The TPV we are talking about here is a dynamically vulcanized thermoplastic elastomer composed of PP+EPDM. It is not difficult to understand that the fluidity of the entire TPV is provided by polypropylene PP, but the proportion of PP in the entire system has a certain range. Yes, for relatively soft products, the polypropylene PP content should not be high, otherwise the hardness will not be reduced. So where do high-flow thermoplastic rubber TPVs start? The following are commonly used methods:
1. Appropriately increase the proportion of PP, and at the same time increase the proportion of oil filling;
2. Choose high melting point polypropylene;
3. Peroxide vulcanization is recommended;
4. Add a certain proportion of lubricant;
5. Reduce the number of fillers;
6. Appropriately reduce the degree of vulcanization, while the size of the EPDM rubber dispersed phase is slightly increased.
1. Dynamic vulcanization after mixing high-flow polypropylene PP and EPDM may cause insufficient residence time in the screw, resulting in incomplete vulcanization;
2. If the PP content is too high, the compression deformation performance will be poor; if the proportion of softening oil is too high, there is a risk of oil leakage;
3. Too much lubricant, there is a risk of precipitation;
4. Reduce the addition of fillers and increase the cost;
5. The degree of vulcanization decreases, the compression deformation increases, the size of the EPDM dispersed phase increases, and the mechanical properties are reduced.
Therefore, it is still difficult to balance the fluidity, mechanical properties, and compression deformation properties of thermoplastic rubber TPV.
The advantage of high-flow TPV is that in the process of injection molding, the viscosity of TPV is reduced, and it is better plasticized, which can reduce injection pressure, speed, and back pressure, improve the window range of injection molding process, and make the appearance of injection molding products smooth and free of internal stress. In injection-bond overmolding, high-flow thermoplastic rubber TPV can bond polyolefin plastics more strongly, such as high-filled PP.
Although the viscosity of thermoplastic rubber TPV is more dependent on the shear rate, increasing the shear rate can greatly reduce the viscosity of TPV, but the shear rate distribution in the injection molding process is not the same, for places farther from the gate, the shear rate dropped a lot, and the viscosity of TPV also increased rapidly. Therefore, increasing the shear rate works well for small products. In addition, an excessively high shear rate can also cause surface burns on injection molded products.
Although the viscosity of high-flow thermoplastic rubber TPV is relatively low, in injection molding, the molding temperature is usually higher than that of conventional TPV, so that with a certain shear rate, the ideal fluidity can be achieved.
Automotive triangular windows, automotive glass packaging, and other thin-walled injection molding products.