Scorch-resistant direct-current cable insulating material and preparation method thereof

Abstract

The invention belongs to the technical field of insulating materials, and discloses a scorch-resistant direct current cable insulating material and a preparation method thereof, and the scorch-resistant direct current cable insulating material comprises the following components in parts by mass: 100 parts of low density polyethylene, 0.15-0.20 part of an antioxidant, 1.6-1.8 parts of a cross-linking agent, and 0.05-0.40 part of a chain transfer agent 2, 4-diphenyl-4-methylpentene. According to the invention, 2, 4-diphenyl-4-methylpentene is used as a chain transfer agent to be added into low-density polyethylene, and the free radical cross-linking reaction of the low-density polyethylene is regulated and controlled, so that the scorching resistance and direct-current breakdown performance of the cross-linked polyethylene cable insulating material are remarkably improved, and meanwhile, a relatively high cross-linking degree is ensured. The cable insulation material provided by the invention has excellent scorch resistance and direct current breakdown performance, and has a good application prospect in the field of long-distance and high-voltage-grade cable insulation manufacturing.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulating materials, and particularly relates to a DC cable insulating material with excellent scorch resistance and a preparation method thereof. Background Art

[0002] With the continuous development of offshore renewable energy, the technology of offshore wind power is becoming increasingly mature, and the requirements for the voltage level and transmission distance of offshore DC power transmission are gradually increasing. Cross-linked polyethylene insulating material is the main insulating form of high-voltage DC cables. At present, it is urgent to improve its long-length extrusion processing performance and insulating performance after cross-linking molding to meet the requirements of long-distance high-voltage DC cables. However, when extruding cross-linked polyethylene insulating material in a long length, local high temperature is likely to occur during the continuous extrusion molding process due to the shearing action of the screw and the heat generated by its own viscosity, which further accelerates the decomposition of the cross-linking agent, promotes the formation of free radicals in the polyethylene molecular chain, and then cross-linking reaction occurs. This premature cross-linking reaction during the processing is called scorch phenomenon. Scorch will cause the premature formation of a cross-linking network inside the insulating material and generate gels. The rheological properties of these gels are quite different from those of the uncross-linked insulating material melt, resulting in poor stability of the melt flow state, affecting the stability of insulating extrusion molding, and ultimately affecting the electrical performance of the high-voltage DC cable after molding. Therefore, in order to improve the scorch resistance of insulating materials, scholars at home and abroad often achieve it by slowing down the cross-linking reaction of low-density polyethylene. Generally, reducing the content of the cross-linking agent or increasing the content of the antioxidant is used to delay the cross-linking reaction. However, although these methods improve the scorch resistance of insulating materials to a certain extent, they will cause a significant decrease in the cross-linking degree of the cross-linked insulation, directly affecting the electrical, thermal, and mechanical properties of the cable insulation. In addition, the presence of additives such as cross-linking agents will produce a large number of by-products, causing insulation defects. If the amount of the cross-linking agent can be reduced while ensuring a high cross-linking degree of the cable insulation, the purity of the cable insulating material will be greatly improved. At present, the mutually restrictive relationship between the scorch resistance and electrical performance of DC cable insulating materials limits the development of high-voltage DC cables towards long distances and high voltage levels. Summary of the Invention

[0003] To solve the problems existing in the prior art, the purpose of the present invention is to provide a DC cable insulating material with excellent scorch resistance and a preparation method thereof. The cable insulating material provided by the present invention has excellent scorch resistance, ensures a high cross-linking degree while improving the purity, and the cross-linked cable insulating material has high DC breakdown performance.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A DC cable insulating material with excellent scorch resistance, in parts by mass, its components include:

[0006] 100 parts of low-density polyethylene, 0.15 to 0.20 parts of 4,4'-thiobis(6-tert-butyl-3-methylphenol), 1.6 to 1.8 parts of crosslinking agent, 0.05 to 0.40 parts of 2,4-diphenyl-4-methylpentene.

[0007] Preferably, the density of the low-density polyethylene is 0.90 to 0.95 g / cm 3 , and the melt mass flow rate under the conditions of 190 °C and 2.16 kg is 1.5 to 2.5 g / 10 min.

[0008] Preferably, the crosslinking agent is dicumyl peroxide.

[0009] Preferably, the scorch resistance time of the scorch-resistant DC cable insulating material is 738 to 1140 s, and the crosslinking degree is 83.05% to 86.91%.

[0010] Preferably, the DC breakdown field strength of the scorch-resistant DC cable insulating material at 24-26 °C is 413.30 to 485.71 kV / mm, and the DC breakdown field strength at 69-71 °C is 287.20 to 356.32 kV / mm.

[0011] The present invention also provides a preparation method of the scorch-resistant DC cable insulating material as described above, including the following processes:

[0012] Melting the low-density polyethylene at a temperature of 115 °C to 120 °C;

[0013] Adding 4,4'-thiobis(6-tert-butyl-o-cresol) to the molten low-density polyethylene, and performing melt blending at a temperature of 115 °C to 120 °C to obtain a mixture M1;

[0014] Adding the crosslinking agent and 2,4-diphenyl-4-methylpentene to the mixture M1, and performing blending at a temperature of 115 °C to 120 °C to obtain a mixture M2;

[0015] Cooling the mixture M2 to obtain the scorch-resistant DC cable insulating material.

[0016] Preferably, the low-density polyethylene is placed in a twin-screw internal mixer and melted at a temperature of 115 °C to 120 °C;

[0017] Among them, the twin-screw rotation speed is 10 to 30 r / min, and the melting time is 10 to 30 min.

[0018] Preferably, 4,4'-thiobis(6-tert-butyl-3-methylphenol) is added to the twin-screw internal mixer and blended with the low-density polyethylene melt to obtain a mixture M1;

[0019] Among them, the blending temperature is 115°C to 125°C, the twin-screw rotation speed is 18 to 30 r / min, and the blending time is 5 to 15 min.

[0020] Preferably, the crosslinking agent and 2,4-diphenyl-4-methylpentene are simultaneously added into a twin-screw internal mixer and blended with the mixture M1 to obtain a mixture M2.

[0021] Among them, the blending temperature is 115°C to 125°C, the twin-screw rotation speed is 18 to 30 r / min, and the blending time is 5 to 10 min.

[0022] Preferably, the mixture M2 is taken out from the cavity of the twin-screw internal mixer and naturally cooled to room temperature to obtain the scorch-resistant cable insulating material.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The composition of the scorch-resistant DC cable insulating material provided by the present invention includes: low-density polyethylene, antioxidant, crosslinking agent, and environmentally friendly chain transfer agent; among them, the antioxidant is 4,4'-thiobis(6-tert-butyl-3-methylphenol), the crosslinking agent is dicumyl peroxide, and the chain transfer agent is 2,4-diphenyl-4-methylpentene. By innovatively adding a chain transfer agent in addition to the antioxidant and crosslinking agent in low-density polyethylene, a compound system is formed, reducing the dosage of the crosslinking agent. The chain transfer agent can regulate the crosslinking process of polyethylene macromolecular free radicals, delay the crosslinking time during processing, and improve the scorch-resistant performance; at the same time, 2,4-diphenyl-4-methylpentene can promote the later free radical crosslinking process of low-density polyethylene, and a denser crosslinked structure can be formed at a low crosslinking agent content, improving the crosslinking degree of crosslinked polyethylene. The crosslinked DC cable insulating material has high DC breakdown performance. The cable insulating material provided by the present invention has excellent scorch-resistant performance and DC breakdown performance, and has good application prospects in the field of manufacturing high-voltage DC cable insulation with long distances and high voltage levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to clarify the present invention more clearly, the following will briefly introduce the drawings required in the embodiments. The drawings in the following description are only embodiments of the present invention. For those of ordinary skill in the art, other drawings of embodiments can also be obtained based on the provided drawings without creative efforts.

[0026] Figure 1 It is a test chart of the scorch-resistant time of the cable insulating materials of all the embodiments and comparative examples provided by the present invention;

[0027] Figure 2It is a comparison chart of the scorch resistance time and gel content of the cable insulation materials of all the embodiments and comparative examples provided by the present invention;

[0028] Figure 3 It is a Weibull distribution diagram of the DC breakdown field strength of the cable insulation materials of all the embodiments and comparative examples provided by the present invention at room temperature (25±1°C).

[0029] Figure 4 It is a Weibull distribution diagram of the DC breakdown field strength of the cable insulation materials of all the embodiments and comparative examples provided by the present invention at high temperature (70±1°C).

[0030] Figure 5 It is a comparison chart of the DC breakdown field strength of the cable insulation materials of all the embodiments and comparative examples provided by the present invention. Detailed Description of the Invention

[0031] The technical solutions in the embodiments of the present invention will be described completely and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] The present invention provides a scorch-resistant DC cable insulation material, the components of which include: low-density polyethylene, hindered phenol antioxidant, crosslinking agent and environmentally friendly chain transfer agent.

[0033] In the cable insulation material provided by the present invention, the low-density polyethylene is low-density polyethylene, and its source has no special limitation and can be a general domestic commercially available brand; the density of the low-density polyethylene in the embodiment is preferably 0.90-0.95 g / cm 3 , and the low-density polyethylene with a density of 0.92 g / cm is used in the following embodiments and comparative examples of the present invention; 3 The melt mass flow rate of the low-density polyethylene (under the conditions of 190°C and 2.16 kg) is preferably 1.5-2.5 g / 10 min, and the low-density polyethylene in the following embodiments and comparative examples of the present invention is 2.3 g / 10 min.

[0034] In the cable insulation material provided by the present invention, the hindered phenol antioxidant is 4,4'-thiobis(6-tert-butyl-3-methylphenol), the crosslinking agent is dicumyl peroxide, and the chain transfer agent is 2,4-diphenyl-4-methylpentene, all of which are generally commercially available.

[0035] In the scorch-resistant DC cable insulation material of the present invention, by mass fraction, the mass fraction of low-density polyethylene is 100 parts, the mass fraction of 4,4'-thiobis(6-tert-butyl-o-cresol) is 0.15 - 0.20 parts; the mass fraction of dicumyl peroxide is 1.6 - 1.8 parts; the mass fraction of 2,4-diphenyl-4-methylpentene is 0.05 - 0.40 parts.

[0036] The preparation method of the above-mentioned scorch-resistant DC cable insulation material of the present invention comprises the following steps:

[0037] Step 1: Weigh low-density polyethylene, antioxidant, cross-linking agent and chain transfer agent respectively according to the above mass fractions for later use;

[0038] Step 2: Add the low-density polyethylene weighed in Step 1 into the cavity of a small twin-screw internal mixer and completely melt it for later use;

[0039] Step 3: Add the antioxidant weighed in Step 1 into the melted low-density polyethylene in Step 2 and blend them in the small twin-screw internal mixer for later use;

[0040] Step 4: Add the dicumyl peroxide and 2,4-diphenyl-4-methylpentene weighed in Step 1 into the mixture in Step 3 simultaneously and blend them in the small twin-screw internal mixer for later use.

[0041] Step 5: Take out the sample from the small twin-screw internal mixer and cool it to room temperature to obtain the scorch-resistant DC cable insulation material of the present invention.

[0042] In the preparation method provided by the present invention, the model of the small twin-screw internal mixer is not particularly limited. The small twin-screw internal mixer (mixing torque rheometer) with the model RM-200C is used in the following examples and comparative examples of the present invention;

[0043] In the preparation method provided by the present invention, the preferred experimental conditions for Step 2 are as follows: the melting temperature is 115°C - 120°C, and the temperature set in the following examples and comparative examples of the present invention is 118°C; the screw speed of the small twin-screw internal mixer is 10 - 30 r / min, and the screw speed set in the following examples and comparative examples of the present invention is 20 r / min; the melting time is 10 - 30 min, and the melting time in the following examples and comparative examples of the present invention is 15 min;

[0044] In the preparation method provided by the present invention, the preferred experimental conditions for step 3 are as follows: the blending temperature is 115°C to 125°C, and the temperature set in the following examples and comparative examples of the present invention is 118°C; the screw speed of the twin-screw small internal mixer is 18 to 30 r / min, and the screw speed set in the following examples and comparative examples of the present invention is 25 r / min, the blending time is 5 to 15 min, and the blending time in the following examples and comparative examples of the present invention is 10 min;

[0045] In the preparation method provided by the present invention, the preferred experimental conditions for step 4 are as follows: the blending temperature is 115°C to 125°C, and the temperature set in the following examples and comparative examples of the present invention is 118°C; the screw speed of the twin-screw small internal mixer is 18 to 30 r / min, and the screw speed set in the following examples and comparative examples of the present invention is 25 r / min; the blending time is 5 to 10 min, and the blending time in the following examples and comparative examples of the present invention is 5 min;

[0046] In the preparation method provided by the present invention, the cooling in step 5 is preferably natural cooling to room temperature, and the laboratory room temperature is 20 to 25°C.

[0047] For the sake of clarity, the following examples and comparative examples are used for detailed description.

[0048] Example 1

[0049] The preparation method of the scorch-resistant DC cable insulating material in this example includes the following steps:

[0050] Add 30 g of low-density polyethylene into a twin-screw small internal mixer, set the screw speed to 20 r / min in the control software, set the temperatures of both the twin-screw and the cavity to 118°C, and the melting time to 15 min; at this time, the low-density polyethylene has completely melted, adjust the twin-screw speed to increase to 25 r / min; after the speed stabilizes, add 0.045 g of 4,4'-thiobis(6-tert-butyl-3-methylphenol) into the cavity, the blending temperature is still set to 118°C, and the blending time is 10 min; then add 0.54 g of dicumyl peroxide and 0.015 g of 2,4-diphenyl-4-methylpentene simultaneously, keep the screw speed and each temperature unchanged, and the blending time is 5 min. Finally, take out the sample and cool it to room temperature to obtain a scorch-resistant DC cable insulating material.

[0051] Example 2

[0052] The preparation method of the scorch-resistant DC cable insulating material in this example includes the following steps:

[0053] Add 30 g of low-density polyethylene into a small twin-screw internal mixer. Set the screw speed to 20 r / min in the control software, and set the temperatures of both the twin-screws and the cavity to 118 °C. The melting time is 15 min. At this time, the low-density polyethylene has been completely melted. Adjust the twin-screw speed to increase to 25 r / min. After the speed is stable, add 0.06 g of 4,4'-thiobis(6-tert-butyl-3-methylphenol) into the cavity. The blending temperature is still set to 118 °C, and the blending time is 10 min. Subsequently, add 0.48 g of dicumyl peroxide and 0.03 g of 2,4-diphenyl-4-methylpentene simultaneously. The screw speed and each temperature remain unchanged, and the blending time is 5 min. Finally, take out the sample and cool it to room temperature to obtain a scorch-resistant DC cable insulating material.

[0054] Example 3

[0055] The preparation method of the scorch-resistant DC cable insulating material in this example includes the following steps:

[0056] Add 30 g of low-density polyethylene into a small twin-screw internal mixer. Set the screw speed to 20 r / min in the control software, and set the temperatures of both the twin-screws and the cavity to 118 °C. The melting time is 15 min. At this time, the low-density polyethylene has been completely melted. Adjust the twin-screw speed to increase to 25 r / min. After the speed is stable, add 0.06 g of 4,4'-thiobis(6-tert-butyl-3-methylphenol) into the cavity. The blending temperature is still set to 118 °C, and the blending time is 10 min. Subsequently, add 0.48 g of dicumyl peroxide and 0.06 g of 2,4-diphenyl-4-methylpentene simultaneously. The screw speed and each temperature remain unchanged, and the blending time is 5 min. Finally, take out the sample and cool it to room temperature to obtain a scorch-resistant DC cable insulating material.

[0057] Example 4

[0058] The preparation method of the scorch-resistant DC cable insulating material in this example includes the following steps:

[0059] Add 30 g of low-density polyethylene into a small twin-screw internal mixer. Set the screw speed to 20 r / min in the control software, and set the temperatures of both the twin-screws and the cavity to 118 °C. The melting time is 15 min. At this time, the low-density polyethylene has been completely melted. Adjust the twin-screw speed to increase to 25 r / min. After the speed is stable, add 0.06 g of 4,4'-thiobis(6-tert-butyl-3-methylphenol) into the cavity. The blending temperature is still set to 118 °C, and the blending time is 10 min. Subsequently, add 0.48 g of dicumyl peroxide and 0.12 g of 2,4-diphenyl-4-methylpentene simultaneously. The screw speed and each temperature remain unchanged, and the blending time is 5 min. Finally, take out the sample and cool it to room temperature to obtain a scorch-resistant DC cable insulating material.

[0060] Comparative Example 1

[0061] A common formulation for cable insulation materials was selected. The low-density polyethylene was the same as that in Examples 1-4. The crosslinking agent was the same dicumyl peroxide as in Examples 1-4, and the antioxidant was the same 4,4'-thiobis(6-tert-butyl-3-methylphenol) as in Examples 1-4. 30 g of low-density polyethylene was added to a small twin-screw internal mixer. The screw speed was set at 20 r / min in the control software, and the temperatures of both the twin-screw and the cavity were set at 118 °C. The melting time was 15 min. At this time, the low-density polyethylene had completely melted, and the twin-screw speed was adjusted to increase to 25 r / min. After the speed stabilized, 0.06 g of 4,4'-thiobis(6-tert-butyl-3-methylphenol) was added to the cavity. The blending temperature was still set at 118 °C, and the blending time was 10 min. Subsequently, 0.54 g of dicumyl peroxide was added simultaneously. The screw speed and each temperature remained unchanged, and the blending time was 5 min. Finally, the sample was taken out and cooled to room temperature to obtain a comparative cable insulation material.

[0062] Comparative Example 2

[0063] A formulation for cable insulation materials that improves the scorch resistance by reducing the crosslinking agent was selected. The low-density polyethylene was the same as that in Examples 1-4. The crosslinking agent was the same dicumyl peroxide as in Examples 1-4, and the antioxidant was the same 4,4'-thiobis(6-tert-butyl-3-methylphenol) as in Examples 1-4. 30 g of low-density polyethylene was added to a small twin-screw internal mixer. The screw speed was set at 20 r / min in the control software, and the temperatures of both the twin-screw and the cavity were set at 118 °C. The melting time was 15 min. At this time, the low-density polyethylene had completely melted, and the twin-screw speed was adjusted to increase to 25 r / min. After the speed stabilized, 0.06 g of 4,4'-thiobis(6-tert-butyl-3-methylphenol) was added to the cavity. The blending temperature was still set at 118 °C, and the blending time was 10 min. Subsequently, 0.48 g of dicumyl peroxide was added simultaneously. The screw speed and each temperature remained unchanged, and the blending time was 5 min. Finally, the sample was taken out and cooled to room temperature to obtain a comparative cable insulation material.

[0064] Comparative Example 3

[0065] A commercially available cable insulation material with the brand name HFDG-4201 was selected, and its components include low-density polyethylene, antioxidant, and crosslinking agent. 30 g of commercial cable insulation pellets were added to a small twin-screw internal mixer. The screw speed was set at 20 r / min in the control software, and the temperatures of both the twin-screw and the cavity were set at 118 °C, with a melting time of 15 min. After the commercial insulation material was completely melted, the screw speed was adjusted to increase to 25 r / min. After the speed stabilized, the internal mixing temperature was maintained at 118 °C, and the internal mixing time was 15 min. Finally, the specimen was taken out and cooled to room temperature to obtain a comparative cable insulation material.

[0066] Performance Test

[0067] Samples of cable insulation materials obtained from each example and comparative example were prepared according to different test requirements, and experimental tests of scorch time, crosslinking degree, and DC breakdown were carried out.

[0068] Experimental specimen for scorch time: Using a flat vulcanizer, each cable insulation material was preheated at 118 °C and 5 Mpa for 5 min, and then hot-pressed at 118 °C and 15 MPa for 5 min to obtain circular thin specimens with a diameter of 25 mm and a thickness of 1 mm for testing.

[0069] Experimental test for scorch time: Using a rotational rheometer to conduct dynamic rheological tests on the above circular thin specimens, the PP25 type rotor was selected, the test temperature was 150 °C, the fixed shear frequency was 3.14 rad / s, the constant strain was 1%, and the process of the storage modulus changing with time was tested. The moment when the storage modulus reached 50000 Pa was defined as the scorch time.

[0070] Experimental specimen for crosslinking degree: Using a flat vulcanizer, the insulation material was preheated at 118 °C and 5 Mpa for 5 min, then hot-pressed at 118 °C and 15 MPa for 5 min, and then hot-pressed at 180 °C and 15 MPa for 15 min to obtain square thin specimens of crosslinked polyethylene with a side length of 100 mm and a thickness of 0.5 mm for testing.

[0071] Experimental test for crosslinking degree: According to the standard JB / T 10437-2004, the gel content test was carried out on the above obtained square thin specimens, and the gel content is the crosslinking degree of the insulation material.

[0072] Experimental specimen for DC breakdown: Using a flat vulcanizer, the insulation material was preheated at 118 °C for 5 min, then hot-pressed at 118 °C and 15 MPa for 5 min, and then hot-pressed at 180 °C and 15 MPa for 15 min to obtain square thin specimens with a side length of 100 mm and a thickness of 0.1 mm for testing.

[0073] DC breakdown experiment test: The HJC-100 type breakdown experiment equipment was used, and spherical-spherical electrodes were selected. The electrode material was brass, the diameter of the electrode was 12.5 mm, and the set voltage rising rate was 1 kV / s. During the experiment, both the electrodes and the test specimens were immersed in transformer oil to prevent surface discharge. Under the conditions of room temperature (25±1°C) and high temperature (70±1°C), 16 effective data points were measured for each specimen, and the Weibull distribution was used to analyze the breakdown data.

[0074] The curves of the storage modulus of different cable insulation materials changing with time are as Figure 1 shown. The scorch resistance time of each specimen was statistically counted at the moment when the storage modulus reached 50,000 Pa. The test results and comparisons of the scorch resistance time of different cable insulation materials are shown in Table 1 and Figure 2 shown.

[0075] Table 1

[0076]

[0077] From Table 1, Figure 1 and Figure 2 it can be seen that the scorch resistance time of the scorch-resistant DC cable insulation material prepared by the present invention is 738 - 1140 s, and the crosslinking degree is 83.05% - 86.91%. Compared with the commonly used cable insulation material formula (Comparative Example 1), adding a chain transfer agent (Example 1) can significantly extend the scorch resistance time; although Comparative Example 2 increased the scorch resistance time by reducing the crosslinking agent content, the crosslinking degree decreased, while Examples 2 - 4 with added chain transfer agents can further increase the scorch resistance time on this basis while maintaining a high crosslinking degree; when the content of the chain transfer agent is 0.2 parts (Example 3), its crosslinking degree is even higher than that of Example 1 and Comparative Example 2 with more crosslinking agents. Therefore, it can be concluded that adding a chain transfer agent realizes improving the scorch resistance performance of the cable insulation material under the condition of low crosslinking agent and high purity, and at the same time can ensure a relatively high crosslinking degree. In addition, the scorch resistance performance of all examples is better than that of the commercial cable insulation material (Comparative Example 3), and the crosslinking degree is also higher than that of the commercial cable insulation material.

[0078] The DC breakdown results of different cable insulation materials at room temperature and high temperature are as Figure 3 and Figure 4 shown, and the data statistics and comparisons are shown in Table 2 and Figure 5 shown.

[0079] Table 2

[0080]

[0081] From Table 2, Figure 3 , Figure 4 and Figure 5It can be seen that the DC breakdown field strength of the scorch-resistant DC cable insulation material obtained in the present invention at room temperature (25 ± 1°C) is 413.30 - 485.71 kV / mm, and at high temperature (70 ± 1°C) is 287.20 - 356.32 kV / mm.

[0082] At room temperature and high temperature, compared with the commonly used cable insulation material formulations (Comparative Example 1 and Comparative Example 2) and commercial cable insulation materials (Comparative Example 3), adding a chain transfer agent at the same crosslinking agent content can improve the DC breakdown field strength of the cable insulation material. When the addition amount of the chain transfer agent is 0.2 parts (Example 3), even with a lower crosslinking agent content, it shows excellent DC breakdown field strength, even higher than the insulation materials containing more crosslinking agents (Example 1 and Comparative Example 2).

[0083] From the above experimental results, it can be seen that by adding 2,4-diphenyl-4-methylpentene as a chain transfer agent to low-density polyethylene in the present invention, regulating its free radical crosslinking reaction, the scorch resistance and DC breakdown performance of the crosslinked polyethylene cable insulation material are significantly improved, while ensuring a relatively high degree of crosslinking. The cable insulation material provided by the present invention has excellent scorch resistance and DC breakdown performance, and has good application prospects in the field of cable insulation manufacturing for long-distance and high-voltage levels.

[0084] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, other embodiments can be achieved without departing from the principle of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, and obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A DC cable insulation material resistant to scorching, characterized in that, In parts by mass, its components include: 100 parts of low-density polyethylene, 0.15 - 0.20 parts of 4,4'-thiobis(6-tert-butyl-3-methylphenol), 1.6 - 1.8 parts of crosslinking agent, 0.05 - 0.40 parts of 2,4-diphenyl-4-methylpentene.

2. The charateristic of a DC cable insulation material resistant to scorching as claimed in claim 1 is that The density of the low-density polyethylene is 0.90 to 0.95 g / cm 3 , and the melt mass flow rate under the conditions of 190 °C and 2.16 kg is 1.5 to 2.5 g / 10 min.

3. The scorch-resistant DC cable insulation material according to claim 1, characterized in that, The crosslinking agent used is dicumyl peroxide.

4. The scorch-resistant DC cable insulating material according to claim 1, characterized in that, The scorch resistance time of the scorch-resistant DC cable insulating material is 738 - 1140 s, and the crosslinking degree is 83.05% - 86.91%.

5. The charateristic of a kind of DC cable insulation material resistant to scorching as claimed in claim 1 is that, The DC breakdown field strength of the scorch-resistant DC cable insulating material is 413.30 - 485.71 kV / mm at 24 - 26 °C, and 287.20 - 356.32 kV / mm at 69 - 71 °C.

6. The preparation method of the scorch-resistant DC cable insulating material according to any one of claims 1-5, characterized in that, It includes the following process: Melt the low-density polyethylene at a temperature of 115 °C - 120 °C; Add 4,4'-thiobis(6-tert-butyl-o-cresol) into the molten low-density polyethylene, and conduct melt blending at a temperature of 115 °C - 120 °C to obtain mixture M1; Add the crosslinking agent and 2,4-diphenyl-4-methylpentene into mixture M1, and conduct blending at a temperature of 115 °C - 120 °C to obtain mixture M2; Cool mixture M2 to obtain the scorch-resistant DC cable insulating material.

7. The preparation method of the scorch-resistant DC cable insulating material according to claim 6, characterized in that, Place the low-density polyethylene in a twin-screw internal mixer and melt it at a temperature of 115 °C - 120 °C; Among them, the twin-screw rotation speed is 10 - 30 r / min, and the melting time is 10 - 30 min.

8. The preparation method of the scorch-resistant DC cable insulating material according to claim 7, characterized in that, Add 4,4'-thiobis(6-tert-butyl-3-methylphenol) into the twin-screw internal mixer and conduct blending with the low-density polyethylene melt to obtain mixture M1; Among them, the blending temperature is 115 °C - 125 °C, the twin-screw rotation speed is 18 - 30 r / min, and the blending time is 5 - 15 min.

9. The preparation method of the scorch-resistant DC cable insulating material according to claim 7, characterized in that, Add the crosslinking agent and 2,4-diphenyl-4-methylpentene into the twin-screw internal mixer simultaneously and conduct blending with mixture M1 to obtain mixture M2; Among them, the blending temperature is 115 °C - 125 °C, the twin-screw rotation speed is 18 - 30 r / min, and the blending time is 5 - 10 min.

10. The preparation method of the scorch-resistant DC cable insulating material according to claim 7, characterized in that Take out mixture M2 from the cavity of the twin-screw internal mixer and naturally cool it to room temperature to obtain the scorch-resistant cable insulating material.

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