GB2113180A - Sealed plastics container - Google Patents

Abstract

A plastic container e.g. for wine has at least two unfoamed plastic walls 2, each of which is separated from the next wall by a layer containing a gas or vapour wherein the gas or vapour contains less than ten volume percent oxygen gas and is not reactive with oxygen under packaging conditions. The layer or layers containing the gas can be entirely gaseous or be a foamed or cellular plastic containing for instance, as little as thirty volume percent gas. The containers minimize the permeation of oxygen from the ambient air into the inside of the container. The outer plastic layer may be supported by a paperboard or wooden container, and the inner plastic container lie within the paperboard or wooden container. Alternatively the container is a double- walled bottle. <IMAGE>

Description

SPECIFICATION Sealed plastics containers This invention concerns sealed plastics containers. More particularly it pertains to multiwall containers having outer and inner walls of unfoamed plastics material. The plastics container has at least two unfoamed plastics walls, each of which is separated from the next wall by a layer containing a gas or vapour wherein the gas or vapour contains less than ten volume percent oxygen gas and is not reactive with oxygen under packaging conditions. The layer or layers containing the gas can be entirely gaseous or be a foamed or cellular plastics containing, for instance, as little as thirty volume percent gas. The containers have a special utility in packaging fluids in bulk where it is desired to minimize the permeation of oxygen from the ambient air into the inside of the container.

It is known to package wines in a flexible plastics container which is inserted into a rigid supporting container such as a paperboard box.

When it is desired to minimize the permeation of atmospheric oxygen into the container, such as in the packaging of wines in such containers, an expensive treatment has been necessary in the past in order to make the inner plastics containers sufficiently impermeable to oxygen. Commonly, the containers are vapour coated with a film of metal in order to minimize the permeability of oxygen into the container.

It is an object of the present invention to provide plastics containers of liquid for the storage of oxygen-sensitive materials in which the permeation of oxygen is minimized without resort to expensive surface treatments of the plastics container wall, and without resort to use of an excessive thickness of the plastics container wall.

According to the present invention then, in a sealed plastics container of liquid which is at essentially atmospheric pressure when at 20"C, the container has at least two unfoamed plastics walls, each of which is separated from the next wall by a layer containing a gas or vapour, and wherein the gas or vapour at the time of initial packaging of the liquid in the container contains less than ten volume per cent oxygen gas and is not reactive with oxygen under packaging conditions. The separating layer or layers can be entirely gaseous or the gas can be contained in a plastics foamed or cellular layer which is at least thirty volume per cent gas. It is immaterial for the purposes of the invention whether the foamed layer is a continuous or open cell foam, or is a closed cell foam, or is a combination thereof.The contents of the package are nonpressurized, i.e., the packaged liquid is at essentially atmospheric pressure when at 200C.

According to a further apsect of the present invention, in a sealed composite plastics container of liquid which is at essentially atmospheric pressure when at 20 C., the container having inner and outer spaced apart unfoamed plastics walls, the inner plastics container wall being within a wooden or paperboard container or box and the outer plastics container wall encompassing the wooden or paperboard container or box which supports the outer container wall, the space between said plastic walls containing a gas or vapour, the gas or vapour at the time of initial packaging of the liquid in the container contains less than ten volume percent elemental oxygen and wherein said gas or vapour is not reactive with oxygen. The box offers support and allows use of structurally relatively weak plastics envelopes.Furthermore, the box provides an opportunity to separate the outermost and innermost plastics walls with whatever volume of barrier gas that is desired, greater volumes giving greater time lags.

The theoretical lag time for permeation of a gas through a laminate of two or more plastics or rubber layers can be calculated according to wellknown equations. (Barrie et al., Diffusion and Solution of Gases in Composite Rubber Membranes, Trans. Faraday Soc. 59, 869-78, "1963"). The so-called "time-lag" is a measure of the time it takes for the rate of diffusion across the barrier to reach a steady state. The time of permeation is plotted against the cumulative total gas permeated, such as oxygen, in milligrams across 100 square inches of the barrier at one atmosphere. After the rate of permeation has reached a steady state, the line plotted on the graph will be a straight line.When this line is extrapolated to the time line, the difference between zero time and the time where the extrapolated line intersects the zero rate on the ordinate is known as the "time-lag".

We have discovered that the general equations for calculating the theoretical time-lag across a multi-layered laminate can also apply to calculation of the time-lag across two or more layers separated by a gas different than the gas to be diffused. Thus, we have found that the total diffusion of the gas, such as oxygen, into a container across plastics layers separated by a gas can be decreased by increasing this time-lag by using something in one of the layers which is far cheaper than a layer of a high barrier plastics, namely, an inert gas such as carbon dioxide or nitrogen or the like. Furthermore, the time-lag can be controlled simply by increasing the thickness or volume of the gas layer. Calculations according to the general formulas in the cited reference bear this out.However, we have further found, surprisingly, that the actual time-lag determined by plotting as described above is much larger than calculations predict.

The invention will now be further described by way of examples with reference to the accompanying drawings, in which: Figure 1 is a side view of a container having liquid therein and made from non-rigid films of plastics separated by an inert gaseous layer, such as nitrogen; Figure 2 is a cross-sectional view taken along the line A-A of Figure 1;; Figure 3 is a sectional view of another form of container having liquid therein and being formed by two rigid bottles, one within the other, sealed at the neck and separated by a space containing the insert gas having a lower content of oxygen than air, i.e., not being over ten volume percent oxygen gas, Figure 4 is a sectional side view of yet another form of container comprising a rigid or a flexible inner plastics container having liquid therein and being located inside an outer container of barrier plastics which can be in the shape of a box or of a cylinder, the space between the outer and inner plastics walls containing the insert gas having a lower content of oxygen than air, i.e. not over 10 volume percent oxygen gas.

Figures 5 and 6 are each sectional side views of composite containers comprising a rigid or flexible inner plastics container having liquid therein and being located inside a rigid box or container of wood or paperboard wherein the box or container is enveloped by a film of barrier plastics, the space between the inner container and the box being filled with the inert gas as in Figure 4. Of course, the gas usually permeates the paperboard or other box wall; and Figure 7 is a similar sectional bag-in-box structure suitable for containing larger quantities of liquids.

In Figures 1 and 2 the container formed by plastics walls 1 contains a liquid 3, such as wine, or a semi-liquid such as ketchup, and the space between plastics walls 1 and 2 is filled with nitrogen or other inert gas. Both the inner and outer walls 1 and 2 are envelopes formed from tubular blown plastics such as poly(ethylene terephthalate). The inner envelope is smaller than the outer envelope and can be placed within it, and then the upper and lower edges are sealed by means of heat along lines 4.For purposes of iilustration a filling spout 5 is shown heat sealed to the walls 1 and 2 and through this the wine can be introduced while air is displaced by the wine, while at the same time, needle-type valves (not shown) can be inserted one into the bottom of wall 2 and another at the top of wall 2 to introduce an inert gas such as nitrogen, and thus flush the air from space between walls 1 and 2.

In Figure 3 an inner bottle of plastics is blow moulded in a known manner, and an outer bottle of plastics is likewise blow moulded. The sizes of the respective bottle necks are such that the neck of the inner bottle fits snugly into the interior of the neck of the outer bottle. To construct the composite container, the outer bottle can be split along the line 12, the inner bottle inserted with a suitable cement around the neck and the neck be thus glued to the inside of the outer neck.

Thereafter, the lower portion of the outer bottle can be heat sealed to the upper portion of the outer bottle. In operation, the same type of needle valves can be used to evacuate the air from the space between walls 10 and 11 of the inner and outer bottles respectively by flushing with an inert gas such as nitrogen, thus creating a nitrogen atmosphere in the space. Thereafter, the small holes would be sealed off, the inner bottle filled with, for example, wine and then the cap (not shown) would be applied.

The structure shown in Figure 5 consists of a rigid or flexible plastics container 21 placed inside a corrugaged or paperboard box 22 or even a wooden box. The outer box is then overwrapped with a film of barrier plastics 23 forming a gas tight outer covering for the box. The outer wrap can be formed from a tube of shrinkable plastics such as oriented poly(ethylene terephthalate) by pulling it over the box, heat-sealing both ends and then shrinking it tightly around the box. Gas for the gas layer is trapped between the inner and outer walls of the plastics container 21 and the box 22 respectively either by forming the outer wrap under a gas flush or by purging through a small hole 24 in the outer wrap and sealing with a barrier tape 26. The barrier tape may be either a heat-seal or pressure sensitve tape with suitable barrier such as a metallized polymer.

Figure 6 shows a structure similar to that of Figure 5 except that the opening to the inner container extends through the outer wrap. The outer wrap is sealed to the inner container at 28 where it extends through the box. A heat-seal or adhesive such as a hot melt is suitable to form a gas tight seal.

Figure 4 shows a structure similar to Figure 5 except that the outer container 1 5 is a rigid box or a cylindrical container formed from a barrier material. The outer box or cylindrical container 1 5 can be made from a barrier plastics or a multilayer plastics incorporating a barrier layer. The cover 1 6 can be either a flexible or rigid material with sufficient barrier properties and is attached and sealed to the box at 1 7 with either a heat seal or an adhesive. Purging of the gas space through hole 19 and sealing at 18 is accomplished as described for the structure shown in Figure 5. A suitable material for the inner container 14, the outer container 1 5 and the lid 16 is again poly(ethylene terephthalate).

A bag-in-box structure, especially suitable for larger sizes of 4 to 6 litres, is shown in Figure 7.

The inner plastic container 31 is usually a flexible bag but can be a rigid plastics. The outer container is a corrugaged or paperboard or even a wooden box 32 overwrapped with a barrier plastic film 33 such as discussed for Figure 5. Containers of the larger sizes can have a spigot 34 for removing the contents. In this case, the outer overwrap can be punctured and the spigot pulled through an opening in the outer container when the contents are dispensed. Purging can be accomplished in much the same way as for the structure shown in Figure 5 through purge hole 36, which can then be covered with barrier tape 37. If desired, a tube can be inserted through the hole to the lower-most reaches in order to flush with nitrogen or other gas.

The spigot in Figure 7 can be of the type shown at the top of page 35 of the June 1982 issue of Package Engineering or any one of the dispenser closures described in U.S. Patent Specification No.

3,400,866.

In all of the embodiments of the invention, the operative gas layer such as nitrogen can be entirely gaseous or can be contained in a foam, open or closed cell, and the space or volume between the two unfoamed plastic container walls is at least thirty volume percent gas.

In an example illustrating the improvement of time-lag when two plastic layers are separated by a nitrogen layer, as compared wth the same thickness of plastic not separated by any gas layer, both systems were tested with an Oxtran 100 permeation tester which is sold by Modern Controls of Mineapolis, Minnesota, U.S.A., which is based on a coulometric detection principle.

In the control experiment two touching films of 3 mils thick poly(ethylene terephthalate) was enclosed between a closed chamber on top and a separate closed chamber on the bottom. To begin with, the closed chamber on top was continually flushed with an atmosphere of nitrogen and the bottom chamber was initially flushed with an atmosphere of nitrogen. The flushing with the nitrogen in the bottom chamber was continued at a slow rate and the effluent tested in the detector instrument of the Oxtran, until no oxygen could be detected. Thereafter, the flow of nitrogen through the bottom chamber was continued and the top chamber was thoroughly flushed with pure oxygen and thereafter a flow of oxygen was maintained to the top chamber under the influence of a pressure control which held the pressure at one atmosphere.Using this setup, the permeation of oxygen through the membrane was continued and the cumulative amount of oxygen determined at timed intervals until a steady state had been reached. Thereafter, the data was plotted and the time-lag determined.

The foregoing procedure was repeated except that a "laminate" of two 3 mils thick films of poly(ethylene terephthalate) were separated by an empty space of 3 mils. The edges of the so-called "laminate" were sealed in order to make a closed volume between the two films. The procedure was carried out as before and, of course, when no oxygen was detected from the bottom chamber, there was also no oxygen in the space between the two plastic films. At this point the top chamber was quickly flushed with oxygen and then the oxygen pressure maintained at one atmosphere as before. Again, the time-lag was determined.

Thus, it was found that the time-lag was 0.19 days in the control and, for the same amount of plastics, was 3.5 days in the structure of the invention with the layer of nitrogen initially filling the space between the two films.

Calculations would have predicted when using the equations referred to hereinbefore that the timelag in the case of the composite separated by the nitrogen layer would have been only 2.5 days.

Calculations show that the calculated time-lag is greatly influenced by the gas layer thickness; in the example above, the calculated time-lag is 22.6 days when the N2 layer is increased from 3 mils to 30 mils.

When it is noted therein that the plastics walls of the outer and inner containers of the composite container or that the adjacent plastic walls of the container are separated or spaced apart, it is not meant to imply that such walls do not touch at some point or points. It will be understood that a large gap such as in parts of Figure 4 coupled with almost no gap at other parts (touching portions of the walls) still averages out to a gas "layer" volume that will increase the time lag according to the present invention.

As used herein, "paperboard" containers include corrugated and fibre containers.

Claims (11)

1. A sealed plastics container of liquid which is at essentially atmospheric pressure when at 200 C, the container having at least two unfoamed plastics walls, each wall being separated from the next wail by a layer containing a gas or vapour, wherein the gas or vapour at the time of initial packaging of the liquid in the container contains less than ten volume per cent elemental oxygen and wherein the gas or vapour is not reactive with oxygen under packaging conditions.

2. A plastics container as claimed in claim 1, wherein at least one of the plastics walls is essentially rigid.

3. A plastics container as claimed in claim 1 or 2, wherein all said plastic walls are essentially rigid.

4. A plastics container as claimed in claim 1, whwerein all wails are non-rigid.

5. A sealed composite plastics container of liquid which is at essentially atmospheric pressure when at 200C, the container having inner and outer spaced apart unfoamed plastics walls, the inner plastics container wall being within a wooden or paperboard container or box and the outer plastics container wall encompassing the wooden or paperboard container or box which supports the outer container wall, the space between said plastic walls containing a gas or vapour, wherein the gas or vapour at the time of initial packaging of the liquid in the container contains less than ten volume percent elemental oxygen and wherein said gas or vapour is not reactive with oxygen.

6. A composite plastic container of claim 5, wherein the inner plastic container wall is essentially rigid.

7. A composite plastic container of claim 5, wherein the inner plastic container wall is nonrigid.

8. A plastics container as claimed in any one of claims 1 to 7, wherein the gas is predominantly nitrogen.

9. A plastics container as claimed in any one of claims 1 to 7, wherein the gas is predominantly carbon dioxide.

1 0. A plastics container as claimed in any one of claims 1 to 7, wherein the gas is contained in the separating layer in a plastic foam and the gas is at least 70 volume per cent of the separating layer.

11. A composite plastic container of any one of claims 5 to 7, wherein the gas is at least partially in a plastics foam and is at least 70 volume percent of the space between the outer and inner unfoamed plastic walls.

1 2. Sealed plastics containers of liquids substantially as herein described with reference to and as illustrated in the accompanying drawings.