How Can Halogen-free Flame-retardant Reinforced PBT Improve Scorch Wire Performance?

How Can Halogen-free Flame-retardant Reinforced PBT Improve Scorch Wire Performance?

PBT materials are crystalline thermoplastic resins with excellent mechanical properties, excellent heat and chemical resistance, and strong electrical insulation, which can be widely used in a variety of electronic and electrical products such as automotive connectors, computers, AC/DC plugs, and transformer bobbins. However, in the field of electronic and electrical appliances, materials are often required to meet certain flame retardant safety evaluation. According to the analysis of the causes of electrical fires in recent years, and wires and other metals in direct contact with the plastic due to metal wire overload or short-circuit and a large number of exothermic ignition is the main cause of fires, so the International Electrotechnical Commission (IEC) on the unattended appliances to develop a flame retardant burning wire test requirements, the current national household electrical appliances 3C certification of unattended appliances for the current-carrying insulating material parts are also mandatory requirements for the performance of burning wire related. The current national 3C certification for household appliances also mandatorily requires the performance of burning wire for current-carrying insulating material components of unattended appliances. At present, the domestic requirements of UL94-V0 flame retardant reinforced PBT has been developed more mature. The traditional way for glass fiber (GF) + halogen flame retardant + antimony trioxide compounding system. But this system can not meet the GWIT, i.e., the requirement of no fire in the whole process within 30s of the application of scorching wire. Next, we will analyze the effects of BPS⁃Sb, halogen-free flame retardant and compound flame retardant on the mechanical properties of reinforced PBT and the scorch wire.

I. Effect of BPS-Sb content on mechanical and scorch wire properties of reinforced PBTs

Table 1 shows the reinforced PBT formulations with different BPS-Sb contents, and Table 2 compares the mechanical and flame retardant properties of reinforced PBTs with a GF content of 30% and different BPS-Sb flame retardant contents. It can be seen that, with the increase in the proportion of flame retardant additive, the system of the burning wire combustion index GWFI and UL 94 vertical combustion rating continues to improve, indicating that the BPS-Sb flame retardant system to cope with the burning wire combustion index GWFI and UL 94 this kind of direct combustion test flame retardant effect of the more efficient, this is because the GWFI and the same as the UL 94 are recorded in the case of withdrawal of the external heat source of the system of autonomous This is because, like UL 94, the GWFI records the extinguishing process of the system when the external heat source is removed.

In the GWIT test, with the increase of BPS-Sb flame retardant, the GWIT is not improved, comparing the 1 formula without flame retardant, we found that the simple halogen flame retardant system has a negative effect on the GWIT, this is because the GWIT record is the process of the external heat source, the whole system of brominated polystyrene is the most thermally unstable existence. Polystyrene is the existence of the worst thermal stability, PBT substrate onset of decomposition temperature of about 380℃, while the brominated polystyrene onset of decomposition temperature is only 310 ~ 330℃, the presence of flame retardants to accelerate the decomposition of the system, the decomposition products are mostly small molecules of low flash point material, so that the system at a much lower temperature by the scorch wire ignition.

II. Effect of different halogen-free flame retardants on the mechanical and scorch wire properties of reinforced PBTs

Table 3 shows the reinforced PBT formulations with different halogen-free flame retardant systems, and Table 4 compares the mechanical properties and flame retardant properties of reinforced PBT with glass fiber content of 30% and different halogen-free flame retardants, and it can be seen from the table that the degree of degradation of the mechanical properties of the material system by the halogen-free flame retardants ADP/MCA/MPP is greater than that of the BPS-Sb flame retardant, which is due to the fact that the halogen-free flame retardant is a small-molecule zwitterionic polymer, which is equivalent to a filler in the system, resulting in a serious loss of mechanical properties. This is because the non-halogenated flame retardants are mostly small molecule zwitterionic polymers with poor compatibility with the matrix resin, which are equivalent to fillers in the system, resulting in a serious loss of mechanical properties, while the brominated polystyrene is a high molecular resin with good compatibility with the system, and the overall mechanical properties are maintained at high levels.

Due to the surface activation treatment, the compatibility of KCP with the matrix resin is greatly improved compared with the conventional halogen-free flame retardants, making the mechanical properties comparable with the brominated polystyrene system. Table 4 flame retardant test results show that the flame retardant effect of a separate halogen-free flame retardant system in general, the burning wire ignition temperature of only ADP in the content of 20% reached 775℃, at this time, the burning wire combustion index is only 800℃, and IEC60335-1 unattended current-carrying parts of the appliance requirements for the GWIT> 850℃, the material's UL vertical combustion rating is only V-1, and the UL vertical combustion rating of the material. The GWIT and GWFI of GF reinforced PBT with 20 parts of MCA, KCP or MPP added are only 725°C and 750°C.

It can be determined that neither the antimony bromide flame retardant system nor the halogen-free flame retardant system, when used alone, can satisfy the relevant burning wire requirements for current-carrying parts of unattended electrical appliances of IEC60335-1.

III. Effect of different types of flame retardant compounding on the mechanical and burning wire properties of reinforced PBTs

Table 5 shows the reinforced PBT formulations with different types of flame retardant compounding, and the formulation design is based on the 4 formulation in Table 1, with equal amount of halogen-free flame retardant compounding.

As can be seen from Table 6, the introduction of phosphorus/nitrogen halogen-free flame retardants in the pure BPS-Sb flame retardant system, the flame retardant properties of the material have been significantly improved, and all the halogen-free flame retardants added 5kg, the material has reached GWIT>775℃, GWFI>850℃. Among them, KCP even reached GWIT>825℃, which is 50℃ higher than the 775℃ required for the scorch wire of current-carrying parts of unattended electrical appliances in EC60335-1. It shows that bromine -nitrogen, bromine-phosphorus, bromine-nitrogen-phosphorus in the system has produced a synergistic effect of flame retardant, the program for flame retardant burning wire test to improve the more obvious. Among them, the carbon-forming halogen-free flame retardant KCP is better compatible with the substrate after surface activation treatment, and the carbon-forming component has lower activation energy, faster start-up speed, and the carbon layer is formed firstly in the pre-combustion period and the carbon layer is more dense, and the carbon layer covers the surface of the combusted material to play a more obvious role in isolating the oxygen.

By adjusting the ratio of BPS-Sb and non-halogenated flame retardants, the effect of the change in the ratio of different types of flame retardants on the mechanical properties of the system and the scorch wire was observed, and the scheme is shown in Table 7.

Table 8 shows that when the proportion of KCP is fixed at 5%, a reduction in the proportion of BPS-Sb flame retardant leads to a decline in the material's flame retardant properties and scorch wire temperature. When the ratio of brominated polystyrene: antimony trioxide: KCP is 10:2:5, the material's UL 94 flame retardancy drops to V-1, with GWIT and GWFI at only 750°C. Upon further increasing the KCP proportion to achieve a brominated polystyrene: antimony trioxide: KCP ratio of 10:2:10, the material's GWIT becomes 775°C, GWFI reaches 960°C, and its UL 94 rating is V-0, meeting the glow wire requirements for unattended electrical current-carrying components as per IEC60335-1. At this point, the material has a low addition ratio of halogenated flame retardants, offering high cost-effectiveness and a strong competitive edge in the market.

IV. Conclusion

1. The single bromine-antimony flame retardant system or halogen-free flame retardant system of the reinforced PBT materials can not meet the IEC60335-1 unattended electrical current-carrying parts of the relevant burning wire requirements.

2. By utilizing the synergistic effect of bromine-nitrogen-phosphorus, compounding halogen-halogen-free flame retardant system can effectively improve the ignition temperature and burning index of reinforced PBT, so as to obtain the reinforced PBT materials that meet the burning wire and flame retardant requirements of the unattended electrical current-carrying parts of IEC60335-1.

3. The addition of halogen-free flame retardants has a greater impact on the mechanical properties of the material, and the surface activation treatment of halogen-free flame retardants can improve its compatibility, thereby reducing the degree of material deterioration.

4. KCP can greatly reduce the addition of bromine antimony flame retardant while meeting UL 94 -V0 to improve GWIT and GWFI, so as to get the cost-effective and more competitive reinforced PBT materials.

YINSU Flame Retardant Company is dedicated to the research and development of flame retardants. Our ADP product is an excellent halogen-free flame retardant that can be used in halogen-free reinforced PBT to improve its scorch wire performance. With its efficient flame retardant properties and good compatibility with the matrix resin, ADP helps to enhance the mechanical properties and flame retardant performance of the material. It plays a significant role in meeting the stringent safety standards of the electrical and electronics industry, providing a reliable solution for halogen-free flame retardant applications.