A reversibly cross-linked polyethylene cable material and preparation method thereof

Abstract

The present invention provides a reversibly cross-linked polyethylene cable material and a preparation method thereof. The raw materials of the reversibly cross-linked polyethylene cable material of the present invention include polyethylene copolymer and coupling agent; the polyethylene copolymer is obtained by copolymerization of polymerization monomers; the polymerization monomers include ethylene, and vinylbenzaldehyde and / or vinylbenzaldehyde derivatives; the coupling agent is selected from polyvalent primary amine compounds. The reversibly cross-linked polyethylene cable material of the present invention has the advantages of excellent heat resistance and wide processing window.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials and relates to a reversible cross-linked polyethylene cable material and a preparation method thereof. Background Art

[0002] Polyethylene has good insulation, easy processing, low temperature resistance and aging resistance, and is an excellent electrical insulation material, but it also has disadvantages such as low temperature resistance and poor creep resistance. After cross-linking, the molecular structure of polyethylene changes from a two-dimensional structure to a three-dimensional network structure, and its electrical properties, heat resistance and physical strength can be greatly improved, broadening its application range.

[0003] Traditional polyethylene cross-linking methods mainly include peroxide cross-linking, radiation cross-linking and silane cross-linking, but the above cross-linking methods are irreversible cross-linking, which will cause the loss of valuable thermoplasticity and make the cable material unable to be reprocessed and recycled.

[0004] Dynamic covalent bonds refer to covalent bonds that can be reversibly broken / bonded after being subjected to specific stimuli (such as heat, light and pH), and the polymer cross-linked network thus formed can achieve topological rearrangement under external influences. It has been reported that reversibly cross-linked polyolefins are obtained through DA reaction. For example, patent CN111072858A reports a polyethylene resin with a cyclopentadiene group as a side group. The polymerization monomers of the polyethylene resin include ethylene and an α-olefin containing a cyclopentadiene group, wherein the cyclopentadiene groups on the α-olefin monomers react with each other through DA reaction to give the obtained polyethylene resin a reversibly cross-linked network structure. The resin undergoes a reverse reaction when heated to above 160°C, decrosslinking the polyethylene, thereby giving the material thermoplasticity. In addition, patent WO2019024633A1 also reports a styrene copolymer with reversible cross-linked bonds, which is obtained by reacting a furan-containing styrene copolymer with a multifunctional maleimide derivative through a DA reaction. The patent also provides the application of the copolymer in cable materials. The reversible cross-linked bonds of the copolymer can be broken at high temperature, so that the cable material has secondary processing properties and can be reused repeatedly.

[0005] However, in many cases, due to the large current transmission per unit cross-sectional area, high heat generation, and high long-term operating temperature of the conductor, higher requirements are placed on the heat resistance level of the insulating material. The reported DA-type reversible cross-linked polyethylene cable material has poor heat resistance, and the viscosity of the cable material drops suddenly when the cross-linking is resolved, which limits its application in high-temperature working environments. Summary of the invention

[0006] The invention provides a reversible cross-linked polyethylene cable material, which has the advantages of excellent heat resistance and wide processing window.

[0007] The present invention also provides a method for preparing a reversibly cross-linked polyethylene cable material, by which a reversibly cross-linked polyethylene cable material with excellent heat resistance and a wide processing window can be simply and quickly prepared.

[0008] The first aspect of the present invention provides a reversibly cross-linked polyethylene cable material, wherein the raw materials of the cable material include a polyethylene copolymer and a coupling agent;

[0009] The polymerizable monomers include ethylene, and vinylbenzaldehyde and / or vinylbenzaldehyde derivatives;

[0010] The coupling agent is selected from polyvalent primary amine compounds.

[0011] The reversibly cross-linked polyethylene cable material as described above, wherein the coupling agent is selected from the compound of formula (I):

[0012] H 2 NR 1 -NH 2 Formula (I)

[0013] In formula (I), R 1 Selected from C1-C12 alkyl, C6-C12 substituted or unsubstituted aryl or C6-C12 substituted or unsubstituted heteroaryl;

[0014] The substituent in the substituted aryl or substituted heteroaryl is selected from C1-C3 alkyl or halogen.

[0015] The reversibly cross-linked polyethylene cable material as described above, wherein R 1 A straight chain alkyl group selected from C2 or C3.

[0016] The reversibly cross-linked polyethylene cable material as described above, wherein the derivative of vinylbenzaldehyde is selected from vinylbenzaldehyde compounds having at least one C1-C6 alkyl substitution on the benzene ring.

[0017] The reversibly cross-linked polyethylene cable material as described above, wherein the mass ratio of the polyethylene copolymer to the coupling agent is 100:(1-20).

[0018] The reversibly cross-linked polyethylene cable material as described above, wherein the polyethylene copolymer comprises 70% to 93% of ethylene units and 5% to 29% of vinylbenzaldehyde units and / or vinylbenzaldehyde derivative units in terms of molar content.

[0019] The reversibly cross-linked polyethylene cable material as described above, wherein the polyethylene copolymer is a low-density polyethylene copolymer.

[0020] The reversibly cross-linked polyethylene cable material as described above, wherein the raw materials of the cable material further include an antioxidant;

[0021] The mass ratio of polyethylene copolymer, coupling agent and antioxidant is 100:(2-15):(0.3-0.7).

[0022] The second aspect of the present invention provides a method for preparing the reversibly cross-linked polyethylene cable material as described above, comprising: mixing the raw materials of the cable material to obtain a mixture; and extruding the mixture to obtain the reversibly cross-linked polyethylene cable material.

[0023] The preparation method as described above, wherein the temperature of the extrusion treatment is 190-230°C.

[0024] The implementation of the present invention has at least the following beneficial effects:

[0025] 1. The present invention obtains a polyethylene cable material having an imine bond covalent cross-linked network structure by reacting the aldehyde group on the side chain of the polyethylene copolymer with the amino group in the coupling agent. The cable material has excellent heat resistance.

[0026] 2. When the polyethylene cable material of the present invention is de-crosslinked, the viscosity of the cable material decreases slowly, which greatly broadens the processing window temperature and processing stability of the cable material, making the processing process simpler and easier to control.

[0027] 3. The preparation method of the reversible cross-linked polyethylene cable material of the present invention can obtain the above-mentioned reversible cross-linked polyethylene cable material with excellent heat resistance and wide processing window by simply mixing and extruding the cable material raw materials. This method has the advantages of being simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a comparison chart of infrared spectra of the cable materials of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0029] Figure 2 This is a comparison chart of infrared spectra of the cable materials of Example 1 and Comparative Example 4. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The first aspect of the present invention provides a reversibly cross-linked polyethylene cable material, wherein the raw materials of the cable material include polyethylene copolymers and coupling agents; the polyethylene copolymers are obtained by copolymerization of polymerization monomers, the polymerization monomers include ethylene, and vinylbenzaldehyde and / or vinylbenzaldehyde derivatives; the coupling agent is selected from polyvalent primary amine compounds.

[0032] The polymerizable monomers include ethylene, and in addition to ethylene, also include at least one of vinylbenzaldehyde and vinylbenzaldehyde derivatives.

[0033] The present invention does not specifically limit the substitution position of the vinyl group on the benzaldehyde, for example, it can be o-vinylbenzaldehyde, m-vinylbenzaldehyde or p-vinylbenzaldehyde, etc. The derivative of vinylbenzaldehyde refers to a compound in which an alkyl substituent is further connected to the benzene ring of vinylbenzaldehyde.

[0034] The polyethylene copolymer of the present invention has an aldehyde group (-CHO) on its side group, and the coupling agent is a polyamine compound, which contains at least two amino groups (-NH 2 ), the aldehyde group and the amino group undergo Schiff base reaction to obtain a reversibly cross-linked polyethylene with a dynamic imine bond cross-linking network.

[0035] Although polyethylene cable materials with dissociated dynamic covalent cross-linked networks represented by DA reaction can be reprocessed, they have narrow processing windows and a sudden drop in viscosity when de-crosslinking, which limits their application and processing difficulty in high temperature environments. The reversibly cross-linked polyethylene cable material of the present invention has a dynamic imine bond cross-linked network, has good heat resistance, and the viscosity of the cable material gradually decreases with the increase of temperature when de-crosslinking, making the processing process simple and easy to control.

[0036] In the present invention, the copolymerization process of the polymerizable monomer is a free radical polymerization process, and a peroxide initiator can be added to the copolymerization reaction to initiate the polymerization reaction. In order to control the polyethylene copolymer obtained by copolymerization to have a suitable molecular weight, a small amount of molecular weight regulator needs to be added to the polymerization system, and the molecular weight regulator can be selected from the molecular weight regulators commonly used in the art, including but not limited to propylene, butene or propane, etc., preferably propylene. The addition amount of the molecular weight regulator is 0 to 5000 ppm, preferably 1000 to 3000 ppm.

[0037] In a specific embodiment, the coupling agent is selected from a compound of formula (I):

[0038] H 2 NR 1 -NH 2 Formula (I)

[0039] In formula (I), R 1Selected from C1-C12 alkyl, C6-C12 substituted or unsubstituted aryl or C6-C12 substituted or unsubstituted heteroaryl;

[0040] The substituent in the substituted aryl or substituted heteroaryl is selected from C1-C3 alkyl or halogen.

[0041] Specifically, the C1-C12 alkyl group may be a straight chain alkyl group or a branched chain alkyl group having 1 to 12 carbon atoms, including but not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, etc. The C1-C6 alkyl group may be a straight chain alkyl group or a branched chain alkyl group having 1 to 6 carbon atoms, including but not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, etc. The C1-C3 alkyl group may be a straight chain alkyl group or a branched chain alkyl group having 1 to 3 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, etc.

[0042] Except for special cases, "aryl" refers to an unsaturated, aromatic, monocyclic or polycyclic fused or covalently linked substituent; "heteroaryl" refers to an aromatic group containing 1 to 4 heteroatoms, typically nitrogen, oxygen, and sulfur.

[0043] The C6-C12 aryl groups include, but are not limited to, phenyl, naphthyl, biphenyl and the like; the C6-C12 heteroaryl groups include, but are not limited to, pyrrolyl, pyridyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl, pyrimidinyl, purinyl, indolyl and the like.

[0044] Furthermore, R in formula (I) 1 Selected from C2 or C3 straight chain alkyl, i.e. ethyl or n-propyl.

[0045] In a specific embodiment, the derivative of vinylbenzaldehyde is selected from vinylbenzaldehyde compounds having at least one C1-C6 alkyl substituted on the benzene ring. Further, the C1-C6 alkyl substituted vinylbenzaldehyde compound is preferably a methyl substituted vinylbenzaldehyde compound.

[0046] In a specific embodiment, the mass ratio of the polyethylene copolymer to the coupling agent in the raw material of the cable material of the present invention is 100:(1-20).

[0047] In a specific embodiment, the polyethylene copolymer includes 70% to 93% of ethylene units and 5% to 29% of vinylbenzaldehyde units and / or vinylbenzaldehyde derivative units according to molar content. Wherein, the polyethylene copolymer includes 5% to 29% of vinylbenzaldehyde units and / or vinylbenzaldehyde derivative units, including the molar content of vinylbenzaldehyde units in the polyethylene copolymer is 5% to 29%, the molar content of vinylbenzaldehyde derivative units in the polyethylene copolymer is 5% to 29%, and the sum of the molar contents of vinylbenzaldehyde units and vinylbenzaldehyde derivative units in the polyethylene copolymer is 5% to 29%. Specifically, the molar content of ethylene units, vinylbenzaldehyde and its derivative units in the copolymer can be determined by infrared spectroscopy. For example, the molar content of aldehyde groups in the copolymer can be determined by infrared spectroscopy, and the content of vinylbenzaldehyde and its derivative units can be determined by the molar content of aldehyde groups.

[0048] The polyethylene copolymer of the present invention is preferably a low-density polyethylene copolymer, which is also called high-pressure polyethylene and has a density of 0.91 g / cm 3 ~0.93g / cm 3 , it has the advantages of excellent electrical insulation performance, good mechanical properties, excellent cost performance and low cost.

[0049] In a specific embodiment, the low-density polyethylene copolymer of the present invention can be prepared by the following preparation method:

[0050] Add polymerization monomers into a high-pressure polyethylene reactor, and carry out a first-stage polymerization reaction of the polymerization monomers at 280°C to 300°C to obtain a first polymerization product; carry out a second-stage polymerization reaction of the first polymerization product at 285°C to 295°C to obtain a second polymerization product; carry out a third-stage polymerization reaction of the second polymerization product at 280°C to 290°C to obtain a third polymerization product; carry out a fourth-stage polymerization reaction of the third polymerization product at 270°C to 285°C to obtain a polyethylene copolymer.

[0051] The above four different stages of polymerization reactions are all initiated by organic peroxides, which are injected at four points through an injection pump to respectively initiate four stages of polymerization reactions.

[0052] Before adding the polymerizable monomers into the reactor, the step of preheating the polymerizable monomers is also included. Preferably, the temperature of the preheated polymerizable monomers is 160°C to 170°C, more preferably 165°C.

[0053] The raw materials of the cable material of the present invention also include antioxidants. Cross-linked polyolefins are prone to aging when used in cable material insulation materials, which deteriorates their cross-linking characteristics, mechanical properties and thermal stability. Adding antioxidants can delay the oxidative aging of oxides.

[0054] The antioxidant of the present invention is preferably at least one selected from hindered phenol antioxidants and phosphite antioxidants. Hindered phenol antioxidants include but are not limited to monohydric hindered phenols and polyhydric hindered phenols, such as butylated hydroxytoluene BHT, antioxidant 1024, antioxidant 3114, antioxidant 1010, and antioxidant 1330; phosphite antioxidants refer to phosphite antioxidants, including but not limited to phenol-free phosphite antioxidants, low-phenol phosphite antioxidants, and phenol-containing phosphite antioxidants, such as antioxidant 168.

[0055] Furthermore, the mass ratio of the polyethylene copolymer, the coupling agent and the antioxidant is 100:(2-15):(0.3-0.7). For example, in a specific embodiment, 80,000 ppm of the coupling agent and 4,000 ppm of the antioxidant are added to each kilogram of the polyethylene copolymer, wherein ppm represents the mass of the coupling agent and the antioxidant as a percentage of the mass of the polyethylene copolymer. In the above embodiment, the mass ratio of the polyethylene copolymer, the coupling agent and the antioxidant is 100:8:0.4.

[0056] The second aspect of the present invention provides a method for preparing the above-mentioned reversibly cross-linked polyethylene cable material, the method comprising: mixing raw materials of the cable material to obtain a mixture; and extruding the mixture to obtain the reversibly cross-linked polyethylene cable material.

[0057] First, the components of the cable material are mixed in a mixer to obtain a mixture; then the mixture is sent to an extruder for mixing and extrusion.

[0058] After extrusion, the process also includes cooling, pelletizing and drying the extrudate to obtain the reversible cross-linked polyethylene cable material of the present invention.

[0059] The mixer of the present invention may be a high-speed mixer, and the extruder includes but is not limited to a single-screw extruder or a twin-screw extruder.

[0060] Furthermore, the mixing of the cable materials can be completed at 0-50°C.

[0061] Furthermore, the temperature of the extrusion treatment is 190-230° C. At this temperature, the extrusion treatment not only completes the molding process of the polyethylene cable material, but also promotes the reaction between the aldehyde group in the polyethylene copolymer and the amino group in the coupling agent, and completes the covalent crosslinking process of the polyethylene copolymer through the imine bond.

[0062] The reversibly cross-linked polyethylene cable material and the preparation method thereof provided by the present invention will be further described in detail below with reference to specific embodiments.

[0063] It should be noted that, in the following examples, unless otherwise specified, the raw materials used can be obtained by commercial purchase or conventional methods, and the experimental methods without specifying specific conditions are conventional methods and conventional conditions well known in the art.

[0064] Example 1

[0065] The preparation method of the reversibly cross-linked polyethylene cable material of this embodiment comprises the following steps:

[0066] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, wherein the temperatures of the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone are 295° C., 285° C., 285° C., and 275° C., respectively, and the reactor pressure is set to 285 MPa. Ethylene and 2-vinylbenzaldehyde are introduced into the reactor at flow rates of 50 t / h and 2.95 t / h, respectively, for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone in sequence, and a molecular weight regulator is introduced at a flow rate of 100 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.17 t / h, and 4-stage polymerization reactions are initiated to prepare a low-density polyethylene copolymer, wherein the aldehyde content in the copolymer is 6.31 mol%;

[0067] Wherein, the initiator is di-tert-butyl peroxide and the molecular weight regulator is propylene.

[0068] 2) Add the low-density polyethylene copolymer, coupling agent and antioxidant obtained in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture at 200° C. through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company), cool the extruded product with circulating water, and then cut it into pellets with a pelletizer. Dry and sieve the pellets to obtain a reversibly cross-linked polyethylene cable material;

[0069] Among them, the coupling agent is ethylenediamine, and the antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:1; the added amount of the coupling agent is 80000ppm per kilogram of low-density polyethylene copolymer, and the added amount of the antioxidant is 4000ppm per kilogram of low-density polyethylene copolymer.

[0070] Example 2

[0071] The preparation method of the reversibly cross-linked polyethylene cable material of this embodiment comprises the following steps:

[0072] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, wherein the temperatures of the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone are 300° C., 297° C., 290° C., and 280° C., respectively, and the pressure of the reactor is set to 285 MPa. Ethylene and 3-vinylbenzaldehyde are introduced into the reactor at a flow rate of 50 t / h and 4.51 t / h, respectively, for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone in sequence, and a molecular weight regulator is introduced at a flow rate of 150 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.20 t / h, and 4-stage polymerization reactions are initiated to prepare a low-density polyethylene copolymer, wherein the aldehyde content in the copolymer is 11.45 mol%;

[0073] Wherein, the initiator is tert-butyl peroxyacetate and the molecular weight regulator is propylene.

[0074] 2) Add the low-density polyethylene copolymer, coupling agent and antioxidant obtained in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture at 200° C. through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company), cool the extruded product with circulating water, and then cut it into pellets with a pelletizer. Dry and sieve the pellets to obtain a reversibly cross-linked polyethylene cable material;

[0075] Among them, the coupling agent is propylene diamine, and the antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1; the added amount of the coupling agent is 90000ppm per kilogram of low-density polyethylene copolymer, and the added amount of the antioxidant is 5000ppm per kilogram of low-density polyethylene copolymer.

[0076] Example 3

[0077] The preparation method of the reversibly cross-linked polyethylene cable material of this embodiment comprises the following steps:

[0078] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, wherein the temperatures of the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone are 300° C., 295° C., 290° C. and 285° C., respectively, and the pressure of the reactor is set to 290 MPa. Ethylene and 2-vinylbenzaldehyde are introduced into the reactor at flow rates of 50 t / h and 2.43 t / h, respectively, for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone in sequence, and a molecular weight regulator is introduced at a flow rate of 150 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.18 t / h, and 4-stage polymerization reactions are initiated to prepare a low-density polyethylene copolymer, wherein the aldehyde content in the copolymer is 5.79 mol%;

[0079] Wherein, the initiator is tert-butyl peroxypivalate and the molecular weight regulator is propylene.

[0080] 2) Add the low-density polyethylene copolymer, coupling agent and antioxidant obtained in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture at 200° C. through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company), cool the extruded product with circulating water, and then cut it into pellets with a pelletizer. Dry and sieve the pellets to obtain a reversibly cross-linked polyethylene cable material;

[0081] Among them, the coupling agent is 1,2-propylenediamine, and the antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:0.5; the added amount of the coupling agent is 60000ppm per kilogram of low-density polyethylene copolymer, and the added amount of the antioxidant is 4500ppm per kilogram of polyethylene.

[0082] Example 4

[0083] The preparation method of the reversibly cross-linked polyethylene cable material of this embodiment comprises the following steps:

[0084] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, wherein the temperatures of the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone are 300° C., 295° C., 290° C. and 285° C., respectively, and the pressure of the reactor is set to 285 MPa. Ethylene and 2-vinylbenzaldehyde are introduced into the reactor at a flow rate of 50 t / h and 2.43 t / h, respectively, for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone in sequence, and a molecular weight regulator is introduced at a flow rate of 50 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.20 t / h, and 4-stage polymerization reactions are initiated to prepare a low-density polyethylene copolymer, wherein the aldehyde content in the copolymer is 10.65 mol%;

[0085] Wherein, the initiator is di-tert-butyl peroxide and the molecular weight regulator is propylene.

[0086] 2) Add coupling agent and antioxidant to the low-density polyethylene copolymer obtained in step 1) and mix them uniformly at high speed, and mix the above components uniformly at high speed to obtain a mixture. The mixture is extruded through a 35-type twin-screw extruder (Belong Keya Nanjing Machinery Company) at 200° C. The extruded product is cooled by circulating water, and then pelletized by a pelletizer. The pellets are dried and sieved to obtain a reversible cross-linked polyethylene cable material;

[0087] Among them, the coupling agent is 1,3-propylenediamine, and the antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1; the added amount of the coupling agent is 70000ppm per kilogram of low-density polyethylene copolymer, and the added amount of the antioxidant is 4000ppm per kilogram of low-density polyethylene copolymer.

[0088] Example 5

[0089] The reversibly cross-linked polyethylene cable material obtained in Example 4 was added again to a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Co., Ltd.) for melting. The melting section temperature of the extruder was 200°C. The melt was extruded at 200°C. The extruded product was cooled and pelletized in a circulating water bath, and then dried and sieved to obtain the final product.

[0090] Example 6

[0091] The reversibly cross-linked polyethylene cable material obtained in Example 5 was added again to a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Co., Ltd.) for melting. The melting section temperature of the extruder was 200°C. The melt was extruded at 200°C. The extruded product was cooled and pelletized in a circulating water bath, and then dried and sieved to obtain the final product.

[0092] Example 7

[0093] The preparation method of the reversibly cross-linked polyethylene cable material of this embodiment comprises the following steps:

[0094] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, wherein the temperatures of the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone are 296° C., 287° C., 285° C. and 280° C., respectively, and the pressure of the reactor is set to 285 MPa. Ethylene and 2-methyl-4-vinylbenzaldehyde are introduced into the reactor at flow rates of 50 t / h and 3.24 t / h, respectively, for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone in sequence, and a molecular weight regulator is introduced at a flow rate of 110 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.18 t / h, and 4-stage polymerization reactions are initiated to prepare a low-density polyethylene copolymer, wherein the aldehyde content in the copolymer is 10.34 mol%;

[0095] Wherein, the initiator is di-tert-butyl peroxide and the molecular weight regulator is propylene.

[0096] 2) Add the low-density polyethylene copolymer, coupling agent and antioxidant obtained in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture at 200° C. through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company), cool the extruded product with circulating water, and then cut it into pellets with a pelletizer. Dry and sieve the pellets to obtain a reversibly cross-linked polyethylene cable material;

[0097] Among them, the coupling agent is p-phenylenediamine, and the antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:1; the added amount of the coupling agent is 90000ppm per kilogram of low-density polyethylene copolymer, and the added amount of the antioxidant is 4500ppm per kilogram of low-density polyethylene copolymer.

[0098] Example 8

[0099] The preparation method of the reversibly cross-linked polyethylene cable material of this embodiment comprises the following steps:

[0100] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, wherein the temperatures of the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone are 295° C., 288° C., 287° C. and 275° C., respectively, and the pressure of the reactor is set to 285 MPa. Ethylene and 2-methyl-4-vinylbenzaldehyde are introduced into the reactor at flow rates of 50 t / h and 4.86 t / h, respectively, for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone in sequence, and a molecular weight regulator is introduced at a flow rate of 150 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.20 t / h, and 4-stage polymerization reactions are initiated to prepare a low-density polyethylene copolymer, wherein the aldehyde content in the copolymer is 14.51 mol%;

[0101] Wherein, the initiator is tert-butyl peroxypivalate and the molecular weight regulator is propylene.

[0102] 2) Add the low-density polyethylene copolymer, coupling agent and antioxidant obtained in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture at 200° C. through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company), cool the extruded product with circulating water, and then cut it into pellets with a pelletizer. Dry and sieve the pellets to obtain a reversibly cross-linked polyethylene cable material;

[0103] Among them, the coupling agent is 2-methyl-p-phenylenediamine, and the antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:1; the amount of the coupling agent added is 110000 ppm per kilogram of low-density polyethylene copolymer, and the amount of the antioxidant added is 5000 ppm per kilogram of low-density polyethylene copolymer.

[0104] Example 9

[0105] The preparation method of the reversibly cross-linked polyethylene cable material of this embodiment comprises the following steps:

[0106] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, wherein the temperatures of the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone are 298° C., 288° C., 287° C. and 275° C., respectively, and the pressure of the reactor is set to 285 MPa. Ethylene and 2-vinylbenzaldehyde are introduced into the reactor at flow rates of 50 t / h and 4.12 t / h, respectively, for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone in sequence, and a molecular weight regulator is introduced at a flow rate of 130 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.18 t / h, and 4-stage polymerization reactions are initiated to prepare a low-density polyethylene copolymer, wherein the aldehyde content in the copolymer is 12.17 mol%;

[0107] Wherein, the initiator is di-tert-butyl peroxide and the molecular weight regulator is propylene.

[0108] 2) Add the low-density polyethylene copolymer, coupling agent and antioxidant obtained in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture at 200° C. through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company), cool the extruded product with circulating water, and then cut it into pellets with a pelletizer. Dry and sieve the pellets to obtain a reversibly cross-linked polyethylene cable material;

[0109] Among them, the coupling agent is 2-chloro-p-phenylenediamine, and the antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:1; the added amount of the coupling agent is 75000ppm per kilogram of low-density polyethylene copolymer, and the added amount of the antioxidant is 7000ppm per kilogram of low-density polyethylene copolymer.

[0110] Comparative Example 1

[0111] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, the temperatures of the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone are 295° C., 285° C., 285° C., and 275° C., respectively, and the reactor pressure is set to 285 MPa. Ethylene is introduced into the reactor at a flow rate of 50 t / h for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone in sequence. At the same time, a molecular weight regulator is introduced at a flow rate of 100 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.17 t / h, and 4-stage polymerization reactions are initiated to prepare low-density polyethylene;

[0112] Wherein, the initiator is di-tert-butyl peroxide and the molecular weight regulator is propylene.

[0113] 2) The low-density polyethylene and antioxidant prepared in step 1) are mixed in a high-speed mixer at high speed to obtain a mixture. The mixture is extruded at 200° C. through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company), the extruded product is cooled by circulating water, and then pelletized by a pelletizer, and the pellets are dried and sieved to obtain polyethylene;

[0114] The antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:1; the amount of the antioxidant added is 4000 ppm per kilogram of low-density polyethylene.

[0115] Comparative Example 2

[0116] 1) Step 1) of this comparative example is consistent with step 1) of Example 1;

[0117] 2) Add the low-density polyethylene copolymer and antioxidant obtained in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture at 200° C. through a 35-type twin-screw extruder (Belonkeya Nanjing Machinery Company), cool the extruded product with circulating water, and then cut it into pellets with a pelletizer. Dry and sieve the pellets to obtain 2-vinylbenzaldehyde grafted modified polyethylene;

[0118] The antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:1; the amount of the antioxidant added is 4000 ppm per kilogram of polyethylene.

[0119] Comparative Example 3

[0120] 1) Step 1) of this comparative example is consistent with step 1) of comparative example 1;

[0121] 2) Add the low-density polyethylene and antioxidant obtained in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company) at 200°C, cool the extruded product with circulating water, and then cut it into pellets with a pelletizer, and then dry and sieve the pellets to obtain polyethylene pellets;

[0122] The antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:1; the amount of the antioxidant added is 4000 ppm per kilogram of low-density polyethylene.

[0123] 3) mixing the polyethylene pellets prepared in step 2) with a peroxide crosslinking agent, and obtaining a cross-linked polyethylene cable material through post-absorption, cooling, and packaging;

[0124] The peroxide crosslinking agent is di-tert-butyl peroxide, and the added amount of the peroxide crosslinking agent is 80,000 ppm per kilogram of polyethylene pellets.

[0125] Comparative Example 4

[0126] The preparation method of the reversibly cross-linked polyethylene cable material of this comparative example comprises the following steps:

[0127] 1) A tubular high-pressure polyethylene reactor with four reaction zones is used as a reaction device, the temperatures of the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone are 295° C., 285° C., 285° C., and 275° C., respectively, and the pressure of the reactor is set to 285 MPa, ethylene and 6-furan-1-hexene are introduced into the reactor at flow rates of 50 t / h and 2.95 t / h, respectively, for preheating, so that the reaction temperature of the preheated material reaches 165° C., and the material is passed through the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone in sequence, and a molecular weight regulator is introduced at a flow rate of 100 kg / h at the inlet of the first reaction zone, and an initiator is injected into the first reaction zone, the second reaction zone, the third reaction zone, and the fourth reaction zone at four points through an injection pump, respectively, and the total amount of initiator added is 0.17 t / h, and 4-stage polymerization reactions are initiated to prepare a low-density polyethylene copolymer;

[0128] Wherein, the initiator is di-tert-butyl peroxide and the molecular weight regulator is propylene.

[0129] 2) Add the low-density polyethylene copolymer, coupling agent and antioxidant mentioned in step 1) into a high-speed mixer, and mix the above components at high speed to obtain a mixture. Extrude the mixture at 200°C through a 35-type twin-screw extruder (Belongkeya Nanjing Machinery Company), cool the extruded product with circulating water, and then cut it into pellets with a pelletizer. Dry and sieve the pellets to obtain a reversible cross-linked polyethylene cable material;

[0130] Among them, the coupling agent is 1,6-bis(maleimido)hexane, and the antioxidant is a mixture of hindered phenol antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 2:1; the added amount of the coupling agent is 80000ppm per kilogram of low-density polyethylene copolymer, and the added amount of the antioxidant is 4000ppm per kilogram of low-density polyethylene copolymer.

[0131] Test Example 1

[0132] The cable materials of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 were subjected to infrared spectroscopy testing, and the testing method was as follows: the samples were pressed into thin sheets less than 2 mm thick above the melting temperature, and the characteristic peaks of the samples were analyzed by Fourier transform infrared spectroscopy (FT-IR).

[0133] Figure 1 This is a comparison chart of infrared spectra of the cable materials of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3; Figure 2 This is a comparison chart of infrared spectra of the cable materials of Example 1 and Comparative Example 4.

[0134] Comparative Example 1 is an uncrosslinked low-density polyethylene cable material, Comparative Example 2 is a low-density polyethylene copolymer cable material prepared from ethylene and vinylbenzaldehyde, Comparative Example 3 is an irreversibly crosslinked low-density polyethylene cable material, and Example 1 is an imine bond reversibly crosslinked low-density polyethylene copolymer cable material prepared from ethylene and vinylbenzaldehyde. Figure 1 It can be seen that the cable material of Comparative Example 2 is at 1725cm -1 The aldehyde absorption peak appeared at 1627cm -1 A C=N bond absorption peak appears at , indicating that the cable material of Example 1 contains an imine bond covalent cross-linked network.

[0135] Example 4 is a reversibly cross-linked polyethylene cable material prepared by DA reaction, Figure 2 It can be seen that the cable material of Comparative Example 4 is at 1197cm -1 The in-plane bending vibration absorption peak of the ring molecule appears at , indicating the formation of a ring structure.

[0136] Test Example 2

[0137] The cable materials obtained in the above embodiments and comparative examples were tested for the following parameters:

[0138] 1. Melt flow rate (MFR): measured in accordance with GB / T 3682.1-2018 at 190°C and 2.16 kg load.

[0139] 2. Density: Tested in accordance with GB / T 1033.2.

[0140] 3. Tensile strength: Tested in accordance with GB / T 1040.3-2006.

[0141] 4. Elongation at break: Tested in accordance with GB / T 1040.3-2006.

[0142] 5. Vicat softening temperature: tested in accordance with GB / T1633-2000.

[0143] 6. Intermediate point constant: tested in accordance with GB / T1409-2006.

[0144] 7. Dielectric loss tangent: Tested in accordance with GB / T1409-2006.

[0145] The test results of the above parameters are shown in Table 1.

[0146] Table 1

[0147]

[0148]

[0149] 1) Compared with the low-density polyethylene prepared in comparative example 1, the tensile strength, elongation at break and Vicat softening temperature of Examples 1 to 9 are significantly improved. Compared with the low-density polyethylene (Comparative example 3) with a pre-embedded cross-linking agent, the performance of Examples 1 to 9 is better than that of Comparative example 3, especially because the cumbersome process steps of pre-embedded cross-linking agent are reduced, the dielectric constant and dielectric loss tangent of the cable material of Examples 1 to 9 are significantly reduced compared with Comparative example 3.

[0150] 2) From the comparison between Example 4, Example 5 and Example 6, it can be seen that the material properties of the cable material of the present invention remain basically unchanged after multiple processing. This is due to the thermally reversible cross-linking function of the cable material of the present invention. The cross-linked structure of the cable material can still be stably restored after repeated processing, which is completely different from the permanent cross-linked network formed by traditional cross-linked polyethylene, thereby giving the cross-linked polymer excellent thermoplastic properties.

[0151] 3) The Vicat softening temperatures of the cable materials of Examples 1 to 9 of the present invention are all higher than those of Comparative Examples 1 to 4, which indicates that the cable materials of the present invention have excellent heat resistance.

[0152] In addition, thanks to the characteristics of the associative dynamic covalent bond, the low-density polyethylene copolymer in the cable material of the present invention still has a cross-linked structure even above the Vicat softening temperature, which makes the melt viscosity of the material decrease slowly, greatly broadening the processing temperature window and processing stability. The thermally reversible cross-linked polyethylene prepared by the present invention fully meets the use requirements of high-voltage polyethylene cable materials.

[0153] In summary, the cable material of the present invention has the remarkable characteristics of being de-crosslinked at high temperature (during processing) and easy to process, and being crosslinked at low temperature (after molding) and having excellent properties during melt processing.

[0154] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A reversibly cross-linked polyethylene cable material, characterized in that: The raw materials of the cable material include polyethylene copolymer and coupling agent; The polyethylene copolymer is obtained by copolymerizing polymerization monomers; the polymerization monomers include ethylene, and vinylbenzaldehyde and / or vinylbenzaldehyde derivatives; The coupling agent is selected from dibasic primary amine compounds; The polyethylene copolymer comprises 70% to 93% of ethylene units and 5% to 29% of vinylbenzaldehyde units and / or vinylbenzaldehyde derivative units in terms of molar content; The mass ratio of the polyethylene copolymer to the coupling agent is 100:(1-20).

2. The reversibly cross-linked polyethylene cable material according to claim 1, characterized in that: The coupling agent is selected from the compound of formula (I): Formula (I) In formula (I), R 1 Selected from C1~C12 alkyl, C6~C12 substituted or unsubstituted aryl or C6~C12 substituted or unsubstituted heteroaryl; Wherein, the substituent in the substituted aryl or substituted heteroaryl is selected from C1-C3 alkyl or halogen.

3. The reversibly cross-linked polyethylene cable material according to claim 2, characterized in that: R 1 A straight chain alkyl group selected from C2 or C3.

4. The reversibly cross-linked polyethylene cable material according to claim 1, characterized in that: The vinylbenzaldehyde derivative is selected from vinylbenzaldehyde compounds having at least one C1-C6 alkyl group substituted on the benzene ring.

5. The reversibly cross-linked polyethylene cable material according to claim 1, characterized in that: The polyethylene copolymer is a low-density polyethylene copolymer.

6. The reversibly cross-linked polyethylene cable material according to claim 1, characterized in that: The raw materials of the cable material also include an antioxidant; The mass ratio of polyethylene copolymer, coupling agent and antioxidant is 100:(2~15):(0.3~0.7).

7. A method for preparing a reversibly cross-linked polyethylene cable material according to any one of claims 1 to 6, characterized in that: include: The raw materials of the cable material are mixed to obtain a mixture; and the mixture is extruded to obtain the reversibly cross-linked polyethylene cable material.

8. The method for preparing a reversibly cross-linked polyethylene cable material according to claim 7, characterized in that: The temperature of the extrusion treatment is 190-230°C.

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