Development of wire and cable flame retardant and flame retardancy Technology

With the accelerating pace of economic construction, the number of large-scale industrial facilities, high-rise commercial buildings, underground buildings and residential buildings is increasing. The total use of cables is bigger and bigger, and the density of laying is also higher. Electric fire accidents caused by short circuit and spontaneous combustion caused by cable aging are more and more frequent, and the loss is becoming more and more serious. This has made people realize that in addition to enhancing awareness of fire safety, strict standards should also be worked out, and all kinds of flame retardant materials for cables should be widely applied to create various kinds of flame-retardant and flame retardant cables.

The design and materials of cable structure has great influence on the fire performance of cable, such as metal clad layer can effectively prevent the cable fire; polyvinyl chloride (PVC), low smoke halogen-free and low smoke (LSZH) have spread and toxic smoke materials, high temperature materials can control the flame. The rational selection of cable flame retardant is one of the key measures to improve the safety performance of cable and reduce the hidden danger of fire.

Two: the flame retardancy mechanism of cable materials

The cable flame retardant material increases the flame retardant components in the system with the matrix polymer (or resin) as the main body, adding plasticizers, heat stabilizers, lubricants, antioxidants, anti ultraviolet agents and so on, so as to prevent the material from being ignited and suppressing the flame propagation.

(1): the combustion behavior and flame retardancy of cable materials

The combustion behavior of cable materials

The combustion behavior of the cable material can be described by the following performance parameters: (1) the difficulty of the ignition of the material. It can be defined by the critical oxygen index (cOI) or the limit oxygen index (LOI). The higher the value, the more difficult the ignition of the material and the spread of the flame are. Usually, COI = 30%, LOI = 23% combustible; flame retardant; LOI in 24% ~ 28% between a flame retardant; LOI in 29% ~ 35% LOI more than 36% high flame retardant. (2) the speed of fire spreading on the surface of the material. (3) fire resistance, that is, the speed of burning through the material. (4) heat release rate (HRR). (5) the difficulty of extinguishing the fire. (6) smoking, including the amount of smoke, the speed of the smoke, and the composition of the smoke. (7) the composition, quantity and rate of production of the toxic gases produced.

Flame retardancy of cable materials

Flame retardant cable materials by chemical or physical methods, change the structure of the polymer, in order to achieve the effect of flame retardant, such as polymer molecules added plays a flame retardant effect of elements, such as bromine, chlorine, phosphorus, antimony, boron; chemical crosslinking or irradiation crosslinking, the linear polymer molecule has become three dimensional mesh and body structure, improve its thermal stability and char yield. Flame retardants can also be added to the matrix polymers. When burning, the flame-retardant components will be flame retarded in different ways and mechanisms in different areas of polymer combustion. There are several ways for flame retardants to be flame-retardant.

(1) the gas phase flame retardancy, that is, in the gas phase, inhibits the free radical of the chain growth in the combustion reaction of the polymer, thus achieving the flame retardancy effect. The flame retardant capture the free radicals in the combustion reaction in the gaseous combustion area, thereby preventing the propagation of the flame, reducing the flame density of the combustion zone, and ultimately decreasing the burning reaction rate until the termination.

(2) the condensed phase flame retardant, that is, to prevent the thermal decomposition of the polymer in the solid phase and prevent the polymer from releasing the combustible gas, thus achieving the flame retardant effect. Flame retardants form glass melting material or foam carbon layer on the polymer surface at high temperature, blocking heat and oxygen and preventing flammable gases from escaping outward, so as to achieve the purpose of flame retardancy.

(3) the heat exchange is interrupted, the heat produced by the polymer is taken away and the polymer is not fed back to the polymer to break down the polymer continuously, thus the flame retardant effect is achieved. The flame retardant has a strong endothermic reaction at high temperature, absorbs part of the heat emitted from combustion, reduces the temperature of the combustible surface, effectively inhibits the formation of flammable gas and prevents the spread of combustion. Flame retardant heat release of combustible gas, the combustible gas will break out of fuel dilution, the combustible gas concentration is reduced to below the limit of combustion; no burning gas also reduces the oxygen concentration in the combustion zone, inhibiting burning continues to be flame retardant.

(4) carbon generation, i.e., the formation of carbon during thermal degradation of polymers, can reduce the production of volatiles, and the sticky carbon layer is covered on the polymer surface, so that polymers can be isolated from flame and make further thermal degradation difficult, and ultimately play a role of flame retardancy. In addition, the carbon layer can also prevent the thermal decomposition of the organism into the gas phase to participate in the combustion process. When the amount of carbon is increased by 1/3, the amount of tobacco is reduced by 1/2, and the flame retardant level of the material is UL94, V-0, and the carbon content should be at least 30%.

(5) synergistic effect, that is, the common effect of each component is greater than the individual effect of each component. The most typical synergistic effect is antimony. Halogen synergism, antimony oxide (commonly used form Sb:O). ) used with chlorinated or brominated flame retardants. In the gas phase, antimony oxide and halogen generated three antimony halide, three antimony halide flame inhibitor, it captures the flame of the H - and HO - free radicals, three antimony halide vapor can stay a long time in the combustion zone, dilute combustible gases, and covered on the surface of polymer and polymer insulation, reduce the decomposition temperature, decomposition rate, carbon formation of the polymer may be closed, prevent flammable gas escape.

There are also a number of antimony halide as a catalyst for coacervation and a catcher that acts as a free radical on the surface of the condensed phase. There are other synergistic effects, such as antimony oxide, non halogen synergistic effect, phosphorus and halogen synergistic effect, nitrogen one halogen synergistic effect, phosphorus and phosphorus synergism and so on.

Three: the selection principle and type of cable material flame retardant

The flame retardant is an additive to prevent the material to be ignited and to inhibit the further spread of the flame. The flame retardants can be divided into two kinds of reaction type and addition type. The reactive flame retardant is introduced into the polymer synthesis process, and the flame retardant is added to the resin, usually a composite flame retardant system.

(1) the principle of selection of flame retardant for cable material

(1) the flame retardants, flame-retardant filler and flame retardant synergist must have good compatibility with the matrix polymer.

(2) the more matching the thermal decomposition of the flame retardant and the matrix polymer, the higher the efficiency of the flame retardant, that is, the less flame retardant can achieve the same flame retardancy effect.

According to the theory and practice has proved a lot, only the flame retardant thermal decomposition curves are lower than the matrix polymer thermal decomposition curves, gas, flame retardant, thermal decomposition of debris material continuously surrounded in polymer matrix around the flame retardant function can effectively (Fig. 2); flame retardant and thermal decomposition curves comparing with the thermal decomposition of the polymer flame retardant effect of the best curve in the low of about 60~75 DEG C; also note that the decomposition temperature and substrate temperature of flame retardant polymer processing, and heat the gap.