Double-layer composite structure cable sheath and preparation method thereof

Abstract

The invention discloses a double-layer composite structure cable sheath and a preparation method thereof, and belongs to the technical field of cable sheath materials. The invention relates to a preparation method of a cable sheath with a double-layer composite structure. The preparation method comprises the following steps: uniformly mixing polyvinyl chloride, an organic ester compatilizer and a metal salt stabilizer to obtain a PVC mixture; caprolactam is subjected to ring opening treatment and then subjected to copolymerization with adipic acid and polyether amine, and modified nylon 6 is obtained; uniformly mixing the modified nylon 6, an aliphatic diester lubricant and an amine stabilizer to obtain a nylon mixture; the cable core passes through a co-extrusion die head, the PVC mixture and the nylon mixture wrap the cable core from inside to outside in a melt co-extrusion mode, and after shaping, the cable sheath of the double-layer composite structure is obtained. The problems of layering, bubbles, poor interface bonding force and the like in combined processing of the nylon layer and the PVC layer are solved. And the obtained cable sheath has high toughness, bending resistance and fluidity.

Description

Technical Field

[0001] This invention relates to the field of cable sheath materials technology, and more specifically to a double-layer composite cable sheath and its preparation method. Background Technology

[0002] Polyamide (nylon) materials, as an emerging cable sheathing material, offer significant advantages. Nylon (PA) is a class of thermoplastic polymers containing amide bonds (-NH-CO-). The interaction of these amide bonds between its molecular chains endows polyamide with a series of unique properties, including high tensile strength, electrical insulation, heat resistance, abrasion resistance, and biocompatibility. These properties make polyamide widely used in various fields such as automotive, electrical cables, textiles, and medical applications. Cable sheaths made of nylon not only possess excellent flexibility, toughness, and abrasion resistance, but also have self-lubricating properties and solvent resistance, effectively preventing damage to the cables from rodents. Furthermore, nylon cable sheaths can withstand extreme environments, such as being buried underground, placed indoors, in tunnels, pipes, or exposed outdoors. They also exhibit resistance to high and low temperatures, meet soil environmental requirements, pose no harm to the surrounding environment, and fully comply with RoHS environmental standards.

[0003] Cable sheaths are typically composed of layers of various materials. Polyvinyl chloride (PVC) is widely used for cable outer sheathing due to its excellent chemical resistance and electrical insulation properties, while nylon serves as the outer layer covering the PVC. For multi-strand cables, an additional PVC layer is added as the outermost layer. PVC's melting point is generally between 170℃ and 180℃, and its processing temperature is approximately 190℃. Therefore, selecting a suitable nylon material as the outer sheath is crucial for ensuring the quality and appearance of the sheath. As one of the five major engineering plastics, PA6 and PA66 are the most representative varieties of nylon, and were the earliest developed and industrialized PA types, accounting for over 90% of total PA production. PA66 has a melting point of around 250℃, which is too high to be combined with PVC for processing; while PA6 has a melting point of around 220℃ and a processing temperature of approximately 240℃. Despite the 50℃ temperature difference between the two, the combined processing of PA6 and PVC still faces many challenges. First, it may be necessary to procure more expensive high-temperature PVC, which undoubtedly increases costs. Second, the bond between the nylon and PVC layers may not be tight enough, easily leading to blistering or breakage of the sheath. Furthermore, long-chain nylons such as PA12 and PA1010 have lower melting points. While they can address some issues, their lower production volume, high price, and significantly lower tensile strength compared to PA6 mean they cannot effectively solve the aforementioned problems. It's important to note that while PA6 and PA66, as commercially available nylon materials, possess high strength, they have poor low-temperature resistance and insufficient toughness. When cable sheathing needs to be used in extreme environments, these shortcomings will significantly limit the material's performance and lifespan, thus affecting safety and economic efficiency. Summary of the Invention

[0004] To address the above problems, this invention provides a double-layer composite cable sheath and its preparation method. This invention solves the problems of delamination, bubbles, and poor interfacial bonding that easily occur during the joint processing of the nylon and PVC layers. Furthermore, modified PA6 has a lower melting point, higher fluidity, and better toughness, endowing the cable sheath with high toughness, bending resistance, and fluidity. This significantly improves the overall cost and service life of the cable. In addition, it reduces processing conditions and significantly reduces energy consumption.

[0005] The first objective of this invention is to provide a method for preparing a double-layer composite cable sheath, comprising the following steps: A PVC mixture is obtained by uniformly mixing polyvinyl chloride, organic ester compatibilizer, and metal salt stabilizer.

[0006] Caprolactam was subjected to ring-opening treatment and copolymerized with adipic acid and polyetheramine. During the copolymerization process, the polyetheramine was inserted into the generated nylon 6 segments to obtain modified nylon 6.

[0007] Modified nylon 6, aliphatic diester lubricant and amine stabilizer are mixed evenly to obtain nylon mixture.

[0008] The cable core is coated from the inside out with a PVC layer formed by the PVC mixture and a nylon layer formed by the nylon mixture through a co-extrusion die. After shaping, a double-layer composite cable sheath is obtained.

[0009] In a preferred embodiment of the present invention, the molar ratio of caprolactam, adipic acid and polyetheramine is 1:0.05~0.12:0.05~0.12.

[0010] In the ring-opening reaction, the reaction temperature is 240℃~260℃ and the reaction time is 6h~8h.

[0011] In the copolymerization reaction, the reaction temperature is 240℃~260℃ and the reaction time is 2h~3h.

[0012] In a preferred embodiment of the present invention, the PVC mixture contains 75% to 85% polyvinyl chloride by mass, 10% to 24% organic ester compatibilizer by mass, and 1% to 5% metal salt stabilizer by mass, totaling 100%.

[0013] In a preferred embodiment of the present invention, the nylon mixture contains 96% to 98% by mass of modified nylon 6, 0.5% to 1.5% by mass of aliphatic diester lubricant, and 1.5% to 2.5% by mass of amine stabilizer, totaling 100%.

[0014] In a preferred embodiment of the present invention, during the melt co-extrusion process, the PVC mixture is added to the first extruder and the nylon mixture is added to the second extruder.

[0015] In the first extruder, the temperature in the feeding zone is 170℃~175℃; the temperature in the compression zone is 180℃~185℃; the temperature in the homogenization zone is 185℃~190℃; and the temperature in the exhaust zone is 190℃~195℃.

[0016] In the second extruder, the temperature in the feeding zone is 190℃~195℃; the temperature in the compression zone is 200℃~210℃; the temperature in the homogenization zone is 210℃~215℃; and the temperature in the exhaust zone is 215℃~220℃.

[0017] The temperature of the co-extrusion die is 200℃~210℃.

[0018] In a preferred embodiment of the present invention, during the cooling and shaping process, the cooling process first proceeds to an air-cooled section with a wind speed of 10 m / s to 15 m / s, and then to a water-cooled section with a water temperature gradient of 25°C to 40°C.

[0019] In a preferred embodiment of the present invention, the organic ester compatibilizer is dioctyl phthalate (DOP), and the metal salt stabilizer is a calcium-zinc composite stabilizer; the calcium-zinc composite stabilizer is obtained by mixing a calcium source and a zinc source in a mass ratio of 2~4:1~3.

[0020] The aliphatic diester lubricant is ethylene bis stearamide (EBS); the amine stabilizer is a hindered amine light stabilizer.

[0021] In a preferred embodiment of the present invention, the calcium source is calcium hydroxide or calcium stearate, and the zinc source is zinc oxide or zinc stearate.

[0022] In a preferred embodiment of the present invention, the hindered amine light stabilizer is one or more of Irganox 1010, Chimassorb 944, or Tinuvin 292.

[0023] The second objective of this invention is to provide a double-layer composite cable sheath prepared by the above-described preparation method.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (0) In the preparation process of this invention, caprolactam, adipic acid, and polyetheramine are used to prepare modified nylon 6. The flexible segments of polyetheramine are embedded in the rigid segments of nylon 6, disrupting the continuity of intramolecular hydrogen bonds, significantly reducing the melting point and improving fluidity. Furthermore, the addition of polyetheramine to nylon 6 reduces crystallinity and thus improves the toughness of nylon 6, manifested as increased impact strength and elongation at break, as well as a decrease in melting point. The melting points of modified nylon 6 and PVC are closer, effectively reducing blistering and delamination caused by the large difference in thermal shrinkage rates between the two materials during processing due to their different melting points. Thus, a double-layer composite cable sheath is obtained by using the melt co-extrusion method of modified nylon 6 and PVC. Combined with the melt co-extrusion process, the blistering rate of the composite sheathed cable obtained by this invention is reduced from the industry average of ≥5 blister / meter to ≤0.5 blister / meter.

[0025] (2) Amine stabilizers can inhibit the oxidative degradation of PVC, while organic ester compatibilizers can enhance the interfacial compatibility between PVC and nylon. The addition of aliphatic diester lubricants can further reduce melt viscosity, allowing for lower PVC extrusion temperatures. This invention achieves PVC / nylon molecular chain interpenetration through temperature matching with organic ester compatibilizers (DOP), increasing interfacial bonding strength by 30%. Furthermore, the ether bonds in polyetheramines provide permanent antistatic properties (volume resistivity ≤ 10). 9 (Ω·cm), no additional conductive agent is needed.

[0026] (3) The PVC layer (twin-screw A zone: 170℃~195℃) and the modified nylon layer (twin-screw B zone: 190℃~220℃) are fused together in the co-extrusion die (200℃~210℃), with a temperature difference ≤15℃ (the temperature difference of conventional PA6 / PVC is >50℃). This achieves the requirement of matching the processing temperature of modified nylon and PVC in the melt co-extrusion process.

[0027] Step-cooling process: First, the air-cooled section with a wind speed of 10m / s~15m / s and a length of 3m~6m is cooled, and then the water-cooled section with a water temperature gradient of 25℃~40℃ is cooled to suppress thermal shrinkage differences and achieve a foaming rate of ≤0.5 bubbles / meter (industry average ≥5 bubbles / meter).

[0028] (4) Compared with the commonly used PA6 sheath (processing temperature 240℃~250℃), modified PA6 (processing temperature 200℃~220℃) effectively reduces the processing temperature, greatly reducing energy consumption in production. In addition, modified PA6 has better fluidity, with a melt index of 25.4 g / 10min, compared with the average of 12.6 g / 10min for existing cable sheath nylon 6, which increases the extrusion speed by 30% and reduces energy consumption by 22%.

[0029] (5) Modified PA6 gives the cable sheath higher toughness and low temperature resistance, and can be used in extreme environments of -40℃. Its impact strength is as high as 25-35kJ / m. 3 It is far higher than the average of 6-11 kJ / m of existing cable sheath nylon 6. 3 The cable's nylon sheath has a tensile strength ≥55MPa and an elongation at break ≥700%, which is close to the average tensile strength of existing nylon 6 cable sheaths (55-65 MPa) but far exceeds the elongation at break of existing nylon 6 cable sheaths (150%-300%). Furthermore, the double-layer composite cable sheath has a maximum bending cycle of ≥9898 times, a maximum bending cycle of ≥9284 times at -40℃, and a maximum bending cycle reduction rate of less than 6.2%. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the preparation process of the present invention.

[0031] Figure 2 The infrared spectra of the modified nylon 6 and nylon 6 prepared in Example 1 are shown.

[0032] Figure 3 The figures show the stretch curves of the cable sheath in Example 1 and Comparative Example 1. Detailed Implementation

[0033] The technical solutions of 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.

[0034] In the preparation of composite sheathed cables, this invention first uses modified nylon 6 instead of conventional nylon 6 as the nylon coating layer, lowering the extrusion temperature of the nylon layer to make it as close as possible to the extrusion temperature of the nylon layer and the PVC layer, thereby reducing blistering caused by different thermal shrinkage between the layers. During processing, a co-extrusion method is used to improve efficiency and further enhance the bonding tightness between the PVC layer and the nylon layer.

[0035] In the composite sheathed cable of this invention, the PVC layer is the insulation layer, and the nylon layer is used to protect the insulation layer. The thickness of the PVC layer and the nylon layer in the composite sheathed cable needs to be customized according to product requirements. The PVC layer thickness of low-voltage cables is 0.5-2.0mm; the PVC layer thickness of medium-voltage cables is 3.0-5.0mm; and the nylon layer thickness of the composite sheathed cable is 0.1-0.8mm. The thickness of the nylon layer will not change due to medium and high voltage cables. An ultrasonic thickness gauge is used on site to measure the PVC layer and the nylon layer.

[0036] During the preparation process, the traction machine speed is adjusted according to different thickness requirements. The traction machine speed of the present invention is 20-30m / min.

[0037] The polyetheramine used in this invention is commercially available ED2000 with a molecular weight of 1900, while commercially available PVC has a molecular weight of 50,000 to 110,000.

[0038] It should be noted that, in the preparation of this invention, the extrusion rates of the first twin-screw extruder and the second twin-screw extruder are not limited, as long as the required thicknesses of the PVC layer and nylon layer in the double-layer composite cable sheath can be achieved.

[0039] Example 1 A method for preparing a double-layer composite cable sheath includes the following steps: S1. Caprolactam and 5% (by mass) of deionized water were added to a high-pressure reactor. The temperature was controlled at 240℃, the pressure at 1.5 MPa, and the reaction time at 6 h. Afterward, the mixture was vented to atmospheric pressure, and the ring-opening rate was calculated to be ≥95% using high-performance liquid chromatography. Adipic acid and polyetheramine were added according to a molar ratio of caprolactam, adipic acid, and polyetheramine of 1:0.05:0.05. The reaction was continued at 240℃ for 2 h, with the pressure maintained at 0.5 MPa. Then, the mixture was vented to atmospheric pressure and reacted under vacuum at -0.1 MPa for 1 h to obtain modified nylon 6, denoted as modified PA6.

[0040] S2. Weigh 0.85 kg of PVC, 0.1 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer according to a mass ratio of 85:10:5, and mix them thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium stearate and zinc stearate in a mass ratio of 2:1.

[0041] Weigh 0.96 kg of modified nylon 6, 0.015 kg of ethylene bis-stearamide and 0.025 kg of light stabilizer (brand name Irganox 1010) in a mass ratio of 96:1.5:2.5 and mix them thoroughly in a high-speed mixer to obtain a nylon mixture.

[0042] S3. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 170℃ in the feeding zone, 180℃ in the compression zone, 185℃ in the homogenization zone, and 190℃ in the exhaust zone.

[0043] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The feed zone temperature of the second twin-screw extruder is 190℃, the compression zone temperature is 200℃, the homogenization zone temperature is 210℃, and the exhaust zone temperature is 215℃. The temperature of the co-extrusion die is set to 200℃, and the traction speed of the traction machine is set to 25m / min. The cable core is passed through the co-extrusion die at a uniform speed. The cable with the sheath first enters a 3m long air-cooling section with a wind speed of 15m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 25℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 15℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling to obtain the composite sheathed cable.

[0044] In the composite sheathed cable prepared in this embodiment, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0045] Example 2 A method for preparing a double-layer composite cable sheath includes the following steps: S1. Caprolactam and 5% (by mass) of deionized water were added to a high-pressure reactor. The temperature was controlled at 240℃, the pressure at 1.5 MPa, and the reaction time at 6 h. Afterward, the mixture was vented to atmospheric pressure, and the ring-opening rate was calculated to be ≥95% using high-performance liquid chromatography. Adipic acid and polyetheramine were added according to a molar ratio of caprolactam, adipic acid, and polyetheramine of 1:0.08:0.08. The reaction was continued at 240℃ for 2 h, with the pressure maintained at 0.5 MPa. Afterward, the mixture was vented to atmospheric pressure and reacted under vacuum at -0.1 MPa for 1 h to obtain modified nylon 6, denoted as modified PA6.

[0046] S2. Weigh 0.85 kg of PVC, 0.1 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer in a mass ratio of 85:10:5. Mix thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium hydroxide and zinc oxide in a mass ratio of 2:1.

[0047] 0.96 kg of modified nylon 6, 0.015 kg of ethylene bis-stearamide, and 0.025 kg of Chimassorb 944 light stabilizer were thoroughly mixed in a high-speed mixer at a mass ratio of 96:1.5:2.5 to obtain a nylon mixture.

[0048] S3. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 170℃ in the feeding zone, 180℃ in the compression zone, 185℃ in the homogenization zone, and 190℃ in the exhaust zone.

[0049] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The feed zone temperature of the second twin-screw extruder is 190℃, the compression zone temperature is 200℃, the homogenization zone temperature is 210℃, and the exhaust zone temperature is 215℃. The temperature of the co-extrusion die is set to 200℃, and the traction speed of the traction machine is set to 25m / min. The cable core is passed through the co-extrusion die at a uniform speed. The cable with the sheath first enters a 3m long air-cooling section with a wind speed of 15m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 25℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 15℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling to obtain the composite sheathed cable.

[0050] In the composite sheathed cable prepared in this embodiment, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0051] Example 3 A method for preparing a double-layer composite cable sheath includes the following steps: S1. Caprolactam and 5% (by mass) of deionized water were added to a high-pressure reactor. The temperature was controlled at 240℃, the pressure at 1.5 MPa, and the reaction time at 6 h. Afterward, the mixture was vented to atmospheric pressure, and the ring-opening rate was calculated to be ≥95% using high-performance liquid chromatography. Adipic acid and polyetheramine were added in a molar ratio of 1:0.1:0.1. The reaction was continued at 240℃ for 2 h, with the pressure maintained at 0.5 MPa. The mixture was then vented to atmospheric pressure and reacted under vacuum at -0.1 MPa for 1 h to obtain modified nylon 6, denoted as modified PA6.

[0052] S2. Weigh 0.8 kg of PVC, 0.15 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer according to a mass ratio of 80:15:5, and mix them thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium stearate and zinc stearate in a mass ratio of 3:2.

[0053] Add the first twin-screw extruder. At the same time, weigh 0.97 kg of modified nylon 6, 0.01 kg of ethylene bis-stearamide and 0.02 kg of Chimassorb 944 light stabilizer in a mass ratio of 97:1.0:2.0 and mix them thoroughly in a high-speed mixer to obtain a nylon mixture.

[0054] S3. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 175°C in the feed zone, 185°C in the compression zone, 190°C in the homogenization zone, and 195°C in the exhaust zone.

[0055] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The temperature of the second twin-screw extruder is 195℃ in the feeding zone, 205℃ in the compression zone, 215℃ in the homogenization zone, and 220℃ in the exhaust zone. The temperature of the co-extrusion die is set to 205℃, and the traction speed of the traction machine is set to 25m / min to uniformly pass the cable core through the co-extrusion die. The cable with the sheath first enters a 5m long air-cooling section with a wind speed of 10m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 30℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 10℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling to obtain the composite sheathed cable.

[0056] In the composite sheathed cable prepared in this embodiment, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0057] Example 4 A method for preparing a double-layer composite cable sheath includes the following steps: S1. Caprolactam and 5% (by mass) of deionized water were added to a high-pressure reactor. The temperature was controlled at 240℃, the pressure at 1.5 MPa, and the reaction time at 6 h. Afterward, the mixture was vented to atmospheric pressure, and the ring-opening rate was calculated to be ≥95% using high-performance liquid chromatography. Adipic acid and polyetheramine were added in a molar ratio of 1:0.1:0.1. The reaction was continued at 240℃ for 2 h, with the pressure maintained at 0.5 MPa. The mixture was then vented to atmospheric pressure and reacted under vacuum at -0.1 MPa for 1 h to obtain modified nylon 6, denoted as modified PA6.

[0058] S2. Weigh 0.8 kg of PVC, 0.15 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer (sodium stearate and zinc oxide in a mass ratio of 3:2) according to a mass ratio of 80:15:5. Mix them thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium stearate and zinc oxide in a mass ratio of 2:1.

[0059] Weigh 0.97 kg of modified nylon 6, 0.01 kg of ethylene bis-stearamide and 0.02 kg of Tinuvin 292 light stabilizer according to a mass ratio of 97:1.0:2.0, and mix them thoroughly in a high-speed mixer to obtain a nylon mixture.

[0060] S3. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 175°C in the feed zone, 185°C in the compression zone, 190°C in the homogenization zone, and 195°C in the exhaust zone.

[0061] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The temperature of the second twin-screw extruder is 195℃ in the feeding zone, 205℃ in the compression zone, 215℃ in the homogenization zone, and 220℃ in the exhaust zone. The temperature of the co-extrusion die is set to 205℃, and the traction speed of the traction machine is set to 25m / min to uniformly pass the cable core through the co-extrusion die. The cable with the sheath first enters a 5m long air-cooling section with a wind speed of 10m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 30℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 10℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling to obtain the composite sheathed cable.

[0062] In the composite sheathed cable prepared in this embodiment, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0063] Example 5 A method for preparing a double-layer composite cable sheath includes the following steps: S1. Caprolactam and 5% (by mass) of deionized water were added to a high-pressure reactor. The temperature was controlled at 240℃, the pressure at 1.5 MPa, and the reaction time at 6 h. Afterward, the mixture was vented to atmospheric pressure, and the ring-opening rate was calculated to be ≥95% using high-performance liquid chromatography. Adipic acid and polyetheramine were added according to a molar ratio of caprolactam, adipic acid, and polyetheramine of 1:0.12:0.12. The reaction was continued at 240℃ for 2 h, with the pressure maintained at 0.5 MPa. Then, the mixture was vented to atmospheric pressure and reacted under vacuum at -0.1 MPa for 1 h to obtain modified nylon 6, denoted as modified PA6.

[0064] S2. Weigh 0.85 kg of PVC, 0.1 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer in a mass ratio of 85:10:5, and mix them thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium hydroxide and zinc stearate in a mass ratio of 4:3.

[0065] 0.98 kg of modified nylon 6, 0.05 kg of ethylene bis-stearamide, and 0.15 kg of Tinuvin 292 light stabilizer were thoroughly mixed in a high-speed mixer at a mass ratio of 98:0.5:1.5 to obtain a nylon mixture.

[0066] S3. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 175°C in the feed zone, 185°C in the compression zone, 190°C in the homogenization zone, and 195°C in the exhaust zone.

[0067] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The feed zone temperature of the second twin-screw extruder is 195℃, the compression zone temperature is 210℃, the homogenization zone temperature is 215℃, and the exhaust zone temperature is 220℃. The temperature of the co-extrusion die is set to 210℃, and the traction speed of the traction machine is set to 25m / min to uniformly pass the cable core through the co-extrusion die. The cable with the sheath first enters a 5m long air-cooling section with a wind speed of 10m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 30℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 10℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling to obtain the composite sheathed cable.

[0068] In the composite sheathed cable prepared in this embodiment, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0069] Example 6 A method for preparing a double-layer composite cable sheath includes the following steps: S1. Caprolactam and 5% (by mass) of deionized water were added to a high-pressure reactor. The temperature was controlled at 260℃, the pressure at 1.5 MPa, and the reaction time at 7 h. Afterward, the mixture was vented to atmospheric pressure, and the ring-opening rate was calculated to be ≥95% using high-performance liquid chromatography. Adipic acid and polyetheramine were added according to a molar ratio of caprolactam, adipic acid, and polyetheramine of 1:0.12:0.12. The reaction was continued at 260℃ for 1 h, with the pressure maintained at 0.5 MPa. The mixture was then vented to atmospheric pressure and reacted under vacuum at -0.1 MPa for 1 h to obtain modified nylon 6, denoted as modified PA6.

[0070] S2. Weigh 0.75 kg of PVC, 0.24 kg of dioctyl phthalate (DOP), and 0.1 kg of calcium-zinc composite stabilizer in a mass ratio of 75:24:1, and mix them thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium hydroxide and zinc stearate in a mass ratio of 4:3.

[0071] 0.98 kg of modified nylon 6, 0.05 kg of ethylene bis-stearamide, and 0.15 kg of Tinuvin 292 light stabilizer were thoroughly mixed in a high-speed mixer at a mass ratio of 98:0.5:1.5 to obtain a nylon mixture.

[0072] S3. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 172°C in the feed zone, 182°C in the compression zone, 187°C in the homogenization zone, and 193°C in the exhaust zone.

[0073] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The temperature of the second twin-screw extruder is 193℃ in the feeding zone, 208℃ in the compression zone, 213℃ in the homogenization zone, and 218℃ in the exhaust zone. The temperature of the co-extrusion die is set to 210℃, and the traction speed of the traction machine is set to 25m / min to uniformly pass the cable core through the co-extrusion die. The cable with the sheath first enters a 5m long air-cooling section with a wind speed of 13m / s for cooling, and then enters a water-cooling section with a water temperature gradient of 40℃ for cooling. Specifically, it passes through a 10m long water-cooling section with a temperature of 5℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 35℃ at a speed of 25m / min for full cooling to obtain the composite sheathed cable.

[0074] In the composite sheathed cable prepared in this embodiment, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0075] Example 6 A method for preparing a double-layer composite cable sheath includes the following steps: S1. Caprolactam and 5% (by mass) of deionized water were added to a high-pressure reactor. The temperature was controlled at 250℃, the pressure at 1.5 MPa, and the reaction time at 8 h. Afterward, the mixture was vented to atmospheric pressure, and the ring-opening rate was calculated to be ≥95% using high-performance liquid chromatography. Adipic acid and polyetheramine were added according to a molar ratio of 1:0.12:0.12. The reaction was continued at 240℃ for 1.5 h, with the pressure maintained at 0.5 MPa. Then, the mixture was vented to atmospheric pressure and reacted under vacuum at -0.1 MPa for 1 h to obtain modified nylon 6, denoted as modified PA6.

[0076] S2. Weigh 0.80 kg of PVC, 0.17 kg of dioctyl phthalate (DOP), and 0.03 kg of calcium-zinc composite stabilizer in a mass ratio of 80:17:3, and mix them thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium hydroxide and zinc stearate in a mass ratio of 4:3.

[0077] 0.98 kg of modified nylon 6, 0.05 kg of ethylene bis-stearamide, and 0.15 kg of Tinuvin 292 light stabilizer were thoroughly mixed in a high-speed mixer at a mass ratio of 98:0.5:1.5 to obtain a nylon mixture.

[0078] S3. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 175°C in the feed zone, 185°C in the compression zone, 190°C in the homogenization zone, and 195°C in the exhaust zone.

[0079] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The feed zone temperature of the second twin-screw extruder is 195℃, the compression zone temperature is 210℃, the homogenization zone temperature is 215℃, and the exhaust zone temperature is 220℃. The temperature of the co-extrusion die is set to 210℃, and the traction speed of the traction machine is set to 25m / min to uniformly pass the cable core through the co-extrusion die. The cable with the sheath first enters a 5m long air-cooling section with a wind speed of 10m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 30℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 10℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling to obtain the composite sheathed cable.

[0080] In the composite sheathed cable prepared in this embodiment, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0081] Comparative Example 1 Compared with Example 5, the difference is that conventional PA6 is added to form the nylon layer. Conventional PA6 is a commercially available product, specifically YH800 from Baling Petrochemical.

[0082] A method for processing a composite sheathed cable includes the following steps: S1. Weigh 0.85 kg of PVC, 0.1 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer according to a mass ratio of 85:10:5, and mix them thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium hydroxide and zinc stearate in a mass ratio of 4:3.

[0083] Nylon 6, ethylene bis-stearamide, and Tinuvin 292 light stabilizer were mixed thoroughly in a high-speed mixer at a mass ratio of 98:0.5:1.5 to obtain a nylon mixture.

[0084] S2. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 175°C in the feed zone, 185°C in the compression zone, 190°C in the homogenization zone, and 195°C in the exhaust zone.

[0085] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The feed zone temperature of the second twin-screw extruder is 195℃, the compression zone temperature is 210℃, the homogenization zone temperature is 215℃, and the exhaust zone temperature is 220℃. The temperature of the co-extrusion die is set to 210℃, and the traction speed of the traction machine is set to 25m / min to uniformly pass the cable core through the co-extrusion die. The cable with the sheath first enters a 5m long air-cooling section with a wind speed of 10m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 30℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 10℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling to obtain a composite sheathed cable.

[0086] In the composite sheathed cable prepared in this comparative example, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0087] Comparative Example 2 The difference from Example 5 is that the melt co-extrusion process was not used; instead, the PVC layer and the nylon layer were extruded separately.

[0088] A method for preparing a double-layer composite cable sheath includes the following steps: S1. Caprolactam and 5% (by mass) of deionized water were added to a high-pressure reactor. The temperature was controlled at 240℃, the pressure at 1.5 MPa, and the reaction time at 6 h. Afterward, the mixture was vented to atmospheric pressure, and the ring-opening rate was calculated to be ≥95% using high-performance liquid chromatography. Adipic acid and polyetheramine were added according to a molar ratio of caprolactam, adipic acid, and polyetheramine of 1:0.12:0.12. The reaction was continued at 240℃ for 2 h, with the pressure maintained at 0.5 MPa. Then, the mixture was vented to atmospheric pressure and reacted under vacuum at -0.1 MPa for 1 h to obtain modified nylon 6, denoted as modified PA6.

[0089] S2. Weigh out 0.85 kg of PVC, 0.1 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer (sodium hydroxide and zinc stearate in a mass ratio of 4:3) at a mass ratio of 85:10:5. Mix thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium hydroxide and zinc stearate in a mass ratio of 4:3.

[0090] The PVC mixture is added to the first twin-screw extruder. The feed zone temperature of the first twin-screw extruder is set to 175℃, the compression zone temperature to 185℃, the homogenization zone temperature to 190℃, and the exhaust zone temperature to 195℃. The traction speed of the traction machine is set to 25m / min to pass the cable core through at a uniform speed. After being cooled and shaped by cold water, the cable material with an insulation layer is obtained.

[0091] S3. Mix 0.98 kg of modified nylon 6, 0.05 kg of ethylene bis-stearamide and 0.15 kg of Tinuvin 292 light stabilizer in a high-speed mixer at a mass ratio of 98:0.5:1.5 to obtain a nylon mixture.

[0092] The nylon mixture is added to a second twin-screw extruder. The feed zone temperature of the second twin-screw extruder is set to 195℃, the compression zone temperature to 210℃, the homogenization zone temperature to 215℃, and the exhaust zone temperature to 220℃. The traction speed of the traction machine is set to 25m / min. The nylon layer is wrapped around the surface of the cable material with the insulation layer obtained in S2, i.e., the PVC layer. The cable with the sheath first enters a 5m long air-cooling section with a wind speed of 10m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 30℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 10℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling, to obtain a composite sheathed cable.

[0093] Comparative Example 3 Compared to Example 5, the difference lies in the addition of conventional PA6 as the nylon layer. The conventional PA6 is a commercially available product, specifically YH800 from Baling Petrochemical. Furthermore, instead of melt co-extrusion, the PVC and nylon layers are extruded separately.

[0094] A method for preparing a double-layer composite cable sheath includes the following steps: S1. Weigh 0.85 kg of PVC, 0.1 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer (sodium hydroxide and zinc stearate in a mass ratio of 4:3) at a mass ratio of 85:10:5. Mix thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium hydroxide and zinc stearate in a mass ratio of 4:3.

[0095] The PVC mixture is added to the first twin-screw extruder. The feed zone temperature of the first twin-screw extruder is set to 175℃, the compression zone temperature to 185℃, the homogenization zone temperature to 190℃, and the exhaust zone temperature to 195℃. The traction speed of the traction machine is set to 25m / min to pass the cable core through it at a uniform speed. After being cooled and shaped by cold water, the cable material with an insulation layer is obtained.

[0096] S2. Mix 0.98 kg of nylon 6, 0.05 kg of ethylene bis-stearamide and 0.15 kg of Tinuvin 292 light stabilizer in a high-speed mixer at a mass ratio of 98:0.5:1.5 to obtain a nylon mixture.

[0097] The nylon mixture is added to the second twin-screw extruder. The feed zone temperature of the second twin-screw extruder is set to 195℃, the compression zone temperature to 210℃, the homogenization zone temperature to 215℃, and the exhaust zone temperature to 220℃. The traction speed of the traction machine is set to 25m / min. The nylon layer is wrapped around the surface of the cable material with the insulation layer obtained in S1, i.e., the PVC layer. The cable with the sheath first enters a 5m long air-cooling section with an air velocity of 10m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 30℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 10℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling, to obtain the composite sheathed cable.

[0098] Comparative Example 4 The difference from Example 5 is that modified PA6 prepared by a one-pot method was added.

[0099] A method for preparing a double-layer composite cable sheath includes the following steps: S1. Add caprolactam and 5% (by mass of caprolactam) of deionized water to a high-pressure reactor. Add adipic acid and polyetheramine to the high-pressure reactor according to the molar ratio of caprolactam, adipic acid and polyetheramine 1:0.12:0.12. Control the temperature at 240℃, the pressure at 1.5MPa, and the reaction time at 6h. Then exhaust the gas to atmospheric pressure to obtain modified nylon 6.

[0100] S2. Weigh out 0.85 kg of PVC, 0.1 kg of dioctyl phthalate (DOP), and 0.05 kg of calcium-zinc composite stabilizer (sodium hydroxide and zinc stearate in a mass ratio of 4:3) at a mass ratio of 85:10:5. Mix thoroughly in a high-speed mixer to obtain a PVC mixture. The calcium-zinc composite stabilizer used in this embodiment is obtained by mixing sodium hydroxide and zinc stearate in a mass ratio of 4:3.

[0101] 0.98 kg of modified nylon 6, 0.05 kg of ethylene bis-stearamide, and 0.15 kg of Tinuvin 292 light stabilizer were thoroughly mixed in a high-speed mixer at a mass ratio of 98:0.5:1.5 to obtain a nylon mixture.

[0102] S3. Add the PVC mixture to the first twin-screw extruder and set the temperature of the first twin-screw extruder to 175°C in the feed zone, 185°C in the compression zone, 190°C in the homogenization zone, and 195°C in the exhaust zone.

[0103] Simultaneously, the nylon mixture is added to the second twin-screw extruder. The feed zone temperature of the second twin-screw extruder is 195℃, the compression zone temperature is 210℃, the homogenization zone temperature is 215℃, and the exhaust zone temperature is 220℃. The temperature of the co-extrusion die is set to 210℃, and the traction speed of the traction machine is set to 25m / min to uniformly pass the cable core through the co-extrusion die. The cable with the sheath first enters a 5m long air-cooling section with a wind speed of 10m / s for cooling treatment, and then enters a water-cooling section with a water temperature gradient of 30℃ for cooling treatment. Specifically, it passes through a 10m long water-cooling section with a temperature of 10℃ at a speed of 25m / min for rapid cooling and shaping, and then continues to pass through a 15m long water-cooling section with a temperature of 40℃ at a speed of 25m / min for full cooling to obtain a composite sheathed cable.

[0104] In the composite sheathed cable prepared in this comparative example, the PVC layer thickness is 2.0 mm and the nylon layer thickness is 0.3 mm.

[0105] The performance of the composite sheathed cables provided in Examples 1-5 and Comparative Examples 1-4 was tested. The bubbling rate was tested as follows: Visual inspection was used to count the total number of bubbles in 1 kilometer of cable material, which was then converted to the number of bubbles per meter. Bending resistance test: Under a bending diameter of 150mm, the maximum number of bends that the composite sheathed cables obtained in the examples and comparative examples could withstand without cracking or breaking was determined. -40℃ bending test: The low-temperature test section of "General Test Methods for Cable Insulation and Sheath" GB / T 2951.14-2008 was used. Tensile strength test of nylon sheath: The peeled nylon film was made into dumbbell-shaped tensile specimens, and then tested according to "Determination of Tensile Properties of Plastics Part 3: Test Conditions for Films and Sheaths" GBT1040.3-2006. Impact strength test of nylon sheath: Modified nylon was made into notched impact specimens as required, and then tested according to "Determination of Impact Strength of Plastic Cantilever Beams" GB / T 1843-2008. Melt flow index test: Melt flow index tests were performed on modified nylon 6 and nylon 6.

[0106] Table 1. Bubble ratio and flexural properties of each embodiment and comparative example. Table 2 Impact properties, tensile properties, and melt flow index of each embodiment and comparative example As can be seen from Tables 1 and 2, the nylon sheath layer obtained in the examples exhibits superior bending performance and low-temperature resistance. Compared with the comparative examples, the number of bends at room temperature for Examples 1 to 5 ranges from 9898 to 11230, significantly higher than the 6584 to 7998 cycles for Comparative Examples 1 to 4. This indicates that the composite sheath cable prepared by this invention has significantly higher toughness than other methods used outside this invention. This is attributed to the modified nylon 6 and the melt co-extrusion method. In this invention, modified nylon 6 is used instead of conventional nylon 6 as the nylon coating layer, reducing the extrusion temperature of the nylon layer and making it as close as possible to the extrusion temperature of the nylon layer and the PVC layer to minimize blistering caused by differences in interlayer thermal shrinkage.

[0107] The co-extrusion process improves efficiency and further enhances the bonding tightness between the PVC layer and the nylon layer.

[0108] Furthermore, tests on the physical properties of the nylon layer revealed that Comparative Example 1, commercially available nylon 6, had low impact strength, low melt flow index, and a high melting point of 224°C, resulting in poor bonding with the PVC layer. Comparative Example 2, the modified PA6 prepared in this invention, exhibited excellent physical properties, but without the melt co-extrusion process, its interfacial bonding remained weak, leading to a decrease in the material's bending count. Comparative Example 3, using conventional cable nylon layer processing methods, yielded the worst results. Comparative Example 4, lacking sufficient caprolactam ring-opening for copolymerization and vacuum polycondensation, resulted in a modified PA6 with a wide molecular weight distribution and high oligomer content, affecting the product's low-temperature resistance, bubble rate, and transparency, significantly reducing its performance. Its foaming rate was slightly higher than that of the modified PA6, and its processed mechanical properties were also weaker.

[0109] Figure 2 The infrared spectra of the modified PA6 prepared in Example 1 and commercially available nylon 6 (PA6) are shown below. Figure 2 It can be seen that the modified PA6 in Example 1 has a significantly higher infrared value at 1100 cm⁻¹. -1 The appearance of COC stretching vibration peaks confirms the introduction of polyetheramine.

[0110] from Figure 3 It can be seen that the tensile properties of the modified PA6 in Example 1, especially its elongation at break, are much higher than those of commercially available PA6 products. This demonstrates the excellent toughness of the modified PA6.

[0111] The double-layer composite cable sheath provided by this invention uses a modified PA6 and PVC system. The raw materials are described in detail below:

[0112] 1. The PVC mixture used in the prepared PVC layer is obtained by mixing polyvinyl chloride, organic ester compatibilizer, and metal salt stabilizer. The following example illustrates the use of dioctyl phthalate (DOP) and a calcium-zinc composite stabilizer: 1.1 In the molecular structure of DOP, the polar ester groups can interact with the polar groups of PVC, allowing them to insert well between the PVC molecular chains. Simultaneously, the non-polar alkyl groups shield the polar groups of PVC, weakening the intermolecular forces and thus improving the plasticity of the plastic. This good compatibility enables DOP to effectively improve the processing and physical properties of PVC, making it more suitable for composite processing with nylon layers. Furthermore, it has low volatility: during cable use, DOP is not easily volatilized, maintaining the long-term stability of the product's performance and ensuring that the insulation and mechanical properties of the cable do not decrease due to plasticizer volatilization. DOP can improve the electrical insulation properties of PVC, which is crucial for cables, effectively preventing safety problems such as leakage and ensuring the safe operation of the cable.

[0113] 1.2 In the calcium-zinc composite stabilizer used in this invention, calcium ions absorb HCl produced by PVC degradation to form stable calcium salts, terminating the degradation chain reaction and delaying material aging. Zinc ions can replace unstable chlorine atoms in PVC molecules to generate stable zinc chloride, while inhibiting double bond formation and reducing discoloration and cross-linking. The synergistic effect of both can compensate for the shortcomings of single metal salts (such as the low efficiency of calcium salts and the tendency of zinc salts to "burn" and cause sudden discoloration), adapting to the higher temperature requirements in cable processing (typically 160℃~200℃), ensuring the stability of the PVC layer during processing and use. Furthermore, while traditional lead salt stabilizers are highly efficient, they contain heavy metals, posing environmental and health risks, and have been restricted in most countries (such as the EU RoHS directive). The calcium-zinc composite stabilizer used in this invention is a lead-free and cadmium-free environmentally friendly product, meeting the cable industry's requirements for environmental protection and low toxicity, and is especially suitable for scenarios where human contact or environmental exposure is possible. It has good compatibility with PVC and DOP, is not prone to precipitation, and avoids affecting the smoothness of the cable surface or the composite effect with the nylon layer. It helps maintain the mechanical properties of PVC (such as flexibility and tensile strength), complementing the high strength of the nylon layer and improving the overall tensile and abrasion resistance of the cable. It has minimal impact on the electrical insulation properties of PVC, meeting the insulation resistance requirements of cables and avoiding the risk of leakage due to improper selection of stabilizers.

[0114] 2. In the nylon layer, the nylon mixture used is obtained by mixing modified nylon 6, aliphatic diester lubricant, and amine stabilizer. Ethylene bis-stearamide (EBS) and hindered amine light stabilizer are used as examples.

[0115] 2.1 Regarding the selection of ethylene bis-stearamide (EBS), the following explanation is provided: 2.1.1 The melting characteristics of modified nylon PA6 and PVC differ significantly: PA6 has a lower melt viscosity; PVC melt viscosity is higher and it is prone to sticking to the mold. In the molecular structure of EBS, the stearamide groups at both ends are polar, while the ethylene chain in the middle is nonpolar. This polar-nonpolar-polar structure allows it to interact with both materials simultaneously: For PVC, the polar groups can form weak interactions with the polar segments (containing chlorine atoms) of PVC, reducing internal friction between PVC molecular chains and lowering melt viscosity; For modified PA6, the polar amide groups can form hydrogen bonds with the amide bonds in the nylon molecule, improving the fluidity of the nylon melt, while the nonpolar segments can form a lubricating layer at the interface between nylon and PVC, reducing interfacial friction between the two materials.

[0116] This dual compatibility is irreplaceable by single polar or non-polar lubricants (such as paraffin and stearic acid), and can avoid processing instability caused by insufficient lubrication (such as sudden increase in extrusion pressure and material retention).

[0117] Furthermore, for the polyetheramine chain segment: the molecule contains ether bonds (-O-) and amino groups (-NH2). The ether bonds are nonpolar flexible chains, while the amino groups are polar groups, resulting in an overall alternating "polar-nonpolar" structure, which combines hydrophilicity and flexibility. EBS has stearamide groups (containing polar amide bonds -CO-NH-) at both ends and an ethylene nonpolar chain in the middle, forming a symmetrical "polar-nonpolar-polar" structure.

[0118] The polyetheramine segments in modified PA6 can form better interactions with the EBS segments, specifically: a. Affinity of polar groups: The amino group (-NH2) of polyetheramine and the amide bond (-CO-NH-) of EBS can be combined through hydrogen bonding (hydrogen bonds are formed between -NH2 and -CO-), which enhances the attraction between molecules.

[0119] b. Compatibility of nonpolar chains: The flexible ether chain (nonpolar) of polyetheramine is similar in structure to the ethylene chain (nonpolar) in the middle of EBS. According to the principle of "like dissolves like", van der Waals forces can be generated to reduce the interfacial repulsion between the two.

[0120] This dual effect of "polar-polar" and "non-polar-non-polar" makes EBS more compatible with polyetheramine segments than with pure nylon 6 segments (pure nylon 6 is mainly composed of amide bonds, and the non-polar segments are relatively short), laying the foundation for the lubrication effect.

[0121] 2.1.2 Synergistic Gains on Material Properties a. Improve lubrication efficiency and processing fluidity The introduction of polyetheramine segments reduces the melt viscosity of modified nylon 6, but may also lead to increased local friction due to the aggregation of polar groups. The strong interaction between EBS and polyetheramine makes it easier for EBS to disperse around the polyetheramine segments rather than simply floating on the material surface: the non-polar chains of EBS can insert into the flexible ether chains of polyetheramine, reducing the entanglement between polyetheramine molecules and further reducing internal melt friction; at the same time, the polar ends of EBS combine with the amino groups of polyetheramine, avoiding excessive migration of EBS to the material surface and thus preventing lubrication failure, making the lubrication effect more durable and stable, especially during high-temperature processing (such as extrusion and injection molding of modified nylon 6), which can significantly reduce melt flow resistance.

[0122] b. Enhance interface compatibility and reduce phase separation In modified nylon 6, there are certain compatibility differences between the nylon 6 segments (rigid and highly polar) and the polyetheramine segments (flexible and less polar), which easily lead to microphase separation. EBS acts as a bridging molecule, with its polar groups at both ends interacting with the amide bonds of nylon 6 and the amino groups of polyetheramine, respectively, while the nonpolar chain in the middle simultaneously binds to the nonpolar portions of both. This helps to alleviate the repulsive forces at the interface between the two phases and reduce the decrease in mechanical properties (such as reduced impact resistance) caused by phase separation.

[0123] c. Optimize material surface properties and migration resistance The hydrophilicity of polyetheramine segments may cause the modified nylon 6 surface to be prone to moisture absorption, while the combination of EBS and polyetheramine can reduce the migration of polyetheramine segments to the surface and reduce moisture absorption; at the same time, due to the strong interaction between EBS and polyetheramine, it is not easy for EBS to precipitate from the inside of the material and form bloom, thus ensuring the smoothness and stability of the material surface (which is especially important for products such as cable sheathing that need to maintain surface properties for a long time).

[0124] 2.2 Reasons for choosing hindered amine light stabilizers (HALS): Advantages of combining HALS with modified nylon 6: Provides protection for both phase segments. 2.2.1 Protection of Nylon 6 segments: Inhibition of amide bond oxidation The photoaging of nylon 6 segments primarily stems from the amide bond breakage induced by ultraviolet radiation and subsequent free radical chain reactions. The mechanism of action of HALS (Hydrogen Alkyl Sulfate) is twofold: firstly, it captures free radicals (such as peroxy and alkoxy radicals) through its amine structure, terminating the chain reaction; secondly, during oxidation, HALS transforms into nitroxide radicals (NO·), a recyclable species that continuously captures new free radicals, resulting in a significantly higher anti-aging efficiency than traditional ultraviolet absorbers (such as benzotriazoles, which can only absorb specific wavelengths of ultraviolet radiation and cannot terminate free radical reactions). This "active free radical scavenging" characteristic prevents the degradation of nylon 6 segments at its source, avoiding material embrittlement and strength reduction.

[0125] 2.2.2 Synergistic effect with polyetheramine segments: Targeted inhibition of ether bond aging In modified nylon 6, the ether bonds in the polyetheramine segments are weak points in photo-oxidation, while the combination of HALS and polyetheramine has unique advantages: Structural compatibility: Polyetheramine segments contain amino groups (-NH2), and the amine groups in HALS molecules (such as piperidine ring structures) have similar polar interactions with amino groups. They can be bound through hydrogen bonds or van der Waals forces, making it easier for HALS to disperse around polyetheramine segments and specifically protecting the easily aging ether bonds; Inhibition of amino catalytic effects: The amino groups of polyetheramines may accelerate photo-oxidation reactions, while the amine structures of HALS can reduce the catalytic activity of amino groups through competitive interactions. At the same time, the nitroxide free radicals generated can preferentially scavenge free radicals near polyetheramine segments, reducing ether bond breakage; Improved weather resistance and durability: The flexibility of polyetheramine segments increases molecular chain mobility, which may accelerate the migration and loss of ordinary light stabilizers. However, the polar interaction between HALS and polyetheramine can reduce this migration and prolong the anti-aging effect.

[0126] Compared to other types of light stabilizers, HALS has the following advantages: a. Wider applicable wavelength range: The natural light exposed to the cable contains ultraviolet rays of the entire wavelength range. HALS does not rely on absorption of specific wavelengths, but responds to oxidation reactions caused by various ultraviolet rays through free radical capture, making it more adaptable to complex light source environments.

[0127] b. Compatibility with PVC system: Modified nylon 6 needs to be combined with PVC. Trace metal ions (such as calcium and zinc in stabilizers) may remain in PVC processing. Traditional ultraviolet absorbers are prone to complexation and failure with metal ions, while the piperidine ring structure of HALS is more stable to metal ions and is not easily affected by PVC system.

[0128] c. Synergistic resistance to thermo-oxidative aging: Cables generate heat due to current during operation. HALS not only resists photoaging but also inhibits thermo-oxidative aging at high temperatures (by eliminating heat-induced free radicals). Other types of light stabilizers (such as UV absorbers) do not have this function and cannot meet the requirements of the "photo-thermal" composite aging environment of cables.

[0129] d. Guarantee of interface stability: The interface between modified nylon 6 and PVC is a weak area for aging. The low migration of HALS (especially after being combined with polyetheramine) can reduce the loss to the interface and prevent the interface from delamination and peeling due to aging. Other light stabilizers (such as small molecule UV absorbers) are prone to migration, which can lead to the failure of interface protection.

[0130] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0131] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a double-layer composite cable sheath, characterized in that, Includes the following steps: A PVC mixture is obtained by uniformly mixing polyvinyl chloride, organic ester compatibilizer, and metal salt stabilizer. After ring-opening treatment of caprolactam, it is copolymerized with adipic acid and polyetheramine. During the copolymerization process, the polyetheramine is inserted into the generated nylon 6 segments to obtain modified nylon 6. Modified nylon 6, aliphatic diester lubricant and amine stabilizer are mixed evenly to obtain nylon mixture; The cable core is coated from the inside out with a PVC layer formed by the PVC mixture and a nylon layer formed by the nylon mixture through a co-extrusion die. After shaping, a double-layer composite cable sheath is obtained.

2. The method for preparing a double-layer composite cable sheath according to claim 1, characterized in that, The molar ratio of caprolactam, adipic acid, and polyetheramine is 1:0.05~0.12:0.05~0.12; In the ring-opening reaction, the reaction temperature is 240℃~260℃, and the reaction time is 6h~8h; In the copolymerization reaction, the reaction temperature is 240℃~260℃ and the reaction time is 2h~3h.

3. The method for preparing a double-layer composite cable sheath according to claim 1, characterized in that, In the PVC mixture, the mass percentage of polyvinyl chloride is 75%~85%, the mass percentage of organic ester compatibilizer is 10%~24%, and the mass percentage of metal salt stabilizer is 1%~5%, totaling 100%.

4. The method for preparing a double-layer composite cable sheath according to claim 1, characterized in that, In the nylon blend, the mass percentage of modified nylon 6 is 96%~98%, the mass percentage of aliphatic diester lubricant is 0.5%~1.5%, and the mass percentage of amine stabilizer is 1.5%~2.5%, totaling 100%.

5. The method for preparing a double-layer composite cable sheath according to claim 1, characterized in that, During the melt co-extrusion process, the PVC mixture is added to the first extruder; the nylon mixture is added to the second extruder. In the first extruder, the temperature in the feeding zone is 170℃~175℃; the temperature in the compression zone is 180℃~185℃; the temperature in the homogenization zone is 185℃~190℃; and the temperature in the exhaust zone is 190℃~195℃. In the second extruder, the temperature in the feeding zone is 190℃~195℃; the temperature in the compression zone is 200℃~210℃; the temperature in the homogenization zone is 210℃~215℃; and the temperature in the exhaust zone is 215℃~220℃. The temperature of the co-extrusion die is 200℃~210℃.

6. The method for preparing a double-layer composite cable sheath according to claim 1, characterized in that, During the shaping process, the water first enters the air-cooled section with a wind speed of 10m / s to 15m / s for cooling, and then enters the water-cooled section for cooling. The water temperature gradient in the water-cooled section is 25℃ to 40℃.

7. The method for preparing a double-layer composite cable sheath according to claim 1, characterized in that, The organic ester compatibilizer is dioctyl phthalate, and the metal salt stabilizer is a calcium-zinc composite stabilizer; the calcium-zinc composite stabilizer is obtained by mixing a calcium source and a zinc source in a mass ratio of 1:0.5~0.75; The aliphatic diester lubricant is ethylene bis-stearamide; the amine stabilizer is a hindered amine light stabilizer.

8. The method for preparing a double-layer composite cable sheath according to claim 7, characterized in that, The calcium source is calcium hydroxide or calcium stearate, and the zinc source is zinc oxide or zinc stearate.

9. The method for preparing a double-layer composite cable sheath according to claim 7, characterized in that, The hindered amine light stabilizer is one or more of Irganox 1010, Chimassorb 944, or Tinuvin 292.

10. A double-layer composite cable sheath prepared by the preparation method according to any one of claims 1 to 9.

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