Cross-linking agent, preparation method, cross-linked polyethylene cable material and cable

Abstract

The invention discloses a cross-linking agent, a preparation method, a cross-linked polyethylene cable material and a cable, and relates to the technical field of cross-linking agents. The invention provides a cross-linking agent for cross-linking polyethylene. The cross-linking agent is a peroxide cross-linking agent with carbon-carbon double bonds at the tail end of a molecular structure. As the tail end of the molecular structure of the peroxide cross-linking agent provided by the invention has a carbon-carbon double bond, the peroxide cross-linking agent provided by the invention has the characteristics of high cross-linking reaction speed, short cross-linking time and few cross-linking byproducts when being used for cross-linking polyethylene, so that a cable with good use stability can be obtained; and moreover, the production efficiency of the high-voltage cable can be effectively improved, the cable degassing time is shortened, the cable degassing energy consumption is reduced, and the production cost is saved.

Description

Technical Field

[0001] This application relates to the field of crosslinking agent technology, and in particular to crosslinking agents, preparation methods, crosslinked polyethylene cable materials, and cables. Background Technology

[0002] In related technologies, when using dicumyl peroxide (DCP) as a crosslinking agent to prepare crosslinked polyethylene cable materials, the peroxide free radicals generated by the thermal decomposition of DCP during the crosslinking process can capture hydrogen atoms from the polyethylene macromolecular chains, thereby forming macromolecular chain free radicals and crosslinking byproducts, such as methane, cumyl alcohol, α-methylstyrene, acetophenone, and isopropylphenyl alcohol. In actual use of such cables, these crosslinking byproducts do not easily migrate from the cable insulation layer and remain there, posing a significant hazard to the safe operation of the cable. Therefore, degassing is usually performed after crosslinking to remove low-boiling-point crosslinking byproducts such as methane. Specifically, the higher the cable voltage rating, the longer the degassing time; cable manufacturers generally require more than 10 days of degassing to remove these crosslinking byproducts. However, this prolonged degassing process leads to low cable production efficiency and high energy consumption costs. Summary of the Invention

[0003] The main purpose of this application is to provide a crosslinking agent, a preparation method, crosslinked polyethylene cable material, and a cable, aiming to solve the technical problem in the prior art that the large number of crosslinking by-products in polyethylene crosslinking leads to low cable production efficiency and high production energy consumption costs.

[0004] To achieve the above objectives, this application proposes a crosslinking agent for crosslinked polyethylene. The crosslinking agent is a peroxide crosslinking agent with carbon-carbon double bonds at the ends of its molecular structure. The structural formula of the crosslinking agent is shown below: ; Where R1 is -C n H 2n-1 (n≥2), R² is -C n H 2n (n≥2), R3 is -C n H 2n+1 (n≥1).

[0005] In one embodiment, when R1 is -C2H3, R2 is -C3H6, and R3 is -C4H9, the crosslinking agent has the following structural formula I: .

[0006] Furthermore, to achieve the above objectives, this application also proposes a method for preparing the aforementioned crosslinking agent, wherein the preparation method is as follows: Tert-butyl hydroperoxide and α,α'-dihydroxy-1,3-diisopropylbenzene were mixed, and a strong oxidizing initiator was added to carry out a first reaction to obtain an intermediate product; wherein, the structural formula II of the intermediate product is shown below: ; After adding iodine to the intermediate product, a second reaction occurs under acidic conditions to obtain the crosslinking agent of structural formula I.

[0007] In one embodiment, the molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene, tert-butyl hydroperoxide, and iodine is 1:(1.2~1.5):(0.1~0.5).

[0008] In one embodiment, the strong oxidizing initiator is a mixture of acetic acid and perchloric acid.

[0009] In one embodiment, the molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene, the acetic acid, and the perchloric acid is 1:(0.1~0.5):(0.1~0.5).

[0010] In one embodiment, when the strong oxidizing initiator is a mixture of acetic acid and perchloric acid, the reaction temperature of the first reaction is 0°C to 10°C, and the reaction duration is 24h to 48h.

[0011] In one embodiment, the mixing of tert-butyl hydroperoxide and α,α'-dihydroxy-1,3-diisopropylbenzene comprises: The α,α'-dihydroxy-1,3-diisopropylbenzene was completely dissolved in dichloromethane; Then add the tert-butyl hydroperoxide and stir to completely mix the tert-butyl hydroperoxide and the α,α'-dihydroxy-1,3-diisopropylbenzene.

[0012] In addition, to achieve the above objectives, this application also proposes a cross-linked polyethylene cable material, which is composed of polyethylene, an antioxidant, and a cross-linking agent as shown in the above structural formula I; The preparation method of the cross-linked polyethylene cable material includes: The polyethylene and the antioxidant are first mixed; After the first mixing is completed, the crosslinking agent of structural formula I is added for a second mixing to obtain a mixture; the mass ratio of the polyethylene, the antioxidant and the crosslinking agent of structural formula I is 100:0.5:3~100:0.2:1; The mixture is removed and cooled to obtain the cross-linked polyethylene cable material.

[0013] In addition, to achieve the above objectives, this application also proposes a cable comprising an insulation layer made of the aforementioned cross-linked polyethylene cable material.

[0014] One or more technical solutions proposed in this application have at least the following technical effects: The peroxide crosslinking agent provided in this application has carbon-carbon double bonds at the end of its molecular structure. Therefore, when using this peroxide crosslinking agent for polyethylene crosslinking, the peroxide crosslinking agent decomposes upon heating to form free radicals. Since these free radicals contain carbon-carbon double bonds and are highly reactive, they can quickly open the carbon-carbon double bonds and form a crosslinked structure with polyethylene, thus achieving rapid crosslinking. After opening the double bonds, one end of the free radical is a macromolecular free radical R2O·, and the other end is an organic free radical ·CH2-R1. Because the organic free radical ·CH2-R1 does not generate the crosslinking byproduct methane during the chain reaction, and the macromolecular free radical R2O· has lower reactivity than the organic free radical ·CH2-R1, polyethylene primarily undergoes a chain reaction with the organic free radical ·CH2-R1 to achieve crosslinking. This can reduce the generation of crosslinking byproducts to a certain extent. Therefore, the crosslinking reaction using the peroxide crosslinking agent provided in this application has the characteristics of fast crosslinking reaction speed, short crosslinking time and few crosslinking by-products. Thus, it can not only obtain cables with good stability, but also effectively improve the production efficiency of high-voltage cables, shorten the cable degassing time, reduce cable degassing energy consumption and save production costs. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A schematic flowchart illustrating the preparation method of the crosslinking agent provided in this application; Figure 2 This is a synthetic route diagram for the first and second reactions in this application; Figure 3 The nuclear magnetic resonance spectrum of the crosslinking agent of structural formula I prepared in Example 1 of this application; Figure 4 The figures show the thermal elongation test results of XLPE cable material in the embodiments and comparative examples of this application; Figure 5 The figure shows the test results of the crosslinking byproduct content of XLPE cable material in the embodiments and comparative examples of this application.

[0017] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0020] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0021] In this application, when numerical intervals (i.e., numerical ranges) are involved, unless otherwise specified, the distribution of selectable numerical values ​​within the numerical interval is considered continuous, and includes the two endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every numerical value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed in this application should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, etc.

[0022] To better understand the technical solution of this application, a brief description of the common processes for cross-linked cables will be given first.

[0023] Currently, the production processes for cross-linked cables in the cable industry are divided into three categories. The first category is peroxide chemical cross-linking, including saturated steam cross-linking, dry chemical cross-linking (also known as inert gas cross-linking), molten salt cross-linking, and silicone oil cross-linking. The second category is silane chemical cross-linking. The third category is radiation cross-linking.

[0024] Peroxide chemical crosslinking is a crosslinking method suitable for high-voltage cables. Its principle involves using an organic peroxide as a crosslinking agent. Under high temperature, the organic peroxide decomposes to generate free radicals. These free radicals then attack polyethylene molecules, abstracting hydrogen atoms to form carbon-hydrogen single bonds, resulting in more stable polyethylene macromolecular free radicals R·. Two adjacent polyethylene macromolecular free radicals R· are connected by a covalent bond (CC bond), thus forming a crosslinked network structure. Common organic peroxides include dicumyl peroxide (DCP) or bis-tert-butyl peroxide (BIPB). This crosslinking method requires high-pressure extrusion equipment, allowing the crosslinking reaction to occur within the barrel. The cable product is then rapidly heated to produce the crosslinked cable product.

[0025] Silane chemical crosslinking involves using polyethylene material containing vinyl silane. After extruding a shielding layer, an insulation layer, and an insulating shielding layer, the insulated core is cooled and coiled, then immersed in hot water at 85-95°C for hydrolytic crosslinking. The principle is that, under the action of an initiator, vinyl silane reacts with molten polyethylene to form a silane graft polymer. This silane graft polymer then undergoes hydrolysis in the presence of a silanol condensation catalyst, completing the hydrolytic crosslinking in water and forming a network of oxo-alkane chain crosslinked structures. This crosslinking process requires not only polyethylene and vinyl silane but also catalysts, initiators, and antioxidants. Because this crosslinking method may increase the moisture content of the insulation layer, it typically only achieves a maximum voltage level of 10KV.

[0026] Irradiation crosslinking, also known as physical crosslinking, utilizes the radiation from a high-energy electron accelerator, where a high-energy electron beam penetrates the insulation layer to generate crosslinks. This crosslinking method does not rely on chemical crosslinking agents. However, due to the limitations of accelerator energy, it can typically only produce cables with voltage ratings not exceeding 10KV, and its advantages are mainly reflected in the manufacturing of cables below 6KV.

[0027] This application discloses a crosslinking agent for crosslinked polyethylene. The crosslinking agent is a peroxide crosslinking agent with carbon-carbon double bonds at the end of its molecular structure. The structural formula of the crosslinking agent is shown below: ; Where R1 is -Cn H 2n-1 (n≥2), R² is -C n H 2n (n≥2), R3 is -C n H 2n+1 (n≥1).

[0028] In one example, R1 is In another example, R1 is In another example, R1 is .

[0029] In this embodiment, the crosslinking agent itself decomposes upon heating to form free radicals as shown below:

[0030] The free radical has a macromolecular free radical R2O· at one end and a double bond at the other end. Therefore, compared with the carbon-hydrogen single bonds formed by other peroxide crosslinking agents, the free radical in this embodiment has a stronger activity because it contains a carbon-carbon double bond. As a result, the free radical itself can quickly open the carbon-carbon double bond without the need for additional means to provide bond energy. After the carbon-carbon double bond is opened, the free radical has a macromolecular free radical R2O· at one end and an organic free radical CH2-R1 formed after the double bond is opened at the other end. The free radical after the carbon-carbon double bond is opened undergoes a double free radical chain reaction with polyethylene to form a crosslinked network structure. That is, the organic free radical CH2-R1 and the macromolecular free radical R2O· abstract hydrogen atoms from the polyethylene molecular chain. The polyethylene molecules after the hydrogen atoms are abstracted are active, and then two adjacent active polyethylene molecules crosslink to form a crosslinked network structure. Since organic free radicals ·CH2-R1 do not generate cross-linking byproducts in chain reactions, and macromolecular free radicals R2O· have lower reactivity than organic free radicals ·CH2-R1, polyethylene is more likely to undergo chain reactions with organic free radicals ·CH2-R1 to achieve cross-linking. That is, more hydrogen atoms on the polyethylene molecular chain are captured by organic free radicals ·CH2-R1 to form a cross-linked network structure, which can reduce the generation of cross-linking byproducts to a certain extent.

[0031] Specifically, since the crosslinking agent provided in this embodiment is a peroxide crosslinking agent, the types of its crosslinking byproducts are the same as those of DCP. The crosslinking byproducts of the crosslinking agent in this embodiment include methane, cumyl alcohol, α-methylstyrene, acetophenone, and isopropylphenyl alcohol, etc. Since polyethylene mainly undergoes chain reactions with the organic free radicals ·CH2-R1 in this crosslinking agent, this can reduce the generation of all the above-mentioned crosslinking byproducts to a certain extent.

[0032] Therefore, it can be seen that using the crosslinking agent provided in this application for crosslinking reaction has the characteristics of fast crosslinking reaction speed, short crosslinking time and few crosslinking by-products, thus enabling the production of cables with good stability.

[0033] In one embodiment, when R1 is -C2H3, R2 is -C3H6, and R3 is -C4H9, the crosslinking agent has the following structural formula I: .

[0034] In this embodiment, the crosslinking agent of structural formula I decomposes upon heating to form free radicals as shown below:

[0035] The free radical has a peroxide free radical RO· at one end and a double bond at the other end. Therefore, compared with the carbon-hydrogen single bonds formed by other peroxide crosslinking agents, the free radical in this embodiment contains a carbon-carbon double bond, making it more susceptible to attack and more active. Consequently, the free radical itself can quickly open the carbon-carbon double bond without the need for additional means to provide bond energy. After the carbon-carbon double bond is opened, the free radical has a peroxide free radical RO· at one end and an organic free radical ·CH2CCH3 at the other end. The free radical after the carbon-carbon double bond is opened undergoes a double free radical chain reaction with polyethylene to form a crosslinked network structure. That is, the organic free radical ·CH2CCH3 and the peroxide free radical RO· abstract hydrogen atoms from the polyethylene molecular chain. The polyethylene molecules that have had hydrogen atoms abstracted are active, and then two adjacent active polyethylene molecules crosslink to form a crosslinked network structure. Therefore, the crosslinking agent provided in this embodiment has the characteristics of fast crosslinking reaction speed and short crosslinking time. Specifically, compared with DCP at the same addition amount, the crosslinking agent of structural formula I in this embodiment can shorten the crosslinking reaction time by more than 10%, and the thermal elongation of the crosslinked polyethylene cable material prepared by this crosslinking agent after crosslinking is better than that of DCP crosslinked polyethylene.

[0036] The crosslinking byproducts of the crosslinking agent in this embodiment include methane, cumyl alcohol, α-methylstyrene, acetophenone, and isopropylphenyl alcohol. Among these, only volatile methane cannot exist stably in the cable. Once the methane content in the cable reaches a critical point, the cable in operation may explode. Furthermore, the slow release of methane during cable use will inevitably affect the electrical and mechanical properties of the cable and may even lead to cable breakdown, causing circuit failure. Other crosslinking byproducts besides methane can be partially removed through degassing. Since these other crosslinking byproducts exist in the cable in liquid form and are relatively stable, they do not pose a threat to the safe operation of the cable if they are not completely removed.

[0037] In this embodiment, the crosslinking agent provides a crosslinking effect on polyethylene. Because the double bonds of the free radicals formed by this crosslinking agent are opened, the peroxide free radical RO· at one end of the free radical has lower reactivity than the organic free radical ·CH2CCH3 at the other end. Furthermore, since the organic free radical ·CH2CCH3 does not generate methane as a crosslinking byproduct during the chain reaction, polyethylene primarily undergoes a chain reaction with the organic free radical ·CH2CCH3. This means that more hydrogen atoms on the polyethylene molecular chain are captured by the organic free radical ·CH2CCH3 to form a crosslinked network structure. This can reduce the generation of crosslinking byproducts, especially methane, to a certain extent. Compared to DCP at the same addition amount, using the crosslinking agent provided in this embodiment can reduce the content of all crosslinking byproducts to about 20%, with the methane content reduced to 1 / 3, thus obtaining a cable with stable performance.

[0038] In related technologies, cross-linked polyethylene (CPE) cable materials are prepared using dicumyl peroxide (DCP) cross-linking agent. After cross-linking, the CPE cable material typically undergoes degassing treatment to remove methane, a low-boiling-point cross-linking byproduct. Specifically, the higher the cable voltage rating, the longer the degassing time. Cable manufacturers generally require more than 10 days of degassing to remove methane. However, this prolonged degassing process leads to low cable production efficiency and high energy consumption costs. In this embodiment, because the methane content of the cross-linking byproduct is significantly reduced, the cable degassing time can be effectively shortened. Specifically, the degassing time can be reduced to 1 / 5 of that of DCP at the same addition amount, thereby effectively improving the production efficiency of high-voltage cables, reducing cable degassing energy consumption, and saving production costs.

[0039] Therefore, it can be seen that using the peroxide crosslinking agent provided in this embodiment for crosslinking reaction has the characteristic of fewer crosslinking byproducts, which can effectively improve cable production efficiency, shorten cable degassing time, reduce cable degassing energy consumption, and save production costs.

[0040] It should also be noted that, based on the different crosslinking characteristics and mechanisms of polymers, the crosslinked polyethylene in this embodiment can be one of medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and low-density polyethylene.

[0041] In addition, to achieve the above objectives, refer to Figure 1 , Figure 1 This application provides a flowchart illustrating the preparation method of the crosslinking agent. The application also proposes a method for preparing the crosslinking agent of the above-mentioned structural formula I, the preparation method comprising steps S100 to S200: In step S100, tert-butyl hydroperoxide and α,α'-dihydroxy-1,3-diisopropylbenzene are mixed, and a strong oxidizing initiator is added to initiate the first reaction to obtain an intermediate product; wherein, the structural formula II of the intermediate product is shown below: .

[0042] The reaction process of the first reaction is as follows: Figure 2 As shown.

[0043] To ensure the reaction is complete, in one possible implementation, the mixing method can be mechanical stirring. After the two reactants are dissolved by continuous mechanical stirring, a strong oxidizing initiator is added and stirring is continued until the reaction is complete.

[0044] In one possible implementation, the molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene to tert-butyl hydroperoxide is 1:(1.2~1.5). In one example, the molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene to tert-butyl hydroperoxide is 1:1.2. At this molar ratio, the conversion rate of the first reaction is over 95%, essentially achieving complete conversion of both raw materials.

[0045] To obtain the intermediate of structural formula II, in one possible embodiment, the strong oxidizing initiator is a mixture of acetic acid and perchloric acid. In this embodiment, perchloric acid generates a strong oxidizing group, which initiates the dehydration reaction of the reactants while protecting the peroxide group from decomposition, to synthesize the intermediate of structural formula II; acetic acid provides an acidic environment to protect the perchloric acid, enabling it to initiate the first reaction. Both are indispensable. In one possible embodiment, the molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene, tert-butylhydrogen peroxide, acetic acid, and perchloric acid is 1:(1.2~1.5):(0.1~0.5):(0.1~0.5).

[0046] Since acetic acid and perchloric acid are strong oxidizing agents, to avoid explosion, in one possible embodiment, the reaction temperature of the first reaction is 0°C to 10°C. In this embodiment, the temperature of the reaction vessel where the first reaction occurs is maintained within the range of 0°C to 10°C before adding a specific molar amount of acetic acid and perchloric acid to initiate the first reaction. In one example, ice can be used to maintain the temperature within the range of 0°C to 10°C. In one example, the reaction vessel can be a flask.

[0047] In order to prevent unreacted perchloric acid from oxidizing the iodine in step S200 and thus failing to obtain the crosslinking agent of structural formula I, in one possible embodiment, the duration of the first reaction is 24h to 48h.

[0048] In step S200, iodine is added to the intermediate product, and a second reaction occurs under acidic conditions to obtain a crosslinking agent of structural formula I.

[0049] The reaction process of the second reaction is as follows: Figure 2 As shown.

[0050] In this embodiment, in order to form a double bond in the intermediate product (a peroxide), the second reaction needs to be carried out under acidic conditions. In one possible embodiment, the acidic condition is the addition of acetic acid, wherein the molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene, tert-butyl hydroperoxide and the acetic acid is 1:(1.2~1.5):(0.1~0.5).

[0051] In this embodiment, iodine is added to induce the formation of double bonds in the intermediate product. After adding iodine, stirring is continued. As the iodine dissolves, a white or pale yellow solid substance precipitates out. Stirring continues until all the solid substance has precipitated out. The white or pale yellow solid substance is the crosslinking agent of structural formula I. To better form double bonds, in one possible embodiment, the molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene, tert-butylhydrogen peroxide, and iodine is 1:(1.2~1.5):(0.1~0.5).

[0052] In this embodiment, after the second reaction occurs under acidic conditions and before obtaining the crosslinking agent of structural formula I, a solid-liquid separation method is used to separate the solid material. After separation, the solid material is washed and dried. In one possible implementation, the solid-liquid separation method can be vacuum filtration or low-temperature freeze drying.

[0053] In one possible implementation, the solid material is cleaned by washing it with dichloromethane 3 to 5 times.

[0054] The preparation method provided in this embodiment has a simple and efficient process route, a high conversion rate, and low energy consumption due to its operation at room temperature, making it economical. Furthermore, the preparation method provided in this embodiment can be synthesized in two steps, resulting in high production efficiency.

[0055] In one possible embodiment, tert-butyl hydroperoxide and α,α'-dihydroxy-1,3-diisopropylbenzene are mixed, comprising: α,α'-dihydroxy-1,3-diisopropylbenzene was completely dissolved in dichloromethane; Then add tert-butyl hydroperoxide and stir to completely mix the tert-butyl hydroperoxide and α,α'-dihydroxy-1,3-diisopropylbenzene.

[0056] In this embodiment, dichloromethane is used as the solvent because it has good solubility for α,α'-dihydroxy-1,3-diisopropylbenzene and is inexpensive. It should also be noted that mineral oil or silicone oil cannot be used as the solvent, as they cannot dissolve the reactant α,α'-dihydroxy-1,3-diisopropylbenzene.

[0057] In one possible implementation, α,α'-dihydroxy-1,3-diisopropylbenzene can be dissolved in a reaction vessel and tert-butyl hydroperoxide can be added to the reaction vessel; in one example, the reaction vessel can be a flask.

[0058] In addition, to achieve the above objectives, this application also proposes a cross-linked polyethylene cable material, which is composed of polyethylene, an antioxidant, and a cross-linking agent as described in structural formula I above.

[0059] In this embodiment, a low-byproduct cross-linked polyethylene cable material was prepared by using a cross-linking agent with a novel chemical structure (Structural Formula I) provided in this application. This cross-linked polyethylene cable material can shorten the degassing time of the cable, which not only reduces production energy consumption and effectively improves the production efficiency of high-voltage cables, but also saves production costs. Specifically, compared with DCP at the same addition amount, the cross-linked polyethylene cable material of this embodiment can reduce the content of all cross-linking byproducts to about 20%, of which the methane content is reduced to 1 / 3, thereby shortening the degassing time to 1 / 5 of that of DCP at the same addition amount.

[0060] It should be noted that the more components a cross-linked polyethylene (XLPE) cable material contains, the worse its electrical properties become. Since the formulation of the XLPE cable material in this embodiment only includes polyethylene, antioxidants, and a cross-linking agent as described in Structural Formula I, the dielectric properties of the XLPE cable material can be guaranteed. It should also be noted that since the cross-linking agent of Structural Formula I used in this embodiment can produce XLPE cable materials with low by-products, it is not necessary to reduce the amount of cross-linking agent added to reduce cross-linking by-products in this embodiment.

[0061] In one embodiment, the polyethylene does not contain carbon-carbon double bonds; and / or the polyethylene is low-density polyethylene.

[0062] Since the crosslinking agent provided in this application can reduce crosslinking byproducts, this application does not have special requirements for the molecular structure of polyethylene. The polyethylene can be highly branched and contain carbon-carbon double bonds, or it can be a commonly used polyethylene without a special molecular structure. Here, a specific molecular structure refers to a highly branched polyethylene containing carbon-carbon double bonds. For cost considerations and to obtain cable materials with excellent performance, in this embodiment, the polyethylene does not contain carbon-carbon double bonds. Therefore, it is not necessary to rely on changing the molecular structure of polyethylene to reduce crosslinking byproducts. This not only helps control raw material costs but also, by not using polyethylene with a special molecular structure, allows for the acquisition of cable materials with excellent processing performance, aging performance, and electrical properties.

[0063] This embodiment does not have any special requirements for the type of polyethylene. The polyethylene can be one of medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and low-density polyethylene. Since low-density polyethylene is commonly used in high-voltage cables, the polyethylene in this embodiment is low-density polyethylene. The resulting low-by-product cross-linked polyethylene cable material can be applied to the insulation layer of high-voltage cables, thereby significantly reducing the cable degassing time and reducing the energy consumption of cable degassing.

[0064] In this embodiment, the polyethylene is low-density polyethylene without carbon-carbon double bonds. This not only allows for better control of the cost of low-byproduct cable material formulations, but also reduces the crosslinking byproducts of low-density polyethylene without carbon-carbon double bonds. At the same time, other properties of low-density polyethylene are not affected, such as processing performance, aging performance, and electrical performance, so as to meet the requirements of high-voltage cables for reduced degassing time and service stability of cable materials.

[0065] The preparation method of cross-linked polyethylene cable material includes steps S300 to S400: Step S300: The polyethylene is first mixed with an antioxidant.

[0066] In one possible implementation, the polyethylene may be low-density polyethylene. In one example, the polyethylene is one of Yangzi Petrochemical-BASF's 2220H, Lanzhou Petrochemical's CL2120P and CL2140P, Shanghai Petrochemical's DJ200, and Wanhua Chemical's 2220H.

[0067] In one possible embodiment, the antioxidant is one or two of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (abbreviated as antioxidant 1010), 4,4'-thiobis(6-tert-butyl-3-methylphenol) (abbreviated as antioxidant 300), 3,5-bis(1,1-dimethylethyl)-4-hydroxyphenylpropionate C13-15 branched and straight-chain alkyl esters (abbreviated as antioxidant 1315), and 2-tert-butyl-6-methylphenol.

[0068] In one possible implementation, the apparatus for the first mixing can be a torque rheometer. In one example, the rotor speed of the torque rheometer is 60 r / min.

[0069] In one possible implementation, the temperature of the first mixing step is below 100°C. In one example, the temperature of the first mixing step is 100°C.

[0070] In one possible implementation, the first mixing time is 5 to 10 minutes. In one example, the first mixing time is 5 minutes.

[0071] In step S400, after the first mixing is completed, a crosslinking agent of structural formula I is added for a second mixing to obtain a mixture; the mass ratio of polyethylene, antioxidant and crosslinking agent of structural formula I is 100:0.5:3~100:0.2:1.

[0072] In one possible implementation, the device for the second mixing process can be a torque rheometer. In one example, the rotor speed of the torque rheometer is 60 r / min.

[0073] Since the mixing temperature needs to be controlled below the temperature at which the crosslinking agent initiates decomposition, in one possible implementation, the second mixing temperature is below 100°C. In one example, the second mixing temperature is 100°C.

[0074] In one possible implementation, the second mixing time is 1 to 2 minutes. In one example, the second mixing time is 2 minutes.

[0075] Step S300: After removing the mixture and cooling it, cross-linked polyethylene cable material is obtained.

[0076] In one possible implementation, cooling is natural cooling.

[0077] To obtain cable material test samples for convenient testing, in one possible embodiment, the mixture is removed and hot-pressed at 13 MPa~15 MPa and 160~180°C for 10~15 minutes, followed by cold pressing at the same pressure and temperature for 5~15 minutes to obtain the sample. In one example, the mixture is removed, hot-pressed at 15 MPa and 180°C for 15 minutes, and then cold-pressed at 15 MPa and 180°C for 10 minutes. In one possible embodiment, the hot-pressing equipment can be a flat vulcanizing machine with a mold size of (10×10×1) mm.

[0078] In addition, to achieve the above objectives, this application also proposes a cable comprising an insulation layer made of the aforementioned cross-linked polyethylene cable material.

[0079] The nominal thickness of the insulation layer is 16mm to 19mm. It should be noted that cross-linked polyethylene (XLPE) cable material is a type of cross-linkable polyethylene cable material. After the XLPE cable material is extruded onto the conductor, it is fed into a cross-linking tube for cross-linking, forming the insulation layer after cross-linking. In one example, the cross-linking time is 60 minutes, and the cross-linking temperature is 160℃.

[0080] The cable is described in accordance with the above embodiments. Since the cable adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0081] The technical features of the technical solution provided in this application will be described more clearly and completely below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Where specific technologies or conditions are not specified in the embodiments, they shall be performed in accordance with the technologies or conditions described in the literature in the art or in accordance with the product instructions. Reagents or instruments used without specified manufacturers are all conventional products that can be obtained commercially.

[0082] Example 1 First, purge the air from the flask with nitrogen and seal it with a rubber stopper. Add 1000 ml of dichloromethane to the flask using a syringe. Under magnetic stirring at 100 rpm, weigh 194.27 g of α,α'-dihydroxy-1,3-diisopropylbenzene and 90.12 g of tert-butyl hydroperoxide into the flask at a molar ratio of 1:1.2. Continue stirring until the two reactants dissolve. Maintain the flask temperature at 10°C using ice. Add 0.1 mol of acetic acid and 0.1 mol of perchloric acid (equivalent to 6 g of acetic acid and 10 g of perchloric acid by mass) to the flask. Continue stirring until no green gas (chlorine) is produced during the reaction. The reaction time is 24 h. After the reaction is complete, a reaction solution is obtained, which contains the intermediate product of structural formula II.

[0083] 0.5 mol of acetic acid and 0.1 mol of iodine were added to the reaction solution. As the iodine dissolved, a pale yellow solid precipitated out. After the iodine was completely dissolved, the reaction was stopped by stirring for another 5 hours. The pale yellow solid was separated from the liquid by vacuum filtration, washed five times with dichloromethane solution, and dried to obtain the crosslinking agent of structural formula I. The NMR spectrum of this crosslinking agent is shown below. Figure 3 As shown.

[0084] Weigh 50g of low-density polyethylene (LDPE) of Yangzi Petrochemical-BASF 2220H and 0.15g of antioxidant 300 and add them to a torque rheometer. The mixing temperature is 100℃, the rotor speed is 60r / min, and the mixing time is 5min. Then add 1g of crosslinking agent of the above-prepared structural formula I to the torque rheometer and continue mixing for 2min. After mixing, the mixture is removed from the torque rheometer. At this point, it is uncrosslinked XLPE cable material. While still hot, it is placed in a flat vulcanizing machine with a mold size of (10×10×1) mm. It is hot-pressed at 15 MPa and 180°C for 15 min, and then cold-pressed at the same pressure for 10 min to prepare a square sample. This square sample is the fully crosslinked XLPE cable material.

[0085] The samples were subjected to thermal elongation testing and cross-linking gas byproduct content testing according to GB / T 2951.21 requirements. The thermal elongation test involved quickly weighing 5g of freshly cross-linked XLPE cable material, placing it in a 70℃ forced-air drying oven, and weighing it every 24 hours, recording the weight (m). i According to the mass loss rate (%) = (5-m) i ) / 5×100 to calculate the mass loss rate.

[0086] Example 2 The only difference between this embodiment and Embodiment 1 is that: 50g of LDPE of grade CL2120P from Lanzhou Petrochemical, 0.075g of antioxidant 1010 and 0.075g of antioxidant 1315, and 0.9g of crosslinking agent of structural formula I.

[0087] Example 3 The cable material preparation method in this embodiment differs from that in Example 1 only in that: 100g of low-density polyethylene (LDPE) of brand name DJ-200 from Shanghai Petrochemical, 0.2g of antioxidant 300, and 1.55g of crosslinking agent of structural formula I.

[0088] Comparative Example 1 The only difference between the cable material preparation method of this comparative example and Example 1 is the addition of 1g of dicumyl peroxide (DCP) crosslinking agent.

[0089] Comparative Example 2 The only difference between the cable material preparation method of this comparative example and Example 1 is that: 50g of LDPE of grade CL2120P from Lanzhou Petrochemical, 0.075g of antioxidant 1010 and 0.075g of antioxidant 1315, and 0.9g of dicumyl peroxide (DCP) crosslinking agent.

[0090] Comparative Example 3 The only difference between the cable material preparation method of this comparative example and Example 1 is that: 100g of low-density polyethylene (LDPE) of brand name DJ-200 from Shanghai Petrochemical, 0.2g of antioxidant 300, 1.25g of dicumyl peroxide, and 0.3g of crosslinking agent (trylpropyl isocyanate).

[0091] The cable materials obtained in Examples 2, 3, 1, 2, and 3 were tested for sample preparation and thermal elongation and crosslinking gas byproduct content according to the test method in Example 1. The thermal elongation test results are as follows: Figure 4 As shown, the test results for the content of crosslinking gas byproducts are as follows: Figure 5 As shown. From Figure 4 It can be seen that, with the same amount of crosslinking agent added, the thermal elongation of the crosslinked polyethylene cable material provided in this application is better than that of DCP crosslinked polyethylene; with the same thermal elongation, the amount of crosslinking agent added in structural formula I of this application can be reduced by about 10%.

[0092] from Figure 5 As can be seen, compared with the comparative example, the technical solution provided in this application reduces the content of all crosslinking by-products by about 20%; under the same degree of crosslinking, the amount of crosslinking agent added in structural formula I of this application can be reduced by more than 10% compared with DCP.

[0093] In contrast, Comparative Example 3, in order to reduce the crosslinking byproducts of DCP, thereby improving the production cycle and efficiency of insulation materials and reducing the product cost and production cost of insulation materials, not only reduced the content of crosslinking agent DCP, but also added a small amount of co-crosslinking agent; the solution provided in this application not only does not require reducing the content of crosslinking agent, but also does not require adding additional co-crosslinking agent.

[0094] All embodiments and comparative examples underwent degassing treatment: In all embodiments and comparative examples, the mixture after mixing was removed from the torque rheometer and allowed to cool naturally to obtain cross-linked polyethylene cable material. After the obtained cross-linked polyethylene cable material was extruded onto a conductor, it was fed into a cross-linking tube for cross-linking. The cross-linking time was 60 minutes and the cross-linking temperature was 160°C. After cross-linking, an insulation layer with a thickness of 16 mm was formed, resulting in six types of high-voltage cables (1600 square millimeter single-core cables). The six types of high-voltage cables were then degassed at a temperature of 70°C.

[0095] Tests showed that Examples 1 and 2 required 2 days for degassing, which reduced the methane content in the cross-linking byproducts of the high-voltage cable insulation layer to below 100 ppm within 2 days. Example 3 required 1.5 days of degassing to reduce the methane content to below 100 ppm, while Comparative Examples 1 and 2 required 7 days, and Comparative Example 3 required 3 days.

[0096] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. A crosslinking agent for crosslinked polyethylene, characterized in that, The crosslinking agent is a peroxide crosslinking agent with carbon-carbon double bonds at the ends of its molecular structure, and the structural formula of the crosslinking agent is shown below: ； Where R1 is -C n H 2n-1 (n≥2), R² is -C n H 2n (n≥2), R3 is -C n H 2n+1 (n≥1).

2. The crosslinking agent for crosslinked polyethylene as described in claim 1, characterized in that, When R1 is -C2H3, R2 is -C3H6, and R3 is -C4H9, the crosslinking agent has the following structural formula I: 。 3. A method for preparing the crosslinking agent as described in claim 2, characterized in that, The preparation method includes: Tert-butyl hydroperoxide and α,α'-dihydroxy-1,3-diisopropylbenzene were mixed, and a strong oxidizing initiator was added to carry out a first reaction to obtain an intermediate product; wherein, the structural formula II of the intermediate product is shown below: ； After adding iodine to the intermediate product, a second reaction occurs under acidic conditions to obtain the crosslinking agent of structural formula I.

4. The method for preparing the crosslinking agent as described in claim 3, characterized in that, The molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene, tert-butyl hydroperoxide, and iodine is 1:(1.2~1.5):(0.1~0.5).

5. The method for preparing the crosslinking agent as described in claim 3, characterized in that, The strong oxidizing initiator is a mixture of acetic acid and perchloric acid.

6. The method for preparing the crosslinking agent as described in claim 5, characterized in that, The molar ratio of α,α'-dihydroxy-1,3-diisopropylbenzene, the acetic acid, and the perchloric acid is 1:(0.1~0.5):(0.1~0.5).

7. The method for preparing the crosslinking agent as described in claim 3, characterized in that, When the strong oxidizing initiator is a mixture of acetic acid and perchloric acid, the reaction temperature of the first reaction is 0℃~10℃, and the reaction time is 24h~48h.

8. The method for preparing the crosslinking agent as described in claim 3, characterized in that, The mixture of tert-butyl hydroperoxide and α,α'-dihydroxy-1,3-diisopropylbenzene comprises: The α,α'-dihydroxy-1,3-diisopropylbenzene was completely dissolved in dichloromethane; Then add the tert-butyl hydroperoxide and stir to completely mix the tert-butyl hydroperoxide and the α,α'-dihydroxy-1,3-diisopropylbenzene.

9. A cross-linked polyethylene cable material, characterized in that, The cross-linked polyethylene cable material is composed of polyethylene, antioxidant, and cross-linking agent of structural formula I as described in claim 2; The preparation method of the cross-linked polyethylene cable material includes: The polyethylene and the antioxidant are first mixed; After the first mixing is completed, the crosslinking agent of structural formula I is added for a second mixing to obtain a mixture; the mass ratio of the polyethylene, the antioxidant and the crosslinking agent of structural formula I is 100:0.5:3~100:0.2:1; The mixture is removed and cooled to obtain the cross-linked polyethylene cable material.

10. A cable, characterized in that, The cable includes an insulation layer made of the cross-linked polyethylene cable material of claim 9.

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