Inclusions in painted surfaces

When painting and coating components, even the smallest surface defects such as craters, specks or bubbles can massively impair the visual impression. While paint craters are generally caused by trace contamination with grease, oil or release agents, spots, pimples or other localized elevations in the paint surface are often caused by the inclusion of foreign particles such as dust particles, metal abrasion, hair or fibres. To reliably avoid such errors, it is first necessary to characterize the shape and composition of the trapped foreign particles as precisely as possible. Together with suitable sample preparation, microanalytical methods such as SEM/EDX, FTIR microscopy or TOF-SIMS can provide valuable information.

Example: On powder-coated aluminum profiles, pimple-shaped elevations are occasionally observed in the paint surface. SEM images of a cross-sectional area through a typical defect show that a foreign particle is trapped in the paint layer, which extends to the paint surface but has no contact with the base material. EDX element analyses only detect aluminum in the area of the inclusion, while the intact coating layer only contains the typical binder elements carbon and oxygen.
Overall, the investigations show that the paint defects are caused by small aluminum chips, which presumably only reach the surface during the coating process and are incorporated into the not yet cured paint layer.