U.S. patent application number 10/326010 was filed with the patent office on 2004-06-24 for film fracture feature for peelable multilayer package lid.
This patent application is currently assigned to Cryovac, Inc.. Invention is credited to Barmore, Charles Rice, Carrouth, Andrew Boyd JR., McDonald, Gregory Edward.
Application Number | 20040118852 10/326010 |
Document ID | / |
Family ID | 32593916 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040118852 |
Kind Code |
A1 |
Barmore, Charles Rice ; et
al. |
June 24, 2004 |
Film fracture feature for peelable multilayer package lid
Abstract
A package for storing and shipping food products incorporates a
multilayer film lid that includes a gas-impermeable exterior layer
and a gas-permeable interior layer. The multilayer film lid is heat
sealed to a flange of a tray upon which the food product is
supported. The gas-impermeable layer may be delaminated from the
gas-permeable layer when it is desired to expose the food to
atmospheric gases. Separation of the gas-impermeable layer from the
gas-permeable layer is facilitated by a film fracture feature
included in the heat seal pattern adjacent a pull tab of the lid.
The film fracture feature concentrates the separation forces
exerted on the tab in a small area so that the gas-permeable layer
of the lid readily breaks at the film fracture feature.
Inventors: |
Barmore, Charles Rice;
(Moore, SC) ; Carrouth, Andrew Boyd JR.;
(Woodruff, SC) ; McDonald, Gregory Edward;
(Simpsonville, SC) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
Cryovac, Inc.
|
Family ID: |
32593916 |
Appl. No.: |
10/326010 |
Filed: |
December 19, 2002 |
Current U.S.
Class: |
220/359.2 ;
220/359.3; 220/359.4 |
Current CPC
Class: |
B65D 77/2044 20130101;
B65D 2577/205 20130101; B65D 2577/2066 20130101; B65D 2577/2091
20130101 |
Class at
Publication: |
220/359.2 ;
220/359.3; 220/359.4 |
International
Class: |
B65D 041/00 |
Claims
What is claimed is:
1. A package for a food product, comprising: a tray for supporting
a food product, the tray defining an upper surface; a multilayer
film lid attached to the upper surface of the tray by a heat seal
that extends about a perimeter surrounding the food product, an
outer edge of the heat seal having two substantially straight
portions that are joined by a corner portion of the heat seal, the
lid having upper and lower layers joined together such that the
upper layer can be peeled from the lower layer, the lower layer
being permeable to oxygen and the upper layer being substantially
impermeable to oxygen, the lid having a pull tab portion that
extends out beyond the corner portion of the heat seal; and a film
fracture feature defined in the corner portion of the heat seal
proximate the pull tab portion, the film fracture feature
comprising a portion of the outer edge of the heat seal formed as a
straight-line segment oriented at a non-perpendicular angle to each
of the two substantially straight portions of the heat seal,
whereby pulling upward on the pull tab portion focuses forces on
said straight-line segment to break the lower layer along the film
fracture feature and thereby initiate fracture between the upper
and lower layers of the lid.
2. The package of claim 1, wherein the film fracture feature
includes a second straight-line segment, the two straight-line
segments intersecting at a vertex.
3. The package of claim 1, wherein the tray includes a bottom wall
for supporting said food product, a side wall extending upwards
from said bottom wall and terminating at a top edge, and a flange
extending outwardly from said top edge of said side wall and
including said upper surface to which said lid is attached by said
heat seal.
4. A package for storing a food product in a modified atmosphere,
comprising: a tray for supporting the food product; and a
multilayer film lid attached to the tray with a heat seal between
the tray and the lid, said heat seal extending substantially
continuously about the product to enclose the food product between
said tray and said lid, said lid comprising a multilayer film
having a first layer and a second layer removably joined together
such that the first layer can be delaminated from the second layer;
wherein the lid includes a pull tab portion and said second layer
is positioned between said first layer and said tray such that the
first layer may be delaminated from the second layer while leaving
said second layer attached to said tray; wherein the heat seal
includes a film fracture feature on an outer edge of the heat seal
proximate to said pull tab portion of said lid, said film fracture
feature comprising a straight-line segment of the outer edge of the
heat seal that intersects another portion of the outer edge of the
heat seal and thereby forms a vertex that acts as a stress riser
for initiation of the delamination of said first layer from said
second layer.
5. The package of claim 4, wherein the tray includes a bottom wall
for supporting said food product, a side wall extending upwards
from said bottom wall and terminating at a top edge, and a flange
connected to said top edge of said side wall, wherein said lid is
connected to the flange by the heat seal.
6. The package of claim 5, wherein said flange provides a
continuous surface that completely surrounds the top edge of said
side wall.
7. The package of claim 6, wherein said tray is generally a
quadrilateral including four of said side walls and four corners at
the intersections between said side walls, and said flange includes
four straight portions respectively joined to the side walls and
four corner portions formed at junctures between said straight
portions of the flange.
8. The package of claim 7, wherein said heat seal includes four
straight portions respectively extending along the four straight
portions of said flange and four corner portions respectively
located at the four corner portions of said flange, and wherein
said film fracture feature is located at one of the corner portions
of the heat seal.
9. The package of claim 8, wherein said flange includes a generally
planar upper surface extending outwardly from said top edge of said
side walls and a stepped surface connected to an outer edge of said
upper surface.
10. The package of claim 9, wherein said film fracture feature of
the heat-seal pattern does not extend outwardly beyond the upper
surface of the flange.
11. The package of claim 9, wherein said generally planar upper
surface of the corner portion of the flange having the film
fracture feature extends to an outer edge of said corner
portion.
12. The package of claim 4, wherein the film fracture feature
includes a second straight-line segment, the two straight-line
segments intersecting at a vertex.
13. The package of claim 4, wherein the film fracture feature
includes at least three straight-line segments that form a vertex
at each intersection of said straight-line segments.
14. The package of claim 4, wherein said first layer includes a
gas-impermeable film.
15. The package of claim 14, wherein said second layer is a
gas-permeable film.
16. A package for storing a food product in a modified atmosphere,
comprising: a tray for supporting said food product thereon
including a bottom wall for supporting said food product, a side
wall extending upwards from said bottom wall and terminating in a
top edge, and a flange connected to the top edge of said side wall,
wherein said tray is generally a quadrilateral including four of
said side walls and four corners at intersections between said side
walls, such that said flange includes four straight portions and
four corner portions; and a lid bonded to said tray with a heat
seal between said tray and said lid, said heat seal extending
substantially continuously about the product to enclose the food
product between said tray and said lid, said lid being a multilayer
film having a first layer and a second layer removably joined
together, said lid having a pull tab portion; wherein said first
layer is gas-impermeable and wherein said second layer is
gas-permeable and is positioned between said first layer and said
tray such that said first layer may be delaminated from said second
layer; wherein said heat seal includes four straight portions
respectively extending along the four straight portions of said
flange and four corner portions respectively located at the four
corner portions of said flange, the pull tab portion of said lid
extending out beyond one of the corner portions of the heat seal;
wherein the corner portion of the heat seal proximate the pull tab
portion includes a film fracture feature comprising a straight-line
segment of an outer edge of the heat seal that intersects another
portion of the outer edge of the heat seal and thereby forms a
vertex that acts as a stress riser for initiation of the
delamination of said first layer from said second layer.
17. The package of claim 16, wherein said flange includes a
generally planar upper surface extending outwardly from said top
edge of said side wall and a stepped surface connected to an outer
edge of said upper surface, and wherein said stepped surface is
absent in the corner portion of the flange at which the film
fracture feature is located such that the upper surface of said
flange at said corner portion extends to an outer edge of the
flange.
18. The package of claim 16, wherein the film fracture feature
includes a second straight-line segment, the two straight-line
segments intersecting at a vertex.
19. A package for storing a food product in a modified atmosphere,
comprising: a tray for supporting the food product; and a
multilayer film lid attached to the tray with a heat seal between
the tray and the lid, said heat seal extending substantially
continuously about the product and creating a heat seal pattern
which encloses the food product between said tray and said lid,
said lid being a multilayer film having a first layer and a second
layer removably joined together such that the first layer can be
delaminated from the second layer; wherein the lid includes a pull
tab portion and said second layer is positioned between said first
layer and said tray such that the first layer may be delaminated
from the second layer while leaving said second layer attached to
said tray; wherein an outside edge of the heat seal pattern defines
a film fracture feature proximate the pull tab portion, said film
fracture feature comprising two line segments of said outside edge
that intersect and thereby form a vertex that acts as a stress
riser for initiation of the delamination of said first layer from
said second layer.
20. The package of claim 19, wherein each of said line segments is
substantially straight.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to packaging for
products, such as fresh red meat or other food products, that are
enclosed between a tray or other support member and a flexible film
lid sealed thereto, wherein a layer of the lid can be peelably
removed from another layer of the lid that remains sealed to the
tray.
BACKGROUND OF THE INVENTION
[0002] Within the meat packaging industry, it is preferable to
package red meats in a container without oxygen to extend the shelf
life of the meat. Oxygen allows bacteria to grow which spoils the
meat; therefore, depriving the packaged meat of oxygen retards the
growth of bacteria. However, by denying the meat of oxygen, the
myoglobin in the meat cannot generate a fresh, naturally appearing
color.
[0003] A device for packaging meat is disclosed in U.S. Pat. No.
5,779,050 to Kocher et al. and assigned to the present assignee,
wherein a multilayer film lid is provided for a meat packing
container. The multilayer film lid consists of an exterior
gas-impermeable layer and an interior gas-permeable layer. The lid
is heat sealed to the oxygen-depleted package containing the meat
product. This system allows the meat to be initially packaged and
shipped in a low-oxygen environment. Before placing the package out
for retail sale, the gas-impermeable layer of the lid is peeled off
so that oxygen reaches the meat through the gas-permeable layer.
This exposure to oxygen allows the meat to "bloom" so that fresh,
naturally appearing colors are generated.
[0004] The multilayer film lid is generally affixed to the
container by heat sealing. In packages of this type, difficulties
have been encountered in delaminating the gas-impermeable layer
from the gas-permeable layer of the lid. In particular, the
gas-impermeable layer sometimes can not be completely removed in
one piece from the gas-permeable layer. If the gas-impermeable
layer fails to properly delaminate from the gas-permeable layer, it
is possible for the heat seal between the lid and the tray to be
damaged in the attempt to remove the gas-impermeable layer.
Therefore, a need exists for a multilayer film lid with an exterior
layer that can be reliably and consistently delaminated from an
interior layer.
BRIEF SUMMARY OF THE INVENTION
[0005] The invention addresses the above needs and achieves other
advantages by providing a package for storing a food product in a
modified atmosphere wherein a heat seal between a lid and a tray
defines a film fracture feature for focusing forces exerted on a
pull tab portion of the lid so as to initiate fracture between the
layers of the lid in a more-reliable and more-consistent manner. In
one embodiment of the invention, the package comprises a tray for
supporting the food product, and a multilayer film lid attached to
an upper surface of the tray by a heat seal that extends about a
perimeter surrounding a food product. An outside edge of the heat
seal has two substantially straight portions that are approximately
perpendicular to each other and are joined by a corner portion of
the heat seal. The lid has upper and lower layers joined together
in such a manner that the upper layer can be peeled from the lower
layer, the lower layer being permeable to oxygen and the upper
layer being substantially impermeable to oxygen. The lid includes a
pull tab portion that extends out beyond the corner portion of the
heat seal. In accordance with the invention, a film fracture
feature is defined in the corner portion of the heat seal proximate
the pull tab portion of the lid. The film fracture feature
comprises a portion of the outside edge of the heat seal formed as
a straight-line segment oriented at a non-perpendicular angle to
each of the two substantially straight portions of the heat seal.
Pulling upward on the pull tab portion focuses the forces on this
straight-line segment to break the lower layer of the film along
the straight-line segment and thereby initiate fracture between the
upper and lower layers of the lid.
[0006] In another embodiment of the invention, the package
comprises a tray for supporting the food product and includes a
bottom wall, a side wall extending upwards from the bottom wall,
and a flange connected to a top surface of the side wall. The
flange extends generally perpendicular to the side wall. The side
walls of the tray form a quadrilateral having four side walls and
four corners at the intersections of the side walls, and the flange
includes four straight portions corresponding to the side walls and
four corner portions corresponding to the corners of the tray.
[0007] The package also includes a lid bonded to the flange of the
tray with a heat seal that extends along the entire upper surface
of the flange; thus, the heat seal includes four straight portions
and four corner portions. The lid includes a pull tab portion that
is not affixed to the tray and extends out beyond the heat seal at
one corner of the flange. The lid is a multilayer film having a
first layer and a second layer that can be peeled apart. The first
layer includes a film that is substantially gas-impermeable and the
second layer is a gas-permeable film and is positioned between the
first layer and the tray such that the first layer may be peeled
from the second layer while leaving the second layer affixed to the
tray. At the corner of the flange that is proximate the pull tab
portion of the lid, the heat seal pattern defines a film fracture
feature on an exterior edge of the heat seal pattern. The film
fracture feature includes at least one straight-line segment that
intersects with at least one of the straight portions of the heat
seal proximate the fourth corner at an obtuse angle. The film
fracture feature acts as a stress riser so that delamination
between the first and second layers of the lid is initiated at the
film fracture feature.
[0008] In another embodiment, the film fracture feature includes
two line segments that intersect to form a vertex in the heat seal
pattern for initiation of the delamination of the first layer from
the second layer.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0009] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale, and wherein:
[0010] FIG. 1 is a perspective view of a package in accordance with
one embodiment of the present invention;
[0011] FIG. 2 is a schematic, cross-sectional view of the package
shown in FIG. 1;
[0012] FIG. 3 is a schematic, partial cross-sectional view of the
package illustrating the removal of the gas-impermeable layer of
the lid;
[0013] FIG. 4 is a schematic, partial cross-sectional of the
package illustrating the removal of the gas-impermeable layer of
the lid, formed as a coextruded, multilayer film;
[0014] FIG. 5 is a top, partial view of the package shown in FIG. 1
illustrating a film fracture feature formed as a single
straight-line segment; and
[0015] FIG. 6 is a top, partial view of the package shown in FIG. 1
illustrating a film fracture feature consisting of multiple
straight-line segments of the heat seal.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present inventions now will be described more fully
hereinafter with reference to the accompanying drawings, in which
some, but not all embodiments of the invention are shown. Indeed,
these inventions may be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein;
rather, these embodiments are provided so that this disclosure will
satisfy applicable legal requirements. Like numbers refer to like
elements throughout.
[0017] FIG. 1 illustrates a peelable, modified-atmosphere package
10 in accordance with the present invention. Such packages are
disclosed in U.S. Pat. Nos. 5,779,050 and 6,032,800, the
disclosures of which are hereby incorporated herein by reference.
Package 10 includes tray 12 having a cavity 14 formed therein and a
food product 16 disposed within the cavity. Tray 12 is preferably
in the form of a tray having a bottom wall 20 and side wall 18 that
extends upwardly from the bottom wall 20. Tray 12 thus defines the
cavity 14, and further includes a peripheral flange 22 extending
outwardly from the top edge of side wall 18. A lid 24 is heat
sealed to flange 22 to enclose the food product 16 within cavity
14. The lid 24 comprises a flexible film structure as further
described below.
[0018] Tray 12 can have any desired configuration or shape, e.g.,
rectangular, round, oval, etc. A preferred configuration, as
illustrated in FIG. 1, is generally rectangular and includes four
side walls 18. Similarly, flange 22 may have any desired shape or
design, including a simple, substantially flat design that presents
a single sealing surface as shown, or a more elaborate design which
presents two or more sealing surfaces. In a preferred embodiment,
flange 22 includes four straight portions corresponding with the
side walls 18 and four corner portions corresponding to the corners
of the tray. In a preferred embodiment illustrated in FIG. 2, the
flange includes an upper surface 23 that extends outward from the
tray side walls 18 and a recessed or stepped surface 42 connected
to and surrounding an outer perimeter of the upper surface 23.
[0019] Suitable materials from which tray 12 can be formed include,
without limitation, polyvinyl chloride, polyethylene terephthalate,
polystyrene, polyolefins such as high density polyethylene or
polypropylene, paper pulp, nylon, polyurethane, etc. The tray may
be foamed or non-foamed as desired, and preferably provides a
barrier to the passage of oxygen therethrough, particularly when
food product 16 is an oxygen-sensitive food product. Tray 12 may
also comprise a material which itself provides a barrier to the
passage of oxygen and may have a substantially gas-impermeable
sealant film (not shown) laminated or otherwise bonded to the inner
or outer surface thereof.
[0020] In the embodiment of FIGS. 1-3, the lid 24 includes an upper
gas-impermeable portion or layer 34 and a lower gas-permeable
portion or layer 32. The two layers 32, 34 are joined together in
such a fashion that the upper layer 34 can be peeled from the lower
layer 32. The upper layer 34 includes a gas-impermeable film, which
can comprise the entirety of the upper layer 34; alternatively, a
gas-impermeable film can be joined to one or more other layers
selected to impart other desired properties to the upper layer; for
instance, in a non-illustrated embodiment the gas-impermeable film
can be sandwiched between two or more other film layers to form the
upper layer 34. The gas-impermeable film of the upper layer
preferably includes a material that provides a substantial barrier
to the passage of gas, particularly oxygen, therethrough. Suitable
materials may include, but are not limited to, vinylidene chloride
copolymer (saran), nylon, polyethylene terephthalate,
ethylene/vinyl alcohol copolymer, and silicon oxides (SiOx).
Gas-permeable layer 32 preferably allows a certain amount of gases
to pass through while generally maintaining a barrier to other
substances such as dirt, dust, or moisture. Gas-permeable layer 32
may also include perforations 36, as illustrated (not to scale) in
FIG. 3, which may be formed by any suitable means, such as
mechanically, chemically, and/or electrically. Examples of such
devices include, but are not limited to, devices that perforate
with laser energy, electrostatic discharge, ultrasonic waves, flame
discharge, needles or other sharp objects, and combinations
thereof. Perforations 36 may range in size from 5 to 2000 microns
in diameter, most preferably 75 to 100 microns in diameter.
Gas-impermeable layer 34 is joined to the top surface of
gas-permeable layer 32 to form the lid 24 prior to the bonding of
lid 24 to flange 22 of tray 12 by a heat seal 30. Lid 24 is
frangible in that the gas-impermeable layer 34 may be delaminated
from gas-permeable layer 32.
[0021] Although food product 16 is illustrated as having a maximum
height which is below the maximum height of tray 12, i.e., the
level at which flange 22 is located, the invention is not limited
to such "low profile" products. Rather, "high profile" products may
also be packaged in accordance with the present invention, i.e.,
those having a maximum height which is above the level at which
flange 22 is located so that the portion of the product which
extends above the level of flange 22 will be in contact with lid
24.
[0022] Referring again to FIG. 2, the lid 24 is affixed to the
upper surface 23 of flange 22 via the heat seal 30. Heat seal 30
preferably extends continuously around the upper surface 23 of
flange 22 to thereby hermetically seal the food product 16 within
package 10. In this manner, lid 24 and tray 12 preferably form a
substantially gas-impermeable enclosure for food product 16 which
substantially completely protects the product from contact with the
surrounding environment including, in particular, atmospheric
oxygen, but also including dirt, dust, moisture, and microbial
contaminates. When food product 16 is oxygen-sensitive, i.e.,
perishable, degradable, or otherwise changeable in the presence of
oxygen, such as fresh red meat products (e.g., beef, veal, lamb,
pork, etc.), poultry, fish, cheese, etc., it is preferred that food
product 16 be packaged in a low-oxygen environment within package
10 to maximize the shelf-life of the product.
[0023] When packaged as shown in FIG. 2, food product 16 can be
maintained under any desired environmental conditions by virtue of
the substantial gas-impermeability of lid 24 (and tray 12) as long
as the gas-impermeable layer 34 remains bonded to the remainder of
lid 24. For example, when food product 16 is a fresh red meat
product, a low-oxygen environment (e.g., less than 0.5% oxygen by
volume) is preferably maintained within cavity 14 to preserve the
meat product during shipping and storage. However, under such
conditions, a fresh red meat product will have a purple color that
is unappealing to consumers. For this reason, when the packaged
product is to be displayed for consumers to purchase, the
gas-impermeable layer 34 of the lid 24 is peeled off such that
atmospheric oxygen can enter the package, thereby causing the fresh
red meat product to re-bloom to a more-appealing red color.
[0024] In the embodiment of FIGS. 1-3, the lid 24 delaminates at
the interface between gas-impermeable layer 34 and gas-permeable
layer 32 when the pull tab of the lid 24 is pulled in the direction
indicated by the arrow in FIG. 3. In this manner, gas-permeable
layer 32 remains bonded by the heat seal 30 to the upper surface 23
of flange 22. However, in another embodiment shown in FIG. 4, a lid
24' is employed that includes a gas-permeable layer comprising a
delaminateable film 38 that splits within itself. Delaminateable
film 38 is preferably a coextruded, multilayer film. When the pull
tab of the lid 24' is pulled, the delaminateable film 38
essentially splits into two portions 38' and 38" along a separation
plane 40. The portion 38' remains attached to the upper layer 34.
The portion 38" remains affixed to the flange 22 and serves as a
gas-permeable film. Delaminateable film 38 can comprise a
gas-permeable film in which the permeability increases as the
thickness decreases. In some cases, the increased oxygen
permeability of the bottom portion 38" may be sufficient to cause
the fresh red meat to re-bloom without any perforation of the film
38"; if not, the entire film 38 or, alternatively, the bottom
portion 38" only, may be perforated as necessary.
[0025] In accordance with the present invention, delamination can
be performed simply and easily just prior to placing the package in
a display case for customer purchase as follows. The pull tab
portion 28 of multilayer film lid 24 is grasped and pulled
generally upwards and backwards (i.e., towards an opposite edge or
corner of the package). In the embodiment of FIG. 3, delamination
occurs between the substantially gas-impermeable layer 34 and the
substantially gas-permeable layer 32. In the embodiment of FIG. 4,
delamination occurs along separation plane 40 and separates
delaminateable film 38 into a top portion 38' and bottom portion
38". Once the substantially gas-impermeable layer 34 has been
removed, oxygen may pass through the substantially gas-permeable
layer 32 or the bottom portion 38" to cause product 16 to
re-bloom.
[0026] Delamination of lid 24 is shown in FIG. 3 in greater detail,
wherein the gas-impermeable layer 34 is shown as it begins to
delaminate from gas-permeable layer 32. Gas-permeable layer 32 is
preferably bonded to the upper surface 23 of flange 22 with a heat
seal 30 that has a greater cohesive strength than the intra-film
cohesive bond strength between gas-impermeable layer 34 and
gas-permeable layer 32. In this manner, when gas-impermeable film
34 is subjected to a delaminating force as indicated by the arrow
in FIG. 3, the lid 24 delaminates such that the gas-permeable
portion 32 remains bonded to tray 12 while the gas-impermeable
portion 34 is removed from the package and discarded. Thus,
gas-permeable layer 32 remains bonded to tray 12 via heat seal
30.
[0027] In the embodiment of FIG. 4, gas-impermeable layer 34 is
preferably bonded to delaminatable film 38 with a bond-strength
that exceeds the intra-film cohesive strength within delaminatable
film 38. Similarly, heat seal 30 preferably results in a bond
between delaminatable film 38 and tray 12 that is also greater than
the intra-film cohesive strength within delaminatable film 38. In
this manner, when lid 24' is subjected to a delaminating force as
indicated by the arrow in FIG. 4, the lid delaminates within
delaminatable film 38 along separation plane 40 such that the
bottom gas-permeable portion 38" remains bonded to tray 12, while
the gas-impermeable portion 34, along with the top portion 38' of
the delaminatable film, is removed from the package and
discarded.
[0028] As noted, to facilitate peeling, the lid 24 preferably
includes a pull tab portion 28. This pull tab portion 28 can be
manually grasped to initiate peeling, and is preferably formed as
disclosed in U.S. Pat. No. 5,779,050, the disclosure of which is
hereby incorporated herein by reference. Peeling is initiated by
grasping and pulling pull tab portion 28 in the direction of the
arrow shown in FIG. 3 and FIG. 4, thus subjecting the heat seal 30
to an upward force. This force is in a direction tending to pull
apart gas-impermeable layer 34 and gas-permeable layer 32, or the
delaminateable film 38, as illustrated in FIG. 3 and FIG. 4,
respectively. The heat seal 30 holds the gas-permeable layer 32 or
the portion 38" intact and secured to tray 12. If a force of
sufficient magnitude is applied, the layer(s) of the lid 24 or 24'
below the gas-impermeable layer 34 is (are) supposed to break at
the heat seal and thereby initiate delamination of the
gas-impermeable film from the rest of the lid as described
above.
[0029] However, in packages 10 with a heat seal pattern similar to
that disclosed in US. Pat. No. 5,779,050, the delamination of the
lid can be problematic. The force exerted on the pull tab of the
lid can cause the flange 22 to bend upward and prevent removal of
gas-impermeable layer 34. The gas-impermeable layer 34 may tear,
resulting in an incomplete removal of the gas-impermeable layer. In
addition, if the lower layer of the lid does not break when the tab
is pulled, the force can rupture the heat seal 30 between the
flange 22 and the lid. Such failures are thought to result
primarily from a non-optimum distribution of the peel force along
the exterior edge of the heat seal 30. The present invention
utilizes a film fracture feature on an exterior edge of the heat
seal 30 to concentrate the force so that the gas-permeable layer 32
reliably breaks at the film fracture feature and thus allows the
gas-impermeable layer 34 to be peeled off without adversely
affecting the gas-permeable layer 32, the flange, or the heat
seal.
[0030] In a preferred embodiment, heat seal 30 includes four
straight portions 31 (FIGS. 1 and 5) respectively extending along
the four straight portions of flange 22, three smoothly curved
corner portions 33 at three of the four corners of flange 22, and a
fourth corner portion 35 (FIG. 5) that includes a film fracture
feature located at the fourth corner of flange 22. The pull tab 28
of the lid extends out beyond the fourth corner portion 35 of the
heat seal. In a preferred embodiment, heat seal 30 is approximately
0.25 inches wide, but the width may vary depending on the
application or material properties.
[0031] FIGS. 1 and 5 depict one embodiment of a film fracture
feature defined by the corner portion 35 of the heat seal 30 for
concentrating peel forces exerted on the tab portion of the lid so
as break the gas-permeable layer 32 of the lid at the film fracture
feature. In this embodiment, the film fracture feature comprises a
straight-line segment 50 of the outer edge of the heat seal 30; by
"outer edge" is meant the edge of the heat seal 30 farther from the
cavity 14 of the package. The straight-line segment 50 is proximate
the pull tab portion 28 of the lid. Straight-line segment 50
intersects at an obtuse angle with each of the straight portions 31
of heat seal 30 on either side of the corner portion 35 of the heat
seal and thereby creates vertices 51 (FIG. 5) at these
intersections. When the pull tab portion 28 is pulled up and back,
the forces are focused on the straight-line segment 50 so as to
initiate fracture of the lower layer 32 of the lid 24.
Additionally, the vertices 51 between the straight-line segment 50
and the straight portions 31 of the heat seal are discontinuities
in the curvature of the outer edge of the heat seal 30 and serve as
stress risers to concentrate the peel force during removal of the
gas-impermeable layer 34 from the gas-permeable layer 32. The
concentration of the peel force on the film fracture feature 50
allows the lower layer 32 of the lid to break at the film fracture
feature and thus permits gas-impermeable layer 34 to be removed in
one piece without disturbing the heat seal 30 between the lower
layer 32 and the upper surface 23 of flange 22.
[0032] Another embodiment of the film fracture feature is
illustrated in FIG. 6, wherein the film fracture feature can be
formed by multiple line segments, such as segments 52 and 54. The
line segments 52 and 54 intersect to form a vertex 56. Line
segments 52 and 54 are preferably straight, but alternatively they
may have a convex or concave shape that nevertheless creates a
vertex at their intersection. Furthermore, the preferred embodiment
of the vertex 56 is defined as a sharp corner, but alternatively
the vertex may comprise a very small radius and still serve as a
stress riser in the outer edge of the heat seal.
[0033] A further problem during the delamination of a package 10 in
the prior art can occur when the heat seal 30 extends outwardly
beyond upper surface 23 of flange 22. As noted, the flange 22
includes upper surface 23 and recessed or stepped surface 42. The
stepped surface 42 extends outward from the outer perimeter of the
upper surface 23 and defines an upward facing surface that is lower
than upper surface 23. This stepped surface 23 is advantageously
utilized during manufacture of package 10 when the material of lid
24 beyond the edges of heat seal 30 is cut. Improper delamination
of the lid may occur if the heat seal 30 onto the interface between
the upper surface 23 and the stepped surface 42. In that case,
exerting a peel force on pull tab portion 28 can cause the flange
22 to bend upward in the direction of the force because of the
orientation of the heat seal 30 on the interface between upper
surface 23 and stepped surface 42.
[0034] To address this issue, packages in accordance with some
embodiments of the present invention include a modified flange
structure at the corner where the pull tab is located. In
particular, as illustrated in FIG. 5, the flange upper surface at
that corner includes a surface 58 that forms an extension of the
upper surface 23 to the outer perimeter of the flange 22. This
surface 58 exists where the stepped surface 42 would otherwise be
located in a non-modified flange. In effect, the top of stepped
surface 42 is raised to the level of the upper surface 23 in the
corner with pull tab portion 28 to create surface 58. Because the
film fracture feature could have various configurations as
exemplified by the different embodiments described herein, the
surface 58 provides additional surface area to ensure the film
fracture feature is confined to the flat upper surface;
additionally, the extended surface 58 allows for some degree of
tolerance in the location of the heat seal relative to the
flange.
[0035] Advantageously, the provision of the film fracture feature
in accordance with the invention does not require any additional
manufacturing steps or materials. The film fracture feature is a
unique shape in the pattern of heat seal 30 and is created when
film 24 and tray 12 are joined together.
[0036] Many modifications and other embodiments of the inventions
set forth herein will come to mind to one skilled in the art to
which these inventions pertain having the benefit of the teachings
presented in the foregoing descriptions and the associated
drawings. Therefore, it is to be understood that the inventions are
not to be limited to the specific embodiments disclosed and that
modifications and other embodiments are intended to be included
within the scope of the appended claims. Although specific terms
are employed herein, they are used in a generic and descriptive
sense only and not for purposes of limitation.
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