EVA (Ethylene Vinyl Acetate) film is commonly used in lamination glass applications due to its distinct properties and advantages. Its adhesion to glass surfaces is a crucial factor in its application, and several methods are used to measure and improve this adhesion.
One of the common tests to measure EVA adhesion is the peel test. In this test, a laminate is made with glass-EVA and a back sheet material that adds stiffness to the test. The glass is fixed at the bottom of the test equipment, and the peel arm consists of the EVA and the back sheet. For a good quality, EVA values of more than 80 N/cm should be obtained, but usually, peel values of more than 100 N/cm can be seen. Another adhesion assessment in the laminated glass industry is the Pummel test. However, due to the lower glass transition temperature of EVA, the classic Pummel test at -18°C can give a distorted result. Therefore, a Pummel test on EVA can be performed at -18°C, but usually, if no large problems occur, the values will always be very high as glass fragments are pushed in the very soft EVA. The adhesion of EVA to glass surfaces is achieved through an organ silane adhesion promoter added to the polymer. The silane side of the coupling agent reacts with the silanol groups on the glass surface, resulting in the release of alcohols. This bonding is a covalent, thus irreversible, bond. This is a significant difference with the PVB system, which is water sensitive and reversible. EVA is produced as dry as possible to avoid reacting with moisture before it can react with the glass surface. After processing, the bonding between glass and EVA is irreversible. EVA, a polyolefin material, does not take up water as easily as PVB, and when it does, the adhesive bonding between the glass surface and the interlayer is much more resistant. The processing of EVA is quite straightforward. It is often laminated using vacuum bag ovens, where the assembly is inserted in a vacuum bag and closed. The vacuum bag is then shifted in an oven. Due to its easy de-airing and high flow, EVA is quite forgiving for the lamination parameters.
In summary, EVA has distinct properties compared to PVB. Its adhesion system is irreversible and not as sensitive to moisture, making it suitable for various applications, especially decorative and aesthetic ones where one would like to encapsulate all sorts of inserts in a laminate.