High-weather-resistant high-flame-retardant polyurethane cable material and preparation method thereof

Abstract

The invention relates to the technical field of cable materials, in particular to a high-weather-resistant high-flame-retardant polyurethane cable material which comprises the following raw material components: polyurethane resin, a phosphorus-nitrogen synergistic flame-retardant system, a weather-resistant modifier, a reinforcing agent and a processing aid, the polyurethane resin is polyester type polyurethane, polyether type polyurethane or polyester-polyether copolymer type polyurethane; the phosphorus-nitrogen synergistic flame-retardant system comprises a phosphorus flame retardant and a nitrogen flame retardant, the phosphorus flame retardant is at least one of triaryl phosphate, triphenyl phosphate or resorcinol bis (diphenyl phosphate), and the nitrogen flame retardant is at least one of triaryl phosphate, triphenyl phosphate and resorcinol bis (diphenyl phosphate). The nitrogen flame retardant is at least one of melamine cyanurate, melamine pyrophosphate or melamine polyphosphate; according to the invention, a phosphorus-nitrogen synergistic flame-retardant system is designed, and the types and proportions of the two flame retardants are reasonably matched to synergistically exert physical barrier and chemical inhibition effects, so that the flame-retardant efficiency is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of cable material technology, specifically to a high weather-resistant and high flame-retardant polyurethane cable material and its preparation method. Background Technology

[0002] Polyurethane cable materials, due to their excellent mechanical toughness and processing adaptability, are widely used in cable insulation and sheathing in outdoor laying, industrial settings, and rail transportation. However, existing polyurethane cable materials have long faced multi-dimensional performance bottlenecks, making it difficult to meet the stringent requirements of use in complex environments.

[0003] In terms of flame retardancy, most products rely on a single type of flame retardant, resulting in low flame retardancy efficiency and difficulty in achieving high-level flame retardancy standards. Some solutions using a phosphorus-nitrogen synergistic system also suffer from discontinuous flame-retardant protective films during combustion due to the lack of optimized ratios of the two flame retardants, leading to dripping and secondary safety hazards. Regarding weather resistance, existing weather-resistant modification systems primarily rely on UV absorbers, neglecting the long-term protective effect of free radical scavenging stabilizers. This makes cable materials susceptible to UV radiation, humidity, and other environmental factors during long-term outdoor use, leading to performance degradation, embrittlement, and cracking, severely shortening their service life. The conflict between mechanical properties and component compatibility is equally prominent. Commonly used reinforcing fillers have weak interfacial bonding with polyurethane resin; their addition not only fails to effectively improve mechanical strength but also easily causes agglomeration, resulting in uneven material performance. Furthermore, existing technologies often focus on improving single properties, failing to address the synergistic conflicts between key properties such as flame retardancy, weather resistance, and mechanical properties. Improving one property often leads to a decline in another, preventing comprehensive optimization of overall performance. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a high weather-resistant and high flame-retardant polyurethane cable material and its preparation method.

[0005] To achieve the above objectives, this invention proposes a high weather-resistant and high flame-retardant polyurethane cable material, comprising the following raw material components: polyurethane resin, a phosphorus-nitrogen synergistic flame-retardant system, a weather-resistant modifier, a reinforcing agent, and processing aids; the polyurethane resin is a polyester-type polyurethane, a polyether-type polyurethane, or a polyester-polyether copolymer polyurethane; the phosphorus-nitrogen synergistic flame-retardant system includes a phosphorus-based flame retardant and a nitrogen-based flame retardant, wherein the phosphorus-based flame retardant is at least one of triaryl phosphate, triphenyl phosphate, or resorcinol bis(diphenyl phosphate), and the nitrogen-based flame retardant is at least one of melamine cyanurate, melamine pyrophosphate, or melamine polyphosphate; the weather-resistant modifier includes an antioxidant, an ultraviolet absorber, and a hindered amine light stabilizer; the reinforcing agent is at least one of nano-silica, nano-calcium carbonate, or nano-mica powder; and the processing aids include a lubricant and an anti-dripping agent.

[0006] Preferably, the polyurethane resin has a hydroxyl value of 18-55 mgKOH / g, and the amount of polyurethane resin used is 55-85 parts by weight; in the phosphorus-nitrogen synergistic flame retardant system, the amount of phosphorus flame retardant is 8-28 parts by weight, the amount of nitrogen flame retardant is 4-18 parts by weight, and the mass ratio of phosphorus flame retardant to nitrogen flame retardant is 1.2:1-5.5:1.

[0007] Preferably, in the weather-resistant modifier, the antioxidant is at least one of antioxidant 1010, antioxidant 1076 or antioxidant 1098, the ultraviolet absorber is at least one of UV-531, UV-327 or UV-326, and the hindered amine light stabilizer is at least one of piperidine or piperazine; the hindered amine light stabilizer accounts for 28%-50% of the total mass of the weather-resistant modifier, and the total amount of the weather-resistant modifier is 1.8-8.5 parts by mass.

[0008] Preferably, the reinforcing agent is a modified reinforcing agent treated with a modifier, wherein the modifier is a silane coupling agent or a titanate coupling agent; the silane coupling agent is at least one of KH550, KH560 or KH570, and the titanate coupling agent is at least one of NDZ-101 or NDZ-201; the amount of the reinforcing agent is 2-12 parts by weight, and the amount of the modifier is 0.8%-2.2% of the total mass of the reinforcing agent.

[0009] Preferably, in the weather-resistant modifier, the amount of the antioxidant is 0.4-2.2 parts by weight, the amount of the ultraviolet absorber is 0.4-2.2 parts by weight, and the amount of the hindered amine light stabilizer is 0.4-2.2 parts by weight.

[0010] Preferably, the grafting rate of the reinforcing agent after treatment with the modifier is not less than 75%; the particle size of the nano-silica is 10-50nm, the particle size of the nano-calcium carbonate is 20-60nm, and the particle size of the nano-mica powder is 30-80nm.

[0011] A method for preparing the aforementioned high weather-resistant and high flame-retardant polyurethane cable material includes the following steps: (1) Flame retardant pretreatment: mix phosphorus-based flame retardant and nitrogen-based flame retardant, add pretreatment agent, and stir at 78-92℃ for 1-2 hours; (2) Modification of reinforcing agent: If the reinforcing agent is a modified reinforcing agent, mix the reinforcing agent and the modifier and stir at 78-92℃ for 0.9-2.1h; (3) Staged mixing: In a twin-screw mixer, the polyurethane resin is first melted at 155-175℃ for 4-6 minutes, and then heated to 165-185℃. Weather-resistant modifier, pretreated flame retardant, reinforcing agent and lubricant are added in sequence and stirred until evenly dispersed. (4) Granulation: The mixed material is fed into a twin-screw extruder and granulated under the following temperature conditions: Zone 1 150-160℃, Zone 2 170-180℃, Zone 3 175-185℃, and Die head 180-190℃.

[0012] Preferably, the pretreatment agent in step (1) is a silane coupling agent or an aluminate coupling agent; the silane coupling agent is KH550 or KH560, and the aluminate coupling agent is DL-411-A; the amount of the pretreatment agent is 0.9%-2.1% of the total mass of the phosphorus-nitrogen synergistic flame retardant system.

[0013] Preferably, in step (3), the stirring time after adding the weather-resistant modifier is 2.5-3.5 min, the stirring time after adding the pretreated flame retardant is 4.5-5.5 min, the stirring time after adding the reinforcing agent is 3.5-4.5 min, and the stirring time after adding the lubricant is 1.5-2.5 min; after adding the lubricant, the anti-dripping agent is added and stirred for 1.5-2.5 min.

[0014] Preferably, the anti-dripping agent is polytetrafluoroethylene micro powder or polyolefin wax micro powder, and the amount of the anti-dripping agent is 0-3.5 parts by weight; the lubricant is at least one of calcium stearate, zinc stearate or ethylene bis-stearamide, and the amount of the lubricant is 0.4-2.2 parts by weight.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention designs a phosphorus-nitrogen synergistic flame retardant system. By rationally matching the types and proportions of the two flame retardants, the physical barrier and chemical inhibition effects are synergistically exerted, which greatly improves the flame retardant efficiency, enabling the cable material to reach a high level of flame retardant standards. At the same time, it effectively inhibits the dripping phenomenon during the combustion process and eliminates secondary safety risks.

[0016] 2. This invention adopts a compound weather-resistant system dominated by free radical scavenging stabilizers, combined with the synergistic effect of antioxidants and ultraviolet absorbers, to delay the aging process of materials from the source, ensuring that the cable material can maintain stable mechanical properties and structural integrity after long-term outdoor use, greatly extending its service life and adapting to harsh climatic environments.

[0017] 3. This invention strengthens the interfacial bonding between the reinforcing filler and the polyurethane resin through modification, effectively preventing filler agglomeration and ensuring performance uniformity while improving the tensile strength and toughness of the material. Furthermore, through innovative processes such as staged mixing and raw material pretreatment, this invention achieves synergistic improvements in key properties such as flame retardancy, weather resistance, and mechanical properties, avoiding the loss of other performance characteristics caused by optimizing a single property.

[0018] The raw material system of this invention has good flexibility and adaptability. The type and ratio of raw materials can be adjusted according to different application scenarios. Moreover, the preparation process does not require special equipment, has high industrial feasibility, is suitable for cable preparation in a variety of scenarios, and has broad application prospects. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0020] Example 1: (1) Raw material dosage (parts by weight): 70g polyester polyurethane (hydroxyl value 35mgKOH / g), TP18, MCA12, 5 weathering agents (10101.5, 1681.5, UV-5311, HALS1), 5g unmodified nano silica, 1g calcium stearate, 0g anti-dripping agent.

[0021] (2) Preparation process: 0.6 parts by weight of flame retardant KH550 was used for pretreatment at 85℃ for 1.5h; in a twin-screw mixer, polyurethane resin was melted at 160-170℃ for 5min, and the temperature was raised to 170-180℃. Weathering agent was added and stirred for 3min, pretreated flame retardant was stirred at high speed for 5min, unmodified nano silica was stirred for 4min, and calcium stearate was stirred at low speed for 2min; granulation was carried out in the twin-screw extruder at 155℃ in zone 1, 175℃ in zone 2, 180℃ in zone 3, and 185℃ at the die head, and injection molded into standard samples.

[0022] Example 2: (1) Raw material dosage: Based on Example 1, the flame retardant was adjusted to TP22 and MCA8 (total dosage 30 parts by mass, phosphorus-nitrogen ratio 2.75:1), while the dosage of other raw materials remained unchanged.

[0023] (2) Preparation process: Same as in Example 1.

[0024] Example 3: (1) Raw material dosage: Based on Example 2, the weathering agent was adjusted to antioxidant 10101.5, antioxidant 1681.5, HALS2 (total dosage 5 parts by mass, UV-531 reduced to 0), and the dosage of other raw materials remained unchanged.

[0025] (2) Preparation process: Same as in Example 1.

[0026] Example 4: (1) Amount of raw materials: Based on Example 3, unmodified nano silica was replaced with KH550 modified nano silica, and the amount of other raw materials remained unchanged.

[0027] (2) Preparation process: Add a step of modifying the reinforcing agent (stir nano silica and 0.05 parts by mass of KH550 at 85°C for 1.5h), the rest is the same as in Example 1.

[0028] Example 5: (1) Raw material dosage: Based on Example 4, add 2 parts by weight of polytetrafluoroethylene micro powder (anti-dripping agent), and keep the dosage of other raw materials unchanged.

[0029] (2) Preparation process: Same as in Example 4, but add anti-dripping agent after calcium stearate during mixing and stir for 2 minutes.

[0030] Example 6: (1) Raw material dosage (parts by weight): polyether polyurethane 72 (hydroxyl value 22mgKOH / g), RDP20, MPP10 (phosphorus-nitrogen ratio 2:1), weathering agent 5.2 (antioxidant 1076 1.6, UV-327 1.0, Tinuvin 770 2.6), KH560 modified nano calcium carbonate 6, EBS 1.2, polyolefin wax micro powder 2.5.

[0031] (2) Preparation process: The flame retardant was pretreated with 0.66 parts by weight of KH560 at 82℃ for 1.8h by stirring; the reinforcing agent was modified with 0.07 parts by weight of KH560 at 82℃ for 1.2h by stirring; in the twin-screw mixer, the resin was melted at 158℃ for 4.5min, and the temperature was raised to 172℃. The weathering agent was added and stirred for 3.2min, the pretreated flame retardant was stirred for 5.2min, the modified reinforcing agent was stirred for 4.2min, EBS was stirred for 2.2min, and the anti-dripping agent was stirred for 2.2min; the twin-screw extruder was granulated at 152℃ in zone one, 173℃ in zone two, 178℃ in zone three, and 183℃ at the die head.

[0032] Example 7: (1) Raw material dosage (parts by mass): Polyester-polyether copolymer polyurethane 68 (hydroxyl value 52mgKOH / g), TPP18, APP9 (phosphorus-nitrogen ratio 2:1), weathering agent 4.8 (antioxidant 1098 1.4, UV-326 1.0, CyasorbUV-3346 2.4), NDZ-101 modified nano mica 8, zinc stearate 1.0, polytetrafluoroethylene micro powder 2.0.

[0033] (2) Preparation process: 0.54 parts by weight of DL-411-A were used for pretreatment at 88℃ for 1.3h; 0.12 parts by weight of NDZ-101 were used for modification at 88℃ for 1.8h; in a twin-screw mixer, the resin was melted at 172℃ for 5.5min, and then heated to 182℃. Weathering agent was added and stirred for 2.8min, pretreated flame retardant was stirred for 4.8min, modified reinforcing agent was stirred for 3.8min, zinc stearate was stirred for 1.8min, and anti-dripping agent was stirred for 1.8min; in a twin-screw extruder, granulation was carried out at 158℃ in zone 1, 178℃ in zone 2, 183℃ in zone 3, and 188℃ at the die head.

[0034] Example 8: (1) Raw material dosage (parts by weight): Polyester polyurethane 82 (hydroxyl value 18mgKOH / g), RDP 25, MCA 5 (phosphorus-nitrogen ratio 5:1), weathering agent 8.2 (antioxidant 1010 2.0, UV-53 12.0, Tinuvin 770 4.2), unmodified nano silica 12, EBS 2.0, anti-dripping agent 3.5.

[0035] (2) Preparation process: 0.60 parts by weight of KH550 were used for pretreatment at 78℃ for 2.0h; in a twin-screw mixer, the resin was melted at 155℃ for 6.0min, and the temperature was raised to 165℃. Weathering agent was added and stirred for 3.5min, pretreated flame retardant was stirred for 5.5min, unmodified reinforcing agent was stirred for 4.5min, EBS was stirred for 2.5min, and anti-dripping agent was stirred for 2.5min; granulation was carried out in the twin-screw extruder at 150℃ in zone 1, 170℃ in zone 2, 175℃ in zone 3, and 180℃ at the die head.

[0036] Comparative Example 1: (1) Raw material usage: In Example 1, TP and MCA were removed, while the usage of other raw materials remained unchanged.

[0037] (2) Preparation process: Same as in Example 1.

[0038] Comparative Example 2: (1) Amount of raw materials: In Example 1, antioxidant 1010, antioxidant 168, UV-531 and HALS were removed, and the amount of other raw materials remained unchanged.

[0039] (2) Preparation process: Same as in Example 1.

[0040] Comparative Example 3: (1) Raw material usage: In Example 1, the flame retardant was replaced with TP30 (MCA was removed), and the usage of other raw materials remained unchanged.

[0041] (2) Preparation process: Same as in Example 1.

[0042] Comparative Example 4: (1) Amount of raw materials: In Example 4, the modified nano-silica was replaced with unmodified nano-silica, and the amount of other raw materials remained unchanged.

[0043] (2) Preparation process: Same as in Example 1 (without the reinforcing agent modification step).

[0044] Comparative Example 5: (1) Amount of raw materials: In Example 1, the hydroxyl value of polyurethane resin was changed to 15 mg KOH / g (lower than the lower limit of 18 mg KOH / g of this invention), while the amount of other raw materials remained unchanged.

[0045] (2) Preparation process: Same as in Example 1.

[0046] Comparative Example 6: (1) Raw material usage: TP:MCA=1:1, HALS content of 20%, unmodified nano-silica, and the rest are the same as in Example 5.

[0047] (2) Preparation process: No flame retardant pretreatment and reinforcing agent modification steps, the rest is the same as in Example 1.

[0048] Comparative Example 7: (1) Amount of raw materials: In Example 8, the hydroxyl value of the resin was changed to 15 mg KOH / g (lower than the extension limit of 18 mg KOH / g), while the amount of other raw materials remained unchanged.

[0049] (2) Preparation process: Same as in Example 8.

[0050] Comparative Example 8: (1) Raw material usage: RDP10 and MPP10 (phosphorus-nitrogen ratio 1:1, lower than the extension limit 1.2:1) in Example 6, the usage of other raw materials remained unchanged.

[0051] (2) Preparation process: Same as in Example 6.

[0052] Comparative Example 9: (1) Preparation process: The flame retardant in Example 7 was not pretreated, and the rest was the same as in Example 7.

[0053] Performance tests are as follows: Testing standards: (1) Flame retardant performance: UL94 vertical flammability rating is tested according to GB / T2408, and oxygen index (LOI) is tested according to GB / T2406. (2) Weather resistance: A 1000-hour xenon lamp aging test was conducted according to GB / T16422.2 (irradiance 0.71W / m²). 2@340nm), according to GB / T2423.4, a 1000h damp heat resistance test (40℃ / 95%RH) was conducted to test the retention rate of tensile strength and elongation at break after aging; (3) Mechanical properties: Tensile strength (tensile rate 50 mm / min) and elongation at break were tested according to GB / T1040. (4) Thermal stability: Thermogravimetric analysis (TGA) was used in a nitrogen atmosphere at a heating rate of 5℃ / min to test the 5% thermal weight loss temperature (T5), 50% thermal weight loss temperature (T50), and char residue at 800℃. (5) Compatibility: The dispersion state of the reinforcing agent was observed using a scanning electron microscope (SEM), and the dispersed particle size was recorded.

[0054] The test results are shown in Tables 1 and 2 below: Table 1: Test Results of Flame Retardancy and Weather Resistance

[0055] Table 2: Test Results of Mechanical and Thermal Stability and Reinforcing Agent Dispersion Properties

[0056] Based on the above test results, the analysis is as follows: (1) The oxygen index of all examples (1-8) is ≥32.0%, of which the oxygen index of examples 4-8 is ≥34.5%, and the UL94 rating is V0. The tensile retention rate after 1000h xenon lamp aging is ≥76%, the damp heat retention rate is ≥68%, and the aging retention rate of examples 3-8 is even ≥84%, which proves that the expanded raw material process combination can stably achieve high flame retardancy and long-term weather resistance.

[0057] (2) Comparative Example 1 is not flame retardant and has an oxygen index of only 20.5%; Comparative Example 2 has an aging retention rate of only 50%; Comparative Example 6 is V1 grade and has molten droplets and an aging retention rate of 72%; Comparative Examples 7 and 8 cannot reach V0 grade. The above results all prove that the parameter range and raw material combination expanded by the present invention are necessary conditions for achieving the performance standard.

[0058] (3) The tensile strength of Examples 4-8 is ≥11.5MPa, of which the tensile strength of Examples 4-7 is ≥17.8MPa, the elongation at break is ≥345%, the carbon residue at 800℃ is ≥9.5%, and the particle size of the reinforcing agent is ≤6μm, which proves that the modification and reinforcement and pretreatment process can effectively improve the mechanical properties, thermal stability and component dispersibility; the tensile strength of Example 8 is 11.5MPa, which still meets the requirements of thin materials, proving the rationality of the parameter boundary expansion.

[0059] (4) Comparative Example 4 has a tensile strength of only 12.3 MPa and a dispersed particle size of 12 μm; Comparative Example 5 has a tensile strength of 10.8 MPa and a T5 of only 275 °C; Comparative Example 9 has a tensile strength of 14.5 MPa and a dispersed particle size of 8 μm. The above results all demonstrate the key role of the modification process and raw material parameter range in performance optimization.

[0060] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only to the claims and their full scope and equivalents.

Claims

1. A high weather-resistant and high flame-retardant polyurethane cable material, characterized in that, The product comprises the following raw material components: polyurethane resin, a phosphorus-nitrogen synergistic flame retardant system, weather-resistant modifier, reinforcing agent, and processing aid; the polyurethane resin is a polyester-type polyurethane, a polyether-type polyurethane, or a polyester-polyether copolymer polyurethane; the phosphorus-nitrogen synergistic flame retardant system includes a phosphorus-based flame retardant and a nitrogen-based flame retardant, wherein the phosphorus-based flame retardant is at least one of triaryl phosphate, triphenyl phosphate, or resorcinol bis(diphenyl phosphate), and the nitrogen-based flame retardant is at least one of melamine cyanurate, melamine pyrophosphate, or melamine polyphosphate; the weather-resistant modifier includes an antioxidant, an ultraviolet absorber, and a hindered amine light stabilizer; the reinforcing agent is at least one of nano-silica, nano-calcium carbonate, or nano-mica powder; and the processing aid includes a lubricant and an anti-dripping agent.

2. The high weather-resistant and high flame-retardant polyurethane cable material according to claim 1, characterized in that, The polyurethane resin has a hydroxyl value of 18-55 mgKOH / g, and the amount of polyurethane resin used is 55-85 parts by weight; in the phosphorus-nitrogen synergistic flame retardant system, the amount of phosphorus flame retardant is 8-28 parts by weight, the amount of nitrogen flame retardant is 4-18 parts by weight, and the mass ratio of phosphorus flame retardant to nitrogen flame retardant is 1.2:1-5.5:

1.

3. The high weather-resistant and high flame-retardant polyurethane cable material according to claim 1, characterized in that, The weather-resistant modifier comprises an antioxidant of at least one of antioxidant 1010, antioxidant 1076, or antioxidant 1098, an ultraviolet absorber of at least one of UV-531, UV-327, or UV-326, and a hindered amine light stabilizer of at least one of piperidine or piperazine. The hindered amine light stabilizer accounts for 28%-50% of the total mass of the weather-resistant modifier, and the total amount of the weather-resistant modifier is 1.8-8.5 parts by mass.

4. The high weather-resistant and high flame-retardant polyurethane cable material according to claim 1, characterized in that, The reinforcing agent is a modified reinforcing agent treated with a modifier, which is a silane coupling agent or a titanate coupling agent; the silane coupling agent is at least one of KH550, KH560 or KH570, and the titanate coupling agent is at least one of NDZ-101 or NDZ-201; the amount of the reinforcing agent is 2-12 parts by mass, and the amount of the modifier is 0.8%-2.2% of the total mass of the reinforcing agent.

5. The high weather-resistant and high flame-retardant polyurethane cable material according to claim 3, characterized in that, In the weather-resistant modifier, the amount of antioxidant is 0.4-2.2 parts by mass, the amount of UV absorber is 0.4-2.2 parts by mass, and the amount of hindered amine light stabilizer is 0.4-2.2 parts by mass.

6. The high weather-resistant and high flame-retardant polyurethane cable material according to claim 4, characterized in that, The reinforcing agent, after being treated with a modifier, has a grafting rate of not less than 75%; the nano-silica has a particle size of 10-50 nm, the nano-calcium carbonate has a particle size of 20-60 nm, and the nano-mica powder has a particle size of 30-80 nm.

7. A method for preparing a high weather-resistant and high flame-retardant polyurethane cable material as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Flame retardant pretreatment: mix phosphorus-based flame retardant and nitrogen-based flame retardant, add pretreatment agent, and stir at 78-92℃ for 1-2 hours; (2) Modification of reinforcing agent: If the reinforcing agent is a modified reinforcing agent, mix the reinforcing agent and the modifier and stir at 78-92℃ for 0.9-2.1h; (3) Staged mixing: In a twin-screw mixer, the polyurethane resin is first melted at 155-175℃ for 4-6 minutes, and then heated to 165-185℃. Weather-resistant modifier, pretreated flame retardant, reinforcing agent and lubricant are added in sequence and stirred until evenly dispersed. (4) Granulation: The mixed material is fed into a twin-screw extruder and granulated under the following temperature conditions: Zone 1 150-160℃, Zone 2 170-180℃, Zone 3 175-185℃, and Die head 180-190℃.

8. The preparation method according to claim 7, characterized in that, The pretreatment agent mentioned in step (1) is a silane coupling agent or an aluminate coupling agent; the silane coupling agent is KH550 or KH560, and the aluminate coupling agent is DL-411-A; the amount of the pretreatment agent is 0.9%-2.1% of the total mass of the phosphorus-nitrogen synergistic flame retardant system.

9. The preparation method according to claim 7, characterized in that, In step (3), the stirring time after adding the weather-resistant modifier is 2.5-3.5 min, the stirring time after adding the pretreated flame retardant is 4.5-5.5 min, the stirring time after adding the reinforcing agent is 3.5-4.5 min, and the stirring time after adding the lubricant is 1.5-2.5 min; after adding the lubricant, add the anti-dripping agent and stir for 1.5-2.5 min.

10. The preparation method according to claim 9, characterized in that, The anti-dripping agent is polytetrafluoroethylene micro powder or polyolefin wax micro powder, and the amount of the anti-dripping agent is 0-3.5 parts by weight; the lubricant is at least one of calcium stearate, zinc stearate or ethylene bis-stearamide, and the amount of the lubricant is 0.4-2.2 parts by weight.

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