Polyethylene pipe resins

Abstract

A polyethylene resin comprising from 44 to 55 wt % of a high molecular weight polyethylene fraction, and from 45 to 56 wt % of a low molecular weight polyethylene fraction; the high molecular weight polyethylene fraction comprising a linear low density polyethylene having a density of from 0.913 to 0.923 g/cm 3 , and an HLMI of from 0.02 to 0.2 g/10 min; and the low molecular weight polyethylene fraction comprising a high density polyethylene having a density of at least 0.969 g/cm 3 and an MI 2 of greater than 100 g/10 min; wherein the relationship between the density D of the resin in g/cm 3 and the weight fraction of the low molecular weight fraction P 1 is defined by 0.055P 1 +0.916<D<0.034P 1 +0.937.

1 . A polyethylene resin comprising from 44 to 55 wt % of a high molecular weight polyethylene fraction, and from 45 to 56 wt % of a low molecular weight polyethylene fraction; 
 the high molecular weight polyethylene fraction comprising a linear low density polyethylene having a density of from 0.913 to 0.923 g/cm 3 , and an HLMI of from 0.02 to 0.2 g/10 min;    and the low molecular weight polyethylene fraction comprising a high density polyethylene having a density of at least 0.969 g/cm 3  and an MI 2  (8/2) of greater than 100 g/10 min;    wherein the relationship between the density D of the resin in g/cm 3  and the weight fraction of the low molecular weight fraction P 1  is defined by 0.055P 1 +0.916<D<0.034P 1 +0.937.    
     
     
         2 . Polyethylene resin according to  claim 1 , having a dynamical viscosity η 0.01 , measured at 0.01 radian/second, of greater than 200,000 Pa.s and a ratio of dynamical viscosities measured at respectively 0.01 and 1 radian/second, η 0.01 /η 1 , of greater than 8.  
     
     
         3 . Polyethylene resin according to  claim 1 , having a time to failure under a stress of 11.2 MPa and at a temperature of 23° C. in a creep test as previously defined performed on a 2 mm thick dogbone-shaped plaque of said resin of greater than 500 hours.  
     
     
         4 . A polyethylene resin having a dynamical viscosity η 0.01 , measured at 0.01 radian/second, of greater than 200,000 Pa.s and a ratio of dynamical viscosities measured at respectively 0.01 and 1 radian/second, η 0.01 η 1 , of greater than 8, and a time to failure, at a stress of 11.2 MPa and a temperature of 23° C., in a creep test as previously defined performed on a 2 mm thick dogbone-shaped plaque of said resin of greater than 500 hours.  
     
     
         5 . Polyethylene resin according to any one of  claims 2  to  4 , wherein the dynamical viscosity η 0.01 , measured at 0.01 radian/second, is greater than 500,000 Pa.s, and the ratio of dynamical viscosities measured at respectively 0.01 and 1 radian/second, η 0.01 η 1 , is greater than 10.  
     
     
         6 . A polyethylene resin according to  claim 1 , wherein the density of the resin is at least 0.945 g/cm 3 .  
     
     
         7 . A polyethylene resin according to  claim 1 , wherein the HLMI of the high molecular weight fraction is from 0.02 to 0.15 g/10 min.  
     
     
         8 . A polyethylene resin according to  claim 1 , wherein the MI 2  of the low molecular weight fraction is from 200 to 1000 g/10 min.  
     
     
         9 . A polyethylene resin according to  claim 1 , wherein the density of the high molecular weight fraction is from 0.915 to 0.922 g/cm 3 .  
     
     
         10 . A polyethylene resin according to  claim 1 , wherein the density of the low molecular weight fraction is from 0.970 to 0.990 g/cm 3 .  
     
     
         11 . A polyethylene resin according to  claim 1 , wherein the polydispersity index D of the low molecular weight fraction is from 2 to 6.  
     
     
         12 . A polyethylene resin according to  claim 1 , wherein the polydispersity index D of the high molecular weight fraction is from 2 to 6.  
     
     
         13 . A polyethylene resin according to  claim 1 , wherein the density is from 0.948 to 0.954 g/cm 3 .  
     
     
         14 . A polyethylene resin according to  claim 1 , wherein the HLMI is from 3 to 50 g/10 min.  
     
     
         15 . A polyethylene resin according to  claim 1 , wherein the relationship between the density D of the resin in g/cm 3  and the weight fraction of the low molecular weight fraction P 1  is defined by 0.055P 1 +0.919<D<0.034P 1 +0.939.  
     
     
         16 . A polyethylene resin according to  claim 1 , wherein the ratio HLMI/MI 5  is at least 30.  
     
     
         17 . A polyethylene resin according to  claim 1 , which has a carbon black dispersion parameter of 2 or better, and a carbon black distribution parameter of B2 or better, as measured by microscopy in accordance to ISO18533, following extrusion and pelletisation in a single pass.  
     
     
         18 . A polyethylene resin according to  claim 17 , wherein the carbon black dispersion parameter is 1 or better, and the carbon black distribution parameter is B1 or better.  
     
     
         19 . (canceled)  
     
     
         20 . A pipe or a fitting comprising a polyethylene resin as defined in  claim 1 .  
     
     
         21 . A process for the preparation of a polyethylene resin having a bimodal molecular weight distribution which comprises; 
 (i) contacting ethylene monomer and a first co-reactant with a catalyst system in a first reaction zone under first polymerization conditions to produce a first polyethylene; and    (ii) contacting ethylene monomer and a second co-reactant with a catalyst system in a second reaction zone under second polymerization conditions to produce a second polyethylene different from the first polyethylene;    wherein the polyethylene resin is as defined in  claim 1  or  4 , and one of the co-reactants is hydrogen and the other is a comonomer comprising a 1-olefin containing from 3 to 12 carbon atoms.    
     
     
         22 . A process according to  claim 21 , wherein each catalyst system comprises (a) a metallocene catalyst component comprising a bis tetrahydroindenyl compound of the general formula (IndH 4 ) 2 R″MQ 2  in which each IndH 4  is the same or different and is tetrahydroindenyl or substituted tetrahydroindenyl, R″ is a bridge which comprises a C 1 -C 4  alkylene radical, a dialkyl germanium or silicon or siloxane, or an alkyl phosphine or amine radical, which bridge is substituted or unsubstituted, M is a Group IV metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atoms or halogen; and (b) a cocatalyst which activates the catalyst component.  
     
     
         23 . A process according to  claim 21 , wherein the first and second polyethylenes are produced in two reactors.  
     
     
         24 . A process according to  claim 23 , wherein the two reactors are connected in series.  
     
     
         25 . A polyethylene resin according to  claim 16 , wherein the ratio of HLMI/MI 5  is at least 35.