Semi-conductive ternary ethylene propylene rubber, and preparation method and application thereof

Abstract

The application discloses a kind of semi-conductive ternary ethylene-propylene rubber and its preparation method and application.Semi-conductive ternary ethylene-propylene rubber preparation raw materials include: ternary ethylene-propylene rubber, plasticizer, reinforcing carbon black, carbon black dispersing agent, sulfur, non-yellowing vulcanization accelerator and auxiliary agent, wherein, non-yellowing vulcanization accelerator includes dithiocarbamate salt vulcanization accelerator, sulfenamide vulcanization accelerator and thiuram vulcanization accelerator.Semi-conductive ternary ethylene-propylene rubber prepared based on the method of the application has no yellowing, no frost spray when contacting with crosslinked cable polyethylene in silicone oil infiltration environment, bonding strength can reach 8.9~10.5 MPa, volume resistivity is ≤60Ω·cm, and has excellent mechanical properties and aging resistance, effectively solves the defects of semi-conductive ternary ethylene-propylene rubber material in application process, such as yellowing, frost spray and insufficient bonding strength, and can be used as high-voltage / ultra-high-voltage cable intermediate joint inner shielding material.

Description

Technical Field

[0001] This invention relates to the field of semiconductive rubber materials technology, and in particular to a semiconductive EPDM rubber, its preparation method and application. Background Technology

[0002] With the rapid development of the power industry towards high voltage and ultra-high voltage, cross-linked cables, due to their excellent electrical insulation, mechanical properties, and aging resistance, have been widely used in power transmission, urban distribution networks, and other fields. As a key connecting component of cross-linked cable lines, the performance of cable joints directly determines the stability and safety of the entire power transmission system. Semi-conductive ethylene propylene diene monomer (EPDM) rubber, due to its good weather resistance, chemical resistance, and controllable electrical properties, has become the preferred shielding material for cable joints. Its core function is to eliminate electric field distortion between the cable insulation layer and the joint's metal components, preventing localized electric field concentration from causing insulation breakdown. Simultaneously, it must achieve tight adhesion with the polyethylene insulation layer of the cross-linked cable to prevent moisture and impurities from intruding, ensuring the joint's sealing performance and electrical reliability.

[0003] In related technologies, semiconductive EPDM rubber still has some shortcomings in practical applications. For example, to improve vulcanization efficiency, most methods use a single vulcanization accelerator (such as EG-5) in combination with a sulfur vulcanization system, or add small molecule plasticizers (such as paraffin oil or naphthenic oil). However, single accelerators are prone to producing byproducts containing chromophores during vulcanization, which migrate to the surface of the polyethylene insulation layer under silicone oil wetting, causing polyethylene yellowing. At the same time, small molecule plasticizers have poor compatibility with the EPDM substrate, are prone to migration and precipitation, causing blooming and further weakening the bonding performance. To address this, researchers have tried using a peroxide vulcanization system to reduce yellowing, but the rigid cross-linked structure it forms reduces the interfacial compatibility with polyethylene, resulting in a significant decrease in bonding strength (usually below 5 MPa). In addition, some researchers have proposed increasing the amount of cross-linking agent or adhesive to alleviate blooming or improve bonding strength, but this often results in rubber hardening, deterioration of processing performance, or the introduction of new small molecule migrants, making it difficult to simultaneously solve problems such as yellowing, blooming, and insufficient bonding.

[0004] Therefore, there is an urgent need to develop a semi-conductive EPDM rubber that can simultaneously achieve no yellowing, no blooming, and high bonding strength, in order to overcome its technical defects of easy yellowing, blooming, and insufficient bonding strength when in contact with cross-linked cable polyethylene in a silicone oil-immersed environment, and to meet the application requirements of shielding materials for intermediate joints of high-voltage and ultra-high-voltage cables. Summary of the Invention

[0005] The first objective of this invention is to provide a semi-conductive EPDM rubber that, when in contact with cross-linked cable polyethylene in a silicone oil-immersed environment, exhibits no yellowing or blooming, has an adhesion strength of 8.9~10.5 MPa, a volume resistivity ≤60Ω·cm, and also possesses excellent mechanical properties and aging resistance.

[0006] The second objective of this invention is to provide a method for preparing semiconductive EPDM rubber.

[0007] The third objective of this invention is to provide an application of semi-conductive EPDM rubber in the preparation of cross-linked cable materials.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a semiconductive EPDM rubber, which comprises, by weight, the following raw materials: 100 parts of EPDM rubber; Plasticizer 20-40 parts; 40-70 parts of reinforcing carbon black; 1-3 parts carbon black dispersant; Sulfur 1-3 parts; 1-3 parts of non-yellowing vulcanization accelerator; 4-7 parts of auxiliary agent; The non-yellowing vulcanization accelerator includes dithiocarbamate vulcanization accelerators, sulfenamide vulcanization accelerators, and thiuram vulcanization accelerators, wherein the weight ratio of the dithiocarbamate vulcanization accelerators, sulfenamide vulcanization accelerators, and thiuram vulcanization accelerators is (0.5~1.5):(0.5~1):(0.2~0.8). The plasticizer is liquid ethylene propylene diene monomer (EPDM) rubber.

[0009] The semiconductive EPDM rubber according to embodiments of the present invention has at least the following beneficial effects: This invention uses EPDM rubber as the base material, employs liquid EPDM rubber as a plasticizer to replace traditional small-molecule plasticizers, and selects a compounded non-yellowing vulcanization accelerator (dithiocarbamates, sulfenamides, and thiurams) in conjunction with a sulfur vulcanization system, along with carbon black dispersant, to prepare a semi-conductive EPDM rubber. The semi-conductive EPDM rubber prepared based on the raw materials of this invention exhibits no yellowing, blooming, or discoloration when in contact with cross-linked cable polyethylene under silicone oil impregnation conditions. It demonstrates a high bond strength of 8.9~10.5 MPa, a low volume resistivity of 37~60 Ω·cm, and a tear strength of 40~43 N / mm. Furthermore, after aging at 135℃ for 168 h, the changes in tensile strength and elongation at break are controlled within 7% and 23%, respectively, exhibiting excellent mechanical properties and aging resistance.

[0010] In some embodiments of the present invention, the third monomer of the EPDM rubber is 5-ethylidene-2-norbornene (ENB), and the content of 5-ethylidene-2-norbornene is 3~10 wt%.

[0011] In some embodiments of the present invention, the ethylene content of the EPDM rubber is 40-60 wt%.

[0012] In some embodiments of the present invention, the Mooney viscosity of the EPDM rubber is 20-40, and the test conditions are ML(1+4), 125°C.

[0013] In some embodiments of the present invention, the molecular weight of the liquid binary ethylene propylene rubber is 40,000 to 60,000.

[0014] In the formulation system of this invention, the use of liquid ethylene propylene diene monomer (EPDM) rubber as a plasticizer, compared to small-molecule plasticizers, helps to further solve problems such as blooming and discoloration. This may be related to the large molecular weight of EPDM rubber, its excellent compatibility with EPDM rubber substrate, and its low tendency to migrate and precipitate. Furthermore, during the secondary vulcanization process, a small number of bonds in the EPDM rubber molecule can participate in the cross-linking reaction, forming a synergistic cross-linking structure with the EPDM rubber substrate and the cross-linked cable polyethylene insulation layer. This also helps to enhance interfacial forces, improve the bonding strength between the rubber and polyethylene, and ensure a bonding strength ≥8 MPa.

[0015] Carbon black dispersants have good lubricating and dispersing effects, which can avoid local performance defects caused by carbon black agglomeration and uneven dispersion of additives, and further enhance the bonding performance with EPDM rubber insulation materials.

[0016] In some embodiments of the present invention, the reinforcing carbon black includes at least one of N330 type carbon black and N550 type carbon black.

[0017] In some embodiments of the present invention, the non-yellowing vulcanization accelerator is 1.7 to 2.8 parts by weight.

[0018] In some embodiments of the present invention, the weight ratio of the dithiocarbamate vulcanization accelerator, the sulfenamide vulcanization accelerator, and the thiuram vulcanization accelerator is (0.5~1.5):(0.5~1):(0.2~0.8).

[0019] This invention employs a combination of thiuram-based, dithiocarbamate-based, and hypoflavinyl amide-based vulcanization accelerators, combined with sulfur to form a synergistic vulcanization system. On one hand, this combination of accelerators ensures thorough reaction and minimizes the generation of byproducts containing chromophores, helping to block the yellowing pathway at its source and ensuring no yellowing occurs upon contact with polyethylene under silicone oil wetting. On the other hand, this composite vulcanization system avoids solubility saturation and migration precipitation caused by excessive use of a single accelerator. The synergistic effect of various accelerators not only improves vulcanization efficiency but also reduces the residue of low-molecular-weight byproducts.

[0020] In some embodiments of the present invention, the dithiocarbamate accelerator is present in parts by weight of 0.5 to 1.5.

[0021] In some embodiments of the present invention, the sulfenamide-based vulcanization accelerator is 0.5 to 1 part by weight.

[0022] In some embodiments of the present invention, the thiuram-based vulcanization accelerator is present in parts by weight of 0.2 to 0.8.

[0023] In some embodiments of the present invention, the dithiocarbamate accelerator includes accelerator BZ (zinc dibutyldithiocarbamate).

[0024] In some embodiments of the present invention, the sulfenamide-based vulcanization accelerator includes an SW accelerator.

[0025] In some embodiments of the present invention, the thiuram-based vulcanization accelerator includes the vulcanization accelerator TBzTD (tetrabenzylthiuram disulfide).

[0026] In some embodiments of the present invention, the proportion of the sulfenamide-based vulcanization accelerator added is less than 0.7%wt.

[0027] Preferably, the addition ratio of the sulfenamide-based vulcanization accelerator is 0.2%wt to 0.7%wt.

[0028] In the formulation system of this invention, sulfur and a non-yellowing sulfidation accelerator can synergistically generate polysulfide crosslinks (-S) through an ionic reaction. x - (x=2-8), accompanied by the decomposition of the promoter producing polar byproducts. This polysulfide bond is highly flexible, and its molecular chain easily penetrates into the gaps between the insulating layers, forming an interpenetrating cross-linked network; simultaneously, the active sulfur reacts with residual free radicals on the surface of the insulating layer to generate a CCS bond transition layer, achieving chemical bonding. Furthermore, the polar groups remaining after the promoter decomposition (such as -SH in thiazoles) generate dipole-dipole interactions with the insulating layer, further enhancing interfacial adsorption.

[0029] In some embodiments of the present invention, the additives include zinc oxide and antioxidants.

[0030] In some embodiments of the present invention, the zinc oxide is 3 to 5 parts by weight, and the antioxidant is 1 to 2 parts by weight.

[0031] In some embodiments of the present invention, the zinc oxide is active zinc oxide.

[0032] In some embodiments of the present invention, the antioxidant is an aniline-type antioxidant.

[0033] In some embodiments of the present invention, the aniline-type antioxidant includes at least one of 4,4'-bis(phenylisopropyl)diphenylamine and 4,4'-dioctyldiphenylamine.

[0034] A second aspect of the present invention provides a method for preparing a semiconductive EPDM rubber as described in the first aspect, comprising the following steps: S1. The EPDM rubber is plasticized and broken down according to the weight parts. S2. Add the aforementioned additives and the carbon black dispersant, and perform a first mixing process to obtain the first rubber compound; S3. Add the reinforcing carbon black and plasticizer to the first rubber compound and perform a second mixing to obtain the second rubber compound; S4. The second rubber compound is subjected to open milling and cooling treatment, and then after the first thin pass treatment, the sulfur and the non-yellowing vulcanization accelerator are added, followed by a second thin pass treatment, and then a first vulcanization and a second vulcanization are performed in sequence to obtain the final product.

[0035] In some embodiments of the present invention, the temperature of the first mixing is 100~130°C and the time is 3~10 min.

[0036] In some embodiments of the present invention, the temperature of the second mixing is 100~130°C and the time is 3~10 min.

[0037] In some embodiments of the present invention, the temperature of the initial melting is 160~180°C and the time is 8~10 min.

[0038] In some embodiments of the present invention, the first thin-pass treatment is performed 2 to 3 times.

[0039] In some embodiments of the present invention, the second thin-pass treatment is performed 8 to 10 times.

[0040] In some embodiments of the present invention, the temperature of the primary vulcanization is 160~175°C, the time is 25~35 min, and the pressure is 10~14 MPa.

[0041] In some embodiments of the present invention, the temperature of the secondary vulcanization is 155~165°C and the time is 90~120 min.

[0042] The secondary vulcanization process of this invention helps to accelerate the full volatilization of residual low-molecular-weight substances (such as accelerator byproducts and unreacted small-molecule components) in the rubber compound, avoiding blooming and discoloration. Secondly, this process helps to promote the participation of a small number of unsaturated bonds in the liquid EPDM plasticizer in the cross-linking reaction, forming a synergistic interpenetrating network with the EPDM substrate and the insulating layer, significantly improving the interfacial bonding strength.

[0043] A third aspect of the present invention provides the use of semiconductive EPDM rubber as described in the first aspect or semiconductive EPDM rubber prepared by the preparation method described in the second aspect in the preparation of cross-linked cable materials.

[0044] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 The results of the yellowing resistance test of the semiconductive EPDM rubber material prepared in Example 1 of this invention are shown.

[0046] Figure 2 The results of the yellowing resistance test of the semiconductive EPDM rubber material prepared in Comparative Example 1 of this invention are shown.

[0047] Figure 3 The results of the yellowing resistance test are for the semiconductive EPDM rubber material prepared in Comparative Example 5 of this invention. Detailed Implementation

[0048] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0049] The terms "preferred," "more preferably," etc., used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0050] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0051] In the description of this invention, the reference term "and / or" includes all and any combination of one or more of the associated listed items. For example, A and / or B includes (A and B) and (A or B).

[0052] In the description of this invention, the ethylene propylene diene monomer (EPDM) rubber was purchased from Jilin Petrochemical Company, with the grade 4050, containing approximately 52.0% ethylene, approximately 7.7% ENB, and a Mooney viscosity of 40. The test conditions were ML(1+4) and 125°C.

[0053] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0054] Example 1 This embodiment provides a semi-conductive EPDM rubber, and the specific raw materials for preparation are shown in Table 1 according to parts by weight.

[0055] Table 1:

[0056] The preparation method of the above-mentioned semiconductive EPDM insulating rubber includes the following steps: S1. Plasticizing and breaking down: According to the above weight parts, plasticize the EPDM rubber in a pressure mixer for 8 minutes to break down the rubber and improve the processing fluidity. S2. First mixing: Add zinc oxide, antioxidant and carbon black dispersant to the EPDM rubber after the above-mentioned rubber breaking, and mix at 120℃ for 5 min to make it evenly dispersed, and the process is complete; S3. Second mixing: Add half of the reinforcing carbon black and half of the plasticizer to the mixture after the first mixing, mix well, then add the remaining reinforcing carbon black and plasticizer, and continue mixing at 120℃ for 5 minutes to make the carbon black and plasticizer evenly dispersed to obtain the rubber compound. S4. Opening and cooling: The above-mentioned mixed rubber compound is opened at 170℃ for 8 minutes, and then cooled and left at 24℃ for 18 hours to eliminate internal stress. S5. Thin pass treatment: The cooled rubber compound is subjected to the first thin pass treatment using a two-roll mill, and the number of thin passes is two. Then, sulfur, vulcanization accelerator BZ, SW accelerator and vulcanization accelerator TBzTD are added, mixed well and immediately subjected to the second thin pass treatment, and the number of thin passes is nine. S6. Vulcanization Treatment: The rubber compound after the above thin-pass treatment is subjected to primary and secondary vulcanization treatments. The primary vulcanization temperature is 165℃, the vulcanization time is 30 min, and the vulcanization pressure is 12 MPa. The secondary vulcanization temperature is 160℃, the vulcanization time is 105 min, and the pressure is atmospheric pressure. After the secondary vulcanization is completed, it is naturally cooled to room temperature to obtain a semi-conductive EPDM rubber sample.

[0057] Example 2 This embodiment provides a semi-conductive EPDM rubber, which differs from Embodiment 1 in that the weight percentages are different, while the other raw materials are the same.

[0058] The specific raw materials for preparing the semiconductive EPDM rubber in this embodiment, based on parts by weight, are shown in Table 2.

[0059] Table 2:

[0060] The preparation method of the above-mentioned semiconductive EPDM insulating rubber is as described in Example 1.

[0061] Example 3 This embodiment provides a semi-conductive EPDM rubber, which differs from Embodiment 1 in that the weight percentages are different, while the other raw materials are the same.

[0062] The specific raw materials for preparing the semi-conductive EPDM rubber in this embodiment, based on parts by weight, are shown in Table 3.

[0063] Table 3:

[0064] The preparation method of the above-mentioned semiconductive EPDM insulating rubber is as described in Example 1.

[0065] Comparative Example 1 This comparative example provides a semi-conductive EPDM rubber, which differs from Example 1 in that the vulcanization-related accelerator is replaced with an equal amount of accelerator EG-5.

[0066] The specific raw materials for preparing the semiconductive EPDM rubber in this comparative example, by weight, are shown in Table 4.

[0067] Table 4:

[0068] The accelerator EG-5 was purchased from Shanghai Ruiba New Materials Technology Co., Ltd.

[0069] The preparation method of the above-mentioned semiconductive EPDM insulating rubber specifically includes the following steps: S1. Plasticizing and breaking down: According to the above weight parts, plasticize the EPDM rubber in a pressure mixer for 8 minutes to break down the rubber and improve the processing fluidity. S2. First mixing: Add zinc oxide, antioxidant and carbon black dispersant to the EPDM rubber after the above-mentioned rubber breaking, and mix at 120℃ for 5 min to make it evenly dispersed, and the process is complete; S3. Second mixing: Add half of the reinforcing carbon black and half of the plasticizer to the mixture after the first mixing, mix well, then add the remaining reinforcing carbon black and plasticizer, and continue mixing at 120℃ for 5 minutes to make the carbon black and plasticizer evenly dispersed to obtain the rubber compound. S4. Opening and cooling: The above-mentioned mixed rubber compound is opened at 170℃ for 8 minutes, and then cooled and left at 24℃ for 18 hours to eliminate internal stress. S5. Thin pass treatment: The cooled rubber compound is subjected to the first thin pass treatment using a two-roll mill, and the number of thin passes is two; then sulfur and accelerator EG-5 are added, mixed well and immediately subjected to the second thin pass treatment, and the number of thin passes is nine. S6. Vulcanization Treatment: The rubber compound after the above thin-pass treatment is subjected to primary and secondary vulcanization treatments. The primary vulcanization temperature is 165℃, the vulcanization time is 30 min, and the vulcanization pressure is 12 MPa. The secondary vulcanization temperature is 160℃, the vulcanization time is 105 min, and the pressure is atmospheric pressure. After the secondary vulcanization is completed, it is naturally cooled to room temperature to obtain a semi-conductive EPDM rubber sample.

[0070] Comparative Example 2 This comparative example provides a semi-conductive EPDM rubber, which differs from Example 1 in that the plasticizer is replaced with an equal amount of white naphthenic oil, while the rest are the same.

[0071] The specific raw materials for preparing the semiconductive EPDM rubber in this comparative example, by weight, are shown in Table 5.

[0072] Table 5:

[0073] The preparation method of the above-mentioned semiconductive EPDM insulating rubber is as described in Example 1.

[0074] Comparative Example 3 This comparative example provides a semiconductive EPDM rubber, which differs from Example 1 in that sulfur is replaced with dicumyl peroxide (DCP) and the vulcanization accelerator is replaced with triallyl isocyanurate (TAIC).

[0075] The specific raw materials for preparing the semiconductive EPDM rubber in this comparative example, by weight, are shown in Table 6.

[0076] Table 6:

[0077] The preparation method of the above-mentioned semiconductive EPDM insulating rubber specifically includes the following steps: S1. Plasticizing and breaking down: According to the above weight parts, plasticize the EPDM rubber in a pressure mixer for 8 minutes to break down the rubber and improve the processing fluidity. S2. First mixing: Add zinc oxide, antioxidant and carbon black dispersant to the EPDM rubber after the above-mentioned rubber breaking, and mix at 120℃ for 5 min to make it evenly dispersed, and the process is complete; S3. Second mixing: Add half of the reinforcing carbon black and half of the plasticizer to the mixture after the first mixing, mix well, then add the remaining reinforcing carbon black and plasticizer, and continue mixing at 120℃ for 5 minutes to make the carbon black and plasticizer evenly dispersed to obtain the rubber compound. S4. Opening and cooling: The above-mentioned mixed rubber compound is opened at 170℃ for 8 minutes, and then cooled and left at 24℃ for 18 hours to eliminate internal stress. S5. Thin pass treatment: The cooled rubber compound is subjected to the first thin pass treatment using a two-roll mill, and the number of thin passes is two; then dicumyl peroxide and triallyl isocyanurate are added, mixed well and immediately subjected to the second thin pass, and the number of thin passes is nine. S6. Vulcanization Treatment: The rubber compound after the above thin-pass treatment is subjected to primary and secondary vulcanization treatments. The primary vulcanization temperature is 165℃, the vulcanization time is 30 min, and the vulcanization pressure is 12 MPa. The secondary vulcanization temperature is 160℃, the vulcanization time is 105 min, and the pressure is atmospheric pressure. After the secondary vulcanization is completed, it is naturally cooled to room temperature to obtain a semi-conductive EPDM rubber sample.

[0078] Comparative Example 4 This comparative example provides a semi-conductive EPDM rubber, which differs from Example 1 in that no carbon black dispersant was added, but otherwise it is the same.

[0079] The specific raw materials for preparing the semiconductive EPDM rubber in this comparative example, by weight, are shown in Table 7.

[0080] Table 7:

[0081] The preparation method of the above-mentioned semiconductive EPDM insulating rubber is as described in Example 1.

[0082] Comparative Example 5 This comparative example provides a semi-conductive EPDM rubber, which differs from Example 1 in that the amount of SW accelerator is increased from 1 part to 1.5 parts, while the rest are the same.

[0083] The specific raw materials for preparing the semiconductive EPDM rubber in this comparative example, by weight, are shown in Table 8.

[0084] Table 8:

[0085] The preparation method of the above-mentioned semiconductive EPDM insulating rubber is as described in Example 1.

[0086] Detection example In this example, the molding properties of the semiconductive EPDM rubber materials prepared in Examples 1-3 and Comparative Examples 1-5 were measured, including hardness, volume resistivity, mechanical properties, aging properties, Mooney viscosity, and vulcanization time T90.

[0087] The test methods for hardness are based on GB / T531.1-2008; the test methods for volume resistivity are based on GB / T2439 2001; the test methods for Mooney viscosity are based on GB / T 1232.1 2016; the test methods for vulcanization time are based on GB / T16584 1996; and the test methods for aging performance, tensile strength, tear strength, and elongation at break are based on GB / T 528 2009.

[0088] The appearance quality inspection method includes: wearing clean gloves, taking a EPDM semiconductive rubber sample cleaned with alcohol, evenly applying a small amount of silicone oil (viscosity 12000, methyl vinyl silicone oil, manufacturer: Changlan Electrical Insulation Materials Co., Ltd.) to the surface, and sandwiching it between two cross-linked polyethylene sheets, ensuring alignment without misalignment. Then, the sample assembly is placed in a pressure device, applying a constant pressure to ensure tight contact between the two. Next, the pressurized sample is placed in a preheated oven at 90℃, maintaining a stable temperature. After 168 hours, the sample is removed, cooled for 30 minutes, and the yellowing is observed and recorded.

[0089] Please refer to Table 9 for the measurement results.

[0090] Table 9

[0091] The above results demonstrate that the semiconductive EPDM rubber prepared by the method of this invention possesses excellent mechanical properties, electrical properties, and aging resistance. The bond strength of all samples exceeds 8.9 MPa (reaching 10.5 MPa in Example 1), the volume resistivity is below 60 Ω·cm, and after aging at 135℃ for 168 h, the changes in tensile strength and elongation at break remain within the acceptable range. 7% and The staining rate should be within 23%, and the appearance should not show yellowing, blooming, or discoloration. Figure 1 The results of the yellowing resistance test of the semiconductive EPDM rubber material prepared by this invention show that the cross-linked polyethylene did not yellow.

[0092] Compared with Example 1, Comparative Example 1 used an equal amount of EG-5 accelerator to replace the variable vulcanization accelerator combination. The results showed that the vulcanization time was shortened to a certain extent, but obvious yellowing appeared on the surface of polyethylene (e.g., Figure 2 As shown in the figure, this may be related to the fact that EG-5 accelerator is prone to producing byproducts containing chromophores during the vulcanization process, which migrate to the polyethylene interface under silicone oil wetting. This indicates that although the single vulcanization accelerator EG-5 has high vulcanization efficiency, it cannot avoid the problem of yellowing. However, the compound vulcanization accelerator system of the present invention can block the generation of chromophores from the source and achieve no yellowing.

[0093] Compared with Example 1, Comparative Example 2 replaced the liquid ethylene propylene diene monomer (EPDM) rubber plasticizer with an equal amount of white naphthenic oil. The results showed that the bond strength decreased from 10.5 MPa to 8.4 MPa (a decrease of about 20%), and blooming appeared on the material surface. This may be related to the small molecular weight of white naphthenic oil, its poor compatibility with EPDM rubber substrate, and its easy migration and precipitation. This indicates that in the formulation system of the present invention, small molecule plasticizers are not conducive to enhancing interfacial bond strength.

[0094] Compared with Example 1, Comparative Example 3 used a peroxide vulcanization system (containing DCP and TAIC) to replace the sulfur and compound accelerator system. The results showed that the bond strength decreased to 7.4 MPa (a decrease of about 30%), and the volume resistivity increased to 109 Ω·cm. It is speculated that this is because the rigid CC crosslinking structure formed by the peroxide reduced the compatibility between the rubber and polyethylene interface. At the same time, the low dispersion efficiency of the peroxide system for carbon black further led to poor conductivity. In contrast, the sulfur and compound accelerator system of the present invention can achieve both high bonding and low resistance.

[0095] Compared with Example 1, Comparative Example 4 did not add carbon black dispersant, and the results showed that the overall performance of the material decreased: the tear strength decreased from 42 N / mm to 38 N / mm, the tensile strength decreased from 15 MPa to 13 MPa, the elongation at break decreased from 368% to 308%, and the change rate of elongation at break after aging deteriorated from -20.9% to -24.3%. This may be related to the uneven dispersion of carbon black and additives, and the inability of a small amount of low molecular weight substances in the formulation to be effectively adsorbed and migrated out.

[0096] Compared to Example 1, Comparative Example 5 increased the amount of SW accelerator from 1.0 part to 1.5 parts, and the results showed that the polyethylene exhibited slight yellowing (e.g. Figure 3 As shown in the figure, it is speculated that this is related to the presence of about 30% sulfenamide accelerators (with benzothiazole rings) in the SW accelerator, which will produce color-developing byproducts when the content exceeds the threshold.

[0097] In summary, this invention provides a semi-conductive EPDM rubber, its preparation method, and its application. Specifically, this invention uses EPDM rubber as the base material, employs liquid EPDM rubber as a plasticizer to replace traditional small-molecule plasticizers, and selects compounded non-yellowing vulcanization accelerators (dithiocarbamates, sulfenamides, and thiurams) in combination with a sulfur vulcanization system. Simultaneously, it incorporates carbon black dispersant and an optimized two-stage mixing and secondary vulcanization process to prepare a semi-conductive EPDM rubber. When in contact with cross-linked cable polyethylene in a silicone oil-immersed environment, it exhibits no yellowing or blooming, with a bonding strength reaching 8.9~10.5 MPa and a volume resistivity ≤60 Ω·cm. Furthermore, it possesses excellent mechanical properties and aging resistance, effectively solving the defects of yellowing, blooming, and insufficient bonding strength present in the application of semi-conductive EPDM rubber materials. It can be used as an inner shielding material for high-voltage / ultra-high-voltage cable intermediate joints.

[0098] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A semiconductive EPDM rubber, characterized in that, The preparation materials include the following by weight: 100 parts of EPDM rubber; Plasticizer 20-40 parts; 40-70 parts of reinforcing carbon black; 1-3 parts carbon black dispersant; Sulfur 1-3 parts; 1-3 parts of non-yellowing vulcanization accelerator; 4-7 parts of auxiliary agent; The non-yellowing vulcanization accelerator includes dithiocarbamate vulcanization accelerators, sulfenamide vulcanization accelerators, and thiuram vulcanization accelerators, wherein the weight ratio of the dithiocarbamate vulcanization accelerators, sulfenamide vulcanization accelerators, and thiuram vulcanization accelerators is (0.5~1.5):(0.5~1):(0.2~0.8). The plasticizer is liquid ethylene propylene diene monomer (EPDM) rubber.

2. The semiconductive EPDM rubber according to claim 1, characterized in that, The third monomer of the EPDM rubber is 5-ethylidene-2-norbornene, and the content of 5-ethylidene-2-norbornene is 3~10 wt%.

3. The semiconductive EPDM rubber according to claim 2, characterized in that, The ethylene content of the EPDM rubber is 40-60 wt%. The Mooney viscosity of the EPDM rubber is 20~40, and the test conditions are ML(1+4), 125℃.

4. The semiconductive EPDM rubber according to claim 1, characterized in that, The reinforcing carbon black includes at least one of N330 type carbon black and N550 type carbon black.

5. The semiconductive EPDM rubber according to claim 4, characterized in that, The addition ratio of the sulfonamide-based vulcanization accelerator is less than 0.7% wt.

6. The semiconductive EPDM rubber according to any one of claims 1 to 5, characterized in that, The additives include zinc oxide and antioxidants.

7. A method for preparing a semiconductive EPDM rubber as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. The EPDM rubber is plasticized and broken down according to the weight parts; S2. Add the aforementioned additives and the carbon black dispersant, and perform a first mixing process to obtain the first rubber compound; S3. Add the reinforcing carbon black and plasticizer to the first rubber compound and perform a second mixing to obtain the second rubber compound; S4. The second rubber compound is subjected to open milling and cooling treatment, and then after the first thin pass treatment, the sulfur and the non-yellowing vulcanization accelerator are added, followed by a second thin pass treatment, and then a first vulcanization and a second vulcanization are performed in sequence to obtain the final product.

8. The preparation method according to claim 7, characterized in that, The temperature of the first mixing step is 100~130℃, and the time is 3~10min; The second mixing process is carried out at a temperature of 100-130℃ for 3-10 minutes. The temperature for the initial refining process is 160~180℃, and the time is 8~10 min.

9. The preparation method according to claim 7 or 8, characterized in that, In step S4, the first thin-pass processing is performed 2 to 3 times; The second thin-pass treatment is repeated 8 to 10 times; The temperature of the first vulcanization is 160~175℃, the time is 25~35min, and the pressure is 10~14 MPa; The secondary vulcanization is carried out at a temperature of 155~165℃ for 90~120 minutes.

10. The use of the semiconductive EPDM rubber as described in any one of claims 1 to 6 in the preparation of cross-linked cable materials.

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