In the case of conventional lamps and lamps based on light-emitting diodes (LEDs) as light sources, glass parts are used and, depending on the function and design, have to be connected to non-glass parts, for example a glass bulb to a heat sink of aluminum; a glass tube to end caps of plastic, etc. Plastic, ceramic and aluminum are often used as the material of the non-glass parts. A known technique for such connections is the adhesive bonding of opposing surfaces with adhesive or sealing substances. A great uncertainty in the adhesive-bonding technique is the lifetime stability over several years. This may differ considerably in the respective adhesive-bonding application, depending on the loading, the adhesive substance used and the design of the adhesive bond. Elaborate tests, long approval times and quality assurance involving a great effort are the direct consequences. In respect of the lifetime stability of adhesive bonds, a distinction is essentially drawn between two failure mechanisms, to be specific on the one hand an adhesive failure or bonding failure and on the other hand a cohesive failure or failure of the strength of the bonding substance. Measures that have been used so far to counteract an adhesive failure include, for example, improved cleaning of the surfaces to be adhesively bonded, activation of the surfaces to be adhesively bonded by special methods of pretreatment (plasma treatment, flame treatment, etc.), increasing the size of the surfaces to be adhesively bonded, use of so-called primers or use of specially formulated adhesive substances. All of these additional methods are cost-intensive.
Measures for reducing the risk of a cohesive failure are based on finding a suitable composition of the adhesive substance and suitable processing of the adhesive substance.