Physico-mechanical characterisation of basecoats for tailored UV-cured multilayered wood coating systems

The durability and aesthetic properties of wood flooring arise from the properties of the coating applied on its surface. Due to their fast-curing speed, high crosslinking density and high durability, UV-curable coatings are often preferred for flat surfaces such as hardwood flooring, tabletops and doors. In the case of hardwood flooring, several types of deteriorations on the coating surface can shatter the perception of the whole product. In the present work, UV-curable formulations with various monomer-oligomer couples were prepared and used as a basecoat within a multilayered wood finishing system. While the topcoat is designed to endure most of the in-use loads, elastic and plastic stresses can reach deeper layers. The aim of this study is to analyze the influence of basecoat composition and thickness on the mechanical behavior of a UVcurable multilayered wood finishing system. First, physical properties such as the average theoretical segment length, glass transition temperature and crosslinking density, of standalone films of the various monomer-oligomer couples were investigated. Then, indentation and scratch resistance tests were performed to understand the role of the basecoats in the overall mechanical response of the multilayered coatings. The thickness of the basecoat applied was found to have a great influence on the mechanical resistance of the finishing system. No direct correlation was established between the basecoat as standalone films and within the multilayered coatings, considering the complexity of such systems several behaviors were detected. A finishing system able to promote overall good scratch resistance and good indentation modulus was obtained for a formulation displaying an equilibrium between the network density and the elasticity.