Generation mechanism of gloss defect for high-glossy injection-molded surface

The gloss defect on a glossy surface is one of the surface defects to be found on injection-molded products. In this paper, the effects of the filling and packing stages on surface gloss are investigated. Based on observations, a generation mechanism of gloss difference is proposed. The difference of the surface gloss can be explained by the replication of the shrinking polymer surface represented by a replication factor. The replication factor is the ratio of melt pressure to surface stiffness, which is influenced by the filling condition and the material properties. The melt pressure as a driving factor to the replication reflects the effect of the flow front speed and viscosity. The surface stiffness as a resisting factor reflects the effect of the flow front speed, mold temperature in the filling stage, and storage modulus. The replication factor shows a high correlation to the surface gloss over a wide range of filling conditions. The proposed mechanism recommends a uniform and high flow front speed and mold temperature to suppress gloss defects.