As for the molding method, application of Heat and Cool (H&C) molding method, in which the metal mold temperature is controlled during the molding process, was investigated to control the crystallization speed of PPGF by metal mold temperature.
With those backgrounds, the cavity temperature that is required to obtain a desired exterior appearance was clarified when PPGF is used for the molding.
Temperature Setting of Mold cavity Required for PPGF
The cavity surface temperature, required to avoid the exposure of glass fibers on the surface of PPGF, was examined using a prototype mold prepared for a part with a shape of a grip handle (Figure 14).
Polypropylene with 30% of chopped glass fibers was used for PPGF material.
On the other hand, as the cavity temperature is set at higher temperatures, the resin becomes capable of reaching the cavity surface and glass fiber exposure in PPGF is suppressed getting a better gloss on the surface of the molded part (Figure 15-b, d).
The results of measurement conducted to confirm the crystallization temperature of PPGF using Differential Scanning Calorimetry (DSC) is shown in Figure 16.
Through the results mentioned above, the target temperature setting of the cavity used for the PPGF molding was defined as 120[degrees]C or above.
The impact on the physical property of the molded part caused by the mold temperature in H&C molding for PPGF has been reported by G.
Influence on Weatherability of PPGF Molded Parts from H&C Molding Method
In this development, we have set a prerequisite of not applying any painting on the grab rail molded with PPGF. The base material of PP is susceptible to ultraviolet rays from the sun causing deterioration that leads to discoloration and cracks.
For glass fiber reinforced resins such as PPGF, the shrinkage of the resin is impeded by the glass fibers because the amount of shrinkage of the matrix resin is larger than that of the glass fiber.