Polypropylene hollow wall winding pipe and preparation method thereof

Abstract

The invention belongs to the technical field of plastic pipe preparation, and particularly relates to a polypropylene hollow wall winding pipe and a preparation method thereof.The preparation method of the polypropylene hollow wall winding pipe comprises the following preparation steps of S1, raw material preparation, S2, base material extrusion, S3, winding forming, S4, welding reinforcement, S5, cooling shaping and S6, aftertreatment and detection. The ring stiffness and low-temperature impact resistance of the pipe can be synchronously improved through a composite modification system, the problem that the pipe is damaged due to low-temperature embrittlement after construction in winter in northern severe cold areas is solved, and deformation caused by insufficient ring stiffness after the pipe is deeply buried in soil is prevented; the pipe can stably adapt to complex scenes such as construction in a severe cold environment and pressure bearing of deeply-buried soil, is not limited by basic use requirements any more, and meanwhile, solves the processing problems of unstable melt flow and mold blockage during extrusion molding.

Description

Technical Field

[0001] This invention relates to the field of plastic pipe manufacturing technology, and in particular to a polypropylene hollow wall spiral pipe and its manufacturing method. Background Technology

[0002] Polypropylene hollow-wall spiral wound pipe, as a new type of plastic pipe, has been widely used in municipal drainage and sewage, industrial wastewater transportation, and agricultural irrigation due to its advantages such as light weight, corrosion resistance, and convenient construction. With the acceleration of urbanization and the increasing environmental protection requirements, the market has set higher standards for the performance of this type of pipe. It not only requires excellent ring stiffness and impact resistance, but also needs to maintain long-term stability under complex environments (such as high temperature, strong ultraviolet radiation, and changes in soil stress), while also taking into account production efficiency and cost control.

[0003] Traditional processes often use single polypropylene resin or simple blending systems. While these can meet the basic needs of municipal drainage and agricultural irrigation, they present an irreconcilable contradiction between improving ring stiffness and optimizing impact resistance. If the focus is on increasing ring stiffness to adapt to deep burial conditions, the impact resistance of the pipe will decrease significantly, and the material will become significantly more brittle at low temperatures, making it prone to breakage under slight external impact. This is especially true in cold northern regions, where pipe breakage due to low-temperature brittleness after winter construction is more prominent, increasing rework costs and affecting project progress. On the other hand, if the focus is on enhancing impact resistance to cope with low-temperature transportation and construction collisions, the ring stiffness of the pipe will be insufficient. This means that after the pipe is buried deep in the soil, it cannot withstand the pressure of the soil's own weight and external loads, making it prone to radial deformation. In severe cases, this can lead to a reduction in the inner diameter of the pipe, poor drainage, or even pipe collapse, increasing the difficulty and cost of later maintenance.

[0004] Accordingly, this application proposes a polypropylene hollow wall wound tube and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a polypropylene hollow wall wound tube and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a polypropylene hollow-wall spiral tube includes the following steps: S1. Raw material preparation: Select homopolymer polypropylene resin with a melt index of 0.8-1.5 g / 10 min as the base material, add composite modification system and quaternary anti-aging composite agent, and mix according to the following mass percentages: homopolymer polypropylene resin 70%-80%, composite modification system 9%-15%, quaternary anti-aging composite agent 0.3%-0.6%; S2, Substrate Extrusion: The S1 mixed raw material is fed into a twin-screw extruder, and the extrusion temperature is set to 155-190℃ and the screw speed is set to 40-55r / min. A continuous Ω-shaped hollow substrate strip is extruded through the die, and wedge-shaped overlapping edges are provided on both sides of the substrate strip. S3. Winding: Prepare modified polyvinyl alcohol adhesive and apply it to the overlapping surface of the substrate tape. Wind the substrate tape to the forming mold at a spiral angle of 35°-42° using a winding machine. Control the spindle speed to 12-18 r / min, the conveying speed to 0.9-1.3 m / min, and the pressure roller pressure to 0.4-0.6 MPa to form a tube blank. S4. Welding reinforcement: Hot air welding is used on the tube blank, and annular reinforcing ribs + radial support strip composite structure are welded at intervals of 180-250mm on the inner wall of the tube blank. S5. Cooling and Shaping: The tube blank is cooled in three stages, and vacuum sizing of the inner wall is carried out during the cooling process; S6. Post-processing and inspection: The inner wall of the tube blank is subjected to plasma treatment, cut into lengths of 6-12m, and after passing tests such as hydraulic pressure test at 0.45MPa for 30 minutes without leakage and ring stiffness test, it is considered a finished product.

[0007] Preferably, the composite modification system in step S1 is composed of the following components in the following mass ratio: maleic anhydride-grafted polypropylene 40%–45%, nano-calcium carbonate-graphene composite powder 30%–35%, and polyolefin elastomer POE 20%–25%.

[0008] Preferably, in the nano-calcium carbonate-graphene composite powder, the mass percentage of graphene is 0.5% to 1.0%; The nano-calcium carbonate-graphene composite powder is prepared through the following steps: Graphene powder was dried in a vacuum drying oven for 2-3 hours to remove adsorbed moisture. 40-80nm nano-calcium carbonate was added to a 1% dilute hydrochloric acid solution with a solid-liquid ratio of 1:10. The solution was stirred at 50°C for 30 minutes to remove surface impurities. After filtration, the solution was washed with deionized water until neutral and dried at 105°C for later use. Pretreated graphene and nano-calcium carbonate were added to an ethanol solution at a solid-liquid ratio of 1:20. The mixture was first mechanically stirred at 800 r / min for 15 min, and then transferred to a 45 kHz, 500 W ultrasonic device for ultrasonic treatment for 30-45 min. The ultrasonic treatment was paused for 2 min every 10 min to avoid overheating and agglomeration. Add 0.8% to 1.2% silane coupling agent KH-570 to the ultrasonically mixed solution. First, dilute it with ethanol to a concentration of 5%, and stir at a constant temperature of 80-85℃ and 300r / min for 2 to 3 hours to allow the coupling agent to be fully grafted onto the powder surface. The modified mixture was vacuum filtered, and the filter cake was dried in a forced-air drying oven at 110-120℃ for 4-5 hours. It was then ground in a planetary ball mill for 30 minutes and passed through a 300-mesh sieve to collect composite powder with a particle size ≤5μm.

[0009] Preferably, the quaternary anti-aging composite agent in step S1 is prepared through the following steps: Antioxidant 1010 and antioxidant 168 were dried in a vacuum drying oven at 60℃ for 1.5h to remove low-boiling-point impurities. Light stabilizer diphenyl diammonium sebate and ultraviolet absorber UV-531 were mixed in a mass ratio of 1:1, and anhydrous ethanol was added in a solid-liquid ratio of 1:5. The mixture was stirred at 40℃ for 20min to prepare a uniform suspension for later use. Weigh out pretreated antioxidant 1010 and antioxidant 168 at a mass ratio of 3:2, add them to a high-speed mixer, and mix at room temperature for 10 minutes. Slowly add the above light stabilizer-UV-531 suspension to the mixer at a mass ratio of 2:1, maintain a speed of 1200 r / min, mix for 15 min, and simultaneously introduce nitrogen gas at a flow rate of 50 mL / min to prevent oxidation of the antioxidant. The mixed anti-aging agent mixture is transferred to a twin-screw granulator to form particles with a diameter of 1-2 mm, and then vacuum dried at 60°C for 2 hours to produce a quaternary anti-aging composite agent.

[0010] Preferably, in step S2, the twin-screw extruder has a length-to-diameter ratio of 40:1, and the extrusion temperature is set in segments: feeding section 155-165℃, compression section 170-180℃, and homogenization section 180-190℃; the surface roughness of the die flow channel Ra≤0.8μm; the inner wall of the cavity of the “Ω”-shaped substrate is provided with 3 to 5 axial reinforcing ribs, wedge-shaped overlapping edges, and the surface is provided with serrated anti-slip texture.

[0011] Preferably, the modified polyvinyl alcohol binder in step S3 is prepared through the following steps: Select polyvinyl alcohol with a degree of polymerization of 1750-1850 and a degree of alcoholysis of 98%-99%, add deionized water, with a solid-liquid ratio of 1:10-1:12, heat to 88-92℃, start stirring, and keep stirring at this temperature for 2.0-2.5 hours. During this period, check with a glass rod every 30 minutes until there are no obvious particles, and a transparent polyvinyl alcohol solution is prepared. Cool the solution to 60-70℃, add 15-25nm nano silica, wherein the nano silica is pre-modified with 0.5% silane coupling agent KH-550, and the amount added is 0.3% to 0.5% of the binder mass. Stir at 600r / min for 10min, and then transfer to a 40kHz, 300W ultrasonic device for ultrasonic dispersion for 20 to 30min. Add 0.1% to 0.2% defoamer to the ultrasonically treated adhesive, stir at 500 r / min for 5 min, let stand for 10 min to remove surface bubbles; test the viscosity of the adhesive and control it at 1500-2000 mPa·s. If the viscosity is too high, add a small amount of deionized water to adjust it, and prepare a modified adhesive with a mass concentration of 6% to 9%.

[0012] Preferably, in step S4, the composite structure of the annular reinforcing rib and the radial support strip is made by extruding the raw materials mixed in step S1 with 1% to 2% glass fiber, and the extrusion temperature is the same as the homogenization temperature in step S2.

[0013] A polypropylene hollow wall spiral wound tube is prepared by a method for preparing a polypropylene hollow wall spiral wound tube.

[0014] The present invention has the following beneficial effects: 1. The composite modification system of this invention can simultaneously improve the ring stiffness and low-temperature impact resistance of pipes. This avoids the problem of pipe breakage due to low-temperature brittleness after construction in frigid northern regions during winter, and also prevents deformation due to insufficient ring stiffness after deep burial. This allows the pipes to stably adapt to complex scenarios such as construction in frigid environments and pressure-bearing deep burial, no longer limited by foundation usage requirements. Simultaneously, this system improves upon the problems of poor compatibility and uneven dispersion of traditional inorganic fillers and resins, solves the processing difficulties of unstable melt flow and mold blockage during extrusion molding, significantly improves production efficiency and product qualification rate, and reduces losses and costs during the production process.

[0015] 2. The quaternary synergistic anti-aging system of this invention, through the synergistic effect of "antioxidant + light stabilization + ultraviolet absorption," can effectively inhibit the degradation reaction of polypropylene pipes during long-term use, preventing short-term embrittlement and cracking caused by factors such as ultraviolet radiation and high temperatures, thus meeting the long-term service life requirements of municipal engineering pipes. Simultaneously, this system reduces the volatilization loss of anti-aging agents during processing, ensuring long-term stable anti-aging effects, eliminating the need for frequent pipe replacements, and reducing subsequent maintenance costs and resource consumption.

[0016] 3. The modified polyvinyl alcohol adhesive of this invention significantly improves bonding strength and water resistance, effectively preventing delamination at the overlap and ensuring the overall structural stability of the pipe. Simultaneously, when used in conjunction with the winding process, this adhesive can resolve issues of overlap gaps and stress concentration, ensuring no leakage during pressure testing. It can stably adapt to high-pressure transportation conditions, avoiding engineering accidents caused by leakage and improving the safety and reliability of the pipe in municipal drainage, industrial wastewater transportation, and other scenarios. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing a polypropylene hollow-wall spiral tube proposed in this invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example 1:

[0019] A polypropylene hollow-wall spiral wound tube and its preparation method, comprising the following steps: Step 1: Raw material preparation: Select homopolymer polypropylene resin with a melt index of 1.0 g / 10 min (pre-dried in a vacuum drying oven at 60℃ for 2 hours to remove adsorbed moisture) as the base material; mix the raw materials according to the following mass percentages: homopolymer polypropylene resin 75%, composite modification system 14.5%, quaternary anti-aging composite agent 0.5%. When mixing, first put the homopolymer polypropylene resin and composite modification system into a high-speed mixer (speed 1000 r / min) for premixing for 5 minutes, then add the quaternary anti-aging composite agent and continue mixing for 8 minutes to ensure that the components are uniform (mixing uniformity ≥98%). The composite modification system consists of 42% maleic anhydride-grafted polypropylene, 33% nano-calcium carbonate-graphene composite powder (graphene mass percentage 0.7%, pre-dried at 110℃ for 4 hours), and 25% polyolefin elastomer POE; the quaternary anti-aging composite agent is made of antioxidant 1010, antioxidant 168, light stabilizer diphenylenediamine sebacate, and ultraviolet absorber UV-531 in a mass ratio of 3:2:2:1 (nitrogen gas is introduced during preparation to prevent oxidation of antioxidants).

[0020] Step 2, Substrate Extrusion: The raw materials mixed in Step 1 are fed uniformly into a twin-screw extruder with a length-to-diameter ratio of 40:1 via a loss-in-weight feeder; the extrusion temperature is set in stages: feeding stage 158-162℃, compression stage 172-178℃, and homogenization stage 182-188℃, with temperature fluctuations in each stage controlled within ±2℃; the screw speed is 45 r / min, and the melt pressure is monitored in real time during operation (maintained at 15-18 MPa). A continuous Ω-shaped hollow substrate strip with wedge-shaped overlapping edges on both sides (with serrated anti-slip texture on the surface, texture depth 0.3mm) and 4 axial reinforcing ribs (rib height 1.5mm, width 2mm) on the inner wall of the cavity is extruded through a mold with a flow channel surface roughness Ra=0.6μm (the mold is wiped with silicone oil before use to prevent material adhesion). After extrusion, the surface temperature of the substrate strip is monitored in real time with an infrared thermometer (controlled at 170-175℃).

[0021] Step 3, Winding Molding: Preparation of Modified Polyvinyl Alcohol Adhesive: Select polyvinyl alcohol with a degree of polymerization of 1800 and a degree of hydrolysis of 98.5%, add deionized water at a solid-liquid ratio of 1:11, heat to 89-91℃ (heating rate 5℃ / min, avoid local overheating), start stirring (300 r / min), keep warm and stir for 2.2 h, checking with a glass rod every 30 min until no obvious particles are found, and a transparent solution is prepared; after cooling to 64-66℃, add 0.4% silane. 15-25nm nano-silica modified with coupling agent KH-550 was stirred at 600r / min for 10min and then ultrasonically dispersed in a 40kHz, 300W ultrasonic device for 25min (pausing for 2min every 10min of ultrasonication to prevent the solution from overheating). Finally, 0.15% defoamer (organosilicon) was added and stirred for 5min. After standing for 10min to remove surface bubbles, the viscosity was controlled at 1700mPa·s (measured with a rotational viscometer at 25℃) and the mass concentration was 7%. The adhesive is evenly applied to the overlapping surface of the substrate strip using a metering roller (the coating thickness is controlled between 0.15 and 0.2 mm, and the coating coverage is 100%). The substrate strip is then wound around the forming mold at a 38° spiral angle using a winding machine (the mold diameter is set to 300 mm according to the pipe specifications). During winding, the tension of the substrate strip is adjusted in real time (maintained at 500 N), and the spindle speed is controlled at 15 r / min, the conveying speed at 1.1 m / min, and the pressure roller pressure at 0.5 MPa (pressure fluctuation ±0.02 MPa) to form a pipe blank (the outer diameter deviation of the pipe blank is ≤ ±0.5 mm).

[0022] Step 4, Welding Reinforcement: Hot air welding is used on the tube blank, with the hot air temperature controlled at 220-230℃ (hot air velocity 1.5m / s). The welding speed is synchronized with the tube blank conveying speed (1.1m / min). Simultaneously, a composite structure of annular reinforcing ribs and radial support strips is welded on the inner wall of the tube blank at intervals of 220mm (interval deviation ±5mm). The cross-section of the annular reinforcing ribs is trapezoidal (top base 8mm, bottom base 10mm, height 5mm), and the radial support strips are spaced 30mm apart. The composite structure is made by extruding the raw materials mixed in Step 1 with the addition of 1.5% glass fiber (3mm in length, modified with silane coupling agent KH-560 in advance). The extrusion temperature is the same as the homogenization temperature in Step 2 (182-188℃). After extrusion, the tube blank is rapidly cooled to below 60℃ by a cooling and shaping sleeve before welding.

[0023] Step 5, Cooling and Shaping: The tube blank is sent into a three-stage cooling water tank (first stage water temperature 25-30℃, second stage 15-20℃, third stage 5-10℃), each stage is 2m long, and the total cooling time is 15min; during the cooling process, the inner wall is vacuum sizing (vacuum degree controlled between -0.08MPa and -0.09MPa), and the inner diameter of the tube blank is monitored in real time (by an online diameter measuring instrument, the measurement frequency is 1 time / second) to ensure that the inner diameter deviation is ≤±0.3mm.

[0024] Step Six, Post-processing and Inspection: The inner wall of the tube blank is subjected to plasma treatment with an argon-oxygen mixed gas (volume ratio 9:1) (treatment power 300W, treatment time 10s / cm²). After treatment, the inner wall contact angle is 28° (measured with a contact angle measuring instrument, and the average value of 3 different measuring points is taken); it is cut to a length of 8m (a toothless saw is used for cutting, and the perpendicularity deviation of the cut surface is ≤0.5°); it undergoes a hydraulic test at 0.45MPa for 30min (the test medium is room temperature clean water, and the pressure increase rate is 0.1MPa / min) with no leakage; the ring stiffness is tested according to GB / T9647-2015 (sampling length 300mm, loading rate 5mm / min) and meets the standard. The tube is free of defects such as bubbles, cracks, and dents in its appearance, and it is then considered a finished product. Example 2:

[0025] A polypropylene hollow wall spiral tube and its preparation method differ from Example 1 in the following aspects: Step 1, raw material preparation: homopolymer polypropylene resin melt index 0.8 g / 10 min (pre-dried in a vacuum drying oven at 55℃ for 2.5 h), mass percentage 80%; composite modification system mass percentage 19.4%, including maleic anhydride grafted polypropylene 45%, nano-calcium carbonate-graphene composite powder (graphene mass percentage 1.0%, pre-dried in a forced-air drying oven at 115℃ for 3.5 h) 30%, polyolefin elastomer POE 25%, pre-mixed for 6 min, then adding anti-aging agent and mixing for 10 min; quaternary anti-aging composite agent mass percentage 0.6% (nitrogen flow rate 60 mL / min during preparation).

[0026] Step 2, substrate extrusion: The feed rate of the mixed raw materials is 18 kg / h, and the melt pressure is maintained at 14-17 MPa; the temperature of the twin-screw extruder is divided into three sections: feeding section 155-160℃, compression section 170-175℃, and homogenization section 180-185℃; the screw speed is 40 r / min; the surface roughness of the die flow channel is Ra=0.7μm, and the inner wall of the Ω-shaped substrate belt cavity contains 3 axial reinforcing ribs (rib height 1.2 mm, width 1.8 mm). The surface temperature of the substrate belt after extrusion is controlled at 165-170℃.

[0027] Step 3, winding molding: Modified polyvinyl alcohol binder solid-liquid ratio 1:10, heating rate 4℃ / min, heat preservation and stirring at 88-90℃ for 2.0h, cooling to 60-62℃, nano silica addition 0.3%, ultrasonic dispersion for 20min (pause for 2min every 8min of ultrasonication), defoamer added and allowed to stand for 12min, viscosity 1500mPa・s, mass concentration 6%; coating thickness 0.12~0.18mm, molding die diameter 200mm, substrate tension 450N; winding helix angle 35°, spindle speed 12r / min, conveying speed 0.9m / min, pressure roller pressure 0.4MPa, tube blank outer diameter deviation ≤±0.4mm.

[0028] Step 4, Welding Reinforcement: Hot air welding temperature 215-225℃, hot air velocity 1.2m / s, welding speed 0.9m / min; the composite structure of annular reinforcing ribs + radial support strips is spaced 180mm apart (interval deviation ±4mm), the cross-section of the annular reinforcing ribs is trapezoidal (top base 7mm, bottom base 9mm, height 4.5mm), and the radial support strips are spaced 28mm apart; glass fiber addition amount 1% (length 2.5mm), after extrusion, it is cooled to below 55℃ before welding.

[0029] Step five is the same as the cooling method in Example 1.

[0030] Step 6, Post-processing and Inspection: Plasma treatment with an argon-oxygen volume ratio of 10:1 and a treatment power of 280W, resulting in an inner wall contact angle of 25°; cutting to a length of 6m (cutting surface perpendicularity deviation ≤0.4°); hydraulic test with a pressure increase rate of 0.08MPa / min, ring stiffness test with a loading rate of 4mm / min; visual inspection showing no obvious defects indicates it is qualified. Example 3:

[0031] A polypropylene hollow-wall spiral wound tube and its preparation method differ from Example 1 in the following aspects: Step 1, raw material preparation: homopolymer polypropylene resin with a melt index of 1.5 g / 10 min (pre-dried in a vacuum drying oven at 65℃ for 1.5 h), accounting for 70% by mass; the composite modification system accounts for 29.7% by mass, including maleic anhydride grafted polypropylene 40%, nano-calcium carbonate-graphene composite powder (graphene mass percentage 0.5%, pre-dried in a forced-air drying oven at 120℃ for 3 h) 35%, and polyolefin elastomer POE 25%. The mixture is pre-mixed for 4 min, and then an anti-aging agent is added and mixed for 9 min; the quaternary anti-aging composite agent accounts for 0.3% by mass (nitrogen flow rate 55 mL / min during preparation).

[0032] Step 2, substrate extrusion: the feed rate of the mixed raw materials is 22 kg / h, and the melt pressure is maintained at 16-19 MPa; the temperature of the twin-screw extruder is divided into three sections: feeding section 160-165℃, compression section 175-180℃, and homogenization section 185-190℃; the screw speed is 55 r / min. The surface roughness of the mold flow channel is Ra=0.8μm. The inner wall of the Ω-shaped substrate strip cavity contains 5 axial reinforcing ribs (rib height 1.8mm, width 2.2mm). The surface temperature of the substrate strip after extrusion is controlled at 175-180℃.

[0033] Step 3, winding molding: Modified polyvinyl alcohol binder solid-liquid ratio 1:12, heating rate 6℃ / min, heat preservation and stirring at 90-92℃ for 2.5h, cooling to 68-70℃, nano silica addition 0.5%, ultrasonic dispersion for 30min (pause for 2min every 12min of ultrasonication), defoamer added and allowed to stand for 8min, viscosity 2000mPa・s, mass concentration 9%; The adhesive coating thickness is 0.18~0.22mm, the forming mold diameter is 400mm, the substrate tension is 550N; the winding helix angle is 42°, the spindle speed is 18r / min, the conveying speed is 1.3m / min, the pressure roller pressure is 0.6MPa, and the outer diameter deviation of the tube blank is ≤±0.6mm.

[0034] Step 5, Welding Reinforcement: Hot air welding temperature 225-235℃, hot air velocity 1.8m / s, welding speed 1.3m / min; the composite structure of annular reinforcing ribs + radial support strips is spaced 250mm apart (interval deviation ±6mm), the cross-section of the annular reinforcing ribs is trapezoidal (top base 9mm, bottom base 11mm, height 5.5mm), and the radial support strips are spaced 32mm apart; glass fiber addition amount 2% (length 3.5mm), after extrusion, it is cooled to below 65℃ before welding.

[0035] Step five is the same as the cooling method in Example 1.

[0036] Step 6, Post-processing and Inspection: Plasma treatment with an argon-oxygen volume ratio of 8:1, a treatment power of 320W, and an inner wall contact angle of 30° after treatment; cutting to a length of 12m (laser positioning is used during cutting, and the perpendicularity deviation of the cutting surface is ≤0.6°); hydraulic test with a pressure increase rate of 0.12MPa / min, ring stiffness test with a loading rate of 6mm / min, and no defects in appearance inspection indicate that it is qualified.

[0037] Comparative Example 1 (excluding nano-calcium carbonate-graphene composite powder in the composite modification system): The difference between this and Example 1 is that the nano-calcium carbonate-graphene composite powder is removed from the composite modification system and replaced with an equal mass of homopolymer polypropylene resin. The specific adjustments are as follows: Raw material preparation: Homopolymer polypropylene resin (melt index 1.0 g / 10 min, vacuum dried at 60℃ for 2 h) mass percentage 75% + 33% (amount of nano-calcium carbonate-graphene composite powder replaced) = 108%. The composite modification system is adjusted to maleic anhydride grafted polypropylene 42%, polyolefin elastomer POE 25% (total percentage 67%), mass percentage 14.5%, and quaternary anti-aging composite agent 0.5% (formula consistent with Example 1); Mixing process: First, the homopolymer polypropylene resin and the composite modification system (without nano powder) are premixed for 5 min in a high-speed mixer at 1000 r / min, then the quaternary anti-aging composite agent is added and mixed for 8 min, with a mixing uniformity ≥95%.

[0038] Steps 2 to 4: All process steps and parameters are completely consistent with those in Example 1 (feeding rate 20kg / h, extrusion temperature 158-188℃, winding spiral angle 38°, plasma treatment parameters, etc. remain unchanged).

[0039] Comparative Example 2 (using a traditional binary anti-aging agent instead of a quaternary anti-aging compound) differs from Example 1 in that a traditional binary anti-aging agent (antioxidant 1010 + UV absorber UV-531 only) replaces the quaternary anti-aging compound. The specific adjustments are as follows: Raw material formulation: The quaternary anti-aging compound agent (0.5%) is replaced with the traditional binary anti-aging agent (antioxidant 1010 0.3% + ultraviolet absorber UV-531 0.2%, without antioxidant 168 and light stabilizer diphenyl disebaic acid). Preparation of binary anti-aging agent: Antioxidant 1010 and UV-531 were vacuum dried at 60℃ for 1.5h, mixed at room temperature for 10min, and added directly in powder form without nitrogen protection or granulation.

[0040] Comparative Example 3 (using a conventional unmodified polyvinyl alcohol binder instead of a modified polyvinyl alcohol binder) differs from Example 1 in that the modified polyvinyl alcohol binder is replaced with a conventional unmodified polyvinyl alcohol binder in the winding process. The specific adjustments are as follows: Step 3, Winding Molding: Traditional Adhesive Preparation: Polyvinyl alcohol with a degree of polymerization of 1800 and a degree of hydrolysis of 98.5% is selected and added to deionized water at a solid-liquid ratio of 1:11. The mixture is stirred at 89-91℃ for 2.2 hours until transparent, without adding nano-silica or defoamer. The viscosity is controlled at 1700 mPa·s (measured at 25℃) and the mass concentration is 7%. Coating Process: Coating was performed using a metered coating roller (thickness 0.15-0.2 mm), with a coating coverage of 95% (due to the absence of nanoparticles, which are prone to sagging); winding parameters were the same as in Example 1 (tension 500 N, spindle speed 15 r / min).

[0041] Steps 1, 2, 4, and 6 are completely identical to those in Example 1 in terms of all process steps and parameters (the composite modified system formulation, extrusion die parameters, and welding interval of the annular reinforcing ribs are all unchanged).

[0042] It should be noted that the performance parameters of the polypropylene hollow-wall spiral wound tubes prepared by the methods described in the above embodiments and comparative examples are as follows: Table 1: Parameter Comparison Table Comparison Projects True impact rate (%) Low-temperature impact strength (kJ / m²) Ring stiffness kN / m² Bond strength at overlap (MPa) Example 1 2 8.5 9.8 2.1 Example 2 3 8.2 9.5 1.9 Example 3 3 8.3 9.6 2.2 Comparative Example 1 12 5.1 6.5 2 Comparative Example 2 3 8.1 9.6 2.1 Comparative Example 3 5 7.8 9.5 1 Specifically, the actual impact rates of Examples 1-3 were 2%, 3%, and 3%, respectively, all at a relatively low level of 2% to 3%, indicating that the pipes had good and stable impact resistance. In contrast, the actual impact rate of Comparative Example 1 was as high as 12% (the acceptable range for the actual impact rate of polypropylene hollow-wall spiral pipe is ≤10%), and Comparative Example 3 was 5%, both significantly higher than the Examples. The composite modified material used in the Examples can be uniformly dispersed in the polypropylene matrix, forming an effective stress dispersion network. When the pipe is impacted, it can quickly disperse the impact energy, inhibiting crack generation and propagation, thereby significantly reducing the actual impact rate. Comparative Example 1, lacking this key composite modified material, could not form an effective stress dispersion structure, resulting in concentrated impact energy and an excessive actual impact rate. Comparative Example 3, due to insufficient performance of the binder and other materials, had a pipe structure that was easily damaged by impact, and its actual impact rate was also higher than the Examples.

[0043] Specifically, the low-temperature impact strengths of Examples 1-3 were 8.5 kJ / m², 8.2 kJ / m², and 8.3 kJ / m², respectively, generally between 8.2 and 8.5 kJ / m², indicating that the pipes still possess good impact toughness at low temperatures. The low-temperature impact strength of Comparative Example 1 was only 5.1 kJ / m², and that of Comparative Example 3 was 7.8 kJ / m², both lower than the Examples. The modified materials used in the Examples exhibit excellent low-temperature toughness; their molecular structure maintains a certain degree of flexibility at low temperatures, preventing the material from becoming brittle. Comparative Example 1 lacked key low-temperature toughening modifiers; at low temperatures, molecular chain movement was restricted, increasing brittleness and drastically reducing impact resistance. Although Comparative Example 3 contained some impact-resistant materials, the synergistic toughening effect was insufficient, and its low-temperature impact resistance was still inferior to the overall level of the Examples.

[0044] Specifically, the overlap bond strengths of Examples 1-3 were 2.1 MPa, 1.9 MPa, and 2.2 MPa, respectively, generally between 1.9 and 2.2 MPa, demonstrating good bonding reliability. The overlap bond strength of Comparative Example 3 was only 1 MPa, far lower than that of the Examples; Comparative Example 1 was 2 MPa, which, although close to some values ​​of the Examples, still showed inferior overall performance compared to the Examples due to its disadvantages in other properties. The modified adhesive used in the Examples contained active groups that could chemically react with the polypropylene substrate, forming strong chemical bonds. Simultaneously, the adhesive itself had a denser structure, significantly improving the overlap bond strength. Comparative Example 3 used a traditional unmodified adhesive, relying solely on physical adsorption for bonding, resulting in weak adhesion and low overlap bond strength.

[0045] In summary, the performance difference between the examples and the comparative examples is essentially due to the difference in the selection of core materials. The nano-calcium carbonate-graphene composite powder determines the upper limit of mechanical properties, the quaternary anti-aging composite agent ensures long-term performance stability, and the modified polyvinyl alcohol binder ensures reliable structural sealing. The presence or absence, modification, and compositional integrity of these three core materials directly lead to differences in key performance aspects of the pipes, such as impact resistance, aging resistance, and bonding sealing. This also proves that the selection and optimization of core materials in this invention are fundamental to overcoming the performance shortcomings of traditional pipes.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a polypropylene hollow-wall spiral wound tube, characterized in that, Includes the following steps: S1. Raw material preparation: Select homopolymer polypropylene resin with a melt index of 0.8-1.5 g / 10 min as the base material, add composite modification system and quaternary anti-aging composite agent, and mix according to the following mass percentages: homopolymer polypropylene resin 70%-80%, composite modification system 9%-15%, quaternary anti-aging composite agent 0.3%-0.6%; S2, Substrate Extrusion: The S1 mixed raw material is fed into a twin-screw extruder, and the extrusion temperature is set to 155-190℃ and the screw speed is set to 40-55r / min. A continuous Ω-shaped hollow substrate strip is extruded through the die, and wedge-shaped overlapping edges are provided on both sides of the substrate strip. S3. Winding: Prepare modified polyvinyl alcohol adhesive and apply it to the overlapping surface of the substrate tape. Wind the substrate tape to the forming mold at a spiral angle of 35°-42° using a winding machine. Control the spindle speed to 12-18 r / min, the conveying speed to 0.9-1.3 m / min, and the pressure roller pressure to 0.4-0.6 MPa to form a tube blank. S4. Welding reinforcement: Hot air welding is used for the tube blank, and annular reinforcing ribs + radial support strip composite structure are welded at intervals of 180-250mm on the inner wall of the tube blank. S5. Cooling and Shaping: The tube blank is cooled in three stages, and vacuum sizing of the inner wall is carried out during the cooling process; S6. Post-processing and inspection: The inner wall of the tube blank is subjected to plasma treatment, cut into lengths of 6-12m, and after passing tests such as hydraulic pressure test at 0.45MPa for 30 minutes without leakage and ring stiffness test, it is considered a finished product.

2. The method for preparing a polypropylene hollow-wall spiral tube according to claim 1, characterized in that, The composite modification system in step S1 is composed of the following components in the following mass ratio: maleic anhydride-grafted polypropylene 40%–45%, nano-calcium carbonate-graphene composite powder 30%–35%, and polyolefin elastomer POE 20%–25%.

3. The method for preparing a polypropylene hollow-wall spiral tube according to claim 2, characterized in that, In the aforementioned nano-calcium carbonate-graphene composite powder, the mass percentage of graphene is 0.5% to 1.0%. The nano-calcium carbonate-graphene composite powder is prepared through the following steps: The graphene powder was dried in a vacuum drying oven for 2-3 hours to remove adsorbed moisture. Add 40-80nm nano-calcium carbonate to 1% dilute hydrochloric acid solution at a solid-liquid ratio of 1:10, stir at 50℃ for 30min to remove surface impurities, filter, wash with deionized water until neutral, and dry at 105℃ for later use. Pretreated graphene and nano-calcium carbonate were added to an ethanol solution at a solid-liquid ratio of 1:

20. The mixture was first mechanically stirred at 800 r / min for 15 min, and then transferred to a 45 kHz, 500 W ultrasonic device for ultrasonic treatment for 30-45 min. The ultrasonic treatment was paused for 2 min every 10 min to avoid overheating and agglomeration. Add 0.8% to 1.2% silane coupling agent KH-570 to the ultrasonically mixed solution. First, dilute it with ethanol to a concentration of 5%, and stir at a constant temperature of 80-85℃ and 300r / min for 2 to 3 hours to allow the coupling agent to be fully grafted onto the powder surface. The modified mixture was vacuum filtered, and the filter cake was dried in a forced-air drying oven at 110-120℃ for 4-5 hours. It was then ground in a planetary ball mill for 30 minutes and passed through a 300-mesh sieve to collect composite powder with a particle size ≤5μm.

4. The method for preparing a polypropylene hollow-wall spiral tube according to claim 1, characterized in that, The quaternary anti-aging composite agent in step S1 is prepared through the following steps: Antioxidant 1010 and antioxidant 168 were dried in a vacuum drying oven at 60℃ for 1.5h to remove low-boiling-point impurities. Light stabilizer diphenyl diammonium sebate and ultraviolet absorber UV-531 were mixed in a mass ratio of 1:1, and anhydrous ethanol was added in a solid-liquid ratio of 1:

5. The mixture was stirred at 40℃ for 20min to prepare a uniform suspension for later use. Weigh out pretreated antioxidant 1010 and antioxidant 168 at a mass ratio of 3:2, add them to a high-speed mixer, and mix at room temperature for 10 minutes. Slowly add the above light stabilizer-UV-531 suspension to the mixer at a mass ratio of 2:1, maintain a speed of 1200 r / min, mix for 15 min, and simultaneously introduce nitrogen gas at a flow rate of 50 mL / min to prevent oxidation of the antioxidant. The mixed anti-aging agent mixture is transferred to a twin-screw granulator to form particles with a diameter of 1-2 mm, and then vacuum dried at 60°C for 2 hours to produce a quaternary anti-aging composite agent.

5. The method for preparing a polypropylene hollow-wall spiral wound tube according to claim 1, characterized in that, In step S2, the twin-screw extruder has a length-to-diameter ratio of 40:1, and the extrusion temperature is set in segments: feeding section 155-165℃, compression section 170-180℃, and homogenization section 180-190℃; the surface roughness of the die flow channel Ra≤0.8μm; the inner wall of the cavity of the "Ω"-shaped substrate is provided with 3 to 5 axial reinforcing ribs, wedge-shaped overlapping edges, and serrated anti-slip texture on the surface.

6. The method for preparing a polypropylene hollow-wall spiral tube according to claim 1, characterized in that, The modified polyvinyl alcohol binder in step S3 is prepared through the following steps: Select polyvinyl alcohol with a degree of polymerization of 1750-1850 and a degree of alcoholysis of 98%-99%, add deionized water, with a solid-liquid ratio of 1:10-1:12, heat to 88-92℃, start stirring, and keep stirring at this temperature for 2.0-2.5 hours. During this period, check with a glass rod every 30 minutes until there are no obvious particles, and a transparent polyvinyl alcohol solution is prepared. Cool the solution to 60-70℃, add 15-25nm nano silica, wherein the nano silica is pre-modified with 0.5% silane coupling agent KH-550, and the amount added is 0.3% to 0.5% of the binder mass. Stir at 600r / min for 10min, and then transfer to a 40kHz, 300W ultrasonic device for ultrasonic dispersion for 20 to 30min. Add 0.1% to 0.2% defoamer to the ultrasonically bonded adhesive, stir at 500 r / min for 5 min, let stand for 10 min, and remove surface bubbles; Test the viscosity of the adhesive and control it within 1500-2000 mPa·s. If the viscosity is too high, add a small amount of deionized water to adjust it, so as to make a modified adhesive with a mass concentration of 6% to 9%.

7. The method for preparing a polypropylene hollow-wall spiral tube according to claim 1, characterized in that, In step S4, the composite structure of the annular reinforcing rib and the radial support strip is made by extruding the raw materials mixed in step S1 with 1% to 2% glass fiber, and the extrusion temperature is the same as the homogenization temperature in step S2.

8. A polypropylene hollow wall spiral wound tube, prepared by the method for preparing a polypropylene hollow wall spiral wound tube according to any one of claims 1-7.

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