High-density polyethylene compositions, method of making the same, injection molded articles made therefrom, and method of making such articles

1. A high-density polyethylene composition that is formulated to be injection molded into an injection-molded bottle cap closure comprising a skirt that axially extends from the periphery of a base, and internal screw threads for securing the cap to a container, and wherein the injection-molded bottle cap closure has improved shrinkage behavior, the composition comprising:

a first component, said first component being a high molecular weight ethylene alpha-olefin copolymer having a density in the range of 0.920 to 0.946 g/cm 3 , and a melt index (I 21.6 ) in the range of 1 to 15 g/10 minutes; and

a second component, said second component being a low molecular weight ethylene polymer having a density in the range of 0.965 to 0.980 g/cm 3 , and a melt index (I 2 ) in the range of 30 to 1500 g/10 minutes;

wherein said high-density polyethylene composition having a melt index (I 2 ) of at least 1 g/10 minutes, a density in the range of 0.950 to 0.960 g/cm 3 ;

wherein said high-density polyethylene composition has a 1% secant modulus in psi of equal or greater to the following relationship: [(7,492,165*density (g/cm 3 )) -6,975,000]psi/(g/cm 3 ));

wherein said high-density polyethylene composition has a molecular weight distribution (Mw/Mn) from 5 to 13; and

wherein said high-density polyethylene composition has a standard deviation of flow direction shrinkage of less than 7 percent across different colors.

2. The high-density polyethylene composition according to claim 1 , wherein said first component having a density in the range of 0.925 to 0.945 g/cm 3 .

3. The high-density polyethylene composition according to claim 1 , wherein said first component having a melt index (I 21.6 ) in the range of 2 to 12 g/10 minutes.

4. The high-density polyethylene composition according to claim 1 , wherein said second component having a density in the range of 0.965 to 0.975 g/cm 3 .

5. The high-density polyethylene composition according to claim 1 , wherein said second component having a melt index (I 2 ) in the range of 40 to 1300 g/10 minutes.

6. The high-density polyethylene composition according to claim 1 , wherein said high-density polyethylene composition having a melt index (I 2 ) of at least 2 g/10 minutes.

7. The high-density polyethylene composition according to claim 1 , wherein said first component having a molecular weight in the range of 150,000 to 300,000.

8. The high-density polyethylene composition according to claim 1 , wherein said second component having a molecular weight in the range of 12,000 to 45,000.

9. The high-density polyethylene composition according to claim 1 , wherein said first component having a density in the range of 0.928 to 0.944 g/cm 3 , and a melt index (I 21.6 ) in the range of 2.5 to 11 g/10 minutes; wherein said second component having a density in the range of 0.965 to 0.975 g/cm 3 , and a melt index (I 2 ) in the range of 50 to 1000 g/10 minutes.

10. A method of producing the high-density polyethylene composition of claim 1 to be injection molded into an injection-molded bottle cap closure comprising a skirt that axially extends from the periphery of a base, and internal screw threads for securing the cap to a container, and wherein the injection-molded bottle cap closure has improved shrinkage behavior, the method comprising the steps of:

introducing ethylene, and an alpha-olefin comonomer into a first reactor;

polymerizing said ethylene in the presence of said alpha-olefin comonomer in said first reactor thereby producing a first component, wherein said first component being a high molecular weight ethylene alpha-olefin copolymer having a density in the range of 0.920 to 0.946 g/cm 3 , and a melt index (I 21 ) in the range of 1 to 15 g/10 minutes;

introducing said first component and additional ethylene into a second reactor;

polymerizing said additional ethylene in said second reactor thereby producing a second component, wherein said second component being a low molecular weight ethylene polymer having a density in the range of 0.965 to 0.980 g/cm 3 , and a melt index (I 2 ) in the range of 30 to 1500 g/10 minutes; and

thereby producing said high-density polyethylene composition, wherein high-density polyethylene composition having a melt index (I 2 ) of at least 1 g/10 minutes, a density in the range of 0.950 to 0.960 g/cm 3 ;

wherein said high-density polyethylene composition has a 1% secant modulus in psi of equal or greater to the following relationship: [(7,492,165*density (g/cm 3 )) -6,975,000] psi/(g/cm 3 ));

wherein said high-density polyethylene composition has a molecular weight distribution (Mw/Mn) from 5 to 13; and

wherein said high-density polyethylene composition has a standard deviation of flow direction shrinkage of less than 7 percent across different colors.

11. A method of producing a manufactured article comprising an injection-molded bottle cap closure that has improved shrinkage behavior, the method comprising the steps of:

injection molding said high-density polyethylene composition of claim 1 thereby forming said manufactured article comprising an injection-molded bottle cap closure, wherein the injection-molded bottle cap closure comprises a skirt that axially extends from the periphery of a base, and internal screw threads for securing the cap to a container.