Silane crosslinking low-smoke halogen-free flame-retardant polyolefin sheath material for slurry resistance and preparation method thereof

Abstract

The invention relates to the technical field of cable materials, and discloses a slurry-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material and a preparation method, the slurry-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material comprises a master batch, a material A, a material B and various materials, a halogen-free flame retardant compound system is adopted, aluminum hydroxide and magnesium hydroxide have a synergistic effect, and the slurry-resistant low-smoke halogen-free flame-retardant polyolefin sheath material is prepared through a silane coupling agent graft modification and dynamic vulcanization process. The flame retardant property, slurry resistance, mechanical property, electrical insulation property and thermal stability are comprehensively improved. The sheath material disclosed by the invention shows excellent durability and comprehensive performance under the conditions of long-term contact with drilling fluid, high temperature, high humidity and extreme weather, overcomes the problems of insufficient flame retardance, poor chemical resistance and poor thermal stability in the prior art, and meets the requirement of environmental protection at the same time. The sheath material not only meets the high-grade requirement on the flame retardant grade, but also has excellent processability and mechanical properties, and is suitable for multi-scene application of cable sheaths under complex working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of cable materials, and specifically to a silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material for resisting mud and a preparation method thereof. Background Art

[0002] At present, most wire and cable materials on the market use halogen-based flame retardants for flame retardant modification. Such flame retardants are widely used due to their excellent flame retardant properties and can significantly reduce the combustion rate of materials through mechanisms such as chemical inhibition and condensed-phase protection. However, during combustion, halogen-based flame retardants will release a large amount of toxic and harmful gases and thick smoke, which not only pose a potential threat to human health but also bring severe challenges to environmental protection. With the continuous enhancement of global environmental awareness, the development of halogen-free low-smoke flame-retardant materials has gradually become a research hotspot in the industry. At the same time, as an important physical modification method, silane cross-linking technology has been widely used to improve the comprehensive performance of polyolefin materials. Through the grafting and cross-linking of silane coupling agents, the heat resistance and electrical properties of materials have been significantly improved.

[0003] Although certain progress has been made in the research and development of halogen-free low-smoke flame-retardant materials and silane cross-linking modification in the prior art, there are still challenges in the coordination and improvement of multiple key properties. For example, a single inorganic flame retardant (such as aluminum hydroxide or magnesium hydroxide) in the flame retardant system requires a relatively high addition amount to achieve the flame retardant effect, but an excessive filler ratio will significantly reduce the mechanical properties and processing properties of the material. In addition, the poor dispersion of the flame retardant and its poor interfacial compatibility with the polyolefin matrix result in unstable material performance in a combustion environment. Although silane cross-linking technology can effectively improve the heat resistance of materials, the existing cross-linking technology is difficult to balance the flame retardant performance and long-term thermal stability, especially when used for a long time at a high temperature (125 °C), the material is prone to oxidative degradation. To address these problems, how to optimize the flame retardant system and cross-linking process to achieve a comprehensive balance of material properties has become a key development direction for halogen-free low-smoke flame-retardant polyolefin sheath materials. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material for resisting mud and a preparation method thereof, which solves the problems of insufficient mud resistance performance of existing polyolefin sheath materials in complex environments, difficulty in achieving a high level of flame retardancy, and difficulty in balancing thermal stability and electrical insulation performance.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material for resisting mud, comprising the following component materials: Masterbatch: 60% - 80%, including: Polyolefin resin: 25 parts - 40 parts; Inorganic flame retardant: 50 parts - 70 parts; Compatibilizer: 3 parts to 6 parts; Antioxidant: 0.2 parts to 0.6 parts; Lubricant: 0.5 parts to 1.5 parts; Antioxidant for rubber: 1 part to 2 parts; Material A: 1% to 5%, including: Silane coupling agent A-172: 1 part to 2 parts; Silane coupling agent A-171: 0.5 part to 1 part; Initiator: 0.1 part to 0.2 part; Masterbatch: 90 parts to 100 parts; Material B: 5% to 15%, including: Color masterbatch: 15 parts to 20 parts; HDPE: 15 parts to 20 parts; Magnesium hydroxide: 40 parts to 60 parts; Antioxidant 405: 5 parts to 10 parts; Antioxidant RD: 5 parts to 10 parts; Silane coupling agent A-172: 0.5 part to 0.8 part; Catalyst dibutyltin dilaurate: 0.2 part to 0.6 part; Lubricant silicone or zinc stearate: 0.5 part to 1 part; Diverse materials: 0.5% to 5%, including: Nano-silica: 0.5 part to 2 parts; Triphenyl phosphite: 0.5 part to 1.5 parts.

[0006] Furthermore, the combination of polyolefin resins (HDPE, POE, EMA) endows the material with hardness, flexibility and oil resistance; the compounding of inorganic flame retardants aluminum hydroxide and magnesium hydroxide provides a halogen-free flame retardant effect, which can absorb heat and reduce temperature and inhibit smoke generation; the compatibilizer improves the dispersion of the flame retardant in the matrix and enhances the overall mechanical properties; the antioxidant and antioxidant for rubber enhance the anti-aging performance of the material, and the lubricant improves the processing fluidity. In Material A, through the compounding and grafting reaction of the coupling agent, the cross-linking efficiency and chemical resistance are improved. In Material B, the flame retardancy and mechanical properties are balanced. At the same time, the catalyst accelerates the silane cross-linking reaction, and the diverse materials play a role in enhancing the mechanical properties of the material and improving the thermal oxidation resistance.

[0007] Preferably, the polyolefin resin includes: HDPE: 15 parts to 20 parts; POE: 3 parts to 8 parts; EMA: 5 parts to 10 parts; Among them, the melt index of HDPE is 0.5 g / 10 min to 2 g / 10 min, the crystallinity is 80% to 90%, the melt index of POE is 2 g / 10 min to 5 g / 10 min, the Shore hardness A is 50 to 60, and the ethyl methacrylate content of EMA is 20% to 30%.

[0008] Furthermore, due to its high crystallinity (80% - 90%), HDPE provides excellent hardness and oil resistance, and the melt index (0.5 g / 10 min - 2 g / 10 min) ensures its good processing fluidity; POE enhances the flexibility and impact resistance of the material through low crystallinity and appropriate melt index (2 g / 10 min - 5 g / 10 min); because EMA contains ethyl methacrylate (20% - 30%), it has strong polarity, significantly improving the oil resistance and reducing the oil absorption rate. The three resins are optimally proportioned and combined, fully balancing the mechanical strength, flexibility and chemical resistance of the sheath material.

[0009] Preferably, the inorganic flame retardant includes 30 parts to 40 parts of aluminum hydroxide and 20 parts to 30 parts of magnesium hydroxide, and the particle size of the flame retardant is 1 μm to 5 μm.

[0010] Furthermore, aluminum hydroxide and magnesium hydroxide decompose and release water vapor at high temperatures, diluting the combustible gases generated during combustion, and at the same time absorbing heat to reduce the surface temperature of the material, playing a flame retardant role. The compounding of the two flame retardants can improve the flame retardant efficiency and reduce the adverse effects of the addition amount of a single flame retardant on the mechanical properties of the material; in addition, the particle size range of 1 μm to 5 μm ensures the uniform dispersion of the flame retardant, contributing to maintaining the overall performance stability of the sheath material.

[0011] Preferably, among the diverse materials, the particle size of nano-silica is 10 nm to 50 nm, and triphenyl phosphite is a phosphite or thioester compound.

[0012] Furthermore, due to its high specific surface area and nano-scale particle size, nano-silica can play a reinforcing role in the material matrix, significantly improving the mechanical properties, wear resistance and durability of the sheath material; at the same time, its uniform dispersion helps to improve the thermal stability and flame retardant properties of the material. Triphenyl phosphite, as a heat stabilizer, improves the thermal oxidation resistance of the material by capturing free radicals and decomposing peroxides, thereby extending the service life of the material.

[0013] Preferably, the diverse materials are prepared based on dynamic vulcanization technology by adding a vulcanizing agent and a crosslinking assistant in a mixer under the conditions of a temperature of 170 °C to 200 °C and a shear rate of 50 rpm to 200 rpm, and the vulcanizing agent is a peroxide or a vulcanized rubber.

[0014] Furthermore, the dynamic vulcanization technology utilizes high temperature and shear force to promote the cross-linking reaction between the vulcanizing agent and the matrix resin in the material, generating a microscopic elastic phase with a three-dimensional network structure, thereby improving the elastic modulus, fatigue resistance, and long-term stability of the sheath material. The synergistic effect of the vulcanizing agent and the cross-linking aid ensures the reliability of the material in extreme environments.

[0015] A method for preparing a silane-crosslinked low-smoke halogen-free flame-retardant polyolefin sheath material for resisting mud, comprising the following steps: S1. Mix the masterbatch, material A, and material B evenly according to a mass ratio of 93 - 95:7 - 5; S2. Extrude and form at 180°C - 220°C through a twin-screw extruder; S3. Conduct silane cross-linking treatment for 24h - 72h in an environment with a humidity of 70% - 90% and a temperature of 60°C - 90°C.

[0016] Furthermore, in step S1, the optimized proportion combination of the masterbatch, material A, and material B achieves a comprehensive balance of material properties; in step S2, the high-temperature extrusion process ensures sufficient mixing of components and suitable processing fluidity; in step S3, the silane cross-linking completes the cross-linking reaction through humidity and temperature control, forming a stable three-dimensional network structure, thereby enhancing the mechanical properties and high-temperature resistance of the sheath material.

[0017] Preferably, in step S1, the masterbatch is prepared through the following steps: (1) Weigh each component according to the formula ratio of the masterbatch in claim 1; (2) Under the temperature condition of 160°C - 190°C, mix each component evenly in a kneader to obtain the masterbatch.

[0018] Preferably, in step S1, material A is prepared through the following steps: (1) Mix the silane coupling agent A-172, the silane coupling agent A-171, and the initiator in proportion; (2) Mix with the masterbatch according to the formula ratio of material A in claim 1; (3) Conduct a graft reaction through a twin-screw extruder at a temperature of 180 - 220°C to obtain material A.

[0019] Preferably, in step S1, material B is prepared through the following steps: (1) Weigh each component according to the formula ratio of material B in claim 1; (2) Mix evenly in a twin-screw extruder under the temperature condition of 180°C - 220°C to obtain material B.

[0020] Preferably, in the step S1, nano-silica and triphenyl phosphite are added during mixing, and then kneading is carried out under the conditions of a dynamic vulcanization process. The particle size of the nano-silica is 10 nm to 50 nm.

[0021] The present invention provides a silane-crosslinked low-smoke and halogen-free flame-retardant polyolefin sheath material for resisting mud and a preparation method thereof. It has the following beneficial effects: 1. The present invention adopts a compound inorganic flame retardant and an optimized silane coupling agent crosslinking system. By constructing a dense three-dimensional network structure, the mud resistance performance of the sheath material is improved. The dispersion uniformity and interfacial compatibility of the flame retardant are fully improved. The sheath material maintains a low oil absorption rate and high hardness during long-term immersion in drilling fluid. Compared with the problem of surface cracking and mechanical property degradation caused by the addition of a single flame retardant in the prior art, the present invention effectively solves the problem of insufficient stability of the sheath material in a mud environment and greatly extends the service life of the cable.

[0022] 2. The present invention adopts a synergistic design of the halogen-free flame retardants aluminum hydroxide and magnesium hydroxide, and introduces a heat stabilizer and nano-silica to optimize the flame retardant system. A large amount of water vapor is released during the combustion of the material to form a protective layer, and the flue gas emission is significantly reduced, containing almost no halogens and other toxic components. Compared with the technical solution of releasing a large amount of corrosive gases during the combustion of traditional halogen-based flame retardant materials, the present invention greatly improves the flame retardant safety, takes into account environmental protection requirements, and effectively solves the defect of excessive flue gas toxicity in a fire environment.

[0023] 3. Through the precise ratio of polyolefin resins and the compound grafting process of silane coupling agents, the present invention realizes the comprehensive optimization of the mechanical strength and electrical insulation performance of the sheath material. The mechanical properties of the material are stable in a marine environment, and the conductivity and insulation are maintained well. Compared with the problems of insulation fluctuation or mechanical property decline caused by uneven dispersion of the flame retardant in the prior art, the present invention solves the deficiency of performance imbalance and can meet the high requirements for durability and electrical performance in a complex marine environment.

[0024] 4. Through the introduction of dynamic vulcanization technology and heat stabilizers, the present invention further enhances the low-temperature flexibility and thermal stability of the sheath material. The anti-aging performance of the material under extreme temperature conditions is greatly improved, and the flexibility also remains excellent. In the prior art, the deficiencies of easy oxidation and degradation of the sheath material in a high-temperature environment or becoming brittle under low-temperature conditions are effectively solved. The technical solution of the present invention broadens the applicable climate range of the product, meets diverse application requirements, and provides better technical support for expanding product varieties. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of the preparation steps of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] Please refer to the attached Figure 1 , Example 1: Preparation of high mud-resistant sheath material Formulation composition: Masterbatch: 70%, including the following components (parts): Polyolefin resin: HDPE (20 parts), POE (5 parts), EMA (7 parts); Inorganic flame retardant: aluminum hydroxide (25 parts), magnesium hydroxide (13 parts); Compatibilizer: maleic anhydride grafted polyethylene (3 parts); Antioxidant: 0.4 part; Silicone lubricant: 0.6 part; Antioxidant 405: 1 part.

[0028] Material A: 4%, including the following components (parts): Silane coupling agent A-172: 1.5 parts; Silane coupling agent A-171: 0.8 part; Initiator: 0.7 part.

[0029] Material B: 20%, including the following components (parts): Color masterbatch: 6 parts; HDPE: 5 parts; Magnesium hydroxide: 8 parts; Antioxidant 405: 2 parts; Catalyst dibutyltin dilaurate: 1 part; Zinc stearate lubricant: 0.5 part.

[0030] Diverse materials: 6%, including the following components (parts): Nano-silica: 2 parts; Triphenyl phosphite: 3 parts.

[0031] Preparation steps: Masterbatch preparation: Mix HDPE, POE, EMA with aluminum hydroxide and magnesium hydroxide, then add the compatibilizer, antioxidant and antioxidant, and mix in a kneader at 170°C and a rotation speed of 60 rpm for 20 minutes. After cooling, masterbatch particles are obtained.

[0032] Preparation of Material A: After uniformly mixing A-172, A-171 and the initiator, the masterbatch is added, and grafting reaction is carried out at 190 °C and a rotation speed of 50 rpm in a twin-screw extruder to obtain Material A.

[0033] Preparation of Material B: The masterbatch, magnesium hydroxide and HDPE are premixed, and then the catalyst and lubricant are added, and extrusion is carried out uniformly under the condition of 200 °C to obtain Material B.

[0034] Processing of the sheath material: The masterbatch, Material A, Material B and various materials are mixed in a ratio of 70:4:20:6, and extrusion molding is carried out through a twin-screw extruder at 200 °C, and then silane cross-linking reaction is carried out for 48 hours in an environment with a humidity of 80% and a temperature of 70 °C.

[0035] Example 2: Preparation of Flame Retardant Ring Sheath Material Formulation Composition: Masterbatch: 65%, including the following components (parts): Polyolefin resin: HDPE (18 parts), POE (6 parts), EMA (8 parts); Inorganic flame retardant: Aluminum hydroxide (23 parts), magnesium hydroxide (12 parts); Compatibilizer: Maleic anhydride grafted ethylene vinyl acetate (4 parts); Antioxidant: 0.3 part; Zinc stearate lubricant: 0.7 part; Antioxidant RD: 1 part.

[0036] Material A: 5%, including the following components (parts): Silane coupling agent A-172: 2 parts; Silane coupling agent A-171: 1 part; Initiator: 1 part.

[0037] Material B: 25%, including the following components (parts): Masterbatch: 5 parts; HDPE: 6 parts; Magnesium hydroxide: 10 parts; Antioxidant 405: 2 parts; Catalyst dibutyltin dilaurate: 2 parts; Silicone lubricant: 0.5 part.

[0038] Various materials: 5%, including the following components (parts): Nano-silica: 2 parts; Triphenyl phosphite: 3 parts.

[0039] Preparation steps: Masterbatch preparation: HDPE, POE, EMA, aluminum hydroxide, and magnesium hydroxide are added to a Banbury mixer in proportion and kneaded for 25 minutes at 180°C. After adding a compatibilizer, an antioxidant, and an anti-aging agent, mixing continues for 10 minutes, and then it is cooled to form pellets.

[0040] A-material preparation: A silane coupling agent A-172, A-171, and an initiator are mixed and then added to the masterbatch, and a grafting reaction is carried out at 190°C. After cooling, the A-material is obtained.

[0041] B-material preparation: The color masterbatch, magnesium hydroxide, and HDPE are mixed evenly, and then a catalyst and a lubricant are added, and it is processed through an extruder at 200°C to obtain the B-material.

[0042] Sheathing material processing: The masterbatch, A-material, B-material, and various materials are mixed in a ratio of 65:5:25:5 and then extruded and formed at 200°C. The materials are placed in an environment with a humidity of 85% and a temperature of 65°C for a crosslinking reaction for 72 hours.

[0043] Example 3: Preparation of a wide-temperature-range sheathing material Formulation composition: Masterbatch: 72%, including the following components (parts): Polyolefin resin: HDPE (20 parts), POE (7 parts), EMA (8 parts); Inorganic flame retardant: Aluminum hydroxide (25 parts), magnesium hydroxide (12 parts); Compatibilizer: Maleic anhydride-grafted polyethylene (3 parts); Antioxidant: 0.5 part; Silicone lubricant: 0.5 part.

[0044] A-material: 3%, including the following components (parts): Silane coupling agent A-172: 1.2 parts; Silane coupling agent A-171: 0.8 part; Initiator: 1 part.

[0045] B-material: 20%, including the following components (parts): Color masterbatch: 5 parts; HDPE: 6 parts; Magnesium hydroxide: 8 parts; Antioxidants 405 and RD: 1 part each; Catalyst dibutyltin dilaurate: 0.5 part.

[0046] Various materials: 5%, including the following components (parts): Nanosilica: 2 parts; Triphenyl phosphite: 3 parts.

[0047] Preparation steps: Masterbatch preparation: Mix polyolefin resin and inorganic flame retardant, then add a compatibilizer, and conduct kneading at 160°C for 15 minutes. Subsequently, add an antioxidant and a lubricant, and continue kneading for 10 minutes. Cool to obtain the masterbatch.

[0048] Preparation of Material A: Mix silane coupling agents A-172 and A-171 with an initiator, add the masterbatch, and conduct grafting reaction with the temperature controlled at 180°C to obtain Material A.

[0049] Preparation of Material B: Mix masterbatch colorant and magnesium hydroxide with HDPE, add a catalyst, and extrude uniformly under the condition of 200°C to obtain Material B.

[0050] Sheathing material processing: Mix each component in a ratio of 72:3:20:5, conduct extrusion molding at 210°C, and then conduct crosslinking reaction in an environment with a humidity of 80% and a temperature of 70°C for 48 hours.

[0051] Comparative Example 1: The masterbatch has no optimized design and does not contain the compounding of silane coupling agents. Component adjustment: Comparative Example 1 is modified based on Example 1, and only the following contents are adjusted: The inorganic flame retardant in the masterbatch is not compounded, and only a single aluminum hydroxide (40%) is used, and magnesium hydroxide is not used; Silane coupling agent A-171 is not used in Material A, and only A-172 (1.5 parts) is used, and the dosage of the initiator is reduced to 0.3 parts; Nano-silica is not added to the diverse materials; only 1.5 parts of triphenyl phosphite is used; Other components remain the same as in Example 1.

[0052] Preparation process: Masterbatch preparation: According to the adjusted masterbatch formula, mix polyolefin resins (HDPE, POE, EMA) with aluminum hydroxide, a compatibilizer, and a lubricant, and conduct kneading at 160°C for 20 minutes to obtain masterbatch particles.

[0053] Preparation of Material A: Mix silane coupling agent A-172 with an initiator, then add them to the masterbatch, and conduct grafting reaction at 190°C to obtain Material A.

[0054] Preparation of Material B: Mix masterbatch colorant with HDPE and magnesium hydroxide evenly, add a catalyst, and process through an extruder at 180°C to obtain Material B.

[0055] Sheathing material processing: Mix the masterbatch, Material A, Material B, and diverse materials in the adjusted ratio, and conduct extrusion molding at 200°C. The wet-heat crosslinking condition is not adopted, and crosslinking is only completed through natural placement.

[0056] Comparative Example 2: Heat stabilizer is not added, and the proportion of the flame retardant is unreasonable. Component adjustment: Comparative Example 2 is modified based on Example 2, and the adjustment contents are as follows: The proportion of polyolefin resin HDPE in the masterbatch is reduced to 14%, and the proportion of POE is increased to 10%; the proportion of EMA remains unchanged (8%); The content of aluminum hydroxide in the inorganic flame retardant is too high (30%), and the content of magnesium hydroxide is too low (5%), and no compounding is formed; Triphenyl phosphate (heat stabilizer) is not added to the diverse materials, and only nano-silica (3%) is added; Material A and Material B are the same as those in Example 2.

[0057] Preparation process: Masterbatch preparation: After mixing the adjusted polyolefin resin with the flame retardant and compatibilizer, it is kneaded at 180 °C for 30 minutes to obtain the masterbatch.

[0058] Material A preparation: The silane coupling agent and initiator are formulated according to the original ratio and then added to the masterbatch, and graft reaction is carried out through a twin-screw extruder at 200 °C to obtain Material A.

[0059] Material B preparation: The masterbatch, HDPE, magnesium hydroxide and catalyst are uniformly mixed and then extruded and molded at 220 °C to obtain Material B.

[0060] Sheathing material processing: The masterbatch, Material A, Material B, and diverse materials are mixed according to the adjusted ratio, and cross-linking reaction is carried out under the conditions of 70% humidity and 65 °C, but the time is shortened to 24 hours.

[0061] Comparative Example 3: The silane coupling agent is completely absent, and no cross-linked network is formed Component adjustment: Comparative Example 3 is modified based on Example 3, and only the following contents are adjusted: Silane coupling agents A-172 and A-171 are completely removed from Material A, and only the initiator (1 part) is retained; The catalyst (such as dibutyltin dilaurate) is not added to Material B; The diverse materials remain the same as those in Example 3 (nano-silica 2%, triphenyl phosphate 3%); The proportions of other components are the same as those in Example 3.

[0062] Preparation process: Masterbatch preparation: According to the masterbatch formula of Example 3, the polyolefin resin is mixed with the flame retardant and then kneaded at 160 °C for 20 minutes to obtain the masterbatch.

[0063] Material A preparation: The silane coupling agent is not added, and the initiator and the masterbatch are directly mixed and simply extruded at 180 °C to obtain uncross-linked Material A.

[0064] Preparation of Material B: Mix the masterbatch, HDPE, and antioxidant according to the formulation in Example 3, without adding a catalyst, and extrude at 200 °C to obtain Material B.

[0065] Processing of the sheath material: Mix the masterbatch, Material A, Material B, and various materials in a ratio of 72:3:20:5, and then extrude and mold at 210 °C. However, no hydrothermal cross-linking treatment is carried out, and it is directly cooled and solidified.

[0066] Experiment 1: Test on the Mud Resistance of the Sheath Material Experiment Description: Experiment Purpose: Compare the chemical resistance of the sheath material samples in Example 1 and Comparative Example 1 in a mud environment, and verify the effects of the compounding of inorganic flame retardants and silane coupling agents on the oil absorption rate, hardness retention, and surface integrity of the sheath material.

[0067] Experiment Steps: Sample Preparation: Use the sheath materials in Example 1 and Comparative Example 1, and adopt the extrusion molding process to prepare standard-sized samples (100 mm × 20 mm × 2 mm) respectively.

[0068] Preparation of the Mud Solution: Prepare a simulated drilling mud solution, the composition of which includes 3% bentonite, 5% NaCl, and the balance deionized water. Adjust the pH value to 10 and keep it at a constant temperature of 80 °C.

[0069] Immersion Test: Immerse the prepared sheath material samples in the mud solution respectively, and set the immersion time to 1 day, 3 days, 7 days, 14 days, and 30 days.

[0070] Performance Test: Determination of the Oil Absorption Rate: Take out the samples at each time point, blot the surface liquid with filter paper, weigh them, and calculate the oil absorption rate.

[0071] Hardness Change Test: Measure the Shore A hardness value of the samples and record the hardness change at each time point.

[0072] Surface Observation: Use an optical microscope to observe whether there are cracks or damages on the surface of the samples, and record the damage conditions.

[0073] Data Recording and Analysis: File the oil absorption rate, hardness change, and surface damage conditions.

[0074] Experimental Data: Table Name: Comparative Test Data on the Mud Resistance of the Sheath Material Immersion time (days) Sample number Oil absorption rate (%) Shore hardness A (change value) Surface damage condition 1 Example 1 0.18 -0.5 None 1 Comparative example 1 0.35 -1.2 Microcracks 3 Example 1 0.22 -1.1 None 3 Comparative example 1 0.52 -2.5 Multiple cracks 7 Example 1 0.29 -1.8 None 7 Comparative example 1 0.75 -4.3 Cracks increase and edges are damaged 14 Example 1 0.40 -3.1 None 14 Comparative example 1 1.10 -6.5 Obvious cracks and local peeling 30 Example 1 0.58 -4.2 Surface slightly discolored 30 Comparative example 1 1.85 -9.0 Large area damaged and completely peeled off Experiment Summary: The compounding optimization of inorganic flame retardants has obviously enhanced the mud resistance of the sheath material. In the flame retardant system of Example 1, through the synergistic effect of aluminum hydroxide and magnesium hydroxide, a more stable material structure is formed. On the contrary, in Comparative Example 1, due to the use of a single flame retardant only, the oil absorption rate increases significantly. Especially after long-term immersion, surface damage becomes inevitable. The fundamental reason for this difference is that the compounding of flame retardants significantly reduces the oil absorption of the resin, while improving the dispersion of fillers and the interfacial bonding force.

[0075] The compounding of silane coupling agents plays an important role in the construction of the crosslinking network of the sheath material. The compounding of A-172 and A-171 in Example 1 effectively improves the crosslinking efficiency. The chemical stability of the material in the mud solution is greatly improved, and the surface hardness only decreases slightly. In Comparative Example 1, due to the lack of the synergistic effect of A-171, the crosslinking network is sparse and of poor quality, and the hardness decreases significantly after immersion. The surface peeling phenomenon after 30 days in the experiment is exactly caused by this.

[0076] The integrity of the sheath material surface is closely related to the crosslinking efficiency. The crosslinking process in Example 1 enhances the bonding force between silane groups and polyolefins under humid and hot conditions, enabling it to maintain integrity in the mud solution for a longer time. In Comparative Example 1, only natural crosslinking treatment is used, and a high-quality network cannot be fully formed, resulting in the gradual expansion of cracks and even large-area damage. This comparison further proves that optimizing the crosslinking system is the key to improving chemical resistance.

[0077] Experiment 2: Flame Retardant Performance Test of Sheath Material Experiment Description: Experiment Purpose: Compare the flame retardant performances of Example 2 and Comparative Example 2, and verify the effects of the optimization of the compounding ratio of inorganic flame retardants and the introduction of heat stabilizers on the flame retardant effect of the material.

[0078] Experiment Steps: Sample Preparation: Use the sheath materials of Example 2 and Comparative Example 2 to prepare flat samples of 100mm×100mm×3mm respectively. Through the compression molding process, the pressure is 5MPa, the temperature is 200℃, and the pressure is maintained for 3 minutes, and then it is cooled and formed.

[0079] Oxygen Index Test: Use an oxygen index tester to measure the limiting oxygen index (LOI) of the samples according to the ASTM D2863 standard.

[0080] The sampling size is 80mm×10mm×3mm, and the oxygen flow rate is set at 100mL / min.

[0081] The test is carried out at room temperature, and the combustion stop time is recorded.

[0082] Horizontal Combustion Test: According to the UL94 horizontal combustion standard, the combustion rating of the test sample is tested.

[0083] The ignition time of the sample is set to 30 seconds, observe the combustion time and the flame spread situation, and record whether there are any dripping substances.

[0084] Smoke Density Test: According to the ASTM E662 standard, the smoke generation rate of the sample during combustion is tested in an optical density chamber.

[0085] The sample size is 50mm×50mm×3mm, and a constant heat flux of 25kW / m² is applied. Record the smoke density value generated by combustion.

[0086] Data Recording and Analysis: Record all data according to the above test methods to ensure sufficient comparison.

[0087] Experimental Data: Table Name: Comparative Test Data of Flame Retardant Properties of Sheathing Materials Sample number Oxygen index (%) Combustion time (seconds) Combustion grade Smoke density (%) Example 2 33.5 12.4 V-0 32 Comparative example 2 27.8 24.6 V-1 48 Example 2 34.1 11.9 V-0 31 Comparative example 2 28.3 22.8 V-1 50 Example 2 33.8 12.2 V-0 33 Comparative example 2 27.5 23.5 V-1 47 Experimental Summary: Example 2 exhibits significantly superior flame retardant properties, and the design of the inorganic flame retardant compound plays a key role. The combination of aluminum hydroxide and magnesium hydroxide releases a large amount of water vapor during combustion, while absorbing heat and reducing the temperature, forming a dense carbonized layer. Compared with the single flame retardant system of Comparative Example 2, the synergistic effect of the compound not only increases the oxygen index, but also effectively inhibits the flame spread. This difference indicates that the reasonable combination of flame retardants can achieve better fire protection while maintaining the structural integrity of the material.

[0088] The addition of heat stabilizer obviously enhances the chemical stability of the sheathing material in the combustion environment. In Example 2, triphenyl phosphite significantly delays the progress of the combustion chain reaction and reduces the combustion rate by capturing free radicals. Due to the lack of heat stabilizer in Comparative Example 2, the flame retardancy of the material shows obvious deficiencies, especially the combustion time is prolonged and the smoke density increases significantly. It can be seen from this that heat stabilizer provides an irreplaceable protective role in a complex combustion environment.

[0089] The smoke density test further reveals the significance of material optimization. The reasonable design of various materials in Example 2 reduces the generation of smoke and the release of toxic substances during the flame retardant process. While in Comparative Example 2, due to the lack of flame retardant and heat stabilizer, the combustion process is more intense and the smoke emission is more significant. This difference once again proves the technical advantages of the inorganic flame retardant compound and the introduction of heat stabilizer, which not only solves the problem of insufficient flame retardant performance, but also takes into account the environmental protection requirements.

[0090] Experiment 3: Mechanical Strength and Environmental Adaptability Test of Sheathing Materials Experimental Instructions: Purpose of the Experiment: By comparing Example 3 with Comparative Example 3, test the mechanical strength, low-temperature impact performance, and heat aging performance of the sheath material, and verify the influence of the introduction of silane coupling agent and cross-linking network on mechanical properties and long-term use stability.

[0091] Experimental Procedures: Sample Preparation: Prepare samples according to the formulations of Example 3 and Comparative Example 3 using the extrusion molding process. The tensile test samples are standard dumbbell shapes (ASTM D638); the impact test sample size is 80 mm × 10 mm × 4 mm; the heat aging test samples are rectangular sheets of 100 mm × 20 mm × 2 mm.

[0092] Tensile Strength and Elongation at Break Test: Use an electronic tensile testing machine to test the tensile strength and elongation at break of the samples according to the ASTM D638 standard.

[0093] The test environment is normal temperature (25 °C), and the tensile speed is set at 50 mm / min. Record the maximum tensile strength and elongation at break of each sample.

[0094] Low-Temperature Impact Test: Test the notched impact strength of the samples in an environment of ~30 °C according to the ASTM D256 standard. Record the impact strength value and observe the fracture morphology of the samples.

[0095] Heat Aging Performance Test: Place the samples in an aging oven at 120 °C for 7 days.

[0096] After aging, retest the tensile strength and elongation at break of the samples and calculate the performance retention rate.

[0097] Data Recording and Analysis: Record the mechanical property indexes of each sample for the test data, and analyze the differences between Example 3 and Comparative Example 3 in mechanical properties and heat aging stability.

[0098] Experimental Data: Table Name: Test Data of Sheath Material Mechanical Strength and Environmental Adaptability Sample number Tensile strength (MPa) Elongation at break (%) <![CDATA[Impact strength (kJ / m ² )]]> Retention rate of tensile strength after aging (%) Example 3 14.8 440 11.3 93.5 Comparative example 3 12.1 330 8.5 74.8 Example 3 15.1 455 10.8 91.7 Comparative example 3 11.8 325 8.2 76.3 Example 3 14.5 435 11.1 94.2 Comparative example 3 12.3 340 8.9 75.5 Experimental Summary: The introduction of silane coupling agent is crucial for improving the mechanical properties of the sheath material. In Example 3, the compounding of silane coupling agents A-172 and A-171 successfully constructed a uniform and dense crosslinked network, significantly enhancing the tensile strength and elongation at break of the material. Compared with Comparative Example 3, due to the absence of silane coupling agent, the chain structure of the material was loose and the degree of crosslinking was insufficient, resulting in a significant decline in mechanical properties. Especially in terms of elongation at break, Example 3 showed obvious flexibility advantages. This difference proves that the construction of the crosslinked network can effectively balance strength and toughness.

[0099] The low-temperature impact performance test further reveals the significance of the silane crosslinking system. Example 3 still maintained a high impact strength at ~30 °C, and the fracture surface of the material was smooth without significant cracks. While in Comparative Example 3, due to the failure to form an effective crosslinked network, it showed high brittleness in the low-temperature environment, and the fracture surface was mostly torn. This indicates that the introduction of silane coupling agent significantly improves the low-temperature adaptability of the material, enabling it to maintain excellent toughness under harsh climate conditions.

[0100] The results of the thermal aging test show that the crosslinked network plays a decisive role in the long-term stability of the material. In Example 3, the combination of silane groups and polyolefin molecular chains significantly improves the thermal oxidation resistance of the material. After aging, the mechanical property retention rate of Example 3 is much higher than that of Comparative Example 3. The latter is more prone to chain breakage and degradation when exposed to high-temperature environments due to the lack of a crosslinking system. This comparison once again verifies the synergistic effect of silane coupling agent, which not only enhances the mechanical properties of the material but also effectively extends its service life.

[0101] Experiment 4: Electrical insulation performance test of the sheath material in a complex environment Experiment description: Experiment purpose: Compare the electrical insulation performance of the sheath materials of Example 1, Example 2, and Example 3 in a complex environment, and verify the improvement effect of formula optimization on the electrical insulation characteristics of the material, especially its performance under long-term immersion in water and high voltage conditions.

[0102] Experiment steps: Sample preparation: Prepare standard cable sheath samples (outer diameter 10 mm, wall thickness 2 mm) from the sheath materials of Example 1, Example 2, and Example 3. After processing each sample, the surface is treated smoothly to ensure no burrs and defects.

[0103] Immersion electrical insulation test: Immerse the samples in a 3.5% NaCl saline solution at a soaking temperature of 25 °C for 24 hours.

[0104] After the soaking is completed, take out the samples, dry the surface moisture with filter paper, measure the volume resistivity using an insulation resistance tester, set the test voltage to 500 V, and record the resistivity values of each sample.

[0105] Arc resistance performance test: Test the arc resistance performance of the samples according to the IEC61621 standard.

[0106] Fix the samples between the electrodes, apply a high voltage of 10 kV (50 Hz), observe the degree of damage to the samples under the action of the arc, and record the arc resistance time.

[0107] Humidity stability test: Place the samples in an environment with a humidity of 90% and a temperature of 60 °C for 72 hours.

[0108] After the treatment, retest the volume resistivity and arc resistance performance, and record the changes in the electrical insulation performance.

[0109] Data recording and analysis: Compare the electrical insulation performance data of the sheath materials in the examples, and analyze the influence of different formulations on the electrical insulation performance.

[0110] Experimental data: Table name: Test data of electrical insulation performance of sheath materials Sample number Initial resistivity (Ω·cm) Arc resistance time (s) Resistivity after wet treatment (Ω·cm) Arc resistance time after wet treatment (s) Example 1 <![CDATA[2.8×10 8 > 43.2 <![CDATA[2.4×10 8 > 40.8 Example 2 <![CDATA[3.5×10 8 > 49.1 <![CDATA[3.2×10 8 > 47.0 Example 3 <![CDATA[4.1×10 8 > 53.5 <![CDATA[3.8×10 8 > 51.7 Example 1 <![CDATA[2.7×10 8 > 42.6 <![CDATA[2.3×10 8 > 41.1 Example 2 <![CDATA[3.4×10 8 > 50.0 <![CDATA[3.1×10 8 > 46.2 Example 3 <![CDATA[4.0×10 8 > 54.0 <![CDATA[3.9×10 8 > 52.4 Experimental summary: The compounding of inorganic flame retardants in the formulation has shown an important role in improving the electrical insulation performance of the materials. The high resistivity performance of Examples 2 and 3 directly comes from the synergistic flame retardant effect of aluminum hydroxide and magnesium hydroxide. The decomposition of aluminum hydroxide generates a protective layer, combined with the endothermic characteristics of magnesium hydroxide, which not only effectively prevents the spread of arc damage but also maintains a relatively high resistivity in a high-humidity environment. Although the electrical insulation performance of Example 1 is acceptable, it is slightly insufficient in terms of humidity stability, indicating that the optimization of the flame retardant ratio has higher requirements for performance balance.

[0111] The cross-linking contribution of the silane coupling agent is more obvious in the arc resistance performance. Example 3 shows the longest arc resistance time in the test, indicating that the construction of its cross-linking network not only enhances the mechanical stability but also significantly improves the material integrity under the action of the arc. Compared with Example 1, the compounding optimization of the silane coupling agent is obviously more conducive to performance maintenance in a complex electric field environment. And due to slightly lower cross-linking degree, the arc resistance performance of Example 2 is slightly lower than that of Example 3 but still better than that of Example 1.

[0112] The humidity stability test reveals the importance of heat stabilizers under extreme conditions. After introducing the heat stabilizer in Example 3, the resistivity decreased the least after treatment at 90% humidity. This further demonstrates that the heat stabilizer protects the molecular structure integrity of the material in a high-humidity environment by decomposing peroxides and capturing free radicals. In contrast, in Example 1, due to the lack of such components, the electrical insulation performance decreased rapidly after wet treatment, verifying again the necessity and advantages of the optimization of diverse materials in the present invention.

[0113] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material for mud resistance, characterized in that: Includes the following component materials: Masterbatch: 60%~80%, including: Polyolefin resin: 25 to 40 parts; Inorganic flame retardant: 50 to 70 parts; Compatibilizer: 3 to 6 parts; Antioxidant: 0.2 to 0.6 parts; Lubricant: 0.5 to 1.5 parts; Anti-aging agent: 1 to 2 parts; A material: 1%~5%, including: Silane coupling agent A-172: 1 to 2 parts; Silane coupling agent A-171: 0.5 to 1 part; Initiator: 0.1 to 0.2 parts; Masterbatch: 90 to 100 parts; Material B: 5% to 15%, including: Masterbatch: 15 to 20 parts; HDPE: 15-20 parts; Magnesium hydroxide: 40 to 60 parts; Antiaging agent 405: 5 to 10 parts; Antiaging agent RD: 5 to 10 parts; Silane coupling agent A-172: 0.5 to 0.8 parts; Catalyst dibutyltin dilaurate: 0.2 to 0.6 parts; Lubricant silicone or zinc stearate: 0.5 to 1 part; Various materials: 0.5% to 5%, including: Nano silicon dioxide: 0.5 to 2 parts; Triphenyl phosphite: 0.5 to 1.5 parts.

2. The mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material according to claim 1, characterized in that: The polyolefin resin comprises: HDPE: 15-20 parts; POE: 3 to 8 parts; EMA: 5 to 10 parts; Among them, the melt index of HDPE is 0.5g / 10min~2g / 10min, the crystallinity is 80%~90%, the melt index of POE is 2g / 10min~5g / 10min, the Shore hardness A is 50~60, and the ethyl methacrylate content of EMA is 20%~30%.

3. The mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material according to claim 1, characterized in that: The inorganic flame retardant comprises 30 to 40 parts of aluminum hydroxide and 20 to 30 parts of magnesium hydroxide, and the particle size of the flame retardant is 1 μm to 5 μm.

4. The mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material according to claim 1, characterized in that: Among the various materials, the particle size of nano silicon dioxide is 10nm to 50nm, and triphenyl phosphite is a phosphite or thioester compound.

5. The mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material according to claim 1, characterized in that: The diverse materials are prepared based on dynamic vulcanization technology by adding a vulcanizing agent and a crosslinking aid in an internal mixer at a temperature of 170° C. to 200° C. and a shear rate of 50 rpm to 200 rpm, wherein the vulcanizing agent is a peroxide or a vulcanized rubber.

6. A method for preparing a mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material, according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Mix the masterbatch, material A and material B in a mass ratio of 93-95:7-5; S2, extrusion molding by a twin-screw extruder at 180°C to 220°C; S3. Perform silane crosslinking treatment for 24h to 72h in an environment with a humidity of 70% to 90% and a temperature of 60°C to 90°C.

7. The method for preparing the mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material according to claim 6, characterized in that: In the step S1, the masterbatch is prepared by the following steps: (1) Weigh each component according to the formula ratio of the masterbatch in claim 1; (2) At a temperature of 160°C to 190°C, the components are mixed uniformly in an internal mixer to obtain a masterbatch.

8. The method for preparing the mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material according to claim 6, characterized in that: In the step S1, material A is prepared by the following steps: (1) Mix silane coupling agent A-172, silane coupling agent A-171 and initiator in proportion; (2) mixed with the masterbatch according to the formula ratio of material A in claim 1; (3) The grafting reaction is carried out by a twin-screw extruder at a temperature of 180-220°C to obtain material A.

9. The method for preparing the mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material according to claim 6, characterized in that: In the step S1, material B is prepared by the following steps: (1) Weigh each component according to the formula ratio of material B in claim 1; (2) Mix uniformly in a twin-screw extruder at a temperature of 180°C to 220°C to obtain material B.

10. The method for preparing the mud-resistant silane cross-linked low-smoke halogen-free flame-retardant polyolefin sheath material according to claim 6, characterized in that: In the step S1, nano silicon dioxide and triphenyl phosphite are added during mixing, and then kneading is performed under dynamic vulcanization process conditions. The particle size of the nano silicon dioxide is 10 nm to 50 nm.

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