Science et Surface was asked to study a problem of white spots in production when dyeing polyamide glue points. An analytical method has been set up to characterise these white spots by linking a morphological and chemical analysis in order to compare with a compliant area of glue.
Observations under the microscope showed a difference in morphology between the areas of compliant and non-compliant glue (white spot) with a slight chemical contrast and the presence of an interface line between tinted and non-tinted areas at the white spots.
The study showed that the white spots are polyester beads, which are located above the dyed polyamide glue points. The fault is therefore not related to a problem with the colour of the glue points, but due to contamination present when the glue was applied.