Semi-conductive ethylene propylene diene monomer and preparation method and application thereof

Abstract

The invention discloses a semiconductive ethylene propylene diene monomer and a preparation method and application thereof. The semiconductive ethylene-propylene-diene monomer is prepared from the following raw materials: ethylene-propylene-diene monomer, zinc oxide, an anti-aging agent, paraffin oil, liquid ethylene-propylene-diene monomer, superconductive carbon black, reinforcing carbon black, a vulcanizing agent and a vulcanizing aid. Wherein the ethylene content of the liquid ethylene-propylene rubber is 60-75wt%, and the molecular weight of the liquid ethylene-propylene rubber is 5000-40000. The semi-conductive ethylene propylene diene monomer adopts a peroxide-vulcanization mixed system, and the semi-conductive ethylene propylene diene monomer prepared by adopting the formula has the advantages of low volume resistivity (less than or equal to 15 omega.cm), high tear strength (greater than or equal to 35 MPa), high tensile strength (greater than or equal to 13 MPa), high bonding strength (greater than or equal to 7 MPa), low rubber content, no color flooding in product appearance and the like; the method can be used for preparing semiconductive materials in the high-voltage and ultrahigh-voltage direct current field.

Description

Technical Field

[0001] The present invention relates to the technical field of rubber materials, and in particular to a semi-conductive ethylene propylene diene monomer rubber and its preparation method and application. Background Art

[0002] Power cable accessories are products that connect cables to power transmission and distribution lines and related power distribution devices, mainly used to ensure the safe operation and efficient connection of cables. Relevant research has found that breakdown accidents are likely to occur during the withstand voltage test of cable accessory products, presumably related to the relatively high volume resistivity of the semi-conductive materials in the products. Its value is one order of magnitude higher than that of the matching cable, and the two cannot be effectively matched, resulting in interface heating and ablation, and finally being broken down.

[0003] In related technologies, to achieve the electrical performance requirements of a lower volume resistivity, when preparing products for high-voltage and extra-high-voltage fields, the formulation system will consider choosing super-conductive carbon black with excellent conductivity as a filler. Among them, the structure of super-conductive carbon black is relatively high, and the usual addition amount is only 1 / 3 of the amount of conventional carbon black used. However, the small addition amount of carbon black will result in a relatively high rubber content in the material, leading to problems such as the material coming off the roll during the mixing process and appearance defects such as wrinkles during the forming process. In addition, when the pure sulfur vulcanization system is used in the formulation system, it can also meet the requirements of lower volume resistivity and surface resistance. However, the rubber compound using the pure sulfur vulcanization system mainly forms -C-S-C- bonds, and the bond energy of -C-S-C- is lower than 284.7 KJ / mol, while the ultraviolet energy range is 300 - 600 KJ / mol, resulting in -C-S-C- being more easily broken under ultraviolet irradiation. Therefore, the rubber compound vulcanized with the sulfur vulcanization system has the defect of easy aging.

[0004] In addition, in the process of manufacturing cable accessory products for high-voltage and extra-high-voltage DC fields, a part of them adopts the reverse molding process, where the insulating components are molded first and then the semi-conductive components are integrally molded. To enhance the bonding performance between the two, a certain component of tackifying resin is usually considered to be added in the formulation design. However, the tackifying resin only plays a physical bonding role. Usually, the resin has a low melting point (<90 °C) and cannot improve the bonding performance of the material under high-temperature conditions. At the same time, for accessory products used in high-voltage and extra-high-voltage fields, there are requirements for no color blooming and other problems on the outer surface of the material. The essence of color blooming is that small molecule volatile components in rubber raw materials and added components, as well as intermediate products of mutual reactions, or small molecule volatile substances in mold release agents, such as specific different groups like carbon-carbon double bonds, carbonyl groups, aldehyde groups, carboxyl groups, azo groups, nitroso groups, -C=S, etc., only absorb light of a certain wavelength. After being irradiated by sunlight, the reflected light shows different colors. These different color groups are collectively referred to as "chromophore / groups". When one or more substances containing chromophores migrate to the surface of the rubber compound, the surface of the rubber compound will carry one or more colors. In semi-conductive materials, due to the presence of many free radicals, hydrogen, hydroxyl groups, carboxyl groups, etc. on the surface of carbon black, the color blooming phenomenon is particularly serious, which not only affects the appearance but also the surface precipitates will affect the material bonding.

[0005] Based on this, there is an urgent need to develop a semi-conductive material with a low volume resistivity, low rubber content, high bonding strength, and no color blooming on the surface. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a semi-conductive ethylene propylene diene monomer (EPDM) rubber, which has the advantages of low volume resistivity, high bonding strength, low rubber content, and no color blooming on the product surface, meeting the performance parameter requirements of semi-conductive materials for high-voltage and extra-high-voltage DC fields, such as Shore A hardness ≤ 60; low volume resistivity (≤ 15 Ω·cm); high tear strength (≥ 35 MPa); high tensile strength (≥ 13 MPa); high bonding strength (≥ 7 MPa); the change rate of tensile strength under aging conditions ≤ 20%, and the change rate of elongation at break ≤ 20%; no color blooming and other problems on the product surface.

[0007] The present invention also provides a preparation method of the semi-conductive ethylene propylene diene monomer (EPDM) rubber.

[0008] The present invention also provides an application of the semi-conductive ethylene propylene diene monomer (EPDM) rubber and its preparation method in the manufacture of cable accessories.

[0009] In the first aspect of the present invention, there is provided a semi-conductive ethylene propylene diene monomer (EPDM) rubber, and its raw materials for preparation include:

[0010] Ethylene propylene diene monomer (EPDM) rubber, zinc oxide, anti-aging agent, paraffin oil, liquid ethylene propylene diene monomer (EPDM) rubber, superconducting carbon black, reinforcing carbon black, vulcanizing agent, vulcanization aid;

[0011] Among them, the ethylene content of the liquid ethylene propylene rubber is 60-75 wt%, and the molecular weight is 5000-40000.

[0012] The semi-conductive ethylene propylene diene monomer rubber according to the embodiment of the present invention has at least the following beneficial effects:

[0013] Using the formula of the present invention to prepare semi-conductive ethylene propylene diene monomer rubber can simultaneously achieve low volume resistivity and surface resistance, high bonding strength, low rubber content, and no color bleeding on the product appearance.

[0014] First of all, the present invention selects ultra-conductive carbon black with fine particles, large specific surface area, and many particles per unit mass as the filler. In the rubber compound system of the present invention, it is mainly stacked in a network chain structure and can form a chain-like conductive structure. Therefore, even with a small addition amount, it has excellent conductive performance. In addition, the formula of the present invention also selects reinforcing carbon black as an auxiliary filler, which helps to reduce the rubber content.

[0015] Secondly, the formula of the present invention selects a peroxide-sulfur vulcanization hybrid system. During the formula optimization process, the inventors found that using a single peroxide vulcanization system, although it has the characteristics of fast vulcanization speed and excellent aging performance, it is not conducive to improving the bonding strength of the material; while using a pure sulfur vulcanization system, although it can meet the requirement of high bonding strength, the aging performance of the material is relatively low. In the peroxide-sulfur vulcanization hybrid system of the present invention, the peroxide vulcanization system is the main one, and sulfur is used as a co-vulcanizing agent. In this hybrid vulcanization system, there are still remaining activators in the rubber material after the first vulcanization, which can directly increase the crosslinking degree with the insulating material during the second vulcanization process, thereby improving the bonding strength from the material structure level.

[0016] In addition, the formula system of the present invention selects ethylene propylene rubber and liquid ethylene propylene rubber as plasticizers. Among them, ethylene propylene rubber is a reactive plasticizer and can participate in the reaction in the peroxide vulcanization system. During the second vulcanization process, it can continue to participate in the crosslinking reaction with the insulating material rubber compound, thereby further improving the bonding strength with the insulating material. And liquid ethylene propylene rubber is a macromolecular plasticizer, which has good compatibility with other components in the system, helps to form a dense and uniform crosslinking network, makes the surface crosslinking density uniform, and avoids local stress concentration and optical differences.

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

[0018]

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

[0020]

[0021]

[0022] In some embodiments of the present invention, the raw material for preparing EPDM rubber contains ethylidene norbornene, and the content of ethylidene norbornene is 3 to 10 wt %.

[0023] In some embodiments of the present invention, the raw material for preparing the EPDM rubber contains ethylene, and the content of the ethylene is 40-60wt%. Within this range, the rubber can be kept with high filling properties, while having good flow properties and processing properties. If the ethylene content is too low, the elasticity increases, resulting in low mechanical properties, which is not conducive to processing. 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 formula of the present invention adopts a vulcanization system, and zinc oxide can be used as an auxiliary agent in the vulcanization system, which has the effects of accelerating the vulcanization speed, improving the vulcanization efficiency, and enhancing the mechanical properties of the rubber material.

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

[0028] Compared with conventional zinc oxide, the particle size of active zinc oxide is small, usually 1 to 100 nm, spherical, with a large specific surface area, and easy to disperse during mixing. In addition, active zinc oxide has relatively higher activity (the grains are refined, the surface electronic structure and microstructure have changed, and a surface effect that ordinary zinc oxide does not have) and excellent adsorption, which can greatly improve the vulcanization efficiency of rubber.

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

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

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

[0032] In some embodiments of the present invention, the DBP (phthalic) adsorption value of the super conductive carbon black > 400 ml / 100 g, and the 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] Dicumyl peroxide can generate stable C-C crosslinking bonds during vulcanization (its chemical stability is superior to the polysulfide bonds of the sulfur system), and it is not easily broken under high temperature or oxidation environment, which helps to significantly improve the aging resistance of the rubber material. In addition, using dicumyl peroxide helps to reduce the adsorption of insulating by-products on the surface of conductive carbon black, thereby maintaining a moderate volume resistivity.

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

[0037] The second aspect of the present invention provides a method for preparing the semi-conductive ethylene propylene diene monomer rubber as described in the first aspect, including the following steps:

[0038] S1: Knead and break the ethylene propylene diene monomer rubber, and add the zinc oxide and part of the liquid ethylene propylene diene monomer rubber, and conduct the first mixing to obtain a zinc oxide masterbatch;

[0039] S2: Add the anti-aging agent to the zinc oxide masterbatch after mixing in step S1, conduct the second mixing, then add the super conductive carbon black, part of the paraffin oil and part of the liquid ethylene propylene diene monomer rubber, conduct the third mixing, and finally add the reinforcing carbon black, and the remaining paraffin oil and the liquid ethylene propylene diene monomer rubber for the fourth mixing to obtain a rubber mixture;

[0040] S3: After the rubber mixture is opened and kneaded, it is cooled and parked, then put into an open mill for thin-pass treatment, and then the vulcanizing agent and the vulcanization aid are added. After the second thin-pass treatment, vulcanization treatment is carried out to obtain the product.

[0041] According to the preparation method of the embodiments of the present invention, it has at least the following beneficial effects:

[0042] The present invention prepares a rubber material by first preparing a zinc oxide masterbatch, which helps to improve the comprehensive properties of the material. Zinc oxide, as a vulcanization accelerator, plays a very important role in the rubber system. It can not only accelerate the vulcanization speed, improve the heat resistance of the material, but also increase the crosslinking density of the material, thereby enhancing the overall mechanical properties of the material. However, due to its fine particles and easy agglomeration, it is not easy to disperse by conventional mixing methods. Making a zinc oxide masterbatch can well 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 the rubber is 5 - 10 min.

[0044] In some embodiments of the present invention, the addition amount of the liquid ethylene propylene rubber during the first mixing process is 1 / 12 - 1 / 16 of the total weight parts of the liquid ethylene propylene rubber.

[0045] In some embodiments of the present invention, the addition amount of the liquid ethylene propylene rubber during the second mixing process is 1 / 2 of the total weight parts of the liquid ethylene propylene rubber.

[0046] In some embodiments of the present invention, in step S2, the paraffin oil is added in two equal amounts. That is, the amount added for the first time is 1 / 2 of the total weight parts of the paraffin oil, and the amount added for the second time is also 1 / 2 of the total weight parts 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 within the range of 100 - 130 °C.

[0048] In some embodiments of the present invention, the times of the first mixing, the second mixing, the third mixing, and the fourth mixing are independently 2 - 5 min.

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

[0050] the time of the second mixing is 2 - 4 min;

[0051] the time of the third mixing is 3 - 5 min;

[0052] the time of the fourth mixing is 3 - 5 min.

[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 mixing time is 6 to 12 minutes.

[0056] In some preferred embodiments of the present invention, the mixing 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 to 175 °C, the vulcanization time is 25 to 35 minutes, and the vulcanization pressure is 10 to 14 MPa.

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

[0060] In a third aspect of the present invention, there is provided an application of the method for preparing the semi-conductive ethylene propylene diene monomer rubber as described in the first aspect or the semi-conductive ethylene propylene diene monomer rubber as described in the second aspect in the preparation of cable accessories.

[0061] Other features and advantages of the present invention will be described in the subsequent specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The present invention will be further described below in conjunction with the drawings and embodiments, wherein:

[0063] Figure 1 is the semi-conductive ethylene propylene diene monomer rubber prepared in Example 1 of the present invention;

[0064] Figure 2 is the semi-conductive ethylene propylene diene monomer rubber prepared in Comparative Example 6 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0065] The concept of the present invention and the technical effects produced will be clearly and completely described below in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0066] The terms "preferably", "more preferably", etc. in the present invention mean embodiments of the present invention that can provide certain beneficial effects in certain cases. However, in the same or other cases, other embodiments may also be preferred. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not available, nor is it intended to exclude other embodiments from the scope of the present invention.

[0067] When a numerical range is disclosed herein, the above range is considered continuous and includes the minimum and maximum values of the range, as well as each value therebetween. Further, when the range refers to integers, each integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0068] In the description of the present invention, the reference term "and / or" includes all and any combinations of one or more of the related listed items.

[0069] In the description of the present invention, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0070] In an embodiment of the present invention, the third monomer of ethylene propylene diene monomer (EPDM, from LANXESS Germany, product number 2650) is ethylidene norbornene (ENB), the content of the ENB is 3 - 10 wt%, the content of ethylene 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, and is purchased from Jiangsu Shuangsheng Zinc Industry Co., Ltd.

[0072] The antioxidant RD is purchased from Shandong Shangshun Chemical Industry Co., Ltd.

[0073] The antioxidant 445 is purchased from SI Group.

[0074] The resistivity of the superconducting carbon black is 0.1 - 10 Ω·cm, and it is purchased from Imerys.

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

[0076] For those not specified with specific conditions in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0077] Example 1:

[0078] This example provides a semi-conductive ethylene propylene diene monomer rubber and its preparation method. By weight, the raw materials for preparing the semi-conductive ethylene propylene diene monomer rubber include the following components:

[0079]

[0080] The above-mentioned preparation method of the semi-conductive ethylene propylene diene monomer rubber includes the following steps:

[0081] S1: According to the above weight fractions, put the formulated amount of ethylene propylene diene monomer rubber into a pressure type internal mixer for plasticizing for 8 minutes to break the rubber;

[0082] S2: Mix all the zinc oxide with the plasticized ethylene propylene diene monomer rubber obtained in step S1, and the formulated amount of 1 / 15 liquid ethylene propylene diene monomer rubber, add them to a pressure type internal mixer and mix for 4 minutes to make a zinc oxide masterbatch;

[0083] S3: Mix the above zinc oxide masterbatch with the formulated amount of antioxidant RD, add them to a pressure type internal mixer and mix for 3 minutes; then add the formulated amount of super conductive carbon black, 1 / 2 of the formulated amount of paraffin oil and 1 / 2 of the formulated amount of liquid ethylene propylene diene monomer rubber and mix for 4 minutes; then add reinforcing carbon black, the remaining paraffin oil and the remaining liquid ethylene propylene diene monomer rubber and mix for 4 minutes to obtain a rubber mixture;

[0084] S4: After discharging, conduct heat treatment, specifically including putting the rubber mixture discharged from the internal mixer on an open mill, kneading at 170 °C for 10 minutes, cooling to room temperature and storing for 24 hours;

[0085] S5: Put the cooled and stored material into an open mill for two passes of thin passing, then add the formulated amount of dicumyl peroxide and sulfur to the open mill, conduct 10 passes of thin passing, and then conduct two vulcanization and sheet making, and cool to obtain the above-mentioned ethylene propylene diene monomer rubber.

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

[0087] Example 2:

[0088] This example provides a semi-conductive ethylene propylene diene monomer rubber and its preparation method. By weight, the raw materials for preparing the semi-conductive ethylene propylene diene monomer rubber include the following components:

[0089]

[0090] The above-mentioned preparation method of the semi-conductive ethylene propylene diene monomer rubber includes the following steps:

[0091] S1: According to the above weight fractions, put the formulated amount of ethylene propylene diene monomer rubber into a pressure kneader for plasticizing for 8 min to break the rubber;

[0092] S2: Mix zinc oxide with the plasticized ethylene propylene diene monomer rubber obtained in step S1 and 1 / 13.3 of the liquid ethylene propylene diene monomer rubber, add them to a pressure kneader and knead for 4 min to make a zinc oxide masterbatch;

[0093] S3: Mix the above zinc oxide masterbatch with the formulated amount of antioxidant RD, add them to a pressure kneader and knead for 3 min; then add the formulated amount of super conductive carbon black, 1 / 2 of the formulated amount of paraffin oil and 1 / 2 of the formulated amount of liquid ethylene propylene diene monomer rubber and knead for 4 min; then add reinforcing carbon black, the remaining paraffin oil and liquid ethylene propylene diene monomer rubber and knead for 4 min to obtain a rubber mixture;

[0094] S4: After discharging, conduct heat treatment, specifically including putting the rubber mixture discharged from the kneader on an open mill, milling at 170 °C for 10 min, cooling to room temperature and storing for 24 h;

[0095] S5: Put the cooled and stored material on an open mill and thin pass it twice, then add the formulated amount of dicumyl peroxide and sulfur to the open mill, thin pass it 10 times, and then conduct two vulcanization processes to make sheets. After cooling, the above ethylene propylene diene monomer 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 normal pressure.

[0097] Example 3:

[0098] This embodiment provides a semi-conductive ethylene propylene diene monomer rubber and a preparation method thereof. According to weight parts, the raw materials for preparing the semi-conductive ethylene propylene diene monomer rubber include the following components:

[0099]

[0100] The above preparation method of the semi-conductive ethylene propylene diene monomer rubber includes the following steps:

[0101] S1: According to the above weight fractions, put the formulated amount of ethylene propylene diene monomer rubber into a pressure kneader for plasticizing for 8 min to break the rubber;

[0102] S2: Mix zinc oxide with the plasticized ethylene propylene diene monomer rubber obtained in step S1 and 1 / 16 of the liquid ethylene propylene diene monomer rubber, add them to a pressure kneader and knead for 4 min to make a zinc oxide masterbatch;

[0103] S3: Mix the above zinc oxide masterbatch with the formula amount of antioxidant RD, add them to a pressure kneader and knead for 3 min; then add the formula amount of super-conductive carbon black, 1 / 2 of the formula amount of paraffin oil and 1 / 2 of the formula amount of liquid ethylene propylene diene monomer (EPDM) and knead for 4 min; then add reinforcing carbon black, the remaining paraffin oil and liquid EPDM and knead for 4 min to obtain a rubber mixture.

[0104] S4: After discharging, conduct heat treatment, specifically including putting the rubber mixture discharged from the kneader on an open mill, kneading at 170 °C for 10 min, cooling to room temperature and storing for 24 h.

[0105] S5: Put the above-cooled and stored material into an open mill and thin-pass it twice, then add the formula amount of dicumyl peroxide and sulfur to the open mill, thin-pass it 10 times, and then conduct two-stage vulcanization and sheet-making. After cooling, the above ethylene propylene diene monomer (EPDM) is obtained.

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

[0107] Comparative Example 1:

[0108] This comparative example provides a semi-conductive ethylene propylene diene monomer (EPDM) and its preparation method. The difference in the preparation raw materials from those of Example 1 is that: no reinforcing carbon black is added to the formula, and it is replaced with the same number of parts of super-conductive carbon black, that is, the dosage of super-conductive carbon black is 45 parts. The other raw materials are the same.

[0109] The semi-conductive ethylene propylene diene monomer (EPDM) of this comparative example is prepared by referring to the method of Example 1.

[0110] Comparative Example 2:

[0111] This comparative example provides a semi-conductive ethylene propylene diene monomer (EPDM) and its preparation method. The difference in the preparation raw materials from those of Example 1 is that: no super-conductive carbon black is added to the formula, and it is replaced with the same number of parts of reinforcing carbon black, that is, the dosage of reinforcing carbon black is 45 parts. The other raw materials are the same.

[0112] The semi-conductive ethylene propylene diene monomer (EPDM) of this comparative example is prepared by referring to the method of Example 1.

[0113] Comparative Example 3:

[0114] This comparative example provides a semi-conductive ethylene propylene diene monomer (EPDM) and its preparation method. The difference in the preparation raw materials from those of Example 1 is that: the liquid ethylene propylene diene monomer (EPDM) is replaced with an equal amount of paraffin oil in the formula, that is, the dosage of paraffin oil is 30 parts. The other raw materials are the same.

[0115] The semi-conductive ethylene propylene diene monomer (EPDM) of this comparative example is prepared by referring to the method of Example 1.

[0116] Comparative Example 4:

[0117] This comparative example provides a semi-conductive ethylene propylene diene monomer rubber and a preparation method thereof. The difference in the preparation raw materials from those of Example 1 is that sulfur is not added, and the other raw materials are the same.

[0118] The semi-conductive ethylene propylene diene monomer rubber of this comparative example was prepared with reference to the method of Example 1.

[0119] Comparative Example 5:

[0120] This comparative example provides a semi-conductive ethylene propylene diene monomer rubber and a preparation method thereof. The difference in the preparation raw materials from those of Example 1 is that dicumyl peroxide is not added, and at the same time, the dosage of sulfur is adjusted to 6 parts, and the other raw materials are the same.

[0121] The semi-conductive ethylene propylene diene monomer rubber of this comparative example was prepared with reference to the method of Example 1.

[0122] Comparative Example 6:

[0123] This comparative example provides a semi-conductive ethylene propylene diene monomer rubber and a preparation method thereof. The difference in the preparation raw materials from those of Example 1 is that liquid ethylene propylene diene monomer rubber is replaced with an equal amount of solid ethylene propylene diene monomer rubber (molecular weight 50,000 - 150,000, ethylene content 72 w%, manufacturer: Exxon, grade: 722), and the other raw material ratios are the same.

[0124] The semi-conductive ethylene propylene diene monomer rubber of this comparative example was prepared with reference to the method of Example 1.

[0125] Comparative Example 7:

[0126] This comparative example provides a semi-conductive ethylene propylene diene monomer rubber and a preparation method thereof. The preparation raw materials are the same as those of Example 1. The difference in the preparation method of this semi-conductive ethylene propylene diene monomer rubber from that of Example 1 is that zinc oxide is not prepared into a masterbatch, and zinc oxide powder is directly added for mixing during the preparation process. It specifically includes the following steps:

[0127] S1: According to the above weight fractions, put the formulated amount of ethylene propylene diene monomer rubber into a pressure type internal mixer for plasticizing for 8 min to break the rubber;

[0128] S2: Mix the plasticized ethylene propylene diene monomer rubber obtained in step S1, 1 / 10 of the formulated amount of liquid ethylene propylene diene monomer rubber, the formulated amount of zinc oxide, and antioxidant RD, and put them into a pressure type internal mixer for mixing for 3 min; then add the formulated amount of super conductive carbon black, 1 / 2 of the formulated amount of paraffin oil, and 1 / 2 of the formulated amount of liquid ethylene propylene diene monomer rubber and mix for 4 min; then add reinforcing carbon black, the remaining paraffin oil, and liquid ethylene propylene diene monomer rubber and mix for 4 min to obtain a rubber mixture;

[0129] S3: After discharging, perform heat treatment, specifically including placing the rubber mixture discharged from the internal mixer in an open mill, kneading at 170 °C for 10 min, cooling to room temperature and storing for 24 h;

[0130] S4: Put the above-mentioned cooled and stored material into an open mill and thin-pass it twice, then add the formula amount of dicumyl peroxide and sulfur into the open mill, thin-pass it 10 times, and then perform two vulcanization and sheet-making processes. After cooling, the above-mentioned ethylene-propylene-diene monomer rubber is obtained.

[0131] In this comparative example, 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 normal pressure.

[0132] Test Example 1: Mechanical property test

[0133] This test example tests the mechanical properties (such as hardness, tear strength, tensile strength, elongation at break, and adhesion strength) of the semi-conductive ethylene-propylene-diene monomer rubber prepared in the above Examples 1-3 and Comparative Examples 1-7. Among them, the test method for hardness is carried out according to the standard of GB / T531.1-2009; the tear strength is in accordance with GB / T 529 2008, and the test methods for tensile strength, elongation at break, and adhesion strength are carried out according to the standard of GB / T 528 2009. There are 5 samples in each group, and the numerical values are taken as the average.

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

[0135] Table 1:

[0136]

[0137] The test results show that the semi-conductive ethylene-propylene-diene monomer rubber material prepared by the present invention has good mechanical properties.

[0138] Compared with Example 1, in Example 2, the anti-aging agent was changed to anti-aging agent 445, and the amounts of super-conductive carbon black, reinforcing carbon black, plasticizer paraffin oil, liquid ethylene-propylene-diene monomer rubber, vulcanizing agent, and vulcanization aids were all taken as the minimum values within the range. The results show that the comprehensive performance has decreased a lot compared with Example 1. It is speculated that due to the large filling amount of ethylene-propylene-diene monomer rubber, the mechanical properties of the material are low, and the carbon black filler content is small, resulting in insufficient material reinforcement.

[0139] Compared with Example 1, in Example 3, the amounts of super conductive carbon black, reinforcing carbon black, plasticizer paraffin oil, liquid ethylene propylene diene monomer rubber, vulcanizing agent and vulcanization aids are all taken as the maximum values within the range. According to the analysis of the final results, its comprehensive performance has not been significantly improved compared with Example 1. It is speculated that there is an optimal ratio for the amounts of carbon black filler, plasticizer and vulcanizing agent. Exceeding their amounts is likely to cause filler agglomeration, over-vulcanization to damage the network structure, etc., and as a result, the comprehensive performance of the material has not been improved instead.

[0140] Compared with Example 1, in Comparative Example 1, reinforcing carbon black was not added, and the amount of super conductive carbon black was increased 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 weakens the tensile properties and ductility of the material, and reinforcing carbon black plays a role in enhancing the mechanical strength in the formula of the present invention. Further, in Comparative Example 2, super conductive carbon black was not added, and the amount of reinforcing carbon black was increased to 45 parts. The results showed that the tensile strength increased to some extent, but a part of the elongation at break was sacrificed.

[0141] Compared with Example 1, there are differences in the content or type of plasticizer (paraffin oil and liquid ethylene propylene diene monomer rubber) in Comparative Examples 3 and 6. Among them, in Comparative Example 3, paraffin oil was used to replace liquid ethylene propylene diene monomer rubber, and the results showed that the mechanical strength increased to some extent, but the bonding strength decreased significantly. In Comparative Example 6, solid ethylene propylene diene monomer rubber was used to replace liquid ethylene propylene diene monomer rubber, and the results showed that the tear strength and tensile strength decreased compared with Example 1, and the elongation at break decreased from 435% to 287%. This shows that using liquid ethylene propylene diene monomer rubber in the formula system of the present invention is more conducive to improving the ductility of the rubber material. Although solid ethylene propylene diene monomer rubber will increase the hardness, it may lead to a significant decrease in tear strength, tensile strength and elongation at break. It is speculated that this is because solid ethylene propylene diene monomer rubber is prone to cause local stress concentration, thereby affecting its ductility. In addition, due to the high Mooney viscosity of solid ethylene propylene diene monomer rubber, it cannot effectively play a plasticizing role, making it difficult to mix the material, and it is easy to have abnormal situations such as uneven carbon black dispersion, resulting in low overall performance of the material.

[0142] Compared with Example 1, there are differences in the vulcanization systems in Comparative Examples 4 and 5. In Comparative Example 4, only DCP was used and sulfur was not added. It showed that its impact on hardness, tear strength and tensile strength was not significant, but the bonding strength decreased from 7.6 MPa to 4.9 MPa, and the elongation at break decreased significantly. It can be seen that adding sulfur as a vulcanization aid in the system of the present invention helps to optimize the crosslinked network structure and enhance the interfacial bonding strength. In the formula of Comparative Example 5, only sulfur was used and DCP was not added. The test results showed that both the tensile strength and hardness decreased, and the elongation at break increased to a certain extent.

[0143] Compared with Example 1, in the preparation process of the semi-conductive ethylene propylene diene monomer rubber material of Comparative Example 7, zinc oxide was not made into a masterbatch, and the results showed that its elongation at break and bonding strength decreased significantly.

[0144] Test Example 2: Detection of volume resistivity and anti-aging performance

[0145] In this test example, the volume resistivity and anti-aging performance of the semi-conductive ethylene propylene diene monomer rubber prepared in the above Examples 1 to 3 and Comparative Examples 1 to 7 were detected. Among them, the test method for volume resistivity was carried out according to the standard of GB / T 2439-2001, and the detection method for anti-aging performance was carried out according to the standard of GB / T 528-2009.

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

[0147] Table 2:

[0148]

[0149] The test results showed that the semi-conductive ethylene propylene diene monomer rubber material prepared by the present invention had moderate volume resistivity and good anti-aging performance. Among them:

[0150] For the resistivity, compared with Example 1, there were differences in the super conductive carbon black and reinforcing carbon black in Comparative Example 1 and Comparative Example 2. In Comparative Example 1, the reinforcing carbon black was replaced with an equal amount of super conductive carbon black, and the results showed that the volume resistivity decreased significantly and the anti-aging performance also decreased significantly. In Comparative Example 2, no super conductive carbon black was added, and the resistivity increased significantly to 115 Ω·cm. In addition, in Comparative Example 5, no dicumyl peroxide was added and the content of sulfur was increased. The results showed that its volume resistivity decreased significantly. It was speculated that on the one hand, sulfur generated polysulfide bonds (S-S bonds) during the vulcanization process, and sulfur atoms might adsorb on the surface of the super conductive carbon black to form a local chemical bonding or physical adsorption layer. This modification enhanced the electron transition efficiency between carbon black particles, thereby improving the conductivity; on the other hand, it might be because high-concentration sulfur could promote a more intensive vulcanization reaction, making the contact between conductive carbon black particles closer and forming a more continuous conductive path.

[0151] For the aging performance, in Comparative Example 5, dicumyl peroxide was not added while the sulfur content was increased. The results showed that the change rate of tensile strength was -18.6% and the change rate of elongation at break was -32.8%. It is speculated that the sulfur crosslinking network is prone to breakage at high temperatures, resulting in significantly deteriorated aging performance. In addition, according to the results of Comparative Example 6, it can be analyzed that liquid ethylene propylene diene monomer (Example 1) is more conducive to maintaining the aging performance than solid ethylene propylene diene monomer (Comparative Example 6). It is speculated that the liquid ethylene propylene diene monomer has better compatibility and can form 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 ethylene propylene diene monomer usually carries more antioxidant groups (such as the shielding effect of unsaturated bonds), which can directly participate in inhibiting oxidation reactions, and its fluidity also helps the uniform distribution of anti-aging agents (such as RD), improving the overall anti-aging ability. However, due to the long molecular chains and high crystallinity of solid ethylene propylene diene monomer, it is easier to form particles or aggregates, resulting in uneven dispersion. And these aggregates may become stress concentration points during vulcanization or use, thus accelerating the aging of the material.

[0152] Test Example 3: Detection of Processability and Appearance Quality

[0153] In this test example, the Mooney viscosity, vulcanization time T90 and other molding properties and appearance quality of the semi-conductive ethylene propylene diene monomer rubber prepared in the above Examples 1 to 3 and Comparative Examples 1 to 7 were detected. The determination method of Mooney viscosity was carried out according to the GB / T 1232.1 2016 standard, and the determination method of vulcanization time was carried out according to the GB / T 16584 1996 standard.

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

[0155] Table 3:

[0156]

[0157]

[0158] The test results showed that the semi-conductive ethylene propylene diene monomer rubber prepared by the examples of the present invention has excellent molding properties and no color blooming on the surface. Taking Example 1 as an example, the semi-conductive ethylene propylene diene monomer rubber prepared by this method is as Figure 1 shown, showing that its surface has no color blooming, and is smooth and delicate, without appearance defects such as wrinkles.

[0159] For molding performance, Comparative Example 6 uses solid EPDM rubber, and its Mooney viscosity reaches 70 (significantly increased). It is speculated that it is due to its poor fluidity and low compatibility with the matrix, which leads to filler agglomeration and a significant increase in viscosity. In addition, the curing time of Comparative Example 5 is significantly improved relative to Example 1. It is speculated that it takes a longer time for high sulfur dosage to form polysulfide crosslinks, and the sulfur vulcanization kinetics are slow. Compared with Example 1, Comparative Example 7 has no change in formula, but in the preparation method, zinc oxide is not prepared into a masterbatch. The results show that the curing time is increased. It is speculated that it is due to the fact that the zinc oxide particles are fine and easy to agglomerate, and the conventional mixing method is not easy to disperse, and the preparation of zinc oxide masterbatch can solve its dispersion problem well.

[0160] Regarding the appearance quality, compared with Example 1, Comparative Example 4 did not add sulfur, but used a peroxide vulcanization system. The results showed that there was a color flooding, which was presumably due to the lack of sulfur, resulting in an incomplete vulcanization network, low surface crosslinking density, exposed fillers, and optical inhomogeneity. In Comparative Example 6, solid EPDM rubber was used to replace liquid EPDM rubber, and the results showed that there was a color flooding phenomenon (such as Figure 2 As shown in the figure, it is speculated that this is caused by the poor fluidity of solid EPDM rubber, filler agglomeration and local concentration differences. When liquid EPDM rubber is used, due to its good compatibility with other components in the system, it helps to form a dense and consistent cross-linked network, making the surface cross-linking density uniform, avoiding local stress concentration and optical differences. In addition, it is worth noting that although no obvious flooding is observed in the rubber material prepared in Comparative Example 7, local white spots or granularity appear, which is speculated to be caused by uneven dispersion of zinc oxide.

[0161] In summary, the present invention provides a semi-conductive EPDM rubber and a preparation method and application thereof. After testing, the semi-conductive EPDM rubber prepared by the method of the present invention has a Shore A hardness of ≤60, a low volume resistivity (≤15Ω.cm), high tear strength (≥35MPa), high tensile strength (≥13MPa), and high bonding strength (≥7MPa); the aging performance (135°C, 168H) results show that the change rate of tensile strength is ≤8%, the change rate of elongation at break is ≤18%, and the product appearance has no defects such as flooding.

[0162] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A semi-conductive ethylene propylene diene monomer rubber, characterized in that, The preparation raw materials include: ethylene propylene diene monomer (EPDM), zinc oxide, antioxidant, paraffin oil, liquid ethylene propylene diene monomer (EPDM), super conducting carbon black, reinforcing carbon black, vulcanizing agent and vulcanization promoter; wherein, the ethylene content of the liquid ethylene propylene diene monomer (EPDM) is 60-75 wt%, and the molecular weight is 5000-40000.

2. The semi-conductive ethylene propylene diene monomer rubber according to claim 1, wherein, By weight parts, the preparation raw materials include:

3. The semi-conductive ethylene propylene diene monomer rubber according to claim 1, characterized in that, The preparation raw materials of the ethylene propylene diene monomer (EPDM) contain ethylidene norbornene, and the content of the ethylidene norbornene is 3-10 wt%; and / or, the preparation raw materials of the ethylene propylene diene monomer (EPDM) contain ethylene, and the content of the ethylene is 40-60 wt%; and / or, the Mooney value of the ethylene propylene diene monomer (EPDM) is 20-40 (M1+4, 125 °C).

4. The semi-conductive ethylene propylene diene monomer rubber according to claim 1, characterized in that, The purity of the zinc oxide is ≥99.5%.

5. The semi-conductive ethylene propylene diene monomer rubber according to any one of claims 1 to 4, characterized in that, The vulcanizing agent includes at least one of dicumyl peroxide and di-tert-butyl peroxide.

6. The semi-conductive ethylene propylene diene monomer rubber according to claim 5, characterized in that, The vulcanization promoter is sulfur.

7. A preparation method of the semi-conductive ethylene propylene diene monomer rubber according to any one of claims 1 to 6, characterized in that, It includes the following steps: S1: Plasticize and break the ethylene propylene diene monomer (EPDM), and add the zinc oxide and part of the liquid ethylene propylene diene monomer (EPDM) for the first mixing to obtain a zinc oxide masterbatch; S2: Add the antioxidant to the zinc oxide masterbatch after mixing in step S1 for the second mixing, then add the super conducting carbon black, part of the paraffin oil and part of the liquid ethylene propylene diene monomer (EPDM) for the third mixing, and finally add the reinforcing carbon black, and the remaining paraffin oil and liquid ethylene propylene diene monomer (EPDM) for the fourth mixing to obtain a rubber mixture; S3: After the rubber mixture is opened and kneaded, it is cooled and parked, then put into an open mill for thin pass treatment, and then the vulcanizing agent and the vulcanization promoter are added. After the second thin pass treatment, vulcanization treatment is carried out to obtain the product.

8. The preparation method according to claim 7, characterized in that, The time of the first mixing, the second mixing, the third mixing and the fourth mixing is independently 2-5 min; and / or, the temperature of the open kneading is 160-180 °C; and / or, the time of the open kneading is 8-10 min.

9. The preparation method according to claim 7 or 8, characterized in that, The vulcanization treatment includes the first vulcanization treatment and the second vulcanization treatment; Preferably, 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; Preferably, the temperature of the second vulcanization is 155-165 °C, the vulcanization time is 90-120 min, and the pressure is normal pressure.

10. Use of the semi-conductive ethylene propylene diene monomer (EPDM) according to any one of claims 1-6 or the preparation method of the semi-conductive ethylene propylene diene monomer (EPDM) according to any one of claims 7-9 in the preparation of cable accessories.

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