A Mold Surface Treatment for Improving Surface Finish of Injection Molded Microcellular Parts

Abstract

Micro-cellular foaming technology draws attention due to the enhancement of mechanical strength, which has been considered as a weak point of current plastic foaming technology. Foam materials produced by this technology offer improved consistency and homogeneity of cell structure, which can result in products with superior properties and uniformity(1). Thus it is widely used for commercial purposes and its market is now growing significantly. However, since the foamed injection parts have swirl marks on its surface, this technology has limited uses such as interior products, in spite of its diverse merits. In this paper, we propose surface treatment of the mold as a way to remove the swirl mark. We injected simple shape specimens with PP and PC/ABS materials and measured the surface quality values such as roughness and gloss. Also we researched the foaming characteristics of both treated and untreated surface using SEM analysis.

Effects of cavity surface temperature on reinforced plastic part surface appearance in rapid heat cycle moulding

“…For CMTC of CIM, the cavity surface temperature during filling process should be much lower than the glass transition temperature or melt temperature of the plastic resin to ensure a short moulding cycle and competitive production efficiency. The low cavity surface temperature makes the polymer melt freeze prematurely and consequently a frozen layer will formed during filling process at the interface between the hot polymer melt and the cold mould cavity, which leads to a series of defects of the final moulded parts, such as flow mark [11,12], weld mark [13,14], swirl mark [15][16][17], roughness [18,19], low gloss [20][21][22], and low replication accuracy [23,24]. For DMTC of RHCM, the cavity surface temperature during filling process has much smaller negative influence on the moulding cycle because the mould can be cooled as soon as possible after filling.…”

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

“…Another possible way to improve the surface quality is counter pressure techniques, particularly the gas counter pressure (GCP) process [19][20][21][22][23], that have been reported to improve effectively the part surface roughness. An example was reported by Bledzki [21] in which the part surface roughness (Rz) decreased from 23 μm to 0.85 μm.…”

Microcellular Foam Injection Molding Process

“…Yoon propose that the glass transition temperature (for the amorphous polymer) or the melt temperature (for the crystalline polymer) is one of the important effect factors on the swirl mark forming [16] . Zhang YT points out that swirl marks always appear near the gate [17] .…”