Hardening of bonding systems
The present invention provides bonding systems comprising a formaldehyde-based (urea-/melamine-/phenol-/resorcinol-formaldehyde or other combination) and/or a polymeric isocyanate resin system composition for bonding ligno-cellulosic materials to form panels and/or shaped products, which contain a resin hardener, also referred to as resin catalyst, characterised in that the hardener is activated by heat.
1. A composite structure comprising:
a mat of ligno-cellulosic materials having at least:
a first layer of the ligno-cellulosic materials combined with a first glue mix, the first glue mix of the first layer including a resin based on at least one of formaldehyde and polymeric isocyanate;
a second layer of the ligno-cellulosic materials combined with a second glue mix, the second glue mix of the second layer also including the resin based on at least one of formaldehyde and polymeric isocyanate; and a third layer of the ligno-cellulosic materials combined with a third glue mix, the third glue mix of the third layer also including the resin based on at least one of formaldehyde and polymeric isocyanate;
a resin hardener formed by a salt having an acid moiety and a base moiety;
wherein one of the acid moiety and the base moiety of the resin hardener is a more volatile moiety, the more volatile moiety activating hardening of the resin in the first glue mix of the first layer upon vaporization; wherein the second and third layers are surface layers of the mat and the first layer is a core layer located therebetween; and
wherein the resin hardener is not in the first glue mix of the first layer, the resin hardener being instead either:
sprayed onto only outer surfaces of surface layers of the mat; or
included in the second and third glue mixes of the second and third layer of the ligno-cellulosic materials, respectively.
2. The composite structure of claim 1 , wherein the resin includes a urea-formaldehyde resin, a melamine-formaldehyde resin, a phenol-formaldehyde resin, a resorcinol-formaldehyde resin or a combination of the aforementioned resins.
3. The composite structure of claim 1 , wherein the resin is derived from the reaction of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) with poly-hydroxy functional compounds.
4. The composite structure of claim 1 , wherein the composite structure is shaped to form a particleboard, a medium density fibreboard, a high density fibreboard, an oriented strand board or plywood.
5. The composite structure of claim 1 , wherein the mat further includes a third layer, both the second and third layers being the surface layers with the first layer being a core layer located therebetween; and
wherein the resin hardener is included in the second glue mix of the second layer and in a third glue mix of the third layer.
6. The composite structure of claim 1 , wherein conventional curing catalysts are in at least the first glue mix.