U.S. patent application number 10/849706 was filed with the patent office on 2004-11-04 for packaging.
This patent application is currently assigned to Constar International, Inc.. Invention is credited to Cochran, Michael Alexander, Folland, Rickworth, Nicholas, James William, Robinson, Melvin Edward Riddell.
Application Number | 20040219320 10/849706 |
Document ID | / |
Family ID | 27263529 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040219320 |
Kind Code |
A1 |
Cochran, Michael Alexander ;
et al. |
November 4, 2004 |
Packaging
Abstract
The present invention provides a wall for a package, which wall
comprises, or includes a layer comprising, a composition comprising
a polymer and capable of scavenging oxygen through the
metal-catalysed oxidation of an oxidisable organic component
thereof. The oxidisable organic component is preferably itself a
polymer, and may be the only polymer in the composition. Preferred
compositions include a blend of 96% polyethylene terephthalate and
4% poly (m-xylyleneadipamide) containing 200 ppm cobalt as
catalyst, with good permeance-versus-time performance (3) when
formed into a bottle.
Inventors: |
Cochran, Michael Alexander;
(Wantage, GB) ; Folland, Rickworth; (Faringdon,
GB) ; Nicholas, James William; (Wantage, GB) ;
Robinson, Melvin Edward Riddell; (Wantage, GB) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
ONE LIBERTY PLACE, 46TH FLOOR
1650 MARKET STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
Constar International, Inc.
|
Family ID: |
27263529 |
Appl. No.: |
10/849706 |
Filed: |
May 20, 2004 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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10849706 |
May 20, 2004 |
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10013985 |
Oct 30, 2001 |
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10013985 |
Oct 30, 2001 |
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09504793 |
Feb 15, 2000 |
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09504793 |
Feb 15, 2000 |
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09244463 |
Feb 4, 1999 |
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09244463 |
Feb 4, 1999 |
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08844515 |
Apr 18, 1997 |
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5955527 |
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08844515 |
Apr 18, 1997 |
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08472841 |
Jun 7, 1995 |
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5639815 |
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08472841 |
Jun 7, 1995 |
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08061939 |
May 17, 1993 |
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08061939 |
May 17, 1993 |
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07668906 |
Mar 13, 1991 |
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07668906 |
Mar 13, 1991 |
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07340416 |
Mar 23, 1989 |
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5021515 |
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Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
C08L 2203/12 20130101;
C08L 77/00 20130101; C08K 5/005 20130101; Y10T 428/26 20150115;
C08L 67/00 20130101; C08L 79/04 20130101; C08K 5/098 20130101; C08L
2310/00 20130101; C08L 23/06 20130101; Y10T 428/31511 20150401;
Y10T 428/2902 20150115; Y10T 428/1352 20150115; Y10T 428/24942
20150115; C08L 77/06 20130101; C08L 67/02 20130101; C08L 23/10
20130101; Y10T 428/2916 20150115; C08L 23/12 20130101; B65D 81/267
20130101; C08K 5/098 20130101; C08L 67/02 20130101; C08L 23/06
20130101; C08L 2666/20 20130101; C08L 23/12 20130101; C08L 2666/20
20130101; C08L 67/00 20130101; C08L 2666/20 20130101; C08L 67/02
20130101; C08L 2666/20 20130101; C08L 67/02 20130101; C08L 77/00
20130101; C08L 23/10 20130101; C08L 2666/20 20130101; C08L 23/12
20130101; C08L 2666/14 20130101; C08L 23/06 20130101; C08L 2666/14
20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B65D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 1987 |
GB |
8717754 |
Mar 12, 1988 |
GB |
8805931 |
Mar 22, 1988 |
GB |
8806752 |
Jul 1, 1988 |
GB |
8815699 |
Jul 6, 1988 |
WO |
PCT/GB88/00532 |
Claims
1-38. (Canceled).
39. A multilayer wall for a package comprising: an
oxygen-scavenging layer comprising an oxidizable polymer and a
transition metal in a positive oxidation state that promotes the
oxidation of the oxidizable polymer; and at least one additional
layer comprising a non-oxidizable polymer wherein the permeability
for oxygen of the non-oxidizable polymer is not more than 6.0
cm.sup.3 mm/(m.sup.2 atm day), wherein the oxygen-scavenging layer
is between the at least one additional layer and the inside of the
package.
40. The multilayer wall of claim 39 wherein the non-oxidizable
polymer in the at least one additional layer is PET.
41. The multilayer wall of claim 39 wherein the transition metal in
the positive oxidation state is cobalt.
42. The multilayer wall of claim 39 wherein the oxidizable polymer
is a polyamide.
43. The multilayer wall of claim 42 wherein the polyamide is
MXD6.
44. The multilayer wall of claim 43 wherein the transition metal in
the positive oxidation state is cobalt.
45. The multilayer wall of claim 43 wherein the non-oxidizable
polymer in the at least one additional layer is PET.
46. The multilayer wall of claim 39 wherein the wall has a
permeance for oxygen that is not more than three-quarters of that
which it would have in the absence of oxygen scavenging
properties.
47. The multilayer wall of claim 39 wherein the wall has a
permeance for oxygen that is not more than 10.0 cm.sup.3/(m.sup.2
atm day) at least in part due to the transition metal promoting the
oxidation of the oxidizable polymer.
48. The multilayer wall of claim 47 wherein the wall has a
permeance for oxygen that is not more than 2.0 cm.sup.3/(m.sup.2
atm day) at least in part due to the transition metal promoting the
oxidation of the oxidizable polymer.
49. The multilayer wall of claim 48 wherein the wall has a
permeance for oxygen that is not more than 0.5 cm.sup.3/(m.sup.2
atm day) at least in part due to the transition metal promoting the
oxidation of the oxidizable polymer.
50. A multilayer wall for a package comprising: at least one
oxygen-scavenging layer comprising an oxidizable polymer and a
transition metal in a positive oxidation state that promotes the
oxidation of the oxidizable polymer; and at least one other layer
comprising a polymer, wherein the permeability for oxygen of the
polymer is not more than 6.0 cm.sup.3 mm/(m.sup.2 atm day).
51. The multilayer wall of claim 50 wherein the transition metal in
the positive oxidation state is cobalt.
52. The multilayer wall of claim 50 wherein the polymer of the at
least one other layer is MXD6.
53. The multilayer wall of claim 50 wherein the transition metal in
the positive oxidation state is cobalt.
54. The multilayer wall of claim 50 wherein the polymer in the at
least one other layer has a permeability for oxygen of not more
than 0.1 cm.sup.3 mm/(m.sup.2 atm day).
55. The multilayer wall of claim 50 wherein the transition metal in
the positive oxidation state is cobalt.
56. The multilayer wall of claim 55 wherein the at least one
oxygen-scavenging layer further comprises PET.
57. The multilayer wall of claim 50 wherein the wall has a
permeance for oxygen that is not more than three-quarters of that
which it would have in the absence of oxygen scavenging
properties.
58. The multilayer wall of claim 50 wherein the wall has a
permeance for oxygen that is not more than 10.0 cm.sup.3/(m.sup.2
atm day) at least in part due to the transition metal promoting the
oxidation of the oxidizable polymer.
59. The multilayer wall of claim 58 wherein the wall has a
permeance for oxygen that is not more than 2.0 cm.sup.3/(m.sup.2
atm day) at least in part due to the transition metal promoting the
oxidation of the oxidizable polymer.
60. The multilayer wall of claim 59 wherein the wall has a
permeance for oxygen that is not more than 0.5 cm.sup.3/(m.sup.2
atm day) at least in part due to the transition metal promoting the
oxidation of the oxidizable polymer.
Description
[0001] The present invention relates to packaging, especially
packaging of oxygen-sensitive materials, most especially of foods
and beverages
[0002] Packaging, whether rigid, semi-rigid, flexible, lidded, or
collapsible, or a combination of these, serves not merely to
contain the material being packaged but, depending on the nature of
the material, to prevent ingress of harmful substances from the
environment. Oxygen from the atmosphere has long been regarded as
one of the most harmful substances for many packaged materials,
especially foodstuffs.
[0003] Packaging made exclusively of glass or metal can provide an
extremely good barrier both to egress of all substances from the
package (especially water and carbon dioxide) and to ingress of all
substances from the environment. Packaging made of polymers in
whole or in part generally performs far less well in both these
respects. This has restricted for many years the use of polymers in
packaging, despite the great advantages of polymers. These
advantages derive from the diversity of polymers themselves in
mechanical, thermal, and optical properties and from the diversity
and adaptability of fabrication techniques for polymers, allowing
flexible bags, rigid containers, and clinging films to be made, the
package wall being homogeneous, laminated, or coated. Compared with
glass and metal packages, polymer packages are generally light and
compared with glass are generally less breakable. There are also
cost advantages with some polymers.
[0004] Polyethylene terephthalate is a major packaging polymer,
used particularly for bottles for carbonated beverages. It is over
twenty times less permeable than polypropylene while still having a
practically significant permeability. There are extremely
impermeable polymers such as copolymers of ethylene and vinyl
alcohol, of vinylidene chloride and vinyl chloride, and of
m-xylylenediamine and adipic acid ("MXD6"); but for practical or
cost reasons these tend to be used as thin layers on or between
polyethylene terephthalate or (in the case of MXD6) for blending
with polyethylene terephthalate, in low per cent quantities, still
leaving practically significant permeability. For instance,
oriented blends of polyethylene terephthalate (96%) and MXD6 (4%)
are about 70% as permeable as polyethylene terephthalate. Chemical
Abstracts, 1984, volume 100, abstract 100: 193165x, being an
abstract of Japanese published patent application 58 160344, gives
some information on these blends.
[0005] We believe that there is considerable potential for
extending the use of polymers by means of oxygen-scavenging
systems. In these, oxygen reacts chemically as it is transmitted
inwards towards the package contents. Accordingly, transmission of
oxygen inwards to the package contents is reduced, not necessarily
with any improvement in the performance of the package with respect
to inward transmission of other substances such as nitrogen or
water vapour or outward transmission of substances.
[0006] Among substances that we believe can then be
more-satisfactorily packaged with polymers we would particularly
mention beers (especially lager beers), wines (especially white
ones), fruit juices, some carbonated soft drinks, fruits, nuts,
vegetables, meat products, baby foods, coffee, sauces, and dairy
products. Almost all foods and beverages are likely to display some
benefit.
[0007] Oxygen-scavenging implies consumption of a material
incorporated in the wall of the package. This will be progressively
consumed, so that the high barrier to oxygen must in principle be
of limited duration. However, the deterioration of the barrier to
oxygen is not necessarily commercially very significant. An
advantage is obtained so long as the rate of such deterioration is
not too great with respect to the time for which the deterioration
can occur prior to consumption of the product. This will depend on
the time from packaging to consumption and also on any relevant
storage times of raw materials, fabricated packaging materials, and
containers prior to their use in packaging the product. Good oxygen
barrier performance over periods as short as one day might be in
principle of use in certain cases, although periods or at least
two, five, ten, twenty, fifty, or hundred days will extend the
range of commercial applications. In respect of the prospective
advantage from reducing barrier over short periods only, it should
be remembered that oxygen entering the package shortly after the
product is packaged has a longer time to react and therefore do
damage than oxygen entering at a time nearer to consumption. It
should also be remembered that in some cases oxygen will be packed
with the product so that improvement of the performance of the
package beyond a certain point may have a relatively insignificant
effect on product quality.
[0008] An early proposal relating to oxygen-scavenging is described
in U.S. Pat. No. 3,856,514 (published in 1971). This describes most
particularly the addition of 0.8% to 2% by weight of antioxidants
to hard polyvinyl chloride. Antioxidants exemplified are
2,2'-methylene-bis-(4-me- thyl-6-t-butylphenol) and
2,2'-dihydroxy-2,3'-dicyclohexyl-5,5'-dimethyldi- phenylmethane.
The best permeability value reported is twenty times lower than
that of the polyvinyl chloride without the antioxidant.
Experimental evidence on the duration of the effect is not
given.
[0009] U.S. Pat. No. 4,048,361 (published in 1977) describes a
multilayer structure in which a barrier layer such as an
acrylonitrile-containing polymer, a terephthalate polyester,
polyvinylidene chloride, a cellulosic material, or an elastomer is
adhered to a layer comprising a carrier such as a polyolefin,
polystyrene, and polyvinyl chloride and an antioxidant. No
quantitative experimental investigation of the barrier properties
is described. The use of antioxidants with polyethylene
terephthalate is not specifically disclosed; in this respect it may
be noted that antioxidants are not added to polyethylene
terephthalate conventionally. (The conventional use of antioxidants
is the suppression of oxidation of polymers, such oxidation in a
package being regarded generally as undesirable.)
[0010] More recently, Rooney has described scavenging systems which
operate by oxidation or organic materials such as
1,3-diphenylbenzofuran when illuminated in the presence of a
dyestuff (Chem. Ind., 1979, 900-901; J.Food Science, 1981, 47,
291-298; Chem. Ind., 1982, 197-198). These systems have the
disadvantage for use with, say, beer bottles that it is not
practical to arrange for each bottle to be illuminated during
storage.
[0011] As well as these proposals to use organic materials as
scavengers there have been proposals to use inorganic reducing
agents as follows: iron powder (Japanese published patent
application 55 106519, published in 1980); hydrogen gas packed with
the product (UK patent 1,188,170, published in 1970); and sulphites
(UK patent specification 1,572,902, published 1980, and European
published patent application 83 826 published 1983). There has been
some commercial application of inorganic reducing agents. However,
special packing procedures are of course necessary if hydrogen is
used, and the use of sulphites and of iron requires special
procedures for wall fabrication because of their poor compatibility
with polymers.
[0012] Some discussion of the conventional measurements and units
of oxygen permeation is appropriate at this point. The measurement
is made by exposing a package wall of area A to a partial pressure
p of oxygen on the one side and to an essentially zero partial
pressure of oxygen on the other. The quantity of oxygen emerging on
the latter side is measured and expressed as a volume rate dV/dt,
the volume being converted to some standard conditions of
temperature and pressure. After a certain time of exposure (usually
a few days) dV/dt is generally found to stabilise, and a P.sub.W
value is calculated from the equation (1).
dV/dt=P.sub.WAp (1)
[0013] P.sub.W in the present specification and claims is called
the permeance of the wall. (Analogy with magnetic permeance and
electrical conductance would suggest that P.sub.W should be
described as "permeance per unit area", but we are following the
nomenclature in Encyclopaedia of Polymer Science and Technology,
Vol.2, Wiley Interscience, 1985, page 178.) The standard conditions
for expressing dV/dt used generally and in this specification are
0.degree. C. and 1 atm (1 atm=101 325 N m.sup.-2). If the thickness
of the area of wall is substantially constant over the area A with
value T and the wall is uniform-through the thickness (i.e. the
wall is not a laminated or coated one) then the permeability of the
material in the direction normal to the wall is calculated from the
equation (2).
dV/dt=P.sub.MAp/T (2)
[0014] For non-scavenging materials, P.sub.W and P.sub.M are to a
reasonable approximation independent of t and p, and P.sub.M of T
although they are often appreciably dependent on other conditions
of the measurement such as the humidity of the atmosphere on the
oxygen-rich side and the temperature of the measurement.
[0015] For oxygen-scavenging walls, P.sub.W and P.sub.M are
functions of t because the concentrations and activity of scavenger
vary with time (particularly as the scavenger is consumed). This
has not prevented us usually from measuring P.sub.W and P.sub.M
reasonably accurately as a function of time (the changes in dV/dt
being relatively gradual once the normal initial equilibration
period of a few days is over). However, it should be recognised
that, whereas after a few days exposure to the measurement
conditions a non-scavenging wall-achieves a steady state in which
dV/dt is equal to the rate of oxygen ingress to the wall, a
scavenging wall achieves an (almost) steady state in which dV/dt is
considerably less than the rate of oxygen ingress to the wall. This
being the case, it is likely that P.sub.W calculated from (1) is a
function of p as well as of t and that P.sub.M in (2) is a function
of p and T as well as of t. P.sub.W and P.sub.M for scavenging
walls are, strictly speaking, not true permeances and
permeabilities at all (since permeation and scavenging are
occurring simultaneously but, rather, apparent ones. However, we
have chosen to retain the conventional terms "permeance" and
"permeability". So long as the conditions of the measurement are
sufficiently specified they are suitable for characterising the
walls in a manner relevant to the packaging user (i.e. in terms of
the oxygen emerging from the wall).
[0016] All values of P.sub.W and P.sub.M hereinafter in this
specification (except where stated otherwise) are to be understood
to refer to conditions in which p=0.21 atm, the relative humidity
on the oxygen-rich side of the wall is 50%, the temperature is
23.degree. C. and (in the case of P.sub.M values) the thickness of
the wall is 0.3 mm. Conditions close to the first three of these,
at least, are conventional in the packaging industry.
[0017] Further, as will be appreciated from the above discussion of
the papers by Rooney, it is possible for P.sub.W and P.sub.M to be
affected by the illumination of the wall under test. All P.sub.W
and P.sub.M values hereinafter, and indeed all references to
oxidation, oxidisability, and oxygen-scavenging properties, refer
to the dark or else to conditions of irradiation not appreciably
contributing to oxygen-scavenging.
[0018] The present invention provides a wall for a package, which
wall comprises, or includes a layer comprising, a composition
comprising a polymer and having oxygen-scavenging-properties,
characterised in that the composition scavenges oxygen through the
metal-catalysed oxidation of an oxidisable organic component
thereof.
[0019] It is important to note in respect of the above and the rest
of the present specification and claims that the oxidisable organic
component may be an oxidisable polymer. The use of an oxidisable
polymer as the oxidisable organic component has the advantage,
broadly speaking, over the use of an oxidisable non-polymeric
component that it is less-likely to affect adversely the properties
of a non-oxidisable polymer with which it is blended. It is
possible for an oxidisable polymer to be used as the sole polymer
in the composition, serving a dual function as polymer and
oxidisable organic component.
[0020] It is to be noted in the same respect that it is of course
possible for two or more polymers, two or more oxidisable organic
components, or two or more catalysts to be used. It is possible
also for a metal catalyst to be used in combination with a
non-metal catalyst. For instance, with some oxidisable organic
components an organic peroxide may be used in combination with the
metal catalyst.
[0021] By "wall for a package" in the present specification and
claims is included (except where the context indicates otherwise)
not only a wall when incorporated into a package structure but also
packaging materials capable of forming walls, such as package
bases, packaging sheet, and so on.
[0022] The word "catalyst" is used in the present specification and
claims in a general way readily understood by the man skilled in
the art, not necessarily to imply that it is not consumed at all in
the oxidation. It is indeed possible that the catalyst may be
converted cyclically from one state to another and back again as
successive quantities of oxidisable component are consumed by
successive quantities of oxygen. However, it may be that some is
lost in side reactions, possibly contributing directly to
oxygen-scavenging in small measure, or indeed that the "catalyst"
is more properly described an an initiator (e.g. generating free
radicals which through branching chain reactions lead to the
scavenging of-oxygen out of proportion to the quantity of
"catalyst").
[0023] Advantageously, the permeance of the wall, for oxygen, is
not more than 10.0 cm.sup.3/(m.sup.2 atm day), preferably-not more
than 5.0 cm.sup.3/(m.sup.2 atm day), more preferably not more than
2.0 cm.sup.3/(m.sup.2 atm day), especially not more than 0.5
cm.sup.3/(m.sup.2 atm day), and most especially not more than 0.1
cm.sup.3/(m.sup.2 atm day).
[0024] Advantageously, the permeance of the wall provided by the
present invention is not more than three-quarters of that which it
would have in the absence of oxygen-scavenging properties,
preferably not more than one half, more preferably not more than
one tenth, especially not more than one twenty-fifth, and most
especially not more than one hundredth.
[0025] Such a permeance should advantageously be maintained for at
least one day when the wall is exposed on both sides to air at
23.degree. C. and 50% relative humidity, and more preferably for
the longer periods referred to in the preliminary discussion
above.
[0026] The necessary scavenging capacity of the wall will generally
have to be greater the greater is the permeance
[0027] in the absence of scavenging properties.
[0028] Accordingly, a good effect even in relative terms is harder
to achieve the higher is this latter permeance. Advantageously,
therefore, the permeance in the absence of oxygen-scavenging
properties is not more than 50 cm.sup.3/(m.sup.2 atm day),
preferably not more than 30 cm.sup.3/(m.sup.2 atm day), most
preferably not more than 18.0 cm.sup.3/(m.sup.2 atm day). A
particularly good effect can be achieved where the said permeance
is in the range from 1.5, preferably 3.0, to 30, preferably 18.0,
cm.sup.3/(m.sup.2 atm-day). While we believe that a good relative
effect should be achievable when said permeances are lower than 1.5
cm.sup.3/(m.sup.2 atm day), the range of commercial applications
seems to us to be relatively limited (generally because this would
involve using in the wall major quantities of existing high barrier
polymers rather than very convenient polymers such as polyethylene
terephthalate).
[0029] The wall may be a rigid one, a flexible sheet, or a clinging
film. It may be Homogenous or a laminate or coated with other
polymers. If it is laminated or coated, then the scavenging
property may reside in a layer of the wall the permeance of which
is relatively high in the absence of scavenging and which alone
would not perform very satisfactorily but which performs
satisfactorily in combination with one or more other layers which
have a relatively low permeance but negligible or insufficient
oxygen-scavenging properties. A single such layer could be used on
the outside of the package since this is the side from which oxygen
primarily comes when the package is filled and sealed. However,
such a layer to either side of the scavenging layer would reduce
consumption of scavenging capacity prior to filling and
sealing.
[0030] The present invention provides in its second aspect a
composition for packaging use which comprises a polymer, an
oxidisable organic component, and a metal catalyst for the
oxidation of the oxidisable organic component.
[0031] The composition provided by the present invention has three
major uses.
[0032] Firstly, it can be used as the material for a wall (uniform
in the direction normal to the wall at least) or else a layer of a
wall providing the major part of the overall barrier. In such a
case, the permeability of the composition for oxygen is
advantageously not more than 3.0, preferably 1.7, more preferably
0.7, especially 0.2, and most especially 0.03 cm.sup.3 mm/(m.sup.2
atm day). The permeability of the composition provided by the
present invention is advantageously not more than three-quarters of
that in the absence of oxygen-scavenging properties, preferably not
more than one half, more preferably not more than one-tenth,
especially not more than one twenty-fifth, and most especially not
more than one-hundredth. The permeability in the absence of
oxygen-scavenging properties is advantageously not more than 17
cm.sup.3 mm/(m.sup.2 atm day), preferably 10, and most preferably
6. A particularly good effect can be achieved for such
permeabilities in the range from 0.5, preferably 1.0, to 10,
preferably 6.0, cm.sup.3 mm/(m.sup.2 atm day).
[0033] Secondly, the composition can be used as a master batch for
blending with another polymer for such use.
[0034] Thirdly, it can be used for forming a layer of a wall which
primarily provides oxygen-scavenging (another layer including
polymer providing gas barrier without significant scavenging), or
as a head-space scavenger (completely enclosed, together with the
package contents, by a package wall).
[0035] The time period for which the permeability is maintained
when the composition is stored in air, as granules or in another
form, is not necessarily critical since storage in sealed
containers or under nitrogen is practical. However, preferably the
permeability should be maintained in air for the periods referred
to above in respect of the wall provided by the invention. More
importantly, however, the permeability should preferably be
maintained when a typical wall is made (0.3 mm thick).
[0036] In a third aspect, the invention provides a package, whether
rigid, semi-rigid, collapsible, lidded, or flexible or a
combination of these, a wall of which is a wall as provided by the
present invention in its first aspect or comprises entirely, as a
layer, or as a blend the composition provided by the invention in
its second aspect.
[0037] Before we proceed to describe the present invention in more
detail (including by means of Examples and an Experiment) it is
appropriate to deal with the question of how one may determine
permeance or permeability that a wall or composition would have in
the absence of scavenging (this permeance or permeability being
referred to several times above). The ratio of permeances or
permeabilities in the presence and absence of scavenging are one
(reciprocal) measure of the size of the scavenging effect, and it
is for this reason that various upper limits on this ratio are
suggested above. (Another measure might be the ratio of the
quantities of oxygen emerging and entering the wall under test, but
this is less practically convenient.) Four methods of determining
the permeances or permeabilities in question will now be described
with particular reference to determining whether a particular
preferred ratio (3/4, 1/2, 1/10 etc. as described above) is
exceeded:-
[0038] (1) The wall under test is exposed to oxygen for a time
sufficiently long that the oxygen permeance or permeability begins
to rise as the oxidisable organic component is consumed. It is of
course not necessary to continue the exposure until no further rise
occurs (i.e. until the scavenging is totally absent). Whenever the
exposure is terminated for a particular sample one can confidently
set a lower limit on permeance or permeability in the absence of
scavenging, and therefore an upper limit on the ratio in
question.
[0039] (2) A wall is prepared for comparison free of catalyst, and
the effect of the catalyst on pure permeation is estimated or (more
likely) reasonably ignored. Some scavenging activity in the absence
of catalyst will not preclude the establishment of the lower and
upper limits referred to in (1).
[0040] (3) In some cases, as will be discussed in more detail
later, the oxygen-scavenging property is still undeveloped until
some time after the forming of a wall, in which case one may take
the largest P.sub.W or P.sub.M value observed before achievement of
maximum barrier as setting a lower limit on P.sub.W or P.sub.M in
the absence of scavenging (results on unequilibrated samples being
ignored, of course).
[0041] (4) In some cases, the oxygen-scavenging effect can be
suppressed by cooling the wall or composition. With due allowance
for the effect of changed temperature, the lower and upper limits
referred to in (1) can be established.
[0042] Of the methods (1) to (4) above, (1) is probably the most
general, although for very good materials the experimental time
could be very long (e.g. exceeding one year) unless accelerating
conditions were used (e.g. higher temperature, high partial
pressures of oxygen). We believe that the walls and compositions in
accordance with the present invention should all display a plot of
permeance or permeability against time of exposure to oxygen
essentially as shown in FIG. 1 attached hereto. However, it being
relatively recently that this invention was made, we do not know
the precise form of the whole curve. It should be noted that a
similar curve for an inert gas such as nitrogen or carbon dioxide
is not to be expected, nor is such a curve to be expected from
known materials of high barrier properties although a long term
increase of permeance or permeability both for oxygen and for
nitrogen or carbon dioxide might occur as a result of general
degradation.
[0043] This indicates a possible fifth method of test, namely
performing comparative experiments with oxygen and an inert gas
while making due allowance for the difference of gas based on
broadly similar conventional materials. The validity of this method
in principle we have confirmed by our finding that bottles made in
accordance with the present invention provide an unexceptional
barrier to loss of carbon dioxide from carbonated water contained
in them.
[0044] The oxidisable component/metal catalyst combination to be
used in accordance with the present invention in all its aspects
may be selected by experimental trial and error such as the man
skilled in the art may readily devise. A good preliminary screening
can be achieved by means of pure scavenging measurements on
granulates (see Example 7 for a possible procedure). A metal
catalyst that is highly effective for one oxidisable organic
component may be less effective for another. The effectiveness may
depend on the precise grade of the organic component or of the
polymer in the composition. It will depend on what fillers,
conventional antioxidants, catalyst residues from polymerisation,
pigments and dyes may be present or added.
[0045] We do not understand fully the role which the metal catalyst
plays in the oxidation, although we regard metals with at least two
positive oxidation states, especially transition metals, as the
most promising catalysts when added in one of the positive
oxidation states, particularly as cations. Thus cobalt added in the
II and III state, rhodium added in the II state, and copper added
in the II state have proved effective with some oxidisable organic
components. Addition in the form of a carboxylate has proved
convenient. Generally speaking, higher levels of catalyst achieve
better scavenging. In the absence of undesired interactions between
the catalyst and the other components (such as depolymerisation) a
weight fraction of metal relative to the total composition of up to
5000 ppm can be readily contemplated. We have found that levels of
at least 10, preferably 50, more preferably 100 ppm of metal can
achieve catalysis (the precise level being determined by trial and
error for a particular overall composition). In wall applications
(as opposed to master batch applications where more catalyst is
used) we have preferred to keep the level of metal below 300, more
preferably 250 ppm.
[0046] In general, where the aim is to modify a non-axidisable
polymer so as to form a wall having scavenging properties the
weight fraction of the oxidisable organic component is likely to
lie in the range from 1 to 7 per cent. However, where the
oxidisable organic component is itself a polymer, then it may,
depending on compatibility, be used in blends over a wide range of
relative proportions with a non-oxidisable polymer or indeed be
used as the sole polymer component of the composition (i.e. weight
fractions from 1 to 100 per cent). Higher weight fractions may be
especially valuable with thin films and/or non-oxidisable polymers
of relatively high permeability when high oxygen ingress rates are
expected. Particularly interesting oxidisable polymers are the
polyamides, especially those containing groups of the formula
-arylene-CH.sub.2--NH--- CO--, conveniently in
--NH--CH.sub.2-arylene-CH.sub.2--NH--CO-alkylene-CO-- - units.
These polyamides are of especial interest with cobalt and rhodium
catalysts. Especially suitable arylene groups are phenylene groups,
particularly m-phenylene groups, which may be alkyl-substituted
and/or condensed with other unsubstituted or alkyl-substituted
aromatic rings. Alkylene and alkyl groups conveniently have from 1
to 10 carbon atoms and may be straight-chain or branched.
Especially suitable alkylene groups are n-butylene groups. MXD6 is
very suitable. Conveniently, the relative viscosity (also called
viscosity ratio) of polyamides containing
--NH--CH.sub.2-arylene-CH.sub.2--NH--CO-alkylene-CO-- groups lies
in the range from 1.5 to 4.5, especially 2.0 to 3.6 (measured for
solutions in 95% aqueous sulphuric acid containing 1 g of polymer
per 100 cm.sup.3 solution).
[0047] Fully aliphatic polyamides are promising, comprising
--CO(CH.sub.2).sub.nCONH(CH.sub.2).sub.mNH-- or
--(CH.sub.2).sub.pCONH-- units (n, m, and p being integers usually
4, 5, or 6), although we have so far not achieved the very good
results which we have achieved with MXD6. In general, the polyamide
may include polymer linkages, side-chains, and end groups not
related to the formal precursors of a simple polyamide (i.e.
compounds having at least two amino groups per molecule together
with those having at least two carboxylic acid groups per molecule,
or aminocarboxylic acids). Conveniently, at least 90 mole per cent
of the polymer's formal precursors will be such. However, a polymer
including a minority of amide linkages would in principle work,
such a polymer perhaps being used as the sole polymeric component
of the composition. Even in such a case, however, one would expect
to include in the composition a concentration of --CONH-- linkages
similar to that which one would use with MXD6--i.e. concentrations
of --CONH-- in the total composition of at least 0.08 mmol/g, most
commonly up to 0.6 mmol/g.
[0048] From a purely chemical standpoint, non-polymeric amides are
attractive as oxidisable organic components. Non-polymeric
compounds containing a group or groups of the formula
-alkylene-CO--NH--CH.sub.2-1,-
3-phenylene-CH.sub.2--NH--CO-alkylene- are of interest, especially
with cobalt and rhodium catalysts. The above comments on alkylene
and 1,3-phenylene groups, made with reference to polymeric amides,
apply here except that n-butylene is not so convenient if an
alkylene group is terminated by H. An example of such a
non-polymeric compound is
n-C.sub.3H.sub.7--CO--NH--CH.sub.2-m-C.sub.6H.sub.4--CH.sub.2--NH--CO-n-C-
.sub.3H.sub.7, which in the presence of cobalt we have found to
scavenge oxygen well, although its suitability for use in
accordance with the present invention needs of course to be
determined by trial and error in a particular application.
[0049] Other non-polymeric oxidisable compounds are also of
interest, for instance conventional antioxidants including
substituted phenols, especially 2,4,6-tri-(t-butyl)phenol.
[0050] Subject to the above preferences on physical properties,
non-oxidisable polymers used according to the present invention in
all its aspects can be chosen with fair freedom, unless there is
some specific inhibition of the scavenging system or other untoward
interaction. In principle, there may be a favourable interaction
(e.g. if the non-oxidisable polymer contains as catalyst residues
metals catalysing the oxidation of the oxidisable organic
component); but in current commercial products the levels are
usually low and the catalyst may be at least partially poisoned
by-the other residues or additives.
[0051] Polymers (formally) or one or more phthalic acids with one
or more organic compounds containing at least two alcoholic hydroxy
groups per molecule can offer fair impermeability in the absence of
scavenging. Preferably, the permeabilities should be less than 6.0
cm.sup.3 mm/(m.sup.2 atm day). Phthalic acid polyesters based on
terephthalic or isophthalic acid are commercially available and
convenient; the hydroxy compounds are typically ethylene glycol
(which may yield diethylene glycol units in situ), and
1,4-di-(hydroxymethyl)-cyclohexane. Conveniently, the intrinsic
viscosity (also called limiting viscosity number) for a phthalic
acid polyester lies in the range from 0.6 to 1.2, especially 0.7 to
1.0 (for o-chlorophenol solvent). 0.6 corresponds approximately to
a viscosity average molecular weight of 59 000, and 1.2 to 112
000.
[0052] In general, the phthalate polyester may include polymer
linkages, side chains, and end groups not related to the formal
precursors of a simple phthalate polyester previously specified.
Conveniently, at least 90 mole per cent will be terephthalic acid
and at least 45 mole per cent an aliphatic glycol or glycols,
especially ethylene glycol.
[0053] Polyolefins blended with a scavenging system have been found
to work, and by lamination or coating with less permeable material
walls of interesting overall barrier properties should be
achievable.
[0054] The composition may, as previously mentioned, include other
components such as pigments, fillers, and dyestuffs. Usually, the
total quantity of such components will be less than 10%, more
usually less than 5%, by weight relative to the whole
composition.
[0055] Compositions which we think may be of especial importance on
the basis of our experiments to date include the following (the
percentages being the weight fractions relative to the total
composition):
[0056] compositions comprising at least 90%, preferably 95%, of
polyethylene terephthalate and/or a polyamide taken together and
having a permeability to oxygen of not more than 0.01 cm.sup.3
mm/(m.sup.2 atm day);
[0057] compositions containing at least 90% of polyethylene
terephthalate, preferably 95%, and having a permeability to oxygen
of not more than 0.3 cm.sup.3 mm/m.sup.2 atm day), and preferably
not more than 0.1 cm.sup.3 mm/(m.sup.2 atm day), and more
preferably not more than 0.03 cm.sup.3 mm/(m.sup.2 atm day),
preferably at least 0.5%, more preferably 1%, and also preferably
less than 7% of the composition consisting of a polyamide; and
[0058] compositions comprising at least 90%, preferably 95%, of a
polyamide and having a permeability to oxygen of not more than 0.01
cm.sup.3 mm/(m.sup.2 atm day).
[0059] The composition provided by the present invention or used in
walls provided by the present invention is preferably formed by
mixing the metal catalyst with the other component or components of
the composition all together or in any sequence. The metal catalyst
is preferably added in the form of a solution or slurry.
Conveniently, the mixing includes or is followed by melt-blending
at a temperature appropriate to the components, commonly in the
range from 100.degree. C. to 300.degree. C. The blending may
immediately precede the formation of the finished article or a
preform or parison, or may be followed by formation of feedstock
for later use, in the production of the finished article. We have
found additions of catalyst in the range of 10 to 250, especially
50 to 200, ppm to be convenient.
[0060] The oxidation catalyst may be added to the monomers from
which one or more polymeric components of a composition are made,
rather than being added as proposed above in a subsequent blending
step. Clearly, if the oxidation catalyst neither interferes with
nor is affected by the-polymerisation process then this may be an
attractive option. If the catalyst interferes or assists with the
polymerisation or is at least partially poisoned by the usual steps
in the polymerisation (as may be the case with cobalt and
polyethylene terephthalate production), then modification or
careful selection of polymerisation protocols will be
necessary.
[0061] In some systems at least, the scavenging properties do not
emerge immediately after the blending, but only after ageing. This
may be because catalyst species have to migrate to relevant sites
in the composition because it is incorporated so as to be present
in the "wrong" phase or because the relevant sites in the
oxidisable component to which they were attached during processing
were very largely oxidised during processing, or because a slow
initiation is involved, or for some other reason. Prolonged ageing
at ordinary temperatures, or ageing accelerated by elevated
temperatures, are in principle possible but are costly. However,
the higher the level of catalyst used, generally the less ageing is
required. Indeed, we have achieved very high barrier to oxygen so
soon after fabrication of walls that any delay is comparable with
or shorter than the normal time required to equilibrate the wall on
the OXTRAN machine, and is unlikely to impose significant cost
penalties. In general, one would seek to achieve high barrier
within 30 days, preferably 20 days, and more preferably 10 days, of
the wall being fabricated if the wall is stored at 23.degree. C.
and 50% relative humidity.
[0062] We shall now consider briefly the packaging structures and
forming techniques that will be appropriate when the present
invention is used for packaging. Where the oxidisable organic
monument is non-polymeric it may have a significant effect on the
forming techniques used, especially on the temperatures that may be
used if the component is volatile. This in turn will affect the
structures that can readily be made. Where, however, the
composition used comprises oxidisable polymer plus catalyst, or
non-oxidisable polymer, oxidisable polymer, plus catalyst, then the
forming techniques and structures can be expected to match those
appropriate to the oxidisable polymer or its blend in the absence
of catalyst; the quantities of catalyst used are likely to be too
small to have much effect on mechanical properties in most
cases.
[0063] Among the techniques that may be in question are moulding
generally, injection moulding, stretch blow moulding, extrusion,
thermoforming, extrusion blow moulding, and (specifically for
multilayer structures) co-extrusion and lamination using adhesive
tie layers orientation, e.g. by stretch blow moulding, of the
polymer is especially attractive with phthalate polyesters and
their blends with MXD6 because of the known mechanical and (in the
latter case) barrier advantages that result.
[0064] In the discussion of wall structures according to the
invention early in this specification, the design considerations
relating to the barrier properties were referred to. However, there
are more general considerations, familiar in the art, which will be
taken into account in practical applications.
[0065] One such consideration is rigidity. If a plastic container
is to be self-supporting when empty, then the thickness of the wall
is likely to lie in the range from 200 to 500 micrometre; such
containers are often referred to as "semi-rigid". More flexible
packaging structures such as meat packs are likely to have wall
thickness in the range from 20 to 200 micrometre. Where thick
structures are required, one may choose to provide only a thin
highly effective scavenging barrier layer supported by mechanically
superior or cheaper relatively poor barriers.
[0066] Another consideration is the requirements for bonding of the
wall made in accordance with the present invention. For instance,
an extra layer may be added to a sheet so as to permit heat sealing
to complete a package structure.
[0067] A further consideration is the protection of the
oxygen-scavenging composition from the package contents or the
environment if direct contact causes any difficulties (e.g.
undesirable chemical reactions or leaching). In such a case a
protective layer will be provided on the appropriate side of the
layer containing the oxygen-scavenging composition.
[0068] For the avoidance of any possible doubt resulting from the
two sets of design considerations for multilayer structures, three
such structures for walls according to the present invention will
now be described, by way of illustration only, by reference to the
FIGS. 3 to 5, each representing schematic sections (not to scale)
of multilayer walls according to the invention.
[0069] In FIG. 3, layer 1 consists of a blend of a first polymer,
an oxidisable organic component, and a metal catalyst. Layers 2 and
3 consist of a second polymer having a permeability much less than
the permeability of the pure first polymer. The overall permeance
performance of the wall is markedly superior to that of a
single-layer wall of the same composition as layers 2 and 3 or of a
single-layer wall of the same composition as layer 1.
[0070] In FIG. 4, layer 1 consists of an oxidisable polymer and a
metal catalyst and alone would have a low permeance. Layer 1 is too
thin for the proposed use and is supported by layers 2 and 3 of a
non-oxidisable polymer which do not significantly reduce the
permeance.
[0071] In FIG. 5, layer 1 consists of a blend of a first polymer,
and oxidisable organic component, and a metal catalyst. Its
permeance is low and it could be economically used at a thickness
appropriate to the proposed use. However, layer 1 is protected from
undesired direct interaction with the package contents and the
environment by layers 2 and 3 of a second polymer which do not
significantly reduce the permeance.
[0072] The present invention will now be further described, by way
of illustration only, by means of the following Examples and an
Experiment.
EXAMPLES 1 TO 5
[0073] The materials used in these Examples were of the grades
specified below. Further information was obtained by our own
measurements or from the manufacturers literature.
[0074] Polyethylene terephthalate, grade B90N, from ICI of UK. This
is a polymer of ethylene glycol with terephthalic acid. It was
found to contain 35 ppm cobalt, 25 ppm sodium, 38 ppm phosphorus,
and 32 ppm antimony, with .ltoreq.1 ppm or copper, germanium, iron,
manganese, and titanium. The intrinsic viscosity in O-chlorophenol
is 0.82.
[0075] MXD6, grade Reny 6001, from Mitsubishi Gas Chemicals of
Japan. This is a polymer of meta-xylylenediamine
H.sub.2NCH.sub.2-m-C.sub.6H.sub.4--C- H.sub.2NH.sub.2 with adipic
acid HO.sub.2C(CH.sub.2).sub.4CO.sub.2H. The relative viscosity of
the polyamide is 2.1, for a solution in 95% aqueous sulphuric acid
containing 1 g of polymer per 100 cm.sup.3 of solution.
[0076] Cobalt Siccatol, from Akzo Chemie ("Siccatol" is a trade
mark). This is a solution in white spirit of C.sub.8-C.sub.10
cobalt carboxylates. The concentration of cobalt (as metal) is 10%
by weight relative to the solution.
[0077] Granules of the polyethylene terephthalate and of the MXD6
were mixed by hand in a tray together with the Siccatol solution in
the relevant proportions. The mixture was then heated at
100.degree. C. for 18 hours in a recirculating dehumidified air
dryer (this to remove water from the two polymers so as to avoid
degradation in injection moulding, as well as incidentally driving
off unevaporated white spirit).
[0078] The mixture was then used to make a preform for a one-litre
cylindrical bottle. The injection moulding was performed on a
Krauss Maffei KM 150 machine. The mass of the preform was
approximately 33 g. The preform was then reheated and blown to form
the bottle with biaxial orientation (i.e. circumferential and
longitudinal orientation). For this, a Corpoplast BMB3 stretch blow
moulding machine was used. The bottle had a wall thickness of 0.3
mm.
[0079] Five bottles were made and tested for oxygen permeance on an
OXTRAN machine 10/50 A made by Mocon Inc of USA. The conditions of
the tests were as set out earlier in this specification.
[0080] Tests were performed at various times after the bottle had
been manufactured. In between tests, the bottles were stored with
air both inside and out. Each test lasts 3 to 4 days until the
bottle (as is usual) "equilibrates" from its storage conditions
(exposed to the atmosphere inside and out) to the test
conditions.
[0081] The various compositions and the test results obtained are
set but in Tables 1 and 2. The permeances per unit area quoted are
calculated from the OXTRAN result on the basis of an oxygen partial
pressure of 0.21 atm and a bottle area of 0.0575 m.sup.2. P.sub.W=O
indicates that no oxygen transmission was detected. The bottle wall
being essentially uniform, they may be converted into
permeabilities in cm.sup.3 mm/(m.sup.2 atm day) for the material by
multiplying them by 0.3.
[0082] For comparison, in Table 2, are also listed the P.sub.W
values observed (or calculated from reported P.sub.M values) for
similar bottles made from the same polymer components in which the
oxygen-scavenging effect is absent (no addition of cobalt). These
figures are approximate, but the spectacular character of the
effect is immediately evident from the comparison.
[0083] The results of Examples 1 and 3 are plotted in FIG. 2.
[0084] A rough calculation for Example 3 based on the comparison
P.sub.W figure indicates that at the time of the last measurement
the bottle will have scavenged at least 0.9 mmol of O.sub.2. The
bottle contains only 0.11 mmol of Co, establishing that the cobalt
functions as a catalyst in the sense previously described.
[0085] The Examples show that, notwithstanding some variability
between samples of similar composition, there is a broad positive
correlation between the extent and duration of scavenging and the
levels of both the oxidisable organic component and the
catalyst.
1TABLE 1 WEIGHT FRACTIONS OF RAW MATERIALS USED TIME IN RELATIVE TO
TOTAL DAYS BALANCE FROM POLYETHYLENE MANU- TEREPHTHALATE FACTURE
WEIGHT OF FIRST WEIGHT FRACTION MEASURE- EXAMPLE FRACTION COBALT
STORAGE MENT No. MXD6 AS METAL CONDITIONS P.sub.W = 0 1 4% 50 ppm
23.degree. C. 10 50% R.H. 2 4% 50 ppm Uncontrolled 3 storage cooler
than 1 3 4% 200 ppm as 1 3 4 2% 50 ppm as 2 10 5 1% 50 ppm as 2
20
[0086]
2TABLE 2 This table gives P.sub.W at time t after first measurement
of P.sub.W = O and a Comparison P.sub.W (no scavenging) for
Examples 1 to 5. EXAMPLE 1 test results t in day 0 24 57 105 150
203 270 1 P W in cm 3 ( m 2 atm day ) 0 0 0.016 0.19 0.6 0.8 1.2
Comparison P.sub.W = 3.0 cm.sup.3/(m.sup.2 atm day) EXAMPLE 2 test
results t in day 0 135 192 207 2 P W in cm 3 ( m 2 atm day ) 0
0.025 0.3 0.35 Comparison P.sub.W = 3.0 cm.sup.3/(m.sup.2 atm day)
EXAMPLE 3 test results t in day 0 31 64 112 157 210 277 3 P W in cm
3 ( m 2 atm day ) 0 0 0.009 0 0.03 0.02 0.02 Comparison P.sub.W =
3.0 cm.sup.3/(m.sup.2 atm day) EXAMPLE 4 test results t in day 0
125 185 200 4 P W in cm 3 ( m 2 atm day ) 0 0.95 1.3 1.4 Comparison
P.sub.W = 3.8 cm.sup.3/(m.sup.2 atm day) EXAMPLE 5 test results t
in day 0 115 175 195 5 P W in cm 3 ( m 2 atm day ) 0 2.7 3.1 3.3
Comparison P.sub.W = 4.2 cm.sup.3/(m.sup.2 atm day)
EXAMPLE 6
[0087] This Example illustrates the use of a master batch.
[0088] MXD6 and Cobalt Siccatol were mixed and injection moulded
into preforms. 2000 ppm cobalt as metal was used by weight relative
to the MXD6.
[0089] The preform was then granulated to make a master batch of
granules. These were then mixed with polyethylene terephthalate to
make further preforms, and these were blown into bottles the same
day. 6% by weight of master batch and 94% by weight of polyethylene
terephthalate were used.
[0090] The procedures were as described in Examples 1 to 6 save
that, of course, polyethylene terephthalate was omitted in the
first stage or the above procedure and Cobalt Siccatol in the
second.
[0091] The bottles achieved a P.sub.W of 0.002 cm.sup.3/(m.sup.2
atm day) within 2 days.
EXAMPLE 7
[0092] This Example directly illustrates the scavenging properties
of compositions in accordance with the invention, and the
dependence of the properties on temperature.
[0093] A preform was made as described in Examples 1 to 5 with the
same ingredients, but the weight fractions of MXD6 and cobalt (on
the same basis) were 2% and 100 ppm respectively.
[0094] The preform was granulated and 25 g samples were sealed into
each of three 60 cm.sup.3 vials having a septum through which the
head space gas could be sampled. The three vials (1 to 3 below)
were stored at different temperatures for 38 days and the head
space gas was analysed. For comparison similar samples without the
added cobalt were stored under similar conditions (vials C1 to C3
below) and the head space gas analysed. The results are summarised
in the following table. The O.sub.2:N.sub.2 ratios are more
reliably determined than the absolute values (themselves normalised
so as to sum to 99%).
3 Storage Volume fraction Volume fraction Vial temperature of
O.sub.2 after of N.sub.2 after No. in .degree. C. 38 days 38 days 1
4.degree. C. 12 87 C1 4.degree. C. 20 79 2 20.degree. C. 8 91 C2
20.degree. C. 20 79 3 55.degree. C. 5 94 C3 55.degree. C. 20 79
[0095] It will be seen that although the scavenging effect is
reduced at 4.degree. C., it is still very appreciable, which is of
course relevant to packaging applications where prolonged
refrigerated or other cool storage may occur.
[0096] A rough calculation for test vial 2 indicates that the
amount of O.sub.2 scavenged over 38 days was 0.24 mmol, whereas the
amount of the sample contained only 0.04 mmol Co, establishing
again that the cobalt functions as a catalyst in the sense
previously described.
EXAMPLE 8
[0097] This Example illustrates the present invention under test
conditions, more closely approaching the actual (aqueous)
conditions in beverage applications. A nominal one-litre bottle was
made as described for Examples 1 to 5, and with the same
composition as the bottle of Example 3.
[0098] The bottle had a volume of 1040 cm.sup.3 and was filled with
1000 cm.sup.3 of water through which nitrogen gas was bubbled
before the bottle was finally sealed with a septum permitting head
space sampling.
[0099] The volume fraction of oxygen in the head space gas was
monitored as a function of time, the bottle being stored in ambient
laboratory conditions.
[0100] The volume fraction was less than 0.2% after 31 days, a very
similar result being obtained with a glass bottle comparison. A
comparison bottle without the added cobalt gave a result of
1.1%.
[0101] The bottles were then subjected to a variety of temperature
conditions (a period at 38.degree. C., 4.degree. C., and ambient)
and after 108 days the results for the example, the glass
comparison, and the comparison without added cobalt were 0.2%,
0.2%, and 2.7%.
EXAMPLE 9
[0102] This Example illustrates the use of a rhodium catalyst
instead of a cobalt catalyst in a system otherwise similar to those
of Examples 1 to 8.
[0103] Polyethylene terephthalate, MXD6, and a solution of rhodium
(II) acetate dimer were mixed and dried overnight at 100.degree. C.
The first two components were of the grades used in Examples 1 to
5. The weight fractions of MXD6 and of rhodium (as metal) relative
to the whole mixture were 4% and 175 ppm respectively.
[0104] A preform for a 296 cm.sup.3 bottle was made on a Meiki 200
injection moulding machine, and the bottle was blown.
Limit-of-detection oxygen transmission was observed on the OXTRAN
machine previously referred to.
EXAMPLE 10
[0105] This Example illustrates the present invention applied to a
polymer other than polyethylene terephthalate. It also demonstrates
the scavenging in an injection-moulded (unblown) container.
[0106] Polypropylene (Solvay grade KL 104) straight from the bag
was mixed-with MXD6 of the-grade used in Examples 1 to 5 which had
been previously dried overnight at 100.degree. C. in a
dehumidifying air dryer and with cobalt Siccatol. Without further
drying, the mixture was injection-moulded to form a cylindrical pot
on a Meiki 200 injection moulding machine. The pot had a wall
thickness of 1.5 mm, was 61 mm diameter, 70 mm high, and had a
surface area of 0.015 m.sup.2
[0107] The weight fractions of MXD6 and cobalt (as metal) relative
to the whole composition were respectively 10% and 200 ppm.
Permeances on the OXTRAN machine of less than 16 cm.sup.3/(m.sup.2
atm day) were observed over 18 days of testing. A comparison
without added cobalt had a permeance of 26 cm.sup.3/(m.sup.2 atm
day).
[0108] This performance indicates a very high rate of scavenging
and implies that the composition may be useful for head space
scavenging or as the scavenging layer in a wall including
additionally a non-scavenging layer of low permeability.
EXAMPLE 11
[0109] This Example illustrates the use of a different scavenging
system once more with polypropylene in place of polyethylene
terephthalate.
[0110] Example 10 was repeated but instead of MXD6, nylon-6,6 of
ICI grade A100 pre-dried as supplied was used. Instead of Cobalt
Siccatol, a solution of copper (II) acetate in methanol was used (7
g/dm.sup.3 concentration). The weight fractions of nylon-6,6 and
copper (as metal) relative to the total composition were 20% and 25
ppm respectively, the balance being polypropylene.
[0111] Pink-coloured bottles were produced which had a permeance of
approximately 6 cm.sup.3/(m.sup.2 atm day) for 22 days of, testing
in the OXTRAN machine. A comparison bottle without added copper had
a permeance of 9 cm.sup.3/(m.sup.2 atm day).
EXAMPLE 12
[0112] This Example illustrates another scavenging system with
another non-oxidisable polymer. The metal catalyst in this case is
assisted by an non-metallic catalyst, and the oxidisable organic
component is non-polymeric.
[0113] The procedure of Example 10 was repeated, but on this
occasion with low density polyethylene instead of polypropylene,
and 2,4,6-tri-(t-butyl)phenol and
2,5-dimethylhexane-2,5-di-(-t-butyl) peroxide instead of MXD6. The
polyethylene was DSM grade Stanylan LD 2308A; the substituted
phenol was the material of Aldrich Chemical Co.Ltd; and the
peroxide was the material of Interox Chemicals Ltd.
[0114] The weight fractions relative to the total composition were
4% substituted phenol, 1% peroxide, 100 ppm cobalt (as metal), and
balance low density polyethylene.
[0115] The permeance was consistently measured as 30-33
cm.sup.3/(m.sup.2 atm day) over a period of 8 days, whereas a
comparison without the added cobalt had values rising monotonically
from its lowest value of 46 cm.sup.3/(m.sup.2 atm day) to 66
cm.sup.3/(m.sup.2 atm day) over the same period.
EXAMPLES 13 TO 20
[0116] It is believed that the foregoing examples provide ample
instruction to the man skilled in the art to put the present
invention into effect, but for the sake of completeness there are
listed in Table 3 various other compositions we have found to
perform well (permeances less than 0.05 cm.sup.3/(m.sup.2 atm day).
The permeances were measured on 0.3 mm walls except in the case of
Example 18, where the wall was 1.5 mm thick.
4TABLE 3 Polymer Oxidisable (balance organic Example of component
and Catalyst and No. composition) weight fraction weight fraction
13 PET MXD6 Co 100 ppm 4% added as Co (II) acetylacetonate 14 PET
MXD6 Co 100 ppm 4% added as Co (III) acetylacetonate 15 PET MXD6 Co
100 ppm 4% added as Co (II) stearate 16 PET MXD6 Co 100 ppm 4%
added as Durham Chemicals Nuosyn 17 PET MXD6 Co 100 ppm 4% added as
Co (II) neodecanoate 18 PETG MXD6 Co 200 ppm 5% added as Cobalt
Siccatol 19 P121 MXD6 Co 100 ppm 5% added as Cobalt Siccatol 20 --
MXD6 Co 200 ppm 100% added as Cobalt Siccatol Notes to Table 3:-
PET, MXD6: grades as in Examples 1 to 5. PETG: a modified PET
including 1,4-di-(hydroxymethyl)-cyclohexane units, Eastman Kodak
grade 6763. P121: another ICI grade of polyethylene terephthalate
suitable in this admixture with MXD6 for extrusion, intrinsic
viscosity in o-chlorophenol 0.85.
Experiment
[0117] Fibres of a material having the same composition as the
master batch in Example 6 were formed into a film and the infra-red
absorption spectrum was observed. An absorption was observed at
1640 cm.sup.-1 which we believe represents an amide carbonyl
absorption.
[0118] The material was then held in air in an oven at 55.degree.
C. for two months and the spectrum was once more observed. A new
albeit relatively small peak was observed at 1740 cm.sup.-1 which
we believe represents a carbonyl absorption distinct from the amide
carbonyl absorption at 1640 cm.sup.-1 (still present).
[0119] The same-effect was observed after holding fibres at
100.degree. C. in air for only 5 days.
[0120] No such effect was observed when MXD6 fibres without cobalt
was held in air at 100.degree. C. for 5 days.
[0121] We believe that the new band may indicate a carbonyl group
formed when the material scavenges oxygen, or possibly the carbonyl
group in the original material whose chemical environment has been
changed, by oxidation.
* * * * *