Note: Descriptions are shown in the official language in which they were submitted.
CA 2961692 2017-03-20
TEAR RESISTANT MONO-AXIALLY ORIENTED PROPYLENE-BASED FILM
Field
[0001] This disclosure relates to a mono-axially oriented propylene-based
film which
exhibits excellent tear resistance and methods of making the same. More
particularly, this
invention relates to a mono-axially oriented, voided film that exhibits
excellent tear resistance
formed from the blending of a voiding agent.
Background
[0002] Polymeric-based films can be used to form tapes for strapping heavy
and bulky
articles such as cartons. In addition, polymeric-based films can be used to
reinforce other
substrates such as corrugated cardboard, cardboard or paperboard backings for
blister packages,
boxes, or envelopes. Furthermore, polymeric-based films can be used as, or
incorporated as part
of, handles for carrying cartons, boxes, bags, or other bulk containers.
Polymeric-based films can
also be used as substrates for adhesive-coated tapes and narrow-width strips
("weaving tapes")
that can be used in woven articles such as sacks, bags, baskets, geo-textiles,
geo-grids, fabrics,
and self-reinforced composites.
[0003] For example, US Patent 2,750,030 describes a high strength pressure-
sensitive
adhesive strapping tape with a lengthwise tensile strength of at least 300
lbs/in. The tape has a
high cross-wise tear strength and a thickness of 5-20 mil. The tape has a film
or paper backing
coated with a tacky rubber-resin pressure-sensitive adhesive which contains an
embedded
monolayer of loosely-twisted or non-twisted yarns of continuous hair-like
glass filaments that
extend continuously from one end of the tape to the other. The cross-wise tear
strength of the
tape is due to the presence of the glass filaments aligned length-wise.
[0004] US Patent 2,753,284 describes a lineally reinforced, high-tensile
adhesive tape for
strapping tape applications and has a tensile strength of at least 100 lbs/in.
The tape has a paper
sheet with two layers of a rubber-resin type pressure-sensitive tacky adhesive
in which mono-
fiber hair-like glass filaments are embedded between the two tacky adhesive
layers. A non-tacky
third adhesive layer is coated over the outermost tacky adhesive layer. The
cross-wise tear
strength of the tape is due to the presence of the glass filaments aligned
linearly.
1
CA 2961692 2017-03-20
[0005] US Patent 4,905,888 describes a handle for packages or cartons
comprising strap-type
foldable carrying tape. The strap-type carrying tape is preferably formed from
a pressure-
sensitive adhesive tape and can be made of woven natural or synthetic fibers.
The carrying tape
can also be reinforced with filament fibers or strips for tear resistance.
[0006] US Patent 7,144,635 describes a tear-resistant laminate comprised of
paper or paper-
board substrate, an adhesive layer, a tear-resistant layer secured to the
adhesive layer, and a heat-
sealable layer. The tear-resistant layer has a tear strength of at least 300
gf in both machine and
cross-direction as measured by Elmendorf tear propation test. The tear-
resistant layer is a
polymeric material and can be biaxially oriented films such as polyester,
nylon, polyolefin, or
high density polyolefins such as metallocene-catalyzed polyethylene.
[0007] US Patent Application Serial No. 14/364,677 (US publication number
US
2014/0322463) describes a uni-directionally oriented film comprised of a
thermoplastic polyester
and a polycarbonate. This type of film can be used for strapping of cartons,
boxes, pallets, etc.,
and may be used as a weaving tape for woven bags, sacks, and containers.
Preferably, the
polyester is a polyethylene terephthalate (PET) resin. Polycarbonate is
blended into the PET film
as a minority component to reduce the tendency of such PET unidirectionally
oriented films from
splitting along the machine direction axis and imparts some impact toughness.
Summary
100081 Disclosed herein is a novel polyolefin-based, monoaxially (or uni-
axially) oriented
film that can be suitable for strapping tape applications and/or other
applications requiring high
tear resistance. In some embodiments, the film can have a high resistance to
cross-direction (or
transverse direction, TD) tearing and can have a machine direction (MD)
tensile strength of
greater than about 75, 80, 85, or 90 lbs/inch width and less than about 130,
120, 115, 110 or 100
lbs/inch width. Preferably, the polyolefin can be a propylene-based polymer.
The tear resistance
may be imparted by voiding of the film in which the voids interrupt or halt
tear propagation
through the film. Without being bound by any theory, it is believed that the
voids provide
termination points for crack/tear propagation and redirects the energy of the
tear propagation
from cross-wise (or transverse-wise) perpendicularly to the machine direction
(along the
direction of the monoaxial orientation) as depicted by Figure 1. It is also
believed that the size
2
CA 2961692 2017-03-20
and shape of these voids can play a role in the effectiveness of terminating
tear propagation, with
smaller, more ovoid or oblong voids being preferred. This can result in a film
with very high
cross-wise or transverse direction tear resistance without using machine-
direction aligned and
embedded fibers or filaments to impart transverse direction tear resistance as
in the prior arts. In
particular, the inventors have found that the disclosed films exhibit very
good transverse tear
resistance even if the film is nicked or cut on the edges of the film to
initiate a transverse tear.
[0009] The described films may be simpler to produce than typical films and
tapes. In some
embodiments, the films can be produced without requiring the use -- or
additional processing
steps ¨ of embedding fibers or filaments. Because the film may not include any
foreign matter
such as glass fibers, the film can be more suitable for recycling scrap or
spent material for other
uses or as part of the production of new strapping tape.
[0010] In an embodiment, a single layer film may be extruded and mono-
axially oriented in
the machine direction. This single layer can be voided, which provides the
transverse direction
tear resistance. In additional multi-layer film embodiments, it is
contemplated to coextrude one
or more skin layers on one or both sides of a void-containing core or base
layer which is mono-
axially oriented in the machine direction. This voided core layer can provide
the transverse
direction tear resistance properties of the multi-layer film. Further
embodiments include voiding
of the coexruded skin layers or intermediate layers adjacent to the core layer
as well. It can also
be contemplated to void the skin layers for tear propagation resistance while
leaving the core
layer un-voided. However, the core layer can be the preferred layer for
voiding as it represents
the bulk of the film mass and the bulk of the voids to terminate crack/tear
propagation. It can be
preferred that the coextruded skin layers be un-voided to provide smoother
outer surfaces more
suitable for printing, laminating, coating, metallizing, or other process
handling. Other
embodiments of the disclosed films can include laminating the disclosed films
to other substrates
including, but not limited to: other unvoided polymeric films or articles,
paper-containing
substrates, cardboard-containing substrates, fabric textiles, non-woven
textiles, meshes, tapes,
etc.
[0011] Voiding of the disclosed films can be accomplished by several means,
including but
not limited to: 1) cavitating agents such as inorganic particles like CaCO3,
Ti02, silica particles,
3
CA 2961692 2017-03-20
glass micro-beads; 2) cavitating agents such as organic polymeric materials
like polybutylene
terephthalate, nylons, polycarbonates, polystyrenes, polymethlymethacrylate;
3) beta-nucleation
of the propylene-based polymer; 4) chemical foaming agents; or 5) combinations
of the above. A
preferred embodiment can be to use chemical foaming agents which provide
relatively large
voids or closed-cell cavities in which there is no physical particle residing
within said void. Such
an embodiment can help reduce the overall density of the voided film in
comparison to a voided
film using inorganic or polymeric cavitating agents wherein such cavitating
agents add their
intrinsic material density to the overall film density.
[0012] The film can also incorporate optional amounts of additives,
including but not limited
to: antiblock additives, slip additives, coloring agents/pigments, antistatic
additives, UV-light
absorbing or blocking additives, fire retardant additives.
[0013] Embodiments of a mono-axially oriented polyolefin film may comprise
a core layer
containing a plurality of voids. The film is oriented at least 4 times in the
machine direction, and
exhibits excellent tear resistance in the transverse direction.
[0014] In some embodiments, the film comprises at least one skin layer. The
at least one
skin layer may be voided or unvoided. In some embodiments, the core layer
comprises a
propylene-based polymer.
[0015] In some embodiments, the core layer comprises CaCO3, Ti02, silica
particles, or
glass micro-beads inorganic voiding particles. In some embodiments, the core
layer comprises
polymeric cavitating or voiding agents such as polybutylene terephthalate,
nylon, polycarbonate,
polystyrene, or polymethlymethacrylate. In some embodiments, the core layer
comprises a
propylene-based polymer and beta-nucleation of the propylene-based polymer to
form a plurality
of voids. In some embodiments, the core layer comprises a chemical foaming
agent as the
voiding agent.
[0016] In some embodiments, the film has a machine direction (MD) tensile
strength of
greater than about 75 lbsf/linear inch width, greater than about 85
lbsf/linear inch width, greater
than about 95 lbsf/linear inch width, or greater than about 100 lbsf/linear
inch width. In some
embodiments, the film has a machine direction tensile strength of about 75-130
lbsf/linear inch
4
CA 2961692 2017-03-20
width, about 85-130 lbsf/linear inch width, about 95-130 lbsf/linear inch
width, or about 100-130
lbsf/linear inch width.
[0017] In some embodiments, the film is a mono-layer film and has a
thickness of 1.5 - 10.0
mil (37.5 ¨ 250 pm) or 2.5 ¨ 5.0 mil before foaming and a thickness of about
2.5 - 18.5 mil (62.5
¨ 462.5 pm) or 3.0 ¨ 5.0 mil after foaming.
[0018] In some embodiments, the film is a multi-layer film and has a
thickness of 1.5 - 10.0
mil (37.5 ¨250 pm) or 2.5 ¨5.0 mil before foaming and a thickness of about 2.5
- 18.5 mil (62.5
¨ 462.5 pm) or 3.0 ¨ 5.0 mil after foaming. In some embodiments, the core
layer or film has a
light transmission % of about 10 - 50% or about 20 ¨ 40 %.
[0019] In some embodiments, the film has a machine direction heat shrinkage
of less than
8%, preferably less than 5%, and more preferably less than 2%.
[0020] An embodiment of a tape comprises a mono-axially oriented polyolefin
film
comprising a core layer containing a plurality of voids, wherein the film is
oriented at least 4
times in the machine direction and exhibits excellent tear resistance in the
transverse direction.
[0021] An embodiment of a method of making a mono-axially oriented
polyolefin film
comprises extruding a film comprising a layer, wherein the layer comprises a
polyolefin (e.g., a
propylene-based polyolefin) and a voiding agent, and orienting the film at
least 4 times in the
machine direction, wherein the film exhibits excellent tear resistance in the
transverse direction.
[0022] In some embodiments, the method further comprises heat setting the
extruded film.
In some embodiments, the method further comprises co-extruding at least one
skin layer that may
not include a voiding agent with the core layer. In some embodiments, the
method forms a
monolayer film.
[0023] In some embodiments, a mono-axially oriented polyolefin film is
described that
comprises a layer comprising a propylene-based polymer and a plurality of
voids formed by a
voiding agent, wherein the film is oriented at least 4 times in the machine
direction.
[0024] The voiding agent can be a chemical foaming agent and can comprises
0.2-3 wt% of
the layer. In some embodiments the density of the film is 0.60-0.89 g/cm3 and
the average void
size of the plurality of voids can be 5000-12000 p.m in width along the MD
axis. The standard
deviation of the average void width can be 2000 p.m or less. In some
embodiments, the film can
CA 2961692 2017-03-20
have a thickness of 1.5-10 mil before foaming and a thickness of 2.5-18.5 mil
after foaming. In
some embodiments, the film comprises at least one skin layer and the skin
layer can be unvoided.
100251 In some embodiments, the voiding agent comprises 1-10 wt% of the
layer. In some
embodiments, the voiding agent comprises CaCO3, Ti02, silica particles, or
glass micro-beads
inorganic void particles, polybutylene terephthalate, nylon, polycarbonate,
polystyrene, or
polymethlymethacrylate, or a beta-nucleation of the propylene-based polymer,
[0026] In some embodiments, the film has a tensile strength of 80-120
lbs/inch width, a
machine direction shrinkage of less than 2%, and/or a light transmission of 20-
40%. In some
embodiments, the film is a mono layer film.
[0027] In some embodiments, a tape is described that comprises the films
disclosed herein.
Specifically, the tape can include a layer comprising a propylene-based
polymer and a plurality of
voids formed by a voiding agent, wherein the film is oriented at least 4 times
in the machine
direction.
[0028] It is understood that aspects and embodiments of the films described
herein include
"consisting" and/or "consisting essentially of' aspects and embodiments. For
all methods, films,
and other aspects described herein, the methods, films, and other aspects can
either comprise the
listed components or steps, or can "consist of' or "consist essentially of'
the listed components
or steps. When a method, film, and other aspect is described as "consisting
essentially of' the
listed components, method, film, and other aspect contains the components
listed, and may
contain other components which do not substantially affect the performance of
the method, film,
and other aspect, but either do not contain any other components which
substantially affect the
performance of the method, film, and other aspect other than those components
expressly listed;
or do not contain a sufficient concentration or amount of the extra components
to substantially
affect the performance of the method, film, and other aspect. When a method is
described as
"consisting essentially of' the listed steps, the method contains the steps
listed, and may contain
other steps that do not substantially affect the outcome of the method, but
the method does not
contain any other steps which substantially affect the outcome of the method
other than those
steps expressly listed.
Brief Description of the Drawings
6
CA 2961692 2017-03-20
[0029] Exemplary embodiments are described with reference to the
accompanying Figures,
in which:
[0030] FIG. 1 is an illustrative embodiment of a voided mono-axially
oriented polyolefin
film that exhibits excellent tear resistance.
[0031] FIG. 2 is an illustration of the void's dimensions within an
embodiment of a mono-
axially oriented polyolefin film that exhibits tear resistance.
Detailed Description
[0032] Described are mono-axially oriented propylene-based films that
exhibit excellent tear
resistance and methods of making the same. In some embodiments, the films can
be produced by
blending a cavitating or foaming agent to produce a voided film which is mono-
axially oriented.
The resulting film has surprisingly good tear resistance properties in the
direction perpendicular
to the orientation direction. Such a film lends itself well to applications
such as, but not limited
to: strapping tape for boxes, cartons, pallets, textile bales; corrugated
cardboard reinforcements;
blister package board packaging; tape fabric; and carrying handles for
cartons, boxes, and the
like; or any applications requiring tear resistance properties. The disclosed
films may be woven
to produce a fabric for use in making sacks, bulk containers, carpet backing,
signage, geo-
textiles, and self-reinforced fabrics. The disclosed films may be tinted or
colored to match
consumer attributes for packaging or cartoning.
[0033] The film or layer may comprise, consist or consist essentially of
the following
materials: 1) a polyolefin or polyolefin blend (for example, a blend
comprising one or more
propylene homopolymers and copolymers); 2) a voiding agent ; and 3) optional
additives,
including but not limited to: antiblock additives, slip additives, coloring
agents/pigments,
antistatic additives, UV-light absorbing or blocking additives, fire retardant
additives.
[0034] Suitable polyolefins can be propylene-based polymers such as
isotactic crystalline
propylene homopolymers and "mini-random" isotactic crystalline ethylene-
propylene
copolymers. "Mini-random" propylene homopolymers are those class of ethylene-
propylene
copolymers in which the ethylene content is fractional, i.e. less than 1 wt%,
typically on the order
of about 0.2-0.8 wt%, and preferably about 0.5-0.7 wt%, of the polymer. These
crystalline
isotactic polypropylenes are generally described as having an isotactic
content of about 90% or
7
CA 2961692 2017-03-20
greater as measured by C13 NMR. Suitable examples of crystalline propylene
homopolymers are
Total Petrochemicals 3271, 3274, and 3373HA; Phillips CH016, CH020, and CR035;
and
Braskem FF018. These resins can also have melt flow rates of about 0.5 to 5
g/10min at 230 , a
melting point of about 160 - 165 C, a crystallization temperature of about 108
¨126 C, a heat of
fusion of about 86 ¨ 110 J/g, a heat of crystallization of about 105 ¨ 111
J/g, and a density of
about 0.90 ¨ 0.91. Higher isotactic content propylene homopolymers (i.e. "high
crystalline"
homopolymers) may also be used. Suitable examples of these include those made
by Total
Petrochemicals 3270 and 3273 grades, Braskem grade HR020F3, and Phillipps 66
CH020XK.
These high crystalline polypropylenes typically have an isotactic content of
93% or greater as
measured by C13 NMR spectra obtained in 1,2,4-trichlorobenzene solutions at
130 C. The %
percent isotactic can be obtained by the intensity of the isotactic methyl
group at 21.7 ppm versus
the total (isotactic and atactic) methyl groups from 22 to 19.4 ppm. These
resins can also have
melt flow rates of about 0.5 to 5 g/10min, a melting point of about 163 - 167
C, a crystallization
temperature of about 108 ¨126 C, a heat of fusion of about 86¨ 110 J/g, a heat
of crystallization
of about 105 ¨ 111 J/g, and a density of about 0.90 ¨ 0.91.
[0035] Other suitable polyolefins can be propylene-containing copolymers
such as
ethylene-propylene copolymers, propylene-butene copolymers, ethylene-propylene-
butene
copolymers, including propylene-containing impact copolymers, and blends
thereof. It can also
be contemplated to blend propylene homopolymers, mini-random homopolymers, and
copolymers as desired. Exemplary propylene-containing copolymers can include:
Total
Petrochemicals Z9421 ethylene-propylene random copolymer elastomer of about
5.0 g/10min
melt flow rate (MFR) at 230 C, melting point of about 120 C, density 0.89
g/cm3, and ethylene
content of about 7 wt% of the polymer; Total Petrochemicals 8473 ethylene-
propylene random
copolymer of about 4.0 MFR at 230 C and ethylene content of about 4.5 wt% of
the polymer;
Sumitomo Chemical SPX78R1 ethylene-propylene-butene random copolymer of about
9.5
g/10min MFR at 230 C, ethylene content of about 1.5 wt%, and butene content of
about 16 wt%
of the polymer; or ExxonMobil Chemical VistamaxxTM ethylene-propylene random
copolymer
elastomers such as grade 3980 FL with an MFR of about 8.3 g/10min at 230 C,
Vicat softening
point of about 80 C, melting point of about 79 C, density of about 0.879
g/cm3, and ethylene
8
CA 2961692 2017-03-20
content of about 8.5 wt%. Other suitable propylene-based copolymers and
elastomers may be
contemplated including but not limited to: metallocene-catalyzed thermoplastic
elastomers like
ExxonMobil's VistamaxxTM 3000 grade, which is an ethylene-propylene elastomer
of about 11
wt% ethylene content, 8 g/10min MFR at 230 C, density of 0.871 g/cm3, Tg of -
20 to -30 C, and
Vicat softening point of 64 C; or ethylene-propylene alpha-olefin copolymer
plastomers of Dow
Chemical's VersifyTM grades, such as grade 3300, which is an ethylene-
propylene plastomer of
about 12 wt% ethylene content, 8 g/10 min MFR at 230 C, density of 0.866
g/cm3, Tg of -28 C,
and Vicat softening point of 29 C; and Mitsui Chemicals TafmerTm grades XM7070
and
XM7080 metallocene-catalyzed propylene-butene random elastomers of about 22
and 26 wt%
butene content, respectively. The Mitsui Tafmer grades are characterized by a
melting point of
75 C and 83 C, respectively; a Vicat softening point of 67 C and 74 C,
respectively; a density of
0.883-0.885 g/cm3; a Tg of about -15 C; a melt flow rate at 230 C of 7.0 g/10
minutes; and a
molecular weight of 190,000-192,000 g/mol. Exemplary impact copolymers can be
an isotactic
ethylene-propylene copolymer with an ethylene-propylene rubber content of
about 10-30 wt% of
the polymer wherein the ethylene content of the rubber is about 10-80 wt% of
the rubber.
Typically, the impact copolymer is manufactured in two reactors. In the first
reactor, propylene
homopolymer is produced and it is conveyed to the second reactor that also
contains a high
concentration of ethylene. The ethylene, in conjunction with the residual
propylene left over
from the first reactor, copolymerizes to form an ethylene-propylene rubber.
The resultant
product has two distinct phases: a continuous rigid propylene homopolymer
matrix and a finely
dispersed phase of ethylene-propylene rubber particles. The rubber content
that is typically used
is in the 10-30 wt% range depending on the desired end-use properties. It is
this mixture of two
phases ¨ the propylene homopolymer matrix and the dispersed phase of ethylene-
propylene
rubber ¨ that provides the impact resistance and toughening properties that
impact copolymers
are known for. Ethylene-propylene impact copolymers are distinctly different
from conventional
ethylene-propylene random copolymers which are typically polymerized in a
single reactor,
generally have a lower ethylene content (typically 0.5 wt% to 6 wt%) wherein
the ethylene
groups are randomly inserted by a catalyst along the polypropylene backbone
chain, and do not
comprise an ethylene-propylene rubber content. A suitable example of ethylene-
propylene
9
CA 2961692 2017-03-20
impact copolymer for the disclosed films is Total Petrochemical's 5571. Total
Petrochemicals
5571 has a melt flow rate of about 7 g/10 minutes at 230 C, a melting point of
about 160-165 C,
a Vicat softening point of about 148 C, and a density of about 0.905 g/cm3.
Another example
of ethylene-propylene impact copolymer can be Total Petrochemical's 4180 with
a melt flow rate
of about 0.7 g/10 minutes at 230 C, a melting point of about 160-165 C, a
Vicat softening point
of about 150 C, and a density of about 0.905 g/cm3. Other suitable ethylene-
propylene impact
copolymers can be Sunoco Chemical's TI-4015-F2 with a melt flow rate of 1.6
g/10minutes at
230 C and a density of about 0.901 g/cm3 and ExxonMobil Chemical's PP7033E2
with a melt
flow rate of about 8 g/10 minutes at at 230 C and a density of about 0.9
g/cm3.
[0036] Isotactic propylene homopolymers, copolymers, and blends thereof
are
particularly preferred for the disclosed films. Other polyolefins that could
also be considered,
however, are ethylene homopolymers such as high density polyethylene, medium
density
polyethylene, low density polyethylene, and linear low density polyethylenes.
These ethylene
homopolymers may also be blended with ethylene copolymers, propylene
copolymers, and/or
propylene homopolymers. Among these types, high density polyethylenes (HDPE)
are preferred,
such as Total Petrochemical's HDPE 9658 (density 0.958 g/cc, MI 0.64 g/10
min), or Total
Petrochemical HDPE 9458 (density 0.958 g/cc, MI 0.45 g/10 min), or Total
Petrochemical
HDPE 9260 (density 0.960 g/cc, MI 2.0 g/10 min).
[0037] In addition, these isotactic crystalline propylene-based resins
may also include
additives such as antiblocking agents and/or slip agents. An amount of
inorganic antiblocking
agent may be optionally added up to 10,000 ppm to the film layer(s) as desired
for film-handling
purposes, winding, antiblocking properties, and control of coefficient of
friction. Preferably
about 300-5000 ppm, and more preferably about 300 ¨ 1000 ppm, of antiblock may
be added.
Suitable antiblock agents comprise those such as inorganic silicas, sodium
calcium
aluminosilicates, crosslinked silicone polymers such as
polymethylsilsesquioxane, and
polymethylmethacrylate spheres. Typical useful particle sizes of these
antiblocks range from 1 ¨
12 um, preferably in the range of 2-6 um. Slip agents such as fatty amides
and/or silicone oils
can also be optionally employed in either or both film layers, either with or
without the inorganic
antiblocking additives, to aid further with controlling coefficient of
friction and web handling
CA 2961692 2017-03-20
issues. Such slip agents are typically migratory and bloom to the surface of
the film. Suitable
types of fatty amides are those such as stearamide or erucamide and similar
types, in amounts of
100-5000 ppm of the layer. Preferably, erucamide can be used at 500-1000 ppm
of the layer. A
suitable silicone oil that can be used is a low molecular weight oil of 350
centistokes which
blooms to the surface readily at a loading of 400-600 ppm of either or both
layers. Antiblock
and slip agents can be conveniently used in the form of masterbatches at
desired loadings for
economy and using desired carrier resins.
[0038] The formation of a plurality of closed cell voids within the
disclosed films can be
critical to imparting the tear resistance of said films. Preferably, the main
layer (also known as
the base layer or core layer) can be the voided layer of a mono-layer or multi-
layer embodiment
as this layer is typically the thickest layer and comprises the bulk mass of
the film. However, in
multi-layer film embodiments, the coextruded "skin" layers adjacent to the
core layer (either on
one side of the core layer or on both sides of the core layer) could be the
voided layer(s) in place
of the core layer or both the skin layers and core layer could be voided.
Voids may be formed
within the respective film layer through cavitation by using inorganic or
organic cavitating agents
well known in the art. Such inorganic cavitating agents can be: calcium
carbonate (CaCO3),
titanium dioxide (Ti02), silica or silicate particles, glass micro-beads, or
other inorganic
particulates and/or minerals. Preferred inorganic cavitating agents can be
calcium carbonate
particles due to its popularity as well as economy. Particle diameter sizes of
the inorganic
cavitating agents can be in the range of about 0.1 ¨2.0 pm. Typical loadings
of the inorganic
cavitating agents can be about 1 ¨ 10 wt% of the layer, preferably about 2-5
wt%. Organic
cavitating agents can be used as well, such as polybutylene terephthalate,
polycarbonate, nylon,
polymethylmethacrylate, polystyrene. Typically, such polymeric cavitating
agents have a higher
Tg than the propylene-based bulk resin of the disclosed films. Typical
loadings of organic
cavitating agents can be about 1-10 wt% of the layer.
[0039] After die-casting the film and quenching, voids or cavities can be
formed by
orientation of the film in the machine direction. Without being bound by any
theory, such
stretching or orientation at certain processing temperatures can form stress
points about the
11
CA 2961692 2017-03-20
cavitating agent particles, resulting in a plurality of closed cell voids or
cavities. These voids
will typically contain the cavitating agent particle within the void.
[0040] A preferred method to produce the voided films disclosed herein can
be to use a
chemical foaming agent (CFA) as the cavitating or voiding agent. Such chemical
foaming agents
degrade under the polymer processing extrusion temperatures, thereby
liberating gases within the
polymer melt. Upon exit from the melt pipe and die, the entrapped gases can
expand, thereby
forming a foamed film layer with a plurality of closed cell voids. The
decomposition of the CFA
can be either exothermic or endothermic. Exothermic CFAs release energy during
decomposition and can include hydrazines and azo compounds. Such compounds can
be
characteristically yellowish in color and should be handled with care to avoid
skin irritation.
Endothermic CFAs consume energy during decomposition, thus requiring
continuous energy
input during the full reaction time and can be usually based on bicarbonate
and citric acid
powders. Such derivatives are also used as food additives, are safer to
handle, and can be
preferred for this reason. In the case of using CFAs to form the voided film
layer, such voids
will typically not contain a solid particle within the void or cavity in
contrast to using inorganic
or polymeric cavitating agents. The amount of CFA to use in the core layer of
the voided film
disclosed herein can be in the range of about 0.2 ¨ 3.0 wt% of the layer,
preferably 0.3 ¨ 1.0
wt%, and more preferably 0.4 ¨ 0.6 wt%. Such chemical foaming agents may be
dry-blended as-
is or as a masterbatch with the polyolefin resin pellets prior to melt
extrusion.
[0041] Suitable chemical foaming agents may be obtained from Bergan
International under
their FoamazolTM brand name, in particular, grade FoamazolTM 63. FoamazolTM 63
is an
endothermic-type CFA, with a melting point of about 110 - 130 C and bulk
density of about 42
lb/ft3 (0.673 g/cm3). Another suitable endothermic chemical foaming agent may
be obtained
from Clariant under their HydrocerolTM brand name, in particular, grade
PEAN698596
masterbatch, with a melting point of about 104 - 115 C and masterbatch
specific gravity of about
0.91 ¨ 0.97.
[0042] The films disclosed herein can be made by dry-blending the component
resins and
materials (e.g. propylene-based polymer blends, chemical foaming agent,
antiblock additives, and
other optional additives such a colorants) and melt-extruded them through a
die at extrusion
12
CA 2961692 2017-03-20
temperatures of about 390-465 F (199-240 C). The die temperature can be about
295-385 F
(146-196 C). The films can also be cast on a chill drum at about 130 F (54 C)
and a casting
speed of about 38.5 fpm (12 mpm). In addition, the films can also be oriented
in the machine
direction (MD) via a series of heated and differentially sped rolls at about
270-280 F (132-
138 C) for the preheat section, and about 205 F (96 C) for the stretching
section. The films can
be heat-set or annealed in the final zones of the MD orientation section at
about 280 F (138 C) to
reduce internal stresses, minimize heat shrinkage of the film, and maintain a
thermally
dimensionally stable mono-axially oriented film. The machine direction mono-
axial orientation
ratio can be about 4.0- 7.0: 1.0, meaning that the film was stretched in the
machine direction at
about 4 - 7 times its original dimension at casting; about 5.0-7.0: 1.0; or
about 6.0-7.0: 1Ø
Preferably, machine direction orientation can be about 6.5:1Ø Production
linespeed after MD
orientation at 6.5:1.0 can be about 250 fpm (76 mpm). Typical total thickness
of the disclosed
films after orientation (and foaming) can range from about 2.0 to 10.0 mil
(200 ¨ 1000G or 50 ¨
250 pm) or about 3.0 ¨ 5.0 mil in thickness. Density of the foamed film can
range from about
0.60 ¨ 0.89 g/cm3, preferred about 0.60 ¨ 0.80 g/cm3, and more preferably
about 0.64 ¨ 0.78
g/cm3. Average void sizes can range from about 5000 ¨ 12,000 pm in width
(along the MD
axis), preferably greater than 6000 pm width, and more preferably 8000 pm or
greater; and
about 10 ¨ 100 pm in height as depicted in Figure 2. Uniformity of the voids
within the film is
desirable and can be characterized by measuring the standard deviation of the
voids' average
width in a representative sample. The preferred standard deviation of the
average void width can
be about 2000 pm or less, and preferably, 1500 pm or less.
[0043] The films disclosed herein may also be discharge-treated on one or
both sides of the
film using methods well-known in the art such as corona or flame or
atmospheric plasma. In
addition, other methods after MD orientation can be used in order to raise the
wetting tension of
the film on one or both sides of the film. Preferably, the film can be treated
on both sides.
Furthermore, the mono-oriented polypropylene-based (MOPP) film can be wound in
roll form.
[0044] The following is a list of materials that were used in the Examples
provided herein:
[0045] Materials:
13
CA 2961692 2017-03-20
= Total Petrochemicals 3274 isotactic crystalline propylene homopolymer:
melt flow rate
1.5 g/10min at 230 C, melting point 163 C, and density 0.905 g/cm3
= Braskem TI4015F propylene-based impact copolymer: melt flow rate 1.6
g/10minutes at
230 C and density 0.901 g/cm3
= Total Petrochemicals 3576XHD isotactic crystalline propylene homopolymer,
containing
ca. 5000ppm Silton0 JC-30 sodium calcium aluminum silicate antiblock particles
of
nominal 3.0
diameter: melt flow rate 8.0 g/10min at 230 C and density 0.905 g/cm3
= Bergan International FoamazolTM 63 chemical foaming agent masterbatch:
melting point
110-130 C and bulk density 42 lb/ft3
= Clariant Hydrocerole PEAN698596 chemical foaming agent masterbatch
= (Optional) Ampacet Blue 463163: blue pigment masterbatch in propylene
homopolymer
carrier resin.
Example and Comparative Examples:
100461
Example 1: A single layer mono-axially oriented film (MOPP) was made using a
ca.
1.5 m-wide mono-axial orientation film-making process with a blend comprising
about 44.1 wt%
Total 3274, about 49.0 wt% Braskem TI4015F, about 4.9 wt% Total 3276XHD, about
1.0 wt%
FoamazolTM 63 masterbatch; and about 1.0 wt% of Ampacet Blue masterbatch (to
impart an blue
tint to the film for aesthetic purposes). A voided film was produced per the
processing
conditions described previously. Specifically, the film was dry-blended and
melt-extruded
through a die at extrusion temperatures of about 390-465 F (199-240 C); die
temperature was
about 295 F (146 C); cast on a chill drum at about 130 F (54 C) and a casting
speed of about
38.5 fpm (12 mpm), and orientation in the machine direction (MD) via a series
of heated and
differentially sped rolls at about 270-280 F (132-138 C) for the preheat
section, and about 205 F
(96 C) for the stretching section. The film was heat-set or annealed in the
final zones of the MD
orientation section at about 280 F (138 C) to reduce internal stresses and
minimize heat
shrinkage of the film and maintain a thermally dimensionally stable mono-
axially oriented film.
The machine direction mono-axial orientation ratio was about 6.5:1.0, meaning
that the film was
stretched in the machine direction at about 6.5 times its original dimension
at casting.
Production linespeed after MD orientation was about 250 fpm (76 mpm).
14
CA 2961692 2017-03-20
[0047] The thickness of the film was about 2.7 mils (67.5 um) thickness of
extruded
polyweight prior to foaming. After foaming/void formation and mono-axial
orientation, the
finished film thickness was about 5.0 mils (125 um) thickness. Density of the
film prior to
foaming/voiding was ca. 0.905 g/cm3 and after foaming /voiding the film
density was ca. 0.60
g/cm3.
100481 Example 2: A film was made similar to Example 1 except that the
extruded
polyweight thickness of the film prior to foaming was about 2.8 mils (70 um).
After foaming
and mono-axial orientation, the finished film thickness was about 5.2 mils
(130 um).
[0049] Example 3: A film was made similar to Example 1 except that Clariant
PEAN698596
was used at about 2.0 wt% of the film. The amount of Total 3274 was about 43.6
wt%; the
amount of Braskem TI4015F was about 48.5 wt%; the amount of Total 3576XHD was
about 4.9
wt%; and about 1.0 wt% Ampacet Blue masterbatch was used. The extruded
polyweight gauge
prior to foaming/voiding was about 2.7 mils (70 um). After foaming/void
formulation, the
finished film thickness was greater than 6.0 mils (125-150 um).
[0050] Comparative Example 1: A film was made similar to Example 1 except
that no
chemical foaming agent was used. The composition was about 44.6 wt% Total
3274; about 49.5
wt% Braskem T14015F; about 4.9 wt% Total 3576XHD; and about 1.0 wt% Ampacet
Blue
masterbatch. The finished film thickness after MD orientation was about 2.7
mils (67.5 um).
[0051] The MOPP film roll Examples were then tested for optics (gloss and
light
transmission), wetting tension, COF, elongation, tensile strength, and tear
resistance.
[0052] The following Tables IA and 1B illustrates the properties of these
Examples:
TABLE 1A
Sample TD Tear MD Heat MD MD/TD MD Appearance
Resistance Shrinkage Tensile Modulus Elongation
Rating % (Thermal Strength kpsi
(1=best; Dimensional 'Winch width
3=poor) Stability)
Ex. 1 1 <2.0 95 30.7 24 Good
Ex. 2 1 <2.0 100 31.3 24 Good
Ex. 3 1 NT^ NP NT" NP Poor
CEx. 1 3 <2.0 160 210 25 Good
TABLE 1B
CA 2961692 2017-03-20
Sample Light Gloss Wetting COF
Transmission (60 ) Tension static/dynamic
ok Dyne-cmicm2
In/Out* In/Out* Out/Out* In/In*
Ex. 1 30.8 39 / 32 42 / 42 0.49 / 0.41 0.57 /
0.48
Ex. 2 29.7 42 / 33 42 / 42 0.48 / 0.38 0.56 /
0.46
Ex. 3 NT^ NT^ NT^ NT^ NT^
CEx. 1 29.0 82/83 42/42 0.67/0.59 0.68/0.60
A Not tested due to poor quality of film appearance.
* -Out" refers to the side of the film that was in contact with the air side
during casting; "In"
refers to the side of the film that was in contact with the casting drum side
during casting.
[0053] As Tables 1A and 1B show, Comparative Example 1 (CEx 1) was a un-
foamed/un-
voided control film. Appearance was very good and consistent with excellent MD
tensile
properties and low heat shrinkage. Gloss values of CEx. 1 were higher than
that of the Examples
due to a smoother surface since CEx. 1 was unvoided. Tensile properties were
also higher than
the Examples due to being an unvoided film. However, when a film sheet of CEx.
1 was torn by
hand at a notch made in the transverse direction side of the film, tear
resistance in the transverse
direction (orthogonal to the orientation direction in the machine direction)
was very poor in that
tearing was initiated and propagated transversely across through the film very
easily with little
effort. Tear resistance property was rated 3 ("poor") where a rating of 1 (-
excellent", no or little
transverse tear through) or 2 ("good", some transverse tear through) is
desirable. CExl's
transverse tear resistance was considered to be poor.
[0054] Example 1 (Ex 1) shows a film with about 1 wt% of the chemical
foaming agent
FoamazolTM 63 to void/foam/cavitate the film layer. Appearance was acceptable
and MD tensile
properties were good at 95 lb/in and 24% MD elongation. MD heat shrinkage was
also very
good at less than 2% shrinkage. This film showed excellent tear resistance in
the transverse
direction and was rated a 1.
[0055] Example 2 (Ex 2) showed a film that was similar to Ex. 1 but was
extruded to be
slightly thicker than Ex. 1 at nominal 5.2 mil (130 p.m) vs. 5.0 mil (125
vim), respectively.
Appearance was acceptable and MD tensile properties were very good at 100
lb/in and 24% MD
elongation. MD heat shrinkage was also very good at less than 2% shrinkage.
This film showed
excellent tear resistance in the transverse direction and was rated a 1.
16
CA 2961692 2017-03-20
[0056] Example 3 (Ex 3) showed a film that used a different chemical
foaming agent, 2 wt%
of Hydrocerol0 PEAN698596 instead of 1 wt% FoamazolTM 63. Unfortunately, void
sizes using
this foaming agent were very large, causing very poor appearance on the film's
surface. Process
modifications were made (MDO stretch temperatures) as well as different
loadings of the
foaming agent (0.5 wt%, 0.8 wt%, 1.0 wt%, and 2 wt%) in an attempt to control
degree of
foaming and void formation. Foaming could only be consistently done at the 2
wt% level (the
lower levels exhibited little or no foaming). In this Example, the film was
considered to be
"over-foamed" with voids that were considered to be too large (bursting
through outer surfaces of
the film) and appearance was very poor. Cavitated or foamed thickness was also
greater than
desired, in excess of 6 mils (150 pm). For this reason, most of the standard
testing was not
conducted since no suitable or consistent enough film was made of this
example. However,
transverse tear resistance was tested and was found to be excellent despite
the large void sizes
and was rated a 1.
[0057] Examples 4 to 9
[0058] Additional Examples 4 - 9 were made similar to Example 1 but with
varying amounts
of FoamazolTM 63 of about 0.4 and 0.6 wt% of the core layer and machine
direction orientation
(MDX) of about 6.2:1.0 and 6.7:1Ø The extrusion temperature melt pipe was
set at ca. 425 F
(218 C) and die temperature was about 375 F (190.5 C). The extruded polyweight
gauge of
these single layer film Examples prior to foaming/voiding was about 2.85 mils
(71.25 lam). After
foaming/void formulation, the finished film thickness ranged from 3.0 -4.0
mils (75-100 [tm).
Table 2A summarizes the formulations and conditions for these Examples.
Table 2A
Example FoamazolTM Total Braskem Total Ampacet MDX Foamed
Film
wt% 3274 TI4015 3576XHD 463163 Thickness
wt% wt% wt% wt% mils (pm)
4 0.4 44.6 49.0 5.0 1.0 6.2 3.0 (75)
0.6 44.4 49.0 5.0 1.0 6.2 3.8(95)
6 0.4 44.6 49.0 5.0 1.0 6.7 3.0 (75)
7 0.6 44.4 49.0 5.0 1.0 6.7 3.2 (80)
8 0.6 44.4 49.0 5.0 1.0 6.2 3.5 (87.5)
17
CA 2961692 2017-03-20
9 0.6 44.4 49.0 5.0 1.0 6.7 4.0 (100)
100591 Tables 2B and 2C summarize some of the properties tested for
Examples 4-9.
Average void width (measured along the longitudinal dimension), void
uniformity (standard
deviation of average void width), voided film density, tear resistance rating,
and both machine
direction (MD) and transverse direction (TD) tensile properties were tested.
Table 2B
Example Void Size Void Film Density Tear Resistance
pm Uniformity g/cm3 Rating
pm 1-3
(1 best;
3=poor)
4 6050 2093 0.838 3
8866 1522 0.642 1
6 1414 NT 0.882 3
7 10,662 1837 0.782 2
8 9189 1571 0.733 2
9 8185 371 0.637 1
Table 2C
Example MD Tensile MD Modulus MD TD Tensile TD
Modulus TD
Strength kpsi Elongation Strength kpsi
Elongation
lbf/in % Ibf/in %
4 118.0 39.3 30.4 9.1 3.0 9.1
5 79.8 21.0 15.3 6.4 1.7 7.9
6 126.1 42.0 30.6 11.5 3.8 4.6
7 100.0 31.3 19.5 9.0 2.8 10.1
8 99.7 28.5 21.1 7.1 2.0 7.8
9 88.8 22.2 14.6 5.6 1.4 6.5
18
CA 2961692 2017-03-20
100601 In Table 2B, Examples 5, 7, 8, and 9 showed the best tear resistance
rating property,
with ratings of at least a "2", indicating good resistance to transverse
direction tear propagation.
Examples 4 and 6 showed the poorest tear resistance property, with a rating of
"3", indicating no
or little resistance to transverse direction tear propagation. It is noted
that the void sizes and
uniformity for Examples 4 and 6 are significantly lower and worse,
respectively, than that of
Examples 5, 7 ¨ 9. It is also noted that the voided film density of Examples 4
and 6 are
significantly higher than that of Examples 5, 7 ¨ 9. Without being bound by
any theory, there
appears to be a correlation between void size/uniformity, voided film density,
and tear resistance
property. Larger-sized voids and more uniform voids appear to be more
favorable for tear
resistance; lower voided film density also appears to correlate to more
favorable tear resistance
property. The exemplary films with good tear resistance appear to have larger
and more
uniform voids ¨ and since they are more voided, these exemplary films will
have a lower density.
Poor tear resistance disclosed films will have smaller (or no) voids; and
consequently, their film
density will be higher. Based on the results of Table 2B, void sizes of
greater than about 6000
pm in width appear to be preferred for good transverse tear resistance
properties; preferably, the
void sizes should be about 8000 pm or more. In some embodiments, the void
sizes are about
6000-12,000 pm or about 8000-12000 pm in width. Void uniformity should be less
than about
2000 pm, and preferably about 1500 pm or less. Similarly, film density should
be less than
about 0.83 g/cm3, preferably less than 0.80, and more preferably, less than
0.70.
[0061] MD tensile strengths for Examples 4-9 were good overall, in
particular Examples 4,
6,7, and 8. Similarly for MD modulus and elongation, Examples 4, 6, 7, and 8
showed the best
values of this Example set. However, Examples 4 and 6 were poorest for tear
resistance.
Examples 7 and 8 showed a good balance of good tear resistance and good
tensile properties.
Test Methods
[0062] The various properties in the above examples were measured by the
following
methods:
[0063] A) Tear Resistance: Tear resistance was tested qualitatively by
notching a piece of
test film on one edge of the transverse direction (or cross-width) side; and
tearing by hand at the
notch to initiate the tear. The notch was made parallel to the transverse
direction of the test film
19
CA 2961692 2017-03-20
with a pair of scissors with notch length approximately 1/4 inch (ca. 6 mm)
and the tear
propagated along the transverse direction. The tear was initiated from the
notch by hand and
observation made as to the ease with which the tear could be propagated across
the transverse
width of the film. The preferred observation for good tear resistance property
was: 1) tearing
could not be initiated and could not be propagated transversely and tear
propagation transferred
to the machine direction only; 2) tearing was difficult to initiate and
difficult to propagate
transversely and tear propagation transferred to the machine direction only;
3) tearing was easily
initiated and easily propagated in the transverse direction. Ratings were as
follows:
1 = No tear propagation or initiation in transverse direction
2 = Some or difficulty in propagating tear in transverse direction
3 = Easy to initiate and propagate tear in transverse direction
[0064] B) Light Transmission of a single sheet of film was measured
substantially in
accordance with ASTM D1003. In some embodiments, the film has a light
transmission of about
10-50%, 20-40%, or about 20-30%.
[0065] C) Gloss was conducted on both sides of a single sheet of film and
was measured
substantially in accordance with ASTM D2457. In some embodiments, the film has
a gloss of 20
or greater.
[0066] D) COF was conducted on both sides of a single sheet of film and was
measured
substantially in accordance with ASTM D1894. In some embodiments, the film has
a COF of
about 0.2 -1.0 or about 0.3-0.7.
[0067] E) Tensile Properties: Modulus, Tensile Strength, Elongation was
conducted in the
MD and/or TD direction of the film substantially in accordance with ASTM D882.
In some
embodiments, the film can have an MD and/or TD tensile strength of at least
about 75 lb/in or at
least about 90 lb/in. In some embodiments, the film can have an MD and/or TD
modulus of at
least about 20 kpsi or at least about 30 kpsi. In some embodiments, the film
can have an MD
and/or TD elongation of at least about 10% or of at least about 15%.
CA 2961692 2017-03-20
[0068] F) Thermal Dimensional Stability (i.e., Heat Shrinkage) was tested
by cutting a strip
of the film 1 inch-wide in the transverse direction by 50 inches long in the
MD direction. This
strip was then immersed in 100 C water for 10 minutes. After this immersion
time, the film strip
was removed, dried with paper towels, and measured again along the MD
direction. The percent
change in dimension from the original MD length was recorded.
[0069] G) Wetting Tension was measured on the discharge-treated side(s) of
the film
substantially in accordance with ASTM 2578-67. In some embodiments, the film
can have a
wetting tension of at least about 36 dynes. In some embodiments, the film can
have a wetting
tension of about 39-42 dynes.
[0070] H) Appearance: Appearance of the film was observed qualitatively. In
essence,
exemplary films that were consistent in appearance were considered acceptable;
films that were
very inconsistent in appearance were considered to be poor.
[0071] I) Void Size and Void Uniformity: Cross-sections of 3 representative
film samples
per Example were taken parallel to the MD direction of the film (orthoganally
to the transverse
direction of the film) and examined via a digital optical microscope (Keyance
model VHX).
Magnification was 30x and the samples were backlit with polarized light to
make the voids more
easily observable. Imaging software integrated with the Keyance digital
microscope was used to
measure the number of voids and void sizes in the field of view. The average
size and standard
deviation were calculated and reported. Void size is defined as the average
dimensional width of
the voids and void uniformity is defined as the standard deviation of the
average void widths.
[0001] J) Film Density: Density of the film was calculated by taking a stack
of 10 sheets (letter
paper size e.g. 8.5 inches by 11 inches) of film and cutting them via a die or
template of area
33.69 cm2 and weighing said cut sheets on an analytical scale. The 10 sheets
are also measured
for thickness using a flat-head micrometer to get an average thickness of the
film. The measured
weight and thickness is then used in a calculation to obtain density:
Weight (g) = Density (g/cm3)
[0072] Thickness (cm) x area (cm')
[0073]
This application discloses several numerical ranges. The numerical ranges
disclosed
inherently support any range or value within the disclosed numerical ranges
even though a
21
CA 2961692 2017-03-20
precise range limitation is not stated verbatim in the specification because
the disclosed subject
matter can be practiced throughout the disclosed numerical ranges.
100741 The above description is presented to enable a person skilled in the
art to make and
use the disclosed subject matter, and is provided in the context of a
particular application and its
requirements. Various modifications to the preferred embodiments will be
readily apparent to
those skilled in the art, and the generic principles defined herein may be
applied to other
embodiments and applications without departing from the scope of the claimed
invention. Thus,
the claimed invention is not intended to be limited to the embodiments shown,
but is to be
accorded the widest scope consistent with the principles and features
disclosed herein.
22
