Harmful substance content requirements. At present, the so-called ordinary environment-friendly wire and cable refers to the cables containing lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers within the scope of EU RoHS regulations. And the wire and cable must not contain environmental hormones and must not contaminate soil and water. Flame-retardant performance, environment-friendly flame-retardant wires and cables have good flame retardant performance. When encountering flames and fire sources, they can prevent the rapid spread and spread of flames, control them within a limited area, and minimize losses. Advanced environmental protection flame-retardant wire: refers to halogen-free environmentally-friendly flame-retardant wire, not only fully meets the requirements of ordinary environmental protection flame-retardant wire, but also does not contain halogen, and will not produce harmful gases and corrosive gases after combustion. According to the requirements of environmental protection, the flame-retardant type wire guarantees that the gas released during combustion has the characteristics of low smoke, halogen-free and low toxicity without deteriorating the flame-retardant rating. In case of fire, in order to ensure that all personnel have escape opportunities, the visual distance shall not be less than 15m, and the visible distance of certain environmentally friendly wire and cable when burning fumes may reach 97m, and the general cable is only 5-8m. Fire-retardant cable insulation is usually used. High-grade environmentally friendly conductors emit white smoke, mainly water vapor, and emit very little smoke.
The temperature rating increases and the current carrying capacity increases. General common PVC wire temperature rating is 70 °C, and environmental protection wire temperature is 105 °C, 125 °C, 150 °C, higher than the normal cable 30 °C ~ 60 °C. After relevant tests, the green wire with the same specification cross-section can be increased by more than 30% to 50% than the flow capacity of the ordinary wire, and the cross-linking degree can even be increased to more than 80%. Halogen-free environmentally friendly conductors are usually cross-linked products. In recent years, the cable industry has generally adopted the irradiation cross-linking process, and the molecular structure of polyolefin materials has been transformed from the original The linear structure is transformed into a mesh structure. This process can improve the operating temperature of the cable and the ability to resist instantaneous high current-carrying capacity in case of a short circuit, and greatly increase the temperature resistance level. Although the cost of advanced environmental protection flame-retardant wires has increased, but taking into account the increase of the current-carrying capacity, the high-quality environmental protection wires are more cost-effective, that is to say, the same current-carrying capacity, and the cost of the advanced environmental protection flame-retardant wires is lower.
So, what is the current state of development of environmentally friendly wire and cable?
In the 1980s, the world began to develop low-smoke halogen-free flame-retardant materials for wire and cable. The advantages of this material are low smoke and non-toxic. When burned by an open flame, metal oxides and water vapor are generated. The low-smoke halogen-free flame-retardant polyolefin is based on a halogen-free polyolefin, and a large amount of magnesium hydroxide or aluminum hydroxide activated by EVA (ethylene-vinyl acetate copolymer) is kneaded in a polyethylene matrix to utilize the hydroxide. When the material is heated and burned, it is decomposed into metal oxides and water to achieve the purpose of flame retardancy. The reaction formula is as follows:
Mg(OH)2→MgO+H2O Endothermic
2Al(OH)3→Al2O3+3H2O Endothermic
The low-smoke halogen-free flame-retardant polyolefin is flame-retarded by the method of heat absorption and metal oxide oxygen isolation. The flame-retardant mechanism is as follows: First, when the wire and cable are burned, the surface hydroxide is decomposed and the reaction is endothermic. The reaction absorbs a large amount of heat in the surrounding air and lowers the temperature of the wire and cable surface. The second is that the generated water molecules absorb a large amount of heat on the surface of the wire and cable, and the water vapor also blocks the oxygen. The third is the metal oxide produced. Encrusting prevents further contact between oxygen and organic matter.
Developed countries have developed halogen-free low-smoke cables in the 1980s and strongly recommend the use of such harmless wire and cable to replace and gradually dispose of toxic PVC wires and cables. This means that the toxicity of halogen-containing cables in the fire is terrible. If the toxicity index of a gas concentration that can cause death in 30 minutes is judged to be 1, then the toxicity index of polyvinyl chloride is 15.01. The halogen-free polyolefin has a toxicity index of 0.79. People can only survive for 2 minutes in the smoke of polyvinyl chloride, and instead of halogen-free materials, people's survival in their smoke can be extended to 40 minutes, which greatly increases the time of escape during a fire. In addition, according to the relevant materials, the light transmittance of the smoke emitted from the flame-retardant PVC cable is less than 15%. That is to say, if the person is in this concentration, the naked eye distance is about 2 meters. Therefore, in the fire, the highly diffused smoke confuses the victim and discerns the direction, prolongs the time spent in the fire, which leads to the further inhalation of smoke and toxic gases and suffocation.
In a large number of tests, it was found that the smoke density and halogen acid gas volatilization of gases released from the combustion of polyolefin-based materials and hydrated metal compounds Al(OH)3 or Mg(OH)3 as flame retardants can reach IEC standard requirements. Al(OH)3 or Mg(OH)2 is an inorganic hydroxide, which has excellent flame retardancy, low toxicity, smoke suppression, and low corrosion, and good smoke suppression, because smoke suppression and resistance Burning is equally important.
Developed countries have always attached great importance to the research, development, and application of low-smoke halogen-free flame-retardant wires and cables and related materials, especially in relatively close-to-construction or high-profile buildings and facilities such as high-rise buildings, subways, stations, airports, power stations, and shopping malls. In recent years, developed countries have restricted the use of lead, cadmium, and other heavy metals such as lead and cadmium, polybrominated biphenyls (PBB), and polybrominated diphenyl ethers (PBDE) in electrical and electronic equipment. The electronics and electronics giants in developed countries have established Their respective "green plans" to prohibit or restrict the use of heavy metals and halogens that are harmful to the human body and the environment, and have carried out a lot of research and development work, has launched a series of "green" electrical and electronic wires and cables. Some countries, such as Switzerland and Germany, strongly oppose the application of PVC, and have already established strict laws that will limit and eventually eliminate the use of PVC.
The development and use of low-smoke halogen-free flame-retardant wires and cables and related materials in China lags behind in developed countries for about 10 years. It was only after 2000 that it gradually got rid of the situation of relying entirely on imports. Now the performance of domestic low-smoke halogen-free flame-retardant wires and cables and related materials has been in compliance with national and international standards, but people's awareness of environmental protection and safety still needs to be improved, and products need to be vigorously promoted.