U.S. patent application number 09/809198 was filed with the patent office on 2001-08-16 for process for the manufacture of a composition comprising ethylene polymers.
This patent application is currently assigned to SOLVAY POLYOLEFINS EUROPE-BELGIUM. Invention is credited to Moens, Bruno, Promel, Michel.
Application Number | 20010014724 09/809198 |
Document ID | / |
Family ID | 3890693 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014724 |
Kind Code |
A1 |
Promel, Michel ; et
al. |
August 16, 2001 |
Process for the manufacture of a composition comprising ethylene
polymers
Abstract
Process for the manufacture of a composition comprising ethylene
polymers, in at least two polymerization reactors connected in
series, according to which, in a first reactor, from 30 to 70% by
weight with respect to the total weight of the composition of an
ethylene homopolymer (A) having a melt flow index MI.sub.2 of 5 to
1000 g/10 min is formed and, in a subsequent reactor, from 30 to
70% by weight with respect to the total weight of the composition
of a copolymer of ethylene and of hexene (B) having a melt flow
index MI.sub.5 of 0.01 to 2 g/10 min is formed. The compositions
obtained by this process exhibit a good compromise between the
processing properties and the mechanical properties, which renders
them capable of being used in the manufacture of articles shaped by
extrusion and extrusion blow-molding, such as films and pipes.
Inventors: |
Promel, Michel; (League
City, TX) ; Moens, Bruno; (Brussels, BE) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
SOLVAY POLYOLEFINS
EUROPE-BELGIUM
44, Rue du Prince Albert, B-1050
Brussels
BE
B-1050
|
Family ID: |
3890693 |
Appl. No.: |
09/809198 |
Filed: |
March 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09809198 |
Mar 16, 2001 |
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09136426 |
Aug 20, 1998 |
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6225421 |
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Current U.S.
Class: |
526/65 ; 526/114;
526/351; 526/75; 526/95 |
Current CPC
Class: |
F16L 9/127 20130101;
C08F 210/16 20130101; C08F 10/02 20130101; C08L 23/04 20130101;
C08L 23/06 20130101; C08F 10/02 20130101; C08F 2/001 20130101; C08L
23/04 20130101; C08L 2666/04 20130101; C08L 23/06 20130101; C08L
2666/04 20130101; C08F 210/16 20130101; C08F 210/08 20130101; C08F
2500/12 20130101; C08F 2500/07 20130101; C08F 2500/13 20130101;
C08F 2500/26 20130101; C08F 210/16 20130101; C08F 210/14 20130101;
C08F 2500/12 20130101; C08F 2500/07 20130101; C08F 2500/13
20130101; C08F 2500/26 20130101; C08F 10/02 20130101; C08F 4/6555
20130101 |
Class at
Publication: |
526/65 ; 526/75;
526/95; 526/114; 526/351 |
International
Class: |
C08F 004/44 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 1997 |
BE |
9700694 |
Claims
1. Process for the manufacture of a composition comprising ethylene
polymers, in at least two polymerization reactors connected in
series, according to which: in a first reactor, ethylene is
polymerized in suspension in a mixture comprising a diluent,
hydrogen, a catalyst based on a transition metal and a cocatalyst,
so as to form from 30 to 70% by weight with respect to the total
weight of the composition of an ethylene homopolymer (A) having a
melt flow index MI.sub.2 of 5 to 1000 g/10 min, the said mixture,
additionally comprising the homopolymer (A), is withdrawn from the
said reactor and is subjected to a reduction in pressure, so as to
degas at least a portion of the hydrogen, then the said at least
partially degassed mixture comprising the homopolymer (A), as well
as ethylene and 1-hexene and, optionally, at least one other
.alpha.-olefin are introduced into a subsequent reactor and the
suspension polymerization is carried out therein in order to form
from 30 to 70% by weight, with respect to the total weight of the
composition, of a copolymer of ethylene and of hexene (B) having a
melt flow index MI.sub.5 of 0.01 to 2 g/10 min.
2. Process according to claim 1, characterized in that the hexene
content in the copolymer (B) is at least 0.4% and at most 10% by
weight.
3. Process according to claim 1, characterized in that the
copolymer (B) is composed essentially of monomer units derived from
ethylene and from 1-hexene.
4. Process according to claim 1, characterized in that the
homopolymer (A) exhibits an MI.sub.2 of at least 50 and not
exceeding 700 g/10 min and that the copolymer (B) exhibits an
MI.sub.5 of at least 0.015 and not exceeding 0.1 g/10 min.
5. Process according to claim 1, characterized in that the diluent
is isobutane.
6. Process according to claim 1, characterized in that the amount
of hydrogen introduced into the first reactor is adjusted so as to
obtain, in the diluent, a molar ratio of hydrogen to ethylene of
0.05 to 1.
7. Process according to claim 1, characterized in that the ratio of
the concentration of hydrogen in the first reactor to the
concentration in the subsequent polymerization reactor is at least
20.
8. Process according to claim 1, characterized in that the amount
of 1-hexene introduced into the subsequent polymerization reactor
is such that, in this reactor, the hexene/ethylene molar ratio in
the diluent is from 0.05 to 3.
9. Process according to claim 1, characterized in that the catalyst
comprises from 10 to 30% by weight of transition metal, from 0.5 to
20% by weight of magnesium, from 20 to 60% by weight of a halogen
and from 0.1 to 10% by weight of aluminium.
10. Composition comprising ethylene polymers comprising from 30 to
70% by weight with respect to the total weight of the composition
of an ethylene homopolymer (A) having a melt flow index MI.sub.2 of
5 to 1000 g/10 min and from 30 to 70% by weight with respect to the
total weight of the composition of a copolymer of ethylene and of
hexene (B) having a melt flow index MI.sub.5 of 0.01 to 2 g/10 min
capable of being obtained by the process according to claim 1.
11. Composition according to claim 10, characterized in that it
exhibits an MI.sub.5 of at least 0.07 and not exceeding 10 g/10 min
and an HLMI/MI.sub.5 ratio of greater than 10.
12. Use of a composition according to claim 10 for the manufacture
of films or of pipes.
13. Pipes obtained by extrusion of a composition according to claim
10.
Description
[0001] The present invention relates to a process for the
manufacture of a composition comprising ethylene polymers,
comprising a homopolymer and a copolymer of ethylene, which makes
use of several polymerization reactors connected in series. It also
relates to the compositions comprising ethylene polymers capable of
being obtained by this process and to their use in the manufacture
of films and pipes.
[0002] Patent Application EP-A-0,603,935 (Solvay) discloses a
process for the preparation of a composition comprising ethylene
polymers comprising an ethylene polymer with a high melt flow index
(MI.sub.2 of 5 to 1000 g/10 min) and an ethylene polymer with a low
melt flow index (MI.sub.5 of 0.01 to 2 g/10 min) in at least two
reactors arranged in series, the ratio by weight of these polymers
being equal to (30 to 70):(70 to 30). This patent application more
specifically discloses a composition, prepared in suspension in
hexane, comprising an ethylene homopolymer having an MI.sub.2 of
168 g/10 min and a copolymer of ethylene and of butene having an
MI.sub.5 of 0.21 g/10 min.
[0003] Patent Application EP-A-0,580,930 discloses a process for
the preparation of a composition comprising ethylene polymers in
two loop reactors in the liquid phase in which, in a first reactor,
ethylene and an alpha-olefin, such as hexene, are introduced, so as
to prepare a copolymer of ethylene and of hexene having a melt flow
index HLMI varying from 0.01 to 5 g/10 min, and then the mixture
resulting from the first reactor is introduced into a second
reactor fed with ethylene, so as to obtain a polymer of ethylene
having an HLMI of greater than 5 g/10 min. As the mixture resulting
from the first reactor still comprises unpolymerized hexene, the
polymer formed in the second reactor is also a copolymer of
ethylene and of hexene.
[0004] The compositions resulting from these processes generally
exhibit processing and mechanical properties which render them
suitable for being used in the manufacture of various shaped
articles.
[0005] The aim of the present invention is to provide a process for
the manufacture of compositions comprising ethylene polymers
exhibiting a better compromise between the processing properties
and the mechanical properties in comparison with the compositions
obtained by the known processes of the state of the art.
[0006] The invention consequently relates to a process for the
manufacture of a composition comprising ethylene polymers, in at
least two polymerization reactors connected in series, according to
which:
[0007] in a first reactor, ethylene is polymerized in suspension in
a mixture comprising a diluent, hydrogen, a catalyst based on a
transition metal and a cocatalyst, so as to form from 30 to 70% by
weight with respect to the total weight of the composition of an
ethylene homopolymer (A) having a melt flow index MI.sub.2 of 5 to
1000 g/10 min,
[0008] the said mixture, additionally comprising the homopolymer
(A), is withdrawn from the said reactor and is subjected to a
reduction in pressure, so as to degas at least a portion of the
hydrogen, then
[0009] the said at least partially degassed mixture comprising the
homopolymer (A), as well as ethylene and 1-hexene and, optionally,
at least one other .alpha.-olefin, are introduced into a subsequent
reactor and the suspension polymerization is carried out therein in
order to form from 30 to 70% by weight, with respect to the total
weight of the composition, of a copolymer of ethylene and of hexene
(B) having a melt flow index MI.sub.5 of 0.01 to 2 g/10 min.
[0010] For the purposes of the present invention, ethylene
homopolymer (A) is understood to denote an ethylene polymer
composed essentially of monomer units derived from ethylene and
substantially devoid of monomer units derived from other olefins.
Copolymer of ethylene and of hexene (3) is understood to denote a
copolymer comprising monomer units derived from ethylene and
monomer units derived from 1-hexene and, optionally, from at least
one other .alpha.-olefin. The other .alpha.-olefin can be selected
from olefinically unsaturated monomers comprising from 3 to 8
carbon atoms (with the exclusion of 1-hexene), such as, for
example, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 3- and
4-methyl-1-pentenes and 1-octene. Preferred .alpha.-olefins are
propylene, 1-butene and 1-octene and more particularly still
1-butene. The copolymer (B) according to the invention generally
comprises at least 90%, in particular at least 94%, by weight of
monomer units derived from ethylene. It preferably comprises at
least 96% by weight of monomer units derived from ethylene. The
content of monomer units derived from 1-hexene in the copolymer
(B), hereinafter referred to as hexene content, is generally at
least 0.4% by weight, in particular at least 0.6% by weight, values
of at least 1% by weight being favourable. The hexene content of
the copolymer (B) is usually at most 10% by weight, preferably at
most 6% by weight. A hexene content which does not exceed 4% by
weight is particularly preferred. For the purposes of the present
invention, the hexene content of the copolymer (B) is measured by
.sup.13C NMR according to the method described in J. C. Randall,
JMS-Rev. Macromol. Chem. Phys., C29(2&3), p. 201-317 (1989),
that is to say that the content of units derived from hexene is
calculated from the measurements of the integrals of the lines
characteristic of hexene (23.4, 34.9 and 38.1 ppm), in comparison
with the integral of the line characteristic of the units derived
from ethylene (30 ppm). A copolymer (B) composed essentially of
monomer units derived from ethylene and from 1-hexene is
particularly preferred.
[0011] For the purposes of the present invention, melt flow index
MI.sub.2, respectively MI.sub.5, is understood to denote the melt
flow indices measured according to ASTM Standard D 1238 (1986) at a
temperature of 190.degree. C. under a load of 2.16 kg, respectively
5 kg. Furthermore, melt flow index HLMI is understood to denote the
melt flow index measured according to ASTM Standard D 1238 (1986)
at a temperature of 190.degree. C. under a load of 21.6 kg.
[0012] The homopolymer (A) according to the invention preferably
exhibits an MI.sub.2 of at least 50, very particularly of at least
90, g/10 min. The MI.sub.2 of the homopolymer (A) preferably does
not exceed 700 g/10 min. The homopolymer (A) advantageously
exhibits an HLMI of at least 100 g/10 min.
[0013] The homopolymer (A) advantageously exhibits an intrinsic
viscosity .eta..sub.A (measured in tetrahydronaphthalene at
160.degree. C.) of at least 0.50 dl/g, preferably of at least 0.58
dl/g. Its intrinsic viscosity generally does not exceed 1.50 dl/g,
preferably it does not exceed 1.00 dl/g. A homopolymer for which
.eta..sub.A does not exceed 0.86 dl/g is particularly
preferred.
[0014] The melt flow index MI.sub.5 of the copolymer (B) according
to the invention is preferably at least 0.015 g/10 min. It
preferably does not exceed 0.1 g/10 min. The copolymer (B)
advantageously exhibits an HLMI of at least 0.1 g/10 min which,
furthermore, does not exceed 20 g/10 min.
[0015] The copolymer (B) generally exhibits an intrinsic viscosity
.eta..sub.B (measured in tetrahydronaphthalene at 160.degree. C.)
of at least 2.20 dl/g. Its intrinsic viscosity .eta..sub.B
generally does not exceed 6.30 dl/g, preferably not 5.90 dl/g. A
copolymer (B) for which the intrinsic viscosity does not exceed
4.00 dl/g is particularly preferred.
[0016] Suspension polymerization is understood to denote the
polymerization in a diluent which is in the liquid state under the
polymerization conditions (temperature, pressure) used, these
polymerization conditions or the diluent being such that at least
50% by weight (preferably at least 70%) of the polymer formed is
insoluble in the said diluent.
[0017] The diluent used in the polymerization process according to
the invention is usually a hydrocarbon-comprising diluent which is
inert with respect to the catalyst, the cocatalyst and the polymer
formed, such as, for example, a linear or branched alkane or a
cycloalkane having from 3 to 8 carbon atoms. The diluent which has
given the best results is isobutane. One advantage of the use of
isobutane lies in particular in its ready recycling. This is
because the use of isobutane makes it possible to recycle the
diluent recovered at the end of the process according to the
invention in the first reactor without having to carry out
exhaustive purification in order to remove the residual hexene.
This is because, as the boiling temperatures of isobutane and of
hexene are far apart, their separation can be carried out by
distillation.
[0018] The amount of ethylene introduced into the first
polymerization reactor and into the subsequent polymerization
reactor is generally adjusted so as to obtain a concentration of
ethylene in the diluent of 5 to 50 g of ethylene per kg of
diluent.
[0019] The amount of hydrogen introduced into the first reactor is
generally adjusted so as to obtain, in the diluent, a molar ratio
of hydrogen to ethylene of 0.05 to 1. In the first reactor, this
molar ratio is preferably at least 0.1. A hydrogen/ethylene molar
ratio which does not exceed 0.6 is particularly preferred.
[0020] The mixture withdrawn from the first reactor, additionally
comprising the homopolymer (A), is subjected to a reduction in
pressure so as to remove (degas) at least a portion of the
hydrogen. The reduction in pressure is advantageously carried out
at a temperature of less than or equal to the polymerization
temperature in the first reactor. The temperature at which the
reduction in pressure is carried out is usually greater than
20.degree. C.; it is preferably at least 40.degree. C. The pressure
at which the reduction in pressure is carried out is less than the
pressure in the first reactor. The pressure-reduction pressure is
preferably less than 1.5 MPa. The pressure-reduction pressure is
usually at least 0.1 MPa. The amount of hydrogen still present in
the at least partially degassed mixture is generally less than 1%
by weight of the amount of hydrogen initially present in the
mixture withdrawn from the first polymerization reactor; this
amount is preferably less than 0.5%. The amount of hydrogen present
in the partially degassed mixture introduced into the subsequent
polymerization reactor is consequently low, or even zero. The
subsequent reactor is preferably also fed with hydrogen. The amount
of hydrogen introduced into the subsequent reactor is generally
adjusted so as to obtain, in the diluent, a molar ratio of hydrogen
to ethylene of 0.001 to 0.1. This molar ratio is preferably at
least 0.004 in this subsequent reactor. It preferably does not
exceed 0.05. In the process according to the invention, the ratio
of the concentration of hydrogen in the diluent in the first
reactor to the concentration in the subsequent polymerization
reactor is usually at least 20, preferably at least 30. A ratio of
concentrations of at least 40 is particularly preferred. This ratio
usually does not exceed 300, preferably not 200.
[0021] The amount of 1-hexene introduced into the subsequent
polymerization reactor is such that, in this reactor, the
hexene/ethylene molar ratio in the diluent is at least 0.05,
preferably at least 0.1. The amount of hexene introduced into the
subsequent reactor is such that the hexene/ethylene molar ratio
does not exceed 3, preferably not 2.8. In the process according to
the invention, the first reactor is not fed with hexene. It is
essential that the first reactor is essentially devoid of 1-hexene.
Consequently, the diluent introduced into the first reactor, which
can be recycled diluent, must be highly depleted in hexene. The
diluent introduced into the first reactor preferably contains less
than 1000 ppm of hexene. In a particularly preferred way, the
diluent introduced into the first polymerization reactor is
essentially devoid of hexene.
[0022] The catalyst used in the process according to the invention
comprises at least one transition metal. Transition metal is
understood to denote a metal from Groups 4, 5 or 6 of the Periodic
Table of the Elements (CRC Handbook of Chemistry and Physics, 75th
edition, 1994-95). The transition metal is preferably titanium
and/or zirconium. Titanium is particularly preferred. In the
process according to the invention, use is preferably made of a
catalyst comprising, in addition to the transition metal,
magnesium. Good results have been obtained with catalysts
comprising:
[0023] from 10 to 30%, preferably from 15 to 20%, by weight of
transition metal,
[0024] from 0.5 to 20%, preferably from 1 to 10%, by weight of
magnesium,
[0025] from 20 to 60%, preferably from 30 to 50%, by weight of
halogen, such as chlorine,
[0026] from 0.1 to 10%, preferably from 0.5 to 5%, by weight of
aluminium;
[0027] the balance generally being composed of elements originating
from the products used in their manufacture, such as carbon,
hydrogen and oxygen. These catalysts are preferably obtained by
coprecipitation of at least one transition metal compound and of a
magnesium compound by means of a halogenated organoaluminium
compound. Such catalysts are known; they have been disclosed
particularly in patents U.S. Pat. No. 3,901,863, U.S. Pat. No.
4,929,200 and U.S. Pat. No. 4,617,360 (Solvay). In the process
according to the invention, the catalyst is preferably introduced
solely into the first polymerization reactor, that is to say that
fresh catalyst is not introduced into the subsequent polymerization
reactor. The amount of catalyst introduced into the first reactor
is generally adjusted so as to obtain an amount of at least 0.5 mg
of transition metal per liter of diluent. The amount of catalyst
usually does not exceed 100 mg of transition metal per liter of
diluent.
[0028] The cocatalyst employed in the process according to the
invention is preferably an organoaluminium compound.
Non-halogenated organoaluminium compounds of formula AlR.sub.3 in
which R represents an alkyl group having from 1 to 8 carbon atoms
are preferred. Triethylaluminium and triisobutylaluminium are
particularly preferred. The cocatalyst is introduced into the first
polymerization reactor. It is also possible to introduce fresh
cocatalyst into the subsequent reactor. The amount of cocatalyst
introduced into the first reactor is generally at least
0.1.times.10.sup.-3 mol per liter of diluent. It usually does not
exceed 5.times.10.sup.-3 mol per liter of diluent. If appropriate,
the amount of fresh cocatalyst introduced into the subsequent
reactor usually does not exceed 5.times.10.sup.-3 mol per liter of
diluent.
[0029] The polymerization temperature is generally from 20 to
130.degree. C. It is preferably at least 60.degree. C. It
preferably does not exceed 115.degree. C. The total pressure at
which the process according to the invention is carried out is
generally from 0.1 MPa to 10 MPa. In the first polymerization
reactor, the total pressure is preferably at least 2.5 MPa. It
preferably does not exceed 5 MPa. In the subsequent polymerization
reactor, the total pressure is preferably at least 1.3 MPa. It
preferably does not exceed 4.3 MPa.
[0030] The duration of polymerization in the first reactor and in
the subsequent reactor is generally at least 20 minutes, preferably
at least 30 minutes. The duration of polymerization usually does
not exceed 5 hours, preferably not 3 hours.
[0031] In order to carry out the process according to the
invention, it is possible to make use of a plant comprising more
than two polymerization reactors connected in series. It is
preferable to restrict the system to two polymerization reactors
connected in series, separated by a device which makes it possible
to carry out the reduction in pressure.
[0032] In the process according to the invention, a suspension
comprising a composition comprising from 30 to 70% by weight of the
homopolymer (A) and from 30 to 70% by weight of the copolymer (B)
is collected at the outlet of the subsequent polymerization
reactor. The composition comprising ethylene polymers can be
separated from the suspension by any known means. The suspension is
usually subjected to a reduction in pressure (final reduction in
pressure), so as to remove the diluent, the ethylene, the hexene
and, optionally, the hydrogen from the composition. According to an
alternative form of the process according to the invention and more
particularly when the diluent is isobutane, the gases exiting from
the first reduction in pressure (intermediate reduction in pressure
between the two polymerization reactors) and from the final
reduction in pressure are mixed, compressed and conveyed to a
distillation unit. This distillation unit is advantageously
composed of one or of two distillation columns in series. Ethylene
and hydrogen are withdrawn at the column top, a mixture of
isobutane and of hexene is withdrawn at the column bottom and
isobutane devoid of hexene is withdrawn from an intermediate plate.
The isobutane-hexene mixture is then recycled in the subsequent
polymerization reactor, whereas the isobutane devoid of hexene is
recycled in the first reactor.
[0033] The process according to the invention makes it possible to
obtain, with a good yield and with a low content of oligomers, a
composition comprising ethylene polymers exhibiting a very good
compromise between the mechanical properties and the processing
properties.
[0034] The invention consequently also relates to a composition
comprising ethylene polymers comprising from 30 to 70% by weight
with respect to the total weight of the composition of an ethylene
homopolymer (A) having a melt flow index MI.sub.2 of 5 to 1000 g/10
min and from 30 to 70% by weight with respect to the total weight
of the composition of a copolymer of ethylene and of hexene (B)
having a melt flow index MI.sub.5 of 0.01 to 2 g/10 min capable of
being obtained by the process according to the invention.
[0035] An essential characteristic of the composition according to
the invention is that it is composed of an intimate and homogeneous
mixture of the homopolymer (A) and of the copolymer (B), the
copolymer (B) being prepared in the presence of the homopolymer
(A). The composition is composed of particles comprising both
homopolymer (A) and copolymer (B).
[0036] The amount of homopolymer (A) in the composition comprising
ethylene polymers according to the invention is preferably at least
40%, more particularly at least 42%, by weight with respect to the
total weight of the composition. The amount of homopolymer (A)
preferably does not exceed 60% by weight. Good results have been
obtained with an amount of homopolymer (A) which does not exceed
58% by weight with respect to the total weight of the
composition.
[0037] The amount of copolymer (B) is preferably at least 40%, more
particularly at least 42%, by weight with respect to the total
weight of the composition. The amount of copolymer (B) preferably
does not exceed 60% by weight. Good results have been obtained with
an amount of copolymer (B) not exceeding 58% by weight with respect
to the total weight of the composition.
[0038] The composition according to the invention generally
comprises at least 95%, preferably at least 99%, by weight of the
combination of the homopolymer (A) and of the copolymer (B). A
composition composed solely of the homopolymer (A) and of the
copolymer (B) is very particularly preferred.
[0039] The composition according to the invention generally
exhibits a melt flow index MI.sub.5 of at least 0.07 g/10 min,
preferably of at least 0.1 g/10 min. The MI.sub.5 of the
composition usually does not exceed 10 g/10 min, preferably not 7
g/10 min. Compositions for which the MI.sub.5 does not exceed 1
g/10 min are particularly preferred. The composition according to
the invention advantageously exhibits an HLMI of at least 2 g/10
min which, furthermore, does not exceed 100 g/10 min.
[0040] An important characteristic of the composition according to
the invention is that it exhibits a broad or bimodal molecular
weight distribution. This characteristic is illustrated by the
ratio of the melt flow indices measured under various loads and
more specifically by the HLMI/MI.sub.5 ratio. The compositions
usually exhibit an HLMI/MI.sub.5 ratio of greater than 10,
preferably greater than 15. The HLMI/MI.sub.5 ratio usually does
not exceed 150. The HLMI/MI.sub.5 ratio preferably does not exceed
50. In the compositions according to the invention, the ratio of
the intrinsic viscosity of the copolymer (B)(.eta..sub.B) to that
of the homopolymer (A)(.eta..sub.A) is generally at least 1.5,
preferably at least 2. The .eta..sub.B/.eta..sub.A ratio generally
does not exceed 12, preferably not 10. A ratio which does not
exceed 7 is particularly preferred.
[0041] In addition, the composition according to the invention
usually exhibits a dynamic viscosity .mu..sub.2, measured at
190.degree. C. at a rate gradient of 100 s.sup.-1, of 10 to 30,000
dpa.multidot.s. In the context of the present invention, the
dynamic viscosity .mu..sub.2 is determined by extrusion of the
polymer at 190.degree. C., through a die with a length of 15 mm and
a diameter of 1 mm, at a constant rate corresponding to a rate
gradient of 100 s.sup.-1 and by measuring the force transmitted by
the piston during its descent. The dynamic viscosity .mu..sub.2 is
then calculated from the relationship .mu..sub.2=233.times.Fp, in
which Fp represents the mean force exerted by the piston, expressed
in daN, during the measuring time of 30 seconds. The cylinder and
the piston of the rheometer which are used for this measurement
correspond to the criteria of that used for the measurement of the
melt flow index according to ASTM Standard D 1238 (1986).
[0042] The compositions according to the invention generally
exhibit a standard density SD, measured according to ASTM Standard
D 792 (on a sample prepared according to ASTM Standard D 1928,
Procedure C), of at least 930 kg/m.sup.3. The compositions
preferably exhibit an SD of greater than 935 kg/m.sup.3.
Compositions which have given good results are those for which the
SD is at least equal to 940 kg/m.sup.3. The SD generally does not
exceed 965 kg/m.sup.3; it preferably does not exceed 960
kg/m.sup.3. Compositions for which the SD is less than 955
kg/m.sup.3 are particularly preferred. The SD of the homopolymer
(A) present in the compositions according to the invention is
generally at least 960 kg/m.sup.3, preferably at least 965
kg/m.sup.3. A homopolymer (A) having an SD of at least 970
kg/m.sup.3 is very particularly preferred. The SD of the copolymer
(B) is generally from 910 to 940 kg/m.sup.3. The SD of the
copolymer (B) is preferably at least 915 kg/m.sup.3. The SD of the
copolymer (B) preferably does not exceed 938 kg/m.sup.3, more
particularly not 935 kg/m.sup.3.
[0043] The compositions according to the invention are suitable for
being employed according to conventional processes for shaping
articles and more particularly according to extrusion and extrusion
blow-moulding processes.
[0044] The compositions according to the invention are well suited
to the manufacture of films. The invention consequently also
relates to the use of a composition according to the invention for
the manufacture of films, in particular by extrusion blow-moulding,
and to the films produced by use of the composition according to
the invention. The compositions according to the invention make it
possible to obtain films exhibiting both a beautiful surface
appearance (absence of defects known as shark skin) and a good
resistance to tearing and to perforation.
[0045] The compositions according to the invention are particularly
well suited to the extrusion of pipes, in particular pipes for the
transportation of pressurized fluids, such as water and gas. The
invention consequently also relates to the use of a composition
according to the invention for the manufacture of pipes. The
manufacture of pipes by extrusion of a composition according to the
invention is advantageously carried out on an extrusion line
comprising an extruder, a sizer and a haul-off device. The
extrusion is generally carried out on an extruder of the
single-screw type and at a temperature of 150 to 230.degree. C. The
sizing of the pipes can be carried out by the creation of a
negative pressure within the pipe and/or by the creation of an
excess pressure outside the pipe.
[0046] The pipes manufactured by means of the compositions
according to the invention are characterized by:
[0047] a good resistance to slow crack propagation or environmental
stress cracking resistance (ESCR), reflected by a failure time
generally of greater than 2000 hours, as measured at 80.degree. C.
on a notched pipe having a diameter of 110 mm and a thickness of 10
mm and under a stress of 4.6 MPa according to the method described
in ISO Standard FIDIS 13479 (1996),
[0048] a good resistance to rapid crack propagation (RCP),
reflected by a halt in crack propagation at an internal pressure
generally at least equal to 12 bar, as measured at 0.degree. C. on
a pipe with a diameter of 110 mm and a thickness of 10 mm according
to the S4 method described in ISO Standard F/DIS 13477 (1996),
and
[0049] a good creep resistance (.tau.), reflected by a failure time
generally of greater than 200 hours (measured at 20.degree. C. on a
pipe having a diameter of 50 mm and a thickness of 3 mm under a
circumferential stress of 12.4 MPa according to ISO Standard
1167).
[0050] The pipes manufactured by means of the compositions
according to the invention are characterized in particular by a
better compromise between the resistance to crack propagation (slow
crack propagation and rapid crack propagation) and the creep
resistance in comparison with the known compositions of the prior
art. The invention consequently also relates to the pipes, more
particularly the pipes for the transportation of pressurized
fluids, obtained by extrusion of a composition according to the
invention.
[0051] It goes without saying that, when they are used for the
molten shaping of articles, the compositions according to the
invention can be mixed with the usual processing additives for
polyolefins, such as stabilizers (antioxidizing agents and/or
anti-UV agents), antistatic agents and processing aids, as well as
pigments. The invention consequently also relates to a mixture
comprising a composition according to the invention and at least
one of the additives described above. The mixtures comprising at
least 95%, preferably at least 97%, by weight of a composition
according to the invention and at least one of the additives
described above are particularly preferred.
[0052] The examples which follow are intended to illustrate the
invention.
[0053] The meanings of the symbols used in these examples and the
units expressing the properties mentioned and the methods for
measuring these properties are explained below.
[0054] Q=content of comonomer in the copolymer (B), expressed as %
by weight. In the case of hexene, the content was measured as
described above; in the case of butene, the butene content was also
measured by NMR according to the method described above, but by
using the lines characteristic of butene (11.18 and 39.6 ppm).
[0055] QT=content of comonomer in the composition, expressed as %
by weight. This amount is measured as explained above for the
comonomer content of the copolymer (B).
[0056] Elmendorf=resistance to tearing measured according to ASTM
Standard D 1922-67; L denotes the measurement in the longitudinal
direction of the film, T denotes the measurement in the transverse
direction of the film.
[0057] DDT=resistance to perforation measured according to ISO
Standard 7765-1 (Dart Drop Test). The values have been expressed in
g per thickness of the film in .mu.m.
[0058] The other symbols have been explained in the
description.
[0059] The values labelled * have been calculated from the values
measured for the polymer manufactured in the reactor 1 and for the
composition resulting from the reactor 2.
EXAMPLES 1, 2, 4 AND 7
[0060] a) Preparation of the catalyst
[0061] Magnesium diethoxide was reacted with titanium tetrabutoxide
for 4 hours at 150.degree. C. in an amount such that the molar
ratio of titanium to magnesium is equal to 2. The reaction product
thus obtained was subsequently chlorinated and precipitated by
bringing the latter into contact with an ethylaluminium dichloride
solution for 90 minutes at 45.degree. C. The catalyst thus
obtained, collected from the suspension, comprises (% by
weight):
[0062] Ti: 17; Cl: 41; Al: 2; Mg: 5.
[0063] b) Preparation of the composition
[0064] The manufacture of a composition comprising ethylene
polymers was carried out in suspension in isobutane in two loop
reactors connected in series separated by a device which makes it
possible continuously to carry out the reduction in pressure.
[0065] Isobutane, ethylene, hydrogen, triethylaluminium and the
catalyst described in point a) were continuously introduced into
the first loop reactor and the polymerization of ethylene was
carried out in this mixture in order to form the homopolymer (A).
The said mixture, additionally comprising the homopolymer (A), was
continuously withdrawn from the said reactor and was subjected to a
reduction in pressure (60.degree. C., 0.7 MPa), so as to remove at
least a portion of the hydrogen. The resulting mixture, at least
partially degassed of hydrogen, was then continuously introduced
into a second polymerization reactor, at the same time as ethylene,
hexene, isobutane and hydrogen, and the polymerization of the
ethylene and of the hexene was carried out therein in order to form
the copolymer (B). The suspension comprising the composition
comprising ethylene polymers was continuously withdrawn from the
second reactor and this suspension was subjected to a final
reduction in pressure, so as to evaporate the isobutane and the
reactants present (ethylene, hexene and hydrogen) and to recover
the composition in the form of a powder, which was subjected to
drying in order to complete the degassing of the isobutane.
[0066] The other polymerization conditions are specified in Table
1.
[0067] The properties of the final compositions are presented in
Table 2.
[0068] c) Use of the composition for the preparation of films.
[0069] The compositions of the various examples were used for the
manufacture of films by extrusion blow-moulding through a die with
a diameter of 100 mm, with a blow ratio (ratio of the diameter of
the bubble to the diameter of the extrusion die) set at 4 and a
neck height of 6 times the diameter of the extrusion die. The
mechanical properties of the films obtained are presented in Table
2.
COMPARATIVE EXAMPLE 3R
[0070] A composition comprising ethylene polymers was manufactured
in the plant and with the catalyst and the cocatalyst described in
Example 1 but by using hexane as diluent and butene as comonomer in
the second reactor. The other conditions are specified in Table
1.
[0071] The properties of the composition obtained are presented in
Table 2.
[0072] Films were manufactured with this composition not in
accordance with the invention under the same conditions as for
Examples 1, 2, 4 and 7. The mechanical properties of the films
obtained are also presented in Table 2.
COMPARATIVE EXAMPLES 5R AND 6R
[0073] A composition comprising ethylene polymers was manufactured
in the plant and with the catalyst and the cocatalyst described in
Example 1 but by using hexene as comonomer in the two
polymerization reactors. The other conditions are specified in
Table 1.
[0074] The properties of the compositions obtained are presented in
Table 2.
[0075] Films were manufactured with these compositions not in
accordance with the invention under the same conditions as for
Examples 1, 2, 4 and 7. The mechanical properties of the films
obtained are also presented in Table 2.
1TABLE 1 EXAMPLE 1 2 3R 4 5R 6R 7 REACTOR 1 diluent isobutane
isobutane hexane isobutane isobutane isobutane isobutane C.sub.2
(g/kg) 9 9 14 10 9 8.8 10 comonomer -- -- -- -- 1-hexene 1-hexene
-- comon./C.sub.2 (mol/mol) 0 0 0 0 0.37 0.37 0 H.sub.2/C.sub.2
(mol/mol) 0.449 0.447 0.437 0.398 0.370 0.428 0.451 T (.degree. C.)
85 85 85 85 85 85 85 residence time (h) 2.20 2.20 2.20 2.20 2.20
2.20 2.20 REACTOR 2 diluent isobutane isobutane hexane isobutane
isobutane isobutane isobutane C.sub.2 (g/kg) 32 33 13 35 35 38 38
comonomer 1-hexene 1-hexene 1-butene 1-hexene 1-hexene 1-hexene
1-hexene comon./C.sub.2 (mol/mol) 1.52 1.41 0.82 2.72 1.76 1.27
1.64 H.sub.2/C.sub.2 (mol/mol) 0.010 0.011 0.009 0.016 0.017 0.021
0.009 T (.degree. C.) 85 85 85 85 85 83 85 residence time (h) 1.23
1.23 1.23 1.27 1.27 1.23 1.23
[0076]
2TABLE 2 EXAMPLE 1 2 3R 4 5R 6R 7 polym. manu- homopolymer
homopolymer homopolymer homopolymer C.sub.2-C.sub.6 C.sub.2-C.sub.6
homopolymer factured react. 1 copo copo weight (%) 45 45 45 55 55
45 45 MI.sub.2 (g/10 min) 99.8 97.6 101.5 116 121 133 102
.eta..sub.A (dl/g) 0.84 0.84 0.84 0.81 0.81 0.79 0.84 SD
(kg/m.sup.3) 968 969 969 968 962 961 967 polym. manu-
C.sub.2-C.sub.6 C.sub.2-C.sub.6 C.sub.2-C.sub.4 C.sub.2-C.sub.6
C.sub.2-C.sub.6 C.sub.2-C.sub.6 C.sub.2-C.sub.6 factured react. 2
copo copo copo copo copo copo copo weight (%) 55 55 55 45 45 55 55
MI.sub.5 * (g/10 min) 0.04 0.05 0.05 0.015 0.015 0.04 0.04 SD *
(kg/m.sup.3) 937.5 935 936.8 926.8 935.7 939.7 936.5 Q * (weight %)
2.84 2.62 2.33 5.07 3.28 2.37 3.05 composition resulting react. 2
QT (weight %) 1.56 1.44 1.28 2.28 1.86 1.62 1.68 MI.sub.5 (g/10
min) 0.31 0.35 0.37 0.23 0.22 0.28 0.30 HLMI (g/10 min) 5.7 6.1 7.4
6.6 6.7 5.7 5.7 SD (kg/m.sup.3) 951 950 951 949 950 949 950
.mu..sub.2 (dPa .multidot. s) 27,200 27,500 25,200 22,600 22,300
26,200 26,600 Film properties film thick. (.mu.m) 29 30 31 32 32 32
28 DDT (g/.mu.m) 8.4 7.6 6.7 10.8 9.5 8.5 10.0 Elmendorf L (g) 26
26 23 42 26 Elmendorf T (g) 355 305 312 379 288
[0077] Table 2 shows that the compositions comprising a homopolymer
and an ethylene/hexene copolymer which are obtained by the process
according to the invention exhibit better mechanical properties
(resistance to tearing and resistance to perforation) in comparison
with a composition comprising butene instead of hexene (Ex. 1 and 2
in comparison with Ex. 3R) and in comparison with compositions
comprising two hexene copolymers (Ex. 4 in comparison with Ex. 5R
and Ex. 7 in comparison with Ex. 6R).
EXAMPLES 8 AND 9R
[0078] These examples were carried out in the plant and with the
catalyst and the cocatalyst described in Example 1. The
polymerization conditions in the two reactors are summarized in
Table 3.
3 TABLE 3 EXAMPLE 8 9R diluent Isobutane Hexane REACTOR 1 C.sub.2
(g/kg) 14.9 10.7 H.sub.2/C.sub.2 0.46 0.38 T (.degree. C.) 85 85
residence time (h) 2.3 3.1 REACTOR 2 C.sub.2 (g/kg) 21.9 14.9
comonomer Hexene Butene comonom./C.sub.2 1.61 0.89 H.sub.2/C.sub.2
0.0048 0.0033 T (.degree. C.) 75 75 residence time (h) 1.3 1.93
[0079] The properties of the final compositions are summarized in
Table 4.
[0080] 997 parts of the composition obtained were mixed with 2
parts of an antioxidizing agent and 1 part of an anti-UV agent and
the mixture was granulated by extrusion in an extruder at a
temperature of 230.degree. C.
[0081] Pipes were then manufactured by extrusion of these granules
on an extruder of single-screw type at 200.degree. C. The
properties measured on these pipes are taken up in Table 4. It is
evident that the composition comprising an ethylene-hexene
copolymer (Ex. 8) exhibits a better compromise between the
resistance to crack propagation (resistance to slow crack
propagation and resistance to rapid crack propagation) and the
creep resistance in comparison with a composition comprising an
ethylene-butene copolymer (Ex. 9R).
4TABLE 4 EXAMPLE 8 9R Polymer manufactured in reactor 1 Homo homo
weight (%) 50.2 50.8 MI.sub.2 (g/10 min) 575 468 .eta..sub.A (dl/g)
0.59 0.62 SD (kg/m.sup.3) 973 972 Polymer manufactured in reactor 2
C.sub.2-C.sub.6 copo C.sub.2-C.sub.4 copo weight (%) 49.8 49.2
MI.sub.5 * (g/10 min) 0.03 0.025 SD * (kg/m.sup.3) 927.1 925.8 Q *
(weight %) 3 2.5 Composition resulting from react. 2 QT (weight %)
1.5 1.24 MI.sub.5 (g/10 min) 0.31 0.31 SD (kg/m.sup.3) 949.6 948.7
.mu..sub.2 (dPa .multidot. s) 22,100 20,500 ESCR (h) >7224 7344
RCP (bar) at 0.degree. C. >12 >12 at -15.degree. C. >12
>12 .tau. (h) 1780 235
EXAMPLE 10
[0082] This example was carried out in the plant of Example 1, with
a catalyst comprising, as % by weight, Ti: 5; Zr: 18; Cl: 45; Al:
5; Mg: 6 and triisobutylaluminium as cocatalyst. The polymerization
conditions in the two reactors are summarized in Table 5.
5 TABLE 5 EXAMPLE 10 Diluent Isobutane REACTOR 1 C.sub.2 (g/kg)
25.2 H.sub.2/C.sub.2 0.47 T (.degree. C.) 85 residence time (h)
3.29 REACTOR 2 C.sub.2 (g/kg) 29.8 Comonomer hexene
comonom./C.sub.2 1.32 H.sub.2/C.sub.2 0.0048 T (.degree. C.) 75
residence time (h) 1.86
[0083] The properties of the final compositions are summarized in
Table 6.
[0084] 997 parts of the composition obtained were mixed with 2
parts of an antioxidizing agent and 1 part of an anti-UV agent and
the mixture was granulated by extrusion in an extruder at a
temperature of 230.degree. C.
[0085] Pipes were then manufactured by extrusion of these granules
on an extruder of single-screw type at 200.degree. C. The
properties measured on these pipes are taken up in Table 6.
6 TABLE 6 EXAMPLE 10 Polymer manufactured in reactor 1 homo weight
(%) 53.4 MI.sub.2 (g/10 min) 400 SD (kg/m.sup.3) 971.8 Polymer
manufactured in reactor 2 C.sub.2-C.sub.6 copo weight (%) 46.6
MI.sub.5 * (g/10 min) 0.04 SD * (kg/m.sup.3) 923.5 Q * (weight %) 3
Composition resulting from react. 2 QT (weight %) 1.4 MI.sub.5
(g/10 min) 0.54 SD (kg/m.sup.3) 948.7 .mu..sub.2 (dPa .multidot. s)
19,000 ESCR (h) >3600
[0086] Belgin Patent Application 09700694 is hereby incorporated
herein by reference.
* * * * *