U.S. patent application number 16/332007 was filed with the patent office on 2019-10-31 for multimodal polyethylene thin film.
This patent application is currently assigned to Thai Polyethylene Co., Ltd.. The applicant listed for this patent is SCG Chemicals Co., Ltd., Thai Polyethylene Co., Ltd.. Invention is credited to Watcharee CHEEVASRIRUNGRUANG, Warachad KLOMKAMOL, Arunsri MATTAYAN, Saranya TRAISILANUN.
Application Number | 20190330390 16/332007 |
Document ID | / |
Family ID | 56920579 |
Filed Date | 2019-10-31 |
United States Patent
Application |
20190330390 |
Kind Code |
A1 |
MATTAYAN; Arunsri ; et
al. |
October 31, 2019 |
MULTIMODAL POLYETHYLENE THIN FILM
Abstract
The present invention relates to a reactor system for a
multimodal polyethylene polymerization process, comprising; (a) a
first reactor; (b) a hydrogen removal unit arranged between the
first reactor and a second reactor comprising at least one vessel
connected with a depressurization equipment, preferably selected
from vacuum pump, compressor, blower, ejector or a combination,
thereof, the depressurization equipment allowing to adjust an
operating pressure to a pressure in a range of 100-200 kPa (abs);
(c) the second reactor; and. (d) a third reactor and the use of a
film thereof.
Inventors: |
MATTAYAN; Arunsri; (Bangkok,
TH) ; TRAISILANUN; Saranya; (Bangkok, TH) ;
CHEEVASRIRUNGRUANG; Watcharee; (Bangkok, TH) ;
KLOMKAMOL; Warachad; (Bangkok, TH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thai Polyethylene Co., Ltd.
SCG Chemicals Co., Ltd. |
Bangkok
Bangkok |
|
TH
TH |
|
|
Assignee: |
Thai Polyethylene Co., Ltd.
Bangkok
TH
SCG Chemicals Co., Ltd.
Bangkok
TH
|
Family ID: |
56920579 |
Appl. No.: |
16/332007 |
Filed: |
September 8, 2017 |
PCT Filed: |
September 8, 2017 |
PCT NO: |
PCT/EP2017/072567 |
371 Date: |
March 11, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 10/02 20130101;
B01J 19/00 20130101; B01J 8/008 20130101; C08J 2423/06 20130101;
C08L 2203/16 20130101; C08L 23/0815 20130101; C08F 2/01 20130101;
C08L 2205/025 20130101; B01D 19/0005 20130101; C08F 2/18 20130101;
B01J 8/22 20130101; C08L 23/06 20130101; C08J 5/18 20130101; C08J
2323/06 20130101; C08L 2207/068 20130101; B01J 19/245 20130101;
B01J 2219/0004 20130101; C08F 2/00 20130101; C08F 2/12 20130101;
C08L 2205/03 20130101; C08J 2423/08 20130101; C08L 23/0815
20130101; C08L 23/0815 20130101; C08L 23/0815 20130101 |
International
Class: |
C08F 10/02 20060101
C08F010/02; B01J 19/24 20060101 B01J019/24; C08L 23/06 20060101
C08L023/06; C08J 5/18 20060101 C08J005/18; B01D 19/00 20060101
B01D019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2016 |
EP |
16188329.3 |
Claims
1. A reactor system for a multimodal polyethylene polymerization
process, comprising; (a) a first reactor; (b) a hydrogen removal
unit arranged between the first reactor and a second reactor
comprising at least one vessel connected with a depressurization
equipment, preferably selected from vacuum pump, compressor,
blower, ejector or a combination thereof, the depressurization
equipment allowing to adjust an operating pressure to a pressure in
a range of 100-200 kPa (abs); (c) the second reactor; and (d) a
third reactor.
2. The reactor system according to claim 1, wherein the
depressurization equipment allows to adjust the operating pressure
in the hydrogen removal unit to a pressure in the range of 103-145
kPa (abs), preferably 104-130 kPa (abs), most preferably 105 to 115
kPa (abs).
3. The reactor system according to claim 1, wherein the hydrogen
removal unit further contains a stripping column for the separation
of hydrogen and a liquid diluent.
4. A process for producing a multimodal polyethylene composition in
the reactor system according to claim 1, comprising; (a)
polymerizing ethylene in an inert hydrocarbon medium in the first
reactor in the presence of a catalyst system, selected from
Ziegler-Natta catalyst or metallocene, and hydrogen in an amount of
0.1-95% by mol with respect to the total gas present in the vapor
phase in the first reactor to obtain a low molecular weight
polyethylene having a weight average molecular weight (Mw) of
20,000 to 90,000 g/mol or medium molecular weight polyethylene
having a weight average molecular weight (Mw) of more than 90,000
to 150,000 g/mol wherein the low molecular weight polyethylene,
respectively the medium molecular weight polyethylene, has a
density at least 0.965 g/cm3, and the low molecular weight
polyethylene has MI.sub.2 in the range from 10 to 1,000 g/10 min
and the medium molecular weight polyethylene has MI.sub.2 in the
range from 0.1 to 10 g/10 min; (b) removing in the hydrogen removal
unit 98.0 to 99.8% by weight of the hydrogen comprised in a slurry
mixture obtained from the first reactor at a pressure in the range
of 103-145 kPa (abs) and transferring the obtained residual mixture
to the second reactor; (c) polymerizing ethylene and optionally
C.sub.4 to C.sub.12 .alpha.-olefin comonomer in the second reactor
in the presence of a catalyst system, selected from Ziegler-Natta
catalyst or metallocene, and in the presence of hydrogen in an
amount obtained in step (b) to obtain a first high molecular weight
polyethylene having a weight average molecular weight (Mw) of more
than 150,000 to 1,000,000 g/mol or a first ultra high molecular
weight polyethylene in the form of a homopolymer or a copolymer
having a weight average molecular weight (Mw) of more than
1,000,000 to 5,000,000 g/mol and transferring a resultant mixture
to the third reactor; and (d) polymerizing ethylene, and optionally
C.sub.4 to C.sub.12 .alpha.-olefin comonomer in the third reactor
in the presence of a catalyst system, selected from Ziegler-Natta
catalyst or metallocene, and hydrogen, wherein the amount of
hydrogen in the third reactor is in a range of 0.1-70% by mol,
preferably 0.1-60% by mol with respect to the total gas present in
the vapor phase in the third reactor or optionally substantial
absence of hydrogen to obtain a second high molecular weight
polyethylene having a weight average molecular weight (Mw) of more
than 150,000 to 1,000,000 g/mol or a second ultra high molecular
weight polyethylene in the form of a homopolymer or copolymer
having a weight average molecular weight (Mw) of more than
1,000,000 to 5,000,000 g/mol.
5. The process according to claim 4, wherein the removing is
removing of 98.0-99.8% by weight of the hydrogen, more preferable
98.0-99.5% by weight, and most preferred 98.0 to 99.1% by
weight.
6. The process according to claim 4, wherein the operation pressure
in the hydrogen removal unit is in the range of 103-145 kPa(abs),
more preferably 104-130 kPa (abs), and most preferred 105 to 115
kPa (abs).
7. A multimodal polyethylene composition obtainable by a process
according to claim 4, comprising; (A) 30 to 65 parts by weight,
preferably 40 to 65 parts by weight, preferably 43 to 52 parts by
weight, most preferred 44 to 50 parts by weight, of the low
molecular weight polyethylene, the low molecular weight
polyethylene having a weight average molecular weight (Mw) of
20,000 to 90,000 g/mol and having a MI.sub.2 from 500 to 1,000 g/10
min according to ASTM D 1238; (B) 8 to 30 party by weight, 8 to 20
parts by weight, preferably 10 to 18 parts by weight, most
preferred 10 to 15 parts by weight, of the first high molecular
weight polyethylene having a weight average molecular weight (Mw)
of more than 150,000 to 1,000,000 g/mol or the first ultra high
molecular weight polyethylene having a weight average molecular
weight (Mw) of more than 1,000,000 to 5,000,000 g/mol; and (C) 30
to 50 parts by weight, preferably 37 to 47 parts by weight, most
preferred 39 to 45 parts by weight, of the second high molecular
weight polyethylene having a weight average molecular weight (Mw)
of more than 150,000 to 1,000,000 g/mol or the second ultra high
molecular weight polyethylene having a weight average molecular
weight (Mw) of more than 1,000,000 to 5,000,000 g/mole, wherein the
density of the first high molecular weight polyethylene or the
first ultra high molecular weight polyethylene and the second high
molecular weight polyethylene or the second ultra high molecular
weight polyethylene are in the range from 0.920 to 0.950
g/cm.sup.3, and wherein the molecular weight distribution of the
multimodal polyethylene composition is from 13 to 60, preferably 20
to 28, preferably from 24 to 28, measured by gel permeation
chromatography.
8. The multimodal polyethylene composition according to claim 7,
wherein the MI.sub.2 is from 600 to 800 g/10 min.
9. The multimodal polyethylene composition according to claim 7,
wherein the molecular weight distribution is from 23 to 28,
preferably from 24 to 26, and more preferably from 25 to 26
measured by gel permeation chromatography.
10. The multimodal polyethylene composition according to claim 7,
wherein the multimodal polyethylene composition has a weight
average molecular weight from 80,000 to 1,300,000 g/mol, preferably
150,000 to 400,000 g/mol, preferably from 200,000 to 350,000 g/mol,
measured by Gel Permeation Chromatography.
11. The multimodal polyethylene composition according to claim 7,
wherein the multimodal polyethylene composition has a number
average molecular weight from 5,000 to 30,000 g/mol, 5,000 to
15,000 g/mol, preferably 7,000 to 12,000 g/mol, measured by Gel
Permeation Chromatography.
12. The multimodal polyethylene composition according to claim 7,
wherein the multimodal polyethylene composition has a Z average
molecular weight from 900,000 to 6,000,000 g/mol, 1,000,000 to
3,000,000 g/mol, preferably from 1,000,000 to 2,500,000 g/mol,
measured by Gel Permeation Chromatography.
13. The polyethylene composition according to claim 7 wherein the
multimodal polyethylene composition has a density from 0.950 to
0.962 g/cm.sup.3, preferably from 0.953 to 0.959 g/cm.sup.3,
according to ASTM D 1505 and/or a melt flow index MI.sub.5 from
0.01 to 50 g/10 min, and/or MI.sub.2 from 0.03 to 0.15 g/10 min
preferably from 0.03 to 0.10 g/10 min.
14. The polyethylene composition according to claim 13, wherein the
MI.sub.5 is from 0.01 to 1 g/10 min.
15. Film comprising the multimodal polyethylene composition
according to claim 7, wherein the film has a thickness from 4 to 40
.mu.m, preferably from 4 to 30 .mu.m, and most preferably 4 to 20
.mu.m.
Description
[0001] The present invention relates to a reactor system for a
multimodal polyethylene polymerization process, a process for
producing a multimodal polyethylene composition using said reactor
system, a multimodal polyethylene composition obtainable this way,
and to a film comprising said multimodal polyethylene
composition.
[0002] The demand of polyethylene resins is increasingly being used
in a variety of applications. As required high performance of
polyethylene for a relatively new plastic, a polymerization process
technology has been developed to support new polymeric material
production. In order for balancing processability and physical
properties of ethylene copolymers, the development in multimodal
polymerization process has been investigated.
[0003] In the prior art, multimodal polyethylene polymerization is
employed to produce polymers having different molecular weights by
creating each resin fraction in separated reactors. A low molecular
weight fraction is produced in a reactor using an excess of
hydrogen to control the molecular weight of the polymer suitable
for providing good processability of the final polymer. A high
molecular weight fraction which has an influence on the physical
properties and is produced under polymerization conditions with low
hydrogen concentration. It is well known in the art that low
molecular weight polymer is preferably produced in a first reactor.
To obtain a multimodal polymer with good physical properties, all
hydrogen from the first reactor should be removed before the
polymerized slurry polymer is passed to a second reactor in which
the production of high molecular weight polymer takes place.
[0004] US2010/0092709 A1 describes a process for preparing bimodal
polyethylene copolymers. The polymerization in a second reactor is
operated at a high temperature with a low
comonomer-to-ethylene-ratio and low hydrogen-to-ethylene-ratio to
obtain resins having improved stress crack resistance and melt
strength.
[0005] U.S. Pat. No. 6,716,936 B1 describes a process for producing
bimodal polyethylene copolymers. A second reactor is operated under
hydrogen depleted polyethylene polymerization by directing a
polyethylene slurry stream from a first reactor to a hydrogen
removal system. Polymerization in both the first and the second
reactors is operated at the bubble point by using propane or
isobutane as a light solvent. The process is suitable for the
production of a bimodal polyethylene for highly homogeneous high
molecular weight resins.
[0006] U.S. Pat. No. 6,291,601 B1 describes a process for producing
a bimodal copolymer with relatively high molecular weight
polyethylene. A hydrogenation catalyst is introduced into a second
reactor to consume residual hydrogen gas from first reactor by
converting hydrogen into ethane leading to a low hydrogen
concentration in the second reactor. Using this technique, the cost
of raw material consumption of both hydrogen and ethylene are
increased due to converting of unreacted gases.
[0007] US 2003/0191251 A1 discloses a process for removing residual
hydrogen from a polymer slurry by using two flash drums placed
between cascade reactors which use light solvent as a diluent. The
addition of make-up solvent to the first flash drum outlet is
required to prevent a slurry transfer pump blocking. Furthermore,
warm make-up solvent is necessary before transferring slurry into
the next flash drum.
[0008] EP 1 655 334 A1 discloses the multimodal production of an
ethylene polymer which is produced in a multistage process with a
MgCl.sub.2-based Ziegler-Natta catalyst. The polymerization stages
are performed in the following order to achieve firstly a ultra
high molecular weight polymer, followed by achieving a low
molecular weight polymer, and finally achieving high molecular
weight polymer in the last step. The polymerization catalyst is
charged to a prepolymerization step to make an ultrahigh molecular
weight fraction.
[0009] WO 2013/144328 describes a composition of multimodal high
density polyethylene which is produced using a Ziegler-Natta
catalyst for use in molding applications. A small fraction of
ultra-high polyethylene of less than 15% by weight is produced in a
third reactor.
[0010] US 2009/0105422 A1 describes a process for producing a
multimodal polyethylene. The polymerization is carried out in three
cascade reactors, wherein the molecular weight of the polymer in
each reactor is controlled by the presence of hydrogen. The
concentration of the hydrogen in each reactor is reduced
subsequently by providing the highest hydrogen concentration in the
first reactor and the lowest hydrogen concentration in the third
reactor.
[0011] WO 2013/113797 describes a process for polyethylene
preparation comprising three main subsequent steps of polymerized
ethylene and at least one other .alpha.-olefin to get the
polyethylene with, respectively, a lower molecular weight ethylene
polymer, a first higher molecular weight ethylene polymer and a
second higher molecular weight ethylene polymer in accordance with
the sequence of a first reactor, a second reactor and a third
reactor.
[0012] Even though many processes for preparing multimodal
polyethylene are known and have been described, there is still a
need for developing new processes for multimodal polymerization,
particularly for further improving the mechanical properties of
polyethylene compositions.
[0013] Therefore, it is the object of the present invention to
provide a reactor system and a process for preparing multimodal
polyethylenes overcoming drawbacks of the prior art, in particular
to enhance the performance of a hydrogen removal unit comprised in
such a reactor.
[0014] It is an further object to provide a multimodal polyethylene
composition overcoming drawbacks of the prior art, in particular
having improved mechanical properties, such as Charpy index.
[0015] A variety of films, which may be applied as the single layer
or to the core or the surface of the multi-layer films, are known
in the art. Likewise, a variety of polymer compositions, in
particular polyethylene compositions, for producing such films are
described.
[0016] WO 2013/144324 A1 discloses a polymer composition comprising
a homopolymer, a first copolymer and a second copolymer of specific
MFR.sub.5, density and molecular weight distribution. The polymer
composition is prepared in a process involving a slurry loop
reactor and two gas phase reactors.
[0017] WO 2006/092378 A1 discloses a film prepared from a polymer
composition having a specific MFR.sub.5 and density and comprising
three constituents, namely a homopolymer and two different
copolymers.
[0018] US 2015/0051364 A1 is related to a multimodal polyethylene
copolymer comprising at least three components and having a
specific density and MFR.sub.21. At least one of the three
components is a copolymer.
[0019] US 2010/0016526 A1 is related to a thin film which may be
produced from bimodal HDPE polymer having specific density. The
composition is prepared by a two stage cascade polymerization with
series using a mixed catalyst system.
[0020] However, in light of the above prior art, there is still a
need to provide multimodal polyethylene compositions for preparing
films and films prepared by using multimodal polyethylene
compositions overcoming drawbacks of the prior art, in particular
high density polyethylene compositions for blown film with improved
properties regarding high output, good bubble stability, high
mechanical strength and high toughness at film thicknesses from 4
to 40 micron or, preferably, less.
[0021] Therefore, it is the further object of the present invention
to provide multimodal polyethylene compositions for preparing films
and films prepared this way overcoming drawbacks of the prior art,
in particular overcoming the drawbacks mentioned above.
[0022] This object is achieved in accordance with the invention
according to the subject-matter of the independent claims.
Preferred embodiments result from the sub-claims.
[0023] The object is first of all achieved by a reactor system for
a multimodal polyethylene polymerization process, comprising;
[0024] (a) a first reactor; [0025] (b) a hydrogen removal unit
arranged between the first reactor and a second reactor comprising
at least one vessel connected with a depressurization equipment,
preferably selected from vacuum pump, compressor, blower, ejector
or a combination thereof, the depressurization equipment allowing
to adjust an operating pressure to a pressure in a range of 100-200
kPa (abs); [0026] (d) the second reactor; and [0027] (e) a third
reactor.
[0028] Preferably, the depressurization equipment allows to adjust
the operating pressure in the hydrogen removal unit to a pressure
in the range of 103-145 kPa (abs), preferably 104-130 kPa (abs),
most preferably 105 to 115 kPa (abs).
[0029] Preferably, the hydrogen removal unit further contains a
stripping column for the separation of hydrogen and a liquid
diluent.
[0030] The object is further achieved by a process for producing a
multimodal polyethylene composition in an inventive reactor system,
comprising (in this sequence);
[0031] (a) polymerizing ethylene in an inert hydrocarbon medium in
the first reactor in the presence of a catalyst system, selected
from Ziegler-Natta catalyst or metallocene, and hydrogen in an
amount of 0.1-95% by mol with respect to the total gas present in
the vapor phase in the first reactor to obtain a low molecular
weight polyethylene having a weight average molecular weight (Mw)
of 20,000 to 90,000 g/mol or medium molecular weight polyethylene
having a weight average molecular weight (Mw) of more than 90,000
to 150,000 g/mol wherein the low molecular weight polyethylene,
respectively the medium molecular weight polyethylene, has a
density at least 0.965 g/cm3, and the low molecular weight
polyethylene has MI2 in the range from 10 to 1,000 g/10 min and the
medium molecular weight polyethylene has MI2 in the range from 0.1
to 10 g/10 min;
[0032] (b) removing in the hydrogen removal unit 98.0 to 99.8% by
weight of the hydrogen comprised in a slurry mixture obtained from
the first reactor at a pressure in the range of 103-145 kPa (abs)
and transferring the obtained residual mixture to the second
reactor;
[0033] (c) polymerizing ethylene and optionally C4 to C12
.alpha.-olefin comonomer in the second reactor in the presence of a
catalyst system, selected from Ziegler-Natta catalyst or
metallocene, and in the presence of hydrogen in an amount obtained
in step (b) to obtain a first high molecular weight polyethylene
having a weight average molecular weight (Mw) of more than 150,000
to 1,000,000 g/mol or a first ultra high molecular weight
polyethylene in the form of a homopolymer or a copolymer having a
weight average molecular weight (Mw) of more than 1,000,000 to
5,000,000 g/mol and transferring a resultant mixture to the third
reactor; and
[0034] (d) polymerizing ethylene, and optionally C4 to C12
.alpha.-olefin comonomer in the third reactor in the presence of a
catalyst system, selected from Ziegler-Natta catalyst or
metallocene, and hydrogen, wherein the amount of hydrogen in the
third reactor is in a range of 0.1-70% by mol, preferably 0.1-60%
by mol with respect to the total gas present in the vapor phase in
the third reactor or optionally substantial absence of hydrogen to
obtain a second high molecular weight polyethylene having a weight
average molecular weight (Mw) of more than 150,000 to 1,000,000
g/mol or a second ultra high molecular weight polyethylene in the
form of a homopolymer or copolymer having a weight average
molecular weight (Mw) of more than 1,000,000 to 5,000,000
g/mol.
[0035] "Substantial absence" in this regard means that hydrogen is
only comprised in the third reactor in an amount which cannot be
avoided by technical means.
[0036] The slurry mixture obtained from the first reactor and
subjected to the step of removing hydrogen in the hydrogen removal
unit contains all of the solid and liquid constituents obtained in
the first reactor, in particular the low molecular weight
polyethylene or the medium molecular weight polyethylene.
Furthermore, the slurry mixture obtained from the first reactor is
saturated with hydrogen regardless the amount of hydrogen used in
the first reactor.
[0037] Preferably, the removing is removing of 98.0 to 99.8% by
weight of the hydrogen, and more preferable 98.0 to 99.5% by
weight, most preferred 98.0 to 99.1% by weight.
[0038] Preferably, the .alpha.-olefin comonomer comprised in the
second reactor and/or in the third reactor is selected from
1-butene and/or 1-hexene.
[0039] Preferably, the operation pressure in the hydrogen removal
unit is in the range of 103-145 kPa (abs) and more preferably
104-130 kPa (abs), most preferred 105 to 115 kPa (abs).
[0040] The weight average molecular weight (Mw) of the low
molecular weight polyethylene, the medium molecular weight
polyethylene, the high molecular weight polyethylene and the ultra
high molecular weight polyethylene described herein are in the
range of 20,000-90,000 g/mol (low), more than 90,000-150,000 g/mol
(medium), more than 150,000-1,000,000 g/mol (high) and more than
1,000,000-5,000,000 g/mol (ultra high) respectively.
[0041] Finally, the object is achieved by a multimodal polyethylene
composition
[0042] obtainable by the inventive process, comprising;
[0043] (A) 30 to 65 parts by weight, preferably 40 to 65 parts by
weight, preferably 43 to 52 parts by weight, most preferred 44 to
50 parts by weight, of the low molecular weight polyethylene, the
low molecular weight polyethylene having a weight average molecular
weight (Mw) of 20,000 to 90,000 g/mol and having a MI.sub.2 from
500 to 1,000 g/10 min, preferably from 600 to 800 g/10 min,
according to ASTM D 1238;
[0044] (B) 8 to 30 parts by weight, preferably 8 to 20 parts by
weight, preferably 10 to 18 parts by weight, most preferred 10 to
15 parts by weight, of the first high molecular weight polyethylene
having a weight average molecular weight (Mw) of more than 150,000
to 1,000,000 g/mol or the first ultra high molecular weight
polyethylene having a weight average molecular weight (Mw) of more
than 1,000,000 to 5,000,000 g/mol; and
[0045] (C) 30 to 50 parts by weight, preferably 37 to 47 parts by
weight, most preferred 39 to 45 parts by weight, of the second high
molecular weight polyethylene having a weight average molecular
weight (Mw) of more than 150,000 to 1,000,000 g/mol or the second
ultra high molecular weight polyethylene having a weight average
molecular weight (Mw) of more than 1,000,000 to 5,000,000 g/mol,
wherein
[0046] the density of the first high molecular weight polyethylene
or the first ultra high molecular weight polyethylene and the
second high molecular weight polyethylene or the second ultra high
molecular weight polyethylene are in the range from 0.920 to 0.950
g/cm3, and
[0047] wherein the molecular weight distribution of the multimodal
polyethylene composition is from 13 to 60, preferably 20 to 60,
preferably 20 to 28, preferably from 24 to 28, measured by gel
permeation chromatography.
[0048] In a further preferred embodiment, the molecular weight
distribution is from 24 to 26, preferably from 25 to 26, measured
by gel permeation chromatography.
[0049] In a preferred embodiment, the multimodal polyethylene
composition has a weight average molecular weight from 80,000 to
1,300,000 g/mol, preferably 150,000 to 400,000 g/mol, preferably
from 200,000 to 350,000 g/mol, measured by Gel Permeation
Chromatography.
[0050] Furthermore, it is preferred, that the multimodal
polyethylene composition has a number average molecular weight from
5,000 to 30,000 g/mol, preferably 5,000 to 15,000 g/mol, preferably
from 7,000 to 12,000 g/mol, measured by Gel Permeation
Chromatography.
[0051] Preferably, the multimodal polyethylene composition has a Z
average molecular weight from 900,000 to 6,000,000 g/mol,
preferably 1,000,000 to 3,000,000 g/mol, preferably from 1,000,000
to 2,500,000 g/mol, measured by Gel Permeation Chromatography.
[0052] Preferably, the multimodal polyethylene composition has a
density from 0.950 to 0.962 g/cm.sup.3 preferably from 0.953 to
0.959 g/cm.sup.3, according to ASTM D 1505 and/or a melt flow index
MI.sub.5 from 0.01 to 50 g/10 min, and/or MI.sub.2 from 0.03 to
0.15 g/10 min preferably from 0.03 to 0.10 g/10 min.
[0053] Finally, the object is achieved by a film comprising the
inventive multimodal polyethylene composition, wherein the film has
a thickness of 4 to 40 .mu.m, preferably 4 to 30 .mu.m, and most
preferably 4 to 20 .mu.m.
[0054] In preferred embodiments of the inventive reactor system,
the inventive process, the inventive multimodal polyethylene
composition and inventive film "comprising" is "consisting of".
[0055] Regarding the inventive film, it is preferred that the film
substantially comprises the inventive multimodal polyethylene
composition, which means that the film does comprise further
constituents only in amounts which do not affect the film
properties regarding output, bubble stability, mechanical strength,
toughness and the like. Most preferred the film is consisting of
the inventive multimodal polyethylene composition.
[0056] In preferred embodiments "parts by weight" is "percent by
weight".
[0057] The above embodiments mentioned to be preferred resulted in
even more improved mechanical properties of the obtained multimodal
polyethylene composition and the film prepared therefrom. Best
results were achieved by combining two or more of the above
preferred embodiments. Likewise, the embodiments mentioned above to
be more or most preferred resulted in the best improvement of
mechanical properties.
[0058] Surprisingly, it was found that by using the inventive
reactor system to produce an inventive multimodal polyethylene
composition by the inventive process allows to form an inventive
film using the inventive composition which is superior over the
prior art. In particular, it was found that by using the inventive
multimodal polyethylene composition a blown film can be prepared
with high output, good bubble stability, high mechanical strength
and high toughness, in particular at a film thickness from 5 to 12
micron.
[0059] The invention concerns a reactor system for multimodal
polyethylene polymerization. The system comprises a first reactor,
a second reactor, a third reactor and a hydrogen removal unit
placed between the first reactor and the second reactor.
[0060] The hydrogen depleted polyethylene from the first reactor
affects the polymerization of high molecular weight in the
subsequent reactors. In particular, high molecular weight leads to
improved mechanical properties of polyethylene that is the
advantage for various product application includes injection
molding, blow molding and extrusion. The catalyst for producing the
multimodal polyethylene resin of this invention is selected from a
Ziegler-Natta catalyst, a single site catalyst including
metallocene-bases catalyst and non-metallocene-bases catalyst or
chromium based might be used, preferably conventional Ziegler-Natta
catalyst or single site catalyst. The catalyst is typically used
together with cocatalysts which are well known in the art.
[0061] Innert hydrocarbon is preferably aliphatic hydrocarbon
including hexane, isohexane, heptane, isobutane. Preferably, hexane
(most preferred n-hexane) is used. Coordination catalyst, ethylene,
hydrogen and optionally .alpha.-olefin comonomer are polymerized in
the first reactor. The entire product obtained from the first
reactor is then transferred to the hydrogen removal unit to remove
98.0 to 99.8% by weight of hydrogen, unreacted gas and some
volatiles before being fed to the second reactor to continue the
polymerization. The polyethylene obtained from the second reactor
is a bimodal polyethylene which is the combination of the product
obtained from the first reactor and that of the second reactor.
This bimodal polyethylene is then fed to the third reactor to
continue the polymerization. The final multimodal (trimodal)
polyethylene obtained from the third reactor is the mixture of the
polymers from the first, the second and the third reactor.
[0062] The polymerization in the first, the second and the third
reactor is conducted under different process conditions. These can
be the variation and concentration of ethylene and hydrogen in the
vapor phase, temperature or amount of comonomer being fed to each
reactor. Appropriate conditions for obtaining a respective homo- or
copolymer of desired properties, in particularly of desired
molecular weight, are well known in the art. The person skilled in
the art is enabled on basis of his general knowledge to choose the
respective conditions on this basis. As a result, the polyethylene
obtained in each reactor has a different molecular weight.
Appropriate conditions for obtaining a respective homo- or
copolymer of desired properties, in particularly of desired
molecular weight, are well known in the art. The person skilled in
the art is enabled on basis of his general knowledge to choose the
respective conditions on this basis. Preferably, low molecular
weight polyethylene is produced in the first reactor, while ultra
high or and molecular weight polyethylene are produced in the
second and third reactor, respectively.
[0063] The term first reactor refers to the stage where the low
molecular weight polyethylene (LMW) or the medium molecular weight
polyethylene (MMW) is produced. The term second reactor refers to
the stage where the first high or ultra high molecular weight
polyethylene (HMW1) is produced. The term third reactor refers to
the stage where the second high or ultra high molecular weight
polyethylene (HMW2) is produced.
[0064] The term LMW refers to the low molecular weight polyethylene
polymer polymerized in the first reactor having a the weight
average molecular weight (Mw) of 20,000-90,000 g/mol.
[0065] The term MMW refers to the medium molecular weight
polyethylene polymer polymerized in the first reactor having a
number average molecular weight (Mn) of 9,000 to 12,000 g/mol and a
weight average molecular weight (Mw) of more than 90,000 to 150,000
g/mol.
[0066] The term HMW1 refers to the high or ultra high molecular
weight polyethylene polymer polymerized in the second reactor
having a weight average molecular weight (Mw) of more than 150,000
to 5,000,000 g/mol.
[0067] The term HMW2 refers to the high or ultra high molecular
weight polyethylene polymer polymerized in the third reactor having
a weight average molecular weight (Mw) of more than 150,000 to
5,000,000 g/mol.
[0068] The LMW or MMW is produced in the first reactorin the
absence of comonomer in order to obtain a homopolymer.
[0069] To obtain the improved polyethylene properties of this
invention, ethylene is polymerized in the first reactor in the
absence of comonomer in order to obtain high density LMW or MMW
polyethylene having density .gtoreq.0.965 g/cm.sup.3 and MI.sub.2
in the range of 10-1000 g/10 min for LMW and 0.1 to 10 g/10 min for
MMW. In order to obtain the target density and MI in the first
reactor, the polymerization conditions are controlled and adjusted.
The temperature in the first reactor ranges from 65-90.degree. C.,
preferably 68-85.degree. C. Hydrogen is fed to the first reactor so
as to control the molecular weight of the polyethylene. The molar
ratio of hydrogen to ethylene in the vapor phase can be varied
depending up on the target MI. However, the preferred molar ratio
ranges from 0.5-8.0, more preferably 3.0-6.0. The first reactor is
operated at pressure between 250 and 900 kPa, preferably 400-850
kPa. An amount of hydrogen present in the vapor phase of the first
reactor is in the range of 20-95% by mole, preferably 50-90% by
mol.
[0070] Before being fed to the second reactor, the slurry obtained
from the first reactor containing LMW or MMW polyethylene
preferably in hexane is transferred to a hydrogen removal unit
which may have a flash drum connected with depressurization
equipment preferably including one or the combination of vacuum
pump, compressor, blower and ejector where the pressure in the
flash drum is reduced so that volatile, unreacted gas, and hydrogen
are removed from the slurry stream. The operating pressure of the
hydrogen removal unit typically ranges from 103-145 kPa (abs),
preferably 104-130 kPa (abs) in which 98.0 to 99.8% by weight of
hydrogen can be removed, preferably 98.0 to 99.5% by weight.
[0071] In this invention, when 98.0 to 99.8% by weight of hydrogen
is removed and the polymerization undergoes under these conditions
of hydrogen content, very high molecular weight polymer can be
achieved this way and Charpy Impact and Flexural Modulus are
improved. It was surprisingly found that working outside the range
of 98.0 to 99.8% by weight of hydrogen removal, the inventive
effect of obtaining very high molecular weight polymer and
improving Charpy Impact an Flexural Modulus could not be observed
to the same extend. The effect was more pronounced in the ranges
mentioned to be preferred.
[0072] The polymerization conditions of the second reactor are
notably different from that of the first reactor. The temperature
in the second reactor ranges from 70-90.degree. C., preferably
70-80.degree. C. The molar ratio of hydrogen to ethylene is not
controlled in this reactor since hydrogen is not fed into the
second reactor. Hydrogen in the second reactor is the hydrogen left
over from the first reactor that remains in slurry stream after
being flashed at the hydrogen removal unit. Polymerization pressure
in the second reactor ranges from 100-3000 kPa, preferably 150-900
kPa, more preferably 150-400 kPa and is controlled by the addition
of inert gas such as nitrogen.
[0073] Hydrogen removal is the comparison result of the amount of
the hydrogen present in the slurry mixture before and after passing
through the hydrogen removal unit. The calculation of hydrogen
removal is performed according to the measurement of gas
composition in the first and the second reactor by gas
chromatography.
[0074] After the substantial amount of hydrogen is removed to
achieve the inventive concentration, slurry from the hydrogen
removal unit is transferred to the second reactor to continue the
polymerization. In this reactor, ethylene can be polymerized with
or without .alpha.-olefin comonomer to form HMW1 polyethylene in
the presence of the LMW or MMW polyethylene obtained from the first
reactor. The .alpha.-olefin comomer that is useful for the
copolymerization includes C.sub.4-12, preferably 1-butene and/or
1-hexene, more preferably 1-butene.
[0075] After the polymerization in the second reactor, the slurry
obtained is transferred to the third reactor to continue the
polymerization.
[0076] The HMW2 is produced in the third reactor by copolymerizing
ethylene with optionally .alpha.-olefin comonomer at the presence
of LMW and HWM1 obtained from the first and second reactor. The
.alpha.-olefin comonomer that is useful for the copolymerization
include C.sub.4_12, preferably 1-butene and/or 1-hexene, more
preferably 1-butene.
[0077] In order to obtain the target density and the target MI in
the third reactor, the polymerization conditions are controlled and
adjusted. However, the polymerization conditions of the third
reactor are notably different from the first and second reactor.
The temperature in the third reactor ranges from 68-90.degree. C.
preferably 68-80.degree. C. Hydrogen is fed to the third reactor so
as to control the molecular weight of polyethylene. The molar ratio
of hydrogen to ethylene can be varied depending up on the target
MI. However, the preferred molar ratio ranges from 0.01-2.0.
Polymerization pressure in the third reactor ranges from 150-900
kPa, preferably 150-400 kPa, and is controlled by the addition of
inert gas such as nitrogen.
[0078] The amount of LMW present in the multimodal polyethylene
composition of the present invention is 40-65 parts by weight. HMW1
present in the polyethylene of the present invention is 8-20 parts
by weight and HMW2 present in the polyethylene of the present
invention is 30-50 parts by weight.
[0079] The final (free-flow) multimodal polyethylene composition is
obtained by separating hexane from the slurry discharged from the
third reactor.
[0080] The resultant polyethylene powder may then be mixed with
antioxidants and optionally additives before being extruded and
granulated into pellets.
[0081] The pellets was then blown into a film using the
conventional tubular blow film process with different thickness and
further evaluated for the film properties.
Definition and Measurement Methods
[0082] MI.sub.2, MI.sub.5, MI.sub.21.6: Melt flow index (MFR) of
polyethylene was measured according to ASTM D 1238 and indicated in
g/10 min that determines the flowability of polymer under testing
condition at 190.degree. C. with load 2.16 kg, 5 kg and 21.6 kg,
respectively.
[0083] Density: Density of polyethylene was measured by observing
the level to which a pellet sinks in a liquid column gradient tube,
in comparison with standards of known density. This method is
determination of the solid plastic after annealing at 120.degree.
C. follow ASTM D 1505.
[0084] Molecular weight and Polydispersity index (PDI): The weight
average molecular weight (Mw), the number average molecular weight
(Mn) and the Z average molecular weight (M.sub.Z) in g/mol were
analysed by gel permeation chromatography (GPC). Polydispersity
index was calculated by Mw/Mn.
[0085] Around 8 mg of sample was dissolved in 8 ml of
1,2,4-trichlorobenzene at 160.degree. C. for 90 min. Then the
sample solution, 200 .mu.l, was injected into the high temperature
GPC with IRS, an infared detector (Polymer Char, Spain) with flow
rate of 0.5 ml/min at 145.degree. C. in column zone and 160.degree.
C. in detector zone. The data was processed by GPC One.RTM.
software, Polymer Char, Spain.
[0086] Intrinsic Viscosity (IV)
[0087] The test method covers the determination of the dilute
solution viscosity of HDPE at 135.degree. C. or Ultra High
Molecular Weight Polyethylene (UHMWPE) at 150.degree. C. The
polymeric solution was prepared by dissolving polymer in Decalin
with 0.2% wt/vol stabilizer (Irganox 1010 or equivalent). The
details are given for the determination of IV followed ASTM
D2515.
[0088] Crystallinity: The crystallinity is frequently used for
characterization by Differential Scanning calorimetry (DSC) follow
ASTM D 3418. Samples were identified by peak temperature and
enthalpy, as well as the % crystallinity was calculated from the
peak area.
[0089] Charpy impact strength: Charpy impact strength is determined
according to ISO179 at 23.degree. C., 0.degree. C. and -20.degree.
C. and showed in the unit kJ/m.sup.2.
[0090] Flexural Modulus: The specimen was prepared and performed
the test according to ISO178. The flexural tests were done using a
universal testing machine equipped with three point bending
fixture.
[0091] Film bubble stability: It was determined during the blown
film process, the axial oscillation of the film bubble was observed
during increasing the nip roll take up speed and continue more than
30 minute. Good bubble stability is defined when film is not
oscillating and bubble is not break.
[0092] Output: The film was blown following the blown film
conditions. Then the film was collected for a minute and weight.
The output of film from unit of g/min is then calculated and
reported in the unit of kg/hr.
[0093] Dart drop impact: This test method follow method A of ASTM
D1709 that covers the determination of the energy that cause
plastic film to fail under specified conditions of free-falling
dart impact. This energy is expressed in terms of the weight of the
falling from a specified height, 0.66.+-.0.01 m, which result in
50% failure of specimens tested.
[0094] Puncture: This testing is in-housed method that a specimen
is clamped without tension between circular plates of a ring clamp
attachment in UTM. A force is exerted against the center of the
unsupported portion of the test specimen by a solid steel rod
attached to the load indicator until rupture of specimen occurs.
The maximum force recorded is the value of puncture resistance
[0095] Tensile and elongation properties of film: The test methods
cover the determination of tensile properties of film (less than
1.0 mm. in thickness) followed ASTM D882. The testing employs a
constant rate of grip separation, 500 mm/min.
[0096] Tear strength: This test method covers the determination of
the average force to propagate tearing through a specified length
of plastic film using an Elmendorf-type tearing tester followed
ASTM D 1922
[0097] Melt strength and Draw down ratio (DD): They are determined
using GOEFFERT Rheotens. The melt extrudate is performed by single
screw extruder with 2 mm die diameter at melt temperature
190.degree. C. the extrudate pass through Rheotens haul-off with
controlled the ramp speed. The haul-off force is record. The
force(N) is collect as a function of draw ratio (DD). Melt strength
and draw down ratio is define as the force at break and draw down
ratio at break respectively.
EXPERIMENTAL AND EXAMPLES
Composition Related Examples
[0098] The medium or high density polyethylene preparation was
carried out in three reactors in series. Ethylene, hydrogen,
hexane, catalyst and TEA (triethyl aluminum) co-catalyst were fed
into a first reactor in the amounts shown in Table 1. A high
activity Ziegler-Natta catalyst was used. The catalyst preparation
is for example described in Hungarian patent application 0800771R.
The polymerization in first reactor was carried out to make a low
molecular weight polyethylene. All of polymerized slurry polymer
from first reactor was then transferred to a hydrogen removal unit
to remove unreacted gas and some of hexane from polymer. The
operating pressure in the hydrogen removal unit was be varied in a
range of 100 to 115 kPa where residual hydrogen was removed more
than 98% by weight but not more than 99.8% by weight from hexane
before transferring to a second polymerization reactor. Some fresh
hexane, ethylene and/or comonomer were fed into second reactor to
produce first high molecular weight polyethylene (HMW1). All of
polymerized polymer from second reactor was fed into the third
reactor which produce second high molecular weight polyethylene
(HMW2). Ethylene, comonomer, hexane and/or hydrogen were fed into
the third reactor.
Comparative Example 1 (CE1)
[0099] A homopolymer was produced in first reactor to obtain a low
molecular weight portion before transferring such polymer to
hydrogen removal unit. Reactant mixture was introduced into the
hydrogen removal unit to separate the unreacted mixture from the
polymer. Residual hydrogen was removed 97.6% by weight when
hydrogen removal unit was operated at pressure of 150 kPa. The low
molecular weight polymer was then transferred to the second reactor
to produce a first high molecular weight polymer. Final, produced
polymer from second reactor was transferred to the third reactor to
create a second high molecular weight polymer. In third, a
copolymerization was carried out by feeding 1-butene as a
comonomer.
Example 1 (E1)
[0100] Example 1 was carried out in the same manner as Comparative
Example 1 except that the hydrogen removal unit was operated at
pressure of 115 kPa. The residual of hydrogen from first reactor
was removed 98.0% by weight. Characteristic properties of these
multimodal polymers are shown in Table 2. As it can be seen, an
improvement of stiffness-impact balance was observed when the
percentage of removed hydrogen residual increased compared with the
properties of Comparative Example 1.
Example 2 (E2)
[0101] Example 2 was carried out in the same manner as Comparative
Example 1 except that the hydrogen removal unit was operated at
pressure of 105 kPa. The residual hydrogen from the first reactor
was removed to an extend of 99.1% by weight. The operational of
hydrogen removal unit under this pressure leads to an expansion of
a polymer properties range. As seen in Table 2, a final melt flow
rate of E2 was lower than a final melt flow rate of CE1 resulted in
an improvement of Charpy impact while still maintained the flexural
modulus.
Comparative Example 2 (CE2)
[0102] Comparative Example 2 was carried out in the same manner as
Comparative Example 1 except that the hydrogen removal unit was
operated at pressure of 102 kPa. The residual of hydrogen from
first reactor was removed to an extend of 99.9% by weight. The
operational of hydrogen removal unit under this pressure leads to
an expansion of a polymer properties range. As seen in Table 2, the
final melt flow rate and a density of CE2 were quite similar to a
final melt flow rate and a density of E2. A decay of Charpy impact
was showed in CE2 compared to E2.
Comparative Example 3 (CE3)
[0103] A homopolymer was produced in a first reactor to obtain a
low molecular weight portion before transferring the polymer to a
hydrogen removal unit. Reactant mixture was introduced into the
hydrogen removal unit to separate the unreacted mixture from the
polymer. Hydrogen residual was removed to an extend of 97.9% by
weight when hydrogen removal unit was operated at pressure of 150
kPa. The low molecular weight polymer was then transferred to a
second reactor to produce a first high molecular weight polymer. In
the second reactor, a copolymerization was carried out by feeding
1-butene as a comonomer. Finally, in-situ bimodal copolymer from
second reactor was transferred to a third reactor to create a
second high molecular weight copolymer portion. Characteristic
properties of this multimodal polymers is shown in Table 2. A
significant improvement in Charpy impact at room temperature could
be obtained by decreasing a density of final polymer when
co-polymer was produced in both the second and the third
reactor.
Example 3 (E3)
[0104] Example 3 was carried out in the same manner as Comparative
Example 3 except that the hydrogen removal unit was operated at
pressure of 105 kPa. The residual of hydrogen from first reactor
was removed to an extend of 98.8% by weight. The polymer obtained
by this process operation had a melt flow rate of 0.195 g/10 min (5
kg loading) lower than such value obtained from CE3. As seen in
Table 2, it revealed an improvement of stiffness-impact balance
when the percentage of removed hydrogen residual increases compared
with the properties of Comparative Example 3.
Comparative Example 4 (CE4)
[0105] A homopolymer was produced in first reactor to obtain a low
molecular weight portion before transferring such polymer to
hydrogen removal unit. Reactant mixture was introduced into the
hydrogen removal unit to separate the unreacted mixture from the
polymer. Residual hydrogen was removed 97.6% by weight when
hydrogen removal unit was operated at pressure of 150 kPa (abs).
The low molecular weight polymer was then transferred to the second
reactor to produce a first high molecular weight polymer. Final,
produced polymer from second reactor was transferred to the third
reactor to create a second high molecular weight polymer. In third,
a copolymerization was carried out by feeding 1-butene as a
comonomer. As seen in Table 2 and 3, the final melt flow rate of
CE4 were quite similar to a final melt flow rate of E5. A decay of
charpy impact and flexural modulus were showed in CE4 compared to
E5, even it showed lower density of E5.
Example 5 (E5)
[0106] Example 5 was carried out in the same manner as Comparative
Example 4 except that the hydrogen removal unit was operated at
pressure of 115 kPa (abs). The residual of hydrogen from first
reactor was removed to an extend of 98.5% by weight. The polymer
obtained by this process operation had a melt flow rate of 48 g/10
min (5 kg loading) lower than such value obtained from CE3. As seen
in Table 2, it revealed an improvement of stiffness-impact balance
when the percentage of removed hydrogen residual increases compared
with the properties of Comparative Example 4.
Example 6 (E6)
[0107] Example 6 was carried out in the same manner as Example 4
except that the comonomer feeding in the third ultra high molecular
weight polyethylene. The polymer produced by this process leads to
an excellent improvement of Charpy impact strength while still
maintained the flexural modulus. As shown in table 2, the inventive
example 6 with IV of 23 dl/g show the high impact strength (one
notched impact without break) and flexural modulus as compared to
comparative samples, however, the melt flow index is unmeasurable
due to high viscosity and high Mw.
TABLE-US-00001 TABLE 1 CE1 E1 E2 CE2 CE3 E3 E4 CE4 E5 E6 W.sub.A, %
55 55 55 55 45 45 30 50 50 30 W.sub.B, % 20 20 20 20 25 25 30 10 10
30 W.sub.C, % 25 25 25 25 30 30 40 40 40 40 First reactor
Polymerization type Homo Homo Homo Homo Homo Homo Homo Homo Homo
Homo Temperature, .degree. C. 80 80 80 80 80 80 80 80 80 80 Total
pressure, kPa 800 800 800 800 800 800 800 800 800 800 Ethylene, g
1,100.72 1,100.70 1,100.86 1,100.74 900.30 900.30 540.50 725.21
725.57 485.70 Hydrogen, g 1.62 1.62 1.55 1.55 2.97 2.99 1.34 1.13
1.13 1.23 Hydrogen removal unit Pressure, kPa (abs) 150 115 105 102
150 105 105 150 115 105 Hydrogen remove, % 97.6 98.0 99.1 99.9 97.9
98.8 98.9 97.7 98.5 98.3 Second reactor Polymerization type Homo
Homo Homo Homo Copo Copo Homo Copo Copo Homo Temperature, .degree.
C. 70 70 70 70 70 70 70 80 80 70 Total pressure, kPa 250 250 250
250 250 250 400 300 300 400 Ethylene, g 400.52 400.81 400.35 400.06
500.17 500.31 540.36 145.35 145.21 485.78 Hydrogen, g 0 0 0 0 0 0 0
0 0 0 1-butene, g 0 0 0 0 18.84 18.91 0 8 8 0 Third reactor
Polymerization type Copo Copo Copo Copo Copo Copo Homo Copo Copo
Copo Temperature, .degree. C. 70 70 70 70 70 70 80 80 80 70 Total
pressure, kPa 400 400 400 400 400 400 600 600 600 600 Ethylene, g
500.74 500.11 500.30 500.63 600.02 601.19 720.60 580.53 580.46
647.54 Hydrogen, g 0 0.001 0.001 0.001 0 0.001 0 0.59 1.37 0
1-butene, g 35.05 30.01 30.03 30.04 60.01 60.04 0 27 27 20.60
W.sub.Ameans percent by weight of Polymer in the first reactor
W.sub.Bmeans percent by weight of Polymer in the second reactor
W.sub.Cmeans percent by weight of Polymer in the third reactor
TABLE-US-00002 TABLE 2 CE1 E1 E2 CE2 CE3 Powder MI.sub.5, 0.474
0.372 0.240 0.242 0.275 g/10 min MI.sub.21, 13.83 10.80 7.38 7.23
6.40 g/10 min Density, 0.9565 0.9578 0.9555 0.9567 0.9441
g/cm.sup.3 IV, dl/g -- -- -- -- -- Mw 276,413 244,279 291,295
319,487 252,160 Mn 8,877 8,724 8,843 8,472 8,016 Mz 2,788,607
2,370,678 3,401,041 4,135,007 1,638,224 PDI 31 28 33 38 31 Pellet
MI.sub.5, 0.436 0.410 0.232 0.199 0.298 g/10 min MI.sub.21, 14.46
11.68 7.876 6.696 7.485 g/10 min Density, 0.9577 0.9574 0.9568
0.9566 0.9442 g/cm.sup.3 IV, dl/g 2.97 3.03 3.52 3.64 3.12 %
Crystallinity, % 64.70 67.24 64.78 66.16 57.49 Charpy, 23.5 29.9
35.3 30.5 47.9 23.degree. C., kJ/m.sup.2 Flexural 1,130 1,210.
1,123 1,123 727 modulus, MPa E3 E4 CE4 E5 E6 Powder MI.sub.5, 0.200
-- 54.80 48.07 NA g/10 min MI.sub.21, 4.81 0.145 641 653 NA g/10
min Density, 0.9438 0.9534 0.9606 0.9590 0.9409 g/cm.sup.3 IV, dl/g
-- 9.00 1.07 1.06 23 Mw 306,468 868,813 77,334 91,752 1,269,336 Mn
7,637 24,107 5,400 6,035 23,450 Mz 2,643,953 5,112,060 667,276
1,027,956 5,262,195 PDI 40 36 14 15 54.13 Pellet MI.sub.5, 0.195 --
60.62 55.47 -- g/10 min MI.sub.21, 4.604 -- 713.1 752.2 -- g/10 min
Density, 0.9440 -- 0.9608 0.9594 -- g/cm.sup.3 IV, dl/g 3.37 9.00
1.0 1.1 23 % Crystallinity, % 54.05 68.23 69.52 65.64 58.20 Charpy,
50.9 84.4 1.5 1.8 85.41 23.degree. C., kJ/m.sup.2 Flexural 785
1,109 1,147 1,196 890 modulus, MPa
Film Related Examples
[0108] To prepare an inventive film from the above compositions, it
was found that a sub-range of multimodal polyethylene compositions
which might be obtained using the inventive reactor system are
particularly preferred. In detail, the compositions suitable to
form the inventive film are as follows and have the following
properties. The following comparative examples refer to the film
related compositions.
[0109] The inventive example E7 was produced follow the inventive
process to make the multimodal polyethylene composition as shown in
table 3. The specific multimodal polyethylene compositions enhance
superior properties of film in particular the ability to make thin
film. The thin film is represented the low thickness of the film
such as 5 micron. It could be also refer to the ability to
down-gauge the film thickness with equivalent properties to
conventional film thickness.
[0110] The inventive example E8 is the multimodal polyethylene
composition produced by inventive process and having polymer as
shown in table 5 in the range of claims with MI.sub.2 of 0.114 g/10
min and density of 0.9570 g/cm3. It shows good processing in film
production and higher output rate with maintaining properties in
particular dart drop impact and puncture resistance at 12 micron
film thickness.
TABLE-US-00003 TABLE 3 Process condition of inventive example 7, E7
and E8 and comparative example 6, CE7 Condition Unit CE7 E7 E8 1st
Reactor Split ratio % 49-50 45-47 45-47 Temperature (.degree. C.)
81-85 81-85 81-85 Pressure kPa 700-750 650-700 580-620 Hydrogen
flow rate NL/h 246 226 248 2nd Reactor Split ratio % 6-8 10-12
10-12 Temperature (.degree. C.) 70-75 70-75 70-75 Pressure kPa
150-300 150-300 150-300 Hydrogen flow rate NL/h 0 0 0 Co-monomer
kg/h 0.031 0.010 0.0135 Comonomer/Ethylene Feed -- 0.018 0.0033
0.0046 H2 removal 99.0 98.9 99.4 Comonomer type -- 1-Butene
1-Butene 1-Butene 3rd Reactor Split ratio % 42-43 42-43 42-43
Temperature (.degree. C.) 70-75 70-75 70-75 Pressure kPa 150-300
150-300 150-300 Hydrogen flow rate NL/h 12.85 13.02 17.28
Co-monomer kg/h 0.052 0.0152 0.0099 Comonomer/Ethylene Feed --
0.0048 0.0013 0.0009 Comonomer type -- 1-Butene 1-Butene
1-Butene
[0111] From the molding composition so prepared, a film was
produced in the following way. The films having different thickness
and output were prepared on the internal blown film machine
comprising a single screw extruder connecting with tubular blow
film apparatus. The temperature setting from extruder to the die is
from 175 to 205.degree. C. The screw speed and nip roll take up
speed to prepare different film thickness in each experiment is
defined in table 4. The film was produced at a blow-up ratio of 4:1
and a neck height of 30 cm with bubble diameter of 23 cm and film
lay flat of 39 cm.
TABLE-US-00004 TABLE 4 Experiment and conditions for film
preparation Experiment 1 Experiment 2 Experiment 3 Blown film
parameter (Ex. 1) (Ex. 2) (Ex. 3) Film thickness 12 5 5 Screw speed
(rpm) 85 85 60 Nip roll take up speed (rpm) 80 150 95 BUR 4:1 4:1
4:1 Neck height (cm) 30 30 30
[0112] The comparative example 4 (CE5) is the commercial resin
EL-Lene.TM. H5604F produced by SCG Chemicals., Co. Ltd. with
MI.sub.2 of 0.03 g/10 min and density of 0.9567 g/cm.sup.3. It is
the bimodal polyethylene produced in slurry cascade process.
[0113] The comparative example 5 (CE6) is the blend of CE4 with
commercial resin LLDPE, Dow.TM. Butene 1211, with MI.sub.2 of 1.0
g/10 min and density of 0.9180 g/cm.sup.3. It is the practical way
in film production to get better film strength in particular dart
drop impact and tear strength.
[0114] The comparative example 6 (CE7) is the multimodal
polyethylene composition produced by the inventive process and
having the composition and molecular weight distribution out of the
specific range of composition for thin film.
[0115] The films were further evaluated for processability and
mechanical properties in both machine direction, MD and transverse
direction, TD as shown in table 5.
TABLE-US-00005 TABLE 5 Properties of polyethylene compositions and
film thereof Properties CE5 CE6 CE7 E7 E8 Resin MI.sub.2, g/10 min
0.03 0.065 0.08 0.08 0.114 MI.sub.2 of LMW NA NA 624 715 722
Density, g/cm.sup.3 0.957 0.952 0.955 0.957 0.957 Density of HMW1,
NA NA 0.921 0.924 0.921 g/cm.sup.3 Density of HMW2, NA NA 0.946
0.947 0.947 g/cm.sup.3 Mn (g/mol) 7,788 8,298 9,579 9,027 8856 Mw
(g/mol) 240,764 276,362 284,257 232,875 228,400 Mz (g/mol)
1,817,918 1,956,827 1,666,188 1,403,576 1,346,144 PDI 30.9 33.3
29.7 25.8 25.7 Melt strength at 0.28 0.25 0.22 0.26 NA break, N
Draw down ratio at 10.5 12.2 12.8 12.5 NA break Film Ex. 1 Ex. 2
Ex. 3 Ex1 Ex1 Ex. 1 Ex. 2 Ex1 Output, kg/hr 16.0 NA 12.8 19.1 20.3
19.7 19.9 20.3 Film thickness, 12 5 5 12 12 12 5 12 micron Screw
speed, rpm 85 85 60 85 85 85 85 85 Nip roll take up 80 150 95 80 80
80 150 80 speed, rpm Blow up ratio, 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1
BUR Bubble Stability Good Bubble Good Good Good Good Good Good
Break Dart drop impact, g 105 -- 113 140 124 159 108 124 Tensile
Strength at 722 -- 889 428 537 895 1068 537 Break (MD), kg/cm.sup.2
Tensile Stregnth at 501 -- 574 320 537 745 499 537 Break (TD),
kg/cm.sup.2 Elongation at 266 -- 52 161 226 417 192 226 Break (MD),
% Elongation at 510 -- 388 390 488 605 365 488 Break (TD), % Tear
Strength 4.14 -- 8.4 7.8 5.5 6.6 2.3 5.5 (MD), g Tear Strength 50
-- 14 49 26 60 27 26 (TD), g Puncture Energy, 26 -- 39 21 29 31 46
29 N-cm/u
[0116] The inventive example 7 shows superior properties of 12
micron film prepared by the same conditions compared to comparative
examples, CE5, CE6 and CE7. The inventive E8 shows maintain film
property and higher output with good bubble stability. In
particular dart drop impact strength, tensile strength of film in
both directions and puncture resistance. Also the film is produced
with higher output.
[0117] Further experiment to make a thin film at 5 micron was
performed in Experiment 2. The Inventive example E7 and E8 show
better draw ability at higher output which can be easily drawn into
5 micron film with good bubble stability and good mechanical
strength. The same experiment was applied to the comparative
example CE5 however bubble break was suddenly found. It was
possible to make the 5 micron film with CE5 only in the case of
lowering output by reducing screw speed and nip roll take up speed
as done in Experiment 3. This is also related to draw down at break
measured by rheoten. The inventive example1 E7 and E8 has higher
draw down at break compared to comparative example CE5.
[0118] Moreover the properties of the 5 micron film made by
inventive example E7 in Experiment 2 are also equivalent to 12
micron film made by CE5 with Experiment 1 in particular dart drop
impact strength, tensile strength at break and puncture resistance.
This also indicated the ability to downgauge the film thickness
without sacrifice of mechanical properties. It was also possible to
obtain good mechanical properties without use of LLDPE as compared
to comparative example CE6.
[0119] These results support that the inventive multimodal
polyethylene composition provide better balance of mechanical
strength with high output for thin film preparation.
[0120] The features disclosed in the foregoing description and in
the claims may, both separately and in any combination, be material
for realizing the invention in diverse forms thereof.
* * * * *