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OAS provides bonding solutions for carbon fibre composites

News International-French

21 Jan 2015

Oxford Advanced Surfaces Limited (OAS) provides an example of how its Onto surface modification technology can be used in the preparation of carbon fibre composites for coating and painting in the automotive industry.

From bumpers and spoilers to dashboards and steering wheels, carbon fibre reinforced plastic (CFRP) is becoming increasingly used in the design of automotive components. Not only is it strong and rigid, it is also light weight, helping to maximise the performance and fuel efficiency of the vehicle and lowering emissions.

Its striking and attractive appearance means that it is often used to make visual components. These parts can be clear coated to protect the structure and create maximum shine of the component, or alternatively the substrate may be painted for a decorative effect. Before applying these finishes, the composite’s surface must be prepared in order to achieve good adhesion of the coating to the substrate and to remove any residual mould release agent. Common approaches to surface preparation of CFRP are sanding or grit blasting. The level of roughening is critical – not enough sanding will result in a poorly adhered coating whereas over sanding will lead to damage of the part, marring the visual appearance. CFRP parts are time- consuming to produce and therefore manufacturing is costly; reducing the rejection rate resulting from poor finishing is therefore clearly desirable.

Onto surface treatments provide a simple and practical solution for bonding coatings and paints to carbon fibre composites. Onto can reduce the extent of the sanding stage and in some cases replace it, decreasing the risk of substrate damage from over sanding as well as drastically reducing the time and effort required to prepare the surface for coating. Each treatment is customised for a particular deposition method for easy application whatever the processing environment. All Onto treatments require a short curing step for activation of the reactive component. Many of company's treatments are coloured but become colourless on heating, helping the user to easily identify when the curing step has been completed. The coated layer of Onto material is extremely thin, allowing the visual aspects of the underlying substrate to be unaffected.

The plastic resin that is chosen for the CFRP can vary. In most cases thermosetting plastics like epoxies are used but more recently people are using thermoplastics because of the processing benefits that they offer as well as for their ease of recycling at end of life. Semi-crystalline thermoplastics are highly resistant to chemicals and cannot usually be bonded to without some kind of surface treatment. In some cases existing surface treatments are just not effective and this means that bonding to thermoplastic based carbon fibre composites can be a barrier to their use. Onto surface treatments can prepare even the most chemically resistant materials for bonding, ensuring that coatings do not delaminate from the substrate over time and enabling you to create innovative products with the advanced materials of your choice.

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