U.S. patent application number 16/332137 was filed with the patent office on 2019-12-12 for multimodal polyethylene screw cap.
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, Saranya TRAISILANUN.
Application Number | 20190374919 16/332137 |
Document ID | / |
Family ID | 56920581 |
Filed Date | 2019-12-12 |
United States Patent
Application |
20190374919 |
Kind Code |
A1 |
TRAISILANUN; Saranya ; et
al. |
December 12, 2019 |
MULTIMODAL POLYETHYLENE SCREW CAP
Abstract
The present invention relates to a reactor system for a
multimodal polyethylene composition comprising; (a) first reactor
(b) 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, a multimodal, polyethylene
composition obtainable this way and a screw cap comprising the
same.
Inventors: |
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: |
56920581 |
Appl. No.: |
16/332137 |
Filed: |
September 8, 2017 |
PCT Filed: |
September 8, 2017 |
PCT NO: |
PCT/EP2017/072588 |
371 Date: |
March 11, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 110/02 20130101;
C08F 2500/02 20130101; C08F 2500/18 20130101; C08L 23/06 20130101;
C08L 2205/025 20130101; B01J 8/008 20130101; B65D 41/04 20130101;
C08L 2205/03 20130101; C08F 2/00 20130101; C08F 2/18 20130101; C08F
2500/05 20130101; B01J 2219/0004 20130101; C08F 2/01 20130101; C08L
23/06 20130101; C08L 23/06 20130101; B01J 8/22 20130101; C08L
2207/068 20130101; C08F 2500/01 20130101; C08F 2/12 20130101; C08L
23/06 20130101; C08L 23/06 20130101; C08L 23/0815 20130101; C08L
23/0815 20130101 |
International
Class: |
B01J 8/00 20060101
B01J008/00; B01J 8/22 20060101 B01J008/22; C08F 110/02 20060101
C08F110/02; C08F 2/01 20060101 C08F002/01; C08F 2/18 20060101
C08F002/18; C08L 23/06 20060101 C08L023/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2016 |
EP |
16188337.6 |
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 a 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; (b) removing in the hydrogen removal unit 98.0 to
99.8% by weight of the hydrogen from 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.4-12
.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 or
a first ultra high molecular weight polyethylene in the form of a
homopolymer or a copolymer and transferring a resultant mixture to
the third reactor; and (d) polymerizing ethylene, and optionally
C.sub.4-12 .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 or a second
ultra high molecular weight polyethylene homopolymer or
copolymer.
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 45 to 65 parts by weight, most preferred 50 to 60 parts
by weight, of the low molecular weight polyethylene having a weight
average molecular weight (Mw) of 20,000 to 90,000 g/mol; (B) 5 to
40 parts by weight, preferably 5 to 30 parts by weight, most
preferred 5 to 20 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) 20
to 60 parts by weight, preferably 25 to 60 parts by weight, most
preferred 35 to 55 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 the
molecular weight distribution of the multimodal polyethylene
composition is from 10 to 60, preferably 10 to 25, preferably 10 to
20, determined by Gel Permeation Chromatography; the isothermal
crystallization half-time of the multimodal polyethylene
composition at a temperature of 123.degree. C. is 7 min or less,
preferably 6 min or less, preferably 2-6 min, according to
Differential Scanning Calorimetry; and a spiral flow length at a
temperature of 220.degree. C. is at least 200 mm, preferably
250-400 mm.
8. The multimodal polyethylene composition according to claim 7,
wherein the spiral flow length at a temperature of 220.degree. C.
is 250-370 mm.
9. The multimodal polyethylene composition according to claim 8,
wherein the multimodal polyethylene composition has an weight
average molecular weight (Mw) from 80,000 to 1,300,00 g/mol,
preferably 80,000 to 250,000 g/mol, preferably 80,000 to 200,000
g/mol, measured by Gel Permeation Chromatography.
10. The multimodal polyethylene composition according to claim 7,
wherein the multimodal polyethylene composition has a number
average molecular weight (Mn) from 5,000 to 30,000 g/mol,
preferably 5,000 to 25,000 g/mol, preferably 6,000 to 20,000 g/mol
measured by Gel Permeation Chromatography.
11. The multimodal polyethylene composition according to claim 7,
wherein the multimodal polyethylene composition has a Z average
molecular weight (Mz) from 700,000 to 6,000,00 g/mol, preferably
700,000 to 2,500,000 g/mol, preferably 700,000 to 2,000,000 g/mol,
more preferably 700,000 to 1,500,000 g/mol measured by Gel
Permeation Chromatography.
12. The polyethylene composition according to claim 7, wherein the
multimodal polyethylene composition has a density 0.950 to 0.965
g/cm3, preferably 0.953 to 0.960 g/cm3, according to ASTM D 1505
and/or MI.sub.2 from 0.1 to 20 g/10 min, preferably from 0.3 to 17
g/10 min, according to ASTM D 1238.
13. Screw cap comprising the multimodal polyethylene composition
according to claim 7.
14. Screw cap according to claim 13 obtainable by injection molding
or compression molding.
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
including a screw cap comprising said multimodal polyethylene
composition and the use thereof.
[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 A 1 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 I 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 1655 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 an 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 ultra high 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 A 1 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
poly ylene 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] Screw caps, for example beverage screw caps and other
closures, which are in particularly used to cap beverage bottles,
especially bottles for carbonated soft drinks, are known in the
art. In particular, there is a variety of polyethylene compositions
for preparing such screw caps.
[0016] WO 2009/077142 A1 discloses a polyethylene molding
composition for producing injection-molded screw caps and closures,
in particular for use together with containers for carbonated
beverage products.
[0017] WO 2007/003530 A1 discloses polyethylene molding
compositions for producing injection-molded finished parts. The
composition is described to be suitable for producing, for example,
closures and bottles. Further described is a use of a multimodal
polyethylene composition.
[0018] U.S. Pat. No. 8,759,448 B2 is related to a polyethylene
molding composition having a multimodal molecular weight
distribution. It is proposed to use the disclosed composition for
preparing caps and closures, transport packaging, houseware and
thin wall packaging applications.
[0019] EP 2365995 B1 discloses a multimodal polyethylene
composition and the use thereof for preparing a single-piece bottle
cap. The multimodal polyethylene composition add nucleating agent
to get faster crystallization rate and altered stress cracking
resistance.
[0020] However, also in light of the above prior art, there is
still the need to provide improved caps, in particular screw caps,
and polymer compositions for preparing the same overcoming
drawbacks of the prior art, in particular to provide polymer
compositions for preparing caps having better processability,
excellent flowability, high stiffness and high environmental
stress-cracking resistance (ESCR).
[0021] It is therefore a further object of the present invention to
provide improved caps and multimodal polyethylene compositions for
preparing the same as well as a method for providing such a
composition overcoming drawbacks of the prior art.
[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 a 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 from 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 C4-12
.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 of more than 150,000 to
1,000,000 g/mol or a first ultra high molecular weight polyethylene
having a weight average molecular weight of more than 1,000,000 to
5,000,000 g/mol in the form of a homopolymer or a copolymer and
transferring a resultant mixture to the third reactor; and
[0034] (d) polymerizing ethylene, and optionally C4-12
.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 of more than 150,000 to 1,000,000 g/mol or
a second ultra high molecular weight polyethylene having a weight
average molecular weight of more than 1,000,000 to 5,000,000 g/mol
homopolymer or copolymer.
[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. F ore,
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.
[0038] Preferably, the .alpha.-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 of 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] Preferably, step (a) results in the low molecular weight
polyethylene or medium molecular weight polyethylene, step (c)
results in high molecular weight polyethylene or the ultra high
molecular weight polyethylene, and step (d) results in high
molecular weight polyethylene or the ultra high molecular weight
polyethylene.
[0041] 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.
[0042] Finally, the object is achieved by a multimodal polyethylene
composition obtainable by the inventive process, comprising;
[0043] (A) 30 to 65 parts by weight, preferably 35 to 65 parts by
weight, preferably 45 to 65 parts by weight, most preferred 50 to
60 parts by weight, of the low molecular weight polyethylene having
a weight average molecular weight (Mw) of 20,000 to 90,000
g/mol;
[0044] (B) 5 to 40 parts by weight, preferably 5 to 30 parts by
weight, most preferred 5 to 20 parts by weight, of the first high
molecular weight polyethylene having a weight average molecular
weight (Mw) of more than 150,000 to 1,000,000g/mol or the first
ultra high molecular weight polyethylene having a weight average
molecular weight (Mw) of more than 1,000,000 to 5,000,000g/mol;
and
[0045] (C) 20 to 60 parts by weight, preferably 25 to 60 parts by
weight, most preferred 35 to 55 parts by weight, of the second high
molecular weight polyethylene having a weight average molecular
weight (Mw) of more 150,000 to 1,000,000g/mol or the second ultra
high molecular weight polyethylene having a weight average
molecular weight (Mw) of more than 1,000,000 to 5,000,000g/mol,
wherein
[0046] the molecular weight distribution of the multimodal
polyethylene composition is from 10 to 60, preferably 10 to 25,
preferably 10 to 20, determined by Gel Permeation
Chromatography;
[0047] the isothermal crystallization half-time of the multimodal
polyethylene composition at temperature of 123.degree. C. is 7 min
or less, preferably 6 min or less, preferably 2-6 min, according to
Differential Scanning Calorimetry; and
[0048] a spiral flow length at a temperature of 220.degree. C. is
at least 200 mm, preferably 250-400 mm.
[0049] Preferably, the spiral flow length at a temperature of
220.degree. C. is 250-370 mm.
[0050] In a preferred embodiment, the multimodal polyethylene
composition has a weight average molecular weight from 80,000 to
1,300,000 g/mol, preferably 80,000 to 250,000 g/mol, preferably
80,000 to 200,000 g/mol, measured by Gel Permeation
Chromatography.
[0051] 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 25,000 g/mol, preferably
6,000 to 20,000 g/mol, measured by Gel Permeation
Chromatography.
[0052] Preferably, the multimodal polyethylene composition has a Z
average molecular weight from 700,000 to 6,000,000 g/mol,
preferably 700,000 to 2,500,000 g/mol, preferably 700,000 to
2,000,000 g/mol, and more preferably 700,000 to 1,500,000 g/mol
measured by Gel Permeation Chromatography.
[0053] Preferably, the multimodal polyethylene composition has a
density 0.950 to 0.965 g/cm.sup.3, preferably 0.953 to 0.960
g/cm.sup.3, according to ASTM D 1505 and/or MI.sub.2 from 0.1 to 20
g/10 min, preferably from 0.3 to 17 g/10 min, according to ASTM D
1238.
[0054] The object is further achieved by a screw cap comprising the
multimodal polyethylene composition according to the invention.
[0055] In this regard, a screw cap (or screw closure) is a
mechanical device which is screwed on and off a "finish" on a
container. It must be engineered to provide an effective seal (and
barrier), to be compatible with the contents, to be easily opened
by the consumer, often to be recloseable, and to comply with
product and package. A screw cap is a common type of closure for
bottles, jars and tubes.
[0056] Most preferred, the screw cap is obtained by injection
molding or compression molding.
[0057] Regarding the inventive screw cap, it is preferred that the
screw cap substantially comprises the inventive multimodal
polyethylene composition, which means that the screw cap does
comprise further constituents only in amounts which do not affect
the cap performances regarding processability (in particular cycle
time), flowability, stiffness and stress crack resistance. Most
preferred, the screw cap is consisting of the inventive multimodal
polyethylene composition.
[0058] In preferred embodiments of the inventive reactor system,
the inventive process and the inventive multimodal polyethylene
composition "comprising" is "consisting of".
[0059] In preferred embodiments "parts by weight" is "percent by
weight".
[0060] The above embodiments mentioned to be preferred resulted in
even more improved mechanical properties of the obtained multimodal
polyethylene composition and the screw caps 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.
[0061] Surprisingly, it was found that using the inventive reactor
system to produce the specific multimodal polyethylene composition
enhance the superior properties for screw cap and closure, in
particular to processability (fast cycle time), flowability,
stiffness and stress crack resistance.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] The polymerization in the first, the second and the third
reactor is conducted under different process conditions. These can
be the variation in 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.
Preferably, low molecular weight polyethylene or medium molecular
weight polyethylene is produced in the first reactor, while high
molecular weight polyethylene or ultra high molecular weight
polyethylene is produced in the second and third reactor
respectively.
[0066] The term first reactor refers to the stage where the low
molecular weight polyethylene (LMW) or the medium molecular weight
polyethylene (W) 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 molecular weight polyethylene or
ultra high molecular weight (HMW2) is produced.
[0067] The term LMW refers to the low molecular weight polyethylene
polymer polymerized in the first reactor having a weight average
molecular weight (Mw) of 20,000-90,000 g/mol.
[0068] The term LMW refers to the medium molecular weight
polyethylene polymer polymerized in the first reactor having a
weight average molecular weight (Mw) of more than 90,000-150,000
g/mol.
[0069] 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 w)of more than 150,000 to
5,000,000 g/mol.
[0070] The term HMW2 refers to the high or ultra high molecular
weight polyethylene polymer polymerized in the third reactor having
the weight average molecular weight (Mw) of more than 150,000 to
5,000,000 g/mol .
[0071] The LMW or MMW is produced in the first reactor in the
absence of comonomer in order to obtain a homopolymer.
[0072] 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
polyethylene or MMW polyethylene having density >0.965
g/cm.sup.3 and MI.sub.2 in the range of 10 to 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 70-90.degree. C., preferably 80-85.degree. C. Hydrogen
is fed to the first reactor so as to control the molecular weight
of the polyethylene. 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 0.1-95% by mole, preferably 0.1-90% by mol.
[0073] 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 and
most preferred 98.0 to 99.1% by weight.
[0074] 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.
[0075] The polymerization conditions of the second reactor are
notably different from that of the first reactor. The temperature
in the second reactor ranges from 65-90.degree. C., preferably
68-80.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, ore preferably 150-400 kPa.
[0076] 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.
[0077] 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 polyethylene or MMW polyethylene obtained
from the first reactor. The .alpha.-olefin comonomer that is useful
for the copolymerization includes C.sub.4-12, preferably 1-butene
and 1-hexene.
[0078] After the polymerization in the second reactor, the slurry
obtained is transferred to the third reactor to continue the
polymerization.
[0079] The HMW2 is produced in the third reactor by copolymerizing
ethylene with optionally .alpha.-olefin comonomer at the presence
of LMW or MMW 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.
[0080] 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. Polymerization
pressure in the third reactor ranges from 150-900 kPa, preferably
150-600 kPa, and is controlled by the addition of inert gas such as
nitrogen.
[0081] The amount of LMW or MMW present in the multimodal
polyethylene composition of the present invention is 30-65 parts by
weight. HMW1 present in the polyethylene of the present invention
is 5-40 p by weight and HMW2 present in the polyethylene of the
present invention is 10-60 parts by weight. It is possible that
HMW1>HMW2 or HMW1<HMW2 depending on the polymerization
conditions employed.
[0082] The final (free-flow) multimodal polyethylene composition is
obtained by separating hexane from the slurry discharged from the
third reactor.
[0083] The resultant polyethylene powder may then be mixed with
antioxidants and optionally additives before being extruded and
granulated into pellets.
DEFINITION AND MEASUREMENT METHODS
[0084] Melt flow index: Melt flow index (MI) of polymer 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 (MI.sub.2), 5 kg (MI.sub.5) and
21.6 kg (MI.sub.21).
[0085] 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.
[0086] 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 in g/mol
were analysed by gel permeation chromatography (GPC).
Polydispersity index was calculated by Mw/Mn. 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 IR5, 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.
[0087] Intrinsic Viscosity (IV): The test method covers the
determination of the dilute solution viscosity of polyethylene at
135.degree. C. or an 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 according to ASTM D 2515.
[0088] Comonomer content: The comonomer content was determined by
high resolution .sup.13C-NMR. 13C-NMR spectra were recorded by 500
MHz ASCEND.TM., Bruker, with cryogenic 10 mm probe. TCB was used as
major solvent with TCE-d2 as locking agent in the ratio of 4:1 by
volume. The NMR experiments were carried on at 120.degree. C., and
the inverse gate 13C (zgig) of pulse program with 90.degree. for
pulse angle were used. The delay time (D1) was set to 10 seconds
for full-spin recovery.
[0089] 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.
[0090] Shear Thinning Index (SHI): It gives an indication as
molecular weight distribution of material. A common measurement
runs viscosity at 190.degree. C. using Dynamic rheometer using 25
mm diameter plate and plate geometry 1 mm gap. SHI (1/100) was
calculated by viscosities at a constant shear stress at 1 kPa and
100 kPa. Generally materials have high SHI means better flowability
of material.
[0091] Viscosity at angular frequency 0.01 [1s] (.eta..sub.0.01):
Rheological parameters are determined by using controlled stress
rheometer model MCR-301 from Anton-Paar. The geometry is
Plate-Plate 25 mm diameter at the measurement gap 1 mm. The dynamic
oscillatory shear performs at angular frequency (.omega.) 0.01-600
rad/s at 190.degree. C. under nitrogen atmosphere. The sample
preparation is performed to circular disk 25 mm by compression
molding at 190.degree. C. Viscosity at 0.01 [1/s] (.eta..sub.0.01)
is obtained from complex viscosity at a specific shear rate 0.01
[1/s].
[0092] Isothermal Crystallization Half-Time (ICHT) and Crystal
growth rate constant (K): The isothermal crystallization half-time
at 123.degree. C. was measured by differential scanning calorimetry
(DSC) to determine the crystallization rate of the sample. The
sample was heated from 30.degree. C. to 200.degree. C. at a heating
rate of 50.degree. C./min and held for 5 min. Then, it was cooled
down to 123.degree. C. at cooling rate 50.degree. C./min and held
for 60 min. The crystal growth rate constant (K) and n were
determined by fitting the data of logarithmic expression of Avrami
equation.
[0093] Spiral flow length: Spiral flow test was carried out by
Fanuc Roboshot S2000i 100B injection molding machine (Screw
diameter 36 mm) with spiral mould at temperature 220.degree. C. and
constant injection pressure 1000 bar. The thickness of specimen is
1 mm. After conditioning sample for 24 hr, the spiral flow length
(mm) was measured.
[0094] Charpy impact strength: The compressed specimen according to
ISO 293 was prepared. Charpy impact strength is determined
according to ISO179 at 23.degree. C. and shown in the unit
kJ/m.sup.2.
[0095] Flexural Modulus: The compressed specimen according to ISO
1872-2 was prepared and performed the test follow ISO 178. The
flexural tests were done using a universal testing machine equipped
with three point bending fixture.
[0096] Full Notch Creep Test (FNCT): The full notch creep test
according to ISO 16770 was the preferred way of measuring the
stress crack resistance of a polymer at constant stress of 6 MPa at
50.degree. C. in 2% Arkopal solution (N=100). The samples were cut
from 6 mm thickness plaques by compression molding follow ISO
1872-2. The specimen (Type C) dimension was 90 mm.times.6
mm.times.6 mm with notch depth of 1 mm. The failure time is
recorded in hr.
EXPERIMENTAL AND EXAMPLES
[0097] 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 commercial
available Ziegler-Natta catalyst was used. The catalyst preparation
is for example described in Hungary patent application 0800771r.
The polymerization in first reactor was carried out to make a low
molecular weight polyethylene or medium 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
(abs) 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 (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.
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 (abs). 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 (abs). 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 (abs). 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 (abs). 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 (abs). 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.
Example 4 (E4)
[0105] A homopolymer was produced in the first reactor to obtain a
medium molecular weight portion before transferring such polymer to
hydrogen removal unit. The hydrogen removal unit was operated at
pressure of 105 kPa (abs) to separate the unreacted mixture from
the polymer. The residual of hydrogen from first reactor was
removed to an extend of 98.9% by weight. The medium molecular
weight polymer was then transferred to the second reactor to
produce a first ultra high molecular weight polymer. Finally,
produced polymer from second reactor was transferred to the third
reactor to create a second ultra high molecular weight polymer. The
second and third reactors are operated under hydrogen depleted
polyethylene polymerization. The processable in-situ ultra high
molecular weight polyethylene is produced by this process operation
leads to an excellent improvement of Charpy impact strength while
still maintained the flexural modulus. The conventional UHMWPE with
very high IV was known that it was unable to measured MI.sub.21.
The inventive example E4 with IV of 9 dl/g shows good melt flow
ability beyond the known art.
Example 6 (E6)
[0106] 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.
[0107] Screw Cap-Related Examples
[0108] The examples of polymer compositions for screw cap-related
this invention regarding the multimodal polyethylenes were
polymerized as shown in Table 1, 2, 3 and 4.
Comparative Example 4 (CE4)
[0109] 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.
Inventive Example 5 (E5)
[0110] 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.
[0111] The properties of the invention from inventive examples E5
were compared to the properties of comparative examples CE4.
Comparative Example 5 (CE5)
[0112] Comparative example 5 (CE5) is a bimodal polyethylene
produced from Ziegler-Natta catalyst. The weight ratio between the
ethylene homopolymer and the ethylene copolymer is in the range of
45:55 to 55:45. A polymer composition comprises a comonomer in an
amount of at least 0.40 mol %.
Comparative Example 6 (CE6)
[0113] Comparative example 6 (CE6) is a commercial multimodal high
density polyethylene Hostalen.RTM. ACP5331 UVB plus.
Inventive Example 7 and 8 (E7 and E8)
[0114] Multimodal polyethylene compositions of inventive examples 7
and 8(E7 and E8) were produced according to the inventive process
with the polymerization condition as shown in Table 3. The
different weight fraction in each reactor was defined and 1-butene
was applied as comonomer in the 2.sup.nd and 3.sup.rd reactor
components. The properties of the invention from inventive examples
7 and 8 (E7 and E7) were compared to the properties of comparative
examples 5 and 6 (CE5 and CE6).
[0115] The characteristics and properties of these multimodal
polyethylenes are shown in Table 4. The comparisons between the
multimodal polymers, but different polymerization process were
illustrated. Surprisingly, the multimodal polyethylene according to
this invention which contain higher Mz and higher shear thinning
shows a significant improvement in processability and stiffness of
inventive examples 7 and 8 (E7 and E8) compare to comparative
examples 5 and 6 (CE5, CE6) and Inventive examples 5 (E5) compare
to comparative example 4 (CE4), respectively.
[0116] The better processability can be investigated in term of
both faster cycle time and higher flowability. Faster cycle time
was determined by the lower crystallization haft time (ICHT) and
higher crystal growth rate (K). The inventive examples 5, 7, and 8
(E5, E7 and E8) show lower ICHT and higher crystal growth rate (K)
than comparative examples 4, 5 and 6 (CE4, CE5 and CE6). It is
supposed that the ultra high molecular weight produced in the
second component following the inventive process can act as a stem
for easier nucleation resulting in faster crystallization rate. The
flowability is normally determined by spiral flow length at
temperature 220.degree. C. The spiral flow length of inventive
example E5 has higher than comparative example 4 (CE4), and
inventive examples 7 and 8 (E7 and E8) have higher than comparative
examples 5 and 6 (CE5 and CE6), even inventive examples have lower
MI than comparative examples.
[0117] The improvement of stiffness compared to CE5 and CE6 were
also investigated. The multimodal polyethylene composition of these
invention examples 7 and 8 (E7 and E8) have better flexural modulus
than comparative examples 5 and 6 (CE5 and CE6) and also the
invention example 5 (E5) has higher flexural modulus than
comparative examples (CE4). Because of the multimodal polyethylene
according to this invention contain higher Mz shows a significant
improvement in stiffness.
[0118] Moreover, the multimodal polyethylene according to this
invention (E8) still has better stress cracking resistance as
measured by FNCT compare to CE5 and CE6. Also the inventive example
7 (E7) showed equivalent FNCT to the bimodal polyethylene (CE5)
even at higher density. This indicated that the inventive
multimodal polyethylene composition provide better processability
and higher stiffness with good balance to stress crack resistance
beyond prior The invention enhanced significantly improvement of
properties for screw cap and closure.
TABLE-US-00001 TABLE 1 Polymerization conditions of multimodal
polyethylenes for Screw cap-related invention in lab reactor 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.A means percent by weight of
Polymer in the first reactor W.sub.B means percent by weight of
Polymer in the second reactor W.sub.C means percent by weight of
Polymer in the third reactor
TABLE-US-00002 TABLE 2 CE1 E1 E2 CE2 CE3 E3 Powder MI.sub.5, g/10
min 0.474 0.372 0.240 0.242 0.275 0.200 MI.sub.21, g/10 min 13.83
10.80 7.38 7.23 6.40 4.81 Density, g/cm.sup.3 0.9565 0.9578 0.9555
0.9567 0.9441 0.9438 IV, dl/g -- -- -- -- -- -- Mw 276,413 244,279
291,295 319,487 252,160 306,468 Mn 8,877 8,724 8,843 8,472 8,016
7,637 Mz 2,788,607 2,370,678 3,401,041 4,135,007 1,638,224
2,643,953 PDI 31 28 33 38 31 40 Pellet MI.sub.5, g/10 min 0.436
0.410 0.232 0.199 0.298 0.195 MI.sub.21, g/10 min 14.46 11.68 7.876
6.696 7.485 4.604 Density, g/cm.sup.3 0.9577 0.9574 0.9568 0.9566
0.9442 0.9440 IV, dl/g 2.97 3.03 3.52 3.64 3.12 3.37 %
Crystalinity, % 64.70 67.24 64.78 66.16 57.49 54.05 Charpy,
23.degree. C., 23.5 29.9 35.3 30.5 47.9 50.9 kJ/m.sup.2 Flexural
modulus, 1,130 1,210 1,123 1,123 727 785 MPa E4 CE4 E5 E6 Powder
MI.sub.5, g/10 min -- 54.80 48.07 NA MI.sub.21, g/10 min 0.145 641
653 NA Density, g/cm.sup.3 0.9534 0.9606 0.9590 0.9409 IV, dl/g
9.00 1.07 1.06 23 Mw 868,813 77,334 91,752 1,269,336 Mn 24,107
5,400 6,035 23,450 Mz 5,112,060 667,276 1,027,956 5,262,195 PDI 36
14 15 54.13 Pellet MI.sub.5, g/10 min -- 60.62 55.47 -- MI.sub.21,
g/10 min -- 713.1 752.2 -- Density, g/cm.sup.3 -- 0.9608 0.9594 --
IV, dl/g 9.00 1.0 1.1 23 % Crystallinity, % 68.23 69.52 65.64 58.20
Charpy, 23.degree. C., 84.4 1.5 1.8 85.41 kJ/m.sup.2 Flexural
modulus, 1,109 1,147 1,196 890 MPa
TABLE-US-00003 TABLE 3 Polymerization conditions of multimodal
polyethylenes for Screw cap-related invention from pilot scale E7
E8 Process Parameters Unit (Inventive) (Inventive) 1.sup.st Reactor
Split ratio % 58-62 48-52 Temperature (.degree. C.) 81-85 81-85
Pressure Bar 5.5-6.0 4.5-5.0 Hexane flow rate L/h 90.0 63.0
Ethylene flow rate L/h 2310.5 1918.0 Hydrogen flow rate NL/h 188.1
104.336 Catalyst flow rate g/h 3.2 3.1 2.sup.nd Reactor Split ratio
% 9-10 12-18 Temperature (.degree. C.) 68-70 68-70 Pressure Bar
1.5-3.0 1.5-3.0 Hexane flow rate L/h 176.2 148.7 Ethylene flow rate
L/h 1051.0 1354 Hydrogen flow rate NL/h 0 0 Comonomer/Ethylene Feed
-- 0.0037 0.00239 H.sub.2 removal 98.89 98.99 Flash pressure 0.054
0.056 Comonomer type -- 1-Butene 1-Butene 3.sup.rd Reactor Split
ratio % 28-33 32-38 Temperature (.degree. C.) 70-75 70-75 Pressure
Bar 1.5-3.0 1.5-3.0 Hexane flow rate L/h 191.6 164.0 Ethylene flow
rate L/h 1980.2 1969.3 Hydrogen flow rate NL/h 39.8 0
Comonomer/Ethylene Feed -- 0.002 0.00849 Production rate kg/h 30.0
25.0 Comonomer type -- 1-Butene 1-Butene
TABLE-US-00004 TABLE 4 Polymer compositions and properties of
multimodal polyethylenees (pellet) for Screw cap-related invention
E5 CE4 E7 E8 CE5 CE6 Properties Inventive Comparative Inventive
Inventive Comparative Comparative MI.sub.2 [g/10 min] 14.6 16.8 0.8
0.5 0.9 2.0 MI.sub.5 [g/10 min] 55.47 60.62 3.16 2.12 3.61 6.54
Density [g/cm.sup.3] 0.9594 0.9608 0.9603 0.9582 0.9584 0.9574 IV
[cm.sup.3/g] 1.10 1.01 2.01 2.39 1.98 1.12 Mn [g/mol] 6,065 7,036
9,600 9,393 8,847 13,459 Mw [g/mol] 85,150 81,171 174,712 183,319
157,896 119,848 Mz [g/mol] 713,636 677,966 1,359,161 1,436,240
1,058,549 765,341 PDI 14 12 18 20 18 9 Comonomer content 0.83 0.67
0.43 0.52 0.50 0.36 [% mol] ICHT @ 123.degree. C. [min] 3.1 3.2 4.1
6.1 8.2 8.7 Crystal growth rate 1.68E-05 1.19E-05 2.7E-06 1.21E-06
1.4E-07 5.8E-07 constant (K) Tm [.degree. C.] 130 130 130 129 130
130 Tc [.degree. C.] 118 118 119 118 117 117 % Crystallinity 66 66
73 66 69 67 SHI (1/100) 12.2 7.0 23.4 26.1 11.4 3.9 .eta..sub.0.01
[Pa s] 2,176 1,283 27,870 38,907 20,343 6,873 Spiral flow length @
350 340 293 282 266 238 220.degree. C. [mm] Flexural modulus 1,196
1,147 1,251 1,258 1,157 1,141 (ISO 178) [MPa] FNCT (ISO 16770) N/A
N/A 17 22 18 8 @ 50.degree. C., 6 MPa, 2% wt Arkopal [hr]
* * * * *