U.S. patent application number 10/114573 was filed with the patent office on 2002-10-31 for metallocene catalyst compositions, processes for making polyolefin resins using such catalyst compositions, and products produced thereby.
Invention is credited to Mink, Robert Ivan, Nowlin, Thomas Edward, Schregenberger, Sandra Denise, Schurzky, Kenneth George, Shirodkar, Pradeep P..
Application Number | 20020160908 10/114573 |
Document ID | / |
Family ID | 23528842 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020160908 |
Kind Code |
A1 |
Mink, Robert Ivan ; et
al. |
October 31, 2002 |
Metallocene catalyst compositions, processes for making polyolefin
resins using such catalyst compositions, and products produced
thereby
Abstract
A catalyst composition for the polymerization of one or more
1-olefins (e.g., ethylene) comprises a transition metal catalyst
precursor and a cocatalyst, the transition metal catalyst precursor
comprising a contact product of an unsubstituted metallocene
compound and an aluminum alkyl compound in a hydrocarbon solvent
solution. In another embodiment, the transition metal catalyst
precursor is bimetallic and contains a non-metallocene transition
metal catalyst component. When a bimetallic catalyst precursor is
used, the resin product exhibits improved properties, and has a
bimodal molecular weight distribution, long chain branching (LCB),
and good bubble stability.
Inventors: |
Mink, Robert Ivan;
(Tarrytown, NY) ; Nowlin, Thomas Edward; (West
Windsor, NJ) ; Schregenberger, Sandra Denise;
(Hillsborough, NJ) ; Shirodkar, Pradeep P.;
(Kingwood, TX) ; Schurzky, Kenneth George;
(Bridgewater, NJ) |
Correspondence
Address: |
ExxonMobil Chemical Company
P.O. Box 2149
Baytown
TX
77522
US
|
Family ID: |
23528842 |
Appl. No.: |
10/114573 |
Filed: |
April 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10114573 |
Apr 1, 2002 |
|
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|
09387186 |
Aug 31, 1999 |
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Current U.S.
Class: |
502/117 ;
502/102; 502/103; 502/150 |
Current CPC
Class: |
C08F 4/65912 20130101;
Y10S 526/943 20130101; C08F 110/02 20130101; C08F 10/00 20130101;
C08F 4/65925 20130101; C08F 110/02 20130101; C08F 2500/07 20130101;
C08F 2500/12 20130101; C08F 2500/20 20130101; C08F 2500/26
20130101; C08F 10/00 20130101; C08F 4/65904 20130101; C08F 10/00
20130101; C08F 4/6546 20130101 |
Class at
Publication: |
502/117 ;
502/102; 502/103; 502/150 |
International
Class: |
B01J 031/00 |
Claims
What is claimed is:
1. A catalyst composition comprising a transition metal catalyst
precursor and a cocatalyst, the transition metal catalyst precursor
comprising a contact product of an unsubstituted metallocene
compound and an aluminum alkyl compound in a hydrocarbon solvent
solution.
2. A catalyst composition comprising a bimetallic transition metal
catalyst precursor and a cocatalyst, the bimetallic transition
metal catalyst precursor comprising: (a) the contact product of an
unsubstituted metallocene compound and an aluminum alkyl compound
in a hydrocarbon solvent solution; and (b) a non-metallocene
transition metal component.
3. The catalyst composition according to claim 1, wherein said
unsubstituted metallocene compound is a complex of a transition
metal of the formula L.sub.xMQ.sub.yQ'.sub.z, in which L represents
an unsubstituted ligand group, M is a transition metal selected
from the group consisting of Group 4 metals, and each of Q and Q'
is a halogen atom, an alkyl group, or a hydrogen atom and Q and Q'
may be the same or different, wherein x is at least 1 and y and z
have values such that x+y+z is equal to the valence of M.
4. The catalyst composition according to claim 1, wherein said
transition metal atom M is zirconium, and said ligand group L is an
unsubstituted cyclopentadienyl group.
5. The catalyst composition according to claim 1, wherein said
aluminum alkyl compound is a trialkylaluminum compound.
6. The catalyst composition according to claim 5, wherein said
trialkylaluminum compound is trimethylaluminum, triethylaluminum,
triisobutylaluminum, or tri-n-octylaluminum.
7. The catalyst composition according to claim 2, wherein said
non-metallocene transition metal component (b) comprises the
reaction product of an optional support, an organomagnesium
compound, an alcohol, and a non-metallocene transition metal
compound.
8. A process for producing a 1-olefin polymer comprising contacting
at least one 1-olefin with the catalyst composition of claim 1
under polymerization conditions.
9. A process for producing a 1-olefin polymer comprising contacting
at least one 1-olefin with the catalyst composition of claim 2
under polymerization conditions.
10. A 1-olefin polymer produced according to the process of claim
8.
11. An ethylene (co)polymer produced in a single reactor having a
bimodal molecular weight distribution, a flow activation energy of
at least about 27 kjoule/mole, a density of from about 0.89 to
about 0.965 g/cc, a melt index of from about 0.01 to about 0.2 g/10
minutes, a high load melt index (HLMI) of from about 2 to about 100
g/10 minutes, and a melt flow ratio (MFR) of from about 40 to about
300.
12. An article of manufacture made from the ethylene (co)polymer of
claim 10.
13. An article of manufacture according to claim 11, wherein said
article is a film having a thickness of up to about 254 microns (10
mils) and an Elmendorf tear resistance in the machine direction of
at least about 236,220 g/m (6 g/mil), and a Dart Drop impact
resistance of at least about 50 g.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to novel catalyst compositions
and to processes for making polyolefin resins using such novel
catalyst compositions, polyolefin resins, and articles made from
such polyolefin resins. In particular, this disclosure relates to
processes for making bimodal polyolefin resins using a novel
catalyst composition comprising a bimetallic transition metal
catalyst precursor and a cocatalyst. This disclosure also relates
to polyolefin resins with improved properties (e.g., improved
bubble stability) having bimodal molecular weight distributions and
long chain branching, as well as articles made from such polyolefin
resins.
BACKGROUND OF THE INVENTION
[0002] Increasing the molecular weight of polyethylene (and
copolymers of ethylene) generally results in enhancing tensile
strength, ultimate elongation, impact strength, puncture
resistance, and toughness of films. However, increasing the
molecular weight of the polyethylene will usually decrease its
processability. By providing a blend of a relatively high molecular
weight (HMW) ethylene polymer with a relatively lower molecular
weight (LMW) ethylene polymer, the desirable characteristics due to
the relatively high molecular weight polymer component can be
retained while, at the same time, improving processability of the
blend material containing the relatively high molecular weight and
low molecular weight polymer components.
[0003] To produce such blends, various alternatives are being
considered in the art, including post reactor or melt blending,
catalysis in a single reactor with a catalyst effective to produce
the blend material, and use of multistage reactors in which
different molecular weight components can be produced sequentially
in each reactor.
[0004] U.S. Pat. No. 2,924,593 to Breslow discloses a process for
producing high molecular weight polyethylene comprising contacting
ethylene with a catalyst composition comprising a
bis(cyclopentadienyl)zi- rconium salt and a metal alkyl compound of
an alkali metal, an alkaline earth metal, or aluminum. In Example
7, the catalyst composition is formed in situ by contacting
bis(cyclopentadienyl)zirconium dichloride, triethylaluminum, and
ethylene in toluene.
[0005] U.S. Pat. No. 4,701,432 to Welborn, Jr. discloses a catalyst
system comprising (i) a metallocene and a non-metallocene
transition metal compound (i.e. a transition metal compound not
containing cyclopentadienyl) supported catalyst component and (ii)
a combination of an organometallic compound of a metal of Groups
IA, IIA, IIB and IIIA of the Periodic Table and an alumoxane
cocatalyst. The catalyst composition is disclosed as being useful
for olefin polymerization, and particularly for the production of
linear low, medium and high density polyethylenes and copolymers of
ethylene with alpha-olefins having 3 or more carbon atoms
(C.sub.3-C.sub.10), cyclic olefins, and/or diolefins having up to
18 carbon atoms.
[0006] U.S. Pat. No. 5,049,535 to Resconi, et al. discloses that
the activity of a catalyst composition obtained from zirconocenes
and trialkylaluminum compounds is extremely low when applied to the
polymerization of ethylene and practically nil for higher olefins
(column 1, lines 10-26). To increase activity, Resconi, et al.
proposed the use of substituted metallocene compounds in
combination with trialkylaluminum compounds.
[0007] U.S. Pat. No. 5,157,008 to Sangokoya, et al. discloses the
production of hydrocarbon solvent solutions of alkylalumoxanes by
mixing trimethylaluminum and a hydrocarbylaluminum compound, which
compound contains at least one hydrocarbyl group having 2 or more
carbon atoms, in a hydrocarbon solvent and thereafter adding water
or a hydrated compound so as to form a solution of alkylaluminoxane
in said solvent.
[0008] U.S. Pat. No. 5,238,892 to Chang discloses an olefin
polymerization catalyst composition comprising a solid product
produced by mixing and reacting a metallocene and an aluminum
alkyl, for example trialkylaluminum, in a hydrocarbon solvent to
form a reaction product, and thereafter adding an undehydrated
support material to the reaction mixture.
[0009] U.S. Pat. No. 5,332,706 to Nowlin, et al. discloses that the
metallocene catalyst must contact the alumoxane (e.g.,
methylalumoxane (MAO)), while the alumoxane is in solution in order
for the metallocene to be activated in a fluidized-bed reactor.
Moreover, the patent discloses that extensive reactor fouling
results when MAO solutions are fed directly into the gas phase
reactor in large enough quantities to provide this liquid contact.
The fouling was found to occur because the MAO solution forms a
liquid film on the interior walls of the reactor, and the catalyst
is activated when it comes into contact with this liquid film,
which in turn leads to the formation of a polymer coating that
grows larder in size until the reactor is fouled.
[0010] U.S. Pat. No. 5,849,653 to Dall'Occo, et al. discloses
catalysts for the polymerization of olefins obtained from
cyclopentadienyl compounds of a transition metal, an organometallic
aluminum compound, and water.
[0011] Japanese Laid-Open Patent Application (Kokai) No. 4-266891
discloses a process for producing a methylisobutylalumoxane having
high activity and excellent solubility in hydrocarbons.
[0012] It would be desirable to provide a catalyst composition that
is capable of producing a bimodal molecular weight distribution
(MWD) polyolefin resin with improved properties (e.g., bubble
stability) having a bimodal molecular weight distribution and long
chain branching. Further, it would be highly desirable to provide a
catalyst composition with high activity from which bimodal
polyolefin resins having long chain branching can be produced,
wherein the polyolefin resins do not require special
post-polymerization tailoring (i.e., the polyolefin resins do not
have to be treated with modifiers, such as oxygen or organic
peroxides, to modify the molecular weight distribution) and yet
possess excellent bubble stability.
SUMMARY OF THE INVENTION
[0013] In one embodiment, a catalyst composition is provided,
wherein the catalyst composition comprises a transition metal
catalyst precursor and a cocatalyst, the transition metal catalyst
precursor comprising the contact product of an unsubstituted
metallocene compound and an aluminum alkyl compound in a
hydrocarbon solvent solution.
[0014] In an alternative embodiment, a catalyst composition is
provided, wherein the catalyst composition comprises a bimetallic
transition metal catalyst precursor and a cocatalyst, the
bimetallic transition metal catalyst precursor comprising:
[0015] (a) the contact product of an unsubstituted metallocene
compound and an aluminum alkyl compound in a hydrocarbon solvent
solution; and
[0016] (b) a non-metallocene transition metal component.
[0017] Further, a process for polymerizing olefins (e.g., ethylene
and/or higher olefins) is provided, wherein the process comprises
contacting one or more olefins with a catalyst composition
comprising a transition metal catalyst precursor and a cocatalyst,
the transition metal catalyst precursor comprising the contact
product of an unsubstituted metallocene compound and an aluminum
alkyl compound in a hydrocarbon solvent solution.
[0018] Alternatively, another process for polymerizing olefins
(e.g., ethylene and/or higher olefins) is provided, wherein the
process comprises contacting one or more olefins with a catalyst
composition comprising a bimetallic transition metal catalyst
precursor and a cocatalyst, the bimetallic transition metal
catalyst precursor comprising:
[0019] (a) the contact product of an unsubstituted metallocene
compound and an aluminum alkyl compound in a hydrocarbon solvent
solution; and
[0020] (b) a non-metallocene transition metal component.
[0021] In yet another embodiment, a polyolefin resin having
improved bubble stability is provided, wherein the polyolefin resin
has a bimodal molecular weight distribution and long chain
branching.
[0022] Further, an ethylene (co)polymer is provided, wherein the
ethylene (co)polymer is produced in a single reactor and has a
bimodal molecular weight distribution, a flow activation energy of
at least about 27 kjoule/mole, a density of from about 0.89 to
about 0.965 g/cc, a melt index of from about 0.01 to about 0.2 g/10
minutes, a high load melt index (HLMI) of from about 2 to about 100
g/10 minutes, and a melt flow ratio (MFR) of from about 40 to about
300.
[0023] Other additional embodiments include various articles made
from the above-described polyolefin resins.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows the bimodal molecular weight distribution of
the resin of Example 4, as measured by Gel Permeation
Chromatography (GPC).
[0025] FIG. 2 shows the bimodal molecular weight distribution of
the resin of Example 5, as measured by GPC.
[0026] FIG. 3 shows the bimodal molecular weight distribution of
the resin of Example 6, as measured by GPC.
[0027] FIG. 4 shows the bimodal molecular weight distribution of
the resin of Example 7, as measured by GPC.
DETAILED DESCRIPTION OF THE INVENTION
[0028] In one aspect, the catalyst composition comprises a
transition metal catalyst precursor and a cocatalyst, the
transition metal catalyst precursor comprising the contact product
of an unsubstituted metallocene compound and an aluminum alkyl
compound (e.g., a trialkylaluminum compound) in a hydrocarbon
solvent solution.
[0029] Useful metallocene compounds include unsubstituted
metallocene compounds that are organometallic coordination
compounds of transition metal compounds. For example, these
metallocene compounds may be complexes of a transition metal of the
formula L.sub.xMQ.sub.yQ'.sub.z. In this formula, L represents an
unsubstituted ligand group (e.g., cyclopentadienyl), M is a
transition metal selected from the group consisting of Group 4
metals of the Periodic Chart of the Elements, as published by
Chemical and Engineering News, 63(5), 27, 1985, such as titanium,
zirconium and hafnium, and each of Q and Q' is a halogen atom, an
alkyl group, or a hydrogen atom and Q and Q' may be the same or
different, wherein x is at least 1 and y and z have values such
that x+y+z is equal to the valence of M. The use of a mixture of
metallocene compounds is also contemplated.
[0030] In the above formula of the metallocene complex, a typical
transition metal atom M is zirconium. As described above, the
ligand group L may be an unsubstituted cyclopentadienyl group,
where x is at least 1 and typically is 2, and x+y+z equals the
valence of M. If the substituents Q and Q' in the above formula of
the metallocene complex are halogen atoms, they belong to the group
of fluorine, chlorine, bromine or iodine, and y+z is 3 or less. If
the substituents Q and Q' in the above formula of the metallocene
complex are alkyl groups, they are typically linear or branched
C.sub.1-C.sub.8 alkyl groups, such as methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, n-pentyl, n-hexyl or n-octyl.
[0031] Suitable metallocene compounds include, but are not limited
to:
[0032] bis(cyclopentadienyl)metal dihalides;
[0033] bis(cyclopentadienyl )metal hydridohalides;
[0034] bis(cyclopentadienyl)metal monoalkyl monohalides; and
[0035] bis(cyclopentadienyl)metal dialkyls;
[0036] wherein the metal is, for example, zirconium, titanium, or
hafnium atom, the halide atoms are, for example, chlorine and the
alkyl groups are C.sub.1-C.sub.6 alkyl groups. Illustrative but
non-limiting examples of metallocene complexes include
[0037] bis(cyclopentadienyl)zirconium dichloride;
[0038] bis(cyclopentadienyl)titanium dichloride;
[0039] bis(cyclopentadienyl)hafnium dichloride;
[0040] bis(cyclopentadienyl)zirconium dimethyl;
[0041] bis(cyclopentadienyl)hafnium dimethyl;
[0042] bis(cyclopentadienyl)zirconium hydridochloride;
[0043] bis(cyclopentadienyl)hafnium hydridochloride; and
[0044] cyclopentadienylzirconium trichloride.
[0045] As previously mentioned, the L.sub.xMQ.sub.yQ'.sub.z
compound is contacted with an aluminum alkyl compound, for example
a trialkylaluminum compound. Contact of these two components is
undertaken in a suitable hydrocarbon solvent, for example a
non-aromatic solvent. The volume of the solvent is sufficient to
produce a solution of the contact product. The solvents which can
be used for this purpose include paraffins of 4 to 10 carbon atoms,
linear or branched, and are exemplified by n-hexane, isohexane,
n-heptane, etc., and their mixtures, as well as cycloalkanes such
as methylcyclopentane, cyclohexane, methylcyclohexane, etc. When
trimethylaluminum is used, the solvent may be an aromatic solvent
such as toluene. Other suitable aromatic solvents include benzene,
xylene or ethylbenzene.
[0046] The aluminum alkyl compounds, typically trialkylaluminum
compounds, which are contacted with the L.sub.xMQ.sub.yQ'.sub.z
compounds are characterized by the formula AlR.sub.3, wherein each
R may be the same or different and is independently an alkyl group,
linear or branched, containing 1 to 12 carbon atoms. For example,
the alkyl groups can be methyl, ethyl, propyl, isopropyl, butyl,
isobutyl, pentyl, isopentyl, hexyl, isohexyl, heptyl, isoheptyl,
octyl, or isooctyl. Representative trialkylaluminum compounds
include, but are not limited to, trimethylaluminum (TMA),
triethylaluminum (TEAL), triisobutylaluminum (TIBA), and
tri-n-octylaluminum (TOA).
[0047] The molar ratio of the aluminum alkyl compound to the
L.sub.xMQ.sub.yQ'.sub.z complex can range from about 2 to about 50,
typically from about 3 to about 40, and most typically from about 4
to about 30.
[0048] The concentration of the metallocene compound in the
hydrocarbon solvent may range from about 0.1 wt % to about 20 wt %,
typically from about 0.5 wt % to about 15 wt %.
[0049] When the transition metal catalyst precursors of the
invention contain two or more L.sub.xMQ.sub.yQ'.sub.z compounds,
they may be contacted individually or separately with the aluminum
alkyl compound.
[0050] The contact product of the transition metal catalyst
precursor is formed by contacting the metallocene and the aluminum
alkyl compound in a suitable hydrocarbon solvent at a temperature
of from about 0.degree. C. to about 100.degree. C., typically from
about 15.degree. C. to about 60.degree. C., for about 1.0 to about
1500 minutes, typically for about 10 to about 180 minutes.
[0051] For example, the contact product of the transition metal
catalyst precursor may be formed by adding a solution of the
trialkylaluminum compound to the metallocene compound to form a
solution of the contact product. Alternatively, the process for
making the contact product of the transition metal catalyst
precursor includes contacting the neat trialkylaluminum compound
with the metallocene compound to form a solution of the contact
product.
[0052] In one alternative embodiment, a bimetallic transition metal
precursor is formed. The bimetallic transition metal catalyst
precursor comprises (a) the contact product of an unsubstituted
metallocene compound and an aluminum alkyl compound in a
hydrocarbon solvent solution, as described above, and (b) a
non-metallocene transition metal component.
[0053] In this embodiment, a wide variety of non-metallocene
transition metal components may be used.
[0054] While not limited thereto, the non-metallocene transition
metal component (b) may be made by reacting an organomagnesium
containing compound, an alcohol, a non-metallocene transition metal
compound, and, optionally, a carrier or support.
[0055] The support, if used, may be inorganic or organic. In
general, the support for the non-metallocene transition metal
catalyst component may be any carrier material which contains
hydroxyl groups. A specific support material for the catalyst
precursor is a particulate, porous, typically inorganic material,
such as an oxide of silicon and/or of aluminum. The support
material is used in the form of a dry powder having an average
particle size of from about 1 micron to about 500 microns. The
surface area of the support should be at least about 3 square
meters per gram (m.sup.2/g), and typically from at least 50
m.sup.2/g up to 400 m.sup.2/g. The support material should be dry,
that is, free of absorbed water. Drying of the support material can
be effected by heating it at about 100.degree. C. to about
1000.degree. C., typically at about 600.degree. C. When the support
is silica, it is heated to at least about 200.degree. C., typically
about 400.degree. C. to about 900.degree. C., and more typically
about 600.degree. C. to about 850.degree. C. The support material
should have at least some active hydroxyl (OH) groups on its
surface to produce the catalyst compositions of this invention. The
number of OH groups on the support surface (silanol groups in the
case of silica) is approximately inversely proportional to the
temperature of drying or dehydration (i.e., the higher the
temperature the lower the hydroxyl group content).
[0056] In one specific embodiment, the support is silica which,
prior to the use thereof in the catalyst precursor synthesis, has
been dehydrated by fluidizing it with nitrogen flow and heating at
about 600.degree. C. for about 4-16 hours to achieve a surface OH
group concentration of about 0.7 millimoles per gram (mmol/g). The
silica is typically a high surface area, amorphous silica (surface
area=300 m.sup.2/g; pore volume of 1.65 cm.sup.3/g), and it is a
material marketed under the tradenames of Davison 952 or Davison
955 by the Davison Chemical Division of W. R. Grace and Company or
Crosfield ES70 by Crosfield Limited. The silica is in the form of
spherical particles, which are obtained by a spray-drying process.
As procured, these silicas are not calcined and thus must be
dehydrated as indicated above.
[0057] The synthesis of the non-metallocene catalyst component (b)
may conveniently be carried out in a series of several consecutive
steps under inert conditions in the absence of water and of
oxygen.
[0058] Support material containing OH groups on their surface is
slurried in a non-polar non-aromatic solvent. The slurry of the
support material in the solvent is prepared by introducing the
support into the solvent, typically while stirring, and heating the
mixture to about 25 to about 70.degree. C., typically to about 40
to about 60.degree. C. Suitable non-polar solvents are materials
which are liquid at reaction temperatures and in which all of the
reactants used later during the catalyst precursor preparation,
i.e., organomagnesium compounds and the non-metallocene transition
metal compounds, are at least partially soluble. Typical non-polar
solvents are alkanes, such as isopentane, hexane, isohexane,
n-heptane, isoheptane, octane, nonane, and decane, although a
variety of other materials including cycloalkanes, such as
cyclohexane and methylcyclohexane can also be used. During the
first stage of the catalyst synthesis, the manufacture of the
intermediate catalyst precursor, aromatic solvents, such as
benzene, toluene and ethylbenzene, may also be employed. The most
typical non-polar solvent is isopentane. Prior to use, the
non-polar solvent should be purified, such as by percolation
through silica gel and/or molecular sieves, to remove traces of
water, oxygen, polar compounds, and other materials capable of
adversely affecting catalyst activity. The temperature of the
slurry is important with respect to its impregnation with a
non-metallocene transition metal compound; that is, temperatures of
the slurry in excess of 90.degree. C. for extended periods may
result in deactivation of the transition metal component added
subsequently. Accordingly, all catalyst precursor synthesis steps
are conducted below 90.degree. C.
[0059] In the second step, the slurry of the support is contacted
with an organomagnesium compound normally provided as a solution.
This solution may contain small quantities of a solubilizing
compound such as a trialkylaluminum. For example, in the case of
butylethylmagnesium (BEM), triethylaluminum may be complexed with
the BEM to solubilize the organomagnesium compound. An example of
such a complex is MAGALA, which is available from Akzo Nobel.
[0060] The organomagnesium compound has the empirical formula
R.sub.mMgR'.sub.n
[0061] where R and R' are the same or different C.sub.2-C.sub.12
alkyl groups, typically C.sub.4-C.sub.10 alkyl groups, more
typically C.sub.4-C.sub.8 alkyl groups, and most typically both R
and R' are butyl groups, and m and n are each 0, 1 or 2, providing
that m+n is equal to the valence of Mg.
[0062] In a specific embodiment of the synthesis of this
non-metallocene catalyst component (b), it is important to add only
such an amount of the organomagnesium compound that will be
deposited, physically or chemically, into the support since any
excess of the organomagnesium compound in the liquid phase may
react with other chemicals used for the catalyst synthesis and
precipitate them outside of the support. The drying temperature of
the support material affects the number of sites on the support
available for the organomagnesium compound: the higher the drying
temperature the lower the number of sites. Thus, the exact molar
ratio of the organomagnesium compound to the OH groups in the
support will vary and must be determined on a case-by-case basis to
assure that only so much of the organomagnesium compound is added
to the solution as will be deposited into the support without
leaving any excess of the organomagnesium compound in the liquid
phase. Thus, the molar ratios given below are intended only as an
approximate guideline and the exact amount of the organomagnesium
compound in this embodiment must be controlled by the functional
limitation discussed above, i.e., it must not be greater than that
which can be deposited into the support. If a greater amount of the
organomagnesium compound is added to the slurry, the excess may
react with the non-metallocene transition metal compound added to
the slurry later, thereby forming a precipitate outside of the
support which is detrimental in the synthesis of the catalyst and
must be avoided. The required amount of the organomagnesium
compound can be determined in any conventional manner, e.g., by
adding the organomagnesium compound to the slurry of the support
until a free organomagnesium compound is detected in the liquid
phase.
[0063] For example, for the silica support, the amount of the
organomagnesium compound added to the slurry may be such that the
molar ratio of Mg to the OH groups on the support is about 0.5:1 to
about 4:1, typically about 0.8:1 to about 3:1, more typically about
0.9:1 to about 2:1 and most typically about 1:1.
[0064] Next, the support treated with the organomagnesium compound
is contacted with an alcohol (R"OH) containing R"O- groups which
are capable of displacing alkyl groups on the magnesium atom. The
amount of the alcohol is effective to provide a [R"OH]:Mg molar
ratio of from about 0.5 to about 2.0, typically from about 0.8 to
about 1.5. The reaction is carried out at a temperature ranging
from about 25.degree. C. to about 800C., typically from about
40.degree. C. to about 70.degree. C.
[0065] The alkyl group R" in the alcohol can contain about 1 to
about 12 carbon atoms, typically about 1 to about 8 carbon atoms;
in the embodiments below, they are alkyl groups containing about 2
to about 4 carbon atoms, particularly 4 carbon atoms. The inclusion
of the alcohol step in the catalyst precursor synthesis produces a
catalyst composition which, relative to the catalyst precursor
prepared without this step, is much more active, requires much less
transition metal (e.g., titanium), and does not interfere with the
performance of the metallocene component in the catalyst.
[0066] Next, the slurry is contacted with a non-metallocene
transition metal compound. During this step, the slurry temperature
must be maintained at about 25 to about 70.degree. C., typically at
about 40 to about 60.degree. C. As noted above, temperatures in
this slurry of about 90.degree. C. or greater result in
deactivation of the non-metallocene transition metal component.
Suitable transition metal compounds used herein are compounds of
metals of Groups 4 and 5, of the Periodic Chart of the Elements, as
published by Chemical and Engineering News, 63(5), 27, 1985,
provided that such compounds are soluble in non-polar solvents.
Non-limiting examples of such compounds are titanium and vanadium
halides, e.g., titanium tetrachloride, vanadium tetrachloride,
vanadium oxytrichloride, titanium and vanadium alkoxides, wherein
the alkoxide moiety has a branched or unbranched alkyl radical of
about 1 to about 20 carbon atoms, typically 1 to about 6 carbon
atoms. For example, the transition metal compounds are titanium
compounds, typically tetravalent titanium compounds. The most
typical titanium compound is TiCl.sub.4. The amount of titanium (or
vanadium) ranges from a Ti/Mg molar ratio of about 0.3 to about
1.5, typically from about 0.50 to about 0.80. Mixtures of such
transition metal compounds may also be used and generally, no
restrictions are imposed on the non-metallocene transition metal
compounds that may be included. Any non-metallocene transition
metal compound that may be used alone may also be used in
conjunction with other transition metal compounds.
[0067] After the addition of the non-metallocene transition metal
compound is complete, in one embodiment of catalyst synthesis, the
slurry solvent is removed by evaporation or filtering to obtain a
free-flowing powder.
[0068] Next, the non-metallocene transition metal component (b) and
the contact product (a) are combined to form the bimetallic
transition metal catalyst precursor. For example, the dried
non-metallocene transition metal catalyst component (b) is
resiurried in a non-polar hydrocarbon (the same as the solvent used
for the preparation of the initial support slurry) and is contacted
with a solution containing the contact product (a). The contact of
(a) and (b) is carried out at temperatures ranging from about
10.degree. C. to about 60.degree. C. and lasts from about 10 to
about 1,000 minutes.
[0069] Optionally, (i) the contact product of the metallocene
compound and the aluminum alkyl compound or (ii) the reaction
product of the contact product (a) and the non-metallocene
transition metal component (b) may be further contacted with a
solution of an alumoxane (e.g., MAO or MMAO, which is a modified
methylalumoxane from Akzo Nobel). The alumoxane is typically
provided in an aromatic or aliphatic solvent such as toluene or
heptane. The use of an alumoxane, in particular MAO, has been found
to provide an improvement in terms of the homogeneity of the
polymer particle morphology. When MAO is used, the molar ratio of
the MAO to the L.sub.xMQ.sub.yQ'.sub.z complex (i.e., Al/M molar
ratio) may be up to about 200.
[0070] The transition metal catalyst precursor or the bimetallic
transition metal catalyst precursor may be used in the form of a
free-flowing particulate form. This is obtained by evaporating the
solvent(s) used during the catalyst precursor synthesis.
[0071] The catalyst composition also comprises an activating
cocatalyst component in addition to the transition metal component.
The cocatalyst may comprise an alumoxane (e.g., MMAO obtained from
Akzo Nobel), optionally an aluminum alkyl (which may be the same or
different as the aluminum alkyl used for the catalyst precursor
synthesis), and optionally water.
[0072] In general, the resins as described herein are made in one
reactor, under suitable reactor conditions. In particular, the
bimodal resins are typically made by polymerizing one or more
olefins (e.g., ethylene) in the presence of the bimetallic catalyst
composition comprising two sources of transition metal each of
which produce different molecular weight polymer.
[0073] For purposes of this disclosure, the term "(co)polymer" or
"polymer" is inclusive of homopolymers, copolymers made from two
different monomers, or interpolymers of more than two types of
monomers (e.g., terpolymers). That is, the term copolymer should be
construed to include not only polymers made from only two different
types of monomers, but also polymers made from three or more
different types of monomers (e.g., a terpolymer). In addition, the
term "(co)polymer" or "polymer" includes random polymers, block
polymers, graft polymers, etc.
[0074] In the polymerization processes described herein, the
polymerization may be conducted in gas phase (e.g., fluidized-bed)
or liquid phase (e.g., slurry).
[0075] In gas phase polymerization, the gaseous monomer feed may,
for example, consist wholly of ethylene or may comprise a
preponderance of ethylene and a minor amount of one or more
comonomers such as a 1-olefin containing from about 3 to about 10
carbon atoms. In particular, the amount of comonomer(s) may be in
the range of, for example, from about 0 to about 30 weight percent,
typically from about 0 to about 20 weight percent, based on the
total weight of polymer produced in the process.
[0076] In particular, the resins according to this disclosure
include 1) a homopolymer of ethylene; or 2) a copolymer of a
preponderance (i.e., greater than 50 wt. %) of ethylene with a
minor amount of one or more 1-olefins containing from about 3 to
about 10 carbon atoms, typically 1-olefin(s) containing from about
4 to about 10 carbon atoms, e.g., 1-butene, 1-pentene, 1-hexene,
4-methyl-1-pentene, 1-octene, 1-decene, and mixtures thereof; or 3)
a mixture of any of the foregoing polymers.
[0077] For example, the polymer product can comprise an amount of
polymerized comonomer which is in the range, for example, of about
0 to 30 weight percent, based on the total weight of polymer.
[0078] In the case of ethylene polymerization, hydrogen is
typically fed to the reactor such that the molar ratio of hydrogen
to ethylene (H.sub.2/C.sub.2 ratio) is, for example, up to about
0.15, typically from about 0.005 to about 0.03.
[0079] The ethylene partial pressure employed in the reactor is
usually no higher than about 1,724 kPa (250 psia), for example in
the range of about 345 kPa (50 psia) to about 1,379 kPa (200 psia),
typically in the range of about 690 kPa (100 psia) to about 1,310
kPa (190 psia).
[0080] If desired for any purpose, e.g., to control superficial gas
velocity or to absorb heat of reaction, an inert gas such as
nitrogen may also be present in the reactor in addition to the
monomer and hydrogen. Thus the total pressure in the reactor may be
in the range, for example, of about 791 kPa (114.7 psia) to about
4,238 kPa (614.7 psia), typically about 1,480 kPa (214.7 psia) to
about 2,859 kPa (414.7 psia).
[0081] The temperature of polymerization in the reactor may be in
the range, for example, of about 60 to about 130.degree. C.,
typically about 70 to about 110.degree. C. The residence time of
the catalyst in the reactor is about 1 to about 8 hours, typically
about 1.5 to about 4 hours in the reactor.
[0082] The resins produced by using the catalyst compositions
containing the bimetallic transition metal catalyst precursor and
the cocatalyst described above are bimodal and also contain
long-chain branching (LCB). By "bimodal," it is meant that there
are two polymer components of different molecular weights, that is
one has a higher relative molecular weight than the other of the
two components. The presence of LCBs is also beneficial for the
bubble stability of the resin during the film blowing process. The
bimodal polyolefin resins described herein do not require special
post-polymerization tailoring (i.e., the polyolefin resins do not
have to be treated with modifiers, such as oxygen or organic
peroxides, to modify the molecular weight distribution) and yet
they possess excellent bubble stability.
[0083] An improvement in bubble stability of the resin during film
production over other bimodal molecular weight resins has been
attributed to the new resins herein. The resins, which are
processed on high stalk extrusion lines, exhibit excellent bubble
stability, a prerequisite to being processed on those lines at high
rates. This improvement in bubble stability has been correlated to
the presence of LCB as measured by the flow activation energy of
the invention resins. It is believed that this property is directly
a result of the catalyst composition used to make them.
[0084] The resins exhibit a characteristic flow activation energy.
It is believed that the high flow activation energy of the products
is indicative of the presence of LCBs, which are known to improve
the bubble stability of blown film resins by increasing their melt
tension. Bubble stability is quantified as the maximum line speed
that can be sustained without increasing bubble oscillations on a
given blown film line. The higher the line speed that the blown
film is being fabricated, the thinner the gauge of the film.
Improved bubble stability is beneficial to a film converter because
it allows the production of a thinner film and/or the achievement
of higher rates with reduced risk of a downed extrusion line.
[0085] The flow activation energy (FAE) of the resins of the
present invention is higher than about 27 kjoule/mole. The FAE
measures the temperature dependencies of dynamic viscosity, and
these measurements are performed at different temperatures using
the RMS 800, over different ranges of temperature, frequency, and
strain. Rheometrics.RTM. Orchestrator 6.4.3 software can be used
for the calculation of FAE. The dynamic properties used herein are
described in ASTM D 4440-84.
[0086] In addition, the density, the melt index (MI), high load
melt index (HLMI), and melt flow ratio (MFR) of the resins
described herein may range as follows:
[0087] Density: about 0.89 to about 0.965 g/cc
[0088] MI: about 0.01 to about 0.5 g/10 minutes
[0089] HLMI: about 2 to about 20 g/10 minutes
[0090] MFR: about 40 to about 200
[0091] The properties of the resins are determined by the following
test methods:
[0092] Density
[0093] ASTM D-1 928
[0094] A plaque is made under controlled cooling conditions.
[0095] ASTM D-1505
[0096] Measurement for density is then made in a density gradient
column; reported as g/cc.
[0097] Melt Index
[0098] ASTM D-1238 (190.degree. C./2160 g)
[0099] (MI)
[0100] Measured at 190.degree. C. reported as grams per 10
minutes.
[0101] High Load
[0102] ASTM D-1238 (190.degree. C./21600 g)
[0103] Melt Index
[0104] Measured at 10 times the weight used in the melt index
(HLMI) test above.
[0105] Melt Flow
[0106] MFR=HLMI/MI
[0107] Ratio (MFR)
[0108] Compositions containing the resins described herein can be
extruded into pipes, injection or blow molded into articles, or
extruded and blown into films. Typically, films can be produced
which are from about 5.08 to about 254 microns (about 0.2 to about
10.0 mils), typically from about 10.16 to about 50.8 microns (about
0.4 to about 2.0 mils), thickness. Blow molded articles include
bottles, containers, fuel tanks and drums.
[0109] For film production, the products may contain any of various
additives conventionally added to polymer compositions such as
processing aids, lubricants, antiblock, stabilizers, antioxidants,
compatibilizers, pigments, etc. These reagents can be employed to
stabilize the products against oxidation and/or improve
processability, appearance, or properties. For example, additive
packages comprising 400-2000 ppm hindered phenol(s); 200-2000 ppm
phosphates; and 250-2000 ppm stearates, for addition to the resin
powders, can be used for pelletization. The polymers can be added
directly to a blown film extruder, e.g., an Alpine extruder, to
produce films having a thickness, for example of about 5.08 to
about 127 microns (about 0.2 to about 5 mils).
[0110] The ethylene polymer product of this invention is capable of
being formed into thin gauge films, e.g., of up to 254 microns (10
mils), of superior mechanical properties, e.g., an Elmendorf tear
resistance in the machine direction (MD Tear, ASTM D1922) of at
least about 236,620 g/m (about 6 g/mil), typically about 314,961 to
about 2,362,205 g/m (about 8 to about 60 g/mil), and more typically
about 393,701 to about 2,362,205 g/m (about 10 to about 60 g/mil),
and a Dart Drop Impact resistance (F50, ASTM D1709) of at least
about 50 g, typically about 100 to about 600 g, and more typically
about 150 to about 600 g.
EXAMPLES
[0111] The following examples illustrate the effectiveness of the
present invention without limiting the scope thereof.
Example 1
[0112] Titanium Component
[0113] 541 grams of Davison grade 955 silica, calcined at
600.degree. C. for 4 hours under nitrogen flow was placed into a
two-gallon stainless steel autoclave containing a stirring paddle.
Next, ca. 2.7 liters of dry isopentane was added to the autoclave
and the stirring rate set at 100 rpm. The temperature of the
silica/isopentane slurry was 50-55.degree. C. Next, 546 mis of
dibutylmagnesium in heptane (0.713 mmol/ml, 389.3 mmol) was added
to the slurry. The contents of the autoclave were stirred for
approximately 1 hour at 50-55.degree. C. Then, 27.43 g (370.1 mmol)
of neat 1-butanol was added and stirring was continued for
approximately 1 hour at 50-55.degree. C. Finally, 44.34 g (233.7
mmol) of titanium tetrachloride was added to the autoclave and
stirring was continued for approximately 1 hour at 50-55.degree. C.
The liquid phase was then removed by evaporation under a nitrogen
purge to yield a free-flowing powder.
Example 2
[0114] Titanium/Zirconium Catalyst Precursor
[0115] A triisobutylaluminum (TIBA)/bis-(cyclopentadienyl)zirconium
dichloride (Cp.sub.2ZrCl.sub.2) contact product was prepared by
adding a solution of TIBA in hexane (1.0 Molar, 378.82 g solution,
545 mmol of Al) to 11.153 g (38.15 mmol) of Cp.sub.2ZrCl.sub.2,
which produced a yellow solution. This solution was then added into
a two-gallon stainless steel autoclave which contained a slurry of
545 g of the Ti component of Example 1 in ca. 2.7 liter of
isopentane heated to 50-55.degree. C. After the addition, the
mixture was stirred for approximately 1 hour at 50-55.degree. C.
Then, MAO in toluene (330.77 g solution, 1655 mmol Al) was added
slowly (in a period of approximately 1 hour) to the mixture at
50-55.degree. C. After the addition, the mixture was stirred for
approximately 1 hour at 50-55.degree. C. and then, the liquid phase
was removed under nitrogen flow to yield a free-flowing powder.
Analyses: 0.98 wt % Mg; 1.28 wt % Ti; 7.9 wt % Al; 0.47 wt %
Zr.
Example 3
[0116] Titanium/Zirconium Catalyst Precursor
[0117] The same procedure as described in Example 2 was used,
except MMAO in heptane was used instead of MAO in toluene. Thus,
422 g of the Ti component of Example 1, 299.42 g solution (431 mmol
of Al) of TIBA in hexane, 8.63 g (29.52 mmol) of
Cp.sub.2ZrCl.sub.2, and 511.3 g solution (1266 mmol Al) of MMAO in
heptane were employed.
[0118] Polymerization Examples
[0119] The Ti/Zr catalyst precursors (Examples 2 and 3) were
activated with a cocatalyst mixture of MMAO, TMA, and H.sub.2O. The
resins were produced in a fluidized-bed reactor under the process
conditions in the Tables below.
[0120] The resins produced from these catalysts were stabilized
with the following additive package (2000 ppm Irganox 1010, 2000
ppm Irgafos 168, 2000 ppm zinc stearate) and compounded on a 1.905
cm (3/4 inch) Brabender extruder under mild conditions (nitrogen
purge and 220.degree. C.). The activation energy of the resultant
pellets was measured on the RMS 800 rheometer as discussed earlier.
The activation energy of 38 kjoule/mole indicated the presence of
long chain branching.
Example 4
[0121] In this example, ethylene and hexene-1 were copolymerized
using the activated bimetallic transition metal catalyst precursor
of Example 2 under the conditions set out in the Table 1 below. The
resin properties are also indicated in Table 1. The bimodal
molecular weight distribution of the resin as measured by Gel
Permeation Chromatography (GPC) is shown in FIG. 1.
1 TABLE 1 Example 2 CATALYST PRECURSOR TIBA, mmol/g Ti component of
Example 1 1.0 Zirconium, mmol/g Ti component of Example 1 0.07 MAO,
mmol/g Ti component of Example 1 3.0 PROCESS Ethylene Partial
Pressure, kPa (psia) 1158 (167.9) Isopentane Partial Pressure, kPa
(psi) 93.1 (13.5) 1-Hexene/Ethylene Molar Ratio, mol/mol 0.007
Hydrogen/Ethylene Molar Ratio mol/mol 0.020 Bed Temp., .degree. C.
90.0 MMAO, ppm 75 TMA, ppm 181 H.sub.2O/C.sub.2H.sub.4 ppmv 11.4
RESIN CHARACTERISTICS HLMI, g/10 min 5.5 MFR 92 Activation Energy,
kjoule/mole 38
Example 5
[0122] Another resin sample was prepared in the fluidized-bed
reactor with the activated catalyst precursor described in Example
2 under the conditions set out in Table 2. This resin was
stabilized with antioxidants (800 ppm Irganox 1010 and 200 ppm
Irgafos 168) and compounded on a Banbury mixer under mild
conditions. The resin was then blown into film on a 50 mm Alpine
extruder equipped with a 100 mm die and 1 mm die gap at 54.4 kg/hr
(120 lb/hr), 4:1 blow up ratio (BUR) and 71.1 cm (28 inch) stalk
height. The process and fabrication conditions are described in the
table below. The bimodal molecular weight distribution of the resin
as measured by Gel Permeation Chromatography (GPC) is shown in FIG.
2, and the resin properties are indicated in Table 2.
2 TABLE 2 Example 2 CATALYST PRECURSOR TIBA, mmol/g Ti Component of
Example 1 1.0 Zirconium, mmol/g Ti Component of Example 1 0.07 MAO,
mmol/g Ti Component of Example 1 3.0 PROCESS Ethylene Partial
Pressure, kPa (psi) 1300 (188.5) Isopentane Partial Pressure, kPa
(psi) 122 (17.7) 1-Hexene/Ethylene Molar Ratio, mol/mol 0.009
Hydrogen/Ethylene Molar Ratio, mol/mol 0.021 Bed Temp., .degree. C.
87.9 MMAO, ppm 85 TMA, ppm 143 H.sub.2O/C.sub.2H.sub.4, ppmv 11.4
RESIN CHARACTERISTICS HLMI, g/10 min 7.3 MFR 142 Density, g/cc
0.9532 BLOWN FILM EVALUATION Melt Pressure, kPa (psi) 38,783 (5625)
Melt Temperature, .degree. C. (.degree. F.) 213 (416) Bubble
Stability (max linespeed, m/min (ft/min)) >91.4 (300) Gauge,
microns (mils) 12.7 (0.5) Dart Drop, F50 g 269 MD Tear, g/m (g/mil)
629,921 (16) TD Tear, g/m (g/mil) 2,795,276 (71)
[0123] The film was blown at very high line speeds (up to the
maximum line speed of 91.4 m/min (300 feet/min)) without
encountering uncontrollable bubble oscillations. This indicated
that the resin has excellent bubble stability. The film properties
of the resin were also good.
Examples 6 and 7
[0124] Additional samples were prepared in the fluidized-bed
reactor using the activated catalyst precursor of Examples 2 and 3
under the conditions set out in Table 3 below. The resin was
stabilized with antioxidants (2000 ppm Irganox 1010, 2000 ppm
Irgafos 168) and compounded on the Banbury mixer under mild
conditions. The process and blown film fabrication conditions are
also described below in Table 3. The bimodal molecular weight
distributions of the resins of Examples 6 and 7, as measured by Gel
Permeation Chromatography (GPC), are shown in FIGS. 3 and 4,
respectively.
3 TABLE 3 Example 6 Example 7 Example 2 Example 3 CATALYST
PRECURSOR TIBA, mmol/g Ti Component of Example 1 1.0 1.0 Zirconium,
mmol/g Ti Component of 0.07 0.07 Example 1 MMAO or MAO, mmol/g Ti
Component of 3.0 3.0 Example 1 PROCESS Ethylene Partial Pressure,
kPa (psi) 1120 1045 (162.5) (151.5) Isopentane Partial Pressure,
kPa (psi) 88.3 88.9 (12.8) (12.9) 1-Hexene/Ethylene Molar Ratio,
mol/mol 0.009 0.008 Hydrogen/Ethylene Molar Ratio, mol/mol 0.015
0.016 Bed Temp., .degree. C. 94.9 95.0 MMAO, ppm 77 173 TMA, ppm
161 165 H.sub.2O/C.sub.2H.sub.4 ppmv 11.4 11.4 RESIN
CHARACTERISTICS HLMI, g/10 min 4.6 6.0 MFR 73 70 Density, g/cc
0.952 0.953 Blown Film Evaluation Melt Pressure, kPa (psi) 43,781
39,990 (6350) (5800) Melt Temperature, .degree. C. (.degree. F.)
212 214 (414) (417) Bubble Stability (max linespeed, m/min >91.4
>91.4 (ft/min)) (300) (300) Gauge, microns (mil) 12.7 12.7 (0.5)
(0.5) Dart Drop, F50 g 481 457 MD Tear, g/m (g/mil) 629,921 669,291
(16) (17) TD Tear, g/m (g/mil) 2,362,205 2,992,126 (60) (76)
[0125] The resins had excellent bubble stability as indicated by
the maximum line speed being greater than the 91.4 m/min (300
ft/min) machine limit. In addition, the films had excellent film
properties as indicated by dart impacts greater than 400 gms and MD
tear values greater than 393,701 g/m (10 g/mil) for a 12.7 microns
(0.5 mil) gauge film.
* * * * *