High-temperature-resistant and flame-retardant cable sheath material for aviation cables and preparation method thereof

Abstract

The application discloses a high-temperature-resistant flame-retardant cable sheath material for aviation cables and a preparation method thereof, which is composed of the following components in parts by weight: 30-60 parts of terpolymer EPDM, 20-50 parts of ethylene-vinyl acetate copolymer, 80-150 parts of aluminum hydroxide, 50-100 parts of magnesium hydroxide, 5-15 parts of zinc borate, 3-10 parts of organic modified montmorillonite, 1-3 parts of composite antioxidant, and 2-6 parts of dicumyl peroxide; S1 mixing in an internal mixer: the components are put into an internal mixer for plasticizing to obtain a mixed rubber; S2 thin pass in an open mill: the mixed rubber is transferred to an open mill, multiple thin passes are performed by adjusting the roll gap, and the rubber sheet is obtained after the bubbles are discharged; S3 extrusion molding: the rubber sheet is put into an extruder, and after being melted and plasticized, the rubber sheet is extruded and coated outside the conductor to form a sheath layer; and S4 radiation crosslinking: the extruded cable is sent into an electron accelerator for electron beam radiation crosslinking to obtain a finished cable sheath; the mechanical property retention rate is high after high-temperature aging, and the high-temperature service life of the aviation cable is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of wire and cable materials technology, specifically to high-temperature resistant and flame-retardant cable sheathing material for aviation cables and its preparation method. Background Technology

[0002] Aviation cables, acting as the "neural network" of aircraft electrical systems, are widely used in engine areas, landing gear, wing wiring, and avionics equipment. Their working environment is characterized by extreme conditions such as high temperature, vibration, oil contamination, and electromagnetic interference. Therefore, stringent technical specifications are imposed on cable sheath materials, mainly including long-term temperature resistance, flame retardancy rating, smoke density, toxic gas release, and mechanical properties such as tear resistance and bending resistance.

[0003] Among commonly used cable sheathing materials, polyvinyl chloride (PVC) is widely used due to its low cost. However, its long-term operating temperature is only 60–105°C, making it prone to aging, embrittlement, and even melting and dripping in the high-temperature areas of aircraft, posing serious safety hazards. Silicone rubber, while possessing excellent heat resistance (up to 180°C), has low tear strength and is expensive, making it difficult to meet the needs of large-scale applications. Ethylene propylene diene monomer (EPDM) rubber has good weather resistance and heat aging resistance, but it is inherently flammable and requires a highly efficient halogen-free flame retardant system to meet aviation standards.

[0004] Current technologies still fall short in achieving an ideal balance between high temperature resistance, high flame retardancy, low smoke toxicity, and mechanical strength. In particular, there is a lack of a comprehensive solution suitable for the aviation environment that combines wide temperature range stability, high-efficiency halogen-free flame retardancy, good processability, and cost-effectiveness. Therefore, developing a novel high-temperature resistant and flame-retardant sheathing material for aviation cables has significant practical and technological value. Summary of the Invention

[0005] The purpose of this invention is to provide a high-temperature resistant and flame-retardant cable sheath material for aviation cables and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the aforementioned objective, the present invention provides the following technical solution: a high-temperature resistant and flame-retardant cable sheath material for aviation cables, comprising, by weight, the following components: 30–60 parts of ethylene propylene diene monomer (EPDM) rubber, 20–50 parts of ethylene-vinyl acetate copolymer, 80–150 parts of aluminum hydroxide, 50–100 parts of magnesium hydroxide, 5–15 parts of zinc borate, 3–10 parts of organically modified montmorillonite, 1–3 parts of composite antioxidant, and 2–6 parts of dicumyl peroxide.

[0007] Preferably, the mass ratio of the EPDM rubber to the ethylene-vinyl acetate copolymer is (1:1)–(3:1), and the mass content of vinyl acetate in the ethylene-vinyl acetate copolymer is 18%–28%.

[0008] Preferably, the aluminum hydroxide is surface modified by a silane coupling agent. The modification method is as follows: γ-aminopropyltriethoxysilane at a mass of 1%–2% of aluminum hydroxide is used and the mixture is stirred at high speed at 80–90°C for 1–2 hours.

[0009] Preferably, it also includes 3–8 parts of aramid staple fiber, wherein the length of the aramid staple fiber is 1–3 mm.

[0010] Preferably, the composite antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1.

[0011] Preferably, the amount of dicumyl peroxide is 3–5 parts, and the organically modified montmorillonite is montmorillonite modified by quaternary ammonium salt intercalation with an interlayer spacing ≥2 nm.

[0012] A preparation process for a high-temperature resistant and flame-retardant cable sheath material for aviation cables includes the following steps: S1 Internal Mixing: EPDM rubber and ethylene-vinyl acetate copolymer are put into an internal mixer for plasticizing. Then, aluminum hydroxide, magnesium hydroxide, zinc borate, organic modified montmorillonite, composite antioxidant, and aramid short fiber are added in sequence and mixed until the material is uniform. Finally, dicumyl peroxide is added and the mixture is continued to be discharged to obtain the compound rubber. S2 open mill thin pass: Transfer the mixed rubber to the open mill, adjust the roller gap to perform thin pass multiple times, remove air bubbles and then sheet to obtain the rubber sheet; S3 Extrusion Molding: The film is fed into the extruder, melted and plasticized, and then extruded to cover the outside of the conductor to form a sheath layer; S4 irradiation crosslinking: The extruded cable is fed into an electron accelerator for electron beam irradiation crosslinking to obtain the finished cable sheath.

[0013] Preferably, the mixing temperature in S1 is 120–140℃, the rotation speed is 40–60 rpm, and the total mixing time is 5–15 min.

[0014] Preferably, the irradiation dose in S4 is 80–150 kGy and the electron beam energy is 2.0–3.0 MeV.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a compound of ethylene propylene diene monomer (EPDM) rubber and ethylene-vinyl acetate copolymer as the matrix, combined with a dual crosslinking mechanism of chemical pre-crosslinking by dicumyl peroxide and electron beam irradiation crosslinking. First, chemical crosslinking is used for initial shaping, and then irradiation crosslinking is used to perfect the three-dimensional network structure, forming a high-density, high-bond-energy crosslinking system. This fully leverages the heat and weather resistance advantages of the saturated main chain of EPDM rubber, while the ethylene-vinyl acetate copolymer enhances filler compatibility. The dual crosslinking network has a higher gel content and better thermal stability, significantly increasing the long-term service temperature and allowing it to withstand higher temperature shocks in the short term. It also exhibits high mechanical property retention after high-temperature aging, effectively extending the high-temperature service life of aviation cables and solving the problems of easy degradation and poor dimensional stability at high temperatures associated with single crosslinking methods. 2. This invention uses aluminum hydroxide and magnesium hydroxide as the main flame retardants, combined with zinc borate and organically modified montmorillonite as synergistic components: the hydroxides decompose upon heating, absorbing a large amount of heat and releasing water vapor to dilute combustible gases; zinc borate catalyzes carbonization in the condensed phase, forming a dense carbon layer to block heat and oxygen; the nanosheet structure of organic montmorillonite creates a labyrinth effect, delaying heat transfer and smoke release. The four components work synergistically from multiple dimensions of the gas and solid phases to exert flame retardant effects; high-level flame retardancy and high oxygen index can be achieved with a relatively low total filler content, resulting in low smoke and non-toxicity during combustion, with no hydrogen halide release, meeting the smoke toxicity standards in the aviation field; at the same time, it avoids the mechanical property degradation caused by ultra-high filler content, achieving a balance between flame retardant performance and mechanical properties, and solving the problems of material embrittlement and poor mechanical properties under high filler content in traditional halogen-free systems; 3. This invention employs a conventional cable processing flow of internal mixing, open milling, extrusion, and irradiation, requiring no special equipment modifications and directly compatible with existing cable production lines. The raw materials are primarily general-purpose rubber and plastic materials, significantly reducing costs compared to high-end solutions such as fluororubber and ceramicized silicone rubber. Furthermore, functional gradation can be achieved through three-layer co-extrusion, controlling the amount of expensive materials used while ensuring performance. It boasts high production efficiency and good batch stability, combining performance and cost advantages to meet the large-scale production needs of aviation cables, solving the problems of difficult processing, high cost, and limited widespread adoption of high-end fire-resistant sheath materials. Attached Figure Description

[0016] Figure 1 A flowchart illustrating the preparation process of the kit of the present invention is shown. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] according to Figure 1 As shown, this invention provides a technical solution: a high-temperature resistant flame-retardant cable sheath material for aviation cables, comprising the following components by weight: 30-60 parts of ethylene propylene diene monomer (EPDM) rubber, with EPDM as the main matrix material and a saturated carbon-carbon bond main chain, possessing natural heat aging resistance, ozone resistance, and weather resistance, providing basic high-temperature resistance for the sheath; 20-50 parts of ethylene-vinyl acetate copolymer, with ethylene-vinyl acetate copolymer as the compound matrix, the vinyl acetate segments being polar, which can improve compatibility with inorganic flame-retardant fillers, improve filler dispersibility, and simultaneously improve material flexibility and processing fluidity; 80-150 parts of aluminum hydroxide; 50-100 parts of magnesium hydroxide, with aluminum hydroxide and magnesium hydroxide as the main halogen-free flame retardants, which absorb a large amount of heat upon heating, releasing water vapor to dilute flammable gases, and the decomposition products are non-toxic metal oxides, halogen-free and low-smoke; the compounding of the two can cover different decomposition temperature ranges, broadening the flame-retardant temperature range; and 5-15 parts of zinc borate. As a flame retardant synergist, it releases water of crystallization upon heating and promotes the formation of a dense carbonized layer in the condensed phase, inhibiting dripping and improving flame retardant efficiency. In synergy with hydroxides, it can reduce the total amount of filler. Organic modified montmorillonite 3-10 parts: Organic modified montmorillonite is a nano-synergistic flame retardant. After quaternary ammonium salt intercalation modification, it can be exfoliated and dispersed in the rubber matrix to form a nanosheet barrier structure, extending the transmission path of heat, smoke and combustible gases, while improving the mechanical strength and dimensional stability of the material. Composite antioxidant 1-3 parts: The composite antioxidant is a hindered phenolic main antioxidant that captures free radicals, and a phosphite auxiliary antioxidant that decomposes hydrogen peroxide. The two work together to inhibit the thermo-oxidative aging chain reaction and improve the long-term thermal aging performance of the material. Dicumyl peroxide 2-6 parts: Dicumyl peroxide is a chemical crosslinking agent. It decomposes upon heating to generate free radicals, which initiate crosslinking of rubber molecular chains. In the extrusion stage, a crosslinking network is initially formed to ensure extrusion shape retention. At the same time, it works synergistically with subsequent irradiation crosslinking to improve the final crosslinking density. The mass ratio of ethylene propylene diene monomer (EPDM) rubber to ethylene-vinyl acetate copolymer is (1:1)–(3:1), and the mass content of vinyl acetate in the ethylene-vinyl acetate copolymer is 18%–28% to optimize the balance between the flexibility and heat resistance of the material. Aluminum hydroxide is surface modified with a silane coupling agent. The modification method is as follows: γ-aminopropyltriethoxysilane at a mass of 1%–2% of aluminum hydroxide is used and stirred at high speed at 80–90℃ for 1–2 hours to enhance its interfacial bonding force with the rubber matrix and improve dispersion uniformity and mechanical properties. It also includes 3–8 parts of aramid short fibers, the length of which is 1–3 mm. The aramid short fibers are used as a reinforcing phase to improve the tear resistance and dimensional stability of the sheath material. The compound antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1, which can effectively inhibit thermo-oxidative aging during processing and use. The amount of dicumyl peroxide is 3–5 parts. The organically modified montmorillonite is quaternary ammonium salt intercalated montmorillonite with an interlayer spacing of ≥2nm. It can work synergistically in the subsequent irradiation crosslinking process to form a stable three-dimensional network structure. A preparation process for a high-temperature resistant and flame-retardant cable sheath material for aviation cables includes the following steps: S1 Internal Mixing: EPDM rubber and ethylene-vinyl acetate copolymer are fed into an internal mixer for plasticizing, which stretches the rubber molecular chains and improves the compatibility of subsequent mixing. Then, aluminum hydroxide, magnesium hydroxide, zinc borate, organic modified montmorillonite, composite antioxidant, and aramid short fiber are added in sequence and mixed until the material is uniform. Finally, dicumyl peroxide is added and the mixture is continued to be discharged to obtain the compound. A step-by-step feeding method is adopted. First, the fillers and additives are fully dispersed. Finally, the crosslinking agent is added in the low-temperature section to avoid premature decomposition of dicumyl peroxide at high temperature, which would lead to scorching and ensure the processing safety and performance uniformity of the compound. S2 open mill thin pass: Transfer the compounded rubber to the open mill, adjust the roller gap to 0.5–1 mm, and perform 5–8 thin passes. Through strong shearing action, the filler agglomerates are further refined, the components are evenly dispersed, and after the air bubbles are removed, the sheet is cut to avoid the presence of pore defects in the finished product, and the film is obtained. S3 Extrusion Molding: The film is fed into a single screw extruder, conveyed in the feeding section, plasticized in the melting section, and homogenized in the homogenizing section before being extruded to cover the outside of the conductor, forming a sheath layer. The extrusion temperature gradually increases along the screw from the feeding section to the die head, and is controlled at 110–130℃ to avoid premature cross-linking due to excessive temperature. S4 Irradiation Crosslinking: The extruded cable is sent into an electron accelerator for electron beam irradiation crosslinking to obtain the finished cable sheath. The electron beam excites the rubber molecules to generate free radicals, which further improves the crosslinking network and enhances the crosslinking density and thermal stability of the crosslinking bonds. In S1, the mixing temperature is 120–140℃, the rotation speed is 40–60 rpm, and the total mixing time is 5–15 min; The irradiation dose in S4 is 80–150 kGy, and the electron beam energy is 2.0–3.0 MeV.

[0019] Working principle: Example 1: Raw material composition (parts by weight): 45 parts of EPDM rubber, 35 parts of ethylene-vinyl acetate copolymer (VA content 20%), 120 parts of silane-modified aluminum hydroxide, 80 parts of magnesium hydroxide, 10 parts of zinc borate, 6 parts of organically modified montmorillonite, 2 parts of antioxidant 1010 / 168 (mass ratio 1:1), 4 parts of dicumyl peroxide, and 5 parts of aramid short fiber.

[0020] Preparation method: S1: Add the above materials to the internal mixer and mix at 130°C for 10 minutes at a speed of 50 rpm; S2: After mixing, the material is discharged and thinned into sheets after passing through a two-mill 6 times. S3: The resulting film is fed into a single-screw extruder and extruded at a die head temperature of 120°C to coat a copper conductor with a diameter of 2.5 mm, forming a sheath layer with a thickness of about 1.2 mm; S4: Place the cable sample under an electron accelerator and crosslink it with electron beam irradiation at a dose of 120 kGy.

[0021] The performance test results are shown in Table 1. Example 2

[0022] Raw material composition (parts by weight): 60 parts of EPDM rubber, 20 parts of ethylene-vinyl acetate copolymer (VA content 20%), 120 parts of silane-modified aluminum hydroxide, 80 parts of magnesium hydroxide, 10 parts of zinc borate, 6 parts of organically modified montmorillonite, 2 parts of antioxidant 1010 / 168 (mass ratio 1:1), 4 parts of dicumyl peroxide, and 5 parts of aramid short fiber.

[0023] The preparation method is the same as in Example 1.

[0024] The performance test results are shown in Table 1. Example 3

[0025] Raw material composition (parts by weight): 45 parts of EPDM rubber, 35 parts of ethylene-vinyl acetate copolymer (VA content 20%), 80 parts of silane-modified aluminum hydroxide, 100 parts of magnesium hydroxide, 10 parts of zinc borate, 6 parts of organically modified montmorillonite, 2 parts of antioxidant 1010 / 168 (mass ratio 1:1), 4 parts of dicumyl peroxide, and 5 parts of aramid short fiber.

[0026] The preparation method is the same as in Example 1.

[0027] The performance test results are shown in Table 1.

[0028] Comparative Example 1: 80 parts of EPDM rubber, 120 parts of silane-modified aluminum hydroxide, 80 parts of magnesium hydroxide, 10 parts of zinc borate, 6 parts of organically modified montmorillonite, 2 parts of antioxidant 1010 / 168 (mass ratio 1:1), 4 parts of dicumyl peroxide, and 5 parts of aramid short fiber.

[0029] The preparation method is the same as in Example 1.

[0030] The performance test results are shown in Table 1.

[0031] Comparative Example 2: Raw material composition (parts by weight): 45 parts of EPDM rubber, 35 parts of ethylene-vinyl acetate copolymer (VA content 20%), 120 parts of silane-modified aluminum hydroxide, 80 parts of magnesium hydroxide, 2 parts of antioxidant 1010 / 168 (mass ratio 1:1), 4 parts of dicumyl peroxide, and 5 parts of aramid short fiber.

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

[0033] The performance test results are shown in Table 1.

[0034] Comparative Example 3: Raw material composition (parts by weight): 45 parts of EPDM rubber, 35 parts of ethylene-vinyl acetate copolymer (VA content 20%), 120 parts of silane-modified aluminum hydroxide, 80 parts of magnesium hydroxide, 10 parts of zinc borate, 6 parts of organically modified montmorillonite, 2 parts of antioxidant 1010 / 168 (mass ratio 1:1), 4 parts of dicumyl peroxide, and 5 parts of aramid short fiber.

[0035] Preparation method: S1: Add the above materials to the internal mixer and mix at 130°C for 10 minutes at a speed of 50 rpm; S2: After mixing, the material is discharged and thinned into sheets after passing through a two-mill 6 times. S3: The resulting film is fed into a single-screw extruder and extruded at a die head temperature of 120°C to coat a copper conductor with a diameter of 2.5 mm, forming a sheath layer with a thickness of about 1.2 mm.

[0036] The performance test results are shown in Table 1.

[0037] The performance test results for each embodiment are summarized below: Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Oxygen index (%) 34.2 33.8 32.5 32.1 29.3 33.5 Smoke density transmittance (%) 80.1 78.5 76.3 74.2 65.8 78.6 Tensile strength (MPa) 14.3 13.8 12.5 11.6 10.8 13.1 Elongation at break (%) 345 330 315 280 265 320 Tear resistance (kN / m) 26.7 25.9 25.2 21.3 20.1 24.5 Strength retention rate (%) after aging at 125℃ for 168 hours 88.5 87.2 86.8 82.4 84 76.3 Gel content (%) 78 76 75 72 74 62 Vertical flammability rating V-0 V-0 V-0 V-1 V-1 V-0 Table 1 In Comparative Example 1, the lack of ethylene-vinyl acetate copolymer resulted in decreased filler compatibility and a decline in both mechanical and flame-retardant properties, demonstrating that the ethylene-vinyl acetate copolymer complex plays a crucial role in improving overall performance. In Comparative Example 2, the lack of synergistic flame-retardant components significantly reduced oxygen index, smoke density, and vertical burning rating, proving that the synergistic system of zinc borate and montmorillonite can significantly improve flame-retardant efficiency. Comparative Example 3, which only used chemical crosslinking, had low gel content and poor performance retention after high-temperature aging, demonstrating that the dual crosslinking system is crucial for improving heat aging resistance.

[0038] In summary, this invention achieves a balance of high temperature resistance, high flame retardancy, low smoke toxicity, and high mechanical strength through multi-component synergistic design. All embodiments meet the performance requirements of aviation cables, and the technical effect is significantly better than existing solutions with single improvements.

[0039] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. High-temperature resistant and flame-retardant cable sheath material for aviation cables, characterized in that: By weight, it consists of the following components: 30–60 parts of ethylene propylene diene monomer (EPDM) rubber, 20–50 parts of ethylene-vinyl acetate copolymer, 80–150 parts of aluminum hydroxide, 50–100 parts of magnesium hydroxide, 5–15 parts of zinc borate, 3–10 parts of organically modified montmorillonite, 1–3 parts of composite antioxidant, and 2–6 parts of dicumyl peroxide.

2. The high-temperature resistant and flame-retardant cable sheath material for aviation cables according to claim 1, characterized in that: The mass ratio of the EPDM rubber to the ethylene-vinyl acetate copolymer is (1:1)–(3:1), and the mass content of vinyl acetate in the ethylene-vinyl acetate copolymer is 18%–28%.

3. The high-temperature resistant and flame-retardant cable sheath material for aviation cables according to claim 1, characterized in that: The aluminum hydroxide is surface modified by a silane coupling agent. The modification method is as follows: γ-aminopropyltriethoxysilane is used at a mass of 1%–2% of aluminum hydroxide, and the mixture is stirred at high speed at 80–90°C for 1–2 hours.

4. The high-temperature resistant and flame-retardant cable sheath material for aviation cables according to claim 1, characterized in that: It also includes 3–8 parts of aramid short fibers, the length of which is 1–3 mm.

5. The high-temperature resistant and flame-retardant cable sheath material for aviation cables according to claim 1, characterized in that: The composite antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:

1.

6. The high-temperature resistant and flame-retardant cable sheath material for aviation cables according to claim 1, characterized in that: The amount of dicumyl peroxide used is 3–5 parts, and the organically modified montmorillonite is montmorillonite modified by quaternary ammonium salt intercalation with an interlayer spacing ≥2 nm.

7. A preparation process for a high-temperature resistant and flame-retardant cable sheath material for aviation cables, applied to the high-temperature resistant and flame-retardant cable sheath material for aviation cables as described in any one of claims 1-6, characterized in that: Includes the following steps: S1 Internal Mixing: EPDM rubber and ethylene-vinyl acetate copolymer are put into an internal mixer for plasticizing. Then, aluminum hydroxide, magnesium hydroxide, zinc borate, organic modified montmorillonite, composite antioxidant, and aramid short fiber are added in sequence and mixed until the material is uniform. Finally, dicumyl peroxide is added and the mixture is continued to be discharged to obtain the compound rubber. S2 open mill thin pass: Transfer the mixed rubber to the open mill, adjust the roller gap to perform thin pass multiple times, remove air bubbles and then sheet the rubber to obtain the sheet; S3 Extrusion Molding: The film is fed into the extruder, melted and plasticized, and then extruded to cover the outside of the conductor to form a sheath layer; S4 irradiation crosslinking: The extruded cable is fed into an electron accelerator for electron beam irradiation crosslinking to obtain the finished cable sheath.

8. The preparation process of the high-temperature resistant and flame-retardant cable sheath material for aviation cables according to claim 7, characterized in that: The mixing temperature in S1 is 120–140℃, the rotation speed is 40–60 rpm, and the total mixing time is 5–15 min.

9. The preparation process of the high-temperature resistant and flame-retardant cable sheath material for aviation cables according to claim 7, characterized in that: The irradiation dose in S4 is 80–150 kGy, and the electron beam energy is 2.0–3.0 MeV.

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