Controlled relative humidity testing for the characterisation of the brittle-tough and glass transition temperatures of coil coating paint films

摘要

It is well known that the brittle-tough (T-BT) and glass (T-g) transition temperatures of a polymer depend on a range of factors including the rate at which an applied stress is delivered, backbone structure and, for thermosetting systems, cross-link density. It is also known that humidity has an effect, but it has been difficult to quantify this. This is a potential problem in the pre-coated metal industry where variations in ambient environmental conditions and line speed, during the forming process, can have detrimental effects. The aim of this work was to quantify the effect of humidity on the TBT and Tg. Modifications to a dynamic mechanical analyser (DMA) and a mechanical tester were made to allow controlled relative humidity (RH) experiments to be performed. Free film samples of coil coatings, based on polyester melamine, were supplied. The glass transitions were measured thermally using the tensile mode of the DMA. The brittle-tough transitions were calculated from a series of isothermal pull-to-break tests performed on the mechanical tester. Reductions in both the brittle-tough (TBT) and glass transition (T-g) temperatures of up to 10degreesC were found as the controlled RH was increased. (C) 2004 Elsevier B.V. All rights reserved.