Note: Descriptions are shown in the official language in which they were submitted.
STABILIZATION OF MIXED CATALYST POLYETHYLENE
FIELD OF THE INVENTION
This invention relates to the stabilization of polyethylene and to processes
to
prepare stabilized polyethylene.
BACKGROUND OF THE INVENTION
Several different types of catalysts systems are known for the production of
polyethylene. Different types of catalysts typically produce different types
of catalyst
residues in polyethylene. The catalyst residues can be associated with the
undesired
development of color in polyethylene. We have observed that the problem of
color
development can be especially troublesome when the polyethylene is made with a
mixed catalyst system that includes at least a first single site catalyst
composition and
a second Ziegler Natta catalyst composition. We have now discovered a method
to
mitigate this problem.
SUMMARY OF THE INVENTION
In an embodiment, the present invention provides a process for stabilizing a
thermoplastic polyolefin product during melt processing conditions wherein
said
thermoplastic polyolefin product is prepared with at least two catalyst
systems and
contains catalyst residues comprising:
a) titanium;
b) aluminum from at least one alumoxane; and
c) magnesium from magnesium chloride;
said process comprising the step of incorporating into said thermoplastic
polyolefin a stabilizer package comprising:
(i) a first phosphite defined by the formula (I);
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RI
R2 0
R3 R4
X ¨0¨AP
R3
R5
R2 0
wherein R1, R2, R4 and R5 each independently denotes a hydrogen atom, an alkyl
group having 1 to 8 carbon atoms, and R3 denotes a hydrogen atom or an alkyl
group
having 1 to 8 carbon atoms; X denotes a single bond, a sulfur atom or a --CHR6
group
(R6 denotes a hydrogen atom, an alkyl group having 1 to 8 carbon atoms or a
cycloalkyl group having 5 to 8 carbon atoms); A denotes an alkylene group
having 1 to
8 carbon atoms or a *--COR7 group (R7 denotes a single bond or an alkylene
group
having 1 to 8 carbon atoms, and * denotes a bonding hand on the side of
oxygen);
and one of Y and Z denotes a hydroxyl group, an alkoxy group having 1 to 8
carbon
atoms or an aralkyloxy group having 7 to 12 carbon atoms, and the other one of
Y and
Z denotes a hydrogen atom or an alkyl group having 1 to 8 carbon atoms);
(ii) a second phosphite that is different from said first phosphite; and
(iii) a hindered phenolic antioxidant;
subjecting said thermoplastic polyolefin product to sufficient temperature to
melt said
polyolefin.
In another embodiment, the invention provides a process for preparing a
thermoplastic polyethylene product comprising:
a process for preparing a thermoplastic polyethylene product comprising:
1) polymerizing polyethylene, optionally with one or more C3-10 alpha
olefins,
under solution polymerization conditions in the presence of a first single
site catalyst
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system comprising an organotitanium catalyst and an aluminoxane cocatalyst to
form
a first polyethylene solution;
2) polymerizing polyethylene, optionally with one or more C3-10 alpha
olefins,
under solution polymerization conditions in the presence of a second catalyst
system
comprising a titanium catalyst; an organoaluminum cocatalyst and magnesium
chloride to form a second polyethylene solution;
3) combining said first polyethylene solution and said second polyethylene
solution to form a combined polyethylene solution;
4) recovering said thermoplastic polyethylene product from said combined
polyethylene solution; and
5) adding to said thermoplastic polyethylene product a stabilizer system
comprising:
(i) a first phosphite defined by the formula (I);
R.: 41 \
X P-0¨A Y
R3
R- ilk 0
wherein R1, R2, R4 and R5 each independently denotes a hydrogen atom, an alkyl
group having 1 to 8 carbon atoms, and R3 denotes a hydrogen atom or an alkyl
group
having 1 to 8 carbon atoms; X denotes a single bond, a sulfur atom or a --CHR6
group
(R6 denotes a hydrogen atom, an alkyl group having 1 to 8 carbon atoms or a
cycloalkyl group having 5 to 8 carbon atoms); A denotes an alkylene group
having 1 to
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8 carbon atoms or a *--COR7 group (R7 denotes a single bond or an alkylene
group
having 1 to 8 carbon atoms, and * denotes a bonding hand on the side of
oxygen);
and one of Y and Z denotes a hydroxyl group, an alkoxy group having 1 to 8
carbon
atoms or an aralkyloxy group having 7 to 12 carbon atoms, and the other one of
Y and
Z denotes a hydrogen atom or an alkyl group having 1 to 8 carbon atoms);
(ii) a second phosphite that is different from said first phosphite; and
(iii) a hindered phenolic antioxidant.
DETAILED DESCRIPTION OF EMBODIMENTS
Definition of Terms
Other than in the examples or where otherwise indicated, all numbers or
expressions referring to quantities of ingredients, extrusion conditions,
etc., used in
the specification and claims are to be understood as modified in all instances
by the
term "about". Accordingly, unless indicated to the contrary, the numerical
parameters
set forth in the following specification and attached claims are
approximations that can
vary depending upon the desired properties that the various embodiments desire
to
obtain. At the very least, and not as an attempt to limit the application of
the doctrine
of equivalents to the scope of the claims, each numerical parameter should at
least be
construed in light of the number of reported significant digits and by
applying ordinary
rounding techniques. The numerical values set forth in the specific examples
are
reported as precisely as possible. Any numerical values, however, inherently
contain
certain errors necessarily resulting from the standard deviation found in
their
respective testing measurements.
It should be understood that any numerical range recited herein is intended to
include all sub-ranges subsumed therein. For example, a range of "1 to 10" is
intended to include all sub-ranges between and including the recited minimum
value
of 1 and the recited maximum value of 10; that is, having a minimum value
equal to or
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greater than 1 and a maximum value of equal to or less than 10. Because the
disclosed numerical ranges are continuous, they include every value between
the
minimum and maximum values. Unless expressly indicated otherwise, the various
numerical ranges specified in this application are approximations.
All compositional ranges expressed herein are limited in total to and do not
exceed 100 percent (volume percent or weight percent) in practice. Where
multiple
components can be present in a composition, the sum of the maximum amounts of
each component can exceed 100 percent, with the understanding that, and as
those
skilled in the art readily understand, that the amounts of the components
actually used
will conform to the maximum of 100 percent.
In order to form a more complete understanding of this disclosure the
following
terms are defined and should be used with the accompanying figures and the
description of the various embodiments throughout.
Herein the term "desired color index" defines a measurement of color, e.g. a
number that correlates with an observer's perception of a color, where the
observer
has normal color vision. Non-limiting examples of color indexes, include "a
Whiteness
Index (WI)" and "a Yellowness Index (YI)"; in this disclosure WI and YI are
measured
according to ASTM E313-10.
As used herein, the term "monomer" refers to a small molecule that may
chemically
react and become chemically bonded with itself or other monomers to form a
polymer.
As used herein, the term "a-olefin" is used to describe a monomer having a
linear hydrocarbon chain containing from 3 to 20 carbon atoms having a double
bond
at one end of the chain.
As used herein, the terms "ethylene polymer" and polyethylene, refer to
macromolecules produced from ethylene monomers and optionally one or more
additional monomers; regardless of the specific catalyst or specific process
used to
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make the ethylene polymer. In the polyethylene art, the one or more additional
monomers are called "comonomer(s)" and often include a-olefins. The term
"homopolymer" refers to a polymer that contains only one type of monomer.
Common
ethylene polymers include high density polyethylene (HDPE), medium density
polyethylene (MOPE), linear low density polyethylene (LLDPE), very low density
polyethylene (VLDPE), ultralow density polyethylene (ULDPE), plastomer and
elastomers. The term ethylene polymer also includes polymers produced in a
high
pressure polymerization processes; non-limiting examples include low density
polyethylene (LDPE), ethylene vinyl acetate copolymers (EVA), ethylene alkyl
acrylate copolymers, ethylene acrylic acid copolymers and metal salts of
ethylene
acrylic acid (commonly referred to as ionomers). The term ethylene polymer
also
includes block copolymers which may include 2 to 4 comonomers. The term
ethylene
polymer also includes combinations of, or blends of, the ethylene polymers
described
above.
The term "ethylene interpolymer" refers to a subset of polymers within the
"ethylene polymer" group that excludes polymers produced in high pressure
polymerization processes; non-limiting examples of polymer produced in high
pressure processes include LOPE and EVA (the latter is a copolymer of ethylene
and
vinyl acetate).
The term "heterogeneous ethylene interpolymers" refers to a subset of
polymers in the ethylene interpolymer group that are produced using a
heterogeneous
catalyst formulation; non-limiting examples of which include Ziegler-Natta or
chromium
catalysts.
The term "homogeneous ethylene interpolymer" refers to a subset of polymers
in the ethylene interpolymer group that are produced using metallocene or
single-site
catalysts. Typically, homogeneous ethylene interpolymers have narrow molecular
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weight distributions, for example gel permeation chromatography (GPC) Mw/Mn
values
of less than 2.8; Mw and Mn refer to weight and number average molecular
weights,
respectively. In contrast, the Mw/Mn of heterogeneous ethylene interpolymers
are
typically greater than the Mw/Mn of homogeneous ethylene interpolymers. In
general,
homogeneous ethylene interpolymers also have a narrow comonomer distribution,
i.e.
each macromolecule within the molecular weight distribution has a similar
comonomer
content. Frequently, the composition distribution breadth index "CDBI" is used
to
quantify how the comonomer is distributed within an ethylene interpolymer, as
well as
to differentiate ethylene interpolymers produced with different catalysts or
processes.
The "CDBI50" is defined as the percent of ethylene interpolymer whose
composition is
within 50% of the median comonomer composition; this definition is consistent
with
that described in U.S. Patent 5,206,075 assigned to Exxon Chemical Patents
Inc. The
CDBI50 of an ethylene interpolymer can be calculated from TREF curves
(Temperature Rising Elution Fractionation); the TREF method is described in
Wild et
al., J. Polym. Sci., Part B, Polym. Phys., Vol. 20 (3), pages 441-455.
Typically the
CDBI50 of homogeneous ethylene interpolymers are greater than about 70%. In
contrast, the CDBI50 of a-olefin containing heterogeneous ethylene
interpolymers are
generally lower than the CDB150 of homogeneous ethylene interpolymers.
It is well known to those skilled in the art, that homogeneous ethylene
interpolymers are frequently further subdivided into "linear homogeneous
ethylene
interpolymers" and "substantially linear homogeneous ethylene interpolymers".
These
two subgroups differ in the amount of long chain branching: more specifically,
linear
homogeneous ethylene interpolymers have less than about 0.01 long chain
branches
per 1000 carbon atoms; while substantially linear ethylene interpolymers have
greater
than about 0.01 to about 3.0 long chain branches per 1000 carbon atoms. A long
chain branch is macromolecular in nature, i.e. similar in length to the
macromolecule
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that the long chain branch is attached to. Hereafter, in this disclosure, the
term
"homogeneous ethylene interpolymer" refers to both linear homogeneous ethylene
interpolymers and substantially linear homogeneous ethylene interpolymers.
Herein, the term "polyolefin" includes ethylene polymers and propylene
polymers; non-limiting examples of propylene polymers include isotactic,
syndiotactic
and atactic propylene homopolymers, random propylene copolymers containing at
least one comonomer and impact polypropylene copolymers or heterophasic
polypropylene copolymers.
The term "thermoplastic" refers to a polymer that becomes liquid when heated,
-- will flow under pressure and solidify when cooled. Thermoplastic polymers
include
ethylene polymers as well as other polymers commonly used in the plastic
industry;
non-limiting examples of other polymers commonly used in film applications
include
barrier resins (EVOH), tie resins, polyethylene terephthalate (PET),
polyamides and
the like.
As used herein the term "monolayer film" refers to a film containing a single
layer of one or more thermoplastics.
As used herein, the terms "hydrocarbyl", "hydrocarbyl radical" or "hydrocarbyl
group" refers to linear or cyclic, aliphatic, olefinic, acetylenic and aryl
(aromatic)
radicals comprising hydrogen and carbon that are deficient by one hydrogen.
As used herein, an "alkyl radical" includes linear, branched and cyclic
paraffin
radicals that are deficient by one hydrogen radical; non-limiting examples
include
methyl (-CH3) and ethyl (-CH2CH3) radicals. The term "alkenyl radical" refers
to linear,
branched and cyclic hydrocarbons containing at least one carbon-carbon double
bond
that is deficient by one hydrogen radical.
As used herein, the term "aryl" group includes phenyl, naphthyl, pyridyl and
other radicals whose molecules have an aromatic ring structure; non-limiting
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examples include naphthylene, phenanthrene and anthracene. An "arylalkyl"
group is
an alkyl group having an aryl group pendant there from; non-limiting examples
include
benzyl, phenethyl and tolylmethyl; an "alkylaryl" is an aryl group having one
or more
alkyl groups pendant there from; non-limiting examples include tolyl, xylyl,
mesityl and
cumyl.
As used herein, the phrase "heteroatom" includes any atom other than carbon
and hydrogen that can be bound to carbon. A "heteroatom-containing group" is a
hydrocarbon radical that contains a heteroatom and may contain one or more of
the
same or different heteroatoms. In one embodiment, a heteroatom-containing
group is
.. a hydrocarbyl group containing from 1 to 3 atoms selected from the group
consisting
of boron, aluminum, silicon, germanium, nitrogen, phosphorous, oxygen and
sulfur.
Non-limiting examples of heteroatom-containing groups include radicals of
imines,
amines, oxides, phosphines, ethers, ketones, oxoazolines heterocyclics,
oxazolines,
thioethers, and the like. The term "heterocyclic" refers to ring systems
having a
.. carbon backbone that comprise from 1 to 3 atoms selected from the group
consisting
of boron, aluminum, silicon, germanium, nitrogen, phosphorous, oxygen and
sulfur.
As used herein the term "unsubstituted" means that hydrogen radicals are
bounded to the molecular group that follows the term unsubstituted. The term
"substituted" means that the group following this term possesses one or more
moieties
that have replaced one or more hydrogen radicals in any position within the
group;
non-limiting examples of moieties include halogen radicals (F, Cl, Br),
hydroxyl
groups, carbonyl groups, carboxyl groups, amine groups, phosphine groups,
alkoxy
groups, phenyl groups, naphthyl groups, Ci to Cio alkyl groups, 02 to Cio
alkenyl
groups, and combinations thereof. Non-limiting examples of substituted alkyls
and
.. aryls include: acyl radicals, alkylamino radicals, alkoxy radicals, aryloxy
radicals,
alkylthio radicals, dialkylamino radicals, alkoxycarbonyl radicals,
aryloxycarbonyl
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radicals, carbomoyl radicals, alkyl- and dialkyl-carbamoyl radicals, acyloxy
radicals,
acylamino radicals, arylamino radicals and combinations thereof.
Herein the term "RI" and its superscript form "Rl" refers to a first reactor
in a
continuous solution polymerization process; it being understood that R1 is
distinctly
.. different from the symbol Ri; the latter is used in chemical formula, e.g.
representing a
hydrocarbyl group. Similarly, the term "R2" and it's superscript form "R2"
refers to a
second reactor, and; the term "R3" and it's superscript form "R3" refers to a
third
reactor.
As used herein, the term "oligomers" refers to an ethylene polymer of low
molecular weight, e.g., an ethylene polymer with a weight average molecular
weight
(Mw) of about 2000 to 3000 daltons. Other commonly used terms for oligomers
include "wax" or "grease". As used herein, the term "light-end impurities"
refers to
chemical compounds with relatively low boiling points that may be present in
the
various vessels and process streams within a continuous solution
polymerization
process; non-limiting examples include, methane, ethane, propane, butane,
nitrogen,
CO2, chloroethane, HCI, etc.
Stabilizer Package
The stabilizer package used in this invention must contain at least three
essential ingredients, namely a first phosphite; a second phosphite and a
hindered
phenolic. Further details are provided below.
First Phosphite
The first phosphite is most broadly defined by formula (I) above. A preferred
species of this first phosphite is 643-(3-tert-butyl-4-hydroxy-5-
methylphenyl)propoxy]-
2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2] dioxaphospepin (CAS Reg. No.
203255-81-
6) and is sold under the trademark name SUMILIZERTm GP by Sumitomo. The use of
this phosphite is described in combination with a polyol (such as
pentaerythritol) in
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U.S. patent no. 7,820,746. A polyol may also be (optionally) used in this
invention but
it is not essential.
Second Phosphite
The second phosphite is different from the first phosphite and may be any of
the phosphites that are conventionally used for the stabilization of
polyolefins. Suitable
examples include:
Simple mono aryl phosphites such as IRGAFOSTM 168 [2,4 di-tertiary butyl
phenyl
phosphite, CAS Registry number 31570-04-41 from BASF; oligomeric phosphites
such
as WESTONTm 705 [CAS Registry Number 939402-02-5] and DOVERPHOSTM
LGP11 [CAS Registry number 1227937-46-3] from Dover Chemical Corporation;
phosphonites such as IRGAFOS PEP-QTM from BASF and diphosphites such as
DOVERPHOSTm9228.
In an embodiment, each of the first and second phosphites is used in amounts
from 100 to 2000 ppm, especially 300 to 1500 ppm and most especially from 400
to
1000 ppm (based on the weight of said thermoplastic polyethylene product).
Hindered Phenolic Antioxidant
The hindered phenolic antioxidant may be any of the molecules that are
conventionally used as primary antioxidants for the stabilization of
polyolefins.
Suitable examples include 2,6-di-tert-butyl-4-methylphenol; 2-tert-buty1-4,6-
dimethylphenol; 2,6-di-tert-butyl-4-ethylphenol; 2,6-di-tert-butyl-4-n-
butylphenol; 2,6-
di-tert-buty1-4isobutylphenol; 2,6-dicyclopenty1-4-methylphenol; 2-(.alpha.-
methylcyclohexyl)-4,6 dimethylphenol; 2,6-di-octadecy1-4-methylphenol; 2,4,6,-
tricyclohexyphenol; and 2,6-di-tert-butyl-4-methoxymethylphenol.
Two (non limiting) examples of suitable hindered phenolic antioxidants are
sold
under the trademarks IRGANOXTM 1010 (CAS Registry number 6683-19-8) and
IRGANOXTM 1076 (CAS Registry number 2082-79-3) by BASF Corporation.
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In an embodiment, the hindered phenolic antioxidant is used in an amount of
from 100 to 2000 ppm, especially from 400 to 1000 ppm (based on the weight of
said
thermoplastic polyethylene product).
(Optional) Long Term Stabilizers
Plastic parts which are intended for long term use preferably contain at least
one
Hindered Amine Light Stabilizer (HALS). HALS are well known to those skilled
in the
art.
When employed, the HALS is preferably a commercially available material and
is used in a conventional manner and amount.
Commercially available HALS include those sold under the trademarks
CHIMASSORBTm 119; CHIMASSORB 944; CHIMASSORB 2020; TINUVINTm 622 and
TINUVIN 770 from Ciba Specialty Chemicals Corporation, and CYASORBTM UV 3346,
CYASORB UV 3529, CYASORB UV 4801, and CYASORB UV 4802 from Cytec
Industries. In some embodiments, TINUVIN 622 is preferred. Mixtures of more
than
one HALS are also contemplated.
Suitable HALS include: bis (2,2,6,6-tetramethylpiperidyI)-sebacate; bis-
5(1,2,2,6,6-pentamethylpiperidy1)-sebacate; n-butyl-3,5-di-tert-butyl-4-
hydroxybenzyl
malonic acid bis(1,2,2,6,6,-pentamethylpiperidyl)ester; condensation product
of 1-
hydroxyethy1-2,2,6,6-tetramethy1-4-hydroxy-piperidine and succinic acid;
condensation
product of N,N'-(2,2,6,6-tetramethylpiperidyI)-hexamethylendiamine and 4-tert-
octylamino-2,6-dichloro-1,3,5-s-triazine; tris-(2,2,6,6-tetramethylpiperidy1)-
nitrilotriacetate, tetrakis-(2,2,6,6-tetramethy1-4-piperidy1)-1,2,3,4butane-
tetra-arbonic
acid; and 1,1'(1,2-ethanediyI)-bis-(3,3,5,5-tetramethylpiperazinone).
Catalysts
Organometallic catalyst formulations that are efficient in polymerizing
olefins
are well known in the art. In the embodiments disclosed herein, at least two
catalyst
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formulations are employed in a continuous solution polymerization process. One
of
the catalyst formulations comprises at least one single-site catalyst
formulation that
produces a homogeneous first ethylene interpolymer. The other catalyst
formulation
comprises at least one heterogeneous catalyst formulation that produces a
heterogeneous second ethylene interpolymer. Optionally a third ethylene
interpolymer
may be produced using the heterogeneous catalyst formulation that was used to
produce the second ethylene interpolymer, or a different heterogeneous
catalyst
formulation may be used to produce the third ethylene interpolymer. In the
continuous
solution process, the at least one homogeneous ethylene interpolymer and the
at least
.. one heterogeneous ethylene interpolymer are solution blended and an
ethylene
interpolymer product is produced; for convenience, this product is referred to
herein as
"thermoplastic polyethylene product."
Single Site Catalyst Formulation
The catalyst components which make up the single site catalyst formulation are
not particularly limited, i.e. a wide variety of catalyst components can be
used. One
non-limiting embodiment of a single site catalyst formulation comprises the
following
three or four components: a bulky ligand-metal complex; an alumoxane co-
catalyst;
an ionic activator and optionally a hindered phenol. In this disclosure: "(i)"
refers to
the amount of "component (i)", i.e. the bulky ligand-metal complex added to
R1; "Op"
refers to "component (ii)", i.e. the alumoxane co-catalyst; "OD" refers to
"component
(iii)" i.e. the ionic activator, and; "(iv)" refers to "component (iv)", i.e.
the optional
hindered phenol.
Non-limiting examples of component (i) are represented by formula (I):
(LA)aM(PI)b(Q)n (I)
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wherein (LA) represents a bulky ligand; M represents a metal atom; PI
represents a
phosphinimine ligand; Q represents a leaving group; a is 0 or 1; b is 1 or 2;
(a+b) = 2;
n is 1 or 2, and; the sum of (a+b+n) equals the valance of the metal M.
Non-limiting examples of the bulky ligand LA in formula (I) include
unsubstituted
or substituted cyclopentadienyl ligands or cyclopentadienyl-type ligands,
heteroatom
substituted and/or heteroatom containing cyclopentadienyl-type ligands.
Additional
non-limiting examples include, cyclopentaphenanthreneyl ligands, unsubstituted
or
substituted indenyl ligands, benzindenyl ligands, unsubstituted or substituted
fluorenyl
ligands, octahydrofluorenyl ligands, cyclooctatetraendiyl ligands,
cyclopentacyclododecene ligands, azenyl ligands, azulene ligands, pentalene
ligands,
phosphoyl ligands, phosphinimine, pyrrolyl ligands, pyrozolyl ligands,
carbazolyl
ligands, borabenzene ligands and the like, including hydrogenated versions
thereof,
for example tetrahydroindenyl ligands. In other embodiments, LA may be any
other
ligand structure capable of q-bonding to the metal M, such embodiments include
both
q3-bonding and q5-bonding to the metal M. In other embodiments, LA may
comprise
one or more heteroatoms, for example, nitrogen, silicon, boron, germanium,
sulfur and
phosphorous, in combination with carbon atoms to form an open, acyclic, or a
fused
ring, or ring system, for example, a heterocyclopentadienyl ancillary ligand.
Other
non-limiting embodiments for LA include bulky amides, phosphides, alkoxides,
aryloxides, imides, carbolides, borollides, porphyrins, phthalocyanines,
corrins and
other polyazomacrocycles.
The metal M in formula (I) may be a Group 4 metal: titanium, zirconium and
hafnium. This invention is especially suitable when M is titanium because we
have
observed severe color formation when the single site catalyst formulation used
in this
invention comprises an organotitanium catalyst.
The phosphinimine ligand, PI, is defined by formula (II):
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(RP)3 P = N - (II)
wherein the RP groups are independently selected from: a hydrogen atom; a
halogen
atom; C1-20 hydrocarbyl radicals which are unsubstituted or substituted with
one or
more halogen atom(s); a C1-8 alkoxy radical; a C6-10 aryl radical; a C6-10
aryloxy radical;
an amido radical; a silyl radical of formula -Si(Rs)3, wherein the Rs groups
are
independently selected from, a hydrogen atom, a C1-8 alkyl or alkoxy radical,
a C6-10
aryl radical, a C6-10 aryloxy radical, or a germanyl radical of formula -
Ge(RG)3, wherein
the RG groups are defined as Rs is defined in this paragraph.
The leaving group Q is any ligand that can be abstracted from formula (I)
forming a catalyst species capable of polymerizing one or more olefin(s). An
equivalent term for Q is an "activatable ligand", i.e. equivalent to the term
"leaving
group". In some embodiments, Q is a monoanionic labile ligand having a sigma
bond
to M. Depending on the oxidation state of the metal, the value for n is 1 or 2
such that
formula (I) represents a neutral bulky ligand-metal complex. Non-limiting
examples of
Q ligands include a hydrogen atom, halogens, C1-20 hydrocarbyl radicals, C1-20
alkoxy
radicals, C5-10 aryl oxide radicals; these radicals may be linear, branched or
cyclic or
further substituted by halogen atoms, Ci-io alkyl radicals, Ci--ro alkoxy
radicals, C6-io
arly or aryloxy radicals. Further non-limiting examples of Q ligands include
weak
bases such as amines, phosphines, ethers, carboxylates, dienes, hydrocarbyl
radicals
having from 1 to 20 carbon atoms. In another embodiment, two Q ligands may
form
part of a fused ring or ring system.
Further embodiments of component (i) of the single site catalyst formulation
include structural, optical or enantiomeric isomers (meso and racemic isomers)
and
mixtures thereof of the bulky ligand-metal complexes described in formula (I)
above.
The second single site catalyst component, component (ii), is an alumoxane
co-catalyst that activates component (i) to a cationic complex. An equivalent
term for
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"alumoxane" is "aluminoxane"; although the exact structure of this co-catalyst
is
uncertain, subject matter experts generally agree that it is an oligomeric
species that
contain repeating units of the general formula (III):
(R)2A10-(Al(R)-0)n-Al(R)2 (III)
where the R groups may be the same or different linear, branched or cyclic
hydrocarbyl radicals containing 1 to 20 carbon atoms and n is from 0 to about
50. A
non-limiting example of an alumoxane is methyl aluminoxane (or MAO) wherein
each
R group in formula (III) is a methyl radical.
Optionally, a third catalyst component (iii) of the single site catalyst
formation is
an ionic activator. In general, ionic activators are comprised of a cation and
a bulky
anion; wherein the latter is substantially non-coordinating. Non-limiting
examples of
ionic activators are boron ionic activators that are four coordinate with four
ligands
bonded to the boron atom. Non-limiting examples of boron ionic activators
include the
following formulas (IV) and (V) shown below:
[R5][B(R7)4]- (IV)
where B represents a boron atom, R8 is an aromatic hydrocarbyl (e.g. triphenyl
methyl
cation) and each R7 is independently selected from phenyl radicals which are
unsubstituted or substituted with from 3 to 5 substituents selected from
fluorine atoms,
C1-4 alkyl or alkoxy radicals which are unsubstituted or substituted by
fluorine atoms;
and a silyl radical of formula -Si(R9)3, where each R9 is independently
selected from
hydrogen atoms and C1-4 alkyl radicals, and; compounds of formula (V):
[(R8)2H][B(R7)4]- (V)
where B is a boron atom, H is a hydrogen atom, Z is a nitrogen or phosphorus
atom, t
is 2 or 3 and R8 is selected from C1_8 alkyl radicals, phenyl radicals which
are
unsubstituted or substituted by up to three C1-4 alkyl radicals, or one R8
taken together
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with the nitrogen atom may form an anilinium radical and R7 is as defined
above in
formula (IV).
In both formula (IV) and (V), a non-limiting example of R7 is a
pentafluorophenyl radical. In general, boron ionic activators may be described
as
salts of tetra(perfluorophenyl) boron; non-limiting examples include
anilinium,
carbonium, oxonium, phosphonium and sulfonium salts of
tetra(perfluorophenyOboron
with anilinium and trityl (or triphenylmethylium). Additional non-limiting
examples of
ionic activators include: triethylammonium tetra(phenyl)boron,
tripropylammonium
tetra(phenyl)boron, tri(n-butyl)ammonium tetra(phenyl)boron, trimethylammonium
tetra(p-tolyl)boron, trimethylammonium tetra(o-tolyl)boron, tributylammonium
tetra(pentafluorophenyl)boron, tripropylammonium tetra(o,p-
dimethylphenyl)boron,
tributylammonium tetra(m,m-dimethylphenyl)boron, tributylammonium tetra(p-
trifluoromethylphenyl)boron, tributylammonium tetra(pentafluorophenyl)boron,
tri(n-
butyl)ammonium tetra(o-tolyl)boron, N,N-dimethylanilinium tetra(phenyl)boron,
N,N-
diethylanilinium tetra(phenyl)boron, N,N-diethylanilinium tetra(phenyl)n-
butylboron,
N,N-2,4,6-pentamethylanilinium tetra(phenyl)boron, di-(isopropyl)ammonium
tetra(pentafluorophenyl)boron, dicyclohexylammonium tetra(phenyl)boron,
triphenylphosphonium tetra(phenyl)boron, tri(methylphenyl)phosphonium
tetra(phenyl)boron, tri(dimethylphenyl)phosphonium tetra(phenyl)boron,
tropillium
tetrakispentafluorophenyl borate, triphenylmethylium tetrakispentafluorophenyl
borate,
benzene(diazonium)tetrakispentafluorophenyl borate, tropillium
tetrakis(2,3,5,6-
tetrafluorophenyl)borate, triphenylmethylium tetrakis(2,3,5,6-
tetrafluorophenyl)borate,
benzene(diazonium) tetrakis(3,4,5-trifluorophenyl)borate, tropillium
tetrakis(3,4,5 -
trifluorophenyl)borate, benzene(diazonium) tetrakis(3,4,5-
trifluorophenyOborate,
tropillium tetrakis(1,2,2-trifluoroethenyl)borate, triphenylmethylium
tetrakis(1 ,2,2-
trifluoroethenyl)borate, benzene(diazonium) tetrakis(1,2,2-
trifluoroethenyl)borate,
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tropillium tetrakis(2,3,4,5-tetrafluorophenyl)borate, triphenylmethylium
tetrakis(2,3,4,5-
tetrafluorophenyl)borate, and benzene(diazonium) tetrakis(2,3,4,5
tetrafluorophenyl)borate. Readily available commercial ionic activators
include N,N-
dimethylanilinium tetrakispentafluorophenyl borate, and triphenylmethylium
tetrakispentafluorophenyl borate.
An optional fourth catalyst component of the single site catalyst formation is
a
hindered phenol, component (iv). Non-limiting example of hindered phenols
include
butylated phenolic antioxidants, butylated hydroxytoluene, 2,4-di-
tertiarybuty1-6-ethyl
phenol, 4,4'-methylenebis (2,6-di-tertiary-butylphenol), 1,3, 5-trimethy1-
2,4,6-tris (3,5-
di-tert-buty1-4-hydroxybenzyl) benzene and octadecy1-3-(3',5'-di-tert-buty1-4'-
hydroxyphenyl) propionate.
Heterogeneous Catalyst Formulations
A number of heterogeneous catalyst formulations are well known to those
skilled in the art, including, Ziegler-Natta (Z/N) and chromium catalyst
formulations.
.. This invention is most relevant to the use of a Z/N catalyst as the
heterogeneous
catalyst formulation because we have observed severe color formation when a
Z/N
catalyst is used.
In this disclosure, embodiments include an in-line Ziegler-Natta catalyst
formulation and a batch Ziegler-Natta catalyst formation. The term "in-line
Ziegler-
Natta catalyst formulation" refers to the continuous synthesis of a small
quantity of
active Ziegler-Natta catalyst and immediately injecting this catalyst into at
least one
continuously operating reactor, wherein the catalyst polymerizes ethylene and
one or
more optional a-olefins to form an ethylene interpolymer. The terms "batch
Ziegler-
Natta catalyst formulation" or "batch Ziegler-Natta procatalyst" refer to the
synthesis of
.. a much larger quantity of catalyst or procatalyst in one or more mixing
vessels that are
external to, or isolated from, the continuously operating solution
polymerization
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process. Once prepared, the batch Ziegler-Natta catalyst formulation, or batch
Ziegler-Natta procatalyst, is transferred to a catalyst storage tank. The term
"procatalyst" refers to an inactive catalyst formulation (inactive with
respect to ethylene
polymerization); the procatalyst is converted into an active catalyst by
adding an alkyl
aluminum co-catalyst. As needed, the procatalyst is pumped from the storage
tank to
at least one continuously operating reactor, where an active catalyst is
formed and
polymerizes ethylene and one or more optional a-olefins to form an ethylene
interpolymer. The procatalyst may be converted into an active catalyst in the
reactor
or external to the reactor.
A wide variety of chemical compounds can be used to synthesize an active
Ziegler-Natta catalyst formulation. The following describes various chemical
compounds that may be combined to produce an active Ziegler-Natta catalyst
formulation. Those skilled in the art will understand that the embodiments in
this
disclosure are not limited to the specific chemical compound disclosed.
An active Ziegler-Natta catalyst formulation may be formed from: a magnesium
compound, a chloride compound, a titanium compound, an alkyl aluminum co-
catalyst
and an aluminum alkyl. In this disclosure: "(v)" refers to "component (v)" the
magnesium compound; the term "(vi)" refers to the "component (vi)" the
chloride
compound; "(vii)" refers to "component (vii)" the metal compound; "(viii)"
refers to
.. "component (viii)" alkyl aluminum co-catalyst, and; "(ix)" refers to
"component (ix)" the
aluminum alkyl. As will be appreciated by those skilled in the art, Ziegler-
Natta
catalyst formulations may contain additional components; a non-limiting
example of an
additional component is an electron donor, e.g. amines or ethers.
A non-limiting example of an active in-line Ziegler-Natta catalyst formulation
can be prepared as follows. In the first step, a solution of a magnesium
compound
(component (v)) is reacted with a solution of the chloride compound (component
(vi))
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to form a magnesium chloride support suspended in solution. Non-limiting
examples
of magnesium compounds include Mg(R1)2; wherein the R1 groups may be the same
or different, linear, branched or cyclic hydrocarbyl radicals containing 1 to
10 carbon
atoms. Non-limiting examples of chloride compounds include R2CI; wherein R2
represents a hydrogen atom, or a linear, branched or cyclic hydrocarbyl
radical
containing 1 to 10 carbon atoms. In the first step, the solution of magnesium
compound may also contain an aluminum alkyl (component (ix)). Non-limiting
examples of aluminum alkyl include Al(R3)3, wherein the R3 groups may be the
same
or different, linear, branched or cyclic hydrocarbyl radicals containing from
1 to 10
carbon atoms. In the second step a solution of the metal compound (component
(vii))
is added to the solution of magnesium chloride and the titanium compound is
supported on the magnesium chloride. Non-limiting examples of suitable metal
compounds include Ti(X) n or TiO(X)n; where; 0 represents oxygen, and; X
represents
chloride or bromide; n is an integer from 3 to 6 that satisfies the oxidation
state of the
metal. Additional non-limiting examples of suitable Ti compounds include Ti
alkyls, Ti
alkoxides (which may be prepared by reacting a metal alkyl with an alcohol)
and
mixed-ligand Ti compounds that contain a mixture of halide, alkyl and alkoxide
ligands. In the third step a solution of an alkyl aluminum co-catalyst
(component (viii))
is added to the Ti compound supported on the magnesium chloride. A wide
variety of
alkyl aluminum co-catalysts are suitable, as expressed by formula (VI):
Al(R4)p(0R5)q(X)r (VI)
wherein the R4 groups may be the same or different, hydrocarbyl groups having
from
1 to 10 carbon atoms; the OR5 groups may be the same or different, alkoxy or
aryloxy
groups wherein R5 is a hydrocarbyl group having from 1 to 10 carbon atoms
bonded
to oxygen; X is chloride or bromide, and; (p+q+r) = 3, with the proviso that p
is greater
than 0. Non-limiting examples of commonly used alkyl aluminum co-catalysts
include
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trimethyl aluminum, triethyl aluminum, tributyl aluminum, dimethyl aluminum
methoxide, diethyl aluminum ethoxide, dibutyl aluminum butoxide, dimethyl
aluminum
chloride or bromide, diethyl aluminum chloride or bromide, dibutyl aluminum
chloride
or bromide and ethyl aluminum dichloride or dibromide.
The process described in the paragraph above, to synthesize an active in-line
Ziegler-Natta catalyst formulation, can be carried out in a variety of
solvents; non-
limiting examples of solvents include linear or branched C5 to C12 alkanes or
mixtures
thereof. To produce an active in-line Ziegler-Natta catalyst formulation the
quantity
and mole ratios of the five components, (v) through (ix), are optimized using
techniques that are well known to those skilled in the art.
Solution Polymerization
A variety of solvents may be used as the process solvent; non-limiting
examples include linear, branched or cyclic C5 to C12 alkanes. Non-limiting
examples
of a-olefins include 1-propene, 1-butene, 1-pentene, 1-hexene and 1-octene.
Suitable
catalyst component solvents include aliphatic and aromatic hydrocarbons. Non-
limiting examples of aliphatic catalyst component solvents include linear,
branched or
cyclic C5-12 aliphatic hydrocarbons, e.g. pentane, methyl pentane, hexane,
heptane,
octane, cyclohexane, methylcyclohexane, hydrogenated naphtha or combinations
thereof. Non-limiting examples of aromatic catalyst component solvents include
benzene, toluene (methylbenzene), ethylbenzene, o-xylene (1,2-
dimethylbenzene), m-
xylene (1,3-dimethylbenzene), p-xylene (1,4-dimethylbenzene), mixtures of
xylene
isomers, hemellitene (1,2,3-trimethylbenzene), pseudocumene (1,2,4-
trimethylbenzene), mesitylene (1,3,5-trimethylbenzene), mixtures of
trimethylbenzene
isomers, prehenitene (1,2,3,4-tetramethylbenzene), durene (1,2,3,5-
tetramethylbenzene), mixtures of tetramethylbenzene isomers,
pentamethylbenzene,
hexamethylbenzene and combinations thereof.
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It is well known to individuals experienced in the art that reactor feed
streams
(solvent, monomer, a-olefin, hydrogen, catalyst formulation, etc.) must be
essentially
free of catalyst deactivating poisons; non-limiting examples of poisons
include trace
amounts of oxygenates such as water, fatty acids, alcohols, ketones and
aldehydes.
.. Such poisons are removed from reactor feed streams using standard
purification
practices; non-limiting examples include molecular sieve beds, alumina beds
and
oxygen removal catalysts for the purification of solvents, ethylene and a-
olefins, etc.
The solution polymerization process used to prepare the polyethylenes used in
this invention preferably uses at least two reactors in series (for
convenience, R1 and
R2).
In the embodiments the operating temperatures of the solution polymerization
reactors can vary over a wide range. For example, the upper limit on reactor
temperatures in some cases may be about 300 C, in other cases about 280 C and
in
still other cases about 260 C; and the lower limit in some cases may be about
80 C, in
other cases about 100 C and in still other cases about 125 C. The second
reactor,
(R2), is normally operated at a higher temperature than the first reactor. The
maximum temperature difference between these two reactors in some cases is
about
120 C, in other cases about 100 C and in still other cases about 80 C; the
minimum
in some cases is about 1 C, in other cases about 5 C and in still other cases
about
10 C. An optional tubular reactor, (R3), may be operated in some cases about
100 C
higher than R2; in other cases about 60 C higher than R2, in still other cases
about
10 C higher than R2 and in alternative cases 0 C higher, i.e. the same
temperature as
R2. The temperature within optional R3 may increase along its length. The
maximum
temperature difference between the inlet and outlet of R3 in some cases is
about
100 C, in other cases about 60 C and in still other cases about 40 C. The
minimum
temperature difference between the inlet and outlet of R3 is in some cases may
be
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0 C, in other cases about 3 C and in still other cases about 10 C. In some
cases R3
is operated an adiabatic fashion and in other cases R3 is heated. R3 is in
series with
R2 and is downstream of R2.
The pressure in the polymerization reactors should be high enough to maintain
the polymerization solution as a single phase solution and to provide the
upstream
pressure to force the polymer solution from the reactors through a heat
exchanger and
on to polymer recovery operations. The operating pressure of the solution
polymerization reactors can vary over a wide range. For example, the upper
limit on
reactor pressure in some cases may be about 45 MPag, in other cases about 30
MPag and in still other cases about 20 MPag; and the lower limit in some cases
may
be about 3 MPag, in other some cases about 5 MPag and in still other cases
about 7
MPag.
Acid Neutralizer (or "Passivator")
A passivator (which may also be referred to as an acid neutralizer) is added
to
a deactivated solution to form a passivated solution. The passivator may be
neat
(100%) passivator, a solution of passivator in a solvent, or a slurry of
passivator in a
solvent. Non-limiting examples of suitable solvents include linear or branched
C5 to
C12 alkanes. In this disclosure, how the passivator is added is not
particularly
important. Suitable passivators are well known in the art, non-limiting
examples
include alkali or alkaline earth metal salts of carboxylic acids (i.e. calcium
stearate) or
hydrotalcites. The quantity of passivator added can vary over a wide range. In
an
embodiment, the molar quantity of passivator added is determined by the total
moles
of chloride compounds added to the solution process, i.e. the chloride
compound
"component (vi)" plus the metal compound "compound (vii)". Optionally, a first
and
second chloride compound and a first and second metal compound may be used,
i.e.
to form the first and second heterogeneous catalyst formulations; in this case
the
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amount of passivator added is determined by the total moles all chloride
containing
compounds. The upper limit on passivator mole ratio (moles passivator)/(total
chlorides) molar ratio may be 20, in some cases 15 and in other cases 10. The
lower
limit on the (passivator)/(total chlorides) molar ratio may be about 0.2, in
some cases
about 0.4 and in still other cases about 0.8. In general, the passivator is
added in the
minimal amount to substantially passivate the deactivated solution.
Flexible Manufactured Articles
The ethylene interpolymer products disclosed herein have improved (lower)
Yellowness Index (YI) and may be converted into a wide variety of flexible
manufactured articles. Non-limiting examples include monolayer or multilayer
films,
such films are well known to those of ordinary experienced in the art. Non-
limiting
examples of processes to prepare such films include blown film and cast film
processes.
Depending on the end-use application, the disclosed ethylene interpolymer
products having improved color may be converted into films that span a wide
range of
thicknesses. Non-limiting examples include, food packaging films where
thicknesses
may range from about 0.5 mil (13 pm) to about 4 mil (102 pm), and; in heavy
duty
sack applications film thickness may range from about 2 mil (51pm) to about 10
mil
(254 pm).
Ethylene interpolymer products having improved color may be used in
monolayer films; where the monolayer may contain more than one ethylene
interpolymer product having improved color and/or additional thermoplastics;
non-
limiting examples of thermoplastics include ethylene polymers and propylene
polymers. The lower limit on the weight percent of the ethylene interpolymer
product
having improved color in a monolayer film may be about 3 wt%, in other cases
about
10 wt% and in still other cases about 30 wt%. The upper limit on the weight
percent of
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the ethylene interpolymer product having improved color in the monolayer film
may be
100 wt%, in other cases about 90 wt% and in still other cases about 70 wt%.
The ethylene interpolymer products having improved color disclosed herein
may also be used in one or more layers of a multilayer film; non-limiting
examples of
multilayer films include three, five, seven, nine, eleven or more layers. The
thickness
of a specific layer (containing an ethylene interpolymer product having
improved color)
within a multilayer film may be about 5%, in other cases about 15% and in
still other
cases about 30% of the total multilayer film thickness. In other embodiments,
the
thickness of a specific layer (containing the ethylene interpolymer product
having
improved color) within a multilayer film may be about 95%, in other cases
about 80%
and in still other cases about 65% of the total multilayer film thickness.
Each
individual layer of a multilayer film may contain more than one ethylene
interpolymer
product having improved color and/or additional thermoplastics.
Additional embodiments include laminations and coatings, wherein mono or
multilayer films containing the disclosed ethylene interpolymer products
having
improved color are extrusion laminated or adhesively laminated or extrusion
coated.
In extrusion lamination or adhesive lamination, two or more substrates are
bonded
together with a thermoplastic or an adhesive, respectively. In extrusion
coating, a
thermoplastic is applied to the surface of a substrate. These processes are
well
.. known to those experienced in the art.
There is a need to improve the color of articles manufactured from ethylene
interpolymer. The color of a manufactured article is an important attribute;
frequently
color is often a customer's first impression of quality. It is essential that
the color of a
manufactured article meets the expectations of the customer. The ethylene
interpolymer products having improved color disclosed herein can be used in a
wide
range of manufactured articles, e.g. articles that comprise one or more films
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(monolayer or multilayer). Non-limiting examples of such manufactured articles
include: food packaging films (fresh and frozen foods, liquids and granular
foods),
stand-up pouches, retortable packaging and bag-in-box packaging; barrier films
(oxygen, moisture, aroma, oil, etc.) and modified atmosphere packaging; light
and
heavy duty shrink films and wraps, collation shrink film, pallet shrink film,
shrink bags,
shrink bundling and shrink shrouds; light and heavy duty stretch films, hand
stretch
wrap, machine stretch wrap and stretch hood films; high clarity films; heavy-
duty
sacks; household wrap, overwrap films and sandwich bags; industrial and
institutional
films, trash bags, can liners, magazine overwrap, newspaper bags, mail bags,
sacks
and envelopes, bubble wrap, carpet film, furniture bags, garment bags, coin
bags,
auto panel films; medical applications such as gowns, draping and surgical
garb;
construction films and sheeting, asphalt films, insulation bags, masking film,
landscaping film and bags; geomembrane liners for municipal waste disposal and
mining applications; batch inclusion bags; agricultural films, mulch film and
green
house films; in-store packaging, self-service bags, boutique bags, grocery
bags, carry-
out sacks and t-shirt bags; oriented films, machine direction and biaxially
oriented
films and functional film layers in oriented polypropylene (OPP) films, e.g.
sealant
and/or toughness layers. Additional manufactured articles comprising one or
more
films containing at least one ethylene interpolymer product having improved
color
include laminates and/or multilayer films; sealants and tie layers in
multilayer films and
composites; laminations with paper; aluminum foil laminates or laminates
containing
vacuum deposited aluminum; polyamide laminates; polyester laminates; extrusion
coated laminates, and; hot-melt adhesive formulations. The manufactured
articles
summarized in this paragraph contain at least one film (monolayer or
multilayer)
comprising at least one embodiment of the disclosed ethylene interpolymer
products
having improved color.
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Desired film physical properties (monolayer or multilayer) typically depend on
the application of interest. Non-limiting examples of desirable film
properties include:
optical properties (gloss, haze and clarity), dart impact, Elmendorf tear,
modulus (1%
and 2% secant modulus), puncture-propagation tear resistance, tensile
properties
(yield strength, break strength, elongation at break, toughness, etc.) and
heat sealing
properties (heat seal initiation temperature and hot tack strength). Specific
hot tack
and heat sealing properties are desired in high speed vertical and horizontal
form-fill-
seal processes that load and seal a commercial product (liquid, solid, paste,
part, etc.)
inside a pouch-like package.
The films used in the manufactured articles described in this section may
optionally include, depending on its intended use, additives and adjuvants in
addition
to the stabilizer package described above. Non-limiting examples of additives
and
adjuvants include, anti-blocking agents, heat stabilizers, slip agents,
processing aids,
anti-static additives, colorants, dyes, filler materials, light stabilizers,
light absorbers,
lubricants, pigments, plasticizers, nucleating agents and combinations
thereof.
Rigid Manufactured Articles
The ethylene interpolymer products disclosed herein having improved (lower)
Yellowness Index (YI) may be converted into a wide variety of rigid
manufactured
articles. Non-limiting examples include: deli containers, margarine tubs,
drink cups
and produce trays; household and industrial containers, cups, bottles, pails,
crates,
tanks, drums, bumpers, lids, industrial bulk containers, industrial vessels,
material
handling containers, bottle cap liners, bottle caps, living hinge closures;
toys,
playground equipment, recreational equipment, boats, marine and safety
equipment;
wire and cable applications such as power cables, communication cables and
conduits; flexible tubing and hoses; pipe applications including both pressure
pipe and
non-pressure pipe markets, e.g. natural gas distribution, water mains,
interior
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plumbing, storm sewer, sanitary sewer, corrugated pipes and conduit; foamed
articles
manufactured from foamed sheet or bun foam; military packaging (equipment and
ready meals); personal care packaging, diapers and sanitary products;
cosmetic,
pharmaceutical and medical packaging, and; truck bed liners, pallets and
automotive
dunnage. The rigid manufactured articles summarized in this paragraph contain
one
or more of the ethylene interpolymer products having improved color or a blend
of at
least one of the ethylene interpolymer products disclosed herein having
improved
color with at least one other thermoplastic.
Such rigid manufactured articles may be fabricated using the following non-
limiting processes: injection molding, compression molding, blow molding,
rotomolding, profile extrusion, pipe extrusion, sheet thermoforming and
foaming
processes employing chemical or physical blowing agents.
The desired physical properties of rigid manufactured articles depend on the
application of interest. Non-limiting examples of desired properties include:
flexural
modulus (1% and 2% secant modulus); tensile toughness; environmental stress
crack
resistance (ESCR); slow crack growth resistance (PENT); abrasion resistance;
shore
hardness; deflection temperature under load; VICAT softening point; IZOD
impact
strength; ARM impact resistance; Charpy impact resistance, and; color
(whiteness
and/or yellowness index).
A further objective of the present disclosure is to provide rigid manufactured
articles comprising ethylene interpolymer products having improved color that
have
improvements in at least one desirable physical property; relative to rigid
manufactured articles formed from comparative ethylene interpolymers.
EXAMPLES
Polymerization of Thermoplastic Polyethylene Product
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The following examples are presented for the purpose of illustrating selected
embodiments of this disclosure; it being understood, that the examples
presented do
not limit the claims presented.
Embodiments of ethylene interpolymer product having improved Yellowness
Index (YI) were produced in a continuous solution polymerization pilot plant
comprising reactors arranged in a series configuration. Methylpentane was used
as
the process solvent (a commercial blend of methylpentane isomers). The volume
of
the first CSTR reactor (R1) was 3.2 gallons (12 L), the volume of the second
CSTR
reactor (R2) was 5.8 gallons (22 L) and the volume of the tubular reactor (R3)
was 4.8
gallons (18 L). Examples of ethylene interpolymer products were produced using
an
R1 pressure from about 14 MPa to about 18 MPa; R2 was operated at a lower
pressure to facilitate continuous flow from R1 to R2. R1 and R2 were operated
in
series mode, wherein the first exit stream from R1 flows directly into R2.
Both CSTR's
were agitated to give conditions in which the reactor contents were well
mixed. The
process was operated continuously by feeding fresh process solvent, ethylene,
1-
octene and hydrogen to the reactors.
The single site catalyst components used were: component (i),
cyclopentadienyl tri(tertiary butyl)phosphinimine titanium dichloride, (Cp[(t-
Bu)3PN]TiC12), hereafter PIC-1; component (ii), methylaluminoxane (MA0-07);
.. component (iii), trityl tetrakis(pentafluoro-phenyl)borate, and; component
(iv), 2,6-di-
tert-butyl-4-ethylphenol. The single site catalyst component solvents used
were
methylpentane for components (ii) and (iv) and xylene for components (i) and
(iii).
Suitable mole ratios of single site catalyst components are: R1 (ii)/(i) mole
ratio =
100.03, i.e. [(MAO-07)/(PIC-1)]; R1 (iv)/(ii) mole ratio = 0.0, i.e. [(2,6-di-
tert-butyl-4-
.. ethylphenol)/(MA0-07)], and; R1 (iii)/(i) mole ratio = 1.1, i.e. [(trityl
tetrakis(pentafluoro-
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phenyl)borate)/(PIC-1)]. The single site catalyst formulation is injected into
R1 using
process solvent.
The in-line Ziegler-Natta catalyst formulation was prepared from the following
components: component (v), butyl ethyl magnesium; component (vi), tertiary
butyl
chloride; component (vii), titanium tetrachloride; component (viii), diethyl
aluminum
ethoxide, and; component (ix), triethyl aluminum. Methylpentane was used as
the
catalyst component solvent. The in-line Ziegler-Natta catalyst formulation was
prepared using the following steps. In step one, a solution of
triethylaluminum and
dibutylmagnesium ((triethylaluminum)/(dibutylmagnesium) molar ratio of 20) was
combined with a solution of tertiary butyl chloride and allowed to react for a
Hold Up
Time (HUT) of about 30 seconds (HUT-1); in step two, a solution of titanium
tetrachloride was added to the mixture formed in step one and allowed to react
for
about 14 seconds (HUT-2), and; in step three, the mixture formed in step two
was
allowed to react for an additional 3 seconds (HUT-3) prior to injection into
R2. The in-
line Ziegler-Natta procatalyst formulation was injected into R2 using process
solvent,
the flow rate of the catalyst containing solvent was about 49 kg/hr, the
temperature of
this line (the second catalyst solution temperature, CST-2) was adjusted. The
in-line
Ziegler-Natta catalyst formulation was formed in R2 by injecting a solution of
diethyl
aluminum ethoxide into R2. In an embodiment, the following mole ratios were
used to
synthesize the in-line Ziegler-Natta catalyst: R2 (vi)/(v) mole ratio = 2.07;
R2 (viii)/(vii)
mole ratio = 1.35, and; R2 (ix)/(vii) mole ratio = 0.35.
Polymerization in the continuous solution polymerization process was
terminated by adding a catalyst deactivator to the third exit stream exiting
the tubular
reactor (R3). The catalyst deactivator used was octanoic acid (caprylic acid),
commercially available from P&G Chemicals, Cincinnati, OH, U.S.A. The catalyst
deactivator was added such that the moles of fatty acid added were 50% of the
total
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molar amount of titanium and aluminum added to the polymerization process; to
be
clear, the moles of octanoic acid added = 0.5 x (moles titanium + moles
aluminum);
this mole ratio was consistently used in all examples.
A two-stage devolatilization process was employed to recover the ethylene
interpolymer product from the process solvent, i.e. two vapor/liquid (V/L)
separators
were used and the second bottom stream (from the second V/L separator) was
passed through a gear pump/pelletizer combination. DHT-4V (hydrotalcite),
supplied
by Kisuma Chemical Industry (Japan) was used as a passivator, or acid
neutralizer, in
the continuous solution process. The CAS Registry number for a suitable
hydrotalcite
.. is 1097-59-9. A slurry of DHT-4V in process solvent was added prior to the
first V/L
separator. The molar amount of DHT-4V added was about 10-fold higher than the
molar amount of chlorides added to the process; the chlorides added were
titanium
tetrachloride and tertiary butyl chloride.
Prior to pelletization the ethylene interpolymer product was stabilized by
adding
a stabilizer package to the ethylene interpolymer product. The components of
the
stabilizer package were dissolved in process solvent and added between the
first and
second V/L separators.
Thermoplastic polyethylene product produced in this manner can contain
catalyst residues in the following amounts: titanium (from Ito 15 ppm);
aluminum
.. (from 10 to 200 ppm) and magnesium (from 10 to 250 ppm).
EXAMPLES
The experiments of the following examples were performed on a co-rotating
twin screw extruder having a screw diameters of 34 mm and length/diameter
ratio =
33.5. The melt temperature was set at 225 C. Output was approximately 13
.. kilograms/hr, at 200 revolutions per minute. Color and melt index (MI) were
measured
after passes 0, 1, 3, and 5. Color measurements were performed in accordance
with
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ASTM standards (yellowness index or "Yl" was determined according to ASTM D
1925). Melt index measurements were conducted using conditions 190 C/2.16 kg
(MI2) and 190 C/21.6 kg (M121)in accordance with ASTM standard D1238.
Differential
scanning calorimetry (DSC) oxidative induction time (01T) experiments are
conducted
in accordance to ASTM D3895 and are reported as the time required before
degradation of a polymer melt occurs when exposed to 200 C and 100% oxygen
atmosphere. Gas fading performance is evaluated by exposing polyethylene
plaques
to an atmospheric fume chamber maintained at 140 F that contains fumes emitted
from a burning natural gas stream, releasing small amounts of NOx gases.
The additives used for the stabilizer package in the examples are as follows.
A01 a hindered phenolic primary antioxidant: Octadecyl 3-(3,5-di-tert-buty1-4-
hydroxyphenyl)propionate (CAS Reg. No. 2082-79-3) (IRGANOXTm1076)
P1: 643-(3-tert-buty1-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-
butyldibenzo[d,f][1,3,2] dioxaphospepin (CAS Reg. No. 203255-81-6)
(SUMILIZERTmGP) ¨within the definition of formula (I), above;
P2: Tris(2-4-di-tert-butylphenyl)phosphite (CAS Reg. No. 31570-04-4)
(IRGAFOSTm168)
Example 1:
The thermoplastic polyethylene product used in all experiments of example 1
was an
ethylene-octene copolymer having a density of about 0.916 g/cc and a melt
index, 12 (as
determined by ASTM D 1238) of about 1.0 grams per 10 minutes. This product was
produced in a solution phase polymerization process using Zeigler-Natta and
single-
site type catalysts in the manner described above. Analysis of a sample of
this polymer
showed the following catalyst residues in parts per million by weight (ppm):
titanium: 7.2
aluminum: 83
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magnesium: 177
TABLE 1
Stabilizer formulations for multiple pass extrusion experiments.
Formulation A01 P1 P2
Cl 1000 0 1000
1E1 500 500 500
1E2 250 500 750
Control formulation (Cl) consists of a conventional stabilizer package
containing 1000 ppm of a phenolic antioxidant, 1000 ppm of a phosphite
antioxidant,
each sold under the trademarks of IRGANOXTM 1076, IRGAFOSTM 168, respectively,
by BASF. Inventive formulation 1 (1E1) contains a ternary blend of
antioxidants
containing 500 ppm of IRGANOXTM 1076, 500 ppm of IRGAFOSTM 168, and 500 ppm
of the hybrid phenolic and phosphite-based antioxidant, sold under the
trademark of
SUM1LIZERTm GP by Sumitomo. Inventive example 2 (1E2) contains 250 ppm of
IRGANOXTM 1076, 750 ppm of IRGAFOSTM 168, and 500 ppm of SUMIL1ZERTm GP.
The purpose of this study was to demonstrate the performance improvement
imparted
through the use of optimized ternary blends of antioxidants.
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TABLE 2
Change in Color (YI) for various additive formulations after multiple
extrusion
pass experiment (225 C) on a twin screw extruder.
Color Extrusion Passes
(YI) 0 1 3 5
Cl -1.93 4.61 12.15
14.69
1E1 -1.61 5.43 10.5
12.73
1E2 -1.78 4.36 7.97
11.07
The compositions were passed through the extruder a total of five times. Color
was measured before the first pass and after passes 1, 3 and 5. All
compositions
became more yellow after being exposed to heat and shear in the extruder.
The observation of one resin as being more 'yellow' than another is generally
perceived as a decrease in resin quality by polyethylene consumers. The data
presented in Table 2 show that the inventive have better color performance
over the
multiple extrusion passes. Reductions in Y1 amount to approximately 2, and 4
units for
1E1 and 1E2 respectively at Pass 3. For reference, differences of 2 Y1 units
are
generally perceptible by eye.
TABLE 3
Change in Melt Index (MI2) after multiple extrusion pass experiment (225 C)
on
a twin screw extruder.
MI2 Extrusion Passes
g/10 minutes 0 1 3 5
Cl 0.98 0.88 0.7 0.51
1E1 0.99 0.93 0.71 0.50
1E2 0.93 0.92 0.81 0.56
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Melt flow rates can have major impacts on how the resins are processed.
Therefore, a retention of melt index stability is desirable as it leads to
more predictable
extrusion performance for polyethylene convertors. Table 3 demonstrates that
1E2 has
good melt flow stability over the 5 extrusion passes when compared against Cl,
despite the lower overall antioxidant loading levels (2000 ppm vs 1500 ppm).
The
combination of reduced color formation with a retention in melt stability is
desirable.
For clarity: the M12 of Cl decreased to 0.51 g/10 minutes and the M12 of 1E2
decreased
to 0.56 g/10 minutes after 5 passes.
TABLE 4
Oxidative induction time (01T) of polyethylene melts exposed to 200 C and
100% 02 atmosphere.
Formulation OIT
(min)
Cl 63.1
tEl 75.0
1E2 81.2
Oxidation induction time (01T) is a measure of the stability of a polymer to
thermal and oxidative stress, and is normally a function of the concentration
of the
primary (phenolic-containing) antioxidant. Higher OIT times are generally
indicative of
higher thermos-oxidative stability of the polyethylene, which is desirable. As
is
demonstrated in Table 4, moderate improvements in thermo-oxidative stability
are
observed in the order 1E2 >1E1 > Cl, demonstrating the effectiveness of
optimized
ternary antioxidant blends for enhanced thermal stability.
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TABLE 5
Gas fading performance of polyethylene formulations exposed to an
atmospheric fume oven at 140 F for 4 weeks.
Days in Atmospheric Fume Chamber
Sample
0 1 3 4 7 14 21 28
Cl 7.38
11.73 15.06 16.65 21.08 26.56 29.91 33.41
1E1 -1.81 -
0.36 1.86 2.71 5.32 10.35 14.23 18.17
1E2 -1.76 -
0.06 2.32 3.24 6.19 11.26 14.97 18.66
Gas fading is a process that occurs as the polymer is exposed to NOx (i.e. NO2
and NO) gases that can be present in low concentration in atmospheres that
contain
combustion products from carbon-based fuels (e.g. natural gas and propane
powered
fork lifts in warehouses). Gas fading is generally believed to be the result
of the NOx
gases interacting with the phenolic antioxidants present in the polymer.
Although the
above example demonstrates an accelerated test, it is clear that the inventive
examples display much lower tendency to gas fade as compared to the
comparative
example, Cl .Y1 values are reported in Table 5. The Y1 of Cl increased from
7.38 to
33.41 after 28 days.
Example 2:
The thermoplastic polyethylene product used in all experiments of example 2
was an ethylene-octene copolymer having a density of about 0.913 g/cc and a
melt
index, 12 (as determined by ASTM D 1238) of about 0.85 grams per 10 minutes.
This
product was produced in a solution phase polymerization process using Zeigler-
Natta
and single-site type catalysts in the manner described above. Polyethylene
resins with
12 values of <1.0 grams per 10 min are typically called 'fractional melt'
resins, and are
generally more difficult to stabilize due to the higher shear stresses
imparted on the
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polymer during processing. Analysis of a sample of this thermoplastic
polyethylene
product showed the following levels of catalyst residues (ppm):
titanium: 7.9
aluminum: 91
magnesium: 182
TABLE 6
Stabilizer formulations for multiple pass extrusion experiments.
Formulation A01 P1 P2
C2 1000 0 1000
1E3 250 500 750
Control formulation (C2) consists of a conventional stabilizer package
containing 1000 ppm of a phenolic antioxidant, 1000 ppm of a phosphite
antioxidant,
each sold under the trademarks of IRGANOXTM 1076, IRGAFOSTM 168, respectively,
by BASF. Inventive example 3 (1E3) contains 250 ppm of IRGANOXTM 1076, 750 ppm
of IRGAFOSTM 168, and 500 ppm of SUMILIZERTm GP. The purpose of this study
was to demonstrate the performance improvement imparted through the use of
optimized ternary blends of antioxidants.
TABLE 7
Change in Color (Y1) for various additive formulations after multiple
extrusion
pass experiment (225 C) on a twin screw extruder.
Color Extrusion Passes
(Y1) 0 1 3 5
C2 -2.48 4.36 8.19
14.74
1E3 -2.61 -0.46 1.98 5.02
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As is evident from the data presented in Table 7, the inventive formulation
(1E3)
result in substantially decreased color formation (YI) as compared to the
comparative
example (C2) over the multiple extrusion passes. Reductions in YI amount to
approximately 6 units for 1E3 as compared to 02 at Pass 3.
TABLE 8
Change in Melt Index (M12) for various additive formulations after multiple
extrusion pass experiment (225 C) on a twin screw extruder.
Color Extrusion Passes
(YI) 0 1 3 5
C2 0.85 0.74 0.59 0.43
1E3 0.83 0.78 0.59 0.44
Table 8 demonstrates that 1E3 has good melt flow stability over the 5
extrusion
passes when compared against 02, despite the lower overall antioxidant loading
levels (2000 ppm vs 1500 ppm).
TABLE 9
Oxidative induction time (01T) of polyethylene melts exposed to 200 C and
100% 02 atmosphere.
Formulation OIT
(min)
C2 61.1
1E3 81.5
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Higher OIT times are generally indicative of higher thermo oxidative stability
of
the polyethylene, which is desirable. As is demonstrated in Table 9, moderate
improvements in thermo-oxidative stability are observed for 1E3 as compared to
C2.
TABLE 10
Gas fading performance of polyethylene formulations exposed to an
atmospheric fume oven at 140 F for 4 weeks.
Sample Days in Atmospheric Fume Chamber
0 1 3 4 7 14 21 28
C2 -2.53 -0.66 2.04 3.2
6.55 13.06 17.77 21.92
1E3 -2.51
-0.86 1.86 2.9 5.91 11.58 15.5 19.16
Although the above example demonstrates an accelerated test, it is clear that
the inventive example 3 (1E3) demonstrates moderately improved resistance to
gas
fading as compared to the comparative example, 02.
Comparative Examples
For clarity, the invention requires that the thermoplastic polyethylene
product is
made with two catalyst systems, namely a single site catalyst system that uses
an
alumoxane cocatalyst and a heterogeneous catalyst system that includes
magnesium
chloride. Color formation has been observed to be especially problematic with
this
catalyst system.
A comparative polyethylene made with a single site catalyst system essentially
the same as described above (in the section entitled Polymerization of
Thermoplastic
Polyethylene Product) was analyzed and found to contain less than 1 ppm Ti;
and 8
ppm Al (from the alumoxane cocatalyst) for a polymer having a melt index (12)
of 1
g/10 minutes and a density of 0.917 g/cc. This polyethylene was stabilized
with a
conventional stabilizer package (500 ppm each of IRGANOXTM 1076 and IRGAFOSTM
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168) and exhibited outstanding color performance, with the Y1 starting at -4.0
and
only increasing to -0.4 after the 5 extrusion pass test described above.
A polyethylene produced with only a Z/N catalyst system substantially as
described above was analyzed and found to contain about 6.5 ppm Ti; 73 ppm Al
and
163 ppm Mg for a polymer having a melt index (12) of 1 gram/10 minutes and a
density
of 0.920 g/cc. This polyethylene was stabilized with a conventional stabilizer
package
500 ppm each of IRGANOXTM 1076 and IRGAFOSTM 168 and exhibited good color
performance, with the Y1 starting at -2.5 and increasing to 7.7 after the 5
extrusion
pass test described above.
In contrast, comparative formulation Cl of example 1 (where the thermoplastic
polyethylene product was produced with a mixed catalyst system) was stabilized
with
two times the conventional stabilization package (1000 ppm each of IRGANOXTM
1076 and IRGAFOSTM 168) exhibited poor color stability (Y1 increase from -1.93
to
14.69).
Whilst not wishing to be bound by theory, it is possible that the aluminoxane
in
the single site catalyst system interacts with catalyst residues from the Z/N
catalyst
system to contribute to the color problem.
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