A high-toughness PP-R pipe material and its preparation method

Abstract

This invention provides a high-toughness PP-R pipe material and its preparation method, belonging to the field of PP pipe technology. The raw materials of the high-toughness PP-R pipe material include: 70 parts PP-R resin, 20 parts PP-elastomer toughening agent, and 10 parts PP-PE toughening agent; the raw materials for preparing the PP-elastomer toughening agent are: PP-R resin, elastomer toughening agent, and polymer-grafted maleic anhydride compatibilizer; the raw materials for preparing the PP-PE toughening agent are: PP-R resin, PP-B resin, metallocene polyethylene, ultra-high molecular weight polyethylene, and ethylene-propylene-based compatibilizer. This invention forms a PP-R / elastomer / PE / PP-B multi-component synergistic composite toughening system through the various components, achieving complementary and synergistic improvement of the properties among the materials, thereby improving the various properties of the PP-R pipe.

Description

[0001] This application is a divisional application. The parent application number is 202310675534.3, the application date is June 8, 2023, and the invention title is "A Synergistic Composite Toughened PP-R Pipe Material and Its Preparation Method and Application". Technical Field

[0002] This invention relates to the field of PP pipe technology, and in particular to a synergistic composite toughened PP-R pipe material, its preparation method, and its application. Background Technology

[0003] Polypropylene (PP) is an abundant and inexpensive raw material. Compared with other general-purpose plastics (PVC, PE, PS), it has advantages such as low density, high strength, good electrical insulation, and ease of processing and molding. It is widely used in daily necessities, packaging, building materials, and other fields. Random copolymer polypropylene (PP-R) is the main type of PP produced. PP-R pipes are currently one of the main cold and hot water transportation pipes used in municipal engineering, residential buildings, and commercial office buildings, and polypropylene pipes have become one of the main basic materials for pipeline applications in my country.

[0004] PP-R pipes are lightweight and high-strength, significantly reducing construction intensity, and their pressure resistance test strength exceeds 5MPa. They exhibit excellent corrosion resistance, wear resistance, and scale resistance. Belonging to the polyolefin family, their molecules contain only carbon and hydrogen elements, making them non-toxic, hygienic, and environmentally friendly. They are heat-resistant and insulating, with a maximum operating temperature of 95℃ and a long-term operating temperature of 60℃, making them suitable for hot water and heating systems, saving substantial energy. The normal service life of these pipes exceeds 50 years. However, because PP is a highly isotactic, semi-crystalline, large-spherulitic polymer, it leads to defects such as low notched impact strength and increased brittleness at low temperatures.

[0005] Research methods for toughening and modifying PP materials have always attracted much attention. To improve the shortcomings of PP performance, various toughening methods have been reported, among which elastomer toughening modification has been considered one of the most effective approaches. Polyolefin elastomers (POEs) are ethylene-octene copolymers. Due to their unique molecular structure, they possess excellent comprehensive properties, including good flowability, corrosion resistance, excellent air permeability, and superior low-temperature resistance. Therefore, they are most commonly used to improve the low-temperature brittleness problem of PP. However, when PP is used as a pipe material, it is necessary to improve its low-temperature toughness while ensuring that its good rigidity is not reduced. However, elastomer toughening modification of PP often comes at the cost of sacrificing rigidity. Furthermore, there are certain differences in the properties of PP and elastomers themselves. Therefore, during blending modification, the elastomer is prone to forming a large-scale, uneven dispersion in the PP, resulting in a decrease in the material's modulus and impact resistance, failing to achieve the desired results, and the improvement in the low-temperature toughness of the finished product is not significant. Summary of the Invention

[0006] The purpose of this invention is to provide a synergistic composite toughened PP-R pipe material, its preparation method and application, wherein the synergistic composite toughened PP-R pipe material has excellent low-temperature toughness and high impact strength.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a synergistic composite toughening modified PP-R pipe material, comprising the following raw materials by mass: 70-85 parts of PP-R resin; 10-20 parts of PP-elastomer toughening agent; 5-10 parts of PP-PE toughening agent; The raw materials for preparing the PP-elastomer toughening agent include: 75-94 parts of PP-R resin, 5-20 parts of elastomer toughening agent, and 1-5 parts of polymer-grafted maleic anhydride compatibilizer. The raw materials for preparing the PP-PE toughening agent include: 75-92 parts of PP-R resin, 1-5 parts of PP-B resin, 5-10 parts of metallocene polyethylene, 1-5 parts of ultra-high molecular weight polyethylene, and 1-5 parts of ethylene-propylene compatibilizer.

[0008] Preferably, the PP-R resin is type III random copolymer polypropylene; and the PP-B resin is a propylene-ethylene block copolymer.

[0009] Preferably, the elastomer toughening agent is one or more of POE, POP, and OBC.

[0010] Preferably, the ethylene content in the POP is ≤20wt%.

[0011] Preferably, the polymer-grafted maleic anhydride compatibilizer includes PP-grafted maleic anhydride compatibilizer or POE-grafted maleic anhydride compatibilizer; the ethylene-propylene-based compatibilizer is an ethylene-propylene-based binary copolymer or an ethylene-propylene-based multi-component copolymer.

[0012] This invention provides a method for preparing the synergistic composite toughening modified PP-R pipe material described in the above technical solution, comprising the following steps: After blending PP-R resin, elastomer toughening agent and polymer-grafted maleic anhydride compatibilizer, the mixture is subjected to first extrusion stretching and granulation in sequence to obtain PP-elastomer toughening agent. After blending PP-R resin, PP-B resin, metallocene polyethylene, ultra-high molecular weight polyethylene and ethylene-propylene compatibilizer, the mixture is subjected to a second extrusion stretching and granulation in sequence to obtain PP-PE toughening agent. After premixing the PP-elastomer toughening agent, PP-PE toughening agent and PP-R resin, the mixture is subjected to a third extrusion stretching and granulation in sequence to obtain a synergistic composite toughened modified PP-R pipe material.

[0013] Preferably, during the first extrusion stretching, the screw extrusion speed is 30~80 r / min and the screw extrusion temperature range is 180~250℃.

[0014] Preferably, during the second extrusion stretching, the screw extrusion speed is 30~80 r / min and the screw extrusion temperature range is 180~230℃; during the third extrusion stretching, the screw extrusion speed is 30~80 r / min and the screw extrusion temperature range is 180~230℃.

[0015] This invention provides the application of the synergistic composite toughening modified PP-R pipe material described in the above technical solution or the synergistic composite toughening modified PP-R pipe material prepared by the preparation method described in the above technical solution in the preparation of PP-R pipes.

[0016] In the synergistic composite toughening modified PP-R pipe material provided by the present invention, due to the addition of the elastomer toughening agent, the elastomer can induce a large number of crazes under the action of external impact force, while the brittle matrix will produce shear yielding. Energy is mainly absorbed by crazes and shear bands, thereby greatly mitigating the impact failure process of the material and increasing the energy of the failure process, thereby improving the toughness of the material at room temperature and low temperature. The addition of PP-B (propylene-ethylene block copolymer) and PE (polyethylene) limits the excessive reduction in tensile strength and yield strength caused by the addition of elastomers, maintaining a balance between rigidity and toughness. Furthermore, the addition of PP-B improves the flowability during PE and PP blend extrusion, making extrusion molding smoother and providing a slight toughening effect, while further enhancing impact resistance. The addition of PE resin reduces the excessive reduction in yield strength of PP-R pipes caused by the addition of elastomers, maintaining a balance between rigidity and toughness. This allows for a reduction in the amount of elastomer added without excessively affecting the rigidity and strength of the pipe. The combined effect of elastomers and PE improves the low-temperature toughness of PP-R pipes. The addition of compatibilizers improves the interfacial bonding of the blends, especially improving the dispersion effect of the elastomer toughening agent and PE, reducing phase separation between PP and the elastomer / PE. This invention forms a multi-component synergistic composite toughening system of PP-R / elastomer / PE / PP-B, achieving complementary and synergistic performance enhancement among the materials, thereby improving the various properties of PP-R pipes.

[0017] The synergistic composite toughening modified PP-R pipe material provided by this invention is suitable for PP-R pipes of different specifications and series. During low-temperature construction in winter, it can reduce the phenomenon of environmental stress cracking of the pipe, improve the overall performance, and enhance the safety of construction personnel. Detailed Implementation

[0018] This invention provides a synergistic composite toughening modified PP-R pipe material, comprising the following raw materials by mass: 70-85 parts of PP-R resin; 10-20 parts of PP-elastomer toughening agent; 5-10 parts of PP-PE toughening agent; The raw materials for preparing the PP-elastomer toughening agent include: 75-94 parts of PP-R resin, 5-20 parts of elastomer toughening agent, and 1-5 parts of polymer-grafted maleic anhydride compatibilizer. The raw materials for preparing the PP-PE toughening agent include: 75-92 parts of PP-R resin, 1-5 parts of PP-B resin, 5-10 parts of metallocene polyethylene, 1-5 parts of ultra-high molecular weight polyethylene, and 1-5 parts of ethylene-propylene compatibilizer.

[0019] Unless otherwise specified, all raw materials required for preparation in this invention are commercially available products well known in the art.

[0020] The raw materials for preparing the synergistic composite toughening modified PP-R pipe material provided by the present invention, by weight, include 70-85 parts of PP-R resin (random copolymer polypropylene resin), preferably 70-80 parts, more preferably 70-75 parts; the random copolymer polypropylene resin is preferably type III random copolymer polypropylene, and the form of the random copolymer polypropylene resin is preferably uncolored granules, colored granules, or powder. In the embodiments of the present invention, PP 4220 is specifically used, which is derived from Yanshan Petrochemical.

[0021] Based on the mass fraction of the PP-R resin, the raw materials for preparing the synergistic composite toughening modified PP-R pipe material provided by the present invention include 10-20 parts of PP-elastomer toughening agent, preferably 15-20 parts.

[0022] In this invention, the raw materials for preparing the PP-elastomer toughening agent include: 75-94 parts of PP-R resin, 5-20 parts of elastomer toughening agent, and 1-5 parts of polymer-grafted maleic anhydride compatibilizer.

[0023] In this invention, the raw materials for preparing the PP-elastomer toughening agent include 75-94 parts of PP-R resin, preferably 80-90 parts, more preferably 82-88 parts, and even more preferably 85-86 parts. In this invention, the PP-R resin used in the PP-elastomer toughening agent is preferably the same as described above, and will not be repeated here.

[0024] In this invention, the raw materials for preparing the PP-elastomer toughening agent include 5-20 parts of elastomer toughening agent, preferably 8-18 parts, and more preferably 10-15 parts. In this invention, the elastomer toughening agent is preferably one or more of POE, POP (ethylene-octene copolymer), and OBC (polyolefin block copolymer). When the elastomer toughening agent is two or more of the above, this invention does not have a special limitation on the ratio of different types of elastomer toughening agents; it can be adjusted according to actual needs. In the POP, the ethylene content is preferably ≤20wt%.

[0025] In this invention, the raw materials for preparing the PP-elastomer toughening agent include 1-5 parts of polymer-grafted maleic anhydride compatibilizer, preferably 2-4 parts, more preferably 2.5-3.5 parts, and even more preferably 3 parts; the polymer-grafted maleic anhydride compatibilizer preferably includes PP-grafted maleic anhydride compatibilizer or POE-grafted maleic anhydride compatibilizer; this invention does not have a special limitation on the type of polymer-grafted maleic anhydride compatibilizer, and commercially available products well known in the art are acceptable, such as DuPont PP-grafted maleic anhydride compatibilizer 21E830 or 50E803; or Dow Chemical POE-grafted maleic anhydride polymer 8150 or 8400.

[0026] Based on the mass fraction of the PP-R resin, the raw materials for preparing the synergistic composite toughening modified PP-R pipe material provided by the present invention include 5 to 10 parts of PP-PE toughening agent, preferably 6 to 9 parts, and more preferably 7 to 8 parts.

[0027] In this invention, the raw materials for preparing the PP-PE toughening agent include: 75-92 parts of PP-R resin, 1-5 parts of PP-B resin, 5-10 parts of metallocene polyethylene, 1-5 parts of ultra-high molecular weight polyethylene, and 1-5 parts of ethylene-propylene compatibilizer.

[0028] In this invention, the raw materials for preparing the PP-PE toughening agent include 75-92 parts of PP-R resin, preferably 80-90 parts, more preferably 82-88 parts, and even more preferably 85-86 parts. The PP-R resin used in the PP-elastomer toughening agent is preferably the same as described above, and will not be repeated here.

[0029] In this invention, the raw materials for preparing the PP-PE toughening agent include 1 to 5 parts of PP-B resin (propylene-ethylene block copolymer), preferably 2 to 4 parts, more preferably 2.5 to 3.5 parts, and even more preferably 3 parts.

[0030] In this invention, the raw materials for preparing the PP-PE toughening agent include 5 to 10 parts of metallocene polyethylene (mPE), preferably 6 to 9 parts, and more preferably 7 to 8 parts.

[0031] In this invention, the raw materials for preparing the PP-PE toughening agent include 1 to 5 parts of ultra-high molecular weight polyethylene (UHMWPE), preferably 2 to 4 parts, more preferably 2.5 to 3.5 parts, and even more preferably 3 parts.

[0032] In this invention, the raw materials for preparing the PP-PE toughening agent include 1 to 5 parts of an ethylene-propylene-based compatibilizer, preferably 2 to 4 parts, more preferably 2.5 to 3.5 parts, and even more preferably 3 parts. In this invention, the ethylene-propylene-based compatibilizer is preferably an ethylene-propylene-based binary copolymer or an ethylene-propylene-based multi-component copolymer, more preferably Dow Chemical 5545, 5565, or 4640.

[0033] This invention provides a method for preparing the synergistic composite toughening modified PP-R pipe material described in the above technical solution, comprising the following steps: After blending PP-R resin, elastomer toughening agent and polymer-grafted maleic anhydride compatibilizer, the mixture is subjected to first extrusion stretching and granulation in sequence to obtain PP-elastomer toughening agent. After blending PP-R resin, PP-B resin, metallocene polyethylene, ultra-high molecular weight polyethylene and ethylene-propylene compatibilizer, the mixture is subjected to a second extrusion stretching and granulation in sequence to obtain PP-PE toughening agent. After premixing the PP-elastomer toughening agent, PP-PE toughening agent and PP-R resin, the mixture is subjected to a third extrusion stretching and granulation in sequence to obtain a synergistic composite toughened modified PP-R pipe material.

[0034] In this invention, the blending is preferably carried out in a high-speed mixer; the present invention does not impose any special limitations on the blending conditions, as long as the materials are mixed evenly according to a process well known in the art. The present invention also does not impose any special limitations on the premixing, as long as the materials are mixed evenly according to a process well known in the art.

[0035] In this invention, the first extrusion stretching, the second extrusion stretching, and the third extrusion stretching are preferably performed in a twin-screw extruder, and the granulation is preferably performed in a granulator; the granulation is preferably cold granulation.

[0036] In this invention, during the first extrusion stretching, the screw extrusion speed is preferably 30~80 r / min, and the screw extrusion temperature range is preferably 180~250℃.

[0037] In this invention, during the second extrusion stretching, the screw extrusion speed is preferably 30~80 r / min, and the screw extrusion temperature range is preferably 180~230℃.

[0038] In this invention, during the third extrusion stretching, the screw extrusion speed is preferably 30~80 r / min, and the screw extrusion temperature range is preferably 180~230℃.

[0039] The present invention does not impose any special limitation on the screw extrusion temperature of each zone of the twin-screw extruder. The temperature can be adjusted according to actual needs within the above temperature range. In the embodiments of the present invention, the specific temperatures of the twin-screw extruder are: 180°C in zone 1, 185°C in zone 2, 195°C in zone 3, 205°C in zone 4, 215°C in zone 5, and 205°C at the die head.

[0040] After completing the third extrusion stretching and granulation, the present invention preferably dries the obtained granules to obtain synergistic composite toughened modified PP-R pipe material; the drying temperature is preferably 70℃, and the drying time is preferably ≥3h.

[0041] This invention provides the application of the synergistically toughened modified PP-R pipe material described in the above-described technical solutions, or the synergistically toughened modified PP-R pipe material prepared by the preparation method described in the above-described technical solutions, in the preparation of PP-R pipes. This invention does not specifically limit the method of application; the corresponding pipe can be prepared using a pipe extrusion machine according to methods well known in the art.

[0042] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0043] In the following embodiments, the present invention does not have a special limitation on the magnitude of the "parts by mass", and g or kg, which are well known in the art, are both acceptable.

[0044] Example 1

[0045] The synergistic composite toughening modified PP-R pipe material provided in this embodiment contains the following raw materials by weight: 70 parts PP-R resin; 20 parts PP-elastomer toughening agent; and 10 parts PP-PE toughening agent. (1) The PP-R resin is a type III random copolymer polypropylene, with the grade PP 4220, manufactured by Yanshan Petrochemical. (2) PP-elastomer toughening agent, based on 100 parts by weight: PP-R resin, 75 parts; The elastomer is a combination of POE, POP and OBC, with a mass ratio of POE, POP and OBC of 5:3:2, 20 parts, brand: Dow Chemical; POE grafted maleic anhydride compatibilizer, 5 parts, brand: Dow Chemical 8150.

[0046] (3) PP-PE toughening agent, calculated per 100 parts by weight: PP-R resin, 75 parts; mPE, 10 parts, ExxonMobil; UHMWPE, 5 parts, Mitsui Chemicals; Ethylene-propylene compatibilizer, 5 parts, brand: Dow Chemical, 5545; PP-B resin, 5 parts, Taiwan Plastics Industry Co., Ltd.; Preparation method: After the elastomer toughening agent, POE-grafted maleic anhydride compatibilizer and PP-R resin were blended in a high-speed mixer, the first extrusion stretching and cooling granulation were performed sequentially using a twin-screw extruder and a granulator. The twin-screw extruder temperatures were 180℃ in zone 1, 185℃ in zone 2, 195℃ in zone 3, 205℃ in zone 4, 215℃ in zone 5, and 205℃ at the die head. The screw speed was 70 r / min to obtain PP / elastomer toughening agent. Metallocene polyethylene, ultra-high molecular weight polyethylene, ethylene-propylene compatibilizer, PP-B resin and PP-R resin were blended in a high-speed mixer, and then subjected to a second extrusion stretching and cooling granulation in sequence using a twin-screw extruder and a granulator. The twin-screw extruder temperatures were 180℃ in zone 1, 185℃ in zone 2, 195℃ in zone 3, 205℃ in zone 4, 215℃ in zone 5, and 205℃ at the die head. The screw speed was 70 r / min to obtain PP / PE toughening agent. After premixing the PP-elastomer toughening agent, PP-PE toughening agent and PP-R resin, the mixture is subjected to a third extrusion stretching and granulation in sequence. The twin-screw extruder temperatures are 180℃ in zone 1, 185℃ in zone 2, 195℃ in zone 3, 205℃ in zone 4, 215℃ in zone 5 and 205℃ at the die head, and the screw speed is 70 r / min. The resulting granules are dried at 70℃ for 3 hours to obtain synergistic composite toughened modified PP-R pipe material.

[0047] Example 2

[0048] The only difference from Example 1 is that: 80 parts of PP-R resin, 15 parts of PP-elastomer toughening agent, and 5 parts of PP-PE toughening agent are used, and the rest are the same as in Example 1.

[0049] Example 3

[0050] The only difference from Example 1 is that: 85 parts of PP-R resin, 10 parts of PP-elastomer toughening agent, and 5 parts of PP-PE toughening agent are used, and the rest are the same as in Example 1.

[0051] Comparative Example 1

[0052] The only difference from Example 1 is that: 80 parts of PP-R resin, 20 parts of PP-elastomer toughening agent, and 0 parts of PP-PE toughening agent are used; otherwise, they are the same as in Example 1.

[0053] Comparative Example 2

[0054] The only difference from Example 1 is that: 80 parts of PP-R resin, 0 parts of PP-elastomer toughening agent, and 20 parts of PP-PE toughening agent are used, while the rest are the same as in Example 1.

[0055] Performance testing

[0056] The pipe material prepared in Example 1 was placed in a pipe extruder to obtain a pipe sample, which is the synergistic composite toughened modified PP-R pipe. The performance of this pipe was compared with that of blank pure PP-R pipe. The test items were: tensile strength, elongation at break, and notched impact strength of simply supported beam at room temperature and low temperature. The test method was GB / T18743. The results are shown in Table 1.

[0057] Table 1. Comparison of performance data of PP-R pipes in Examples 1-3

[0058] As shown in Table 1, compared with the blank pure PP-R pipe, the low-temperature toughness (notched impact strength of a simply supported beam at -20℃) of the synergistic composite toughening modified PP-R pipe of the present invention has been significantly improved, and the decrease in tensile yield strength will not affect the normal use of the pipe, and it is not lower than the requirements of our company's standard (tensile yield stress ≥21MPa).

[0059] The comparison between Examples 1-3 and Comparative Examples 1-2 illustrates that in the composite toughening modification system, the amount of PP / elastomer toughening agent added cannot be too little or not added at all. Insufficient addition leads to insignificant improvement in low-temperature toughness, and the performance may even be worse than adding only a single blended toughening agent (as in Comparative Example 1). In Example 1, the addition amount is optimal; compared to Comparative Examples 1-2, low-temperature toughness is improved without sacrificing tensile yield strength.

[0060] The comparison between Examples 1-3 and Comparative Examples 1-2 illustrates that a single blended toughening system is far less effective in achieving the desired performance balance than a multi-component synergistic composite toughening system. While Comparative Example 1 showed improved low-temperature toughness, its tensile strength decreased and fell below the company's standard requirements. Comparative Example 2, although its tensile strength did not decrease significantly and met the standard requirements, showed limited improvement in low-temperature toughness, failing to meet the requirements for low-temperature use.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-toughness PP-R pipe material, characterized in that, The following raw materials are included in the preparation by mass parts: 70 parts PP-R resin; 20 parts PP-elastomer toughening agent; 10 parts PP-PE toughening agent; The raw materials for preparing the PP-elastomer toughening agent are: PP-R resin, elastomer toughening agent and polymer-grafted maleic anhydride compatibilizer, and the mass ratio of the PP-R resin, elastomer toughening agent and polymer-grafted maleic anhydride compatibilizer is 75:20:

5. The elastomer toughening agent includes POE, POP and OBC, and the mass ratio of POE, POP and OBC is 5:3:2; The raw materials for preparing the PP-PE toughening agent are: PP-R resin, PP-B resin, metallocene polyethylene, ultra-high molecular weight polyethylene, and ethylene-propylene compatibilizer. The mass ratio of PP-R resin, PP-B resin, metallocene polyethylene, ultra-high molecular weight polyethylene, and ethylene-propylene compatibilizer is 75:5:10:5:

5. The PP-R resin is a type III random copolymer polypropylene; The PP-B resin is a propylene-ethylene block copolymer; The polymer-grafted maleic anhydride compatibilizer is a POE-grafted maleic anhydride compatibilizer. The ethylene-propylene compatibilizer is an ethylene-propylene multi-component copolymer.

2. The high-toughness PP-R pipe material according to claim 1, characterized in that, The ethylene content in the POP is ≤20wt%.

3. A method for preparing a high-toughness PP-R pipe material according to any one of claims 1 to 2, characterized in that, Includes the following steps: 1) After blending PP-R resin, elastomer toughening agent and polymer-grafted maleic anhydride compatibilizer, the mixture is subjected to first extrusion stretching and granulation in sequence to obtain PP-elastomer toughening agent. 2) After blending PP-R resin, PP-B resin, metallocene polyethylene, ultra-high molecular weight polyethylene and ethylene-propylene compatibilizer, the mixture is subjected to a second extrusion stretching and granulation in sequence to obtain PP-PE toughening agent. 3) After premixing the PP-elastomer toughening agent, PP-PE toughening agent and PP-R resin, the mixture is subjected to a third extrusion stretching and granulation in sequence to obtain a high-toughness PP-R pipe material; There is no requirement for the order of steps 1) and 2).

4. The preparation method according to claim 3, characterized in that, During the first extrusion stretching, the screw extrusion speed is 70 r / min, the screw extrusion temperature range is 180~215℃, and the screw extrusion temperature is 180℃ in zone 1, 185℃ in zone 2, 195℃ in zone 3, 205℃ in zone 4, 215℃ in zone 5, and 205℃ at the die head.

5. The preparation method according to claim 4, characterized in that, During the second extrusion stretching, the screw extrusion speed is 70 r / min, the screw extrusion temperature range is 180~215℃, and the screw extrusion temperature is 180℃ in zone 1, 185℃ in zone 2, 195℃ in zone 3, 205℃ in zone 4, 215℃ in zone 5, and 205℃ at the die head.

6. The preparation method according to claim 5, characterized in that, During the third extrusion stretching, the screw extrusion speed is 70 r / min, the screw extrusion temperature range is 180~215℃, and the screw extrusion temperature is 180℃ in zone 1, 185℃ in zone 2, 195℃ in zone 3, 205℃ in zone 4, 215℃ in zone 5, and 205℃ at the die head.

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