Rubber compound for lightweight EPDM (Ethylene-Propylene-Diene Monomer) sealing strip and preparation process thereof

Abstract

The invention relates to the field of rubber materials, in particular to a rubber compound for a lightweight EPDM (Ethylene-Propylene-Diene Monomer) sealing strip and a preparation process of the rubber compound. The rubber compound for the light-weight EPDM sealing strip at least comprises the following raw materials in parts by mass: 90-130 parts of EPDM raw rubber, 15-25 parts of a rubber composition, 40-60 parts of reinforcing filler, 25-35 parts of a softening plasticizer, 1.5-4.5 parts of a cross-linking agent and 3-6 parts of a foaming agent. The finally prepared rubber compound for the light-weight EPDM sealing strip can maintain excellent physical and mechanical properties and processing stability, has good material corrosion resistance, water resistance, moisture resistance and other properties, still has good comprehensive properties such as elasticity and aging resistance on the premise of maintaining light weight, and is suitable for popularization and application. Therefore, the ever-increasing requirements of modern industry on high-performance sealing materials are met.

Description

Technical Field

[0001] This application relates to the field of rubber materials, and more specifically to a lightweight EPDM sealing strip compound and its preparation process. Background Technology

[0002] With the continuous development of modern industrial technology, sealing materials are increasingly widely used in transportation vehicles, construction, and other fields, and the requirements for sealing performance, durability, and material cost are constantly increasing. Among many sealing materials, ethylene propylene diene monomer (EPDM) rubber has become one of the preferred materials for manufacturing sealing strips due to its excellent weather resistance, ozone resistance, and heat resistance. EPDM sealing strips are widely used in doors, windows, curtain walls, and automobile bodies, playing a role in waterproofing, dustproofing, sound insulation, and shock absorption. In order to meet practical applications, EPDM raw rubber is usually mixed with various fillers, vulcanizing agents, plasticizers, antioxidants, and other additives through a compounding process to prepare a stable compound, which is then formed into the final sealing strip product through extrusion, vulcanization, and other processes.

[0003] Currently, most mainstream EPDM sealing strip compounds on the market employ high-filler systems to reduce costs and improve processing performance. Commonly used fillers such as carbon black, calcium carbonate, and talc are added in large quantities to the compound. Simultaneously, to improve the flowability and vulcanization characteristics of the compound, appropriate amounts of plasticizers and processing aids are usually added. However, while high filler content reduces raw material costs to some extent, it also leads to problems such as increased compound density, decreased elasticity, and increased compression set, affecting the resilience and long-term sealing performance of the sealing strip. Furthermore, traditional formulation systems often rely on high rubber content and complex additive combinations to maintain physical and mechanical properties, resulting in a large overall weight of the compound, which is not conducive to lightweight design requirements.

[0004] In recent years, although some studies have attempted to improve the overall performance of EPDM compounds by introducing novel reinforcing fillers or optimizing vulcanization systems, practical applications still face problems such as poor dispersibility, high processing difficulty, and significant cost increases. Furthermore, most existing EPDM compound formulations still fall short in ensuring good extrusion surface finish and dimensional stability, easily leading to process defects such as scorching, extrusion distortion, or uneven vulcanization, which in turn affect the appearance quality and installation compatibility of sealing strips. More importantly, many current EPDM compound systems struggle to balance lightweighting with maintaining excellent mechanical properties. Summary of the Invention

[0005] In summary, existing EPDM sealing strip compound technologies still face significant technical bottlenecks in terms of overall performance, including material corrosion resistance, waterproofing, moisture resistance, physical and mechanical properties, and processing stability, making it a crucial challenge for those skilled in the art. This application proposes a lightweight EPDM sealing strip compound and its preparation process. The resulting lightweight EPDM sealing strip compound maintains excellent physical and mechanical properties and processing stability while retaining good corrosion resistance, waterproofing, and moisture resistance. Furthermore, it maintains a lightweight profile while exhibiting good elasticity and aging resistance, thus meeting the growing demand for high-performance sealing materials in modern industry.

[0006] A lightweight EPDM sealing strip compound, by weight, comprises at least the following raw materials: 90-130 parts of EPDM raw rubber, 15-25 parts of rubber composition, 40-60 parts of reinforcing filler, 25-35 parts of softening plasticizer, 1.5-4.5 parts of crosslinking agent, and 3-6 parts of foaming agent.

[0007] Preferably, the mass ratio of the EPDM raw rubber, the rubber composition, and the softening plasticizer is (10~12):(1.7~2.1):(2.6~3).

[0008] Preferably, the mass ratio of the EPDM raw rubber, the rubber composition, and the softening plasticizer is (10.5~11):(1.9~2):(2.6~2.8).

[0009] Preferably, the rubber composition is a combination of brominated butyl rubber and hydrogenated carboxylated nitrile rubber.

[0010] Preferably, the mass ratio of the brominated butyl rubber to the hydrogenated carboxylated nitrile rubber is (6~8):(1.5~2.5).

[0011] Preferably, the mass ratio of the brominated butyl rubber to the hydrogenated carboxylated nitrile rubber is (6~7):(1.5~2).

[0012] Preferably, the brominated butyl rubber is Bromobutyl 2222, manufactured by ExxonMobil, USA.

[0013] Preferably, the hydrogenated carboxylated nitrile rubber is Zetpol 4310, manufactured by Zeon Corporation of Japan.

[0014] The addition of brominated butyl rubber and hydrogenated carboxylated nitrile rubber in this application is ingeniously complementary. While achieving material lightweighting, it not only does not weaken the core performance of the EPDM matrix, but also significantly enhances its overall performance. In particular, the combination of these two specific types of raw materials undergoes partial compatibility and chain segment entanglement during the mixing process, forming a reinforced structural network with EPDM as the continuous phase. This network effectively blocks the penetration of small molecules such as water vapor and corrosive gases, thereby greatly improving the material's waterproof, moisture-resistant, and corrosion-resistant properties. Furthermore, the other component bears and disperses external stress, thus maintaining a high-strength skeletal support while ensuring a sufficiently lightweight compound, ultimately ensuring strong and robust overall performance.

[0015] Preferably, the reinforcing filler is precipitated silica or spherical calcium carbonate.

[0016] Preferably, the reinforcing filler is precipitated silica.

[0017] Preferably, the average particle size of the precipitated silica is 400~600 nm.

[0018] Preferably, the softening plasticizer is at least one selected from naphthenic oil, paraffin oil, dioctyl phthalate, dioctyl adipate, and vegetable oil.

[0019] Preferably, the softening plasticizer is paraffin oil and / or dioctyl phthalate.

[0020] Preferably, the softening plasticizer is paraffin oil.

[0021] Preferably, the crosslinking agent is dicumyl peroxide or benzoyl peroxide.

[0022] Preferably, the foaming agent is at least one selected from 4,4'-oxobis(benzenesulfonyl)hydrazine, azodicarbonamide, p-toluenesulfonyl hydrazine, and 5-phenyltetrazole.

[0023] Preferably, the foaming agent is 4,4'-oxobisbenzenesulfonylhydrazine or azodicarbonamide.

[0024] Preferably, the foaming agent is azodicarbonamide.

[0025] Preferably, the lightweight EPDM sealing strip compound, by weight, further comprises: 8-15 parts of functional resin, 2-5 parts of crosslinking agent, 1-3 parts of antioxidant, and 2-4 parts of processing aid.

[0026] Preferably, the mass ratio of the EPDM raw rubber to the functional resin is (10~12):(0.9~1.3).

[0027] Preferably, the mass ratio of the EPDM raw rubber to the functional resin is (10.5~11):(1~1.1).

[0028] Preferably, the functional resin is a composition of liquid silane-modified end-capped polyether and hydrogenated cycloalkane resin.

[0029] Preferably, the mass ratio of the liquid silane-modified end-capped polyether to the hydrogenated cycloalkane resin is (3~4):(5~7).

[0030] Preferably, the mass ratio of the liquid silane-modified end-capped polyether to the hydrogenated cycloalkane resin is (3.2~3.5):(6~6.5).

[0031] Preferably, the liquid silane-modified end-capped polyether is S203H, manufactured by Beyotime Biotechnology, China.

[0032] Preferably, the hydrogenated cycloalkane resin is Regalite R9100, manufactured by Eastman Chemical Company of the United States.

[0033] By adding two raw materials to the functional resin, the weather resistance, corrosion resistance, and long-term waterproofing of the compound are significantly improved while maintaining its lightweight properties. During vulcanization, these two components physically entangle and weakly chemically interact with the EPDM polymer chains, acting as internal plasticizers and interfacial bridges within the rubber matrix. They also form a hydrophobic and flexible molecular layer on the material surface, effectively blocking water molecule penetration. Simultaneously, the hydrogenated cycloalkane resin, as a thermoplastic tackifying resin, not only improves processing fluidity, but its saturated cyclic structure also acts as a protective structure, uniformly dispersed in the compound. Together with the silane raw material, it constructs a continuous protective network, absorbing and dissipating ultraviolet light energy and thermal stress, significantly improving phenomena such as material cracking, hardening, and sealing failure caused by environmental aging.

[0034] Preferably, the crosslinking agent is triallyl isocyanurate or zinc dimethacrylate.

[0035] Preferably, the crosslinking agent is triallyl isocyanurate.

[0036] Preferably, the antioxidant is tris(2,4-di-tert-butylphenyl) phosphite or 2,2'-methylenebis(4-methyl-6-tert-butylphenol).

[0037] Preferably, the antioxidant is tris(2,4-di-tert-butylphenyl) phosphite.

[0038] Preferably, the processing aid is at least one of polyethylene wax, fatty alcohol polyoxyethylene ether, erucamide, and oleamide.

[0039] Preferably, the processing aid is a combination of polyethylene wax and erucamide.

[0040] Preferably, the mass ratio of the polyethylene wax to erucamide is (1.5~2.5):(0.4~0.8).

[0041] Preferably, the mass ratio of the polyethylene wax to erucamide is (1.8~2):(0.5~0.6).

[0042] A preparation process for a lightweight EPDM sealing strip compound includes the following steps: S1: Mixing EPDM raw rubber in an internal mixer at 60-65℃ for 2-3 minutes, then sequentially adding functional resin, reinforcing filler, softening plasticizer, antioxidant, and processing aid. After all materials are added, mixing is carried out at 70-100℃ for 4-5 minutes. After completion, the masterbatch is discharged and transferred to a two-roll mill; S2: Cooling the masterbatch on the two-roll mill by wrapping it with rollers. After the roller temperature stabilizes at 60-65℃, the remaining raw materials are added and mixed. Then, the mixture is transferred back to the internal mixer and mixed at 50-70℃ for 2-3.5 minutes. When the temperature inside the mill reaches 85-95℃, the masterbatch is discharged immediately; S3: After discharge, the rubber compound is thinly passed through a triangular loop 6-8 times to homogenize the discharged compound and remove air bubbles. Finally, it is sheeted to obtain the final product.

[0043] The beneficial effects of this application are: 1. The lightweight EPDM sealing strip compound finally obtained in this application can maintain excellent physical and mechanical properties and processing stability, while also possessing good material corrosion resistance, waterproof and moisture resistance, and good elasticity and aging resistance while maintaining lightweight properties. This provides a solution to the existing problems of lightweight compound technology and meets the growing demand of modern industry for high-performance sealing materials.

[0044] 2. The addition of brominated butyl rubber and hydrogenated carboxylated nitrile rubber in this application is ingeniously complementary. While achieving material lightweighting, it does not weaken the core performance of the EPDM matrix, but rather significantly enhances its comprehensive performance. Together, they form a reinforced structural network with EPDM as the continuous phase, which can effectively block the penetration of small molecules such as water vapor and corrosive gases, thereby greatly improving the waterproof, moisture-resistant and corrosion-resistant properties of the material. On the other hand, it can also bear and disperse external stress, thus maintaining a high-strength skeleton support while ensuring that the rubber compound is sufficiently lightweight, ultimately ensuring strong and powerful comprehensive performance.

[0045] 3. The addition of the two functional resin raw materials in this application significantly improves the weather resistance, corrosion resistance and long-term waterproofing ability of the sealing strip while maintaining the lightweight characteristics of the rubber compound. During the vulcanization process, these two components can physically entangle and weakly chemically interact with the EPDM polymer chains, playing the role of internal plasticizer and interface bridging in the rubber matrix. They also form a hydrophobic and flexible molecular layer on the material surface, effectively blocking the penetration of water molecules. Together with the silane raw material, they form a continuous protective network, significantly improving the phenomena of material cracking, hardening and sealing failure caused by environmental aging, thereby giving the sealing strip excellent and durable comprehensive protective performance in harsh environments. Detailed Implementation

[0046] (1) Example 1 A lightweight EPDM sealing strip compound, by weight, comprises: 110 parts EPDM raw rubber, 20 parts rubber composition, 45 parts reinforcing filler, 26.5 parts softening plasticizer, 3.2 parts crosslinking agent, 4.2 parts foaming agent, 10 parts functional resin, 2.8 parts co-crosslinking agent, 1.5 parts antioxidant, and 2.6 parts processing aid.

[0047] The EPDM raw rubber is TER4038, made by LVE from South Korea.

[0048] The rubber composition is a combination of brominated butyl rubber and hydrogenated carboxylated nitrile butadiene rubber in a mass ratio of 7:2. The brominated butyl rubber is Bromobutyl 2222, manufactured by ExxonMobil, USA; the hydrogenated carboxylated nitrile butadiene rubber is Zetpol 4310, manufactured by Zeon, Japan.

[0049] The reinforcing filler is precipitated silica with an average particle size of 500 nm.

[0050] The softening plasticizer is paraffin oil; the crosslinking agent is dicumyl peroxide; the foaming agent is azodicarbonamide; the co-crosslinking agent is triallyl isocyanurate; and the antioxidant is tris(2,4-di-tert-butylphenyl) phosphite.

[0051] The functional resin is a composition of liquid silane-modified end-capped polyether and hydrogenated cycloalkane resin in a mass ratio of 3.5:6.5. The liquid silane-modified end-capped polyether is S203H, manufactured by Beyotime Biotechnology, China; the hydrogenated cycloalkane resin is Regalite R9100, manufactured by Eastman Chemical Company, USA.

[0052] The processing aid is a composition of polyethylene wax and erucamide in a mass ratio of 2:0.6.

[0053] A preparation process for a lightweight EPDM sealing strip compound includes the following steps: S1: EPDM raw rubber is mixed in an internal mixer at 65°C for 3 minutes. Then, functional resin, reinforcing filler, softening plasticizer, antioxidant, and processing aid are added sequentially. After all materials are added, the mixture is mixed at 85°C for 4 minutes. After completion, the rubber is discharged to obtain masterbatch, which is then transferred to a two-roll mill. S2: The masterbatch is cooled by wrapping it with rollers on the two-roll mill. After the roller temperature stabilizes at 65°C, the remaining raw materials are added and mixed. Then, the mixture is transferred back to the internal mixer and mixed at 60°C for 3 minutes. When the temperature inside the mill reaches 90°C, the rubber is discharged immediately. S3: After discharge, the rubber compound is thinly passed through a triangular loop 6-8 times to homogenize the discharged rubber compound and remove air bubbles. Finally, the rubber is sheeted to obtain the final product.

[0054] (2) Example 2 This embodiment differs from Embodiment 1 only in the following aspects: A lightweight EPDM sealing strip compound, by weight, comprises the following raw materials: 100 parts EPDM raw rubber, 17.5 parts rubber composition, 45 parts reinforcing filler, 29 parts softening plasticizer, 3.2 parts crosslinking agent, 4.2 parts foaming agent, 10 parts functional resin, 2.8 parts co-crosslinking agent, 1.5 parts antioxidant, and 2.6 parts processing aid.

[0055] The remaining implementation methods are the same.

[0056] (3) Example 3 This embodiment differs from Embodiment 1 only in the following aspects: A lightweight EPDM sealing strip compound, by weight, comprises the following raw materials: 120 parts EPDM raw rubber, 20 parts rubber composition, 45 parts reinforcing filler, 26.5 parts softening plasticizer, 3.2 parts crosslinking agent, 4.2 parts foaming agent, 9 parts functional resin, 2.8 parts co-crosslinking agent, 1.5 parts antioxidant, and 2.6 parts processing aid.

[0057] The remaining implementation methods are the same.

[0058] (4) Comparative Example 1 This comparative example differs from Example 1 only in the following aspects: A lightweight EPDM sealing strip compound, by weight, comprises: 110 parts EPDM raw rubber, 9.5 parts rubber composition, 45 parts reinforcing filler, 26.5 parts softening plasticizer, 3.2 parts crosslinking agent, 4.2 parts foaming agent, 13 parts functional resin, 2.8 parts co-crosslinking agent, 1.5 parts antioxidant, and 2.6 parts processing aid.

[0059] The remaining implementation methods are the same.

[0060] (5) Comparative Example 2 This comparative example differs from Example 1 only in the following aspects: A lightweight EPDM sealing strip compound, by weight, comprises: 110 parts EPDM raw rubber, 25 parts rubber composition, 45 parts reinforcing filler, 26.5 parts softening plasticizer, 3.2 parts crosslinking agent, 4.2 parts foaming agent, 4.5 parts functional resin, 2.8 parts co-crosslinking agent, 1.5 parts antioxidant, and 2.6 parts processing aid.

[0061] The remaining implementation methods are the same.

[0062] (6) Comparative Example 3 The only difference between this comparative example and Example 1 is that the functional resin is a composition of liquid silane-modified end-capped polyether and hydrogenated cycloalkane resin in a mass ratio of 5:3.

[0063] The remaining implementation methods are the same.

[0064] (7) Comparative Example 4 The only difference between this comparative example and Example 1 is that the functional resin is a composition of liquid silane-modified end-capped polyether and hydrogenated cycloalkane resin in a mass ratio of 1:9.

[0065] The remaining implementation methods are the same.

[0066] (8) Comparative Example 5 The only difference between this comparative example and Example 1 is that the rubber composition is a combination of brominated butyl rubber and hydrogenated carboxylated nitrile rubber in a mass ratio of 8.5:0.5.

[0067] The remaining implementation methods are the same.

[0068] (9) Comparative Example 6 This comparative example differs from Example 1 only in the following way: the rubber composition is a combination of brominated butyl rubber and hydrogenated carboxylated nitrile rubber in a mass ratio of 1:2.

[0069] The remaining implementation methods are the same.

[0070] (10) Comparative Example 7 The only difference between this comparative example and Example 1 is that the reinforcing filler is kaolin with an average particle size of 0.2 μm.

[0071] The remaining implementation methods are the same.

[0072] Performance testing 1. Density test: The compound rubber products prepared in the examples and comparative examples were tested with a density meter, and the average value of 10 density tests was recorded in Table 1.

[0073] 2. Mechanical properties: The test was conducted in accordance with ISO 37. The results were the average of 10 tests for tensile strength and elongation at break, and recorded in Table 1.

[0074] 3. Compression set: The test is conducted according to ISO 815-1, and the results are the average of 10 tests and recorded in Table 1.

[0075] 4. Hot air aging: The test is conducted according to ISO 188, and the result is the average of 10 tests of tensile strength change rate, which is recorded in Table 1.

[0076] 5. Liquid resistance: The test is conducted in accordance with ISO 1817. The results are the average of 10 tests of volume expansion rate in standard oil No. 1 and recorded in Table 1.

[0077] Table 1 Performance Test Results

[0078] Examples 1-3 demonstrate superior performance compared to Comparative Examples 1-7. The functional resins and rubber compositions used in these examples, as defined in this application, work in conjunction with other technical solutions. This not only avoids the performance contradictions inherent in the EPDM rubber system but also significantly enhances its overall performance. A continuous, reinforced structural network is constructed, effectively blocking the penetration of small molecules such as water vapor and corrosive gases. Furthermore, the physical entanglement and weak chemical interactions of the polymer chains act as internal plasticizers and interfacial bridges within the rubber matrix. A hydrophobic and flexible molecular layer is formed on the material surface, effectively preventing water molecule penetration. Together with the silane raw material, a continuous protective network is constructed, significantly improving phenomena such as material cracking, hardening, and sealing failure caused by environmental aging. This endows the sealing strip with excellent and durable comprehensive protective performance under harsh environments. In contrast, Comparative Examples 1-7 employ different non-defined technical solutions, resulting in a significant reduction in the technical effects of their respective solutions within the system, and a marked weakening of their effectiveness, ultimately affecting the overall comprehensive performance of the compound.

Claims

1. A millbase for light weight EPDM weather stripping, characterized by: The raw materials include, in parts by mass, EPDM raw rubber 90-130, rubber composition 15-25, reinforcing filler 40-60, softening plasticizer 25-35, crosslinking agent 1.5-4.5, and foaming agent 3-6. The rubber composition is a combination of brominated butyl rubber and hydrogenated carboxyl nitrile rubber, with a mass ratio of (6-8):(1.5-2.5).

2. The compound for light-weight EPDM weather stripping according to claim 1, characterized in that: The mass ratio of the EPDM raw rubber, rubber composition and softening plasticizer is (10-12):(1.7-2.1):(2.6-3).

3. The compound for light-weight EPDM weather stripping according to claim 2, characterized in that: The reinforcing filler is precipitated white carbon black or spherical calcium carbonate.

4. The compound for light-weight EPDM weather stripping according to claim 3, characterized in that: The softening plasticizer is at least one of naphthenic oil, paraffin oil, dioctyl phthalate, dioctyl adipate and vegetable oil.

5. The compound for light-weight EPDM weather stripping according to claim 4, characterized in that: The crosslinking agent is dicumyl peroxide or benzoyl peroxide.

6. The compound for light-weight EPDM weather stripping according to claim 1, wherein: The raw materials for the light-weight EPDM sealing strip compound further include, in parts by mass, functional resin 8-15, auxiliary crosslinking agent 2-5, antioxidant 1-3 and processing aid 2-4.

7. The compound for light-weight EPDM weather stripping according to claim 6, characterized in that: The mass ratio of the EPDM raw rubber and functional resin is (10-12):(0.9-1.3).

8. The compound for light-weight EPDM weather stripping according to claim 7, characterized in that: The functional resin is a combination of liquid silane-modified capped polyether and hydrogenated naphthenic hydrocarbon resin, with a mass ratio of (3-4):(5-7).

9. The compound for light-weight EPDM weather stripping according to claim 8, characterized in that: The auxiliary crosslinking agent is triallyl isocyanurate or zinc dimethyl acrylate.

10. A process for the preparation of a compound according to any one of claims 6 to 9, characterized in that: The method specifically includes the following steps: S1: The EPDM raw rubber is mixed in a Banbury mixer at 60-65℃ for 2-3 min, and then the functional resin, reinforcing filler, softening plasticizer, antioxidant and processing aid are added in sequence. After all the materials are added, mixing is carried out at 70-100℃ for 4-5 min, and then the compound is discharged to complete the masterbatch, which is then moved to an open mill; S2: The masterbatch is cooled by roller wrapping in the open mill, and after the roller temperature stabilizes at 60-65℃, the remaining raw materials are mixed and then moved back to the Banbury mixer for mixing at 50-70℃ for 2-3.5 min. When the temperature in the mixer reaches 85-95℃, the compound is immediately discharged; S3: After the compound is discharged, the compound is thinned, and the triangular bag is punched 6-8 times to homogenize the compound and remove air bubbles, and then the compound is sheeted.

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