TPV (thermoplastic vulcanizate)-based semiconductive shielding material for power cable and preparation method of TPV-based semiconductive shielding material

Abstract

The invention relates to a TPV-based semiconductive shielding material for a power cable. The TPV-based semiconductive shielding material comprises the following raw material components in percentage by mass: 35-45% of polypropylene resin; 20-30% of ethylene propylene diene monomer; 1-5% of nitrile rubber; 1-2% of vinyl silane; 0.5-1% of an initiator; 2-5% of a catalyst; 15-30% of a conductive agent; 0.5-1% of a lubrication dispersant; and 0.5-1% of an anti-aging agent. A ternary composite base material of polypropylene (PP), ethylene propylene diene monomer (EPDM) and nitrile rubber (NBR) and auxiliaries such as vinyl silane, an initiator, a catalyst and a conductive agent are adopted, and quadruple material modification of melt grafting, dynamic vulcanization, controllable degradation and blending dispersion is completed at the same time through the hot shearing effect of a double-screw extruder. The prepared TPV-based semi-conductive shielding material has good conductivity, and an extruded power cable semi-conductive shielding layer has high surface smoothness.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cable materials, and relates to a semiconductive shielding material, in particular to a TPV-based semiconductive shielding material for power cables and a preparation method thereof. BACKGROUND

[0002] Traditional cross-linked polyethylene (XLPE) insulated power cables have problems such as high manufacturing energy consumption, complex degassing process, and non-recyclable material after retirement. Polypropylene (PP) has advantages such as non-cross-linking, recyclability, and high-temperature resistance, and a polypropylene insulated power cable prepared therefrom has become a substitute for traditional XLPE insulated power cables. At present, the preparation of polypropylene power cable insulation material has preliminarily formed three major technical routes, and the development of a matching polypropylene semiconductive shielding material still faces some technical bottlenecks.

[0003] The semiconductive shielding layer is an important component of 10KV and above power cables, and is generally formed into a "inner shielding layer-insulation layer-outer shielding layer" composite structure through a three-layer co-extrusion process. The inner and outer semiconductive shielding material layers are respectively in equipotential with the cable conductor and the metal shielding layer, so that a smooth interface is formed between the insulation layer and the high-voltage potential and the ground potential, thereby playing the roles of eliminating the burrs or protrusions on the surface of the metal conductor, uniformly distributing the interface electric field, suppressing the excessively high local field strength, and preventing partial discharge. The semiconductive shielding material is generally composed of a resin base material, a conductive agent, a cross-linking agent, an antioxidant, and a lubricant therefor. At present, ethylene-vinyl acetate copolymer (EVA) and ethylene-butyl acrylate copolymer (EBA) based cross-linked semiconductive shielding materials are relatively mature in commercialization. With the green and low-carbon transformation of the cable industry, polypropylene insulated power cables have become an industry hotspot, but the development of thermoplastic (non-cross-linked) semiconductive shielding materials matching the polypropylene insulated power cables is still in the verification stage. The power cable standards and the power cable preparation process require that the polypropylene semiconductive inner shielding material has good mechanical properties, high-temperature resistance, low-temperature resistance, low resistivity, easy processability, a smooth surface of the shielding layer after extrusion, and easy peeling between the insulation layer. How to balance various properties has become a technical bottleneck to be solved in the industry.

[0004] The elastomer blending route is a cost-effective way to toughen polypropylene. Through physical blending, the elastomer is dispersed in the polypropylene matrix in the form of microscopic particles to form a uniform "island-in-sea" structure, thereby achieving the purpose of reducing the bending modulus and improving the low-temperature flexibility of polypropylene. Although blending elastomers in polypropylene can improve the bending modulus and low-temperature flexibility, it often leads to a decrease in the tensile strength and heat resistance of the blended material. Moreover, the polypropylene / elastomer "island-in-sea" structure formed by physical blending is not thermodynamically stable. When heated, the molecular chains between the material will undergo de-entanglement, and the polypropylene / elastomer material will undergo phase separation, resulting in a significant deterioration of the mechanical properties after heat aging. The Chinese invention patent with the authorization announcement number CN115850869B discloses a method of using POE elastomer blending to improve the elongation at break and impact resistance of polypropylene. However, as an ethylene-based elastomer, POE is not compatible with polypropylene in terms of co-crystallization and thermodynamics.

[0005] The Chinese invention patent with the authorization announcement number CN105037964B discloses a TPV material with good mechanical properties and processing performance, which can be applied in the field of electric wires and cables. Common TPV materials are prepared by reaction extrusion, in which polypropylene (PP) and ethylene propylene diene rubber (EPDM) undergo physical blending and rubber vulcanization reaction in the presence of a crosslinking agent. This process is called "dynamic vulcanization". The crosslinking agent systems commonly used in the modified plastic industry are peroxide vulcanization systems and phenolic resin vulcanization systems. Both are thermally initiated crosslinking reactions, and the dynamic vulcanization speed is uncontrollable, which is prone to scorching. Once scorching occurs, the viscosity of EPDM increases sharply, and it is difficult to uniformly disperse the vulcanized EPDM in the form of small particles in the PP matrix, resulting in a TPV material with performance that cannot meet the expected requirements. SUMMARY

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a TPV-based semiconductive shielding material for power cables.

[0007] To achieve the above-mentioned purpose, the present invention provides a TPV-based semiconductive shielding material for power cables, which comprises the following raw material components by mass percentage:

[0008]

[0009] Optimally, the polypropylene resin is a mixture composed of one or more selected from homopolymer polypropylene (PPH) and block copolymer polypropylene (PPB), and the melt index (MFI) of the polypropylene resin is 1-3 g / 10 min, and the melting point (Tm) is ≥ 150℃.

[0010] Optimally, the ethylene content of the ethylene propylene diene rubber is 45-75%, the ethylidene norbornene (ENB) content is 2-5%, and the Mooney viscosity (ML1+4) at 125℃ is 40-100.

[0011] Optimally, the Mooney viscosity ML1+4 of the nitrile rubber at 100℃ is 30-100.

[0012] Optimally, the vinyl silane is a mixture consisting of one or more selected from A-151 silane, A-171 silane and A-172 silane.

[0013] Optimally, the initiator is a mixture consisting of one or more selected from dicumyl peroxide, benzoyl peroxide and di-tert-butyl peroxide isopropyl benzene.

[0014] Optimally, the catalyst is a dibutyl tin dilaurate master batch with LLDPE as carrier, the mass concentration of dibutyl tin dilaurate in the master batch is 0.5-2wt%.

[0015] Optimally, the conductive agent is conductive carbon black, which is high-structure acetylene carbon black, DBP absorption value is ≥150ml / 100g.

[0016] Optimally, the lubricating dispersing agent is a mixture consisting of one or more selected from magnesium 12-hydroxystearate, ethylene bis 12-hydroxystearic amide and hyperbranched polymer lubricant, and the antioxidant is antioxidant TMQ.

[0017] Another object of the present application is to provide a preparation method of the TPV-based semi-conductive shielding material for power cable, comprising the following steps:

[0018] Mixing the formula amount of the polypropylene resin, ethylene propylene terpolymer rubber, nitrile rubber, antioxidant and catalyst in proportion to prepare a resin premix;

[0019] Adding the formula amount of the vinyl silane and initiator into a container to stir and mix to prepare a silane liquid premix;

[0020] Adding the formula amount of the conductive agent and lubricating dispersing agent into a sonic resonance mixer to mix to prepare a conductive agent powder premix;

[0021] Setting the temperature of the twin-screw extruder to 160-230℃, and then feeding the resin premix, the silane liquid premix and the conductive agent powder premix into the twin-screw extruder respectively, and the extruded melt is prepared into a granular TPV-based semi-conductive shielding material by air cooling and granulation.

[0022] Thanks to the above technical solution, the present application has the following advantages compared with the prior art:

[0023] (1) The TPV-based semi-conductive shielding material for power cables is prepared by using polypropylene (PP), ethylene propylene diene rubber (EPDM) and nitrile rubber (NBR) as a ternary composite base material, and by using vinyl silane, initiator, catalyst and conductive agent as auxiliary agents to complete the four material modifications of "melt grafting + dynamic vulcanization + controllable degradation + blending dispersion" simultaneously through the heat shearing action of a double screw extruder.

[0024] (2) The EPDM-g-Si formed by melt grafting of EPDM and vinyl silane can improve the interfacial compatibility between the conductive agent and the polymer base material, and can improve the dispersity of the conductive agent in the polymer base material under the synergistic action of the dispersant, so that the conductive agent forms a uniformly distributed conductive network in the polymer base material, and the prepared TPV-based semi-conductive shielding material for power cables has good conductivity, and the semi-conductive shielding layer of the power cable has high surface smoothness.

[0025] (3) The PP, EPDM and NBR and the peroxide initiator are subjected to "peroxide crosslinking type dynamic vulcanization" under the heat shearing action of the double screw extruder, and the EPDM-g-Si formed by melt grafting of EPDM and vinyl silane is subjected to "silane crosslinking type dynamic vulcanization" under the action of the catalyst and the trace amount of moisture contained in the conductive agent. Under the joint action of the two dynamic vulcanizations, the PP and the EPDM and NBR blend to form a TPV material with an interpenetrating network structure, which has excellent mechanical properties and heat resistance, and effectively avoids the problems of decreased heat resistance and phase separation after heat aging which are faced by the conventional PP and elastomer direct blending technical route.

[0026] (4) The PP tends to be subjected to controllable degradation under the action of the peroxide, so that the TPV-based semi-conductive shielding material for power cables has good processing fluidity, and still has thermoplasticity after service, and has good recyclability.

[0027] (5) A small amount of nitrile rubber NBR is mixed in the TPV-based semi-conductive shielding material for power cables, so that the polarity of the material can be controlled, the peeling strength between the TPV-based semi-conductive shielding material for power cables and the polypropylene insulation layer of the power cable can be reduced, and the performance requirement of easy peeling of the shielding layer can be realized. DETAILED DESCRIPTION

[0028] The TPV-based semi-conductive shielding material for power cables comprises the following raw material components in mass percentage: polypropylene resin 35-45%; ethylene propylene diene rubber 20-30%; nitrile rubber 1-5%; vinyl silane 1-2%; initiator 0.5-1%; catalyst 2-5%; conductive agent 15-30%; lubricating dispersant 0.5-1%; anti-aging agent 0.5-1%.

[0029] The preparation method of the TPV-based semi-conductive shielding material for power cables comprises the following steps: uniformly mixing the formula amount of the polypropylene resin, the ethylene propylene diene rubber, the nitrile rubber, the antioxidant and the catalyst in proportion to prepare a resin premix; stirring and mixing the formula amount of the vinyl silane and the initiator in a container to prepare a silane liquid premix; adding the formula amount of the conductive agent and the lubricating dispersant into a sonic resonance mixer to mix and prepare a conductive agent powder premix; setting the temperature of a double screw extruder at 160-230 DEG C, and then feeding the resin premix, the silane liquid premix and the conductive agent powder premix into the double screw extruder, and the extruded melt is granulated by air cooling to prepare a granular TPV-based semi-conductive shielding material.

[0030] A TPV-based semi-conductive shielding material is prepared by using a ternary composite substrate of polypropylene (PP), ethylene propylene diene rubber (EPDM) and nitrile rubber (NBR) and additives such as vinyl silane, initiator, catalyst and conductive agent to complete the four material modifications of "melt grafting + dynamic vulcanization + controllable degradation + blending dispersion" simultaneously through the thermal shearing action of a double screw extruder. The EPDM-g-Si formed by the melt grafting of EPDM and vinyl silane can improve the interfacial compatibility between the conductive agent and the polymer substrate, and improve the dispersity of the conductive agent in the polymer substrate under the synergistic action of the dispersant, so that the conductive agent forms a uniformly distributed conductive network in the polymer substrate. The prepared TPV-based semi-conductive shielding material has good conductivity, and the extruded semi-conductive shielding layer of the power cable has high surface smoothness. The PP, EPDM and NBR undergo "peroxide crosslinking type dynamic vulcanization" under the thermal shearing action of the double screw extruder, and the EPDM-g-Si formed by the melt grafting of EPDM and vinyl silane undergoes "silane crosslinking type dynamic vulcanization" under the action of the catalyst and the trace amount of water contained in the conductive agent. Under the combined action of the two dynamic vulcanizations, the PP and EPDM and NBR blend to form an interpenetrating network structure of the TPV material, which has excellent mechanical properties and heat resistance, effectively avoiding the problems of decreased heat resistance and phase separation after heat aging faced by the conventional PP and elastomer direct blending technology route. The PP tends to undergo controllable degradation under the action of the peroxide, so that the TPV-based semi-conductive shielding material has good processing fluidity, and the TPV-based semi-conductive shielding material after service still has thermoplasticity and good recyclability. A small amount of nitrile rubber NBR is added into the TPV-based semi-conductive shielding material to regulate the polarity of the material, reduce the peeling strength between the TPV-based semi-conductive shielding material and the polypropylene insulation layer of the power cable, and realize the performance requirement of easy peeling of the shielding layer.

[0031] The polypropylene resin is a mixture consisting of one or more selected from the group consisting of homopolymer polypropylene PPH and block copolymer polypropylene PPB, the melt index MFI of the polypropylene resin is 1-3 g / 10 min, the melting point Tm is ≥ 150°C. The ethylene mass content of the above-mentioned ethylene propylene rubber is 45-75%, the ethylidene norbornene ENB mass content is 2-5%, the Mooney viscosity ML1+4 at 125°C is 40-100. The Mooney viscosity ML1+4 of the above-mentioned nitrile rubber at 100°C is 30-100. The above-mentioned vinyl silane is a mixture consisting of one or more selected from the group consisting of A-151 silane, A-171 silane and A-172 silane. The above-mentioned initiator is a mixture consisting of one or more selected from the group consisting of dicumyl peroxide, benzoyl peroxide and di-tert-butyl peroxide isopropyl benzene. The above-mentioned catalyst is a dibutyl tin dilaurate master batch with LLDPE as the carrier, the mass concentration of dibutyl tin dilaurate in the master batch is 0.5-2 wt%. The above-mentioned conductive agent is conductive carbon black, which is high-structure acetylene carbon black, the DBP absorption value is ≥ 150 ml / 100 g. The above-mentioned lubricating dispersing agent is a mixture consisting of one or more selected from the group consisting of magnesium 12-hydroxystearate, ethylene bis 12-hydroxystearamide and hyperbranched polymer lubricant, and the antioxidant is antioxidant TMQ.

[0032] The application will be further described in detail below in combination with specific examples, but the application is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not marked are conventional conditions in the industry.

[0033] Examples 1-4 and Comparative Examples 1-12

[0034] Examples 1-4 and Comparative Examples 1-12 respectively provide a TPV-based semiconductive shielding material for power cables, and the specific raw material amounts are shown in Tables 1 and 2.

[0035] Table 1 Raw material composition table of TPV-based semiconductive shielding material for power cables (Examples 1-4 and Comparative Examples 1-4, unit: kg)

[0036]

[0037] Table 2 Raw material composition table of TPV-based semiconductive shielding material for power cables (Comparative Examples 5-9, unit: kg)

[0038]

[0039] Note: polypropylene resin uses Qilu Petrochemical block copolymer polypropylene PPB EPS30R (melt index MFI = 1.5 g / 10 min, melting point Tm = 163℃); ethylene propylene rubber uses Jilin Petrochemical EPDM J-2070 (ethylene mass content 56.5%; ethylbenzene ENB mass content 2.0%, Mooney viscosity ML1+4 at 125℃ is 45); butyl nitrile rubber uses Lanzhou Petrochemical NBR 3305 (Mooney viscosity ML1+4 at 100℃ is 50); vinyl silane uses vinyl trimethoxysilane manufactured by Jiangxi Chen Guang New Materials Co., Ltd., brand A-171; initiator uses dicumyl peroxide DCP manufactured by Jiangsu Daoming Chemical Co., Ltd.; catalyst uses dibutyl tin dilaurate mother granules produced by Anhui Chuzhou Dewei New Materials Co., Ltd., brand B1, the mass concentration of dibutyl tin dilaurate in the mother granules is 1%wt; conductive agent uses acetylene carbon black Li-EH700 produced by Jiaozuo Hexing Chemical Industry Co., Ltd., its DBP absorption value is 446ml / 100g; lubricating dispersing agent uses ethylene bis 12-hydroxy stearamide produced by Jiangxi Dongyuan Technology Co., Ltd., brand EBH; antioxidant uses antioxidant TMQ produced by Sainto Chemical Technology Co., Ltd.

[0040] The preparation method of the TPV-based semiconductive shielding material for power cables in the above embodiments 1-4 is as follows:

[0041] First step, raw material pre-mixing: using a high-speed mixer to mix polypropylene PPB EPS30R, ethylene propylene rubber EPDM J-2070, butyl nitrile rubber NBR 3305, antioxidant TMQ and catalyst B1 in proportion to obtain resin pre-mixing material;

[0042] Mix vinyl A-171 and initiator DCP in proportion in a container to obtain silane liquid pre-mixing material;

[0043] Add conductive agent acetylene carbon black Li-G30 and lubricating dispersing agent ethylene bis 12-hydroxy stearamide EBH into a sonic resonance mixer, and the conductive agent and the lubricating dispersing agent are microscopically diffused and mixed under the action of 60Hz sound wave to obtain conductive agent powder pre-mixing material for standby.

[0044] Second step, using a double screw extruder with a length-diameter ratio of 48:1 as the production equipment, feeding the resin premix into the double screw extruder through the loss weight metering scale, injecting the silane liquid premix into the double screw extruder through the loss weight diaphragm pump, and feeding the conductive agent powder premix into the double screw extruder through the side feeding; the temperature of the double screw extruder is set to 160-230°C (in this application, it is set to 180°C, which has no effect on the performance of the product in this temperature range), so that all raw materials complete the four simultaneous modifications of "melt grafting + dynamic vulcanization + controllable degradation + blending dispersion" in the extruder under the action of the heat shearing of the double screw extruder; the extruded melt is prepared into granular TPV-based semi-conductive shielding material products through air cooling and granulation.

[0045] Comparative Example 1: In the formula, the proportion of PPB EPS30R is 36%, the proportion of A-171 silane is reduced to 0.4%, and the other raw materials and proportions are the same as in Example 1, and the preparation method is unchanged.

[0046] Comparative Example 2: In the formula, the proportion of PPB EPS30R is 35.5%, and DCP is not contained, and the other raw materials and proportions are the same as in Example 1, and the preparation method is unchanged.

[0047] Comparative Example 3: In the formula, the proportion of PPB EPS30R is increased to 60%, and the proportion of EPDM J-2070 is reduced to 5%, and the other raw materials and proportions are the same as in Example 1, and the preparation method is unchanged.

[0048] Comparative Example 4: In the formula, the proportion of PPB EPS30R is reduced to 10%, and the proportion of EPDM J-2070 is increased to 55%, and the other raw materials and proportions are the same as in Example 1, and the preparation method is unchanged.

[0049] Comparative Example 5: In the formula, the proportion of EPDM J-2070 is reduced to 10%, and the proportion of NBR 3305 is increased to 16%, and the other raw materials and proportions are the same as in Example 2, and the preparation method is unchanged.

[0050] Comparative Example 6: In the formula, the proportion of EPDM J-2070 is increased to 26%, and NBR 3305 is not contained, and the other raw materials and proportions are the same as in Example 2, and the preparation method is unchanged.

[0051] Comparative Example 7: In the formula, the proportion of PPB EPS30R is increased to 57%, and the proportion of Li-G30 is reduced to 10%, and the other raw materials and proportions are the same as in Example 2, and the preparation method is unchanged.

[0052] Comparative Example 8: In the formula, the proportion of PPB EPS30R is reduced to 25%, and the proportion of Li-G30 is increased to 42%, and the other raw materials and proportions are the same as in Example 2, and the preparation method is unchanged.

[0053] Comparative Example 9, the proportion of PPB EPS30R in the formula is increased to 40%, does not contain EBH, other raw materials and the same ratio as Example 3, the preparation method is unchanged;

[0054] Comparative Example 10, the proportion of PPB EPS30R in the formula is increased to 41%, does not contain A-171 silane, does not contain EBH, other raw materials and the same ratio as Example 3, the preparation method is unchanged;

[0055] Comparative Example 11, the formula is the same as Example 1, the preparation method variable is to use a double screw extruder with a length-diameter ratio of 36:1, and other process conditions remain unchanged;

[0056] Comparative Example 12, the formula is the same as Example 1, the preparation method variable is to set the temperature of the double screw extruder to fluctuate between 120-140℃, and other process conditions remain unchanged;

[0057] The TPV-based semiconductive shielding material for power cables prepared in Examples 1-4 and Comparative Examples 1-12 is subjected to performance testing according to the following test items and test methods.

[0058] Performance testing:

[0059] Specific test items and test methods are as follows:

[0060] Mechanical properties (tensile strength, elongation at break) test method: test according to the method described in GB / T 1040.3-2006, tensile speed is 50mm / min;

[0061] Thermal extension test method (evaluate heat resistance): use type II dumbbell-shaped samples, draw upper and lower marks at 2cm intervals in the middle section, place under a load of 0.2MPa in a 150℃ oven for 15min, read the length L after extension of the upper and lower marks, and the thermal extension calculation method is: thermal extension = L-2 / 2x100%;

[0062] Air heat aging performance (evaluate heat resistance and phase separation problem) test method: test according to the method described in GB / T 2951.12, heat aging conditions are 135℃x168h;

[0063] Low temperature impact embrittlement performance (evaluate low temperature performance) test method: test according to the method described in GB / T 5470-2008, low temperature impact catalyst temperature is -40℃;

[0064] 20℃ volume resistivity, 90℃ volume resistivity test method: test according to the method described in GB / T 3048.3;

[0065] The melt flow rate MFI (230℃, 2.16kg) is tested according to the method described in GB / T 3682.1-2018.

[0066] The test method for the smoothness of the extruded sheet (the number of protrusions, the size of protrusions) is as follows: 500g of the TPV-based semiconductive shielding material prepared in the application is extruded into a continuous 0.5mm-thick strip-shaped sheet through a 2mm×50mm die at a temperature setting of 150℃, 180℃, 190℃, 200℃ and a screw rotation speed of 80rpm using a φ20 single-screw extruder provided by Harbin Hap Electrical Technology Co., Ltd. Five random points of the extruded strip-shaped sheet are observed under a scanning electron microscope, and the number of protrusions and the size of protrusions at each point are recorded. The average number of protrusions and the average size of protrusions of the TPV-based semiconductive shielding material prepared in the examples and the comparative examples are obtained by summation and averaging.

[0067] The test method for the peel strength is as follows: the method described in Appendix B of JB / T 10738-2007 is used for testing, in which the cable insulation is a thermoplastic polypropylene insulation material.

[0068] Performance determination: the performance compliance is evaluated according to the material indicators of PYJBJ type in JB / T 10738-2007.

[0069] The products of Examples 1-4 and Comparative Examples 1-12 are subjected to the above-mentioned performance tests, and the results are shown in Tables 3 and 4.

[0070] Table 3 Performance test results of each example and comparative example (I)

[0071]

[0072] Table 4 Performance test results of examples and comparative examples (II)

[0073]

[0074]

[0075] As can be seen from the performance test data of each example in Tables 3 and 4, the TPV-based semiconductive shielding materials for power cables prepared in Examples 1, 2, 3 and 4 all have good mechanical properties, high-temperature resistance, low-temperature resistance, low resistivity, easy processing, smooth surface of the shielding layer after extrusion, and moderate peel strength between the shielding layer and the insulation layer.

[0076] Compared with Example 1, the heat extension of Comparative Example 1 and Comparative Example 2 is obviously large, the tensile strength / elongation at break is small, and the change rate of mechanical properties after heat aging is >30%, which exceeds the standard requirement. This shows that the addition of small amount of A717 silane and no addition of DCP initiator leads to the failure of dynamic crosslinking between EPDM and PP, thus the TPV material with effective interpenetrating network structure cannot be formed, the mechanical properties are poor, the heat resistance is reduced, and the mechanical properties after heat aging are seriously deteriorated. The formulation of Comparative Example 2 does not contain DCP initiator, and thus the controllable rheological degradation of PP cannot be achieved, so the melt flow rate is much smaller than that of Example 1, and the processability is poor.

[0077] Compared with Example 1, the brittle failure number of -40℃ low temperature impact of Comparative Example 3 is 26 / 40, and the cold resistance is unqualified. This shows that when the addition amount of EPDM is too small, the toughening effect of PP is not obvious, and thus the cold resistance is poor. At the same time, the volume resistivity of Comparative Example 3 is small, which shows that when the addition amount of EPDM is too small, the conductive agent acetylene black cannot be filled into the high crystalline PP resin, and thus a uniform and continuous conductive network cannot be formed, and thus the resistivity is high.

[0078] Compared with Example 1, the tensile strength of Comparative Example 4 is obviously low and unqualified, and the melt flow rate is too small and the flowability is poor. This shows that when the addition amount of EPDM is too large, the strength of the prepared TPV material is low due to the poor strength of EPDM rubber itself. At the same time, too much EPDM forms an excessive vulcanized rubber component in the TPV material, and the thermoplasticity of the material as a whole is poor and the flowability is reduced.

[0079] Compared with Example 2, the peel strength of Comparative Example 5 is small and the peel strength of Comparative Example 6 is large, which shows that the peel strength between the TPV-based semi-conductive shielding material and the polypropylene cable insulation layer can be adjusted by adjusting the addition amount of nitrile rubber NBR. The more the addition amount of nitrile rubber, the easier the TPV-based semi-conductive shielding material is to peel. In view of the requirement of JB / T 10738-2007 standard that the peel strength between the peelable shielding material and the insulation layer is 10-45 N / cm, the reasonable addition amount of nitrile rubber should be set as 1-5% according to Example 1, Example 2, Example 3 and Example 4.

[0080] Compared with Example 2, the volume resistivity of Comparative Example 7 is obviously high because the content of conductive agent acetylene black is less than 15%, which does not meet the requirement of JB / T 10738-2007 standard. While the volume resistivity of Comparative Example 8 is small because the content of conductive agent acetylene black is more than 30%, but the mechanical properties of Example 8 are poor, the low temperature impact embrittlement performance at -40℃ is slightly poor, and the agglomeration effect caused by the high content of acetylene black leads to the large number of protrusions on the surface of the extruded sheet and the large size of the protrusions, and the surface smoothness is poor.

[0081] Compared with Example 3, the mechanical properties of Comparative Example 9 and Comparative Example 10 are poor, the low-temperature impact embrittlement at -40℃ is poor, the volume resistivity is high, the number of protrusions on the surface of the extruded sheet is high, and the size of the protrusions is large, indicating that the addition of a lubricating dispersant in the formula can cause uneven dispersion of the conductive agent acetylene black, agglomeration of acetylene black, and thus poor mechanical properties (agglomeration of acetylene black in the material forms defects), low-temperature impact embrittlement (agglomeration of acetylene black in the material forms defects, poor toughness), high volume resistivity (uneven dispersion of acetylene black cannot form a continuous conductive network), and large number and size of protrusions on the surface of the extruded sheet (agglomerated conductive carbon black forms protrusions). Compared with Comparative Example 9, the mechanical properties of Comparative Example 10 are poorer, the volume resistivity is higher, and the size of the protrusions on the surface of the extruded sheet is larger, indicating that the lack of silane in the formula of Comparative Example 10 cannot form a silane-grafted EPDM macromolecular coupling agent, and the dispersion effect of acetylene black is not as good as that of Comparative Example 9.

[0082] Compared with Example 1, the length-diameter ratio of the twin-screw extruder used in Comparative Example 11 is only 36:1, which is two less than the length-diameter ratio of 48:1 of the twin-screw extruder used in Example 1. The residence time of the raw materials in the extruder is short, and the four simultaneous modifications of "melt grafting + dynamic vulcanization + controllable degradation + blending dispersion" cannot be completely achieved, so the performance is not as good as that of Example 1.

[0083] Compared with Example 1, the temperature setting of the screw extruder used in Comparative Example 12 is 120-140℃, which is too low. The plasticization of the raw materials in the extruder is not sufficient, and the melt temperature does not reach the required temperature value for the "melt grafting + dynamic vulcanization + controllable degradation" reaction. The "melt grafting + dynamic vulcanization + controllable degradation" cannot be completely achieved, so the performance is not as good as that of Example 1.

[0084] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A TPV-based semi-conductive shielding material for power cables, characterized in that: It includes the following raw material components in percentage by mass: Polypropylene resin 35~45%; EPDM rubber 20~30%; Nitrile rubber 1~5%; Vinylsilane 1~2%; Initiator 0.5~1%; Catalyst 2~5%; Conductive agent 15~30%; Lubricating dispersant 0.5~1%; Antiaging agent 0.5~1%.

2. The TPV-based semiconductive shielding material for power cable according to claim 1, characterized in that: The polypropylene resin is a mixture of one or more selected from homopolymer polypropylene (PPH) and block copolymer polypropylene (PPB). The polypropylene resin has a melt index (MFI) of 1-3 g / 10 min and a melting point (Tm) of ≥150° C.

3. The TPV-based semiconductive shielding material for power cable according to claim 1, characterized in that: The ethylene mass content of the EPDM rubber is 45-75%, the ethylidene norbornene (ENB) mass content is 2-5%, and the Mooney viscosity ML1+4 at 125° C. is 40-100.

4. The TPV-based semiconductive shielding material for power cable according to claim 1, characterized in that: The Mooney viscosity ML1+4 of the nitrile rubber at 100° C. is 30-100.

5. The TPV-based semiconductive shielding material for power cable according to claim 1, characterized in that: The vinyl silane is a mixture of one or more selected from A-151 silane, A-171 silane and A-172 silane.

6. The TPV-based semiconductive shielding material for power cable according to claim 1, characterized in that: The initiator is a mixture of one or more selected from dicumyl peroxide, benzoyl peroxide and di-tert-butyl peroxyisopropylbenzene.

7. The TPV-based semiconductive shielding material for power cable according to claim 1, characterized in that: The catalyst is a dibutyltin dilaurate masterbatch with LLDPE as a carrier, and the mass concentration of dibutyltin dilaurate in the masterbatch is 0.5-2wt%.

8. The TPV-based semiconductive shielding material for power cable according to claim 1, characterized in that: The conductive agent is conductive carbon black, which is high-structure acetylene carbon black and has a DBP absorption value of ≥150 ml / 100 g.

9. The TPV-based semiconductive shielding material for power cable according to claim 1, characterized in that: The lubricating dispersant is a mixture of one or more selected from 12-hydroxy magnesium stearate, ethylene bis 12-hydroxy stearamide and a hyperbranched polymer lubricant, and the antioxidant is the antioxidant TMQ.

10. The method for preparing the TPV-based semiconductive shielding material for power cables according to any one of claims 1 to 9, characterized in that: The following steps are involved: The polypropylene resin, EPDM rubber, nitrile rubber, antioxidant and catalyst are mixed in proportion to prepare a resin premix; Adding the formulated amount of the vinyl silane and the initiator into a container and stirring and mixing to prepare a silane liquid premix; Adding the conductive agent and lubricating dispersant in the formula amount into an acoustic resonance mixer and mixing them to prepare a conductive agent powder premix; The temperature of the twin-screw extruder is set to 160-230° C., and then the resin premix, the silane liquid premix and the conductive agent powder premix are fed into the twin-screw extruder respectively. The extruded melt is granulated by air cooling to prepare a granular TPV-based semi-conductive shielding material.

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