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. 2020 Sep 15;12(9):2100.
doi: 10.3390/polym12092100.

Causes of the Gloss Transition Defect on High-Gloss Injection-Molded Surfaces

Jinsu Gim  1 , Eunsu Han  2 , Byungohk Rhee  2 , Walter Friesenbichler  3 , Dieter P Gruber  4
Affiliations

Causes of the Gloss Transition Defect on High-Gloss Injection-Molded Surfaces

Jinsu Gim et al. Polymers (Basel). .

Abstract

The gloss transition defect of injection-molded surfaces should be mitigated because it creates a poor impression of product quality. Conventional approaches for the suppression of the gloss transition defect employ a trial-and-error approach and additional equipment. The causes of the generation of a low-gloss polymer surface and the surface change during the molding process have not been systematically analyzed. This article proposes the causes of the generation of a low-gloss polymer surface and the occurrence of gloss transition according to the molding condition. The changes in the polymer surface and gloss were analyzed using gloss and topography measurements. The shrinkage of the polymer surface generates a rough topography and low glossiness. Replication to the smooth mold surface compensates for the effect of surface shrinkage and increases the surface gloss. The surface stiffness and melt pressure influence the degree of mold surface replication. The flow front speed and mold temperature are the main factors influencing the surface gloss because they affect the development rate of the melt pressure and the recovery rate of the surface stiffness. Therefore, the mold design and process condition should be optimized to enhance the uniformity of the flow front speed and mold temperature.

Keywords: gloss transition defect; injection molding; mold surface replication; shrinkage; surface analysis; surface defect; surface gloss.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Example of the gloss defect on a high-gloss injection-molded surface.
Figure 2
Figure 2
Injection molds: (a) mold type A, (b) fixed plate of the mold type B, and (c) moving plate of mold type B
Figure 3
Figure 3
Cavity pressure under different packing pressure conditions.
Figure 4
Figure 4
Gloss distribution measurement using the IPA technique [35,36]: (a) measurement setup and (b) intensity profile and contrast distribution.
Figure 5
Figure 5
Determination of the root-mean-square (RMS) roughness (Sq) and lateral correlation length (Lc) using the height–height correlation function (HHCF).
Figure 6
Figure 6
Surface measurement result: (a) surface gloss and (b) topography parameters.
Figure 7
Figure 7
Surface topography molded by various flow-front speeds (FFS); (a) 31.6 mm/s, (b) 100 mm/s, (c) 316 mm/s, and (d) 1000 mm/s.
Figure 8
Figure 8
Comparison of the measured and predicted surface gloss.
Figure 9
Figure 9
Contrast distribution of the short-shot specimen.
Figure 10
Figure 10
Fountain flow and melt pressure development at the flow front.
Figure 11
Figure 11
Rough surface at the flow front.
Figure 12
Figure 12
Surface gloss under various molding conditions.
Figure 13
Figure 13
Effect of the molding conditions on the surface gloss.
Figure 14
Figure 14
Effect of the flow front speed fluctuation on the gloss transition defect; (a) flow front speed fluctuation 25–250 mm/s, (b) flow front speed fluctuation 50–250 mm/s, and (c) flow front speed fluctuation 100–250 mm/s.
Figure 15
Figure 15
Effect of the packing pressure on the gloss transition defect caused by the flow fluctuation 25–250 mm/s; (a) without packing pressure, and (b) with 500 bar of packing pressure.
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