A polypropylene-based composite insulation material and a method for preparing the same

Abstract

The application discloses a kind of polypropylene-based composite insulating material and preparation method thereof, it is related to insulating material technical field.The application first uses 4-vinyl-1,2-benzenedicarboxylic acid and rare earth metal coordination preparation rare earth nucleating agent, again through compounding surface modification hexagonal boron nitride whisker as modified filler, make it maintain original insulating level of matrix while constructing heat conduction path, both cooperate to improve material thermal stability and dielectric property, modified filler is fused mixed extrusion preparation functional masterbatch with polypropylene;Functional masterbatch, polypropylene, initiator and auxiliary agent are melt blended, and then semi-finished product is obtained by double-screw extrusion granulation;After the semi-finished product is remelted and flow-cast, recrystallization annealing is carried out, the shear action in flow-casting process is used to induce the in-plane directional arrangement of hexagonal boron nitride whisker, then cooling is controlled under direct current electric field, polypropylene molecular chain is oriented using external electric field and the crystalline morphology is controlled, and finally polypropylene composite insulating material is obtained.

Description

Technical Field

[0001] This invention relates to the field of insulating materials technology, specifically to a polypropylene-based composite insulating material and its preparation method. Background Technology

[0002] Currently, the practical application of polypropylene insulation materials in high-voltage power transmission scenarios is consistently hampered by the technical challenge of synergistically optimizing the thermal field and crystal morphology. Most mainstream production processes currently employ a single physical blending method to add thermally conductive fillers. While this approach can improve the material's thermal conductivity to some extent, the disordered dispersion of the fillers within the matrix easily leads to localized heat accumulation, creating a temperature gradient within the insulation layer. The increase in temperature not only intensifies the thermal motion of polymer molecular chains, lowering the migration barrier for charge carriers within the material, but also triggers thermal relaxation of the crystal structure, resulting in decreased crystallinity, crystal form transformation, and ultimately, a direct decrease in dielectric strength and an increase in leakage current.

[0003] On the other hand, the application of traditional nucleating agents often focuses on increasing the crystallization rate, neglecting the balance between the nucleation process and crystal integrity. Under the influence of thermal history, problems such as coarse crystal lamellae and weakened grain boundary strength easily arise, creating potential pathways for the formation of electric trees. Particularly noteworthy is the failure of current processes to precisely control the distribution of fillers and the orientation of molecular chains, resulting in poor continuity of the thermally conductive network and difficulty in effectively curbing localized overheating. Furthermore, in the melt processing stage, the interfacial bonding strength between the filler and the matrix is ​​insufficient, easily leading to micropores and defects at the interface. These areas become sources of charge accumulation and space charge packet generation, further exacerbating the distortion of the electric field.

[0004] The aforementioned problems are intertwined, causing the insulation performance of existing polypropylene insulation materials to exhibit an irreversible decline when subjected to the combined effects of long-term thermal aging and electric fields, making it difficult to meet the stringent requirements for the material's heat resistance and electrical stability. Summary of the Invention

[0005] The purpose of this invention is to provide a polypropylene-based composite insulating material and its preparation method, so as to solve the problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a polypropylene-based composite insulating material, comprising the following components by mass fraction: 70-100 parts of polypropylene, 15-35 parts of modified masterbatch, 0.1-0.3 parts of initiator and 0.5-2 parts of antioxidant; The polypropylene-based composite insulation material is obtained by melt blending the above components, followed by twin-screw extrusion granulation to obtain a semi-finished product, then casting the semi-finished product, recrystallizing and annealing it, and finally controlling the cooling under a DC electric field. The modified masterbatch is prepared by melt blending 25-45 parts of polypropylene, 1-3 parts of modified rare earth nucleating agent, and 0.5-2.5 parts of hexagonal boron nitride whiskers. The modified rare earth nucleating agent is prepared by coordination of 4-vinyl-1,2-phthalic acid and rare earth metal salt.

[0007] Furthermore, the polypropylene resin is isotactic polypropylene, with a density of 0.90–0.94 g / cm³, a melt flow rate of 1.7–3.1 g / 10 min, and an isotacticity > 97%.

[0008] Furthermore, the initiator is dicumyl peroxide.

[0009] Furthermore, the antioxidant is selected from at least one of hindered phenolic antioxidants and phosphite antioxidants.

[0010] Furthermore, the rare earth metal salt is lanthanum nitrate hexahydrate or lanthanum chloride hexahydrate.

[0011] Furthermore, a method for preparing a polypropylene-based composite insulating material includes the following preparation steps: (1) Dissolve 4-vinyl-1,2-phthalic acid in 20wt% ethanol aqueous solution, disperse by ultrasonication, adjust pH to 7~8, continue stirring and dropwise add rare earth metal salt solution, adjust pH to 6.5~7.5 after dropwise addition, stir reaction at 50~60℃ for 3~5h, filter, wash, dry, grind to pass through 200 mesh to obtain modified rare earth nucleating agent; (2) Polypropylene, modified rare earth nucleating agent and hexagonal boron nitride whiskers are melt-blended using a twin-screw extruder. The reaction temperature is 170-210℃ and the reaction time is 1-5 min. After extrusion, the mixture is granulated and dried to obtain modified masterbatch. (3) Add polypropylene, modified masterbatch, initiator and antioxidant to a mixer and mix for 0.5h. Then add the uniformly mixed material to a twin-screw extruder for melt blending, extrusion granulation to obtain a semi-finished product, remelt the semi-finished product, and after casting, perform recrystallization annealing and cooling under the condition of applying a DC electric field to obtain a polypropylene-based composite insulation material.

[0012] Furthermore, in step (1), the rare earth metal salt solution is prepared by dissolving the rare earth metal salt in deionized water to a concentration of 100~120g / L.

[0013] Furthermore, in step (1), the molar ratio of rare earth metal salt and 4-vinyl-1,2-phthalic acid is 1:1.5~2.

[0014] Furthermore, in step (2), the hexagonal boron nitride whiskers are hexagonal boron nitride whiskers that have been surface modified using KH-550.

[0015] Furthermore, the recrystallization annealing process in step (3) involves heating to 120-130°C at a rate of 5-10°C / min and holding for 5-15 minutes.

[0016] Furthermore, in step (3), the electric field strength is 1-5 kV / mm, the cooling rate is 0.5-2℃ / min, until the temperature drops to 90-95℃, the DC electric field is turned off, and cooling continues to room temperature.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: First, a rare earth nucleating agent is prepared using 4-vinyl-1,2-phthalic acid and rare earth metal coordination. The two carboxyl groups of 4-vinyl-1,2-phthalic acid chelate with the rare earth metal, thereby improving the nucleation efficiency and the crystallization behavior of polypropylene. This enhances the material's rigidity and impact resistance. At the same time, a double bond is introduced on the surface of the rare earth nucleating agent, providing an active site for subsequent reactions. Then, surface-modified hexagonal boron nitride whiskers are compounded as a modified filler. The high electrical resistance and low dielectric constant of hexagonal boron nitride allow it to maintain the original insulation level of the matrix while constructing thermally conductive pathways. The combination of the two improves the thermal stability and dielectric properties of the material. The modified filler is melt-mixed with polypropylene and extruded to prepare a functional masterbatch. Secondly, the functional masterbatch, polypropylene, initiator, and additives are melt-blended and then granulated by twin-screw extrusion to obtain a semi-finished product. In the molten state, the double bonds on the surface of the rare earth nucleating agent undergo graft polymerization with the polypropylene chain segments, strengthening the bonding force between the filler and the matrix and preventing interface delamination. The semi-finished product is remelted and cast, and then recrystallized and annealed. The shearing action during the casting process induces the hexagonal boron nitride whiskers to align in-plane, forming a continuous heat-conducting network, improving heat dissipation efficiency, eliminating local overheating inside the insulation layer, suppressing the decrease in dielectric strength and the risk of electrical treeing caused by temperature rise, and further improving the insulation performance of the composite material. Subsequently, cooling is controlled under a DC electric field, and the external electric field is used to induce the orientation of the polypropylene molecular chains and regulate the crystal morphology, finally obtaining the polypropylene composite insulation material. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The test methods for various indicators of the polypropylene-based composite insulation material prepared in the following embodiments are as follows: Tensile strength: Polypropylene-based composite insulation materials prepared in the same mass as those in Examples 1-5 and Comparative Examples 1-5 were tested according to GB / T 1040.2-2006 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics". The specimen type was 1B and the tensile rate was 50 mm / min.

[0020] Simply supported beam impact strength: Polypropylene-based composite insulation materials prepared in Examples 1-5 and Comparative Examples 1-5 of the same mass were tested according to GB / T 1043.1-2008 "Determination of impact properties of simply supported beams of plastics - Part 1: Non-instrumental impact test" and the test specimens were unnotched specimens.

[0021] Crystallinity: Polypropylene-based composite insulation materials prepared in Examples 1-5 and Comparative Examples 1-5 of equal mass were analyzed according to GB / T 19466.3-2004 "Differential Scanning Calorimetry (DSC) for Plastics - Part 3: Determination of Melting and Crystallization Temperatures and Enthalpies". The calculation formula is: X c = ×100%, where ΔH m The melting enthalpy is ΔH0 (enthalpy of 100% crystallization of polypropylene), which is taken as 207 J / g.

[0022] Thermal conductivity: Polypropylene-based composite insulating materials prepared in the same mass of Examples 1-5 and Comparative Examples 1-5 were tested according to ASTM D5470-17 "Standard Test Method for Thermal Conductivity of Electrical Insulating Materials" using the steady-state heat flow method.

[0023] Volume resistivity: Polypropylene-based composite insulating materials prepared in the same mass as those in Examples 1-5 and Comparative Examples 1-5 were tested according to GB / T 31838.2-2019 "Dielectric and resistive properties of solid insulating materials - Part 2: Resistive properties (DC method) - Volume resistivity and volume resistivity", with an applied voltage of 1000 V and a charging time of 60 s.

[0024] Power frequency breakdown field strength: Polypropylene-based composite insulation materials prepared in Examples 1-5 and Comparative Examples 1-5 of the same mass were tested according to GB / T 1408.1-2016 "Electrical strength test method for insulating materials - Part 1: Power frequency test", using 25mm diameter spherical electrodes, a voltage rise rate of 1.0kV / s, and transformer oil as the medium.

[0025] Example 1 (1) Dissolve 4-vinyl-1,2-phthalic acid in 20wt% ethanol aqueous solution at 12 times its mass, disperse by ultrasonication at 40kHz for 10min, adjust pH to 7 by adding 1mol / L sodium hydroxide solution, continue to add rare earth metal salt solution by stirring at 400r / min at a dropping rate of 1 drop / second, adjust pH to 6.5 by dilute nitric acid after addition, stir and react at 300r / min at 50℃ for 3h, filter, wash, dry to constant weight in vacuum drying oven at 60℃, grind through a 200-mesh sieve to obtain modified rare earth nucleating agent; the rare earth metal salt is lanthanum nitrate hexahydrate; the lanthanum nitrate solution is prepared by dissolving lanthanum nitrate hexahydrate in deionized water to prepare a 100g / L solution; the molar ratio of lanthanum nitrate hexahydrate to 4-vinyl-1,2-phthalic acid is 1:1.5; (2) 25 parts of polypropylene, 1 part of modified rare earth nucleating agent and 0.5 parts of hexagonal boron nitride whiskers were added to a twin-screw extruder for melt blending. The reaction temperature was 170℃ and the reaction time was 1min. The mixture was then extruded, granulated and dried to obtain modified masterbatch. The hexagonal boron nitride whiskers were obtained by dispersing hexagonal boron nitride whiskers with an aspect ratio ≥50 in anhydrous ethanol, adding 4% KH-550 by weight of the whiskers, refluxing and stirring at 80℃ for 3h, filtering and drying at 80℃. (3) 70 parts of polypropylene, 15 parts of modified masterbatch, 0.1 parts of initiator dicumyl peroxide and 0.5 parts of antioxidant 1010 are added to a mixer and mixed for 0.5 h. The mixture is then added to a twin-screw extruder for melt blending. The screw speed is 40 r / min and the barrel temperature is 155℃ in zone 1, 165℃ in zone 2, 175℃ in zone 3 and 180℃ in zone 4. The mixture is extruded and granulated to obtain a semi-finished product. After remelting, the semi-finished product is cast into a sheet with a thickness of 0.5 mm and then recrystallized and annealed: the temperature is raised to 120℃ at 5℃ / min and held for 5 min. The temperature is then lowered to 90℃ at 0.5℃ / min under a DC electric field of 1 kV / mm. The direction of the DC electric field is parallel to the direction of the casting to match the shear orientation direction of the whiskers. After the electric field is turned off, the mixture is naturally cooled to room temperature to obtain a polypropylene-based composite insulating material.

[0026] Example 2 (1) Dissolve 4-vinyl-1,2-phthalic acid in 12 times its mass of 20wt% ethanol aqueous solution, disperse by ultrasonication at 40kHz for 12min, adjust the pH to 7.2 by adding 1mol / L sodium hydroxide solution, and continue to add rare earth metal salt solution by stirring at 450r / min at a dropping rate of 1.5 drops / second. After the addition is complete, adjust the pH to 7.0 with dilute nitric acid, stir and react at 55℃ and 350r / min for 4h, filter, wash, dry in a vacuum drying oven at 70℃ to constant weight, grind and pass through a 200-mesh sieve to obtain modified rare earth nucleating agent; the rare earth metal salt is lanthanum chloride hexahydrate; the lanthanum chloride solution is prepared by dissolving lanthanum chloride hexahydrate in deionized water to prepare a 110g / L solution; the molar ratio of lanthanum chloride hexahydrate to 4-vinyl-1,2-phthalic acid is 1:1.8; (2) 35 parts of polypropylene, 2 parts of modified rare earth nucleating agent and 1.5 parts of hexagonal boron nitride whiskers were added to a twin-screw extruder for melt blending. The reaction temperature was 190℃ and the reaction time was 3 min. The mixture was then extruded, granulated and dried to obtain modified masterbatch. The hexagonal boron nitride whiskers were obtained by dispersing hexagonal boron nitride whiskers with an aspect ratio ≥ 50 in anhydrous ethanol, adding 4% KH-550 by weight of the whiskers, refluxing and stirring at 80℃ for 3 h, filtering and drying at 80℃. (3) 85 parts of polypropylene, 25 parts of modified masterbatch, 0.2 parts of initiator dicumyl peroxide, and 1.2 parts of antioxidant 168 were added to a mixer and mixed for 0.5 h. The mixture was then added to a twin-screw extruder for melt blending. The screw speed was 45 r / min, and the barrel temperature was 158℃ in zone 1, 168℃ in zone 2, 178℃ in zone 3, and 183℃ in zone 4. The mixture was extruded and granulated to obtain a semi-finished product. After remelting, the semi-finished product was cast into a sheet with a thickness of 1.2 mm and then recrystallized and annealed: the temperature was raised to 125℃ at 8℃ / min and held for 10 min. The temperature was then lowered to 92℃ at 1.2℃ / min under a DC electric field of 3 kV / mm. The direction of the DC electric field was parallel to the direction of the casting to match the shear orientation direction of the whiskers. After the electric field was turned off, the mixture was allowed to cool naturally to room temperature to obtain a polypropylene-based composite insulating material.

[0027] Example 3 (1) Dissolve 4-vinyl-1,2-phthalic acid in 12 times its mass of 20wt% ethanol aqueous solution, disperse by ultrasonication at 40kHz for 13min, add 1mol / L sodium hydroxide solution to adjust pH to 7.5, continue to add rare earth metal salt solution by stirring at 500r / min at a dropping rate of 1.8 drops / second, adjust pH to 7.2 with dilute nitric acid after addition, stir and react at 58℃ and 380r / min for 4.5h, filter, wash, dry in a vacuum drying oven at 75℃ to constant weight, grind through a 200-mesh sieve to obtain modified rare earth nucleating agent; the rare earth metal salt is lanthanum nitrate hexahydrate; the lanthanum nitrate solution is prepared by dissolving lanthanum nitrate hexahydrate in deionized water to prepare a 115g / L solution; the molar ratio of lanthanum nitrate hexahydrate to 4-vinyl-1,2-phthalic acid is 1:1.9; (2) 40 parts of polypropylene, 2.5 parts of modified rare earth nucleating agent and 2 parts of hexagonal boron nitride whiskers were added to a twin-screw extruder for melt blending. The reaction temperature was 200℃ and the reaction time was 4min. The mixture was then extruded, granulated and dried to obtain modified masterbatch. The hexagonal boron nitride whiskers were obtained by dispersing hexagonal boron nitride whiskers with an aspect ratio ≥50 in anhydrous ethanol, adding 4% KH-550 by weight of the whiskers, refluxing and stirring at 80℃ for 3h, filtering and drying at 80℃. (3) 90 parts of polypropylene, 30 parts of modified masterbatch, 0.25 parts of initiator dicumyl peroxide and 1.5 parts of antioxidant 126 were added to a mixer and mixed for 0.5 h. The mixture was then added to a twin-screw extruder for melt blending. The screw speed was 48 r / min and the barrel temperature was 159℃ in zone 1, 169℃ in zone 2, 179℃ in zone 3 and 184℃ in zone 4. The mixture was extruded and granulated to obtain a semi-finished product. After remelting, the semi-finished product was cast into a sheet with a thickness of 1.5 mm and then recrystallized and annealed: the temperature was raised to 128℃ at 9℃ / min and held for 12 min. The temperature was then lowered to 94℃ at 1.5℃ / min under a DC electric field of 4 kV / mm. The direction of the DC electric field was parallel to the direction of the casting to match the shear orientation direction of the whiskers. After the electric field was turned off, the mixture was allowed to cool naturally to room temperature to obtain a polypropylene-based composite insulating material.

[0028] Example 4 (1) Dissolve 4-vinyl-1,2-phthalic acid in 12 times its mass of 20wt% ethanol aqueous solution, disperse by ultrasonication at 40kHz for 14min, adjust pH to 7.8 by adding 1mol / L sodium hydroxide solution, continue to add rare earth metal salt solution by stirring at 550r / min at a dropping rate of 1.9 drops / second, adjust pH to 7.4 by dilute nitric acid after addition, stir and react at 59℃ and 390r / min for 4.8h, filter, wash, dry to constant weight in a vacuum drying oven at 78℃, grind through a 200-mesh sieve to obtain modified rare earth nucleating agent; the rare earth metal salt is lanthanum chloride hexahydrate; the lanthanum chloride solution is prepared by dissolving lanthanum chloride hexahydrate in deionized water to prepare a 118g / L solution; the molar ratio of lanthanum chloride hexahydrate to 4-vinyl-1,2-phthalic acid is 1:1.95; (2) 42 parts of polypropylene, 2.8 parts of modified rare earth nucleating agent and 2.2 parts of hexagonal boron nitride whiskers were added to a twin-screw extruder for melt blending. The reaction temperature was 205℃ and the reaction time was 4.5 min. The mixture was then extruded, granulated and dried to obtain modified masterbatch. The hexagonal boron nitride whiskers were obtained by dispersing hexagonal boron nitride whiskers with an aspect ratio ≥50 in anhydrous ethanol, adding 4% KH-550 by weight of the whiskers, refluxing and stirring at 80℃ for 3 h, filtering and drying at 80℃. (3) 95 parts of polypropylene, 32 parts of modified masterbatch, 0.28 parts of initiator dicumyl peroxide, and 1.8 parts of antioxidant 1010 were added to a mixer and mixed for 0.5 h. The mixture was then added to a twin-screw extruder for melt blending. The screw speed was 49 r / min, and the barrel temperature was 160℃ in zone 1, 170℃ in zone 2, 180℃ in zone 3, and 185℃ in zone 4. The mixture was extruded and granulated to obtain a semi-finished product. After remelting, the semi-finished product was cast into a sheet with a thickness of 1.8 mm and then recrystallized and annealed: the temperature was raised to 129℃ at 9.5℃ / min and held for 14 min. The temperature was then lowered to 94℃ at 1.8℃ / min under a DC electric field of 4.5 kV / mm. The direction of the DC electric field was parallel to the direction of the casting process to match the shear orientation direction of the whiskers. After the electric field was turned off, the mixture was allowed to cool naturally to room temperature to obtain a polypropylene-based composite insulating material.

[0029] Example 5 (1) Dissolve 4-vinyl-1,2-phthalic acid in 12 times its mass of 20wt% ethanol aqueous solution, disperse by ultrasonication at 40kHz for 15min, adjust pH to 8 by adding 1mol / L sodium hydroxide solution, continue to add rare earth metal salt solution by stirring at 600r / min at a dropping rate of 2 drops / second, adjust pH to 7.5 by dilute nitric acid after addition, stir and react at 60℃ and 400r / min for 5h, filter, wash, dry to constant weight in a vacuum drying oven at 80℃, grind through a 200-mesh sieve to obtain modified rare earth nucleating agent; the rare earth metal salt is lanthanum nitrate hexahydrate; the lanthanum nitrate solution is prepared by dissolving lanthanum nitrate hexahydrate in deionized water to prepare a 120g / L solution; the molar ratio of lanthanum nitrate hexahydrate to 4-vinyl-1,2-phthalic acid is 1:2; (2) 45 parts of polypropylene, 3 parts of modified rare earth nucleating agent and 2.5 parts of hexagonal boron nitride whiskers were added to a twin-screw extruder for melt blending. The reaction temperature was 210℃ and the reaction time was 5min. The mixture was then extruded, granulated and dried to obtain modified masterbatch. The hexagonal boron nitride whiskers were obtained by dispersing hexagonal boron nitride whiskers with an aspect ratio ≥50 in anhydrous ethanol, adding 4% KH-550 by weight of the whiskers, refluxing and stirring at 80℃ for 3h, filtering and drying at 80℃. (3) 100 parts of polypropylene, 35 parts of modified masterbatch, 0.3 parts of initiator dicumyl peroxide and 2 parts of antioxidant 168 were added to a mixer and mixed for 0.5 h. The mixture was then added to a twin-screw extruder for melt blending. The screw speed was 50 r / min and the barrel temperature was 160℃ in zone 1, 170℃ in zone 2, 180℃ in zone 3 and 185℃ in zone 4. The mixture was extruded and granulated to obtain a semi-finished product. After remelting, the semi-finished product was cast into a sheet with a thickness of 2 mm and then recrystallized and annealed: the temperature was raised to 130℃ at 10℃ / min and held for 15 min. The temperature was then lowered to 95℃ at 2℃ / min under a 5 kV / mm DC electric field. The direction of the DC electric field was parallel to the direction of the casting to match the shear orientation direction of the whiskers. After the electric field was turned off, the mixture was naturally cooled to room temperature to obtain a polypropylene-based composite insulating material.

[0030] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that step (2) is omitted, and step (3) is changed to: 90 parts of polypropylene, 2 parts of modified rare earth nucleating agent, 1.5 parts of hexagonal boron nitride whiskers, 0.025 parts of initiator dicumyl peroxide, and antioxidant 126 1.5 parts were added to a mixer and mixed for 0.5 hours. The uniformly mixed material was then added to a twin-screw extruder for melt blending, extruded and granulated to obtain a semi-finished product. The semi-finished product was remelted, cast into a film with a thickness of 1.5 mm, and then recrystallized and annealed. It was then cooled under a DC electric field to obtain a polypropylene-based composite insulation material. The screw speed was 48 r / min, and the extruder barrel temperature was set as follows: Zone 1 159℃, Zone 2 169℃, Zone 3 179℃, and Zone 4 184℃. The recrystallization annealing process was to heat the material to 128℃ at a rate of 9℃ / min and hold it for 12 min. The electric field strength was 4 kV / mm, and the cooling rate was 1.5℃ / min until the temperature dropped to 94℃. The DC electric field was then turned off, and the material was cooled to room temperature. The remaining steps were the same as in Example 3.

[0031] Comparative Example 2 The difference between Comparative Example 2 and Example 3 lies in step (2). Step (2) is changed to: polypropylene, lanthanum nitrate hexahydrate and hexagonal boron nitride whiskers are melt-blended using a twin-screw extruder at a reaction temperature of 190°C for 4.5 min. After extrusion, the mixture is granulated and dried to obtain modified masterbatch. The modified masterbatch is prepared by melt-blending 40 parts of polypropylene, 2 parts of lanthanum nitrate hexahydrate and 2 parts of hexagonal boron nitride whiskers. The hexagonal boron nitride whiskers are hexagonal boron nitride whiskers that have been surface-modified using KH-550. The remaining steps are the same as in Example 3.

[0032] Comparative Example 3 The difference between Comparative Example 3 and Example 3 lies in step (3). Step (3) is changed to: 90 parts of polypropylene, 30 parts of modified masterbatch, 0.025 parts of initiator dicumyl peroxide and 1.5 parts of antioxidant 126 are added to a mixer and mixed for 0.5 hours. Then, the uniformly mixed material is added to a twin-screw extruder for melt blending and extrusion granulation to obtain a semi-finished product. The semi-finished product is directly subjected to recrystallization annealing and cooled under the condition of applying a DC electric field to obtain a polypropylene-based composite insulation material. The screw speed is 48 r / min, and the temperature inside the extruder barrel is set as follows: Zone 1 159℃, Zone 2 169℃, Zone 3 179℃, Zone 4 184℃. The recrystallization annealing process is to heat up to 128℃ at 9℃ / min and hold for 12 minutes. The electric field strength is 4kV / mm, the cooling rate is 1.5℃ / min, until the temperature drops to 94℃, the DC electric field is turned off, and cooling continues to room temperature. The remaining steps are the same as in Example 3.

[0033] Comparative Example 4 The difference between Comparative Example 4 and Example 3 lies in step (3). Step (3) is changed to: 90 parts of polypropylene, 30 parts of modified masterbatch, 0.025 parts of initiator dicumyl peroxide, and 1.5 parts of antioxidant 126 are added to a mixer and mixed for 0.5 hours. The mixture is then added to a twin-screw extruder for melt blending. The screw speed is 48 r / min, and the barrel temperature is 159°C in zone 1, 169°C in zone 2, 179°C in zone 3, and 184°C in zone 4. The mixture is then extruded and granulated to obtain a semi-finished product. After remelting, the semi-finished product is cast into a sheet with a thickness of 1.5 mm. Without recrystallization annealing, the sheet is directly cooled to 94°C at a rate of 1.5°C / min under a 4 kV / mm DC electric field. After the electric field is turned off, the sheet is naturally cooled to room temperature to obtain a polypropylene-based composite insulating material. The remaining steps are the same as in Example 3.

[0034] Comparative Example 5 The difference between Comparative Example 5 and Example 3 lies in step (3). Step (3) is changed to: 90 parts of polypropylene, 30 parts of modified masterbatch, 0.025 parts of initiator dicumyl peroxide, and 1.5 parts of antioxidant 126 are added to a mixer and mixed for 0.5 hours. The mixture is then added to a twin-screw extruder for melt blending. The screw speed is 48 r / min, and the barrel temperature is 159°C in zone 1, 169°C in zone 2, 179°C in zone 3, and 184°C in zone 4. The mixture is then extruded and granulated to obtain a semi-finished product. After remelting, the semi-finished product is cast into a sheet with a thickness of 1.5 mm and then recrystallized and annealed: the temperature is raised to 128°C at 9°C / min, held for 12 minutes, and then cooled naturally to room temperature without applying an electric field to obtain a polypropylene-based composite insulating material. The remaining steps are the same as in Example 3.

[0035] Example of effect Table 1 below shows the performance analysis results of the polypropylene-based composite insulating materials of Examples 1 to 5 and Comparative Examples 1 to 5 of the present invention.

[0036] Table 1 A comparison of the experimental data from the examples and comparative examples reveals that the polypropylene-based composite insulating material prepared by this invention exhibits excellent comprehensive performance. In terms of mechanical properties, the tensile strength of each example reaches 22.6–24.0 MPa, and the impact strength reaches 6.5–8.2 kJ / m², demonstrating a good balance between stiffness and toughness. Regarding thermal conductivity, thanks to the in-plane orientation of the hexagonal boron nitride whiskers induced by casting shearing and the synergistic optimization of the crystal structure by rare earth nucleating agents, the thermal conductivity of the examples reaches 0.27–0.35 W / (m·K), which is generally superior to most comparative examples, with Example 5 reaching the highest value of 0.35 W / (m·K). In terms of dielectric properties, the volume resistivity of each example reaches 3.8 × 10⁻⁶. 15 ~5.8×10 15The thermal conductivity reaches 140~158 kV / mm at power frequency, with a maximum strength of Ω·cm. Notably, as the BN whisker content increases, the thermal conductivity continuously improves, but the breakdown field strength drops slightly after reaching its peak in Example 3, indicating that excessive filler may introduce trace interface defects, suggesting the existence of an optimal filler ratio. Comparative Examples 4 and 5, lacking annealing or electric field treatment respectively, exhibited better breakdown field strengths than other comparative examples, but still lower than Example 3, demonstrating that the synergistic effect of shear-induced whisker orientation and electric field-induced molecular chain orientation is key to achieving optimal performance. In summary, this invention achieves a good balance between high thermal conductivity and high insulation, meeting the performance requirements of high-voltage power cable insulation materials.

[0037] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A polypropylene-based composite insulating material, characterized in that, By mass fraction, it includes the following components: 70-100 parts polypropylene, 15-35 parts modified masterbatch, 0.1-0.3 parts initiator, and 0.5-2 parts antioxidant; The polypropylene-based composite insulation material is obtained by melt blending the above components, followed by twin-screw extrusion granulation to obtain a semi-finished product, then casting the semi-finished product, recrystallizing and annealing it, and finally controlling the cooling under a DC electric field. The modified masterbatch is prepared by melt blending 25-45 parts of polypropylene, 1-3 parts of modified rare earth nucleating agent, and 0.5-2.5 parts of hexagonal boron nitride whiskers. The modified rare earth nucleating agent is prepared by coordination of 4-vinyl-1,2-phthalic acid and rare earth metal salt.

2. The polypropylene-based composite insulating material according to claim 1, characterized in that, The initiator is dicumyl peroxide.

3. The polypropylene-based composite insulating material according to claim 2, characterized in that, The antioxidant is selected from at least one of hindered phenolic antioxidants and phosphite antioxidants.

4. The polypropylene-based composite insulating material according to claim 1, characterized in that, The rare earth metal salt is lanthanum nitrate hexahydrate or lanthanum chloride hexahydrate.

5. A method for preparing a polypropylene-based composite insulating material according to any one of claims 1-4, characterized in that, The preparation steps include the following: (1) Dissolve 4-vinyl-1,2-phthalic acid in 20wt% ethanol aqueous solution, disperse by ultrasonication, adjust pH to 7~8, continue stirring and dropwise add rare earth metal salt solution, adjust pH to 6.5~7.5 after dropwise addition, stir reaction at 50~60℃ for 3~5h, filter, wash, dry, grind to pass through 200 mesh to obtain modified rare earth nucleating agent; (2) Polypropylene, modified rare earth nucleating agent and hexagonal boron nitride whiskers are melt-blended using a twin-screw extruder. The reaction temperature is 170-210℃ and the reaction time is 1-5 min. After extrusion, the mixture is granulated and dried to obtain modified masterbatch. (3) Add polypropylene, modified masterbatch, initiator and antioxidant to a mixer and mix for 0.5h. Then add the uniformly mixed material to a twin-screw extruder for melt blending, extrusion granulation to obtain a semi-finished product, remelt the semi-finished product, and after casting, perform recrystallization annealing and cooling under the condition of applying a DC electric field to obtain a polypropylene-based composite insulation material.

6. The method for preparing a polypropylene-based composite insulating material according to claim 5, characterized in that, The rare earth metal salt solution in step (1) is prepared by dissolving rare earth metal salt in deionized water to a concentration of 100~120g / L.

7. The method for preparing a polypropylene-based composite insulating material according to claim 5, characterized in that, In step (1), the molar ratio of rare earth metal salt and 4-vinyl-1,2-phthalic acid is 1:1.5~2.

8. The method for preparing a polypropylene-based composite insulating material according to claim 5, characterized in that, In step (2), the hexagonal boron nitride whiskers are hexagonal boron nitride whiskers that have been surface modified using KH-550.

9. The method for preparing a polypropylene-based composite insulating material according to claim 5, characterized in that, The recrystallization annealing process in step (3) involves heating to 120-130°C at a rate of 5-10°C / min and holding for 5-15 minutes.

10. The method for preparing a polypropylene-based composite insulating material according to claim 5, characterized in that, In step (3), the electric field strength is 1-5 kV / mm, the cooling rate is 0.5-2℃ / min, until the temperature drops to 90-95℃, the DC electric field is turned off, and cooling continues to room temperature.

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