Two-Component Injection Molding as a Noise Countermeasure for Polycarbonate Glazing 2017-01-1817
Polycarbonate (PC) glazing as a one-for-one glass replacement offers a 50% weight reduction, but exhibits several dB lower sound transmission loss (STL) in the low frequency range where tire and engine noise are dominant. In the high frequency range where wind noise is dominant, PC glazing offers an STL at least comparable to its glass counterpart, and an STL exceeding glass when this frequency range encompasses the glass coincidence frequency. However, a key value proposition of PC glazing is the opportunity for feature integration afforded by the injection molding process generally used for forming such glazing. Two-component (2K) molding fuses a second shot of plastic material behind, and along the perimeter of, the transparent PC first shot. This second shot can incorporate features and implement functions that require additional components attached or peripheral to a glass version. In effect, a portion of the weight reduction entitlement for PC glazing is transferred to the host vehicle, such that the weight reduction of the glazing itself is less than 50%. Moreover, the second shot tends to stiffen the PC glazing relative to the first shot alone. We show experimentally that these two effects contribute to making the low frequency STL of a 2K PC rear window intermediate between the first shot alone and the comparable glass version. Thus, integration operates as a noise countermeasure for glazing weight reduction. Injection molded PC glazing can also be designed for reduced aerodynamic (high frequency) noise, further improving its noise profile versus glass.