Note: Descriptions are shown in the official language in which they were submitted.
CA 02280910 1999-08-10
POUCHES FOR PACKAGING FLOWABLE MATERIALS
This invention relates to a pouch used in consumer
packaging made from certain film structures useful for packag-
ing flowable materials, for example liquids such as milk.
U. S. Patent Nos. 4,503,102, 4,521,437 and 5,288,531
disclose the preparation of polyethylene film for use in the
manufacture of a disposable pouch for packaging of liquids
such as milk. U. S. Patent No. 4,503,102 discloses pouches
made from a blend of a linear ethylene copolymer copolymerized
from ethylene and an alpha-olefin at the C4 to C10 range and
an ethylene-vinyl acetate polymer copolymerized from ethylene
and vinyl acetate. The linear polyethylene copolymer has a
density of from 0.916 to 0.930 g/cm3 and a melt index of from
0.3 to 2.0 g/10 minutes. The ethylene-vinyl acetate polymer
has a weight ratio of ethylene to vinyl acetate from 2.2:1 to
24:1 and a melt index of from 0.2 to 10 g/10 minutes. The
blend disclosed in U. S. Patent No. 4,503,102 has a weight
ratio of linear low density polyethylene to ethylene-vinyl
acetate polymer of from 1.2:1 to 4:1. U. S. Patent No.
4,503,102 also discloses laminates having as a sealantfilm
the aforementioned blend.
U. S. Patent No. 4,521,437 describes pouches made
from a sealant film which is from 50 to 100 parts of a linear
copolymer of ethylene and octene-1 having a density of from
0.916 to 0.930 g/cm3 and a melt index of 0.3 to 2.0 g/10
minutes and from 0 to 50 parts by weight of at least one
polymer selected from the group consisting of a linear
copolymer of ethylene and a C4-C10-alpha-olefin having a
density of from 0.916 to 0.930 g/cm3 and a melt index of from
0.3 to 2.0 g/10 minutes, a high-pressure polyethylene having
a density of from 0.916 to 0.924 g/cm3 and a melt index of
from 1 to 10 g/10 minutes and blends thereof. The sealant
film disclosed in the U. S. Patent No. 4,521,437 was selected
on the basis of providing (a) pouches with a M-test value
substantially smaller, at the same film thickness, than that
obtained for pouches made with film of a blend of 85 parts
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of a linear ethylene/butene-1 copolymer having a density of
0.919 g/cm3 and a melt index of 0.75 g/10 minutes and 15 parts
of a high pressure polyethylene having a density of 0.918
g/cm3 and a melt index of 8.5 g/10 minutes, or (b) an M(2)-
test value of less than 12~, for pouches having a volume of
from greater than 1.3 to 5 liters, or (c) an M(1.3)-test value
of less than 5~ for pouches having a volume of from 0.1 to 1.3
liters. The M, M(2) and M(1.3)-tests are defined pouch drop
tests in U. S. Patent No. 4,521,437. The pouches may also be
made from composite films in which the sealant film forms at
least the inner layer. But the high-pressure polyethylene
described in U. S. Patent No. 4,521,437 is not described as
having a high melt strength and all of the high-pressure poly-
ethylene resins employed in the examples have a melt index
greater than 1 g/10 minutes. Furthermore, there is teaching
in U. S. Patent No. 4,521,437 that for ethylene polymer blends
melt strength does not correlate with hot tack strength or
leaker performance.
U. S. Patent No. 5,288,531 discloses pouches made
from a film structure having a blend of (a) from 10 to 100
percent by weight of at least one polymeric seal layer of an
ultra low density linear ethylene copolymer interpolymerized
from ethylene and at least one alpha-olefin in the range of
C3-C10 with a density of from 0.89 g/cm3 to less than 0.915
g/cm3 and (b)
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WO 98/34844 PCT/US97/01671
from 0 to 90 percent by weight of at least one polymer selected from the group
consisting of a
linear copolymer of ethylene and a C3-C~e-alpha-olefin having a density of
greater than 0.916
g/cm3 and a melt index of from 0.1 to 10 g/10 minutes, a high-pressure low
density
polyethylene having a density of from 0.916 to 0.930 g/cm3 and a melt index of
from 0.1 to 10
g/10 minutes, or ethylene-vinyl acetate copolymer having a weight ratio of
ethylene to vinyl
acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10 g/10 minutes.
The heat seal layer in
the U.S. Patent No. 5,288,531 provides improved hot tack strength and lower
heat seal initiation
temperature to a two-layer or three-layer coextruded multilayer film structure
described therein.
The polyethylene pouches known in the prior art have some deficiencies. The
1o problems associated with films known in the prior art relate to the sealing
properties and
performance properties of the film for preparing pouches, In particular, prior
art films made
into pouches in general have a high incident of "leakers", i.e., seal defects
such as pinholes
which develop at or near the seal in which flowable material, for example milk
escapes from the
pouch. Although the seal and pertormance properties of the prior art films
have been generally
satisfactory, there is still a need in the industry for better seal and
performance properties in
films for manufacture of hermetically seated pouches containing flowable
materials. More
particularly, there is a need for improved sealing properties of the film such
as hot tack and
melt strength in order to improve the processability of the film and to
improve pouches made
from the films.
2o For example, the line speed of known packaging equipment used for
manufacturing pouches such as form, fill and seal machines, is currently
limited by the sealing
properties of the film used in the machines. Prior art polyethylene films have
low melt
strength. Therefore, the speed at which a form, fill and seal machine can
produce a pouch is
limited and, thus, the number of pouches produced on a form, fill and seal
machine is limited.
If the melt strength is increased, then the speed of a form, fill and seal
machine can be
increased and, thus, the number of pouches produced can be increased. Until
the present
invention, many have attempted to improve sealing properties of the polymeric
composition
used in pouch film without success.
It is desired to provide a polyethylene film structure for a pouch container
3 o having improved melt strength with performance properties as good or
better than the known
prior art pouch films.
It is also desired to provide a film structure for a pouch container which can
be
processed through a form fill and seal machine as a monofayer film.
It is further desired to provide a pouch made from the aforementioned film
structures such that the pouch has a reduced failure rate.
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The present invention provides a pouch containing a flowable material, said
pouch being made from a film structure with at least one seal layer of a
polymeric composition.
comprising: (a) from 10 to 100 percent, based on the total weight of said
composition, of a
mixture of (1) from 5 to 95 percent by weight, based on 100 weight parts of
said mixture, of
, linear ethylene copolymer interpolymerized from ethylene and at least one
alpha-olefin in the
range of C3-C18 and having a density from 0.916 to 0.940g/cm3 and a melt index
of less than
10gh0 minutes, and a molecular weight distribution, MwlMn, ratio of greater
than 4.0, and a
peak melting point greater than 100°C as measured by a differential
scanning colorimeter, and
(2) from 5 to 95 percent by weight, based on 100 weight parts of said mixture,
of high pressure
io low density polyethylene having a density from 0.916 to 0.930g1cm3, a melt
index of less than
ig/10 minutes and melt strength greaser Than 10 cN as determined using a
Gottfert Rheotens
unit at 190°C; and (b) from 0 to 90 percent, based on the total weight
of said composition, of at
least one copolymer selected from the group consisting of an ethylene-vinyl
acetate copolymer
having a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a
melt index of from 02
to 108110 minutes.
One embodiment of the present invention is a pouch made from. a two-layer
coextruded film containing an outer layer of linear low density polyethylene
and an inner seal
layer of the aforementioned polymeric composition.
Another embodiment of the present invention is a pouch made from a three-
2o layer coextruded film containing an outer layer and a core layer of linear
low density
polyethylene and an inner seal layer of the aforementioned polymeric
composition.
Another aspect of the present invention is a process for preparing the
aforementioned pouch.
Yet another embodiment of the present invention is a pouch made from a three-
2s layer coextruded film containing an outer layer and a core layer of high
pressure low density
polyethylene and an inner seal layer of the aforementioned polymeric
composition.
It has been discovered that the film structures for the pouches of.the present
invention have an improved melt strength and heat seal strength, particularly
the end-seal
strength. Use of the films for making pouches of the present invention in
form, fill and seal
so machines leads to machine speeds higher than currently obtainable with the
use of
commercially available film.
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Also according to the present invention, there is
provided a pouch containing a flowable material, said pouch
being made from a multilayer film structure comprising: a
first layer of polymeric composition comprising: (a) from 10
to 100 percent, based on the total weight of said
composition, of a mixture of (1) from 5 to 95 percent by
weight, based on 100 weight parts of said mixture, of linear
ethylene copolymer interpolymerized from ethylene and at
least one alpha-olefin in the range of C3-C18 and having a
density from 0.916 to 0.940g/cm3 and a melt index of less
than 10g/10 minutes, and a molecular weight distribution,
Mw/Mn, ratio of greater than 4.0, and a peak melting point
greater than 100°C as measured by a differential scanning
colorimeter, and (2) from 5 to 95 percent by weight, based
on 100 weight parts of said mixture, of high pressure low
density polyethylene having a density from 0.916
to 0.930g/cm3, a melt index of less than 1g/10 minutes and
melt strength greater than 10 cN as determined using a
Gottfert Rheotens unit at 190°C; and b) from 0 to 90
percent, based on the total weight of said composition, of
an ethylene-vinyl acetate copolymer having a weight ratio of
ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt
index of from 0.2 to 10g/10 minutes; and at least one second
layer of linear ethylene copolymer interpolymerized from
ethylene and at least one alpha-olefin in the range of C3-C1a
and having a density from 0.916 to 0.940g/cm3 and a melt
index of from 0.1 to 10g/10 minutes.
According to the present invention, there is
further provided a film structure of a polymeric composition
for a packaging application comprising: (a) from 10 to 100
percent, based on the total weight of said composition, of a
mixture of (1) from 5 to 95 percent by weight, based on 100
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weight parts of said mixture, of linear ethylene copolymer
interpolymerized from ethylene and at least one alpha-olefin
in the range of C3-Cla and having a density from 0.916 to
0.940g/cm3 and a melt index of less than 10g/10 minutes, and
a molecular weight distribution, Mw/Mn, ratio of greater
than 4.0, and a peak melting point greater than 100°C as
measured by a differential scanning colorimeter, and (2)
from 5 to 95 percent by weight, based on 100 weight parts of
said mixture, of high pressure low density polyethylene
having a density from 0.916 to 0.930g/cm3, a melt index of
less than 1g/10 minutes and melt strength greater than 10 cN
as determined using a Gottfert Rheotens unit at 190°C; and
(b) from 0 to 90 percent, based on the total weight of said
composition, of an ethylene-vinyl acetate copolymer having a
weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1
and a melt index of from 0.2 to 10g/10 minutes.
According to the present invention, there is
further provided a process for preparing a pouch containing
a flowable material comprising forming a film structure by
either blown tube extrusion or cast extrusion, forming the
film structure into a tubular member and transversely heat-
sealing opposite ends of the tubular member, said tubular
member comprising a film structure for a pouch container
with at least one seal layer of a polymeric composition
comprising: (a) from 10 to 100 percent, based on the total
weight of said composition, of a mixture of (1) from 5 to 95
percent by weight, based on 100 weight parts of said
mixture, of linear ethylene copolymer interpolymerized from
ethylene and at least one alpha-olefin in the range of C3-Cla
and having a density from 0.916 to 0.940g/cm3 and a melt
index of less than 10g/10 minutes, and a molecular weight
distribution, Mw/Mn, ratio of greater than 4.0, and a peak
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melting point greater than 100°C as measured by a
differential scanning colorimeter, and (2) from 5 to 95
percent by weight, based on 100 weight parts of said
mixture, of high pressure low density polyethylene having a
density from 0.916 to 0.930g/cm3, a melt index of less than
1g/10 minutes and melt strength greater than 10 cN as
determined using a Gottfert Rheotens unit at 190°C; and (b)
from 0 to 90 percent, based on the total weight of said
composition, of at least one copolymer selected from the
group consisting of an ethylene-vinyl acetate copolymer
having a weight ratio of ethylene to vinyl acetate
from 2.2:1 to 24:1 and a melt index of from 0.2 to 10g/10
minutes.
According to the present invention, there is
further provided a process for preparing a pouch containing
a flowable material comprising forming a film structure by
either blown tube extrusion or cast extrusion, forming the
film structure into a tubular member and transversely heat-
sealing opposite ends of the tubular member, said tubular
member comprising: a first layer of polymeric composition
comprising: (a) from 10 to 100 percent, based on the total
weight of said composition, of a mixture of (1) from 5 to 95
percent by weight, based on 100 weight parts of said
mixture, of linear ethylene copolymer interpolymerized from
ethylene and at least one alpha-olefin in the range of C3-C18
and having a density from 0.916 to 0.940g/cm3 and a melt
index of less than 10g/10 minutes, and a molecular weight
distribution, Mw/Mn, ratio of grater than 4.0, and a peak
melting point greater than 100°C as measured by a
differential scanning colorimeter, and (2) from 5 to 95
percent by weight, based on 100 weight parts of said
mixture, of high pressure low density polyethylene having a
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density from 0.916 to 0.930g/cm3, a melt index of less than
1g/10 minutes and melt strength greater than 10 cN as
determined using a Gottfert Rheotens unit at 190°C; and (b)
from 0 to 90 percent, based on the total weight of said
composition, of at least one copolymer selected from the
group consisting of an ethylene-vinyl acetate copolymer
having a weight ratio of ethylene to vinyl acetate
from 2.2:1 to 24:1 and a melt index of from 0.2 to 10g/10
minutes; at least one second layer of linear ethylene
copolymer interpolymerized from ethylene and at least one
alpha-olefin in the range of C3-Cls and having a density
from 0.916 to 0.0940g/cm3 and a melt index of from 0.1
to 10g/10 minutes.
Brief Description of the Drawings
Fig. 1 shows a perspective view of a pouch package
of an embodiment of the present invention.
Fig. 2 shows a perspective view of another pouch
package of an embodiment of the present invention.
Fig. 3 shows a partial, enlarged cross-sectional
view of the film structure of a pouch of an embodiment of
the present invention.
Fig. 4 shows another partial, enlarged cross-
sectional view of the film structure of a pouch of an
embodiment of the present invention.
Fig. 5 shows yet another partial, enlarged cross-
sectional view of the film structure of a pouch of an
embodiment of the present invention.
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Fig. 6 is a graphical illustration of end seal
strength versus melt strength.
The pouch of an embodiment of the present
invention, for example as shown in Figure 1 and 2, for
packaging flowable materials is manufactured from a
monolayer film structure of a polymeric seal layer which is
a blend of a linear low density polyethylene and a high
pressure low density polyethylene having a high melt
strength. The blend can also contain an ethylene
vinylacetate copolymer.
"Melt strength" which is also referred to in the
relevant art as "melt tension" is defined and quantified
herein to mean the stress or force (as applied by a wind-up
drum equipped with a strain cell) required to draw a molten
extrudate at some specified rate above its melting point as
it passes through the die of a standard plastometer such as
the one described in ASTM D1238-E. Melt strength values,
which are reported herein in centi-Newtons (cN), are
determined using a Gottfert Rheotens at 190°C. In general,
for ethylene cx-olefin interpolymers and high pressure
ethylene polymers, melt strength tends to increase with
increased molecular weight, or with broadening of the
molecular weight distribution and/or with increased melt
flow ratios. The melt strength of the high pressure low
density polyethylene of the present invention is greater
than 10 cN as determined using a Gottfert Rheotens unit at
190°C, preferably from 13 to 40 cN, and most preferably 15
to 25 cN. Further, the melt strength of the polymeric
composition of the present invention is greater than 10 cN
as determined using Gottfert Rheotens unit at 190°C,
preferably from 15 to 70 cN, and most preferably 15 to 50.
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One component of the polymer composition of an
embodiment of the present invention is a polyethylene
referred to hereinafter as "linear low density polyethylene"
("LLDPE"). An example of a commercially available LLDPE is
DOWLEX'"" 2045 (Trademark of and commercially available from
The Dow Chemical Company). The LLDPE is generally a linear
copolymer of ethylene and a minor amount of an a-olefin
having from 3 to 18 carbon atoms, preferably from 4 to 10
carbon atoms and most preferably 8 carbon atoms. The LLDPE
for the polymeric composition of the present invention has a
density of greater than 0.916 g/cm3, more preferably
from 0.916 to 0.940 g/cm3, most preferably from 0.918
to 0.926 g/cm3; generally has a melt index of less
than 10g/10 minutes, preferably from 0.1 to 10g/10 minutes,
most
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preferably from 0.5 to 2gh0 minutes and generally has an (,ollz ratio of from
0.1 to 20,
preferably from 5 to 20, and most preferably 7 to 20.
The LLDPE can be prepared by the continuous, batch or semi-batch solution,
slurry or gas phase polymerization of ethylene and one or more optional a-
olefin comonomers
- in the presence of a Ziegler Natta catalyst, such as by the process
disclosed in U.S. Patent No.
4,076,698 to Anderson et al .
Suitable a-olefin for the LLDPE of the present invention are represented by
the
following formula:
CHZ = CHR
1o where R is a hydrocarbyi radical having from one to twenty carbon atoms.
The
interpolymerization process can be a solution, slurry or gas phase technique
or combinations
thereof. Suitable a-olefin for use as comonomers include 1-propylene, 1-
butane,
1-isobutylene, 1-pentane, 1-hexane, 4-methyl-1-pentane, 1-heptene and 1-
octane, as well as
other monomer types such as styrene, halo- or alkyl-substituted styrenes,
tetrafluoro-ethylene,
vinyl benzocyclobutane, 1,4-hexadiene, 1,7-actadiene, and cycloalkenes, e.g.,
cyclopentene,
cyclohexene and cyclooctene. Preferably, the a-olefin will be 1-butane, 1-
pentane,
4-methyl-1-pentane, 1-hexane, 1-heptene, 1-octane, or mixtures thereof. More
preferably, the a-
olefin will be 1-hexane, 1-heptene, 1-octane, or mixtures thereof, as
coatings, profiles and films
fabricated with the resultant extrusion composition will have especially
improved abuse
properties where such higher a-olefins are utilized as comonomers. However,
most
preferably, the a-olefin will be 1-octane and the polymerization process will
be a continuous
solution process.
The molecular weight distribution of the ethylene a-olefin interpolymer
compositions and the high pressure ethylene polymer compositions are
determined by gel
permeation chromatography (GPC) on a Waters 150 high temperature
chromatographic unit
equipped with differential refractometer and three columns of mixed porosity.
The columns are
supplied by Polymer Laboratories and are commonly packed with pore sizes of
103, ,10°,105
and 106. The solvent is 1,2,4-trichiorobenzene, from which 0.3 percent by
weight solutions of
the samples are prepared for injection. The flow rate is 1.0
milliliters/minute, unit operating
temperature is 140°C and the injection size is 100 microiiters.
The molecular weight determination with respect to the polymer backbone is
deduced by using narrow molecular weight distribution polystyrene standard
(from Polymer
Laboratories) in conjunction with their elution volumes. The equivalent
polyethylene molecular
weights are determined by using appropriate Mark-Houwink coefficients for
polyethylene and
polystyrene (as described by Williams and Ward in Journal of Polymer Science,
Polymer
Letters, Vol. 6, p. 621, 1968) to derive the following equation:
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WO 98/34844 PCT/iJS97/01671
"'polyethylene -_ a * (""polystyrene)b.
In this equation, a = 0.4316 and b = 1Ø Weight average molecular weight, Mw,
is
calculated in the usual manner according to the following formula: M", -__ ~
w, x M,, where w,
and M, are the weight fraction and molecular weight, respectively, of the i'"
fraction eluting from
- the GPC column.
For LLDPE, the Mw/Mn is preferably 2 to 7, especially 4.
It is believed that the use of LDPE having high melt strength in a film
structure
for pouches of the present invention (1 ) provided a pouch that can be
fabricated at a fast rate
through a form, fill and seal machine, and (2) provides a pouch package having
few leakers,
1o particularly when the pouch of the present invention is compared to pouches
made with linear
low density polyethylene, low density polyethylene or a combination thereof.
With reference to Figures 3 to 5, the film structure of the pouch of the
present
invention also includes a multilayer or composite film structure 30,
preferably containing the
above-described polymer seal layer being the inner layer of the pouch.
As will be understood by those skilled in the art, the multilayer film
structure for
the pouch of the present invention may contain various combination of film
layers as long as
the seal layer forms part of the ultimate film structure. The multilayer film
structure for the
pouch of the present invention may be a coextruded film, a coated film or a
laminated film. The
film structure also included the seal layer in combination with a barrier film
such as polyester,
2 o nylon, EVOH, polyvinylidene dichloride (PVDC) such as SARANTM (Trademark
of The Dow
Chemical Company) and metallized films. The end use for the pouch tends to
dictate, in a large
degree, the selection of the other material or materials used in combination
with the seal layer
film. The pouches described herein will refer to seal layers used at least on
the inside of the
pouch.
One embodiment of the film structure 30 for the pouch of the present
invention,
shown in Figure 3, comprises seal layer 31 of a blend of LLDPE and high melt
strength LDPE of
this invention and at least one polymeric outer layer 32. The polymeric outer
layer 32 is
preferably a polyethylene film layer, more preferably a LLDPE. An example of a
commercially
available LLDPE is DOWLEXTM 2045 (Trademark of the commercially available from
The Dow
3 o Chemical Company). The thickness of the outer layer 32 may be any
thickness so long as the
seal layer 31 has a minimum thickness of 0.1 mil (2.5 microns).
Another embodiment of the film structure 30 for the pouch of the present
invention, shown in Figure 4, comprises the polymeric layer 32 sandwiched
between two
polymeric seal layers 31.
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Still another embodiment of the film structure 30 for the pouch of the present
invention, shown in Figure 5, comprises at least one polymeric core layer 33
between at least
one polymeric outer layer 32 and at least one polymeric seal layer 31. The
polymeric layer 33
may be the same LLDPE film layer as the outer layer 32 or preferably a
different LLDPE, and
more preferably an LLDPE, for example DOWLEX's'M 204S (Trademark of and
commercially
available from The Dow Chemical Company) that has a higher density than the
outer layer 32.
The thickness of the core layer 33 may be any thickness so long as the seal
layer 31 has a
minimum thickness of 0.1 mil (2.5 microns).
The ultimate film thickness of the final film product used for making the
pouch
lo of the present invention is from 0.5 mil (12.7 microns) to 10 mils (254
microns), preferably from
1 mil (25.4 microns) to 5 mils (127 microns); more preferably from 2 mils
(50.8 microns) to 4
mils (100 microns).
Additives, known to those skilled in the art, such as anti-block agents, slip
additives, UV stabilizers, pigments and processing aids may be added to the
polymers from
15 which the pouches of the present invention are made.
As can be seen from the different embodiments of the present invention shown
in Figure 3-5, the film structure for the pouches of the present invention has
design flexibility.
Different LLDPE can be used in the outer and core layers to optimize specific
film properties
such as film stiffness. Thus, the film can be optimized for specific
applications such as for a
2o vertical form, film and seal machine.
The polyethylene film structure used to make a pouch of the present invention
is made by either the blown tube extrusion method or the cast extrusion
method, methods well
known in the art. The blown tube extrusion method is described, for example,
in Modern
Plastics Mid-October 1989 Encyclopedia Issue, Volume 66, Number 11, pages 264
to 266. The
25 cast extrusion method is described, for example, in Modern Plastics Mid-
October 1989
Encyclopedia Issue, Volume 66, Number 11, pages 256 to 257.
Embodiments of the pouches of the present invention, shown in Figure 1 and 2
are hermetically sealed containers filled with "flowable materials". By
"flowable materials" it is
meant, materials which are flowable under gravity or which may be pumped. The
term
30 "flowable materials" does not include gaseous materials. The ffowable
materials include
liquids for example milk, water, fruit juice, oil; emulsions for example ice
cream mix, soft
margarine; pastes for example meat pates, peanut butter; preservers for
example jams, pie
fillings marmalade; jellies; doughs; ground meat for example sausage meat;
powders for
example gelatin powders, detergents; granular solids for example nuts, sugar;
and like
35 materials. The pouch of the present invention is particularly useful for
liquid foods for example
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milk. The flowable material may also include oleaginous liquids for example
cooking oil or
motor oil.
Once the film structure for the pouch of the present invention is made, the
film
structure is cut to the desired width for use in conventional pouch-forming
machines. The
~ embodiments of the pouch of the present invention shown in Figures 1 and 2
are made in so-
called form, fill and seal machines well known in the art. With regard to
Figure 1, there is
shown a pouch 10 being a tubular member 11 having a longitudinal lap seal 12
and transverse
seals 13 such that, a "pillow-shaped" pouch is formed when the pouch is filled
with flowable
material.
1o With regard to Figure 2, there is shown a pouch 20 being a tubular member
21
having a peripheral fin seal 22 along three sides of the tubular member 21,
for example, the top
seal 22a and the longitudinal side seals 22b and 22c. and having a-bottom
substantially
concave or "bowl-shaped" member 23 sealed to the bottom portion of the tubular
member 21
such that when viewed in cross-section, longitudinally, substantially a semi-
circular or "bowed-
shaped" bottom portion is formed when the pouch is filled with flowable
material. The pouch
shown in Figure 2 is an example of so-called "Enviro-Pak" pouch known in the
art.
The pouch manufactured according to the present invention is preferably the
pouch shown in Figure 1 made on so-called vertical form, fill and seal (VFFS)
machines well
known in the art. Examples of commercially available VFFS machines include
those
2o manufactured by Hayssen, Thimonnier, Tetra Pak, or Prepac. A VFFS machine
is described in
the following reference: F. C. Lewis, "Form-Fill-Seal," Packaging
Encyclopedia, page 180, 1980.
In a VFFS packaging process, a sheet of the plastic film structure described
herein is red into a VFFS machine where the sheet is formed into a continuous
tube in a. tube-
forming section. The tubular member is formed by sealing the longitudinal
edges of the film
z s together -- either by lapping the plastic film and sealing the film using
an inside/outside seal or
by fin sealing the plastic film using an insidelinside seal. Next, a sealing
bar seals the tube
transversely at one end being the botlom of the "pouch", and then the fill
material, for example
milk, is added to the "pouch.° The sealing bar then seals the top end
of the pouch and either
burns through the plastic film or cuts the film, thus, separating the formed
completed pouch
3o from the tube. The process of making a pouch with a VFFS machine is
generally described in
U.S. Patent Nos. 4,503,102 and 4,521,437 .
The capacity of the pouches of the present invention may vary. Generally, the
pouches may contain from 5 milliliters to 10 liters, preferably from 1
milliliter to 8 liters, and
more preferably from 1 milliliter to 5 liters of flowable material.
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WO 98/34844 PCT/US97/01671
The film structure for the pouch of the present invention has precisely
controlled strength. The use of the film structure described in the present
invention for making
a pouch results in a stronger pouch, and, therefore, more preferably, the
pouch contains fewer
use-related leakers. The use of a LLDPE and LDPE blend in the seal layer of
the present
invention in a two or three-layer coextruded film product will provide a film
structure that can
be used for making pouches at a faster rate in the VFFS and such pouches
produced will
contain fewer leakers.
With the trend in today's consumer packaging industry moving toward
providing the consumer with more environmentatly friendly packages, the
polyethylene pouch
lo of the present invention is a good alternative. The use of the polyethylene
pouch for packaging
consumer liquids such as milk has its advantages over containers used in the
past: the glass
bottle, paper carton, and high density polyethylene jug. The previously used
containers
consumed large amounts of natural resources in their manufacture, required a
significant
amount of space in landfill, used a large amount of storage space and used
more energy in
15 temperature control of the product (due to the heat transfer properties of
the container).
The polyethylene pouch of the present invention made of thin polyethylene
film,
used for liquid packaging, offers many advantages over the containers used in
the past. The
polyethylene pouch (1) consumes less natural resources, (2) requires less
space in a landfill,
(3) can be recycled, (4) can be processed easily, (5) requires less storage
space, (6) uses less
2o energy for storage (heat transfer properties of package), (7) can be safety
incinerated and (S)
can be reused, for example, the empty pouch can be used for other applications
such as
freezer bags, sandwich bags, and general purpose storage bags.
The polymeric resins described in Table I herein below were used to prepare
samples of blown films shown in the Examples and Comparative Examples.
25 Table I: Resin Properties
Resin Name Type Melt Index,Density, M rength,
dg/min. glcc cN
AFFINITY PL SLEP 1.0 0.903 3.9
1880
DOWLEX 2045 LLDPE 1.0 0.920 6
LDPE 1351 LDPE (tube) 0.22 0.923 19
XU 60021.62 LDPE 0.5 0.919 25
(autoclave)
LDPE 609C LDPE (tube) 0.88 0.924 10
LDPE 526 I LDPE (tube) 1.0 0.903 ?
_g_
CA 02280910 1999-08-10
WO 98/34844 PCT/US97/01671
The composition of various LDPE and LLDPE blends and their melt strength is
shown in Table Il herein below.
Table II: Men Strength of Resin Blends
Blend DesignationDescription (*) Melt Strength (cN)
1 DOWLEX 2045 6.4
2 AFFINITY PL 1880 3.9
3 LDPE 5261 12.1
4 LDPE 1351 19.5
LDPE 609C 12.1
6 LDPE XU60021.62 24.3
7 DOWLEX 2045/10% 1351 10.4
8 DOWLEX 2045/20% 1351 16.0
9 DOWLEX 2045/30% 1351 19.7
DOWLEX 2045/10% 609C 9.5
11 DOWLEX 2045/20% 609C 11.7
12 DOWLEX 2045/30% 609C 13.4
13 DOWLEX 2045/10% XU60021.6211.5
14 DOWLEX 2045/20% XU60021.6224.2
DOWLEX 2045/30% XU60021.6230.4
16 AFFINITY PL 10% 1880 5.9
17 AFFINITY PL 20% 1351 9.4
18 AFFINITY PL 30% 1351 9.7
19 AFFINITY PL 10% 5261 4.9
AFFINITY PL 20% 5261 5.8
21 AFFINITY PL 30% 5261 6.6
22 AFFINITY PL 10% XU60021.628.4
23 AFFINITY PL 20% XU60021.6212.3
24 AFFINITY PL 30% XU60021.6214.7
(*) % refers to percent by weight of LDPE in the blend
A 5kg sample of each blend shown in Table II was processed through a Leistritz
twin screw extruder. The melt strength of the blends were determined using a
Gottfert
Rheotoens unit.
Erucamide, a siip agent; Si02, an antiblock agent; and a processing aid were
added to each of the resins described in Table I such that the final
concentrations of the
1o additives were as follows: 1200 pprii Erucamide; 2500 ppm Si02.
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Film structures produced were subjected to physical testing to determine its
various properties including:
(1) Puncture, using method ASTM D3763;
(2) Dart Impact, using ASTM D17o9, Method A;
(3) Elmendorf Tear, using ASTM D1922;
(4) Tensiles, using ASTM D882;
(5) 1% and 2% Secant Modulus, using ASTM D882;
(6) Hot Tack Strength, using method described hereinbelow; and
(7) Heat Seal Strength, using method described hereinbelow;
1o The hot tack strength of sample films was measured using the "DTC Hot Tack
Test Method," which measures the force required to separate a heat seal before
the seal has
had a chance to fully cool (crystallize). This simulates the filling of
material into a pouch before
the seal has had a chance to cool.
The "DTC Hot Tack Test Method" is a test method using a DTC Hot Tack Tester
i5 Model #52D according to the following conditions:
Specimen Width: 25.4 mm
Sealing Time: 0.5 seconds
Sealing Pressure: 0.27 N/mm/mm
Delay Time: 0.5 seconds
Peel Speed: 150 mmlseconds
Number of Samples/Temperature5
Temperature Increments: 5C
Temperature Range: 75C - 150C
The heat seal strength of sample films was measured using the "DTC Heat Seal
Strength Test Method," which is measure designed to measure the force required
to separate a
2o seal after the material has cooled to 23°C temperature. The film
samples were exposed to a
relative humidity of 50 percent and a temperature of 23°C for a minimum
of 24 hours prior to
testing.
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The "DTC Heat Seal Strength Test Method" uses a DTC Hot Tack Tester Model
#52D, wherein the heat seal portion of the tester is used, according to the
following conditions:
Specimen Width: 25.4 mm
Seating Time: 0.5 seconds
Sealing Pressure: 0.27 N/mm/mm
Number of SampleslTemperature 5
Temperature Increments: 5°C
Temperature Range: 80°C -150°C
The seal strength of the film samples was determined using an Instron Tensile
Tester Model #1122 according to the following test conditions:
Direction of Pull: 90 to seal
Crosshead Speed: 500 mm/minute
Full Scale Load: 5 kg
Number of Samptes/Threshold:1 percent of
FSL
Break Criterion: 80 percent
Gauge Length: 2.0 inches
(50.8 millimeters)
Sampte Width: 1.0 inch
(25.4 millimeters)
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Table III:
Multilaysr (A/B/A) Fiims for Physical Property Testing
Example Resin Blend in Layer A Resin Blend in LayerOverall
B
No. Gauge
(Mils)
1 A* AFFINITY PL 1880 + 20% DOWLEX 2045 + 20% 2.46
LDPE 135 I LDPE
135 I
1 B AFFINITY PL 1880 + 20% DOWLEX 2045 + 80% 2.49
LDPE 135 I LDPE
135 I
2 AFFINITY PL 1$80 + 20% DOWLEX 2045 + 20% 2.50
LDPE 503 I LDPE
503 I
3 AFFINITY PL 1880 + 20% DOWLEX 2045 + 20% 2.10
LDPE 526 I LDPE
526 I
4 AFFINITY PL 1880 + 20% DOWLEX 2045 + 20% 2.50
XU60021.62 I
XU60021.62
Comp. AFFINITY PL 1880 ? 2.54
A
(*) % refers to percent by weight of LDPE in the blend
Physical properties of films show in Table III are reported in Table IV below,
and
the results of hottack and heat seal strength are reported in Table V.
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WO 98/34844 PCT/US97/01671
Table IV: Physical Properties of Multilayer Films
AFF AFF AFF AFF AFF AFF AFFINITY
1880+2 1880+ 1880+1880 1880 1880 1880
+
0% 20% 20% 20% + +
XU
1351 1351 1351 60021.620% 20%
80% Id 3MIL 2 5031 5261
IN
core)
Gauge mil 2.49 3.18 2.46 2.50 2.50 2.10 2.54
Etmertdorf f M253D
Tear
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Table VI: HottacklHeat Seaf Strength
Hot Tack Strength, N/in
DOWLEX DOWLEX 2045 DOWLEX 2045DOWLEX 2045
2045 + + +
20% LDPE 20% LDPE 20%
1351
609C XU60021.62
TEMPERATURE
C
90 0.23 0.14 0.22 0.19
95 0.17 0.21 0.15 0.19
100 0.64 0.62 0.66 0.68
105 1.91 1.91 1.85 1.79
110 2.47 2.86 2.55 2.83
l 15 3.28 3.47 3.30 3.59
120 2.64 3.04 2.73 3.17
125 2.51 2.96 2.63 3.16
130 2.38 2.86 2.56 3.13
135 2.35 2.73 2.32 2.89
140 2.27 2.48 2.16 2.62
145 2.17 2.35 2.14 2.39
150 1.96 2.21 2.09 2.12
155 1.99 1.91 1.85 1.89
l 60 1.65 1.78 1.80 1.84
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CA 02280910 2004-O1-22
77252-51
Table VII: Neat Seal Strength, inn
DOWLEX 2045DOWLEX 2045DOWLEX 2045 DOWLEX
2045
+ + +
20% LOPE 20% LDP 20%
1351
609C XU60021.62
TEMPERATURE
C
100 026 020 0.19 0.26
105 0.51 0.72 0.51 0.71
110 4.28 4.88 4.10 4.95
115 4.71 5.76 5.15 6.14
120 5.52 7.09 6.00 7.83
125 5.71 7.01 6.50 7.79
130 6.02 7.07 6.60 7.82
135 5.33 7.37 5.90 7.70
140 6.11 7.50 6.75 8.00
145 5.56 7.01 6.06 7.75
150 5.27 7.53 6.33 7.70
155 4.86 7.74 6.48 8.25
160 5.68 7.75 6.50 8.69
The present invention is illustrated by the following examples but is not to
be
limited thereby.
Examples 1-3 and Comparative Examples A
The film samples described in Table III were made as a monolayer using a
TM
Macro blown film line. The extruder was 2-112 inches (6.4 cm) in diameter and
had a 24:1 UD
i0 ratio and a barrier screw with a Maddock mixing head. A 6 inch (15.2 cm)
diameter die was
used with a 60 mil (1,524 microns) die gap for the manufacture of the test
films. The fabrication
conditions for the blown film five were a blow-up ratio of 2.5 and a melt
temperature of 220°C.
Examples 4-6 and Comparative Example B
The films described in Table Ill were slit to a width of 15 inches (38.1 cm)to
~5 produce 2-liter milk pouches using a Prepac IS6 Vertical, Form, Fill and
Seal machine located at
a commercial dairy. The unit packaged 2-liter milk filled pouches at the rate
of 30 pouches per
minute per filling head under normal operating conditions. For each film
tested, approximately
16-20 milk-filled pouches were collected. They were inspected for initial seal
integrity. 6-8
-16-
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WO 98/34844 PCT/US97/0167I
pouches were tested on site for heat seal strength and 10 pouches were
drained, washed and
dried for further evaluation.
The seal strength was determined using an Instron Tensile Tester Model #1122.
Sample were expose to a relative humidity of 50% and 23°C for 24-48
hours prior to testing.
_ The Instron test conditions were as follows:
Direction of pull: 90° to seal
Crosshead speed: 500 mm/min.
Full Scale Load: 5 kg
Threshold: 1% of FSL
Break Criterion 80%
Gauge length: 2.0 in. (50.8 mm)
Sample width: 1.0 in. (25.4 mm)
The initial examination of end seal integrity involved three steps:
i) Determination Of On-Line Leakers
ii) Subjective Seat Strength Test
lfl iii) Visual Examination of End Seals
-17-
CA 02280910 2004-O1-22
77252-51
On Line Leakers
On line leakers were only seen with the pouches made from the DOWLEX 2045.
No leakers were seen with the other films.
Subjective Seal Stren4th Test
The subjective seal strength test involved squeezing the pouch from one end
until the pouch either yielded or the seal failed. Table Vlll shows that no
seal failures were seen
with the pouches made with 20% 1351 or XU 60021.62.
Visual Examination of End Seals
The DOWLEX 2045 films were found to have significant seat thinning and end
1o seal stringers as shown in Table IX. The pouches made with 20% 609C were
found to have
some seal thinning and some end seat stringers. No seal thinning or stringers
were found with
the 20% 1351 and XU 60021.62 films.
End Seal Strength
Ten 2-liter milk pouches were tested for end seal strength using an Instron
Tensile Tester Model # 4206, under same conditions described in connection
with the
determination of heat seat strength hereinabove.
The seal strengths are shown in Table X. Seal strength was found to increase
as the melt strength of the blend increased. This finding is graphically
illustrated in Fig. 6
using a blend of 80% by weight of LLDPE and 20% by weight of LDPE, except the
first data
2o point having melt strength of 6.4 cN did not contain any LDPE. No
correlation was evident
between LDPE melt index and seal strength.
Microscopy Examination of End Seals
The stringer regions and edge regions of the pouches were cryo-sectioned and
examined using light microscopy techniques. Table XI summarizes the results.
The films made with 20% 1351 and XU 60021.62 showed very little seal thinning
and no end seal stringers (fine polymer filaments coming from the seat area),
while the films
made with 100% DOWLEX 2045 had significant seal thinning and stringers.
Seal Region Film Thinntn4
The weakest part of a good seal is typically the film just in front of the
seal bead.
3 o Any thinning of this film results in lower seal strengths since this is
the region that fails when
the seal is stressed. Comparing the melt strength of the resin blends (Table
II) with the amount
of film thinning seen with the pouches made with a commercial VFFS unit (Table
XI), it is seen
that, as the melt strength of the resin blend increased, the amount of film
thinning decreased.
_18_
CA 02280910 1999-08-10
WO 98/34$44 PCT/US97/016'1l
No correlation was seen between film thinning (Table XI) and melt index of
LDPE in resin
blends (Table 1).
Seal Bead
Comparing seal bead thickness (Table XI) to resin blend melt strength (Table
II)
and LDPE melt index (Table I), it is seen that there is a strong correlation
between melt strength
and bead thickness, and no correlation between LDPE melt index and seal bead
thickness.
Higher melt strength blends resulted in thicker seal beads.
Table VIII: Liconsa Dairy Prepac VFFS Evaluation
Subjective Seal Strengths
Run # LLDPE LDPE % LDPE # Pouches# Seal
Tested Failure
1 DOWLEX 2045 0 7 3
2 DOWLEX 2045 6096 20 8 2
3 DOWLEX 2045 1351 20 ~ 6 0
4 DOWLEX 2045 XU.62 20 7 0
Table IX: Liconsa Dairy Prepac VFFS Evaluation
Visual Examination of End Seals
Run # LLDPE LDPE % LDPE Visual Examination
of Seal
1 DOWLEX 2045 -- 0 heavy stringers,
seal
thinning
2 DOWLEX 2045 609C 20 heavy stringers,
seal
thinning
3 DOWLEX 2045 1351 20 no stringers
4 DOWLEX 2045 XU.62 20 no stringers
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WO 98/34844 PCT/US97/01671
Table X: Prepac VFFS
Pouch End Seal Strength
Run # LLDPE MI LDPE MI % LDPE Seai Strength,
Ib/in
1 DOWLEX 2045 -- 0 5.31
2 DOWLEX 2045 609C 20 5.78
3 DOWLEX 2045 135C 20 6.79
4 DOWLEX 2045 XU.62 20 7.01
Table XI: Prepac
VFFS Microscopy Analysis Summary
# DescriptionComments Seal Bead*Film **Film Reduction
ThicknessThicknesThicknessin Film
~m s Before Thickness,
N111 .Seal, %
m
1 DOWLEX sever 139 65.5 43.1 34
thinning
and
drawing
of
seal area
many seat
stringers
2 DOWLEX some 130 63.2 50.0 21
2045 + thinning,
20% LDPE some
609C stringers
3 DOWLEX good, no 176 60.8 56.9 6
2045 + thinning,
no
20% LDPE stringers
1351
4 DOWLEX good, no 228 61.3 60.2 2
2045 + thinning,
no
20% XU strings
60021.62
*measured 550~m from seal
**measured cross section at thinnest part of film before the seal
-20-
CA 02280910 1999-08-10
WO 98/34844 - PCT/US97/01671
The following polymeric resin blends shown in Table XII were used to further
illustrate the advantages of this invention:
Table X11: Resin Blends
Blend Description Blend Description
1 DOWLEX 2045
2 DOWLEX + 10% LDPE XU 60021.62
3 DOWLEX + 20% LDPE XU 60021.62
4 DOWLEX + 30% LDPE XU 60021.62
DOWLEX + 40% LDPE XU 60021.62
6 DOWLEX + 50% LDPE XU 60021.62
7 DOWLEX + 60% LDPE XU 60021.62
DOWLEX + 70% LDPE XU 60021.62
DOWLEX + 80% LDPE XU 60021.62
DOWLEX + 90% LDPE XU 60021.62
(') % refers to percent by
weight of the amount of
LDPE in various blends.
The resin blends of Table XII were used to fabricate 2.8 mil (71 microns)thick
films using a MACROS blown film line having a barrier screw with a diameter of
2 1/2 inches
10 (63.5 mm, 24:1 UD ratio and Maddock mixing head. A six inch (15.2 cm) die
with a 60 mil (1524
microns) die gap was used. A Macro dual lip air ring supplied with chilled air
was used. Each
resin was blended to a target of 1200 ppm erucamide slip and 2500 ppm Si02
antiblock. Each
film was tested for hottack and heat seal strength, values reported in Table
XIII and Table XIV,
respectively.
-21-
Image
CA 02280910 1999-08-10
WO 98/34844 PGT/US97/01671
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-23-
CA 02280910 1999-08-10
WO 98/34844 PCT/US97/Q16'71
The hottack strength was determined using a DTC Hottack Tester Model #D52D
under the conditions described hereinabove. The test films were heat sealed
using the DTC
Hottack Tester Model #D52D under the conditions described hereinabove. The
heat seal
s - strength was determined using an Instron Tensile Tester Model #1122. Test
samples were
exposed to a relative humidity of 50 percent and 23°C for 24 to 48
hours prior to testing. The
Instron test conditions were the same as described hereinabove.
From the results of hottack and heat seal tests shown in Table XIII and Table
XIV, it is seen that the maximum hottack strength was reached with the 50
percent DOWLEX
io 2045/50 percent XU 80021.62 blend. The highest hest seal strenght were also
seen with the 50
percent DOWLEX 2045!50 percent XU 60021.62 blend.
-24-
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WO 98/34844 PCT/C1S97/01671
Expected hottack strength was calculated as per the following:
TABLE XV:
HOTTACK = (0.5 X LLDPE hottack) + (0.5 X LDPE hottack)
PredictedDOWLEX LDPE 1351 DOWLEX 2045 DOWLEX 2045
+ 20% + 20%
vs. Actual2045
Hottack LDPE 1351- LDPE 1351-
ACTUAL
Strength EXPECTED
Temp.
(C)
95 0.29 0.18 0.24 0.27
100 0.45 0.22 0.33 0.35
105 1.76 0.56 1.16 0.97
110 2.40 0.81 i.60 2.19
115 2.82 0.86 1.84 3.i8
120 2.96 0.74 1.85 3.41
125 2.77 0.69 1.73 3.54
130 2.54 0.69 1.62 3.34
135 2.40 0.64 1.52 3.10
140 2.31 0.64 1.47 3.05
145 2.32 0.60 1.46 2.87
150 2.18 0.56 1.37 2.74
The results of predicted versus actual hottack strength are shown in Table XV.
It can be seen that the actual hottack strength of the present invention is
significantly higher
than the predicted level, indicating a clearly synergistic effect.
-25-
