Materials for wires and cables can be divided into conductive materials, insulating materials, protective layer materials, shielding materials, filling materials, etc. according to their use parts and functions. According to material properties, it can be divided into metals (copper, aluminum, aluminum alloy, steel), plastics (PVC, PE, PP, XLPE/XL-PVC, PU, TPE/PO), rubber, etc.
1、 Polyvinyl chloride (PVC)
PVC is generally used as insulation and protective layer material. PVC is used as wire and cable insulation, which is not easy to burn, aging resistant, oil resistant, chemical resistant, impact resistant and easy to color; However, due to the large dielectric constant, it is generally only used as the insulating material of low-voltage cables and control cables.
The performance of PVC as the sheath of wires and cables: it has good wear resistance, can resist oil, acid, alkali, bacteria, moisture and sunlight, and has self extinguishing performance on the role of flame; The minimum working temperature of PVC sheath is -40 ℃, and the high temperature resistance can reach 105 ℃.
2、 Polyethylene (PE)
General physical properties of PE: white wax, translucent, soft and tough, slightly elongated, lighter than water, non-toxic: combustion characteristics: flammable, continue to burn after leaving the fire, the upper end of the flame is yellow and the lower end is blue, melting and dripping when burning, giving off the smell of paraffin burning; The melting point range of polyethylene processing is 132~135 ℃, the ignition temperature is 340 ℃, and the spontaneous combustion temperature is 390 ℃.Polyethylene (PE) is generally divided into LDPE, MDPE, HDPE and FMPE.
LDPE: low density polyethylene is the lightest kind of polyethylene series, also known as low-pressure polyethylene. Its structural characteristics are nonlinear. It has low crystallinity and softening point, good flexibility, elongation, electrical insulation, transparency, and high impact strength. Low density polyethylene has poor mechanical strength and low heat resistance. In addition, an obvious weakness is its poor resistance to environmental stress cracking.
MDPE: medium density polyethylene, also known as medium pressure polyethylene and Philip polyethylene, its performance is similar to that of high density polyethylene.
HDPE: compared with low-density polyethylene, high-density polyethylene, also known as high-pressure polyethylene, has excellent comprehensive properties, such as improving heat resistance and mechanical strength (such as tensile length, bending strength, compression strength, shear strength), and improving the barrier performance against water vapor and gas. It has superior environmental stress cracking resistance.
FMPE: foamed PE is the most widely used foam material. The dielectric constant of chemically foamed foam polyethylene can be reduced to about 1.55. If a new process of physical foaming is adopted, that is, inert gas (nitrogen or air) is injected into molten polyethylene during extrusion to foam, foam polyethylene with small bubble size can be prepared. The foaming degree can be controlled between 35-40%, and more than 40% can be achieved. Its dielectric constant can be reduced to about 1.20. Moreover, due to the absence of chemical foaming agent, the insulation does not contain foaming agent residue, and the dielectric loss can be greatly reduced, The loss has reached the level of air insulation.
3、 Ethylene vinyl acetate copolymer (EVA)
EVA is a kind of thermoplastic with rubber like elasticity. Its performance is closely related to the content of vinyl acetate (VA): the smaller VA is, the more it looks like high-pressure polyethylene, while the more VA is, the more it looks like rubber. EVA Nuo high-pressure polyethylene with low VA content is soft and has good impact strength. It is suitable for making composite materials.
EVA has good elasticity, low-temperature flexibility, chemical resistance and weather resistance. When used together with LDPE, it can improve the environmental cracking resistance, impact resistance, soft hardness and the adhesion between conductor and insulation of LDPE.
4.Tetrapolypropylene (PP)
Polypropylene has a specific gravity of 0.89-0.91, which is the smallest of commonly used plastics at present. It has excellent mechanical strength, the highest softening temperature among thermoplastic resins, and good low temperature resistance and aging resistance; The optical rotation resistance is only slightly poor, but it can be improved by adding stabilizer through copolymerization.
