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Common insulation materials and main properties of flame retardant cables
The performance of the flame retardant cable is determined by the oxygen index of the material used. The higher the oxygen index, the better the flame retardant performance of the flame retardant cable. However, at the same time, some other properties are lost, which increases the difficulty of operation and the cost of materials.
The flame retardant cable must pass the standard clock C test requirements to require the oxygen index of the insulation material to reach 30, and if it is required to reach the B and A sheath materials and fillers, use flame retardant materials.
Flame retardant cables are mainly made of halogen-free flame retardant materials and halogen-containing flame retardant materials.
1.Halogen-free flame retardant materials
Polyolefin is a halogen-free material. It is composed of hydrocarbons. It decomposes carbon dioxide and water during combustion without producing significant smoke and harmful gases. Polyolefins mainly include polyethylene (PE) and ethylene acetate polymer (E-VA). These materials are not flame retardant by themselves, and inorganic flame retardants and phosphorus flame retardants need to be added to be processed into practical halogen-free flame retardant materials. However, due to the lack of polar groups on the molecular chain of non-polar substances It is hydrophobic and has poor affinity with inorganic flame retardants, making it difficult to bond firmly. In order to improve the surface activity of polyolefins, surfactants can be added to the formula; or polymers containing polar groups are blended in the polyolefins to blend, thereby increasing the amount of flame retardant fillers, improving the mechanical properties of the materials and Processing performance, while obtaining better flame retardancy.
2.Low-smoke, low-halogen flame retardant materials
Mainly for polyvinyl chloride and chlorosulfonated polyethylene. Add CaCO3 and A (lOH) 3 to the polyvinyl chloride formulation. Zinc borate and MoO3 can reduce the HCL release and smoke generation of flame retardant polyvinyl chloride, thereby improving the flame retardancy of the material and reducing the emissions of halogen, acid mist and smoke, but it may cause the oxygen index to decrease slightly. When the amount of additives is large, the mechanical and electrical properties of the material will also be reduced.
3.Halogen-containing flame retardant materials
Due to the liberation of hydrogen halides during combustion and heating, hydrogen halides can capture the active radical HO radicals, thereby delaying or extinguishing the combustion of the material and achieving the purpose of flame retardancy. Commonly used materials are polyvinyl chloride, neoprene, chlorosulfonated polyethylene, and ethylene-propylene rubber.
(1) Flame retardant polyvinyl chloride (PVC): Because PVC is cheap, has good insulation properties, and good flame retardancy, it is widely used in ordinary flame retardant wires and cables. In order to improve the flame retardancy of PVC, halogen flame retardant (decabromodiphenyl ether), chlorinated paraffin and synergistic flame retardant are often added to the formula to improve the flame retardancy of polyvinyl chloride.
(2) Ethylene-propylene rubber (EPDM): It is a non-polar hydrocarbon. It has excellent electrical properties, high insulation resistance, and low dielectric loss. However, ethylene-propylene rubber is a flammable material. The degree of cross-linking of ethylene-propylene rubber must be reduced. Only by reducing the molecular weight of the low-molecular-weight substances produced by the molecular chain disconnection can the flame retardancy of the material be improved. As the degree of crosslinking of ethylene-propylene rubber increases, the oxygen index increases. For example, DC (P-cumene peroxide), TAIC (triacryl cyanurate), and HVA (2N, N m-phenylene bismarimide) can be added to the formulation. Increase the oxygen index by 10 to 15.
In another method, adding an inorganic flame retardant filler to ethylene-propylene rubber can also increase the oxygen index. Commonly used fillers are A (lOH) 3, which can release crystal water at high temperatures and absorb a large amount of heat to achieve a flame retardant effect. However, adding a large amount of filler will reduce the mechanical and electrical properties of the material (such as reduced tensile strength and elongation). Therefore, the filler cannot exceed 150 parts. In order to obtain better flame retardant properties and maintain high mechanical properties, it is necessary to appropriately reduce the flame retardant filler and appropriately add other flame retardants.