A high dielectric performance polypropylene cable insulation material resistant to long-term electrical aging and a preparation method thereof

Abstract

The present invention proposes a polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging and a preparation method thereof, and belongs to the technical field of electrical material synthesis and preparation. In terms of mass fraction, the cable insulation material comprises 40 to 60 parts of polypropylene, 20 to 40 parts of polymer elastomer, 10 to 20 parts of thermal conductive filler, and 1 to 3 parts of free radical regulated voltage stabilizer. Among them, the voltage stabilizer is a small molecule compound containing a xanthate group, and the general structural formula is:, R1 is one of methyl, ethyl, isopropyl or n-butyl, which has a regulating effect on the free radical reaction during the electrical aging and thermal oxidation aging of polypropylene. The present invention proposes to mix polypropylene and a voltage stabilizer that can regulate the free radical reaction uniformly, obtain a blended masterbatch after melt blending, extrusion, cooling, drying, and pelletizing, and then mix the blended masterbatch with the polymer elastomer and melt extrude to obtain a polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging.

Description

Technical Field

[0001] The invention relates to the technical field of electrical material synthesis and preparation, and in particular to a polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging and a preparation method thereof. Background Art

[0002] Compared with traditional cross-linked polyethylene cable insulation materials, polypropylene cable insulation materials are resistant to high temperatures, with long-term working temperatures of up to 100~120°C. They also have higher breakdown strength and volume resistivity, and the production process is relatively simple, without the need for vulcanization. They have high production efficiency, low energy consumption, and are green and environmentally friendly, and can effectively improve cable operation stability and safety.

[0003] However, due to the lack of a stable chemical cross-linking structure, polypropylene cable insulation materials have experienced serious electrical treeing after being loaded with large currents during service, which directly leads to a decrease in the insulation strength of polypropylene cable insulation materials and affects the stability and safety of cable operation. How to effectively inhibit the electrical treeing of polypropylene insulation materials is an urgent problem to be solved in the development and application of polypropylene insulation materials.

[0004] Adding voltage stabilizer is a traditional modification method for power cable insulation materials, which can significantly improve the polymer insulation material's ability to suppress and tolerate electrical treeing, and has the advantages of being cheap and easy to operate. Currently, the commonly used voltage stabilizers are aromatic ketone compounds, which have good conjugation characteristics and electron delocalization, resulting in generally high electron affinity. However, such voltage stabilizers have a small molecular weight and are difficult to be uniformly distributed in the polypropylene in a long-term stable manner when doped in polypropylene under melt blending conditions. They are prone to migration and precipitation, which may cause their effects to gradually degrade.

[0005] In addition, the research on the initiation and growth of electrical dendrites in polymer insulating materials shows that its main mechanisms include electron injection and extraction, electrophotodegradation, and trap theory of non-radiative energy transfer. The starting point of these theories is to consider the generation of macromolecular free radicals through energy release under the condition of local electric field concentration, so the key to the problem is how to eliminate these macromolecular free radicals. Currently, the commonly used free radical scavengers are antioxidants and anti-aging additives, but both can only passively capture and annihilate free radicals, and it is difficult to achieve controllable and continuous and stable removal of internal free radical reactions during the service of cable insulation materials. Therefore, the improvement of the electrical aging resistance of polypropylene cable insulation materials by the two is limited. Summary of the invention

[0006] In view of the current state of the art, the present invention proposes a polypropylene cable insulation material with high dielectric properties that is resistant to long-term electrical aging and a preparation method thereof. Polypropylene is used as a polymer matrix, and polymer elastomers, functional fillers and additives are introduced to improve the mechanical properties and thermal conductivity of the material. At the same time, a free radical-regulated voltage stabilizer containing a xanthate structure is added. The free radical-regulated voltage stabilizer can effectively regulate the free radical reaction under the thermal field and the concentrated electric field, delay or even avoid the occurrence of electrical tree formation, thereby greatly extending the service life of the cable material. In addition, a two-step extrusion method is adopted in the process, so that the free radical-regulated voltage stabilizer and the filler can be stably retained in the polypropylene phase, which not only solves the problem that the commonly used voltage stabilizer cannot be effective for a long time, but also avoids the serious weakening of the dielectric properties caused by the aggregation of fillers in the polymer elastomer. Furthermore, the introduction of the polymer elastomer synergistically regulates the crystallization behavior of polypropylene, changes the polypropylene crystal structure, and enables the cable insulation material to have both excellent mechanical properties and dielectric properties.

[0007] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0008] The present invention provides a polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging and a preparation method thereof. The cable insulation material comprises, by weight, 40 to 60 parts of polypropylene, 20 to 40 parts of polymer elastomer, 10 to 20 parts of thermal conductive filler, and 1 to 3 parts of free radical regulated voltage stabilizer.

[0009] In one embodiment of the present invention, the free radical regulated voltage stabilizer is a small molecule compound containing a xanthate group, and its general structural formula is ;

[0010] Wherein, R1 is one of methyl, ethyl, isopropyl or n-butyl.

[0011] In one embodiment of the present invention, the polypropylene has a melting point of 150-165°C and a molecular weight of 4×10 6 ~1×10 7 g / mol, isotacticity is 20.0~40.0%, melt flow rate is 1.0~3.0 g / 10min at 230℃ / 2.16 kg, and Shore hardness (D) is 60~65.

[0012] In one embodiment of the present invention, the polymer elastomer is one or more of a polyolefin elastomer, a styrene-butadiene-styrene block copolymer, a styrene-ethylene-butylene-styrene block copolymer, and a thermoplastic polyurethane elastomer.

[0013] In one embodiment of the present invention, the thermally conductive filler is one or more of boron nitride, silicon nitride, aluminum nitride, and artificial diamond.

[0014] The present invention also proposes a method for preparing a polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging, which comprises at least the following steps:

[0015] Purification of the free radical regulated voltage stabilizer: diluting the free radical regulated voltage stabilizer with tetrahydrofuran, pouring it into n-hexane for precipitation, filtering to obtain a filter cake, re-dissolving the filter cake with tetrahydrofuran, pouring it into petroleum ether to obtain a precipitate, filtering the precipitate, washing it, and vacuum drying it at 30-40° C. for 24-48 h to obtain a free radical regulated voltage stabilizer;

[0016] Preparation of blending masterbatch: the purified free radical regulated voltage stabilizer, polypropylene and thermal conductive filler are mixed at a high speed of 1500-2000 r / min for 10-15 min, the obtained blend is melt-blended and extruded in an extruder at 230-290° C., and pelletized after cooling and drying to obtain blending masterbatch;

[0017] Preparation of high dielectric performance polypropylene cable insulation material resistant to long-term electrical aging: the blended masterbatch and the polymer elastomer are mixed at a high speed of 1500-2000 r / min for 10-15 min, and then placed in a wire and cable extruder at a temperature of 170-290°C for melt extrusion, and then cooled and solidified, while adjusting the take-up speed of the traction machine to control the shrinkage rate of the insulation material, and then dried and pelletized to obtain the high dielectric performance polypropylene insulation material resistant to long-term electrical aging.

[0018] In one embodiment of the present invention, in the step of re-dissolving the filter cake, the volume ratio of the tetrahydrofuran to the petroleum ether is 1:5-1:10.

[0019] The present invention proposes a polypropylene cable insulation material with high dielectric properties that is resistant to long-term electrical aging and a preparation method thereof. The use of a free radical regulating voltage stabilizer can effectively capture free radicals generated by electrical and thermal aging, thereby increasing the service life of the insulation material. At the same time, the voltage stabilizer can be inserted into the polypropylene chain segment, combined with the introduction of a polymer elastomer, to coordinately regulate the polypropylene crystal structure, so that the insulation material has both good mechanical properties and high dielectric properties. The preparation process of the present invention is simple and has great industrial production value. DETAILED DESCRIPTION

[0020] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0021] The technical solution of the present invention is further described in detail below in conjunction with several embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0022] The present invention provides a polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging and a preparation method thereof. The polypropylene (PP) has a melting point of 160°C and a molecular weight of 6×10 6 g / mol, isotacticity is 34.0%, melt flow rate is 3.0 g / 10min at 230°C / 2.16 kg, Shore hardness (D) is 65, in Example 1 and Comparative Examples 2-3 of the present invention, the free radical-regulated voltage stabilizer is di-n-butyl xanthate disulfide (CPB), in Example 2, the free radical-regulated voltage stabilizer is diisopropyl xanthate disulfide (DIP), in Example 3, the free radical-regulated voltage stabilizer is tetrathiodiester (TETD), and in Example 4, the free radical-regulated voltage stabilizer is dimethyl xanthate disulfide (DMS). In Comparative Example 1, the antioxidant used is antioxidant 1010 (AO).

[0023] In one embodiment of the present invention, the polymer elastomer is one or more of a polyolefin elastomer, a styrene-butadiene-styrene block copolymer, a styrene-ethylene-butylene-styrene block copolymer, and a thermoplastic polyurethane elastomer. In Example 1, the polymer elastomer is a polyolefin elastomer (POE) having a density of 0.87 g / cm 3 , the melt flow rate is 2.5 g / 10min at 190℃ / 2.16 kg, the Shore hardness (D) is 47, the elongation at break is 480%, and the tensile strength is 8.7 MPa; in Examples 2 and 4, the polymer elastomer is a styrene-ethylene-butylene-styrene block copolymer (SEBS), the styrene content of which is 29% and the density is 0.91 g / cm 3 , the melt flow rate is 6.0 g / 10 min at 230°C / 2.16 kg, the Shore hardness (D) is 60, the elongation at break is 370.0%, and the tensile strength is 31.0 MPa; in Example 3 and Comparative Examples 1-2, the polymer elastomer is a combination of POE and SEBS.

[0024] In one embodiment of the present invention, the thermally conductive filler is one or two of boron nitride, silicon nitride, aluminum nitride, and artificial diamond species; in Examples 1 to 3, the thermally conductive filler is boron nitride (BN), in Example 4, the thermally conductive filler is aluminum nitride (AlN), and in Comparative Examples 1 and 3, the thermally conductive filler is a combination of BN and AlN.

[0025] The raw material components and mass proportions required for preparing the cable sheath materials in the following examples and comparative examples are shown in Table 1.

[0026]

[0027] Example 1

[0028] Referring to Table 1, the preparation of polypropylene cable insulation material in this embodiment is carried out according to the following steps:

[0029] Purification of the free radical regulated voltage stabilizer: diluting the free radical regulated voltage stabilizer with tetrahydrofuran, pouring it into n-hexane for precipitation, filtering to obtain a filter cake, re-dissolving the filter cake with tetrahydrofuran, pouring it into petroleum ether to obtain a precipitate, filtering the precipitate, washing it, and vacuum drying it at 40° C. for 36 h to obtain a free radical regulated voltage stabilizer;

[0030] Preparation of blended masterbatch: The purified free radical regulated voltage stabilizer, polypropylene and thermal conductive filler are mixed at a high speed of 1500 r / min for 15 min, and the obtained blend is melt-blended and extruded in an extruder at 230-290° C., and pelletized after cooling and drying to obtain a blended masterbatch;

[0031] Preparation of high dielectric performance polypropylene cable insulation material resistant to long-term electrical aging: the blended masterbatch and the polymer elastomer are mixed at a high speed of 2000 r / min for 10 minutes and then placed in a wire and cable extruder at a temperature of 170-290°C for melt extrusion, followed by cooling and curing, while adjusting the take-up speed of the traction machine to control the shrinkage rate of the insulation material, and then drying and pelletizing to obtain the high dielectric performance polypropylene insulation material resistant to long-term electrical aging.

[0032] Example 2

[0033] The raw materials and formula of this example are shown in Table 1, and the preparation process is the same as that of Example 1.

[0034] Example 3

[0035] The raw materials and formula of this example are shown in Table 1, and the preparation process is the same as that of Example 1.

[0036] Example 4

[0037] The raw materials and formula of this example are shown in Table 1, and the preparation process is the same as that of Example 1.

[0038] Comparative Example 1

[0039] Referring to Table 1, the preparation of polypropylene cable insulation material in this embodiment is carried out according to the following steps:

[0040] Preparation of blending masterbatch: AO, PP and thermal conductive filler are mixed at a high speed of 1500 r / min for 15 min, the obtained blend is melt-blended and extruded in an extruder at 230-290°C, and pelletized after cooling and drying to obtain blending masterbatch;

[0041] Preparation of polypropylene cable insulation material: The blended masterbatch and the polymer elastomer are mixed at a high speed of 2000 r / min for 10 minutes, and then placed in a wire and cable extruder at a temperature of 170-290°C for melt extrusion, and then cooled and solidified. At the same time, the take-up speed of the traction machine is adjusted to control the shrinkage rate of the insulation material. After drying, pelletizing is performed to obtain the polypropylene insulation material with high dielectric properties that is resistant to long-term electrical aging.

[0042] Comparative Example 2

[0043] The raw materials and formula of this comparative example are shown in Table 1, and its preparation process is the same as that of Example 1.

[0044] Comparative Example 3

[0045] Referring to Table 1, the preparation of polypropylene cable insulation material in this embodiment is carried out according to the following steps:

[0046] Purification of the free radical regulated voltage stabilizer: diluting the free radical regulated voltage stabilizer with tetrahydrofuran, pouring it into n-hexane for precipitation, filtering to obtain a filter cake, re-dissolving the filter cake with tetrahydrofuran, pouring it into petroleum ether to obtain a precipitate, filtering the precipitate, washing it, and vacuum drying it at 40° C. for 36 h to obtain a free radical regulated voltage stabilizer;

[0047] Preparation of polypropylene cable insulation material: The purified free radical regulated voltage stabilizer, PP and thermal conductive filler are mixed at a high speed of 1500r / min for 15 minutes, and the obtained blend is melt-blended and extruded in an extruder at 230-290°C, and then cooled and solidified. At the same time, the take-up speed of the traction machine is adjusted to control the shrinkage rate of the insulation material. After drying, pelletizing is performed to obtain the polypropylene insulation material with high dielectric properties that is resistant to long-term electrical aging.

[0048] The performance of the polypropylene cable insulation materials prepared in the above embodiments and comparative examples was tested, and the test results are shown in Table 2.

[0049]

[0050] The above-mentioned embodiments 1-4 and comparative examples 1-3 were subjected to a constant voltage accelerated aging test, the lowest withstand voltage level was set to 50 kV / mm, and three withstand voltage levels of 55, 60 and 65 kV / mm were selected, and the material breakdown failure time t was recorded. The test results are shown in Table 3.

[0051]

[0052] As shown in Tables 2 and 3, the various properties of Examples 1 to 4 are compared with those of Comparative Examples 1 to 3. Among them, Example 1 and Comparative Examples 2 to 3 use a free radical-regulated voltage stabilizer CPB, Example 2 uses a radical-regulated voltage stabilizer DIP, Example 3 uses a free radical-regulated voltage stabilizer TETD, Example 4 uses a free radical-regulated voltage stabilizer DMS, and Comparative Example 1 uses an antioxidant 1010. Compared with Comparative Example 1, the breakdown failure time of Examples 1 to 4 at different withstand voltage levels is significantly increased, proving that the four free radical-regulated voltage stabilizers can significantly improve the electrical aging properties of polypropylene composite materials. Compared with Comparative Example 1, the dielectric constants of Examples 1 to 4 are significantly improved. Compared with Comparative Example 1, when the same filler is added, the dielectric loss of Examples 1 to 4 is lower. It can be seen that the free radical-regulated voltage stabilizer significantly improves the dielectric properties of the material. Compared with Comparative Example 2, Example 1 has a longer failure time under low voltage conditions, indicating that the addition of thermally conductive fillers inhibits electrical aging behavior to a certain extent. This may be because the thermally conductive fillers make the overall temperature rise of Example 1 slower and reduce the activity of free radical reactions. Compared with Comparative Example 3, Examples 1 to 4 have better elongation at break and tensile strength, indicating that the introduction of polymer elastomers can improve the mechanical properties of the system.

[0053] In summary, the present invention proposes a polypropylene cable insulation material with high dielectric properties that is resistant to long-term electrical aging and a preparation method thereof. Polypropylene is used as a polymer matrix, and polymer elastomers, functional fillers and additives are introduced to improve the mechanical properties of the material. At the same time, a free radical-regulated voltage stabilizer containing a xanthate structure is designed and synthesized, and the free radical reaction under a concentrated electric field is effectively regulated. At the same time, a two-step extrusion method is adopted in the process, so that the voltage stabilizer can stably exist between polypropylene chain segments, effectively avoiding the occurrence of electrical treeing, greatly extending the service life of the cable material, and combined with the introduction of the polymer elastomer, the crystallization behavior of polypropylene is synergistically regulated to change its crystal structure, so that the cable insulation material has both excellent mechanical properties and dielectric properties.

[0054] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as the above-mentioned features and the technical features with similar functions disclosed in this application (but not limited to) being replaced with each other.

[0055] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging, characterized in that: The cable insulation material is composed of 40 to 60 parts of polypropylene, 20 to 40 parts of polymer elastomer, 10 to 20 parts of thermal conductive filler, and 1 to 3 parts of free radical regulated voltage stabilizer by weight; the free radical regulated voltage stabilizer is a small molecule compound containing a xanthate group, and the general structural formula is Wherein, R1 is one of methyl, ethyl, isopropyl or n-butyl.

2. The polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging according to claim 1, characterized in that: The polypropylene has a melting point of 150-165° C., a molecular weight of 4×106-1×107 g / mol, an isotacticity of 20.0-40.0%, a melt flow rate of 1.0-3.5 g / 10 min at 230° C. / 2.16 kg, and a Shore hardness (D) of 60-65.

3. The polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging according to claim 1, characterized in that: The thermal conductive filler is a mixture of one or more of boron nitride, silicon nitride, aluminum nitride and artificial diamond.

4. The polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging according to claim 1, characterized in that: The polymer elastomer is a mixture of one or more of polyolefin elastomer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer and thermoplastic polyurethane elastomer.

5. The method for preparing a polypropylene cable insulation material with high dielectric properties and resistance to long-term electrical aging according to any one of claims 1 to 4, characterized in that: The preparation process includes at least the following steps: (1) Purification of a free radical-regulated voltage stabilizer: diluting the voltage stabilizer with tetrahydrofuran, and pouring it into n-hexane for precipitation, and filtering to obtain a filter cake. The filter cake is redissolved with tetrahydrofuran, and poured into petroleum ether to obtain a precipitate. The precipitate is filtered, washed, and vacuum-dried at 30 to 40° C. for 24 to 48 hours to obtain a free radical-regulated voltage stabilizer. In the step of redissolving the filter cake, the volume ratio of the tetrahydrofuran to the petroleum ether is 1:5 to 1:10; (2) Preparation of a blended masterbatch: The purified free radical-regulated voltage stabilizer, polypropylene, and thermally conductive filler obtained in step (1) are mixed at a high speed of 1500 to 2000 r / min for 10 to 15 min, and the resulting blend is melt-blended and extruded in an extruder at 230 to 290° C., cooled, dried, and pelletized to obtain a blended masterbatch; (3) Preparation of high dielectric performance polypropylene cable insulation material resistant to long-term electrical aging: The blended masterbatch obtained in step (2) is mixed with a polymer elastomer at a speed of 1500 to 2000 r / min for 10 to 15 minutes, and then placed in a wire and cable extruder at a temperature of 170 to 290° C. for melt extrusion, and then cooled and solidified. At the same time, the take-up speed of the traction machine is adjusted to control the shrinkage rate of the insulation material. After drying, the polypropylene insulation material with high dielectric performance that is resistant to long-term electrical aging is obtained by pelletizing.

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