Without time-consuming and cost-intensive pretreatment operations such as padding and flame treatment, SMC parts are still very susceptible to suffer defects by coating processes. Incomplete curing causes post-curing reactions, emissions, and thermal weight loss in the coating process. In addition, the surface properties are considerably changed during the post-curing and in dependence of the coating process conditions (temperature, curing time) and the SMC formulation, which affects the coating behavior of the material.
Within a project sponsored by the Federal Ministry of Education and Research (BMBF), scientists of the Leibniz-Institut für Polymerforschung Dresden e. V. (IPF) have shown that an electron treatment of the SMC parts before coating can prevent these problems.
The electron treatment ensures complete curing within a short period of time and an energy-efficient way, thus avoiding post curing at a later stage. Fogging is drastically reduced or even suppressed. In addition, the electron treatment leads to functionalization and hydrophilic properties of the SMC surface, which has a positive effect on wetting, flow, and adhesive strength of the coating layers.
To get optimum effects, electron energy and dose must be precisely tuned according to the SCM formulation and the molding conditions.
For the novel technology a patent application has been filed. At present, its suitability for use in industrial coating of 3D SMC parts is validated within another BMBF-sponsored project.
Compact electron accelerators, which are available on the market, will allow to integrate the additional process step in line at reasonable costs.
Contact: Dr. Michaela Gedan-Smolka