A flame retardant ethylene propylene rubber and its preparation method and its application in high voltage DC cable accessories

Abstract

The present invention provides a flame retardant EPDM rubber and a preparation method thereof and an application thereof in high-voltage DC cable accessories, belonging to the technical field of wires and cables. The present invention adds a flame retardant to the EPDM rubber, thereby giving the EPDM rubber flame retardant or self-extinguishing properties and strong tensile tearing properties. The present invention improves the flame retardant properties of the EPDM rubber by improving the preparation process of the EPDM rubber, the selection of the flame retardant and the addition amount, thereby expanding its scope of application, and while improving the flame retardant properties of the EPDM rubber, ensures that its electrical properties and mechanical properties are not affected, thereby meeting the performance requirements of the high-voltage DC cable accessories.

Description

Technical Field

[0001] The invention belongs to the technical field of electric wires and cables, and in particular relates to a flame-retardant ethylene-propylene rubber and a preparation method thereof and application thereof in high-voltage direct current cable accessories. Background Art

[0002] In recent years, with the economic development and growing demand for electricity in my country, my country's power system has been continuously developing towards higher voltage levels to meet the needs of power load. As a key part of the DC transmission network system, the insulation safety and reliability of high-voltage DC cables are closely related to the stability of the entire high-voltage DC transmission network, and cable accessories are an indispensable part of the high-voltage DC cable system. The insulation inside the cable accessories is generally composed of two parts: the main cable insulation XLPE and the accessory enhanced insulation. Cable accessories have long been the weakest and most important insulation link in the cable structure. Operation experience shows that under the action of long-term DC voltage in the DC cable, the temperature of the reinforced insulation inside the cable accessories will be much higher than the temperature of the cable's own XLPE. Once the cable system is short-circuited due to a fault, the temperature of the cable accessories will rise sharply again, and there is a risk of spontaneous combustion, which greatly affects the safe operation and stability of the high-voltage DC cable system.

[0003] The insulation materials currently used for cable accessories are mainly ethylene propylene diene rubber (EPDM) and silicone rubber (SiR). SiR has better electrical strength and arc resistance, better insulation reliability, and EPDM has extremely excellent high elasticity, good elongation at break and low hardness, which is very convenient for on-site installation and laying. Therefore, EPDM is widely used as the main insulating material in DC cable accessories.

[0004] However, the biggest disadvantage of this material is its flammability, with an oxygen index of only 19. In particular, it is easy to smolder, posing a potential risk of combustion, and its aging performance in humid conditions is not good enough; its mechanical strength is also relatively poor among rubber materials. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a flame retardant ethylene propylene rubber and a preparation method thereof and application thereof in high voltage DC cable accessories. The present invention combines process improvement with material selection to prepare a flame retardant rubber having good mechanical and electrical properties, thereby meeting the performance requirements of high voltage DC cable accessories.

[0006] The present invention is achieved through the following technical solutions:

[0007] The first object of the present invention is to provide a flame retardant ethylene-propylene rubber, which comprises the following components, by weight: 65-80 parts of ethylene-propylene rubber, 90-110 parts of flame retardant, 2-3 parts of coupling agent, 4-6 parts of zinc oxide, 0.5-1.5 parts of stearic acid, 2-5 parts of antioxidant, 50-60 parts of clay, 3-5 parts of paraffin oil, 20-25 parts of white carbon black, 10-15 parts of silicon carbide, 1-3 parts of sulfur, 3-4 parts of vulcanization accelerator, and 4-5 parts of vulcanizing agent.

[0008] Clay has a certain reinforcing effect in rubber, which can improve the mechanical properties of rubber, give it excellent wear resistance, water resistance and chemical resistance, and increase the hardness of unvulcanized rubber. The role of silicon carbide is to improve the accumulation of DC space charge.

[0009] In one embodiment of the present invention, the flame retardant is selected from EVM and magnesium hydroxide.

[0010] In one embodiment of the present invention, the coupling agent is selected from silane coupling agents.

[0011] In one embodiment of the present invention, the vulcanization accelerator is selected from one or more of TAIC, TMTD-80 and DM.

[0012] In one embodiment of the present invention, the vulcanizing agent is selected from one or more of BIBP, DTDM, IS90-65 and DCP.

[0013] In one embodiment of the present invention, the following components are included in parts by weight: 65-80 parts of EPDM rubber, 20-30 parts of EVM, 70-80 parts of magnesium hydroxide, 2-3 parts of silane coupling agent, 4-6 parts of zinc oxide, 0.5-1.5 parts of stearic acid, 2-5 parts of antioxidant, 50-60 parts of clay, 3-5 parts of paraffin oil, 20-25 parts of white carbon black, 10-15 parts of silicon carbide, 1-3 parts of sulfur, 3-4 parts of vulcanization accelerator, and 4-5 parts of vulcanizing agent.

[0014] The second object of the present invention is to provide the use of the flame retardant ethylene propylene rubber in high voltage DC cable accessories.

[0015] The third object of the present invention is to provide a method for preparing a flame retardant ethylene-propylene rubber, comprising the following steps:

[0016] (1) EPDM rubber and EVM are mixed, and white carbon black is added in batches and kneaded to obtain a mixture; wherein the EPDM rubber, EVM and white carbon black are allowed to stand after each kneading to allow the white carbon black to be fully dispersed;

[0017] (2) zinc oxide, stearic acid, antioxidant, paraffin oil, white carbon black, clay, and flame retardant are sequentially added to the mixture obtained in step (1), and the mixture is thinly passed through. Then, sulfur, a cross-linking agent, and a vulcanizing agent are added, and the mixture is thinly passed through and then vulcanized to obtain the flame-retardant EPDM rubber.

[0018] In one embodiment of the present invention, in step (1), the standing time is 20 min-40 min.

[0019] In one embodiment of the present invention, in step (2), the number of thin passes is 2 to 8 times.

[0020] In one embodiment of the present invention, in step (2), the vulcanization conditions are: temperature of 160° C.-170° C., time of 30 min-40 min, and pressure of 10 MPa-15 MPa.

[0021] In one embodiment of the present invention, in step (2), the amount of white carbon black added each time is 4 to 5 parts, divided into 3 to 4 times.

[0022] Flame retardant selection:

[0023] (1) Inorganic hydrated metal compound flame retardant:

[0024] Commonly used inorganic hydrated metal flame retardants are aluminum hydroxide and magnesium hydroxide. However, as an inorganic flame retardant, aluminum hydroxide has low flame retardant efficiency, and the flame retardant effect is not obvious when added in small doses. At the same time, the addition of inorganic fillers will affect the compatibility between rubber materials and it is difficult to distribute evenly in the rubber matrix, which can easily cause stress concentration and reduce the comprehensive mechanical properties of the material. The presence of magnesium hydroxide has the disadvantage that a large amount of addition is required to achieve the corresponding flame retardant effect.

[0025] (2) EVM is made of ethylene and vinyl acetate copolymers and has certain thermosetting properties. Compared with EVA, the VA (vinyl acetate) content in ethylene-vinyl acetate rubber is higher, about 40%-80%. Its combustion smoke is small, and it is an ideal low-smoke halogen-free flame retardant material. There are no unsaturated double bonds on the main chain of the EVM molecule, and its chemical properties are stable. It has good weather aging resistance and outstanding heat resistance. It can also maintain good mechanical properties at 175°C. Because it is a polar rubber, it is also oil-resistant. At the same time, its coloring is stable, and basically no toxic gases are produced during combustion. The smoke emission is low. The light flux per unit area measured by the smoke density meter is higher than that of ordinary rubber, and its flame retardant properties are superior. The oxygen index can reach more than 40 by adding halogen-free flame retardants such as magnesium hydroxide and aluminum hydroxide.

[0026] Therefore, the present invention selects magnesium hydroxide (06B) and EVM as flame retardants in the preparation of flame retardant EPDM insulating rubber.

[0027] Since the particles of white carbon black are easily aggregated into large particles in EPDM rubber, their structure changes, hindering their interaction with EPDM rubber materials, reducing the vulcanization effect, making the stirring flow performance of the material worse, increasing the time used for its curing, and affecting its tensile properties. Therefore, in the present invention, white carbon black should be poured into the rubber material in batches, and each addition should be paused and left to stand for 30 minutes to allow the white carbon black to be fully dispersed. And the amount added each time should be as small as possible.

[0028] In one embodiment of the present invention, the present invention provides a method for preparing a flame retardant ethylene-propylene rubber, wherein the EPDM rubber comprises the following components in parts by weight: 75 parts of EPDM rubber, 25 parts of EVM, 75 parts of flame retardant magnesium hydroxide, 2 parts to 3 parts of silane coupling agent, 4 parts to 6 parts of zinc oxide, 0.5 parts to 1.5 parts of stearic acid, 2 parts to 5 parts of antioxidant, 50 parts to 60 parts of clay, 3 parts to 5 parts of paraffin oil, 20 parts to 25 parts of white carbon black, 10 parts to 15 parts of silicon carbide, 1 part to 3 parts of sulfur, 3 parts to 4 parts of vulcanization accelerator TAIC, and 4 parts to 5 parts of vulcanizing agent BIBP.

[0029] The preparation method comprises the following steps:

[0030] First, EPDM and EVM are used as raw materials for standby. EPDM and white carbon black are first mixed. Note that white carbon black should be poured into the silicone rubber material in batches. Each time it is added, it needs to be paused for 30 minutes to allow the white carbon black to be fully dispersed. Since white carbon black has a strong viscosity, the amount added each time should be as small as possible; then add EVM and continue mixing. Other small materials are added in the order of zinc oxide, stearic acid, antioxidants RD and MB, paraffin oil, white carbon black, clay, and flame retardant; put the material that has been taken out and put it into the open mill for thinning twice, and then add the formula amount of S, TAIC and BIBP to the open mill, and thin it 10 times, and then vulcanize and make films; the vulcanization temperature is 165℃, the vulcanization time is 35min, and the vulcanization pressure is 14MPa.

[0031] The above technical solution of the present invention has the following advantages compared with the prior art:

[0032] (1) The present invention solves the problems of difficulty in dispersing magnesium hydroxide flame retardant in rubber matrix and affecting the compatibility of rubber matrix and other fillers by improving the preparation process; the accumulation of space charge during operation is also greatly reduced by dispersing the distribution of fillers, so that the safety performance of cable system operation is greatly guaranteed;

[0033] (2) The present invention develops a new type of high-efficiency halogen-free flame retardant compounding system, determines the optimal addition method of various fillers, and achieves low-smoke halogen-free flame retardancy without affecting the properties of rubber materials (especially mechanical properties and electrical properties);

[0034] (3) The present invention adds flame retardants to EPDM to give EPDM flame retardancy or self-extinguishing properties and strong tensile tearing properties. The present invention improves the flame retardancy of EPDM by improving the preparation process of EPDM, the selection of flame retardants and the amount of addition, thereby expanding its scope of application, and ensuring that its electrical and mechanical properties are not affected while improving the flame retardancy of EPDM;

[0035] (4) The present invention discusses the influence of the amount of auxiliary materials such as EVM and magnesium hydroxide on the self-extinguishing time and the afterburning performance of EPDM through multiple experiments, designs the optimal formula of flame-retardant EPDM, and thus manufactures EPDM with better flame retardant effect and stronger tensile tearing performance, thereby increasing its application range. The results show that when the amount of aluminum hydroxide in 75 parts of EPDM and 25 parts of EVM is 75 parts, the combustion oxygen index (OI value) of EPDM can reach 38%, and both the mechanical properties and electrical properties are maintained. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0037] Example 1

[0038] The present embodiment provides a flame retardant ethylene-propylene rubber, comprising the following components in parts by weight: 75 parts of EPDM rubber, 3 parts of silane coupling agent, 5 parts of zinc oxide, 1 part of stearic acid, 4 parts of antioxidant, 50 parts of clay, 4 parts of paraffin oil, 21 parts of white carbon black, 13 parts of silicon carbide, 2 parts of sulfur, 3 parts of vulcanization accelerator TAIC, and 5 parts of vulcanizing agent BIBP.

[0039] Preparation method of EPDM rubber:

[0040] (1) First, blend EPDM in a mixer at 80°C and 60r / min, and then mix the blend with white carbon black. Note that the white carbon black should be added to the blend in batches. After each mixing of EPDM and white carbon black, let it stand for 30 minutes to allow the white carbon black to complete the migration process and fully disperse. Since white carbon black has a strong viscosity, the amount added each time should be as small as possible;

[0041] (2) Then, zinc oxide, stearic acid, antioxidants RD and MB, paraffin oil, white carbon black, and clay are added in sequence. The material taken out and left to stand is put into an open mill and thinned twice. Then, the formulated amount of S, TAIC, and BIBP are added to the open mill and thinned 10 times. Then, the material is vulcanized and sheeted to obtain flame-retardant EPDM rubber. The vulcanization temperature is 165°C, the vulcanization time is 35 minutes, and the vulcanization pressure is 14 MPa.

[0042] Example 2

[0043] The present embodiment provides a flame retardant ethylene-propylene rubber, comprising the following components in parts by weight: 75 parts of EPDM rubber, 25 parts of EVM, 75 parts of flame retardant magnesium hydroxide, 3 parts of silane coupling agent, 5 parts of zinc oxide, 1 part of stearic acid, 4 parts of antioxidant, 50 parts of clay, 4 parts of paraffin oil, 21 parts of white carbon black, 13 parts of silicon carbide, 2 parts of sulfur, 3 parts of vulcanization accelerator TAIC, and 5 parts of vulcanizing agent BIBP.

[0044] Preparation method of EPDM rubber:

[0045] (1) First, blend EPDM and EVM in an internal mixer at 80°C and 60r / min, and then mix the blend with white carbon black. Note that white carbon black should be added to the blend in batches. After each mixing of EPDM, EVM and white carbon black, let it stand for 30 minutes to allow the white carbon black to complete the migration process and fully disperse. Since white carbon black has a strong viscosity, the amount added each time should be as small as possible;

[0046] (2) Then, zinc oxide, stearic acid, antioxidants RD and MB, paraffin oil, white carbon black, clay, and flame retardant are added in sequence. The material taken out and left to stand is put into an open mill and thinned twice. Then, the formulated amount of S, TAIC, and BIBP are added to the open mill and thinned 10 times. Then, vulcanization is performed to obtain flame-retardant EPDM rubber. The vulcanization temperature is 165°C, the vulcanization time is 35 minutes, and the vulcanization pressure is 14 MPa.

[0047] Example 3

[0048] The present embodiment provides a flame retardant ethylene-propylene rubber, comprising the following components in parts by weight: 75 parts of EPDM rubber, 25 parts of EVM, 75 parts of flame retardant magnesium hydroxide, 2 parts of silane coupling agent, 4 parts of zinc oxide, 1.5 parts of stearic acid, 2 parts of antioxidant, 60 parts of clay, 3 parts of paraffin oil, 20 parts of white carbon black, 15 parts of silicon carbide, 1 part of sulfur, 3 parts of vulcanization accelerator TAIC, and 5 parts of vulcanizing agent BIBP.

[0049] Preparation method of EPDM rubber:

[0050] (1) First, blend EPDM and EVM in an internal mixer at 80°C and 60r / min, and then mix the blend with white carbon black. Note that white carbon black should be added to the blend in batches. After each mixing of EPDM, EVM and white carbon black, let it stand for 30 minutes to allow the white carbon black to complete the migration process and fully disperse. Since white carbon black has a strong viscosity, the amount added each time should be as small as possible;

[0051] (2) Then, zinc oxide, stearic acid, antioxidants RD and MB, paraffin oil, white carbon black, clay, and flame retardant are added in sequence. The material taken out and left to stand is put into an open mill and thinned twice. Then, the formulated amount of S, TAIC, and BIBP are added to the open mill and thinned 10 times. Then, vulcanization is performed to obtain flame-retardant EPDM rubber. The vulcanization temperature is 165°C, the vulcanization time is 35 minutes, and the vulcanization pressure is 14 MPa.

[0052] Example 4

[0053] The present embodiment provides a flame retardant ethylene-propylene rubber, comprising the following components in parts by weight: 75 parts of EPDM rubber, 25 parts of EVM, 75 parts of flame retardant magnesium hydroxide, 3 parts of silane coupling agent, 6 parts of zinc oxide, 0.5 parts of stearic acid, 5 parts of antioxidant, 50 parts of clay, 5 parts of paraffin oil, 25 parts of white carbon black, 10 parts of silicon carbide, 3 parts of sulfur, 4 parts of vulcanization accelerator TAIC, and 4 parts of vulcanizing agent BIBP.

[0054] Preparation method of EPDM rubber:

[0055] (1) First, blend EPDM and EVM in an internal mixer at 80°C and 60 r / min, and then mix the blend with silica. Note that silica should be added to the blend in batches. After each mixing of EPDM, EVM and silica, let it stand for 30 minutes to allow silica to complete the migration process and be fully dispersed.

[0056] (2) Then, zinc oxide, stearic acid, antioxidants RD and MB, paraffin oil, white carbon black, clay, and flame retardant are added in sequence. The material taken out and left to stand is put into an open mill and thinned twice. Then, the formulated amount of S, TAIC, and BIBP are added to the open mill and thinned 10 times. Then, vulcanization is performed to obtain flame-retardant EPDM rubber. The vulcanization temperature is 165°C, the vulcanization time is 35 minutes, and the vulcanization pressure is 14 MPa.

[0057] Comparative Example 1

[0058] This comparative example is similar to Example 2, except that the standing time in step (1) is changed to 10 min.

[0059] Comparative Example 2

[0060] This comparative example is similar to Example 2, except that the standing time in step (1) is changed to 20 minutes.

[0061] Comparative Example 3

[0062] This comparative example is similar to Example 2, except that the white carbon black is not mixed first but added together with other fillers.

[0063] Comparative Example 4

[0064] This comparative example is similar to Example 2, except that no magnesium hydroxide flame retardant filler is added, and only EVM is added.

[0065] Test Case

[0066] The hardness, tear strength, tensile strength, elongation at break, volume resistivity, DC breakdown strength positive electrode, DC breakdown strength negative electrode, space charge density, and oxygen index of the flame retardant EPDM rubber obtained in the above examples and comparative examples were tested (refer to GB / T 2951-2008 and GB / T 3048-2007). The specific test results are shown in Table 1:

[0067] Table 1 Comparison of EPDM rubber properties between the embodiment and the comparative example

[0068]

[0069]

[0070] It can be seen from the data of Example 1 and Example 2 that when the new process preparation method is used, the changes in the electrical properties and mechanical properties of the rubber are minimal. Although there is a slight decrease, they still meet the use conditions of the DC cable, and the flame retardant properties have a qualitative leap.

[0071] It can be seen from the data of Example 2 and Comparative Examples 1 and 2 that the control of the standing time after each mixing of EPDM, EVM and white carbon black is also crucial. If the time is too short, white carbon black cannot complete the migration, and the viscosity of white carbon black itself makes it very easy for white carbon black to aggregate in the material. If magnesium hydroxide flame retardant filler is added at this time, especially after the addition of ultrafine magnesium hydroxide, magnesium hydroxide will form a large area of ​​agglomeration, resulting in a large amount of space charge accumulation inside the material, which will greatly reduce the electrical and mechanical properties of the rubber, greatly affecting the operation safety of DC cable accessories.

[0072] It can be seen from the data of Comparative Example 3 that if white carbon black is not mixed in advance and is added in batches, it will have a huge side effect on the performance of the entire material, whether it is electrical properties, mechanical properties or flame retardant properties.

[0073] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A flame retardant ethylene-propylene rubber, characterized in that: The composition comprises the following components by weight: 65-80 parts of EPDM rubber, 90-110 parts of flame retardant, 2-3 parts of coupling agent, 4-6 parts of zinc oxide, 0.5-1.5 parts of stearic acid, 2-5 parts of antioxidant, 50-60 parts of clay, 3-5 parts of paraffin oil, 20-25 parts of white carbon black, 10-15 parts of silicon carbide, 1-3 parts of sulfur, 3-4 parts of vulcanization accelerator and 4-5 parts of vulcanizing agent. The flame retardant is selected from EVM and / or magnesium hydroxide; The method for preparing the flame retardant ethylene-propylene rubber is characterized by comprising the following steps: (1) EPDM rubber and EVM are mixed, and white carbon black is added in batches for internal mixing to obtain a mixture; wherein the EPDM rubber, EVM and white carbon black are allowed to stand for 30-40 minutes after each internal mixing to allow the white carbon black to be fully dispersed; (2) adding zinc oxide, stearic acid, antioxidant, paraffin oil, white carbon black, clay, and flame retardant to the mixture obtained in step (1) in sequence, and performing thin-passing, and then adding sulfur, a cross-linking agent, and a vulcanizing agent, and performing vulcanization after continuing thin-passing, to obtain the flame-retardant EPDM rubber; In step (1), the amount of white carbon black added each time is 4 to 5 parts, divided into 3 to 4 times.

2. The flame retardant EPDM rubber according to claim 1, characterized in that: The coupling agent is selected from silane coupling agents.

3. The flame retardant ethylene-propylene rubber according to claim 1, characterized in that: The vulcanization accelerator is selected from one or more of TAIC, TMTD-80 and DM.

4. The flame retardant EPDM rubber according to claim 1, characterized in that: The vulcanizing agent is selected from one or more of BIBP, DTDM, IS90-65 and DCP.

5. Use of the flame retardant ethylene propylene rubber according to any one of claims 1 to 4 in high voltage DC cable accessories.

6. The preparation method according to claim 1, characterized in that: In step (2), the number of thin passes is 2 to 8 times.

7. The preparation method according to claim 1, characterized in that: In step (2), the vulcanization conditions are: temperature of 160°C-170°C, time of 30min-40min, and pressure of 10MPa-15MPa.

Images