FRP moulded components manufactured without release agents
14 November 2012
Up to now, releasing components from moulds has called for release agents. The problem is that the residues of these agents left behind must then be removed at cost.
Now, there is an alternative: a specially coated release film that leaves no residues. “Our film can be applied to structures of all kinds and makes it easy to release components from moulds,” says Dr Matthias Ott, project manager at the Plasma Technology and Surfaces (PLATO) section of the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM). “It features a 0.3 micrometer thick plasma-polymer release layer that leaves no residues on the surface of the component.”
This coating on the film is based on development work conducted at the IFAM on producing non-stick component moulds using a low-pressure plasma process. First, the mould to be coated is placed in a plasma reactor and atmospheric pressure is reduced to one ten thousandth of normal level. Next, layering gases are fed into the reactor and a plasma is ignited. Molecules containing silicon or carbon that are injected into the plasma are deposited as a thin layer. Since the molecules are highly reactive, they bond very well with the mould.
The snag is that plasma reactors are, at best, five cubic meters in volume, which means only relatively small moulds can be coated. So the researchers in Bremen, together with experts from Fraunhofer IFAM’s Project Group Joining and Assembly (FFM) in Stade, decided to strike out in a new direction.
“We wanted to make the process available for big components too, for instance in aircraft manufacturing, by means of an appropriate release film,” says Gregor Grasl, FFM project manager. While release films are already commercially available, they are very stiff. This means they cannot be deep drawn and are suited only to simple mould contours. The IFAM scientists, on the other hand, are using a film that, while tough, also demonstrates up to 300 percent elasticity. What’s more, at less than 0.1mm it is extremely thin. “That means it can also be applied to curved or structured surfaces without creasing,” says Grasl.
The challenge that had to be overcome was how to get the coating to stick to the film. “We developed a plasma process which relaxes the release layer. Put another way, the layer enters a state of equilibrium as soon as the plasma is turned off and no more highly reactive particles are formed, and the molecules it contains then organise themselves such that the surface no longer exhibits any reactive groups,” explains Ott.
As a result, the resin of the composite part does not bond with the release layer, but the release layer bonds very well with the film – not detaching even when subjected to forces such as extreme stretching. In contrast to the films available to date, this new film leaves no residues of release agents on fibre-reinforced plastic (FRP) components. “We are using what amounts to a new class of materials that, by virtue of their chemical structure, are harder than classic polymers,” says Ott.
The film, known as FlexPLAS, has already demonstrated that it can cope with real-life production demands in the FFM development lab.