Preparation method, material and application of ethylene propylene rubber blended insulating material

Abstract

The invention relates to an ethylene propylene rubber blending insulating material preparation method, material and application, and the method comprises the following steps: weighing ethylene propylene diene monomer, isotatic polypropylene, an inorganic filler and an auxiliary agent, carrying out melt blending on the ethylene propylene diene monomer and the isotatic polypropylene in a torque rheometer at 170-190 DEG C and 30-60 r / min, sequentially adding the inorganic filler and the auxiliary agent, shearing for 10-15 minutes until the torque is stable, and carrying out extrusion molding to obtain the ethylene propylene rubber blending insulating material. Discharging and granulating to obtain particles, and uniformly introducing dicumyl peroxide into the particles by adopting an infiltration method to obtain particles in which the vulcanizing agent is pre-distributed; and putting the granules into a mold, pre-pressing for 5-10 minutes at 120 DEG C and 20 MPa, then transferring to a press vulcanizer, carrying out hot pressing and exhausting for 5 times at 160-200 DEG C and 20 MPa, continuously vulcanizing for 5-10 minutes, cooling and demolding to obtain the flaky blended rubber sheet.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment technology, and in particular to a method for preparing, materials for, and applications of ethylene propylene rubber blended insulation materials. Background Technology

[0002] The safe and reliable operation of electrical equipment, such as cables for offshore wind turbine torsion carriers, places comprehensive demands on insulation materials, requiring high breakdown field strength, high volume resistivity, controllable thermal conductivity, and stability over a wide temperature range. Existing rubber-based insulation materials often struggle to achieve this balance under operating conditions of 25–90°C: maintaining flexibility and fatigue resistance while ensuring stable insulation and heat dissipation performance under elevated temperatures.

[0003] When isotactic polypropylene is introduced into EPDM rubber to form a blend system, the performance improvement is accompanied by a structural trade-off: as the isotactic polypropylene content increases, the crystallinity of the material increases and the interphase interface layer thickens, the diffusion, entanglement and adsorption of interfacial chain segments are enhanced, which can serve as "crystallization physical crosslinking points + interfacial constraints" to jointly enhance interchain interactions, thereby significantly improving strength, breakdown field strength, volume resistivity and thermal conductivity, and the improvement is more obvious at high temperatures; however, at the same time, it will cause a decrease in elongation at break and elasticity, and may lead to an increase in dielectric loss, forming an inherent contradiction between "strengthening and toughness" and "insulation and loss".

[0004] The information disclosed in the background section is only for enhancing the understanding of the background of this invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] This invention provides a method for preparing an ethylene propylene rubber blended insulating material, the material itself, and its applications. An appropriate amount of isotactic polypropylene is compounded into a ternary ethylene propylene rubber matrix, and a melt-blending and molding method is used to ensure that the distributed crystalline physical crosslinking points and the synergistic effect of the two-phase interface layer are within a controllable range, forming a stable mesoscopic structural network. Under this structural constraint, the material achieves synergistic improvement in mechanical, dielectric, and thermal properties and temperature stability within the temperature range of 25℃ to 90℃; and achieves a comprehensive balance of mechanical, dielectric, and thermal properties while maintaining flexibility.

[0006] A method for preparing an ethylene propylene rubber blend insulation material includes:

[0007] Step a: Weigh out EPDM rubber, isotactic polypropylene, inorganic fillers and additives, wherein the mass fraction of isotactic polypropylene is 0% to 15%, and the additives include antioxidants and paraffin wax.

[0008] Step b: Ethylene propylene diene monomer (EPDM) rubber and isotactic polypropylene (IPM) are melt-blended in a torque rheometer at 170–190℃ and 30–60 r / min. Inorganic fillers and additives are added sequentially, and the mixture is sheared for 10–15 minutes until the torque stabilizes. The mixture is then discharged and granulated to obtain particles. During the blending process, IPM forms a microcrystalline structure and serves as a physical crosslinking point. Combined with the segment diffusion, entanglement, and adsorption of the two-phase interface layer of EPDM rubber and IPM, a mesoscopic network structure with enhanced inter-chain interaction and defect suppression capabilities is constructed.

[0009] Step c: Dicumyl peroxide is uniformly introduced into the granules using an impregnation method to obtain granules with pre-distributed vulcanizing agent;

[0010] Step d: Place the granules in a mold and pre-press at 120°C and 20MPa for 5–10 minutes. Then transfer them to a flat vulcanizing machine and hot-press and degas 5 times at 160–200°C and 20MPa. Continue vulcanizing for 5–10 minutes, cool and demold to obtain sheet-like blended rubber sheets.

[0011] In the method for preparing an ethylene propylene rubber blend insulation material, in step b, ethylene propylene rubber is first added and allowed to soften before isotactic polypropylene and inorganic fillers are added in batches alternately.

[0012] In the method for preparing an ethylene propylene rubber blended insulating material, in step c, the amount of dicumyl peroxide is 1–3 parts per 100 parts of rubber.

[0013] In the method for preparing an ethylene propylene rubber blended insulating material, the inorganic filler is selected from at least one of surface-modified kaolin, nano zinc oxide, and lead oxide, and the total amount added is 5% to 20% of the total mass of the material.

[0014] In the method for preparing an ethylene propylene rubber blend insulation material, the inorganic filler is a surface-modified inorganic filler treated with a silane coupling agent or fatty acid to enhance its interfacial compatibility with the polymer matrix and reduce phase separation defects.

[0015] In the method for preparing an ethylene propylene rubber blend insulation material, the crystallinity of the material is 0.3% to 6.2%.

[0016] An ethylene propylene rubber blend insulation material is prepared according to the aforementioned method for preparing an ethylene propylene rubber blend insulation material.

[0017] The ethylene propylene rubber blend insulation material described above is composed of the following components in mass percentage:

[0018] EPDM rubber: 84.5%~99.5%;

[0019] Isotactic polypropylene: 0%–15%;

[0020] Inorganic fillers and additives: balance.

[0021] In the aforementioned ethylene propylene rubber blend insulation material, the isotactic polypropylene has a mass fraction of 5%, and the material simultaneously meets the following performance indicators within a temperature range of 25℃ to 90℃:

[0022] Tensile strength at 25℃ ≥12.5MPa, and at 90℃ ≥2.5MPa;

[0023] Volume resistivity at 90℃ ≥3.5×10¹³Ω·m;

[0024] At 25℃, the breakdown field strength is ≥39kV / mm and the decrease with increasing temperature is less than that of pure EPDM rubber.

[0025] Thermal conductivity at 25℃ ≥0.185W / (m·K), an improvement of ≥15% compared to pure EPDM rubber;

[0026] Elongation at break ≥400%.

[0027] An application of the ethylene propylene rubber blend insulation material in the field of electrical insulation, used to manufacture insulation layers for power cables, support components for gas-insulated switchgear, insulators for offshore wind power torsion cables, or insulating components in rail transit electrical systems.

[0028] Compared with existing technologies, this invention has the following advantages: The temperature stability of the structure of this invention is significantly improved, enabling the blended material to achieve a synergistic improvement in breakdown field strength, volume resistivity, and thermal conductivity with minimal fluctuations within the temperature range of 25℃ to 90℃, while obtaining higher tensile strength while ensuring necessary flexibility. Using 5% isotactic polypropylene as a representative ratio, within the temperature range of 25℃ to 90℃, the breakdown strength remains at 39kV / mm~44kV / mm, the resistivity at 3.76×10^13Ω·m~3.56×10^14Ω·m, the elongation at break at 400%~600%, the relative permittivity at 2.85~3.05, and the thermal conductivity at 0.185W / (m·K)~0.198W / (m·K). This achieves a synergistic improvement in mechanical, dielectric, and thermal properties and temperature stability; meeting the comprehensive requirements of strength, insulation, and processability for cables and electrical insulation components. Attached Figure Description

[0029] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0030] In the attached diagram:

[0031] Figure 1 This is a schematic diagram illustrating the bulk density test results at room temperature for EPDM rubber samples with different polypropylene content provided in one embodiment of this disclosure. Figure 1 In figure (a), the relationship between density and PP content is shown. Figure 1 (b) Relationship between crosslinking density and PP content;

[0032] Figure 2 This is a surface morphology diagram of ethylene propylene rubber with different PP contents provided in one embodiment of this disclosure;

[0033] Figure 3 (a) is the DSC curve of a blend system provided in an embodiment of this disclosure. Figure 3 Figure (b) is a schematic diagram showing the relationship between the crystallinity of the blend system and the PP content.

[0034] Figure 4 This is a schematic diagram illustrating the relationship between the tensile properties of ethylene propylene rubber with different PP contents and temperature, provided in one embodiment of this disclosure. Figure 4 In Figure (a), the relationship between tensile strength and temperature is shown. Figure 4 (b) Relationship between elongation at break and temperature; Figure 4 (c) shows the relationship between the elastic modulus and temperature;

[0035] Figure 5 This is a schematic diagram illustrating the relationship between the resistivity of ethylene propylene rubber with different PP contents and temperature, provided in one embodiment of this disclosure.

[0036] Figure 6 This is a schematic diagram illustrating the relationship between the breakdown field strength and temperature of ethylene propylene rubber with different PP contents according to an embodiment of this disclosure;

[0037] Figure 7 This is a schematic diagram illustrating the relationship between the relative permittivity, tanδ, and temperature of blended rubbers with different polypropylene content according to an embodiment of this disclosure. Figure 7 (a) Relationship between relative permittivity and temperature. Figure 7 (b) The relationship between tanδ and temperature;

[0038] Figure 8 This is a schematic diagram illustrating the relationship between the thermal conductivity and temperature of ethylene propylene rubber with different PP contents according to an embodiment of this disclosure.

[0039] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0040] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0041] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0042] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0043] like Figures 1 to 8 As shown, the preparation method of ethylene propylene rubber blend insulation material includes the following steps:

[0044] Step a, weigh EPDM rubber, isotactic polypropylene, inorganic filler and additives, wherein the mass fraction of isotactic polypropylene is 0% to 15%, and the additives include antioxidant (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) and paraffin wax;

[0045] Step b: Ethylene propylene diene monomer (EPDM) rubber and isotactic polypropylene (IPM) are melt-blended in a torque rheometer at 180°C and 60 r / min. Inorganic fillers and additives are added sequentially, and the mixture is sheared for 15 minutes until the torque stabilizes. The mixture is then discharged and granulated to obtain particles. During the blending process, IPM forms a microcrystalline structure and serves as a physical crosslinking point. Combined with the segment diffusion, entanglement, and adsorption of the two-phase interface layer of EPDM rubber and IPM, a mesoscopic network structure with enhanced inter-chain interaction and defect suppression capabilities is constructed.

[0046] Step c: Dicumyl peroxide is uniformly introduced into the granules using an impregnation method to obtain granules with pre-distributed vulcanizing agent;

[0047] Step d: Place the granules in a mold and pre-press them at 120°C and 20MPa for 10 minutes. Then transfer them to a flat vulcanizing machine and hot-press them at 180°C and 20MPa, venting them 5 times. Continue vulcanizing for 10 minutes, then cool and demold to obtain sheet-like blended rubber sheets.

[0048] In a preferred embodiment of the method for preparing an ethylene propylene rubber blend insulation material, in step b, ethylene propylene rubber is first added and allowed to soften before isotactic polypropylene and inorganic fillers are added in batches alternately.

[0049] In a preferred embodiment of the method for preparing an ethylene propylene rubber blend insulation material, in step c, the amount of dicumyl peroxide is 1–3 parts per 100 parts of rubber.

[0050] In a preferred embodiment of the method for preparing an ethylene propylene rubber blend insulation material, the inorganic filler is selected from at least one of surface-modified kaolin, nano zinc oxide, and lead oxide, and the total amount added is 5% of the total mass of the material.

[0051] In a preferred embodiment of the method for preparing an ethylene propylene rubber blend insulation material, the inorganic filler is a surface-modified inorganic filler treated with a silane coupling agent or fatty acid to enhance its interfacial compatibility with the polymer matrix and reduce phase separation defects.

[0052] In a preferred embodiment of the method for preparing an ethylene propylene rubber blend insulation material, the crystallinity of the material is 0.3% to 6.2%.

[0053] An ethylene propylene rubber blend insulation material is prepared according to the aforementioned method for preparing an ethylene propylene rubber blend insulation material.

[0054] The ethylene propylene rubber blend insulation material described above is composed of the following components in mass percentage:

[0055] EPDM rubber: 84.5%~99.5%;

[0056] Isotactic polypropylene: 0%–15%;

[0057] Inorganic fillers and additives: balance.

[0058] In the aforementioned ethylene propylene rubber blend insulation material, the isotactic polypropylene has a mass fraction of 5%, and the material simultaneously meets the following performance indicators within a temperature range of 25℃ to 90℃:

[0059] Tensile strength at 25℃ ≥12.5MPa, and at 90℃ ≥2.5MPa;

[0060] Volume resistivity at 90℃ ≥3.5×10¹³Ω·m;

[0061] At 25℃, the breakdown field strength is ≥39kV / mm and the decrease with increasing temperature is less than that of pure EPDM rubber.

[0062] Thermal conductivity at 25℃ ≥0.185W / (m·K), an improvement of ≥15% compared to pure EPDM rubber;

[0063] Elongation at break ≥400%.

[0064] An application of an ethylene propylene rubber blend insulation material in the field of electrical insulation, used to manufacture insulation layers for power cables, support components for gas-insulated switchgear, insulation for offshore wind power torsion cables, or insulation components in rail transit electrical systems.

[0065] In one embodiment, an ethylene propylene rubber blend insulation material with synergistically regulated isotactic polypropylene content is composed of ethylene propylene diene monomer (EPDM) and isotactic polypropylene (iPP), wherein the mass fraction of iPP is 0% to 15%, and the remainder is EPDM and conventional additives; the blend material has a mesoscopic structure formed by the interleaved distribution of iPP crystalline regions and EPDM amorphous regions, wherein the iPP crystalline structure is distributed in the EPDM matrix as "physical crosslinking points" and forms molecular chain entanglement and adsorption structures at the two-phase interface layer, which is used to synergistically improve the tensile strength, volume resistivity, breakdown field strength and thermal conductivity of the material.

[0066] In the aforementioned blended insulating material, the mass fraction of iPP is 5%, and within this range, the material achieves a comprehensive balance of mechanical, dielectric, and thermal properties within a temperature range of 25℃ to 90℃.

[0067] Tensile strength ≥12.5MPa (25℃), and maintains ≥2.5MPa at 90℃;

[0068] Volume resistivity ≥3.5×10¹³Ω·m (90℃);

[0069] The breakdown field strength is ≥39kV / mm (25℃) and the temperature stability is better than that of pure EPDM;

[0070] Thermal conductivity ≥0.185W / (m·K) (25℃), which is more than 15% higher than that of pure EPDM;

[0071] The elongation at break is ≥400%, maintaining good flexibility.

[0072] The blended insulating material further comprises at least one inorganic filler selected from surface-modified kaolin, nano zinc oxide, and lead oxide, as well as antioxidants, paraffin wax, and peroxide curing agents; the inorganic filler is surface-treated to enhance interfacial compatibility with the polymer matrix, and its content is 5–20 wt% of the total mass.

[0073] The blended insulating material contains 4–6% iPP by mass and exhibits stable breakdown field strength (≥39kV / mm), high volume resistivity (≥3.5×10¹³Ω·m@90℃) and improved thermal conductivity (≥0.185W / (m·K)) within a working temperature range of 25–90℃, making it suitable for electrical insulation in high-temperature and high-field-strength environments.

[0074] In the blended insulating material, the crystallinity of the material increases linearly with the increase of iPP content, and the crystallinity reaches about 3.5% when the iPP content is 5%. DSC test shows that there is an obvious melting endothermic peak near 150℃, indicating that iPP has successfully crystallized and participated in the formation of physical cross-linking network.

[0075] A method for preparing a blended insulating material includes the following steps:

[0076] (a) Weigh out EPDM, iPP, inorganic filler, antioxidant, paraffin and additives according to the formula;

[0077] (b) EPDM and iPP are melt-blended in a torque rheometer at 170–190°C and 30–60 r / min. Inorganic fillers and additives are added sequentially, and sheared for 10–15 minutes until the torque is stable. The mixture is then discharged and granulated.

[0078] (c) Dicumyl peroxide (DCP) is uniformly introduced into the obtained granules by impregnation method to obtain granules with pre-distributed vulcanizing agent;

[0079] (d) Place the granules in a mold and pre-press them at 120°C and 20MPa for 5–10 minutes. Then transfer them to a flat vulcanizing machine and hot-press them at 160–200°C and 20MPa for 5 times while venting. Continue vulcanizing for 5–10 minutes, then cool and demold to obtain sheet-like blended rubber sheets.

[0080] In the preparation method described above, in step (b), EPDM base material is first added and allowed to soften, and then iPP and inorganic fillers are added alternately in batches to promote uniform dispersion; in step (c), the amount of DCP used is 1-3 parts per 100 parts of rubber.

[0081] In the preparation method described above, a controllable amount of isotactic polypropylene (iPP) is added to EPDM. The microcrystalline structure formed by iPP during the blending process is used as a "physical cross-linking point". Combined with the chain segment diffusion, entanglement and adsorption of the EPDM / iPP two-phase interface layer, a mesoscopic network structure with enhanced inter-chain interaction and defect suppression ability is constructed. Thus, the mechanical strength, insulation performance and thermal conductivity of the material are improved simultaneously without significantly sacrificing toughness.

[0082] In the preparation method described above, the amount of iPP added is controlled within the range of 5wt% to achieve a significant improvement in tensile strength, volume resistivity, breakdown field strength and thermal conductivity, while keeping the increase in dielectric loss (tanδ) within an acceptable range and maintaining an elongation at break ≥400%.

[0083] The blended insulating material is used to manufacture insulation layers for power cables, supports for gas-insulated switchgear (GIS), insulators for offshore wind power torsion cables, or high-reliability insulating components in rail transit electrical systems.

[0084] In one embodiment, the blended insulating material is prepared as a EPDM / isotactic polypropylene blend film using melt blending and hot pressing. The processing temperature of EPDM is approximately 160–180°C, and the melting temperature of isotactic polypropylene is approximately 160–170°C; therefore, a molding temperature range of 170–190°C is used during processing. By adjusting the mass fraction of isotactic polypropylene from 0% to 15% (preferably approximately 5%), a mesoscopic structure synergistic between the dispersed crystalline region and the interface layer is constructed, thereby achieving a comprehensive improvement in mechanical, dielectric, and thermal properties, as well as temperature stability.

[0085] In one embodiment, the preparation method steps are as follows:

[0086] Weigh the EPDM rubber base material and isotactic polypropylene separately according to the target formula, and place the surface-modified kaolin, nano zinc oxide, and sieved lead oxide and other inorganic powders on clean weighing paper for later use; separately weigh appropriate amounts of paraffin wax and antioxidants. To ensure accurate proportioning, first prepare the organic phases (EPDM rubber and isotactic polypropylene) separately for use, and then prepare the inorganic fillers and additives, ensuring that the order of addition is consistent with the subsequent blending process;

[0087] The processing temperature was set to 170℃ and the rotation speed to 30 r / min in the torque rheometer. A small amount of EPDM rubber granules was first added to clean and lubricate the cavity. Then, the weighed EPDM base material was added according to the specified ratio. After it softened sufficiently by heating, isotactic polypropylene, surface-modified kaolin, antioxidant, and sieved lead oxide were added sequentially, alternating with the aforementioned inorganic fillers, allowing the material to fully melt and disperse under high shear for approximately 10 minutes. Subsequently, the equipment temperature was adjusted to 120℃, nano-zinc oxide was added, and shearing continued until the torque stabilized (reaching torque equilibrium). The material was then discharged and sheared into approximately 3mm particles, serving as intermediate material before molding.

[0088] Dicumyl peroxide (DCP) was uniformly introduced into the above-mentioned particles using an impregnation method, allowing the vulcanizing agent to be fully impregnated and distributed inside and on the surface of the particles, resulting in granular samples with good flowability and uniformity. This step is beneficial for the uniform vulcanization reaction during subsequent hot pressing, reducing the phenomenon of insufficient or excessive cross-linking in certain areas.

[0089] Calculate and weigh the required granules based on the mold cavity volume and the measured sample density, and evenly disperse them in the mold. Cover the top and bottom of the mold with polyester film and place it between steel plates to prevent sticking and facilitate demolding. Place the molded sample into a preheating device with a temperature of 120℃ and a pressure of 20MPa. Preheat for about 5 minutes to soften and initially spread the granules, and then apply pressure for about 5 minutes to pre-press the material into sheets, so that the material is evenly spread in the mold cavity, air gaps are eliminated, and the density is increased.

[0090] Transfer the steel plate containing the sample and the mold to a flat vulcanizing machine. Set the temperature to 180℃ (or select 160 / 180 / 200℃ as needed), and maintain the pressure at 20MPa. First, hot-press for approximately 5 minutes, then perform 5 venting operations to remove gases generated during vulcanization and prevent the formation of pores. After venting, continue hot-pressing for approximately 5 minutes to complete vulcanization and shaping. After hot-pressing, remove the steel plate and cool it using water cooling or other methods. Demold to obtain a square sheet of blended rubber.

[0091] This invention yields a polymer insulating material with a "dispersed crystalline region-interface layer synergy" mesoscopic structure. This mesoscopic structure is formed by the interlacing of crystalline lamellar layers of isotactic polypropylene and amorphous regions of EPDM rubber. Compared to the original EPDM rubber matrix, its temperature stability is significantly improved, enabling the blend to achieve a synergistic increase in breakdown field strength, volume resistivity, and thermal conductivity with minimal fluctuations within the temperature range of 25℃ to 90℃, while maintaining higher tensile strength while ensuring necessary flexibility. Using 5% isotactic polypropylene as a representative ratio, within the temperature range of 25℃ to 90℃, the breakdown strength remains at 39kV / mm to 44kV / mm, the resistivity at 3.76×10^13Ω·m to 3.56×10^14Ω·m, the elongation at break at 400% to 600%, the relative permittivity at 2.85 to 3.05, and the thermal conductivity at 0.185W / (m·K) to 0.198W / (m·K).

[0092] Example

[0093] Specific implementation examples include EPDM rubber / isotactic polypropylene polymer insulation materials (isotactic polypropylene iPP mass fraction of 0%, 2.5%, 5%, 10%, and 15%).

[0094] The polymer insulating material is prepared by melt blending and flat hot pressing (the molding temperature range is approximately 170–190°C).

[0095] The polymer insulating material has a two-phase interleaved mesoscopic structure, in which the crystalline structure of isotactic polypropylene acts as a physical cross-linking point, and the interface layer contains chain segment diffusion and entanglement.

[0096] The bulk density test results of EPDM rubber samples with different polypropylene content at room temperature are as follows: Figure 1 As shown in Figure (a), the density of isotactic polypropylene blended with EPDM rubber decreases slightly with increasing isotactic polypropylene content, from 1.21 g / cm³ at 0 PP to 1.11 g / cm³ at 15 PP. For high-voltage, thick-insulated wind power twisted cables, with a fixed insulation thickness, a higher insulation material density results in a heavier cable, significantly increasing the difficulty of construction, laying, maintenance, and cable replacement. Therefore, while ensuring insulation performance, a lower density results in a lighter cable, which is more beneficial for practical engineering applications.

[0097] The crosslinking density of ethylene propylene rubber with different PP contents was tested using the equilibrium swelling method. The crosslinking density of the ethylene propylene rubber samples was calculated by the mass change of the samples before and after swelling in cyclohexane for 168 hours. The test results are as follows: Figure 1As shown in (b), the results indicate that the crosslinking density of ethylene propylene rubber (EPR) decreases slightly with increasing PP content, from approximately 2.49 × 10⁻⁴ mol / cm³ with 0% PP to approximately 2.31 × 10⁻⁴ mol / cm³ with 15% PP. However, the overall change in crosslinking density is not significant, ranging from ±0.2 × 10⁻⁴ mol / cm³. Due to its inherent structure, PP is difficult to crosslink, so the crosslinking process is dominated by EPR. Specifically, under heat, the molecular bonds of the peroxide vulcanizing agent break, decomposing into highly reactive free radicals, namely alkoxy free radicals. These free radicals, due to their high reactivity, can substitute highly reactive hydrogen atoms in the side chain groups of EPR, thereby generating highly reactive vulcanization centers in the side chain. These vulcanization centers readily react with each other, coupling into high-bond-energy vulcanization bonds. The crosslinking density test results show that increasing PP content has no effect on the crosslinking process of EPR and has little impact on the connections between macromolecules in the EPR matrix structure.

[0098] The surface morphology of ethylene propylene rubber with different PP contents and the results of EDS energy dispersive spectroscopy are as follows: Figure 2 As shown, in the EPDM rubber system, polypropylene is uniformly distributed in the matrix as the dispersed phase. If the polypropylene / EPDM rubber or inorganic filler is severely incompatible with the matrix, it will weaken the interfacial molecular interactions and chain segment entanglement / adsorption, leading to filler-matrix separation, increased defects, and performance degradation. In the actual comparison, except for the different mass fraction of polypropylene, the type and amount of filler were the same; SEM / EDS (×1000) showed that a large amount of filler was uniformly distributed on the surface of each formulation. Except for some aggregation of nano zinc oxide due to size effect, there was no obvious accumulation, indicating that increasing the polypropylene content has no significant effect on the dispersion / accumulation behavior of the filler.

[0099] The heat flux curves of five EPDM rubbers with different PP contents were tested using differential scanning calorimetry. The test results are as follows: Figure 4 As shown in (a), the crystallinity was calculated by integrating the area of ​​the melt peak near the polypropylene crystallization melting temperature of 150℃. The calculation results are shown in Figure 1. Figure 4As shown in (b), with the increase of polypropylene content, the melting endothermic peak area near the crystallization temperature of polypropylene segments (150℃) continuously increases, meaning that the crystallinity of EPDM rubber continuously increases with the increase of PP content, from 0.32% at 0% PP to 6.11% at 15% PP. The crystallinity is basically linearly related to the increase of PP content. In addition, the crystallization melting temperature of the blended rubber is slightly increased. This is because during the cross-linking process of EPDM, the cross-linking network formed includes polypropylene, which to some extent restricts the movement of polypropylene molecular chains. At the same time, at the interface between the amorphous region of polypropylene and the contacting amorphous region of EPDM, molecular chain segments diffuse between the two phases, improving interfacial compatibility. Inorganic fillers such as nanoparticles further reduce the interfacial tension between the two phases, enhancing interfacial compatibility, ultimately resulting in an increase in the crystallization melting temperature.

[0100] The tensile properties of ethylene propylene rubber with different polypropylene content were tested using a universal testing machine at different temperatures (25℃, 50℃, 70℃, 90℃). The test results are as follows: Figure 4As shown. Tensile strength and elongation at break characterize the strength and toughness of a material. Higher tensile strength and elongation at break indicate better strength and toughness. Elastic modulus characterizes a material's ability to resist elastic deformation, i.e., its elasticity. A higher elastic modulus indicates greater stiffness and poorer elasticity. At different temperatures, the tensile strength of ethylene propylene rubber continuously increases with increasing PP content. At room temperature (around 25℃), it increases from 11.17 MPa with 0% PP to 14.07 MPa with 15% PP, an increase of 2.9 MPa. However, the elongation at break continuously decreases with increasing PP content. At 15% PP, the elongation at break is only 468.19%, a decrease of 203.6% compared to 671.83% with 0% PP, a significant decrease. The elastic modulus, representing material stiffness, also increases, rising from 2.24 MPa with 0% PP to [missing value]. The tensile strength and elastic modulus of ethylene propylene rubber increased by 24.64 MPa to 26.88 MPa, indicating a significant increase in material stiffness but a significant decrease in elasticity, which is detrimental to performance improvement. With increasing temperature, both the tensile strength and elastic modulus of ethylene propylene rubber decrease, while the elongation at break initially increases and then decreases. At a high temperature (90℃), the tensile strength increases from 1.24 MPa for 0% PP to 2.79 MPa for 15% PP, the elongation at break decreases from 313.73% for 0% PP to 278.31% for 15% PP, and the elastic modulus increases from 0.98 MPa for 0% PP to 2.34 MPa for 15% PP. All five ethylene propylene rubbers with different PP contents met the specified mechanical property standards of 300% minimum elongation at break and 6.5 MPa minimum tensile strength under normal temperature testing conditions. In general, the tensile strength increases slightly with the increase of PP content, and increases significantly when the PP content reaches 5%. The elongation at break decreases slightly with the increase of PP content, and decreases significantly after the PP content reaches 10%. The elastic modulus also increases significantly after the PP content reaches 10%.

[0101] The ratios of high-temperature and room-temperature parameters of various mechanical properties of ethylene propylene rubber with different PP contents were plotted as thermal stability parameters. Figure 5 As shown in the figure, the thermal stability of tensile strength increases with increasing PP content, while the thermal stability of elongation at break first increases and then decreases, and the thermal stability of elastic modulus continuously decreases. With increasing polypropylene content, polypropylene and EPDM rubber form an interpenetrating interface layer due to their good compatibility. Within the interface, chain segments diffuse and generate physical effects such as entanglement and adsorption. Furthermore, under the influence of peroxides, some chemical bonding may occur, enhancing the overall interaction between molecular chains. Simultaneously, the crystalline structure of polypropylene acts as a "physical cross-linking point," improving tensile strength. However, the reduced free slippage of chain segments decreases the material's ability to relieve stress, making it easier for microscopic damage to accumulate and transform into macroscopic cracks, leading to decreased toughness and elongation at break. Increased crystallinity also increases modulus and decreases elasticity. Considering strength, toughness, elasticity, and temperature stability, a polypropylene content of approximately 5% is preferable; excessively high content is detrimental.

[0102] The resistivity of EPDM rubber blends with different polypropylene content was tested. Before testing, the samples were wiped clean with anhydrous ethanol and dried. The entire test was conducted in a constant temperature oven. The resistivity of the samples was measured at four temperatures: 25℃, 50℃, 70℃, and 90℃, under the same conditions. The results are as follows: Figure 5 As shown. Combined with the aforementioned changes in crystallinity, increasing the mass percentage of polypropylene added is equivalent to increasing the length of the crystallizable molecular chain segments in the blend system. Therefore, the crystallinity of the blend system continuously increases, forming crystalline structures that act similarly to physical cross-linking points, strengthening the connection between molecular chains in the blend system, reducing defects in the system, and consequently increasing the resistivity of the system. The resistivity increases from 3.56 × 10¹⁴ Ω·m at 0% PP to 9.95 × 10¹⁴ Ω·m at 15% PP, an increase of 6.4 × 10¹⁴ Ω·m. With increasing test temperature, different PP contents... The resistivity of ethylene propylene rubber (EPR) decreases across the board. At a high temperature (90℃), the resistivity of 0% EPR decreases to 1.88 × 10¹³ Ω·m, and that of 15% EPR decreases to 9.06 × 10¹³ Ω·m, representing a significant decrease of more than an order of magnitude. However, the decrease is smaller for blended rubbers compared to pure EPR, with high-temperature resistivity dropping to 7%–9% of the room-temperature resistivity (increasing with increasing PP content). Pure EPR's resistivity at high temperatures is only 5%, meaning that increasing PP content can improve the resistivity of EPR at different temperatures and enhance its temperature stability. Volume resistivity depends on the number, mobility, and charge of charge carriers. Increasing temperature increases carrier concentration and mobility, leading to a near-linear decrease in resistivity with temperature. Increasing the polypropylene content thickens the interfacial layer and forms crystalline "physical cross-linking points," raising the transition barrier and inhibiting migration, thereby improving resistivity and its temperature stability; this constraint remains effective up to 90℃. For wind power special cables, higher resistivity can reduce temperature rise, reduce the risk of overheating and failure, and improve operational safety.

[0103] Figure 6 This describes the relationship between the breakdown field strength and temperature of EPDM rubber with different PP contents. The dielectric breakdown field strength is determined by both electrical and thermal breakdown. At the interface layer, polypropylene and EPDM rubber undergo segment penetration, entanglement, and adsorption, which restricts the movement of chain segments in the amorphous region, makes the chain arrangement more regular, and reduces filler-matrix interface defects. Simultaneously, polypropylene crystallization increases the degree of order. These two factors synergistically enhance the breakdown field strength, and as the polypropylene content increases, the interface layer and crystalline regions increase, further increasing the breakdown field strength. At approximately 90℃, the above structure remains relatively stable; therefore, the breakdown field strength is still higher than that of pure EPDM rubber, and the temperature stability also increases with increasing polypropylene content.

[0104] The dielectric constant and loss temperature spectra of EPDM rubber blends with different polypropylene content were tested, and the test results are as follows: Figure 7As shown, with increasing polypropylene content, the dielectric constant of EPDM rubber decreases, which is beneficial for a more uniform electric field within the cable and an improved insulation utilization coefficient. Dielectric loss generally shows an upward trend, but the rate of increase gradually decreases. This is because the interaction between polypropylene crystallization and the two-phase interface layer makes the molecular chains more regular, restricts chain segment orientation and residual polarization, and suppresses leakage current. Simultaneously, the obstruction of dipole orientation leads to a certain increase in loss at low to medium content levels. In summary, a balance should be struck between the benefits of reduced dielectric constant and the costs of increased loss, and an appropriate polypropylene content of approximately 5% is recommended.

[0105] The thermal conductivity of ethylene propylene rubber blends with different PP contents was tested, and the test results are as follows: Figure 8 As shown in the figure, the results indicate that the thermal conductivity of ethylene propylene rubber (EPR) increases with increasing PP content at different temperatures. At room temperature (25℃), the thermal conductivity of EPR increases from 0.163 (W / (m·K)) with 0% PP to 0.354 (W / (m·K)) with 15% PP. At 50℃, the thermal conductivity increases from 0.157 (W / (m·K)) with 0% PP to 0.339 (W / (m·K)) with 15% PP. At 70℃, the thermal conductivity increases from 0.15 (W / (m·K)) with 0% PP to 0.322 (W / (m·K)) with 15% PP. Further increasing the temperature to 90℃, the thermal conductivity increases from 0.137 (W / (m·K)) with 0% PP to 0.306 (W / (m·K)) with 15% PP. However, the thermal conductivity of EPDM rubbers with varying PP content decreases with increasing temperature. Overall, blends with high PP content exhibit higher thermal conductivity at all temperatures, which is beneficial for the application of EPDM rubber in cable insulation materials.

[0106] Examples show that the addition of 5% by mass of isotactic polypropylene can improve the overall performance of the blend. Specifically:

[0107] (1) The mechanical, dielectric, and thermal properties of the blended materials change monotonically with the addition of isotactic polypropylene, specifically showing an improvement in dielectric properties, thermal properties, and tensile strength, as well as a deterioration in elongation at break and modulus of elasticity. Considering the requirements of wind power torsion cables for the elongation at break and modulus of elasticity of ethylene propylene rubber materials, it is believed that the ethylene propylene rubber blend system with 5% isotactic polypropylene has the best comprehensive performance. Compared with the one without isotactic polypropylene, its tensile strength at 25℃ and 90℃ increased by 13% and 47%, respectively; its breakdown field strength increased by 23% and 32%, respectively; its resistivity increased by 10% and 75%, respectively; and its thermal conductivity increased by 19% and 27%, respectively.

[0108] (2) As the content of isotactic polypropylene increases, the interfacial layer formed between the isotactic polypropylene and EPDM rubber molecular chains also increases accordingly. Diffusion occurs between the two-phase chain segments or molecular chains within the interfacial layer, generating interactions, including physical effects such as molecular chain entanglement and adsorption, as well as cross-linking reactions involving peroxides. These effects enhance the connections between macromolecules in the EPDM rubber system, thereby restricting the movement of macromolecular chain segments. On the other hand, the crystalline structure formed by isotactic polypropylene acts as a physical cross-linking point, enhancing the tensile strength, insulation properties, and thermal conductivity of the blend system while leading to a deterioration in the toughness, elasticity, and dielectric loss properties of the EPDM rubber. Therefore, to ensure the elasticity and toughness of the blended rubber, the content of isotactic polypropylene should not be too high. When the mass fraction of isotactic polypropylene is 5%, the various properties of the EPDM rubber can be significantly improved.

[0109] Isotactic polypropylene (iPP) was selected as the functional modifying phase and introduced into an ethylene propylene diene monomer (EPDM) matrix to form a two-phase blend structure. Utilizing the high crystallinity of iPP, distributed microcrystalline regions were formed in the amorphous EPDM matrix, serving as "physical crosslinking points" to enhance the interaction between molecular chains. A mesoscopic network structure with a synergistic "crystallization-interface" relationship was constructed. The iPP crystalline regions formed a physical crosslinking network in EPDM, improving mechanical strength and thermal stability. Molecular chain diffusion, entanglement, and adsorption occurred at the interface between the EPDM and iPP phases, forming a thickened interface layer, reducing phase separation and defects, and improving interfacial bonding. Synergistic performance improvement: Comprehensive optimization of mechanical, dielectric, and thermal properties was achieved. It was found that the optimal overall performance was achieved when the iPP mass fraction was 4–6%. Too low (<4%) resulted in limited reinforcement; too high (>10%) led to a sharp decrease in toughness, a dramatic increase in elastic modulus, and an increase in dielectric loss.

[0110] Furthermore, iPP, as a highly crystalline polymer, forms nano- to micron-scale lamellar structures within an amorphous EPDM matrix during melt blending and cooling. These crystalline regions act as "physical crosslinking points," effectively restricting the free movement of the EPDM main chain and the expansion of free volume at high temperatures, significantly improving the tensile strength and high-temperature dimensional stability of the material. Simultaneously, due to the certain chemical similarity between iPP and EPDM (both are hydrocarbon polymers), interdiffusion, entanglement, and van der Waals adsorption of molecular chain segments occur at the interface between the two phases, forming a transition interface layer with controllable thickness. This interface layer not only enhances the interphase bonding force and suppresses the generation of micropores and phase separation defects, but also reduces electric field concentration and carrier migration channels by increasing local order, thereby significantly improving volume resistivity and breakdown field strength. Crucially, this invention discovers that when the amount of iPP added is 5%, the crystal density and interfacial area reach an optimal balance: on the one hand, a sufficient number of physical cross-linking points and interfacial constraints are enough to significantly improve strength, insulation and thermal conductivity (the improvement in thermal conductivity stems from the suppression of phonon scattering by the ordered structure of the crystalline region and the reduction of interfacial thermal resistance); on the other hand, it avoids problems such as a sharp increase in rigidity, a sharp drop in elongation at break (from >600% to <300%) and an uncontrollable increase in dielectric loss (tanδ) caused by excessive iPP (>10%).

[0111] Furthermore, the preparation process employs a strategy of "batch alternating feeding + impregnation method for introducing vulcanizing agent" to ensure uniform dispersion of iPP and uniform vulcanization reaction, preventing local agglomeration or uneven cross-linking from damaging the integrity of the mesoscopic structure. The resulting blend exhibits excellent comprehensive performance stability over a wide temperature range of 25℃–90℃: the breakdown field strength remains at 38–44kV / mm, the volume resistivity at 90℃ is still above 3.5×10¹³Ω·m, the thermal conductivity is more than 15% higher than pure EPDM, and the elongation at break remains ≥400%, fully meeting the multiple requirements of high-end applications such as offshore wind power torsion cables for "high strength, high insulation, good flexibility, and heat dissipation capabilities." In summary, this invention, through precise control of composition, structure, and process, achieves for the first time synergistic optimization of mechanical, dielectric, and thermal properties in a single rubber matrix, breaking through the performance bottleneck of traditional insulation materials where "strengthening inevitably leads to embrittlement, and high insulation is difficult to achieve high thermal conductivity."

[0112] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for preparing an ethylene propylene rubber blend insulating material, characterized in that, Includes the following steps: Step a: Weigh out EPDM rubber, isotactic polypropylene, inorganic fillers and additives, wherein the mass fraction of isotactic polypropylene is 0% to 15%, and the additives include antioxidants and paraffin wax. Step b: Ethylene propylene diene monomer (EPDM) rubber and isotactic polypropylene (IPM) are melt-blended in a torque rheometer at 170–190℃ and 30–60 r / min. Inorganic fillers and additives are added sequentially, and the mixture is sheared for 10–15 minutes until the torque stabilizes. The mixture is then discharged and granulated to obtain particles. During the blending process, IPM forms a microcrystalline structure and serves as a physical crosslinking point. Combined with the segment diffusion, entanglement, and adsorption of the two-phase interface layer of EPDM rubber and IPM, a mesoscopic network structure with enhanced inter-chain interaction and defect suppression capabilities is constructed. Step c: Dicumyl peroxide is uniformly introduced into the particles using an impregnation method to obtain granules with pre-distributed vulcanizing agent. Step d: Place the granules in a mold and pre-press at 120°C and 20MPa for 5–10 minutes. Then transfer them to a flat vulcanizing machine and hot-press and degas 5 times at 160–200°C and 20MPa. Continue vulcanizing for 5–10 minutes, cool and demold to obtain sheet-like blended rubber sheets.

2. The method for preparing an ethylene propylene rubber blend insulating material according to claim 1, characterized in that, Preferably, in step b, EPDM rubber is added first and allowed to soften before isotactic polypropylene and inorganic fillers are added in batches alternately.

3. The method for preparing an ethylene propylene rubber blend insulating material according to claim 1, characterized in that, In step c, the amount of dicumyl peroxide used is 1–3 parts per 100 parts of rubber.

4. The method for preparing an ethylene propylene rubber blend insulating material according to claim 1, characterized in that, The inorganic filler is selected from at least one of surface-modified kaolin, nano zinc oxide, and lead oxide, and the total amount added is 5% to 20% of the total mass of the material.

5. The method for preparing an ethylene propylene rubber blend insulating material according to claim 1, characterized in that, The inorganic filler is a surface-modified inorganic filler treated with silane coupling agents or fatty acids to enhance its interfacial compatibility with the polymer matrix and reduce phase separation defects.

6. The method for preparing an ethylene propylene rubber blend insulating material according to claim 1, characterized in that, The crystallinity of the material is 0.3% to 6.2%.

7. An ethylene propylene rubber blend insulation material, characterized in that, It is prepared by a method for preparing an ethylene propylene rubber blend insulating material according to any one of claims 1-6.

8. The ethylene propylene rubber blend insulating material according to claim 7, characterized in that, Composed of the following components by mass percentage composition: EPDM rubber: 84.5%~99.5%; Isotactic polypropylene: 0%–15%; Inorganic fillers and additives: balance.

9. An application of the ethylene propylene rubber blend insulating material as described in any one of claims 7-8 in the field of electrical insulation, characterized in that, Used for manufacturing insulation layers for power cables, supports for gas-insulated switchgear, insulators for offshore wind power torsion cables, or insulating components in rail transit electrical systems.

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