Flame-retardant and heat-conducting ethylene propylene diene monomer foaming sealing gasket and preparation method thereof

Abstract

The invention relates to a flame-retardant and heat-conducting EPDM (Ethylene-Propylene-Diene Monomer) foaming sealing gasket and a preparation method thereof and belongs to the technical field of rubber materials. The sealing gasket takes ethylene propylene diene monomer as a matrix, and the core is that 8-25 parts of expandable graphene grafted and modified by an epoxy silane coupling agent is added as a functional filler, and 10-30 parts of epoxidized soybean oil is matched as a bio-based active plasticizer. In a peroxide cross-linking system, the three components form an integrated cross-linking network through chemical reaction, so that the sealing gasket has good heat conductivity, flame retardance and stability. The preparation method is controllable in process and suitable for industrial production. The sealing gasket is suitable for new energy automobile battery packs, energy storage equipment and other occasions with comprehensive requirements for sealing, heat dissipation and fire prevention.

Description

Technical Field

[0001] This invention belongs to the field of rubber material technology and relates to a flame-retardant and thermally conductive EPDM foamed sealing gasket and its preparation method. Background Technology

[0002] Ethylene propylene diene monomer (EPDM) rubber is widely used in various applications requiring long-term sealing due to its excellent weather resistance, ozone resistance, and elasticity, such as new energy vehicle battery packs, electronic appliance housings, and building curtain walls. However, traditional EPDM foam gaskets have significant shortcomings in flame retardancy and heat dissipation, making it difficult to meet the growing demands for thermal management and fire safety in electronic devices. Existing technologies typically employ physical blending to add flame retardants (such as aluminum hydroxide and brominated flame retardants) or thermally conductive fillers (such as aluminum nitride and alumina) to improve the material's flame retardancy or thermal conductivity, respectively. While this method is simple, it often leads to a decline in the material's mechanical properties, processing difficulties, and the easy migration and precipitation of functional components, resulting in severe performance degradation after long-term use. It cannot simultaneously achieve flame retardancy, heat dissipation, elasticity, and long-term stability. For example, adding large amounts of flame-retardant fillers can significantly deteriorate the foam structure, affecting sealing performance; while the introduction of high thermal conductivity fillers often leads to material brittleness and decreased resilience.

[0003] To address these issues, researchers have attempted to utilize novel nanomaterials such as expandable graphene, leveraging its combined thermal conductivity and high-temperature expansion and flame-retardant properties. However, graphene exhibits poor dispersibility and agglomeration in rubber matrices, particularly in foaming systems, where its layered structure easily disrupts cell uniformity, leading to product performance degradation. Furthermore, conventional physical blending cannot resolve the migration issues of plasticizers and functional fillers, resulting in rapid performance degradation of products under aging conditions such as heat, oxygen, and other media, impacting service life and reliability.

[0004] Therefore, developing an EPDM foam sealing material that can synergistically achieve high-efficiency flame retardancy, active heat dissipation, excellent elasticity, and long-term stability has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant and thermally conductive EPDM foamed sealing gasket and its preparation method, which has both good flame-retardant and thermally conductive properties.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, the present invention provides a flame-retardant and thermally conductive EPDM rubber foam sealing gasket, the raw materials of which, by weight, include: 100 parts of EPDM rubber; 8-25 parts of surface-modified expandable graphene; 10-30 parts of bio-based plasticizer; 20-50 parts of reinforcing filler; 1-5 parts of peroxide crosslinking agent; 3-10 parts of chemical foaming agent; The surface-modified expandable graphene is prepared by grafting with an epoxy silane coupling agent.

[0007] As used in this text, "surface-modified expandable graphene" refers to the covalent grafting of an epoxy-based silane coupling agent onto the graphene surface via an acid-catalyzed hydrolysis-condensation reaction, which is the core functional filler of this invention. This modification not only improves the dispersibility of graphene in a hydrophobic rubber matrix, but more importantly, introduces active epoxy groups. This allows it to not only chemically bond with the EPDM rubber matrix through peroxide radical initiation, but also to produce synergistic effects at the molecular level with bio-based plasticizers that also have an epoxy structure.

[0008] The "expandable graphene" is a functional nanomaterial prepared from natural flake graphite through processes such as oxidation, intercalation, and exfoliation.

[0009] Preferably, the epoxy silane coupling agent is γ-glycidoxypropyltrimethoxysilane. This specific coupling agent is chosen for two reasons: First, the silanol groups generated after hydrolysis can undergo condensation reactions with oxygen-containing groups (such as -OH) on the surface of expandable graphene, achieving covalent grafting and thus establishing a strong chemical bridge between the graphene and the rubber matrix. Second, its epoxy groups share reactive homology with other epoxy compounds in the system (such as epoxidized soybean oil), and can synergistically participate in the construction of the peroxide-induced ring-opening crosslinking network.

[0010] Preferably, the bio-based plasticizer is epoxidized soybean oil. It is not only an environmentally friendly plasticizer but also an active crosslinking aid. The multiple epoxy groups on its molecular chain allow it to integrate into the rubber network through chemical reactions, thereby avoiding the migration loss of traditional plasticizers and achieving the dual purpose of plasticization and network flexibility. Simultaneously, its epoxy-epoxy interaction with modified graphene helps to form a more uniform composite material system.

[0011] Preferably, the reinforcing filler is a compound filler of carbon black and silica. Carbon black provides excellent reinforcing effect and certain thermal conductivity; silica (silica) can significantly improve the processing performance and tear strength of the rubber compound and reduce heat generation.

[0012] In the peroxide vulcanization system of this invention, the chemical reaction rate between the silanol groups on the surface of silica and the epoxy compounds (epoxidized soybean oil and epoxy silanes) is relatively low. The main interaction is the physical adsorption of free radicals, which has been compensated for by appropriately increasing the amount of peroxide. The possible trace chemical bonding helps to further improve the interfacial affinity between silica and the rubber matrix.

[0013] Preferably, the peroxide crosslinking agent is dicumyl peroxide (DCP). It is one of the most commonly used peroxide crosslinking agents for EPDM rubber. It can efficiently generate active free radicals and simultaneously initiate the carbon-hydrogen bond breaking and crosslinking of EPDM rubber as well as the ring-opening reaction of epoxy groups. It is the key initiator for constructing the chemical synergistic network.

[0014] Preferably, the chemical foaming agent is azodicarbonamide (AC) or 4,4'-oxobisbenzenesulfonyl hydrazine (OBSH). This helps to obtain closed-cell foam with uniform pores and a fine structure, maintaining the elasticity, sealing performance, and lightweight of the gasket.

[0015] The core mechanism of this invention is as follows: surface modification of expandable graphene is performed using an epoxy silane coupling agent to introduce active epoxy groups; under the initiation of free radicals generated by the peroxide crosslinking agent, the epoxy groups of the surface-modified expandable graphene and the epoxy groups of the bio-based plasticizer covalently bond with the EPDM rubber molecular chain, thereby constructing a three-dimensional chemical crosslinking network integrating "rubber-plasticizer-functional filler".

[0016] First, chemically bonded modified graphene becomes a stable functional node in the network, achieving uniform dispersion while efficiently constructing thermally conductive pathways and leveraging its flame-retardant properties through thermal expansion, thus integrating flame retardancy and heat dissipation. Second, bio-based plasticizers are anchored in the network through chemical action, preventing migration and volatilization and achieving long-term plasticization. Simultaneously, the chemical anchoring of graphene also prevents its aggregation and detachment, jointly ensuring the long-term stability of the material's mechanical and functional properties. Third, covalent bonds greatly enhance the interfacial bonding between components, enabling the material to maintain excellent foaming structure, high resilience, and low compression set even with the addition of high-functionality fillers, achieving an excellent balance between multifunctionality and basic mechanical properties.

[0017] Secondly, the present invention provides a method for preparing a flame-retardant and thermally conductive EPDM rubber foam sealing gasket, comprising the following steps: (1) EPDM rubber, bio-based plasticizer, reinforcing filler and the surface-modified expandable graphene are mixed to obtain a premixed rubber; (2) Then, the premixed rubber is added to the peroxide crosslinking agent and the chemical foaming agent, and mixed evenly to obtain the compounded rubber; (3) Place the compounded rubber in a mold preheated to 170-185°C, close the mold, and maintain an initial pressure of 12-18 MPa for 2-5 minutes; then reduce the pressure to 5-10 MPa and continue to maintain the pressure for 8-15 minutes. After demolding, the sealing gasket is obtained.

[0018] Preferably, in step (1), the mixing temperature is 90-110℃ and the mixing time is 4-6 minutes. Using a higher mixing temperature aims to fully plasticize the rubber and ensure good dispersion and wetting of fillers such as modified graphene.

[0019] Preferably, in step (2), the mixing temperature is 50-60℃. Adding the crosslinking agent and foaming agent at a lower temperature is to prevent the peroxide from decomposing prematurely and the foaming agent from foaming too early, thus ensuring processing safety and the storage stability of the rubber compound.

[0020] The first high pressure (12-18MPa) in step (3) mainly serves to inhibit the decomposition of the foaming agent in the early stage of vulcanization, ensure that the rubber compound fills the cavity densely, and create conditions for uniform nucleation.

[0021] The second stage, pressure reduction and holding (5-10 MPa): After the initial formation of the cross-linked network, provides adequate space to allow for the decomposition of the foaming agent and the controlled growth of cells. The temperature (170-185℃) at this stage can promote the synergistic occurrence of three key reactions: peroxide decomposition initiating cross-linking, epoxy group ring-opening reaction, and foaming agent (AC) decomposition.

[0022] Thirdly, the present invention provides a sealing assembly comprising the flame-retardant and thermally conductive EPDM foam sealing gasket described in the first aspect.

[0023] This sealing assembly is suitable for applications requiring comprehensive sealing, vibration reduction, fire resistance (flame retardancy), and heat dissipation. Examples include: battery pack enclosure sealing for new energy vehicles, waterproof and dustproof sealing for energy storage equipment cabinets, and housing sealing for high-power-density electronic devices.

[0024] The beneficial effects of this invention are: This invention constructs a chemically bonded "ternary synergistic network" to firmly anchor modified expandable graphene and epoxidized soybean oil within a rubber matrix, enabling the material to possess both highly efficient thermal conductivity pathways and excellent thermal expansion and flame-retardant properties. Simultaneously, this chemical network structure effectively improves plasticizer migration and filler detachment, protecting the material's performance under long-term aging conditions. Detailed Implementation

[0025] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0026] The expandable graphene can be prepared by chemical oxidation intercalation, exfoliation, and post-treatment steps of natural graphite or expandable graphite. For example: Take 5.0 g of expandable graphite, add 120 mL of concentrated sulfuric acid, and cool to below 5°C in an ice-water bath. Slowly add 15.0 g of potassium permanganate in portions, and after the addition is complete, react at 25°C for 2 hours. Then slowly add 250 mL of deionized water, and finally transfer to a 95°C water bath to react for 30 minutes. Slowly add 50 mL of 30% hydrogen peroxide solution. The resulting product is centrifuged, washed, and dried to obtain oxidized expandable graphene.

[0027] The surface-modified expandable graphene is prepared by the following steps: expanding graphene is dispersed in an ethanol-water solution, a silane coupling agent is added, and the reaction is carried out at 60-80℃ and under acidic conditions of pH 4-5 for 4-8 hours. After washing and drying, the graphene is obtained.

[0028] Unless otherwise specified, all raw materials and instruments used in the following examples and comparative examples are commercially available. The term "surface-modified expandable graphene" refers to a product obtained by grafting oxidized expandable graphene with γ-glycidyl etheroxypropyltrimethoxysilane (KH-560).

[0029] Example 1 A flame-retardant and thermally conductive EPDM foam sealing gasket includes: Raw material composition: 100 parts of EPDM 4045 rubber, 8 parts of surface-modified expandable graphene, 10 parts of epoxidized soybean oil, 10 parts of carbon black, 10 parts of silica, 1 part of dicumyl peroxide, and 3 parts of azodicarbonamide.

[0030] Preparation method: (1) Plasticize the raw EPDM rubber in a thin pass on a two-roll mill (roller temperature 100℃) for 2 minutes. Add epoxidized soybean oil, carbon black, silica and surface-modified expandable graphene in sequence, mix for 5 minutes until all components are evenly dispersed to obtain a premixed rubber. Sheet and cool.

[0031] (2) Second stage mixing: The premixed rubber is re-rolled on the open mill (roller temperature 55℃), dicumyl peroxide and foaming agent are added, and the mixture is mixed for 4 minutes until uniform to obtain the compounded rubber. Sheet it out and let it stand for later use.

[0032] (3) Compression molding vulcanization foaming: Cut an appropriate amount of the compound rubber and place it in a flat vulcanization mold preheated to 180°C. After closing the mold, apply a pressure of 15 MPa and hold the pressure for 3 minutes; then reduce the pressure to 7 MPa and continue to hold the pressure for 12 minutes.

[0033] After demolding, the sample is placed in a 150°C forced-air oven for 2 hours to obtain the flame-retardant and thermally conductive EPDM foam sealing gasket sample.

[0034] Example 2 A flame-retardant and thermally conductive EPDM foam sealing gasket includes: Raw material composition: 100 parts of EPDM 4045 rubber, 18 parts of surface-modified expandable graphene, 20 parts of epoxidized soybean oil, 15 parts of carbon black, 15 parts of silica, 3 parts of dicumyl peroxide, and 6 parts of 4,4'-oxobisbenzenesulfonyl hydrazine.

[0035] The preparation method is the same as in Example 1.

[0036] Example 3 A flame-retardant and thermally conductive EPDM foam sealing gasket includes: Raw material composition: 100 parts of EPDM 4045 rubber, 25 parts of surface-modified expandable graphene, 30 parts of epoxidized soybean oil, 15 parts of carbon black, 15 parts of silica, 5 parts of dicumyl peroxide, and 10 parts of 4,4'-oxobisbenzenesulfonyl hydrazine.

[0037] The preparation method is the same as in Example 1.

[0038] Comparative Example 1 Its formula is basically the same as that of Example 2, except that an equal amount of homologous unmodified expandable graphene is used instead of surface-modified expandable graphene.

[0039] The preparation method is the same as in Example 1.

[0040] Comparative Example 2 Its formula is basically the same as that of Example 2, except that an equal amount of dioctyl phthalate is used instead of epoxidized soybean oil.

[0041] The preparation method is the same as in Example 1.

[0042] Comparative Example 3 Its formulation is basically the same as that of Example 2, except that an equal amount of oxidized expandable graphene physically modified with titanate coupling agent (NDZ-201) is used instead of surface-modified expandable graphene.

[0043] The preparation method is the same as in Example 1.

[0044] Comparative Example 4 Its formula is basically the same as that of Example 2, except that no graphene filler is added, and its proportion is replaced by an equal amount of silica.

[0045] The preparation method is the same as in Example 1.

[0046] Performance testing: 1. Thermal conductivity test: Referring to ASTM D5470, a steady-state heat flow thermal conductivity meter was used. The sample was prepared into a flat sheet of specified thickness and placed between two temperature control plates. After thermal equilibrium was reached, the steady-state heat flux density passing through the sample, the sample thickness, and the temperature difference between the two sides were measured to calculate the thermal conductivity, expressed in W / (m·K).

[0047] 2. Vertical Burning Performance Test: The test is conducted according to the UL 94 V test method. A strip specimen is suspended vertically, with its lower end in contact with a flame at a specified height for a specified time, after which it is removed. The flaming time, flaming time, and whether the specimen ignites the cotton below are recorded. Based on the criteria in the standard, its flame retardancy rating (V-0, V-1, or V-2) is determined.

[0048] 3. Tensile strength test: According to GB / T 528-2009, the dumbbell-shaped specimen is stretched at a specified speed using a universal testing machine until it breaks. The maximum tensile force and the original cross-sectional area of ​​the specimen are recorded, and the tensile strength is calculated. The unit is expressed in MPa.

[0049] 4. Compression set test: Refer to GB / T 7759.1-2015. Hold the cylindrical specimen at the specified temperature (70℃) and compression rate (25%) for a certain time (22 hours). After unloading, allow it to recover at room temperature for a specified time and measure the percentage difference between the final thickness and the original thickness.

[0050] 5. Thermal Aging Performance Test: Place the sample in a thermal aging chamber at a specified temperature (125℃) for a continuous period of time (72 hours). After aging, remove the sample and acclimate it in a standard laboratory environment (23℃, 50% RH) for at least 16 hours, then test its tensile strength and thermal conductivity again. Calculate the performance retention rate as a percentage of the performance value after aging compared to the initial value.

[0051] Data from Examples 1-3 show that the thermal conductivity and flame retardancy of the material systematically increase as the amount of surface-modified expandable graphene increases from 8 parts to 25 parts. Comparative Example 1 demonstrates that without epoxy-based silane chemical grafting, graphene cannot effectively participate in network construction, resulting in weak interfacial bonding.

[0052] Comparative Example 3 showed an initial thermal conductivity close to that of Comparative Example 2, demonstrating that physical modification aids dispersion; however, its flame retardant rating (V-1) and key aging performance retention were reduced, proving that the performance advantage of this invention stems from the covalently cross-linked network constructed by epoxy groups, rather than simple physical dispersion. Comparative Example 2 highlights that epoxidized soybean oil can improve plasticization through chemical bonding. Comparative Example 4 almost completely lost its thermal conductivity and flame retardant properties, demonstrating that expandable graphene is the core component for achieving the dual functions of this invention.

[0053] This invention constructs a stable chemical bonding network through synergistic design involving epoxy silane modification, co-crosslinking of epoxidized soybean oil, and peroxide-induced modification, thereby obtaining a product that combines thermal conductivity, flame retardancy, mechanical properties, and stability.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A fire-retardant, heat-conductive, ethylene-propylene-diene rubber foamed gasket, characterized in that, Raw materials thereof include, by weight parts: Ethylene-propylene-diene rubber 100 parts; Surface-modified expandable graphene 8-25 parts; Bio-based plasticizer 10-30 parts; Reinforcing filler 20-50 parts; Peroxide crosslinking agent 1-5 parts; Chemical foaming agent 3-10 parts; The surface-modified expandable graphene is prepared by grafting modification with an epoxy silane coupling agent.

2. The fire-retardant, heat-conductive, EPDM foam gasket of claim 1, wherein, The epoxy silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

3. The fire-retardant, heat-conductive, EPDM foam gasket of claim 1, wherein, The bio-based plasticizer is epoxidized soybean oil.

4. The fire-retardant, heat-conductive, EPDM foam gasket of claim 1, wherein, The reinforcing filler is a compounded filler of carbon black and white carbon black.

5. The fire-retardant, heat-conductive, EPDM foam gasket of claim 1, wherein, The peroxide crosslinking agent is dicumyl peroxide.

6. The fire-retardant, heat-conductive, EPDM foam gasket of claim 1, wherein, The chemical foaming agent is azodicarbonamide or 4,4'-oxybisbenzenesulfonylhydrazide.

7. A method of making a flame-retardant, heat-conductive, EPDM foam gasket according to any one of claims 1-6, characterized in that, The method comprises the following steps: (1) mixing ethylene-propylene-diene rubber, bio-based plasticizer, reinforcing filler, and the surface-modified expandable graphene to obtain a premixed rubber; (2) then adding the premixed rubber to a peroxide crosslinking agent and a chemical foaming agent, and mixing uniformly to obtain a mixed rubber; (3) placing the mixed rubber in a mold preheated to 170-185°C, closing the mold, and maintaining an initial pressure of 12-18 MPa for 2-5 minutes; then reducing the pressure to 5-10 MPa, continuing to maintain the pressure for 8-15 minutes, and obtaining the sealing gasket after demolding.

8. The preparation method according to claim 7, characterized in that, In step (1), the mixing temperature is 90-110°C, and the mixing time is 4-6 minutes.

9. The preparation method according to claim 7, characterized in that, In step (2), the mixing temperature is 50-60°C.

10. A seal assembly characterized by, A flame-retardant and heat-conductive ethylene-propylene-diene rubber foamed sealing gasket comprising the sealing gasket according to any one of claims 1-6.

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