Note: Descriptions are shown in the official language in which they were submitted.
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FREEZER STORAGE BAG
This invention generally concerns the packaging of food, particularly meat.
The
invention was made during attempts to make improved functional "freezer bags"
for
repackaging and freezer storing uncooked red meat by the ultimate consumer in
a manner
that reduces so tailed "freezer burn". However, various aspects of the
invention also apply to
the commercial packaging or repackaging of food, such as by a supermarket or
even by
butchers at a slaughterhouse. Other aspects of the invention include methods
for preparing
the improved freezer bags; methods for using the bags; the packages of meat;
and certain
types of thermoplastic film being particularly suitable for use as meat-
contacting packaging
material.
Reciosable plastic storage bags are extremely old in the art. Today, plastic
bags
are typically available to the public in cartons identified for specific
recommended "end use"
(such as Storage Bags, Heavy Duty Freezer Bags, Vegetable Bags, Trash Bags).
Often the bag
itself is labeled by "end use", for example "ZtPLOC° BRAND Heavy Duty
Freezer Bags".
The term "freezer bag" is hereby defined as a bag having significant
functional
utility in the storage of food in a freezer. "Freezer Bags" are typically
available in the following
sizes: 2 gallon; 1 gallon; pleated 1/2 gallon; quart; and pint.
The term "freezer burn" is hereby defined as the name for the dehydration that
occurs when unpackaged or improperly packaged food is stored in the low
humidity
atmosphere of a freezer (see "Packaging Foods With Plastics", by Wilmer A.
Jenkins and James
P. Harrington, published in 1991 by Technomic Publishing Co., Inc., at page
305). Consumers
typically describe freezer burn in terms of three main visual attributes: ice
crystal formation,
product dehydration, and color change.
Freezer burn has remained a major complaint among consumers despite the
commercial success of thick plastic freezer bags. In the short term, freezer
burn can be a
reversible process. In the Tong term, however, freezer burn causes a complex
deterioration of
food quality involving undesirable texture changes followed by chemical
changes such as
degradation of pigments and oxidative rancidity of lipids. Taste, aroma, mouth
feel and color
can all be ruined. Freezer burn of raw red meat is particularly critical
because of its impact
upon the color of the meat.
Aforementioned "Packaging Foods With Plastics" provides an excellent state of
the art summary, with all the information on (commercial) "packaging fresh red
meat collected
i n Chapter Seven". Curiously, the book does not appear to mention freezer
burn, apart from
defining it in the glossary.
"Keeping Food Fresh" is the title of an article in "Consumer Reports", for
March,
1994, at pages 143-147. The article is too recent to be available as prior art
againstthis U.S.
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VVO 97/29966 , PCT/US96/02135
patent application. Nevertheless its contents are of interest in showing the
absence of certain
types of prior art, and therefore enhancing the patentability of the present
invention.
The "Consumer Reports" article attempts to answer the question as to which
packaging material (plastic, aluminum, waxed paper, bags, wraps or reusable
containers) do
the best job of (1 ) keeping food fresh for "the long haul", (2) at lowest
overall cost, and (3) with
minimum adverse environmental impact. 1t "top rates" ZIPLOC~ Pleated Freezer
Bags (at page
145). It poi nts out that food stored in plastic containers can suffer from
freezer burn if the
container contains too much air. Concerning "wraps" (plastic films and freezer
papers) it
advised against double wrapping because of cost and environmental reasons and
"our tests
1 p showed that double wrapping doesn't afford much extra protection any way".
Nowhere does
the article disclose or suggest the invention described hereinafter.
The patent literature contains descriptions of various types of bag having
liners or
double walls including some space between the walls. Some of these patents
relate to the
transportation and storage of food. U_S. Patent 4,211,091 (Campbell) concerns
an "Insulated
1 S Lunch Bag". U.5. Patent 4,211,267 (Skovgaard) describes a "Carrying Bag"
for "getting home
with frozen food before it thaws". U.S. Patent 4,797,010 (assigned to Nabisco
Brands) discloses
a duplex paper bag as a "reheatable, resealable package for fried food". U.S.
Patent 4,358,466
(assigned to The Dow Chemical Company) relates to an improved "Freezer To
Microwave Oven
Bag". The bag is formed of two wing shaped pouches on each side of an upright
spout. U.5.
20 Patent 5,005,679 (Hjelle) concerns "Tote Bags Equipped With A Cooling
Chamber". All of these
food bags appear to have very thick food contacting walls compared to the
invention described
hereinafter. None of these patents appear to focus on freezer burn.
Books on "Home Freezing" are of interest to this invention. Concerning
"Wrapping Meat for the Freezer", the book "Rodale's Complete Book of Home
Freezing" by
25 Marilyn Hodges and the Rodale Test Kitchen staff (1984) suggested the
hardly convenient
method of wrapping meat chunks in a single layer of freezer paper and "sucking
out the air
with a straw" (trying to avoid getting blood into one's mouth) in order to
reduce the amount
of dehydration in the freezer (see page 173).
There is clearly still a great need to improve existing methods of packaging
fresh
30 meat, as determined by consumer surveys, coupled with the fact that there
is a huge retail
market in the U.S. alone, consuming multi millions of dollars worth of plastic
packaging
materials annually.
In contrast to the known prior art, it has now been surprisingly discovered
that
certain types of multiple walled .plastic bags (defined herein as "multibags")
are better than
35 corresponding single wall freezer bags (having equal or greater weight than
the multiple
walled bags) for use as a functional freezer bag for preserving meat without
freezer burn.
In its broadest scope, the present invention provides a freezer bag
for the storage of meat without producing "freezer burn" comprising:
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CA 02246277 2003-06-19
a multibag having at least a thermoplastic inner liner bag and a
thermoplastic outer support bag, the inner liner bag having a first sidewall
and a
second sidewall attached together along respective lateral edges forming edge
seals, each sidewall having a top edge, and the liner bag having a folded edge
defining the bottom of the liner bag,
the outer support bag having two sidewalls attached together along
respective lateral edges forming edge seals, each sidewall having top edges
defining the opening to the multibag and the support bag having a folded edge
defining the bottom of the multibag,
the top edges of the liner bag being attached to an inner surface of
each respective sidewall of the support bag,
wherein the support bag has a nominal respective sidewall
thickness of 33 pm to 76 Nm (1.3 to 3.0 mils), and
the liner bag has a nominal sidewall thickness of 7.6 Nm to 25 pm
(0.3 to 1.0 mil).
Further according to the present invention is a process for making
multibags for storage of meat without "freezer burn" having at least an inner
liner
bag and an outer support bag comprising the steps of;
forwarding a first thermoplastic film web having a thickness of 33
Nm to 76 pm (1.3 to 3 mils) and a first transverse web width between parallel
edges;
forwarding at least a second thermoplastic film web having a
thickness of 7.6 Nm to 25 Nm (0.3 to 1.0 mil) and a second transverse web
width
between parallel edges, the second transverse web width being smaller than the
width of the first thermoplastic film;
overlaying the second thermoplastic film web onto the first
thermoplastic film web between the parallel edges of the first film web;
attaching the second thermoplastic film web to the first
thermoplastic film web along the parallel edges of the second thermoplastic
film
web;
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CA 02246277 2003-06-19
longitudinally folding the films in the transverse direction to form the
bottom of the bag; and
transversely seat cutting the folded films to form bags.
Further according to the present invention is an apparatus for
making multibags for storage of meat without "freezer burn" having at least an
inner liner bag and an outer support bag comprising:
means for forwarding a first thermoplastic film web having a
thickness of 33 Nm to 76 Nm (1.3 to 3 mils) and a first transverse web width
between parallel edges;
means for forwarding at least a second thermoplastic film web
having a thickness of 7.6 ~Im - 25 Nm (0.3 to 1.0 mil) and a second transverse
web width between parallel edges, the second transverse web width being
smaller than the width of the first thermoplastic film;
means for overlaying the second thermoplastic film web onto the
first thermoplastic film web between the parallel edges of the first film web;
means for attaching the second thermoplastic film web along the
parallel edges of the second thermoplastic film;
means for longitudinally folding the films in the transverse direction
to form the bottom of the bag; and
means for transversely seal cutting the folded films to form bags.
FIG. 1 A is a front elevational view of a prior art reclosable thermoplastic
single
wall bag having a zipper.
FIG. 1 B is a cross-sectional view taken along reference line 1 B-1 B of FIG.
1A.
F1G. 2A is a front elevational view of a double wall bag in accordance with
the
present invention, (i) having a thin inner wall or liner, and (ii) having
"common side seals"
between the inner and outer walls and, optionally, (iii) a vent through the
outer wall to
connect the space between the inner and outer walls to the atmosphere outside
the outer wall.
FIG. 2B is a partial cross-sectional view taken along line 2B-2B of FIG. 2A.
FIG. 2C is a partial cross-sectional view taken along line 2C-2C of FIG. 2A.
FIG. 3A is a front elevational view of another double wall bag of the present
invention, with "separate side seals" and having the liner bag attached
longitudinally across
the total length of inside surfaces of the support bag sidewalls.
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FIG. 3B is a partial cross-sectional view taken along tine 3B-3B of FIG. 3A.
FIG. 3C is a cross-sectional view taken along line 3C-3C of FIG. 38.
FIG. 4A is a front elevational view of a further double wall bag of the
present
invention having the liner bag attached tongitudinatly across a portion of the
total length of
the inside surfaces of support bag sidewalls, wherein the space between the
liner bag and
support bag wails is connected with the space within the finer bag.
FIG. 4B is a partial cross-sectional view taken along line 4B-4B of FlG. 4A.
FIG. 4C is a partial cross-sectional view taken along tine 4C-A.C of FIG. 4B.
FIG. 5A is a front elevational view of a 3-layer mufti bag of the present
invention
having an inner film Layer between the liner bag and the support bag, wherein
the liner bag
has microholes throughout its surface.
FIG. 5B is a partial cross-sectional view along line 5B-5B of FIG. 5A.
FIG. 5C is a partial cross-sectional view along line 5C-5C of FIG. 5A showing
an
optional third inner layer between liner bag and support bag of FIG. 5A.
FIG. 6A is a front elevational view of a package of "meat in a closed bag" of
the
invention.
FIG. 6B is a cross-sectional view taken along reference line 6B-6B of FIG 6A.
FIG. 7 is a diagrammatic flow diagram for one manual process of the present
invention for making experimental freezer bags.
FIG. 8 is a diagrammatic flow diagram for a process of the present invention
for
making freezer bags having a common edge seal between the liner bag and
support bag.
Figure 9A is a front elevationat view of a double wall bag in accordance with
the
present invention, having a finer bag prepared from a textured,
particutarlyembossed film on
at least the inside surface.
Figure 98 is a cross sectional view taken along reference line 9B-9B of Figure
9A.
Figure 9C is an enlarged cross sectional view of a blanket seal for attaching
the
top edges of the liner bag to the sidewalls of the support bag.
Figure 9D is an enlarged cross sectional view of another embodiment of a
blanket
seal for attaching the top edges of the Ii ner bag to the sidewalls of the
support bag.
Figure 10 is an isometric view of one process for preparing and blanket
seating
bags of the present i nvention.
Figures 11-16 are enlarged cross sectional and plan views of various preferred
embossing patterns for embossing the either or both liner bag surfaces.
Figure 17 is a cross sectional view of a preferred process of making the bags
of the
present invention.
Certain terms used in this specification are hereby defined as follows:
"Multiwall bag" is a bag having wails made up of more than one Layer.
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A "double bag" is two bags, one within the other, which double bag can be
separated into two separate bags, which separate bags can then reform the
double bag (as for
bagging groceries at a supermarket).
A "duplex bag" is hereby defined as an integral bag consisting of an outer
support bag and an inner liner bag, wherein the liner bag is partly (but not
completely) joined
to the support bag.
A "multibag" is hereby defined as an integral bag having at least an outer
support bag and an inner liner bag, wherein the liner bag is partly (but not
completely) joined
to the support bag; and optionally additional layers between the liner bag and
the support
bag. The simplest form of a multibag is a duplex bag.
An embodiment of the multibag of the present invention is shown generally in
FIGS. 2A-2C. As shown in FIG. 2A, multibag 10 comprises an outer bag or
support bag 12 and an
inner bag or liner bag 11. Support bag 12 is defined by edge seals 21, 21' and
folded edge 26
shown by line DC. Support bag 12 has a reusable closure means i4, such as a
mateable male
and female closure, for releasably closing multibag 10. Support bag 12 has a
venting means
such as vent hole 99 through sidewall 19. Liner bag 11 has edge seals shown by
lines ad and be
and a folded edge 24 defined by fine dc. Liner bag 11 and support bag 12 share
edge seals, that
is, edge seats shown by lines ad and be are common with a portion of the total
length of edge
seals 21, 21'.
Referring to F1G5. 2A and 2B, finer bag top edges 28, 28' are attached
longitudinally across inside surfaces 20, 20' of support bag sidewafls 19, 19'
forming liner bag
throat or opening 13. The liner bag is longitudinally attached to the support
bag at a
preselected distance from multibag opening 15. Alternate means of attaching
liner bag top
edges 28, 28' to support bag sidewaf fs 19, 19' are described below.
As shown in more detail in FIGS. 2B and 2C, support bag sidewalls 19, 19' and
liner
bag sidewalis 17, 17' are generally separable from one another except at edge
seals shown by
lines ad, bc, and attachment ab and have a space 23 therebetween. As shown in
FIG. 2B, liner
bag 11 is attached longitudinally across support bag sidewalls i9, 19' at
finer bag edges 28, 28'
such that when closure 14 is puffed apart to form opening 15, foodstuffs are
placed into the
liner bag 11 through opening 15 and liner bag opening 13 and the food stuff
contacts the liner
bag 11 and with minor manipulation of the bag, the liner bag 11 conforms to
the shape of the
foodstuff as shown in FIG. 6A and 6B.
Closure means 14 may be any reusable closure. Examples of useful reusable
closures and how they are made and attached to bags are found in for example,
U.S. Patent No.
4.56t,109, U.S. Patent No. 4,363,345, U.S. Patent No. 4,528,224, and U.S.
Patent No. 5,070,584.
One or more vent holes 99 may generally be placed anywhere through at least
one sidewal I 19 or 19' of support bag 12 or anywhere through at least one
liner bag sidewall 17
or 1T or through both sidewaffs of both finer bag and support bag or through
one sidewall of
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each of liner bag and support bag. One or more vent holes 99 may also be
placed through
either liner bag folded edge 24 or support bag folded edge 26 or both liner
bag and support
bag folded edges 24, 26. Support bag t 2 preferably has more than one vent
hole 99 and the
vent hole 99 is preferably in a sidewall 19 of the support bag 12 below the
sea! area where the
liner bag 11 is attached to the sidewalls 19, 19' of the support bag 12. Vent
hole 99 provides
venting of the support bag 12 to the surrounding atmosphere and permits an air
space 23
between sidewalls 17, 1 T of liner bag 11 and sidewalls 19, 19' of support bag
12.
Venting to the outside atmosphere increases the amount of cling or surface
area
contact of the liner bag film to meat. Venting permits the inner finer to
cling to the meat by
allowing the liner bag to move more independently of the support bag than it
otherwise
would if the space between the two film Layers was closed and of a fixed
volume. The support
bag film is generally more stiff than the liner bag film and the stiffer
support bag film tends to
pull the liner bag off of the meat if no venting occurs. Having vent holes in
the support bag
also prevent air bubblesfrom forming in between the film layers and prevent
the film layers
from sticking togetherduring manufacture of the multibag.
The number and diameter of the vent holes in either or both the Jiner bag and
support bag should be as few and as smal I as possible so to make the holes
less visible to the
consumer. However, the vent holes need to be large enough to allow the
continuous expelling
of air from between film layers during manufacture and to allow the consumer
to hand-expel
air from between the liner bag and support bag during use. Thus, the number of
vent holes
needed in either or both bags will generally vary with the size of the vent
holes.
Generally, there is at least one vent hole in either the support bag or the I
finer bag
and practically there is no upper limit to the number of vent holes in either
or both of the liner
and support bags. The number of vent holes in either the liner bag or support
bag or in both
liner bag and support bags may vary from at least 1 to 28, preferably the
number of vent holes
range from 6 to 28 and more preferably range in number from 9 to 17.
Generally, the
diameters of *he vent holes are greater than 450 microns, preferably from 450
to 750 microns,
and more preferably from 450 to 500 microns in diameter.
The means of attaching a liner bag to a support bag to form a muttibag of the
present invention may be any means known in the art. The liner bag may be
attached
continuously and uniformly along liner bag top edges or attached in a
discontinuous or
intermittent manner along liner bag top edges. Useful examples of attaching
means known in
the art include hot air hem sealing, extrusion lamination (extruded
thermoplastic film between
the film layers), hot melt adhesive (placed over or under the top edges of the
liner bag), heated
bar heat sealing, ultrasonic sealing, heated rollers or belts, adhesive film
strips, infrared sealing,
radio frequency sealing, or vibration welding. The liner bag may also be
attached to the
support bag during manufacture by means of post-applying closure profiles onto
and over
edges of liner bag film described hereinafter. Use of any of the above means
of attaching two
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film webs largely depends on the chemical and physical characteristics of the
film webs used to
make the liner bag and the support bag. Preferably, liner bag i 1 is attached
to support hag 12
along top edges 28, 28' by means of a hinge-type blanket seal 97 described in
more detail
hereinafter and shown in FtG. 9C.
To use a muitibag of the present invention, the user would place the food or
meat
to be packaged into the finer bag through the opening in the multibag, stroke
the food or
meat with the hand through the bag thereby causing the liner bag to conform to
the external
geometry of the food or meat at the meats surface 9 and thereby exhausting air
from the liner
bag, and thereafter close the support bag while avoiding significant re-entry
of air into the
liner bag. FIGS. 6A and 6B show meat 300 packaged in a muttibag having an
inner liner bag 11
and an outer support bag 12.
Another embodiment of the maltibag of the present invention is shown in
multibag 40 of FIG. 3A and in FIGS. 3B-3C. Muitibag 40 comprises a liner bag
41 and a support
bag 42. Support bag 42 has a reusable closure means 14 and edge seals 44, 44'
joining sidewalls
46, 46' (FIG. 4B) and a folded edge 26. Liner bag 41 has edge seals shown by
lines ad and be
joining sidewalls 49, 49' (FIG. 4B) and a folded edge 24. Referring to FIGS.
3B and 3A, top edges
48, 48' of liner bag 41 are attached longitudinally across inside surfaces 43,
43' of support bag
sidewalls 46, 46' forming liner bag opening 13. Edge seals be and ad of liner
bag 41 are
"separate" from edge seals 44, 44' of support bag 42, in contrast to edge
seals be and ad of
multibag 10 shown in FIG. 2A which are "common" with a portion of edge seals
21, 21' of
support bag 26. As in the embodiment shown in FIG. 2A, support bag sidewalls
46, 46' and liner
bag sidewal Is 49, 49' have a space 23 therebetween. The liner bag 41 may be
attached to
support bag 42 along liner bag top edges 48, 48' by attaching means described
hereinbefore.
Preferably, liner bag 41 is attached to support bag 42 along liner bag top
edges 48, 48' by
means of a hinge-type blanket seal 97, described hereinafter and shown in more
detail in FIG.
9C.
Another embodiment of the multibag of the present invention is shown in
mufti bag 50 of FIG. 4A and in FIGS. 4B-4C. Multibag 50 comprises a liner bag
51 and a support
bag 52 having a reusable closure means 14 near the top of the bag. Liner bag
51 defines edge
seals ad and be joining sidewalls 57, 5T (FIG. 4B) and has folded edge 54.
Support bag has edge
seals 60, 60' joining sidewalls 58, 58' (FIG. 4B) and has a folded edge 56. As
shown more clearly
in FIG. 4B, liner bag top edges 53, 53' are attached longitudinally across to
inside surfaces 59 of
sidewalk 58, 58' along line ab as shown in FiG. 4A. In this embodiment, liner
bag 51 and
support bag 52 have separate edge seals. As shown in more detail in F1G5. 4A
and 4C, top edges
of 1 i ner bag S3, 53' are not attached to support bag sidewalls 58, 58'
across the total
longitudinal width of sidewalk 58, 58'. This attachment of liner bag 51 to
support bag 52
creates openings 63 into support bag 52 adjacent liner bag edge seals ad and
bc. The opening
63 into support bag 52 is open to the atmosphere when closure 14 is open. The
liner bag 51
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may be attached to support bag 52 along liner bag top edges 53, 53' by
attaching means
described hereinbefore.
Another embodiment of a multibag of the present invention is shown in multibag
70 of FIG. 5A and in FIGS. 5B-5C. Multibag 70 comprises generally liner bag 71
and support bag
72 having a reusable closure means 14. Liner bag 71 is defined by edge seals
shown by lines ad
and be joining sidewails 80, 80' (FIG. 5B) and has folded edge 74. Support bag
is defined
generally by edge seals 73, 73' (FIG. 5B) joining sidewails 82, 82' and has
folded edge 76.
Viewing FIGS. 5A and 5C, liner bag 71 has a plurality of microholes 78
(described below)
through sidewalls 80, 80'. Referring to FIG. 5B, top edges of I finer bag 83,
83' are heat sealed
i ntermittently across the longitudinal length of sidewalis 82, 82' forming
holes 75 and attached
areas 79. Top edges of liner bag 83, 83' attached to support bag sidewalls 82,
82' defines
opening 81 to finer bag. Referring to FIG. 5C, multibag 70 has an inner film
layer 77
sandwiched in between liner bag 71 and support bag 72.
Holes 75 and sealed areas 79 are formed from intermittent heat sealing of
liner
bag top edges 83, 83' to support bag sidewails 82, 82'. Holes 75 are the areas
of i finer bag top
edges 83, 83' that are not attached to support bag sidewails 82, 82'. In this
embodi ment of the
present invention, the top edges of liner bag 83, 83' are heat sealed
intermittently to support
bag sidewalls 82, 82' where portions of inner layer 77 have been removed. In
this embodiment,
inner film layer 77 is made of a material for example, that is not heat
sealable to either liner
bag or support bag. However, liner bag may be attached to support bag with an
intermittent
seal in any embodiment of the present invention. A discontinuous or
intermittent attachment
or seal of a liner bag to a support bag may atso be made using conventional
adhesives, hot melt
adhesives, or hot air hem sealing or other sealing means described
hereinbefore as is know in
the art.
Holes 75 open to the inside of the support bag and to the atmosphere when
closure means 14 is open, to allow the user to remove air from in between the
liner bag and the
support bag so to enhance the cling of the liner bag to the meat. Holes 75 are
only along the
poi nt of attachment of the liner bag to the support bag. Holes 75 perform
essentially the same
function as vent holes 99 but are typically much larger than vent holes 99 and
microholes 78.
Microholes 78 are generally uniformly distributed across the entire surface of
at
least one sidewall of a bag. Vent holes, on the other hand, are not generally
uniformly
distributed across the entire surface of at least one sidewail of a bag.
Microholes 78 are
distinguishable between vent holes 99 in that vent holes 99 are few in
comparison to the
number of microhoies that would be present in a sidewail of a bag. Normally, a
multibag of
the present invention would not have both microholes and vent holes since the
microholes
would permit ai r to escape as wel I as al I ow water to permeate through from
the meat to the
inner film tayer. Both *he support bag and the liner bag may have microholes
through
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respective sidewalls. Preferably, only the liner bag of the multibag shown in
FIGS. 5A-5C has
microholes.
In practice, foodstuffs such as meat would be placed into multibag 70 and the
meat would contact the liner bag 71. Water would permeate through microhoies
78 of liner
bag 71 and the water would be adsorbed by hydroscopic inner film layer 77 and
the inner layer
77 would swell slightly causing the liner bag 7i to uniformly contact the
meat's surface.
Uniform contact of the ii ner bag with meat prevents the meat from being
freezer burned.
By "uniformly distributed" it is meant that the microholes are substantially
identically and substantially evenly spaced apart from each other over the
entire surface area
0 of a sidewall or film web. The microholes are preferably in a polka-dot like
matrix or pattern.
Generally, the microholes have a diameter of from 50 to 950 microns,
preferably have a
diameter of from 100 to 500 microns and more preferably have a diameter of
from 200 to 300
microns. Generally, the number of microholes per until area is from 3
microhoiestin2 (0.465
microholes/cm2) to 8i microholes/ in2 (12.56 microholeslcm2). Preferably, the
hole density is
15 from 5 microholes/in2 (0.775 microholes/cm2) to 50 microholes/in2 (7.75
microholeslcm2) and
more preferably from 8 to 30 microhoies/in2 (1.24 microholeslcm2 to 4.65
microholes/cm2>. A
process and apparatus for microperforating films are described in U.S. Patent
5,405,561.
Generally, a third layer or inner film layer 77 may be made of the same or
different materials than those used to make the liner and support bags. Useful
materials
20 include thermoplastic polymers, cellufosic polymers, paper, cotton,
polyvinyl alcohol, a plastic
fiber matrix such as TYVEXT"" (availabte from DuPont), a paiyester fabric such
as RAYONT"' or
DACRONs'", an elastic fabric such as LYCRAT"", or a generally hygroscopic
material in the form of
a film. Preferably, inner film layer 77 is film of a hygroscopic material, for
example a cellulose
ether or a polyvinyl alcohol. More preferably, the inner fif m layer is a film
made from a
25 hYdroxypropyl methyl cellulose resin such as METHOCEL, (Trademark of The
Dow Chemical
Company) available from Polymer Films, Inc., Rockville, CT.
A preferred embodiment of a multibag of the present invention is shown in
multibag 90 of F1G. 9A. Multibag 90 is comprised of a liner bag 91 and a
support bag 92 having
a reusable closure means 14. Liner bag 91 is defined by edge seals ad and be
and a folded edge
30 24. Support bag 92 is defined by edge seals 89, 89' and folded edge 26.
Liner bag 91 and
support bag 92 share edge seals ad and bc. Referring to FIGS. 9A and 9B, top
edges 95, 95' of
liner bag 91 are attached to sidewails 96, 96' of support bag 92
longitudinally across inside
surfaces 101, 101' by a blanket seal 97 in the machine direction. Top edges
95, 95' attached to
support bag sidewafls 96, 96' define the finer bag opening. Liner bag
sidewalls 94, 94' and
35 support bag sidewalls 96, 96' are generally separable except at edge seals
ad, be and blanket
seal 97 (described hereinafter) forming a space 23 therebetween as shown in
FIG. 9B. Support
bag 92 has a plurality of vent holes 99 through its sidewall 96 below blanket
seal 97. Liner bag
92 has textured inner surfaces 98 as shown in FIGS. 9A and 9B. Preferably, the
textured surfaces
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98 are embossed. Vent holes 99 may also be through a liner bag sidewall 94,
94' below blanket
seal 97.
As shown more particularly in FIG. 9C, a hinge-type blanket seal 97 is formed
by
overlaying a sealing band 100 of extruded material over the top edges of the
liner bag 95 inthe
machine direction of the liner bag and support bag film. The process of
applying a sealing
band and forming a blanket seal is described hereinafter. The sealing band 100
is attached to
the support bag sidewalls generally at area 103 and is attached to the liner
bag to edges
general 1y at area 102. The top edges of the finer bag are not heat sealed to
the support bag
sidewails in this embodiment. Attaching sealing band 100 to both sidewall 96
and top edge 95
creates a hinge-like attachment whereby top edge 95 may be pulled away from
sidewal I 96 and
form a T-shape at the point of attachment. The strength of the attachment of
the seating band
to the support bag and the liner bag is preferably such that the liner bag
film will fail during a
T-shape pull test. The sealing band 100 used to form a hinge-type blanket seal
may be made
from any suitable thermopias*ic material or combination of thermoplastic
materials that are
heat sealable to at least the portions of the thermoplastic films to be
joined. Preferably, the
sealing band is polyethylene and more preferably, low density polyethylene or
other materials
which are compatible with the support and liner bag materials hereinafter
described.
Another type of blanket seal useful in the present invention is a blanket seal
which attaches to both the support and liner bag materials and also causes the
liner bag
material to heat seal to the support bag. As shown i n FIG. 9D, heat seal type
blanket seal 110
comprises sealing band 112 applied over the top edges of the liner bag 95 and
contacting
support bag 96 and being attached generally at areas 114 and 116. The liner
bag top edge 95 is
heat sealed and rigidly attached to the support bag 96 generally at area 118.
The heat seal type
blanket seat is formed when the sealing band can transfer enough heat through
the liner bag
film to cause it to heat seal to the support bag fitm. A sufficient amount of
heat transfer from
the sealing band is transferred if the sealing band temperature, heat
capacity, and mass are
sufficiently high, and the liner bag film is sufficiently thin and has a
sufficiently low sealing
temperature. Sealing band 112 may be made of the same materials described
hereinbefore as
useful for seating band 100. The support and finer bag materials as
hereinafter described must
be heat sealable to each other in order to form a heat seal type blanket seal.
Surprisingly, by texturing orembossing the film of the finer bag, the liner
bag film
has improved performance. The improved performance of the embossed liner bag
film is
attributed to an increased surface area of the film which provides greater
cling to a meat
surfate than an unembossed liner. Embossing also effectively reduces the
overall stiffness of
the film which also improves cling of the liner bag film to the meat surface.
Generally, any embossed pattern may be used on the liner bag or on the support
bag. Useful embossing patterns and shapes include for example elongated
diamonds (FIG. 11),
honey-combs (FIG. 12), squares, spheres (FIG. i3), triangles (FIG. 14), cones
(FIG. 15), pyramids
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{FIG. 16). U niform, discrete geometric patterns also provide channeling of
air during the
expellation of air from between the film layers. Other embossed patterns
useful in the present
invention and their manufacture are described in U.S. Patent No. 5,113,555.
Preferably, the
embossed pattern on the finer bag is an elongated diamond and more preferably
is a square or
uniform shaped diamond which has a pyramid shape in cross section. Preferably,
embossed
patterns protrude from the inner surface of the finer bag so to contact meat
or other
foodstuffs. Generally, the density of the embossed elements that make up the
pattern an the
liner bag may be from 6 to 50 units per linear inch of the surface of liner
bag, and preferably
from 10 to 20 units per linear inch of the surface of liner bag.
Generally, the support bag and liner hag of the multibags of the present
invention are made from a thermoplastic material or a blend of thermoplastic
materials and
can be comprised of the same or different material. The fil ms may be made by
a conventional
cast or blown film process. Useful thermoplastics include for example
polyotefins such as high
density polyethylene (HDPE), low density polyethylene (LDPE), linear low
density polyethylene
{LLDPE), and polypropylene (PP); thermoplastic elastomers such as styrenic
block copolymers,
polyolefin blends, elastomeric alloys, thermoplastic polyurethanes,
thermoplastic copolyesters,
and thermoplastic pofyamides; polymers and copolymers of polyvinyl chloride
(PVC),
polyvinylidene chloride (PVDC) , saran polymers, ethylenelvinyl acetate
copolymers, cellulose
acetates, polyethylene terephthatate (PET), ionomer (Surfyn), polystyrene,
polycarbonates,
styrene acrylonitrile, aromatic polyesters, linear polyesters, thermoplastic
polyvinyl alcohais
and useful materials listed hereinbefore that may be used to make an inner
film layer.
Preferably, the support bag and the liner bag are both made of polyethylene
and more
preferably from a blend of low density polyethylene (LDPE) (0.92 density) and
linear low
density polyethylene (LLDPE) (0.925 density). Preferably, the liner bag film
has a density of less
than 0.930 g/cc.
Generally, the film of the liner bag of the multibags of the present invention
have
a Transverse Direction 2 Percent Secant Modufus (TDSM) of less than 40,000
pounds per square
inch (psi) (2.75 x 108 Pa), and preferably less than 27,000 psi (1.86 x 108
Pa) as determined in
accordance with ASTM D 832-83, Method A with a jaw gap of 4 inches, a specimen
width of 1
inch, an initial strain rate of 0.25 inches/inchJminute, and a crosshead speed
of 1 inch/minute.
The modulus of a film in either the transverse or machine direction of the
film is generally a
measurement of the stiffness of the film. Typically, thermoplastic polyolefin
films that are
prepared by cast fil m processes that are known in the art have a TDSM of less
than 27,000 psi
(1.86 x 108 Pa). Thermoplastic polyolefin films that are prepared by well
known blown-film
processes have a TDSM of from 20,000 to 40,000 psi (9.30 x 10~ to 1.86 x 1 O8
Pa). Examples of
commercially available resins that would result in cast or blown films having
these tensile
properties include, for example, LDPE 748 and LDPE 690 from The Dow Chemical
Company.
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Another useful characteristic of the film of the liner bag is the Z number.
The Z
number is defined by the formula:
t3 X TDSM
where t is the thickness of the film in mils and TDSM is the transverse
direction modulus as
defined above. The Z number describes the relative stiffness of the film as a
function ofthe
film's thickness and modulus. Generally, the liner bag film has a Z number of
Less than 60,000 _
mil3 psi (6.7 mm3.kPa). Preferably, the liner bag film has a Z number of less
than 20,000 mil3 psi
(2.2 mm3~kPa), more preferably from 2,000 to 10,000 mil3 psi (0.22 to 1.1
mm3~kPa), and even
more preferably, from 3,000 to 6,000 mii3 psi {0.33 to 0.66 mm3~kPa).
Preferably, the support bag has a Z value in a range of from 50,000 to 150,000
mil3 psi (5.6to 16.9 mm3~kPa).
Generally, the support bag will have a nominal sidewall thickness of from 1 to
4
mils (25.4 to 102 microns), preferably from 1.3 to 3.0 mils (33 to 76
microns), and more
preferably from 1.5 to 2.0 mils (38 to 50.8 microns). Nominal thickness refers
to the thickness of
the film prior to any surface treatment such as scoring, texturing, and
embossing.
Generally, the liner bag will have a nominal sidewall thickness of less than 2
mils
{50.8 microns) and preferably from 0.3 to 1.0 mil (7.6 to 25.4 microns) and
more preferably has a
nominal sidewall thickness of from 0.5 to 0.7 mil (73 to 17.8 microns).
Preferably, the inner surface of the liner bag has a contact angle in the
range of
from 65° to 75° at 20°C relative to raw beef meat juice
as determined by advancing eontart
angle determination using a contact goniometer for example Model No. A-100
available from
Rame-Hart. Contact angle is defined as the angle formed between a horizontal
substrate and a
line tangent to the surface of a drop of liquid at the point where the surface
of the liquid drop
meet the horizontal substrate. The contact angle is a function of the surface
tension of the
liquid. The lower degree of contact angle indicates a higher degree of wetting
or adhesion of
the liquid to the substrate.
The method of measuring the contact angle is as follows: 1. Drops of the
liquid
to be measured (about 1 microliter) are place on the measuring surface (liner
bag film) of the
contact goniometer. 2. The contact angles are measured on both sides of each
of five drops. 3.
Step two is repeated on different sections of the I finer bag surface and the
results are averaged
to determine a mean contact angle. Examples of film that have a contact angle
of between 65°
to 75° at 20°C relative to raw beet meat juice include a blend
of LDPE and LLDPE available from
The Dow Chemical Company.
The multibags of the present invention may also have one or more layers of
film
or substrate between the support bag and the liner bag. Useful films and
substrates include
those materials listed above for the liner bag and the support bag and also
include papers,
cellulose polymers, fabrics, and elastic fabrics.
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The multibags of the present invention may also be made of films having
different colors so to highlight the bag-in-a-bag structure to the consumer.
For example, the
ii ner bag and support bag may be of a different color or tint or each or both
may be opaque or
clear.
The multibags of the present invention may also contain a liner bag andlor a
support bag that comprises a film or substrate that has been corona treated to
improve the
wetting characteristic of the film and thereby improve the meat adhering
and/or printing
characteristic of the film. Preferably, the inside surface or food contacting
surface of the liner
bag is corona treated. Useful teachings describing the process of corona
treating plastic films
0 are described in U.S. Patent No. 5,328,705.
The multibags of the present invention may also have a printed area on the
support and/or the liner bag. Printed areas are used as a write-on surface or
a write-on patch
to record information relating to the contents of the bag. The write-on
surface may also be
strategically placed on the support and/or liner bag to hide vent holes.
j 5 The multibags of the present invention may also have a liner bag and/or a
support bag that is pleated.
While not bound by any particular theory, it is believed that the means by
which
the multibags of the present invention prevent freezer burn of meats is that a
thin, inner layer
of film in the form of a bag which clings and conforms to the surface ofthe
meat and therefore
20 prevents moisture loss and excludes air from the meat surface. Excluding
moisture loss and air
from the meat surface reduces the formation of ice crystals that lead to
freezer burn or
dehydration of the meat.
FlG. 7 shows a block diagram of a process for hand making the multibags of the
present invention. As described in step illustrated by box 200, an inner liner
film of
25 polyethylene is cut to size and the edge seals of an existing polyethylene
freezer bag are cut off
and the freezer bag is unfolded. In step illustrated by box 270, the finer
film is overlayed onto
the unfoided freezer bag and aligned such that the edges of the liner film are
between the
closure profiles of the freezer bag, in step illustrated by box 220, the liner
film is attached to
the freezer bag film with a bar type heat sealer thereby heat sealing the two
films together
30 along the parallel edges of the liner film. In step illustrated by box 230,
the attached films are
folded such that the closure profiles are matched and the edges of the films
are sealed to make
a multibag. The sealed edges are formed by conventional heat sealing. In step
illustrated by
box 240, the excess thermoplastic is trimmed and the bag is inspected for
integrity. The bag or
bags are then packed in a dispenser as shown in step illustrated by box 250.
35 A process according to the present invention for making a multibag having
at
least an inner finer bag and an outer support bag generally comprises the
steps of forwarding a
first thermoptastic film web having a thickness of greater than 1 mil and a
first transverse web
width between parallel edges, forwarding at least a second thermoplastic film
web having a
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thickness of less than 2 mil and a second transverse web width, the second
transverse web
width being smaller than the width of the first thermoplastic film, overlaying
the second
thermoplastic film web onto the first thermoplastic film web between the
parallel edges of the
first film web, attaching the second thermoplastic film to the first
thermoplastic film along
parallel edges of the second thermoplastic film, folding the films in the
transverse direction,
and seal cutting the folded films to form bags.
FIG. 8 is a diagrammatic flow diagram for one embodiment of the process of the
present invention. As shown in step illustrated by box 300, the liner film or
second film may be
extruded orsuppiied from an unwind stand. Extrusion of the iinerfilm may be by
blown or cast
extrusion of thermoplastic material as is known in the art. Step illustrated
by box 310 provides
that the support or firstthermoplastic film is extruded having zippertype
closure profiles on
each respective film edge. The extrusion may be either conventional castor
blown film. An
example of an integral cast film process is described in U.S. Patent No.
4,263,079. Preferably,
both of the films are cast extruded. In step illustrated by box 320, the inner
or second film is
~ 5 added or overiayed onto the first film. The second film is aligned such
that the edges of the
second film are between the closure profiles of the first film. The overlaying
and alignment of
the second fitm onto the first film is done using conventional guide means
such as rollers and
nip rolls. In step illustrated by box 330, the parallel edges of the liner or
second film are heat
sealed to the support or first film. The films may be heat sealed together
using conventional
heat seating means such as a heated bar sealer, a hot air hem sealer,
extrusion lamination,
heated rollers and belts. Preferably, the films are seated together by a hinge-
type blanket seal.
The process step for forming a blanket seal is described hereinafter. In step
illustrated by box
340, the attached films web is folded and the closure profiles are joined. The
web may be
folded by conventional folding means known in the art. In step illustrated by
box 350, the the
folded film web is seal cut to form bags, the bags are stacked, and the
stacked bags are packed
into a container. The attached films may be folded and seal cut into bags as
described in U.S.
Patent No. 5,062,825. Preferably, the male and female closure elements are
interlocked after
folding of the films and prior to seal cutting. The finished bags may be
stacked, delivered, and
then packed into containers as described in U.S. Patent No. 5,302,080, U.S.
Patent No. 5,108,085
and U.S. Patent No. 5,185,987. The process of the present invention for making
a multibag of
at least two bags contemplates attaching together more than two film webs.
Either one or both of the first and second films my be textured by for example
embossing. Either or both of the film webs may be corona treated prior to or
after being
attached together. Preferably, the second thermoplastic film is corona treated
and embossed
prior to overlaying the second film onto the firstthermoplastic film.
The second or liner film web may be microperforated prior to being overlayed
onto the first or support film web using a process and an apparatus described
in U.S. Patent No.
5,405,567 .
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Vent holes 99 may be placed in either or both of the film webs using any fi#m
puncturing means or method known in the art such as a process and apparatus
similar to the
process and apparatus described in U.S. Patent No. 5,405,561. Vent holes may
also be made in
either or both film webs using a laser or a puncturing means having pins
protruding from a
rubber roller. Preferably, vent holes 99 in the film are made by perforating
the film with a non-
heated perforating means. Preferably, at least one vent hole 99 is placed in
the support or first
thermoplastic film web below the seas attaching the film webs prior to
overlaying the films.
The vent hole 99 in the support film web prevents air becoming trapped between
the webs and
forming a bubble or wrinkling the film when passing through compression rolls
or during
folding of the web.
Preferably, the closure profi les on the first thermoplastic film are formed
and
applied after the film webs are attached together. The closure profiles may be
extruded
through a die to form the desired profile and then applied to the film post-
extrusion as is
known in the art. An example of an extrusion and post-application process of
closure profiles is
described in U.S. Patent No. 5,049,223.
A preferred process for making the film web used for making multibags of the
present invention is shown in FIG. 17 and a process for attaching the two film
webs is shown in
FIG. 10. FiG. 17 is a schematic side view of the process providing and
attaching film webs 400
and F1G. 10 is an isometric view of a process for attaching the film webs
together prior to
forming bags. Referring to FIG. 17, process 400 generally comprises a means
for providing a
support or first film web 410, a means for providing a (finer or second film
web 430, tension
controt means 440 and a sealing or attaching means shown general 1y as 450.
Means 410
generally comprises an extrusion means 412 in extrusion alignment with a cast
rol l 416.
Extrusion means 412 extrudes a thermoplastic material 413 onto cast roll 416
to form a support
or first film web 414. The means for providing the first film web may also be
any means known
in the art and may be an extrusion process as described in U.S. Patent No.
5,049,223. Film web
414 passes through a conventional gauge control means 418 to a corona
treatment means 420
wherein the first film web 414 is corona treated as described hereinbefore, to
prepare the film
for later optional printing.
A liner or second film web 432 is provided by a roll or unwind stand 431. The
second film 432 may also be provided by a conventional blown or cast film
process as is know in
the art. The second film web has a transverse web width that is smallerthan
the transverse web
width of the first film web 414. Film webs 4i 4 and 432 are fed in to tension
control means such
as nip rol is 440 so as to match the strain of each of the films. Matching the
strain of the films is
described hereinafter in more detail. The first and second film webs 414 and
432 are aligned
and overlayed at roll 434 forming web 436. Web 436 is fed into a sealing means
shown
generally as 450. Web 436 changes orientation at roll 438 and is fed into
sealing means 450.
Sealing means 450 generally comprises an extrusion means or extruder 452, roll
454 and
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compression roll 456. A preferred seating means is shown in FIG. 10 and
described below.
Extruder 452 provides a sealing band 458. Sealing band 458 is fed onto web 436
and overlaps
the parallel edge of liner or second film 432. The sealing band 458 on web 436
passes between
roll 454 and compression rol I 456 and forming a blanket'seal. Extrusion means
or extruder 456
provides closure profiles 460. Closure profiles 460 are attached to the
opposed parallel edges
of the first film 414 as described in for example U.S. Patent 5,049,223
forming a web having a
blanket seat and closure profiles, web 462. Web 462 having closure profiles
isthen folded,
sealed and cut, stacked, and packed as shown and described in FIG. 8.
Either or both of the film webs may be textured or corona treated as described
hereinbefore. Either or both of the film webs may be microperforated or have
vent holes
placed therein as described above.
The second thermoplastic film or liner film may be attached to the first
thermoplastic film or support film by means of an extruded blanket seal
(overlaps edge of liner
film) as earlier described with respect to FIGS. 9C and 9D, hot air hem
seating, extrusion
lamination (extruded thermoplastic film between the film layers), hot melt
adhesive (placed
over or under the edge of *he top film layer), ultrasonic sealing, heated
rollers or belts,
adhesive film strips, infrared sealing, radio frequency sealing, or vibration
welding. Use of any
of the above means of attaching two film webs largely depends on the chemical
and physical
characteristics of the film webs. Preferably, the liner film is attached to
the support film using
an extruded hinge-type blanket seal 97 as shown in FIG. 9C and hereinafter
described. The
process shown in FIG 17 may be a continuous process or a step process.
Preferably, the process
is continuous.
FIG. 10 shows a process for attaching the second thermoplastic film web 432 to
the first thermoplastic film web 414 and is indicated generally as process
450a. Referring to
FIG. 10, in attaching a second thermoplastic film web 432 to a
firstthermoptastic film web 414
along parallel edges 470 of the second thermoplastic film web according to the
present
invention, the second thermoplastic film web 432 is aligned with and overlayed
onto a first
thermoplastic film web 414 forming film web 436. The film webs pass between
nip rolls 472
and pass under a sealing band extruder 452. A sealing band 458 of molten
thermoptastic
material is extruded onto *he advancing webs in the machine direction so as to
overlap the
edge 470 of the second film web and thereby contact and attach to both film
webs securing the
films together. The attached film webs are fed through a set of compression or
pinch rolls 454,
456 forming a blanket seal 459. A conventional second sealing band extruder
(not shown) is
used to seal the opposite parallel edge of the second film web to the first
film web. Film web
436 having a blanket seal 459 then passes through conventional guide rolls 474
and 476 so to
orient the web 436 for folding and seal cutting to form bags.
The blanket seat 459 may be either a hinge-type blanket seal 97 (FIG. 9C) or a
heat
seal type blanket seal 110 (FIG. 9D). Preferably, the blanket seat 459 is hi
nge-type. Some of the
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advantages of the blanket seating process include films may be attached
continuously at a
relatively high process rate, the blanket seal appears strong and
aesthetically pleasing to
consumers, the process is insensitive to other process variations, and it does
not produce a film
tail as does other processes known in the art.
Generally, the sealing bands may be applied in any fashion so as to attach the
two
films together. Preferably, the first thermoplastic film has mateable male and
female closure
elements along opposing edges of the film web and the seating bands are
applied equidistant
from their respective closure profiles. More preferably, the sealing bands are
applied
equidistant from the respective edges of the first thermoplastic film such
that mateable mate
0 and female closure elements may be applied to the support or first
thermoplastic film after the
film webs are attached.
Generally, the seating band may be made from any suitable thermoplastic
material or combi nation of thermoplastic materials that are heat sealable to
at least the
portions of the thermoplastic films to be joined. Preferably, the sealing band
is polyethylene
and more preferably, tow density polyethylene. An example of a suitable
commercially
available LDPE useful in the present invention is LDPE 748, commercially
available from The
Dow Chemical Company.
When forming a hinge-type blanket seal, the width of the sealing band may
generally range from 3 mm to the width of the support or first film web.
Preferably the width
of the seal l ng band ranges from 3 to 76 mm, and more preferably has a width
of from 6 to 19
mm.
Generally, the sealing band used to form a hinge-type blanket seal has a
thickness
of from 13 to 254 microns (0.5 to 10 miss) and preferably has a thickness of
from 25 to 51
microns (1 to 2 mils) and more preferably from 25.5 microns to 38.2 microns
(1.0 to 1.5 mils).
The sealing bands may be tinted, colored, or textured so to highlight the bag-
in-
a-bag structure to the consumer.
Since the sealing, band normally does not heat seal the second film to the
first
film, the sealing band may advantageously be used to attach films that
otherwise could not be
heat sealed together. However, if the seating band temperature, heat capacity,
and mass are
sufficient, and the liner film has an appropriate thickness and sealing
temperature, the
extruded seating band will transfer enough heat through the linerfiim to heat
seal it to the
support film.
Generally, the width of the finer or second film web is less than or smaller
than
the width of the first film web so that any portion of the seal band does not
hang over the edge
of the firstfilm web after being applied. Preferably, the width of the liner
or second film is
smaller than that of the width of the first film such that male and female
closure profiles may
be attached along opposed parallel edges of the first film web.
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General 1y, it is known i n the art that to attach two webs together, it is
desirable to
match the % stretch, or strain, i n the two webs at the point they are joined.
Matching the
strain avoids a cross direction curling (CD Curl) phenomenon from occurring
when the tension
is released. In the machine direction, the tension in each web can be related
as follows:
In the elastic region, 6 = E~ = T
t
Where:
c5 = Stress (psi)
E = Modulus of Elasticity (psi)
~ = Strain (in/in)
T = Tension (PLI)
t = Thickness (in)
Rearranging gives
~=5aT
E tE
To avoid machine direction (MD) puckering when an inner finer film is attached
to an outer
film,
Set~Liner = ~Outerfilm
tr-finer ~L''t inter
TLiner - TOuter ~ tOuter ~ EOuter
For elastic films, it is known in the art that a material under tension in the
machine direction will contract or "Neck-in" in the cross direction as a
function of a material
property known as Poisson's ratio, v. Poisson's ratio is a ratio of lateral
strain to axial strain and
is typically 0.3 for polyethylene. Using Poisson's ratio to relate the lateral
strain to the axial
strain, and following a similar derivation as above, the conditions required
to match CD Strain
and avoid MD Curl is as follows:
Vow diner EEL
TLiner ' TOuter
vLiner ~ tOuter ~ EOuter
In practice, it is generally desirable to match the strain in both the machine
and
tross directions. The puckering can be minimized by a variety of means,
including: attaching
webs that are similar in modulus and/or attaching webs that are similar in
Poisson's ratio. ,
For a given set of materials, the puckering can be minimized by running at low
tension where the films are attached, so there will be less recovery.
Depending on the .
application, the cross direction puckering can sometimes be considered
insignificant compared
to the machine direction.
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Thus it is desirable to maintain a relatively low tension in both webs, and
have
matched machine direction strain in the webs at the point where they are
joined. It is generally
known in the art that a recommended tension in the machine direction range to
effectively
transport webs is from 10- 25°/a of the yield tension, measured in PLI.
Film tracking may
become less precise at tensions below 10°r6 of the yield tension. While
the MD tension in each
web can be maintained from 0-100% of the yield point, it has been found that
above 25% of
the yield point, there is a danger of localized thin spots in the web actually
exceeding the yield
point of the film, resulting in non-elastic stretching. It has been found that
for successful
attachment of extruded sealing bands, *he tension is preferably run in the
range of 2-15°r6 of
the yield tension in the machine direction.
For the preferred embodiment, it has been found advantageous to use
lightweight idler roils with low friction bearings, to minimize the drag
between the liner film
supply point and the point where a blanket seal is applied. Even then, the
tension in the liner
fil m at the supply point is often so low that there becomes a trade-off
between low enough
~ 5 tension to avoid puckering or stretching, and high enough tension to give
adequate tracking.
As a result, the embodiment shown in Figure 10 has a set of nip rolls between
the two web
supply points and the point where a blanket seal is applied. Then the tension
the two webs can
be matched at somewhat higher, for example, 15°r6 of the yield point
tension, prior to the nip
rolls. Nip rolls allow different tension control zones. The strain in the webs
can be matched by
appropriate tension control between the supply points and the nip roll. The
compression tuff is
run at slightly lower speed that the nip rolls so to release some of the MD
tension, reducing it to
the desired 2-15°r6 range for blanket band sealing. A second set of nip
rolls could optionally be
added such that each web would run through a separate nip, and could have
separate tension
control, just prior to joining of the separate film webs as shown in FIG. 17.
Referri ng back to the process shown i n FIG. 17, the tension of the I finer
or second
thermoplastic film is generally controlled in the range of from 0.05 to 1
pound per linear inch
width (PLi) (0.6 mil PE) by using a set of compressing or nip rollers 440 as
in known in the art. in
the preferred embodiment, each of the film webs pass through nip rolls so to
match the strain
on each of the films. Thus, the tension of each of the film webs may be
different in order to
match the s*rain on each of the films. Alignment of the liner or second film
may be
accomplished by using conventional edge guiding systems and/or edge trimming
of the film
web to width.
Referring to FIG. 10, the tension of the combined films is generally
controlled in
the range of from 0.02 to 2.0 PLI (PE films) after the sealing band is applied
to avoid stretching
of the warm bands. The tension of the combined film webs may be controlled by
conventional
nip rollers 472. Stretching of the blanket bands may produce a "wave" and/or
puckering in the
final product.
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An alternate process according to the present invention for heat sealing at
least
two film webs comprises the steps of providing at least first and second film
webs capable of
being heat sealed together, overlaying the second film web onto the first film
web, providing
at least one sealing band of material having a temperature, mass, and heat
capacity sufficient
to heat seal the second thermoplastic film to the first thermoplastic film,
and applying said
band of sealing material to the overiayed film webs. This process is the same
as the process
shown in FIG. 10, except that the sealing band extruder 452 may be placed
above any portion
of the film web 436 so to heat seal the film webs together i n the machine
direction at any point
across the web. Preferably, the seal i ng band is compressed between rol lets
454, 456 after
having been applied. Multiple sealing band extruders 452 are used to provide
multiple seating
bands 458 along the machine direction of the film web so as to form multiple
heat seal type
blanket bands as shown in F1G. 9D. The film webs may be provided by extrusion
or from an
unwind stand. The film webs to be heat sealed may be made of any thermoplastic
materials
capable of being heat sealed together including those materials described
hereinbefore. The
film webs may have the same width or be of different widths. Generally, the
sealing band may
be made of any extrudable material capable of heat sealing to film webs
together. Preferably,
the sealing band is made from thermoplastic materials including for exampte
LDPE 748
available from The Dow Chemical Company.
Generally, the sealing band has a temperature, heat capacity, and mass
sufficient
2p to heat seal two films together. Generally, the temperature of the sealing
band is the
temperature at which the particular material may be extruded without
degrading.
Generally, the thickness of the film to be heat seated should of a thickness
so to
allow heat transfer from the sealing band to the film to heat seal the film to
the underlying
film web. Generally, the thickness of the sealing band used to form a heat
seal type blanket
seal may range from 0.5 to 10 mil (13 to 254 microns). Preferably, the sealing
band for a heat
seal type blanket seal has a thickness of from 1.5 to 3.0 mil (38 to 76
microns) and more
preferably has a thickness of from 1.5 to 2 mil (38 to 50.8 microns).
General 1y, the width of the sealing band used to form a heat seal type
blanket
seal ranges from 3 mm to the width of the support or first film web,
preferably the width of the
sealing band ranges from 3 to 76 mm, and more preferably has a width of from 6
to 19 mm.
Another process according to the present invention for attaching at least two
fitm
webs comprises the steps of providing at least first and second film webs
having first and
second widths respectively, the second width being smaller than the first
width, overlaying the
second film web onto the first film web between parallel edges of the first
film web, providing
at least one band of sealing material, and applying said band of sealing
material along and
over parallel edges of the second film web. Preferably, the sealing band 458
is applied to the
film webs by one or more extruders 452 (FIG. 10). Extruders 452 may be placed
at any point
above the film webs so to be capable of attaching the film webs together by
forming a hinge-
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type blanket seal in the machine direction. For example, multiple extruders
452 may be
staggered above the paral fel edges of three or more fi f m webs so to attach
the fi f m webs
together in succession. Preferably, the sealing band 452 is compressed between
rollers 454, 456
after haul ng been applied to the parallel edges of the fi Im web or webs.
Preferably, the sealing bands 458 used to form hinge-type blanket seals are
applied equidistant from the respective edges of the first thermoplastic film.
Generally, the
sealing band may be made from any suitable thermoplastic material or
combination of
thermoplastic materials that are heat sealable to at feast the portions of the
film webs to be
joined. The fif m webs to be joined may be for example thermoplastic as
described
hereinbefore, non-thermoplastic, fabrics, nonwovens, and coextruded films. The
film
substrates are attached together by the sealing band as shown in FIG. 9C.
When forming a hinge type blanket seal, the width of the sealing band may
generally range from 3 mm to the width of the support or first film web,
preferably the width
of the sealing band ranges from 3 to 76 mm, and more preferably has a width of
from 6 to 19
mm.
Generally, the sealing band used to form a hinge-type blanket seal has a
thickness
of from 13 to 254 microns (0.5 to 10 mils) and preferably has a thickness of
from 25 to 50.8
microns (1 to 2 mils) and more preferably from 25.5 microns to 38.2 microns
(1.0 to 1.5 mils).
EXAMPLES OF THE INVENTION
The experimental work that led to the aspects of the invention claimed
hereinafter involved time-consuming hand fabrication of numerous different
types of
"multibag" defined above; repackaging of meat in the multibags; and evaluation
of the
performance of the multibags retative to each other and other controls being
commercially
available freezer bags, during and after many months of storage in a freezer.
The experimental work involved the sequential evaluation of three main types
of
prototype, types A, B, and C described below.
TYPE-A PROTOTYPES
Type-A prototypes were all three layer multibags made essentially in
accordance
with Figures 5A, 5B and 5C having a support bag, a finer bag, a third layer,
and vent holes for
venting the space between the Ifner bag and the support to the space within
the Ii ner bag.
More specifically, Type-A1 multibags were fabricated as follows:
a. A support bag being an outer layer of polyethylene film (used for making
ZIPLOC~ storage bag 1.75 mil (44.4 microns));
b. A finer bag being an inner layer of polyethylene film 1.75 mil (44.4
microns)
thick with 800 microholes having hole diameters of 10 microns as vent holes to
permit moisture
to move freely into and out of the middle layer; and
c. A third layer being a hygroscopic film having a thickness of 1.5 mil (38
microns)
and moisture content of around 10 percent by weight (METHOCEL~ cellulose
ethers film made
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by Polymer Films, inc.-Rockville, CT). METHOCEL~ is a registered trademark of
The Dow
Chemical Company. More specifically, typical properties of the film are found
in the June, t986
data sheet of Polymer Films Inc., for product named "EM IIDO Water Soluble
Film". The
product was identified as having the primary constituent being Hydroxypropyl
Methyl
Cellulose Resin having CAS No of 009004-65-3.
Further, it will be noted from Figure 5A that the edge seals AD and BC of the
support bag are essentially "common" with the edge seals ad and be of the
liner bag.
TYPE-B PROTOTYPES
Type-B prototypes were all three layer muftibags essentially similar to the
Type-A
prototypes except that the liner bag had a thickness of 1.2 mil (30.5
microns)(instead of 1.75 mil
(44.4 microns)); and except the liner bag had no microholestherein and that
the space
between the finer bag and the support bag was essentially completely unvented.
TYPE-C PROTOTYPES
Type-C prototypes were all multibags of the duplex variety as shown in Figures
~ 5 2A, 2B, 2C, 3A, 3B, 3C, 4A, 4B and 4C and having a support bag having a
thickness of 1.75 mil
(44.4 microns) and a liner bag having a thickness of 0.6 mil without any
"third layer or wall"
between the liner bag and the support bag.
The Type-C mufti bags were given a secondary classification (denoted by the
letter
"C" or the letter "S" dependent upon whether the bags had "common edge seals"
or
20 ~~separate edge seals". The liner's edge seals are shown on the tines ad
and be in Figures 2A, 3A
and 4A. The edge seals of the support bag are shown by the lines AD and BC in
Figures 2A, 3A
and 4A. Clearly, in Figure 2A the edge seals are essentially "common"; whereas
in Figures 3A
and 4A the edge seals are "separate".
The bags were fabricated by hand. FIG. 7 is a diagrammatic flow diagram for
25 maki ng Type-CC multibags.
The Type-C multibags were given a tertiary classification (1, 2, or 3)
according to
whether the space between the support bag and the finer bag was (1) vented to
the space
within the liner bag (as shown in Figure 4C); ar (2) not vented (as shown in
Figures 3A, 3B and
3C); or (3) vented to the surrounding atmosphere (as shown by the vent 99 in
dotted line in
30 Figures 2A and 2B).
EVALUATION PROCEDURE
Ali prototype multibags were essentially evaluated relative to control bags in
the
following way by actually using the bags as potential freezer bags containing
boneless beef
steak.
35 1. Beef steak samples were initially weighed before packing in the bags.
Each
bag had one beef steak. The bags were placed in a commercial freezer with a
set point of 0°F (-
17.8°C).
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2. The freezer was occasionally opened and closed for the purpose of observing
the samples.
3. Physical observation (including bags conformation around steaks, formation
of
ice crystals, visible dry spots, and discoloration) were made daily during the
first two weeks and
then once every week for the next eight months for prototypes Type-A and Type-
B. Type-C was
physical 1y observed over a period of three months. Frozen beef steaks were
photographed in
color both inside and outside the bags, then thawed and photographed again.
4. Percent weight toss and the amount of drips were measured on the thawed
steaks. Amount of drips is defined as the blood-like fluid exuding from frozen
meat upon
thawi ng.
5. "Unexpected effects" were noted as appropriate.
SHORT TERM RESULTS - TYPES A. B AND C
Various Type-A prototypes and Type-B prototypes were evaluated
simultaneously, and sequentially in a staggered manner.
~ 5 Type-A1 described above was evaluated because the film was hygroscopic and
in
the hope that it might help to prevent moisture escaping from the meat during
storage in the
freezer.
However, an unexpected result occurred almost immediately. In particular it
was
discovered that with hygroscopic fi Im layer between the liner bag and the
support bag, the
20 hY9roscopic layer and the liner bag changed shape very rapidly and
"conformed" to the shape
of the beef steak. In other words it was highly beneficial in excluding air
from the space
around the beef steak.
It came as a second major surprise when the Type-B multibag also tightly
conformed the liner bag around the steak as a short term phenomenon.
25 The apparent success of the Type-B multibag led to design of the Type-C
multibag. Two types of Type-C bags were evaiua*ed: Type-CC2 and Type-CS2.
Again a
surprisingly result occurred. The Type-CC2 multibag appears to conform more
easily to the
shape of the beef steak at packaging and "before" the beef steak package is
placed in the
freezer as shown in Figure 6A. V1/ith hindsight, it is possibte to make
various speculations based
30 upon the fact that the unvented bag essentially has constant mass of air
between the liner bag
and the support bag.
LONG TERM RESU LTS - TYPES A AND B
Beef steaks in regular freezer bags (control) developed many large ice
crystals and
severe discoloration (bright red color faded into faint brown). Severe freezer
burn, as
35 evidenced by large discolored dry spots, was observed on the steak in both
frozen and thawed
states.
Beef steaks in the Type-A three layer multibags (with a perforated inner
layer)
were in excellent condition. Formation of ice crystals was significantly
reduced, the bright red
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color was maintained and no discoloration was observed. No freezer burn on the
surface of the
steaks was observed.
The Type-B three layer multibags with nonperforated film as the inner layer
showed similar results to those obtained with Type-A multibags.
A key hindsight observation that may explain the significant difference in
quality
performance between the control bags and the three layer bags is that the
middle and inner
layers of the three layer bags had tightly conformed around the steak which
resulted in
reducing air pockets and subsequent formation of ice crystals.
A comparison of weight toss and amount of drips between treatments showed
that weight loss of the steaks correlated well with the amount of formation of
ice crystals. Beef
steaks stored in regular freezer bags had a severe weight loss (20.5%) in
eight months and the
amount of drips was 2.06%. Beef steaks stored in the three layer bags (with a
perforated inner
layer) had a significantly less weight toss (4.3°~) than the control
and the amount of drips was
1.93°r6. The least amount of weight toss (1.9%) and drips (0.26%) was
measured with steaks
stored in the three layer bags (with nonperforated inner layer). The
difference in performance
between the three layer bags and control bags relate to the ability of the
three layer bags to
conform tightly around the meat, which fed to minimizing air pockets. As a
result of
conforming, the dehydration process, that leads to freezer burn, was reduced
significantly.
It was concluded that the qual ity of frozen beef steaks, stored in the Type-A
and
TYpe-B three layer multibags was superior compared to regular freezer storage
bags (control).
The freezer burn was minimized significantly due to the conforming of the
inner and middle
layers of the three layer bags onto the beef steaks.
LONG TERM RESULTS-TYPE-C
The Type-CC2 and Type-CS2 multibags also performed significantly better than
the commercially available freezer bags used as control. Their superior
performance can be
attributed, with the benefit of hindsight, to the tendency of the liner bag to
"conform" to the
food and minimize the headspace available for ice formation. It should perhaps
be noted that
performance advantages of these prototypes were less significant in tests with
irregularly
shaped food such as broccoli and chicken with bones.
Various properties of the Type-C liner bag and support bag were measured and
compared with the corresponding properties of the commercially available
freezer bags. For
example, the Relative Stiffness (as determined by the equation: Z = t3 X TDSM)
of the Type-C
liner was 1 to 2 orders of magnitude lower than commercially available
"freezer bags" (for
example 5,300 cubic mils psi (0.59 mm3~kPa) compared with 304,000 cubic mils
psi (34
mm3~kPa)).
Another experiment involved comparing a Type-CC multibag as described
hereinbefore with a Type-CC multibag having an embossed liner bag. The
experiment included
the repacking of 5 different types of meat and the evaluation of the muitibags
against each
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other and a commercially available freezer bag using a simplified 5 level
rating scale. The
control bags tested were ZIPLOC brand FREEZER BAGS (control).
PROTOTYPES
The multibags used were duplex bags having a support bag sidewall thickness of
1.75 mil (44.4 microns) and a liner bag sidewall thickness of 0.6 mil (15.2
microns). One
multibag had an embossed liner hereinafter designated "embossed liner" and the
other
multibag had a plain or smooth liner, hereinafterdesignated "plain liner."
Both multibags
were constructed of polyethylene. The embossed pattern on the embossed liner
bag was
uniform diamonds at 16 diamonds per Liner inch.
Five samples of each of ground beef, denver steak, boneless/skinless chicken
breast, fish fillet, and pork loin rib chop were placed into plain liner
multibags, embossed liner
multibags and Z1PLOC brand FREEZER BAGS. Each bag had one piece of meat. The
bags were
placed in a commercial freezer with a set point or 0°F. The freezer was
opened at various
intervals to observe and evaluate the samples.
STING SCALE
A rating scale was developed to visually rate ice crystal formation on the
surface
of the meat samples tested. The rating levels are: "< Low-Low," "Low-Medium
(Low-Med),"
Medium (Med)," "Medium-High (Med-Hi)," and "High."
" < Low-Low" means no or very small and very fine ice crystals present on the
meat surface in ice crystal patches of from 1/4 to 1/2 square inches (1.6 to
3.2 cm2) in area and
no freezer burn present.
"Low-Med" means early development of three dimensional ice crystals on the
meat surface due to some film lifting and no freezer burn present on film
contacted meat
su rfaces.
"Med" means numerous ice crystals present on the meat surface in patches
having an area or greater than 1/2 square inch (3.2 cm2), at least 1/4 of the
total meat surface
area having lost film contact, and minor or no freezer burn present.
"Med-Hi" means numerous three dimensional ice crystals present on over 1/3 of
the meat surface due to greater loss of film contact and freezer burn is
present.
° High" means ice crystals present over at least 1/2 of the total
surface area of the
meat and/or freezer burn present.
RESU LTS
The results of the freezer tests at freezing times of 17 weeks and 8 months
are
shown below in Table 1. The numbers in each rating category are the number of
meat samples
(out of five tested) having that particular rating attribute in the particular
time period. The
results show that both of the muitibags of the present invention prevented ice
crystal
formation and freezer burn on meats tested compared with the performance of a
control.
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TABLE 1
SAMPLE Low- Low- Med. Med. High
Hil
Low Med
_ _ 17 Weeks
Groun Bee
embossed liner 4 0 1 0 0
plain liner 4 0 1 0 0
Control 0 0 4 1 0
Denver Steak
embossed liner 3 1 1 0 0
plain liner 4 0 1 0 0
Control 0 0 3 0 2
BonelessJSkinless
Ck. Brt
embossed liner 5 0 0 0 0
plain liner 5 0 0 0 0
Control 0 2 2 0 1
Fish Fillet
embossed liner 4 0 0 0 1
plain finer 0 1 4 0 0
Control 0 0 0 0 5
Pork Loin R~ Chop
embossed liner 5 0 0 0 0
plain liner 5 0 0 4 1
Control 0 0 0 4 1
8 Months
Ground Beef _
embossed liner 5 0 0 0 0
plain liner 5 0 0 0 0
Control 0 0 5 0 0
Denver Steak
embossed liner 5 0 0 0 0
plain liner 5 0 0 0 0
Control 0 0 0 5 0
Bonetess/Skiniess
Ck. Brt
embossed liner 5 0 0 0 0
plain finer 5 0 0 0 0
Control 0 0 5 0 0
Fish Fillet
embossed liner 4 0 1 0 0
plain liner 4 0 1 0 0
Control 0 0 0 0 5
Pork Loin Rib Chop
embossed liner 5 0 0 0 0
plain liner 2 0 3 0 0
Control 0 0 0 3 2
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Although specific embodiments of the present invention have been described, it
is to be understood that modifications and variations may be found by those
skiiled in the art
which are within the spirit and scope of the invention.
10
20
30
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