Processing methods and materials for improving the properties of isotactic polypropylene blends with ethylene propylene rubber

Abstract

A processing method and material for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber (EPR) are disclosed. The method involves weighing EPR, isotactic polypropylene, and additives, and then melt-blending them to obtain premixed granules. The premixed granules are loaded into a mold and pre-pressed at 120°C and 20 MPa for 5–10 minutes. Hot-pressing crosslinking is then performed at a crosslinking temperature of 20 MPa for 10–15 minutes, followed by venting. The material is then cooled and demolded to obtain an isotactic polypropylene blended EPR rubber blended insulating material. The crosslinking density and crystallinity of the isotactic polypropylene are controlled by adjusting the crosslinking temperature, thereby achieving a synergistic improvement in mechanical and dielectric properties.

Description

Technical Field

[0001] This invention relates to the field of ethylene propylene rubber technology, and in particular to a processing method and materials for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber. Background Technology

[0002] As the capacity of wind turbine generators continues to increase, their associated torsion cables face unprecedented insulation challenges. As the "blood vessels" connecting the tower and the generator, torsion cables not only need to withstand frequent mechanical torsional stresses during long-term operation, but also need to operate under multi-physical field coupling conditions at high voltage levels (66kV / 110kV) and high temperatures (continuous operation at 90℃) caused by conductor heating. While traditional ethylene propylene diene monomer (EPDM) insulation materials possess excellent flexibility, their heat creep resistance and high-temperature dielectric strength often have an inverse relationship, making it difficult to simultaneously meet the stringent requirements of "high mechanical fatigue life" and "high-temperature, high-field-strength insulation."

[0003] To improve the heat resistance and insulation properties of EPDM, existing technologies commonly employ isotactic polypropylene (iPP) blending modification of EPDM, utilizing the high-melting-point crystalline phase of iPP to reinforce the matrix. In the most similar industrial implementation schemes, the preparation process typically follows the traditional rubber processing principles of "efficiency first" and "crosslinking first." That is, in pursuit of extremely high production efficiency and a dense chemical crosslinking network (to prevent high-temperature deformation), existing processes tend to set high or extremely high vulcanization crosslinking temperatures (typically ≥200℃ or higher). Those skilled in the art generally believe that the higher the crosslinking temperature, the faster the decomposition of peroxides (such as DCP), the higher the density of chemical crosslinking points formed, and the better the heat resistance and mechanical strength of the material. Therefore, maximizing the degree of crosslinking has become the mainstream direction of existing technology development, without in-depth consideration or refined control of the microstructural evolution during the crosslinking process, especially the interference of the crosslinking network on the crystalline phase. Ignoring the inhibitory effect of chemical crosslinking on physical crystallization, current technologies blindly pursue high crosslinking temperatures (such as 200℃ and above). While this has successfully constructed dense chemical crosslinking networks, current processing methods lack quantitative control over the antagonistic (competitive) relationship between the chemical crosslinking network (formed by the vulcanizing agent) and the physical crystallization network (formed by iPP crystallization). This often leads to a dilemma where the prepared insulating materials suffer from either a low crosslinking temperature and poor heat resistance (loose network), or a high crosslinking temperature and low breakdown (restricted crystallization). Current technologies have failed to find the "golden balance" that can both lock in the matrix and preserve the crystal domains.

[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 processing method and material for improving the electrical and mechanical properties of isotactic polypropylene blends with ethylene propylene rubber. It constructs a synergistic microstructure of chemical and physical dual networks, and precisely controls the crosslinking temperature within a thermodynamic equilibrium window, ensuring the formation of a sufficiently dense chemical crosslinking network in the EPDM matrix, with a crosslinking density ≥ 2.4 × 10⁻⁶. -4 mol / cm 3 Simultaneously, the degree of freedom of iPP molecular chains in arranging into the crystal lattice is preserved to the maximum extent, avoiding "stifling" crystallization due to excessively rapid cross-linking. This achieves a nonlinear synergistic improvement in mechanical and electrical properties at high temperatures, resulting in an insulating material that combines high chemical cross-linking density with high crystal retention (≥2.2%). This material effectively solves the problem of wind power torsion cables "breaking under heat" at 90℃, while maintaining excellent elongation at break (toughness), achieving a technological leap from single-performance optimization to comprehensive structural balance.

[0006] A processing method for improving the electrical and mechanical properties of isotactic polypropylene blends of ethylene propylene rubber includes:

[0007] Premixed granules were prepared by melt blending EPDM rubber, isotactic polypropylene and additives.

[0008] The premixed granules are loaded into a mold and pre-compressed at 120°C and 20MPa for 5–10 minutes.

[0009] Hot-press crosslinking is performed at the crosslinking temperature at a pressure of 20 MPa for 10–15 minutes, followed by venting. After cooling and demolding, isotactic polypropylene blended with ethylene propylene rubber blended insulating material is obtained. By adjusting the crosslinking temperature, the crosslinking density and crystallinity of isotactic polypropylene are controlled, thereby achieving a synergistic improvement in mechanical and dielectric properties.

[0010] In the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the amount of isotactic polypropylene added in ethylene propylene rubber, isotactic polypropylene and additives is 3-8 wt%, and the crosslinking temperature is 160-200℃.

[0011] In the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the isotactic polypropylene is added at a rate of 5 wt% in the ethylene propylene rubber, isotactic polypropylene, and additives, the crosslinking temperature is 180℃, and the crosslinking density of the isotactic polypropylene blended ethylene propylene rubber blended insulating material is ≥2.5×10⁻⁶. -4 mol / cm 3 Crystallinity ≥ 2.1, high tensile strength ≥ 12.5 MPa @ 25℃, volume resistivity ≥ 3.0 × 10⁻⁶ 1 3 Ω·m@90℃.

[0012] In the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the additives include surface-modified kaolin, nano zinc oxide, lead oxide, antioxidant, paraffin wax and peroxide vulcanizing agent, and the additives are 1-3 parts per 100 parts of ethylene propylene rubber.

[0013] In the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the additives include inorganic fillers and peroxide vulcanizing agents. The inorganic fillers include modified kaolin or nano ZnO, and the peroxide vulcanizing agent is dicumyl peroxide. Premixed particles are prepared by melt blending of ethylene propylene rubber, isotactic polypropylene, and inorganic fillers. Dicumyl peroxide is added at 120°C to avoid premature crosslinking at high temperature.

[0014] In the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the melt blending is carried out in a torque rheometer at a processing temperature of 170–190℃, a rotation speed of 30–60 r / min, and a mixing time of 10–15 minutes; inorganic fillers and organic phases are added alternately to promote dispersion.

[0015] In the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, hot-press crosslinking is performed in a flat vulcanizing machine. Before hot-press crosslinking, dicumyl peroxide is uniformly introduced into the premixed particles by impregnation.

[0016] An isotactic polypropylene blended with ethylene propylene rubber isomeric insulating material, which is made according to a processing method for improving the electrical and mechanical properties of isotactic polypropylene blended with ethylene propylene rubber.

[0017] In a preferred embodiment of the isotactic polypropylene blended with ethylene propylene rubber (EPR) insulating material, when the amount of isotactic polypropylene added to the EPR, isotactic polypropylene, and additives is 3-8 wt% and the crosslinking temperature is 160–200℃, the isotactic polypropylene blended with EPR has the following performance characteristics:

[0018] The crosslinking density is 2.0–2.8 × 10⁻⁶. -4 mol / cm 3 ;

[0019] Crystallinity is 2.1–2.7%;

[0020] Tensile strength at 25℃ ≥12.0MPa, elongation at break ≥450%;

[0021] Volume resistivity at 90℃ ≥3.0×10 1 3 Ω·m, breakdown field strength ≥35kV / mm;

[0022] Relative permittivity ≤3.1, tanδ≤0.02, 1kHz, 25℃.

[0023] In a preferred embodiment of the isotactic polypropylene blended with ethylene propylene rubber blended insulating material, when the amount of isotactic polypropylene added to the ethylene propylene rubber, isotactic polypropylene, and additives is 5 wt%, and the crosslinking temperature is 180°C, the material exhibits the following characteristics in the temperature range of 25–90°C:

[0024] Resistivity temperature stability is better than ±15% variation;

[0025] The breakdown field strength temperature stability is better than ±12% variation;

[0026] The increase in dielectric loss is the smallest, with tanδ increasing by no more than 50% during the heating process.

[0027] Compared with the prior art, the present invention has the following advantages: The present invention uses crosslinking temperature as a performance control variable, which has a competitive influence on the "crosslinking network" and "crystallization structure" in the EPDM / iPP blend system, and proposes an optimal process window (180℃) accordingly, thereby realizing the systematic optimization of the comprehensive performance of the material. Attached Figure Description

[0028] 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.

[0029] In the attached diagram:

[0030] Figures 1(a) to 1(b) are schematic diagrams of samples of isotactic polypropylene blended with ethylene propylene rubber blended insulating material provided in an embodiment of the present disclosure, wherein Figure 1(a) is a granular sample and Figure 1(b) is a square sheet sample;

[0031] Figure 2 This is a surface morphology diagram of ethylene propylene rubber at different crosslinking temperatures provided in one embodiment of this disclosure;

[0032] Figures 3(a) to 3(b) are schematic diagrams illustrating the effect of crosslinking temperature on the density and crosslinking density of ethylene propylene rubber according to an embodiment of this disclosure. Figure 3(a) shows the relationship between the density of ethylene propylene rubber and the crosslinking temperature, and Figure 3(b) shows the relationship between the crosslinking density and the crosslinking temperature.

[0033] Figure 4 This is a relationship between crystallinity and crosslinking temperature provided in one embodiment of the present disclosure;

[0034] Figures 5(a) to 5(c) are schematic diagrams showing the relationship between the tensile properties of ethylene propylene rubber and the crosslinking temperature according to an embodiment of the present disclosure. Figure 5(a) shows the tensile strength at different crosslinking temperatures, Figure 5(b) shows the elongation at break at different crosslinking temperatures, and Figure 5(c) shows the elastic modulus at different crosslinking temperatures.

[0035] Figure 6 This is a schematic diagram illustrating the relationship between the resistivity of ethylene propylene rubber and temperature at different crosslinking temperatures, provided in one embodiment of this disclosure.

[0036] Figure 7 This is a schematic diagram illustrating the relationship between the breakdown field strength of ethylene propylene rubber at different crosslinking temperatures and temperature, provided in one embodiment of this disclosure.

[0037] Figures 8(a) to 8(b) are schematic diagrams showing the relationship between the relative permittivity and tanδ of blended rubbers with different crosslinking temperatures provided in an embodiment of this disclosure. Figure 8(a) shows the relationship between the relative permittivity and temperature, and Figure 8(b) shows the relationship between tanδ and temperature.

[0038] Figure 9 This is a schematic diagram illustrating the relationship between the thermal conductivity and temperature of ethylene propylene rubber at different crosslinking temperatures, provided in one 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] As shown in Figure 1(a) to Figure 9 As shown, the processing method for improving the electrical and mechanical properties of isotactic polypropylene blends of ethylene propylene rubber includes the following steps:

[0044] Premixed granules were prepared by melt blending EPDM rubber, isotactic polypropylene and additives.

[0045] The premixed granules are loaded into a mold and pre-compressed at 120°C and 20MPa for 5–10 minutes.

[0046] Hot-press crosslinking is performed at the crosslinking temperature at a pressure of 20 MPa for 10–15 minutes, followed by venting. Cooling and demolding yields an isotactic polypropylene blend with ethylene propylene rubber as an insulating material. The 120°C pre-pressing process softens and densifies the premixed particles before significant premature crosslinking, reducing interparticle porosity and improving material spread uniformity within the mold. The 20 MPa pressure promotes particle adhesion and reduces internal voids and interface defects. The pre-pressing time is controlled at 5–10 minutes to ensure basic compaction while avoiding excessive heat history that could affect subsequent crosslinking and crystallization. Furthermore, hot-pressing at the crosslinking temperature for 10–15 minutes with venting allows the peroxide vulcanizing agent to fully function, forming a more uniform crosslinked network. Venting also reduces volatiles and residual gas retention, minimizing internal porosity and improving the material's mechanical and electrical insulation properties. After employing the aforementioned pre-pressing and hot-pressing processes, the resulting sheets are well-formed with smooth surfaces, and exhibit good thickness consistency among different samples, which is beneficial for subsequent comparative evaluation of crosslinking density, crystallinity, and electrical properties. By adjusting the crosslinking temperature to control the crosslinking density and isotactic polypropylene crystallinity, a synergistic improvement in mechanical and dielectric properties can be achieved.

[0047] In a preferred embodiment of the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the amount of isotactic polypropylene added in the ethylene propylene rubber, isotactic polypropylene and additives is 3-8 wt%, and the crosslinking temperature is 160-200℃.

[0048] In a preferred embodiment of the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the isotactic polypropylene is added at 5 wt% of the ethylene propylene rubber, isotactic polypropylene, and additives, the crosslinking temperature is 180℃, and the crosslinking density of the isotactic polypropylene blended ethylene propylene rubber blended insulating material is ≥2.5×10⁻⁶.-4 mol / cm 3 Crystallinity ≥ 2.1, high tensile strength ≥ 12.5 MPa @ 25℃, volume resistivity ≥ 3.0 × 10⁻⁶ 1 3 Ω·m@90℃.

[0049] In a preferred embodiment of the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the additives include surface-modified kaolin, nano zinc oxide, lead oxide, antioxidant, paraffin wax, and peroxide vulcanizing agent, and the additives are 1-3 parts per 100 parts of ethylene propylene rubber.

[0050] In a preferred embodiment of the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the additives include inorganic fillers and peroxide vulcanizing agents. The inorganic fillers include modified kaolin or nano ZnO, and the peroxide vulcanizing agent is dicumyl peroxide. Premixed particles are prepared by melt blending of ethylene propylene rubber, isotactic polypropylene, and inorganic fillers. Dicumyl peroxide is added at 120°C to avoid premature crosslinking at high temperature.

[0051] In a preferred embodiment of the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, the melt blending is carried out in a torque rheometer at a processing temperature of 170–190°C, a rotation speed of 30–60 r / min, and a mixing time of 10–15 minutes; inorganic fillers and organic phases are added alternately to promote dispersion.

[0052] In a preferred embodiment of the processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, hot-press crosslinking is performed in a flat vulcanizing machine. Before hot-press crosslinking, dicumyl peroxide is uniformly introduced into the premixed particles using an impregnation method.

[0053] An isotactic polypropylene blended with ethylene propylene rubber as an insulating material, which is made according to the aforementioned processing method for improving the electrical and mechanical properties of isotactic polypropylene blended with ethylene propylene rubber.

[0054] In a preferred embodiment of the isotactic polypropylene blended with ethylene propylene rubber (EPR) insulating material, when the amount of isotactic polypropylene added to the EPR, isotactic polypropylene, and additives is 3-8 wt% and the crosslinking temperature is 160–200℃, the isotactic polypropylene blended with EPR has the following performance characteristics:

[0055] The crosslinking density is 2.0–2.8 × 10⁻⁶. -4 mol / cm 3 ;

[0056] Crystallinity is 2.1–2.7%;

[0057] Tensile strength at 25℃ ≥12.0MPa, elongation at break ≥450%;

[0058] Volume resistivity at 90℃ ≥3.0×10 1 3 Ω·m, breakdown field strength ≥35kV / mm;

[0059] Relative permittivity ≤3.1, tanδ≤0.02, 1kHz, 25℃.

[0060] In a preferred embodiment of the isotactic polypropylene blended with ethylene propylene rubber blended insulating material, when the amount of isotactic polypropylene added to the ethylene propylene rubber, isotactic polypropylene, and additives is 5 wt%, and the crosslinking temperature is 180°C, the material exhibits the following characteristics in the temperature range of 25–90°C:

[0061] Resistivity temperature stability is better than ±15% variation;

[0062] The breakdown field strength temperature stability is better than ±12% variation;

[0063] The increase in dielectric loss is the smallest, with tanδ increasing by no more than 50% during the heating process.

[0064] In one embodiment, excessively high crosslinking density creates a strong confinement effect at the microscopic level. The dense network structure acts like a cage, locking up the molecular chains and severely hindering the diffusion and orderly arrangement of iPP molecular chains towards the crystal nucleus, leading to a significant decrease in the crystallinity of iPP (and even causing crystal phase fragmentation and imperfection). This practice of sacrificing physical crystal domains for chemical crosslinking directly destroys the deep-level traps that capture charge carriers in the material, causing the breakdown field strength of the material to decrease rather than increase at 90°C. The dual mechanism of increased crosslinking density, enhanced molecular chain bonding, and improved performance, versus excessively high crosslinking temperature, inhibited crystallization, and decreased stability, provides a quantifiable basis for regulation. Focusing on the optimal temperature point of 180°C, highlighting performance advantages, crosslinking at 180°C: while maintaining high strength, the temperature stability of resistivity and breakdown field strength is optimal, and the dielectric loss degradation is minimal. The crosslinking temperature is 180°C, and the material obtained at this temperature has both high crosslinking density (≥2.5×10⁻⁶). -4 mol / cm 3 It possesses moderate crystallinity (≥2.1%), high tensile strength (≥12.5MPa@25℃), and high volume resistivity (≥3.0×10⁻⁶). 13 Ω·m@90℃) and good dielectric temperature stability (resistivity and breakdown field strength fluctuate little with temperature).

[0065] In one embodiment, the isotactic polypropylene blended with ethylene propylene rubber blended insulation material is used as a torsion cable material.

[0066] This invention uses EPDM as the matrix and iPP as the modified phase, and takes "crosslinking temperature" as the core control variable. A series of insulating materials were prepared by selecting three characteristic temperature points (160℃ - under-crosslinked region, 180℃ - equilibrium region, and 200℃ - over-crosslinked region). Through correlation analysis between microstructure and macroscopic properties, the competitive mechanism of "crosslinked network restricting crystal growth" was revealed, and the optimal process window was determined.

[0067] I. Preparation process and microstructure

[0068] 1. Homogeneous blending and dispersion

[0069] Process Description: First, the components are melt-blended at 170°C using a torque rheometer. An alternating feeding method is employed to ensure uniform dispersion of iPP (5wt%) and inorganic fillers (modified kaolin, nano-ZnO, etc.) within the EPDM matrix. Subsequently, DCP vulcanizing agent is added at 120°C to prevent premature cross-linking at high temperatures.

[0070] Morphological characterization: The sheet-like samples prepared as shown in Figures 1(a) to 1(b) have smooth surfaces. Figure 2 As shown by scanning electron microscopy (SEM), the filler particles maintained good dispersion in the matrix at crosslinking temperatures of 160℃, 180℃, and 200℃, with no obvious agglomeration. This eliminates the possibility of performance differences due to uneven dispersion, proving that subsequent performance changes are entirely due to the alteration of the matrix network structure by the crosslinking temperature.

[0071] II. Microstructure Evolution

[0072] 1. Linear increase in crosslinking density

[0073] As shown in Figure 3(b), as the crosslinking temperature increases from 160℃ to 200℃, the crosslinking density of the material exhibits a significant linear increasing trend (from 2.03×10⁻⁶). -4 mol / cm 3 Increased to 2.76×10 -4 mol / cm 3 This is in line with kinetic expectations; the high temperature accelerates the decomposition of dicumyl peroxide (DCP), forming a denser "chemically cross-linked network." While existing technologies generally consider a higher degree of cross-linking to be better, this invention has discovered its negative effects.

[0074] 2. Nonlinear suppression of crystallinity

[0075] like Figure 4As shown, the crystallinity of iPP decreases inversely with increasing crosslinking temperature. At 160℃, the crystallinity is approximately 2.7%, while at 200℃, it significantly decreases to 2.12%. This data directly confirms the network antagonism effect proposed in this invention. At 200℃, the excessively rapid crosslinking reaction quickly locks the EPDM molecular chains, forming a dense, rigid network. This dense network generates a strong spatial confinement effect, restricting the diffusion and orderly arrangement of iPP molecular chains towards the crystal nucleus like a cage, preventing iPP from effectively growing complete crystal domains. This indicates that simply pursuing a high crosslinking temperature (200℃) severely damages the material's "physical crystallization network."

[0076] Macro performance response

[0077] 1. The "rigid-flexible balance" of mechanical properties

[0078] Tensile strength ( Figure 5a Elongation at break (E): The strength increases monotonically with increasing crosslinking temperature, with the highest strength (12.98 MPa) observed at 200℃, consistent with the crosslinking reinforcement theory. Figure 5b Extreme values ​​were observed. The elongation at break of the 180℃ sample exhibited optimal values ​​in both the room temperature and high temperature ranges (especially reaching a peak of approximately 700% at 50℃). This indicates that the network structure at 180℃ possesses sufficient cross-linking points to transfer stress while retaining appropriate molecular chain flexibility. For wind power torsion cables, elongation at break (toughness) is more important than strength alone. The 180℃ process endows the material with an optimal structure to resist repeated torsional fatigue.

[0079] 2. The "High-Temperature Steady State" of Resistivity and Breakdown Field Strength

[0080] Volume resistivity ( Figure 6 At a high temperature of 90℃, the resistivity of the samples at 180℃ and 200℃ was significantly better than that of the sample at 160℃. This indicates that the cross-linked network must reach a certain density to limit ion migration at high temperatures.

[0081] Breakthrough field strength ( Figure 7 The crosslinking density of the 200℃ sample is key evidence for determining the optimal temperature window. Although the 200℃ sample has the highest crosslinking density, its breakdown field strength does not show an absolute advantage at high temperatures and decreases rapidly with temperature. In contrast, the 180℃ sample maintains excellent stability across the entire temperature range (25-90℃). Insulation performance depends on the "deep traps." The 160℃ sample has too shallow traps (loose crosslinking); although the 200℃ sample has dense crosslinking, its crystallinity is damaged (reduced physical traps), resulting in insufficient high-temperature withstand voltage. Only the 180℃ sample achieves a dual synergy of "chemical network locking of chain segments" and "physical crystal domain blocking of electrons," which plays a positive role in maintaining insulation performance at high temperatures.

[0082] 3. Auxiliary verification of dielectric and thermal properties (refer to Figures 8(a) to 8(b)). Figure 9 )

[0083] Thermal conductivity ( Figure 9 As the crosslinking temperature increases, the thermal conductivity increases significantly (reaching 0.26 W / (m·K) at 200℃). This is because the dense network reduces phonon scattering. Although the thermal conductivity of the sample at 180℃ (0.195 W / (m·K)) is slightly lower than that at 200℃, it still meets the engineering heat dissipation requirements and comprehensively balances insulation and mechanical properties.

[0084] This invention experimentally demonstrates that the "crosslinking temperature" is not a simple linear process parameter. 180℃ is not merely an intermediate temperature, but a crucial thermodynamic equilibrium window. At this temperature, the material overcomes the thermal instability defects of low crosslinking degree while avoiding the suppression of crystal phase structure by excessively high crosslinking degree, successfully constructing a dual-network synergistic structure of "high crosslinking density + high crystal retention rate," achieving a perfect balance between high-temperature insulation and high mechanical toughness required for wind power torsion cables.

[0085] Furthermore, the crosslinking temperature was used as the core control variable, limited to the range of 160-200℃, with 180℃ being particularly preferred as the optimal process temperature. This result indicates that in the system described in this application, a higher crosslinking temperature is not necessarily better. Within the thermodynamic equilibrium window of 180℃, the dicumyl peroxide (DCP) vulcanizing agent can form a sufficiently dense chemical crosslinking network (crosslinking density ≥ 2.4 × 10⁻⁶) at a moderate decomposition rate. -4 mol / cm 3 This precise temperature control avoids excessive restriction on the molecular chain movement of isotactic polypropylene (iPP) by an overly rapid crosslinking reaction. This allows the material to achieve both sufficient heat resistance and maximum retention of iPP's crystallinity (crystallization retention ≥ 2.2%), thus achieving optimal synergy between the chemical crosslinking network and the physical crystallization network.

[0086] This invention achieves a microstructure where the crosslinking network and crystalline structure are relatively coordinated through precise control of the 180℃ crosslinking temperature. The chemical crosslinking network (formed by chemical bonds between EPDM molecular chains) provides the basis for the material's thermal stability and mechanical strength, effectively locking molecular chain segments and preventing thermal deformation at high temperatures. The physical crystalline network (formed by iPP crystal domains) constructs numerous deep-level traps within the material. These traps effectively capture high-energy charge carriers, significantly improving the breakdown field strength of the material under 90℃ high-temperature conditions. The synergistic effect of these two networks enables the material to maintain both excellent insulation performance (excellent stability of breakdown field strength within the 25-90℃ temperature range) and good mechanical toughness (peak elongation at break reaches approximately 700% at 50℃), contributing to improved insulation stability of wind power torsion cable insulation materials under high-temperature conditions. An alternating feeding method was used during the melt blending process at 170℃. This technique ensured the uniform dispersion of isotactic polypropylene (5wt%) and inorganic fillers (modified kaolin, nano-ZnO, etc.) in the ethylene propylene rubber matrix. The uniformly dispersed iPP phase can form a uniformly distributed crystalline network during subsequent crosslinking, avoiding performance inhomogeneity caused by local aggregation. The uniformly dispersed inorganic fillers can effectively improve the thermal conductivity of the material (the thermal conductivity of the sample at 180℃ reached 0.195 W / (m·K)), improving the heat dissipation performance of the material. At the same time, the nanofillers can further increase the deep trap density and improve the insulation performance. This uniformly dispersed microstructure provides a good foundation for the subsequent crosslinking temperature control, ensuring the consistency and reliability of the material properties.

[0087] This invention employs a staged temperature control process: "170℃ melt blending → 120℃ addition of vulcanizing agent → 160-200℃ crosslinking." This technique offers multiple advantages. First, the 170℃ melt blending temperature ensures sufficient melting and uniform dispersion of all components without premature decomposition of the vulcanizing agent. Second, cooling the material to 120℃ before adding the vulcanizing agent effectively prevents premature crosslinking at high temperatures, ensuring the controllability of the subsequent crosslinking process. Finally, vulcanization and crosslinking are carried out within the 160-200℃ range, with the optimal crosslinking temperature of 180℃ achieving the best balance between chemical crosslinking and physical crystallization. This staged temperature control process provides a reliable technological guarantee for preparing insulating materials with excellent comprehensive properties.

[0088] By precisely controlling the crosslinking temperature at 180℃, this invention achieves a crosslinking density (≥2.4×10⁻⁶). -4 mol / cm 3The synergistic optimization of crosslinking density and crystal retention rate (≥2.2%) has significant technical benefits: on the one hand, a sufficiently high crosslinking density ensures the thermal stability of the material at 90℃, effectively limiting ion migration at high temperatures, resulting in a significantly better volume resistivity than samples with low crosslinking density (160℃); on the other hand, a high crystal retention rate ensures the presence of sufficient deep-level traps in the material, which can effectively capture high-energy electrons and prevent electron avalanche breakdown, allowing the breakdown field strength of the material to maintain excellent stability at high temperatures. This synergistic optimization enables the material to possess both excellent insulation performance and good mechanical toughness under high-temperature conditions, perfectly meeting the requirements of wind power torsion cables under complex operating conditions.

[0089] This invention establishes a quantitative correlation between microstructure and macroscopic properties by revealing the competitive mechanism of "crosslinked network-limited crystal growth." This correlation regulation has significant technical implications: it enables engineers to precisely control the microstructure (crosslinking density, crystallinity) of materials by adjusting a single process parameter—crosslinking temperature—thereby achieving targeted optimization of macroscopic properties (breakdown field strength, elongation at break, thermal conductivity, etc.). This mechanism-based targeted regulation method overcomes the limitations of traditional "trial and error" methods, providing scientific theoretical guidance and a reliable process path for the preparation of high-performance insulating materials.

[0090] 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 processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber, characterized in that, Includes the following steps: Premixed granules were prepared by melt blending EPDM rubber, isotactic polypropylene and additives. The premixed granules are loaded into a mold and pre-compressed at 120°C and 20MPa for 5–10 minutes. Hot-press crosslinking is performed at the crosslinking temperature at a pressure of 20 MPa for 10–15 minutes, followed by venting. After cooling and demolding, isotactic polypropylene blended with ethylene propylene rubber blended insulating material is obtained. By adjusting the crosslinking temperature, the crosslinking density and crystallinity of isotactic polypropylene are controlled, thereby achieving a synergistic improvement in mechanical and dielectric properties.

2. The processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber according to claim 1, characterized in that, Preferably, in the EPDM rubber, isotactic polypropylene and additives, the amount of isotactic polypropylene added is 3-8 wt%, and the crosslinking temperature is 160-200℃.

3. The processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber according to claim 1, characterized in that, In the ethylene propylene diene monomer (EPDM) rubber, isotactic polypropylene, and additives, the isotactic polypropylene is added at 5 wt%, the crosslinking temperature is 180℃, and the crosslinking density of the isotactic polypropylene-EPDM rubber blend insulation material is ≥2.5×10⁻⁶. -4 mol / cm 3 Crystallinity ≥ 2.1, high tensile strength ≥ 12.5 MPa @ 25℃, volume resistivity ≥ 3.0 × 10⁻⁶ 13 Ω·m@90℃.

4. The processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber according to claim 1, characterized in that, The additives include surface-modified kaolin, nano zinc oxide, lead oxide, antioxidant, paraffin wax, and peroxide vulcanizing agent, and the additives are 1-3 parts per 100 parts of EPDM rubber.

5. The processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber according to claim 1, characterized in that, The additives include inorganic fillers and peroxide vulcanizing agents. The inorganic fillers include modified kaolin or nano ZnO, and the peroxide vulcanizing agent is dicumyl peroxide. Premixed particles are prepared by melt blending EPDM rubber, isotactic polypropylene and inorganic fillers. Dicumyl peroxide is added at 120°C to avoid premature cross-linking at high temperature.

6. The processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber according to claim 1, characterized in that, The melt blending was carried out in a torque rheometer at a processing temperature of 170–190°C, a rotation speed of 30–60 r / min, and a mixing time of 10–15 minutes; inorganic fillers and organic phases were added alternately to promote dispersion.

7. The processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber according to claim 1, characterized in that, Hot-press crosslinking is carried out in a flat vulcanizing machine. Before hot-press crosslinking, dicumyl peroxide is uniformly introduced into the premixed particles by impregnation.

8. An isotactic polypropylene blended with ethylene propylene rubber blended insulating material, characterized in that, It is made by a processing method for improving the electrical and mechanical properties of isotactic polypropylene blended ethylene propylene rubber according to any one of claims 1-7.

9. The isotactic polypropylene blended with ethylene propylene rubber blended insulating material according to claim 8, characterized in that, In ethylene propylene diene monomer (EPDM) rubber, isotactic polypropylene (IPM), and additives, when the amount of IPM added is 3-8 wt% and the crosslinking temperature is 160–200℃, the IPM-EPDM blended insulating material has the following performance characteristics: The crosslinking density is 2.0–2.8 × 10⁻⁶. -4 mol / cm 3 ; Crystallinity is 2.1–2.7%; Tensile strength at 25℃ ≥12.0MPa, elongation at break ≥450%; Volume resistivity at 90℃ ≥3.0×10 13 Ω·m, breakdown field strength ≥35kV / mm; Relative permittivity ≤3.1, tanδ≤0.02, 1kHz, 25℃.

10. The isotactic polypropylene blended with ethylene propylene rubber blended insulating material according to claim 8, characterized in that, When the amount of isotactic polypropylene added to EPDM rubber, isotactic polypropylene, and additives is 5 wt%, and the crosslinking temperature is 180℃, the material exhibits the following characteristics in the temperature range of 25–90℃: Resistivity temperature stability is better than ±15% variation; The breakdown field strength temperature stability is better than ±12% variation; The increase in dielectric loss is the smallest, with tanδ increasing by no more than 50% during the heating process.

Images