Title of Invention

COATED PIPES HAVING IMPROVED MECHNICAL PROPERTIES AND A METHOD OF PRODUCTION THEREOF

Abstract The present invention deals with coated pipes having a layer of multimodal polyethylene. The multimodal ethylene copolymer is a copolymer of ethylene with one or more alpha-olefin comonomers having from 6 to 10 carbon atoms and has a weight average molecular weight of from 70000 g/mol to 250000 g/mol. the ratio of the weight average molecular weight to the number average molecular weight, Mw/Mn. of from 15 to 50, a melt index MFR2 of from 0.05 g/10min to 5g/10 min, a melt index MFR5 of from 0.5 to 10 g/10 min and a density of from 930 kg/m3 to 955 kg/m3. The pipes can be coated with high throughput and good production economy. The coatings have good mechanical properties.
Full Text COATED PIPES HAVING IMPROVED MECHANICAL PROPERTIES AND A METHOD OF
PRODUCTION THEREOF
Objective of the invention
The present invention is directed to polymer coated pipes. More specifically, the present
invention is directed to coated metal pipes having an improved resistance to stress cracking
for a given density of the coating. In addition, the present invention is directed to a method of
producing such coated metal pipes with a high throughput and good production economy.
Technical background and prior art
The use of bimodal or multimodal ethylene polymers in coating of steel pipes is known from
EP-A-837915. However, even though the document teaches that the coatings have good
mechanical properties there still exists a need to further improve the slow crack growth
resistance and improve the balance between the stiffness and stress cracking resistance of
the coating composition.
Summary of the invention
The present invention provides polyethylene coated metal pipes that have an improved
resistance against stress cracking and/or can be used at a wide range of service
temperature.
One aspect of the present invention is to provide a pipe comprising an inner surface, an
outer surface layer (A) and a coating layer (B) covering said outer surface (A), wherein the
coating layer (B) comprises a coating composition (B-2) comprising a multimodal copolymer
of ethylene and one or more alpha-olefin comonomers having from 6 to 10 carbon atoms (B-
1), wherein the multimodal ethylene copolymer (B-1) has a weight average molecular weight
of from 70000 g/mol to 250000 g/mol, a melt index MFR2 of from 0.05 g/10 min to 5 g/10 min,
a melt index MFR5 of from 0.5 to 10 g/10 min and a density of from 930 kg/m3to 950 kg/m3.
Another aspect of the present invention is to provide pipes comprising an inner surface and
an outer surface layer (A) and a coating layer (B) wherein
the coating layer (B) comprises a coating composition (B-2) comprising a multimodal
copolymer of ethylene and one or more alpha-olefin comonomers having from 6 to 10 carbon
atoms (B-1), wherein the multimodal ethylene copolymer (B-1) further comprises
(B-1-1) from 40 to 60 %, based on the weight of the multimodal ethylene copolymer (B-1), of
a low molecular weight ethylene homopolymer component, said low molecular weight
ethylene homopolymer having a weight average molecular weight of from 5000 g/mol to
70000 g/mol; and
(B-1-2) from 60 to 40 %, based on the weight of the multimodal ethylene copolymer (B-1), of
a high molecular weight ethylene copolymer component, said high molecular weight ethylene
copolymer having a weight average molecular weight of from 100000 g/mol to 700000 g/mol;
and
the multimodal ethylene copolymer has a weight average molecular weight of from 70000
g/mol to 250000 g/mol and a melt index MFR2 of from 0.05 g/10 min to 5 g/10 min, preferably
from 0.1 to 1.2 g/10 min and more preferably 0.2 - 0.8. Preferably, it further has an MFR5 of
0.5 to 10 g/10 min, more preferably from 1.0 to 5.0 g/10 min. Preferably still it has a density
of from 930 kg/m3 to 950 kg/m3.
The third aspect of the present invention is providing a method for producing the coated
pipes as disclosed above. The process comprises the steps of:
providing a pipe having an outer surface layer (A);
applying a coating composition (B-2) onto the pipe outer surface layer (A) to form a coating
layer (B), wherein the coating composition (B-2) comprises a multimodal copolymer of
ethylene and one or more alpha-olefin comonomers having from 6 to 10 carbon atoms (B-1),
wherein the multimodal ethylene copolymer (B-1) has a weight average molecular weight of
from 70000 g/mol to 250000 g/mol, a melt index MFR2 of from 0.05 g/10 min to 5 g/10 min, a
melt index MFR5 of from 0.5 to 10 g/10 min and a density of from 930 kg/m3 to 950 kg/m3.
The fourth aspect of the present invention is to provide a process for producing coated pipes
comprising the steps of:
(i) polymerising ethylene, in a first polymerisation stage, in the presence of a polymerisation
catalyst, hydrogen, ethylene and optionally an inert diluent to produce a low molecular weight
ethylene homopolymer (B-1-1) having a weight average molecular weight of from 5000 g/mol
to 70000 g/mol and which constitutes from 40 to 60 % by weight of the multimodal ethylene
copolymer (B-1); and
(ii) polymerising, in a second polymerisation stage, ethylene and one or more alpha-olefin
comonomers having from 6 to 10 carbon atoms in the presence of a polymerisation catalyst,
ethylene, one or more alpha-olefin comonomers having 6 to 10 carbon atoms and optionally
hydrogen and/or an inert diluent to produce a high molecular weight copolymer of ethylene
and one or more alpha-olefin comonomers having from 6 to 10 carbon atoms (B-1-2) having
a weight average molecular weight of from 200000 g/mol to 700000 g/mol, which high
molecular weight ethylene component (B-1-2) constitutes from 40 to 60 % by weight of the
multimodal ethylene copolymer (B-1); and wherein said first and said second polymerisation
step are performed as successive polymerisation steps with the polymer product produced in
any previous step being present in the subsequent step(s) and wherein said first step and
said second step can be performed in any order and wherein the resulting multimodal
ethylene copolymer (B-1) has a weight average molecular weight of from 70000 g/mol to
250000 g/mol and a melt index MFR2 of from 0.05 g/10 min to 5 g/10 min, a melt index MFR5
of from 0.5 to 10 g/10 min and a density of from 930 kg/m3 to 950 kg/m3;
(iii) recovering said multimodal ethylene copolymer;
(iv) obtaining the coating composition (B-2) comprising 80 to 100 % by weight, preferably
from 85 to 100 % by weight and in particular from 90 to 99 % by weight of the multimodal
ethylene copolymer (B-1), optional additives and optional other polymers;
(iv) applying said coating composition (B-2) onto the pipe (A) to form the coating layer (B)
The coated pipes according to the present invention exhibit a good stress crack resistance
as measured by the CTL method described elsewhere in this patent application, typically of
at least 60 hours, preferably of at least 100 hours. Thus, at a given density of the multimodal
ethylene copolymer (B-1) the coating composition (B-2) comprising the multimodal ethylene
copolymer (B-1) has an increased CTL compared to the prior art compositions.
The pipe coating process allows the preparation of coated pipes having good mechanical
properties with a high throughput.
Detailed description
Multimodal ethylene copolymer
The multimodal ethylene copolymer (B-1) is a copolymer of ethylene and one or more alpha-
olefin comonomers having from 6 to 10 carbon atoms. The multimodal ethylene copolymer
has a weight average molecular weight of 70000 to 250000 g/mol, a melt index MFR2 of from
0.05 to 5 g/10 min, preferably from 0.1 to 1.2 g/10 min, and more preferably from 0.2 to 1.0
g/10 min. Preferably, it further has an MFR5 of 0.5 to 10 g/10 min, more preferably from 1.0
to 5.0 g/10 min. Furthermore, the multimodal ethylene copolymer has a density of from 930
to 950 kg/m3, preferably from 933 to 944 kg/m3 and more preferably from 936 to 944 kg/m3.
When the multimodal ethylene copolymer (B-1) has the comonomers selected from alpha-
olefins having from 6 to 10 carbon atoms the coating composition (B-2) has the improved
mechanical properties. If comonomers having a lower number of carbon atoms are used, the
composition does not have the advantageous mechanical properties. On the other hand, if
comonomers having a higher number of carbon atoms are used the incorporation of the
comonomer is slower and it becomes more difficult to produce the copolymer (B-1).
When the multimodal copolymer (B-1) has the weight average molecular weight between
70000 and 250000 g/mol and a melt index MFR2 within the range of 0.05 to 5 g/10 min the
coating composition (B-2) has a good processability and good mechanical properties. If the
molecular weight is lower than the specified range and/or the melt index is higher than the
specified range the coating composition has inferior mechanical properties. On the other
hand, if the molecular weight is higher than the specified range and/or the melt index is lower
than the specified range the coating composition has a poor processability. By poor
processability is meant a low throughput, poor neck-in behaviour and/or line breaks during
the coating process.
Preferably the multimodal ethylene copolymer (B-1) has a broad molecular weight
distribution as indicated by the ratio of weight average molecular weight to the number
average molecular weight, Mw/Mn, of from 15 to 50, preferably from 20 to 40 and in
particular from 25 to 40. When the ratio of the weight average molecular weight to the
number average molecular weight is within these limits the multimodal ethylene copolymer
(B-1) has a good combination between processability and homogeneity.
The multimodal ethylene copolymer (B-1) advantageously comprises from 40 to 60 % by
weight, based on the multimodal ethylene copolymer (B-1), of low molecular weight ethylene
homopolymer component (B-1-1). The low molecular weight ethylene homopolymer
component (B-1-1) has a weight average molecular weight of from 5000 to 70000 g/mol,
preferably form 15000 to 50000 g/mol. Preferably the low molecular weight ethylene
homopolymer component (B-1-1) has a melt index MFR2 of from 100 to 1500 g/10 min, more
preferably from 150 to 1000 g/10 min. Preferably still, the low molecular weight ethylene
homopolymer component (B-1-1) has a density of at least 969 kg/m3, more preferably of 971
to 978 kg/m3.
It should be understood that within the meaning of the present invention the term
"homopolymer" is used to mean a linear ethylene polymer which essentially consists of
ethylene repeating units. It may contain trace amount of units derived from other
polymerisable monomers, but it should contain at least about 99.9 % by mole of ethylene
repeating units, based on all the repeating units present in the low molecular weight ethylene
homopolymer component.
The multimodal ethylene copolymer (B-1) advantageously also comprises from 40 to 60 % by
weight, based on the multimodal ethylene copolymer (B-1), a high molecular weight
copolymer of ethylene and alpha-olefins having from 6 to 10 carbon atoms (B-1-2). The high
molecular weight copolymer component (B-1-2) has a weight average molecular weight of
from 100000 to 700000 g/mol, preferably 150000 to 300000 g/mol. Preferably, it further has a
content of alpha-olefin comonomers having from 6 to 10 carbon atoms of 0.5 to 10 % by
mole, preferably from 1 to 5 % by mole, based on the total number of moles of repeating
units in the high molecular weight copolymer component (B-1-2).
It should be understood that within the meaning of the present invention the term "copolymer
of ethylene and alpha-olefins having from 6 to 10 carbon atoms" is used to mean an ethylene
polymer which essentially consists of ethylene repeating units and repeating units derived
from alpha-olefins having from 6 to 10 carbon atoms. It may contain trace amount of units
derived from other polymerisable monomers, but it should contain at least about 99.9 % by
mole of above-mentioned repeating units, based on all the repeating units present in the high
molecular weight ethylene copolymer component.
The inventors have found that when the low molecular weight component (B-1-1) and the
high molecular weight component (B-1-2) as described above are present in the multimodal
ethylene copolymer (B-1) the advantageous properties of the multimodal ethylene polymer
(B-1) and the coating composition (B-2) are conveniently obtained.
!n addition to the two components referred above the multimodal ethylene copolymer (B-1)
may contain up to 20 % by weight of other polymer components. The amount ant the
properties of such additional polymer components may be selected freely provided that the
properties of the multimodal ethylene copolymer and of the two above-mentioned
components are those discussed above and that the properties of the multimodal ethylene
copolymer (B-1) are still within the limits specified herein.
Polymerisation process
The multimodal ethylene copolymer may be produced in any suitable polymerisation process
known in the art. Preferably the multimodal ethylene copolymer is produced in a sequential
polymerisation process comprising at least two polymerisation zones operating at different
conditions to produce the multimodal copolymer. The polymerisation zones may operate in
slurry, solution, or gas phase conditions or their combinations. Suitable processes are
disclosed, among others, in WO-A-92/12182 and WO-A-96/18662.
Catalyst
The polymerisation is conducted in the presence of an olefin polymerisation catalyst. The
catalyst may be any catalyst which is capable of producing all components of the multimodal
ethylene copolymer. Suitable catalysts are, among others, Ziegler - Natta catalysts based on
a transition metal, such as titanium, zirconium and/or vanadium or metallocene catalysts or
late transition metal catalysts, as well as their mixtures. Especially Ziegler - Natta catalysts
and metallocene catalysts are useful as they can produce polymers within a wide range of
molecular weight with a high productivity.
Suitable Ziegler- Natta catalysts preferably contain a magnesium compound, an aluminium
compound and a titanium compound supported on a particulate support.
The particulate support can be an inorganic oxide support, such as silica, alumina, titania,
silica-alumina and silica-titania. Preferably, the support is silica.
The average particle size of the silica support can be typically from 10 to 100 µm. However,
it has turned out that special advantages can be obtained if the support has an average
particle size from 15 to 30 µm, preferably from 18 to 25 µm. Alternatively, the support may
have an average particle size of from 30 a 80 µm, preferably from 30 to 50 µm. Examples of
suitable support materials are, for instance, ES747JR produced and marketed by Ineos
Silicas (former Crossfield), and SP9-491, produced and marketed by Grace.
The magnesium compound is a reaction product of a magnesium dialkyl and an alcohol. The
alcohol is a linear or branched aliphatic monoalcohol. Preferably, the alcohol has from 6 to
16 carbon atoms. Branched alcohols are especially preferred, and 2-ethyl-1-hexanol is one
example of the preferred alcohols. The magnesium dialkyl may be any compound of
magnesium bonding to two alkyl groups, which may be the same or different. Butyl-octyl
magnesium is one example of the preferred magnesium dialkyls.
The aluminium compound is chlorine containing aluminium alkyl. Especially preferred
compounds are aluminium alkyl dichlorides and aluminium alkyl sesquichlorides.
The titanium compound is a halogen containing titanium compound, preferably chlorine
containing titanium compound. Especially preferred titanium compound is titanium
tetrachloride.
The catalyst can be prepared by sequentially contacting the carrier with the above mentioned
compounds, as described in EP-A-688794 or WO-A-99/51646. Alternatively, it can be
prepared by first preparing a solution from the components and then contacting the solution
with a carrier, as described in WO-A-01/55230.
Another, especially preferred, group of suitable Ziegler - Natta catalysts contain a titanium
compound together with a magnesium halide compound without an inert support. Thus, the
catalyst contains a titanium compound on a magnesium dihalide, like magnesium dichloride.
Such catalysts are disclosed, for instance, in WO-A-2005/118655 and EP-A-810235.
The Ziegler- Natta catalyst is used together with an activator. Suitable activators are metal
alkyl compounds and especially aluminium alkyl compounds. These compounds include alkyl
aluminium halides, such as ethylaluminium dichloride, diethylaluminium chloride,
ethylaluminium sesquichloride, dimethylaluminium chloride and the like. They also include
trialkylaluminium compounds, such as trimethylaluminium, triethylaluminium, tri-
isobutylaluminium, trihexylaluminium and tri-n-octylaluminium. Furthermore they include
alkylaluminium oxy-compounds, such as methylaluminiumoxane,
hexaisobutylaluminiumoxane and tetraisobutylaluminiumoxane. Also other aluminium alkyl
compounds, such as isoprenylaluminium, may be used. Especially preferred activators are
trialkylaluminiums, of which triethylaluminium, trimethylaluminium and tri-isobutylaluminium
are particularly used.
The amount in which the activator is used depends on the specific catalyst and activator.
Typically triethylaluminium is used in such amount that the molar ratio of aluminium to the
transition metal, like Al/Ti, is from 1 to 1000, preferably from 3 to 100 and in particular from
about 5 to about 30 mol/mol.
As discussed above, also metallocene catalysts may be used to produce the multimodal
ethylene copolymer. Suitable metallocene catalysts are known in the art and are disclosed,
among others, in WO-A-95/12622, WO-A-96/32423, WO-A-97/28170, WO-A-98/32776,
WO-A-99/61489, WO-A-03/010208, WO-A-03/051934, WO-A-03/051514, WO-A-
2004/085499, EP-A-1752462 and EP-A-1739103.
Polymerisation
The polymerisation zone where the low molecular weight ethylene homopolymer is produced
typically operates at a temperature of from 20 to 150 °C, preferably from 50 to 110 °C and
more preferably from 60 to 100 °C. The polymerisation may be conducted in slurry, gas
phase or solution.
The catalyst may be transferred into the polymerisation zone by any means known in the art.
It is thus possible to suspend the catalyst in a diluent and maintain it as homogeneous slurry.
Especially preferred it is to use oil having a viscosity form 20 to 1500 mPa-s as diluent, as
disclosed in WO-A-2006/063771. It is also possible to mix the catalyst with a viscous mixture
of grease and oil and feed the resultant paste into the polymerisation zone. Further still, it is
possible to let the catalyst settle and introduce portions of thus obtained catalyst mud into the
polymerisation zone in a manner disclosed, for instance, in EP-A-428054. The
polymerisation zone may also be preceded by a prepolymerisation zone, in which case the
mixture withdrawn from the prepolymerisation zone is directed into the polymerisation zone.
Into the polymerisation zone is also introduced ethylene, optionally an inert diluent, and
optionally hydrogen and/or comonomer. The low molecular weight ethylene homopolymer
component is produced in a first polymerisation zone and the high molecular weight ethylene
copolymer component is produced in a second polymerisation zone. The first polymerisation
zone and the second polymerization zone may be connected in any order, i.e. the first
polymerisation zone may precede the second polymerisation zone, or the second
polymerisation zone may precede the first polymerisation zone or, alternatively,
polymerisation zones may be connected in parallel. However, it is preferred to operate the
polymerisation zones in cascaded mode.
As it was disclosed above, the low molecular weight homopolymer is produced in the first
polymerisation zone. Into the first polymerisation zone are introduced ethylene, hydrogen
and optionally an inert diluent. Comonomer is not introduced into the first polymerisation
zone. The polymerisation in the first polymerisation zone is conducted at a temperature
within the range of from 50 to 115 °C, preferably from 80 to 110 °C and in particular from 90
to 105 °C. The pressure in the first polymerisation zone is from 1 to 300 bar, preferably from
5 to 100 bar.
The polymerisation in the first polymerisation zone may be conducted in slurry. Then the
polymer particles formed in the polymerisation, together with the catalyst fragmented and
dispersed within the particles, are suspended in the fluid hydrocarbon. The slurry is agitated
to enable the transfer of reactants from the fluid into the particles.
The polymerisation usually takes place 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. An especially preferred diluent
is propane, possibly containing minor amount of methane, ethane and/or butane.
The ethylene content in the fluid phase of the slurry may be from 2 to about 50 % by mole,
preferably from about 3 to about 20 % by mole and in particular from about 5 to about 15 %
by mole. The benefit of having a high ethylene concentration is that the productivity of the
catalyst is increased but the drawback is that more ethylene then needs to be recycled than if
the concentration was lower.
The slurry polymerisation may be conducted in any known reactor used for slurry
polymerisation. Such reactors include a continuous stirred tank reactor and a loop reactor. It
is especially preferred to conduct the polymerisation in 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 US-A-
4582816, US-A-3405109, US-A-3324093, EP-A-479186 and US-A-5391654.
It is sometimes advantageous to conduct the slurry polymerisation above the critical
temperature and pressure of the fluid mixture. Such operation is described in US-A-5391654.
The amount of hydrogen is adjusted based on the desired melt flow rate and it also depends
on the specific catalyst used. For many generally used Ziegler - Natta catalysts the molar
ratio of hydrogen to ethylene is from 100 to 1000 mol/kmol, preferably from 200 to 800
mol/kmol and in particular from 300 to 800 mol/kmol.
The polymerisation in the first polymerisation zone may also be conducted in gas phase. A
preferable embodiment of gas phase polymerisation reactor is a fluidised bed reactor. There
the polymer particles formed in the polymerisation are suspended in upwards moving gas.
The gas is introduced into the bottom part of the reactor. The upwards moving gas passes
the fluidised bed wherein a part of the gas reacts in the presence of the catalyst and the
unreacted gas is withdrawn from the top of the reactor. The gas is then compressed and
cooled to remove the heat of polymerisation. To increase the cooling capacity it is sometimes
desired to cool the recycle gas to a temperature where a part of the gas condenses. After
cooling the recycle gas is reintroduced into the bottom of the reactor. Fluidised bed
polymerisation reactors are disclosed, among others, in US-A-4994534, US-A-4588790, EP-
A-699213, EP-A-628343, FI-A-921632, FI-A-935856, US-A-4877587, FI-A-933073 and EP-
A-75049.
In gas phase polymerisation using a Ziegler - Natta catalyst hydrogen is typically added in
such amount that the ratio of hydrogen to ethylene is from 500 to 10000 mol/kmol, preferably
from 1000 to 5000 mol/kmol to obtain the desired molecular weight of the low molecular
weight ethylene homopolymer component.
The high molecular weight copolymer of ethylene and at least one alpha-olefin having 6 to 10
carbon atoms is produced in the second polymerisation zone. Into the second polymerisation
zone are introduced ethylene, alpha-olefin having 6 to 10 carbon atoms, hydrogen and
optionally an inert diluent. The polymerisation in second polymerisation zone is conducted at
a temperature within the range of from 50 to 100°C, preferably from 60 to 100oC and in
particular from 70 to 95 °C. The pressure in the second polymerisation zone is from 1 to 300
bar, preferably from 5 to 100 bar.
The polymerisation in the second polymerisation zone may be conducted in slurry. The
polymerisation may then be conducted along the lines as was discussed above for the first
polymerisation zone.
The amount of hydrogen is adjusted based on the desired melt flow rate and it also depends
on the specific catalyst used. For many generally used Ziegler - Natta catalysts the molar
ratio of hydrogen to ethylene is from 0 to 50 mol/kmol, preferably from 10 to 35 mol/kmol.
Furthermore, the amount of alpha-olefin having from 6 to 10 carbon atoms is adjusted to
reach the targeted density. The ratio of the alpha-olefin to ethylene is typically from 100 to
500 mol/kmol, preferably from 150 to 350 mol/kmol.
The polymerisation in the second polymerisation zone may also be conducted in gas phase.
In gas phase polymerisation using a Ziegler- Natta catalyst hydrogen is typically added in
such amount that the ratio of hydrogen to ethylene is from 5 to 100 mol/kmol, preferably from
10 to 50 mol/kmol to obtain the desired molecular weight of the high molecular weight
ethylene copolymer component (B-1-2). The amount of alpha-olefin having from 6 to 10
carbon atoms is adjusted to reach the targeted density. The ratio of the alpha-olefin to
ethylene is typically from 100 to 500 mol/kmol, preferably from 150 to 350 mol/kmol.
Coating composition
The coating composition (B-2) comprises the multimodal ethylene copolymer (B-1) and
eventual additives and other polymers. Preferably the coating composition (B-2) comprises
from 80 to 100 % by weight, more preferably from 85 to 100 % by weight and in particular
from 90 to 99 % by weight of the multimodal ethylene copolymer (B-1).
In addition to the multimodal ethylene copolymer (B-1) the coating composition (B-2) typically
contains conventional additives known in the art. Such additives are, among others,
antioxidants, process stabilizers, UV-stabilizers, pigments and acid scavengers.
Suitable antioxidants and stabilizers are, for instance, 2,6-di-tert-butyl-p-cresol, tetrakis-
[methylene-3-(3',5-di-tert-butyl-4'hydroxyphenyl)propionate]methane, octadecyl-3-3(3'5'-di-
tert-butyl-4'-hydroxyphenyl)propionate, dilaurylthiodipropionate, distearylthiodipropionate,
tris-(nonylphenyl)phosphate, distearyl-pentaerythritol-diphosphite and tetrakis(2,4-di-tert-
butylphenyl)-4,4'-biphenylene-diphosphonite.
Some hindered phenols are sold under the trade names of Irganox 1076 and Irganox 1010.
Commercially available blends of antioxidants and process stabilizers are also available,
such as Irganox B225 marketed by Ciba-Geigy.
Suitable acid scavengers are, for instance, metal stearates, such as calcium stearate and
zinc stearate. They are used in amounts generally known in the art, typically from 500 ppm to
10000 ppm and preferably from 500 to 5000 ppm.
Carbon black is a generally used pigment, which also acts as an UV-screener. Typically
carbon black is used in an amount of from 0.5 to 5 % by weight, preferably from 1.5 to 3.0 %
by weight. Preferably the carbon black is added as a masterbatch where it is premixed with a
polymer, preferably high density polyethylene (HDPE), in a specific amount. Suitable
masterbatches are, among others, HD4394, sold by Cabot Corporation, and PPM1805 by
Poly Plast Muller. Also titanium oxide may be used as an UV-screener.
In addition the coating composition (B-2) may contain further polymers, such as carrier
polymers used in additive masterbatches. The amount and nature of such polymers may be
chosen freely within the limits discussed above as long as the properties of the coating
composition are not negatively affected.
It is also possible to add a suitable amount of the adhesion polymer into the coating
composition (B-2) to improve the adhesion between the pipe and the coating layer. In this
way the amount of the polymer used in the adhesion layer may be reduced and in some
cases it may be possible to eliminate the adhesion layer altogether.
Preferably, the coating composition (B-2) has a flow rate ratio FRR5/2 of from 2 to 10,
preferably from 2 to 6 and in particular from 3 to 5. Preferably still, it has a flow rate ratio
FRR21/5 of 15 to 40, more preferably from 20 to 35 and/or a shear thinning index SHI2.7/210 of
from 25 to 100.
The coating composition (B-2) preferably has a high resistance to environmental stress
cracking. Thus, preferably the coating composition has a stress cracking resistance, as
measured by CTL (Constant Tensile Load) at 60 °C and 5 MPa of at least 60 h, more
preferably of at least 80 h and especially preferably of at least 100 h.
Preferably the coating composition (B-2) has a wear index of at most 30, more preferably of
at most 25.
Especially preferably the coating composition (B-2) has a balance between the density of the
multimodal ethylene copolymer (B-1) and the CTL so that the coating composition (B-2) has
a value of CTL of at least 60 hours and comprises a multimodal ethylene copolymer (B-1)
having a density of 930 to 950 kg/m3, more preferably has a CTL of at least 80 hours and
comprises a multimodal ethylene copolymer having a density of 933 to 944 kg/m3, and in
particular has a CTL of at least 100 hours and comprises a multimodal ethylene copolymer
having a density of 936 to 944 kg/m3.
Coating layer
The coated pipe has a coating layer (B) which comprises the coating composition (B-2). The
coating layer (B) comprises at least 75 % by weight, preferably at least 80 % by weight and
more preferably at least 90 % by weight of the coating composition (B-2), based on the total
weight of the coating layer (B). Especially preferably, the coating layer (B) consists of the
coating composition (B-2).
Pipe coating and coated pipe
It is preferable to properly prepare the surface of the pipe before coating as it is known in the
art. The pipe surface is typically inspected for any rust, dirt, flaws, discontinuities, and metal
defects. All the excess material needs be removed from the pipe surface to make sure that
the coating is properly adhered to the pipe. Suitable cleaning methods include air and water
high pressure washing, grit or shot blasting and mechanical brushing. Also acid wash and
chromate pre-treatment is sometimes used.
Typically the pipes are heated with induction heating up to about 200 °C. The temperature is
adjustable depending on the line speed and the material being used in the corrosion
preventing layer (C). When the epoxy Teknos AR8434 is used the steel pipe is preferably
heated to 190 °C. The temperature decreases slightly during the coating process.
If epoxy powder (at 23 °C) is used it is typically sprayed on with epoxy guns, where the
speed of the rotating pipe is about 9 m/min. The thickness of the epoxy and other coating
materials are set in accordance with end use specified requirements. Normal thickness value
for the epoxy layer (on-shore installations) is from 70 to 200 µm, such as 135 µm.
Materials that may be used in the corrosion protection layer (C) are, for instance, epoxy
resins and organosilicon compounds. Examples of suitable epoxy resins are phenol-based
epoxies and amine-based epoxies. These kinds of epoxies are sold, among others, under
trade names of AR8434 (of Teknos), Scotchkote 226N (of 3M) and PE50-7191 (of BASF).
Suitable organosilicon compounds have been disclosed in EP-A-1859926.
The extrusion of the adhesive (D) and the coating (B) layer may be performed, for instance,
with two single screw extruders. They may have a diameter of, for instance, from 30 to 100
mm, such as 60 mm, and a length of from 15 to 50 L/D, such as 30 L/D. The temperature is
typically controlled in several zones and the temperature of the PE adhesive (D) and coating
(B) layer after the die is from 190 to 300 °C, such as 225 and 250°C, respectively. Die widths
are from 50 to 300 mm, such as 110 mm and 240 mm for the adhesive layer and coating
layer, respectively. Both adhesive and the coating layer are usually rolled tightly onto the
pipe with a silicone pressure roller. The thickness of the adhesive layer (D) is typically from
200 to 400 µm, such as 290 µm. The thickness of the coating layer (B) is typically from 1 to 5
mm, preferably from 2 to 4 mm, such as 3.2 mm.
Materials suitable to be used in the adhesion layer (D) are, for instance, acid or acid
anhydride grafted olefin polymers, like polyethylene or polypropylene. Suitable polymers are,
among others, fumaric acid modified polyethylene, fumaric acid anhydride modified
polyethylene, maleic acid modified polyethylene, maleic acid anhydride modified
polyethylene, fumaric acid modified polypropylene, fumaric acid anhydride modified
polypropylene, maleic acid modified polypropylene and maleic acid anhydride modified
polypropylene. Examples of especially suitable adhesion plastics are given in EP-A-1316598.
After the coating the coated pipe is cooled, for instance by providing water flow on the coated
pipe surface.
The coated pipes according to the present invention have improved mechanical properties,
such as very high resistance to stress cracking. Further, the multimodal ethylene copolymer
(B-1) contained in the coating composition (B-2) has a broad molecular weight distribution,
allowing the coated pipes to be produced with high throughput and good production
economy.
Examples
Methods
CTL
CTL is determined by using a method similar to ISO 6252:1992 as follows.
The samples are prepared by pressing a plaque at 180 °C and 10 MPa pressure with a total
length of 125 to 130 mm and a width at its ends of 21 ± 0.5 mm. The plaque then is milled
into the correct dimensions in a fixture on two of the sides with a centre distance of both
holders of 90 mm and a hole diameter of 10 mm. The central (narrow) part of the plaque has
a parallel length of 30 ± 0.5 mm, a width of 9 ± 0.5 mm, and a thickness of 6 ± 0.5 mm.
A front notch of 2.5 mm depth is then cut into the sample with a razor blade fitted into a
notching machine (PENT-NOTCHER, Norman Brown engineering), the notching speed is 0.2
mm/min. On the two remaining sides side grooves of 0.8 mm are cut which should be
coplanar with the notch. After making the notches, the sample is conditioned in 23 ±1°C and
50 % relative humidity for at least 48 h. The samples are then mounted into a test chamber in
which the active solution (10 % solution of IGEPAL CO-730 in deionised water, chemical
substance: 2-(4-nonyl-phenoxy)ethanol) is kept at 60 °C temperature. The samples are
loaded with a dead weight corresponding to an initial stress of about 5 MPa and at the
moment of breakage an automatic timer is shut off. The average of at least two
measurements is reported.
The sample and the notch applied to the sample are shown in Figure 1, in which:
A: total length of the specimen125 to 130 mm
B: distance between the centre points of the holders 90 mm
C: width of the specimen at the end 21 ±0.5 mm
D: hole diameter 10 mm
E: side grooves 0.8 mm
F: thickness of plaque 6 ± 0.2 mm
G: width of narrow parallel part 9 ± 0.5 mm
H: main notch 2.5 + 0.02 mm
The length of the narrow section of the specimen was 30 ± 0.5 mm.
GPC
The weight average molecular weight Mw and the molecular weight distribution (MWD =
Mw/Mn wherein Mn is the number average molecular weight and Mw is the weight average
molecular weight) is measured by a method based on ISO 16014-4:2003 and ASTM D 6474-
99. A Waters GPCV2000 instrument, equipped with refractive index detector and online
viscosimeter was used with 2 x GMHXL-HT and 1x G7000H columns from Tosoh Bioscience
and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol)
as solvent at 140 °C and at a constant flow rate of 1 mL/min. 209.5 uL of sample solution
were injected per analysis. The column set was calibrated using universal calibration
(according to ISO 16014-2:2003) with 15 narrow MWD polystyrene (PS) standards in the
range of 1 kg/mol to 12 000 kg/mol. Mark Houwink constants were used for polystyrene and
polyethylene (K: 19 x 10"3 mL/g and a: 0.655 for PS, and K: 39 x10"3 mL/g and a: 0.725 for
PE). All samples were prepared by dissolving 0.5 - 3.5 mg of polymer in 4 mL (at 140 °C) of
stabilized TCB (same as mobile phase) and keeping for max. 3 hours at 160 °C with
continuous shaking prior sampling in into the GPC instrument.
Melt Index, Melt Flow Rate, Flow Rate Ratio (Ml, MFR, FRR):
Melt Index (Ml) or Melt Flow Rate (MFR)
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 melt viscosity of the polymer. The MFR is determined at
190°C for PE. The load under which the melt flow rate is determined is usually indicated as a
subscript, for instance MFR2 is measured under 2.16 kg load, MFR5 is measured under 5 kg
load or MFR21 is measured under 21.6 kg load.
Flow Rate Ratio (FRR)
The quantity FRR (flow rate ratio) is an indication of molecular weight distribution and
denotes the ratio of flow rates at different loads. Thus, FRR21/2 denotes the value of
MFR21/MFR2.
Neck-in
Neck-in was given as a width of the film after the 110 mm die in mm. In this test series neck-
in is registered at the maximum peripheral speed of pipe the molten film can manage without
variations in width. The neck-in was measured at a winding speed of 20 RPM.
Peel strength
Adhesion of polymer on steel was tested by Instron 1122 peel strength test equipment
according to DIN 30670. A strip of 3 cm width is cut of the coating layer. The other end of the
strip is fastened to pulling equipment and the pulling strength is measured during the peeling
of the strip from the steel with a pulling speed of 10 mm/min. The results are expressed as N
per cm. The peel strength was measured from the coatings produced at a screw speed of 50
RPM.
Pipe coating
A steel pipe with a diameter of 114 mm was cleaned to remove the excess material from its
surface. The pipe was then heated with induction heating to 190 °C. Epoxy powder (Teknos
AR8434) was then sprayed onto the pipe surface with the rotating speed of the line of 9
m/min so that the thickness of the epoxy layer was 135 urn. Then an adhesion plastic, a
maleic acid anhydride grafted polyethylene adhesive, prepared according to composition 2 in
EP 1 316 598 A1, was extruded onto the pipe by using a Barmag single screw extruder with
an L/D ratio of 24 and a diameter of 45 mm and where the temperature of the melt after the
die was 225 °C. The die width was 110 mm. Simultaneously the composition of Example 1
was then extruded onto the adhesion layer by using a Krauss-Maffei extruder having a
diameter of 45 mm and the L/D ratio of 30. The die width was 240 mm and the temperature
of the melt after the die was 250 °C. The coating was conducted at extruder screw speeds of
25, 50 and 100 RPM. At the screw speed of 25 RPM five different winding speeds were run,
namely 9, 15, 20, 25 and 30 RPM.
Rheology
Rheological parameters such as Shear Thinning Index SHI and Viscosity were determined
by using a Anton Paar Phisica MCR 300 Rheometer on compression moulded samples
under nitrogen atmosphere at 190 °C using 25 mm diameter plates and plate and plate
geometry with a 1.2 mm gap. The oscillatory shear experiments were done within the linear
viscosity range of strain at frequencies from 0.05 to 300 rad/s (ISO 6721-1). Five
measurement points per decade were made.
The values of storage modulus (G'), loss modulus (G") complex modulus (G*) and complex
viscosity (?*) were obtained as a function of frequency (?). ?100 is used as abbreviation for
the complex viscosity at the frequency of 100 rad/s.
Shear thinning index (SHI), which correlates with MWD and is independent of Mw, was
calculated according to Heino ("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, and "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).
SHI value is obtained by calculating the complex viscosities at given values of complex
modulus and calculating the ratio of the two viscosities. For example, using the values of
complex modulus of 1 kPa and 100 kPa, then ?*(1 kPa) and ?*(100 kPa) are obtained at a
constant value of complex modulus of 1 kPa and 100 kPa, respectively. The shear thinning
index SHI1/100 is then defined as the ratio of the two viscosities ?*(1 kPa) and ?*(100 kPa), i.e.
?(1)/?(100).
It is not always practical to measure the complex viscosity at a low value of the frequency
directly. The value can be extrapolated by conducting the measurements down to the
frequency of 0.126 rad/s, drawing the plot of complex viscosity vs. frequency in a logarithmic
scale, drawing a best-fitting line through the five points corresponding to the lowest values of
frequency and reading the viscosity value from this line.
Shore Hardness
Shore D hardness was determined according to ISO 868-2003. The measurement was done
on round disks having a diameter of 35 mm and thickness of 4 mm and which were punched
from compression moulded sheets having a thickness of 4 mm. The sheet was moulded
according to ISO 1872-2 at 180 °C with a cooling rate 15 °C/min. Finally, the plaques are
conditioned at 23 °C at 50 % relative humidity for at least two days.
Five measurements per sample are made. The measurement points are selected so that
there is at least 10 mm distance to the edge of the disc and at least 6 mm distance to the
nearest previous measurement point.
During the measurement a specified indenter (type D durometer) is forced into the test
specimen under specified conditions (a mass of 5 kg). After 15 s the mass is removed, and
the depth of penetration is measured.
Wear index
Wear index is determined by conducting Taber abrasion test on plaques according to ASTM
D 4060.
The specimen is a 2 mm thick 100x100 mm compression moulded plaque having a hole with
6.3 mm diameter at the centre. The specimen has been thermostated for at least 24 hours at
23 °C temperature and 50 % relative humidity. The test is done by using CS-17 abrasion
wheel. The wheel is adjusted by placing the specimen in the device and running the wheel
50 cycles. The specimen is then carefully cleaned and weighed after which the specimen is
placed in the testing device and the test is started. The wear index (I) is calculated as:

where A = weight of the specimen before the abrasion, B = weight of the specimen after the
abrasion and C = number of abrasion cycles.
The adjustment of the wheel is done at the beginning of each test and after 500 cycles.
Density:
Density of the polymer was measured according to ISO 1183-2 / 1872-2B.
Tensile Strength:
Tensile strength properties were determined according to ISO 527-2. Compression moulded
specimens of type 1A were used, which were prepared according to ISO 1872-2B.
Strain at Yield:
Strain at yield (in %) was determined according to ISO 527-2. The measurement was
conducted at 23 °C temperature with an elongation rate of 50 mm/min.
Stress at Yield:
Stress at yield (in MPa) was determined according to ISO 527-2. The measurement was
conducted at 23 °C temperature with an elongation rate of 50 mm/min.
Tensile Modulus
Tensile modulus (in MPa) was determined according to ISO 527-2. The measurement was
conducted at 23 °C temperature with an elongation rate of 1 mm/min.
Tensile Break:
Tensile break was determined according to ISO 527-2. The measurement was conducted at
23 °C temperature with an elongation rate of 50 mm/min.
DSC:
The Melting Temperature (Tm) and the Crystallization Temperature (Tcr) were measured with
Mettler TA820 differential scanning calorimeter (DSC) on 3±0.5 mg samples. Both
crystallization and melting curves were obtained during 10°C/min cooling and heating scans
between -10 - 200°C. Melting and crystallization temperatures were taken as the peaks of
endotherms and exotherms, respectively. The degree of crystallinity was calculated by
comparison with heat of fusion of a perfectly crystalline polyethylene, i.e. 290 J/g.
Comonomer content:
13C-NMR analysis was used to determine the comonomer content of the samples. Samples
were prepared by dissolving approximately 0.100 g of polymer and 2.5 ml of solvent in a 10
mm NMR tube. The solvent was a 90/10 mixture of 1,2,4-trichlorobenzene and benzene-d6.
Samples were dissolved and homogenised by heating the tube and its contents at 150 C in a
heating block.
The proton decoupled carbon-13 single pulse NMR spectra with NOE were recorded on a
Joel ECX 400 MHz NMR spectrometer. The acquisition parameters used for the experiment
included a flip-angle of 45 degrees, 4 dummy scans, 3000 transients and a 1.6 s acquisition
time, a spectral width of 20kHz, temperature of 125 C, WALTZ decoupling and a relaxation
delay of 6.0 s. The processing parameters used included zero-filling to 32k data points and
apodisation using an exponential window function with in 1.0 Hz artificial line broadening
followed by automatic zeroth and first order phase correction and automatic baseline
correction.
Comonomer contents were calculated using integral ratios taken from the processed
spectrum using the assignments described in JC. Randall's work (JMS - Rev. Macromol.
Chem. Phys., C29(2&3), 201-317 (1989) using:
E = (\alphaB + \alphaH + \betaB + \betaH + \gammaB + \gammaH + \delta++)/2
B = (methine B + 2B + 1B)/3
H = (methine H + 4H + 3H + 2H)/4
where methine is the CH branch site, alpha, beta, gamma the carbon sits adjacent to the CH
i.e. CH, alpha, beta, gamma, delta. \delta++ is the bulk CH2 site and the 1,2,3 and 4 sites
representing the various carbon sites along the branch with the methyl group being
designated 1.
CE = 100%*E/(E+B+H)
CB = 100%*B/(E+B+H)
CH = 100%*H/(E+B+H)
Example 1
A loop reactor having a volume of 50 dm3 was operated continuously at a temperature of 60
°C and a pressure of 62 bar. Into the reactor were introduced 41 kg/h of propane diluent, 2
kg/h of ethylene and 35 g/h of hydrogen. In addition 6.3 g/h of a solid polymerisation catalyst
component sold by BASF under a trade name of Lynx 200 was introduced into the reactor
together with triethylaluminium cocatalyst so that the ratio of aluminium to titanium was 30
mol/mol. The rate of polymer production was about 1.8 kg/h.
The slurry from the 50 dm3 loop reactor was withdrawn and transferred continuously to
another loop reactor having a volume of 500 dm3 and which was operated at a temperature
of 95 °C and a pressure of 60 bar. Into the reactor were introduced additional propane
diluent, ethylene and hydrogen. The ethylene concentration in the fluid mixture was 3.6 mol-
%, based on the total number of moles in the fluid mixture, and the rate of polymer
production was about 30 kg/h. The conditions and data can be seen in Table 1.
The slurry from the loop reactor was withdrawn by using settling legs into a flash vessel
operated at a temperature of 50 °C and a pressure of 3 bar where the hydrogen and major
part of the hydrocarbons was removed from the polymer. The ethylene homopotymer was
directed into a fluidised bed gas phase reactor operated at 85 °C temperature and 20 bar
pressure. Into the reactor were introduced additional ethylene, 1-hexene comonomer,
hydrogen and nitrogen as inert gas. The ethylene concentration was 16 mol-%, based on the
total number of moles in the gas mixture, and the other conditions and data are shown in
Tablet
The resulting polymer powder was dried from hydrocarbons and mixed with 3000 ppm of
Irganox B225, 1000 ppm of calcium stearate and 2.4 % of carbon black, based on the final
composition. The mixture was then extruded into pellets by using a CIM90P twin screw
extruder (manufactured by Japan Steel Works). The properties of the polymer and the
composition are shown in Table 2.
The resulting composition was used in coating a steel pipe as described above in the
description of the methods under the title "Pipe coating". Data is shown in Table 2.
Example 2 and Reference Example 3R
The procedure of Example 1 was repeated except that conditions were as shown in Table 1.
The polymer data is shown in Table 2.
Reference Example 4R
The multimodal ethylene polymer was similar to Polyethene #3 of Example 2 of EP 837915.
It can be seen from the data that in Examples 1 and 2 where 1-hexene had been used as a
comonomer in the high molecular weight copolymer component clearly had a higher ESCR
than the Reference Examples 3R and 4R having 1-butene as a comonomer. Furthermore,
the Examples 1 and 2 have a slightly higher tensile modulus corresponding to a specific
density than the Reference Examples 3R and 4R.
Claims
1. A pipe comprising an inner surface, an outer surface layer (A) and a coating
layer (B) covering said outer surface layer (A), wherein the coating layer (B)
comprises a coating composition (B-2) comprising a multimodal ethylene
copolymer (B-1), being a copolymer of ethylene and one or more alpha-olefin
comonomers having from 6 to 10 carbon atoms, wherein the multimodal ethylene
copolymer (B-1) has a weight average molecular weight of from 70000 g/mol to
250000 g/mol, a melt index MFR2, determined according to ISO 1133 at 190°C
under a load of 2.16 kg, of from 0.05 g/10 min to 5 g/10 min, a melt index MFR5,
determined according to ISO 1133 at 190°C under a load of 5 kg, of from 0.5 to
10 g/10 min, a density of from 930 kg/m3 to 950 kg/m3, and a ratio of weight
average molecular weight to number average molecular weight, Mw/Mn, of from
15 to 50.
2. The pipe according to claim 1 wherein the multimodal ethylene copolymer (B-
1) has a ratio of weight average molecular weight to number average molecular
weight, Mw/Mn, of from 20 to 40 and in particular from 25 to 40.
3. The pipe according to claim 1 or claim 2 wherein the coating composition (B-
2) has a stress cracking resistance, as measured by CTL (Constant Tensile
Load) at 60 °C and 5 MPa, preferably of at least 80 h and more preferably of at
least 100 h.
4. The pipe according to any one of the preceding claims wherein the multimodal
ethylene copolymer (B-1) has a density of 933 kg/m3 to 944 kg/m3, preferably
936 kg/m3 to 944 kg/m3.
5. The pipe according to claim 1 or 2 wherein the coating composition (B-2) has
a melt index MFR2, determined according to ISO 1133 at 190°C under a load of
2.16 kg, of 0.1 to 1.2 g/10 min, preferably from 0.2 to 1.0 g/10 min and MFR5,
determined according to ISO 1133 at 190°C under a load of 5 kg, of 1.0 to 5.0
g/10 min.
6. The pipe according to any one of the preceding claims wherein the pipe is a
metal pipe.
7. The pipe according to any one of the preceding claims wherein the outer
surface layer (A) is covered by a corrosion preventing layer (C) which is further
covered by the coating layer (B).
8. The pipe according to claim 7 wherein the corrosion preventing layer (C) is
covered by an adhesive layer (D), which is further covered by the coating layer
(B).
9. The pipe according to any one of claims 1 to 6 wherein the outer surface layer
(A) is covered by an adhesive layer (D), which is further covered by the coating
layer (B).
10. The pipe according to any one of preceding claims wherein the coating layer
(B) comprises from 75 to 100 % by weight, preferably from 80 to 100 % by
weight, more preferably from 90 to 100 % by weight and in particular 100 % by
weight based on the total weight of the coating layer (B) of the coating
composition (B-2) comprising the multimodal ethylene copolymer (B-1).
11. The pipe according to any one of the preceding claims wherein the coating
composition (B-2) comprises from 80 to 100 % by weight, preferably from 85 to
100 % by weight and in particular from 90 to 99 % by weight of the multimodal
ethylene copolymer (B-1).
12. The pipe according to any one of the preceding claims wherein the
multimodal ethylene copolymer (B-1) further comprises
(B-1 -1) from 40 to 60 %, based on the weight of the multimodal ethylene
copolymer (B-1), a low molecular weight ethylene homopolymer component, said
low molecular weight ethylene homopolymer component (B-1-1) having a weight
average molecular weight of from 5000 g/mol to 70000 g/mol; and
(B-1-2) from 60 to 40 %, based on the weight of the multimodal ethylene
copolymer (B-1), a high molecular weight ethylene copolymer component, said
high molecular weight ethylene copolymer component (B-1-2) being a copolymer
of ethylene with one or more alpha-olefin comonomers having from 6 to 10
carbon atoms and having a weight average molecular weight of from 100000
g/mol to 700000 g/mol.
13. The pipe according to any one of the preceding claims wherein the coating
composition (B-2) has a flow rate ratio FRR21/5of 15 to 40, which is the ratio
MFR21/MFR5 where MFR21 and MFR5 are determined according to ISO 1133 at
190 °C under loads of 21.6 kg and 5 kg, respectively, preferably from 20 to 35.
14. The pipe according to any one of the preceding claims wherein the coating
composition (B-2) has an SHI2 7/210 of from 25 to 100, where the SHI2.7/210 is
determined from oscillatory shear experiments within the linear viscosity range
of strain at frequencies from 0.05 to 300 rad/s according to ISO 6721-1 as the
ratio of the complex viscosities ?(2.7 kPa)/ ?(210 kPa).
15. A process for producing a coated pipe, comprising the steps of:
providing a pipe having an outer surface layer (A);
applying a coating composition (B-2) onto the pipe outer surface layer (A) to
form a coating layer (B), wherein the coating composition (B-2) comprises a
multimodal ethylene copolymer (B-1), being a copolymer of ethylene and one or
more alpha-olefin comonomers having from 6 to 10 carbon atoms, wherein the
multimodal ethylene copolymer (B-1) has a weight average molecular weight of
from 70000 g/mol to 250000 g/mol, a melt index MFR2, determined according to
ISO 1133 at 190°C under a load of 2.16 kg, of from 0.05 g/10 min to 5 g/10 min,
a melt index MFR5, determined according to ISO 1133 at 190°C under a load of
5 kg, of from 0.5 to 10 g/10 min, of from 0.5 to 10 g/10 min and a density of from
930 kg/m3 to 950 kg/m3, and a ratio of weight average molecular weight to
number average molecular weight, Mw/Mn, of from 15 to 50.
16. A process according to claim 15 comprising the steps of:
(i) polymerising ethylene, in a first polymerisation stage, in the presence of a
polymerisation catalyst, hydrogen, ethylene and optionally an inert diluent to
produce a low molecular weight ethylene homopolymer component (B-1-1)
having a weight average molecular weight of from 5000 g/mol to 70000 g/mol
and which constitutes from 40 to 60 % by weight of the multimodal ethylene
copolymer (B-1);
(ii) polymerising, in a second polymerisation stage, ethylene and one or more
alpha-olefin comonomers having from 6 to 10 carbon atoms in the presence of a
polymerisation catalyst, ethylene, one or more alpha-olefin comonomers having
6 to 10 carbon atoms and optionally hydrogen and/or an inert diluent to produce
a high molecular weight ethylene copolymer component (B-1-2), being a
copolymer of ethylene and one or more alpha-olefin comonomers having from 6
to 10 carbon atoms (B-1-2) and having a weight average molecular weight of
from 200000 g/mol to 700000 g/mol, which high molecular weight ethylene
copolymer component (B-1-2) constitutes from 40 to 60 % by weight of the
multimodal ethylene copolymer (B-1); and wherein said first and said second
polymerisation step are performed as successive polymerisation steps with the
polymer product produced in any previous step being present in the subsequent
step(s) and wherein said first step and said second step can be performed in any
order;
(iii) recovering said multimodal ethylene copolymer (B-1);
(iv) obtaining the coating composition (B-2) comprising 80 to 100 % by weight,
preferably from 85 to 100 % by weight and in particular from 90 to 99 % by
weight of the multimodal ethylene copolymer (B-1), optional additives and
optional other polymers; and
(iv) applying said coating composition (B-2) onto the pipe outer surface layer (A)
to form the coating layer (B).
17. The process according to claim 16, wherein the polymerisation step (i) is
performed in a polymerisation stage preceding the polymerisation step (ii).
18. The process according to claim 16 wherein the polymerisation step (ii) is
performed in a polymerisation stage preceding the polymerisation step (i).
19. The process according to any one of claims 16 to 18 wherein the
polymerisation is conducted in the presence of a polymerisation catalyst
comprising a solid component comprising titanium, halogen and magnesium,
optionally supported on a particulate support, together with an aluminium alkyl
cocatalyst
20. The process according to claim 19 wherein the catalyst comprises a titanium
compound and a magnesium dihalide without an inert inorganic oxide support.
21. The process according to claim 19 or claim 20 wherein the solid catalyst
component is introduced into the first polymerisation step and is therefrom
transferred into the subsequent step(s) and where no additional solid catalyst
component is introduced into said subsequent step(s).
22. The process according to any one of the claims 15 to 21 wherein a corrosion
preventing layer (C) is applied onto the pipe outer surface layer (A) before
coating it with the coating layer (B).
23. The process according to claim 22 wherein an adhesive layer (D) is applied
onto the corrosion preventing layer (C) before coating it with the coating layer
(B).
24. The process according to any one of claims 15 to 21, wherein an adhesive
layer (D) is applied onto the pipe outer surface layer (A) before coating it with
the coating layer (B).
25. The process according to any one of claims 15 to 24 wherein the multimodal
ethylene copolymer (B-1) has a ratio of weight average molecular weight to
number average molecular weight, Mw/Mn, of from 20 to 40 and in particular
from 25 to 40.
26. The process according to any one of claims 15 to 24 wherein the coating
composition (B-2) has an SHI2.7/210 of from 25 to 100, where the SHI2 7/210 is
determined from oscillatory shear experiments within the linear viscosity range
of strain at frequencies from 0.05 to 300 rad/s according to ISO 6721-1 as the
ratio of the complex viscosities ?(2.7 kPa)/ ?(210 kPa).



The present invention deals with coated pipes having a layer of multimodal polyethylene. The multimodal ethylene
copolymer is a copolymer of ethylene with one or more alpha-olefin comonomers having from 6 to 10 carbon atoms and has a weight
average molecular weight of from 70000 g/mol to 250000 g/mol. the ratio of the weight average molecular weight to the number
average molecular weight, Mw/Mn. of from 15 to 50, a melt index MFR2 of from 0.05 g/10min to 5g/10 min, a melt index MFR5
of from 0.5 to 10 g/10 min and a density of from 930 kg/m3 to 955 kg/m3. The pipes can be coated with high throughput and good
production economy. The coatings have good mechanical properties.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=oXmbyZWXlSuNk/kIJrRdSw==&loc=wDBSZCsAt7zoiVrqcFJsRw==


Patent Number 272079
Indian Patent Application Number 1733/KOLNP/2010
PG Journal Number 12/2016
Publication Date 18-Mar-2016
Grant Date 16-Mar-2016
Date of Filing 13-May-2010
Name of Patentee BOREALIS TECHNOLOGY OY
Applicant Address P. O. BOX 330, FIN-06101 PORVOO FINLAND
Inventors:
# Inventor's Name Inventor's Address
1 ANKER, MARTIN TÖLTVÄGEN 2, S-425, 43 HISINGS KARRA SWEDEN
2 FREDRIKSEN, SIW, BODIL TYRISVINGEN 2, N-3290 STAVERN NORWAY
3 BENTZROD, PÅL, CHRISTAIN STORGATAN 54, N-3290 STAVERN NORWAY
4 BÄCKMAN, MATS FORSSTENAGATAN 4H, S-416, 51 GÖTEBORG SWEDEN
5 LEIDEN, LEIF HEMÄNGSVAGEN 28, FIN-07130 ANDERSBÖLE FINLAND
6 VAHTERI, MARKKU TAPANI LÖFVINGINKATU 2-4 B 9, FIN-06100 PORVOO FINLAND
7 REKONEN, PETRI JAKARINKATU 2 E 8, FIN-06100 PORVOO FINLAND
PCT International Classification Number C09D 123/06
PCT International Application Number PCT/EP2008/010407
PCT International Filing date 2008-12-08
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 07024736.6 2007-12-20 EUROPEAN UNION