Cross-linkable polyethylene insulation material and its application, cross-linked polyethylene insulation material and its preparation method and application

Abstract

This invention relates to the field of polymer processing technology, and discloses a crosslinkable polyethylene insulation material and its application, a crosslinkable polyethylene insulation material and its preparation method and application. The crosslinkable polyethylene insulation material comprises low-density polyethylene, an antioxidant, and a crosslinking agent; the amount of antioxidant relative to 100 parts by weight of low-density polyethylene is... a Parts by weight; the amount of antioxidant used reduces the activation energy of the crosslinking reaction in crosslinkable polyethylene insulation. E It is 40-70 kJ / mol; 。 The polyethylene insulation material made from this crosslinkable polyethylene insulation material can improve scorch resistance and degassing efficiency without affecting the electrical performance of the cable.

Description

Technical Field

[0001] This invention relates to the field of polymer processing technology, specifically to a crosslinkable polyethylene insulating material and its application, and a crosslinkable polyethylene insulating material and its preparation method and application. Background Technology

[0002] Due to their technological advantages in long-distance, low-loss, and high-capacity power transmission, high-voltage direct current (HVDC) cables have been widely used in cross-border power grid interconnection, island power supply, and large-scale wind power grid integration. In recent years, the rapid growth of offshore wind power capacity has created vast opportunities for the development of HVDC cables, especially HVDC submarine cables. Cross-linked polyethylene (XLPE), due to its excellent electrical, mechanical, and environmental adaptability, is widely used as the main insulation material for high-voltage cables.

[0003] For a long time, my country's high-voltage XLPE insulation materials have been monopolized by international giants such as Borealis and Dow Chemical. Currently, the development of domestic high-voltage DC insulation materials is mainly in the cable type testing and pre-qualification testing verification stage, and there are no domestically produced DC cables that are in operation. For high-voltage DC submarine cables that can easily reach hundreds of kilometers in length, it is necessary to extend the extrusion length of the insulated core to reduce the number of factory joints. Therefore, the long-length extrusion process of the insulated core and the degassing post-treatment process are key technologies for submarine cable manufacturing.

[0004] Long-length extrusion of insulated wire cores presents a rigorous test of the scorch resistance and extrusion stability of insulation materials. Currently, the scorch resistance of domestically produced insulation materials is insufficient to meet the requirements of long-length extrusion processes, with continuous extrusion times generally within 10 days. Furthermore, due to the generally high amount of crosslinking agents in the formulation, pre-crosslinked and other scorched particles are easily generated during extrusion, leading to a reduction in the electrical performance of the insulation. Given the long continuous production cycle of long-length submarine cables, the degassing post-treatment stage requires shortening the degassing time to improve production efficiency. Moreover, crosslinking byproducts, especially liquid byproducts, are difficult to remove, directly affecting the electrical performance and long-term operational reliability of the cable insulation. High crosslinking byproduct content also prolongs degassing time and reduces production efficiency. Therefore, reducing the content of crosslinking agents and crosslinking byproducts is crucial for improving the electrical performance of the insulation. DC insulation materials have extremely high requirements for cleanliness, minimizing the types of small-molecule additives to avoid introducing chemical impurities. However, current methods for improving the scorch resistance of insulation materials mainly rely on adding anti-scorch agents and other additive components. The addition of small-molecule additives can easily increase DC conductivity, thereby reducing the electrical performance of the insulation. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that the electrical properties, scorch resistance and degassing efficiency of insulation materials for high voltage DC cables cannot be improved in a coordinated manner in the existing technology, and to provide a cross-linkable polyethylene insulation material and its application, as well as a cross-linked polyethylene insulation material and its preparation method and application.

[0006] Through extensive research, the inventors of this invention discovered that there is a correlation between the activation energy of the crosslinking reaction of low-density polyethylene in crosslinkable polyethylene insulation materials for cables and the electrical properties, scorch resistance, and degassing efficiency of the cable insulation material. However, in the current crosslinkable polyethylene insulation materials, the activation energy of the crosslinking reaction of low-density polyethylene is relatively high, the molecular chain mobility of low-density polyethylene is poor, and free diffusion is hindered, ultimately resulting in the inability to simultaneously achieve the desired electrical properties, scorch resistance, and degassing performance of the resulting cable insulation material. Furthermore, the inventors discovered that compounding antioxidants with at least two double bonds at the end with low-density polyethylene can significantly reduce the activation energy of the crosslinking reaction of low-density polyethylene, thereby simultaneously improving the electrical properties, scorch resistance, and degassing properties of cable insulation materials. In particular, the inventors found that by selecting appropriate types of antioxidants and controlling the amount of antioxidants so that the activation energy of the crosslinking reaction of the composition composed of antioxidants and low-density polyethylene is between 40-70 kJ / mol, the crosslinking reaction efficiency and scorch resistance of crosslinkable polyethylene insulation materials can be effectively balanced. This allows for the improvement of the electrical properties, scorch resistance, and degassing properties of cable insulation materials without the addition of initiators and co-crosslinking agents.

[0007] To achieve the above objectives, the first aspect of the present invention provides a crosslinkable polyethylene insulation material, wherein the crosslinkable polyethylene insulation material comprises low-density polyethylene, an antioxidant, and a crosslinking agent, and does not contain an initiator or a co-crosslinking agent;

[0008] The amount of antioxidant used relative to 100 parts by weight of low-density polyethylene is: a Parts by weight;

[0009] Among them, the amount of antioxidant used reduces the activation energy of the crosslinking reaction of crosslinkable polyethylene insulation material. E It is 40-70 kJ / mol;

[0010]

[0011] in, E The activation energy of the crosslinking reaction of the composition consisting of antioxidant and low-density polyethylene is kJ / mol. E LDPE The activation energy for the crosslinking reaction of low-density polyethylene is kJ / mol. E AO The intrinsic activation energy of the antioxidant is given in kJ / mol. bIt is 0.3-1; c The number of terminal double bonds in an antioxidant; n The value is 2.

[0012] A second aspect of the present invention provides a method for preparing cross-linked polyethylene insulation material, wherein the method includes:

[0013] After preheating the antioxidant in the above-mentioned crosslinkable polyethylene insulation material, it is first mixed with low-density polyethylene to obtain an intermediate material. Then, the molten crosslinking agent is mixed with the intermediate material for a second time, and after a first heat preservation, it is cooled to obtain the crosslinkable polyethylene insulation material. The antioxidant is a liquid antioxidant.

[0014] or;

[0015] The low-density polyethylene and antioxidant in the above-mentioned crosslinkable polyethylene insulation material are melt-extruded and granulated to obtain an intermediate material; the molten crosslinking agent is mixed with the intermediate material in a third process and then kept warm for a second time, and then cooled to obtain the crosslinkable polyethylene insulation material, wherein the antioxidant is a solid antioxidant;

[0016] Crosslinkable polyethylene insulation material is crosslinked to obtain crosslinked polyethylene insulation material.

[0017] A third aspect of the present invention provides a cross-linked polyethylene insulating material prepared by the above method.

[0018] The fourth aspect of the present invention provides the application of the above-mentioned cross-linkable polyethylene insulation material or the above-mentioned cross-linked polyethylene insulation material in high-voltage DC cables.

[0019] Through the above technical solutions, the crosslinkable polyethylene insulation material and its application, as well as the crosslinkable polyethylene insulation material and its preparation method and application provided by the present invention, achieve the following beneficial effects:

[0020] The polyethylene insulation material made from the cross-linkable polyethylene insulation material provided by this invention can improve the scorch resistance and degassing efficiency without affecting the electrical performance of the cable.

[0021] Furthermore, the present invention employs a specific type of antioxidant in crosslinkable polyethylene insulation material for cables. This not only promotes the formation of a three-dimensional crosslinking network of carbon free radicals on the polyethylene molecular chain, effectively reducing the amount of crosslinking agent used, but also effectively avoids the "scorching" phenomenon that occurs during the storage or processing of crosslinkable polyethylene insulation material. It also reduces the content of crosslinking byproducts formed due to the presence of crosslinking agents, thereby further improving the electrical properties, scorch resistance, and degassing efficiency of cables made from polyethylene insulation material. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The first aspect of the present invention provides a crosslinkable polyethylene insulation material, wherein the crosslinkable polyethylene insulation material comprises low-density polyethylene, an antioxidant and a crosslinking agent, and does not contain an initiator and a co-crosslinking agent;

[0024] The amount of antioxidant used is a parts by weight relative to 100 parts by weight of low-density polyethylene.

[0025] Among them, the amount of antioxidant used reduces the activation energy of the crosslinking reaction of crosslinkable polyethylene insulation material. E It is 40-70 kJ / mol;

[0026]

[0027] E The activation energy of the crosslinking reaction of the composition consisting of antioxidant and low-density polyethylene is kJ / mol. E LDPE The activation energy for the crosslinking reaction of low-density polyethylene is kJ / mol. E AO The intrinsic activation energy of the antioxidant is given in kJ / mol. b The effective coefficient of the double bond functional group of the antioxidant is between 0.3 and 1; c The number of terminal double bonds in an antioxidant; n The value is 2.

[0028] In this invention, n is the reaction order in which the antioxidant participates in the crosslinking reaction.

[0029] In this invention, the activation energy of the crosslinking reaction of the low-density polyethylene is... E LDPE Intrinsic activation energy of antioxidants E AO The results were obtained using differential scanning calorimetry (DSC).

[0030] In this invention, the crosslinkable polyethylene insulation material does not contain initiators or co-crosslinking agents. This reduces the total amount of additives and the content of small molecule byproducts, ensuring the ultra-cleanliness of the obtained crosslinkable polyethylene insulation material while still ensuring a high degree of crosslinking and a long scorch resistance time, which is beneficial for the long-term stable extrusion of the insulation material.

[0031] In one specific embodiment of the present invention, the activation energy of the crosslinking reaction of the low-density polyethylene is... E LDPE The value is 110-160 kJ / mol, preferably 120-150 kJ / mol.

[0032] In one specific embodiment of the present invention, the antioxidant is a hindered amine antioxidant, whose intrinsic activation energy is... E AO It is 90-140 kJ / mol.

[0033] In one specific embodiment of the present invention, the antioxidant is a hindered phenolic antioxidant with intrinsic activation energy... E AO It is 100-140 kJ / mol.

[0034] According to the present invention, the amount 'a' of the antioxidant is calculated according to the following formula:

[0035] a = A × M o / N ;

[0036] Where A is 0.0008-0.0015 / (g / mol), M o The molar mass of the antioxidant is expressed in g / mol. N The number of hydroxyl or amino functional groups in the antioxidant.

[0037] In this invention, A is an empirical parameter for the amount of antioxidant used in the art, which is determined based on the type of antioxidant, the relative molecular mass of the antioxidant, and the number of effective antioxidant groups in the antioxidant.

[0038] In this invention, b The effective coefficient of the double bond functional group in antioxidants refers to the ability of double bonds in antioxidants to replace traditional crosslinking agents. It is related to the type of double bond, the content of double bonds, the steric hindrance of double bonds, and the electronic cloud effect of double bonds in antioxidants.

[0039] In this invention, b Determined by the following method:

[0040] (1) Mix antioxidant or crosslinking agent with 100 parts by weight of LDPE to obtain insulating material (antioxidant) and insulating material (crosslinking agent); wherein, in the insulating material (antioxidant) and insulating material (crosslinking agent), the amount of antioxidant and crosslinking agent is such that the molar concentration of double bond in the antioxidant is equal to the molar concentration of peroxide group in the crosslinking agent;

[0041] (2) The gel content S of the insulating material (antioxidant) and the insulating material (crosslinking agent) were tested according to JB / T 10437-2024 respectively;

[0042] (3) Calculate the crosslinking density of insulation material 1 and insulation material 2 respectively according to the following;

[0043] ;

[0044] in, .

[0045] In this invention, c The number of terminal double bonds in the antioxidant, c≥2.

[0046] In a preferred embodiment of the present invention, b It is 0.6-0.9.

[0047] According to the present invention, the crosslinking agent is an organic peroxide crosslinking agent relative to 100 parts by weight of low-density polyethylene, and the actual amount of crosslinking agent used is: d Parts by weight, of which, d = d 0– a × c × M c × b / ( M o × f );

[0048] d 0 = target gelation rate / ( f × K × c );

[0049] Where c represents the number of terminal double bonds in the antioxidant; b The effective coefficient of the double bond functional group of the antioxidant; M c The molar mass of the crosslinking agent is expressed in g / mol. M o The molar mass of the antioxidant is expressed in g / mol. f The number of peroxide groups in the crosslinking agent molecule; d 0 represents the theoretical amount of pure crosslinking agent, in parts by weight; c It is 0.7-0.9; 16 is the molar mass of oxygen atoms, g / mol; K is 50-60.

[0050] In this invention, the calculation of the actual amount of crosslinking agent involves only numerical calculations and not unit calculations.

[0051] In this invention, the "peroxide group" is the -OO- group in the crosslinking agent.

[0052] In this invention, c The actual utilization rate of peroxide free radicals is a key indicator for measuring the efficiency of crosslinking reactions, and it is affected by various factors such as the crosslinking system and reaction conditions. c The specific value is an empirical value in this field.

[0053] In this invention, K is an empirical constant, determined based on the thermal elongation test results of cross-linked polyethylene insulation material. The specific test method refers to standard GB / T 2951.21-2008.

[0054] In this invention, gel ratio refers to the proportion of insoluble gel portion in cross-linked polyethylene insulation material to the total mass, reflecting the degree to which polyethylene molecular chains form a three-dimensional network structure. The unit is %, and gel ratio is usually used in engineering to characterize the degree of cross-linking of materials.

[0055] In this invention, for insulation materials meeting the application requirements of 100-500kV high-voltage DC cables, the gelation rate is 80-90%, which is the "target gelation rate" described in this invention. In this invention, the theoretical dosage of pure crosslinking agent is determined based on the target gelation rate. d 0 is 0.8-2, preferably 1-1.8.

[0056] In this invention, by adjusting the actual amount of crosslinking agent under the above conditions, it is possible to maintain good crosslinking characteristics at low crosslinking agent content, reduce the impact of crosslinking byproducts, especially liquid byproducts such as acetophenone and α-methylstyrene, on DC conductivity and space charge distortion rate, thereby improving the electrical performance of insulation materials, shortening cable degassing time, and improving cable production efficiency.

[0057] In a preferred embodiment of the present invention, the crosslinkable polyethylene insulation material is composed of low-density polyethylene, antioxidant and crosslinking agent.

[0058] In a preferred embodiment of the present invention, the antioxidant has three or more terminal double bonds.

[0059] According to the present invention, the antioxidant is selected from at least one of acrylate antioxidants, allylamine antioxidants, and allylphenol antioxidants.

[0060] In this invention, in order to further avoid introducing impurities that could affect the electrical properties of the cross-linked polyethylene insulation material, preferably, the antioxidant has a purity of analytical grade ≥99.5%.

[0061] In this invention, there is no particular limitation on the specific type of acrylate antioxidant, as long as it meets the aforementioned requirements for antioxidants. For example, the acrylate antioxidant is selected from bisphenol A glycerol dimethacrylate (CAS: 1565-94-2) (with 2 terminal double bonds) and / or bisphenol A epoxy acrylate (CAS: 71281-65-7) (with 2 terminal double bonds).

[0062] In this invention, there is no particular limitation on the specific type of allylamine antioxidant, as long as it meets the aforementioned requirements for antioxidants. For example, the allylamine antioxidant is selected from antioxidant 5057 (CAS: 68411-46-1) (the number of terminal double bonds in the antioxidant is 2) and / or m-xylenediacrylamide (CAS: 2842-63-9) (the number of terminal double bonds in the antioxidant is 2).

[0063] In this invention, there is no particular limitation on the specific type of allylphenol antioxidant, as long as it meets the aforementioned requirements for antioxidants. For example, the allylphenol antioxidant is selected from at least one of 2,4,6-triallylphenol (CAS: 20490-22-6) (with 3 terminal double bonds), 4,4'-sulfonylbis[2-(2-propenyl)]phenol (CAS: 41481-66-7) (with 2 terminal double bonds), and 2,6-diallyl-p-cresol (CAS: 6630-76-8) (with 2 terminal double bonds).

[0064] According to the present invention, the weight-average molecular weight of the low-density polyethylene is 50,000-100,000 g / mol.

[0065] According to the present invention, the number average molecular weight of the low-density polyethylene is 10,000-25,000 g / mol.

[0066] According to the present invention, the molecular weight distribution of the low-density polyethylene is 4-7.

[0067] According to the present invention, the melt flow rate of the low-density polyethylene at 190°C and 2.16 kg is 1.2-2.2 g / 10 min.

[0068] According to the present invention, the density of the low-density polyethylene is 0.918-0.922 g / cm³. 3 .

[0069] In this invention, when at least one of the weight-average molecular weight, number-average molecular weight, molecular weight distribution, melt flow rate, and density of low-density polyethylene meets the above-mentioned range, it indicates that the content of low-molecular-weight substances in low-density polyethylene is low, which can further reduce the amount of crosslinking agent used and further reduce the content of impurities in the obtained crosslinked polyethylene insulation material.

[0070] Furthermore, the weight-average molecular weight of the low-density polyethylene is 60,000-90,000 g / mol.

[0071] Furthermore, the number-average molecular weight of the low-density polyethylene is 12,000-30,000 g / mol.

[0072] Furthermore, the low-density polyethylene has a molecular weight distribution of 4-6.

[0073] Furthermore, the low-density polyethylene has a melt flow rate of 1.8-2 g / 10 min at 190°C and 2.16 kg.

[0074] Furthermore, the density of the low-density polyethylene is 0.919-0.921 g / cm³. 3 .

[0075] According to the present invention, a It is 0.1-0.6. d It is 0.6-0.8.

[0076] In this invention, when the amounts of antioxidant and crosslinking agent in the polyethylene insulation material meet the above-mentioned ranges, the allyl or allyl double bond in the antioxidant can play a crosslinking role, which can reduce the amount of peroxide crosslinking agent and does not require the addition of other crosslinking agent components, thereby ensuring the target gel rate.

[0077] Furthermore, a The value is 0.15-0.45. d It ranges from 0.8 to 1.2.

[0078] In this invention, there is no particular limitation on the type of crosslinking agent, which can be a conventional type of crosslinking agent in the art. For example, the crosslinking agent is selected from one or two of the following: dicumyl peroxide (DCP), tert-butyl peroxide, benzoyl peroxide (BPO), 1,4-di-tert-butylperoxypropylbenzene (BIPB), and 2,5-dimethyl-2,5-bis-(tert-butylperoxy)hexane (bis(di-2-pentane)).

[0079] A second aspect of the present invention provides a method for preparing cross-linked polyethylene insulating material, wherein the method includes:

[0080] After preheating the antioxidant in the above-mentioned crosslinkable polyethylene insulation material, it is first mixed with low-density polyethylene to obtain an intermediate material. Then, the molten crosslinking agent is mixed with the intermediate material for a second time, and after a first heat preservation, it is cooled to obtain the crosslinkable polyethylene insulation material. The antioxidant is a liquid antioxidant.

[0081] or;

[0082] The low-density polyethylene and antioxidant in the above-mentioned crosslinkable polyethylene insulation material are melt-extruded and granulated to obtain an intermediate material; the molten crosslinking agent is mixed with the intermediate material in a third process and then kept warm for a second time, and then cooled to obtain the crosslinkable polyethylene insulation material, wherein the antioxidant is a solid antioxidant;

[0083] Crosslinkable polyethylene insulation material is crosslinked to obtain crosslinked polyethylene insulation material.

[0084] In this invention, when cross-linked polyethylene insulation material is prepared using the specific method described above, a high degree of cross-linking can be achieved with a relatively low cross-linking agent content. This reduces DC conductivity and space charge distortion rate, improving the electrical performance of the cross-linked polyethylene insulation material under a DC field. It also extends the scorch resistance time of the cross-linkable polyethylene insulation material, facilitating its long-term stable extrusion. Simultaneously, reducing the amount of cross-linking agent effectively reduces cross-linking byproducts and shortens the degassing time of the cable.

[0085] In this invention, there are no particular limitations on the equipment used for the first mixing, the second mixing, and the third mixing. The mixing can be carried out in conventional mixing equipment in the art, such as a mixing absorption tank.

[0086] The antioxidant is a liquid antioxidant.

[0087] The preheated antioxidant is first mixed with low-density polyethylene to obtain an intermediate material. Then, the molten crosslinking agent is secondly mixed with the intermediate material, followed by a first heat preservation and cooling to obtain a crosslinkable polyethylene insulation material. The antioxidant is a liquid antioxidant.

[0088] In this invention, by preheating the antioxidant and crosslinking agent, the antioxidant and crosslinking agent are better and more uniformly dispersed, ultimately resulting in a crosslinked polyethylene insulation material that has both excellent scorch resistance and excellent electrical properties, as well as high degassing efficiency.

[0089] According to the present invention, the conditions for the first mixing include: a mixing temperature of 50-90 °C and a mixing time of 10-30 min.

[0090] According to the present invention, the conditions for the second mixing include: a mixing temperature of 50-90°C and a mixing time of 10-30 min.

[0091] According to the present invention, the conditions for the first heat preservation include: heat preservation temperature of 60-85 ℃; heat preservation time of 14-30 h.

[0092] In this invention, when the conditions for controlling the first mixing, the second mixing, or the first heat preservation meet the above-mentioned range, it is possible to ensure that the liquid antioxidant, the molten crosslinking agent, and the intermediate material are in a "liquid state," thereby achieving uniform dispersion of the antioxidant, the crosslinking agent, and the low-density polyethylene, and significantly reducing the number of process steps.

[0093] In this invention, "liquid" refers to liquid antioxidants, crosslinking agents, and intermediate materials in a flowable state.

[0094] Furthermore, the conditions for the first mixing include: a mixing temperature of 60-80°C, preferably 65-75°C; and a mixing time of 15-20 min.

[0095] Furthermore, the conditions for the second mixing include: a mixing temperature of 60-80°C, preferably 65-75°C; and a mixing time of 15-25 min.

[0096] Furthermore, the conditions for the first heat preservation include: a heat preservation temperature of 65-85℃, preferably 70-80℃; and a heat preservation time of 16-28h, preferably 16-24h.

[0097] In this invention, in order to ensure that the low-density polyethylene, antioxidant and crosslinking agent are fully and uniformly mixed, preferably, the preheated antioxidant is sprayed into the low-density polyethylene; and / or, the molten crosslinking agent is sprayed into the intermediate material.

[0098] According to the present invention, the spraying rates of the preheated antioxidant and the molten crosslinking agent are each 0.5-1 L / min.

[0099] In this invention, when the spraying speed of the preheated antioxidant and the molten crosslinking agent is controlled to meet the above-mentioned range, it can ensure that the liquid antioxidant has sufficient time to mix with the low-density polyethylene and that the molten crosslinking agent has sufficient time to mix with the intermediate material. At the same time, it avoids the local aggregation of the crosslinking agent and the antioxidant, thereby achieving uniform dispersion of the antioxidant, crosslinking agent and low-density polyethylene, and significantly reducing the number of process steps.

[0100] Furthermore, the spraying rates of the preheated antioxidant and the molten crosslinking agent are each 0.6-0.8 L / min.

[0101] According to the present invention, the crosslinking conditions include: a crosslinking temperature of 160-220°C, a crosslinking time of 10-25 min, and a crosslinking pressure of 10-25 MPa.

[0102] In this invention, crosslinking under the above conditions enables the double bonds in the peroxide crosslinking agent and antioxidant to fully undergo crosslinking reaction, thereby increasing the degree of crosslinking of the crosslinked polyethylene insulation material.

[0103] Furthermore, the crosslinking conditions include: a crosslinking temperature of 170-220℃, preferably 175-185℃, a crosslinking time of 15-20 min, and a crosslinking pressure of 15-20 MPa.

[0104] The antioxidant is a solid antioxidant.

[0105] Low-density polyethylene and an antioxidant are melt-extruded and granulated to obtain an intermediate material; the molten crosslinking agent is mixed with the intermediate material in a third process, followed by a second heat preservation, and then cooled to obtain a crosslinkable polyethylene insulation material, wherein the antioxidant is a solid antioxidant.

[0106] In this invention, there are no particular limitations on the equipment used for melt extrusion; conventional equipment in the art, such as reciprocating single-screw extruders and / or twin-screw extruders, can be used.

[0107] According to the present invention, the conditions for melt extrusion include: a melt extrusion temperature of 110-150°C and a melt extrusion rotation speed of 150-300 rpm.

[0108] According to the present invention, the conditions for the third mixing include: a mixing temperature of 50-90°C and a mixing time of 10-30 min.

[0109] According to the present invention, the conditions for the second heat preservation include: heat preservation temperature of 60-85°C; heat preservation time of 14-30h.

[0110] In this invention, when the conditions of melt extrusion, third mixing, or second heat preservation meet the above-mentioned range, the antioxidant and crosslinking agent can achieve uniform dispersion.

[0111] Furthermore, the conditions for melt extrusion include: a melt extrusion temperature of 120-130°C and a melt extrusion rpm of 200-250 rpm.

[0112] Furthermore, the conditions for the third mixing include: a mixing temperature of 60-80℃, preferably 65-75℃; and a mixing time of 15-25 min.

[0113] Furthermore, the conditions for the second insulation include: an insulation temperature of 65-85℃, preferably 70-80℃; and a mixing time of 16-28h, preferably 16-24h.

[0114] In this invention, in order to ensure that the low-density polyethylene, antioxidant and crosslinking agent are fully and uniformly mixed, preferably, the molten crosslinking agent is sprayed into the intermediate material.

[0115] According to the present invention, the spraying rate of the molten crosslinking agent is 0.5-1 L / min.

[0116] In this invention, controlling the spraying speed of the molten crosslinking agent to meet the above-mentioned range can avoid local accumulation and better achieve uniform dispersion of the crosslinking agent.

[0117] Furthermore, the spraying rate of the molten crosslinking agent is 0.6-0.8 L / min.

[0118] According to the present invention, the crosslinking conditions include: a crosslinking temperature of 160-220°C, a crosslinking time of 10-25 min, and a crosslinking pressure of 10-25 MPa.

[0119] In this invention, crosslinking under the above conditions enables the double bonds in the peroxide crosslinking agent and antioxidant to fully undergo crosslinking reaction, thereby increasing the degree of crosslinking of the crosslinked polyethylene insulation material.

[0120] Furthermore, the crosslinking conditions include: a crosslinking temperature of 170-220℃, preferably 175-185℃, a crosslinking time of 15-20 min, and a crosslinking pressure of 15-20 MPa.

[0121] A third aspect of the present invention provides a cross-linked polyethylene insulating material prepared by the above method.

[0122] The fourth aspect of the present invention provides the application of the above-mentioned cross-linkable polyethylene insulation material or cross-linked polyethylene insulation material in high-voltage DC cables.

[0123] The present invention will be described in detail below through embodiments. In the following embodiments,

[0124] (1) Activation energy test method:

[0125] Differential scanning calorimetry (DSC) was used, based on the Arrhenius equation (Equation 1), to determine the peak temperature T of the reaction at four different heating rates (10 K / min, 15 K / min, 20 K / min, 25 K / min). A straight line was fitted using the Kissinger method, and the slope of the line was calculated. m Then, the activation energy is calculated using Equation 2:

[0126] Formula 1;

[0127] From Equation 1, we can deduce that m= -E a / R;

[0128] Therefore, E = -m × R (Equation 2);

[0129] in, k This is the reaction rate constant, in seconds. -1 (First-order reaction) R The gas constant is 8.314 J / mol. K and T are absolute temperatures (K), A is the pre-exponential factor, and s -1 .

[0130] (2) Thermal extension test method: Refer to standard GB / T 2951.21-2008.

[0131] (3) Scorch resistance test method: Performed in accordance with GB / T 16584-1996, the test temperature is 160℃, and T is defined as follows: S1 To withstand scorching time.

[0132] (4) Method for testing methane gas concentration:

[0133] Methane content was determined using non-dispersive infrared spectroscopy (NDIR). The specific testing method was as follows: 50g of test sample was placed in a sample bag containing 200mL of argon gas, sealed, and allowed to stand for 12 hours. The gas was then introduced into the NDIR spectrometer for content determination. The sampling system used PTFE tubing. The instrument measured the attenuation of infrared light at specific wavelengths using the characteristic infrared absorption peaks at 3.3 μm (main absorption peak) and 7.66 μm (secondary absorption peak) according to Lambert-Beer's law, and the methane concentration was calculated using Equation 3.

[0134] According to the Lambert-Beer law,

[0135] c = P × log(I 0 / I) Formula 3

[0136] in, c The molar concentration of methane (unit: mol / m³). I 0 represents the intensity of infrared light at a specific wavelength incident on the sample cell; I The intensity of infrared light after passing through the sample (containing methane gas); P For calibration constant ( P = 1 / (ε×L) (This is calibrated by the instrument manufacturer using standard concentration gases). For bimodal instruments, calibration is performed separately for 3.3 μm and 7.66 μm. P 1 and P 2. During actual measurement, the absorbance is automatically switched according to the magnitude (generally using the main peak at 3.3μm, and in special cases using the secondary peak at 7.66μm to avoid saturation of the main peak at high concentrations).

[0137] At low concentrations: c = P 1 × log(I 0 / I)

[0138] At high concentrations: c = P 2 × log(I 0 / I)

[0139] Low concentration means the absorption peak intensity at 3.3 micrometers did not reach the instrument's maximum value during the test; high concentration means the absorption peak intensity at 3.3 micrometers reached the instrument's maximum value during the test, and the peak intensity at 7.66 micrometers was then used as the concentration calculation value.

[0140] (5) Measurement of electrical conductivity of cross-linked polyethylene insulation material:

[0141] Conductivity current was measured using a picoammeter and a standard two-electrode testing system. The sample thickness was (200±10) µm. Before testing, the sample was heated to 50 °C. o In an oven at temperature C, the sample is short-circuited for at least 24 hours. The sample is then placed between the upper and lower electrodes of the testing system and short-circuited again at room temperature for approximately 30 minutes, until the short-circuit current on the picoammeter decreases to less than 0.02A. At 70℃, the electric field strength is increased from 10kV / mm in 10kV / mm increments until it reaches 30kV / mm, and the ammeter data is recorded.

[0142] (6) Space charge test (electric field distortion rate) of cross-linked polyethylene insulation material:

[0143] Space charge testing was performed using the pulse electroacoustic (PEA) method. The sample thickness was (200±10) µm. Before testing, the sample was heated to 50 °C. o The material was short-circuited in an oven at temperature C for more than 24 hours, at a test temperature of 70℃ and an electric field strength of 30kV / mm. By analyzing the acoustic signal, information on the charge distribution and electric field distortion in the material was obtained.

[0144] Low-density polyethylene (LDPE-1) has a number-average molecular weight of 14,118 g / mol, a weight-average molecular weight of 62,190 g / mol, a molecular weight distribution of 4.39, and a density of 0.920 g / cm³. 3 The melt flow rate is 1.9 g / 10 min (190 °C, 2.16 kg), and the activation energy for the crosslinking reaction is 144 kJ / mol.

[0145] Low-density polyethylene (LDPE-2) has a number-average molecular weight of 16,688 g / mol, a weight-average molecular weight of 80,774 g / mol, a molecular weight distribution of 4.8, and a density of 0.918 g / cm³. 3 The melt flow rate is 1.85 g / 10 min (190 °C, 2.16 kg), and the activation energy for the crosslinking reaction is 146 kJ / mol.

[0146] Low-density polyethylene (LDPE-3) has a number-average molecular weight of 14670 g / mol, a weight-average molecular weight of 71130 g / mol, a molecular weight distribution of 4.85, and a density of 0.919 g / cm³. 3 The melt flow rate is 1.9 g / 10 min (190 °C, 2.16 kg), and the activation energy for the crosslinking reaction is 140 kJ / mol.

[0147] Antioxidant 1,2,4,6-triallylphenol, with 3 terminal double bonds, molar mass 214 g / mol, intrinsic activation energy... E AO It has a concentration of 121 kJ / mol, N is 1, and is a liquid antioxidant.

[0148] Antioxidant 2, Antioxidant 5057 (reaction product of N-phenylaniline and 2,4,4-trimethylpentene (CAS No.: 68411-46-1), with 2 terminal double bonds, molar mass 393 g / mol, intrinsic activation energy...) E AO It has a strength of 110 kJ / mol and a nitrogen content of 1. It is a solid powder antioxidant.

[0149] Antioxidant 3, Bisphenol A epoxy acrylate, with 2 terminal double bonds, molar mass 485 g / mol, intrinsic activation energy E AO It has a concentration of 113 kJ / mol, an N concentration of 2, and is a liquid antioxidant.

[0150] Antioxidant 4, Antioxidant 300, 4,4'-Thiobis(6-tert-butyl-3-methylphenol), 0 terminal double bonds, molar mass 359 g / mol, intrinsic activation energy E AO It has a concentration of 165 kJ / mol and an N concentration of 2; it is a solid powder antioxidant.

[0151] Antioxidant 5,2,2'-diallylbisphenol A, with 2 terminal double bonds, molar mass 308 g / mol, intrinsic activation energy E AO It has a concentration of 138 kJ / mol, an N concentration of 2, and is a liquid antioxidant.

[0152] Crosslinking agent, bis(2,5), molar mass M c The number of peroxide groups is 290 g / mol. f It is 2. c It is 0.7.

[0153] In the following embodiments of the present invention, 1 part by weight is 1g.

[0154] Example

[0155] The effective coefficient b of double bond functional groups of different antioxidants

[0156] (1) Antioxidants (antioxidant 1, antioxidant 2, antioxidant 3, antioxidant 4 and antioxidant 5) and crosslinking agents are mixed with 100 parts by weight of LDPE and then added to different insulating materials; wherein, in different insulating materials, the amount of antioxidants and crosslinking agents is such that the molar concentration of double bonds in different antioxidants is equal to the molar concentration of peroxide groups in crosslinking agents;

[0157] (2) The gel content S of different insulating materials was tested according to JB / T 10437-2024;

[0158] (3) Calculate the crosslinking density of different insulating materials according to the following;

[0159] ;

[0160] in, .

[0161] The results are shown in Table 1.

[0162] Table 1

[0163]

[0164] Crosslinkable polyethylene insulation material formulation design

[0165] (1) The dosage of different antioxidants a in crosslinkable polyethylene insulation material is determined according to the following formula. The dosage of antioxidants is shown in Table 2.

[0166] a = A M o / N

[0167] in, M o The molar mass of the antioxidant is expressed in g / mol. N The number of hydroxyl or amino functional groups; A It is 0.0011 / (g / mol).

[0168] (2) Different types of antioxidants were mixed with 100 parts by weight of low-density polyethylene to obtain a mixture. The crosslinking activation energy E of the mixture was calculated according to the following formula, and the results are shown in Table 2.

[0169] , where n is 2.

[0170] (3) Based on the target gelation rate (87%), determine the theoretical amount of pure crosslinking agent (double 2,5) according to the following formula.d 0 = target gelation rate / ( f × K × c ),in, K The value is 55. c The value is 0.7. f The value is 2, and the theoretical amount of pure crosslinking agent (double 2,5) is calculated. d 0 = 1.2 parts by weight.

[0171] Table 2

[0172]

[0173] As can be seen from Table 2, the actual amount of crosslinking agent d in crosslinkable polyethylene insulation is only related to the type and amount of antioxidant. For crosslinkable polyethylene insulation with the same type of antioxidant, the actual amount of crosslinking agent is the same.

[0174] (4) For different types of antioxidants, according to the formula d = d 0– a × c × M c × b / ( M o × f The actual amount of crosslinking agent (double 2,5) used in the crosslinkable polyethylene insulation material was calculated, and the results are shown in Table 3.

[0175] Table 3

[0176]

[0177] (5) The final formulation of cross-linkable polyethylene insulation material is determined through steps (1) to (4) as shown in Table 4.

[0178] Table 4

[0179]

[0180] Comparative Example 7

[0181] The formulation of crosslinkable polyethylene insulation material is as follows: 100 parts by weight of LDPE-3, 0.17 parts by weight of antioxidant 5, 1.2 parts by weight of bis(2,5)-diphenyltrimethylammonium chloride, and 0.3 parts by weight of triallyl polyisocyanate.

[0182] Preparation of cross-linked polyethylene insulation materials

[0183] The crosslinkable polyethylene insulation material designed according to the aforementioned method is used to prepare crosslinked polyethylene insulation materials, wherein the liquid antioxidant is prepared according to method A; and the solid antioxidant is prepared according to method B.

[0184] Method A

[0185] Liquid antioxidants were preheated and sprayed onto low-density polyethylene for the first mixing to obtain an intermediate material. Molten crosslinking agents were then sprayed onto the intermediate material for a second mixing and a first heat preservation period. After cooling, crosslinkable polyethylene insulation material was obtained. The conditions for the first mixing included a mixing temperature of 70°C and a mixing time of 20 minutes. The conditions for the second mixing included a mixing temperature of 75°C and a mixing time of 20 minutes. The conditions for the first heat preservation included a heat preservation temperature of 80°C and a heat preservation time of 20 hours. The spraying rate of the liquid antioxidants and crosslinking agents was 0.6 L / min. The types and amounts of low-density polyethylene, antioxidants, and crosslinking agents are detailed in Table 4.

[0186] Crosslinkable polyethylene insulation material is obtained by hot pressing at 180℃ and 15MPa for 15 minutes to crosslink it.

[0187] Method B

[0188] Low-density polyethylene and a solid antioxidant are melt-extruded and granulated in a twin-screw extruder to obtain an intermediate material. Molten crosslinking agent is sprayed onto the intermediate material for a third mixing and a second heat preservation process, followed by cooling to obtain crosslinkable polyethylene insulation material. The melt extrusion conditions include: a temperature of 130℃ and a rotation speed of 250 rpm; the third mixing conditions include: a mixing temperature of 75℃ and a mixing time of 25 min; the second heat preservation conditions include: a heat preservation temperature of 70℃ and a heat preservation time of 24 h; and the crosslinking agent spraying rate is 0.7 L / min. The types and amounts of low-density polyethylene, antioxidant, and crosslinking agent are detailed in Table 4.

[0189] Crosslinkable polyethylene insulation material is obtained by hot pressing at 180℃ and 15MPa for 15 minutes to crosslink it.

[0190] The properties of the cross-linked polyethylene insulation material prepared above were tested, and the results are shown in Table 5.

[0191] Table 5

[0192]

[0193] As can be seen from Tables 1-5, by selecting specific types of antioxidants, when the activation energy of the crosslinking reaction of the composition composed of antioxidants and low-density polyethylene meets the range of 40-70 kJ / mol, the resulting crosslinked polyethylene insulation material can have a suitable degree of crosslinking (with appropriate elongation under thermal extension load), a long scorch resistance time, low crosslinking by-products, and low DC conductivity and space charge distortion rate. This indicates that the crosslinked polyethylene insulation material obtained in this way can take into account scorch resistance, electrical properties, and degassing efficiency.

[0194] As can be seen from the test results of Example 1 and Comparative Example 1 in Table 5, Example 1, with a lower crosslinking agent content, can achieve the same degree of crosslinking as Comparative Example 1 with a 1.5% crosslinking agent content. Example 1 has a longer scorch resistance time, lower total amount of additives and crosslinking byproduct content, lower DC conductivity and space charge distortion rate, and better electrical properties.

[0195] Comparing the test results of Example 1 and Comparative Example 2 in Table 5, Comparative Example 2 showed a larger elongation under load, indicating a lower degree of crosslinking within the reactant material. To further improve the degree of crosslinking, it is necessary to increase the content of the crosslinking agent or add a co-crosslinking agent (Comparative Example 3). However, increasing the content of the additives reduces the scorch resistance time and increases the ion content and crosslinking byproduct content in the system, resulting in higher DC conductivity and space charge distortion rate.

[0196] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A cross-linkable polyethylene insulation material, characterized in that, The crosslinkable polyethylene insulation material includes low-density polyethylene, antioxidants, and crosslinking agents, but does not contain initiators or co-crosslinking agents; The amount of antioxidant used relative to 100 parts by weight of low-density polyethylene is: a Parts by weight; Among them, the amount of antioxidant used reduces the activation energy of the crosslinking reaction of crosslinkable polyethylene insulation material. E It is 40-70 kJ / mol; in, E The activation energy of the crosslinking reaction of the composition consisting of antioxidant and low-density polyethylene is kJ / mol. E LDPE The activation energy for the crosslinking reaction of low-density polyethylene is kJ / mol. E AO The intrinsic activation energy of the antioxidant is given in kJ / mol. b It is 0.3-1; c The number of terminal double bonds in an antioxidant; n It is 2; c≥2； Relative to 100 parts by weight of low-density polyethylene, the crosslinking agent is an organic peroxide crosslinking agent, and the actual amount of crosslinking agent used is... d Parts by weight; of which, d = d 0– a × c × M c × b / ( M o × f ); d 0 = target gelation rate / ( f × K × γ ); in, c The number of terminal double bonds in an antioxidant; M c The molar mass of the crosslinking agent is expressed in g / mol. b The effective coefficient of the double bond functional group of the antioxidant; M o The molar mass of the antioxidant is expressed in g / mol. f The number of peroxide groups in the crosslinking agent molecule; d 0 represents the theoretical amount of pure crosslinking agent, in parts by weight; γ It is 0.7-0.9; 16 is the molar mass of oxygen atoms, g / mol; K is 50-60; Dosage of antioxidants a Calculated using the following formula: a = A M o / N ； Where A is 0.0008-0.0015 / (g / mol), M o The molar mass of the antioxidant is expressed in g / mol. N The number of hydroxyl or amino functional groups in the antioxidant.

2. The cross-linkable polyethylene insulation material according to claim 1, wherein, The crosslinkable polyethylene insulation material is composed of low-density polyethylene, antioxidants, and crosslinking agents.

3. The cross-linkable polyethylene insulation material according to claim 1, wherein, The antioxidant contains at least three terminal double bonds.

4. The crosslinkable polyethylene insulation material according to claim 1, wherein, The antioxidant is selected from at least one of acrylate antioxidants, allylamine antioxidants, and allylphenol antioxidants.

5. The cross-linkable polyethylene insulation material according to claim 4, wherein, The antioxidant is a liquid antioxidant or a solid antioxidant.

6. The crosslinkable polyethylene insulation material according to claim 1, wherein, The low-density polyethylene has a weight-average molecular weight of 50,000-100,000 g / mol. And / or, the number average molecular weight of the low-density polyethylene is 10,000-25,000 g / mol; And / or, the molecular weight distribution of the low-density polyethylene is 4-7; And / or, the low-density polyethylene has a melt flow rate of 1.2-2.2 g / 10 min at 190°C and 2.16 kg; And / or, the density of the low-density polyethylene is 0.918-0.922 g / cm³. 3 .

7. The cross-linkable polyethylene insulation material according to any one of claims 1-6, wherein, a It is 0.1-0.

6. d It ranges from 0.6 to 1.

8.

8. A method for preparing cross-linked polyethylene insulating material, characterized in that, The method includes: After preheating the antioxidant in the crosslinkable polyethylene insulation material according to any one of claims 1-7, it is first mixed with low-density polyethylene to obtain an intermediate material. Then, the molten crosslinking agent is mixed with the intermediate material for a second time, and after a first heat preservation, it is cooled to obtain the crosslinkable polyethylene insulation material, wherein the antioxidant is a liquid antioxidant. or; The low-density polyethylene and antioxidant in the crosslinkable polyethylene insulation material according to any one of claims 1-7 are melt-extruded and granulated to obtain an intermediate material; the molten crosslinking agent and the intermediate material are mixed for a third time and then kept warm for a second time, and then cooled to obtain the crosslinkable polyethylene insulation material, wherein the antioxidant is a solid antioxidant; Crosslinkable polyethylene insulation material is crosslinked to obtain crosslinked polyethylene insulation material.

9. The method according to claim 8, wherein, The conditions for the first mixing include: a mixing temperature of 50-90℃; and a mixing time of 10-30 min. And / or, the conditions for the second mixing include: a mixing temperature of 50-90°C; and a mixing time of 10-30 min; And / or, the conditions for the first insulation include: insulation temperature of 60-85℃; insulation time of 14-30h; And / or, the crosslinking conditions include: a crosslinking temperature of 160-220℃, a crosslinking time of 10-25 min, and a crosslinking pressure of 10-25 MPa.

10. The method according to claim 8, wherein, The conditions for melt extrusion include: a melt extrusion temperature of 110-150℃ and a melt extrusion rotation speed of 150-300 rpm; And / or, the conditions for the third mixing include: a mixing temperature of 50-90°C; and a mixing time of 10-30 min; And / or, the conditions for the second insulation include: insulation temperature of 60-85℃; insulation time of 14-30h.

11. The method according to claim 8, wherein, The preheated antioxidant is sprayed onto the low-density polyethylene. And / or, spray the molten crosslinking agent into the intermediate material.

12. The method according to claim 11, wherein, The spraying rates of the preheated antioxidant and the molten crosslinking agent are each 0.5-1 L / min.

13. A cross-linked polyethylene insulating material prepared by the method according to any one of claims 8-12.

14. The application of the crosslinkable polyethylene insulation material according to any one of claims 1-7 or the crosslinked polyethylene insulation material according to claim 13 in high-voltage DC cables.

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