Cellulose gypsum based substrate with increased water resistance and strength by surface application of polymeric diphenylmethane diisocyanate

Abstract

The disclosed invention consists of an improved gypsum based, cellulosic containing board and method for applying a resin to an untreated board at a spray station where pMDI resin is sprayed onto the front and back side of the board. A resin distribution system is used to supply the spray nozzles with pMDI. Optionally, a second spray station is included, if desired, to add additional pMDI resin over the surface of the board to achieve complete coverage. The improvement is an increased water resistance and flexural strength.

What is claimed is:  
     
         1 . A water-resistant structural panel comprising: 
 gypsum and cellulose fibers, the cellulose fibers being present at a surface of said structural panel; and    a matrix of a polyurethane resin and said cellulose fibers formed at and below said surface of said structural panel to create a water-resistant barrier at said surface.    
     
     
         2 . The water-resistant structural panel of  claim 1 , wherein said panel has a flexural strength increase from about 20% to about 35%.  
     
     
         3 . The water-resistant structural panel of  claim 1 , wherein said panel has a water absorption rate of about 0.5 grams of water per a 2 hour period.  
     
     
         4 . The water-resistant structural panel of  claim 1 , wherein said surface has an increase in scuff resistance.  
     
     
         5 . The water-resistant structural panel of  claim 1  wherein said surface has a decrease in the amount of dust generated during handling.  
     
     
         6 . A method of applying a non-aqueous polymeric resin to a gypsum based board having cellulosic fibers at its surface including the steps of: 
 providing a gypsum based substrate;    providing a spray system having nozzles;    pumping the polymeric resin through said nozzles;    uniformly applying the polymeric resin onto said substrate by spraying the polymeric resin onto said substrate, thereby transferring the polymeric resin from said nozzles to said substrate; and    allowing the polymeric resin to cure within said substrate.    
     
     
         7 . A method in accordance with  claim 6  wherein the step of pumping the polymeric resin to said nozzles includes the step of providing a resin distribution system to continuously pump the polymeric resin to said nozzles.  
     
     
         8 . A method in accordance with  claim 6  wherein the step of uniformly applying the polymeric resin onto said substrate retains the thickness of the board.  
     
     
         9 . A method in accordance with  claim 6  wherein the step of providing a spray system having nozzles includes the placement of said nozzles within from about 8 inches to about 10 inches from the gypsum based substrate.  
     
     
         10 . A method in accordance with  claim 6  wherein the step of providing a spray system having nozzles includes nozzles that have a fan spray pattern.  
     
     
         11 . A method in accordance with  claim 6  wherein the step of providing a spray system having nozzles includes the separation of said nozzles by about 3 inches.  
     
     
         12 . A product made in accordance with the method of  claim 6 .  
     
     
         13 . A spray apparatus for applying a non-aqueous polymeric resin to a gypsum based substrate having cellulosic fibers at its surface including: 
 a spray bar having nozzles;    means for supplying the polymeric resin and spraying said polymeric resin onto said gypsum based substrate.    
     
     
         14 . The spray apparatus in accordance with  claim 13  wherein the means for supplying the polymeric resin to said nozzles is a resin distribution system.  
     
     
         15 . The spray apparatus in accordance with  claim 13  wherein said nozzles are placed from about 8 inches to about 10 inches from said gypsum based substrate.  
     
     
         16 . The spray apparatus in accordance with  claim 13  wherein said nozzles have a fan spray pattern.  
     
     
         17 . The spray apparatus in accordance with  claim 13  wherein said nozzles spray the polymeric resin at a rate from about 9 pounds to about 25 pounds per 1000 square feet.