Low dielectric loss polyolefin insulation material and method of making same

Abstract

The application discloses a kind of low dielectric loss polyolefin insulating materials and preparation method thereof.Material raw materials include isotactic polypropylene, ethylene-1-octene copolymer, polar antioxidant, hydrogen bond network building agent, full hydrogenated alicyclic petroleum resin and amorphous area concentration trigger agent.Preparation method is: polar antioxidant and hydrogen bond network building agent are prepared complex master batch by heating shearing;Residual raw materials are dry mixed to obtain matrix material;Matrix material is fed into twin-screw extruder by main feed inlet, and complex master batch is pressed into melt mixing extrusion by side feeder;After stepwise temperature control annealing, it is cooled and cut into particles.The hydrogen bond network formed by antioxidant and building agent is used to constrain polar group, combined with trigger agent to induce crystallization, so that petroleum resin is enriched in amorphous area to fill free volume.This mechanism increases the activation energy of polar group flipping, inhibits its orientation polarization under alternating electric field, while maintaining the heat-aging resistance of insulating material, reduces high-frequency dielectric loss.

Description

Technical Field

[0001] This invention relates to the field of polymer insulating materials technology, specifically to low dielectric loss polyolefin insulating materials and their preparation methods. Background Technology

[0002] Polyolefin materials, due to the non-polar nature of their main chain, possess low intrinsic dielectric constant and dielectric loss, and are commonly used as insulation layers for high-frequency communication cables and high-voltage transmission cables. To meet the requirements for heat and oxygen aging resistance during long-term cable operation, hindered phenolic antioxidants are typically added to the polyolefin matrix in industrial production. These antioxidants contain polar groups such as phenolic hydroxyl and ester groups in their molecular structure. When the insulating material is subjected to an alternating electric field, these small polar molecule groups undergo orientation polarization within the amorphous region of the polymer, leading to a significant increase in high-frequency dielectric loss and consequently affecting the signal transmission quality and operational stability of the cable.

[0003] To address the issue of increased dielectric loss caused by polar antioxidants, existing conventional treatment methods have corresponding technical limitations. Directly reducing the proportion of polar antioxidants leads to insulation materials failing long-term thermal aging tests, severely shortening the actual service life of cables. Some solutions attempt to synthesize novel macromolecular or non-polar antioxidants to replace traditional hindered phenolic additives, but this approach faces challenges such as complex molecular structure design, cumbersome synthesis steps, and high manufacturing costs, making large-scale industrial application difficult. Furthermore, in solutions that use surface-modified inorganic nanofillers to physically adsorb polar molecules, the nanofillers are prone to agglomeration in the polymer melt, forming numerous heterogeneous defect interfaces within the material. These defect interfaces easily accumulate space charge under an electric field, not only failing to effectively suppress high-frequency dielectric loss but also reducing the breakdown field strength of the insulation material. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the technical problem solved by this invention is that existing polyolefin insulating materials typically contain antioxidants with polar groups to meet heat and oxygen aging resistance requirements. Under the action of an alternating electric field, the polar groups undergo orientation polarization within the polymer matrix, leading to an increase in the high-frequency dielectric loss of the material.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a low dielectric loss polyolefin insulating material, employing the following technical solution: A low dielectric loss polyolefin insulating material, wherein the insulating material is made from raw materials comprising the following parts by weight: isotactic polypropylene: 80.0-90.0 parts; ethylene-1-octene copolymer: 10.0-20.0 parts; polar antioxidant: 0.5-1.5 parts; hydrogen bond network building agent: 1.0-3.0 parts; fully hydrogenated alicyclic petroleum resin: 5.0-10.0 parts; amorphous region concentration triggering agent: 0.1-0.3 parts. Wherein, the polar antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; the hydrogen bond network building agent is ethylene bis-stearamide; and the amorphous region concentration triggering agent is dimethyl dibenzyl sorbitol.

[0007] By employing the above technical solution, the high-frequency dielectric loss of insulating materials is reduced. The mechanism of this invention mainly lies in the synergistic effect between the components: First, the phenolic hydroxyl groups in the polar antioxidant structure act as hydrogen bond donors, interacting with the amide groups in the hydrogen bond network building agent structure as hydrogen bond acceptors to form an intermolecular hydrogen bond network. This network increases the activation energy for spatial rotation of polar groups, restricting the rotational freedom of polar small molecules under an electric field. Second, the amorphous region concentration trigger dissolves in the molten polyolefin system and preferentially self-assembles to form a nucleation network during material extrusion and cooling, promoting dense crystallization of isotactic polypropylene. The regular arrangement of polymer chains forms crystalline regions. Due to the exclusivity of the crystal lattice, the crystalline regions repel the fully hydrogenated alicyclic petroleum resin, polar antioxidant, and hydrogen bond network building agent into the amorphous region of the polymer. Subsequently, the high crystallinity of isotactic polypropylene leads to a reduction in the absolute volume of the amorphous region. The enrichment of fully hydrogenated alicyclic petroleum resins in the amorphous region fills the free volume between polymer segments, increasing the local glass transition temperature and reducing the segment mobility in the amorphous region. Ultimately, the polar groups of the polar antioxidant are chemically constrained by the intermolecular hydrogen bond network and physically compressed by the enrichment of the fully hydrogenated alicyclic petroleum resin. This dual constraint mechanism increases the steric hindrance of polar group flipping, making its dipole relaxation time longer than the period of the high-frequency alternating electric field. The polar groups cannot flip with the change of electric field, thereby suppressing orientation polarization and reducing the dielectric loss of the material.

[0008] Preferably, the raw materials are in the following weight proportions: 85.0 parts isotactic polypropylene; 15.0 parts ethylene-1-octene copolymer; 1.0 part polar antioxidant; 2.0 parts hydrogen bond network building agent; 7.5 parts fully hydrogenated alicyclic petroleum resin; and 0.2 parts amorphous region concentration trigger. By adopting the above technical solution, the proportions of each component reach thermodynamic equilibrium, and the material maintains its mechanical strength while achieving stable suppression of dielectric loss.

[0009] Preferably, the isotactic polypropylene has an isotacticity greater than or equal to 97%, a crystallinity of 50%–65%, and a melt flow rate of 2.0–4.0 g / 10 min under conditions of 230°C and a load of 2.16 kg; the ethylene-1-octene copolymer has a mass fraction of 20%–30% of 1-octene copolymer units and a density of 0.865–0.875 g / cm³. By adopting the above technical solution, a continuous phase matrix that meets the processing and molding requirements of the insulation layer is provided, ensuring the mechanical strength and flexibility of the material.

[0010] Preferably, the fully hydrogenated alicyclic petroleum resin has a degree of hydrogenation greater than or equal to 99.5%, a bromine value less than or equal to 2.0 gI2 / 100 g, and a ring and ball softening point of 120.0–140.0 °C. By adopting the above technical solution, the non-polar properties and thermal stability of the resin are guaranteed, ensuring that the component is compatible with the polyolefin matrix.

[0011] Preferably, the polar antioxidant has a purity of ≥98.0% and a melting point of 110.0–125.0℃; the hydrogen bond network building agent has a purity of ≥98.0%, a total amine value of ≤3.0 mgKOH / g, an acid value of ≤7.0 mgKOH / g, and a melting point of 140.0–146.0℃. By adopting the above technical solution, the intermolecular hydrogen bond assembly process is ensured to be unaffected by impurities, thus ensuring the locking efficiency of polar groups.

[0012] Secondly, the present invention provides a method for preparing a low dielectric loss polyolefin insulating material, which adopts the following technical solution: A method for preparing a low dielectric loss polyolefin insulating material includes the following steps: S1, placing a polar antioxidant and a hydrogen bond network building agent in a mixer, and obtaining an antioxidant-EBS complex masterbatch under heating and shearing conditions; S2, mixing isotactic polypropylene, ethylene-1-octene copolymer, fully hydrogenated alicyclic petroleum resin and an amorphous region concentration trigger uniformly to obtain a matrix physical mixture; S3, feeding the matrix physical mixture obtained in step S2 into the main feed port of a twin-screw extruder, feeding the antioxidant-EBS complex masterbatch obtained in step S1 into the side feeder of the twin-screw extruder, mixing in situ at a melt temperature of 190-210°C and extruding it into a melt strip; S4, passing the extruded melt strip through a first annealing section and a second annealing section for stepped temperature-controlled annealing, and then cooling and pelletizing to obtain the low dielectric loss polyolefin insulating material.

[0013] By adopting the above technical solution, the material formulation system and processing technology are combined. Step S1 promotes the pre-formation of intermolecular hydrogen bond networks in the components under an independent heating and shearing environment, avoiding the direct entry of polar antioxidants into the high-temperature extruder and resulting in early oxidation and consumption. Step S3 adopts a side-feeding method to shorten the residence time of the hydrogen bond network in the high-temperature melt and maintain the integrity of the complex structure. Step S4 introduces stepped temperature-controlled annealing, allowing the polymer chain segments to obtain relaxation time above the glass transition temperature, eliminating the non-equilibrium free volume generated by rapid cooling, promoting the amorphous region of the polymer to reach thermodynamic equilibrium, fixing the spatial distribution of the hydrogen bond network and additive molecules, and ensuring the stability of the material's dielectric properties.

[0014] Preferably, in step S1, the specific process parameters for preparing the antioxidant-EBS complex masterbatch are as follows: under a slightly positive pressure nitrogen atmosphere, the stirring paddle speed is controlled at 1500–2500 rpm, causing the material temperature of the mixture to rise at a rate of 10–15 °C / min; when the actual material temperature reaches 145.0–155.0 °C, this temperature is maintained for constant mixing for 15–20 min, followed by cooling to 20–30 °C. By adopting the above technical solution, conditions for component melting and molecular collision are provided, promoting the spontaneous formation of hydrogen bonds, while the slightly positive pressure nitrogen atmosphere prevents the polar antioxidant from undergoing thermo-oxidative degradation under high-temperature conditions.

[0015] Preferably, in step S3, the length-to-diameter ratio of the twin-screw extruder is 40:1 to 48:1, and the screw speed is 150 to 250 rpm. After the matrix physical mixture reaches a completely molten state in the twin-screw extruder barrel, the antioxidant-EBS complex masterbatch is continuously pressed into the melt. By adopting the above technical solution, it is ensured that the matrix resin and the fully hydrogenated alicyclic petroleum resin reach a miscible state before the polar complex is introduced, thus avoiding the agglomeration and precipitation of polar substances.

[0016] Preferably, in step S4, the specific process parameters for the stepped temperature-controlled annealing are as follows: the ambient temperature of the first annealing section is 110.0–120.0℃, and the residence time of the material strip in the first annealing section is 3.0–5.0 min; the ambient temperature of the second annealing section is 70.0–80.0℃, and the residence time of the material strip in the second annealing section is 3.0–5.0 min. By adopting the above technical solution, the crystallization kinetics of polypropylene are controlled. The first annealing section promotes the formation of the nucleating agent network and induces rapid growth of the crystal regions, while the second annealing section promotes the rearrangement and shrinkage of the amorphous chain segments, thereby achieving densification of the physical space.

[0017] Preferably, in step S2, the mixing is performed by dry mixing at a room temperature of 20–30°C and a rotation speed of 300–500 rpm for 5–10 minutes. By adopting the above technical solution, the dry powder material is dispersed and mixed on a physical scale.

[0018] This invention provides a low dielectric loss polyolefin insulating material and its preparation method. It has the following beneficial effects:

[0019] 1. This invention reduces the high-frequency dielectric loss of polyolefin insulating materials. By premixing an antioxidant containing polar groups with ethylene bis-stearamide, an intermolecular hydrogen bond network is formed, raising the activation energy barrier for the spatial rotation of polar groups. Simultaneously, dimethyl dibenzyl sorbitol induces polypropylene crystallization, repelling the fully hydrogenated alicyclic petroleum resin to the amorphous region to fill the free volume. This technical solution restricts the activity space of polar groups under an alternating electric field, thereby suppressing the orientation polarization process and effectively reducing the dielectric loss of the material.

[0020] 2. This invention reduces dielectric loss while maintaining the heat and oxygen aging resistance of the insulating material. Instead of controlling dielectric loss by reducing the conventional amount of polar antioxidants, this method utilizes intermolecular hydrogen bonds to spatially confine the polar groups. This non-covalent interaction between components does not destroy the chemical activity of the hindered phenolic structure in the antioxidant molecule, allowing it to still function as a free radical scavenger within the polymer matrix, thus ensuring the insulation material meets the required anti-aging lifespan under long-term heated operating conditions.

[0021] 3. This invention improves the physical stability of the material's internal structure and ensures process feasibility. The preparation method incorporates a stepped temperature-controlled annealing step, allowing the polymer segments after extrusion to relax above the glass transition temperature, eliminating the non-equilibrium free volume generated by conventional water bath quenching processes. This annealing process promotes a dense thermodynamic equilibrium in the polymer's amorphous regions, fixing the spatial distribution of hydrogen bonds and additives, preventing additive migration and precipitation due to the drastic reduction in the amorphous region's accommodating space, and ensuring the overall production process is fully compatible with existing extrusion equipment. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

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

[0024] Please see the appendix Figure 1 This invention provides a low dielectric loss polyolefin insulating material and its preparation method.

[0025] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0026] The density of isotactic polypropylene is 0.90 g / cm³ to 0.91 g / cm³, and the melt mass flow rate at 230°C and 2.16 kg load is 2.0 g / 10 min to 4.0 g / 10 min.

[0027] The ethylene-1-octene copolymer has a mass fraction of 20% to 30% of 1-octene copolymer units, a density of 0.865 g / cm³ to 0.875 g / cm³, and a melt mass flow rate of 1.0 g / 10 min to 5.0 g / 10 min under conditions of 190 °C and 2.16 kg load.

[0028] Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] is commonly known as antioxidant 1010, with CAS number 6683-19-8.

[0029] Ethylene bis-stearamide has the CAS number 110-30-5 and a melting point of 140.0℃ to 146.0℃.

[0030] The fully hydrogenated dicyclopentadiene petroleum resin has the CAS number 68132-00-3, a degree of hydrogenation greater than or equal to 99.5%, and a softening point of 120.0℃ to 140.0℃ using the ring and ball method.

[0031] 1,3:2,4-Di(3,4-dimethylbenzyl)sorbitol is commonly known as the nucleating agent DMDBS, with CAS number 135861-56-2.

[0032] Preparation Example 1:

[0033] This preparation example provides an antioxidant-EBS complex masterbatch, comprising the following steps:

[0034] 1000g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 2000g of ethylene bis-stearamide were added to a high-speed mixer with a temperature-controlled jacket. Nitrogen gas with a purity of 99.9% was introduced to replace the mixture and maintain a slightly positive pressure nitrogen atmosphere in the mixing chamber. High-speed stirring was started, and the stirring paddle speed was set to 2000 rpm, so that the material temperature of the mixing system increased at a rate of 12℃ / min. When the actual material temperature reached 150.0℃, the temperature was maintained and mixed for 18 minutes. After the temperature was maintained, the bottom discharge valve was opened to discharge the material into a low-speed cold mixer with a water-cooled jacket, where it was cooled to 25℃ at a speed of 75 rpm to obtain antioxidant-EBS complex masterbatch.

[0035] Preparation Example 2:

[0036] This preparation example provides an antioxidant-EBS complex masterbatch, comprising the following steps:

[0037] 1000g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 2000g of ethylene bis-stearamide were added to a high-speed mixer with a temperature-controlled jacket. Nitrogen gas with a purity of 99.9% was introduced to replace the mixture and maintain a slightly positive pressure nitrogen atmosphere in the mixing chamber. High-speed stirring was started, and the stirring paddle speed was set to 1500 rpm. The jacket heating was activated to increase the temperature of the mixed system at a rate of 10℃ / min. When the actual temperature of the material reached 145.0℃, it was kept at this temperature for 15 minutes. After the temperature was kept constant, the bottom discharge valve was opened to discharge the material into a low-speed cold mixer with a water-cooled jacket. The mixture was cooled to 20℃ at a speed of 50 rpm to obtain antioxidant-EBS complex masterbatch.

[0038] Preparation Example 3:

[0039] This preparation example provides an antioxidant-EBS complex masterbatch, comprising the following steps:

[0040] 1000g of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 2000g of ethylene bis-stearamide were added to a high-speed mixer with a temperature-controlled jacket. Nitrogen gas with a purity of 99.9% was introduced to replace the mixture and maintain a slightly positive pressure nitrogen atmosphere in the mixing chamber. High-speed stirring was started, and the stirring paddle speed was set to 2500 rpm, so that the material temperature of the mixing system increased at a rate of 15℃ / min. When the actual material temperature reached 155.0℃, it was kept at this temperature for 20 minutes. After the temperature was kept constant, the bottom discharge valve was opened to discharge the material into a low-speed cold mixer with a water-cooled jacket, where it was cooled to 30℃ at a speed of 100 rpm to obtain antioxidant-EBS complex masterbatch.

[0041] Example 1:

[0042] This embodiment provides a low dielectric loss polyolefin insulating material and its preparation method, including the following steps: 85.0 parts of isotactic polypropylene, 15.0 parts of ethylene-1-octene copolymer, 7.5 parts of fully hydrogenated alicyclic petroleum resin, and 0.2 parts of dimethyl dibenzyl sorbitol are added to a low-speed mixer and dry-mixed at 400 rpm for 8 minutes at 25°C to obtain a matrix physical mixture; a co-rotating parallel twin-screw extruder with a length-to-diameter ratio of 44:1 is used, and the temperatures of each heating section from the feed port to the die head are set sequentially as follows: Zone 1 165°C, Zone 2 185°C, Zone 3 200°C, Zone 4 205°C, Zone 5 205°C, and Zone 6 200°C, with the die head temperature set to 205°C; the twin-screw extruder is started, the screw speed is set to 200 rpm, and the matrix physical mixture is added through a main loss-in-weight feeder. The main feed inlet of the extruder; 3.0 parts of the antioxidant-EBS complex masterbatch prepared in Preparation Example 1 are added to the side feeder. After the matrix material reaches a molten state in the extruder barrel, the complex masterbatch is continuously pressed into the three-zone melt of the extruder for in-situ mixing through the side feed screw; the extruded material is extruded through the die head to form a continuous melt strip with a diameter of 2.5 mm; the strip is sequentially annealed in two independently temperature-controlled air bath traction channels. The ambient temperature of the first annealing section is controlled at 115.0℃ and the residence time is controlled at 4.0 min. The ambient temperature of the second annealing section is controlled at 75.0℃ and the residence time is controlled at 4.0 min; after the stepped annealing, the strip enters the room temperature air cooling zone to cool to 25℃ and is cut by a rotary pelletizer to obtain cylindrical insulating material particles with a length of 3.5 mm.

[0043] Example 2:

[0044] This embodiment provides a low dielectric loss polyolefin insulating material and its preparation method, including the following steps: 90.0 parts of isotactic polypropylene, 10.0 parts of ethylene-1-octene copolymer, 5.0 parts of fully hydrogenated alicyclic petroleum resin, and 0.1 parts of dimethyl dibenzyl sorbitol are added to a low-speed mixer and dry-mixed at 300 rpm for 5 minutes at 20°C to obtain a matrix physical mixture; a co-rotating parallel twin-screw extruder with a length-to-diameter ratio of 40:1 is used, and the temperatures of each heating section from the feed port to the die head are set sequentially as follows: Zone 1 160°C, Zone 2 180°C, Zone 3 195°C, Zone 4 200°C, Zone 5 200°C, and Zone 6 195°C, with the die head temperature set to 200°C; the twin-screw extruder is started, the screw speed is set to 150 rpm, and the matrix physical mixture is added through a main loss-in-weight feeder. The main feed inlet of the extruder; 1.5 parts of the antioxidant-EBS complex masterbatch prepared in Preparation Example 2 are added to the side feeder. After the matrix material reaches a molten state in the extruder barrel, the complex masterbatch is continuously pressed into the three-zone melt of the extruder through the side feed screw for in-situ mixing; the extruded material is extruded through the die head to form a continuous melt strip with a diameter of 2.0 mm; the strip is sequentially annealed in two independently temperature-controlled air bath traction channels. The ambient temperature of the first annealing section is controlled at 110.0℃ and the residence time is controlled at 3.0 min. The ambient temperature of the second annealing section is controlled at 70.0℃ and the residence time is controlled at 3.0 min; after the stepped annealing, the strip enters the room temperature air cooling zone to cool to 25℃ and is cut by a rotary pelletizer to obtain cylindrical insulating material particles with a length of 3.0 mm.

[0045] Example 3:

[0046] This embodiment provides a low dielectric loss polyolefin insulating material and its preparation method, including the following steps: 80.0 parts of isotactic polypropylene, 20.0 parts of ethylene-1-octene copolymer, 10.0 parts of fully hydrogenated alicyclic petroleum resin, and 0.3 parts of dimethyl dibenzyl sorbitol are added to a low-speed mixer and dry-mixed at 500 rpm for 10 minutes at 30°C to obtain a matrix physical mixture; a co-rotating parallel twin-screw extruder with a length-to-diameter ratio of 48:1 is used, and the temperatures of each heating section from the feed port to the die head are set sequentially as follows: Zone 1 170°C, Zone 2 190°C, Zone 3 205°C, Zone 4 210°C, Zone 5 210°C, and Zone 6 205°C, with the die head temperature set to 210°C; the twin-screw extruder is started, the screw speed is set to 250 rpm, and the matrix physical mixture is fed through a main loss-in-weight feeder. The antioxidant-EBS complex masterbatch prepared in Preparation Example 3 was added to the main feed inlet of the extruder. 4.5 parts of the masterbatch was added to the side feeder. Once the matrix material reached a molten state in the extruder barrel, the masterbatch was continuously pressed into the three-zone melt of the extruder via the side feed screw for in-situ mixing. The extruded material was extruded through the die head to form a continuous melt strip with a diameter of 3.0 mm. The strip underwent stepped annealing through two independently temperature-controlled air bath traction channels. The ambient temperature of the first annealing stage was controlled at 120.0℃, and the residence time was controlled at 5.0 min. The ambient temperature of the second annealing stage was controlled at 80.0℃, and the residence time was controlled at 5.0 min. After stepped annealing, the strip was cooled to 25℃ in a room temperature air-cooling zone and cut using a rotary pelletizer to obtain cylindrical insulating material particles with a length of 4.0 mm.

[0047] Example 4:

[0048] This embodiment provides a low dielectric loss polyolefin insulating material and its preparation method, including the following steps: 85.0 parts of isotactic polypropylene, 15.0 parts of ethylene-1-octene copolymer, 7.5 parts of fully hydrogenated alicyclic petroleum resin, and 0.2 parts of dimethyl dibenzyl sorbitol are added to a low-speed mixer and dry-mixed at 400 rpm for 8 minutes at 25°C to obtain a matrix physical mixture; a co-rotating parallel twin-screw extruder with a length-to-diameter ratio of 44:1 is used, and the temperatures of each heating section from the feed port to the die head are set sequentially as follows: Zone 1 165°C, Zone 2 185°C, Zone 3 200°C, Zone 4 205°C, Zone 5 205°C, and Zone 6 200°C, with the die head temperature set to 205°C; the twin-screw extruder is started, the screw speed is set to 200 rpm, and the matrix physical mixture is added through a main loss-in-weight feeder. The main feed inlet of the extruder; 3.0 parts of the antioxidant-EBS complex masterbatch prepared in Preparation Example 1 are added to the side feeder. After the matrix material reaches a molten state in the extruder barrel, the complex masterbatch is continuously pressed into the three-zone melt of the extruder for in-situ mixing through the side feed screw; the extruded material is extruded through the die head to form a continuous melt strip with a diameter of 2.5 mm; the strip is sequentially annealed in two independently temperature-controlled air bath traction channels. The ambient temperature of the first annealing section is controlled at 115.0℃ and the residence time is controlled at 3.0 min. The ambient temperature of the second annealing section is controlled at 75.0℃ and the residence time is controlled at 3.0 min; after the stepped annealing, the strip enters the room temperature air cooling zone to cool to 25℃ and is cut by a rotary pelletizer to obtain cylindrical insulating material particles with a length of 3.5 mm.

[0049] Example 5:

[0050] This embodiment provides a low dielectric loss polyolefin insulating material and its preparation method, including the following steps: 85.0 parts of isotactic polypropylene, 15.0 parts of ethylene-1-octene copolymer, 7.5 parts of fully hydrogenated alicyclic petroleum resin, and 0.2 parts of dimethyl dibenzyl sorbitol are added to a low-speed mixer and dry-mixed at 400 rpm for 8 minutes at 25°C to obtain a matrix physical mixture; a co-rotating parallel twin-screw extruder with a length-to-diameter ratio of 44:1 is used, and the temperatures of each heating section from the feed port to the die head are set sequentially as follows: Zone 1 165°C, Zone 2 185°C, Zone 3 200°C, Zone 4 205°C, Zone 5 205°C, and Zone 6 200°C, with the die head temperature set to 205°C; the twin-screw extruder is started, the screw speed is set to 200 rpm, and the matrix physical mixture is added through a main loss-in-weight feeder. The main feed inlet of the extruder; 3.0 parts of the antioxidant-EBS complex masterbatch prepared in Preparation Example 1 are added to the side feeder. After the matrix material reaches a molten state in the extruder barrel, the complex masterbatch is continuously pressed into the three-zone melt of the extruder for in-situ mixing through the side feed screw; the extruded material is extruded through the die head to form a continuous melt strip with a diameter of 2.5 mm; the strip is sequentially annealed in two independently temperature-controlled air bath traction channels. The ambient temperature of the first annealing section is controlled at 115.0℃ and the residence time is controlled at 5.0 min. The ambient temperature of the second annealing section is controlled at 75.0℃ and the residence time is controlled at 5.0 min; after the stepped annealing, the strip enters the room temperature air cooling zone to cool to 25℃ and is cut by a rotary pelletizer to obtain cylindrical insulating material particles with a length of 3.5 mm.

[0051] Comparative Example 1:

[0052] Compared with Example 1, the differences are as follows: ethylene bis-stearamide, fully hydrogenated alicyclic petroleum resin and dimethyl dibenzyl sorbitol are not added to the formulation; the preparation step of antioxidant-EBS complex masterbatch and the step-annealing step are omitted in the preparation process; 1.0 part of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is added directly in the initial dry mixing stage of the matrix; the extruded strip is directly placed into a 25°C room temperature water bath for rapid cooling and shaping; all other aspects are the same.

[0053] Comparative Example 2:

[0054] Compared with Example 1, the difference is that: ethylene bis-stearamide is not added to the formulation; the preparation step of antioxidant-EBS complex masterbatch is omitted in the preparation process, and 1.0 part of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is directly added in the initial dry mixing stage of the matrix, and the rest are the same.

[0055] Comparative Example 3:

[0056] The difference from Example 1 is that no fully hydrogenated alicyclic petroleum resin is added to the formulation, but all other aspects are the same.

[0057] Comparative Example 4:

[0058] The difference from Example 1 is that dimethyl dibenzyl sorbitol is not added to the formulation, but all other aspects are the same.

[0059] Comparative Example 5:

[0060] Compared with Example 1, the difference is that the preparation step of antioxidant-EBS complex masterbatch is omitted in the preparation process. Instead, 1.0 part of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 2.0 part of ethylene bis-stearamide are directly added and mixed in the initial dry mixing stage of the matrix and fed uniformly through the main feed port of the twin-screw extruder. All other aspects are the same.

[0061] Comparative Example 6:

[0062] Compared with Example 1, the difference is that after the extruded material is extruded through the die head in the preparation process, it is not subjected to stepped annealing, but is directly placed into a 25°C room temperature water bath for rapid cooling and shaping. All other aspects are the same.

[0063] Test Example 1

[0064] This test uses Fourier transform infrared spectroscopy to examine the changes in the molecular structure of the pure component and the premixed masterbatch, and to verify the construction of the hydrogen bond network between the antioxidant and ethylene bis-stearamide.

[0065] Pure pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] powder, pure ethylene bis-stearamide powder, the antioxidant-EBS complex masterbatch obtained in Preparation Example 1, and the polyolefin insulating materials prepared in each example and comparative example were taken. The polyolefin insulating materials were cryogenically pulverized into powder by liquid nitrogen for later use. Samples were prepared using the potassium bromide tableting method. 1.4 mg to 1.7 mg of the powder sample to be tested was weighed and 165 mg to 185 mg of dry pure potassium bromide powder was added. The powder was then ground evenly in an agate mortar. The ground powder was placed in a tablet press and pressed into thin sheets at a pressure of 10.5 MPa. The Fourier transform infrared spectrometer was turned on, and the scanning wavenumber range was set to 4000 cm⁻¹ to 400 cm⁻¹, the spectral resolution was 4 cm⁻¹, and the number of scans was 32. After performing a background scan on the pure potassium bromide blank pellet, each sample pellet was placed in the optical path for transmission spectral scanning. The transmittance and corresponding wavenumber data were recorded, and the characteristic absorption peak positions of specific functional groups in each sample were extracted.

[0066] The characteristic absorption peak positions of specific functional groups in each sample were extracted using the infrared spectrometer's accompanying software and recorded in Table 1.

[0067] Table 1. Peak position data of infrared characteristic absorption peaks of pure components and complex masterbatches

[0068] Sample Name Phenolic hydroxyl OH stretching vibration peak / cm⁻¹ Ester group C=O stretching vibration peak / cm⁻¹ Amide NH stretching vibration peak / cm⁻¹ Amide C=O stretching vibration peak / cm⁻¹ Pure antioxidant 1010 3645.7 1741.2 / / Pure ethylene bis-stearamide / / 3297.8 1643.1 Preparation of Complex Masterbatch in Example 1 3411.3 1737.5 3283.4 1631.8 Example 1 3414.2 1738.6 3285.1 1633.5 Example 2 3415.8 1739.1 3286.4 1634.2 Example 3 3412.5 1737.9 3284.2 1632.7 Example 4 3414.7 1738.4 3285.5 1633.9 Example 5 3413.9 1738.2 3284.8 1633.1 Comparative Example 1 3643.5 1740.8 / / Comparative Example 2 3644.1 1741.0 / / Comparative Example 3 3416.3 1739.5 3287.1 1635.4 Comparative Example 4 3415.9 1739.2 3286.8 1634.9 Comparative Example 5 3638.2 1740.1 3294.5 1641.7 Comparative Example 6 3422.4 1739.8 3289.3 1636.5

[0069] The absorption peak of the OH stretching vibration of the free phenolic hydroxyl group in the structure of pure antioxidant 1010 is located at 3645.7 cm⁻¹. After premixing, the OH stretching vibration peak in Preparation Example 1 shifted to 3411.3 cm⁻¹. The free amide C=O stretching vibration peak of pure ethylene bis-stearamide is located at 1643.1 cm⁻¹, shifting to 1631.8 cm⁻¹ in Preparation Example 1; the amide NH stretching vibration peak shifted from 3297.8 cm⁻¹ to 3283.4 cm⁻¹. In the insulating materials of Examples 1 to 5, all characteristic absorption peaks maintained the same redshift state. In Comparative Examples 1 and 2, without the addition of ethylene bis-stearamide, the phenolic hydroxyl OH stretching vibration peak remained in the high wavenumber region above 3643 cm⁻¹; in Comparative Example 5, the premixing step was omitted and the peaks were directly blended, resulting in a significant reduction in the shift amplitude of each characteristic peak.

[0070] The redshift of the characteristic absorption peak towards lower wavenumbers is a spectral feature of hydrogen bond formation. Under high temperature and shear conditions, the phenolic hydroxyl group of the antioxidant undergoes non-covalent interaction with the amide group of ethylene bis-stearamide. The phenolic hydroxyl group acts as a hydrogen bond donor, and the hydrogen atom and the amide carbonyl oxygen atom, which acts as a hydrogen bond acceptor, undergo electron cloud density rearrangement, weakening the force constants of the OH bond and C=O bond, resulting in a decrease in stretching vibration energy and a drop in absorption frequency.

[0071] Test results show that the premixing process forms a hydrogen bond network between the antioxidant and ethylene bis-stearamide, and this network persists in the polymer matrix of the insulating material after melt extrusion. When polyolefin insulating materials are subjected to an alternating electric field, polar groups are prone to orientation polarization reversal in the amorphous region of the polymer, resulting in dielectric loss. The hydrogen bond network physically constrains the polar groups, raising the activation energy barrier for spatial rotation and making the dipole relaxation time longer than the period of the high-frequency alternating electric field. The high-frequency electric field cannot drive the polar groups to undergo homing reversal, thus suppressing the orientation polarization process and reducing the high-frequency dielectric loss of the material.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low dielectric loss polyolefin insulating material, characterized in that, The insulating material is made from the following raw materials in parts by weight: isotactic polypropylene: 80.0-90.0 parts; ethylene-1-octene copolymer: 10.0-20.0 parts; polar antioxidant: 0.5-1.5 parts; hydrogen bond network building agent: 1.0-3.0 parts; fully hydrogenated alicyclic petroleum resin: 5.0-10.0 parts; amorphous region concentration triggering agent: 0.1-0.3 parts; wherein the polar antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; the hydrogen bond network building agent is ethylene bis-stearamide; and the amorphous region concentration triggering agent is dimethyl dibenzyl sorbitol.

2. The low dielectric loss polyolefin insulating material according to claim 1, characterized in that, The raw materials are in the following weight proportions: 85.0 parts isotactic polypropylene; 15.0 parts ethylene-1-octene copolymer; 1.0 part polar antioxidant; 2.0 parts hydrogen bond network building agent; and 7.5 parts fully hydrogenated alicyclic petroleum resin. 0.2 parts of amorphous region concentration trigger.

3. The low dielectric loss polyolefin insulating material according to claim 1, characterized in that, The isotactic polypropylene has an isotacticity greater than or equal to 97%, a crystallinity of 50% to 65%, and a melt mass flow rate of 2.0 to 4.0 g / 10 min under conditions of 230°C and 2.16 kg load; the ethylene-1-octene copolymer has a mass fraction of 20% to 30% of 1-octene copolymer units and a density of 0.865 to 0.875 g / cm³.

4. The low dielectric loss polyolefin insulating material according to claim 1, characterized in that, The fully hydrogenated alicyclic petroleum resin has a degree of hydrogenation greater than or equal to 99.5%, a bromine value less than or equal to 2.0 gI2 / 100 g, and a ring and ball softening point of 120.0–140.0 °C.

5. The low dielectric loss polyolefin insulating material according to claim 1, characterized in that, The polar antioxidant has a purity of ≥98.0% and a melting point of 110.0–125.0℃; the hydrogen bond network building agent has a purity of ≥98.0%, a total amine value of ≤3.0mgKOH / g, an acid value of ≤7.0mgKOH / g, and a melting point of 140.0–146.0℃.

6. A method for preparing the low dielectric loss polyolefin insulating material according to any one of claims 1-5, characterized in that, Includes the following steps: S1. The polar antioxidant and the hydrogen bond network building agent are placed in a mixer and an antioxidant-EBS complex masterbatch is prepared under heating and shearing conditions. S2. The isotactic polypropylene, ethylene-1-octene copolymer, fully hydrogenated alicyclic petroleum resin and amorphous region concentration trigger are mixed evenly to prepare a matrix physical mixture. S3. The matrix physical mixture prepared in step S2 is fed into the main feed port of a twin-screw extruder, and the antioxidant-EBS complex masterbatch prepared in step S1 is fed into the side feeder of the twin-screw extruder. The mixture is in situ mixed at a melt temperature of 190-210°C and extruded into a melt strip. S4. The extruded melt strip is subjected to stepped temperature-controlled annealing in the first annealing section and the second annealing section, and then cooled and pelletized to obtain a low dielectric loss polyolefin insulating material.

7. The method for preparing the low dielectric loss polyolefin insulating material according to claim 6, characterized in that, In step S1, the specific process parameters for preparing the antioxidant-EBS complex masterbatch are as follows: under a slightly positive pressure nitrogen atmosphere, the stirring speed is controlled at 1500-2500 rpm, so that the material temperature of the mixing system rises at a rate of 10-15℃ / min; when the actual material temperature reaches 145.0-155.0℃, the temperature is maintained at this constant temperature for 15-20 min, and then cooled to 20-30℃.

8. The method for preparing the low dielectric loss polyolefin insulating material according to claim 6, characterized in that, In step S3, the length-to-diameter ratio of the twin-screw extruder is 40:1 to 48:1, and the screw speed is 150 to 250 rpm. After the matrix physical mixture reaches a completely molten state in the barrel of the twin-screw extruder, the antioxidant-EBS complex masterbatch is continuously pressed into the melt.

9. The method for preparing the low dielectric loss polyolefin insulating material according to claim 6, characterized in that, In step S4, the specific process parameters for stepped temperature-controlled annealing are as follows: the ambient temperature of the first annealing section is 110.0~120.0℃, and the residence time of the material strip in the first annealing section is 3.0~5.0min; the ambient temperature of the second annealing section is 70.0~80.0℃, and the residence time of the material strip in the second annealing section is 3.0~5.0min.

10. The method for preparing the low dielectric loss polyolefin insulating material according to claim 6, characterized in that, In step S2, the mixing is performed by dry mixing at a speed of 300-500 rpm for 5-10 minutes at a room temperature of 20-30°C.

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