Note: Descriptions are shown in the official language in which they were submitted.
CA 02731809 2011-02-14
LAMINATE FOR PACKAGING HYGROSCOPIC MATERIALS, POUCHES MADE
THEREFROM, AND METHOD FOR MANUFACTURING SAME
FIELD OF THE INVENTION
The present invention relates to a laminate with a very low rate of water
vapour transmission,
which is particularly suitable for packaging flowable hygroscopic solids in
pelleted form.
BACKGROUND OF THE INVENTION
Most dry packaged goods are vulnerable to environmental moisture. In humid
environments,
moisture absorbed by the product through its packaging can have a number of
undesirable
effects on the shelf life and usefulness of the contents, depending on the
packaged product.
For instance, crystalline or powder substances can absorb moisture and become
clumped.
Biologically active chemicals can become hydrolyzed following water
absorption. Absorbed
water will hasten the spoilage of many dry food materials. Such materials
which have the
characteristic of tending to absorb moisture from the air are termed
"hygroscopic".
To combat this problem, there have been many developments in packaging
materials in order
to produce low Moisture or Water Vapour Transmission Rates (commonly
abbreviated to
"MVTR" or "WVTR") through the packaging. Depending on the value of the
packaged
contents and the extent to which it is crucial to minimize WVTR, the amount
invested in
engineering for the packaging and the quantity of materials used to construct
it will vary. For
instance, dry food stuffs such as flour and sugar are moisture sensitive but
they are also
inexpensive and are typically sold at a high rate of turnover, and therefore
do not require very
long periods of storage. Limited moisture entering the package does not
generally cause
significant problems for the contained product. These materials are often
simply packaged in
multi layers of coated kraft paper which are relatively inexpensive and deemed
to provide
sufficient protection. A WVTR in the range of 6.0 g of water per 100 square
inches of
packaging material per 24 hours, at the standard testing conditions of 90%
relative humidity,
38 degrees Celcius, is considered commercially acceptable for these types of
products.
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Items such as solid pet food pellets are somewhat more sensitive to moisture
entry, as moisture
tends to increase the rate of spoilage of such protein and fat containing
products. Further, if
the pet food clumps, it decreases the flowability of the product, which is
problematic for the
consumer. Manufacturers therefore tend to utilize a packaging material with
lower rates of
WVTR, in the range of 0.4-0.8 g/100 square inches per 24 hours in standard
testing conditions.
Such packaging is often comprised of polyethylene laminated to kraft paper, or
all-plastic
laminates, as such materials are relatively inexpensive and are found to have
sufficiently low
WVTR.
The overall goal in terms of packaging hygroscopic materials is to make a
packaging that
provides adequate product protection, and at the same time is economically
viable to produce.
Some hygroscopic materials are very sensitive to humidity, are also
sufficiently expensive, and
may require storage for longer periods of time before use, in order to justify
investment in a
packaging treatment that greatly minimizes WVTR. The resin pellets used in the
manufacture
of materials such as laminates or plastic containers or bags, such as pellets
of nylon or ethylene
vinyl alcohol, are available from a number of chemical suppliers including
DUPONTTM,
BASFTM, and HONEYWELLTM. Such materials are provided as granular pellets as
this is the
format that is most convenient to work with in terms of laminate
manufacturing.
Such pellets are highly hygroscopic. They have a very low tolerance to
environmental
humidity, requiring WVTR in the range of 0.05-0.08 grams of water per 100
square inches per
24 hours under standard testing conditions. Moisture causes the pellets to
rapidly degrade, and
given their expense and often long periods of storage, this would present a
significant
economic problem for the many industrial consumers of such products. Moisture
further
causes the pellets to clump, which reduces the ability of the user to pour the
pellets into
vehicles such as hoppers during the manufacturing process, to accurately pour
specific
measured amounts, or to readily mix the pellets with other solid granular
materials.
A known effective barrier material which imparts the feature of low WVTR to
packaging is
metal foil, most commonly aluminum foil. Foil is typically used as a
protective layer when
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packaging resin pellets. However, foil can be relatively brittle and easily
punctured or torn.
Given that pelleted resins tend to be hard and may have sharp edges,
additional measures have
been necessary to make the package puncture-resistant. Such packages have
therefore been
further lined with a protective plastic layer in addition to the aluminum
foil.
A further practical requirement for packaging such industrial grade products
is good
sealability. The packaging will typically be made into large pouches or bags
which may
contain anywhere from twenty to forty kilograms of pellets. Such pouches must
be able to
withstand rough handling conditions during transport and shipping, vibrations
and bouncing
during travel, as well as being dropped from moderate heights during delivery
without
breakage or bursting at the seams of the pouch.
Given the above requirements, the type of package used in the industry for
packaging
hygroscopic resin pellets has been thick, heavy, and expensive to manufacture.
The typical
prior art package has included a layer of aluminum foil as well as a further
protective polymer
layer on the package interior in order to shield the aluminum foil from
contact with the resin
pellets. The aluminum foil has further been attached to several layers of
heavy gauge kraft
paper. This combination provides the low WVTR necessary for such product, but
is both
bulky and expensive to manufacture. The packaging is relatively thick, in the
range of 9-10
mils. Given rising fuel costs resulting in increased shipping expenses for
heavier goods, and
the scarcity of resources needed to manufacture such bulky packaging, it would
be
advantageous to have a thinner, lighter material that is less expensive to
manufacture but
which has the required low WVTR, puncture resistance, and sealability.
SUMMARY OF THE INVENTION
The present invention provides a packaging laminate designed particularly for
packaging
highly hygroscopic, pelleted, flowable materials. Described herein is a
multilayer laminate
which incorporates a layer of polymeric material which has had a thin film of
metal deposited
onto it by vapour coating. This layer combined with a further effective
moisture barrier layer
provides the low WVTR in the range required by such highly hygroscopic
materials. This
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laminate can be used with or without additional structural layers of paper or
plastic, to form
bags that have the features of very low WVTR, excellent puncture resistance,
and excellent
heat sealability.
In one embodiment the invention relates to a packaging material incorporating
a heat sealable
layer of oriented polypropylene or polyethylene terephthalate upon which has
been deposited a
thin coating of aluminum. This metallized layer is further adhered to a
multilayer laminate
which is comprised of linear low and/or high density polyethylenes. This
combined structure
can then be adhered or laminated to one or more plies of paper or heavy
plastic, both of which
function to provide structure and strength to the laminate. This packaging
material has the
required very low level of WVTR, and is also particularly strong and puncture
resistant. The
oriented polypropylene layer further shows excellent heat sealing
characteristics.
The present invention is also directed to a method of manufacturing the
laminate of the
invention. A layer of polymeric material is provided with a heat sealable
surface on one side,
and a metallized surface on the other. A multilayer laminate is separately
prepared by blown
tube co-extrusion. The multilayer laminate is then adhered to the metallized
side of the
oriented polypropylene, and the entire resulting structure may then optionally
be adhered to a
ply of structural material such as kraft paper or a relatively thick
structural plastic sheet having
a gauge in the range of 5 mil. Further plies of structural material may also
be added. The
resulting multilayer structure forms a packaging material that can then be
used to make bags
that are particularly suitable for packaging pelleted hygroscopic materials.
In a further aspect, the present invention is directed to a bag formed of the
laminate of the
present invention for packaging pelleted hygroscopic materials.
In a still further aspect, the present invention is also directed to a method
of forming the bag
made from the laminate of the present invention.
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BRIEF DESCRIPTION OF THE FIGURES
The present invention will now be better understood with reference to the
detailed description
and tables and to the accompanying figures in which:
Figure 1 is a drawing of a pouch that can be constructed using the laminate of
the invention;
and
Figure 2 is a graph demonstrating the heat sealability of the test packaging
as compared to a
traditional foil laminate.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a novel packaging laminate designed
particularly for packaging
highly hygroscopic, pelleted, flowable materials. It is a multilayer structure
which
incorporates a layer of a polymeric material which has had a thin film of
aluminum deposited
onto it by vapour coating. This layer combined with a further effective
moisture barrier layer
provides the low WVTR in the range required by such highly hygroscopic
materials.
In one embodiment, the present invention provides a multi-layer laminate
having a core layer
comprising a first outer layer comprised of linear low density polyethylene,
low density
polyethylene, and anti-block agent; an inner layer comprised of linear low
density
polyethylene, low density polyethylene, and slip additive; and a second outer
layer comprised
of linear low density polyethylene, low density polyethylene, and anti-block
agent. The multi-
layer laminate includes a metallized layer of polymeric material having a heat
sealable surface
and a metallized surface wherein the metallized surface is adhered to the
second outer layer
and optionally a structural layer selected from a paper or a plastic that is
adhered to the first
outer layer. The multi-layer laminate has a water vapour transmission rate of
less than 0.05
g/100 square inches/24 hours measured at 38 degrees Celcius and 90 % relative
humidity. In
an alternative embodiment the water vapour transmission rate is less than
0.005 g/100 square
inches/24 hours measured at 38 degrees Celcius and 90 % relative humidity.
CA 02731809 2011-02-14
In one embodiment, the multi-layer laminate has an average energy to break of
at least 8.0
pounds per inch. In another embodiment the multi-layer laminate has an average
energy to
break of at least 9.0 pounds per inch.
In one embodiment, the multi-layer laminate has an average puncture of at
least 3.0 feet per
pounds force per inches cubed. In another embodiment, the multi-layer laminate
has an
average puncture of at least 4.0 feet per pounds force per inches cubed.
Tables 1 and 2 show sample formulations of the multi-layer laminate described
herein. As set
out therein, there are essentially three components to the multi-layer
laminate of the invention:
A. a metallized layer such as a metallized biaxially oriented polypropylene
which will face the
interior of any bag made using the laminate of the invention; B. a three-layer
core laminate
with barrier properties, and C. one to three outer structural layers of kraft
paper which will be
located to the exterior of any bag made using the laminate of the invention.
In terms of the metallized layer, as set out in both sample formulations, a
biaxially oriented
polypropylene was chosen as the base for this layer. Polypropylene is a
material with good
heat sealing characteristics, and the process of aligning it in two directions
(i.e. biaxial
orientation) is known to improve the strength of the film, the modulus
(resistance to stretching)
and also to improve the moisture barrier properties of the film because of the
increased
crystallinity of the polymers, all of which are features imparted by the
orientation process.
An alternate embodiment for the metallized layer could comprise polyethylene
terephthalate
film, which may be engineered to have good moisture barrier properties, and
which may be
coated on one side with a metal coating. A heat sealable layer could then be
formed on or
adhered to the opposite side of the film.
In terms of the three-layer core laminate, the ingredients of sample
formulations are provided
in tables 1 and 2 respectively. In one embodiment, the multi-layer laminate
includes a core
comprising a middle and two outer layers formed of quantities of linear low
density
polyethylene and low density polyethylene. Also included in the formulations
are additives
typically used in the film manufacturing process. Antiblock additives are
included in order to
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minimize adhesion between adjacent sheets of film. Polymer processing aids
were added in
order to enhance the extrusion abilities of the film being made. Slip
additives are added in
order to reduce the surface coefficient of friction of the laminates being
formed. Each of these
types of additives are available from a number of chemical supply companies.
In one embodiment the three components of the core of the multi-layer laminate
include outer
layers comprising linear low density polyethylene. The multi-layer laminate
core comprises
first and second outer layers each comprising from about 88 to about 92%
linear low density
polyethylene, from about 6 to about 10% low density polyethylene, and from
about 1 to about
2% antiblock agent; and an inner layer comprising from about 88 to about 92%
linear low
density polyethylene, from about 6 to about 10% low density polyethylene, and
from about 1
to about 2% slip agent.
Set out in Table 1 is an example of the multi-layer laminate of this
embodiment including a
structural layer of kraft paper.
TABLE 1
LLDPE Formulation
Package Exterior Side
kraft Paper
1-3 plies
Core Layer
Layer A (25%): 90.50 % linear low density polyethylene
8.00 % low density polyethylene
1.50 % antiblock agent
Layer B (50%): 90.40 % linear low density polyethylene
8.00 % low density polyethylene
1.60% slip agent
Layer C (25%): 90.50 % linear low density polyethylene
8.00 % low density polyethylene
1.50 % antiblock agent
Metallized layer
Metallized biaxially oriented polypropylene
Package Interior Side
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In an alternative embodiment, the formulation for the three-layer core
laminate comprises a
middle layer formed from high density polyethylene, low density polyethylene,
and very low
density polyethylene. The two outer layers are identical in composition and
are formed
principally from linear low density polyethylene and low density polyethylene.
Antiblock,
polymer processing aids, and slip agents are also used in this formulation. In
one embodiment
the multi-layer laminate comprises first and second outer layers each
comprising from about
77 to about 82% linear low density polyethylene, from about 15 to about 19%
low density
polyethylene, from about 2 to about 4% antiblock agent, from about 0.5 to
about 1.5 %
polymer processing aid; and an inner layer comprising from about 70 to about
77% high
density polyethylene, from about 13 to about 17% low density polyethylene,
from about 8 to
about 12 % very low density polyethylene, and from about 0.5 to about 1.5%
slip agent.
Set out in table 2 is an example of the multi-layer laminate of this
embodiment including a
structural layer of kraft paper.
TABLE 2
HDPE Formulation
Package Exterior Side
kraft Paper
1-3 plies
Core Layer
Layer A (25%): 79.00 % linear low density polyethylene
17.00 % low density polyethylene
3.00 % antiblock agent
1.00 % polymer processing aid
Layer B (50%): 73.90 % high density polyethylene
15.00 % low density polyethylene
10.00 % very low density polyethylene
1.10 % slip agent
Layer C (25%): 79.00 % linear low density polyethylene
17.00 % low density polyethylene
3.00 % antiblock agent
1.00 % polymer processing aid
Metallized layer
Metallized biaxially oriented polypropylene
Package Interior Side
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Following formation of the three-layer laminate, the next step in the
manufacturing process is
the adhesion of the three-layer laminate to the metallized layer, which can be
accomplished by
any known method.
The combined three layer barrier and the metallized biaxially oriented
polypropylene can then
be attached to a further structural layer such as kraft paper. Paper is a
convenient material,
particularly for the outermost layer, as it has a high coefficient of friction
and therefore can be
used to make packages with good stackability. Paper is also readily printed
on. The combined
laminate may be adhered to a single ply of paper, which may in turn be adhered
to further plies
of paper, prior to converting into bags or any other desired packaging
structure.
Instead of paper, another possible embodiment is an all plastic bag in which
the barrier films
are laminated to structural plastic having a thickness in the range of 5 mil.
In another
embodiment the structural plastic layer is at least 4 mil thick. A material
may be chosen for the
outer plastic which provides a high coefficient of friction, and the plastic
may be printable as
well.
EXAMPLE
The following detailed example will make reference to Table 1 above. A three
layer core
laminate is formed in accordance with the recipe provided. Layer A contains
90.50% linear
low density polyethylene (the SCLAIRTM brand purchased from NOVATM), 8.00% low
density polyethylene (purchased from DOWTM), and 1.50% antiblock agent. Layer
A
comprises 25% of the total mass of the three-layer laminate. Layer C is
identical in
composition and mass to layer A. Layer B contains 90.40% linear low density
polyethylene
(also the SCLAIRTM brand from NOVATM), 8.00% low density polyethylene (from
DOWTM),
and 1.60% of a slip agent. Layer B comprises the remaining 50% of the mass of
the three-
layer laminate. The three layers A, B, and C are co-extruded by standard
methods of blown
tube co-extrusion. The three-layer core laminate is formed to have a thickness
of 1.2 mil.
Following cooling and rolling, the three-layer laminate is then adhered to a
metallized
biaxially oriented polypropylene film with a vaporized aluminum deposit on one
side, and a
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heat sealable surface on the other side. An appropriate product is available
from Celplast
Metallized Products LimitedTM under the name FOILMET BOPPTM, and was used
successfully. This film is 0.70 mil thick, is metallized on one side, and is
heat sealable on the
other, and thus incorporates the necessary sealant layer. The heat sealable
layer can be sealed
to itself or to another surface using heated crimp sealer jaws or similar heat
sealing apparatus.
A solventless adhesive, such as the aromatic polyurethane adhesive called DURO-
FLEXTM
37-9451 available from NATIONAL STARCH TM is then applied, and the laminates
are
adhered together using a standard roll to roll laminator. The newly formed
laminate is then
cured for 24 hours.
The entire laminate is then adhered to one ply of paper using a standard
adhesive applied in
rows. Kraft Unbleached SPK paper available from TOLKOTM Marketing and Sales
Ltd. has
been successfully used. Further plies of outer paper may also be adhered using
standard
methods. When adhered to two additional plies of outer paper, the thickness of
the material is
between 6.5-7.0 mils. The material is then ready for conversion into bags.
Another aspect of the invention is a bag formed using the laminate of the
invention, after it has
been further adhered to additional plies of paper as described above. This
provides a versatile
packaging material in terms of the types of bags that may be formed from it,
as the inside
polypropylene layer may be sealed both to itself, and to an outer surface of
the bag.
The structures of bags used for packaging are known in the art. A sample bag
structure is
shown in perspective view in figure 1. Following the appropriate cutting of
the packaging
material, the bag may be formed to have side gussets I and 2, a lap seal 5
along the bag's
longitudinal axis formed by the application of heat, an open mouth 3 for later
filling of the bag,
and a closed pinch bottom 4 which is also sealed by heat.
The foregoing steps constitute the preferred method by which the laminate and
bag of the
present invention are made. However, it will be apparent to those of skill in
the art that
variations may be applied to the steps in the method without departing from
the scope of the
invention. All such similar substitutes and modifications apparent to those
skilled in the art
CA 02731809 2011-02-14
are deemed to be within the spirit, scope, and concept of the invention as
defined by the
claims.
Laminates of this invention comprise an arrangement of polymeric layers and a
metallized
layer that each contribute both individually and collectively to improving
moisture barrier
properties, puncture resistance, and sealability, producing a unique set of
beneficial properties.
These properties are described in further detail with reference to tables 3-7
and figure 2.
Table 3 shows WVTR results using a standard testing method, ASTM E96-05, the
"Standard
Test Method for Water Vapor Transmission of Materials". Three samples were
tested: two
laminates of the invention and a control. The two laminates of the invention
were formulated
in accordance with the specifications provided in tables 1 and 2 respectively
(the LLDPE
embodiment and the HDPE embodiment). A traditional foil/paper laminate was
used as a
control.
TABLE 3
WVTR Test Results using ASTM E96-05
Sample WVTR (g/100 square inches/24 hours)
Control: traditional foil laminate 0.0129
Test Laminate (LLDPE embodiment) 0.00645
Test Laminate (HDPE embodiment) 0.0194
In accordance with ASTM E96-05, laminate samples of a standard size (0.0645
metres
squared) were tested in conditions of 23 +/- 2 degrees Celcius, with 50 +/- 2%
relative
humidity. Specified volumes of water were placed into water-impermeable
containers which
were then sealed with laminates using a sealant comprised of 60%
microcrystalline wax and
40% refined crystalline paraffin wax. The containers were then weighed before
and after
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testing to determine the average mass loss which could be attributed to water
exiting the
container through the laminate. Testing took place over a 45 day period.
As set out in table 3, the LLDPE embodiment achieved a WVTR of 0.00645 g/100
inches2/24
hours. The control traditional foil laminate had a WVTR of 0.0129 g/100
inches2/24 hours.
While the HDPE embodiment had a higher WVTR of 0.0194 g/100 inches2/24 hours,
it is still
a very low WVTR that renders the HDPE embodiment commercially acceptable for
packaging
highly hygroscopic materials.
Table 4 shows WVTR results using another standard testing method, ASTM F372,
in which
both the LLDPE and HDPE embodiments were tested against the traditional foil
laminate as a
control. The equipment used for this test was the MOCON PERMATRANTM 3/60, with
films
being conditioned in the instrument for 24 hours prior to measurements being
taken. The
effective surface area of the samples tested was 10 square centimetres, and
the carrier gas used
was nitrogen. The temperature was 38 degrees Celcius with a humidity of 90 +/-
3 %. As set
out in figure 5, the LLDPE again performed better than the traditional foil
control, achieving a
WVTR of 0.0017 g/100 inches2/24 hours as compared to the 0.0018 g/100
inches2/24 hours
measured for the traditional foil control. The HDPE embodiment was found to
have a WVTR
of 0.0019 g/100 inches2/24 hours, which is higher than the control or the
LLDPE embodiment,
but still well within the range required for packaging highly hygroscopic
materials.
TABLE 4
WVTR Test Results using ASTM F372
Sample WVTR (g/100 square inches/24 hours)
Control: traditional foil laminate 0.0018
Test Laminate (LLDPE embodiment) 0.0017
Test Laminate (HDPE embodiment) 0.0019
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Results were confirmed for the LLDPE embodiment using a further test. Table 5
shows the
test results for Water Vapour Transmission using ASTM D 3079-94, "Standard
Test Method
for Water Vapour Transmission of Flexible Heat-Sealed Packages for Dry
Products", also
known in the industry as the "Jungle Room" test. This test is commonly used
for assessing
packaging materials to determine the amount of humidity that will reach the
contents of the
package. The test involves weighing empty packages, then filling them with a
quantity of
dessicant, such as calcium chloride. The packages are then sealed, and placed
for
predetermined times in environments of controlled temperature and humidity, at
37.8 +/- 1.1
degrees Celcius, and 90 +l- 2% relative humidity. The packages are weighed
afterwards, the
weight of the empty packages being subtracted from that of the dessicant-
filled packages. The
difference in weight will be the amount of water vapour that entered the
package during the
test.
TABLE 5
Jungle Room Test Results (ASTM D 3079-94)
Sample Water Weight Gain in 28 days
A: Test Invented Laminate 19.78 g
B: Traditional Foil 2.54 g
C: Kraft Standard Package 207.71 g
As detailed in table 5, three types of package materials were tested: A: the
test laminate
(LLDPE embodiment), B: a traditional foil laminate used as a control, and as a
further
comparative control, C: a standard laminate for packaging moderately moisture-
sensitive
materials. In this test, sample C was a multi-walled kraft bag lined with
HDPE, which is used
commercially to package dry pet food.
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For each of the types of package materials A-C, samples were sealed empty or
sealed with
dessicant. All samples were placed in the conditioning chambers with
temperature and
humidity conditions as set out above. Following set periods, the packages were
weighed
inside the conditioning chamber to determine weight gain over the total test
period, 28 days.
Weight gain of the empty control samples was deemed to be water absorption of
the paper
exterior packaging. Weight gain of the dessicant-containing samples was deemed
to be a
function of both water absorption of the paper packaging, and water absorption
of the
contained dessicant material due to water vapour transmission through the test
samples. The
difference between the test samples and control samples was considered to
reflect the extent to
which packages A-C allowed the transmission of water to reach the package
contents.
As seen in table 5, sample C which represents a standard package for
moderately hygroscopic
materials, allowed the passage of 207.71 grams of water into the package over
the test period.
Sample B, the traditional heavy foil laminate packaging (having layers of
aluminum foil,
polymer, and three plies of kraft paper) was much less permeable to water,
allowing the
passage of 2.54 grams of water. Sample A, the invented laminate (LLDPE
embodiment),
allowed the passage of 19.78 grams of water over the 28 day period, which
provides results
sufficiently close to the much heavier traditional laminate to be commercially
viable for
packaging such highly hygroscopic pellets. In other words, the Sample A
results show that the
invented laminate has low enough WVTR to be considered functionally comparable
with the
traditional heavy foil laminate package.
The results of the testing shown in tables 3, 4 and 5 reveal that the invented
laminates have
comparable WVTR to the traditional heavy foil laminate packaging (having
layers of
aluminum foil, polymer, and three plies of kraft paper). As the invented
laminate is far less
expensive to manufacture, and uses less material than the traditional foil
laminate, yet has
excellent WVTR in the range required, it may be concluded that the traditional
foil laminate
may be considered overengineered for the purpose it needs to fulfill.
The strength of the LLDPE embodiment of the invention was also assessed. Table
6 shows the
results of standard puncture testing of the laminate. A traditional foil
laminate was again used
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as a control, and tested against the LLDPE embodiment. For all test samples,
the two outer
plies of Daft paper were removed. All tests were therefore conducted on the
laminate when
adhered to only one outer layer of kraft paper.
TABLE 6
Puncture Test Data
Test Parameter Traditional Foil Test Laminate
Laminate Control
Average Elongation at Break 0.42 inches 0.68 inches
Average Energy to Break 4.7 lbs/inch 9.5 lbs/inch
Average Puncture 1.7 feet/lb force/inches3 4.1 feet/lb force/inches3
Average Peak Load 37.2 lb force 40.2 lb force
In the puncture testing method used, strips of laminate were clamped by their
edges in a testing
machine under controlled conditions of temperature and humidity. A probe was
then used to
penetrate the laminates at controlled speeds, until rupture occurred.
Measurements were taken
from which the puncture-resistance of the laminates could be assessed.
As set out in table 6, the first parameter measured for each of the samples
was the Average
Elongation at Break, which is the average amount of stretch in the laminate
prior to breakage
by the probe as described above. As shown, the LLDPE embodiment of the
invention showed
significantly higher elongation at break of 0.68 inches, as compared to 0.42
inches for the
traditional foil laminate control. This shows that the LLDPE embodiment has
greater
resistance to puncture than the control.
The next parameter measured was the Average Energy to Break, which is the
number of
pounds of force per inch required for the probe to displace the laminate. The
traditional foil
laminate control required 4.7 pounds of force to displace the laminate by one
inch. The
LLDPE embodiment is much stronger, requiring 9.5 pounds of force. In this
test, the LLDPE
embodiment therefore tolerated more than double the force of the control. This
result again
shows the excellent puncture resistance of the LLDPE embodiment.
CA 02731809 2011-02-14
The next parameter measured was the "Average Puncture", measured in feet per
pounds of
force per inches3. The Average Puncture of a given film is the energy needed
per unit area to
puncture the film, taking into account the contact surface area of the probe,
and the thickness
of the film. The traditional foil control required 1.7 feet/lb force/inches3
whereas the LLDPE
embodiment required 4.1 feet/lb force/inches3, almost 2.5 times that amount.
The final parameter measured was the Average Peak Load, which is the averaged
maximum
pounds of force that was needed to break the film. The LLDPE embodiment again
performed
better than the traditional foil control in this regard, requiring 40.2 lb of
force versus 37.2 lb of
force for the control.
The results set out in table 6 demonstrate that the LLDPE embodiment of the
invented
laminate is stronger and more puncture-resistant than the currently used
traditional foil
laminate. This is a beneficial characteristic, particularly when the invented
laminate is used to
package heavy quantities of pelleted hygroscopic materials.
Finally, it is also functionally important that the laminate and packaging
formed by it have
good sealing characteristics so that a firm closure can be made of the
package. There are many
known ways of sealing a package, but the most convenient method is by applying
heat through
clamping jaws.
Figure 2 displays the heat sealing profile of the package of the invention. In
this graph, the
invented package is termed "Met-tech (LLDPE)", and was formulated using the
specifications
provided in table 1, with three plies of kraft paper. The LLDPE embodiment was
compared to
a traditional foil laminate package also incorporating three plies of kraft
paper. The variable
temperature applied to create the seal is set out on the X axis, and the peel
strength required to
separate the seals after a cooling period is set out on the Y axis. The seals
were created using a
dwell time of 0.3 seconds, and an applied pressure of 40 psi. These parameters
are in the
range typically used in commercial operations.
As shown by figure 2, the laminate of the invention displays superior sealing
characteristics.
While the seal initiation temperatures of the invented laminate and the
control are the same at
16
CA 02731809 2011-02-14
160 degrees, even at that temperature the seal of the invented laminate is
stronger than that of
the control. This superiority in strength continues up to the point where the
temperature
reaches 200 degrees Celcius. This provides the invented laminate with a
"sealing window" of
160 degrees to 200 decrees Celcius, over which strong seals can be
demonstrated.
In commercial terms, bags formed of the laminate provided to customers for
filling and sealing
can therefore be used with a wider variety of heat sealing apparatus, which
will work as long
as their temperatures land within the sealing window. The seal initiation
temperature of 160
degrees is relatively low for a laminate being sealed through several plies of
paper. The low
seal initiation temperature means that in commercial applications, less energy
will be required
to heat seal at this lower temperature, and the laminate is more tolerant to
any inadequacies in
the customer's heat sealing equipment. The contents of the package are also
exposed to less
heat during filling and sealing, which is a further beneficial feature of this
invention.
Within the scope of the claims set out below, a person of skill in the art may
make adjustments
to the formulations and steps described above. Therefore, while the invention
has been
described with reference to specific embodiments thereof, it will be
appreciated that numerous
variations, modifications, and embodiments are possible, and are to be
regarded as being
within the spirit and scope of the invention.
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