Note: Descriptions are shown in the official language in which they were submitted.
2ri~i~~~~
~iULTI-PLY BACKSEAMABLE FILM
FTELD OF TILE INVENTION
The field of the invention is a packaging film from
which bags and casings can. be made which have improved struc-
tural soundness so that they may be fully aharacteri~ed as
"cook-in." The term "cook-in" as used herein is intended to
refer to packaging material structurally capable of withstand-
ing exposure to time-temperature conditions while containing a
food product.
This invention relates generally to thermoplastic films
suitable for cook-in packaging; and more particularly to food
cook-in films. These films may have food contact surf ace
characteristics which promote binding adherence to a contained
food product during cook-in. The films of the invention exhib-
it improved hot and cold seal strength, improved optics and
are more readily processable than known films. The present
invention is particularly directed to backseamed casings.
PRIOR ART
Cook-in packaged'foods are essentially foods cooked in
the package in which they are distributed to the consumer and
which may be consumed with or without warming. Cook-in time-
temperature conditions typically refer to a long slow cook,
for example, submersion in hot water at about 55°C to about
65°C for about 1 to about 4 hours. These conditions are repre-
5/920915.1/SPECFLDR
~ n.
sentative of institutional c~o~ g~requirements. Submersion
at about 7 0 ° C to about 10 0 ° C f or up to about 12 hours
repre-
sents the limiting case. Under such conditions, a cook-in
packaging material should maintain seal integrity, i.e., any
heat sealed seams should resist being pulled apart during
cook-in. The film should also be heat sealable to itself and,
the packaging film substantially conformable to the contained
food product. Preferably, this substantial conformability is
achieved by the film being heat shrinkable under these condi-
tions so as to form a tightly fitting package, i.e., the film
should be heat shrinkable under these time-temperature condi-
tions and should possess sufficient shrink energy so that
submerging the packaged food product in hot water will shrink
the packaging film snugly around the contained product, and
especially up to about 55o monoaxial and/or biaxial shrink-
age.
The film may also have food product adherence to re-
strict "cook-oft" or collection of juices between the surface
of the contained food product and the food contact surface of
the packaging material during cook-in, thereby increasing
product yield. More particularly, in the types of multilayer
films wherein the first "sealing and food contact" layer is of
the type of material that adheres to a contained food product
during cook-in, this first layer may alternatively be referred
to as the "adhering layer." As used herein, the term "adhere"
is intended to mean that the food contact surface of the film
bonds during cook-in to the contained food product to an ex-
tent sufficient to substantially prevent accumulation of flu-
ids between the ~ilm and the contained product.
A heat shrinkable, cook-in film is described by Oberle
et al, U. S. Patent No. 4,469,742 that includes a first "seal-
ing or food contact" layer of a nonlipophillic polymeric mate-
rial which has a softening point greater than that of the
following shrink layer; a second layer, of an ethylene homopol-
ymer or copolymer melt bonded to the first layer; a third or
adhesive layer, melt bonded to the second layer, of a chemical-
5/920915.1/SPECFLDR
2
1y modified polyethylene beir~'~ ~~r'a~~.~tively cross-linkable
and having functional groups with a relatively strong affinity
for the following barrier layer; a fourth or barrier layer of
a hydrolyzed ethylene vinyl acetate copolymer melt bonded to
the third layer; a fifth or adhesive layer as in said third
layer, melt bonded to the fourth layer; and a sixth or abuse
layer, melt bonded to the fifth layer. In one embodiment, the
first "sealing and food contact" layer is an ionomer, a metal
salt neutralized copolymer of an olefin and a carboxylic acid,
representatively Surlyn(TM), which is a type of material that
adheres to a contained meat product during cook-in. This
Surlyn(TM) layer also functions as a protein-adhering layer.
In another embodiment, the sealing layer is a propylene-
ethylene random copolymer having from to to 6o by weight of
ethylene: The patent also describes a method for making the
film including full coextrusion and selective irradiation and
orientation.
In the conventional method of manufacturing heat shrink-
able film as described by Oberle et al, a tubular orientation
process is utilized wherein a primary tube of the film is
biaxially oriented by formation of a bubble to create internal
pressure and induce stretching in the transverse direction and
with the use of pinch rolls at different speeds to induce
stretching in the machine direction. The films of the present
invention are easily oriented with the incidence of bubble
breakage during orientation minimized, and in some cases,
eliminated. The stretched bubble is then collapsed, and may
be wound up as flattened, seamless, tubular film to use later
to make bags, e~.g., either end-seal bags typically made by
transversely heat sealing across the width of flattened tubing
followed by severing the tubing so that the transverse seal
forms the bag bottom, or side-seal bags in which the trans-
verse heat seals farm the bag sides and one edge of the tubing
forms the bag bottom. Such bags are typically used by placing
the food product in the bag, evacuating the bag, and either
heat sealing the bag mouth or gathering and applying a metal
clip around the gathered mouth of the bag to form a seal.
5/920915.1/SPECELDR
3
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Alternatively, the collapsed tube may be slit into a film or
two, or more films, depending on the width desired. The film
can then be folded longitudinally about a forming shoe with
opposed edges being joined in a lap seal in order to form a
backseamed casing. Backseamed casings are often desirable
when process limitations preclude formation of an oriented
tube or sufficiently small diameter for a given cook-in appli-
catian. However, the lap seal of such a casing requires that
the inner layer of the cook-in material (optionally an adher-
ing layer) is heat sealable to the outermost layer. This
required sealing compatibility is most easily achieved by
providing inner and outer layers of identical chemical composi-
tion. However, the inner and outer layers need not be identi-
cal as long as their respective compositions are sufficiently
compatible for forming seals which are delamination resistant
under rigorous cook-in conditions.
Formation of a backseamed .tube from a film may be by a
continuous or ~an intermittent process. By the intermittent
process the film is typically sealed to form a length of tub
ing required for a given end-use application and then cut
transversely. As the film indexes forward and the sealing and
cutting steps are repeated, a series of tubular .casings of the
desired diameter and length are provided. The casings may be
clipped at one end for subsequent stuffing and clipping of the
opposite end or they may be heat sealed and treated as bags
produced from seamless tubing. Alternatively, an intermittent
process may be employed for forming a continuous tube so long
as the individually formed seals have at least some overlap.
By the continuous process the entire length of the film is
sealed to form a continuous tuba for later clipping, stuffing
and clipping.
Cook-in tubing, whether seamless or backseamed, may be
shirred; that is, folded or pleated into a relatively short
length for ease of handling during stuffing. Regardless of
the method of manufacture, the bag or casing is then immersed
in hot water at. approximately the same temperature at which
5/920915.1/SPECFLDR
4
the film was stretch oriented, typically about 160° to 205°F.
(61° to 96°C), hot water immersion being one of the quickest
and most economical means of transferring sufficient heat to
the film to shrink it uniformly. Alternatively, the bag, film
or casing may serve as a liner of a cooking mold.
A plastic, adhering cook-in package such as a casing is
described by Schirmer, in U. S. Patent No. 4,606,922 as well
as a method for enhancing yield of a cook-in packaged meat
product.' The method includes first providing an adhering
cook-in container including a flexible thermoplastic envelope
being substantially conformable to a contained meat product
and having an inner meat-contacting surface of a selectively
irradiated ionomer, then conforming the container about a
selected meat product and cooking the packaged product, where-
upon the inner surface of the envelope bonds to the meat prod-
uct substantially to prevent cook-out of fluids.
A flexible plastic adhering cook-in package is de-
scribed by Thompson in U. S. Patent No. 4,411,919, as well as
a method for enhancing yield of cook-in packaged meat prod-
uct. The method includes: providing an adhering cook-in
package comprising a flexible plastic container substantially
conformable to a selected meat product and having an inner
meat product contacting surface of polymeric olefin. This
container is subjected to an energetic radiation surface treat-
ment in the presence of oxygen sufficient to cause the inner
surface to adhere to the meat product during cook-in, the
container having been formed from hot blown tubular film. The
package is conformed about a selected meat product followed by
cooking the packaged product, whereupon the inner surface
adheres to the meat product to substantially prevent cook-out
of fluids.
Erk pt al, U. S. Patent No. 4,303,711, describes a
tubular film consisting of biaxially stretched plastic materi-
al for packing and casing, paste type foodstuffs that are
heated after packing or are packed in a hot fluid state. The
5/920915.1/SPECFLDR
f1 C1
film is a mixture of approximately 50-99 parts by weight of at
least one aliphatic polyamide and approximately 1-50 parts by
weight of one or more members of the group consisting of an
ionomer resin, a modified ethylene vinyl acetate copolymer and
a modified polyolefin.
Erk et al, U. S. Patent No. 4,601,929, relates to a
single layer of polyamide film for packing and casing food-
stuffs in paste form, especially foodstuffs that are packed
when hot or are subject to heat treatment after packing.
Ghiradello et al, U. S. Patent No. 4,568,580, relates
to an article of manufacture for packaging food products com-
prising a first film section having at least one surface com-
prising a copolyamide obtained by random copolymerization of
precursor monomers of at least two different.polyamides. The
article includes a second film section of a film having a
surface comprising the aforesaid copolyamide and at least one
heat weld between the copolyamide surfaces of said first and
second film sections. The article is capable of withstanding
heat treatment at temperatures from 70°C to 120°C for at least
minutes without suffering damage to the heat weld.
Oberle, U. S. Patent No. 4,855,183 discloses a cook-in
film having a first food contact layer comprising a polyamide
composition.
obey 1e, U.S. Patent No. 4,762,748 describes a cook-in
shrink film characterized by the presence of ethylene alkyl
acrylate copolymer in core layer and abuse layers, in adhesive
layers, or both. The sealing layer is selected from the group
consisting of a propylene ethylene copolymer, an ionomer, a
blend of a linear low density polyethylene and an ionomer, and
a blend. of a linear low density polyethylene and an ethylene
acrylic acid copolymer.
Schirmer, U.S. Patent No. 4,448,792, describes a cook-
in shrink bag having a sealing and food contact layer of a
5/920915.1/SPECFLDR
6
:~. ~l ~ ~ 8 ~~
propylene homopolymer or copolymer, preferably a propylene-
ethylene copolymer of low ethylene content. A core layer
adjacent the sealing layer is a blend of a propylene homopoly-
mer or copolymer. Also included are a barrier layer, an abuse
layer and adhesive layers sandwiching the barrier.
Oberle, U.S. Patent No. 4,879,124, describes a perforat-
ed cook-in shrink bag. Preferable materials for the sealing
layer include ethylene-acrylic acid copolymers, ethylene
methacrylic acid copolymers, ionomers and blends of such.
Schirmer, U.S. Patent No. 4,608,302, describes oriented
..S
films from propylene copolymers and unplasticized Saran which
are suitable for use in the packaging of prepared food prod-
ucts. A core layer may comprise an ethylene vinyl acetate
copolymer having a vinyl acetate content if from loo to 12o by
weight and a fractional melt index. The core layer is adja-
cent a sealing layer which is a propylene homopolymer or
copolymer which may be a propylene ethylene copolymer.
Bekele, U.S. Patent No. 4,909,726, describes an impact
resistant film for chub packaging. Various layers may contain
?a.' polymeric materials of fractional melt index.
Mueller, U.S. Patent No. 4,977,022, describes a barrier
=w stretch film with at least one interior layer which may com
prise an ethylene vinyl acetate copolymer of fractional melt
index.
Schirmer, ~.U.S. Patent No. 4,937,112, describes a film
for chub packaging which includes an olefin sealing layer and
a core layer adjacent the sealing layer which comprises a
polymeric material of high molecular weight and fractional
melt index selected from the group consisting of high density
.;
polyethylene, low density polyethylene and ethylene vinyl
acetate copolymer.
5/920915.1/SPECFLDR
7
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U.5. Patent No. 4,495,249 issued to Ohya et al disclos-
es a multi-layer laminate film with a core layer of a
hydrolized ethylene-vinyl acetate copolymer, and two outer
layers of a mixture of copolymer of ethylene and vinyl acetate
and a copolymer of propylene and ethylene or linear low densi-
ty polyethylene. The multilayer laminate film of the refer-
ence can be made heat shrinkable and has gas barrier proper-
ties.
U.5. Patent No. 4,182,457 (Yamada et al) discloses a
container with an EVOH core, adhesive layers, and additional
layers of e.g. polypropylene or ethylene propylene copolymer.
U.5. Patent No. 4,511,610 (Yazaki et al) discloses a
container with an EVOH core, adhesive layers, and additional
layers of e.g. polypropylene or ethylene propylene copolymer.
U.5. Patent No. 4,405,667 issued to Christensen et al
appears to di$close a retortable pouch having a linear low
density polyethylene heat seal layer, a second layer of a
blend of linear low density polyethylene and propylene
ethylene copolymer, optional third, fourth, and fifth layers
of propylene ethylene copolymer, a sixth layer of an anhydride
modified polypropylene, a seventh layer of nylon, an eighth
layer of EVOH and a ninth layer o:r nylon.
U.S. Patent No. 4,532,189 issued to Mueller discloses a
shrink film having two skin layers each comprising e.g. a
blend of polypropylene and ethylene propylene copolymer.
Also of interest is U.S. Patent No. 4,400,428 issued to
Rosenthal et a1 which discloses a composite film having a
biaxially oriented polypropylene based film (BOPP) laminated
on at least one surface with a multilayer structure including
a gas barrier layer of a hydrolyzed ethylene vinyl acetate
copolymer and a layer adaacent to the base film, and a heat
sealable outer layer which may be, for example, modified
propylene/ethylene copolymer.
/ 9 2 0 915 .1 / SPECELIaR
8
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EPO Patent Application No. 0149321 discloses a heat
shrinkable tubular film having a gas barrier layer of
vinylidene chloride copolymer, outer layers of polyolefin such
as ethylene propylene copolymer, polypropylene and mixtures
thereof, at least one intermediate layer of for example a
polyamide, and adhesive layers disclosed between any of the
above layers.
U.K. Patent Application GB 2,139,948A discloses a
multilayer, preferably coextruded fiber-layer heat sealable
film having a surface layer of a heat sealable polymer such as
linear low density polyethylene of LLDPE blended With other
polymers such as EVA, an EVOH layer, and a layer of
polypropylene. These layers can be bonded by polymeric adhe-
sive tie layers.
U.K. Patent Application GB 2,221,649 discloses a compos-
ite film with improved heat shrinkable properties comprising a
core layer of a copolymer or propylene and one or more alpha-
olefins having a Vicat softening point of 70-110°C and two
outer layers of a crystalline polypropylene resin having a
melting point of 135-150°C.
EPO Patent Application No. 435498-A is directed to a
multilayer heat-shrinkable film which includes a heat sealing
layer which is a copolymer of propylene and at least two other
alpha-olefins .
Japanese Patent Application 3063133-A is directed to a
heat shrinkable ~multilayer film which includes at least one
layer which is a blend of an aliphatic polyamide and a non'
crystalline polyamide.
Japanese Patent Application 3121842-A is directed to a
packaging material which contains an inner layer which is a
polyamide/polyethylene blend.
5/920915.1/SPECFLDR
,.... 9
CA 02106889 2002-12-19
64536-832
German Patent Application 3943024-A is directed to
a monolayer casing which is a blend of nylon 6 and a
copolyamide.
Summary of the Invention
The present invention provides a novel cook-in
film which is readily biaxially oriented. Further, the
present invention provides a novel cook-in film that has
improved biaxial orientability as a tube by means of forming
a bubble wherein bubble breakage is substantially minimized
or eliminated. Further, the present invention provides a
method for manufacturing such a novel cook-in film wherein
the sealing layer comprises a blend of a propylene based
copolymer and an ethylene alpha-olefin copolymer. Further,
the present invention provides a method for manufacturing
such a novel cook-in film wherein the outermost layer
comprises a blend of a propylene based copolymer and an
ethylene alpha-olefin copolymer. The present invention also
provides a cook-in film with good elastic recovery for a
tight package appearance. Still further, the present
invention provides a cook-in film which can be formed into
backseamed casings.
These as well as other aspects of the invention
are achieved by providing a heat-shrinkable multilayer film
which has a heat sealing outer layer of a blend of about 50%
to about 95% by weight of a propylene based copolymer and
from about 5% to about 50% by weight of a homogeneous
ethylene alpha-olefin copolymer having a density below about
0.90 g/cc. Such aspects are further achieved by providing
such a film which also includes at least one layer
containing a polyamide, a copolyamide, an amorphous
copolyamide, or blends of such.
CA 02106889 2002-12-19
64536-832
Additional aspects and advantages of the invention
will be set forth in part in the description which follows
and in part will be apparent to a person with ordinary skill
in the art from the description, or may be learned by
practice of the invention. The advantages of the invention
may be realized and attained by means of the
instrumentalities and combinations particularly pointed out
in the appended claims.
Detailed Description ef the Invention
The present invention is directed generally to multi-
layer heat shrinkable films which have a heat sealing layer
which is a blend of a propylene based copolymer and a homoge-
neous ethylene alpha-olefin copolymer with a density below
about 0.90 g/cc. Specifically, films with improved process-
ability and heat seal characteristics in accordance with the
present invention have the structure: (inner sealing and food
contact layer)/(nylon layer)/outer sealing layer) or (inner
sealing and food cor_tact layer)/(nylon layer)/(barrier lay-
er)/(outer sealing layer). Here again, the inner sealing and
food contact layer is a blend of a propylene based copolymer
with an ethylene a~ pha-of efin copoiT .~er having a densi ty below
about 0.90 g/cc. 'the propylene based copolymer is preferably
an ethylene propylene copolymer which contains from about 94°-,
to about 99-% by wei ght of propylene and from about 1% to about
6o by weight of ethylene.
Alternatively, the propylene based copolymer may be a
copolymer of propylene with ethylene and butene. Such
ethylene propylene butene copolymer should preferably contain
from about 90% to about 99o by weight of propylene, from about
1% to about 6% by weight of ethylene, and from about to to
abcut 10 o by weight oz butene. It SilOUld be noted that nor
11
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,~. ~~ t.u .~ LV
purposes of the present specification, the term "copolymer" is
intended to broadly describe the products of polymerization of
two or more comonomers.
Although the present heat sealing layer may comprise
anywhere from 50o to about 95a by weight of such propylene
based copolymer, a more preferred range is 70% to about 85%
with 750 of the heat sealing layer being the optimum amount of
such copolymer. As noted above, the propylene based copolymer
is blended with a homogeneous ethylene alpha-olefin copolymer
which has a density below about 0.90 g/cc.
Ethylene alpha-olefins are, generally speaking,
copolymers of ethylene with one or more comonamers selected
from C3 to about C1o alpha olefins but especially compris-
es ethylene copolymers with CQ to about C1o alpha olefins
such as butane-1, pentane-1, hexane-1, octane-l, and the like,
in which the polymer molecules comprise long chains with few
side chains or. branches and sometimes are referred to as lin-
ear polymers. These polymers are obtained by low pressure
polymerization processes and the side branching which is
present will be short compared to non-linear ethylenes.
Ethylene/alpha-olefin copolymers have a density in the range
of fram about 0.860 g/cc to about 0.940 g/cc. The term linear
low density polyethylene is generally understood to include
that group of ethylene/alpha-olefin copolymers which fall into
the density range of about 0.915 to about 0.940 g/cc. Some-
times linear polyethylene in the density range from about
0.926 to about 0.940 is referred to a linear medium density
polyethylene (LMDPE). Lower density ethylene alpha olefins
may be referred to as very low density polyethylene (VLDPE,
typically used to refer to the ethylene butane copolymers
supplied by Union Carbide) and ultra-low density polyethylene
(ULDPE,. typically used to refer to the ethylene octane
copolymers supplied by Dow). It should be noted although
specific density ranges is for VLDPE, ULDPE, LLDPE, and LMDPE
have been set forth herein, that no bright line can be drawn
for density classification and such will vary by supplier.
5/920915.1/SPECFLDR
12
Heretofore, conventional ethylene alpha-olefins have
been produced by Ziegler-Natta catalyst polymerization. The
traditional Ziegler-Natta homogeneous system includes a metal
halide activated by a metal alkyl cocatalyst. These are sys-
tems in which there are various oxidation states of the metal,
and a variety of ligand environments, depending upon where the
site is located in the catalyst, all leading to a relatively
broad molecular weight distribution and a generally heteroge-
neous composition. Generally speaking, Ziegler-rT~tta cata-
lysts incorporate comonomer poorly and produce some polymer
chains with much comonomer and others with substantially
less. Fox example, with conventional Ziegler-Natta catalysis,
a linear ethylene alpha-olefin having an average of l00
comonomer may have a range of Oo to 40% comonomer in any given
individual chain.
Recently a new type of ethylene based linear polymers
have been introduced. These new resins are produced by
metallacene catalyst polymerization and are characterized by
narrow or more homogenous compositional properties, such as
molecular weight distribution, than resins produced by conven-
tianal Ziegler-Natta polymerization processes. Conventional
Ziegler-Natta polymerization systems have discreet catalyst
composition differences which axe manifested as different
catalyst reaction sites with each site having different reac-
tion rates and selectivities. Metallocene catalyst systems
are characterized as a single identifiable chemical type which
has a singular rate in selectivity. Thus the conventional
systems produce resins that reflect the differential character
of the different catalyst sites while resins produced by
metallocene systems reflect the single catalytic site. Howev-
er, it should be noted that at least some previously available
ethylene based linear polymers exhibited the physical and
compositional properties achieved by the present metallocene
catalyzed polyolefins. Although not produced by metallocene
catalysis, such copolymers were produced by non-metallocene
single cite catalysts yielding resins which achieve the homoge-
neity of metallocene catalyzed resins. An example of such are
5/920915.1/SPECFLDR
13
CA 02106889 2002-12-19
64536-832
the resins sold under the trade-mark Tafmer(TM) by Mitsui.
Both metallocene catalyzed ethylene alpha olefins and the
Tafmer-type of resins are appropriate for use in the heat seal
layer of the present invention.
Thus, the ethylene alpha-olefin of the present heat
sealing layer is a homogeneous metallocene catalyzed resin or,
at least, a single site catalyzed resin such as a Tafmer. The
density is limited to below about 0.90 g/cc in order to aid in
processability of the overall film structure and for improved
sealing. The homogeneous ethylene alpha-olefin employed is
preferably an ethylene butene copolymer or an ethylene
propylene copolymer which will exhibit excellent compatibility
with the propylene-based resin. The ethylene alpha-olef in
will comprise from about 5o to about 50o by weight of the heat
sealing layer, most preferably between 15% and 300.
The present film structure further includes at least
one polyamide or nylon-containing layer. Such layer is
present to impart elastic recovery properties to the overall
structure. Specifically, in a cook-in application, as noted
above, the food product is literally cooked in the film pack-
age. Because the present film is biaxially oriented it
shrinks during cooking to closely conform to the enclosed food
product. After cooking, the product is typically 'chilled
which, at least in the case of a meat product, often results
in product shrinkage. It is desirable that the film have good
elastic recovery in order to tightly conform to the meat dur-
ing such shrinkage.
It is generally known that nylons provide such elastic
recovery properties to thermoplastic films. For purposes of
the present invention, various combinations of polyamides,
copolyamides and amorphous nylons were investigated for deter-
mining a preferred combination of processability, stiffness
imparting properties and elastic recovery. A layer of nylon
6/12 was found to produce the optimum combination of proper-
ties for the present invention.
14
CA 02106889 2002-12-19
64536-832
Thus, the invention preferably comprises the foregoing
(inner sealing and food contact layer)/(nylon layer)/(outer
sealing layer) and in further embodiments the structure:
(inner sealing and food contact layer)/(nylon layer)/(barrier
layer)/(outer sealing layer). Each of the layers may also be
optionally banded to one anothEr by a tie layer as well.
The food contact layer can optionally be subjected to
an energetic radiation treatment, including, but not limited
to corona discharge, plasma, flame, ultraviolet, and high
energy electron treatment. For instance, the food contact
layer may be selectively irradiated with high energy electrons
which advantageously may be accomplished during irradiation of
the overall multilayer film structure for cook-in integrity,
as further discussed below. Radiation dosages are referred to
herein in terms of the radiation unit "RAD," with one million
RADS or a megarad being designated as "MR." A suitable radia -
tion dosage of high energy electrons is in the range of up to
about 12 MR, more preferably about 2 to about 9 MR.
The adhesive or tie layer will also comprise any poly
mer that will have excellent adhesion to the barrier layer and
the core layer or the abuse layer or both the core layer and
the abuse layer. The various polyethylenes includ~,ng the
polyethylene copolymers as described herein and the ethylene
vinyl acetate copolymers are useful as tie layers employed
according to the present invention. Preferably, the tie layer
comprises an anhydride modified alpha-olef in copolymer having
rubber moieties such as is contained in the core layer, dis
TM
cussed above. A preferred resin is T~:ror 1203 from Morton
International. Also suitable is BynelTM4107 from du Pont.
However, any of the various adhesives well known in the art of
film making may be employed, such as, for example, the Plexar
(TM) adhesives supplied by Chemplex Co.
The term "ethylene vinyl acetate copolymer" (EVA) as
used herein for a type of polyethylene refers to a copolymer
formed from ethyl:vw.:.~ and v,~njl a~~~~tate monomers wherein the
CA 02106889 2002-12-19
64536-832
ethylene derived units in the copolymer are present in major
amounts and the vinyl acetate derived units in the copolymer
are present in minor amounts. EVA is known not only for hav-
ing structural strength, as ethylene alpha-olefin polymer
does, but also for providing excellent adhesion to an adjacent
layer, which. decrease or even obviate the need for an "adhe-
sive." EVA copolymers can be hydrolyzed to ethylene vinyl
alcohol copolymers, (EVOH), which are employed principally as
a barrier layer according to the present invention. For en-
hanced orientability a modifier such as an ethylene/acrylic
esterfmaleic anhydride terpolymer may be blended with the
present EVOH barrier layer.
The term "oriented" is also used herein interchangeably
with the term "heat shrinkable," these terms designating a
material which has been stretched and set by cooling while
substantially retaining its stretched dimensions. An oriented
(i.e. heat shrinkable) material will tend to return to its
original unstretched (unextended) dimensions when heated to an
appropriate elevated temperature.
The cook-in film of the present invention is preferably
oriented and is formed by extrusion processes especially art-
known coextrusion methods. It is initially cooled by, for
example, cascading water quenching, after which it is reheated
to within its orientation temperature range and oriented by
stretching. The stretching to orient may be accomplished in
many ways such as, for example, by "blown bubble" techniques
or "tenter framing." These processes are well known to those
skilled in the art and refer to orientation procedures whereby
the material is stretched in the cross or transverse direction
(TD) and/or in the longitudinal or machine direction (MD).
After being stretched, the film is quickly quenched while
substantially retaining its stretched dimensions to cool the
film rapidly and thus set or lock in the oriented molecular
configuration.
16
~'~_~""''~
If a film having little or no orientation is desired,
e.g. nonoriented or non-heat shrinkable film, the film may be
formed from a nonorientable material or, if formed from an
orientable material may be "hot blown." In forming a hot
blown film, the film is not cooled immediately after extrusion
or coextrusion but rather is first stretched shortly after
extrusion while the film is still at an elevated temperature
abave the orientation temperature range of the material.
Thereafter, the film is cooled, by well known methods. Those
having skill in the art are familiar with this process and the
fact that the resulting film has substantially unoriented
characteristics. Other methods for forming unoriented films
are well known such as cast extrusion or cast coextrusion
methods.
As noted, the film layers may be formed by coextrusion,
with additional layers thereafter being extrusion coated there-
on to form multilayer films. Two multilayer tubes may also be
formed with one of the tubes thereafter being extrusion coated
or laminated onto the other. The extrusion coating method of
film formation is preferable to coextruding the entire film
when it is desired to subject one or more layers of the film
to a treatment which may be harmful to one or more of the
other layers. This may be done where it is desired to irradi-
ate one or more layers of a film with high energy electrons
where the film contains a baxrier layer of one or more
copolymers of vinylidene chloride (e.g., Saran(TM)), such as
vinylidene chloride and vinyl chloride or vinylidene chloride
and methyl acrylate as well as vinylidene chloride with ethyl
acrylate or acryl.onitrile.
Films of this type would, for example, comprise those
where the barrier layer is a Saran(TM) layer in addition to or
instead . of an EVOH layer . Those skilled in the art generally
recognise that irradiation with high energy electrons is gener-
ally harmful to such Saran(TM) barrier layer compositions, as
irradiation may degrade and discolor Saran(TM), making it turn
brown. Thus, if full coextrusion followed by high energy
5/920915.1/SPECFLDR
17
_ c~ °,'.i ~ ' .
electron irradiation of the multilayer structure is carried
out on a film having a barrier layer containing a Saran(TM)
layer, the irradiation should be conducted at low levels and
with care. Alternatively, this may be avoided by extruding a
first layer or layers, subjecting the layer or layers to high
energy electron irradiation and thereafter applying the
Saran(TM) barrier layer and, for that matter, other layers
(which may or may not have been irradiated) sequentially onto
the outer surf ace of the extruded previously irradiated tube.
This sequence allows for high energy electron irradiation of
the first layer or layers without subjecting the Saran(TM)
barrier layer to harmful discoloration.
Thus, as used herein the term "extrusion" or the term
°'extruding" is intended to include coextrusion, extrusion
coating, or combinations thereof.
The above general outline for manufacturing of films is
not meant to be all inclusive since such processes are well.
known as set forth in U. S. Patent Nos. 4,274,900; 4,229,241;
4,194,039; 4,188,443; 4,048,428; 3,821,182 and 3,022,543.
5/920915.1/SPECE'LDR
.. 1 8
~~.~~'~?j?~
EXAMPLES
An attempt was made to produce the following film struc-
tures. Tt was believed that the polyamide composition of the
internal layers would provide good elastic recovery properties
to a conventional inner sealant / tie / barrier / tie / outer
sealant structure. However, these comparative film structures
proved difficult and sometimes impossible to orient. Relative
percent thicknesses for each layer are also given.
manr.~ T
Layers
1 2 3 4 5 6 7
Tnner Tie Nylon Barrier Nylon Tie Out,
Sealant Seal:
Comp.
Ex. 1
EPC-1 R-AD PA(90%) EVOH PA(90%) R-AD EPC
APA (10%) APA (10%)
7.35% 8.82% 7.35% 8.82% 29.41% 29.41% 8.8
Comp.
Ex. 2
EPC-1 P-AD ~ PA(90%) EVOH PA(90%) P-AD EPC
APA ( :10 APA ( 10 % )
% )
29.41% 8.82% 7.35% 8.82% 7.35% 8.82% 29.4
Comp.
Ex. 3
EPC-1 R=AD PA(90%) EVOH PA(90%) R°AD EPC
APA (10%) APA (10%)
31.75% 9.52%- 3.97% 9.52% 3.97% 9.52% 31.7
Comp.
Ex. 4
EPC-1 R-AD PA(90%) EVOH-2 PA(90%) R-AD EPC
APA (10%) APA (10%)
31.75% 9.52% 3.97% 9.52% 3.97% 9.52% 31.7'
5/920915.1/SPECFLDR
19
~~.~~~'j?.~
comp.
Ex. 5
EPC-1 R-AD PA(85%) EVOH PA(85%) R-AD EPC
APA (15%) APA (15%)
31.75% 9.52% 3.97% 9.52% 3.97% 9.52% 31.7
Comp.
Ex. 6
EPC-1 R-AD PA(85%) EVOH(85%~A(85%)R-AD EPC
APA (15%) M (15%I~PA (15%)
31.75% 9.52% 3.97% 9.52% 3.97% 9.52% 31.7
Comp.
Ex. 7
EPC-1 R-AD PA(93%) EVOH-2 PA(93%) R-AD EPC
APA (7%) APA (7%)
31.75% 9.52% 3.97% 9.52% 3.97% 9.52% 31.7
Comp.
Ex. 8
EPC-1 P-AD PA(90%) EVOH-2 PA(90%) P-AD EPC
APA (10%) APA (10%)
30.30% 11.36% 3.79% 9.09% 3.79% 11.36% 30.3
comp.
Ex. 9
EPC-1 P-AD PA(90%) EVOH-2 PA(90%) P-AD EPC
APA ( 10% APA ( 10% )
)
31.50% 11.81% 1.97% 9.45% 1.97% 11.81% 31.5
The following film structures, all containing a
blend of a propylene-based copolymer and an ethylene alpha-
olefin in the sealant were readily processed with little or
no difficulty in orientation. It should be noted that the
structures of the present Examples include polyamide-contain-
ing layers of comparable thicknesses to those of Comparative
Examples 1 - 9 above. In those earlier structures the
polyamide was split into twn separate layers to sandwich the
barrier layer and to provide a palindromic, film structure.
It was believed that a symmetrical structure would preclude
curling. However, for the present Examples it was determined
that the stiffness of the barrier layer balanced that of a
single polyamide-containing layer to prevent curling.
5/920915.1/SPECFLDR
,. ,. , ?_ 0
f-, p cu~
'_ ;.i ;. ~ it
TABLE II
Layers
1 2 3 4 5 6
Inner Tie Nylon Barrier Tie Outer
Sealant Sealant
EX. 1
EPC-1(75%) R-AD CPA-1(80%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA (20%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 2
EPC-1(75%) R-AD CPA-1(80%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA (20%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 3
EPC-1(75%) R-AD CPA-1(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA (10%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 4
EPC-1(75%) R-AD CPA-1(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA (10%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 5
EPC1(75%) ,R-AD CPA-2(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA (10%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 6'
EPC-1(75%) R-AD CPA-2(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA (10%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 7
EPC-1(75%) R-AD CPA-1(60%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-2 (40%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 8
EPC-1(75%) R-AD CPA-1(60%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-2 (40%) M (115%) EAO-1(25%)
24.24% 15.'15% 12.90% 9.09% 15.15%24.24%
Ex. 9
EPC-1(75%) R-AD PA-1(60%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-1 (40%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 10
EPC-1(75%) R-AD PA-1(60%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-1 (40%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
5/920915.1/S~ECFLDR
21
,e ~ !' f '
C ~ f .,? y f
~ .)_ 4,~ ~.~ ,. J .J e~
Ex. 11
EPC-1(75%) R-AD PA-1(60%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-2 (40%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 12
EPC-1(75%) R-AD PA-1(60%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-2 (40%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 13
EPC-1(75%) R-AD PA-1(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA (10%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 14
EPC-1(75%) R-AD PA-1(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA (10%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.240
Ex. 15
EPC-1(75%) R-AD CPA-1 EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 16
EPC-1(75%) R-AD CPA-1 EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) . M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 17
EPC-1(75%) R-AD CPA-3 EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) M (15%) EAO°1(25%)
25.00% 15.63% 9.37% 9.37% 15.63%25.00%
Ex. 18
EPC-1(75%)R-AD CPA-1(70%) EVOH(85%)R-ADEPC1(75%)
EAO1(25%) CPA-4(30%) M (15%) EAO1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 19
EPC1(75%) R-AD CPA-4(50%) EVOH(85%)R-ADEPC-1(75%)
EAO1(25%) CPA-1(500) M (15%) EAO-1(25%)
25.00% 15.63% 9.37% 9.37% 15.63%25.00%
Ex. 20
EPC-1(750)R-AD CPA-4(70%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-1(30%) M (15%) EAO-1(25%)
25.00% 15.63% 9.37% 9.37% 15.63%25.00%
Ex. 21
EPC-1(75%) R-AD PA-2(60%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-4(40%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
5/920915.1/SPECFLDR
22
.. .
~~ 4/
Ex. 22
EPC-1(75%)R-AD PA-2(60%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) CPA-4(40%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.240
Ex. 23
EPC-1(75%)R-AD CPA-3(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA(10%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 24
EPC-1(75%)R-AD CPA-2(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA(10%) M (15%) EAO-1(25%)
25.81% 16.13% 6.45% 9.68% 16.13%25.81%
Ex. 25
EPC-1(75%) R-AD CPA-2(90%) EVOH(85%)R-ADEPC-1(75%)
EAO-1(25%) APA(10%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 26
EPB(75%) R-AD CPA-3(40%) EVOH(85%)R-AD EPB(75%)
EAO-1(25%) GPA°1(60%) M (15%) EAO-1(25%)
24.24% 15.15% 12.90% 9.09% 15.15%24.24%
Ex. 27
EPC-2(75%) R-AD CPA-3(40%) EVOH(85%)R-ADEPC-2(75%)
EAO-1 ( 25 % ) ~ CPA-1 ( 60 % ) M ( 15 % ) EAO-1 ( 25 % )
24.24% 15.15% 22.90% 9.09% 15.15%24.24%
Ex. 28
EPC-2(75%) R-AD CPA--4 EVOH R-ADEPC-2(75%)
EAO-1(25%) EAO-1(25%)
23.33% 16.66% 13.33% 6.66% 16.66%23.33%
Ex. 29
EPC-2(75%) R-AD CPA-4(70%) EVOH R-ADEPC-2(75%)
EAO-1(25%) CPA-1(30%) EAO-1(25%)
23.33% 16.66% 13.33% 6.66% 16.66%23.33%
Ex: 30
EPB(75%) R-AD CPA-4(70%) EVOH R-AD EPB(75%)
EAO-1(25%) CPA-1(30%) EAO-1(25%)
22.67% 17.00% 12.59% 6.17% 16.37%25.19%
Ex. 31
EPB(75%) R-AD CPA-4 EVOH R-AD EPB(75%)
EAO-1(25%) EAO-1(25%)
23.12% 16.87% 12.50% 6.25% 16.25%25.00%
Ex. 32
EPB(75%) R-AD CPA-4 EVOH R-AD EPB(75%)
EAO-1(25%) EAO-1(25%)
27.7$% 13.89% 11.11% 5.55% 13.89%27.78%
5/920915.1/SPECFI~DR
23
CA 02106889 2002-12-19 '
64536-832
Ex. 33
EPC-2 ( 60 a ) R-AD CPA-1 ( '>0 a ) EVOH R-ADEPC-2 ( 60 0 )
EAO-1(40%) CPA-4(500) EAO-1(40x)
26 . 44°, 14 _ 67.° 7 . 6'p'~ 6 _ 75° __I5 . 31°
29 . 23 ~ _
Ex. 34
EPC-2 ( 60 0 ) R-AD PA-1 ( 90 0 ) EVOI3 R-ADEPC-2 ( 60 0 )
EAO-1 ( 40 0 ) CPA-1 ( 1_0 0 ) EAO-1 ( 40 ~ )
26 . 44°-" ' 14 . 61. ~ -l . 6'-~° 6 _ 75° 1.5 .
31.° 29 . 23 0
In the Foregoing Exampl_~s ~~he following materials
were employed:
EPC-1 F'inaM8473 sold by Fina, a
prorylen~/ethyl~ne copolymer
wit_.h 3 . I_ ~ ethylene .
EPC-Z Eltn.TMP KJ 409 sold by Solway,
a pr~p~y'_~ne ethy l ene copolymer
with 3 . 2~~; ethylene .
EPB w531Dr~old by Sumitomo, an
ethylene propy7_ene butene
copolyrner .
R-AD an ethylene alpha-olefin
copolymer, Tymor('"M) 1203 sold
by Morton INtl., rubber and
malc~~_c anhydride grafted.
P-AD F3ynelME30Z sold by Dupont, an
anhyctrl_de c; rafted polypropylFne.
1M
PA or PA-1 8209 F'2d Sold by Al Lied, Nylon
6.
TM
PA-2 Vestamid 1,1940 Natural so~'d by
Hul:~ America, Inc. contains
Irc~anox 1098, an antioxidant,
anti calcium stearate.
APA
Celar PA 3526 sold by DuPcnt,
' an amorphous nylon.
TM
CPA-1 Xh 3303 sold by E~mser, a
Nylon 6 G/6 10.
TM
CPA-2 CF62BSE sold by Emser, a
Nylon C / 0 9 .
'1'M
CPA-3 Ultra.mid C35 sold by HASF , a
Nylon 666..
TM
CPA-4 Grilcn ~~'6S sold by Emser, a
Nylon 6/12.
~4
CA 02106889 2002-12-19
64536-832
EVOH Ethylene vinyl.~Mlcohol
copolymer, Evai~ a~C-E105A sold
by Eval of America.
EVOH-2 ECG--156B~ sold by Eval of
America, an ethylene vinyl alco-
hol copolymer.
M ~ an ethylene - acrylic ester -
maleic anhydride copolymer modi-
fier.
EAO-1 Tafmer A-4085 sold by Mitsui, a
homogeneous ethylene butene
copolymer, density = 0.885 g/cc.
CA 02106889 2002-12-19
64536-832
EAO-1 Lower density ethylene
alpha-olefin copolymer ATTANE(TM)
4203, sold 'ay Dow Chemical,
ethylene polymerized with 1-
octene having a den=pity of
0.905 g/cc
EAO-2 ethylene 1-octene copolymer,
Dowlex(TM) 2045 ~~old by Dow
Chemical
EBA EA 705-009TM so7_d by Quantum
Chemical Company, e-~.hylene
butyl acrvlate copolymer having
a butyl acrylate content oz 50
by weight.
COLOR-1 whi~._o c~i-or concentrate, EPE
102.4-C~~:>old by Teknor Color, a
50 o TiOzI 50 o LDPE blend.
The foregoing description of preferred embodiments
of the invention have been presented for purpose: of illustra-
tion and description. It is not intended to be exhaustive or
to limit the invention to the prec:i.se form disclosed, and
modifications and variations are possible in light of the
above teachings or may be acquired from practice of the inven-
tion- The embodiments were chosen and described in order to
explain the principles of the invention and its practical
application to enable one skilled in the art to utilize the
invention in various embodiments and with various modifica-
tions as are suited to the particular use contemplated. I'or
example, although backseamed casings are discussed herein,
thermoplastic films employing the present seal layer and
other strucr~ural layers are also within the scope cf the
present invention. It is intended that the scope of the
invention be defined by the claims appended hereto, an~vtheir
equivalents.
26
