Polypropylene cable insulation layer capable of preventing electrical tree branches and performance detection method thereof

Abstract

The invention relates to the technical field of cable insulation sheaths, and particularly discloses an anti-electric-tree polypropylene cable insulation layer and a performance detection method thereof. The invention discloses a polypropylene cable insulation layer capable of preventing electrical treeing. The cable insulation layer is prepared from the following raw materials in parts by weight: 50-90 parts of modified polypropylene, 5-15 parts of ethylene-vinyl acetate copolymer, 3-8 parts of modified filler and 0.1-1 part of antioxidant, the modified polypropylene is prepared from the following raw materials: polypropylene, 4-propenyloxy-2-hydroxybenzophenone, dicumyl peroxide and a styrene derivative; the modified filler is prepared from the following raw materials: nano particles, gamma-aminopropyltriethoxysilane and an organic solvent.

Description

Technical Field

[0001] The present application relates to the technical field of cable insulation sheaths, and in particular to an anti-electrical tree polypropylene cable insulation layer and a performance detection method thereof. Background Art

[0002] Polypropylene insulated cables have broad application prospects in the fields of future urban center power transmission, offshore wind power grids, etc. due to their material advantages such as low carbon and environmental protection, high operating temperature, excellent dielectric properties, and process advantages of short production cycle. However, the commonly used polypropylene insulated cables will experience electrical treeing after a period of use. Electrical treeing is a micron-level discharge destruction channel formed by local breakdown caused by local electric field concentration caused by defects such as impurities and bubbles in the insulating material. Because of its shape similar to tree branches, it is called electrical treeing. Once electrical treeing occurs, it will develop at an extremely fast speed. Once the electrical treeing grows to penetrate the insulation layer, a breakdown failure will occur, thus affecting the safe operation of the cable. Therefore, it is urgent to develop a cable insulation layer with better anti-electrical treeing performance. Summary of the invention

[0003] In order to develop a cable insulation layer with good anti-electrical treeing performance, the present application provides a polypropylene cable insulation layer with anti-electrical treeing and a performance detection method thereof.

[0004] In the first aspect, the present application provides a polypropylene cable insulation layer for preventing electric tree branches, which adopts the following technical scheme: a polypropylene cable insulation layer for preventing electric tree branches, wherein the raw materials of the cable insulation layer include the following components in parts by weight: 50 to 90 parts of modified polypropylene, 5 to 15 parts of ethylene-vinyl acetate copolymer, 3 to 8 parts of modified filler, and 0.1 to 1 part of antioxidant; the raw materials of the modified polypropylene include polypropylene, 4-propyleneoxy-2-hydroxybenzophenone, diisopropyl peroxide, and a styrene derivative; the raw materials of the modified filler include nanoparticles, γ-aminopropyltriethoxysilane, and an organic solvent.

[0005] By adopting the above technical scheme, dicumyl peroxide in the modified polypropylene can induce free radicals of the matrix, so that 4-propyleneoxy-2-hydroxybenzophenone is grafted on the polypropylene, the migration and precipitation of 4-propyleneoxy-2-hydroxybenzophenone are inhibited, and the anti-electrical treeing performance of the modified polypropylene is improved. Styrene derivatives and 4-propyleneoxy-2-hydroxybenzophenone can jointly inhibit the macromolecular degradation of polypropylene. The nanoparticles are modified by using γ-aminopropyltriethoxysilane to improve the dispersion performance of the nanoparticles. γ-aminopropyltriethoxysilane can also couple the modified polypropylene with ethylene-vinyl acetate copolymer. The combination of ethylene-vinyl acetate copolymer and nanoparticles can improve the anti-electrical treeing performance of the cable insulation layer.

[0006] In a specific embodiment, the method for preparing the modified polypropylene comprises the following steps: Add diisopropylbenzene peroxide into ethanol and stir evenly to obtain an initiator solution; Under the protection of nitrogen, 4-propyleneoxy-2-hydroxybenzophenone and styrene derivatives were added to polypropylene, and stirred evenly to obtain a mixture A; The initiator solution was added dropwise to the mixed material A, and then stirred for reaction at 100-110° C., and then deionized water was added to continue the reaction, filtered, and dried to obtain modified polypropylene.

[0007] By adopting the above technical scheme, dicumyl peroxide is first dissolved in ethanol to obtain an initiator solution, 4-propyleneoxy-2-hydroxybenzophenone is grafted onto polypropylene, and styrene derivatives inhibit the macromolecular degradation of polypropylene, thereby obtaining modified polypropylene with good anti-electrical treeing performance.

[0008] In a specific embodiment, the weight ratio of the 4-propyleneoxy-2-hydroxybenzophenone, the styrene derivative, and the polypropylene is 1:(3-5):(45-55).

[0009] By adopting the above technical scheme, the ratio of 4-propyleneoxy-2-hydroxybenzophenone, styrene derivatives and polypropylene is further limited, thereby increasing the grafting rate of 4-propyleneoxy-2-hydroxybenzophenone and further improving the performance of the modified polypropylene.

[0010] In a specific embodiment, the method for preparing the modified filler comprises the following steps: Adding γ-aminopropyltriethoxysilane and an organic solvent into water, stirring and mixing evenly to obtain a spraying liquid; The nanoparticles are stirred and mixed evenly, and during the stirring process, a spraying liquid is sprayed into the nanoparticles. After the spraying is completed, the nanoparticles are stirred and dried to obtain a modified filler.

[0011] By adopting the above technical scheme, γ-aminopropyltriethoxysilane is dissolved in an organic solvent to obtain a spray liquid, and then the spray liquid is sprayed on the nanoparticles, stirred evenly, and dried, so that the γ-aminopropyltriethoxysilane is wrapped on the nanoparticles, the modification of the nanoparticles is completed, and a modified filler is obtained.

[0012] In a specific embodiment, the nanoparticles include a mixture of zinc oxide and titanium dioxide.

[0013] By adopting the above technical solution, zinc oxide can reduce the injection of charges and inhibit the accumulation of space charges, and titanium dioxide can produce a large number of deep traps to prevent the growth of electrical trees. Therefore, the combination of the two can improve the anti-electrical tree performance of the cable insulation layer.

[0014] In a specific embodiment, the weight ratio of the spraying liquid to the nanoparticles is 1:(13-14).

[0015] By adopting the above technical solution, the ratio of the spraying liquid to the nanoparticles is further limited, the modification effect of the nanoparticles is improved, and the γ-aminopropyltriethoxysilane can be better coated.

[0016] In a specific embodiment, the method for preparing the polypropylene cable insulation layer comprises the following steps: The modified polypropylene, ethylene-vinyl acetate copolymer, modified filler and antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the cable conductive core to form a polypropylene cable insulation layer.

[0017] By adopting the above technical scheme, the raw materials of modified polypropylene, ethylene-vinyl acetate copolymer, modified filler and antioxidant are firstly stirred and mixed evenly, and then extruded, dried and cooled to obtain a polypropylene cable insulation layer with good anti-electrical tree performance.

[0018] In the second aspect, the present application provides a method for detecting the performance of a polypropylene cable insulation layer for preventing electric branches, which adopts the following technical solution: A method for detecting the performance of an insulating layer of a polypropylene cable for preventing electric tree branches comprises the following steps: Sample preparation: The polypropylene cable insulation layer is made into n samples with a thickness of 4 mm, and each sample is 5 cm long and 1 cm wide; Detection: Insert the needle electrode into the sample 2mm deep, and observe the time of electrical tree formation for each sample at a voltage of 20kV, which are t1, t2, t3~tn in sequence, and calculate the average initiation time t of electrical tree formation, t=(t1+t2+t3+~+tn) / n.

[0019] By adopting the above technical solution, according to the average initiation time, the longer the average initiation time is, the better the anti-electrical tree performance of the cable insulation layer is.

[0020] In summary, the present application includes at least one of the following beneficial technical effects: 1. The dicumyl peroxide in the modified polypropylene in the present application can initiate free radicals of the matrix, so that 4-propyleneoxy-2-hydroxybenzophenone is grafted on the polypropylene, inhibiting the migration and precipitation of 4-propyleneoxy-2-hydroxybenzophenone, improving the anti-electrical treeing performance of the modified polypropylene, and the styrene derivatives and 4-propyleneoxy-2-hydroxybenzophenone can jointly inhibit the macromolecular degradation of polypropylene; the nanoparticles are modified by γ-aminopropyltriethoxysilane, which improves the dispersion performance of the nanoparticles, and γ-aminopropyltriethoxysilane can also couple the modified polypropylene with ethylene-vinyl acetate copolymer. The combination of ethylene-vinyl acetate copolymer and nanoparticles can improve the anti-electrical treeing performance of the cable insulation layer; 2. The zinc oxide in the modified filler in the present application can reduce the injection of charges and inhibit the accumulation of space charges, and the titanium dioxide can produce a large number of deep traps to prevent the growth of electrical dendrites. Therefore, the combination of the two can improve the anti-electrical dendrite performance of the obtained cable insulation layer; 3. The detection method in this application calculates the average initiation time. The longer the average initiation time is, the better the anti-electrical tree performance of the cable insulation layer is. DETAILED DESCRIPTION

[0021] The present application is further described in detail below with reference to the embodiments.

[0022] All raw materials in the examples can be obtained from the market, among which the styrene derivative is St, and the zinc oxide and titanium dioxide are both nano-grade.

[0023] Preparation Example Preparation Example 1 Preparation Example 1 provides a method for preparing modified polypropylene, comprising the following steps: Add dicumyl peroxide to ethanol and stir evenly to dissolve the dicumyl peroxide completely to obtain an initiator solution; Under the protection of nitrogen, 4-propyleneoxy-2-hydroxybenzophenone and styrene derivatives are added to polypropylene, and stirred evenly to obtain a mixture A; wherein the weight ratio of 4-propyleneoxy-2-hydroxybenzophenone, styrene derivatives and polypropylene is 1:2:40; the weight ratio of diisopropylbenzene peroxide and styrene derivatives is 1:40; The initiator solution was added dropwise to the mixture A, and then stirred and reacted at 105°C for 30 minutes, and then deionized water was added and stirred and reacted for 3 hours, filtered, and dried to obtain modified polypropylene; wherein the weight ratio of deionized water to polypropylene was 1:1.

[0024] Preparation Example 2 The difference between Preparation Example 2 and Preparation Example 1 is that the weight ratio of 4-propyleneoxy-2-hydroxybenzophenone, styrene derivative, and polypropylene is 1:3:45; the remaining steps are consistent with Preparation Example 1.

[0025] Preparation Example 3 The difference between Preparation Example 3 and Preparation Example 1 is that the weight ratio of 4-propyleneoxy-2-hydroxybenzophenone, styrene derivative and polypropylene is 1:4:50; the remaining steps are consistent with Preparation Example 1.

[0026] Preparation Example 4 The difference between Preparation Example 4 and Preparation Example 1 is that the weight ratio of 4-propyleneoxy-2-hydroxybenzophenone, styrene derivative and polypropylene is 1:5:55; the remaining steps are consistent with Preparation Example 1.

[0027] Preparation Example 5 The difference between Preparation Example 5 and Preparation Example 1 is that the weight ratio of 4-propyleneoxy-2-hydroxybenzophenone, styrene derivative and polypropylene is 1:6:60; the remaining steps are consistent with Preparation Example 1.

[0028] Preparation Example 6 Preparation Example 6 provides a method for preparing a modified filler, comprising the following steps: Add γ-aminopropyltriethoxysilane and an organic solvent into water, stir and mix evenly to obtain a spray liquid; wherein the organic solvent is ethanol; and the weight ratio of γ-aminopropyltriethoxysilane, the organic solvent, and water is 5:18:2; The nanoparticles are stirred and added into a mixer and mixed evenly. During the stirring process, the spraying liquid is sprayed onto the nanoparticles. After the spraying is completed, stirring is continued for 0.5 h, and the mixture is dried at 110° C. for 2 h to obtain a modified filler; wherein the nanoparticles are a mixture of zinc oxide and titanium dioxide, and the weight ratio of zinc oxide to titanium dioxide is 1:1; the weight ratio of the spraying liquid to the nanoparticles is 1:13.

[0029] Preparation Example 7 The difference between Preparation Example 7 and Preparation Example 6 is that the weight ratio of the spraying liquid to the nanoparticles is 1:13.5; the remaining steps are consistent with Preparation Example 6.

[0030] Preparation Example 8 The difference between Preparation Example 8 and Preparation Example 6 is that the weight ratio of the spraying liquid to the nanoparticles is 1:14; the remaining steps are consistent with Preparation Example 6.

[0031] Preparation Example 9 The difference between Preparation Example 9 and Preparation Example 7 is that the nanoparticles are zinc oxide; the remaining steps are consistent with Preparation Example 7.

[0032] Preparation Example 10 The difference between Preparation Example 10 and Preparation Example 7 is that the nanoparticles are titanium dioxide; the remaining steps are consistent with Preparation Example 7. Example

[0033] Example 1 Embodiment 1 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 1, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 6, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0034] Example 2 Embodiment 2 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 2, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 6, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0035] Example 3 Embodiment 3 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 3, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 6, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0036] Example 4 Embodiment 4 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 4, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 6, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0037] Example 5 Embodiment 5 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 5, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 6, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0038] Example 6 Embodiment 6 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 3, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 7, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0039] Example 7 Embodiment 7 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 3, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 8, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0040] Example 8 Embodiment 8 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 3, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 9, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0041] Example 9 Embodiment 9 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of the modified polypropylene in Preparation Example 3, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 10, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0042] Example 10 Embodiment 10 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 70 kg of the modified polypropylene in Preparation Example 3, 10 kg of ethylene-vinyl acetate copolymer, 5.5 kg of the modified filler in Preparation Example 7, and 0.5 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0043] Embodiment 11 Embodiment 11 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 90 kg of the modified polypropylene in Preparation Example 3, 15 kg of ethylene-vinyl acetate copolymer, 8 kg of the modified filler in Preparation Example 7, and 1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0044] Comparative Example Comparative Example 1 Comparative Example 1 provides a method for preparing an anti-electrical tree polypropylene cable insulation layer, comprising the following steps: 50 kg of polypropylene, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of the modified filler in Preparation Example 6, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0045] Comparative Example 2 Comparative Example 2 provides a method for preparing an insulating layer of a polypropylene cable having an anti-electrical tree structure, comprising the following steps: 55 kg of the modified polypropylene in Preparation Example 1, 3 kg of the modified filler in Preparation Example 6, and 0.1 kg of an antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried, and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the conductive core of the cable to form a polypropylene cable insulation layer; wherein the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

[0046] Comparative Example 3 Comparative Example 3 provides a method for preparing a polypropylene cable insulation layer for preventing electric tree branches, comprising the following steps: 50 kg of modified polypropylene in Preparation Example 1, 5 kg of ethylene-vinyl acetate copolymer, 3 kg of filler and 0.1 kg of antioxidant were stirred and mixed uniformly to obtain a mixture B; then the mixture B was melt-extruded and granulated, dried and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material was extruded on the cable conductive core to form a polypropylene cable insulation layer; wherein the antioxidant was pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; and the filler was a mixture of zinc oxide and titanium dioxide, and the weight ratio of zinc oxide to titanium dioxide was 1:1.

[0047] Performance testing Anti-electrical treeing performance: The polypropylene cable insulation layer is made into n samples with a thickness of 4 mm, and the length of each sample is 5 cm and the width is 1 cm. In this application, n is 20; the needle electrode is inserted into the sample 2 mm deep, and the time of electrical treeing of each sample is observed under a voltage of 20 kV, and recorded as t1, t2, t3~tn in sequence. The average initiation time t of electrical treeing is calculated, t=(t1+t2+t3+~+tn) / n. The longer the average initiation time, the better the anti-electrical treeing performance of the cable insulation layer.

[0048] Table 1 Performance test results of cable insulation layer sample Average initiation time (min) Example 1 30.2 Example 2 33.8 Example 3 34.2 Example 4 34.0 Example 5 31.1 Example 6 35.8 Example 7 35.0 Example 8 31.3 Example 9 31.5 Example 10 36.9 Embodiment 11 36.0 Comparative Example 1 22.5 Comparative Example 2 25.6 Comparative Example 3 25.1 Combining Example 1 and Comparative Examples 1-3, the anti-electrical treeing performance of the cable insulation layer in Example 1 is the best. It can be seen that when preparing the insulation layer, the raw material is polypropylene grafted with 4-propyleneoxy-2-hydroxybenzophenone, and γ-aminopropyltriethoxysilane-modified nanoparticles and ethylene-vinyl acetate copolymer are added. The combination of the two improves the anti-electrical treeing performance of the prepared cable insulation layer.

[0049] In combination with Examples 1-5, the cable insulation layer in Examples 2-4 has good anti-electrical treeing performance. It can be seen that when preparing modified polypropylene, the ratio of 4-propyleneoxy-2-hydroxybenzophenone, styrene derivatives, and polypropylene is preferably 1: (3-5): (45-55), and the performance of the modified polypropylene obtained is better.

[0050] Combining Example 3, Example 6 and Example 7, the anti-electrical tree performance of the cable insulation layer in Example 6 is the best. It can be seen that when preparing the modified filler, when the weight ratio of the spray liquid to the nanoparticles is 1: (13-14), increasing the amount of nanoparticles added, the modification effect of the nanoparticles shows a trend of first increasing and then decreasing.

[0051] In combination with Example 6, Example 8 and Example 9, the cable insulation layer in Example 6 has the best anti-electrical treeing performance. It can be seen that when preparing the modified filler, the nanoparticles are preferably a mixture of zinc oxide and titanium dioxide. Zinc oxide can reduce the injection of charges and inhibit the accumulation of space charges. Titanium dioxide can produce a large number of deep traps to prevent the growth of electrical trees. Therefore, the use of nanoparticles composed of the two can improve the anti-electrical treeing performance of the prepared cable insulation layer.

[0052] Combining Example 6, Example 10 and Example 11, the anti-electrical tree performance of the cable insulation layer in Example 10 is the best. It can be seen that when preparing the insulation layer, increasing the amount of raw materials used, the anti-electrical tree performance of the cable insulation layer shows a trend of first increasing and then decreasing.

[0053] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A polypropylene cable insulation layer for preventing electric branches, characterized in that: The raw materials of the cable insulation layer include the following components in parts by weight: 50-90 parts of modified polypropylene, 5-15 parts of ethylene-vinyl acetate copolymer, 3-8 parts of modified filler, and 0.1-1 part of antioxidant; the raw materials of the modified polypropylene include polypropylene, 4-propyleneoxy-2-hydroxybenzophenone, diisopropyl peroxide, and styrene derivatives; the raw materials of the modified filler include nanoparticles, γ-aminopropyltriethoxysilane, and an organic solvent.

2. The polypropylene cable insulation layer for preventing electric branches according to claim 1 is characterized in that: The preparation method of the modified polypropylene comprises the following steps: Add diisopropylbenzene peroxide into ethanol and stir evenly to obtain an initiator solution; Under the protection of nitrogen, 4-propyleneoxy-2-hydroxybenzophenone and styrene derivatives were added to polypropylene, and stirred evenly to obtain a mixture A; The initiator solution was added dropwise to the mixed material A, and then stirred for reaction at 100-110° C., and then deionized water was added to continue the reaction, filtered, and dried to obtain modified polypropylene.

3. The polypropylene cable insulation layer for preventing electric branches according to claim 2 is characterized in that: The weight ratio of the 4-propyleneoxy-2-hydroxybenzophenone, the styrene derivative and the polypropylene is 1:(3-5):(45-55).

4. The polypropylene cable insulation layer for preventing electric branches according to claim 1 is characterized in that: The preparation method of the modified filler comprises the following steps: Adding γ-aminopropyltriethoxysilane and an organic solvent into water, stirring and mixing evenly to obtain a spraying liquid; The nanoparticles are stirred and mixed evenly, and during the stirring process, a spraying liquid is sprayed into the nanoparticles. After the spraying is completed, the nanoparticles are stirred and dried to obtain a modified filler.

5. The polypropylene cable insulation layer for preventing electric branches according to claim 4 is characterized by: The nanoparticles include a mixture of zinc oxide and titanium dioxide.

6. The polypropylene cable insulation layer for preventing electric branches according to claim 5, characterized in that: The weight ratio of the spraying liquid to the nanoparticles is 1:(13-14).

7. The polypropylene cable insulation layer for preventing electric branches according to claim 1 is characterized by: The preparation method of the polypropylene cable insulation layer comprises the following steps: The modified polypropylene, ethylene-vinyl acetate copolymer, modified filler and antioxidant are stirred and mixed uniformly to obtain a mixture B; the mixture B is then melt-extruded and granulated, dried and cooled to obtain a polypropylene cable insulation material, and then the polypropylene cable insulation material is extruded onto the cable conductive core to form a polypropylene cable insulation layer.

8. A method for testing the performance of the insulation layer of a polypropylene cable for preventing electric tree branches according to any one of claims 1 to 7, characterized in that: The following steps are involved: Sample preparation: The polypropylene cable insulation layer is made into n samples with a thickness of 4 mm, and each sample is 5 cm long and 1 cm wide; Detection: Insert the needle electrode into the sample at a depth of 2mm. Under a voltage of 20kV, observe the time of electrical treeing of each sample, which are t1, t2, t3~tn in sequence. Calculate the average initiation time t of electrical treeing, t=(t1+t2+t3+~+tn) / n.