Polypropylene insulated dc cable and method for producing the same

Abstract

The application belongs to the field of cable insulation material preparation, and particularly relates to a polypropylene insulation direct current cable and a preparation method thereof. The polypropylene insulation material of the direct current cable provided by the application comprises the following components in parts by weight: 100 parts of PP, 5-15 parts of EPDM, and 1-5 parts of nano-MgO. The application solves the phenomenon that the EPDM particles show poor dispersibility on the PP matrix by improving the preparation process (increasing the extrusion pressure and injection molding temperature, and stepwise cooling). By adding the nano-filler EPDM elastomer, the flexibility and anti-twisting ability of the polypropylene insulation are improved, and the interfacial polarization phenomenon between the EPDM elastomer and the polypropylene is improved, so that the mechanical properties and the electrical properties can be improved at the same time.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of cable insulation material preparation, and particularly relates to a polypropylene insulation direct current cable and a preparation method thereof. BACKGROUND

[0002] In recent years, with the economic development and the increasing demand for electricity, the power system is continuously developed to a higher voltage level to meet the demand for power load. As a key part of the direct current transmission network system, PP (polypropylene) is a highly competitive and potential high-voltage direct current insulation cable material, and is a general-purpose thermoplastic plastic with excellent performance. PP is widely used in many fields of life such as medical devices, mechanical equipment parts, chemical containers, clothing, automobiles and the like due to its excellent electrical insulation, light specific gravity, chemical corrosion resistance, heat resistance and the like. PP also shows better thermal stability, sufficient mechanical flexibility and excellent electrical performance at high temperature. In addition, PP is a main product of petrochemical industry, and has low cost. Moreover, the thermoplastic property of PP makes it easier to recycle and reprocess. Therefore, PP can be considered as a promising recyclable and environmentally friendly direct current cable insulation material. However, due to its own characteristics such as large elastic modulus, strong rigidity, poor anti-aging performance, large brittleness at low temperature, and the like, the electrical performance of PP will decrease under the working conditions of high temperature and high electric field, especially the accumulation of space charges under high temperature and high electric field, which cannot meet the requirements of high-voltage direct current cable insulation materials.

[0003] At present, the modification is mainly through blending, nano-particle doping, nucleating agent and chemical grafting. Through the modification of PP, the physical and chemical properties of PP are improved to meet the requirements of high-voltage cable insulation materials.

[0004] 1. Blending modification: due to the addition of elastomers, the rigidity of PP is reduced and the toughness is improved, but the charges generated by the interface polarization between different phases and the electrode injection charges will also reduce the dielectric properties of the material.

[0005] 2. Nano-particle doping modification: when the interface contact between nano-particles and polymers is not good and the interaction is weak, the composite material will separate the nano-particles from the polymers when subjected to strong external force, which will damage the integrity of the material.

[0006] 3. The β spherulite structure generated by adding β nucleating agent is loose, and can slip to dissipate energy when subjected to external force. Moreover, the deep traps introduced by β can inhibit the injection of space charges, so as to improve the mechanical properties and dielectric properties at the same time. However, it is difficult to ensure the dispersity of the nucleating agent in large-scale production.

[0007] Although the addition of EPDM elastomer makes the rigidity of PP decrease and toughness increase, the addition of a large amount of elastomer can form an interface in the composite material. Due to the difference in the relative dielectric constant and electrical conductivity between the elastomer and the polymer matrix, polarization phenomenon can occur at the interface. The polarization process can accumulate space charge, thereby causing electric field distortion. In addition, the EPDM particles exhibit poor dispersibility on the PP matrix, and the particle size difference between the particles is large. SUMMARY

[0008] The application improves the preparation process of polypropylene and the selection of nano-doped elastomer, expands the application range, improves the mechanical properties of polypropylene, ensures that the electrical properties are not negatively affected, and improves the problem of space charge accumulation of polypropylene insulation under high temperature and high field.

[0009] In order to solve the above technical problems, the application provides the following technical scheme:

[0010] The application provides a preparation method of a polypropylene insulation direct current cable, comprising the following steps:

[0011] S11: twisting to prepare a conductor core;

[0012] S12: using three-layer co-extrusion from the inside to the outside to prepare a conductor shielding layer, a polypropylene insulation layer and an insulation shielding layer on the conductor core, to obtain a crosslinked core; the polypropylene insulation layer is obtained by extruding a nano-doped EPDM elastomer through an extruder; the nano-doped EPDM elastomer is obtained by mixing 100 parts of polypropylene (PP), 5-15 parts of ethylene-propylene-diene rubber (EPDM) and 1-5 parts of nano-magnesium oxide by weight;

[0013] 1. Selection of elastomer:

[0014] (1) EVA

[0015] EVA is connected to each other in the PP matrix, and too much destroys the regularity of PP molecules.

[0016] (2) EPDM

[0017] Although the EPDM particles exhibit poor dispersibility on the PP matrix, and the particle size difference between the particles is large, the difference between the particles can be reduced by doping EPDM with nano-filler and then blending with PP. In addition, by adjusting the production process, the problem of poor dispersibility of EPDM on the PP matrix can be completely improved.

[0018] 2. Selection of nano-doping agent:

[0019] Nanometer ZnO, Al2O3, MgO and TiO2 can all inhibit space charge and improve the DC breakdown strength of insulation. However, nanometer MgO can change the electrical properties of PP more and is more likely to be widely used as high-voltage DC cable insulation material.

[0020] Therefore, the application modifies polypropylene by using EPDM and nanometer MgO.

[0021] During the extrusion, the temperature zones are set as follows: 1 zone 175℃, 2 zone 180℃, 3 zone 190℃, 4 zone 195℃, 5 zone 195℃, 6 zone 195℃, 7 zone 200℃, 8 zone 200℃, 9 zone 200℃.

[0022] S13: The crosslinked core is cooled by a temperature reduction channel, and the temperature zones are set as follows: 1 zone 190℃, 2 zone 160℃, 3 zone 130℃, 4 zone 120℃, 5 zone 110℃, 6 zone 100℃, 7 zone 60℃, 8 zone 30℃.

[0023] S14: The surface of the crosslinked core cooled in step S13 is sequentially subjected to metal shielding, cabling, inner sheath extrusion, armor loading and outer sheath extrusion to obtain the polypropylene insulation DC cable.

[0024] Preferably, the extruder is selected from a 175 type screw extruder.

[0025] Preferably, the nanometer doped EPDM elastomer is composed of 100 parts of polypropylene, 15 parts of ethylene propylene rubber and 5 parts of nanometer magnesium oxide by weight.

[0026] Preferably, the conductor shielding layer is obtained by extrusion through a 75 type screw extruder.

[0027] Further, during the extrusion of the conductor shielding layer, the temperature zones are set as follows: 1 zone 165℃, 2 zone 180℃, 3 zone 190℃, 4 zone 195℃, 5 zone 200℃, 6 zone 200℃, 7 zone 200℃.

[0028] Preferably, the insulation shielding layer is obtained by extrusion through a 90 type screw extruder.

[0029] Further, during the extrusion of the insulation shielding layer, the temperature zones are set as follows: 1 zone 165℃, 2 zone 180℃, 3 zone 185℃, 4 zone 195℃, 5 zone 200℃, 6 zone 200℃.

[0030] The application also provides a polypropylene insulation DC cable prepared by the above preparation method.

[0031] Through multiple experimental verification preparation process, the extrusion temperature, cooling temperature gradient, and the influence of the blending ratio, thus the manufacture of a good mechanical properties and electrical properties of polypropylene class insulation.

[0032] The results show that: when 100 parts of PP and 15 parts of EPDM and 5 parts of MgO, the mechanical properties and electrical properties of polypropylene insulation reach the optimal.

[0033] EPDM particles in the PP matrix dispersion is poor, the particle size gap is larger.

[0034] The technical scheme of the present application has the following advantages compared with the prior art:

[0035] 1. By improving the preparation process (increasing the extrusion pressure and injection molding temperature, step cooling) to solve the phenomenon of poor dispersion of EPDM particles in the PP matrix.

[0036] 2. By adding nano filler EPDM elastomer, improve the flexibility and anti-warping ability of polypropylene insulation, and improve the interface polarization phenomenon between EPDM elastomer and polypropylene, so as to ensure that the mechanical properties are improved, and the electrical properties are also improved. DETAILED DESCRIPTION

[0037] The present application will be further described below in conjunction with specific examples, so that those skilled in the art can better understand the present application and can be implemented, but the examples are not as a limitation on the present application.

[0038] Example 1

[0039] The standard steps are as follows:

[0040] 1) using 100 parts of polypropylene, 15 parts of ethylene propylene rubber, 5 parts of nano magnesium oxide to prepare nano-doped EPDM elastomer;

[0041] 2) twisted to prepare the conductor core;

[0042] 3) the crosslinked wire core is prepared by a three-layer co-extrusion production line; the conductor shielding layer, the insulation shielding layer and the polypropylene insulation layer are prepared by a 75 type screw extruder, a 90 type screw extruder and a 175 type screw extruder, respectively.

[0043] 4) the extrusion screw temperature of the conductor shielding layer adopts 7 partitions, and the temperature of each partition is: 165°C for the first partition, 180°C for the second partition, 190°C for the third partition, 195°C for the fourth partition, 200°C for the fifth partition, 200°C for the sixth partition, and 200°C for the seventh partition; 5) the polypropylene insulation layer adopts a modified polypropylene material, and the screw temperature is set in a ladder mode, specifically: 175°C for the first partition, 180°C for the second partition, 190°C for the third partition, 195°C for the fourth partition, 195°C for the fifth partition, 195°C for the sixth partition, 200°C for the seventh partition, 200°C for the eighth partition, and 200°C for the ninth partition;

[0044] 6) the extrusion screw temperature of the insulation shielding layer adopts 6 partitions, and the temperature of each partition is: 165°C for the first partition, 180°C for the second partition, 185°C for the third partition, 195°C for the fourth partition, 200°C for the fifth partition, and 200°C for the sixth partition;

[0045] 7) the crosslinked core is prepared and passes through a cooling channel, and the temperature of each partition is: 190°C for the first partition, 160°C for the second partition, 130°C for the third partition, 120°C for the fourth partition, 110°C for the fifth partition, 100°C for the sixth partition, 60°C for the seventh partition, and 30°C for the eighth partition;

[0046] 8) metal shielding, cabling, inner sheath extrusion, armoring, and outer sheath extrusion are sequentially performed to obtain a product cable.

[0047] Example 2

[0048] The standard steps are as follows:

[0049] 1) a nano-doped EPDM elastomer is prepared by using 100 parts of polypropylene, 5 parts of EPDM, and 1 part of nano magnesium oxide by weight;

[0050] 2) a conductor core is prepared by twisting;

[0051] 3) the crosslinked core is prepared by using a three-layer co-extrusion production line; the conductor shielding layer, the insulation shielding layer, and the polypropylene insulation layer are prepared by using a 75-type screw extruder, a 90-type screw extruder, and a 175-type screw extruder, respectively;

[0052] 4) the extrusion screw temperature of the conductor shielding layer adopts 7 partitions, and the temperature of each partition is: 165°C for the first partition, 180°C for the second partition, 190°C for the third partition, 195°C for the fourth partition, 200°C for the fifth partition, 200°C for the sixth partition, and 200°C for the seventh partition; 5) the polypropylene insulation layer adopts a modified polypropylene material, and the screw temperature is set in a ladder mode, specifically: 175°C for the first partition, 180°C for the second partition, 190°C for the third partition, 195°C for the fourth partition, 195°C for the fifth partition, 195°C for the sixth partition, 200°C for the seventh partition, 200°C for the eighth partition, and 200°C for the ninth partition;

[0053] 6) The extrusion screw temperature of the insulation shielding layer adopts 6 partitions, and the temperature of each partition is: 165℃ for the first partition, 180℃ for the second partition, 185℃ for the third partition, 195℃ for the fourth partition, 200℃ for the fifth partition, and 200℃ for the sixth partition;

[0054] 7) After the cross-linking core is prepared, it passes through a cooling channel, and the temperature of each partition is: 190℃ for the first partition, 160℃ for the second partition, 130℃ for the third partition, 120℃ for the fourth partition, 110℃ for the fifth partition, and 100℃ for the sixth partition; 60℃ for the seventh partition; and 30℃ for the eighth partition;

[0055] 8) Metal shielding, cabling, inner sheath extrusion, armor fitting, and outer sheath extrusion are sequentially performed to obtain the product cable.

[0056] Example 3

[0057] The standard steps are as follows:

[0058] 1) A nano-doped EPDM elastomer is prepared by using 100 parts of polypropylene, 5 parts of ethylene-propylene-diene rubber, and 5 parts of nano-magnesium oxide by weight;

[0059] 2) The conductor core is prepared by twisting;

[0060] 3) The cross-linking core is prepared by using a three-layer co-extrusion production line; the conductor shielding layer, the insulation shielding layer, and the polypropylene insulation layer are prepared by using a 75-type screw extruder, a 90-type screw extruder, and a 175-type screw extruder, respectively;

[0061] 4) The extrusion screw temperature of the conductor shielding layer adopts 7 partitions, and the temperature of each partition is: 165℃ for the first partition, 180℃ for the second partition, 190℃ for the third partition, 195℃ for the fourth partition, 200℃ for the fifth partition, 200℃ for the sixth partition, and 200℃ for the seventh partition; 5) The polypropylene insulation layer adopts modified polypropylene material, and the screw temperature is set in a ladder shape, specifically: 175℃ for the first partition, 180℃ for the second partition, 190℃ for the third partition, 195℃ for the fourth partition, 195℃ for the fifth partition, 195℃ for the sixth partition, 200℃ for the seventh partition, 200℃ for the eighth partition, and 200℃ for the ninth partition;

[0062] 6) The extrusion screw temperature of the insulation shielding layer adopts 6 partitions, and the temperature of each partition is: 165℃ for the first partition, 180℃ for the second partition, 185℃ for the third partition, 195℃ for the fourth partition, 200℃ for the fifth partition, and 200℃ for the sixth partition;

[0063] 7) After the cross-linking core is prepared, it passes through a cooling channel, and the temperature of each partition is: 190℃ for the first partition, 160℃ for the second partition, 130℃ for the third partition, 120℃ for the fourth partition, 110℃ for the fifth partition, and 100℃ for the sixth partition; 60℃ for the seventh partition; and 30℃ for the eighth partition;

[0064] 8) Metal shielding, cabling, inner sheath extrusion, armor fitting, and outer sheath extrusion are sequentially performed to obtain the product cable.

[0065] Comparative Example 1

[0066] The cooling gradient of the cooling is decreased by 30℃ per time;

[0067] The specific steps are as follows:

[0068] 1) Using 100 parts of polypropylene, 5 parts of ethylene propylene rubber, and 5 parts of nano magnesium oxide to prepare a nano-doped EPDM elastomer by weight;

[0069] 2) Twisting to prepare a conductor core;

[0070] 3) The crosslinked core is prepared by a three-layer co-extrusion production line; the conductor shielding layer, the insulation shielding layer, and the polypropylene insulation layer are prepared by a 75 type screw extruder, a 90 type screw extruder, and a 175 type screw extruder, respectively;

[0071] 4) The extrusion screw temperature of the conductor shielding layer is divided into 7 zones, and the temperature of each zone is: Zone 1 165℃, Zone 2 180℃, Zone 3 190℃, Zone 4 195℃, Zone 5 200℃, Zone 6 200℃, Zone 7 200℃; 5) The polypropylene insulation layer uses modified polypropylene material, and the screw temperature is set in a ladder shape, specifically: Zone 1 175℃, Zone 2 180℃, Zone 3 190℃, Zone 4 195℃, Zone 5 195℃, Zone 6 195℃, Zone 7 200℃, Zone 8 200℃, Zone 9 200℃;

[0072] 6) The extrusion screw temperature of the insulation shielding layer is divided into 6 zones, and the temperature of each zone is: Zone 1 165℃, Zone 2 180℃, Zone 3 185℃, Zone 4 195℃, Zone 5 200℃, Zone 6 200℃;

[0073] 7) After the crosslinked core is prepared, it passes through a cooling channel, and the cooling gradient of the cooling is decreased by 30℃ per time;

[0074] 8) Metal shielding, cabling, inner sheath extrusion, armoring, and outer sheath extrusion are sequentially performed to obtain a product cable.

[0075] Comparative Example 2

[0076] Comparative Example 2: The above steps are completely the same, and EPDM without doping nano MgO is added;

[0077] The specific steps are as follows:

[0078] 1) Using 100 parts of polypropylene and 5 parts of ethylene propylene rubber to prepare a nano-doped EPDM elastomer by weight, without adding nano magnesium oxide;

[0079] 2) Twisting to prepare a conductor core;

[0080] 3) The crosslinked core is prepared by a three-layer co-extrusion production line; the conductor shielding layer, the insulation shielding layer and the polypropylene insulation layer are respectively prepared by a 75 type screw extruder, a 90 type screw extruder and a 175 type screw extruder;

[0081] 4) The extrusion screw temperature of the conductor shielding layer is divided into seven zones, and the temperature of each zone is: zone 1 165℃, zone 2 180℃, zone 3 190℃, zone 4 195℃, zone 5 200℃, zone 6 200℃, and zone 7 200℃; 5) The polypropylene insulation layer uses a modified polypropylene material, and the screw temperature is set in a ladder form, specifically: zone 1 175℃, zone 2 180℃, zone 3 190℃, zone 4 195℃, zone 5 195℃, zone 6 195℃, zone 7 200℃, zone 8 200℃, and zone 9 200℃;

[0082] 6) The extrusion screw temperature of the insulation shielding layer is divided into six zones, and the temperature of each zone is: zone 1 165℃, zone 2 180℃, zone 3 185℃, zone 4 195℃, zone 5 200℃, and zone 6 200℃;

[0083] 7) After the crosslinked core is prepared, it passes through a cooling channel, and the cooling gradient is decreased by 30℃ per time;

[0084] 8) The metal shielding, cabling, inner sheath extrusion, armoring and outer sheath extrusion are sequentially performed to obtain the product cable.

[0085] Comparative Example 3

[0086] The steps are the same as those in Example 1, and EPDM and MgO are directly added into PP, respectively.

[0087] Comparative Example 4

[0088] The steps are the same as those in Example 1, and the proportions of EPDM and MgO are changed; wherein, 100 parts of PP, 20 parts of EPDM and 10 parts of MgO are used by weight.

[0089] Effect Evaluation 1

[0090] It is found that the crystallization behavior of the EPDM and PP blend shows that the crystallization temperature and the crystal nucleation rate of the blend increase after the addition of EPDM, which indicates that EPDM has a nucleation effect on PP. The crystal growth rate decreases, which indicates that the crystal size becomes smaller, i.e. the ball becomes smaller. As a result, EPDM reduces the crystallinity of PP, and the crystallization temperature of PP is about 115℃, so the present application adopts a more intensive ladder type cooling to ensure its original crystallinity.

[0091] 1) Compared with Example 2, it can be found that by the preparation method of the present application, the electrical properties of PP can be improved, and the mechanical properties of PP can also be improved.

[0092] 2) By comparing Example 2 with Comparative Example 1, it is found that increasing the cooling temperature gradient results in a decrease in mechanical and electrical properties, because the increase in the cooling temperature gradient results in less crystallization of PP, leading to a larger amorphous region.

[0093] 3) By comparing Example 2 with Comparative Example 2, it is found that adding EPDM elastomer alone can improve the mechanical properties of PP, but because the addition of EPDM forms an interface with PP, resulting in the presence of polarized charges, which leads to a decrease in electrical properties.

[0094] 4) By comparing Example 2 with Comparative Example 3, it is found that adding EPDM and MgO separately, rather than mixing them together in advance, results in a decrease in both electrical and mechanical properties, because the addition of the two separately results in uneven filling of MgO into EPDM, which partially results in the phenomenon in 3), leading to a decrease in electrical properties.

[0095] Table 1 Performance test of Examples and Comparative Examples

[0096]

[0097] Obviously, the above examples are merely examples for clarity and do not limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. Here, it is not necessary and impossible to exhaust all embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for preparing a polypropylene insulated DC cable, characterized in that, Includes the following steps: S11: Stranding to prepare the conductor core; S12: A conductor shielding layer, a polypropylene insulation layer, and an insulation shielding layer are sequentially prepared from the inside to the outside of the conductor core using a three-layer co-extrusion process to obtain a cross-linked wire core; the polypropylene insulation layer is obtained by extruding nano-doped EPDM elastomer through an extruder; by weight, the nano-doped EPDM elastomer is obtained by mixing 100 parts of polypropylene, 5-15 parts of EPDM rubber, and 1-5 parts of nano-magnesium oxide; the temperature zones during the extrusion of the polypropylene insulation layer are set as follows: Zone 1 175℃, Zone 2 180℃, Zone 3 190℃, Zone 4 195℃, Zone 5 195℃, Zone 6 195℃, Zone 7 200℃, Zone 8 200℃, Zone 9 200℃; By weight, the nano-doped EPDM elastomer is composed of 100 parts polypropylene, 15 parts EPDM rubber, and 5 parts nano-magnesium oxide; the extrusion temperature zones for the conductor shielding layer are set as follows: Zone 1 165℃, Zone 2 180℃, Zone 3 190℃, Zone 4 195℃, Zone 5 200℃, Zone 6 200℃, and Zone 7 200℃; the extrusion temperature zones for the insulating shielding layer are set as follows: Zone 1 165℃, Zone 2 180℃, Zone 3 185℃, Zone 4 195℃, Zone 5 200℃, and Zone 6 200℃. S13: The cross-linked core is cooled in zones through a cooling channel, with the temperature zones set as follows: Zone 1 190℃, Zone 2 160℃, Zone 3 130℃, Zone 4 120℃, Zone 5 110℃, Zone 6 100℃, Zone 7 60℃, and Zone 8 30℃. S14: The cross-linked core surface after being cooled in sections in step S13 is subjected to metal shielding, cabling, inner sheath extrusion, armoring and outer sheath extrusion in sequence to obtain the polypropylene insulated DC cable.

2. The preparation method according to claim 1, characterized in that, The extruder is selected from a 175-type screw extruder.

3. The preparation method according to claim 1, characterized in that, The conductor shielding layer is obtained by extrusion using a 75-type screw extruder.

4. The preparation method according to claim 1, characterized in that, The insulating shielding layer is obtained by extrusion using a 90-type screw extruder.

5. A polypropylene insulated DC cable prepared by the preparation method according to any one of claims 1-4.

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