27.5 kV-grade thermoplastic polypropylene cable material for electrified railway and preparation method of 27.5 kV-grade thermoplastic polypropylene cable material

Abstract

The invention provides a 27.5 kV-grade thermoplastic polypropylene cable material for an electrified railway and a preparation method of the 27.5 kV-grade thermoplastic polypropylene cable material, and belongs to the technical field of cable insulating materials. Comprising the following components: 50-60% of modified polypropylene; 15-20% of ethylene propylene rubber; 10 to 12% of polyethylene; 5%-6% of mica powder; 1-2.3% of an antioxidant; 2 to 3 percent of glass fiber and 0.1 to 0.3 percent of rare earth. The prepared modified polypropylene insulating material has more excellent high temperature resistance, thermal shock resistance and water tree resistance, has the advantage of being more environmentally friendly and low temperature resistance compared with an XLPE cable material, and is more suitable for the field of electrified railways.

Description

Technical Field

[0001] The invention relates to a 27.5 kV-grade thermoplastic polypropylene cable material for electrified railways and a preparation method thereof, belonging to the technical field of cable insulation materials. Background Art

[0002] With the rapid development of electrified railways, the performance requirements for cables are getting higher and higher. At present, cross-linked polyethylene (XLPE) is commonly used as the insulation material for electrified railway cables.

[0003] Although traditional XLPE materials meet the use requirements to a certain extent, they are still insufficient in terms of environmental protection, weather resistance, heat resistance, etc.: cross-linked polyethylene is a thermosetting polymer, and the cross-linking and degassing process in the manufacturing process consumes high energy and produces carbon emissions. After the cable is retired, the insulation cannot be recycled and reused. Incineration, cracking, landfill and other treatment methods not only consume a lot of energy, but also have a great negative impact on the environment.

[0004] Under the national "dual carbon" background, XLPE insulated cables can no longer meet the needs of green and sustainable contemporary social and economic development. The development of thermoplastic insulation materials that can replace XLPE insulation is an important direction for the development of cable insulation.

[0005] Compared with XLPE cables, polypropylene cables are not only environmentally friendly and recyclable after retirement, but also have many advantages in manufacturing and application: for example, in cable manufacturing, the energy consumption of the cross-linking process and the degassing process can be greatly reduced; there is no need for a degassing process, and there are fewer by-product impurities inside the insulation; polypropylene materials are cheap, and the production of cables has cost advantages, etc.

[0006] At present, there is no thermoplastic polypropylene cable product with a voltage level of 27.5 kV on the market. Therefore, the art is in urgent need of a 27.5 kV grade thermoplastic polypropylene cable material for electrified railways and a preparation method thereof. Summary of the invention

[0007] The purpose of the present invention is to solve the problem that thermoplastic polypropylene cable products with a voltage level of 27.5 kV have not yet appeared in the market in the prior art.

[0008] In order to achieve the purpose of solving the above-mentioned problems, the technical solution adopted by the present invention is to provide a 27.5kV grade thermoplastic polypropylene cable material for electrified railways and a preparation method thereof.

[0009] The first aspect of the present invention provides a 27.5 kV grade thermoplastic polypropylene cable material for electrified railways, comprising the following components:

[0010] Modified polypropylene 50-60%; EPDM 15-20%; Polyethylene 10-12%; Mica powder 5%-6%; Antioxidant 1-2.3%; Glass fiber 2%-3%, Rare earth 0.1%-0.3%;

[0011] The percentages of the various substances are by mass. The modified polypropylene is an ethylene-propylene block copolymer structure, and its chemical structure is as follows: Figure 3 shown.

[0012] The second aspect of the present invention provides a method for preparing the above-mentioned 27.5kV grade thermoplastic polypropylene cable material for electrified railways, comprising the following steps: weighing the components according to mass ratio, drying and mixing the materials uniformly, and then feeding the mixed materials into a feeding hopper of a twin-screw extruder, and subjecting the materials to high-speed shearing, extrusion, stranding, cooling and granulation by the twin-screw.

[0013] During the mixing process, polypropylene and EPDM are melt-blended. EPDM can induce silver streaks and shear bands after being subjected to external forces, absorbing part of the energy generated by external force impact, thereby converting the brittle fracture of polypropylene caused by external force impact into tough fracture, improving the toughness of polypropylene and reducing the elastic modulus of PP. At the same time, the polyethylene structure is introduced into the main chain of polypropylene to form Figure 2 The ethylene-propylene block copolymer structure shown reduces or destroys the continuous chain structure of polypropylene, hinders the crystalline arrangement of polymer molecules, thereby reducing the crystallinity of polypropylene and further improving the toughness.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The modified polypropylene insulation material prepared by the present invention has better high temperature resistance, heat shock resistance and water tree resistance, and has the advantages of being more environmentally friendly and having low temperature resistance than XLPE cable materials, and is more suitable for the field of electrified railways. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the microscopic phase model of modified polypropylene in this application;

[0017] Figure 2 Schematic diagram of the ethylene-propylene block copolymer structure of the modified polypropylene in this application;

[0018] Figure 3 This is the infrared spectrum of the modified polypropylene in this application. DETAILED DESCRIPTION

[0019] In order to make the present invention more clearly understood, a preferred embodiment is described in detail with reference to the accompanying drawings as follows:

[0020] like Figure 1-3As shown, the present invention provides a 27.5 kV grade thermoplastic polypropylene cable material for electrified railway and a preparation method thereof.

[0021] Example 1

[0022] Weigh 50-60% modified polypropylene, 15-20% ethylene-propylene rubber, 10-12% polyethylene, 5%-6% mica powder, 1-2.3% antioxidant, 2%-3% glass fiber, and 0.1%-0.3% rare earth according to mass ratio, and bake and mix the materials evenly. Then, feed the mixed materials into the feeding hopper of the twin-screw extruder, and through high-speed shearing, extrusion, drawing, cooling, and granulation of the twin-screw, 27.5kV grade thermoplastic polypropylene cable material for electrified railways is obtained.

[0023] According to the cable industry standard, the temperature resistance level of the cable is divided into 90℃, 105℃, 125℃ and 150℃. The evaluation method of the temperature resistance level of the cable is: the material is subjected to aging test at different temperatures, and the change rate of elongation at break is 50% as the end point of aging, and the aging days of the material at different temperatures are obtained. Then, the aging days and aging temperature are linearly correlated by linear regression to obtain a linear relationship curve. Then, the maximum operating temperature is determined according to the life of the cable.

[0024] The aging temperature requirement for the corresponding XLPE insulation material in IEC 60502-1:2004 is 135°C and the time is 168h. If the thermal aging test is passed, it can be considered that the long-term maximum operating temperature of the material is 90°C.

[0025] In T / CEEIA591-2022 "Thermoplastic Polypropylene Insulated Power Cable with Rated Voltage 6kV (Um=7.2kV) to 35kV (Um=40.5kV)", the corresponding aging temperature requirement for polypropylene insulation material is 150℃ and the time is 168h. If the heat aging test is passed, it can be considered that the long-term maximum operating temperature of the material is 105℃.

[0026] Results of thermal aging test: The insulation layer of the modified polypropylene cable in the invention was sampled and placed in a thermal aging box at 150°C for 168 hours. The insulating material maintained a good shape at high temperature. The change rate of tensile strength before and after insulation aging was +10%, and the change rate of elongation at break before and after insulation aging was -1%, both of which met the "less than or equal to 25%" requirement in the T / CEEIA591-2022 standard, and the thermal aging test performance was qualified.

[0027] The material test performance indicators prove that the polypropylene has been modified. Compared with pure polypropylene, the notched impact strength of the modified polypropylene insulation material in the invention is increased from 4kJ / m 2 Increase to 10kJ / m 2The flexural modulus increased from 600MPa to 1200MPa, and the tensile yield stress increased from 20MPa to 16MPa, indicating that the toughness of the modified polypropylene is significantly improved, the flexibility is increased, and the mechanical properties are greatly improved.

[0028] During the mixing process, polypropylene and EPDM are melt-blended. EPDM can induce silver streaks and shear bands after being subjected to external forces, absorbing part of the energy generated by external force impact, thereby converting the brittle fracture of polypropylene caused by external force impact into tough fracture, improving the toughness of polypropylene and reducing the elastic modulus of PP. At the same time, the polyethylene structure is introduced into the main chain of polypropylene to form Figure 2 The ethylene-propylene block copolymer structure shown reduces or destroys the continuous chain structure of polypropylene, hinders the crystalline arrangement of polymer molecules, thereby reducing the crystallinity of polypropylene and further improving the toughness.

[0029] Figure 3 This is the infrared spectrum of 27.5kV polypropylene insulation material. It can be seen from the figure that the polypropylene insulation material has obvious PE characteristic peaks at 719cm-1 and 729cm-1, indicating that there are some relatively long PE segments introduced by copolymerization modification in the modified PP, proving that the material has formed an ethylene-propylene block copolymer structure and the modification is successful.

[0030] Comparative Example 1

[0031] The cross-linked polyethylene (XLPE) insulation material can only pass the 135°C, 168h heat aging test in the heat aging test, but cannot pass the 150°C, 168h heat aging test. In the 150°C, 168h heat aging test, the cross-linked polyethylene insulation layer samples are severely deformed, and the change rate of tensile strength before and after insulation aging and the change rate of elongation at break before and after insulation aging are greater than 50%, which does not meet the requirements.

[0032] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and equivalent changes made by using the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A 27.5kV grade thermoplastic polypropylene cable material for electrified railways, characterized in that: Includes the following components: Modified polypropylene 50-60%; EPDM 15-20%; Polyethylene 10-12%%; Mica powder 5%-6%; antioxidant 1-2.3%; glass fiber 2%-3%, rare earth 0.1%-0.3%; The percentages of various substances are by mass, and the modified polypropylene is an ethylene-propylene block copolymer structure.

2. A method for preparing a 27.5 kV grade thermoplastic polypropylene cable material for electrified railways as claimed in claim 1, characterized in that: The method comprises the following steps: weighing the components according to the mass ratio, drying the materials and mixing them evenly, and then feeding the mixed materials into the feeding hopper of the twin-screw extruder, and then undergoing high-speed shearing, extrusion, stranding, cooling and granulation by the twin-screw.

Images