Structure-scratch properties relationships of acrylate photo-polymerizable protective coatings for thermoplastic substrates

Abstract

International audienceThe relationships between the composition and the scratch resistance of clear photo-polymerized protective coatings for thermoplastic substrates were studied in relation with their thermomechanical properties. For this purpose, dynamic mechanical analyses of free-standing films were compared to micro-scratch tests of thick or thin coatings deposited on polycarbonate. In these experiments, the depth indented by the tip, the elastic recovery of the material, the residual depth of the scratch, and the load at which the first crack appears, were analyzed. Different coatings close in formulation were studied. First, the proportion of a specific difunctional monomer featuring a hard structure was varied in order to change the crosslinking density of the polymer network. The thermomechanical properties were consequently modified at high temperature, but remained similar at 23 degrees C, whereas at this temperature, the scratch properties of the coating evolved with its composition. The addition of 5 wt% alumina or silica nanopartides did not modify the thermomechanical properties or the scratch resistance of the coatings, even if a more concentrated filler layer was observed near the surface of the coating. Nevertheless, the consequent incorporation of a new diacrylate monomer in the polymer matrix delayed the ductile-brittle transition. Finally the substitution of petro-based monomers by slightly different bio-based compounds led to a change of the scratch behavior of the thickest coatings (150 mu m-thick), and increased the critical load for the thinnest coatings (15 mu m-thick). It comes out that micro-scratch tests allow a finer comparison of the samples

Effect of bio‐based monomers on the scratch resistance of acrylate photopolymerizable coatings

“…As for the critical load [Fig. (d)], the improvement is remarkable with respect to a classical petro‐based formulation that showed a 1.9 N critical load under the same test conditions, that is, an increase ranging from ∼60% for Bio 12 to ∼175% for Bio 13. All the studied coatings are thus effective in terms of protection against scratches.…”

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

“…The purpose of an HC in general is to increase the hardness and scratch resistance via a hard coat layer over the substrate surface. An HC can involve an organic oxide, epoxy resin, polyurethane silicone, or polyacrylate, showing plastic deformation on scratches [64][65][66]. Xu et al reported a study wherein UV-cured acrylates were used as a hard coating for a PMMA/PC substrate, and the properties were tested using the pencil hardness test and progressive normal scratch test [67].…”