Polypropylene compositions and polypropylene insulated cable materials and their applications, high voltage DC cables

Abstract

This invention relates to the field of cable insulation materials, and discloses a polypropylene composition, a polypropylene insulated cable material, their applications, and high-voltage DC cables. The polypropylene composition comprises random copolymer polypropylene, a propylene-based elastomer, an antioxidant, and a voltage stabilizer; wherein the voltage stabilizer is an aromatic ketone compound containing at least two benzene rings. In this polypropylene composition, the random copolymer polypropylene and the propylene-based elastomer exhibit good compatibility, effectively preventing phase separation and thus giving the polypropylene insulated cable material excellent mechanical properties. Furthermore, by employing a specific type of voltage stabilizer, high-energy electrons can be captured, space charge accumulation reduced, and breakdown field strength increased, enabling the polypropylene insulated cable material made from this polypropylene composition to simultaneously possess excellent mechanical and electrical properties.

Description

Technical Field

[0001] This invention relates to the field of cable insulation materials, specifically to a polypropylene composition and polypropylene insulated cable material and their applications, and high-voltage DC cables. Background Technology

[0002] High-voltage direct current (HVDC) transmission is an important means of high-voltage, high-capacity, long-distance power transmission and regional power grid interconnection. Thermoplastic polypropylene (PP), due to its excellent electrical insulation properties, high heat resistance, high mechanical strength, good chemical corrosion resistance, and recyclability, meets the requirements of green environmental protection and low carbon emissions, making it an important direction for future power cable research.

[0003] However, polypropylene (PP) exhibits drawbacks such as high rigidity at room temperature and low toughness at low temperatures, making it unsuitable for meeting the basic mechanical performance requirements of DC cables and necessitating modification. Elastomer blending modification of PP materials is considered one of the effective methods to improve PP toughness and flexural modulus. Currently, commonly studied elastomer additives include ethylene propylene rubber (EPR), ethylene propylene diene monomer (EPDM), polyolefin elastomers (POE), and hydrogenated styrene-butadiene block copolymers (SEBS). While these elastomer blending modifications can improve the performance defects of PP materials to some extent, some insurmountable problems remain. For example, a large number of interfacial regions exist between the blended elastomer and PP, leading to varying degrees of reduction in the electrical properties of PP blend insulation, severely affecting the reliability of cable insulation. In cross-linked polyethylene cable insulation materials, the addition of graftable aromatic ketone voltage stabilizers can improve its electrical resistance; however, the matrix is ​​a cross-linked system, and the voltage stabilizer relies on a grafting reaction to achieve compatibility, making it unsuitable for direct application to thermoplastic PP / elastomer systems.

[0004] Traditional elastomer blending and the addition of voltage stabilizers present a dilemma of "performance trade-offs": elastomer toughening inevitably leads to phase interface defects, resulting in a decline in electrical properties; general voltage stabilizers are unevenly dispersed and easily migrate in PP / elastomer systems, making it difficult to balance mechanical and electrical properties.

[0005] Therefore, there is an urgent need to develop a multi-component synergistic and process-adaptable modification scheme to address the core pain points of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and provide a polypropylene composition and polypropylene insulated cable material and their applications, as well as high-voltage DC cables. The polypropylene insulated cable material made from this composition can effectively suppress space charge accumulation and electric field distortion, and has excellent breakdown resistance.

[0007] To achieve the above objectives, a first aspect of the present invention provides a polypropylene composition comprising random copolymer polypropylene, a propylene-based elastomer, an antioxidant, and a voltage stabilizer. The voltage stabilizer is an aromatic ketone compound containing at least two benzene rings.

[0008] A second aspect of the present invention provides a polypropylene insulated cable material, which is prepared from the polypropylene composition as described above.

[0009] A third aspect of the present invention provides the use of the polypropylene composition as described above or the polypropylene insulated cable material as described above in high-voltage DC cables.

[0010] A fourth aspect of the present invention provides a high-voltage DC cable, wherein the insulation layer of the high-voltage DC cable comprises the polypropylene composition as described above or the polypropylene insulating cable material as described above.

[0011] Through the above technical solution, the present invention can achieve at least the following beneficial effects: In this polypropylene composition, the random copolymer polypropylene and propylene-based elastomer have good compatibility, which can effectively prevent phase separation and thus give the polypropylene insulated cable material excellent mechanical properties. In addition, by using a specific type of voltage stabilizer, high-energy electrons can be captured, space charge accumulation can be reduced and breakdown field strength can be improved, so that the polypropylene insulated cable material made from this polypropylene composition can have both excellent mechanical and electrical properties. Detailed Implementation

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] The first aspect of the present invention provides a polypropylene composition comprising random copolymer polypropylene, propylene-based elastomer, antioxidant and voltage stabilizer; The voltage stabilizer is an aromatic ketone compound containing at least two benzene rings.

[0014] In this invention, random copolymer polypropylene refers to a thermoplastic polymer material formed by random copolymerization of propylene as the main component and ethylene as the comonomer (usually with a content of less than 10%).

[0015] In this invention, propylene-based elastomer refers to a copolymer obtained by polymerization of propylene as the main component and ethylene and / or α-olefins (such as 1-butene) as comonomers, with the comonomer content being above 10 wt%, typically 10-20 wt%.

[0016] In this invention, aromatic ketones have the conventional meaning in the art, referring to a class of compounds with... The compound has a structure in which at least one of R1 and R2 is an aryl group, and the carbonyl group is directly attached to at least one benzene ring. The inventors of this invention have discovered that using an aromatic ketone compound containing at least two benzene rings as a voltage stabilizer in the composition system of this invention can trap high-energy electrons, reduce space charge accumulation, and increase the breakdown field strength, and can effectively suppress the migration of the voltage stabilizer, so that the polypropylene insulated cable material made from this polypropylene composition can simultaneously possess excellent mechanical and electrical properties.

[0017] According to the present invention, preferably, the random copolymer polypropylene and the propylene-based elastomer are used as the basis, wherein the random copolymer polypropylene is 70-90 parts by weight and the propylene-based elastomer is 10-30 parts by weight.

[0018] In this invention, the mechanical properties of polypropylene insulated cable material can be effectively improved with a small amount of propylene-based elastomer added, resulting in better economic benefits.

[0019] More preferably, based on the total weight of the random copolymer polypropylene and the propylene-based elastomer, the random copolymer polypropylene is 75-85 parts by weight and the propylene-based elastomer is 15-25 parts by weight.

[0020] According to the present invention, preferably, the antioxidant is 0.1-1 parts by weight and the voltage stabilizer is 0.1-0.5 parts by weight, based on the total weight of 100 parts by weight of random copolymer polypropylene and propylene-based elastomer.

[0021] In this invention, the amounts of antioxidant and voltage stabilizer meet the above-mentioned ranges, which is more conducive to improving the electrical resistance of polypropylene insulated cable material while ensuring mechanical properties.

[0022] More preferably, the antioxidant is 0.1-0.5 parts by weight and the voltage stabilizer is 0.1-0.3 parts by weight, based on the total weight of 100 parts by weight of random copolymer polypropylene and propylene-based elastomer.

[0023] According to the present invention, preferably, the density of the random copolymer polypropylene is 0.89-0.91 g / cm³. 2 .

[0024] According to the present invention, preferably, the melting temperature of the random copolymer polypropylene is 140-160°C.

[0025] According to the present invention, preferably, the content of ethylene units in the random copolymer polypropylene is 0.5-4 wt%. For example, it can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.1 wt%, 3.2 wt%, 3.3 wt%, 3.4 wt%, 3.5 wt%, 3.6 wt%, 3.7 wt%, 3.8 wt%, 3.9 wt%, or 4 wt%, or it can be a range consisting of any two of the above values, or any intermediate value within that range.

[0026] According to the present invention, preferably, the random copolymer polypropylene has a melt index of 0.1-2 g / 10 min at 230°C and 2.16 kg.

[0027] According to the present invention, preferably, the weight-average molecular weight of the random copolymer polypropylene is 300,000-700,000 g / mol.

[0028] In this invention, at least one characteristic parameter of the random copolymer polypropylene satisfies the above-mentioned range, which is more conducive to balancing the mechanical and electrical properties of polypropylene insulated cable material, and makes the mechanical properties of polypropylene insulation material better while ensuring electrical performance.

[0029] More preferably, the content of ethylene units in the random copolymer polypropylene is 1-3.5 wt%.

[0030] According to the present invention, preferably, the density of the propylene-based elastomer is 0.86-0.89 g / cm³. 2 .

[0031] According to the present invention, preferably, the glass transition temperature of the propylene-based elastomer is ≤-20°C.

[0032] According to the present invention, preferably, in the propylene-based elastomer, the comonomer is ethylene and / or 1-butene.

[0033] According to the present invention, preferably, the tensile strength of the propylene-based elastomer is 10-20 MPa.

[0034] According to the present invention, preferably, the elongation at break of the propylene-based elastomer is ≥800%.

[0035] According to the present invention, preferably, the weight-average molecular weight of the propylene-based elastomer is 100,000-300,000 g / mol.

[0036] In this invention, at least one characteristic parameter of the propylene-based elastomer satisfies the above-mentioned range, which is more conducive to balancing the mechanical and electrical properties of polypropylene insulated cable material, and makes the mechanical properties of polypropylene insulation material better while ensuring electrical performance.

[0037] More preferably, the content of comonomer in the propylene-based elastomer is 10-15 wt%. For example, it can be 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, 14 wt%, 14.5 wt%, or 15 wt%, or it can be a range consisting of any two of the above values, or any intermediate value within that range.

[0038] According to the present invention, preferably, the dipole moment of the voltage stabilizer is 0.5-4 Debye.

[0039] In this invention, the dipole moment is calculated using density functional theory (DFT).

[0040] According to the present invention, preferably, the LUMO energy level of the voltage stabilizer is ≤-1eV.

[0041] In this invention, the LUMO energy level is calculated using density functional theory (DFT).

[0042] According to the present invention, preferably, the 5wt% thermogravimetric temperature of the voltage stabilizer is ≥280°C.

[0043] In this invention, the 5wt% thermogravimetric temperature is tested by thermogravimetric analysis. It refers to the temperature at which the mass loss of the material reaches 5wt% of its initial mass under nitrogen atmosphere and heating rate of 10℃ / min.

[0044] In this invention, when at least one of the parameters of the voltage stabilizer, including the dipole moment, LUMO energy level, and 5wt% thermogravimetric temperature, meets the above-mentioned range, it is more conducive to capturing high-energy electrons, reducing space charge accumulation, and increasing the breakdown field strength, effectively suppressing the migration of the voltage stabilizer, and further improving the mechanical and electrical properties of the cable material.

[0045] More preferably, the voltage stabilizer has a dipole moment of 2.5-4 Debye.

[0046] More preferably, the LUMO energy level of the voltage stabilizer is ≤-2eV.

[0047] More preferably, the voltage stabilizer has a 5wt% thermogravimetric temperature of ≥300℃.

[0048] According to the present invention, preferably, the antioxidant includes a primary antioxidant and a secondary antioxidant.

[0049] According to the present invention, preferably, the weight ratio of the primary antioxidant to the voltage stabilizer is 1:1-5.

[0050] In this invention, the weight ratio of the main antioxidant to the voltage stabilizer within the above-mentioned range is more conducive to capturing free radicals generated in polypropylene during processing and decomposing hydrogen peroxide, effectively inhibiting the thermo-oxidative degradation chain reaction, ensuring the molecular weight stability of polypropylene during processing, and ultimately maintaining the mechanical properties and long-term stability of the material.

[0051] More preferably, the weight ratio of the primary antioxidant to the voltage stabilizer is 1:2-4.

[0052] According to the present invention, preferably, the weight ratio of the primary antioxidant to the secondary antioxidant is 1:0.5-2.

[0053] According to the present invention, preferably, the primary antioxidant is a hindered phenolic compound.

[0054] More preferably, in order to further cooperate with the voltage stabilizer to inhibit free radical degradation and improve the electrical properties of the polypropylene insulated cable material, the main antioxidant is a thiobisphenol compound.

[0055] In some specific embodiments of the present invention, the primary antioxidant is at least one of 4,4'-thiobis(6-tert-butyl-3-methylphenol), 2,2'-thiobis[ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 2,2'-thiobis(6-tert-butyl-4-methylphenol).

[0056] In this invention, the type of co-antioxidant can be a conventional choice in the art, for example, it can be a phosphite compound.

[0057] In some specific embodiments of the present invention, the co-antioxidant is at least one of tris(2,4-di-tert-butylphenyl) phosphite and pentaerythritol diisodecyl phosphite.

[0058] In some particularly preferred embodiments of the present invention, the inventors have ingeniously discovered that when the voltage stabilizer has a dipole moment of 0.5-4 Debye, a LUMO energy level ≤ -1eV, and a 5wt% thermogravimetric temperature ≥ 280℃, based on the total weight of the random copolymer polypropylene and the propylene-based elastomer, the random copolymer polypropylene comprises 75-85 parts by weight, and the propylene-based elastomer comprises 15-25 parts by weight; the content of ethylene units in the random copolymer polypropylene is 0.5-4wt%; the content of comonomers in the propylene-based elastomer is 10-15wt%; the antioxidant includes a primary antioxidant and a secondary antioxidant; based on the total weight of 100 parts by weight of the random copolymer polypropylene and the propylene-based elastomer, the antioxidant comprises 0.1-0.5 parts by weight, the weight ratio of the primary antioxidant to the secondary antioxidant is 1:0.5-2, and the weight ratio of the primary antioxidant to the voltage stabilizer is 1:2-4.

[0059] When the preferred embodiment described above is adopted, the DC breakdown field strength of the polypropylene insulation material can reach over 480 kV / mm, and the average charge density is less than 10 C / cm². 3 The electric field distortion is less than 5%, and the tensile strength can be maintained above 35MPa.

[0060] A second aspect of the present invention provides a polypropylene insulated cable material, which is prepared from the polypropylene composition as described above.

[0061] According to the present invention, preferably, the DC breakdown field strength of the polypropylene insulated cable material at 25℃±2℃ is ≥400kV / mm.

[0062] According to the present invention, preferably, the average charge density of the polypropylene insulated cable material under a polarized electric field of 20 kV / mm is ≤16 C / cm². 3 .

[0063] According to the present invention, preferably, the electric field distortion of the polypropylene insulated cable material under a polarized electric field of 20 kV / mm is ≤10%.

[0064] According to the present invention, preferably, the tensile strength of the polypropylene insulated cable material is ≥30MPa.

[0065] In this invention, the preparation method of the polypropylene insulated cable material can be arbitrarily selected according to actual needs. This invention exemplarily provides a preparation method comprising: After random copolymer polypropylene, propylene-based elastomer and antioxidant are first mixed, the product of the first mixture is second mixed with voltage stabilizer, and then extruded to obtain the polypropylene insulation material.

[0066] In this invention, the first mixing is carried out in a mixer.

[0067] Preferably, the conditions for the first mixing include: a temperature of 180-200℃, a rotation speed of 30-60 r / min, and a time of 10-20 min.

[0068] In this invention, the extrusion conditions include: a temperature of 150-200℃ and a screw speed of 150-200 r / min.

[0069] In some specific embodiments of the present invention, the temperature of the first extrusion zone is 150-155°C, and the temperature of subsequent zones gradually increases, with the discharge temperature being 195-200°C. The total number of temperature zones and the temperature gradient can be selected according to actual needs, and this will not be elaborated further in this invention.

[0070] In this invention, when the antioxidant includes a primary antioxidant and a secondary antioxidant, in order to further improve the uniformity of material mixing, the preparation method further includes mixing the primary antioxidant and the secondary antioxidant before performing the first mixing.

[0071] In this invention, the preparation method further includes filtering and granulating the material after extrusion. The filtering and granulation methods can be conventional choices in the art, and will not be described in detail here.

[0072] A third aspect of the present invention provides the use of the polypropylene composition as described above or the polypropylene insulated cable material as described above in high-voltage DC cables.

[0073] A fourth aspect of the present invention provides a high-voltage DC cable, wherein the insulation layer of the high-voltage DC cable comprises the polypropylene composition as described above or the polypropylene insulating cable material as described above.

[0074] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention, and are not intended to limit the present invention.

[0075] Unless otherwise specified, all reagents and materials used in the following examples were purchased from reputable chemical reagent suppliers and were of analytical purity.

[0076] In the following examples and comparative examples, the density of the random copolymer polypropylene is 0.9 g / cm³. 2 The melting temperature is 141.4℃, the ethylene unit content is 3.3wt%, the melt index at 230℃ and 2.16kg is 0.26g / 10min, and the weight average molecular weight is 612,700g / mol.

[0077] The density of the propylene-based elastomer is 0.874 g / cm³. 2It has a glass transition temperature of -25℃, an ethylene unit content of 11wt%, a tensile strength of 18.6MPa, an elongation at break of 800%, and a weight-average molecular weight of 230,500g / mol.

[0078] Voltage stabilizer 1: 3,5-dibenzyloxyacetophenone, with a dipole moment of 3.5 Debye, a LUMO energy level of -2.2 eV, and a thermal weight loss temperature of 312℃ at 5wt%.

[0079] Voltage stabilizer 2: 5,5'-methylenebis(2-hydroxy-4-methoxybenzophenone), with a dipole moment of 2.1 Debye, a LUMO energy level of -1.8 eV, and a thermal weight loss temperature of 327 °C at 5 wt%.

[0080] The voltage stabilizer 3 in the comparative example is dibenzyltoluene, with a dipole moment of 0.5 Debye, a LUMO energy level of -1.2 eV, and a thermal weight loss temperature of 383 °C at 5 wt%.

[0081] Example 1 (1) 0.1 parts by weight of 4,4'-thiobis(6-tert-butyl-3-methylphenol) and 0.1 parts by weight of tris(2,4-di-tert-butylphenyl) phosphite were stirred and premixed at room temperature at a stirring speed of 60 r / min to obtain a compound antioxidant; (2) Add 80 parts by weight of random copolymer polypropylene, 20 parts by weight of propylene-based elastomer and 0.2 parts by weight of compound antioxidant into a mixer (temperature 200℃, time 2min, speed 60rpm) and mix evenly. (3) The product of step (2) is mixed with 0.1 parts by weight of 3,5-dibenzyloxyacetophenone and then extruded using a twin-screw extruder at a speed of 180 r / min. The extruder is set to zone 1 (150℃), zone 2 (155℃), zone 3 (160℃), zone 4 (165℃), zone 5 (170℃), zone 6 (180℃), zone 7 (190℃), zone 8 (200℃), zone 9 (200℃), and material temperature (200℃). The filter screen is 500 mesh. After water cooling and granulation, polypropylene insulated cable material A1 is obtained.

[0082] Example 2-11 Polypropylene insulated cable materials A2-A11 were prepared according to the method of Example 1, except that the amount and type of each raw material added are shown in Table 1.

[0083] Comparative Examples 1-7 Polypropylene insulated cable materials D1-D7 were prepared according to the method of Example 1, except that the amount and type of each raw material added are shown in Table 1.

[0084] Table 1

[0085] Continued from Table 1

[0086] Continued from Table 1

[0087] Among them, 'a' is purchased from ExxonMobil and has the brand name Vistamaxx. TM 6102FL is a propylene-based elastomer with an ethylene unit content of 16 wt%. b is random copolymer polypropylene, grade M250E, purchased from Shanghai Petrochemical, with an ethylene unit content of 5.1 wt%. c is an ethylene-propylene terpolymer (EPDM) purchased from Mitsui, Japan, with the grade 3072EM. The ethylene unit content is 64wt%, the ethylene-norbornene content is 5.4wt%, and the propylene unit content is 30.6wt%. d is a polyolefin elastomer (POE) purchased from Dow Chemical, brand name ENGAGE™ 8842, with an ethylene unit content of 76 wt% and an octene unit content of 24 wt%. e is a block copolymer polypropylene, grade K8303, purchased from Yanshan Petrochemical, with a propylene block content of 95.1 wt% and an ethylene block content of 4.9 wt%.

[0088] Test case The polypropylene insulated cable materials prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 2.

[0089] The DC breakdown strength was tested in accordance with GB / T 1408.2-2016, with a test temperature of (25±2)℃ and a test piece thickness of (0.2±0.01)mm.

[0090] Average charge density and electric field distortion were measured using a pulsed electroacoustic (PEA) system with a sample thickness of 200 ± 10 μm. A polarization electric field of 20 kV / mm was applied to the sample and held for 30 min.

[0091] Average charge density per unit volume in the sample ( q(t) The formula for calculating ) is:

[0092] In the formula, L Where is the thickness of the sample, in meters (m). q(x、 t) Represents the polarization time as t At that time, the sample inside x Space charge density at the location.

[0093] The formula for calculating electric field distortion is as follows:

[0094] In the formula, E max It is the maximum electric field intensity distorted by space charge during the polarization process of the sample, kV / mm; E 0 represents the applied polarization field strength, in kV / mm; in this invention, it is 20 kV / mm.

[0095] Tensile strength was tested in accordance with GB / T1040.1-2018.

[0096] Table 2

[0097] As can be seen from Table 2, the polypropylene insulated cable material provided by the present invention not only has excellent electrical properties such as high DC breakdown field strength, low average charge density and low electric field distortion, which can ensure the stability of cable use, but also has excellent tensile strength, excellent comprehensive performance and excellent application value.

[0098] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polypropylene composition, characterized in that, The polypropylene composition includes random copolymer polypropylene, propylene-based elastomer, antioxidant, and voltage stabilizer. The voltage stabilizer is an aromatic ketone compound containing at least two benzene rings.

2. The polypropylene composition according to claim 1, wherein, Based on the total weight of the random copolymer polypropylene and the propylene-based elastomer, the random copolymer polypropylene is 70-90 parts by weight and the propylene-based elastomer is 10-30 parts by weight. And / or, based on the total weight of 100 parts by weight of random copolymer polypropylene and propylene-based elastomer, the antioxidant is 0.1-1 parts by weight and the voltage stabilizer is 0.1-0.5 parts by weight.

3. The polypropylene composition according to claim 1 or 2, wherein, The density of the random copolymer polypropylene is 0.89-0.91 g / cm³. 2 ; And / or, the melting temperature of the random copolymer polypropylene is 140-160°C; And / or, in the random copolymer polypropylene, the content of ethylene units is 0.5-4 wt%; And / or, the random copolymer polypropylene has a melt index of 0.1-2 g / 10 min at 230°C and 2.16 kg; And / or, the weight-average molecular weight of the random copolymer polypropylene is 300,000-700,000 g / mol.

4. The polypropylene composition according to any one of claims 1-3, wherein, The density of the propylene-based elastomer is 0.86-0.89 g / cm³. 2 ; And / or, the glass transition temperature of the propylene-based elastomer is ≤-20°C; And / or, in the propylene-based elastomer, the comonomer is ethylene and / or 1-butene; Preferably, the content of comonomer in the propylene-based elastomer is 10-15 wt%. And / or, the tensile strength of the propylene-based elastomer is 10-20 MPa; And / or, the elongation at break of the propylene-based elastomer is ≥800%; And / or, the weight-average molecular weight of the propylene-based elastomer is 100,000-300,000 g / mol.

5. The polypropylene composition according to any one of claims 1-4, wherein, The voltage stabilizer has a dipole moment of 0.5-4 Debye; And / or, the LUMO level of the voltage stabilizer is ≤-1eV; And / or, the voltage stabilizer has a 5wt% thermogravimetric temperature ≥280°C.

6. The polypropylene composition according to any one of claims 1-5, wherein, The antioxidants include primary antioxidants and secondary antioxidants; Preferably, the weight ratio of the primary antioxidant to the voltage stabilizer is 1:1-5, more preferably 1:2-4; Preferably, the weight ratio of the primary antioxidant to the secondary antioxidant is 1:0.5-2; Preferably, the primary antioxidant is a hindered phenolic compound, and more preferably a thiobisphenol compound.

7. A polypropylene insulated cable material, characterized in that, The polypropylene insulated cable material is prepared from the polypropylene composition according to any one of claims 1-6.

8. The polypropylene insulated cable material according to claim 7, wherein, The DC breakdown field strength of the polypropylene insulated cable material at 25℃±2℃ is ≥400kV / mm; And / or, the average charge density of the polypropylene insulated cable material under a polarized electric field of 20 kV / mm is ≤16 C / cm³. 3 ; And / or, the electric field distortion of the polypropylene insulated cable material under a polarized electric field of 20kV / mm is ≤10%; And / or, the tensile strength of the polypropylene insulated cable material is ≥30MPa.

9. The use of the polypropylene composition according to any one of claims 1-6 or the polypropylene insulated cable material according to claim 7 or 8 in high-voltage DC cables.

10. A high-voltage DC cable, characterized in that, The insulation layer of the high-voltage DC cable comprises the polypropylene composition according to any one of claims 1-6 or the polypropylene insulated cable material according to claim 7 or 8.

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