Pipe comprising ethylene base polymer

Abstract

The pipe of the present invention comprises an ethylene base polymer comprising ethylene and an α-olefin having 3 to 20 carbon atoms, wherein (A) a maximum value of the residual stress is 0.13 MPa or less; (B) the crystallinity is 0.630 to 0.850; (C) a gradient of the crystallinity against a thickness of the pipe is 0.465 or less; and (D) the pipe has a thickness of 5 to 50 mm. It is excellent in a durability, a rigidity and an impact resistance and suited to uses for large diameter pipes receiving a high internal pressure.

What is claimed is:  
     
         1 . A pipe comprising an ethylene base polymer comprising ethylene and an α-olefin having 3 to 20 carbon atoms, wherein (A) a maximum value of the residual stress is 0.13 MPa or less; (B) the crystallinity is 0.630 to 0.850; (C) a gradient of the crystallinity against a thickness of the pipe is 0.465 or less; and (D) the pipe has a thickness of 5 to 50 mm.  
     
     
         2 . The pipe as described in  claim 1 , wherein the pipe has a tie molecule-forming probability of 0.12 or more.  
     
     
         3 . The pipe as described in  claim 1 , wherein the ethylene base polymer has a melt index of 0.02 to 0.18 g/10 minutes and a complex viscosity coefficient of 1×10 3  to 4×10 3  Pa·sec at a frequency of 100 sec −1 .  
     
     
         4 . The pipe as described in  claim 1 , wherein the hoop stress which is determined by applying a hydrostatic pressure to the pipe at a temperature of 20° C. is 12.00 MPa or more at a breaking time of 1000 hours.  
     
     
         5 . The pipe as described in  claim 1 , wherein according to ISO 13479, the pipe is provided on a surface thereof with 4 notches (notch depth rate: 20%) and has a breaking time of 165 hours or longer which is measured at a temperature of 80° C. under a pressure of 0.92 MPa, and the pipe having a notch depth rate of 40% has a breaking time of 20 hours or longer.  
     
     
         6 . A pipe comprising an ethylene base polymer comprising ethylene and an α-olefin having 3 to 20 carbon atoms, wherein according to ISO 13479, the pipe is provided on a surface thereof with 4 notches (notch depth rate: 20%) and has a breaking time of 165 hours or longer which is measured at a temperature of 80° C. under a pressure of 0.92 MPa, and the pipe having a notch depth rate of 40% has a breaking time of 20 hours or longer.