Polyethylene composition for pipe and pipe coating applications

Patent metadata

Field	Value
Publication number	US-9527934-B2
Application number	US-201414896843-A
Country	US
Kind code	B2
Filing date	Sep 24, 2014
Priority date	Oct 10, 2013
Publication date	Dec 27, 2016
Grant date	Dec 27, 2016

Abstract

The present application relates to a polyethylene composition comprising a base resin being a copolymer of ethylene with at least one alpha olefin comonomer having from 3 to 12 carbon atoms, the base resin having a density of more than 940.0 kg/m 3 and equal to or less than 952.5 kg/m 3 , determined according to ISO 1 183-1:2004, wherein the composition has a melt flow rate MFR5 (190° C., 5 kg) of 0.10 to 3.0 g/10 min, determined according to ISO 1 133, a storage modulus of G (2 kPa) of 600 Pa to 900 Pa, a shear thinning index SHI2.7/210 of 20 to 50 and the composition has an elongation at break (EB) at −45° C. in dependence of the molar comonomer content (mol. CC) of the base resin following the following equation EB[%]>175[%/mol %]·mol. CC[mol %], whereby the elongation at break (EB) is determined according to ISO 527-1 at a temperature of −45° C. and the molar co-monomer content (mol. CC) reflects the molar content of alpha-olefin comonomer units in the total content of monomer units of the base resin, an article comprising such a polyethylene composition and the use of such a polyethylene composition for the production of an article.

First claim

The invention claimed is:

1. A polyethylene composition comprising
a base resin being a copolymer of ethylene with at least one alpha olefin comonomer having from 3 to 12 carbon atoms, the base resin having a density of more than 940.0 kg/m 3 and equal to or less than 952.5 kg/m 3 , determined according to ISO 1183-1:2004,
wherein the composition has a melt flow rate MFR 5 (190° C., 5 kg) of 0.10 to 3.0 g/10 min, determined according to ISO 1133, a storage modulus of G′ (2 kPa) of 600 Pa to 900 Pa, a shear thinning index SHI 2.7/210 of 20 to 50 and
the composition has an elongation at break (EB) at −45° C. in dependence of the molar comonomer content (mol. CC) of the base resin following the following equation
EB[%]≧175[%/mol %]·mol. CC[mol %],

whereby the elongation at break (EB) is determined according to ISO 527-1 at a temperature of −45° C. and the molar comonomer content (mol. CC) reflects the molar content of alpha-olefin comonomer units in the total content of monomer units of the base resin.

2. The polyethylene composition according to claim 1 having a polydispersity index PI within the range of equal to or higher than 1.5 Pa −1 and equal to or less than 3.0 Pa −1 .

3. The polyethylene composition according to claim 1 , wherein the base resin has a content of units derived from at least one alpha olefin comonomer having from 3 to 12 carbon atoms of 0.1 to 3.0 mol.-%.

4. The polyethylene composition according to claim 1 , wherein the composition has a tensile modulus (23° C.) of at least 900 MPa.

5. The polyethylene composition according to claim 1 , wherein the composition has a Charpy Notched Impact Strength at 0° C. of at least 10 kJ/m 3 .

6. The polyethylene composition according to claim 1 , wherein the composition has a flow rate ratio FRR 21/5 , being the ratio of MFR 21 to MFR 5 , of 15 to 40.

7. The polyethylene composition according to claim 1 , wherein the composition has a complex viscosity at 0.05 rad/s eta* 0.05 rad/s of 100 000 Pa·s to 220 000 Pa·s.

8. The polyethylene composition according to claim 1 , wherein the composition has a molecular weight distribution, being the ratio of Mw/Mn, of 10 to 30.

9. The polyethylene composition according to claim 1 , wherein the base resin comprises at least two ethylene homo- or copolymer fractions (A) and (B) being different in their weight average molecular weight M w ,
wherein fraction (A) is an ethylene homopolymer and fraction (B) is a copolymers of ethylene and at least one alpha-olefin comonomer units with 3 to 12 carbon atoms,
whereby fraction (A) has a melt flow rate MFR 2 (190°, 2.16 kg) of 100 to 400 g/10 min, and
wherein fraction (A) is present in an amount of 44 to 54 wt.-% with respect to the base resin.

10. A polyethylene composition obtainable by a multistage process, the multistage process comprising
a) polymerizing ethylene in the presence of
a silica supported Ziegler Natta catalyst having a molar composition of the catalyst including
Al 1.30 to 1.65 mol/kg silica,
Mg 1.25 to 1.61 mol/kg silica,
Ti 0.70 to 0.90 mol/kg silica

and having a mean particle size (D50) of 7 to 15 μm, preferably of 8 to 12 μm
in a first reactor
for obtaining an intermediate material, the intermediate material having a has a melt flow rate MFR 2 (190°, 2.16 kg) of 100 to 400 g/10 min; and

b) transferring the reaction product to gas phase reactor
(i) feeding ethylene and comonomer to the gas phase reactor
(ii) further polymerizing the intermediate

to obtain a base resin having a density of more than 940.0 kg/m 3 and equal to or less than 952.5 kg/m 3 , determined according to ISO 1183-1:2004,
c) extruding the base resin into a polyethylene composition having a melt flow rate MFR 5 (190° C., 5 kg) of 0.10 to 3.0 g/10 min, determined according to ISO 1133, a storage modulus of G′ (2 kPa) of 600 Pa to 900 Pa, a shear thinning index SHI 2.7/210 of 20 to 50, and the composition has an elongation at break (EB) at −45° C. in dependence of the molar comonomer content (mol. CC) of the base resin following the following equation
EB[%]≧175[%/mol %]·mol. CC[mol %],

whereby the elongation at break (EB) is determined according to ISO 527-1 at a temperature of −45° C. and the molar comonomer content (mol. CC) reflects the molar content of alpha-olefin comonomer units in the total content of monomer units of the base resin.

11. An article comprising the polyethylene composition according to claim 1 .

12. The article according to claim 11 being a pipe or pipe fitting.

13. The article according to claim 11 being a pipe, the outer surface of which is coated with a coating layer comprising a polyethylene composition which comprises
a base resin being a copolymer of ethylene with at least one alpha olefin comonomer having from 3 to 12 carbon atoms, the base resin having a density of more than 940.0 kg/m 3 and equal to or less than 952.5 kg/m 3 , determined according to ISO 1183-1:2004,
wherein the composition has a melt flow rate MFR 5 (190° C., 5 kg) of 0.10 to 3.0 g/10 min, determined according to ISO 1133, a storage modulus of G′ (2 kPa) of 600 Pa to 900 Pa, a shear thinning index SHI 2.7/210 of 20 to 50 and
the composition has an elongation at break (EB) at −45° C. in dependence of the molar comonomer content (mol. CC) of the base resin following the following equation
EB[%]≧175[%/mol %]·mol. CC[mol %],

whereby the elongation at break (EB) is determined according to ISO 527-1 at a temperature of −45° C. and the molar comonomer content (mol. CC) reflects the molar content of alpha-olefin comonomer units in the total content of monomer units of the base resin.

14. An article comprising the polyethylene composition according to claim 10 .

15. The article according to claim 14 being a pipe or pipe fitting.

16. The article according to claim 11 being a pipe, the outer surface of which is coated with a coating layer comprising a polyethylene composition obtainable by
a multistage process, the multistage process comprising
d) polymerizing ethylene in the presence of
a silica supported Ziegler Natta catalyst having a molar composition of the catalyst including
Al 1.30 to 1.65 mol/kg silica,
Mg 1.25 to 1.61 mol/kg silica,
Ti 0.70 to 0.90 mol/kg silica

and having a mean particle size (D50) of 7 to 15 μm, preferably of 8 to 12 μm
in a first reactor
for obtaining an intermediate material, the intermediate material having a has a melt flow rate MFR 2 (190°, 2.16 kg) of 100 to 400 g/10 min; and

e) transferring the reaction product to gas phase reactor
(iii) feeding ethylene and comonomer to the gas phase reactor
(iv) further polymerizing the intermediate

to obtain a base resin having a density of more than 940.0 kg/m 3 and equal to or less than 952.5 kg/m 3 , determined according to ISO 1183-1:2004,
f) extruding the base resin into a polyethylene composition having a melt flow rate MFR 5 (190° C., 5 kg) of 0.10 to 3.0 g/10 min, determined according to ISO 1133, a storage modulus of G′ (2 kPa) of 600 Pa to 900 Pa, a shear thinning index SHI 2.7/210 of 20 to 50, and the composition has an elongation at break (EB) at −45° C. in dependence of the molar comonomer content (mol. CC) of the base resin following the following equation
EB[%]≧175[%/mol %]·mol. CC[mol %],

whereby the elongation at break (EB) is determined according to ISO 527-1 at a temperature of −45° C. and the molar comonomer content (mol. CC) reflects the molar content of alpha-olefin comonomer units in the total content of monomer units of the base resin.

Assignees

• Borealis Ag

Inventors

• Buryak Andrey
• Stubenrauch Kurt

Classifications

• C09D123/06 Primary

  Polyethylene · CPC title

• C08F210/08

  Butenes · CPC title

• C08F4/6492

  containing aliphatic unsaturation · CPC title

• C08F210/16

  Copolymers of ethene with alpha-alkenes, e.g. EP rubbers · CPC title

• C08L23/0815

  with aliphatic 1-olefins containing one carbon-to-carbon double bond · CPC title