Polyethylene-based semi-conductive sheath material and preparation method and application thereof

Abstract

The invention belongs to the technical field of cable materials, and particularly relates to a polyvinyl semi-conductive sheath material and further discloses a preparation method and application of the polyvinyl semi-conductive sheath material. The polyvinyl semiconductive sheath material is prepared by blending two or more metallocene linear low density polyethylene (mLLDPE) with different properties, two or more conductive fillers with different structures and different conductive properties, and auxiliaries such as a semipolar copolymer, a dispersant, an antioxidant, a lubricant and an acid acceptor. The material has excellent and stable conductivity and higher working temperature, the PTC effect is weaker and even the negative temperature coefficient (NTC) effect is weaker at the high working temperature, and in addition, the material also has better low temperature resistance and mechanical property.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable materials, and specifically relates to a polyethylene-based semiconductive sheath material and further discloses a preparation method and application thereof. The semiconductive sheath material of the present invention can be used to prepare an outer semiconductive sheath of a high-voltage cable and an outer semiconductive sheath of a submarine cable and a URD type cable. Background Art

[0002] In the manufacturing process of ultra-high voltage cables with a rated voltage of 110kV and above, a layer of graphite powder needs to be coated on the cable sheath as a semi-conductive layer. Its main function is to discharge the induced charge on the sheath to the contact body (such as the earth) through the semi-conductive layer to increase the current carrying capacity of the cable. At the same time, the staff can also calculate the outer sheath resistance and judge the quality of the cable sheath by detecting the current in the outer sheath loop. However, due to the defects of poor environmental protection, the graphite coating method is very easy to fall off after coating, which may lead to uneven coating and other shortcomings, and is gradually eliminated.

[0003] In order to solve the problems existing in the above-mentioned graphite coating, the method generally recognized in the market is to extrude a semi-conductive layer on the outer sheath instead of the graphite coating. Since the semi-conductive layer has very good conductivity, when it is used as the outer sheath of submarine cables and URD type cables, it can also effectively absorb the electric field in the cable, thereby making the electric field distribution in the cable more uniform, thereby protecting the insulation layer of the cable from damage. In addition, the semi-conductive layer can also play a role in waterproofing and corrosion resistance. Therefore, the performance of the semi-conductive layer material directly affects the quality of the cable. At present, the semi-conductive layer sheath materials commonly used in the market are generally prepared by adding conductive fillers and other additives to polyolefin resins or polyvinyl chloride resins. For semi-conductive materials based on polyolefin resins, the properties of polyolefin resins and conductive fillers determine the quality of the semi-conductive layer materials.

[0004] For example, Chinese patent CN109467783A discloses a polyethylene / carbon nanotube conductive material and a preparation method thereof, wherein polyethylene, carbon nanotubes and other fillers and additives are prepared by conventional processing methods, but there are problems such as high cost of carbon nanotubes and excessive material cost. Another example is Chinese patent CN109593256A discloses an anti-ultraviolet semi-conductive polyethylene sheath material and its application, wherein the resin used in the sheath material is mainly linear low-density polyethylene, and the material has poor aging performance under high temperature conditions, and the conductive fillers used are carbon nanotubes and graphene, resulting in excessive material cost. Other schemes such as Chinese patents CN102295796A, CN113527795A, CN111234362A, CN102863686A or CN114685874A all disclose a material system using a blend of PE resin and one or more modified resins such as ethylene-vinyl acetate copolymer (EVA), polyolefin elastomer (POE), and ethylene butyl acrylate (EBA). Such modified resins can accommodate a large amount of conductive fillers and improve the mechanical properties of the material, including toughness and resistance to environmental stress cracking. However, such resins have low melting points and Vicat softening points, which results in a lower operating temperature of the semi-conductive layer material.

[0005] In addition, the semi-conductive layer material made of the conventional conductive filler has a positive temperature coefficient (PTC). The PTC effect refers to the phenomenon that the resistance of the material increases as the external temperature rises. The rated operating temperature of the high-voltage cable is generally 70-90°C, which is in the PTC region of the semi-conductive composite material. Therefore, as the ambient temperature rises, the PTC effect can increase the volume resistivity of the material, and the corresponding cable induced potential increases, affecting the partial discharge of the cable operation and increasing the heat of the cable metal sheath, thereby greatly affecting the transmission power of the cable and reducing the current carrying capacity of the cable.

[0006] Therefore, the art expects to develop a semi-conductive sheath material with stable electrical conductivity, high operating temperature, good low temperature resistance and mechanical properties. Summary of the invention

[0007] To this end, the technical problem to be solved by the present invention is to provide a polyethylene-based semi-conductive sheath material, which has excellent and stable electrical conductivity and a high operating temperature, a weak PTC effect at a high operating temperature, or even a weak negative temperature coefficient (NTC) effect, and also has good low temperature resistance and mechanical properties, and can be used to prepare an outer semi-conductive sheath of a high-voltage cable, as well as an outer semi-conductive sheath of a submarine cable and a URD type cable;

[0008] The second technical problem to be solved by the present invention is to provide a method for preparing the polyethylene-based semi-conductive sheath material and its use in preparing the outer semi-conductive sheath of a high-voltage cable.

[0009] In order to solve the above technical problems, the polyethylene-based semiconductive sheath material described in the present invention comprises the following raw material components in parts by weight:

[0010] 40-60 parts by weight of low melt flow rate metallocene linear low density polyethylene mLLDPE1;

[0011] 40-60 parts by weight of high melt flow rate metallocene linear low density polyethylene mLLDPE2;

[0012]

[0013] Preferably, the polyethylene-based semiconductive sheath material comprises the following raw material components in parts by weight:

[0014] Low melt flow rate metallocene linear low density polyethylene mLLDPE1 45-55 parts by weight;

[0015] 45-55 parts by weight of high melt flow rate metallocene linear low density polyethylene mLLDPE2;

[0016]

[0017] Specifically, in the polyethylene-based semiconductive sheath material, the total amount of mLLDPE1 and mLLDPE2 is 100 parts by weight.

[0018] Specifically, the polyethylene-based semiconductive sheath material, the low melt flow rate metallocene linear low-density polyethylene mLLDPE1 is used for blow molding film material, and the density is 0.914-0.920g / cm 3 , the melt mass flow rate (MFR) is 0.8-2.5g / 10min, the impact damage mass of the blown film is not less than 600g, and it has the characteristics of high strength and high toughness. The MFR is a measured value at 190°C and 2.16kg load, the impact damage mass is measured according to the B method in GB / T 9639.1-2008, and the film sample thickness is 30μm. Specifically, in the present invention, the mLLDPE1 resin used in the present invention can be F181ZU of Sinopec Qilu Branch, HPR18H10AX of PetroChina Daqing Petrochemical, 1018CA of ExxonMobil of the United States, SP1520 of Mitsui Chemicals of Japan, etc.

[0019] Specifically, the polyethylene-based semiconductive sheath material, the high melt flow rate metallocene linear low-density polyethylene mLLDPE2 is used for film material for tape casting, and the density is 0.914-0.920 g / cm 3, the melt mass flow rate MFR is 3.5-4.5g / 10min. Specifically, in the present invention, the mLLDPE2 resin used in the present invention can be F184Z of Sinopec Qilu Branch, 5220G of Dow Chemical, 4518PA of ExxonMobil, XP9500 of Daelim, South Korea, etc.

[0020] The present invention has found through multiple tests that the mLLDPE1 resin with higher impact damage quality has a narrow molecular weight distribution and excellent mechanical properties. It can still maintain high mechanical properties after adding a large amount of inorganic fillers, so it has high inorganic filling capacity, but due to its narrow molecular weight distribution and large viscosity, it has poor processing performance; while the mLLDPE2 resin also has a narrow molecular weight distribution and a regular molecular chain structure, but has a low molecular weight and good processing performance, has greater wettability and coating properties for inorganic fillers, and can improve the dispersion effect of inorganic fillers and the low-temperature brittleness of materials. Therefore, the present invention selects two mLLDPE resins that have a complementary effect after adding a large amount of inorganic fillers, and can obtain materials with excellent mechanical properties and processing properties by matching them in a certain proportion.

[0021] Specifically, the polyethylene-based semi-conductive sheath material and the low specific surface area conductive filler have a specific surface area of ​​30-160 m 2 / g, oil absorption value (DBP) is 90-300ml / 100g; preferably, the low specific surface area conductive filler can be superconducting furnace carbon black, acetylene carbon black and other carbon blacks. Superconducting furnace carbon black is preferred, and its oil absorption value is 90-300ml / 100g, preferably 90-150ml / 100g, and its specific surface area is 30-160m 2 / g, preferably 40-100m 2 / g. The oil absorption value is measured according to GB / T 3780.2-2017 standard, and the specific surface area is measured according to GB / T 10722-2014 standard. Specifically, in the present invention, the conductive carbon black of the present invention can be Yongdong YD-250C, Yongdong YD-280C, Lianke LK2105, Cabot Carbon Black VXC200, Cabot Carbon Black VXC68, etc.

[0022] Specifically, the polyethylene-based semi-conductive sheath material and the high specific surface area conductive filler have a specific surface area of ​​≥800m 2 / g; Preferably, the high specific surface area conductive filler includes conductive carbon black and / or multi-walled carbon nanotubes, that is, it can be a high specific surface area conductive carbon black or multi-walled carbon nanotubes (MWNTs), preferably a high specific surface area conductive carbon black, whose specific surface area is ≥800m 2 / g, preferably ≥1200m 2 / g. Specifically, in the present invention, the high specific surface area conductive carbon black of the present invention can be Cabot carbon black BP2000, Akzo Nobel carbon black EC-600JD, etc. The outer diameter of MWNTs is 5-50nm, the inner diameter is 2-20nm, the length is 0.5-50μm, and the specific surface area is ≥60m 2 / g. The preferred outer diameter is 10-30nm, the inner diameter is 5-10nm, the length is 10-30μm, and the specific surface area is 110-260m 2 / g. Specifically, in the present invention, the MWNTs of the present invention can be FloTubes produced by Beijing Tianna Technology Co., Ltd. TM 9000, TNM3 and MS1235 of Chengdu Research Institute of Organic Chemistry, Chinese Academy of Sciences, etc.

[0023] The polyethylene-based semi-conductive sheath material of the present invention has a conductive composite material whose conductivity changes with the increase of the external temperature, which is affected by the thermal expansion effect of the matrix volume, causing the spacing between the conductive particles to increase, blocking the conductive path composed of the conductive particles, causing the volume resistivity to increase, and is also affected by the thermal excitation effect of the surface electrons of the conductive particles, causing the electron movement ability to increase and the volume resistivity to decrease. The change of conductivity with temperature is the total result of the superposition of these two factors. The composite material of the low specific surface area conductive filler has a PTC effect, which is mainly affected by the first factor. The high specific surface area conductive carbon black in the high specific surface area conductive filler has a very high specific surface area, a small particle size, and a very high structure. In the relatively low temperature region before the melting point of the matrix, the volume expansion effect is not obvious, and the volume resistivity caused by the enhanced surface electron movement ability is dominant, and the composite material has an NTC effect. MWNTs have a large aspect ratio and are curled and entangled at room temperature. As the external temperature increases, the curled MWNTs long chain elongates, causing the conductive path to increase, resulting in the composite material also having an NTC effect before the melting point of the matrix. Under the synergistic effect of two conductive fillers with different structures and different conductive properties, the PTC effect of the composite material can be reduced. If the content of the high specific surface area conductive filler is relatively high, the composite material may even have a weak NTC effect.

[0024] The semi-conductive sheath material of the present invention needs to have a higher conductivity, that is, a lower volume resistivity, and therefore needs to add more conductive fillers. However, too high a filler content will reduce the mechanical properties and processing properties of the material. The two mLLDPE film raw material resins used have good flexibility, ductility, mechanical strength and heat resistance, strong corrosion resistance, and good environmental stress cracking resistance, which can effectively guarantee the application performance of the sheath material.

[0025] Specifically, the polyethylene-based semi-conductive sheath material, the semi-polar copolymer is a low molecular weight semi-polar copolymer, preferably, the semi-polar copolymer includes a mixture of one or more of polyester polyol copolymers, polyether polyol copolymers, and hydroxy acrylic resins. Since the two conductive fillers, especially the high specific surface area conductive fillers, have a large specific surface area, are easy to aggregate and difficult to disperse, and MWNTs also have mutual entanglement between aggregates. Therefore, the present invention introduces a low molecular weight semi-polar copolymer to increase the dispersibility of the conductive filler, improve the adhesion between the conductive filler and the resin, and improve the conductive properties and mechanical properties of the material. The semi-polar copolymer can also be used as a lubricant for the composite material and a diluent and dispersant for the conductive filler. The semi-polar copolymer used in the present invention can be a mixture of one or more of polyester polyols, polyether polyols, hydroxy acrylic resins, etc., with a molecular weight of 180-8000, preferably 180-6000.

[0026] Specifically, the polyethylene-based semiconductive sheath material, the dispersant includes polyethylene wax PEW, preferably with a molecular weight of 2000-6000; the dispersant used in the present invention is polyethylene wax (PEW), and the molecular weight is preferably 3000-4000.

[0027] Specifically, the polyethylene-based semiconductive sheath material, the antioxidant includes one or a mixture of a mixture of hindered phenol antioxidants (1010, 1076), phosphite antioxidants (168), thioester antioxidants (DLTDP, DLTP), and thio-hindered phenol antioxidants (300).

[0028] Specifically, the polyethylene-based semiconductive sheath material and the lubricant include silicone masterbatch and / or fluorine-containing polymer processing aid PPA.

[0029] Specifically, the polyethylene-based semiconductive sheath material, the acid absorber includes a polyolefin acid absorber, preferably calcium stearate and / or zinc stearate.

[0030] The present invention also discloses a method for preparing the polyethylene-based semiconductive sheath material, comprising the following steps:

[0031] (1) taking selected amounts of the high specific surface area conductive filler, the semi-polar copolymer, the low specific surface area conductive filler, and the dispersant and mixing them to obtain a first mixed material for later use;

[0032] (2) taking selected amounts of the low melt flow rate metallocene linear low density polyethylene mLLDPE1, the high melt flow rate metallocene linear low density polyethylene mLLDPE2, an antioxidant, a lubricant and an acid absorbent and mixing them to obtain a second mixture for standby use;

[0033] (3) respectively feeding the first mixed material and the second mixed material into different feeding ports of a twin-screw extruder, and performing melt extrusion granulation to obtain the product.

[0034] Specifically, the preparation method of the polyethylene-based semiconductive sheath material is:

[0035] In the step (1), the mixing temperature of the mixing step is 100-120° C.; and / or,

[0036] In the step (1), the stirring speed of the mixing step is 800-1200 rpm; and / or,

[0037] In the step (1), the stirring time of the mixing step is 10-20 min; and / or,

[0038] In the step (2), the temperature of the mixing step is 30-55° C.; and / or,

[0039] In the step (2), the stirring speed of the mixing step is 250-350 rpm; and / or,

[0040] In the step (2), the stirring time of the mixing step is 3-8 min; and / or,

[0041] In the step (3), the temperature of the melt extrusion step is 180-200° C.; and / or,

[0042] In the step (3), the second mixture is fed into the main feeding port of the twin-screw extruder, and the first mixture 3 is fed into the side feeding port of the twin-screw extruder.

[0043] Specifically, the step (1) further comprises the step of grinding the high specific surface area conductive filler and the semi-polar copolymer after mixing, and then adding the low specific surface area conductive filler and the dispersant to mix.

[0044] The invention also discloses the use of the polyethylene-based semi-conductive sheath material or the polyethylene-based semi-conductive sheath material prepared by the method in preparing cable material sheaths.

[0045] The invention also discloses a cable material sheath and a cable prepared from the polyethylene-based semi-conductive sheath material or the polyethylene-based semi-conductive sheath material prepared by the method.

[0046] The polyethylene-based semi-conductive sheath material of the present invention is prepared by blending two or more metallocene linear low-density polyethylenes (mLLDPE) with different properties and two or more conductive fillers with different structures and different conductive properties, as well as semi-polar copolymers, dispersants, antioxidants, lubricants, acid absorbers and other additives. The material has excellent and stable conductive properties and a high operating temperature, a weak PTC effect at high operating temperature or even a weak negative temperature coefficient (NTC) effect, and also has good low temperature resistance and mechanical properties. It effectively solves the problems of low operating temperature, large PTC effect, and increased volume resistivity of current polyolefin semi-conductive sheath materials as the operating temperature rises.

[0047] The polyethylene-based semi-conductive sheath material of the present invention adopts two mLLDPE with different performance characteristics as the basic resin of the material, and the basic resin does not contain resins with low melting points such as EVA and POE, so that the prepared semi-conductive sheath material has a higher working temperature; and two conductive fillers with different structures and different conductive properties are used as the conductive agent of the material, so that the prepared semi-conductive sheath material has a weaker PTC effect or even a weaker NTC effect, and the conductivity does not change much with the increase of temperature; and the conductive filler is treated with a semi-polar copolymer, so that the dispersibility of the conductive filler and the adhesion between the conductive filler and the resin can be improved, and the conductive property and mechanical property of the composite material can be improved.

[0048] The polyethylene-based semiconductive sheath material of the present invention utilizes the synergistic effect of two conductive fillers with different structures and different conductive properties to prepare a composite material with a weak PTC effect or even a weak NTC effect; and simultaneously utilizes mLLDPE with high strength, high toughness and high inorganic filling and a mLLDPE with good fluidity as a matrix to prepare a semiconductive sheath material with good processing performance, mechanical properties and heat resistance. DETAILED DESCRIPTION

[0049] In order to better understand the present invention, the present invention is further described below in conjunction with the embodiments, the purpose is to better understand the content of the present invention. Therefore, the following embodiments are only illustrative and do not limit the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the contents of the present invention.

[0050] Examples 1-5

[0051] The present invention is as follows: Examples 1-5, the raw material composition and proportion (by weight) of the sheath material are shown in Table 1 below.

[0052] The components used in the following embodiments 1-5 of the present invention are all commercially available products, and the relevant information is as follows:

[0053] The mLLDPE1 resin is F181ZU produced by Sinopec Qilu Branch, with a density of 0.918 g / cm 3 , MFR is 1.0g / 10min;

[0054] The mLLDPE2 resin is F184Z produced by Sinopec Qilu Branch, with a density of 0.918 g / cm 3 , MFR is 3.5g / 10min;

[0055] EVA is V6110M produced by BASF-YPC Co., Ltd., with MFR of 1.0g / 10min and VA content of 26.5%;

[0056] The low specific surface area conductive filler is carbon black VXC68 produced by Cabot Corporation of the United States, with a DBP of 123ml / 100g and a specific surface area of ​​68m 2 / g;

[0057] The high specific surface area conductive filler is carbon black BP2000 produced by Cabot Corporation of the United States, with a specific surface area of ​​1475m 2 / g;

[0058] The semi-polar copolymer is polypropylene glycol of the polyether polyol class, which is PPG-200 produced by Hai'an Petrochemical Plant in Jiangsu Province, with a molecular weight of 200;

[0059] The antioxidant was antioxidant 300 produced by Zibo Vanke Chemical Co., Ltd.;

[0060] The lubricant PPA was FX-5920A produced by 3M Company of the United States;

[0061] The acid absorbent is commercially available zinc stearate.

[0062] Table 1 Raw material formula of Examples 1-5 (parts by weight)

[0063]

[0064]

[0065] The method for preparing the sheath material described in Examples 1-5 of the present invention comprises the following steps:

[0066] (1) First, the two selected conductive fillers are dried, and the dried high specific surface area conductive filler and the semi-polar copolymer are weighed according to the formula and mixed evenly in a high-speed mixer, the mixing temperature is 110° C., the stirring speed is 1000 rpm, and the mixing time is 15 min, and the mixture is put into a dry ball mill for grinding, and the grinding time is 20 minutes; then the dried low specific surface area conductive filler and dispersant PE wax are added to the mixture, and the mixture is weighed according to the formula and mixed evenly in a high-speed mixer, the mixing temperature is 110° C., the stirring speed is 1000 rpm, and the mixing time is 15 min, to obtain a first mixture;

[0067] (2) mLLDPE1 resin, mLLDPE2 resin, antioxidant, lubricant, and polyolefin acid absorber were weighed according to the formula and mixed evenly in a high-speed mixer at a mixing temperature of 45° C., a stirring speed of 300 rpm, and a mixing time of 5 min to obtain a second mixture;

[0068] (3) feeding the second mixture into a main feeding port of a co-rotating twin-screw extruder with a side feeding port, feeding the first mixture into the side feeding port, and melt-extruding and granulating at 180° C., and drying to obtain the product.

[0069] Comparative Examples 1-6

[0070] The present invention is as follows: Comparative Examples 1-6, the raw material composition and proportion (by weight) of the sheath material are shown in Table 2 below.

[0071] The present invention is as follows: Comparative Examples 1-6, the components used are all commercially available products, and the relevant information is the same as that of Examples 1-5.

[0072] Table 2 Comparative Examples 1-6 Formula

[0073] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 mLLDPE1 resin 52 100 - 52 52 55 mLLDPE2 resin 48 - 100 48 - 45 EVA - - - - 48 - Low surface area conductive filler 40 32 35 32 32 30 High surface area conductive filler - 3 - 3 3 - Semi-polar copolymer - 0.2 - - 0.2 0.1 PE wax 2.7 2.5 2.7 2.7 2.5 2.0 Antioxidants 1.0 1.0 1.0 1.0 1.0 1.0 Lubricants 0.1 0.1 0.1 0.1 0.1 0.08 Acid absorbent 0.3 0.3 0.3 0.3 0.3 0.1

[0074] In the comparative example 1 of the present invention, the conductive fillers in Example 4 are all replaced with conductive fillers with low specific surface area, the amount is 40 parts by weight, the PE wax is 2.7 parts by weight, and the other formulas and amounts are the same as those in Example 4; the specific preparation process is carried out in the following manner:

[0075] (1) drying a low specific surface area conductive filler, adding PE wax, weighing according to a formula, and mixing in a high-speed mixer at a mixing temperature of 110° C., a stirring speed of 1000 rpm, and a mixing time of 15 min to obtain a first mixture;

[0076] (2) mLLDPE1 resin, mLLDPE2 resin, antioxidant, lubricant, and polyolefin acid absorber were weighed according to the formula and mixed evenly in a high-speed mixer at a mixing temperature of 45° C., a stirring speed of 300 rpm, and a mixing time of 5 min to obtain a second mixture;

[0077] (3) feeding the second mixture into a main feeding port of a co-rotating twin-screw extruder with a side feeding port, feeding the first mixture into the side feeding port, and melt-extruding and granulating at 180° C., and drying to obtain the product.

[0078] In the comparative example 2 of the present invention, all the resins in Example 4 are replaced with mLLDPE1 resin in an amount of 100 parts, and the rest of the formula, amount and preparation process are the same as those in Example 4.

[0079] In the comparative example 3 of the present invention, all the resins in Example 4 are replaced with mLLDPE2 resin in an amount of 100 parts, all the conductive fillers are replaced with low specific surface area conductive fillers in an amount of 35 parts, the total amount of PE wax is 2.7 parts, and the remaining formulas and amounts are the same as in Example 4, and the specific preparation process is the same as in Comparative Example 1.

[0080] In the comparative example 4 of the present invention, the semi-polar copolymer in Example 4 is replaced by PE wax, and the total amount of PE wax is 2.7 parts. The remaining formulas, amounts and preparation processes are the same as those in Example 4, but the semi-polar copolymer in step 2 is replaced by an equal amount of PE wax.

[0081] In the comparative example 5 of the present invention, the mLLDPE2 resin in Example 4 is replaced by an equal amount of EVA, and the rest of the formula, dosage and implementation method are the same as in Example 4.

[0082] In the comparative example 6 of the present invention, all the conductive fillers in Example 1 are replaced with low specific surface area conductive fillers, and the amount is 30 parts. The other formulas and amounts are the same as in Example 1, and the preparation process is the same as in Comparative Example 1, but step 2 is changed to weighing the dried low specific surface area conductive filler, semi-polar copolymer and dispersant according to the formula and then putting them into a high-speed mixer for uniform mixing, and the other processes remain unchanged.

[0083] Experimental example

[0084] The properties of the sheath materials prepared in the above-mentioned embodiments 1-5 and comparative examples 1-6 were tested respectively, wherein the thermal deformation performance was tested according to GB / T 8815-2008. The test results are shown in Tables 3-4 below.

[0085] Table 3 Performance test results of Examples 1-5

[0086]

[0087] Table 4 Comparative Example Performance Test Results

[0088]

[0089]

[0090] It can be seen from the test results in Tables 3-4 above that without using conductive carbon black with high specific surface area (Comparative Examples 1, 3 and 6), the sheath material has a more obvious PTC effect, and the volume resistivity at 90°C is much higher than the volume resistivity at 25°C; when only mLLDPE resin with good mechanical properties but poor fluidity is used (Comparative Example 2), the sheath material is difficult to process; when only mLLDPE resin with good fluidity is used (Comparative Example 3), the tensile strength of the sheath material is low; without using semi-polar copolymer to treat conductive filler (Comparative Example 4), the tensile strength and conductivity of the sheath material prepared therefrom are low, and it also has a larger PTC effect; and when Comparative Example 5 uses EVA resin with a low melting point, the thermal deformation of the composition is large, and the tensile strength is also lower than the tensile strength of the composition of Example 4.

[0091] The sheath material of the present invention has excellent and stable electrical conductivity and a relatively high operating temperature. The PTC effect at high operating temperature is relatively weak or even has a relatively weak negative temperature coefficient (NTC) effect. In addition, it also has relatively good low temperature resistance and mechanical properties.

[0092] The embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A polyethylene-based semiconductive sheath material, characterized in that: The raw material components include the following parts by weight:

2. The polyethylene-based semiconductive sheath material according to claim 1, characterized in that: The raw material components include the following parts by weight:

3. The polyethylene-based semiconductive sheath material according to claim 1 or 2, characterized in that: The total amount of mLLDPE1 and mLLDPE2 is 100 parts by weight.

4. The polyethylene-based semiconductive sheath material according to any one of claims 1 to 3, characterized in that: The density of the low melt flow rate metallocene linear low density polyethylene mLLDPE1 is 0.914-0.920 g / cm 3 , the melt mass flow rate MFR is 0.8-2.5g / 10min, and the impact damage mass of the blown film is not less than 600g; The density of the low melt flow rate metallocene linear low density polyethylene mLLDPE2 is 0.914-0.920 g / cm 3 , the melt flow rate MFR is 3.5-4.5g / 10min.

5. The polyethylene-based semiconductive sheath material according to any one of claims 1 to 4, characterized in that: The specific surface area of ​​the low specific surface area conductive filler is 30-160m 2 / g, and an oil absorption value DBP of 90-300ml / 100g; preferably, the low specific surface area conductive filler includes conductive carbon black; The specific surface area of ​​the high specific surface area conductive filler is ≥800m 2 / g; Preferably, the high specific surface area conductive filler includes conductive carbon black and / or multi-walled carbon nanotubes.

6. The polyethylene-based semiconductive sheath material according to any one of claims 1 to 5, characterized in that: The semi-polar copolymer is a low molecular weight semi-polar copolymer. Preferably, the semi-polar copolymer comprises one or a mixture of polyester polyol copolymers, polyether polyol copolymers, and hydroxy acrylic resins; and / or, The dispersant comprises polyethylene wax PEW, preferably with a molecular weight of 2000-6000; and / or, The antioxidant includes one or a mixture of a mixture of hindered phenol antioxidants, phosphite antioxidants, thioester antioxidants, and thio-hindered phenol antioxidants; and / or, The lubricant includes silicone masterbatch and / or fluorine-containing polymer processing aid PPA; and / or, The acid scavenger includes a polyolefin acid scavenger, preferably calcium stearate and / or zinc stearate.

7. A method for preparing the polyethylene-based semiconductive sheath material according to any one of claims 1 to 6, characterized in that: The steps include: (1) taking selected amounts of the high specific surface area conductive filler, the semi-polar copolymer, the low specific surface area conductive filler, and the dispersant and mixing them to obtain a first mixed material for later use; (2) taking selected amounts of the low melt flow rate metallocene linear low density polyethylene mLLDPE1, the high melt flow rate metallocene linear low density polyethylene mLLDPE2, an antioxidant, a lubricant and an acid absorbent and mixing them to obtain a second mixture for standby use; (3) respectively feeding the first mixed material and the second mixed material into different feeding ports of a twin-screw extruder, and performing melt extrusion granulation to obtain the product.

8. The method for preparing the polyethylene-based semiconductive sheath material according to claim 7, characterized in that: In the step (1), the mixing temperature of the mixing step is 100-120° C.; and / or, In the step (1), the stirring speed of the mixing step is 800-1200 rpm; and / or, In the step (1), the stirring time of the mixing step is 10-20 min; and / or, In the step (2), the temperature of the mixing step is 30-55° C.; and / or, In the step (2), the stirring speed of the mixing step is 250-350 rpm; and / or, In the step (2), the stirring time of the mixing step is 3-8 min; and / or, In the step (3), the temperature of the melt extrusion step is 180-200° C.; and / or, In the step (3), the second mixture is fed into the main feeding port of the twin-screw extruder, and the first mixture 3 is fed into the side feeding port of the twin-screw extruder.

9. Use of the polyethylene-based semiconductive sheath material according to any one of claims 1 to 6 or the polyethylene-based semiconductive sheath material prepared by the method according to claim 8 or 9 for preparing cable material sheaths.

10. Cable material sheath and cable made from the polyethylene-based semiconductive sheath material according to any one of claims 1 to 6 or the polyethylene-based semiconductive sheath material prepared by the method according to claim 8 or 9.

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