Title of Invention

MULTIMODAL POLYETHYLENE COMPOSITION WITH IMPROVED HOMOGENEITY

Abstract A polyethylene composition is disclosed. The polyethylene composition comprising a base resin which comprises: (A) a first ethylene homo- or copolymer fraction, and (B) a second ethylene homo- or copolymer fraction, wherein fraction (A) has a lower weight average molecular weight than fraction (B), the ratio of the MFR2 of fraction (A) and the MFR5 of the base resin being from 200 to 1500, and the composition has a white spot area of 1 % or below.
Full Text Multimodal Polyethylene Composition with Improved Homogeneity
The present invention concerns a multimodal, preferably bimodal,
polyethylene composition comprising two ethylene homo- or copolymer
fractions with different molecular weight having improved homogeneity.
Furthermore, the present invention relates to a process for the production of
such a composition as well as to the use of such a composition for the
production of a pipe.
Multimodal polyethylene compositions are frequently used e.g. for the
production of pipes due to their favourable physical and chemical
properties as e.g. mechanical strength, corrosion resistance and long-term
stability. When considering that the fluids, such as water or natural gas,
transported in a pipe often are pressurized and have varying temperatures,
usually within a range of 0°C to 50°C, it is obvious that the polyethylene
composition used for pipes must meet demanding requirements.
For multimodal polymers comprising more than one polymer fraction with
different molecular weight, homogeneity is known to be a critical property,
because low degrees of homogeneity adversely affect e.g. the surface
properties and other properties of the polymer composition. For obtaining a
sufficient degree of homogeneity, mixing of the different fractions the
composition is consisting of must be reached down to the microscopic
scale.
When compounding multimodal polymer compositions e.g. for the
production of pipes, so-called "white spots" occur in the compounded
material. These white spots usually have a size of below 10 to about 50
micrometer and consist of high molecular weight polymer particles that

have not been adequately compounded in the composition. Further, when
compounding polymer compositions e.g. for the production of films, gel
particles with a size of about 0.01 to 1 mm often occur. These gel particles
also consist of high molecular weight polymer particles not adequately
compounded and appear as disfiguring inhomogeneities in the finished
film. Still further, inhomogeneities in multimodal polymer compositions
may also cause waviness of the surface of articles produced thereof.
As a measure for the homogeneity in multimodal resins the ISO 18553 test
can be applied. ISO 18553 originally is a method for rating pigmented
spots,' i.e. serves to determine how well pigments are dispersed in a
polymer. As the dispersion of the pigment is dependent on the overall
homogeneity of the polymer because inhomogeneities of the polymer are
not coloured by the pigment, ISO 18553 can also be used as a measure for
the homogeneity of a polymer by counting the non-coloured white spots
and rating them according to the ISO 18553 scheme.
As a further measure for the homogeneity of a polymer, the white spot area
test has been developed which to a far extent is based on the modified ISO
18553 white spot rating test as described in the above paragraph. This test
is described in detail below.
It is known that homogeneity of a multimodal polymer composition can be
improved by applying multiple compounding steps and/or particular
compounding conditions to the resin coming from the reactor. These
measures, however, have the disadvantage that they are associated with a
significant increase in production costs for the composition.
It is, therefore, an object of the present invention to provide a multimodal
polyethylene composition, in particular for the use as a pipe material, with

improved homogeneity and thus improved properties, including improved
surface properties. In particular, it is an object of the present invention to
provide such a multimodal polyethylene composition having improved
homogeneity directly after its production. At the same time, the
composition should have good processing and good mechanical properties.
The present invention thus provides in a first embodiment a polyethylene
composition comprising a base resin which comprises
(A) a first ethylene homo- or copolymer fraction, and
(B) a second ethylene homo- or copolymer fraction,
wherein fraction (A) has a lower molecular weight than fraction (B), the
ratio of the MFR2 of fraction (A) and the MFR5 of the base resin being
from 200 to 1500 and the composition has a white spot area of 1 % or
below.
The homogeneity of the composition in terms of its white spot area is
measured after a single compounding step as defined in detail below.
Usually, the composition, measured after said single compounding step, has
a white spot area of 0.01 to 1 %.
Preferably, the composition measured after said single compounding step,
has a white spot area of 0.7 % or below, usually then 0.01 to 0.7 %
Preferably, the polyethylene composition, measured after a single
compounding step, has a rating in the ISO 18553 white spot rating test of
below 4.5, more preferably below 3.
In a second embodiment, the present, invention provides a polyethylene
composition comprising a base resin comprising

(A) a first ethylene homo- or copolymer fraction, and
(B) a second ethylene homo- or copolymer fraction,
wherein fraction (A) has a lower molecular weight than fraction (B), the
ratio of the MFR2 of fraction (A) and the MFR5 of the base resin being
from 200 to 1500 and the composition has a rating in the ISO 18553 white
spot rating test of below 4.5.
As for the first embodiment, the measurement of the homogeneity in terms
of the ISO 18553 white spot rating test is carried out after said single
compounding step. Usually, the composition, after said single
compounding step, has a rating in the ISO 18553 white spot rating test of
0.01 to below 4.5.
Preferably, the composition has a rating in the ISO 18553 white spot rating
test of below 3, usually then between 0.01 and below 3.
The polyethylene compositions according to the invention have an
improved microscopic mixing directly after their production, which is
demonstrated by the fact that already after a single, usual compounding
step a resin with an excellent homogeneity is obtained. Thus, the
composition combines good mechanical with good surface properties and
hence e.g. an improved impact strength with an improved appearance of the
final product.
The term "molecular weight" as used herein denotes the weight average
molecular weight Mw,
The term "base resin" means the entirety of polymeric components in the
polyethylene composition according to the invention, usually making up at
least 90 wt% of the total composition. Preferably, the base resin is

consisting of fractions (A) and (B), optionally further comprising a
prepolymer fraction in an amount of up to 20 wt%, more preferably up to
10 wt% and most preferably up to 5 wt% of the total base resin.
In addition to the base resin, usual additives for utilization with
polyolefms, such as pigments (for example carbon black), stabilizers
(antioxidant agents), antacids and/or anti-UVs, antistatic agents and
utilization agents (such as processing aid agents) may be present in the
polyethylene composition. Preferably, the amount of these additives is 10
wt% or below, further preferred 8 wt% or below, of the total composition.
Preferably, the composition comprises carbon black in an amount of 8 wt%
or below, further preferred of 1 to 4 wt%, of the total composition.
Further preferred, the amount of additives different from carbon black is 1
wt% or less, more preferably 0.5 wt% or less.
Usually, a polyethylene composition comprising at least two polyethylene
fractions, which have been produced under different polymerisation
conditions resulting in different (weight average) molecular weights for the
fractions, is referred to as "multimodal". The prefix "multi" relates to the
number of different polymer fractions the composition is consisting of.
Thus, for example, a composition consisting of two fractions only is called
"bimodar.
The form of the molecular weight distribution curve, i.e. the appearance of
the graph of the polymer weight fraction as function of its molecular
weight, of such a multimodal polyethylene will show two or more maxima
or at least be distinctly broadened in comparison with the curves for the
individual fractions.

For example, if a polymer is produced in a sequential multistage process,
utilising reactors coupled in series and using different conditions in each
reactor, the polymer fractions produced in the different reactors will each
have their own molecular weight distribution and weight average molecular
weight. When the molecular weight distribution curve of such a polymer is
recorded, the individual curves from these fractions are superimposed into
the molecular weight distribution curve for the total resulting polymer
product, usually yielding a curve with two or more distinct maxima.
In the following, preferred features for both embodiments of the
polyethylene composition according to the invention are described.
In the polyethylene, composition according to the invention, fraction (A)
preferably has an MFR2 of at least 100 g/10min, more preferably at least
200 g/10min, and most preferably at least 300 g/10min.
Furthermore, in the polyethylene composition, fraction (A) preferably has
an MFR2 of 2000 g/10min or less, more preferably of 1500 g/10min or less,
and most preferably of 1000 g/10min or less.
The base resin preferably has an MFR5 of 1 g/10min or below, more
preferably of 0.8 g/10min or below, more preferably of 0.6 g/10min or
below, and most preferably 0.4 g/10min or below.
Furthermore, the base resin preferably has an MFR5 of 0.01 g/10min or
higher, more preferably of 0.05 g/10min or higher, and most preferably of
0.1 g/10min or higher.
Preferably, in the polyethylene composition according to the invention the
weight ratio of fractions (A):(B) in the base resin is 30:70 to 70:30.
Furthermore, fraction (A) preferably is an ethylene homopolymer.

Fraction (A) preferably has a density of 950 kg/m3 or higher, more
preferably 960 kg/m3 or higher.
" Further preterred, "the weight average molecular weight of fraction (A) is
from 5,000 g/mol to 100,000 g/mol, more preferably is from 7,000 to
90,000 g/mol, and most preferably is from 10,000 to 80,000 g/mol.
In the polyethylene composition according to the invention fraction (B)
preferably is a copolymer of ethylene with at least one further alpha-olefin
comonomer.
Preferably, the alpha-olefin comonomer of fraction (B) is having from 4 to
8 carbon atoms, and more preferably is selected from 1-butene, 1-hexene,
4-methyl-1-pentene and 1-octene.
Fraction (B) preferably has a density of 954 kg/m3 or lower, more
preferably of 952 kg/m3 or lower, still more preferably of 950 kg/m3 or
lower, and most preferably of 940 kg/m3 or lower.
Base resin preferably has a density of lower than 960 kg/m3.
The weight average molecular weight of the base resin preferably is from
100,000 g/mol to 1,000,000 g/mol.
Preferably, the composition has a white spot area of 0.7 % or below,
usually between 0.01 to 0.7 %
The polyethylene composition according to any the invention preferably
has a shear thinning index SHI(2.7/210) of at least 5, more preferably at least
10, still more preferably at least 20 and most preferably at least 40.

Furthermore, the polyethylene composition preferably has a shear thinning
index SHI(2.7/210) of 300 or less, more preferably 290 or less, still more
preferably 220 or less and most preferably 200 or less.
The SHI is the ratio of the viscosity of the polyethylene composition at
different shear stresses. In the present invention, the shear stresses at 2.7
kPa and 210 kPa are used for calculating the SHI2.7/210 which may serve as a
measure of the broadness of the molecular weight distribution.
Furthermore, the polyethylene composition preferably has a viscosity at a
shear stress of 2.7 kPa η(2.7) of 10,000 to 500,000 Pas, more preferably of
50,000 to 400,000 Pas, and most preferably of 75,000 to 350,000 Pas.
Where herein preferred features of fractions (A) and/or (B) of the
composition of the present invention are given, these values are generally
valid for the cases in which they can be directly measured on the respective
fraction, e.g. when the fraction is separately produced or produced in the
first stage of a multistage process.
However, the base resin may also be and preferably is produced in a
multistage process wherein e.g. fractions (A) and (B) are produced in
subsequent stages. In such a case, the properties of the fractions produced
in the second and third step (or further steps) of the multistage process can
either be inferred from polymers, which are separately produced in a single
stage by applying identical polymerisation conditions (e.g. identical
temperature, partial pressures of the reactants/diluents, suspension medium,
reaction time) with regard to the stage of the multistage process in which
the fraction is produced,- and by using a catalyst on which no previously
produced polymer is present. Alternatively, the properties of the fractions
produced in a higher stage of the multistage process may also be calculated,

e.g. in accordance with B. Hagstrom, Conference on Polymer Processing
(The Polymer Processing Society), Extended Abstracts and Final
Programme, Gothenburg, August 19 to 21, 1997, 4:13.
Thus, although not directly measurable on the multistage process products,
the properties of the fractions produced in higher stages of such a
multistage process can be determined by applying either or both of the
above methods. The skilled person will be able to select the appropriate
method.
The polyethylene composition according the invention preferably is
produced so that at least one of fractions (A) and (B), preferably (B), is
produced in a gas-phase reaction.
Further preferred, one of the fractions (A) and (B) of the polyethylene
composition, preferably fraction (A), is produced in a slurry reaction,
preferably in a loop reactor, and one of the fractions (A) and (B),
preferably fraction (B), is produced in a gas-phase reaction.
Further, the polyethylene base resin preferably is produced in a multistage
process. Polymer compositions produced in such a process are also
designated as "in-situ"-blends.
A multistage process is defined to be a polymerisation process in which a
polymer comprising two or more fractions is produced by producing each
or at least two polymer fraction(s) in a separate reaction stage, usually with
different reaction conditions in each stage, in the presence of the reaction
product of the previous stage which comprises a polymerisation catalyst.
Accordingly, it is preferred that fraction (A) and (B) of the polyethylene
composition are produced in different stages of a multistage process.

Preferably, the multistage process comprises at least one gas phase stage in
which, preferably, fraction (B) is produced.
Further preferred, traction (B) is produced in a subsequent stage in the
presence of fraction (A) which has been produced in a previous stage.
It is previously known to produce multimodal, in particular bimodal, olefin
polymers, such as multimodal polyethylene, in a multistage process
comprising two or more reactors connected in series. As an example of this
prior art, mention may be made of EP 517 868, which is hereby
incorporated by way of reference in its entirety, including all its preferred
embodiments as described therein, as a preferred multistage process for the
production of the polyethylene composition according to the invention.
Preferably, the main polymerisation stages of the multistage process are
such as described in EP 517 868, i.e. the production of fractions (A) and
(B) is carried out as a combination of slurry polymerisation for fraction
(A)/gas-phase polymerisation for fraction (B). The slurry polymerisation is
preferably performed in a so-called loop reactor. Further preferred, the
slurry polymerisation stage precedes the gas phase stage.
Optionally and advantageously, the main polymerisation stages may be
preceded by a prepolymerisation, in which case up to 20 % by weight,
preferably 1 to 10 % by weight, more preferably 1 to 5 % by weight, of the
total base resin is produced. The prepolymer is preferably an ethylene
homopolymer (HDPE). At the prepolymerisation, preferably all of the
catalyst is charged into a loop reactor and the prepolymerisation is
performed as a slurry polymerisation. Such a prepolymerisation leads to
less fine particles being produced in the following reactors and to a more
homogeneous product being obtained in the end.

In the production of the base resin Ziegler-Natta (ZN) or metallocene
catalysts are preferably used, more preferably Ziegler-Natta catalysts.
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 non-
silica supported ZN catalyst, and most preferably MgCl2-based ZN catalyst.
The Ziegler-Natta catalyst further preferably comprises a group 4 (group
numbering according to new IUPAC system) metal compound, preferably
titanium, magnesium dichloride and aluminium.
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 WO2004055068 and
WO2004055069 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.
The resulting end product consists of an intimate mixture of the polymers
from the two reactors, the different molecular weight distribution curves of
these polymers together forming a molecular weight distribution curve
having a broad maximum or two maxima, i.e. the end product is a bimodal
polymer mixture.
It is preferred that the multimodal base resin of the polyethylene
composition according to the invention is a bimodal polyethylene mixture
consisting of fractions (A) and (B), optionally further comprising a small

prepolymerisation fraction in the amount as described above. 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.
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.
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 °C, more preferably is 90 to 105°C, and
most preferably is 92 to 100°C, and the temperature in the gas-phase
reactor preferably is 70 to 105 °C, more preferably is 75 to 100°C, and
most preferably is 82 to 97°C.
A chain-transfer agent, preferably hydrogen, is added as required to the
reactors, and preferably 200 to 800 moles of H2/kmoles of ethylene are
added to the reactor, when the LMW fraction is produced in this reactor,
and 0 to 50 moles of H2/kmoles of ethylene are added to the gas phase
reactor when this reactor is producing the HMW fraction.

Preferably, the base resin of the polyethylene composition is produced with
a rate of at least 5 tons/h, more preferably at least 10 ton/h, and most
preferablv at least 15 tons/h.
The composition of the invention preferably if produced in a process
comprising compounding step, wherein the composition of the base resin,
i.e. the blend, which is typically obtained as a base resin powder from the
reactor, is extruded in an extruder and then pelletised to polymer pellets in
a manner known in the art.
Optionally, additives or other polymer components can be added to the
composition during the compounding step in the amount as described
above. Preferably, the composition of the invention obtained from the
reactor is compounded in the extruder together with additives 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 as supplied
by Japan steel works, Kobe steel or Farrel-Pomini, e.g. JSW 460P.
In one embodiment, the extrusion step is carried out using production rates
of at least 400, at least 500, at least 1000 kg/h may be used in said
compounding step.
In another embodiment the compounding step can be effected with
production rate of that least 5 tons/h, preferably at least 15 tons/h, more
preferably at least 20 or 25 tons/h or even at least 30 or more tons/h, such
as at least 50, such 1-50, preferably 5-40, 10-50, in some embodiments 10-
25 tons/h.

Alternatively, production rates at least 20 tons/h, preferably at least 25
tons/h, even at least 30 tons/h, e.g. 25-40 tons/h may be desired during the
compounding step.
The present multimodal polyethylene composition of the invention enables
such production rates within the property window of the invention, i.e. with
various property combinations of MFR's of the fractions and of final base
resin variations together with excellent homogeneity, just to mention few.
Preferably, in said extrusion step, a total SEI (specific energy input) of the
extruder may be at least 150, 150-400, 200-350, 200-300 kWh/ton.
It is known that the temperature of the polymer melt may vary in the
extruder, the highest (max) melt temperature of the composition in the
extruder during the extrusion step is typically more than 150°C., suitably
between 200 to 350°C, preferably 250 to 310°C, more pref. 250 to 300°C.
The benefit of the invention is that an excellent homogeneity can be
obtained without extensive mixing, already by effecting once the
compounding step, e.g. the preferable extrusion with production rates as
defined above, and additionally, together with the high level homogeneity
desirable polymer properties can be achieved/maintained.
Furthermore, the present invention relates to a process for the production of
a polyethylene composition as described hereinbefore comprising the steps
of
i) polymerising ethylene monomers, and optionally one or more
alpha-olefin comonomers, in the presence of a Ziegler-Natta
catalyst to obtain a first ethylene homo- or copolymer fraction
(A)

ii) polymerising ethylene monomers, and optionally one or more
alpha-olefin comonomers, in the presence of a Ziegler-Natta
catalyst to obtain a second ethylene homo- or copolymer
fraction (B) having a higher average molecular weight than
fraction (A)
wherein the second polymerisation step is carried out in the presence of the
polymerization product of the first step.
Preferably, the polymerization to obtain fraction (A) is carried out in a loop
reactor.
Furthermore, the polymerization to obtain fraction (B) is preferably carried
out in a gas phase reactor.
The first polymerisation step preferably is preceded by a prepolymerisation
step in which preferably at most 20 wt%, more preferably at most 10 wt%
and still more preferably at most 5 wt% of the total base resin is produced.
Still further, the present invention relates to an article, preferably a pipe,
comprising a polyethylene composition as described above or obtainable by
a process as described above, and to the use of such a polyethylene
composition for the production of an article, preferably a pipe.
Experimental and Examples
1. Definitions and measurement methods
a) Molecular weight
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. A waters 150CV plus instrument was
used with column 3 x HT&E styragel from Waters (divinylbenzene) and
trichlorobenzene (TCB) as solvent at 140 °C. The column set was
calibrated using universal calibration with narrow MWD PS standards (the
Mark Howings constant K: 9.54*10-5 and a: 0.725 for PS, and K: 3.92*10-4
and a: 0.725 for PE). The ratio of Mw and Mn is a measure of the broadness
of the distribution, since each is influenced by the opposite end of the
"population".
b) Density
Density is measured according to ISO 1872, Annex A.
c) Melt Flow Rate/Flow Rate Ratio
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 is determined at 190°C and
may be determined at different loadings such as 2.16 kg (MFR2), 5 kg
(MFR5) or 21.6 kg (MFR21).
The quantity FRR (flow rate ratio) is an indication of molecular weight
distribution and denotes the ratio of flow rates at different loadings. Thus,
FRR21/5 denotes the value of MFR21/MFR5.
d) Rheological parameters
Rheological parameters such as Shear Thinning Index SHI and Viscosity
are determined by using a rheometer, preferably a Rheometrics Phisica

MCR 300 Rheometer. The definition and measurement conditions are
described in detail on page 8 line 29 to page 11, line 25 of WO 00/22040.
e) Measurement of Homogeneity
The polymer composition according to the present invention has an
improved homogeneity directly after its production in the polymerisation
reactor. However, as, first, homogeneity is usually measured only on a
compounded composition, and, second, the way in which compounding is
carried out has a decisive influence on the homogeneity of the compounded
composition, it is important that the compounding conditions to which the
composition is subjected and the compounding equipment used are/is
clearly defined before homogeneity of the composition is determined, e.g.
in terms of the white spot area test or the modified ISO 18553 white spot
rating test as described below.
Accordingly, homogeneity of the compositions described herein is
determined after a single compounding step only, which is to be carried out
as follows:
The base resin powder coming from the reactor is transferred, e.g. via
intermediate holding tanks (50-250 tons), to the compounding unit without
extra handling like grinding or cooling or similar processes.
The powder is then poured into the inlet of the compounder together with
the appropriate amounts of additives. The additives can be, typically,
stearates, antioxidants, UV-stabilisers, or pigments/carbon blacks. The
additives can be added as a pure component or as a master batch with a PE
carrier.

The base resin plus additives are then passed through the compounding unit
only once.
No material that has passed the compounder once is allowed to be
transferred back to the inlet of the compounder for further work nor is it
allowed to pass the compounded material further to a second processing
unit.
The idea of the single compounding step is that a reactor powder is allowed
only one single pass through the compounding unit.
The equipment to be used for the single compounding step is a twin-screw
extruder like counter rotating equipment as supplied by Japan steel works,
e.g. CIM JSW 460P or equivalent equipment.
Typical compounding conditions in the single compounding step used in
CIM JSW 460P having a screw diameter of 460 mm are:
production: 25 to 30 tons/h
mixer specific energy input (SEI): 260 kWh/ton
gear pump SEI: 19 kWh/ton
Temp, before gear pump: 290 °C
Temp, after gear pump: 300 °C
suction pressure gear pump: 1.6 bar
mixer speed: 400 rpm
The white spot area of the once compounded composition is determined at
least partly following ISO 18553, as follows:

A sample of a composition (including a pigment to make the
inhomogeneities visible, e.g. carbon black in an amount of around 2.5 wt%)
which is obtained after a single compounding step as described above, is
analysed by first obtaining 6 microtome cuts of 6 different parts of the
sample (thickness The cuts are evaluated at a magnification of 100, and the size, i.e. the part
of the surface, of the non-coloured inclusions ("white spots", agglomerates,
particles) on a total surface of each cut of 0.7 mm2 is determined. All white
spots with a diameter > 5 microns are counted. The "white spot area" is
then expressed as the averaged fraction of the white spots on the total
surface of the sample cut.
f) Measurement of homogeneity - Rating in modified ISO 18553 white
spot rating test
In addition to the white spot area test, homogeneity complementary is
determined according to the modified ISO 18553 white spot rating test. In
this test, inhomogeneities of the composition present after a single
compounding step as described above, which appear as white spots, are
determined and rated according to the rating scheme given in ISO 18553.
The lower the composition is rated in this test, the better is the
homogeneity of the composition.
2. Polyethylene compositions
Production of polyethylene compositions base resins was performed in a
multistage reaction comprising a first polymerisation stage in slurry in a

50 dm3 loop reactor, followed by transferring the slurry to a 500 dm3 loop
reactor wherein polymerisation was continued in slurry to produce the low
molecular weight component (fraction (A)), and a second polymerisation in
a gas phase reactor in the presence of the product from the second loop
reactor to produce the comonomer containing high molecular weight
component (fraction (B)). As comonomer, butene-1 has been used.
As a catalyst, Lynx 200 available from Engelhard Corporation Pasadena,
U.S.A. has been used for all examples according to the invention.
In comparative example 1, a catalyst prepared according to example 1 of
EP 0 688 794 has been used.
The polymerisation conditions applied and the properties of the polymers
obtained are listed in Table 1.
After production of fraction (B) (and hence the complete base resin), the
obtained polymer powder was transferred to an extruder where it was
compounded together with 2.5 wt% carbon black according to the
procedure described under item e) above.



WE CLAIM:
1. A polyethylene composition comprising a base resin which comprises:
(A) a first ethylene homo- or copolymer fraction, and
(B) a second ethylene homo- or copolymer fraction,
wherein fraction (A) has a lower weight average molecular weight than fraction (B),
the ratio of the MFR2 of fraction (A) and the MFR5 of the base resin being from 200 to 1500,
and the composition has a white spot area of 1 % or below.
2. A polyethylene composition comprising-a base resin comprising:
(A) a first ethylene homo- or copolymer fraction, and
(B) a second ethylene homo- or copolymer fraction,
wherein fraction (A) has a lower weight average molecular weight than fraction (B), the ratio
of the MFR2 of fraction (A) and the MFR5 of the base resin being from 200 to 1500, and the
composition has a rating in the ISO 18553 white spot rating test of below 4.5.
3. A polyethylene composition as claimed in claim 1 wherein the composition has a
rating in the ISO 18553 white spot rating test of below 4.5.
4. A polyethylene composition as claimed in claims 1, 2 or 3 wherein fraction (A) has an
MFR2 of 100 g/10min or more.
5. A polyethylene composition as claimed in any of the preceding claims
wherein the base resin has an MFR5 of 1 g/10min or below.
6. A polyethylene composition as claimed in any of the preceding claims wherein the
weight ratio of fractions (A):(B) in the base resin is 30:70 to 70:30.

7. A polyethylene composition as claimed in any of the preceding claims wherein the
MFR5 of the composition is 0.6 g/10min or below.
8. A polyethylene composition as claimed in any of the preceding claims wherein
fraction (A) is an ethylene homopolymer.
9. A polyethylene composition as claimed in any of the preceding claims wherein
fraction (A) has a density of 950 kg/m3 or higher.
10. A polyethylene composition as claimed in any of the preceding claims wherein
fraction (B) is a copolymer of ethylene with at least one further alpha-olefin comonomer.
11. A polyethylene composition as claimed in any of the preceding claims wherein
fraction (B) has a density of lower than 954 kg/m3.
12. A polyethylene composition as claimed in any of the preceding claims wherein the
composition has a SHI (2.7/210) of 5 to 300.
13. A polyethylene composition as claimed in any of the preceding claims wherein the
base resin has been produced in a multistage process.
14. A process for the production of a polyethylene composition as claimed in any of the
preceding claims comprising the steps of:
i) polymerising ethylene monomers, and optionally one or more alpha-olefin
comonomers, in the presence of a Ziegler-Natta catalyst to obtain a first ethylene homo- or
copolymer fraction (A)

ii) polymerising ethylene monomers, and optionally one or more alpha-olefin
comonomers, in the presence of a Ziegler-Natta catalyst to obtain a second ethylene homo- or
copolymer fraction (B) having a higher average molecular weight than fraction (A).
wherein the second polymerisation step is carried out in the presence of the
polymerization product of the first step.
15. A process as claimed in claim 14 wherein the polymerization to obtain fraction (A) is
carried out in a slurry reactor.
16. A process as claimed in claims 14 or 15 wherein the polymerization to obtain fraction
(B) is carried out in a gas phase reactor.
17. An article comprising a polyethylene composition as claimed in any of claims 1 to 13.
18. An article as claimed in claim 17 wherein the article is a pipe.


A polyethylene composition is disclosed. The polyethylene composition comprising a
base resin which comprises: (A) a first ethylene homo- or copolymer fraction, and (B) a
second ethylene homo- or copolymer fraction, wherein fraction (A) has a lower weight
average molecular weight than fraction (B), the ratio of the MFR2 of fraction (A) and the
MFR5 of the base resin being from 200 to 1500, and the composition has a white spot area of
1 % or below.

Documents:

01212-kolnp-2007-abstract.pdf

01212-kolnp-2007-assignment.pdf

01212-kolnp-2007-claims1.0.pdf

01212-kolnp-2007-claims1.1.pdf

01212-kolnp-2007-correspondence others 1.1.pdf

01212-kolnp-2007-correspondence others.pdf

01212-kolnp-2007-description complete.pdf

01212-kolnp-2007-form 1.pdf

01212-kolnp-2007-form 3 1.1.pdf

01212-kolnp-2007-form 3.pdf

01212-kolnp-2007-form 5.pdf

01212-kolnp-2007-gpa.pdf

01212-kolnp-2007-international exm report.pdf

01212-kolnp-2007-international publication.pdf

01212-kolnp-2007-international search report.pdf

01212-kolnp-2007-pct others.pdf

01212-kolnp-2007-pct request.pdf

01212-kolnp-2007-priority document.pdf

1212-KOLNP-2007-(23-01-2012)-CORRESPONDENCE.pdf

1212-KOLNP-2007-ABSTRACT 1.1.pdf

1212-KOLNP-2007-AMANDED CLAIMS.pdf

1212-KOLNP-2007-ASSIGNMENT.pdf

1212-KOLNP-2007-CORRESPONDENCE.1.2.pdf

1212-KOLNP-2007-CORRESPONDENCE.pdf

1212-KOLNP-2007-DESCRIPTION (COMPLETE) 1.1.pdf

1212-KOLNP-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

1212-KOLNP-2007-EXAMINATION REPORT.pdf

1212-KOLNP-2007-FORM 1-1.1.pdf

1212-KOLNP-2007-FORM 18 1.1.pdf

1212-kolnp-2007-form 18.pdf

1212-KOLNP-2007-FORM 2.pdf

1212-KOLNP-2007-FORM 3-1.2.pdf

1212-KOLNP-2007-FORM 3.pdf

1212-KOLNP-2007-FORM 5.pdf

1212-KOLNP-2007-FORM-27.pdf

1212-KOLNP-2007-GPA.pdf

1212-KOLNP-2007-GRANTED-ABSTRACT.pdf

1212-KOLNP-2007-GRANTED-CLAIMS.pdf

1212-KOLNP-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

1212-KOLNP-2007-GRANTED-FORM 1.pdf

1212-KOLNP-2007-GRANTED-FORM 2.pdf

1212-KOLNP-2007-GRANTED-SPECIFICATION.pdf

1212-KOLNP-2007-OTHERS 1.1.pdf

1212-KOLNP-2007-PA.pdf

1212-KOLNP-2007-PRIORITY DOCUMENT.pdf

1212-KOLNP-2007-REPLY TO EXAMINATION REPORT.pdf

1212-KOLNP-2007-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf


Patent Number 249678
Indian Patent Application Number 1212/KOLNP/2007
PG Journal Number 44/2011
Publication Date 04-Nov-2011
Grant Date 02-Nov-2011
Date of Filing 05-Apr-2007
Name of Patentee BOREALIS TECHNOLOGY OY
Applicant Address P.O. BOX 330, FIN-06101 PORVOO
Inventors:
# Inventor's Name Inventor's Address
1 BÄCKMAN, MATS FORSSTENAGATAN 4H, S-416 51 GÖTEBORG
2 VAN PRAET, ERIK LEMING 103, B-3220 HOLSBEECK
3 VAN MARION, REMKO HINTSCHIGGASSE 1, AT-1100 WIEN
4 GUSTAFSSON, BILL DRAGONVÄGEN 8, S-444 41 STENUNGSUND
PCT International Classification Number C08L 23/06
PCT International Application Number PCT/EP2005/011719
PCT International Filing date 2005-11-02
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 04026093.7 2004-11-03 EUROPEAN UNION