COATING FAILURE ANALYSIS
of point defects (case 21)
What’s the cause of the coating failure?
A manufacturer of luminescent screens for medical X-ray imaging had a problem with the presence of point defects in topcoats of screens in a test production. An urgent coating failure analysis was needed to identify the cause of this defect.
Several point defects were analyzed with an optical microscope and by means of a scanning electron microscope (SEM). Microtome cross-sections through the point defect were prepared and examined.
Coating failure explained and fixed
At the surface of the protective topcoat, the defects had the appearance of collapsed bubbles. In the cross-sections, cavities were found directly below the point defects.
Through discussion with the customer, it was concluded that (incompletely blended) gel particles in the binder formulation were the most probable cause of the coating failure. The excessive amount of solvent in these particles was responsible for the cavities and bubble formation at the surface.
Based on this analysis, the customer decided to run another test production with an alternative binder/solvent combination, which was successful.
Agfa-Labs has a long history of analyzing and resolving coating failures due to exogenous contamination, for example by dust particles.
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