Note: Descriptions are shown in the official language in which they were submitted.
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CONTROLLED ATMOSPHERE PACKAGE WITH DOUBLE COVER
BACKGROUND OF THE INVENTION
The present invention relates generally to packages for fresh red meat.
s Particularly, this invention is directed to the packaging of food products
such that
the packaged product may be maintained in one condition under certain
~ circumstances and then converted to another condition. Specifically,
packages in
accordance with the present invention provide for distribution of a packaged
product in a low oxygen environment and for introduction of oxygen to the
to product surface at a supermarket or other retail outlet. Such inlxoduction
of
oxygen is achieved either by permeation of oxygen through a film in contact
with
the product surface or through an exchange of atmospheric oxygen with a low
oxygen gaseous atmosphere contained around the product.
While a wide variety of food products can be packaged in accordance with
15 the teachings of this invention, it is particularly advantageous in
connection with
the packaging of fresh red meat such that the meat may be transported in a low
oxygen atmosphere, that is, preferably 0.5~ 02 or less, most preferably 0.05%
02 or
less, and then caused to bloom when it reaches a supermarket by exposure to
oxygen.
20 Historically, large sub-primal cuts of meat have been butchered and
packaged in each supermarket. This, however, can be inefficient a.nd result in
certain undesirable additional costs. For example, all cuts from a large sub-
primal
must be sold at once. Instead it would be preferable to permit they meat to be
butchered and packaged at a central facility which benefits from economies of
scale
25 and thereafter shipped to individual supermarkets such as is done, for
example,
with many poultry products.
In the past, the goal of central fresh red meat processing has not been
achievable because most consumers prefer to buy meat which is reddened in
color
as a result of exposure to oxygen. However, the meat maintains its reddened
color
s o for approximately one to three days and, thereafter, turns a brown color
which is
undesirable to most consumers.
Therefore, if the meat was butchered and packaged in a gas permeable
(hereinafter "permeable") film, as is typical at retail, at a central location
and then
shipped to another location for eventual sale, in all likelihood, by i:he time
the
35 package reached the retail outlet the meat would have undergone the
transformation to the brown color and would be effectively unsalable.
Conversely,
if the meat was butchered and packaged at a central location in a gas-
impermeable
(hereinafter "impermeable") film, either under vacuum or with vacuum and a low
oxygen gas flush, and then shipped to another location for eventual wile, the
meat
1
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would reach the retail outlet having a purple color which is typical of meat
prior to
exposure to oxygen. Heretofore, marketing efforts to teach the consumer about
the
harmlessness of the purple color have proved to be difficult. And, if the gas
impermeable film was a component of a conventional package having a tray which
s is overwrapped or lidded with a film and which contains a low oxygen '
atmosphere, the impermeable film would have to be removed and replaced with a
permeable film in order to allow for bloom of the meat to a bright red color
prior to '
display for the consumer, negating to a large extent the benefits of a central
processing facility.
so A variety of packages have been developed in an effort to provide a means
for transporting meat in a low oxygen environment and for quickly and easily
introducing oxygen to the meat at the retail outlet immediately prior to
display to
the consumer.
One approach to solving this problem has involved the development of
15 peelable films. That is, films have been developed which readily delaminate
into
permeable and impermeable portions. Such a film is sealed to a support member,
such as a tray, which contains the meat product, thereby forming a gas
impermeable package for distribution. At the retail outlet, the gas
impermeable
portions are peeled from the film leaving a permeable film sealed to the tray
and,
2 o therefore, a gas permeable package which allows the meat to bloom to
bright red
because of the exchange with atmospheric oxygen.
The peelable film may extend over the contained product and be sealed to
the periphery of the tray as a lid or it may be heated and draped over the
product
under vacuum to form to a vacuum skin package. However, for both types of
2 s packages the principal drawback is the relatively low gas transmission
rate of the
permeable film portion after removal of the impermeable portion. That is,
although the permeable portion of the peelable film has a much higher gas
transmission rate than that of the entire film prior to delamination, 5,000 to
25,000
cc/m2/24 hrs./atm. at 73°F as compared to 0 to 50 cc/m2/24 hrs./atm. at
73°F prior
s o to delamination, it is still too low to effect bloom of the packaged meat
in a low
oxygen gaseous atmosphere in a short period of time, except in areas of
intimate
permeable film to meat contact.
Most of the other approaches to achieving the goal of central fresh red meat
processing have involved the development of a variety of dual web packages of
the
35 type having a permeable film covering the meat product and an impermeable
film,
which is removed at the retail outlet, covering the permeable film wherein the
permeable film and the impermeable film are separate, discreet films.
Examples of these types of packages include dual overwrap packages
wherein a permeable film is wrapped around the meat and its support member
2
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WO 96!39342 PCTlUS96109047
and an impermeable film is wrapped about the permeable film; dual. lid
packages
which include a permeable lid and an impermeable lid sealed to the periphery
of
the support member; and packages with a head space which allows for the
introduction of a treating gas, typically nitrogen, carbon dioxide or some
mixture
~ s of the two, between a permeable film adjacent to the meat product and an
impermeable upper web. '$ut, as sis the case with the peelable films discussed
above, each of these dual web packages are limited in their effectiveness by
the
permeability of the permeable film. Typical gas transmission rates for
commercially viable gas permeable films are 5,000 to 25,000 cc/mz/2~I
hrs./atm. at
so 73°F which is too low to effect rapid red meat bloom by exchange of
the low
oxygen gases out and the atmospheric oxygen in.
~ further package developed to allow for central fresh red meat processing
includes a gas impermeable upper lid with a valve defined in the lid. The
package
may include a treating gas between the packaged pleat and the upper lid during
15 distribution which is withdrawn through the valve and replaced with an
oxygen-
rich gas. Although a rapid bloom is possible with this system, it has the
disadvantages of requiring trained operators at the retail outlet and
relatively
expensive equipment to exchange each package thus negating the cost savings of
a
central processing facility. The presence of the valve has the further
disadvantage
20 of creating a package appearance which is different from that which
consumers are
accustomed to seeing for meat packaging. Further, a gas space betty een the
meat
product and the impermeable film is required to maintain a bloomed color which
yields an underfilled package appearance.
Yet another package developed to allow for central fresh red meat
2s processing provides for an excellent exchange of gases and rapid
introduction of
oxygen in which an upper impermeable web covers a lower permeable web which
includes unsealed areas in the seal of the permeable web to the tray. However,
the
intermittent sealed and nonsealed areas are formed by an altered sealing head
which comprises a series of sealing "fingers" rather than a conventional,
continuous
so sealing surface.
Thus, it is an object of the present invention to provide a package which
allows for central processing of fresh red meat with minimal processing
required at
retail.
It is yet another object of the present invention to provide a package which
s5 is similar in appearance to that which consumers are accustomed to seeing
for meat
packaging.
It is a further object of the present invention to provide a package which
allows for rapid bloom of fresh red meat.
3
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64536-937
It is yet another object of the present invention
to provide a package which may be assembled, filled and
sealed at a central processing facility on conventional
equipment.
SUMMARY OF THE INVENTION
According to one aspect of the present invention,
there is provided a packaged product comprising: a product;
a support member having a cavity receiving the
product and a peripheral flange; a permeable film sealed to
the support member at a sealed area about the circumference
of said flange for enclosing the product; a discontinuity in
the sealed area between the permeable film and the flange of
the support member, wherein said discontinuity is formed by
a nonsealable powder present between the permeable film and
the flange at the sealed area, whereby a channel is formed
between the permeable film and the flange at the
discontinuity; and an impermeable film enclosing the
permeable film and the discontinuity.
According to another aspect of the present
invention, there is provided a packaged product comprising:
a product; a support member having a cavity receiving the
product and a peripheral flange; a permeable film sealed to
the support member at a sealed area about the circumference
of said flange for enclosing the product; a discontinuity in
' 25 the sealed area between the permeable film and the flange of
the support member, wherein said discontinuity is formed by
a sealable drawstring present between the permeable film and
the flange at the sealed area, whereby removal of said
drawstring provides at least one channel defined by the
permeable film and the flange; and an impermeable film
enclosing the permeable film and the discontinuity.
4
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64536-937
According to still another aspect of the present
invention, there is provided a packaged product comprising:
a product; a support member having a cavity receiving the
product and a peripheral flange, wherein said support member
is a barrier foam tray comprising a foamed substrate and a
barrier sealant film laminated thereto; a permeable film
sealed to the support member at a sealed area about the
circumference of said flange for enclosing the product; a
discontinuity in the sealed area between the permeable film
and the flange of the support member, said discontinuity
formed by a substance present between the permeable film and
the flange at the sealed area; and an impermeable film
enclosing the permeable film and the discontinuity.
According to yet another aspect of the present
invention, there is provided a packaged product comprising:
a product; a support member having a cavity receiving the
product and a peripheral flange; a permeable gasket sealed
to said flange about the circumference thereof; a permeable
film sealed to the permeable gasket, thereby enclosing the
product; and an impermeable film enclosing the permeable
film and the gasket.
According to a further aspect of the present
invention, there is provided a packaged product comprising:
a product: a support member having a cavity receiving the
product and a peripheral flange; a permeable film sealed to
the support member at said flange for enclosing the product;
at least one channel defined by the permeable film and the
support member, said channel being defined by at least one
depressed groove in the flange thereby creating an unsealed
area; and an impermeable film enclosing the permeable film,
the at least one channel and the unsealed area whereby
removal of said impermeable film allows for free flow of
4a
CA 02223240 2004-12-16
64536-937
gases through said at least one channel, into and out of
said package.
4b
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WO 96!39342 PCTlUS96/09~47
BRIEF DESCRIPTION OF THE DRAWINGS
A detailed description of preferred embodiments of the invention follows,
with reference to the accompanying drawings, wherein:
Fig. 1 is a perspective view of a package, according to the invention;
~ 5 Fig. 2 is an enlarged sectional view of a flange of a package, according
to the
invention, showing the seals of the permeable film and channels defined within
the
flange;
Fig. 3 is a cross-section of the package of Fig. 1, showing the seals of the
permeable and impermeable films;
1 o Fig. 4 is a perspective view of a package, according to the invention;
Fig. 5 is an enlarged sectional view of the flange of the package of Fig. 4
after rennoval of the impermeable film;
Fig. 6 is a perspective view of a package, according to the invention;
Fig. 7 is an enlarged sectional view of the flange of the package of Fig. 6
15 during one possible mode of operation;
Fig. 8 is an enlarged sectional view of a flange of a package, according to
the
invention, showing a gasket sealed to the permeable film and to the' flange
after
removal of the impermeable film; and
Fig. 9 is a cross-section of the package of Fig. 8 with the impermeable film
2 0 sealed to the flange.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a package for products, particularly fresh
red meat products, having a tray, an inner non-barrier or permeable fylm
sealed to
2s the flange of the tray, and an outer barrier or impermeable film sealed to
the flange
of the tray, wherein unsealed areas between the permeable film and the tray
provide for a rapid introduction of oxygen into the tray cavity upon rE~moval
of the
outer impermeable film. The unsealed areas may either provide open channels
into the tray cavity, or may contain foreign objects which, upon removal of
the
so impermeable film, provide such open channels or which have an exceptionally
high oxygen permeability such that an open channel is not required :Eor rapid
gas
exchange.
Generally, open channels between the permeable film and the flange of the
tray are formed by either ridges defined within the tray flange or a.
nonsealable
s5 substance applied to the flange, the sealing surface of the permeable film
or both.
The former is illustrated in Figure 1 of the drawings which shows a package 10
in
accordance with the present invention having a tray or support member 12 with
a
cavity 14 for receiving a product 16 and a peripheral upper flange 18 which
includes inner flange portion 20 and outer flange portion 22 separated by
CA 02223240 1997-12-02
WO 96/39342 PCT/US96/09047
depression 24. Depression 24 allows for trimming of any film sealed to the
inner
flange portion 20 and provides a clear delineation between the sealing area
for an
inner permeable film and an outer impermeable film.
In the present embodiment, inner flange portion 20 includes grooves 21
s defined therein and spaced about the perimeter of the flange. A top
impermeable
film 26 is sealed to the support member at outer flange portion 22.
Preferably, a
peelable seal is formed between the impermeable film 26 and outer flange
portion
22 such that the outer impermeable film may be readily removed from the
package
at retail.
1 o Figure 2 is an enlarged sectional view of the flange 18 of package 10
after
removal of impermeable film 26. Permeable film 28 is sealed to the support
member at inner flange portion 20. However, grooves 21 defined in inner flange
portion 20 provide for open channels between the tray cavity 14 and depression
24.
When impermeable film 26 is sealed to outer flange portion 22, depression 24
is
15 enclosed, as is shown in Figure 3. However, upon removal of film 26,
depression
24 and grooves 21 define open channels into tray cavity 14. Preferably, during
packaging the tray cavity 14 is flushed with a low oxygen gas such as, for
example,
nitrogen, carbon dioxide, or, preferably, a mixture of the two. Removal of
impermeable film 26 allows for a rapid release of the low oxygen gases
contained
2 o within the package and for a rapid introduction of oxygen into the package
thereby
blooming the packaged fresh red meat product.
Open channels between the permeable film and the flange of the tray which
are formed by a nonsealable substance applied to the flange, the sealing
surface of
the permeable film or both are represented in Figure 4 and 5 of the drawings.
25 Figure 4 shows a package 30 in accordance with the present invention having
a
tray or support member 32 with a cavity 34 for receiving a product 36 and a
flange
38 which includes inner flange portion 40 and outer flange portion 42
separated by
depression 44.
In the present embodiment, nonsealed areas 43 are defined between inner
so flange portion 40 and permeable film 48 and are spaced about the perimeter
of the
flange. As can be seen from the drawing of Figure 4, the top impermeable film
46
is sealed to the support member at outer flange portion 42. Hereagain, it is
preferred that a peelable seal is formed between the impermeable film 46 and
outer
flange portion 42 such that the outer impermeable film may be readily removed
ss from the package at retail.
Figure 5 is an enlarged sectional view of the flange 38 of package 30 after
removal of impermeable film 46. Permeable film 48 is sealed to the support
member at inner flange portion 40 but with the nonsealed areas 43 providing
open
channels between the tray cavity 34 and the external atmosphere. Upon removal
of
6
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WO 96/39342 PCTlUS96/09047
impermeable film 46, nonsealed areas 43 define open channels into tray cavity
34
allowing for a release of any contained low oxygen gases and a rapid
introduction
of oxygen and, therefore, rapid blooming of any packaged fresh red meat
product.
Unlike the embodiment of Figures 1 - 3, the present embodiment does not
require
' s that the depression between the inner and outer flange portions is
employed in
forming the open channels between the tray cavity and the atmosphere. Thus, a
- single flange tray may be employed in the present embodiment so long as the
impermeable film seal is formed external to the permeable film seal, either at
the
upper surface of the single flange or in an overwrap configuration. However, a
1 o dual flange tray such as is illustrated here has the advantage of
facilitating the
packaging process because the depression between the two flange portions
allows
for uniform trimming of the permeable film after sealing.
The nonsealed areas of package 30 of Figures 4 and 5 are formed by the
inclusion of a nonsealable material at the sealing surface of the permeable
film, the
15 inner flange or both. Examples of nonsealable materials which may be
employed
in accordlance with the present invention include solids such as corn st;~rch
or other
powders, liquids such as olefin glycols and nonsealable gels.
The nonsealable material may be applied to the surface of the film, the
flange or both or may optionally be incorporated into the surface of eitl:~er
structure
2o during its manufacture. That is, both the film and the support ;member are
comprised of one or more polymeric resins. The film may be either a monolayer
or
a multilayer structure. The layer which is sealed to the support member is
comprised of a resin or a blend of resins which are capable of forming a seal,
preferably a heat seal, with the flange of the support member. Similarly, the
2s support member, which must be gas impermeable, is at least partially
comprised
of one or more polymeric resins. One preferred support member structure for
use
in the present invention is a barrier foamed tray comprising a foamed
substrate of
a resin such as polystyrene or polypropylene with a barrier sealant film
laminated
thereto. Non-foamed polymeric materials or pulp or paperboard may also be
s o employed in the base tray as long as the upper surface is coated or
laminated with
a material which is capable of forming a seal, preferably a heat seal, with
the
permeable film and the impermeable film.
Sealability between the support member and the permeable and
impermeable films depends on a variety of factors including melting point,
35 softening point and crystallinity of the resins employed in the sealing
layers, the
r
type of seal to be formed and the degree of sealing desired. For example, in
the
seal between the support member flange and the impermeable film it is
generally
preferred that a peelable seal is formed in order to allow for ready removal
of the
impermeable film at retail. The provision of a nonsealable resin, one, for
example,
CA 02223240 1997-12-02
WO 96/39342 PCT/~JS96/09047
with a melting point and corresponding softening point too high to form heat
seals
at the desired sealing temperature, spaced throughout the sealing surface of
one of
the members to be sealed will result in nonsealed areas.
Because it is necessary to form an airtight seal between the support member
s outer flange portion and the impermeable film, it is generally preferred
that such
nonsealable resin not be included in the support member sealing surface,
although
it would be possible to provide a resin which is not sealable to the permeable
film
but is sealable to the impermeable film. Instead, it is preferred that such a
nonsealable resin be incorporated into the sealing surface of the permeable
film.
s o That is, stripes of a nonsealing resin are incorporated into the sealing
surface of the
permeable film during its manufacture. During packaging, as a roll of the
permeable film is employed to cover the product in the tray cavity and is
sealed to
the inner flange portion of the tray about the periphery thereof, the stripes
of
nonsealable resin form nonsealed areas such as are shown at Figure 5. The
1s impermeable film encloses the product but upon its removal the nonsealed
areas
provide open channels allowing for a rapid introduction of oxygen to the
packaged
product.
Figures 6 and 7 illustrate an alternative embodiment of the present
invention wherein the means for forming nonsealed areas in the seal between
the
2 o permeable film and the support member flange is a foreign object, here a
drawstring, present at the seal which forms an open channel upon its removal.
Figure 6 shows a package 50 in accordance with the present invention having a
tray or support member 52 with a cavity 54 for receiving a product 56. Unlike
the
trays shown for all of the other embodiments of the present invention, support
2s member 52 has a single flange 58. Although a dual flange tray may be
employed in the present embodiment, this embodiment is especially adaptable
for
use with a conventional single flange tray. A drawstring 61 is provided
between
permeable film 68 and flange 58 and is incorporated into the seal between the
two.
Preferably, the drawstring is coated with a sealable substance so that it is
sealed to
s o the flange and the film, rather than being merely physically trapped
within the
seal. However, the drawstring may be either coated or non-coated such that it
either seals well (as with a sealable resin coating), seals loosely (such as
may be
achieved with a wax coating), or does not seal at all to the flange and the
film.
For the present embodiment there is no open channel into tray cavity 54
3s until one is made by removal of the drawstring at retail as is illustrated
in Figure 7.
Although Figure 7 demonstrates removal of the drawstring 61 by pulling it
along
the length of the sealed area between permeable film 68 and flange 58 to form
an
enlarged open channel, it is also within the scope of the present invention to
pull
s
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WO 96/39342 PCTlITS96/09047
the drawstring straight from the package to form smaller channels having
dimensions substantially equal to the those of the drawstring itself.
Although the present embodiment may employ separate permeable and
impermeable films, it is unique in that there is no need for the imperxrteable
film to
enclose an open channel or channels because there are no open charunels until
the
package is handled at retail. Thus, the permeable and impermeable films may
' comprise a single film which can be delaminated into permeable and
:impermeable
webs. Such a multilayer film is sealed to the tray flange with the permeable
layer
or layers adjacent to the tray and the impermeable layer or layers forming an
to uppermost surface. At retail the impermeable web is delaminated from the
film
leaving the permeable web sealed to the tray. The drawstring is then removed
to
form open channels into the tray cavity in order to allow for the rapid
introduction
of oxygen to the packaged fresh red meat. As an alternative, an impermeable
film
may be sealed to or laminated to a permeable film during packaging for the
same
end result at retail.
As with many of the other embodiments of the invention described herein,
the impermeable film can be integral with and peelable from the permeable film
and thus sealed at the same location on the single flange; or, the impermeable
film
can comprise a separate film overlying the permeable film and optionally
sealed at
2 o a separate location on the flange. As a further alternative the present
package may
include an impermeable film only. The removal of one or more dravwstrings may
be employed to form open channels for sufficient gas exchange without the use
of a
permeable film.
If, however, a dual flange, dual film approach is employed, the drawstring
may advantageously be tucked into the depression between the flange portions
such than it does not extend into the seal between the outer flange portion
and the
impermeable film and out of the package itself during transport. Thus,
possible
contamination of the drawstring and, consequently, the package can be avoided.
As an alternative to a foreign object at the flange/permeable film seal which
so is removed in order to provide for a gas exchange at retail, Figures 8 and
9 show
an object which is not removed but which provides for an introduction of
oxygen
upon removal of an upper impermeable web. Figure 9 shows a cross-section of
package 70 in accordance with the present invention having a tray or support
member 72 with a cavity 74 for receiving a product and an flange 78 which
includes inner flange portion 80 and outer flange portion 82 separated by
depression 84.
In the present embodiment, inner flange portion 80 has sealed to the upper
surface thereof a permeable gasket 81 which extends about the perimeter of the
tray at that upper surface and a permeable film sealed over the gasl<:et along
the
9
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WO 96/39342 PCT/US96/09047
inner flange. The permeable gasket can be continuous around the entire inner
flange or a segment, depending upon the oxygen permeability required for the
package or other factors. A top impermeable film 86 is sealed to the support
member at outer flange portion 82. Hereagain, it is preferred that a peelable
seal is
formed between the impermeable film 86 and outer flange portion 82 such that
the
outer impermeable film may be readily removed from the package at retail.
Figure 8 is an enlarged sectional view of the flange 78 of package 70 after '
removal of impermeable film 86. Permeable film 88 is sealed to the gasket 81
which is sealed to inner flange portion 80. Optionally, a gasket may be
applied to
1 o the flange with an adhesive and then heat sealed to the permeable film.
Gasket 81
may be perforated or porous but preferably has a permeability allowing for gas
diffusion into the package equivalent to a package having a permeable film
having
an oxygen transmission rate of greater than about 100,000 cc/m2/24 hr.~1
atm.~73°F.
Furthermore, as an alternatfve, a smaller object which is porous, perforated,
or has
at least one channel defined therethrough may be contained between and sealed
to
permeable film 88 and inner flange portion 80 without being a gasket, such as
the
segment described above. That is, one or more of such highly transmissible
objects
may be contained within that seal in order to allow for a release of any
contained
low oxygen gases and a rapid introduction of oxygen into the tray cavity upon
2 o removal of the impermeable film. Inter alia, the term "discontinuities" as
used
herein therefore includes, for example, the nonsealed areas or channels
described
above that are formed by a nonsealable substance, a nonsealable portion of the
permeable film or substrate, a foreign object, e.g. a drawstring, and/or a
permeable gasket.
The permeable film or web of the present invention is an oxygen permeable
or non-barrier film or skin which may be a formable or stretchable material.
Typical polymeric materials for the present permeable film may include any
material which may be securely sealed and bonded to the support member, such
as
polyethylene or any of a variety of ethylene copolymers including, for
example,
s o ethylene vinyl acetate, ethylene acrylate copolymers, ethylene acrylic
acid
copolymers including metal neutralized salts thereof, and ethylene alpha-
olefin
copolymers. Such ethylene alpha-olefins may be heterogeneous or homogeneous
in nature. That is, ethylene alpha-olefins which have been formed by
conventional
Zeigler-Natta catalysis and are heterogeneous in nature, such as linear low
density
s5 polyethylene (LLDPE), are within the scope of the present invention as well
as .
such copolymers which are formed by single site catalysis, such as any of a
variety
of forms of metallocene catalyst technology, and are homogeneous in nature are
also within the scope of the present invention. A preferred permeable film for
use
to
CA 02223240 1997-12-02
WO 96/39.342 PCT/LJS96/09047
in accordance with the present invention is a symmetrical, five layer oriented
film
having the structure:
EVA / LLDPE / EVA / LLDPE / EVA
although a wide variety of permeable films may be employed.
' S The impermeable film or web of the present invention may be any suitable
barrier layer, film or laminate which is substantially impermeable to gas such
as
' oxygen so that a fresh meat product contained in a vacuum or other low
oxygen
atmosphere possesses an enhanced shelf life over a package without the barrier
layer. Suitable polymeric materials having gas barrier properties for use in
the
io present invention include ethylene vinyl alcohol copolymers, vinylidene
chloride
copolymers (PVDC) such as vinylidene chloride vinyl chloride or vinylidene
chloride methyl acrylate. Laminates of a sealable film and a barriier
structure
which includes a barrier layer and a tough, non-forming material such as a
biaxially oriented nylon or biaxially oriented polyester are especially
preferred for
15 use as the impermeable lidding of the present inventive packages. A
preferred
impermeable web has the structure:
biax nylon / PVDC // EVA / LLDPE / seal
wherein the double slashes (//) indicate adhesive lamination of thE~ two webs,
although a variety of laminates and multilayer films may be employed as the
2 o impermeable web of the present invention.
Generally, the films or webs which may be employed in accordance with the
present invention may be monolayer or mulHlayer. Multilayer films may be
employed when all of the properties required of the film cannot be achieved by
a
single polymeric component or a blend of polymers in a single layer. For
example,
2s an impermeable film to be sealed to a tray in all likelihood will comprise
a
multilayer film because several properties are needed including peelable
sealability, oxygen barrier and impact properties, and outer abuse properties.
Thus, the film employed will most likely contain three layers at a minimum: a
seal
layer, a barrier layer and an outer abuse layer. Further internal layers such
as
so adhesive layers and bulk layers may also be included. Laminates of sealable
films
and nonforming materials such as biaxially oriented polyester or biaxially
oriented
nylon are also within the scope of the present invention and are widely
recognized
as superior lidstocks for tray-type packages.
The foregoing description of preferred embodiments of the invention has
. s5 been presented for purposes of illustration and description. It is not
intended to be
exhaustive or to limit the invention to the precise form disclosed, and
modifications and variations are possible in light of the above teachings or
may be
acquired from practice of the invention. The embodiments were chosen and
described) in order to explain the principles of the invention and its
practical
11
CA 02223240 1997-12-02
WO 96/39342 PCT/US96/09047
application to enable one skilled in the art to utilize the invention in
various
embodiments and with various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be defined by the
claims appended hereto, and their equivalents.
s
12
