Polyethylene resin, and pipes and pipe joints using same

Abstract

A polyethylene resin superior in both moldability and long-term physical properties and suitable for both pipe and pipe joint, the polyethylene resin having a density of 0.915 to 0.955 g.cm −3 , a melt flow rate of not more than 0.20 dg.min as measured at 190° C. and at a load of 2.16 kgf, a melt flow rate of 17.0 to 70.0 dg.min −1 as measured at 190° C. and at a load of 21.6 kgf, a zero shear viscosity (η 0 ) of 200,000 to 2,000,000 Pa.s, a characteristic time constant (τ 0 ) of 50 to 500 sec., and a ratio (τ 0 /η 0 ) of 1.0×10 −4 to 4.0×10 −4 Pa −1 , the zero shear viscosity (η 0 ) being obtained by approximating a dynamic melt viscosity (η*), unit: Pa.s) with equation [1], the dynamic melt viscosity (η*) being obtained by measurement using a rheometer at 190° C., at a parallel plate spacing of 1.5 mm, at a distortion of 10% to 15% and in the frequency (ω) range of 100 to 0.01 rad.s −1 : η *= η 0 1 + ( τ 0    ·    ω ) n [ 1 ] where n is a parameter.

What is claimed is:  
     
         1 . A polyethylene resin superior in both moldability and long-term physical properties and suitable for both pipe and pipe joint, said polyethylene resin having a density of 0.915 to 0.955 g.cm −3 , a melt flow rate of not more than 0.20 dg.min −1  as measured at 190° C. and at a load of 2.16 kgf, a melt flow rate of 17.0 to 70.0 dg.min −1  as measured at 190° C. and at a load of 21.6 kgf, a zero shear viscosity (η 0 ) of 200,000 to 2,000,000 Pa.s, a characteristic time constant (τ 0 ) of 50 to 500 sec., and a ratio (τ 0 /η 0 ) of 1.0×10 −4  to 4.0×10 −4  Pa −1 , said zero shear viscosity (η 0 ) being obtained by approximating a dynamic melt viscosity (η*, unit: Pa.s) with equation [1], said dynamic melt viscosity (η*) being obtained by measurement using a rheometer at 190° C., at a parallel plate spacing of 1.5 mm, at a distortion of 10% to 15% and in the frequency (ω) range of 100 to 0.01 rad.s −1 :  
             η   *=       η   0       1   +       (       τ   0                ·              ω     )     n                 [   1   ]                       

 where n is a parameter.  
 
     
     
         2 . A pipe formed by extrusion of the polyethylene resin set forth in    claim 1   .  
     
     
         3 . A pipe joint formed by injection molding of the polyethylene resin set forth in    claim 1   .  
     
     
         4 . A combination of the pipe set forth-in    claim 2    and the pipe joint set forth in    claim 3   .