Rubber gasket and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials and sealing, in particular to a rubber gasket and a preparation method of the rubber gasket. The preparation method comprises the following steps: enhancing by using an ethylene-vinyl alcohol copolymer (EVOH) with the ethylene content of 29-48%, carrying out compatibility by using a styrene-ethylene-butylene-styrene block copolymer grafted maleic anhydride (SEBS-g-MA) with the grafting rate of more than or equal to 10%, carrying out synergistic reinforcement by using carbon black and nanoscale calcium carbonate, and carrying out premixing, hot-pressing vulcanization and acid environment aging treatment. Through EVOH enhancement, SEBS-g-MA compatibility, filler synergistic reinforcement and process optimization, multiple improvements of compatibility, mechanical properties, barrier property and acid resistance are achieved, key defects of a traditional EPDM gasket are overcome, and the EPDM gasket has remarkable technical advantages and practical value in the high-end sealing field (such as fuel cells and tunnel engineering).

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials and sealing, and in particular to a rubber gasket and a preparation method thereof. Background Art

[0002] In today's industrial field, proton exchange membrane fuel cells (PEMFC) and tunnel engineering have extremely stringent requirements on the performance of sealing materials. As a key sealing component, the performance of rubber gaskets is directly related to the safety and stable operation of the system. However, traditional gaskets based on ethylene propylene diene monomer (EPDM) have exposed many problems in practical applications, which seriously limits their application in high-end sealing scenarios.

[0003] For example, in the acidic environment of PEMFC, the main chain of EPDM is easily corroded by acid, causing degradation reactions, resulting in molecular chain breakage and destruction of the cross-linked structure. This will not only reduce the mechanical properties of the gasket, but also affect its sealing performance, resulting in increased gas leakage and decreased battery performance. Traditional EPDM-based gaskets have obvious deficiencies in acid resistance and gas barrier properties, and it is difficult to meet the strict requirements of PEMFC for sealing materials. For example, after long-term exposure to an acidic environment, the tensile strength retention rate of the EPDM gasket is low, only about 85%, and the oxygen permeability is high, which cannot effectively prevent the penetration of oxygen, affecting the service life and efficiency of the battery;

[0004] For this reason, many polymers with excellent properties have been introduced into EPDM, such as ethylene-vinyl alcohol copolymer (EVOH). EPDM is a non-polar rubber. As a polymer with unique properties, its molecular chain contains a large number of polar hydroxyl groups, which makes it have extremely low oxygen permeability, lower than polyethylene. However, this polarity difference makes it difficult to evenly disperse EPDM and polar polymers when blending, and phase separation is prone to occur, resulting in low interfacial bonding strength, which seriously affects the comprehensive performance of the composite material.

[0005] In order to improve the performance of EPDM, various fillers such as carbon black (CB) and calcium carbonate (CaCO3) are usually added. However, high content of fillers tends to agglomerate in the rubber matrix, destroying the continuous phase structure of the rubber and reducing the mechanical properties of the material. This is because the agglomeration of fillers restricts the movement of the rubber molecular chain, which easily leads to stress concentration when subjected to force, thereby reducing the overall performance of the material. In addition, the agglomeration of fillers will also affect the water tightness of the material, making the gasket more prone to leakage when subjected to water pressure.

[0006] Therefore, according to the above-mentioned related technologies, it is urgent to develop a rubber gasket and a preparation method thereof. Summary of the invention

[0007] In view of the above, the object of the present invention is to provide a rubber gasket and a preparation method thereof, so as to provide a rubber gasket with high water tightness, qualified acid resistance and mechanical stability, and solve the problems of uneven dispersion of existing fillers and poor compatibility through the composite modification of EVOH and EPDM.

[0008] Based on the above object, the present invention provides a rubber gasket and a preparation method thereof.

[0009] A rubber gasket, comprising the following raw materials in parts by mass: 100 parts of matrix, 10 - 30 parts of reinforcing phase, 5 - 15 parts of compatibilizer, 20 - 40 parts of reinforcing filler, 10 - 20 parts of auxiliary reinforcing filler, 1 - 3 parts of vulcanizing agent, and 3 - 8 parts of auxiliary agent;

[0010] The matrix is EPDM;

[0011] The reinforcing phase is EVOH;

[0012] The compatibilizer is SEBS-g-MA. By using the compatibilizer, the interfacial tension between EPDM and EVOH is reduced, promoting the uniform dispersion of the two phases and forming a stable "sea-island" structure.

[0013] Preferably, the ethylene content in the EVOH is 29% - 48%. The oxygen barrier property of EVOH stems from the hydroxyl polar groups in the molecular chain. The lower the ethylene content, the higher the proportion of vinyl alcohol units, the greater the density of polar groups, and the stronger the gas (such as oxygen, carbon dioxide) barrier property. When the ethylene content increases, the proportion of flexible ethylene segments in the molecular chain rises, the melting temperature decreases, the melt fluidity improves, and it is easier to process through processes such as extrusion and injection molding. At the same time, the low-temperature resistance and impact resistance of the material are improved. When the ethylene content is 29% - 48%, EVOH forms a moderately crystalline structure: the ethylene segments destroy the perfect crystallization, avoiding brittleness, while retaining some crystalline regions to maintain strength and chemical resistance.

[0014] Preferably, the grafting rate of the SEBS-g-MA ≥ 10%. As a compatibilizer, the styrene-ethylene-butene-styrene (SEBS) block in the molecular structure of SEBS-g-MA provides compatibility with the non-polar EPDM matrix, while the grafted maleic anhydride (MA) groups form polar interactions with the hydroxyl groups (-OH) of the polar reinforcing phase EVOH through ester bonds or hydrogen bonds. A grafting rate ≥ 10% means that there are at least 10 parts of MA groups in every 100 parts of SEBS, ensuring sufficient polar sites to bind with EVOH, significantly reducing the interfacial tension between EPDM (non-polar) and EVOH (polar). A low grafting rate (such as < 10%) will result in insufficient MA groups, and EVOH is prone to agglomeration in EPDM to form large-sized particles. When the grafting rate ≥ 10%, the MA groups effectively anchor EVOH, reducing its dispersion size to the nanoscale, forming a uniform "sea-island" structure, and avoiding stress concentration. A high grafting rate enables SEBS-g-MA to form physical / chemical cross-linking bridges at the EPDM and EVOH interface, improving the load transfer efficiency between the two phases. High grafting rate → sufficient MA groups → strong polar interactions → low interfacial tension → uniform dispersion of EVOH and filler → strong interfacial adhesion → excellent mechanical / barrier properties → acid resistance and sealing reliability.

[0015] Preferably, the reinforcing filler is carbon black, and the carbon black is any one of N550 carbon black and N330 carbon black, and the average particle size of the carbon black is 40 - 50 nm.

[0016] Preferably, the co-reinforcing filler is nano calcium carbonate.

[0017] Preferably, the vulcanizing agent is dicumyl peroxide.

[0018] Preferably, the additives are obtained by mixing zinc oxide and stearic acid in a mass ratio of 2 - 5:1 - 3.

[0019] A preparation method of a rubber gasket includes the following steps:

[0020] Step S1. Premixing: After plasticizing EPDM, sequentially add EVOH, compatibilizer, reinforcing filler, and co-reinforcing filler, and mix at 60 °C for 20 - 30 min to form a uniform premix.

[0021] Step S2. Add the vulcanizing agent and additives, and hot press and vulcanize at 160 °C, 100 - 150 bar for 15 - 20 min.

[0022] Step S3. Post-treatment: Aging treatment in an acidic environment for 400 - 800 h.

[0023] In step S1, due to the hygroscopicity of EVOH, it needs to be dried in a vacuum oven at 80 - 90 °C for 4 - 6 h before use to remove moisture to avoid generating bubbles during the vulcanization process. The compatibilizer is added to the vulcanized EPDM synchronously with EVOH. During the mixing process at 60 °C, the styrene segment of SEBS-g-MA is compatible with EPDM, and the maleic anhydride group forms a polar interaction with the hydroxyl group of EVOH, improving the compatibility between the two phases.

[0024] The nano-calcium carbonate as the auxiliary reinforcing filler in step S1 is surface-modified before use. The process of the surface modification is as follows: surface treatment is carried out using stearic acid or titanate coupling agent, the treatment concentration is 1 - 3%, and it is mixed with calcium carbonate (10 - 20 parts) in a high-speed mixer for 10 - 15 min to make the filler surface lipophilic. The purpose of the surface modification is to improve the compatibility with non-polar EPDM and reduce agglomeration.

[0025] Preferably, the process of the plasticization in step S1 is as follows:

[0026] The EPDM raw rubber is put into an open mill and plasticized at 20 - 30 °C. The rubber molecular chains are broken by the shear force of the rollers. The plasticization time is 10 - 15 min until the surface of the rubber compound is smooth and there is no obvious block structure. The roll gap of the open mill is 0.5 - 1 mm, and the rotation speed is 20 - 30 rpm. The purpose of the plasticization is to break the molecular structure of EPDM, reduce the molecular weight, improve the plasticity and fluidity, and facilitate subsequent mixing.

[0027] Preferably, the addition timing of the vulcanizing agent in step S2 is the post-mixing stage. After the pre-mixing of EPDM, EVOH, compatibilizer, and filler is completed, it is added before hot pressing and vulcanizing at 160 °C to avoid early vulcanization.

[0028] Preferably, in the additives in step S3, zinc oxide is a vulcanization activator, and stearic acid promotes the dispersion of zinc oxide. The two work together to improve the vulcanization efficiency.

[0029] In the present invention, SEBS-g-MA effectively reduces the interfacial tension between EPDM and EVOH, reduces the dispersed size of the reinforcing phase from the micron level to the nanometer level, and optimizes the compatibility of the system.

[0030] The beneficial effects of the present invention:

[0031] The present invention provides a rubber gasket and its preparation method. Through reasonable raw material ratios and specific preparation processes, it effectively solves the deficiencies of traditional EPDM-based gaskets in terms of compatibility, mechanical properties, barrier properties, and acid resistance. The specific beneficial effects are as follows:

[0032] In the present invention, SEBS-g-MA is used as a compatibilizer. The styrene segment in its molecular structure can be anchored in the EPDM matrix, and the maleic anhydride group forms a polar interaction with the hydroxyl group of EVOH, reducing the interfacial tension between the two phases, effectively inhibiting the phase separation of EVOH and EPDM, making the reinforcing phase EVOH more uniformly dispersed in the matrix. Moreover, the reinforcing filler carbon black and the co-reinforcing filler nano-calcium carbonate can, under the action of the compatibilizer, reduce the agglomeration phenomenon, form a uniform filler network, avoid stress concentration, and enhance the overall stability of the material.

[0033] In the present invention, EVOH as a polar reinforcing phase, together with carbon black and nano-calcium carbonate, acts with its high hardness and rigidity to significantly improve the tensile strength, hardness and compression deformation resistance of the gasket. The C-C crosslinking bonds formed by the dicumyl peroxide vulcanizing agent, combined with the 160 °C hot press vulcanization process, enhance the crosslinking density, improve the elastic recovery ability, reduce the long-term compression set, and ensure the sealing stability of the gasket under high pressure.

[0034] The hydroxyl groups in the EVOH molecule effectively hinder the diffusion of oxygen. After being compounded with the EPDM matrix, the oxygen permeability of the gasket is significantly reduced, which is suitable for scenarios with high gas barrier requirements such as PEMFC. The aging treatment in an acidic environment promotes the formation of a dense oxide layer on the material surface. Combining with the interfacial stabilizing effect of SEBS-g-MA, the degradation of the EPDM main chain caused by acid erosion is reduced, the retention rate of tensile strength is increased, and the service life in an acidic environment is extended.

[0035] The present invention adopts a step-by-step mixing process to ensure the uniform dispersion of each component and avoid the agglomeration of fillers. The hot press vulcanization parameters balance the crosslinking efficiency and production efficiency, which is suitable for industrial production. By adjusting the EVOH content and the filler ratio, the present invention can be flexibly adapted to PEMFC seals (requiring acid resistance and high gas tightness) and tunnel joint waterproofing (requiring high water tightness, anti-deformation, and high-pressure water penetration resistance), and has broad application prospects.

[0036] Through EVOH reinforcement, SEBS-g-MA compatibilization, filler synergistic reinforcement and process optimization, the present invention realizes multiple improvements in compatibility, mechanical properties, barrier properties and acid resistance, solves the key defects of traditional EPDM gaskets, and has significant technical advantages and practical value in high-end sealing fields (such as fuel cells and tunnel engineering). Detailed Embodiments

[0037] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in detail with reference to specific embodiments.

[0038] The reinforcing filler used in the present invention is any one of N550 carbon black and N330 carbon black with an average particle size of 40 - 50 nm;

[0039] In the present invention, the ethylene content in the EVOH used is 29%-48%;

[0040] In the present invention, the grafting rate of SEBS-g-MA used is ≥10%.

[0041] Example 1: A preparation method of a rubber gasket, comprising the following steps:

[0042] S1. Put the EPDM raw rubber into an open mill and carry out plasticizing at 20°C. The rubber molecular chains are broken by the roller shear force. The plasticizing time is 10 min until the surface of the rubber compound is smooth and there is no obvious block structure. The roll gap of the open mill is 0.5 mm and the rotation speed is 20 rpm. The purpose of plasticizing is to destroy the molecular structure of EPDM, reduce the molecular weight, improve the plasticity and fluidity, and facilitate subsequent mixing to obtain plasticized EPDM;

[0043] S2. EVOH needs to be dried in a vacuum oven at 80°C for 4 h before use to remove moisture to avoid generating bubbles during the vulcanization process, and obtain pretreated EVOH;

[0044] S3. The auxiliary reinforcing filler nano calcium carbonate is surface modified before use. The process is as follows: surface treatment is carried out with stearic acid or titanate coupling agent, and the treatment concentration is 1-2-2.5-3%. The purpose of surface modification is to improve the compatibility with non-polar EPDM and reduce agglomeration to obtain modified auxiliary reinforcing filler;

[0045] S4. Premixing: Add 10 g of pretreated EVOH, 5 g of SEBS-g-MA, 20 g of carbon black and 10 g of nano calcium carbonate to 100 g of plasticized EPDM in sequence, and mix at 60°C for 20 min to form a uniform premix. The compatibilizer SEBS-g-MA and EVOH are added to the plasticized EPDM synchronously. During the mixing process at 60°C, the styrene segment of SEBS-g-MA is compatible with EPDM, and the maleic anhydride group forms a polar interaction with the hydroxyl group of EVOH. SEBS-g-MA effectively reduces the interfacial tension between EPDM and EVOH, reduces the dispersed size of the reinforcing phase from the micron level to the nano level, promotes the uniform dispersion of the two phases, forms a stable "sea-island" structure, and optimizes the compatibility of the system;

[0046] S5. Mix zinc oxide and stearic acid in a mass ratio of 2:1 to obtain an auxiliary agent. Zinc oxide is a vulcanization activator, and stearic acid promotes the dispersion of zinc oxide. The two synergistically improve the vulcanization efficiency;

[0047] S6. Add 1 g of dicumyl peroxide and 3 g of additives to the homogeneous premix, and hot press and vulcanize at 160 °C and 100 bar for 15 min to obtain a mixed material. The addition timing of the vulcanizing agent dicumyl peroxide is in the post-mixing stage. After the premixing of EPDM, EVOH, compatibilizer, and filler is completed, it is added before hot press vulcanization at 160 °C to avoid early vulcanization;

[0048] S7. Post-treatment: Aging treatment of the mixed material in an acidic environment for 400 - 500 - 600 - 800 h to obtain a rubber gasket.

[0049] Example 2: A method for preparing a rubber gasket, comprising the following steps:

[0050] S1. Put the EPDM raw rubber into an open mill and carry out plasticizing at 23 °C. The rubber molecular chains are broken by the roller shear force. The plasticizing time is 12 min until the surface of the rubber compound is smooth and there is no obvious block structure. The roller gap of the open mill is 0.7 mm and the rotation speed is 23 rpm. The purpose of plasticizing is to destroy the molecular structure of EPDM, reduce the molecular weight, improve plasticity and fluidity, and facilitate subsequent mixing to obtain plasticized EPDM;

[0051] S2. EVOH needs to be dried in a vacuum oven at 83 °C for 4.5 h before use to remove moisture to avoid generating bubbles during the vulcanization process, and obtain pretreated EVOH;

[0052] S3. The nano-calcium carbonate as a reinforcing filler is surface-modified before use. The process is as follows: Surface treatment is carried out with stearic acid or titanate coupling agent, and the treatment concentration is 2%. The purpose of surface modification is to improve the compatibility with non-polar EPDM and reduce agglomeration to obtain modified reinforcing filler;

[0053] S4. Premixing: Add 20 g of pretreated EVOH, 10 g of SEBS-g-MA, 25 g of carbon black, and 13 g of nano-calcium carbonate to 100 g of plasticized EPDM in sequence, and mix at 60 °C for 23 min to form a homogeneous premix. The compatibilizer SEBS-g-MA is added to the plasticized EPDM synchronously with EVOH. During the mixing process at 60 °C, the styrene segment of SEBS-g-MA is compatible with EPDM, and the maleic anhydride group forms a polar interaction with the hydroxyl group of EVOH. SEBS-g-MA effectively reduces the interfacial tension between EPDM and EVOH, reduces the dispersed size of the reinforcing phase from the micron level to the nano level, promotes the uniform dispersion of the two phases, forms a stable "sea-island" structure, and optimizes the compatibility of the system;

[0054] S5. Mix zinc oxide and stearic acid in a mass ratio of 3:2 to obtain an additive. Among them, zinc oxide is a vulcanization activator, and stearic acid promotes the dispersion of zinc oxide. The two cooperate to improve the vulcanization efficiency;

[0055] S6. Add 2 g of dicumyl peroxide and 5 g of additives to the homogeneous premix, and hot press and vulcanize at 160 °C and 120 bar for 17 min to obtain a mixed material. The addition timing of the vulcanizing agent dicumyl peroxide is in the post-mixing stage. After the premixing of EPDM, EVOH, compatibilizer, and filler is completed, it is added before hot press vulcanization at 160 °C to avoid early vulcanization;

[0056] S7. Post-treatment: Aging treatment of the mixed material in an acidic environment for 500 h to obtain a rubber gasket.

[0057] Example 3: A method for preparing a rubber gasket, comprising the following steps:

[0058] S1. Put the EPDM raw rubber into an open mill and carry out plasticizing at 28 °C. The rubber molecular chains are broken by the roller shear force. The plasticizing time is 14 min until the surface of the rubber compound is smooth and there is no obvious block structure. The roller gap of the open mill is 0.9 mm, and the rotational speed is 27 rpm. The purpose of plasticizing is to destroy the molecular structure of EPDM, reduce the molecular weight, improve plasticity and fluidity, and facilitate subsequent mixing to obtain plasticized EPDM;

[0059] S2. EVOH needs to be dried in a vacuum oven at 87 °C for 5 h before use to remove moisture to avoid generating bubbles during the vulcanization process to obtain pretreated EVOH;

[0060] S3. The nano calcium carbonate as a reinforcing filler is surface modified before use. The process is as follows: surface treatment is carried out with stearic acid or titanate coupling agent, and the treatment concentration is 2.5%. The purpose of surface modification is to improve the compatibility with non-polar EPDM and reduce agglomeration to obtain modified reinforcing filler;

[0061] S4. Premixing: Add 25 g of pretreated EVOH, 12 g of SEBS-g-MA, 30 g of carbon black, and 16 g of nano calcium carbonate to 100 g of plasticized EPDM in sequence, and mix at 60 °C for 26 min to form a homogeneous premix. The compatibilizer SEBS-g-MA is added to the plasticized EPDM synchronously with EVOH. During the mixing at 60 °C, the styrene segment of SEBS-g-MA is compatible with EPDM, and the maleic anhydride group forms a polar interaction with the hydroxyl group of EVOH. SEBS-g-MA effectively reduces the interfacial tension between EPDM and EVOH, reduces the dispersed size of the reinforcing phase from the micron level to the nano level, promotes the uniform dispersion of the two phases, forms a stable "sea-island" structure, and optimizes the compatibility of the system;

[0062] S5. Mix zinc oxide and stearic acid in a mass ratio of 4:2.5 to obtain an additive. Zinc oxide is a vulcanization activator, and stearic acid promotes the dispersion of zinc oxide. The two work together to improve the vulcanization efficiency;

[0063] S6. Add 2.5 g of dicumyl peroxide and 7 g of additives to the homogeneous premix, and hot press and vulcanize at 160 °C and 140 bar for 19 min to obtain a mixed material. The addition timing of the vulcanizing agent dicumyl peroxide is in the post-mixing stage. After the premixing of EPDM, EVOH, compatibilizer, and filler is completed, it is added before hot press vulcanization at 160 °C to avoid early vulcanization;

[0064] S7. Post-treatment: Age the mixed material in an acidic environment for 400 - 500 - 600 - 800 h to obtain a rubber gasket.

[0065] Example 4: A method for preparing a rubber gasket, comprising the following steps:

[0066] S1. Put the EPDM raw rubber into an open mill and carry out plasticizing at 30 °C. The rubber molecular chains are broken by the shearing force of the rollers. The plasticizing time is 15 min until the surface of the rubber compound is smooth and there is no obvious block structure. The roller gap of the open mill is 1 mm and the rotation speed is 30 rpm. The purpose of plasticizing is to break the molecular structure of EPDM, reduce the molecular weight, improve plasticity and fluidity, and facilitate subsequent mixing to obtain plasticized EPDM;

[0067] S2. EVOH needs to be dried in a vacuum oven at 90 °C for 6 h before use to remove moisture to avoid generating bubbles during the vulcanization process, and obtain pretreated EVOH;

[0068] S3. The nano calcium carbonate as the reinforcing filler is surface-modified before use. The process is as follows: Use stearic acid or titanate coupling agent for surface treatment, and the treatment concentration is 1 - 2 - 2.5 - 3%. The purpose of surface modification is to improve the compatibility with non-polar EPDM and reduce agglomeration to obtain modified reinforcing filler;

[0069] S4. Premixing: Sequentially add 30 g of pretreated EVOH, 15 g of SEBS-g-MA, 40 g of carbon black, and 20 g of nano calcium carbonate to 100 g of plasticized EPDM, and mix at 60 °C for 30 min to form a homogeneous premix. The compatibilizer SEBS-g-MA is added to the plasticized EPDM synchronously with EVOH. During the mixing process at 60 °C, the styrene segment of SEBS-g-MA is compatible with EPDM, and the maleic anhydride group forms a polar interaction with the hydroxyl group of EVOH. SEBS-g-MA effectively reduces the interfacial tension between EPDM and EVOH, reduces the dispersed size of the reinforcing phase from the micron level to the nano level, promotes the uniform dispersion of the two phases, forms a stable "sea-island" structure, and optimizes the compatibility of the system;

[0070] S5. Mix zinc oxide and stearic acid in a mass ratio of 5:3 to obtain an additive. Zinc oxide is a vulcanization activator, and stearic acid promotes the dispersion of zinc oxide. The two work together to improve the vulcanization efficiency;

[0071] S6. Add 3 g of dicumyl peroxide and 8 g of additives to the homogeneous premix, and hot-press and vulcanize at 160 °C and 150 bar for 20 min to obtain a mixed material. The addition timing of the vulcanizing agent dicumyl peroxide is in the post-mixing stage. After the preparation of the premix of EPDM, EVOH, compatibilizer, and filler is completed, it is added before hot-press vulcanization at 160 °C to avoid early vulcanization;

[0072] S7. Post-treatment: Aging treatment of the mixed material is carried out for 800 h in an acidic environment to obtain a rubber gasket.

[0073] Comparative Example 1:

[0074] In this comparative example, compared with Example 1, no reinforcing filler was added during the preparation of the rubber gasket, and the remaining steps and parameters were the same. This comparative example will not be repeated here, and finally a rubber gasket was obtained.

[0075] Comparative Example 2:

[0076] In this comparative example, compared with Example 1, only "SEBS-g-MA" was replaced with "SEBS" with equal molecular weight, and the remaining steps and parameters were the same. This comparative example will not be repeated here, and finally a rubber gasket was obtained.

[0077] Comparative Example 3:

[0078] In this comparative example, compared with Example 1, only "additives" was replaced with "zinc oxide", and the remaining steps and parameters were the same. This comparative example will not be repeated here, and finally a rubber gasket was obtained.

[0079] Comparative Example 4:

[0080] In this comparative example, compared with Example 1, only "EVOH with an ethylene content of 29%-48%" was replaced with "EVOH with an ethylene content of 9%", and the remaining steps and parameters were the same. This comparative example will not be repeated here, and finally a rubber gasket was obtained.

[0081] Comparative Example 5:

[0082] In this comparative example, compared with Example 1, only "EVOH with an ethylene content of 29%-48%" was replaced with "EVOH with an ethylene content of 69%", and the remaining steps and parameters were the same. This comparative example will not be repeated here, and finally a rubber gasket was obtained.

[0083] Comparative Example 6:

[0084] In this comparative example, compared with Example 1, only "SEBS-g-MA with a grafting rate ≥ 10%" was replaced with "SEBS-g-MA with a grafting rate of 4%", and the remaining steps and parameters were the same. This comparative example will not be repeated here, and finally a rubber gasket was obtained.

[0085] Performance Test:

[0086] 1. Tensile Strength and Elongation at Break: Refer to ASTM D412 "Test Method for Rubber Tensile Properties", use a universal material testing machine (such as Instron 5967), make the sample into a dumbbell-shaped specimen with a gauge length of 50 mm, stretch at a speed of 500 mm / min, and record the maximum tensile load and elongation at break;

[0087] 2. Hardness Test: Refer to ASTM D2240 "Test Method for Rubber Hardness (Shore A Type)", use a Shore A hardness tester (such as SANTAM SHD05), evenly select 5 points on the surface of the sample, read the hardness value after applying pressure for 15 s, and take the average value;

[0088] 3. Compression Set: Refer to ASTM D395 "Test Method for Rubber Compression Set (Method B, 70°C × 24 h)", use a compression fixture and a constant temperature oven, compress the cylindrical sample (Φ13 mm × 6 mm) to 75% of its original thickness, keep it at 70°C for 24 h, then release and recover for 30 min, measure the residual thickness, and calculate the compression set rate: H0 is the original thickness, H r is the thickness after recovery, and Hs is the thickness during compression;

[0089] 4. Oxygen Permeability: Refer to ASTM D3985 "Test Method for Oxygen Permeability of Plastic Films and Sheets (Differential Pressure Method)", use an oxygen permeability tester (such as MOCON OXTRAN 2 / 22), test at a temperature of 25°C, humidity of 0%, differential pressure of 1 atm, and sample thickness of 1 mm, and record the oxygen permeation amount per unit time;

[0090] 5. Acid Resistance Test (Tensile Strength Retention Rate): Environmental Simulation: Refer to the acidic environment of PEMFC, immerse the sample in a 12.5 ppm H2SO4 + 1.8 ppm HF solution, age at 80°C for 800 h, and then test the tensile strength according to ASTM D412 after aging to calculate the retention rate:

[0091] 6. Watertightness Test: Refer to the STUVA method, simulate the water pressure scenario of tunnel joints, use a water pressure test device, install the sample on the joint simulation device, apply a lateral offset (such as 6 mm), gradually increase the water pressure until leakage occurs, and record the critical water pressure value (unit: bar); The results are shown in Table 1-6 below:

[0092] Table 1

[0093]

[0094]

[0095] Table 2

[0096] Project Compression permanent deformation / % <![CDATA[Oxygen permeability / (cc·m -2 ·day -1 ·atm -1 )]]> Example 1 9.7 15.3 Example 2 8.5 12.8 Example 3 7.2 10.5 Example 4 6.8 8.3 Comparative Example 1 18.2 25.7 Comparative Example 2 25.3 32.1 Comparative Example 3 15.5 20.3 Comparative Example 4 12.0 18.5 Comparative Example 5 10.5 16.0 Comparative Example 6 22.1 28.9

[0097] Table 3

[0098]

[0099]

[0100] Table 4

[0101]

[0102] Table 5

[0103]

[0104] Table 6

[0105]

[0106] Data analysis:

[0107] (I) Acid resistance test (tensile strength retention rate): The retention rates of Examples 1-4 were 92%-95%, those of Comparative Examples 1-3 and 6 were lower than 90%, and those of Comparative Examples 4-5 were about 90%. The interfacial stabilizing effect of SEBS-g-MA inhibited the breakage of the EPDM main chain in an acidic environment. The nanoscale dispersion of EVOH reduced interfacial defects and avoided interfacial debonding caused by the penetration of acidic media (for example, the retention rate of Comparative Example 2 was only 80% due to the lack of compatibilizer).

[0108] (II) Matching degree of water tightness test and engineering application: Example 1 withstood 28 bar (6 mm offset), far exceeding Comparative Examples 1-6 (10-20 bar), meeting the requirements of the "high pressure + offset" working conditions for tunnel sealing. Low filler agglomeration (the filler in Example 1 was evenly dispersed) provided a continuous sealing barrier. SEBS-g-MA improved the interfacial bonding strength and avoided slip leakage at the interface between the gasket and the joint under water pressure.

[0109] (III) Oxygen permeability and compatibility with PEMFC application: The oxygen permeability of Example 4 was 8.3 cc·m-2·day-1·atm-1, superior to that of traditional EPDM (about 20) and Comparative Example 2 (32.1). The adsorption and barrier effect of the hydroxyl polar groups of EVOH on oxygen, combined with the multi-layer barrier formed by the nanoscale dispersion, conformed to the dual oxygen barrier mechanism of "polar groups + tortuous path".

[0110] (4) Comparative Example 2 (without compatibilizer): Tensile strength ↓49.6%, oxygen permeability ↑111%, compression set ↑160%. It is proved that SEBS-g-MA is the core element to solve the compatibility of EPDM / EVOH, and there is no alternative solution (for example, the performance cannot be restored after replacing Comparative Example 2 with SEBS), indicating that the blending of polar / non-polar polymers must rely on compatibilizers to reduce the interfacial tension, otherwise phase separation will lead to performance failure, that is, it also indicates the necessity of "grafting rate ≥10%"; Comparative Examples 4-5 (abnormal ethylene content in EVOH): When the ethylene content is 9%, due to the too high crystallinity of EVOH, although the oxygen barrier property is theoretically higher, the compatibility with EPDM is poor (the polarity difference is too large), and the actual permeability has not been significantly reduced (18.5 vs 15.2 of Example 1), proving that 29% is the lower limit of the compatibility-oxygen barrier balance. When the ethylene content is 69%, due to too many ethylene segments, the polarity of EVOH is insufficient, the compatibility with EPDM is improved but the oxygen barrier property is decreased (permeability 16.0 vs 15.2 of Example 1), verifying that 48% is the upper limit of the oxygen barrier property-processability balance.

[0111] (5) In the examples, the tensile strength increases from 12.7→30.1 MPa with the increase of the total amount of fillers (carbon black + calcium carbonate) (20 + 10→40 + 20 parts), which conforms to the "filler reinforcement effect"; however, the elongation at break decreases from 415%→320%, reflecting the "fillers restricting the movement of rubber chains". In the present invention, the total amount of fillers is 30-60 parts (Examples 1-4) to avoid agglomeration caused by excessive amounts (such as the filler network is incomplete in Comparative Example 1 without additives). The vulcanization temperature of 160 °C can ensure that DCP decomposes to generate sufficient free radicals (decomposition temperature 120-180 °C) to form high-strength C-C crosslinking bonds (compression set of the examples ≤10%). The pressure is 100-150 bar: High pressure promotes the uniform dispersion of fillers and avoids the residual bubbles (defects may occur without this process).

[0112] (6) Data tests show that the present invention has the following advantages:

[0113] 1. Core innovation of interfacial engineering: A grafting rate of SEBS-g-MA ≥10% achieves the nano-level dispersion of EVOH, solves the problem of polar / non-polar blending, and makes the improvement of mechanical and barrier properties inevitable (verified by Comparative Examples 2 and 6 in the opposite direction).

[0114] 2. Synergistic design of fillers: The combination of carbon black (reinforcement) + nano calcium carbonate (compatibilization), through surface modification and step-by-step mixing, forms a "strong interfacial bond + uniform network", improving the stiffness while maintaining flexibility (hardness of Example 1 is 68 Shore A, elongation at break is 415%).

[0115] 3. Precision of parameter range: The ethylene content of EVOH is 29%-48%, and SEBS-g-MA is 5-15 parts. This is the "compatibility-performance" golden range verified by data, avoiding failures caused by extreme values (such as Comparative Examples 4-5, 6).

[0116] In this application, the ethylene content in EVOH is 29%-48%. The oxygen barrier property of EVOH stems from the polar hydroxyl groups in the molecular chain. The lower the ethylene content, the higher the proportion of vinyl alcohol units, the greater the density of polar groups, and the stronger the gas (such as oxygen, carbon dioxide) barrier property. When the ethylene content increases, the proportion of flexible ethylene segments in the molecular chain rises, the melting temperature decreases, the melt fluidity improves, and it is easier to process through processes such as extrusion and injection molding. At the same time, the low-temperature resistance and impact resistance of the material are improved. When the ethylene content is 29%-48%, EVOH forms a moderate crystalline structure: the ethylene segments destroy the complete crystallization, avoiding brittleness, while retaining some crystalline regions to maintain strength and chemical resistance. The grafting rate of SEBS-g-MA ≥ 10%. As a compatibilizer, the styrene-ethylene-butene-styrene (SEBS) block in the molecular structure of SEBS-g-MA provides compatibility with the non-polar EPDM matrix, while the grafted maleic anhydride (MA) groups form polar interactions with the hydroxyl groups (-OH) of the polar reinforcing phase EVOH through ester bonds or hydrogen bonds. A grafting rate ≥ 10% means that there are at least 10 parts of MA groups in every 100 parts of SEBS, ensuring sufficient polar sites to bind with EVOH, significantly reducing the interfacial tension between EPDM (non-polar) and EVOH (polar). A low grafting rate (such as <10%) will result in insufficient MA groups, and EVOH is prone to agglomeration in EPDM to form large-sized particles. When the grafting rate ≥ 10%, the MA groups effectively anchor EVOH, reducing its dispersion size to the nanoscale and forming a uniform "sea-island" structure, avoiding stress concentration. A high grafting rate enables SEBS-g-MA to form physical / chemical cross-linking bridges at the interface between EPDM and EVOH, improving the load transfer efficiency between the two phases. High grafting rate → sufficient MA groups → strong polar interaction → low interfacial tension → uniform dispersion of EVOH and filler → strong interfacial adhesion → excellent mechanical / barrier properties → acid resistance and sealing reliability.

[0117] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

[0118] This invention is intended to cover all such alternatives, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention shall be included within the scope of protection of this invention.

Claims

1. A rubber gasket, characterized in that: The invention comprises the following raw materials by weight: 100 parts of matrix, 10-30 parts of reinforcing phase, 5-15 parts of compatibilizer, 20-40 parts of reinforcing filler, 10-20 parts of auxiliary reinforcing filler, 1-3 parts of vulcanizing agent, and 3-8 parts of auxiliary agent; The matrix is ​​EPDM; The reinforcing phase is EVOH; The compatibilizer is SEBS-g-MA.

2. The rubber gasket according to claim 1, characterized in that: The ethylene content in the EVOH is 29%-48%.

3. The rubber gasket according to claim 1, characterized in that: The grafting rate of the SEBS-g-MA is ≥10%.

4. The rubber gasket according to claim 1, characterized in that: The reinforcing filler is carbon black.

5. The rubber gasket according to claim 1, characterized in that: The auxiliary reinforcing filler is nano-scale calcium carbonate.

6. The rubber gasket according to claim 1, characterized in that: The vulcanizing agent is dicumyl peroxide.

7. The rubber gasket according to claim 1, characterized in that: The auxiliary agent is obtained by mixing zinc oxide and stearic acid in a mass ratio of 2-5:1-3.

8. A method for preparing a rubber gasket, characterized in that: The following steps are involved: Step S1. Premixing: After EPDM is plasticized, EVOH, compatibilizer, reinforcing filler and auxiliary reinforcing filler are added in sequence, and the mixture is mixed at 60°C for 20-30 minutes; Step S2. Add vulcanizing agent and additives, and hot press vulcanize at 160°C and 100-150 bar for 15-20 minutes; Step S3. Post-treatment: Acidic environment aging treatment for 400-800 hours.

9. The method for preparing a rubber gasket according to claim 8, characterized in that: The process of mastication in step S1 is as follows: Put the EPDM raw rubber into an open mill and plasticize it at 20-30℃. The rubber molecular chain is broken by the shear force of the rollers. The plasticizing time is 10-15 minutes, until the surface of the rubber is smooth and there is no obvious block structure. The roller spacing of the open mill is 0.5-1mm and the rotation speed is 20-30rpm.

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