Polyethylene cable insulation material and process for its production

Abstract

This invention relates to the field of polyethylene insulation materials and discloses a polyethylene cable insulation material and its preparation method. The method includes: (1) blending an antioxidant, an anti-scorching agent, and low-density polyethylene by gravity metering, extruding, and then water-cooling and pelletizing to obtain granules; (2) preheating the granules by gravity metering and then sequentially mixing and impregnating them with a peroxide; the anti-scorching agent is 1,1-diphenylethylene and / or 2,4-diphenyl-4-methyl-1-pentene. The method provided by this invention can prepare a polyethylene cable insulation material with anti-scorching properties and high cleanliness. Furthermore, the performance of ultra-high voltage polyethylene cables above 110KV produced using the polyethylene cable insulation material provided by this invention is stable, and the scorching time is longer. Therefore, the polyethylene cable insulation material provided by this invention is suitable for the production of long-cycle cables.

Description

Technical Field

[0001] This invention relates to the field of polyethylene insulation materials, and more specifically to polyethylene cable insulation materials and their preparation methods. Background Technology

[0002] Currently, polyethylene is the main raw material for power cable insulation materials both domestically and internationally. This is because cross-linked polyethylene (XLPE) can significantly improve its creep resistance, corrosion resistance, and environmental stress cracking resistance, as well as its heat resistance, thus increasing the maximum operating temperature of the cable.

[0003] Currently, medium and high voltage power cables mainly use two methods to produce polyethylene cable insulation materials. The first is the compounding and extrusion granulation method: antioxidants and crosslinking agents are blended with polyethylene, and then directly granulated using a screw extruder to produce polyethylene insulation material. However, this method can result in pre-crosslinking during processing; simultaneously, compounding needs to be carried out at the decomposition temperature of the crosslinking agent, thus causing uneven dispersion of high-melting-point additives and uneven plasticization, which seriously affects product quality. The second method is the post-absorption method: additives and polyethylene are compounded, filtered, and granulated to obtain clean polyethylene particles; then, the crosslinking agent is impregnated with the preheated polyethylene particles for a period of time to obtain a relatively clean polyethylene insulation material.

[0004] Currently, cable material manufacturers widely use the post-absorption method to produce high-voltage and ultra-high-voltage cable materials. Even with the post-absorption method, if the insulation material formula is not upgraded, during the production of long cables (with a production cycle exceeding one week), the extruder filter screen may scorch, and the pre-crosslinked material may disperse into the cable as impurities, posing a risk of cable breakdown.

[0005] With the development of my country's infrastructure, there is an increasing need for long cables with fewer interfaces and for laying long cables in special environments. Therefore, there is an urgent need to produce high-performance, ultra-clean cable insulation materials.

[0006] CN107828116A discloses a scorch-resistant insulation material for high-voltage DC cables, characterized in that, by weight, the raw materials of the insulation material include: 90-100 parts of low-density polyethylene, 0.1-5 parts of metal oxide, 0.1-1.5 parts of antioxidant, 0.5-2.5 parts of crosslinking agent, 0.1-3 parts of co-crosslinking agent, and 0.1-3 parts of scorch-resistant agent; the low-density polyethylene has a number-average molecular weight of 4000-60000 and a density of 0.91-0.93 g / cm³. 3The crosslinking agent is a mixture selected from one or more of N-cyclohexylthiophthalimide, triallyl isocyanurate, and trimethylolpropane trimethacrylate; the anti-scorching agent is a mixture selected from one or more of 2-benzothiazolyl-N-morpholino sulfide, N-phenyl-N-[(trichloromethyl)thio]benzenesulfonamide, and morpholino-4-dithiocarboxylic acid-4-morpholino ester; and the crosslinking agent is diisophenylpropene peroxide. Although the insulating material produced by this prior art possesses a temperature resistance rating above 90°C and anti-scorching properties, the prior art uses excessive additives, especially metal oxides. In cases of uneven mixing, the resulting product is prone to charge concentration, leading to breakdown.

[0007] CN103756010A discloses an anti-scorching chemically cross-linked insulation material, characterized by being prepared from the following raw materials in parts by weight: 100 parts low-density polyethylene, 1-3 parts cross-linking agent, 0.2-0.5 parts antioxidant, 0.1-0.5 parts anti-scorching agent, and 0.05-0.2 parts lubricant. While this prior art can solve the scorching phenomenon caused by the cross-linking agent remaining in the screw for a long time during the extrusion of chemically cross-linked cables, the prior art involves high-speed stirring of the antioxidant, which results in some loss and affects the subsequent addition effect. Furthermore, the low-density polyethylene resin is subjected to a single mixing and single blending extrusion, which creates a strong shearing effect on the base resin of the cable material, affecting the cross-linking and mechanical properties of the final cable material product. Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a polyethylene cable insulation material that is resistant to scorching and has extremely low impurity content (high cleanliness).

[0009] To achieve the above objectives, a first aspect of the present invention provides a method for preparing polyethylene cable insulation material, the method comprising:

[0010] (1) Under the condition that the number of dust particles with a diameter ≥ 0.5 μm in each cubic meter of air is less than 40,000 and the number of dust particles with a diameter > 5 μm is less than 500, antioxidants, anti-scorching agents and low-density polyethylene are blended and extruded by gravity metering and then water-cooled and pelletized to obtain pellets with an average particle size of 1-5 mm.

[0011] (2) The granules are preheated by gravity metering and then mixed and impregnated with peroxide in sequence;

[0012] The antioxidant is selected from at least one of 4,4′-thiobis(6-tert-butyl-3-methylphenol), 2,2′-thiobis(6-tert-butyl-4-methylphenol), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and tris(2,4-di-tert-butylphenyl)phosphite;

[0013] The anti-scorching agent is 1,1-diphenylethylene and / or 2,4-diphenyl-4-methyl-1-pentene;

[0014] The density of the low-density polyethylene is 0.900-0.950 g / cm³. 3 The melt index is 1.5-3 g / 10 min, and the molecular weight distribution is 5-7.

[0015] The weight ratio of the low-density polyethylene, the antioxidant, the anti-scorching agent, and the peroxide is 100:0.05-1:0.1-3:1.6-2.8.

[0016] A second aspect of the present invention provides a polyethylene cable insulation material prepared by the method described in the first aspect above.

[0017] This invention improves the post-absorption process for producing polyethylene cable insulation materials, enabling the entire production process to be carried out under clean and enclosed conditions. At the same time, all materials are transported by gravity, which avoids dust generated by external forces and material friction, effectively reducing the introduction of impurities. In addition, anti-scorching additives are added to the materials along with other additives to obtain a polyethylene cable insulation material that is resistant to scorching and has high cleanliness.

[0018] When using the polyethylene cable insulation material prepared by the method provided by this invention to produce cables, the production cycle can reach more than 10 days when the production extrusion volume is 120-150 tons / day, the filter screen does not scorch, and the cables prepared have a wider range of applications. Detailed Implementation

[0019] 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.

[0020] In this invention, the molecular weight distribution is obtained using gel permeation chromatography (GPC).

[0021] As previously described, a first aspect of the present invention provides a method for preparing polyethylene cable insulation material, the method comprising:

[0022] (1) Under the condition that the number of dust particles with a diameter ≥ 0.5 μm in each cubic meter of air is less than 40,000 and the number of dust particles with a diameter > 5 μm is less than 500, antioxidants, anti-scorching agents and low-density polyethylene are blended and extruded by gravity metering and then water-cooled and pelletized to obtain pellets with an average particle size of 1-5 mm.

[0023] (2) The granules are preheated by gravity metering and then mixed and impregnated with peroxide in sequence;

[0024] The antioxidant is selected from at least one of the following: 4,4′-thiobis(6-tert-butyl-3-methylphenol) (antioxidant 300), 2,2′-thiobis(6-tert-butyl-4-methylphenol) (antioxidant 2246S), 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 tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168);

[0025] The anti-scorching agent is 1,1-diphenylethylene and / or 2,4-diphenyl-4-methyl-1-pentene;

[0026] The density of the low-density polyethylene is 0.900-0.950 g / cm³. 3 The melt index is 1.5-3 g / 10 min, and the molecular weight distribution is 5-7.

[0027] The weight ratio of the low-density polyethylene, the antioxidant, the anti-scorching agent, and the peroxide is 100:0.05-1:0.1-3:1.6-2.8.

[0028] In a preferred embodiment, the antioxidant is selected from at least one of 4,4′-thiobis(6-tert-butyl-3-methylphenol), 2,2′-thiobis(6-tert-butyl-4-methylphenol), and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0029] Preferably, in step (1), the number of dust particles with a diameter ≥ 0.5 μm in each cubic meter of air is less than 36,000.

[0030] In a preferred embodiment, in step (1), the number of dust particles with a diameter > 5 μm in each cubic meter of air is less than 300.

[0031] Preferably, in step (1), the density of the low-density polyethylene is 0.910-0.930 g / cm³. 3 The melt index is 1.8-2.5 g / 10 min, and the molecular weight distribution is 5.5-6.5.

[0032] Preferably, in step (1), the average particle size of the granules is 2-3 mm.

[0033] In a preferred embodiment, in step (2), the peroxide is selected from at least one of the following: tert-butyl peroxyisopropyl carbonate, tert-butyl perlaurate, tert-butyl peracetic acid, tert-butyl peroxybenzoate, tert-butyl perphthalate, 2,5-dimethyl-2,5-bis(benzoyl peroxide)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane, dicumyl peroxide, tert-butyl cumyl peroxide, and tert-butyl hydroperoxide.

[0034] Preferably, in step (1), the anti-scorching agent is a combination of 1,1-diphenylethylene and 2,4-diphenyl-4-methyl-1-pentene in a weight ratio of 0.1-3:1. The inventors of this invention have discovered that the polyethylene cable insulation material obtained under this preferred condition possesses good scorching resistance and high cleanliness, while also exhibiting better mechanical properties.

[0035] More preferably, in step (1), the anti-scorching agent is a combination of 1,1-diphenylethylene and 2,4-diphenyl-4-methyl-1-pentene in a weight ratio of 0.1-1:1.

[0036] Preferably, the weight ratio of the low-density polyethylene, the antioxidant, the anti-scorching agent and the peroxide is 100:0.05-0.5:0.1-2:1.8-2.2.

[0037] According to a preferred embodiment, in step (1), the conditions for the blend extrusion include: being carried out in a screw extruder at a temperature of 150-230°C and a screw speed of 150-500 rpm. More preferably, in step (1), the conditions for the blend extrusion include: being carried out in a screw extruder at a temperature of 150-200°C and a screw speed of 150-350 rpm.

[0038] According to another preferred embodiment, in step (1), the conditions for water-cooled pelletizing include a temperature of 3-10°C.

[0039] Preferably, in step (2), the preheating conditions include a temperature of 40-85°C and a time of 1-35 hours. More preferably, in step (2), the preheating conditions include a temperature of 45-80°C and a time of 10-30 hours.

[0040] In a preferred embodiment, in step (2), the mixing conditions include: mixing under stirring conditions, a temperature of 40-80°C, and a time of 10-50 min.

[0041] According to a preferred embodiment, the granules are conveyed through a closed pipeline containing deionized water and then centrifugally dried.

[0042] It should be noted that the present invention does not impose any particular restrictions on the conditions for centrifugal drying, as long as the surface of the granules is free of moisture.

[0043] Preferably, in step (2), the immersion conditions include a temperature of 40-80°C and a time of 8-30 hours. More preferably, in step (2), the immersion conditions include a temperature of 50-70°C and a time of 8-24 hours.

[0044] As previously stated, a second aspect of the present invention provides a polyethylene cable insulation material prepared by the method described in the first aspect.

[0045] The present invention will be described in detail below through examples.

[0046] In the following examples, unless otherwise specified, all raw materials used were commercially purchased.

[0047] In the following examples, unless otherwise specified, the amount of low-density polyethylene used is 30 kg.

[0048] raw material:

[0049] Low-density polyethylene

[0050] Low-density polyethylene I: Grade: 9202, density: 0.922 g / cm³ 3 The melt flow index was 2.2 g / 10 min, and the molecular weight distribution was 6; it was purchased from Yanshan Petrochemical Company.

[0051] antioxidants

[0052] Antioxidant I: Antioxidant 300;

[0053] Antioxidant II: Antioxidant 1010;

[0054] Antioxidant III: Antioxidant 1076 + 168 are compounded at a weight ratio of 1:0.5;

[0055] Anti-scorching agent

[0056] Anti-scorching agent I: 1,1-diphenylethylene;

[0057] Anti-scorch agent II: 2,4-diphenyl-4-methyl-1-pentene;

[0058] Anti-scorching agent III: Hydroquinone;

[0059] Peroxide: Dicumyl peroxide (DCP)

[0060] Example 1

[0061] (1) Under the condition that the number of dust particles with a diameter ≥ 0.5 μm in each cubic meter of air is less than 35200 and the number of dust particles with a diameter > 5 μm is less than 293, antioxidant I, anti-scorching agent I and low-density polyethylene are blended and extruded by gravity metering and then water-cooled and pelletized to obtain granules with uniform particle size.

[0062] The conditions for blend extrusion are as follows: it is carried out in a twin-screw extruder with a feeding section temperature of 155°C, a melting section temperature of 170°C, a shearing temperature of 175°C, a die nozzle temperature of 175°C, and a screw speed of 350 rpm.

[0063] The conditions for water-cooled pelletizing are: temperature 5℃;

[0064] (2) The granules are transported through a closed pipeline containing deionized water and centrifugally dried until the surface of the granules is free of moisture.

[0065] Then, the dried granules were preheated by gravity metering and then mixed and impregnated with peroxide in sequence to prepare polyethylene cable insulation material C1.

[0066] The weight ratio of low-density polyethylene, antioxidant, anti-scorching agent and peroxide is 100:0.2:0.2:2;

[0067] The preheating conditions are: temperature 70℃, time 10h;

[0068] The mixing conditions were: mixing under stirring conditions, at a temperature of 70°C, for a time of 40 minutes;

[0069] The soaking conditions were: temperature 70℃ and time 18h.

[0070] Example 2

[0071] This embodiment uses a method similar to that of Embodiment 1, except that:

[0072] Antioxidant I was replaced by antioxidant II by weight, and the amount of anti-scorching agent was adjusted so that the weight ratio of low-density polyethylene, antioxidant, anti-scorching agent and peroxide was 100:0.2:0.17:2; all other conditions were the same as in Example 1, and polyethylene cable insulation material C2 was prepared.

[0073] Example 3

[0074] This embodiment uses a method similar to that of Embodiment 1, except that:

[0075] Replace anti-scorching agent I by weight with a combination of anti-scorching agent I and anti-scorching agent II in a weight ratio of 2:1;

[0076] All other conditions were the same as in Example 1, and polyethylene cable insulation material C3 was prepared.

[0077] Example 4

[0078] This embodiment uses a method similar to that of Embodiment 1, except that:

[0079] Replace antioxidant I with antioxidant III by weight;

[0080] All other conditions were the same as in Example 1, and polyethylene cable insulation material C4 was prepared.

[0081] Example 5

[0082] This embodiment uses a method similar to that of Embodiment 1, except that:

[0083] Replace antioxidant I with antioxidant III by weight and adjust the soaking time to 24 hours;

[0084] All other conditions were the same as in Example 1, and polyethylene cable insulation material C5 was prepared.

[0085] Comparative Example 1

[0086] This comparative example was conducted using a method similar to that of Example 1, except that:

[0087] The amount of peroxide and the impregnation time were adjusted to 24 hours, so that the weight ratio of low-density polyethylene, antioxidant, anti-scorching agent and peroxide was 100:0.2:0.2:1.5; all other conditions were the same as in Example 1, and polyethylene cable insulation material DC1 was prepared.

[0088] Comparative Example 2

[0089] This comparative example was conducted using a method similar to that of Example 1, except that:

[0090] Replace anti-scorching agent I with anti-scorching agent III by weight, and adjust the impregnation time to 30h;

[0091] All other conditions were the same as in Example 1, and polyethylene cable insulation material DC2 was prepared.

[0092] Comparative Example 3

[0093] This comparative example was conducted using a method similar to that of Example 1, except that:

[0094] Anti-scorching agent I is not used;

[0095] All other conditions were the same as in Example 1, and polyethylene cable insulation material DC3 was prepared.

[0096] Comparative Example 4

[0097] This comparative example was conducted using a method similar to that of Example 1, except that:

[0098] The amount of peroxide and the impregnation time were adjusted to 30 hours, so that the weight ratio of low-density polyethylene, antioxidant, anti-scorching agent and peroxide was 100:0.2:0.2:3; all other conditions were the same as in Example 1, and polyethylene cable insulation material DC4 was prepared.

[0099] Comparative Example 5

[0100] This comparative example was conducted using a method similar to that of Example 4, except that:

[0101] The amount of peroxide was adjusted so that the weight ratio of low-density polyethylene, antioxidant, anti-scorching agent and peroxide was 100:0.2:0.2:3; all other conditions were the same as in Example 1, and polyethylene cable insulation material DC5 was prepared.

[0102] Test case

[0103] The polyethylene cable insulation materials prepared in the examples and comparative examples were subjected to the performance tests shown in Table 1, and the test results are shown in Table 2.

[0104] Table 1

[0105]

[0106] Table 2

[0107]

[0108] Continued from Table 2

[0109]

[0110]

[0111] As shown in Table 2, the method provided by this invention can produce polyethylene cable insulation materials with high scorch resistance and cleanliness. Furthermore, the ultra-high voltage polyethylene cables (110KV and above) produced using the polyethylene cable insulation material provided by this invention exhibit stable performance and longer scorch resistance. Therefore, the polyethylene cable insulation material provided by this invention is suitable for the production of long-cycle cables.

[0112] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing polyethylene cable insulation material, characterized in that, The method includes: (1) Under the condition that the number of dust particles with a diameter ≥ 0.5 μm in each cubic meter of air is less than 40,000 and the number of dust particles with a diameter > 5 μm is less than 500, antioxidants, anti-scorching agents and low-density polyethylene are blended and extruded by gravity metering and then water-cooled and pelletized to obtain pellets with an average particle size of 1-5 mm. (2) The granules are preheated by gravity metering and then mixed and impregnated with peroxide in sequence; The antioxidant is selected from at least one of 4,4'-thiobis(6-tert-butyl-3-methylphenol), 2,2'-thiobis(6-tert-butyl-4-methylphenol), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and tris(2,4-di-tert-butylphenyl)phosphite; The anti-scorching agent is a combination of 1,1-diphenylethylene and 2,4-diphenyl-4-methyl-1-pentene in a weight ratio of 0.1-3:

1. The density of the low-density polyethylene is 0.900-0.950 g / cm³. 3 The melt index is 1.5-3 g / 10 min, and the molecular weight distribution is 5-7. The weight ratio of the low-density polyethylene, the antioxidant, the anti-scorching agent, and the peroxide is 100:0.05-1:0.1-3:1.6-2.

8.

2. The method according to claim 1, wherein, In step (1), the number of dust particles with a diameter ≥ 0.5 μm in each cubic meter of air is less than 36,000; and / or, In step (1), the number of dust particles with a diameter > 5 μm in each cubic meter of air is less than 300.

3. The method according to claim 1 or 2, wherein, In step (1), the density of the low-density polyethylene is 0.910-0.930 g / cm³. 3 Melt index of 1.8-2.5 g / 10 min, molecular weight distribution of 5.5-6.5; and / or, In step (1), the average particle size of the granules is 2-3 mm.

4. The method according to claim 1 or 2, wherein, In step (2), the peroxide is selected from at least one of the following: tert-butyl peroxyisopropyl carbonate, tert-butyl peroxylaurate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxyphthalate, 2,5-dimethyl-2,5-bis(benzoyl peroxide)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumyl peroxide, tert-butyl cumyl peroxide, and tert-butyl hydroperoxide.

5. The method according to claim 1 or 2, wherein, The weight ratio of the low-density polyethylene, the antioxidant, the anti-scorching agent, and the peroxide is 100:0.05-0.5:0.1-2:1.8-2.

2.

6. The method according to claim 1 or 2, wherein, In step (1), the conditions for the co-extrusion include: being carried out in a screw extruder at a temperature of 150-230°C and a screw speed of 150-500 rpm; and / or, In step (1), the conditions for water-cooled pelletizing include a temperature of 3-10℃.

7. The method according to claim 1 or 2, wherein, In step (2), the preheating conditions include: temperature 40-80℃ and time 1-35h.

8. The method according to claim 1 or 2, wherein, In step (2), the mixing conditions include: mixing under stirring conditions, at a temperature of 40-80°C, for a time of 10-50 min; and / or, In step (2), the conditions for immersion include: a temperature of 40-80°C and a time of 10-30 hours.

9. A polyethylene cable insulation material prepared by the method according to any one of claims 1-8.

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