U.S. patent application number 12/004059 was filed with the patent office on 2009-01-01 for polyolefin composition for rotomolding.
This patent application is currently assigned to Borealis Technology Oy. Invention is credited to Arild Follestad, Knut Fosse, Espen Ommundsen.
Application Number | 20090004417 12/004059 |
Document ID | / |
Family ID | 8181753 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090004417 |
Kind Code |
A1 |
Follestad; Arild ; et
al. |
January 1, 2009 |
Polyolefin composition for rotomolding
Abstract
A polymer composition suitable for rotomoulding comprising I) An
ethylene homopolymer or copolymer with at least one other
C.sub.3-10 a olefin, having a melt flow rate of 0.5 to 30, a
molecular weight distribution (Mw/Mn) of less than 4, an Mw of
50,000 to 110,000, a density of 0.940 g/cm.sup.3 to 0.970
g/cm.sup.3 and a melting point of 100 to 145.degree. C.; or I) a
propylene homopolymer or copolymer with at least one other
C.sub.2-10 .alpha. olefin, having a melt flow rate of 0.5 to 30, a
molecular weight distribution (Mw/Mn) of less than 4, an Mw of
150,000 to 300,000, and a melting point of 100 to 170.degree. C.;
and II) an ethylene homo or copolymer with at least one other
C.sub.3-10 .alpha.-olefin, having a melt flow rate of within 40% of
the melt flow rate of component (I), a molecular weight
distribution of (Mw/Mn) of less than 4, an Mw of within 30% of the
Mw of component (I), a density of 0.880 g/cm.sup.3 to 0.940
g/cm.sup.3 said density being at least 0.010 g/cm.sup.3 less than
the density of component (I) and a melting point of at least 5+ C.
less than that of component (I); or II) a propylene homo or
copolymer with at least one other C.sub.2-10 .alpha.-olefin having
a melt flow rate of within 40% of the melt flow rate of component
(I), a molecular weight distribution of (Mw/Mn) of less than 4, an
Mw of within 30% of the Mw of component (I), and a melting point of
at least 10.degree. C. less than that of component (I).
Inventors: |
Follestad; Arild;
(Stathelle, NO) ; Ommundsen; Espen; (Langesund,
NO) ; Fosse; Knut; (Skien, NO) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
Borealis Technology Oy
Porvoo
FI
|
Family ID: |
8181753 |
Appl. No.: |
12/004059 |
Filed: |
December 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10469601 |
Jan 13, 2004 |
7332543 |
|
|
PCT/GB02/00904 |
Mar 1, 2002 |
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12004059 |
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Current U.S.
Class: |
428/36.92 ;
264/310; 525/240 |
Current CPC
Class: |
C08L 23/10 20130101;
C08L 2205/02 20130101; C08L 23/0815 20130101; C08L 2205/06
20130101; C08L 23/0815 20130101; C08L 2666/04 20130101; C08L
2666/04 20130101; Y10T 428/1397 20150115; C08L 2314/06 20130101;
C08L 23/10 20130101 |
Class at
Publication: |
428/36.92 ;
525/240; 264/310 |
International
Class: |
B29D 22/00 20060101
B29D022/00; B29C 41/06 20060101 B29C041/06; C08L 23/08 20060101
C08L023/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2001 |
EP |
01301873.4 |
Claims
1-19. (canceled)
20. A polymer composition suitable for rotomoulding comprising I)
an ethylene copolymer with at least one other C.sub.3-10
.alpha.-olefin, having a melt flow rate of 0.5 to 30 g/10 min, a
molecular weight distribution (Mw/Mn) of less than 4, an Mw of
50,000 to 110,000, a density of 0.940 g/cm.sup.3 to 0.970
g/cm.sup.3 and a melting point of 100 to 145.degree. C.; and II) an
ethylene copolymer with at least one other C.sub.3-10
.alpha.-olefin, having a melt flow rate of within 40% of the melt
flow rate of component (I), a molecular weight distribution of
(Mw/Mn) of less than 4, an Mw of within 30% of the Mw of component
(I), a density of 0.880 g/cm.sup.3 to 0.940 g/cm.sup.3 said density
being at least 0.010 g/cm.sup.3 less than the density of component
(I) and a melting point of at least 5.degree. C. less than that of
component (I).
21. A composition as claimed in claim 20 wherein both components
(I) and (II) are made by single site catalysts.
22. A composition as claimed in claim 20 wherein the melting point
of component (II) is at least 10.degree. C. less than that of
component (I).
23. A composition as claimed in claim 20 wherein component (II) is
an ethylene copolymer with butene, hexene or octene.
24. A composition as claimed in claim 20 wherein component (II) is
an ethylene copolymer with hexene.
25. A composition as claimed in any one of claims 21 to 23 wherein
the melt flow rates of components (I) and (II) are 4 to 10 g/10
min.
26. A composition as claimed in claim 20 wherein the melt flow
rates of components (I) and (II) 6 to 8 g/10 min.
27. A composition as claimed in claim 20 wherein the molecular
weight distribution of the composition is less than 4.
28. A composition as claimed in claim 20 wherein the density of
component (II) is 0.910 g/cm.sup.3 to 0.930 g/cm.sup.3.
29. A composition as claimed in claim 20 wherein the density of
composition is in the range 0.925 to 0.950 g/cm.sup.3.
30. A composition as claimed in claim 20 wherein the density of
composition is in the range 0.930 to 0.940 g/cm.sup.3.
31. A composition as claimed in claim 20 wherein the melting point
of component (I) is in the range 125.degree. C. to 135.degree. C.
and the melting point of component (II) is in the range 100.degree.
C. to 125.degree. C.
32. A composition as claimed claim 20 wherein the molecular weight
distribution each of components (I) and (II) is less than 3.
33. A composition as claimed in claim 20 wherein the ratio of
component (I) to (II) is from 4:1 to 1:4.
34. A rotomoulded article formed from a polymer composition as
claimed in claim 20.
35. An article as claimed in claim 34 being a liquid container.
36. A process for the preparation of a rotomoulded article
comprising rotomoulding a composition comprising I) an ethylene
copolymer with at least one other C.sub.3-10 .alpha.-olefin, having
a melt flow rate of 0.5 to 30 g/10 min, a molecular weight
distribution (Mw/Mn) of less than 4, an Mw of 50,000 to 110,000, a
density of 0.940 g/cm.sup.3 to 0.970 g/cm.sup.3 and a melting point
of 100 to 145.degree. C.; and II) an ethylene copolymer with at
least one other C.sub.3-10 .alpha.-olefin, having a melt flow rate
of within 40% of the melt flow rate of component (I), a molecular
weight distribution of (Mw/Mn) of less than 4, an Mw of within 30%
of the Mw of component (I), a density of 0.880 g/cm.sup.3 to 0.940
g/cm.sup.3 said density being at least 0.010 g/cm.sup.3 less than
the density of component (I) and a melting point of at least
5.degree. C. less than that of component (I).
37. A process as claimed in claim 36 wherein rotomoulding is
effected at a rotation speed of 9/1.4 RPM; heating for 13 minutes
in oven at 270.degree. C.; fan assisted cooling for 10 minutes
followed by 6 minutes ambient cooling in the absence of a fan.
38. A rotomoulded article as claimed in claim 34 wherein both
components (I) and (II) are made by metallocene catalysts.
Description
[0001] This application is a divisional of U.S. application Ser.
No. 10/469,601 filed Jan. 13, 2004, now allowed, which in turn is
the US national phase of international application PCT/GB02/00904
filed 01 Mar. 2002, which designated the US.
[0002] This invention relates to the use of a particular polymer
composition in for example, rotational moulding as well as to the
polymer composition itself, to rotomoulding processes using the
same and to rotomoulded articles made from the polymer composition.
More specifically, the invention concerns the use of a polymer
composition which comprises at least two components formed by
single site catalysis having particular molecular weight
distributions, comonomer compositions and densities.
[0003] Rotational moulding is a moulding process in which a
particulate polymer, the moulding powder, is filled into a mould
which is placed into an oven and rotated so that the polymer melts
and coats the inside surface of the mould. In order to ensure that
the moulded product is defect free, the moulding powder must have a
relatively small particle size and should preferably be uniform in
particle size and composition. Where, as is normal, the moulding
powder has to contain colouring agents or other additives, e.g.
stabilisers, the moulding powder is conventionally produced by
grinding polymer pellets extruded from stabilised reactor grain
powder to the correct particle size for rotation of moulding,
usually this the colours or other additives being added in with the
polymer pellets are mixed into the ground and moulding powder
[0004] A wide variety of articles may be prepared by rotational
moulding. In particular rotational moulding is used in the
manufacture of large objects such as liquid containers, e.g. tanks,
boats, as well as in a large number of household areas, e.g. in the
manufacture of toys.
[0005] The nature of the polymer rotomoulded depends very much on
the nature of the article to be made. For example, if a chemical
tank is being made, then the polymer used should be one which is
not degraded by the chemical and one which has particular
mechanical properties so that the container does not break under
stress. Polymers used for the manufacture of toys must be
completely non-toxic and again must be strong to prevent breakage.
Articles for outdoor use such as boats must also be resistant to
degradation from by the elements, e.g. sunlight, rain, frost or
seawater. The mechanical properties of the rotomoulding powders are
therefore critical.
[0006] Another important property is rheology and it is also
critical that this is favourable. Rheology is a measure of
non-Newtonian solid flow and it is crucial that flow be within
certain limits to ensure that product properties are ideal.
[0007] Moreover, when making objects where a well defined shape is
required, it is also desired that the eventual rotomoulded product
does not warp, i.e. that the sides of a product remain
undistorted.
[0008] A variety of polymers may be successfully rotomoulded
although homo and copolymers of ethylene and homo and copolymers of
propylene may in particular be mentioned. However, the nature of
the catalyst used to make the polymer has a significant bearing on
the rotomouldability of the polymer.
[0009] In rotomoulding, polymers produced from single site
catalysts give rise to products having excellent mechanical
properties and enable rotomoulding to be carried out over a much
shorter period of time.
[0010] Polymers produced from single site catalysts tend to have a
narrow molecular weight distribution and copolymers produced from
single site catalysts tend to have narrow comonomer distribution.
These properties gives rise to increased environmental stress
cracking resistance and improvements in other mechanical
properties.
[0011] However, the narrow distribution of comonomers as compared
to a Ziegler-Natta produced polymer, results in a much narrower
melting and crystallisation behaviour.
[0012] The sharp melting behaviour makes the polymer very sensitive
to processing temperature and, without wishing to be limited by
theory, it is believed that this causes severe warpage in
rotomoulding products. Hence, the mechanical property benefits of
using a polymer made by single site catalysis are offset by
increased warpage.
[0013] Polymers produced using Ziegler-Natta catalysts have much
broader melting/crystallisation windows than polymers made by
single site catalysis and hence tend to produce rotomoulding
products with much less warpage.
[0014] However, due to the broad comonomer distribution and broad
molecular weight distribution mechanical properties, especially
ESCR and rheology are not so favourable.
[0015] There still remains therefore, the need to find a polymer
suitable for rotational moulding that can give rise to products
having both low warpage and excellent rheological and mechanical
properties.
[0016] It has now been surprisingly found that by forming, e.g.
blending, a particular mix of polymers, preferably made by single
site catalysis a polymer composition may be produced which not only
has excellent mechanical and rheological properties but also does
not warp after rotomoulding since its processing window is
broadened.
[0017] A blend of polymers having, depending on the monomers
involved, similar molecular weights and similar melt flow rates but
different densities, melting points or comonomer distributions has
surprisingly been found to give rise to a composition which shows
an overall narrow molecular weight distribution and hence excellent
mechanical and rheological properties and has a broadened
processing window which eliminates warpage normally associated with
single site materials.
[0018] Hence, viewed from one aspect the invention provides a
polymer composition suitable for rotomoulding comprising
[0019] I) a first ethylene homo or copolymer with at least one
other C.sub.3-10 .alpha.-olefin, having a melt flow rate (MFR) of
0.5 to 30, preferably 3 to 15, especially 6 to 8, a molecular
weight distribution (Mw/Mn) of less than 4, preferably less than
3.5, especially less than 3, an Mw of 50,000 to 110,000, a density
of 0.940g/cm.sup.3 to 0.970 g/cm.sup.3 and a melting point of 100
to 145.degree. C.;
[0020] OR
[0021] I) a propylene homo or copolymer with at least one other
C.sub.2-10 .alpha.-olefin, having a melt flow rate of 0.5 to30,
preferably 3 to 15, especially 6 to 8, a molecular weight
distribution (Mw/Mn) of less than 4, preferably less than 3.5,
especially less than 3, an Mw of 150,000 to 300,000, and a melting
point of 100 to 170.degree. C.;
[0022] and
[0023] II) a second ethylene homo or copolymer with at least one
other C.sub.3-10 .alpha.-olefin, having a melt flow rate of within
40%, preferably 20% of the melt flow rate of component (I), a
molecular weight distribution of (Mw/Mn) of less than 4, an Mw of
within 30%, preferably20% of the Mw of component (I), a density of
0.880 g/cm.sup.3 to 0.940 g/cm.sup.3 said density being at least
0.010 g/cm.sup.3 less than the density of component (I) and a
melting point of at least 5.degree. C., preferably at least
10.degree. C. less than that of component (I)
[0024] OR
[0025] II) a propylene homo or copolymer with at least one other
C.sub.2-10 .alpha.-olefin having a melt flow rate of within 40%,
preferably 20% of the melt flow rate of component (I), a molecular
weight distribution of (Mw/Mn) of less than 4, an Mw of within 30%,
preferably 20% of the Mw of component (I), and a melting point of
at least 10.degree. C. less than that of component (I).
[0026] Viewed from another aspect the invention provides a polymer
composition suitable for rotomoulding comprising as hereinbefore
described wherein said composition has a molecular weight
distribution (Mw/Mn) of less than 4, an Mw of within 30%,
preferably 20% of the Mw of component (I), and an Mn within 30%,
preferably 20% of the Mw of component (I).
[0027] In an especially preferred embodiment, the invention
provides a polymer composition suitable for rotomoulding
comprising
[0028] I) an ethylene homopolymer having a melt flow rate of 0.5 to
30, preferably 3 to 15, especially 6 to 8, a molecular weight
distribution (Mw/Mn) of less than 4, preferably less than 3.5,
especially less than 3, an Mw of 50,000 to 110,000, a density of
0.940 g/cm.sup.3 to 0.970 g/cm.sup.3 and a melting point of 100 to
145.degree. C.;
[0029] and
[0030] II) an ethylene copolymer with at least one C.sub.3-10
.alpha.-olefin having a melt flow rate of within 40%, preferably20%
of the melt flow rate of component (I), a molecular weight
distribution of (Mw/Mn) of less than 4, an Mw of within 30%,
preferably 20% of the Mw of component (I), a density of 0.880
g/cm.sup.3 to 0.940 g/cm.sup.3, preferably 910 g/cm.sup.3 to 0.930
g/cm.sup.3 said density being at least 0.010 g/cm.sup.3 less than
the density of component (I) and a melting point of at least
10.degree. C. less than that of component (I).
[0031] Viewed from another aspect the invention provides the use of
a polymer composition as hereinbefore described in
rotomoulding.
[0032] Viewed from yet another aspect the invention provides a
process for the preparation of an article comprising rotomoulding a
composition as herein before defined.
[0033] Viewed from yet another aspect the invention provides an
article comprising a polymer composition as hereinbefore described,
especially a rotomoulded article.
[0034] Viewed from yet another aspect the invention provides a
process for the preparation of a polymer composition as
hereinbefore described wherein said composition is produced in at
least two reactors in cascade or parallel, e.g. two slurry phase
reactors or two gas phase reactors, especially a slurry phase
followed by gas phase reactor.
[0035] Viewed from another aspect the invention provides a process
for the preparation of a polymer composition as hereinbefore
described comprising blending components (I) and (II) in
conventional blending apparatus, preferably a micropellet
extruder.
[0036] Viewed from another aspect the invention provides a process
for the preparation of a polymer composition as hereinbefore
described said process comprising the use of at least two
catalysts, preferably metallocene catalysts, e.g. a dualsite
catalyst preferably a dualsite metallocene catalyst.
[0037] Unless otherwise stated densities are measured according to
ISO 1183-1987 (E). MFR is measured according to ISO 1133-1997
(D-for PE/M for PP). The melting point of polyethylene is measured
by heating the polymer from room temperature to 200.degree. C. at a
heat rate of 10.degree. C./min. Thee polymer is maintained at
200.degree. C. for 5 mins and then cooled to -10.degree. C. at a
cool rate of 10.degree. C./min and maintained at -10.degree. C. for
1 minute. The polymer is then heated to 200.degree. C. at a heat
rate of 10.degree. C./min and the melting point is taken on this
second heat run. For polypropylene the procedure is identical
except that heating takes place to 225.degree. C. and cooling is
effected to 20.degree. C. GPC analyses were carried out under the
following conditions:
[0038] Equipment: Waters 150 CV plus no. 1115
[0039] Detector: Refractive Index (RI) and Viscosity detector
[0040] Calibration: Narrow molecular weight distribution PS 1.
Columns: 3.times.HT6E styragel from Waters(140.degree. C.).
[0041] Components (I) and (II) may be copolymers of ethylene or
propylene with at least one other C.sub.2-10 .alpha.-olefin.
Suitable comonomers include ethylene, propylene, 1-butene,
1-hexene, 1-octene etc. Clearly, ethylene is only a suitable
comonomer when the major monomer is propylene and propylene is only
a suitable comonomer where the major monomer is ethylene. Diolefins
may also be employed as comonomers especially those having two
terminal double bonds, e.g. butadiene. In a preferred embodiment,
where component (I) or (II) is a copolymer, it is a copolymer of
ethylene with octene, butene or hexene, especially butene or
hexene.
[0042] Component (I) or (II) may also be a homopolymer of propylene
having no or only a few crystallinity disrupting units, e.g. less
than 5 units per 100 propylene linkages. By crystallinity
disrupting units it is meant a unit that disrupts the regular
structure of the polymer, i.e. an atactic unit in syndiotactic or
isotactic propylene polymers. In one embodiment, both components
(I) and (II) should be propylene homopolymers in which component
(I) is preferably a syndiotactic or isotactic propylene component
and component (II) is preferably an amorphous propylene
homopolymer. In a less preferred embodiment component (I) may be a
polypropylene homopolymer and component (II) may be a propylene
copolymer.
[0043] In another less preferred embodiment both components may be
ethylene homopolymers in which component (II) comprises a high
degree of short chain branching.
[0044] In a final and most preferred embodiment, component (I) may
be an ethylene homopolymer and component (II) may be an ethylene
copolymer.
[0045] The polymer components (I) and (II) should preferably have
similar melt flow rates, i.e. the melt flow rate of component (II)
should not differ from the melt flow rate of component (I) by
greater than 40%, e.g. 20%, preferably no more than 10%, especially
no more than 5%. The melt flow rate of the components should be in
the range 0.5 to 30, preferably 1 to 20, more preferably 3 to 15,
e.g. 4 to 10, especially 6 to 8, most especially about 6. In a
highly preferred embodiment both components (I) and (II) have a MFR
of about 6.
[0046] The melt flow rate of the entire composition should also be
in the range 0.5 to 30, preferably 1 to 20, more preferably 2 to
15, e.g. 4 to 10, especially 6 to 8, most especially about 6.
[0047] The molecular weight distribution (MWD) of both components
should be approximately the same, e.g. within 10%, and the MWD must
be narrow, e.g. an (Mw/Mn) of less than 4, preferably less than
3.5, especially less than 3. The MWD of the entire composition
should also preferably be less than 4, especially less than
3.5.
[0048] Whilst the Mw and Mn ranges may vary within wide limits the
Mw/Mn ratio remains low, i.e. less than 4. In a preferred
embodiment the Mw and Mn of both components are also similar. For a
polyethylene homopolymer or copolymer suitable Mw values are in the
range 50000 to 110000, especially 65000 to 85000. For a propylene
homopolymer or copolymer suitable Mw values are Mw of 150,000 to
300,000. The Mw of component(II) should be within 30%, preferably
20% of the Mw of component (I).
[0049] For compositions based on ethylene, the densities of the two
components should be different, i.e. component (II) should have a
density at least 0.010 g/cm.sup.3, especially 0.020 g/cm.sup.3
different from component (I). For ethylene homo and copolymers,
preferably component (I) should have a density in the range 0.940
to 0.970 g/cm.sup.3 and component (II) should have a density in the
range of 0.880 to 0.940 g/cm.sup.3, preferably in the range 0.910
g/cm.sup.3 to 0.930 g/cm.sup.3, said density preferably being at
least 0.010 g/cm.sup.3 less than the density of component (I).
[0050] For compositions based on ethylene, the density of the
entire composition is preferably in the range 0.925 to 0.50
g/cm.sup.3 preferably 930 to 0.940 g/cm.sup.3.
[0051] The two components must also have different crystallinity
properties, i.e. components (I) and (II) should have different
melting points. This may be achieved by providing copolymers with
differing comonomer contents or for a composition containing only
homopolymers by providing a polymer having differing numbers of
crystallinity disrupting units (e.g. short chain branches).
[0052] Where component (I) is an ethylene homo or copolymer it may
have a melting point of 100 to 145.degree. C. Where component (I)
is a propylene copolymer or propylene homopolymer it should have a
melting point of 100 to 170.degree. C.
[0053] Component (II) should have a melting point which differs
from that of component (I) by at least 5.degree. C., preferably at
least 10.degree. C., especially at least 20.degree. C. In the case
of a propylene homopolymer, component (II) may also be amorphous
and may therefore have no defined melting point. Such a structure
is deemed to have a melting point at least 10.degree. C. less than
(and in effect infinitely less) than component (I).
[0054] Thus an especially preferred composition according to the
invention is a composition in which component (I) is an ethylene
homopolymer having an MFR of 6 to 8, a molecular weight
distribution of less than 3, an Mw of 65,000 to 100,000, an Mn of
20,000 to 60,000, a density of 0.945 to 0.970 g/cm.sup.3 and a
melting point of 125 to 135.degree. C.; and component (II) is an
ethylene copolymer with hexene having an MFR of 6 to 8, a molecular
weight distribution of less than 3, an Mw of 65,000 to 100,000, an
Mn of 20,000 to 60,000, a density of 0.910 to 0.940 g/cm.sup.3 and
a melting point of 100 to 125.degree. C.
[0055] In order to prepare the required polymer for rotomoulding,
components (I) and (II) may be blended using conventional blending
or compounding technology. The components (I) and (II) may be mixed
in any convenient ratio to ensure that the desired properties are
obtained. Preferably however, the ratio of component (I) to (II) is
from 95:5 to 5:95, preferably 9:1 to 1:9, especially 4:1 to 1:4,
more especially 1:2 to 2:1.
[0056] Components (I) and (II) may also be used in conjunction with
other polymers in the blend such as rotomoulding polymer grades and
some Ziegler-Natta polymers. Moreover, it is within the scope of
the invention to use a further polymer component (III) which also
has a MWD and MFR similar to components (I) and (II) but has a
still different comonomer distribution hence producing a multimodal
comonomer distribution.
[0057] The polymer composition described above gives rise to
rotomoulded articles with excellent mechanical and rheological
properties and low warpage.
[0058] The components are preferably produced using a single site
catalyst, e.g. metallocene catalyst or potentially a dualsite
catalyst. However, where component (I) or (II) is a homopolymer
Ziegler-Natta catalysis may be employed. This is not however,
preferred. Suitable metallocene catalysts for use in the invention
may be any conventional metallocene catalyst. As used herein, the
term metallocene is used to refer to all catalytically active
metal: .eta.-ligand complexes in which a metal is complexed by one,
two or more open chain or closed ring .eta.-ligands. The use of
bridged bis-.eta.-ligand metallocenes, single .eta.-ligand "half
metallocenes", and bridged .eta.-.sigma. ligand "scorpionate"
metallocenes is particularly preferred. The metal in such complexes
is preferably a group 4A, 5A, 6A, 7A or 8A metal or a lanthanide or
actinide, especially a group 4A, 5A or 6A metal, particularly Zr,
Hf or Ti. The .eta.-ligand preferably comprises .eta..sup.4 or
.eta..sup.5 open chain or .eta..sup.5-cyclopentadienyl ring,
optionally with a ring or chain carbon replaced by a heteroatom
(e.g. N, B, S or P), optionally substituted by pendant or fused
ring substituents and optionally linked by bridge (e.g. a 1 to 4
atom bridge such as(CH.sub.2).sub.2, C(CH.sub.3).sub.2 or
Si(CH.sub.3).sub.2) to a further optionally substituted homo or
heterocyclic cyclopentadienyl ring. The ring substituents may for
example be halo atoms or alkyl groups optionally with carbons
replaced by heteroatoms such as O, N and Si, especially Si and O
and optionally substituted by mono or polycyclic groups such as
phenyl or naphthyl groups. Suitable .eta.-ligands, include those of
formula II discussed above. Examples of such homo or heterocyclic
cyclopentadienyl ligands are well known in the art (see e.g.
EP-A-416815, W096/04290, EP-A-485821, EP-A-485823, U.S. Pat. No.
5,276,208 and U.S. Pat. No. 5,145,819).
[0059] Besides the .eta.-ligand, the metallocene complex used
according to the invention may include other ligands; typically
these may be halide, hydride, alkyl, aryl, alkoxy, aryloxy, amide,
carbamide or other two electron donor groups. Any hydrocarbyl
ligand here will generally contain up to 20 carbons, preferably up
to 10 carbons, e.g. up to 6 carbons.
[0060] Metallocene catalysts are conventionally employed in the
presence of a cocatalyst. Suitable cocatalysts are well known and
include alkyl metal compounds, in particular alumoxanes. Suitable
alumoxanes include C.sub.1-10 alkyl alumoxanes, e.g. methyl
alumoxane (MAO) and isobutyl alumoxanes (e.g. tetra and
hexaisobutyl alumoxane, TIBAO and HIBAO), especially MAO. Alumoxane
co-catalysts are described by Hoechst in WO-A-94/28034. These are
considered cyclic or cage like oligomers having up to 40,
preferably 3 to 20, --[Al(R'')O]-- repeat units (where R'' is
hydrogen, C.sub.1-10 alkyl, preferably methyl, or C.sub.6-18 aryl
or mixtures thereof).
[0061] If desired the metallocene or metallocene/ cocatalyst
mixture may be used in unsupported form or it may be precipitated
and used as such. However the metallocene or its reaction product
with the cocatalyst is preferably introduced into the
polymerization reactor in supported form, e.g. impregnated into a
porous particulate support, as is well known in the art.
[0062] The particulate support material used is preferably an
organic or inorganic material, e.g. a polymer (such as for example
polyethylene, polypropylene, an ethylenepropylene copolymer,
another polyolefin or polystyrene or a combination thereof). Such
polymeric supports may be formed by precipitating a polymer or by a
prepolymerization, e.g. of monomers used in the polymerization for
which the catalyst is intended. However, the support is especially
preferably a metal or pseudo metal oxide such as silica, alumina or
zirconia or a mixed oxide such as silica-alumina, in particular
silica, alumina or silica-alumina.
[0063] Especially preferably the support is a porous material so
that the metallocene may be loaded into the pores of the support,
e.g. using a process analogous to those described in W094/14856
(Mobil), W095/12622 (Borealis) and W096/00243 (Exxon). The particle
size is not critical but is preferably in the range 5 to 200 .mu.m,
more preferably 10 to 80 .mu.m.
[0064] Before loading, the particulate support material is
preferably calcined, i.e. heat treated, preferably under a
non-reactive gas such as nitrogen. This treatment is preferably at
a temperature in excess of 100.degree. C., more preferably
200.degree. C. or higher, e.g. 200-800.degree. C., particularly
about 300.degree. C. The calcination treatment is preferably
effected for several hours, e.g. 2 to 30 hours, more preferably
about 10 hours.
[0065] A cocatalyst, e.g. an alumoxane or an ionic catalyst
activator (such as a boron or aluminium compound, especially a
fluoroborate) may also be mixed with or loaded onto the catalyst
support material. This may be done subsequently or more preferably
simultaneously to loading of the metallocene, for example by
including the cocatalyst in the solution of the metallocene or, by
contacting the metallocene loaded support material with a solution
of the cocatalyst or catalyst activator, e.g. a solution in an
organic solvent. Alternatively however, any such further material
may be added to the metallocene loaded support material in the
polymerization reactor or shortly before dosing of the catalyst
material into the reactor.
[0066] In this regard, as an alternative to an alumoxane it may be
preferred to use a fluoroborate catalyst activator, especially a
B(C.sub.6F.sub.5).sub.3 or more especially a
.sup.eB(C.sub.6F.sub.5).sub.4 compound, such as
C.sub.6H.sub.5N(CH.sub.3).sub.2H:B(C.sub.6F.sub.5).sub.4 or
(C.sub.6H.sub.5).sub.3C:B(C.sub.6F.sub.5).sub.4. Other borates of
general formula (cation.sup.+).sub.a (borate.sup.-).sub.b where a
and b are positive numbers, may also be used.
[0067] Both components (I) and (II) may be prepared simultaneously
using a dualsite catalyst, i.e. a catalyst carrying two active
metallocene sites on a single support, one site designed to give a
component (I) and the other designed to give component (II).
[0068] The polymerisation is typically conducted in the presence of
a diluent. As a diluent, a linear, branched or cyclic saturated
hydrocarbon such as butane, propane, pentane, hexane, heptane,
octane, cyclohexane or methylcyclohexane may be used.
[0069] Polymerisation to produce the polymer for use in the
invention may take place in the slurry, solution or gas phase.
Slurry phase polymerisation can be conducted under standard slurry
conditions.
[0070] For slurry reactors, the reaction temperature will generally
be in the range 60 to 110.degree. C. (e.g.80-110.degree. C.), the
reactor pressure will generally be in the range 5 to 80 bar (e.g.
25-65 bar), and the residence time will generally be in the range
0.3 to 5 hours (e.g. 0.5 to 2 hours). The diluent used will
generally be an aliphatic hydrocarbon having a boiling point in the
range -70 to +100.degree. C., especially isobutane or propane.
[0071] For solution phase reactors, the reaction temperature used
will generally be in the range 130 to 270.degree. C., the reactor
pressure will generally be in the range 20 to 400 bar and the
residence time will generally be in the range 0.1 to 1 hour. The
solvent used will commonly be a hydrocarbon with a boiling point in
the range 80-200.degree. C.
[0072] For gas phase reactors, the reaction temperature used will
generally be in the range 60 to 115.degree. C. (e.g. 70 to
110.degree. C.), the reactor pressure will generally be in the
range 10 to 25 bar, and the residence time will generally be 1 to 8
hours. The gas used will commonly be a non-reactive gas such as
nitrogen together with monomer (e.g. ethylene).
[0073] In order to ensure that copolymer particles are in the
correct size for rotational moulding the products of any
polymerisation reaction may be converted to powder form or
pelletized to a particle size of approximately 0.1 to 0.5 mm,
preferably 0.3 mm using standard technology. Hence, suitably sized
pellets may be prepared by grinding.
[0074] Alternatively micropellets may be produced using the
technique described in WO 00/35646 which is hereby incorporated by
reference. By this method a mixture of polyolefin and optionally at
least one additive is extruded in melt form through a die and
pelletised to give particles having a particular size distribution.
The particles are then dried to very low levels of moisture to
improve rotomouldability.
[0075] Alternatively, the polymerisation, using a dualsite or
multisite catalyst, can be set up such that the reactor powder is
suitable for use without further manipulation. In one embodiment of
the invention rotomoulding may be carried out by combining polymer
powder with a masterbatch of UV-stabiliser-loaded polyolefin powder
in line with the teaching of WO00/11065 which is hereby
incorporated by reference.
[0076] The polymer powder or pellets can comprise any standard
additives e.g. one or more selected from colouring agents,
stabilisers, antioxidants, UV-absorbers, anti-static agents,
lubricants and fillers.
[0077] Rotational moulding may take place under standard
conditions. The polymer powder is placed in the mould which is then
transferred to an oven and rotated, preferably about two axes to
distribute the polymer powder over the hot surfaces of the mould.
The heating cycle is continued until all of the powder has melted
and formed a thick, continuous layer within the mould. The mould is
then removed from the oven and cooled until the resin has
solidified. The moulded part is then removed.
[0078] The length of time which the mould must be heated depends on
the nature of the article being moulded, the amount of resin
present and the temperature of the oven. Typical rotomoulding
temperatures are 230.degree. C. to 350.degree. C., more
particularly 260.degree. C. to 320.degree. C. Heating time is
chosen such that the inner air temperature in the mould is
160.degree. C. to 300.degree. C., more preferably 170.degree. C. to
250.degree. C. This temperature can be measured using a
Rotolog.RTM. or similar equipment to monitor the temperature or it
may be chosen based on previous experience. Cooling may be carried
out under a stream of air, water spray or mist or simply in ambient
air at room temperature. A combination of these methods may also be
employed. Preferably cooling is achieved using a combination of
blown air followed by ambient air or just blown air. Cooling times
are normally of similar magnitude to heating times or slightly
longer. Slow cooling reduces the amount of warpage present in a
rotomoulded article however, it is a purpose of the invention to
provide polymer compositions which can be cooled more rapidly
without increases in warpage compared to conventional single site
polymers. The moulded tank may be removed from its mould at any
convenient time although it is preferred if it is removed when it
has cooled to a temperature of 60.degree. C. to 100.degree. C.
[0079] The skilled artisan is able to manipulate the temperature,
time and rotation speed/ratio within a rotomoulding apparatus to
ensure that well-formed moulded articles are produced.
[0080] Particularly preferred rotomoulding conditions are Rotation
Speed 9/1.4 RPM; heating for 13 minutes in oven at 270.degree. C.;
fan assisted cooling for 10 minutes followed by ambient air cooling
for 6 minutes.
[0081] The polymer composition of the invention may also have
utility outside the field of rotomoulding. It is envisaged that the
composition may give benefits in thermoforming due to the broadened
processing window which the polymers exhibit. In particular polymer
compositions of this type may be useful in the replacement of PVC.
The polymer compositions may also be useful in film and injection
moulding applications and this forms a yet further aspect of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0082] FIG. 1 graphically depicts test results in accordance with
Example 3.
[0083] FIG. 2 graphically depicts test results in accordance with
Example 6.
[0084] The invention will now be further illustrated with reference
to the following non-limiting examples and figures.
EXAMPLE 1
[0085] Two polymer components A and B were prepared as described in
Annex 1 below. The catalyst used was made from (nBu-Cp)ZrC12 and
MAO impregnated on a support of calcined silica. Polymerisations
took place in a bench scale semibatch reactor with hydrogen
premixed in Component A is an ethylene homopolymer made from a
single site catalyst having a density of 0.957 g/cm.sup.3, an Mw of
77000, an Mn of 28000 giving a Mw/Mn of 2.7, a melting point of
132.degree. C. and a MFR of 6.
[0086] Component B is an ethylene/hexene copolymer having a density
of 0.923 g/cm.sup.3, a Mw of 67000 and Mn of 31000 giving an Mw/Mn
of2.1, an MFR of8 and a melting point of 120.degree. C. These
components were compounded together, optionally with further
polyethylene reactor powders, RP1 and RP2 having a density of 0.934
g/cm.sup.3 and an MFR of 6 or a density of 0.939 g/cm.sup.3 and an
MFR of 6 respectively. The polymer blend was completed by the
addition of an antioxidant and a slip agent.
[0087] The polymer blends prepared are shown in Table 1 below:
TABLE-US-00001 TABLE 1 Sample Comp. A RP1 RP2 Comp. B 934Y 18% 25%
57% -- 934A 64% -- -- 36% 934B 32% 50% -- 18% 934C 16% 75% -- 9%
934D 8% 87.5% -- 4.5% 934Ref -- 100% -- --
[0088] All blends were made to a total of 4 kg which resulted in
approximately 3.8 kg of granules. These blends were then ground
leaving at least 2.8 kg of powder. The overall density of each
blend was 0.934 g/cm.sup.3, except 934Y which had a density of
0.940 g/cm.sup.3.
[0089] In addition, some commercially available polymer grades were
readied for rotomoulding.
[0090] RM 8403, an ethylene/hexene copolymer available from
Borealis A/S, is a polymer produced from a metallocene catalyst
having the following properties: Mw=75000, Mn=34000, MWD=2.2, MFR
6, density 940 g/cm.sup.3, melting point 125.degree. C., heat of
fusion 194 J/g, cryst Temp 110.degree. C., heat of cryst -158
J/g.
[0091] RM 8343, an ethylene/hexene copolymer available from
Borealis A/S, is a polymer produced from a metallocene catalyst
having the following properties: Mw 76000, Mn=34000, MWD=2.2 MFR 6,
density 934 g/cm.sup.3 melting point 123.degree. C., heat of fusion
176 J/g, cryst Temp 108.degree. C., heat of cryst -156 J/g.
[0092] ME8152, an ethylene/butene copolymer available from Borealis
A/S, is a polymer produced from a Ziegler-Natta catalyst having the
following properties: Mw101000, Mn25000, MWD 4.1, MFR 3.5, density
934 g/cm.sup.3, melting point 125.degree. C., heat of fusion 180
J/g, cryst Temp 110.degree. C.
[0093] The properties of each blend are further explained in the
table below
TABLE-US-00002 934ref 934A 934B 934C 934D 934Y Density 935.1 934.9
935.3 935.3 934.6 940.6 Melt pt 123.4 127 125 124.4 123.7 127 heat
of fusion 163 163 164 164 160 182 cryst T 109 112.3 110.6 110 109.6
112.6 heat of cryst -155 -151 -153 -154 -148 -173
EXAMPLE 2
[0094] Samples were rotomoulded under one or more of the following
sets of conditions to form boxes.
Rotomoulding Serial 1
[0095] No preheating; Rotation Speed 9/1.4 RPM; heating for 13
minutes in oven at 270.degree. C.; fan assisted cooling for 10
minutes followed by 6 minutes ambient cooling in the absence of a
fan. 700 g of polymer employed; Max mould temperature 227.degree.
C., mould temperature at start 35.degree. C.
Rotomoulding Serial 3
[0096] Mould was preheated to 60.degree. C.; Rotation Speed 4/2;
heating for 13 minutes in oven at 2700; fan assisted cooling for 30
minutes. 700 g of polymer employed; Max mould temperature
227.degree. C., mould temperature at start 60.degree. C.
[0097] The boxes resulting from the rotomoulding were cubes having
sides of approximately 20 cm. The edges of the boxes were
trimmed.
EXAMPLE 3
[0098] Warpage of the rotomoulded boxes was measured on five of the
six cube walls (not the top wall). A ruler with a micrometer was
used diagonally on each side of the box. Results are depicted in
Table 2 relative to results achieved with ME8152.
TABLE-US-00003 TABLE 2 Box Average Warpage ME8152 - Roto Serial 3
100% ME8152 - Roto Serial 1 66% RM8343 - Roto Serial 3 143% RM8343
- Roto Serial 1 92% 934A - Roto Serial 3 72% 934A - Roto Serial 1
38%
[0099] These results are graphically depicted in FIG. 1.
EXAMPLE 4
[0100] Thickness variation in the walls of the boxes was measured
by taking five wall thickness measurements from each side of the
boxes. Average thickness variation is standard deviation for all
points of each box relative to ME8152. The results are depicted in
Table 3 below.
TABLE-US-00004 TABLE 3 Box Thickness variation ME8152 - Roto Serial
3 100% ME8152 - Roto Serial 1 38% RM8343 - Roto Serial 3 115%
RM8343 - Roto Serial 1 33% 934A - Roto Serial 3 53% 934A - Roto
Serial 1 59%
[0101] The figures used to produce these tables are as follows:
TABLE-US-00005 sample 934A 934A RM8343 RM8343 ME8152 ME8152 warpage
0.938 1.78 2.264 3.55 1.63 2.47 thckns 3.44 3.53 3.54 3.58 3.49
3.64
[0102] (In which columns 1, 3 and 5 comprise rotomoulding Serial 1
results and columns 2, 4 and 6 comprise rotomoulding serial 3
results).
Discussion
[0103] Blends with the broadest comonomer distribution have
significantly less warpage and thickness variation than the
reference materials. Moreover, an analysis of the crystal lattice
structure of 934A reveals a much finer crystal structure which
should make the material more robust to morphological changes. The
appearance of the boxes made with 934A was also improved and fewer
air bubbles are formed in the rotomoulded article.
EXAMPLE 5
[0104] Mechanical Properties. The following tests were employed to
test the mechanical properties of the boxes produced.
[0105] Tensile Modulus: IS0527-1 (1993)
[0106] Instrument Falling Weight (IFW) ISO 6603-2: 1989
[0107] Circular disks with diameter 60 mm are used with a
hemispherical striker of mass 10 kg and 20 mm diameter. Falling
height 1 m at a velocity of 4.4m/s at -20.degree. C. Rupture was
ductile.
[0108] ESCR-ASTM D1693-97/ISO 1872-2:1997
[0109] Standardised specimens are notched and stressed before being
lowered into a solution of detergent at 50.degree. C. (Detergent
10% Antarox (Igepal) CO-630. Specimen thickness 2 mm. Examination
every 4 hours and calculation is based on probability of 50% broken
samples.
[0110] Density-ISO 1183: 1987
TABLE-US-00006 934 Mechanical Data Ref 934 A 934 B 934 C 934 D 934
Y RM8343 RM8403 ME8152 ESCR 10% F50 33 24 21 25 36 10 Series 1 9/1,
4 13-10-6 Tensile properties Tensile Mpa 620 680 660 650 620 800
585 710 600 modulus sStress at Mpa 18 18 18 18 18 21.5 17.5 20 17
yield Strain at % 13 11 12 12 12 11 13 12 13 yield FWI AT
-20.degree. c. Max force N/mm 1430 1390 1400 1410 1410 1470 1425
1490 1310 Total energy J 19 19 19 19 19 19 19 20 15 at break Total
Mm 24 24 24 25 24 23 24 23 22 deformation Density 937.2 937.4 936
933.4 Series 2 9/1, 4 13-30 Tensile properties Tensile Mpa 630 670
630 755 740 610 modulus Stress at Mpa 18 18 18 21 20.5 17 yield
Strain at % 12 11 12 11 13 13 yield FWI AT -20.degree. c. Max force
N/mm 1440 1420 1420 1470 1480 13 Total energy J0 mm 19 19 19 19 18
16 at break Total 24 24 24 23 23 22 deformation Series 3 4/2 13/30
Tensile Properties Tensile Mpa 640 700 670 680 645 795 615 705 600
modulus Stress at Mpa 18 18 18 18.5 18 22 17.5 20 16.5 yield Strain
at % 11.5 11 12 12.5 12 11 12.5 12.5 11 yield FWI AT -20.degree. c.
Max force N/mm 1220 1190 1190 1210 1210 1270 1200 1260 1100 Total
energy 17 17 17 17 17 17 16 16 13 at break Total 24 25 24 24 24 24
24 24 23 deformation Density 936.8 937 9 935.7 927.5
[0111] 934Y has the most favourable tensile and impact properties
but has lower ESCR. Overall, compositions of the invention show
improved warpage, stiffness, morphology and comparable or improved
ESCR. Grade 934A has also been found to have increased high
temperature stiffness.
EXAMPLE 6
[0112] The warpage and thickness data (in mm) for rotomoulding
serial 1 with all blends is displayed in the first two tables
below. Data for serial 3 is displayed in the further two tables.
These results are graphically depicted in FIG. 2.
TABLE-US-00007 Roto Serial 1 results sample 934Ref 934A 934B 934C
934D warpage 2.226 0.938 1.54 1.706 1.734 thckns 3.51 3.44 3.48
3.52 3.47 sample 934Y RM8343 RM8403 ME8152 warpage 1.842 2.264
2.272 1.626 thckns 3.411 3.54 3.40 3.49
TABLE-US-00008 Roto Serial 3 results sample 934Ref 934A 934B 934C
934D Warpage 3.642 1.78 2.56 2.87 2.37 thckns 3.52 3.53 3.59 3.53
3.54 sample 934Y RM8343 RM8403 ME8152 Warpage 2.712 3.548 3.946
2.474 thckns 3.47 3.58 3.44 3.64
[0113] As will be seen, the warpage results for the compositions
934Y, 934A, 934B, 934C and 934D are better than the results
obtained using the available commercial grades.
EXAMPLE 7
[0114] The following metallocenes are used in this example.
Me.sub.2Si(9Flu).sub.2ZrCl.sub.2 (A-metallocene) which produces
amorphous atactic polypropylene and rac
Me.sub.2Si(2MeIndenyl).sub.2 ZrCl.sub.2 (B-metallocene) which
produces isotactic polypropylene. These catalysts are available
from Boulder.
Dualsite Catalyst Preparation
[0115] Preparation of catalyst "60/40" in the Table in Example 8--A
pretreated silica carrier, calcined at 600.degree. C. was
transferred to a small bottle with stirrer bar. The carrier was
wetted with toluene (5.5 ml per 2 g carrier). A solution of 2.5 ml
of 30% MAO in toluene, 38.4 mg of A-metallocene and 33.4 mg of
B-metallocene was prepared and stirred for 30 mins. This solution
is added dropwise to 5.5 ml of toluene containing 2 g of silica
carrier and stirred for 20 minutes and left overnight. The catalyst
is then dried in nitrogen for 2 hours at 40.degree. C.,
[0116] The other catalysts in Example 8 were made analogously to
"60/40" maintaining the total molar metallocene concentration
constant.
EXAMPLE 8
[0117] The dry catalyst is fed into a 2 L reactor under nitrogen.
650 ml propylene is added to the reactor and prepolymerisation is
initiated for 8 minutes at 15.degree. C. The temperature is rapidly
raised to 70.degree. C. and polymerisation takes place in the
absence of hydrogen. The reactor conditions are described in the
Table below.
TABLE-US-00009 Dual site Run Temp. Mg weight Extra TEA, catalyst in
no .degree. C. Time H.sub.2 cat polymer 1M (A54) mol % (B/A) 6301
70.degree. C. 40 min 0 220 200 g 0.3 ml 100/0 6303 70.degree. C. 60
min 0 200 15 g 0.1 ml 0/100 6314 70.degree. C. 30 min 0 230 190 g
0.25 ml 90/10 6315 70.degree. C. 30 min 0 210 190 g 0.25 ml 60/40
6316 70.degree. C. 60 min 0 230 130 g 0.25 ml 20/80 6317*
70-80.degree. C. .sup. 55 min 0 210 175 g 0.3 ml 20/80 Mw Mn MWD
6301 whole polymer 185 000 82 000 2.3 6301 crystalline phase 185
000 82 000 2.3 6303 whole polymer 190 000 55 000 3.3 6303 XS phase
185 000 55 000 3.3 6314 whole polymer 190 000 80 000 2.4 6314
crystalline phase 190 000 80 000 2.4 6315 whole polymer 210 000 80
000 2.6 6315 crystalline phase 210 000 100 000 2.1 6316 whole
polymer 240 000 105 000 2.2 6316 crystalline phase 230 000 105 000
2.2
Results
[0118] The properties of the resulting polymers are described in
the table above. The polymer components produced form a composition
which is expected to be ideal for rotomoulding due to the almost
identical Mw and Mn values but differing melting point properties
of the isotactic and amorphous components.
[0119] Runs 6316 and 6317 give rise to a polymer composition having
xylene soluble fractions of 16 and 19 wt % respectively. (The
polymer is boiled in xylene at 137.degree. C. for 30 minutes,
cooled filtered and the crystalline phase precipitated). The
polymer compositions are surprisingly free-flowing powders and it
is believed that never before have free flowing polypropylene
polymer compositions been prepared having such high xylene soluble
fractions. This forms a further aspect of the invention. The high
xylene soluble fraction is believed to give rise to a softer
polymer which may warp less on rotomoulding.
[0120] Thus viewed from a further aspect the invention provides a
free-flowing polypropylene homopolymer powder having a xylene
soluble fraction of at least 7 wt %, preferably at least 12 wt %.
Preferably said powder is produced in a polymerisation stage by a
catalyst system comprising two different active sites.
[0121] Viewed from another aspect the invention provides a free
flowing propylene homo or copolymer powder comprising components A
and B wherein:
[0122] Component A has a crystalline melting point; and
[0123] Component B has a melting point at least 10.degree. C. lower
than that of component A, preferably 30.degree. C., especially
component B is amorphous, has an Mn of at least 25000 g/mol.
preferably at least 40000 g/mol and has a comonomer content of less
than 20 wt %, preferably less than 5 wt %;
[0124] said powder having an Mw of at least 75000 g/mol, a xylene
soluble fraction of at least 7 wt %, preferably at least 12 wt
%.
[0125] The catalyst used to manufacture said free flowing powder is
also new. Thus viewed from another aspect the invention provides a
solid, preferably supported multisite catalyst comprising two
metallocenes A' and B';
[0126] metallocene A' comprising two optionally substituted indenyl
groups bridged via the 1-position of the indenyl, said metallocene
having C.sub.2 symmetry and preferably comprising a group 4A metal
and a methyl substituent at the 2-position of each ring;
[0127] metallocene B' comprising two optionally substituted .eta.5
ligands, at least one of which is a fluorenyl ligand bridged via
the 9-position of the fluorenyl, said metallocene B' having C.sub.s
symmetry and preferably comprising a group 4A metal. In a further
preferred embodiment, both .eta.-5 ligands are fluorenyl
ligands.
EXAMPLE 9
[0128] Two polymer components RM8343 and component A' were
prepared. Component A' is an ethylene homopolymer prepared in an
identical fashion to Component A.
[0129] Polymer blends are prepared as shown in Table 4 below
TABLE-US-00010 TABLE 4 Test Unit RM8343 50/50* Comp A' density
Kg/m3 934.5 945 960.7 melt pt .degree. C. 123.7 129.4 134.4 tens
mod MPa 620 950 1330 warpage Mm 2.2 1.3 deformed 50/50 mix of
RM8343 and Comp A'. Warpage was tested by following the procedure
of Rotomoulding Serial 1 except oven heating was carried out for 14
mins, fan cooling for 16 mins with no subsequent air cooling.
[0130] The results show that the combination of RM8343 and Comp A'
results in a surprisingly low level of warpage. Moreover, the
tensile modulus of the blend is still high giving excellent
stiffness, an ideal property for rotomoulding.
TABLE-US-00011 Annex 1 PREPARATION OF COMPONENTS A & B USING
(nBu-Cp).sub.2ZrCl.sub.2/MAO ON SILICA Cal temp (.degree.
c.)/Loading (%) 600/100 600/100 600/100 600/100 600/100 600/100
600/100 600/100 IMP Dry-mix Dry-mix Dry-mix Dry-mix Dry-mix Dry-mix
Dry-mix Dry-mix Reac temp 94 94 94 94 85 85 85 85 Reac pres (bar
25.5 25.5 25.5 25.5 23.1 23.1 23.1 23.1 Etene partial pressure
(bar) 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 Eten H2 ratio (ppm H2) 420
420 420 420 650 650 650 440 C6/Etene-Cascade (Wt % C8) 0.00 0.00
0.00 0.00 6.00 6.00 6.00 6.00 TOTAL RUN TIME (min) 60 60 60 60 60
60 60 60 MFR2 (powder) 6.1 6.4 6.8 6.2 8.1 8.5 8.3 6.5 MFR21
(powder) 95 105 121 103 123.0 122 120 110 FFR (powder) 15.6 16.4
17.8 16.6 15.2 14.4 14.5 16.9 DENSITY (powder kg/dm3 0.9573 0.9577
0.9563 0.9568 0.9224 0.9214 0.9216 0.9245 COMPONENT A COMPONENT
B
* * * * *