U.S. patent application number 15/107431 was filed with the patent office on 2017-01-05 for polyethylene composition for pipe applications with improved sagging properties.
The applicant listed for this patent is ABU DHABI POLYMERS COMPANY LIMITED (BOROUGE), BOREALIS AG. Invention is credited to Mohana Murali ADHYATMA BHATTAR, Jarmo HARJUNTAUSTA, Antti TYNYS.
Application Number | 20170002187 15/107431 |
Document ID | / |
Family ID | 49916789 |
Filed Date | 2017-01-05 |
United States Patent
Application |
20170002187 |
Kind Code |
A1 |
TYNYS; Antti ; et
al. |
January 5, 2017 |
POLYETHYLENE COMPOSITION FOR PIPE APPLICATIONS WITH IMPROVED
SAGGING PROPERTIES
Abstract
The present invention relates to a polyethylene composition
comprising, a base resin (A) comprising a copolymer of ethylene and
at least one comonomer selected from alpha-olefins having from
three to twelve carbon atoms, wherein the ethylene copolymer
comprises a low molecular weight component (A-1) and a high
molecular weight component (A-2) with the low molecular weight
component (A-1) having a lower weight average molecular weight than
the high molecular weight component (A-2), (B) carbon black in an
amount of 1.0 to 10 wt % based on the total amount of the
polyethylene composition, and (C) optional further additives other
than carbon black.
Inventors: |
TYNYS; Antti; (Abu Dhabi,
AE) ; HARJUNTAUSTA; Jarmo; (Helsinki, FI) ;
ADHYATMA BHATTAR; Mohana Murali; (Abu Dhabi, AE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ABU DHABI POLYMERS COMPANY LIMITED (BOROUGE)
BOREALIS AG |
Abu Dhabi
Wien |
|
AE
AT |
|
|
Family ID: |
49916789 |
Appl. No.: |
15/107431 |
Filed: |
December 22, 2014 |
PCT Filed: |
December 22, 2014 |
PCT NO: |
PCT/EP2014/003462 |
371 Date: |
June 22, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08L 2203/18 20130101;
C08L 23/0815 20130101; F16L 9/12 20130101; C08L 2308/00 20130101;
C08K 3/04 20130101; C08L 2314/02 20130101; C08L 23/06 20130101;
C08L 23/0815 20130101; C08L 23/06 20130101; C08K 3/04 20130101 |
International
Class: |
C08L 23/08 20060101
C08L023/08; F16L 9/12 20060101 F16L009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2013 |
EP |
13006049.4 |
Claims
1-15. (canceled)
16. A polyethylene composition comprising, a base resin (A)
comprising a copolymer of ethylene and at least one comonomer
selected from alpha-olefins having from three to twelve carbon
atoms, wherein the ethylene copolymer comprises a low molecular
weight component (A-1) and a high molecular weight component (A-2)
with the low molecular weight component (A-1) having a lower weight
average molecular weight than the high molecular weight component
(A-2), (B) carbon black in an amount of 1.0 to 10 wt % based on the
total amount of the polyethylene composition, and (C) optional
further additives other than carbon black; wherein the base resin
(A) has a density of equal to or more than 943 kg/m.sup.3 to equal
to or less than 957 kg/m.sup.3, determined according to ISO 1183,
and the composition has a melt flow rate MFR.sub.5 (190.degree. C.,
5 kg) of equal to or more than 0.12 g/10 min to equal to or less
than 0.20 g/10 min, determined according to ISO 1133, a shear
thinning index SHI.sub.2.7/210 of equal to or more than 80 to equal
to or less than 130 and a viscosity at a constant shear stress of
747 Pa, eta.sub.747, of equal to or more than 700 kPas to equal to
or less than 1200 kPas.
17. The polyethylene composition according to claim 16, wherein the
low molecular weight component (A-1) is an ethylene
homopolymer.
18. The polyethylene composition according to claim 16, wherein the
low molecular weight component (A-1) has a melt flow rate MFR.sub.2
(190.degree. C., 2.16 kg) of 200 g/10 min to 400 g/10 min,
determined according to ISO 1133.
19. The polyethylene composition according to claim 16, wherein the
high molecular weight component (A-2) is a copolymer of ethylene
and a comonomer selected from alpha-olefins having from three to
twelve carbon atoms.
20. The polyethylene composition according to claim 16, wherein the
weight ratio of the low molecular weight component (A-1) to the
high molecular component (A-2) is from 45:55 to 55:45.
21. The polyethylene composition according to claim 16, wherein the
composition has a melt flow rate MFR.sub.21 (190.degree. C., 21.6
kg) of 5.6 g/10 min to 7.0 g/10 min, determined according to ISO
1133.
22. The polyethylene composition according to claim 16, wherein the
composition has a density of equal to or more than 953 kg/m.sup.3
to equal to or less than 967 kg/m.sup.3, determined according to
ISO 1183.
23. The polyethylene composition according to claim 16, wherein the
composition has a shear thinning index SHI.sub.5/200 of equal to or
more than 50 to equal to or less than 100.
24. The polyethylene composition according to claim 16, wherein the
composition has at least one, preferably both, of the following
properties a) a weight average molecular weight, Mw, of 250 to 360
kg/mol, more preferably 260 to 340 kg/mol, and/or b) Mz value of
1600 to 2500 kg/mol, preferably 1700 to 2200 kg/mol, even more
preferably 1750 to 2150 kg/mol.
25. The polyethylene composition according to claim 16, wherein the
composition has a molecular weight distribution Mw/Mn, of at least
25, preferably 30 to 50, more preferably 30 to 45.
26. The polyethylene composition according to claim 16, wherein the
composition has a tensile modulus of equal to or less than 1250
MPa, determined according to ISO 527-2:1993.
27. A polyethylene composition obtainable by a multistage process,
the process comprising a) polymerizing ethylene in the presence of
a Ziegler-Natta catalyst for obtaining an intermediate material, b)
transferring the intermediate material to a gas phase reactor (i)
feeding ethylene and an alpha-olefin comonomer having from 3 to 12
carbon atoms to the gas phase reactor (ii) further polymerizing the
intermediate material to obtain a base resin (A) which comprises
the intermediate material polymerized in step a) and a material
polymerized in step b) which has a higher weight average molecular
weight as the intermediate material of step a), wherein the base
resin (A) has a density of equal to or more than 943 kg/m.sup.3 to
equal to or less than 957 kg/m.sup.3, determined according to ISO
1183, c) extruding the base resin (A) in the presence of 1 to 10 wt
% carbon black (B), based on the amount of the polyethylene
composition, and optional further additive(s) (C), into a
polyethylene composition having a melt flow rate MFR.sub.5
(190.degree. C., 5 kg) of equal to or more than 0.12 g/10 min to
equal to or less than 0.20 g/10 min, determined according to ISO
1133 (type II), a shear thinning index SHI.sub.2.7/210 of equal to
or more than 80 to equal to or less than 130 and a viscosity at a
constant shear stress of 747 Pa, eta.sub.747, of equal to or more
than 700 kPas to equal to or less than 1200 kPas.
28. An article comprising the polyethylene composition according to
claim 16.
29. The article according to claim 28 being a pipe or pipe fitting,
preferably pipe having a wall thickness of at least 60 mm.
30. An article comprising the polyethylene composition of claim
27.
31. The article according to claim 30 being a pipe or pipe fitting
leaving a wall thickness of at least 60 mm.
Description
[0001] The present invention relates to a polyethylene composition,
particularly a polyethylene composition for pipe applications. The
invention further relates to a process for the production of said
polyethylene composition and an article, particularly a pipe,
comprising said polyethylene composition.
BACKGROUND OF THE INVENTION
[0002] Pipes constructed from polymer materials have a multitude of
uses, such as fluid transport, i.e. the transport of liquids,
slurries and gases, e.g. water or natural gas. During transport, it
is normal for the fluid to be pressurized. Moreover, the
transported fluid may have varying temperatures, usually within the
range from about 0.degree. C. to about 50.degree. C. Such
pressurized pipes are preferably constructed from polyolefin
plastics, usually unimodal or bimodal ethylene plastics such as
medium density polyethylene (MDPE; density: 930-942 kg/m.sup.3) and
high density polyethylene (HDPE; density: 942-965 kg/m.sup.3).
[0003] The expression "pressure pipe" used herein refers to a pipe
which, when used, is subjected to a positive pressure, that is the
pressure inside the pipe being higher than the pressure outside the
pipe.
[0004] Polymeric pipes are generally manufactured by extrusion, or,
to a small extent, by injection moulding. A conventional plant for
extrusion of polymer pipes comprises an extruder, a die-head, a
calibrating device, cooling equipment, a pulling device, and a
device for cutting and/or for coiling up the pipe.
[0005] The manufacture of polyethylene materials for use in
pressure pipes is discussed in an article by Scheirs et al
(Scheirs, Bohm, Boot and Leevers: PE100 Resins for Pipe
Applications, TRIP Vol. 4, No. 12 (1996) pp. 408-415). The authors
discuss the production technology and properties of PE100 pipe
materials. They point out the importance of proper comonomer
distribution and molecular weight distribution in order to optimize
slow crack growth and rapid crack propagation.
[0006] Whilst properties of conventional polymer pipes are
sufficient for many purposes, enhanced properties may also be
desired, for instance in applications requiring high pressure
resistance, i.e. pipes that are subjected to an internal fluid
pressure for long and/or short periods of time.
[0007] A problem when manufacturing large diameter pipes,
particularly from multimodal polymer material, is that it is
difficult to maintain uniform dimensions all over the pipe. This is
due to gravity flow of the polymer melt, causing it to flow from
the upper part of the pipe to the lower part (often called
"sagging"). Thus, the wall thickness at the upper part of the pipe
becomes smaller than at the lower part of the pipe. The sagging
problem is particularly pronounced for thick-walled large diameter
pipes, such as pipes with a wall thickness of at least 60 mm.
[0008] The above described sagging problem has been discussed in
German patent application DE 19604196 A1. It discloses a process to
manufacture a large-bore, thick walled pipe of polyethylene. The
pipe is extruded through a ring formed die and cooled on both inner
and outer surfaces. This double sided cooling is said to eliminate
the deformation of the pipe due to gravity-induced flow of the melt
emerging from the die.
[0009] International patent application WO 00/22040 discusses the
improvement of the polyethylene composition for addressing the
sagging problem. It was said that a bimodal polyethylene
composition with a high viscosity at a low shear stress of 747 Pa
improves sagging behavior of the polymeric melt.
[0010] There is a need for polyethylene compositions especially for
pressure pipe applications which show low sagging behavior so that
they are suitable for large diameter pipes with wall thicknesses of
at least 60 mm and an optimized balance of properties as regards
mechanical properties, pressure resistance and processability.
SUMMARY OF THE INVENTION
[0011] The present invention relates to a polyethylene composition
comprising, preferably consisting of,
[0012] a base resin (A) comprising [0013] a copolymer of ethylene
and at least one comonomer selected from alpha-olefins having from
three to twelve carbon atoms, [0014] wherein the ethylene copolymer
comprises a low molecular weight component (A-1) and a high
molecular weight component (A-2) with the low molecular weight
component (A-1) having a lower weight average molecular weight than
the high molecular weight component (A-2),
[0015] (B) carbon black in an amount of 1.0 to 10 wt % based on the
total amount of the polyethylene composition, and
[0016] (C) optional further additives other than carbon black;
[0017] wherein the base resin (A) has a density of equal to or more
than 943 kg/m.sup.3 to equal to or less than 957 kg/m.sup.3,
determined according to ISO 1183, and
[0018] the composition has a melt flow rate MFR.sub.5 (190.degree.
C., 5 kg) of equal to or more than 0.12 g/10 min to equal to or
less than 0.20 g/10 min, determined according to ISO 1133, a shear
thinning index SHI.sub.2.7/210 of equal to or more than 80 to equal
to or less than 130 and a viscosity at a constant shear stress of
747 Pa, eta.sub.747, of equal to or more than 700 kPas to equal to
or less than 1200 kPas.
[0019] The polyethylene composition according to the invention
surprisingly not only show a low sagging tendency as can be seen
from a high viscosity at a low shear stress of 747 Pa, but also an
improved balance of properties as regards mechanical properties,
such as tensile properties, pressure resistance in the pressure
pipe test and processability which can be seen in the rheological
properties such as a higher shear thinning index.
[0020] The present invention further provides a polyethylene
composition obtainable by a multistage process, the multistage
process comprising [0021] a) polymerizing ethylene in the presence
of a Ziegler-Natta catalyst for obtaining an intermediate material,
[0022] b) transferring the intermediate material to a gas phase
reactor [0023] (i) feeding ethylene and an alpha-olefin comonomer
having from 3 to 12 carbon atoms to the gas phase reactor [0024]
(ii) further polymerizing the intermediate material [0025] to
obtain a base resin (A) which comprises the intermediate material
polymerized in step a) and a material polymerized in step b) which
has a higher weight average molecular weight as the intermediate
material of step a), wherein the base resin (A) has a density of
equal to or more than 943 kg/m.sup.3 to equal to or less than 957
kg/m.sup.3, determined according to ISO 1183, [0026] c) extruding
the base resin (A) in the presence of 1 to 10 wt % carbon black
(B), based on the amount of the polyethylene composition, and
optional further additive(s) (C), into a polyethylene composition
having a melt flow rate MFR.sub.5 (190.degree. C., 5 kg) of equal
to or more than 0.12 g/10 min to equal to or less than 0.20 g/10
min, determined according to ISO 1133, a shear thinning index
SHI.sub.2.7/210 of equal to or more than 80 to equal to or less
than 130 and a viscosity at a constant shear stress of 747 Pa,
eta.sub.747, of equal to or more than 700 kPas to equal to or less
than 1200 kPas.
[0027] In a further aspect, the present invention provides an
article comprising the polyethylene composition according to the
present invention.
[0028] In yet a further aspect, the present invention is concerned
with the use of the inventive polyethylene composition for the
production of an article.
[0029] Thereby, it is preferred that the article relates to a pipe
or a pipe fitting, more preferably a pipe with a large wall
thickness such as at least 60 mm.
[0030] Definitions
[0031] A polyethylene composition according to the present
invention denotes a polymer derived from at least 50 mol-% ethylene
monomer units and additional comonomer units.
[0032] An ethylene homopolymer thereby denotes a polymer consisting
essentially of ethylene monomer units. Due to the requirements of
large-scale polymerization it may be possible that the ethylene
homopolymer includes minor amounts of comonomer units, which
usually is below 0.1 mol %, preferably below 0.05 mol %, most
preferably below 0.01 mol % of the ethylene homopolymer.
[0033] An ethylene copolymer denotes a polymer consisting of
ethylene monomer units and comonomer units in an amount of at least
0.1 mol %. In an ethylene random copolymer the comonomer units are
randomly distributed in the polymer chain.
[0034] The term `base resin (A)` denotes the polymeric component of
the composition.
[0035] The term `different` denotes that a polymeric component
differs from another polymeric component in at least one
measureable property. Suitable properties for differentiating
polymeric components are weight average molecular weight, melt flow
rate MFR.sub.2 or MFR.sub.5, density or comonomer content.
[0036] General
[0037] Base resin (A)
[0038] The base resin (A) comprises a copolymer of ethylene and at
least one comonomer selected from alpha-olefins having from three
to twelve carbon atoms (referred herein also as ethylene
copolymer).
[0039] Preferably the alpha olefin comonomers of the ethylene
copolymer are selected from alpha olefins having from 4 to 8 carbon
atoms, such as 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene.
Especially preferred are 1-butene and 1-hexene. Mostly preferred is
1-hexene.
[0040] The ethylene copolymer may further comprise further
comonomer units different from alpha olefin comonomers such as
dienes, polar comononers or silicon containing comonomers. It is,
however, preferred that the ethylene copolymer only contains alpha
olefin monomers as comonomer units.
[0041] The ethylene copolymer comprises a low molecular weight
component (A-1) and a high molecular weight component component
(A-2). The low molecular weight component (A-1) differs from the
high molecular weight component (A-2) by having a lower weight
average molecular weight.
[0042] Preferably the base resin consists of the copolymer of
ethylene and at least one comonomer, more preferably one comonomer,
selected from alpha-olefins having from three to twelve carbon
atoms.
[0043] The ethylene copolymer may further comprise further polymer
component(s) different to the low molecular weight component (A-1)
and the high molecular weight component (A-2). The further polymer
component(s) can be introduced to the ethylene copolymer, the base
resin or the polyethylene composition either by melt mixing or
compounding or in an additional reaction stage of the multi-stage
process for producing base resin of the polyethylene
composition.
[0044] Components (A-1) and (A-2) differ in their weight average
molecular weight in that that component (A-2) has a higher weight
average molecular weight as component (A-1). The differences in
weight average molecular weight can be seen from the melt flow rate
MFR.sub.2 of component (A-1) which is higher than the melt flow
rate MFR.sub.5 of the polyethylene composition.
[0045] The MFR.sub.2 (2.16 kg, 190.degree. C.) of component (A-1)
is equal to or more than 200 g/10 min, preferably equal to or more
than 220 g/10 min, most preferably equal to or more than 240 g/10
min.
[0046] Further, the MFR.sub.2 (2.16 kg, 190.degree. C.) of
component (A-1) is equal to or less than 400 g/10 min, preferably
equal to or less than 390 g/10 min, more preferably equal to or
less than 380 g/10 min.
[0047] Component (A-1) can be a homopolymer or copolymer of
ethylene.
[0048] Component (A-1) in one embodiment can be a copolymer of
ethylene with one or more alpha-olefins having from 3 to 12 carbon
atoms. Preferably the alpha olefin comonomers are selected from
alpha olefins having from 4 to 8 carbon atoms, such as 1-butene,
1-hexene, 4-methyl-1-pentene and 1-octene. Especially preferred are
1-butene and 1-hexene.
[0049] The ethylene copolymer of component (A-1) preferably has a
density of equal to or more than 955 kg/m.sup.3 and of equal to or
less than 965 kg/m.sup.3, more preferably of equal to or more than
963 kg/m.sup.3, and most preferably of equal to or more than 961
kg/m.sup.3.
[0050] However, it is preferred that component (A-1) is an ethylene
homopolymer. The homopolymer preferably has a density of at least
970 kg/m.sup.3 and preferably of more than 970 kg/m.sup.2.
[0051] Further, component (A-1) is preferably present in the base
resin in an amount of 40 to 55 wt.-%, more preferably 45 to 54
wt.-%, most preferably 47 to 53 wt.-%, with respect to the base
resin.
[0052] The high molecular weight component (A-2) is preferably a
copolymer of ethylene and at least one alpha-olefin comonomers,
preferably one alpha-olefin comonomer, with 3 to 12 carbon
atoms.
[0053] Thereby, the alpha-olefin comonomer(s) used in the
ethylene/alpha-olefin copolymer of the high molecular weight
component (A-2) preferably are different to that/those used in the
optional ethylene/alpha-olefin copolymer of the low molecular
weight component (A-1).
[0054] Preferably the alpha olefin comonomer(s) of component (A-2)
is/are selected from alpha olefins having from 4 to 8 carbon atoms,
such as 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene.
Especially preferred are 1-butene and 1-hexene and mostly preferred
is 1-hexene.
[0055] Component (A-2) may further comprise further comonomer units
different from alpha olefin comonomers such as dienes, polar
comononers or silicon containing comonomers. It is, however,
preferred that the component (A-2) only contains alpha olefin
monomers as comonomer.
[0056] It is especially preferred that the component (A-2) contains
either 1-butene and/or 1-hexene as comonomer. Mostly preferred is
1-hexene as comonomer for component (A-2).
[0057] The content of units derived from at least one alpha olefin
comonomer having from 3 to 12 carbon atoms in component (A-2) is
preferably 0.3 to 2.5 mol %, more preferably 0.4 to 2.0 mol %.
[0058] Further, component (A-2) is preferably present in the base
resin in an amount of 60 to 45 wt.-%, more preferably 55 to 46
wt.-%, and most preferably 53 to 47 wt.-%, with respect to the base
resin.
[0059] The weight ratio of the low molecular weight component (A-1)
to the high molecular weight component (A-2) is from 40:60 to
55:45, preferably from 45:55 to 54:46, most preferably from 47:53
to 53:47.
[0060] Optionally, the ethylene copolymer further comprises a
prepolymer fraction. The prepolymer fraction preferably is an
ethylene homopolymer or copolymer. The optional prepolymer fraction
is preferably present in an amount of 0 to 5 wt.-%, more preferably
in an amount of 0.2 to 3.5 wt.-% and most preferably in an amount
of 0.5 to 2.5 wt.-%.
[0061] As regards the amount of the different polyethylene
components (A-1) and (A-2) in the ethylene copolymer and the weight
ratios of components (A-1) and (A-2) the optional prepolymer
fraction is counted to the amount and the weight of component
(A-1).
[0062] In one embodiment of the present invention the ethylene
copolymer consists only of above defined components (A-1) and
(A-2).
[0063] In another embodiment of the present invention the ethylene
copolymer consists of components (A-1) and (A-2) and a prepolymer
fraction as defined above.
[0064] The base resin (A) preferably consists of the low molecular
weight component (A-1), the high molecular weight component (A-2)
and the optional prepolymer as the polymer components.
[0065] The base resin (A) preferably has a density of equal to or
more than 945 kg/m.sup.3, more preferably of equal to or more than
947 kg/m.sup.3.
[0066] The base resin (A) preferably has a density of equal to or
less than 955 kg/m.sup.3, more preferably of equal to or less than
953 kg/m.sup.3 and most preferably of equal to or less than 952
kg/m.sup.3.
[0067] The content of units derived from at least one alpha olefin
comonomer having from 3 to 12 carbon atoms in the base resin (A) is
preferably 0.05 to 2.0 mol %, more preferably 0.10 to 1.5 mol %,
most preferably 0.20 to 1.0 mol %.
[0068] The base resin (A) is preferably present in the polyethylene
composition in an amount of more than 80 wt %, more preferably in
an amount of 85 to 99 wt %, most preferably in an amount of 90 to
98 wt %, based on the total amount of the polyethylene composition
(100 wt %).
[0069] Polyethylene Composition
[0070] In addition to the base resin, the polymer composition may
comprise and preferably comprises usual additives (C) for
utilization with polyolefins, such as stabilizers (e.g. antioxidant
agents), metal scavengers and/or UV-stabilizers, antistatic agents
and utilization agents (such as processing aid agents). Preferably,
the amount of these additives (C) is 10 wt % or below, more
preferably 8 wt % or below, more preferably 5 wt % or below, of the
composition (100 wt %).
[0071] Further preferred, the amount of additives (C) different
from carbon black is 0 wt % to 1 wt %, more preferably 0.001 wt %
to 0.8 wt %.
[0072] The polyethylene composition comprises carbon black (B) in
an amount of 1.0 to 10 wt %, preferably 1.5 to 9.0 wt %, more
preferably 1.8 to 8.0 wt %, still more preferably 1.8 to 7.0 wt %,
still more preferably 1.8 to 5.0 wt %, still more preferably 1.8 to
4.5 wt % and most preferably 1.8 to 4.0 wt %, based on the total
amount of the composition.
[0073] Carbon black (B) can be added to polymer composition as such
(neat) or in form of so-called master batch (CBMB), in which carbon
black, and optionally further additives (C) as defined above, are
contained in concentrated form in a carrier polymer.
[0074] The optional carrier polymer of carbon black masterbatch is
not calculated to the amount of the polymer components present in
the polyethylene composition. In other words, it is to be
understood that carbon black (B) and optional additive(s) (C) may
be added to the polymer composition in form of a masterbatch, i.e.
together with a carrier polymer. In such case the carrier polymer
is not considered as polymer component(s), but is calculated into
the amount (wt %) of carbon black (B) or, respectively, into the
amount (wt %) of additive(s) (C).
[0075] The amount of the optional carrier polymer of the carbon
black master batch is 0 to 5 wt % based on the total amount of the
polymer composition (100 wt %).
[0076] The polyethylene composition according to the present
invention has a melt flow rate MFR.sub.5 (190.degree. C., 5 kg) of
equal to or more than 0.12 g/10 min, preferably equal to or more
than 0.13 g/10 min, and most preferably equal to or more than 0.14
g/10 min.
[0077] Further, the polyethylene composition has a melt flow rate
MFR.sub.5 (190.degree. C., 5 kg) of equal to or less than 0.20 g/10
min, preferably equal to or less than 0.19 g/10 min.
[0078] The polyethylene composition according to the present
invention preferably has a melt flow rate MFR.sub.21 (190.degree.
C., 21.6 kg) of equal to or more than 5.6 g/10 min, more preferably
equal to or more than 5.9 g/10 min.
[0079] Further, the polyethylene composition preferably has a melt
flow rate MFR.sub.21 (190.degree. C., 21.6 kg) of equal to or less
than 7.0 g/10 min, preferably equal to or less than 6.5 g/10 min,
and most preferably equal to or less than 6.4 g/10 min.
[0080] The MFR.sub.2 (190.degree. C., 2.16 kg), MFR.sub.5
(190.degree. C., 5 kg) and the MFR.sub.21 (190.degree. C., 21.6 kg)
are determined according to ISO 1133.
[0081] The polyethylene composition according to the present
invention preferably has a density of equal to or more than 956 to
964 kg/m.sup.3, determined according to ISO 1183-1:2004.
[0082] The polyethylene composition has a shear thinning index
SHI.sub.2.7/210 of 80 to 130, more preferably a shear thinning
index SHI.sub.2.7/210 of 90 to 125, and most preferably a shear
thinning index SHI.sub.2.7/210 of 95 to 120.
[0083] The polyethylene composition preferably has a shear thinning
index SHI.sub.5/200 of 50 to 100, more preferably a shear thinning
index SHI.sub.5/200 of 55 to 90, and most preferably a shear
thinning index SHI.sub.5/200 of 60 to 80.
[0084] The shear thinning indexes SHI.sub.2.7/210 and SHI.sub.5/200
are a rheological measure indicating the broadness of the polymer.
Thus SHI can be modified e.g. by varying the relative amounts of
low and high molecular weight material (via split of the reactors)
and/or by varying the molecular weights of the respective low and
high molecular weight materials for example by variation of the
chain transfer agent feed, as evident to a skilled person.
[0085] The polyethylene composition has a viscosity eta.sub.747 of
equal to or more than 700 kPas, more preferably of equal to or more
than 750 kPas.
[0086] The viscosity eta.sub.747 of the polyethylene composition is
preferably equal to or less than 1200 kPas, most preferably equal
to or less than 1000 kPas.
[0087] The viscosity eta.sub.747 is measured at a very low,
constant shear stress of 747 Pa and is inversely proportional to
the gravity flow of the polyethylene composition. I.e. the higher
eta.sub.747 the lower the sagging of the polyethylene composition.
Herein the higher eta.sub.747 indicates the presence of high
molecular weight polymer chains and higher molecular weight Mz and
also higher Mw.
[0088] The polyethylene composition according to the present
invention preferably has a complex viscosity at 0.05 rad/s eta* of
170 000 Pas to 300 000 Pas, more preferably 200 000 Pas to 275 000
Pas, and most preferably 220 000 Pas to 250 000 Pa s.
[0089] The polyethylene composition according to the present
invention preferably has a complex viscosity at 300 rad/s eta* of
1050 Pas to 1500 Pa s, more preferably 1080 Pas to 1250 Pa s, and
most preferably 1100 Pas to 1200 Pa s.
[0090] The polyethylene composition according to the present
invention preferably has a weight average molecular weight, Mw, in
the range of 250 to 360 kg/mol, more preferably 260 to 340
kg/mol.
[0091] The polyethylene composition according to the present
invention preferably has a Mz value in the range of 1600 to 2500
kg/mol, preferably 1700 to 2200 kg/mol even more preferably 1750 to
2150 kg/mol. Mz indicates the portion (amount) and the Mw of the
very high molecular weight fraction.
[0092] Further the polyethylene composition preferably has a
molecular weight distribution, being the ratio of the weight
average molecular weight to the number average molecular weight,
Mw/Mn, of at least 25, preferably 30 to 50, more preferably 30 to
45, most preferably 32 to 42.
[0093] The polyethylene composition of the invention with the
specific property balance between density, MFR, viscosity at low
shear stress and shear thinning index provide not only low sagging
behavior but also highly advantageous mechanical properties e.g.
for pipe applications (expressed e.g. as tensile modulus), and
processability properties, when the polyethylene composition is
processed to articles, preferably pipes, as well as desirable
resistance to internal pressure when tested using pipe samples of
the polyethylene composition.
[0094] The composition according to the present invention has a
tensile modulus, determined according to ISO 527-2:1993 at a
temperature of 23.degree. C. of equal to or less than 1250 MPa,
preferably of equal to or less than 1200 MPa, and most preferably
of equal to or less than 1100 MPa. The lower limit of the tensile
modulus at 23.degree. C. is usually not lower than 800 MPa,
preferably not lower than 950 MPa.
[0095] In a further aspect, the present invention is concerned with
a polyethylene composition obtainable by a multistage process, the
multistage process comprising [0096] a) polymerizing ethylene in
the presence of a Ziegler-Natta catalyst for obtaining an
intermediate material, [0097] b) transferring the intermediate
material to a gas phase reactor [0098] (i) feeding ethylene and an
alpha-olefin comonomer having from 3 to 12 carbon atoms to the gas
phase reactor [0099] (ii) further polymerizing the intermediate
material [0100] to obtain a base resin (A) which comprises the
intermediate material polymerized in step a) and a material
polymerized in step b) which has a higher weight average molecular
weight as the intermediate material of step a), wherein the base
resin (A) has a density of equal to or more than 943 kg/m.sup.3 to
equal to or less than 957 kg/m.sup.3, determined according to ISO
1183, [0101] c) extruding the base resin (A) in the presence of 1
to 10 wt % carbon black (B), based on the amount of the
polyethylene composition, and optional further additive(s) (C),
into a polyethylene composition having a melt flow rate MFR.sub.5
(190.degree. C., 5 kg) of equal to or more than 0.12 g/10 min to
equal to or less than 0.20 g/10 min, determined according to ISO
1133 (type II), a shear thinning index SHI.sub.2.7/210 of equal to
or more than 80 to equal to or less than 130 and a viscosity at a
constant shear stress of 747 Pa, eta.sub.747, of equal to or more
than 700 kPas to equal to or less than 1200 kPas.
[0102] The base resin (A) and the polyethylene composition
obtainable by the above described multistage process are preferably
further defined by the properties of the base resin (A) and the
polyethylene composition described above or in claims.
[0103] Most preferably the polyethylene composition consists of the
base resin (A), carbon black (B) and optional further additives
other than carbon black (C).
[0104] Article
[0105] In yet a further aspect, the present invention is concerned
with an article comprising, preferably consisting of, the
polyethylene composition as described above or below in claims.
[0106] Thereby, in the preferred embodiment of the present
invention the article is a pipe or pipe fitting comprising,
preferably consisting of, the polyethylene composition as described
above or below in claims. Most preferably the article is a pipe,
especially a pipe with a wall thickness of at least 60 mm.
[0107] Process
[0108] The polyethylene compositions of the present invention are
usually made by a multi-stage process, i.e. a process which makes
use of at least two reactors, one for producing a lower molecular
weight component (A-1) and a second for producing a higher
molecular weight component (A-2). These reactors may be employed in
parallel, in which case the components must be mixed after
production. More commonly, the reactors are employed in series,
such that the products of one reactor are used as the starting
material in the next reactor, e.g. one component is formed in the
first reactor and the second is formed in the second reactor in the
presence of the first component. In this way, the two components
are more intimately mixed, since one is formed in the presence of
the other.
[0109] The polymerization reactions used in each stage may involve
conventional ethylene homo-polymerization or copolymerization
reactions, e.g. gas phase, slurry phase, liquid phase
polymerizations, using conventional reactors, e.g. loop reactors,
gas phase reactors, batch reactors, etc.
[0110] The polymerization may be carried out continuously or
batchwise, preferably the polymerization is carried out
continuously.
[0111] Known two-stage processes are for instance liquid
phase-liquid phase processes, gas phase-gas phase processes and
liquid phase-gas phase processes. It is also known that these
two-stage processes can further be combined with one or more
additional polymerization steps selected from gas phase, slurry
phase or liquid phase polymerization processes.
[0112] Multimodal polyethylene compositions of the present
invention are preferably produced in a multistage process, where
lower molecular weight and higher molecular weight polymers
(components A-1 and A-2) are produced in different polymerization
steps, in any order.
[0113] A high molecular weight (HMW) polymer component (=relatively
low density) (A-2) can be prepared in the first polymerization step
and a low molecular weight (LMW) polymer component (=relatively
high density) (A-1) in the second polymerization step. This can be
referred to as the reverse mode. Alternatively, the low molecular
weight polymer component (A-1) can be prepared in the first
polymerization step and the high molecular weight polymer component
(A-2) in the second polymerization step. This can be referred to as
the normal mode and is preferred.
[0114] A two-stage process can, for example be a slurry-slurry or a
gas phase-gas phase process, particularly preferably a slurry-gas
phase process. Optionally the process according to the invention
can comprise one or two additional polymerization steps.
[0115] The slurry and gas phase stages may be carried out using any
conventional reactors known in the art. A slurry phase
polymerization may, for example, be carried out in a continuously
stirred tank reactor; a batch-wise operating stirred tank reactor
or a loop reactor. Preferably slurry phase polymerization is
carried out in a loop reactor. In such reactors the slurry is
circulated with a high velocity along a closed pipe by using a
circulation pump. Loop reactors are generally known in the art and
examples are given, for instance, in U.S. Pat. No. 4,582,816, U.S.
Pat. No. 3,405,109, U.S. Pat. No. 3,324,093, EP-A-479186 and U.S.
Pat. No. 5,391,654.
[0116] The term gas phase reactor encompasses any mechanically
mixed, fluidized bed reactor, fast fluidized bed reactor or settled
bed reactor or gas phase reactors having two separate zones, for
instance one fluidized bed combined with one settled bed zone.
Preferably the gas phase reactor for the second polymerization step
is a fluidized bed reactor.
[0117] The slurry and gas phase processes are well known and
described in the prior art.
[0118] In a preferred embodiment of the invention the low molecular
weight (LMW) component (A-1) is produced first and the high
molecular weight (HMW) component (A-2) is produced in the presence
of LMW component (A-1). In this case the LMW component is the first
polyethylene component (A-1) and the HMW component is the second
polyethylene component (A-2).
[0119] The polymerisation catalysts for the production of the base
resin may include coordination catalysts of a transition metal,
such as Ziegler-Natta (ZN), metallocenes, non-metallocenes,
Cr-catalysts etc. The catalyst may be supported, e.g. with
conventional supports including silica, Al-containing supports and
magnesium dichloride based supports. Preferably the catalyst is a
ZN catalyst, more preferably the catalyst is a non-silica supported
ZN catalyst, and most preferably a MgCl.sub.2-based ZN
catalyst.
[0120] The Ziegler-Natta catalyst further preferably comprises a
group 4 (group numbering according to new IUPAC system) metal
compound, preferably titanium, magnesium dichloride and
aluminum.
[0121] The catalyst may be commercially available or be produced in
accordance or analogously to the literature. For the preparation of
the preferable catalyst usable in the invention, reference is made
to WO 2004/055068 and WO 2004/055069 of Borealis and EP 0 810 235.
The content of these documents in its entirety is incorporated
herein by reference, in particular concerning the general and all
preferred embodiments of the catalysts described therein as well as
the methods for the production of the catalysts. Particularly
preferred Ziegler-Natta catalysts are described in EP 0 810
235.
[0122] The resulting end product consists of an intimate mixture of
the polymers from the reactors, the different
molecular-weight-distribution curves of these polymers together
forming a molecular-weight-distribution curve having a broad
maximum or several maxima, i.e. the end product is a multimodal
polymer mixture.
[0123] It is preferred that the multimodal polyethylene composition
according to the invention is a bimodal polyethylene mixture
consisting of polymer components (A-1) and (A-2), optionally
further comprising a small prepolymerisation fraction. It is also
preferred that this bimodal polymer mixture has been produced by
polymerisation as described above under different polymerisation
conditions in two or more polymerisation reactors connected in
series. Owing to the flexibility with respect to reaction
conditions thus obtained, it is most preferred that the
polymerisation is carried out in a loop reactor/a gas-phase reactor
combination.
[0124] Preferably, the polymerisation conditions in the preferred
two-stage method are so chosen that the comparatively low-molecular
polymer having no content of comonomer is produced in one stage,
preferably the first stage, owing to a high content of
chain-transfer agent (hydrogen gas), whereas the high-molecular
polymer having a content of comonomer is produced in another stage,
preferably the second stage. The order of these stages may,
however, be reversed.
[0125] In the preferred embodiment of the polymerisation in a loop
reactor followed by a gas-phase reactor, the polymerisation
temperature in the loop reactor preferably is 85 to 115.degree. C.,
more preferably is 90 to 105.degree. C., and most preferably is 92
to 100.degree. C., and the temperature in the gas-phase reactor
preferably is 70 to 105.degree. C., more preferably is 75 to
100.degree. C., and most preferably is 82 to 97.degree. C. The
pressure in the loop reactor is typically from 1 to 150 bar,
preferably from 1 to 100 bar and the pressure in the gas phase
reactor is typically at least 10 bar, preferably at least 15 bar
but typically not more than 30 bar, preferably not more than 25
bar.
[0126] The polymerisation in the slurry phase reactor usually takes
place in an inert diluent, typically a hydrocarbon diluent which is
selected from a group comprising C.sub.3 to C.sub.8 hydrocarbons,
such as methane, ethane, propane, n-butane, isobutane, hexanes such
as n-hexane, heptanes, octanes etc. or their mixtures. Preferably
the diluent is a low boiling hydrocarbon having from 1 to 4 carbon
atoms or a mixture of such hydrocarbons. An especially preferred
diluent is propane, possibly containing minor amounts of methane,
ethane and/or butane. The inert diluent can be the same or
different in the different polymerisation steps.
[0127] The ethylene content in the fluid phase of the slurry in the
slurry phase reactor may be from 0.5 to 50% by mole, preferably
from 1 to 20% by mole, and in particular from 2 to 10% by mole.
[0128] In a preferred embodiment of a gas phase reactor, the
polymerization takes place in a fluidised bed gas phase reactor
where an olefin is polymerised in the presence of a polymerisation
catalyst in an upwards moving gas stream. The reactor typically
contains a fluidised bed comprising the growing polymer particles
containing the active catalyst located above a fluidisation grid.
The polymer bed is fluidised with the help of a fluidisation gas
comprising the olefin monomer, eventually comonomer(s), eventually
chain growth controllers or chain transfer agents, such as
hydrogen, and eventually inert gas.
[0129] Also antistatic agent(s) may be introduced into the gas
phase reactor if needed. Suitable antistatic agents and methods to
use them are disclosed, amongst others, in U.S. PAt. No. 5,026,795,
U.S. Pat. No. 4,803,251, U.S. Pat. No. 4,532,311, U.S. Pat. No.
4,855,370 and EP-A-560 035. They are usually polar compounds and
include, amongst others, water, ketones, aldehydes alcohols.
[0130] A chain-transfer agent, preferably hydrogen, is added as
required to the reactors, and preferably 500 to 1200 moles of
H.sub.2/kmoles of ethylene are added to the reactor, when the LMW
component (A-1) is produced in this reactor, and 0 to 100 moles of
H.sub.2/kmoles of ethylene are added to the gas phase reactor when
this reactor is producing the HMW component (A-2).
[0131] The polymerization process may further comprise a
pre-polymerisation step which precedes the polymerisation steps.
The purpose of the pre-polymerisation is to polymerise a small
amount of polymer onto the catalyst at a low temperature and/or a
low monomer concentration. By pre-polymerisation it is possible to
improve the performance of the catalyst in slurry and/or modify the
properties of the final polymer. The pre-polymerisation step may be
conducted in slurry or gas phase. Preferably the pre-polymerisation
is conducted in slurry.
[0132] Thus, the pre-polymerisation step may be conducted in a loop
reactor. The pre-polymerisation is then preferably conducted in an
inert diluent, typically a hydrocarbon diluent such as methane,
ethane, propane, n-butane, isobutane, pentanes, hexanes, heptanes,
octanes etc., or their mixtures. Preferably the diluent is a low
boiling hydrocarbon having from 1 to 4 carbon atoms or a mixture of
such hydrocarbons. The most preferred diluent is propane.
[0133] The temperature in the pre-polymerisation step is typically
from 0.degree. C. to 90.degree. C., preferably from 20.degree. C.
to 80.degree. C. and more preferably from 40.degree. C. to
70.degree. C.
[0134] The pressure is not critical and is typically from 1 bar to
150 bar, preferably from 10 bar to 100 bar.
[0135] The amount of monomer is typically such that from 0.1 grams
to 1000 grams of monomer per one gram solid catalyst component is
polymerised in the pre-polymerisation step. As the person skilled
in the art knows, the catalyst particles recovered from a
continuous pre-polymerisation reactor do not all contain the same
amount of pre-polymer. Instead, each particle has its own
characteristic amount which depends on the residence time of that
particle in the pre-polymerisation reactor. As some particles
remain in the reactor for a relatively long time and some for a
relatively short time, then also the amount of pre-polymer on
different particles is different and some individual particles may
contain an amount of pre-polymer which is outside the above limits.
However, the average amount of pre-polymer on the catalyst
typically is within the limits specified above.
[0136] In addition to ethylene monomer it is possible to use one or
more alpha-olefin comonomers in the pre-polymerisation step if
desired. Suitable comonomers are, for example, 1-butene, 1-hexene,
4-methyl-1-pentene, 1-octene and their mixtures.
[0137] It is however preferred that in the pre-polymerization step
an ethylene homopolymer prepolymer fraction is polymerized.
[0138] The molecular weight of the pre-polymer may be controlled by
hydrogen as it is known in the art. Further, antistatic additives
may be used to prevent the particles from adhering to each other or
the walls of the reactor, as disclosed in WO-A-96/19503 and
WO-A-96/32420.
[0139] The catalyst components are preferably all introduced to the
pre-polymerisation step. However, where the solid catalyst
component and the cocatalyst can be fed separately it is possible
that only a part of cocatalyst is introduced into the
pre-polymerisation stage and the remaining part into the subsequent
polymerisation stages. Also in such cases it is necessary to
introduce as much cocatalyst into the pre-polymerisation stage as
necessary to obtain a sufficient polymerisation reaction.
[0140] The polymerization conditions as well as the feed streams
and the residence time in the reactors are preferably adapted as
such to produce a base resin (A) as described above or in the
claims below.
[0141] Carbon Black (B), and optionally additives (C) or other
polymer components, are added to the composition during the
compounding step in the amount as described above. Preferably, the
polyethylene composition of the invention obtained from the reactor
is compounded in the extruder together with carbon black (B) and
optional additives (C) in a manner known in the art.
[0142] The composition of the invention, preferably if produced in
a process comprising a compounding step, wherein the composition,
i.e. the blend, which is typically obtained as a polyolefin base
resin powder from the reactor, is extruded in an extruder and then
pelletized to polymer pellets in a manner known in the art. The
extruder may be e.g. any conventionally used extruder. As an
example of an extruder for the present compounding step may be
those supplied by Japan Steel works, Kobe Steel or Farrel-Pomini,
e.g. JSW 460P or JSW CIM90P.
[0143] Use
[0144] Furthermore, the present invention relates to an article,
preferably a pipe or pipe fitting, preferably pipe, and to the use
of such a polyethylene composition for the production of an
article, preferably a pipe or pipe fitting, most preferably a pipe.
Especially preferred are pipes with a wall thickness of at least 60
mm, more preferably at least 75 mm.
[0145] Pipes can be produced from the polyethylene composition
according to the present invention according to the methods known
in the art. Thus, according to one preferred method the
polyethylene composition is extruded through an annular die to a
desired internal diameter, after which the polyethylene composition
is cooled.
[0146] The pipe extruder preferably operates at a relatively low
temperature and therefore excessive heat build-up should be
avoided. Extruders having a high length to diameter ratio L/D more
than 15, preferably of at least 20 and in particular of at least 25
are preferred. The modern extruders typically have an L/D ratio of
from about 30 to 35.
[0147] The polymer melt is extruded through an annular die, which
may be arranged either as end-fed or side-fed configuration. The
side-fed dies are often mounted with their axis parallel to that of
the extruder, requiring a right-angle turn in the connection to the
extruder. The advantage of side-fed dies is that the mandrel can be
extended through the die and this allows, for instance, easy access
for cooling water piping to the mandrel.
[0148] After the plastic melt leaves the die it is calibrated to
the correct diameter. In one method the extrudate is directed into
a metal tube (calibration sleeve). The inside of the extrudate is
pressurised so that the plastic is pressed against the wall of the
tube.
[0149] According to another method the extrudate leaving the die is
directed into a tube having a perforated section in the centre. A
slight vacuum is drawn through the perforation to hold the pipe
against the walls of the sizing chamber.
[0150] After the sizing the pipe is cooled, typically in a water
bath having a length of about 5 metres or more.
[0151] The fittings can be produced by conventional moulding
processes, like injection moulding processes, which are well known
to a skilled person.
EXAMPLES
[0152] 1. Definitions
[0153] a) Melt Flow Rate
[0154] The melt flow rate (MFR) is determined according to ISO 1133
and is indicated in g/10 min. The MFR is an indication of the
flowability, and hence the processability, of the polymer. The
higher the melt flow rate, the lower the viscosity of the polymer.
The MFR.sub.5 of polyethylene is measured at a temperature of
190.degree. C. and a load of 5 kg, the MFR.sub.2 of polyethylene at
a temperature of 190.degree. C. and a load of 2.16 kg and the
MFR.sub.21 of polyethylene is measured at a temperature of
190.degree. C. and a load of 21.6 kg. The quantity FRR (flow rate
ratio) denotes the ratio of flow rates at different loads. Thus,
.sub.FRR2115 denotes the value of MFR.sub.21/MFR.sub.5.
[0155] b) Density
[0156] Density of the polymer was measured according to ISO
1183-1:2004 Method A on compression moulded specimen prepared
according to EN ISO 1872-2 (February 2007) and is given in
kg/m.sup.3.
[0157] c) Comonomer Content
[0158] Quantitative nuclear-magnetic resonance (NMR) spectroscopy
was used to quantify the comonomer content of the polymers.
[0159] Quantitative .sup.13C{.sup.1H} NMR spectra recorded in the
molten-state using a Bruker Advance III 500 NMR spectrometer
operating at 500.13 and 125.76 MHz for .sup.1H and .sup.13C,
respectively. All spectra were recorded using a .sup.13C optimized
7 mm magic-angle spinning (MAS) probehead at 150.degree. C. using
nitrogen gas for all pneumatics. Approximately 200 mg of material
was packed into a 7 mm outer diameter zirconia MAS rotor and spun
at 4 kHz. This setup was chosen primarily for the high sensitivity
needed for rapid identification and accurate quantification {[1],
[2], [6]}. Standard single-pulse excitation was employed utilizing
the transient NOE at short recycle delays of 3 s {[1], [3]) and the
RSHEPT decoupling scheme {[4], [5]}. A total of 1024 (1 k)
transients were acquired per spectrum. This setup was chosen due to
its high sensitivity towards low comonomer contents.
[0160] Quantitative .sup.13C{.sup.1H) NMR spectra were processed,
integrated and quantitative properties determined using custom
spectral analysis automation programs. All chemical shifts are
internally referenced to the bulk methylene signal (.delta.+) at
30.00 ppm {[9]}.
[0161] Characteristic signals corresponding to the incorporation of
1-hexene were observed {[9]} and all contents calculated with
respect to all other monomers present in the polymer.
H=I*.sub.B4
[0162] With no other signals indicative of other comonomer
sequences, i.e. consecutive comonomer incorporation, observed the
total 1-hexene comonomer content was calculated based solely on the
amount of isolated 1-hexene sequences:
H.sub.total=H
[0163] Characteristic signals resulting from saturated end-groups
were observed. The content of such saturated end-groups was
quantified using the average of the integral of the signals at
22.84 and 32.23 ppm assigned to the 2 s and 3 s sites
respectively:
S=(1/2)*(I.sub.2S+I.sub.3S)
[0164] The relative content of ethylene was quantified using the
integral of the bulk methylene (.delta.+) signals at 30.00 ppm:
E=(1/2)*I.sub..delta.+
[0165] The total ethylene comonomer content was calculated based on
the bulk methylene signals and accounting for ethylene units
present in other observed comonomer sequences or end-groups:
E.sub.total=E+( 5/2)*B+( 3/2)*S
[0166] The total mole fraction of 1-hexene in the polymer was then
calculated as:
fH=(H.sub.total/(E.sub.total+H.sub.total)
[0167] The total comonomer incorporation of 1-hexene in mole
percent was calculated from the mole fraction in the usual
manner:
H [mol %]=100*fH
[0168] The total comonomer incorporation of 1-hexene in weight
percent was calculated from the mole fraction in the standard
manner:
H [wt %]=100*(fH*84.16)/((fH*84.16)+((1-fH)*28.05))
[0169] [1] Klimke, K., Parkinson, M., Piel, C., Kaminsky, W.,
Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006;
207:382.
[0170] [2] Parkinson, M., Klimke, K., Spiess, H. W., Wilhelm, M.,
Macromol. Chem. Phys. 2007; 208:2128.
[0171] [3] Pollard, M., Klimke, K., Graf, R., Spiess, H. W.,
Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules
2004; 37:813.
[0172] [4] Filip, X., Tripon, C., Filip, C., J. Mag. Reson. 2005,
176, 239.
[0173] [5] Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and
Brown, S. P., Mag. Res. in Chem. 2007, 45, S1, S198.
[0174] [6] Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M.,
Gaborieau, M., Polymer 50 (2009) 2373.
[0175] [7] Zhou, Z., Muemmerle, R., Qiu, X., Redwine, D., Cong, R.,
Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 2007, 187,
225.
[0176] [8] Busico, V., Carbonniere, P., Cipullo, R., Pellecchia,
R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28,
1128.
[0177] [9] J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys.
1989, C29, 201.
[0178] d) Dynamic Shear Measurements (Frequency Sweep
Measurements)
[0179] The characterization of polymer melts by dynamic shear
measurements complies with ISO standards 6721-1 and 6721-10. The
measurements were performed on an Anton Paar MCR501 stress
controlled rotational rheometer, equipped with a 25 mm parallel
plate geometry. Measurements were undertaken on compression moulded
plates using nitrogen atmosphere and setting a strain within the
linear viscoelastic regime. The oscillatory shear tests were done
at 190.degree. C. applying a frequency range between 0.0154 and 500
rad/s and setting a gap of 1.2 mm.
[0180] In a dynamic shear experiment the probe is subjected to a
homogeneous deformation at a sinusoidal varying shear strain or
shear stress (strain and stress controlled mode, respectively). On
a controlled strain experiment, the probe is subjected to a
sinusoidal strain that can be expressed by
.gamma.(t)=.gamma..sub.0 sin(.omega.t) (1)
[0181] If the applied strain is within the linear viscoelastic
regime, the resulting sinusoidal stress response can be given
by
.sigma.(t)=.sigma..sub.0 sin(.omega.t+.delta.) (2)
[0182] where .sigma..sub.0, and .gamma..sub.0 are the stress and
strain amplitudes, respectively; .omega. is the angular frequency;
.delta. is the phase shift (loss angle between applied strain and
stress response); t is the time.
[0183] Dynamic test results are typically expressed by means of
several different rheological functions, namely the shear storage
modulus, G', the shear loss modulus, G'', the complex shear
modulus, G*, the complex shear viscosity, .eta.*, the dynamic shear
viscosity, .eta.', the out-of-phase component of the complex shear
viscosity, .eta.'', and the loss tangent, tan .eta., which can be
expressed as follows:
G ' = .sigma. 0 .gamma. 0 cos .delta. [ Pa ] ( 3 ) G '' = .sigma. 0
.gamma. 0 sin .delta. [ Pa ] ( 4 ) G * = G ' + G '' [ Pa ] ( 5 )
.eta. * = .eta. ' - .eta. '' [ Pa s ] ( 6 ) .eta. ' = G '' .omega.
[ Pa s ] ( 7 ) .eta. '' = G ' .omega. [ Pa s ] ( 8 )
##EQU00001##
[0184] Besides the above mentioned rheological functions one can
also determine other rheological parameters such as the so-called
elasticity index EI(x). The elasticity index EI(x) is the value of
the storage modulus, G', determined for a value of the loss
modulus, G'', of x kPa and can be described by equation 9.
EI(x)=G' for (G''=x kPa) [Pa] (9)
[0185] For example, the EI(5 kPa) is defined by the value of the
storage modulus G', determined for a value of G'' equal to 5
kPa.
[0186] The determination of so-called Shear Thinning Indexes is
done, as described in equation 10.
SHI ( x / y ) = Eta * for ( G * = xkPa ) Eta * for ( G * = ykPa ) [
Pa ] ( 10 ) ##EQU00002##
[0187] For example, the SHI.sub.(2.7/210) is defined by the value
of the complex viscosity, in Pas, determined for a value of G*
equal to 2.7 kPa, divided by the value of the complex viscosity, in
Pas, determined for a value of G* equal to 210 kPa.
[0188] The values of storage modulus (G'), loss modulus (G''),
complex modulus (G*) and complex viscosity (.eta.*) were obtained
as a function of frequency (.omega.).
[0189] Thereby, e.g. .eta.*.sub.300 rad/s (eta*.sub.300 rad/s) is
used as abbreviation for the complex viscosity at the frequency of
300 rad/s and .eta.*.sub.0.05 rad/s (eta*.sub.0.05 rad/s) is used
as abbreviation for the complex viscosity at the frequency of 0.05
rad/s.
[0190] The values are determined by means of a single point
interpolation procedure, as defined by Rheoplus software. In
situations for which a given G* value is not experimentally
reached, the value is determined by means of an extrapolation,
using the same procedure as before. In both cases (interpolation or
extrapolation), the option from Rheoplus "Interpolate y-values to
x-values from parameter" and the "logarithmic interpolation type"
were applied.
REFERENCES
[0191] [1] Rheological characterization of polyethylene fractions"
Heino, E. L., Lehtinen, A., Tanner J., Seppala, J., Neste Oy,
Porvoo, Finland, Theor. Appl. Rheol., Proc. Int. Congr. Rheol, 11th
(1992), 1, 360-362
[0192] [2] The influence of molecular structure on some rheological
properties of polyethylene", Heino, E. L., Borealis Polymers Oy,
Porvoo, Finland, Annual Transactions of the Nordic Rheology
Society, 1995.).
[0193] [3] Definition of terms relating to the non-ultimate
mechanical properties of polymers, Pure & Appl. Chem., Vol. 70,
No. 3, pp. 701-754, 1998.
[0194] e) Eta 747 Pa (Sagging):
[0195] One method which correlates well with the sagging
properties, and is used in connection with the present invention
relates to the rheology of the polymer and is based on
determination of the viscosity of the polymer at a very low,
constant shear stress. A shear stress of 747 Pa has been selected
for this method. The viscosity of the polymer at this shear stress
is determined at a temperature of 190.degree. C. and has been found
to be inversely proportional to the gravity flow of the polymer,
i.e. the greater the viscosity the lower the gravity flow.
[0196] The determination of the viscosity at 747 Pa shear stress is
made by using a rotational rheometer, which can be a constant
stress rheometer as for example an Anton Paar MCR Series Rheometer.
Rheometers and their function have been described in "Encyclopedia
of Polymer Science and Engineering", 2nd Ed., Vol. 14, pp. 492-509.
The measurements are performed under a constant shear stress
between two 25 mm diameter plates (constant rotation direction).
The gap between the plates is 1.2 mm. An 1.2 mm thick polymer
sample is inserted between the plates.
[0197] The sample is temperature conditioned during 2 min before
the measurement is started. The measurement is performed at
190.degree. C. After temperature conditioning the measurement
starts by applying the predetermined stress. The stress is
maintained during 1800 s to let the system approach steady state
conditions. After this time the measurement starts and the
viscosity is calculated.
[0198] The measurement principle is to apply a certain torque to
the plate axis via a precision motor. This torque is then
translated into a shear stress in the sample. This shear stress is
kept constant. The rotational speed produced by the shear stress is
recorded and used for the calculation of the viscosity of the
sample.
[0199] f) Molecular Weight
[0200] Molecular weight averages (Mz, Mw and Mn), Molecular weight
distribution (MWD) and its broadness, described by polydispersity
index, PDI=Mw/Mn (wherein Mn is the number average molecular weight
and Mw is the weight average molecular weight) were determined by
Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003
and ASTM D 6474-99 using the following formulas:
M n = i = 1 N A i ( A i / M i ) ( 1 ) M w = i = 1 N ( A i .times. M
i ) A i ( 2 ) M z = i = 1 N ( A i .times. M i 2 ) ( A i / M i ) ( 3
) ##EQU00003##
[0201] For a constant elution volume interval .DELTA.V.sub.i, where
A.sub.i and M.sub.i are the chromatographic peak slice area and
polyolefin molecular weight (MW).
[0202] A PolymerChar GPC instrument, equipped with infrared (IR)
detector was used with 3.times. Olexis and 1.times. Olexis Guard
columns from Polymer Laboratories and 1,2,4-trichlorobenzene (TCB,
stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) as
solvent at 160.degree. C. and at a constant flow rate of 1 mL/min.
200 .mu.L of sample solution were injected per analysis. The column
set was calibrated using universal calibration (according to ISO
16014-2:2003) with at least 15 narrow MWD polystyrene (PS)
standards in the range of 0.5 kg/mol to 11 500 kg/mol. Mark Houwink
constants for PS, PE and PP used are as described per ASTM D
6474-99. All samples were prepared by dissolving 5.0-9.0 mg of
polymer in 8 mL (at 160.degree. C.) of stabilized TCB (same as
mobile phase) for 2.5 hours for PP or 3 hours for PE at 160.degree.
C. under continuous gentle shaking in the autosampler of the GPC
instrument.
[0203] g) Tensile Modulus (23.degree. C.)
[0204] As a measure for stiffness, the tensile modulus (E-modulus)
of the compositions was measured at 23.degree. C. on compression
molded specimens according to ISO 527-2:1993. The specimens (1B
type) were cut from plaques of 4 mm thickness prepared by
compression molding according to ISO 293:2004 using the conditions
defined in chapter 3.3 of ISO 1872-2:2007. The modulus was measured
at a speed of 1 mm/min.
[0205] h) Tensile Properties (23.degree. C.)
[0206] The tensile strength, including tensile stress at yield,
strain at yield and elongation at break (i.e. tensile strain at
break) is measured according to ISO 527-1 (cross head speed 50
mm/min) at a temperature of 23.degree. C.
[0207] i) Pressure Test on Un-Notched Pipes (PT); Resistance to
Internal Pressure
[0208] The resistance to internal pressure has been determined in a
pressure test on pressure test on un-notched 32 mm SDR 11 pipes
having a length of 450 mm is carried out in water-inside and
water-outside environment according to ISO 1167-1:2006. End caps of
type A were used. The time to failure is determined in hours. The
following conditions were applied: hoop stress of 5.5 MPa at a
temperature of 80.degree. C.
[0209] 2. Materials
a) Inventive Example Ex1
[0210] Into a first loop reactor having a volume of 50 dm.sup.3 and
operating at a temperature of 60.degree. C. and a pressure of 65
bar propane (C3, 50 kg/h), ethylene (C2, 2 kg/h), and hydrogen (H2,
10 g/h) were introduced for conducting a pre-polymerization step.
In addition a commercially available, solid polymerisation catalyst
component Lynx 200.TM. sold by BASF Catalyst LLC was introduced
into the reactor together with triethylaluminium cocatalyst so that
the ratio of aluminium to titanium was 15 mol/mol. The
polymerization rate was 1.9 kg/h.
[0211] The slurry was withdrawn intermittently from the
prepolymerization reactor and directed to a second loop reactor
having a volume of 500 dm.sup.3 and operating at a temperature of
95.degree. C. and a pressure of 65 bar. Additionally, propane,
ethylene and hydrogen were fed to the second loop reactor whereby
the ethylene concentration and the hydrogen to ethylene ratio for
example Ex 1 are listed in Table 1. The production split, the
density and melt index of the polymer fractions produced in the
second loop reactor are listed in Table 1.
[0212] The slurry was withdrawn intermittently from the second loop
reactor by using settling legs and directed to a gas phase reactor.
The gas phase reactor was operated at a temperature of 85.degree.
C. and a pressure of 20 bar. Additional ethylene, 1-hexene
comonomer, and hydrogen were fed whereby the ethylene
concentration, the 1-hexene to ethylene ratio and the hydrogen to
ethylene ratio as well as the production split and the density of
the polymers of example Ex 1 withdrawn from the gas phase reactor
are listed in Table 1.
[0213] The resulting polymer was purged with nitrogen (about 50
kg/h) for one hour, stabilised with commercial stabilisers, 1100
ppm of Irganox 1010, 1100 ppm Irgafos 168 and 1500 ppm Ca-stearate
and then extruded together with 3.0 wt % carbon black to pellets in
a counter-rotating twin screw extruder CIM90P (manufactured by
Japan Steel Works) The temperature profile in each zone was
90/120/190/250.degree. C.
[0214] The properties of the compounded composition are shown in
Table 1.
b) Comparative Example CE2
[0215] As comparative example CE2 commercially available black
bimodal HDPE grade for PE100 pipes (for thick wall pipes) has been
tested. The properties of the PE100 HDPE resin are shown in Table
1.
c) Pipe Preparation
[0216] The compounded compositions of Inventive Example Ex1 and
Comparative Examples CE1 were extruded to SDR 11 pipes for the
pressure resistance tests in a Battenfeld 1-60-35-B extruder at a
screw speed of about 200 rpm, and the conditions as listed in Table
2. The temperature profile in each barrel zone was
220/210/210/210/210.degree. C.
[0217] The results of the pipe tests are shown in Table 2.
TABLE-US-00001 TABLE 1 Polymerization conditions Ex1
Prepolymerizer: Temperature [.degree. C.] 60 Pressure [bar] 65
Split [wt %] 2.3 Loop: Temperature [.degree. C.] 95 Pressure [bar]
65 H.sub.2/C.sub.2 [mol/kmol] 1050 C.sub.2-concentration [mol %]
2.6 Production Rate [kg/h] 37 Split [wt %] 48.7 MFR.sub.2 [g/10
min] 325 Density [kg/m.sup.3] 970 Gas phase: Temperature [.degree.
C.] 85 Pressure [bar] 20 H.sub.2/C.sub.2 [mol/kmol] 12.6
C.sub.6/C.sub.2 [mol/kmol] 68 C.sub.2-concentration [mol %] 15
Production Rate [kg/h] 38 Split [wt %] 49 Density [kg/m.sup.3] 949
Composition Properties: Ex. 1 CE2 Density [kg/m.sup.3] 962 961
MFR.sub.5 [g/10 min] 0.16 0.17 MFR.sub.21 [g/10 min] 6.2 6.6
FRR.sub.21/5 39 39 Mw [kg/mol] 285 267 Mz [kg/mol] 1885 1705 MWD
(Mw/Mn) 36 19 Eta (0.05 rad/s) [Pa s] 234000 282000 Eta (300 rad/s)
[Pa s] 1141 1265 SHI.sub.2.7/210 109 72 SHI.sub.5/200 69 49
Eta.sub.747 [kPa s] 868 870 C.sub.6 content [mol %] 0.80 Tensile
Modulus [MPa] 1042 1300 Tensile Strength [MPa] 28.4 37 Tensile
Stress at yield [MPa] 28.4 25 Elongation at break [%] 640 760
TABLE-US-00002 TABLE 2 Pipe Properties Ex1 Pipe Extrusion Melt
Pressure, 32 mm [bar] 315 Melt Temperature, 32 mm [.degree. C.] 200
Melt Pressure, 110 mm [bar] 321 Melt Temperature, 110 mm [.degree.
C.] 190 Pressure Test 80.degree. C., 5.5 MPa [h] 240 Failure mode D
Failure mode: D = ductile failure mode B = brittle failure mode
* * * * *