Newsletter_0420151

While both traditional joining techniques (e.g. rivets or screws) and bonding technologies are used to attach metallic parts, for joining metal and plastic materials the use of adhesive technology is predominant. There are typical differences between metals and plastics, for example in terms of temperature sensitivity, brittleness and surface finish. Therefore traditional joining techniques frequently cannot be used to join metal and plastic materials.

Plastics are made up of polymer chains. A wide variety of plastics are suitable for bonding, to varying degrees: plastics with high surface energy are well suited while materials with low surface energy are more problematic. Low surface energy plastics include, for example, PP, PE, PS, HDPE, LDPE, NBR and EPDM. All of those materials feature specific surface energies of less than 40 mN/m. Mold release agents, plasticizers in PVC and undefined mixtures of recycled material may result in further challenges for self-adhesive solutions.

In any case, special glue for plastics with low surface energy should be chosen, the viscoelastic properties of the adhesive material should be adjusted according to the surface conditions and the surfaces to be joined should be cleaned to remove dust, oil and release agents, and be dry.

Metals have surface energy (typically 1000-5000 mN/m), which are well suited for bonding. The selection of the adhesive technology to be applied depends very much on how the metal surface is treated. In addition to the properties of the metal and plastics to be bonded, the connection requirements have to be defined. Which requirements regarding shear and tensile forces, splitting and peeling forces have to be fulfilled? Do dynamic forces and environmental influences such as humidity, high and low temperatures need to be considered? Chemical resistance to solvents, acids or alkalis may need to be taken into account.

There is no universal self-adhesive solution for bonding metals and plastics. Depending on the materials selected, their surfaces and the customer’s requirements, application-specific solutions may have to be defined.

Our engineers will be pleased to advise you on your choice of self-adhesive solution. Please contact our consultants.

 

The bonding of nonpolar polyolefin such as PP or PE is very difficult due to the low surface energy (about 30-35 mN/m). Usually, the surfaces have to be treated with costly surface preparation methods using primers, plasma or corona. The polymer chains on the plastic surface are broken by the impact of energetic particles and, in their new form of polar molecules, can make chemical connections. The latest generation of two-component adhesives makes the structural bonding of low-surface energy materials possible without surface pretreatment. In the field of adhesive tape technology, there are promising approaches, which are suitable for bonding different materials, e.g. GRP with PE depending on the requirements (e.g. heat, cold, humidity or UV resistance).

Our team is available to discuss the variety of material combinations that can be used to achieve an optimal adhesive solution. Our engineers will be pleased to advise you on your choice of self-adhesive solution.

Please contact our specialists.

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