A high-impact double-walled corrugated pipe and a method for manufacturing the same

Abstract

The application discloses a kind of high impact resistance double-wall corrugated pipes and preparation methods thereof, relate to plastic pipe technical field, the high impact resistance double-wall corrugated pipe includes outer corrugated wall and the inner smooth wall integrally formed with the outer corrugated wall, the outer corrugated wall with the inner smooth wall is prepared by polyolefin composite material through co-extrusion, vacuum shaping;The polyolefin composite material includes high-density polyethylene, alpha-olefin ethylene copolymer, linear low-density polyethylene, compatible toughening agent, surface-modified inorganic rigid filler and auxiliary agent;By adding alpha-olefin ethylene copolymer in the HDPE system within a certain density and melt mass flow rate range, it forms dispersed flexible toughening phase in polyethylene continuous phase.Under the action of low-temperature impact load, flexible phase can induce the formation of silver line and shear band, absorb impact energy, thereby significantly improving the impact resistance of double-wall corrugated pipe at-20 DEG C.

Description

Technical Field

[0001] This invention relates to the field of plastic pipe technology, and in particular to a high-impact double-wall corrugated pipe and its preparation method. Background Technology

[0002] Polyethylene double-wall corrugated pipes typically consist of an outer corrugated wall and an inner smooth wall. The outer wall has a ring-shaped corrugated structure, which improves the pipe's ring stiffness, while the inner wall remains smooth, reducing transport resistance. These pipes are widely used in municipal drainage, agricultural irrigation and drainage, road drainage, communication sheathing, and underground sewage systems.

[0003] Most existing double-wall corrugated polyethylene pipes use high-density polyethylene (HDPE) as the main raw material. HDPE has high rigidity, corrosion resistance, and processing stability. However, under conditions such as low-temperature construction, winter transportation, backfill impact, and foundation settlement, the outer corrugated wall of the pipe is prone to concentrated impact loads. When the ambient temperature is low, the toughness of ordinary HDPE material decreases, and whitening, cracking, or brittle failure easily occurs at the crests of the outer wall, affecting the laying safety and service life of the pipe.

[0004] To improve the impact resistance of polyethylene double-wall corrugated pipes, existing technologies typically employ toughening methods such as adding elastomers, reducing resin density, or increasing the content of soft components. However, simply increasing the amount of elastomer often reduces the material modulus, causing a decrease in pipe ring stiffness and making it difficult to meet the load-bearing capacity requirements of buried pipes. While simply adding inorganic fillers can improve rigidity, it can easily lead to uneven dispersion of the filler in the polyethylene matrix, forming stress concentration points and thus reducing low-temperature impact performance.

[0005] Furthermore, existing double-wall corrugated pipes typically use the same extrusion formula for both the outer corrugated wall and the inner smooth wall. While this method is simple, it doesn't fully consider the stress differences between the outer and inner walls. The outer corrugated wall directly bears the loads from transportation, construction, backfilling, and external impacts, requiring higher low-temperature impact toughness. The inner smooth wall primarily serves as a support and conveyor, necessitating greater dimensional stability, ring stiffness, and inner wall flatness. Using the exact same high-toughness formula for both the inner and outer walls would result in a decrease in overall stiffness; using a standard HDPE formula would lead to insufficient impact resistance of the outer wall.

[0006] Therefore, there is an urgent need to provide a double-walled corrugated pipe material and its preparation method that can significantly improve low-temperature impact resistance while maintaining ring stiffness, ring flexibility and processing stability. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: to address the problems of insufficient impact resistance of existing HDPE double-wall corrugated pipes in low-temperature environments, easy decrease in ring stiffness after toughening, uneven dispersion of inorganic fillers which easily causes stress concentration, and difficulty in taking into account the impact resistance of the outer wall and the support performance of the inner wall when using the same formula for the inner and outer walls, the present invention provides a high-impact double-wall corrugated pipe and its preparation method.

[0008] This invention toughens a polyethylene system at low temperature using α-olefin ethylene copolymer, improves the interfacial bonding between α-olefin ethylene copolymer and HDPE using a compatibility toughening agent, compensates for stiffness loss caused by elastic components using surface-modified inorganic rigid fillers, and achieves higher impact toughness on the outer corrugated wall and maintains high stiffness and dimensional stability on the inner smooth wall through a differentiated co-extrusion process for the inner and outer walls, thereby obtaining a high-impact double-wall corrugated pipe with excellent comprehensive performance.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a high-impact double-wall corrugated pipe, the high-impact double-wall corrugated pipe comprising an outer corrugated wall and an inner smooth wall integrally formed with the outer corrugated wall, the outer corrugated wall and the inner smooth wall being prepared by co-extrusion and vacuum shaping of polyolefin composite material.

[0010] The polyolefin composite material comprises, by weight, the following: 75-88 parts high-density polyethylene, 8-18 parts α-olefin ethylene copolymer, 3-10 parts linear low-density polyethylene, 1-4 parts compatibility toughening agent, 5-15 parts inorganic rigid filler, 1-3 parts carbon black masterbatch, 0.2-0.8 parts antioxidant, 0.2-1.0 parts lubricant, and 0.1-0.5 parts processing aid.

[0011] The α-olefin ethylene copolymer is an elastomer or plastic formed by copolymerizing ethylene with C4-C8 α-olefins, with a density of 0.860-0.910 g / cm³ and a melt mass flow rate of 0.5-5.0 g / 10 min.

[0012] The α-olefin ethylene copolymer can be one or a combination of two or more of ethylene-octene copolymer, ethylene-butene copolymer, and ethylene-hexene copolymer. Preferably, the ethylene-octene copolymer accounts for 50%-100% of the mass of the α-olefin ethylene copolymer.

[0013] The high-density polyethylene has a density of 0.945-0.965 g / cm³ and a melt flow rate of 0.2-1.2 g / 10 min. The mass ratio of the high-density polyethylene to the α-olefin ethylene copolymer is 100:(10-22).

[0014] The compatibility toughening agent is one or a combination of two or more of maleic anhydride-grafted polyethylene, glycidyl methacrylate-grafted polyethylene, and ethylene-acrylate copolymer, and the grafting rate of the compatibility toughening agent is 0.5%-1.5%.

[0015] The inorganic rigid filler is one or a combination of two or more of the following: surface-modified calcium carbonate, talc, and wollastonite. The inorganic rigid filler has a D50 particle size of 0.8-3.0 μm, a D97 particle size ≤10 μm, and a moisture content ≤0.2%. It is surface-modified with stearic acid, silane coupling agent, or titanate coupling agent to improve its dispersibility and interfacial bonding in the polyolefin matrix.

[0016] The outer corrugated wall has a wall thickness of 1.5-6.0 mm at the crest and 1.0-4.5 mm at the trough, while the inner smooth wall has a wall thickness of 1.2-5.0 mm. A continuous annular cavity structure is formed between the outer corrugated wall and the inner smooth wall.

[0017] In one embodiment, the outer corrugated wall and the inner smooth wall are made of the same polyolefin composite material.

[0018] In another preferred embodiment, the content of α-olefin ethylene copolymer in the outer corrugated wall is 2-6 parts by weight higher than the content of α-olefin ethylene copolymer in the inner smooth wall. This differentiated design enables the outer corrugated wall to have higher low-temperature impact absorption capacity, while maintaining higher stiffness, dimensional stability, and inner wall flatness of the inner smooth wall.

[0019] In the drop hammer impact test at -20℃, the impact strength of the high-impact double-wall corrugated pipe is at least 30% higher than that of the same specification pure HDPE double-wall corrugated pipe.

[0020] The present invention also provides a method for preparing the above-mentioned high-impact double-wall corrugated pipe, comprising the following steps: S1. Weigh out the high-density polyethylene, α-olefin ethylene copolymer, linear low-density polyethylene, compatibility toughening agent, inorganic rigid filler, carbon black masterbatch, antioxidant, lubricant and processing aid by weight. S2. The high-density polyethylene, α-olefin ethylene copolymer, linear low-density polyethylene, compatibility toughening agent and inorganic rigid filler are put into a high-speed mixer and mixed for 3-8 minutes. Then carbon black masterbatch, antioxidant, lubricant and processing aid are added and mixed for another 2-5 minutes to obtain a premix. S3. The premixed material is fed into a twin-screw extruder for melt blending, extrusion, cooling and pelletizing to obtain polyolefin composite material particles; S4. Add the outer wall polyolefin composite material particles to the outer wall extruder and the inner wall polyolefin composite material particles to the inner wall extruder. The content of α-olefin ethylene copolymer in the outer wall polyolefin composite material particles is 2-6 parts by weight higher than the content of α-olefin ethylene copolymer in the inner wall polyolefin composite material particles. Co-extrusion through a composite die forms a tube blank with an outer corrugated wall and an inner smooth wall. S5. The tube blank is introduced into the double-wall corrugated forming module, and after vacuum adsorption, cooling and shaping, traction and cutting, the high impact-resistant double-wall corrugated tube is obtained.

[0021] In step S3, the temperatures from zone one to the die head of the twin-screw extruder are controlled sequentially as follows: 160-175℃, 170-185℃, 180-195℃, 185-205℃, and 190-210℃. The screw speed is 180-350 r / min, and the vacuum exhaust pressure is -0.06 to -0.09 MPa.

[0022] In step S4, the melt temperature of the outer wall extruder is 185-210℃, and the melt temperature of the inner wall extruder is 180-205℃.

[0023] In step S5, the temperature of the molding module is 15-35℃, the vacuum degree is -0.03 to -0.08MPa, and the traction speed is 0.3-2.5m / min.

[0024] Compared with existing technologies, this invention provides a high-impact double-wall corrugated pipe and its preparation method, which has the following beneficial effects: By adding an α-olefin ethylene copolymer with a specific density and melt flow rate range to the HDPE system, a dispersed flexible toughening phase is formed in the continuous polyethylene phase. Under low-temperature impact loads, the flexible phase can induce the formation of crazes and shear bands, absorbing impact energy, thereby significantly improving the impact resistance of the double-wall corrugated pipe at -20℃.

[0025] This invention does not employ a simple method of increasing the elastomer content. Instead, it limits the α-olefin ethylene copolymer to 8-18 parts by weight and combines it with 5-15 parts by weight of surface-modified inorganic rigid filler. This design can improve low-temperature toughness while maintaining the ring stiffness of the pipe, preventing insufficient ring stiffness or corrugated wall collapse due to excessive toughening.

[0026] This invention employs a compatibility toughening agent to improve the interfacial bonding between HDPE, α-olefin ethylene copolymer, and inorganic rigid filler. By having the grafted groups of the compatibility toughening agent interact with the filler surface or polar interface, the risk of filler agglomeration and interfacial debonding is reduced, allowing impact loads to be effectively transferred between the matrix and the filler, thus preventing the inorganic filler from becoming a brittle crack initiation point.

[0027] This invention limits the inorganic rigid filler to calcium carbonate, talc, or wollastonite surface-modified with stearic acid, silane coupling agent, or titanate coupling agent, and limits the D50 particle size to 0.8-3.0 μm, the D97 particle size to ≤10 μm, and the moisture content to ≤0.2%. This particle size range is beneficial for the uniform dispersion of the filler and also provides stiffness reinforcement, improving the ring stiffness and dimensional stability of the pipe.

[0028] This invention employs a differentiated co-extrusion structure for the inner and outer walls, resulting in an α-olefin ethylene copolymer content in the outer corrugated wall that is 2-6 parts by weight higher than that in the inner smooth wall. The outer corrugated wall bears the main external impact load, and the higher α-olefin ethylene copolymer content improves low-temperature impact resistance. The inner smooth wall maintains a relatively low α-olefin ethylene copolymer content, which helps to maintain ring stiffness, inner wall smoothness, and dimensional stability, thereby achieving a synergistic balance between outer wall toughness and overall stiffness.

[0029] The preparation method of this invention adopts a twin-screw melt blending granulation and a double-wall corrugated pipe co-extrusion molding process. The process route is highly compatible with existing polyethylene double-wall corrugated pipe production lines and is easy to implement industrially. Attached Figure Description

[0030] Figure 1 In Embodiment 2 of the present invention, the outer corrugated wall of the high-impact double-wall corrugated pipe is... SEM image of the cross section after a drop hammer impact at 20℃; Figure 2 This is a SEM image of the low-temperature impact cross-section of the outer corrugated wall of the pure HDPE double-wall corrugated pipe, which is Comparative Example 1 of this invention. Figure 3 This is a TEM image of the α-olefin ethylene copolymer dispersed phase in the polyolefin composite material of Example 2 of the present invention; Figure 4 This is a SEM image of the low-temperature impact fracture surface of the composite material without compatibility toughening agent in Comparative Example 5 of this invention. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Please see Figures 1-4 This invention provides a technical solution for a high-impact double-wall corrugated pipe and its manufacturing method: In the following examples and comparative examples, the double-wall corrugated pipes prepared are all of the same specification, with a nominal inner diameter of DN / ID300, a target ring stiffness grade of SN8, and a wall thickness controlled at the crest of the outer corrugated wall of 3.0-3.5 mm, at the trough of 2.0-2.4 mm, and at the thickness of the inner smooth wall of 2.0-2.6 mm. Unless otherwise specified, 3-8 parts of carbon black masterbatch are used, with a carbon black content of 35%-50% in the masterbatch; the antioxidant is a compound of hindered phenolic antioxidants and phosphite antioxidants; the lubricant is polyethylene wax; and the processing aid is a fluoropolymer processing aid.

[0033] The "impact strength" mentioned in this specification refers to the critical impact energy corresponding to a true impact rate (TIR) ​​≤ 10% at -20℃, under the test conditions specified in the currently valid standard for testing the impact resistance of thermoplastic pipes. The critical impact energy is calculated based on the mass of the falling hammer, the acceleration due to gravity, and the height of the falling hammer. The higher the critical impact energy, the stronger the pipe's low-temperature impact resistance.

[0034] The “pure HDPE double-wall corrugated pipe of the same specification” mentioned in this specification refers to a double-wall corrugated pipe made using the same pipe specifications, the same corrugated structure, the same molding equipment and the same processing conditions, with HDPE as the main resin and the addition of conventional carbon black masterbatch, antioxidants and lubricants.

[0035] Example 1 The polyolefin composite material for the outer wall comprises, by weight, the following: 75 parts high-density polyethylene, 10 parts α-olefin ethylene copolymer, 3 parts linear low-density polyethylene, 1 part compatibility toughening agent, 5 parts calcium carbonate surface modified with stearic acid, 1 part carbon black masterbatch, 0.2 parts antioxidant, 0.2 parts lubricant, and 0.1 parts processing aid.

[0036] The polyolefin composite material for the inner wall comprises, by weight, the following: 77 parts high-density polyethylene, 8 parts α-olefin ethylene copolymer, 3 parts linear low-density polyethylene, 1 part compatibility toughening agent, 5 parts calcium carbonate surface modified with stearic acid, 1 part carbon black masterbatch, 0.2 parts antioxidant, 0.2 parts lubricant, and 0.1 parts processing aid.

[0037] The α-olefin ethylene copolymer is an ethylene-octene copolymer with a density of 0.890 g / cm³ and a melt flow rate of 1.0 g / 10 min. The high-density polyethylene has a density of 0.955 g / cm³ and a melt flow rate of 0.45 g / 10 min. The compatibility toughening agent is maleic anhydride-grafted polyethylene with a grafting rate of 0.8%. The calcium carbonate D50 has a particle size of 1.5 μm.

[0038] The preparation method is as follows: S1. Weigh out the raw materials for the outer wall and the raw materials for the inner wall according to the above formula.

[0039] S2. High-density polyethylene, ethylene-octene copolymer, linear low-density polyethylene, maleic anhydride grafted polyethylene and stearic acid surface-modified calcium carbonate are respectively added to a high-speed mixer and mixed for 3 minutes. Then carbon black masterbatch, antioxidant, lubricant and processing aid are added and mixed for another 2 minutes to obtain premix for outer wall and premix for inner wall.

[0040] S3. The premixed materials for the outer wall and the premixed materials for the inner wall are fed into a twin-screw extruder for melt blending and granulation. The temperatures from zone one to the die head of the twin-screw extruder are 160℃, 170℃, 180℃, 185℃, and 190℃ respectively, the screw speed is 180 r / min, and the vacuum exhaust pressure is -0.06 MPa, to obtain polyolefin composite material particles for the outer wall and polyolefin composite material particles for the inner wall.

[0041] S4. Add the polyolefin composite material particles for the outer wall to the outer wall extruder, and add the polyolefin composite material particles for the inner wall to the inner wall extruder. The melt temperature of the outer wall extruder is 185℃, and the melt temperature of the inner wall extruder is 180℃. The tube blank is formed by co-extrusion through the composite die.

[0042] S5. The tube blank is introduced into the double-wall corrugated forming module. The forming module temperature is 15℃, the vacuum degree is -0.03MPa, and the traction speed is 0.3m / min. After vacuum adsorption, cooling and shaping, traction and cutting, a high-impact double-wall corrugated pipe is obtained.

[0043] Example 2 The polyolefin composite material for the outer wall comprises, by weight, the following: 82 parts high-density polyethylene, 15 parts α-olefin ethylene copolymer, 6 parts linear low-density polyethylene, 2.5 parts compatibility toughening agent, 10 parts calcium carbonate surface modified with silane coupling agent, 2 parts carbon black masterbatch, 0.5 parts antioxidant, 0.6 parts lubricant, and 0.3 parts processing aid.

[0044] The polyolefin composite material for the inner wall comprises, by weight, the following: 85 parts high-density polyethylene, 12 parts α-olefin ethylene copolymer, 6 parts linear low-density polyethylene, 2.5 parts compatibility toughening agent, 10 parts calcium carbonate surface modified with silane coupling agent, 2 parts carbon black masterbatch, 0.5 parts antioxidant, 0.6 parts lubricant, and 0.3 parts processing aid.

[0045] The α-olefin ethylene copolymer is an ethylene-octene copolymer with a density of 0.875 g / cm³ and a melt flow rate of 2.0 g / 10 min. The high-density polyethylene has a density of 0.958 g / cm³ and a melt flow rate of 0.60 g / 10 min. The compatibility toughening agent is maleic anhydride-grafted polyethylene with a grafting rate of 1.0%. The calcium carbonate D50 has a particle size of 1.2 μm.

[0046] The preparation method is as follows: S1. Weigh out the raw materials for the outer wall and the raw materials for the inner wall according to the above formula.

[0047] S2. High-density polyethylene, ethylene-octene copolymer, linear low-density polyethylene, maleic anhydride grafted polyethylene and calcium carbonate surface modified with silane coupling agent are respectively added to a high-speed mixer and mixed for 5 minutes. Then carbon black masterbatch, antioxidant, lubricant and processing aid are added and mixed for another 3 minutes to obtain premix for outer wall and premix for inner wall.

[0048] S3. The premixed materials for the outer wall and the premixed materials for the inner wall are fed into a twin-screw extruder for melt blending and granulation. The temperatures from zone one to the die head of the twin-screw extruder are 168℃, 178℃, 188℃, 195℃, and 200℃ respectively, the screw speed is 260 r / min, and the vacuum exhaust pressure is -0.08 MPa, to obtain polyolefin composite material particles for the outer wall and polyolefin composite material particles for the inner wall.

[0049] S4. Add the polyolefin composite material particles for the outer wall to the outer wall extruder, and add the polyolefin composite material particles for the inner wall to the inner wall extruder. The melt temperature of the outer wall extruder is 198℃, and the melt temperature of the inner wall extruder is 193℃. The tube blank is formed by co-extrusion through the composite die.

[0050] S5. The tube blank is introduced into the double-wall corrugated forming module. The forming module temperature is 25℃, the vacuum degree is -0.06MPa, and the traction speed is 1.2m / min. After vacuum adsorption, cooling and shaping, traction and cutting, a high-impact double-wall corrugated pipe is obtained.

[0051] Example 3 The polyolefin composite material for the outer wall comprises, by weight, the following: 88 parts high-density polyethylene, 18 parts α-olefin ethylene copolymer, 10 parts linear low-density polyethylene, 4 parts compatibility toughening agent, 15 parts talc powder surface modified with titanate coupling agent, 3 parts carbon black masterbatch, 0.8 parts antioxidant, 1.0 part lubricant, and 0.5 parts processing aid.

[0052] The polyolefin composite material for the inner wall comprises, by weight, the following: 88 parts high-density polyethylene, 12 parts α-olefin ethylene copolymer, 10 parts linear low-density polyethylene, 4 parts compatibility toughening agent, 15 parts talc powder surface modified with titanate coupling agent, 3 parts carbon black masterbatch, 0.8 parts antioxidant, 1.0 part lubricant, and 0.5 parts processing aid.

[0053] The α-olefin ethylene copolymer is a blend of ethylene-octene copolymer and ethylene-hexene copolymer in a mass ratio of 7:3, with a density of 0.885 g / cm³ and a melt flow rate of 3.0 g / 10 min. The high-density polyethylene has a density of 0.965 g / cm³ and a melt flow rate of 0.90 g / 10 min. The compatibility toughening agent is a blend of maleic anhydride-grafted polyethylene and ethylene-acrylate copolymer, with a grafting rate of 1.2%. The talc powder D50 particle size is 2.0 μm.

[0054] The preparation method is as follows: S1. Weigh out the raw materials for the outer wall and the raw materials for the inner wall according to the above formula.

[0055] S2. High-density polyethylene, α-olefin ethylene copolymer, linear low-density polyethylene, compatibility toughening agent and talc powder modified with titanate coupling agent are respectively added to a high-speed mixer and mixed for 8 minutes. Then carbon black masterbatch, antioxidant, lubricant and processing aid are added and mixed for another 5 minutes to obtain premix for outer wall and premix for inner wall.

[0056] S3. The premixed materials for the outer wall and the premixed materials for the inner wall are fed into a twin-screw extruder for melt blending and granulation. The temperatures from zone one to the die head of the twin-screw extruder are 175℃, 185℃, 195℃, 205℃, and 210℃ respectively, the screw speed is 350 r / min, and the vacuum exhaust pressure is -0.09 MPa, to obtain polyolefin composite material particles for the outer wall and polyolefin composite material particles for the inner wall.

[0057] S4. Add the polyolefin composite material particles for the outer wall to the outer wall extruder, and add the polyolefin composite material particles for the inner wall to the inner wall extruder. The melt temperature of the outer wall extruder is 210℃, and the melt temperature of the inner wall extruder is 205℃. The tube blank is formed by co-extrusion through the composite die.

[0058] S5. The tube blank is introduced into the double-wall corrugated forming module. The forming module temperature is 35℃, the vacuum degree is -0.08MPa, and the traction speed is 2.5m / min. After vacuum adsorption, cooling and shaping, traction and cutting, a high-impact double-wall corrugated pipe is obtained.

[0059] Example 4 Both the outer and inner walls are made of the same polyolefin composite material, comprising, by weight: 82 parts high-density polyethylene, 13 parts α-olefin ethylene copolymer, 6 parts linear low-density polyethylene, 2 parts compatibility toughening agent, 10 parts wollastonite surface modified with silane coupling agent, 2 parts carbon black masterbatch, 0.5 parts antioxidant, 0.6 parts lubricant, and 0.3 parts processing aid.

[0060] The α-olefin ethylene copolymer is an ethylene-octene copolymer with a density of 0.880 g / cm³ and a melt flow rate of 2.5 g / 10 min. The high-density polyethylene has a density of 0.956 g / cm³ and a melt flow rate of 0.55 g / 10 min. The compatibility toughening agent is glycidyl methacrylate-grafted polyethylene with a grafting rate of 0.9%. The wollastonite D50 has a particle size of 2.5 μm.

[0061] The preparation steps in this embodiment are basically the same as those in Example 2, except that the same polyolefin composite material particles are added to both the outer wall extruder and the inner wall extruder.

[0062] Example 5 The polyolefin composite material for the outer wall comprises, by weight, the following: 80 parts high-density polyethylene, 14 parts α-olefin ethylene copolymer, 5 parts linear low-density polyethylene, 2 parts compatibility toughening agent, 8 parts calcium carbonate and talc composite filler modified with stearic acid, 2 parts carbon black masterbatch, 0.4 parts antioxidant, 0.5 parts lubricant, and 0.2 parts processing aid.

[0063] The polyolefin composite material for the inner wall comprises, by weight, the following: 84 parts high-density polyethylene, 10 parts α-olefin ethylene copolymer, 5 parts linear low-density polyethylene, 2 parts compatibility toughening agent, 8 parts calcium carbonate and talc composite filler modified with stearic acid, 2 parts carbon black masterbatch, 0.4 parts antioxidant, 0.5 parts lubricant, and 0.2 parts processing aid.

[0064] The α-olefin ethylene copolymer is a blend of ethylene-butene copolymer and ethylene-octene copolymer in a mass ratio of 4:6, with a density of 0.895 g / cm³ and a melt flow rate of 1.8 g / 10 min. The composite filler has a calcium carbonate to talc mass ratio of 6:4 and a D50 particle size of 1.8 μm.

[0065] The preparation steps in this embodiment are basically the same as those in Example 2.

[0066] Example 6 The polyolefin composite material for the outer wall comprises, by weight, the following: 78 parts high-density polyethylene, 16 parts α-olefin ethylene copolymer, 8 parts linear low-density polyethylene, 3 parts compatibility toughening agent, 12 parts calcium carbonate surface modified with silane coupling agent, 2.5 parts carbon black masterbatch, 0.6 parts antioxidant, 0.8 parts lubricant, and 0.4 parts processing aid.

[0067] The polyolefin composite material for the inner wall comprises, by weight, the following: 82 parts high-density polyethylene, 11 parts α-olefin ethylene copolymer, 8 parts linear low-density polyethylene, 3 parts compatibility toughening agent, 12 parts calcium carbonate surface modified with silane coupling agent, 2.5 parts carbon black masterbatch, 0.6 parts antioxidant, 0.8 parts lubricant, and 0.4 parts processing aid.

[0068] The α-olefin ethylene copolymer is an ethylene-octene copolymer with a density of 0.870 g / cm³ and a melt flow rate of 1.5 g / 10 min. The high-density polyethylene has a density of 0.952 g / cm³ and a melt flow rate of 0.50 g / 10 min. The compatibility toughening agent is maleic anhydride-grafted polyethylene with a grafting rate of 1.1%. The calcium carbonate D50 has a particle size of 1.0 μm.

[0069] The preparation steps in this embodiment are basically the same as those in Example 2.

[0070] Comparative Example 1 uses 100 parts high-density polyethylene, 2 parts carbon black masterbatch, 0.5 parts antioxidant, 0.6 parts lubricant, and 0.3 parts processing aid. It does not contain α-olefin ethylene copolymer, linear low-density polyethylene, compatibility toughening agent, or inorganic rigid filler. The pipe specifications, outer corrugated wall dimensions, inner smooth wall dimensions, co-extrusion equipment, and molding process parameters of this comparative example are the same as those of Example 2.

[0071] Comparative Example 2 differs only in that neither the polyolefin composite material for the outer wall nor the polyolefin composite material for the inner wall contains α-olefin ethylene copolymer, and both are supplemented with an equal weight of high-density polyethylene. The remaining components and preparation methods are the same as in Example 2.

[0072] Comparative Example 3 differs only in that: the content of α-olefin ethylene copolymer in the polyolefin composite material for the outer wall is 4 parts, the content of α-olefin ethylene copolymer in the polyolefin composite material for the inner wall is 4 parts, and it is supplemented with an equal weight of high-density polyethylene. The remaining components and preparation methods are the same as in Example 2.

[0073] Comparative Example 4 differs only in that the content of α-olefin ethylene copolymer in the polyolefin composite material for the outer wall is 24 parts, the content of α-olefin ethylene copolymer in the polyolefin composite material for the inner wall is 20 parts, and the content of high-density polyethylene is reduced accordingly. The remaining components and preparation methods are the same as in Example 2.

[0074] Comparative Example 5 differs only in that: no compatibility toughening agent is added, and an equal part by weight of high-density polyethylene is used to make up the difference; the remaining components and preparation methods are the same as in Example 2.

[0075] Comparative Example 6 differs only in that the inorganic rigid filler used is unmodified calcium carbonate with the same particle size as in Example 2, while the other components and preparation methods are the same as in Example 2.

[0076] Comparative Example 7 differs only in that the content of α-olefin ethylene copolymer in the polyolefin composite material used for the outer wall is 12 parts, and the content of α-olefin ethylene copolymer in the polyolefin composite material used for the inner wall is 15 parts. That is, the content of α-olefin ethylene copolymer in the outer wall is lower than that in the inner wall. The total amount of other components, the types of materials, and the preparation methods are the same as in Example 2.

[0077] Performance testing methods To verify the technical effect of the present invention, DN / ID300 double-wall corrugated pipes of the same specifications were prepared according to Examples 1 to 6 and Comparative Examples 1 to 7. All pipes were placed in an environment of 23℃±2℃ and 50%±10% relative humidity for 48 hours before testing.

[0078] 1. Low-temperature drop hammer impact test The low-temperature drop hammer impact test was conducted according to GB / T 14152-2001 "Test Method for Resistance to External Impact of Thermoplastic Pipes - Clockwise Rotation Method".

[0079] After conditioning the specimens at -20℃ for 4 hours, a drop hammer impact test was conducted. By varying the drop hammer height and impact energy, the occurrence of cracks, penetrating failure, or significant brittle fracture was recorded, and the true impact rate (TIR) ​​was calculated. The highest impact energy that the pipe could withstand when TIR ≤ 10% was taken as the critical impact energy, expressed in J.

[0080] The low-temperature shock gain rate is calculated using the following formula: Low-temperature impact improvement rate = (critical impact energy of example or comparative example - critical impact energy of comparative example 1) / critical impact energy of comparative example 1 × 100.

[0081] 2. Ring stiffness test The ring stiffness test was conducted according to GB / T 9647-2015, "Determination of Ring Stiffness of Thermoplastic Pipes". The test temperature was 23℃±2℃, and the compression speed was determined according to the standard requirements. The load on the specimen under the specified deformation was recorded, and the ring stiffness was calculated in kN / m².

[0082] 3. Ring flexibility test The ring flexibility test was conducted according to GB / T 39385-2020, "Determination of Ring Flexibility of Thermoplastic Pipes for Plastic Piping Systems". The pipe was radially compressed to a specified deformation, and the presence of internal wall cracking, external wall cracking, delamination, reverse bending failure, or structural instability was observed. The presence of cracks or delamination at 30% radial deformation was used as the evaluation index.

[0083] 4. Oxidation induction time test The oxidation induction time was tested according to GB / T 19472.1-2019 "Buried Polyethylene (PE) Structural Wall Piping Systems - Part 1: Polyethylene Double Wall Corrugated Pipes", and the differential scanning calorimetry method was used for determination. The test temperature was 200℃, and the oxidation induction time was recorded in minutes.

[0084] 5. Longitudinal Retraction Rate Test The longitudinal shrinkage rate test was conducted according to GB / T 6671-2001, "Determination of Longitudinal Shrinkage Rate of Thermoplastic Pipes". After treating the sample at a specified temperature for a specified time, the change rate of the sample length was measured, expressed in percent.

[0085] 6. Tensile property test Tensile property testing was conducted in accordance with GB / T 8804.3-2003 "Determination of tensile properties of thermoplastic pipes - Part 3: Polyolefin pipes". The test items included tensile yield stress and elongation at break, which were used to evaluate the toughness and processing stability of the pipe material.

[0086] Figure 1 In the figure, the cross-section is rough, with obvious plastic tearing, crack deflection and micropore structure. The filler is relatively uniformly dispersed, indicating that the material undergoes significant plastic deformation and effectively absorbs impact energy during the impact process.

[0087] Figure 2 In the middle section, the cross-section is relatively flat overall, the main crack propagation path is obvious, and it is accompanied by local stepped cross-section and brittle failure characteristics, indicating that pure HDPE has weak plastic deformation ability under low temperature impact and the crack is prone to rapid propagation.

[0088] Figure 3 In the figure, the dark, nearly circular or elliptical areas represent the α-olefin ethylene copolymer-enriched dispersed phase, while the light-colored areas represent the HDPE continuous matrix. The dispersed phases are relatively uniform in size and distribution, with no obvious large-scale agglomeration, indicating that the compatibility-toughening system is conducive to the formation of a stable flexible dispersed structure.

[0089] Figure 4 As shown in the figure, the cross-section is relatively flat, but there are pull-out holes and interface debonding around the filler particles. The cracks extend along the interface between the matrix and the filler, indicating that when no compatibility toughening agent is added, the bonding between the phase interfaces is insufficient, and the impact energy is difficult to dissipate effectively.

[0090] Test Results Table 1. Low-temperature impact resistance and structural mechanical properties of each embodiment and comparative example.

[0091] As shown in Table 1, the critical impact energy of Examples 1 to 6 under the condition of -20℃ is significantly higher than that of the pure HDPE reference pipe, with an improvement rate of 34.4%-62.2%, all of which meet the requirement of "improving by no less than 30% compared with the same specification of pure HDPE double-wall corrugated pipe".

[0092] Comparative Example 2, without the addition of α-olefin ethylene copolymer, had a critical impact energy of only 196 J, which was only 8.9% higher than that of the pure HDPE reference tube. This indicates that α-olefin ethylene copolymer is a key technical feature for improving low-temperature impact resistance.

[0093] In Comparative Example 3, the content of α-olefin ethylene copolymer was lower than the range specified in this invention, the critical impact energy was 214 J, and the improvement rate was only 18.9%, which did not meet the high impact resistance index specified in this invention. This indicates that when the content of α-olefin ethylene copolymer is too low, the flexible phase is insufficient and cannot effectively absorb low-temperature impact energy.

[0094] In Comparative Example 4, the content of α-olefin ethylene copolymer was higher than the limit specified in this invention. Although the critical impact energy reached 312J, the ring stiffness decreased to 6.7kN / m², which is lower than the stiffness level usually required for SN8 grade. Furthermore, local buckling occurred in the ring flexibility test, indicating that excessive α-olefin ethylene copolymer content will weaken the rigidity and structural stability of the material.

[0095] Comparative Example 5, without the addition of a compatibility toughening agent, had a critical impact energy of 228 J, representing a 26.7% improvement, which did not meet the 30% performance improvement requirement. Furthermore, it exhibited localized whitening and slight interfacial cracks during the 30% ring flexibility test. These results indicate that, in the absence of a compatibility toughening agent, the interfacial bonding between the flexible phase of the α-olefin ethylene copolymer and the continuous phase of HDPE, as well as between the inorganic rigid filler and the polyolefin matrix, is insufficient. Under low-temperature impact loading, this makes the interface prone to debonding and crack propagation.

[0096] Comparative Example 6 used unmodified inorganic rigid fillers with a critical impact energy of 220 J, representing an increase of 22.2%. Localized whitening and slight cracking were observed during ring flexibility testing. These results indicate that while unmodified inorganic fillers can provide a certain level of stiffness, they are prone to agglomeration in polyolefin matrices. These agglomerated particles form localized stress concentration points under impact loads, making crack initiation and propagation more likely.

[0097] In Comparative Example 7, the content of α-olefin ethylene copolymer on the outer wall was lower than that on the inner wall. Although the total α-olefin ethylene copolymer content in the formulation was close to that of Example 2, the low-temperature impact absorption capacity of the outer corrugated wall was insufficient, with a critical impact energy of only 229 J and an improvement rate of 27.2%, failing to meet the 30% improvement requirement. This result indicates that, based on the total mass of each polyolefin composite material being 100%, the differentiated structural design, where the mass percentage of α-olefin ethylene copolymer in the outer corrugated wall is 2-6 percentage points higher than that in the inner smooth wall, plays a crucial role in improving external impact resistance.

[0098] Table 2. Thermal stability, dimensional stability, and tensile properties of each embodiment and comparative example.

[0099] As shown in Table 2, the oxidation induction time for Examples 1 to 6 was 36-41 min, indicating that the antioxidant system used in this invention can meet the thermal stability requirements during the processing and use of polyethylene double-wall corrugated pipes. The longitudinal shrinkage rate for Examples 1 to 6 was 1.2%-1.6%, indicating good dimensional stability of the pipes.

[0100] Examples 2 and 6 exhibit high elongation at break, at 680% and 705% respectively, while maintaining ring stiffness within the range of 8.7-9.2 kN / m². This demonstrates that the present invention achieves a balance between toughness and rigidity through the synergistic effect of α-olefin ethylene copolymer, compatible toughening agent, and surface-modified inorganic rigid filler.

[0101] In Comparative Example 4, due to the excessively high content of α-olefin ethylene copolymer, the tensile yield stress decreased to 18.9 MPa, and the longitudinal shrinkage rate increased to 2.6%, indicating that excessive flexible components lead to a decrease in material strength and dimensional stability. This result demonstrates the rationality of limiting the α-olefin ethylene copolymer content to 8-18 parts by weight in this invention.

[0102] Comparative Examples 5 and 6, by omitting the compatibility toughening agent or using unmodified fillers, both exhibited insufficient low-temperature impact resistance, but their failure mechanisms differed. Comparative Example 5 primarily showed interfacial debonding and crack propagation due to insufficient interfacial bonding; Comparative Example 6 primarily showed localized stress concentration and crack initiation due to uneven filler dispersion. These two examples demonstrate, from different perspectives, the necessity of compatibility toughening agents and filler surface modification in the formulation system of this invention.

[0103] Results Analysis 1. Effect of α-olefin ethylene copolymer on low-temperature impact resistance Examples 1 through 6 all used α-olefin ethylene copolymer as the low-temperature toughening component. Due to its low density and good chain segment mobility, the α-olefin ethylene copolymer forms a dispersed flexible phase within the HDPE matrix. When the pipe is subjected to a drop hammer impact at -20°C, the flexible phase absorbs the impact energy and induces localized plastic deformation in the matrix, thereby delaying crack propagation.

[0104] Data from Comparative Examples 2 and 3 show that when no α-olefin ethylene copolymer is added or its content is less than 8 parts by weight, the improvement in low-temperature impact performance is insufficient. Data from Comparative Example 4 shows that when the α-olefin ethylene copolymer content is higher than 18 parts by weight, although the impact performance is improved, the ring stiffness and dimensional stability decrease significantly. Therefore, this invention limits the α-olefin ethylene copolymer content to 8-18 parts by weight, which achieves a better balance between impact resistance and ring stiffness.

[0105] 2. The effect of compatibility toughening agents on interfacial bonding In Example 2, after adding 2.5 parts by weight of maleic anhydride-grafted polyethylene, the low-temperature critical impact energy reached 285J, while in Comparative Example 5, without the addition of a compatibility toughening agent, the critical impact energy decreased to 228J, with an improvement rate of only 26.7%, which did not reach the 30% improvement level required by the present invention.

[0106] The failure mechanism of Comparative Example 5 was mainly due to insufficient interfacial bonding. Due to the lack of a compatibility toughening agent, the interfacial bonding between the flexible phase of the α-olefin ethylene copolymer and the continuous phase of HDPE was insufficient, and a stable interface was also difficult to form between the inorganic rigid filler and the polyolefin matrix. When the pipe was subjected to low-temperature impact, the impact energy could not be effectively transferred and dissipated between the phases, but instead preferentially debonded along the weak areas of the interface, leading to localized whitening and microcrack propagation. Therefore, the compatibility toughening agent in this invention is not merely an additive, but a key component for establishing a stable interface between the continuous phase, the flexible phase, and the filler.

[0107] 3. The effect of surface-modified inorganic rigid fillers on the rigidity-toughness balance Examples 1 to 6 all used inorganic rigid fillers that were surface-modified with stearic acid, silane coupling agents, or titanate coupling agents. After surface modification, the compatibility between the filler surface and the polyolefin matrix is ​​improved, the filler is easier to disperse uniformly, and the ring stiffness of the pipe can be improved without significantly sacrificing impact toughness.

[0108] Comparative Example 6 used unmodified calcium carbonate. Although the ring stiffness remained at 9.1 kN / m², the low-temperature critical impact energy decreased to 220 J, with an improvement rate of only 22.2%. Furthermore, localized whitening and slight cracks appeared in the ring flexibility test. These results indicate that unmodified inorganic fillers are difficult to maintain uniform dispersion in a polyolefin matrix and easily form agglomerated particles. These agglomerated particles act as localized hard defects during impact, easily causing stress concentration and inducing crack initiation.

[0109] Therefore, although both Comparative Examples 5 and 6 exhibit insufficient low-temperature impact resistance, the causes differ. Comparative Example 5 focuses on failure caused by "insufficient interfacial bonding," while Comparative Example 6 focuses on failure caused by "uneven filler dispersion and stress concentration." Both examples demonstrate that the compatibility toughening agent and the surface-modified inorganic rigid filler in this invention have different but complementary mechanisms of action. Together with the α-olefin ethylene copolymer, they constitute a key formulation system for achieving a balance between high impact resistance and high ring stiffness.

[0110] 4. The impact of differentiated co-extrusion design for inner and outer walls In Example 2, the content of α-olefin ethylene copolymer on the outer wall was 15 parts, and on the inner wall it was 12 parts, with the outer wall containing 3 parts by weight more than the inner wall. The critical impact energy reached 285 J, and the ring stiffness remained at 9.2 kN / m². In Example 6, the content of α-olefin ethylene copolymer on the outer wall was 5 parts by weight more than that on the inner wall, and the critical impact energy was further increased to 292 J.

[0111] Comparative Example 7 had an α-olefin ethylene copolymer content of 12 parts on the outer wall and 15 parts on the inner wall, meaning the α-olefin ethylene copolymer content on the outer wall was lower than that on the inner wall. Although the overall material usage was close to that of Example 2, its critical impact energy was only 229 J, failing to meet the requirement of a 30% increase compared to the pure HDPE reference pipe. This indicates that the external impact of the double-walled corrugated pipe is mainly borne by the outer corrugated wall, and only by configuring a higher content of α-olefin ethylene copolymer in the outer corrugated wall can the external impact energy be absorbed more effectively.

[0112] This invention does not simply involve adding elastomers to HDPE. Instead, it selects α-olefin-ethylene copolymers within a specific density and melt flow rate range to ensure good compatibility and low-temperature flexibility with the polyethylene matrix. Limiting the α-olefin-ethylene copolymer to 8-18 parts by weight improves low-temperature impact resistance while avoiding excessive toughening that could reduce ring stiffness. Introducing a compatibility toughening agent creates a more stable interfacial structure between the flexible phase, the HDPE matrix, and the inorganic rigid filler, preventing debonding and crack propagation due to insufficient interfacial bonding. Surface-modified inorganic rigid fillers compensate for modulus loss caused by the elastic components and prevent unmodified filler agglomeration that forms stress concentration points, thereby maintaining the pipe's ring stiffness and structural stability. A differentiated co-extrusion structure is used, where the mass percentage of α-olefin-ethylene copolymer in the outer corrugated wall is 2-6 percentage points higher than that in the inner smooth wall, based on the total mass of the respective polyolefin composite materials (100%). This concentrates the impact-resistant components on the main impact-bearing areas while maintaining the inner wall's support performance.

[0113] The aforementioned technical features work together to enable all six embodiments to increase the low-temperature drop hammer impact strength by at least 30% compared to the pure HDPE reference pipe at -20℃, while maintaining ring stiffness, ring flexibility, thermal stability, and dimensional stability. This result demonstrates that the present invention resolves the contradiction between the existing double-wall corrugated pipe's "insufficient low-temperature toughness" and "decreased stiffness after toughening," exhibiting outstanding substantive features and significant progress.

[0114] The high-impact double-wall corrugated pipe of the present invention is composed of high-density polyethylene, α-olefin ethylene copolymer, linear low-density polyethylene, compatible toughening agent, inorganic rigid filler and conventional additives. The raw materials are sourced from stable sources. The preparation process includes steps such as high-speed mixing, twin-screw melt blending and granulation, dual-machine co-extrusion, vacuum shaping, cooling traction and cutting. It has good compatibility with existing polyethylene double-wall corrugated pipe production equipment.

Claims

1. A high-impact double-wall corrugated pipe, characterized in that, The high-impact double-wall corrugated pipe includes an outer corrugated wall and an inner smooth wall integrally formed with the outer corrugated wall. The outer corrugated wall and the inner smooth wall are prepared by co-extrusion and vacuum shaping of polyolefin composite material. The polyolefin composite material comprises, by weight, the following: The composition includes 75-88 parts high-density polyethylene, 8-18 parts α-olefin ethylene copolymer, 3-10 parts linear low-density polyethylene, 1-4 parts compatibility toughening agent, 5-15 parts inorganic rigid filler, 1-3 parts carbon black masterbatch, 0.2-0.8 parts antioxidant, 0.2-1.0 parts lubricant, and 0.1-0.5 parts processing aid; the α-olefin ethylene copolymer content in the outer corrugated wall is 2-6 parts by weight higher than the α-olefin ethylene copolymer content in the inner smooth wall. The α-olefin ethylene copolymer is an elastomer or plastic formed by copolymerizing ethylene with C4-C8 α-olefins, with a density of 0.860-0.910 g / cm³ and a melt flow rate of 0.5-5.0 g / 10 min; the melt flow rate is determined according to GB / T 3682.1, with test conditions of 190℃ and 2.16 kg. The polyolefin composite material is melt-blended and granulated by a twin-screw extruder, and then extruded into a double-wall corrugated pipe to obtain the high-impact double-wall corrugated pipe. Linear low-density polyethylene can improve melt ductility and co-extrusion stability, enhance the mold adhesion of the preform during vacuum adsorption molding, and improve low-temperature toughness together with α-olefin ethylene copolymer. The high-impact double-wall corrugated pipe is subjected to an external impact test at -20℃ according to GB / T 14152-2001. The critical impact energy corresponding to the true impact rate TIR≤10% characterizes the low-temperature impact resistance performance. The critical impact energy is not less than 30% higher than that of a pure HDPE reference pipe prepared under the same specifications, the same corrugated structure, and the same molding conditions.

2. The high-impact double-wall corrugated pipe according to claim 1, characterized in that, The α-olefin ethylene copolymer is one or a combination of two or more of ethylene-octene copolymer, ethylene-butene copolymer, and ethylene-hexene copolymer; preferably, the mass percentage of ethylene-octene copolymer in the α-olefin ethylene copolymer is 50%-100%.

3. The high-impact double-wall corrugated pipe according to claim 1, characterized in that, The high-density polyethylene has a density of 0.945-0.965 g / cm³ and a melt flow rate of 0.2-1.2 g / 10 min. The melt flow rate is determined according to GB / T 3682.1 under the conditions of 190℃ and 2.16 kg. The mass ratio of the high-density polyethylene to the α-olefin ethylene copolymer is 100:(10-22).

4. The high-impact double-wall corrugated pipe according to claim 1, characterized in that, The compatibility toughening agent is one or a combination of two or more of maleic anhydride-grafted polyethylene, glycidyl methacrylate-grafted polyethylene, and ethylene-acrylate copolymer; when the compatibility toughening agent is maleic anhydride-grafted polyethylene or glycidyl methacrylate-grafted polyethylene, its grafting rate is 0.5%-1.5%.

5. A high-impact double-wall corrugated pipe according to claim 1, characterized in that, The inorganic rigid filler is one or more of the following: surface-modified calcium carbonate, talc, and wollastonite. The D50 particle size of the inorganic rigid filler is 0.8-3.0 μm, the D97 particle size is ≤10 μm, and the moisture content is ≤0.2%. It is surface-modified with stearic acid, silane coupling agent, or titanate coupling agent to improve its dispersibility and interfacial bonding in the polyolefin matrix.

6. A high-impact double-wall corrugated pipe according to claim 1, characterized in that, The outer corrugated wall has a wall thickness of 1.5-6.0 mm at the crest and 1.0-4.5 mm at the trough, while the inner smooth wall has a wall thickness of 1.2-5.0 mm. A continuous annular cavity structure is formed between the outer corrugated wall and the inner smooth wall.

7. A high-impact double-wall corrugated pipe according to claim 1, characterized in that, The outer corrugated wall and the inner smooth wall are made of the same material, or the content of α-olefin ethylene copolymer in the outer corrugated wall is 2-6 parts by weight higher than the content of α-olefin ethylene copolymer in the inner smooth wall.

8. A method for preparing a high-impact double-wall corrugated pipe as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Weigh out the high-density polyethylene, α-olefin ethylene copolymer, linear low-density polyethylene, compatibility toughening agent, inorganic rigid filler, carbon black masterbatch, antioxidant, lubricant and processing aid by weight. S2. The high-density polyethylene, α-olefin ethylene copolymer, linear low-density polyethylene, compatibility toughening agent and inorganic rigid filler are put into a high-speed mixer and mixed for 3-8 minutes. Then carbon black masterbatch, antioxidant, lubricant and processing aid are added and mixed for another 2-5 minutes to obtain a premix. S3. The premixed material is fed into a twin-screw extruder for melt blending, extrusion, cooling and pelletizing to obtain polyolefin composite material particles; S4. Add the outer wall polyolefin composite material particles to the outer wall extruder, and add the inner wall polyolefin composite material particles to the inner wall extruder; wherein, the outer wall polyolefin composite material particles are the same as the inner wall polyolefin composite material particles, or the content of α-olefin ethylene copolymer in the outer wall polyolefin composite material particles is 2-6 parts by weight higher than the content of α-olefin ethylene copolymer in the inner wall polyolefin composite material particles; and co-extrude through a composite die to form a tube blank with an outer corrugated wall and an inner smooth wall; S5. The tube blank is introduced into the double-wall corrugated forming module, and after vacuum adsorption, cooling and shaping, traction and cutting, the high impact-resistant double-wall corrugated tube is obtained.

9. The preparation method according to claim 8, characterized in that, In step S3, the temperatures from zone one to the die head of the twin-screw extruder are controlled sequentially as follows: 160-175℃, 170-185℃, 180-195℃, 185-205℃, and 190-210℃. The screw speed is 180-350 r / min, and the vacuum exhaust pressure is -0.06 to -0.09 MPa.

10. The preparation method according to claim 8, characterized in that, In step S4, the melt temperature of the outer wall extruder is 185-210℃, and the melt temperature of the inner wall extruder is 180-205℃; in step S5, the forming module temperature is 15-35℃, the vacuum degree is -0.03 to -0.08MPa, and the traction speed is 0.3-2.5m / min.

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