Process for producing smooth strand-based siding or structural panels using secondary pressing
A process for producing a smooth-sided strand-based siding or wood structural panel using a secondary pressing process. The secondary pressing process is performed after the primary process completes pressing and consolidation of the substrate/board. The secondary process applies and cures the overlay after applying a water spray on the hot board immediately out of the primary process press, and before overlay application. The application of the water spray causes the surface of the board to swell and cure. A settling period follows to allow the top surface particles and strands to swell along with absorption and evaporation of the moisture. This is followed by surface sanding to remove the telegraphing and produce a smooth surface, which is then followed by lamination of the overlay(s). The process is completed by post-lamination treatment and coating of the board.
1. A manufacturing process for producing a smooth-sided strand-based product, comprising the steps of:
blending cellulosic strands with one or more additives or chemicals;
forming a mat from said cellulosic strands;
applying heat and pressure to the mat in a primary pressing process to form a board;
trimming the board to form a master blank;
while the master blank is still heated from the primary pressing process, and prior to application of one or more overlays to a surface of the master blank, pre-telegraphing the cellulosic strands in the surface of the master blank by causing said cellulosic strands to swell, wherein the step of pre-telegraphing comprises
causing the cellulosic strands in the surface to swell by applying a water-based spray to said surface sufficient to elevate the moisture content of the master blank to approximately 3% moisture content, wherein the water-based spray comprises water and one or more chemicals or hydrophobic agents;
covering the master blank; and
storing the covered master blank for a settling period of approximately 14 days to allow said cellulosic strands to swell;
after the settling period, and prior to application of one or more overlays to the surface of the master blank, removing imperfections in the pre-telegraphed surface by sanding the pre-telegraphed surface;
applying one or more overlays to the surface; and
applying heat and pressure to the master blank in a secondary pressing process to adhere the one or more overlays to the surface of the master blank;
wherein the mat comprises a first surface and a second surface, and further comprising the step of pressing a texture in the first surface of the mat during the primary pressing process;
further wherein the step of pre-telegraphing is applied to the second surface.
2. The manufacturing process of claim 1 , further comprising applying cellulosic fines to a surface of the mat prior to the primary pressing process.
3. The manufacturing process of claim 1 , wherein the secondary pressing process uses platen surface temperatures no greater than approximately 450 degrees F.
4. The manufacturing process of claim 1 , wherein the step of forming the mat from said cellulosic strands comprising first forming a bottom surface layer of cellulosic strands, then forming a center core layer over the bottom surface layer, then forming a top surface layer over the center core layer.
5. The manufacturing process of claim 4 , wherein the cellulosic strands forming the top surface layer differ in size between larger and finer, and forming the top surface layer comprises depositing the larger cellulosic strands first so that finer cellulosic strands are situated more closely to the top surface of the mat.
6. The manufacturing process of claim 4 , wherein the cellulosic strands forming the bottom surface layer differ in size between larger and finer, and forming the bottom surface layer comprises depositing the finer cellulosic strands first so that finer cellulosic strands are situated more closely to the bottom surface of the mat.
7. The manufacturing process of claim 1 , wherein two overlays are applied, first a cushion overlay to reduce further telegraphing of the first surface, and then a final overlay as a finished surface.
8. The manufacturing process of claim 1 , further comprising post-press processing the master blank to produce a finished panel.