U.S. patent application number 12/223439 was filed with the patent office on 2009-01-15 for hermetically sealable, easy-opeanable, flexible container of heat-shrinklable thermoplastic material.
Invention is credited to Felice Ursino.
Application Number | 20090017239 12/223439 |
Document ID | / |
Family ID | 36716860 |
Filed Date | 2009-01-15 |
United States Patent
Application |
20090017239 |
Kind Code |
A1 |
Ursino; Felice |
January 15, 2009 |
Hermetically Sealable, Easy-Opeanable, Flexible Container of
Heat-Shrinklable Thermoplastic Material
Abstract
A plastic bag for the manufacture of an easy-openable,
hermetically sealed package, comprises a multi-layer
heat-shrinkable film folded and/or heat-sealed to itself to form a
flexible container with two closed side edges, a closed bottom side
edge and an open top side, wherein said multi-layer heat-shrinkable
film comprises a first outer heat-sealing layer (a), a second outer
layer (b) and directly adhered to the heat-sealing layer (a) an
internal layer (c) of a blend of at least two resin components that
are only partially compatible so that said layer (c) will fail when
a transversal force of from about 4 to about 9.5 N/25.4 mm is
applied thereto. Preferably the bag is an ES bag and comprises an
unsealed area extending beyond the factory bottom seal where the
front and rear panels of the bag are separately graspable and
usable as tabs to be pulled apart to initiate opening of the
package. Also claimed is the packaged product comprising said
plastic bag.
Inventors: |
Ursino; Felice; (Milan,
IT) |
Correspondence
Address: |
CRYOVAC, INC.;SEALED AIR CORP
P.O. BOX 464
DUNCAN
SC
29334
US
|
Family ID: |
36716860 |
Appl. No.: |
12/223439 |
Filed: |
January 25, 2007 |
PCT Filed: |
January 25, 2007 |
PCT NO: |
PCT/EP2007/000635 |
371 Date: |
July 30, 2008 |
Current U.S.
Class: |
428/34.9 |
Current CPC
Class: |
B65D 75/26 20130101;
B32B 7/06 20130101; B32B 2250/24 20130101; B31B 2155/00 20170801;
B32B 2439/46 20130101; C08L 23/0869 20130101; B32B 27/306 20130101;
B32B 2307/736 20130101; B32B 2307/7242 20130101; B31B 70/00
20170801; B31B 2160/10 20170801; C08L 51/06 20130101; C08L 2666/02
20130101; B32B 27/32 20130101; C08L 2666/02 20130101; B32B 2307/31
20130101; B32B 27/304 20130101; Y10T 428/1328 20150115; B31B
2155/003 20170801; B32B 2270/00 20130101; C08L 23/0876 20130101;
B32B 27/08 20130101; B32B 27/308 20130101; C08L 23/0853 20130101;
B65D 75/5855 20130101; C08L 23/20 20130101; B32B 27/34 20130101;
C08L 23/0869 20130101; C08L 23/0876 20130101 |
Class at
Publication: |
428/34.9 |
International
Class: |
B65D 75/26 20060101
B65D075/26; B65B 53/02 20060101 B65B053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2006 |
EP |
06001912.2 |
Claims
1: A plastic bag for the manufacture of an easy-openable,
hermetically sealed package, said plastic bag comprising a
multi-layer heat-shrinkable film folded and/or heat-sealed to
itself to form a flexible container with two closed side edges, a
closed bottom side edge and an open top side, wherein said
multi-layer heat-shrinkable film comprises a first outer
heat-sealing layer (a), a second outer layer (b) and directly
adhered to the heat-sealing layer (a) an internal layer (c) of a
blend of at least two resin components that are only partially
compatible so that said layer (c) will fail when a transversal
force of from about 4 to about 9.5 N/25.4 mm is applied
thereto.
2: The plastic bag of claim 1 which comprises an unsealed area
extending beyond one of the seals forming the bag, where the front
and rear panels of the bag itself are separately graspable and
usable as tabs to be pulled apart to initiate opening of the
package.
3: The plastic bag of claim 2 wherein said unsealed area beyond one
of the seals forming the bag is present only along a small portion
of the seal length.
4: The plastic bag of claim 2 wherein the seal beyond which the
unsealed area extends, has a width less than about 4 mm.
5: The plastic bag of claim 1 which is an end seal bag.
6: A packaged product comprising i) an easy-openable, hermetically
sealed, plastic bag comprising a multi-layer heat-shrinkable film
folded and/or heat-sealed to itself to form a closed flexible
container, wherein said multi-layer heat-shrinkable film comprises
at least a first outer heat-sealable layer (a), a second outer
layer (b) and directly adhered to the heat-sealing layer (a) an
internal layer (c) of a blend of at least two resin components that
are only partially compatible so that said layer (c) will fail when
a transversal force of from about 4 to about 9.5 N/25.4 mm is
applied thereto, and ii) a product packaged in said bag, said
plastic bag having an unsealed area extending beyond one of the
seals of the package where the front and rear panels of the bag are
separately graspable and usable as opening tabs.
7: The packaged product of claim 6 wherein the seal in the plastic
bag beyond which the unsealed area extends has a width less than
about 4 mm.
8: The package of claim 6 wherein the plastic bag is an end seal
bag.
9: The package of claim 8 wherein the seal beyond which the
unsealed area extends is the factory bottom seal.
10: The package of claim 9 wherein said unsealed area is present
only along a small portion of the bottom seal length.
11: The package of claim 6 wherein the product is packaged under
vacuum and the plastic bag is heat-shrunk around the product.
12: The plastic bag of claim 1 wherein the blend of resins for
internal layer (c) comprises from about 35 wt. % to about 80 wt. %
of a copolymer of ethylene and acrylic or methacrylic acid and in
particular an ionomer, from about 15 wt. % to about 30 wt. % of a
modified ethylene-vinyl acetate, and from about 2 wt. % to about 50
wt. % of a polybutene and preferably comprises from about 40 wt. %
to about 70 wt. % of an ionomer, from about 15 wt. % to about 30
wt. % of a modified ethylene-vinyl acetate, and from about 10 wt. %
to about 30 wt. % of a polybutene.
13: The plastic bag of claim 6, wherein the blend of resins for
internal layer (c) comprises from about 35 wt. % to about 80 wt. %
of a copolymer of ethylene and acrylic or methacrylic acid and in
particular an ionomer, from about 15 wt. % to about 30 wt. % of a
modified ethylene-vinyl acetate, and from about 2 wt. % to about 50
wt. % of a polybutene and preferably comprises from about 40 wt. %
to about 70 wt. % of an ionomer, from about 15 wt. % to about 30
wt. % of a modified ethylene-vinyl acetate, and from about 10 wt. %
to about 30 wt. % of a polybutene.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a flexible container of
heat-shrinkable thermoplastic material, such as a bag or pouch,
that can be sealed in a tight, hermetic manner, to encase a
product, providing for a package that can withstand the
conventional handling without accidentally rupturing and thus
safely securing the packaged product, and at the same time can be
opened by hand, i.e., without using scissors, knives, or other
cutting and dangerous devices, when this is desired.
BACKGROUND OF THE INVENTION
[0002] Food and other items are often packaged in flexible
containers of thermoplastic material, such as pre-formed bags with
one end open through which the product to be packaged is inserted
into the bag, or pouches that are formed starting from a flat or
folded film sealed around the product to be packaged, which are
then closed by heat-sealing the open end(s).
[0003] Particularly with food products, the flexible container is
very often made of heat-shrinkable thermoplastic material. In such
a case, first the product is loaded into the flexible container,
then air is removed and the open end of the container is closed by
a heat-sealing step, and finally the sealed and vacuumized package
is submitted to a heat-treatment to get the shrink of the packaging
material tightly around the packaged product. While the opening of
plastic bags and pouches is a problem that in general needs
improving, in case of vacuumized and shrunk bags opening of the end
package to reach the packaged product may become a real problem if
no cutting tools are available. It is therefore desirable to
provide the flexible container with so-called easy-opening means,
i.e., a feature or a combination of features that would enable the
end user to easily open the package by hand.
[0004] U.S. Pat. No. 3,516,537 addresses this problem by creating a
tab in the skirt of a heat-shrinkable bag extending beyond the
factory seal of the bag, by means of a cut at a right angle to said
factory seal. To open the package the tab is gripped with the
fingers of one hand and pulled up and across the bottom of the
package, while the packaged product is held with the other hand.
The entrance edge of the tab, being directed at a right angle to
the seal, will tear into and through the factory seal. As the tab
is pulled across the package, the package will tear open
predominantly following the sealed seam. This solution however can
be employed only with products that would not be damaged by a
certain pressure (such as the pressure exerted by pulling up the
tab with one hand while keeping down the product with the other)
such as the turkey specifically illustrated in U.S. Pat. No.
3,516,537.
[0005] A similar approach, with similar drawbacks, has been
described in U.S. Pat. No. 3,641,732, where a laminated tear tab
extending outwardly and substantially perpendicular to the package
is formed by the fusion of a suitable portion of the wrapping
material.
[0006] A different approach has been followed in e.g., U.S. Pat.
Nos. 3,391,851, and 5,413,412 where a tear tab is sealed over a
perforation line on a heat-shrunk container or on a heat-shrinkable
bag. The drawbacks in these solutions are mainly related to the
risk that the accidental detachment of the adhered tear tab would
expose the perforations thus leading to a loss of vacuum within the
package.
[0007] Still another approach has been described in U.S. Pat. No.
4,958,735 and provides for the adhesion of a thick strip of non
shrinkable thermoplastic material adhered to the un-shrunk portion
of an otherwise shrunk package, said thick strip bearing a weakness
line dividing it into two manually graspable sections to be used as
tear tabs and pulled into the opposite directions to open the
package. While this system has certain advantages, because for
instance there is no need to keep the packaged product while
opening the package and there are no risks for the packaged product
if the tear tabs detach from the bag, the manufacture of such a
package would be very complicated and difficult to apply on
industrial scale. Furthermore the opening of the package will occur
through a tear of the shrunk film in the longitudinal direction
thus destroying the whole container.
[0008] There is therefore still a need for flexible containers
provided with improved easy opening means.
OBJECT AND SUMMARY OF THE INVENTION
[0009] It is thus an object of the present invention to provide an
easy-openable flexible container of heat-shrinkable thermoplastic
material that can be sealed in a tight, hermetic manner, to safely
secure the packaged product, can be employed for the packaging of
any type of products, and can be manufactured easily.
[0010] In a first aspect the present invention concerns a plastic
bag for the manufacture of an easy-openable, hermetically sealed
package, said plastic bag comprising a multi-layer heat-shrinkable
film folded and/or heat-sealed to itself to form a flexible
container with two closed side edges, a closed bottom side edge and
an open top side, wherein said multi-layer heat-shrinkable film
comprises a first outer heat-sealing layer (a), a second outer
layer (b) and directly adhered to the heat-sealing layer (a) an
internal layer (c) of a blend of at least two resin components that
are only partially compatible so that said layer (c) will fail when
a transversal force of from about 4 to about 9.5 N/25.4 mm is
applied thereto.
[0011] As used herein the term "bag" is inclusive of end-seal (or
ES) bags, which have an open top, seamless (i.e., folded, unsealed)
side edges, and a seal across the bottom of the bag,
transverse-seal (or TS) bags, which have an open top, a seamless
bottom edge and each of the side edges with a seal therealong, and
L-sealed (or LS) bags, which have an open top, a sealed bottom, one
transverse-seal along a first side edge and a seamless second side
edge.
[0012] In a preferred embodiment of this first aspect, the bag
comprises an unsealed area extending beyond one of the factory
seals forming the bag, where the front and rear panels of the bag
itself are separately graspable and usable as tabs to be pulled
apart to initiate opening of the package. In a most preferred
embodiment, said unsealed area beyond the factory seal is present
only along a small portion of the seal length to further facilitate
the opening of the bag by concentrating the force on a limited
width of the seal.
[0013] Preferably the plastic bag is an ES bag.
[0014] In a second aspect the present invention concerns a packaged
product comprising i) an easy-openable, hermetically sealed,
plastic bag made from a multi-layer heat-shrinkable film folded
and/or heat-sealed to itself to form a closed container, wherein
said multi-layer heat-shrinkable film comprises at least a first
outer heat-sealable layer (a), a second outer layer (b) and
directly adhered to the heat-sealing layer (a) an internal layer
(c) of a blend of at least two resin components that are only
partially compatible so that said layer (c) will fail when a
transversal force of from about 4 to about 9.5 N/25.4 mm is applied
thereto, and ii) a product packaged in said bag, said plastic bag
having an unsealed area extending beyond one of the seals of the
package where the front and rear panels of the bag are separately
graspable and usable as opening tabs.
[0015] In a preferred embodiment of said second aspect, the bag is
an ES bag. In a more preferred embodiment the bag is an ES bag and
the unsealed area is extending beyond the factory end seal and,
even more preferably, said unsealed area is present only along a
small portion of the bottom seal length.
[0016] Preferably in said second aspect the product is packaged
under vacuum and the plastic bag is heat-shrunk around the
product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a perspective view of a shrunk bag according to
one embodiment of the present invention where the tear tabs extend
beyond the seal closing the bag mouth;
[0018] FIG. 2 is a top view of an ES bag according to a preferred
embodiment of the present invention;
[0019] FIG. 3 is a top view of a tubing from which the ES bags of
FIG. 2 are manufactured by using a suitably selected cutting
profile;
[0020] FIG. 4 is a perspective view of a shrunk bag where the
starting bag is the bag of FIG. 2;
[0021] FIG. 5 is a top view of a series of TS bags according to the
present invention with a side tear tab;
[0022] FIG. 6a to 6c are representational top view of particular
shapes of possible tear tabs.
DEFINITIONS
[0023] As used herein, the term "film" is used in a generic sense
to include any flexible plastic web, regardless of whether it is
film or sheet. Typically, films of and used in the present
invention have however a thickness of 150 .mu.m or less, preferably
a thickness of 140 .mu.m or less, and more preferably a thickness
of 120 .mu.m or less.
[0024] As used herein, the phrases "inner layer" and "internal
layer" refer to any film layer having both of its principal
surfaces directly adhered to another layer of the film.
[0025] As used herein, the phrase "outer layer" refers to any film
layer having only one of its principal surfaces directly adhered to
another layer of the film
[0026] As used herein, the phrase "innermost layer", when referred
to the multi-layer film used in the manufacture of the flexible
container, means the outer layer of said multi-layer film which in
the end package will be closest to the packaged product relative to
the other layers of the film.
[0027] As used herein, the phrase "outermost layer", when referred
to the multi-layer film used in the manufacture of the flexible
container means the outer layer of said multi-layer film which in
the end package will be furthest from the packaged product relative
to the other layers of the film.
[0028] As used herein, the phrases "seal layer", "sealing layer",
"heat seal layer", and "sealant layer", refer to an outer layer
involved in the sealing of the film to itself.
[0029] As used herein the term "factory seal" refers to any and all
seals necessary to convert a film tubing or a flat film into a bag
having an open top. Such seals are made at the bag-making factory
and hence are herein termed to be "factory seals".
[0030] As used herein, the term "core" and the phrase "core layer",
refer to any inner film layer that preferably has a function other
than serving as an adhesive or compatibilizer for adhering two
layers to one another.
[0031] As used herein, the phrase "tie layer" refers to any inner
film layer having the primary purpose of adhering two layers to one
another.
[0032] As used herein, the phrase "machine direction", herein
abbreviated "MD", refers to a direction "along the length" of the
film, i.e., in the direction of the film as the film is formed
during extrusion and/or coating.
[0033] As used herein, the phrase "transverse direction", herein
abbreviated "TD", refers to a direction across the film,
perpendicular to the machine or longitudinal direction. As used
herein, the phrases "heat-shrinkable," "heat-shrink," and the like,
refer to the tendency of the film to shrink upon the application of
heat, i.e., to contract upon being heated, such that the size of
the film decreases while the film is in an unrestrained state. As
used herein said term refer to films with a free shrink in each of
the machine and the transverse directions, as measured by ASTM D
2732, of at least 5% at 95.degree. C.
[0034] As used herein, the term "polymer" refers to the product of
a polymerization reaction, and is inclusive of homo-polymers, and
co-polymers, whereas the term "co-polymer" refers to polymers
formed by the polymerization reaction of at least two different
monomers, thus including, for example, also ter-polymers.
[0035] As used herein, the phrase "heterogeneous polymer" refers to
polymerization reaction products of relatively wide variation in
molecular weight and relatively wide variation in composition
distribution, i.e., typical polymers prepared, for example, using
conventional Ziegler-Natta catalysts.
[0036] As used herein, the phrase "homogeneous polymer" refers to
polymerization reaction products of relatively narrow molecular
weight distribution and relatively narrow composition distribution.
Homogeneous polymers are structurally different from heterogeneous
polymers, in that homogeneous polymers exhibit a relatively even
sequencing of co-monomers within a chain, a mirroring of sequence
distribution in all chains, and a similarity of length of all
chains, i.e., a narrower molecular weight distribution. This term
includes those homogeneous polymers prepared using metallocene, or
other single-site type catalysts, as well as those homogenous
polymers that are obtained using Ziegler Natta catalysts in
homogenous catalysis conditions.
[0037] As used herein, the term "polyolefin" refers to any
polymerized olefin, which can be linear, branched, cyclic,
aliphatic, aromatic, substituted, or unsubstituted. More
specifically, included in the term polyolefin are homo-polymers of
olefin, co-polymers of olefin, co-polymers of an olefin and an
non-olefinic co-monomer co-polymerizable with the olefin, such as
vinyl monomers, modified polymers thereof, and the like. Specific
examples include polyethylene homo-polymer, polypropylene
homo-polymer, polybutene homo-polymer, ethylene-.alpha.-olefin
co-polymer, propylene-.alpha.-olefin co-polymer,
butene-.alpha.-olefin co-polymer, ethylene-unsaturated ester
co-polymer, ethylene-unsaturated acid co-polymer, (e.g.
ethylene-ethyl acrylate co-polymer, ethylene-butyl acrylate
co-polymer, ethylene-methyl acrylate co-polymer, ethylene-acrylic
acid co-polymer, and ethylene-methacrylic acid co-polymer),
ethylene-vinyl acetate copolymer, ionomer resin, polymethylpentene,
etc.
[0038] As used herein the term "modified polyolefin" is inclusive
of modified polymer prepared by co-polymerizing the homo-polymer of
the olefin or co-polymer thereof with an unsaturated carboxylic
acid, e.g., maleic acid, fumaric acid or the like, or a derivative
thereof such as the anhydride, ester or metal salt or the like. It
is also inclusive of modified polymers obtained by incorporating
into the olefin homo-polymer or co-polymer, by blending or
preferably by grafting, an unsaturated carboxylic acid, e.g.,
maleic acid, fumaric acid or the like, or a derivative thereof such
as the anhydride, ester or metal salt or the like.
[0039] As used herein, the phrase "ethylene-.alpha.-olefin
copolymer" refers to such heterogeneous materials as linear low
density polyethylene (LLDPE) with a density usually in the range of
from about 0.915 g/cm.sup.3 to about 0.930 g/cm.sup.3, linear
medium density polyethylene (LMDPE) with a density usually in the
range of from about 0.930 g/cm.sup.3 to about 0.945 g/cm.sup.3, and
very low and ultra low density polyethylene (VLDPE and ULDPE) with
a density lower than about 0.915 g/cm.sup.3; and homogeneous
polymers such as metallocene-catalyzed EXACT.TM. and EXCEED.TM.
homogeneous resins obtainable from Exxon, single-site AFFINITY.TM.
resins obtainable from Dow, and TAFMER.TM. homogeneous
ethylene-.alpha.-olefin copolymer resins obtainable from Mitsui.
All these materials generally include co-polymers of ethylene with
one or more co-monomers selected from
(C.sub.4-C.sub.10)-.alpha.-olefin such as butene-1, hexene-1,
octene-1, etc., in which the molecules of the copolymers comprise
long chains with relatively few side chain branches or cross-linked
structures.
[0040] As used herein, the term "adhered", as applied to film
layers, broadly refers to the adhesion of a first layer to a second
layer either with or without an adhesive, a tie layer or any other
layer therebetween. In contrast, as used herein, the phrase
"directly adhered" is defined as adhesion of the subject layer to
the object layer, without a tie layer, adhesive, or other layer
therebetween. As used herein, the word "between", as applied to a
layer expressed as being between two other specified layers,
includes both direct adherence of the subject layer to the two
other layers it is between, as well as a lack of direct adherence
to either or both of the two other layers the subject layer is
between, i.e., one or more additional layers can be imposed between
the subject layer and one or more of the layers the subject layer
is between.
[0041] As used herein the term "gas-barrier" when referred to a
layer or to an overall structure, is used to identify layers or
structures characterized by an Oxygen Transmission Rate (evaluated
at 23.degree. C. and 0% R.H. according to ASTM D-3985) of less than
500 cm.sup.3/m.sup.2daybar.
[0042] As used herein the wording "only partially compatible", when
applied to the polymer components of the blend of layer (c), is
intended to refer to the individual components of a polymer blend
that exhibit a sufficient interfacial adhesion to held them in
contact with one another, at their interfaces, under the intended
conditions of use, but that do not allow the layer containing their
blend to maintain its mechanical integrity when submitted to a
given stress, in this case a transversal force in the range of from
about 4 to about 9.5 N/25.4 mm.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0043] The multi-layer heat-shrinkable film that can suitably be
employed for the manufacture of the easy-peelable and hermetically
sealable bag of the present invention contains at least three
layers, a first outer heat-sealing layer (a), a second outer layer
(b) and, directly adhered to the heat-sealing layer (a), an
internal cohesive failure layer (c).
[0044] The internal cohesive failure layer (c) comprises a blend of
at least two resin components that are only partially compatible
and are selected in such a way that said layer (c) will fail, by an
internal rupture substantially along a plane parallel to the layer
itself, when a transversal force of from about 4 to about 9.5
N/25.4 mm is applied thereto. Blends of polymer components that can
be used for layer (c) are for instance those described in
EP-B-192,131 comprising an ionomer with a melt flow index lower
than 5 and a modified ethylene-vinyl acetate copolymer with a
remarkably higher melt flow index, whereby the melt flow indices of
the two polymers in said layer (c) differ by at least 10; or those
described in WO 99/54398 comprising three components, i.e., a
copolymer of ethylene and acrylic or methacrylic acid and in
particular an ionomer, a modified EVA and a polybutene; or those
described in US 2002/0172834 which comprise polybutene, an ionomer,
and EVA or an alkyl ester of (meth)acrylic acid in suitable
proportions, and the whole content of these documents is
incorporated herein by reference.
[0045] Preferred blends for layer (c) are those comprising from
about 35 wt. % to about 80 wt. % of a copolymer of ethylene and
acrylic or methacrylic acid and in particular an ionomer, from
about 15 wt. % to about 30 wt. % of a modified ethylene-vinyl
acetate, and from about 2 wt. % to about 50 wt. % of a
polybutene.
[0046] Particularly preferred blends for layer (c) are those
comprising from about 40 wt. % to about 70 wt. % of an ionomer,
from about 15 wt. % to about 30 wt. % of a modified ethylene-vinyl
acetate, such as for instance an ethylene-vinyl acetate carbon
monoxide copolymer, and from about 10 wt. % to about 30 wt. % of a
polybutene.
[0047] Other blends of only partially compatible resins may be
employed for layer (c) provided however they will lead to a
breakage of the layer when a transversal force of from about 4 to
about 9.5 N/25.4 mm is applied thereto. If layer (c) does fail when
a transversal force lower than about 4 N/25.4 mm is applied
thereto, the bag obtained from the film containing such layer might
not withstand the pressure exerted in the loading step by the most
conventional automatic loading systems and therefore there might be
leakages in the packages made thereby. If layer (c) fails only when
a transversal force higher than about 9.5 N/25.4 mm is applied
thereto, the package obtained from the multi-layer film containing
such layer (c) will not be easy-openable. The force required to
break such a layer (c) is measured in accordance with ASTM F88-94
using specimens 25.4 mm in width and 300 mm in length made by
heat-sealing two strips of a three-layer film where layer (c) is
sandwiched between two thin polyolefin layers. The two strips are
manually separated until their edges may be fixed respectively into
the lower and upper clamps of an Instron dynamometer. The Instron
is then started, at a crosshead speed of 30 cm/min with a
full-scale load of 2 kg, and peel the specimen apart by
delaminating layer (c) into two portions.
[0048] The heat-sealable layer (a) of the multi-layer film suitable
for the manufacture of the easy-openable bag according to the
present invention will comprise one or more resins independently
selected from the group consisting of polyethylene homo-polymer,
heterogeneous or homogeneous ethylene-.alpha.-olefin copolymer,
ethylene-vinyl acetate co-polymer, ethylene-ethyl acrylate
co-polymer, ethylene-butyl acrylate co-polymer, ethylene-methyl
acrylate co-polymer, ethylene-ethyl methacrylate co-polymer,
ethylene-butyl methacrylate co-polymer, ethylene-methyl
methacrylate co-polymer, ethylene-acrylic acid co-polymer,
ethylene-methacrylic acid co-polymer, ionomer and blends thereof in
any proportion. Preferred resins will be ethylene-vinyl acetate
copolymers, linear ethylene-.alpha.-olefin copolymers, homogeneous
or heterogeneous, and blends of two or more of these resins.
Particularly preferred resins for the heat-sealable layer (a) will
comprise homogeneous and heterogeneous ethylene-.alpha.-olefin
copolymers with a density comprised between about 0.890 and about
0.925 g/cm.sup.3, and more preferably with a density comprised
between about 0.895 and about 0.915 g/cm.sup.3 and blends thereof
in any proportions. The preferred resins for the heat-sealable
layer (a) will have a seal initiation temperature
.ltoreq.110.degree. C., more preferably a seal initiation
temperature .ltoreq.105.degree. C., and yet more preferably a
sealing initiation temperature .ltoreq.100.degree. C.
[0049] Heat-sealable layer (a) will be the innermost layer in the
end package and is the layer involved in the heat-sealing of the
film to itself for the manufacture of the flexible container and of
the end package. The thickness of said first outer layer (a) would
not be higher than 20 .mu.m, preferably not higher than 18 .mu.m
and even more preferably not higher than 15 .mu.m. Typically it
will have a thickness higher than 6 .mu.m and preferably higher
than 8 .mu.m to provide for a hermetic seal. Representative
thickness values for the heat-sealable layer (a) are preferably in
the range 10-15 .mu.m.
[0050] For the other outer layer (b), which will be the outermost
layer in the flexible container and in the end package, any
thermoplastic material can be employed, such as any polyolefin,
modified polyolefin or any blend thereof. Polyamides or
copolyamides and polyesters or copolyesters may also be
employed.
[0051] The polyamide/copolyamide resins that could be used for the
outer layer (b) may be aliphatic nylons e.g., nylon 6, nylon 11,
nylon 12, nylon 66, nylon 69, nylon 610, nylon 612, and copolymer
nylons including nylon 6/9, nylon 6/10, nylon 6/12, nylon 6/66,
nylon 6/69, and aromatic nylons, such as 6I, 6I/6T, MXD6, MXD6/MXDI
as well as blends thereof.
[0052] Preferred thermoplastic polyesters may include those
obtained from an acid component comprising an aromatic dibasic
acid, such as terephthalic acid or isophthalic acid, and a glycol
component comprising an aliphatic glycol, an alicyclic glycol or an
aromatic glycol, such as ethylene glycol, diethylene glycol or
cyclohexane dimethanol. The use of a co-polyester, formed starting
from two or three species of acid component or/and of glycol
component, would be preferred.
[0053] Preferred polyolefin resins for the outer layer (b) are
ethylene homo-polymers and ethylene co-polymers. More preferred are
ethylene-.alpha.-olefin copolymers, particularly those with a
density of from about 0.895 to about 0.935 g/cm.sup.3, and more
preferably of from about 0.900 and about 0.930 g/cm.sup.3,
ethylene-vinyl acetate copolymers, particularly those with a vinyl
acetate content of from about 4 to about 14% by weight, ionomers,
and their blends.
[0054] The thickness of said outer layer (b) typically will depend
on the number of layers in the overall structure and on their
thickness in view of the total thickness desired for the flexible
container. It will thus be generally comprised between about 2 and
about 20 .mu.m, and preferably between about 3 and about 15
.mu.m.
[0055] According to a preferred embodiment of the present invention
the multi-layer film also comprises a core gas-barrier layer (d)
that comprises at least one gas barrier resin generally selected
from vinylidene chloride copolymers (PVDC), ethylene-vinyl alcohol
copolymers (EVOH), polyamides and acrylonitrile-based copolymers.
Preferred resins are typically PVDC, EVOH, polyamides/copolyamides
and blends of EVOH with polyamides/copolyamides.
[0056] The most preferred resin is PVDC. This term includes
copolymers of vinylidene chloride and at least one
mono-ethylenically unsaturated monomer copolymerizable with
vinylidene chloride. The mono-ethylenically unsaturated monomer may
be used in a proportion of 2-40 wt. %, preferably 4-35 wt. %, of
the resultant PVDC. Examples of the mono-ethylenically unsaturated
monomer may include vinyl chloride, vinyl acetate, vinyl
propionate, alkyl acrylates, alkyl methacrylates, acrylic acid,
methacrylic acid, and acrylonitrile. The vinylidene chloride
copolymer can also be a ter-polymer. It is particularly preferred
to use a copolymer with vinyl chloride or (C.sub.1-C.sub.8)-alkyl
(meth)acrylate, such as methyl acrylate, ethyl acrylate or methyl
methacrylate, as the comonomers. It is also possible to use a blend
of different PVDC such as for instance a blend of the copolymer of
vinylidene chloride with vinyl chloride with the copolymer of
vinylidene chloride with methyl acrylate. The PVDC may contain
suitable additives as known in the art, i.e. stabilisers,
antioxidizers, plasticizers, hydrochloric acid scavengers, etc.
that may be added for processing reasons or/and to control the
gas-barrier properties of the resin.
[0057] Ethylene-vinyl alcohol copolymers will be preferably
employed when a particularly good flexibility is required or when a
fully coextruded, irradiated structure is manufactured because EVOH
withstands irradiation without being degraded, up to a very high
energy level. It will be used alone or admixed with a polyamide or
copolyamide. Polyamides and copolyamides can also be employed alone
as gas-barrier resins. Particularly preferred in this case are the
aromatic polyamides/copolyamides such as the polyamide formed by
polycondensation between methaxylyenediamine and adipic acid, the
polyamide formed from hexamethylenediamine and terephthalic acid
and/or isophthalic acid and the copolyamide formed from
methaxylyenediamine, adipic acid and isophthalic acid. In general
amorphous or semi-crystalline polyamides/copolyamides are
preferred.
[0058] Once the gas-barrier resin has been selected, its thickness
will be set to provide for the desired oxygen transmission rate
(OTR). High barrier structures will have an OTR below 100
cm.sup.3/daym.sup.2atm and preferably below 80
cm.sup.3/daym.sup.2atm and will be particularly suitable for meat
packaging, including fresh red meat and processed meat. Higher OTR
will be preferred for packaging e.g. most of the cheeses where
generally OTR of from about 100 to about 400 cm.sup.3/daym.sup.2atm
are preferred and from about 150 to about 350
cm.sup.3/daym.sup.2atm mostly preferred.
[0059] Typically the thickness of the barrier layer ranges from
about 2 to about 10 .mu.m, preferably from about 3 to about 8
.mu.m, and more preferably from about 3.5 to about 7 .mu.m.
[0060] Additional layers, such as for instance tie layers, to
improve interlayer adhesion, may be present.
[0061] Tie layers may be disposed between the respective layers in
case where a sufficient adhesion is not ensured between adjacent
layers. The adhesive resin may preferably comprise one or more
polyolefins, one or more modified polyolefins or a blend of the
above. Specific, not limitative, examples thereof may include:
ethylene-vinyl acetate copolymers, ethylene-(meth)acrylate
copolymers, ethylene-.alpha.-olefin copolymers, any of the above
modified with carboxylic or preferably anhydride functionalities,
elastomers, and a blend of these resins.
[0062] If the structure contains tie layers their thickness is
generally comprised between about 0.5 and about 7 .mu.m, and
preferably between about 2 and about 5 .mu.m.
[0063] Other layers may be present in the overall structure such as
bulky structural layers to increase the thickness of the overall
structure as desired, oxygen scavenging layers, additional
gas-barrier layers, etc. as known in the art.
[0064] Typically the overall thickness of the film for use in the
manufacture of the flexible containers of the present invention
will be between about 35 and about 120 .mu.m, preferably between
about 40 and about 110 .mu.m, and even more preferably between
about 45 and about 100 .mu.m.
[0065] In all the film layers, the polymer components may contain
appropriate amounts of additives normally included in such
compositions. Some of these additives are preferably included in
the outer layers or in one of the outer layers, while some others
are preferably included in the outer layers or in one of the outer
layers, while some others are preferably added to inner layers.
These additives include slip and anti-block agents such as talc,
waxes, silica, and the like, antioxidants, stabilizers,
plasticizers, fillers, pigments and dyes, cross-linking inhibitors,
cross-linking enhancers, UV absorbers, antistatic agents, anti-fog
agents or compositions, and the like additives known to those
skilled in the art of packaging films.
[0066] The films according to the present invention are
heat-shrinkable.
[0067] Preferably they show a % free shrink in each direction of at
least 10% at 95.degree. C. and more preferably a % free shrink at
95.degree. C. higher than 20 in at least one direction, and even
more preferably a % free shrink at 95.degree. C. higher than 20 in
each direction.
[0068] Preferred films are also those showing a % free shrink
higher than 10 in each direction at a temperature of 90.degree. C.
and more preferred those showing a % free shrink higher than 10 in
each direction at a temperature of 85.degree. C.
[0069] The films according to the present invention can be
manufactured by the so-called trapped-bubble process, which is a
known process typically used for the manufacture of heat-shrinkable
films for food contact packaging. According to said process, the
multilayer film is co-extruded through a round die to obtain a tube
of molten polymeric material which is quenched immediately after
extrusion without being expanded, optionally cross-linked, then
heated to a temperature which is above the Tg of all the resins
employed and below the melting temperature of at least one of the
resins employed, typically by passing it through a hot water bath,
or alternatively by passing it through an IR oven or a hot air
tunnel, and expanded, still at this temperature by internal air
pressure to get the transversal orientation and by a differential
speed of the pinch rolls which hold the thus obtained "trapped
bubble", to provide the longitudinal orientation. Typical
orientation ratios will be comprised between about 2 and about 6 in
each direction and preferably between about 3 and about 5 in each
direction. After being stretched, the film is quickly cooled while
substantially retaining its stretched dimensions to somehow freeze
the molecules of the film in their oriented state and rolled for
further processing.
[0070] Cross-linking is typically obtained by passing the flattened
tubing through an irradiation vault where it is irradiated by
high-energy electrons. Depending on the characteristics desired,
this irradiation dosage can vary from about 20 to about 200 kGy,
preferably from about 30 to about 150 kGy.
[0071] Depending on the number of layers in the structure it may be
advisable or necessary to split the co-extrusion step: a tube will
first be formed of a limited number of layers, with layer (a) on
the inside of the tube; this tube will be quenched quickly and
before submitting it to the orientation step it will be
extrusion-coated with the remaining layers, again quenched quickly,
optionally cross-linked, and then passed to the orientation. During
the extrusion-coating the tube will be slightly inflated just to
keep it in the form of a tube and avoid that it collapses. The
coating step can then be simultaneous, by coextruding all the
remaining layers altogether, so as to simultaneously adhere all of
them, one over the other, to the quenched tube obtained in the
first coextrusion step, or this coating step can be repeated as
many times as the layers which are to be added.
[0072] The extrusion-coating step is clearly also required when a
film only partially cross-linked is desired. As an example, in the
case of barrier structures comprising a PVDC layer which might be
degraded/discoloured by irradiation, it might be desiderable to
avoid cross-linking of the PVDC layer. In this case the irradiation
step will be performed after the extrusion of the first group of
layers, which would not comprise the PVDC barrier layer, and before
the extrusion-coating.
[0073] Alternatively, the film according to the present invention
may be obtained by flat extrusion (co-extrusion or extrusion
coating) and biaxial stretching by a simultaneous or a sequential
tenter process.
[0074] Still alternatively the film according to the present
invention may be obtained by heat- or glue-laminating separately
obtained webs each containing only part of the film sequence of
layers.
[0075] In a preferred embodiment the film is obtained as a seamless
tubular film and it is then converted into end sealed (ES) bags by
transversely sealing and severing across the seamless tubular film
as it lays flat. Alternatively it is converted into transverse
sealed (TS) bags by slitting the seamless tubular film along one of
its edges and then transversely seal and severe the thus obtained
center-folded film into bags, where the side seals are the sealing
and severing seams and the bottom of the bag is the unslit edge of
the film.
[0076] Other bag and pouch making methods known in the art may be
readily adapted to make receptacles from the multilayer film
according to the present invention.
[0077] The seal(s) along the bottom and/or side edges of the
flexible containers of the invention can be at the very edge itself
(e.g., seals of a type commonly referred to in this art as "trim
seals" where sealing of e.g. the bottom of one bag will generate
the open mouth of the following bag and in such a case the opening
tabs to be grasped when opening of the package is desired, will be
created in the bag portion which extends beyond the seal closing
the open mouth of the package. This embodiment is illustrated in
FIG. 1, where 1 is the product packaged in the bag 2, 3 indicates
the trim end seal, 4 is one of the seamless (folded) side edges of
the ES bag, 5 is the seal closing the mouth of the bag, 6 is the
skirt extending beyond seal 5 and 7a and 7b are the shaped portions
of the unsealed front and rear panels of the bag which extend
beyond the seal 5. By grasping said two tabs 7a and 7b and pulling
them in laterally opposite directions, it will then be possible to
easily initiate opening of the bag.
[0078] However, in general, the factory seals are made using an
impulse-type heat-sealing apparatus which utilizes a heat-sealing
bar which is quickly heated and then quickly cooled. The
heat-sealing bar may be straight or possibly shaped, e.g.,
typically with a curved shape, and is associated with cutting
means, generally parallel to the sealing bar and at a short
distance thereof. The heat-sealing means and the cutting means will
operate simultaneously and while the heat-sealing means will seal
the bottom of one bag, the associated cutting means will create the
open mouth in the following one. This will generate bags where the
seals are spaced inwardly (roughly 0.5-1.5 cm) from the container
side and/or bottom edges with a so-called "skirt" of the unsealed
front and rear panels extending beyond the seal and having a
dimension corresponding to the distance between the sealing means
and the cutting means. When a flexible container according to a
preferred embodiment of the present invention is desired, where
suitably shaped opening tabs of unsealed material extend beyond one
of the factory seals, it will thus be sufficient to modify the
profile of the cutting means accordingly, while maintaining the
shape of the heat-sealing bar unchanged.
[0079] In both cases, in order to get the best results in terms of
easy openability of the package, the width of the seal, be it a
factory seal or the seal made in the packaging process to close the
mouth of the package, will be less than about 4 mm, more preferably
less than about 3.5 mm, and typically comprised between about 1 and
about 3 mm, e.g., 1 to 2 mm.
[0080] With reference to the Figures, FIG. 2 is a top view of an ES
bag according to a preferred embodiment of the present invention.
In said FIG. 10 is the bottom factory seal of the bag, 11 and 12
are the side folded edges, 13 is the open mouth of the bag, 14 is
the skirt beyond the bottom factory seal 10 and 15 is that part of
the skirt 14 where the unsealed rear and front panels (15a and 15b)
are suitably shaped to be separately graspable and thus usable as
opening tabs.
[0081] FIG. 3 is a perspective view of a lay-flat tubing from which
the bag of FIG. 2 is made. In said FIG. 3, 20 is the seamless
tubing in a lay-flat configuration, 21 and 22 are the side folded
edges of the tubing, 23 is the end seal of the first bag formed 24,
25 is the skirt of the same bag 24 which extends beyond the factory
seal, 26 are the opening tabs of bag 24, i.e. the area in said
skirt 25 where the two unsealed rear and front panels will be
separately grasped by the user and pulled apart to open the bag 24,
27 is the mouth of the next bag 28, having the complementary shape,
29 is the end seal of bag 28, is the skirt of said bag 28, and 31
are the opening tabs of bag 28.
[0082] FIG. 4 represents a perspective view of a package obtained
from a bag according to FIG. 2, where the package is shrunk
following vacuumization and heat-sealing of the bag mouth. In said
FIG. 4, 40 is the product packaged, 41 is the bag, 42 is the bottom
factory seal, 43 is the skirt extending beyond the bottom factory
seal, 44a and 44b are the two opening tabs in the rear and front
panels of the shrunk bag that will be pulled in laterally opposite
directions to initiate and propagate opening of the bag, 45 is one
of the two folded side edges and 46 is the top seal to close the
bag.
[0083] FIG. 5 is a top view of a series of TS serrated bags, where
50 is a first TS bag, 51 is the bottom folded edge, 52 is the open
mouth of bag 50, 53 and 54 are the side seals of bag 50, 55 are the
tabs cut into the side skirt 56 extending beyond the factory side
seal 53, 57 is the serration between said bag 50 and the next one
58, 59 is one side seal of bag 58, the other being indicated with
numeral 60, 61 is the folded bottom edge of bag 58, and 62 is the
open mouth, 63 is the tab cut into the side skirt 64 extending
beyond the factory side seal 60, and 65 is the serration between
said bag 58 and the next one, not illustrated in said Figure.
[0084] FIGS. 6a to 6c are top views of details of ES bags according
to a preferred embodiment of the invention wherein alternative
shapes of the profile of the opening tabs are illustrated. In these
FIGS. 70a, 70b, and 70c indicate the bottom factory seal of the ES
bag, 71a, 71b, and 71c are the skirt extending beyond the
respective factory seals and 72a, 72b, and 72c are alternative
shapes for the opening tabs in the superposed panels.
[0085] As illustrated in these figures, preferably the opening tabs
have a limited dimension as this will allow to concentrate the
force of the user to initiate breaking of the seal and therefore
opening of the bag, in a direction perpendicular to the direction
in which the tabs are pulled. Preferably the opening tabs will have
a size suitable to be grasped by the hands of the user and will
extend beyond the factory seal only along a small portion of the
factory seal length, typically not exceeding 50%, preferably not
exceeding 30% and more preferably not exceeding 20% of the length
of the factory seal. With reference to the FIGS. 6a, 6b, and 6c,
73a, 73b, and 73c, indicate the length of the factory seal along
which the opening tabs respectively extend. In all those cases the
opening tabs are of a size suitable to allow grasping by the hands
of the user, while the length of the factory seal along which they
extend, as well their positioning, may vary to a great extent.
[0086] When the package has to be opened, the end user will keep
the package by the opening tabs and pull them in laterally opposite
directions. The seal adjacent to the tab will then be opened by
breaking the heat-sealing layer (a), through the cohesive failure
layer (c) in the sealing area, and again breaking the heat-sealing
layer (a) below the sealing area but leaving the other layers
unaffected. Thus there will be no breakage of the bag but only its
opening and no encapsulation. In packaging, the product will be
loaded into a heat-shrinkable bag made of the film of the
invention, the bag will normally be evacuated, and the open end
thereof will be closed by heat-sealing, optionally creating opening
tabs in the skirt extending beyond the seal closing the open mouth,
if opening tabs extending beyond any of the factory seals are not
already present in the pre-formed bag. Following vacuumization and
heat-sealing the packaging material will be heat shrunk by applying
heat. This can be done, for instance, by immersing the filled bag
into a hot water bath or conveying it through a hot water shower or
a hot air tunnel, or by infrared radiation. The heat treatment will
produce a tight wrapping that will closely conform to the contour
of the product therein.
[0087] An easy-openable, hermetically sealable, bag according to
the present invention has wide applications, particularly for food
packaging applications, e.g., for the packaging of meat, such as
beef and poultry, processed meat, such as ham, mortadella, wurstel,
and dairy products, particularly hard cheeses. The bag will have
heat-sealing properties that will allow it to survive the process
of being filled, evacuated, sealed, closed, heat shrunk, boxed,
shipped, unloaded, and stored at the retail supermarket, without
loosing the hermeticity, while it will also have an easy opening
feature that will allow opening of the package by hand, i.e.,
without using scissors, knives, or other cutting and dangerous
devices, when this is desired.
[0088] The invention can be further understood by reference to the
following examples that are merely illustrative and are not to be
interpreted as a limitation to the scope of the present invention
that is defined by the appended claims.
EXAMPLE
[0089] A six layer structure has been prepared by coextrusion of a
substrate consisting of a first (sealing) outer layer (a), an
adjacent cohesive failure layer (c), and a bulk layer (f), followed
by quenching of the extruded three layer tubular film, irradiation
at 64 kGy and extrusion coating thereof with a barrier layer (e),
an adhesive layer (d) and the outer layer (c). The end extruded
tube is then rapidly cooled and biaxially oriented by passing it
through a hot water bath (about 95-98.degree. C.), then inflating
to get transverse orientation and stretching to get longitudinal
orientation. The orientation ratios were about 3.5.times.3.5.
[0090] The resins used for the different layers and the partial
thicknesses of each layer are reported in the Table below.
TABLE-US-00001 Thickness layer Resin or resin composition (.mu.m)
(a) 80% of metallocene ethylene-.alpha.-olefin copolymer 13 with d
= 0.902 g/cm.sup.3 and MI = 6 g/10 min (Affinity .TM.PL1280G) and
20% of heterogeneous ethylene-.alpha.-olefin copolymer with d =
0.911 g/cm.sup.3 and MI = 6 g/10 min (Stamylex .TM. 08-076F by DSM)
(c) 58% of ionomer (Na methacrylate) with d = 0.94 7 g/cm.sup.3 and
MI = 1.3 g/10 min (Surlyn .RTM. 1601 by DuPont) 22% of
Ethylene-vinyl acetate/carbon monoxide copolymer (24% Vinyl
Acetate) with d = 1 g/cm.sup.3 and MI = 35 g/10 min (Elvalloy .TM.
741A) and 20% of polybutylene with d = 0.908 g/cm.sup.3 and MI = 1
g/10 min (Polybutene-1 PB8640M by Basell) (f) 50% of heterogeneous
ethylene-.alpha.-olefin copolymer 24 with d = 0.920 g/cm.sup.3 and
MI = 1 g/10 min (Dowlex .TM. 2045E by Dow) and 50% of
ethylene-vinyl acetate copolymer (13 wt. % VA) MI = 0.4 g/10 min
(Evatane .TM. 1003 VN 4 by Elf-Atochem) (e) PVDC containing 2 wt. %
of plasticisers and 1 wt. % 5 of stabilizers (d) 80% of maleic
anhydride-modified linear low 6 density polyethylene d = 0.913
g/cm.sup.3 and MI = 1.7 g/10 min and 20% of ethylene-vinyl acetate
modified with ethylene acrylic acid copolymer (Bynel .TM. 3101 by
Du Pont) (b) co-polyamide nylon 6/66 (85/15) (Ultramid .RTM. C35 by
3 BASF) Melt Flow Indexes (MFI's) are measured by ASTM D-1238,
Condition E, 190.degree. C./2.16 kg and are reported in grams/10
minutes. Unless otherwise specifically indicated, all percentages
are by weight.
[0091] The % free shrink at 90.degree. C. was measured according to
ASTM D 2732 by immersing for 5 seconds specimens of the structure
(10 cm.times.10 cm) into a hot water bath set at 90.degree. C. and
then calculating the % free shrink in each direction by the
equation
% free shrink=(L.sub.0-L.sub.f)/L.sub.0.times.100
wherein (L.sub.0 is the initial length of side and L.sub.f is the
length of side after shrinking).
[0092] The film of Example 1 showed a % free shrink (LD/TD) at
90.degree. C. of 30/40.
[0093] The tubing of oriented material was flattened and converted
into ES bags 350 mm.times.500 mm, by means of an impulse sealer set
at the following conditions: 160 cycle/min at 16 mA of impulse. The
cut profile was modified to give bags with the opening tabs as
indicated in FIG. 2, the dimensions of said tabs were 80 mm in
length and 60 mm in maximum width.
[0094] The seal strength of these bags has been measured by means
of the Parallel Plate Burst Test. In this test each bag was
confined between two metal plates based about 10 cm apart within a
chamber and inflated until its seal fails. In particular each bag
was clamped in a fixture provided with a hose and the open mouth of
the bag was clamped around the hose. Air was pumped through the
hose whereby the bag was inflated. The two metal plates restrained
the two sides of each bag respectively. For each bag the pressure
was increased via the hose at the rate of 1 inch of water pressure
per second until the seal for that bag burst open.
[0095] The seal strength of these bags has also been measured by
the Variable Pressure Hot Burst Test that is a test to determine
the seal quality of shrinkable materials at different temperatures.
The approach with this test is to immerse total sealed areas into
hot water and after a predetermined dwell time, increase the
pressure inside the bag at a constant rate of approximately 25.4 mm
of water per second until the seal fails. The millimeters of water
pressure, at the level at which the seal fails, are recorded.
Minimum specifications are expressed in mm for each bag width.
[0096] The results obtained with the bags tested in the Parallel
Plate Burst Test and in the Variable Pressure Hot Burst Test were
respectively 170 IOWP and 100 mbar, values both perfectly in line
with the product specification.
[0097] The easy-openability of these bags was then tested by
loading them with a product (2 kg), vacuumizing in a Cryovac.RTM.
VC 12 vacuum chamber, heat-sealing the open mouth and finally
shrinking in hot (95.degree. C.) water. The shrunk packages were
allowed to cool, dried, and then easily opened by hands by pulling
the opening tabs in the two laterally opposite directions.
* * * * *