WATERBASED FORMALDEHYDE FREE ADHESIVES

摘要

There is described a formaldehyde-free laminating adhesive, optionally the with less than 3% by weight of co-solvent(s), the adhesive comprising: (I) a polyurethane that comprises from 30 % to 65 % by weight of hard segments, the polyurethane being obtained and/or obtainable from a first polyurethane dispersion (PUD) comprising the reaction product of (A) an organic isocyanate and (B) at least one chain extender reacting in a respective stoichiometric ratio (NCO to NCO reactive group) from 1:1 to 1:2.5 and; optionally the NCO reactive group(s) of the chain extender comprises one or more hydrazinyl-like group(s) (denoting isocyanate reactive groups selected from the group comprising, preferably consisting of: -NRNR2(hydrazinyl groups); -CONRNR2 (hydrazidyl groups), -NRCONRNR2 (semicarbazidyl groups); and -ONR2 (oxyamine groups), where each R is independently selected from H or C1-10hydrocarbo); and (II) optionally a second polymer obtained and/or obtainable from a polymer precursor comprising at least one unsaturated moiety, preferably an ethylenically unsaturated group, and where optionally the second polymer may be iminated; with the provisos that: (a) when the first polyurethane does not comprise hydrazinyl-like group(s) then the second polymer is iminated; and (ß) when the second polymer is un-iminated or is absent then the first polyurethane comprises hydrazinyl-like group(s). These adhesives may be used to adhere surface veneers to wood and/or to laminate the layers within plywood.