High toughness impact resistant cable protection pipe

Abstract

The application relates to the technical field of cable protection pipes, and discloses a high-toughness impact-resistant cable protection pipe which is made of a base premix, a swelling modification pretreatment material and a delay capturing agent master batch. The base premix comprises high-density polyethylene, poly-1-butene and a processing aid; the swelling pretreatment material is prepared by hot mixing, swelling and quenching of ultrahigh molecular weight polyethylene and industrial white oil; and the delay capturing agent master batch is made of calcined diatomite and high-flow high-density polyethylene. During preparation, the base premix and the swelling pretreatment material are jointly added into a co-rotating twin-screw extruder, and the delay capturing agent master batch is added into the extruder through side feeding in the middle and rear sections; after the extruded pipe blank is vacuum-diametered and surface-hardened, the pipe blank enters a normal-pressure hot water cooling box to perform thermodynamic annealing and shaping. Through swelling treatment, the toughening phase disperses and absorbs impact energy, the master batch adsorbs free low-molecular substances, and residual internal stress is released through hot water annealing, so that the impact toughness and long-term mechanical properties of the pipe material are improved.

Description

Technical Field

[0001] This invention relates to the field of cable protection pipe technology, specifically a high-toughness, impact-resistant cable protection pipe. Background Technology

[0002] High-density polyethylene (HDPE) pipes are widely used in underground cable protection projects due to their good corrosion resistance and insulation properties. However, conventional HDPE cable protection pipes suffer from insufficient toughness when subjected to strong external mechanical impacts, making them prone to brittle fracture. To improve the impact resistance of the pipes, the industry has attempted to introduce ultra-high molecular weight polyethylene (UHMWPE) as a toughening component into the matrix. However, UHMWPE has a high molecular weight, resulting in poor compatibility when blended with conventional HDPE. When the two are directly mixed and extruded, phase separation occurs within the system due to differences in melt flowability, making it difficult to fully plasticize. This not only fails to form a uniform dispersed phase to absorb impact energy but also leads to fluctuations in the overall mechanical properties of the material.

[0003] Furthermore, introducing low-molecular-weight substances such as oils to improve the blending performance of ultra-high molecular weight polyethylene (UHMWPE) and the matrix resin can introduce new problems. These low-molecular-weight substances tend to be in a free state in the extruded pipe system. During storage and use, these free low-molecular-weight substances gradually migrate to and precipitate on the pipe surface. This precipitation phenomenon leads to oil stain defects on the pipe surface, severely affecting the appearance quality of the pipe and reducing the interfacial bonding strength of the materials. Simultaneously, under long-term underground burial and geostress, the creep resistance of conventional high-density polyethylene materials is limited, making it difficult to guarantee the long-term mechanical stability of the pipe system and prone to structural deformation. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-toughness, impact-resistant cable protection pipe, aiming to solve the problems in existing technologies such as the easy phase separation caused by direct blending of ultra-high molecular weight polyethylene, the easy migration and precipitation of low molecular weight substances introduced during processing to the pipe surface, and the insufficient long-term creep resistance and mechanical stability of conventional matrix materials.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a high-toughness, impact-resistant cable protection pipe, made from raw materials comprising the following parts by weight: Matrix premix: 100 parts high-density polyethylene, 3-6 parts poly-1-butene, and 0.5-1.0 parts processing aids; Swelling modified pretreatment material: 8-15 parts ultra-high molecular weight polyethylene, 1-3 parts industrial white oil; delayed capture agent masterbatch: 3-6 parts.

[0006] This invention uses ultra-high molecular weight polyethylene (UHMWPE) as the toughening phase. Due to its high molecular weight, direct blending with high-density polyethylene (HDPE) results in phase separation and difficulty in plasticization. This invention employs industrial white oil for swelling modification pretreatment of UHMWPE. Under the high-speed frictional heating effect of hot mixing, white oil molecules penetrate into the interstices of the UHMWPE molecular chains, increasing the space for chain segment movement. Subsequently, a rapid cooling treatment fixes the UHMWPE molecular chains in a swollen state. This allows the swollen modified pretreatment material to be distributed as a dispersed phase within the HDPE matrix during subsequent extrusion, forming a two-phase dispersion structure. When the pipe is subjected to external impact, this dispersed phase can absorb and dissipate the impact energy, blocking the propagation of microcracks, thereby improving the impact toughness of the pipe.

[0007] Meanwhile, poly-1-butene is introduced into the formulation to synergistically toughen and provide creep resistance. To address the issue of free precipitation of low-molecular-weight substances such as white oil during extrusion and storage, this invention introduces a delayed-release trapping agent masterbatch. This masterbatch is added via side feeding in the middle to later stages of the extruder. Utilizing the porous structure of calcined diatomaceous earth, it adsorbs free low-molecular-weight substances in the later stages of melt blending, preventing their migration and precipitation onto the pipe surface, thereby ensuring the appearance quality and interfacial bonding strength of the pipe.

[0008] Preferably, the processing aid specifically comprises antioxidant 1010, antioxidant 168, and calcium stearate; and the amount of antioxidant 1010 is 0.15-0.25 parts, the amount of antioxidant 168 is 0.15-0.25 parts, and the amount of calcium stearate is 0.2-0.5 parts. The hindered phenolic antioxidant and phosphite antioxidant are combined with a lubricant to ensure the thermal stability of the material under heated processes.

[0009] In one specific embodiment, the delayed capture agent masterbatch is made from 60 parts by weight of calcined diatomaceous earth and 40 parts by weight of high-flowability high-density polyethylene as a carrier resin. The high-flowability carrier resin ensures that the diatomaceous earth is uniformly dispersed into the melt system within the limited blending time of the main extruder.

[0010] The present invention also provides a manufacturing process for the above-mentioned high-toughness impact-resistant cable protection pipe, comprising the following specific steps: Calcined diatomaceous earth and polyethylene as carrier resin are weighed and mixed in a conventional mixer. Then, the mixture is fed into a twin-screw extruder. The extruded material strips are cooled with water and then cut into cylindrical masterbatches by a pelletizer to obtain the delayed capture agent masterbatch. Ultra-high molecular weight polyethylene is added to a hot mixer and stirred. Industrial white oil is added evenly to the hot mixer. Then the speed is increased and the material is heated and kneaded by high-speed friction between the materials. After the time is reached, the pneumatic discharge valve is opened and the material is discharged into the cold mixer below for low-speed stirring and cooling. The swollen modified pretreated material is then discharged. High-density polyethylene, poly-1-butene, and processing aids are mixed in a conventional mixer, and the discharged material is the matrix premix. The swelling modified pretreatment material and the matrix premix are simultaneously added to the main feed hopper of the co-rotating twin-screw extruder. In the middle and rear section of the co-rotating twin-screw extruder, the delayed capture agent masterbatch is fed into the melt being blended through the side feeder. After thorough mixing, it is extruded through the pipe extrusion die to form a high-temperature pipe blank. The high-temperature tube blank first enters the vacuum sizing sleeve to rapidly cool and harden the surface of the tube blank to form a rigid shell, thus obtaining the tube. The sizing tube then enters the atmospheric pressure hot water cooling box for thermodynamic annealing and phase transformation shaping. The tube then enters the final stage ambient temperature spray water box to be completely cooled to room temperature. The fully cooled and shaped pipe is pulled by a tracked traction machine and cut to a fixed length to obtain a high-toughness, impact-resistant cable protection pipe.

[0011] In the shaping and cooling stage of the above-mentioned preparation process, after the tube blank is hardened on the surface of the vacuum sizing sleeve, it enters the atmospheric pressure hot water cooling tank. The hot water environment releases the residual internal stress generated in the tube during the extrusion and sizing process, preventing the tube from deforming due to internal stress shrinkage in the later stage; at the same time, the suitable water temperature provides thermodynamic conditions to promote the crystal transformation process of poly-1-butene in the tube system, making the polymer crystals arrange regularly, thereby improving the long-term mechanical stability of the tube.

[0012] Preferably, in the step of preparing the delayed capture agent masterbatch: calcined diatomaceous earth and high-flowability high-density polyethylene are put into a conventional mixer and mixed at room temperature at a speed of 300-500 rpm for 5-10 minutes; the temperature of each section of the twin-screw extruder is set as follows: feeding section 150-160℃, melting section 170-180℃, homogenization section 180-190℃, die head section 180-190℃, and the screw speed is set to 200-300 rpm.

[0013] Preferably, in the step of preparing the swelling modified pretreatment material: when starting the stirring in the hot mixer, the initial speed is set to 300-500 rpm; after adding industrial white oil, the speed is increased to 1500-2000 rpm, so that the system temperature rises to 105-115℃, and the material is kneaded at a constant temperature for 15-20 minutes; after being discharged into the cold mixer, the material is cooled to 30-40℃ within 3-5 minutes under low-speed stirring at 100-200 rpm.

[0014] Preferably, in the step of preparing the matrix premix: after adding high-density polyethylene, poly-1-butene and processing aids into a conventional mixer, they are mixed at room temperature at a speed of 300-500 rpm for 5-10 minutes.

[0015] Preferably, in the extrusion step of the co-rotating twin-screw extruder: the temperature of each section of the co-rotating twin-screw extruder is set as follows: Zone 1 165-175℃, Zone 2 175-185℃, Zones 3 to 6 180-190℃, Die head flange and die area 180-190℃, and the main screw speed is set as 150-250 rpm.

[0016] Preferably, in the sizing and annealing steps: the length of the vacuum sizing sleeve is 2 to 3 meters, the temperature of the circulating cooling water in the vacuum sizing sleeve is controlled at 15 to 25°C, and the vacuum degree is set to ~0.04MPa to ~0.08MPa; the length of the atmospheric pressure hot water cooling tank is 10 to 15 meters, and the temperature of the circulating water is controlled at 85 to 90°C.

[0017] This invention provides a high-toughness, impact-resistant cable protection pipe. It has the following beneficial effects: 1. This invention employs industrial white oil for swelling modification pretreatment of ultra-high molecular weight polyethylene (UHMWPE) followed by low-speed rapid cooling and shaping, thereby fixing the UHMWPE molecular chains in a swollen state. This feature allows the UHMWPE to be distributed as a dispersed phase within the high-density polyethylene matrix during subsequent extrusion. When subjected to external impact, this dispersed phase can absorb and dissipate impact energy, preventing microcrack propagation, thus improving the impact toughness of the pipe and solving the problem of phase separation that easily occurs when directly blending UHMWPE.

[0018] 2. In the middle and later stages of extrusion blending, this invention adds a delayed-capture agent masterbatch made of calcined diatomaceous earth and high-flowability high-density polyethylene via side feeding. Utilizing the porous structure of calcined diatomaceous earth, it adsorbs free low-molecular-weight substances in the system during the later stages of melt blending, preventing these substances from migrating and precipitating onto the pipe surface, thereby ensuring the surface quality of the pipe and the bonding strength of the material interface.

[0019] 3. In the extrusion and shaping stage, the surface-hardened tube blank is placed in an atmospheric pressure hot water cooling tank for annealing. The hot water environment can release the residual internal stress generated during the extrusion and sizing process, preventing the tube from deforming due to stress shrinkage during later use; at the same time, this temperature condition can promote the crystal transformation of poly-1-butene in the system, making the polymer crystals arrange regularly and stabilizing the long-term mechanical properties of the tube. Attached Figure Description

[0020] Figure 1 This is the differential scanning calorimeter in Test Example 1 of this invention.

[0021] Figure 2 This is the X-ray diffraction pattern of the pipe sample in Test Example 1 of this invention.

[0022] Figure 3 This is the tensile stress-strain curve of the pipe sample in Test Example 3 of this invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: This example provides a manufacturing process for a high-toughness, impact-resistant cable protection pipe, including the following steps: 60 parts by weight of calcined diatomaceous earth and 40 parts by weight of high-flowability high-density polyethylene were weighed as the carrier resin. The above materials were fed into a conventional mixer and mixed for 8 minutes at 400 rpm at room temperature. The mixed material was then fed into a twin-screw extruder, with the extruder temperatures set as follows: feeding section 155°C, melting section 175°C, homogenizing section 185°C, and die head section 185°C. The screw speed was set to 250 rpm. After water cooling, the extruded material was cut into cylindrical masterbatches using a pelletizer to obtain the delayed capture agent masterbatch.

[0025] Add 12 parts by weight of ultra-high molecular weight polyethylene to a hot mixer and start stirring, setting the initial speed to 400 rpm. Add 2 parts by weight of industrial white oil evenly to the hot mixer via spraying, then increase the speed to 1750 rpm. Heat is generated through high-speed friction between the materials, raising the system temperature to 110°C, and the mixture is kneaded at this temperature for 18 minutes. After the time is reached, the pneumatic discharge valve is instantly opened, discharging the material into a cold mixer with an activated circulating cooling water jacket. Under low-speed stirring at 150 rpm, the material is cooled to 35°C within 4 minutes, yielding the swollen modified pretreated material.

[0026] 100 parts by weight of high-density polyethylene, 4.5 parts by weight of poly-1-butene, and 0.8 parts by weight of processing aids (specifically composed of 0.2 parts by weight of antioxidant 1010, 0.2 parts by weight of antioxidant 168, and 0.4 parts by weight of calcium stearate) are added into a conventional mixer and mixed at 400 rpm for 8 minutes at room temperature. The resulting material is the matrix premix.

[0027] The obtained swollen modified pretreated material and the obtained matrix premix were simultaneously added to the main feed hopper of a co-rotating twin-screw extruder equipped with a side feeder. The extruder temperatures were set as follows: Zone 1 170℃, Zone 2 180℃, Zones 3 to 6 185℃, and the die head flange and die area 185℃. The main screw speed was set to 200 rpm. In the middle and rear section of the extruder, 4.5 parts by weight of the prepared delayed capture agent masterbatch was fed into the melt being blended via the side feeder. After thorough mixing, the materials were extruded through the pipe extrusion die to form a high-temperature pipe blank.

[0028] The high-temperature tube blank first enters a 2.5-meter-long vacuum sizing sleeve. The circulating cooling water temperature inside the sleeve is controlled at 20℃, and the vacuum degree is set to -0.06MPa, allowing the tube blank surface to rapidly cool and harden, forming a rigid outer shell. The sized tube then enters a 12-meter-long atmospheric pressure hot water cooling tank. Inside the tank, there is no vacuum negative pressure, and the circulating water temperature is controlled at 88℃ for thermodynamic annealing and phase transformation shaping. The tube then enters a final stage ambient temperature spray water tank for complete cooling to room temperature. The fully cooled and shaped tube is then pulled by a tracked traction machine and cut to a fixed length.

[0029] Example 2: This example provides a manufacturing process for a high-toughness, impact-resistant cable protection pipe, including the following steps: 60 parts by weight of calcined diatomaceous earth and 40 parts by weight of high-flowability high-density polyethylene were weighed as the carrier resin. The above materials were fed into a conventional mixer and mixed at 500 rpm for 10 minutes at room temperature. The mixed material was then fed into a twin-screw extruder, with the extruder temperatures set as follows: feeding section 160°C, melting section 180°C, homogenizing section 190°C, and die head section 190°C. The screw speed was set to 300 rpm. After water cooling, the extruded material was cut into cylindrical masterbatches using a pelletizer to obtain the delayed capture agent masterbatch.

[0030] Add 15 parts by weight of ultra-high molecular weight polyethylene to a hot mixer and start stirring, setting the initial speed to 500 rpm. Add 3 parts by weight of industrial white oil evenly to the hot mixer via spraying, then increase the speed to 2000 rpm. Heat is generated through high-speed friction between the materials, raising the system temperature to 115°C, and the mixture is kneaded at this temperature for 20 minutes. After the time is reached, the pneumatic discharge valve is instantly opened, discharging the material into a cold mixer with an activated circulating cooling water jacket. Under low-speed stirring at 200 rpm, the material is cooled to 40°C within 5 minutes, yielding the swollen modified pretreated material.

[0031] 100 parts by weight of high-density polyethylene, 6 parts by weight of poly-1-butene, and 1.0 part by weight of processing aids (specifically composed of 0.25 parts by weight of antioxidant 1010, 0.25 parts by weight of antioxidant 168, and 0.5 parts by weight of calcium stearate) are added into a conventional mixer and mixed at 500 rpm for 10 minutes at room temperature. The resulting material is the matrix premix.

[0032] The obtained swollen modified pretreated material and the obtained matrix premix were simultaneously added to the main feed hopper of a co-rotating twin-screw extruder equipped with a side feeder. The extruder temperatures were set as follows: Zone 1 175℃, Zone 2 185℃, Zones 3 to 6 190℃, and the die head flange and die area 190℃. The main screw speed was set to 250 rpm. In the middle and rear section of the extruder, 6 parts by weight of the prepared delayed capture agent masterbatch were fed into the melt being blended via the side feeder. After thorough mixing, the materials were extruded through the pipe extrusion die to form a high-temperature pipe blank.

[0033] The high-temperature tube blank first enters a 3-meter-long vacuum sizing sleeve. The circulating cooling water temperature inside the sleeve is controlled at 25℃, and the vacuum degree is set to -0.08MPa, allowing the tube blank surface to cool and harden rapidly, forming a rigid outer shell. The sized tube then enters a 15-meter-long atmospheric pressure hot water cooling tank. Inside the tank, there is no vacuum negative pressure, and the circulating water temperature is controlled at 90℃ for thermodynamic annealing and phase transformation shaping. The tube then enters a final stage ambient temperature spray water tank for complete cooling to room temperature. The fully cooled and shaped tube is then pulled by a tracked traction machine and cut to a fixed length.

[0034] Example 3: This example provides a manufacturing process for a high-toughness, impact-resistant cable protection pipe, including the following steps: Weigh 60 parts by weight of calcined diatomaceous earth and 40 parts by weight of high-flowability high-density polyethylene as the carrier resin. Add the above materials to a conventional mixer and mix for 5 minutes at 300 rpm at room temperature. Then, feed the mixed material into a twin-screw extruder. The extruder temperatures for each section are set as follows: feeding section 150°C, melting section 170°C, homogenizing section 180°C, and die head section 180°C. The screw speed is set to 200 rpm. After water cooling, the extruded material is cut into cylindrical masterbatches using a pelletizer to obtain the delayed capture agent masterbatch.

[0035] Eight parts by weight of ultra-high molecular weight polyethylene were added to a hot mixer, and stirring was started with an initial speed of 300 rpm. One part by weight of industrial white oil was evenly added to the hot mixer via spraying, and then the speed was increased to 1500 rpm. The system temperature was raised to 105°C by high-speed friction between the materials, and kneaded at this temperature for 15 minutes. After the time was reached, the pneumatic discharge valve was opened instantly, discharging the material into a cold mixer with a pre-operated circulating cooling water jacket. The material was cooled to 30°C within 3 minutes by stirring at a low speed of 100 rpm, and the swollen modified pretreated material was then discharged.

[0036] 100 parts by weight of high-density polyethylene, 3 parts by weight of poly-1-butene, and 0.5 parts by weight of processing aids (specifically composed of 0.15 parts by weight of antioxidant 1010, 0.15 parts by weight of antioxidant 168, and 0.2 parts by weight of calcium stearate) are added into a conventional mixer and mixed at 300 rpm for 5 minutes at room temperature. The resulting material is the matrix premix.

[0037] The obtained swollen modified pretreated material and the obtained matrix premix were simultaneously added to the main feed hopper of a co-rotating twin-screw extruder equipped with a side feeder. The extruder temperatures were set as follows: Zone 1 165℃, Zone 2 175℃, Zones 3 to 6 180℃, and the die head flange and die area 180℃. The main screw speed was set to 150 rpm. In the middle and rear section of the extruder, 3 parts by weight of the prepared delayed capture agent masterbatch were fed into the melt being blended via the side feeder. After thorough mixing, the materials were extruded through the pipe extrusion die to form a high-temperature pipe blank.

[0038] The high-temperature tube blank first enters a 2-meter-long vacuum sizing sleeve. The circulating cooling water temperature inside the sleeve is controlled at 15℃, and the vacuum degree is set to -0.04MPa, allowing the tube blank surface to cool and harden rapidly, forming a rigid outer shell. The sized tube then enters a 10-meter-long atmospheric pressure hot water cooling tank. Inside the tank, there is no vacuum negative pressure, and the circulating water temperature is controlled at 85℃ for thermodynamic annealing and phase transformation shaping. The tube then enters a final stage ambient temperature spray water tank for complete cooling to room temperature. The fully cooled and shaped tube is then pulled by a tracked traction machine and cut to a fixed length.

[0039] Comparative Example 1: Compared with Example 1, the difference is that the hot-cold two-stage solid-phase micro-swelling pretreatment of ultra-high molecular weight polyethylene was not performed. Industrial white oil was removed from the formulation; 12 parts by weight of untreated ultra-high molecular weight polyethylene powder were directly mixed with the matrix premix at room temperature and fed into the main feed hopper. All other aspects were the same.

[0040] Comparative Example 2: The difference from Example 1 is that poly-1-butene was not added to the matrix premix formulation. Everything else is the same.

[0041] Comparative Example 3: Compared with Example 1, the difference is that no delayed capture agent masterbatch was prepared, and the side feeding step of the extruder was eliminated. An equivalent weight of powdered calcined diatomaceous earth (2.7 parts by weight) and high-flowability high-density polyethylene (1.8 parts by weight) were directly added to the matrix premix and fed in at once from the main feed hopper. Everything else was the same.

[0042] Comparative Example 4: Compared with Example 1, the difference is that the atmospheric pressure thermodynamic annealing phase transformation shaping was eliminated in the tube blank forming process. After passing through a 2.5-meter vacuum sizing sleeve, the tube blank directly entered a conventional spray water tank with a length of 12 meters and a constant water temperature of 20°C for rapid cooling and shaping throughout the process. Everything else was the same.

[0043] Test Example 1: Experimental Procedure: Differential scanning calorimetry (DSC) was used for testing. The test subjects included commercially available pure ultra-high molecular weight polyethylene (UHMWPE) powder reference samples and the swollen modified pretreated material prepared in Example 1. Samples of 5.2 to 6.8 mg were taken and placed in standard aluminum crucibles. Under a nitrogen atmosphere, the temperature was increased from 25°C to 180°C at a rate of 10°C / min. Heat flow data during the heating phase were recorded, and the peak melting temperature, enthalpy of fusion, and peak half-width were extracted.

[0044] X-ray diffraction was used for testing. The test subjects included the pipe samples prepared in Example 1 and Comparative Example 4. Sheet-shaped samples with a thickness of 2 mm were cut along the extrusion direction of the pipe. Kα radiation from a copper target was used, with a tube voltage of 40 kV and a tube current of 40 mA. The scanning range was set to 2θ = 5° to 30°, and the scanning step size was 0.02°. X-ray diffraction data of the samples were recorded. Peak separation and fitting were performed on the characteristic diffraction peaks of poly(1-butene) crystal form I and II, as well as the diffraction peaks of the polyethylene matrix. After background subtraction, the percentage of the integrated area of ​​the characteristic peaks of poly(1-butene) crystal form I and II, and other unassigned peaks was calculated.

[0045] Experimental data: Table 1. Differential Scanning Calorimetry Test Data ; Table 2. X-ray diffraction crystal form test data. ; Note: The area percentage of other unassigned peaks in the table refers to the area percentage of weak peaks other than the characteristic diffraction peaks of crystal form I and crystal form II, as well as the residual peaks after amorphous scattering or background subtraction; the data in Tables 1 and 2 are representative or average results after repeated tests.

[0046] Experimental conclusions: Based on Table 1 and... Figure 1 According to the data, the peak melting temperature of pure ultra-high molecular weight polyethylene powder is approximately 142.3℃, and the corresponding enthalpy of melting is 186.7 J / g. Figure 1The solid line shows a concentrated endothermic peak around 142℃. The melting peak temperature of the pretreated material in Example 1 shifts towards a lower temperature range to 138.4℃, with a melting enthalpy of 162.2 J / g. Figure 1 The dashed line shows a shift in peak position and an increase in peak half-width at half-maximum (HWHM). This change in thermal parameters reflects the penetration of industrial white oil into the amorphous region on the surface of polymer particles. The entry of white oil molecules increases the free space between polymer chain segments to a certain extent, making the chain structure more relaxed. This results in a decrease in the energy required for material melting and a lower melting temperature. The corresponding cooling process restricts the retraction of molecular chains, allowing white oil molecules to remain on the surface of the material. This is beneficial for improving the powder's flowability in subsequent processes.

[0047] According to Table 2 and Figure 2 According to the data, the relative area ratio of the characteristic peak of poly-1-butene crystal form I in the pipe of Example 1 was 89.1%. Figure 2 The solid line exhibits a characteristic diffraction peak near 2θ = 9.8°, while the relative area proportion of crystal form II is relatively low. In Comparative Example 4, the relative area proportion of crystal form I in the pipe is 27.6%, and the relative area proportion of crystal form II is 65.4%. Figure 2 The dashed line indicates a characteristic diffraction peak for poly(1-butene) crystal form II around 11.3°. Poly(1-butene) tends to form crystal form II initially during the initial cooling process from the molten state. Single-stage cooling with cold water rapidly reduces the mobility of polymer molecular chains, causing many crystal forms II to be fixed without undergoing phase transformation. Example 1 employed atmospheric pressure hot bath annealing, providing a constant thermal environment for the rearrangement of polymer chain structures and promoting the transformation of poly(1-butene) from crystal form II to crystal form I. Compared to cold water cooling, the gentler temperature gradient alleviates the internal stress generated in the matrix resin during the crystallization shrinkage stage, helping to reduce interfacial defects caused by uneven shrinkage at the two-phase interface.

[0048] Test Example 2: Unless otherwise specified, in the following test examples, the pipes prepared in Examples 1 to 3 and each comparative example are all pipes of the same specification, with a nominal outer diameter of 110 mm and a nominal wall thickness of 5.0 mm.

[0049] Experimental Procedure: A current monitoring recorder was used to collect the operating load data of the main motor of the extruder. The test subjects included Example 1, Comparative Example 1, and Comparative Example 3. After the equipment entered the stable extrusion stage, the overall machine current data was continuously recorded for 60 minutes. The average current and current fluctuation rate during this period were calculated, and the material flow status at the feed inlet of the feeding section was recorded.

[0050] Pipe dimensions were measured using vernier calipers and an ultrasonic thickness gauge. The test subjects included fixed-length pipes from Example 1 and Comparative Example 4. Five measurement sections were randomly selected along the pipe's axial direction, and the maximum and minimum outer diameters, as well as the pipe wall thickness, were measured at the same section. The maximum difference in outer diameter, the average ellipticity, and the maximum deviation in wall thickness were calculated.

[0051] Experimental data: Table 3. Record of Process Flow Field Stability and Feed Inlet Status ; Table 4. Test Data on Pipe Dimensional Stability ; Note: For each performance test, at least 5 parallel samples were tested. The data in the table are the average values ​​of the parallel test results.

[0052] Experimental Conclusions: According to the data in Table 3, the average current of Example 1 was 182.4 A, with a current fluctuation rate of 3.14%, and the material flow from the feed port was smooth. The average current of Comparative Example 1 was 197.6 A, with a current fluctuation rate of 15.27%, accompanied by intermittent feeding delays. Considering the differences in operating parameters, Comparative Example 1 did not add industrial white oil for swelling treatment. The ultra-high molecular weight polyethylene powder was directly mixed with the matrix resin at room temperature, which easily caused electrostatic agglomeration due to dry friction, resulting in local density differences in the material entering the extruder screw, causing oscillations in the extruder torque and current. The average current of Comparative Example 3 was 214.3 A, with a current fluctuation rate of 29.83%. Intermittent material bridging occurred at the feed port, accompanied by local backflow. After short-term discharge and traction stabilization, pipe samples for subsequent performance testing could still be obtained, but its continuous extrusion stability was significantly reduced. Comparative Example 3 eliminated the diatomaceous earth masterbatch and side feeding steps, directly adding the powder to the main material. Powdered diatomaceous earth increases the dry friction between materials in the screw compression section. Simultaneously, the uncoated diatomaceous earth pre-absorbs the white oil components released from the surface of the pretreated material, altering the lubrication state of the material in the initial melting stage, leading to increased flow resistance and inducing material blockage or feeding fluctuations. Example 1 uses side-feeding with diatomaceous earth masterbatch. By coating the calcined diatomaceous earth with carrier resin and shifting the side-feeding position backward, the direct exposure of inorganic powder in the feeding and compression sections is reduced. This reduces the impact of dry friction and the pre-absorption of white oil by the calcined diatomaceous earth on the lubrication state in the initial melting stage, maintaining the stable operation of the extrusion process.

[0053] According to the data in Table 4, the maximum outer diameter difference of the pipe in Example 1 was 0.85 mm, the ellipticity was 0.76%, and the maximum wall thickness deviation was 0.21 mm. The maximum outer diameter difference of the pipe in Comparative Example 4 was 3.42 mm, the ellipticity was 3.11%, and the maximum wall thickness deviation was 0.87 mm. Considering the differences in cooling processes, Comparative Example 4 used a 20°C cold water sizing process throughout, where the outer layer of the pipe solidified after contact with cold water, while the inner wall and core remained in a high-temperature molten state. The difference in cooling rates between the inner and outer layers caused shrinkage stress in the radial section of the pipe, resulting in flattening deformation of the pipe blank under the combined effects of traction and its own gravity. Example 1 used thin-shell sizing combined with 88°C atmospheric pressure hot water annealing. A short-term cooling process using a vacuum sizing sleeve was used to establish the outer shell of the pipe, followed by a hot bath to slow down the overall cooling rate and reduce the temperature gradient in the thickness direction of the pipe. This spatiotemporal decoupling operation reduced the residual internal stress caused by asynchronous shrinkage of each layer, maintaining the shape and dimensional accuracy of the pipe after cooling and sizing.

[0054] Test Example 3: Implementation steps: A pipe ring stiffness testing machine was used for testing. The test objects included pipes from Examples 1 to 3, Comparative Example 3, and Comparative Example 4, which were extruded and left to stand for 24 hours. A 300mm long pipe segment was cut along the axial direction of the pipe as a sample. The sample was placed horizontally between the upper and lower parallel pressure plates of the testing machine, and the compression speed was set to 10mm / min. The load when the vertical deformation of the sample reached 3% of the inner diameter of the pipe was recorded, and the ring stiffness value was calculated.

[0055] Tensile tests were conducted using a universal testing machine. The test subjects included the pipes from Examples 1 to 3, Comparative Example 3, and Comparative Example 4. Type 1B dumbbell-shaped standard specimens were cut along the axial direction of the pipes. The tensile speed was set to 50 mm / min at an ambient temperature of 23°C. Load and displacement data during the tensile process were recorded, and the stress value at the yield point of the specimen was extracted.

[0056] Experimental data: Table 5. Static Test Data of Pipes ; Note: For each performance test, at least 5 parallel samples were tested. The data in the table are the average values ​​of the parallel test results.

[0057] Experimental conclusion: According to the data in Table 5, the ring stiffness of Examples 1 to 3 is 11.82 kN / m. 2 Up to 13.05 kN / m 2 The tensile yield stress is between 25.9 MPa and 27.5 MPa. Figure 3The curve represented by the solid line in Example 1 exhibits a high slope in the initial stage and shows a distinct yield peak near the stress value of 26.8 MPa. The average ring stiffness of Comparative Example 3 is 8.16 kN / m. 2 The average tensile yield stress is 21.2 MPa. Figure 3 The curve in Comparative Example 3, represented by the dashed line, has a gentler initial slope, and the yield peak shifts towards lower stress. Comparative Example 3 does not include the side-feeding process of diatomaceous earth masterbatch; instead, powdered diatomaceous earth is fed in a single step. The early addition of powder alters the distribution of white oil in the material. Free white oil components diffuse into the high-density polyethylene matrix. White oil molecules interpenetrate between the molecular chains of high-density polyethylene, increasing the free space between chain segments and producing a plasticizing effect, causing the pipe matrix to soften and reducing the material's ability to withstand external pressure and tensile loads. Example 1 uses side-feeding to add diatomaceous earth, utilizing its porous structure to adsorb free white oil, reducing the diffusion of white oil into the high-density polyethylene matrix and maintaining the original stiffness of the matrix material.

[0058] According to the data in Table 5, the average tensile yield stress of Comparative Example 4 was 22.7 MPa, which is lower than that of Example 1. (Combined with...) Figure 3 The curve in Comparative Example 4, represented by the dashed line, shows a similar initial stress increase trend to Example 1, but exhibits an earlier yield transition at a lower stress level. The tube blank in Comparative Example 4 was directly cooled in a 20°C water bath after extrusion. The rapidly decreasing temperature shortened the relaxation time of the polymer molecular chain segments, and residual internal stress was retained within the tube due to differences in the shrinkage rates of each layer. Simultaneously, under these cooling conditions, poly-1-butene formed and retained crystal form II, without transforming to crystal form I. When tensile force was applied, the internal residual stress and the applied load superimposed, causing the material to yield at a lower stress level. Example 1, using an atmospheric pressure hot bath annealing process, provided a temperature environment that delayed freezing of the polymer chains, promoted the release of residual internal stress, and facilitated the phase transformation of poly-1-butene to crystal form I, thereby improving the basic tensile strength of the tube.

[0059] Test Example 4: Experimental Procedure: Low-temperature impact testing was conducted using a pendulum impact testing machine. The test subjects included extruded pipes from Examples 1 to 3, and Comparative Examples 1, 2, and 4. Standard rectangular specimens were cut along the axial direction of the pipes, and a V-notch was machined in the middle of each specimen. The specimens were placed in a -20°C low-temperature environment chamber for 4 hours. The specimens were then removed and a simply supported beam impact test was performed within a specified time. The energy absorbed upon fracture was recorded, and the notched impact strength was calculated.

[0060] Interfacial compatibility testing was conducted using a dynamic thermomechanical analyzer. The test subjects included pipes from Example 1, Comparative Example 1, and Comparative Example 2. Strip samples with dimensions of 50 mm in length, 10 mm in width, and 2 mm in thickness were obtained by cutting. A single cantilever beam test mode was used, with a test frequency of 1 Hz, a heating rate of 3 °C / min, and a scanning temperature range of -50 °C to 120 °C. During the test, the loss tangent data of the material was continuously recorded, and the tanδ main peak temperature, tanδ main peak value, and tanδ main peak half-width were extracted.

[0061] Experimental data: Table 6. Low-Temperature Notched Impact Strength Test Data for Pipes ; Table 7. Dynamic Thermomechanical Analysis Test Data Table ; Note: The tanδ main peak temperature and half-peak width are used to characterize the chain segment relaxation behavior and the width of the interface transition zone in the polymer blend system; at least 5 parallel samples were used for each performance test, and the data in the table are the average values ​​of the parallel test results.

[0062] Experimental conclusion: According to the data in Table 6, the -20℃ notched impact strength of Examples 1 to 3 is 46.5 kJ / m. 2 Up to 51.2 kJ / m 2 Between. The average notched impact strength of Comparative Example 1 decreased to 12.3 kJ / m. 2 Based on the dynamic thermomechanical analysis data in Table 7, the tanδ main peak temperature of Comparative Example 1 is 24.3℃, lower than 38.6℃ of Example 1, and its tanδ main peak half-width is 18.7℃, significantly smaller than 34.2℃ of Example 1. Comparing the operation process, Comparative Example 1 did not undergo modification treatment with white oil, and the ultra-high molecular weight polyethylene particles maintained a dense, highly crystalline state. During the melt mixing stage, the dense ultra-high molecular weight polyethylene is difficult to interpenetrate with the high-density polyethylene matrix, forming an interfacial isolation zone between them. Under external impact loads, the unfused ultra-high molecular weight polyethylene particles act as stress concentration points, inducing the propagation of internal cracks in the material, leading to a decrease in impact resistance. Example 1 utilized white oil to increase the activity space of the surface chain segments of ultra-high molecular weight polyethylene, promoting the entanglement of polymer macromolecules and matrix resin. As shown in Table 7, the tanδ main peak temperature of Example 1 shifts towards higher temperatures compared to Comparative Example 1, and the half-peak width of the main peak increases, indicating that the distribution range of the chain segment relaxation process in the material becomes wider, reflecting the widening of the transition zone at the interface between the two phases of the polymer blend and the improvement of the degree of interface fusion.

[0063] According to the data in Table 6, the average notched impact strength of Comparative Example 2 is 16.8 kJ / m. 2As shown in Table 7, the half-maximum width of the tanδ main peak in Comparative Example 2 is 24.6℃, which is less than 34.2℃ in Example 1, indicating that the transition zone at the two-phase interface in Comparative Example 2 is narrower, and the interface buffering effect is weaker than that in Example 1. Poly-1-butene was not added to the formulation of Comparative Example 2. There are differences in the crystallization rate and shrinkage rate between high-density polyethylene and ultra-high molecular weight polyethylene. During the cooling and shaping stage after extrusion, localized interface separation occurs at the two-phase interface due to asynchronous cooling and shrinkage. The poly-1-butene added in Example 1 has a similar non-polar chain structure to polyethylene resins, which can form a flexible transition layer at the interface between high-density polyethylene and ultra-high molecular weight polyethylene. Through chain segment diffusion, physical entanglement, and synergistic shrinkage during cooling and crystallization, it reduces stress concentration at the two-phase interface. When the pipe is subjected to instantaneous impact, this flexible transition layer can absorb and dissipate some of the energy during the impact load transmission process, thereby improving the low-temperature impact resistance of the pipe.

[0064] According to the data in Table 6, the average notched impact strength of Comparative Example 4 is 24.1 kJ / m. 2 In contrast to the cooling process conditions, the tube blank in Comparative Example 4 was directly immersed in a 20°C cold water bath after extrusion. The outer resin layer of the tube blank rapidly shrank in volume under the action of the cold water. Under cooling conditions, the rapid shrinkage of the high-density polyethylene matrix applied tensile stress to the still fragile blend interface, causing tearing and damage at the polymer interface. Example 1, using a hot bath annealing process, mitigated the cooling rate difference between the inner and outer layers of the tube, reduced the volume shrinkage stress during the curing stage, protected the structural integrity of the polymer blend interface, and maintained the impact resistance of the tube under low-temperature conditions.

Claims

1. A high-toughness, impact-resistant cable protection pipe, characterized in that, Made from the following ingredients in parts by weight: Matrix premix: 100 parts high-density polyethylene, 3-6 parts poly-1-butene, and 0.5-1.0 parts processing aids; Swellable modified pretreatment material: 8-15 parts ultra-high molecular weight polyethylene, 1-3 parts industrial white oil; Delayed capture agent masterbatch: 3-6 parts.

2. The high-toughness, impact-resistant cable protection pipe according to claim 1, characterized in that: The processing aid is specifically composed of antioxidant 1010, antioxidant 168 and calcium stearate; and the antioxidant 1010 is 0.15-0.25 parts, the antioxidant 168 is 0.15-0.25 parts, and the calcium stearate is 0.2-0.5 parts.

3. The high-toughness, impact-resistant cable protection pipe according to claim 2, characterized in that: The delayed capture agent masterbatch is made from 60 parts by weight of calcined diatomaceous earth and 40 parts by weight of high-flowability high-density polyethylene as a carrier resin.

4. The high-toughness, impact-resistant cable protection pipe according to claim 3, characterized in that, The preparation of the high-toughness, impact-resistant cable protection tube includes the following steps: Calcined diatomaceous earth and high-flowability high-density polyethylene as carrier resin are weighed and mixed in a conventional mixer. Then, the mixture is fed into a twin-screw extruder. The extruded material strips are cooled by water and then cut into cylindrical masterbatches by a pelletizer to obtain the delayed capture agent masterbatch. The ultra-high molecular weight polyethylene is put into a hot mixer and stirred. The industrial white oil is added evenly to the hot mixer. Then the speed is increased and the material is heated and kneaded by high-speed friction between the materials. After the time is reached, the pneumatic discharge valve is opened and the material is discharged into the cold mixer below for low-speed stirring and cooling. The swollen modified pretreatment material is obtained by discharging the material. The high-density polyethylene, the poly-1-butene and the processing aid are put into a conventional mixer and mixed. The discharged material is the matrix premix. The swelling modified pretreatment material and the matrix premix are simultaneously added to the main feed hopper of a co-rotating twin-screw extruder. In the middle and rear section of the co-rotating twin-screw extruder, the delayed capture agent masterbatch is fed into the melt being blended through a side feeder. After thorough mixing, the mixture is extruded through a pipe extrusion die to form a high-temperature pipe blank. The high-temperature tube blank first enters a vacuum sizing sleeve to rapidly cool and harden the surface of the tube blank to form a rigid shell, thus obtaining the tube. The sizing tube is then placed in an atmospheric pressure hot water cooling tank for thermodynamic annealing and phase transformation shaping. The tube is then placed in a final ambient temperature spray water tank to be completely cooled to room temperature. The fully cooled and shaped pipe is pulled by a tracked traction machine and cut to a fixed length to obtain the high-toughness impact-resistant cable protection pipe.

5. The high-toughness, impact-resistant cable protection pipe according to claim 4, characterized in that, In the step of obtaining the delayed capture agent masterbatch: After the calcined diatomaceous earth and the high-flowability high-density polyethylene are put into the conventional mixer, they are mixed at room temperature at a speed of 300-500 rpm for 5-10 minutes. The temperature settings for each section of the twin-screw extruder are as follows: The feeding section is set at 150–160°C, the melting section at 170–180°C, the homogenization section at 180–190°C, the die head section at 180–190°C, and the screw speed is set at 200–300 rpm.

6. The high-toughness, impact-resistant cable protection pipe according to claim 4, characterized in that, In the step of obtaining the swollen modified pretreated material: When starting the mixing process in the hot mixer, the initial rotation speed is set to 300-500 rpm; After adding the industrial white oil, increase the rotation speed to 1500-2000 rpm, raise the system temperature to 105-115°C, and knead at the system temperature for 15-20 minutes. After being fed into the cold mixer, the material is cooled to 30-40°C within 3-5 minutes under low-speed stirring at 100-200 rpm.

7. The high-toughness, impact-resistant cable protection pipe according to claim 4, characterized in that, In the step of obtaining the matrix premix: After the high-density polyethylene, the poly-1-butene, and the processing aid are put into the conventional mixer, they are mixed at room temperature at a speed of 300-500 rpm for 5-10 minutes.

8. The high-toughness, impact-resistant cable protection pipe according to claim 4, characterized in that, In the step of forming the high-temperature tube blank: The temperature settings for each section of the co-rotating twin-screw extruder are as follows: Zone 1: 165-175℃, Zone 2: 175-185℃, Zones 3 to 6: 180-190℃, Die head flange and die area: 180-190℃, Main screw speed set to 150-250 rpm.

9. The high-toughness, impact-resistant cable protection pipe according to claim 4, characterized in that, In the step of rapidly cooling and hardening the surface of the tube blank to form a rigid outer shell: The length of the vacuum sizing sleeve is 2 to 3 meters, the temperature of the circulating cooling water inside the vacuum sizing sleeve is controlled at 15 to 25°C, and the vacuum degree is set to -0.04 MPa to -0.08 MPa.

10. The high-toughness, impact-resistant cable protection pipe according to claim 4, characterized in that, In the step of thermodynamic annealing phase transformation shaping: The length of the atmospheric pressure hot water cooling tank is 10 to 15 meters, and the circulating water temperature is controlled at 85 to 90°C.

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