Functional Coating: Atmospheric Pressure Plasma Treatment On 3D Printed Polymer Surfaces

3D-printed components have an unmistakable advantage: they have a very free shape. But when it comes to coating, especially when other materials are subsequently functionalized, this free form may become a problem. The free form of the 3D components makes them inaccessible to many coating processes, especially low-pressure ones. In addition, it is difficult to combine 3D printing processes such as fused deposition modelling (FDM) with low-pressure coating processes such as sputter deposition, evaporation, plasma-assisted chemical vapour deposition.

The actual material surface is an important influencing factor that significantly determines the usability of many plastic materials. The aim is to change surface chemistry through coating and functionalisation processes. In the case of coatings, the layer-forming material brings the required chemical groups with it, while functionalization causes the chemical groups to couple directly to the surface.

The aim is to create surfaces that strengthen or reduce adhesion to other coatings or materials, reduce migration of plasticizers and improve mechanical or chemical resistance to environmental influences.

Dr Thomas Neubert, project manager at the Fraunhofer Institute for Thin Films and Surface Technology in Braunschweig, Germany, writes in an article in the journal ‘Plastverarbeiter‘ that one solution could be to use the atmospheric pressure plasma process, which can be integrated into FDM systems in the form of plasma jets.

Combination Of 3D Printing And Plasma Jet Coating

At the Fraunhofer Institute, so-called dielectrically impeded discharges (DBE) are used. High voltages lead to an electrical gas-discharge in a gap between two electrodes, which serves as the actual energy source. It has been shown that the combination of 3D printing and plasma jet coating also successfully coats the inner surfaces of the polymer implants. Depending on the structure density, the working gas flow and the precursor vapour pressure, the coatings penetrated several millimetres into the polymer structure. It is also possible to pulse the electrical power of the plasma jet, thereby possibly increasing the density of the nucleophilic groups on the substrate surface.

The concentration on such a process becomes clear when one considers that atmospheric pressure plasma processes – compared to other gas-phase coating processes – are characterized by low investment costs, high treatment speeds and good scalability. In addition, there are various industrially established treatment sources for flat, curved or three-dimensional substrates.