Note: Descriptions are shown in the official language in which they were submitted.
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BACKSEAMED CASING AND PACKAGED PRODUCT INCORPORATING SAME
This application is a divisional of Canadian
Patent Application Serial No. 2,233,948 filed Oct. 7, 1996.
Field of the Invention
The present invention relates generally to
multilayer films, and particularly to multilayer films
suitable for use in backseamed casings for packaging meat
products. The present invention is particularly related to
backseamed casings suitable for packaging protein-containing
food products in which the film adheres to the food product,
and especially to those having a relatively high protein
content, also called 'low-fat' food products, such as
poultry, ham, roast beef, etc. The present invention is
also directed to packages.
Background of the Invention
Processed meat products, such as poultry and ham,
are often packaged in a flexible, thermoplastic, heat-
shrinkable film tubing commonly referred to as a casing.
Although some casings have a lay-flat width of 6-20 inches,
some products, such as ham, etc., are quite often packaged
in a casing of smaller lay-flat width, e.g., a width of from
3 to 6 inches. Such casings often may need to have a
precisely-controlled width, because the packages are stated
as having a given weight, which is uniform among packages,
and the packages also have product sliced at uniform
intervals, with each package containing the same number of
slices. Thus, variations in casing width can result in both
an undesirable degree of variation in overall package
weight, as well as an undesirable degree of variation in
slice weights.
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Thus, there is a need for a casing having a small
and uniform diameter. However, it is relatively difficult
to make a narrow width, heat-shrinkable seamless casing
having a precisely controlled width, using a commercially
feasible process. Consequently, there is a need for some
other process for making a narrow-width, precisely-width-
controlled casing.
Some backseamed casings are known to be casings of
small and uniform diameter. Small-diameter backseamed
casings are known which have a precisely controlled casing
width, i.e., a lay-flat width independent of film extrusion
variations. In the production of backseamed casings
(e.g., using a backseaming machine such as a Nishibe2m
HSP-250-SA backseaming machine obtained from Nishibe Kikai
Co. Ltd. of Nagoya, Japan), a flat sheet of film is folded
longitudinally by passage over a "forming shoe". A forming
shoe is a part of the backseaming machine which the film is
passed under and around, i.e., so that the initially flat
film is reconfigured as a tube, having a longitudinal
overlap and seal therealong (lap-sealed backseamed casing),
or with film longitudinal edges abutted against one another
(butt-sealed backseamed casing), with the width of the tube
being determined by the circumference of the forming shoe.
A longitudinal lap or butt seal is then applied while the
film is between the forming shoe and a sealing device,
resulting in a lap-sealed backseamed casing, or a butt-
sealed backseamed casing. Butt-seal casings utilize a butt-
seal tape sealed to the inside or the outside surface of the
casing film, along both sides of the abutting longitudinal
seam of the casing film. In either event, the resulting
tubing, termed a "backseamed casing," is sealed or clipped
at its ends after being filled with a meat product. For
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some uses, the meat product is thereafter cooked while in
the backseamed casing.
It would be desirable to provide a highly uniform,
small diameter backseamed casing suitable for cook-in end
use, the casing being made from a film which adheres to
high-protein meat products, such as certain grades of ham
and turkey. Of course, it would also be desirable to
provide the backseamed casing with a backseam seal which
survives the cook-in process.
It is known that a polar surface is needed for
adhesion of a film to a meat product. Adhesion of the film
to the meat is frequently needed in order to prevent
"purge", i.e., "cook-out", which can occur during the
cooking of the meat packaged in the film if the film does
not adhere to the meat during cook-in. A polar film surface
can be provided by using: (a) polar resin in the film layer
in contact with the meat, and/or (b) surface modification,
such as corona treatment, of the film surface in contact
with the meat. Typically, polar polymers used for meat
adhesion include: ethylene/unsaturated acid copolymer,
anhydride-containing polyolefin, and polyamide.
Film-to-meat adhesion is known to be enhanced by
corona treatment of the surface of the film to which the
meat is to be adhered. However, corona treatment alters the
film surface in a manner which can, on occasion, result in
an inferior seal, i.e., a seal more likely to leak than if
the film surface is not corona treated. This "leaky seal
problem" can be avoided by "buffing off" the corona
treatment in the area of the seal, so that the advantageous
effects of the corona treatment, i.e., greater meat
adhesion, can be retained on the majority of the meat-
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contact surface of the film, while at the same time
avoiding, in the area of the seal, the seal-quality problem
caused by the corona treatment. However, the buffing step
is undesirable, as it is an additional processing step which
renders the casing manufacture more complex and costly.
Furthermore, the buffing step is frequently inconsistent.
Since the backseaming process is generally carried
out after the corona treatment, shrinkage of the film
against the forming shoe (during backseaming), coupled with
forwarding the film over the forming shoe after shrinkage,
results in the rubbing of the film against the forming shoe
edges. This rubbing reduces or destroys corona treatment,
at least in the area in which the film rubs against the
forming shoe. As a result, backseamed casings containing
corona treated films can exhibit purge at the locations at
which the film rubs against the forming shoe. Furthermore,
corona treatment can be inconsistent, at least with respect
to prevention of purge for products having an intermediate
protein content. It would be desirable that the casing film
has a consistent and adequate level of protein/meat
adhesion. As a result, it would be desirable to provide a
corona-treatment-free backseamed casing which prevents purge
from products relatively high in protein, where the adhesion
of the casing film to the meat product is uniform over the
film.
Thus, it would be desirable to provide a
backseamed casing of small and uniform diameter which is
heat-shrinkable and suitable for cook-in end use, exhibits
good purge-resistance and good seal strength, can be
economically manufactured, does not produce significant meat
pull-off upon being stripped from a cooked meat product, and
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which provides a good oxygen barrier, in order to provide
good shelf life to the cooked meat product.
Heat-shrinkable films having an outer layer
capable of providing meat adhesion, which are otherwise
suitable for use as backseamed casings, have been found to
have the undesirable characteristic of necking down on the
forming shoe during the backseaming process. The necking
down on the forming shoe is believed to be due to shrinkage
of the film during the heat sealing step of the backseaming
operation. That is, the heat sealing step can cause
substantial film shrinkage in an area extending outward from
the seal, causing the edges of the casing to neck down on
the forming shoe. The result of necking down is a casing
having "ruffled edges", i.e., visible nonuniformities in the
casing. In an extreme case, necking down results in the
rupture of the film, as the shrinking of the film against
the forming shoe places so much force on the film that the
film ruptures. Thus, it would be desirable to provide a
casing film which does not shrink down (i.e., "neck down")
on the forming shoe during the backseaming operation.
Summary of the Invention
It has been discovered that the presence of an
inner layer comprising a polyamide, preferably a high
modulus polyamide, provides, if the polyamide layer makes up
at least 5 percent of the total film thickness, a film which
does not neck down on the forming shoe during the
backseaming operation. Although the reasons why the inner
polyamide layer prevent necking down on the forming shoe are
not currently known with certainty, it is believed that
various factors, including heat transfer, shrink
characteristics, etc. bring about the discovered advantage
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of not necking down on the forming shoe. Furthermore, the
inner polyamide layer also helps to provide a better quality
casing film by making the casing film easier to orient,
facilitating faster backseaming speeds, and also imparting
enhanced seal strength, toughness, pin-hole resistance and
elastic recovery to the casing film.
It has also been discovered that in the case of
anhydride-containing polyolefin, if the anhydride
functionality is of the order of 1 weight percent or less,
the polymer often does not provide adequate meat adhesion to
intermediate-protein-containing meat products, or low-
protein-containing meat products. On the other hand,
polymers such as polyamide can, in some instances, provide
too much meat-adhesion and tend to pull meat off during
unpackaging of the meat, thereby destroying the smooth
surface desired upon separating the casing film from the
cooked meat product, and also contributing to yield loss.
Polyamides are also relatively expensive polymers. Thus, it
would be desirable to provide a casing having a film
providing adequate meat adhesion to prevent purge, while
being able to strip the film from the meat without meat
pull-off due to too much adhesion of the film to the cooked
meat product. However, it has been found that adequate meat
adhesion can be obtained using an anhydride-containing
polyolefin having an anhydride functionality of at least
1 percent.
The parent Canadian Patent Application Serial
No. 2,233,948 invention is directed to a backseamed casing
comprising a heat-shrinkable casing film. The heat
shrinkable film comprises a first layer, a second layer, a
third layer and a fourth layer, with the first and third
layers being outer layers and the second and fourth layers
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being between the first layer and the third layer. The
first outer layer serves as an inside casing layer, and
comprises a first polyolefin. The first polyolefin
comprises at least one member selected from the group
consisting of: (i) ethylene/unsaturated acid copolymer,
propylene/unsaturated acid copolymer, and butene/unsaturated
acid copolymer, wherein the unsaturated acid is present in
an amount of at least 4 weight percent, based on the weight
of the copolymer; and (ii) anhydride-containing polyolefin
comprising an anhydride-functionality, wherein the anhydride
functionality is present in an amount of at least 1 weight
percent, based on the weight of the anhydride-containing
polyolefin. The second layer comprises at least one member
selected from the group consisting of polyester, and first
polyamide. The third layer serves as an outside casing
layer, and comprises at least one member selected from the
group consisting of second polyolefin, polystyrene, and
second polyamide. The second layer has a thickness of at
least 5% of a total thickness of the heat-shrinkable casing
film. The fourth layer serves as an 02 layer and comprises
at least one member selected from the group consisting of
ethylene/vinyl alcohol copolymer, polyvinylidene chloride,
polyamide, polyalkylene carbonate, and polyester.
According to a first aspect of the present
invention there is provided a backseamed casing comprising a
heat-shrinkable casing film comprising: (A) a first outer
layer serving as an inside casing layer, the first outer
layer comprising a first polyolefin, the first outer layer
having a surface energy level of less than about
34 dynes/cm, with the proviso that a blend of
propylene/ethylene copolymer and homogeneous ethylene/alpha-
olefin copolymer having a density of less than 0.90 g/cc
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does not make up the majority of the first outer layer;
(B) a second layer comprising at least one member selected
from the group consisting of polyester and first polyamide;
(C) a third layer serving as an outside casing layer, the
third outer layer comprising at least one member selected
from the group consisting of a second polyolefin,
polystyrene and second polyamide; and wherein the second
layer is between the first layer and the third layer, and
the second layer has a thickness of at least about 5% of a
total thickness of the heat-shrinkable casing film.
In a lap-sealed backseamed casing according to the
invention, preferably the first polyolefin has a vicat
softening point of at least 70 C, more preferably at least
80 C, in order to provide a desired level of seal strength.
However, in a butt-sealed backseamed casing according to
this third aspect of the present invention, the vicat
softening point of the first polyolefin may be less
critical. More preferably, the first polyolefin is a
relatively non-polar polymer, preferably having a surface
energy level of less than 32 dynes/cm.
The second layer preferably comprises the first
polyamide. More preferably, the first polyamide comprises
at least one member selected from the group consisting of
polyamide 6, polyamide 66, polyamide 9, polyamide 10,
polyamide 11, polyamide 12, polyamide 69, polyamide 610,
polyamide 612, polyamide 61, polyamide 6T, and copolymers
thereof. Still more preferably, the first polyamide
comprises at least one member selected from the group
consisting of polyamide 6, polyamide 66 and
copolyamide 6/66.
Preferably, the second layer and the fourth layer
are directly adhered.
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As a second aspect, the present invention is
directed to a package comprising a cooked meat product
within a backseamed casing. The backseamed casing is
according to the first aspect of the present invention
described herein, and the cooked meat product is adhered to
a meat-contact surface of the casing film.
If a non-corona treated backseamed casing
(or equivalent thereof) according to the first aspect of the
present aspect is used, the cooked meat product preferably
comprises at least one member selected from the group
consisting of turkey and fish, wherein the meat product
comprises fat in an amount of from 1 to 10 weight percent,
preferably 2 to 6 percent, and more preferably from
3 to 5 percent.
Brief Description of the Drawings
Figure 1 illustrates a cross-sectional view of a
lap-seal backseamed casing in accord with the present
invention.
Figure 2 illustrates an enlarged cross-sectional
view of a first preferred casing film suitable for use in
the lap-seal backseamed casing illustrated in Figure 1.
Figure 3 illustrates an enlarged cross-sectional
view of a second preferred casing film suitable for use in
the lap-seal backseamed casing illustrated in Figure 1.
Figure 4 illustrates an enlarged cross-sectional
view of a third preferred casing film suitable for use in
the lap-seal backseamed casing illustrated in Figure 1.
Figure 5 illustrates a cross-sectional view of a
butt-seal backseamed casing in accord with the present
invention.
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Figure 6 illustrates an enlarged cross-sectional
view of a first preferred casing film suitable for use in
the butt-seal backseamed casing illustrated in Figure S.
Figure 7 illustrates an enlarged cross-sectional
view of a first preferred butt-seal tape film suitable for
use in the butt-seal backseamed casing illustrated in
Figure 5.
Figure 8 illustrates a schematic view of a process
for making a preferred heat-shrinkable casing film and/or
butt-seal tape film, for use in a backseamed casing in
accord with the present invention.
Figure 9 illustrates a perspective view of a first
package according to the present invention.
Figure 10 illustrates a perspective view of a
second package according to the present invention.
Detailed Description of the Invention
As used herein, the term "package" and the phrase
"packaged product" refer to an article in which a product
(preferably a food product, more preferably a meat-
containing food product) is encased in a packaging film.
As used herein, the phrase "lay-flat film" refers
to a film that has been extruded as a wide, thin-walled,
circular tube, usually blown, cooled, then gathered by
converging sets of rollers and wound up in flattened form.
The phrase "lay-flat width", refers to half of the
circumference of the inflated film tube.
As used herein, the phrase "backseamed casing"
refers to any casing (a tubular film) having a longitudinal
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seal. For example, a lap-seal backseamed casing can be
formed: by folding a film strip over a forming shoe of a
horizontal sealing machine, and applying a longitudinal seal
thereto where the film overlaps, e.g. using a Nishibe Model
HSP-250-SA sealing machine; or a TotaniTM Model FD-350C
sealing machine obtained from Totani Giken Kogyo Co., Ltd.,
of Kyoto, Japan; or, by folding a film strip over a forming
shoe of a vertical form fill and seal machine, and applying
a longitudinal seal thereto where the film overlaps,
e.g., using an ONPACK-2002 (TM) sealing machine, obtained
from Orihiro Company, Ltd., of Tomioka City, Japan. A lap-
sealed casing could also use a tape-film in between the
areas where the film overlaps, to facilitate sealing. A
butt-seal backseamed casing can be formed: by folding a film
strip over a forming shoe of a horizontal sealing machine,
with opposing longitudinal edges abutting one another,
i.e., in non-overlapping relation to one another; and
thereafter, by applying a butt-seal tape film over the
abutting edges, followed by sealing the butt-seal tape film
across and along the abutting edges, so that a sealed tube
is formed.
For the backseamed casings according to the
present invention, the composition in the second layer can
be present either in one or more layers of the casing film.
If the composition is present in more than one layer, the
layers are preferably so positioned as to provide reasonable
symmetry to the film, thus providing a relatively flat,
curl-free film.
Preferably, the backseamed casing according to the
present invention has a lay-flat width of at less than
10 inches; more preferably, from 1 to 10 inches, still more
preferably, from 2 to 8 inches; yet still more preferably,
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from 3 to 7 inches, and yet still even more preferably, from
4 to 6 inches. It is believed that for any given film to be
backseamed, the problem of necking down on the forming shoe
becomes worse as the lay-flat width of the casing is
reduced.
Heat-shrinkable multilayer films of the invention
preferably have a substantially symmetrical cross-section,
with respect to both layer thickness and layer chemical
composition, in order to provide the film with relatively
low curl. For example, for a 3-layer casing film according
to the backseamed casing of the present invention, the ratio
of a/b is preferably from 0.7-1.3, more preferably from
0.8-1.2, and even more preferably from 0.9-1.1; wherein,
'a' is the thickness of the first outer layer and 'b' is the
thickness of the second outer layer. For a preferred six-
layer casing film in accordance with the backseamed casing
of the present invention, the ratio of the sums of the
thickness of the first layer plus the fifth layer to the sum
of the second layer plus the sixth layer is preferably from
0.7-1.3; more preferably from 0.8 to 1.2; and still more
preferably, from 0.9 to 1.1.
The heat-shrinkable casing film according to the
present invention preferably has a free shrink of from
5-70 percent in one or both directions (i.e., longitudinal
direction "L", also referred to as "machine direction", and
transverse direction, "T") at 185 F, determined according to
ASTM D 2732; more preferably, from 10-50 percent at 185 F;
still more preferably, from 15-35 percent at 86 C (185 F).
Preferably, the casing film is biaxially oriented, and
preferably the film has a free shrink, at 85 C (185 F), of
at least 10 percent in each direction (L and T); more
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preferably, at least 15 percent in each direction.
Preferably, the casing film has a total free shrink of from
30 to 50 percent (L+T) at 85 C (185 F). For a butt seal
backseamed casing, the butt seal tape film can be either a
heat-shrinkable film or a non-heat-shrinkable film.
As used herein, the term "sealed" refers to any
and all means of closing a package, such as heat sealing via
hot air and/or heated bar, ultrasonic, radio frequency
sealing, and even the use of clips on, for example, a
shirred casing, etc. As used herein, the phrase "heat seal"
refers to a seal formed by contacting the film with a hot
element, e.g., using a hot bar, hot wire, hot air, etc.
Preferably, the seal in the backseamed casing
according to the present invention has a seal strength of at
least 3 pounds per inch (as measured on an *Instron, per
ASTM F88); more preferably, from 0.893 - 17.86 kg/cm
(5 to 100 lb/in); still more preferably,
from 1.25 - 8.93 kg/cm (7 to 50 lb/in); yet still more
preferably, from 1.786 - 5.358 kg/cm (10 to 30 lb/in); and
yet still more preferably, from 2.679 - 3.572 kg/cm
(15 to 20 lb/in).
As used herein, the phrase "butt seal" refers to a
seal formed by butting opposing film edges together and
thereafter sealing regions in the vicinity of the abutted
edges to a butt seal tape, as shown in Figure 5.
As used herein, the phrase "lap seal" refers to a
seal formed by lapping a film over itself to form a package
by sealing an inside surface of the film to an outside
surface of the film, as shown in Figure 4.
*Trade-mark
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As used herein, the phrase "meat-contact layer",
refers to a layer of a multilayer film which is in direct
contact with the meat-containing product packaged in the
film. The meat-contact layer is an outer layer, in order to
be in direct contact with the meat product. The meat-
contact layer is an inside layer in the sense that in the
packaged meat product, the meat-contact layer is the
innermost film layer in direct contact with the food.
As used herein, the phrase "meat-contact surface"
refers to a surface of a meat-contact layer which is in
direct contact with the meat in the package.
As used herein, the phrase "meat-adhesion", and
"adhered", refer to maintaining direct contact between the
meat surface and the meat-contact surface of the film, so
that there is an absence of fat or a substantial amount of
free moisture, e.g., juices emitted outside of the meat
product, commonly referred to as "purge". In general, there
is an absence of a substantial amount of free moisture if
the level of free moisture is from 0 to 2%, based on the
weight of the meat product before cooking. Preferably the
amount of free moisture is from 0 to 1%, more preferably,
0 to 0.5%, and still preferably from 0 to 0.1 percent based
on the weight of the meat product before cooking.
As used herein, the phrase "cook-in" refers to the
process of cooking a product packaged in a material capable
of withstanding exposure to long and slow cooking conditions
while containing the food product, for example cooking at
57 C to 121 C (i.e, 135 F-250 F) for 2-12 hours, preferably
57 C to 95 C (i.e, 135 F-203 F) for 2-12 hours. Cook-in
packaged foods are essentially pre-packaged, pre-cooked
foods which may be directly transferred to the consumer in
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this form. These types of foods may be consumed with or
without warming. Cook-in packaging materials maintain seal
integrity, and in the case of multilayer films are
delamination resistant. Cook-in films may also be heat-
shrinkable under cook-in conditions so as to form a tightly
fitting package. Cook-in films preferably have a tendency
for adhesion to the food product, thereby preventing "cook-
out", i.e., "purge", which is the collection of juices
between the outer surface of the food product and the meat-
contact surface of the film, i.e., the surface in direct
contact with the meat. Additional optional characteristics
of films for use in cook-in applications include
delamination-resistance, low 02 permeability, heat-
shrinkability representing 20-50% biaxial shrinkage at 85 C
(185 F), and optical clarity.
As used herein, "EVOH" refers to ethylene vinyl
alcohol copolymer. EVOH includes saponified or hydrolyzed
ethylene vinyl acetate copolymers, and refers to a vinyl
alcohol copolymer having an ethylene comonomer, and prepared
by, for example, hydrolysis of vinyl acetate copolymers.
The degree of hydrolysis is preferably at least 50% and more
preferably at least 85%.
As used herein, the term "barrier", and the phrase
"barrier layer", as applied to films and/or film layers, is
used with reference to the ability of a film or film layer
to serve as a barrier to 02.
As used herein, the term "lamination", and the
phrase "laminated film", refer to the process, and resulting
product, made by bonding together two or more layers of film
or other materials. Lamination can be accomplished by
joining layers with adhesives, joining with heat and
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pressure, corona treatment, and even spread coating and
extrusion coating. The term laminate is also inclusive of
coextruded multilayer films comprising one or more tie
layers.
As used herein, the term "oriented" refers to a
polymer-containing material which has been stretched at an
elevated temperature (the orientation temperature), followed
by being "set" in the stretched configuration by cooling the
material while substantially retaining the stretched
dimensions. Upon subsequently heating unrestrained,
unannealed, oriented polymer-containing material to its
orientation temperature, heat shrinkage is produced almost
to the original unstretched, i.e., pre-oriented dimensions.
More particularly, the term "oriented", as used herein,
refers to oriented films, wherein the orientation can be
produced in one or more of a variety of manners.
As used herein, the phrase "orientation ratio"
refers to the multiplication product of the extent to which
the plastic film material is expanded in several directions,
usually two directions perpendicular to one another.
Expansion in the machine direction is herein referred to as
"drawing", whereas expansion in the transverse direction is
herein referred to as "stretching". The degree of
orientation is also referred to as the orientation ratio, or
sometimes as the "racking ratio".
As used herein, the term "monomer" refers to a
relatively simple compound, usually containing carbon and of
low molecular weight, which can react to form a polymer by
combining with itself or with other similar molecules or
compounds.
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As used herein, the term "comonomer" refers to a
monomer which is copolymerized with at least one different
monomer in a copolymerization reaction, the result of which
is a copolymer.
As used herein, the term "polymer" refers to the
product of a polymerization reaction, and is inclusive of
homopolymers, copolymers, terpolymers, etc. In general, the
layers of a film can consist essentially of a single
polymer, or can have still additional polymers blended
therewith.
As us-ed herein, the term "homopolymer" is used
with reference to a polymer resulting from the
polymerization of a single monomer, i.e., a polymer
consisting essentially of a single type of repeating unit.
As used herein, the term "copolymer" refers to
polymers formed by the polymerization reaction of at least
two different monomers. For example, the term "copolymer"
includes the copolymerization reaction product of ethylene
and an alpha-olefin, such as 1-hexene. However, the term
"copolymer" is also inclusive of, for example, the
copolymerization of a mixture of ethylene, propylene,
1-hexene, and 1-octene.
As used herein, the term "polymerization" is
inclusive of homopolymerizations, copolymerizations,
terpolymerizations, etc., and includes all types of
copolymerizations such as random, graft, block, etc. In
general, the polymers, in the films used in accordance with
the present invention, can be prepared in accordance with
any suitable polymerization process, including slurry
polymerization, gas phase polymerization, and high pressure
polymerization processes.
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As used herein, the term "copolymerization" refers
to the simultaneous polymerization of two or more monomers.
As used herein, a copolymer identified in terms of
a plurality of monomers, e.g., "propylene/ethylene
copolymer", refers to a copolymer in which either monomer
copolymerizes in a higher weight or molar percent. However,
the first listed monomer preferably is polymerized in a
higher weight percent than the second listed monomer, and,
for copolymers which are terpolymers, quadripolymers, etc.,
preferably, the first monomer copolymerizes in a higher
weight percent than the second monomer, and the second
monomer copolymerizes in a higher weight percent than the
third monomer, etc.
As used herein, terminology employing a "/" with
respect to the chemical identity of a copolymer (e.g., "an
ethylene/alpha-olefin copolymer"), identifies the comonomers
which are copolymerized to produce the copolymer. Such
phrases as "ethylene alpha-olefin copolymer" is the
respective equivalent of "ethylene/alpha-olefin copolymer."
As used herein, the phrase "heterogeneous polymer"
refers to polymerization reaction products of relatively
wide variation in molecular weight and relatively wide
variation in composition distribution, i.e., polymers made,
for example, using conventional Ziegler-Natta catalysts.
Heterogeneous polymers are useful in various layers of the
film used in the present invention. Such polymers typically
contain a relatively wide variety of chain lengths and
comonomer percentages.
As used herein, the phrase "heterogeneous
catalyst" refers to a catalyst suitable for use in the
polymerization of heterogeneous polymers, as defined above.
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Heterogeneous catalysts are comprised of several kinds of
active sites which differ in Lewis acidity and steric
environment. Ziegler-Natta catalysts are heterogeneous
catalysts. Examples of Ziegler-Natta heterogeneous systems
include metal halides activated by an organometallic co-
catalyst, such as titanium chloride, optionally containing
magnesium chloride, complexed to trialkyl aluminum and may
be found in patents such as U.S. Patent No. 4,302,565, to
GOEKE, et. al., and U.S. Patent No. 4,302,566,
to KAROL, et. al.
As used herein, the phrase "homogeneous polymer"
refers to polymerization reaction products of relatively
narrow molecular weight distribution and relatively narrow
composition distribution. Homogeneous polymers are useful
in various layers of the multilayer film used in the present
invention. Homogeneous polymers exhibit a relatively even
sequencing of comonomers within a chain, the mirroring of
sequence distribution in all chains, and the similarity of
length of all chains, and are typically prepared using
metallocene, or other single-site type catalysis.
More particularly, homogeneous ethylene/alpha-
olefin copolymers may be characterized by one or more
methods known to those of skill in the art, such as
molecular weight distribution (Mw/Mn), composition
distribution breadth index (CDBI), and narrow melting point
range and single melt point behavior. The molecular weight
distribution (Mw/Mn), also known as polydispersity, may be
determined by gel permeation chromatography. The
homogeneous ethylene/alpha-olefin copolymers useful in this
invention will have a(Mw/Mõ) of less than 2.7. Preferably,
the (Mw/Mn) will have a range of 1.9 to 2.5. More
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preferably, the (Mw/Mn) will have a range of 1.9 to 2.3. The
composition distribution breadth index (CDBI) of such
homogeneous ethylene/alpha-olefin copolymers will generally
be greater than 70 percent. The CDBI is defined as the
weight percent of the copolymer molecules having a comonomer
content within 50 percent (i.e., plus or minus 50%) of the
median total molar comonomer content. The CDBI of linear
polyethylene, which does not contain a comonomer, is defined
to be 100%. The Composition Distribution Breadth Index
(CDBI) is determined via the technique of Temperature Rising
Elution Fractionation (TREF). CDBI determination clearly
distinguishes the homogeneous copolymers used in the present
invention (narrow composition distribution as assessed by
CDBI values generally above 70%) from heterogeneous polymers
such as VLDPEs available commercially which generally have a
broad composition distribution as assessed by CDBI values
generally less than 55%. The CDBI of a copolymer is readily
calculated from data obtained from techniques known in the
art, such as, for example, temperature rising elution
fractionation as described, for example, in Wild et. al.,
J. Poly. Sci. Poly. Phys. Ed., Vol. 20, p.441 (1982).
Preferably, the homogeneous ethylene/alpha-olefin copolymers
have a CDBI greater than 70%, i.e., a CDBI of from
70% to 99%. In general, the homogeneous ethylene/alpha-
olefin copolymers in the multilayer films of the present
invention also exhibit a relatively narrow melting point
range, in comparison with "heterogeneous copolymers",
i.e., polymers having a CDBI of less than 55%. Preferably,
the homogeneous ethylene/alpha-olefin copolymers exhibit an
essentially singular melting point characteristic, with a
peak melting point (Tm), as determined by Differential
Scanning Colorimetry (DSC), of from 60 C to 110 C.
Preferably, the homogeneous copolymer has a DSC peak Tm of
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from 90 C to 110 C. As used herein, the phrase "essentially
single melting point" means that at least 80%, by weight, of
the material corresponds to a single Tm peak at a temperature
within the range of from 60 C to 110 C, and essentially no
substantial fraction of the material has a peak melting
point in excess of 115 C., as determined by DSC analysis.
DSC measurements are made on a Perkin ElmerTM System 7
Thermal Analysis System. Melting information reported are
second melting data, i.e., the sample is heated at a
programmed rate of 10 C./min. to a temperature below its
critical range. The sample is then reheated (2nd melting)
at a programmed rate of 10 C/min.
A homogeneous ethylene/alpha-olefin copolymer can,
in general, be prepared by the copolymerization of ethylene
and any one or more alpha-olefin. Preferably, the alpha-
olefin is a C3-C20 a-monoolefin, more preferably, a
C4-C12 a-monoolefin, still more preferably, a
C4-C8 a-monoolefin. Still more preferably, the alpha-olefin
comprises at least one member selected from the group
consisting of butene-1, hexene-1, and octene-1, i.e.,
1-butene, 1-hexene, and 1-octene, respectively. Most
preferably, the alpha-olefin comprises octene-1, and/or a
blend of hexene-1 and butene-1.
Processes for preparing homogeneous polymers are
disclosed in U.S. Patent No. 5,206,075, U.S. Patent
No. 5,241,031, and PCT International Application
WO 93/03093. Further details regarding the production and
use of one genus of homogeneous ethylene/alpha-olefin
copolymers are disclosed in U.S. Patent No. 5,206,075, to
HODGSON, Jr.; U.S. Patent No. 5,241,031, to MEHTA;
PCT International Publication Number WO 93/03093, in the
name of Exxon Chemical Company; PCT International
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Publication Number WO 90/03414, in the name of Exxon
Chemical Patents, Inc. Still another genus of homogeneous
ethylene/alpha-olefin copolymers is disclosed in U.S. Patent
No. 5,272,236, to LAI, et. al., and U.S. Patent
No. 5,278,272, to LAI, et. al.
As used herein, the term "polyolefin" refers to
any polymerized olefin, which can be linear, branched,
cyclic, aliphatic, aromatic, substituted, or unsubstituted.
More specifically, included in the term polyolefin are
homopolymers of olefins, copolymers of olefins, copolymers
of an olefin and an non-olefinic comonomer copolymerizable
with the olefin, such as vinyl monomers, modified polymers
thereof, and the like. Specific examples include propylene
homopolymers, ethylene homopolymers, poly-butene,
propylene/alpha-olefin copolymers, ethylene/alpha-olefin
copolymers, butene/alpha-olefin copolymers, ethylene/vinyl
acetate copolymers, ethylene/ethyl acrylate copolymers,
ethylene/butyl acrylate copolymers, ethylene/methyl acrylate
copolymers, ethylene/acrylic acid copolymers,
ethylene/methacrylic acid copolymers, modified polyolefin
resins, ionomer resins, polymethylpentene, etc. The
modified polyolefin resins include modified polymers
prepared by copolymerizing (grafting) the homopolymer of the
olefin or copolymer thereof with an unsaturated carboxylic
acid, e.g., maleic acid, fumaric acid or the like, or a
derivative thereof such as the anhydride, ester or metal
salt or the like. It could also be obtained by
incorporating into the olefin homopolymer or copolymer, an
unsaturated carboxylic acid, e.g., maleic acid, fumaric acid
or the like, or a derivative thereof such as the anhydride,
ester or metal salt or the like.
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As used herein, terms identifying polymers, such
as "polyamide", "polyester", "polyurethane", etc., are
inclusive of not only polymers comprising repeating units
derived from monomers known to polymerize to form a polymer
of the named type, but are also inclusive of comonomers,
derivatives, etc., which can copolymerize with monomers
known to polymerize to produce the named polymer.
Derivatives also include ionomers of the polymer(s). For
example, the term "polyamide" encompasses both polymers
comprising repeating units derived from monomers, such as
caprolactam, which polymerize to form a polyamide, as well
as copolymers derived from the copolymerization of
caprolactam with a comonomer which when polymerized alone
does not result in the formation of a polyamide.
Furthermore, terms identifying polymers are also inclusive
of "blends" of such polymers with other polymers of a
different type.
As used herein, the phrase "anhydride
functionality" refers to any form of anhydride
functionality, such as the anhydride of maleic acid, fumaric
acid, etc., whether blended with one or more polymers,
grafted onto a polymer, or copolymerized with a polymer,
and, in general, is also inclusive of derivatives of such
functionalities, such as acids, esters, and metal salts
derived therefrom.
As used herein, the phrase "modified polymer", as
well as more specific phrases such as "modified ethylene
vinyl acetate copolymer", and "modified polyolefin" refer to
such polymers having an anhydride functionality, as defined
immediately above, grafted thereon and/or copolymerized
therewith and/or blended therewith. Preferably, such
modified polymers have the anhydride functionality grafted
23
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on or polymerized therewith, as opposed to merely blended
therewith.
As used herein, the phrase "anhydride-modified
polymer" refers to one or more of the following:
(1) polymers obtained by copolymerizing an anhydride-
containing monomer with a second, different monomer, and
(2) anhydride grafted copolymers, and (3) a mixture of a
polymer and an anhydride-containing compound.
As used herein, the phrase "ethylene alpha-olefin
copolymer", and "ethylene/alpha-olefin copolymer", refer to
such heterogeneous materials as linear low density
polyethylene (LLDPE), and very low and ultra low density
polyethylene (VLDPE and ULDPE); and homogeneous polymers
such as metallocene catalyzed polymers such as EXACT (TM)
materials supplied by Exxon, and TAFMER (TM) materials
supplied by Mitsui Petrochemical Corporation. These
materials generally include copolymers of ethylene with one
or more comonomers selected from C4 to Clo alpha-olefins such
as butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in
which the molecules of the copolymers comprise long chains
with relatively few side chain branches or cross-linked
structures. This molecular structure is to be contrasted
with conventional low or medium density polyethylenes which
are more highly branched than their respective counterparts.
LLDPE, as used herein, has a density usually in the range of
from 0.91 grams per cubic centimeter to 0.94 grams per cubic
centimeter. Other ethylene/alpha-olefin copolymers, such as
the long chain branched homogeneous ethylene/alpha-olefin
copolymers available from the Dow Chemical Company, known as
AFFINITY (TM) resins, are also included as another type of
ethylene alpha-olefin copolymer useful in the present
invention.
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In general, the ethylene/alpha-olefin copolymer
comprises a copolymer resulting from the copolymerization of
from 80 to 99 weight percent ethylene and from
1 to 20 weight percent aipha-olefin. Preferably, the
ethylene alpha-olefin copolymer comprises a copolymer
resulting from the copolymerization of from 85 to 95 weight
percent ethylene and from 5 to 15 weight percent alpha-
olefin.
As used herein, the phrases "inner layer" and
"internal layer" refer to any layer, of a multilayer film,
having both of its principal surfaces directly adhered to
another layer of the film.
As used herein, the phrase "outer layer" refers to
any film layer of a multilayer film having only one of its
principal surfaces directly adhered to another layer of the
film.
As used herein, the phrase "inside layer" refers
to the outer layer, of a multilayer film packaging a
product, which is closest to the product, relative to the
other layers of the multilayer film.
As used herein, the phrase "outside layer" refers
to the outer layer, of a multilayer film packaging a
product, which is furthest from the product relative to the
other layers of the multilayer film.
As used herein, the phrase "directly adhered", as
applied to film layers, is defined as adhesion of the
subject film layer to the object film layer, without a tie
layer, adhesive, or other layer therebetween. In contrast,
as used herein, the word "between", as applied to a film
layer expressed as being between two other specified layers,
CA 02561490 2006-10-13
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includes both direct adherence of the subject layer between
to the two other layers it is between, as well as including
a lack of direct adherence to either or both of the two
other layers the subject layer is between, i.e., one or more
additional layers can be imposed between the subject layer
and one or more of the layers the subject layer is between.
As used herein, the term "core", and the phrase
"core layer", as applied to multilayer films, refer to any
internal film layer which has a primary function other than
serving as an adhesive or compatibilizer for adhering two
layers to one another. Usually, the core layer or layers
provide the multilayer film with a desired level of
strength, e.g., modulus, and/or optics, and/or added abuse
resistance, and/or specific impermeability.
As used herein, the phrases "seal layer" and
"sealant layer", with respect to multilayer films, refers to
an outer film layer, or layers, involved in the sealing of
the film to itself or another layer. It should also be
recognized that in general, the outer 0.5 to 3 mils of a
film can be involved in the sealing of the film to itself or
another layer. With respect to packages having only fin-
type seals, as opposed to lap seals, the phrase "sealant
layer" generally refers to the inside film layer of a
package, as well as supporting layers adjacent this sealant
layer often being sealed to itself, and frequently serving
as a food contact layer in the packaging of foods.
As used herein, the phrase "tie layer" refers to
any internal layer having the primary purpose of adhering
two layers to one another.
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As used herein, the phrase "skin layer" refers to
an outside layer of a multilayer film in packaging a
product, this skin layer being subject to abuse.
As used herein, the phrase "bulk layer" refers to
any layer of a film which is present for the purpose of
increasing the abuse-resistance, toughness, modulus, etc.,
of a multilayer film. Bulk layers generally comprise
polymers which are inexpensive relative to other polymers in
the film which provide some specific purpose unrelated to
abuse-resistance, modulus, etc.
As used herein, the term "extrusion" is used with
reference to the process of forming continuous shapes by
forcing a molten plastic material through a die, followed by
cooling or chemical hardening. Immediately prior to
extrusion through the die, the relatively high-viscosity
polymeric material is fed into a rotating screw of variable
pitch, which forces it through the die.
As used herein, the term "coextrusion" refers to
the process of extruding two or more materials through a
single die with two or more orifices arranged so that the
extrudates merge and weld together into a laminar structure
before chilling, i.e., quenching. Coextrusion can be
employed in film blowing, free film extrusion, and extrusion
coating processes.
As used herein, the phrase "machine direction",
herein abbreviated "MD", refers to a direction "along the
length" of the film, i.e., in the direction of the film as
the film is formed during extrusion and/or coating.
As used herein, the phrase "transverse direction",
herein abbreviated "TD", refers to a direction across the
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film, perpendicular to the machine or longitudinal
direction.
As used herein, the phrase "free shrink" refers to
the percent dimensional change in a 10 cm x 10 cm specimen
of film, when subjected to selected heat, as measured by
ASTM D 2732, as known to those of skill in the art.
According to the first aspect of the present
invention as set forth above, if the first polyolefin
comprises ethylene/unsaturated acid, propylene/unsaturated
acid, and/or butene/unsaturated acid, preferably the
unsaturated acid mer is present in an amount of from
4 to 30 weight percent, based on the weight of the
copolymer; more preferably, from 7 to 20 percent; still more
preferably, from 8 to 15 percent; and, yet still more
preferably, from 9 to 13 percent. Depending upon the meat
product, if the unsaturated acid monomer is present in an
amount less than 6 weight percent, sufficient purge-
resistance may not be achieved upon cooking the meat product
in the casing. On the other hand, if the amount of
unsaturated acid monomer is present in an amount greater
than 20 weight percent, the softening point of the
unsaturated acid copolymer may be too low to facilitate film
production and/or obtain satisfactory seal strength for
cook-in end use. Thus, the optimal level of unsaturated
acid monomer depends on the manner in which the film is
produced, and the particular end-use of the film, e.g., the
type of meat being packaged, and the cook-in conditions.
If the first polyolefin comprises anhydride-
containing polyolefin comprising an anhydride-functionality,
preferably the anhydride functionality is present in an
amount of from 1 to 10 weight percent, based on the weight
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of the anhydride-containing polyolefin; more preferably,
from 2 to 5 weight percent.
In a lap-sealed backseamed casing according the
present invention, preferably the first polyolefin has a
vicat softening point of at least 70 C, more preferably at
least 80 C, and still more preferably at least 90 C, in
order to provide a desired level of seal strength. However,
in a butt-sealed backseamed casing according to the present
invention, in which a butt-tape film is sealed to the outer
surface of the third film layer, the lower-limit of the
softening point of the first polyolefin may be less
critical.
Preferably, the first polyolefin is present in the
first outer layer in an amount of from 10 to 50 weight
percent, based on the weight of the first layer; more
preferably, in an amount of from 10 to 30 percent; and still
more preferably, in an amount of from 15 to 25 percent.
As the third polyolefin, LLDPE is more preferred
than propylene/ethylene copolymer because LLDPE produces a
seal having less "pucker", if the second polyolefin also
comprises LLDPE and the casing is a lap-seal backseamed
casing. The third polyolefin provides the first layer with
a high melting point resin, which is advantageous for cook-
in end use, where the casing is subjected to relatively high
temperatures for a relatively long period of time.
Preferably, the third polyolefin has a melting point less
than 160 C; more preferably, less than 140 C, and still more
preferably, less than 130 C. Preferably, the third
polyolefin has a vicat softening point of at least 80 C,
more preferably, at least 90 C, and still more preferably,
at least 100 C.
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'64536-943D
In the second layer, the first polyamide
preferably comprises at least one member selected from the
group consisting of polyamide 6, polyamide 66, polyamide 9,
polyamide 10, polyamide 11, polyamide 12, polyamide 69,
polyamide 610, polyamide 612, polyamide 61, polyamide 6T,
and copolymers thereof; more preferably, at least one member
selected from the group consisting of polyamide 6, polyamide
66 and polyamide 6/66. Preferably, the first polyamide has
a melting point of at least 350 F; more preferably, at least
370 F; still more preferably, at least 390 F.
Preferably, the second layer further comprises a
third polyamide having a melting point of less than 176.67 C
(350 F). Preferably, the second layer comprises:
(a) polyamide 6 in an amount of from 40 to 90 weight
percent, based on the weight of the second layer; and
(b) copolyamide 6/12 in an amount of from 10 to 60 weight
percent, based on the weight of the second layer, wherein
the copolyamide 6/12 comprises caprolactam monomer in an
amount of from 30 to 70 weight percent (more preferably,
40 to 60 weight percent). Preferably, the first polyamide
has a melting point above 076.61 C (350 F), and the third
polyamide has a melting point below 176.67 C (350 F), as
this combination has been found to produce a combination of
modulus, orientability, seal strength, and pinhole-
resistance which is preferred.
Preferably, the second polyolefin comprises at
least one member selected from the group consisting of
polyethylene homopolymer, polyethylene copolymer,
polypropylene homopolymer, polypropylene copolymer,
polybutene homopolymer, and polybutene copolymer. More
preferably, the second polyolefin comprises at least one
member selected from the group consisting of ethylene/alpha-
CA 02561490 2006-10-13
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olefin copolymer, propylene/alpha-olefin copolymer,
butene/alpha-olefin copolymer, ethylene/unsaturated ester
copolymer, and ethylene/unsaturated acid copolymer. Still
more preferably, the second polyolefin comprises at least
one member selected from the group consisting of linear low
density polyethylene (LLDPE), propylene/ethylene copolymer,
and propylene/butene copolymer. Yet still more preferably,
the second polyolefin comprises LLDPE. In a lap-seal
backseam casing according to the present invention,
preferably the second polyolefin and the third polyolefin
are the same polymer.
If the fifth and sixth layers each comprise
polystyrene or polyurethane, they may be the same
.polystyrene and/or polyurethane, or different polystyrenes
and/or polyurethanes. In serving as tie layers, preferably
the fifth and sixth layers each assist the adhesion of the
preferably polyolefinic first and third layers to the
polyamide layer, as well as to the 02-barrier layer, if
present.
The butt-seal tape film is chosen so that it is
seal-compatible with the sealant surface of the casing film.
Preferably, the butt-seal tape film comprises polyolefin as
an outer sealing layer. More preferably, the butt-seal tape
film further comprises an 02-barrier layer. Still more
preferably, the butt-seal tape film further comprises two
tie layers, i.e., a tie layer between the 02-barrier layer
and each of the two outer layers, each of which comprise
polyolefin. Preferably, the butt-seal tape film is heat-
shrinkable, and preferably, the butt-seal tape film
comprises an outer sealing layer comprising polyolefin
having a melting point of from about 90 C-150 C; more
preferably, from about 100 C-130 C.
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The seal layer of the butt-seal tape film is an
outer film layer which preferably comprises at least one
member selected from the group consisting of polyethylene
homopolymer, polyethylene copolymer, polypropylene
homopolymer, polypropylene copolymer, polybutene
homopolymer, and polybutene copolymer; more preferably,
ethylene/alpha-olefin copolymer, propylene/alpha-olefin
copolymer, butene/alpha-olefin copolymer,
ethylene/unsaturated ester copolymer, and
ethylene/unsaturated acid copolymer; still more preferably,
linear low density polyethylene (LLDPE), propylene/ethylene
copolymer, and propylene/butene copolymer.
In the casing film according to the third aspect
of the present invention, all of the various polymers
present in each of the film layers are preferably as
described above according to the first aspect of the present
invention, except that the first polyolefin of the first
layer has surface energy of less than 34 dynes/cm, more
preferably, less than 32 dynes/cm. Thus, in the third
aspect of the present invention, the first polyolefin
preferably comprises at least one member selected from the
group consisting of polyethylene homopolymer, polyethylene
copolymer, polypropylene homopolymer, polypropylene
copolymer, polybutene homopolymer, and polybutene copolymer.
More preferably, the first polyolefin comprises at least one
member selected from the group consisting of ethylene/alpha-
olefin copolymer, propylene/alpha-olefin copolymer,
butene/alpha-olefin copolymer, ethylene/unsaturated acid
copolymer, and ethylene/unsaturated ester copolymer. Still
more preferably, the first polyolefin comprises at least one
member selected from the group consisting of linear low
density polyethylene (LLDPE), propylene/ethylene copolymer,
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*64536-943D
and propylene/butene copolymer. Yet still more preferably,
the first polyolefin comprises LLDPE.
Preferably, the multilayer film has a shrink
tension of at least 68.95 RPa (10 psi), more preferably,
from 138.90 - 6895 RPa (20-1000 psi), still more preferably,
from 689.5 - 4136.9 RPa (100 to 600 psi); and yet still more
preferably, from 2068.4 - 3497.4 RPa (300 to 500 psi).
A preferred backseamed casing according to the
present invention comprises a multilayer heat shrinkable
film comprising a meat-adhesion layer comprising a polar
polymer, which provides a high level of meat adhesion,
especially to intermediate/high protein-containing meat
products. Although this film can be corona treated, the
film of the invention does not require corona treatment in
order to exhibit a desired level of meat adhesion with
products such as turkey, good-to-intermediate quality ham,
and roast beef. However, the backseamed casing film of the
present invention can be corona treated in order to provide
an enhanced level of adhesion, especially with high fat
products. Typically, films which by themselves have a
relatively low level of meat-adhesion exhibit the 'buffing-
off' problem described above, at least at the backseamed
edges thereof. However, the films of the present invention
have an advantage in that respect. Because the untreated
films already have an acceptable level of meat-adhesion to
intermediate-quality meat products, even when the corona
treatment is buffed-off the surface during the backseaming
operation, there is sufficient protein-adhesion from the
polymer to prevent purge or fatting-out. Thus, the ultimate
package still has an acceptable level of adhesion.
Optionally, corona treatment could also be carried out after
the backseamed tubing is made. Here, too, if a relatively
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low-meat-adhering-polymer is used as the inside casing layer
and the resulting backseamed tubing is then corona treated,
substantial purge (also known as cook-out and fatting-out)
can occur on a strip at the edge of the backseamed tubing,
where there is insufficient corona treatment (inherent in
the process used to internally corona treat). However, the
corona treatment of a film surface which already has an
enhanced level of meat-adhesion (as is the case in the
present invention) reduces or eliminates the purge or cook-
loss at the casing lay flat edges (which, as described
above, have not been substantially treated). Thus, the
backseamed casing of the present invention avoids the
"buffing off problem" associated with corona treatment,
while at the same time achieving a satisfactory level of
meat adhesion to various different kinds of protein-
containing meat products.
As described above, the second layer of the casing
film must have a thickness of at least 5% of a total
thickness of the heat-shrinkable casing film. That is, if
the thickness of the second layer is less than 5 percent of
the total thickness of the film, the second layer may not
perform adequately in preventing the film from shrinking
down against the forming shoe.
If the heat-shrinkable casing film in the
backseamed casing is made by orienting a tape which is
heated over a very short time period, such as a tape heated
by infrared radiation, the thickness of the second layer
could be as high as 70%, based on the thickness of the
multilayer film. However, if the film is heated over a
relatively long time period, such as being heated in hot
water, the preferred polyamides tend to crystallize to a
relatively high level before the orientation step, which
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produces problems during the orientation step (the rate of
crystallization depends on the type of polyamide used). In
this latter situation, typically, the greater the thickness
of the second layer, the more difficult it is to orient to
obtain the resulting casing film. This forces a practical
limit on the maximum percentage thickness of the second
layer (especially when the most preferred polyamides are
used), based on the total thickness of the multilayer casing
film. Thus, if hot-water is used as the orientation medium,
the second layer of the casing film preferably has a
thickness of from 5 to 50 percent of the total thickness of
the casing film; more preferably, from 5 to 40 percent;
still more preferably, from 10 to 30 percent; and yet still
more preferably, from 10 to 20 percent, based on a total
thickness of the multi-layer film.
It has been discovered that the second layer,
which preferably comprises polyamide, serves to prevent
necking down on the forming shoe during the backseaming
process. Necking down typically occurs during the
backseaming process when the film is drawn so tightly around
the forming shoe (as a result of the film shrinking due to
the heat generated outwards from the seal area during the
backseaming process) that it cannot be forwarded. The
presence of the second layer, significantly reduces the
necking down of the film by reducing that region of the film
which shrinks due to the propagation of heat outward from
the heat seal bar.
Preferably, the backseamed casing of the present
invention comprises a casing film having from
3 to 20 layers; more preferably, from 4 to 12 layers; still
more preferably, from 6 to 10 layers.
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Preferably, the multilayer casing film used in the
backseamed casing according to the present invention can
have any total thickness desired, so long as the film
provides the desired properties for the particular packaging
operation in which the film is used. Preferably, the casing
film used in the present invention has a total thickness,
i.e., a combined thickness of all layers, of from
0.0127 - 0.254 mm (0.5 to 10 mils (1 mil equals
0.001 inch)); more preferably, from 0.0254 - 0.2032 mm
(1 to 8 mils); and still more preferably, from
0.0508 - 0.1016 mm (2 to 4 mils).
It should be noted that the modulus of the casing
film should be high enough that so that the film does not
stretch to an undesirable degree during the backseaming
process. Preferably, the casing film has a modulus of at
least 137895 RPa (20,000 psi); more preferably, from
206842 - 30,000 to 1723690 RPa (250,000 psi); still more
preferably, from 275790 - 1034204 RPa
(40,000 to 150,000 psi.); yet still more preferably, from
310264 - 82737 RPa (45,000 to 120,000); and even yet still
more preferably, from 344738 - 482633 RPa
(50,000 to 70,000 psi). It should be kept in mind that if
the modulus of the casing film is too high, problems could
occur after backseaming, e.g., the film could flex-crack
when being wound up after backseaming or cause difficulty in
tracking. Furthermore, too high a modulus is especially
undesirable if the film is to be used as a casing which is
to undergo shirring, as films of too high a modulus may
flex-crack during shirring. On the other hand, if the
modulus of the film is too low, the film tends to stretch
too much during backseaming, thereby producing backseamed
casing of low quality in that it does not backseam
36
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acceptably, has a wavy appearance, and/or has ruffled edges,
and/or seal pucker, and/or does not track well through the
machine.
Figure 1 illustrates lap-seal backseamed casing 11
according to the present invention. Lap-seal backseamed
casing 11 comprises heat-shrinkable casing film 12, which is
sealed to itself at backseam lap-seal 13.
Figure 2 illustrates an enlarged cross-sectional
view of heat-shrinkable casing film 12, which is especially
suited to the packaging of meat. In Figure 2, casing film
12 comprises: first layer 14, second layer 16, third layer
18, fourth layer 20, fifth layer 22, sixth layer 24, seventh
layer 26, and eighth layer 28.
First layer 14 is an outer film layer which serves
as an inside layer of the casing film. First layer 14 has
outer meat-contact surface 15 for direct contact, and
adhesion to, the meat being packaged in casing 11.
Preferably, first layer 14 has a thickness of from
0.1 to 3 mils; more preferably, from 0.2 to 1 mil; still
more preferably, from 0.3 to 0.8 mil; and yet still more
preferably, 0.5 mils. First layer 14 comprises a polar
polymer which preferably has a surface energy greater than
32 dynes/cm, more preferably greater than 34 dynes/cm, and
still more preferably greater than 36 dynes/cm. Preferably,
first layer 14 comprises a first polyolefin comprising at
least one member selected from the group consisting of:
(i) ethylene/unsaturated acid copolymer,
propylene/unsaturated acid copolymer, and butene/unsaturated
acid copolymer, wherein the unsaturated acid (mer) is
present in an amount of at least 4 weight percent, based on
the weight of the copolymer; and
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(ii) anhydride-containing polyolefin comprising an
anhydride-functionality, wherein the anhydride functionality
is present in an amount of at least 1 weight percent, based
on the weight of the anhydride-containing polyolefin;
More preferably, first layer 14 comprises a first
polyolefin comprising at least one member selected from the
group consisting of:
(i) ethylene/unsaturated acid copolymer,
propylene/unsaturated acid copolymer, and butene/unsaturated
acid copolymer, wherein the unsaturated acid (monomer) is
present in an amount of from 6-30%, more preferably from
about 7-20%, still more preferably from 8-15%, and yet still
more preferably, from 9-13%, based on the weight of the
copolymer; and
(ii) anhydride-containing polyolefin comprising an
anhydride-functionality, wherein the anhydride functionality
is present in an amount of from 1 to 10 weight percent,
based on the weight of the anhydride-containing polyolefin;
more preferably from 2 to 5 weight percent.
If the first polyolefin comprises unsaturated acid
copolymer, if the unsaturated acid monomer is present in an
amount less than 6 weight percent, sufficient purge
resistance may not be achieved. On the other hand, if the
amount of unsaturated acid (monomer) in the copolymer is
greater than 20 weight percent, the softening point of the
unsaturated acid copolymer may be too low to facilitate
processing into film and/or obtain satisfactory seal
strength during cooking. The preferred unsaturated acid
(monomer) level may vary depending on the end application,
i.e., the type of meat product to be adhered to.
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In any backseamed casing according to the present
invention, preferably, the inside film layer (which serves
as a food-contact layer, and, in the lap seal backseamed
casing according to the present invention also serves as a
sealant layer) does not comprise a blend of
propylene/ethylene copolymer and homogeneous ethylene/alpha-
olefin copolymer having a density of less than 0.90. That
is, if this blend makes up the majority of the seal layer,
the seal strength may be less than preferred. Furthermore,
if this blend makes up the majority of the seal layer, no
core layer of polyester and/or first polyamide is required
in order to backseam the film without a detrimental degree
of necking down on the forming shoe.
Multilayer film 12 may be used in either a lap-
seal backseamed casing or a butt-seal backseamed casing. In
a lap-seal backseamed casing such as casing 11, preferably
the first polyolefin has a vicat softening point of at least
70 C, more preferably at least 80 C, in order to retain good
seal strength during cook-in. However, for a butt-sealed
backseamed casing, the lower-limit of the softening point of
the first polyolefin may be less critical, as it is both the
softening point of the third layer of the casing film, as
well as the softening point of the sealant layer of the
butt-seal tape film, which govern sealability and seal
strength during cooking.
Preferably, first layer 14 further comprises a
third polyolefin comprising at least one member selected
from the group consisting of polyethylene homopolymer,
polyethylene copolymer, polypropylene homopolymer,
polypropylene copolymer, polybutene homopolymer, and
polybutene copolymer. More preferably, the third polyolefin
comprises at least one member selected from the group
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consisting of ethylene/alpha-olefin copolymer,
propylene/alpha-olefin copolymer, butene/alpha-olefin
copolymer, ethylene/unsaturated acid copolymer, and
ethylene/unsaturated ester copolymer. Even more preferably,
the third polyolefin comprises at least one member selected
from the group consisting of linear low density polyethylene
(LLDPE), propylene/ethylene copolymer, and propylene/butene
copolymer. Preferably, the third polyolefin has a vicat
softening point of at least 80 C, more preferably, at least
90 C, and even more preferably at least 100 C. Preferably,
the first polyolefin is present in an amount of from about
10-50%, more preferably, in an amount of from about 10-30%,
and even more preferably, in an amount of from about 15-25%,
based on the composition of the first outer layer.
The third polyolefin provides first layer 14 with
a higher softening point polymer to enhance the stability of
the film, and seals thereof, during cook-in. Furthermore,
the dilution of the polar polymer with a relatively non-
polar polymer, i.e., the third polyolefin, does not
significantly decrease the purge-resistance characteristics
of the first layer of the casing film. Preferably, first
layer 14 comprises a blend of 80 weight percent LLDPE and
20 weight percent ethylene/unsaturated acid copolymer.
Second layer 16 is an inner film layer which is
between first layer 14 and third layer 18. Second layer 16
provides casing film 11 with the characteristic of
undergoing the backseaming operation without necking down on
the forming shoe. Second layer 16 also helps to provide a
better quality casing film by making casing film 12 easier
to orient, and facilitating faster backseaming speeds, and
also imparting enhanced seal strength, toughness, pin-hole
resistance and elastic recovery to casing film 12. Second
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layer 16 preferably comprises at least one member selected
from the group consisting of polyester, and first polyamide,
i.e., polymers having relatively high modulus and/or
relatively high elastic recovery. More preferably, second
layer 16 comprises the first polyamide; still more
preferably, at least one member selected from the group
consisting of polyamide 6, polyamide 66, polyamide 9,
polyamide 10, polyamide 11, polyamide 12, polyamide 69,
polyamide 610, polyamide 612, polyamide 61, polyamide 6T, as
well as copolymers prepared from copolymerization of any one
or more of the monomers used in the preparation of any of
these polyamides; and yet still more preferably, at least
one member selected from the group consisting of
polyamide 6, polyamide 66 and polyamide 6/66. Preferably,
the first polyamide has a melting point of at least 176.67 C
(350 F); more preferably, at least 370 F; even more
preferably, at least 390 F. Preferably, second layer 16 has
a thickness of from about 0.05 to 1 mil; preferably, from
0.1 to 0.5 mil; more preferably, from about 0.2 to 0.4 mil,
and still more preferably, about 0.3 mils.
Preferably, second layer 16 further comprises a
third polyamide having a melting point of less than about
350 F. Preferably, second layer 16 comprises:
(a) polyamide 6 in an amount of from about 40 to 90 weight
percent, based on the weight of the first inner layer; and
(b) copolyamide 6/12 in an amount of from about
10 to 60 weight percent, based on the weight of the first
inner layer, wherein the copolyamide 6/12 comprises
caprolactam (mer) in an amount of from about 30 to 70 weight
percent, based on the weight of the copolyamide; more
preferably, from about 40 to 60 weight percent.
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Third layer 18 is an outer film layer which serves
as an outside abuse-resistant and heat-seal layer of
casing 11. Preferably, third layer 18 has a thickness of
from about 0.1 to 3 mils; more preferably, from about
0.2 to 1 mil; still more preferably, from about
0.3 to 0.8 mil; and, yet still more preferably, about
0.35 to 0.65 mil.
Preferably, third layer 18 comprises at least one
member selected from the group consisting of second
polyolefin, polystyrene, second polyamide, polyester,
polymerized ethylene/vinyl alcohol copolymer, polyvinylidene
chloride, polyether, polyurethane, polycarbonate, and
starch-containing polymer; more preferably, third layer 18
comprises the second polyolefin; still more preferably, at
least one member selected from the group consisting of
polyethylene homopolymer, polyethylene copolymer,
polypropylene homopolymer, polypropylene copolymer,
polybutene homopolymer, and polybutene copolymer; yet still
more preferably, third layer 18 comprises at least one
member selected from the group consisting of ethylene/alpha-
olefin copolymer, propylene/alpha-olefin copolymer,
butene/alpha-olefin copolymer, ethylene/unsaturated ester
copolymer, and ethylene/unsaturated acid copolymer; and yet
still even more preferably, third layer 18 comprises at
least one member selected from the group consisting of
linear low density polyethylene (LLDPE), propylene/ethylene
copolymer, and propylene/butene copolymer.
In a lap-seal backseam casing, the second
polyolefin and the third polyolefin are preferably the same
polymer.
Preferably, the second polyolefin has a vicat
softening point of at least 80 C, more preferably, at least
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90 C, and even more preferably at least 100 C. The
softening point of the second polyolefin needs to be high
enough for the casing to survive cook-in.
Fourth layer 20 is an internal layer which is
between first layer 14 and third layer 18, and preferably
comprises a polymer having relatively high oxygen barrier
characteristics. Preferably, fourth layer 20 has a
thickness of from about 0.05 to 2 mils; more preferably,
from 0.05 to 0.5 mil; still more preferably, from
0.1 to 0.3 mil; and yet still more preferably, from about
0.12 to 0.17 mils. In general, fourth layer 20 comprises at
least one member selected from the group consisting of
polymerized ethylene vinyl alcohol (EVOH), polyvinylidene
chloride, fourth polyamide, polyalkylene carbonate, and
polyester; preferably, at least one member selected from the
group consisting of polymerized ethylene vinyl alcohol and
fourth polyamide; more preferably, polymerized ethylene
vinyl alcohol; still more preferably, polymerized ethylene
vinyl alcohol having about 44 mole percent ethylene.
Fifth layer 22 and sixth layer 24 are tie layers
in casing film 12. Fifth layer 22 is between first layer 14
and second layer 16; sixth layer 24 is between second
layer 16 and third layer 18. As a general rule, tie layers
should have a relatively high degree of compatibility with
barrier layers, such as polymerized EVOH, or the polyamide
layer, as well as non-barrier layers, such as polymerized
ethylene alpha-olefin copolymer. The composition, number,
and thickness of tie layers is as known to those of skill in
the art. Preferably, fifth layer 22 and sixth layer 24 each
have a thickness of from about 0.05 to 2 mils; more
preferably, from about 0.05 to 0.5 mil; still more
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preferably, from about 0.1 to 0.3 mil; and yet still more
preferably, from about 0.12 to 0.17 mils.
Preferably, fifth layer 22 comprises at least one
member selected from the group consisting of fourth
polyolefin, polystyrene and polyurethane; more preferably,
at least one member selected from the group consisting of
modified ethylene/alpha-olefin copolymer, modified
ethylene/unsaturated ester copolymer, and modified
ethylene/unsaturated acid copolymer. Preferably, sixth
layer 24 comprises at least one member selected from the
group consisting of fifth polyolefin, polystyrene and
polyurethane; more preferably, at least one member selected
from the group consisting of modified ethylene/alpha-olefin
copolymer, modified ethylene/unsaturated ester copolymer,
and modified ethylene/unsaturated acid copolymer.
Seventh layer 26 is a core layer between first
layer 14 and second layer 16. Seventh layer 26 provides the
multilayer casing film 12 film with desired abuse, shrink,
and optical characteristics, and preferably comprises a
polymer having relatively low cost while providing these
characteristics. Preferably, seventh layer 26 has a
thickness of from about 0.1 to 3 mils; more preferably, from
0.2 to 1.5 mils; still more preferably, from 0.3 to 1 mil;
and yet still more preferably, from about 0.50 to 0.80 mils.
Preferably, seventh layer 26 comprises at least one member
selected from the group consisting of polyolefin, polyamide,
polyester, and polyurethane; more preferably, polyolefin;
still more preferably, at least one member selected from the
group consisting of ethylene/alpha-olefin copolymer,
propylene/alpha-olefin copolymer, butene/alpha-olefin
copolymer, ethylene/unsaturated ester copolymer, and
ethylene/unsaturated acid copolymer; and yet still more
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preferably, a blend of 80 weight percent ethylene vinyl
acetate copolymer (having 6 weight percent vinyl acetate
mer) with 20 weight percent high density polyethylene.
Eighth layer 28 is a core layer between second
layer 16 and third layer 18. Eighth layer 18 also provides
the multilayer film with desired abuse, shrink, and optical
characteristics, and preferably comprises a polymer having
relatively low cost while providing these attributes. In
general, eighth layer 28 can have a thickness of from about
0.1 to 3 mils; preferably, from 0.2 to 1.5 mil; more
preferably, from 0.3 to 1 mil; and still more preferably,
from about 0.50 to 0.80 mils. In general, eighth layer 28
comprises at least one member selected from the group
consisting of polyolefin, polyamide, polyester, and
polyurethane; preferably, polyolefin; more preferably at
least one member selected from the group consisting of
ethylene/alpha-olefin copolymer, propylene/alpha-olefin
copolymer, butene/alpha-olefin copolymer,
ethylene/unsaturated ester copolymer, and
ethylene/unsaturated acid copolymer; still more preferably,
a blend of 80 weight percent ethylene vinyl acetate
copolymer (having 6 weight percent vinyl acetate) with
20 weight percent ethylene/unsaturated acid copolymer.
Seventh layer 26 and eighth layer 28 are typically
chosen in composition and layer thickness so as to provide a
relatively flat, curl-free, heat-shrinkable casing film.
Preferably, seventh layer 26 and eighth layer 28 have a
composition and thickness so as to provide the multilayer
film with as much cross-sectional symmetry as possible.
Cross-sectional symmetry provides the film with the desired
characteristics of low curl and low floppiness.
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If "a" represents a sum of the thicknesses of the
first, fifth, and seventh layers, and "b" represents a sum
of the thicknesses of the second, sixth, and eighth layers,
then preferably, a:b is from about 0.5:1 to 1.5:1, more
preferably 0.7:1 to 1.3:1, still more preferably, from about
0.8:1 to 1.2:1.
In casing 11, backseam seal 13 can be formed using
any one or more of a wide variety of sealing devices, as
known to those of skill in the art, such as heat sealing via
hot air and/or heated bar and/or hot wire, ultrasonic
sealing, radio frequency sealing, etc. However, a preferred
sealing mechanism is the use of a heated seal bar which
provides for better sealability and can provide better
ultimate seal strength, thus providing seals capable of
surviving the cooking process.
Figure 3 illustrates alternative preferred six-
layer, heat-shrinkable casing film 30 suitable for use as a
lap-seal casing as illustrated in Figure 1, as well as a
butt-seal casing as illustrated in Figure 5. As with
multilayer film 12 of Figure 2, multilayer film 30 is also
especially suited to the packaging of meat products which
are thereafter subjected to cook-in. Casing film 30
comprises first layer 32, second layer 34, third layer 36,
fourth layer 38, fifth layer 40, and sixth layer 42.
First layer 32 is an outer film layer which serves
as an inside casing film layer, and accordingly is a meat-
contact layer which is analogous to first layer 14 of
Figure 2. When in the form of casing, first layer 32 has
inside meat-contact surface 33 for direct contact with, and
adhesion to, the meat within the casing. If casing film 30
is used to make lap-seal casing 11 as illustrated in
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Figure 1, first layer 32 is sealed to second layer 34 at
backseam lap seal 13, this seal being located where a
portion of outer surface 33 overlaps an outside surface of
casing film 30. First layer 32 has the same general and
preferred thickness and chemical composition as first layer
14 of Figure 2. However, first layer 32 most preferably has
a thickness of 0.8 mils.
Second layer 34 is a core layer between first
layer 32 and third layer 36, and in general is analogous to
second layer 16 of Figure 2. Second layer 34 has the same
general and preferred thickness and chemical composition as
second layer 16 of Figure 2.
Third film layer 36 is an outer film layer which
serves as an outside, abuse-resistant heat-seal layer of
casing 11. Preferably, third layer 36 is analogous to third
layer 18 of Figure 1. Third layer 36 has the same general
and preferred thickness and chemical composition as third
layer 18 of Figure 1. However, third layer 36 most
preferably has a thickness of about 0.8 mils.
Fourth layer 38 is an inner layer between first
layer 32 and third layer 36, and in general is analogous to
fourth layer 20 of Figure 2. Fourth layer 38 has the same
general and preferred thickness and chemical composition as
fourth layer 20 of Figure 2.
Fifth layer 40 is a tie layer between first
layer 32 and second layer 34, and in general is analogous to
fifth layer 22 of Figure 2. Fifth layer 40 has the same
general and preferred thickness and chemical composition as
fifth layer 22 of Figure 2.
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Sixth layer 42 is a tie layer between second
layer 34 and third layer 36, and in general is analogous to
sixth layer 24 of Figure 2. Sixth layer 42 has the same
general and preferred thickness and chemical composition as
sixth layer 24 of Figure 2.
Figure 4 illustrates an alternative preferred
three-layer, heat-shrinkable, multi-layer casing film 44
suitable for use as a lap-seal casing 11 as illustrated in
Figure 1. As with multilayer film 12 of Figure 2, multi-
layer film 44 is also especially suited to the packaging of
meat products which are thereafter subjected to cook-in.
Casing film 44 comprises first layer 46, second layer 48,
and third layer 50.
First layer 46 is an outer film layer which serves
as an inside casing film layer, and is a meat-contact layer
which is analogous to first layer 14 of Figure 2. When in
the form of a casing, first layer 46 of multilayer film 44
has inside meat-contact surface 47 for direct contact with,
and adhesion to, the meat within the casing. If casing
film 44 is used to make lap-seal casing 11 as illustrated in
Figure 1, first layer 46 is sealed to third layer 50 at
backseam lap seal 13, this seal being located where a
portion of inside surface 47 overlaps a portion of outside
surface 51 of casing film 44. Preferably, first layer 46
has the same thickness and chemical composition as first
layer 14 of Figure 2; more preferably, first layer 46
comprises a modified polyolefin for improved bonding to
second layer 48; still more preferably, first layer 46
comprises anhydride-modified LLDPE as the third polyolefin.
Also, more preferably, first layer 46 has a thickness of
1.0 mil.
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Second layer 48 is a core layer between first
layer 46 and third layer 50, and in general is analogous to
second layer 16 of Figure 2. Second layer 48 has the same
general and preferred thickness and chemical composition as
second layer 16 of Figure 2.
Third layer 50 is an outer abuse-resistant layer
and heat-seal layer, which is analogous to third layer 18 of
Figure 2. Preferably, third layer 50 has the same thickness
and chemical composition as third layer 18 of Figure 2.
However, third layer 50 further comprises a modified
polyolefin for improved bonding to second layer 48; more
preferably, third layer 50 comprises, as the second
polyolefin, 100 weight percent anhydride-modified LLDPE.
Also, more preferably, third layer 50 has a thickness of
1.0 mil.
Figure 5 illustrates a cross-sectional view of
butt-seal backseamed casing 52, in accordance with the
present invention. Butt-seal backseamed casing 52 comprises
heat-shrinkable casing film 54 having abutting longitudinal
edges 56 and 58, and butt-seal tape 60, one side of which is
sealed to outside surface 55 of casing film 54,
seals 59 and 61 being in regions adjacent to and along
longitudinal edges 56 and 58. In this manner, a tubular
casing is provided in which a product can be packaged,
especially a meat product which is thereafter subjected to
cook-in while packaged in butt-seal backseamed casing 52.
Figure 6 illustrates preferred heat-shrinkable,
multilayer film 62 for use as casing film 54 in butt-seal
backseamed casing 52 illustrated in Figure 5. Multilayer
film 62 comprises first layer 64, second layer 66, third
layer 68, fourth layer 70, fifth layer 72, and sixth
layer 74.
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First film layer 64 is a meat-contact and meat
adhesion which is analogous to first layer 32 of the film of
Figure 3. First film layer 64 serves as an inside casing
layer, and provides meat-contact surface 65 for direct
contact with, and adhesion to, meat packaged in the casing
which is thereafter subjected to cook-in. Preferably, first
layer 64 has the same thickness and chemical composition as
first layer 32 of Figure 3.
Second layer 66 is an inner film layer which
serves as a casing core layer which reduces or eliminates
necking down on the forming shoe during the backseaming
operation. Second layer 66 is between first layer 64 and
third layer 68, and is analogous to second layer 34 of the
film of Figure 3. Preferably, second layer 66 has the same
thickness and chemical composition as second layer 34.
Third layer 68 is an outer film layer which serves
as an outside casing abuse-resistance and heat-seal layer,
and is analogous to third layer 36 of the film of Figure 3.
Preferably, third layer 68 has the same thickness and
chemical composition as third layer 36.
Fourth layer 70 is an inner film layer which
serves as an 02-barrier layer, is between first film layer
64 and third film layer 68, and is analogous to fourth layer
38 in film 30 of Figure 3. Preferably, fourth layer 70 has
the same thickness and chemical composition as fourth
layer 38.
Fifth layer 72 is an inner film layer which serves
as a tie layer, and is between first film layer 64 and
second film layer 66, and is analogous to fifth layer 40 in
film 30 of Figure 3. Preferably, fifth layer 72 has the
same thickness and chemical composition as fifth layer 40.
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Sixth layer 74 is an inner film layer which serves
as a tie layer, and is between second film layer 66 and
third film layer 68, and is analogous to sixth layer 42 in
film 30 of Figure 3. Preferably, sixth layer 74 has the
same thickness and chemical composition as sixth layer 42.
Figure 7 illustrates preferred heat-shrinkable,
multilayer film 76 for use as butt-seal tape film 60 in
butt-seal backseamed casing 52 illustrated in Figure S.
Multilayer film 76 comprises first layer 78, second
layer 80, third layer 82, fourth layer 84, and fifth
layer 86.
First layer 78 is an outer film layer which serves
as a heat-seal layer, and is analogous to third layer 68 of
film 62 illustrated in Figure 6. First layer 78 serves as
the outer layer of butt-seal tape film 60 which is sealed to
outside surface 55 of casing film 54, i.e., to form
seals 59 and 61 (see Figure 5). Preferably, first layer 78
has the same thickness and chemical composition as third
layer 68.
Second layer 80 is an inner film layer between
first layer 78 and third layer 82, serves as an 02-barrier
layer, and is analogous to fourth layer 38 of multilayer
film 30 illustrated in Figure 3. Preferably, second
layer 80 has the same thickness and chemical composition as
fourth layer 38.
Third layer 82 is an outer film layer which serves
as a butt-seal tape abuse-resistance layer, and is analogous
in composition to third layer 68 of film 62 illustrated in
Figure 6. Preferably, third layer 82 has the same thickness
and chemical composition as third layer 68.
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Fourth layer 84 is an inner film layer which
serves as a tie layer, is between first layer 78 and second
layer 80, and is analogous to fifth layer 40 of film 30
illustrated in Figure 3. Preferably, fourth layer 84 has
the same thickness and chemical composition as fifth
layer 40.
Fifth layer 86 is an inner film layer which serves
as a tie layer, is between second layer 80 and third layer
82, and is analogous to sixth layer 42 of film 30
illustrated in Figure 3. Preferably, fifth layer 86 has the
same thickness and chemical composition as sixth layer 42.
It should be noted that the butt-seal tape film
need not have a core layer of polyamide or polyester which
prevents the butt-seal tape film from necking down on the
forming shoe. This is due to the fact that the butt-seal
tape occupies so little of the overall structure of the
butt-sealed backseamed casing, that the shrinkage of the
tape film during the backseaming operation has little
tendency to cause necking down on the forming shoe.
Backseamed casings 11 and 52 (illustrated in
Figures 1 and 5, respectively) which use films 12, 30, 44,
62, and 76 (illustrated in Figures 2, 3, 4, 6, and 7,
respectively), are suited to many different forms of
packaging in accordance with the present invention,
including shirred casings, bags, etc.
Figure 8 illustrates a preferred process for
making casing film and/or butt-seal tape film for in
accordance with the present invention. For example,
Figure 8 illustrates a preferred process for making the
films illustrated in Figures 2, 3, 4, 6, and 7. In the
process illustrated in Figure 8, solid polymer beads (not
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illustrated) are fed to a plurality of extruders (for
simplicity, only extruder 88 is illustrated). Inside
extruders 88, the polymer beads are degassed, following
which the resulting bubble-free melt is forwarded into die
head 90, and extruded through an annular die, resulting in
tubing tape 92 which is preferably from about 15 to 30 mils
thick, and preferably has a lay-flat width of from about
2 to 10 inches.
After cooling or quenching by water spray from
cooling ring 94, tubing tape 92 is collapsed by pinch
rolls 96, and is thereafter fed through irradiation vault 98
surrounded by shielding 100, where tubing tubing 92 is
irradiated with high energy electrons (i.e., ionizing
radiation) from iron core transformer accelerator 102.
Tubing tape 92 is guided through irradiation vault 98 on
rolls 104. Preferably, tubing tape 92 is irradiated to a
level of from about 40-100 kGy, resulting in irradiated
tubing tape 106. Irradiated tubing tape 106 is wound upon
windup roll 108 upon emergence from irradiation vault 98,
forming irradiated tubing tape coil 110.
After irradiation and windup, windup roll 108 and
irradiated tubing tape coil 110 are removed and installed as
unwind roll 112 and unwind tubing tape coil 114, on a second
stage in the process of making the film as ultimately
desired. Irradiated tubing 106, being unwound from unwind
tubing tape coil 114, is then passed over guide roll 116,
after which irradiated tubing 106 is passed through hot
water bath tank 118 containing hot water 120. Irradiated
tubing 106 is then immersed in hot water 120 (preferably
having a temperature of about 185-210 F) for a period of
about 20-60, i.e., for a time period long enough to bring
the film up to the desired temperature for biaxial
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orientation. Thereafter, hot, irradiated tubular tape 122
is directed through nip rolls 124, and bubble 126 is blown,
thereby transversely stretching hot, irradiated tubular
tape 122 so that an oriented film tube 128 is formed.
Furthermore, while being blown, i.e., transversely
stretched, nip rolls 130 have a surface speed higher than
the surface speed of nip rolls 124, thereby resulting in
longitudinal orientation. As a result of the transverse
stretching and longitudinal drawing, oriented film tube 128
is produced, this blown tubing preferably having been both
stretched in a ratio of from about 1:1.5 to 1:6, and drawn
in a ratio of from about 1:1.5 to 1:6. More preferably, the
stretching and drawing are each performed at a ratio of from
about 1:2 to 1:4. The result is a biaxial orientation of
from about 1:2.25 to 1:36, more preferably, 1:4 to 1:16.
While bubble 126 is maintained between pinch
rolls 124 and 130, oriented film tube 128 is collapsed by
rollers 132, and thereafter conveyed through pinch rolls 130
and across guide roll 134, and then rolled onto.wind-up
roll 136. Idler roll 138 assures a good wind-up. The
resulting multilayer film can be used to form backseamed
casings, etc., which, in turn, can be used for the packaging
of meat products, in accordance with the present invention.
The films of the examples set forth below were
prepared according to the process described immediately
above. These examples provide additional details on the
backseamed casings, their use in the packaging of a meat
product, and the unexpected results obtained from the use of
the casing film during the backseaming process, and
subsequent packaging and cook-in of the meat product.
The polymer components used to fabricate
multilayer casing film and butt-seal tape film according to
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the present invention may also contain appropriate amounts
of additives typically included in such compositions. These
additives include slip agents such as talc, antioxidants,
fillers, dyes, pigments, radiation stabilizers, antistatic
agents, elastomers, and like additives known to those of
skill in the art of packaging films.
The backseamed casings according to the present
invention comprise casing films and butt-seal tape films
which can be prepared by any means known to those of skill
in the art, e.g., via coextrusion and/or extrusion coating,
and/or lamination. However, preferably the films are
produced by coextrusion.
The backseamed casing according to the present
invention preferably comprises a casing film (and butt-seal
tape film) which comprises a crosslinked polymer network.
Although the crosslinked polymer network can be produced in
one or more of a variety of manners, such as chemical
crosslinking and/or irradiation, preferably the crosslinked
polymer network is produced by the irradiation of a tape or
film. Either some or all of the layers of the multilayer
film can comprise crosslinked polymer networks.
In the irradiation process, the film is subjected
to an energetic radiation treatment, such as high energy
electron treatment, which induces cross-linking between
molecules of the irradiated material. The irradiation of
polymeric films is disclosed in U.S. Patent NO. 4,064,296,
to BORNSTEIN, et. al. BORNSTEIN, et. al. discloses the use
of ionizing radiation for crosslinking the polymer present
in the film.
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Radiation dosages are referred to herein in terms
of the radiation unit "RAD", with one million RADS, also
known as a megarad, being designated as "MR", or, in terms
of the radiation unit kiloGray (kGy), with 10 kiloGray
representing 1 MR, as is known to those of skill in the art.
A suitable radiation dosage of high energy electrons is in
the range of up to about 16-166 kGy, more preferably about
44-139 kGy, and still more preferably, 50-80 kGy.
Preferably, irradiation is carried out by an electron
accelerator and the dosage level is determined by standard
dosimetry methods.
As used herein, the phrases "corona treatment" and
"corona discharge treatment" refer to subjecting the
surfaces of thermoplastic materials, such as polyolefins, to
corona discharge, i.e., the ionization of a gas such as air
in close proximity to a film surface. The ionization is
initiated by a high voltage passed through a nearby
electrode, causing oxidation and other changes to the film
surface.
Corona treatment of polymeric materials is
disclosed in U.S. Patent No. 4,120,716, to BONET, issued
October 17, 1978. BONET discloses improved adherence
characteristics of polyethylene, by subjecting of the
polyethylene to corona treatment, in order to oxidize the
surface thereof. U.S. Patent No. 4,879,430, to HOFFMAN,
discloses the use of corona discharge for the treatment of
plastic webs for use in meat cook-in packaging, with the
corona treatment of the inside surface of the web increasing
the adhesion of the film to the proteinaceous material.
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Although corona treatment is a method of treatment
of the multilayer film of the present invention, plasma
treatment of the film may also be used.
Figure 9 illustrates a perspective view of
package 140 in accordance with the present invention, and
Figure 10 illustrates a cross-sectional view through
section 10-10 of Figure 9. Package 140 comprises lap-seal
casing 144 which encases meat product 146, with casing 144
being closed at both ends by clips 142, with only one clip
being illustrated in Figure 9. The lap seal portion of
casing 144 comprises longitudinal outer casing film edge 148
and longitudinal inner casing film edge 150, as well as
overlap region 152 which contains the backseam seal.
Casing 144 comprises a multilayer casing film in accordance
with the backseamed casing of the present invention. The
casing film can be, for example, any one or more of
preferred multilayer films 12, 30, 44, or 62, as described
in detail above. Furthermore, although package 140 as
illustrated comprises a lap-seal casing, alternatively the
package can comprise a butt-seal casing (preferably, as
illustrated in Figure 5), in which latter instance the
casing further comprises a butt-seal tape, preferably as
described above and as illustrated in Figures 5 and 7. In
Figures 9 and 10, product 146 in the package is preferably
meat, more preferably cooked meat, and preferably inside
surface 154 of casing 144 is adhered to the meat product
during cook-in.
The packaged product can be made by a process
comprising: (A) filling a backseamed casing with a meat
product, whereby a filled casing is formed; (B) closing the
ends of the filled casing so that the meat product is
encased by the backseamed casing, whereby a chub is formed;
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and (C) cooking the meat product encased in the backseamed
casing by subjecting the chub to cook-in, so that the meat
product adheres to the inside surface of the casing. The
backseamed casing is a backseamed casing according to the
present invention, preferably a preferred backseamed casing
according to the present invention.
Although in general the product in the package can
be any cooked meat product, preferably the cooked meat
product comprises at least one member selected from the
group consisting of poultry, ham, beef, lamb, goat, horse,
fish, liver sausage, mortadella, and bologna; more
preferably, poultry, ham, beef and bologna; even more
preferably, ham and roast beef.
The invention is illustrated by the following
examples, which are provided for the purpose of
representation, and are not to be construed as limiting the
scope of the invention. Unless stated otherwise, all
percentages, parts, etc. are by weight.
EXAMPLE 1
A 3-3/4 inch wide (lay flat dimension) tube,
called a "tape", was produced by the coextrusion process
described above and illustrated in Figure 8, wherein the
tape cross-section (from inside of tube to outside of tube)
was as follows:
0.0762 mm (3.0 mils) of LLDPE#1 (80%) and Ionomer
#1 (20%) /
0.08728 mm (3.2 mils) of a blend of EVA#1 (80%)
and LMDPE#1 (20%)
/
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0.04572 mm (1.8 mil) of anhydride grafted
LLDPE#2 /
0.04064 mm (1.6 mils) of a blend of Nylon#1 (50%)
and Nylon#2 (50%) /
0.02032 mm (0.8 mil) of EVOH/
0.02032 mm (0.8 mils) of anhydride grafted
LLDPE#2 /
0.06858 mm (2.7 mils) of a blend of EVA#1 (80%)
and LMDPE#1 (20%) /
0.0889 mm (3.5 mils) of LLDPE #3.;
wherein:
LLDPE#1 was DOWLEXO 2045.03 linear low density
polyethylene, obtained from Dow Plastics, of Freeport,
Texas;
Ionomer#1 was SURLYNO 1650 zinc-based ionomer of
ethylene/methacrylic acid copolymer, obtained from
E.I. DuPont de Nemours, of Wilmington, Delaware;
LLDPE#2 was TYMORO 1203 linear low density
polyethylene having an anhydride functionality grafted
thereon, obtained from Morton International, of Chicago,
Illinois;
EVA#1 was PE 5269T (TM) ethylene vinyl acetate
copolymer, obtained from Chevron Chemical Company of
Houston, Texas;
EVOH was EVALO LC-E105A polymerized ethylene vinyl
alcohol, obtained from Eval Company of America, of Lisle,
Illinois;
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LMDPE#1 was DOWLEXO 2037 linear medium density
polyethylene, obtained from Dow Plastics, of Freeport,
Texas;
NYLON#1 was ULTRAMIDO B4 polyamide 6, obtained
from BASF corporation of Parsippany, New Jersey;
NYLON#2 was GRILONO CF6S polyamide 6/12, obtained
from EMS-American Grilon Inc., of Sumter, S.C.;
LLDPE#3 was DOWLEXO 2244A linear low density
polyethylene, obtained from Dow Plastics of Freeport, Texas;
All the resins were extruded between 380 F and
500 F, and the die was heated to approximately 420 F. The
extruded tape was cooled with water and flattened, the
flattened width being 3-3/4 inches wide in a lay-flat
configuration. The tape was then passed through a scanned
beam of an electronic cross-linking unit, where it received
a total dosage of 64 kilo Grays (kGy), which is the
equivalent of 4.5 mega Rads (MR). After irradiation, the
flattened tape was passed through hot water for about a
third of a minute, the hot water having a temperature of
from about 208 F to 210 F. The resulting heated tape was
inflated into a bubble and oriented into a film tubing
having a lay-flat width of 9-3/4 inches and a total
thickness of 2.3 mils. The bubble was very stable and the
optics and appearance of the film were good. The film
tubing was determined to have 18% free shrinkage in the
longitudinal direction and 29% free shrinkage in the
transverse direction, when immersed in hot water for about
8 seconds, the hot water being at a temperature of 185 F,
i.e., using ASTM method D2732-83.
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The film tubing, made as described immediately
above, was then slit so that it was converted into film
sheet. The film sheet was folded longitudinally around a
forming shoe with opposing lengthwise film sheet edges being
overlapped. Thereafter, a lap-seal backseam casing was made
by applying a heat seal (using a hot seal bar, more
particularly a Nishibe Model HSP-250-SA sealing machine)
longitudinally over the overlapping regions of the film
sheet. During the backseaming operation, the film was
positioned so that the outside layer of the film tubing
(before it was slit) formed the outside layer of the
backseamed casing, with the inside layer of the film tubing
forming the inside layer of the backseamed casing. The film
backseamed well, i.e., without necking down around the
forming shoe to the extent that the film ruptured or the
process was interrupted.
The resulting backseamed casing, having with a
lay-flat width of about 4 inches, was then clipped at one
end and filled with chopped ham emulsion from the open end.
The casing was then closed with a second metal clip and the
section of meat-filled casing was cut free of the remainder
of the casing, forming a package which comprises the lap-
seal backseamed casing and the ham emulsion encased in the
casing. Several such packages were produced, and were
thereafter cooked for about 4 hours at from about
145 F - 170 F in a high humidity environment. The cooked
casings were then cooled in a cooler kept at 32 F for
several hours. The resulting chilled packages were then
examined for purge and found to have no purge between the
cooked meat product and the casing film. Also, several
samples of backseamed casing were made, each containing
water as the packaged medium, and a mixture of 0.1% mineral
oil and 99.9% water. These casings were evaluated for seal
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strength survivability by cooking at 180 F for 12 hrs, and
were found to have acceptable seal strength.
The backseamed casing was also shirred. The
shirred casings were found to have acceptable seal strength,
with very few or no pinholes being detected.
EXAMPLE 2
A 3-3/4 inch wide (lay flat dimension) tape is
produced by the coextrusion process described above in
Figure 8, wherein the tape cross-section (from inside to
outside) is as follows:
0.1524 mm (6.0 mils) of LLDPE#3 (80%) and ION#l
(20%) /
0.02794 mm (1.1 mil) of anhydride grafted
LLDPE#2 /
0.0508 mm (2.0 mils) of a blend of Nylon#1 (50%)
and Nylon#2 (50%) /
0.02794 mm (1.1 mil) of EVOH /
0.02794 mm (1.1 mils) of anhydride grafted
LLDPE#2 /
0.1524 mm 96.0 mils) of LLDPE #3,
wherein all the resins are as identified in
Example 1 above. All the resins are extruded at a
temperature of from about 380 F to 500 F, and the die is at
approximately 420 F. The extruded tape is cooled with water
and flattened, the flattened width being 3-3/4 inches wide,
in a lay-flat configuration. The tape is then passed
through a scanned beam of an electronic cross-linking unit,
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where it receives a total dosage of 64 kilo Grays (kGy),
which is the equivalent of 4.5 mega Rads (MR). After
irradiation, the flattened tape is passed through hot water
at 208 F to 210 F for a period of about a third of a minute,
immediately after which the heated tape is inflated into a
bubble, and is oriented into tubing having a lay-flat width
of 9-3/4 inches and a total thickness of 2.3 mils. The
bubble is stable and the optics and appearance of the film
are good. The resulting film has 18% free shrinkage in the
longitudinal direction and 29% free shrinkage in the
transverse direction when it is immersed in hot water at
185 F, i.e., using ASTM method D2732-83.
The film tubing, made as described immediately
above, is then slit lengthwise, converting the film tubing
into film sheet. The film sheet is folded longitudinally
around a forming shoe with longitudinally opposing edges
being overlapped, with the overlapping regions thereafter
being joined by applying a heat seal, using a hot-seal bar,
longitudinally over the overlap, to form a lap seal using a
Nishibe Model HSP-250-SA sealing machine. During the
backseaming operation, the film is positioned so that the
outside layer of the film tubing (before it is slit)
corresponds with the outside layer of the backseamed casing,
with the inside layer of the film tubing corresponding with
the inside layer of the backseamed casing. The film
backseams well.
The resulting backseamed casing, having a lay-flat
width of about 4 inches, is then clipped at one end and
filled with chopped ham emulsion from the open end. The
tubing is then closed with a second metal clip and the
section of meat-filled casing is cut free of the remainder
of the casing, forming a package which comprises the lap-
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seal backseamed casing and the ham emulsion encased in the
casing. Several packages are so made. Each of the packages
is cooked for about 4 hours from 145 F -170 F in a high
humidity environment. The cooked packages are then cooled
in a cooler kept at 32 F for several hours. The resulting
cooked, chilled packages are examined for purge and found to
have no purge between the cooked meat product and the inside
surface of the backseamed casing.
Several additional packages are made from the
backseamed casing, each of these packages containing a
product comprising 99.9% water and 0.1% mineral oil. These
casings are evaluated for seal strength survivability by
cooking at 180 F for 12 hours, and are found to have
acceptable seal strength.
EXAMPLE 3
A 3-3/4 inch wide (lay flat dimension) tubular
tape is produced according to Example 1. The tape cross-
section (from inside of tube to outside of tube) is as
follows:
0.1524 mm (6.0 mils) of Terpolyolefin#1/
0.02794 mm (1.1 mil) of anhydride grafted
LLDPE#2 /
0.0508 mm (2.0 mils) of a blend of Nylon#1 (50%)
and Nylon#2 (50%) /
0.02794 mm (1.1 mils) of EVOH /
0.02794 mm (1.1 mils) of anhydride grafted
LLDPE#2 /
0.1524 mm (6.0 mils) of LLDPE #3,
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wherein:
Terpolyolefin#1 is LOTADERO 3210 ethylene/butyl
acrylate/maleic anhydride terpolymer, comprising about
3% anhydride functionality, obtained from Elf Atochem North
America, Inc., of Philadelphia, PA, and all the other resins
are as identified in Example 1 above.
All the resins are extruded between
380 F and 500 F, and the die is at approximately 420 F. The
extruded tape is cooled with water and flattened, the
flattened width being 3-3/4 inches wide, in a lay-flat
configuration. The tape is then passed through a scanned
beam of an electronic cross-linking unit, where it receives
a total dosage of 64 kilo Grays (kGy), which is the
equivalent of 4.5 mega Rads (MR). After irradiation, the
flattened tape is passed through hot water at
208 F to 210 F, inflated into a bubble, and oriented into
tubing having a lay-flat width of 9-3/4 inches and a total
thickness of 2.3 mils. The bubble is stable and the optics
and appearance of the resulting tubing film are good. The
tubing film has 18% free shrinkage in the longitudinal
direction and 29% free shrinkage in the transverse
direction, when immersed in hot water for 8 seconds at
185 F, i.e., according to ASTM method D2732-83.
The tubing film is then slit into film. The film
is folded longitudinally around a forming shoe with opposing
longitudinal edges being overlapped, with the overlapping
regions then being joined by applying a heat seal (using a
hot-seal bar) longitudinally over the overlap, to form a
lap-seal backseamed casing, using a Nishibe Model HSP-250-SA
sealing machine. During the backseaming operation, the film
is positioned so that the layer which corresponds with the
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outside layer of the film tubing (before it is slit) forms
the outside layer of the resulting backseamed casing, with
the layer which corresponds with the inside layer of the
film tubing forms the inside layer of the resulting lap-seal
backseamed casing. The film backseams well, i.e., without
necking down on the forming shoe to the extent that the film
either ruptures or interrupts the process.
This resulting backseamed casing, having a lay-
flat width of about 4 inches, is then clipped at one end and
filled from the open end with chopped ham emulsion. The
tubing is then closed with a second metal clip, resulting in
a package, with the package thereafter being cooked for
about 4 hours from 145 F -170 F in a high humidity
environment. The packages containing cooked ham emulsion
are then cooled in a cooler for several hours, the cooler
having a temperature of about 32 F. The resulting chilled
packages are then examined for purge and found to have no
purge between the product and the plastic material.
Several other backseamed casings are filled with a
mixture of 99.9% water and 0.1% mineral oil. These casings
are evaluated for seal strength survivability by cooking at
180 F for 12 hrs, and are found to have acceptable seal
strength.
EXAMPLE 4
A 3-3/4 inch wide (lay flat dimension) annular
tape, was produced by the coextrusion process described
above and illustrated in Figure 5, wherein the tape cross-
section (from inside to outside) was as follows:
0.07112 mm (2.8 mils) of EMAA#1 /
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0.08382 mm (3.3 mils) of a blend of EVA#l (80%)
and HDPE#l (20%) /
0.02286 mm (0.9 mils) of anhydride grafted
LLDPE#2 /
0.04572 mm (1.8 mils) of a blend of Nylon#1 (50%)
and Nylon#2 (50%) /
0.02794 mm (1.1 mils) of EVOH /
0.04064 mm (1.6 mils) of anhydride grafted
LLDPE#2 /
0.05588 mm (2.2 mils) of a blend of EVA#1 (80%)
and HDPE#1 (20%) /
0.07874 mm (3.1 mils) of LLDPE #3,
wherein:
EMAA#1 was NUCREL ARX 84-2 ethylene/methacrylic
acid copolymer, obtained from E.I. DuPont de Nemours, of
Wilmington, Delaware;
HDPE#1 is FORTIFLEX J60-500C-147 high density
polyethylene, obtained from Solvay Polymers, Inc., Deer
Park, Texas; and
all other resins are as identified in Example 1
above.
All the resins were extruded at a temperature of
from about 380 F to 500 F, and the die was heated to
approximately 420 F. The extruded tape was cooled with
water and flattened, the flattened width being 3-3/4 inches
wide, in a lay-flat configuration. The tape was then passed
through a scanned beam of an electronic cross-linking unit,
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where it received a total dosage of 64 kilo Grays (kGy),
which is the equivalent of 4.5 mega Rads (MR). After
irradiation, the flattened tape was passed through hot water
at 208 F to 210 F, inflated into a bubble, and oriented into
film tubing having a lay-flat width of 9-3/4 inches and a
total thickness of 2.3 mils. The bubble was very stable and
the optics and appearance of the film tubing were good. The
resulting film tubing had 18% free shrinkage in the
longitudinal direction and 29% free shrinkage in the
transverse direction, when immersed for 8 seconds in hot
water at 185 F, i.e., using ASTM method D2732-83.
The film tubing, made as described immediately
above, was then slit longitudinally, thereby converting the
film tubing into film sheet. The film sheet was folded
longitudinally around a forming shoe, with opposing
longitudinal edges being overlapped, with the overlapping
regions of the film sheet thereafter being joined by
applying a heat seal (using a hot-seal bar) longitudinally
over the overlap, using a Nishibe Model HSP-250-SA sealing
machine. During the backseaming operation, the film was
positioned so that the outside layer of the film tubing
(before it was slit) corresponds to the outside layer of the
resulting backseamed casing, with the inside layer of the
film tubing corresponding to the inside layer of the
backseamed casing. The film backseamed well and appeared to
have acceptable seal strength. The film was also evaluated
for protein adhesion and found to have satisfactory purge
resistance with an intermediate quality ham product.
EXAMPLE 5
A 5-3/4 inch wide (lay flat dimension) annular
tape was produced by the coextrusion process described above
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and illustrated in Figure 8, wherein the tape cross-section
(from inside the tube to outside the tube) was as follows:
0.0762 mm (3.0 mils) of LLDPE#3 (80%) and EAA#1
(20%) /
0.08636 mm (3.4 mils) of a blend of EVA#1 (60%),
HDPE#1 (20%) and PIG#1 (20%)/
0.03048 mm (1.2 mil) of anhydride grafted
LLDPE#2 /
0.04308 mm (1.7 mils) of a blend of Nylon#1 (50%)
and Nylon#2 (50%) /
0.0254 mm (1.0 mils) of EVOH /
0.02794 mm (1.1 mils) of anhydride grafted
LLDPE#2 /
0.06858 mm (2.7 mils) of a blend of EVA#1 (60%),
EAA#1(20%) and PIG#1 (20%)/
0.08636 mm (3.4 mils) of LLDPE #3,
wherein:
EAA#1 is PRIMACORO 1410 ethylene/acrylic acid
copolymer, obtained from The Dow Chemical Company, of
Midland, Michigan;
PIG#1 is EPE 10214-C opaque white color
concentrate, obtained from Teknor Color Company, of
Pawtucket, R.I.;
all other resins were as identified in
Examples 1-4, above.
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All the resins were extruded at a temperature of
from about 380 F to 500 F, and the die was heated to
approximately 420 F. The extruded tape was cooled with
water and flattened, the flattened width being 5-3/4 inches,
in a lay-flat configuration. The tape was then passed
through a scanned beam of an electronic cross-linking unit,
where it received a total dosage of 64 kilo Grays (kGy),
which is the equivalent of 4.5 mega Rads (MR). After
irradiation, the flattened tape was passed through hot water
for about a third of a minute, the hot water having a
temperature of from about 208 F to 210 F. Immediately upon
emerging from the hot water bath, the heated tape was
inflated into a bubble, and oriented into a film tubing
having a lay-flat width of 15 inches and a total thickness
of 2.3 mils. The bubble was very stable and the optics and
appearance of the film tubing were good. The resulting film
tubing had 18% free shrinkage in the longitudinal direction
and 29% free shrinkage in the transverse direction when
immersed in hot water at 185 F for 8 seconds, i.e., using
ASTM method D2732-83.
The tubing, made as described immediately above,
was then slit into film, and was converted into a lap-seal
backseamed casing in the manner described in Example 1,
above. The film backseamed very well.
The lap-seal backseamed casing, having a lay-flat
width of about 4 inches, was then clipped at one end and
filled with chopped ham emulsion from the open end. The
casing was then closed with a second metal clip, and the
section of meat-filled casing is cut free of the remainder
of the casing, forming a package which comprises the lap-
seal backseamed casing and the ham emulsion encased in the
casing. Several packages were produced in this manner, with
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the packages thereafter being cooked for about 4 hours at a
temperature of from 145 F to 170 F, in a high humidity
environment. The resulting cooked casings were then cooled
in a cooler kept at 32 F for several hours. The resulting
chilled casings were then examined for purge and found to
have no purge between the product and the plastic material.
Several additional packages were produced, these
additional packages using the same backseamed casing, but
encasing a product containing 99.9% water and 0.1% mineral
oil. These casings were evaluated for seal strength
survivability by cooking at 180 F for 12 hrs, and were found
to have acceptable seal strength.
The slit film was also corona-treated to a surface
energy level of 62 dynes/cm, and then immediately folded
(and overlapped) longitudinally about a second forming shoe
having a size so that the resulting lap-seal backseamed
casing had a lay-flat width of about 5-1/4 inches. This
backseamed casing was then clipped at one end and filled
with liver sausage emulsion from the open end. The casing
was then closed with a second metal clip, and the section of
meat-filled casing was cut free of the remainder of the
casing, forming a package which comprised the lap-seal
backseamed casing and the liver sausage emulsion encased in
the casing. Several packages were produced in this manner,
with the packages thereafter being cooked for about 4 hours
from 145 F -170 F in a high humidity environment. The
resulting packages containing cooked meat were then cooled
in a cooler kept at 32 F for several hours. The resulting
chilled packages were then examined for purge and found to
have good purge-resistance at the casing lay-flat edges,
i.e., where the edges had rubbed against the forming shoe.
Thus, even though the corona treatment at the casing lay-
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flat edges had been 'buffed off', there was still sufficient
affinity of the untreated meat-contact surface of the casing
(comprising ethylene/acrylic acid copolymer) to the liver
sausage to prevent fatting out at that location.
The above backseamed casing was also shirred. The
shirred casings were found to have acceptable seal strength,
with very few or no pinholes being detected.
EXAMPLE 6
A 5-inch tape was produced by the coextrusion
process described above and illustrated in Figure 8, wherein
the tape cross-section (from inside of tube to outside of
tube) was as follows:
0.0762 mm (3.0 mils) of LLDPE #4 /
0.127 mm (5.0 mils) of a blend of EVA#2 (80%) and
LLDPE #1 ( 2 0 0) /
0.0254 mm (1.0 mil) of anhydride grafted LLDPE#2 /
0.0635 mm (2.5 mils) of Nylon#2 /
0.02794 mm (1.1 mils) of EVOH /
0.04064 mm (1.6 mils) of anhydride grafted
LLDPE#2 /
0.06096 (2.4 mils) of a blend of EVA#2 (80%) and
LLDPE#1 (20%)/
0.0762 mm (3.0 mils) of LLDPE #3, and
wherein:
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LLDPE#4 was PLEXARO PX 360 anhydride grafted
linear low density polyethylene, obtained from Quantum
Chemical Company, of Cincinnati, Ohio;
EVA#2 was ELVAXO 3128 ethylene/vinyl acetate
copolymer, obtained from E.I. DuPont de Nemours & Co., of
Wilmington, Delaware; and
and all other the resins are as identified in
Examples 1-5, above.
The tape was made and oriented into 15-inch wide
tubing film in the manner described in Example 1, above.
One significant difference between this film and the films
of Examples 1-5 is that the film of this example has a core
layer comprising only Nylon #2, i.e., nylon 6/12, rather
than containing the blend of nylon 6 and nylon 6/12. The
tape oriented acceptably, though it's orientability was/is
significantly inferior to that of the tapes of Examples 1-5.
The film tubing was converted into film sheet,
which in turn was converted into lap-seal backseamed casing
in the manner described in Example 1, above. The film
backseamed acceptably, though not as well as the films of
Examples 1-5. Also, when evaluated for seal strength, it
was/is discovered that, while the backseamed tubing of this
example probably had acceptable seal strength, it's seal
strength was/is inferior to that of the films of
Examples 1-5.
EXAMPLE 7 (Comparative)
A 5-1/8 inch, lay-flat width, annular tape was
produced by the coextrusion process described above and
illustrated in Figure 8, wherein the tape cross-section
(from inside the tube to outside the tube) was as follows:
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0.08128 mm (3.2 mils) of LLDPE #4 /
0.132 mm (5.2 mils) of a blend of EVA#2 (65%),
LLDPE #1 (20%) and PIG#1 (15%) / 0.9 mils of anhydride
grafted LLDPE#2 /
0.02286 mm (0.9 mils) of anhydride grafted
LLDPE#2 /
0.01778 mm (0.7 mils) of a blend of Nylon#1 (50%)
and Nylon#2 (50%) /
0.02794 mm (1.1 mil) of EVOH /
0.04318 mm (1.7 mils) of anhydride grafted
LLDPE#2 /
0.04826 mm (1.9 mils) of a blend of EVA#2 (650),
LLDPE#1 (20%) and PIG#1 (15%) /
0.08128 mm (3.2 mils) of LLDPE#3,
wherein all the resins are as identified in
Examples 1-6 above.
All the resins were extruded at a temperature of
from about 380 F and 530 F, and the die was heated to
approximately 420 F. The extruded tape was cooled with
water and flattened, and had a width of about 5-1/8 inches.
This tape was then passed through the scanned beam of an
electronic crosslinking unit where the tape received a total
dosage of 64 kGy. After irradiation, the flattened tape was
passed through hot water for about a third of a minute, the
hot water having a temperature of from about 204 F to 210 F.
The resulting heated tape was then inflated into a bubble in
a manner so that the heated tape was converted into a
biaxially oriented film tubing. The oriented film tubing
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had a lay-flat width of 15 inches. The multilayer film
having a total thickness of 2.3 mils, and a free shrink in
the longitudinal direction of about 18 percent, and
29 percent in the transverse direction. Free shrink was
determined by immersing the film in hot water at 185 F for
about 8 seconds, i.e., using ASTM method D2732-83.
The tubing, made as described immediately above,
was then slit into film. The film was folded longitudinally
about a forming shoe with opposed edges being joined by
applying a heat seal longitudinally over the overlapping
regions of the film, in an attempt to form a lap seal using
a Nishibe Model HSP-250-SA sealing machine. During the
backseaming operation, the film was positioned so that the
outside layer of the tubing (before it was slit)
corresponded with the outside layer of the backseamed
tubing, with the inside layer of the tubing corresponding
with the inside layer of the backseamed tubing. However,
during this backseaming step, the film necked down a
substantial degree on the forming shoe, resulting in
intermittent film rupture. Thus, the film was not
backseamable.
EXAMPLE 8 (Comparative)
A 3-1/2 inch lay-flat annular tape was produced by
the coextrusion process described above and illustrated in
Figure 8, wherein the tape cross-section (from inside of
tube to outside of tube) was as follows:
0.8128 mm (3.2 mils) of LLDPE #4 /
0.12446 mm (4.9 mils) of a blend of EVA#2 (65%),
LLDPE #1 (20%) and PIG#1 (15%) /
0.0254 mm (1.0 mil) of anhydride grafted LLDPE#2 /
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0.0635 mm (2.5 mils) of a blend of Nylon#1 (50%)
and Nylon#2 (50%)
/
0.03084 mm (1.2 mil) of EVOH /
0.04064 mm (1.6 mils) of anhydride grafted
LLDPE#2 /
0.04826 mm (1.9 mils) of a blend of EVA#2 (65%),
LLDPE#1 (20%), and PIG#1 (15%) /
0.08128 mm (3.2 mils) of LLDPE #3,
wherein all resins are as identified in Example 7
(Comparative), as set forth above.
The tape was made and oriented into 10 inch tubing
film in a manner as described above in Example 7
(Comparative). The only substantial difference between the
film of this example and the film of Example 7 (Comparative)
is the thickness of the nylon core layer, i.e., in this
example, the nylon core layer was about 3 1/2 times as thick
as the thickness of the nylon core layer in the film of
Example 7 (Comparative).
The resulting film tubing was converted into film
sheet and was thereafter further converted into a backseamed
casing, these conversion processes being carried out in the
same manner as set forth in Example 7 (Comparative), above.
However, contrary to the film of Example 7 (Comparative),
this film did not undergo substantial necking down on the
forming shoe, and underwent backseaming successfully.
Nevertheless, the resulting backseamed casing of
this example is not an example of the present invention
because it does not have sufficient purge resistance.
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However, this example demonstrated that a minimum thickness
of the nylon core layer is critical to the backseamability
of a heat-shrinkable film.
The backseamed casing was also shirred. The
shirred casings were found to have acceptable seal strength,
with very few or no pinholes being detected.
EXAMPLE 9 (Comparative)
A 5-1/8 inch tubular tape was produced by the
coextrusion process described above and illustrated in
Figure 8, wherein the tape cross-section (from inside of
tube to outside of tube) was as follows:
0.0762 mm (3.0 mils) of a blend of LLDPE #4 (90%)
and NYLON#2 (10%) /
0.1321 mm (5.2 mils) of a blend of LLDPE #2 (80%)
and EAO#1 (25%)
/
0.0508 mm (2.0 mil) of anhydride grafted LLDPE#2 /
0.02794 mm (1.1 mil) of EVOH /
0.04318 mm (1.7 mils) of anhydride grafted
LLDPE#2 /
0.08128 mm (3.2 mils) of a blend of LLDPE#2 (80%)
and EAO#1 (20%) /
0.0762 mm (3.0 mils) of LLDPE#3,
wherein EAO#1 was EXACT 4011 (TM) homogeneous
ethylene/alpha-olefin copolymer, obtained from the Exxon
Chemical Company, of Baytown, Texas; and all other resins
are as identified in Examples 1-5 and Comparatives 1-2
above.
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All the resins were extruded at a temperature of
from about 380 F to 530 F, and the die was at a temperature
of about 420 F. The extruded tape was cooled with water and
flattened, the flattened width being 5-1/8 inches. This
tape was then passed through the scanned beam of an
electronic crosslinking unit where it received a total
dosage of 64 kGy. After irradiation, the flattened tape was
passed through hot water for about a third of a minute, the
hot water having a temperature of from about 204 F to 210 F.
Upon emerging from the hot water, the resulting heated tape
was immediately inflated into a bubble, and oriented to
result in an oriented film tube having a lay-flat width of
14 inches. This film had a total thickness of 2.3 mils.
The tape did not orient as well as the films described in
Example 1, 4, 5, 7 (comparative), and 8 (comparative), due
to the absence of the nylon core layer. The film had a free
shrink of about 25 percent in the longitudinal direction,
and about 29 percent in the transverse direction. Free
shrink was determined by immersing the film in hot water for
about 8 seconds, the water having a temperature of about
185 F, i.e., using ASTM method D2732-83.
The tubing film was converted into film sheet
which was backseamed as described in Example 1. However,
during backseaming the film necked down severely on the
forming shoe (much more severely than in the case of
Example 7 (Comparative), thereby rupturing itself and
disrupting the process. Thus, this film was not a viable
backseamable film. Thus, not only did the absence of the
nylon core layer affect orientability of the film, but the
resulting film also was not backseamable. This comparative
example highlights the importance of the nylon core layer,
for backseaming as well as orientability.
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EXAMPLE 10 (Comparative)
A 5-1/8 inch tubular tape was produced by the
coextrusion process as described above and illustrated in
Figure 8, wherein the tape cross-section (from inside the
tube to outside the tube) was as follows:
0.762 mm (3.0 mils) of a blend of LLDPE#4 (80%)
and NYLON#2 (20%) /
0.1524 mm (6.0 mils) of a blend of LLDPE#2 (80%)
and EAO# 1( 2 0 0) /
0.0254 mm (1.0 mil) of anhydride grafted LLDPE#2 /
0.04064 mm (1.6 mils) of a blend of NYLON#1 (50%)
and NYLON#2 (50%) /
0.0254 mm (1.0 mil) of EVOH /
0.04318 mm (1.7 mils) of anhydride grafted
LLDPE#2 /
0.0762 mm (3.0 mils) of a blend of LLDPE#2 (80%)
and EAO# 1( 2 0 0) /
0.0762 mm (3.0 mils) of LLDPE#3,
wherein all resins are as identified in
Examples 1-9 above. The tape was coextruded and oriented
into 14 inch wide tubing film as described above in
Example 9 (Comparative). The only substantial difference
between this film and the film of Example 9 (Comparative)
was the incorporation of the nylon core layer in the film of
this example. The film oriented acceptably and far superior
to the film of Example 9 (Comparative). The tubing was then
slit into film and was backseamed by a process as described
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in Example 1 above. The film backseamed well, and exhibited
good seal strength.
However, even though the film of this example
backseamed acceptably, it is not a preferred film because it
exhibited insufficient protein adhesion, i.e., insufficient
purge-resistance. However, a comparison of the
backseamability of this film with the backseamability and
orientability of the film of Example 9(Comparative),
indicate that the presence of the nylon core layer is
critical to both backseamability and orientability of the
resulting heat-shrinkable film.
EXAMPLE 11 (Comparative)
A 5-inch tubular tape was produced by the
coextrusion process described above and illustrated in
Figure 8, wherein the tape cross-section (from inside the
tube to outside the tube) was as follows:
0.08128 mm (3.2 mils) of LLDPE #4 /
0.11684 mm (4.6 mils) of a blend of EVA#2 (80%)
and LLDPE #1 (20%) /
0.0254 mm (1.0 mil) of anhydride grafted LLDPE#2 /
0.04826 mm (1.9 mils) of a blend of Nylon#1 (50%)
and Nylon#2 (50%) /
0.02794 mm (1.1 mil) of EVOH /
0.04826 mm (1.9 mils) of anhydride grafted
LLDPE#2 /
0.08128 mm (3.2 mils) of a blend of EVA#2 (80%)
and LLDPE#1 (20%)/
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0.07874 mm (3.1 mils) of LLDPE #3, and
wherein all the resins are as identified in
Example 7 (Comparative), above. The tape was made and
oriented into 15 inch lay-flat width film tubing in the
manner described above in Example 8 (Comparative). The only
substantial difference between this film of this example and
the film of Example 8 (Comparative) is that the film of this
example was pigmented. The film was converted into film
sheet and was backseamed as described in Example 1, above.
The film sheet backseamed well. The backseamed casing was
then used to prepare a number of packages which contained
intermediate quality ham emulsion. The ham emulsion was
prepared, cooked, and chilled in the manner described in
Example 1. The resulting chilled packages were found to
have significant and unacceptable purge between the meat-
contact surface and the cooked meat product. Thus, this
example indicates that the protein-adhesion characteristic
of Plexar PX 360 anhydride-containing polyolefin resin,
which comprises less than about 1/2% anhydride
functionality, is insufficient for purge resistance with
intermediate or poor quality ham products, i.e., products
which are relatively low in protein, and are therefore more
difficult for obtaining film-to-meat adhesion. The ham
product was the same as the ham product used in Example 1.
The film sheet was also corona-treated to a
surface energy level of 62 dynes/cm, and thereafter
backseamed, with the resulting backseamed casing being used
as described immediately above, i.e., to package
intermediate quality ham product. In an examination of the
chilled casings, purge was found at areas of the casing
corresponding to the lay-flat edges, i.e., where the edges
had rubbed against the forming shoe, thereby causing
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insufficient protein adhesion. The rubbing of the edges on
the forming shoe presumably "buffed" the corona treated
surface at that location. The buffing off of the corona
treatment by the forming shoe resulted in too little purge
resistance. Without corona treatment, the purge-resistance
afforded by the anhydride-containing meat-contact resin
(Plexar PX360, which comprises less than 1% anhydride
functionality), without corona treatment (since it had been
buffed off), is insufficient to prevent fatting out. The
liver sausage product used is the same product used in the
liver sausage cook-testing of Example S.
The backseamed casing was also shirred. The
shirred casings were found to have acceptable seal strength,
with very few or no pinholes being detected.
EXAMPLE 12 (Comparative]
A 4-inch tape was produced by the coextrusion
process described above in Figure 8 wherein the tape cross-
section (from inside of tube to outside of tube) was as
follows:
0.0762 mm (3.0 mils) of EPC#1 /
0.127 mm (5.0 mils) of a blend of EVA#3 (70%) and
EAO#2 (30%) /
0.03556 mm (1.4 mil of anhydride grafted LLDPE#2 /
0.03048 mm (1.2 mils) of EVOH /
0.03302 mm (1.3 mils) of anhydride grafted
LLDPE#2 /
0.127 mm (5.0 mils) of EPC#l,
and wherein:
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EPC#l was ELTEX P KS409, a propylene/ethylene
copolymer, obtained from Solvay Polymers, Inc., of
Deer Park, Texas.
EVA#3 was PE1651CS28, 6.5% EVA copolymer, obtained
from Rexene Corporation, of Dallas, Texas.
EAO#2 was TAFMER (TM) P-0480, an
ethylene/propylene copolymer, obtained from Mitsui
Petrochemical Industries, Ltd., of Tokyo, Japan; and
all the other resins are as identified in
Example 1 above.
The tape was made and oriented into 12 inch wide
tubing film in a manner as described in Example 1, above.
The tape oriented acceptably, though the orientability of
the tape was inferior to the orientability of the tape of
Example 1, probably because the tape of Example 1 contained
a core layer comprising nylon.
The casing film, made as described immediately
above, was then slit into film sheet. The film sheet was
then corona treated on a flat-sheet corona treater to
achieve a surface energy level of about 48 dynes/cm on the
inside layer of the tubing film, i.e., the outer film layer
which was to form the corona-treated inside layer of the
casing. After corona treating, the film sheet was folded
longitudinally about a forming shoe with opposing edges
being overlapped as described above. The resulting
overlapping region of the film was then joined by applying a
heat seal longitudinally to the overlap, to form a lap seal,
using a Nishibe Model HSP-250-SA sealing machine. During
the backseaming operation, the film was positioned so that
the corona-treated surface formed the inside layer of the
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resulting lap-seal casing. Although the film did not
contain a core layer comprising nylon and/or polyester, the
film backseamed acceptably. It is believed that the
presence of the outer film layers comprising
propylene/ethylene copolymer assisted in preventing the film
from shrinking back so tightly against the forming shoe that
the process would have been interrupted.
The backseamed casing was then used to prepare a
number of packages which contained liver sausage. The
packages were prepared, cooked, and chilled in the manner
described in Example 1. While the lap-seal backseamed
casing was found to have reasonable seal strength, it was
not as preferred as the casing of the present invention, due
to less seal strength during cook-in, and more seal pucker
after cook-in, compared with the casing films of
Examples 1 and S. Furthermore, it was found that during
cook-in fatting out occurred at regions corresponding with
the casing lay-flat edges, i.e., where the corona-treatment
had been buffed off by the forming shoe.
EXAMPLE 13
A 5-inch tape was produced by the coextrusion
process described above.and illustrated in Figure 8, wherein
the tape cross-section (from inside of tube to outside of
tube) was as follows:
0.09398 mm (3.7 mils) of a blend of EPC#2 and
EAO#3 /
0.06858 mm (2.7 mils) of anhydride grafted
LLDPE#2 /
0.0508 mm (2.0 mils) of Nylon#2/
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0.0254 mm (1.0 mils) of EVOH /
0.06604 mm (2.6 mils) of anhydride grafted
LLDPE#2 /
0.1016 mm (4.0 mils) of a blend of EPC#2 and
EAO#3,
and wherein:
EPC#2 was NOBLEN (TM) W531D propylene/ethylene
copolymer, obtained from Sumitomo Chemical Company,
Limited, of Tokyo, Japan;
EAO#3 was TAFMER (TM) A-4085, an ethylene-butene
copolymer obtained from Mitsui Petrochemical Industries,
Ltd., of Tokyo, Japan; and
all the other resins are as identified in Example
1 above.
The tape was made and oriented into 14-inch wide
tubing film in a manner as described in Example 1, above.
The tape oriented acceptably, though the orientability of
the tape was inferior to the orientability of the tape of
Example 1, probably because the tape of Example 1 contained
a core layer comprising a more preferred nylon composition.
The casing film, made as described immediately
above, was then slit into film sheet and corona treated and
backseamed in the manner described in Example 12, above.
The film backseamed acceptably. After making chubs from the
casing film packed with liver sausage and subjecting the
chubs to cook-in as described in Example 12, the lap-seal
backseamed casing was found to have reasonable seal
strength, it was not as preferred as the casing of the
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present invention, due to less seal strength during cook-in,
and more seal pucker after cook-in, compared with the casing
films of Examples 1 and 5. Furthermore, it was found that
during cook-in fatting out occurred at regions corresponding
with the casing lay-flat edges, i.e., where the corona-
treatment had been buffed off by the forming shoe.
EXAMPLE 14
A 5-1/2-inch tape was produced by the coextrusion
process described above in Figure 8 wherein the tape cross-
section (from inside of tube to outside of tube) was as
follows:
0.0711 mm (2.8 mils) of EPC#1 /
0.14986 mm (5.9 mils) of a blend of EVA#3 (70%)
and EAO#2 (30%) /
0.0381 mm (1.5 mil) of anhydride grafted LLDPE#2 /
0.03048 mm (1.2 mils) of EVOH /
0.0762 mm (3.0 mils) of NYLON#2/
0.02286 mm (0.9 mils) of anhydride grafted
LLDPE#2 /
0.06096 mm (2.4 mils) of a blend of EVA#3 (70%)
and EAO#2 (30%) /
0.07366 mm (2.9 mils) of EPC#1,
and wherein:
all the resins are as identified in Example 1 & 7
above.
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The tape was made and oriented into 16-inch wide
tubing film by a process as described above in Example 1.
Although the tape oriented acceptably, the orientability of
the tape was inferior to the orientability of the tape of
Example 1, probably because the tape of Example 1 contained
a core layer comprising a more preferred nylon composition.
The casing film, made as described immediately
above, was then slit into film sheet and corona treated and
backseamed in the manner described in Example 12, above.
The film backseamed acceptably. The resulting lap-seal
backseamed casing was then shirred, with the shirred casing
then being evaluated for seal strength. The results
indicated that while the seal strength of the shirred
casings was good, the shirring process resulted in a low but
more than preferred rate of formation of pinholes alongside
the backseam.
The results obtained from Examples 1-6, which are
according to the present invention, as well as the results
obtained from Examples 7-14, reveal several important and
unexpected results obtained by the present invention.
First, it has been discovered that a core layer of
nylon substantially reduces, or prevents, film neck-down on
the forming shoe during the backseaming process, so long as
the nylon core layer has at least a certain minimum
thickness. While the amount of nylon needed probably
depends on a variety of factors, such as composition of the
remainder of the film, overall physical properties, etc., it
appears that the nylon layer needs to have a thickness of at
least about 5%, based on the total thickness of the
multilayer film, if necking down on the forming shoe is to
be substantially reduced or prevented.
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Second, the selection of the type of nylon can
have a significant impact on the performance of the film,
not just with regard to backseamability, but also with
regard to other desired characteristics, such as improved
orientability, improved sealability, improved seal strength,
and improved pinhole-resistance. Whereas seal strength is
simply the strength of the seal as measured by ability to
withstand cook-in, sealability is the ease of sealing,
i.e., incorporates a sealing window temperature, seal
consistency between batches, and seal reliability during
cook-in. For example, a comparison of the performance of
the backseamed casings according to Example 6 versus
Example 11 reveals that the core layer of a blend of
nylon 6 (50%) and nylon 6/12 (50%), provides better tape
orientability, better sealability, better backseamability,
and better seal strength. The influence of the nylon core
layer on backseamability is unexpected in that it cannot be
explained by the modulus, free shrink, or shrink force
imparted by the nylon-containing layer. Moreover, the
significant influence of the nyloncore layer on seal
strength is unexpected in that the nylon core layer is not
serving as a sealant layer.
Third, a comparison of Examples 12-14 with
themselves and with Examples 1-11 indicates several
advantages of the backseamed casing according to the present
invention. First, although the core layer comprising
polyester and/or first nylon, or first nylon having a
melting point of at least 300 F, provides advantages in
backseamability, i.e., of prevention of necking down on the
forming shoe, this advantage can in some cases (depending on
the remainder of the film composition) be obtained even
without the presence of such a core layer, as is apparent
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from a comparison of Example 12 (Comparative) with Example
13 (Comparative). Second, a comparison of Example 13
(Comparative) with Examples 1 and 5 indicates that even if a
nylon core layer is present and the film backseams
acceptably, outer layers comprising propylene/ethylene
copolymers are associated with seal puckering, which is
aesthetically and commercially less than preferred, as well
as a less than preferred level of seal cook-in survival.
Third, a comparison of Example 14 with Examples 1 and 5
indicates that the casings according to Examples 1 and 5
shirred without detectable pinhole formation, in contrast to
the comparative casing of Example 14. Also, a comparison of
Examples 6, 13, and 14 with Examples 1 and 5, indicates that
a more preferred nylon composition can significantly enhance
the orientability of the tape during the formation of the
film tubing.
Although the present invention has been described
with reference to the preferred embodiments, it is to be
understood that modifications and variations of the
invention exist without departing from the principles and
scope of the invention, as those skilled in the art will
readily understand. Accordingly, such modifications are in
accordance with the claims set forth below.
89
