Thermoplastic insulating material resistant to treeing and process for its preparation and use

Abstract

The application belongs to the technical field of polymers, and discloses a kind of thermoplastic insulating material resistant to electrical treeing and a preparation method and application thereof.The thermoplastic insulating material contains alkenyl monomer-containing graft-modified propylene polymer, optional propylene polymer, auxiliary agent and optional elastomer;The auxiliary agent contains antioxidant and voltage stabilizer;In the thermoplastic insulating material, the content of alkenyl monomer-containing structural unit in the graft state is 0.1-6wt%, and the content of xylene-soluble matter is 0-70wt%;The melt flow rate of the thermoplastic insulating material under a load of 2.16kg at 230℃ is 0.2-7g / 10min;The bending modulus of the thermoplastic insulating material is 150-1600MPa.The thermoplastic insulating material has stable electrical treeing resistance, and can be used stably for a long time at high temperature and high field strength.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polymers, and particularly relates to a treeing-resistant thermoplastic insulating material, a preparation method of the treeing-resistant thermoplastic insulating material, and application of the treeing-resistant thermoplastic insulating material in a cable. BACKGROUND

[0002] In order to meet the requirements of environmental protection and sustainable development, research on a new recyclable non-crosslinked polyolefin cable insulating material has become a hot spot in the field of insulating materials. Polypropylene has become the most concerned research direction due to its excellent electrical insulation performance and low price. Under the action of an electric field, defects such as impurities and air gaps in the cable insulating layer cause local charge aggregation, leading to local breakdown, and then forming a treeing nanoscale discharge damage channel, which is called an electrical tree. Once the electrical tree grows through the insulating layer, an electrical fault will occur. Therefore, it is necessary to reduce the occurrence of electrical trees in cable insulating materials.

[0003] One method of inhibiting the growth of electrical trees is to add a voltage stabilizer to the insulating material. Voltage stabilizers are compounds that can introduce charge traps to capture high-energy electrons and reduce the local electric field strength, such as phenylethanone and benzophenone compounds. However, such additives have small molecular weights and are prone to migration under long-term working conditions, leading to a decrease in insulating performance.

[0004] In "Preparation of Polypropylene Grafted 4-Propoxyenyl-2-Hydroxybenzophenone Material" (Functional Materials, 2018, 49(11): 11080-11084) by Zhang Wenlong, polypropylene resistivity is improved by using 4-propoxyenyl-2-hydroxybenzophenone modification through melt grafting. However, the monomer grafting rate is low, and melt grafting can cause degradation of polypropylene, generating impurities and reducing the mechanical properties of the material, which is not suitable for cable insulating materials.

[0005] In patent document CN109384998B, aromatic ketone side chains are modified on SEBS, and then blended with polypropylene to improve the treeing voltage and avoid precipitation of voltage stabilizers. However, the solution method for SEBS modification is complicated and costly, and the long-term stability of the treeing resistance effect has not been proven. SUMMARY

[0006] In view of the deficiencies in the prior art, the purpose of the present application is to provide a treeing-resistant thermoplastic insulating material, a preparation method thereof and application thereof. The thermoplastic insulating material has stable treeing-resistant performance and can be used stably for a long time under high temperature and high field strength.

[0007] The first aspect of the present application provides a thermoplastic insulating material resistant to electrical treeing, which contains an alkenyl monomer grafted propylene polymer, an optional propylene polymer, an auxiliary agent, and an optional elastomer; the auxiliary agent contains an antioxidant and a voltage stabilizer;

[0008] In the thermoplastic insulating material, the content of the alkenyl monomer structure unit in the grafted state is 0.1-6wt%, the content of xylene soluble is 0-70wt%; the melt flow rate of the thermoplastic insulating material under a load of 2.16kg at 230℃ is 0.2-7g / 10min; the flexural modulus of the thermoplastic insulating material is 150-1600MPa.

[0009] The second aspect of the present application provides a preparation method of the above-mentioned thermoplastic insulating material resistant to electrical treeing, which comprises: mixing the alkenyl monomer grafted propylene polymer, the optional propylene polymer, the auxiliary agent, and the optional elastomer, melt extruding and granulating to obtain the thermoplastic insulating material;

[0010] The auxiliary agent contains an antioxidant, a voltage stabilizer, an optional copper inhibitor, and an optional processing aid.

[0011] The third aspect of the present application provides the application of the above-mentioned thermoplastic insulating material resistant to electrical treeing in cables.

[0012] The thermoplastic insulating material of the present application has stable electrical treeing resistance, and is suitable for long-term use under high temperature and high field strength. In the present application, a relatively inexpensive monomer is introduced into a propylene polymer in a grafted manner, and the obtained modified material has a functional group with good compatibility with a voltage stabilizer, which can reduce the migration of the voltage stabilizer, and obtain a long-acting stable voltage effect. This method is low in cost, simple in operation, flexible in regulation, suitable for large-scale preparation of materials, and has good industrial application potential.

[0013] Other features and advantages of the present application will be described in detail in the following specific embodiments. DETAILED DESCRIPTION

[0014] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0015] According to the first aspect of the present application, the present application provides a thermoplastic insulating material resistant to electrical treeing, which contains an alkenyl monomer grafted propylene polymer, an optional propylene polymer, an auxiliary agent, and an optional elastomer; the auxiliary agent contains an antioxidant and a voltage stabilizer;

[0016] The content of the monomer structural unit containing alkenyl group in the graft state in the thermoplastic insulating material is 0.1-6wt%, the content of xylene soluble is 0-70wt%; the melt flow rate of the thermoplastic insulating material under the load of 230℃, 2.16kg is 0.2-7g / 10min; the bending modulus of the thermoplastic insulating material is 150-1600MPa.

[0017] Preferably, the content of the monomer structural unit containing alkenyl group in the graft state in the thermoplastic insulating material is 0.5-5wt%, preferably 1-4wt%, the content of xylene soluble is 0.5-65wt%; the melt flow rate of the thermoplastic insulating material under the load of 230℃, 2.16kg is 0.5-5g / 10min, preferably 1-3.5g / 10min; the bending modulus of the thermoplastic insulating material is 200-1200MPa, preferably 400-1000MPa.

[0018] In the present application, the propylene polymer can be a propylene homopolymer or a propylene copolymer with homogeneous structure or heterogeneous structure, the content of the comonomer in the propylene polymer is 0-25wt%, preferably 0-20wt%; the melt flow rate of the propylene polymer under the load of 230℃, 2.16kg is 0.5-10g / 10min, preferably 1-7g / 10min, the melting temperature Tm is 110-180℃, preferably 120-170℃.

[0019] According to the present application, the comonomer of the propylene copolymer can be at least one selected from the group consisting of ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene, preferably ethylene and / or 1-butene.

[0020] In the present application, the monomer containing alkenyl group is at least one selected from the group consisting of aromatic olefin monomer, siloxane monomer containing unsaturated double bond, acrylate monomer and acrylic monomer; preferably acrylate monomer and / or aromatic olefin monomer; more preferably styrene and / or glycidyl methacrylate.

[0021] According to the present application, the thermoplastic insulating material contains at least one propylene polymer grafted and modified by the monomer containing alkenyl group. That is, the propylene polymer grafted and modified by the monomer containing alkenyl group in the thermoplastic insulating material can be a single propylene polymer grafted and modified by the monomer containing alkenyl group, or two or more propylene polymers grafted and modified by the monomer containing alkenyl group.

[0022] The propylene polymer grafted and modified by the monomer containing alkenyl group in the present application can be prepared by the conventional method in the prior art, as long as the use requirement is met. Preferably, the propylene polymer grafted and modified by the monomer containing alkenyl group is prepared by the following method:

[0023] a. The propylene polymer is placed in a closed reactor, and inert gas is replaced;

[0024] b. The radical initiator and the olefinic monomer are added to the closed reactor, and mixed by stirring;

[0025] c. The co-solvent is optionally added, and the reaction system is optionally swelled;

[0026] d. The dispersant is optionally added, the reaction system is heated to the grafting reaction temperature, and the grafting reaction is carried out;

[0027] e. The reaction product is optionally filtered and dried, and the propylene polymer grafted with the olefinic monomer is obtained.

[0028] According to the present application, the inert gas can be various inert gases commonly used in the art, including but not limited to nitrogen, argon.

[0029] In the present application, the radical initiator is selected from peroxide radical initiators; the peroxide radical initiator is preferably selected from at least one of dibenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dodecanoyl peroxide, tert-butyl benzene peroxide, diisopropyl peroxydicarbonate, tert-butyl peroxy(2-ethylhexanoate), and dicyclohexyl peroxydicarbonate.

[0030] According to the present application, the amount of the olefinic monomer can be 1-12%, preferably 1.5-9%, and more preferably 1.7-7%, based on the mass of the propylene polymer.

[0031] The mass ratio of the amount of the radical initiator to the amount of the olefinic monomer is 0.1-6:100, and preferably 0.5-5:100.

[0032] According to the present application, the co-solvent is an organic solvent having a swelling effect on the olefin polymer, and the co-solvent is preferably selected from at least one of benzene, toluene, xylene, chlorobenzene, tetrahydrofuran, diethyl ether, acetone, hexane, cyclohexane, decalin, and heptane. The amount of the co-solvent is 1-30%, and preferably 10-25%, based on the mass of the propylene polymer.

[0033] In the present application, the swelling conditions include that the swelling temperature can be 30-60°C, and the time can be 1-5 hours.

[0034] According to the present application, the dispersant is water or an aqueous sodium chloride solution. The water is deionized water, and the aqueous sodium chloride solution can be used at any conventional concentration. The amount of the dispersant is 50-300%, based on the mass of the propylene polymer.

[0035] In the present application, the temperature of the grafting reaction is 80-130°C, preferably 85-120°C; the time is 0.5-10 hours, preferably 1-6 hours.

[0036] According to the present application, all materials in the grafting reaction system can be added at one time or at different stages of the reaction.

[0037] According to the present application, the auxiliary agent contains an antioxidant, a voltage stabilizer, optionally an anti-copper agent and optionally a processing aid.

[0038] The antioxidant is selected from at least one of hindered phenolic antioxidants, hindered amine antioxidants, phosphite antioxidants and thio antioxidants. The antioxidant is preferably at least one of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)mesitylene, N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, 2,2'-thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2',2-oxamidyl-bis-[ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionate, n-octadecyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-thiobis(6-tert-butyl-3-methylphenol), triphenyl phosphite, tris[2,4-di-tert-butylphenyl]phosphite, dilauryl thiodipropionate.

[0039] The voltage stabilizer is an aromatic compound, preferably a derivative of acetophenone and / or benzophenone, more preferably 2,4-dihydroxybenzophenone and / or acetophenone.

[0040] The anti-copper agent can be at least one of N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, 2,2-oxamidyl-bis[ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionic acid and N-salicyloylaminophthalimide.

[0041] The processing aid is selected from at least one of fluorine-containing compounds, polypropylene wax, polyethylene wax, fatty acid esters and mineral oil, preferably at least one of polypropylene wax, fatty acid esters and mineral oil.

[0042] In the present application, the elastomer can be an elastomer commonly used in the art, preferably selected from at least one of POE, PBE, EPR, EPDM, SEBS and SBS.

[0043] According to the second aspect of the present application, the present application provides a preparation method of the above-mentioned thermoplastic insulating material resistant to electrical treeing, which comprises: mixing the propylene polymer grafted with alkenyl monomer, optional propylene polymer, auxiliary agent and optional elastomer, melt-extruding and granulating to obtain the thermoplastic insulating material;

[0044] The auxiliary agent contains antioxidant, voltage stabilizer, optional copper inhibitor and optional processing aid.

[0045] According to the present application, the amount of the propylene polymer grafted with alkenyl monomer is greater than 50%, preferably greater than 55%, and more preferably greater than 60%, based on the total mass of the propylene polymer grafted with alkenyl monomer, propylene polymer and elastomer; the amount of the antioxidant is 1000-5000 ppm, preferably 1500-4000 ppm; the amount of the voltage stabilizer is 0.1-5%, preferably 0.3-3%; when the processing aid is contained, the amount of the processing aid is 0.5-4%, preferably 0.8-2%; when the copper inhibitor is contained, the amount of the copper inhibitor is 1000-5000 ppm, preferably 1500-4000 ppm.

[0046] In addition, according to the product requirements, other auxiliary agents such as anti-aging agent can be added in the present application, and the types and amounts of other auxiliary agents are conventional and known to those skilled in the art.

[0047] In the present application, the melt-extruding and granulating can be carried out by using conventional equipment in the prior art, and the preferred equipment is a twin-screw extruder. The temperature of the melt-extruding and granulating can be 180-250°C, preferably 185-230°C, and more preferably 190-220°C.

[0048] The third aspect of the present application provides the use of the above-mentioned thermoplastic insulating material resistant to electrical treeing in cables.

[0049] The thermoplastic insulating material of the present application can be used as an insulating material in the field of cables, and the specific use mode can be carried out according to conventional insulating materials.

[0050] The substances and parameters not defined in the present application can be selected according to the prior art, which are conventional technical means in the art.

[0051] The present application will be further described below in combination with examples, but is not limited by these examples.

[0052] In the following preparation examples, examples and comparative examples, the relevant data are obtained according to the following test methods:

[0053] 1. Determination of the comonomer content in propylene polymer:

[0054] The comonomer content was determined by quantitative Fourier transform infrared (FTIR) spectroscopy. The correlation of the determined comonomer content was calibrated by quantitative nuclear magnetic resonance (NMR) spectroscopy. The quantitative 13 The calibration method of the results obtained from C-NMR spectroscopy was performed according to the conventional method in the art.

[0055] 2. Determination of xylene solubles content (XS):

[0056] The test was performed according to the method specified in GB / T 24282-2009.

[0057] 3. Determination of grafting degree GD (n) The test was performed according to the method specified in GB / T 24282-2009.

[0058] 2-4 g of the grafting product was placed in a Soxhlet extractor and extracted with an organic solvent (ethyl acetate was used for aromatic olefin monomers, acrylate monomers, and acrylic monomers; acetone was used for silane monomers) for 24 hours to remove unreacted monomers and their homopolymers, obtaining a pure grafting product, which was dried and weighed to calculate the parameter grafting degree GD. (n) The grafting degree GD represents the grafting rate of the propylene polymer containing an alkenyl monomer in the material. The content of the structural unit containing the alkenyl monomer in the grafting state in the thermoplastic insulating material is represented by GD. In the present application, the calculation formula of GD is as follows:

[0059]

[0060]

[0061] In the above formula, w0 is the mass of the propylene polymer; w1 is the mass before extraction of the grafting product; and w2 is the mass after extraction of the grafting product. In the case where the thermoplastic insulating material contains more than one grafting product, m n1 is the mass of the first propylene polymer containing an alkenyl monomer modified material, m n2 is the mass of the second propylene polymer containing an alkenyl monomer modified material, and so on; and mproduct is the mass of the thermoplastic insulating material.

[0062] 4. Determination of melt flow rate (melt index) MFR:

[0063] The test was performed according to the method specified in GB / T 3682-2018 using a melt index instrument of type 7026 of CEAST company at 230℃ under a load of 2.16 kg.

[0064] 5. Determination of melting temperature (melting point) Tm:

[0065] The melting process and crystallization process of the material are analyzed by differential scanning calorimeter. The specific operation is: under the protection of nitrogen, 5-10 mg of sample is measured from 20 to 200 DEG C by three-stage temperature measurement method, and the change of heat flow reflects the melting and crystallization process of the material, so as to calculate the melting temperature Tm.

[0066] 6. Determination of flexural modulus:

[0067] Determined according to the method specified in GB / T 9341-2008.

[0068] 7. Electric tree length

[0069] Sample preparation and testing refer to "Guo F, Wang YJ, Yue HJ, et al. Temperature characteristics of periodic DC and AC electric trees in XLPE and MgO / XLPE nanocomposites [J]. High Voltage Technology, 2018, 044(005): 1459-1466." The thickness of the sample is 1 mm.

[0070] The reagents used in the preparation examples, examples and comparative examples are as follows:

[0071] Benzoyl peroxide (BPO), BLENZON TECHNOLOGY CO., LTD.;

[0072] Lauryl peroxide (LPO), BLENZON TECHNOLOGY CO., LTD.;

[0073] Tert-butyl 2-ethylhexanoate peroxide (OT), Adamas Reagent Co., Ltd.;

[0074] Styrene (St), BLENZON TECHNOLOGY CO., LTD.;

[0075] Glycidyl methacrylate (GMA), BLENZON TECHNOLOGY CO., LTD.;

[0076] Xylene, BLENZON TECHNOLOGY CO., LTD.;

[0077] Antioxidant: antioxidant 1035, antioxidant 1010, antioxidant 168, antioxidant 697, Shanghai Kaijin Chemical Industry;

[0078] Processing aid (lubricant): PP wax 2602 (Clariant), PPA5920A (3M Company, USA);

[0079] Anti-copper agent: MD-1024, MDA-5, Shanghai Kaijin Chemical Industry;

[0080] Voltage stabilizer: UV-0 (Shanghai Kaijin Chemical Industry), phenylacetone (BLENZON TECHNOLOGY CO., LTD.);

[0081] Elastomers: Vistamaxx 6102, Vistamaxx 6202, ExxonMobil;

[0082] Propylene polymers as shown in Table 1:

[0083] Table 1

[0084]

[0085] Preparation Examples 1-5

[0086] The propylene polymer powder is weighed into a reaction kettle with mechanical stirring, the reaction system is closed and deoxygenated by nitrogen replacement. The initiator and the mixture containing the alkenyl monomer are added and mixed with the powder for 15-20 minutes, the dispersant or the swelling aid is optionally added, the materials are optionally heated and swelled, and then heated to the reaction temperature for 2-6 hours. After the reaction is completed, the system is cooled, the dispersant water is optionally filtered out, and the product is dried at 70°C for 4 hours to obtain the propylene polymer grafted and modified with the alkenyl monomer. The specific reaction conditions and product properties are shown in Tables 2 and 3.

[0087] Table 2

[0088]

[0089] Table 3

[0090]

[0091] Examples 1-5

[0092] The alkenyl monomer grafted and modified propylene polymer (modified propylene polymer), antioxidant, voltage stabilizer, copper inhibitor, processing aid, optional propylene polymer, and optional elastomer are weighed, and the amounts of the materials are measured by mass fraction, mass percentage, or mass ppm. After the materials are mixed by a high-speed mixer, they are fed into a twin-screw extruder for melt extrusion and granulation to obtain a thermoplastic insulating material. The specific preparation conditions and material properties are shown in Tables 4 and 5, respectively.

[0093] Comparative Examples 1-3

[0094] Comparative Example 1 is set up in the same way as Example 1, except that no voltage stabilizer is added. Comparative Example 2 is set up in the same way as Example 1, except that the unmodified propylene polymer is used instead of the modified propylene polymer in Example 1. Comparative Example 3 is set up in the same way as Example 1, except that the amount of the voltage stabilizer is higher. The specific preparation conditions and material properties are shown in Tables 4 and 5, respectively.

[0095] Table 4

[0096]

[0097]

[0098] Table 5

[0099]

[0100] The materials prepared in the examples and comparative examples were prepared into two groups of samples according to the test method, one group was directly tested for electrical tree, i.e. the initial electrical tree; the other group was placed in an air environment at 135℃ for 10 days, and then the electrical tree was tested again, to obtain the treated electrical tree. The specific results are shown in Table 6.

[0101] Table 6

[0102]

[0103] The present application simulates the operating conditions of cable insulation materials at high temperature for a long time, tests the long-term electrical tree growth resistance of the sample, and compares the results of the comparative examples and the comparative examples. It can be found that the sample of the present application has long-term electrical properties. Comparing the data of Example 1 and Comparative Example 1, it can be seen that the sample without voltage stabilizer has more obvious electrical tree growth. Comparing the data of Example 1 and Comparative Example 2, it can be seen that the sample using ungrafted modified polypropylene has poor electrical tree resistance after a period of time, indicating that the migration of the voltage stabilizer causes performance degradation. Comparing the data of Example 1 and Comparative Example 3, it can be seen that the amount of voltage stabilizer is higher than the limit range of the present application, and the electrical tree performance of the sample is not further improved.

[0104] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A thermoplastic insulating material resistant to treeing, characterized in that, The thermoplastic insulating material contains propylene polymer grafted with alkenyl group-containing monomer, optional propylene polymer, auxiliary agent, and optional elastomer; the auxiliary agent contains antioxidant and voltage stabilizer; the alkenyl group-containing monomer is aromatic alkenyl monomer and / or glycidyl methacrylate; the voltage stabilizer is aromatic compound; the amount of the voltage stabilizer is 0.1-5% based on the total mass of the propylene polymer grafted with alkenyl group-containing monomer, propylene polymer, and elastomer; In the thermoplastic insulating material, the content of alkenyl group-containing monomer structure unit in grafting state is 0.1-6wt%, the content of xylene soluble is 0-70wt%; the melt flow rate of the thermoplastic insulating material under 230℃ and 2.16kg load is 0.2-7g / 10min; the bending modulus of the thermoplastic insulating material is 150-1600MPa.

2. The tree-retardant thermoplastic insulating material of claim 1, wherein, In the thermoplastic insulating material, the content of alkenyl group-containing monomer structure unit in grafting state is 0.5-5wt%, the content of xylene soluble is 0.5-65wt%; the melt flow rate of the thermoplastic insulating material under 230℃ and 2.16kg load is 0.5-5g / 10min; the bending modulus of the thermoplastic insulating material is 200-1200MPa.

3. The tree-retardant thermoplastic insulating material of claim 2, wherein, In the thermoplastic insulating material, the content of alkenyl group-containing monomer structure unit in grafting state is 1-4wt%; the melt flow rate of the thermoplastic insulating material under 230℃ and 2.16kg load is 1-3.5g / 10min; the bending modulus of the thermoplastic insulating material is 400-1000MPa.

4. The tree-retardant thermoplastic insulating material of claim 1, wherein, The propylene polymer is propylene homopolymer or propylene copolymer, and the content of comonomer in the propylene polymer is 0-25wt%; the melt flow rate of the propylene polymer under 230℃ and 2.16kg load is 0.5-10g / 10min, and the melting temperature Tm is 110-180℃; The alkenyl group-containing monomer is styrene and / or glycidyl methacrylate.

5. The tree-retardant thermoplastic insulating material of claim 4, wherein, The content of comonomer in the propylene polymer is 0-20wt%; the melt flow rate of the propylene polymer under 230℃ and 2.16kg load is 1-7g / 10min, and the melting temperature Tm is 120-170℃.

6. The resistance treeing thermoplastic insulating material of claim 4, wherein, The comonomer of the propylene copolymer is at least one selected from ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene.

7. The tree-retardant thermoplastic insulating material of claim 6, wherein, The comonomer of the propylene copolymer is ethylene and / or 1-butene.

8. The tree-retardant thermoplastic insulating material of any of claims 1-7, wherein, The thermoplastic insulating material contains at least one propylene polymer grafted with alkenyl group-containing monomer.

9. The tree-retardant thermoplastic insulating material of claim 8, wherein, The propylene polymer grafted with alkenyl group-containing monomer is prepared by the following method: a. Put the propylene polymer into a closed reactor, and perform inert gas replacement; b. Add free radical initiator and alkenyl group-containing monomer into the closed reactor, and stir to mix; c. Optionally add cosolvent, and optionally swell the reaction system; d. Optionally add dispersant, heat the reaction system to grafting reaction temperature, and perform grafting reaction; e. Optionally filter and dry the reaction product, to obtain propylene polymer grafted with alkenyl group-containing monomer.

10. The tree-retardant thermoplastic insulating material of claim 9, wherein, The radical initiator is selected from peroxide radical initiators; The amount of the olefin group-containing monomer is 1 to 12% by mass based on the mass of the propylene polymer. The mass ratio of the amount of the radical initiator to the amount of the olefin group-containing monomer is 0.1 to 6:

100.

11. The tree-retardant thermoplastic insulating material of claim 9, wherein, The peroxide radical initiator is selected from at least one of dibenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, lauroyl peroxide, dodecanoyl peroxide, t-butyl peroxybenzoate, diisopropyl peroxydicarbonate, t-butyl peroxy(2-ethylhexanoate), and dicyclohexyl peroxydicarbonate.

12. The tree-retardant thermoplastic insulating material of claim 9, wherein, The amount of the olefin group-containing monomer is 1.5 to 9% by mass based on the mass of the propylene polymer.

13. The tree-retardant thermoplastic insulating material of claim 12, wherein, The amount of the olefin group-containing monomer is 1.7 to 7% by mass based on the mass of the propylene polymer.

14. The tree-retardant thermoplastic insulating material of claim 9, wherein, The mass ratio of the amount of the radical initiator to the amount of the olefin group-containing monomer is 0.5 to 5:

100.

15. The tree-retardant thermoplastic insulating material of claim 9, wherein, The co-swelling agent is selected from at least one of benzene, toluene, xylene, chlorobenzene, tetrahydrofuran, diethyl ether, acetone, hexane, cyclohexane, decalin, and heptane; the amount of the co-swelling agent is 1 to 30% by mass based on the mass of the propylene polymer; The temperature of the swelling is 30 to 60°C for 1 to 5 hours. The dispersant is water or an aqueous sodium chloride solution; the amount of the dispersant is 50 to 300% by mass based on the mass of the propylene polymer; The temperature of the grafting reaction is 80 to 130°C for 0.5 to 10 hours.

16. The tree-retardant thermoplastic insulating material of claim 15, wherein, The amount of the co-swelling agent is 10 to 25% by mass based on the mass of the propylene polymer.

17. The tree-retardant thermoplastic insulating material of claim 15, wherein, The temperature of the grafting reaction is 85 to 120°C for 1 to 6 hours.

18. The tree-retardant thermoplastic insulating material of claim 1, wherein, The antioxidant is selected from at least one of hindered phenol-based antioxidants, hindered amine-based antioxidants, phosphite-based antioxidants, and thio-based antioxidants; The voltage stabilizer is a phenylacetone-based and / or benzophenone-based derivative.

19. The tree-retardant thermoplastic insulating material of claim 18, wherein, The antioxidant is at least one of tetrakis[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]pentaerythritol ester, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)mesitylene, N,N'-bis[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine, 2,2'-thiobis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2',2-oxamidobis-[ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)]propionate, n-octadecyl β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 4,4'-thiobis(6-t-butyl-3-methylphenol), triphenyl phosphite, tris[2,4-di-t-butylphenyl]phosphite, dilauryl thiodipropionate.

20. The tree-retardant thermoplastic insulating material of claim 18, wherein, The voltage stabilizer is 2,4-dihydroxybenzophenone and / or phenylacetone.

21. The tree-retardant thermoplastic insulating material of claim 18, wherein, The auxiliary agent contains an anti-copper agent and a processing aid; the anti-copper agent is at least one of N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, 2,2-oxamido-bis[ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionic acid and N-salicyloylphthalimide; the processing aid is at least one selected from a fluorine-containing compound, a polypropylene wax, a polyethylene wax, a fatty acid ester and a mineral oil.

22. The tree-retardant thermoplastic insulating material of claim 21, wherein, The processing aid is at least one of a polypropylene wax, a fatty acid ester and a mineral oil.

23. The tree-retardant thermoplastic insulating material of claim 18, wherein, The elastomer is at least one selected from POE, PBE, EPR, EPDM, SEBS and SBS.

24. The method of making a resistance to treeing thermoplastic insulating material according to any one of claims 1 to 23, characterized in that, The preparation method comprises: mixing the propylene polymer grafted and modified with an alkenyl monomer, an optional propylene polymer, an auxiliary agent and an optional elastomer, melt-extruding and granulating to obtain the thermoplastic insulating material. The auxiliary agent contains an antioxidant, a voltage stabilizer, an optional anti-copper agent and an optional processing aid.

25. The method of making a resistance to treeing thermoplastic insulating material of claim 24, wherein, The amount of the propylene polymer grafted and modified with an alkenyl monomer is greater than 50% based on the total mass of the propylene polymer grafted and modified with an alkenyl monomer, the propylene polymer and the elastomer; the amount of the antioxidant is 1000-5000 ppm; the amount of the voltage stabilizer is 0.3-3%; the amount of the processing aid is 0.5-4%; and the amount of the anti-copper agent is 1000-5000 ppm. The temperature of the melt-extruding and granulating is 180-250°C.

26. The method of making a resistance to treeing thermoplastic insulating material of claim 25, wherein, The amount of the propylene polymer grafted and modified with an alkenyl monomer is greater than 55% based on the total mass of the propylene polymer grafted and modified with an alkenyl monomer, the propylene polymer and the elastomer.

27. The method of making a resistance to treeing thermoplastic insulating material of claim 26, wherein, The amount of the propylene polymer grafted and modified with an alkenyl monomer is greater than 55% based on the total mass of the propylene polymer grafted and modified with an alkenyl monomer, the propylene polymer and the elastomer.

28. The method of making a resistance to treeing thermoplastic insulating material of claim 25, wherein, The amount of the antioxidant is 1500-4000 ppm.

29. The method of making a resistance to treeing thermoplastic insulating material of claim 25, wherein, The amount of the processing aid is 0.8-2%.

30. The method of making a resistance to treeing thermoplastic insulating material of claim 25, wherein, The amount of the anti-copper agent is 1500-4000 ppm.

31. The method of making a resistance to treeing thermoplastic insulating material of claim 25, wherein, The temperature of the melt-extruding and granulating is 185-230°C.

32. The method of making a resistance to treeing thermoplastic insulating material of claim 31, wherein, The temperature of the melt-extruding and granulating is 190-220°C.

33. Use of the treeing-resistant thermoplastic insulating material of any one of claims 1-23 or prepared by the preparation method of any one of claims 24-32 in a cable.

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