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Technical Paper -
The aim of this work was to determine the minimum surface cleanliness of aluminum substrates required for good and reproducible silicone rubber adhesion. Aluminum substrates were prepared, ranging from “contaminated” to different degrees of “cleaned”. The surface energy of the substrate was determined by contact angle measurement. The surfaces were also compared using simplified methods, such as wettability test or by the use of inks with known surface tension. Silicone rubber was then compression molded onto the cleaned and primed substrates. The silicone rubber adhesion was then evaluated by lap shear testing, before and after aging in boiling water. It was concluded that in order to obtain strong and stable interface, exhibiting mainly cohesive failure between the aluminum and silicone rubber, the surface energy of the subset before priming should be >45 mJ/m2 including a polar component of >10 mJ/m2. This corresponded to a hydrophobicity class of the substrate of >6 according to IEC 62073.