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, zinc oxide, antioxidant, paraffin oil, liquid binary ethylene-propylene rubber, superconducting carbon black, reinforcing carbon black, vulcanizing agent and vulcanizing aid;Wherein, the ethylene content of the liquid binary ethylene-propylene rubber is 60-75wt%, and the molecular weight is 5000-40000.Semi-conductive ternary ethylene-propylene rubber of the application selects peroxide-vulcanization mixed system, and semi-conductive ternary ethylene-propylene rubber prepared by the formulation of the application has the advantages of low volume resistivity (≤15Ω·cm), high tear strength (≥35MPa), high tensile strength (≥13MPa), high adhesive strength (≥7MPa), low gum content and product appearance not color, etc., and can be used for preparing semi-conductive material in the field of high-voltage ultra-high voltage direct current.

Description

Technical Field

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

[0002] Power cable accessories are products that connect cables to power transmission and distribution lines and related power distribution equipment, primarily used to ensure the safe operation and efficient connection of cables. Related research has found that cable accessories are prone to breakdown during withstand voltage tests, presumably due to the high volume resistivity of the semiconducting materials in the products. This resistivity is an order of magnitude higher than that of the matched cable, preventing effective matching and leading to interface heating and ablation, ultimately resulting in breakdown.

[0003] In related technologies, to achieve the electrical performance requirements of low volume resistivity, when preparing products for high-voltage and ultra-high-voltage applications, the formulation system often considers using superconducting carbon black with excellent conductivity as a filler. Superconducting carbon black has a relatively high structural integrity, and its addition amount is typically only 1 / 3 of that of conventional carbon black. However, the small amount of carbon black added results in a higher rubber content in the material, leading to problems such as material slippage during mixing and wrinkles and other appearance defects during molding. Furthermore, while a pure sulfur vulcanization system can also meet the requirements for low volume resistivity and surface resistivity, rubber compounds using a pure sulfur vulcanization system mainly form -CSC- bonds. The energy of the -CSC- bond is below 284.7 KJ / mol, while the energy range of ultraviolet light is 300-600 KJ / mol. This makes the -CSC- bonds more prone to breakage under ultraviolet irradiation, thus resulting in rubber compounds vulcanized using a sulfur vulcanization system exhibiting a tendency to age easily.

[0004] Furthermore, in the manufacturing process of cable accessories for high-voltage and ultra-high-voltage DC applications, some utilize a reverse molding process, first molding the insulating components and then composite molding the semi-conductive components. To enhance the bonding performance between the two, a certain component of tackifying resin is typically added to the formulation design. However, tackifying resin only provides physical bonding, and its low melting point (<90℃) prevents it from improving the bonding performance of the material under high-temperature conditions. Simultaneously, for accessories used in high-voltage and ultra-high-voltage applications, the outer surface of the material must be free of iridescence. Iridescence is essentially caused by small volatile molecules in rubber raw materials and additives, as well as their reaction intermediates, or small volatile molecules in release agents. These small volatile groups, such as carbon-carbon double bonds, carbonyl groups, aldehyde groups, carboxyl groups, azo groups, nitroso groups, and -C=S, absorb only certain wavelengths of light. When exposed to sunlight, the reflected light exhibits different colors. These groups are collectively called "chromophores / chromophores." When one or more substances containing chromophores migrate to the surface of the rubber compound, the surface acquires one or more colors. In semiconductive materials, carbon black has a large number of free radicals, hydrogen, hydroxyl, carboxyl groups and other groups on its surface, so the iridescence phenomenon is particularly serious. It not only affects the appearance, but the surface exudates also affect the adhesion of the material.

[0005] Therefore, there is an urgent need to develop a semiconductive material with low volume resistivity, low adhesive content, high bonding strength, and no color cast. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a semi-conductive EPDM rubber, which possesses advantages such as low volume resistivity, high bond strength, low rubber content, and a non-coloring appearance. It meets the performance parameter requirements for semi-conductive materials used in high-voltage and ultra-high-voltage DC applications, such as Shore A hardness ≤60; low volume resistivity (≤15Ω·cm); high tear strength (≥35MPa); high tensile strength (≥13MPa); high bond strength (≥7MPa); tensile strength change rate under aging conditions ≤20%; elongation at break change rate ≤20%; and a non-coloring appearance.

[0007] The present invention also proposes a method for preparing semiconductive EPDM rubber.

[0008] This invention also proposes the application of a semi-conductive EPDM rubber and its preparation method in the manufacture of cable accessories.

[0009] In a first aspect, the present invention provides a semiconductive EPDM rubber, the raw materials for which are prepared include:

[0010] EPDM rubber, zinc oxide, antioxidant, paraffin oil, liquid EPDM rubber, superconducting carbon black, reinforcing carbon black, vulcanizing agent, vulcanization aid;

[0011] The liquid ethylene propylene diene monomer (EPDM) rubber contains 60-75 wt% ethylene and has a molecular weight of 5000-40000.

[0012] The semiconductive EPDM rubber according to embodiments of the present invention has at least the following beneficial effects:

[0013] The semi-conductive EPDM rubber prepared using the formulation of this invention can simultaneously achieve low volume resistivity and surface resistivity, high bond strength, low rubber content, and no color blemishes in the product appearance.

[0014] First, this invention selects superconducting carbon black with fine particles, large specific surface area, and a high particle size per unit mass as a filler. In the adhesive system of this invention, it mainly accumulates in a network chain structure, forming a chain-like conductive structure. Therefore, even with a small amount added, it still exhibits excellent conductivity. Furthermore, the formulation of this invention also uses reinforcing carbon black as an auxiliary filler, which helps to reduce the adhesive content.

[0015] Secondly, the formulation of this invention uses a peroxide-vulcanization mixed system. During the formulation optimization process, the inventors found that while a single peroxide vulcanization system has advantages such as fast vulcanization speed and excellent aging performance, it is not conducive to improving the bonding strength of the material. On the other hand, while a pure sulfur vulcanization system can achieve high bonding strength requirements, the material's aging performance is relatively low. In the peroxide-vulcanization mixed system of this invention, the peroxide vulcanization system is the main component, and sulfur acts as a co-vulcanizing agent. In this mixed vulcanization system, the rubber material still has residual activators after the first vulcanization, which can directly improve the degree of crosslinking with the insulating material during the second vulcanization process, thereby improving the bonding strength from the material structure level.

[0016] Furthermore, the formulation system of this invention uses ethylene propylene diene monomer (EPDM) rubber and liquid EPDM rubber as plasticizers. EPDM rubber, as a reactive plasticizer, participates in the reaction during the peroxy vulcanization system and continues to participate in the crosslinking reaction with the insulating material during the secondary vulcanization process, thereby further improving the bonding strength with the insulating material. Liquid EPDM rubber, as a macromolecular plasticizer, has good compatibility with other components in the system, which helps to form a dense and consistent crosslinking network, resulting in uniform surface crosslinking density and avoiding localized stress concentration and optical differences.

[0017] In some embodiments of the present invention, the raw materials for preparation include, by weight:

[0018]

[0019] In some embodiments of the present invention, the raw materials for preparation include, by weight:

[0020]

[0021]

[0022] In some embodiments of the present invention, the raw material for preparing EPDM rubber includes ethylene-bis(norbornene), and the content of ethylene-bis(norbornene) is 3-10 wt%.

[0023] In some embodiments of the present invention, the raw material for preparing EPDM rubber includes ethylene, and the ethylene content is 40-60 wt%. Within this range, the rubber compound can maintain high filling properties while also having good flow properties and processing performance. If the ethylene content is too low, the elasticity increases, leading to lower mechanical properties and making processing difficult. If the ethylene content is too high, the elasticity decreases and the filling properties are poor.

[0024] In some embodiments of the present invention, the Mooney value of the EPDM rubber is 20 to 40 (M1+4, 125°C).

[0025] In some embodiments of the present invention, the purity of the zinc oxide is ≥99.5%.

[0026] The material formulation of this invention employs a vulcanization system, in which zinc oxide can be used as an additive to accelerate vulcanization, improve vulcanization efficiency, and enhance the mechanical properties of the rubber compound.

[0027] In some embodiments of the present invention, the zinc oxide is active zinc oxide.

[0028] Compared to conventional zinc oxide, activated zinc oxide has a smaller particle size, typically ranging from 1 to 100 nm, exhibiting a spherical shape and a larger specific surface area, making it easier to disperse during compounding. Furthermore, activated zinc oxide possesses relatively higher activity (due to finer grains, changes in surface electronic and microstructure, resulting in surface effects not found in ordinary zinc oxide) and excellent adsorption properties, which can significantly improve the vulcanization efficiency of rubber.

[0029] In some embodiments of the present invention, the antioxidant is an aniline-type antioxidant. In the formulation system of the present invention, the use of an aniline-type antioxidant helps to improve the resistance of the rubber compound to thermo-oxidative aging.

[0030] In some embodiments of the present invention, the resistivity of the superconducting carbon black is 1.0 to 1.5 Ω·m.

[0031] In some embodiments of the present invention, the apparent specific volume of the superconducting carbon black is 4.0–5.0 cm³. 3 / g; ash content 1.5–2.0%.

[0032] In some embodiments of the present invention, the superconducting carbon black has a DBP (phthalic acid) adsorption value > 400 ml / 100 g and an iodine adsorption value (specific surface area) > 950 mg / g.

[0033] In some embodiments of the present invention, the vulcanizing agent includes at least one of dicumyl peroxide (DCP) and di-tert-butyl peroxide (DTBP).

[0034] In some preferred embodiments of the present invention, the vulcanizing agent is dicumyl peroxide.

[0035] During vulcanization, dicumyl peroxide generates stable C-C crosslinks (whose chemical stability is superior to that of polysulfide bonds in sulfur systems). These crosslinks are not easily broken under high temperatures or oxidizing environments, which helps to significantly improve the aging resistance of rubber materials. In addition, the use of dicumyl peroxide helps to reduce the adsorption of insulating byproducts on the surface of conductive carbon black, thereby maintaining a suitable volume resistivity.

[0036] In some embodiments of the present invention, the vulcanizing aid is sulfur.

[0037] 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:

[0038] S1: The EPDM rubber is plasticized and broken down, and the zinc oxide and part of the liquid EPDM rubber are added for the first mixing to obtain zinc oxide masterbatch.

[0039] S2: Add the antioxidant to the zinc oxide masterbatch after mixing in step S1, and perform a second mixing. Then add the superconducting carbon black, part of the paraffin oil and part of the liquid ethylene propylene diene monomer (EPDM) rubber, and perform a third mixing. Finally, add the reinforcing carbon black, the remaining paraffin oil and the liquid EPDM rubber, and perform a fourth mixing to obtain a rubber mixture.

[0040] S3: After the rubber mixture is milled, it is cooled and left to stand. Then it is put into the mill for thin-pass treatment. The vulcanizing agent and the vulcanizing aid are added. After a second thin-pass treatment, the mixture is vulcanized to obtain the final product.

[0041] The preparation method according to embodiments of the present invention has at least the following beneficial effects:

[0042] This invention prepares rubber materials by first preparing zinc oxide masterbatch, which helps improve the overall performance of the materials. Zinc oxide, as a vulcanization aid, plays a very important role in rubber systems. It can not only accelerate the vulcanization speed and improve the heat resistance of the material, but also increase the crosslinking density of the material, thereby improving the overall mechanical properties of the material. However, due to its fine particles and tendency to agglomerate, it is not easy to disperse using conventional mixing methods. Preparing zinc oxide masterbatch can effectively solve its dispersion problem, and also helps to reduce the vulcanization time.

[0043] In some embodiments of the present invention, in step S1, the time for plasticizing and breaking down the rubber is 5 to 10 minutes.

[0044] In some embodiments of the present invention, the amount of liquid ethylene propylene diene monomer (EPDM) rubber added during the first mixing process is 1 / 12 to 1 / 16 of the total weight of liquid EPDM rubber.

[0045] In some embodiments of the present invention, the amount of liquid ethylene propylene diene monomer (EPDM) rubber added during the second mixing process is 1 / 2 of the total weight of liquid EPDM rubber.

[0046] In some embodiments of the present invention, in step S2, the paraffin oil is added in two equal parts. That is, the first addition is 1 / 2 of the total weight of the paraffin oil, and the second addition is also 1 / 2 of the total weight of the paraffin oil.

[0047] In some embodiments of the present invention, the temperatures of the first mixing, the second mixing, the third mixing, and the fourth mixing are independently selected from any temperature in the range of 100 to 130°C.

[0048] In some embodiments of the present invention, the time for the first mixing, the second mixing, the third mixing and the fourth mixing is independently 2 to 5 minutes.

[0049] In some preferred embodiments of the present invention, the first mixing time is 3 to 5 minutes;

[0050] The second mixing time is 2-4 minutes;

[0051] The third mixing time is 3-5 minutes;

[0052] The fourth mixing time is 3 to 5 minutes.

[0053] In some embodiments of the present invention, the temperature of the open mill is 160–180°C.

[0054] In some preferred embodiments of the present invention, the temperature of the open mill is 165-175°C.

[0055] In some embodiments of the present invention, the refining time is 6 to 12 minutes.

[0056] In some preferred embodiments of the present invention, the refining time is 8 to 10 minutes.

[0057] In some embodiments of the present invention, the vulcanization treatment includes a first vulcanization treatment and a second vulcanization treatment.

[0058] In some embodiments of the present invention, the temperature of the first vulcanization is 160-175°C, the vulcanization time is 25-35 min, and the vulcanization pressure is 10-14 MPa.

[0059] In some embodiments of the present invention, the temperature of the second vulcanization is 155-165°C, the vulcanization time is 90-120 min, and the pressure is atmospheric pressure.

[0060] A third aspect of the present invention provides the application of the method for preparing semiconductive EPDM rubber as described in the first aspect or the method for preparing semiconductive EPDM rubber as described in the second aspect in the preparation of cable accessories.

[0061] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0062] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0063] Figure 1 The semi-conductive EPDM rubber prepared in Example 1 of this invention;

[0064] Figure 2 This is a semi-conductive EPDM rubber prepared in Comparative Example 6 of the present invention. Detailed Implementation

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] In an embodiment of the present invention, the third monomer of the EPDM rubber (Lanxess, Germany, product number 2650) is ethylene-bis(norbornene) (ENB), the content of which is 3-10 wt%, the content of which is 40-60 wt%, and the Mooney value is 20-40 (M1+4, 125°C).

[0071] The zinc oxide is active zinc oxide with a particle size of 20-100 nm, purchased from Jiangsu Shuangsheng Zinc Industry Co., Ltd.

[0072] Antioxidant RD was purchased from Shandong Shangshun Chemical Co., Ltd.

[0073] Anti-aging agent 445 was purchased from San Lecter, USA.

[0074] The superconducting carbon black has a resistivity of 0.1–10 Ω·cm and was purchased from Ehrlich, Switzerland.

[0075] The liquid ethylene propylene diene monomer (EPDM) rubber has an ethylene content of 60-75 wt% and a molecular weight of 5000-40000 (purchased from Dongguan Shenghao Plastic Raw Materials Co., Ltd., product number SH7228).

[0076] 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.

[0077] Example 1:

[0078] This embodiment provides a semiconductive EPDM rubber and its preparation method. The raw materials for preparing the semiconductive EPDM rubber, by weight, include the following components:

[0079]

[0080] The preparation method of the above-mentioned semiconductive EPDM rubber includes the following steps:

[0081] S1: According to the above weight fraction, put the formula amount of EPDM rubber into a pressure mixer and plasticize for 8 minutes to break the rubber.

[0082] S2: Mix all the zinc oxide with the plasticized EPDM rubber obtained in step S1 and 1 / 15 of the formula amount of liquid EPDM rubber, add it to a pressure mixer and mix for 4 minutes to make zinc oxide masterbatch.

[0083] S3: Mix the above zinc oxide masterbatch and the antioxidant RD in the formula amount, and mix in a pressure mixer for 3 minutes; then add the superconducting carbon black, 1 / 2 of the paraffin oil and 1 / 2 of the liquid EPDM rubber in the formula amount and mix for 4 minutes; then add the reinforcing carbon black, the remaining paraffin oil and the remaining liquid EPDM rubber and mix for 4 minutes to obtain a rubber mixture;

[0084] S4: After discharge, heat treatment is carried out, specifically including placing the rubber mixture discharged from the internal mixer into a two-mill, mixing at 170°C for 10 minutes, cooling to room temperature and standing for 24 hours;

[0085] S5: Put the cooled and stored material into the open mill and pass it through the mill twice. Then add the formula amount of dicumyl peroxide and sulfur to the open mill, pass it through the mill 10 times, and then vulcanize it twice to form sheets. After cooling, the above EPDM rubber is obtained.

[0086] In this embodiment, the temperature of the first vulcanization is 160°C, the vulcanization time is 35 min, and the vulcanization pressure is 14 MPa; the temperature of the second vulcanization is 165°C, the vulcanization time is 120 min, and the pressure is atmospheric pressure.

[0087] Example 2:

[0088] This embodiment provides a semiconductive EPDM rubber and its preparation method. The raw materials for preparing the semiconductive EPDM rubber, by weight, include the following components:

[0089]

[0090] The preparation method of the above-mentioned semiconductive EPDM rubber includes the following steps:

[0091] S1: According to the above weight fraction, put the formula amount of EPDM rubber into a pressure mixer and plasticize for 8 minutes to break the rubber.

[0092] S2: Mix zinc oxide with the plasticized EPDM rubber obtained in step S1 and 1 / 13.3 liquid EPDM rubber, add it to a pressure mixer and mix for 4 minutes to make zinc oxide masterbatch.

[0093] S3: Mix the above zinc oxide masterbatch and the antioxidant RD in the formula, and mix in a pressure mixer for 3 minutes; then add the superconducting carbon black, half of the paraffin oil and half of the liquid EPDM rubber in the formula and mix for 4 minutes; then add the reinforcing carbon black, the remaining paraffin oil and liquid EPDM rubber and mix for 4 minutes to obtain a rubber mixture;

[0094] S4: After discharge, heat treatment is carried out, specifically including placing the rubber mixture discharged from the internal mixer into a two-mill, mixing at 170°C for 10 minutes, cooling to room temperature and standing for 24 hours;

[0095] S5: Put the cooled and stored material into the open mill and pass it through the mill twice. Then add the formula amount of dicumyl peroxide and sulfur to the open mill, pass it through the mill 10 times, and then vulcanize it twice to form sheets. After cooling, the above EPDM rubber is obtained.

[0096] In this embodiment, the temperature of the first vulcanization is 160°C, the vulcanization time is 35 min, and the vulcanization pressure is 14 MPa; the temperature of the second vulcanization is 165°C, the vulcanization time is 120 min, and the pressure is atmospheric pressure.

[0097] Example 3:

[0098] This embodiment provides a semiconductive EPDM rubber and its preparation method. The raw materials for preparing the semiconductive EPDM rubber, by weight, include the following components:

[0099]

[0100] The preparation method of the above-mentioned semiconductive EPDM rubber includes the following steps:

[0101] S1: According to the above weight fraction, put the formula amount of EPDM rubber into a pressure mixer and plasticize for 8 minutes to break the rubber.

[0102] S2: Mix zinc oxide with the plasticized EPDM rubber obtained in step S1 and 1 / 16 liquid EPDM rubber, add it to a pressure mixer and mix for 4 minutes to make zinc oxide masterbatch.

[0103] S3: Mix the above zinc oxide masterbatch and the antioxidant RD in the formula, and mix in a pressure mixer for 3 minutes; then add the superconducting carbon black, half of the paraffin oil and half of the liquid EPDM rubber in the formula and mix for 4 minutes; then add the reinforcing carbon black, the remaining paraffin oil and liquid EPDM rubber and mix for 4 minutes to obtain a rubber mixture;

[0104] S4: After discharge, heat treatment is carried out, specifically including placing the rubber mixture discharged from the internal mixer into a two-mill, mixing at 170°C for 10 minutes, cooling to room temperature and standing for 24 hours;

[0105] S5: Put the cooled and stored material into the open mill and pass it through the mill twice. Then add the formula amount of dicumyl peroxide and sulfur to the open mill, pass it through the mill 10 times, and then vulcanize it twice to form sheets. After cooling, the above EPDM rubber is obtained.

[0106] In this embodiment, the temperature of the first vulcanization is 160°C, the vulcanization time is 35 min, and the vulcanization pressure is 14 MPa; the temperature of the second vulcanization is 165°C, the vulcanization time is 120 min, and the pressure is atmospheric pressure.

[0107] Comparative Example 1:

[0108] This comparative example provides a semi-conductive EPDM rubber and its preparation method. The difference between the raw materials and those in Example 1 is that reinforcing carbon black is not added to the formulation; instead, an equal amount of superconducting carbon black is used, i.e., the amount of superconducting carbon black is 45 parts. All other raw materials are the same.

[0109] The semiconductive EPDM rubber in this comparative example was prepared according to the method in Example 1.

[0110] Comparative Example 2:

[0111] This comparative example provides a semi-conductive EPDM rubber and its preparation method. The difference between the raw materials and those in Example 1 is that superconducting carbon black is not added to the formulation; instead, an equal amount of reinforcing carbon black is used, i.e., the amount of reinforcing carbon black is 45 parts. All other raw materials are the same.

[0112] The semiconductive EPDM rubber in this comparative example was prepared according to the method in Example 1.

[0113] Comparative Example 3:

[0114] This comparative example provides a semiconductive EPDM rubber and its preparation method. The difference between the raw materials and those in Example 1 is that an equal amount of paraffin oil is used to replace the liquid EPDM rubber in the formulation, i.e., the amount of paraffin oil is 30 parts. All other raw materials are the same.

[0115] The semiconductive EPDM rubber in this comparative example was prepared according to the method in Example 1.

[0116] Comparative Example 4:

[0117] This comparative example provides a semiconductive EPDM rubber and its preparation method. The difference between the raw materials used in this preparation and those in Example 1 is that sulfur was not added, while the other raw materials are the same.

[0118] The semiconductive EPDM rubber in this comparative example was prepared according to the method in Example 1.

[0119] Comparative Example 5:

[0120] This comparative example provides a semiconductive EPDM rubber and its preparation method. The difference between the raw materials used in this preparation method and those in Example 1 is that dicumyl peroxide is not added, and the amount of sulfur is adjusted to 6 parts, while the other raw materials are the same.

[0121] The semiconductive EPDM rubber in this comparative example was prepared according to the method in Example 1.

[0122] Comparative Example 6:

[0123] This comparative example provides a semiconductive EPDM rubber and its preparation method. The difference between the raw materials and those in Example 1 is that the liquid EPDM rubber is replaced with an equal amount of solid EPDM rubber (molecular weight 50,000 to 150,000, ethylene content 72w, manufacturer: Exxon, grade: 722), while the proportions of the other raw materials are the same.

[0124] The semiconductive EPDM rubber in this comparative example was prepared according to the method in Example 1.

[0125] Comparative Example 7:

[0126] This comparative example provides a semi-conductive EPDM rubber and its preparation method, using the same raw materials as in Example 1. The difference between this preparation method and Example 1 is that zinc oxide is not prepared as a masterbatch; instead, zinc oxide powder is directly added and mixed during the preparation process. Specifically, the method includes the following steps:

[0127] S1: According to the above weight fraction, put the formula amount of EPDM rubber into a pressure mixer and plasticize for 8 minutes to break the rubber.

[0128] S2: Mix the plasticized EPDM rubber obtained in step S1, 1 / 10 of the formula amount of liquid EPDM rubber, the formula amount of zinc oxide and antioxidant RD, and mix them in a pressure mixer for 3 minutes; then add the formula amount of superconducting carbon black, 1 / 2 of the formula amount of paraffin oil and 1 / 2 of the formula amount of liquid EPDM rubber and mix for 4 minutes; then add the reinforcing carbon black, the remaining paraffin oil and liquid EPDM rubber and mix for 4 minutes to obtain a rubber mixture;

[0129] S3: After discharge, heat treatment is carried out, specifically including placing the rubber mixture discharged from the internal mixer into a two-mill, mixing at 170°C for 10 minutes, cooling to room temperature and standing for 24 hours;

[0130] S4: Put the cooled and rested material into the open mill and pass it through the mill twice. Then add the formula amount of dicumyl peroxide and sulfur to the open mill, pass it through the mill 10 times, and then vulcanize it twice to form sheets. After cooling, the above EPDM rubber is obtained.

[0131] In this comparative example, the temperature of the first vulcanization was 160℃, the vulcanization time was 35 min, and the vulcanization pressure was 14 MPa; the temperature of the second vulcanization was 165℃, the vulcanization time was 120 min, and the pressure was atmospheric pressure.

[0132] Test Example 1: Mechanical Performance Testing

[0133] This test example examines the mechanical properties (such as hardness, tear strength, tensile strength, elongation at break, and bond strength) of the semiconductive EPDM rubbers prepared in Examples 1-3 and Comparative Examples 1-7. Hardness was tested according to GB / T 531.1-2009; tear strength was tested according to GB / T 529 2008; and tensile strength, elongation at break, and bond strength were tested according to GB / T 528 2009. Five samples were used in each group, and the average values ​​were taken.

[0134] The test results are shown in Table 1:

[0135] Table 1:

[0136]

[0137] Test results show that the semi-conductive EPDM rubber material prepared by this invention has good mechanical properties.

[0138] Compared with Example 1, the antioxidant in Example 2 was changed to antioxidant 445. The amounts of superconducting carbon black and reinforcing carbon black, plasticizer paraffin oil and liquid EPDM rubber, as well as vulcanizing agent and vulcanizing aid were all taken as the minimum within the range. The results showed that the overall performance was significantly lower than that of Example 1. It is speculated that this is because the EPDM rubber has a large filler content, resulting in lower material mechanical properties, and the carbon black filler content is too small, resulting in insufficient material reinforcement.

[0139] Compared to Example 1, the amounts of superconducting carbon black and reinforcing carbon black, plasticizer paraffin oil and liquid EPDM rubber, as well as vulcanizing agent and vulcanizing aid in Example 3 were all taken at their maximum values ​​within the specified range. Based on the final results analysis, its overall performance was not significantly improved compared to Example 1. It is speculated that there is an optimal ratio for the amounts of carbon black filler, plasticizer, and vulcanizing agent; exceeding these amounts can easily lead to filler agglomeration, excessive vulcanization damaging the network structure, etc., resulting in no improvement in the overall performance of the material.

[0140] Compared to Example 1, Comparative Example 1 did not add reinforcing carbon black, but increased the amount of superconducting carbon black to 45 parts. The results showed that the tensile strength decreased from 15 MPa (Example 1) to 10 MPa, and the elongation at break decreased from 435% to 298%. This indicates that the removal of reinforcing carbon black significantly weakened the tensile properties and ductility of the material. In the formulation of this invention, reinforcing carbon black plays a role in improving mechanical strength. Furthermore, Comparative Example 2 did not add superconducting carbon black, but increased the amount of reinforcing carbon black to 45 parts. The results showed that the tensile strength was improved, but some elongation at break was sacrificed.

[0141] Compared to Example 1, Comparative Examples 3 and 6 show differences in the content or type of plasticizers (paraffin oil and liquid EPDM rubber). In Comparative Example 3, paraffin oil was used instead of liquid EPDM rubber, resulting in improved mechanical strength but significantly reduced adhesive strength. In Comparative Example 6, solid EPDM rubber was used instead of liquid EPDM rubber, resulting in decreased tear strength and tensile strength compared to Example 1, and a decrease in elongation at break from 435% to 287%. This indicates that using liquid EPDM rubber in the formulation system of this invention is more beneficial for improving the ductility of the rubber material. While solid EPDM rubber increases hardness, it may lead to a significant decrease in tear strength, tensile strength, and elongation at break. This is presumably because solid EPDM rubber is prone to localized stress concentration, thus affecting its ductility. Furthermore, due to the high Mooney viscosity of solid EPDM rubber, it cannot effectively act as a plasticizer, making material mixing difficult and prone to abnormalities such as uneven carbon black dispersion, resulting in lower overall material performance.

[0142] Compared to Example 1, the vulcanization systems in Comparative Examples 4 and 5 differ. Comparative Example 4 used only DCP without adding sulfur, showing little effect on hardness, tear strength, and tensile strength, but the bond strength decreased from 7.6 MPa to 4.9 MPa, while the elongation at break significantly decreased. This demonstrates that adding sulfur as a vulcanization aid in the system of this invention helps optimize the crosslinking network structure and enhance interfacial bonding strength. In the formulation of Comparative Example 5, only sulfur was used without adding DCP. The test results showed a decrease in tensile strength and hardness, while the elongation at break increased to some extent.

[0143] Compared with Example 1, in Comparative Example 7, zinc oxide was not made into masterbatch during the preparation of the semiconductive EPDM rubber material, and the results showed that its elongation at break and bond strength were significantly reduced.

[0144] Test Example 2: Volume Resistivity and Anti-aging Performance Testing

[0145] This test example examines the volume resistivity and anti-aging properties of the semiconductive EPDM rubbers prepared in Examples 1-3 and Comparative Examples 1-7. The volume resistivity test method is performed according to GB / T2439 2001 standard, and the anti-aging property test method is performed according to GB / T 528 2009 standard.

[0146] The test results are shown in Table 2.

[0147] Table 2:

[0148]

[0149] Test results show that the semi-conductive EPDM rubber material prepared by this invention has moderate volume resistivity and good anti-aging properties. Specifically:

[0150] Regarding resistivity, there were differences between the superconducting carbon black and reinforcing carbon black in Comparative Examples 1 and 2 compared to Example 1. In Comparative Example 1, the reinforcing carbon black was replaced with an equal amount of superconducting carbon black, resulting in a significant decrease in volume resistivity and a marked decrease in anti-aging performance. In contrast, Comparative Example 2, without the addition of superconducting carbon black, showed a significant increase in resistivity to 115 Ω·cm. Furthermore, Comparative Example 5, without the addition of dicumyl peroxide and with an increased sulfur content, showed a significant decrease in volume resistivity. This is presumably due to two factors: firstly, sulfur generates polysulfide bonds (SS bonds) during sulfidation, and sulfur atoms may adsorb onto the surface of the superconducting carbon black, forming a local chemical bond or physical adsorption layer. This modification enhances the electronic transition efficiency between carbon black particles, thereby improving conductivity; secondly, high concentrations of sulfur may promote a more concentrated sulfidation reaction, resulting in tighter contact between conductive carbon black particles and the formation of a more continuous conductive pathway.

[0151] Regarding aging performance, Comparative Example 5, without the addition of dicumyl peroxide but with increased sulfur content, showed a tensile strength change rate of -18.6% and a breakage elongation change rate of -32.8%. This is presumably due to the sulfur crosslinking network being prone to breakage at high temperatures, resulting in significant deterioration of aging performance. Furthermore, based on the results of Comparative Example 6, it can be concluded that liquid EPDM (Example 1) is better at maintaining aging performance than solid EPDM (Comparative Example 6). This is presumably because liquid EPDM has better compatibility, enabling the formation of a more uniform crosslinking network during vulcanization, which is more conducive to reducing local stress concentration and delaying the generation and propagation of microcracks. In addition, liquid EPDM typically carries more antioxidant groups (such as the shielding effect of unsaturated bonds), which can directly participate in inhibiting oxidation reactions. Its fluidity also helps in the uniform distribution of antioxidants (such as RD), improving overall anti-aging ability. Solid ethylene propylene diene monomer (EPDM) rubber, due to its longer molecular chains and higher crystallinity, is more likely to form particles or agglomerates, resulting in uneven dispersion. Furthermore, these agglomerates may become stress concentration points during vulcanization or use, thereby accelerating material aging.

[0152] Test Example 3: Processability and Appearance Quality Inspection

[0153] This test example examines the molding properties and appearance quality of the semiconductive EPDM rubbers prepared in Examples 1-3 and Comparative Examples 1-7, including Mooney viscosity and vulcanization time T90. The Mooney viscosity was determined according to GB / T 1232.1-2016, and the vulcanization time was determined according to GB / T16584-1996.

[0154] The test results are shown in Table 3.

[0155] Table 3:

[0156]

[0157]

[0158] Test results show that the semi-conductive EPDM rubber prepared using the embodiments of the present invention has excellent molding performance and no discoloration in appearance. Taking Example 1 as an example, the semi-conductive EPDM rubber prepared using this method is as follows: Figure 1 As shown, its surface is free of discoloration, smooth and delicate, and free of wrinkles or other appearance defects.

[0159] Regarding molding performance, Comparative Example 6 used solid ethylene propylene diene monomer (EPDM) rubber, with a Mooney viscosity reaching 70 (significantly increased). This is presumably due to its poor flowability and low compatibility with the matrix, leading to filler agglomeration and a substantial increase in viscosity. Furthermore, the vulcanization time of Comparative Example 5 was significantly longer than that of Example 1, presumably because the high sulfur content requires a longer time to form polysulfide crosslinks, and sulfur vulcanization kinetics are slower. Comparative Example 7 had the same formulation as Example 1, but the zinc oxide was not prepared as a masterbatch. The results showed an increased vulcanization time, presumably because the zinc oxide particles are fine and easily agglomerate, making them difficult to disperse using conventional mixing methods. Preparing a zinc oxide masterbatch effectively solves this dispersion problem.

[0160] Regarding appearance quality, compared to Example 1, Comparative Example 4 did not add sulfur and used a peroxide vulcanization system. The results showed iridescence, presumably due to the incomplete vulcanization network caused by sulfur deficiency, resulting in low surface crosslinking density, exposed fillers, and optical inhomogeneity. In Comparative Example 6, solid EPDM rubber was used instead of liquid EPDM rubber, and the results showed iridescence (e.g., ...). Figure 2 As shown in the figure, the poor flowability of solid EPDM rubber, filler agglomeration, and local concentration differences are presumably the cause. However, when liquid EPDM rubber is used, its good compatibility with other components in the system helps form a dense and consistent cross-linked network, resulting in uniform surface cross-linking density and avoiding local stress concentration and optical differences. Furthermore, it is worth noting that although no obvious iridescence was observed in the rubber material prepared in Comparative Example 7, local white spots or a grainy texture appeared, presumably due to uneven dispersion of zinc oxide.

[0161] In summary, this invention provides a semi-conductive EPDM rubber, its preparation method, and its application. Testing shows that the semi-conductive EPDM rubber prepared using this method exhibits a Shore A hardness ≤60, low volume resistivity (≤15Ω·cm), high tear strength (≥35MPa), high tensile strength (≥13MPa), and high bond strength (≥7MPa). Aging performance (135℃, 168H) results show that the tensile strength change rate is ≤8%, the elongation at break change rate is ≤18%, and the product appearance shows no discoloration or other defects.

[0162] 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 consists of the following raw materials in parts by weight: 80-120 parts EPDM rubber, 2-8 parts zinc oxide, 0.5-3 parts antioxidant, 5-25 parts paraffin oil, 5-25 parts liquid EPDM rubber, 15-35 parts superconducting carbon black, 5-35 parts reinforcing carbon black, 2-10 parts vulcanizing agent and 0.2-1.5 parts vulcanizing aid; The liquid ethylene propylene diene monomer (EPDM) rubber has an ethylene content of 60-75 wt% and a molecular weight of 5000-40000. The vulcanizing agent is dicumyl peroxide, and the vulcanizing aid is sulfur. The semiconductive EPDM rubber is prepared by the following method: S1: The EPDM rubber is plasticized and broken down, and the zinc oxide and part of the liquid EPDM rubber are added for the first mixing to obtain zinc oxide masterbatch. S2: Add the antioxidant to the zinc oxide masterbatch after mixing in step S1, and perform a second mixing. Then add the superconducting carbon black, part of the paraffin oil and part of the liquid ethylene propylene diene monomer (EPDM) rubber, and perform a third mixing. Finally, add the reinforcing carbon black, the remaining paraffin oil and the liquid EPDM rubber, and perform a fourth mixing to obtain a rubber mixture. S3: After the rubber mixture is milled, it is cooled and left to stand. Then it is put into the mill for thin-pass treatment. The vulcanizing agent and the vulcanizing aid are added. After a second thin-pass treatment, the mixture is vulcanized to obtain the final product.

2. The semiconductive EPDM rubber according to claim 1, characterized in that, The raw materials for preparing the EPDM rubber include ethylene-bis(norbornene), and the content of ethylene-bis(norbornene) is 3-10 wt%. And / or, the raw materials for preparing EPDM rubber include ethylene, wherein the ethylene content is 40-60 wt%; And / or, the Mooney viscosity of the EPDM rubber is 20~40, and the test conditions are: M1+4, 125℃.

3. The semiconductive EPDM rubber according to claim 1, characterized in that, The purity of the zinc oxide is ≥99.5%.

4. A method for preparing a semiconductive EPDM rubber as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: The EPDM rubber is plasticized and broken down, and the zinc oxide and part of the liquid EPDM rubber are added for the first mixing to obtain zinc oxide masterbatch. S2: Add the antioxidant to the zinc oxide masterbatch after mixing in step S1, and perform a second mixing. Then add the superconducting carbon black, part of the paraffin oil and part of the liquid ethylene propylene diene monomer (EPDM) rubber, and perform a third mixing. Finally, add the reinforcing carbon black, the remaining paraffin oil and the liquid EPDM rubber, and perform a fourth mixing to obtain a rubber mixture. S3: After the rubber mixture is milled, it is cooled and left to stand. Then it is put into the mill for thin-pass treatment. The vulcanizing agent and the vulcanizing aid are added. After a second thin-pass treatment, the mixture is vulcanized to obtain the final product.

5. The preparation method according to claim 4, characterized in that, The time for the first mixing, the second mixing, the third mixing, and the fourth mixing is 2-5 minutes each; And / or, the temperature of the open mill is 160~180℃; And / or, the refining time is 8-10 minutes.

6. The preparation method according to claim 4 or 5, characterized in that, The vulcanization process includes a first vulcanization process and a second vulcanization process.

7. The preparation method according to claim 6, characterized in that, The temperature of the first vulcanization is 160~175℃, the vulcanization time is 25~35min, and the vulcanization pressure is 10~14MPa.

8. The preparation method according to claim 6, characterized in that, The second vulcanization is carried out at a temperature of 155-165°C, for a vulcanization time of 90-120 minutes, and at atmospheric pressure.

9. The application of the semi-conductive EPDM rubber according to any one of claims 1 to 3 or the preparation method of the semi-conductive EPDM rubber according to any one of claims 4 to 8 in the preparation of cable accessories.

Images