Polypropylene-based high-voltage cable semiconductive shielding material, preparation method and cable

Abstract

The application relates to the technical field of cable materials, and discloses a polypropylene-based high-voltage cable semi-conductive shielding material, a preparation method thereof and a cable. The polypropylene-based high-voltage cable semi-conductive shielding material comprises the following components in parts by weight: 49-56 parts of impact copolymerized polypropylene, 21-24 parts of propylene-ethylene copolymerized elastomer, 20-30 parts of conductive carbon black, 0.5-5 parts of cobalt ferrite nanoparticles, 0.1-0.35 parts of an antioxidant, 1-2 parts of a dispersing agent and 1-2 parts of a lubricant. Compared with the prior art, the semi-conductive shielding material has good mechanical properties, excellent electrical properties and excellent space charge injection inhibition capacity by determining the ratio of the impact copolymerized polypropylene and the propylene-ethylene copolymerized elastomer and the content of the cobalt ferrite nanoparticles.

Description

TECHNICAL FIELD

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

[0002] As the core facility of modern power transmission systems, high-voltage cables play an important role in urban power grid construction, power transmission projects across water areas and submarine cable systems due to their technical advantages of long-distance, high-load and low-energy power transmission. In the composite structure of the cable, the shielding layer made of a semiconductor material has a dual core function: on the one hand, it can effectively fill the structural defects between the conductor and the insulating layer, and on the other hand, it can promote more uniform electric field distribution through interface electric field regulation. This special functional layer has irreplaceable protective value for maintaining the long-term stable operation and safety performance of the cable equipment under complex working conditions.

[0003] At present, the problem of space charge greatly restricts the development of direct current cable transmission technology and is a key factor limiting the improvement of direct current transmission voltage level. The accumulation of space charge will first cause electric field distortion, resulting in excessive local electric field strength of the insulation and causing partial discharge. This will accelerate the aging of the dielectric and reduce the performance of the cable insulation material, and on the other hand, it may induce the formation of discharge channels and even cause insulation breakdown. As an environmentally friendly material, polypropylene resin (PP) has a limited application range due to its high hardness and brittleness. In order to solve this problem, low modulus elastomers are usually added to polypropylene to reduce the hardness. However, with the blending of elastomers, structural changes occur in PP, which leads to changes in carrier trap distribution and thus affects the behavior of space charge. It is generally believed that the contact interface between the semiconductive shielding layer and the main insulation layer is the main channel for charge injection. Therefore, the interface quality of the shielding layer plays an important role in regulating the charge injection process, and how to improve the interface quality of the shielding layer has become an important problem to be solved to improve the space charge injection inhibition capability. SUMMARY

[0004] In view of this, the present application provides a polypropylene-based semiconductive shielding material for high-voltage cables, a preparation method thereof and a cable. The semiconductive shielding material provided by the present application has good mechanical properties, excellent electrical properties and excellent space charge injection inhibition capability by determining the ratio of impact copolymerized polypropylene and propylene-ethylene copolymer elastomer and the content of cobalt ferrite nanoparticles.

[0005] The technical solution of the present application is as follows:

[0006] In a first aspect, the present application provides a polypropylene-based semiconductive shielding material for high-voltage cables, comprising the following components by weight:

[0007] 49-56 parts of impact copolymerized polypropylene, 21-24 parts of propylene-ethylene copolymer elastomer, 20-30 parts of conductive carbon black, 0.5-5 parts of cobalt ferrite nanoparticles, 0.1-0.35 parts of antioxidant, 1-2 parts of dispersant, 1-2 parts of lubricant;

[0008] The cobalt ferrite nanoparticles are obtained by co-precipitation method by adding a precipitant to the hydrate of ferric salt and the hydrate of cobalt salt.

[0009] Further, the preparation method of the cobalt ferrite nanoparticles comprises the following steps:

[0010] Mix 5-11 parts of the hydrate of ferric salt and 2-3 parts of the hydrate of cobalt salt by weight fraction, and dissolve them in 100 parts of deionized water, and heat to 50-65℃ under stirring at 130-180 rpm to obtain a mixture; add 40-60 parts of precipitant to the mixture and react and cool, and wash with distilled water and anhydrous ethanol for 2-5 times respectively, and dry to obtain the cobalt ferrite nanoparticles;

[0011] The precipitant is sodium hydroxide solution with a concentration of 5-8M.

[0012] Further, the hydrate of ferric salt includes at least one of ferric sulfate nine hydrate, ferric chloride six hydrate, ferric nitrate nine hydrate; the hydrate of cobalt salt includes at least one of cobalt chloride six hydrate, cobalt nitrate six hydrate, cobalt sulfate seven hydrate, cobalt acetate four hydrate.

[0013] Further, the impact copolymerized polypropylene includes propylene homopolymer and ethylene-propylene copolymer rubber phase; the physical and chemical property parameters of the impact copolymerized polypropylene include at least one of density 0.85-0.95 g / cm 3 , crystallinity 25-35%, melting point 145-165℃, melt index under 230℃×2.16kg load is 2.0-3.0 g / 10min.

[0014] Further, the mass percentage of ethylene in the propylene-ethylene copolymer elastomer is 5-15%; the physical and chemical property parameters of the propylene-ethylene copolymer elastomer include at least one of crystallinity 3-10%, melting point 40-50℃, melt index under 190℃×2.16kg load is 0.8-1.8 g / 10min.

[0015] Further, the carbon black oil absorption value of the conductive carbon black is 140-160 mL / 100g.

[0016] Further, the antioxidant includes at least one of hindered phenolic antioxidant, phosphite antioxidant and thio-phenolic antioxidant; the dispersant includes at least one of oleic acid amide and ethylene bis-stearamide; and the lubricant includes at least one of zinc stearate and pentaerythritol.

[0017] In a second aspect, based on the same inventive concept, the present application provides a preparation method of the polypropylene-based semi-conductive shielding material of any one of the first aspect, comprising the following steps:

[0018] The conductive carbon black, the antioxidant, the dispersant and the lubricant are mixed to obtain a conductive carbon black masterbatch; the impact copolymerized polypropylene and the propylene-ethylene tool elastomer are melt blended with the conductive carbon black masterbatch to obtain a polypropylene-based semi-conductive shielding material masterbatch; and the polypropylene-based semi-conductive shielding material masterbatch is melt blended with the cobalt ferrite nanoparticles to obtain the polypropylene-based semi-conductive shielding material.

[0019] Further, the melt blending manner includes at least one of internal mixing and extrusion.

[0020] In a third aspect, based on the same inventive concept, the present application provides a cable comprising the polypropylene-based semi-conductive shielding material of any one of the first aspect or prepared by the preparation method of any one of the second aspect.

[0021] Compared with the prior art, the embodiments of the present application have at least the following advantages or beneficial effects:

[0022] The polypropylene-based semi-conductive shielding material provided by the present application determines the compatibility ratio of the impact copolymerized polypropylene and the propylene-ethylene copolymer elastomer, and introduces cobalt ferrite nanoparticles as a functional additive, which synergistically optimizes the key properties of the matrix material mechanical properties and the shielding layer electrically conductive stability and space charge inhibition. Compared with the prior art, the mechanical, electrical and space charge protection properties of the semi-conductive shielding material are synergistically improved, meeting the actual use requirements of high-voltage direct current cables. Specifically:

[0023] 1. Compared with the existing shielding material that simply uses homopolymer polypropylene as the matrix, the present application selects impact copolymerized polypropylene as the supporting matrix of the composite material. The matrix is composed of propylene homopolymer and ethylene-propylene copolymer rubber phase. The propylene homopolymer provides crystallinity to ensure high mechanical strength, and the ethylene-propylene copolymer rubber phase imparts flexibility to the material, which makes the impact copolymerized polypropylene itself have excellent mechanical properties and flexibility.

[0024] 2. At the same time, the propylene-ethylene copolymer elastomer has high interface compatibility due to containing similar ethylene-propylene random segments and high rigidity propylene segment structure, which can further improve the low-temperature impact strength and toughness of the matrix, fundamentally solving the technical bottleneck of high hardness, brittleness and low-temperature cracking of traditional polypropylene-based shielding materials, and ensuring the mechanical requirements of cable laying and long-term service.

[0025] 3. Compared with the existing technical solution relying on the internal trap of the insulating layer to regulate space charge, the application introduces cobalt ferrite nanoparticles as a functional additive. The particles have high dielectric constant and variable valence transition metal ions. On the one hand, under the action of an external direct current electric field, they can produce significant interface polarization effect, forming an induced electric field opposite to the direction of the external electric field, effectively weakening the driving force of carrier injection from the conductor to the insulating layer, thereby inhibiting the accumulation of space charge in the adjacent insulating medium. On the other hand, the surface metal cations can provide a Coulomb potential well, which has a strong electrostatic attraction to the migrating electrons, hindering their crossing of the shielding layer / insulating layer interface and further reducing charge injection. Under the dual action, efficient control of space charge accumulation is achieved, avoiding the drawbacks of charge regulation lag and easy electric field distortion in traditional solutions.

[0026] 4. The cobalt ferrite nanoparticles introduced in the application help to improve the dispersion state of the conductive filler in the polypropylene matrix. The nanoscale CoFe2O4 can fill the gaps between carbon black particles, making the shielding layer more dense and reducing partial discharge caused by microvoids, resulting in a more uniform and dense internal structure of the shielding layer. This not only helps to maintain a stable conductive network, but also improves the uniformity of the interface electric field distribution, thereby achieving excellent space charge suppression effect without significantly increasing the amount of conductive filler. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0028] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the application can be purchased from the market or prepared by existing methods.

[0029] In view of the technical problems existing in the prior art, according to one aspect of the embodiments of the present disclosure, a polypropylene-based high-voltage cable semi-conductive shielding material is provided, which comprises the following components by weight:

[0030] 49-56 parts of impact copolymerized polypropylene, 21-24 parts of propylene-ethylene copolymer elastomer, 20-30 parts of conductive carbon black, 0.5-5 parts of cobalt ferrite nanoparticles, 0.1-0.35 parts of antioxidant, 1-2 parts of dispersant, 1-2 parts of lubricant;

[0031] The cobalt ferrite nanoparticles are obtained by co-precipitation of a hydrate of a ferric salt and a hydrate of a cobalt salt by adding a precipitant.

[0032] Specifically, the preparation method of the cobalt ferrite nanoparticles comprises: mixing 5-11 parts of a hydrate of a ferric salt and 2-3 parts of a hydrate of a cobalt salt by weight, dissolving them in 100 parts of deionized water, heating to 50-65℃ under stirring at 130-180 rpm, to obtain a mixture; adding 40-60 parts of a precipitant to the mixture and reacting and cooling, washing with distilled water and anhydrous ethanol for 2-5 times, and drying to obtain the cobalt ferrite nanoparticles.

[0033] In some examples, the hydrate of the ferric salt includes at least one of ferric sulfate nonahydrate, ferric chloride hexahydrate, and ferric nitrate nonahydrate; and the hydrate of the cobalt salt includes at least one of cobalt chloride hexahydrate, cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, and cobalt acetate tetrahydrate.

[0034] It should be noted that the precipitant used in the embodiments of the present application is sodium hydroxide solution, and the concentration is 5-8M.

[0035] In some examples, the weight fraction of the impact copolymerized polypropylene can be selected from any value between 49-56 parts; and the weight fraction of the ethylene-propylene copolymer elastomer can be selected from any value between 21-24 parts.

[0036] For example, the weight fraction of the conductive carbon black includes but is not limited to 20 parts, 22 parts, 25 parts, 27 parts, or 30 parts; and the weight fraction of the cobalt ferrite nanoparticles includes but is not limited to 0.5 parts, 1 part, 3 parts, 5 parts.

[0037] In some examples, the impact copolymerized polypropylene includes a propylene homopolymer and an ethylene-propylene copolymer rubber phase, the density of the impact copolymerized polypropylene is 0.85-0.95 g / cm 3 , the crystallinity is 25-35%, the melting point is 145-165℃, and the melt index under a load of 230℃×2.16kg is 2.0-3.0 g / 10min.

[0038] In some examples, the mass percentage of ethylene in the propylene-ethylene copolymer elastomer is 5-15%, the crystallinity of the propylene-ethylene copolymer elastomer is 3-10%, the melting point is 40-50℃, and the melt index under a load of 190℃×2.16kg is 0.8-1.8 g / 10min.

[0039] In some examples, the carbon black oil absorption number of the conductive carbon black is 140-160 mL / 100g.

[0040] In some examples, the antioxidant includes at least one of a hindered phenolic antioxidant, a phosphite antioxidant, and a thio-phenolic antioxidant; the dispersant includes at least one of an oleic acid amide and an ethylene bis-stearamide; and the lubricant includes at least one of a zinc stearate and a pentaerythritol.

[0041] According to another aspect of the embodiments of the present application, a preparation method of a polypropylene-based high-voltage cable semi-conductive shielding material is also provided, which specifically includes: mixing conductive carbon black, an antioxidant, a dispersant, and a lubricant to obtain a conductive carbon black masterbatch; melt blending an impact copolymerized polypropylene, a propylene-ethylene tool elastomer, and the conductive carbon black masterbatch to obtain a polypropylene-based semi-conductive shielding material masterbatch; and melt blending the polypropylene-based semi-conductive shielding material masterbatch and cobalt ferrite nanoparticles to obtain the polypropylene-based high-voltage cable semi-conductive shielding material.

[0042] In some examples, the temperature for melt blending is 180-220°C, for example, the temperature for melt blending includes but is not limited to 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, or 220°C.

[0043] In some examples, the time for melt blending is 10-15 min.

[0044] In some examples, the rotational speed for melt blending is 80-150 r / min, for example, the rotational speed for melt blending includes but is not limited to 80 r / min, 85 r / min, 90 r / min, 95 r / min, 100 r / min, 105 r / min, 110 r / min, 115 r / min, 120 r / min, 130 r / min, 140 r / min, 145 r / min, or 150 r / min.

[0045] In some examples, the way for melt blending includes at least one of internal mixing and extrusion.

[0046] According to still another aspect of the embodiments of the present application, a cable is also provided, which includes the polypropylene-based high-voltage cable semi-conductive shielding material of any one of the first aspect or is prepared by the preparation method of any one of the second aspect.

[0047] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. The experimental methods in the following examples, if no specific conditions are noted, are generally determined according to national standards. If there is no corresponding national standard, the methods are determined according to the general international standards, conventional conditions, or the conditions suggested by the manufacturers.

[0048] Example 1

[0049] This example 1 provides a polypropylene-based high-voltage cable semiconductive shielding material, which comprises the following components by weight:

[0050] 50 parts of impact copolymerized polypropylene, 22 parts of propylene-ethylene copolymerized elastomer, 25 parts of conductive carbon black, 0.5 parts of cobalt ferrite nanoparticles, 1 part of dispersant, 1 part of lubricant, and 0.5 parts of antioxidant.

[0051] The impact copolymerized polypropylene has a density of 0.9 g / cm 3 , a crystallinity of 30%, a melting point of 162°C, a melt index of 2.5 g / 10 min under a load of 230°C x 2.16 kg, and the impact copolymerized polypropylene comprises homopolymerized polypropylene and ethylene-propylene copolymerized rubber phase.

[0052] The propylene-ethylene copolymerized elastomer has a crystallinity of 5%, a melting point of 45°C, a melt index of 1.2 g / 10 min under a load of 190°C x 2.16 kg, and the mass percentage of ethylene in the propylene-ethylene copolymerized elastomer is 11%.

[0053] The conductive carbon black has an oil absorption value of 148 ml / 100 g.

[0054] The dispersant is vinyl bis-stearamide, the lubricant is zinc stearate, and the antioxidant is 4,4'-thio-bis(6-tert-butyl-3-methylphenol).

[0055] The preparation method of the cobalt ferrite nanoparticles is as follows: 5.406 g of a trivalent iron salt hydrate and 2.375 g of a divalent cobalt salt hydrate are mixed and dissolved in 100 mL of deionized water, heated to 60°C with stirring at 150 rpm, to obtain a mixture; 50 mL of 6M sodium hydroxide solution is added to the mixture and reacted and cooled, washed with distilled water and anhydrous ethanol for 3 times respectively, and dried to obtain cobalt ferrite nanoparticles.

[0056] Among them, the trivalent iron salt hydrate is FeCl3·6H2O, and the divalent cobalt salt hydrate is CoCl2·6H2O.

[0057] The preparation method of the polypropylene-based high-voltage cable semi-conductive shielding material is: placing the impact copolymerized polypropylene, propylene-ethylene copolymer elastomer and conductive carbon black in a banbury mixer for melt blending to obtain a polypropylene-based semi-conductive shielding masterbatch, and then melt blending the polypropylene-based semi-conductive shielding masterbatch and cobalt ferrite nanoparticles in the banbury mixer to obtain the polypropylene-based high-voltage cable semi-conductive shielding material.

[0058] The melt blending process is: temperature 180℃, time 15 minutes, and rotation speed 100r / min.

[0059] Example 2

[0060] This example 2 provides a polypropylene-based high-voltage cable semi-conductive shielding material, which is only different from example 1 in that:

[0061] The impact copolymerized polypropylene is 49 parts, and the cobalt ferrite nanoparticles are 1 part.

[0062] Example 3

[0063] This example 3 provides a polypropylene-based high-voltage cable semi-conductive shielding material, which is only different from example 1 in that:

[0064] The impact copolymerized polypropylene is 49 parts, the propylene-ethylene copolymer elastomer is 21 parts, and the cobalt ferrite nanoparticles are 2 parts.

[0065] Example 4

[0066] This example 4 provides a polypropylene-based high-voltage cable semi-conductive shielding material, which is only different from example 1 in that:

[0067] The impact copolymerized polypropylene is 48 parts, the propylene-ethylene copolymer elastomer is 21 parts, and the cobalt ferrite nanoparticles are 3 parts.

[0068] Example 5

[0069] This example 5 provides a polypropylene-based high-voltage cable semi-conductive shielding material, which is only different from example 1 in that:

[0070] The impact copolymerized polypropylene is 47 parts, the propylene-ethylene copolymer elastomer is 20 parts, and the cobalt ferrite nanoparticles are 5 parts.

[0071] Example 6

[0072] This example 6 provides a polypropylene-based high-voltage cable semi-conductive shielding material, which is only different from example 1 in that:

[0073] The hydrate of the ferric salt is Fe(NO3)3·9H2O, and the addition amount is 8.08g; the hydrate of the cobalt salt is Co(NO3)2·6H2O, and the addition amount is 2.91g.

[0074] Example 7

[0075] This Example 7 provides a polypropylene-based high-voltage cable semiconductive shielding material, which is distinguished from Example 1 only in that:

[0076] The hydrate of the ferric salt is Fe2(SO4)3·9H2O, and the added amount is 11.24 g. The hydrate of the cobalt salt is CoSO4·7H2O, and the added amount is 2.81 g.

[0077] Example 8

[0078] This Example 8 provides a polypropylene-based high-voltage cable semiconductive shielding material, which is distinguished from Example 1 only in that:

[0079] The dispersant is oleic acid amide, and the lubricant is pentaerythritol.

[0080] Comparative Example 1

[0081] This comparative example provides a polypropylene-based high-voltage cable semiconductive shielding material, which is distinguished from Example 1 only in that:

[0082] The propylene-ethylene copolymer elastomer is replaced by 21 parts of ethylene-octene copolymer elastomer, and no cobalt ferrite nanoparticles are added, so as to verify the influence of replacing the propylene-ethylene copolymer elastomer and not adding the cobalt ferrite nanoparticles on the technical effect.

[0083] Comparative Example 2

[0084] This comparative example provides a polypropylene-based high-voltage cable semiconductive shielding material, which is distinguished from Example 1 only in that:

[0085] The propylene-ethylene copolymer elastomer is replaced by 21 parts of ethylene-octene copolymer elastomer, and no cobalt ferrite nanoparticles are added, so as to verify the influence of replacing the propylene-ethylene copolymer elastomer and not adding the cobalt ferrite nanoparticles on the technical effect.

[0086] Comparative Example 3

[0087] This comparative example provides a polypropylene-based high-voltage cable semiconductive shielding material, which is distinguished from Example 1 only in that:

[0088] The propylene-ethylene copolymer elastomer is replaced by 21 parts of styrene-butadiene-styrene block copolymer, and no cobalt ferrite nanoparticles are added, so as to verify the influence of replacing the propylene-ethylene copolymer elastomer and not adding the cobalt ferrite nanoparticles on the technical effect.

[0089] The weight fractions of the raw materials in the above examples and comparative examples are shown in Tables 1 and 2:

[0090] Table 1 Weight fraction data of raw materials in each example

[0091] Components (parts by weight) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Impact copolymer polypropylene 50 49 49 48 47 48 48 50 Propylene-ethylene copolymer elastomer 22 22 21 21 20 21 21 22 Conductive carbon black 25 25 25 25 25 25 25 25 Cobalt ferrite nanoparticles 0.5 1 2 3 5 3 3 0.5 Dispersant 2 2 2 2 2 2 2 2 Lubricant 1 1 1 1 1 1 1 1 Antioxidant 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

[0092] Table 2 Data of weight parts of raw materials of comparative examples

[0093] Components (parts by weight) Comparative Example 1 Comparative Example 2 Comparative Example 3 Impact copolymer polypropylene 50 50 50 Propylene-ethylene copolymer elastomer 21 0 0 Ethylene-octene copolymer elastomer 0 21 0 Styrene-butadiene-styrene block copolymer 0 0 21 Conductive carbon black 25 25 25 Cobalt ferrite nanoparticles 0 0 0 Dispersant 2 2 2 Lubricant 1 1 1 Antioxidant 0.5 0.5 0.5

[0094] In order to better understand the application, the polypropylene-based high-voltage cable semiconductive shielding material obtained in the above examples and comparative examples was cut into test samples for volume resistivity, mechanical properties and electric voice pulse method after hot pressing at 180°C. The volume resistivity at 23°C and 90°C was tested based on GB / T3048.2, the elongation at break was tested based on GB / T1040.2, and the space charge characteristics were tested based on GB / T 31489.1-2015. The test results are shown in Table 3:

[0095] Table 3 Test data of product performance of examples and comparative examples

[0096] Group Volume resistivity at 23°C (Ω-cm) Volume resistivity at 90°C (Ω-cm) Elongation at break (%) Average charge density (C / m 3 ) Maximum field distortion rate (%) Example 1 12.2 50.3 492.3 2.5 14.4 Example 2 9.6 21.9 510.2 2.4 9.6 Example 3 6.7 13.5 505.2 2.4 8.7 Example 4 16.7 55.6 508.7 2.2 6.1 Example 5 20.9 59.8 500.8 2.6 17.7 Example 6 8.4 15.6 509.1 2.3 10.6 Example 7 9.2 18.3 497.7 2.2 7.7 Example 8 16.4 65.8 488.6 2.5 15.1 Comparative Example 1 37.9 154.4 485.6 2.8 20.5 Comparative Example 2 35.7 115.8 193.4 3.3 19.8 Comparative Example 3 52.8 200.6 394.4 3.5 25.3

[0097] According to the experimental data in Tables 1 and 2, we can determine the relevance of material component adjustment and performance change. From Example 1 to Example 5, by gradually increasing the content of cobalt ferrite nanoparticles (from 0.5 parts to 5 parts) and keeping the content of carbon black unchanged, the volume resistivity at 23°C showed a downward trend first and then an upward trend with the increase of the addition amount, reaching a minimum value of 6.7Ω·cm at Example 3 (2 parts), which was about 82.3% lower than 37.9Ω·cm of Comparative Example 1; the volume resistivity at 90°C decreased more significantly, which was only 13.5Ω·cm at Example 3, which was 84.7% lower than 154.4Ω·cm of Comparative Example 1, showing excellent high-temperature conductivity stability.

[0098] However, when the addition amount exceeds 3 parts (Example 5), the volume resistivities at 23°C and 90°C rebound to 20.9Ω·cm and 59.8Ω·cm, respectively, which are still significantly lower than those of Comparative Example 1, indicating that excessive addition leads to a rebound in resistivity, but does not completely offset its improvement.

[0099] The elongation at break of all examples is maintained between 485.6% and 510.2%, which is comparable to 500.8% of Comparative Example 1, indicating that the addition of 0.5 parts to 5 parts of cobalt ferrite nanoparticles has little negative impact on the toughness of the material, and the shielding material still has excellent flexibility, which can meet the long-term bending and installation requirements of high-voltage cables.

[0100] After adding cobalt ferrite nanoparticles, the space charge suppression effect of the material is obviously improved. With the content increasing from 0 parts (Comparative Example 1) to 3 parts (Example 4), the maximum field distortion rate continuously decreases from 20.5% to 6.1%, and the average charge density continuously decreases from 2.8 C / m 3Stepwise decrease to 2.2 C / m 3 , indicating a significant reduction in space charge accumulation. When the cobalt ferrite nanoparticle content continues to increase to 5 parts (Example 5), the suppression effect is weakened, and the maximum field distortion rate rises to 17.7%, and the average charge density rises to 2.6 C / m 3 .

[0101] Overall, the space charge suppression capability shows a trend of first increasing and then decreasing with the increase of the cobalt ferrite additive amount, and reaches the optimum at 3 parts. This trend is due to the dual action mechanism of cobalt ferrite nanoparticles: on the one hand, its high dielectric constant (ε ≈ 13~15) produces strong polarization under an applied electric field, forming an induced electric field (Ein) in the opposite direction, effectively weakening the charge injection driving force of the conductor / shielding layer to the insulating layer; on the other hand, the unoccupied d orbitals of Co 2+ and Fe 3+ can provide a Coulomb potential well to capture migrating electrons and hinder them from crossing the shielding layer / insulating layer interface.

[0102] The outstanding advantages of the present application are: by introducing functional cobalt ferrite nanoparticles into the polypropylene-based semiconductive shielding layer, the space charge injection path is blocked from the source, rather than relying on the internal trap regulation of the insulating layer. Cobalt ferrite has good compatibility with the polypropylene matrix and is uniformly dispersed, which can build an active protective layer in the shielding layer with polarization shielding and carrier capture capability. This design ingeniously utilizes the electronic structure and dielectric properties of transition metal ferrite, significantly improving the insulation reliability of the HVDC cable system without significantly changing the traditional shielding material formula system, providing key material support for the development of high-voltage grade polypropylene insulation DC cables.

[0103] Various embodiments of the present application can exist in a range of forms; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the described range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) within the indicated range.

[0104] The foregoing is considered as illustrative only of the principles of the application. Numerous modifications and changes will readily occur to those skilled in the art, and it is intended to embrace all such modifications and changes that fall within the scope of the application. Accordingly, the application is not to be restricted in scope to the specific embodiments disclosed herein but is to be accorded the full scope that the principles and novel features request appropriately granted.

Claims

1. A polypropylene-based semiconductive shielding material for high-voltage cables, characterized in that, The components include the following parts by weight: 49-56 parts impact-resistant copolymer polypropylene, 21-24 parts propylene-ethylene copolymer elastomer, 20-30 parts conductive carbon black, 0.5-5 parts cobalt ferrite nanoparticles, 0.1-0.35 parts antioxidant, 1-2 parts dispersant, and 1-2 parts lubricant; The cobalt ferrite nanoparticles are synthesized by co-precipitation of hydrates of trivalent iron salts and hydrates of divalent cobalt salts with the addition of a precipitant.

2. The material according to claim 1, characterized in that, The preparation method of the cobalt ferrite nanoparticles includes the following steps: Mix 5-11 parts by weight of ferric salt hydrate and 2-3 parts by weight of divalent cobalt salt hydrate and dissolve in 100 parts by weight of deionized water. Heat to 50-65°C with stirring at 130-180 rpm to obtain a mixture. Add 40-60 parts by weight of precipitant to the mixture and react and cool. Wash with distilled water and anhydrous ethanol 2-5 times respectively, and dry to obtain the cobalt ferrite nanoparticles. The precipitant is a sodium hydroxide solution with a concentration of 5-8M.

3. The material according to claim 2, characterized in that, The hydrates of the trivalent iron salts include at least one of ferric sulfate nonahydrate, ferric chloride hexahydrate, and ferric nitrate nonahydrate; the hydrates of the divalent cobalt salts include at least one of cobalt chloride hexahydrate, cobalt nitrate hexahydrate, cobalt sulfate heptahydrate, and cobalt acetate tetrahydrate.

4. The material according to claim 1, characterized in that, The impact-resistant copolymer polypropylene comprises a propylene homopolymer and an ethylene-propylene copolymer rubber phase; the physicochemical properties of the impact-resistant copolymer polypropylene include a density of 0.85-0.95 g / cm³. 3 It has at least one of the following characteristics: crystallinity of 25-35%, melting point of 145-165℃, and melt index of 2.0-3.0 g / 10 min at 230℃ × 2.16 kg load.

5. The material according to claim 1, characterized in that, The propylene-ethylene copolymer elastomer contains 5-15% ethylene by mass; the physicochemical properties of the propylene-ethylene copolymer elastomer include at least one of the following: crystallinity 3-10%, melting point 40-50℃, and melt index of 0.8-1.8 g / 10 min at 190℃ × 2.16 kg load.

6. The material according to claim 1, characterized in that, The conductive carbon black has an oil absorption value of 140-160 mL / 100 g.

7. The material according to claim 1, characterized in that, The antioxidant includes at least one of hindered phenolic antioxidants, phosphite antioxidants, and thiophenolic antioxidants; the dispersant includes at least one of oleamide and ethylene bis-stearamide; and the lubricant includes at least one of zinc stearate and pentaerythritol.

8. A method for preparing a polypropylene-based semiconductive shielding material for high-voltage cables according to any one of claims 1-7, characterized in that, Includes the following steps: Conductive carbon black, antioxidant, dispersant and lubricant are mixed to obtain conductive carbon black masterbatch; impact-resistant copolymer polypropylene and propylene-ethylene copolymer elastomer are melt-blended with the conductive carbon black masterbatch to obtain polypropylene-based semiconductive shielding material masterbatch; the polypropylene-based semiconductive shielding material masterbatch is melt-blended with cobalt ferrite nanoparticles to obtain polypropylene-based high-voltage cable semiconductive shielding material.

9. The method according to claim 8, characterized in that, The melt blending method includes at least one of mixing and extrusion.

10. A cable, characterized in that, The material includes the polypropylene-based high-voltage cable semi-conductive shielding material according to any one of claims 1-7, or the polypropylene-based high-voltage cable semi-conductive shielding material prepared by the method of any one of claims 8-9.