Decorative Chromium Coatings on Polycarbonate Substrate for the Automotive Industry

Abstract

Metal-coated plastic parts are replacing traditional metallic materials in the automotive industry. Sputtering is an alternative technology that is more environmentally friendly than electrolytic coatings. Most metalized plastic parts are coated with a thin metal layer (~100–200 nm). In this work, the challenge is to achieve thicker films without cracking or without other defects, such as pinholes or pores. Chromium coatings with different thicknesses were deposited onto two different substrates, polycarbonate with and without a base coat, using dc magnetron sputtering in an atmosphere of Ar. Firstly, in order to improve the coating adhesion on the polymer surface, a plasma etching treatment was applied. The coatings were characterized for a wide thickness range from 800 nm to 1600 nm. As the thickness of the coatings increased, there was an increase in the specular reflectivity and roughness of the coatings and changes in morphology due to the columnar growth of the film and a progressive increase in thermal stresses. Furthermore, a decrease in the hardness and the number of pinholes was noticed. The maximum thickness achieved without forming buckling defects was 1400 nm. The tape tests confirmed that every deposited coating showed a good interface adhesion to both polymers.

Corrosion Resistance in Artificial Perspiration of Cr-Based Decorative Coatings

“…All coatings had perfect adhesion ( Figure 3 ), where the edges of the cut were completely smooth, and none of the small squares that made up the grid were detached after removing the tape. The good adhesion behavior is also exponentiated by the acrylate layer between the coating and the substrate even for the CrN/CrO coating, whose surface seems cracked due to residual stress caused by the difference in coefficients of thermal expansion of the two materials in contact [ 25 , 26 ], but ultimately the adhesion of the coating was not affected.…”

A Comprehensive Outlook of Scope within Exterior Automotive Plastic Substrates and Its Coatings

“…Further, an issue with chromate plating has been the inability to achieve thicker films (>100 nm) in the fear of coating delamination. In that regard, Ponte et al [10] recently published a research study wherein a defect-free thicker film (800-1600 nm) with and without a base coat was coated onto an initially plasma-treated substrate. With an optimum thickness of 1400 nm, an increase in the spectral reflectivity and morphology changes were observed (via scanning electron and atomic force microscopy) in thicker films by virtue of the thermal stress increase and film columnar growth.…”

“…Being an interesting aspect of plastic substrates, these transparent coatings can be lightweight alternatives to glass coatings, though the former is a little more prone to scratch and wear [9]. To that extent, polycarbonate plastic has essentially gained attention due to its transparency, impact resistance, and weatherability, especially in auto headlamp covers and signage [10]. It goes without saying that coatings on both substrates also need to pass the common property requirements of stiffness, tensile strength, flexibility, stone chip resistance, etc.…”

PVD for Decorative Applications: A Review

“…PVD coatings can be deposited on several substrates, such as, Ti, Al, Cu alloys, steel, and even plastics (e.g., polycarbonate [85]). Corrosion-resistant substrates are preferred because PVD coatings' corrosion performances are highly dependent on the microstructure.…”