Thermoplastic elastomer TPE (Thermoplastic Elastomer), also known as artificial rubber or synthetic rubber. Its products not only have the high elasticity, aging resistance, and oil resistance of traditional cross-linked vulcanized rubber, but also have the characteristics of convenient processing and wide processing methods for ordinary plastics. TPE plastic is mainly composed of two parts, one is plastic as the continuous phase, and the other is rubber as the dispersed phase. Usually rubber needs to be combined with softening oil or plasticizer. Vulcanizing agents and some auxiliary additives are also essential. In addition, in order to reduce costs or improve certain aspects of performance, some inorganic fillers will also be added. According to the material composition, it can be divided into: styrene (SBS, SIS, SEBS, SEPS), olefin (TP0, TPV), diene (TPB, TPI), vinyl chloride (TPVC, TCPE), urethane ( TPU), esters (TPEE), amides (TPAE), organic fluorines (TPF), silicones and vinyls, etc., cover almost all areas of synthetic rubber and synthetic resins. Listed below are several common TPE components.
However, there are many components in the TPE thermoplastic elastomer formulation system. Due to the differences in the structure and properties of the components, the mechanism is not clear, which brings great difficulty to the flame retardant treatment. There will also be great safety hazards during the use process, which gives TPE The use of the product brings certain limitations. So, what difficulties may TPE flame-retardant treatment encounter?
1, the choice of flame retardant is difficult
The flame retardant has poor compatibility with the substrate. When the amount of flame retardant added in the elastic system is slightly larger, especially in the halogen-free flame retardant, the elastic modulus, flexibility, mechanical properties, and abrasion resistance of TPS will be greatly reduced, the fluidity of the melt will become poor, and the elastomer will be difficult. Molded, and flame retardant migration is prone to occur on the surface, which constitutes environmental pollution.
2, the flame retardant mechanism is not clear
TPS system is mainly a multiphase mixed structure of rubber, polyolefin resin, plasticizer and filler. Although there are relatively mature formulations and examples for halogen-free flame retardant polyolefin resins. However, the flame-retardant mechanisms of SEBS, polyolefin-based PP and PE are actually different. It is difficult for a flame retardant to flame-retardate multiple plastic components at the same time.
3, plasticizer reduces flame retardancy
TPE plastics often need to add plasticizers (white oil) in order to reduce the hardness and make the hand feel softer, usually with 26#, 32# white oil, 70# white oil as the main four types. Due to the difference in limiting oxygen index and fluidity of the four oils, and the natural flammability of oils greatly reduces the flame retardancy of elastomers, how to solve the relationship between plasticizers and flame retardants when producing low-hardness products? Choosing the type of white oil is very important.
Based on the difficulties that may be encountered above, what are the actual problems that may be encountered during the processing of flame-retardant TPE? What are the corresponding solutions?
1, the wire surface is not smooth
TPE wire processing often occurs. It is usually caused by improper temperature adjustment and uneven mixing of flame retardants. It may also be caused by incorrect mold selection. Of course, it has a lot to do with the material formulation. Experienced manufacturers will eliminate equipment problems and find the right temperature after repeated adjustments. However, engineers should be cautious about selecting suitable materials and specific formulas. It is recommended to communicate more with the raw material supplier, know the physical properties of the material and processing precautions, and choose the right material, it will get twice the result with half the effort! TPU wire is better than TPE wire surface processing.
2, precipitation on the wire surface
So far there is no material that can guarantee no precipitation at all. The specific precipitation performance is: the surface is white, oily or misty. With current technology, this problem has not been solved yet. It is recommended that customers choose a material with a slight whitening surface when choosing, and this precipitation will not affect its physical and electrical properties. Do not use materials with oil on the surface, as they will easily fall off and peel off during use. In addition, the precipitation is also divided into serious and serious. The precipitation of good materials is slight, and it is not easy to occur in a short period of time, even if it occurs with a gentle hand rub.
3, the surface is white and peeling off the glue
whitening is caused by the addition of PP and PE components in the material, which can be improved. There are also some manufacturers that do not clarify their products, but TPE is more difficult than TPU. If the skin is peeled and the glue is lost, the level is very general. What I want to talk about here is the formula! Craftsmanship!
4, processing difficulty
The performance of elastomers is relatively slow in processing speed, which is about 50% slower than that of PVC. The temperature is not easy to adjust, and a lot of materials will be wasted when adjusting the machine. In addition, the machine must be washed before the material is prepared, and the waste is not small. These are inevitable. In production, it sometimes happens that everything is normal in the front-end production and there are problems in the back-end processing. It needs to be explained here that the secondary card material is risky and should be used with caution.
The flame-retardant TPE/TPU plastic is a very unique material. The TPE/TPU flame-retardant problem still requires more work in the selection of materials, formulas and processes. In general, it is recommended to use liquid flame retardants to reduce the hardness while improving the flame retardancy, reduce the amount of powder flame retardants, can improve the transparency of the product, and use a compatibilizer to improve the compatibility of the flame retardant with the substrate It can improve the precipitation and greatly enhance the mechanical properties; in the process, special screw distribution is used to improve the dispersion of the flame retardant in the system, improve the flame retardant efficiency, and improve the appearance; adopt a new type of silicone flame retardant, and the condensed phase flame retardant mechanism is formed. The cracked carbon layer with strong oxidation resistance improves the flame retardant efficiency.