Influence of Decorative Film Thickness on Molding Quality of MIM-IMD Products

JIN Xin; LIANG Xiangjing; HUANG Changyi; HUANG Zhenmin; YAN Kui; GUO Wei

doi:10.3969/j.issn.1674-6457.2025.07.025

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Journal of Netshape Forming Engineering ›› 2025, Vol. 17 ›› Issue (7) : 236-245. DOI: 10.3969/j.issn.1674-6457.2025.07.025

Advanced Manufacturing Technology and Equipment

Influence of Decorative Film Thickness on Molding Quality of MIM-IMD Products

JIN Xin¹, LIANG Xiangjing^1,*, HUANG Changyi¹, HUANG Zhenmin², YAN Kui^3a, GUO Wei^3b

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Abstract

The work aims to investigate the regulation mechanism of polypropylene (PP) decorative film thickness on the properties of microcellular foaming-in-mold decorating (MIM-IMD) injection molded products, to optimize the bubble structure, surface quality and mechanical properties. Using the MIM-IMD process, mechanical tests were conducted on samples with different film thicknesses by controlling the thickness of the decorative film (0.10-0.30 mm), and combined with scanning electron microscopy (SEM) to observe the blister hole structure and the surface morphology. When the thickness of the decorative film increased, the maximum diameter of core layer vesicles rose perpendicular to the direction of the melt flow, the average diameter and density of vesicles rose and then fell; and parallel to the direction of the melt flow, the thickness of the core layer decreased, the average diameter of vesicles rose, the density of vesicles rose and then fell, and the average diameter and density of vesicles on the coated side was higher than that on the non-film side; When the film thickness was 0.1 mm, the surface defects of the foamed parts were fewer and the surface roughness was the lowest, and the pores and depressions increased with the increase of the film thickness. The tensile strength, bending strength and impact strength of the foamed part surface showed an upward trend as the film thickness increased. Decorative film thickness significantly affects the asymmetric distribution of the bubble structure. When the thickness of the decorative film increases, the hysteresis effect is enhanced, the melt temperature on the coated side increases, providing more time for the growth of the vesicles. When the film thickness is more than 0.2 mm, the gas escape is intensified, and the quality of the vesicles decreases. The decorative film is effective in improving the surface quality. But after the increase in the thickness of the film, the film can be heated to higher temperatures by the melt, resulting in the increase of the surface defects in the foamed parts. The decorative film improves the mechanical properties of the foamed parts by improving the internal structure of the vesicles, and the increased thickness of the film can further enhance the protection of the substrate.

Key words

polypropylene / microcellular injection molding / in-mold decoration / microstructure / mechanical properties

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JIN Xin, LIANG Xiangjing, HUANG Changyi, HUANG Zhenmin, YAN Kui, GUO Wei. Influence of Decorative Film Thickness on Molding Quality of MIM-IMD Products[J]. Journal of Netshape Forming Engineering. 2025, 17(7): 236-245 https://doi.org/10.3969/j.issn.1674-6457.2025.07.025

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Funding

; Fund：Youth Fund of National Natural Science Foundation of China (51605356); Education Reform and Development Project of “Integration of Industry and Education, Cooperation between Schools and Enterprises” of China Electronic Labor Society (Ceal2024163)