Extruded plastic lumber and method of manufacture

Abstract

A composite reinforced plastic lumber article, such as a board or a plank having a generally rectangular cross-section, is formed by extruding a wood particle/polymer composition through an extrusion die which forms a corrugated or relatively thin sheet cross-section core part. The core part is compressed to push corrugations closer together and then cooled in a two-stage cooling process with water spray and submersion followed by vacuum and air blast drying of the article, followed by extruding an outer coating of the same composition over the core part. A continuous plank-like composite article is thus formed and is cooled after the outer coating is extruded over the core part. Opposed surfaces of the article may be embossed to provide a woodgrain appearance. The two-stage article forming process provides more rapid cooling of the material to enhance the speed of production of reinforced plastic lumber articles and the like.

What is claimed is:  
     
         1 . An extruded plastic lumber article comprising: 
 a core part formed of a polymer material and having a cross-section which is compressed after extrusion through an extrusion die; and    a polymer coating disposed over the surfaces of said core part to encapsulate said core part to form said article.    
     
     
         2 . The article set forth in  claim 1  wherein: 
 said core part is formed to have a cross-section comprising repeated corrugations between one side of said core part and an opposite side of said core part.  
 
     
     
         3 . The article set forth in  claim 1  wherein: 
 opposed surfaces of said coating are embossed.  
 
     
     
         4 . The article set forth in  claim 1  wherein: 
 the composition of said core part and said coating comprises one of polypropylene and polyethylene.  
 
     
     
         5 . The article set forth in  claim 1  wherein: 
 the composition of one of said core part and said coating comprises one of reinforced polyethylene and polypropylene.  
 
     
     
         6 . The article set forth in  claim 5  wherein: 
 said one of said polypropylene and polyethylene is reinforced by wood particles.  
 
     
     
         7 . The article set forth in  claim 6  wherein: 
 the composition of said core part and said coating comprises about 25% wood flour and 75% polypropylene, by weight.  
 
     
     
         8 . A plastic lumber article comprising: 
 a core part having a cross section comprising repeated corrugations extending between one side of said core part and an opposite side of said core part, said core part being formed of a reinforced polymer; and    a coating disposed over the surfaces of said core part to encapsulate said core part, said coating being formed of one of a polymer and a reinforced polymer.    
     
     
         9 . The article set forth in  claim 8  wherein: 
 said corrugations are compressed to be substantially contiguous with each other.  
 
     
     
         10 . The article set forth in  claim 8  wherein: 
 said core part is reinforced by wood particles dispersed throughout said core part.  
 
     
     
         11 . The article set forth in  claim 8  wherein: 
 said article is reinforced by at least one sheet of metal foil disposed between said core part and said coating.  
 
     
     
         12 . The article set forth in  claim 8  wherein: 
 said coating is reinforced by wood particles.  
 
     
     
         13 . The article set forth in  claim 8  wherein: 
 the composition of said core part and said coating comprises one of wood particles dispersed in polypropylene or polyethylene.  
 
     
     
         14 . The article set forth in  claim 8  formed by a process which includes: 
 extruding said core part;  
 cooling said core part after extrusion thereof; and  
 extruding said coating over said core part.  
 
     
     
         15 . The article set forth in  claim 8  formed by a process which includes: 
 compressing said corrugations to be substantially contiguous with each other before encapsulating said core part in said coating.  
 
     
     
         16 . The article set forth in  claim 15  formed by a process which includes: 
 cooling said core part after compressing said corrugations.  
 
     
     
         17 . The article set forth in  claim 16  formed by a process which includes: 
 passing said core part though a water spray to cool said core part.  
 
     
     
         18 . The article set forth in  claim 16  formed by a process which includes: 
 supporting at least opposite sides and a third side of said core part by support rollers while cooling said core part.  
 
     
     
         19 . The article set forth in  claim 8  formed by a process which includes: 
 providing an embossing on at least one surface of said article after disposing said coating over said core part.  
 
     
     
         20 . The article set forth in  claim 8  formed by a process which includes: 
 cooling said article after disposing said coating on said core part by passing said article in a continuous extrudate thereof through a quantity of cooling liquid.  
 
     
     
         21 . The article set forth in  claim 20  formed by the process which includes: 
 blowing pressure air over said article after removal of said article from said cooling liquid to remove liquid from the surfaces thereof.  
 
     
     
         22 . The article set forth in  claim 8  formed by a process which includes: 
 passing said core part through a vacuum chamber before disposing said coating over said core part.  
 
     
     
         23 . The article set forth in  claim 8  formed by a process which includes: 
 pulling said article through an extruder to apply said coating.  
 
     
     
         24 . The article set forth in  claim 8  formed by a process which includes: 
 pulling said article through a set of embossing rollers and a cooling liquid tank with a pulling apparatus engaged with said article at a point downstream of said tank in the direction of movement of said article.  
 
     
     
         25 . A method for forming an extruded plastic lumber article comprising a core part formed of a reinforced polymer material encapsulated by a coating of a polymer material disposed over the surfaces of said core part, said method comprising the steps of: 
 forming said core part to have a cross section comprising repeated corrugations extending between one side of said core part and an opposite side of said core part;    cooling said core part after formation thereof;    extruding said coating over said core part to form said article;    cooling said article to reduce the temperature thereof; and    cutting said article into discrete lengths.    
     
     
         26 . The method set forth in  claim 25  including the steps of: 
 compressing said corrugations toward each other after forming said corrugations.  
 
     
     
         27 . The method set forth in  claim 26  including the steps of: 
 cooling said core part with a cooling liquid after compressing said corrugations.  
 
     
     
         28 . The method set forth in  claim 27  including the steps of: 
 supporting said core part by support roller means while cooling said core part.  
 
     
     
         29 . The method set forth in  claim 27  including the step of: 
 applying a vacuum to said core part after cooling said core part to remove moisture therefrom.  
 
     
     
         30 . The method set forth in  claim 27  including the step of: 
 blowing pressure air over said core part to remove cooling liquid from the surfaces thereof.  
 
     
     
         31 . The method set forth in  claim 25  including the step of: 
 embossing at least one surface of said article after extruding said coating over said core part.  
 
     
     
         32 . The method set forth in  claim 25  including the step of: 
 cooling said article after extruding said coating by passing said article in a continuous extrudate thereof through a quantity of cooling liquid.