Terpolymer ethylene propylene rubber based functional filler composition and method of making the same

Abstract

This invention provides a EPDM rubber-based functional filler composition and its preparation method, relating to the field of polymer composite materials technology. The composition includes EPDM rubber, thermally conductive and insulating fillers, flame-retardant fillers, and ceramicized composite powder fillers. The ceramicized composite powder filler comprises kaolin raw material and calcined kaolin, with the calcined kaolin content not less than 35%. The invention achieves high-efficiency flame retardancy through a synergistic flame-retardant system of aluminum hydroxide (ATH) and ceramicized composite powder fillers. ATH has endothermic decomposition properties, releasing water vapor to dilute combustible gases, while the kaolin raw material can further absorb heat and delay the temperature rise of the matrix. Calcined kaolin serves as a pre-fabricated ceramic skeleton, which, in conjunction with a flux, forms a dense ceramic protective layer. When mixed with the kaolin raw material, it provides a synergistic effect between the skeleton and the flame-retardant material, improving flame-retardant performance.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to EPDM rubber-based functional filler compositions and their preparation methods, which can be used as cable insulation layers, cable sheaths, and insulating components of electrical equipment. Background Technology

[0002] EPDM (Ethylene-Propylene-Diene Monomer) is a random terpolymer obtained by copolymerizing ethylene, propylene, and non-conjugated dienes. The EPDM molecular backbone has a highly saturated carbon chain structure, contains no polar substituents, and exhibits excellent resistance to heat and oxygen aging, weathering, chemical resistance, and good electrical insulation properties. It is widely used in the insulation and sheathing of wires and cables, as well as sealing materials.

[0003] In applications where safety and reliability are extremely critical, such as mining cables and high-voltage wiring harnesses for new energy vehicles, EPDM insulation materials must simultaneously meet multiple performance requirements, including high insulation, high thermal conductivity, and flame retardancy. However, EPDM itself has a low thermal conductivity (typically below 0.3 W / (m·K)), is flammable, and has a limiting oxygen index of approximately 18.6% for pure EPDM vulcanizate. Currently, the industry uses the method of preparing EPDM-based functional filler compositions, adding functional fillers to the EPDM matrix to improve performance.

[0004] For example, when kaolin is added to EPDM, the dielectric and mechanical properties of the composite filler material are improved when the kaolin content is about 30 wt%. When aluminum hydroxide (ATH) is added to EPDM, it has a flame-retardant effect. When ceramic materials (silicon dioxide, montmorillonite, and sodium silicate are sintered and then ground into powder) are added to EPDM, the EPDM can be sintered into a ceramic body with a certain strength at a combustion temperature of 200℃-800℃, thus blocking the continued combustion of the flame.

[0005] There is currently a lack of an EPDM-based functional filler composition and its preparation method that can simultaneously achieve the triple functions of high thermal conductivity, high insulation, and high fire resistance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a EPDM-based functional filler composition and its preparation method, which solves the technical problems that existing EPDM-based filler compositions cannot simultaneously achieve high thermal conductivity, high electrical insulation, and efficient fire resistance, and that the filler dispersion is uneven and the mechanical properties need to be improved.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The EPDM-based functional filler composition comprises the following components in parts by weight: 100 parts of EPDM rubber; 5-30 parts of thermally conductive and insulating filler; 10-50 parts of flame-retardant filler; 10-40 parts of ceramicized composite powder filler; Interface modifier 1-5 parts; 1-5 parts of vulcanizing aid; Other adjuvants: 1-3 parts; The thermally conductive insulating filler comprises hexagonal boron nitride nanosheets and / or boron nitride nanosheets; The ceramicized composite powder filler comprises kaolin raw material and calcined kaolin, and the content of calcined kaolin is not less than 35%. The composition has a volume resistivity of not less than 1×10¹⁴ Ω·cm and a thermal conductivity of not less than 0.5 W / (m·K) after vulcanization.

[0008] The synergistic flame-retardant system of aluminum hydroxide (ATH) and ceramic composite powder filler achieves high-efficiency flame retardancy. ATH has endothermic decomposition, releasing water vapor to dilute flammable gases, and kaolin raw material can further absorb heat and delay the temperature rise of the matrix. Calcined kaolin serves as a pre-fabricated ceramic skeleton, which, together with flux, forms a dense ceramic protective layer. When mixed with kaolin raw material, it provides the synergistic effect of the skeleton and the flame-retardant material, improving the flame-retardant performance. (After the cable is subjected to prolonged flame exposure, its surface material may carbonize, but the residual voids formed by the kaolin raw material and calcined kaolin prevent the surface material from burning continuously, thus completely solving the problem of flame transmission from the cable surface.) Preferably, the flame-retardant filler is one or more of aluminum hydroxide, magnesium hydroxide, and ammonium polyphosphate.

[0009] The preferred method for preparing calcined kaolin is as follows: Kaolin raw material is mixed with flux and then calcined at 800℃~1000℃ for 2~4 hours to obtain ceramic body. The ceramic body is then ground into powder to obtain calcined kaolin.

[0010] Preferably, the mass ratio of raw kaolin to calcined kaolin in the ceramicized composite powder filler is 1:0.4 to 0.7.

[0011] Preferably, the vulcanizing aid includes a vulcanizing agent and a vulcanizing co-agent, wherein the vulcanizing agent is a peroxide vulcanizing agent and the vulcanizing co-agent is a polyfunctional acrylate or maleimide vulcanizing co-agent.

[0012] Preferably, the other additives are one or more of the following: dispersants, lubricants, antistatic agents, colorants, thickeners, anti-scorching agents, smoke suppressants, antibacterial agents, and anti-aging agents.

[0013] The preparation method of the EPDM rubber-based functional filler composition includes the following steps: S1. Mix raw kaolin with flux and calcine at 800℃~1000℃ for 2~4 hours to obtain ceramic body. Grind the ceramic body into powder to obtain calcined kaolin powder. S2. The calcined kaolin powder obtained in step S1 is mixed with raw kaolin at a mass ratio of 1:0.4 to 0.7 to obtain ceramicized composite powder filler. S3. Plasticize EPDM rubber in an internal mixer at 40-60°C for 2-5 minutes; then add thermally conductive and insulating filler, flame-retardant filler, ceramicized composite powder filler, interface modifier and other additives to the internal mixer, and mix at 80-130°C for 5-15 minutes to obtain a mixed rubber compound. S4. Add the compounded rubber to the rubber extruder and wrap it around the cable conductor through the extruder head to form an insulation layer; S5. A continuous vulcanization process is used to continuously vulcanize the cable covered with an insulation layer through a vulcanization pipeline.

[0014] Preferably, the average particle size of the calcined kaolin powder obtained in step S1 is 1 μm to 10 μm.

[0015] Preferably, the mixing in step S1 adopts a segmented feeding method. First, thermally conductive and insulating filler, flame-retardant filler and ceramic composite powder filler are added and mixed for 3 to 8 minutes. Then, interface modifier and other additives are added and mixed for another 3 to 8 minutes.

[0016] EPDM is a non-polar material, while inorganic functional fillers mostly have polar surfaces. The lack of chemical affinity between the two leads to the easy aggregation of fillers within the EPDM matrix. This invention modifies the filler surface by adding an interface modifier (silane coupling agent KH-550), thereby enhancing the interfacial bonding between the filler and the EPDM matrix.

[0017] The process employs a segmented feeding and mixing method. First, the functional filler is mixed with EPDM raw rubber to initially disperse the filler. Then, an interface modifier is added to uniformly coat the filler surface. Finally, other additives are added. This process facilitates the uniform distribution of different types of fillers in the matrix and avoids the agglomeration and uneven dispersion of fillers caused by the traditional one-time feeding method. The resulting EPDM-based functional filler composition exhibits excellent mechanical properties.

[0018] Preferably, the vulcanization temperature of the continuous vulcanization process in step S5 is 160–200°C, and the pressure inside the vulcanization pipeline is 0.5–3.0 MPa.

[0019] This invention provides a ternary ethylene propylene diene monomer (EPDM) rubber-based functional filler composition and its preparation method. It possesses the following beneficial effects: Traditional EPDM has a thermal conductivity typically below 0.3 W / (m·K), making it difficult to dissipate heat quickly. This leads to the continuous accumulation of Joule heat within the insulation layer, accelerating the material's thermo-oxidative aging. This invention introduces hexagonal boron nitride nanosheets, which possess excellent thermal conductivity and electrical insulation properties, to construct a highly efficient thermally conductive network within the EPDM matrix. The in-plane thermal conductivity of the hexagonal boron nitride nanosheets reaches as high as 2000 W / (m·K), far exceeding that of bulk hexagonal boron nitride. This improved thermal conductivity effectively dissipates the Joule heat generated during cable operation, reducing the operating temperature rise of the insulation layer, slowing down the thermo-oxidative aging process, thereby extending the cable's service life and increasing its current carrying capacity.

[0020] EPDM vulcanizate has a limiting oxygen index of only about 18.6%, classifying it as a flammable material. This invention achieves highly efficient flame retardancy through a synergistic flame retardant system of aluminum hydroxide (ATH) and ceramic composite powder filler. Aluminum hydroxide undergoes endothermic decomposition, releasing water vapor to dilute flammable gases, while raw kaolin can further absorb heat and delay the temperature rise of the matrix. Calcined kaolin serves as a pre-fabricated ceramic skeleton, which, together with flux, forms a dense ceramic protective layer. When mixed with raw kaolin, it provides a synergistic effect between the skeleton and the flame-retardant material, improving flame retardant performance. (After a cable is subjected to prolonged flame exposure, its surface material may carbonize, but the residual voids formed by the raw kaolin and calcined kaolin prevent continuous combustion of the surface material, thus completely solving the problem of flame transmission from the cable surface.) Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example

[0022] This invention provides a EPDM rubber-based functional filler composition, which, by mass parts, comprises: 100 parts of EPDM raw rubber (Keltan 2470L), 8 parts of hexagonal boron nitride nanosheets (BNNSs), 40 parts of aluminum hydroxide (ATH), 30 parts of ceramicized composite powder filler, 2 parts of silane coupling agent (KH-550), 2.5 parts of dicumyl peroxide (DCP), 1.5 parts of triallyl isocyanurate (TAIC), 1 part of antioxidant RD, and 1 part of stearic acid.

[0023] The preparation method of calcined kaolin is as follows: raw kaolin and low melting point glass powder (flux) are mixed at a mass ratio of 1:0.4, and calcined at 800℃ for 3 hours to obtain ceramic body. The ceramic body is then ground into powder with an average particle size of 5μm to obtain calcined kaolin powder.

[0024] Kaolin raw material and calcined kaolin were mixed at a mass ratio of 1:0.5 to obtain ceramic composite powder filler.

[0025] EPDM rubber was plasticized in an internal mixer at 50°C for 3 minutes; then, hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), ceramicized composite powder filler, silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid were added to the internal mixer in a segmented feeding manner.

[0026] Specifically, first add hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), and ceramic composite powder filler, and mix for 5 minutes. Then add silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid, and continue mixing for 5 minutes. Then discharge the adhesive at 110℃ to obtain the mixed rubber compound.

[0027] The compounded rubber is added to a rubber extruder and then wrapped around the cable conductor through the extruder head to form an insulation layer.

[0028] A continuous vulcanization process is adopted, with a vulcanization temperature of 170℃ and a pressure of 1.5MPa inside the vulcanization pipeline, to continuously vulcanize the cable covered with an insulation layer. Example

[0029] This invention provides a EPDM rubber-based functional filler composition, which, by mass parts, comprises: 100 parts of EPDM raw rubber (Keltan 2470L), 22 parts of hexagonal boron nitride nanosheets (BNNSs), 32 parts of aluminum hydroxide (ATH), 36 parts of ceramicized composite powder filler, 2 parts of silane coupling agent (KH-550), 1.5 parts of dicumyl peroxide (DCP), 1.5 parts of triallyl isocyanurate (TAIC), 1 part of antioxidant RD, and 1 part of stearic acid.

[0030] The preparation method of calcined kaolin is as follows: raw kaolin and low melting point glass powder (flux) are mixed at a mass ratio of 1:0.5, and calcined at 800℃ for 3 hours to obtain ceramic body. The ceramic body is then ground into powder with an average particle size of 5μm to obtain calcined kaolin powder.

[0031] Kaolin raw material and calcined kaolin were mixed at a mass ratio of 1:0.5 to obtain ceramic composite powder filler.

[0032] EPDM rubber was plasticized in an internal mixer at 50°C for 3 minutes; then, hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), ceramicized composite powder filler, silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid were added to the internal mixer in a segmented feeding manner.

[0033] Specifically, first add hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), and ceramic composite powder filler, and mix for 5 minutes. Then add silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid, and continue mixing for 5 minutes. Then discharge the adhesive at 110℃ to obtain the mixed rubber compound.

[0034] The compounded rubber is added to a rubber extruder and then wrapped around the cable conductor through the extruder head to form an insulation layer.

[0035] A continuous vulcanization process is adopted, with a vulcanization temperature of 170℃ and a pressure of 1.5MPa inside the vulcanization pipeline, to continuously vulcanize the cable covered with an insulation layer. Example

[0036] This invention provides a EPDM rubber-based functional filler composition, which, by mass parts, comprises: 100 parts of EPDM raw rubber (Keltan 2470L), 26 parts of hexagonal boron nitride nanosheets (BNNSs), 45 parts of aluminum hydroxide (ATH), 32 parts of ceramicized composite powder filler, 2 parts of silane coupling agent (KH-550), 1.5 parts of dicumyl peroxide (DCP), 1.5 parts of triallyl isocyanurate (TAIC), 1 part of antioxidant RD, and 1 part of stearic acid.

[0037] The preparation method of calcined kaolin is as follows: raw kaolin and low melting point glass powder (flux) are mixed at a mass ratio of 1:0.6, and calcined at 800℃ for 3 hours to obtain ceramic body. The ceramic body is then ground into powder with an average particle size of 5μm to obtain calcined kaolin powder.

[0038] Kaolin raw material and calcined kaolin were mixed at a mass ratio of 1:0.4 to obtain ceramic composite powder filler.

[0039] EPDM rubber was plasticized in an internal mixer at 50°C for 3 minutes; then, hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), ceramicized composite powder filler, silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid were added to the internal mixer in a segmented feeding manner.

[0040] Specifically, first add hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), and ceramic composite powder filler, and mix for 5 minutes. Then add silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid, and continue mixing for 5 minutes. Then discharge the adhesive at 110℃ to obtain the mixed rubber compound.

[0041] The compounded rubber is added to a rubber extruder and then wrapped around the cable conductor through the extruder head to form an insulation layer.

[0042] A continuous vulcanization process is adopted, with a vulcanization temperature of 170℃ and a pressure of 1.5MPa inside the vulcanization pipeline, to continuously vulcanize the cable covered with an insulation layer.

[0043] Comparative Example 1 (containing only raw kaolin, not calcined kaolin) This comparative example provides an embodiment of the present invention that provides a EPDM rubber-based functional filler composition, which, by mass parts, comprises: 100 parts of EPDM raw rubber (Keltan 2470L), 22 parts of hexagonal boron nitride nanosheets (BNNSs), 32 parts of aluminum hydroxide (ATH), 36 parts of kaolin raw material, 2 parts of silane coupling agent (KH-550), 1.5 parts of dicumyl peroxide (DCP), 1.5 parts of triallyl isocyanurate (TAIC), 1 part of antioxidant RD, and 1 part of stearic acid.

[0044] EPDM rubber was plasticized in an internal mixer at 50°C for 3 minutes; then, hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), kaolin raw material, silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid were added to the internal mixer in a segmented feeding manner.

[0045] Specifically, first add hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), and kaolin raw materials, and mix for 5 minutes. Then add silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid, and continue mixing for 5 minutes. Then discharge the adhesive at 110℃ to obtain the mixed rubber compound.

[0046] The compounded rubber is added to a rubber extruder and then wrapped around the cable conductor through the extruder head to form an insulation layer.

[0047] A continuous vulcanization process is adopted, with a vulcanization temperature of 170℃ and a pressure of 1.5MPa inside the vulcanization pipeline, to continuously vulcanize the cable covered with an insulation layer.

[0048] Comparative Example 2 (excluding raw kaolin, containing only calcined kaolin) This comparative example provides an embodiment of the present invention that provides a EPDM rubber-based functional filler composition, which, by mass parts, comprises: 100 parts of EPDM raw rubber (Keltan 2470L), 22 parts of hexagonal boron nitride nanosheets (BNNSs), 32 parts of aluminum hydroxide (ATH), 36 parts of calcined kaolin, 2 parts of silane coupling agent (KH-550), 1.5 parts of dicumyl peroxide (DCP), 1.5 parts of triallyl isocyanurate (TAIC), 1 part of antioxidant RD, and 1 part of stearic acid.

[0049] The preparation method of calcined kaolin is as follows: raw kaolin and low melting point glass powder (flux) are mixed at a mass ratio of 1:0.5, and calcined at 800℃ for 3 hours to obtain ceramic body. The ceramic body is then ground into powder with an average particle size of 5μm to obtain calcined kaolin powder.

[0050] EPDM rubber was plasticized in an internal mixer at 50°C for 3 minutes; then, hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), calcined kaolin powder, silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid were added to the internal mixer in a segmented feeding manner.

[0051] Specifically, first add hexagonal boron nitride nanosheets (BNNSs), aluminum hydroxide (ATH), and calcined kaolin powder, mix for 5 minutes, then add silane coupling agent (KH-550), dicumyl peroxide (DCP), triallyl isocyanurate (TAIC), antioxidant RD, and stearic acid, continue mixing for 5 minutes, and discharge the adhesive at 110℃ to obtain the mixed rubber compound.

[0052] The compounded rubber is added to a rubber extruder and then wrapped around the cable conductor through the extruder head to form an insulation layer.

[0053] A continuous vulcanization process is adopted, with a vulcanization temperature of 170℃ and a pressure of 1.5MPa inside the vulcanization pipeline, to continuously vulcanize the cable covered with an insulation layer.

[0054] Sample preparation Cable samples covered with insulation layers obtained from each of the embodiments (Example 1, Example 2, Example 3) and the comparative examples (Comparative Example 1, Comparative Example 2) were taken.

[0055] Testing methods (a) Volume resistivity The test was conducted according to GB / T 3048.5-2007 "Test Methods for Electrical Performance of Wires and Cables". A 5m long insulated core sample was taken, the sheath was stripped from the end to expose the conductor, and then sealed with a heat-shrinkable plastic cap. The sample was then immersed in water, and the insulation resistance between the conductor and the water was measured. The test voltage was 500V, and the sample was equilibrated for 24 hours in an environment of (23±2)℃ and (50±5)%RH.

[0056] (ii) Thermal conductivity A sample was cut from the cable insulation layer, and a disc-shaped sample with a diameter of 50.8 mm was cut using a circular cutter. The sample was placed between the hot and cold plates of the heat flux and thermal conductivity meter, and a compressive load of 0.28 MPa was applied. The heat flow and temperature difference through the sample under steady state were measured, and the thermal conductivity was calculated.

[0057] (iii) Breakdown strength (dielectric strength) The test shall be conducted in accordance with GB / T 1695. The conductor shall be removed from the insulated wire core to form an insulating sheet of uniform thickness. The sample shall be placed between two electrodes and a 50 Hz power frequency voltage shall be applied at a specified voltage increase rate until dielectric breakdown occurs. The breakdown voltage divided by the sample thickness shall be the breakdown strength.

[0058] (iv) Flame retardant rating (vertical combustion) The test was conducted according to UL94, "Tests for flammability of plastic materials for use in equipment and appliance components." A 125mm × 13mm strip sample was cut from the cable insulation and placed in an environment of 23±2℃ and 50±5%RH for 48 hours, followed by aging in a 70℃ oven for 168 hours. The sample was fixed vertically, with a flame height of 20mm. After the flame was applied for 10 seconds, it was removed, and the afterflame time was recorded to determine the flame retardancy rating.

[0059] The cable samples covered with insulation layers obtained from each embodiment (Example 1, Example 2, Example 3) and the comparative examples (Comparative Example 1, Comparative Example 2) were tested, and the results are shown in Table 1 below:

[0060] Table 1 It is evident that the performance of Example 2 is superior to that of Example 1, Example 3, Comparative Example 1, and Comparative Example 2. Its performance advantages are reflected in the following aspects: (1) Synergistic formulation of hexagonal boron nitride nanosheets (BNNSs) and ceramic composite powder filler: In Example 2, the amount of hexagonal boron nitride nanosheets (BNNSs) was 22 parts and the amount of ceramic composite powder filler was 36 parts; compared with Example 1 and Example 3 (which increased the amount of hexagonal boron nitride nanosheets (BNNSs)), the thermal conductivity network of Example 2 was more complete, the thermal conductivity was increased by 18.1%, and the volume resistivity was reduced from 1.6×10¹ 5 Ω·cm increased to 2.1×10¹5 Ω·cm.

[0061] (2) Optimization of Aluminum Hydroxide (ATH) Dosage: In Example 2, the amount of aluminum hydroxide (ATH) was 32 parts, lower than the 40 parts in Example 1 and the 45 parts in Example 3. Aluminum hydroxide (ATH) decomposes and absorbs heat at high temperatures, but excessive aluminum hydroxide (ATH) will dilute the volume fraction of the thermally conductive filler and reduce the continuity of the thermally conductive network. At the same time, the thermal conductivity of aluminum hydroxide (ATH) particles themselves is low (about 0.2 to 0.3 W / (m·K)), and excessive filling will hinder the transfer of heat between fillers. In Example 2, the amount of aluminum hydroxide (ATH) was controlled at 32 parts, which ensured the flame retardant effect (UL94 V-0, afterflame time t1 / t2 only 1.8 / 2.3s) while avoiding excessive dilution of thermal conductivity, thus achieving the best balance between thermal conductivity and flame retardancy.

[0062] (3) Optimal blending of raw kaolin and calcined kaolin: In Example 2, the mass ratio of raw kaolin to calcined kaolin was 1:0.5, that is, the proportion of raw material was about 66.7% and the proportion of calcined material was about 33.3%. Compared with Example 1 (raw material: calcined material = 1:0.5, but the total amount of filler was low, only 30 parts), Example 2 increased the total amount of ceramic composite powder filler to 36 parts, while maintaining the optimal blending ratio of 1:0.5, which improved both the ceramic effect and the insulation performance. Compared to Example 3 (raw material: calcined material = 1:0.4, with a relatively low proportion of calcined material), Example 2 has a higher proportion of calcined kaolin, which provides a more sufficient pre-made ceramic skeleton and ceramic seed crystals, resulting in better breakdown strength (89.2 kV / mm vs 82.3 kV / mm) and thermal conductivity (1.24 W / (m·K) vs 1.12 W / (m·K)).

[0063] Comparing the data of Example 2 with Comparative Examples 1 and 2, it is evident that Comparative Example 2, containing only calcined kaolin, while providing a pre-fabricated ceramic framework and seed crystals, lacks the chemical ceramic-forming activity of the kaolin raw material. The process of removing crystal water from the kaolin raw material at high temperature is an endothermic reaction, effectively absorbing heat and delaying the temperature rise of the EPDM matrix, thus buying time for the ceramicization reaction. The lack of raw material means the loss of this important physical cooling mechanism, resulting in a significantly prolonged afterflame time. The ceramic phase generated by the in-situ reaction of kaolin raw material and flux at high temperature can cooperate with the pre-fabricated framework of calcined kaolin to form a denser and more continuous overall structure. When only calcined kaolin is present, there is insufficient bonding force between ceramic particles, gaps exist between fillers, and flame retardant performance decreases. Moreover, calcined kaolin has lost its crystal water and surface-active groups, which may result in weaker interfacial bonding with the EPDM matrix, leading to lower breakdown strength and volume resistivity compared to Example 2.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A EPDM-based functional filler composition, characterized in that, By mass, it includes the following components: 100 parts of EPDM rubber; 5-30 parts of thermally conductive and insulating filler; 10-50 parts of flame-retardant filler; 10-40 parts of ceramicized composite powder filler; Interface modifier 1-5 parts; 1-5 parts of vulcanizing aid; Other adjuvants: 1-3 parts; The thermally conductive insulating filler comprises hexagonal boron nitride nanosheets and / or boron nitride nanosheets; The ceramicized composite powder filler comprises kaolin raw material and calcined kaolin, and the content of calcined kaolin is not less than 35%. The volume resistivity of the composition after vulcanization is not less than 1×10⁻⁶. 14 Ω·cm, thermal conductivity not less than 0.5 W / (m·K).

2. The EPDM-based functional filler composition according to claim 1, characterized in that: The flame-retardant filler is one or more of aluminum hydroxide, magnesium hydroxide, and ammonium polyphosphate.

3. The EPDM-based functional filler composition according to claim 1, characterized in that: The preparation method of calcined kaolin is as follows: Kaolin raw material is mixed with flux and then calcined at 800℃~1000℃ for 2~4 hours to obtain ceramic body. The ceramic body is then ground into powder to obtain calcined kaolin.

4. The EPDM-based functional filler composition according to claim 3, characterized in that: The mass ratio of raw kaolin to calcined kaolin in the ceramicized composite powder filler is 1:0.4 to 0.

7.

5. The EPDM-based functional filler composition according to claim 1, characterized in that: The vulcanization aid includes a vulcanizing agent and a vulcanizing co-agent. The vulcanizing agent is a peroxide vulcanizing agent, and the vulcanizing co-agent is a polyfunctional acrylate or maleimide vulcanizing co-agent.

6. The EPDM-based functional filler composition according to claim 1, characterized in that: The other additives are one or more of the following: dispersants, lubricants, antistatic agents, colorants, thickeners, anti-scorching agents, smoke suppressants, antibacterial agents, and anti-aging agents.

7. A method for preparing a EPDM-based functional filler composition, characterized in that, Includes the following steps: S1. Mix raw kaolin with flux and calcine at 800℃~1000℃ for 2~4 hours to obtain ceramic body. Grind the ceramic body into powder to obtain calcined kaolin powder. S2. The calcined kaolin powder obtained in step S1 is mixed with raw kaolin at a mass ratio of 1:0.4 to 0.7 to obtain ceramicized composite powder filler. S3. Plasticize EPDM rubber in an internal mixer at 40-60°C for 2-5 minutes; then add thermally conductive and insulating filler, flame-retardant filler, ceramicized composite powder filler, interface modifier and other additives to the internal mixer, and mix at 80-130°C for 5-15 minutes to obtain a mixed rubber compound. S4. Add the compounded rubber to the rubber extruder and wrap it around the cable conductor through the extruder head to form an insulation layer; S5. A continuous vulcanization process is used to continuously vulcanize the cable covered with an insulation layer through a vulcanization pipeline.

8. The method for preparing the EPDM-based functional filler composition according to claim 7, characterized in that: The average particle size of the calcined kaolin powder obtained in step S1 is 1 μm to 10 μm.

9. The method for preparing the EPDM-based functional filler composition according to claim 7, characterized in that: The mixing process in step S1 adopts a segmented feeding method. First, thermally conductive and insulating filler, flame-retardant filler and ceramic composite powder filler are added and mixed for 3 to 8 minutes. Then, interface modifier and other additives are added and mixed for another 3 to 8 minutes.

10. The method for preparing the EPDM-based functional filler composition according to claim 1, characterized in that: The vulcanization temperature of the S5 step continuous vulcanization process is 160–200℃, and the pressure inside the vulcanization pipeline is 0.5–3.0 MPa.

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