Polypropylene insulated direct current power cable

Abstract

This invention relates to the field of cable manufacturing technology and discloses a polypropylene insulated DC power cable. The polypropylene insulated DC power cable provided by this invention includes: a cable conductor; an insulation layer covering the outer periphery of the cable conductor; and an outer sheath covering the outer periphery of the insulation layer. The polypropylene insulated DC power cable provided by this invention has a volume resistivity of up to 5.5 × 10⁻⁶. 14 The DC breakdown field strength can reach 70kV / mm, exhibiting excellent insulation performance. The polypropylene insulated DC power cable provided by this invention has a tensile strength of up to 29.8MPa, an elongation at break of up to 435%, and a Shore D hardness of up to 64, demonstrating excellent mechanical properties. Furthermore, the polypropylene insulated DC power cable provided by this invention retains 93.8% of its tensile strength and 90.1% of its elongation at break after heat aging, exhibiting excellent aging resistance.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, and more specifically, to a polypropylene insulated DC power cable. Background Technology

[0002] Traditional high-voltage DC cables mostly use cross-linked polyethylene (XLPE) insulation. This material requires high-temperature cross-linking, has a complex production process, consumes a lot of energy, and is difficult to recycle after use, making it less environmentally friendly. Furthermore, XLPE easily accumulates space charge under a DC electric field, leading to decreased insulation performance and aging over long-term operation, making it difficult to meet the requirements for higher voltages and longer lifespans.

[0003] Polypropylene (PP) materials have advantages such as no cross-linking required, recyclability, high temperature resistance, and good insulation properties, making them an ideal insulation material for next-generation environmentally friendly power cables. However, ordinary PP has poor toughness, is prone to brittleness, and also suffers from defects such as space charge accumulation and insufficient breakdown strength under a DC electric field.

[0004] Currently, it is difficult to simultaneously improve the mechanical properties, insulation properties, and long-term stability of polypropylene cables through simple blending and modification. Therefore, developing a polypropylene insulated cable with superior overall performance suitable for high-voltage DC applications and its preparation method is of significant practical importance. Summary of the Invention

[0005] The purpose of this invention is to provide a polypropylene insulated DC power cable.

[0006] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention: A polypropylene insulated DC power cable, comprising: Cable conductor; An insulating layer that covers the outer periphery of the cable conductor; An outer sheath, which covers the outer periphery of the insulating layer.

[0007] Furthermore, the cable conductor is made of multiple strands twisted together.

[0008] Furthermore, the insulating layer is an insulating material, and the method for preparing the insulating material includes the following steps: 1) Preparation of activated polypropylene powder; 2) Preparation of functionalized POE nanofillers; 3) Insulating materials are prepared using the activated polypropylene powder obtained in step 1) and the functionalized POE nanofiller obtained in step 2) as raw materials.

[0009] Furthermore, in step 1), the preparation of activated polypropylene powder specifically includes the following steps: 1) Homopolymer polypropylene, syndiotactic polypropylene and polybutene-1 are mixed and subjected to gradient vacuum drying and plasma activation treatment in sequence to obtain pre-activated polypropylene powder; The mass ratio of homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s), and polybutene-1 (PB-1) is 100:(4-8):(1-3). The process parameters for the gradient vacuum drying are as follows: First stage, vacuum degree -0.08MPa, temperature 65~75℃, heat preservation drying for 1h; Second stage, vacuum degree -0.08MPa, temperature 80~90℃, heat preservation drying for 2h. The plasma activation process parameters are as follows: argon to oxygen volume ratio of 3:1, gas pressure of 100 Pa, power of 80 W, and activation time of 8 to 12 min. 2) Mix silane coupling agent (KH-550), water and ethanol, and hydrolyze to obtain silane coupling agent hydrolysate; The mass ratio of the silane coupling agent, water, and ethanol is 1:4:20. Specifically, the hydrolysis is performed at 50°C for 30 minutes. 3) The silane coupling agent hydrolysate obtained in step 2) is atomized and sprayed into the preliminarily activated polypropylene powder obtained in step 1). After the spraying is completed, the mixture is stirred and dried to obtain the activated polypropylene powder. The mass ratio of the pre-activated polypropylene powder to the silane coupling agent is 100: (0.1-0.2). Specifically, the stirring and mixing process involves controlling the stirring speed to be 1000 r / min and stirring and mixing for 4 to 6 minutes. Specifically, the drying process involves drying at 80°C for 2 hours.

[0010] Furthermore, in step 2), the preparation of functionalized POE nanofillers specifically includes the following steps: 1) Maleic anhydride, acrylic acid and benzoyl peroxide were added to the ethylene-octene copolymer and extruded to granulate, thus obtaining MAH-AA-g-POE particles; The mass ratio of the ethylene-octene copolymer, maleic anhydride, acrylic acid, and benzoyl peroxide is (15-25):(0.8-2):(0.3-0.8):(0.2-0.5). The process parameters for the extrusion granulation are: extrusion temperature 150-160℃, screw speed 130r / min; 2) Place the MAH-AA-g-POE particles obtained in step 1) in an acetone solution, ultrasonically clean them, centrifuge and dry them to obtain functionalized POE powder; Specifically, the ultrasonic cleaning involves controlling the ultrasonic power to 200W and performing ultrasonic cleaning for 30 minutes. Specifically, the drying process involves drying at 80°C for 2 hours. 3) Mix β-nucleating agent, nano titanium dioxide, nano boron nitride, composite antioxidant and calcium stearate, stir to obtain nanofiller; The composite antioxidant is composed of antioxidant 1010 and antioxidant 168 mixed in a mass ratio of 2:1. The mass ratio of the β-nucleating agent, nano-titanium dioxide, nano-boron nitride, composite antioxidant, and calcium stearate is (1-2):(0.5-1):(0.5-1):(3-5):0.5. Specifically, the stirring process involves: first controlling the stirring speed to 500 r / min and stirring at low speed for 2-3 minutes, then controlling the stirring speed to 1500 r / min and stirring at high speed for 6-10 minutes. 4) Mix the functionalized POE powder obtained in step 2) and the nanofiller obtained in step 3), stir, and obtain the functionalized POE-nanofiller; The mass ratio of the functionalized POE powder to the nanofiller is (2-4):1; Specifically, the stirring process involves controlling the stirring speed to be 500 r / min and stirring at low speed for 10 minutes.

[0011] Furthermore, in step 3), the preparation of the insulating material specifically includes the following steps: 1) Activated polypropylene powder is fed into the main feed port of the twin-screw extruder, and functionalized POE nanofiller is fed into the side feed port of the twin-screw extruder. The in-situ grafting reaction is carried out using a segmented temperature-controlled shearing process to obtain PP-POE composite material. The process parameters for the segmented temperature-controlled shearing process are as follows: Feeding section: temperature 140~150℃, screw speed 100r / min; Melting section: temperature 160~170℃, screw speed 120r / min; Core section: temperature 175~185℃, screw speed 150r / min; Homogenization section: temperature 170~175℃, screw speed 130r / min; Head section: Temperature 165~170℃, screw speed 110r / min; The grafting rate of the in-situ grafting reaction needs to be controlled between 1.2% and 1.8%. 2) The PP-POE composite material obtained in step 1 is extruded and then subjected to electric field-cooling synergistic gradient induction to obtain the insulating material. The extrusion molding process parameters are: extrusion temperature 165~175℃, extrusion pressure 15~20MPa, and screw speed 120r / min; The process parameters induced by the electric field-cooling synergistic gradient are as follows: First stage: electric field strength 10kV / mm, temperature 130~140℃, processing time 20min; Second stage: electric field strength 5kV / mm, temperature 90~110℃, processing time 30min; Third stage: electric field strength 0kV / mm, temperature 70~90℃, processing time 30min.

[0012] Furthermore, the outer protective layer is an outer protective material, which includes polyethylene.

[0013] Second technical solution of the present invention The above-mentioned method for preparing a polypropylene insulated DC power cable includes the following steps: 1) The insulating material is wrapped around the outer periphery of the cable conductor, shrunk and shaped to obtain the insulation layer; 2) Wrap the outer sheath material around the outer periphery of the insulation layer obtained in step 1) to obtain the outer sheath layer; Further, in step 1), the process parameters for shrinkage and shaping are: shaping temperature 110-130℃, and heat preservation and shaping for 5-10 minutes; Further, in step 2), the process parameters for shrinkage and shaping are: shaping temperature 120-130℃, and heat preservation and shaping for 10-15 minutes.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a polypropylene insulated DC power cable with a volume resistivity of up to 5.5 × 10⁻⁶. 14 Ω·m, DC breakdown field strength can reach 70kV / mm, and it has good insulation properties; The polypropylene insulated DC power cable provided by this invention has a tensile strength of up to 29.8 MPa, an elongation at break of up to 435%, and a Shore D hardness of up to 64, exhibiting excellent mechanical properties. The present invention provides a polypropylene insulated DC power cable, which has a tensile strength retention rate of up to 93.8% and an elongation at break retention rate of up to 90.1% after heat aging, and has good aging resistance.

[0015] This invention provides a polypropylene insulated DC power cable that employs a composite strategy of "ternary matrix activation" and "functionalized POE-nanofiller" at the material design level. By blending homopolymer polypropylene, syndiotactic polypropylene, and polybutene-1, followed by gradient drying and plasma activation, different regular structures are introduced at the molecular chain level, providing a more active interface for subsequent modification. Simultaneously, POE is first grafted with maleic anhydride and acrylic acid as dual monomers, and then combined with fillers containing β-nucleating agents and nanoparticles, achieving multiple functions such as toughening, nucleation, insulation enhancement, and anti-aging.

[0016] This invention provides a polypropylene insulated DC power cable that combines "segmented temperature-controlled in-situ grafting" with "electric field-cooling synergistic gradient induction" processes at the manufacturing level. The former ensures a controllable and uniform chemical reaction between the modifier and the polypropylene matrix by precisely controlling the temperature and shear force in different sections of a twin-screw extruder, achieving uniform dispersion at the nanoscale. The latter applies an external electric field that is gradually withdrawn from high to low during the material molding and cooling process. This electric field can effectively guide the ordered arrangement of polymer molecular chains, promote the formation of β-crystals and orient nanofillers, thereby greatly suppressing the accumulation of space charge and significantly improving the DC breakdown field strength. Detailed Implementation

[0017] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0018] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0019] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0020] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0021] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0022] The following embodiments illustrate a method for preparing a polypropylene insulated DC power cable, comprising the following steps: 1. Preparation of activated polypropylene powder 1) Homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s), and polybutene-1 (PB-1) were mixed in a mass ratio of 100:(4-8):(1-3), and then subjected to gradient vacuum drying and plasma activation treatment in sequence to obtain pre-activated polypropylene powder. The process parameters for the gradient vacuum drying are as follows: First stage, vacuum degree -0.08MPa, temperature 65~75℃, heat preservation drying for 1h; Second stage, vacuum degree -0.08MPa, temperature 80~90℃, heat preservation drying for 2h. The plasma activation process parameters are as follows: argon to oxygen volume ratio of 3:1, gas pressure of 100 Pa, power of 80 W, and activation time of 8 to 12 min. 2) Mix silane coupling agent (KH-550), water and ethanol according to the mass ratio of silane coupling agent, water and ethanol 1:4:20, and hydrolyze at 50℃ for 30 min to obtain silane coupling agent hydrolysate; 3) According to the mass ratio of pre-activated polypropylene powder to silane coupling agent of 100: (0.1~0.2), the hydrolysate of silane coupling agent obtained in step 2) is atomized and sprayed into the pre-activated polypropylene powder obtained in step 1). After the spraying is completed, the stirring speed is controlled at 1000 r / min, and the mixture is stirred for 4~6 min. The mixture is then dried at 80℃ for 2 h to obtain the activated polypropylene powder. 2. Preparation of Functionalized POE Nanofillers 1) According to the mass ratio of ethylene-octene copolymer (POE), maleic anhydride (MAH), acrylic acid (AA), and benzoyl peroxide (BPO) of (15-25): (0.8-2): (0.3-0.8): (0.2-0.5), the ethylene-octene copolymer is first crushed to 80-100 mesh, and then maleic anhydride, acrylic acid, and benzoyl peroxide are added to the ethylene-octene copolymer. The mixture is then extruded and granulated to obtain MAH-AA-g-POE particles. The process parameters for the extrusion granulation are: extrusion temperature 150-160℃, screw speed 130r / min; 2) Place the MAH-AA-g-POE particles obtained in step 1) in an acetone solution, control the ultrasonic power to 200W, ultrasonically clean for 30 minutes, centrifuge, dry at 80℃ for 2 hours, and pulverize to 80-100 mesh to obtain functionalized POE powder. 3) Mix the β-nucleating agent, nano-titanium dioxide, nano-boron nitride, composite antioxidant and calcium stearate in a mass ratio of (1-2):(0.5-1):(0.5-1):(3-5):0.5. First, control the stirring speed at 500 r / min and stir at low speed for 2-3 min. Then, control the stirring speed at 1500 r / min and stir at high speed for 6-10 min to obtain the nano filler. The composite antioxidant is composed of antioxidant 1010 and antioxidant 168 mixed in a mass ratio of 2:1. 4) Mix the functionalized POE powder obtained in step 2) and the nanofiller obtained in step 3) according to the mass ratio of functionalized POE powder to nanofiller of (2-4):1, control the stirring speed to 500 r / min, stir at low speed for 10 min, and obtain the functionalized POE-nanofiller. 3. Preparation of insulating materials 1) According to the reasonable mass ratio of activated polypropylene powder to functionalized POE nanofiller of 100:(8~15), the activated polypropylene powder obtained in step 1 is fed into the main feed port of the twin-screw extruder, and the functionalized POE nanofiller obtained in step 2 is fed into the side feed port (located at the front 1 / 3 of the extruder) of the twin-screw extruder. The in-situ grafting reaction is carried out by segmented temperature-controlled shearing process (grafting rate is controlled at 1.2~1.8%) to obtain PP-POE composite material. The process parameters for the segmented temperature-controlled shearing process are as follows: Feeding section: temperature 140~150℃, screw speed 100r / min; Melting section: temperature 160~170℃, screw speed 120r / min; Core section: temperature 175~185℃, screw speed 150r / min; Homogenization section: temperature 170~175℃, screw speed 130r / min; Head section: Temperature 165~170℃, screw speed 110r / min; 2) The PP-POE composite material obtained in step 1) is extruded and then subjected to electric field-cooling synergistic gradient induction to obtain the insulating material. The extrusion molding process parameters are: extrusion temperature 165~175℃, extrusion pressure 15~20MPa, and screw speed 120r / min; The process parameters induced by the electric field-cooling synergistic gradient are as follows: First stage: electric field strength 10kV / mm, temperature 130~140℃, processing time 20min; Second stage: electric field strength 5kV / mm, temperature 90~110℃, processing time 30min; Third stage: electric field strength 0kV / mm, temperature 70~90℃, treatment time 30min; 4. Preparation of polypropylene insulated DC power cables 1) Wrap the insulating material obtained in step 3 around the outer periphery of the cable conductor, shrink and shape it to obtain an insulating layer; The shrinkage and shaping process parameters are as follows: shaping temperature 110-130℃, heat preservation and shaping for 5-10 minutes; 2) Wrap the outer sheath material around the outer periphery of the insulation layer obtained in step 1), shrink and shape it to obtain the outer sheath; The outer protective material is polyethylene; The shrinkage and shaping process parameters are as follows: shaping temperature 120-130℃, heat preservation and shaping for 10-15 minutes.

[0023] Example 1 A polypropylene insulated DC power cable 1. Preparation of activated polypropylene powder 1) Homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s), and polybutene-1 (PB-1) were mixed in a mass ratio of 100:6:2, and then subjected to gradient vacuum drying and plasma activation treatment in sequence to obtain preliminarily activated polypropylene powder. The process parameters for the gradient vacuum drying are as follows: First stage, vacuum degree -0.08MPa, temperature 70℃, and heat preservation drying for 1 hour; Second stage, vacuum degree -0.08MPa, temperature 85℃, and heat preservation drying for 2 hours. The process parameters for plasma activation are as follows: argon to oxygen volume ratio of 3:1, gas pressure of 100Pa, power of 80W, and activation time of 10min. 2) Mix silane coupling agent (KH-550), water and ethanol according to the mass ratio of silane coupling agent, water and ethanol 1:4:20, and hydrolyze at 50℃ for 30 min to obtain silane coupling agent hydrolysate; 3) According to the mass ratio of pre-activated polypropylene powder to silane coupling agent of 100:0.2, the hydrolysate of silane coupling agent obtained in step 2) is atomized and sprayed into the pre-activated polypropylene powder obtained in step 1). After the spraying is completed, the stirring speed is controlled at 1000 r / min, and the mixture is stirred for 5 min. Then, it is dried at 80℃ for 2 h to obtain the activated polypropylene powder. 2. Preparation of Functionalized POE Nanofillers 1) According to the mass ratio of ethylene-octene copolymer (POE), maleic anhydride (MAH), acrylic acid (AA), and benzoyl peroxide (BPO) of 20:1.4:0.5:0.3, the ethylene-octene copolymer is first crushed to 80-100 mesh, and then maleic anhydride, acrylic acid, and benzoyl peroxide are added to the ethylene-octene copolymer, and then extruded and granulated to obtain MAH-AA-g-POE particles; The process parameters for the extrusion granulation are: extrusion temperature 155℃, screw speed 130r / min; 2) Place the MAH-AA-g-POE particles obtained in step 1) in an acetone solution, control the ultrasonic power to 200W, ultrasonically clean for 30 minutes, centrifuge, dry at 80℃ for 2 hours, and pulverize to 80-100 mesh to obtain functionalized POE powder. 3) The β-nucleating agent, nano titanium dioxide, nano boron nitride, composite antioxidant and calcium stearate were mixed according to the mass ratio of 1.5∶0.8∶0.8∶4∶0.5. First, the stirring speed was controlled at 500 r / min and stirred at low speed for 3 min. Then, the stirring speed was controlled at 1500 r / min and stirred at high speed for 8 min to obtain the nano filler. The composite antioxidant is composed of antioxidant 1010 and antioxidant 168 mixed in a mass ratio of 2:1. 4) Mix the functionalized POE powder obtained in step 2) and the nanofiller obtained in step 3) according to a mass ratio of 3:1, control the stirring speed to 500 r / min, and stir at low speed for 10 min to obtain the functionalized POE-nanofiller. 3. Preparation of insulating materials 1) With a reasonable mass ratio of activated polypropylene powder to functionalized POE nanofiller of 100:12, the activated polypropylene powder obtained in step 1 is fed into the main feed port of the twin-screw extruder, and the functionalized POE nanofiller obtained in step 2 is fed into the side feed port (located at the front 1 / 3 of the extruder) of the twin-screw extruder. The in-situ grafting reaction is carried out using a segmented temperature-controlled shearing process (grafting rate controlled at 1.2-1.8%) to obtain PP-POE composite material. The process parameters for the segmented temperature-controlled shearing process are as follows: Feeding section: temperature 145℃, screw speed 100r / min; Melting section: temperature 165℃, screw speed 120r / min; Core section: temperature 180℃, screw speed 150r / min; Homogenization section: temperature 170℃, screw speed 130r / min; Head section: Temperature 165℃, screw speed 110r / min; 2) The PP-POE composite material obtained in step 1) is extruded and then subjected to electric field-cooling synergistic gradient induction to obtain the insulating material. The extrusion molding process parameters are: extrusion temperature 170℃, extrusion pressure 15MPa, and screw speed 120r / min. The process parameters induced by the electric field-cooling synergistic gradient are as follows: First stage: Electric field strength 10kV / mm, temperature 135℃, processing time 20min; Second stage: Electric field strength 5kV / mm, temperature 100℃, processing time 30min; Third stage: Electric field strength 0kV / mm, temperature 80℃, processing time 30min; 4. Preparation of polypropylene insulated DC power cables 1) Wrap the insulating material obtained in step 3 around the outer periphery of the cable conductor, shrink and shape it to obtain an insulating layer; The shrinkage and shaping process parameters are as follows: shaping temperature 120℃, heat preservation and shaping for 8 minutes; 2) Wrap the outer sheath material around the outer periphery of the insulation layer obtained in step 1), shrink and shape it to obtain the outer sheath; The outer protective material is polyethylene; The shrinkage and shaping process parameters are as follows: shaping temperature 125℃, heat preservation and shaping for 12 minutes.

[0024] Example 2 A polypropylene insulated DC power cable 1. Preparation of activated polypropylene powder 1) Homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s), and polybutene-1 (PB-1) were mixed in a mass ratio of 100:4:1 and then subjected to gradient vacuum drying and plasma activation treatment in sequence to obtain pre-activated polypropylene powder. The process parameters for the gradient vacuum drying are as follows: First stage, vacuum degree -0.08MPa, temperature 65℃, and heat preservation drying for 1 hour; Second stage, vacuum degree -0.08MPa, temperature 80℃, and heat preservation drying for 2 hours. The plasma activation process parameters are as follows: argon to oxygen volume ratio of 3:1, gas pressure of 100Pa, power of 80W, and activation time of 8min. 2) Mix silane coupling agent (KH-550), water and ethanol according to the mass ratio of silane coupling agent, water and ethanol 1:4:20, and hydrolyze at 50℃ for 30 min to obtain silane coupling agent hydrolysate; 3) According to the mass ratio of pre-activated polypropylene powder to silane coupling agent of 100:0.1, the hydrolysate of silane coupling agent obtained in step 2) is atomized and sprayed into the pre-activated polypropylene powder obtained in step 1). After the spraying is completed, the stirring speed is controlled at 1000 r / min, and the mixture is stirred for 4 min. Then, it is dried at 80℃ for 2 h to obtain the activated polypropylene powder. 2. Preparation of Functionalized POE Nanofillers 1) According to the mass ratio of ethylene-octene copolymer (POE), maleic anhydride (MAH), acrylic acid (AA) and benzoyl peroxide (BPO) of 15:0.8:0.3:0.2, the ethylene-octene copolymer is first crushed to 80-100 mesh, and then maleic anhydride, acrylic acid and benzoyl peroxide are added to the ethylene-octene copolymer, and then extruded and granulated to obtain MAH-AA-g-POE particles; The process parameters for the extrusion granulation are: extrusion temperature 150℃, screw speed 130r / min; 2) Place the MAH-AA-g-POE particles obtained in step 1) in an acetone solution, control the ultrasonic power to 200W, ultrasonically clean for 30 minutes, centrifuge, dry at 80℃ for 2 hours, and pulverize to 80-100 mesh to obtain functionalized POE powder. 3) Mix the β-nucleating agent, nano titanium dioxide, nano boron nitride, composite antioxidant and calcium stearate in a mass ratio of 1:0.5:0.5:3:0.5. First, control the stirring speed to 500 r / min and stir at low speed for 2 min. Then, control the stirring speed to 1500 r / min and stir at high speed for 6 min to obtain the nano filler. The composite antioxidant is composed of antioxidant 1010 and antioxidant 168 mixed in a mass ratio of 2:1. 4) Mix the functionalized POE powder obtained in step 2) and the nanofiller obtained in step 3) according to a mass ratio of 2:1, control the stirring speed to 500 r / min, and stir at low speed for 10 min to obtain the functionalized POE-nanofiller. 3. Preparation of insulating materials 1) With a reasonable mass ratio of activated polypropylene powder to functionalized POE nanofiller of 100:8, the activated polypropylene powder obtained in step 1 is fed into the main feed port of the twin-screw extruder, and the functionalized POE nanofiller obtained in step 2 is fed into the side feed port (located at the front 1 / 3 of the extruder) of the twin-screw extruder. The in-situ grafting reaction is carried out using a segmented temperature-controlled shearing process (grafting rate controlled at 1.2-1.8%) to obtain PP-POE composite material. The process parameters for the segmented temperature-controlled shearing process are as follows: Feeding section: temperature 140℃, screw speed 100r / min; Melting section: temperature 160℃, screw speed 120r / min; Core section: temperature 175℃, screw speed 150r / min; Homogenization section: temperature 170℃, screw speed 130r / min; Head section: Temperature 165℃, screw speed 110r / min; 2) The PP-POE composite material obtained in step 1) is extruded and then subjected to electric field-cooling synergistic gradient induction to obtain the insulating material. The extrusion molding process parameters are: extrusion temperature 165℃, extrusion pressure 15MPa, and screw speed 120r / min. The process parameters induced by the electric field-cooling synergistic gradient are as follows: First stage: electric field strength 10kV / mm, temperature 130℃, processing time 20min; Second stage: Electric field strength 5kV / mm, temperature 90℃, processing time 30min; Third stage: Electric field strength 0kV / mm, temperature 70℃, processing time 30min; 4. Preparation of polypropylene insulated DC power cables 1) Wrap the insulating material obtained in step 3 around the outer periphery of the cable conductor, shrink and shape it to obtain an insulating layer; The process parameters for shrinkage and shaping are as follows: shaping temperature 110℃, heat preservation and shaping for 5 minutes; 2) Wrap the outer sheath material around the outer periphery of the insulation layer obtained in step 1), shrink and shape it to obtain the outer sheath; The outer protective material is polyethylene; The shrinkage and shaping process parameters are as follows: shaping temperature 120℃, heat preservation and shaping for 10 minutes.

[0025] Example 3 A polypropylene insulated DC power cable 1. Preparation of activated polypropylene powder 1) Homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s), and polybutene-1 (PB-1) were mixed in a mass ratio of 100:8:3, and then subjected to gradient vacuum drying and plasma activation treatment in sequence to obtain preliminarily activated polypropylene powder. The process parameters for gradient vacuum drying are as follows: First stage, vacuum degree -0.08MPa, temperature 75℃, and heat preservation drying for 1 hour; Second stage, vacuum degree -0.08MPa, temperature 90℃, and heat preservation drying for 2 hours. The plasma activation process parameters are as follows: argon to oxygen volume ratio of 3:1, gas pressure of 100Pa, power of 80W, and activation time of 12min. 2) Mix silane coupling agent (KH-550), water and ethanol according to the mass ratio of silane coupling agent, water and ethanol 1:4:20, and hydrolyze at 50℃ for 30 min to obtain silane coupling agent hydrolysate; 3) According to the mass ratio of pre-activated polypropylene powder to silane coupling agent of 100:0.2, the hydrolysate of silane coupling agent obtained in step 2) is atomized and sprayed into the pre-activated polypropylene powder obtained in step 1). After the spraying is completed, the stirring speed is controlled at 1000 r / min, and the mixture is stirred for 6 min. Then, it is dried at 80℃ for 2 h to obtain the activated polypropylene powder. 2. Preparation of Functionalized POE Nanofillers 1) According to the mass ratio of ethylene-octene copolymer (POE), maleic anhydride (MAH), acrylic acid (AA), and benzoyl peroxide (BPO) of 25∶2∶0.8∶0.5, the ethylene-octene copolymer is first crushed to 80-100 mesh, and then maleic anhydride, acrylic acid, and benzoyl peroxide are added to the ethylene-octene copolymer, and then extruded and granulated to obtain MAH-AA-g-POE particles; The process parameters for the extrusion granulation are: extrusion temperature 160℃, screw speed 130r / min; 2) Place the MAH-AA-g-POE particles obtained in step 1) in an acetone solution, control the ultrasonic power to 200W, ultrasonically clean for 30 minutes, centrifuge, dry at 80℃ for 2 hours, and pulverize to 80-100 mesh to obtain functionalized POE powder. 3) Mix the β-nucleating agent, nano titanium dioxide, nano boron nitride, composite antioxidant and calcium stearate in a mass ratio of 2:1:1:5:0.5. First, control the stirring speed to 500 r / min and stir at low speed for 3 min. Then control the stirring speed to 1500 r / min and stir at high speed for 10 min to obtain the nano filler. The composite antioxidant is composed of antioxidant 1010 and antioxidant 168 mixed in a mass ratio of 2:1. 4) The functionalized POE powder obtained in step 2) and the nanofiller obtained in step 3) are mixed according to a mass ratio of 4:1. The stirring speed is controlled at 500 r / min and the mixture is stirred at low speed for 10 min to obtain the functionalized POE-nanofiller. 3. Preparation of insulating materials 1) With a reasonable mass ratio of activated polypropylene powder to functionalized POE nanofiller of 100:15, the activated polypropylene powder obtained in step 1 is fed into the main feed port of the twin-screw extruder, and the functionalized POE nanofiller obtained in step 2 is fed into the side feed port (located at the front 1 / 3 of the extruder) of the twin-screw extruder. The in-situ grafting reaction is carried out using a segmented temperature-controlled shearing process (grafting rate controlled at 1.2-1.8%) to obtain PP-POE composite material. The process parameters for the segmented temperature-controlled shearing process are as follows: Feeding section: temperature 150℃, screw speed 100r / min; Melting section: temperature 170℃, screw speed 120r / min; Core section: temperature 185℃, screw speed 150r / min; Homogenization section: temperature 175℃, screw speed 130r / min; Head section: Temperature 170℃, screw speed 110r / min; 2) The PP-POE composite material obtained in step 1) is extruded and then subjected to electric field-cooling synergistic gradient induction to obtain the insulating material. The extrusion molding process parameters are: extrusion temperature 175℃, extrusion pressure 20MPa, and screw speed 120r / min. The process parameters induced by the electric field-cooling synergistic gradient are as follows: First stage: Electric field strength 10kV / mm, temperature 140℃, processing time 20min; Second stage: Electric field strength 5kV / mm, temperature 110℃, processing time 30min; Third stage: Electric field strength 0kV / mm, temperature 90℃, processing time 30min; 4. Preparation of polypropylene insulated DC power cables 1) Wrap the insulating material obtained in step 3 around the outer periphery of the cable conductor, shrink and shape it to obtain an insulating layer; The process parameters for shrinkage and shaping are as follows: shaping temperature 130℃, heat preservation and shaping for 10 minutes; 2) Wrap the outer sheath material around the outer periphery of the insulation layer obtained in step 1), shrink and shape it to obtain the outer sheath; The outer protective material is polyethylene; The shrinkage and shaping process parameters are as follows: shaping temperature 130℃, heat preservation and shaping for 15 minutes.

[0026] Comparative Example 1 A polypropylene insulated DC power cable Same as Example 1, except that in step 1, the preparation of activated polypropylene powder, step 1) is: Homopolymer polypropylene was subjected to gradient vacuum drying and plasma activation treatment in sequence to obtain pre-activated polypropylene powder. The process parameters for the gradient vacuum drying are as follows: First stage, vacuum degree -0.08MPa, temperature 70℃, and heat preservation drying for 1 hour; Second stage, vacuum degree -0.08MPa, temperature 85℃, and heat preservation drying for 2 hours. The plasma activation process parameters are as follows: argon to oxygen volume ratio of 3:1, gas pressure of 100 Pa, power of 80 W, and activation time of 10 min.

[0027] Comparative Example 2 A polypropylene insulated DC power cable Same as Example 1, except that in step 1, the preparation of activated polypropylene powder, step 1) is: According to the mass ratio of homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s), and polybutene-1 (PB-1) of 100:6:2, the homopolymer polypropylene, syndiotactic polypropylene, and polybutene-1 were mixed and then subjected to vacuum drying and plasma activation treatment in sequence to obtain preliminarily activated polypropylene powder. The process parameters for vacuum drying are: vacuum degree -0.08MPa, temperature 70℃, and heat preservation drying for 3 hours. The plasma activation process parameters are as follows: argon to oxygen volume ratio of 3:1, gas pressure of 100 Pa, power of 80 W, and activation time of 10 min.

[0028] Comparative Example 3 A polypropylene insulated DC power cable Same as Example 1, except that in step 1, the preparation of activated polypropylene powder, step 1) is: According to the mass ratio of homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s) and polybutene-1 (PB-1) of 100:6:2, the homopolymer polypropylene, syndiotactic polypropylene and polybutene-1 were mixed and subjected to gradient vacuum drying to obtain preliminarily activated polypropylene powder. The process parameters for gradient vacuum drying are as follows: First stage, vacuum degree -0.08MPa, temperature 70℃, and heat preservation drying for 1 hour; Second stage, vacuum degree -0.08MPa, temperature 85℃, and heat preservation drying for 2 hours.

[0029] Comparative Example 4 A polypropylene insulated DC power cable Same as Example 1, except that the preparation of activated polypropylene powder in step 1 is... 1) The homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s), and polybutene-1 (PB-1) are mixed in a mass ratio of 100:6:2, and then subjected to gradient vacuum drying and plasma activation treatment in sequence to obtain the activated polypropylene powder. The process parameters for the gradient vacuum drying are as follows: First stage, vacuum degree -0.08MPa, temperature 70℃, and heat preservation drying for 1 hour; Second stage, vacuum degree -0.08MPa, temperature 85℃, and heat preservation drying for 2 hours. The plasma activation process parameters are as follows: argon to oxygen volume ratio of 3:1, gas pressure of 100 Pa, power of 80 W, and activation time of 10 min.

[0030] Comparative Example 5 A polypropylene insulated DC power cable Same as Example 1, except that in step 2, the preparation of functionalized POE nanofiller, maleic anhydride and acrylic acid grafting are omitted, and in subsequent steps, POE particles are used instead of MAH-AA-g-POE particles to prepare polypropylene insulated DC power cables.

[0031] Comparative Example 6 A polypropylene insulated DC power cable Same as Example 1, except that in step 2, the preparation of functionalized POE nanofiller is omitted, and in subsequent steps, functionalized POE powder is used instead of functionalized POE nanofiller to prepare polypropylene insulated DC power cable.

[0032] Comparative Example 7 A polypropylene insulated DC power cable Same as Example 1, except that in step 3, the preparation of the insulating material, step 2) is: The PP-POE composite material obtained in step 1) is extruded and then subjected to electric field gradient induction to obtain the insulating material. The extrusion molding process parameters are: extrusion temperature 170℃, extrusion pressure 15MPa, and screw speed 120r / min. The process parameters induced by the electric field gradient are as follows: First stage: Electric field strength 10kV / mm, processing time 20min; Second stage: Electric field strength 5kV / mm, processing time 30min; Third stage: electric field strength 0kV / mm, processing time 30min.

[0033] Comparative Example 8 A polypropylene insulated DC power cable Same as Example 1, except that in step 3, the preparation of the insulating material, step 2) is: The PP-POE composite material obtained in step 1) is extruded and then subjected to cooling gradient induction to obtain the insulating material. The extrusion molding process parameters are: extrusion temperature 170℃, extrusion pressure 15MPa, and screw speed 120r / min. The process parameters induced by the cooling gradient are as follows: First stage: Temperature 135℃, processing time 20min; Second stage: Temperature 100℃, processing time 30min; Third stage: Temperature 80℃, processing time 30min.

[0034] Comparative Example 9 A polypropylene insulated DC power cable Same as Example 1, except that in step 3, the preparation of the insulating material, step 2) is: The PP-POE composite material obtained in step 1) is extruded and then subjected to electric field-cooling synergistic induction to obtain the insulating material. The extrusion molding process parameters are: extrusion temperature 170℃, extrusion pressure 15MPa, and screw speed 120r / min. The process parameters induced by the electric field-cooling synergy are as follows: Electric field strength 5kV / mm, temperature 100℃, processing time 80min.

[0035] Performance verification The insulation performance of the polypropylene insulated DC power cables prepared in Examples 1-3 and Comparative Examples 1-9 was tested, and the test results are shown in Table 1.

[0036] As shown in Table 1, the polypropylene insulated DC power cable provided by this invention has a volume resistivity of up to 5.5 × 10⁻⁶. 14 It has a DC breakdown field strength of up to 70 kV / mm and excellent insulation properties.

[0037] The mechanical properties of the polypropylene insulated DC power cables prepared in Examples 1-3 and Comparative Examples 1-9 were tested, and the test results are shown in Table 2.

[0038] As shown in Table 2, the polypropylene insulated DC power cable provided by this invention has a tensile strength of up to 29.8 MPa, an elongation at break of up to 435%, and a Shore D hardness of up to 64, exhibiting excellent mechanical properties.

[0039] The polypropylene insulated DC power cables prepared in Examples 1-3 and Comparative Examples 1-9 were tested for aging resistance. The test results are shown in Table 3.

[0040] As shown in Table 3, the polypropylene insulated DC power cable provided by this invention has a tensile strength retention rate of up to 93.8% and a breaking elongation retention rate of up to 90.1% after heat aging, demonstrating good aging resistance.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A polypropylene insulated DC power cable, characterized in that, The polypropylene insulated DC power cable includes: Cable conductor; An insulating layer that covers the outer periphery of the cable conductor; An outer sheath, which covers the outer periphery of the insulating layer.

2. The polypropylene insulated DC power cable according to claim 1, characterized in that, The insulating layer is an insulating material, and the method for preparing the insulating material includes the following steps: S1 is used to prepare activated polypropylene powder; S2 preparation of functionalized POE nanofillers; S3 uses the activated polypropylene powder obtained in step 1) and the functionalized POE nanofiller obtained in step 2) as raw materials to prepare insulating materials.

3. The polypropylene insulated DC power cable according to claim 2, characterized in that, In step S1, the preparation of activated polypropylene powder specifically includes the following steps: 1) Homopolymer polypropylene, syndiotactic polypropylene and polybutene-1 are mixed and subjected to gradient vacuum drying and plasma activation treatment in sequence to obtain pre-activated polypropylene powder; 2) Mix silane coupling agent (KH-550), water and ethanol, and hydrolyze to obtain silane coupling agent hydrolysate; 3) Atomize the silane coupling agent hydrolysate obtained in step 2) into the preliminarily activated polypropylene powder obtained in step 1). After the spraying is completed, stir and mix, and dry to obtain the activated polypropylene powder.

4. A polypropylene insulated DC power cable according to claim 3, characterized in that, In step 1), the mass ratio of homopolymer polypropylene (PP-HC), syndiotactic polypropylene (PP-s), and polybutene-1 (PB-1) is 100:(4-8):(1-3).

5. A polypropylene insulated DC power cable according to claim 2, characterized in that, In step S2, the preparation of functionalized POE nanofillers specifically includes the following steps: 1) Maleic anhydride, acrylic acid and benzoyl peroxide were added to the ethylene-octene copolymer and extruded to granulate, thus obtaining MAH-AA-g-POE particles; 2) Place the MAH-AA-g-POE particles obtained in step 1) in an acetone solution, ultrasonically clean them, centrifuge and dry them to obtain functionalized POE powder. 3) Mix β-nucleating agent, nano titanium dioxide, nano boron nitride, composite antioxidant and calcium stearate, stir to obtain nanofiller; 4) Mix the functionalized POE powder obtained in step 2) and the nanofiller obtained in step 3), stir, and obtain the functionalized POE-nanofiller.

6. A polypropylene insulated DC power cable according to claim 5, characterized in that, In step 1), the mass ratio of the ethylene-octene copolymer, maleic anhydride, acrylic acid, and benzoyl peroxide is (15-25):(0.8-2):(0.3-0.8):(0.2-0.5). In step 3), the mass ratio of the β-nucleating agent, nano-titanium dioxide, nano-boron nitride, composite antioxidant, and calcium stearate is (1-2):(0.5-1):(0.5-1):(3-5):0.

5. In step 4), the mass ratio of the functionalized POE powder to the nanofiller is (2-4):

1.

7. A polypropylene insulated DC power cable according to claim 2, characterized in that, In step S3, the preparation of the insulating material specifically includes the following steps: 1) Activated polypropylene powder is fed into the main feed port of the twin-screw extruder, and functionalized POE nanofiller is fed into the side feed port of the twin-screw extruder. The in-situ grafting reaction is carried out using a segmented temperature-controlled shearing process to obtain PP-POE composite material. 2) The PP-POE composite material obtained in step 1 is extruded and then subjected to electric field-cooling synergistic gradient induction to obtain the insulating material.

8. A polypropylene insulated DC power cable according to claim 7, characterized in that, In step 2), the process parameters induced by the electric field-cooling synergistic gradient are: First stage: electric field strength 10kV / mm, temperature 130~140℃, processing time 20min; Second stage: electric field strength 5kV / mm, temperature 90~110℃, processing time 30min; Third stage: electric field strength 0kV / mm, temperature 70~90℃, processing time 30min.

9. A method for preparing a polypropylene insulated DC power cable as described in any one of claims 1 to 8, characterized in that, Includes the following steps: 1) The insulating material is wrapped around the outer periphery of the cable conductor, shrunk and shaped to obtain the insulation layer; 2) Wrap the outer sheath material around the outer periphery of the insulation layer obtained in step 1) to obtain the outer sheath.

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