DK159199B - Oxygen-absorbing plastic structures for improving their resistance to oxygen transmission, container incorporating such structures and method for protecting oxygen-sensitive products against oxidation - Google Patents

Description

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The invention relates to oxygen-absorbing plastic structures to improve its resistance to oxygen transmission, containers including such structures, and to methods for protecting oxygen-sensitive products from oxidation.

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This specification relates to improved polymeric materials intended for packaging foodstuffs and the like, as well as containers made of such polymeric materials. Containers used for food packaging are often subjected to harsh processing conditions, e.g. during retort treatment for sterilization purposes. Containers that can be retorted and methods of manufacture are mentioned in our international patent applications filed under PCT and published under Nos. W081 / 00230 and W081 / 00231 on Feb. 5.

1981. The present invention can be applied to the subject discussed in each of the 15 aforementioned international applications.

It has already been proposed to use blow molded multilayer pool containers with barrier layers to reduce oxygen penetration through the container wall to protect the food or beverages packed therein against oxidation. The problem of oxygen penetration is well known and mitigated by a suitable barrier material. In addition, such surfactants have been used or proposed in multi-layer structures in connection with oxygen scavenging systems for the absorption of all oxygen that may pass through the barrier layer or remain in the compartment of the packed and processed food or beverage. More specifically, the specification of U.S. Patent No. 4,048,361 discloses a food container made with a barrier material within which there is a support layer containing a "getter". The "getter" may be an absorbent for all gas passing through the barrier layer. An alternative solution includes a barrier layer on each side of the carrier layer whereby oxygen from the food or from outside oxygen will slowly be absorbed by the "getter". In this patent, the particular "getter" is generally referred to, and patent 35 relates more specifically to a container shape or construction. In the specification of US Patent No. 3,586,514, the use of anti-oxidants mixed with a plaster barrier layer is mentioned to reduce the penetration of oxygen into beer in a container.

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2 of the specification of US Patent No. 3,429,717 discloses a barrier layer comprising Saran® in a foil sandwich with an antioxidant! in uniform distribution among the Saran-1agene. This patent describes that the antioxidant medium must be selected depending on the film, the product to be wrapped, as well as the light and heat conditions to which the package will be exposed.

From the disclosure of U.S. Patent No. 4,113,652, it is known that the presence of ammonium salts or water in an oxygen scavenger may extend the period before the oxygen scavenger becomes effective. Increasing the amount of water or ammonium salts in the oxygen scavenger will extend its latency period. This patent only mentions a latency period of up to 50 hours. As will be appreciated in the light of the present disclosure, such a latency period is impractical for many food containers from a commercial point of view.

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Various oxygen scavenging agents are known. In the specification of US Patent No. 2,825,651, an oxygen removal system which includes hydrates, e.g. an anhydrous sodium sulfite catalyzed by copper sulfate pentahydrate. Such an oxygen scavenger is included as a pellet within a protective package for placement in the container's free space. The problem of using the invention of this patent in practice is pointed out in the specification of US Patent 25 No. 4,113,652.

More relevant to multi-layer containers is U.S. Patent No. 4,041,209. This patent discloses an aqueous solution of a reducing sulfite salt disposed between a very blocking outer layer and a smaller blocking inner layer, a structure which allows the extraction of oxygen from the free space, so that the solution can react with the leaking oxygen, and thus delay inward oxygen flow from the outside. There is neither mentioned nor proposed regulation or activation of the solution in this patent. Activation is an important aspect of the present invention.

From the above, it appears that a plastic structure (e.g., a container) containing a scavenger or a "getter" to enhance its resistance to passage of gases, such as 3

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oxygen, is known from U.S. Patent No. 4,048,361 or U.S. Patent No. 3,586,514. The present invention is based on such a structure, and is intended to provide improvements thereof, i.a. making the structure activatable, when desired, to an oxygen-absorbing state.

A successful oxygen scavenging system must remain passive or inert to maintain its oxygen-collecting capacity until the food is sealed in the container. Containers are often stored empty on 10 stocks for several months before use. Therefore, there is a need for means whereby the scavenger in a multilayer vessel will remain passive until the oxygen scavenging activity is most advantageous. The patent literature does not meet this need to which the present invention is directed.

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The present invention provides a plastic structure including a scavenger for improving its resistance to oxygen transmission therethrough, characterized in that it is a laminate comprising a plurality of 20 solid polymer layers, at least one of which comprises a dry oxygen scavenger composition. wherein the scavenger composition is made capable of exhibiting a longer passive state, under which it does not substantially react with oxygen, and wherein the composition can be activated to an active oxygenophilic state, under which it is directly reactive with oxygen when moisture originating from the ambient environment is allowed to reach and moisten the composition wherein the composition is associated with a protective polymer material either in the layer containing the composition or in another layer or layers of the structure so that it is selectively protected therefrom from moisture where it is protective material is resistant to moisture penetration at ambient temperature, but has increased moisture permeability at elevated temperature, e.g. at above 93.3 ° C, so that when the structure is exposed to elevated temperature and moisture, the protective material, e.g.

35 under retort conditions, can be made moisture permeable and allow moisture to come into contact with and moisten the composition, thereby activating it from its passive to its active state.

The invention also provides a plastic structure including one

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4 is a scavenger for improving its resistance to oxygen transmission therethrough, characterized in that it comprises a solid polymeric layer which includes a dry oxygen scavenger composition wherein the scavenger composition has been capable of exhibiting a longer passive state, under which it does not react substantially with oxygen, and the composition can be activated to an active oxygenophilic state, under which it is directly reactive with oxygen when moisture from the surrounding environment is allowed to reach and moisten the composition, 10 wherein polymer The yoke is resistant to moisture penetration at ambient temperature, but has increased moisture permeability at elevated temperature, e.g. above 93.3 ° C so that the protective material, by exposing the structure to elevated temperature and moisture, e.g. under retort conditions, moisture permeability can be made to allow moisture to contact and moisten the composition, thereby activating it from its passive to its active state.

This structure can be used as an insert or piece that is simply placed in a container or package to protect the contents after activation to the oxygenophilic state. An oxygen barrier is not essential in this case.

The structure of the invention may also be embodied as a container which is co-injected, coextruded, blow molded or thermoformed. Such a container may be characterized by a wall including an outer olefin layer, an oxygen barrier layer, a polymer layer comprising the composition and an inner olefin layer, the olefinic agent or an additional layer or layer of the wall comprising the material which is substantially impervious to moisture, to protect the composition at ambient temperature, but which is permeable to moisture by e.g. retort temperatures, whereby moisture can reach and activate the composition to an active, oxygenophilic state.

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The present invention also provides a method for protecting an oxidizable product from degradation by oxidation during storage, the process being characterized in that it comprises the steps of: (a) forming a container from 5

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a plastic structure having a plurality of solid polymeric layers, at least one of which includes a dry oxygen scavenger composition, wherein the scavenger composition has been made capable of exhibiting a longer passive state during which it does not substantially react with oxygen and the composition can be activated to an active oxygenophilic state under which it is directly reactive with oxygen when moisture from outside the structure is allowed to reach and moisten the composition, wherein the composition is associated with a protective polymer material in either the layer 10 itself containing the composition or another layer or layers of the structure so that it is selectively protected against moisture, whereby the protective material is resistant to moisture penetration at ambient temperature, but has increased moisture permeability at elevated temperature, e.g. (b) filling the container with the product and hermetically sealing it around the product, and (c) subjecting the sealed container to elevated levels of temperature and moisture to make the protective material moisture permeable to allow; that moisture contacts and wets the composition and transforms it from its passive to its active state to absorb moisture in the container.

The invention will now be explained in detail by way of examples.

The present invention encompasses an oxygen scavenger which can be successfully and simply activated at the precise time when it is most needed and provides inexpensive, simple, reliable multi-layer pole container form structures.

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A composite wall structure for a polymer container suitable for food products can be constructed from a plurality of layers, each selected for specific functions. The outer and inner layers are usually structural and protective layers selected to hold outer elements out, respectively, to accommodate the foodstuffs. Between these layers are materials which are intended to control the undesirable penetration of oxygen. The outermost layer, designed to impart structural integrity to the structure, may be a thermoplastic olefin material due to its low cost, in light processing and physical properties. The inner layer also has a structural function and can also be formed from materials that are compatible with food products, cheap and easy to mold.

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A thermoplastic oxygen barrier layer is placed between the two structural layers. Suitable blocking materials may include ethylene vinylal carbon copolymers such as EVAL® manufactured by Kuraray of Osaka,

Japan, Saran® and similar materials having low permeability for oxygen transmission. It is advantageous to place the oxygen barrier layer between a pair of outer and inner protective layers to provide a combination of packaging properties. An adhesive material may be included between the barrier layer and the adjacent layers to ensure good integrity between the outer and inner layers and the barrier layer.

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It is known that food items packed in e.g. Metal containers using traditional methods with canned double-closed ends will contain a certain amount of gases in the free space and contained oxygen, and the latter will react with some food items. It is desirable to keep the gases in the free space to a minimum, to provide reliable end closure with hermetic seal, and it is also important to minimize the amount of oxygen present which may react with the contents of the container. Oxygen penetration into plastic containers is a further problem which is not of importance to the metal box manufacturer. Thus, an oxygen absorbing system for food protection may be required, especially in plastic containers.

Limiting the oxidation of the food will help prevent its degradation. Change in color, nutritional value and taste 30 may be directly related to degradation due to oxygen associated with the foods. In a multilayer plastic container, a system for absorbing oxygen is very important because an oxygen barrier, no matter how excellent, reduces the penetration of oxygen into the container only. Thus, a system which will absorb oxygen passing through the barrier layer and located between the barrier layer and the food items is desirable. It is more particularly desirable to have an oxygen absorption system which has a greater affinity for oxygen than the foods. Ideally, such a system should be able to absorb oxygen faster than the food as well 7

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as it should have a stronger affinity for oxygen than the foods have.

The oxygen absorption system should not be activated until the food is wrapped. Containers having an oxygen-absorbing system must therefore be capable of being manufactured and stored with the oxygen-absorbing system in a passive state until the precise time when oxygen absorption is required, at which time the system will be activated. Without an activatable absorption system and having a passive and active state, its usability could be severely impaired during empty storage prior to packing. The yield of a non-activated oxygen absorption system will be limited and will require the containers to be used immediately after manufacture. Such a restriction is impractical for commercial use and hermetic packaging of food products.

An oxygen absorption system with an adjustable chemical behavior is desirable. Such a system includes a palladium catalyst for combining hydrogen and oxygen in the water-producing vessel. In the specification of U.S. Patent No. 3,712,848 and U.S. Patent No. 4,125,632, a system of this type is disclosed which is activated by flushing the container with a gas mixture comprising hydrogen. A system like this is expensive because of the cost of palladium and the extra process step needed for activation.

The present invention seeks to make use of the commonly used filling and processing equipment and operations or preferably through the normal retort treatment after filling to activate an oxygen absorption system. Desirably, filling the container does not only cause activation.

This system can maintain its passive state until activated, e.g. by the sterilization procedures used after packaging and during treatment.

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The system may involve activation by moisture penetration through the walls of the multilayer polymer container. This withdrawal can occur during packaging, processing or sterilization. Raised temperature during packaging or sterilization is another 8

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variable factor which increases the penetration of water into the oxygen absorber to activate this. Heating for activation is often desirable and in some cases this may be a necessary step. More specifically, in the dry state, the oxygen absorber is passive, but upon contact with moisture from the normal processing it becomes activated and begins to react with oxygen.

Previously, antioxidants have been added to polymer resins to produce containers and to materials to be filled therein to inhibit oxidation. It is also known that certain antioxidants have the ability to react with oxygen, but usually to a very limited extent. The difference between direct oxygen absorption and the effect of typical antioxidants is relevant to the present invention, which seeks to make use of a direct oxygen absorber system, in contrast to most of the previous work using antioxidants such as propyl gallate and butylated hydroxyanisole, di-tertiary. -butyl paracresol (see US Patent No. 4,048,361). It is important to understand that typical antioxidants act differently than systems that directly absorb oxygen. More specifically, antioxidants are usually present in a small percentage to complete the degradation process in the material in which it is mixed, e.g. the plastic container itself or its contents. A system such as the one used herein that directly absorbs oxygen is capable of reacting at a considerable rate with a much greater amount of oxygen than the antioxidants would, and it is also used at relatively high concentrations. The chemical difference is that the oxygen absorbing system only chemically reacts with oxygen, and although the antioxidants can react with molecular oxygen, the primary effect of an antioxidant is to interfere with the free radicals involved in oxidative degradation.

The concept of activation is only partially understood in the description of U.S. Patent No. 2,316,804, in which materials which do not initially have antioxidant activity in the presence of elevated temperatures and organic packaging compositions develop a distinct oxygen scavenging effect. However, these materials are unsuitable for containers produced by melt extrusion, since the high production temperatures would activate the oxygen absorption of

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early.

A preferred embodiment of the invention comprises 5 layers of thermoplastic material, the outer and inner layers being either polyolefin layers or olefin layers and the inner layer being an oxygen barrier layer.

There are adhesive layers between the barrier layer and the olefin layers to ensure structural integrity. One or the other or both adhesive layers may comprise an oxygen absorbing system. It is preferred to place the oxygen absorbing system between the oxygen barrier lid and the food. A number of such absorbent systems could be used in the adhesive layer. The choice of system depends on the special processing conditions of the container as well as the amount of oxygen absorption desired.

A preferred multilayer vessel has outer and inner olefin layers that can withstand transmission of water vapor at room temperature, but at elevated temperature, e.g. during retort treatment, they allow water vapor to enter the oxygen-absorbing system. It is the water vapor which is the activating agent.

In the patent literature, systems for enclosing a package in a container for reaction in the presence of moisture in the food are mentioned, see e.g. German Publication Publication No. 28 27 247, published 4 Jan. 1979 (corresponds to GB No. 2,000,431). It is recognized that it is possible to use a wet sulfite salt for oxygen absorption. According to German Publication No. 28 27 247, the sulfite salt is wetted by a flowing salt with which it is mixed. This patent discloses the use of a scavenger composition comprising at least 3 components. In the patent, it is neither acknowledged nor suggested that potassium sulphite is in itself an effluent.

However, the necessary water is introduced either by using the hydrated form of the salt or by contact with water in the food.

There is no specific mention of activation by the regulated use of water to activate the oxygen-absorbing system, nor any understanding of the finding that the water vapor mobility of a vessel wall protecting the sulfite salt can be 1000 times greater at raising the temperature thereof from 21 to 121 ° C, which is the case when polyethylene and polypropylene are used as the inner and outer layers. There is also no mention that

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10 other temperature ranges or machining conditions will effect activation with other structural resin layers.

The structure of the present invention contains compositions which become oxygenophilic and react with oxygen when dissolved by absorption of pervasive water vapor. Some water-soluble salts can become very oxygenophilic in this liquid state.

The term "liquid state" as used herein is used to denote the state of chemicals which are either being dissolved 2q or have been dissolved by absorption of moist steam. Although most inorganic salts flow when the relative humidity approaches 100%, the present invention is best carried out with chemicals (called liquid salts) which flow at lower humidity, e.g. below approx. 85%.

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A liquid composition comprises at least one liquid salt and a material which absorbs oxygen when wetted. The flow and oxygen absorption can both be properties of a salt, as is the case with potassium sulfite; alternatively, these properties may be weighed by a cooperative mixture of salts such as potassium acetate and sodium sulfite. A dry composition in the vessel wall can be transferred to a fluid state as water vapor permeates during the retort treatment step. Then the moisture is captured by the walls because their ability to transfer moisture decreases 1000 25 times upon cooling. The activation or triggering is therefore achieved by this combination.

Potassium sulfite is an excellent material for use in the present invention as an oxygen absorber due to its flux, and it exhibits only oxygenophilic character in the wet state. Potassium sulphite can be used alone or in conjunction with other liquefying salts, especially those salts which flow at lower relative humidity to affect activation time. There is no problem in using potassium sulfite in food-grade containers, since potassium sulfite is an approved food additive (FDA approved, for example).

The invention may be practiced in the manufacture of multilayer polymer containers by injection molding or extrusion methods or by

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thermoforming. Such multi-layer plastic containers can then be sold to food and beverage packaging companies without concern that the oxygen-absorbing system will degrade in the time between manufacture and use. More preferably, the preferred structure has an olefin layer that protects the oxygen absorption system from moisture so that it does not become highly oxygenophilic until it is retorted. Packaging a wet food in a container of the preferred construction and design will result in a gradual activation of the oxygen absorption system. Potassium sulphite is particularly well suited for use as an oxygen scavenger because it can be readily activated by the retort treatment and has sufficient thermal stability to be used in thermoplastic processes such as injection molding.

To test the oxygen absorption activation mechanism, a number of square layers of 5 layers were collected. Such a plate was prepared as follows. The outer layers were cut from a 0.38 mm thick polyolefin sheet which was a melt blend of 50 parts polyethylene and 50 parts polypropylene. The central layer was a 0.05 mm thick sheet of ethylene-vinylal carbon copolymer (GLD sold by Nippon Goshei Co., Ltd., 2 Japan). The interlaced adhesive layers were a modified polyolefin ("Plexar" sold by Chemplex Inc., Rolling Meadows, Illinois) in which potassium sulfite was melt blended in an amount of 20% by weight. These adhesive layers were approx. 0.05 mm thick. The separate layers were then stacked and melt-pressed together to produce a 2g integral plate in which the outer olefin layers meet only at the edges to completely protect the inner layers from ambient moisture. Additional sets of plates were prepared in which disodium phosphate was used instead of potassium sulfite in the adhesive layer. Since disodium phosphate does not absorb oxygen, the latter plates were used as a control.

The plates were autoclaved at 121 ° C for various times and then analyzed on a MoCon oxygen permeability tester. In this instrument, both sides of the plates can be flushed with nitrogen gas. The gas-2g current from the lower side is passed over an oxygen detector. Under perfect conditions, the reading on this detector should be zero; In practice, leakage causes a small reading, known as the baseline.

Plates containing an active oxygen scavenger lower the baseline because the leaking oxygen is absorbed. This method can 12

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used to identify the plates which absorb oxygen. Table 1 compares the values obtained during the nitrogen gas flushing of non-retort treated and retort treated plates.

TABLE 1

Agent in adhesive layer K2S03 Na2HP0 ^

Autoclaving time (min.) 0 0 30 30 45 45 60 60 120 120

Baseline reading (mV) 0.03 0.03 0.02 0.03 0.02 0.02 0.02 0.02 0.03 0.03

The results indicate that 30 minutes autoclaving is the minimum requirement to begin oxygen absorption with this composition, while 45 minutes autoclaving activates it.

For further testing, thermoforming cylindrical containers were prepared from a coextruded multilayer sheet.

These containers had a diameter of 10.3 cm and a depth of 11.3 cm. The container body consisted of 6 layers. The oxygen scavenger K2SO3 was mixed in a carrier material comprising high density polyethylene (HDPE) which was placed next to the inner polyolefin layer. The latter was a structural layer of a melt mixture of 50 parts high density polyethylene (HDPE) and 50 parts polypropylene (PP). The outer layer structure of the container was from the inner surface to the outer surface as follows: 0.30 mm HDPE-PP / 0.10 mm HDPE with 30 wt% K2 SO3 / 0.02 mm Plexar / 0.05 mm EVAL® / 0, 02mm "Plexar" / 0.30mm HDPE-PP blend. EVAL® is an ethylene vinylal carbon copolymer manufactured by Kuraray Chemical Co., Ltd., Japan. A group of 5-layer containers without the K2SO3 layer were also prepared for control. The layer composition for these control containers was: 0.38 mm HDPE-PP / 0.02 "Plexar" / 0.05 mm EVAL® / 0.02 mm "Plexar" / 0.38 mm HDPE-PP. The containers were filled with hot water (71 ° C) and double seamed with 35 metal yokes containing two small rubber tins. The clearance between the water in the container and the lid was approx. 4.76 mm high.

At specified storage times after retort treatment (at 121 ° C) or hot filling (71 ° C), a sample was taken from the gas in the free space 13

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through a slurry and analyzed for oxygen and nitrogen using gas chromatography. The oxygen concentrations in the free space (determined as a ratio of oxygen to oxygen + nitrogen) are listed in Table 2. The concentration in the hot-filled but not autoclaved vessel is less than that of air (0.21) because the hot water cooler, its increased affinity for oxygen will decrease the (^ concentration in the free space.

Thus, it is clear that the autoclaved containers are activated to absorb oxygen as the oxygen level in the free space decreases as a function of time, while the oxygen level in the non-autoclaved container is constant as a function of time. This provides a further demonstration of the efficacy of the system for activating oxygen absorption.

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TABLE 2A

Content 02 (cm3)

Originally 3 months

No additives 10 34 10 K2S03 11 8

Table 2A shows results accumulated over a 3-month period for containers retorted at 121 ° C for 2 hours with the results given in Table 15 2 for the K2SO3 containers. These containers were packed and retorted with water and then stored for 18 3 days. Then they were emptied and filled with 10 cm of water to maintain 100% relative humidity inside the containers. The space above the water was filled with approx. 99% nitrogen and 1% oxygen. Thus, at 20 and sealed, the containers were stored for 3 months in an environment comprising 100% oxygen at atmospheric pressure and a relative humidity of 75%. For control, a container without additives was treated in the same way and stored in the same way. It is clear from Table 2A that the K2 SO3-containing container not only prevented penetration, but also absorbed 3 cm 3 of oxygen from the free space. The container without scavenger allowed 24 cm of oxygen to enter the container. The decrease in oxygen concentration in the free space over the 3-month period clearly shows the capturing effect of K2S03.

Although the above-described containers according to the invention have a 6-1 layer structure, it may be preferable to use fewer layers. One can, for example. choose to use a 5-layer structure where the potassium sulfite has been mixed in an adhesive layer. The system discussed in detail above exhibits a widespread passive state which, thanks to the fluctuating behavior of the system, changes abruptly to its active oxygeno-file state. Other systems may have a less widespread passive state and may also be utilized, provided treatment can be initiated that triggers a major change in the activity of the oxygenophilic state.

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A system which after activation with water is an effective oxygen scavenging system is a mixture of a heat treated gelatin and a strong base. Gelatin will generally not capture oxygen, but it will do so after a heat treatment, either alone or in the presence of base, at 149 ° C for more than 5 minutes.

The following examples illustrate the effectiveness of this system. The composition used for the Examples is 10 wt% Type A gelatin and 20 wt% NaOH in a 70 wt% carrier material consisting of "Plexar". This composition was mixed in a Braben-der mixing head at 204 ° C for 20 minutes and then pressed to ca. 0.05 mm thick foils.

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The foil is capable of rapidly collecting 170 cm of oxygen per day. 15 grams of gelatin when the film is saturated with moisture. One of the conditions suitable for saturating the composition is to retort the exposed film at 121 ° C for 2 hours.

The oxygen scavenging rate is extremely slow if the film of this gelatin composition is protected with a moisture barrier layer to reduce the moisture penetration of the composition. The following table illustrates the rate of oxygen scavenging of a film of the gelatin composition which is not retorted and protected on both sides by a 0.38 mm thick HDPE layer (moisture barrier layer).

TABLE 3 3 cm "caught" per grams of gelatin (22.8 ° C)

Shelf life 37 days 58 days 108 days 30 Relative humidity during storage 44% 0 6 8 75% 0 10 41 100% 9 24 61 35

It is to be understood that the rate of capture of the composition 02 can be controlled by the moisture protection layer and the storage conditions. Absorption will occur after the materials are exposed to moist air for extended periods of time. This shows that while 17

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retort treatment provides immediate activation, it is also possible to obtain activation without retort treatment.

The gelatinous system is effective as an oxygen scavenging system, but produces unpleasant odors when exposed to elevated temperatures for extended periods of time. Where containers are to be made by melt processing of plastics (containing the present oxygen scavenging systems), it is preferred to use a thermally stable system such as potassium sulfite as the oxygen scavenging system.

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The structures described above had the oxygen barrier layer at or near the center of the laminate, flanked on both sides by a structural layer (polyolefin). There are alternative constructions that will function satisfactorily and are within the scope of the invention. An example is a multi-layer structure with thin layers of an oxygen barrier on the outside. The mass of the sidewall would be a structural plastic layer in which an oxygen scavenging system is embedded. The structural layer serves as a means of protecting the oxygen scavenging system within the structural layer from premature activation, although a negligible amount of the oxygen scavenging system near the surface of the structural layer can be activated before the product is packaged. Such a can or package could be made with a polyolefin wall containing a potassium sulfite dispersion and a Saran® or epoxy coating on the outside. Although outer oxygen blocking agents are preferred, they can be omitted or replaced with pure polyolefin. In this case, it is necessary to embed more oxygen scavenger in its host layer or structural layer.

Finally, a piece (chip) may be used in place of a pellet or packet of powder by placing the piece within a sealed container. An advantage of integrated designs is that this avoids the problem of dry powder in packets that break and contaminate the packaged product. The piece could be any of the listed designs, the choice depending on how it is used.

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Although a preferred system has been shown and described, it is to be understood that there are many other fluent compositions and polymeric materials which, when used in combination, will exhibit the necessary activating ability for an oxygenophilic state, and therefore 18

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enables the successful use of the blend for packaging in the commercial processing of foods.

Multilayer structures comprising an oxygen barrier layer associated with at least one side thereof with a structural layer comprising an activatable oxygen scavenging system may be of a flexible or rigid nature. Flexible structures can be used to produce bag or bag type food packaging, while rigid structures can be used to make plastic containers which e.g. has the known form commonly associated with food or beverage cans.

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Claims (21)

A PI structure comprising a scavenger for improving its resistance to oxygen transmission therethrough, characterized in that it is a laminate comprising a plurality of solid polymer layers, at least one of which comprises a dry oxygen scavenger composition wherein the scavenger composition is made. capable of exhibiting a longer passive state under which it does not substantially react with oxygen, and wherein the composition can be activated to an active oxygenophilic state, under which it is directly reactive with oxygen when moisture derived from the surrounding environment is allowed to reach and moisten the composition wherein the composition is associated with a protective polymeric material either in the layer containing the composition or in another layer or layers of structure so that it is selectively protected therefrom from moisture where the protective material is resistant to for moisture penetration at o ambient temperature, but has increased moisture permeability at elevated temperature, e.g. at above 93.3 ° C, so that when the structure is exposed to elevated temperature and moisture, the protective material, e.g. under retort conditions, moisture permeability can be made and allow moisture to contact and moisten the composition, thereby activating it from its passive to its active state. Plastic structure according to claim 1, characterized in that the protective material is substantially impervious to moisture at temperatures below 37.8 ° C. Plastic structure according to claim 1 or 2, characterized in that the scavenger-containing layer is arranged between two layers of the protective material. Plastic structure according to claim 1 or 2, characterized in that it comprises at least one barrier layer which is an oxygen barrier polymer such as ethylene vinylal carbon copolymer. Plastic structure according to claim 4, characterized in that the protective material constitutes the layer including the collecting agent composition and that one oxygen barrier layer is arranged on each side thereof. 6. A plastic structure according to claim 4, characterized in that the scavenger-containing layer is arranged on one side of the oxygen barrier layer and that another polymer layer, e.g. of the protective material is placed on the other side of the barrier layer. Plastic structure according to claim 4, characterized in that it comprises an oxygen barrier layer laminated to a layer of the protective material with the scavenger-containing layer therebetween, wherein the latter layer e.g. comprises an adhesive polymer. Plastic structure according to claim 7, characterized in that a second layer of protective material is arranged on the opposite side of the oxygen barrier cover relative to the scavenger-containing layer. The plastic structure according to claim 8, characterized in that it comprises an additional layer disposed between the oxygen barrier cover and the second protective material layer, which further layer e.g. comprises an adhesive polymer and optionally includes an oxygen scavenging composition composition. Plastic structure according to claim 4, characterized in that an oxygen barrier layer is sandwiched in a sandwich-like manner between two layers of the protective material, such as e.g. is a polyolefin or olefin material and that between the barrier layer and each of the protective material layers is a polymeric adhesive layer wherein either or both adhesive layers comprise the oxygen scavenger composition. 30 Plastic structure according to claim 4, characterized in that the oxygen barrier cover is sandwiched between a first and a second layer of the protective material, a layer of polymer adhesive being adhered to each side of the barrier layer and adhering this layer (a) to the first protective material layer and (b) to the scavenger-containing layer disposed between the barrier layer and the second protective material layer. Plastic structure according to any one of claims 1-11, characterized in that the protective material is an olefin polymer or copolymer, e.g. a melt blend of polyethylene and polypropylene in substantially the same weight proportions. Plastic structure according to any one of claims 1-12, characterized in that the composition contains a liquid compound which becomes oxygenophilic in the liquid state. Plastic structure according to claim 13, characterized in that the composition contains a sulfite salt such as potassium sulfite. Plastic structure according to any one of claims 1-12, characterized in that the composition is a mixture of a base, e.g. sodium hydroxide, and gelatin, the gelatin having been heat-treated in the presence or absence of the base. Plastic structure according to claim 15, characterized in that the heat treatment comprises increasing the temperature of the gelatin alone or of the mixture with the base to over 149 ° C for more than 5 minutes. 20 A plastic structure comprising a scavenger for improving its resistance to oxygen transmission therethrough, characterized in that it comprises a solid polymer. ag which includes a dry oxygen scavenger composition wherein the scavenger composition has been made capable of exhibiting a longer passive state during which it does not substantially react with oxygen and the composition can be activated to an active oxygenophilic state under which it is directly reactive with oxygen when moisture derived from the ambient environment is allowed to reach and moisten the composition wherein the polymer layer is resistant to moisture permeation at ambient temperature but has increased moisture permeability at elevated temperature, e.g. above 93.3 ° C so that the protective material, by exposing the structure to elevated temperature and moisture, e.g. under retort conditions, moisture permeability can be made to allow moisture to contact and moisten the composition, thereby activating it from its passive to its active state. Plastic structure according to any one of the preceding claims, characterized in that it is in the form of a polymeric chip ("chip") for inclusion in a sealed package for the absorption of oxygen therein. A container with a wall comprising the structure of any one of claims 1-17, which container e.g. is made by a coextrusion, co-injection or thermo-forming process. A method of protecting an oxidizable product from degradation by oxidation during storage, characterized in that it comprises the steps of: (a) forming a container from a plastic structure having a plurality of solid polymer layers, at least one of which includes a dry oxygen scavenger composition; wherein the scavenger composition has been made capable of exhibiting a longer passive state during which it does not substantially react with oxygen, and that the composition can be activated to an active oxygenophilic state, under which it is directly reactive with oxygen when moisture originating from the environment for the structure is allowed to reach and moisten the composition, wherein the composition is associated with a protective polymer material in either the layer itself containing the composition or another layer or layers of the structure, thereby being selectively protected from moisture, wherein the protective material is resistant to moisture permeation at ambient temperature, but has increased moisture permeability at elevated temperature, e.g. (b) filling the container with the product and hermetically sealing it around the product, and (c) subjecting the sealed container to elevated levels of temperature and moisture to make the protective material moisture permeable to allow the moisture comes into contact with and wets the composition and transforms it from its passive to its active state to absorb moisture in the container. Process according to claim 20, characterized in that the final step is carried out by a high temperature sterilization method when the product is a food.