An insulating material, its preparation and use

Abstract

The application relates to the field of power cable insulation, and discloses an insulation material and a preparation method and application thereof. The method comprises the following steps: granulating low-density polyethylene and an antioxidant to obtain granulated material; mixing a crosslinking agent with the granulated material to obtain mixed material; and heating the mixed material to obtain the insulation material; the low-density polyethylene has a weight average molecular weight of 60,000-120,000, a molecular weight distribution index of 3-7, a carbon-carbon double bond content of 0.7-1.1 carbon-carbon double bonds per 1000 carbon atoms, and a melt mass flow rate of 0.5-5 g / 10 min under the test conditions of 190 DEG C and 2.16 kg. The insulation material prepared by the method has a good application prospect in the field of power cable insulation.

Description

Technical Field

[0001] This invention relates to the field of power cable insulation, specifically to an insulating material, its preparation method, and its application. Background Technology

[0002] LDPE (low-density polyethylene) can be classified into two types based on the type of reactor used for production: batch reactor and tubular reactor. Both batch and tubular reactor methods involve free radical polymerization, resulting in a linear polyethylene chain with numerous branches. LDPE produced by the batch reactor method has a wider molecular weight distribution compared to LDPE produced by the tubular reactor method.

[0003] Meanwhile, LDPE has a symmetrical molecular structure and the dipole moment of the entire molecule is equal to zero. It is a typical nonpolar material with a very small dielectric constant, making it an ideal insulating material that is widely used in the field of wires and cables.

[0004] Because LDPE has a linear structure, its mechanical properties and heat resistance are relatively low, limiting its applications. Crosslinking technology can transform the linear structure of LDPE into a three-dimensional network structure of crosslinked polyethylene (XLPE), improving the material's creep resistance, corrosion resistance, and resistance to environmental stress cracking. Other mechanical properties, such as tensile strength and low-temperature performance, are also improved to some extent. In particular, its heat resistance is significantly enhanced, thereby increasing its maximum operating temperature and reducing the requirements for short-circuit and overload protection in power lines, making XLPE the preferred material for power cable insulation.

[0005] Crosslinking methods for LDPE include peroxide crosslinking, silane crosslinking, and irradiation crosslinking.

[0006] The silane crosslinking method requires water to complete the crosslinking reaction, so it can only be used for the production of medium and low voltage cables. The radiation crosslinking method relies on electron beam irradiation to complete the crosslinking, and is only suitable for thin-walled insulated cables. The peroxide crosslinking method has a wider range of applications. In the current technology, the insulation materials produced by the peroxide injection process are generally only used for medium and low voltage power cables. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing cable insulation materials with good mechanical properties and high heat resistance.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for preparing an insulating material, the method comprising the following steps: (1) Low-density polyethylene and antioxidant are granulated to obtain granulated material; (2) The crosslinking agent is brought into contact with and mixed with the granulated material to obtain a mixture; (3) The mixture is heated to obtain the insulating material; The mass ratio of the low-density polyethylene, the antioxidant, and the crosslinking agent is 1:0.001-0.01:0.012-0.025; The low-density polyethylene is produced by tubular method, and the weight-average molecular weight of the low-density polyethylene is 60,000-120,000, the molecular weight distribution index is 3-7, the carbon-carbon double bond content is 0.7-1.1 carbon-carbon double bonds per 1000 carbon atoms, and the melt mass flow rate under the test conditions of 190℃ and 2.16kg is 0.5-5g / 10min.

[0009] A second aspect of the present invention provides an insulating material prepared by the method described in the first aspect above.

[0010] A third aspect of the present invention provides the application of the insulating material described in the second aspect above in the field of power cable insulation materials.

[0011] The method for preparing insulating materials provided by this invention is simple and highly operable. The insulating material prepared by this method has good mechanical properties and excellent thermal aging performance; at the same time, the gel content of this insulating material is ≥86wt%, and the elongation under thermal load is ≤60%, which shows excellent application prospects in power cable materials, and is especially suitable for use in the field of high voltage or ultra-high voltage cable insulation. Detailed Implementation

[0012] 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.

[0013] As previously described, a first aspect of the present invention provides a method for preparing an insulating material, the method comprising the following steps: (1) Low-density polyethylene and antioxidant are granulated to obtain granulated material; (2) The crosslinking agent is brought into contact with and mixed with the granulated material to obtain a mixture; (3) The mixture is heated to obtain the insulating material; The mass ratio of the low-density polyethylene, the antioxidant, and the crosslinking agent is 1:0.001-0.01:0.012-0.025; The low-density polyethylene is produced by tubular method, and the weight-average molecular weight of the low-density polyethylene is 60,000-120,000, the molecular weight distribution index is 3-7, the carbon-carbon double bond content is 0.7-1.1 carbon-carbon double bonds per 1000 carbon atoms, and the melt mass flow rate under the test conditions of 190℃ and 2.16kg is 0.5-5g / 10min.

[0014] In this invention, the molecular weight distribution index is the ratio of weight-average molecular weight to number-average molecular weight.

[0015] Preferably, the molecular weight distribution index of the low-density polyethylene is 3.5-6.5, more preferably 4.0-5.6. The inventors of this invention have discovered that, under this preferred condition, the resulting insulating material better meets the insulation requirements of power cables and exhibits better heat resistance.

[0016] According to a preferred embodiment, the method further includes: preparing the low-density polyethylene by the following method before performing the granulation process: The low-density polyethylene is obtained by polymerizing ethylene, an initiator, and a molecular weight regulator. The initiator is selected from at least one of tert-butyl peroxynedecanoate, tert-butyl peroxynepentanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxybenzoate and tert-butyl peracetate. The molecular weight regulator is propylene and / or ethane.

[0017] Preferably, the initiator is tert-butyl peroxyneodecanate.

[0018] In a preferred embodiment, the molecular weight regulator is propylene.

[0019] Preferably, the polymerization reaction conditions include a temperature of 240-255°C and a pressure of 250-320 MPa. The inventors of this invention have discovered that, under this preferred condition, the low-density polyethylene obtained, when used in the preparation of insulating materials, is beneficial for improving the crosslinking properties of the low-density polyethylene. The resulting insulating material exhibits better mechanical properties and heat resistance, and can better meet the requirements of power cables for insulating materials.

[0020] Preferably, the weight ratio of the ethylene, the initiator, and the molecular weight regulator is 1:(1×10⁻⁶). -5 -5×10 -5 ): (1×10 -2 -5×10 -2 ).

[0021] Preferably, the flow rate of the molecular weight regulator is 200-450 kg / h.

[0022] In this invention, the polymerization reaction is carried out in a tubular reactor.

[0023] This invention does not impose any particular requirements on the type of tubular reactor, and those skilled in the art can select one as needed. For example, the tubular reactor is a tubular reactor with a length of 900-1500 m.

[0024] Preferably, in step (1), the granulation conditions include a temperature of 170-210℃.

[0025] Preferably, the granulation process is carried out in a twin-screw extruder.

[0026] In a preferred embodiment, the average diameter of the filter screen used in the die head of the twin-screw extruder is 13-48 μm.

[0027] According to a preferred embodiment, the method further includes: in step (2), before the contact mixing, the granulated material is preheated and then the preheated granulated material is contact mixed with the crosslinking agent to obtain a mixture.

[0028] Preferably, the crosslinking agent is applied in liquid form.

[0029] Preferably, in step (2), the liquid crosslinking agent is sprayed onto the preheated granulated material to achieve the contact mixing.

[0030] The present invention does not have any special requirements for the spraying method, as long as the spraying is uniform, and those skilled in the art can choose according to their needs.

[0031] Preferably, the preheating conditions include: a temperature of 50-80°C and a time of 30-90 minutes.

[0032] In a preferred embodiment, in step (3), the conditions for the heat treatment include: a temperature of 50-80°C and a time of 8-24 hours.

[0033] Preferably, the method further includes, in step (3), cooling the material obtained by the heat treatment to obtain the insulating material. The present invention does not have particular requirements for the cooling method; those skilled in the art can choose according to their needs.

[0034] In a preferred embodiment, the antioxidant is 4,4'-thiobis(6-tert-butyl-3-methylphenol), 2,2'-thiobis[ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and tris(2,4-di-tert-butyl)phosphite in a mass ratio of 1:0.1-0.5:0.1-0.5. The inventors of this invention have discovered that, in this preferred embodiment, the resulting insulating material exhibits superior thermal aging properties.

[0035] Preferably, the crosslinking agent is selected from at least one of dicumyl peroxide, 1,3-bis(tert-butylperoxyisopropyl)benzene, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and more preferably dicumyl peroxide.

[0036] As previously stated, a second aspect of the present invention provides an insulating material prepared by the method described in the first aspect.

[0037] In a preferred embodiment, the insulating material has a gel content ≥86wt% and a thermal elongation ≤60%.

[0038] As previously stated, the third aspect of the present invention provides the application of the insulating material described in the second aspect in the field of power cable insulation.

[0039] The present invention will be described in detail below through examples. Unless otherwise specified, the instruments, reagents, and materials involved in the following examples are all conventional instruments, reagents, and materials, which can be obtained through legitimate commercial channels. Unless otherwise stated, all reagents used are commercially available analytical grade products.

[0040] Tubular reactor: ExxonMobil Chemical Company, USA.

[0041] Stirred reactor: Sumitomo Chemical Co., Ltd., Japan.

[0042] Initiator: tert-butyl peroxyneodecanate.

[0043] Molecular weight regulator: propylene.

[0044] Antioxidants: Antioxidant I: 4,4'-thiobis(6-tert-butyl-3-methylphenol), 2,2'-thiobis[ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butyl)phosphite in a mass ratio of 1:0.2:0.2.

[0045] Antioxidant II: 4,4'-thiobis(6-tert-butyl-3-methylphenol), 2,2'-thiobis[ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butyl)phosphite in a mass ratio of 1:0.2:0.8.

[0046] Crosslinking agent: dicumyl peroxide.

[0047] Low-density polyethylene: LDPE-D2: Weight average molecular weight is 75,000, carbon-carbon double bond content is 0.84 carbon-carbon double bonds per 1000 carbon atoms, molecular weight distribution index is 6.4, melt mass flow rate is 7.5 g / 10 min under test conditions of 190℃ and 2.16 kg, grade is LD608.

[0048] Preparation Example 1: This preparation example illustrates the preparation of low-density polyethylene according to the formulation and process parameters in Table 1 by a method including the following steps.

[0049] Ethylene, an initiator, and a molecular weight regulator are polymerized in a tubular reactor to obtain the low-density polyethylene, named LDPE-1.

[0050] Unless otherwise specified, the remaining preparation examples follow the same process as Preparation Example 1, except for the raw material formulation and process parameters, as shown in Table 1. Any parts not listed are the same as those in Preparation Example 1.

[0051] Comparative Preparation Example 1 This comparative preparation example was prepared using a method similar to that of Preparation Example 1. The difference is that the polymerization reaction was carried out in a batch reactor (batch reactor method) in this preparation example. All other steps were the same as in Preparation Example 1, and low-density polyethylene was obtained, which was named LDPE-D1.

[0052] Table 1 Preparation Example 1 Preparation Example 2 Preparation Example 3 Preparation Example 4 Preparation Example 5 Ethylene flow rate (kg / h) 27000 28000 Same as preparation example 1 Same as preparation example 1 Same as preparation example 1 Initiator flow rate (kg / h) 0.30 0.30 Same as preparation example 1 Same as preparation example 1 Same as preparation example 1 Flow rate (kg / h) of molecular weight regulator 350 300 Same as preparation example 1 270 270 Polymerization reaction Temperature / °C 255 Same as preparation example 1 Same as preparation example 1 Same as preparation example 1 Same as preparation example 1 Pressure / MPa 285 Same as preparation example 1 265 265 260 Naming of low-density polyethylene LDPE-1 LDPE-2 LDPE-3 LDPE-4 LDPE-5 Example 1 This embodiment prepares the insulating material using the following steps: (1) In a twin-screw extruder (the average diameter of the filter screen used in the die head is 45 μm), low-density polyethylene (LDPE-1) and antioxidant are granulated in sequence to obtain granulated material; (2) The granulated material is preheated, and then the crosslinking agent is sprayed onto the preheated granulated material to achieve contact mixing and obtain a mixture; (3) The mixture is subjected to heat treatment and cooling in sequence to obtain the insulating material; The granulation process is carried out at a temperature of 190℃. The preheating temperature is 70℃ and the time is 50min; The heat treatment temperature was 65℃, and the time was 16 hours. The mass ratio of the low-density polyethylene (5 kg), antioxidant, and crosslinking agent is 1:0.002:0.02.

[0053] Examples 2 to 5 were all carried out using a method similar to that of Example 1, except that the types of low-density polyethylene were different, namely, the low-density polyethylene LDPE-2 to LDPE-5 prepared in the aforementioned preparation examples were used respectively, and the remaining steps were the same as in Example 1.

[0054] Example 6 This embodiment uses a method similar to that of Example 1, except that antioxidant II of equal mass is used to replace antioxidant I in Example 1, and the remaining steps are the same as in Example 1.

[0055] Comparative Example 1 This comparative example was conducted using a method similar to that of Example 1, except that: in this comparative example, LDPE-D1 of equal mass was used to replace LDPE-1 in Example 1, and the remaining steps were the same as in Example 1.

[0056] Comparative Example 2 This comparative example was conducted using a method similar to that of Example 1, except that: in this comparative example, LDPE-D2 of equal mass was used to replace LDPE-1 in Example 1, and the remaining steps were the same as in Example 1.

[0057] Comparative Example 3 This comparative example was conducted using a method similar to that of Example 1. The difference is that, while keeping the amount of LDPE-1 (low-density polyethylene) constant, the mass ratio of low-density polyethylene, antioxidant, and crosslinking agent was adjusted to 1:0.02:0.02. All other steps were the same as in Example 1.

[0058] Comparative Example 4 This comparative example was conducted using a method similar to that of Example 1. The difference is that, while keeping the amount of LDPE-1 (low-density polyethylene) constant, the mass ratio of low-density polyethylene, antioxidant, and crosslinking agent was adjusted to 1:0.002:0.03. All other steps were the same as in Example 1.

[0059] Test case The performance of the low-density polyethylene obtained in the aforementioned preparation example and the performance of the insulating material obtained in the example were analyzed according to the test methods in Table 2 below. The performance test results of the low-density polyethylene are shown in Table 3, and the performance test results of the insulating material are shown in Table 4.

[0060] Table 2

[0061] Note: Molecular weight includes weight-average molecular weight and number-average molecular weight.

[0062] Table 3

[0063] Table 4 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Tensile stress / MPa 22.5 23.4 21.8 23.6 24.2 21.9 Fracture tensile strain / % 540 550 550 560 560 530 Tensile stress after aging / MPa 23.3 22.9 23.1 22.5 25.5 20.5 Tensile strain at break after aging / % 560 560 580 540 520 510 Elongation under heat load / % 58 57 60 55 59 59 Gel content / % 86.5 86.8 86.3 87.2 86.6 85.6 Electrical strength (kV / mm) 42.4 43.1 44.5 43.6 45.0 40.2 <![CDATA[Dielectric loss factor / ×10 -4 > 1.3 1.2 1.2 1.3 1.1 1.6 Dielectric constant 2.23 2.25 2.24 2.20 2.21 2.26 <![CDATA[Volume resistivity × 10 14 Ω·m]]> 12.3 10.6 10.2 16.3 11.6 8.3 Continued from Table 4 Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile stress / MPa 22.5 22.4 18.5 21.5 20.8 Tensile stress after aging / MPa 23.3 20.1 16.5 26.8 25 Fracture tensile strain / % 540 460 430 500 510 Tensile strain at break after aging / % 560 440 390 450 410 Elongation under heat load / % 58 85 68 65 56 Gel content / % 86.5 71.5 83.5 84.2 87.6 Electrical strength (kV / mm) 42.4 38.5 39.3 41.2 40.6 <![CDATA[Dielectric loss factor / ×10 -4 > 1.3 1.5 1.7 1.6 1.5 Dielectric constant 2.23 2.28 2.27 2.25 2.25 <![CDATA[Volume resistivity × 10 14 Ω·m]]> 12.3 7.6 5.2 7.3 10.3 The results above show that the insulating material prepared by the method of the present invention has good mechanical properties and excellent thermal aging performance. Moreover, the gel content of the insulating material is ≥86wt%, and the elongation under thermal load is ≤60%, making it very suitable for application in the field of power cable insulation materials.

[0064] 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 method for preparing an insulating material, characterized in that, The method includes the following steps: (1) Low-density polyethylene and antioxidant are granulated to obtain granulated material; (2) The crosslinking agent is brought into contact with and mixed with the granulated material to obtain a mixture; (3) The mixture is heated to obtain the insulating material; The mass ratio of the low-density polyethylene, the antioxidant, and the crosslinking agent is 1:0.001-0.01:0.012-0.025; The low-density polyethylene is produced by tubular method, and the weight-average molecular weight of the low-density polyethylene is 60,000-120,000, the molecular weight distribution index is 3-7, the carbon-carbon double bond content is 0.7-1.1 carbon-carbon double bonds per 1000 carbon atoms, and the melt mass flow rate under the test conditions of 190℃ and 2.16kg is 0.5-5g / 10min.

2. The method according to claim 1, wherein, The method further includes: preparing the low-density polyethylene by the following method prior to the granulation process: The low-density polyethylene is obtained by polymerizing ethylene, an initiator, and a molecular weight regulator. The initiator is selected from at least one of tert-butyl peroxynedecanoate, tert-butyl peroxynepentanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxybenzoate and tert-butyl peracetate. The molecular weight regulator is propylene and / or ethane.

3. The method according to claim 2, wherein, The conditions for the polymerization reaction include: a temperature of 240-255℃ and a pressure of 250-320MPa.

4. The method according to claim 2 or 3, wherein, The weight ratio of the ethylene, the initiator, and the molecular weight regulator is 1:(1×10⁻⁶). -5 -5×10 -5 ): (1×10 -2 -5×10 -2 ).

5. The method according to any one of claims 1-4, wherein, In step (1), the granulation conditions include a temperature of 170-210℃; And / or, in step (3), the conditions for the heat treatment include: a temperature of 50-80°C and a time of 8-24h.

6. The method according to any one of claims 1-5, wherein, The antioxidants are 4,4'-thiobis(6-tert-butyl-3-methylphenol), 2,2'-thiobis[ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and tris(2,4-di-tert-butyl)phosphite in a mass ratio of 1:0.1-0.5:0.1-0.

5.

7. The method according to any one of claims 1-6, wherein, The crosslinking agent is selected from at least one of dicumyl peroxide, 1,3-bis(tert-butylperoxyisopropyl)benzene, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, preferably dicumyl peroxide.

8. An insulating material prepared by the method according to any one of claims 1-7.

9. The insulating material according to claim 8, wherein, The insulating material has a gel content of ≥86wt% and a thermal elongation at load ≤60%.

10. The application of the insulating material according to claim 8 or 9 in the field of power cable insulation materials.

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