Veneering or covering boards, esp. chipboard, using urea! resin glue - with addn. of hardener system contg. strong acid before or during pressing

摘要

In covering surfaces (boards) with veneers, films, impregnated papers etc. by applying an (extended) urea resin glue to =1 of the surfaces and curing under pressure, opt. at elevated temp., a hardener system contg. a strong acid and/or substance with strongly acidic reaction is added before or on pressing. The hardener system pref. also contains film-forming substances and/or conventional additives (antifoam, wetting agent etc.) and has pH 4, pref. 2. The process is used esp. in the prodn. of chipboard and in veneering. The hardener system pref. contains (organic) acids with a m. pt. above room temp., pref. (ar)aliphatic or aromatic dicarboxylic acids (malonic, phthalic and/or sulphonic acids), Lewis acids (AlCl3, ZnCl2), acid anhydride amides or hydrazides or readily hydrolysed salts of a strong acid with a weak base. A buffered hardener may be added. PVA, cellulose (derivs), starch (degradation prods polyvinylpyrrolidone, poly(meth)acrylic acid salts, (co) polyacrylamides and other paper finishing film-forming binders can be added. The resin concn. is 0.5-50 pref. 5-20 wt. % and the pressing temp. 100-150 degrees C or, if wood with a high moisture content or colour-sensitive veneers are used, below 100 degrees C.