U.S. patent application number 11/504257 was filed with the patent office on 2006-12-07 for very low density polyethylene blends.
This patent application is currently assigned to UNIVATION TECHNOLOGIES, LLC. Invention is credited to James McLeod Farley, Paul Masten German, Richard W. Halle, George Panagopoulos.
Application Number | 20060276594 11/504257 |
Document ID | / |
Family ID | 32069440 |
Filed Date | 2006-12-07 |
United States Patent
Application |
20060276594 |
Kind Code |
A1 |
German; Paul Masten ; et
al. |
December 7, 2006 |
Very low density polyethylene blends
Abstract
Blends of very low density polyethylene produced using
metallocene catalysts (mVLDPE) and linear low density polyethylene
(LLDPE) are disclosed. The polymer blends include a
metallocene-catalyzed VLDPE polymer having a density of less than
0.916 g/cm.sup.3, the VLDPE polymer preferably being linear and
without long chain branching, and a LLDPE polymer having a density
of from 0.916 to 0.940 g/cm.sup.3. The polymer blends are
particularly suitable in blown and cast film applications.
Inventors: |
German; Paul Masten;
(Friendswood, TX) ; Farley; James McLeod; (League
City, TX) ; Halle; Richard W.; (Houston, TX) ;
Panagopoulos; George; (Cypress, TX) |
Correspondence
Address: |
UNIVATION TECHNOLOGIES LLC
5555 SAN FELIPE, SUITE 1950
HOUSTON
TX
77056
US
|
Assignee: |
UNIVATION TECHNOLOGIES, LLC
Houston
TX
|
Family ID: |
32069440 |
Appl. No.: |
11/504257 |
Filed: |
August 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10297777 |
Oct 28, 2003 |
7125933 |
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PCT/US01/20077 |
Jun 22, 2001 |
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11504257 |
Aug 10, 2006 |
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60213571 |
Jun 22, 2000 |
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60243208 |
Oct 25, 2000 |
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60270802 |
Feb 23, 2001 |
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60278315 |
Mar 23, 2001 |
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60278567 |
Mar 23, 2001 |
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60278560 |
Mar 23, 2001 |
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Current U.S.
Class: |
525/240 |
Current CPC
Class: |
C08L 2205/025 20130101;
C08L 23/04 20130101; C08L 23/0815 20130101; C08L 2314/06 20130101;
C08L 23/0815 20130101; C08L 23/04 20130101; B32B 27/322 20130101;
C08L 2205/02 20130101; C08L 2205/03 20130101; C08L 2666/06
20130101; Y10T 428/31938 20150401; C08L 2666/06 20130101 |
Class at
Publication: |
525/240 |
International
Class: |
C08L 23/04 20060101
C08L023/04 |
Claims
1-2. (canceled)
3. A multilayer film, comprising a first layer and a second layer,
at least one of the layers comprising a polymer blend composition,
the polymer blend composition comprising: (i) a copolymer derived
from ethylene and one or more C.sub.3-C.sub.20 alpha olefin
comonomers, said copolymer having: a) a comonomer content of from 5
to 15 wt. %, b) a density of less than 0.916 g/cm.sup.3, c) a
composition distribution breadth index in the range of from 55% to
70%, d) a molecular weight distribution Mw/Mn of from 2 to 3, e) a
molecular weight distribution Mz/Mw of less than 2, and f) a
bi-modal composition distribution; and (ii) a linear low density
polyethylene polymer having a density of from 0.916 to 0.940
g/cm.sup.3.
4. (canceled)
5. An article, comprising a substrate and a film disposed on the
substrate, the film comprising a polymer blend composition, the
polymer blend composition comprising: (i) a copolymer derived from
ethylene and one or more C.sub.3-C.sub.20 alpha olefin comonomers,
said copolymer having: a) a comonomer content of from 5 to 15 wt.
%, b) a density of less than 0.916 g/cm.sup.3, c) a composition
distribution breadth index in the range of from 55% to 70%, d) a
molecular weight distribution Mw/Mn of from 2 to 3, and e) a
molecular weight distribution Mz/Mw of less than 2; and (ii) a
linear low density polyethylene polymer having a density of from
0.916 to 0.940 g/cm.sup.3.
6. The multi-layer film, or the article of claim 5, wherein the
copolymer is produced using an unbridged bis-Cp metallocene
catalyst system.
7. The multi-layer film, or the article of claim or 5, wherein the
copolymer is produced in a gas phase polymerization process.
8. The multi-layer film, or the article of claim or 5, wherein the
copolymer is produced in a gas phase polymerization process at a
pressure in the range of from 100 psig to 1000 psig.
9. The multi-layer film, or the article of claim or 5, wherein the
copolymer is produced using an unbridged bis-Cp metallocene
catalyst system in a gas phase polymerization process at a pressure
in the range of from 100 psig to 1000 psig.
10. The multi-layer film of claim 3, wherein the copolymer has a
melt index of 5 g/10 minutes or less.
11. The article of claim 4 5, wherein the copolymer has a melt
index of 5 g/10 minutes or more.
12-13. (canceled)
14. A multilayer film, comprising a first layer and a second layer,
at least one of the layers comprising a polymer blend composition,
the polymer blend composition comprising: (a) a
metallocene-catalyzed linear very low density polyethylene polymer
having: (i) a density of less than 0.916 g/cm.sup.3, (ii) a
composition distribution breadth index of 50 to 85% by weight,
(iii) a molecular weight distribution Mw/Mn of 2 to 3, (iv) a
molecular weight distribution Mz/Mw of less than 2, and (v) two
peaks in a TREF measurement, (b) a linear low density polyethylene
polymer having a density of from 0.916 to 0.940 g/cm.sup.3.
15. (canceled)
16. An article, comprising a substrate and a film disposed on the
substrate, the film comprising a polymer blend composition, the
polymer blend composition comprising: (a) a metallocene-catalyzed
linear very low density polyethylene polymer having: (i) a density
of less than 0.916 g/cm.sup.3, (ii) a composition distribution
breadth index of 50 to 85% by weight, (iii) a molecular weight
distribution Mw/Mn of 2 to 3, and (iv) a molecular weight
distribution Mz/Mw of less than 2, and (b) a linear low density
polyethylene polymer having a density of from 0.916 to 0.940
g/cm.sup.3.
17. The multi-layer film, or the article of claim 14 or 16, wherein
the very low density polyethylene polymer is a gas-phase
metallocene produced very low density polyethylene polymer.
18. The multi-layer film, or the article of claim 14 or 16, wherein
the very low density polyethylene polymer has a density of from
0.900 to 0.915 g/cm.sup.3.
19. The multi-layer film, or the article of claim 14 or 16, wherein
the very low density polyethylene polymer is a comonomer of
ethylene and at least one comonomer selected from the group
consisting of C.sub.3 to C.sub.12 alpha olefins.
20. The multi-layer film, or the article of claim 14 or 16, wherein
the linear low density polyethylene polymer is a
metallocene-catalyzed linear low density polyethylene polymer.
21. The multi-layer film, or the article of claim 14 or 16, wherein
the linear low density polyethylene polymer is a gas-phase
metallocene produced linear low density polyethylene polymer.
22. The multi-layer film, or the article of claim 14 or 16, wherein
the linear low density polyethylene polymer is a Ziegler-Natta
produced linear low density polyethylene polymer.
23. The multi-layer film, or the article of claim 14 or 16, wherein
the linear low density polyethylene polymer has a melt index of
from 0.5 to 20 g/10 min.
24. The multi-layer film, or the article of claim 14 or 16, wherein
the linear low density polyethylene polymer is a comonomer of
ethylene and at least one comonomer selected from the group
consisting of C.sub.3 to C.sub.12 linear alpha olefins.
25. The multi-layer film, or the article of claim 14 or 16, wherein
the blend comprises 5-80% by weight of the very low density
polyethylene polymer and 95-20% by weight of the linear low density
polyethylene polymer, based on the total weight of the very low
density polyethylene and linear low density polyethylene
polymers.
26. The multi-layer film, or the article of claim 14 or 16, wherein
the blend further comprises a second very low density polyethylene
polymer having a density of less than 0.916 g/cm.sup.3.
27. The multi-layer film; or the article of claim 14 or 16, wherein
the blend further comprises a second linear low density
polyethylene polymer having a density of from 0.916 to 0.940
g/cm.sup.3.
28. The multi-layer film of claim 14, wherein the very low density
polyethylene polymer has a melt index of 5 g/10 min or less.
29. The multilayer film of claim 14, wherein the multilayer film
comprises at least layers including a top layer, a bottom layer,
and a middle layer.
30. The multilayer film of claim 29, wherein one of the top layer
and the bottom layer comprises the polymer blend composition.
31. The multilayer film of claim 29, wherein the top layer and the
bottom layer comprise the polymer blend composition.
32. The multilayer film of claim 29, wherein the middle layer
comprises the polymer blend composition.
33. The multilayer film of claim 14, wherein the film has a dart
drop value of at least 5 g/.mu.m.
34. The multilayer film of claim 14, wherein at least one layer
does not include the polymer blend and comprises a very low density
polyethylene, a low density polyethylene, a linear low density
polyethylene, a medium density polyethylene, a high density
polyethylene, an ethylene-acrylic acid copolymer, an ethylene-vinyl
acetate copolymer, an ethylene-methacrylic acid copolymer, an
ethylene-vinyl alcohol copolymer, polyvinylidene chloride,
polyethylene terephthalate, oriented polypropylene, nylon, or a
mixture thereof.
35. The article of claim 16, wherein the very low density
polyethylene polymer has a melt index of 5 g/10 min or more.
36. The article of claim 16, wherein the film comprises a monolayer
film.
37. The article of claim 16, wherein the film comprises a
multilayer film.
38. The article of claim 16, wherein the film is extrusion coated
on the substrate.
39. The article of claim 16, wherein the film is laminated to the
substrate.
40. The article of claim 16, wherein the substrate is selected from
the group consisting of glass, plastic, metal foil, and paper.
Description
1. FIELD OF THE INVENTION
[0001] The present invention relates generally to polyolefin blends
and films produced from polyolefin blends. More specifically, the
present invention is directed to blends of very low density
polyethylene produced using metallocene catalysts and linear low
density polyethylene, and films formed of such blends.
2. BACKGROUND
[0002] Various types of polyethylenes are known in the art. Low
density polyethylene ("LDPE") can be prepared at high pressure
using free radical initiators, or in gas phase processes using
Ziegler-Natta or vanadium catalysts, and typically has a density in
the range of 0.916-0.940 g/cm.sup.3. LDPE is also known as
"branched" or "heterogeneously branched" polyethylene because of
the relatively large number of long chain branches extending from
the main polymer backbone. Polyethylene in the same density range,
i.e., 0.916 to 0.940 g/cm.sup.3, which is linear and does not
contain long chain branching is also known; this "linear low
density polyethylene" ("LLDPE") can be produced with conventional
Ziegler-Natta catalysts or with metallocene catalysts. Relatively
higher density LDPE, typically in the range of 0.928 to 0.940
g/cm.sup.3, is sometimes referred to as medium density polyethylene
("MDPE"). Polyethylenes having still greater density are the high
density polyethylenes ("HDPEs"), i.e., polyethylenes having
densities greater than 0.940 g/cm.sup.3, and are generally prepared
with Ziegler-Natta catalysts. Very low density polyethylene
("VLDPE") is also known. VLDPEs can be produced by a number of
different processes yielding polymers with different properties,
but can be generally described as polyethylenes having a density
less than 0.916 g/cm.sup.3, typically 0.890 to 0.915 g/cm.sup.3 or
0.900 to 0.915 g/cm.sup.3.
[0003] U.S. Pat. Nos. 5,272,236 and 5,278,272 disclose
polyethylenes termed "substantially linear ethylene polymers"
("SLEPs"). These SLEPs are characterized as having a polymer
backbone substituted with about 0.01 long chain branches/1000
carbons to about 3 long chain branches/1000 carbons, more
preferably from about 0.01 long chain branches/1000 carbons to
about 1 long chain branches/1000 carbons, and especially from about
0.05 long chain branches/1000 carbons to about 1 long chain
branches/1000 carbons. As used in U.S. Pat. Nos. 5,272,236 and
5,278,272, "long chain branching" is defined as a chain length of
at least about 6 carbons, above which the length cannot be
distinguished using .sup.13C NMR spectroscopy. It is further
disclosed that the long chain branch can be as long as about the
same length as the length of the polymer backbone.
[0004] As used in the present disclosure, the term "linear" is
applied to a polymer that has a linear backbone and does not have
long chain branching; i.e., a "linear" polymer is one that does not
have the long chain branches characteristic of a SLEP polymer.
[0005] Blends of polyethylenes are also known. Blending has been
used to form polymer compositions having altered properties, such
as melt index and various processability characteristics. Blending
has also been used to form polymer compositions having properties
enhanced for particular end uses. For example, polymer blends have
been used to form cast or extruded films with altered film
properties, such as toughness, tear resistance, shrink properties,
and other desired film characteristics.
[0006] U.S. Pat. No. 5,972,444 discloses a polyolefin shrink film
made from a polymer mixture which includes a first ethylene polymer
component having a single differential scanning calorimetry (DSC)
melting peak or a single Analytical Temperature Rising Elution
Fractionation (ATREF) peak and a second ethylene polymer component
having one or more DSC melting peaks, wherein the density
differential between the two component polymers about 0 to about
0.03 g/cm.sup.3. Preferably, the first ethylene polymer component
is a substantially linear ethylene polymer (SLEP) and the second
component polymer is a heterogeneously branched linear ethylene
polymer. Commonly assigned PCT publication WO 98/21276 discloses
similar films.
[0007] U.S. Pat. No. 5,707,751 discloses shrink film compositions
comprising precise combinations of "narrow, substantially singular"
melting point polyethylene with a higher melting point (by at least
about 10.degree. C.) polyethylene.
[0008] U.S. Pat. No. 5,382,631 discloses polymer blends and single
or multilayer films made from the blends. The blends are made from
components having a narrow molecular weight distribution (e.g.,
Mw/Mn 3) and a narrow composition distribution (e.g., CDBI>50%).
The blend components of the blend can all have the same molecular
weight but different comonomer contents, the same comonomer content
but different molecular weights, or comonomer contents which
increase with molecular weight. The blends have either Mw/Mn>3
and/or CDBI<50%, and combinations of each, and can be bimodal
with respect to either or both molecular weight and/or comonomer
content. The blends are generally free of blend components having
both a higher average molecular weight and a lower average
comonomer content than another blend component.
[0009] U.S. Pat. Nos. 5,907,943 and 5,922,441 disclose a
thermoplastic stretch wrap film containing at least three layers,
the inner layer of which comprises a blend of a "low dispersity
polymer" and either a high pressure low density polyethylene resin,
a very low density polyethylene resin or a combination thereof. The
low dispersity polymer has a density of from about 0.88 to 0.94
g/cm.sup.3.
3. SUMMARY
[0010] In one embodiment, the present invention is directed to a
polymer blend, the blend including a very low density polyethylene
(VLDPE) polymer having a density of less than 0.916 g/cm.sup.3, and
a linear low density polyethylene (LLDPE) polymer, having a density
of from 0.916 to 0.940 g/cm.sup.3. Preferably the VLDPE and LLDPE
polymers are metallocene-catalyzed polymers.
[0011] In another embodiment, the present invention is directed to
a polymer blend, the blend including a metallocene-produced VLDPE
polymer, preferably a gas-phase metallocene-produced VLDPE polymer,
the VLDPE polymer being a copolymer of ethylene and at least one
C.sub.3 to C.sub.12 alpha olefin and having a density of from 0.900
to 0.915 g/cm.sup.3 and a melt index of from 0.5 to 20 g/10 min;
and a metallocene-produced LLDPE polymer, the LLDPE polymer being a
copolymer of ethylene and at least one C.sub.3 to C.sub.12 alpha
olefin and having a density of from 0.916 to 0.940 g/cm.sup.3 and a
melt index of from 0.5 to 20 g/10 min. The blend can include, for
example, 5-85% by weight of the VLDPE polymer and 95-15% by weight
of the LLDPE polymer, based on the total weight of the VLDPE and
LLDPE polymers.
[0012] In another embodiment, the present invention is directed to
a polymer blend, the blend including a gas-phase
metallocene-produced VLDPE polymer, the VLDPE polymer being a
copolymer of ethylene and 1-butene, 1-hexene, 4-methyl-1-pentene,
or 1-octene and having a density of from 0.910 to 0.915 g/cm.sup.3,
a melt index of from 0.5 to 20 g/10 min, a composition distribution
breadth index of 60 to 80 wt %, and a molecular weight distribution
(Mw/Mn) of 2.2 to 2.8; and a metallocene-produced LLDPE polymer,
the LLDPE polymer being a copolymer of ethylene and 1-butene,
1-hexene, 4-methyl-1-pentene or 1-octene and having a density of
from 0.916 to 0.925 g/cm.sup.3 and a melt index of from 0.5 to 20
g/10 min. In this embodiment, the blend preferably includes 10-50%
by weight of the VLDPE polymer and 90-50% by weight of the LLDPE
polymer, based on the total weight of the VLDPE and LLDPE
polymers.
[0013] In one embodiment, the present invention is directed to a
VLDPE/LLDPE polymer blend, the blend including a
metallocene-produced VLDPE polymer comprising an ethylene copolymer
with a comonomer content of 25% or less by weight, preferably 20%
or less by weight, and more preferably 15% or less by weight.
[0014] In another embodiment, the present invention is directed to
monolayer films formed from the polymer blends of the
invention.
[0015] In another embodiment, the present invention is directed to
multilayer films, wherein at least one layer of the multilayer film
is formed of a polymer blend of the invention.
[0016] In other embodiments, the invention is directed to articles
including the films of the invention, articles wrapped with the
films of the invention, and substrates coated with the films of the
invention.
4. DETAILED DESCRIPTION
[0017] 4.1 The VLDPE Component
[0018] The polymer blends and films of the present invention
include a very low density polyethylene (VLDPE) polymer. As used
herein, the terms "very low density polyethylene" polymer and
"VLDPE" polymer refer to a polyethylene copolymer having a density
of less than 0.916 g/cm.sup.3. Polymers having more than two types
of monomers, such as terpolymers, are also included within the term
"copolymer" as used herein. The comonomers that are useful in
general for making VLDPE copolymers include .alpha.-olefins, such
as C.sub.3-C.sub.20 .alpha.-olefins and preferably C.sub.3-C.sub.12
.alpha.-olefins. The .alpha.-olefin comonomer can be linear or
branched, and two or more comonomers can be used, if desired.
Examples of suitable comonomers include linear C.sub.3-C.sub.12
.alpha.-olefins, and .alpha.-olefins having one or more
C.sub.1-C.sub.3 alkyl branches, or an aryl group. Specific examples
include propylene; 1-butene, 3-methyl-1-butene;
3,3-dimethyl-1-butene; 1-pentene; 1-pentene with one or more
methyl, ethyl or propyl substituents; 1-hexene with one or more
methyl, ethyl or propyl substituents; 1-heptene with one or more
methyl, ethyl or propyl substituents; 1-octene with one or more
methyl, ethyl or propyl substituents; 1-nonene with one or more
methyl, ethyl or propyl substituents; ethyl, methyl or
dimethyl-substituted 1-decene; 1-dodecene; and styrene. It should
be appreciated that the list of comonomers above is merely
exemplary, and is not intended to be limiting. Preferred comonomers
include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene,
1-hexene, 1-octene and styrene, more preferably 1-butene, 1-hexene,
and 1-octene.
[0019] Although not generally preferred, other useful comonomers
include polar vinyl, conjugated and non-conjugated dienes,
acetylene and aldehyde monomers, which can be included in minor
amounts in terpolymer compositions. Non-conjugated dienes useful as
co-monomers preferably are straight chain, hydrocarbon di-olefins
or cycloalkenyl-substituted alkenes, having 6 to 15 carbon atoms.
Suitable non-conjugated dienes include, for example: (a) straight
chain acyclic dienes, such as 1,4-hexadiene and 1,6-octadiene; (b)
branched chain acyclic dienes, such as 5-methyl-1,4-hexadiene;
3,7-dimethyl-1,6-octadiene; and 3,7-dimethyl-1,7-octadiene; (c)
single ring alicyclic dienes, such as 1,4-cyclohexadiene;
1,5-cyclo-octadiene and 1,7-cyclododecadiene; (d) multi-ring
alicyclic fused and bridged ring dienes, such as tetrahydroindene;
norbornadiene; methyl-tetrahydroindene; dicyclopentadiene (DCPD);
bicyclo-(2.2.1)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl
and cycloalkylidene norbornenes, such as 5-methylene-2-norbornene
(MNB), 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene,
5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene,
and 5-vinyl-2-norbornene (VNB); and (e) cycloalkenyl-substituted
alkenes, such as vinyl cyclohexene, allyl cyclohexene, vinyl
cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene, and vinyl
cyclododecene. Of the non-conjugated dienes typically used, the
preferred dienes are dicyclopentadiene, 1,4-hexadiene,
5-methylene-2-norbornene, 5-ethylidene-2-norbornene, and
tetracyclo-(.DELTA.-11,12)-5,8-dodecene. Particularly preferred
diolefins are 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene,
dicyclopentadiene (DCPD), norbornadiene, and 5-vinyl-2-norbornene
(VNB). Note that throughout this description the terms
"non-conjugated diene" and "diene" are used interchangeably.
[0020] It should be appreciated that the amount of comonomer used
will depend upon the desired density of the VLDPE polymer and the
specific comonomers selected. For one embodiment of the VLDPE
polymer comprising an ethylene/butene copolymer, the molar ratio of
butene to ethylene should be from about 0.015 to 0.035, preferably
from 0.020 to 0.030. For one embodiment of the VLDPE polymer
comprising an ethylene/hexene copolymer, the molar ratio of hexene
to ethylene should be from about 0.015 to 0.035, preferably from
0.020 to 0.030. For one embodiment of the VLDPE polymer comprising
an ethylene/octene copolymer, the molar ratio of octene to ethylene
should be from about 0.015 to 0.035, preferably from 0.020 to
0.030. In general, the comonomer may be present in an amount of 25%
or less by weight, preferably 20% or less by weight and more
preferably 15% or less by weight. In one embodiment, the comonomer
may be present in an amount of 5% or more by weight. It is
well-understood in the art that, for a given comonomer, the density
of the VLDPE polymer produced therefrom decreases as the comonomer
content increases. One skilled in the art can readily determine the
appropriate comonomer content appropriate to produce a VLDPE
polymer having a desired density.
[0021] The VLDPE polymer has a density of less than 0.916
g/cm.sup.3, and preferably at least 0.890 g/cm.sup.3, more
preferably at least 0.900 g/cm.sup.3. Thus, a preferred density
range for the VLDPE polymer is 0.900 g/cm.sup.3 to 0.915
g/cm.sup.3. Alternate lower limits of the VLDPE polymer density
include 0.905 g/cm.sup.3 or 0.910 g/cm.sup.3.
[0022] The VLDPE polymer is further characterized by a melt index
(MI) of from 0.5 to 20 g/10 min (dg/min), as measured in accordance
with ASTM-1238 condition E. In one or more specific embodiments,
alternative lower limits--for the melt index include 0.7 and 1.0
g/10 min, and alternative upper limits for the melt index include
5, 10, 12 and 15 g/10 min, with melt index ranges from any lower
limit to any upper limit being within the scope of the
invention.
[0023] In one embodiment, the VLDPE polymer is made in a
metallocene-catalyzed polymerization process. As used herein, the
terms "metallocene-catalyzed VLDPE," "metallocene-produced VLDPE,"
or "m-VLDPE" refer to a VLDPE polymer having the density and melt
index properties described herein, and being produced in the
presence of a metallocene catalyst. One skilled in the art will
recognize that a metallocene-catalyzed VLDPE polymer has measurable
properties distinguishable from a VLDPE polymer having the same
comonomers in the same weight percentages but produced from a
different process, such as a conventional Ziegler-Natta
polymerization process.
[0024] The terms "metallocene" and "metallocene catalyst precursor"
as used herein mean compounds having a Group 4, 5 or 6 transition
metal (M), with a cyclopentadienyl (Cp) ligand or ligands which may
be substituted, at least one non-cyclopentadienyl-derived ligand
(X), and zero or one heteroatom-containing ligand (Y), the ligands
being coordinated to M and corresponding in number to the valence
thereof. The metallocene catalyst precursors generally require
activation with a suitable co-catalyst (referred to as an
"activator"), in order to yield an "active metallocene catalyst",
i.e., an organometallic complex with a vacant coordination site
that can coordinate, insert, and polymerize olefins. The
metallocene catalyst precursor is preferably one of, or a mixture
of metallocene compounds of either or both of the following
types:
[0025] (1) Cyclopentadienyl (Cp) complexes which have two Cp ring
systems for ligands. The Cp ligands form a sandwich complex with
the metal and can be free to rotate (unbridged) or locked into a
rigid configuration through a bridging group. The Cp ring ligands
can be like or unlike, unsubstituted, substituted, or a derivative
thereof, such as a heterocyclic ring system which may be
substituted, and the substitutions can be fused to form other
saturated or unsaturated rings systems such as tetrahydroindenyl,
indenyl, or fluorenyl ring systems. These cyclopentadienyl
complexes have the general formula.
(Cp.sup.1R.sup.1.sub.m)R.sup.3.sub.n(Cp.sup.2R.sup.2.sub.p)MX.sub.q
wherein: Cp.sup.1 and Cp.sup.2 are the same or different
cyclopentadienyl rings; R.sup.1 and R.sup.2 are each,
independently, a halogen or a hydrocarbyl, halocarbyl,
hydrocarbyl-substituted organometalloid or halocarbyl-substituted
organometalloid group containing up to about 20 carbon atoms; m is
0 to 5; p is 0 to 5; two R.sup.1 and/or R.sup.2 substituents on
adjacent carbon atoms of the cyclopentadienyl ring associated
therewith can be joined together to form a ring containing from 4
to about 20 carbon atoms; R.sup.3 is a bridging group; n is the
number of atoms in the direct chain between the two ligands and is
0 to 8, preferably 0 to 3; M is a transition metal having a valence
of from 3 to 6, preferably from group 4, 5, or 6 of the periodic
table of the elements and is preferably in its highest oxidation
state; each X is a non-cyclopentadienyl ligand and is,
independently, a hydrogen, a halogen or a hydrocarbyl,
oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted
organometalloid, oxyhydrocarbyl-substituted organometalloid or
halocarbyl-substituted organometalloid group containing up to about
20 carbon atoms; and q is equal to the valence of M minus 2.
[0026] (2) Monocyclopentadienyl complexes which have only one Cp
ring system as a ligand. The Cp ligand forms a half-sandwich
complex with the metal and can be free to rotate (unbridged) or
locked into a rigid configuration through a bridging group to a
heteroatom-containing ligand. The Cp ring ligand can be
unsubstituted, substituted, or a derivative thereof such as a
heterocyclic ring system which may be substituted, and the
substitutions can be fused to form other saturated or unsaturated
rings systems such as tetrahydroindenyl, indenyl, or fluorenyl ring
systems. The heteroatom containing ligand is bound to both the
metal and optionally to the Cp ligand through the bridging group.
The heteroatom itself is an atom with a coordination number of
three from Group 15 or a coordination number of two from group 16
of the periodic table of the elements. These mono-cyclopentadienyl
complexes have the general formula
(Cp.sup.1R.sup.1.sub.m)R.sup.3.sub.n(Y.sub.rR.sup.2)MX.sub.s
wherein: each R.sup.1 is independently, a halogen or a hydrocarbyl,
halocarbyl, hydrocarbyl-substituted organometalloid or
halocarbyl-substituted organometalloid group containing up to about
20 carbon atoms, "m" is 0 to 5, and two R.sup.1 substituents on
adjacent carbon atoms of the cyclopentadienyl ring associated there
with can be joined together to form a ring containing from 4 to
about 20 carbon atoms; R.sup.3 is a bridging group; "n" is 0 to 3;
M is a transition metal having a valence of from 3 to 6, preferably
from group 4, 5, or 6 of the periodic table of the elements and is
preferably in its highest oxidation state; Y is a heteroatom
containing group in which the heteroatom is an element with a
coordination number of three from Group 15 or a coordination number
of two from group 16, preferably nitrogen, phosphorous, oxygen, or
sulfur; R.sup.2 is a radical selected from a group consisting of
C.sub.1 to C.sub.20 hydrocarbon radicals, substituted C.sub.1 to
C.sub.20 hydrocarbon radicals, wherein one or more hydrogen atoms
is replaced with a halogen atom, and when Y is three coordinate and
unbridged there may be two R.sup.2 groups on Y each independently a
radical selected from the group consisting of C.sub.1 to C.sub.20
hydrocarbon radicals, substituted C.sub.1 to C.sub.20 hydrocarbon
radicals, wherein one or more hydrogen atoms is replaced with a
halogen atom, and each X is a non-cyclopentadienyl ligand and is,
independently, a hydrogen, a halogen or a hydrocarbyl,
oxyhydrocarbyl, halocarbyl, hydrocarbyl-substituted
organometalloid, oxyhydrocarbyl-substituted organometalloid or
halocarbyl-substituted organometalloid group containing up to about
20 carbon atoms, "s" is equal to the valence of M minus 2.
[0027] Examples of biscyclopentadienyl metallocenes of the type
described in group (1) above for producing the m-VLDPE polymers of
the invention are disclosed in U.S. Pat. Nos. 5,324,800; 5,198,401;
5,278,119; 5,387,568; 5,120,867; 5,017,714; 4,871,705; 4,542,199;
4,752,597; 5,132,262; 5,391,629; 5,243,001; 5,278,264; 5,296,434;
and 5,304,614.
[0028] Illustrative, but not limiting, examples of suitable
biscyclopentadienyl metallocenes of the type described in group (1)
above are the racemic isomers of: [0029]
.mu.-(CH.sub.3).sub.2Si(indenyl).sub.2M(Cl).sub.2; [0030]
.mu.-(CH.sub.3).sub.2Si(indenyl).sub.2M(CH.sub.3).sub.2; [0031]
.mu.-(CH.sub.3).sub.2Si(tetrahydroindenyl).sub.2M(Cl).sub.2; [0032]
.mu.-(CH.sub.3).sub.2Si(tetrahydroindenyl).sub.2M(CH.sub.3).sub.2;
[0033]
.mu.-(CH.sub.3).sub.2Si(indenyl).sub.2M(CH.sub.2CH.sub.3).sub.2;
and [0034]
.mu.-(C.sub.6H.sub.5).sub.2C(indenyl).sub.2M(CH.sub.3).sub.2;
wherein M is Zr or Hf.
[0035] Examples of suitable unsymmetrical cyclopentadienyl
metallocenes of the type described in group (1) above are disclosed
in U.S. Pat. Nos. 4,892,851; 5,334,677; 5,416,228; and 5,449,651;
and in the publication J. Am. Chem. Soc. 1988, 110, 6255.
[0036] Illustrative, but not limiting, examples of preferred
unsymmetrical cyclopentadienyl metallocenes of the type described
in group (1) above are: [0037]
.mu.-(C.sub.6H.sub.5).sub.2C(cyclopentadienyl)(fluorenyl)M(R).sub.2;
[0038]
.mu.-(C.sub.6H.sub.5).sub.2C(3-methylcyclopentadienyl)(fluorenyl)-
M(R).sub.2; [0039]
.mu.-(CH.sub.3).sub.2C(cyclopentadienyl)(fluorenyl)M(R).sub.2;
[0040]
.mu.-(C.sub.6H.sub.5).sub.2C(cyclopentadienyl)(2-methylindenyl)M(CH.sub.3-
).sub.2; [0041]
.mu.-(C.sub.6H.sub.5).sub.2C(3-methylcyclopentadienyl)(2-methylindenyl)M(-
Cl).sub.2; [0042]
.mu.-(C.sub.6H.sub.5).sub.2C(cyclopentadienyl)(2,7-dimethylfluorenyl)M(R)-
.sub.2; and [0043]
.mu.-(CH.sub.3).sub.2C(cyclopentadienyl)(2,7-dimethylfluorenyl)M(R).sub.2-
; wherein M is Zr or Hf, and R is C.sub.1 or CH.sub.3.
[0044] Examples of suitable monocyclopentadienyl metallocenes of
the type described in group (2) above are disclosed in U.S. Pat.
Nos. 5,026,798; 5,057,475; 5,350,723; 5,264,405; 5,055,438; and in
WO 96/002244.
[0045] Illustrative, but not limiting, examples of preferred
monocyclopentadienyl metallocenes of the type described in group
(2) above are: [0046]
.mu.-(CH.sub.3).sub.2Si(cyclopentadienyl)(1-adamantylamido)M(R).sub.2;
[0047]
.mu.-(CH.sub.3).sub.2Si(3-tertbutylcyclopentadienyl)(1-adamantyla-
mido)M(R).sub.2; [0048]
.mu.-(CH.sub.2(tetramethylcyclopentadienyl)(1-adamantylamido)M(R).sub.2;
[0049]
.mu.-(CH.sub.3).sub.2Si(tetramethylcyclopentadienyl)(1-adamantyla-
mido)M(R).sub.2; [0050]
.mu.-(CH.sub.3).sub.2C(tetramethylcyclopentadienyl)(1-adamantylamido)M(R)-
.sub.2; [0051]
.mu.-(CH.sub.3).sub.2Si(tetramethylcyclopentadienyl)(1-tertbutylamido)M(R-
).sub.2; [0052]
.mu.-(CH.sub.3).sub.2Si(fluorenyl)(1-tertbutylamido)M(R).sub.2;
[0053]
.mu.-(CH.sub.3).sub.2Si(tetramethylcyclopentadienyl)(1-cyclododecylamido)-
M(R).sub.2; and [0054]
.mu.-(C.sub.6H.sub.5).sub.2C(tetramethylcyclopentadienyl)(1-cyclododecyla-
mido)M(R).sub.2; wherein M is Ti, Zr or Hf, and R is Cl or
CH.sub.3.
[0055] Other organometallic complexes that are useful catalysts for
the VLDPE polymers described herein are those with diimido ligand
systems, such as are described in WO 96/23010. Other references
describing suitable organometallic complexes include
Organometallics, 1999, 2046; PCT publications WO 99/14250, WO
98/50392, WO 98/41529, WO 98/40420, WO 98/40374, WO 98/47933; and
European publications EP 0 881 233 and EP 0 890 581.
[0056] The metallocene compounds and/or other organometallic
complexes are contacted with an activator to produce an active
catalyst. One class of activators is noncoordinating anions, where
the term "noncoordinating anion" (NCA) means an anion which either
does not coordinate to the transition metal cation or which is only
weakly coordinated to the transition metal cation, thereby
remaining sufficiently labile to be displaced by a neutral Lewis
base. "Compatible" noncoordinating anions are those which are not
degraded to neutrality when the initially formed complex
decomposes. Further, the anion will not transfer an anionic
substituent or fragment to the cation so as to cause it to form a
neutral four coordinate metallocene compound and a neutral
by-product from the anion. Noncoordinating anions useful in
accordance with this invention are those which are compatible,
stabilize the metallocene cation in the sense of balancing its
ionic charge in a +1 state, yet retain sufficient lability to
permit displacement by an ethylenically or acetylenically
unsaturated monomer during polymerization. Additionally, the anions
useful in this invention will be large or bulky in the sense of
sufficient molecular size to largely inhibit or prevent
neutralization of the metallocene cation by Lewis bases other than
the polymerizable monomers that may be present in the
polymerization process. Typically the anion will have a molecular
size of greater than or equal to about 4 angstroms.
[0057] An additional method of making metallocene catalysts uses
ionizing anionic pre-cursors which are initially neutral Lewis
acids but form the cation and anion upon ionizing reaction with the
metallocene compounds. For example, tris(pentafluorophenyl) boron
acts to abstract an alkyl, hydride or silyl ligand from the
metallocene compound to yield a metallocene cation and a
stabilizing non-coordinating anion; see, EP-A-0 427 697 and EP-A-0
520 732. Metallocene catalysts for addition polymerization can also
be prepared by oxidation of the metal centers of transition metal
compounds by anionic precursors containing metallic oxidizing
groups along with the anion groups; see EP-A-0 495 375.
[0058] Examples of suitable activators capable of ionic
cationization of the metallocene compounds of the invention, and
consequent stabilization with a resulting noncoordinating anion,
include:
trialkyl-substituted ammonium salts such as:
[0059] triethylammonium tetraphenylborate; [0060] tripropylammonium
tetraphenylborate; [0061] tri(n-butyl)ammonium tetraphenylborate;
[0062] trimethylammonium tetrakis(p-tolyl)borate; [0063]
trimethylammonium tetrakis(o-tolyl)borate; [0064] tributylammonium
tetrakis(pentafluorophenyl)borate; [0065] tripropylammonium
tetrakis(o,p-dimethylphenyl)borate; [0066] tributylammonium
tetrakis(m,m-dimethylphenyl)borate; [0067] tributylammonium
tetrakis(p-trifluoromethylphenyl)borate; [0068] tributylammonium
tetrakis(pentafluorophenyl)borate; and [0069] tri(n-butyl)ammonium
tetrakis(o-tolyl)borate; N,N-dialkyl anilinium salts such as:
[0070] N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate;
[0071] N,N-dimethylaniliniumtetrakis(heptafluoronaphthyl)borate;
[0072] N,N-dimethylanilinium tetrakis(perfluoro-4-biphenyl)borate;
[0073] N,N-dimethylanilinium tetraphenylborate; [0074]
N,N-diethylanilinium tetraphenylborate; and [0075]
N,N-2,4,6-pentamethylanilinium tetraphenylborate; dialkyl ammonium
salts such as: [0076] di-(isopropyl)ammonium
tetrakis(pentafluorophenyl)borate; and [0077] dicyclohexylammonium
tetraphenylborate; and triaryl phosphonium salts such as: [0078]
triphenylphosphonium tetraphenylborate; [0079]
tri(methylphenyl)phosphonium tetraphenylborate; and [0080]
tri(dimethylphenyl)phosphonium tetraphenylborate.
[0081] Further examples of suitable anionic precursors include
those including a stable carbonium ion, and a compatible
non-coordinating anion. These include: [0082] tropillium
tetrakis(pentafluorophenyl)borate; [0083] triphenylmethylium
tetrakis(pentafluorophenyl)borate; [0084]
benzene(diazonium)tetrakis(pentafluorophenyl)borate; [0085]
tropillium phenyltris(pentafluorophenyl)borate; [0086]
triphenylmethylium phenyl-(trispentafluorophenyl)borate; [0087]
benzene(diazonium)phenyl-tris(pentafluorophenyl)borate; [0088]
tropillium tetrakis(2,3,5,6-tetrafluorophenyl)borate; [0089]
triphenylmethylium tetrakis(2,3,5,6-tetrafluorophenyl)borate;
[0090] benzene(diazonium)tetrakis(3,4,5-trifluorophenyl)borate;
[0091] tropillium tetrakis(3,4,5-trifluorophenyl)borate; [0092]
benzene(diazonium)tetrakis(3,4,5-trifluorophenyl)borate; [0093]
tropillium tetrakis(3,4,5-trifluorophenyl)aluminate; [0094]
triphenylmethylium tetrakis(3,4,5-trifluorophenyl)aluminate; [0095]
benzene(diazonium)tetrakis(3,4,5-trifluorophenyl)aluminate; [0096]
tropillinum tetrakis(1,2,2-trifluoroethenyl)borate; [0097]
triphenylmethylium tetrakis(1,2,2-trifluoroethenyl)borate; [0098]
benzene(diazonium)tetrakis(1,2,2-trifluoroethenyl)borate; [0099]
tropillium tetrakis(2,3,4,5-tetrafluorophenyl)borate; [0100]
triphenylmethylium tetrakis(2,3,4,5-tetrafluorophenyl)borate; and
[0101]
benzene(diazonium)tetrakis(2,3,4,5-tetrafluorophenyl)borate.
[0102] Where the metal ligands include halide moieties, for
example,
(methyl-phenyl)silylene(tetra-methyl-cyclopentadienyl)(tert-butyl-amido)z-
irconium dichloride), which are not capable of ionizing abstraction
under standard conditions, they can be converted via known
alkylation reactions with organometallic compounds such as lithium
or aluminum hydrides or alkyls, alkylalumoxanes, Grignard reagents,
etc. See EP-A-0 500 944, EP-A1-0 570 982 and EP-A1-0 612 768 for
processes describing the reaction of alkyl aluminum compounds with
dihalide substituted metallocene compounds prior to or with the
addition of activating anionic compounds. For example, an aluminum
alkyl compound may be mixed with the metallocene prior to its
introduction into the reaction vessel. Since the alkyl aluminum is
also suitable as a scavenger (as described below), its use in
excess of that normally stoichiometrically required for akylation
of the metallocene will permit its addition to the reaction solvent
with the metallocene compound. Normally, alumoxane would not be
added with the metallocene, so as to avoid premature activation,
but can be added directly to the reaction vessel in the presence of
the polymerizable monomers when serving as both scavenger and
alkylating activator.
[0103] Alkylalumoxanes are additionally suitable as catalyst
activators, particularly for those metallocenes having halide
ligands. An alumoxane useful as a catalyst activator typically is
an oligomeric aluminum compound represented by the general formula
(R--Al--O).sub.n, which is a cyclic compound, or
R(R--Al--O).sub.nAlR.sub.2, which is a linear compound. In these
formulae, each R or R.sub.2 is a C.sub.1 to C.sub.5 alkyl radical,
for example, methyl, ethyl, propyl, butyl or pentyl, and "n" is an
integer from 1 to about 50. Most preferably, R is methyl and "n" is
at least 4, i.e., methylalumoxane (MAO). Alumoxanes can be prepared
by various procedures known in the art. For example, an aluminum
alkyl may be treated with water dissolved in an inert organic
solvent, or it may be contacted with a hydrated salt, such as
hydrated copper sulfate suspended in an inert organic solvent, to
yield an alumoxane. Generally, however prepared, the reaction of an
aluminum alkyl with a limited amount of water yields a mixture of
the linear and cyclic species of the alumoxane.
[0104] Optionally, a scavenging compound is also used. The term
"scavenging compound" as used herein refers to those compounds
effective for removing polar impurities from the reaction solvent.
Such impurities can be inadvertently introduced with any of the
polymerization reaction components, particularly with solvent,
monomer and comonomer feed, and adversely affect catalyst activity
and stability by decreasing or even eliminating catalytic activity,
particularly when a metallocene cation-noncoordinating anion pair
is the catalyst system. The polar impurities, or catalyst poisons,
include water, oxygen, oxygenated hydrocarbons, metal impurities,
etc. Preferably, steps are taken before provision of such into the
reaction vessel, for example, by chemical treatment or careful
separation techniques after or during the synthesis or preparation
of the various components, but some minor amounts of scavenging
compound will still normally be required in the polymerization
process itself. Typically, the scavenging compound will be an
organometallic compound such as the Group-13 organometallic
compounds of U.S. Pat. Nos. 5,153,157 and 5,241,025; EP-A-0 426
638; WO-A-91/09882; WO-A-94/03506; and WO-A-93/14132. Exemplary
compounds include triethyl aluminum, triethyl borane, tri-isobutyl
aluminum, isobutyl aluminumoxane, those having bulky substituents
covalently bound to the metal or metalloid center being preferred
to minimize adverse interaction with the active catalyst.
[0105] The catalyst system is optionally supported, typically on an
inorganic oxide or chloride or a material such as polyethylene,
polypropylene or polystyrene. These catalysts can include partially
and/or fully activated precursor compositions. The catalysts may be
modified by prepolymerization or encapsulation. Specific
metallocenes and catalyst systems useful in practicing the
invention are disclosed in WO 96/11961, and WO 96/11960. Other
non-limiting examples of metallocene catalysts and catalyst systems
are discussed in U.S. Pat. Nos. 4,808,561, 5,017,714, 5,055,438,
5,064,802, 5,124,418, 5,153,157 and 5,324,800. Still other
organometallic complexes and/or catalyst systems are described in
Organometallics, 1999, 2046; PCT publications WO 96/23010, WO
99/14250, WO 98/50392, WO 98/41529, WO 98/40420, WO 98/40374, WO
98/47933; and European publications EP 0 881 233 and EP 0 890
581.
[0106] In a preferred embodiment, the VLDPE polymer is made using a
gas-phase, metallocene-catalyzed polymerization process. As used
herein, the term "gas phase polymerization" refers to
polymerization of monomers in a fluidized bed. In this embodiment,
the VLDPE polymer may be made by polymerizing alpha-olefins in the
presence of a metallocene catalyst under reactive conditions in a
gas phase reactor having a fluidized bed and a fluidizing medium.
In a specific embodiment, the VLDPE polymer can be made by
polymerization in a single reactor (as opposed to multiple
reactors). As discussed in greater detail below, a variety of gas
phase polymerization processes may be used. For example,
polymerization may be conducted in uncondensed or "dry" mode,
condensed mode, or "super-condensed mode." In a specific
embodiment, the liquid in the fluidizing medium can be maintained
at a level greater than 2 weight percent based on the total weight
of the fluidizing medium.
[0107] The material exiting the reactor includes the VLDPE polymer
and a stream containing unreacted monomer gases. Following
polymerization, the polymer is recovered. In certain embodiments,
the stream can be compressed and cooled, and mixed with feed
components, whereupon a gas phase and a liquid phase are then
returned to the reactor.
[0108] Generally, in carrying out the gas phase polymerization
processes described herein, the reactor temperature can be in the
range of 50.degree. C. to 110.degree. C., sometimes higher.
However, the reactor temperature should not exceed the melting
point of the VLDPE being formed. A typical reactor temperature is
80.degree. C. The reactor pressure should be 100 to 1000 psig (0.7
to 7 MPa), preferably 150 to 600 psig (1 to 4 MPa), more preferably
200 to 500 psig (1.4 to 3.5 MPa) and most preferably 250 to 400
psig (1.7 to 2.8 MPa).
[0109] Preferably, the process is operated in a continuous cycle. A
specific, non-limiting embodiment of the gas phase polymerization
process that is operated in a continuous cycle will now be
described, it being understood that other forms of gas
polymerization may also be used.
[0110] A gaseous stream containing one or more monomers is
continuously passed through a fluidized bed under reactive
conditions in the presence of a catalyst as described above. This
gaseous stream is withdrawn from the fluidized bed and recycled
back into the reactor. Simultaneously, polymer product may be
withdrawn from the reactor and new monomer or monomers are added to
replace the reacted monomer(s). In one part of the cycle, in a
reactor, a cycling gas stream is heated by the heat of
polymerization. This heat is removed in another part of the cycle
by a cooling system external to the reactor. Heat generated by the
reaction may be removed in order to maintain the temperature of the
gaseous stream inside the reactor at a temperature below the
polymer and catalyst degradation temperatures. Further, it is often
desirable to prevent agglomeration or formation of chunks of
polymer that cannot be removed as product. This may be accomplished
in a variety of ways known in the art, such as, for example,
through control of the temperature of the gaseous stream in the
reaction bed to a temperature below the fusion or sticking
temperature of the polymer particles produced during the
polymerization reaction.
[0111] Heat should be removed, since the amount of polymer produced
in the fluidized bed polymerization process is generally related to
the amount of heat that can be withdrawn from a reaction zone in a
fluidized bed within the reactor. During the gas phase
polymerization process, heat can be removed from the gaseous
recycle stream by cooling the stream outside the reactor. The
velocity of the gaseous recycle stream in a fluidized bed process
should be sufficient to maintain the fluidized bed in a fluidized
state. In certain conventional fluidized bed reactors, the amount
of fluid circulated to remove the heat of polymerization is often
greater than the amount of fluid required for support of the
fluidized bed and for adequate mixing of the solids in the
fluidized bed. However, to prevent excessive entrainment of solids
in a gaseous stream withdrawn from the fluidized bed, the velocity
of the gaseous stream should be regulated.
[0112] The recycle stream can be cooled to a temperature below the
dew point, resulting in condensing a portion of the recycle stream,
as described in U.S. Pat. Nos. 4,543,399 and 4,588,790. As set
forth in those patents, the resulting stream containing entrained
liquid should be returned to the reactor without the aforementioned
agglomeration and/or plugging that may occur when a liquid is
introduced during the fluidized bed polymerization process. For
purposes of this patent, this intentional introduction of a liquid
into a recycle stream or reactor during the process is referred to
generally as a "condensed mode" operation of the gas phase
polymerization process. As taught by the above mentioned patents,
when a recycle stream temperature is lowered to a point below its
dew point in condensed mode operation, an increase in polymer
production is possible, as compared to production in a
"non-condensing" or "dry" mode, because of increased cooling
capacity. Also, a substantial increase in space time yield, the
amount of polymer production in a given reactor volume, can be
achieved by operating in condensed mode--with little or no change
in product properties. Also, in certain condensed mode operations,
the liquid phase of the two-phase gas/liquid recycle stream mixture
remains entrained or suspended in the gas phase of the mixture. The
cooling of the recycle stream to produce this two-phase mixture
results in a liquid/vapor equilibrium. Vaporization of the liquid
occurs when heat is added or pressure is reduced. The increase in
space time yields are the result of this increased cooling capacity
of the recycle stream which, in turn, is due both to the greater
temperature differential between the entering recycle stream and
the fluidized bed temperature and to the vaporization of condensed
liquid entrained in the recycle stream. In a specific non-limiting
embodiment of the process described herein, a condensed mode of
operation is utilized.
[0113] In operating the gas phase polymerization process to obtain
the VLDPE polymer, the amount of polymer and catalyst, the
operating temperature of the reactor, the ratio of comonomer(s) to
monomer and the ratio of hydrogen to monomer should be determined
in advance, so that the desired density and melt index can be
achieved.
[0114] Although a variety of gas polymerization processes may be
used to make the polyolefins of the present inventions, including
non-condensed or dry mode, it is preferred to use any one of a
variety of condensed mode processes, including the condensed mode
processes described in the above patents, as well as improved
condensed mode gas polymerization processes, such as those
disclosed in U.S. Pat. No. 5,462,999, and 5,405,922. Other types of
condensed mode processes are also applicable, including so-called
"supercondensed mode" processes, as discussed in U.S. Pat. Nos.
5,352,749 and 5,436,304.
[0115] The condensable fluids that can be used in one of the
condensed mode gas phase polymerization operations may include
saturated or unsaturated hydrocarbons. Examples of suitable inert
condensable fluids are readily volatile liquid hydrocarbons, which
may be selected from saturated hydrocarbons containing from 2 to 8
carbon atoms. Some suitable saturated hydrocarbons are propane,
n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane,
isohexane, and other saturated C.sub.6 hydrocarbons, n-heptane,
n-octane and other saturated C.sub.7 and C.sub.8 hydrocarbons, or
mixtures thereof. The preferred inert condensable hydrocarbons are
C.sub.4 and C.sub.6 saturated hydrocarbons. The condensable fluids
may also include polymerizable condensable comonomers such as
olefins, alpha-olefins, diolefins, diolefins containing at least
one alpha-olefin or mixtures thereof including some of the
aforementioned monomers which may be partially or entirely
incorporated into the polymer product.
[0116] The preferred gas-phase, metallocene VLDPE polymers can be
further characterized by a narrow composition distribution. As is
well known to those skilled in the art, the composition
distribution of a copolymer relates to the uniformity of
distribution of comonomer among the molecules of the polymer.
Metallocene catalysts are known to incorporate comonomer very
evenly among the polymer molecules they produce. Thus, copolymers
produced from a catalyst system having a single metallocene
component have a very narrow composition distribution, in that most
of the polymer molecules will have roughly the same comonomer
content, and within each molecule the comonomer will be randomly
distributed. By contrast, conventional Ziegler-Natta catalysts
generally yield copolymers having a considerably broader
composition distribution, with comonomer inclusion varying widely
among the polymer molecules.
[0117] A measure of composition distribution is the "Composition
Distribution Breadth Index" ("CDBI"). The definition of Composition
Distribution Breadth Index (CDBI), and the method of determining
CDBI, can be found in U.S. Pat. No. 5,206,075 and PCT publication
WO 93/03093. From the weight fraction versus composition
distribution curve, the CDBI is determined by establishing the
weight percentage of a sample that has a comonomer content within
50% of the median comonomer content on each side of the median. The
CDBI of a copolymer is readily determined utilizing well known
techniques for isolating individual fractions of a sample of the
copolymer. One such technique is Temperature Rising Elution
Fractionation (TREF) as described in Wild, et al., J. Poly. Sci.,
Poly. Phys. Ed., vol. 20, p. 441 (1982).
[0118] To determine CDBI, a solubility distribution curve is first
generated for the copolymer. This may be accomplished using data
acquired from the TREF technique described above. This solubility
distribution curve is a plot of the weight fraction of the
copolymer that is solubilized as a function of temperature. This is
converted to a weight fraction versus composition distribution
curve. For the purpose of simplifying the correlation of
composition with elution temperature, all fractions are assumed to
have a Mn.gtoreq.15,000, where Mn is the number average molecular
weight of the fraction. Any low weight fractions present generally
represent a trivial portion of the VLDPE polymers. The remainder of
this description and the appended claims maintain this convention
of assuming all fractions have Mn.gtoreq.15,000 in the CDBI
measurement.
[0119] The VLDPE polymers can also be characterized by molecular
weight distribution (MWD). Molecular weight distribution (MWD) is a
measure of the range of molecular weights within a given polymer
sample. It is well known that the breadth of the MWD can be
characterized by the ratios of various molecular weight averages,
such as the ratio of the weight average molecular weight to the
number average molecular weight, Mw/Mn, or the ratio of the
Z-average molecular weight to the weight average molecular weight,
Mz/Mw.
[0120] Mz, Mw and Mn can be measured using gel permeation
chromatography (GPC), also known as size exclusion chromatography
(SEC). This technique utilizes an instrument containing columns
packed with porous beads, an elution solvent, and detector in order
to separate polymer molecules of different sizes. In a typical
measurement, the GPC instrument used is a Waters chromatograph
equipped with ultrastyro gel columns operated at 145.degree. C. The
elution solvent used is trichlorobenzene. The columns are
calibrated using sixteen polystyrene standards of precisely known
molecular weights. A correlation of polystyrene retention volume
obtained from the standards, to the retention volume of the polymer
tested yields the polymer molecular weight.
[0121] Average molecular weights M can be computed from the
expression: M = i .times. N i .times. M i n + 1 i .times. N i
.times. M i n ##EQU1## where N.sub.i is the number of molecules
having a molecular weight M.sub.i. When n=0, M is the number
average molecular weight Mn. When n=1, M is the weight average
molecular weight Mw. When n=2, M is the Z-average molecular weight
Mz. The desired MWD function (e.g., Mw/Mn or Mz/Mw) is the ratio of
the corresponding M values. Measurement of M and MWD is well known
in the art and is discussed in more detail in, for example, Slade,
P. E. Ed., Polymer Molecular Weights Part II, Marcel Dekker, Inc.,
NY, (1975) 287-368; Rodriguez, F., Principles of Polymer Systems
3rd ed., Hemisphere Pub. Corp., NY, (1989) 155-160; U.S. Pat. No.
4,540,753; Verstrate et al., Macromolecules, vol. 21, (1988) 3360;
and references cited therein.
[0122] The VLDPE polymers are preferably linear polymers without
long chain branching. As used in the present disclosure, the term
"linear" is applied to a polymer that has a linear backbone and
does not have long chain branching; i.e., a "linear" polymer is one
that does not have the long chain branches characteristic of a SLEP
polymer as defined in U.S. Pat. Nos. 5,272,236 and 5,278,272. Thus,
a "substantially linear" polymer as disclosed in those patents is
not a "linear" polymer because of the presence of long chain
branching.
[0123] One embodiment of the VLDPE polymers have one or more of the
following characteristics, in addition to the density and other
parameters described herein:
[0124] (a) a composition distribution CDBI of 50 to 85%,
alternatively 60 to 80%, or 55 to 75%, or 55% or more to 70% or
less;
[0125] (b) a molecular weight distribution Mw/Mn of 2 to 3,
alternatively 2.2 to 2.8;
[0126] (c) a molecular weight distribution Mz/Mw of less than 2;
and
[0127] (d) the presence of two peaks in a TREF measurement.
[0128] Particularly preferred VLDPEs having some or all of these
characteristics are the gas phase metallocene-produced VLDPEs
described above.
[0129] Two peaks in the TREF measurement as used in this
specification and the appended claims means the presence of two
distinct normalized ELS (evaporation mass light scattering)
response peaks in a graph of normalized ELS response (vertical or y
axis) versus elution temperature (horizontal or x axis with
temperature increasing from left to right) using the TREF method
disclosed in the EXAMPLES section below. A "peak" in this context
means where the general slope of the graph changes from positive to
negative with increasing temperature. Between the two peaks is a
local minimum in which the general slope of the graph changes from
negative to positive with increasing temperature. "General trend"
of the graph is intended to exclude the multiple local minimums and
maximums that can occur in intervals of 2.degree. C. or less.
Preferably, the two distinct peaks are at least 3.degree. C. apart,
more preferably at least 4.degree. C. apart, even more preferably
at least 5.degree. C. apart. Additionally, both of the distinct
peaks occur at a temperature on the graph above 20.degree. C. and
below 120.degree. C. where the elution temperature is run to
0.degree. C. or lower. This limitation avoids confusion with the
apparent peak on the graph at low temperature caused by material
that remains soluble at the lowest elution temperature. Two peaks
on such a graph indicates a bi-modal composition distribution (CD).
Bimodal CD may also be determined by other methods known to those
skilled in the art. One such alternate method for TREF measurement
than can be used if the above method does not show two peaks is
disclosed in B. Monrabal, "Crystallization Analysis Fractionation:
A New Technique for the Analysis of Branching Distribution in
Polyolefins," Journal of Applied Polymer Science, Vol. 52, 491-499
(1994).
[0130] A preferred balance of properties, particularly in film
applications, according to the invention is achieved when the long
chain branching of the VLDPE is reduced. Therefore, with respect to
the catalyst structures described above, bis-Cp structures are
preferred over mono-Cp structures, unbridged structures are
preferred over bridged structures, and unbridged bis-Cp structures
are the most preferred. Preferred catalyst systems which will
minimize or eliminate long chain branching to produce polymers
substantially free of or free of long chain branching are based on
un-bridged bis-Cp zirconocenes, such as but not limited to
bis(1-methyl-3-n-butyl cyclopentadiane)zirconium dichloride.
[0131] Symmetric metallocenes may be used to produce a VLDPE
polymer of the present invention. Symmetric metallocenes include,
but are not limited to, bis(methylcyclopentadienyl)zirconium
dichloride, bis(1,3-dimethylcyclopentadienyl)zirconium dichloride,
bis(1,2-dimethylcyclopentadienyl)zirconium dichloride,
bis(1,2,4-trimethylcyclopentadienyl)zirconium dichloride,
bis(1,2,3-trimethylcyclopentadienyl)zirconium dichloride,
bis(tetramethylcyclopentadienyl)zirconium dichloride,
bis(pentamethylcyclopentadienyl)zirconium dichloride,
bis(ethylcyclopentadienyl)zirconium dichloride,
bis(propylcyclopentadienyl)zirconium dichloride,
bis(butylcyclopentadienyl)zirconium dichloride,
bis(isobutylcyclopentadienyl)zirconium dichloride,
bis(pentylcyclopentadienyl)zirconium dichloride,
bis(isopentylcyclopentadienyl)zirconium dichloride,
bis(cyclopentylcyclopentadienyl)zirconium dichloride,
bis(phenylcyclopentadienyl)zirconium dichloride,
bis(benzylcyclopentadienyl)zirconium dichloride,
bis(trimethylsilylmethylcyclopentadienyl)zirconium dichloride,
bis(cyclopropylmethylcyclopentadienyl)zirconium dichloride,
bis(cyclopentylmethylcyclopentadienyl)zirconium dichloride,
bis(cyclohexylmethylcyclopentadienyl)zirconium dichloride,
bis(propenylcyclopentadienyl)zirconium dichloride,
bis(butenylcyclopentadienyl)zirconium dichloride,
bis(1,3-ethylmethylcyclopentadienyl)zirconium dichloride,
bis(1,3-propylmethylcyclopentadienyl)zirconium dichloride,
bis(1,3-butylmethylcyclopentadienyl)zirconium dichloride,
bis(1,3-isopropylmethylcyclopentadienyl)zirconium dichloride,
bis(1,3-isobutylmethylcyclopentadienyl)zirconium dichloride,
bis(1,3-methylcyclopentylcyclopentadienyl)zirconium dichloride, and
bis(1,2,4-dimethylpropylcyclopentadienyl)zirconium dichloride.
[0132] Unsymmetric metallocenes may be used to produce a VLDPE
polymer of the present invention. Unsymmetric metallocenes include,
but are not limited to,
cyclopentadienyl(1,3-dimethylcyclopentadienyl)zirconium dichloride,
cyclopentadienyl(1,2,4-trimethylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(tetramethylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(pentamethylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(propylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(butylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(pentylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(isobutylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(cyclopentylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(isopentylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(benzylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(phenylcyclopentadienyl)zirconium
dichloride,
cyclopentadienyl(1,3-propylmethylcyclopentadienyl)zirconium
dichloride,
cyclopentadienyl(1,3-butylmethylcyclopentadienyl)zirconium
dichloride,
cyclopentadienyl(1,3-isobutylmethylcyclopentadienyl)zirconium
dichloride,
cyclopentadienyl(1,2,4-dimethylpropylcyclopentadienyl)zirconium
dichloride,
(tetramethylcyclopentadienyl)(methylcyclopentadienyl)zirconium
dichloride,
(tetramethylcyclopentadienyl)(1,3-dimethylcyclopentadienyl)zirconium
dichloride,
(tetramethylcyclopentadienyl)(1,2,4-trimethylcyclopentadienyl)zirconium
dichloride,
(tetramethylcyclopentadienyl)(propylcyclopentadienyl)zirconium
dichloride,
(tetramethylcyclopentadienyl)(cyclopentylcyclopentadienyl)zirconium
dichloride,
(pentamethylcyclopentadienyl)(methylcyclopentadienyl)zirconium
dichloride,
(pentamethylcyclopentadienyl)(1,3-dimethylcyclopentadienyl)zirconium
dichloride,
(pentamethylcyclopentadienyl)(>1,2,4-trimethylcyclopentadienyl)zirconi-
um dichloride,
(pentamethylcyclopentadienyl)(propylcyclopentadienyl)zirconium
dichloride,
(pentamethylcyclopentadienyl)(cyclopentylcyclopentadienyl)zirconium
dichloride,
cyclopentadienyl(ethyltetramentylcyclopentadienyl)zirconium
dichloride,
cyclopentadienyl(propyltetramentylcyclopentadienyl)zirconium
dichloride,
(methylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconium
dichloride,
(1,3-dimethylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconiu-
m dichloride,
(1,2,4-trimethylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirco-
nium dichloride,
(propylcyclopentadienyl)(propyltetramentylcyclopentadienyl)zirconium
dichloride, cyclopentadienyl(indenyl)zirconium dichloride,
(methylcyclopentadienyl)(indenyl)zirconium dichloride,
(1,3-dimethylcyclopentadienyl)(indenyl)zirconium dichloride,
(1,2,4-trimethylcyclopentadienyl)(indenyl)zirconium dichloride,
(tetramethylcyclopentadienyl)(indenyl)zirconium dichloride,
(pentamethylcyclopentadienyl)(indenyl)zirconium dichloride,
cyclopentadienyl(1-methylindenyl)zirconium dichloride,
cyclopentadienyl(1,3-dimethylindenyl)zirconium dichloride,
cyclopentadienyl(1,2,3-trimethylindenyl)zirconium dichloride,
cyclopentadienyl(4,7-dimethylindenyl)zirconium dichloride,
(tetramethylcyclopentadienyl)(4,7-dimethylinde>nyl)zirconium
dichloride,
(pentamethylcyclopentadienyl)(4,7-dimethylindenyl)zirconium
dichloride, cyclopentadienyl(5,6-dimethylindenyl)zirconium
dichloride,
(pentamethylcyclopentadienyl)(5,6-dimethylindenyl)zirconium
dichloride, and
(tetramethylcyclopentadienyl)(5,6-dimethylindenyl)zirconium
dichloride.
[0133] The preferred method for producing the catalyst of the
invention is described below and can be found in U.S. application
Ser. Nos. 265,533, filed Jun. 24, 1994, now abandoned, and 265,532,
filed Jun. 24, 1994, now abandoned, both are hereto fully
incorporated by reference in their entirety. In a preferred
embodiment, the metallocene catalyst component is typically
slurried in a liquid to form a metallocene solution and a separate
solution is formed containing an activator and a liquid. The liquid
can be any compatible solvent or other liquid capable of forming a
solution or the like with at least one metallocene catalyst
component and/or at least one activator. In the preferred
embodiment the liquid is a cyclic aliphatic or aromatic
hydrocarbon, most preferably toluene. The metallocene and activator
solutions are preferably mixed together and added to a porous
support such that the total volume of the metallocene solution and
the activator solution or the metallocene and activator solution is
less than four times the pore volume of the porous support, more
preferably less than three times, even more preferably less than
two times, and more preferably in the 1-1.5 times to 2.5-4 times
range and most preferably in the 1.5 to 3 times range. Also, in the
preferred embodiment, an antistatic agent is added to the catalyst
preparation.
[0134] In one embodiment, the metallocene catalyst is prepared from
silica dehydrated at 600.degree. C. The catalyst is a commercial
scale catalyst prepared in a mixing vessel with and agitator. An
initial charge of 1156 pounds (462 Kg) toluene is added to the
mixer. This was followed by mixing 925 pounds (421 Kg) of 30
percent by weight methyl aluminoxane in toluene. This is followed
with 100 pounds (46 Kg) of 20 percent by weight
bis(1,3-methyl-n-butyl cyclopentadienyl)zirconium dichloride in
toluene (20.4 pounds (9.3 Kg) of contained metallocene). An
additional 144 pounds (66 Kg) of toluene is added to the mixer to
rinse the metallocene feed cylinder and allowed to mix for 30
minutes at ambient conditions. This is followed by 54.3 pounds (25
Kg) of an AS-990 in toluene, surface modifiers solution, containing
5.3 pounds (2.4 Kg) of contained AS-990. An additional 100 pounds
(46 Kg) of toluene rinsed the surface modifier container and was
added to the mixer. The resulting slurry is vacuum dried at 3.2
psia (70.6 kPa) at 175.degree. F. (79.degree. C.) to a free flowing
powder. The final catalyst weight was 1093 pounds (497 Kg). The
catalyst can have a final zirconium loading of 0.40% and an
aluminum loading of 12.0%.
[0135] In one preferred embodiment a substantially homogenous
catalyst system is preferred. For the purposes of this patent
specification and appended claims, a "substantially homogenous
catalyst" is one in which the mole ratio of the transition metal of
the catalyst component, preferably with an activator, is evenly
distributed throughout a porous support.
[0136] The procedure for measuring the total pore volume of a
porous support is well known in the art. Details of one of these
procedures is discussed in Volume 1, Experimental Methods in
Catalytic Research (Academic Press, 1968) (specifically see pages
67-96). This preferred procedure involves the use of a classical
BET apparatus for nitrogen absorption. Another method well know in
the art is described in Innes, Total porosity and Particle Density
of Fluid Catalysts By Liquid Titration, Vol. 28, No. 3, Analytical
Chemistry 332-334 (March, 1956).
[0137] The mole ratio of the metal of the activator component to
the transition metal of the metallocene component is in the range
of ratios between 0.3:1 to 1000:1, preferably 20:1 to 800:1, and
most preferably 50:1 to 500:1. Where the activator is an ionizing
activator as previously described the mole ratio of the metal of
the activator component to the transition metal component is
preferably in the range of ratios between 0.3:1 to 3:1. component
to the transition metal component is preferably in the range of
ratios between 0.3:1 to 3:1.
[0138] Typically in a gas phase polymerization process a continuous
cycle is employed where in one part of the cycle of a reactor, a
cycling gas stream, otherwise known as a recycle stream or
fluidizing medium, is heated in the reactor by the heat of
polymerization. This heat is removed in another part of the cycle
by a cooling system external to the reactor. (See for example U.S.
Pat. Nos. 4,543,399, 4,588,790, 5,028,670, 5,352,749, 5,405,922,
5,436,304, 5,453,471 and 5,462,999 all of which are fully
incorporated herein by reference.)
[0139] Generally in a gas fluidized bed process for producing
polymer from monomers a gaseous stream containing one or more
monomers is continuously cycled through a fluidized bed in the
presence of a catalyst under reactive conditions. The gaseous
stream is withdrawn from the fluidized bed and recycled back into
the reactor. Simultaneously, polymer product is withdrawn from the
reactor and new or fresh monomer is added to replace the
polymerized monomer.
[0140] In one embodiment of the process of the invention the
process is essentially free of a scavenger. For the purposes of
this patent specification and appended claims the term "essentially
free" means that during the process of the invention no more than
10 ppm of a scavenger based on the total weight of the recycle
stream is present at any given point in time during the process of
the invention.
[0141] In another embodiment of the process of the invention the
process is substantially free of a scavenger. For the purposes of
this patent specification and appended claims the term
"substantially free" is defined to be that during the process of
the invention no more than 50 ppm of a scavenger based on the total
weight of a fluidized bed is present at any given point in time
during the process of the invention.
[0142] In one embodiment during reactor start-up to remove
impurities and ensure polymerization is initiated, a scavenger is
present in an amount less than 300 ppm, preferably less than 250
ppm, more preferably less than 200 ppm, even more preferably less
than 150 ppm, still more preferably less than 100 ppm, and most
preferably less than 50 ppm based on the total bed weight of a
fluidized bed during the first 12 hours from the time the catalyst
is placed into the reactor, preferably up to 6 hours, more
preferably less than 3 hours, even more preferably less than 2
hours, and most preferably less than 1 hour and then the
introduction of the scavenger is halted.
[0143] In another embodiment of the process of the invention the
scavenger is present in an amount sufficient until the catalyst of
the invention has achieved a catalyst productivity on a weight
ratio basis of greater than 1000 grams of polymer per gram of the
catalyst, preferably greater than about 1500, more preferably
greater than 2000, even more preferably greater than 2500, and most
preferably greater than 3000.
[0144] In another embodiment of the process of the invention during
start-up the scavenger is present in an amount sufficient until the
catalyst of the invention has achieved a catalyst productivity 40
percent of that of steady-state, preferably less than 30 percent,
even more preferably less than 20 percent and most preferably less
than 10 percent. For the purposes of this patent specification and
appended claims "steady state" is the production rate, weight of
polymer being produced per hour.
[0145] The productivity of the catalyst or catalyst system is
influenced by the main monomer, (i.e., ethylene or propylene)
partial pressure. The preferred mole percent of the monomer,
ethylene or propylene, is from about 25 to 90 mole percent and the
monomer partial pressure is in the range of from about 75 psia (517
kPa) to about 300 psia (2069 kPa), which are typical conditions in
a gas phase polymerization process.
[0146] When a scavenger is utilized in the process of the invention
the scavenger can be introduced typically into the reactor directly
or indirectly into the recycle stream or into any external means
capable of introducing the scavenger into the reactor. Preferably
the scavenger enters into the reactor directly, and most preferably
directly into the reactor bed or below the distributor plate in a
typical gas phase process, preferably after the bed is in a
fluidized state. In one embodiment the scavenger can be introduced
once, intermittently or continuously to the reactor system.
[0147] The scavenger used in the process of the invention is
introduced to the reactor at a rate equivalent to 10 ppm to 100 ppm
based on the steady state, production rate, and then scavenger
introduction is stopped.
[0148] In yet another embodiment particularly during start-up the
scavenger when used is introduced at a rate sufficient to provide
an increase in catalyst productivity on a weight ratio basis of a
rate of 200 grams of polymer per gram of catalyst per minute,
preferably at a rate of 300, even more preferably at a rate of 400
and most preferably at a rate of 500.
[0149] In another embodiment, the mole ratio of the metal of the
scavenger to the transition metal of the metallocene catalyst
component equals about, about 0.2 multiplied by the ppm of a
scavenger based on the production rate multiplied by the catalyst
productivity in kilograms of polymer per gram of catalyst. The
range of the mole ratio is from about 300 to 10. In a preferred
embodiment, where an alkyl aluminum is used as the scavenger the
mole ratio is represented as aluminum (Al) to transition metal, for
example, zirconium, where the moles of. Al are based on the total
amount of scavenger used.
[0150] It is also preferred that hydrogen not be added to the
system simultaneously with the scavenger. It is also within the
scope of this invention that the scavenger can be introduced on a
carrier separate from that used when a supported metallocene
catalyst system is used in the process of the invention.
[0151] Fines for the purpose of this patent specification and
appended claims are polymer particles less than 125 mu in size.
Fines of this size can be measured by using a standard 120 mesh
unit sieve screen. In a preferred embodiment the amount of
scavenger present in the reactor at any given point in time during
the process of the invention the level of fines less than 125 mu is
less than 10%, preferably less than 1%, more preferably less than
0.85% to less than 0.05%.
[0152] It is within the scope of the invention that a system
external to the reactor for removing scavengers introduced in the
process of the invention from the recycle stream may be used. This
would then prevent the recycle of the scavenger back into the
reactor and prevent scavenger build-up in the reactor system. It is
preferred that such a system is placed prior to the heat exchanger
or compressor in the recycle stream line. It is contemplated that
such a system would condense the scavenger out of the fluidizing
medium in the recycle stream line. It would be preferred that the
fluidizing medium is treated to remove the scavenger, see for
example U.S. Pat. No. 4,460,755, incorporated herein by
reference.
[0153] It is also contemplated by the process of the invention that
scavenger can be intermittently introduced during the process
wherein greater than 90%, preferably greater than 95% of all the
scavenger introduced is removed from the recycle stream. It is also
contemplated by this invention that the catalyst or catalyst system
or components thereof of the invention can be used upon start-up as
a scavenger, however, this would be an expensive procedure.
[0154] In the most preferred embodiment of the invention the
process is a gas phase polymerization process operating in a
condensed mode. For the purposes of this patent specification and
appended claims the process of purposefully introducing a recycle
stream having a liquid and a gas phase into a reactor such that the
weight percent of liquid based on the total weight of the recycle
stream is greater than about 2.0 weight percent is defined to be
operating a gas phase polymerization process in a "condensed
mode".
[0155] In one embodiment of the process of the invention the weight
percent of liquid in the recycle stream based on the total weight
of the recycle stream is in the range of about 2 to about 50 weight
percent, preferably greater than 10 weight percent and more
preferably greater than 15 weight percent and even more preferably
greater than 20 weight percent and most preferably in the range
between about 20 and about 40 percent. However, any level of
condensed can be used depending on the desired production rate.
[0156] In another embodiment of the process of the invention the
amount of scavenger utilized if any is used should be in a mole
ratio less than 100, preferably less than 50, more preferably less
than about 25 based on the mole ratio of the metal of the
transition metal scavenger to the transition metal of the
metallocene where the scavenger is an aluminum containing
organometallic compound and the transition metal of the metallocene
is a Group 4 metal then the mole ratio above is based on the moles
of aluminum to the moles of the Group 4 metal of the catalyst.
[0157] Fouling is a term used to describe the collection of polymer
deposits on surfaces in a reactor. Fouling is detrimental to all
parts of a polymerization process, including the reactor and its
associated systems, hardware, etc. Fouling is especially disruptive
in areas restricting gas flow or liquid flow. The two major areas
of primary concern are the heat exchanger and distributor plate
fouling. The heat exchanger consists of a series of small diameter
tubes arranged in a tube bundle. The distributor plate is a solid
plate containing numerous small diameter orifices through which the
gas contained in a recycle stream is passed through before entering
the reaction zone or distributed into a bed of solid polymer in a
fluidized bed reactor such as described in U.S. Pat. No. 4,933,149,
incorporated herein by reference.
[0158] Fouling manifests itself as an increase in the pressure drop
across either the plate, cooler, or both. Once the pressure drop
becomes too high, gas or liquid can no longer be circulated
efficiently by the compressor, and it is often necessary to shut
the reactor down. Cleaning out the reactor can take several days
and is very time consuming and costly. Fouling can also occur in
the recycle gas piping and compressor, but usually accompanies
plate and cooler fouling.
[0159] To quantify the rate of fouling it is useful to define a
fouling factor, F. F is the fraction of the area of a hole that is
fouled. If F=0 (0%) then there is no fouling. Conversely, if F=1
(100%) the hole is completely plugged. It is possible to relate the
fouling to the pressure drop, DELTA P, at a given time in terms of
the pressure drop of a clean system, DELTA P0. As fouling increases
DELTA P increases and is larger than the initial pressure drop,
DELTA P0. F is given by the following expressions: [See equation in
original] (I) Cooler Fouling [See Original Patent for Chemical
Structure Diagram] (II) In general, when F is greater than about
0.3 to about 0.4 (30-40%) a reactor shutdown is inevitable.
Preferably, F is less than 40%, preferably less than 30%, even more
preferably less than 20%, still more preferably less than 15% and
most preferably less than 10% to 0%. The rate of fouling, the
change in F as a function of time, is used to quantify fouling. If
no fouling occurs the rate of fouling is zero. A minimum acceptable
rate of fouling for a commercial operation is about 12
percent/month or 0.4 percent/day, preferably less than 0.3
percent/day, even more preferably less than 0.2 percent/day and
most preferably less than 0.1 percent/day.
[0160] Particle size is determined as follows; the particle size is
measured by determining the weight of the material collected on a
series of U.S. Standard sieves and determining the weight average
particle size.
[0161] Fines are defined as the percentage of the total
distribution passing through 120 mesh standard sieve.
[0162] In one embodiment, the process is operated using a
metallocene catalyst based on bis(1,3-methyl-n-butyl
cyclopentadienyl)zirconium dichloride is described in this example.
It shows the fouling effect of operating a commercial reactor using
TEAL. This example includes information from a startup of a
commercial reactor on metallocene catalyst.
[0163] Possible optimizations of the gas phase polymerization
process and additional catalyst preparations are disclosed in U.S.
Pat. Nos. 5,763,543, 6,087,291, and 5,712,352, and PCT published
applications WO 00/02930 and WO 00/02931.
[0164] Although the VLPDE polymer component of the VLDPE/LLDPE
blends of the invention has been discussed as a single polymer,
blends of two or more such VLDPE polymers, preferably two or more
m-VLDPE polymers, having the properties described herein are also
contemplated.
[0165] 4.2 The LLDPE Component
[0166] The polymer blend also includes a linear low density
polyethylene (LLDPE) polymer. As used herein, the terms "linear low
density polyethylene" polymer and "LLDPE" polymer refer to a
homopolymer or preferably copolymer of ethylene having a density of
from 0.916 to 0.940 g/cm.sup.3. Polymers having more than two types
of monomers, such as terpolymers, are also included within the term
"copolymer" as used herein. The comonomers that are useful in
general for making LLDPE copolymers include .alpha.-olefins, such
as C.sub.3-C.sub.20 .alpha.-olefins and preferably C.sub.3-C.sub.12
.alpha.-olefins. The .alpha.-olefin comonomer can be linear or
branched, and two or more comonomers can be used, if desired.
Examples of suitable comonomers include linear C.sub.3-C.sub.12
.alpha.-olefins, and .alpha.-olefins having one or more
C.sub.1-C.sub.3 alkyl branches, or an aryl group. Specific examples
include propylene; 3-methyl-1-butene; 3,3-dimethyl-1-butene;
1-pentene; 1-pentene with one or more methyl, ethyl or propyl
substituents; 1-hexene with one or more methyl, ethyl or propyl
substituents; 1-heptene with one or more methyl, ethyl or propyl
substituents; 1-octene with one or more methyl, ethyl or propyl
substituents; 1-nonene with one or more methyl, ethyl or propyl
substituents; ethyl, methyl or dimethyl-substituted 1-decene;
1-dodecene; and styrene. It should be appreciated that the list of
comonomers above is merely exemplary, and is not intended to be
limiting. Preferred comonomers include propylene, 1-butene,
1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and styrene.
[0167] Other useful comonomers include polar vinyl, conjugated and
non-conjugated dienes, acetylene and aldehyde monomers, which can
be included in minor amounts in terpolymer compositions.
Non-conjugated dienes useful as co-monomers preferably are straight
chain, hydrocarbon di-olefins or cycloalkenyl-substituted alkenes,
having 6 to 15 carbon atoms. Suitable non-conjugated dienes
include, for example: (a) straight chain acyclic dienes, such as
1,4-hexadiene and 1,6-octadiene; (b) branched chain acyclic dienes,
such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; and
3,7-dimethyl-1,7-octadiene; (c) single ring alicyclic dienes, such
as 1,4-cyclohexadiene; 1,5-cyclo-octadiene and
1,7-cyclododecadiene; (d) multi-ring alicyclic fused and bridged
ring dienes, such as tetrahydroindene; norbornadiene;
methyl-tetrahydroindene; dicyclopentadiene (DCPD);
bicyclo-(2.2.1)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl
and cycloalkylidene norbornenes, such as 5-methylene-2-norbornene
(MNB), 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene,
5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene,
and 5-vinyl-2-norbornene (VNB); and (e) cycloalkenyl-substituted
alkenes, such as vinyl cyclohexene, allyl cyclohexene, vinyl
cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene, and vinyl
cyclododecene. Of the non-conjugated dienes typically used, the
preferred dienes are dicyclopentadiene, 1,4-hexadiene,
5-methylene-2-norbornene, 5-ethylidene-2-norbornene, and
tetracyclo-(.DELTA.-11,12)-5,8-dodecene. Particularly preferred
diolefins are 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene,
dicyclopentadiene (DCPD), norbornadiene, and 5-vinyl-2-norbornene
(VNB).
[0168] The amount of comonomer used will depend upon the desired
density of the LLDPE polymer and the specific comonomers selected.
One skilled in the art can readily determine the appropriate
comonomer content appropriate to produce an LLDPE polymer having a
desired density.
[0169] The LLDPE polymer has a density of 0.916 g/cm.sup.3 to 0.940
g/cm.sup.3, and preferably from 0.916 g/cm.sup.3 to 0.925
g/cm.sup.3. The LLDPE polymer can have a melt index of from 0.5 to
20 g/10 min (dg/min), as measured in accordance with ASTM-1238
condition E. Alternative lower limits for the melt index include
0.7 and 1.0 g/10 min, and alternative upper limits for the melt
index include 5, 10, 12 and 15 g/10 min, with melt index ranges
from any lower limit to any upper limit being within the scope of
the invention.
[0170] The LLDPE polymer can be produced using any conventional
polymerization process and suitable catalyst, such as a
Ziegler-Natta catalyst or a metallocene catalyst.
Metallocene-catalyzed LLDPEs (m-LLDPE) are preferred. Particularly
preferred m-LLDPEs are the gas-phase, metallocene catalyzed LLDPEs
described in WO 94/26816. Examples of suitable LLDPEs include the
metallocene LLDPEs commercially available under the trade name
EXCEED.TM. from ExxonMobil Chemical Co., Houston, Tex., the
Ziegler-Natta LLDPEs available as ExxonMobil LL series LLDPEs, from
ExxonMobil Chemical Co., Houston, Tex., and the DOWLEX.TM. LLDPE
resins available from Dow Chemical Co.
[0171] Although the LLPDE polymer component of the VLDPE/LLDPE
blends of the invention has been discussed as a single polymer,
blends of two or more such LLDPE polymers, preferably two or more
metallocene-catalyzed LLDPE polymers, having the properties
described herein are also contemplated.
[0172] 4.3 VLDPE-LLDPE Blends
[0173] In one embodiment, the present invention provides a polymer
blend, the blend including a VLDPE polymer and an LLDPE polymer.
The blend can include any of the VLDPE polymers described herein,
preferably a metallocene-catalyzed VLDPE polymer, and more
preferably a gas-phase produced metallocene catalyzed VLDPE
polymer. The blend can include any of the LLDPE polymers described
herein, preferably a metallocene-catalyzed LLDPE polymer, and more
preferably a gas-phase produced metallocene catalyzed LLDPE
polymer.
[0174] The blends can be formed using conventional equipment and
methods, such a by dry blending the individual components and
subsequently melt mixing in a mixer, or by mixing the components
together directly in a mixer, such as a Banbury mixer, a Haake
mixer, a Brabender internal mixer, or a single or twin-screw
extruder including a compounding extruder and a side-arm extruder
used directly downstream of a polymerization process. Additionally,
additives can be included in the blend, in one or more components
of the blend, and/or in a product formed from the blend, such as a
film, as desired. Such additives are well known in the art, and can
include, for example: fillers; antioxidants (e.g., hindered
phenolics such as IRGANOX.TM. 1010 or IRGANOX.TM. 1076 available
from Ciba-Geigy); phosphites (e.g., IRGAFOS.TM. 168 available from
Ciba-Geigy); anti-cling additives; tackifiers, such as polybutenes,
terpene resins, aliphatic and aromatic hydrocarbon resins, alkali
metal and glycerol stearates and hydrogenated rosins; UV
stabilizers; heat stabilizers; antiblocking agents; release agents;
anti-static agents; pigments; colorants; dyes; waxes; silica;
fillers; talc and the like.
[0175] The blends include at least 5 weight percent and up to 85
weight percent of the VLDPE polymer, and at least 15 weight percent
and up to 95 weight percent of the LLDPE polymer, with these weight
percents based on the total weight of the VLDPE and LLDPE polymers
of the blend. Alternative lower limits of the VLDPE polymer can be
10%, 20%, 30% or 40% by weight. Alternative upper limits of the
VLDPE polymer can be 80%, 70%, 60% or 50% by weight. Ranges from
any lower limit to any upper limit are within the scope of the
invention. Preferred blends include from 5 to 85%, alternatively
from 10-50% or from 10-30% by weight of the VLDPE polymer. The
balance of the weight percentage is the weight of the LLDPE polymer
component.
[0176] In one preferred embodiment, the polymer blend includes a
metallocene-catalyzed VLDPE polymer having a density of less than
0.916 g/cm.sup.3, and an LLDPE polymer having a density of from
0.916 to 0.940 g/cm.sup.3.
[0177] In another preferred embodiment, the polymer blend includes
a gas-phase metallocene-produced VLDPE polymer, the VLDPE polymer
being a copolymer of ethylene and at least one C.sub.3 to C.sub.12
alpha olefin and having a density of from 0.900 to 0.915 g/cm.sup.3
and a melt index of from 0.5 to 20 g/10 min; and a
metallocene-produced LLDPE polymer, the LLDPE polymer being a
copolymer of ethylene and at least one C.sub.3 to C.sub.12 alpha
olefin and having a density of from 0.916 to 0.925 g/cm.sup.3 and a
melt index of from 0.5 to 20 g/10 min, wherein the blend includes
5-85% by weight of the VLDPE polymer and 95-15% by weight of the
LLDPE polymer, preferably 10-50% by weight of the VLDPE polymer and
90-50% by weight of the LLDPE polymer, based on the total weight of
the VLDPE and LLDPE polymers.
[0178] In any of these embodiments, the VLDPE polymer, the LLDPE
polymer, or both, can be blends of such polymers. I.e., the VLDPE
polymer component of the blend can itself be a blend of two or more
VLDPE polymers having the characteristics described herein, and
alternatively or additionally, the LLDPE polymer component of the
blend can itself be a blend of two or more LLDPE polymers having
the characteristics described herein.
[0179] 4.4 Films
[0180] Polymer blends of the present invention are particularly
suitable for film applications. It has been surprisingly found that
films formed from polymer blends of the invention exhibit improved
properties, particularly improved dart impact and puncture
properties, relative to conventional films. The VDLPE/LLDPE polymer
blends of the invention can be used to form cast or blown films
having a single layer (monolayer films) or multiple layers
(multilayer films). When used in multilayer films, the VLDPE/LLDPE
polymer blends can be used in any layer of the film, or in more
than one layer of the film, as desired. When more than one layer of
the film is formed of a VLDPE/LLDPE polymer blend of the present
invention, each such layer can be individually formulated; i.e.,
the layers formed of the VLDPE/LLDPE polymer can be the same or
different chemical composition, density, melt index, thickness,
etc., depending upon the desired properties of the film.
[0181] To facilitate discussion of different film structures of the
invention, the following notation is used herein. Each layer of a
film is denoted "A" or "B", where "A" indicates a conventional film
layer as defined below, and "B" indicates a film layer formed of
any of the VLDPE/LLDPE polymer blends of the present invention.
Where a film includes more than one A layer or more than one B
layer, one or more prime symbols (', '', ''', etc.) are appended to
the A or B symbol to indicate layers of the same type (conventional
or inventive) that can be the same or can differ in one or more
properties, such as chemical composition, density, melt index,
thickness, etc., within the range of these parameters defined
herein. Finally, the symbols for adjacent layers are separated by a
slash (/). Using this notation, a three-layer film having an inner
layer of a VLDPE/LLDPE polymer blend of the invention disposed
between two outer, conventional film layers would be denoted
A/B/A'. Similarly, a five-layer film of alternating
conventional/inventive layers would be denoted A/B/A'/B'/A''.
Unless otherwise indicated, the left-to-right or right-to-left
order of layers does not matter, nor does the order of prime
symbols; e.g., an A/B film is equivalent to a B/A film, and an
A/A'/B/A'' film is equivalent to an A/B/A'/A'' film, for purposes
of the present invention. The relative thickness of each film layer
is similarly denoted, with the thickness of each layer relative to
a total film thickness of 100 (dimensionless) is indicated
numerically and separated by slashes; e.g., the relative thickness
of an A/B/A' film having A and A' layers of 10 .mu.m each and a B
layer of 30 .mu.m is denoted as 20/60/20.
[0182] For the various films described herein, the "A" layer can be
formed of any material known in the art for use in multilayer films
or in film-coated products. Thus, for example, the A layer can be
formed of a polyethylene homopolymer or copolymer, and the
polyethylene can be, for example, a VLDPE, a low density
polyethylene (LDPE), an LLDPE, a medium density polyethylene
(MDPE), or a high density polyethylene (HDPE), as well as other
polyethylenes known in the art. The polyethylene can be produced by
any suitable process, including metallocene-catalyzed processes and
Ziegler-Natta catalyzed processes. Further, the A layer can be a
blend of two or more such polyethylenes, and can include additives
known in the art. Further, one skilled in the art will understand
that the layers of a multilayer film must have the appropriate
viscosity match.
[0183] In multilayer structures, one or more A layers can also be
an adhesion-promoting tie layer, such as PRIMACOR.TM.
ethylene-acrylic acid copolymers available from The Dow Chemical
Co., and/or ethylene-vinyl acetate copolymers. Other materials for
A layers can be, for example, foil, nylon, ethylene-vinyl alcohol
copolymers, polyvinylidene chloride, polyethylene terephthalate,
oriented polypropylene, ethylene-vinyl acetate copolymers,
ethylene-acrylic acid copolymers, ethylene-methacrylic acid
copolymers, graft modified polymers, other polyethylenes, such as
HDPE, LDPE, LMDPE, and MDPE, and paper.
[0184] The "B" layer is formed of a VLDPE/LLDPE polymer blend of
the invention, and can be any of such blends described herein. In
one embodiment, the B layer is formed of a blend of a
metallocene-catalyzed VLDPE polymer having a density of less than
0.916 g/cm.sup.3 and an LLDPE polymer having a density of from
0.916 to 0.940 g/cm.sup.3. In another embodiment, the B layer is
formed of a blend comprising: (a) a gas-phase metallocene-produced
VLDPE copolymer of ethylene and at least one C.sub.3 to C.sub.12
alpha olefin and having a density of from 0.900 to 0.915 g/cm.sup.3
and a melt index of from 0.5 to 10 g/10 min; and (b) a
metallocene-produced LLDPE copolymer of ethylene and at least one
C.sub.3 to C.sub.12 alpha olefin and having a density of from 0.916
to 0.925 g/cm.sup.3 and a melt index of from 0.5 to 10 g/10 min. In
one embodiment, the B layer is formed of a blend comprising a
gas-phase metallocene-produced VLDPE having a melt index having the
lower limits of 0.5 g/10 min or more, 0.7 g/10 min or more, 1 g/10
min or more and having the upper limits of 5 g/10 min or less, 3
g/10 min or less, or 2 g/10 min or less, with melt index ranges
from any lower limit to any upper limit being within the scope of
the invention. In one preferred embodiment, the B layer is formed
of a blend as described herein, wherein the VLDPE component of the
blend has one or more of the following characteristics, in addition
to the density, melt index, and other parameters described
herein:
[0185] (a) a composition distribution CDBI of 50 to 85%,
alternatively 60 to 80%, or 55 to 75%, or 55% or more to 70% or
less;
[0186] (b) a molecular weight distribution Mw/Mn of 2 to 3,
alternatively 2.2 to 2.8;
[0187] (c) a molecular weight distribution Mz/Mw of less than 2;
and
[0188] (d) the presence of two peaks in a TREF measurement.
[0189] As noted above, when the multilayer film has two or more B
layers, the B layers can be the same, or can differ in thickness,
chemical composition, density, melt index, CDBI, MWD, or other
properties, within the range of parameters consistent with the
inventive polymer blends.
[0190] The thickness of each layer of the film, and of the overall
film, is not particularly limited, but is determined according to
the desired properties of the film. Typical film layers have a
thickness of about 1 to 1000 .mu.m, more typically about 5 to 100
.mu.m, and typical films have an overall thickness of 10 to 100
.mu.m.
[0191] In one embodiment, the present invention provides a
single-layer (monolayer) film formed of any of the VLDPE/LLDPE
polymer blends of the invention; i.e., a film having a single layer
which is a B layer as described above.
[0192] In other embodiments, and using the nomenclature described
above, the present invention provides multilayer films with any of
the following exemplary structures:
[0193] (a) two-layer films, such as A/B and B/B';
[0194] (b) three-layer films, such as A/B/A', A/A'/B, B/A/B' and
B/B'/B'';
[0195] (c) four-layer films, such as A/A'/A''/B, A/A'/B/A'',
A/A'/B/B', A/B/A'/B', A/B/B'/A', B/A/A'/B', A/B/B'/B'', B/A/B'/B''
and B/B'/B''/B''';
[0196] (d) five-layer films, such as A/A'/A''/A'''/B,
A/A'/A''/B/A''', A/A'/B/A''/A''', A/A'/A''/B/B', A/A'/B/A''/B',
A/A'/B/B'/A'', A/B/A'/B'/A'', A/B/A'/A''/B, B/A/A'/A''/B',
A/A'/B/B'/B'', A/B/A'/B'/B'', A/B/B'/B''/A', B/A/A'/B'/B'',
B/A/B'/A'/B'', B/A/B'/B''/A', A/B/B'/B''/B''', B/A'/B''/B''',
B/B'/A/B''/B''', and B/B'/B''/B'''/B'''';
[0197] and similar structures for films having six, seven, eight,
nine or more layer. It should be appreciated that films having
still more layers can be formed using the polymer blends of the
invention, and such films are within the scope of the
invention.
[0198] In any of the embodiments above, one or more A layers can be
replaced with a substrate layer, such as glass, plastic, paper,
metal, etc., or the entire film can be coated or laminated onto a
substrate. Thus, although the discussion herein has focussed on
multilayer films, the films of the polymer blends of the present
invention can also be used in as coatings; e.g., films formed of
the inventive polymer blends, or multilayer films including one or
more layers formed of the inventive polymer blends, can be coated
onto a substrate such as paper, metal, glass, plastic and other
materials capable of accepting a coating. Such coated structures
are also within the scope of the present invention.
[0199] As described below, the films can be extrusion cast films or
blown films. The films can further be embossed, or produced or
processed according to other known film processes.
[0200] The films can be tailored to specific applications by
adjusting the thickness, materials and order of the various layers,
as well as the additives in each layer. Films according to the
invention can be used as cling films, stretch films, shipping
sacks, produce bags, lamination films, liners, diaper films, or for
a variety of other suitable end-use applications that will be
apparent to those skilled in the art.
[0201] 4.4.1 Film Properties
[0202] Film properties can be measured by techniques well known in
the art, and specifically described in the Examples herein. It has
been surprisingly found that films of the present invention show
improved strength and puncture properties, relative to films formed
of, for example, LLDPE/LLDPE blends. Specifically, in particular
embodiments, the films of the present invention have dart drop
values of at least 5 g/.mu.m, preferably at least 6 g/.mu.m, more
preferably at least 8 g/.mu.m, and still more preferably at least 9
.mu.m/g, as determined by the procedures described in the Examples
section herein. Dart impact and other film properties are explained
in more detail in the Examples herein.
[0203] 4.5 Producing Films and Coatings
[0204] Films may be formed by any number of well known extrusion or
coextrusion techniques. Any of the blown or chill roll techniques
commonly used are suitable. For example, the composition can be
extruded in a molten state through a flat die and then cooled to
form a film. Alternatively, the composition can be extruded in a
molten state through an annular die and then blown and cooled to
form a tubular, blown film, which can then be axially slit and
unfolded to form a flat film. Films of the invention may be
unoriented, uniaxially oriented or biaxially oriented. Physical
properties of the film may vary from those of the polymer blend,
depending on the film forming techniques used.
[0205] As a specific example, cast films can be prepared using a
pilot scale commercial cast film line machine as follows. Pellets
of the polymeric blend are melted at temperatures ranging from
about 250.degree. C. to about 300.degree. C., with the specific
melt temperature being chosen to match melt viscosities of the
various resins. The melts are conveyed to a coextrusion adapter
that combines the melt flows into a multilayer, coextruded
structure. This layered flow is distributed through a single
manifold film extrusion die to the desired width. The die gap
opening is typically about 0.025 inches (about 600 .mu.m). The
material is then drawn down to the final gauge. The material draw
down ratio is typically about 21:1 for 0.8 mil (20 .mu.m) films. A
vacuum box or air knife can be used to pin the melt exiting the die
opening to a primary chill roll maintained at about 90.degree. F.
(32.degree. C.).
[0206] As another example, blown films can be prepared as follows.
The polymer composition is introduced into the feed hopper of an
extruder, such as a 63.5 mm Egan extruder that is water-cooled,
resistance heated, and has an L/D ratio of 24:1. The film can be
produced using a 15.24 cm Sano die with a 2.24 mm die gap, along
with a Sano dual orifice non-rotating, non-adjustable air ring. The
film is extruded through the die into a film that was cooled by
blowing air onto the surface of the film. The film is drawn from
the die typically forming a cylindrical film that is cooled,
collapsed and optionally subjected to a desired auxiliary process,
such as slitting, treating, sealing or printing. The finished film
can be wound into rolls for later processing, or can be fed into a
bag machine and converted into bags. A particular blown film
process and apparatus suitable for forming films according to
embodiments of the present invention is described in U.S. Pat. No.
5,569,693.
[0207] Multiple-layer films may be formed by methods well known in
the art. The materials forming each layer may be coextruded through
a coextrusion feedblock and die assembly to yield a film with two
or more layers adhered together but differing in composition.
Coextrusion can be adapted to cast film or blown film processes.
Multiple-layer films may also be formed by extrusion coating
whereby a substrate material is contacted with the hot molten
polymer as the polymer exits the die. For instance, an already
formed polypropylene film may be extrusion coated with an ethylene
copolymer film as the latter is extruded through the die.
Multiple-layer films may also be formed by combining two or more
single layer films prepared as described above. The total thickness
of multilayer films may vary based upon the application desired. A
total film thickness of about 5-100 .mu.m, more typically about
10-50 .mu.m, is suitable for most applications. Those skilled in
the art will appreciate that the thickness of individual layers for
multilayer films may be adjusted based on desired end use
performance, resin or copolymer employed, equipment capability and
other factors.
[0208] Yet, another aspect of the invention relates to an article
formed by extrusion coating. For example, a substrate material can
be contacted with the hot molten polymer as the polymer exits the
die. For instance, an already formed polypropylene film may be
extrusion coated with an ethylene copolymer film as the latter is
extruded through the die. Extrusion coatings are generally
processed at higher temperatures than cast films, typically about
600.degree. F., in order to promote adhesion of the extruded
material to the substrate. Other extrusion coating processes are
known in the art, including those described, for example, in U.S.
Pat. Nos. 5,268,230, 5,178,960 and 5,387,630. In one embodiment,
the present invention is directed to a VLDPE/LLDPE film or coating
on a flexible substrate such as paper, metal foil or the like,
wherein the film or coating is formed of a VLDPE/LLDPE polymer
blend. The coating may be a monolayer film or a multi-layer film.
The substrate can also be stock for milk cartons, juice containers,
films, etc. In one embodiment, the coating is formed of a blend
comprising a gas-phase metallocene-produced VLDPE, the VLDPE having
a melt index having the lower limits of 5 g/10 min or more, 7 g/10
min or more, 9 g/10 min or more, 13 g/10 min or more, 14 g/10 min
or more, 15 g/10 min and having the upper limit of 20 g/10 min or
less, with melt index ranges from any lower limit to the upper
limit being within the scope of the invention.
[0209] The films and coatings of the present invention are also
suitable for use in laminate structures; i.e., with a film or a
coating as described herein disposed between two substrates. These
films and coatings are also suitable
[0210] 4.6 Applications
[0211] There are many potential applications of films produced from
the polymer blends described herein. These films can be made into
other forms, such as tape, by any one of a number of well known
cutting, slitting, and/or rewinding techniques. They may be useful
as stretch, sealing, or oriented films.
[0212] Typical applications include:
[0213] packaging, such as bundling, packaging and unitizing a
variety of products including various foodstuffs, rolls of carpet,
liquid containers and various like goods normally containerized
and/or palletized for shipping, storage, and/or display;
[0214] flexible food packaging, including frozen food
packaging;
[0215] bags, such as trash bags and liners, industrial liners,
shipping sacks and produce bags; and
[0216] surface protection applications, with or without stretching,
such as in the temporary protection of surfaces during
manufacturing, transportation, etc.
[0217] Surfaces of the films of this invention can be modified by
known and conventional post-forming techniques such as corona
discharge, chemical treatment, flame treatment, and the like.
5. EXAMPLES
[0218] Materials and Methods
[0219] Metallocene catalysts for the polymerization of the
inventive VLDPE were prepared according to the methods as described
above for an unbridged bis-Cp structure (such as a
bis(1,3-methyl-n-butyl cyclopentadienyl)zirconium dichloride).
[0220] Cast films were prepared using a pilot scale commercial cast
film line machine as described above. The material melt temperature
was approximately 550.degree. F. (290.degree. C.). The die gap
opening was nominally 0.025 inches (0.63 mm). An air knife was used
to pin the melt exiting the die opening to a primary chill roll
maintained at about 80.degree. F. (27.degree. C.). The films
described in the following Examples were prepared as three-layer
A/B/A films or A/A'/A films (comparative), with relative
thicknesses in the ratio 15:70:15 for the three layers A:B:A. For
simplicity, the outer "A" layers are labeled without prime symbols
as these layers are the same in the following examples. The
composition of the "A" and "B" layers is defined below.
[0221] Tensile strength values (tensile yield, ultimate tensile
strength, elongation at break and elongation at yield) were
measured (machine direction ("MD") and transverse direction ("TD"))
in accordance with ASTM D882-97. The film gauge was measured using
ASTM D5947-96 Method C, except that the micrometer calibration was
performed annually with a commercially available gauge block
(Starret Webber 9, JCV1&2).
[0222] The ACD protocol is an analytical-scale TREF (Temperature
Rising Elution Fractionation) test for semi-crystalline copolymers
to characterize the composition distribution (CD). A sample is
dissolved in a good solvent, cooled slowly to allow crystallization
on a support, and then re-dissolved and washed from the support by
heating during elution. Polymer chains are fractionated by
differences in their crystallization temperature in solution, which
is a function of composition (and defect structure). A mass
detector provides concentration vs. elution temperature data; CD
characterization is obtained by applying a calibration curve (i.e.,
mole % comonomer vs. temperature) established using narrow-CD
standards. Two in-house Visual Basic programs are used for data
acquisition and analysis.
[0223] There are really two distributions provided by the ACD test:
[0224] Solubility Distribution (weight fraction vs. solubility
temperature)--measured directly. [0225] Composition Distribution
(weight fraction vs. comonomer content)--obtained by applying the
calibration curve to the solubility distribution.
[0226] Emphasis is usually placed on characterization of the CD.
However, the solubility distribution can be of equal or greater
importance when: [0227] A calibration curve has not been
established for the polymer of interest. [0228] The MW of the
sample is low, or the MWD is broad enough that a significant
portion of the sample is low MW (M<20k). Under these
circumstances, the reported CD is influenced by the MW-dependence
of solubility. The calibration curve must be corrected for the
effect of MW to give the true CD, which requires a priori knowledge
of the relative influence of MW and composition on solubility for a
given sample. In contrast, the solubility distribution correctly
accounts for contributions from both effects, without trying to
separate them.
[0229] Note that the solubility distribution should depend on
solvent type and crystallization/dissolution conditions. If
correctly calibrated, the CD should be independent of changes in
these experimental parameters.
[0230] Composition Distribution Breadth Index (CDBI) was measured
using the following instrumentation: ACD: Modified Waters 150-C for
TREF (Temperature Rising Elution Fractionation) analysis (includes
crystallization column, by-pass plumbing, timing and temperature
controllers); Column: 75 micron glass bead packing in (High
Pressure Liquid Chromotography) HPLC-type column; Coolant: Liquid
Nitrogen; Software: "A-TREF" Visual Basic programs; and Detector:
Polymer Laboratories ELS-1000. Run conditions for the CDBI
measurements were as follows: TABLE-US-00001 GPC settings Mobile
phase: TCE (tetrachlororethylene) Temperature: column compartment
cycles 5-115.degree. C., injector compartment at 115.degree. C. Run
time: 1 hr 30 min Equilibration time: 10 min (before each run) Flow
rate: 2.5 mL/min Injection volume: 300 .mu.L Pressure settings:
transducer adjusted to 0 when no flow, high pressure cut-off set to
30 bar Temperature controller settings. Initial Temperature:
115.degree. C. Ramp 1 Temperature: 5.degree. C. Ramp time = 45
Dwell time = 3 min min Ramp 2 Temperature: 115.degree. C. Ramp time
= 30 Dwell time = 0 min min Alternative temperature controller
settings if two peaks are not exhibited in a TREF measurement.
Initial Temperature: 115.degree. C. Ramp 1 Temperature: 5.degree.
C. Ramp time = 12 Dwell time = 3 min hrs Ramp 2 Temperature:
115.degree. C. Ramp time = 12 Dwell time = 0 min hrs In some case,
longer ramp times may be needed to show two peaks in a TREF
measurement. ELS settings Nebulizer temperature: 120.degree. C.
Evaporator temperature: 135.degree. C. Gas flow rate: 1.0 slm
(standard liters per minute) Heated transfer line temperature:
120.degree. C.
[0231] Melt Index was determined according to ASTM D-1238-95. Melt
index is reported in units of g/10 min, or the numerically
equivalent units of dg/min.
[0232] Density (g/cm.sup.3) was determined using chips cut from
plaques compression/molded in accordance with ASTM D-1928-96
Procedure C, aged in accordance with ASTM D618 Procedure A, and
measured according to ASTM D1505-96.
[0233] Elmendorf tear was determined in accordance with ASTM
D1922-94a. The film gauge was measured according to ASTM D374-94
Method C, except that the micrometer calibration was performed
annually with a commercially available gauge block (Starret Webber
9, JCV1 &2).
[0234] 1% Secant (both MD and TD) was determined in accordance with
ASTM D882-97. The film gauge was measured according to ASTM
D5947-96 Method C, except that the micrometer calibration was
performed annually with a commercially available gauge block
(Starret Webber 9, JCV1&2).
[0235] Dart Drop values were measured in accordance with ASTM
D1709-98 Method A. The film gauge was measured according to ASTM
D374-94 Method C, except that the micrometer calibration was
performed annually with a commercially available gauge block
(Starret Webber 9, JCV1&2).
[0236] The probe puncture energy test was conducted using an
Instron Universal tester that records a continuous reading of the
force (stress) and penetration (strain) curve. A 6 inch by 6 inch
(15 cm by 15 cm) film specimen was securely mounted to a
compression load cell to expose a test area 4 inches (10 cm) in
diameter. Two HDPE slip sheets each 2 in by 2 in (5 cm.times.5 cm)
and each approximately 0.25 mil (6.35 .mu.m) thick were loosely
placed on the test surface. A 3/4 in (1.9 cm) diameter elongated
matte finished stainless steel probe, traveling at a constant speed
of 10 in/min (25 cm/min) was lowered into the film, and a
stress/strain curve was recorded and plotted. The "puncture force"
was the maximum force (lb or N) encountered. The machine was used
to integrate the area under the stress/strain curve, which is
indicative of the energy consumed during the penetration to rupture
testing of the film, and is reported as "puncture energy" or "break
energy" (inlb or J). The probe penetration distance was not
recorded in this test.
[0237] Haze (%) was determined according to ASTM D1003-97 using the
alternate Haze Shortcut Procedure.
[0238] Gloss (unitless, sometimes reported as "GU") at 45 degrees
was determined according to ASTM D2457-97.
[0239] Gauge: film gauge was measured according to ASTM D374-94
Method C, except that the micrometer calibration was performed
annually with a commercially available gauge block (Starret Webber
9, JCV1&2).
[0240] Shrink (%) was determined in the machine direction (MD) and
transverse direction (TD) as follows. A 100 mm circle is cut from
the film. The machine direction is marked, then the specimen is
talced and then heated. The amount of shrinkage is measured in both
MD and TD, and is reported as % MD shrinkage and % TD
shrinkage.
[0241] For measurements of film properties, the film samples were
annealed by heating for 48 hours at 140.degree. F. (60.degree. C.)
prior to testing.
[0242] In the following Examples, resins produced by various
suppliers were used to demonstrate the unique and advantageous
properties of the polymer blend compositions and films of the
present invention. It should be understood that the specific
numerical values of various parameters of these resins described
below are nominal values.
[0243] EXACT.RTM. 3132 is a plastomer made using metallocene
catalyst in a high pressure bulk polymerization process having a
nominal density of 0.9031 g/cm.sup.3, available from ExxonMobil
Chemical Co., Houston, Tex.
[0244] EXCEED.TM. ECD-147 is gas-phase metallocene-produced LLDPE
ethylene/hexene copolymer with a Melt Index of 3.5 dg/min, a
density of 0.921 g/cm.sup.3, a melting point of 120.degree. C., a
CDBI of approximately 60-80%, an MWD (Mw/Mn) of approximately
2.5-2.6, and a Melt Flow Rate (121/12) of approximately 16-18,
available from ExxonMobil Chemical Co., Houston, Tex.
[0245] EXCEED.TM. ECD-320 is a gas-phase metallocene produced LLDPE
ethylene/hexene copolymer with a Melt Index of 1.0 dg/min and a
density of 0.916 g/cm.sup.3, available from ExxonMobil Chemical
Co., Houston, Tex.
[0246] EXCEED.TM. ECD-321 is a gas-phase metallocene produced VLDPE
ethylene/hexene copolymer with a Melt Index of 1.0 dg/min, a
density of 0.912 g/cm.sup.3, a melting point of 116.5.degree. C., a
CDBI of approximately 60-80%, an MWD (Mw/Mn) of approximately
2.5-2.6, and a Melt Flow Rate (121/12) of approximately 16-18,
available from ExxonMobil Chemical Co., Houston, Tex.
[0247] EXCEED.TM. 350D60 is a linear low density polyethylene made
using metallocene catalyst in a gas phase polymerization process
having a nominal density of 0.918 g/cm.sup.3, available from
ExxonMobil Chemical Co., Houston, Tex.
[0248] EXCEED.TM. 357C32 is a gas-phase metallocene produced
m-LLDPE ethylene/hexene copolymer with a Melt Index of 3.5 dg/min,
a density of 0.917 g/cm.sup.3, and a melting point of 115.degree.
C., available from ExxonMobil Chemical Co., Houston, Tex.
[0249] ExxonMobil LL-1001 is a gas-phase Ziegler-Natta produced
LLDPE ethylene/butene copolymer blown film resin having a Melt
Index of 1.0 dg/min, a density of 0.918 g/cm.sup.3, and a melting
point of 121.degree. C., available from ExxonMobil Chemical Co.,
Houston, Tex.
[0250] ExxonMobil LL-1002 is a Ziegler-Natta LLDPE ethylene/butene
copolymer blown film resin having a Melt Index of 2.0 dg/min, a
density of 0.918 g/cm.sup.3, and a melting point of 121.degree. C.,
available from ExxonMobil Chemical Co., Houston, Tex.
[0251] LL-3003 is a Ziegler-Natta LLDPE ethylene/hexene copolymer
cast film resin having a Melt Index of 3.2 dg/min, a density of
0.9175 g/cm.sup.3, a CDBI of approximately 35%, a melting point of
124.degree. C., and a Melt Flow Rate (121/12) of approximately
27-30, available from ExxonMobil Chemical Co., Houston, Tex.
[0252] ExxonMobil LL-3001 is a linear low density polyethylene made
using Ziegler-Natta catalyst in a gas phase polymerization process
having a nominal density of 0.917 g/cm and a nominal melt index of
1 dg/min, available from ExxonMobil Chemical Co., Houston, Tex.
[0253] Dow Affinity 1840 is very low density polyethylene made
using metallocene catalyst in a solution polymerization process
having a nominal density of 0.9104 g/cm.sup.3, available from Dow
Chemical Co.
[0254] Dow Attane 4201 is a very low density polyethylene made
using Ziegler-Natta catalyst in a solution polymerization process
having a nominal density of 0.9132 g/cm.sup.3, available from Dow
Chemical Co.
[0255] In the data tables following, the names of several
commercial EXCEED.TM. resins are abbreviated. Each occurrence of
the abbreviated name should be interpreted as identifying a
particular EXCEED.TM. resin. EXCEED.TM. and EXACT.RTM. are
trademarks of ExxonMobil Chemical Co., Houston, Tex.
Example 1A
[0256] Certain VLDPE polymer resins of the inventions herein were
prepared using gas phase polymerization using metallocene catalyst
systems as disclosed elsewhere herein. The invention resins are
identified below in Table I as Samples A, G, H (EXCEED.TM. 321,
0.9129 g/cm.sup.3), and I. The co-monomers used to make Samples A,
G, H, and I were ethylene and hexene. Fluidized gas phase reactors
were operated to produce the resulting copolymers.
[0257] The polymerizations were conducted in the continuous gas
phase fluidized bed reactors. The fluidized beds of those reactors
were made up of polymer granules. The gaseous feed streams of
ethylene and hydrogen were introduced below each reactor bed into
the recycle gas line. Hexene comonomer was introduced below the
reactor bed. An inert hydrocarbon (isopentane) was also introduced
to each reactor in the recycle gas line, to provide additional heat
capacity to the reactor recycle gases. The individual flow rates of
ethylene, hydrogen and hexene comonomer were controlled to maintain
fixed composition targets. The concentration of the gases were
measured by an on-line gas chromatograph to ensure relatively
constant composition in the recycle gas stream.
[0258] The solid catalyst was injected directly into the fluidized
beds using purified nitrogen. The catalyst rates were adjusted to
maintain constant production rate. The reacting beds of growing
polymer particles were maintained in a fluidized state by a
continuous flow of the make up feed and recycle gas through each
reaction zone. To maintain constant reactor temperatures, the
temperature of the recycle gas was continuously adjusted up or down
to accommodate any changes in the rate of heat generation due to
the polymerization.
[0259] The fluidized bed was maintained at a constant height by
withdrawing a portion of the bed at a rate equal to the formation
of the particulate product. The product was transferred to a purger
vessel to remove entrained hydrocarbons.
[0260] Specifically, the properties of certain "invention"
polymers, i.e., those made in accordance with the gas
polymerization processes corresponding to the invention, using
metallocene catalysts, were compared with certain "comparative"
polymers, i.e., polymers made in accordance with non-invention
methods.
[0261] Referring now to the comparative examples, Sample B was made
using a comparative polymer, specifically, a linear low density
polyethylene (EXCEED.TM. 350D60, 0.9189 g/cm.sup.3) made using
metallocene catalyst in a gas phase polymerization process. Sample
C was made using a linear low density polyethylene (ExxonMobil
LL-3001, 0.9199 g/cm.sup.3) made using Ziegler-Natta catalyst in a
gas phase polymerization process. Sample D was made using a
plastomer (EXACT.RTM. 3132, 0.9031 g/cm.sup.3) made using
metallocene catalyst in a high pressure bulk polymerization
process. Sample E was made using a very low density polyethylene
(Dow Attane 4201, 0.9132 g/cm.sup.3) made using Ziegler-Natta
catalyst in a solution polymerization process. Sample F was made
using a very low density polyethylene (Dow Affinity 1840, 0.9104
g/cm.sup.3) made using metallocene catalyst in a solution
polymerization process. Sample J was made using a linear low
density polyethylene (EXCEED.TM. ECD-320, 0.9178 g/cm.sup.3) made
using metallocene catalyst in a gas phase polymerization process.
Sample K was made using a linear low density polyethylene
(EXCEED.TM. 350D60, 0.9183 g/cm.sup.3) made using metallocene
catalyst in a gas phase polymerization process.
[0262] The resin densities, melt index test results, and
characterization data are set forth in Table 1 below. Comparative
examples of samples B-F and J-K are denoted in the table by an
asterisk (*). TABLE-US-00002 TABLE 1 Resin Properties A B* C* D* E*
F* Resin m-VLDPE m-LLDPE ZN- m- ZN- m-VLDPE (EXCEED LLDPE Plastomer
VLDPE (Affinity 350D60) (LL- (EXACT (Attane 1840) 3001) 3132) 4201)
Density (g/cm.sup.3) Molded 0.9129 0.9189 0.9199 0.9031 0.9132
0.9104 Rheology MI (I2) 1.07 1.17 1.10 1.09 1.00 0.96 HLMI (I21)
18.50 19.14 30.03 18.03 30.37 35.54 Ratio (I21/I2) 17.29 16.36
27.30 16.54 30.37 37.02 MI Swell 1.12 1.08 1.17 1.01 1.14 1.23
Hexene Content Wt % 9.6 7.1 GPC-HT Mn 50612 48653 Mw 100908 100064
Mw/Mn 1.99 2.06 Mz/Mw 1.66 1.69 Mz + 1/Mw 2.46 2.52 ACD CDBI 64.5
6.7 % Solubles 0.6 0.6 DSC (Celsius) 2.sup.nd melt-Peak 118.34
120.70 124.56 118.00 105.68 2.sup.nd peak 103.41 109.62 99.64
123.25 3.sup.rd peak 103.62 Delta H (J/g) 112.06 126.96 128.45
94.76 112.45 108.61 Crystallization-Peak 2.sup.nd peak 3.sup.rd
peak Delta H (J/g) -118.11 -129.63 -130.28 -96.17 -114.28 -114.41 G
H I J* K* Resin m-VLDPE m-VLDPE m-VLDPE m-LLDPE m-LLDPE (ECD-321)
(ECD-320) (EXCEED 350D60) Density (g/cm.sup.3) Molded 0.9114 0.9129
0.9130 0.9178 0.9183 Rheology MI (I2) 0.97 1.17 1.07 1.14 1.12 HLMI
(I21) 17.04 18.18 17.39 18.13 17.41 Ratio (I21/I2) 17.56 15.5 16.3
15.9 15.6 MI Swell 1.10 1.13 1.13 1.12 1.13 Hexene Content Wt %
10.2 10.4 10.0 8.2 7.2 GPC-HT Mn 52016 45411 44528 44050 46928 Mw
102647 101795 103827 103123 103842 Mw/Mn 1.97 2.24 2.33 2.34 2.21
Mz/Mw 1.61 1.73 1.75 1.74 1.73 Mz + 1/Mw 2.29 2.66 2.71 2.65 2.66
ACD CDBI 55.3 71.8 66.4 62.5 72.7 % Solubles 1.1 1.2 1.2 1.7 2.3
DSC (Celsius) 2.sup.nd melt-Peak 117.83 116.50 116.07 119.37 118.03
2.sup.nd peak 101.72 100.81 100.43 106.36 107.76 3.sup.rd peak
Delta H (J/g) 109.84 113.44 122.44 131.67 132.32
Crystallization-Peak 102.37 102.76 105.33 103.27 2.sup.nd peak
89.42 89.96 94.87 94.51 3.sup.rd peak 60.58 61.33 64.74 66.16 Delta
H (J/g) -112.19 -121.36 -122.46 -132.01 -130.65
[0263] The following Examples 1-15 show the properties of
three-layer films formed from conventional materials (comparative)
and from polymer blends according to the present invention. Each
film was of the three-layer A/A'/A (comparative) or A/B/A
structure, with the outer A layers being the same in all examples,
and the three layers in a thickness ratio of 15/70/15. The A layers
were formed of LL3003, a Ziegler-Natta LLDPE ethylene/hexene
copolymer cast film resin. The materials and methods are as
described above.
Examples 1-3 (Comparative)
[0264] Conventional A/A'/A three-layer films were formed for
comparison to the inventive films. The inner layer (A') was formed
of an mLLDPE resin having a nominal density of 0.917 g/cm.sup.3
(EXCEED.TM. 357C32, Example 1) or an mLLDPE resin having a nominal
density of 0.921 g/cm.sup.3 (EXCEED.TM. 147, Examples 2 and 3).
Table 2 shows the film properties. TABLE-US-00003 TABLE 2 Example 1
Example 2 Example 3 (Comparative) (Comparative) (Comparative) Outer
Layer Composition ZN-LLDPE ZN-LLDPE ZN-LLDPE (LL3003) (LL3003)
(LL3003) Inner Layer Composition 100% m-LLDPE 100% m-LLDPE 100%
m-LLDPE (ECD357C32) (ECD147) (ECD147) Inner Layer Resin Density,
g/cm.sup.3 0.917 0.921 0.921 Inner Layer Resin MI, g/10 min 3.5 3.5
3.5 Tensile Strength @ Yield MD, psi (MPa) 1164 (8.03) 1226 (8.45)
1207 (8.32) TD, psi (MPa) 1217 (8.39) 1214 (8.37) 1087 (7.49) at
200% MD, psi (MPa) 1931 (13.3) 1889 (13.0) 2171 (15.0) Ultimate
Tensile MD, psi (MPa) 9873 (68.1) 9029 (62.3) 9622 (66.3) TD, psi
(MPa) 7384 (50.9) 6672 (46.0) 6362 (43.9) Elongation @ Yield MD, %
8.0 8.2 8.7 TD. % 10.4 7.9 6.7 Break Elongation MD, % 547 549 455
TD, % 758 796 726 1% Secant MD, psi (MPa) 16682 (115).sup. 18010
(124).sup. 15971 (110).sup. TD, psi (MPa) 19112 (132).sup. 21142
(146).sup. 18864 (130).sup. Elmendorf Tear MD, g 234 204 95 TD, g
655 649 550 MD, g/mil (g/.mu.m) 252 (9.93) 215 (8.46) 119 (4.69)
TD, g/mil (g/.mu.m) 699 (27.5) 710 (28.0) 688 (27.1) Dart Drop g
149 117 91 g/mil (g/.mu.m) 159 (6.26) 127 (5.00) 114 (4.49) Average
Gauge, mil (.mu.m) 0.94 (24) 0.92 (23) 0.80 (20) Haze, % 1.8 1.8
1.6 Gloss @ 45 degrees 89 89 90.7 Puncture Peak Force, lb (N) 9.62
(42.8) 9.48 (42.2) 8.79 (39.1) Peak Force, lb/mil (N/.mu.m) 10.23
(1.79) 10.3 (1.80) 10.99 (1.92) Break Energy, in lb (J) 33.55
(3.79) 33.3 (3.76) 27.83 (3.14) Break Energy, in lb/mil (mJ/.mu.m)
35.69 (159) 36.2 (161) 34.79 (155) Shrink: MD, % 24 26 44 TD, % 1 0
1 Film Density, g/cm.sup.3 0.9127 0.9141
Examples 4-5
[0265] Three-layer films were made as in Examples 1-3, using either
conventional polymer blends (comparative) or polymer blends of the
invention, for the inner layer. In Example 4, the inner layer was a
blend of 10% by weight m-VLDPE (EXCEED.TM. 321, density 0.912
g/cm.sup.3) and 90% by weight m-LLDPE (EXCEED.TM. 147, density
0.921 g/cm.sup.3). Example 5 is a comparative example. The inner
layer was a blend of 10% by weight m-LLDPE (EXCEED.TM. 320, density
0.916 g/cm.sup.3) and 90% by weight of a second m-LLDPE, EXCEED.TM.
147. Thus, Examples 4 and 5 differ only in that the polymer blend
forming the inner layer was an m-VLDPE/m-LLDPE blend in Example 4
(inventive), and an m-LLDPE/m-LLDPE blend in Example 5
(comparative). Table 3 shows the data. For further comparison, the
data averaging Examples 2 and 3, wherein the inner layer was 100%
m-LLDPE (EXCEED.TM. 147) is also shown. TABLE-US-00004 TABLE 3
Example 5 Examples 2-3 Example 4 (Comparative) (Comparative) Outer
Layer Composition ZN-LLDPE ZN-LLDPE ZN-LLDPE (LL3003) (LL3003)
(LL3003) Inner Layer Composition 10% m-VLDPE 10% m-LLDPE 100%
m-LLDPE (ECD321) (ECD320) (ECD147) 90% m-LLDPE 90% m-LLDPE (ECD147)
(ECD147) Inner Layer Resin Density, g/cm.sup.3 10% 0.912 10% 0.916
0.921 g/cm.sup.3 90% 0.921 90% 0.921 Inner Layer Resin MI, g/10 min
10% 1.0 10% 1.0 100% 3.5 90% 3.5 90% 3.5 Tensile Strength @ Yield
MD, psi (MPa) 1220 (8.41) 1142 (7.87) 1216 (8.39) TD, psi (MPa)
1186 (8.18) 1124 (7.75) 1150 (7.93) at 200% MD, psi (MPa) 1924
(13.3) 1982 (13.7) 2030 (14.0) Ultimate Tensile MD, psi (MPa) 9344
(64.4) 9659 (66.6) 9325 (64.3) TD, psi (MPa) 7028 (48.5) 6280
(43.3) 6517 (44.9) Elongation @ Yield MD, % 8.4 8.7 8.4 TD. % 7.4
8.3 7.3 Break Elongation MD, % 522 475 502 TD, % 775 696 761 1%
Secant MD, psi (MPa) 19395 (134).sup. 16924 (117).sup. 16990
(117).sup. TD, psi (MPa) 20599 (142).sup. 19165 (132).sup. 20003
(138).sup. Elmendorf Tear MD, g 218 115 149 TD, g 651 511 599 MD,
g/mil (g/.mu.m) 234 (9.2) 139 (5.5) 167 (6.6) TD, g/mil (g/.mu.m)
693 (27.3) 616 (24.3) 699 (27.5) Dart Drop: g 126 98 104 g/mil
(g/(.mu.m) 137 (5.39) 120 (4.72) 120 (4.74) Average Gauge, mil
(.mu.m) 0.92 (23) 0.82 (21) 0.86 (22) Haze (%) 1.7 1.6 1.7 Gloss @
45 degrees 90 91.8 89.8 Puncture Peak Force, lb (N) 9.49 (42.2)
9.17 (40.8) 9.13 (40.6) Peak Force, lb/mil (N/.mu.m) 10.31 (1.81)
11.18 (1.96) 10.64 (1.86) Break Energy, in lb (J) 32.32 (3.65)
31.34 (3.54) 30.56 (3.45) Break Energy, in lb/mil (mJ/.mu.m) 35.13
(156) 38.22 (170) 35.49 (158) Shrink MD, % 29 43 35 TD, % -4 -1 0.5
Film Density, g/cm.sup.3 0.9143
Examples 6-9
[0266] Three-layer films were made as in Examples 1-3, using either
conventional polymer blends (comparative) or polymer blends of the
invention, for the inner layer. In Example 6, the inner layer was a
blend of 20% by weight m-VLDPE (EXCEED.TM. 321, density 0.912
g/cm.sup.3) and 80% by weight m-LLDPE (EXCEED.TM. 147, density
0.921 g/cm.sup.3). Examples 7-9 are comparative examples. In
Examples 7-9, the inner layer was a blend of: (a) 20% by weight
m-LLDPE (EXCEED.TM. 320, density 0.916 g/cm.sup.3) and 80% by
weight of a second m-LLDPE (EXCEED.TM. 147, density 0.921
g/cm.sup.3), in Example 7; (b) 20% by weight of a Ziegler-Natta
LLDPE (LL1001, density 0.918 g/cm.sup.3) and 80% by weight of an
m-LLDPE (EXCEED.TM. 147, density 0.921 g/cm.sup.3), in Example 8;
and (c) 20% by weight of a Ziegler-Natta LLDPE (LL1002, density
0.918 g/cm.sup.3) and 80% by weight of an m-LLDPE (EXCEED.TM. 147,
density 0.917 g/cm.sup.3), in Example 9. Example 8 and 9 differ in
the Melt Index of the ZN-LLDPE; LL1001 in Example 8 has a Melt
Index of 1.0 dg/min, and LL1002 in Example 9 has a Melt Index of
2.0 dg/min. Table 4 shows the data. TABLE-US-00005 TABLE 4 Example
7 Example 8 Example 9 Example 6 (Comparative) (Comparative)
(Comparative) Outer Layer Composition ZN-LLDPE ZN-LLDPE ZN-LLDPE
ZN-LLDPE (LL3003) (LL3003) (LL3003) (LL3003) Inner Layer
Composition 20% m-VLDPE 20% m-LLDPE 20% ZN-LLDPE 20% ZN-LLDPE
(ECD321) (ECD320) (LL1001) (LL1002) 80% m-LLDPE 80% m-LLDPE 80%
m-LLDPE 80% m-LLDPE (ECD147) (ECD147) (ECD147) (ECD147) Inner Layer
Resin Density, g/cm.sup.3 20% 0.912 20% 0.916 20% 0.918 20% 0.918
80% 0.921 80% 0.921 80% 0.921 80% 0.917 Inner Layer Resin MI, g/10
min 20% 1.0 20% 1.0 20% 1.0 20% 2.0 80% 3.5 80% 3.5 80% 3.5 80% 3.5
Tensile Strength @ Yield MD, psi (MPa) 1134 (7.82) 1181 (8.14) 1274
(8.78) 1230 (8.48) TD, psi (MPa) 1205 (8.31) 1128 (7.78) 1302
(8.98) 1242 (8.56) at 200% MD, psi (MPa) 1933 (13.3) 2020 (13.9)
1937 (13.4) 1845 (12.7) Ultimate Tensile MD, psi (MPa) 9660 (66.6)
9914 (68.3) 8920 (61.5) 8484 (58.5) TD, psi (MPa) 6790 (46.8) 6725
(46.4) 5870 (40.5) 5663 (39.0) Elongation @ Yield MD, % 7.5 9.5 8.8
8.5 TD. % 9.1 7.5 9.7 8.5 Break Elongation MD, % 521 466 535 568
TD, % 746 705 867 838 1% Secant MD, psi (MPa) 17687 (122).sup.
15163 (105).sup. 16815 (116).sup. 17889 (123).sup. TD, psi (MPa)
20089 (139).sup. 18131 (125).sup. 18487 (127).sup. 21207 (146).sup.
Elmendorf Tear MD, g 246 131 163 117 TD, g 681 494 683 620 MD,
g/mil (g/.mu.m) 268 (10.6) 154 (6.06) 171 (6.73) 127 (5.00) TD,
g/mil (g/.mu.m) 724 (28.5) 588 (23.1) 712 (28.0) 660 (26.0) Dart
Drop g 149 113 95 88 g/mil (g/.mu.m) 164 (6.46) 133 (5.24) 102
(4.02) 95 (3.74) Gauge, mil (.mu.m) Average 0.91 (23) 0.85 (22)
0.93 (24) 0.93 (24) Low 0.87 (22) 0.81 (21) 0.91 (23) 0.91 (23)
High 0.94 (24) 0.89 (23) 0.94 (24) 0.94 (24) Haze (%) 1.7 1.6 1.5
1.6 Gloss 45 degrees 88 91.3 90 91 Puncture Peak Force, lb (N) 9.77
(43.5) 9.49 (42.2) 9.17 (40.8) 8.55 (38.0) Peak Force, lb/mil
(N/.mu.m) 10.74 (1.88) 11.17 (1.96) 9.86 (1.73) 9.19 (1.61) Break
Energy, in lb (J) 32.25 (3.64) 29.68 (3.35) 31.60 (3.57) 27.68
(3.13) Break Energy, in lb/mil (mJ/.mu.m) 35.44 (158) 34.92 (155)
33.98 (151) 29.76 (132) Shrink MD, % 30 46 39 38 TD, % -3 -1 -8 -5
Film Density, g/cm.sup.3 0.9135 0.9154 0.9144
[0267] Table 4 illustrates some surprising features of the films of
the present invention. The inventive sample (Example 6) having an
inner layer of a m-VLDPE/m-LLDPE blend shows increased dart drop
values compared to films having an inner layer of an
m-LLDPE/m-LLDPE blend (Example 7) or ZN-LLDPE/m-LLDPE blends
(Examples 8 and 9). Additionally, Example 6 shows better puncture
resistance, as shown by the higher values for peak force (N) and
break energy.
Examples 10-11 (Comparative)
[0268] Examples 10-11 are comparative examples. Three-layer films
were made as in Examples 1-3. The inner layer was a blend of: (a)
20% by weight of a Ziegler-Natta LLDPE (LL1001, density 0.918
g/cm.sup.3) and 80% by weight of an m-LLDPE (EXCEED.TM. 357C32,
density 0.917 g/cm.sup.3), in Example 10; and (b) 20% by weight of
a Ziegler-Natta LLDPE (LL1002, density 0.918 g/cm.sup.3) and 80% by
weight of an m-LLDPE (EXCEED.TM. 357C32, density 0.917 g/cm.sup.3),
in Example 11. Examples 10 and 11 differ in the Melt Index of the
ZN-LLDPE; LL1001 in Example 10 has a Melt Index of 1.0 dg/min, and
LL1002 in Example 11 has a Melt Index of 2.0 dg/min. Table 5 shows
the data. The data for Example 6 (inventive) are repeated for
comparison. TABLE-US-00006 TABLE 5 Example 10 Example 11 Example 6
(Comparative) (Comparative) Outer Layer Composition ZN-LLDPE
ZN-LLDPE ZN-LLDPE (LL3003) (LL3003) (LL3003) Inner Layer
Composition 20% m-VLDPE 20% ZN-LLDPE 20% ZN-LLDPE (ECD321) (LL1001)
(LL1002) 80% m-LLDPE 80% m-LLDPE 80% m-LLDPE (ECD147) (ECD357)
(ECD357) Inner Layer Resin Density, g/cm.sup.3 20% 0.912 20% 0.918
20% 0.918 80% 0.921 80% 0.917 80% 0.917 Inner Layer Resin MI, g/10
min 20% 1.0 20% 1.0 20% 2.0 80% 3.5 80% 3.5 80% 3.5 Tensile
Strength @ Yield MD, psi (MPa) 1134 (7.82) 1126 (7.76) 1154 (7.96)
TD, psi (MPa) 1205 (8.31) 1166 (8.04) 1139 (7.85) at 200% MD, psi
(MPa) 1933 (13.3) 1825 (12.6) 1828 (12.6) Ultimate Tensile MD, psi
(MPa) 9660 (66.6) 8725 (60.2) 8790 (60.6) TD, psi (MPa) 6790 (46.8)
6145 (42.4) 5613 (38.7) Elongation @ Yield MD, % 7.5 7.9 8.6 TD. %
9.1 7.6 7.6 Break Elongation MD, % 521 543 581 TD, % 746 845 822 1%
Secant MD, psi (MPa) 17687 (122).sup. 18009 (124).sup. 17521
(121).sup. TD, psi (MPa) 20089 (139).sup. 20322 (140).sup. 20659
(142).sup. Elmendorf Tear MD, g 246 204 106 TD, g 681 690 650 MD,
g/mil (g/.mu.m) 268 (10.6) 215 (8.46) 112 (4.4) TD, g/mil (g/.mu.m)
724 (28.5) 726 (28.6) 694 (27.3) Dart Drop: g 149 94 88 g/mil
(g/.mu.m) 164 (6.46) 100 (3.94) 97 (3.82) Average Gauge, mil
(.mu.m) 0.91 (23) 0.94 (24) 0.91 (23) Haze (%) 1.7 1.7 1.8 Gloss 45
degrees 88 89 90 Puncture Peak Force, lb (N) 9.77 (43.5) 9.53
(42.4) 9.05 (40.3) Peak Force, lb/mil (N/.mu.m) 10.74 (1.88) 10.13
(1.77) 9.95 (1.74) Break Energy, in lb (J) 32.25 (3.64) 30.46
(3.44) 28.93 (3.27) Break Energy, in lb/mil (mJ/.mu.m) 35.44 (158)
32.40 (144) 31.79 (141) Shrink MD, % 30 48 46 TD, % -3 -11 -10 Film
Density, g/cm.sup.3 0.9135 0.9141 0.9138
[0269] Comparing Example 6 with the conventional films of Examples
10 and 11, the films of the present invention show higher dart drop
and puncture values than films having as an inner layer a
conventional ZN-LLDPE/m-LLDPE blend.
Examples 12-13
[0270] Three-layer films were made as in Examples 1-3, using either
conventional polymer blends (comparative) or polymer blends of the
invention, for the inner layer. In Example 12, the inner layer was
a blend of 30% by weight m-VLDPE (EXCEED.TM. 321, density 0.912
g/cm.sup.3) and 70% by weight m-LLDPE (EXCEED.TM. 147, density
0.921 g/cm.sup.3). Example 13 is a comparative example. In Example
13, the inner layer was a blend of: 30% by weight of an m-LLDPE
(EXCEED.TM. 320, density 0.916 g/cm.sup.3) and 70% by weight of a
second m-LLDPE (EXCEED.TM. 147, density 0.921 g/cm.sup.3). Table 6
shows the data. TABLE-US-00007 TABLE 6 Example 13 Example 12
(Comparative) Outer Layer Composition ZN-LLDPE ZN-LLDPE (LL3003)
(LL3003) Inner Layer Composition 30% m-VLDPE 30% m-LLDPE (ECD321)
(ECD320) 70% m-LLDPE 70% m-LLDPE (ECD147) (ECD147) Inner Layer
Resin Density, g/cm.sup.3 30% 0.912 30% 0.916 70% 0.921 70% 0.921
Inner Layer Resin MI, g/10 min 30% 1.0 30% 1.0 70% 3.5 70% 3.5
Tensile Strength @ Yield MD, psi (MPa) 1077 (7.43) 1183 (8.16) TD,
psi (MPa) 1114 (7.68) 1132 (7.81) at 200% MD, psi (MPa) 1909 (13.2)
2193 (15.1) Ultimate Tensile MD, psi (MPa) 9926 (68.4) 9955 (68.6)
TD, psi (MPa) 6998 (48.3) 6570 (45.3) Elongation @ Yield MD, % 7.1
8.9 TD. % 7.2 8.7 Break Elongation MD, % 515 437 TD, % 727 710 1%
Secant MD, psi (MPa) 16870 (116).sup. 15772 (109).sup. TD, psi
(MPa) 20007 (138).sup. 18356 (127).sup. Elmendorf Tear MD, g 225
106 TD, g 620 509 MD, g/mil (g/.mu.m) 237 (9.33) 129 (5.08) TD,
g/mil (g/.mu.m) 646 (25.4) 613 (24.1) Dart Drop: g 226 112 g/mil
(g/.mu.m) 246 (9.69) 138 (5.43) Average Gauge, mil (.mu.m) 0.92
(23) 0.81 (21) Haze (%) 1.7 1.5 Gloss 45 degrees 87 91.5 Puncture
Peak Force, lb (N) 10.58 (47.1) 9.41 (41.9) Peak Force, lb/mil
(N/.mu.m) 11.50 (2.01) 11.61 (2.03) Break Energy, in lb (J) 37.07
(4.19) 32.07 (3.62) Break Energy, in lb/mil (mJ/.mu.m) 40.29 (179)
39.60 (176) Shrink MD, % 36 44 TD, % -6 0 Film Density, g/cm.sup.3
0.9125
[0271] Comparing Example 12 with the conventional film of Example
13, the films of the present invention show higher dart drop and
puncture values (peak force (N) and break energy) than films having
as an inner layer a conventional ZN-LLDPE/m-LLDPE blend.
Examples 14-15
[0272] Three-layer films were made as in Examples 1-3, using either
conventional polymer blends (comparative) or polymer blends of the
invention, for the inner layer. In Example 14, the inner layer was
a blend of 50% by weight m-VLDPE (EXCEED.TM. 321, density 0.912
g/cm.sup.3) and 50% by weight m-LLDPE (EXCEED.TM. 147, density
0.921 g/cm.sup.3). Example 15 is a comparative example. In Example
15, the inner layer was a blend of: 50% by weight of an m-LLDPE
(EXCEED.TM. 320, density 0.916 g/cm.sup.3) and 50% by weight of a
second m-LLDPE (EXCEED.TM. 147, density 0.921 g/cm.sup.3). Table 7
shows the data. TABLE-US-00008 TABLE 7 Example 15 Example 14
(Comparative) Outer Layer Composition ZN-LLDPE ZN-LLDPE (LL3003)
(LL3003) Inner Layer Composition 50% m-VLDPE 50% m-LLDPE (ECD321)
(ECD320) 50% m-LLDPE 50% m-LLDPE (ECD147) (ECD147) Inner Layer
Resin Density, g/cm.sup.3 50% 0.912 50% 0.916 50% 0.921 50% 0.921
Inner Layer Resin MI, g/10 min 50% 1.0 50% 1.0 50% 3.5 50% 3.5
Tensile Strength @ Yield MD, psi (MPa) 1069 (7.37) 1141 (7.87) TD,
psi (MPa) 1014 (6.99) 1108 (7.64) at 200% MD, psi (MPa) 2212 (15.3)
2188 (15.1) Ultimate Tensile MD, psi (MPa) 10527 (72.6) 10351
(71.4) TD, psi (MPa) 6972 (48.1) 6814 (47.0) Elongation @ Yield MD,
% 9.7 9.2 TD. % 7.9 8.0 Break Elongation MD, % 412 426 TD, % 660
679 1% Secant MD, psi (MPa) 14883 (103).sup. 16013 (110).sup. TD,
psi (MPa) 16977 (117).sup. 18557 (128).sup. Elmendorf Tear MD, g
142 128 TD, g 378 421 MD, g/mil (g/.mu.m) 171 (6.73) 156 (6.14) TD,
g/mil (g/.mu.m) 450 (17.7) 507 (20.0) Dart Drop: g 220 128 g/mil
(g/.mu.m) 262 (10.3) 154 (6.06) Average Gauge, mil (.mu.m) 0.84
(21) 0.83 (21) Haze (%) 1.5 1.5 Gloss 45 degrees 90.5 92.1 Puncture
Peak Force, lb (N) 9.35 (41.6) 9.75 (43.4) Peak Force, lb/mil
(N/.mu.m) 11.13 (1.95) 11.74 (2.06) Break Energy, in lb (J) 30.08
(3.40) 32.43 (3.66) Break Energy, in lb/mil (mJ/.mu.m) 35.80 (159)
39.07 (174) Shrink MD, % 42 50 TD, % -3 -2 Film Density,
g/cm.sup.3
[0273] Comparing Example 14 with the conventional film of Example
15, the films of the present invention show higher dart drop values
than films having as an inner layer a conventional ZN-LLDPE/m-LLDPE
blend.
[0274] All patents, test procedures, and other documents cited
herein, including priority documents, are fully incorporated by
reference to the extent such disclosure is not inconsistent with
this invention and for all jurisdictions in which such
incorporation is permitted.
* * * * *