Polymeric structural panel

Abstract

A polymeric twin wall board which includes a first substantially planar sheet forming the upper side of the board, a second substantially planar sheet forming the underside of the board and a plurality of spaced longitudinally extending webs connecting the first substantially planar sheet to the second substantially planar sheet wherein the difference between the level of the top surface of the first substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extending webs is no more than about 1% of the average distance between adjacent longitudinally extending webs.

The claims defining the invention are as follows:  
     
         1 . A polymeric twin wall board which includes a first substantially planar sheet forming the upper side of the board, a second substantially planar sheet forming the underside of the board and a plurality of spaced longitudinally extending webs connecting the first substantially planar sheet to the second substantially planar sheet wherein the difference between the level of the top surface of the first substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extending webs is no more than about 0.1% of the average distance between adjacent longitudinally extending webs.  
     
     
         2 . A polymeric twin wall board as claimed in  claim 1  wherein the difference between the level of the top surface of the first substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extending webs is no more than about 0.5% of the average distance between adjacent longitudinally extending webs.  
     
     
         3 . A polymeric twin wall board as claimed in either one of claims  1  or  2  wherein the longitudinally extending webs are equally spaced.  
     
     
         4 . A polymeric twin wall board as claimed in any one of  claims 1  to  3  wherein the difference between the level of the outer surface of the second substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the second substantially planar sheet intermediate any of the adjacent webs is no more than about 1% of the average distance between adjacent longitudinally extending webs.  
     
     
         5 . A polymeric twin wall board as claimed in  claim 4  wherein the difference between the level of the outer surface of the second substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the second substantially planar sheet intermediate any of the adjacent webs is no more than about 0.5% of the average distance between adjacent longitudinally extending webs.  
     
     
         6 . A polymeric twin wall board as claimed in any one of the previous claims which includes longitudinally extending webs which are separated by a distance of between 2.0 to 5.0 mm.  
     
     
         7 . A polymeric twin wall board as claimed in  claim 6  wherein the difference between the level of the top surface of the first substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extending webs is no more than 0.020 mm.  
     
     
         8 . A polymeric twin wall board as claimed in  claim 7  wherein the difference between the level of the top surface of the first substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extending webs is no more than 0.010 mm.  
     
     
         9 . A polymeric twin wall board as claimed in any one of  claims 1  to  8  wherein the first and second substantially planar sheets are of equal thickness and the thickness is between 0.1 to 0.3 mm.  
     
     
         10 . A polymeric twin wall board as claimed in any one of the previous claims made from a homopolymer or copolymer of polypropylene.  
     
     
         11 . A polymeric twin wall board as claimed in any one of the previous claims wherein the thermal conductivity of the polymer used for the manufacture of the board is greater than 0.20 W/m.K.  
     
     
         12 . A polymeric twin wall board as claimed in  claim 11  wherein the thermal conductivity of the polymeric material is between 0.25 to 0.35 W/m.K.  
     
     
         13 . A polymeric twin wall board as claimed in any one of the previous claims wherein the polymeric material from which the board is made has a crystalline freezing point above 112° C.  
     
     
         14 . A polymeric twin wall board as claimed in  claim 13  wherein the crystalline freezing point of the polymeric material is more than 120° C. and less than 150° C.  
     
     
         15 . A process for the manufacture of a polymeric twin wall board which includes, extruding a molten polymeric material through a die configured to produce a board having opposed first and second substantially planar sheets separated by a plurality of transverse longitudinally extending webs, and delivering the said extruded material into a cavity bounded by upper and lower platens where the extruded material is cooled to form a solidified board, wherein a sufficiently high vacuum is applied to at least one side of the extruded polymeric material whilst in the cavity so that the difference between the level of the top surface of the first substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extended webs in the solidified board is no more than about 1% of the distance between adjacent longitudinally extending webs.  
     
     
         16 . A process for the manufacture of a polymeric twin wall board as claimed in  claim 15  wherein the vacuum applied to at least one side of the extruded polymeric material whilst in the cavity is sufficiently high so that the difference between the level of the top surface of the first substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extending webs in the solidified board is no more than about 0.5% of the distance between adjacent longitudinally extending webs.  
     
     
         17 . A process as claimed in either one of claims  15  or  16  wherein a vacuum is applied to both sides of the extruded polymeric material.  
     
     
         18 . A process for the manufacture of a polymeric twin wall board which includes, extruding a molten polymeric material through a die configured to produce a board having opposed first and second substantially planar sheets separated by a plurality of transverse longitudinally extending webs where the distance between adjacent webs is between 2.0 to 5.0 mm and delivering the said extruded material into a cavity bounded by upper and lower platens where the extruded material is cooled to form a solidified board, wherein a sufficiently high vacuum is applied to at least one side of the extruded polymeric material whilst in the cavity so that the difference between the level of the top surface of the first substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extending webs in the solidified board is no more than about 0.020 mm.  
     
     
         19 . A process for the manufacture of a polymeric twin wall board as claimed in  claim 18  wherein the difference between the level of the top surface of the substantially planar sheet adjacent to its juncture with any of the longitudinally extending webs and the level of the top surface of the first substantially planar sheet intermediate any of the adjacent longitudinally extending webs in the solidified board is no more than 0.010 mm.  
     
     
         20 . A process for the manufacture of a polymeric twin wall board as claimed in any one of  claims 15  to  19  wherein the upper and lower platens are substantially flat and are cooled so that the temperature of the surface of the platens is 7° C. or lower at the time of delivering the said extruded material into the cavity bounded by the said platens.  
     
     
         21 . A process for the manufacture of a polymeric twin wall board as claimed in  claim 20  wherein the temperature of the surface of both platens is between 2.0 to 6.0° C. at the time of delivering the said extruded material into the cavity bounded by the said platens.  
     
     
         22 . A process for the manufacture of a polymeric twin wall board as claimed in any one of  claims 15  to  21  wherein the polymeric material used has a crystalline freezing point which is more than 120° C. and less than 150° C.  
     
     
         23 . A process for the manufacture of a polymeric twin wall board as claimed in  claim 22  wherein the crystalline freezing point of the polymeric material is more than 125° C.  
     
     
         24 . A process for the manufacture of a polymeric twin wall board as claimed in any one of  claims 15  to  23  wherein the polymeric material has a thermal conductivity greater than 0.20 W/m.K.  
     
     
         25 . A process for the manufacture of a polymeric twin wall board as claimed in  claim 24  wherein the polymeric material has a thermal conductivity of between 0.25 to 0.35 W/m.K.  
     
     
         26 . A process for the manufacture of a polymeric twin wall board as claimed in any one of  claims 15  to  21  wherein said polymeric material is a modified or unmodified polyolefin having a thermal conductivity of greater than 0.20 W/m.K and a crystalline freezing point more than 120° C. and less than 150° C., wherein the vacuum applied to at least one side of the extruded polymeric material is at least −150 mBar.  
     
     
         27 . A process for the manufacture of a polymeric twin wall board as claimed in  claim 26  wherein the vacuum applied to at least one side of the extruded polymeric material whilst in the cavity is between −175 mBar and −300 mBar.  
     
     
         28 . A process for the manufacture of a polymeric twin wall board as claimed in any one of the previous claims wherein the vacuum applied is constant and the extrudate is held in place while the solidifying process takes place.  
     
     
         29 . A process for the manufacture of a polymeric twin wall board as claimed in any one of  claims 15  to  28  further including the step of transferring the solidified product into a cavity between a further pair of platens where a vacuum in the order of −30 to −50 mBar is applied.  
     
     
         30 . A polymeric twin wall board substantially as hereinbefore described with reference to what is shown in any one of the drawings.  
     
     
         31 . A process for the manufacture of a polymeric twin wall board as hereinbefore described with reference to what is shown in any one of the drawings.