Biaxial orientation cable protection tube

Abstract

The biaxial orientation cable protection tube is prepared from the following raw materials in parts by mass: 100 parts of PVC (Polyvinyl Chloride) resin, 5 to 15 parts of plasticizer, 3 to 8 parts of maleic anhydride grafted EVA (Ethylene Vinyl Acetate), 2 to 5 parts of heat stabilizer, 0.5 to 1.5 parts of lubricant and 5 to 10 parts of filler, the plasticizer at least comprises pyridyl modified adipic acid polyester; the preparation method of the biaxial orientation cable protection tube comprises the following steps: uniformly mixing raw materials of the cable protection tube, and performing melt extrusion to obtain a tube blank; spraying an aqueous solution containing metal ions to the surface of the pipe blank; and heating the cooled tube blank to an orientation temperature, carrying out synchronous biaxial stretching, and carrying out cooling and shaping. According to the invention, the problems of tensile tear and collapse caused by insufficient melt strength in the biaxial orientation process of plasticized and toughened modified PVC can be effectively solved.

Description

Technical Field

[0001] This application relates to the field of PVC materials, and in particular to a biaxially oriented cable protection tube. Background Technology

[0002] Biaxially oriented polyvinyl chloride (PVC-O) cable protection pipes are widely used in underground power and communication engineering due to their excellent ring stiffness, impact resistance, and dimensional stability. By applying axial traction and radial internal pressure to the PVC pipe blank in a highly elastic state, the molecular chains are arranged in an orderly bidirectional manner, thereby significantly improving the mechanical properties.

[0003] However, to meet the demands of cold regions, existing technologies often introduce small-molecule plasticizers (such as DOP) and rubber-based impact modifiers (such as CPE, MBS, and EVA) into PVC systems to improve low-temperature brittleness. While these additives can improve flexibility, they severely weaken the melt strength and high elastic modulus of the material within the orientation temperature window. This causes the pipe to experience localized necking, tearing, or even collapse during simultaneous biaxial stretching due to its inability to withstand biaxial tension, making stable and continuous production difficult. Furthermore, small-molecule plasticizers are prone to migration and precipitation, leading to hardening and brittleness of the pipe after long-term use, further limiting their application in high-end cable protection. Summary of the Invention

[0004] This application aims to solve the problem of tensile tearing and collapse caused by insufficient melt strength in the biaxial orientation process of plasticized and toughened modified PVC.

[0005] This application provides a biaxially oriented cable protection tube, comprising the following raw materials in parts by weight: 100 parts PVC resin, 5-15 parts plasticizer, 3-8 parts maleic anhydride-grafted EVA, 2-5 parts heat stabilizer, 0.5-1.5 parts lubricant, and 5-10 parts filler; wherein the plasticizer comprises at least pyridine-modified adipic acid polyester; the preparation method of the biaxially oriented cable protection tube comprises: mixing the raw materials of the cable protection tube, melt-extruding to obtain a tube blank; spraying an aqueous solution containing metal ions onto the surface of the tube blank; heating the cooled tube blank to the orientation temperature, performing synchronous biaxial stretching, and cooling and shaping to obtain the final product.

[0006] In any of the above technical solutions, the pyridyl-modified adipic acid polyester is prepared by esterification polycondensation of adipic acid, pyridine dicarboxylic acid, and propylene glycol in a molar ratio of 1:0.05 to 0.1:1.1 to 1.2.

[0007] In any of the above technical solutions, the number-average molecular weight of the pyridyl-modified adipic acid polyester is 2000 to 4000.

[0008] In any of the above technical solutions, the pyridine dicarboxylic acid is 2,5-pyridine dicarboxylic acid or 2,6-pyridine dicarboxylic acid.

[0009] In any of the above technical solutions, the metal ions are selected from Ni. 2+ Zn 2+ Cu 2+ One or more of them.

[0010] In any of the above technical solutions, the concentration of metal ions in the aqueous solution is 0.01–0.1 mol / L, the aqueous solution temperature is 55–70℃, and the spraying rate is 80–120 mL / m³. 2 Surface area of ​​tube blank.

[0011] This application achieves a tube reinforcement mechanism that is "non-interfering during processing and self-reinforcing during orientation" by introducing pyridine-modified adipic acid polyester and maleic anhydride-modified EVA, along with improvements to the cooling spray process. Specifically, during the tube blank cooling stage after extrusion, the residual heat of the tube body is used to spray metal ions (such as Zn) in the cooling water. 2+ It rapidly penetrates the surface layer and forms polydentate coordination bonds with the carboxyl groups provided by maleic anhydride-grafted EVA and the pyridine nitrogen atoms and terminal carboxyl groups in the pyridine-modified adipic acid polyester. Due to the strong coordination ability of the pyridine ring, it can construct stable five- or six-membered chelate rings with transition metal ions, thereby building a three-dimensional coordination crosslinking network in situ within the pipe before orientation. This network remains intact at the orientation temperature, significantly improving the high elastic modulus and tensile strength, effectively supporting the synchronous biaxial stretching process and preventing tearing and collapse. Simultaneously, the extremely low migration rate of the high molecular weight polyester backbone further anchors the plasticizing segments through coordination, fundamentally inhibiting precipitation and ensuring long-term cold resistance.

[0012] It should be noted that maleic anhydride-modified EVA has both good toughening effect and good compatibility with PVC resin matrix. This ensures that the coordination network can be effectively dispersed in the resin matrix and play a good reinforcing role.

[0013] In any of the above technical solutions, after rinsing with an aqueous solution containing metal ions, the tube blank is placed in a cooling water tank to cool it to below 40°C.

[0014] In any of the above technical solutions, the orientation temperature is 100-130℃.

[0015] In any of the above technical solutions, the VA content in the maleic anhydride-grafted EVA is 30-50 wt%.

[0016] In any of the above technical solutions, the maleic anhydride grafting rate of the maleic anhydride-grafted EVA is 0.3 to 1.0 wt%.

[0017] In any of the above technical solutions, the axial stretching ratio of the synchronous biaxial stretching is 1.5 to 2.0, and the radial stretching ratio is 1.8 to 2.5.

[0018] In any of the above technical solutions, the filler is a modified filler with surface-grafted siloxane groups.

[0019] In any of the above technical solutions, the method for preparing the modified filler is as follows: The surface of the filler was modified using a vinyl silane coupling agent to obtain a vinylated filler; Vinylated fillers are hydrosilylated with hydrogen-containing silanes to obtain siloxane-modified fillers.

[0020] In any of the above technical solutions, the mass ratio of the filler, vinyl silane coupling agent, and hydrogen-containing silane is 100:3-6:2-5.

[0021] In any of the above technical solutions, the hydrogen-containing silane is selected from one or more of trimethoxysilane, triethoxysilane, methyldimethoxysilane, and ethyldimethoxysilane.

[0022] In any of the above technical solutions, the filler is an inorganic microsphere with a sphericity of not less than 0.8, selected from at least one of spherical silica, spherical calcium carbonate, or spherical talc.

[0023] Preferably, the vinyl silane coupling agent is selected from vinyltrimethoxysilane or vinyltriethoxysilane.

[0024] This application employs siloxane-modified fillers with a sphericity ≥0.8, which not only reduces physical obstacles to the orientation of PVC molecular chains but also plays a synergistic reinforcing role during cooling water spraying. Specifically, water penetration into the pipe material induces hydrolysis and condensation of the siloxane groups grafted onto the filler surface, forming a local Si-O-Si network. This network interpenetrates with the metal-pyridine / carboxylic acid coordination system, constituting an organic-inorganic hybrid reinforcing phase. A flexible siloxane layer grafted with vinylsilane and hydrogen siloxane via hydrosilylation improves the filler's dispersion in the PVC matrix and provides stress buffering at the two-phase interface, preventing stress concentration and microcracks during tensile testing. These two reinforcing mechanisms work synergistically in time (water-triggered during cooling) and space (from the surface to the subsurface), jointly ensuring the structural integrity of the highly flexible PVC system during biaxial orientation.

[0025] In summary, this application has the following beneficial effects: This application introduces a synergistic system of pyridine-modified adipic acid polyester and maleic anhydride-grafted EVA, combined with a pre-orientation metal ion spray cooling process. This allows for the in-situ construction of a coordination crosslinking network before biaxial stretching without sacrificing extrusion processability, significantly improving the mechanical strength of the pipe at the orientation temperature and effectively preventing tearing and collapse during stretching. Simultaneously, the high-molecular-weight polyester plasticizer greatly reduces the risk of migration and precipitation, ensuring long-term low-temperature resistance. Combined with high-sphericity siloxane-modified fillers, the silicon-oxygen network formed during cooling further enhances interfacial bonding and overall structural stability, while minimizing interference with molecular chain orientation due to the spherical morphology. The overall solution achieves simultaneous improvement in flexibility, orientation, and long-term durability, making it suitable for the production of high-performance biaxially oriented PVC cable protection pipes. Detailed Implementation

[0026] Preparation Example Preparation Example 1-1, pyridyl-modified adipic acid polyester, was prepared according to the following operation: In a reaction flask equipped with a stirrer, water separator, nitrogen inlet tube, and thermometer, 730.8 g (5.0 mol) of adipic acid, 66.8 g (0.3 mol) of 2,6-pyridinedicarboxylic acid, and 466.5 g (6.0 mol) of 1,2-propanediol were added, followed by 1.2 g of tetrabutyl titanate catalyst. Under high-purity nitrogen protection, the mixture was slowly heated to 160°C and reacted for 2 hours for esterification, with the water content reaching over 90% of the theoretical value. The temperature was then raised to 210°C and gradually reduced to ≤10 mmHg, continuing the polycondensation reaction for another 3 hours. After the reaction was complete, the mixture was discharged while hot, cooled, and sliced ​​to obtain a pale yellow transparent solid. Gel permeation chromatography determined the number-average molecular weight to be 3100.

[0027] Preparation Examples 1-2: Pyridyl-modified adipic acid polyester was prepared according to the following procedure: In a reaction flask equipped with a stirrer, water separator, nitrogen inlet tube, and thermometer, 730.8 g (5.0 mol) of adipic acid, 41.3 g (0.25 mol) of 2,6-pyridinedicarboxylic acid, and 408.2 g (5.25 mol) of 1,2-propanediol were added, followed by 0.9 g of tetrabutyl titanate catalyst. Under high-purity nitrogen protection, the mixture was slowly heated to 150°C and reacted for 2.5 h for esterification, resulting in a water content exceeding 90% of the theoretical value. The temperature was then raised to 205°C and gradually reduced to ≤10 mmHg, continuing the polycondensation reaction for another 2.5 h. After the reaction was complete, the mixture was discharged while hot, cooled, and sliced ​​to obtain a pale yellow transparent solid. Gel permeation chromatography determined the number-average molecular weight to be 2200.

[0028] Preparation Examples 1-3: Pyridyl-modified adipic acid polyesters were prepared according to the following procedures: In a reaction flask equipped with a stirrer, water separator, nitrogen inlet tube, and thermometer, 730.8 g (5.0 mol) of adipic acid, 82.5 g (0.5 mol) of 2,6-pyridinedicarboxylic acid, and 466.5 g (6.0 mol) of 1,2-propanediol were added, followed by 1.5 g of tetrabutyl titanate catalyst. Under high-purity nitrogen protection, the mixture was slowly heated to 165 °C and reacted for 1.5 h for esterification, with the water content exceeding 90% of the theoretical value. The temperature was then raised to 215 °C and gradually reduced to ≤10 mmHg, continuing the polycondensation reaction for another 3.5 h. After the reaction was complete, the mixture was discharged while hot, cooled, and sliced ​​to obtain a pale yellow transparent solid. Gel permeation chromatography determined the number-average molecular weight to be 3800.

[0029] Preparation Examples 1-4, pyridyl-modified adipic acid polyesters, differ from Preparation Example 1-1 in that 2,6-pyridinedicarboxylic acid is replaced with an equimolar amount of adipic acid.

[0030] Preparation Example 2-1, siloxane-modified filler, was prepared according to the following method: In a reaction flask equipped with a reflux condenser, stirrer, and dropping funnel, 100 g of spherical silica (average particle size 1.5 μm, sphericity approximately 0.85), 400 mL of ethanol, and 30 mL of water were added and ultrasonically dispersed for 30 min. The temperature was raised to 80 °C, and 4.5 g of vinyltriethoxysilane was added dropwise. The mixture was kept at this temperature and stirred for 4 h to perform surface grafting. After filtration, the silica was washed three times with ethanol and dried under vacuum at 80 °C for 12 h to obtain the vinylated filler. This filler was redispersed in 300 mL of toluene, and 3.5 g of methyldimethoxysilane and 0.1 g of Karstedt platinum catalyst (Pt content 2%) were added. The mixture was reacted at 85 °C for 5 h to perform hydrosilylation. After cooling, the filler was filtered, washed successively with toluene and ethanol, and dried at 100 °C for 12 h to obtain the siloxane-modified filler.

[0031] Preparation Example 2-2, siloxane-modified filler, was prepared according to the following method: In a reaction flask equipped with a reflux condenser, stirrer, and dropping funnel, 100 g of spherical calcium carbonate (average particle size 1-2 μm, sphericity approximately 0.9), 360 mL of ethanol, and 20 mL of water were added and ultrasonically dispersed for 30 min. The temperature was raised to 80 °C, and 3.3 g of vinyltriethoxysilane was added dropwise. The mixture was kept at this temperature and stirred for 3.5 h to perform surface grafting. After filtration, the mixture was washed three times with ethanol and vacuum dried at 80 °C for 12 h to obtain the vinylated filler. This filler was redispersed in 300 mL of toluene, and 2.2 g of methyldimethoxysilane and 0.1 g of Karstedt platinum catalyst (Pt content 2%) were added. The mixture was reacted at 80 °C for 4 h to perform hydrosilylation. After cooling, the filler was filtered, washed successively with toluene and ethanol, and dried at 100 °C for 12 h to obtain the siloxane-modified filler.

[0032] Preparation Example 2-3, siloxane-modified filler, was prepared according to the following method: In a reaction flask equipped with a reflux condenser, stirrer, and dropping funnel, 100 g of spherical silica (average particle size 1.5 μm, sphericity approximately 0.85), 450 mL of ethanol, and 30 mL of water were added and ultrasonically dispersed for 30 min. The temperature was raised to 85 °C, and 5.8 g of vinyltriethoxysilane was added dropwise. The mixture was kept at this temperature and stirred for 4 h to perform surface grafting. After filtration, the silica was washed three times with ethanol and dried under vacuum at 80 °C for 12 h to obtain the vinylated filler. This filler was redispersed in 300 mL of toluene, and 4.8 g of methyldiethoxysilane and 0.13 g of Karstedt platinum catalyst (Pt content 2%) were added. The mixture was reacted at 90 °C for 5 h to perform hydrosilylation. After cooling, the silica was filtered, washed successively with toluene and ethanol, and dried at 100 °C for 12 h to obtain the siloxane-modified filler.

[0033] Preparation Examples 2-4, vinyl-modified fillers, were prepared according to the following method: In a reaction flask equipped with a reflux condenser, stirrer, and dropping funnel, 100 g of spherical silica (average particle size 1.5 μm, sphericity approximately 0.85), 400 mL of ethanol, and 30 mL of water were added and ultrasonically dispersed for 30 min. The temperature was raised to 80 °C, and 4.5 g of vinyltriethoxysilane was added dropwise. The mixture was kept at this temperature and stirred for 4 h to perform surface grafting. After filtration, the sample was washed three times with ethanol and dried under vacuum at 80 °C for 12 h to obtain the vinyl-modified filler.

[0034] Preparation Example 2-5, siloxane modified filler, differs from Preparation Example 2-1 in that an equal amount of glass fiber (average length 3-6 mm, average diameter 11-13 μm) replaces spherical silica (average particle size 1.5 μm, sphericity approximately 0.85).

[0035] In the following examples, the PVC resin used is Xinjiang Tianye SG-5 type PVC; the heat stabilizer is an organotin heat stabilizer (MARK17 MOK N5 octyltin mercaptan); the lubricant is a calcium stearate / paraffin compound (mass ratio 1:1); and maleic anhydride-grafted EVA (VA content 40wt%, maleic anhydride grafting rate 0.6wt%).

[0036] Example 1: A biaxially oriented cable protection tube is prepared according to the following steps: 10 kg of PVC resin, 1 kg of pyridyl-modified adipic acid polyester (Preparation Example 1-1), 0.5 kg of maleic anhydride-grafted EVA, 0.3 kg of organotin heat stabilizer, 0.1 kg of lubricant, and 0.75 kg of siloxane-modified filler (Preparation Example 2-1) were added to a high-speed mixer and hot-mixed at 110°C for 8 min. The mixture was then transferred to a cold mixer and cooled to below 40°C to obtain a uniform dry mix. The dry mix was added to a conical twin-screw extruder with the following temperature settings: feeding section 145°C, compression section 165°C, metering section 180°C, and die head 185°C. The melt temperature was controlled at 178±2°C. The extruded tube blank was then extruded through an annular die. Immediately after leaving the die, the tube blank entered a spray cooling section, where it was first sprayed with a 60°C, 0.05 mol / L zinc nitrate aqueous solution via an annular atomizing nozzle at a spray rate of approximately 100 mL / m. 2 The tube blank surface area is measured, and then it enters a 25℃ main cooling water bath to reduce the tube blank temperature to below 40℃. The cooled tube blank is then sent to a heating furnace and uniformly heated to an orientation temperature of 115℃, and then sent to a biaxial stretching device: first, axial traction is applied (stretching ratio 1.7), while simultaneously 1.2MPa nitrogen gas is introduced for radial expansion (stretching ratio 2.1), achieving synchronous biaxial stretching. After stretching, it is immediately quenched and shaped in a 25℃ cooling water bath to obtain a biaxially oriented cable protection tube.

[0037] Example 2: A biaxially oriented cable protection tube is prepared according to the following steps: 10 kg of PVC resin, 0.55 kg of pyridyl-modified adipic acid polyester (Preparation Example 1-2), 0.3 kg of maleic anhydride-grafted EVA, 0.2 kg of organotin heat stabilizer, 0.06 kg of lubricant, and 0.53 kg of siloxane-modified filler (Preparation Example 2-2) were added to a high-speed mixer and hot-mixed at 105°C for 10 min. The mixture was then transferred to a cold mixer and cooled to below 40°C to obtain a uniform dry mix. The dry mix was added to a conical twin-screw extruder with the following temperature settings: feeding section 140°C, compression section 160°C, metering section 175°C, and die head 180°C. The melt temperature was controlled at 172±2°C. The extruded tube blank was then extruded through an annular die. Immediately after leaving the die, the tube blank entered a spray cooling section, where it was first sprayed with a 65°C, 0.02 mol / L zinc nitrate aqueous solution via an annular atomizing nozzle at a spray rate of approximately 120 mL / m. 2 The tube blank surface area is measured, and then it enters a main cooling water bath at 25±2℃ to reduce the tube blank temperature to below 40℃. The cooled tube blank is then sent to a heating furnace and uniformly heated to an orientation temperature of 105℃, and then sent to a biaxial stretching device: first, axial traction is applied (stretching ratio 1.5), while simultaneously 1.0MPa nitrogen gas is introduced for radial expansion (stretching ratio 1.9), achieving synchronous biaxial stretching. After stretching, it is immediately quenched and shaped in a 25℃ cooling water bath to obtain a biaxially oriented cable protection tube.

[0038] Example 3: A biaxially oriented cable protection tube is prepared according to the following steps: 10 kg of PVC resin, 1.5 kg of pyridyl-modified adipic acid polyester (Preparation Examples 1-3), 0.8 kg of maleic anhydride-grafted EVA, 0.45 kg of organotin heat stabilizer, 0.15 kg of lubricant, and 1 kg of siloxane-modified filler (Preparation Examples 2-3) were added to a high-speed mixer and hot-mixed at 115°C for 8 minutes. The mixture was then transferred to a cold mixer and cooled to below 40°C to obtain a uniform dry mix. The dry mix was added to a conical twin-screw extruder with the following temperature settings: feeding section 150°C, compression section 170°C, metering section 185°C, and die head 190°C. The melt temperature was controlled at 180±2°C. The extruded tube blank was then extruded through an annular die. Immediately after leaving the die, the tube blank entered a spray cooling section, where it was first sprayed with a 60°C, 0.1 mol / L zinc nitrate aqueous solution via an annular atomizing nozzle at a spray rate of approximately 100 mL / m. 2 The tube blank surface area is measured, and then it enters a main cooling water bath at 25±2℃ to reduce the tube blank temperature to below 40℃. The cooled tube blank is then sent to a heating furnace and uniformly heated to an orientation temperature of 125℃, and then sent to a biaxial stretching device: first, axial traction is applied (stretching ratio 2.0), while simultaneously 1.5MPa nitrogen gas is introduced for radial expansion (stretching ratio 2.4), achieving synchronous biaxial stretching. After stretching, it is immediately quenched and shaped in a 20℃ cooling water bath to obtain a biaxially oriented cable protection tube.

[0039] Example 4, a biaxially oriented cable protection tube, differs from Example 1 in that an equal amount of vinyl-modified filler from Preparation Example 2-4 is used to replace the siloxane-modified filler from Preparation Example 2-1.

[0040] Example 5, a biaxially oriented cable protection tube, differs from Example 1 in that an equal amount of the siloxane-modified filler from Example 2-5 is used to replace the siloxane-modified filler from Example 2-1.

[0041] Comparative Example Comparative Example 1, a biaxially oriented cable protection tube, differs from Example 1 in that an equal amount of pyridyl-modified adipic acid polyester prepared in Examples 1-4 is used instead of the pyridyl-modified adipic acid polyester prepared in Example 1-1.

[0042] Comparative Example 2, a biaxially oriented cable protection tube, differs from Example 1 in that an equal amount of dioctyl phthalate is used to replace the pyridyl-modified adipic acid polyester used in Preparation Example 1-1.

[0043] Comparative Example 3 is a biaxially oriented cable protection tube, which differs from Example 1 in that an equal amount of EVA (VA content 40wt%) was used to replace the maleic anhydride-grafted EVA (VA content 40wt%) in Preparation Example 1-1.

[0044] Comparative Example 4, a biaxially oriented cable protection tube, differs from Example 1 in that it uses a deionized aqueous solution at 35°C instead of a solution containing Zn at 35°C. 2+ The surface was cooled by spraying with a 0.02 mol / L zinc nitrate aqueous solution.

[0045] Performance testing Experiment 1: Evaluation of the molding stability of the biaxial orientation process In the production process of the examples and comparative examples, 10-meter-long pipes with an outer diameter of 80 mm and a wall thickness of 3.0 mm were continuously produced and cut into 10-cm-long samples. The morphological changes of the pipe blanks during the heating, stretching, and shaping stages were observed and measured. Any of the following conditions were judged as "defective products": 1. Local thinning in the axial or radial direction (thickness deviation > ±25%); 2. Surface cracking or perforation; 3. Out-of-roundness of the pipe body (ovality > 5%). The number of defective products was counted, and the defect rate (%) was calculated as (number of defective products / 100) × 100%.

[0046] Experiment 2: Ring Stiffness Test Three specimen segments with a length of (300±20) mm were randomly cut from each group of pipes produced in the various embodiments and comparative examples. The prepared specimens were conditioned for 24 hours in a standard laboratory environment at (23±2)℃ and (50±10)% relative humidity. A ring stiffness testing machine equipped with a parallel loading plate and an inner diameter measurement system was used according to GB / T 9647-2015 "Determination of Ring Stiffness of Thermoplastic Pipes". The specimen was placed vertically at the center of the lower platen of the testing machine. Pressure was applied to the specimen at a constant compression rate (causing a relative radial deformation of 3%±1% per minute). The ring stiffness value of each individual specimen was recorded. The specimen was rotated approximately 120° and 240° relative to the first loading position, and the above steps were repeated twice. The arithmetic mean of the three measurements was taken as the final ring stiffness result for this batch of conduits.

[0047] Test 3: Low-temperature performance and low-temperature stability (anti-migration properties) test (1) From the finished pipes obtained in each embodiment and comparative example, 12 pipe sections with a length of 200 mm were cut from each group as samples, and 6 samples were randomly selected and placed in a -20℃ low temperature chamber for 2 hours for pretreatment. Then, the test was carried out in accordance with the requirements of GB / T 14152-2001 "Test Method for External Impact Resistance of Thermoplastic Pipes - Clockwise Rotation Method". Test conditions: impact hammer mass 0.5 kg, impact energy 4.9 J, hammer head diameter: 25 mm, test temperature -20℃. Test steps: place the sample horizontally on the V-shaped support; impact different positions in sequence according to the "clockwise rotation method"; record whether the sample breaks (cracks penetrating the pipe wall are considered as failure); calculate the initial true impact rate TIR1 (%) = (number of broken samples / total number of impacts) × 100%; the lower the TIR value, the better the impact resistance and low temperature resistance.

[0048] (2) The other 6 samples were placed in a forced-air drying oven at 70℃ for 20 days to accelerate thermal aging. After the thermal aging was completed, the samples were taken out and placed in a standard environment (23±2℃, relative humidity 50±10%) for 24 hours, and then placed in a low temperature chamber at -20℃ for 2 hours for pretreatment. Then, the drop hammer impact test was carried out according to the test method and steps in (1) to measure the aging true impact rate TIR2.

[0049] Table 1 Performance Test Results Experimental data analysis: Compared to Example 1, Example 4 (using vinyl-modified filler instead of siloxane-modified filler) showed a decline in all performance aspects, indicating that siloxane groups play a crucial role in improving aging impact resistance and tensile stability. This may be because while vinyl filler improves dispersibility, it lacks hydrolyzable siloxane groups, making it unable to form a Si-O-Si network during cooling. This results in insufficient interfacial stress buffering capacity, making it prone to microcracks during stretching and easily fractured under external impact. Furthermore, the plasticizer anchoring effect is weak during long-term use, leading to a significant decrease in toughness after aging.

[0050] Example 5 (using glass fiber instead of spherical silica) showed deterioration in molding defect rate, ring stiffness and initial TIR1 index. The reason may be that glass fiber is an irregular filler with a large aspect ratio and sharp edges, which hinders the orderly arrangement and orientation of PVC chain segments during biaxial stretching and forms stress concentration points at the fiber ends, resulting in local tearing and deterioration of mechanical properties.

[0051] Comparative Example 1 (adipic acid polyester without pyridine groups) performed significantly worse in all indicators, suggesting that the pyridine group is crucial for the coordination of metal ions. This may be because ordinary polyesters only contain carboxyl groups, which are less effective with Zn. 2+The weak coordination ability prevents the formation of a stable multi-toothed chelate structure, resulting in insufficient enhancement of network strength at the orientation temperature and limited anchoring ability for plasticized segments, leading to accelerated migration after aging.

[0052] Comparative Example 2 (where DOP replaced pyridyl polyester as a plasticizer) showed a comprehensive deterioration in defect rate, ring stiffness, and TIR2, indicating that small-molecule plasticizers severely weaken orientation feasibility and long-term stability. This may be because, compared to adipic acid polyester plasticizers, small-molecule DOP significantly reduces the high-elastic modulus, causing the tube blank to tear under tension; simultaneously, DOP is more prone to migration and precipitation, leading to hardening and brittleness of the material after aging, and a sharp decline in impact resistance.

[0053] Comparative Example 3 (ordinary EVA replaced with maleic anhydride-grafted EVA) showed poorer defect rate and TIR2 (20%), indicating that the carboxyl functional group plays an important role in the construction of the coordination network. This may be because ordinary EVA lacks a carboxyl group and cannot bind with Zn. 2+ Effective coordination prevents the coordination network from effectively penetrating and dispersing within the PVC resin matrix to form a denser reinforcing network. Insufficient reinforcing network strength leads to decreased interphase bonding.

[0054] Comparative Example 4 (Deionized water replacing Zn) 2+ The solution showed a significant decrease in all performance indicators, indicating that spraying with an aqueous solution of metal ions is a key step in achieving in-situ enhancement. This may be due to the absence of Zn. 2+ If the pyridine / carboxyl group coordination crosslinking cannot be triggered, the pipe material will rely solely on the strength of the matrix itself at the orientation temperature, which is insufficient to support high tensile strength. Furthermore, without coordination anchoring, the plasticizer still has a certain tendency to migrate.

[0055] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A biaxially oriented cable protection pipe, characterized in that, The raw materials include the following parts by weight: 100 parts PVC resin, 5-15 parts plasticizer, 3-8 parts maleic anhydride grafted EVA, 2-5 parts heat stabilizer, 0.5-1.5 parts lubricant, and 5-10 parts filler. The plasticizer comprises at least pyridyl-modified adipic acid polyester; The preparation method of the biaxially oriented cable protection tube includes: mixing the raw materials of the cable protection tube, melting and extruding to obtain a tube blank; spraying an aqueous solution containing metal ions onto the surface of the tube blank; heating the cooled tube blank to the orientation temperature, performing synchronous biaxial stretching, and cooling and shaping to obtain the tube blank.

2. The biaxially oriented cable protection pipe according to claim 1, characterized in that, The pyridyl-modified adipic acid polyester is prepared by esterification polycondensation of adipic acid, pyridine dicarboxylic acid, and propylene glycol in a molar ratio of 1:0.05-0.1:1.1-1.

2.

3. The biaxially oriented cable protection pipe according to claim 1, characterized in that, The number-average molecular weight of the pyridyl-modified adipic acid polyester is 2000–4000.

4. The biaxially oriented cable protection pipe according to claim 2, characterized in that, The pyridine dicarboxylic acid is 2,5-pyridine dicarboxylic acid or 2,6-pyridine dicarboxylic acid.

5. The biaxially oriented cable protection pipe according to claim 1, characterized in that, The metal ions are selected from Ni. 2+ Zn 2+ Cu 2+ One or more of the following; the concentration of metal ions in the cooling water is 0.01–0.1 mol / L.

6. The biaxially oriented cable protection pipe according to claim 1, characterized in that, The filler is a modified filler with surface-grafted siloxane groups.

7. The biaxially oriented cable protection pipe according to claim 6, characterized in that, The modified filler is prepared by: The surface of the filler was modified using a vinyl silane coupling agent to obtain a vinylated filler; Vinylated fillers are hydrosilylated with hydrogen-containing silanes to obtain siloxane-modified fillers.

8. The biaxially oriented cable protection pipe according to claim 7, characterized in that, The mass ratio of the filler, vinyl silane coupling agent, and hydrogen-containing silane is 100:3-6:2-5.

9. The biaxially oriented cable protection pipe according to claim 7, characterized in that, The hydrogen-containing silane is selected from one or more of trimethoxysilane, triethoxysilane, methyldimethoxysilane, and ethyldimethoxysilane.

10. The biaxially oriented cable protection pipe according to any one of claims 1 to 9, characterized in that, The filler is an inorganic microsphere with a sphericity of not less than 0.8, selected from at least one of spherical silica, spherical calcium carbonate, or spherical talc.

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