Chemical Surface Modification of Polycarbonate at Injection Molding - Process and Surface Characterization
Jürgen Nagel, Matthias Bräuer, Bernd Hupfer, Dieter Lehmann
Institute of Polymer Research Dresden e.V.
Germany

Keywords: surface modification, injection molding, melt reactions

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The surface of plastic parts has often a low surface energy and needs to be modified. Commercial processes are plasma and flame treatment, which always has to be made in a separate stage. Since the effect mostly vanishes after a short time, this activation has to be done shortly before the plastic part is bonded or lacquered.
A new method has been developed for the surface modification and activation, respectively, of polycarbonate. In the first step the mould has to be wetted with a solution of reactive macromolecular modifier which contain amine or aliphatic hydroxyl groups. After evaporation of the solvent a thin film of the modifier retains on the mould surface. At the injection step the hot melt front hits the modifier, and a reaction takes place which attaches the modifier covalently to the melt surface and, thus, to the surface of the later plastic part.
In the contribution the chemical and physical basics are analyzed. The methods is described in detail. The surface of the modified parts is analyzed by contact angle, electrokinetic potential, and by ATR-FTIR spectra, fluorescence and uv/vis absorption spectroscopy. Spectroscopic labels are used to characterize the reactivity of the functional chemical groups at the surface. The conclusions are supported by DSC investigations of the melt reaction. The experiments reveal that the macromolecular modifier is bound covalently to the plastic part surface. The modified surface contains reactive groups which can be used for further processes. The effect is permanent.
With the new method a plasma or flame treatment may be saved for some applications. The method may be transferable to other polymers and other molding processes. Applications of surfaces modified with the new method may be wetting/dewetting, reactive bonding, improvement of paint adhesion, metallization, and electrical surface conductivity for instance.