Patent ID: 6623600
Filing Date: 2003-09-23
Classification: B01D,B27K

Abstract:
A method of performing an impregnating treatment on a resin-containing wood substrate using a fluid in supercritical state as 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 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 to improve surface properties of the treated wood substrate, and (v) withdrawing the treated wood substrate from the chamber, characterized in that the releasing step (iv) comprises the features: (a) starting releasing the pressure at a rate which, if it were continued until atmospheric pressure were reached, would cause exudation of resin from the interior of the wood substrate to the surface thereof due to bubble forming expansion of the fluid dissolved in the resin in step (iii), (b) interruption said releasing at a first pressure level, (c) increasing the pressure to a second level above said first level but below the pressure maintained in step (iii), (d) immediately after reaching said second pressure level resuming pressure release to decrease the pressure to a third level below said first level, (e) subsequently at least once repeating a release operation comprising pressure increase to a level below the maximum level of the immediately preceding release operation, instantly followed by pressure decrease to a level below the minimum level of the immediately preceding release operation, wherein the number of release operations in (e) and the pressure levels in each of these operations as well as in the steps (b), (c) and (d) are previously fixed on basis of simple experiments, using relevant specimens of wood or resin, to obtain a shorter total release time (a)+, (b)+, (c)+, (d)+ and (e)+, than would have been possible if the pressure were released by a continuous, uninterrupted withdrawal of the fluid for a predetermined time.