Patent ID: 6517907
Filing Date: 2003-02-11
Classification: B05D,B27K

Abstract:
A method of performing an impregnating treatment on a resin-containing wood substrate using a fluid in supercritical state as a delivering solvent medium, which fluid in supercritical state is soluble in the resin present in the wood substrate, comprising the steps of(i) introducing the wood substrate into a pressure tight treatment chamber, (ii) introducing a stream comprising said fluid into the chamber and adjusting the pressure and temperature therein to ensure the fluid being present in supercritical state and to promote penetration of the fluid and any substances dissolved therein into the wood substrate, (iii) maintaining contact between the wood substrate and the fluid in supercritical state and the fluid in supercritical state for a time period sufficient to obtain the desired penetration, whereby also a certain dissolution of the fluid into the resin takes place, (iv) after a possible purging of the chamber with said fluid in supercritical state, releasing the pressure in the chamber down to ambient pressure, and (v) withdrawing the treated wood substrate containing the dissolved fluid and any substances dissolved therein from the chamber, characterized in that the releasing step (iv) comprises the features:(a) starting releasing the pressure, (b) recovering the fluid exhausted from the chamber during this release, (c) before harmful exudation of resin to the surface of the wood substrate takes place, displacing at least partially the resin-soluble fluid in the chamber by a second fluid being less soluble in resin that the displaced fluid, and (d) continuing the pressure release of the chamber without harmful exudation of resin to the surface of the wood substrate, at a rate which would have caused such resin exudation if the displacement defined in (c) were omitted.