Crack-resistant melamine/formaldehyde-impregnated paper-decorated panels using blocked isocyanates as a temperature-responsive crosslinker

Melamine–formaldehyde (MF) resin-impregnated paper-decorated panels are prone to surface cracking, which can be reduced by changing the brittle structure of the MF resin. To increase the curing degree and toughness of the resin, a hexamethylene diisocyanate trimer blocked with methyl ethyl ketoxime (ME-HDI-tri) was used as a temperature-responsive crosslinker. This latent crosslinking agent only worked above 120 °C, which prevented it from participating in cross-linking reactions during the preparation of the impregnated paper. The chemical structures of the modified MF resins (ME-HDI-tri-MF) were characterized by Fourier-transform infrared (FTIR) spectroscopy. The curing behaviors of the MF resins were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). Impregnated paper was prepared with ME-HDI-tri-MF, and its tensile strength and elongation at break were tested. Blockboard was prepared with ME-HDI-tri-MF, and its cracking and corrosion resistance were tested. The absorption peak of the methylene chain was observed in the FTIR spectrum of ME-HDI-tri-MF after curing, which indicated that ME-HDI-tri participated in the curing reaction of the MF resin. With the addition of ME-HDI-tri 5 %, the curing temperature of the MF resin decreased from 142 °C to 130 °C, and the ultimate tensile stress and elongation at break of the modified impregnated paper increased by 97.70 % and 86.25 %, respectively. The cracking and corrosion resistance of the decorated panel prepared with ME-HDI-tri-MF were also improved. After adding 3 % ME-HDI-tri, the surface cracking of the decorated panels was prevented, which extended the service life and broadened the application range of the decorated panels.