Note: Descriptions are shown in the official language in which they were submitted.
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MULTILAYER FILMS HAVING TUNABLE STRAIN HARDENING
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No.
62/450,772 filed on January 26, 2017, the entire disclosure of which is hereby
incorporated by
reference.
TECHNICAL FIELD
[0002] Embodiments of the present disclosure are generally related to
multilayer films, and
are specifically related to multilayer films including LDPE.
BACKGROUND
[0003] Multilayer films can include films such as cast films or blown
films, which may
include silage wrap, stretch wrap, and surface protective films. Linear low
density polyethylene
(LLDPE) and/or high density polyethylene (HDPE) are widely used for producing
multilayer
films with high tensile strength and high impact strength. Conventional
attempts to optimize
film tensile strength and yield strength by blending polymers have yielded
films with increased
yield strength, but impact strengths that were lower than films made from one
of the components
used in the blend.
[0004] Accordingly, there is a need to develop multilayer films having
increased strain
hardening and yield strength while enabling the film to remain stretchable.
SUMMARY
[0005] Embodiments are directed to multilayer cast films comprising low
density
polyethylene (LDPE) having a density of 0.918 g/cc to 0.931 g/cc and a melt
index (I2) of from
0.15 g/10 min to 6 g/10 min. The multilayer films may yield improved strain
hardening and
yield strength.
[0006] According to one embodiment, a multilayer cast film includes a cling
layer, a release
layer, and at least one core layer disposed between the cling layer and the
release layer. The
cling layer includes an ultra low density polyethylene (ULDPE), a propylene
interpolymer, or
blends thereof. The ULDPE has a density of 0.895 g/cc to 0.915 g/cc and a melt
index (12) of
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from 2 g/10 min to 10 g/10 min when measured according to ASTM D1238 at 190 C
and 2.16
kg load. The propylene interpolymer includes at least 60 wt.% units derived
from propylene and
between 1 and 40 wt% units derived from ethylene, and has a density of from
0.840 g/cm3 to
0.900 g/cm3, a highest differential scanning calorimetry (DSC) melting peak
temperature of
from 50.0 C to 120.0 C, a melt flow rate, MFR2, of from 1 g/10 min to 100
g/10 min when
measured according to ASTM D1238 at 230 C and 2.16 kg load, and a molecular
weight
distribution (MWD) of less than 4Ø The release layer includes a first linear
low density
polyethylene (first LLDPE) having a density of from 0.915 to 0.938 g/cc and a
melt index of
from 0.5 g/10 min to 10 g/10 min. Each of the core layers includes a second
linear low density
polyethylene (second LLDPE) having a density of from 0.905 to 0.930 g/cc and a
melt index of
from 0.5 g/10 min to 10 g/10 min. One or more of the cling layer, the release
layer, or the at
least one core layer further includes a low density polyethylene having a
density of 0.918 g/cc to
0.931 g/cc and a melt index (I2) of from 0.15 g/10 min to 6 g/10 min. The
multilayer cast film
includes from 3 wt% to 7 wt%, based on a total amount of polymers present in
the multilayer
cast film, of the low density polyethylene (LDPE). The multilayer cast film is
defined by at least
one of the following properties: a tensile ultimate elongation in the machine
direction of less
than 300%, as measured in accordance with ASTM D882; a natural draw ratio
(NDR) of less
than 250%; or a Highlight ultimate stretch of less than 300%, as measured in
accordance with
ASTM D4649. Additionally, the multilayer cast film exhibits a machine
direction tensile
strength at second yield of greater than 21.0 MPa for a film having a
thickness of 10 microns or
more in accordance with ASTM D882.
[0007] Additional features and advantages of the embodiments will be set
forth in the
detailed description which follows, and in part will be readily apparent to
those skilled in the art
from that description or recognized by practicing the embodiments described
herein, including
the detailed description which follows, the claims, as well as the appended
drawings.
[0008] It is to be understood that both the foregoing and the following
description describe
various embodiments and are intended to provide an overview or framework for
understanding
the nature and character of the claimed subject matter. The accompanying
drawings are
included to provide a further understanding of the various embodiments, and
are incorporated
into and constitute a part of this specification. The drawings illustrate the
various embodiments
described herein, and together with the description serve to explain the
principles and operations
of the claimed subject matter.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a graph depicting the tensile stress (vertical axis) as a
function of the stretch
% (horizontal axis) for the films of Comparative Sample A and Sample 1;
[0010] FIG. 2 is a graph depicting the tensile stress (vertical axis) as a
function of the stretch
% (horizontal axis) for the films of Samples 2-5; and
[0011] FIG. 3 is a graph depicting the tensile stress (vertical axis) as a
function of the stretch
% (horizontal axis) for the films of Comparative Samples B and C and Samples 6
and 7.
DETAILED DESCRIPTION
[0012] In various embodiments, multilayer films, for example, multilayer
cast films, include
a cling layer, a release layer, and at least one core layer disposed between
the cling layer and the
release layer. According to various embodiments, at least one of the layers
includes LDPE
polymer having a density of 0.918 g/cc to 0.931 g/cc. Without being bound by
theory, these
multilayer films have improved strain hardening and yield strength while
maintaining stretch.
[0013] As used herein, "polyethylene" means polymers comprising greater
than 50% by
weight of units which have been derived from ethylene monomer. This includes
polyethylene
homopolymers or copolymers (meaning units derived from two or more
comonomers). Common
forms of polyethylene known in the art include Low Density Polyethylene
(LDPE); Linear Low
Density Polyethylene (LLDPE); Ultra Low Density Polyethylene (ULDPE); Very Low
Density
Polyethylene (VLDPE); single site catalyzed Linear Low Density Polyethylene,
including both
linear and substantially linear low density resins (m-LLDPE); and High Density
Polyethylene
(HDPE). These polyethylene materials are generally known in the art; however
the following
descriptions may be helpful in understanding the differences between some of
these different
polyethylene resins.
[0014] The term "ULDPE" is defined as a polyethylene-based copolymer having
a density in
the range of 0.895 to 0.915 g/cc.
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[0015] The term "LDPE" may also be referred to as "high pressure ethylene
polymer" or
"highly branched polyethylene" and is defined to mean that the polymer is
partly or entirely
homopolymerized or copolymerized in autoclave or tubular reactors at pressures
above 14,500
psi (100 MPa) with the use of free-radical initiators, such as peroxides (see
for example U.S.
Pat. No. 4,599,392, incorporated herein by reference). LDPE resins typically
have a density in
the range of 0.916 to 0.940 g/cc.
[0016] The term "LLDPE", includes both resin made using the traditional
Ziegler-Natta
catalyst systems as well as single-site catalysts such as metallocenes
(sometimes referred to as
"m-LLDPE"). LLDPEs contain less long chain branching than LDPEs and include
the
substantially linear ethylene polymers which are further defined in U.S. Pat.
No. 5,272,236, U.S.
Pat. No. 5,278,272, U.S. Pat. No. 5,582,923 and U.S. Pat. No. 5,733,155; the
homogeneously
branched linear ethylene polymer compositions such as those in U.S. Pat. No.
3,645,992; the
heterogeneously branched ethylene polymers such as those prepared according to
the process
disclosed in U.S. Pat. No. 4,076,698; and/or blends thereof (such as those
disclosed in U.S. Pat.
No. 3,914,342 or U.S. Pat. No. 5,854,045). The linear PE can be made via gas-
phase, solution-
phase or slurry polymerization or any combination thereof, using any type of
reactor or reactor
configuration known in the art, including but not limited to gas and solution
phase reactors.
[0017] The term "HDPE" refers to polyethylenes having densities greater
than about 0.940
g/cc, which are generally prepared with Ziegler-Natta catalysts, chrome
catalysts or even
metallocene catalysts.
[0018] As stated above, various embodiments include multilayer films having
at least three
layers, including a cling layer, a release layer, and at least one core layer.
Cling layers, for
example, may enable the multilayer film to cling to itself when the film is
wrapped on a load.
The release layer does not have to have non-cling characteristics, but it does
typically exhibit
lower cling characteristics than the cling layer. For ease of handling,
manufacture and
recyclability, the polyethylene(s) that is used in the release layer may be
the same or similar to
the polyethylene(s) used in the cling layer and any core layers.
[0019] In various embodiments, the cling layer includes an ultra low
density polyethylene
(ULDPE), a propylene interpolymer, or a blend thereof. In embodiments, the
cling layer
includes a ULDPE. The ULDPE may have a density of 0.895 g/cm3 to 0.915 g/cm3,
or from
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0.900 g/cm3 to 0.910 g/cm3, or from 0.902 g/cm3 to 0.906 g/cm3. Moreover, the
ULDPE may
have a melt index (I2) of from 2 g/10 min to 10 g/10 min when measured
according to ASTM
D1238 at 190 C and 2.16 kg load. In further embodiments, the 12 may be from 2
g/10 min to 8
g/10 min, or from 2 g/10 min to 6 g/10 min. Commercially available ULDPEs
suitable for use
include, by way of example and not limitation, ULDPEs available under the
tradename
ATTANETm from The Dow Chemical Company (Midland, MI).
[0020] In embodiments, the cling layer additionally or alternatively
includes a propylene
interpolymer. The propylene interpolymer includes at least 60 wt% units
derived from
propylene and between 1 and 40 wt% units derived from ethylene. For example,
the propylene
interpolymer may include from 60 wt% to 99 wt% units derived from propylene,
from 65 wt%
to 95 wt% units derived from propylene, from 70 wt% to 90 wt% units derived
from propylene,
from 75 wt% to 87 wt% units derived from propylene, or even from 80 wt% to 85
wt% units
derived from propylene and from 1 wt% to 40 wt% units derived from ethylene,
from 5 wt% to
35 wt% units derived from ethylene, from 10 wt% to 30 wt% units derived from
ethylene, from
13 wt% to 25 wt% units derived from ethylene, or even from 15 wt% to 20 wt%
units derived
from ethylene. In embodiments, the propylene interpolymer has a density of
from 0.840 g/cc
and 0.900 g/cc, from 0.850 g/cc to 0.890 g/cc, or from 0.860 to 0.870 g/cc. In
embodiments, the
propylene interpolymer has a highest differential scanning calorimetry (DSC)
melting peak
temperature of from 50.0 C to 120.0 C, from 100.0 C to 117.0 C, or even
from 105.0 C to
115 C. In embodiments, the propylene interpolymer has a melt flow rate, MFR2,
of from 1 g/10
min to 100 g/10 min when measured according to ASTM D1238 at 230 C and 2.16
kg load.
For example, the propylene interpolymer may have a melt flow rate, MFR2, of
from 1 g/10 min
to 100 g/10 min, from 1.25 g/10 min to 50 g/10 min, from 1.5 g/10 min to 25
g/10 min, from
1.75 g/10 min to 20 g/10 min, from 2 g/10 min to 10 g/10 min, or from 2.5 g/10
min to 5 g/10
min. Furthermore, in embodiments, the propylene interpolymer has a molecular
weight
distribution (MWD), Mw/Mõ, of less than 4Ø For example, the propylene
interpolymer may
have an MWD of from 1 to 4, from 1.5 to 3.9, or from 2 to 3.8. Various
commercial propylene
interpolymers are considered suitable, for example, VISTAMAXXTm from the Exxon
Mobil
Chemical Company.
[0021] Although in one or more embodiments the cling layer may include a ULDPE
or a
propylene interpolymer, it is contemplated that in some embodiments, the cling
layer may
include a blend of a ULDPE and a propylene interpolymer. In further
embodiments, additional
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polymers may be added to the cling layer, such as LDPEs, LLDPEs, and the like.
Accordingly,
in one embodiment, the cling layer includes from 3 wt% to 100 wt% of ULDPE,
propylene
interpolymer, or both. In a further embodiment, the cling layer includes from
20 wt% to 80 wt%
of ULDPE, propylene interpolymer, or both. In yet another embodiment, the
cling layer includes
from 20 wt% to 40 wt% of ULDPE, propylene interpolymer, or both. By way of
example and
not limitation, in some embodiments, the cling layer includes about 30% ULDPE,
propylene
interpolymer, or both and about 70% LLDPE, while in other embodiments, the
cling layer
includes about 100% ULDPE, propylene interpolymer, or both.
[0022] In some embodiments, the cling layer may include up to about 20 wt%
LDPE
polymer (sometimes referred to herein as LDPE resin), from 4 wt% to 15 wt%
LDPE polymer,
or, in some embodiments, from 4 wt% to 10 wt% LDPE polymer.
[0023] As will be described in greater detail below, the LDPE polymer may
be included in
other layers in addition to or as an alternative to inclusion in the cling
layer. In various
embodiments, any layer including LDPE may include from greater than 0 wt% to
20 wt%
LDPE, from greater than 0 wt% to 15 wt% LDPE, from 0.01 wt% to 15 wt% LDPE, or
from 0.5
wt% to 15 wt% LDPE. In other words, each layer in the multilayer film includes
a maximum of
15 wt% or even 20 wt% LDPE, but may alternatively be free of LDPE. Various
embodiments
provide a multilayer film including from about 3 wt% to about 7 wt% LDPE based
on a total
weight of the multilayer film.
[0024] The LDPE may have a density of from 0.915 g/cc to 0.931 g/cc, from
0.915 g/cc to
0.925 g/cc, or even from 0.918 g/cc to 0.924 g/cc. In some embodiments, the
LDPE has a
density of from 0.918 g/cc to 0.931 g/cc. The LDPE may have a melt index (I2)
ranging from
0.15 g/10 min to 6 g/10 min, from 0.15 g/10 min to 4 g/10 min, from 0.2 g/10
min to 6 g/10 min,
from 0.2 g/10 min to 5 g/10 min, from 0.2 g/10 min to 2 g/10 min, from 0.2
g/10 min to 1 g/10
min, or from 0.75 g/10 min to 2 g/10 min when measured according to ASTM D1238
at 190 C
and 2.16 kg load. The LDPE may further be characterized by molecular weight
distribution
(MWD). For example, in various embodiments, the LDPE has an MWD from 3.5 to
10, from 4
to 10, or from 5 to 9. As used herein, the MWD is defined as Mw/Mõ, where Mw
is a weight
average molecular weight and M,, is a number average molecular weight.
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[0025] The LDPEs may be well-known, commercially available LDPEs, and may be
made
by any one of a variety of processes, such as those described above.
Commercially available
LDPEs include but are not limited to LDPEs available under the tradenames
AGILITYTm and
DOW, including but not limited to DOWTM LDPE 310E, from The Dow Chemical
Company
(Midland, MI).
[0026] In some embodiments, the cling layer may further include one or more
LLDPEs.
Suitable LLDPEs may include, for example, one or more of the LLDPEs described
hereinbelow.
For example, in some embodiments, the cling layer includes an LLDPE having a
density of from
0.905 to 0.930 g/cc and a melt index (I2) of from 0.5 g/10 min to 10 g/10 min
when measured
according to ASTM D1238 at 190 C and 2.16 kg load. The LLDPE may further be
characterized by a MWD of from 3.5 to 5.0, or from 3.5 to 4.5, as measured by
GPC. In various
embodiments, the LLDPE may further be characterized by a comonomer
distribution breadth
index (CDBI) of less than 70%. As used herein, CDBI is defined as the weight
percent of the
polymer molecules having a comonomer content within 50 percent of the median
total molar
comonomer content. It represents a comparison of the comonomer distribution in
the polymer to
the comonomer distribution expected for a Bernoullian distribution.
[0027] In embodiments, the LLDPE of the core layer is an ethylene/C4-C20
alpha-olefin
interpolymer, or in further embodiments, an ethylene/C5-C20 alpha-olefin
interpolymer, an
ethylene/C4-C8 alpha-olefin interpolymer (C4-C8-LLDPE), or an ethylene/C6-C12
interpolymer
(C6-C12-LLDPE). The term "interpolymer" is used herein to indicate a
copolymer, or a
terpolymer, or the like. That is, at least one other comonomer is polymerized
with ethylene to
make the interpolymer. For example, in some embodiments, the LLDPE may be an
ethylene/C5
terpolymer, while in other embodiments, the LLDPE may be an ethylene/C4-C20
copolymer.
[0028] The ethylene/C5-C20 alpha-olefin interpolymer may have a density of
from 0.915 g/cc
to 0.925 g/cc, from 0.916 g/cc to 0.920 g/cc, or from 0.917 to 0.919 g/cc. In
various
embodiments, the ethylene/C5-C20 alpha-olefin interpolymer has a melt index
(I2) ranging from
0.25 g/10 min to 10 g/10 min, from 0.5 g/10 min to 5 g/10 min, or from 0.75
g/10 min to 4 g/10
min when measured according to ASTM D1238 at 190 C and 2.16 kg load.
[0029] The C6-C12-LLDPE may be a copolymer including ethylene and at least
one C6-C12 a-
olefin comonomer. The C6-C12 a-olefin comonomer may be, for example, 1-hexene,
1-octene,
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or the like. Accordingly, in some embodiments, the C6-C12-LLDPE may be, by way
of example
and not limitation, hexene-LLDPE (C6-LLDPE) or octene-LLDPE (C8-LLDPE). The C6-
C12-
LLDPE may be a well-known, commercially available C6-C12-LLDPE, and may be
made by any
one of a wide variety of processes including, but not limited to, solution,
gas or slurry phase
processes. Additionally, such processes may be Ziegler-Natta catalyzed or
constrained
geometry catalyzed, or the like. In some embodiments, the C6-C12-LLDPE is a
Ziegler-Natta
catalyzed resin. Commercially available C6-C12-LLDPEs include but are not
limited to C6-C12-
LLDPEs available under the tradenames DOWLEXTm (including, but not limited to,
DOWLEXTm 2645G) and ATTANETm (including, but not limited to, ATTANETm 4607GC
and
ATTANETm 4404G) from The Dow Chemical Company (Midland, MI). Other
commercially
available C6-C12-LLDPEs include those available under the tradenames ENABLETM
(including,
but not limited to, ENABLE Tm 2010) and EXCEEDTM (including, but not limited
to,
EXCEEDTM 3518) from the Exxon Mobil Chemical Company.
[0030] The C6-C12-LLDPE may have a density of from 0.900 to 0.940 g/cc,
from 0.916 g/cc
to 0.920 g/cc, or from 0.915 to 0.925 g/cc. In various embodiments, the C6-C12-
LLDPE has a
melt index (I2) ranging from 0.25 g/10 min to 10 g/10 min, from 0.5 g/10 min
to 2 g/10 min,
from 0.8 g/10 min to 4.5 g/10 min, or even from 1 g/10 min to 3 g/10 min.
[0031] The C4-C8-LLDPEs may have a density of from 0.900 g/cc to 0.940
g/cc, from 0.916
g/cc to 0.920 g/cc, or from 0.915 to 0.925 g/cc. The C4-C8-LLDPEs may include
well-known,
commercially available C4-C8-LLDPEs, and may be made by any one of a wide
variety of
processes including, but not limited to, solution, gas or solution, gas or
slurry phase processes.
Additionally, such processes may be Ziegler-Natta catalyzed or constrained
geometry catalyzed,
or the like. In some embodiments, the C4-C8-LLDPE is a Ziegler-Natta catalyzed
resin. In
various embodiments, the C4-C8-LLDPEs or butene-LLDPE has a melt index (I2)
ranging from
0.5 g/10 min to 4 g/10 min or from 1 g/10 min to 2 g/10 min when measured
according to
ASTM D1238 at 190 C and 2.16 kg load.
[0032] The C4-C8-LLDPEs may include butene-LLDPEs. These may include well-
known,
commercially available butene-LLDPEs made by any one of a wide variety of
processes
including, but not limited to, solution, gas or slurry phase, Ziegler-Natta or
constrained geometry
catalyzed, or the like. Commercially available butene-LLDPEs include but are
not limited to
butene-LLDPEs available under the tradenames CEFORTM, for example, CEFORTm
1221P and
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CEFORTM 1211P from The Dow Chemical Company (Midland, MI), or SABIC LLDPE
218B
from Saudi Arabia Basic Industries Corporation (Saudi Arabia).
[0033] In specific embodiments, the cling layer may include butene-LLDPEs,
hexene-
LLDPEs, octene-LLDPEs, or combinations thereof. Various amounts are
contemplated for the
LLDPE's in the cling layer. For example, the cling layer may include from 10
wt% to 95 wt%
LLDPE, or from 20 wt% to 90 wt% LLDPE, or from 50 wt% to 80 wt% LLDPE, or from
60
wt% to 80 wt% LLDPE. Various amounts are contemplated for the LLDPEs in the
release layer.
For example, the release layer may include from 10 wt% to 100 wt% LLDPE, or
from 20 wt%
to 90 wt% LLDPE.
[0034] As stated above, the multilayer film further includes a release
layer. In various
embodiments, the release layer includes at least one LLDPE, for example,
butene-LLDPE,
hexene-LLDPE, or combinations thereof.
[0035] In some embodiments, the release layer may further include at least
one LDPE
polymer. The LDPE polymer may, for example, be any of the LDPE polymers
described above.
In embodiments, the release layer may include up to about 20 wt% LDPE polymer,
from 3 wt%
to 20 wt% LDPE polymer, or, in some embodiments, from 3 wt% to 10 wt% LDPE
polymer.
That said, the LDPE polymer is only present from 3 wt% to 7 wt% based on a
total amount of
polymers of the multilayer film.
[0036] Furthermore, the multilayer film further includes at least one core
layer disposed
between the cling layer and the release layer. In various embodiments, at
least one core layer
may be in contact with the cling layer and/or the release layer. In other
embodiments, additional
layers may be disposed between the cling layer and the core layer and/or
between the release
layer and the core layer. Each core layer of the multilayer film includes at
least one LLDPE. In
various embodiments, the core layer(s) may be used to provide strain
hardening. Strain
hardening occurs when areas of material which have already been strained
become stiffer,
transferring subsequent elongation into areas which are unstrained. Although
in various
embodiments, a single core layer will be discussed and described, it is
contemplated that in some
embodiments, multiple core layers may be employed.
[0037] Various LLDPEs may be included in the core layer, including but not
limited to the
LLDPEs described above. For example, in embodiments, the LLDPE may have a
density of
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from 0.905 to 0.930 g/cc and a melt index (I2) of from 0.5 g/10 min to 10 g/10
min when
measured according to ASTM D1238 at 190 C and 2.16 kg load.
[0038] In some embodiments, the core layer includes an LLDPE that is the
same as an
LLDPE included in the release layer, while in other embodiments, the LLDPE of
the core layer
is different from the LLDPE included in the release layer. Moreover, the LLDPE
of the core
layer may be the same as or different from an LLDPE included in the cling
layer. In some
embodiments, each of the cling layer, the release layer, and the core layer
includes a different
LLDPE, while in other embodiments, two or more layers may include the same
LLDPE. In
other words, in some embodiments, two or more LLDPEs in the cling layer, the
release layer,
and the core layer may be different from each other. By "a different LLDPE,"
it is meant that
the LLDPEs may differ in density, melt index, catalyst, process, or some other
aspect. In some
embodiments, one or more core layers may include one or more butene-LLDPEs,
such as those
described above. For example, in one embodiment, the multilayer film includes
three core
layers: two outer core layers and an inner core layer. In this embodiment, the
inner core layer
may include a butene-LLDPE and each of the outer core layers may include an
ethylene/C5-C20
alpha-olefin interpolymer.
[0039] In further embodiments, the core layer may be made from a solution
including an
LDPE and a C6-C12 comonomer LLDPE copolymer (C6-C12-LLDPE) blend. In some
embodiments, the core layer may be made from a solution including an LDPE and
a C6-C8-
LLDPE blend. Accordingly, in some embodiments, the C6-C12-LLDPE may be, by way
of
example and not limitation, hexene-LLDPE (C6-LLDPE) or octene-LLDPE (C8-
LLDPE).
[0040] In some embodiments, the core layer may further include at least one
LDPE polymer.
The LDPE polymer may, for example, be any of the LDPE polymers described
hereinabove. In
embodiments, the core layer may include up to about 20 wt% LDPE polymer, from
3 wt% to 20
wt% LDPE polymer, or, in some embodiments, from 3 wt% to 10 wt% LDPE polymer
based on
a total amount of polymers present in the core layer. In some embodiments in
which the
multilayer film includes two or more core layers, at least one of the core
layers includes from 3
wt% to 20 wt% LDPE polymer, or, in some embodiments, from 3 wt% to 10 wt% LDPE
polymer based on a total amount of polymers present in that core layer.
Reiterating the proviso
above, the LDPE polymer is present in from 3 wt% to 7 wt% based on a total
amount of
polymers of the multilayer film.
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[0041] It is contemplated that the multilayer film may include multiple
layers including
various combinations of LLDPEs, and one or more layers may include an LDPE. As
one
example, the multilayer film may include a cling layer including at least
ULDPE, a release layer
including a first LLDPE, and at least one core layer including a second LLDPE.
In another
example, the multilayer film may include a cling layer including at least
ULDPE, a release layer
including a first LLDPE and from 3 wt% to 20 wt% LDPE, and at least one core
layer including
a second LLDPE. In another example, the multilayer film may include a cling
layer including at
least ULDPE, a release layer including a first LLDPE, and two core layers
including a second
LLDPE, at least one of the core layers also including from 3 wt% to 20 wt%
LDPE. In another
example, the multilayer film may include a release layer including a first
LLDPE, at least one
core layer including a second LLDPE, and a cling layer including at least
ULDPE and a third
LLDPE. In some embodiments, one or more of the LLDPEs is formed in the
presence of a
Ziegler-Natta catalyst and is characterized by a MWD of from 3.5 to 5.0, or
from 3.5 to 4.5, as
measured using GPC and a CDBI of less than 70%.
[0042] In embodiments, at least one LLDPE may be an ethylene-butene copolymer
and
another LLDPE in the multilayer film may be an ethylene/C5-C20 alpha-olefin
interpolymer. For
example, the multilayer film may include a cling layer including at least
ULDPE, a release layer
including an ethylene-butene copolymer, and at least one core layer including
an ethylene/C5-
C20 alpha-olefin interpolymer. As another example, the multilayer film may
include a cling
layer including at least ULDPE and an ethylene-butene copolymer, a release
layer including an
LLDPE, and at least one core layer including an ethylene/C5-C20 alpha-olefin
interpolymer. In
still another example, the multilayer film may include a cling layer including
at least ULDPE, a
release layer including an LLDPE, and at least three core layers. An inner
core layer may
include an ethylene-butene copolymer, while the two outer core layers may
include an
ethylene/C5-C20 alpha-olefin interpolymer. Other combinations are also
contemplated.
[0043] The multilayer film of various embodiments may be constructed from two
or more
film layers by any film lamination and/or coextrusion technique and using any
blown or cast
film extrusion and lamination equipment known in the art. For example,
multilayer film
structures may be prepared using coextrusion techniques, such as, by cast
coextrusion
techniques.
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[0044] The multilayer film may have a thickness of from 5 p.m to 15 p.m,
from 6 p.m to 13
p.m, from 6 p.m to 12 p.m, from 6 p.m to 9 p.m, from 8 p.m to 15 p.m, or from
10 p.m to 15 p.m. In
various embodiments, the core layer has a thickness of from 30% to 70% based
on a total
thickness of the multilayer film. In some embodiments, the core layer has a
thickness of from
40% to 60% based on the total thickness of the multilayer film. In other
embodiments, the core
layer has a thickness of from 50% to 70% based on the total thickness of the
multilayer film. In
still other embodiments, the core layer has a thickness of from about 50% to
about 90% of the
total thickness of the film.
[0045] One or more layers of the multilayer film may further comprise one
or more additives.
Such additives include, but are not limited to, dyes, lubricants, fillers,
pigments, antioxidants,
processing aids, UV stabilizers, release agents, anti-blocking agents, and
combinations thereof.
The multilayer films may contain any amounts of such additives, such as from 0
wt% to 10 wt%
based on a weight of the layer.
[0046] Without being bound by theory, the tunable strain hardening
properties may be
characterized by one or more of the properties detailed below.
[0047] The multilayer films of various embodiments herein may have a
tensile ultimate
elongation in the machine direction of less than 350%, less than 325%, less
than 300% or even
less than 250% when measured in accordance with ASTM D882.
[0048] The multilayer films described herein typically exhibit a machine
direction ("MD")
tensile strength of at least 20 MPa, as measured in accordance with ASTM D882.
In some
embodiments, the machine direction tensile strength of the multilayer film is
from about 35 to
80 MPa, from 40 to 75 MPa, or from 42 to 72 MPa.
[0049] Moreover, the multilayer films described herein may exhibit a
natural draw ratio
(NDR) of less than about 250%. As used herein, the NDR is determined from a
stress-
elongation measurement of ASTM D882, as the elongation at the intersection of
a line drawn
through a linear portion of the strain hardening region and a line drawn
through a linear portion
of the yield plateau region. The lines are calculated as linear regression
fits to the data in the
linear portions of the curves. The specific range of data points subjected to
the linear regression
analysis can be chosen by changing the lower elongation limit in steps of, for
example, 5%,
keeping the overall range constant at, for example, 50% (e.g., 50-100%, 55-
105%, 60-110%,
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etc.), and determining the range which gives the lowest sum of squared
differences between
predicted and actual data. Additional details on calculating the NDR may be
found in U.S.
Patent No. 7,601,409, which is hereby incorporated by reference in its
entirety.
[0050] In various embodiments, the multilayer film exhibits a machine
direction tensile stress
at second yield of greater than 19.0 MPa, or greater than 21.0 MPa for a film
having a thickness
of 10 microns or more in accordance with ASTM D882.
In various embodiments, the
multilayer film has at least one of the following properties: a tensile
ultimate elongation in the
machine direction of less than 300% as measured in accordance with ASTM D882,
a NDR of
less than 250%, or a Highlight ultimate stretch of less than 300% as measured
in accordance
with ASTM D4649.
[0051] In practice, the multilayer film may be wrapped around an article,
including but not
limited to food, or a group of articles to form a unitized package. The
unitized package may be
at least partially held together by the retaining force applied by the
multilayer film, which is
stretched during the wrapping. Wrapping may be performed by positioning the
article or group
of articles on a platform or turntable, which is rotated to take up the
multilayer film from a
continuous roll. Braking tension may be applied to the multilayer film roll to
subject the
multilayer film to continuous tensioning or stretching force. Alternatively,
an operator may
hand hold the roll of multilayer film and walk around the article or group of
articles to be
wrapped, applying the multilayer film to the article or group of articles.
Test Methods
[0052] Unless otherwise specified, test methods were performed as follows:
[0053] Density is measured in accordance with ASTM D 792, and is reported
in grams per
cubic centimeter (g/cc or g/cm3).
[0054] Melt Index (I2) is measured in accordance with ASTM D 1238 at 190 C
and a 2.16
kg load, and is reported in grams eluted per 10 minutes.
[0055] Melt Flow Rate, MFR2, for propylene-based polymers is measured in
accordance
with ASTM D 1238-10, Condition 230 C/2.16 kg, and is reported in grams eluted
per 10
minutes.
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Gel Permeation Chromatography (GPC)
Propylene Interpolymers
[0056]
The chromatographic system consisted of a PolymerChar GPC-IR (Valencia, Spain)
high temperature GPC chromatograph, equipped with an internal IR5 infra-red
detector (IR5)
coupled to a Precision Detectors (Now Agilent Technologies) 2-angle laser
light scattering (LS)
detector Model 2040, and followed by a PolymerChar 4-capillary viscosity
detector (three
detectors in series). For all light scattering measurements, the 15 degree
angle was used for
measurement purposes. The autosampler oven compartment was set at 160
Celsius, and the
column compartment was set at 150 Celsius. The columns used were four,
Agilent "Mixed A"
columns, each 30 cm, and each packed with 20-micron linear mixed-bed
particles. The
chromatographic solvent used was 1,2,4-trichlorobenzene, which contained 200
ppm of
butylated hydroxytoluene (BHT). The solvent source was nitrogen sparged. The
injection
volume was 200 microliters, and the flow rate was 1.0 milliliters/minute.
[0057] Calibration of the GPC column set was performed with 21 narrow
molecular weight
distribution, polystyrene standards with molecular weights ranging from 580 to
8,400,000 g/mol.
These standards were arranged in 6 "cocktail" mixtures, with at least a decade
of separation
between individual molecular weights.
The standards were purchased from Agilent
Technologies. The polystyrene standards were prepared at "0.025 grams in 50
milliliters of
solvent" for molecular weights equal to, or greater than, 1,000,000, g/mol,
and at "0.05 grams in
50 milliliters of solvent" for molecular weights less than 1,000,000 g/mol.
The polystyrene
standards were dissolved at 80 C, with gentle agitation, for 30 minutes.
[0058]
The equivalent polypropylene molecular weights are determined by using
appropriate
Mark-Houwink coefficients for polypropylene (as described by Th.G. Scholte,
N.L.J. Meijerink,
H.M. Schoffeleers, and A.M.G. Brands, J. Appl. Polym. Sci., 29, 3763 ¨ 3782
(1984),
incorporated herein by reference) and polystyrene (as described by E. P.
Otocka, R. J. Roe, N.
Y. Hellman, P. M. Muglia, Macromolecules, 4, 507 (1971) incorporated herein by
reference) in
the Mark-Houwink equation (EQ 1), which relates intrinsic viscosity to
molecular weight. The
instantaneous molecular weight (1\4(pp)) at each chromatographic point is
determined by EQ 2,
using universal calibration and the Mark-Houwink coefficients as defined in EQ
1. The number-
average, weight-average, and z-average molecular weight moments, Mn, Mw, and
Mz are
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calculated according to EQ 3, EQ 4, and EQ 5, respectively, wherein IR is the
baseline-
subtracted infra-red measurement signal height of the polymer elution peak at
each
chromatographic point (i).
{ul}=KMa (EQ 1)
where Kpp = 1.90E-04, app = 0.725 and Kps = 1.26E-04, aps = 0.702
A 3rd-order polynomial was used to fit the polystyrene calibration points.
1
aps +1 a +1
(K M PP
M (PP) = PS PS
(EQ 2)
PP
IR
Mn(GPC) = _________________
(
IR/ (EQ 3)
(PP),
i
1(IRi * M (pp)i)
MW(GPC) = (EQ 4)
IRi
1(IRi * M (pp)i2)
MZ(GPC) = _________________
(EQ 5)
(Mi * M (pp) i)
LLDPE and LDPE Polymers
[0059] For the LLPDE and LDPE samples, the polystyrene standard peak molecular
weights
(IR 5 detector) were converted to polyethylene molecular weights using EQ 6
(as described in
Williams and Ward, J. Polym. Sci., Polym. Let., 6, 621 (1968))
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M (PE) = A(111 ps) where A = 0.4315 and B =1 (EQ 6)
A third order polynomial was used to fit the respective polyethylene-
equivalent calibration
points. A small adjustment to A (from approximately 0.415 to 0.44) was made to
correct for
column resolution and band-broadening effects, such that NIST standard NBS
1475 was
obtained at 52,000 g/mol (Mw). The number-average, weight-average, and z-
average molecular
weight moments, Mn, Mw, and Mz are calculated according to EQ 7, EQ 8, and EQ
9,
respectively, wherein IR is the baseline-subtracted infra-red measurement
signal height of the
polymer elution peak at each chromatographic point (i).
IR,
Mn(GPC) = _________________
I
IR/ (EQ 7)
(PE),
i
* M (PE)i)
MW(GPC) = (EQ 8)
IRi
1(IRi* M (pE)i 2 )
MZ(GPC) = _________________
t (EQ 9)
URi* M (PE)i)
Crystallization Elution Fractionation (CEF) Method
[0060] The Crystallization Elution Fractionation (CEF) technology is
conducted according to
Monrabal et al, Macromol. Symp. 257, 71-79 (2007). The CEF instrument is
equipped with an
IR-4 or IR-S detector (such as that sold commercially from PolymerChar, Spain)
and a two
angle light scattering detector Model 2040 (such as those sold commercially
from Precision
Detectors). A 10 micron guard column of 50 mm x 4.6 mm (such as that sold
commercially from
PolymerLabs) is installed before the IR-4 or IR-S detector in the detector
oven. Ortho-
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dichlorobenzene (ODCB, 99% anhydrous grade) and 2,5-di-tert-butyl-4-
methylphenol (BHT)
(such as commercially available from Sigma-Aldrich) are obtained. Silica gel
40 (particle size
0.2-0.5 mm) (such as commercially available from EMD Chemicals) is also
obtained. The silica
gel is dried in a vacuum oven at 160 C for at least two hours before use.
ODCB is sparged with
dried nitrogen (N2) for one hour before use. Dried nitrogen is obtained by
passing nitrogen at
<90 psig over CaCO3 and 5A molecular sieves. ODCB is further dried by adding
five grams of
the dried silica to two liters of ODCB or by pumping through a column or
columns packed with
dried silica between 0.1 ml/min to 1.0 ml/min. Eight hundred milligrams of BHT
are added to
two liters of ODCB if no inert gas such as N2 is used in purging the sample
vial. Dried ODCB
with or without BHT is hereinafter referred to as "ODCB-m." A sample solution
is prepared by,
using the autosampler, dissolving a polymer sample in ODCB-m at 4 mg/ml under
shaking at
160 C for 2 hours. 300 0_, of the sample solution is injected into the
column. The temperature
profile of CEF is: crystallization at 3 C/min from 110 C to 30 C, thermal
equilibrium at 30 C
for 5 minutes (including Soluble Fraction Elution Time being set as 2
minutes), and elution at 3
C/min from 30 C to 140 C. The flow rate during crystallization is 0.052
ml/min. The flow
rate during elution is 0.50 ml/min. The IR-4 or IR-S signal data is collected
at one data
point/second.
[0061] The CEF column is packed with glass beads at 125 p.m 6% (such as
those
commercially available with acid wash from MO-SCI Specialty Products) with 1/8
inch stainless
tubing according to U.S. 8,372,931. The internal liquid volume of the CEF
column is between
2.1 ml and 2.3 ml. Temperature calibration is performed by using a mixture of
NIST Standard
Reference Material linear polyethylene 1475a (1.0 mg/ml) and Eicosane (2
mg/ml) in ODCB-m.
The calibration consists of four steps: (1) calculating the delay volume
defined as the
temperature offset between the measured peak elution temperature of Eicosane
minus 30.00 C;
(2) subtracting the temperature offset of the elution temperature from the CEF
raw temperature
data. It is noted that this temperature offset is a function of experimental
conditions, such as
elution temperature, elution flow rate, etc.; (3) creating a linear
calibration line transforming the
elution temperature across a range of 30.00 C and 140.00 C such that NIST
linear
polyethylene 1475a has a peak temperature at 101.00 C, and Eicosane has a
peak temperature
of 30.00 C, (4) for the soluble fraction measured isothermally at 30 C, the
elution temperature
is extrapolated linearly by using the elution heating rate of 3 C/min. The
reported elution peak
temperatures are obtained such that the observed comonomer content calibration
curve agrees
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with those previously reported in U.S. Patent No. 8,372,931, which is hereby
incorporated by
reference.
Comonomer Distribution Breadth Index (CDBI)
[0062] The CDBI is calculated using the methodology described in
WO/93/03093, which is
hereby incorporated by reference, from data obtained from CEF. CDBI is defined
as the weight
percent of the polymer molecules having a comonomer content within 50 percent
of the median
total molar comonomer content. It represents a comparison of the comonomer
distribution in the
polymer to the comonomer distribution expected for a Bernoullian distribution.
[0063] CEF is used to measure the short chain branching distribution (SCBD)
of the
polyolefin. A CEF molar comonomer content calibration is performed using 24
reference
materials (e.g., polyethylene octene random copolymer and ethylene butene
copolymer) with a
narrow SCBD having a comonomer mole fraction ranging from 0 to 0.108 and a Mw
from
28,400 to 174,000 g/mole. The ln (mole fraction of ethylene), which is the ln
(comonomer mole
fraction), versus 1/T (K) is obtained, where T is the elution temperature in
Kelvin of each
reference material. The comonomer distribution of the reference materials is
determined using
13C NMR analysis in accordance with techniques described, for example, in U.S.
Patent No.
5,292,845 (Kawasaki, et al.) and by J. C. Randall in Rev. Macromol. Chem.
Phys., C29, 201-
317.
Differential Scanning Calorimetry (DSC)
[0064] DSC is used to measure the melting and crystallization behavior of a
polymer over a
wide range of temperatures. For example, the TA Instruments Q1000 DSC,
equipped with an
RCS (refrigerated cooling system) and an autosampler is used to perform this
analysis. The
instrument is first calibrated using the software calibration wizard. A
baseline is obtained by
heating a cell from -80 C to 280 C without any sample in an aluminum DSC
pan. Sapphire
standards are then used as instructed by the calibration wizard. Next, 1 to 2
milligrams (mg) of a
fresh indium sample are analyzed by heating the standards sample to 180 C,
cooling to 120 C
at a cooling rate of 10 C/minute, and then keeping the standards sample
isothermally at 120 C
for 1 minute. The standards sample is then heated from 120 C to 180 C at a
heating rate of 10
C/minute. Then, it is determined that indium standards sample has heat of
fusion (Hf) = 28.71
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0.50 Joules per gram (J/g) and onset of melting = 156.6 C 0.5 C. Test
samples are then
analyzed on the DSC instrument.
[0065] During testing, a nitrogen purge gas flow of 50 ml/min is used. Each
sample is melt
pressed into a thin film at about 175 C; the melted sample is then air-cooled
to room
temperature (approx. 25 C). The film sample is formed by pressing a "0.1 to
0.2 gram" sample
at 175 C at 1,500 psi, and 30 seconds, to form a "0.1 to 0.2 mil thick" film.
A 3-10 mg, 6 mm
diameter specimen is extracted from the cooled polymer, weighed, placed in a
light aluminum
pan (ca 50 mg), and crimped shut. Analysis is then performed to determine its
thermal
properties.
[0066] The thermal behavior of the sample is determined by ramping the
sample temperature
up and down to create a heat flow versus temperature profile. First, the
sample is rapidly heated
to 180 C, and held isothermal for five minutes, in order to remove its
thermal history. Next, the
sample is cooled to -40 C, at a 10 C/minute cooling rate, and held
isothermal at -40 C for five
minutes. The sample is then heated to 150 C (this is the "second heat" ramp)
at a 10 C/minute
heating rate. The cooling and second heating curves are recorded. The cool
curve is analyzed
by setting baseline endpoints from the beginning of crystallization to -20 C.
The heat curve is
analyzed by setting baseline endpoints from -20 C to the end of melt. The
values determined
are peak melting temperature (Tn,), peak crystallization temperature (TA onset
crystallization
temperature (Tc onset), heat of fusion (Hf) (in Joules per gram), and the
calculated %
crystallinity for polyethylene samples using: % Crystallinity for PE =
((Hf)/(292 J/g)) x 100, and
the calculated % crystallinity for polypropylene samples using: %
Crystallinity for PP =
((Hf)/165 J/g)) x 100. The heat of fusion (Hf) and the peak melting
temperature are reported
from the second heat curve. Peak crystallization temperature and onset
crystallization
temperature are determined from the cooling curve.
13C-NMR
Sample Preparation
[0067] The samples are prepared by adding approximately 2.7 g of a 50/50
mixture of
tetrachloroethane-d2/orthodichlorobenzene containing 0.025 M Cr(AcAc)3 to 0.25
g sample in
a Norell 1001-7 10 mm NMR tube. The samples are dissolved and homogenized by
heating the
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tube and its contents to 150 C using a heating block and vortex mixer. Each
sample is visually
inspected to ensure homogeneity.
Data Acquisition Parameters
[0068] The data is collected using a Bruker 400 MHz spectrometer equipped
with a Bruker
Dual DUL high-temperature CryoProbe. The data is acquired using 320 transients
per data file,
a 6 sec pulse repetition delay, 90 degree flip angles, and inverse gated
decoupling with a sample
temperature of 120 C. All measurements are made on non-spinning samples in
locked mode.
Samples are allowed to thermally equilibrate for 7 minutes prior to data
acquisition. The 13C
NMR chemical shifts are internally referenced to the mmmm pentad at 21.90 ppm
or the EEE
triad at 30.0 ppm.
Data Analysis
[0069] Composition is determined using the assignments from S. Di Martino
and M.
Kecichtermans, "Determination of the Composition of Ethylene-Propylene-Rubbers
Using 13C-
NMR Spectroscopy," Journal of Applied Polymer Science, Vol. 56, 1781-1787
(1995), and
integrated C13 NMR spectra to solve the vector equation s=fM where M is an
assignment
matrix, s is a row vector representation of the spectrum, and f is a mole
fraction composition
vector. The elements of f are taken to be triads of E and 0 with all
permutations of E and 0.
The assignment matrix M is created with one row for each triad in f and a
column for each of the
integrated NMR signals. The elements of the matrix are integral values
determined by reference
to the assignments in Ref. 1. The equation is solved by variation of the
elements of f as needed
to minimize the error function between s and the integrated C13 data for each
sample. This is
easily executed in Microsoft Excel using the Solver function.
[0070] Elmendorf Tear is measured in machine direction (MD) and transverse
direction (TD)
in accordance with ASTM D1922.
[0071] Tensile strength values (at yield, at 2nd yield, at break,
elongation at break, energy to
break, and stress) are measured in the machine direction (MD) with a ZWICK
model Z010 with
TestXpertII software according to ASTM D882. Tensile Yield Strength (or yield
point) is
defined as the first inflection points or local maximum at the lowest strain
(elongation) in a
stress-strain curve from ASTM D882. Tensile 2nd Yield Strength is defined as
the second
inflection point or second local maximum at higher strain than the yield
point, which resides
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typically between strain at yield point and start of yield plateau region
(typically less than 100%
strain) from ASTM D882.
[0072] Dart Impact Strength (sometimes termed "dart drop") is measured
according to
ASTM D1709 Method A, at 26 inches 0.4 inches (66 cm 1 cm) height and
polished
aluminum hemispherical head of 38.10 0.13 mm in diameter.
[0073] Puncture resistance is measured on a ZWICK model Z010 with
TestXpertII software.
The specimen size is 6" x 6" and at least 5 measurements are made to determine
an average
puncture value. A 1000 Newton load cell is used with a round specimen holder.
The specimen is
a 4 inch diameter circular specimen. The Puncture resistance procedures follow
ASTM D5748-
95 standard, with modification to the probe described here. The puncture probe
is a 1/2 inch
diameter ball shaped polished stainless steel probe. There is no gauge length;
the probe is as
close as possible to, but not touching, the specimen. The probe is set by
raising the probe until it
touched the specimen. Then the probe is gradually lowered, until it is not
touching the specimen.
Then the crosshead is set at zero. Considering the maximum travel distance,
the distance would
be approximately 0.10 inch. The crosshead speed used is 250 mm/minute. The
thickness is
measured in the middle of the specimen. The thickness of the film, the
distance the crosshead
traveled, and the peak load are used to determine the puncture by the
software. The puncture
probe is cleaned after each specimen. The puncture force at break is the
maximum peak load at
break (in Newtons) and the puncture energy is the area under the curve of the
load/elongation
curve (in Joules).
[0074] Highlight values (ultimate stretch and stretch force) were measured
on a Highlight
Film test stand, Highlight Industries Inc. (Michigan, USA). The Highlight
measurements follow
ASTM D4649 standard. A film supply roll is placed on the film mandrel, where
film is
unwound and threaded through two pre-stretching rubber rollers, and finally
collected at the
take-up mandrel. The test selector switch was positioned to
"Ultimate/Quality", and the "Light"
setting was selected for thin gauge films. The Highlight ultimate stretch was
conducted using
the Film Ultimate Test feature on the test software, which starts at a minimal
stretch percentage
and progressively increases the film stretch to the film's ultimate stretch
level. The test speed is
56 meters/minute, and at least 2 measurements are made to determine the
average ultimate
stretch. The Highlight stretch force is measured using the force transducer
located between the
pre-stretching rubber rollers, recorded periodically throughout the
experiment.
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Examples
[0075] The following examples are provided to illustrate various
embodiments, but are not
intended to limit the scope of the claims. All parts and percentages are by
weight unless
otherwise indicated. Further, a description of the raw materials used in the
examples is as
follows:
[0076] DOWLEXTm 2645G is a C6-LLDPE copolymer having a melt index (I2) of 0.85
g/10
min and a density of 0.918 g/cc, available from The Dow Chemical Company
(Midland, MI);
[0077] DOWLEXTm 2607G is a C6-LLDPE copolymer having a melt index (I2) of 2.3
g/10
min, a density of 0.918 g/cc, available from The Dow Chemical Company
(Midland, MI);
[0078] LOTRENETm FE8000 LDPE is an LDPE having a melt index (I2) of 0.8 g/10
min and
a density of 0.923 g/cc as measured in accordance with ASTM D1505, available
from Qatar
Petrochemical Company Ltd. (Qatar);
[0079] VISTAMAXXTm 6102 is a propylene interpolymer including 16.0 wt%
ethylene and
having a melt flow rate (MFR2) of 3 g/ 10 min, a Tn, of 105.54 C (measured
using DSC), and a
density of 0.862 g/cc as measured in accordance with ASTM D1505, available
from the Exxon
Mobil Chemical Company (Spring, TX);
[0080] DOW Tm LDPE 310E is an LDPE having a melt index (I2) of 0.75 g/10 min
and a
density of 0.923 g/cc, available from The Dow Chemical Company (Midland, MI);
[0081] DOW Tm Butene 1221G1 is a butene-LLDPE having a melt index (I2) of 2.0
g/10 min
and a density of 0.918 g/cc, available from The Dow Chemical Company (Midland,
MI);
[0082] DOW Tm Butene 1211G1 is a butene-LLDPE having a melt index (I2) of
1.0 g/10 min
and a density of 0.918 g/cc, available from The Dow Chemical Company (Midland,
MI);
[0083] SABIC LLDPE 218B is a butene-LLDPE copolymer, having a melt index (I2)
of 2.0
g/10 min, a density of 0.918 g/cc, available from Saudi Arabia Basic
Industries Corporation
(Saudi Arabia);
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[0084] ENABLETM 2010 is a C6-LLDPE copolymer prepared using a metallocene
catalyst
and a gas phase polymerization process, having a melt index (I2) of 1.0 g/10
min and a density
of 0.920 g/cc, available from the Exxon Mobil Chemical Company;
[0085] EXCEEDTM 3518 is a C6-LLDPE copolymer prepared using a metallocene
catalyst
and a gas phase polymerization process, having a melt index (I2) of 3.5 g/10
min and a density
of 0.918 g/cc, available from the Exxon Mobil Chemical Company;
[0086] ATTANETm 4607GC is a C6-ULDPE copolymer, having a melt index (I2) of
4.0 g/10
min and a density of 0.904 g/cc, available from The Dow Chemical Company
(Midland, MI);
and
[0087] ATTANETm 4404G is a C8-ULDPE copolymer, having a melt index (I2) of 4.0
g/10
min and a density of 0.904 g/cc, available from The Dow Chemical Company
(Midland, MI).
[0088] To fabricate the films in the following Examples, a multilayer cast
film lines were
used. Extruder configurations and operating temperatures are provided in Table
1 below. Also
provided in Table 1 below are die temperatures, chill roll temperatures, line
speed, and other
operating parameters. The Examples demonstrate the capability of fabricating
multilayer films
having tunable strain hardening over a wide range of line speed and throughput
machine
configurations, shown in Table 1, from 260 to 700 m/min and from 175 to 1400
kg/hr,
respectively.
Table 1: Multilayer Film Fabrication Conditions
Fabrication conditions Example 1 Example 2 Example 3
Egan Davis
Machine maker Torninova SML
Standard
Die type Coat-hanger Coat-hanger Coat-hanger
Die width (m) .9144 2 3
Die gap (mm) 0.508 0.7 0.7
No. of layers 5 5 7
Layer configuration A:B:C:D:E A:B:C:B:D A:B:D:C:D:B:E
Layer ratio (%) 10:15:50:15:10 12:25:26:25:12 12:16:16:12:16:16:12
A, E = 50.8 A, D = 55 A, C, E = 60
Screw diameter (mm) B, C, D = 63.5 B = 120 B, D = 90
C =70
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A, C, E= 28
Screw length (L/D) 30 30
B, D = 33
Melt temperature ( C) 270 260 265
Die temperature ( C) 270 265 270
Air gap (mm) 88.9 25 20
Total throughput (kg/hr) 175 420 1400
Chill-roller temperature ( C) 21 26 27
Line Speed (m/min) 260 450 700
Example]
[0089] Table 2 below lists Comparative Sample A, which includes various
multiple layers
including LLDPEs but lacking LDPE, and Sample 1, which is an embodiment of the
present
multilayer film composition. In particular, Comparative Sample A includes a
core layer of C6-
LLDPE encapsulated by layers including various LLDPEs while Sample 1 includes
a core layer
of butene-LLDPE and LDPE encapsulated by layer of various LLDPEs. In
Comparative
Sample A and Sample 1, layer A corresponds to the cling layer.
Table 2: Multilayer Film Compositions
Layer Film
Layer configuration and composition ratio (%
Thickness
thickness) (um)
A: 70 wt% Butene 1221G1 + 30 wt% ATTANETm 4404G
B: 60 wt% Butene 1221G1 + 40 wt% EXCEED Tm 3518
Comparative 10/15/50/
C: ENABLETm 2010 12.5
Sample A 15/10
D: 60 wt% Butene 1221G1 + 40 wt% EXCEEDTm 3518
E: Butene 1221G1
A: 70 wt% Butene 1211G1 + 30 wt% ATTANETm 4404G
B: DOWLEXTm 2645G
10/15/50/
Sample 1 C: 90 wt% Butene 1211G1 + 10 wt% LDPE 310E 12.5
15/10
D: DOWLEXTm 2645G
E: Butene 1211G1
[0090] Each of the films of Comparative Sample A and Sample 1 were fabricated
on a
multilayer cast film line according to the conditions provided for Example 1
in Table 1 above.
Each of the multilayer cast films were subjected to numerous tests, including
puncture testing,
tear resistance, dart impact, and tensile elongation testing. The results are
presented in Table 3.
The results of the tensile yield and elongation tests are presented in FIG. 1.
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Table 3: Tensile, Puncture, Tear Resistance, and Dart Impact Test
Results
Comparative
Sample 1
Sample A
Film thickness (microns) 12.5 12.5
Tensile Strength at Yield MD (MPa) 10.5 12.7
Tensile Strength at 2' Yield MD (MPa) 19.7 22.1
Tensile Strength at Break MD (MPa) 43.6 44.7
Tensile Ultimate Elongation MD (%) 325.7 249.1
Tensile Energy to Break MD (J) 1.14 0.8
Natural Draw Ratio (NDR) (%) 233.8 183.6
Tensile Stress at NDR (MPa) 26.5 29.1
Puncture Force at Break (N) 27.34 23.73
Puncture Energy at Break (J) 1.99 1.53
Elmendorf Tear MD (1600 g) 0.59 0.24
Elmendorf Tear TD (1600 g) 3.20 3.84
Dart Impact - Method A 74.5 59.5
Highlight Ultimate Stretch (%) 218.1 256.1
Highlight Stretch Force, 150% Stretch (kgf) 25.8 27.7
[0091] As shown in Table 3 and FIG. 1, the multilayer film of Sample 1
(plot 102) exhibited
higher tensile yield and strain hardening at the second yield point than
Comparative Sample A
(plot 100). Specifically, the multilayer film of Sample 1 had a second yield
point 104 of 22.1
MPa at a stretch % of 57.5%, while the film of Comparative Sample A (plot 100)
had a second
yield point 106 of 19.7 MPa at a stretch % of approximately 80%. Although an
increased
toughness was expected for the film of Comparative Sample A (compared to films
including
only ENABLE Tm 2010) due to the inclusion of EXCEED Tm 3518, the multilayer
film of Sample
1 nonetheless was able to achieve high tear resistance (TD) with balanced
toughness,
particularly for film having a 12.5 p.m thickness. Also, the Sample 1 (plot
102) achieved a
tensile ultimate elongation in the machine direction of 249% (point 114) at
the desired less than
300% for low stretch films, whereas Comparative Sample A (plot 100) exceeded
300% and
measured at 325.7%.
[0092] FIG. 1 also shows that the tensile stress at yield (108) for
Sample 1 was 12.7 MPa.
The NDR 110 is also marked on FIG. 1 for Sample 1, as is the tensile stress at
NDR 112 for
Sample 1, to illustrate how these values are obtained. FIG. 1 also includes
the tensile stress at
break 114 for Sample 1, which corresponds to an elongation at break of 249.1%.
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Example 2
[0093] Table 4 below lists Samples 2-5, which are embodiments of the
present multilayer
film composition. In particular, Samples 2-5 include LDPE in at least two
different inner layers
and two different C6-LLDPE in at least two different layers. Samples 2-5
include a core layer
with either a single C6-LLDPE or two different C6-LLDPE and do not include
LDPE in the core
layer. In Samples 2-5, layer A corresponds to the cling layer.
Table 4: Multilayer Film Compositions
Film
Layer ratio
Layer configuration and composition Thickness
(% thickness)
(PO
A: 7 wt% VISTAMAXXTm 6102 + 93 wt% SabicL)
LLDPE 218B
B: 94 wt% DOWLEXTm 2607G +6 wt% LOTRENETm
FE8000 LDPE
Sample 2 C: 80 wt%
DOWLEXTm 2645G + 20 wt% DOWLEXTm 12/25/26/25/12 8
2607G
B: 94 wt% DOWLEXTm 2607G +6 wt% LOTRENETm
FE8000 LDPE
D: DOWLEXTm 2607G
A: 7 wt% VISTAMAXXTm 6102 + 93 wt% Sabicu
LLDPE 218B
B: 90 wt% DOWLEXTm 2607G + 10 wt%
LOTRENETm FE8000 LDPE
Sample 3 C: 80 wt%
DOWLEXTm 2645G + 20 wt% DOWLEXTm 12/25/26/25/12 8
2607G
B: 90 wt% DOWLEXTm 2607G + 10 wt%
LOTRENETm FE8000 LDPE
D: DOWLEXTm 2607G
A: 7 wt% VISTAMAXXTm 6102 + 93 wt% SabicL)
LLDPE 218B
B: 90 wt% DOWLEXTm 2607G + 10 wt%
LOTRENETm FE8000 LDPE
Sample 4 12/25/26/25/12
8
C: DOWLEXTm 2645G
B: 90 wt% DOWLEXTm 2607G + 10 wt%
LOTRENETm FE8000 LDPE
D: DOWLEXTm 2607G
A: 7 wt% VISTAMAXXTm 6102 + 93 wt% Sabicu
LLDPE 218B
B: 94 wt% DOWLEXTm 2607G +6 wt% LOTRENETm
FE8000 LDPE
Sample 5 12/25/26/25/12
8
C: DOWLEXTm 2645G
B: 94 wt% DOWLEXTm 2607G +6 wt% LOTRENETm
FE8000 LDPE
D: DOWLEXTm 2607G
[0094] Each of the films of Samples 2-5 were fabricated on a multilayer
cast film line
according to the conditions provided for Example 2 in Table 1 above. Each of
the multilayer
cast films were subjected to numerous tests, including puncture testing, tear
resistance, dart
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impact, and tensile elongation testing. The results are presented in Table 5.
The results of the
tensile yield and elongation tests are presented in FIG. 2.
Table 5: Tensile, Puncture, Dart Impact, and Tear Resistance Test Results
Sample 2 Sample 3 Sample 4 Sample 5
Film thickness (microns) 8 8 8 8
Tensile Strength at Yield MD (MPa) 10.7 13.4 13.9 12.5
Tensile Strength at 2nd Yield MD (MPa) 19.6 25.2 26.6 23.4
Tensile Strength at Break MD (MPa) 42.1 42.2 49.9 52.5
Tensile Ultimate Elongation MD (%) 241.1 225.1 227.0 245.7
Tensile Energy to Break MD (J) 0.59 0.6 0.65 0.65
NDR (%) 195.0 150.0 137.0 191.8
Tensile Strength at NDR (MPa) 26.5 29.2 30.9 31.1
Puncture Force at Break (N) 19.88 20.52 18.02 19.51
Puncture Energy at Break (J) 1.27 1.21 0.91 1.16
Elmendorf Tear MD (1600 g wt.) (g) 0.14 0.09 0.07 0.1
Elmendorf Tear TD (1600 g wt.) (g) 3.36 3.62 3.28 2.81
Dart Impact - Method A 27 27 29.5 32
Highlight Ultimate Stretch (%) 151.0 155.5 125.6 180.9
Highlight Stretch Force, 100% stretch
17.87 20.98 21.11 18.20
(kgf)
[0095] As shown in Table 5 and FIG. 2, each of Samples 2 (plot 202), 3
(plot 204), 4 (plot
206), and 5 (plot 208) exhibit an improved second yield strength than
expected. Furthermore,
without being bound by theory it is believed that the tensile strength at 2nd
yield point can be
tuned with low percentage of LDPE from 3% to 7%. In particular, it is shown
that 5% LDPE
overall in the film structure from two different formulations (Samples 3 and
4) exhibit higher
tensile strength at 2nd yield than films containing 3% LDPE (Samples 2 and 5).
[0096] Furthermore, Table 5 and FIG. 2 show that Sample 2 has an NDR 203 of
195%,
Sample 3 has an NDR 205 of 150%, Sample 4 has an NDR 207 of 137%, and Sample 5
has an
NDR 209 of 191.8%. Accordingly, each of Samples 2-5 exhibits an NDR below
250%, and
Tensile Ultimate Elongation MD and Highlight Ultimate Stretch values of less
than 300%. Of
particular distinction, the thin 8 micron films can be produced in cast film
fabrication at 450
m/min line speed with good draw-down behavior, as shown in Table 1, while
maintaining high
level of mechanical film performance.
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Example 3
[0097] Table 6 below lists Comparative Sample B, which includes various
multiple layers
including LLDPEs but lacking LDPE, Comparative Sample C, which includes
various C6-
LLDPEs in core, encapsulating, and release layers and does not include LDPE,
and Samples 6
and 7, which are embodiments of the present multilayer film composition.
Samples 6 and 7
include a LDPE in two separate inner layers, two different C6-LLDPEs in at
least two different
inner layers, and a core layer (layer C) that includes a blend of two
different C6-LLDPEs without
LDPE. In Comparative Samples B and C and Samples 6-7, layer E corresponds to
the cling
layer.
Table 6: Multilayer Film Compositions
Film
Layer ratio (%
Layer configuration and composition Thickness
thickness)
(PO
A: EXCEED Tm 3518
B: 70 wt% Sabic LLDPE 218B +30 wt%ENABLETm
2010
D: ENABLE Tm 2010
C: ENABLE Tm 2010
Comparative D: ENABLE Tm 2010 12/16/16/12/16/
Sample B B: 70 wt% Sabic LLDPE 218B +
30 wt%ENABLETm 16/12
2010
E: 91 wt% Sable LLDPE 218B + 9 wt%
VISTAMAXXTm 6102
A: DOWLEXTm 2607G
B: DOWLEXTm 2607G
D: DOWLEXTm 2607G
C: 25 wt% DOWLEXTm 2607G +75 wt% DOWLEXTm
Comparative 12/16/16/12/16/
2645G 10
Sample C 16/12
D: DOWLEXTm 2607G
B: DOWLEXTm 2607G
E: 91 wt% DOWLEXTm 2607G + 9 wt%
VISTAMAXXTm
A: DOWLEXTm 2607G
B: DOWLEXTm 2607G
D: DOWLEXTm 2607G + 10 wt% LDPE 310E
C: 25 wt% DOWLEXTm 2607G +75 wt% DOWLEXTm
12/16/16/12/16/
Sample 6 2645G 10
16/12
D: DOWLEXTm 2607G + 10 wt% LDPE 310E
B: DOWLEXTm 2607G
E: 91 wt% DOWLEXTm 2607G +9 wt%
VISTAMAXXTm
A: DOWLEXTm 2607G
B: DOWLEXTm 2607G
D: DOWLEXTm 2607G + 16 wt% LDPE 310E 12/16/16/12/16/
Sample 7 10
C: 25 wt% DOWLEXTm 2607G +75 wt% DOWLEXTm 16/12
2645G
D: DOWLEXTm 2607G + 16 wt% LDPE 310E
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B: DOWLEXTm 2607G
E: 91 wt% DOWLEXTm 2607G +9 wt%
VISTAMAXXTm
[0098] Each of the films of Comparative Samples B and C and Samples 6-7 were
fabricated
on a multilayer cast film line according to the conditions provided for
Example 3 in Table 1
above. In each of the films, the cling is approximately 1% overall in
structure. Accordingly, for
a 10 p.m thick film in which the cling layer is 12% of the thickness, the
cling is about 9% in the
cling layer.
[0099] Each of the multilayer cast films were subjected to numerous
tests, including puncture
testing, tear resistance, dart impact, and tensile elongation testing.
Highlight ultimate stretch and
Highlight stretch force data was not available for Comparative Sample B. The
results are
presented in Table 7. The results of the tensile yield and elongation tests
are presented in FIG.
3.
Table 7: Tensile, Puncture, and Tear Resistance Test Results
Comparative Comparative
Sample 6 Sample 7
Sample B Sample C
Film thickness (microns) 10 10 10 10
Tensile Strength at Yield MD (MPa) 11.9 12.1 12.8 14.6
Tensile Strength at 2nd Yield MD
26.4 20.1 21.2 23.9
(MPa)
Tensile Strength at Break MD (MPa) 48.7 48.2 49.0 51.6
Tensile Ultimate Elongation MD (%) 248.5 281.3 274.1 284.0
Tensile Energy to Break MD (J) 0.89 0.95 0.93 1.02
NDR (%) 188.3 200.5 194.0 193.0
Tensile Strength at NDR (MPa) 33.3 27.7 27.2 30.4
Puncture Force at Break (N) 25.24 22.35 22.11 18.96
Puncture Energy at Break (J) 1.49 1.50 1.48 1.11
Elmendorf Tear MD (1600 g wt.) (g) 0.24 0.19 0.19 0.12
Elmendorf Tear TD (1600 g wt.) (g) 2.82 3.36 2.97 2.44
Highlight Ultimate Stretch (%) N.D. 236.2 210.7 240.6
Highlight Stretch Force, 100%
N.D. 22.8 23.3 24.7
Stretch (kgf)
[00100] As shown in Table 7 and FIG. 3, Sample 6 (plot 304) and Sample 7 (plot
306)
demonstrate an improved second yield strength over Comparative Sample C (plot
302) and a
comparable second yield strength to that of Comparative Sample B (plot 300),
which lacks
LDPE. These results demonstrate the ability to tune both the tensile strength
at 2nd yield and the
strain % of 2nd yield point via low levels of LDPE between 3-7 wt.% (i.e.
increasing LDPE
percentage increases the tensile strength at 2nd yield), to tailor the
yielding of the film during
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stretch. Furthermore, the films of Samples 6 and 7 achieve low levels of
stretch as demonstrated
by an NDR at less than 250% (305 and 307, respectively), and Highlight
Ultimate Stretch and
Tensile ultimate elongation MD at less than 300%. The NDR 305 of Sample 6 and
the NDR
307 of Sample 7 are less than the NDR 303 of Comparative Sample C and are
similar to the
NDR 301 of Comparative Sample B, which lacks LDPE. Of particular distinction,
Samples 6
and 7 are successfully fabricated on a fast cast co-extrusion film line (700
m/min) and at high
throughput (1400 kg/hr), as shown in Table 1, to demonstrate good draw-ability
and high output
capability, respectively, for thin 10 micron films.
[00101] It is further noted that terms like "preferably," "generally,"
"commonly," and
"typically" are not utilized herein to limit the scope of the claimed
invention or to imply that
certain features are critical, essential, or even important to the structure
or function of the
claimed invention. Rather, these terms are merely intended to highlight
alternative or additional
features that may or may not be utilized in a particular embodiment of the
present disclosure.
[00102] It will be apparent that modifications and variations are possible
without departing
from the scope of the disclosure defined in the appended claims. More
specifically, although
some aspects of the present disclosure are identified herein as preferred or
particularly
advantageous, it is contemplated that the present disclosure is not
necessarily limited to these
aspects.
