CN113571234B - A high performance polypropylene thermoplastic cable - Google Patents

Abstract

The invention belongs to the field of electricity, and relates to a high-performance polypropylene thermoplastic cable. The cable includes: at least one conductor and at least one electrically insulating layer surrounding the conductor; wherein the material of the electric insulating layer is at least one polypropylene grafted heterocycle modified material; the modified polypropylene grafted heterocycle material comprises structural units derived from copolymerized polypropylene and structural units derived from alkenyl-containing heterocycle monomers; the modified material of the polypropylene grafted heterocycle is characterized in that the content of structural units which are derived from heterocyclic monomers containing alkenyl and are in a grafted state in the modified material of the polypropylene grafted heterocycle is 0.5-6wt%. The cable has higher working temperature, and has the advantages of thinner thickness of an electric insulation layer, better heat dissipation and smaller weight under the condition of ensuring the same voltage level and insulation level.

Description

A high performance polypropylene thermoplastic cable

Technical Field

The invention belongs to the electrical field, and in particular relates to a high-performance polypropylene thermoplastic cable.

Background Art

At present, cross-linked polyethylene is commonly used as the insulation material for high-voltage DC cables at home and abroad. Its working temperature is generally 70℃, and the long-term working design field strength is about 12kV/mm. At present, with the further increase of the operating voltage and transmission capacity of high-voltage DC cables, the operating environment of cable insulation has become more stringent due to the further increase of temperature and electric field strength, which puts forward higher requirements on the performance of cable insulation materials, that is, it still has strong insulation performance under higher temperature and electric field strength conditions. However, the working temperature of traditional cross-linked polyethylene has reached its use limit and cannot be further improved. Therefore, it is urgent to develop DC cables using new high-temperature and high-field insulation materials to meet the requirements of cable systems working under high voltage and large capacity conditions.

At present, the manufacturing of cross-linked polyethylene insulated DC cables mostly adopts a three-layer co-extrusion extruded insulation preparation method. The extrusion process is mainly divided into three steps: heating and melting of the insulating material, cross-linking (vulcanization), and cooling and molding. Cross-linking initiators are generally used to make polyethylene molecules undergo cross-linking reactions, which makes the production process of the cable more complicated. In addition, due to the introduction of cross-linking initiators, cross-linking byproduct impurities are inevitably introduced into the main insulation, which will have a certain negative impact on the insulation performance of the finished cable. In addition, cross-linked polyethylene is a thermosetting plastic that cannot be recycled, and its high-temperature decomposition products are extremely harmful to the environment. Therefore, in order to simplify the production process of cables, improve the final quality of cable insulation, and eliminate the possible harm to the environment, it is necessary to find a new type of thermoplastic recyclable cable insulation material and its preparation process to replace the traditional polyethylene material and its cross-linking process, so as to realize the manufacturing and engineering application of low-cost, high-performance, recyclable insulated power cables.

Summary of the invention

The purpose of the present invention is to overcome the problem that existing cable products cannot meet the requirements of stable operation under high temperature and high field strength, and to provide a high-performance polypropylene thermoplastic cable. The cable uses a modified material of polypropylene grafted heterocyclic as the main insulation layer. Compared with existing cables, it can still maintain or even have a higher volume resistivity and stronger breakdown resistance at higher operating temperatures, and its mechanical properties can also meet the cable use requirements.

The present invention provides a high-performance polypropylene thermoplastic cable, the cable comprising:

at least one conductor and at least one electrically insulating layer surrounding said conductor;

Wherein, the material of the electrical insulating layer is at least one modified material of polypropylene grafted with heterocyclic rings;

The modified material of polypropylene grafted heterocycles comprises structural units derived from copolymerized polypropylene and structural units derived from heterocyclic monomers containing alkenyl groups; based on the weight of the modified material of polypropylene grafted heterocycles, the content of structural units derived from heterocyclic monomers containing alkenyl groups and in a grafted state in the modified material of polypropylene grafted heterocycles is 0.5-6wt%, preferably 0.5-4wt%.

The core of the present invention is to use a new material as the electrical insulation layer of the cable. Therefore, the present invention has no special restrictions on the form and specific structure of the cable, and can adopt various conventional cable forms (DC or AC, single core or multi-core) and corresponding structures in the field. In the cable of the present invention, except that the electrical insulation layer adopts the new grafted modified polypropylene material, the other layer structures and other layer materials can be selected conventionally in the field.

The cable of the present invention may be a DC cable or an AC cable; preferably a DC cable; more preferably, the cable is a medium-high voltage DC cable or an ultra-high voltage DC cable. In the present invention, low voltage (LV) means a voltage lower than 1 kV, medium voltage (MV) means a voltage in the range of 1 kV to 40 kV, high voltage (HV) means a voltage higher than 40 kV, preferably higher than 50 kV, and ultra-high voltage (EHV) means a voltage of at least 230 kV.

According to a preferred embodiment of the present invention, the cable has at least one cable core, and each of the cable cores includes, from the inside to the outside, a conductor, an optional conductor shielding layer, an electrical insulation layer, an optional electrical insulation shielding layer, and an optional metal shielding layer. The conductor shielding layer, the electrical insulation shielding layer, and the metal shielding layer can be provided as required, and are generally used in cables above 6 kV.

In addition to the above structures, the cable may further include an armor and/or a sheath layer.

The cable of the present invention can be a single-core cable or a multi-core cable. For a multi-core cable, the cable can also include a filling layer and/or a tape layer. The filling layer is formed by a filling material filled between each core. The tape layer is coated on the outside of all cores to ensure that the core and the filling layer are round, prevent the core from being scratched by the armor, and play a flame retardant role.

In the cable of the present invention, the conductor is a conductive element usually made of metal material, preferably aluminum, copper or other alloys, including one or more metal wires. The DC resistance and the number of single wires of the conductor must meet the requirements of GB/T 3956. The preferred conductor adopts a compact stranded circular structure with a nominal cross-sectional area of less than or equal to ^800mm2 ; or adopts a split conductor structure with a nominal cross-sectional area of greater than or equal to ^1000mm2 , and the number of conductors is not less than 170.

In the cable of the present invention, the conductor shielding layer can be a covering layer made of materials such as polypropylene, polyolefin elastomer and carbon black, with a volume resistivity of less than 1.0Ω·m at 23°C and a volume resistivity of less than 3.5Ω·m at 90°C, a melt flow rate of 0.01 to 30g/10min at 230°C and a load of 2.16kg, preferably 0.05 to 20g/10min, more preferably 0.1 to 10g/10min, and more preferably 0.2 to 8g/10min; tensile strength ≥12.5MPa; elongation at break ≥150%. The thickness of the thinnest point of the conductor shielding layer is not less than 0.5mm, and the average thickness is not less than 1.0mm.

In the cable of the present invention, the material of the electrical insulation layer is at least one modified material of polypropylene grafted heterocycles, which means that the substrate constituting the electrical insulation layer is the modified material of polypropylene grafted heterocycles, and in addition to the modified material of polypropylene grafted heterocycles, it may also contain other components, such as polymer components or additives, preferably additives, such as any one or more of antioxidants, stabilizers, processing aids, flame retardants, water tree retardant additives, acid or ion scavengers, inorganic fillers, voltage stabilizers and anti-copper agents. The types and amounts of additives are conventional and known to those skilled in the art.

The method for preparing the electric insulating layer of the present invention can also adopt conventional methods in the field of cable preparation, for example, the modified material of polypropylene grafted heterocycle is mixed with various optional additives, granulated by a twin-screw extruder, and then the obtained granules are extruded by an extruder to prepare the electric insulating layer. Generally, the conductor shielding material and the modified material granules of polypropylene grafted heterocycle can be co-extruded to form a structure of conductor shielding layer + electric insulating layer, or a structure of conductor shielding layer + electric insulating layer + electric insulating shielding layer. The specific operations can all adopt conventional methods and process conditions in the field.

Due to the use of the modified material of polypropylene grafted heterocycles, the thickness of the electrical insulating layer of the present invention can be only 50% to 95% of the nominal thickness of the XLPE insulating layer in GB/T 12706. Preferably, the thickness of the electrical insulating layer is 70% to 90% of the nominal thickness of the XLPE insulating layer in GB/T12706; the eccentricity is not greater than 10%.

In the cable of the present invention, the electrical insulation shielding layer can be a covering layer made of materials such as polypropylene, polyolefin elastomer and carbon black, with a volume resistivity of less than 1.0Ω·m at 23°C and a volume resistivity of less than 3.5Ω·m at 90°C. The melt flow rate at 230°C and 2.16kg load is 0.01-30g/10min, preferably 0.05-20g/10min, further preferably 0.1-10g/10min, and more preferably 0.2-8g/10min; the tensile strength is ≥12.5MPa; the elongation at break is ≥150%. The thickness of the thinnest point of the electrical insulation shielding layer is not less than 0.5mm, and the average thickness is not less than 1.0mm.

In the cable of the present invention, the metal shielding layer may be a copper tape shielding layer or a copper wire shielding layer.

In the cable of the present invention, the filling layer may be made of a polymer material, such as PE/PP/PVC or recycled rubber material.

In the cable of the present invention, the tape layer/armor layer is usually a metal covering layer made of a copper wire metal cage, a lead or aluminum metal sheath, etc., which wraps the outer surface of the electrical insulation shielding layer and has a DC volume resistivity of ≤1000Ω·m at room temperature.

In the cable of the present invention, the material of the sheath layer can be any one of polyvinyl chloride, polyethylene or low-smoke halogen-free material. The sheath layer includes both an inner sheath layer and an outer sheath layer.

Each of the above-mentioned layer structures can be prepared by conventional methods in the art. For example, the conductor shielding layer, the electrical insulation layer, and the sheath layer can be formed by extrusion coating with an extruder, and the metal shielding layer and the armor can be formed by wrapping.

In the modified material of polypropylene grafted heterocycle used in the present invention, the "structural unit" means that it is a part of the modified material of polypropylene grafted heterocycle, and its form is not limited. Specifically, the "structural unit derived from copolymerized polypropylene" refers to the product formed by copolymerized polypropylene, which includes both the "group" form and the "polymer" form. The "structural unit derived from alkenyl-containing heterocyclic monomers" refers to the product formed by alkenyl-containing heterocyclic monomers, which includes both the "group" form and the "monomer" form, and also the "polymer" form. The "structural unit" can be a repeating unit or a non-repeating independent unit.

In the present invention, the structural unit derived from the alkenyl group-containing heterocyclic monomer "in a grafted state" refers to the structural unit derived from the alkenyl group-containing heterocyclic monomer covalently linked (grafted) to the copolymerized polypropylene.

In the present invention, the meaning of "comonomer" of copolymerized polypropylene is well known to those skilled in the art, and refers to a monomer copolymerized with propylene.

According to the present invention, preferably, the graft modified polypropylene material is obtained by grafting copolymerized polypropylene and an olefinic heterocyclic monomer, preferably by solid phase grafting. The grafting reaction of the present invention is a free radical polymerization reaction, therefore, the "grafted state" refers to the state in which the reactant is connected with another reactant after free radical polymerization. The connection includes both direct connection and indirect connection.

During the grafting reaction, the alkenyl-containing heterocyclic monomers can polymerize to form a certain amount of ungrafted polymers. The term "graft-modified polypropylene material" of the present invention includes both the product (crude product) directly obtained by grafting copolymerized polypropylene and alkenyl-containing heterocyclic monomers, and the pure graft-modified polypropylene obtained by further purifying the product.

According to the present invention, the modified material of the polypropylene grafted heterocycle as the electrical insulating layer material preferably has at least one of the following characteristics: a melt flow rate at 230°C and a load of 2.16 kg of 0.01 to 30 g/10 min, preferably 0.05 to 20 g/10 min, further preferably 0.1 to 10 g/10 min, more preferably 0.2 to 5 g/10 min; a flexural modulus of 20 to 900 MPa, more preferably 50 to 600 MPa; an elongation at break ≥ 200%, preferably an elongation at break ≥ 300%; and a tensile strength greater than 5 MPa, preferably 10 to 40 MPa.

In addition, in terms of electrical properties, the modified material of polypropylene grafted heterocycle has at least one of the following characteristics:

- The working temperature of the modified material of polypropylene grafted heterocycle is ≥ 90°C, preferably 90-160°C;

- The breakdown field strength E _g of the modified material of polypropylene grafted heterocycle at 90° C. is ≥190 kV/mm, preferably 190 to 800 kV/mm;

- the breakdown field strength change rate ΔE/E obtained by dividing the difference ΔE between the breakdown field strength _Eg of the modified material grafted with heterocyclic polypropylene at 90°C and the breakdown field strength E of the copolymerized polypropylene at 90°C by the breakdown field strength E of the copolymerized polypropylene at 90°C is greater than 1%, preferably 1.5% to 50%, more preferably 2% to 35%, and further preferably 5% to 25%;

- the DC volume resistivity ρ _vg of the modified material of polypropylene grafted heterocycle at 90°C and 15 kV/mm field strength is ≥7×10 ¹² Ω·m, preferably 7×10 ¹² Ω·m to 1.0×10 ²⁰ Ω·m;

- the ratio of the DC volume resistivity ρ _vg of the modified material of the polypropylene grafted heterocycle at 90°C and 15 kV/mm field strength to the DC volume _resistivity ρ _v of the copolymerized polypropylene at 90°C and 15 kV/mm _field strength is greater than 1, preferably 1.1 to 20, more preferably 1.2 to 10, and further preferably 1.3 to 4;

- The dielectric constant of the modified material of polypropylene grafted with heterocyclic rings at 90°C and 50 Hz is greater than or equal to 2.0, preferably 2.0 to 2.5.

According to the present invention, the copolymerized polypropylene (the basic polypropylene in the present invention) is a propylene copolymer containing ethylene or a higher α-olefin or a mixture thereof. Specifically, the comonomer of the copolymerized polypropylene is selected from at least one of C ₂ -C ₈ α-olefins other than propylene. The C ₂ -C ₈ α-olefins other than propylene include, but are not limited to: at least one of ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene, preferably ethylene and/or 1-butene, and more preferably, the copolymerized polypropylene consists of propylene and ethylene.

The copolymerized polypropylene of the present invention can be a heterophasic propylene copolymer. The heterophasic propylene copolymer can contain a propylene homopolymer or a propylene random copolymer matrix component (1), and another propylene copolymer component (2) dispersed therein. In the propylene random copolymer, the comonomer is randomly distributed on the main chain of the propylene polymer. Preferably, the copolymerized polypropylene of the present invention is a heterophasic propylene copolymer prepared in situ in a reactor by an existing process.

According to a preferred embodiment, the heterophasic propylene copolymer comprises a propylene homopolymer matrix or a random copolymer matrix (1), and a propylene copolymer component (2) containing one or more ethylene or higher α-olefin comonomers dispersed therein. The heterophasic propylene copolymer may be an island-in-sea structure or a bicontinuous structure.

In the art there are two types of heterophasic propylene copolymers known, heterophasic propylene copolymers containing propylene random copolymers as matrix phase or heterophasic propylene copolymers containing propylene homopolymers as matrix phase. The random copolymer matrix (1) is a copolymer formed by randomly distributed comonomer parts in the polymer chain, in other words, consisting of an alternating sequence of two monomer units of random length (including single molecules). Preferably, the comonomer in the matrix (1) is selected from ethylene or butene. Particularly preferably, the comonomer in the matrix (1) is ethylene.

Preferably, the propylene copolymer (2) dispersed in the homopolymer or copolymer matrix (1) of the heterophasic propylene copolymer is substantially amorphous. The term "substantially amorphous" means here that the propylene copolymer (2) has a lower crystallinity than the homopolymer or copolymer matrix (1).

According to the present invention, in addition to the above-mentioned composition characteristics, the copolymerized polypropylene has at least one of the following characteristics: a comonomer content of 0.5 to 40 mol%, preferably 0.5 to 30 mol%, preferably 4 to 25 wt%, and more preferably 4 to 22 wt%; a xylene soluble content of 2 to 80 wt%, preferably 18 to 75 wt%, further preferably 30 to 70 wt%, and more preferably 30 to 67 wt%; a comonomer content in the solubles of 10 to 70 wt%, preferably 10 to 50 wt%, and more preferably 20 to 35 wt%; and a ratio of the intrinsic viscosity of the solubles to the polypropylene of 0.3 to 5, preferably 0.5 to 3, and more preferably 0.8 to 1.3.

According to the present invention, preferably, the copolymerized polypropylene also has at least one of the following characteristics: the melt flow rate at 230°C and 2.16kg load is 0.01-60g/10min, preferably 0.05-35g/10min, and more preferably 0.5-8g/10min; the melting temperature Tm is above 100°C, preferably 110-180°C, more preferably 110-170°C, more preferably 120-170°C, and more preferably 120-166°C. The weight average molecular weight is preferably 20×10 ⁴ to 60×10 ⁴ g/mol. The basic polypropylene with high Tm has satisfactory impact strength and flexibility at both low and high temperatures. In addition, when using the basic polypropylene with high Tm, the grafted modified polypropylene of the present invention has the advantage of being able to withstand higher working temperatures. The copolymerized polypropylene of the present invention is preferably a porous granular or powdery resin.

According to the present invention, preferably, the copolymerized polypropylene also has at least one of the following characteristics: a flexural modulus of 10 to 1000 MPa, preferably 50 to 600 MPa; an elongation at break of ≥ 200%, preferably an elongation at break of ≥ 300%. Preferably, the copolymerized polypropylene has a tensile strength greater than 5 MPa, preferably 10 to 40 MPa.

The copolymerized polypropylene of the present invention may include, but is not limited to, any commercially available polypropylene powder suitable for the present invention, such as NS06 of Sinopec Wuhan Petrochemical, SPF179 of Sinopec Qilu Petrochemical, etc., and may also be produced by the polymerization process described in Chinese patents CN1081683, CN1108315, CN1228096, CN1281380, CN1132865C and CN102020733A, etc. Commonly used polymerization processes include the Spheripol process of Basell, the Hypol process of Mitsui Chemicals, the Borstar PP process of Borealis, the Unipol process of DOW Chemicals, the Innovene gas phase process of INEOS (formerly BP-Amoco), etc.

The alkenyl-containing heterocyclic monomer of the present invention may be any alkenyl-containing heterocyclic compound that can be polymerized by free radicals, and may be selected from at least one of imidazole containing alkenyl substituents, pyrazole containing alkenyl substituents, carbazole containing alkenyl substituents, pyrrolidone containing alkenyl substituents, pyridine or pyridinium salt containing alkenyl substituents, piperidine containing alkenyl substituents, caprolactam containing alkenyl substituents, pyrazine containing alkenyl substituents, thiazole containing alkenyl substituents, purine containing alkenyl substituents, morpholine containing alkenyl substituents and oxazoline containing alkenyl substituents; preferably, the alkenyl-containing heterocyclic monomer is a monoalkenyl-containing heterocyclic monomer.

Specifically, the alkenyl-containing heterocyclic monomer can be selected from: at least one of 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-allylimidazole, 1-vinylpyrazole, 3-methyl-1-vinylpyrazole, vinylcarbazole, N-vinylpyrrolidone, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine, vinylpyridine N-oxide, vinylpyridinium salt, vinylpiperidine, N-vinylcaprolactam, 2-vinylpyrazine, N-vinylpiperazine, 4-methyl-5-vinylthiazole, N-vinylpurine, vinylmorpholine and vinyloxazoline.

The polypropylene grafted heterocyclic modified material of the present invention can be prepared by a method comprising the following steps: in the presence of an inert gas, a reaction mixture comprising copolymerized polypropylene and an olefin-containing heterocyclic monomer is subjected to a solid phase grafting reaction to obtain the polypropylene grafted heterocyclic modified material.

The grafting reaction of the present invention can be carried out by referring to various conventional methods in the art, preferably a solid phase grafting reaction. For example, active grafting points are formed on the copolymerized polypropylene in the presence of a grafting alkenyl-containing heterocyclic monomer, or active grafting points are first formed on the copolymerized polypropylene and then treated with a grafting monomer. The grafting points can be formed by treatment with a free radical initiator, or by high-energy ionizing radiation or microwave treatment. Free radicals generated in the polymer as a result of chemical or radiation treatment form grafting points on the polymer and initiate polymerization of monomers at these points.

Preferably, the grafting point is initiated by a free radical initiator and the grafting reaction is further carried out. In this case, the reaction mixture also includes a free radical initiator; further preferably, the free radical initiator is selected from a peroxide free radical initiator and/or an azo free radical initiator.

Among them, the peroxide free radical initiator is preferably selected from at least one of dibenzoyl peroxide, diisopropyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dodecyl peroxide, tert-butyl perbenzoate, diisopropyl peroxydicarbonate, tert-butyl peroxy (2-ethylhexanoate) and dicyclohexyl peroxydicarbonate; the azo free radical initiator is preferably azobisisobutyronitrile and/or azobisisoheptylnitrile.

More preferably, the grafting point is initiated by a peroxide-based free radical initiator and further the grafting reaction proceeds.

In addition, the grafting reaction of the present invention can also be carried out by the methods described in CN106543369A, CN104499281A, CN102108112A, CN109251270A, CN1884326A and CN101492517B.

Under the premise of meeting the above product characteristics, the present invention has no particular limitation on the amount of each component used in the grafting reaction. Specifically, the mass ratio of the free radical initiator to the heterocyclic monomer containing an olefin group can be 0.1 to 10:100, preferably 0.5 to 5:100. The mass ratio of the heterocyclic monomer containing an olefin group to the copolymerized polypropylene can be 0.3 to 12:100, preferably 0.5 to 10:100.

The process conditions of the grafting reaction are not particularly limited in the present invention. Specifically, the grafting reaction temperature can be 30 to 130° C., preferably 60 to 120° C.; the grafting reaction time can be 0.5 to 10 h, preferably 1 to 5 h.

In the present invention, the "reaction mixture" includes all materials added to the grafting reaction system. The materials can be added at one time or at different stages of the reaction.

The reaction mixture of the present invention may further include a dispersant, which is preferably water or an aqueous solution of sodium chloride. The mass amount of the dispersant is preferably 50 to 300% of the mass of the copolymerized polypropylene.

The reaction mixture of the present invention may further include an interfacial agent, which is an organic solvent having a swelling effect on polyolefins, preferably at least one of the following organic solvents having a swelling effect on copolymerized polypropylene: ether solvents, ketone solvents, aromatic hydrocarbon solvents, and alkane solvents; more preferably at least one of the following organic solvents: chlorobenzene, polychlorinated benzene, alkanes or cycloalkanes with _{a C6} or higher content, benzene, _C1 - _C4 alkyl substituted benzene, _C2 - _C6 fatty ethers, _C3 - _C6 fatty ketones, and decalin; further preferably at least one of the following organic solvents: benzene, toluene, xylene, chlorobenzene, tetrahydrofuran, ether, acetone, hexane, cyclohexane, decalin, and heptane. The mass content of the interfacial agent is preferably 1-30% of the mass of the copolymerized polypropylene, and more preferably 10-25%.

The reaction mixture of the present invention may further include an organic solvent as a solvent for dissolving the solid free radical initiator, and the organic solvent preferably includes at least one of C2 _{- C5} alcohols, _C2 - _C4 ethers and _C3 - _C5 ketones, more preferably includes at least one of _C2 - _C4 alcohols, C2 _{- C3} ethers and _C3 - _C5 ketones, and most preferably includes at least one of ethanol, ether and acetone. The mass content of the organic solvent is preferably 1-35% of the mass of the copolymerized polypropylene.

In the preparation method of the polypropylene grafted heterocyclic modified material of the present invention, the definitions of the olefinic heterocyclic monomer and copolymerized polypropylene are the same as those mentioned above and will not be repeated here.

According to the present invention, the preparation method of the modified material of polypropylene grafted heterocycle can be selected from one of the following methods:

Mode 1, the preparation method comprises the following steps:

a. placing the copolymerized polypropylene in a closed reactor and replacing it with an inert gas;

b. adding a free radical initiator and an olefin-containing heterocyclic monomer into the closed reactor and stirring to mix;

c. optionally adding an interfacial agent, and optionally causing the reaction system to swell;

d. optionally adding a dispersant, heating the reaction system to the grafting reaction temperature, and performing the grafting reaction;

e. After the reaction is completed, filtering (when using an aqueous phase dispersant) and drying are optionally performed to obtain the modified material of the polypropylene grafted heterocycle.

More specifically, the preparation method comprises the following steps:

a. placing the copolymerized polypropylene in a closed reactor and replacing it with an inert gas;

b. dissolving the free radical initiator in the alkenyl-containing heterocyclic monomer to prepare a solution, adding the solution to a closed reactor containing copolymerized polypropylene, and stirring to mix;

c. adding 0 to 30 parts of an interfacial agent, and optionally allowing the reaction system to swell at 20 to 60 ° C for 0 to 24 hours;

d. Add 0 to 300 parts of dispersant, heat the system to the graft polymerization temperature of 30 to 130 ° C, and react for 0.5 to 10 hours;

e. After the reaction is completed, filtering (when using an aqueous phase dispersant) and drying are optionally performed to obtain the modified material of the polypropylene grafted heterocycle.

Mode 2, the preparation method comprises the following steps:

a. placing the copolymerized polypropylene in a closed reactor and replacing it with an inert gas;

b. mixing an organic solvent and a free radical initiator and adding the mixture to the closed reactor;

c. removing the organic solvent;

d. adding an alkenyl-containing heterocyclic monomer, optionally adding an interfacial agent, and optionally causing the reaction system to swell;

e. optionally adding a dispersant, heating the reaction system to the grafting reaction temperature, and performing the grafting reaction;

f. After the reaction is completed, filtering (when using an aqueous phase dispersant) and drying are optionally performed to obtain the polypropylene grafted heterocyclic modified material.

More specifically, the preparation method comprises the following steps:

a. placing the copolymerized polypropylene in a closed reactor and replacing it with an inert gas;

b. mixing an organic solvent and a free radical initiator to prepare a solution and adding it to a closed reactor containing copolymerized polypropylene;

c. removing the organic solvent by purging with an inert gas or by vacuum;

d. adding an alkenyl-containing heterocyclic monomer, adding 0 to 30 parts of an interfacial agent, and optionally allowing the reaction system to swell at 20 to 60° C. for 0 to 24 hours;

e. Add 0 to 300 parts of dispersant, heat the system to the graft polymerization temperature of 30 to 130 ° C, and react for 0.5 to 10 hours;

f. After the reaction is completed, filtering (when using an aqueous phase dispersant) and drying are optionally performed to obtain the modified material of the polypropylene grafted heterocycle.

According to the method of the present invention, if there are volatile components in the system after the reaction is completed, the method of the present invention preferably includes a step of devolatilization, which can be carried out by any conventional method, including vacuum extraction or use of a stripping agent at the end of the grafting process. Suitable stripping agents include, but are not limited to, inert gases.

As described above, the "polypropylene grafted heterocyclic modified material" of the present invention includes both the product (crude product) directly obtained by grafting copolymerized polypropylene and heterocyclic monomers containing alkenyl groups, and the grafted modified polypropylene pure product obtained by further purifying the product. Therefore, the preparation method of the present invention may optionally include a step of purifying the crude product. The purification may be carried out by various conventional methods in the art, such as extraction.

The present invention does not particularly limit the grafting efficiency of the grafting reaction, but a higher grafting efficiency is more conducive to obtaining a polypropylene grafted heterocyclic modified material with desired properties through a one-step grafting reaction. Therefore, it is preferred to control the grafting efficiency of the grafting reaction to be 30-100%, and more preferably 35-80%. The concept of the grafting efficiency is well known to those skilled in the art, and refers to the amount of heterocyclic monomer grafted/the total amount of heterocyclic monomer fed to the reaction.

The inert gas of the present invention can be any inert gas commonly used in the art, including but not limited to nitrogen and argon.

The cable of the present invention can be prepared by various conventional preparation processes in the art, and the present invention has no particular limitation thereto.

According to a specific embodiment of the present invention, the preparation method of the cable is as follows:

Preparation of the conductor: a plurality of single-filament conductors (such as aluminum) are compressed and twisted together to obtain a conductor core; or a wire bundling operation is performed, and then the single-filament conductors after the wire bundling are twisted together to obtain a conductor core.

Preparation of particles of the modified material of polypropylene grafted with heterocycles: the modified material of polypropylene grafted with heterocycles is mixed with optional additives and granulated by a twin-screw extruder.

Preparation of conductor shielding layer and electrical insulation layer: The conductor shielding material and the modified material particles of the above-mentioned polypropylene grafted heterocycle are co-extruded and coated on the outside of the conductor core through an extruder to form a conductor shielding layer + electrical insulation layer, or to form a conductor shielding layer + electrical insulation layer + electrical insulation shielding layer (outer shielding layer).

Preparation of metal shielding layer: Copper tape or copper wire is wrapped around the electrical insulation layer (electrical insulation shielding layer) to form a metal shielding layer.

Preparation of the inner sheath layer: The sheath layer pellets are extruded outside the metal shielding layer through an extruder to form the inner sheath layer.

Preparation of armor: Use galvanized steel/stainless steel/aluminum alloy to make steel wire or steel belt armor, which is wrapped around the inner sheath layer with a single layer of armor in the left direction or a double layer of armor with an inner layer in the right direction and an outer layer in the left direction. The steel wire or steel belt armor should be tight to minimize the gap between adjacent steel wires/steel belts.

Preparation of outer sheath layer: The sheath layer pellets are extruded outside the armor through an extruder to form an outer sheath layer.

Finally, the high-performance polypropylene thermoplastic cable is obtained.

Compared with existing cables, the cable of the present invention can still maintain or even have a higher volume resistivity and stronger breakdown resistance at a higher operating temperature, and its mechanical properties can also meet the cable use requirements. Under the condition of ensuring the same voltage level and insulation level, the electrical insulation layer made of the modified material of polypropylene grafted heterocycle has the advantages of thinner thickness, better heat dissipation and smaller weight than the electrical insulation layer of conventional cables. Therefore, the cable has a wider range of applications.

Other features and advantages of the present invention will be described in detail in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

FIG1 is a schematic diagram of the three-dimensional structure of a cable in a specific embodiment of the present invention.

Description of Reference Numerals

1- conductor; 2- conductor shielding layer; 3- electrical insulation layer; 4- electrical insulation shielding layer; 5- metal shielding layer; 6- inner sheath layer; 7- armor; 8- outer sheath layer.

DETAILED DESCRIPTION

The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

In the following examples and comparative examples:

1. Determination of comonomer content in copolymerized polypropylene:

The comonomer content is determined by quantitative Fourier transform infrared (FTIR) spectroscopy. The correlation of the determined comonomer content is calibrated by quantitative nuclear magnetic resonance (NMR) spectroscopy. The calibration method based on the results obtained by quantitative ¹³ C-NMR spectroscopy is carried out according to conventional methods in the art.

2. Determination of xylene soluble content, comonomer content in soluble matter and intrinsic viscosity ratio of soluble matter/copolymerized polypropylene:

The test was conducted using the CRYST-EX instrument from Polymer Char. Trichlorobenzene was used as solvent, the temperature was raised to 150°C for dissolution, the temperature was kept constant for 90 minutes, a sample was taken for testing, the temperature was then lowered to 35°C, the temperature was kept constant for 70 minutes, and a sample was taken for testing.

3. Determination of weight average molecular weight of copolymer polypropylene:

High temperature GPC was used for determination. The PL-GPC 220 gel permeation chromatograph of Polymer Laboratory was used. The sample was dissolved in 1,2,4-trichlorobenzene at a concentration of 1.0 mg/ml. The test temperature was 150°C and the solution flow rate was 1.0 ml/min. The molecular weight of polystyrene was used as the internal reference to develop a standard curve. The molecular weight and molecular weight distribution of the sample were calculated based on the elution time.

4. Determination of melt flow rate MFR:

According to the method specified in GB/T 3682-2018, the melt index was measured using a CEAST 7026 melt indexer at 230°C and a load of 2.16 kg.

5. Determination of melting temperature Tm:

Differential scanning calorimetry was used to analyze the melting and crystallization processes of the material. The specific operation was as follows: Under nitrogen protection, 5 to 10 mg of sample was measured from 20°C to 200°C using a three-stage temperature rise and fall measurement method, and the change in heat flow reflected the melting and crystallization process of the material, thereby calculating the melting temperature Tm.

6. Determination of grafting efficiency GE and parameter M1:

2-4 g of the grafted product was placed in a Soxhlet extractor and extracted with ethyl acetate for 24 hours to remove unreacted monomers and homopolymers to obtain a pure grafted product, which was dried and weighed to calculate the parameters M1 and grafting efficiency GE.

The parameter M1 represents the content of the structural unit derived from the heterocyclic monomer containing an olefin group in the modified material of the polypropylene grafted heterocyclic ring. In the present invention, the calculation formulas of M1 and GE are as follows:

In the above formula, _w0 is the mass of the PP matrix; _w1 is the mass of the grafted product before extraction; _w2 is the mass of the grafted product after extraction; and _w3 is the mass of the added heterocyclic monomer.

7. Determination of DC volume resistivity:

The determination was carried out according to the method specified in GB/T 1410-2006.

8. Determination of breakdown field strength:

The determination was carried out according to the method specified in GB/T 1408-2006.

9. Determination of tensile strength:

The determination was carried out according to the method specified in GB/T 1040.2-2006.

10. Determination of flexural modulus:

The determination was carried out according to the method specified in GB/T 9341-2008.

11. Determination of elongation at break:

The determination was carried out according to the method specified in GB/T 1040-2006.

12. Determination of dielectric constant and dielectric loss factor:

The determination was carried out according to the method specified in GB/T 1409-2006.

13. Determination of the main insulation conductivity (resistivity) ratio of the cable:

The test is carried out according to the method specified in Appendix A of TICW 7.1-2012. The main insulation conductivity ratio is equal to the main insulation conductivity of the cable at 90°C divided by the main insulation conductivity of the cable at 30°C.

14. Cable insulation space charge injection test (determination of electric field distortion rate):

The cable insulation space charge injection test shall be carried out according to the method specified in Appendix B of TICW 7.1-2012.

15. DC withstand voltage test:

At room temperature, the cable is continuously pressurized with 1.85 times the rated voltage of negative polarity for 2 hours. If there is no breakdown or discharge, it passes, otherwise it fails.

16. Load cycle test:

The cable is heated to 90℃ at the rated operating temperature and pressurized with 1.85 times the rated voltage for 8 hours, then cooled naturally and the voltage is removed for 16 hours, and the cycle is repeated for 12 days. If no breakdown occurs, it is considered to have passed.

The starting materials used in the examples are described in Table A below.

Table A

name describe Copolymer polypropylene 1* Reference CN101679557A described method homemade Copolymer polypropylene 2* Reference CN101679557A described method homemade Copolymer polypropylene 3* Reference CN101679557A described method homemade Copolymer polypropylene 4* Reference CN101058654A described method homemade Polypropylene T30S Homopolymer polypropylene, Sinopec Zhenhai Refining & Chemical Benzoyl peroxide J&K Chemicals 4-Vinylpyridine J&K Chemicals Poly (4-vinylpyridine) Sigma-Aldrich LLC.

* Copolymer polypropylene 1: Copolymer polypropylene used in Example 1.

* Copolymer polypropylene 2: Copolymer polypropylene used in Example 2.

* Copolymer polypropylene 3: Copolymer polypropylene used in Example 3.

* Copolymer polypropylene 4: Copolymer polypropylene used in Example 4.

Example 1

The basic copolymerized polypropylene powder with the following characteristics was selected: ethylene content of comonomer 18.1wt%, xylene soluble content 48.7wt%, comonomer content in solubles 31.9wt%, solubles/copolymerized polypropylene intrinsic viscosity ratio 0.89, weight average molecular weight 34.3×10 ⁴ g/mol, MFR 1.21g/10min at 230°C and 2.16kg load, Tm=143.4°C, breakdown field strength (90°C) 236kV/mm, DC volume resistivity (90°C, 15kV/mm) 1.16E13Ω·m, and fine powder less than 40 mesh was removed by sieving. 2.0kg of the above basic copolymerized polypropylene powder was weighed and added into a 10L reactor with mechanical stirring, the reaction system was sealed, and nitrogen was replaced for deoxygenation. 1.2 g of dibenzoyl peroxide and 40 g of 4-vinylpyridine were added, stirred and mixed for 30 min, swelled at 50 ° C for 30 min, heated to 90 ° C, and reacted for 4 hours. After the reaction, nitrogen was purged to cool down to obtain polypropylene-g-4-vinylpyridine material product C1. The performance parameters of the obtained product were tested, and the results are shown in Table 1.

Example 2

The basic copolymerized polypropylene powder with the following characteristics was selected: ethylene content of comonomer 14.7wt%, xylene soluble content 41.7wt%, comonomer content in solubles 34.5wt%, solubles/copolymerized polypropylene intrinsic viscosity ratio 0.91, weight average molecular weight 36.6×10 ⁴ g/mol, MFR 1.54g/10min at 230°C and 2.16kg load, Tm=164.9°C, breakdown field strength (90°C) 248kV/mm, DC volume resistivity (90°C, 15kV/mm) 7.25E12Ω·m, and fine powder less than 40 mesh was removed by sieving. 2.0kg of the above basic copolymerized polypropylene powder was weighed and added into a 10L reactor with mechanical stirring, the reaction system was sealed, and nitrogen was replaced for deoxygenation. 2.2 g of dibenzoyl peroxide and 100 g of 4-vinylpyridine were added, stirred and mixed for 30 min, swelled at 50 ° C for 60 min, heated to 95 ° C, and reacted for 4 hours. After the reaction, nitrogen was purged to cool down to obtain polypropylene-g-4-vinylpyridine material product C2. The performance parameters of the obtained product were tested, and the results are shown in Table 1.

Example 3

The basic copolymerized polypropylene powder with the following characteristics was selected: ethylene content of comonomer 20.1wt%, xylene soluble content 66.1wt%, comonomer content in solubles 29.5wt%, solubles/copolymerized polypropylene intrinsic viscosity ratio 1.23, weight average molecular weight 53.8×10 ⁴ g/mol, MFR 0.51g/10min at 230°C and 2.16kg load, Tm=142.5°C, breakdown field strength (90°C) 176kV/mm, DC volume resistivity (90°C, 15kV/mm) 5.63E12Ω·m, and fine powder less than 40 mesh was removed by sieving. 2.0kg of the above basic copolymerized polypropylene powder was weighed and added into a 10L reactor with mechanical stirring, the reaction system was sealed, and nitrogen was replaced for deoxygenation. 4.5 g of dibenzoyl peroxide and 150 g of 4-vinylpyridine were added, stirred and mixed for 30 min, swelled at 50 ° C for 30 min, heated to 90 ° C, and reacted for 4 hours. After the reaction, nitrogen was purged to cool down to obtain polypropylene-g-4-vinylpyridine material product C3. The performance parameters of the obtained product were tested, and the results are shown in Table 1.

Example 4

The content of ethylene in the comonomer is 4.8wt%, the content of xylene solubles is 19.2wt%, the content of comonomer in the solubles is 17.6wt%, the ratio of solubles to copolymerized polypropylene intrinsic viscosity is 1.04, the weight average molecular weight is 29.2×10 ⁴ g/mol, the MFR at 230°C and 2.16kg load is 5.37g/10min, Tm=163.3°C, the breakdown field strength (90°C) is 322kV/mm, the DC volume resistivity (90°C, 15kV/mm) is 1.36E13Ω·m, and the fine powder less than 40 mesh is removed by sieving. Weigh 2.0kg of the above basic copolymerized polypropylene powder and add it into a 10L reactor with mechanical stirring, close the reaction system, and replace with nitrogen for deoxygenation. 3g of dibenzoyl peroxide was dissolved in 100g of acetone, and the obtained acetone solution was added to the reaction system, heated to 40°C, purged with nitrogen for 30min to remove acetone, and then 60g of N-vinyl pyrrolidone was added, stirred and mixed for 30min, heated to 100°C, and reacted for 1 hour. After the reaction was completed, the temperature was cooled to obtain a polypropylene-gN-vinyl pyrrolidone material product C4. The various performance parameters of the obtained product were tested, and the results are shown in Table 1.

Example 5

Weigh 2.0 kg of the basic copolymerized polypropylene powder of Example 1, add it to a 10L reactor with mechanical stirring, close the reaction system, and replace with nitrogen for deoxygenation. Add 4.5 g of dibenzoyl peroxide and 200 g of 4-vinyl pyridine, stir and mix for 30 min, swell at 50 ° C for 30 min, heat to 90 ° C, and react for 4 hours. After the reaction is completed, nitrogen is purged to cool down to obtain polypropylene-g-4-vinyl pyridine material product C5. The performance parameters of the obtained product are tested, and the results are shown in Table 1.

Comparative Example 1

Weigh 2.0 kg of T30S powder (breakdown field strength (90°C) is 347 kV/mm, DC volume resistivity (90°C, 15 kV/mm) is 1.18E13 Ω·m) from which fine powder less than 40 mesh is removed by sieving, and add it to a 10L reactor with mechanical stirring, close the reaction system, and replace with nitrogen for deoxygenation. Add 1.2 g of dibenzoyl peroxide and 40 g of 4-vinylpyridine, stir and mix for 30 min, swell at 50°C for 30 min, heat to 90°C, and react for 4 hours. After the reaction is completed, nitrogen is purged to cool down to obtain polypropylene-g-4-vinylpyridine material product D1. The performance parameters of the obtained product are tested, and the results are shown in Table 1.

Comparative Example 2

The basic copolymerized polypropylene powder with the following characteristics was selected: ethylene content of comonomer 18.1wt%, xylene soluble content 48.7wt%, comonomer content in solubles 31.9wt%, solubles/copolymerized polypropylene intrinsic viscosity ratio 0.89, weight average molecular weight 34.3×10 ⁴ g/mol, MFR 1.21g/10min at 230°C and 2.16kg load, Tm=143.4°C, breakdown field strength (90°C) 236kV/mm, DC volume resistivity (90°C, 15kV/mm) 1.16E13Ω·m, and fine powder less than 40 mesh was removed by sieving. 2.0kg of the above basic copolymerized polypropylene powder was weighed and added into a 10L reactor with mechanical stirring, the reaction system was sealed, and nitrogen was replaced for deoxygenation. 7.5 g of dibenzoyl peroxide and 300 g of 4-vinylpyridine were added, stirred and mixed for 30 min, swelled at 50 ° C for 30 min, heated to 90 ° C, and reacted for 4 hours. After the reaction, nitrogen was purged to cool down to obtain polypropylene-g-4-vinylpyridine material product D2. The performance parameters of the obtained product were tested, and the results are shown in Table 1.

Comparative Example 3

A basic copolymerized polypropylene powder having the following characteristics was selected: 18.1wt% ethylene content of comonomer, 48.7wt% xylene soluble content, 31.9wt% comonomer content in solubles, 0.89 solubles/copolymerized polypropylene intrinsic viscosity ratio, 34.3×10 ⁴ g/mol weight average molecular weight, 1.21g/10min at 230°C and 2.16kg load, Tm=143.4°C, 236kV/mm breakdown field strength (90°C), 15kV/mm DC volume resistivity, 1.16E13Ω·m, and fine powder less than 40 mesh was removed by sieving. 2000g of the above basic copolymerized polypropylene powder was weighed, mixed with 40g poly-4-vinyl pyridine, and mixed using a screw extruder to obtain blend D3. The performance parameters of the obtained product were tested, and the results are shown in Table 1.

Comparing the data of Example 1 and Comparative Example 1, it can be seen that the bending modulus of the polypropylene-g-heterocyclic material obtained by using T30S powder as the base powder is too high, the mechanical properties of the material are poor, and it cannot meet the processing requirements of the insulating material.

Comparing the data of Example 1 and Comparative Example 2, it can be seen that excessive addition of heterocyclic monomers (too high M1 value) will lead to a decrease in the breakdown field strength and volume resistivity of the obtained polypropylene-g-heterocyclic material, affecting the electrical properties of the material.

By comparing the data of Example 1 and Comparative Example 3, it can be seen that the use of the mixed heterocyclic polymer method leads to a significant decrease in the breakdown field strength and volume resistivity of the material, which greatly affects the electrical properties of the material.

In summary, it can be seen from the data in Table 1 that the significant decrease in the bending modulus makes the modified material of the polypropylene grafted heterocycle of the present invention have good mechanical properties, and compared with the copolymerized polypropylene without grafting the heterocyclic monomer containing olefinic group, the breakdown field strength of the grafted product is improved, indicating that the modified material of the polypropylene grafted heterocycle of the present invention also has good electrical properties.

In addition, it can be seen from the dielectric constant and dielectric loss data that grafting modification does not affect the dielectric constant and dielectric loss of the material, and the material of the present invention meets the necessary conditions for insulation.

Example A

Preparation of the conductor: 76 aluminum monofilaments with a diameter of 2.5 mm were tightly compressed and twisted to obtain an aluminum conductor inner core.

Preparation of polypropylene grafted heterocyclic modified material particles: Blend the following components by mass: 100 parts of polypropylene grafted heterocyclic modified material obtained in Example 1, 0.3 parts of antioxidant 1035. Use a twin-screw extruder to granulate at a speed of 300 r/min and a granulation temperature of 210-230°C.

Preparation of conductor shielding layer and insulating layer: Conductor shielding material PSD_WMP-00012 (Zhejiang Wanma Co., Ltd.) and the above-mentioned polypropylene grafted heterocyclic modified material particles are co-extruded and coated on the outside of the conductor core through an extruder to form a conductor shielding layer + electrical insulation layer, or to form a conductor shielding layer + electrical insulation layer + electrical insulation shielding layer (outer shielding layer), and the extrusion temperature is 190-210°C.

Preparation of the metal shielding layer: 25 T1 copper wires with a diameter of 0.3 mm are wrapped around the electrical insulation layer (electrical insulation shielding layer) to form a metal shielding layer.

Preparation of the inner sheath layer: PVC particles of brand St-2 (Dongguan Haichuang Electronics Co., Ltd.) are extruded outside the metal shielding layer through an extruder to form an inner sheath layer.

Preparation of armor: Use 50 304 stainless steel wires with a diameter of 6.0 mm to make the steel wire armor. The single-layer armor is wrapped leftward on the inner sheath layer. The armor is tight to minimize the gap between adjacent steel wires.

Preparation of the outer sheath layer: PVC particles of brand St-2 (Dongguan Haichuang Electronics Co., Ltd.) are extruded outside the armor through an extruder to form an outer sheath layer.

Finally, the high-performance polypropylene thermoplastic cable is obtained. The three-dimensional structure schematic diagram of the cable is shown in FIG1 .

According to the above method, a cable with an energy level of 10 kV is prepared based on the material of Example 1. The cable conductor cross-sectional area is 400 mm ² , the average thickness of the conductor shielding layer is 1.07 mm, the average thickness of the electrical insulation layer is 2.64 mm, the average thickness of the electrical insulation shielding layer is 1.00 mm, the average thickness of the metal shielding layer is 1.00 mm, the cable insulation eccentricity is 5.4%, the average thickness of the armor is 5.94 mm, the average thickness of the inner sheath layer is 2.25 mm, and the average thickness of the outer sheath layer is 2.40 mm.

Test Case A

The prepared cable was tested. The main insulation conductivity test result of the cable: the conductivity ratio of the cable at 90°C and 30°C was 52.1. The cable insulation space charge injection test result: the electric field distortion of the cable was 16.2%. The DC withstand voltage test result: the cable passed without breakdown and discharge. The load cycle test result: the cable passed without breakdown.

Example B

Preparation of the conductor: A plurality of aluminum monofilament conductors are bundled, and then the bundled monofilament conductors are twisted to obtain an aluminum conductor inner core.

Preparation of polypropylene grafted heterocyclic modified material particles: Blend the following components by weight: 100 parts of polypropylene grafted heterocyclic modified material obtained in Example 2-5, 0.3 parts of antioxidant 1010/168/calcium stearate (mass ratio 2:2:1). Use a twin-screw extruder to granulate at a speed of 300 r/min and a granulation temperature of 210-230°C.

Preparation of conductor shielding layer and insulating layer: Conductor shielding material PSD_WMP-00012 (Zhejiang Wanma Co., Ltd.) and the above-mentioned polypropylene grafted heterocyclic modified material particles are co-extruded and coated on the outside of the conductor core through an extruder to form a conductor shielding layer + electrical insulation layer, or to form a conductor shielding layer + electrical insulation layer + electrical insulation shielding layer (outer shielding layer), and the extrusion temperature is 160-210°C.

Preparation of metal shielding layer: T1 copper is used to wrap copper tape outside the electrical insulation layer (electrical insulation shielding layer) to form a metal shielding layer.

Preparation of the inner sheath layer: PVC particles of brand St-2 (Dongguan Haichuang Electronics Co., Ltd.) are extruded outside the metal shielding layer through an extruder to form an inner sheath layer.

Preparation of armor: Use 304 stainless steel to make steel wire armor with a nominal diameter of 1.25mm. The single-layer armor is wrapped leftward on the inner sheath layer. The armor is tight to minimize the gap between adjacent steel wires.

Preparation of the outer sheath layer: PVC particles of brand St-2 (Dongguan Haichuang Electronics Co., Ltd.) are extruded outside the armor through an extruder to form an outer sheath layer.

Finally, the high-performance polypropylene thermoplastic cable is obtained. The three-dimensional structure schematic diagram of the cable is shown in FIG1 .

According to the above method, cables with energy levels within the range of 6-35 kV are prepared based on the materials of Examples 2-5, respectively. The cable conductor cross-sectional area is 240-400 mm ² , the conductor shielding layer thickness is 1-3 mm, the electrical insulation layer thickness is 2-8 mm, the electrical insulation shielding layer thickness is 0.5-1.5 mm, the armor thickness is 0.5-1 mm, the inner sheath layer thickness is 1-2 mm, and the outer sheath layer thickness is not less than 1.8 mm.

Test Case B

The cables were tested. The main insulation conductivity test results of the cables: the conductivity ratio of each cable at 90°C and 30°C was less than 100. The cable insulation space charge injection test results: the electric field distortion of each cable was less than 20%. The DC withstand voltage test results: all cables had no breakdown and discharge phenomenon, and passed. The load cycle test results: all cables had no breakdown phenomenon, and passed.

It can be seen that the cable using the modified material of polypropylene grafted heterocycle as the main insulating layer of the present invention has a higher operating temperature than the existing cables, and can still maintain or even have a higher volume resistivity and stronger breakdown resistance at a higher operating temperature. Under the condition of ensuring the same voltage level and insulation level, the electrical insulation layer made of the modified material of polypropylene grafted heterocycle has the advantages of thinner thickness, better heat dissipation and lighter weight than the electrical insulation layer of conventional cables.

The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

The endpoints and any values of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

Claims (64)

1. A high-performance polypropylene thermoplastic cable, characterized in that the cable comprises: at least one conductor and at least one electrically insulating layer surrounding said conductor; Wherein, the material of the electrical insulating layer is at least one modified material of polypropylene grafted with heterocyclic rings; The modified material of polypropylene grafted heterocycles is composed of structural units derived from copolymerized polypropylene and structural units derived from heterocyclic monomers containing alkenyl groups; based on the weight of the modified material of polypropylene grafted heterocycles, the content of structural units derived from heterocyclic monomers containing alkenyl groups and in a grafted state in the modified material of polypropylene grafted heterocycles is 0.5-6wt%. 2. The cable according to claim 1, wherein the content of the structural unit derived from the heterocyclic monomer containing an olefin group and in the grafted state in the modified material of polypropylene grafted heterocyclic is 0.5 to 4 wt% based on the weight of the modified material of polypropylene grafted heterocyclic. 3. The cable according to claim 1, wherein the cable has at least one cable core, and each of the cable cores comprises, from inside to outside, a conductor, an optional conductor shielding layer, an electrical insulation layer, an optional electrical insulation shielding layer, and an optional metal shielding layer. 4. The cable according to claim 3, wherein the cable further comprises an armor and/or a sheath layer. 5. The cable according to claim 3, wherein the cable further comprises a filling layer and/or a tape layer. The cable according to claim 1 , wherein the cable is a DC cable or an AC cable. The cable according to claim 6 , wherein the cable is a direct current cable. 8. The cable according to any one of claims 1 to 7, wherein the modified material of the polypropylene grafted heterocycle has at least one of the following characteristics: a melt flow rate of 0.01 to 30 g/10 min at 230°C and a load of 2.16 kg; a flexural modulus of 20 to 900 MPa; an elongation at break ≥ 200%; and a tensile strength greater than 5 MPa. 9 . The cable according to claim 8 , wherein the modified material of polypropylene grafted with heterocycle has a melt flow rate of 0.05 to 20 g/10 min at 230° C. and a load of 2.16 kg. 10 . The cable according to claim 9 , wherein the modified material of polypropylene grafted with heterocycle has a melt flow rate of 0.1 to 10 g/10 min at 230° C. and a load of 2.16 kg. 11 . The cable according to claim 10 , wherein the modified material of polypropylene grafted with heterocycle has a melt flow rate of 0.2 to 5 g/10 min at 230° C. and a load of 2.16 kg. 12. The cable according to claim 8, wherein the flexural modulus of the modified material of polypropylene grafted with heterocycles is 50 to 600 MPa. 13. The cable according to claim 8, wherein the elongation at break of the modified material of polypropylene grafted with heterocycles is ≥300%. 14. The cable according to claim 8, wherein the tensile strength of the modified material of polypropylene grafted with heterocycles is 10 to 40 MPa. 15. The cable according to any one of claims 1 to 7, wherein the modified material of polypropylene grafted with heterocycle has at least one of the following characteristics: - The working temperature of the modified material of polypropylene grafted heterocycle is ≥90°C; - The breakdown field strength E _g of the modified material of polypropylene grafted heterocycle at 90° C. is ≥190 kV/mm; - the breakdown field strength change rate ΔE/E obtained by dividing the difference ΔE between the breakdown field strength _Eg of the modified material grafted with heterocyclic polypropylene at 90°C and the breakdown field strength E of the copolymerized polypropylene at 90°C by the breakdown field strength E of the copolymerized polypropylene at 90°C is greater than 1%; - The DC volume resistivity ρ _vg of the modified material of polypropylene grafted with heterocyclic rings at 90°C and 15kV/mm field strength is ≥7×10 ¹² Ω·m; - the ratio of the DC volume resistivity ρ _vg of the modified material of the polypropylene grafted heterocycle at 90°C and 15 kV/mm field strength to the DC volume resistivity ρ _v of the copolymerized polypropylene at 90°C and 15 kV/mm field strength ρ _vg/ ρ _v is greater than 1; -The dielectric constant of the modified material of polypropylene grafted with heterocycles at 90°C and 50Hz is greater than or equal to 2.0. 16. The cable according to claim 15, wherein the working temperature of the modified material of polypropylene grafted with heterocycle is 90-160°C. 17. The cable according to claim 15, wherein the modified material of polypropylene grafted with heterocycle has a breakdown field strength _Eg of 190-800 kV/mm at 90°C. 18. The cable according to claim 15, wherein the breakdown field strength change rate ΔE/E obtained by dividing the difference ΔE between the breakdown field strength _Eg of the modified material grafted with heterocyclic polypropylene at 90°C and the breakdown field strength E of the copolymerized polypropylene at 90°C by the breakdown field strength E of the copolymerized polypropylene at 90°C is 1.5% to 50%. 19. The cable according to claim 18, wherein the breakdown field strength change rate ΔE/E obtained by dividing the difference ΔE between the breakdown field strength _Eg of the modified material grafted with heterocyclic polypropylene at 90°C and the breakdown field strength E of the copolymerized polypropylene at 90°C by the breakdown field strength E of the copolymerized polypropylene at 90°C is 2% to 35%. 20. The cable according to claim 19, wherein the breakdown field strength change rate ΔE/E obtained by dividing the difference ΔE between the breakdown field strength _Eg of the modified material grafted with heterocyclic polypropylene at 90°C and the breakdown field strength E of the copolymerized polypropylene at 90°C by the breakdown field strength E of the copolymerized polypropylene at 90°C is 5% to 25%. 21. The cable according to claim 15, wherein the modified material of polypropylene grafted with heterocycle has a DC volume resistivity _ρvg of 7× ^1012Ω ·m to 1.0× ^1020Ω ·m at 90°C and a field strength of 15 kV/mm. 22. The cable according to claim 15, wherein the ratio (ρ vg/ ρ v) of the DC volume resistivity ρ _vg of the modified material of the polypropylene grafted heterocycle at 90°C and a field strength of 15 kV/ _mm to the DC volume resistivity ρ _v of the copolymer _{polypropylene} at 90°C and a field strength of 15 kV/mm is 1.1 to 20. 23. The cable according to claim 22, wherein the ratio ρ vg/ ρ _v of the DC volume resistivity ρ vg of the modified material of the polypropylene grafted heterocycle at 90°C and a field strength of 15 kV/mm to the DC volume _resistivity ρ _v of the copolymer polypropylene at 90°C and a field strength of 15 kV/mm is 1.2 to ₁₀ . 24. The cable according to claim 23, wherein the ratio ρ vg/ ρ _v of the DC volume resistivity ρ vg of the modified material of polypropylene grafted heterocycle at 90°C and 15 kV/mm field strength to the DC volume resistivity ρ _v of the copolymer polypropylene at 90°C and 15 kV _{/ mm} field strength is 1.3 to 4. 25. The cable according to claim 15, wherein the dielectric constant of the modified material of polypropylene grafted with heterocycles is 2.0 to 2.5 at 90°C and 50 Hz. 26. The cable according to any one of claims 1 to 7, wherein the copolymerized polypropylene has at least one of the following characteristics: a comonomer content of 0.5 to 40 mol%; a xylene soluble content of 2 to 80 wt%; a comonomer content in the solubles of 10 to 70 wt%; and a characteristic viscosity ratio of the solubles to the polypropylene of 0.3 to 5. 27. The cable according to claim 26, wherein the comonomer content of the copolymerized polypropylene is 0.5 to 30 mol%. 28. The cable according to claim 27, wherein the comonomer content of the copolymerized polypropylene is 4 to 25 wt%. 29. The cable according to claim 28, wherein the comonomer content of the copolymerized polypropylene is 4 to 22 wt%. 30. The cable according to claim 26, wherein the copolymerized polypropylene has a xylene soluble content of 18 to 75 wt%. 31. The cable according to claim 30, wherein the copolymerized polypropylene has a xylene soluble content of 30 to 70 wt%. 32. The cable according to claim 31, wherein the copolymerized polypropylene has a xylene soluble content of 30 to 67 wt%. 33. The cable according to claim 26, wherein the comonomer content in the soluble matter of the copolymerized polypropylene is 10 to 50 wt%. 34. The cable according to claim 33, wherein the comonomer content in the soluble matter of the copolymerized polypropylene is 20 to 35 wt%. 35. The cable according to claim 26, wherein the intrinsic viscosity ratio of the soluble matter of the copolymerized polypropylene to the polypropylene is 0.5-3. 36. The cable according to claim 35, wherein the intrinsic viscosity ratio of the soluble matter of the copolymerized polypropylene to the polypropylene is 0.8 to 1.3. 37. The cable according to any one of claims 1 to 7, wherein the copolymerized polypropylene has at least one of the following characteristics: a melt flow rate of 0.01 to 60 g/10 min at 230°C and a load of 2.16 kg; a melting temperature Tm of above 100°C; and a weight average molecular weight of 20× ¹⁰⁴ to 60× ¹⁰⁴ g/mol. 38. The cable according to claim 37, wherein the copolymerized polypropylene has a melt flow rate of 0.05 to 35 g/10 min at 230°C and a load of 2.16 kg. 39. The cable according to claim 38, wherein the copolymerized polypropylene has a melt flow rate of 0.5 to 8 g/10 min at 230°C and a load of 2.16 kg. 40. The cable according to claim 37, wherein the melting temperature Tm of the copolymerized polypropylene is 110-180°C. The cable according to claim 40, wherein the melting temperature Tm of the copolymerized polypropylene is 110-170°C. 42. The cable according to claim 41, wherein the melting temperature Tm of the copolymerized polypropylene is 120-170°C. 43. The cable according to claim 42, wherein the melting temperature Tm of the copolymerized polypropylene is 120-166°C. 44. The cable according to any one of claims 1 to 7, wherein the comonomer of the copolymerized polypropylene is at least one selected from _C2 to _C8 α-olefins other than propylene. 45. The cable according to claim 44, wherein the comonomer of the copolymerized polypropylene is selected from at least one of ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. 46. The cable according to claim 45, wherein the comonomer of the copolymerized polypropylene is ethylene and/or 1-butene. 47. The cable of claim 46, wherein the copolymerized polypropylene consists of propylene and ethylene. 48. The cable according to any one of claims 1 to 7, wherein the alkenyl-containing heterocyclic monomer is selected from at least one of imidazole containing alkenyl substituents, pyrazole containing alkenyl substituents, carbazole containing alkenyl substituents, pyrrolidone containing alkenyl substituents, pyridine or pyridinium salt containing alkenyl substituents, piperidine containing alkenyl substituents, caprolactam containing alkenyl substituents, pyrazine containing alkenyl substituents, thiazole containing alkenyl substituents, purine containing alkenyl substituents, morpholine containing alkenyl substituents and oxazoline containing alkenyl substituents. The cable according to claim 48, wherein the heterocyclic monomer containing an alkenyl group is a heterocyclic monomer containing a monoalkenyl group. 50. The cable according to claim 48, wherein the alkenyl-containing heterocyclic monomer is selected from at least one of 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-allylimidazole, 1-vinylpyrazole, 3-methyl-1-vinylpyrazole, vinylcarbazole, N-vinylpyrrolidone, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine, vinylpyridine N-oxide, vinylpyridinium salt, vinylpiperidine, N-vinylcaprolactam, 2-vinylpyrazine, N-vinylpiperazine, 4-methyl-5-vinylthiazole, N-vinylpurine, vinylmorpholine and vinyloxazoline. 51. The cable according to any one of claims 1 to 7, wherein the modified material of polypropylene grafted with heterocyclic ring is prepared by solid phase grafting reaction of copolymerized polypropylene and heterocyclic monomer containing olefin group. 52. The cable according to claim 51, wherein the preparation method of the modified material of polypropylene grafted with heterocycle comprises: subjecting a reaction mixture comprising copolymerized polypropylene and an olefin-containing heterocyclic monomer to a grafting reaction in the presence of an inert gas to obtain the modified material of polypropylene grafted with heterocycle. 53. The cable of claim 52, wherein the reaction mixture further comprises a free radical initiator. 54. The cable according to claim 53, wherein the free radical initiator is selected from peroxide-based free radical initiators and/or azo-based free radical initiators. 55. The cable according to claim 54, wherein the peroxide-based free radical initiator is selected from at least one of dibenzoyl peroxide, diisopropyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dodecyl peroxide, tert-butyl perbenzoate, diisopropyl peroxydicarbonate, tert-butyl peroxy (2-ethylhexanoate) and dicyclohexyl peroxydicarbonate; and the azo-based free radical initiator is azobisisobutyronitrile and/or azobisisoheptylonitrile. 56. The cable according to claim 53, wherein the mass ratio of the free radical initiator to the olefinic heterocyclic monomer is 0.1 to 10:100. 57. The cable according to claim 56, wherein the mass ratio of the free radical initiator to the olefinic heterocyclic monomer is 0.5 to 5:100. 58. The cable according to claim 52, wherein the mass ratio of the heterocyclic monomer containing an olefin group to the copolymerized polypropylene is 0.3 to 12:100. 59. The cable according to claim 58, wherein the mass ratio of the heterocyclic monomer containing alkenyl group to the copolymerized polypropylene is 0.5 to 10:100. 60. The cable according to claim 52, wherein the grafting reaction is carried out at a temperature of 30 to 130°C and for a time of 0.5 to 10 hours. 61. The cable according to claim 60, wherein the temperature of the grafting reaction is 60-120°C and the time is 1-5 hours. 62. A cable according to any one of claims 52-61, wherein the reaction mixture further comprises at least one of the following components: a dispersant, an interface agent and an organic solvent, the mass content of the dispersant is 50 to 300% of the mass of the copolymer polypropylene, the mass content of the interface agent is 1 to 30% of the mass of the copolymer polypropylene, and the mass content of the organic solvent is 1 to 35% of the mass of the copolymer polypropylene. 63. The cable according to claim 62, wherein the preparation method comprises the following steps: a. placing the copolymerized polypropylene in a closed reactor and replacing it with an inert gas; b. adding a free radical initiator and an olefin-containing heterocyclic monomer into the closed reactor and stirring to mix; c. optionally adding an interfacial agent, and optionally causing the reaction system to swell; d. optionally adding a dispersant, heating the reaction system to the grafting reaction temperature, and performing the grafting reaction; e. After the reaction is completed, filtering is optionally performed, and the modified material of the polypropylene grafted heterocycle is obtained after drying. 64. The cable according to claim 62, wherein the preparation method comprises the following steps: a. placing the copolymerized polypropylene in a closed reactor and replacing it with an inert gas; b. mixing an organic solvent and a free radical initiator and adding the mixture to the closed reactor; c. removing the organic solvent; d. adding an alkenyl-containing heterocyclic monomer, optionally adding an interfacial agent, and optionally causing the reaction system to swell; e. optionally adding a dispersant, heating the reaction system to the grafting reaction temperature, and performing the grafting reaction; f. After the reaction is completed, filtering is optionally performed, and the modified material of the polypropylene grafted heterocycle is obtained after drying.

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