Pipe having improved high temperature resistance
The present invention relates to a pipe made of a polyethylene composition comprising a polyethylene base resin, which comprises c. an ethylene copolymer as fraction (A), and d. an ethylene homo- or copolymer as fraction (B), with fraction (A) having a lower molecular weight than fraction (B), wherein the polyethylene base resin is obtainable in a polymerization process in which a single-site catalyst (SSC) is used in the polymerization of at least one of fractions (A) and (B), the base resin having (i) a density of below 940 kg/m 3 , and (ii) a MFR 5 at 190° C./5.00 kg of at least 0.20 g/10 min, and the polyethylene composition having a time to failure of at least 250 h measured according to ISO 1167 at 95° C. and 4.3 MPa.
1. A pipe made of polyethylene composition comprising a polyethylene base resin, which comprises:
a. a copolymer of ethylene and C 4 to C 20 alpha-olefin comonomers as fraction (A), wherein ethylene copolymer (A) has a density of from 925 to below 940 kg/m 3 , and
b. an ethylene copolymer and an alpha-olefin comonomer with 4 or more carbon atoms as fraction (B);
wherein the comonomer content of fraction (A) is between 0.1 and 3.0 mol % and the comonomer content of fraction (B) is between 0.1 and 2.0 mol %;
with fraction (A) having a lower molecular weight than fraction (B), wherein the polyethylene base resin is obtained by a polymerization process in which fraction (A) and fraction (B) are polymerised in the presence of the same single-site catalyst (SSC), the base resin having:
(i) a density of below 940 kg/m 3 , and
(ii) a MFR 5 at 190° C./5.00 kg of at least 0.20 g/10 min;
wherein the polyethylene composition has a time to failure of at least 250 h measured according to ISO 1167 at 95° C. and 4.3 MPa;
wherein the polyethylene composition has a flexural modulus below 700 MPa measured according to ISO 178; and
wherein the polyethylene base resin has an SHI (2.7/210) of below 20.
2. The pipe according to claim 1 , wherein fraction (A) has a melt flow rate MFR 2 of 10 to 300 g/10 min.
3. The pipe according to claim 1 , wherein in the base polyethylene resin the weight ratio between fraction (A) and fraction (B) is between 60:40 to 40:60.
4. The pipe according to claim 1 , wherein the molecular weight distribution (MWD) of the polyethylene base resin is from 5 to 25.
5. The pipe according to claim 1 , wherein the SHI (5/300) is below 35.
6. The pipe according to claim 1 , wherein the viscosity of the polyethylene base resin at a shear rate of 0.05 kPa (eta 0.05 ) is at least 15,000 kPa.
7. The pipe according to claim 1 , wherein the polyethylene composition has a Charpy impact strength at 0° C. of at least 8 kJ/m 2 , measured according to ISO 179.
8. The pipe according to claim 1 , wherein the polyethylene composition has an RCP-S4 value of +2° C. or lower, measured according to ISO 13477.
9. The pipe according to claim 1 , wherein the polyethylene composition has a modulus of elasticity from 400 to 900 MPa according to ISO 527.
10. A process for the manufacturing of a pipe, wherein a polyethylene composition comprising a polyethylene base resin, which comprises:
a. a copolymer of ethylene and C 4 to C 20 alpha-olefin comonomers as fraction (A), wherein ethylene copolymer (A) has a density of from 925 to below 940 kg/m 3 , and
b. an ethylene copolymer and an alpha-olefin comonomer with 4 or more carbon atoms as fraction (B); wherein the comonomer content of fraction (A) is between 0.1 and 3.0 mol % and the comonomer content of fraction (B) is between 0.1 and 2.0 mol %;
with fraction (A) having a lower molecular weight than fraction (B), wherein the polyethylene base resin is obtained by a polymerization process in which fraction (A) and fraction (B) are polymerized in the presence of the same single-site catalyst (SSC), the base resin having:
(i) a density of below 940 kg/m 3 , and
(ii) a MFR 5 at 190° C./5.00 kg of at least 0.20 g/10 min;
the polyethylene composition having a time to failure of at least 250 h measured according to ISO 1167 at 95° C. and 4.3 MPa;
wherein the polyethylene composition has a modulus of elasticity below 700 MPa measured according to ISO 178; and
the SHI (2.7/210) of the polyethylene base resin is below 20;
is formed into a pipe.