Adhesives

Owing to the requirements, 14 adhesives from various manufacturers made it onto the shortlist, including acrylate, epoxy resin, and polyurethane adhesives, see Table 1. The acrylates are 1-part products. Curing is carried out with a spe­cial lamp, preferably using UV radiation. The adhesive can cure within just a few minutes, depending on the intensity of the radiation. The epoxy resins are 2-part products consisting of resin and hardener, which are mixed together in the ratio specified by the manufacturer. The curing starts to take place at room temperature immediately after mixing. Increasing the strength by curing at a higher temperature was not used because this would be very difficult to accom­plish for the intended application. The polyurethanes are also 2-part products that cure at room temperature. Owing to the planar geometry of the adhesive joints, 1-part adhesives that cure using the moisture in the air cannot be consid­ered. In larger planar joints, moisture could not migrate sufficiently into the inner part of the joint. Hence, the curing of the adhesive processes slowly and may not be fully completed. Silicone adhesives, which cure by polycondensa­tion, are also not suitable for this joint geometry. The gaseous condensates can­not escape from the inner parts of the joints and this may lead to impairments and weak curing.