Print-through Phenomenon on the Surface of GFRP: Pilot Study

Unsaturated polyester filled with coloring agent is commonly used as the surface material of a GFRP yacht and is called a gel-coating layer. The reflection on the gel-coating layer surface will be imperfect if twists and wrinkles exist on the gel-coating surface. This phenomenon is called print-through phenomenon (PTP) in this investigation. The PTP seriously reduces the beauty of a yacht and therefore limits the application of GFRP to the yacht. Therefore, it is urgent to solve the PTP problem. The first goal of this study is to objectively define and quantitatively measure the existence of PTP and its level. The surface of the gel-coating layer of GFRP is scanned by using the portable high resolution surface roughness and form measurement instrument. Based on a large number of experiments, the average parameter, arithmetic mean deviation (Ra), and the peak parameter, the altitude of the surface profile (Rt), are proposed to determine the existence of PTP and its level. The second goal of this study is to consider the causes of PTP happening and find out the factors that can influence it. Through experimental observations and qualitative analysis, it is believed that PTP is related to the non-uniform residual stress in the gel-coating layer of GFRP. So, any factors which can produce the non-uniform residual stress in the gel-coating layer can influence PTP, such as the shrinkage of the resin during its hardening chemical reaction and the atmospheric pressure during the Seemann composite resin infusion molding process (SCRIMP). After ascertaining what causes PTP, research methods that can be used to reduce PTP will then be studied.