There are two commonly used methods to mold porous plastic parts. The first method mixes a blowing agent with the injected polymer during the molding process to create the desired voids. This mix-on-the-fly method is easy to implement but the size and distribution of the voids are random and difficult to control.
The second method is similar to the sintering process in powder metallurgy, where powder metals are heated under pressure to near but just below the melting temperature until the particles fuse with each other. For plastics, granulated polymers are injected into a heated die and sintered together. By carefully controlling the temperature and the pressure, the size and distribution of the pores can be more accurately controlled.
Porous media molding has a wide variety of filtration, venting, wicking, and diffusion applications, such as air filter, water filters, sterilization vents, hydrostatic vents, air freshener wicks, adhesive applicators, marker/highlighter nips, and aquarium bubblers, just to name a few.
Many polymers can be used in porous media molding. The common ones are