Using thermally insulated polymer film for mold temperature control to improve surface quality of microcellular injection molded parts

Microcellular injection molding provides many advantages over conventional foams and their unfoamed counterparts, but its applications are limited by visible surface quality problems such as silver streaks and swirl marks. In this study, a mold temperature control method was proposed which a thermally insulated composite polymer film (82%PET+18%PC) stick on the surface of mold core is used to achieve heat transfer delay at the plastic's melt-mold surface interface during the microcellular injection molding process to improve surface quality of molded parts. Effect of film thickness on the part surface quality, was also investigated using surface roughness measurements and visual inspection of the molded parts. It was found that the surface quality of parts can be greatly improved without a significant increase in cycle time when comparing with parts molded without polymer film. The surface roughness can decreases from 5.6 to 1.8 pm when polymer film thickness increases from 0.125 to 0.188 mm. Meanwhile, the flow marks of gas bubbles on the part surface can be removed completely at film thickness of 0.188 mm. The usefulness by stick a polymer film on the surface of mold core for mold temperature control in improving part surface quality during microcellular injection molding has been successfully demonstrated. (C) 2008 Elsevier Ltd. All rights reserved.