High-temperature-resistant EPDM (Ethylene-Propylene-Diene Monomer) rubber compound suitable for salt bath vulcanization for engine sheath and preparation method thereof

Abstract

The invention relates to the technical field of rubber compound materials, and particularly discloses a high-temperature-resistant EPDM rubber compound suitable for salt bath vulcanization for an engine sheath and a preparation method of the high-temperature-resistant EPDM rubber compound. The invention discloses a high-temperature-resistant EPDM rubber compound for an engine sheath. The high-temperature-resistant EPDM rubber compound specifically comprises the following components in parts by weight: 100-150 parts of EPDM raw rubber, 90-150 parts of filler, 25-45 parts of paraffin oil, 4-7 parts of magnesium oxide, 1-3 parts of a dispersing agent, 1-3 parts of a thermal oxidation anti-aging agent, 4-8 parts of a cross-linking agent and 2-5 parts of an assistant cross-linking agent, the EPDM raw rubber is formed by mixing oil-extended EPDM 10675C and low Mooney viscosity EPDM S505A; the filler is prepared from fast extruding furnace black N550, semi-reinforced carbon black N774, silane modified kaolin and PEG (Polyethylene Glycol) 4000. According to the method provided by the invention, the extrusion processability and high temperature resistance of the rubber material can be effectively balanced, and the prepared rubber compound is suitable for salt bath vulcanization.

Description

Technical Field

[0001] This application relates to the technical field of compound rubber materials, specifically to a high-temperature resistant EPDM compound rubber suitable for salt bath vulcanization of engine sheaths and its preparation method. Background Technology

[0002] Currently, the EPDM compound rubber used in traditional engine housings mostly adopts a sulfur vulcanization system, which has limited heat resistance. Although it can maintain short-term stability under the normal operating temperature of 120-150℃ in the engine compartment, long-term use is prone to problems such as cross-linking network degradation, increased hardness, and loss of elasticity. In local high-temperature areas of the engine compartment (such as near the turbocharger, where the instantaneous temperature can reach 200℃), housings made of ordinary EPDM compound rubber will crack and become brittle within 3-6 months, leading to exposed wiring harnesses, causing circuit failures and even safety hazards.

[0003] To overcome the high-temperature resistance bottleneck, peroxide vulcanization systems, due to their ability to form stable carbon-carbon crosslinks, theoretically allow EPDM compounds to be used for extended periods at 150-200℃. However, traditional peroxide vulcanization relies heavily on vulcanizing tanks, whose slow, low-temperature vulcanization characteristics result in low production efficiency and high costs. In contrast, salt bath vulcanization offers advantages such as a high-temperature environment and rapid vulcanization within 1-3 minutes. Furthermore, the uniform heat transfer through the salt medium during vulcanization effectively prevents localized over- or under-vulcanization. However, salt bath vulcanization faces challenges in compound compatibility: Firstly, it easily generates porosity defects during extrusion vulcanization. EPDM compounds often employ a lower hardness design to ensure flexibility. Low-hardness compounds tend to have higher volatile content in plasticizers and other additives. Combined with the fact that peroxides are prone to premature decomposition due to localized shear heat during high-speed extrusion, the generated gases cannot be expelled in time. These gases are then trapped and form porosity after rapid vulcanization in the salt bath, leading to decreased product density and reduced mechanical properties (such as tensile strength). Secondly, the fluidity compatibility of the compound is poor under high-speed extrusion conditions. Low-hardness rubber compounds have low viscosity, but the dispersion stability of peroxides decreases under the combined action of screw shearing and die shearing during high-speed extrusion. At the same time, the frictional resistance between the rubber compound and the equipment flow channel changes, making it difficult to accurately match the flowability with the extrusion speed and vulcanization rhythm.

[0004] Therefore, developing an EPDM compound that can fully leverage the high-temperature resistance of peroxides and is compatible with the rapid salt bath vulcanization process has become the key to solving the industry's dual demands for "high performance" and "high efficiency". Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a high-temperature resistant EPDM compound suitable for salt bath vulcanization of engine sheaths and its preparation method.

[0006] In the first aspect, this application provides a high-temperature resistant EPDM compound for engine sheaths, specifically comprising the following components in parts by weight: 100-150 parts of EPDM raw rubber, 90-150 parts of filler, 25-45 parts of paraffin oil, 4-7 parts of magnesium oxide, 1-3 parts of dispersant, 1-3 parts of thermo-oxidative antioxidant, 4-8 parts of crosslinking agent, and 2-5 parts of co-crosslinking agent; The EPDM raw rubber is composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 5-8:5-7. The filler was prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 5-7:3-5:1-3:0.1-0.3.

[0007] This application requires the mixed rubber compound to have good flowability for online extrusion vulcanization, facilitating molding through the extruder screw and die, and avoiding excessive extrusion pressure, surface roughness, or material breakage due to excessively high viscosity; however, it also cannot suffer from melt fracture or dimensional instability due to excessively low viscosity. Furthermore, it aims to reduce the use of paraffin oil to avoid the formation of porosity due to excessive low-molecular-weight substances. Therefore, the EPDM raw rubber needs to be selected using a combination of high Mooney-extended EPDM 10675C and low Mooney-extended EPDM S505A to meet extrusion performance requirements while maintaining a certain level of Mooney viscosity.

[0008] In the filler system selected in this application: high-structure fast-extrusion carbon black N550 has good processing fluidity and can impart good physical and mechanical properties to the product, but its aggregates are dendritic and easily form a network structure, which can easily adsorb peroxides or bubbles, increasing the risk of porosity; medium-low structure semi-reinforcing carbon black N774 can reduce the adsorption of peroxides and avoid uneven local crosslinking and bubble generation during vulcanization, but its insufficient reinforcing efficiency affects the product strength. Therefore, a specific amount of fast-extrusion carbon black N550 and semi-reinforcing carbon black N774 are used together. During salt bath vulcanization, volatile residual low-molecular-weight substances and gaseous products from the decomposition of peroxide vulcanization systems in the rubber compound cannot escape in time due to the liquid state of the salt bath medium. These products tend to accumulate inside the rubber product, forming pores. Adding an appropriate amount of silane-modified kaolin to the rubber compound can effectively suppress these pore defects. The working principle is as follows: silane-modified kaolin is uniformly dispersed in the rubber compound, forming a dense network structure that acts as a physical barrier, hindering the free diffusion and aggregation of gas molecules and reducing the probability of bubble nucleation. Simultaneously, silane-modified kaolin can appropriately increase the viscosity of the rubber compound, reducing its flowability during extrusion. PEG4000 can coat the surface of filler particles, reducing the interaction between fillers and thus promoting filler dispersion in the rubber matrix, improving system uniformity, and reducing extrusion pressure. PEG itself has certain lubricating properties, which can further reduce the viscosity of the rubber compound, improve demolding properties, and enhance the surface smoothness of the extruded product. This ensures that the filler can fully function and guarantees the controllability of the vulcanization process at high temperatures.

[0009] This application uses high flash point, low volatility paraffin oil to reduce the volatilization of low molecular weight substances during high-temperature peroxide salt bath volatilization, thus avoiding the impact of product cross-section pores on product performance; at the same time, it ensures the stability of the volatilization system and avoids fluctuations in volatilization speed or a decrease in crosslinking density due to oil volatilization.

[0010] This application selects bis(2,5-diphenyl) peroxide as a crosslinking agent with a high-temperature half-life suitable for salt bath vulcanization temperature (200-300℃). Its half-life is about 1 minute at 200℃. When used in conjunction with a co-crosslinking agent, it can optimize vulcanization efficiency, increase crosslinking density and improve the performance of rubber products through synergistic effect. At the same time, the addition of MgO (zinc-free formulation design avoids heavy metal pollution from saline wastewater) can neutralize the acidic byproducts (such as tert-butyl alcohol) produced by the decomposition of bis(2,5-diphenyl) peroxide, stabilizing the vulcanization system. It ensures that the crosslinking reaction and gas release are synchronized, avoiding the generation of a large amount of gas that cannot be discharged due to excessively rapid decomposition.

[0011] Preferably, the high-temperature resistant EPDM compound for engine sheaths specifically comprises the following components in parts by weight: 120-140 parts EPDM raw rubber, 110-130 parts filler, 30-40 parts paraffin oil, 5-6 parts magnesium oxide, 1.5-2.5 parts dispersant, 1.5-2.5 parts thermo-oxidative antioxidant, 5-7 parts crosslinking agent, and 3-4 parts co-crosslinking agent.

[0012] Preferably, the EPDM raw rubber is composed of oil-extended EPDM 10675C and low Mooney EPDMS505A in a weight ratio of 7-8:5-6.

[0013] In one specific implementation, the weight ratio of oil-extended EPDM 10675C and low Mooney EPDMS505A in the EPDM raw rubber can be 7:5, 7:6, 8:5, or 8:6.

[0014] Experimental analysis shows that the use of the above-mentioned weight ratio of oil-extended EPDM 10675C and low Mooney EPDMS505A to form EPDM raw rubber can further improve the performance of the compounded rubber product.

[0015] Preferably, the filler is prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 6-7:3-4:1-2:0.15-0.25.

[0016] In one specific implementation, the filler can be prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in weight ratios of 6.5:3.5:1.5:0.2 and 6:3:1:0.2.

[0017] Experimental analysis shows that the filler prepared by this application using the above-mentioned weight ratio of fast-extrusion carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 can further improve the performance of the compounded rubber product.

[0018] Preferably, the method for preparing the silane-modified kaolin in the filler is as follows: Kaolin was placed in an ethanol-water solution containing 0.8-1.5 wt% silane coupling agent KH-550 and stirred at 60-70℃ for 2-3 hours. Then it was dried at 80-90℃ for 4-6 hours to obtain silane-modified kaolin. The ethanol-water solution was composed of a mixture of ethanol and water in a volume ratio of 8-10:1, and the pH was adjusted to 4-5 with acetic acid.

[0019] Preferably, the method for preparing the filler is as follows: After mixing fast-extrusion carbon black N550 and semi-reinforcing carbon black N774, add 5-8% of the total mass of carbon black in ethanol as a dispersion medium. Ball mill for 2-3 hours at a ball-to-material ratio of 7-9:1 and a rotation speed of 300-400 r / min. Then dry at 70-80℃ for 3-4 hours and pulverize through a 200-mesh sieve to obtain carbon black mixed powder. Mix the silane-modified kaolin and carbon black powder evenly at a speed of 800-1000 r / min, heat to 60-70℃, add PEG4000, then heat to 80-90℃, increase the speed to 1200-1500 r / min, and stir for 30-50 min. The material temperature is reduced to below 40℃, and it is crushed through a 200-mesh sieve to obtain the filler.

[0020] Preferably, the dispersant is L-24; the thermo-oxidative antioxidant is 445.

[0021] Preferably, the crosslinking agent is dipentyl dithiocarbonate; the co-crosslinking agent is TMPTMA.

[0022] Secondly, this application provides a method for preparing the high-temperature resistant EPDM compound for the engine sheath, specifically including the following steps in sequence: (1) Mixing: Put EPDM raw rubber, magnesium oxide, dispersant, and thermo-oxidative antioxidant into a mixer, and reduce the pressure of the top plug to 5-7 bar at a speed of 40-50 r / min for 70-90 s; Add filler and paraffin oil, and at a speed of 20-40 r / min, lower the top plug and apply a pressure of 5-7 bar until the temperature reaches 110-120℃; Maintain the top bolt in the high position for 8-15 seconds at a rotation speed of 20-40 r / min; At a rotation speed of 10-20 r / min, lower the top bolt and apply a pressure of 2-4 bar until the temperature reaches 130-140℃; Add crosslinking agent and co-crosslinking agent, maintain a speed of 10-20 r / min, lower the top bolt and apply a pressure of 2-4 bar for 15-30 seconds, and after the temperature is ≤140℃, open the discharge door and discharge the rubber compound to the open mill below to obtain the semi-finished rubber compound. (2) Post-processing: The semi-finished rubber compound is cooled by passing it through two open mills with a roller temperature of ≤60℃, followed by rubber filtration, rubber sheeting, cooling and storage.

[0023] In one specific implementation, the top bolt is lowered at a speed of 10-20 r / min, and the pressure of 2-4 bar is applied until the temperature reaches 130-140°C; Add crosslinking agent and co-crosslinking agent, and maintain a pressure of 2-4 bar with the top jack lowered at a speed of 10-20 r / min for 15-30 seconds. At the same time, after the temperature is ≤140℃ (the temperature of the reaction system will rise during the pressure maintenance period; the temperature needs to be controlled not to exceed 140℃ during the pressure process before unloading), open the discharge door and discharge the rubber compound to the open mill below to obtain the semi-finished rubber compound.

[0024] In one specific implementation, the specific steps of the rubber sheeting, cooling and storage are as follows: the filtered rubber compound is passed through a selected mold and is divided into multiple strips of fixed width and thickness and then sequentially immersed in a cold water tank and a release agent tank from the rubber filter; the rubber strips are then suspended in a cooling box for cooling and drying; when the temperature of the rubber sheet drops below 35°C, the rubber sheet is stacked and packaged.

[0025] Thirdly, this application provides the application of the high-temperature resistant EPDM compound in engine sheaths.

[0026] In summary, the technical solution of this application has the following effects: The compound provided in this solution solves the problem of adapting the poor flowability of the salt bath extrusion section of the engine sleeve to the problem of poor flowability of the rapid extrusion by precisely selecting the raw rubber type and matching the types of fillers "fast extrusion carbon black N550, semi-reinforcing carbon black N774, silane modified kaolin, PEG4000", as well as the synergistic optimization of the ratio of crosslinking agent and co-crosslinking agent.

[0027] The compound rubber provided in this solution presents a dense state as an engine cover, with no visible pore defects.

[0028] The compound provided by this solution can meet the extrusion speed of salt bath vulcanization, enabling continuous production and improving production efficiency. Furthermore, the salt medium provides uniform heat transfer during vulcanization, effectively preventing local over- or under-vulcanization, thus improving product quality and reducing manufacturing costs.

[0029] The compound provided by this solution successfully integrates the high-temperature resistance advantage of the peroxide vulcanization system with the rapid salt bath vulcanization process, effectively solving the industry's dual challenges of "high performance" and "high efficiency". Detailed Implementation

[0030] The present application will be further described in detail below with reference to embodiments, comparative examples and performance test results. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0031] Example

[0032] Examples 1-5 Examples 1-5 provide a high-temperature resistant EPDM compound for engine sheaths and its preparation method.

[0033] The difference in the above embodiments is that the amount of each raw material component is different, as shown in Table 1.

[0034] The preparation method of the high-temperature resistant EPDM compound for engine sheaths suitable for salt bath vulcanization in the above embodiments is as follows.

[0035] (1) Mixing EPDM raw rubber (composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 7:6), along with magnesium oxide, dispersant L-24, and thermo-oxidative antioxidant 445, was fed into an internal mixer. The mixer was operated at 45 rpm with the top plug lowered and a pressure of 6 bar applied, and maintained for 80 seconds. The oil-extended EPDM 10675C and low Mooney EPDM S505A were supplied by Arlanxyn.

[0036] Filler (prepared from fast-extrusion carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 6.5:3.5:1.5:0.2) and paraffin oil were added, and the mixture was heated to 110℃ by reducing the pressure by 6 bar under a rotating speed of 30 r / min. The filler was prepared by placing kaolin in an ethanol-water solution containing 1 wt% silane coupling agent KH-550, stirring at 65℃ for 3 h, and then drying at 85℃ for 5 h to obtain silane-modified kaolin. The ethanol-water solution consisted of a mixture of ethanol and water in a volume ratio of 9:1, and the pH was adjusted to 4.5 with acetic acid. Mix 65g of fast-extrusion carbon black N550 and 35g of semi-reinforcing carbon black N774, then add 6g of ethanol (6% of the total carbon black mass). Ball mill for 3 hours at a ball-to-material ratio of 8:1 and a rotation speed of 350r / min. Then dry at 75℃ for 4 hours and pulverize through a 200-mesh sieve to obtain a carbon black mixed powder. Mix 15g of silane-modified kaolin and the carbon black mixed powder evenly at a rotation speed of 900r / min, heat to 65℃, add 2g of PEG4000, then heat to 85℃, increase the rotation speed to 1400r / min, and stir for 40 minutes. When the material temperature drops below 40℃, pulverize through a 200-mesh sieve to obtain the filler.

[0037] Maintain the top bolt at a speed of 30 r / min for 10 seconds; this process allows the moisture and low molecular weight substances in the rubber compound, which reaches 110°C, to evaporate.

[0038] At a rotation speed of 15 r / min, the top plug is lowered and the pressure is increased by 3 bar until the temperature reaches 130℃; this process mainly involves the further dispersion of raw rubber and various compounding agents, and secondly, the compounded rubber can achieve good flowability.

[0039] Add crosslinking agent dipentyl dithiocarbonate and co-crosslinking agent TMPTMA, maintain a speed of 15 r / min and a pressure of 3 bar for 20 seconds with the top bolt lowered, and after the temperature is ≤140℃, open the discharge door and discharge the rubber compound to the open mill below to obtain the semi-finished rubber compound.

[0040] (2) Post-processing Cooling and filtration of open mill: The semi-finished rubber compound is cooled by passing it through two open mills with a roller temperature of ≤60℃, and then it enters the rubber filter for filtration. Rubber compound sheeting, cooling, and storage: After filtration, the rubber compound is passed through a selected mold and cut into multiple strips of fixed width and thickness, which are then sequentially immersed in a cold water tank and a release agent tank from the rubber filter. The rubber strips are then suspended in a cooling box for cooling and drying. Once the temperature of the rubber sheets drops below 35°C, they are stacked and packaged.

[0041] Table 1. Amounts of each raw material component in Examples 1-5 and Comparative Examples 1-2

[0042] Examples 6-7 Examples 6-7 respectively provide a high-temperature resistant EPDM compound for engine sheaths and its preparation method.

[0043] The difference between the above embodiments and Embodiment 1 is that the type of EPDM raw rubber is different, as shown below.

[0044] In Example 6: the EPDM raw rubber was composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 8:5.

[0045] In Example 7: the EPDM raw rubber was composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 5:7.

[0046] All other process parameters in the above embodiments are the same as those in Embodiment 1.

[0047] Examples 8-10 Examples 8-10 respectively provide a high-temperature resistant EPDM compound for engine sheaths and its preparation method.

[0048] The difference between the above embodiments and Embodiment 1 is that the type of packing is different, as shown below.

[0049] In Example 8, the filler was prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 6:4:1:0.25.

[0050] In Example 9, the filler was prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 7:3:2:0.15.

[0051] In Example 10: The filler was prepared from fast extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 5:5:3:0.1.

[0052] All other process parameters in the above embodiments are the same as those in Embodiment 1.

[0053] Comparative Example Comparative Examples 1-2 Comparative Examples 1 and 2 respectively provide an EPDM compound and its preparation method.

[0054] The difference between the above comparative example and Example 1 is that the amount of each component in the EPDM compound is different, as shown in Table 1.

[0055] All other process parameters in the above comparative examples are the same as those in Example 1.

[0056] Comparative Examples 3-6 Comparative Examples 3-6 each provide an EPDM compound and its preparation method.

[0057] The difference between the above comparative example and Example 1 is as follows:

[0058] In Comparative Example 3: the EPDM raw rubber was composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 3:7.

[0059] In Comparative Example 4, the filler was obtained by directly mixing fast extruded carbon black N550, semi-reinforcing carbon black N774, kaolin (unmodified) and PEG4000 in a weight ratio of 6.5:3.5:1.5:0.2.

[0060] In Comparative Example 5, the filler was prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG2000 in a weight ratio of 6.5:3.5:1.5:0.2.

[0061] In Comparative Example 6, the filler was prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 3.5:6.5:4:0.5.

[0062] All other process parameters in the above comparative examples are the same as those in Example 1.

[0063] Performance testing (1) Compatibility with salt bath sulfidation process (1.1) Viscosity: According to the test method of GB / T 1232.1-2016, the compound rubber sample prepared in the example or comparative example was kept at a fixed temperature of 100℃ (close to the temperature before extrusion of salt bath vulcanized rubber) and a rotation speed of 2r / min for 4min, and the viscosity of the sample was tested.

[0064] (1.2) Appearance of the product: The compound rubber sample prepared in the example or comparative example is extruded using a Φ30mm single screw extruder (die head temperature 65℃, screw speed 45r / min) at an extrusion speed of 30m / min to obtain EPDM rubber material for sealing sheaths; observe whether there are any defects on the surface of the extruded product, such as scratches or bubbles.

[0065] (2) Tensile strength: The tensile strength of the compound samples prepared in the examples or comparative examples shall be determined in accordance with GB / T 528.

[0066] (3) High temperature resistance: The compound rubber samples prepared in the examples or comparative examples were placed in an aging test chamber, left to stand at 150°C for 168 hours, and then taken out and allowed to cool naturally to room temperature before the tensile strength was measured again. The tensile strength retention rate was calculated. Tensile strength retention rate = (tensile strength of the sample after the high temperature resistance test / tensile strength of the original sample) × 100%.

[0067] Test results are shown in Table 2.

[0068] Table 2 Performance test results of the compound rubber in the examples and comparative examples

[0069] As shown in Table 2 above, the mixed rubber compound prepared using the technical solution provided in this application has a viscosity of 42.7-49.8 MPa·s at 100℃, exhibiting good flowability and excellent extrusion processability. The surface of the rubber compound products treated with salt bath vulcanization is free of defects such as scratches and bubbles. Furthermore, the tensile strength retention rate of the mixed rubber after aging at 150℃ for 168 hours is ≥81%. These test performance results demonstrate that the method provided in this application, through precise synergy of the types and amounts of each raw material component, can effectively balance the extrusion processability and high-temperature resistance of the rubber compound, making it suitable for salt bath vulcanized rubber products.

[0070] By comparing the test results of Examples 1-5 and Comparative Examples 1-2, it can be seen that the amount of each raw material component has a significant impact on the performance of the mixed rubber. In Comparative Examples 1-2, the prepared mixed rubber samples had poor performance, poor flowability, and were unsuitable for salt bath vulcanization; moreover, they had poor high-temperature resistance. In contrast, the mixed rubber product prepared in this application, by precisely adjusting the amount of each raw material component, exhibits excellent extrusion processability and high-temperature resistance.

[0071] Comparing the test results of Examples 1, 6-7, and Comparative Example 3, it can be seen that the type of EPDM raw rubber has a significant impact on the performance of the blended rubber product. In Comparative Example 3, the EPDM raw rubber was composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 3:7, and the resulting blended rubber sample exhibited poor high-temperature resistance. In contrast, the EPDM raw rubber prepared in this application, composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 5-8:5-7, produces a blended rubber product with excellent extrusion processability and high-temperature resistance.

[0072] By comparing the test results of Examples 1, 8-10, and Comparative Examples 4-6, it can be seen that the type of filler has a significant impact on the performance of the mixed rubber products. In Comparative Example 4, the filler was obtained by directly mixing fast-extruded carbon black N550, semi-reinforcing carbon black N774, unmodified kaolin, and PEG4000 in a weight ratio of 6.5:3.5:1.5:0.2. In Comparative Example 5, the filler was prepared by mixing fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG2000 in a weight ratio of 6.5:3.5:1.5:0.2. In Comparative Example 6, the filler was prepared by mixing fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 3.5:6.5:4:0.5. The resulting mixed rubber samples exhibited poor extrusion processability and high-temperature resistance. In contrast, the filler prepared by this application using fast-extrusion carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 has excellent extrusion processability and high-temperature resistance properties.

[0073] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A high-temperature resistant EPDM compound for engine sheaths, characterized in that, Specifically, it includes the following components by weight: 100-150 parts EPDM raw rubber, 90-150 parts filler, 25-45 parts paraffin oil, 4-7 parts magnesium oxide, 1-3 parts dispersant, 1-3 parts thermo-oxidative antioxidant, 4-8 parts crosslinking agent, and 2-5 parts co-crosslinking agent; The EPDM raw rubber is composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 5-8:5-7. The filler was prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 5-7:3-5:1-3:0.1-0.

3.

2. The high-temperature resistant EPDM compound for engine sheaths according to claim 1, characterized in that, Specifically, it includes the following components by weight: 120-140 parts EPDM raw rubber, 110-130 parts filler, 30-40 parts paraffin oil, 5-6 parts magnesium oxide, 1.5-2.5 parts dispersant, 1.5-2.5 parts thermo-oxidative antioxidant, 5-7 parts crosslinking agent, and 3-4 parts co-crosslinking agent.

3. The high-temperature resistant EPDM compound for engine sheaths according to claim 1, characterized in that, The EPDM raw rubber is composed of oil-extended EPDM 10675C and low Mooney EPDM S505A in a weight ratio of 7-8:5-6.

4. The high-temperature resistant EPDM compound for engine sheaths according to claim 1, characterized in that, The filler was prepared from fast-extruded carbon black N550, semi-reinforcing carbon black N774, silane-modified kaolin, and PEG4000 in a weight ratio of 6-7:3-4:1-2:0.15-0.

25.

5. The high-temperature resistant EPDM compound for engine sheaths according to claim 1, characterized in that, The method for preparing the silane-modified kaolin in the filler is as follows: Kaolin was placed in an ethanol-water solution containing 0.8-1.5 wt% silane coupling agent KH-550 and stirred at 60-70℃ for 2-3 hours. Then it was dried at 80-90℃ for 4-6 hours to obtain silane-modified kaolin. The ethanol-water solution was composed of a mixture of ethanol and water in a volume ratio of 8-10:1, and the pH was adjusted to 4-5 with acetic acid.

6. The high-temperature resistant EPDM compound for engine sheaths according to claim 1, characterized in that, The method for preparing the filler is as follows: After mixing fast-extrusion carbon black N550 and semi-reinforcing carbon black N774, add 5-8% of the total mass of carbon black in ethanol as a dispersion medium. Ball mill for 2-3 hours at a ball-to-material ratio of 7-9:1 and a rotation speed of 300-400 r / min. Then dry at 70-80℃ for 3-4 hours and pulverize through a 200-mesh sieve to obtain carbon black mixed powder. Mix the silane-modified kaolin and carbon black powder evenly at a speed of 800-1000 r / min, heat to 60-70℃, add PEG4000, then heat to 80-90℃, increase the speed to 1200-1500 r / min, and stir for 30-50 min. The material temperature is reduced to below 40℃, and it is crushed through a 200-mesh sieve to obtain the filler.

7. The high-temperature resistant EPDM compound for engine sheaths according to claim 1, characterized in that, The dispersant is L-24; the thermo-oxidative antioxidant is 445.

8. The high-temperature resistant EPDM compound for engine sheaths according to claim 1, characterized in that, The crosslinking agent is dipentyl dithiocarbonate; the co-crosslinking agent is TMPTMA.

9. The method for preparing high-temperature resistant EPDM compound for engine sheaths according to any one of claims 1-8, characterized in that, Specifically, the following steps are performed sequentially: (1) Mixing: Put EPDM raw rubber, magnesium oxide, dispersant, and thermo-oxidative antioxidant into a mixer, and reduce the pressure of the top plug to 5-7 bar at a speed of 40-50 r / min for 70-90 s; Add filler and paraffin oil, and at a speed of 20-40 r / min, lower the top plug and apply a pressure of 5-7 bar until the temperature reaches 110-120℃; Maintain the top bolt in the high position for 8-15 seconds at a rotation speed of 20-40 r / min; At a rotation speed of 10-20 r / min, lower the top bolt and apply a pressure of 2-4 bar until the temperature reaches 130-140℃; Add crosslinking agent and co-crosslinking agent, maintain a speed of 10-20 r / min, lower the top bolt and apply a pressure of 2-4 bar for 15-30 seconds, and after the temperature is ≤140℃, open the discharge door and discharge the rubber compound to the open mill below to obtain the semi-finished rubber compound. (2) Post-processing: The semi-finished rubber compound is cooled by passing it through two open mills with a roller temperature of ≤60℃, followed by rubber filtration, rubber sheeting, cooling and storage.

10. The application of the high-temperature resistant EPDM compound as described in any one of claims 1-8 in engine sheaths.

Images