Establishment of Gas Counter Pressure Technology and Its Application to Improve the Surface Quality of Microcellular Injection Molded Parts

Abstract

The purpose of this study is to establish the Gas Counter Pressure (GCP) technology in combined with microcellular injection molding process. The application of gas into the mold cavity during the melt injection period provides a counter force against the melt front advancement, restricting the foaming process during the melt filling stage. Various gas counter pressures from 0 bar up to 300 bar and gas holding times of 0 to 10 s after filling completion were employed for investigating their relevant effect. It was found that when gas counter pressure is greater than 100 bar, foaming does not appear in the skin layer if no holding time is applied after melt-filling. As gas counter pressure increases, thickness of the solid skin layer without foaming also increases. Employment of holding time after melt-filling also assists foaming restriction in the melt core area. If a holding time of 10 s is applied combined with a counter pressure greater than 100 bar, foaming is completely restricted resulting in a transparent PS sample part. The part surface of those subjected to foaming-restriction in the skin layer also appears to be smooth and glossy. For the black PS parts molded via microcellular injection combined with gas counter pressure, it appears the same gloss quality as that achieved by conventional injection molding.

Advances in microcellular injection moulding

“…79 Also, the investigation demonstrated that by combining both GCP and elevated mould temperatures, an increase in both the surface quality and cellular morphology can be achieved. 79 The results obtained by Chen et al 80 also proved that GCP is effective at reducing surface defects. In particular, when processing a PS polymer, a surface roughness improvement of more than 90% was achieved.…”

“…Furthermore, it was found that when applying a holding time of 10 s, the parts exhibited no foaming until the melt is solidified. 80 Lee et al 81 proposed a combination of both GCP and core-back processing with high density PE (HDPE). to produce Class A surface finishes.…”

Structure and mechanical properties of polystyrene foams made through microcellular injection molding via control mechanisms of gas counter pressure and mold temperature

“…When the gas counter pressure is greater than the critical pressure, then the melt may retain as a single phase without any foaming as long as the counter pressure applies. Recently, a more detailed study of the surface quality of microcellular injection molded parts was investigated using GCP technology [24]. It was found that when the GCP is greater than a certain value, a foaming free part surface can be achieved.…”

Characterization of microcellular plastics for weight reduction in automotive interior parts

“…Gas Counter Pressure (GCP) technique consists of pressurizing to a high pressure the mold cavity, allowing filling by the polymer/gas system but restricting foaming, as pressure drop does not occur [109]. Thus, fracture cells on the melt flow front is inhibited and swirl marks are eliminated.…”