A rubber sealing gasket compound and method of making the same

Abstract

The application belongs to the technical field of rubber and plastic material sealing gaskets, and particularly relates to a rubber sealing gasket and a preparation method thereof. The rubber sealing gasket comprises, by mass fraction, the following raw materials: ethylene-propylene-diene monomer (EPDM) rubber, ethylene-vinyl acetate rubber, filler, modified layered filler, zinc oxide, coupling agent, plasticizer, processing aid, antioxidant, compatibilizer, vulcanization accelerator and vulcanizing agent. The ethylene-vinyl acetate rubber, compatibilizer and modified layered filler are introduced into the EPDM matrix, which not only effectively enhances the bonding strength of the rubber matrix and the metal interface, but also improves the dispersibility and compatibility of the modified layered filler in the rubber, realizes high-strength bonding with the metal and excellent medium resistance. While maintaining high mechanical properties and low compression permanent deformation of the material, the long-term sealing reliability of the material under severe working conditions in the fields of aerospace and high-end automobiles is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of rubber and plastic sealing gasket technology, specifically relating to a metal-rubber sealing gasket compound with excellent sealing performance, reliability, and durability, and resistance to media aging, as well as its preparation method. It is particularly suitable for metal-rubber composite sealing components in fields such as automotive air conditioning systems, aerospace hydraulic and pneumatic systems, and high-end equipment manufacturing. Background Technology

[0002] With the rapid development of modern industrial technology, especially in the automotive, aerospace, and precision machinery industries, the operating environments of fluid transmission systems are becoming increasingly demanding. In the automotive air conditioning sector, the air conditioning system is a complex, closed system composed of numerous connecting pipes. It circulates high-temperature, high-pressure gaseous refrigerant and low-temperature, high-pressure liquid refrigerant, accompanied by the lubricating flow of refrigeration oil, placing extremely high demands on the sealing gaskets' resistance to various media. In the aerospace and aircraft manufacturing sectors, the sealing environment is even harsher. Aircraft hydraulic actuation systems (such as landing gear and flap control) often use phosphate ester-based flame-retardant hydraulic oils, while environmental control systems involve various cooling media. These systems not only require sealing materials to possess excellent resistance to swelling from polar media but also to maintain elasticity over a wide temperature range.

[0003] Therefore, extremely stringent requirements are placed on the sealing performance of the sealing gaskets on the flange faces of each interface of the system. They must effectively resist the corrosion of refrigerants and other substances for a long time and ensure zero leakage.

[0004] It is against this backdrop that rubber-metal composite gaskets were developed. In rubber-metal gaskets, the metal skeleton provides structural rigidity, bearing the majority of the bolt preload, ensuring extremely high mechanical strength and dimensional stability, and providing excellent blow-out resistance. Through a vulcanization bonding process, the rubber is encapsulated within the sealing groove of the metal skeleton. Under the action of bolt preload, the rubber undergoes elastic deformation, achieving effective sealing with extremely low compression. Furthermore, it has relatively low requirements for the flatness and roughness of the flange surface, forming extremely high line contact stress with the flange surface, thus achieving a highly reliable and effective seal.

[0005] When ethylene propylene diene monomer (EPDM) rubber is used in aerospace-grade or automotive-grade metal-rubber gaskets, appropriately increasing the vinyl content helps enhance the physical and mechanical properties, heat resistance, and weather resistance of the compound. This has a significant advantage in ensuring the long-term sealing reliability of metal-rubber gaskets in new environmentally friendly refrigerant environments. However, as the vinyl content increases, the crystallinity changes, leading to a weakening of the interfacial bonding force between the rubber and the metal skeleton, and a significant decrease in adhesion. During the operation of the rubber gasket, when the preload exceeds the adhesive strength between the metal and the rubber gasket, the interface may peel or debond, resulting in seal failure and leakage. Under the high-frequency vibration of aircraft engines or the bumpy road conditions of automobiles, once the preload exceeds the adhesive strength, the interface is very prone to peeling, leading to seal failure.

[0006] Currently, research in the field of metal-rubber gaskets mainly focuses on structural design. For example, existing patents CN222669252U, CN119585551A, and CN222458342U primarily address the geometric configuration of the gasket, aiming to improve sealing performance through mechanical structural innovation. However, they neglect in-depth research on the rubber formulation material itself, especially its interfacial adhesion and resistance to media aging.

[0007] In terms of formulation and interfacial bonding, current mainstream research, such as patents CN112608524B and CN116731406A, focuses on enhancing the adhesion between rubber and steel wire by adding metal adhesion promoters. In the field of thermal insulation materials, a few researchers, such as Wang Lianqing and Wang Y, have used methods such as matrix grafting modification and constructing epoxy hybrid networks to introduce polar functional groups into the rubber matrix to strengthen the metal-rubber bonding strength.

[0008] Regarding the above research, compared to using traditional adhesion promoters to improve the adhesion between high-ethylene-content EPDM and metals, although a strong interfacial bond can be formed initially, the oxidation reaction of rubber molecular chains catalyzed by metal ions such as cobalt salts during vulcanization and service accelerates the thermo-oxidative aging process, leading to hardening, embrittlement, and a decline in dynamic fatigue performance. In contrast, while grafting in a large number of polar functional groups essentially increases the reactivity of the rubber and enhances the adhesion strength between the rubber and metal, introducing too many polar groups increases the affinity of EPDM for the refrigerant medium environment of automotive air conditioning systems, resulting in a decrease in anti-swelling ability and significantly sacrificing the EPDM rubber's resistance to media aging.

[0009] Regarding resistance to various media, most researchers have adopted methods such as modifying the vulcanization system to increase crosslinking density, changing the filler system by using multiple types of carbon black, and directly using layered fillers. Among these, synergistically using fillers with different dimensional structures in the matrix to construct a "multi-dimensional, multi-scale" composite barrier network can further improve the durability and service life of gaskets in harsh environments. However, the interfacial interactions between different fillers and the rubber matrix, as well as between different fillers themselves, remain the core challenge and key technological bottleneck that needs to be addressed.

[0010] Therefore, given the various problems and challenges of the aforementioned metal-rubber composite sealing materials, the development of a new type of metal-rubber sealing gasket material that can adapt to the harsh working conditions in the aerospace and high-end automotive fields, and has excellent sealing performance, reliability, and durability, with high adhesion and resistance to media aging, has become an urgent need for development. Summary of the Invention

[0011] To address the key technical bottlenecks of existing rubber-metal gaskets, such as the difficulty in balancing adhesive strength and media resistance, and the poor interfacial bonding of fillers with multiple dimensions, this invention provides a rubber gasket compound with high adhesion and resistance to media aging, as well as its preparation method.

[0012] To achieve the above objectives, the technical solution adopted by this invention is as follows: the rubber sealing gasket material is composed of the following parts by weight: 80-100 parts of EPDM rubber 1-10 parts of ethylene-vinyl acetate rubber 20-100 parts of filler 1-5 parts of modified layered filler 2-8 parts zinc oxide 1-5 parts of coupling agent 2-8 parts plasticizer Processing aids 1-6 parts Anti-aging agent 2-6 parts 1-8 parts compatibilizer 1-6 parts of vulcanization accelerator 1-5 parts of vulcanizing agent Furthermore, the EPDM rubber includes one or more of ENB-EPDM, VNB-EPDM, DCPD-EPDM, and HD-EPDM. Preferably, the EPDM rubber is ENB-EPDM, with a Mooney viscosity [ML (1+4) 125℃] of 10~100MU; an ethylene content of 40~80%; and a third monomer content of 5~15%. Too low a third monomer content will lead to inconsistent vulcanization rates in the blended rubber compound.

[0013] Furthermore, the ethylene-vinyl acetate rubber is an ethylene-vinyl acetate copolymer rubber containing epoxy groups, preferably an ethylene-vinyl acetate-glycidyl methacrylate rubber EVM-GMA with a Mooney viscosity [ML (1+4) 100℃] of 20±10MU; the vinyl acetate (VA) content is about 40~60 wt%, and the glycidyl methacrylate (GMA) content is about 2.0%~10.0%.

[0014] Furthermore, the filler includes inorganic fillers such as carbon black and silica, and a mixture of unsaturated carboxylic acid metal salts. The carbon black is composed of carbon blacks with different particle sizes and structures; the carbon black is one or more of reinforcing carbon black, semi-reinforcing carbon black, medium-particle thermal cracking carbon black, and spray-dried carbon black; preferably, the average particle size of the carbon black is 10-200 nanometers, and the nitrogen adsorption specific surface area is 10-150 m². 2 / g, DBP oil absorption value 50~150cm 3 / 100g; the nitrogen adsorption specific surface area of ​​the precipitated silica is 20~300m². 2 / g, DBP oil absorption value 50~400cm 3 / 100g; the unsaturated carboxylic acid metal salt is zinc acrylate, zinc methacrylate, zinc dimethacrylate, magnesium methacrylate, etc.; the modified layered filler is one or more of organic modified montmorillonite, modified boron nitride, modified graphene, modified MXene and surface modified talc.

[0015] Further optimization: Inorganic fillers (carbon black, silica): Modified layered fillers: Unsaturated carboxylates are used in combination at a mass ratio of (40~80): (1~5): (10~20).

[0016] Further optimization: The modified layered filler is a filler that has undergone surface chemical modification treatment in order to enhance the compatibility and interfacial bonding force between the filler and the rubber matrix.

[0017] Preferably, the organically modified montmorillonite can be prepared by cation exchange modification of sodium-based montmorillonite using a quaternary ammonium salt containing active functional groups (such as epoxy groups).

[0018] For example, epichlorohydrin is first reacted with long-chain alkyl tertiary amines (such as octadecyl dimethyl tertiary amine) to synthesize quaternary ammonium salts containing epoxy groups as modifiers; then, the modifier is used to carry out a cation exchange reaction with sodium-based montmorillonite to prepare organically modified montmorillonite.

[0019] Preferably, the surface-modified talc powder can be obtained by surface grafting modification of talc powder using silane coupling agents (such as KH-550, KH-560, A-172, etc.).

[0020] Furthermore, the plasticizer includes polyester plasticizers such as adipic acid polyester plasticizer, sebacic acid polyester plasticizer, etc., or one or more combinations of trimellitates and phthalates; the coupling agent is a silane coupling agent such as vinylsilane, aminosilane, epoxysilane, mercaptosilane, and methacryloxysilane, etc.; the processing aid is stearic acid, zinc stearate, etc.

[0021] Furthermore, antioxidants include one or more combinations of amines, phenols, heterocyclic compounds, phosphites, and protective waxes.

[0022] Furthermore, the compatibilizer includes maleic anhydride-grafted ethylene propylene diene monomer (MAH-g-EPDM).

[0023] Furthermore, the vulcanization accelerator includes one or more combinations of trimethylolpropane triacrylate (TMPTA), ethylene glycol diacrylate (EGDA), trimethylolpropane trimethacrylate (TMPTAMA), ethylene glycol dimethacrylate (EGDMA), zinc diacrylate (ZDA), zinc dimethacrylate (ZDMA), triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), and 1,2-polybutadiene (1,2-PBR).

[0024] Furthermore, the vulcanizing agent includes one or more of the following: dicumyl peroxide; 2,4-di-tert-butyl peroxide; 2,5-di(tert-butylperoxy)-2,5-dimethylhexane; tert-butylcumyl peroxide; 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn-3; tert-butylperoxy-isopropenylcumyl peroxide; m-di(tert-butylperoxy)diisopropylbenzene; p-di(tert-butylperoxy)diisopropylbenzene; dicumyl peroxide; 1,1-di(tert-butylperoxy)cyclohexane; n-butyl 4,4-di(tert-butylperoxy)valerate; ethyl 3,3-di(tert-butylperoxy)butyrate; and tert-butyl peroxide benzoate.

[0025] This invention first introduces ethylene-vinyl acetate-glycidyl methacrylate copolymer rubber (EVM-GMA) into ethylene propylene diene monomer (EPDM) rubber, utilizing its highly polar functional groups to effectively improve the adhesion strength to the metal interface. Simultaneously, by adding the compatibilizer maleic anhydride grafted onto EPDM rubber (MAH-g-EPDM), the compatibilizer is grafted onto EPDM rubber, improving the compatibility between EVM-GMA and the EPDM matrix. This optimized compatibility system also creates highly uniform dispersion conditions for the subsequently introduced modified layered filler. By adjusting the types and amounts of EVM-GMA, the compatibilizer MAH-g-EPDM, and the modified layered filler, a rubber sealing gasket material is finally prepared.

[0026] The method for preparing the above-mentioned rubber sealing gasket includes the following steps: (1) First, put EPDM rubber, ethylene-vinyl acetate-glycidyl methacrylate rubber and compatibilizer into a mixer for plasticizing. Stir at a speed of 20~40r / min for 1~3min to obtain a uniformly mixed blend. (2) Weigh the fillers (carbon black, silica, modified layered fillers and unsaturated carboxylates) and mix them evenly in a mixer; then add processing aids, antioxidants, coupling agents, zinc oxide and half of the fillers to the blend, and continue to stir at a speed of 20~50r / min for 4~8min. (3) When the internal mixer reaches 70~100℃, add the remaining half of the filler and plasticizer, and stir at a speed of 20~50r / min until the temperature of the internal mixer reaches 110~130℃. (4) Put the compound obtained in step (3) into the open mill, adjust the roller speed to 20~40r / min, then adjust the roller gap to 0.2~0.6mm, and use the turning machine to feed the material for 3~5 minutes; adjust the roller gap to 2~4mm and let it stand for 16~24 hours after the sheet is produced. (5) Adjust the roller gap of the open mill to 2-4 mm, wrap the rollers, add vulcanization accelerator and vulcanizing agent again, cut the rubber on the left and right and pound the rubber 2-5 times each, then adjust the roller gap to 0.2-0.6 mm, and use the turning machine to place the material for 3-5 minutes; adjust the roller gap to 0.1-0.3 mm, make triangular wrapping and thin passage 5-6 times, then adjust the roller gap to 2-4 mm, sheet out, cool and stand for 12-24 hours to obtain the compound rubber; (6) The pretreatment of the metal skeleton includes degreasing and cleaning, sandblasting, phosphating or silanizing and other chemical treatments. Finally, in the coating stage, the adhesive Chemosil produced by Lord Company is applied. ® 512 was diluted with isopropanol at a 1:1 ratio, and the dry film thickness was controlled within the range of 10-20 μm using a uniform coating method. After coating, the substrate was allowed to air dry at room temperature for 30 minutes, and finally, the treated substrate was sealed and stored in a dry environment.

[0027] (7) After the compound obtained in step (5) is left to stand for 12 to 24 hours, it is vulcanized with the pretreated metal skeleton obtained in step (6) to obtain the metal-rubber sealing gasket compound; wherein the vulcanization pressure is 10 to 15 MPa, the vulcanization temperature is 170 to 190°C, and the vulcanization time is 5 to 15 minutes.

[0028] In step 1) of this invention, the compatibilizer maleic anhydride grafted onto EPDM rubber is carried out through the following steps: (1) Heat the internal mixer to 170°C and add ethylene propylene diene monomer (EPDM) after the temperature stabilizes, so that it is completely melted. Then add ethylene propylene diene monomer (MAH) and initiator benzoyl peroxide (BPO), and EPDM:MAH:BPO are melt-grafted in a ratio of 100:5:0.1 for 10 min to obtain MAH-g-EPDM.

[0029] (2) Place the melt-grafted MAH-g-EPDM in a Soxhlet extractor, add acetone and reflux at 85°C for 24 h to allow it to swell fully in order to remove unreacted grafted monomers and possible MAH copolymers. Then place it in a vacuum drying oven at 70°C for 12 h to obtain purified MAH-g-EPDM.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects: To address the stringent requirements placed on materials by aerospace hydraulic systems and automotive air conditioning sealing systems under long-term coupled environments of heat, media (refrigerant / phosphate ester hydraulic oil), mechanical stress, and high-frequency vibration, this study innovatively designed and optimized a traditional EPDM rubber system. The core strategy lies in introducing EVM-GMA and the compatibilizer MAH-g-EPDM, along with synergistic modification of layered fillers, to achieve an integrated performance improvement from interfacial chemical bonding to the bulk barrier structure. This systematically solves the industry challenge of simultaneously achieving adhesive durability and resistance to media swelling.

[0031] Firstly, EPDM was selected and a highly stable chemical bonding interface was constructed using EVM-GMA. During vulcanization, the epoxy groups in the EPDM molecular chain undergo a ring-opening reaction with the active groups in the metal adhesive pretreatment layer, forming a strong covalent bond bridge. This not only significantly improves the initial bond strength but also ensures that the bonding interface will not fail due to physical adsorption or ionic bond disruption under harsh conditions such as thermal aging and refrigerant immersion. It can withstand high-frequency vibrations and alternating loads during aircraft flight or vehicle operation, significantly enhancing its anti-peeling ability.

[0032] Meanwhile, this solution completely abandons traditional cobalt salt adhesive accelerators, fundamentally avoiding the catalytic effect of metal ions on rubber aging, effectively delaying the aging rate of the material matrix and the bonding interface, and achieving simultaneous optimization of bonding strength and anti-aging performance. Furthermore, the appropriate addition of EVM-GMA to the EPDM matrix does not completely graft hybridize EPDM into a polar rubber, but rather, by introducing a small amount of EVM-GMA, it efficiently enhances interfacial adhesive activity while maintaining the non-polar characteristics of the EPDM matrix as much as possible. Its low affinity with polar refrigerant media is preserved, thus allowing the material to inherit the inherent and excellent anti-swelling ability of EPDM rubber.

[0033] When polar EVM-GMA is introduced into a non-polar EPDM matrix, the inherent polarity difference leads to weak interphase bonding. To avoid rubber cohesive failure (R-type failure) under the working stress of the rubber gasket, resulting in sealing failure and leakage, MAH-g-EPDM is introduced as a highly efficient "molecular bridge" compatibilizer. The main chain of this compatibilizer is completely compatible with the EPDM matrix and can be firmly "anchored" in the matrix through chain entanglement and co-vulcanization. Meanwhile, the maleic anhydride (MAH) functional groups of its side chains can form strong interactions and hydrogen bonds with the ester groups, epoxy groups of EVM-GMA, and polar groups on the surface of the modified filler. This unique amphiphilic structure effectively improves the compatibility of EPDM and EVM-GMA, strengthens the phase interface, and promotes the uniform dispersion and improved physical and mechanical properties of subsequent fillers.

[0034] Based on the optimized interface described above, a multi-dimensional, multi-scale composite barrier network is constructed by using fillers with different dimensional structures in synergy within the matrix. With the assistance of MAH-g-EPDM, the modified layered fillers are uniformly dispersed in the rubber matrix, achieving a strong and robust bond between the filler-matrix and filler-filler interfaces. The synergistic interaction of fillers of different dimensions creates a dense physical barrier network within the matrix, significantly extending the penetration path of small refrigerant molecules. This systematically improves the overall swelling resistance and long-term media stability of the rubber compound, providing a crucial material solution for metal-rubber gaskets in automotive air conditioning systems and aerospace hydraulic systems. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0036] The following examples further illustrate preferred embodiments within the scope of the present invention. These examples are merely illustrative and not intended to limit the scope of the invention, as many variations can be made to the invention without departing from its essence and scope.

[0037] The terms “comprising,” “including,” “containing,” “having,” “comprising,” or other variations thereof are intended to cover non-closed inclusion, and no distinction is made between these terms. The term “comprising” means that other steps and components may be added without affecting the final result. The term “comprising” also includes the terms “consisting of” and “substantially consisting of”. The compositions and methods / processes of the present invention may comprise, consist of, and substantially consist of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein.

[0038] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0039] The tensile properties were tested according to GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber"; the tear strength was tested according to GB / T 529-2008 "Determination of Tear Strength of Vulcanized Rubber or Thermoplastic Rubber"; the hot air aging performance was tested according to GB / T 3512-2014 "Accelerated Aging and Heat Resistance Test of Vulcanized Rubber or Thermoplastic Rubber in Hot Air"; the compression set was tested according to GB / T 7759.1-2015 "Determination of Compression Set of Vulcanized Rubber or Thermoplastic Rubber - Part 1: Under Normal or High Temperature Conditions"; the adhesive strength was tested according to GB / T 11211-2009 "Determination of Adhesion Strength between Vulcanized Rubber or Thermoplastic Rubber and Metal - Two-Plate Method"; and the permeability coefficient was tested according to GB / T7755.1-2018 "Determination of Air Permeability of Vulcanized Rubber or Thermoplastic Rubber - Part 1: Differential Pressure Method".

[0040] Table 1-1 Parts by weight of raw materials for comparative example series and embodiment series

[0041] Remark: ① Arlanx Newtech's EPDM Keltan 2470C has an ethylene content of 70.5%, a Mooney viscosity [ML1+4 (125℃)] of 22MU, and a third monomer content of 4.5%. ② Arlanx Newtech's ethylene propylene diene monomer (EPDM) rubber Keltan 5470C has an ethylene content of 66%, a Mooney viscosity [ML1+4 (125℃)] of 55MU, and a third monomer content of 4.6%. ③ Arlanx Newtech's EPDM Keltan 2650C has an ethylene content of 46%, a Mooney viscosity [ML1+4 (125℃)] of 25MU, and a third monomer content of 6.0%. ④ Alangxin Technology Co., Ltd.'s ethylene-vinyl acetate-glycidyl methacrylate rubber EVM-GMA, brand name Levapren NPG, Mooney viscosity [ML (1+4) 100℃] is 20±10MU; vinyl acetate (VA) content is approximately 60 wt%, and glycidyl methacrylate (GMA) content is approximately 2.9%~3.0%; ⑤ Cabot N774 carbon black, with a particle size of 80-170 nanometers and a nitrogen adsorption surface area of ​​approximately 25-35 m². 2 / g; DBP oil absorption value approximately 72 cm 3 / 100g; ⑥ Cabot N330 carbon black, with a particle size of 28-36 nanometers and a nitrogen adsorption surface area of ​​approximately 80 m². 2 / g; DBP oil absorption value approximately 102 cm 3 / 100g; ⑦ Evonik Degussa Ultrasil VN3GR, a granulated silica product, has a nitrogen adsorption surface area of ​​approximately 180 m². 2 / g; ⑧ Zinc dimethacrylate (ZDMA) from Qingdao Zhongxiang Company; ⑨ The coupling agent A-172 produced by Shanghai Ruiba New Materials Co., Ltd. has the chemical name vinyltrimethoxysilane; ⑩ The antioxidant MB produced by Weilin New Material Technology Co., Ltd. has the chemical name 2-thiol-benzimidazole; The antioxidant 445 produced by Shandong Shangshun Chemical Co., Ltd. has the chemical name 4,4'-bis(α,α-dimethylbenzyl)diphenylamine. The BIBP vulcanizing agent produced by Jiangsu Qiangsheng Functional Chemical Co., Ltd. has the chemical name 2,4-di-tert-butyl peroxide cumene. The accelerator TAIC produced by Jiangsu Qiangsheng Functional Chemical Co., Ltd. has the chemical name triallyl isocyanurate.

[0042] The organic-modified montmorillonite in the modified layered packing material is processed through the following steps: (1) Dissolve an appropriate amount of epichlorohydrin in ethanol solvent and heat to 70°C. Slowly add octadecyl dimethyl tertiary amine, with a molar ratio of epichlorohydrin to octadecyl dimethyl tertiary amine of 1.2:1. Stir mechanically at 200 r / min for 5 h and cool to room temperature. Distill the above solution under reduced pressure using a rotary evaporator, and wash three times with ethanol to obtain a pale yellow paste, i.e., epoxy quaternary ammonium salt.

[0043] (2) Take cation-exchanged sodium-based montmorillonite and epoxy quaternary ammonium salt, add deionized water, and disperse by ultrasonication. Slowly add epoxy quaternary ammonium salt dropwise to the montmorillonite suspension. The mass ratio of cation-exchanged sodium-based montmorillonite to epoxy quaternary ammonium salt is 1:0.5. Heat to 65℃, mechanically stir at 500 r / min for 6 h, centrifuge the mixture, wash, vacuum dry at 80℃ for 24 h, grind and pass through a 500 mesh sieve to obtain white powdery organic modified montmorillonite.

[0044] The surface modification of talc powder in modified layered fillers is carried out through the following steps: (1) Mix 1.2% of the silane coupling agent by mass of talc with a certain amount of ethanol-water mixed solvent (ethanol:water volume ratio of 8:2). Stir at 400 r / min for 1 hour at 40°C to generate active silanol.

[0045] (2) Add talc powder to an appropriate amount of deionized water, disperse it ultrasonically, and prepare a suspension with a solid content of 20%. Transfer the talc powder suspension to a reaction vessel, heat it to 70°C, and slowly add the silane hydrolysate to the talc powder slurry. Stir mechanically at 400 r / min for 3 h. After the reaction is complete, cool the mixed slurry to room temperature. Filter and wash repeatedly with ethanol to remove adsorbed and unreacted silane. Dry under vacuum at 100°C for 16 h, grind and pass through a 500-mesh sieve to obtain dry, loose, and uniform surface-modified talc powder.

[0046] Comparative Example A1-1

[0047] A method for preparing a metal-rubber sealing gasket includes the following steps: (1) First, put EPDM Keltan2470C into a mixer for plasticizing and stir for 3 minutes at a speed of 40 r / min.

[0048] (2) Weigh the fillers (carbon black, silica and unsaturated carboxylate ZDMA), mix them evenly in a mixer, then add the processing aid (stearic acid), antioxidant (antioxidant MB, antioxidant 445), coupling agent A-172, zinc oxide and half of the fillers to the rubber compound, and continue to stir at a speed of 40 r / min for 4 min. (3) When the internal mixer reaches 70°C, add the remaining half of the filler and plasticizer (polypropylene adipate), and stir at 40 r / min until the internal mixer reaches 110°C. (4) Put the compound obtained in step (3) into the open mill, adjust the roller speed to 20r / min, adjust the roller gap to 0.2mm, and turn the material over for 3 minutes; adjust the roller gap to 2mm and let it stand for 16 hours after the sheet is produced.

[0049] (5) Adjust the roller gap of the open mill to 2mm, wrap the rollers, add vulcanization accelerator TAIC and vulcanizing agent BIBP again, cut the rubber on the left and right and pound the rubber 3 times each, then adjust the roller gap to 0.2mm, and place the material on the turning machine for 3 minutes; adjust the roller gap to 0.1mm, make triangular wrapping and thin passage 6 times, then adjust the roller gap to 4mm, sheet out, cool and stand for 12 hours to obtain the compound rubber; (6) The pretreatment of the metal skeleton includes degreasing and cleaning, sandblasting, phosphating or silanizing and other chemical treatments. Finally, in the coating stage, the adhesive Chemosil is applied. ® 512 was diluted with isopropanol at a 1:1 ratio, and the dry film thickness was controlled within the range of 10-20 μm using a uniform coating method. After coating, the substrate was allowed to air dry at room temperature for 30 minutes, and finally, the treated substrate was sealed and stored in a dry environment.

[0050] (7) After the rubber material obtained in step (5) is left to stand for 12 hours, it is vulcanized with the pretreated metal skeleton obtained in step (6) to obtain the metal-rubber sealing gasket rubber material.

[0051] The vulcanization pressure was 15 MPa, the vulcanization temperature was 170℃, and the vulcanization time was based on the process positive vulcanization time t measured by the vulcanizer. 90 Sure.

[0052] The obtained rubber sealing gasket material and product performance test results are shown in Table 1-2.

[0053] Comparative Example A1-2

[0054] The preparation method is the same as that of Comparative Example A1-1, except that in the first step, Keltan 2650C EPDM rubber with low vinyl content is added to completely replace Keltan 2470C EPDM rubber in equal amounts. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-2.

[0055] Comparative Examples A1-3

[0056] The preparation method is the same as that of Comparative Example A1-1, except that in the first step, EPDM 5470C is added to replace EPDM 2470C. In addition to Keltan 5470C, EVM-GMA is also added for blending, with a ratio of 5470C:EVM-GMA of 80:20, while the total amount of rubber remains unchanged. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-2.

[0057] Comparative Examples A1-4

[0058] The preparation method is the same as that of Comparative Example A1-1, except that in the first step, Keltan 2470C, Keltan 2650C, and MAH-g-EPDM are added and blended, with a ratio of 2470C:2650C:MAH-g-EPDM of 60:25:15, while the total amount of rubber remains unchanged. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-2.

[0059] Comparative Examples A1-5

[0060] The preparation method is the same as that of Comparative Example A1-1, except that in the first step, Keltan 5470C, EVM-GMA, and MAH-g-EPDM are added for blending, with a ratio of 5470C:EVM-GMA:MAH-g-EPDM of 65:20:15, and the total amount of rubber remains unchanged. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-2.

[0061] Example B1-1

[0062] The preparation method is the same as that of Comparative Example A1-1, except that in the first step, EPDM rubber Keltan 5470C is added to completely replace EPDM rubber Keltan 2470C in equal amounts, keeping the total amount of rubber constant. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-2.

[0063] Example B1-2

[0064] The preparation method is the same as that of Comparative Example A1-1, except that Keltan 2470C and Keltan 2650C are added and blended in the first step, with a ratio of 2470C:2650C of 60:40, while the total amount of rubber remains unchanged. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-2.

[0065] Examples B1-3

[0066] The preparation method is the same as in Example B1-1, except that in the first step, in addition to adding Keltan 5470C, EVM-GMA is also added for blending, with a 5470C:EVM-GMA ratio of 90:10, and the total amount of rubber remains unchanged. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-2.

[0067] Examples B1-4

[0068] The preparation method is the same as in Examples B1-2, except that in the first step, MAH-g-EPDM is added to partially replace Keltan 2650C, with the ratio of 2470C:2650C:MAH-g-EPDM being 60:35:5, while keeping the total amount of rubber constant. The resulting rubber sealing gasket compound and product performance tests are shown in Tables 1-2.

[0069] Examples B1-5

[0070] The preparation method is the same as in Examples B1-3, except that in the first step, MAH-g-EPDM is added to partially replace Keltan 5470C, with the ratio of 5470C:EVM-GMA:MAH-g-EPDM being 85:10:5, while the total amount of rubber remains unchanged. The resulting rubber sealing gasket compound and product performance tests are shown in Tables 1-2.

[0071] Table 1-2 Performance Testing of Rubber Sealing Gasket Compounds and Products

[0072] Note: R134a is an environmentally friendly hydrofluorocarbon refrigerant for automotive air conditioning systems, with tetrafluoroethane as its main component; ND11 is a refrigeration lubricant for automotive air conditioning compressors.

[0073]

[0074] As can be seen from Tables 1-1 and 1-2: (1) As can be seen from Comparative Example A1-1, although EPDM with high vinyl content has excellent physical and mechanical properties and resistance to heat and oxygen aging, its non-polar characteristics result in poor adhesion to metals. The high crystallinity of vinyl leads to excessive compression set of the rubber compound, resulting in poor sealing performance of the rubber gasket and failing to meet the application requirements. As can be seen from Comparative Example A1-2, although EPDM with low vinyl content has relatively good adhesion, the low vinyl content leads to a decrease in the regularity of the molecular chain, which deteriorates its tensile strength, modulus, and resistance to heat and oxygen aging. In addition, the relatively loose crosslinking network makes it easier to penetrate and swell in R134a and its mixture with ND11 oil, resulting in insufficient resistance to media aging and failing to meet the application requirements. By comparing Example B1-1 with Comparative Examples A1-1 and A1-2, the example uses EPDM with higher vinyl content, which improves the adhesion strength between the rubber compound and the metal, while slightly reducing the resistance to heat and oxygen aging and the resistance to media aging. By comparing Examples B1-2 with Comparative Examples A1-1 and A1-2, the physical and mechanical properties, compression set properties, heat and oxygen aging resistance, and resistance to R134a and its mixture with ND11 oil were significantly improved after blending EPDM with high and low ethylene content compared to Comparative Example A1-2. The adhesive properties also showed a certain increase compared to Comparative Example A1-1.

[0075] (2) By comparing Examples B1-3 with Example B1-1, the introduction of an appropriate amount of EVM-GMA not only improves the physical and mechanical properties and the resistance to heat and oxygen aging, but also significantly improves the adhesion between the adhesive and the metal, achieving synergistic optimization of high adhesion and high resistance to heat and oxygen aging. However, its aging resistance is still insufficient in R134a and its mixture with ND11 oil. By comparing Examples B1-3 with Comparative Example A1-3, when the amount of EVM-GMA added is small, it can play a reinforcing role as a dispersed phase; however, when the amount added is too large, the difference in compatibility between EPDM and EVM-GMA will lead to an increase in interfacial defects between the two phases, which will cause a serious decline in physical and mechanical properties and aging resistance. This shows that an appropriate amount of EVM-GMA within 1 to 10 parts can meet the performance requirements.

[0076] (3) Comparing Examples B1-4 with Example B1-2, it can be seen that adding an appropriate amount of MAH-g-EPDM can improve the physical and mechanical properties and heat and oxygen aging resistance of the adhesive, and appropriately improve the adhesion performance between the adhesive and metal. Comparing Examples B1-4 with Comparative Examples A1-4, it can be seen that although adding excessive amounts of MAH-g-EPDM further improves its physical and mechanical properties, adhesive strength, and heat and oxygen aging resistance, its resistance to R134a and its mixture with ND11 oil deteriorates severely, failing to meet the usage requirements. This indicates that an appropriate amount of MAH-g-EPDM within 1-8 parts can meet the performance requirements.

[0077] (4) A comparison of Examples B1-5 and Comparative Examples A1-5 shows that the compatibilizing effect of MAH-g-EPDM has a saturation threshold. Exceeding the optimal dosage, excess MAH-g-EPDM forms an independent third phase in the matrix, becoming a new stress defect point and leading to a deterioration in various properties. A comparison of Examples B1-5 and B1-3 shows that introducing MAH-g-EPDM into the EPDM / EVM-GMA blend system can act as a highly efficient compatibilizer to improve the interfacial compatibility between the two phases and promote the dispersion of EVM-GMA, thereby synergistically improving physical and mechanical properties, adhesive strength, and resistance to heat and oxygen aging, while reducing resistance to media. Therefore, subsequent research on formulation optimization should focus on further improving its resistance to media based on the existing "high adhesion and resistance to heat and oxygen aging," to further refine the coordination and unity between high adhesion and high durability.

[0078] Table 1-3 Parts by weight of raw materials for comparative example series and embodiment series

[0079] Comparative Example A2-1

[0080] A method for preparing a metal-rubber sealing gasket includes the following steps: (1) First, put EPDM Keltan5470C, ethylene-vinyl acetate-glycidyl methacrylate rubber EVM-GMA and compatibilizer MAH-g-EPDM into a mixer for plasticizing. Stir at 40 r / min for 3 min to obtain a uniformly mixed blend.

[0081] (2) Weigh the fillers (carbon black, silica, unsaturated carboxylate ZDMA and unmodified montmorillonite), mix them evenly in a mixer, and then add the processing aid (stearic acid), antioxidant (antioxidant MB, antioxidant 445), coupling agent A-172, zinc oxide and half of the fillers to the rubber compound, and continue to stir at a speed of 40 r / min for 4 min; (3) When the internal mixer reaches 70°C, add the remaining half of the filler and plasticizer (polypropylene adipate), and stir at 40 r / min until the internal mixer reaches 110°C. (4) Put the compound obtained in step (3) into the open mill, adjust the roller speed to 20r / min, adjust the roller gap to 0.2mm, and turn the material over for 3 minutes; adjust the roller gap to 2mm and let it stand for 16 hours after the sheet is produced.

[0082] (5) Adjust the roller gap of the open mill to 2mm, wrap the rollers, add vulcanization accelerator TAIC and vulcanizing agent BIBP again, cut the rubber on the left and right and pound the rubber 3 times each, then adjust the roller gap to 0.2mm, and place the material on the turning machine for 3 minutes; adjust the roller gap to 0.1mm, make triangular wrapping and thin passage 6 times, then adjust the roller gap to 4mm, sheet out, cool and stand for 12 hours to obtain the compound rubber; (6) The pretreatment of the metal skeleton includes degreasing and cleaning, sandblasting, phosphating or silanizing and other chemical treatments. Finally, in the coating stage, the adhesive Chemosil is applied. ® 512 was diluted with isopropanol at a 1:1 ratio, and the dry film thickness was controlled within the range of 10-20 μm using a uniform coating method. After coating, the substrate was allowed to air dry at room temperature for 30 minutes, and finally, the treated substrate was sealed and stored in a dry environment.

[0083] (7) After the rubber material obtained in step (5) is left to stand for 12 hours, it is vulcanized with the pretreated metal skeleton obtained in step (6) to obtain the metal-rubber sealing gasket rubber material.

[0084] The vulcanization pressure was 15 MPa, the vulcanization temperature was 170℃, and the vulcanization time was based on the process positive vulcanization time t measured by the vulcanizer. 90 Sure.

[0085] The obtained rubber sealing gasket material and product performance tests are shown in Table 1-4.

[0086] Comparative Example A2-2

[0087] The preparation method is the same as that of Comparative Example A2-1, except that the amount of unmodified montmorillonite used in the second step is 4 parts. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-4.

[0088] Comparative Examples A2-3 and A2-4

[0089] The preparation method for Comparative Example A2-3 is the same as that for Comparative Example A2-1, except that the amount of unmodified talc powder used in the second step is 2 parts. The amount of unmodified talc powder used in Comparative Example A2-4 is 4 parts. The resulting rubber sealing gasket compounds and product performance tests are shown in Tables 1-4.

[0090] Comparative Example A2-5

[0091] The preparation method is the same as that of Comparative Example A2-1, except that in the second step, organically modified montmorillonite and surface-modified talc powder are used, each in a dosage of 5 parts. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-4.

[0092] Examples B2-1 and B2-2

[0093] Example B2-1 was prepared using the same method as Comparative Example A2-1, except that the unmodified montmorillonite in the second step was replaced with organically modified montmorillonite; all other operations were the same as in A2-1. Example B2-2 used 4 parts of organically modified montmorillonite, and all other operations were the same as in B2-1. The resulting rubber sealing gasket compound and product performance tests are shown in Tables 1-4.

[0094] Examples B2-3 and B2-4

[0095] The preparation method for Example B2-3 is the same as that for Comparative Example A2-3, except that the unmodified talc powder in the second step is replaced with surface-modified talc powder; other operations are the same as in A2-3. In Example B2-4, the amount of surface-modified talc powder is 4 parts; other operations are the same as in B2-3. The resulting rubber sealing gasket compound and product performance tests are shown in Tables 1-4.

[0096] Example B2-5

[0097] The preparation method is the same as that of Comparative Example A2-5, the difference being that in the second step, the amount of organically modified montmorillonite and surface-modified talc is 2 parts each. The resulting rubber sealing gasket compound and product performance tests are shown in Table 1-4.

[0098] Table 1-4 Performance Testing of Rubber Sealing Gasket Compounds and Products

[0099] As can be seen from Tables 1-3 and 1-4: (1) By comparing Example B2-1 with Comparative Example A2-1, Example B2-3, and Comparative Example A2-3, the addition of a small amount of layered filler can appropriately improve the physical and mechanical properties, heat and oxygen aging resistance, and media aging resistance of the rubber compound. However, the addition of modified layered filler has a more significant effect on improving the performance of the rubber matrix. This is because, with the assistance of MAH-g-EPDM, the modified layered filler can be uniformly dispersed in the rubber matrix, achieving a strong and tough bond between the filler and the matrix and between the filler and the filler interface. Fillers of different dimensions work together to build a dense physical barrier network in the matrix. Especially in terms of media aging resistance, the multi-dimensional fillers work together to form a maze effect, which greatly extends the penetration path of refrigerant R134a and its mixture with ND11 oil, thereby greatly improving the overall swelling resistance and long-term media stability of the rubber compound.

[0100] (2) By comparing Example B2-2 with Comparative Example A2-2, Example B2-4, and Comparative Example A2-4, the addition of 4 parts of unmodified layered filler significantly reduced the physical and mechanical properties, heat and oxygen aging resistance, and resistance to refrigerant R134a and its mixture with ND11 oil. This is because the unmodified filler has poor compatibility with rubber, and when the unmodified layered filler exceeds the load-bearing capacity of the matrix, its dispersibility deteriorates, leading to severe filler agglomeration. These agglomerates, as stress concentration points, are prone to becoming the origin of microcracks during stress, heat and oxygen, or medium aging, accelerating material failure and severely degrading performance. Using the same number of modified layered fillers, due to their interaction with the compatibilizer MAH-g-EPDM, the dispersibility is fundamentally improved, effectively avoiding the sharp decline in the above-mentioned properties, thus maintaining good performance stability even at higher filler contents.

[0101] (3) By comparing Example B2-5 with Examples B2-2 and B2-4, the same amount of modified layered filler was added. Example B2-5, by using two different modified layered fillers in synergy, allowed the layered fillers of different particle sizes, shapes, and surface chemistry to overlap and complement each other in the matrix, which could more effectively cover a wider scale range, construct a multi-scale composite barrier network, form a more complete and dense barrier, and fill the inherent defects in the single layered filler network. Therefore, compared with adding the same amount of single layered filler, it can further improve the resistance to media aging. By comparing Example B2-5 with Comparative Example A2-5, when an excessive amount of modified layered filler was added, the physical and mechanical properties, compression set, resistance to thermo-oxidative aging, and resistance to refrigerant R134a and its mixed media aging with ND11 oil were severely degraded, failing to meet the usage requirements. This shows that an appropriate amount of modified layered filler within 1 to 5 parts can meet the performance requirements.

[0102] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rubber sealing gasket compound, characterized in that, The rubber sealing gasket material, by weight, has the following composition: 80-100 parts of EPDM rubber 1-10 parts of ethylene-vinyl acetate rubber 20-100 parts of filler 1-5 parts of modified layered filler 2-8 parts zinc oxide 1-5 parts of coupling agent 2-8 parts plasticizer Processing aids 1-6 parts Anti-aging agent 2-6 parts 1-8 parts compatibilizer 1-6 parts of vulcanization accelerator 1-5 parts of vulcanizing agent; Among them, ethylene-vinyl acetate rubber is an ethylene-vinyl acetate copolymer rubber containing epoxy groups; The filler is a mixture of inorganic filler and unsaturated carboxylic acid metal salt; the inorganic filler is one or more of carbon black and silica; the modified layered filler is organic modified montmorillonite obtained by cation exchange modification of sodium-based montmorillonite with quaternary ammonium salt containing epoxy groups or surface modified talc obtained by surface grafting modification of talc with silane coupling agent; the compatibilizer is maleic anhydride-grafted polyolefin.

2. The rubber sealing gasket compound as described in claim 1, characterized in that, The ethylene propylene diene monomer (EPDM) rubber is specifically one or more of ENB-EPDM, VNB-EPDM, DCPD-EPDM, and HD-EPDM; the ethylene-vinyl acetate copolymer rubber containing epoxy groups is ethylene-vinyl acetate-glycidyl methacrylate copolymer rubber.

3. The rubber sealing gasket compound as described in claim 1, characterized in that, The unsaturated carboxylic acid metal salt is one or more combinations of zinc acrylate, zinc dimethacrylate, and magnesium methacrylate.

4. The rubber sealing gasket compound as described in claim 1, characterized in that, The coupling agent is a silane coupling agent; the plasticizer is one or more combinations of polyesters, trimellitic esters, and phthalates; the processing aid is one or more combinations of stearic acid and zinc stearate; and the antioxidant is one or more combinations of amines, phenols, heterocyclic compounds, phosphites, and protective waxes.

5. The rubber sealing gasket compound as described in claim 1, characterized in that, The compatibilizer is specifically maleic anhydride-grafted ethylene propylene diene monomer (MAH-g-EPDM).

6. The rubber sealing gasket compound as described in claim 1, characterized in that, The vulcanization accelerator is one or more combinations of trimethylolpropane triacrylate (TMPTA), ethylene glycol diacrylate (EGDA), trimethylolpropane trimethacrylate (TMPTMA), ethylene glycol dimethacrylate (EGDMA), zinc diacrylate (ZDA), zinc dimethacrylate (ZDMA), triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), and 1,2-polybutadiene (1,2-PBR). The vulcanizing agent is one or more of the following: dicumyl peroxide; 2,4-di-tert-butyl peroxide; 2,5-di(tert-butylperoxy)-2,5-dimethylhexane; 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn-3; m-di(tert-butylperoxy)diisopropylbenzene; p-di(tert-butylperoxy)diisopropylbenzene; dicumyl peroxide; 1,1-di(tert-butylperoxy)cyclohexane; n-butyl-4,4-di(tert-butylperoxy)valerate; ethyl-3,3-di(tert-butylperoxy)butyrate; and tert-butylperoxybenzoate.

7. The method for preparing the rubber sealing gasket compound according to any one of claims 1-6, characterized in that, The preparation method steps are as follows: (1) First, put EPDM rubber, ethylene-vinyl acetate rubber and compatibilizer into a mixer for plasticizing to obtain a uniformly mixed blend. (2) Weigh the filler and modified layered filler and mix them evenly in a mixer; then add the processing aid, antioxidant, coupling agent, zinc oxide, and half of the filler and modified layered filler that were mixed evenly in the mixer to the blend, and continue to mix. (3) When the internal mixer reaches 70~100℃, add the remaining half of the aforementioned filler and modified layered filler and plasticizer that are mixed evenly in the mixer, and mix until the temperature reaches 110~130℃. (4) Put the compound obtained in step (3) into the open mill, adjust the roller speed to 20~40r / min, then adjust the roller gap to 0.2~0.6mm, and use the turning machine to feed the material for 3~5 minutes; adjust the roller gap to 2~4mm and let it stand for 16~24 hours after the sheet is produced. (5) Adjust the roller gap of the open mill to 2~4mm, wrap the rollers, add vulcanization accelerator and vulcanizing agent again, mix evenly to obtain rubber sealing gasket material.

8. A metal-rubber composite sealing gasket, characterized in that, It comprises a metal skeleton and a rubber layer covering the metal skeleton, the rubber layer being formed by vulcanization of the rubber sealing gasket compound as described in any one of claims 1-6.

9. The metal-rubber composite sealing gasket according to claim 8, characterized in that, The preparation method of the metal-rubber composite sealing gasket is as follows: first, the metal is pretreated, and then the rubber sealing gasket material according to any one of claims 1-6 is vulcanized with the pretreated metal skeleton to obtain the metal-rubber sealing gasket material; wherein, the vulcanization pressure is 10~15MPa and the vulcanization temperature is 170~190℃.

10. The metal-rubber composite sealing gasket according to claim 8, characterized in that, A chemical bonding interface, primarily based on covalent bonds, is formed between the rubber part and the metal.

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