Method for extending the effective life of an oxygen scavenger in a container wall

Abstract

A method of filling a container, and thereby extending the effective life of an oxygen scavenger, includes providing a container having an oxygen scavenger material, introducing product contents and a liquefied gas into the container to displace at least a portion of the air within the headspace, and capping or otherwise sealing the container. Displacing oxygen from the headspace diminishes the available oxygen within the container that can permeate into the container sidewall, thereby extending the effective life of the scavenger.

Description

BACKGROUND

[0001] This invention relates to processing and filling containers, and more particularly to processing and/or filling containers having an oxygen scavenging material.

[0002] Polyethylene terephthalate (“PET”), polypropylene, or other thermoplastic materials are often employed for forming containers for comestible products, such as food and beverages—especially beer, juices, and the like. Containers suitable for filling processes at which elevated temperatures are employed (including for example filling a container with a product that is at an elevated temperature, pasteurizing a container after filling, and the like) will be referred to herein as “hot-fillable.” Hot-fillable containers generally are blow molded and a heat set process during which the containers are subjected to elevated temperatures for predetermined time periods in order to increase crystallization and decrease orientation of the polymer. Heat setting, which increases crystallinity, is beneficial, among other things, to reduce shrinkage of the container at elevated temperature. Container configurations, blow molding techniques, and heat setting techniques for both hot-fillable containers are well known.

[0003] Typically, hot-fillable containers are not designed to withstand positive internal pressures, but rather such designs focus on maintaining an appropriate and desirable shape during vacuum deformation upon cooling of the contents after capping. Thus, collapsible or deformable portions are often formed in the container wall, and the hot-fillable base is typically designed to withstand only negative pressure. U.S. Pat. No. 5,251,424, entitled “Method Of Packaging Products In Plastic Containers,” which is incorporated herein in its entirety, describes a method of hot filling a plastic container that includes introducing liquid nitrogen into the container prior to capping for providing a positive internal pressure. The '424 patent states that advantages of such a technique include eliminating vacuum panels, enabling reduction of container thickness, and control of the headspace volume. Numerous references disclose introducing nitrogen into metal cans prior to application of a can end.

[0004] PET and many other plastics suitable for containers are permeable to oxygen, whether the container is hot-fillable or is suitable for another filling process. Thus, the shelf life of comestible products in PET or other plastic containers is limited or decreased by oxygen permeation through the container surfaces, and comestible products packaged in such containers are subject to spoilage. Pressurizing a container formed entirely of PET with liquid nitrogen would likely have little effect on product shelf life. Thus, in efforts to reduce oxygen permeation, an oxygen barrier may be employed. For example, a multilayer container may include an outermost and an innermost layer (that is, forming the container chamber surface) of virgin PET, with an oxygen barrier material, such as EVOH, therebetween. Often, tie layers are employed between EVOH and PET.

[0005] The commercial acceptance of containers employing conventional barrier layers has been limited at least in part because the effectiveness of the oxygen barrier is less than commercially desired, even if additional coatings or layers are employed. Oxygen scavenging compounds in a container wall are often employed rather than barrier layers described above. For example, U.S. Pat. Nos. 5,955,527; 5,639,815; 5,049,624; and/or 5,021,515 (which will be referred to as the “Packaging” patents) disclose an oxygen scavenging material that is suitable for use in bottles in hot-fillable and other containers. Oxygen scavenging compounds have a finite effective life (that is, useful life) because eventually the oxidizable material oxidizes to a degree that enables oxygen to permeate through the container wall (that is, the oxidizable material is essentially used up).

[0006] Thus, there is a need for container technology that extends the effective life of an oxygen scavenger or the shelf life of a product in a container.

SUMMARY OF THE INVENTION

[0007] In a conventional container that includes an oxygen scavenging material in the container wall, oxygen is available to permeate both from outside the container (that is, from the ambient atmosphere) into the oxygen scavenging material and from within the container (that is, from the enclosed chamber) into the oxygen scavenging material. Oxygen is typically available from inside the container because it is present in the container headspace upon capping, and also possibly because it is dissolved in the product. The oxidizable material in the container wall portion surrounding the headspace may have a diminished effective life compared with other portions of the container wall because of the oxygen permeation from both inside and outside the container in circumstances in which the concentration of oxygen (and/or the mass transfer rate of the oxygen into the container wall) is greater in the headspace than in the product

[0008] Displacing oxygen from within the container headspace prior to capping diminishes the (molar) quantity and/or partial pressure of oxygen inside the container, thereby diminishing the amount of oxygen that is available to permeate from inside the container into the container wall. We have found that displacing some oxygen from the headspace increases the effective life of the oxygen scavenger in the container wall in the region of the headspace.

[0009] Diminishing the oxygen partial pressure within the container has little effect on the gross rate of oxygen permeation from outside the container into the oxidizable material in the container wall, yet it diminishes the oxygen available within the container for permeating in an outward direction into the oxidizable material of the container wall. Thus, the effective life of the oxidizable material, especially in the portion defining or proximate to the headspace, is extended by the degree of decrease in oxygen permeation from within the container into the container wall.

[0010] A method of extending effective life of an oxygen scavenging material disposed in a container wall employs the phenomenon described above. The method includes providing a container that has a wall comprising an oxygen scavenging material. The container wall may be formed either of multiple layers or a monolayer. The multiple layers preferably include a discrete layer that includes an oxidizable compound sandwiched between layers that substantially lack oxygen scavenging capabilities, such as polyethylene terephthalate (“PET”), polypropylene, or other suitable material. The monolayer preferably is a blend of an oxidizable material with a conventional plastic.

[0011] The container is filled with a product and a dose of liquefied gas up to a fill line, which is spaced apart from the rim of the container to form a headspace. Upon introducing the liquefied gas into the container, at least a portion of the liquefied gas vaporizes and displaces at least a portion of the air in the container headspace. Upon the displacement of at least some of the air from the headspace, a closure or liner is applied to the container to seal the container. The liquefied gas within the container then continues to vaporize to form a positive total pressure within the container. U.S. patent application Ser. No.______ (Attorney Docket Number CC-3412), entitled “Method For Diminishing Delamination of A Multilayer Plastic Container,” which discloses related or complimentary technology, is incorporated herein by reference in its entirety.

[0012] In hot-fill applications that would otherwise be subject to vacuum deformation upon cooling of the contents, providing a positive pressure within the container by liquefied gas dosing enables the elimination or diminished size of vacuum panels or other collapsible or deformable portions of the container, and may also enable a lighter-weight container and control over the headspace. Further, the combination of an oxygen scavenger in the container wall with liquefied gas dosing is beneficial for product shelf life. In this regard, displacing a portion of the air present in the headspace by introducing a dose of liquefied gas extends the life of the oxygen scavenger in the container wall in the region of the headspace. Extending the effective life of the oxygen scavenger, and thus likely extending the product shelf life, applies to hot-filling and non-hot-filling applications.

BRIEF DESCRIPTION OF THE FIGURES

[0013] FIG. 1 is a flow chart illustrating steps according to the present invention;

[0014] FIG. 2 is a diagrammatic view of a monolayer container wall;

[0015] FIG. 3 is a diagrammatic view of a three layer container wall;

[0016] FIG. 4 is a view of a portion of a container package with which the present invention may be employed; and

[0017] FIG. 5 is a perspective view of the container shown in FIG. 4.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0018] A method of extending the effective life of a container that includes an oxygen scavenging material is provided. The present invention may be employed with any type of container, including: injection blow-molded bottles, extrusion blow-molded bottles, and bottles formed by any other process; heat set bottles suitable for hot-fillable applications and non-heat set bottles; and jars or containers suitable for foods, sauces, and the like.

[0019] FIGS. 4 and 5 illustrate merely one embodiment of a container 9 with which the present invention may be employed. Container 9 preferably is a heat set container capable of withstanding filling with a beverage at hot-fill temperatures, which typically is about 190 degrees F., with volumetric shrinkage of only a few percent. Heat set processes for forming containers are well known by persons familiar with plastic container manufacturing and design.

[0020] Container 9 is capable of withstanding internal positive pressures contemplated to be encountered in liquefied gas dosing applications, as well as in pressure filling applications. The particular internal pressure rating or design point of a container may be chosen according to the particular parameters of the application, such as desired internal pressure at a given temperature, carbonization of the product, container configuration, container wall material properties, resistance to abuse, and the like. Such parameters will be understood by persons familiar with container design and technology.

[0021] Container 9 includes a base 12, a body 14, a dome 16, a neck 18, and a finish 20. Base 12 preferably has a substantially continuous contact ring or standing ring on which the container rests. Body 14 extends upwardly from base 12, and is preferably substantially continuous. Because the liquefied gas pressurizes container 9, as explained more fully below, vacuum panels or other features that flex upon internal vacuum are unnecessary. Thus, body 14 preferably is substantially cylindrical. Body 14 may optionally grip portions. In this regard, finger indentations 22 may be formed in body 14 to aid gripping.

[0022] Dome 16 extends upwardly from body 14, and yields to neck 18. Preferably, neck 18 is substantially cylindrical or slightly tapered. Preferably, neck 18 is sufficient long to provide an adequate headspace such that spilling of the product is unlikely upon initial opening of the closure. Finish 20 is disposed at the top of neck 18. Further description of container 9 is described in co-pending, concurrently filed U.S. patent application Ser. No. ______ , entitled “Pressurizable Container With Contact Ring” (Attorney Docket Number CC-3438), which is incorporated by reference herein in its entirety.

[0023] Container 9 may be formed of any material comprising any oxygen scavenger. The wall of container 9 may be formed in any configuration, including multiple layers or a single layer. In this regard, FIG. 2 illustrates a container wall 30 that is formed of a single, substantially uniform composition that includes an oxygen scavenger. FIG. 3 illustrates a container wall formed in multiple layers 32, 34, and 36. Outer and inner layers 32 and 36 preferably are a virgin plastic material, such a polyethylene terephthalate, polypropylene, or other suitable material. Sandwich between outer and inner layers 32 and 36 is an intermediate layer 34, which preferably includes an oxygen scavenger. The present invention encompasses any combination of layers, including walls formed of more than three layers and walls having additional coatings.

[0024] Preferably, the oxygen scavenger includes an oxidizable organic component and a metal catalyst for the oxidation of the oxidizable organic component. The oxidizable organic component preferably is a polymer, such as a polyamide and especially MXD6, which is a condensation polymer of m-xylylenediamine and adipic acid. The metal catalyst may include cobalt, copper, rhodium compounds and/or other suitable substances. A suitable material for the oxygen scavenger layer is OXBAR™, which is available from Crown Cork & Seal Company, Philadelphia, Pa. U.S. Pat. Nos. 5,955,527; 5,639,815; 5,049,624; and/or 5,021,515, each of which is incorporated by reference in its entirety, disclose technology relating to such a scavenger. The present invention is not limited to the preferred oxygen scavenger, but rather encompasses employing any such substance capable of such oxidation.

[0025] Further, particular features or configuration of container 9 are employed to illustrate an embodiment of a container on which the present invention may be employed. The present invention, however, is not limited to the particular features or configuration of the container. Rather, the invention encompasses a container of any configuration, including without limitation cylindrical and non-cylindrical containers, containers of any dome shape or lacking a dome, containers of any neck configuration or lacking a neck, and containers having any standing ring configuration, a footed configuration, and the like.

[0026] Referring again to the figures to illustrate the present method, a container, such as container 9, is provided to a filling station for filling a comestible product, such as juice, sauces, and/or the like. The product is filled up to a predetermined fill line, which is illustrated by reference numeral 24 in FIGS. 4 and 5. Preferably, the product is introduced at conventional hot-fill temperatures, such as 180 to 190 degrees F. The product may be filled by any type of gravity filling process in which the product is allowed to flow into container 9 under atmospheric conditions or at a low head pressure, a pressure filling process in which the product is pumped into container such that the container encounters a positive internal pressure (typically a few pounds per square inch), or other filling method.

[0027] A predetermined dose of liquefied gas is introduced into container 9 either just prior to, concurrently with, or after introduction of the product into container 9. The liquefied gas preferably is an inert gas, and even more preferably is liquefied nitrogen. The liquefied gas may be introduced into the container prior to, concurrently with, or after the product in introduced into the container. The product filling system and liquefied gas delivery system are schematically represented by reference numerals 42 and 44, respectively, in FIG. 5. Equipment and systems for filling plastic containers is well known. Similarly, equipment and systems for introducing liquefied nitrogen or other inert gas into containers, especially metal cans, is well known. Any conventional equipment and systems may be employed to accomplish such steps.

[0028] Upon filling the container up to fill line 24, a headspace 28 is formed between fill line 24 and the top lip of container 9. The gas in the headspace upon filling in a conventional process typically has a composition like that of the atmosphere. In this regard, under gravity filling conditions, container 9 is essentially open (or at least not sealed air-tight) during the filling process. Similarly, under pressure filling conditions, the container is open to the atmosphere prior to filling and prior to capping.

[0029] According to the present invention, the liquefied gas, which vaporizes upon being introduced into container 9, displaces at least some of the oxygen in headspace 28. Closure 26, which is diagrammatically shown in dashed lines in FIG. 4, is applied to finish 20 while at least some of the oxygen is displaced to seal container 9. Similarly, a liner, which may also be represented by reference numeral 26, may be applied. Upon application of closure (and/or liner) 26, container 9 is sealed. Because at least some of the oxygen was displaced from headspace 28 upon sealing, the composition of the gas in headspace 28 includes an elevated partial pressure or concentration of nitrogen (or other gas making up the liquefied gas) and a diminished partial pressure or concentration of oxygen, compared with ambient conditions.

[0030] The diminished oxygen partial pressure within headspace 28 provides fewer molecules that may migrate into the container wall 11 or 36 compared with an oxygen partial pressure in the headspace of conventionally filled containers or filling by other means. Similarly, the diminished quantity of available oxygen in the headspace will also extend the life of an oxygen scavenger that is formed as part of the liner.

[0031] The present invention encompasses any oxygen partial pressure in the sealed headspace below ambient (that is, about 3.1 psi) when the contents reach equilibrium, ambient temperature. Each of the exemplary pressures provided below are the pressure in the headspace immediately upon capping, regardless of the headspace gas or product temperature, although it is understood that such pressures will vary upon cooling of the product. Vaporization of any liquefied gas in the product after capping may increase the total pressure in the headspace. Preferably, the oxygen partial pressure in the sealed headspace is below about 2.75 psi, which provides a measurable increase in the effective life of the oxygen scavenger, or even more preferably below about 2.3 psi, even more preferably below about 1.54 psi, and even more preferably below about 0.77 psi.

[0032] The present invention is illustrated with respect to a particular container, although the present invention is not limited to the particular container configuration or materials described herein. Rather, the present invention encompasses employing any container configuration, container material, or container manufacturing method. Further, the present invention encompasses any filling technique. Even though the present invention provides advantages in hot-filling applications, the present invention also encompass including filling at any temperature in any type of process. Reference should be made to the claims to ascertain the scope of the present invention.

Claims

1. A method for extending effective life of an oxygen scavenger that is disposed in the wall of a container, comprising the steps of:

a. providing the container formed of a material comprising the oxygen scavenger;

b. introducing a comestible product into the container, thereby forming a headspace between a product fill line a rim of the container;

c. introducing a quantity of liquefied gas into the container;

d. enabling vaporized liquefied gas to displace at least a portion of air in the headspace; and

e. capping the container so as to maintain low oxygen partial pressure within the headspace relative to ambient atmospheric pressure, thereby diminishing the amount of oxygen available to permeate from inside the container into the oxygen scavenger.

2. The method of claim 1 wherein the container wall includes an outer layer of PET, an interior layer of an oxygen scavenging compound comprising nylon, and an inner layer of PET for contacting the product.

3. The method of claim 1 wherein the container wall includes a single layer comprising a blend of an oxidizable polymer and a non-oxidizable polymer.

4. The method of claim 1 wherein the container wall includes a blend of an oxygen scavenger material and polyethylene terephthalate.

5. The method of claim 1 wherein the oxygen scavenger is an oxidizable organic component and a metal catalyst.

6. The method of claim 5 wherein the organic component is a polymer.

7. The method of claim 5 wherein the organic component is a polyamide.

8. The method of claim 5 wherein the organic component a condensation polymer of m-xylylenediamine and adipic acid.

9. The method of claim 1 wherein the liquefied gas forms a positive total pressure inside the container after the capping step (e).

10. The method of claim 9 wherein the introducing step (b) includes introducing the comestible product into the container at an elevated temperature.

11. The method of claim 10 wherein the oxygen partial pressure within the headspace is below about 3.1 psi.

12. The method of claim 1 wherein the oxygen partial pressure within the headspace is below about 2.75 psi upon capping.

13. The method of claim 1 wherein the oxygen partial pressure within the headspace is below about 2.3 psi upon capping.

14. The method of claim 1 wherein the oxygen partial pressure within the headspace is below about 1.54 psi upon capping.

15. The method of claim 1 wherein the oxygen partial pressure within the headspace is below about 0.77 psi upon capping.

16. The method of claim 1 wherein capping step (e) thereby forms an oxygen partial pressure gradient across the container wall.

17. The method of claim 1 wherein the quantity of liquefied gas is sufficient to maintain a positive total pressure within the container upon cooling to ambient temperature.

18. The method of claim 1 wherein the quantity of liquefied gas is sufficient to maintain a positive total pressure within the container upon cooling to approximately 50 degrees F.

19. The method of claim 1 wherein the quantity of liquefied gas is sufficient to maintain a positive total pressure within the container upon cooling to approximately 40 degrees F.

20. The method of claim 1 wherein the quantity of liquefied gas is such that the container has a substantially atmospheric pressure upon cooling to ambient temperature.

21. The method of claim 1 wherein the liquefied gas comprises liquefied nitrogen.

22. The method of claim 1 wherein the liquefied gas is an inert gas.

23. The method of claim 1 wherein the liquefied gas is liquefied nitrogen.