DEPTH PROFILING OF ACRYLIC MELAMINE FORMALDEHYDE COATINGS/

The depth dependences of the glass transition temperature, the crossli nk density, and the triazine/styrene and nitrogen/carbon ratios have b een investigated in acrylic/melamine coatings. Depth profiles were det ermined by using a microtome technique which produced slices large eno ugh (5 x 5 cm) to employ as analytical tools dynamic mechanical analys is, differential scanning calorimetry, and elemental analysis. The tri azine/styrene ratios were derived from infrared absorption spectra. De pending on the cure conditions, gradients perpendicular to the coating surface were observed for the glass transition temperature, the cross link density, and the triazine/styrene infrared absorbance ratio, For 30 min cure time, these gradients existed in coatings cured below 160 degrees C. The nitrogen/carbon ratios of the crosslinked. resins, dete rmined from elemental analysis and X-ray photoelectron spectroscopy, s tayed constant in samples in which the other parameters investigated c hanged with depth. The gradients of the glass transition temperature a nd crosslink density are believed to originate from a shift of the che mical reaction equilibrium of the crosslinking reaction. Trapped isobu tanol, a reaction by-product, is assumed to be responsible for this sh ift.