U.S. patent application number 09/138991 was filed with the patent office on 2001-12-13 for process for making a packaged product.
Invention is credited to MIZE, JR., JAMES A., NOEL, DAVID C..
Application Number | 20010051200 09/138991 |
Document ID | / |
Family ID | 22288943 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051200 |
Kind Code |
A1 |
NOEL, DAVID C. ; et
al. |
December 13, 2001 |
PROCESS FOR MAKING A PACKAGED PRODUCT
Abstract
A packaged product comprises a boneless food product comprising
at least one member selected from the group consisting of meat and
cheese. The food product has added liquid thereon, for example
brine which has been injected into (and is exuding from) a meat
product, or brine in which cheese has been soaking. The film
article surrounds the boneless food product, and is in contact with
both the boneless food product and the added liquid. The film
article exhibits a Standard Drop Test-Boneless failure rate of less
than 60 percent. A packaging process involves placing the boneless
food product into a film article, which may be a bag, pouch, or
casing, the boneless food product having added liquid thereon. The
added liquid on the surface of the meat product contaminates an
inside surface of the film article which is to be sealed. The film
article is then sealed across an open end thereof, the seal being
made through the contamination on the inside surface of the meat
product. The resulting film article exhibits a Standard Drop
Test--Boneless failure rate of less than 60 percent.
Inventors: |
NOEL, DAVID C.; (GREER,
SC) ; MIZE, JR., JAMES A.; (SIMPSONVILLE,
SC) |
Correspondence
Address: |
CRYOVAC INC
P O BOX 464
DUNCAN
SC
29334
|
Family ID: |
22288943 |
Appl. No.: |
09/138991 |
Filed: |
August 24, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09138991 |
Aug 24, 1998 |
|
|
|
09102256 |
Jun 22, 1998 |
|
|
|
Current U.S.
Class: |
426/129 ;
426/410; 426/641 |
Current CPC
Class: |
B65D 2275/02 20130101;
B65D 81/22 20130101; B65D 85/76 20130101; B32B 27/08 20130101; B65D
75/002 20130101 |
Class at
Publication: |
426/129 ;
426/410; 426/641 |
International
Class: |
B65D 085/00; A23B
004/00 |
Claims
What is claimed is:
1. A packaged product comprising: (A) a boneless food product
comprising at least one member selected from the group consisting
of meat and cheese, the food product having an added liquid
thereon; (B) a film article which is both surrounding and in
contact with both the food product and the added liquid, wherein
the film article exhibits a Standard Drop Test failure rate of less
than 60 percent.
2. The packaged product according to claim 1, wherein the film
article comprises a heat-shrinkable film.
3. The packaged product according to claim 1, wherein the film
article exhibits a Standard Drop Test failure rate of less than 50
percent.
4. The packaged product according to claim 3, wherein the film
article exhibits a Standard Drop Test failure rate of less than 40
percent.
5. The packaged product according to claim 1, wherein the food
product comprises meat.
6. The packaged product according to claim 5, wherein the meat
product comprises at least one member selected from the group
consisting of pork and beef.
7. The packaged product according to claim 6, wherein the meat
product comprises brine-injected pork.
8. The packaged product according to claim 1, wherein the added
liquid comprises brine.
9. The packaged product according to claim 8, wherein the brine is
present in an amount of from about 1 percent to 30 percent, based
on the weight of the product.
10. The packaged product according to claim 1, wherein the film
article comprises a multilayer film having a seal layer which
comprises a homogeneous ethylene/alpha-olefin copolymer.
11. The packaged product according to claim 1, wherein the film
article comprises a multilayer film having a thickness of from
about 1.5 to 3 mils.
12. The packaged product according to claim 1, wherein the film
article comprises a multilayer film having a free shrink of from
about 15 to 60 percent in at least one direction.
13. The packaged product according to claim 1, wherein the film
article comprises a multilayer film having a shrink tension of from
about 50 to 350 psi in a first direction, and from about 300 to
1000 psi in a second direction.
14. The packaged product according to claim 1, wherein the film
article comprises a multilayer film having an inside layer
comprising at least one member selected from the group consisting
of polyolefin, polyamide, polyester, polyvinyl chloride, and
ionomer.
15. A packaging process comprising: (A) making a film article
comprising at least one member selected from the group consisting
of a bag, a pouch, and a casing, the article having an open top;
(B) placing into the film article a boneless food product having
added liquid thereon, the boneless food product depositing liquid
contamination onto a region of an inside surface of the film
article which is to be sealed after the boneless food product is
placed into the film article, the liquid contamination comprising
the added liquid; and (C) heat sealing across the open top of the
film article after the boneless food product has been placed
therein, the heat-sealing being carried out through the liquid
contamination deposited onto the inside surface of the film
article, whereby a packaged product is formed; and wherein the film
article exhibits a Standard Drop Test failure rate of less than 60
percent.
16. The process according to claim 15, wherein the process further
comprises evacuating atmosphere from within the film article after
the boneless food product is placed into the film article but
before the heat sealing across the open top of the film
article.
17. The process according to claim 15, wherein the boneless food
product comprises meat, and wherein brine is injected into the meat
before the meat is placed into the film article.
18. The process according to claim 15, wherein the film article
comprises a heat shrinkable film, and the process further comprises
heat shrinking the film article after heat sealing across the open
top of the film article.
19. The process according to claim 18, wherein the film article is
an end-seal bag, and the heat-shrinkable film has a free shrink at
185.degree. F. of from about 15 to about 60 percent in a machine
direction, and a free shrink at 185.degree. F. of from about 15 to
about 60 percent in a transverse direction.
20. The process according to claim 18, wherein the film article is
an end-seal bag, and the heat-shrinkable film has a shrink tension
at 185.degree. F. in a machine direction of from about 50 to about
350 psi, and a shrink tension at 185.degree. F. in a transverse
direction of from about 310 to about 1000 psi, and wherein the
shrink tension in the transverse direction is at least 120 of the
shrink tension in the machine direction.
21. The process according to claim 15, wherein the article
comprises at least one member selected from the group consisting of
end-seal bag, side-seal bag, casing, and pouch, with the first
direction being parallel to a length of the film article, and the
second direction being perpendicular to the length of the film
article.
22. The process according to claim 15, wherein the boneless food
product comprises at least one member selected from the group
consisting of meat and cheese.
23. The process according to claim 15, wherein the boneless food
product comprises brine-injected meat.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a packaged product in which
an article, such as a bag, pouch, or casing, is used to package a
product, such as food. The invention also relates to a process for
making the packaged product according to the present invention.
BACKGROUND OF THE INVENTION
[0002] Injecting fresh meat with liquid, such as brine, is a means
to tenderize the meat. The brine interacts with the muscle
proteins, with the resulting liquid mixture exuding from the meat.
During packaging, the liquid which is on the surface of such
injected meat products is a blend of the injected brine, muscle
proteins, and natural juices and blood from the meat product. This
liquid blend tends to smear onto the packaging film in the region
to be sealed. The liquid blend is difficult to seal through. We
have analyzed the seal strength of seals made under conditions of
this type of contamination, and have discovered that the strength
of seals made through the liquid blend can be even more than 80%
less than the strength of seals made without the liquid blend being
present in the seal area while the seal is made.
[0003] While some processors have successfully solved this
weak-seal problem with equipment and line layouts which prevent
contamination of the seal area with brine, other processors
continue to have significant problems. Moreover, it has been found
that high-shrinking bags exacerbate the seal failure problem. That
is, as the bag shrinks, the seal contacts the product which puts
pressure on the seal, which can cause seal failure as the seal
shrinks tightly up against the product.
[0004] One solution to the seal failure problem has been to provide
an oversized shrink bag, so that the seal is made far enough from
the product that the shrinkage of the bag does not result in the
seal contacting the product within the bag. Although this may
reduce the seal failure problem, it causes other problems. More
particularly, it produces a packaged product of lesser aesthetic
value due to excess film extending outward from the product being
packaged. Secondly, the excess film provides an envelope which
tends to collect juices from the meat product, which are unsightly
and also exhibit an accelerated spoilage rate relative to the
remainder of the meat product. It would also be desirable to avoid
the seal failure problem while also avoiding the problems of
diminished aesthetic appearance due to excess film, unsightly juice
accumulation in the envelope of the excess film, and reduced shelf
life due to accelerated spoilage rates caused by the juice which
accumulates in the envelope of the excess film. The inventors of
the present invention have arrived at a solution to these
problems.
SUMMARY OF THE INVENTION
[0005] We have discovered that seal failure rates can be
dramatically reduced for the packaging of a boneless meat product
in which the meat has been injected with brine, without using an
oversized bag and while providing a package in which the film is
shrunk tightly against the meat product. We have discovered that
bags made from particular films can be sealed through a
brine-containing liquid blend, with significantly fewer seal
failures even after the film is shrunk tightly against the boneless
meat product. Moreover, it has been found that the use of lower
shrink tension and/or lower free shrink can assist in reducing the
seal failure due to the seal pulling down tightly against the
product being packaged during shrinkage of the film after it is
sealed around the product. Our invention enables us to package a
product using a bag which is sized closer to the size of the
product, thereby providing a final packaged product with an
appearance which is of greater aesthetic appeal, i.e., versus the
use of an oversized bag.
[0006] Using a highly abusive test, we have assessed a seal failure
rate of about 66 percent using bags which are currently in
commercial use for the packaging of brine-injected boneless pork
products. However, through the use of bags made from films of
particular polymers (especially metallocene-catalyzed
ethylene/alpha-olefin copolymers in the seal layer), as well as by
providing the film with a relatively low free shrinkage (and/or
substantially lesser shrink tension) in a direction which, in
general, is perpendicular to the seal made through the
contamination, we have discovered that we can reduce the seal
failure rate to a level as low as 26 percent, using the same highly
abusive test. This is a 60 percent reduction in seal failure rate,
using a test we believe to be significantly more abusive than the
actual conditions of use of the packaged products. In view of the
substantial improvement in seal integrity during our highly abusive
testing, we believe that in commercial use our packaged products
will exhibit a seal failure rate which is a substantial improvement
over the seal failure rate currently being experienced in the
commercial market.
[0007] As a first aspect, the present invention is directed to a
packaged product comprising: (A) a boneless food product comprising
at least one member selected from the group consisting of meat and
cheese, the food product having a free liquid additive thereon; and
(B) a film article which is both surrounding and in contact with
both the food product and the free liquid. The film article
exhibits a Standard Drop Test failure rate of less than 60 percent;
more preferably, less than 55 percent; still more preferably less
than 50 percent; yet still more preferably, less than 45 percent;
still more preferably, less than 40 percent; still more preferably,
less than 35 percent; still more preferably, less than 30 percent;
still more preferably, less than 25 percent; still more preferably,
less than 20 percent; still more preferably, less than 15
percent.
[0008] Preferably, the film article comprises a heat-shrinkable
film. Preferably, the film is a multilayer film comprising a seal
layer comprising a homogeneous ethylene/alpha-olefin copolymer.
Preferably, the film has a thickness of from about 1.5 to 3 mils;
more preferably, from about 1.8 to 2.7 mils; still more preferably,
from about 2 to 2.4 mils. Preferably, the film has a free shrink of
from about 15 to 60 percent in at least one direction; more
preferably, from about 20 to 50 percent. Preferably, the film has a
shrink tension of from about 50 to 350 pounds per square inch
(i.e., "psi") in a first direction, and from about 300-1000 in a
second direction, more preferably, from about 100 to 200 psi the
first direction, and from about 360 to 600 psi in the second
direction. Shrink tension is measured in accordance with ASTM D
2838, the entirety of which is hereby incorporated by reference
thereto.
[0009] If the film article is an end-seal bag, preferably the first
direction is the machine direction (i.e., longitudinal direction),
so that a seal made through liquid contamination is forced against
the product by the shrink tension in the first direction. Likewise,
if the film article is a side-seal bag, preferably the first
direction is the transverse direction. Preferably, the second
direction has a shrink tension of at least about 120 percent of the
shrink tension of the first direction; more preferably, from about
150 to 2000 percent of the shrink tension of the first direction;
still more preferably, from about 150 to 350 percent of the shrink
tension of the first direction; and, yet still more preferably,
from about 150 to 300 percent of the shrink tension of the second
direction.
[0010] Preferably, the multilayer film has a seal layer comprising
at least one member selected from the group consisting of
polyolefin, polyamide, polyester, polyvinyl chloride, and ionomer;
more preferably, homogeneous ethylene/alpha-olefin copolymer,
ethylene/unsaturated ester copolymer (especially ethylene/vinyl
acetate copolymer), and ionomer. Preferably, the seal layer
comprises homogeneous ethylene/alpha-olefin copolymer in an amount
of at least about 90 weight percent. A particularly preferred seal
layer comprises homogeneous ethylene/alpha-olefin copolymer in an
amount of about 80 percent, based on layer weight, and linear low
density polyethylene in an amount of about 20 percent, based on
layer weight. Preferably, the multilayer film further comprises an
O.sub.2-barrier layer, which in turn preferably comprises at least
one member selected from the group consisting of ethylene/vinyl
alcohol copolymer, polyvinylidene chloride (PVDC), polyalkylene
carbonate, polyamide, polyethylene naphthalate, polyester,
polyacrylonitrile. Preferably, the film comprises a crosslinked
polymer network, which is preferably obtained by irradiation of one
or more layers of the film. If the multilayer film comprises an
O2-barrier layer, preferably the film further comprises one or more
adhesive layers (i.e., "tie" layers) to enhance interlayer adhesion
of the various film layers to one another.
[0011] Preferably, the free liquid additive comprises brine.
Preferably, the brine is present in an amount of from about 1
percent to 30 percent, based on the weight of the product; more
preferably, from about 5 to 25 percent; still more preferably, from
about 6 to 20 percent; yet still more preferably, from about 10 to
12 percent, or from about 16 to 18 percent. Preferably, the food
product comprises meat. Preferably, the meat product comprises at
least one member selected from the group consisting of poultry,
pork, beef, lamb, goat, horse, and fish; more preferably, at least
one member selected from the group consisting of poultry, pork,
beef, and lamb; still more preferably, at least one member selected
from the group consisting of pork and beef; yet still more
preferably, brine-injected pork.
[0012] As a second aspect, the present invention is directed to a
packaging process comprising: (A) making a film article having an
open top, (B) placing into the film article a boneless food product
having an added liquid thereon, and (C) heat sealing across the
open top of the film article. The film article comprises at least
one member selected from the group consisting of a bag, a pouch,
and a casing. When being placed into the film article, the boneless
food product deposits liquid contamination onto a region of an
inside surface of the film article before the film article is
sealed across the top thereof. The liquid contamination comprises
the added liquid. Upon sealing across the top of the film article
and through the liquid contamination, a packaged product is formed.
The film article exhibits a Standard Drop Test failure rate of less
than 60 percent.
[0013] Preferably, the process further comprises evacuating
atmosphere from within the film article after the boneless food
product is placed into the film article but before the heat sealing
across the open top of the film article. Preferred films, food
products, and added liquids are as set forth above in the first
aspect of the present invention. Preferably, brine is injected into
a boneless meat product before the meat product is placed into the
film article. Preferably, the film article comprises at least one
member selected from the group consisting of an end-seal bag, a
side-seal bag, a casing, and a pouch, with the first direction
being parallel to a length of the article, and the second direction
being perpendicular to the length of the article. If the first
direction is a machine direction and the second direction is a
transverse direction, preferably the article is an end-seal bag,
casing, or pouch; if the first direction is the transverse
direction and the second direction is the machine direction,
preferably the article is a side-seal bag. If the film article is a
casing, it can be either seamless or backseamed. If the film
article is a pouch, it can be an L-seal pouch or a U-seal
pouch.
[0014] As a third aspect, the present invention is directed to a
packaged product comprising a bone-in meat product having a free
liquid additive thereon, and a film article which is both
surrounding and in contact with both the bone-in meat product and
the free liquid. The film article exhibits a Standard Drop Test
failure rate of less than 30 percent. More preferably, the film
article exhibits a Standard Drop Test failure rate of less than 25
percent; still more preferably, less than 20 percent; yet still
more preferably, less than 15 percent; and still more preferably,
less than 10 percent. Preferred films are as described above in the
first and second aspects of the present invention. Preferred
boneless meat products include bone-in beef, pork, lamb, foul
(including chicken, turkey, etc.), fish, goat, and horse.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates an end-seal bag in lay-flat view, the bag
being useful in a packaged product according to the present
invention.
[0016] FIG. 2 illustrates a cross-sectional view taken through
section 2-2 of FIG. 1.
[0017] FIG. 3 illustrates a side-seal bag in lay-flat view, the bag
being useful in a packaged product according to the present
invention.
[0018] FIG. 4 illustrates a cross-sectional view taken through
section 4-4 of FIG. 3.
[0019] FIG. 5 illustrates a schematic view of a preferred process
for making a multilayer film useful in the packaged product of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] As used herein, the phrase "added liquid" refers to any
liquid which is added to the food product, i.e., to the surface of
the food product and/or within the structure of the food product.
Examples of added liquids include brine, spice solutions, etc.,
injected into meat products, or used as soaking solutions for
cheese. Ultimately, a portion of the added liquid remains within
the food product at the time of packaging, while another portion of
the added liquid exudes onto the surface (or remains on the
surface) of the food product at the time of packaging. It is this
added liquid which is on the surface of the food product, i.e., not
within the food product, which is available to contaminate the
inside surface of the film article which is to be sealed. The added
liquid which contaminates the inside surface of the film article is
responsible for the lowering of the strength of the resulting seal.
In the present invention, brine is a preferred added liquid. As
used herein, the term "brine" is inclusive of a solution of salt
(e.g. sodium chloride) in water, regardless of whether or not other
salts are also present, such as various phosphate-containing salts.
Preferably, the brine contains salt in an amount of from about 3 to
20 percent, based on the weight of the solution.
[0021] As used herein, the phrase "free liquid" refers to liquid
that is in a package which contains a food product, the liquid
being in the package but not contained within the food product.
That is, a free liquid is not being held within the boneless-food
product. For example, "purge", which is known by those of skill in
the art as being natural juice exuded from fresh meat, is
considered to be a free liquid once the liquid exudes from the meat
product. Moreover, liquid that is present on the surface of a meat
product is also considered to be a free liquid. Still further, if a
liquid (such as brine) is injected into a meat product and
thereafter exudes from the meat product, the liquid that exudes
from the meat product is likewise considered to be free liquid,
even though the liquid is not a natural juice within the meat
product.
[0022] As used herein, the term "film" is used in a generic sense
to include plastic web, regardless of whether it is film or sheet.
Preferably, films of and used in the present invention have a
thickness of 0.25 mm or less. As used herein, the term "package"
refers to packaging materials used in the packaging of a
product.
[0023] Preferably, the film according to the present invention
comprises a total of from 3 to 20 layers; more preferably, from 4
to 12 layers; and still more preferably, from 5 to 9 layers. The
multilayer film of 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, especially desired drop test results.
[0024] As used herein, the phrases "seal layer", "sealing layer",
"heat seal layer", and "sealant layer", refer to an outer layer, or
layers, involved in the sealing of the film to itself, another
layer of the same or another film, and/or another article which is
not a film. Although it should also be recognized that up to the
outer 3 mils of a film can be involved in the sealing of the film
to itself or another layer, the phrase "seal layer," and the like,
refer herein only to the outer layer(s) which is to be heat-sealed
to itself, another film, etc. Any inner layers which contribute to
the sealing performance of the film are herein designated as
"seal-assist" layers. With respect to packages having only fin-type
seals, as opposed to lap-type seals, the phrase "sealant layer"
generally refers to the inside layer of a package, the inside layer
being an outer layer which frequently also serves as a food contact
layer in the packaging of foods. However, in a multilayer film, the
composition of the other layers (within 3 mils of the inside
surface) can also affect sealability and seal strength.
[0025] Sealant layers employed in the packaging arts have included
the genus of thermoplastic polymer, which includes thermoplastic
polyolefin, polyamide, polyester, polyvinyl chloride, and ionomer.
Preferred polymers for the sealant layer include homogeneous
ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer,
and ionomer.
[0026] As used herein, the term "heat-seal," and the phrase
"heat-sealing," refer to any seal of a first region of a film
surface to a second region of a film surface, wherein the seal is
formed by heating the regions to at least their respective seal
initiation temperatures. The heating can be performed by any one or
more of a wide variety of manners, such as using a heated bar, hot
wire, hot air, infrared radiation, ultrasonic sealing, etc.
Heat-sealing is the process of joining two or more thermoplastic
films or sheets by heating areas in contact with each other to the
temperature at which fusion occurs, usually aided by pressure.
Heat-sealing is inclusive of thermal sealing, melt-bead sealing,
impulse sealing, dielectric sealing, and ultrasonic sealing.
[0027] As used herein, the term "barrier," and the phrase "barrier
layer," as applied to films and/or layers, is used with reference
to the ability of a film or layer to serve as a barrier to one or
more gases. In the packaging art, oxygen (i.e., gaseous O.sub.2)
barrier layers have included, for example, ethylene/vinyl alcohol
copolymer, polyvinylidene chloride (PVDC), polyalkylene carbonate,
polyamide, polyethylene naphthalate, polyester, polyacrylonitrile,
etc., as known to those of skill in the art. However, in the
present invention the O.sub.2-barrier layer preferably comprises
either EVOH or polyvinylidene chloride, the PVDC comprising a
thermal stabilizer (i.e., HCl scavenger, e.g., epoxidized soybean
oil) and a lubricating processing aid, which, for example,
comprises one or more acrylates.
[0028] As used herein, the phrases "abuse layer", as well as the
phrase "puncture-resistant layer", refer to any layer which serves
to resist abrasion, puncture, and other potential causes of
reduction of package integrity, as well as potential causes of
reduction of package appearance quality. 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.
[0029] As used herein, the term "core", and the phrase "core
layer", as applied to multilayer films, refer to any internal layer
which preferably has a 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, i.e., modulus, and/or optics, and/or added abuse
resistance, and/or specific impermeability.
[0030] As used herein, the phrase "tie layer" refers to any
internal layer having the primary purpose of adhering two layers to
one another. In one preferred embodiment, tie layers can comprise
any polymer having a polar group grafted thereon, so that the
polymer is capable of covalent bonding to polar polymers such as
polyamide and ethylene/vinyl alcohol copolymer. Preferred polymers
for use in tie layers include, but are not restricted to,
ethylene/unsaturated acid copolymer, ethylene/unsaturated ester
copolymer, anhydride-grafted polyolefin, polyurethane, and mixtures
thereof.
[0031] 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.
[0032] As used herein, the phrases "food-contact layer" and
"meat-contact layer", refer to a layer of a multilayer film which
is in direct contact with the food/meat in the package comprising
the film. The food-contact/meat-contact layer is an outer layer of
the multilayer film, in the sense that the
food-contact/meat-contact layer is in direct contact with the meat
product within the package. The food-contact/meat-contact layer is
an inside layer in the sense that with respect to the packaged food
product/meat product, the food-contact/meat-contact layer is the
inside layer (i.e., innermost layer) of the package, this inside
layer being in direct contact with the food/meat.
[0033] As used herein, the phrase "food-contact surface" and
"meat-contact surface" refers to an outer surface of a food-contact
layer/meat-contact layer, this outer surface being in direct
contact with the food/meat within the package.
[0034] As used herein, "EVOH" refers to ethylene/vinyl alcohol
copolymer, i.e., polymerized ethylene vinyl alcohol. 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, or by chemical reactions with polyvinyl alcohol. The
degree of hydrolysis is preferably at least 50%, and more
preferably, at least 85%. Preferably, the EVOH comprises from about
28 to about 48 mole % ethylene, more preferably, from about 32 to
about 44 mole % ethylene, and even more preferably, from about 38
to about 44 mole % ethylene.
[0035] 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.
[0036] 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". For
films extruded through an annular die, stretching is usually
obtained by "blowing" the film to produce a bubble. For such films,
drawing is usually obtained by passing the film through two sets of
powered nip rolls, with the downstream set having a higher surface
speed than the upstream set, with the resulting draw ratio being
the surface speed of the downstream set of nip rolls divided by the
surface speed of the upstream set of nip rolls. The degree of
orientation is also referred to as the orientation ratio, or
sometimes as the "racking ratio".
[0037] 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 film, perpendicular to the machine or
longitudinal direction.
[0038] As used herein, the phrases "heat-shrinkable,"
"heat-shrink," and the like, refer to the tendency of a film,
generally an oriented film, to shrink upon the application of heat,
i.e., to contract upon being heated, such that the size (area) of
the film decreases while the film is in an unrestrained state.
Likewise, the tension of a heat-shrinkable film increases upon the
application of heat if the film is restrained from shrinking. As a
corollary, the phrase "heat-contracted" refers to a heat-shrinkable
film, or a portion thereof, which has been exposed to heat such
that the film or portion thereof is in a heat-shrunken state, i.e.,
reduced in size (unrestrained) or under increased tension
(restrained).
[0039] As used herein, the phrase "free shrink" refers to the
percent dimensional change in a 10 cm.times.10 cm specimen of film,
when subjected to selected heat (i.e., at a certain temperature),
with the quantitative determination being carried out according to
ASTM D 2732, as set forth in the 1990 Annual Book of ASTM
Standards, Vol. 08.02, pp.368-371, which is hereby incorporated, in
its entirety, by reference thereto.
[0040] As used herein, the phrase "heat-shrinkable" is used with
reference to all films which exhibit a total free shrink (i.e.,
L+T) of at least 10 percent at 185.degree. F. The multilayer film
used in the present invention preferably has a total free shrink
(i.e., L+T before shrinkage) of at least 40 percent at 185.degree.
F. Moreover, the film preferably has a free shrink of at least 15
percent at 185.degree. F. in the machine direction, and at least 15
percent at 185.degree. F. in the transverse direction. "Total free
shrink" is determined by summing the percent free shrink in the
machine direction 25 with the percentage of free shrink in the
transverse direction. For example, a film which exhibits, at
185.degree. F., 30 percent free shrink in the transverse direction
and 20 percent free shrink in the machine direction, has a "total
free shrink" at 185.degree. F. of 50 percent.
[0041] The multilayer films of the invention can be annealed or
heat-set to reduce the free shrink either slightly, substantially
or completely.
[0042] 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.
[0043] 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. A film layer can consist of a single
polymer (with or without non-polymeric additives), or can have
still additional polymers together therewith, i.e., blended
therewith.
[0044] As used 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 mer, i.e., repeating unit.
[0045] 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. The term copolymer is also
inclusive of polymers produced by reaction, such as graft
copolymer, block copolymer, and random copolymer.
[0046] 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. 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.
[0047] As used herein, the term "copolymerization" refers to the
simultaneous polymerization of two or more monomers to result in a
copolymer. 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 may copolymerize in a higher
weight or molar percent than the other monomer or monomers.
However, the first listed monomer preferably polymerizes 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.
[0048] For addition polymers, copolymers are identified, i.e.,
named, in terms of the monomers from which the copolymers are
produced. For example, the phrase "propylene/ethylene copolymer"
refers to a copolymer produced by the copolymerization of both
propylene and ethylene, with or without additional comonomer(s). A
copolymer comprises recurring "mers" derived from the monomers from
which the copolymer is produced, e.g., a propylene/ethylene
copolymer comprises propylene mer units and ethylene mer units.
[0049] 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. As used herein,
"ethylene alpha-olefin copolymer" is the equivalent of
"ethylene/alpha-olefin copolymer."
[0050] 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., typical polymers prepared, for example, using
conventional Ziegler-Natta catalysts. Heterogeneous polymers are
useful in various layers of the film used in the present invention.
Although there are a few exceptions (such as TAFMER.TM. linear
homogeneous ethylene/alpha-olefin copolymers produced by Mitsui
Petrochemical Corporation, using Ziegler-Natta catalysts),
heterogeneous polymers typically contain a relatively wide variety
of chain lengths and comonomer percentages.
[0051] 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 are
structurally different from heterogeneous polymers, in that
homogeneous polymers exhibit a relatively even sequencing of
comonomers within a chain, a mirroring of sequence distribution in
all chains, and a similarity of length of all chains, i.e., a
narrower molecular weight distribution. Furthermore, homogeneous
polymers are typically prepared using metallocene, or other
single-site type catalysis, rather than using Ziegler Natta
catalysts.
[0052] 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
(M.sub.w/M.sub.n), composition distribution breadth index (CDBI),
and narrow melting point range and single melt point behavior. The
molecular weight distribution (M.sub.w/M.sub.n), also known as
polydispersity, may be determined by gel permeation chromatography.
The homogeneous ethylene/alpha-olefin copolymers useful in this
invention generally have (M.sub.w/M.sub.n) of less than 2.7;
preferably from about 1.9 to about 2.5; more preferably, from about
1.9 to about 2.3. The composition distribution breadth index (CDBI)
of such homogeneous ethylene/alpha-olefin copolymers will generally
be greater than about 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 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 about 70%, i.e., a CDBI of from about 70% to about 99%. The
homogeneous ethylene/alpha-olefin copolymers in the multilayer
films to be used in 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 (T.sub.m), as determined by Differential
Scanning Colorimetry (DSC), of from about 60.degree. C. to about
105.degree. C. Preferably the homogeneous copolymer has a DSC peak
T.sub.m of from about 80.degree. C. to about 100.degree. C. As used
herein, the phrase "essentially single melting point" means that at
least about 80%, by weight, of the material corresponds to a single
T.sub.m peak at a temperature within the range of from about
60.degree. C. to about 105.degree. C., and essentially no
substantial fraction of the material has a peak melting point in
excess of about 115.degree. C., as determined by DSC analysis. DSC
measurements are made on a Perkin Elmer System 7 Thermal Analysis
System. Melting information reported are second melting data, i.e.,
the sample is heated at a programmed rate of 10.degree. C./min. to
a temperature below its critical range. The sample is then reheated
(2nd melting) at a programmed rate of 10.degree. C./min. The
presence of higher melting peaks is detrimental to film properties
such as haze, and compromises the chances for meaningful reduction
in the seal initiation temperature of the final film.
[0053] A homogeneous ethylene/alpha-olefin copolymer can be
prepared by the copolymerization of ethylene and any one or more
alpha-olefins. Preferably, the alpha-olefin is a C.sub.3-C.sub.20
alpha-monoolefin, more preferably, a C.sub.4-C.sub.12
alpha-monoolefin, still more preferably, a C.sub.4-C.sub.8
alpha-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.
[0054] Processes for preparing and using homogeneous polymers are
disclosed in U.S. Pat. No. 5,206,075, U.S. Pat. No. 5,241,031, and
PCT International Application WO 93/03093, each of which is hereby
incorporated by reference thereto, in its entirety. Further details
regarding the production and use of homogeneous
ethylene/alpha-olefin copolymers are disclosed in PCT International
Publication Number WO 90/03414, and PCT International Publication
Number WO 93/03093, both of which designate Exxon Chemical Patents,
Inc. as the Applicant, and both of which are hereby incorporated by
reference thereto, in their respective entireties.
[0055] Still another genus of homogeneous ethylene/alpha-olefin
copolymers is disclosed in U.S. Pat. No. 5,272,236, to LAI, et.
al., and U.S. Pat. No. 5,278,272, to LAI, et. al., both of which
are hereby incorporated by reference thereto, in their respective
entireties.
[0056] 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
olefin, copolymers of olefin, 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 polyethylene homopolymer, polypropylene
homopolymer, polybutene, ethylene/alpha-olefin copolymer,
propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer,
ethylene/unsaturated ester copolymer, ethylene/unsaturated acid
copolymer, (especially ethyl acrylate copolymer, ethylene/butyl
acrylate copolymer, ethylene/methyl acrylate copolymer,
ethylene/acrylic acid copolymer, ethylene/methacrylic acid
copolymer), modified polyolefin resin, ionomer resin,
polymethylpentene, etc. Modified polyolefin resin is inclusive of
modified polymer prepared by copolymerizing 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.
[0057] 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. 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 mixtures, blends, etc. of such polymers with
other polymers of a different type.
[0058] 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 on or polymerized therewith, as opposed to merely blended
therewith.
[0059] As used herein, the phrase "anhydride-containing polymer"
and "anhydride-modified polymer", refer 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.
[0060] 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 EXACT.TM.
linear homogeneous ethylene/alpha olefin copolymer resins
obtainable from the Exxon Chemical Company, of Baytown, Tex., and
TAFMER.TM. linear homogeneous ethylene/alpha-olefin copolymer
resins obtainable from the Mitsui Petrochemical Corporation. All
these materials generally include copolymers of ethylene with one
or more comonomers selected from C.sub.4 to C.sub.10 alpha-olefin
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. The heterogeneous
ethylene/alpha-olefin commonly known as LLDPE has a density usually
in the range of from about 0.91 grams per cubic centimeter to about
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 homogeneous ethylene/alpha-olefin copolymer useful in the
present invention.
[0061] The ethylene/alpha-olefin copolymer comprises a copolymer
resulting from the copolymerization of from about 80 to about 99
weight percent ethylene and from 1 to about 20 weight percent
alpha-olefin. Preferably, the ethylene/alpha-olefin copolymer
comprises a copolymer resulting from the copolymerization of from
about 85 to about 95 weight percent ethylene and from about 5 to
about 15 weight percent alpha-olefin.
[0062] 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.
[0063] As used herein, the phrase "outer layer" refers to any layer
of film having less than two of its principal surfaces directly
adhered to another layer of the film. The phrase is inclusive of
monolayer and multilayer films. In multilayer films, there are two
outer layers, each of which has a principal surface adhered to only
one other layer of the multilayer film. In monolayer films, there
is only one layer, which, of course, is an outer layer in that
neither of its two principal surfaces are adhered to another layer
of the film.
[0064] 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. "Inside layer" also is used with reference to the
innermost layer of a plurality of concentrically arranged layers
simultaneously coextruded through an annular die.
[0065] 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. The phrase "outside layer" also is used with
reference to the outermost layer of a plurality of concentrically
arranged layers coextruded through an annular die.
[0066] As used herein, the term "adhered" is inclusive of films
which are directly adhered to one another using a heat-seal or
other means, as well as films which are adhered to one another
using an adhesive which is between the two films. As used herein,
the phrase "directly adhered", as applied to layers, is defined as
adhesion of the subject layer to the object layer, without a tie
layer, adhesive, or other layer therebetween. In contrast, as used
herein, the word "between", as applied to a layer expressed as
being between two other specified layers, 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.
[0067] 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, i.e., an extruder, which forces the
polymeric material through the die.
[0068] 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.
[0069] At least a portion of the multilayer film of the present
invention is preferably irradiated to induce crosslinking. In the
irradiation process, the film is subjected to one or more energetic
radiation treatments, such as corona discharge, plasma, flame,
ultraviolet, X-ray, gamma ray, beta ray, and high energy electron
treatment, each of which induces cross-linking between molecules of
the irradiated material. The irradiation of polymeric films is
disclosed in U.S. Pat. No. 4,064,296, to BORNSTEIN, et. al., which
is hereby incorporated in its entirety, by reference thereto.
BORNSTEIN, et. al. discloses the use of ionizing radiation for
crosslinking the polymer present in the film.
[0070] To produce crosslinking, a suitable radiation dosage of high
energy electrons is employed, preferably using an electron
accelerator, with a dosage level being determined by standard
dosimetry methods. Other accelerators such as a Van de Graaf or
resonating transformer may be used. The radiation is not limited to
electrons from an accelerator since any ionizing radiation may be
used. The ionizing radiation can be used to crosslink the polymers
in the film. Preferably, the film is irradiated at a level of from
about 30 kGy to about 207 kGy, more preferably from about 30 kGy to
about 140 kGy. As can be seen from the descriptions of preferred
films for use in the present invention, the most preferred amount
of radiation is dependent upon the film and its end use.
[0071] 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 initiated by a high voltage passed
through a nearby electrode, and causing oxidation and other changes
to the film surface, such as surface roughness.
[0072] Corona treatment of polymeric materials is disclosed in U.S.
Pat. No. 4,120,716, to BONET, issued Oct. 17, 1978, herein
incorporated in its entirety by reference thereto. BONET discloses
improved adherence characteristics of the surface of polyethylene
by corona treatment, to oxidize the polyethylene surface. U.S. Pat.
No. 4,879,430, to HOFFMAN, also hereby incorporated in its entirety
by reference thereto, 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 to increase
the adhesion of the meat to the adhesion of the meat to the
proteinaceous material. The films of this invention can be
corona-treated in a preferred embodiment.
[0073] Various combinations of layers can be used in the formation
of the multilayer films for use in the present invention. Only 4-,
6-, and 7-layer preferred embodiments are provided here as
illustrations. The multilayer films useful in the present invention
can also comprise additional layers or fewer layers. Thus,
modifications and variations may be utilized without departing from
the principles and scope of the invention, as those skilled in the
art will readily understand.
[0074] Preferably, the film is produced by casting an annular tape
which is thereafter oriented at least 2:1 in at least 1 direction;
more preferably, from about 2:1 to about 10:1 in at least one
direction, still more preferably, at least 2.5:1 to 5:1 in at least
one direction.
[0075] FIG. 1 is a schematic of a preferred end seal bag 10, in a
lay-flat position, this bag being in accord with the present
invention; FIG. 2 is a cross-sectional view of bag 10 taken through
section 2-2 of FIG. 1. Viewing FIGS. 1 and 2 together, bag 10
comprises bag film 11, top edge 12 defining an open top, first bag
side edge 13, second bag side edge 14, bottom edge 15, and end seal
16.
[0076] FIGS. 3 and 4 illustrate side-seal bag 18. FIG. 3
illustrates a schematic of side seal bag 18, in a lay-flat view;
FIG. 4 illustrates a cross-sectional view taken through section 44
of FIG. 3. With reference to FIGS. 3 and 4 together, side seal bag
18 is comprised of bag film 19, top edge 20 defining an open top,
bottom edge 21, first side seal 22, and second side seal 23.
[0077] In addition to the bag-type packaging articles illustrated
in FIGS. 1-4 and described above, the packaging article can also be
a casing made from a flexible packaging film, i.e., a film tubing.
The casing can be a seamless casing or a backseamed casing, the
latter being a casing having a seam running the length of the
tubing. Backseamed casings include both lap-seal backseamed casings
as well as butt-sealed backseamed casings, the latter utilizing a
butt-seal tape which is sealed to the casing film, as is known to
those of skill in the art. Another type of packaging article which
can be utilized is generally referred to as a "pouch," which is
generally made from two rectangular pieces of flexible packaging
film of the same dimensions, which are sealed to one another along
3 edges, leaving the unsealed fourth edges to form the open top,
into which a product can be inserted.
[0078] FIG. 5 illustrates a schematic view of a first preferred
process for making films according to the present invention. As
illustrated in FIG. 5, solid polymer beads (not illustrated) are
fed to a plurality of extruders 28 (for simplicity, only one
extruder is illustrated). Inside extruders 28, the polymer beads
are forwarded, melted, and degassed, following which the resulting
bubble-free melt is forwarded into die head 30, and extruded
through an annular die, resulting in tubing 32 which is preferably
about 10 to 20 mils thick.
[0079] After cooling or quenching by water spray from cooling ring
34, tubing 32 is collapsed by pinch rolls 36, and is thereafter fed
through irradiation vault 38 surrounded by shielding 40, where
tubing 32 is irradiated with high energy electrons (i.e., ionizing
radiation) from iron core transformer accelerator 42. Tubing 32 is
guided through irradiation vault 38 on rolls 44. Preferably, tubing
32 is irradiated to a level of from about 40 kGy to about 120
kGy.
[0080] After irradiation, irradiated tubing 46 is directed through
pinch rolls 48, following which irradiated tubing 46 is slightly
inflated, resulting in trapped bubble 50. However, at trapped
bubble 50, the tubing is not significantly drawn longitudinally, as
the surface speed of nip rolls 52 are about the same speed as nip
rolls 48. Furthermore, irradiated tubing 46 is inflated only enough
to provide a substantially circular tubing without significant
transverse orientation, i.e., without stretching.
[0081] Slightly inflated, irradiated tubing 46 is passed through
vacuum chamber 54, and thereafter forwarded through coating die 56.
Annular coating stream 58 is melt extruded from coating die 56 and
coated onto slightly inflated, irradiated tube 50, to form two-ply
tubular film 60. Coating stream 58 preferably comprises an
O.sub.2-barrier layer, which does not pass through the ionizing
radiation. Further details of the above-described coating step are
generally as set forth in U.S. Pat. No. 4,278,738, to BRAX et. al.,
which is hereby incorporated by reference thereto, in its
entirety.
[0082] After irradiation and coating, two-ply tubing film 60 is
wound up onto windup roll 62. Thereafter, windup roll 62 is removed
and installed as unwind roll 64, on a second stage in the process
of making the tubing film as ultimately desired. Two-ply tubular
film 60, from unwind roll 64, is unwound and passed over guide roll
66, after which two-ply tubular film 60 passes into hot water bath
tank 68 containing hot water 70. The now collapsed, irradiated,
coated tubular film 60 is immersed in hot water 70 (preferably at a
temperature of from about 185.degree. F. to 210.degree. F.) for a
period of from about 10 to about 100 seconds, i.e., for a time
period in order to bring the film up to the desired temperature for
biaxial orientation.
[0083] Thereafter, irradiated tubular film 60 is directed through
nip rolls 72, and bubble 74 is blown, thereby transversely
stretching tubular film 60. Furthermore, while being blown, i.e.,
transversely stretched, nip rolls 76 draw tubular film 60 in the
longitudinal direction, as nip rolls 76 have a surface speed higher
than the surface speed of nip rolls 72. As a result of the
transverse stretching and longitudinal drawing, irradiated, coated
biaxially-oriented blown tubing film 78 is produced, this blown
tubing preferably having been both stretched in a ratio of from
about 1:1.5 to about 1:6, and drawn at a ratio of from about 1:1.5
to about 1:6; more preferably, the stretching and drawing are each
performed a ratio of from about 1:2 to about 1:4. The result is a
biaxial orientation of from about 1:2.25 to about 1:36, more
preferably, from about 1:4 to about 1:16. While bubble 74 is
maintained between pinch rolls 72 and 76, blown tubing 78 is
collapsed by rollers 80, and thereafter conveyed through pinch
rolls 76 and across guide roll 82, and then rolled onto wind-up
roll 84. Idler roll 86 assures a good wind-up.
[0084] 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.
Examples 1-4
[0085] Four different ethylene-based heat-shrinkable, coextruded
multilayer films were prepared by a process as schematically
illustrated in FIG. 5 (described above). Each of the films was
converted into a plurality of end-seal bags. For each of the four
different bag types, some of the bags were sealed shut in the
absence of any product being placed within the bag. For the
remaining bags of each type, a brine-injected pork product was
placed within the bag, with the brine/meat juice blend, being on
the surface of the meat product, contaminating the area to be the
area to be sealed. The average seal strengths of the bags were as
follows:
1TABLE 1 Avg. Seal Strength of % Reduction in Seal Avg. Seal
Strength of Bag with Brine Strength Due to Brine Film Identity
Clean Bag Seal (lb/in) Contamination (lb/in) on Seal Area 1 10.92
2.73 75.0 2 10.16 1.62 84.1 3 11.48 3.50 69.5 4 9.45 3.35 64.6
[0086] The results in Table 1 clearly establish that seal strength
is greatly reduced if the seal is made through brine in admixture
with pork purge. The clean bag seal strengths of from 9.45 to 11.48
lb/in establishes that the chemical composition of the film was not
responsible for the low seal strength obtained in the presence of
the combination of brine and purge. Taken in total, the results
indicate that the combination of purge and brine was responsible
for lowering the seal strength in an amount of from about 64.6% to
about 84.1%.
Example 5
[0087] A 7-layer, partially-irradiated, extrusion-coated, biaxially
oriented, heat-shrinkable, O.sub.2-barrier film was produced by a
process as illustrated in FIG. 5, described above. In the process,
a tape containing the first, second, and third layers was
coextruded as a substrate which was irradiated to a level of 71
kGy. Thereafter, the fourth, fifth, sixth, and seventh layers were
extrusion coated onto the irradiated substrate. In this manner, the
layer comprising PVDC-MA was not subjected to irradiation. The
orientation of the resulting 22 mil thick tape, i.e., to form the
oriented, heat-shrinkable film, was carried out by immersing the
tape in hot water at 197.degree. F., followed by immediate
immersion in hot water at 192.degree. F., followed immediately by
orientation. The tape was oriented 3.5X in the longitudinal
direction, and 3.5X in the transverse direction. The resulting film
had a thickness of 2.2 mils. The film had a free shrink at
185.degree. F. in the longitudinal direction of 37 percent, and a
free shrink at 185.degree. F. in the transverse direction of 53
percent. The various layers of the tape had the following
composition and thickness:
2TABLE 2 Layer Layer Thickness Designation Layer Chemical Identity
(mils) First Homogeneous ethylene/alpha-olefin 5 copolymer #1
Second 90% homogeneous ethylene/alpha-olefin #2 9 10% rubber Third
EVA #1 1 Fourth PVDC/MA 2 Fifth EMA 1 Sixth Homogeneous
ethylene/alpha-olefin #2 2.5 Seventh Homogeneous
ethylene/alpha-olefin #3 1.5
[0088] In Table 2 above, the identity of the resins used was as
follows. First, "homogeneous ethylene/alpha-olefin #1" was
AFFINITY.TM. PL 1280 single site catalyzed, long chain branched
ethylene/octene copolymer which had a density of 0.900 g/cc, and a
melt index of 6.0 g/10 min, obtained from The Dow Chemical Company
of Midland, Mich.
[0089] "Homogeneous ethylene/alpha-olefin #2" was DPF 1150.01
single-site-catalyzed ethylene/octene copolymer which had a density
of 0.901 g/cc, and a melt index of 0.9 g/10 min., and was obtained
from The Dow Chemical Company of Midland, Mich.
[0090] "Homogeneous ethylene/alpha-olefin #3" was AFFINITY.TM.-0
PL1850 single-site-catalyzed, long chain branched, ethylene/octene
copolymer which had a density of 0.902 g/cc, and a melt index of
3.0 g/10 min., and was obtained from The Dow Chemical Company of
Midland, Mich.
[0091] "Rubber" was BUNA EP-T-2370P ethylene/propylene/diene
(5-ethyledene 2-norbornene) resin which had a density of 0.867
g/cc, a melt index of 2.0 g/10 min, and which was obtained from
Bayer Inc., Rubber Division, of Akron, Ohio.
[0092] "EVA #1" was LD-713.93 ethylene/vinyl acetate copolymer
which had a vinyl acetate content of 15 percent, a density of 0.934
g/cc, and a melt index of 3.5 g/l 10 min., and which was obtained
from the Exxon Chemical Company of Baytown, Tex.
[0093] "PVDC/MA" was a blend of: (a) 96% XU32034.06 polyvinylidene
chloride/methyl acrylate copolymer which contained 91.5% PVDC and
8.5% methyl acrylate, obtained from The Dow Chemical Company, of
Midland, Mich.; (b) 2% PLAS CHEK.TM. 775 epoxidized soy bean oil
obtained from the Bedford Chemical Division of Ferro Corporation,
of Bedford, Mass.; and (c) 2% METABLEN.RTM. L-1000 butyl
acrylate/methyl methacrylate/butyl methacrylate terpolymer having a
density of 1.14 g/cc and obtained from Elf Atochem NA, Inc., of
Philadelphia, Pa.; the blend of (a), (b), and (c) had a density of
1.69 g/cc.
[0094] "EMA" was EMAC SP 1305.TM. ethylene/methyl acrylate
copolymer having a density of 0.944 g/cc and a melt index of 2.0
g/10 min, and was obtained from the Chevron Chemical Company of
Houston, Tex.
Example 6
[0095] Another 7-layer partially-irradiated, extrusion-coated,
biaxially oriented, heat-shrinkable, O.sub.2-barrier film was
produced in by the process as illustrated in FIG. 5, and in
accordance with the description of Example 5, above. As is apparent
from Table 3 below, the composition of each of the film layers was
the same, but the thicknesses of the layers were different from the
film of Example 5. The orientation of the resulting 17.6 mil thick
tape, i.e., to form the oriented, heat-shrinkable film, was carried
out by immersing the tape in hot water at 197.degree. F., followed
by immediate immersion in hot water at 192.degree. F., followed
immediately by orientation. The tape was oriented 2.8X in the
longitudinal direction, and 3.5X in the transverse direction. The
resulting film had a thickness of 2.2 mils. The film had a free
shrink at 185.degree. F. in the longitudinal direction of 36
percent, and a free shrink at 185.degree. F. in the transverse
direction of 48 percent. The various layers of the tape had the
following composition and thickness:
3TABLE 3 Layer Layer Thickness Designation Layer Chemical Identity
(mils) First Homogeneous ethylene/alpha-olefin 4 copolymer #1
Second 90% homogeneous ethylene/alpha-olefin #2 7.2 10% rubber
Third EVA #1 0.8 Fourth PVDC/MA 1.6 Fifth EMA 0.8 Sixth Homogeneous
ethylene/alpha-olefin #2 2 Seventh Homogeneous
ethylene/alpha-olefin #3 1.2
Example 7
[0096] Another 7-layer partially-irradiated, extrusion-coated,
biaxially oriented, heat-shrinkable, O.sub.2-barrier film was
produced in by the process as illustrated in FIG. 5, and in
accordance with the description of Example 6, above, except that
the orientation of the resulting 17.6 mil thick tape, i.e., to form
the oriented, heat-shrinkable film, was carried out by immersing
the tape in hot water at 205.degree. F., followed by immediate
immersion in hot water at 200.degree. F., followed immediately by
orientation. The tape was oriented 2.8X in the longitudinal
direction, and 3.5X in the transverse direction. The resulting film
had a thickness of 2.2 mils. The film had a free shrink at
185.degree. F. in the longitudinal direction of 18 percent, and a
free shrink at 185.degree. F. in the transverse direction of 39
percent.
Example 8
[0097] Another 7-layer partially-irradiated, extrusion-coated,
biaxially oriented, heat-shrinkable, O.sub.2-barrier film was
produced in by the process as illustrated in FIG. 5, and in
accordance with the description of Example 6, above, except that
the orientation of the resulting 17.6 mil thick tape, i.e., to form
the oriented, heat-shrinkable film, was carried out by immersing
the tape in hot water at 202.degree. F., followed by immediate
immersion in hot water at 192.degree. F., followed immediately by
orientation. The tape was oriented 2.8X in the longitudinal
direction, and 3.5X in the transverse direction. The resulting film
had a thickness of 2.2 mils. The film had a free shrink at
185.degree. F. in the longitudinal direction of 36 percent, and a
free shrink at 185.degree. F. in the transverse direction of 53
percent.
Example 9
[0098] Another 7-layer partially-irradiated, extrusion-coated,
biaxially oriented, heat-shrinkable, O.sub.2-barrier film was
produced in by the process as illustrated in FIG. 5, and unless
otherwise indicated, in accordance with the description of Example
5, above. Table 4, below, sets forth the composition and relative
thicknesses of each of the various layers of the film of this
example. The orientation of the resulting 22 mil thick tape, i.e.,
to form the oriented, heat-shrinkable film, was carried out by
immersing the tape in hot water at 197.degree. F., followed by
immediate immersion in hot water at 191 .degree. F., followed
immediately by orientation. The tape was oriented 3.5X in the
longitudinal direction, and 3.5X in the transverse direction. The
resulting film had a thickness of 2.2 mils. The film had a free
shrink at 185.degree. F. in the longitudinal direction of 37
percent, and a free shrink at 185.degree. F. in the transverse
direction of 46 percent. The various layers of the tape had the
following composition and thickness:
4TABLE 4 Layer Layer Thickness Designation Layer Chemical Identity
(mils) First Homogeneous ethylene/alpha-olefin 5 copolymer #1
Second 90% homogeneous ethylene/alpha-olefin #2 9 30% LLDPE#1 10%
rubber Third EVA #1 1 Fourth PVDC/MA 2 Fifth EMA 1 Sixth
Homogeneous ethylene/alpha-olefin #2 2.5 Seventh Homogeneous
ethylene/alpha-olefin #3 1.5
[0099] In Table 4 above, "LLDPE #1 was DOWLEX.TM.2045.03
ethylene/octene copolymer which had a density of 0.920 g/cc, and a
melt index of 1.1 g/10 min., and was obtained from The Dow Chemical
Company of Midland, Mich.
Example 10
[0100] A 4-layer partially-irradiated, extrusion-coated, biaxially
oriented, heat-shrinkable, O.sub.2-barrier film was produced by a
process as illustrated in FIG. 5, described above. In the process,
a tape containing the first and second layers was coextruded as a
substrate which was irradiated to a level of 64 kGy. Thereafter,
the third and fourth layers were extrusion coated onto the
irradiated substrate. In this manner, the layer comprising PVDC-MA
was not subjected to irradiation. The orientation of the resulting
25 mil thick tape, i.e., to form the oriented, heat-shrinkable
film, was carried out by immersing the tape in a preheat water bath
containing water at a temperature of 210.degree. F., followed by
immediate immersion in a hot water bath containing water also at
210.degree. F., followed immediately by orientation. The tape was
oriented 3.5X in the longitudinal direction, and 3.5X in the
transverse direction. The resulting film had a thickness of 2.32
mils. The film had a free shrink at 185.degree. F. in the
longitudinal direction of 21 percent, and a free shrink at
185.degree. F. in the transverse direction of 30 percent. The
various layers of the tape had the following composition and
thickness:
5TABLE 5 Layer Layer Thickness Designation Layer Chemical Identity
(mils) First 80% homogeneous ethylene/alpha-olefin 5 copolymer #1,
and 20% LLDPE #2 Second 85% LLDPE#1 12 15% EBA Third PVDC/MA 2
Fourth 90% EVA #2 6 10% HDPE
[0101] In Table 5 above, "LLDPE #2" was ESCORENE.TM. LL3003.32
ethylene/hexene copolymer which had a density of 0.9175 g/cc, and a
melt index of 3.2 g/10 min., and was obtained from the Exxon
Chemical Company of Baytown, Tex.
[0102] "EBA" was SP 1802 ethylene/butyl acrylate copolymer, having
a butyl acrylate mer content of 18%, a density of 0.928 g/cc, and a
melt index of 0.5 g/10 min, and was obtained from the Chevron
Chemical Company, of Houston, Tex.
[0103] "EVA #2" was ESCORENE.TM. LD-318.92 ethylene/vinyl acetate
copolymer which had a vinyl acetate content of 9 percent, a density
of 0.930 g/cc, and a melt index of 2.0 g/10 min., and which was
obtained from the Exxon Chemical Company of Baytown, Tex.
[0104] "HDPE" was FORTIFLEX.TM. T60-500-119 high density
polyethylene, having a density of 0.961 g/cc, and a melt index of
6.2 g/10 min., and which was obtained from Solvay Polymers, Inc.,
of Houston, Tex.
Example 11
[0105] A 7-layer partially-irradiated, extrusion-coated, biaxially
oriented, heat-shrinkable, O.sub.2-barrier film was produced by a
process as illustrated in FIG. 5, described above. In the process,
a tape containing the first, second, and third layers was
coextruded as a substrate which was irradiated to a level of 71
kGy. Thereafter, the fourth, fifth, sixth, and seventh layers were
extrusion-coated onto the irradiated substrate. In this manner, the
layer comprising PVDC-MA was not subjected to irradiation. The
orientation of the resulting 22.2 mil thick tape, i.e., to form the
oriented, heat-shrinkable film, was carried out by immersing the
tape in hot water at 197.degree. F., followed by immediate
immersion in hot water at 192.degree. F., followed immediately by
orientation. The tape was oriented 3.6X in the longitudinal
direction, and 3.55X in the transverse direction. The resulting
film had a thickness of 2.2 mils. The film had a free shrink at
185.degree. F. in the longitudinal direction of 32 percent, and a
free shrink at 185.degree. F. in the transverse direction of 43
percent. The various layers of the tape had the following
composition and thickness:
6TABLE 6 Layer Layer Thickness Designation Layer Chemical Identity
(mils) First 80% homogeneous ethylene/alpha-olefin 4.9 copolymer #1
20% LLDPE #2 Second 60% homogeneous ethylene/alpha-olefin #2 9.0
30% LLDPE#1 10% rubber Third EVA #1 1.0 Fourth PVDC/MA 1.9 Fifth
EMA 1.0 Sixth Homogeneous ethylene/alpha-olefin #2 2.6 Seventh 85%
homogeneous ethylene/alpha-olefin #3, 1.8 and 15% LLDPE #1
Example 12 (Comparative)
[0106] A 6-layer partially-irradiated, extrusion-coated, biaxially
oriented, heat-shrinkable, O.sub.2-barrier film was produced by a
process as illustrated in FIG. 5, described above. In the process,
a tape containing the first and second layers was coextruded as a
substrate which was irradiated to a level of 64 kGy. Thereafter,
the third, fourth, fifth, and sixth layers were extrusion-coated
onto the irradiated substrate. In this manner, the layer comprising
PVDC-MA was not subjected to irradiation. The orientation of the
resulting 21.1 mil thick tape, i.e., to form the oriented,
heat-shrinkable film, was carried out by immersing the tape in hot
water at 193.degree. F., followed by immediate immersion in hot
water at 180.degree. F., followed immediately by orientation. The
tape was oriented 3.2X in the longitudinal direction, and 3.7X in
the transverse direction. The resulting film had a thickness of 1.8
mils. The film had a free shrink at 185.degree. F. in the
longitudinal direction of 48 percent, and a free shrink at
185.degree. F. in the transverse direction of 60 percent. The
various layers of the tape had the following composition and
thickness:
7TABLE 7 Layer Layer Thickness Designation Layer Chemical Identity
(mils) First Homogeneous ethylene/alpha-olefin copolymer 5 #1
Second EVA #1 8.4 Third PVDC/MA 2.2 Fourth EMA 1.0 Fifth
Homogeneous ethylene/alpha-olefin #4 3.0 Sixth 85% homogeneous
ethylene/alpha-olefin #4, 1.5 and 2% Antiblock Masterbatch
[0107] In Table 7 above, "homogeneous ethylene/alpha-olefin #4" was
AFFINITY.TM. PF1140 single-site-catalyzed, long chain branched,
ethylene/octene copolymer which had a density of 0.8965 g/cc, and a
melt index of 1.6 g/10 min., and was obtained from The Dow Chemical
Company of Midland, Mich.
[0108] "Antiblock Masterbatch" was L-7118-AB antiblock masterbatch
in which 20% talc was present in an AFFINITY.TM.
ethylene/alpha-olefin copolymer carrier, obtained from Bayshore
Industrial of LaPorte, Tex., the masterbatch had a density of 1.039
and a melt index of 5.5 g/10 min.
Example 13 (Comparative)
[0109] A 7-layer partially-irradiated, extrusion-coated, biaxially
oriented, heat-shrinkable, O.sub.2-barrier film was produced by a
process as illustrated in FIG. 5, described above. In the process,
a tape containing the first, second, and third layers was
coextruded as a substrate which was irradiated to a level of 50
kGy. Thereafter, the fourth, fifth, sixth, and seventh layers were
extrusion-coated onto the irradiated substrate. In this manner, the
layer comprising PVDC-MA was not subjected to irradiation. The
orientation of the resulting 23.8 mil thick tape, i.e., to form the
oriented, heat-shrinkable film, was carried out by immersing the
tape in hot water at 205.degree. F., followed by immediate
immersion in hot water at 195.degree. F., followed immediately by
orientation. The tape was oriented 3.5X in the longitudinal
direction, and 4X in the transverse direction. The resulting film
had a thickness of 1.93 mils. The film had a free shrink at
185.degree. F. in the longitudinal direction of 31 percent, and a
free shrink at 185.degree. F. in the transverse direction of 45
percent. The various layers of the tape had the following
composition and thickness:
8TABLE 8 Layer Layer Thickness Designation Layer Chemical Identity
(mils) First 80% homogeneous ethylene/alpha-olefin 5.5 copolymer
#1, and 20% LLDPE #2 Second EVA #3 9.1 Third EVA #3 1.0 Fourth
PVDC/MA 2.2 Fifth EVA #2 0.8 Sixth EVA#2 3.9 Seventh 90% EVA #2,
and 1.3 10% HDPE
[0110] In Table 8 above, "EVA #3 was ESCORENE.TM. LD 720.92
ethylene/vinyl acetate copolymer which had a vinyl acetate content
of 19 percent, a density of 0.940 g/cc, and a melt index of 1.5
g/10 min., and which was obtained from the Exxon Chemical Company
of Baytown, Tex.
The "Standard Drop Test"
[0111] The Standard Drop Test was conducted as follows. First,
boneless pork sirloin pieces were injected with a brine-based
injection solution. The brine-based injection solution contained
about 5 percent sodium chloride and about 1.1 percent phosphate.
The boneless pork sirloin pieces were injected with the brine
solution in an amount of about 11 percent, based on the weight of
the boneless sirloin pieces.
[0112] About 41/2 pounds of injected pork sirloin pieces were then
placed in a test bag (preferably, an end-seal bag) having a
lay-flat width of from about 8 to 91/2 inches, and a length of
about 18 inches. The seal area of the bag was kept free of
contamination by loading the meat into the bag using a loading
horn. Then, the seal area of the bag (i.e., a portion of the inside
surface of the bag through which the seal was to be made) was
intentionally contaminated from about 5 to 6 milliliters of a
brine/purge seal contamination solution which was evenly dispersed
onto the inside surface of the bag, in the area to be sealed.
[0113] The brine/purge seal contamination solution was prepared as
follows: 500 milliliters of the brine solution, which was the same
as the injection solution discussed above, as mixed with 500
milliliters of pork purge (i.e., blood) and 100 g of lean pork
muscle. This mixture was then blended until liquefied, and was
chilled to a temperature of from about 32.degree. to 45.degree. F.
for at least 1 hour prior to use.
[0114] After the brine/purge seal contamination solution was
applied to the seal area of the bag, the bag was heat sealed using
a Cryovac.TM. 8600-B18 rotary chamber vacuum packaging machine.
While in the Cryovac.RTM. 8600-B18 rotary chamber vacuum packaging
machine, the atmosphere within the bag was evacuated to a level of
about 2-3 torr, and while the bag was evacuated, it was closed
around the product by heat sealing, the seal being made through
that portion of the bag to which the brine/purge seal contamination
solution had been applied. The sealing parameters were as follows:
seal voltage: 76 amps, seal time: 0.5 seconds; machine speed: 30
packages per minute. The seal was made within about 4 inches of the
injected pork sirloin pieces. After sealing, the resulting package
was shrunk in a Cryovac.TM. BFT6570 E shrink tunnel which operated
with a water temperature of 195.degree. F. and a belt speed of 55
ft/min.
[0115] Five of the resulting packages were placed in a 15 inches
wide, by 231/2 inches long by 9 inches deep, with the box material
(corrugated paper board) being about 1/8 inch thick. The box
containing the 5 packages was then dropped from a height of 34"
onto a level, flat, hard surface, so that the bottom surface of the
box lands flat on the hard surface. After dropping, the five
packages were removed from the box, inflated with air, and
submerged in water to determine if the seal made from the
Cryovac.TM. 8600 B-18 packaging machine had failed, i.e., whether
the seal was leaking. Any air bubbles which came from this seal
indicated a leak.
[0116] A total of 50 replications were conducted in order to
establish the performance criteria, i.e., the failure rate, which
was reported in terms of the percent of the bags which exhibited
leaking at the seal. Leaks occurring at an area other than the seal
are discarded, i.e., do not contribute to the test result. In
conducting the replications, no box was used (i.e., dropped) more
than three times. Moreover, the sirloin pieces were used no more
than 5 times, i.e., no more than 5 replications. The sirloin pieces
were maintained at a temperature of from about 32.degree. F. to
45.degree. F. Between each replication the sirloin pieces were
submerged in the brine solution for a minimum of 5 minutes before
repackaging. The temperature of the brine solution was maintained
between 32.degree. F. and 45.degree. F.
9TABLE 9 Results of Standard Drop Test for Films of Examples 5
through 13 Standard Drop Test Film of Example No. (% leakers) 5 36
6 34 7 36 8 26 9 32 10 36 11 30 12 (Comparative) 86 13
(Comparative) 66
[0117] The results set forth in Table 9, above, show that the films
of Examples 5-11, when used in a Standard Drop Test, exhibited a
percent leaker rate of from 26-36 percent. In contrast, the films
of Examples 12 and 13, both of which are comparative examples,
exhibited a percent leaker rate of 86 percent and 66 percent,
respectively.
[0118] It is not completely understood why the films of Examples 12
and 13 did not perform as well in the Standard Drop Test as did the
films of Examples 5-11. However, it is believed that if the film
shrinks in the shrink tunnel so that the seal (made through the
brine-containing contamination) is forced too tightly against the
meat product, the weakness of this seal will cause a higher
percentage of such bags to fail during the Standard Drop Test. The
film of Example 12 (Comparative) had a significantly higher free
shrink and shrink tension in the direction perpendicular to the
seal made through the contamination. Factors also believed to
affect film performance in the Standard Drop Test include seal
layer composition (homogeneous ethylene/alpha-olefin copolymer
appeared to perform better), film thickness (thicker films appeared
to perform better), film free shrink and shrink tension in the
direction perpendicular to the seal made through the contamination
(low free shrink and shrink tension appeared to perform better),
amount and type of contamination in the area to be sealed (less
contamination is better), type of meat product (including size,
shape, meat species, etc), and presence or absence of bone in the
meat product.
[0119] In addition to the use of bags for carrying out the process
of the present invention (and making the packaged product of the
present invention), the multilayer film can be a tubular casing,
preferably a shirrable casing. Preferably, the casing is used for
the packaging of food products, especially boneless meat products
and processed meat products. Among the types of meat which can be
packaged in the films and packages according to the present
invention are poultry, pork, beef, sausage, lamb, goat, horse, and
fish. Preferably, the casing of the present invention is used in
the packaging of pork, poultry, beef, and sausage products.
[0120] The polymer components used to fabricate multilayer films
according to the present invention may also contain appropriate
amounts of other additives normally included in such compositions.
These include slip agents such as talc, antioxidants, fillers,
dyes, pigments and dyes, radiation stabilizers, antistatic agents,
elastomers, and the like additives known to those of skill in the
art of packaging films.
[0121] All ranges within all of the above-disclosed ranges are
expressly included within this specification. Moreover, layers
which are adjacent or directly adhered to one another are
preferably of differing chemical composition, especially differing
polymeric composition. All reference to ASTM tests are to the most
recent, currently approved and published version of the ASTM test
identified, as of the priority filing date of this application.
[0122] Although the present invention has been described in
connection with the preferred embodiments, it is to be understood
that modifications and variations may be utilized without departing
from the principles and scope of the invention, as those skilled in
the art will readily understand. Accordingly, such modifications
may be practiced within the scope of the following claims.
* * * * *