Oriented strand boards

Abstract

Oriented strand board (OSB), comprising a core layer and two face layers, whereby the face layers comprise an adhesive composition, wherein the adhesive composition in at least one of the face layers comprises a resin composition comprising melamine, formaldehyde, optionally urea and aromatic hydroxyl compounds, wherein the molar ratio of melamine to formaldehyde is 1:0.84.0, the molar ratio of melamine to urea is 1:0-2.0 and the molar ratio of melamine to aromatic hydroxyl compounds is 1:0-2.0. In a preferred embodiment, both the face layers and the core layer comprise the said adhesive composition. The OSB's according to the invention can meet the OSB/3 and even the OSB/4 requirements in the EN 300 standards.

1 . Oriented strand board (OSB), comprising a core layer and two face layers, whereby at least the core layer comprises an adhesive composition, wherein the adhesive composition in the core layer comprises a resin composition comprising melamine, formaldehyde, optionally urea and optionally an aromatic hydroxyl compound, and wherein the molar ratio of melamine to formaldehyde is 1:0.8-1:9, the molar ratio of melamine to urea is 1:0-1:6, and the molar ratio of melamine to aromatic hydroxyl compound is 1:0-1:2. 
   
   
       2 . Oriented strand board according to  claim 1 , wherein the resin in the adhesive composition of the core layer has a molar ratio of melamine to formaldehyde of 1:0.8-1:4 and a molar ratio of melamine to urea of 1:0-1:2. 
   
   
       3 . Oriented strand board according to  claim 1 , wherein the amount of resin in the core layer is 2.5-8 wt % dry resin/dry wood. 
   
   
       4 . Oriented strand board according to  claim 1 , wherein the amount of urea in the core layer is 0-0.025 kg/kg core layer. 
   
   
       5 . Oriented strand board according to  claim 1 , wherein the OSB has a thickness swell lower than 15 or 12% according to the OSB/3 or OSB/4 standard, respectively. 
   
   
       6 . Oriented strand board according to  claim 1 , wherein the OSB has an internal bond value after boiling according to the OS/3 or OSB/4 standard. 
   
   
       7 . Process for the preparation of an oriented strand board (OSB), comprising the steps of:
 a) preparing an adhesive composition comprising a resin composition comprising melamine, formaldehyde, optionally urea and an aromatic hydroxyl compound, wherein the molar ratio of melamine to formaldehyde is 1:0.8-1:9, the molar ratio of melamine to urea is 1:0-1:6 and the molar ratio of melamine to aromatic hydroxyl compound is 1:0-2.0;   b) treating wood strands with the adhesive composition;   c) scattering adhesive-treated wood strands for a face layer, a core layer on top of the face layer, and again a face layer on top of the core layer, whereby the wood strands of at least the core layer were treated with the adhesive composition prepared in a);   d) pressing the wood strands, whereby the adhesive composition is at least partially cured, to form an OSB.   
   
   
       8 . Process according to  claim 7 , wherein the resin composition as used in step a) has a molar ratio of melamine to formaldehyde of 1:0.8-1:4, and a molar ratio of melamine to urea of 1:0-1:2. 
   
   
       9 . Process according to  claim 7 , wherein the wood strands of the face layers and of the core layer were treated with an adhesive composition as prepared in step a).