Effects of manufacturing variables on surface quality and distribution of melamine formaldehyde resin in paper laminates

Paper impregnated and coated with thermosetting resins is commonly used as a decorative and protective laminate for wood composites. The paper laminates are manufactured in a paper treater by impregnating décor paper with a mixture of melamine (MF) and urea formaldehyde (UF) resin or UF resin. This resin is then cured, and the paper is coated with a protective layer of MF resin. There is ongoing pressure to reduce the production cost of the laminates by increasing paper treatment speeds and minimizing the consumption of the expensive MF resin. Attempts to implement such strategies often result in poor quality laminates that contain defects (unfilled pores) in the MF coating. Examination of the relationship between UF resin treatment and paper type on the surface quality and distribution of MF resin in treated and pressed laminates revealed that the level of UF resin treatment strongly influenced the quality of the MF coating in laminates. Low levels of UF resin treatment (< 25.0 g m^-2) are associated with high levels of coating defects, and certain paper types in particular are prone to develop such defects. Scanning electron microscopy and Raman microscopy reveal that defects in MF coatings occur when MF resin flows from the surface of paper into voids that have not been filled by UF resin. The implications of these findings for the manufacture of protective laminates for use in low-pressure melamine panels are discussed briefly.