Dye marking of phenoplast impregnated materials - which alters under press and high temp

摘要

Certain dyes are used for the marking of phenoplast impregnated base materials for the prepn. of coatings or for the surface prepn. of industrial materials, e.g. Kraft paper. The dyes show a colour alteration under press. conditions at elevated temp. in the presence of the phenoplast resins, which is masked by the colour of the crosslinked condensation resin. The dye may be used to distinguish between differently treated base materials.