Anti-cracking fatigue-resistant low-temperature elastic air spring composite rubber material and preparation process thereof

Abstract

The present application relates to a kind of anti-cracking fatigue-resistant low-temperature elastic good air spring composite rubber material, by weight parts, including the following components: natural rubber (NR): 70-85 parts;Butadiene rubber (BR): 15-30 parts;Maleic anhydride grafting ethylene-propylene-diene rubber (EPDM-g-MAH): 10-15 parts;Brominated butyl rubber (BIIR): 3-8 parts, preferably 5 parts;Epoxy carbon nanotube: 5-10 parts;Reinforcing filler: 40-60 parts;Peroxide vulcanizing agent: 1.0-2.5 parts;Sulfur: 0.3-0.8 parts;Co-vulcanizing agent and active agent: 2-5 parts;Anti-aging system: 3-6 parts;Processing aid: 1-3 parts;Tackifying resin: 2-5 parts.The scheme strengthens the compatibility and interfacial adhesion between EPDM phase and NR / BR matrix.This makes EPDM phase long-term, stable ozone-resistant nature, from the root to eliminate the generation of surface cracking.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to an air spring rubber material for automobile suspension systems and its preparation method, specifically an air spring composite rubber material and its preparation process that combines excellent ozone crack resistance, dynamic fatigue resistance and low-temperature elasticity. Background Technology

[0002] As a core component of automotive suspension systems, air springs directly impact ride comfort, safety, and lifespan. Their rubber air bladders are constantly exposed to air, enduring high-frequency, high-amplitude dynamic stress and strain, and subjected to the combined effects of environmental factors such as ozone, oxygen, and alternating high and low temperatures. This makes them highly susceptible to ozone cracking on their surface and internal thermo-oxidative aging due to dynamic heat generation, ultimately leading to fatigue failure. In cold regions, the low-temperature embrittlement of rubber materials is particularly pronounced.

[0003] Currently, while air spring compounds primarily composed of natural rubber (NR) possess excellent fatigue heat generation properties and high strength, the large number of unsaturated double bonds in their molecular chains results in extremely poor ozone resistance. Conventional techniques employ a combination of physical protective waxes and chemical antioxidants, but their protective effect is limited under harsh ozone environments and continuous dynamic loads. Directly using ethylene propylene diene monomer (EPDM), known for its ozone resistance, is also problematic due to the poor compatibility and difficulty in co-curing between NR and EPDM, leading to a weak two-phase interface that severely impairs the material's mechanical properties, particularly its dynamic fatigue performance.

[0004] While existing technologies employ methods such as dynamic vulcanization and the addition of compatibilizers to improve NR / EPDM blends, problems remain, including complex processes, insufficient interfacial reinforcement, and insignificant reduction in dynamic heat generation. These limitations make it difficult to simultaneously meet the comprehensive requirements of high ozone resistance, high fatigue resistance, and low-temperature elasticity. Therefore, developing an air spring rubber material that combines these excellent properties has significant industrial application value. Summary of the Invention

[0005] The present invention proposes an air spring composite rubber material with good overall performance and feasible process, and its preparation process, which solves the problem that the air spring rubber material used in the prior art is difficult to achieve excellent ozone crack resistance, excellent dynamic fatigue resistance and good low temperature elasticity.

[0006] The technical solution of this invention is implemented as follows: A composite rubber material for air springs with good crack resistance, fatigue resistance, and low-temperature elasticity, characterized in that it comprises the following components by weight: Natural rubber (NR): 70-85 parts; Butadiene rubber (BR): 15-30 parts; Maleic anhydride-grafted EPDM-g-MAH: 10-15 parts; Brominated butyl rubber (BIIR): 3-8 parts; Epoxidized carbon nanotubes: 5-10 parts; Reinforcing filler: 40-60 parts; Peroxide vulcanizing agent: 1.0-2.5 parts; Sulfur: 0.3-0.8 parts; Vulcanizing agent and activator: 2-5 parts; Anti-aging system: 3-6 parts; Processing aids: 1-3 parts; Tackifying resin: 2-5 parts.

[0007] Furthermore, the natural rubber is SMR20 or SCR5 standard rubber; the butadiene rubber is the BR9000 series with a high cis-1,4 structure.

[0008] Furthermore, the epoxy group content of the epoxide carbon nanotubes is 3-8 wt%, the tube diameter is 10-30 nm, and the length is 5-20 μm.

[0009] Furthermore, the reinforcing filler is a compound system of highly dispersible silica and carbon black N330, wherein silica accounts for 30-60% of the total weight of the reinforcing filler.

[0010] Furthermore, the anti-aging system is a composite system of antioxidant 4020, antioxidant RD and microcrystalline wax, with a weight ratio of (1.5-2.5):1:(2-3).

[0011] Further, the peroxide vulcanizing agent is dicumyl peroxide (DCP) or bis-(tert-butylperoxide)benzene (BIPB); the vulcanizing co-agent is triallyl isocyanurate (TAIC) or trimethylolpropane trimethacrylate (TMPTMA).

[0012] Furthermore, the brominated butyl rubber comprises 5 parts by weight.

[0013] A preparation process for an air spring composite rubber material with good crack resistance, fatigue resistance, and low-temperature elasticity, characterized by the following steps: S1: First stage mixing: In an internal mixer, the natural rubber, butadiene rubber, brominated butyl rubber, and maleic anhydride-grafted EPDM rubber as described in any one of claims 1-7 are added sequentially and plasticized for 1-2 minutes; then half of the reinforcing filler, epoxidized carbon nanotubes, processing aids, and tackifying resin are added and mixed at 130-150°C for 3-5 minutes, and the glue is discharged to obtain a first stage masterbatch; S2: Two-stage mixing: Put the first-stage masterbatch and the remaining half of the reinforcing filler and anti-aging system into the internal mixer, mix at 140-155℃ for 3-4 minutes, discharge the glue, cool to room temperature, and obtain the second-stage masterbatch; S3: Thin pass processing on open mill: On an open mill with a roll gap of 0.5-1mm, thin pass 10 times to obtain three sections of masterbatch; S4: Final mixing and vulcanization: In a two-roll mill or a three-stage masterbatch at a temperature ≤100℃, add the peroxide vulcanizing agent, sulfur, vulcanizing aid and activator in sequence. After mixing evenly, pass through a thin sheet to obtain the final rubber. S5: Vulcanization molding: After filtering the final rubber compound, it is combined with the cord fabric and subjected to compression molding vulcanization at 160-170℃ and 10-20MPa pressure. The vulcanization time is 1.2-1.5 times the normal vulcanization time (t90) of the rubber compound to obtain the air spring product.

[0014] The final refining temperature in step S4 shall not exceed 100℃.

[0015] An air spring, characterized in that the air spring is made of the composite rubber material as described in any one of claims 1-7, or is prepared by the manufacturing process as described in any one of claims 8-9.

[0016] In summary, compared with the prior art, the air spring composite rubber material and its preparation process provided by the present invention, which have good crack resistance, fatigue resistance, and low-temperature elasticity, have the following significant advantages: Exceptional Ozone Cracking Resistance: The innovative design incorporates maleic anhydride-grafted ethylene propylene diene monomer (EPDM-g-MAH) with reactive functional groups. These MAH groups react with active sites or co-curing agents on the NR / BR molecular chain during vulcanization, achieving chemical bonding. This allows the ozone-resistant EPDM phase to be firmly bonded to the main rubber matrix through "chemical anchoring," rather than simple physical blending. The addition of brominated butyl rubber (BIIR) as a polymeric interfacial compatibilizer further enhances the compatibility and interfacial adhesion between the EPDM phase and the NR / BR matrix. This enables the EPDM phase to maintain its inherent ozone resistance for a long period, effectively preventing surface cracking at its source.

[0017] Excellent dynamic fatigue resistance and low heat generation: The addition of BR significantly improves the low-temperature elasticity of the rubber compound and reduces hysteresis loss. Epoxy carbon nanotubes are a key innovation: on the one hand, their nanotube structure has an extremely high aspect ratio and strength, providing excellent reinforcement; on the other hand, the epoxy groups on their surface can chemically react with the rubber molecular chains to form a robust "polymer-nanotube" interface, effectively dissipating energy and reducing internal friction during dynamic deformation, thereby significantly reducing dynamic heat generation. Combined with a peroxide / sulfur semi-effective vulcanization system, a stable three-dimensional network is constructed, mainly composed of strong CC crosslinking bonds supplemented by an appropriate amount of polysulfide bonds. The network has high strength and low stress relaxation, jointly ensuring the fatigue resistance of the material under long-term alternating loads.

[0018] Significant low-temperature performance: The NR / BR matrix itself has excellent low-temperature performance, and the addition of BIIR further improves the flexibility of the compound. The unique "chemically compatible" design avoids interfacial embrittlement caused by phase separation, ensuring that the material maintains high elasticity at low temperatures (such as -40℃), meeting the needs of use in cold regions.

[0019] High process feasibility: The preparation process of this invention is based on conventional rubber processing equipment. Through an optimized two-stage mixing process, it ensures good dispersion of key components such as epoxidized carbon nanotubes and EPDM-g-MAH, and avoids premature decomposition of peroxides. The process is stable and easy to realize industrial production. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example

[0021] This embodiment discloses a composite rubber material for air springs that is resistant to cracking, fatigue, and has good low-temperature elasticity. The formula, by weight, is as follows: Natural rubber (NR): 80 parts Butadiene rubber (BR): 20 parts Maleic anhydride-grafted EPDM-g-MAH: 10 parts Brominated Butyl Rubber (BIIR): 5 parts Epoxy carbon nanotubes: 5 parts Silica: 30 parts Carbon black N330: 20 parts Dicumyl peroxide (DCP): 1.5 parts Sulfur: 0.5 parts Triallyl isocyanurate (TAIC): 1.0 part Zinc oxide: 5 parts Stearic acid: 2 parts Anti-aging system (4020 / RD / wax): 2 / 1 / 2 parts Processing aid (zinc stearate): 2 parts Tackifying resin (p-tert-butylphenol resin): 2 parts Preparation process: S1: First stage mixing: In a Banbury mixer, natural rubber, butadiene rubber, brominated butyl rubber, and maleic anhydride-grafted EPDM rubber are added in sequence and plasticized for 1.5 minutes; then half the amount of silica, carbon black N330, all the epoxidized carbon nanotubes, processing aids and tackifying resin are added and mixed at 140°C for 4 minutes, and the glue is discharged to obtain the first stage masterbatch.

[0022] S2: Two-stage mixing: Put the first-stage masterbatch, the remaining half of the silica, carbon black N330, and the entire anti-aging system into a mixer and mix at 150°C for 3.5 minutes. Discharge the masterbatch and cool it to room temperature to obtain the second-stage masterbatch.

[0023] S3: Thin pass processing on open mill: On an open mill with a roll gap of 0.8mm, thin pass 10 times to obtain three sections of masterbatch.

[0024] S4: Final mixing and vulcanization: In a two-roll mill (roll temperature ≤ 90℃), add the three-stage masterbatch, followed by DCP, sulfur, TAIC, zinc oxide, and stearic acid in sequence. After mixing evenly, pass through a thin sheet to obtain the final rubber.

[0025] S5: Vulcanization molding: After filtering the final rubber, it is compounded with the cord fabric and molded and vulcanized at 165℃ and 15MPa pressure. The vulcanization time is 1.3 times that of t90 to obtain the air spring product. Example

[0026] The formula is basically the same as that in Example 1, except that: Maleic anhydride-grafted EPDM-g-MAH rubber: 12 parts Epoxidized carbon nanotubes: 7 parts Silica: 35 parts Carbon black N330: 15 parts DCP: 1.8 servings The remaining components and dosages are the same as in Example 1.

[0027] The preparation process is the same as in Example 1. Example

[0028] The recipe is as follows: Natural rubber (NR): 75 parts Butadiene rubber (BR): 25 parts Maleic anhydride-grafted EPDM-g-MAH rubber: 15 parts Brominated Butyl Rubber (BIIR): 5 parts Epoxy carbon nanotubes: 10 parts Silica: 40 parts Carbon black N330: 10 parts DCP: 2.0 copies Sulfur: 0.5 parts TAIC: 1.0 copy Zinc oxide: 5 parts Stearic acid: 2 parts Anti-aging system (4020 / RD / wax): 2 / 1 / 2 parts Processing aids: 2 parts Tackifying resin: 2 parts The preparation process is the same as in Example 1.

[0029] Comparative Example 1 (Simple blending of traditional NR / EPDM) The recipe is as follows: Natural rubber (NR): 80 parts Butadiene rubber (BR): 20 parts Plain EPDM (ungrafted): 10 copies Silica: 50 parts Sulfur: 2.5 parts Zinc oxide: 5 parts Stearic acid: 2 parts Anti-aging agent 4020: 2 parts Anti-aging agent RD: 1 part Microcrystalline wax: 2 parts Processing aids: 2 parts Tackifying resin: 2 parts It does not contain brominated butyl rubber, epoxidized carbon nanotubes, peroxide vulcanizing agents, or vulcanizing aids.

[0030] Preparation process: conventional two-stage mixing method, sulfur and accelerator are added during the final refining, and the vulcanization conditions are 151℃×90.

[0031] Comparative Example 2 (non-epoxy carbon nanotubes and BIIR) The recipe is as follows: Natural rubber (NR): 80 parts Butadiene rubber (BR): 20 parts Maleic anhydride-grafted EPDM-g-MAH rubber: 12 parts Silica: 50 parts DCP: 1.5 servings Sulfur: 0.5 parts TAIC: 1.0 copy Zinc oxide: 5 parts Stearic acid: 2 parts Anti-aging system (4020 / RD / wax): 2 / 1 / 2 parts Processing aids: 2 parts Tackifying resin: 2 parts No brominated butyl rubber or epoxidized carbon nanotubes are added.

[0032] The preparation process is the same as in Example 1.

[0033] Examples 1-3 and Comparative Examples 1-2 The formula composition is shown in Table 1.

[0034]

[0035] Comparative Example 1: NR as the main component, high sulfur vulcanization, and simple blending with ordinary EPDM.

[0036] Comparative Example 2: No epoxidized carbon nanotubes and brominated butyl rubber were added.

[0037] Examples 1-3: These are solutions of the present invention, the difference being the amount of epoxidized carbon nanotubes and EPDM-g-MAH used.

[0038] Table 1: Formulations of Examples and Comparative Examples (parts by weight) Preparation process: carried out according to the process described in the foregoing invention.

[0039] Performance testing: The above-mentioned rubber compounds were subjected to vulcanization characteristic tests, and samples were prepared according to standards. Their physical and mechanical properties, ozone aging resistance (40℃, 50pphm ozone concentration, 20% tensile strength, and observation of crack appearance time), dynamic compression heat generation (Goodrich fatigue testing machine, 55℃), and low-temperature resilience (TR test, -40℃) were tested. The results are shown in Table 2.

[0040] Table 2: Performance Test Results of Examples and Comparative Examples

[0041] Results analysis: Comparative Example 1 (Traditional Formula): Although it has high strength, it has extremely poor ozone resistance (cracking after 170h) and high dynamic heat generation (25℃).

[0042] Comparative Example 2 (without nanotubes and BIIR): Ozone resistance was significantly improved, but strength and tear strength decreased, and dynamic heat generation was only reduced (22°C), indicating insufficient interface strengthening and heat generation control.

[0043] Examples 1-3 (of this invention): While maintaining excellent mechanical properties, ozone resistance reached over 1000 hours without cracking, dynamic compression fatigue temperature rise was significantly reduced to 15-18℃, and low-temperature resilience was excellent. Among them, Example 2 showed the best overall performance, achieving the optimal balance of crack resistance, fatigue resistance, low heat generation, and low-temperature elasticity.

[0044] In summary, this invention, through the synergistic design concept of "reactive compatibility" and "nano-reinforcement / friction reduction" and supplemented by an optimized composite vulcanization system, has successfully prepared an air spring rubber material with excellent comprehensive performance, which is particularly suitable for use in harsh environments and has broad application prospects.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite rubber material for air springs with good crack resistance, fatigue resistance, and low-temperature elasticity, characterized in that, By weight, it comprises the following components: Natural rubber (NR): 70-85 parts; Butadiene rubber (BR): 15-30 parts; Maleic anhydride-grafted EPDM-g-MAH: 10-15 parts; Brominated butyl rubber (BIIR): 3-8 parts; Epoxidized carbon nanotubes: 5-10 parts; Reinforcing filler: 40-60 parts; Peroxide vulcanizing agent: 1.0-2.5 parts; Sulfur: 0.3-0.8 parts; Vulcanizing agent and activator: 2-5 parts; Anti-aging system: 3-6 parts; Processing aids: 1-3 parts; Tackifying resin: 2-5 parts.

2. The air spring composite rubber material according to claim 1, characterized in that, The natural rubber is SMR20 or SCR5 standard rubber; the butadiene rubber is the BR9000 series with high cis-1,4 structure.

3. The air spring composite rubber material according to claim 1, characterized in that, The epoxide carbon nanotubes have an epoxy group content of 3-8 wt%, a diameter of 10-30 nm, and a length of 5-20 μm.

4. The air spring composite rubber material according to claim 1, characterized in that, The reinforcing filler is a compound system of highly dispersible silica and carbon black N330, wherein silica accounts for 30-60% of the total weight of the reinforcing filler.

5. The air spring composite rubber material according to claim 1, characterized in that, The anti-aging system is a composite system of antioxidant 4020, antioxidant RD and microcrystalline wax, with a weight ratio of (1.5-2.5):1:(2-3).

6. The air spring composite rubber material according to claim 1, characterized in that, The peroxide vulcanizing agent is dicumyl peroxide (DCP) or bis-(tert-butylperoxide)benzene (BIPB); the co-vulcanizing agent is triallyl isocyanurate (TAIC) or trimethylolpropane trimethacrylate (TMPTMA).

7. The air spring composite rubber material according to claim 1, characterized in that, The brominated butyl rubber is present in 5 parts by weight.

8. A preparation process for a composite rubber material for air springs with good crack resistance, fatigue resistance, and low-temperature elasticity, characterized in that, Includes the following steps: S1: First stage mixing: In an internal mixer, the natural rubber, butadiene rubber, brominated butyl rubber, and maleic anhydride-grafted EPDM rubber as described in any one of claims 1-7 are added sequentially and plasticized for 1-2 minutes; then half of the reinforcing filler, epoxidized carbon nanotubes, processing aids, and tackifying resin are added and mixed at 130-150°C for 3-5 minutes, and the glue is discharged to obtain a first stage masterbatch; S2: Two-stage mixing: Put the first-stage masterbatch and the remaining half of the reinforcing filler and anti-aging system into the internal mixer, mix at 140-155℃ for 3-4 minutes, discharge the glue, cool to room temperature, and obtain the second-stage masterbatch; S3: Thin pass processing on open mill: On an open mill with a roll gap of 0.5-1mm, thin pass 10 times to obtain three sections of masterbatch; S4: Final mixing and vulcanization: In a two-roll mill or a three-stage masterbatch at a temperature ≤100℃, add the peroxide vulcanizing agent, sulfur, vulcanizing aid and activator in sequence. After mixing evenly, pass through a thin sheet to obtain the final rubber. S5: Vulcanization molding: After filtering the final rubber compound, it is combined with the cord fabric and subjected to compression molding vulcanization at 160-170℃ and 10-20MPa pressure. The vulcanization time is 1.2-1.5 times the normal vulcanization time (t90) of the rubber compound to obtain the air spring product.

9. The preparation process of the air spring composite rubber material with good crack resistance, fatigue resistance, and low-temperature elasticity according to claim 8, characterized in that, The final refining temperature in step S4 shall not exceed 100℃.

10. An air spring, characterized in that, The air spring is made of the composite rubber material described in any one of claims 1-7, or by the preparation process described in any one of claims 8-9.

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