Processing and Weathering of Sol-Gel Clearcoats for Coil-Coated Steel

Abstract

Clearcoats provide long-term aesthetics and protection for underlying coating systems, increasing product lifetimes. However, organic clearcoats are predominantly produced using fossil-fuel feedstocks. In search of a sustainable alternative, an experimental investigation was conducted on the development of glass-like clearcoats produced using the sol-gel process. The processing of sol-gel clearcoats over a pigmented polyurethane coating was studied by modifying the sol-gel solution pH, ageing, curing, precursor chemistry and deposition techniques. Under optimal formulation and processing conditions, defect-free sol-gel clearcoats were produced that have the potential to be scaled up to a coil-coating line using existing technologies. Mechanical testing demonstrated the coatings had excellent adhesion, hardness, and flexibility. Furthermore, accelerated laboratory weathering tests revealed the sol-gel coatings had superior degradation resistance compared to the organic coatings tested, resulting in negligible colour changes and higher gloss retention after 4000 h of exposure. The durability and environmental benefits of sol-gel clearcoats highlight their potential as a replacement for traditional organic clearcoats in a variety of applications.

Improving the Corrosion Performance of Organically Coated Steel Using a Sol–Gel Overcoat

“…The peak at 950 cm −1 corresponds to Si–OH bending and the peak at 790 cm −1 corresponds to Si–O–Si bending vibration [ 42 ]. The presence of only the Si–O–Si vibration for the 2.5% TEOS coating was unexpected based on previous works [ 34 , 40 , 41 ]. The presence of all the expected peaks in the 10% TEOS coatings suggests that polysiloxane network formation has occurred at this concentration.…”

“…The peak at 950 cm −1 corresponds to Si-OH bending and the peak at 790 cm −1 corresponds to Si-O-Si bending vibration [42]. The presence of only the Si-O-Si vibration for the 2.5% TEOS coating was unexpected based on previous works [34,40,41].…”

“…In comparison, sol–gel coatings are thinner, can improve the corrosion performance on metallic surfaces, offer improved hardness and scratch resistance and provide hydrophobic properties. Recently published work demonstrated that sol–gels offer a potential replacement for organic clearcoats as they improved the mechanical and UV degradation performance whilst being substantially thinner [ 34 ]. The work demonstrated that TEOS-based sol–gel coatings can be applied to PU substrates, but further work was required to determine whether there is scope for industrial applications.…”