example, the range of "10% to 30%" should be understood to include any subranges, such as 10% to 15%, 12% to 18%, 20% to 30%, etc., as well as all integers including values of 10%, 11%, 12%, 13% and the like up to 30%, and should also be understood to include any value between valid integers within the stated range, such as 10.5%, 15.5%, 25.5%, and the like.

[0036] Hereinafter, a detailed description is given of the present disclosure.

[0037] The present disclosure pertains to a rubber compound composition in which the electrical insulation resistance of a rubber material for a hose is drastically increased (about 100 times) in order to reduce galvanic corrosion due to a potential difference between a rubber hose and a clamp. When the amount of an inorganic filler is increased in order to simply increase electrical resistance in typical materials, electrical resistance may be increased but the product is not formed properly (upon hose extrusion, distortion or shape change occurs) or the properties thereof may be greatly deteriorated. Thus, it may be difficult or impossible to satisfy durability performance, such as burst pressure and negative pressure resistance required of hoses. Hence, the type and amount of base polymer and the amount of plasticizer (paraffin oil) are optimized to overcome the above problems and to significantly increase the durability and corrosion resistance of the clamp. In the rubber composition according to the present disclosure, state / aging properties are maintained at levels equivalent to those of conventional rubber hoses for vehicles, and simultaneously, electrical insulation resistance is greatly improved. The improvement thereof is confirmed through observed material / product / system durability.

[0038] Various aspects of the present disclosure are described below.

[0039] An aspect of the present disclosure pertains to a rubber composition for preventing galvanic corrosion. The rubber composition includes a base polymer, a reinforcing agent, an anti-aging agent, an activating agent, a plasticizer and a crosslinking agent. The base polymer includes a first ethylene propylene diene monomer(EPDM) rubber and a second EPDM rubber. The first EPDM rubber is EPDM including 8% to 10% of 5-ethylidene-2-norbornene (ENB). The second EPDM rubber is EPDM including 70% to 75% of ethylene. The weight ratio of the first EPDM rubber and the second EPDM rubber is 30 to 50 : 50 to 70.

[0040] In an aspect of the present disclosure, the rubber composition has electrical insulation resistance (10 7< Ω·cm) of 50 or more.

[0041] In the present disclosure, the EPDM rubber is an ethylene-propylene-diene terpolymer. The diene includes any one selected from the group comprising or consisting of ENB, dicyclopentadiene (DCPD), 1,4-pentadiene, cyclohexadiene andcyclic or bridged diene.

[0042] In an embodiment, EPDM having high heat resistance and weather resistance is used by blending EPDM having high ENB content (8 to 10%) with EPDM having high ethylene content (70 to 75%). EPDM having high ENB content may increase softness because of the increased ENB content. Thus, the EPDM may exhibit good processability and may be favorably applied to extruded products, but may deteriorate properties such as scorch stability, elongation, thermal aging, and the like. On the other hand, EPDM having high ethylene content may ensure desirable mechanical properties and may thus exhibit durability such as burst pressure required of hoses. However, when added in excess, increased crystallinity and thus poor processability may result. In order to ensure these advantages at the same time, two kinds of EPDM are blended, and may thus be optimally compounded. The first EPDM rubber and the second EPDM rubber are used at a weight ratio of 30 to 50 : 50 to 70, thereby ensuring both of the above advantages at the same time.

[0043] The reinforcing agent includes carbon black and an inorganic filler. Based on 100 parts by weight of the base polymer, the amount of the carbon black is 30 to 50 parts by weight and the amount of the inorganic filler is 25 to 45 parts by weight.

[0044] In an aspect of the present disclosure, the carbon black has dibutyl phthalate (DBP) absorption (ml / 100g) of 40 to 150 and I2 (mg / g) of 10 to 50.

[0045] In an aspect of the present disclosure, the inorganic filler is silica. The silica has Brunauer, Emmett, and Teller (BET) surface area (m 2< / g) of 180 to 230 and a density (g / l) of 120 to 160.

[0046] The reinforcing agent comprises an inorganic filler (silica) as a base in order to ensure the electrical insulation properties required of the above material. Moreover, carbon black is blended in order to ensure fatigue resistance and robustness against permanent deformation, which are typically required of hoses. The reinforcing agent is used in an optimal blending amount because dispersibility in a rubber phase is very useful from the viewpoint of durability. Superior durability is obtained when the carbon black is used in an amount of 30 to 50 parts by weight and the inorganic filler is used in an amount of 25 to 45 parts by weight based on 100 parts by weight of the base polymer.

[0047] In an aspect of the present disclosure, the amount of the anti-aging agent is 0.5 to 1.5 parts by weight based on 100 parts by weight of the base polymer. The anti-aging agent is N'-isopropyl-N-phenyl-phenylene diamine.

[0048] In an aspect of the present disclosure, the amount of the activating agent is 1.5 to 6 parts by weight based on 100 parts by weight of the base polymer. The activating agent is at least one of zinc oxide and stearic acid.

[0049] In an aspect of the present disclosure, the activating agent includes zinc oxide and stearic acid. The amount of zinc oxide is 2 to 4 parts by weight based on 100 parts by weight of the base polymer. The amount of stearic acid is 0.5 to 1.5 parts by weight based on 100 parts by weight of the base polymer.

[0050] The amount of the plasticizer is 1.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer.

[0051] The plasticizer is paraffin oil.

[0052] In an embodiment, when the inorganic filler is added in excess relative to the amount of carbon black, the Mooney viscosity of the resulting compound may be greatly increased (hardened). Hence, the amount of the plasticizeris adjusted for optimal compounding, thereby attaining desired product extrudability. The amount of the plasticizer is 1.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer. Given the above range, desired product extrudability may be attained.

[0053] In an aspect of the present disclosure, the amount of the crosslinking agent is 0.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer.

[0054] In an aspect of the present disclosure, the crosslinking agent is sulfur.

[0055] Another aspect of the present disclosure pertains to a rubber hose for a vehicle including the above rubber composition.

[0056] Still another aspect of the present disclosure pertains to a method of preparing the rubber composition. The method includes mixing a base polymer with a reinforcing agent, an anti-aging agent, an activating agent, and a plasticizer and mixing the mixed polymer with a crosslinking agent.

[0057] In still another aspect of the present disclosure, the base polymer includes a first EPDM rubber and a second EPDM rubber. The first EPDM rubber is EPDM including 8% to 10% of ENB. The second EPDM rubber is EPDM including 70% to 75% of ethylene.T he weight ratio of the first EPDM rubber and the second EPDM rubber is 30 to 50 : 50 to 70.

[0058] In still another aspect of the present disclosure, the reinforcing agent includes carbon black and an inorganic filler. Based on 100 parts by weight of the base polymer, the amount of the carbon black is 30 to 50 parts by weight and the amount of the inorganic filler is 25 to 45 parts by weight.

[0059] In still another aspect of the present disclosure, the amount of the anti-aging agent is 0.5 to 1.5 parts by weight based on 100 parts by weight of the base polymer. The amount of the activating agent is 1.5 to 6 parts by weight based on 100 parts by weight of the base polymer.

[0060] In still another aspect of the present disclosure, the amount of the plasticizer is 1.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer.

[0061] A better understanding of the present disclosure is given through the following preparation examples, examples, and test examples. However, these preparation examples, examples, and test examples are merely set forth to illustrate the present disclosure but are not to be construed as limiting the scope of the present disclosure.Preparations of Examples 1-7 and Comparative Examples 1-7

[0062] In order to prepare engine mount compositions having improved heat resistance and fatigue resistance, components were compounded in the amounts shown in the following tables to thus manufacture specimens.

[0063] EPDM was masticated for 3 min using a kneader, mixed together with are inforcing agent, an anti-aging agent, a processing adjuvant, and a plasticizer, kneaded for 3 to 4 min, and cleaned for 1 to 2 min, thus obtaining a final carbon master batch(CMB)compound. The CMB compound was mixed with a crosslinking agent using a roll mixer. The rubber composition thus obtained was measured for appropriate vulcanization time using a rheometer and was then heated and pressed at 160 kgf / cm 2< using a hot press, thereby manufacturing vulcanized specimens.

[0064] Specific compositions are shown in Tables 1 and 2 below. These Tables 1 and 2 are shown in FIG. 3.Test Example 1. Comparison of properties

[0065] In order to evaluate the rubber specimens and products manufactured above, the following items were tested. The results thereof are compared and evaluated. Hardness: Measurement with dumbbell No. 3 in accordance with KS M 6784 Tensile strength and elongation: Measurement with dumbbell No. 3 in accordance with KS M 6782 Electrical insulation resistance and product-bursting strength: Measurement in accordance with company standard (MS263-19)

[0066] The test results are shown in Tables 1 and 2 below. These Tables 1 and 2 are shown in FIG. 3. [Table 1]ItemsExample7Example1Example2Example3Example4Example5Example6CompoundingPolymerEPDM (High ENB)40305040404040EPDM (High Ethylene)60705060606060Reinforcing agentCarbon black (FEF)40404030504040Silica35353545253535Anti-aging agentN'-isopro pyl-N-phenyl - phenylene diamine1111111Process ing adjuvan tZnO3333333Steari c Acid1111111Plastic izerParaff in oil2.52.52.52.52.51.53.5Crossli nking agentSulfur1111111CZ1111111State propert iesHardness (Hs)66676465666663Tensile strength (kgf / cm 2< )110120113105119123102Elongation (%)430390400380410350330Electrical insulation resistance (10 7< Ω·cm)140120130139115138135Product-bursting strength (kgf / cm 2< )201919.51720.319.118.7Product formabilityGoodGoodGoodGoodGoodGoodGood [Table 2] ItemsComparative Example 1ComparativeExample 2ComparativeExample 3ComparativeExample 4ComparativeExample 5ComparativeExample 6ComparativeExample 7CompoundingPolymerEPDM (High ENB)206040404040100EPDM (High Ethyl ene)8040606060600Reinfo rcing agentCarbon black (FEF)40402060404070Silica3535551535350Anti-aging agentN'-isopr opyl-N-phenyl-phenylene diamine1111111Proces sing adjuvantZnO3333333Stearic Acid1111111PlasticizerParaf fin oil2.52.52.52.50.54.52.5Crossl inking agentSulfu r1111111CZ1111111State prope rtiesHardness (Hs)70635966705865Tensile strength (kgf / cm 2< )115957310612389110Elongation (%)310310180380450250350Electrical insulation resistance (10 7< Ω·cm)1281321601.61391101.6Product-bursting strength (kgf / cm 2< )-14.5-19.2-12.319.5Product formabilityImpossibleGoodImpossibleGoodImpossibleGoodGood

[0067] In order to set the EPDM blending ratio, the components were compounded as in Examples 1 and 2 and Comparative Examples1 and 2, and thus the material properties and part performance were confirmed. When the ratio of EPDM having high ENB content and EPDM having high ethylene content was 30-50 : 70-50 part per hundred (phr), electrical insulation resistance, and durability required of parts were satisfied. When the amount of EPDM having high ENB content was greater than the upper limit thereof, mechanical properties (bursting strength) required of products were problematic. On the other hand, when the amount thereof was less than the lower limit thereof, the resulting material was excessively hardened, thus causing a problem of poor product processability (hose extrusion).

[0068] In order to set the reinforcing agent blending ratio, the components were compounded as in Examples 3 and 4 and Comparative Examples 3 and 4, and thus the material properties and part performance were confirmed. When the ratio of carbon black(FEF type) and inorganic filler (silica) was 30-50 : 25-45 phr, electrical insulation resistance, and durability required of parts were satisfied. When the amount of carbon black was greater than the upper limit thereof, electrical insulation resistance was not improved, and when the amount of silica was greater than the upper limit thereof, the filler was not dispersed. Thus, continuous extrusion was not possible upon product formation, undesirably making it difficult or impossible to form parts.

[0069] In order to set the amount of the plasticizer so as to ensure formability, the components were compounded as in Examples 5 and 6 and Comparative Examples 5 and 6, and thus the material properties and part performance were confirmed. When the amount of the plasticizer was 1.5 to 3.5 phr, the material properties and part performance were satisfied. When the amount thereof was less than the lower limit thereof, crosslinking density was increased and thus the product was not extruded. On the other hand, when the amount thereof was greater than the upper limit thereof, mechanical properties (bursting strength) of products were unsatisfactory.

[0070] Based on the test results, the properties of Example 7according to the present disclosure were vastly superior.Test Example 2. Comparison with properties of conventional product

[0071] Example 7, the properties of which were found to be vastly superior in Test Example 1,was used as a developed product. The properties thereof were compared with those of a conventional product in accordance with company standard MS263-19.

[0072] The conventional product was that of Comparative Example 7.

[0073] The results of comparison of the properties thereof are shown in Table 3 below. [Table 3]ItemsMS263 -19Evaluation resultRemarkConventional productDevelope d productState propertie sHardness60±5 or 70±56566Room temperatureTensilestrengt h (kgf / cm 2< )100 ↑110112Elongation (%)300 ↑350430AgingChange in hardness0 to +20+7+10130°C x 168hrTensile strength change (%)+25% ↓+16+5Elongation change (%)-60% ↓-51-45Liquid resistanceChange in hardness-5 to +10-3+2Antifreeze 50% aqueous solution 115°C x 360 hrTensile strength change (%)-20% ↓-2+2Elongation change (%)-40% ↓-35-25Compressed permanent shrinkage (%)High temperature65 ↓4046120°C x 70hrOzone resistanceNo CrackNo CrackNo Crack100pphm x 72hrElectrical insulation resistance (Ω·cm)10 6< 1.6 x 10 -7< 1.4 x 10 9< 100 times improvement over conventional product

[0074] As described above, it can be confirmed that the developed product (Example 7) of the present disclosure exhibited properties capable of minimizing galvanic corrosion between metal clips that are essentially used for hose fixing.

[0075] Accordingly, whether galvanic corrosion was actually minimized was evaluated through the following Test Example 3.Test Example 3. Evaluation of corrosion of clip for hose connection of conventional product and developed product

[0076] The conventional product and the developed product were measured for corrosion of a clip used for hose connection in accordance with CCT-A and MS619-10.

[0077] The evaluation times were 30 cycles, 40 cycles, and 80 cycles, and the test results are shown in FIG. 4.

[0078] As shown in FIG. 4, corrosion resistance of the clamp was improved compared to the conventional product. In the conventional product, initial corrosion occurred at the 30 th< cycle and complete corrosion occurred at the 80 th< cycle. In contrast, the developed product did not corrode even at the 80 th< cycle. Therefore, it can be concluded that the corrosion resistance in the present disclosure was improved 200% or more compared to the conventional product.

Claims

1. A rubber composition for preventing galvanic corrosion, the rubber composition comprising: a base polymer, a reinforcing agent, an anti-aging agent, an activating agent, a plasticizer, and a crosslinking agent, wherein the base polymer comprises a first ethylene propylene diene monomer(EPDM)rubber and a second EPDM rubber, wherein the first EPDM rubber is EPDM comprising 8% to 10% of 5-ethylidene-2-norbornene (ENB), wherein the second EPDM rubber is EPDM comprising 70% to 75% of ethylene, wherein a weight ratio of the first EPDM rubber and the second EPDM rubber is 30 to 50 : 50 to 70, wherein the reinforcing agent comprises carbon black and an inorganic filler, and wherein, based on 100 parts by weight of the base polymer, an amount of the carbon black is 30 to 50 parts by weight and an amount of the inorganic filler is 25 to 45 parts by weight, and wherein the plasticizer is paraffin oil, and wherein an amount of the plasticizer is 1.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer.

2. The rubber composition of claim 1, wherein the rubber composition has electrical insulation resistance (107 Ω·cm) of 50 or more.

3. The rubber composition of claim 1, wherein the carbon black has dibutyl phthalate (DBP) absorption(ml / 100g) of 40 to 150 and I2 (mg / g) of 10 to 50, and wherein the inorganic filler is silica, and wherein the silica has Brunauer, Emmett, and Teller (BET) surface area (m2 / g) of 180 to 230 and a density (g / l) of 120 to 160.

4. The rubber composition of one of claims 1-3, wherein an amount of the anti-aging agent is 0.5 to 1.5 parts by weight based on 100 parts by weight of the base polymer, and wherein the anti-aging agent is N'-isopropyl-N-phenyl-phenylene diamine.

5. The rubber composition of one of claims 1-4, wherein the activating agent comprises zinc oxide and stearic acid, wherein an amount of the zinc oxide is 2 to 4 parts by weight based on 100 parts by weight of the base polymer, and wherein an amount of the stearic acid is 0.5 to 1.5 parts by weight based on 100 parts by weight of the base polymer.

6. The rubber composition of one of claims 1-5, wherein an amount of the crosslinking agent is 0.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer.

7. The rubber composition of one of claims 1-6, wherein the crosslinking agent is sulfur.

8. A rubber hose for a vehicle, the rubber hose comprising: a rubber composition having a base polymer, a reinforcing agent, an anti-aging agent, an activating agent, a plasticizer, and a crosslinking agent, wherein the base polymer comprises a first ethylene propylene diene monomer(EPDM) rubber and a second EPDM rubber, wherein the first EPDM rubber is EPDM comprising 8% to 10% of 5-ethylidene-2-norbornene (ENB), wherein the second EPDM rubber is EPDM comprising 70% to 75% of ethylene, and wherein a weight ratio of the first EPDM rubber and the second EPDM rubber is 30 to 50 : 50 to 70.

9. A method of preparing a rubber composition, the method comprising: mixing a base polymer with a reinforcing agent, an anti-aging agent, an activating agent, and a plasticizer; and mixing the mixed polymer with a crosslinking agent, wherein the base polymer comprises a first EPDM rubber and a second EPDM rubber, the first EPDM rubber is EPDM comprising 8% to 10% of 5-ethylidene-2-norbornene (ENB), the second EPDM rubber is EPDM comprising 70% to 75% of ethylene, and a weight ratio of the first EPDM rubber and the second EPDM rubber is 30 to 50 : 50 to 70.

10. The method of claim 9, wherein the reinforcing agent comprises carbon black and an inorganic filler, and wherein, based on 100 parts by weight of the base polymer, an amount of the carbon black is 30 to 50 parts by weight and an amount of the inorganic filler is 25 to 45 parts by weight.

11. The method of one of claims 9-10, wherein an amount of the anti-aging agent is 0.5 to 1.5 parts by weight based on 100 parts by weight of the base polymer, and wherein an amount of the activating agent is 1.5 to 6 parts by weight based on 100 parts by weight of the base polymer.

12. The method of one of claims 9-11, wherein an amount of the plasticizer is 1.5 to 3.5 parts by weight based on 100 parts by weight of the base polymer.