STUDIES INTO THE LIFE-EXPECTANCY OF INSULATING GLASS UNITS

Insulating glass units are exposed to a variety of environmental factors, such as temperature and atmospheric pressure fluctuations, wind loads, working loads, sunlight, water and water vapour. The service life of a sealed insulating glass unit critically depends on the perfect functioning of the edge seal under these environmental influences. The water vapour permeability of the secondary insulating glass sealant plays only a subordinate role in the life expectancy of a dual-seal insulating glass unit, since the resistance of the edge seal to water vapour diffusion is determined almost exclusively by the low water vapour permeability of the PIB primary seal. On the other hand, great importance must be attached to the viscoelastic properties of the secondary insulating glass sealants, particularly to their tensile stress behaviour and their elastic recovery, as these properties affect the ability of the primary seal to function. In the case of gas-filled insulating glass units, the gas permeability of the secondary seal exerts a great influence on the gas leakage rate, since the gas permeabilities of organic primary and secondary sealants are approximately equal. When silicone sealants are used for the production of gas-filled insulating glass units, additional measures must be taken to ensure a gas-tight edge seal.