Grafting type semiconductive shielding material and preparation method thereof

Abstract

The application discloses a grafted semiconductive shielding material and a preparation method thereof, and belongs to the technical field of high-voltage cable materials and preparation thereof. The application solves the problems of uneven dispersion of conductive fillers in the matrix resin and poor high-temperature stability of volume resistivity in the existing semiconductive shielding material. The grafted modified additive containing a polar group is added to an ethylene-butyl acrylate copolymer, is initiated by an initiator, and is bonded to the ethylene-butyl acrylate copolymer macromolecular chain through melt grafting. The polar group on the grafted modified additive can interact with the conductive fillers, improve the dispersibility of the conductive fillers in the copolymer matrix, reduce the high-temperature thermal expansion of the copolymer matrix, reduce the distance between the conductive filler aggregates at high temperatures, make the original conductive network not easy to be damaged, effectively reduce the volume resistivity of the semiconductive shielding material, improve the high-temperature stability of the semiconductive shielding material, and reduce the positive temperature coefficient (PTC) effect.

Description

Technical Field

[0001] This invention relates to a grafted semiconductive shielding material and its preparation method, belonging to the technical field of high-voltage cable materials and their preparation. Background Technology

[0002] High-voltage cables, as key power equipment for high-voltage power transmission, play a vital role in urban power transmission, cross-river and cross-sea power transmission. Semiconductor shielding is an important component of high-voltage AC / DC cables, eliminating defects such as gaps and protrusions at the interface between the cable insulation and the metal conductor and the metal shield. It also ensures uniform electric field distribution in the insulation layer, suppresses excessively high local field strength, and prevents partial discharge. Its quality directly affects the safe operation and service life of high-voltage cables. Volume resistivity is a key performance indicator for evaluating semiconductor shielding layers; the lower the value, the higher the shielding effect. However, within a certain temperature range, the volume resistivity of semiconductor shielding layers gradually increases with increasing temperature, exhibiting a significant positive temperature coefficient of resistance (PTC) characteristic. High-voltage cables have a rated operating temperature of 70℃ or 90℃, which falls within the PTC region of the semiconductor shielding layer. Therefore, how to reduce the PTC effect of semiconductor shielding materials and improve the temperature stability of their volume resistivity is a key issue in the research of semiconductor shielding materials for high-voltage cables. Current technologies typically require adding conductive fillers to the matrix resin to prepare semiconductive shielding materials and adjust their volume resistivity. However, conductive fillers often suffer from insufficient conductivity and uneven dispersion, leading to increased volume resistivity and reduced high-temperature stability of the semiconductive shielding material. This can negatively impact the electric field distribution within the cable. Furthermore, excessive conductive fillers can affect the mechanical properties of the shielding material, further reducing the safe and stable operation of the cable. Therefore, improving the compatibility of conductive fillers with the matrix resin, enhancing their dispersibility within the matrix resin, reducing the volume resistivity of the semiconductive shielding material, and suppressing the PTC effect have become important development directions for semiconductive shielding materials. Summary of the Invention

[0003] This invention addresses the problems of uneven dispersion of conductive fillers in the matrix resin and poor high-temperature stability of volume resistivity in existing semiconductive shielding materials by providing a grafted semiconductive shielding material and its preparation method.

[0004] The technical solution of this invention:

[0005] One objective of this invention is to provide a grafted semiconductive shielding material, which is made from the following raw materials in parts by weight: 100 parts ethylene-butyl acrylate copolymer, 0.2 to 3 parts initiator, 20 to 70 parts conductive carbon black, 0 to 10 parts second conductive filler, and 0.02 to 5 parts grafting modifier; the grafting modifier contains active groups that can be grafted onto the ethylene-butyl acrylate copolymer.

[0006] Furthermore, the graftable active groups contained in the grafting modified additive are C=C double bonds.

[0007] Furthermore, the grafting modification additive is maleic anhydride or allyl chloroacetate.

[0008] Further specifying, the initiator is one or a mixture of several of the following: dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and bis-tert-butylperoxyisopropylbenzene.

[0009] Furthermore, the initiator is specified as 0.5 to 3 parts of dicumyl peroxide.

[0010] Furthermore, the initiator is specified as 0.5 to 3 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0011] Furthermore, the initiator is specified as 0.2 to 2 parts of bis-tert-butylperoxyisopropylbenzene.

[0012] Further specifying, the second conductive filler is graphite nanopowder and / or carbon nanotubes.

[0013] A second objective of this invention is to provide a method for preparing the above-mentioned grafted semiconductive shielding material, the method comprising the following steps:

[0014] Step 1: Dry the ethylene-butyl acrylate copolymer, carbon black and the second conductive filler in a vacuum oven at 60°C for 24 hours. Then, melt the ethylene-butyl acrylate copolymer in a torque rheometer and add the second conductive filler. Mix the mixture for 2 to 10 minutes at a temperature of 80 to 130°C and a rotation speed of 30 to 80 r / min to obtain the masterbatch.

[0015] Step 2: Add the masterbatch and ethylene-butyl acrylate copolymer together into a torque rheometer to melt, then add carbon black, grafting modifier and initiator in sequence, and mix for 8-20 minutes at a temperature of 80-130℃ and a speed of 30-80 r / min to obtain a graftable semiconductive blend.

[0016] Step 3: The graftable semiconductive blend is placed in a flat vulcanizing machine and hot-pressed at a temperature of 80-130℃ and a pressure of 10-20MPa. Then, it is transferred to a flat vulcanizing machine at a temperature of 140-200℃ and a pressure of 10-20MPa for grafting and crosslinking for 10-60 minutes, and then cooled to obtain the grafted semiconductive shielding material.

[0017] Further specified, the melting temperature of the ethylene-butyl acrylate copolymer is 100-120℃, and the torque rheometer speed is 50-70 r / min.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The present invention uses grafting and crosslinking initiators, and utilizes the graftable active groups of grafting modified additives to connect the polar groups contained therein to the ethylene-butyl acrylate copolymer macromolecular chain to prepare grafted semiconductive shielding material. The semiconductive shielding material has low volume resistivity, high resistivity high temperature stability, and good mechanical properties.

[0020] (2) The present invention uses a grafting method to attach polar groups to the macromolecular chain of ethylene-butyl acrylate copolymer, so that the polar groups are uniformly and densely distributed in the ethylene-butyl acrylate copolymer matrix, which improves the compatibility between the copolymer and carbon black and the second conductive filler, and improves the dispersion of the conductive filler in the copolymer matrix, thereby reducing the volume resistivity of the semiconductive shielding material.

[0021] (3) The present invention utilizes the interaction between polar groups and conductive fillers to significantly reduce the high-temperature thermal expansion of the grafted ethylene-butyl acrylate copolymer matrix, reduce the distance between conductive filler aggregates at high temperatures, make the original conductive network of conductive fillers less likely to be destroyed, effectively improve the conductivity of semi-conductive shielding material at high temperatures, and reduce its PTC effect. Attached Figure Description

[0022] Figure 1 Infrared spectra of ethylene-butyl acrylate copolymer film samples before and after grafting and crosslinking reactions in Example 1;

[0023] Figure 2 Scanning electron microscope images of the semiconductive shielding materials prepared for different embodiments, wherein a is Comparative Example 1, b is Example 1, c is Example 2, d is Example 3, and e is Example 4;

[0024] Figure 3 A comparison of the volume resistivity of the semiconductive shielding materials prepared in different embodiments as a function of temperature. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0029] The ethylene-butyl acrylate copolymer (EBA), model 1770, used in the following examples was purchased from Repsol, Spain; dicumyl peroxide (DCP) was purchased from AkzoNobel, Netherlands; 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (vulcanizing agent bis(2,5-dimethyl)propane) was purchased from Wengjiang Chemical Reagent Co., Ltd., Guangdong, China; bis(tert-butylperoxy)propane (vulcanizing agent BIPB) was purchased from Wengjiang Chemical Reagent Co., Ltd., Guangdong, China; carbon black (CB), model VULCANX C500, was purchased from Cabot Corporation, USA; carbon nanotubes (CNT), model MWNT-1020, with a purity >98%, particle size 10-20 nm, length 5-15 μm, and specific surface area 40-300 m² / g. 2 / g, purchased from Shenzhen Nanoport Co., Ltd., China; maleic anhydride (MAH), purchased from Shanghai McLean Biochemical Technology Co., Ltd., China; allyl chloroacetate (CAAE), purchased from Shanghai McLean Biochemical Technology Co., Ltd., China.

[0030] Example 1

[0031] The steps for preparing the semiconductive shielding material in this embodiment are as follows:

[0032] Step 1: Add 70g of ethylene-butyl acrylate copolymer to a torque rheometer and melt it at 110℃ and 50r / min. After melting, add 30g of carbon black and mix for 5min under the same conditions. Then add 1g of maleic anhydride and mix for 5min. Finally, add 1g of dicumyl peroxide and continue mixing for 3min to obtain a graftable semiconducting blend.

[0033] Step 2: The obtained graftable semiconductive blend is placed in a flat vulcanizing machine and hot-pressed at a temperature of 110℃ and a pressure of 15MPa. Then it is transferred to a flat vulcanizing machine at a temperature of 175℃ and a pressure of 15MPa for grafting and crosslinking for 30 minutes. After cooling, maleic anhydride-grafted ethylene-butyl acrylate copolymer-based semiconductive shielding material is obtained.

[0034] To verify the grafting of maleic anhydride into ethylene-butyl acrylate copolymer, the infrared spectra of the ethylene-butyl acrylate copolymer film before and after the grafting and crosslinking reactions were measured. The results are as follows: Figure 1 As shown. By Figure 1 It can be seen that after grafting and cross-linking reactions, maleic anhydride at 1850 and 1786 cm⁻¹... -1 The stretching vibration peak intensity of the carbonyl C=O group remained almost unchanged, and at 888 cm⁻¹ -1 The disappearance of the out-of-plane bending vibration peak of the =CH group indicates that the C=C double bond in maleic anhydride opened during the grafting and crosslinking reaction, verifying that maleic anhydride was successfully grafted onto the ethylene-butyl acrylate copolymer macromolecular chain. The dispersibility of carbon black in maleic anhydride-grafted ethylene-butyl acrylate copolymer / carbon black semiconductive shielding material is as follows: Figure 2 As shown in (b), the volume resistivity of the semiconductive shielding material changes with temperature as follows: Figure 3 As shown.

[0035] Example 2

[0036] The steps for preparing the semiconductive shielding material in this embodiment are as follows:

[0037] Step 1: Add 68g of ethylene-butyl acrylate copolymer to a torque rheometer and melt it at 120℃ and 60r / min. After melting, add 32g of carbon black and mix for 4min under the same conditions. Then add 0.5g of maleic anhydride and mix for 4min. Finally, add 1.8g of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and continue mixing for 2min to obtain a graftable semiconducting blend.

[0038] Step 2: The obtained graftable semiconductive blend is placed in a flat vulcanizing machine and hot-pressed at a temperature of 120℃ and a pressure of 12MPa. Then it is transferred to a flat vulcanizing machine at a temperature of 180℃ and a pressure of 12MPa for grafting and crosslinking for 20 minutes. After cooling, maleic anhydride-grafted ethylene-butyl acrylate copolymer-based semiconductive shielding material is obtained.

[0039] The dispersibility of carbon black in maleic anhydride-grafted ethylene-butyl acrylate copolymer / carbon black semiconductive shielding material is as follows: Figure 2 As shown in (c), the volume resistivity of the semiconductive shielding material changes with temperature as follows: Figure 3 As shown.

[0040] Example 3

[0041] The steps for preparing the semiconductive shielding material in this embodiment are as follows:

[0042] Step 1: Add 65g of ethylene-butyl acrylate copolymer to a torque rheometer and melt it at 100℃ and 70r / min. After melting, add 35g of carbon black and mix for 6min under the same conditions. Then add 1g of allyl chloroacetate and mix for 6min. Finally, add 0.7g of bis-tert-butylperoxyisopropylbenzene and continue mixing for 3min to obtain a graftable semiconducting blend.

[0043] Step 2: The obtained graftable semiconductive blend is placed in a flat vulcanizing machine and hot-pressed at a temperature of 100℃ and a pressure of 18MPa. Then, it is transferred to a flat vulcanizing machine at a temperature of 165℃ and a pressure of 18MPa for grafting and crosslinking for 50 minutes. After cooling, a semiconductive shielding material based on chloropropyl acetate grafted ethylene-butyl acrylate copolymer is obtained.

[0044] The dispersibility of carbon black in allyl chloroacetate-grafted ethylene-butyl acrylate copolymer / carbon black semiconductive shielding material is as follows: Figure 2 As shown in (d), the volume resistivity of the semiconductive shielding material changes with temperature as follows: Figure 3 As shown.

[0045] Example 4

[0046] The steps for preparing the semiconductive shielding material in this embodiment are as follows:

[0047] Step 1: Add 70g of ethylene-butyl acrylate copolymer to a torque rheometer and melt it at 115℃ and 55r / min. After melting, add 10g of carbon nanotubes and mix under the same conditions for 6min to obtain the masterbatch. Add 16g of the masterbatch and 56g of ethylene-butyl acrylate copolymer to the torque rheometer and melt it at 115℃ and 55r / min. After melting, add 28g of carbon black and mix under the same conditions for 4min. Then add 0.3g of maleic anhydride and mix for 5min. Finally, add 1.5g of dicumyl peroxide and continue mixing for 3min to obtain a graftable semiconducting blend.

[0048] Step 2: The obtained graftable semiconductive blend is placed in a flat vulcanizing machine and hot-pressed at a temperature of 115℃ and a pressure of 15MPa. Then it is transferred to a flat vulcanizing machine at a temperature of 170℃ and a pressure of 15MPa for grafting and crosslinking for 40 minutes. After cooling, maleic anhydride-grafted ethylene-butyl acrylate copolymer-based semiconductive shielding material is obtained.

[0049] The dispersibility of carbon black in maleic anhydride-grafted ethylene-butyl acrylate copolymer / carbon black / carbon nanotube semiconductive shielding material is as follows: Figure 2 As shown in (e), the volume resistivity of the semiconductive shielding material changes with temperature as follows: Figure 3 As shown.

[0050] Comparative Example 1

[0051] The steps for preparing the semiconductive shielding material in this comparative example are as follows:

[0052] Step 1: Add 70g of ethylene-butyl acrylate copolymer to a torque rheometer and melt it at 110℃ and 50r / min. After melting, add 30g of carbon black and mix for 5min under the same conditions. Then add 1g of dicumyl peroxide and continue mixing for 3min to obtain a semiconductive blend.

[0053] Step 2: The obtained semiconductive blend is placed in a flat vulcanizing machine and hot-pressed at a temperature of 110℃ and a pressure of 15MPa. Then it is transferred to a flat vulcanizing machine at a temperature of 175℃ and a pressure of 15MPa, crosslinked for 30 minutes, and then cooled to obtain pure ethylene-butyl acrylate copolymer-based semiconductive shielding material.

[0054] The dispersibility of carbon black in pure ethylene-butyl acrylate copolymer / carbon black semiconductive shielding material is as follows Figure 2 As shown in (a), the volume resistivity of the semiconductive shielding material changes with temperature as follows: Figure 3 As shown.

[0055] Example of results:

[0056] (1) Analysis and explanation of the above data:

[0057] Depend on Figure 2 As shown in Figures a, b, and c, the carbon black exhibits poor dispersibility in the pure ethylene-butyl acrylate copolymer-based semiconductive shielding material prepared in Comparative Example 1, with obvious agglomeration. However, the dispersibility of carbon black in the grafted ethylene-butyl acrylate copolymer-based semiconductive shielding materials prepared in Examples 1 and 2 is significantly improved, with more uniform dispersion and no obvious agglomeration. Figure 3 It can be seen that the volume resistivity of the grafted ethylene-butyl acrylate copolymer-based semiconductive shielding material prepared in Examples 1 and 2 is significantly lower than that of the pure ethylene-butyl acrylate copolymer-based semiconductive shielding material prepared in Comparative Example 1. The polar groups of the grafted maleic anhydride are uniformly and densely distributed in the ethylene-butyl acrylate copolymer matrix, which can improve the compatibility between the copolymer matrix and carbon black, increase the dispersion of carbon black in the copolymer matrix, and thus reduce the volume resistivity of the semiconductive shielding material.

[0058] Comparing with Comparative Example 1, the volume resistivity of the grafted ethylene-butyl acrylate copolymer-based semiconductive shielding materials prepared in Examples 1 and 2 increases less with increasing temperature, indicating a reduced PTC effect. At 90°C, their volume resistivity is also less than 100 Ω·cm. Semiconductive shielding materials for high-voltage cables require a resistivity below 100 Ω·cm at room temperature and below 350 Ω·cm at operating temperatures of 70°C or 90°C. Therefore, the resistivity of the grafted ethylene-butyl acrylate copolymer-based semiconductive shielding materials prepared in Examples 1 and 2 fully meets the requirements for semiconductive shielding materials for cables, and their performance far exceeds these requirements.

[0059] (2) The swelling rates of the semiconductive shielding materials prepared in Example 1, Example 2 and Comparative Example 1 in xylene at different temperatures were compared, and the results are shown in Table 1 below:

[0060] Table 1

[0061] 30℃ 70℃ 90℃ Example 1 41.84％ 324.82％ 516.84％ Example 2 41.86％ 290.6％ 535.47％ Comparative Example 1 41.04％ 371.54％ 578.57％

[0062] As shown in the table above, at higher temperatures, the swelling rate of the grafted ethylene-butyl acrylate copolymer-based semiconductive shielding materials prepared in Examples 1 and 2 is significantly lower than that of the pure ethylene-butyl acrylate copolymer-based semiconductive shielding material prepared in Comparative Example 1. Maleic anhydride grafting can reduce the swelling rate of the ethylene-butyl acrylate copolymer-based semiconductive shielding material in good solvents. The polar groups of maleic anhydride grafted onto the ethylene-butyl acrylate copolymer can react physically or chemically with carbon black, limiting the swelling of the ethylene-butyl acrylate copolymer in good solvents at higher temperatures. That is, the grafted ethylene-butyl acrylate copolymer matrix is ​​less likely to expand at higher temperatures, reducing the distance between carbon black aggregates at high temperatures and making the original carbon black conductive network less likely to be destroyed. Therefore, as the temperature increases, the volume resistivity of the maleic anhydride grafted ethylene-butyl acrylate copolymer-based semiconductive shielding material will not increase sharply, and the PTC effect will be weakened. Grafting modification additives containing polar groups can effectively improve the high-temperature stability of the resistivity of the semiconductive shielding material.

[0063] (3) The mechanical properties of the semiconductive shielding materials prepared in Examples 1 to 4 and Comparative Example 1 were compared, and the results are shown in Table 2 below:

[0064] Table 2

[0065] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Tensile strength (MPa) 19.94 22.67 22.41 19.31 19.86 Elongation at break (%) 310.23 380.19 405.83 336.17 255.66

[0066] As shown in the table above, compared with Comparative Example 1, the tensile strength and elongation at break of the grafted ethylene-butyl acrylate copolymer-based semiconductive shielding materials prepared in Examples 1 and 2 of the present invention are improved. The tensile strength and elongation at break of the grafted ethylene-butyl acrylate copolymer-based semiconductive shielding material prepared in Example 3 are comparable. However, the tensile strength of the grafted ethylene-butyl acrylate copolymer-based semiconductive shielding material prepared in Example 4 is comparable, but the elongation at break is reduced.

[0067] From a comprehensive performance perspective, grafted semiconductive shielding material meets the requirements of high-voltage cable semiconductive shielding material for electrical and mechanical properties. Carbon black has good dispersibility in semiconductive shielding material, and semiconductive shielding material has low resistivity, high resistivity high-temperature stability and excellent mechanical properties, making it an excellent high-voltage cable semiconductive shielding material.

[0068] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A grafted semiconductive shielding material, characterized in that, It is made from the following raw materials in parts by weight: 100 parts ethylene-butyl acrylate copolymer, 0.2-3 parts initiator, 20-70 parts conductive carbon black, 0-10 parts second conductive filler, and 0.02-5 parts grafting modifier. The grafting modification additive is maleic anhydride or allyl chloroacetate; the initiator is one or a mixture of several of dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and bis-tert-butylperoxyisopropylbenzene.

2. The grafted semiconductive shielding material according to claim 1, characterized in that, The initiator is 0.5 to 3 parts of dicumyl peroxide.

3. The grafted semiconductive shielding material according to claim 1, characterized in that, The initiator is 0.5 to 3 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

4. The grafted semiconductive shielding material according to claim 1, characterized in that, The initiator is 0.2 to 2 parts of bis-tert-butylperoxyisopropylbenzene.

5. The grafted semiconductive shielding material according to claim 1, characterized in that, The second conductive filler is graphite nanopowder and / or carbon nanotubes.

6. A method for preparing the grafted semiconductive shielding material according to claim 1, characterized in that, include: Step 1: Dry the ethylene-butyl acrylate copolymer, conductive carbon black and the second conductive filler in a vacuum oven at 60°C for 24 hours. Then, melt the ethylene-butyl acrylate copolymer in a torque rheometer and add the second conductive filler. Mix the mixture for 2 to 10 minutes at a temperature of 80 to 130°C and a rotation speed of 30 to 80 r / min to obtain the masterbatch. Step 2: Add the masterbatch and ethylene-butyl acrylate copolymer together into a torque rheometer to melt, then add conductive carbon black, grafting modifier and initiator in sequence, and mix for 8-20 minutes at a temperature of 80-130℃ and a rotation speed of 30-80 r / min to obtain a graftable semiconductive blend. Step 3: The graftable semiconductive blend is placed in a flat vulcanizing machine and hot-pressed at a temperature of 80~130℃ and a pressure of 10~20MPa. Then it is transferred to a flat vulcanizing machine at a temperature of 140~200℃ and a pressure of 10~20MPa for grafting and crosslinking for 10~60 minutes, and then cooled to obtain the grafted semiconductive shielding material.

7. The method for preparing the grafted semiconductive shielding material according to claim 6, characterized in that, The melting temperature of the ethylene-butyl acrylate copolymer is 100~120℃, and the speed of the torque rheometer is 50~70 r / min.

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