Polyethylene and its applications, polyethylene compositions and crosslinked polyethylene insulation cable materials

Abstract

The application relates to the field of polymers, in particular to a kind of polyethylene and its application, polyethylene composition and crosslinked polyethylene insulated cable material.The polyethylene has 10-20 tertiary carbon atoms per 1000 carbon atoms and 0.1-0.2 vinyl groups per 1000 carbon atoms.The polyethylene in the application can improve the scorch resistance and heat resistance of crosslinked polyethylene insulated cable material, and further obtain super-high voltage cable applicable to 330 kV and above.

Description

Technical Field

[0001] This invention relates to the field of polymers, specifically to polyethylene and its applications, polyethylene compositions, and cross-linked polyethylene insulated cable materials. Background Technology

[0002] High-performance high-voltage insulation materials are a crucial component of power cables, directly impacting their safety, reliability, and service life. They are vital for urban power grid construction and the comprehensive utilization of new energy sources. Currently, most high-performance high-voltage insulation materials utilize cross-linked polyethylene (XLPE) insulation. XLPE insulation is prepared by extruding polyethylene insulating material and then undergoing a cross-linking reaction. Compared to traditional insulation materials, it offers significant advantages. It not only possesses better electrical resistance and higher heat resistance, but also exhibits excellent mechanical properties, corrosion resistance, and creep resistance, resulting in a wider range of applications. Especially in long-distance ultra-high-voltage power transmission scenarios, its advantages are unparalleled by other insulation materials.

[0003] To meet the demands of long-distance ultra-high-voltage power transmission, power cables require long extrusion lengths during production. However, the extrusion channels for polyethylene insulation are typically long, and prolonged extrusion leads to uneven temperature distribution within the channels, causing localized hot spots. This results in the decomposition of the crosslinking agent and premature crosslinking of the insulation. Higher temperatures or longer residence times in high-temperature regions increase the likelihood of scorching. The resulting gel-like substance easily clogs the channels, reducing the extrusion length and production efficiency of the cable. Therefore, improving the scorch resistance of the insulation material is crucial for ensuring the long-term extrusion molding of power cables. Summary of the Invention

[0004] The purpose of this invention is to overcome the defect of poor scorch resistance of polyethylene cable insulation materials containing polyethylene in the prior art, and to provide a new polyethylene that can improve the scorch resistance of cable insulation materials when used as cable insulation materials, and ultimately obtain ultra-high voltage cables suitable for 330 kV and above.

[0005] The inventors of this invention have discovered that, based on polyethylene having the required density and melt flow rate, by controlling the number of tertiary carbon atoms and vinyl groups in polyethylene within a specific range, the scorch resistance of polyethylene cable insulation material can be improved, ultimately resulting in ultra-high voltage cables suitable for 330 kV and above.

[0006] Based on this, the first aspect of the present invention provides a polyethylene having 10-20 tertiary carbon atoms / 1000 carbon atoms and 0.1-0.2 vinyl atoms / 1000 carbon atoms.

[0007] The second aspect of the present invention provides a method for preparing the polyethylene described in the first aspect of the present invention, wherein the method comprises: ethylene monomer undergoing a free radical polymerization reaction in the presence of an initiator and a terminator, wherein the initiator has at least two injection points, and the first initiator at the first injection point includes initiator I, initiator II, and initiator III, wherein the mass ratio of initiator I, initiator II, and initiator III is 1:2-3:3-4; the amount of terminator is 1%-1.5% of the mass of ethylene; the reaction temperature is 170-300°C, and the reaction pressure is 225-235 MPa.

[0008] The third aspect of the present invention provides the application of the polyethylene described in the first aspect of the present invention in cables.

[0009] A fourth aspect of the present invention provides a polyethylene composition comprising the polyethylene described in the first aspect of the present invention.

[0010] The fifth aspect of the present invention provides a cross-linked polyethylene insulated cable material, said cross-linked polyethylene insulated cable material being made of the polyethylene composition described in the fourth aspect of the present invention.

[0011] Although the mechanism is not very clear, experiments have shown that the polyethylene provided in this invention has a structural feature of 10-20 tertiary carbon atoms / 1000 carbon atoms and 0.1-0.2 vinyl atoms / 1000 carbon atoms, which makes the polyethylene cable insulation material containing the polyethylene described in this invention have excellent anti-scorching properties, and thus can obtain ultra-high voltage cables suitable for 330 kV and above. Attached Figure Description

[0012] Figure 1 This is a flowchart of a method for preparing polyethylene according to one embodiment of the present invention; Figure 2 This is a schematic diagram of the initiator injection points of reactor R1 during the preparation of polyethylene in one embodiment of the present invention.

[0013] Explanation of reference numerals in the attached figures Figure 2 In the formula, A: di-tert-butyl peroxide; C: tert-butyl peroxide; S: tert-butyl peroxide (2-ethylhexanoate). Detailed Implementation

[0014] 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.

[0015] During their research on polyethylene, the inventors of this invention discovered that, under the premise of having a suitable melt flow rate and density, by controlling the vinyl content and the number of tertiary carbon atoms in the polyethylene structure, the resulting polyethylene has excellent comprehensive properties. For example, polyethylene cable insulation materials containing the polyethylene described in this invention have excellent anti-scorching properties, and ultimately, cross-linked polyethylene cable insulation materials with excellent heat resistance can be obtained.

[0016] Based on this, the first aspect of the present invention provides a polyethylene having 10-20 tertiary carbon atoms / 1000 carbon atoms and 0.1-0.2 vinyl atoms / 1000 carbon atoms.

[0017] The inventors of this invention discovered that the number of tertiary carbon atoms in polyethylene is much greater than the number of vinyl groups. By controlling the vinyl content and the number of tertiary carbon atoms in polyethylene within the aforementioned specific range, the scorch resistance of the polyethylene cable insulation material containing this invention can be improved. Furthermore, the cable insulation material prepared from this insulation material meets the standards for 330 kV and above ultra-high voltage cable materials in terms of crosslinking degree. The reason for this may be that the vinyl groups in the polyethylene molecule promote the formation of a crosslinking network during processing, thereby increasing the collision probability of free radicals at intermolecular branching points. This, in turn, promotes crosslinking reactions between these free radicals. The vinyl content, to a certain extent, determines the rate of the crosslinking reaction.

[0018] According to the present invention, "vinyl" refers to a group containing a carbon-carbon double bond, such as CH2=CH-, specifically allyl. All individual values ​​and subranges of polyethylene having 0.1-0.2 vinyl groups per 1000 carbon atoms are included in the present invention. For example, polyethylene has 0.1 vinyl groups per 1000 carbon atoms, 0.12 vinyl groups per 1000 carbon atoms, 0.13 vinyl groups per 1000 carbon atoms, 0.14 vinyl groups per 1000 carbon atoms, 0.15 vinyl groups per 1000 carbon atoms, 0.16 vinyl groups per 1000 carbon atoms, 0.18 vinyl groups per 1000 carbon atoms, 0.19 vinyl groups per 1000 carbon atoms, 0.2 vinyl groups per 1000 carbon atoms, or any range consisting of two of the above values. In a preferred embodiment of the present invention, polyethylene has 0.14-0.18 vinyl groups per 1000 carbon atoms.

[0019] According to the present invention, all individual values ​​and sub-ranges of polyethylene having 10-20 tertiary carbon atoms / 1000 carbon atoms are included in the present invention. For example, polyethylene having 10 tertiary carbon atoms / 1000 carbon atoms, 11 tertiary carbon atoms / 1000 carbon atoms, 13 tertiary carbon atoms / 1000 carbon atoms, 15 tertiary carbon atoms / 1000 carbon atoms, 16.4 tertiary carbon atoms / 1000 carbon atoms, 17.4 tertiary carbon atoms / 1000 carbon atoms, 18 tertiary carbon atoms / 1000 carbon atoms, 19 tertiary carbon atoms / 1000 carbon atoms, 20 tertiary carbon atoms / 1000 carbon atoms, or any range consisting of any two of the above values. In a preferred embodiment of the present invention, the polyethylene has 13-20 tertiary carbon atoms / 1000 carbon atoms.

[0020] According to the present invention, the melt mass flow rate of the polyethylene measured at 190°C and a load of 2.16 kg is 1-5 g / 10 min; and / or, the density of the polyethylene is 0.915-0.930 g / cm³. 3 .

[0021] In this invention, when the melt flow rate and / or density of polyethylene meet the above-mentioned ranges, the composition containing polyethylene can be made suitable for the standards of 330 kV and above ultra-high voltage cable materials.

[0022] According to the present invention, all individual values ​​and sub-ranges of melt mass flow rate of polyethylene measured at 190°C and 2.16 kg load for 1-5 g / 10 min are included in the present invention, for example, melt mass flow rates of 1 g / 10 min, 1.2 g / 10 min, 1.5 g / 10 min, 1.6 g / 10 min, 1.8 g / 10 min, 2.1 g / 10 min, 2.3 g / 10 min, 2.5 g / 10 min, 2.8 g / 10 min, 3 g / 10 min, 3.2 g / 10 min, 3.5 g / 10 min, 3.6 g / 10 min, 3.8 g / 10 min, 4.1 g / 10 min, 4.3 g / 10 min, 4.5 g / 10 min, 4.8 g / 10 min, or 5 g / 10 min measured at 190°C and 2.16 kg load.

[0023] According to the present invention, the density of polyethylene is 0.915-0.930 g / cm³. 3 All individual values ​​and sub-ranges are included in this invention, for example, the density of polyethylene is 0.915 g / cm³. 3 0.916 g / cm 3 0.917 g / cm3 0.918 g / cm 3 0.919 g / cm 3 0.920 g / cm 3 0.921 g / cm 3 0.922 g / cm 3 0.923 g / cm 3 0.925 g / cm 3 0.927g / cm 3 0.929 g / cm 3 0.930 g / cm 3 , or a range consisting of any two of the above values.

[0024] Those skilled in the art will know that polymers are not composed of compounds of a single molecular weight. Even if polymers have the same chemical composition, most of them are composed of homologous polymers with the same elemental composition but different molecular weights and structures. The chemical composition distribution of polymers can be obtained by temperature wash fractionation (TREF). The chemical composition or structure of different temperature fractions have different effects on the final polyethylene product. The inventors further discovered that controlling the vinyl content and the number of tertiary carbon atoms in high-temperature fractions, especially the 75°C and 80°C fractions, can further improve the scorch resistance of polyethylene insulation materials and the heat resistance of cross-linked polyethylene insulation materials.

[0025] In this invention, the chemical composition of polyethylene can be obtained by the temperature wash fractionation (TREF) method T30-T85, but this should not be construed as limiting the invention. Based on the aim of ensuring that the polyethylene insulation material containing the polyethylene of this invention has better scorch resistance and that the cross-linked polyethylene insulation material prepared therefrom has better heat resistance, according to a preferred embodiment of the invention, the 80°C fraction of the polyethylene temperature wash fraction has 15-25 tertiary carbon atoms / 1000 carbon atoms. All individual values ​​and sub-ranges of 15-25 tertiary carbon atoms / 1000 carbon atoms in the 80°C fraction of the polyethylene temperature wash fraction are included in this invention. For example, the 80°C fraction of the polyethylene temperature wash fraction has 15 tertiary carbon atoms / 1000 carbon atoms. The number of tertiary carbon atoms per 1000 carbon atoms is 16, 17.9, 18.6, 19.8, 20.1, 21, 22, 23, 24, 25, or any two of the above values. Preferably, the polyethylene fraction subjected to a heated washing process at 80°C has 17-22 tertiary carbon atoms per 1000 carbon atoms.

[0026] In this invention, based on the aim of ensuring that the polyethylene insulation material containing the polyethylene of this invention has better scorch resistance, and at the same time that the cross-linked polyethylene insulation material prepared therefrom has better heat resistance, in a preferred embodiment, the polyethylene heated to 75°C fraction has 13-18 tertiary carbon atoms / 1000 carbon atoms. All individual values ​​and sub-ranges of 13-18 tertiary carbon atoms / 1000 carbon atoms in the polyethylene heated to 75°C fraction are included in this invention. For example, the polyethylene heated to 75°C fraction... The polyethylene fraction having 13 tertiary carbon atoms / 1000 carbon atoms, 14.1 tertiary carbon atoms / 1000 carbon atoms, 14.9 tertiary carbon atoms / 1000 carbon atoms, 15.2 tertiary carbon atoms / 1000 carbon atoms, 16.2 tertiary carbon atoms / 1000 carbon atoms, 17 tertiary carbon atoms / 1000 carbon atoms, 18 tertiary carbon atoms / 1000 carbon atoms, or any two of the above values, is preferably a 75°C fraction with 14-17 tertiary carbon atoms / 1000 carbon atoms.

[0027] In a preferred embodiment, the 70°C fraction of the polyethylene subjected to a preheating rinse has 17-24 tertiary carbon atoms per 1000 carbon atoms. All individual values ​​and sub-ranges of 17-24 tertiary carbon atoms per 1000 carbon atoms in the 70°C fraction of the polyethylene subjected to a preheating rinse are included in this invention, for example, the 70°C fraction of the polyethylene subjected to a preheating rinse has 17 tertiary carbon atoms per 1000 carbon atoms, 18 tertiary carbon atoms per 1000 carbon atoms, 18.7 tertiary carbon atoms per 1000 carbon atoms, 19 tertiary carbon atoms per 1000 carbon atoms, etc. The number of tertiary carbon atoms per 1000 carbon atoms is 0.8, 20.2, 20.5, 21, 22, 23, 24, or any two of the above values. Preferably, the polyethylene fraction subjected to a 70°C warming rinse has 18-21 tertiary carbon atoms per 1000 carbon atoms.

[0028] In a preferred embodiment, the 65°C fraction of the polyethylene subjected to a preheating rinse has 19-26 tertiary carbon atoms per 1000 carbon atoms. All individual values ​​and sub-ranges of 19-26 tertiary carbon atoms per 1000 carbon atoms in the 65°C fraction of the polyethylene subjected to a preheating rinse are included in this invention. For example, the 65°C fraction of the polyethylene subjected to a preheating rinse has 19 tertiary carbon atoms per 1000 carbon atoms, 20 tertiary carbon atoms per 1000 carbon atoms, 21.6 tertiary carbon atoms per 1000 carbon atoms, etc. The number of carbon atoms is 00, 22.5 tertiary carbon atoms / 1000 carbon atoms, 23 tertiary carbon atoms / 1000 carbon atoms, 23.5 tertiary carbon atoms / 1000 carbon atoms, 24 tertiary carbon atoms / 1000 carbon atoms, 25 tertiary carbon atoms / 1000 carbon atoms, 26 tertiary carbon atoms / 1000 carbon atoms, or any two of the above values. Preferably, the polyethylene rinsing fraction at 65°C has 21-25 tertiary carbon atoms / 1000 carbon atoms.

[0029] In a preferred embodiment, the 80°C fraction of the polyethylene has 0.04-0.1 vinyl atoms per 1000 carbon atoms. All individual values ​​and sub-ranges of 0.04-0.1 vinyl atoms per 1000 carbon atoms in the 80°C fraction of the polyethylene are included in this invention. For example, the 80°C fraction of the polyethylene has 0.04 vinyl atoms per 1000 carbon atoms, 0.05 vinyl atoms per 1000 carbon atoms, 0.06 vinyl atoms per 1000 carbon atoms, 0.07 vinyl atoms per 1000 carbon atoms, 0.08 vinyl atoms per 1000 carbon atoms, 0.09 vinyl atoms per 1000 carbon atoms, 0.1 vinyl atoms per 1000 carbon atoms, or any range consisting of any two of the above values. Preferably, the 80°C fraction of the polyethylene has 0.06-0.09 vinyl atoms per 1000 carbon atoms.

[0030] In a preferred embodiment, the 75°C fraction of the polyethylene has 0.02-0.07 vinyl atoms per 1000 carbon atoms. All individual values ​​and sub-ranges of 0.02-0.07 vinyl atoms per 1000 carbon atoms in the 75°C fraction of the polyethylene are included in this invention. For example, the 75°C fraction of the polyethylene has 0.02 vinyl atoms per 1000 carbon atoms, 0.03 vinyl atoms per 1000 carbon atoms, 0.04 vinyl atoms per 1000 carbon atoms, 0.05 vinyl atoms per 1000 carbon atoms, 0.06 vinyl atoms per 1000 carbon atoms, 0.07 vinyl atoms per 1000 carbon atoms, or any range consisting of two of the above values. Preferably, the 75°C fraction of the polyethylene has 0.03-0.06 vinyl atoms per 1000 carbon atoms.

[0031] In a preferred embodiment, the 70°C fraction of the polyethylene subjected to a preheating rinse has 0.05-0.16 vinyl atoms per 1000 carbon atoms. All individual values ​​and sub-ranges of 0.05-0.16 vinyl atoms per 1000 carbon atoms in the 70°C fraction of the polyethylene subjected to a preheating rinse are included in this invention, for example, 0.05 vinyl atoms per 1000 carbon atoms, 0.07 vinyl atoms per 1000 carbon atoms, 0.08 vinyl atoms per 1000 carbon atoms, etc. The preferred polyethylene fraction for a 70°C heated washing process has 0.07-0.15 vinyl groups per 1000 carbon atoms, or a range consisting of 1000 carbon atoms, 0.09 vinyl groups per 1000 carbon atoms, 0.1 vinyl groups per 1000 carbon atoms, 0.11 vinyl groups per 1000 carbon atoms, 0.13 vinyl groups per 1000 carbon atoms, 0.15 vinyl groups per 1000 carbon atoms, 0.16 vinyl groups per 1000 carbon atoms, or any two of the above values.

[0032] In a preferred embodiment, the polyethylene 65°C wash fraction has 0.1-0.2 vinyl groups per 1000 carbon atoms, for example, 0.1 vinyl groups per 1000 carbon atoms, 0.12 vinyl groups per 1000 carbon atoms, 0.14 vinyl groups per 1000 carbon atoms, 0.15 vinyl groups per 1000 carbon atoms, 0.16 vinyl groups per 1000 carbon atoms, 0.18 vinyl groups per 1000 carbon atoms, 0.19 vinyl groups per 1000 carbon atoms, 0.2 vinyl groups per 1000 carbon atoms, or any range of two of the above values. Preferably, the polyethylene 65°C wash fraction has 0.12-0.19 vinyl groups per 1000 carbon atoms.

[0033] According to the present invention, further research has found that, under the premise of the same vinyl content, the more high molecular weight fractions there are, the faster the material scorches, while the more low molecular weight fractions there are, the lower the final degree of cross-linking of the material. In order to further increase the scorch resistance of products processed using polyethylene, in a preferred embodiment, the weight-average molecular weight of the polyethylene is 70,000 to 120,000. All individual values ​​and sub-ranges of the weight-average molecular weight of polyethylene from 70,000 to 120,000 are included in the present invention. For example, the weight-average molecular weight of the polyethylene is 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000, 105,000, 110,000, 115,000, 120,000, or any two of the above values. In a preferred embodiment, the weight-average molecular weight of the polyethylene is 80,000 to 100,000.

[0034] According to the present invention, based on the aim of ensuring that the polyethylene insulation material containing the polyethylene of the present invention has better scorch resistance, and at the same time that the cross-linked polyethylene insulation material prepared therefrom has better heat resistance, in a preferred embodiment, the weight-average molecular weight of the polyethylene heated to 80°C fraction is 140,000-220,000. All individual values ​​and sub-ranges of the weight-average molecular weight of the polyethylene heated to 80°C fraction are included in the present invention. For example, the weight-average molecular weight of the polyethylene heated to 80°C fraction is 140,000, 150,000, 160,000, 170,000, 180,000, 185,000, 190,000, 195,000, 200,000, 210,000, 220,000, or any range of two of the above values. In a preferred embodiment, the weight-average molecular weight of the polyethylene heated to 80°C fraction is 170,000-190,000.

[0035] In a preferred embodiment, the weight-average molecular weight of the polyethylene fraction washed at 75°C is 150,000 to 230,000. All individual values ​​and sub-ranges of the weight-average molecular weight of the polyethylene fraction washed at 75°C are included in this invention. For example, the weight-average molecular weight of the polyethylene fraction washed at 75°C is 150,000, 160,000, 170,000, 180,000, 185,000, 190,000, 195,000, 200,000, 210,000, 220,000, 230,000, or any range of two of the above values. In a preferred embodiment, the weight-average molecular weight of the polyethylene fraction washed at 75°C is 180,000 to 200,000.

[0036] According to the present invention, the weight-average molecular weight of the 70°C fraction and the 65°C fraction of polyethylene after rinsing were further analyzed. As long as the purpose of the present invention can be achieved, the present invention does not have a special limitation on the weight-average molecular weight of the 70°C fraction of polyethylene after rinsing. The following embodiments are only illustrative embodiments and should not be construed as limiting the present invention.

[0037] According to a preferred embodiment of the present invention, the weight-average molecular weight of the polyethylene fraction washed at 70°C is 50,000 to 110,000. All individual values ​​and sub-ranges of the weight-average molecular weight of the polyethylene fraction washed at 70°C are included in the present invention, for example, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 90,000, 100,000, 110,000, or any range of two of the above values. In a preferred embodiment, the weight-average molecular weight of the polyethylene fraction washed at 70°C is 60,000 to 100,000.

[0038] According to a preferred embodiment of the present invention, the weight-average molecular weight of the polyethylene fraction washed at 65°C is 25,000-60,000. All individual values ​​and sub-ranges of the weight-average molecular weight of the polyethylene fraction washed at 65°C are included in the present invention, such as 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, or any range of two of the above values. In a preferred embodiment, the weight-average molecular weight of the polyethylene fraction washed at 65°C is 35,000-50,000.

[0039] According to the present invention, based on the aim of ensuring that the polyethylene insulation material containing the polyethylene of the present invention has better scorch resistance, and at the same time that the cross-linked polyethylene insulation material prepared therefrom has better heat resistance, in a preferred embodiment, the molecular weight distribution of the polyethylene is not higher than 5.3, preferably 3.5-5.3. All individual values ​​and sub-ranges of the molecular weight distribution of polyethylene in the range of 3.5-5.3 are included in the present invention. For example, the molecular weight distribution of the polyethylene is 3.5, 3.8, 4.0, 4.1, 4.2, 4.3, 4.5, 4.8, 5.0, 5.3, or any two of the above values. In a preferred embodiment, the molecular weight distribution of the polyethylene is 4.5-5.

[0040] According to the present invention, based on the aim of ensuring that the polyethylene insulation material containing the polyethylene of the present invention has better scorch resistance, and at the same time that the cross-linked polyethylene insulation material prepared therefrom has better heat resistance, in a preferred embodiment, the molecular weight distribution of the polyethylene in the 80°C heated washing fraction is not higher than 6, preferably 3-4. All individual values ​​and sub-ranges of the molecular weight distribution of the polyethylene in the 80°C heated washing fraction being 3-4 are included in the present invention. For example, the molecular weight distribution of the polyethylene in the 80°C heated washing fraction is 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any range of two of the above values.

[0041] In a preferred embodiment, the molecular weight distribution of the polyethylene fraction washed at 75°C is not higher than 6, preferably 3-4. All individual values ​​and sub-ranges of the molecular weight distribution of the polyethylene fraction washed at 75°C being 3-4 are included in this invention. For example, the molecular weight distribution of the polyethylene fraction washed at 75°C being 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any range consisting of any two of the above values.

[0042] According to a preferred embodiment of the present invention, the molecular weight distribution of the polyethylene fraction washed at 70°C is not higher than 5, preferably 3-4.5. All individual values ​​and sub-ranges of the molecular weight distribution of the polyethylene fraction washed at 70°C being 3-4.5 are included in the present invention, for example, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, or any range of two of the above values.

[0043] According to a preferred embodiment of the present invention, the molecular weight distribution of the polyethylene fraction washed at 65°C is not higher than 4, preferably 1.5-3. All individual values ​​and sub-ranges of the molecular weight distribution of the polyethylene fraction washed at 65°C being 1.5-3 are included in the present invention, for example, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, or any range of two of the above values.

[0044] Those skilled in the art will know that the melting temperature is related to the physical properties and processing characteristics of polyethylene. As long as the vinyl content and the number of tertiary carbon atoms in polyethylene meet the requirements of the present invention, those skilled in the art can select the melting temperature of polyethylene according to the actual application requirements of polyethylene. In one embodiment, the melting temperature of the polyethylene is 105-111℃.

[0045] According to the present invention, as long as the purpose of the present invention can be achieved, the melting temperature of each temperature fraction of polyethylene is not particularly limited. Preferably, the melting temperature of the 80°C grade of the polyethylene is 109-112°C; preferably, the melting temperature of the 75°C grade of the polyethylene is 106-108°C; preferably, the melting temperature of the 70°C grade of the polyethylene is 105-108°C; preferably, the melting temperature of the 65°C grade of the polyethylene is 102-105°C.

[0046] According to a preferred embodiment of the present invention, the content of the polyethylene in the 65-80°C heated washing fraction is 66-94 wt%, preferably 82-90 wt%.

[0047] According to a preferred embodiment of the present invention, the content of the polyethylene in the 75°C heated washing fraction is 35-45 wt%. All individual values ​​and sub-ranges of the 35-45 wt% content of the polyethylene in the 75°C heated washing fraction are included in the present invention, for example, 35 wt%, 36 wt%, 37 wt%, 40 wt%, and 45 wt%. In a preferred embodiment, the content of the polyethylene in the 75°C heated washing fraction is 36-40 wt%. Thus, the polyethylene-containing polyethylene insulation material has good scorch resistance, and the finally obtained cross-linked polyethylene insulation material has good heat resistance.

[0048] According to a preferred embodiment of the present invention, the content of the polyethylene heated to 80°C fraction is 15-25 wt%, and all individual values ​​and sub-ranges of the polyethylene heated to 80°C fraction content of 15-25 wt% are included in the present invention, for example, 15 wt%, 18 wt%, 20 wt%, 21 wt%, 25 wt%. In a preferred embodiment, the polyethylene heated to 80°C fraction is 17-21 wt%. Thus, the polyethylene insulation material containing the polyethylene of the present invention has good scorch resistance, and the finally obtained cross-linked polyethylene insulation material has good heat resistance.

[0049] According to a preferred embodiment of the present invention, the content of the polyethylene fraction heated to 80°C is not higher than 0.1 wt%.

[0050] Cleanliness has a significant impact on the electrical properties of polyethylene products during use. According to a preferred embodiment of the present invention, the polyethylene does not contain impurities larger than 200 µm.

[0051] In this invention, the impurity refers to carbonized polyethylene.

[0052] The polyethylene described in this invention can be prepared using conventional equipment. Simultaneously, the process conditions are controlled and adjusted to ensure that the polyethylene obtained from the polymerization of ethylene meets the structural and physicochemical parameters of the polyethylene described in this invention, particularly achieving a structure of 10-20 tertiary carbon atoms / 1000 carbon atoms and 0.1-0.2 vinyl atoms / 1000 carbon atoms. For example, the polyethylene described in this invention can be prepared by high-pressure free radical polymerization, i.e., in the presence of an initiator, ethylene monomer undergoes a free radical polymerization reaction. The polymerization reaction is very rapid and can be carried out continuously, i.e., continuously feeding ethylene raw materials and an initiator for high-pressure free radical polymerization. The reactor for the high-pressure free radical polymerization reaction can be a conventional reactor in the art, such as an autoclave reactor or a tubular reactor, preferably a tubular reactor.

[0053] In a preferred embodiment of the present invention, in order to obtain polyethylene having 10-20 tertiary carbon atoms / 1000 carbon atoms and 0.1-0.2 vinyl atoms / 1000 carbon atoms as described in the present invention, the polyethylene is prepared according to the following method: In the presence of an initiator and a terminator, ethylene monomer undergoes a free radical polymerization reaction. The initiator has at least two injection points, and the first initiator at the first injection point includes initiator I, initiator II, and initiator III. The mass ratio of initiator I, initiator II, and initiator III is 1:2-3:3-4. The amount of terminator is 1%-1.5% of the mass of ethylene. The reaction temperature is 170-300℃, and the reaction pressure is 225-235 MPa.

[0054] raw material: For the raw materials, the monomer is ethylene. During high-pressure free radical polymerization, an initiator is required. Any initiator that can generate free radicals under high-pressure free radical polymerization conditions is suitable for this invention. In one embodiment, the initiator is a peroxide initiator, such as di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate). During the polymerization reaction, a terminator can be added to control the molecular weight of polyethylene. The terminator can be a conventional terminator in the art, preferably using C3 or higher olefins to provide double bonds, such as propylene. To ensure high purity of polyethylene, the raw materials such as ethylene and propylene are refined to ensure that the ethylene content is above 99.98 wt% and the content of impurities affecting the reaction is below 5%. ppm, as those skilled in the art will know, the specific types of impurities that affect the reaction, such as hydrogen, alkynes, etc.; in one embodiment, the amount of initiator is 0.03%-0.1% of the mass of fresh ethylene; in one embodiment, the amount of terminator is 1%-1.5% of the mass of fresh ethylene; Compression steps: Free radical polymerization is carried out under high pressure. Fresh ethylene and a terminator (e.g., propylene) are introduced into a compression unit and compressed to the required pressure, typically 225-235 MPa. The compression unit generally consists of 2-5 compressors connected in series. The ethylene is sequentially compressed through the compressors to 225-235 MPa. For example, refer to… Figure 1 Fresh ethylene and a terminator (e.g., propylene) are sequentially compressed to 225-235 MPa by compressor K1 and secondary compressor K2. During the compression step, recycled ethylene and the terminator can be introduced at feasible points in the compression step according to the pressure of the recycled ethylene (i.e., the unreacted ethylene obtained by separation) and the terminator itself. Alternatively, the unreacted ethylene can be pressurized to a feasible point in the compression step and then introduced.

[0055] High-pressure free radical polymerization reaction steps: An ethylene-containing mixture is fed into a tubular reactor for high-pressure free radical polymerization in the presence of an initiator. The initiator can be injected at multiple points in the tubular reactor, for example, 2-7. Since high-pressure free radical polymerization is exothermic, continuous cooling is controlled during the reaction. For example, circulating water is used for cooling during the reaction, with the circulating water and reactants in a countercurrent heat exchange state, thereby controlling the reaction temperature peak (referred to as the temperature peak) and the initiation temperature (minimum temperature). The pressure of the high-pressure free radical polymerization reaction can be controlled through a compression step. In one embodiment, the reaction pressure is 225-235 MPa; in another embodiment, the reaction temperature is 170-300°C; in yet another embodiment, [refer to...]. Figure 2 There are four initiator injection points. Preferably, the first initiator at the first injection point is a mixture of di-tert-butyl peroxide (initiator A), tert-butyl peroxide (initiator C), and tert-butyl peroxide (2-ethylhexanoate) (initiator S), with a preferred mass ratio of 1:2-3:3-4, more preferably 1:2.5:3.2. The amount of the first initiator is preferably 0.012-0.014% of the mass of fresh ethylene. The second initiator at the second injection point is di-tert-butyl peroxide (initiator A) and tert-butyl peroxide (initiator C), with a preferred mass ratio of 1:2-3, more preferably 1:2.5. The amount of the second initiator is preferably 0.008-0.012% of the mass of fresh ethylene. The third initiator at the third injection point is tert-butyl peroxide (2-ethylhexanoate) (initiator S), with a preferred amount of... The amount of fresh ethylene is 0.008-0.01% of its mass; the fourth initiator at the fourth injection point is tert-butyl peroxide (2-ethylhexanoate) (i.e., initiator S), preferably 0.007-0.008% of the mass of fresh ethylene; in one embodiment, the temperature peak of each reaction zone is independently 290-300°C; in addition, those skilled in the art can select a suitable length of reaction zone according to the amount of polymerization reaction to be carried out. In one embodiment, the length ratio of the first reaction zone, the second reaction zone, the third reaction zone and the fourth reaction zone is (1.2-1.4):(0.8-1.2):(0.8-1.2):(0.8-1.2), preferably 1.35:1:1:1; wherein the definition of the reaction zone refers to the position where the reactants and the initiator delivered at the initiator injection point mix and come into contact, up to the position of the next initiator injection point.

[0056] Separate cycle steps: The product obtained by high-pressure free radical polymerization contains polyethylene, low molecular weight compounds, and unreacted ethylene. The pressure of the product after the reaction is high. The product pressure can be reduced from the reaction pressure to the separation pressure required by the pressure regulating valve at the outlet of the tubular reactor. The separation is generally carried out first in a high-pressure separator (the separation pressure is generally 10-40 MPa), and then in a low-pressure separator (the separation pressure is generally 0.1-0.5 MPa). The separation operation is a conventional operation in the art, and the inventor will not elaborate on it in this invention. The purpose of the separation is to recover most of the unreacted raw materials and remove low molecular weight compounds. The separated material contains a large amount of unreacted ethylene. Generally, the unreacted material from the low-pressure separator is first pressurized in a booster and then mixed with fresh ethylene and a terminator (e.g., propylene). The unreacted material from the high-pressure separator is introduced into the reactor R1 at feasible points in the compression step according to its own pressure to continue the reaction.

[0057] Extrusion granulation: The molten polyethylene product from the bottom of the low-pressure separator enters the extrusion granulator for extrusion granulation. The low-density polyethylene obtained during the extrusion granulation process can be continuously inspected online by an optical inspection instrument with a resolution of 40 µm or higher. The qualified materials are classified according to cleanliness through a three-way valve in accordance with conventional methods in the art. After drying, the granules are pneumatically conveyed into the deaeration silo and the blending silo for further processing. Finally, the product is sent to the packaging line. To ensure the cleanliness of the polyethylene product, the ion content in the pelleting water is less than 10 ppm, the circulation time is less than 8 hours, and the impurity content in the pneumatic conveying system is less than 10 ppm. The extrusion granulator is cleaned before granulation.

[0058] In this invention, the molecular weight and distribution of polyethylene, the number of tertiary carbon atoms, and the vinyl content are all affected by the reaction temperature peak, reaction pressure, and the amount of raw materials added in the polymerization reaction. The density of polyethylene is highly correlated with its crystallinity, and the melt index of polyethylene is highly correlated with its molecular weight and molecular weight distribution. To achieve the objectives of this invention, those skilled in the art can adjust the process conditions to achieve polyethylene with 10-20 tertiary carbon atoms / 1000 carbon atoms and 0.1-0.2 vinyl atoms / 1000 carbon atoms.

[0059] According to the present invention, such as Figure 1-2As shown, in one embodiment, the method for preparing polyethylene includes: fresh ethylene and propylene (the terminator) are compressed at a certain flow rate (e.g., the flow rate of fresh ethylene is 20-30 t / h, and the flow rate of propylene is 65-70 g / s) by a primary compressor K1. The pressure increases from 2.5-2.8 MPa at the inlet to approximately 25-29 MPa. After exiting the primary compressor K1, the material enters a secondary compressor K2 for compression. The pressure increases to the required pressure of 225-235 MPa for the reactor and then enters reactor R1. Four initiators are injected into reactor R1 through initiator injection points at the starting positions of reaction zones 1-4 to initiate the polymerization reaction. The polymerization reaction is exothermic. During the reaction, circulating water is used for cooling to control the reaction temperature peak and initiation temperature. There are a total of 13 reaction cooling zones in the four reaction sections. The circulating water and the reactants exchange heat in a countercurrent manner. The temperature range is 170℃-300℃, and the reaction pressure is 225-235 MPa. At a pressure of approximately 25 MPa, the conversion rate of ethylene monomer is about 28%-32%. At the end of reactor R1, the polyethylene produced by the reaction and the unreacted ethylene enter the high-pressure separator S1 for separation. The separation pressure is about 25 MPa. The unreacted ethylene from the high-pressure separator S1 enters the secondary compressor K2 at a certain flow rate (e.g., 37 t / h) for compression and then enters reactor R1 to continue the reaction. The molten polyethylene product from the bottom of the low-pressure separator S2 enters the extrusion granulator R1 for granulation. After drying, the granules are pneumatically conveyed into the deaeration silo and blending silo for further processing. Finally, the product is sent to the packaging line. To ensure the high purity of polyethylene, ethylene and propylene are refined to ensure that the ethylene content is above 99.98 wt% and the content of impurities affecting the reaction (hydrogen, alkynes, etc.) is below 5 ppm. The ion content in the pelletizing water is controlled to be below 10 ppm, the circulation time is below 8 hours, and the impurity content in the pneumatic conveying system is below 10 ppm. The screws of the low-pressure separator S2 and the extrusion granulator P1 are cleaned before each production run. Base material is not discharged when the unit is started or stopped or production fluctuates. The transition time for switching high-voltage cable base material grades is doubled, and qualified products are cut only after stability is confirmed. The water replenishment of the pelletizing water tank is increased to ensure that the hourly overflow rate of pelletizing water is above 30% of the total water volume. During the production of high-voltage cable base material, the frequency of analysis and inspection of melt index, color particles, particle size, and tailing particles is doubled.

[0060] In this invention, polyethylene can be used in different products as needed. As a non-limiting application, the second aspect of this invention provides the application of the polyethylene described in the first aspect of this invention in cables.

[0061] The inventors of this invention have discovered that the polyethylene in this invention is particularly suitable for the preparation of cable products, and the degree of crosslinking of the cable insulation material obtained can reach the standard of 330 kV and above ultra-high voltage cable materials.

[0062] A third aspect of the present invention provides a polyethylene composition comprising the polyethylene described in the first aspect of the present invention.

[0063] The composition containing the polyethylene of the present invention has excellent scorch resistance. In a preferred embodiment, the scorch rate of the polyethylene composition is not higher than 0.18 N·m / s, preferably 0.09-0.15 N·m / s.

[0064] The polyethylene in this invention is particularly suitable for cross-linked articles, and according to a preferred embodiment of the invention, the composition is capable of cross-linking.

[0065] In this invention, "capable of crosslinking" is a technical term commonly used in the art, specifically referring to the ability of a composition containing the polyethylene of this invention to be crosslinked, for example, by forming bridging between polymer chains through free radicals.

[0066] According to a preferred embodiment of the present invention, the composition contains a crosslinking agent.

[0067] According to the present invention, there is no particular limitation on the specific type of crosslinking agent, and those skilled in the art can select it as needed. Preferably, the crosslinking agent is a peroxide, and examples of peroxides include tert-butyl cumene peroxide, tert-butyl cumene peroxide, dicumene peroxide, 1,3-bis(tert-butyl peroxide), 1,4-bis(tert-butyl peroxide), tert-butyl peroxide, 2,5-dimethyl-2,5-bis(benzoyl)peroxy-hexane, etc., with dicumene peroxide being the most preferred.

[0068] According to a preferred embodiment of the present invention, the content of the crosslinking agent in the composition is 1-2 wt% of the polyethylene mass.

[0069] Other functional additives, such as antioxidants, may be added to the polyethylene composition of the present invention as needed. In one embodiment, the polyethylene composition further contains antioxidants, which can be conventional antioxidants in the art, such as hindered phenolic antioxidants. Examples of hindered phenolic antioxidants include N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine (antioxidant 1098), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076), and 4,4'-thiobis(6-tert-butyl-m-cresol) (antioxidant 300), with antioxidant 1010 being preferred.

[0070] According to a preferred embodiment of the present invention, the antioxidant content in the composition is 0.1-0.5 wt%.

[0071] According to the present invention, the components of the polyethylene composition can be stored separately or mixed as needed, for example, to form a mixture for use. Specifically, the mixture can be used as a polyethylene insulation material to prepare subsequent cross-linked polyethylene cable insulation materials. In one embodiment, the polyethylene insulation material can be prepared according to the following steps: (1) Polyethylene and antioxidant are added to a continuous internal mixer and mixed at a temperature of 180℃-190℃. The mixed material is then filtered to remove impurities. The material after impurity removal is extruded and granulated by twin screws. After being cooled by pure water, it is transported to a purified polyethylene drying system for dehydration and drying. The dried product is then transported to a drum mixer and kept at 70℃-80℃. (2) Spray the crosslinking agent heated to the molten state onto the surface of the granules in the drum mixer. After spraying, continue to keep it warm for 4-7 hours, and then cool it to room temperature to obtain polyethylene insulation material.

[0072] A fourth aspect of the present invention provides a cross-linked polyethylene insulated cable material, said cross-linked polyethylene insulated cable material being made from the polyethylene composition described in the third aspect of the present invention.

[0073] The preparation method of the cross-linked polyethylene insulated cable material in this invention can be carried out according to conventional preparation methods in the art, and will not be described in detail here.

[0074] The cross-linked polyethylene insulated cable material of this invention has a high degree of cross-linking. According to a preferred embodiment of this invention, the degree of cross-linking of the cross-linked polyethylene insulated cable material is not less than 82%. For example, the degree of cross-linking is 82%, 83%, 85%, 89%, or any range of two of the above values.

[0075] Unless otherwise stated in the specification, the following methods are used for property determination in the context of this invention.

[0076] The melt flow index of polyethylene was tested according to GB / T 3682, with a load of 2.16 kg and a temperature of 190℃. The density of polyethylene was determined according to GB / T 1033.2, using the D method, and tested after boiling for 30 minutes. The weight-average molecular weight and molecular weight distribution of polyethylene were determined by gel permeation chromatography (GPC). The solvent and mobile phase were both 1,2,4-trichlorobenzene (containing 0.025% antioxidant 2,6-dibutyl-p-cresol). The column temperature was 150℃ and the flow rate was 1.0 ml / min. Narrow-distribution polystyrene standards were used for general calibration. The vinyl group (CH2=CH) of polyethylene was tested using a 600 M nuclear magnetic resonance spectrometer, in accordance with SH / T 1775-2012. 75 mg of sample was placed in a 5 mm sample tube, 0.5 mL of solvent was added, and the sample tube was kept in a constant temperature bath at 140℃ for 3-4 hours to ensure uniform dispersion. The prepared sample tube was then placed in a nuclear magnetic resonance spectrometer and stabilized at 125℃ for 30 min before scanning. The number of scans was set to 32. After scanning, the proton NMR spectrum was processed. The isolated hydrogen atom peak in -CH2- in the polymer was calibrated to 1.13 ppm. At this time, the multiplet at 5.59 ppm was attributed to the hydrogen atom of CHR in CH2=CHR, the multiplet at 4.77 ppm was attributed to the hydrogen atom of CH2 in CH2=CHR, and the multiplet at 0.72 ppm was attributed to the hydrogen atom of -CH3. The area of ​​the multiplet at 5.59 ppm (CH2=CH) was set to 1. Then, the peaks at 4.77 ppm, 1.13 ppm and 0.72 ppm were integrated respectively, and the resulting peak areas were recorded as a, b and c respectively. The vinyl content of polyethylene was calculated by the formula (6+3a) / (6b+4c). The number of tertiary carbon atoms in polyethylene was determined using a 600 M nuclear magnetic resonance spectrometer and a Fourier transform infrared spectrometer. Using linear low-density polyethylene (LLDPE) as an internal standard, carbon spectra of different grades of LLDPE were measured, and the tertiary carbon content was calculated. Specifically, different grades of linear low-density polyethylene were prepared into discs with a thickness of approximately 0.2 mm, and their infrared spectra (resolution 2 cm⁻¹) were measured. -1 The infrared spectrum is plotted with absorbance as the ordinate. Given that the absorbance of a given group or its derivative is linearly related to its concentration, a fourth derivative of the infrared spectrum is calculated. This yields the infrared derivative spectrum, with the fourth derivative of absorbance as the ordinate and wavenumber as the abscissa. The 1340 cm⁻¹ value in the derivative spectrum is then calculated. -1 The peak height of the characteristic peak of -CH (representing a tertiary carbon atom) was used to quantitatively analyze the tertiary carbon atoms of the internal standard (linear low-density polyethylene) using carbon spectroscopy. In the carbon spectrum, the peaks of linear low-density polyethylene were concentrated in the range of 5-50 ppm, with the peak near 39.73 ppm being the tertiary carbon atom peak. The area of ​​this peak was set to 1, and then the content of tertiary carbon atoms in linear low-density polyethylene was calculated by integrating the other peaks of polyethylene. The peak height at 1340 cm⁻¹ in the fourth derivative spectrum was used as the reference value. -1 Peak height and 2019 cm⁻¹ in the original infrared spectrum -1 Peak height ratio h 1340 / h 2019 With the y-axis as the tertiary carbon content N in linear low-density polyethylene as the x-axis, establish the equation for the tertiary carbon atom concentration curve as follows:y= 0.00707 N+ 0.13921, R 2 =0.9997, then the original infrared spectrum and fourth derivative spectrum of the polyethylene to be tested were measured, and the value at 1340 cm⁻¹ in the fourth derivative spectrum was calculated. -1 Peak height and 2019 cm⁻¹ in the original infrared spectrum -1 Peak height ratio h 1340 / h 2019 Substitute this ratio into the equation for the tertiary carbon atom concentration curve to calculate its tertiary carbon content.

[0077] The melting temperature of polyethylene was determined by differential scanning calorimetry (DSC) according to ASTM D 3418, with a heating rate of 10 °C / min. Temperature-elution fractionation method: Approximately 6-8 g of sample is packed into a material column. The dissolution temperature is set at 160℃, and the solvent is o-dichlorobenzene (with 0.1 wt% BHT added as an antioxidant to prevent polymer degradation during temperature-elution). The dissolved sample is transferred to a fractionation column and then cooled to room temperature at a rate of 3.5℃ / min. Elution temperatures are set at 30℃, 35℃, 45℃, 55℃, 65℃, 70℃, 75℃, 80℃, and 85℃. At each elution temperature, the temperature equilibration time is set at 45 min. The eluent is collected and cooled to room temperature. Then, most of the solvent is evaporated using a rotary evaporator (rotary evaporation temperature 120℃, vacuum degree -0.096MPa) for recycling. The remaining eluent is mixed with 2 volumes of ethanol. A precipitate will form in the flask. The precipitate is collected and washed using a Buchner funnel. The resulting solid is vacuum dried at 40℃ to constant weight, which is the target fraction at the corresponding temperature.

[0078] The degree of crosslinking (gel content) test shall be performed in accordance with the provisions of GB / T 18474-2001.

[0079] Scorch resistance was assessed using a Brabender internal mixer at a temperature of 140℃, a screw speed of 60 r / min, a mixing time of 15 min, and a feed rate of 40 g. The changes in torque and material temperature of the polyethylene insulation material under shear were tested. The slope of the torque curve was used as the scorch rate (k), directly reflecting the scorch resistance of the insulation material. A higher scorch rate (k) indicates poorer scorch resistance, and vice versa.

[0080] The present invention will be described in detail below through embodiments.

[0081] The structural characteristics, physicochemical parameters, and test results of polyethylene in the following examples and comparative examples are shown in Table 1.

[0082] Example 1 Reference Figure 1-2 The refined fresh ethylene feedstock and the terminator propylene were drawn into reactor R1 at flow rates of 22 t / h and 68 g / s, respectively, at a pressure of 230 MPa and a temperature of 150℃. A mixture A of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) is injected into reaction zone 1 at a flow rate of 2.9 kg / h (the mass ratio of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) is 1:2.5:3.2). A mixture B of di-tert-butyl peroxide and tert-butyl peroxide is injected into reaction zone 2 at a flow rate of 2.28 kg / h (the mass ratio of di-tert-butyl peroxide and tert-butyl peroxide is 1:2.5). Di-tert-butyl peroxide is injected into reaction zones 3 and 4 at flow rates of 1.95 kg / h and 1.63 kg / h, respectively. The pressure is increased to 230 MPa before entering reactor R1 to initiate the polymerization reaction. Cooling is achieved through cooling water during the reaction process, controlling the peak reaction temperature in each reaction zone to approximately 290℃ and the reaction pressure to 235 MPa. MPa, the lengths of reaction zone 1, reaction zone 2, reaction zone 3 and reaction zone 4 are 540 m, 400 m, 400 m and 400 m respectively; The product obtained from the reaction is depressurized and cooled before being separated from the unreacted gas. The molten polyethylene product separated from the bottom of the low-pressure separator S2 enters the extrusion granulator P1 for granulation to obtain low-density polyethylene. The obtained low-density polyethylene and antioxidant are added in proportion to a continuous internal mixer for mixing at a mixing temperature of 190°C. After that, it is extruded and granulated to obtain granules, which are then conveyed to a rotary drum mixer and kept at 75°C. The antioxidant is 1010, and the amount of antioxidant added is 0.25% of the mass of low-density polyethylene. Dicumyl peroxide heated to a molten state is sprayed onto the surface of the granules in a rotary drum mixer. The amount of dicumyl peroxide added is 1.6% of the mass of low-density polyethylene. After spraying, the material is kept at a constant temperature for 5 hours and then cooled to room temperature to obtain polyethylene insulation material.

[0083] Example 2 Reference Figure 1-2 The refined fresh ethylene feedstock and the terminator propylene were drawn into reactor R1 at flow rates of 22 t / h and 70 g / s, respectively, at a pressure of 230 MPa and a temperature of 150℃. A mixture A of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) was injected into reaction zone 1 at a flow rate of 2.8 kg / h (the mass ratio of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) was 1:2.5:3.2). A mixture B of di-tert-butyl peroxide and tert-butyl peroxide was injected into reaction zone 2 at a flow rate of 2.1 kg / h (the mass ratio of di-tert-butyl peroxide and tert-butyl peroxide (2:2.5) was injected into reaction zone 3 and reaction zone 4, respectively, at flow rates of 1.9 kg / h and 1.6 kg / h, respectively. The pressure was increased to 230. MPa is introduced into the reactor to initiate the polymerization reaction. The reaction is cooled by cooling water during the process, and the reaction temperature peak of each reaction zone is controlled to be about 285℃, and the reaction pressure is 235MPa. The lengths of reaction zone 1, reaction zone 2, reaction zone 3 and reaction zone 4 are 540 m, 400 m, 400 m and 400 m, respectively. The product obtained from the reaction is depressurized and cooled before being separated from the unreacted gas. The molten polyethylene product separated from the bottom of the low-pressure separator S2 enters the extrusion granulator P1 for granulation to obtain low-density polyethylene. The obtained low-density polyethylene and antioxidant are added to a continuous internal mixer in proportion. The mixing temperature is 190℃. After being mixed evenly, the mixture is extruded and granulated to obtain granules. The granules are then heated to 75℃ and conveyed to a rotary drum mixer and kept at 75℃. The antioxidant is 1010, and the amount of antioxidant added is 0.25% of the mass of low-density polyethylene. Dicumyl peroxide, heated to a molten state, is sprayed onto the surface of the granules. The amount of dicumyl peroxide added is 1.6% of the mass of low-density polyethylene. After spraying, the material is kept at a constant temperature for 5 hours and then cooled to room temperature to obtain polyethylene insulation material.

[0084] Example 3 Reference Figure 1-2 The refined fresh ethylene feedstock and the terminator propylene were drawn into reactor R1 at flow rates of 22 t / h and 68 g / s, respectively, at a pressure of 225 MPa and a temperature of 150℃. A mixture A of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) is injected into reaction zone 1 at a flow rate of 2.9 kg / h (the mass ratio of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) is 1:2.5:3.2). A mixture B of di-tert-butyl peroxide and tert-butyl peroxide is injected into reaction zone 2 at a flow rate of 2.28 kg / h (the mass ratio of di-tert-butyl peroxide and tert-butyl peroxide (2:2.5) is injected into reaction zone 3 and reaction zone 4 at flow rates of 1.95 kg / h and 1.63 kg / h, respectively. The pressure is increased to 230 MPa before entering the reactor to initiate the polymerization reaction. Cooling is achieved using cooling water during the reaction, controlling the peak reaction temperature to approximately 290°C and the reaction pressure to 225 MPa. MPa, the lengths of reaction zone 1, reaction zone 2, reaction zone 3 and reaction zone 4 are 540 m, 400 m, 400 m and 400 m respectively; The product obtained from the reaction is depressurized and cooled before being separated from the unreacted gas. The molten polyethylene product separated from the bottom of the low-pressure separator S2 enters the extrusion granulator P1 for granulation to obtain low-density polyethylene. The obtained low-density polyethylene and antioxidant are added to a continuous internal mixer in proportion. The mixing temperature is 190℃. After uniform mixing, the mixture is extruded and granulated to obtain granules. The granules are then heated to 75℃ and conveyed to a rotary drum mixer and kept at 75℃. The antioxidant is 1010, and the amount of antioxidant added is 0.25% of the mass of low-density polyethylene. Dicumyl peroxide, heated to a molten state, is sprayed onto the surface of the granules. The amount of dicumyl peroxide added is 1.6% of the mass of low-density polyethylene. After spraying, the material is kept at a constant temperature for 5 hours and then cooled to room temperature to obtain polyethylene insulation material.

[0085] Example 4 Reference Figure 1-2 The refined fresh ethylene feedstock and the terminator propylene are drawn into reactor R1 at flow rates of 22 t / h and 65 g / s, respectively, at a pressure of 225 MPa and a temperature of 150℃. A mixture A of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) is injected into reaction zone 1 at a flow rate of 2.8 kg / h (the mass ratio of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) is 1:2.5:3.2). A mixture B of di-tert-butyl peroxide and tert-butyl peroxide is injected into reaction zone 2 at a flow rate of 2.1 kg / h (the mass ratio of di-tert-butyl peroxide and tert-butyl peroxide is 1:2.5). Di-tert-butyl peroxide is injected into reaction zones 3 and 4 at flow rates of 1.9 kg / h and 1.6 kg / h, respectively. The pressure is increased to 225 MPa before entering the reactor, thereby initiating the polymerization reaction. During the reaction, cooling water is used to control the reaction temperature peak of each reaction zone to be approximately 280℃, and the reaction pressure to be 225 MPa. The product obtained from the reaction is depressurized and cooled before being separated from the unreacted gas. The molten polyethylene product separated from the bottom of the low-pressure separator S2 enters the extrusion granulator P1 for granulation to obtain low-density polyethylene. The obtained low-density polyethylene and antioxidant are added to a continuous internal mixer in proportion. The mixing temperature is 190℃. After being mixed evenly, the mixture is extruded and granulated to obtain granules. The granules are then heated to 75℃ and conveyed to a rotary drum mixer and kept at 75℃. The antioxidant is 1010, and the amount of antioxidant added is 0.25% of the mass of low-density polyethylene. Dicumyl peroxide, heated to a molten state, is sprayed onto the surface of the granules. The amount of dicumyl peroxide added is 1.6% of the mass of low-density polyethylene. After spraying, the material is kept at a constant temperature for 5 hours and then cooled to room temperature to obtain polyethylene insulation material.

[0086] Comparative Example 1 Reference Figure 1-2 The refined fresh ethylene feedstock and the terminator propylene are drawn into reactor R1 at flow rates of 22 t / h and 60 g / s, respectively, at a pressure of 215 MPa and a temperature of 150℃. A mixture A of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) is injected into reaction zone 1 at a flow rate of 3 kg / h (mass ratio of di-tert-butyl peroxide, tert-butyl peroxide, and tert-butyl peroxide (2-ethylhexanoate) is 1.5:2.2:3). A mixture B of di-tert-butyl peroxide and tert-butyl peroxide is injected into reaction zone 2 at a flow rate of 2.4 kg / h (mass ratio of di-tert-butyl peroxide and tert-butyl peroxide (1:2.5)). Di-tert-butyl peroxide is injected into reaction zones 3 and 4 at flow rates of 2.2 kg / h and 1.7 kg / h, respectively. The pressure is increased to 215 MPa before entering the reactor, thus initiating the polymerization reaction. During the reaction, cooling water is used to control the reaction temperature peak at approximately 295°C, and the reaction pressure is 215 MPa. MPa; the lengths of reaction zone 1, reaction zone 2, reaction zone 3, and reaction zone 4 are 540 m, 400 m, 400 m, and 400 m, respectively; The product material obtained from the reaction is depressurized and cooled before being separated from the unreacted gas. The molten polyethylene product separated from the bottom of the low-pressure separator S2 enters the P1 extrusion granulator for granulation to obtain low-density polyethylene. The obtained low-density polyethylene and antioxidant are added to a continuous internal mixer in proportion. The mixing temperature is 190℃. After being mixed evenly, the mixture is extruded and granulated to obtain granules. Then, the granules are heated to 75℃ and conveyed to a rotary drum mixer and kept at 75℃. The antioxidant is 1010, and the amount of antioxidant added is 0.25% of the mass of low-density polyethylene. Dicumyl peroxide, heated to a molten state, is sprayed onto the surface of the granules. The amount of dicumyl peroxide added is 1.6% of the mass of low-density polyethylene. After spraying, the material is kept at a constant temperature for 5 hours and then cooled to room temperature to obtain polyethylene insulation material.

[0087] Comparative Example 2 Low-density polyethylene A (Qilu Petrochemical grade 7042 polyethylene) and antioxidant were added to a continuous internal mixer in a certain proportion. The mixing temperature was 190℃. After uniform mixing, the mixture was filtered and then extruded by a twin-screw extruder. The mixture was cooled by pure water and then sent to a purified polyethylene drying system for dehydration and drying to obtain granules. The granules were then heated to 75℃ and sent to a rotary drum mixer and kept at 75℃. The antioxidant was 1010, and the amount of antioxidant added was 0.25% of the mass of low-density polyethylene. Dicumyl peroxide, heated to a molten state, is sprayed onto the surface of the granules. The amount of dicumyl peroxide added is 1.6% of the mass of low-density polyethylene. After spraying, the material is kept at a constant temperature for 5 hours and then cooled to room temperature to obtain polyethylene insulation material.

[0088] Comparative Example 3 Low-density polyethylene B (Borealis's grade LS4258DCE polyethylene insulation material, purified using dichloromethane as solvent via a Soxhlet extractor to remove antioxidants and crosslinking agents) and antioxidants were added in proportion to a continuous internal mixer at a mixing temperature of 190°C. After uniform mixing, the mixture was filtered and then extruded by a twin-screw extruder. The granules were cooled with pure water and then conveyed to a purified polyethylene drying system for dehydration and drying to obtain granules. The granules were then heated to 75°C and conveyed to a rotary drum mixer and kept at 75°C. The antioxidant used was 1010, and the amount of antioxidant added was 0.25% of the mass of low-density polyethylene. Dicumyl peroxide, heated to a molten state, is sprayed onto the surface of the granules. The amount of dicumyl peroxide added is 1.6% of the mass of low-density polyethylene. After spraying, the material is kept at a constant temperature for 5 hours and then cooled to room temperature to obtain polyethylene insulation material.

[0089] Comparative Example 4 Low-density polyethylene C (Borealis's grade LS4201EHV polyethylene insulation material, purified using dichloromethane as solvent via a Soxhlet extractor to remove antioxidants and crosslinking agents) and antioxidants were added in proportion to a continuous internal mixer at a mixing temperature of 190°C. After uniform mixing, the mixture was filtered and then extruded by a twin-screw extruder. The granules were cooled with pure water and then conveyed to a purified polyethylene drying system for dehydration and drying to obtain granules. The granules were then heated to 75°C and conveyed to a rotary drum mixer and kept at 75°C. The antioxidant used was 1010, and the amount of antioxidant added was 0.25% of the mass of low-density polyethylene. Dicumyl peroxide, heated to a molten state, is sprayed onto the surface of the granules. The amount of dicumyl peroxide added is 1.6% of the mass of low-density polyethylene. After spraying, the material is kept at a constant temperature for 5 hours and then cooled to room temperature to obtain polyethylene insulation material.

[0090] Table 1 Test Results

[0091] As shown in Table 1, the polyethylene provided by the present invention has a low scorch rate when used in cross-linked polyethylene cable insulation material, and the insulation material made from the cross-linked polyethylene cable insulation material has a high degree of cross-linking. This indicates that the polyethylene of the present invention exhibits good scorch resistance and heat resistance when used in cross-linked polyethylene cable insulation material.

[0092] 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 combinations of 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 polyethylene, characterized in that, The polyethylene has 10-20 tertiary carbon atoms / 1000 carbon atoms and 0.1-0.2 vinyl atoms / 1000 carbon atoms.

2. The polyethylene according to claim 1, wherein, The polyethylene has a melt mass flow rate of 1-5 g / 10 min measured at 190°C and a load of 2.16 kg; and / or, the polyethylene has a density of 0.915-0.930 g / cm³. 3 .

3. The polyethylene according to claim 1 or 2, wherein, The polyethylene rinsing fraction at 80°C has: 15-25 tertiary carbon atoms / 1000 carbon atoms, preferably 17-22 tertiary carbon atoms / 1000 carbon atoms; 0.04-0.1 vinyl atoms / 1000 carbon atoms, preferably 0.06-0.09 vinyl atoms / 1000 carbon atoms; and / or The polyethylene rinsing fraction at 75°C has: 13-18 tertiary carbon atoms / 1000 carbon atoms, preferably 14-17 tertiary carbon atoms / 1000 carbon atoms; 0.02-0.07 vinyl atoms / 1000 carbon atoms, preferably 0.03-0.06 vinyl atoms / 1000 carbon atoms.

4. The polyethylene according to any one of claims 1-3, wherein, The polyethylene rinsing fraction at 70°C has: 17-24 tertiary carbon atoms / 1000 carbon atoms, preferably 18-21 tertiary carbon atoms / 1000 carbon atoms; 0.05-0.16 vinyl atoms / 1000 carbon atoms, preferably 0.07-0.15 vinyl atoms / 1000 carbon atoms; and / or The polyethylene rinsing fraction at 65°C has: 19-26 tertiary carbon atoms / 1000 carbon atoms, preferably 21-25 tertiary carbon atoms / 1000 carbon atoms; 0.1-0.2 vinyl atoms / 1000 carbon atoms, preferably 0.12-0.19 vinyl atoms / 1000 carbon atoms.

5. The polyethylene according to any one of claims 1-4, wherein, The polyethylene has a weight-average molecular weight of 70,000-120,000, preferably 80,000-100,000; and / or The weight-average molecular weight of the polyethylene fraction washed at 80°C is 140,000-220,000, preferably 170,000-190,000; and / or The polyethylene fraction subjected to a 75°C warm-wash process has a weight-average molecular weight of 150,000-230,000, preferably 180,000-200,000; and / or The polyethylene fraction subjected to a 70°C warm-wash process has a weight-average molecular weight of 50,000-110,000, preferably 60,000-100,000; and / or The weight-average molecular weight of the polyethylene fraction obtained by rinsing at 65°C is 25,000-60,000, preferably 35,000-50,000.

6. The polyethylene according to any one of claims 1-5, wherein, The polyethylene has a molecular weight distribution not higher than 5.3, preferably 3.5-5.3, more preferably 4.5-5; and / or The molecular weight distribution of the polyethylene fraction subjected to 80°C warming wash is not higher than 6, preferably 3-4; and / or The molecular weight distribution of the polyethylene fraction obtained by rinsing at 75°C is not higher than 6, preferably 3-4; and / or The molecular weight distribution of the polyethylene fraction subjected to a 70°C warm-up washing process is not higher than 5, preferably 3-4.5; and / or The molecular weight distribution of the polyethylene fraction subjected to a 65°C heating rinse is not higher than 4, preferably 1.5-3.

7. The polyethylene according to any one of claims 1-6, wherein, The melting temperature of the polyethylene is 105-111℃; and / or The melting temperature of the polyethylene fraction subjected to 80°C warming scrubbing is 109-112°C; and / or The melting temperature of the polyethylene fraction subjected to a 75°C heating wash is 106-108°C; and / or The melting temperature of the polyethylene fraction subjected to a 70°C heating wash is 105-108°C; and / or The melting temperature of the polyethylene fraction subjected to a 65°C heating wash is 102-105°C.

8. The polyethylene according to any one of claims 1-7, wherein, The content of the polyethylene in the 65-80°C heated washing fraction is 66-94 wt%, preferably 82-90 wt%; and / or The content of the polyethylene in the 75°C heated washing fraction is 35-45 wt%, preferably 36-40 wt%; and / or The content of the polyethylene in the 80°C heated washing fraction is 15-25 wt%, preferably 17-21 wt%; and / or The content of the polyethylene fraction heated to 80°C or higher is not higher than 0.1 wt%.

9. The polyethylene according to any one of claims 1-8, wherein, The polyethylene does not contain impurities larger than 200 µm.

10. A method for preparing the polyethylene according to any one of claims 1-9, characterized in that, The method includes: ethylene monomer undergoing free radical polymerization in the presence of an initiator and a terminator, wherein the initiator has at least two injection points, and the first initiator at the first injection point includes initiator I, initiator II, and initiator III, wherein the mass ratio of initiator I, initiator II, and initiator III is 1:2-3:3-4; the amount of terminator is 1%-1.5% of the mass of ethylene; the reaction temperature is 170-300℃, and the reaction pressure is 225-235 MPa.

11. The preparation method according to claim 10, wherein, The amount of the first initiator is 0.012-0.014% of the ethylene mass; And / or, the initiator I comprises di-tert-butyl peroxide; the initiator II comprises tert-butyl peroxide; and the initiator III comprises tert-butyl peroxide (2-ethylhexanoate).

12. The preparation method according to claim 10 or 11, wherein, There are at least four injection points for the initiator; The first initiator at the first injection point includes initiator I, initiator II and initiator III, wherein the mass ratio of the first initiator, the second initiator and the third initiator is 1:2-3:3-4; The second initiator at the second injection point includes initiator I and initiator II, wherein the mass ratio of initiator I to initiator II is 1:2-3; The third initiator at the third injection point and the third initiator at the fourth injection point are each independently initiator III.

13. The method according to claim 12, wherein, The amount of the first initiator is 0.012-0.014% of the mass of ethylene; the amount of the second initiator is 0.008-0.012% of the mass of ethylene; the amount of the third initiator is 0.008-0.01% of the mass of ethylene; and the amount of the fourth initiator is 0.007-0.008% of the mass of ethylene.

14. The use of the polyethylene according to any one of claims 1-9 in cables.

15. A polyethylene composition, characterized in that, The composition comprises the polyethylene as described in any one of claims 1-9.

16. The polyethylene composition according to claim 15, wherein, The scorch rate of the composition is not higher than 0.18 N·m / s, preferably 0.09-0.15 N·m / s.

17. The composition according to claim 15 or 16, wherein, The composition is crosslinkable; and / or The composition contains a crosslinking agent; Preferably, The crosslinking agent is selected from peroxides; and / or In the composition, the content of crosslinking agent is 1-2 wt% of the polyethylene mass.

18. The composition according to any one of claims 15-17, wherein, The composition contains antioxidants; Preferably, The antioxidant is selected from hindered phenolic antioxidants; and / or The antioxidant content in the composition is 0.1-0.5 wt%.

19. A cross-linked polyethylene insulated cable material, characterized in that, The cross-linked polyethylene insulated cable material is made of the polyethylene composition according to any one of claims 11-14; Preferably, the degree of cross-linking of the cross-linked polyethylene insulated cable material is not less than 82%.

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