Carbon Black-Containing Crosslinked Polyethylene Pipe Having Resistance To Chlorine And Hypochlorous Acid

Abstract

Pipe or tubing of crosslinked polyethylene (“PEX”) containing less than 2% by wt. carbon black provides improved resistance to oxidizing agents such as chlorine and hypochlorous acid in water. The pipe may be further protected with a thin tubular core (inner layer) of high density polyethylene or chlorinated polyethylene. The pipe may optionally have an oxygen barrier layer, such as poly(ethylene-co-vinyl alcohol) (“EVOH”), contiguously disposed radially outward from the carbon-containing PEX layer. The pipe is suitable for potable water applications and for hot water radiant heating systems.

1 . A pipe or tubing of crosslinked polyethylene (“PEX”) having a wall of substantially uniform thickness in the range from 1.78 mm to 17.29 mm having dispersed therein less than 2% by weight of carbon black having a particle size less than 27 nm (nanometers).  
     
     
         2 . The pipe of  claim 1  wherein the carbon black is present in an amount in the range from 0. 1% to 1.75% by wt. in the PEX.  
     
     
         3 . The pipe of  claim 1  wherein the carbon black is present in an amount in the range from 0.25% to 1.25% by wt. in the PEX.  
     
     
         4 . The pipe of  claim 1  wherein the carbon black is present in an amount in the range from 0.4% to 0.90% by wt. in the PEX.  
     
     
         5 . The pipe of  claim 4  wherein the PEX is crosslinked by a silane grafting process.  
     
     
         6 . A process for producing a multilayer pipe comprising co-extruding: 
 (a) an inner relatively thick-walled tubular layer of crosslinked polyethylene (PEX) crosslinkable to a gel content of at least 65% and containing from 0.1% to about 1.75% by weight carbon black; and,    (b) an outer tubular layer of PEX free of carbon black, crosslinklable to a gel level content of at least 65%, contiguously disposed radially outward from the inner layer and melt-bonded thereto, wherein the outer tubular layer of PEX is color-coded for installation in a chosen service, and the combined thickness of the inner and outer tubular layers meets specifications of an applicable piping code.    
     
     
         7 . The process of  claim 6 , including, extruding an inner tubular core layer of protective polymer having a substantially uniform wall thickness at least 0.025 mm (mil) but no more than 1.52 mm (0.060″), the protective polymer being selected from the group consisting of high density polyethylene (“HDPE”) and chlorinated polyethylene (“PE”) having a maximum wall thickness from about 28 to 100 times smaller than the nominal diameter of pipe in the range from 7 mm (0.25″) to 152 mm (6″), ratio 28 being attributable to small diameter non-SDR-9 piping, and ratio 100 being attributable to the larger diameter SDR-9 pipe, wherein the HDPE has a density in the range from 0.941 g/cc to 0.963 g/cc, and the chlorinated PE has a chlorine content in the range from 5 to about 50% by weight.  
     
     
         8 . A crosslinked polyethylene composition (PEX) having improved resistance to oxidation and ultraviolet light comprising from 0.1 to less than 2.0 weight percent of carbon black, wherein said crosslinked polyethylene was crosslinked by a silane grafting method.  
     
     
         9 . The composition of  claim 8  wherein said carbon black is present at a level from 0.1 to 1.75 weight percent.  
     
     
         10 . The composition of  claim 9  wherein said carbon black is present at a level from about 0.25 to about 1.25 weight percent.  
     
     
         11 . The composition of  claim 10  wherein said carbon black is present at a level from about 0.40 to about 0.90 weight percent.  
     
     
         12 . A composition of  claim 8  wherein said carbon black has a particle size of less than 27 nm.  
     
     
         13 . A composition of  claim 12  wherein said carbon black has a particle size of less than 22 nm.  
     
     
         14 . A composition of  claim 13  wherein said carbon black has a particle size of less than 20 nm.  
     
     
         15 . A composition of  claim 8  wherein said crosslinked polyethylene was crosslinked using silane grafting.  
     
     
         16 . A composition of  claim 15  further comprising at least one antioxidant.