Lightweight multiwall sheet with high stiffness and method of making it

Abstract

A multiwall sheet (30) comprising a first wall (2); a second wall (4); a plurality of ribs (8) extended between the first and second walls (2, 4); and a plurality of mid-ribs (6), wherein one mid-rib (6) extends between each two adjacent ribs (8), wherein the mid-ribs (6) extend at a mid-rib angle (18) relative to an adjoining rib (8), and wherein the mid-rib angle (18) is not 90° relative to a rib (8) to which it attaches, wherein the mid-ribs (6) attach only to adjacent ribs (8), and wherein the mid-ribs (6) do not attach to either the first or second walls (2, 4).

1 . A multiwall sheet comprising:
 a first wall;   a second wall;   a plurality of ribs extended between the first and second walls; and   a plurality of mid-ribs, wherein one mid-rib extends between each two adjacent ribs, wherein the mid-ribs extend at a mid-rib angle relative to an adjoining rib, and wherein the mid-rib angle is not 90° relative to a rib to which it attaches, wherein the mid-ribs attach only to adjacent ribs, and wherein the mid-ribs do not attach to either the first or second walls.   
     
     
         2 . The multiwall sheet of  claim 1 , wherein an initial end of a mid-rib is attached to a first rib at a first initial offset distance measured from a inside surface of the first wall. 
     
     
         3 . The multiwall sheet of  claim 2 , wherein the first initial offset distance is 10% to 90% of a total sheet thickness. 
     
     
         4 . A multiwall sheet of  claim 1 , wherein adjacent mid-ribs form a mid-rib pattern comprising a repeating mid-rib pattern, an alternating mid-rib pattern, or a combination comprising at least one of the foregoing patterns. 
     
     
         5 . A multiwall sheet of  claim 1 , wherein the sheet has a total sheet thickness of 4 mm to 100 mm. 
     
     
         6 . A multiwall sheet of  claim 1 , wherein the first wall has a thickness of 0.1 mm to 10 mm. 
     
     
         7 . A multiwall sheet of  claim 1 , wherein the second wall has a thickness of 0.1 mm to 10 mm. 
     
     
         8 . A multiwall sheet of  claim 1 , wherein the plurality of ribs each has a thickness of 0.1 mm to 10 mm. 
     
     
         9 . A multiwall sheet of  claim 1 , wherein the plurality of mid-ribs each has a thickness of 0.02 mm to 2 mm. 
     
     
         10 . A multiwall sheet of  claim 1 , wherein the sheet comprises a plastic material. 
     
     
         11 . A multiwall sheet of  claim 10 , wherein the plastic material comprises homopolymers and copolymers of a polycarbonate, a polyester, a polyacrylate, a polyamide, a polyetherimide, a polyphenylene ether, or a combination comprising at least one of the foregoing. 
     
     
         12 . A multiwall sheet of  claim 1 , wherein a maximum sheet deflection is less than or equal to 70 mm, at a wind pressure of 1000 N/m 2 . 
     
     
         13 . A multiwall sheet of  claim 1 , wherein a sheet deflection under a suction condition is 75% to 125% of the sheet deflection under a pressurized condition of the same magnitude as the suction condition. 
     
     
         14 . A multiwall sheet of  claim 1 , wherein a rib spacing is 10% to 1,000% of a total sheet thickness. 
     
     
         15 . A multiwall sheet of  claim 1 , wherein a rib spacing is equal to a total sheet thickness. 
     
     
         16 . An article comprising the multiwall sheet of  claim 1 . 
     
     
         17 . A method of making a multiwall sheet, comprising:
 forming a multiwall sheet;   wherein the multiwall sheet comprises   a first wall;   a second wall;   a plurality of ribs extended between the first and second walls; and   a plurality of mid-ribs, wherein one mid-rib extends between each two adjacent ribs, wherein the mid-ribs extend at a mid-rib angle relative to an adjoining rib, and wherein the mid-rib angle is not 90° relative to a rib to which it attaches, wherein the mid-ribs attach only to adjacent ribs, and wherein the mid-ribs do not attach to either the first or second walls.   
     
     
         18 . The method of  claim 17 , wherein forming a multiwall sheet comprises extruding, coextruding, injection molding or a combination comprising at least one of the foregoing. 
     
     
         19 . The method of  claim 17 , further comprising cutting the multiwall sheet. 
     
     
         20 . The method of  claim 17 , further comprising processing the multiwall sheet in a secondary operation.