Note: Descriptions are shown in the official language in which they were submitted.
WO 94/07379 PGT/US93/09125
1
IMPROVED OXYGEN SCAVENGING COMPOSITIONS
7P'OR LOW TEMPERATURE U8E
Field of the Invention
The invention generally relates to compositions,
articles and methods for scavenging oxygen in
environments containing oxygen-sensitive products,
particularly food and beverage products. These
materials have high oxygen absorption rates at low
temperatures.
Background of the Invention
It is well known that regulating the exposure of
oxygen-sensitive products to oxygen maintains and
enhances the quality and "shelf-life" of the product.
For instance, by limiting the oxygen exposure of
oxygen sensitive food products in a packaging system,
the quality of the food product is maintained, and
food spoilage is avoided. In addition such packaging
also keeps the product in inventory longer, thereby
reducing costs incurred from waste and having to
restock inventory. In the food packaging industry,
several means for regulating oxygen exposure have
already been developed. These means include modified
atmosphere packaging (MAP) and oxygen barrier film
packaging.
One method currently being used is through
"active packaging," whereby the package for the food
product is modified in some manner to regulate the
food product's exposure to oxygen. See Labuza and
Breene, "Application of 'Active Packaging' for
Improvement of Shelf Life and Nutritional Quality of
Fresh and Extended Shelf-Life Foods," Journal of Food
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rocessina and Preservation, Vol. 13, pp. 1-69 (1989).
The inclusion of oxygen scavengers within the cavity
of the package is one form of active packaging.
Typically, such oxygen scavengers are in the form of t
sachets which contain a composition which scavenges
the oxygen through oxidation reactions. One sachet
contains iron-based compositions which oxidize to
their ferric states. Another type of sachet contains
unsaturated fatty acid salts on a particulate
adsorbent. See U. S. Patent 4,908,151. Yet another
sachet contains metal/polyamide complex. See PCT
Application 90/00578.
However, one disadvantage of sachets is the need
for additional packaging operations to add the sachet
to each package. A further disadvantage arising from
the iron-based sachets is that certain atmospheric
conditions (e.g., high humidity, low COZ level) in the
package are sometimes required in order for scavenging
to occur at an adequate rate.
Another means for regulating the exposure to
oxygen involves incorporating an oxygen scavenger into
the packaging structure itself. Through the
incorporation of the scavenging material in the
package itself rather than by addition of a separate
scavenger structure (e.g., a sachet) to the package, a
more uniform scavenging effect throughout the package
is achieved. This may be especially important where
there is restricted air flow inside the package. In
addition, such incorporation can provide a means of
intercepting and scavenging oxygen as it is passing
through the walls of the package (herein referred to '
as an "active oxygen barrier"), thereby maintaining
the lowest possible oxygen level throughout the
package.
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One attempt to prepare an oxygen-scavenging wall
involves the incorporation of inorganic powders and/or
salts. See European Applications 367,835; 366,254;
367,390; and 370,802. However, incorporation of these
powders and/or salts causes degradation of the wall's
transparency and mechanical properties such as tear
strength. In addition, these compounds can lead to
processing difficulties, especially in the fabrication
of thin layers such as thin films. Even further, the
scavenging rates for walls containing these compounds
appear to be unsuitable for many commercial oxygen-
scavenging applications, e.g. such as those in which
sachets are employed.
The oxygen scavenging systems disclosed in
European Applications 301,719 and 380,319 as well as
disclosed in PCT 90/00578 and 90/00504 illustrate
another attempt to produce an oxygen-scavenging wall.
These patent applications disclose incorporating a
metal catalyst-polyamide oxygen scavenging system into
the package wall. This system has a low rate of
oxygen scavenging which is not generally suitable for
creating an internal oxygen level of less than 0.1~
(starting with air) within a period of four weeks or
less at room temperature, as is typically required for
headspace oxygen scavenging applications. See
Mitsubishi Gas Chemical Company, Inc.'s literature
titled "AGELESS~-A New Age in Food Preservation" (date
unknown).
Further, in regards to the incorporation of the
polyamide/catalyst system into the package wall,
polyamides are typically incompatible with the
thermoplastic polymers, e.g. ethylene-vinyl acetate
copolymers and low density polyethylenes, typically
used to make flexible package walls. Even further,
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when polyamides are used by themselves to make a flexible
package wall, they may result in inappropriately stiff
structures. Polyamides also incur processing difficulties
and higher costs when compared with the costs of
thermoplastic polymers typically used to make flexible
packaging. Even further, they are sometimes difficult to
heat seal. Thus, all of these are factors to consider when
selecting materials for packages, especially flexible
packages and when selecting systems for reducing oxygen
exposure of packaged products.
Materials having commercially usable oxygen
absorption rates and capacities as well as good handling
properties for use in flexible packaging are disclosed in
copending Canadian Application Serial No. 2,062,083, filed
February 18, 1992 (issued March 26, 2002). Methods of
inducing oxygen absorption are disclosed in
U.S. Patent 5,211,875, issued May 18, 1993.
Summary of the Invention
The invention provides a composition which is
effective as an oxygen scavenger and is suitable for
incorporating into layers used in articles containing
oxygen-sensitive products. Further, the invention provides
an oxygen scavenging composition which is compatible with
the materials typically used to prepare such layers. The
invention also provides compositions for scavenging oxygen
which can be used in a flexible layer in a multilayer
article containing oxygen-sensitive products. Further the
invention provides a novel composition suitable for use in
packaging of food and beverage products. Even further, the
invention provides oxygen scavenging articles which have
high oxygen absorption rates (at least 10 cc Oz/m2oday),
preferably greater than 30) at low temperatures (<10'C).
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Such articles would be particularly useful for foods
benefiting from both a reduced oxygen environment and
refrigerated storage.
Most oxygen scavenging compositions have very low
oxygen absorption rates at low temperatures (polyamides,
syndiotactic-1,2-polybutadiene); however, some novel
compositions do not suffer from this limitation. Such
materials include atactic-1,2-polybutadiene, EPDM rubbers,
polyoctenamer, and 1,4-polybutadiene.
The invention is intended for use in coextruded
films, cap liners etc. Of materials that scavenge oxygen,
in general, those most desired for low temperature oxygen
scavenging have a low degree of crystallinity (<30~), and a
1 ow Tg ( < -15 ° C ) .
:15 In one aspect, the invention provides an oxygen
scavenging composition in the form of a film, said
composition comprising: (1) an oxygen scavenging system
consisting essentially of: (a) an ethylenically unsaturated
hydrocarbon polymer having a weight average molecular weight
of at least about 1,000, and a glass transition temperature
(Tg) of lower than -25°C and a crystallinity of less than 30
percent, and (b) from 10 to 10,000 ppm of transition metal
in the form of a transition metal salt; and (2) a
photoinitiator or mixtures of photoinitiators; said
2,5 composition has an oxygen absorption rate of at least 10 cc
OZ per mz per day at a temperature of 4°C and an oxygen
absorption capacity of at least 250 cc oxygen per m2 per mil
thickness.
The above-mentioned aspects and others will be
apparent from the description that follows.
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Description of the Invention
The invention can be used in packaging articles
having several forms. Suitable articles include, but are
not limited to, rigid containers, flexible bags, or
combinations of both. Typical rigid or semi-rigid articles
include plastic, paper or cardboard cartons or bottles such
as juice containers, soft drink containers, thermoformed
trays or cups which have wall thicknesses in the range of
100 to 1000 micrometers.
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Typical flexible bags include those used to package
many food items, and will likely have thicknesses of 5
to 250 micrometers. In addition the walls of such
articles often comprise multiple layers of material.
This invention can be used~in one, some or all of
those layers.
Though it may be preferable from the standpoint
of packaging convenience and/or scavenging
effectiveness to employ the invention as an integral
part of the package wall, the invention can also be
used as a non-integral packaging component, e.g.
coatings, bottle cap liners, adhesive or non-adhesive
sheet inserts, sealants or fibrous mat inserts.
Besides packaging articles for food and beverage,
packaging for other oxygen-sensitive products can
benefit from the invention. Such products would be
pharmaceuticals, oxygen sensitive medical products,
corrodible metals or products such as electronic
devices, etc.
The ethylenically unsaturated hydrocarbon (a) may
be either substituted or unsubstituted. As defined
herein, an unsubstituted ethylenically unsaturated
hydrocarbon is any compound which possesses at least
one aliphatic carbon-carbon double bond and comprises
100% by weight carbon and hydrogen. A substituted
ethylenically unsaturated hydrocarbon is defined
herein as an ethylenically unsaturated hydrocarbon
which possesses at least one aliphatic carbon-carbon
double bond and comprises about 50% - 99% by weight
carbon and hydrogen. Preferable substituted or
unsubstituted ethylenically unsaturated hydrocarbons
are those having two or more ethylenically unsaturated
groups per molecule. More preferably, it is a
polymeric compound having three or more ethylenically
WO 94/07379 ~ ~ PCT/US93/09125
unsaturated groups and a molecular weight equal to or
greater than 1,000 weight average molecular weight.
Preferred examples of unsubstituted ethylenically
unsaturated hydrocarbons include, but are not limited
to, diene polymers such as polyisoprene, (e. g., trans-
polyisoprene), polybutadiene (especially 1,2-
polybutadienes, which are defined as those
polybutadienes possessing greater than or equal to 50~
1,2 microstructure), and copolymers thereof, e.g.
styrene-butadiene. Such hydrocarbons also include
polymeric compounds such as polypentenamer,
polyoctenamer, and other polymers prepared by olefin
metathesis; diene oligomers such as squalene; and
polymers or copolymers derived from dicyclopentadiene,
norbornadiene, 5-ethylidene-2-norbornene, or other
monomers containing more than one carbon-carbon double
bond (conjugated or non-conjugated). These hydro-
carbons further include carotenoids such as ~-carotene.
Preferred substituted ethylenically unsaturated
hydrocarbons include, but are not limited to, those
with oxygen-containing moieties, such as esters,
carboxylic acids, aldehydes, ethers, ketones,
alcohols, peroxides, and/or hydroperoxides. Specific
examples of such hydrocarbons include, but are not
limited to, condensation polymers such as polyesters
derived from monomers containing carbon-carbon double
bonds; unsaturated fatty acids and their partially
polymerized derivatives such as oleic, ricinoleic,
dehydrated ricinoleic, and linoleic acids and
derivatives thereof, e.g. esters. Such hydrocarbons
also include polymers or copolymers derived from
(meth)allyl (meth)acrylates.
The composition used may also comprise a mixture
of two or more of the substituted or unsubstituted
ethylenically unsaturated hydrocarbons described
above.
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As will also be evident, ethylenically
unsaturated hydrocarbons which are appropriate for
forming solid transparent layers at room temperature
are preferred for scavenging oxygen in the packaging
articles described above. For most applications where
transparency is necessary, a layer which allows at
least 50% transmission of visible light is acceptable.
When making transparent oxygen-scavenging layers
according to this invention, 1,2-polybutadiene is
especially preferred as component (a). For instance,
1,2-polybutadiene can exhibit transparency, mechanical
properties and processing characteristics similar to
those of polyethylene. In addition, this polymer is
found to retain its transparency and mechanical
integrity even after most or all of its oxygen
capacity has been consumed, and even when little or no
diluent resin is present. Even further, 1,2-
polybutadiene exhibits a relatively high oxygen
capacity and, once it has begun to scavenge, it
exhibits a relatively high scavenging rate as well.
Most oxygen scavenging compositions have very low
oxygen absorption rates at low temperatures. This is
a disadvantage when oxygen absorption is needed, for
example, under refrigerated conditions. The preferred
oxygen scavengers of this invention have high oxygen
absorption rates (at least 10 cc OZ/(mzday),
preferably greater than 30) at temperatures (<10C).
Of materials that scavenge oxygen, in general, those
most desired for low temperature oxygen scavenging
have a low degree of crystallinity (<30%) and a low
glass transition temperature (Tg <-15C), preferably
<-25, more preferably <-40C. Materials which meet
these criteria include atactic-1,2-polybutadiene
(greater than 50% atactic) EPDM rubbers (typically -58
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to -50C, polyoctenamer (Tg about -75C) and 1,4-
polybutadiene (greater than 50% 1,4 microstructure, Tg
typically -60 to -75C), as well as partially
polymerized unsaturated fatty acids. One of ordinary
skill in the art will recognize that the above-
described polymers can exist in multiphase
compositions. In such a case, it is the Tg of the
phases) containing the ethylenic unsaturation which
need to meet the above-described criteria.
As indicated above, (b) is a transition metal
catalyst. While not being bound by any particular
theory, suitable metal catalysts are those which can
readily interconvert between at least two oxidation
states. See Sheldon, R. A.; Kochi, J. K.; "Metal-
Catalyzed Oxidations of Organic Compounds" Academic
Press, New York 1981.
Preferably, (b) is in the form of a transition
metal salt, with the metal selected from the first,
second or third transition series of the Periodic
Table. Suitable metals include, but are not limited
to, manganese II or III, iron II or III, cobalt II or
III, nickel II or III, copper I or II, rhodium II, III
or IV, and ruthenium. The oxidation state of the
metal when introduced is not necessarily that of the
active form. The metal is preferably iron, nickel or
copper, more preferably manganese and most preferably
cobalt. Suitable counterions for the metal include,
but are not limited to, chloride, acetate, stearate,
palmitate, 2-ethylhexanoate, neodecanoate or
naphthenate. Particularly preferable salts include
cobalt (II) 2-ethylhexanoate and cobalt (II)
neodecanoate. The metal salt may also be an ionomer,
in which case a polymeric counterion is employed.
Such ionomers are well known in the art.
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When making layers, such as film layers, from
compositions wherein (a) is a polymeric compound such
as polybutadiene, polyisoprene or copolymers thereof
or polypentenamer, etc., the layer can be prepared
5 directly from (a). On the other hand, (a) and
transition metal catalyst (b) may be further combined
with one or more polymeric diluents, such as
thermoplastic polymers which are typically used to
form film layers in plastic packaging articles. Even
to in the event (a) is a thermoplastic polymer, e.g.
polybutadiene, it is sometimes suitable to include one
or more additional polymeric diluents. In the
manufacture of certain packaging articles well known
thermosets can also be used as the polymeric diluent.
Selecting combinations of diluent and (a) depends
on the properties desired. Polymers which can be used
as the diluent include, but are not limited to,
polyethylene terephthalate (PET), polyethylene, low or
very low density polyethylene, ultra-low density
polyethylene, linear low density polyethylene,
polypropylene, polyvinyl chloride, polystyrene, and
ethylene copolymers such as ethylene-vinyl acetate,
ethylene-alkyl (meth)acrylates, ethylene-(meth)acrylic
acid and ethylene-(meth)acrylic acid ionomers. In
rigid articles such as beverage containers PET is
often used. See European Application 301,719. Blends
of different diluents may also be used. However, as
indicated above, the selection of the polymeric
diluent largely depends on the article to be
manufactured and the end use. Such selection factors
are well known in the art.
If a diluent polymer such as a thermoplastic is
employed, it should further be selected according to
its compatibility with the ethylenically unsaturated
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hydrocarbon selected for (a). In some instances, the
clarity, cleanliness, effectiveness as an oxygen
scavenger, barrier properties, mechanical properties
and/or texture of the article can be adversely
affected by a blend containing a polymer which is
incompatible with (a). For instance, it has been
found that when (a) is dehydrated castor oil, a less
"greasy" film is prepared from a blend with ethylene-
acrylic acid copolymer than with ethylene vinyl
acetate copolymer.
Further additives may also be included in the
composition to impart properties desired for the
particular article being manufactured. Such additives
include, but are not necessarily limited to, fillers,
pigments, dyestuffs, antioxidants, stabilizers,
processing aids, plasticizers, fire retardants, anti-
fog agents, etc.
The mixing of the components listed above is
preferably accomplished by melt-blending at a
temperature in the range of 50C to 300C. However
alternatives such as the use of a solvent followed by
evaporation may also be employed. The blending may
immediately precede the formation of the finished
article or preform or precede the formation of a
feedstock or masterbatch for later use in the
production of finished packaging articles. When
making film layers or articles from oxygen-scavenging
compositions, (co)extrusion, solvent casting,
injection molding, stretch blow molding, orientation,
thermoforming, extrusion coating, coating and curing,
lamination or combinations thereof would typically
follow the blending.
The amounts of (a), (b), optional polymeric
diluents and additives, vary depending on the article
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to be manufactured and its end use. These amounts
also depend on the desired oxygen scavenging capacity,
the desired oxygen scavenging rate, and the particular
materials selected.
For instance, the primary function of (a) is to
react irreversibly with oxygen during the scavenging
process, and the primary function of (b) is to
facilitate this process. Thus, to a large extent, the
amount of (a) will affect the oxygen capacity of the
composition, i.e., affect the amount of oxygen that
the composition can consume, and the amount of (b)
will affect the rate at which oxygen is consumed. It
also thus follows that the amount of (a) is selected
in accordance with the scavenging capacity needed for
a particular application, and the amount of (b) is
selected in accordance with the scavenging rate
needed. Typically, the amount of (a) may range from 1
to 99%, preferably from 10 to 99%, by weight of the
composition or layer in which both (a) and (b) are
present (herein referred to as the "scavenging
component", e.g., in a coextruded film, the scavenging
component would comprise the particular layers) in
which (a) and (b) are present together). Typically,
the amount of (b) may range from 0.001 to 1% (10 to
10,000 ppm) of the scavenging component, based on the
metal content only (excluding ligands, counterions,
etc.). In the event the amount of (b) is about 0.5%
or less, it follows that (a) and/or the diluent will
comprise substantially all of the composition.
If one or more diluent polymers are used, those
polymers may comprise, in total, as much as 99% by
weight of the scavenging component.
Any further additives employed would normally not
comprise more than 10% of the scavenging component,
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with preferable amounts being less than 5% by weight
of the scavenging component.
As mentioned above, the oxygen scavenging
composition may be used in a flexible or rigid single
layer or multilayer article. The layers comprising
the composition may be in several forms. They may be
in the form of stock films, including "oriented" or
"heat shrinkable" films, which may ultimately be
processed as bags, etc. The layers may also be in the
form of sheet inserts to be placed in a packaging
cavity. In rigid articles such as beverage
containers, thermoformed trays or cups, the layer may
be within the container's walls. Even further, the
layer may also be in the form of a liner placed with
or in the container's lid or cap. The layer may even
be coated or laminated onto any one of the articles
mentioned above.
In multilayered articles, the oxygen scavenging
layer may be included with layers such as, but not
necessarily limited to, "oxygen barriers", i.e. layers
of material having an oxygen transmission rate equal
to or less than 500 cubic centimeters per square meter
(cc/m2) per day per atmosphere at room temperature,
i.e. about 25C. Typical oxygen barriers comprise
polyethylene vinyl alcohol), polyacrylonitrile,
polyvinyl chloride, poly(vinylidene dichloride),
polyethylene terephthalate, silica, and polyamides.
Copolymers of certain materials described above, and
metal foil layers, can also be employed.
The additional layers may also include one or
more layers which are permeable to oxygen. In one
preferred embodiment, especially for flexible
packaging for food, the layers include, in order
starting from the outside of the package to the
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innermost layer of the package, (i) an oxygen barrier
layer, (ii) a layer comprising the invention, i.e. the
scavenging component as defined earlier, and
optionally, (iii) an oxygen permeable layer. Control
of the oxygen barrier property of (i) allows a means
to regulate the scavenging life of the package by
limiting the rate of oxygen entry to the scavenging
component (ii), and thus limiting the rate of
consumption of scavenging capacity. Control of the
oxygen permeability of layer (iii) allows a means to
set an upper limit on the rate of oxygen scavenging
for the overall structure independent of the
composition of the scavenging component (ii). This
can serve the purpose of extending the handling
lifetime of the films in the presence of air prior to
sealing of the package. Furthermore, layer (iii) can
provide a barrier to migration of (a), (b), other
additives, or by-products of scavenging into the
package interior. Even further, layer (iii) may also
improve the heat-sealability, clarity and/or
resistance to blocking of the multilayer film.
The multilayered articles can be prepared using
coextrusion, coating and/or lamination. In addition
to oxygen barrier and oxygen permeable layers, further
layers such as adhesive layers may be adjacent to any
of the layers listed above. Compositions suitable for
adhesive layers include those well known in the art,
such as anhydride functional polyolefins.
To determine the oxygen scavenging capabilities
of the invention, the rate of oxygen scavenging can be
calculated by measuring the time elapsed before the
article depletes a certain amount of oxygen from a
sealed container. For instance, a film comprising the
scavenging component can be placed in an air-tight,
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sealed container of a certain oxygen containing
atmosphere, e.g. air which typically contains 20.6
oxygen by volume. Then, over a period of time,
samples of the atmosphere inside the container are
5 removed to determine the percentage of oxygen
remaining.
When an active oxygen barrier is required, a
useful scavenging rate can be as low as 0.05 cc oxygen
(OZ) per gram of (a) in the scavenging component per
10 day in air at 25C and at 1 atmosphere pressure.
However, the composition of this invention has the
capability of rates equal to or greater than 0.5 cc
oxygen per gram of (a) per day, thus making it
suitable for scavenging oxygen from within a package,
15 as well as suitable for active oxygen barrier
applications. The composition is even capable of more
preferable rates equal to or greater than 5.0 cc OZ per
gram of (a) per day.
Generally, film layers suitable for use as an
active oxygen barrier can have a scavenging rate as
low as 1 cc oxygen per square meter per day when
measured in air at 25C and 1 atmosphere pressure.
However, a layer of this invention is capable of a
scavenging rate greater than 10 cc oxygen per square
meter per day, and preferably has an oxygen scavenging
rate equal to or greater than about 25 cc oxygen per
square meter per day under the same conditions, thus
making it suitable for scavenging oxygen from within a
package, as well as suitable for active oxygen barrier
applications. Under different temperature and
atmospheric conditions, the scavenging rates of the
composition and layers of the invention will be
different. The rates at room temperature and one
atmosphere were measured because they best represent
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the conditions under which the invention will be
exposed in many instances.
In an active oxygen barrier application, it is
preferable that the combination of oxygen barriers and
any oxygen scavenging activity create an overall
oxygen transmission rate of less than about 1.0, more
preferably less than 0.5, and even more preferably
less than .1 cubic centimeters per square meter per
day per atmosphere at 25C. It is also preferable
that the oxygen scavenging capacity is such that this
transmission rate is not exceeded for at least two
days. See European Application 301,719. Another
definition of acceptable oxygen scavenging is derived
from testing actual packages. In actual use, the
scavenging rate requirement will largely depend on the
internal atmosphere of the package, the contents of
the package and the temperature at which it is stored.
In actual use, it has been found that the scavenging
rate of the oxygen scavenging article or package
should be sufficient to establish an internal oxygen
level of less than 0.1~ in less than about four weeks.
See Mitsubishi literature su ra.
In a packaging article according to this
invention, the scavenging rate capability will depend
primarily on the amount and nature of (a) and (b), and
secondarily on the amount and nature of other
additives (e. g., diluent polymer, antioxidant, etc.)
which are present in the scavenging component, as well
as the overall manner in which the package is
fabricated, e.g., surface area/volume ratio.
The oxygen scavenging capacity of an article
comprising the invention can be measured by
determining the amount of oxygen consumed until the
article becomes ineffective as a scavenger. The
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scavenging capacity of the package will depend
primarily on the amount and nature of (a) present in
the scavenging component.
In actual use, the oxygen scavenging capacity
requirement of the article will largely depend on
three parameters of each application:
(1) the quantity of oxygen initially present in
the package,
(2) the rate of oxygen entry into the package
in the absence of the scavenging property,
and
(3) the intended shelf life for the package.
The scavenging capacity of the composition can be
as low as 1 cc oxygen per gram, but is preferably at
least 10 cc oxygen per gram, and more preferably at
least 50 cc oxygen per gram. When such compositions
are in a layer, the layer will preferably have an
oxygen capacity of at least 250 cc oxygen per square
meter per mil thickness and more preferably at least
1200 cc and more preferably 2400 cc oxygen per square
meter per mil thickness.
Other factors may also affect oxygen scavenging
and should be considered when selecting compositions
for the scavenging. These factors include but are not
limited to temperature, relative humidity, and the
atmospheric environment in the package.
El~alaple 1
MASTERBATCB PREPARATION
A masterbatch comprising transition metal
catalyst was prepared by a continuous compounding and
pelletizing operation. In particular, a dry blend of
polyethylene vinylacetate), having a 9~ vinylacetate
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1s
content (EVA-9), and pellets of TEN-CEM~ cobalt
neodecanoate catalyst (22.5% cobalt by weight) from
Mooney Chemicals, was placed in the hopper of a
BRABENDER~ counter-rotating, intermeshing, twin screw
extruder, equipped with a strand die. The amount of
catalyst used was 2.3% by weight, to give 5000 ppm
cobalt in the masterbatch. The extruder was
maintained at 120°C, with the die at 110°C. The
resulting strand was fed through a water bath to cool
and then dried with an air knife. The strand was then
fed into a KILLION~ pelletizer. The resulting
pellets, herein referred to as the "cobalt
masterbatch", were then used in the formulations
illustrated below.
A second masterbatch containing 10% benzophenone
photoinitiator (Aldrich) and 5000 ppm TEN-CEM~ cobalt
was prepared by the same method. The second
masterbatch is herein referred to as "cobalt,
benzophenone masterbatch°°.
Comparison
A multilayer, blown film was prepared by
coextrusion using the cobalt, benzophenone masterbatch
prepared above. The resulting film was a two layer
structure having a thickness of about 3 mils. One
layer comprised polyethylene vinylacetate) about 1-
1.5 mils thick, and the other (scavenging) layer
comprised 90% syndiotactic-1,2-polybutadiene (RB830,
Japan Synthetic Rubber, Tg -15°C, crystallinity 29%)
and 10% cobalt benzophenone masterbatch. Samples of
various sizes (indicated as 891 cm2 or 963 cm2 in this
example), were W irradiated for 5 minutes on an
Amergraph'~ blacklight unit (about 3.2 mW/cm2) and then
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sealed in barrier bags containing 39o cc of air.
Samples were then either stored at room temperature or
were refrigerated (3-4 °c). Gas samples (4 cc) were
withdrawn from the bags through an adhesive rubber
strip, and were analyzed on a Mocon~" model LC-700F
oxygen analyzer. The following data indicate the
drastic effect that refrigerated storage.can have on
oxygen scavenging rate.
Time Room Tem~ R~igerated
(Days) 891 cm 963 cm2
Percent O~ Percent 02
0 20.6 20.6
1 0.364 ---
2 0. 000
3 --- 18.8
14 0.000 ~ 13.3 I
.- T _.
21 ___ 6.9
31 ___ 0.84
35 0.000 0.000
These data give a room temperature scavenging
2o rate of 450 cc OZ/mz/day, and a refrigerated rate of 24
cc o2/m2/day. The ratio of the room temperature rate
to the refrigerated is therefore about 19 to 1.
Example 2
A formulation was prepared in a Brabender mixing
chamber which consisted of EPDM rubber (VistalonT3708,
Exxon) and :10% by weight cobalt benzophenone
masterbatch. Films were pressed and tested as
described above. These data indicate that the
CA 02146026 2003-O1-30
64536-9f30
- 20 -
scavenging rate of some materials is less affected by
temperature.
Time oom Temp. RefricLerated
(days) 110 cm2 108 cm2
Percent O~ Percent OZ,
0 20.6 20.6
1 --- 20.2
3 -_- .18 . 8
4 10.1 ---
1.3 11.8
10 13 --- 10.3
14 0.000 ---
30 --- 4.6
78 --- 0.008
These data give a room temperature scavenging
rate of about 174 cc O2/m2/day, and a refrigerated rate
of about 32 cc OZ/m2/day. This gives a room temperature
to refrigerated rate ratio of 5.4 to 1.
Exammple 3
A formulation was prepared in a Brabender mixing
chamber which consisted of EPDM rubber (Vistalon 3708,
Exxon) with 20% by weight polyoctenamer (Vestenamer TM
6213, Hiils), and 10% by weight cobalt benzophenone
TM
masterbatch. Vestenamer 6213 is < 10% crystalline at
room temperature, and has a T8 = -75 °C. Films were
pressed and tested as described above. These data
indicate a synergistic effect in the scavenging rate
of this blend, as well as less of a temperature
effect.
WO 94/07379 PCT/US93/09125
21
Time Room Temp. Refrigerated
( days ) 10 2 cm2 8 7 cmz
Percent 02 Percent O
0 20.6 20.6
1 7.9 17.9
2 4.08 14.2
5 0.31 9.1
8 0.000 6.4
12 --- 4.55
26 --- 2.78
A masterbatch was prepared as in Example 1,
except that the amount of cobalt was 1.5% by weight
and the amount of benzophenone was 5% by weight.
These data give a room temperature scavenging
rate of about 330 cc OZ/m2/day, and a refrigerated rate
of about 100 cc OZ/m2/day. This gives a room
temperature to refrigerated rate ratio of 3.3 to 1.
~~t~ple 4
A masterbatch was prepared as in Example l,
except that the amount of cobalt was 1.5% by weight
and the amount of benzophenone was 5% by weight. Two
multilayer shrink barrier structures were prepared by
a double pass extrusion coating process. The inner
(heat seal) polyolefin layers were e-beam irradiated
prior the first coating pass, which deposited the
oxygen scavenging layer. A second pass deposited the
poly(vinylidene dichloride) barrier layers and the
outer polyolefin abuse layers. The tubing was then
biaxially oriented about 13 to 1, giving 1.4-1.5 mil
of polyolefin between the interior of the tube, and
the scavenging layer, about 0.55 mil of scavenging
WO 94/07379 PCT/US93/09I25
22
layer, and about 0.2 mil barrier layer in the final
structure. In the first structure (I), the scavenging
layer consisted of 60% EPDM (Vistalon 3708, Exxon),
30% polyoctenamer (Vestenamer 6213, Hiils), and 10%
S
cobalt/benzophenone masterbatch. The second structure
(II) had a scavenging layer consisting of 90%
syndiotactic-1,2-poly(butadiene) (RB830, JSR), and 10%
cobalt/benzophenone masterbatch. The final structures
were fashioned into bags, which were W irradiated 5
minutes on each side as described above. In room
temperature tests, bags were inflated with 600 cc of
air. In refrigerated tests, 150 cc of air was used.
Samples were removed and tested for oxygen
concentration as described above.
T ime I ~, I I ~I
days Room Temp. ~tefria. Room Refria.
6 51 cm2 3 91 cm2 Temp- ~ 17 cm2
% OZ % O2 647 Cm2 % O2
% OZ
0 20.6 20.6 20.6 20.6
1 16.4 18.2 20.3 ---
3 7.90 --- 19.8 20.6
5 --- 4.50 --- ---
g ___ ___ ___ 20.3
g ___ 0.24 ___ ___
14 0.00 --- 11.0 20.3
15 ___ 0.07 ___ ___
21 0.00 --- 7.30 20.3
29 --- --- 4.20 20.3
These data give a room temperature scavenging
rate for structure I of about 136 cc 02/m2~day and a
refrigerated rate of about 53 cc 02/m2 ~ day giving a
WO 94/07379 PGT/US93/09I25
23
room temperature to refrigerated rate ratio of 2.6 to
1. For structure II, these data give a room
r
temperature scavenging rate of about 98.4 cc 02/m2~day
and a refrigerated rate of only 0.4 cc 02/m2~day giving
a
a room temperature to refrigerated rate ratio of 246
to 1. These data further indicate that in oriented,
multilayer structures, the drop in scavenging rate
with temperature for the RB830 based scavenging
systems is even greater.
~snmple 5
A masterbatch was prepared as in Example 4. A
formulation was prepared in a Brabender° mixing chamber
consisting of 70% syndiotactic-1,2-poly(butadiene)
(RB830, JSR), 20% atactic-1,2-poly(butadiene) (Edison
Polymer Innovation Corp., MW = 40,000), and 10%
cobalt/benzophenone masterbatch. Films were pressed
with a surface area of 200 cm2, irradiated for 5
minutes as described above, and sealed in barrier
bags with 600 cc of air for room temperature samples,
and 150 cc air for refrigerated samples. Oxygen was
monitored as described above. These data indicate
that atactic-1,2-poly(butadiene) is useful to improve
the refrigerated scavenging rate.
WO 94/07379 PCT/US93/09125
24
Time Room Temp. Refria.
days $ O2 % ~2 i
0 20.6 20.6
1 17.2 20.0
6 10.1 16.8
19 4.90 8.90
26 3.70 4.90
35 2.94 2.26
43 2.31 1.08
These data indicate a room temperature scavenging
rate of about 128 cc O2/(m2~d), and a refrigerated
scavenging rate of about 34 cc OZ/(m2~d), giving a room
temperature to refrigerated rate ratio of 3.8 to 1.
