U.S. patent application number 09/044043 was filed with the patent office on 2001-08-30 for oxygen-scavenging compositions and articles.
Invention is credited to CHEN, STEPHEN Y., CHIANG, WEILONG L., TSAI, BOH C., VENKATESHWARAN, LAKSHMI N..
Application Number | 20010018480 09/044043 |
Document ID | / |
Family ID | 21930213 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010018480 |
Kind Code |
A1 |
CHIANG, WEILONG L. ; et
al. |
August 30, 2001 |
OXYGEN-SCAVENGING COMPOSITIONS AND ARTICLES
Abstract
Oxygen-scavenging compositions comprising an oxidizable metal
component, an electrolyte component and a solid, non-electrolytic,
acidifying component. When blended with soft, flexible polymeric
resins, these compositions exhibit good oxygen-scavenging
performance with improved oxidation efficiency relative to
compositions containing an oxidizable metal component, an
electrolyte, and an acidifying component combined with a more rigid
thermoplastic resins. Selection of a thermally stable
non-electrolytic, acidifying component is important when melt
compounding the compositions into polymeric resins and particularly
for extrusion coating applications. The compositions can be used
directly as an oxygen absorbent resin melt-fabricated into a wide
variety of oxygen-scavenging packaging articles or as concentrates
in combination with other thermoplastic resins.
Inventors: |
CHIANG, WEILONG L.;
(NAPERVILLE, IL) ; TSAI, BOH C.; (INVERNESS,
IL) ; CHEN, STEPHEN Y.; (WHEATON, IL) ;
VENKATESHWARAN, LAKSHMI N.; (FREEHOLD, NJ) |
Correspondence
Address: |
CIBA SPECIALTY CHEMICALS CORPORATION
PATENT DEPARTMENT
540 WHITE PLAINS RD
P O BOX 2005
TARRYTOWN
NY
10591-9005
US
|
Family ID: |
21930213 |
Appl. No.: |
09/044043 |
Filed: |
March 18, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09044043 |
Mar 18, 1998 |
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08483302 |
Jun 7, 1995 |
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5744056 |
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08483302 |
Jun 7, 1995 |
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08249758 |
May 25, 1994 |
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08249758 |
May 25, 1994 |
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08092722 |
Jul 16, 1993 |
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Current U.S.
Class: |
524/417 ;
428/327 |
Current CPC
Class: |
B01D 53/04 20130101;
B01D 2257/80 20130101; C08J 3/226 20130101; C08J 2323/06 20130101;
C08K 3/30 20130101; C08J 2423/00 20130101; B01D 53/46 20130101;
C08K 3/01 20180101; Y10T 428/254 20150115; B01D 2253/202 20130101;
B22F 1/16 20220101; A23L 3/3436 20130101; B01D 53/02 20130101; C08K
3/32 20130101; B01D 2257/104 20130101 |
Class at
Publication: |
524/417 ;
428/327 |
International
Class: |
C08K 003/32; B32B
005/16 |
Claims
We claim:
1. An oxygen-scavenging composition comprising an oxidizable metal
component, an electrolyte component, and a non-electrolytic
acidifying component that is thermally stable at thermoplastic
resin melt fabrication temperatures.
2. The oxygen-scavenging composition of claim 1 wherein the
non-electrolytic acidifying component is thermally stable above
200.degree. C.
3. The oxygen-scavenging composition of claim 2 wherein the
non-electrolytic acidifying component is selected from the group
consisting of monocalcium phosphate, potassium acid pyrophosphate,
magnesium sulfate, sodium metaphosphate, sodium trimetaphosphate,
sodium hexametaphosphate, aluminum sulfate, aluminum potassium
sulfate and combinations thereof.
4. The oxygen-scavenging composition of claim 1 wherein the
non-electrolytic acidifying component is thermally stable above
270.degree. C.
5. The oxygen-scavenging composition of claim 4 wherein the
non-electrolytic acidifying component is selected from the group
consisting of calcined products of: monocalcium phosphate, sodium
acid pyrophosphate, sodium metaphosphate, sodium trimetaphosphate,
sodium phosphate monobasic, sodium hexametaphosphate, potassium
phosphate monobasic, potassium acid pyrophosphate and combinations
thereof.
6. The oxygen-scavenging composition of claim 4 wherein the
non-electrolytic acidifying component consists of calcined sodium
acid pyrophosphate, calcined monocalcium phosphate and combinations
thereof.
7. The oxygen-scavenging composition of claim 1 comprising about 10
to about 200 parts by weight electrolyte component and
non-electrolytic acidifying component per 100 parts by weight
oxidizable metal.
8. An oxygen-scavenging composition comprising an oxidizable metal
component, an electrolyte component, a non-electrolytic acidifying
component and a polymeric resin with a 1% secant modulus less than
about 25,000 p.s.i. and/or a Shore D Hardness less than about
45.
9. The oxygen-scavenging composition of claim 8 wherein the
polymeric resin is selected from the group consisting of:
metallocene polyethylenes, styrene-rubber block copolymers, very
low density polyethylenes, ultra low density polyethylenes, and
elastomeric homopolypropylene.
10. The oxygen-scavenging composition of claim 9 wherein the
polymeric resin is metallocene polyethylene.
11. The oxygen-scavenging composition of claim 9 wherein the
polymeric resin is a styrene-rubber block copolymer.
12. The oxygen-scavenging composition of claim 11 wherein the
styrene-rubber block copolymer is selected from the group
consisting of styrene ethylene-butylene block copolymer, styrene
butadiene block copolymer, and styrene isobutylene block
copolymer.
13. The oxygen-scavenging composition of claim 8 comprising about 5
to about 150 parts by weight of the oxidizable metal plus
electrolyte plus acidifying components per hundred parts by weight
of the polymeric resin.
14. The oxygen-scavenging composition of claim 8 wherein the
acidifying component is selected from the group consisting of
sodium acid pyrophosphate, monocalcium phosphate, calcined sodium
acid pyrophosphate and calcined monocalcium phosphate.
15. The oxygen-scavenging composition of claim 8 in the form of a
fabricated article.
16. The oxygen-scavenging composition of claim 8 in the form of a
concentrate.
17. The oxygen-scavenging composition of claim 16 further blended
with a second polymeric resin in the form of a fabricated
article.
18. The oxygen-scavenging composition of claim 16 further
comprising at least one polymeric resin having a 1% secant modulus
and Shore D Hardness greater than or equal to the concentrate
resin.
19. An oxygen-scavenging composition comprising iron, sodium
chloride, and a non-electrolytic acidifying component selected from
the group consisting of: sodium acid pyrophosphate, monocalcium
phosphate, calcined sodium acid pyrophosphate or calcined
monocalcium phosphate or mixtures thereof; in a polymeric resin
with a 1% secant modulus less than about 25,000 p.s.i. and/or a
Shore D Hardness less than about 45, wherein the weight ratio of
sodium chloride to the non-electrolytic acidifying component is
about 10/90 to about 90/10 and about 50 to about 200 parts by
weight sodium chloride and non-electrolytic acidifying component
are present per hundred parts by weight iron.
20. An oxygen-scavenging composition comprising an oxidizable metal
component, an electrolyte component, a non-electrolytic acidifying
component in a polymeric resin with a 1% secant modulus less than
about 20,000 p.s.i. and/or a Shore D Hardness less than about 42.
Description
[0001] This is a continuation-in-part of copending application Ser.
No. 08/483,302 filed Jun. 7, 1995, which is a continuation-in-part
of application Ser. No. 08/249,758 filed May 25, 1994, now
abandoned, which is a divisional of application Ser. No. 08/092,722
filed Jul. 16, 1993, now abandoned.
FIELD OF THE INVENTION
[0002] This invention relates to oxygen-scavenging compositions
having utility in packaging and other applications.
BACKGROUND OF THE INVENTION
[0003] Products sensitive to oxygen, particularly foods, beverages
and medicines, deteriorate or spoil in the presence of oxygen. One
approach to reducing these difficulties is to package such products
with packaging materials containing at least one layer of a
so-called "passive" gas barrier film that can act as a physical
barrier to transmission of oxygen but does not react with oxygen.
Films obtained from ethylene vinyl alcohol copolymer (EVOH) or
polyvinylidene dichloride (PVDC) are commonly used for this purpose
due to their excellent oxygen barrier properties. By physically
blocking transmission of oxygen, these barrier films can maintain
or substantially maintain initial oxygen levels within a package.
Because passive barrier films can add cost to a packaging
construction and do not reduce levels of oxygen already present in
the packaging construction, however, there is a need for effective,
lower cost alternatives and improvements.
[0004] An approach to achieving or maintaining a low oxygen
environment inside a package is to use a packet containing an
oxygen absorbent material. The packet, also sometimes referred to
as a pouch or sachet, is placed in the interior of the package
along with the product. Sakamoto et al. discloses oxygen absorbent
packets in Japan Laid Open Patent Application No. 121634/81 (1981).
A typical ingredient used in the oxygen scavenger carried in the
packet is reduced iron powder which can react with oxygen to form
ferrous oxide or ferric oxide, as disclosed in U.S. Pat. No.
4,856,650. Also, it is known to include in the packet, along with
iron, a reaction promoter such as sodium chloride, and a
water-absorbing agent, such as silica gel, as described in U.S.
Pat. No. 4,992,410. Japan Laid Open Patent Application No. 82-24634
(1982) discloses an oxygen absorber composition comprising 100
parts by weight (pbw) iron powder, 2 to 7 pbw ammonium chloride, 8
to 15 pbw aqueous acid solution and 20 to 50 pbw of a slightly
water soluble filler such as activated clay. Japan Laid Open Patent
Application No. 79-158386 (1979) discloses an oxygen arresting
composition comprising a metal, such as iron, copper or zinc, and
optionally, a metal halide such as sodium chloride or zinc chloride
at a level of 0.001 to 100 pbw to 1 pbw of metal and a filler such
as clay at a level of 0.01 to 100 pbw to 1 pbw of metal.
[0005] Although oxygen absorbent or scavenger materials used in
packets can react chemically with oxygen in the package, also
sometimes referred to as "headspace oxygen", they do not prevent
external oxygen from penetrating into the package. Therefore, it is
common for packaging in which such packets are used to include
additional protection such as wrappings of passive barrier films of
the type described above. This adds to product costs. With many
easy-to-prepare foods, another difficulty with oxygen scavenger
packets is that consumers may mistakenly open them and consume
their contents together with the food. Moreover, the extra
manufacturing step of placing a packet into a container can add to
the cost of the product and slow production. Further, oxygen
absorbent packets are not useful with liquid products.
[0006] In view of these disadvantages and limitations, it has been
proposed to incorporate directly into the walls of a packaging
article a so-called "active" oxygen absorber, i.e., one that reacts
with oxygen. Because such a packaging article is formulated to
include a material that reacts with oxygen permeating its walls,
the packaging is said to provide an "active-barrier" as
distinguished from passive barrier films which block transmission
of oxygen but do not react with it. Active-barrier packaging is an
attractive way to protect oxygen-sensitive products because it not
only can prevent oxygen from reaching the product from the outside
but also can absorb oxygen present within a container.
[0007] One approach for obtaining active-barrier packaging is to
incorporate a mixture of an oxidizable metal (e.g., iron) and an
electrolyte (e.g., sodium chloride) into a suitable resin, melt
process the result into monolayer or multilayer sheets or films and
form the resulting oxygen scavenger-containing sheets or films into
rigid or flexible containers or other packaging articles or
components. This type of active-barrier is disclosed in Japan Laid
Open Patent Application No. 56-60642 (1981), directed to an
oxygen-scavenging sheet composed of a thermoplastic resin
containing iron, zinc or copper and a metal halide. Disclosed
resins include polyethylene and polyethylene terephthalate. Sodium
chloride is the preferred metal halide. Component proportions are
such that 1 to 500 parts metal halide are present per 100 parts
resin and 1 to 200 parts metal halide are present per 100 parts
metal. Similarly, U.S. Pat. No. 5,153,038 discloses plastic
multilayer vessels of various layer structures formed from a resin
composition formed by incorporating an oxygen scavenger, and
optionally a water absorbing agent, in a gas barrier resin. The
oxygen scavenger can be a metal powder such as iron, low valence
metal oxides or reducing metal compounds. The oxygen scavenger can
be used in combination with an assistant compound such as a
hydroxide, carbonate, sulfite, thiosulfite, tertiary phosphate,
secondary phosphate, organic acid salt or halide of an alkali metal
or alkaline earth metal. The water absorbing agent can be an
inorganic salt such as sodium chloride, calcium chloride, zinc
chloride, ammonium chloride, ammonium sulfate, sodium sulfate,
magnesium sulfate, disodium hydrogenphosphate, sodium
dihydrogenphosphate, potassium carbonate or sodium nitrate. The
oxygen scavenger can be present at 1 to 1000 weight % based on
weight of the barrier resin. The water absorbing agent can be
present at 1 to 300 weight % based on weight of the barrier
resin.
[0008] One difficulty with scavenger systems incorporating an
oxidizable metal (e.g., iron) and a metal halide (e.g., sodium
chloride) into a thermoplastic layer is the inefficiency of the
oxidation reaction. To obtain sufficient oxygen absorption in
active-barrier packaging, high loadings of scavenger composition
are often used. This typically requires that sheets, films and
other packaging layer or wall structures containing a scavenging
composition be relatively thick. This, in turn, contributes to cost
of the packaging material and may preclude attainment of thin
packaging films having adequate oxygen-scavenging capabilities.
[0009] Another oxygen-scavenging composition, disclosed in U.S.
Pat. No. 4,104,192, comprises a dithionite and at least one
compound having water of crystallization or water of hydration.
Listed among these compounds are various hydrated sodium salts,
including carbonate, sulfate, sulfite and phosphates; sodium
pyrophosphate decahydrate is specifically mentioned. As disclosed
in Table 1, Example 1 of the patent, sodium pyrophosphate
decahydrate was the least effective of the compounds tested. In
addition, use of hydrate containing compounds may not suitable in
oxygen-scavenging resins that require high temperature processing.
Thus, while a variety of approaches to maintaining or reducing
oxygen levels in packaged items have been advanced, there remains a
need for improved oxygen-scavenging compositions and packaging
materials utilizing the same.
[0010] An object of the present invention is to provide improved
oxygen-scavenging compositions and packaging. Another object is to
provide low cost, oxygen-scavenging compositions of improved
efficiency. Another object is to provide oxygen-scavenging
compositions that can be used effectively, even at relatively low
levels, in a wide range of active-barrier packaging films and
sheets, including laminated and coextruded multilayer films and
sheets. Another object is to provide active-barrier packaging
containers that can increase the shelf-life of oxygen-sensitive
products by slowing the passage of external oxygen into the
container, by absorbing oxygen present inside the container or
both. Other objects will be apparent to those skilled in the
art.
SUMMARY OF THE INVENTION
[0011] These objects can be attained according to the invention by
providing oxygen-scavenging compositions comprising at least one
oxidizable metal component, at least one electrolyte component and
at least one solid, non-electrolytic acidifying component.
Optionally, a water-retentive binder and/or polymeric resin can be
included in the composition, if desired. For particularly efficient
oxygen absorption and cost effective formulations, the oxidizable
metal component comprises iron, the electrolyte component comprises
sodium chloride and the solid, non-electrolytic, acidifying
component comprises sodium acid pyrophosphate. In one embodiment,
the invented compositions are provided in the form of a powder or
granules for use in packets. In another embodiment, the
compositions include or are added to a thermoplastic resin and are
used in fabrication of articles by melt processing methods.
Concentrates comprising the compositions or their components and at
least one thermoplastic resin also are provided and offer
advantages in melt processing operations. For the embodiments that
include a thermoplastic resin, thermally stable acidifying
components are preferred and provide a more aesthetically pleasing
film or article. Preferred thermoplastic resins are soft, flexible
resins which enable the oxygen-scavenging composition to absorb
oxygen more efficiently. The invented compositions also are
provided in the form of packaging structures and components
thereof.
[0012] As used herein, the term "electrolyte compound" means a
compound which substantially dissociates in the presence of water
to form positive and negative ions. By "solid, non-electrolytic
acidifying component" or, simply, "acidifying component," is meant
a component comprising a material which is normally solid and
which, in dilute aqueous solution, has a pH less than 7 and
disassociates only slightly into positive and negative ions.
DESCRIPTION OF THE INVENTION
[0013] The invented compositions are oxygen-scavenging compositions
that exhibit improved oxygen-absorption efficiency relative to
known, oxidizable metal-electrolyte systems, such as iron and
sodium chloride, as a result of inclusion in the compositions of a
non-electrolytic, acidifying component. In the presence of
moisture, the combination of the electrolyte and the acidifying
components promotes reactivity of metal with oxygen to a greater
extent than does either alone. Consequently, oxygen absorption
efficiency of the invented compositions is greater than that of
known compositions. For a given weight of oxygen-scavenging
composition, the invented compositions provide greater scavenging
capability than conventional materials, other things being equal.
Alternatively, less of the invented composition is needed to
provide a given level of oxygen-scavenging capability than if
conventional materials are used, other things being equal.
[0014] Advantageously, when incorporated into thermoplastic resins
used for making packaging articles and components, the improved
efficiency of the invented compositions can lead to reductions in
not only oxygen scavenger usage but, also, resin usage because the
lower loading levels permitted by the invented compositions
facilitate downgauging to thinner or lighter weight packaging
structures.
[0015] Another advantage of the invented compositions when used in
fabrication of articles by melt processing is that one or more of
the components of the composition can be provided in the form of a
concentrate in a thermoplastic resin, thereby facilitating
convenient use of the compositions and tailoring of scavenging
compositions to particular product requirements.
[0016] The oxygen-scavenging composition of the present invention
comprises an oxidizable metal component, an electrolyte component,
and a solid, non-electrolytic, acidifying component. Optionally,
the composition also comprises a water-absorbing binder component.
The composition can also comprise a polymeric resin if desired. The
composition can be packaged in an enclosure to form a packet
suitable for placement in the interior of a package. The enclosure
can be made from any suitable material that is permeable to air but
not permeable to the components of the oxygen-scavenging
composition or the product to be packaged to a degree that would
allow intermingling of the oxygen-scavenging composition with
products with which it might be packaged. Suitably, the enclosure
is constructed of paper or air-permeable plastic. The composition
also can be incorporated into polymeric resins for use in making
fabricated articles, for example by melt processing, spraying and
coating techniques.
[0017] Suitable oxidizable metal components comprise at least one
metal or compound thereof capable of being provided in particulate
or finely divided solid form and of reacting with oxygen in the
presence of the other components of the composition. For
compositions to be used in packaging applications, the component
also should be such that, both before and after reaction with
oxygen, it does not adversely affect products to be packaged.
Examples of oxidizable metals include iron, zinc, copper, aluminum,
and tin. Examples of oxidizable metal compounds include ferrous
sulfate, cuprous chloride and other iron (II) and copper (I) salts
as well as tin (II) salts. Mixtures also are suitable. Oxidizable
metal components consisting entirely or mostly of reduced iron
powder are preferred because they are highly effective in terms of
performance, cost and ease of use.
[0018] The invented compositions also comprise an electrolyte
component and a solid, non-electrolytic, acidifying component.
These components function to promote reaction of the oxidizable
metal with oxygen. While either such component promotes oxidation
in the absence of the other, the combination is more effective than
either alone.
[0019] Suitable electrolyte components comprise at least one
material that substantially disassociates into positive and
negative ions in the presence of moisture and promotes reactivity
of the oxidizable metal component with oxygen. Like the oxidizable
metal component, it also should be capable of being provided in
granular or powder form and, for compositions to be used in
packaging, of being used without adversely affecting products to be
packaged. Examples of suitable electrolyte components include
various electrolytic alkali, alkaline earth and transition metal
halides, sulfates, nitrates, carbonates, sulfites and phosphates,
such as sodium chloride, potassium bromide, calcium carbonate,
magnesium sulfate and cupric nitrate. Combinations of such
materials also can be used. A particularly preferred electrolyte
component, both for its cost and performance, is sodium
chloride.
[0020] The acidifying component comprises a solid, non-electrolytic
compound that produces an acidic pH, i.e., less than 7, preferably
less than 5, in dilute aqueous solution. The component
disassociates into positive and negative ions only slightly in
aqueous solution. As with the oxidizable metal and electrolyte
components, for compositions to be used in packaging applications,
the acidifying component should be capable of being used without
adversely affecting products to be packaged. For applications in
which the invented compositions include or are to be used with a
thermoplastic resin, the acidifying component also should have
sufficient thermal stability to withstand melt compounding,
processing, and fabrication into the final article or film. The
term thermal stability as used herein means that the acidifying
component decomposes only insubstantially, if at all, at the normal
processing temperature of the polymer from which the film or
article is fabricated. The acidifier is considered to have
decomposed when it no longer functions for its intended purpose or
the films and articles fabricated from the thermoplastic resin
contain a significant number of bubbles and voids due to the loss
of water or hydrate. For example, some acidifying components have a
thermal decomposition temperature below typical thermoplastic
processing temperatures. Thus, when these acidifying components are
blended into the polymer they thermally decompose into another
material and no longer act as an acidifier. Other acidifying
components will not thermally decompose and continue to function as
acidifiers, but may lose water or hydrate at higher processing
temperatures. This loss of water or hydrate during fabrication will
cause voids or bubbles to appear in the final film or article.
[0021] Suitable materials include various organic and inorganic
acids and their salts. Depending on the end-use application,
particular groups of acidifying components are preferred. For the
embodiment directed to use in a packet or sachet, organic acids and
their salts can be used. For example citric acid, anhydrous citric
acid, citric acid monosodium salt, citric acid disodium salt,
salicylic acid, ascorbic acid, tartaric acid, ammonium sulfate,
ammonium phosphate, nicotinic acid, aluminum ammonium sulfate and
sodium phosphate monobasic. Combinations of such materials may also
be used. These acidifying components are not preferred for use in
resin applications because their thermal decomposition temperature
is below the compounding temperature of common packaging resins.
The thermal decomposition temperature of some common organic acids
are as follows: salicylic acid (98.degree. C.); citric acid
(175.degree. C.); ascorbic acid (193.degree. C.); and tartaric acid
(191.degree. C.).
[0022] When the oxygen-scavenging compositions of the present
invention are compounded into thermoplastic resins such as
polyethylene, using polymer compounding or melt-fabrication
operations, preferred acidifying components are those that are
thermally stable--i.e., do not thermally decompose and do not lose
water or hydrate--at typical film processing temperatures which
range from about 200.degree. C. to about 260.degree. C. Examples
include: potassium acid pyrophosphate, calcium acid pyrophosphate,
monocalcium phosphate, magnesium sulfate, disodium dihydrogen
pyrophosphate, also known as sodium acid pyrophosphate, sodium
metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate,
aluminum sulfate and aluminum potassium sulfate. Combinations of
these materials may also be used. The dehydration temperature of
sodium acid pyrophosphate and monocalcium phosphate is 266.degree.
C. and 235.degree. C. respectively.
[0023] It has been discovered that although these acidifying
components are thermally stable at normal resin processing
temperatures, they are less stable at higher processing
temperatures, such as those used for extrusion coating which range
from about 270.degree. C. to about 340.degree. C. At these higher
processing temperatures some acidifying components liberate water
which creates voids and bubbles in the films and articles
manufactured. These voids and bubbles give the final films and
articles an unpleasant appearance, and if the voids and bubbles are
large enough, may reduce the films ability to scavenge oxygen. In
order to obtain the improved oxygen-scavenging benefits of the
acidifying component without compromising the quality of the film,
dehydrated derivatives of certain acidifying components are used.
Conveniently, dehydration may be accomplished by calcination in a
furnace or kiln. The calcining process drives off the water from
the acidifying component prior to its compounding and use in a high
temperature fabrication operation. In this manner, the water is not
driven off during the extrusion film coating process and the
formation of voids and bubbles is prevented. Preferably, no more
than 500 ppm of water remain in the oxygen-scavenging resin
composition, and more preferably no more than 100 ppm.
[0024] In addition, the water may be driven off during the initial
melt compounding of the oxygen-scavenging composition to form
oxygen-scavenging resin pellets. These pellets are then
subsequently processed or fabricated into the final article or
film. Since the water is driven off during the initial
melt-compounding, and not during fabrication, formation of voids
and bubbles in the film or article is avoided.
[0025] For such high temperature extrusion coating process,
preferred acidifying components are those that are thermally stable
above 270.degree. C. Examples include calcined products of:
monocalcium phosphate, monomagnesium phosphate, magnesium sulfate,
disodium dihydrogen pyrophosphate, also known as sodium acid
pyrophosphate, sodium metaphosphate, sodium trimetaphosphate,
sodium phosphate monobasic, sodium hexametaphosphate, aluminum
sulfate, potassium phosphate monobasic, potassium acid
pyrophosphate, aluminum potassium sulfate and combinations thereof.
Sodium metaphosphate, sodium trimetaphosphate, and sodium
hexametaphosphate are all intermediates of the sodium acid
pyrophosphate calcining process. Extrusion coated packaging films
and articles made from oxygen-scavenging resins containing a metal
compound, an electrolyte and a calcined acidifying component, are
free of voids and bubbles and exhibit improved oxygen absorption
rates and capacity compared to those scavenging resins that contain
no acidifying component. The thermal decomposition temperature of
calcined monocalcium phosphate is 375.degree. C. and calcined
sodium acid pyrophosphate or sodium hexametaphosphate is
550.degree. C.
[0026] Components of the invented oxygen-scavenging compositions
are present in proportions effective to provide oxygen-scavenging
effects. Preferably, at least one part by weight electrolyte
component plus acidifying component is present per hundred parts by
weight oxidizable metal component, with the weight ratio of
electrolyte component to acidifying component ranging from about
99:1 to about 1:99. More preferably, at least about 10 parts
electrolyte plus acidifying components are present per 100 parts
oxidizable metal component to promote efficient usage of the latter
for reaction with oxygen. There is no upper limit on the amount of
electrolyte plus acidifier relative to metal from this standpoint
although little or no gain in oxidation efficiency is seen above
about 200 parts per 100 parts metal and economic and processing
considerations may favor lower levels. In order to achieve an
advantageous combination of oxidation efficiency, low cost and ease
of processing and handling, about 30 to about 150 parts electrolyte
plus acidifying component per 100 parts metal component are most
preferred.
[0027] An optional water-absorbing binder can also be included in
the invented compositions, if desired, to further enhance oxidation
efficiency of the oxidizable metal. The binder can serve to provide
additional moisture which enhances oxidation of the metal in the
presence of the promoter compounds. The binder is dry when it is
added to the oxygen-scavenging composition and absorbs moisture
from the products packages in the final article or during retort.
Water-absorbing binders suitable for use generally include
materials that absorb at least about 5 percent of their own weight
in water and are chemically inert. Examples of suitable binders
include diatomaceous earth, boehmite, kaolin clay, bentonite clay,
acid clay, activated clay, zeolite, molecular sieves, talc,
calcined vermiculite, activated carbon, graphite, carbon black, and
the like. It is also contemplated to utilize organic binders,
examples including various water absorbent polymers as disclosed in
Koyama et al., European Patent Application No. 428,736. Mixtures of
such binders also can be employed. Preferred binders are bentonite
clay, kaolin clay, and silica gel. When used, the water-absorbent
binder preferably is used in an amount of at least about five parts
by weight per hundred parts by weight of the oxidizable metal,
electrolyte and acidifying components. More preferably, about 15 to
about 100 parts of binder per hundred parts metal are present as
lesser amounts may have little beneficial effect while greater
amounts may hinder processing and handling of the overall
compositions without offsetting gain in oxygen-scavenging
performance. When a binder component is used in compositions
compounded into plastics, the binder most preferably is present in
an amount ranging from about 10 to about 50 parts per hundred parts
metal to enhance oxidation efficiency at loading levels low enough
to ensure ease of processing.
[0028] A particularly preferred oxygen-scavenging composition
according to the invention comprises iron powder as the metal
component, sodium chloride as the electrolyte and sodium acid
pyrophosphate or monocalcium phosphate as the acidifying component,
with about 10 to about 150 parts by weight sodium chloride plus
sodium acid pyrophosphate or monocalcium phosphate being present
per hundred parts by weight iron and the weight ratio of sodium
chloride to sodium acid pyrophosphate or monocalcium phosphate
being about 10:90 to about 90:10. Optionally, up to about 100 parts
by weight water absorbing binder per hundred parts by weight of the
other components also are present. Most preferably, the composition
comprises iron powder, about 5 to about 100 parts sodium chloride
and about 5 to about 70 parts sodium acid pyrophosphate per hundred
parts iron and up to about 50 parts binder per hundred parts of the
other components.
[0029] According to another aspect of this invention, there is
provided an oxygen scavenger resin composition comprising at least
one plastic resin and the above-described oxygen-scavenging
composition, with or without the water-absorbent binder component.
The selection of the acidifying component will depend on the melt
fabrication temperature of the plastic resin. Sodium acid
pyrophosphate and monocalcium phosphate are thermally stable above
200.degree. C., while calcined products of sodium acid
pyrophosphate and calcined products of monocalcium phosphate are
stable above 270.degree. C.
[0030] Any suitable polymeric resin into which an effective amount
of the oxygen-scavenging composition of this invention can be
incorporated and that can be formed into a laminar configuration,
such as film, sheet or a wall structure, can be used as the plastic
resin in the compositions according to this aspect of the
invention. Thermoplastic and thermoset resins can be used. Examples
of thermoplastic polymers include polyamides, such as nylon 6,
nylon 66 and nylon 612, linear polyesters, such as polyethylene
terephthalate, polybutylene terephthalate and polyethylene
naphthalate, branched polyesters, polystyrenes, styrene block
copolymers such as those comprising styrene blocks and rubber
blocks comprising ethylene, propylene, isoprene, butadiene,
butylene or isobutylene polymer blocks or combinations thereof,
polycarbonate, polymers of unsubstituted, substituted or
functionalized olefins such as polyvinyl chloride, polyvinylidene
dichloride, polyacrylamide, polyacrylonitrile, polyvinyl acetate,
polyacrylic acid, polyvinyl methyl ether, ethylene vinyl acetate
copolymer, ethylene methyl acrylate copolymer, polyethylenes
(including, high, low, and linear low density polyethylenes and
so-called metallocene polyethylenes), polypropylene,
ethylene-propylene copolymers, poly(1-hexene),
poly(4-methyl-1-pentene), poly(1-butene), poly(3-methyl-1-butene),
poly(3-phenyl-1-propene) and poly(vinylcyclohexane). Homopolymers
and copolymers are suitable as are polymer blends containing one or
more of such materials. Thermosetting resins, such as epoxies,
oleoresins, unsaturated polyester resins and phenolics also are
suitable.
[0031] Preferred polymers are thermoplastic resins having oxygen
permeation coefficients greater than about 2.times.10.sup.-12
cc-cm/cm.sup.2-sec-cm Hg as measured at a temperature of 20.degree.
C. and a relative humidity of 0% because such resins are relatively
inexpensive, easily formed into packaging structures and, when used
with the invented oxygen-scavenging compositions, can provide a
high degree of active barrier protection to oxygen-sensitive
products. Examples of these include polyethylene terephthalate and
polyalpha-olefin resins such as high, low and linear low density
polyethylene and polypropylene. Even relatively low levels of
oxygen-scavenging composition, e.g., about 5 to about 15 parts per
hundred parts resin, can provide a high degree of oxygen barrier
protection to such resins. Among these preferred resins,
permeability to oxygen increases in the order polyethylene
terephthalate ("PET"), polypropylene ("PP"), high density
polyethylene ("HDPE"), linear low density polyethylene ("LLDPE"),
and low density polyethylene ("LDPE"), other things being equal.
Accordingly, for such polymeric resins, oxygen scavenger loadings
for achieving a given level of oxygen barrier effectiveness
increase in like order, other things being equal.
[0032] According to a preferred embodiment of the invention, the
thermoplastic resin comprises a soft resin with a flexible
molecular chain. Such soft resins with the flexibility of rubber,
such as polyalpha-olefins polymerized using metallocene catalysts
(also known as plastomers) and thermoplastic elastomers, show
unexpectedly superior oxygen absorption efficiency when compared to
more rigid thermoplastic resins, all other conditions being equal.
It is believed that the flexible molecular structure of soft resins
facilitates the migration and intimate contact of the
oxygen-scavenging components. This close contact promotes the
oxidation reaction which leads to unexpectedly higher oxygen
absorption efficiency (cc O.sub.2/gm Fe) compared to harder and
more rigid polymeric resins. The softness and flexibility of a
resin can be determined by examining several properties including
its 1% secant modulus (ASTM D 882-3) and its Shore Hardness (ASTM D
2240). Measuring either of the properties will provide a good
indication of whether a resin will exhibit improved oxygen
efficiency. Typically, improved oxygen absorption efficiency can be
found in resins with a 1% secant modulus less than 25,000 p.s.i.
and/or a Shore D Hardness less than 45. Preferred resins have a 1%
secant modulus less than about 20,000 p.s.i. and/or a Shore D
Hardness less than about 42. Sample carrier resins, their secant
modulus and Shore Hardness are listed in Example 11, Table II.
[0033] Preferred, soft, flexible resins according to this
embodiment of the invention are polyalpha-olefins polymerized using
metallocene catalysts such as metallocene polyethylenes ("mPE") and
metallocene polypropylenes ("mPP"). mPEs are copolymers of ethylene
with at least one higher alpha-olefin of about 4-8 carbons such as
butene, hexene and octene with comonomer levels from about 1-25%.
mPEs also have a narrow molecular weight
distribution--(MW).sub.W/(MW).sub.n--of about 2 to 5. Specific
examples include Dow Affinity resins, Dow/Dupont Engage resins and
Exxon Exact resins. These mPEs are described in the literature as
linear, short chain branched polymer chains with high comonomer
content, narrow comonomer distribution and uniform, narrow
molecular weight distribution. The 1% secant modulus range for mPEs
is about 2,500 to about 9,000 p.s.i., and the Shore D Hardness from
about 29 to about 41. By contrast, the conventional multi-site
Zieglar-Natta-catalyzed polyolefins (e.g. "LLDPE") are linear with
broad comonomer distribution and broader molecular weight
distribution of about 6 to 8, and traditional radical-initiated
polyolefins (e.g. "LDPE") contain no comonomers, are highly
branched with long and short chain branches, and have a broad
molecular weight distribution of about 10 to 14. Conventional LDPE
resins have a 1% secant modulus from about 25,000 p.s.i. to about
38,000 p.s.i. and a Shore D Hardness from about 45-55. LLDPE resins
have a 1% secant modulus from about 30,000 to about 75,000 and a
Shore D Hardness from about 45-55. Polypropylene has a 1% secant
modulus range from about 160,000 to about 230,000 p.s.i. and a
Shore D Hardness from about 65 to about 85. As carrier resins for
the oxygen-scavenging component, mPEs have shown superior oxygen
absorption rates and capacities relative to oxygen scavenger
carrier resins comprising conventional LDPE, LLDPE and PP.
[0034] Another group of preferred, soft, flexible resins that show
improved oxygen absorption efficiency are styrene block copolymers
such as those comprising styrene blocks and rubber blocks of
ethylene, propylene, isoprene, butadiene, butylene or isobutylene
or combinations thereof. ("styrene-rubber block copolymers").
Styrene-rubber block copolymers consist of block segments of
polymerized styrene monomer units and rubber monomer units such as
butadiene, isoprene and ethylene-butylene. The styrene/rubber ratio
in the copolymers can vary widely, but typically from 15-40 parts
styrene blocks to 60-85 parts rubber blocks. The rubber units give
these block copolymers their flexibility and elasticity. The 1%
secant modulus of these block copolymers is from about 150 to about
2000 p.s.i. Their Shore D Hardness is from about 5 to about 15. As
suggested above, this flexibility and softness facilitates
migration and intimate contact between the oxygen-scavenging
components--i.e., the oxidizable metal component, electrolyte
component and solid, non-electrolytic, acidifying component--which
promotes the efficient oxidation of the metal component.
[0035] A specific example of such block copolymers are Shell's G
and D series Kraton.RTM. rubber polymers which are soft, flexible,
elastic, thermoplastics. Shell's G series Kraton.RTM. consists of
styrene-ethylene-butylene-styrene block copolymers ("SEBS"), and
the D series consists of styrene-butadiene-styrene block copolymer
("SBS"). Another example is a styrene-isobutylene-styrene block
copolymer ("SIBS").
[0036] In addition to metallocene-catalyzed polyolefins and
styrene-rubber block copolymers, soft, flexible resins such as very
low density polyethylene ("VLDPE"), ultra low density polyethylene
("ULDPE"), elastomeric forms of polypropylene such as elastomeric
homopolypropylene ("EHPP"), and elastomeric copolymer polypropylene
can also be used as the carrier resin to enhance oxygen absorption
efficiency. ULDPE and VLDPE have a 1% secant modulus from about
18,000 to about 20,000 p.s.i. and a Shore D Hardness of about 42.
Elastomeric forms of PP have a Shore D of about 20 and 1% secant
modulus of about 1,800 p.s.i. Selection of the polymeric resin will
depend upon several factors including the end-use packaging
application, the level of oxygen absorption required, and whether
or not the oxygen-scavenging composition in the polymeric resin
will be further blended with the same or distinct resin.
[0037] In selecting a thermoplastic resin for use or compounding
with the oxygen-scavenging composition of the invention, the
presence of residual antioxidant compounds in the resin can be
detrimental to oxygen absorption effectiveness. Phenol-type
antioxidants and phosphite-type antioxidants are commonly used by
polymer manufacturers for the purpose of enhancing thermal
stability of resins and fabricated products obtained therefrom.
Specific examples of these residual antioxidant compounds include
materials such as butylated hydroxytoluene,
tetrakis(methylene(3,5-di-t-butyl-4-hydroxyhydro-cinnamate)methane
and triisooctyl phosphite. Such antioxidants are not to be confused
with the oxygen scavenger components utilized in the present
invention. Generally, oxygen absorption of the scavenger
compositions of the present invention is improved as the level of
residual antioxidant compounds is reduced. Thus, commercially
available resins containing low levels of phenol-type or
phosphite-type antioxidants, preferably less than about 1600 ppm,
and most preferably less than about 800 ppm, by weight of the
resin, are preferred (although not required) for use in the present
invention. Examples are Dow Chemical Dowlex 2032 linear low density
polyethylene (LLDPE); Union Carbide GRSN 7047 LLDPE; Goodyear PET
"Traytuf" 9506; and Eastman PETG 6763. Commercially available mPEs
such as Exxon Exact, Dow Affinity, and Dow/Dupont Engage have
acceptable levels of antioxidants and styrene-rubber block
copolymers such as Kraton.RTM. have suitable levels as well.
Measurement of the amount of residual antioxidant can be performed
using high pressure liquid chromatography.
[0038] When used in combination with resins, the oxidizable metal,
electrolyte and acidifying components of the invented
oxygen-scavenging compositions, and any optional water-absorbent
binder that may be used, are used in particulate or powder form.
Particle sizes of 50 mesh or smaller are preferred to facilitate
melt-processing of oxygen scavenger thermoplastic resin
formulations. For use with thermoset resins for formation of
coatings, particle sizes smaller than the thickness of the final
coating are employed. The oxygen scavenger can be used directly in
powder or particulate form, or it can be processed, for example by
melt compounding or compaction-sintering, into pellets to
facilitate further handling and use.
[0039] Processing aids may also be used when the oxygen scavenging
components are combined with resins. For example, flouropolymers
such as Dynamar FX-9613 and FX-5920A available from Dyneon can be
added to the melt compounding process to reduce the melt fracture
of the polymer matrix and possibly reduce the die pressure.
Preferably, 50 ppm-5000 ppm of flouropolymer may be added, more
preferably 200 ppm-2000 ppm, and most preferably 500 ppm-1000 ppm
of flouropolymer may be added to the oxygen-scavenging resin
comprised of oxidizable metal, electrolyte, acidifying component,
and the carrier resin of the present invention.
[0040] The mixture of oxidizable metal component, electrolyte
component, acidifying component and optional water-absorbent binder
can be added directly to a thermoplastic polymer compounding or
melt-fabrication operation, such as in the extrusion section
thereof, after which the molten mixture can be advanced directly to
a film or sheet extrusion or coextrusion line to obtain monolayer
or multilayer film or sheet in which the amount of
oxygen-scavenging composition is determined by the proportions in
which the composition and resin are combined in the resin feed
section of the extrusion-fabrication line. Alternatively, the
mixture of oxidizable metal component, electrolyte component,
acidifying component and optional binder can be compounded into
masterbatch concentrate pellets, which can be further let down into
packaging resins for further processing into extruded film or
sheet, or injection molded articles such as tubs, bottles, cups,
trays and the like. Soft, flexible resins with a 1% Secant modulus
less than 25,000 p.s.i. and a Shore D Hardness less than 45 are
more preferred carrier resins for the concentrate pellets because
they promote greater oxygen absorption efficiency when used in
combination with more rigid packaging resins. Soft, flexible resins
with a 1% Secant modulus less than about 20,000 p.s.i. and a Shore
D Hardness less than about 42 are particularly preferred. Again,
examples of such resins include mPEs, styrene-rubber block
copolymers, VLDPE, ULDPE, and elastomeric forms of polypropylene.
Particularly preferred carrier resins are styrene-butadiene block
copolymers and metallocene polyethylenes.
[0041] The degree of mixing of oxidizable metal, electrolyte and
acidifying components and, if used, optional binder component has
been found to affect oxygen absorption performance of the
oxygen-scavenging compositions, with better mixing leading to
better performance. Mixing effects are most noticeable at low
electrolyte plus acidifying components to oxidizable metal
component ratios and at very low and very high acidifying component
to electrolyte component ratios. Below about 10 parts by weight
electrolyte plus acidifying components per hundred parts by weight
metal component, or when the weight ratio of either the electrolyte
or acidifying component to the other is less than about 10:90, the
oxygen scavenger components are preferably mixed by aqueous slurry
mixing followed by oven drying and grinding into fine particles.
Below these ratios, mixing by techniques suitable at higher ratios,
such as by high-intensity powder mixing, as in a Henschel mixer or
a Waring powder blender, or by lower intensity mixing techniques,
as in a container on a roller or tumbler, may lead to variability
in oxygen uptake, particularly when the compositions are
incorporated into thermoplastic resins and used in melt processing
operations. Other things being equal, it has been found that
oxygen-scavenging compositions prepared by slurry mixing have the
highest oxygen absorption efficiency or performance, followed in
order by compositions prepared using high intensity solids mixers
and roller/tumbler mixing techniques. However, when mixing a
composition containing a calcined acidifying component for use in a
high temperature application, non-slurry mixing techniques are
preferred.
[0042] Other factors that may affect oxygen absorption performance
of the invented oxygen-scavenging compositions include surface area
of articles incorporating the compositions, with greater surface
area normally providing better oxygen absorption performance. The
amount of residual moisture in the water-absorbent binder, if used,
also can affect performance with more moisture in the binder
leading to better oxygen absorption performance. However, there are
practical limits on the amount of moisture that should be present
in the binder because too much can cause premature activation of
the oxygen scavenger composition as well as processing
difficulties. The moisture can also cause poor aesthetics, such as
bubbles and voids, in fabricated products. Especially those
fabricated at high temperatures.
[0043] When incorporated into thermoplastic resins and used for
fabrication of articles by melt processing techniques, the nature
of the resin also can have a significant effect. Thus when the
invented oxygen-scavenging compositions are used with amorphous
and/or oxygen permeable polymers such as polyolefins or amorphous
polyethylene terephthalate, higher oxygen absorption is seen than
when the compositions are used with crystalline and/or oxygen
barrier polymers such as crystalline polyethylene terephthalate and
EVOH. Superior oxygen absorption efficiency is observed when the
invented compositions are used with soft, flexible resins such as
metallocene catalyzed polyolefins and styrene-rubber block
copolymers.
[0044] When used with thermoplastic resins, the oxygen-scavenging
compositions can be incorporated directly into the resin in amounts
effective to provide the desired level of oxygen-scavenging
ability. When so-used, preferred oxygen scavenger levels will vary
depending on the choice of resin, configuration of the article to
be fabricated from the resin and oxygen-scavenging capability
needed in the article. Use of resins with low inherent viscosity,
e.g., low molecular weight resins, normally permits higher loadings
of scavenger composition without loss of processability.
Conversely, lesser amounts of oxygen scavenger may facilitate use
of polymeric materials having higher viscosities. Preferably, at
least about 2 parts by weight oxygen-scavenging composition are
used per 100 parts by weight resin. Loading levels above about 200
parts per hundred parts resin generally do not lead to gains in
oxygen absorption and may interfere with processing and adversely
affect other product properties. More preferably, loading levels of
about 5 to about 150 parts per hundred are used to obtain good
scavenging performance while maintaining processability. Loading
levels of about 5 to about 15 parts per hundred are particularly
preferred for fabrication of thin films and sheets. For films and
sheets made directly from resin concentrates, loading levels of
about 5 to about 100 parts oxygen-scavenging composition per
hundred parts resin are preferred, 5 to 50 parts most
preferred.
[0045] Preferred oxygen scavenger resin compositions for
fabrication of packaging articles comprise at least one
thermoplastic resin and about 5 to about 150 parts by weight
oxygen-scavenging composition per hundred parts by weight resin,
more preferably 5 to about 50 parts, with the oxygen-scavenging
composition comprising iron powder, sodium chloride and sodium acid
pyrophosphate. About 10 to about 200 parts by weight sodium
chloride and sodium acid pyrophosphate per hundred parts by weight
iron are present in the scavenging composition, more preferably
about 30 to about 130 parts and the weight ratio of sodium chloride
to sodium acid pyrophosphate is about 10:90 to about 90:10. Up to
about 50 parts by weight water-absorbent binder per hundred parts
by weight of resin and oxygen scavenger also can be included.
Especially preferred compositions of this type comprise
polypropylene, high, low or linear low density polyethylene or
polyethylene terephthalate as the resin, about 5 to about 30 parts
by weight oxygen scavenger per hundred parts by weight resin, about
5 to about 100 parts by weight sodium chloride and about 5 to about
70 parts by weight sodium acid pyrophosphate per hundred parts by
weight iron and up to about 50 parts by weight binder per hundred
parts by weight iron plus sodium chloride plus sodium acid
pyrophosphate.
[0046] Another preferred composition for packaging articles
comprises a soft, flexible resin such as mPE or a styrene-rubber
block copolymer, and about 5 to about 150 parts by weight oxygen
scavenger per hundred parts by weight resin, with the
oxygen-scavenging composition comprising iron powder, sodium
chloride and sodium acid pyrophosphate or monocalcium phosphate.
The oxygen scavenger is about 5 to about 150 parts by weight sodium
chloride and about 5 to about 100 parts by weight sodium acid
pyrophosphate or monocalcium phosphate per hundred parts by weight
iron.
[0047] When packaging articles are manufactured using a high
temperature fabrication process, use of calcined sodium acid
pyrophosphate or calcined monocalcium phosphate as acidifying
components are preferred to prevent the formation of bubbles and
voids in the fabricated article.
[0048] While the oxygen-scavenging composition and resin can be
used in a non-concentrated form for direct fabrication of
scavenging sheets or films (i.e., without further resin dilution),
it also is beneficial to use the oxygen-scavenging composition and
resin in the form of a concentrate. When so-used, the ability to
produce a concentrate with low materials cost weighs in favor of
relatively high loadings of scavenger that will still permit
successful melt compounding, such as by extrusion pelletization.
Thus concentrate compositions according to the invention preferably
contain at least about 10 parts by weight oxygen-scavenging
composition per hundred parts by weight resin and more preferably
about 30 to about 150 parts per hundred. Suitable resins for such
oxygen-scavenging concentrate compositions include any of the
thermoplastic polymer resins described herein. Low melt viscosity
resins facilitate use of high scavenger loadings and typically are
used in small enough amounts in melt fabrication of finished
articles that the typically lower molecular weight of the
concentrate resin does not adversely affect final product
properties. Preferred carrier resins are polypropylene, high
density, low density and linear low density polyethylenes, and
polyethylene terephthalate. Preferred among those are
polypropylenes having melt flow rates (ASTM D1238) of about 1 to
about 40 g/10 min, polyethylenes having melt indices (ASTM D1238)
of about 1 to about 20 g/10 min and polyethylene terephthalates
having inherent viscosities (ASTM D2857) of about 0.6 to about 1 in
phenol/trichloroethane.
[0049] A most preferred carrier resin for the concentrate
compositions are the soft, flexible resins as indicated by a Shore
D Hardness less than 45 and/or a secant modulus less than 25,000
p.s.i. Particularly preferred are those resins with a 1% Secant
modulus less than about 20,000 p.s.i. and a Shore D Hardness less
than about 42. These concentrate resins preferably contain about 30
to about 150 parts by weight oxygen-scavenging component per
hundred parts by weight resin and most preferably about 75 to about
125 parts by weight oxygen-scavenging composition per 100 parts by
weight resin. The oxygen-scavenging composition is preferably about
25 to 125 parts by weight sodium chloride and about 25 to 75 parts
by weight acidifying component selected from sodium acid
pyrophosphate, monocalcium phosphate, calcined sodium acid
pyrophosphate or calcined monocalcium phosphate per 100 parts by
weight iron. For fabrication of thin films from these concentrates,
loading levels of about 5-150 parts oxygen-scavenging composition
to 100 parts resin is preferred, and about 10-100 parts
oxygen-scavenging composition to hundred parts resin is more
preferred, and 10-50 parts oxygen-scavenging composition to hundred
parts resin is most preferred. Concentrates and films produced in
accordance with the above, exhibit superior oxygen absorption
capabilities.
[0050] When concentrates are used to fabricate oxygen-scavenging
films and packaging articles, such concentrates can be used alone
or in combination with a thermoplastic resin that is either the
same or distinct from the carrier resin. Thus, the concentrate can
be comprised of a soft flexible resin and the film resin selected
from polypropylene, polyethylene, polyethylene terephthalate or any
other suitable resin depending on the final packaging structure.
Likewise, both the carrier resin and the film or packaging resin
can be comprised of the same or distinct soft, flexible resin or
the same or distinct more rigid thermoplastic resin. Preferably, at
least the carrier resin is of the soft, flexible type to achieve
superior oxygen absorption capabilities.
[0051] It also is contemplated to utilize various components of the
oxygen-scavenging composition or combinations of such components to
form two or more concentrates that can be combined with a
thermoplastic resin and fabricated into an oxygen-scavenging
product. An advantage of using two or more concentrates is that the
electrolyte and acidifying components can be isolated from the
oxidizable metal until preparation of finished articles, thereby
preserving full or essentially full oxygen-scavenging capability
until actual use and permitting lower scavenger loadings than would
otherwise be required. In addition, separate concentrates permit
more facile preparation of differing concentrations of the
electrolyte and acidifying components and/or water absorbent binder
with the oxidizable metal and also enable fabricators to
conveniently formulate a wide range of melt-processible resin
compositions in which oxygen-scavenging ability can be tailored to
specific end use requirements. Preferred components or combinations
of components for use in separate concentrates are (1) acidifying
component; (2) combinations of oxidizable metal component with
water absorbing binder component; and (3) combinations of
electrolyte and acidifying components.
[0052] A particularly preferred component concentrate is a
composition comprising an acidifying component such as sodium acid
pyrophosphate, monocalcium phosphate, calcined sodium acid
pyrophosphate or calcined monocalcium phosphate and a thermoplastic
resin. Such a concentrate can be added in desired amounts in melt
fabrication operations utilizing thermoplastic resin that already
contains, or to which will be added, other scavenging components,
such as an oxidizable metal or combination thereof with an
electrolyte, to provide enhanced oxygen-scavenging capability.
Especially preferred are concentrates containing about 10 to about
150 parts by weight sodium acid pyrophosphate, calcined sodium acid
pyrophosphate, or calcined monocalcium phosphate per hundred parts
by weight resin. The concentrate resin may be selected from any
number of resins such as with polypropylene, polyethylene and
polyethylene terephthalate, with soft flexible resins being the
most preferred with mPEs and styrene-rubber block copolymers giving
the best results.
[0053] Polymeric resins that can be used for incorporating the
oxygen-scavenging compositions into internal coatings of cans via
spray coating and the like are typically thermoset resins such as
epoxy, oleoresin, unsaturated polyester resins or phenolic based
materials.
[0054] This invention also provides articles of manufacture
comprising at least one melt-fabricated layer incorporating the
oxygen-scavenging compositions as described above. Because of the
improved oxidation efficiency afforded by the invented
oxygen-scavenging compositions, the scavenger-containing layer can
contain relatively low levels of the scavenger. The articles of the
present invention are well suited for use in flexible or rigid
packaging structures. In the case of rigid sheet packaging
according to the invention, the thickness of the oxygen-scavenging
layer is preferably not greater than about 100 mils, and is most
preferably in the range of about 10 to about 50 mils. In the case
of flexible film packaging according to the invention, the
thickness of the oxygen scavenger layer is preferably not greater
than about 10 mils and, most preferably, about 0.5 to about 8 mils.
As used herein, the term "mils" is used for its common meaning,
i.e., one-thousandth of an inch. Packaging structures and
fabricated articles according to the invention can be in the form
of films or sheets, both rigid and flexible, as well as container
or vessel walls and liners as in trays, cups, bowls, bottles, bags,
pouches, boxes, films, cap liners, can coatings and other packaging
constructions. Both monolayer and multilayer structures are
contemplated.
[0055] The oxygen-scavenging composition and resin of the present
invention afford active-barrier properties in articles fabricated
therefrom and can be melt processed by any suitable fabrication
technique into packaging walls and articles having excellent oxygen
barrier properties without the need to include layers of costly gas
barrier films such as those based on EVOH, PVDC, metallized
polyolefin or polyester, aluminum foil, silica coated polyolefin
and polyester, etc. The oxygen scavenger articles of the present
invention also provide the additional benefit of improved
recyclability. Scrap or reclaim from the oxygen-scavenging resin
can be easily recycled back into plastic products without adverse
effects. In contrast, recycle of EVOH or PVDC gas barrier films may
cause deterioration in product quality due to polymer phase
separation and gelation occurring between the gas barrier resin and
other resins making up the product. Nevertheless, it also is
contemplated to provide articles, particularly for packaging
applications, with both active and passive oxygen barrier
properties through use of one or more passive gas barrier layers in
articles containing one or more active barrier layers according to
the invention. Thus, for some applications, such as packaging for
food for institutional use and others calling for long shelf-life,
an oxygen-scavenging layer according to the present invention can
be used in conjunction with a passive gas barrier layer or film
such as those based on EVOH, PVDC, metallized polyolefins or
aluminum foil.
[0056] The present invention is also directed to a packaging wall
containing at least one layer comprising the oxygen-scavenging
composition and resin described above. It should be understood that
any packaging article or structure intended to completely enclose a
product will be deemed to have a "packaging wall," as that term is
used herein, if the packaging article comprises a wall, or portion
thereof, that is, or is intended to be, interposed between a
packaged product and the atmosphere outside of the package and such
wall or portion thereof comprises at least one layer incorporating
the oxygen-scavenging composition of the present invention. Thus,
bowls, bags, liners, trays, cups, cartons, pouches, boxes, bottles
and other vessels or containers which are intended to be sealed
after being filled with a given product are covered by the term
"packaging wall" if the oxygen-scavenging composition of the
invention is present in any wall of such vessel (or portion of such
wall) which is interposed between the packaged product and the
outside environment when the vessel is closed or sealed. One
example is where the oxygen-scavenging composition of the invention
is fabricated into, or between, one or more continuous
thermoplastic layers enclosing or substantially enclosing a
product. Another example of a packaging wall according to the
invention is a monolayer or multilayer film or sheet containing the
present oxygen-scavenging composition used as a cap liner in a
beverage bottle (i.e., for beer, wine, fruit juices, etc.) or as a
wrapping material.
[0057] An attractive active-barrier layer is generally understood
as one in which the kinetics of the oxidation reaction are fast
enough, and the layer is thick enough, that most of the oxygen
permeating into the layer reacts without allowing a substantial
amount of the oxygen to transmit through the layer. Moreover, it is
important that this "steady state" condition exist for a period of
time appropriate to end use requirements before the scavenger layer
is spent. The present invention affords this steady state, plus
excellent scavenger longevity, in economically attractive layer
thicknesses, for example, less than about 100 mils in the case of
sheets for rigid packaging, and less than about 10 mils in the case
of flexible films. For rigid sheet packaging according to the
present invention, an attractive scavenger layer can be provided in
the range of about 10 to about 30 mils, while for flexible film
packaging, layer thicknesses of about 0.5 to about 8 mils are
attractive. Such layers can function efficiently with as little as
about 2 to about 10 weight % oxygen scavenger composition based on
weight of the scavenger layer.
[0058] In fabrication of packaging structures according to the
invention, it is important to note that the oxygen-scavenging resin
composition of the invention is substantially inactive with respect
to chemical reaction with oxygen so long as the water activity of
the composition is less than about 0.2-0.3. In contrast, the
composition becomes active for scavenging oxygen when the water
activity is at or above about 0.2-0.3. Water activity is such that,
prior to use, the invented packaging articles can remain
substantially inactive in relatively dry environments without
special steps to maintain low moisture levels. However, once the
packaging is placed into use, most products will have sufficient
moisture to activate the scavenger composition incorporated in the
walls of the packaging article. In the case of a hypothetical
packaging article according to the invention having an intermediate
oxygen-scavenging layer sandwiched between inner and outer layers,
the scavenging layer of the structure, in which the
oxygen-scavenging composition of the present invention is
contained, will be active for chemical reaction with oxygen
permeating into the scavenging layer if the following equation is
satisfied: 1 a = d i ( WVTR ) o a o + d o ( WVTR ) j a i d j ( WVTR
) o + d o ( WVTR ) i 0.2 - 0.3
[0059] where:
[0060] d.sub.i is the thickness in mils of the inner layer;
[0061] d.sub.o is the thickness in mils of the outer layer;
[0062] a.sub.o is the water activity of the environment outside the
packaging article (i.e., adjacent the outer layer);
[0063] a.sub.i is the water activity of the environment inside the
packaging article (i.e., adjacent the inner layer);
[0064] a is the water activity of the scavenging layer;
[0065] (WVTR).sub.o is the water vapor transmission rate of the
outer layer of the packaging wall in gm.mil/100 in. sq.day at
100.degree. F. and 90% RH according to ASTM E96; and
[0066] (WVTR).sub.i is the water vapor transmission rate of the
inner layer of the packaging wall in gm.mil/100 in. sq. day at
100.degree. F. and 90% RH according to ASTM E96.
[0067] For monolayer packaging constructions in which a layer
incorporating the oxygen-scavenging composition is the only layer
of the packaging wall, the package will be active for oxygen
absorption provided a.sub.o or a.sub.i is greater than or equal to
about 0.2-0.3.
[0068] To prepare a packaging wall according to the invention, an
oxygen-scavenging resin formulation is used or the
oxygen-scavenging composition, or its components or concentrates
thereof, is compounded into or otherwise combined with a suitable
packaging resin whereupon the resulting resin formulation is
fabricated into sheets, films or other shaped structures.
Formulations or concentrates using soft, flexible resins as the
carrier resin may be compounded or combined with any suitable
packaging resin including but not limited to polypropylene,
polyethylene, or polyethylene terephthalate. Extrusion,
coextrusion, blow molding, injection molding, extrusion coating and
any other sheet, film or general polymeric melt-fabrication
technique can be used. Sheets and films obtained from the oxygen
scavenger composition can be further processed, e.g. by coating or
lamination, to form multilayered sheets or films, and then shaped,
such as by thermoforming or other forming operations, into desired
packaging walls in which at least one layer contains the oxygen
scavenger. Such packaging walls can be subjected to further
processing or shaping, if desired or necessary, to obtain a variety
of active-barrier end-use packaging articles. The present invention
reduces the cost of such barrier articles in comparison to
conventional articles which afford barrier properties using passive
barrier films.
[0069] As a preferred article of manufacture, the invention
provides a packaging article comprising a wall, or combination of
interconnected walls, in which the wall or combination of walls
defines an enclosable product-receiving space, and wherein the wall
or combination of walls comprises at least one wall section
comprising an oxygen-scavenging layer comprising (i) a polymeric
resin, preferably a thermoplastic resin or a thermoset resin, most
preferably a thermoplastic resin selected from the group consisting
of polyolefins, polystyrenes and polyesters, and most preferably
soft, flexible resins with a 1% secant modulus less than 25,000
p.s.i. and Shore D Hardness less than 45; (ii) an oxidizable metal
preferably comprising at least one member selected from the group
consisting of iron, copper, aluminum, tin and zinc, and most
preferably about 1 to about 100 parts iron per hundred parts by
weight of the resin; (iii) an electrolyte component and (iv) a
solid, non-electrolytic, acidifying component which in the presence
of water has a pH of less than 7, with about 5 to about 150 parts
by weight of electrolyte and acidifying components per hundred
parts by weight iron preferably being present and the weight ratio
of the acidifying component to electrolyte component preferably
being about 5/95 to about 95/5; and, optionally, a water-absorbent
binder. In such articles, sodium chloride is the most preferred
electrolyte component and sodium acid pyrophosphate is most
preferred as the acidifying component, with the weight ratio of
sodium acid pyrophosphate to sodium chloride most preferably
ranging from about 10/90 to about 90/10. For articles made by high
temperature extrusion coating process, calcined sodium acid
pyrophosphate or calcined monocalcium phosphate are the most
preferred acidifying component.
[0070] A particularly attractive packaging construction according
to the invention is a packaging wall comprising a plurality of
thermoplastic layers adhered to one another in bonded laminar
contact wherein at least one oxygen-scavenging layer is adhered to
one or more other layers which may or may not include an
oxygen-scavenging composition. It is particularly preferred,
although not required, that the thermoplastic resin constituting
the major component of each of the layers of the packaging wall be
the same, so as to achieve a "pseudo-monolayer". Such a
construction is easily recyclable.
[0071] An example of a packaging article using the packaging wall
described above is a two-layer or three-layer dual ovenable tray
made of crystalline polyethylene terephthalate ("C-PET") suitable
for packaging pre-cooked single-serving meals. In a three-layer
construction, an oxygen-scavenging layer of about 10 to 20 mils
thickness is sandwiched between two non-scavenging C-PET layers of
3 to 10 mils thickness. The resulting tray is considered a
"pseudo-monolayer" because, for practical purposes of recycling,
the tray contains a single thermoplastic resin, i.e., C-PET. Scrap
from this pseudo-monolayer tray can be easily recycled because the
scavenger in the center layer does not detract from recyclability.
In the C-PET tray, the outer, non-scavenging layer provides
additional protection against oxygen transmission by slowing down
the oxygen so that it reaches the center layer at a sufficiently
slow rate that most of the ingressing oxygen can be absorbed by the
center layer without permeating through it. The optional inner
non-scavenging layer acts as an additional barrier to oxygen, but
at the same time is permeable enough that oxygen inside the tray
may pass into the central scavenging layer. It is not necessary to
use a three layer construction. For example, in the above
construction, the inner C-PET layer can be eliminated. A tray
formed from a single oxygen-scavenging layer is also an attractive
construction.
[0072] The pseudo-monolayer concept can be used with a wide range
of polymeric packaging materials to achieve the same recycling
benefit observed in the case of the pseudo-monolayer C-PET tray.
For example, a package fabricated from polypropylene or
polyethylene can be prepared from a multilayer packaging wall
(e.g., film) containing the oxygen-scavenging composition of the
present invention. In a two-layer construction the scavenger layer
can be an interior layer with a non-scavenging layer of polymer on
the outside to provide additional barrier properties. A sandwich
construction is also possible in which a layer of
scavenger-containing resin, such as polyethylene, is sandwiched
between two layers of non-scavenging polyethylene. Alternatively,
polypropylene, polystyrene or another suitable resin can be used
for all of the layers.
[0073] Another example of a packaging article according to the
invention is a film or packaging wall fabricated from low density
polyethylene, polypropylene, PET or any other suitable resin and an
oxygen-scavenging concentrate of a soft, flexible resin such as mPE
or styrene-rubber block copolymers. For example, oxygen-scavenging
concentrate pellets comprised of mPE can be melt-blended with LDPE
resin to form a film of LDPE with regions of mPE which contain the
oxygen-scavenging composition. Alternatively, oxygen-scavenging
concentrate pellets comprised of styrene-butadiene block copolymer
can be melt-blended with PET for form a package wall of PET with
regions of styrene-butadiene block copolymer which contain the
oxygen-scavenging composition. In this manner, the film or package
wall can be composed of whatever resin is required for the
particular packaging application without sacrificing the superior
oxygen absorption capabilities of the soft flexible resins.
[0074] Various modes of recycle may be used in the fabrication of
packaging sheets and films according to the invention. For example,
in the case of manufacturing a multilayer sheet or film having a
scavenging and non-scavenging layer, reclaim scrap from the entire
multilayer sheet can be recycled back into the oxygen-scavenging
layer of the sheet or film. It is also possible to recycle the
multilayer sheet back into all of the layers of the sheet.
[0075] Packaging walls and packaging articles according to the
present invention may contain one or more layers which are foamed.
Any suitable polymeric foaming technique, such as bead foaming or
extrusion foaming, can be utilized. For example, a packaging
article can be obtained in which a foamed resinous layer
comprising, for example, foamed polystyrene, foamed polyester,
foamed polypropylene, foamed polyethylene or mixtures thereof, can
be adhered to a solid resinous layer containing the
oxygen-scavenging composition of the present invention.
Alternatively, the foamed layer may contain the oxygen-scavenging
composition, or both the foamed and the non-foamed layer can
contain the scavenging composition. Thicknesses of such foamed
layers normally are dictated more by mechanical property
requirements, e.g. rigidity and impact strength, of the foam layer
than by oxygen-scavenging requirements.
[0076] Packaging constructions such as those described above can
benefit from the ability to eliminate costly passive barrier films.
Nevertheless, if extremely long shelf life or added oxygen
protection is required or desired, a packaging wall according to
the invention can be fabricated to include one or more layers of
EVOH, nylon or PVDC, or even of metallized polyolefin, metallized
polyester, or aluminum foil. Another type of passive layer which
may be enhanced by an oxygen-scavenging resin layer according to
the present invention is silica-coated polyester or silica-coated
polyolefin. In cases where a multilayer packaging wall according to
the invention contains layers of different polymeric compositions,
it may be preferable to use adhesive layers such as those based on
ethylene-vinyl acetate copolymer or maleated polyethylene or
polypropylene, and if desired, the oxygen scavenger of the present
invention can be incorporated in such adhesive layers. It is also
possible to prepare the oxygen-scavenging composition of the
present invention using a gas barrier resin such as EVOH, nylon or
PVDC polymer in order to obtain a film having both active and
passive barrier properties.
[0077] While the focus of one embodiment of the invention is upon
the incorporation of the oxygen-scavenging composition directly
into the wall of a container, the oxygen-scavenging compositions
also can be used in packets, as a separate inclusion within a
packaging article where the intent is only to absorb headspace
oxygen.
[0078] A primary application for the oxygen-scavenging resin,
packaging walls, and packaging articles of the invention is in the
packaging of perishable foods. For example, packaging articles
utilizing the invention can be used to package milk, yogurt, ice
cream, cheese; stews and soups; meat products such as hot dogs,
cold cuts, chicken, beef jerky; single-serving pre-cooked meals and
side dishes; homemade pasta and spaghetti sauce; condiments such as
barbecue sauce, ketchup, mustard, and mayonnaise; beverages such as
fruit juice, wine, and beer; dried fruits and vegetables; breakfast
cereals; baked goods such as bread, crackers, pastries, cookies,
and muffins; snack foods such as candy, potato chips, cheese-filled
snacks; peanut butter or peanut butter and jelly combinations,
jams, and jellies; dried or fresh seasonings; and pet and animal
foods; etc. The foregoing is not intended to be limiting with
respect to the possible applications of the invention. Generally
speaking, the invention can be used to enhance the barrier
properties in packaging materials intended for any type of product
which may degrade in the presence of oxygen.
[0079] Still other applications for the oxygen-scavenging
compositions of this invention include the internal coating of
metal cans, especially for oxygen-sensitive food items such as
tomato-based materials, baby food and the like. Typically the
oxygen-scavenging composition can be combined with polymeric resins
such as thermosets of epoxy, oleoresin, unsaturated polyester
resins or phenolic based materials and the material applied to the
metal can by methods such as roller coating or spray coating.
[0080] The examples provided below are for purposes of illustration
and are not intended to limit the scope of invention.
[0081] For purposes of the following examples, oxygen-scavenging
performance was measured according to an Oxygen Absorption Test
performed in a 500 ml glass container containing the
oxygen-scavenging composition in the form of powder, concentrate
pellet or film. Distilled water or an aqueous salt solution in an
open vial was placed inside the glass container next to the samples
to be tested in order to control the relative humidity in the
container. The container was then sealed and stored at the test
temperature. The residual oxygen concentration in the headspace of
the container was measured initially and then periodically using a
Servomex Series 1400 Oxygen Analyzer or MOCON Oxygen Analyzer. The
amount of oxygen absorbed by the test sample was determined from
the change in the oxygen concentration in the headspace of the
glass container. The test container had a headspace volume of about
500 ml and contained atmospheric air so that about 100 ml of oxygen
were available for reaction with the iron. Test samples having an
iron content of about 0.5 gm Fe were tested. For the test system,
iron oxidized from metal to FeO has a theoretical oxygen absorption
level of 200 cc O.sub.2/gm Fe and iron oxidized from metal to
Fe.sub.2O.sub.3 has a theoretical oxygen absorption level of 300 cc
O.sub.2/gm Fe. In all of the examples, oxygen scavenger component
percentages are in weight percents based on total weight of the
compositions, whether film, powder or pellet, tested for oxygen
absorption.
EXAMPLE 1
[0082] Various powder mixtures of iron powder (SCM Iron Powder
A-131); sodium chloride (Morton pulverized salt, Extra Fine 200);
bentonite clay (Whittaker, Clarke & Davis, WCD-670); anhydrous
sodium acid pyrophosphate ("SAP"), Na.sub.2H.sub.2P.sub.2O.sub.7
(Sigma #7758-16-9); sodium pyrophosphate decahydrate ("SPH"),
Na.sub.4P.sub.2O.sub.7.10H.sub.2O (Aldrich 22, 136-8) and anhydrous
sodium pyrophosphate ("SPA"), Na.sub.4P.sub.2O.sub.7 (Aldrich
32,246-6) were prepared as described below. Upon water absorption,
SAP has a pH of 4 and SPH and SPA each has a pH of 10. The
bentonite clay had been dried separately overnight at 250.degree.
C. in a vacuum oven. The desired weights of ingredients were dry
blended in a Waring blender and the blended ingredients were stored
under a nitrogen atmosphere. Samples 1-1 and 1-2 and comparative
samples Comp 1-A through Comp 1-I were tested for oxygen absorption
at test conditions of 168 hr, a relative humidity of 100% and a
temperature of 22.degree. C. Results are tabulated below. This
Example demonstrates that the oxygen-scavenging compositions of
this invention employing iron, sodium chloride and SAP provide
equivalent or better oxygen absorbing efficiency than compositions
of iron and sodium chloride with or without clay. Comparative
compositions with iron, sodium chloride and SPH or SPA exhibit
considerably lower oxygen absorption values. Also, comparative
compositions with iron and clay, SAP, SPH or SPA all exhibited very
low values of oxygen absorption with no electrolyte compound,
sodium chloride, present.
1 Powder NaCl, Additive, cc O.sub.2 No. Fe, % % Additive % Clay, %
gm Fe 1-1 50 37.5 SAP 12.5 0 204 1-2 44.4 33.3 SAP 11.1 11.1 169
Comp 1-A 100 0 -- 0 0 5 Comp 1-B 57.1 42.9 -- 0 0 202 Comp 1-C 50
37.5 -- 0 12.5 204 Comp 1-D 50 37.5 SPH 12.5 0 74 Comp 1-E 50 37.5
SPA 12.5 0 44 Comp 1-F 80 0 -- 0 20 39 Comp 1-G 80 0 SAP 20 0 17
Comp 1-H 80 0 SPH 20 0 2 Comp 1-I 80 0 SPA 20 0 2
EXAMPLE 2
[0083] A dry-mix preparation of oxygen scavenger ingredients was
carried out in the following manner: Iron powder (SCM Iron Powder
A-131); sodium chloride 24(Morton pulverized salt, Extra Fine 200);
bentonite clay (Whittaker, Clarke & Davis, WCD-670) and
anhydrous sodium acid pyrophosphate (SAP),
Na.sub.2H.sub.2P.sub.2O.sub.7 (Sigma #7758-16-9) were dry blended
in a Waring blender at a weight ratio of Fe:NaCl:bentonite
clay:Na.sub.2H.sub.2P.sub.2O.sub.7 of 4:3:1:2. The bentonite clay
had been dried separately overnight at 250.degree. C. in a vacuum
oven. The blended oxygen scavenger ingredients were stored under
nitrogen. A concentrate of oxygen scavenger and polymer resin was
prepared from a 50/50 weight ratio of linear low density
polyethylene granules (GRSN 7047, Union Carbide) and the oxygen
scavenger composition by tumble mixing in a bucket/bottle roller
for ten minutes to obtain a homogeneous mixture. The resultant
powder blend was fed directly to the hopper of a 19 mm conical
corotating twin-screw extruder equipped with a strand die. The zone
temperatures of the extruder barrel were set as follows: zone
1--215.degree. C., zone 2--230.degree. C., zone 3--230.degree. C.,
and strand die-- 230.degree. C. The extrudate was cooled with
room-temperature water in a water bath and chopped into pellets
with a pelletizer. The pellets were dried overnight at 100.degree.
C. in a vacuum oven and stored under nitrogen.
EXAMPLE 3
[0084] Low density polyethylene oxygen-scavenging films were
prepared by extruding a mixture containing 80 parts by weight (pbw)
low density polyethylene pellets (DOW 526 I, Dow Chemical) having a
nominal oxygen permeation coefficient (OPC) of
1.5-2.1.times.10.sup.-10 cc-cm/cm.sup.2-sec-cm Hg, as measured at a
temperature of 20.degree. C. and a relative humidity of 0%, and 20
pbw of an oxygen-scavenging composition in the form of a
concentrate prepared according to the procedure described in
Example 2. The concentrates contained various amounts of iron,
sodium chloride, bentonite clay and SAP as tabulated below with the
weight ratio of sodium chloride to iron maintained at about 0.75:1.
Films were prepared using a Haake Rheomex 245 single screw extruder
(screw diameter--19 mm; L/D ratio--25:1). The zone temperatures of
the extruder barrel were set as follows: zone 1--245.degree. C.,
zone 2--250.degree. C., zone 3--250.degree. C. and die--230.degree.
C. Nominal thicknesses of the extruded films were 5 mils. Tabulated
below is the amount of oxygen absorbed by each of the film samples
as measured by the Oxygen Absorption Test described above at test
conditions of 168 hr, a relative humidity of 100% and a temperature
of 22.degree. C. This example demonstrates that at a given weight
ratio of sodium chloride to iron, addition of SAP significantly
increases the oxygen absorption of the low density polyethylene
oxygen-scavenging film.
2 Film No. Iron, % NaCl, % SAP, % Clay, % ccO.sub.2gm Fe 3-1 4.00
3.00 2.00 1.00 92 3-2 4.44 3.33 1.11 1.11 50 3-3 4.71 3.53 0.59
1.18 51
EXAMPLE 4
[0085] Low density polyethylene oxygen-scavenging films were
prepared by the same procedure as described in Example 3. The low
density polyethylene films contained various amounts of iron,
sodium chloride, bentonite clay and SAP as tabulated below with the
weight ratio of SAP to iron held constant at a value of 0.5:1.
Tabulated below is the amount of oxygen absorbed by each of the
film samples as measured by the Oxygen Absorption Test described
above at test conditions of 168 hr, a relative humidity of 100% and
a temperature of 22.degree. C. This example demonstrates that for
low density polyethylene films containing iron, SAP and sodium
chloride at a given weight ratio of SAP to iron, sodium chloride
increased the oxygen-scavenging capacity of the low density
polyethylene film and that as the amount of sodium chloride was
increased, the oxygen-scavenging capacity of the film also
increased.
3 Film No. Iron, % NaCl, % SAP, % Clay, % ccO.sub.2gm Fe 4-1 5.56
0.28 2.78 1.39 33 4-2 5.33 0.67 2.67 1.33 56 4-3 5.13 1.03 2.56
1.28 60 4-4 4.00 3.00 2.00 1.00 92
EXAMPLE 5
[0086] Concentrates of the ingredient mixtures of Example 4 and
polymer resin were prepared at a 50/50 weight ratio with linear low
density polyethylene granules (GRSN 7047, Union Carbide) by tumble
mixing the components in a bucket/bottle roller for ten minutes to
obtain a homogeneous mixture. The resulting blends were formed into
pellets by the procedure described in Example 2 and the
concentrates were mixed with low density polyethylene pellets (Dow
5261, Dow Chemical) in a 1:4 weight ratio and these pellet blends
formed into films for oxygen-scavenging testing. The films were
tested at conditions of 168 hr, a relative humidity of 100% and a
temperature of 22.degree. C. The amount of thermoplastic polymer in
the film was 90 weight % and the compositions of the remaining
components are tabulated below together with the oxygen absorbed.
This example demonstrates that the oxygen-scavenging composition of
this invention comprising a thermoplastic resin, iron, sodium
chloride and SAP provides equivalent or better oxygen absorbing
efficiency than the thermoplastic resin, iron and sodium chloride,
with or without clay. Comparative compositions with a thermoplastic
resin, iron, sodium chloride and SPH or SPA all exhibit
considerably lower oxygen absorption values. Also, comparative
compositions with no electrolyte compound, sodium chloride, present
all exhibited very low values of oxygen absorption. The water of
hydration of the SPH led to processing difficulties during film
extrusion.
4 Powder NaCl, Additive, cc O.sub.2 No. Fe, % % Additive % Clay, %
gm Fe 5-1 5.00 3.75 SAP 1.25 0 54 5-2 4.44 3.33 SAP 1.11 1.11 40
Comp 5-A 10.0 0 -- 0 0 0.3 Comp 5-B 5.71 4.29 -- 0 0 23 Comp 5-C
5.00 3.75 -- 0 1.25 27 Comp 5-D 5.00 3.75 SPH 1.25 0 4 Comp 5-E
5.00 3.75 SPA 1.25 0 5 Comp 5-F 8.00 0 -- 0 2.00 1 Comp 5-G 8.00 0
SAP 2.00 0 3 Comp 5-H 8.00 0 SPH 2.00 0 0.6 Comp 5-I 8.00 0 SPA
2.00 0 0.5
COMPARATIVE EXAMPLE A
[0087] Comparative, extruded low density polyethylene films were
prepared by extruding a mixture containing 80 pbw low density
polyethylene pellets (DOW 526 I, Dow Chemical) and 20 pbw of
concentrates prepared according to Example 2 with various amounts
of citric acid tripotassium salt ("CATP") as the additive. Citric
acid tripotassium salt upon water absorption has a pH of 9. The
extruded films were prepared according to the method described in
Example 3 with the films having nominal thicknesses of 5 mils. The
amounts of oxygen absorbed by the film samples as measured by the
Oxygen Absorption Test described above at test conditions of 168
hr, a relative humidity of 100% and a temperature of 22.degree. C.
are given below. This comparative example demonstrates that citric
acid tripotassium salt, having a pH greater than 7 upon water
absorption, when added to NaCl is ineffective in enhancing
oxygen-scavenging properties. Comparative films B-3 and B4 with
only SAP or sodium chloride as the additive exhibited oxygen
absorption values of 3 and 26 cc O.sub.2/gm Fe, respectively.
5 Film NaCl, CATP, SAP, Clay, cc O.sub.2 No. Iron, % % % % % gm Fe
B-1 4.44 3.33 1.11 0 1.11 0 B-2 4.00 3.00 2.00 0 1.00 1 B-3 5.71 0
10 0 2.86 1.43 3 B-4 5.00 3.75 0 0 1.25 26
EXAMPLE 6
[0088] Low density polyethylene films were prepared by extruding a
mixture containing 80 pbw low density polyethylene pellets (DOW 526
I, Dow Chemical) and 20 pbw of a concentrate prepared according to
Example 2 with various amounts of nicotinic acid ("NIT") and sodium
chloride. Nicotinic acid upon water absorption has a pH of 4-5. The
extruded films were prepared according to the method described in
Example 3 with the films having nominal thicknesses of 5 mils. The
amount of oxygen absorbed by the film samples as measured by the
Oxygen Absorption Test described above after 168 hr at a relative
humidity of 100% and a temperature of 22.degree. C. is tabulated
below. This example demonstrates that nicotinic acid in combination
with sodium chloride can improve oxygen-scavenging ability and that
nicotinic acid without the electrolyte compound, sodium chloride,
was not effective in increasing the oxygen-scavenging ability of
the composition.
6 cc O.sub.2 Iron, % NaCl, % Clay, % NIT, % gm Fe 4.00 3.00 1.00
2.00 49 5.71 0 1.43 2.86 4
EXAMPLE 7
[0089] Low density polyethylene oxygen-scavenging films were
prepared by extruding a mixture containing 80 pbw low density
polyethylene pellets (DOW 526 I, Dow Chemical) having a nominal OPC
of 1.5-2.1.times.10.sup.-1- 0 cc-cm/cm.sup.2-sec-cm Hg, as measured
at a temperature of 20.degree. C. and a relative humidity of 0%,
and 20 pbw of concentrates containing various amounts of iron,
sodium chloride, bentonite clay and SAP as tabulated below in the
manner described according to Example 2. The film was prepared
using a Haake Rheomex 245 single screw extruder (screw diameter--19
mm; L/D ratio--25:1). The zone temperatures of the extruder barrel
were set as follows: zone 1--245.degree. C., zone 2--250.degree.
C., zone 3--250.degree. C. and die--230.degree. C. The extruded
films had nominal thicknesses of 5 mils. The amounts of oxygen
absorbed by the film samples as measured by the Oxygen Absorption
Test at test conditions of 168 hr, a relative humidity of 100% and
a temperature of 22.degree. C. are given below. This example
demonstrates good oxygen absorption performance even at low levels
of electrolyte plus acidifying components but that oxygen
absorption was erratic at low electrolyte to acidifier ratios. The
latter results are believed to have been caused by difficulties in
effectively mixing the compositions with low levels of sodium
chloride.
7 cc O.sub.2 Iron, % NaCl, % SAP, % Clay, % gm Fe 5.6 0.3 2.8 1.4
55 6.5 0.3 1.6 1.6 69 7.1 0.4 0.7 1.8 50 7.4 0.4 0.4 1.9 44 7.6 0.4
0.2 1.9 49 5.7 0.06 2.8 1.4 45 6.6 0.07 1.7 1.7 19 7.4 0.07 0.7 1.8
29 7.6 0.08 0.4 1.9 15 7.8 0.08 0.2 2.0 46
EXAMPLE 8
[0090] Low density polyethylene oxygen-scavenging films were
prepared by extruding a mixture containing 80 pbw low density
polyethylene pellets (DOW 526 I, Dow Chemical) having a nominal OPC
of 1.5-2.1.times.10.sup.-1- 0 cc-cm/cm.sup.2-sec-cm Hg, as measured
at a temperature of 20.degree. C. and a relative humidity of 0%,
and 20 pbw of concentrates prepared according to Example 2 with
iron, bentonite clay, citric acid and sodium chloride. Upon water
absorption, citric acid has a pH of 1-2. The films were prepared
according to the method described in Example 3 with the extruded
films having nominal thicknesses of 5 mils. The amounts of oxygen
absorbed by the film samples as measured by the Oxygen Absorption
Test described above at test conditions of 168 hr, a relative
humidity of 100% and a temperature of 22.degree. C. are given
below. This example demonstrates that with an acidifier compound of
high acidity, the amount of oxygen absorbed was significantly
increased.
8 Citric cc O.sub.2 Additive Iron, % NaCl, % Acid, % Clay, % gm Fe
0 5.00 3.75 0 1.25 26 Citric Acid 4.44 3.33 1.11 1.11 174 Citric
Acid 4.00 3.00 2.00 1.00 197
EXAMPLE 9
[0091] Two separate concentrate preparations of various oxygen
scavenger ingredients were carried out in the following manner: In
one concentrate, iron powder (SCM iron Powder A-131); sodium
chloride (Morton pulverized salt, Extra Fine 325); and bentonite
clay (Whittaker, Clarke & Davis, WCD-670) were mixed in a high
intensity Henschel mixer in a weight ratio of Fe:NaCl:bentonite
clay of 4:3:1. The mixed ingredients were fed at a 50:50 by weight
ratio with linear low density polyethylene powder (Dowlex 2032, Dow
Chemical) to a Werner & Pfleiderer ZSK-40 twin-screw extruder
to form concentrate pellets. A second concentrate of 25 weight
percent of anhydrous sodium acid pyrophosphate, (Sigma #7758-16-9)
with linear low density polyethylene powder was also prepared in a
ZSK-40 twin-screw extruder. Films of polyethylene terephthalate
("PET") (nominal OPC of 1.8-2.4.times.10.sup.-12
cc-cm/cm.sup.2-sec-cm Hg), polypropylene ("PP") (nominal OPC of
0.9-1.5.times.10.sup.-10 cc-cm/cm.sup.2-sec-cm Hg), low density
polyethylene ("LDPE") and linear low density polyethylene ("LLDPE")
with various combinations of the above concentrates were extruded.
In all of the films, the weight ratio of sodium chloride to iron
was held constant at 0.75:1. The amounts of oxygen absorbed by
these film samples as measured by the Oxygen Absorption Test at
test conditions of 168 hr, a temperature of 22.degree. C. and a
relative humidity of 100% are tabulated below.
9 cc O.sub.2 Resin Fe, % NaCl, % SAP, % Clay, % gm Fe PET 5.00 3.75
0 1.25 10 PET 4.00 3.00 1.00 1.00 14 PET 4.00 3.00 2.00 1.00 14 PP
5.00 3.75 0 1.25 28 PP 4.00 3.00 1.00 1.00 46 PP 4.00 3.00 2.00
1.00 50 LLDPE 5.00 3.75 0 1.25 39 LLDPE 4.00 3.00 1.00 1.00 99
LLDPE 4.00 3.00 2.00 1.00 98 LDPE 5.00 3.75 0 1.25 29 LDPE 4.00
3.00 1.00 1.00 41 LDPE 4.00 3.00 2.00 1.00 48
EXAMPLE 10
[0092] Two separate concentrates were prepared by the same
procedure as in Example 9. One concentrate consisted of iron powder
(SCM iron powder A-131); sodium chloride (Morton pulverized salt,
Extra Fine 325); bentonite clay (Whittaker, Clarke & Davis,
WCD-670); and linear low density polyethylene resin (Dowlex 2032,
Dow Chemical) in a weight ratio of Fe:NaCl:bentonite clay:LLDPE of
4:3:1:8. The second concentrate consisted of sodium acid
pyrophosphate (Sigman #7758-16-9) and linear low density
polyethylene (Dowlex 2032, Dow Chemical) in a weight ratio of
SAP:LLDPE of 1:3. Low density polyethylene oxygen-scavenging films
were prepared by the same procedure as described in Example 3 using
a Haake Rheomex 245 single screw extruder. The film processing
temperatures varied from nominal 243.degree. C. to nominal
260.degree. C. to nominal 288.degree. C. At nominal 243.degree. C.,
the zone temperatures of the extruder barrel were set as follows:
zone 1--241.degree. C., zone 2--243.degree. C., zone 3--
243.degree. C. and die--218.degree. C. At nominal 260.degree. C.,
the zone temperatures of the extruder barrel were set as follows:
zone 1--254.degree. C., zone 2--260.degree. C., zone 3--260.degree.
C. and die-- 232.degree. C. At nominal 288.degree. C., the zone
temperatures of the extruder barrel were set as follows: zone
1--282.degree. C., zone 2--285.degree. C., zone 3--288.degree. C.
and die--252.degree. C. At the higher processing temperatures, the
resulting films were found to contain voids believed to have been
caused by decomposition of sodium acid pyrophosphate. Thermal
gravimetric analysis of sodium acid pyrophosphate powder heated
from room temperature to about 610.degree. C. at a rate of about
10.degree. C./minute indicated weight loss occurring from about 260
to 399.degree. C., corresponding to loss of water from sodium acid
pyrophosphate, thus suggesting decomposition thereof to NaPO.sub.3.
Based on these observations, it is believed that the higher
processing temperatures used in this example led to decomposition
of the sodium acid pyrophosphate that was originally used to sodium
metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate,
each having a pH in the range of 4-6 in aqueous solution, or a
combination thereof. The amounts of oxygen absorbed by these film
samples as measured by the Oxygen Absorption Test at test
conditions of 168 hr, a temperature of 22.degree. C. and a relative
humidity of 100% are tabulated below.
10 Nominal Film Film Processing cc O.sub.2 No. Temp., .degree. C.
Iron, % NaCl, % SAP, % Clay, % gm Fe 10-1 243 4.44 3.33 1.11 1.11
40 10-2 288 4.44 3.33 1.11 1.11 53 10-3 260 11.11 8.33 2.78 2.78 48
10-4 288 11.11 8.33 2.78 2.78 77
EXAMPLE 11
[0093] A dry-mix preparation of oxygen scavenger ingredients was
carried out in the following manner: Iron powder (SCM A-131);
sodium chloride (Morton EF325); and sodium acid pyrophosphate
(Monsanto SAP-28) were mixed at 2/2/1 weight ratio of Fe/NaCl/SAP
in an intensive mixing Henschel mixer. The mixing time was about 80
seconds. The powder mixture was compounded into nineteen separate
resins as shown in the Table below at a 1/1 weight ratio on a
twin-screw ZSK-30 extruder. The zone temperatures of the extruder
barrel were set as follows: zone 1--140-200.degree. C., zone
2--220-280.degree. C., zone 3--230-270.degree. C., zone
4--220-260.degree. C., zone 5--220-260.degree. C., zone
7--200-250.degree. C. The melt temperature of the extrudate was in
the range of 180-280.degree. C. The extrudate was cooled and
chopped into concentrate pellets of oxygen scavenger resin
designated Concentrates I-XV and Concentrates A-D. The resulting
concentrates were measured for oxygen-scavenging performance
according to the Oxygen Absorption Test described above at 72 hr (3
day), 168 hr (7 days), and 672 hr (28 days). The results are
tabulated below in Table I and the 1% Secant Modulus and Shore D
Hardness are shown in Table II. This Example demonstrates that the
oxygen-scavenging compositions of this invention employing iron,
sodium chloride and SAP in a soft, flexible resin provide better
oxygen absorbing efficiency than identical compositions in more
rigid polyethylenes and polypropylenes such as in concentrates
A-D.
11TABLE I Oxygen Absorption Performance of Oxygen-Scavenging
Concentrate Pellets in Various Carrier Resins Concentrate Resin
Composition 20 wt % Iron 20 wt % Salt 10 wt % SAP 50 wt % Carrier
Resin Oxygen Scavenger Concentrate Oxygen Absorption (cc O.sub.2/gm
Fe) Conc @ 22.degree. C., 100% RH No. Carrier Resin Type 3 days 7
days 28 days comonomer I Dow Affinity mPE/octene 38,43 55,59 91,95
PF1140 II Dow/DuPont mPE/octene 39,41 55,58 90,96 Engage 8440 III
Exxon Exact mPE/hexene 35 52 86 3131 IV Exxon Exact mPE/butene 37
53 79 4053 V Exxon Exact mPE/hexene 53 71 109 4151 VI Amcco EHPP
mPP/none 31 45 76 Styrene:Rubber VII Shell Kraton SBS/35:65 135 166
185 D2103 VIII Shell Kraton SBS/30:70 88 125 160 D2104 IX Shell
Kraton SEBS/22:78 55 85 121 G2109 X Shell Kraton SEBS/37:63 37 61
105 G2701 XI Shell Kraton SEBS/30:70 42 65 108 G2705 XII Shell
Kraton SEBS/21:79 81 105 138 G2706 XIII SIBS SIBS/30:70 58 79 97
comonomer XIV Carbide ULDPE Unipol/higher 69 103 137 ETS9064 XV Dow
VLPDE LP Solution/ 42 58 88 Attane 4202 higher olefin A Dow Dowlex
Ziegler-Natta/ 25 35 61 LLDPE2032 higher olefin B Amoco PP7200p
Ziegler-Natta/ 13 21 39 none C Dow LDPE6401 Radical/none 20 31 60 D
Westlake LDPE Radical/none 20 32 55 EF412
[0094]
12TABLE II Shore Hardness and Secant Modulus Properties of Carrier
Resins for Oxygen-Scavenging Composition Conc 1% Secant No. Carrier
Resin Type Shore D Modulus comonomer I Dow Affinity mPE/octene 35.6
5,155 PF1140 II Dow/DuPont mPE/octene 37.2 6,600 Engage 8440 III
Exxon Exact mPE/hexene 40.6 8,448 3131 IV Exxon Exact mPE/butene
29.9 2,866 4053 V Exxon Exact mPE/hexene 37.7 6,563 4151 VI Amcco
EHPP mPP/none 19.5 1,837 Styrene:Rubber VII Shell Kraton SBS/35:65
19.0 1,386 D2103 VIII Shell Kraton SBS/30:70 8.1 829 D2104 IX Shell
Kraton SEBS/22:78 10.3 454 G2109 X Shell Kraton SEBS/37:63 12.8
1,706 G2701 XI Shell Kraton SEBS/30:70 9.1 1,126 G2705 XII Shell
Kraton SEBS/21:79 5.9 188 G2706 XIII SIBS SIBS/30:70 10.9 337
Comonomer XIV Carbide ULDPE Unipol/higher 42.0 20,000 ETS9064 XV
Dow VLPDE LP Solution/ 42.1 18,900 Attane 4202 higher olefin A Dow
Dowlex Ziegler-Natta/ 47.5 37,115 LLDPE2032 higher olefin B Amoco
PP7200p Ziegler-Natta/ 72.4 176,000 none C Dow LDPE6401
Radical/none 46.1 26,526 D Westlake LDPE Radical/none 46.2 26,385
EF412
[0095] The oxygen absorption results of Example 11 demonstrate that
oxygen-scavenging compositions in soft, flexible resins absorb more
oxygen per gram of iron than more rigid, hard resins such as LDPE,
LLDPE and PP. Although there is not a linear relationship between
the softness and flexibility of a resin and oxygen-absorption,
there is a demonstrated improvement between soft, flexible resins
on the whole and hard, rigid resins. All of the resins with a Shore
D below 45 and 1% secant modulus below about 25,000 p.s.i. absorbed
more oxygen per gram of iron than those resins with a Shore D
greater than 45 and 1% secant modulus greater than 25,000 p.s.i. It
is believed that the flexible molecular structure of soft resins
facilitates the intimate contact of the oxygen-scavenging
components. This enables the electrolyte and acidifying component
to promote the oxidation of the iron in the resin.
[0096] As shown in Table I, the styrene-butadiene-styrene block
copolymers of the Kraton.RTM. D series work particularly well. This
improved oxygen absorption may be in part due to the absorption of
oxygen by the carbon-carbon double bonds in the butadiene segments
of the styrene-butadiene block-copolymer.
EXAMPLE 12
[0097] Low density polyethylene oxygen-scavenging films were
prepared by blending each of the nineteen concentrates of Example
11, having the same Shore D and 1% secant Modulus properties listed
above, with Dow LDPE 640i resin at a 1/1 ratio, and preparing
extruded films using a single Haake extruder. The zone temperatures
of the extruder barrel were set as follows: zone 1--190.degree. C.,
zone 2--200.degree. C., zone 3-- 210.degree. C., and die
zone--200.degree. C. The extruded films had a nominal thickness of
5 mils. The resulting films, designated Film I-XV and Comparative
Film A-D, were measured for oxygen-scavenging performance according
to the Oxygen Absorption Test described above at 72 hr (3 day), 168
hr (7 days), and 672 hr (28 days). The results are tabulated below.
This Example demonstrates that the oxygen-scavenging LDPE films of
this invention employing iron, sodium chloride and SAP in a soft,
flexible carrier resin concentrate blended with the LDPE resin
provide better oxygen absorbing efficiency than identical
compositions in more rigid polyethylene and polypropylene
concentrates A-D blended with LDPE film resin.
13TABLE III Oxygen Absorption Performance of Extrusion Films
Containing Oxygen-Scavenging Compositions in Various Carrier Resins
Extrusion Film Composition 50 wt % Concentrate Resin from Table I
50 wt % LDPE Film Resin Oxygen Scavenger Concentrate Oxygen
Absorption (cc O.sub.2/gm Fe) Conc @ 22.degree. C., 100% RH No.
Carrier Resin Type 3 days 7 days 28 days comonomer I Dow Affinity
mPE/octene 77 96 126 PF1140 II Dow/DuPont mPE/octene 54 64 84
Engage 8440 III Exxon Exact mPE/hexene 82 100 127 3131 IV Exxon
Exact mPE/butene 64 73 92 4053 V Exxon Exact mPE/hexene 75 88 116
4151 VI Amcco EHPP mPP/none 73 85 94 Styrene:Rubber VII Shell
Kraton SBS/35:65 110 128 143 D2103 VIII Shell Kraton SBS/30:70 85
95 111 D2104 IX Shell Kraton SEBS/22:78 104 156 187 G2109 X Shell
Kraton SEBS/37:63 47 64 81 G2701 XI Shell Kraton SEBS/30:70 47 62
79 G2705 XII Shell Kraton SEBS/21:79 63 69 84 G2706 XIII SIBS
SIBS/30:70 80 107 122 comonomer XIV Carbide ULDPE Unipol/higher 57
68 87 ETS9064 XV Dow VLPDE LP Solution/ 66 88 119 Attane 4202
higher olefin A Dow Dowlex Ziegler-Natta/ 36 40 61 LLDPE2032 higher
olefin B Amoco PP7200p Ziegler-Natta/ 18 28 43 none C Dow LDPE6401
Radical/none 44 57 79 D Westlake LDPE Radical/none 44 51 65
EF412
[0098] The oxygen absorption results of Example 12 demonstrate that
oxygen-scavenging compositions in soft, flexible resin concentrates
that are further blended with LDPE to form LDPE films, absorb more
oxygen per gram of iron than those same compositions in more rigid,
hard concentrate resins further blended with LDPE to form LDPE
films. Comparison of the results from Example 11 to Example 12,
shows that some resins absorbed oxygen more effectively in
concentrate form. But, overall, the soft, flexible carrier resins
performed better than the hard, rigid carrier resins in
concentrates and films. It is believed that the difference between
concentrate vs. film absorption results may be due to the
compatibility of the concentrate carrier and film resin. We believe
that if the concentrate carrier resin is miscible in the film resin
when blended with the film resin, the regions of soft, flexible
resin containing the oxygen-scavenging composition may not exist.
If those regions do not exist, the hard, stiff film resin may
effect the oxygen absorption ability of the oxygen-scavenging
composition in the same manner the hard, stiff resins lower
absorption in the resin concentrate form. For example, the Kraton G
series absorbs more oxygen per gram of iron in the concentrate form
versus the LDPE film. This may be due to the fact that
styrene-ethylene-butylene styrene block copolymers are readily
miscible in LDPE. This miscibility may cause the break down of the
soft, flexible resin regions, leaving the oxygen-scavenging
components in the more rigid LDPE resin.
EXAMPLE 13
[0099] In accordance with Example 11, a dry-mix preparation of
oxygen scavenger ingredients was carried out in the following
manner: Iron powder (SCM A-131); sodium chloride (Morton EF325);
and sodium acid pyrophosphate (Monsanto SAP-28) were mixed at 2/2/1
ratio of Fe/NaCl/SAP in an intensive mixing Henschel mixer. The
powder mixture was compounded into two separate resins (Dow/DuPont
Engage 8440 and Dow Affinity PF1140) at a 1/1 weight ratio on a
twin-screw ZSK-30 extruder to make concentrate pellets of oxygen
scavenger resin designated Concentrates C-1 and C-2. Polypropylene
oxygen-scavenging films were prepared by blending each of the
concentrates with Amoco PP6219 polypropylene resin at a 1/1 ratio,
and preparing 5 ml extrusion films using a single screw Haake
extruder in accordance with Example 12. The resulting films,
designated F-1 and F-2, were measured for oxygen-scavenging
performance according to the Oxygen Absorption Test described above
at 72 hr (3 day), 168 hr (7 days), and 672 hr (28 days). The
results are tabulated below. This Example demonstrates that mPE is
as effective as a carrier resin in polypropylene as a diluent as it
is when LDPE is the diluent.
[0100] Concentrate Resin Composition:
14 20 wt % Iron 20 wt % Salt 9 wt % Clay 10 wt % SAP 50 wt %
Carrier Resin Conc. No. Carrier Resin Type/comonomer C-1 Dow/DuPont
Engage 8440 mPE/octene C-2 Dow Affinity PP1140 mPE/octene Extrusion
Film Composition 50 wt % Concentrate Resin C1-C2 50 wt % Amoco
PP6219 Film Resin Oxygen Scavenger Extrusion Film Oxygen Absorption
(cc O.sub.2/gm Fe) @ 22.degree. C., 100% RH Film No. Concentrate 3
days 7 days 28 days F-1 C-1 56 77 108 F-2 C-2 59 96 110
[0101] The following Examples 14-16 demonstrate the effect of
dehydrated acidifying components on the appearance and
oxygen-absorption of the oxygen-scavenging films. In each of the
Examples below, a high extrusion temperature--above 270.degree.
C.-- was used to approximate the high temperature extrusion coating
process temperature.
EXAMPLE 14
Calcination of SAP
[0102] Commercial food-grade sodium acid pyrophosphate
(Na.sub.2H.sub.2P.sub.2O.sub.7, Monsanto SAP-28) was calcined at
350.degree. C. for 2 hours in a microwave furnace to give a
dehydrated product. The weight loss during calcination was 8.1 wt
%. The pH of a 0.1 wt % aqueous slurry/solution of dehydrated SAP
was 5.6. The dehydrated SAP was ground and sifted into a fine
powder, and then mixed with iron powder (SCM A-131), salt powder
(Morton EF325) at 2/2/1 weight ratio of iron/salt/dehydrated SAP in
an intensive mixing Waring mixer. The powder mixture was further
mixed with Exxon LLDPE resin powder (Escorene LL-5002.09) at 1/3
ratio of inorganic/resin in the mixer.
[0103] The mixture of oxygen scavenger components and resin was
compounded into an oxygen scavenger resin composition, and further
made into extruded film on a Haake extruder at 310.degree. C. The
extruder temperature profile was 280, 295, 310, and 265.degree. C.
at Zone 1, 2, 3 and 4 (die). The polymer melt temperature was
310.degree. C. The extruded film (designated Film I) showed clean
and smooth appearance with no voids or bubbles in the film. The
oxygen absorption performance of the film sample was measured and
found to be good, as shown in Table IV.
[0104] For comparison, commercial food-grade sodium acid
pyrophosphate (Na.sub.2H.sub.2P.sub.2O.sub.7, Monsanto SAP-28) was
used without calcination. The pH of the 0.1 wt % aqueous
slurry/solution of SAP was 4.2. It was mixed with iron powder (SCM
A-131), salt powder (Morton EF325) at 2/2/1 weight ratio of
iron/salt/SAP in an intensive mixing Waring mixer. The powder
mixture was further mixed with Exxon LLDPE resin powder (Escorene
LL-5002.09) at 1/3 ratio of inorganic/resin in the mixer.
[0105] The mixture of oxygen scavenger components and resin was
compounded into an oxygen scavenger resin, and further made into
extruded film on a Haake extruder at 310.degree. C. The extruder
temperature profile was 280, 295, 310, and 265.degree. C. at Zone
1, 2, 3 and 4 (die). The polymer melt temperature was 310.degree.
C. The extruded film (designated Film A) showed poor appearance
with many large voids and bubbles in the film. The oxygen
absorption performance of the film sample was measured and found to
be very good, as shown in Table IV.
EXAMPLE 15
Calcination of MCP
[0106] Commercial food-grade monocalcium phosphate monohydrate
(CaH.sub.4(PO.sub.4).sub.2.H.sub.2O, Rhone-Poulenc Regent 12xx) was
calcined at 350.degree. C. for 2 hours in a microwave furnace to
give a dehydrated product. The weight loss during calcination was
18.6 wt %. The pH of the 0.1 wt % aqueous slurry/solution of
dehydrated MCP was 3.0.
[0107] It was ground and sifted into a fine powder, and then mixed
with iron powder (SCM A-131), salt powder (Morton EF325) at 2/2/1
weight ratio of iron/salt/dehydrated MCP in an intensive mixing
Waring mixer. The powder mixture was further mixed with Exxon LLDPE
resin powder (Escorene LL-5002.09) at 1/3 ratio of inorganic/resin
in the mixer.
[0108] The mixture of oxygen scavenger components and resin was
compounded into an oxygen scavenger resin, and further made into
extruded film on a Haake extruder at 310.degree. C. The extruder
temperature profile was 280, 295, 310, and 265.degree. C. at Zone
1, 2, 3 and 4 (die). The polymer melt temperature was 310.degree.
C. The extruded film (designated Film II) showed clean and smooth
appearance with no voids or bubbles in the film. The oxygen
absorption performance of the film sample was measured and found to
be good, as shown in Table IV.
[0109] For comparison, commercial food-grade monocalcium phosphate
monohydrate (CaH.sub.4(PO.sub.4).sub.2.H.sub.2O, Rhone-Poulenc
Regent 12xx) was used without calcination. The pH of the 0.1 wt %
aqueous (slurry) solution of MCP was 4.0. It was mixed with iron
powder (SCM A-131), salt powder (Morton EF325) at 2/2/1 weight
ratio of iron/salt/MCP in an intensive mixing Waring mixer. The
powder mixture was further mixed with Exxon LLDPE resin powder
(Escorene LL-5002.09) at 1/3 ratio of inorganic/resin in the
mixer.
[0110] The mixture of oxygen scavenger components and resin was
compounded into an oxygen scavenger resin, and further made into
extruded film on a Haake extruder at 310.degree. C. The extruder
temperature profile was 280, 295, 310, and 265.degree. C. at Zone
1, 2, 3 and 4 (die). The polymer melt temperature was 310.degree.
C. The extruded film (designated Film B) showed poor appearance
with many large voids and bubbles in the film. The oxygen
absorption performance of the film sample was measured and found to
be very good, as shown in Table IV.
EXAMPLE 16
Calcination of STMP
[0111] Commercial food-grade sodium trimetaphosphate
((NaPO.sub.3).sub.3, Monsanto STMP) was calcined at 350.degree. C.
for 1 hour in a microwave furnace to give a dehydrated product. The
weight loss during calcination was 0.5 wt %. The pH of the 0.1 wt %
aqueous slurry/solution of dehydrated STMP was 5.4. It was ground
and sifted into a fine powder, and then mixed with iron powder (SCM
A-131), salt powder (Morton EF325) at 2/2/1 weight ratio of
iron/salt/dehydrated STMP in an intensive mixing Waring mixer. The
powder mixture was further mixed with Exxon LLDPE resin powder
(Escorene LL-5002.09) at 1/3 ratio of inorganic/resin in the
mixer.
[0112] The mixture of oxygen scavenger and resin was compounded
into an oxygen scavenger resin, and further made into extruded film
on a Haake extruder at 310.degree. C. The extruder temperature
profile was 280, 295, 310, and 265.degree. C. at Zone 1, 2, 3 and 4
(die). The polymer melt temperature was 310.degree. C. The extruded
film (designated Film III) showed clean and smooth appearance with
no voids or bubbles in the film. The oxygen absorption performance
of the film sample was measured and found to be good, as shown in
Table IV.
[0113] For comparison, commercial food-grade sodium
trimetaphosphate ((NaPO.sub.3).sub.3, Monsanto STMP) was used
without calcination. The pH of the 0.1 wt % aqueous (slurry)
solution of STMP was 5.2. It was mixed with iron powder (SCM
A-131), salt powder (Morton EF325) at 2/2/1 weight ratio of
iron/salt/STMP in an intensive mixing Waring mixer. The powder
mixture was further mixed with Exxon LLDPE resin powder (Escorene
LL-5002.09) at 1/3 ratio inorganic/resin in the mixer.
[0114] The mixture of oxygen scavenger and resin was compounded
into an oxygen scavenger resin, and further made into extruded film
on a Haake extruder at 310.degree. C. The extruder temperature
profile was 280, 295, 310, and 265.degree. C. at Zone 1, 2, 3 and 4
(die). The polymer melt temperature was 310.degree. C. The extruded
film (designated Film C) showed somewhat poor appearance with
minor/small voids and bubbles in the film. The oxygen absorption
performance of the film sample was measured and found to be good,
as shown in Table IV.
COUNTER EXAMPLE D
No Acidifying Component
[0115] Iron powder (SCM A-131) and salt powder (Morton EF325) were
mixed at 1/1 ratio in an intensive mixing Waring mixer. No
acidifying component was used in the formulation. The powder
mixture was further mixed with Exxon LLDPE resin powder (Escorene
LL-5002.09) at 1/3 ratio of inorganic/resin in the mixer.
[0116] The mixture of oxygen scavenger and resin was compounded
into an oxygen scavenger resin, and further made into extruded film
on a Haake extruder at 310.degree. C. The extruder temperature
profile was 280, 295, 310, and 265.degree. C. at Zone 1, 2, 3 and 4
(die). The polymer melt temperature was 310.degree. C. The extruded
film (designated Film D) showed clean and smooth appearance with no
voids or bubbles in the film. The oxygen absorption performance of
the film sample was measured and found to be poor, as shown in
Table IV.
15TABLE IV Oxygen Absorption Performance of Oxygen-Scavenging Films
Oxygen Absorption (cc O.sub.2/gm Fe) after 6 days Sample ID pH
Modifier Film Appearance @ 22.degree. C., 100% RH Film I Calcined
Good, no voids 44.0 SAP Film II Calcined Good, no voids 65.5 MCP
Film III Calcined Good, no voids 38.5 STMP Film A SAP Poor, many
large 165 voids Film B MCP Poor, many large 158 voids Film C STMP
Somewhat poor, 53.0 minor voids Film D No Good, no voids 12.2
acidifying component
[0117] The oxygen-absorption results of Table IV demonstrate two
important points. First, that use of an acidifying component
improves the oxygen absorption of the iron regardless of whether
the acidifying component contains hydrate or is dehydrated. Second,
that there is a trade-off between oxygen absorption and film
appearance when using hydrated versus dehydrated acidifying
components. If the fabrication temperature of the film or article
is below the dehydration temperature of the hydrated acidifying
component, then the hydrated acidifying component may be used
without the creation of voids or bubbles. If, however, the
fabrication temperature is above the dehydration temperature of the
hydrated acidifying component, a calcined acidifying component
should be used. Although the oxygen absorption decreases when
calcined acidifying components are used, the film appearance is
smooth with no voids or bubbles. The selection of acidifying
component will depend on the end-use application, but an acidifying
component--hydrated or calcined--should always be used to achieve
increased oxygen absorption.
* * * * *