NO892049L - POLYMER MOVIES WITH HOEY OXYGEN BARRIERS. - Google Patents

Description

The present invention relates to polymeric films and in particular such films which provide a high oxygen barrier. The present invention is particularly directed to such films which are exposed to moisture at some point during their expected useful life.

Ethylene vinyl alcohol copolymers (EVOH) are known to act as an oxygen barrier in multilayer films. Vinylidene chloride copolymers (VDC) are also known to have oxygen barrier properties. The oxygen barrier properties of the VDC and EVOH copolymers are, however, affected differently by the humidity in the environments in which the polymers are used. The VDC copolymer has relatively less oxygen barrier than EVOH copolymers with low ethylene content, and in some cases higher ethylene content, but it is relatively insensitive to changes in humidity. Namely, its oxygen barrier properties are generally about the same at high humidities as at low humidities. While there are some variations in the oxygen barrier as the humidity changes, these variations are quite moderate.

EVOH with a low ethylene content has a much better oxygen barrier than VDC at low humidity. EVOH with higher ethylene content has a better oxygen barrier than some VDC copolymers at low humidity. However, the EVOH copolymers are quite sensitive to the humidity to which they are exposed, so that at high humidity, e.g. over approx. 75-80$, the oxygen barrier properties of the EVOH copolymer are less effective, and are thus less desirable than the properties of the VDC copolymer. At humidity above approx. 75-80$ namely the oxygen transfer rate for the EVOH copolymer is typically higher than the oxygen transfer rates for the VDC copolymer.

Oxygen transfer rates as described and discussed herein are based on comparison of 0.025 mm EVOH copolymer versus 0.025 mm VDC copolymer, except where otherwise noted.

Thus, while low ethylene content EVOH copolymers are generally preferred for use in low humidity environments, the VDC copolymer is typically considered better for film that will be exposed to high humidity environments.

Higher ethylene EVOH copolymers have somewhat higher oxygen transfer rates than both lower ethylene PVOH and some VDC copolymers. EVOH with a higher ethylene content has a medium moisture sensitivity. Therefore, since EVOH is generally easier to process than the VDC copolymer, in some cases EVOH copolymers with higher ethylene content are preferred for conventional application.

However, it has generally been the practice to use VDC copolymers for films that will be exposed to high humidity environments for some period of their service life, in order to gain at least the barrier properties that come with the VDC copolymer, while the higher oxygen transfer rates of PVOH- the copolymer is avoided in environments with higher humidity. On the other hand, when constant low humidity is expected on the outside of the package, the lower oxygen transfer rate of PVOH with low ethylene content is generally preferred, f to achieve extended shelf life.

A disadvantage of this practice has been that a gasket exposed to higher humidity for only a portion of its service life has conventionally used a VDC copolymer barrier layer, and thus has not been able to take advantage of the lower oxygen transfer rates of PVOH with low ethylene content during those periods of service life where the relative humidity is low enough for the gasket and its contents to benefit from the use of PVOH copolymer instead of VDC copolymer. It would therefore be desirable to produce a film which provides the high oxygen barrier of PVOH at lower humidities, and where its oxygen barrier properties are less sensitive to humidity variations, and is particularly less sensitive to high humidity. Indeed, it would be desirable to have a film that has the advantages of the lower oxygen transfer rate of low ethylene content PVOH at lower humidities, while also having the advantage of the more stable oxygen barrier provided by VDC copolymer at higher humidities.

The present invention is thus aimed at polymeric films with several layers which have low oxygen transfer rates corresponding to the barrier provided by EVOH at low humidity, in combination with oxygen transfer rates which generally correspond to the barrier provided by VDC copolymer at high humidity. The films of the invention can provide at least the barrier properties of the VDC copolymer at all times, and can advantageously provide the better barrier properties of EVOH during periods when the relative humidity is less than, e.g. about. 75$.

The present invention provides a multi-layer polymer film with good oxygen barrier properties over a wide range of humidity conditions. According to the invention, a multilayer polymer film has a first layer of ethylene vinyl alcohol copolymer, a second layer of a vinylidene chloride copolymer, and preferably a third, adhesive layer between the first and second layers. The adhesive layer preferably provides adhesion of at least approx. 39.4 g/cm width, as determined by peel strength, of at least one of the layers of vinylidene chloride copolymer and ethylene vinyl alcohol copolymer. Examples of the composition of the third adhesive layer are EVA with a high vinyl acetate (VA) content, especially greater than 15$ VA, mixtures and copolymers of polypropylene, homopolymer or copolymer (PP) with EVA, ethylene methyl acrylate (EMA), anhydride modified polypropylene homopolymer or — copolymer (MPP), and anhydride-modified ethylene vinyl acetate (MEVA). In preferred embodiments, the water vapor transmission rate (WVTR) between the first layer of EVOH and a first outer surface of the film, through the VDC copolymer, is less than the WVTR between the EVOH layer and the second outer surface of the film, away from the VDC copolymer . Typically, the ratio of WVTR through VDC to the first surface, and WVTR to the second surface is no more than approx. 0.25/1.

The films according to the invention preferably comprise a fourth sealing layer, the second layer of vinylidene chloride copolymer being between the first EVOH layer and the fourth sealing layer. Preferred compounds for the sealing layer are selected from the group consisting of olefin-based polymers and copolymers and mixtures thereof. Examples of sealing layer compounds for use at high temperatures are polypropylene homopolymers and copolymers and polyethylene with a resin density of at least approx. 0.940, preferably at least approx. 0.950. Examples of sealing layer compounds for use at lower temperatures are EVA, low density polyethylene (LDPE), medium density polyethylene (MDPE), ionomers, and linear low density polyethylene (LLDPE), including densities as low as, e.g. about. 0.890. A fifth adhesive layer may be placed between the second layer of VDC copolymer and the fourth sealing layer. Examples of materials useful in the mixture in the fifth layer are EVA copolymers comprising more than approx. 15$ vinyl acetate, blends and copolymers of PP and EVA, EMA, MPP and MEVA.

As a particular example of a film according to the invention, mention can be made of a polymer film with, in order, a first layer comprising EVOH, a second layer comprising an EVA with more than approx. 15$ vinyl acetate, a third layer comprising a VDC copolymer, a fourth layer comprising an EVA with more than approx. 15$ vinyl acetate, and a fifth layer comprising LLDPE.

A second particular example of a film according to the invention is a multilayer film with, in order, a first layer comprising EVOH, a second layer comprising an anhydride modified polypropylene, a third layer comprising a VDC copolymer, a fourth layer comprising an anhydride modified polypropylene and a fifth polypropylene-based layer.

A third particular example of polymeric films according to the invention has, in order, a first layer comprising EVOH, a second layer comprising an anhydride-modified EVA copolymer, a third layer comprising a VDC copolymer, a fourth layer comprising an anhydride-modified EVA copolymer and a fifth layer comprising LLDPE.

In the many embodiments of the films according to the invention, it is preferred, although not necessary, that a single adhesive layer is placed between the layers of PVOH and VDC copolymer, and is in surface-to-surface contact with both the PVOH layer and the VDC layer , thereby providing an adhesion of at least 39.4 g/cm width to both the first and second layers.

In one family of films according to the present invention, the films comprise a coextruded multilayer film with a first layer comprising vinylidene chloride copolymer, and a second layer coextruded with the vinylidene chloride copolymer and comprising ethylene vinyl alcohol. It is preferred, although not necessary, that the coextruded films comprise the above-mentioned intermediate adhesive layer placed between the VDC copolymer layer and the EVOH layer.

In some embodiments of the invention, the VDC copolymer comprises vinylidene chloride-vinyl chloride copolymer. The other embodiments are a preferred copolymer vinylidene chloride-methyl acrylate copolymer.

In terms of making the films of the invention, one method of making them is to co-extrude the EVOH and VDC copolymer, including forming the EVOH into a first layer with an annular mold at a first temperature, forming the VDC copolymer into a second layer with an annulus at a second temperature significantly lower than the first temperature, combining the first and second layers to form a multilayer film, and coextruding and cooling the film. Preferably, the first temperature for forming the EVOH copolymer is about 193°C to 216°C. The EVOH and VDC copolymer layers are preferably co-extruded simultaneously through a single co-extrusion die, and are preferably formed into a ring shape in substantially the same time.

Another and preferred method for producing the multilayer polymer films according to the invention comprises the steps of treating a first mixture comprising EVOH in a first extruder and thereby producing a first melt stream, treating a second mixture comprising a VDC copolymer in a second extruder and thereby producing a second melt stream, and process, in a third extruder, thereby producing a third melt stream of a polymeric mixture which can be bound in the molten state to at least one of the first and second mixtures to provide in the solid state one of peel strength in the contact surface of at least about . 39.4 g/cm width. The first, second and third melt streams are then fed into a coextrusion die, either an annular die or a linear die. In the die, the melt streams are combined, the third melt stream being between the first and second melt streams. The combined melt streams are then formed into a multi-layer film in the die, and extruded out of the die as a co-extruded film and then cooled.

The invention can also be described as a packaging system comprising a multi-layered packaging material which cooperatively defines a package, the packaging material comprising a first layer comprising EVOH, and a second layer comprising a VDC copolymer placed between the first layer and the product, a product in the package, and environment on the outer surface of the wrapping material with a lower humidity than the humidity on the inner surface of the wrapping material. In the wrapping material, the step-increasing WVTR between the first layer of EVOH and a first surface of the wrapping material, through the VDC copolymer, is less than the step-increasing WVTR between the EVOH layer and the second surface of the film, away from the VDC copolymer.

The wrapping material in such a wrapping system preferably comprises a fourth heat-sealable layer between the product and the second VDC copolymer layer and a fifth layer, comprising a second binder layer, between the second VDC copolymer layer and the fourth heat-sealable layer. A preferred blend for the fourth layer comprises LLDTE, and for the fifth layer EVA copolymer. In some embodiments, however, the fourth layer comprises a propylene-based polymer blend, and the fifth layer comprises a carboxy-modified, propylene-based polymer blend. The third and fifth binding layers can also, as mentioned above, comprise anhydride-modified EVA, especially when the fourth, heat-sealable layer comprises LLDPE.

Regarding certain embodiments of the packaging systems according to the invention carried out by coextruded films according to the invention, the packaging system comprises a coextruded, multi-layer thermoplastic film, a product within this film as part of the packaging system and an environment on the outer surface of the film having a lower moisture than the moisture on the inner surface of the wrapping material. The film has a first layer comprising EVOH, and a second layer comprising VDC copolymer which is placed between the first EVOH layer and the product.

For those gaskets that will be exposed to high humidity during the expected service life of the gasket, it is preferred that the WVTR between the first layer of EVOH and the inner surface of the film is less than the WVTR between the EVOH layer and the second (outer) surface of the film , away from the VDC copolymer.

As mentioned in connection with the production of films according to the invention, it is preferred in the seals to use a third layer of an adhesive, polymeric material between the first and second layers of EVOH and VDC respectively.

The invention can also be considered a method for producing a packaged product. The first step in this process involves choosing suitable materials and layer structures and producing a multilayer polymer film. The film has a first layer comprising an EVOH copolymer, a second layer comprising a VDC copolymer and a third bonding layer between the first and second layers, WVTR between the first layer of EVOH and at least one outer surface of the film, through the VDC copolymer, is less than the WVTR between the EVOH layer and the other, outer surface of the film, away from the VDC copolymer. After manufacturing the polymeric film, the method comprises forming the film into a packaging container with the other outer surface of the film, to which water vapor can most easily transfer from the EVOH layer, placed against the outside of the package, and placing a product in the container in which the product produces a moisture concentration inside the package that is greater than the ambient humidity outside the package. The manufactured packaging container is then closed and sealed with the moisture, or moisture-producing contents, within. In such a gasket, the layer of VDC copolymer acts as a moisture barrier to protect the EVOH from moisture inside the gasket, whereby moisture in the EVOH and between the EVOH and the outer surface of the gasket is transferred to the outer surface, and from there to the surrounding environment with lower humidity, faster than it is transferred through the VDC copolymer to the EVOH layer. Thus, the moisture content of the EVOH copolymer usually reflects the ambient humidity conditions outside the package, more than the humidity conditions inside the package. The lower the ratio of WVTR to the inside of the gasket and WVTR to the outside of the gasket is closer, the EVOH will reflect the moisture conditions outside.

The embodiments of the gaskets according to the invention which provide lower WVTR ratios, such as e.g. not larger than approx. 0.25/1, preferably approx. 0.15/1, more preferably approx. 0.05/1, allows EVOH to reflect the ambient humidity conditions in the external environment, and is advantageously adapted for processing in an environment with high humidity, such as e.g. a retort autoclave, and then returned to an environment with lower humidity, such as the surrounding atmosphere. In films thus prepared and processed by such a method, the wrapping film absorbs moisture from the high humidity environment and then releases this moisture, particularly that between the EVOH copolymer and the outer surface of the package, to the low humidity environment on the outer the surface of the gasket. The result of such a treatment, including the absorption of the moisture and the release of the moisture, is that the oxygen barrier in the wrapping film is reduced to only approx. the level of oxygen barrier provided by the less moisture-sensitive VDC copolymer layer, when the film absorbs the moisture, and reverts to about the level of oxygen barrier provided by the EVOH copolymer when the film releases moisture into and to the lower humidity environment. Fig. 1 shows a cross-section of a two-layer film according to the invention. Fig. 2 shows a cross-section of a three-layer film according to the invention. Fig. 3 shows a cross-section of a four-layer film according to the invention. Figures 4 and 6 show cross-sections of five-layer films according to the invention. Fig. 5 shows a cross-section of a seven-layer film according to the invention. Fig. 7 shows a general setup for an extrusion apparatus for producing the films according to the invention. Fig. 8 shows a cross-section of a nozzle from fig. 7, and film cooling apparatus used with the extrusion apparatus from fig. 7, together with a cross-section of a five-layer film produced in the die. Fig. 9 shows a pillow that is made with film according to the invention. Fig. 10 shows a cross-section of a package made from a semi-solid container and a lid made from a film according to the invention. Fig. 11 graphically shows the relative oxygen permeabilities for representative EVOH and VDC copolymers. Fig. 12 graphically shows the oxygen permeability of films according to the invention and shows a comparison with the oxygen permeability of a single layer film of EVOH with a comparable EVOH thickness. Fig. 13 graphically shows the advantage of the combination of an EVOH layer and a VDC layer in a film, compared to using only EVOH with the same combined thickness. Figures 1-6 show cross-sections of representative films according to the invention. It should be noted that in the drawings the first digit in the numbering sequence indicates the figure number and the second and third digits indicate the element being identified. As regards fig. 1, the two-layer film is designated as a whole by No. 110. In fig. 2, the total film (here a three-layer film) is identified by the number 210. In a similar way

the films in figures 3, 4, 5 and 6 are identified with the numbers 310, 410, 510 and 610 respectively.

Each of the films according to the invention has as essential components a first layer comprising ethylene vinyl alcohol copolymer and a second layer of vinylidene chloride copolymer, and the simplest form of the invention can contain only these two layers as shown in fig. 1, where layer 112 comprises the ethylene vinyl alcohol copolymer and layer 114 comprises the vinylidene chloride copolymer.

While the two-layer film in fig. 1 is satisfactory for providing some of the properties that are desirable in the films according to the invention, namely an oxygen barrier that is relatively insensitive to moisture, preferred films contain additional layers that provide additional desirable features. In particular with reference to fig. 1, it is determined that there is minimal attraction between the EVOH layer and the VDC layer. Thus, it is preferred to introduce an adhesive layer as at 216 in fig. 2 between the EVOH layer 112 and the VDC layer 214. A typical adhesive composition useful in layer 16 is EVA with more than approx. 15$ VA, and usually varying from approx. 18 to approx. 38$ VA. Another typical adhesive is a blend or copolymer of EVA with polypropylene, either homopolymer or copolymer. Still other acceptable adhesives are EMA, anhydride-modified polypropylene, homopolymer or copolymer, and anhydride-modified ethylene vinyl acetate. The anhydride modifications referred to may be copolymer units, or may be mixtures of the modified material with unmodified polymeric material. Other suitable polymeric adhesives will be obvious to the person skilled in the field of polymer films.

The films of fig. 2 is better than the films on fig. 1 in that they typically provide increased adhesion between the EVOH layer 12 and the VDC layer 114, using the adhesive layer 16.

In order for the films according to the invention to have the ability to effectively and economically produce gaskets by using adhesion in the films according to the invention, it is desirable to include in the film a sealing layer 318 which is illustrated in fig. 3, whereby the film can be produced into a package, e.g. a bag, by heat sealing, which is made around the periphery of the shaped container. The composition of the sealing layer 318 is selected for its temperature tolerance as well as its adaptability to be combined in the film structuring. Examples of sealing layer mixtures for use at high temperatures such as e.g. in retort structures that are exposed to treatment conditions up to approx. 135°C, sealing layer mixtures are therefore based on polypropylene homopolymer or copolymer, and polyethylene with a resin density of at least approx. 0.940, preferably at least approx. 0.950. Examples of sealing layer compounds for use at lower temperatures are EVA, LDPE, MDPE, ionomers and LLDPE including densities as low as approx. 0.890. Higher density LLDPE can also sometimes be used for use at higher temperatures. Modifying additives can of course be used where appropriate. Thus, the film in fig. 3 a first layer 312 of EVOH, a second layer 314 of VDC, a third adhesive layer 316 and the sealing layer 318.

In fig. 4, the EVOH layer is designated as 412 and the VDC layer is designated as 414. The adhesive layer 416 corresponds to the adhesive layers 216 and 316 which are similarly designated for Figures 2 and 3. The layer 418 corresponds to the sealing layer designated as 318 in FIG. 3. The layer 420 is an adhesive between the VDC copolymer layer 414 and the sealing layer 418, and is introduced for the purpose of improving the adhesion between the layers 414 and 418. The composition of the adhesive layer 420 can be selected from the materials indicated for the composition of the adhesive layer 16. Thus materials will typically be EVA with a vinyl acetate content greater than approx. 15$, blends and copolymers of EVA with polypropylene, EMA, MPP and MEVA. While the compositions of the adhesive layers 16 and 20 can be the same and are preferred to be the same in order to achieve simplicity in the chemistry of the structure, it is very acceptable that different materials are used for the layers 16 and 20. This is particularly desirable when the adhesion between the corresponding layers are improved by choosing different adhesive materials for layers 16 and 20.

The adhesive layer 161 can be used to achieve adhesion to either the EVOH layer 212, or the VDC layer 214, or both. When the adhesive layer 16 is bonded to only one of the layers 12 and 14, it is in surface-to-surface contact with only this layer, and is then in surface-to-surface contact with other contributing layers (not shown) between layer 16 and the other of layers 12 and 14. In the preferred embodiments, however, adhesive layer 16 is in surface-to-surface contact with, and thus bonded to, both layers 212 and 214. Similarly, adhesive layer 420 may be in surface-to-surface contact with, and therefore bonded to, only one of the VDC layer 14 and the sealing layer 18, in which case it is then in surface-to-surface contact with an intermediate layer (not shown) between layer 420 and the other of layers 14 and 18. It however, it is again preferred that the adhesive layer 420 is in contact with both layer 14 and layer 18, and thus binds these two layers directly together.

The films according to the invention can be produced using a number of methods. The methods may include such steps as extrusion, coextrusion, lamination, extrusion-lamination, coextrusion-lamination, and the like. The preferred method for making films according to the invention is the coextrusion process, with its resulting good economy. In the coextrusion process, it is preferred that all the layers in the film are coextruded simultaneously through a single die. Tubular coextrusion is acceptable. However, an example of a preferred method for the efficient production of films according to the invention is the casting extrusion process, where mixtures for the many layers are processed through corresponding extruders to produce melt streams which are then fed into a coextrusion die. In the nozzle, the melt streams are combined and converted into the multilayer film which is extruded from the nozzle opening, preferably on a cooling roll where the polymers are cooled and fixed.

Fig. 7 illustrates in block diagram form a combination of apparatus 724 for use in the molding extrusion of five-layer films according to the invention, which e.g. 410 in fig. 4. Extruders 726, 728, 729 and 730 are used to process four separate polymer blends corresponding to layers 412, 414, 416, 418 and 420, layers 416 and 420 having the same composition for the purposes of this illustration. Extruder 726 processes the PVOH for layer 12. Extruder 728 processes the VDC copolymer for layer 14. Extruder 729 processes the adhesive for layers 16 and 20. Extruder 730 processes the sealant for layer 18. The melt streams 840 and 842 (see Fig. 8) from extruders 728 respectively and 729, pass through connecting tubes 734 and 737 to a combining intermediate piece, shown by dashed line in FIG. 8 where they combine with the adhesive melt stream 842 which is located on both sides of the VDC melt stream 840 to thus form a three-layer melt stream 848 which is fed to die 838. The melt streams 844 and 846 from extruders 726 and 730 respectively pass through connecting tubes 732 and 736 directly to die 838. In the coextrusion die 38, the melt streams 844 and 846 are combined with the three-layer melt stream 848 to produce the five-layer melt stream in the die which is extruded from the die 38.

When the five-layer melt stream is extruded from die 38, it is cast onto a cooling roll 850 which is maintained at a controlled temperature, e.g. 32°C, and which is conductive to fixing the film 810 when making the film comprising the five layers 812, 814, 816, 818 and 820. After the film is made in the die and fixed on the cooling roll 850, it is either tied up, or is further processed according to conventional film processes.

Figs. 9 and 10 indicate packages which can be easily produced using films according to the invention, and in particular films which comprise a sealing layer 18. The bag 942 shown in fig. 9, is typically made by bringing two sheets of the film into surface-to-surface relationship with each other and providing heat seals 943 around the periphery. Alternatively, part of the sheet material can be folded in on itself so that the corresponding sealing layer parts face the inside of the fold, and so that seals are formed between the surfaces that face each other in the folded sheet.

Another example of gaskets that can be produced using the films according to the invention is the one shown at 1044 in fig. 10. A container 1046 is typically formed using a thermoforming process from a sheet that is typically thicker than the films that are usually produced in the present invention. The films according to the invention are between approx. 0.025 and approx. 0.63 mm thick, but are preferably between 0.038 and 0.25 mm thick. The preferred thicknesses provide films that have a high degree of flexibility, the films being thus usable in various flexible packaging applications. Thicker films can be produced, but they are typically more expensive than necessary to provide the benefits of flexible packaging films.

In the case of the packing shown in fig. 10, the lower wrapping portion 1046 is a pre-made container made of a thicker material, such as by thermoforming a sheet between 1 and 2 mm thick, to obtain a container having a thickness of the order of 0.25-0.75 mm at the bottom of the container. This provides a container that has a degree of stiffness that is typically desirable in packages of this type. The lid 1010 in the package is a film according to the invention which e.g. illustrated in Figures 1-6.

When producing sealed gaskets using films according to the invention, the sealing layer 18 can be used to produce seals where such are available. Where there is no sealing layer as part of the film 10, additional adhesive materials will typically be used between the surfaces that face each other in order to be sealed together. Where a sealing layer 18 is used, parts of the surfaces facing each other are brought into surface-to-surface contact when the seal is formed between the respective opposing film parts.

The vinylidene chloride copolymer used in the films according to the invention can be any of the available vinylidene chloride copolymers, especially those containing vinyl chloride or acrylate comonomers, especially methyl acrylate. Vinylidene chloride-vinyl chloride copolymers have a typical extrusion temperature of approx. 154 to approx. 166°C in contrast to typical ethylene vinyl alcohol copolymers, which have extrusion temperatures typically above 191°C. When producing the films according to the invention by means of the coextrusion process, the melt streams are thus produced in the corresponding extruders at the desired temperatures, and the melt streams are exposed to alternating temperatures only in the die. Since a higher temperature is required for EVOH than for VDC, at least part of the die is kept at the higher temperature to ensure its continuous fluidity in the die. The VDC copolymer is then exposed to at least a portion of the higher temperature required by the EVOH during at least a portion of its passage through the die during manufacture, along with the other melt streams, to form the multilayer film that is extruded from the die. Thus, EVOH is produced in the form of a melt stream and finally into a film form at a higher temperature, e.g. 199 to 210°C, while the vinylidene chloride copolymer is made into a melt stream at a lower temperature, e.g. about. 154 to 166°C. The temperatures during the melt treatment of EVOH and the VDC copolymers naturally depend on the particular copolymers being treated. A vinylidene chloride-vinyl chloride copolymer is preferably treated between 160 and 166°C, while a vinylidene chloride-methyl acrylate copolymer is preferably treated at a slightly lower temperature, such as e.g. 154 to 160°C.

A significant feature of the invention lies in providing correct arrangements of the layers in the manufacture of the films, and of the films in the manufacture of packs according to the invention, and especially those packs containing products that produce high humidity inside the pack than those present in the expected ambient conditions on the outside of the package. Particularly in cases where the interior of the package exhibits a higher humidity than the conditions outside the package, it is highly desirable to arrange the films according to the invention in the package so that the vinylidene chloride copolymer layer 14 lies between the product and the ethylene vinyl alcohol copolymer. In this arrangement, the VDC copolymer acts as a moisture barrier between the EVOH and the moisture inside the gasket, thus regulating the growing moisture transmission from the inside of the gasket, through the VDC copolymer layer to the EVOH layer. It is also important that the barrier against moisture penetration between the EVOH layer and the outer side of the gasket is significantly smaller than the moisture barrier between the EVOH layer and the inner side of the gasket. Thus, the packing films according to the invention for use in connection with moist products provide the layers which are placed inwards from the EVOH layer a greater moisture barrier than any layers which may be placed outwards from the EVOH. In films according to the invention, the VDC copolymer is primarily responsible for providing a good moisture barrier in the film. Thus, in the gaskets, it is placed towards the inside of the gasket, from the EVOH layer 12, in cases where the moisture inside the gasket is greater than the moisture outside the gasket.

Fig. 1-4 shows EVOH as the outer surface of the film for simplicity. And especially where a film according to the invention is produced using a coextrusion process, it is preferred that the EVOH is an outer layer of the layers that are coextruded, as in fig. 1-4.

However, it is preferred that a material which is more resistant to harsh treatment constitutes the outer layer of the film, when it is produced into a package. Thus, a layer 522 of a material that resists rough treatment is typically mounted, such as e.g. polyethylene terephthalate (PET), polyamide, polycarbonate, or the like, on the EVOH layer 12, e.g. by means of an adhesive layer 523 which e.g. a curing type urethane adhesive. The adhesive in layer 523 is naturally chosen in light of the special compositions of layers 512 and 522.

Fig. 5 represents a typical 0.63 mm thick film according to the invention for which the moisture barrier can be calculated. For the purposes of determining the moisture barrier, the adhesive layers 516, 520 and 523 are all considered to be less than 0.0025 mm thick, and to provide nominal, growing moisture barrier, so their contribution is ignored for convenience in calculating moisture barrier properties. The EVOH layer 512 forms the base layer from which the growing moisture barrier is calculated. Growing moisture barriers the barrier provided by a small increase in film thickness. The increments chosen for comparison here correspond to the thicknesses between the corresponding layer contact rafts. In this example, the EVOH layer is 0.013 mm thick.

The VDC copolymer is vinylidene chloride-methyl acrylate copolymer (VDC-MA) and is 0.13 mm thick. The sealing layer 518 is LLDPE and is 0.025 mm thick. The layer resistant to rough treatment is PET, and is 0.013 mm thick. Outside of EVOH, the moisture transfer rate depends on the outer layers, namely 0.013 mm of PET, and is approx. 40 g/m<2>day at 60$ relative humidity. Inward from the EVOH, the increasing moisture transfer rate is a combination of the velocities of the inner layers that are between the EVOH layer and the inner film surface, namely the VDC copolymer layer 14 and

The LLDPE layer 518. The combined speed is approx. 1.6 g/m<2>day. Thus, the ratio between the growing moisture transfer rate for the inner layers and the growing moisture transfer rate for the outer layers is approx. 1.6/40, or approx. 0.04/1.

In the above illustration, both the EVOH layer and the VDC layer were 0.013 mm thick, with a total thickness of 0.025 mm for the two layers. When the thicknesses of the two layers are rearranged so that the VDC layer is made as thin as possible while still being subjected to coextrusion, its thickness is approx. 0.0025 mm. If the EVOH layer is thickened accordingly so that the sum of the thicknesses remains 0.025 mm, this then becomes 0.023 mm thick. If it is otherwise kept like this, the increasing moisture transfer rate in such a film for the layers inwards from the EVOH layer is approx. 6 g/m<2>day. The growing moisture transfer rate for the layers outside the EVOH layer remains at 40 g/m<2>day. In this case, the ratio between the growing moisture transfer rates for the inner layers and the outer layers is thus approx. 6/40, or approx. 0.15/1.

The ratio between the growing moisture transfer rates for the inner layers and the outer layers shall not be more than approx. 0.25/1, preferably no more than approx. 0.15/1 and is generally no more than approx. 0.15/1 and is generally no more than 0.05/1 for the preferred films of the invention, which exhibit the desired excellent oxygen barrier along with the reduced sensitivity to moisture. The total V/VTR through the entire thickness of the wrapping material must furthermore be low enough to provide a stable moisture content in the packaged product, and is usually less than approx. 6 g/m<2>day, when the VDC layer is VDC-MA and is 0.0025 mm thick and the relative humidity outside is approx. 60$. This generally provides fairly adequate moisture barrier properties for VDC copolymer layer 14. Of course, other materials also contribute to providing a moisture barrier, depending on the film structure, the relative layer thickness and the ambient conditions at the film surfaces.

Thus, by providing the higher moisture barrier increase in the inner layers, the films gain the ability to release moisture from the EVOH layer to a lower humidity environment outside the package faster than moisture is transferred to the EVOH layer from inside the package. Where the moisture barrier for the outer layers is relatively low, the moisture in the EVOH layer 12 thus follows close to the moisture to which the outside of the package is exposed. When the outside of the package is exposed to high humidity, the EVOH layer absorbs moisture, which greatly reduces the contribution of the EVOH layer to the oxygen barrier. But the VDC layer is not affected in this way. Its oxygen barrier contribution remains approximately constant. Thus, the oxygen barrier of the wrapping film is maintained at approximately the level to which the VDC copolymer contributes.

Once the lower humidity is restored outside the package, the moisture in the EVOH layer is rapidly released to the low humidity outer environment through any outer layers that provide a low moisture barrier. When the moisture in the EVOH layer is released quickly, the barrier properties of the EVOH layer are restored accordingly.

The oxygen barrier properties of representative EVOH and vinylidene chloride copolymers are illustrated in Fig. 11. All tests represent oxygen transfer rate (OTR) for films 0.025 mm thick. As shown there, conventional vinylidene chloride-vinyl chloride copolymer (VDC-VC) has an OTR of approx. 2.25 g g/m<2>day. VDC-MA has an OTR of approx. 0.85 g/m<2>day. Fig. 11 shows that the OTR for the VDC copolymers does not vary much with varying humidity. Fig. 11 also shows that the OTR of EVOH films is less than the OTR of some of the VDC films at low humidity, but is greater than the OTR of VDC films at high humidity. The OTR for EVOH containing 32$ ethylene is e.g. about. 0.15 g/m<2>day with 0$ relative humidity (R.H.), while the OTR for VDC-MA is approx. 0.85, and for VDC-VC is approx. 2.25. At approx. 75$ R.H. the OTR for VDC-MA and EVOH is roughly the same. Over approx. 75$ R.H. the OTR of the EVOH film is worse, but it is still better than the OTR of the VDC-VC, up to approx. 92$ R.H.

As can be seen from fig. 11, the OTR for EVOH is affected, as can be seen from fig. 11 thus has EVOH containing at least 40$ ethylene, generally an OTR equal to or greater than the OTR of VDC-MA at all humidities. But, it is still better than OTR for VDC-VC up to approx. 85-90$ R.H.

In some applications in which the films according to the invention are intended to be used, the films are temporarily exposed to high humidity and high temperature, such as e.g. by retort treatment in a high temperature autoclave, followed by return to a lower humidity and lower temperature environment after the treatment is complete. During the autoclave treatment period, which typically uses steam or hot water, the wrapping film, including the EVOH layer 12, absorbs moisture from the hot water or steam of the process. The absorbed moisture naturally causes the oxygen barrier properties of the EVOH layer to decrease in accordance with the known sensitivity of EVOH under conditions of high temperature and high humidity. However, the VDC copolymer layer 14 is not affected in this way. Indeed, it retains its oxygen-barrier properties at the same general level in humid environments as well as in dryness, as can be seen from fig. 11. During the autoclave treatment, the oxygen barrier properties of the film thus reflect the properties of the VDC copolymer layer 14. After the autoclave treatment is finished and the package is removed from the high humidity environment, the wrapping film releases the moisture that was taken up in the autoclave process from the EVOH layer 12 outwards to the outer surface of the package. The outer layer or layers of the gasket thus release their moisture outwards from the EVOH layer to the surroundings with lower humidity. When the moisture is released, and especially when the moisture leaves the EVOH layer 12, the oxygen barrier properties of the EVOH layer 12 are restored accordingly. Thus, at any time when the gasket is in a low humidity environment, the oxygen barrier properties of the gasket generally reflect the oxygen barrier properties of the EVOH layer at these low humidities. There is naturally a recovery time period where EVOH layers are in the process of reaching equilibrium with the external environment, whether they are moist or dry, where the oxygen barrier properties of the gasket are intermediate.

Special examples of films according to the invention will now be described, the following structures being representative of films which exhibit the desirable properties of films according to the invention:

/EVOH/EVA/VDC/EVA/LLPDE/

/EVOH/MPP/VDC/MPP/PPE/

/EVOH/MEVA/VDC/MEVA/LLPDE/

/PET/urethane adhesive/EVOH/MEVA/VDC/MEVA/LLPDE/

MPP = anhydride-modified polypropylene

MEVA = anhydride modified ethylene vinyl acetate

Example 1

A four-layer film as illustrated in fig. 3 is produced. EVOH is GL-ET from Nippon Gohsei with an ethylene content of 38$. The inner layer 16 is Plexar 2965, an anhydride-modified EVA. Layer 14 is vinylidene chloride-vinyl chloride copolymer. Layer 18 is an EVA mixture containing approx. 9$ vinyl acetate. The film is produced by co-extrusion of the polymers in the production of the four-layer film. The temperature for EVOH when it enters the nozzle is approx. 201°C. The temperature of Plexar 2965 when it enters the nozzle is approx. 177°C. The temperature of the VDC copolymer as it enters the die is approx. 163°C. The temperature for EVA comprising layer 18 varies between 182 and 204°C during the experiment. The multiple polymers are formed into tubular layers and a tubular tape is extruded from the annular die with a thickness of approximately 0.38 mm. Samples of the tape are then thermoformed in the production of containers which have a base area of 10 x 10 cm and a height of 5 cm. The thickness of the resulting thermoformed material is approximately 0.038 mm. The oxygen barrier for the resulting material appears in Table 1.

The oxygen permeabilities in Table 1 are determined using an Oxtran Oxygen Analyzer by exposing the inner surface of the film to 100% humidity. The outer surface of the film is then exposed to humidities of 50, 75 or 100$, and the oxygen transfer is measured. Thus, by measuring the oxygen transfer rate where there is a humidity difference across the two surfaces, the performance of the film in a package containing a wet product, and where the outside of the package is exposed to the normally lower humidity in the external environment, i.e. 50$ or 75$ relative humidity, is simulated, and therefore calculated.

If a dry product is packaged, a good oxygen barrier is similarly achieved by placing the EVOH layer between the VDC layer and the product, since the dry product then represents the dry side of the wrapping film. For heat-sealable packaging films where these embodiments are used, the EVOH layer 12 is between the VDC layer and the sealing layer 18. Representative of such films is the one shown in fig. 6. In fig. 6, layers 612, 614, and 616 represent the EVOH layer, the VDC layer, and the intermediate adhesive layer, respectively. Layer 618 is the sealing layer as illustrated in Figures 3 and 4. Layer 624 is an adhesive such as those described for layers 216, 316 and 416.

Example 2

A five-layer film as in fig. 4 is cast extruded. The EVOH layer consists of Soarnel D from Nippon Gohsei. The ethylene content of Soarnol D is 29$. The VDC copolymer in layer 14 is Dow 119 vinylidene chloride-methyl acrylate copolymer. The vinylidene chloride copolymer contains additives for the typical heat stabilization needs. The sealing layer 18 consists of Dow 3010 linear low density polyethylene. The composition of adhesive layers 16 and 20 is in both cases Plexar 326 anhydride-modified EVA.

The temperatures in the melt streams of EVOH and LLDPE are both approx. 204°C at the entrance to the nozzle. The temperature of the adhesive Plexar 326 is approximately 160°C at the entrance to the nozzle. The temperature of the Dow 119 vinylidene chloride methacrylate copolymer is approximately 157°C at the nozzle entrance. The material is then combined in the die, and a multi-layer film such as that shown in fig. 4. The film extruded from the die is approximately 0.07 mm thick. The EVOH layer is approx. 0.007 mm thick. The VDC copolymer is approximately 0.014 mm thick. The inner layers of Plexar 360 are approximately 0.0025 mm thick. LLDPE is approximately 0.038 mm thick.

The thus produced film is then tested for oxygen transmission in a range of relative humidities as described in example 1. When the film is tested with the EVOH layer towards the low humidity side, which simulates that the VDC copolymer lies between the EVOH and the moist product, the oxygen permeability is measured which is illustrated in fig. 12 with the solid line "A". When the arrangement of the film is reversed so that the EVOH is between the VDC copolymer and the wet side of the film, the oxygen transfer rate as illustrated by curve "B" in Fig. 12. Curve "C" in fig. 12 represents the calculated oxygen transfer rate for a single layer film of the same Soarnol D EVPH, the same thickness as the thickness of the EVOH layer in the film of Example 2, namely 0.007 mm thick. Fig. 12 therefore shows (curve B) that when the EVOH is turned towards the inside of the package, which is simulated by the high humity side of the oxygen tester, the oxygen permeability is relatively constant at all humidities present on the other surface of the film, namely that represented by the outside of the package surface, and approximates the oxygen permeability of the VDC-MA copolymer layer at the stated thickness of 0.015 mm of VDC-MA. Correspondingly, curve "A" indicates that with the EVOH layer placed towards the outside of the package, namely with the VDC copolymer between the EVOH layer and the product, and where the EVOH layer can release moisture to an environment with lower humidity, namely below approx. 75$ R.H. the oxygen permeability of the film is lower than the oxygen permeability of the VDC copolymer, and is rather regulated by the good oxygen barrier properties of the EVOH layer. Gaskets made with films according to the invention, and where the VDC copolymer is suitably placed between the EVOH layer and the product, and where the EVOH layer can release moisture to the environment near the outer surface of the gasket, result in the gasket having the advantages of the EVOH layer's lower oxygen permeability at lower humidities, e.g. under approx. 75$ relative humidity as shown in fig. 12, and yet does not have the extreme oxygen sensitivity characteristic of films where EVOH is the sole source of the oxygen barrier. Rather, the maximum oxygen permeability of the film is regulated by the VDC copolymer so that it never exceeds the level of oxygen permeability normally associated with the corresponding VDC copolymer of the thickness used.

Example 3

A film is coextruded as in Example 2, making appropriate adjustments in the melt processing temperatures of the various polymers. Layer 12 is EVOH. Layer 14 is vinylidene chloride-methyl acrylate copolymer. Layers 16 and 22 are OF-500 anhydride-modified polypropylenes from Mitsui Petro-chemical. Sikt 418 is a propylene ethylene copolymer.

Example 4

A film is produced as in example 3. Layer 12 is EVOH. Layer 14 is a vinylidene chloride-methyl acrylate copolymer. Layer 18 is linear low density polyethylene. Layers 16 and 20 comprise ethylene vinyl acetate copolymer containing approx. 28$ vinyl acetate.

Example 5

A film is prepared as in Example 4, except that the composition of layer 14 is vinylidene chloride-vinyl chloride copolymer.

Example 6

A film is prepared as in Example 4. Each of the adhesive layers, as in 16 and 20, is approximately 0.0025 mm thick. EVOH contains 32% ethylene and layer 12 is 0.013 mm thick. VDC is VDC-MA and layer 14 is 0.013 mm thick. The sealing layer 18 is LLDPE with a thickness of approx. 0.025 mm. A 0.013 mm thick film of PET is adhesively laminated to the EVOH layer using a curing type urethane adhesive to produce a 7-layer film as shown in Fig. 5.

Combination example 6

A 0.063 mm thick film is produced as in example 6 except that an additional 0.013 mm layer of EVOH is used instead of the 0.013 mm thick VDC-MA layer and the adhesive layer 16.

Oxygen permeation rates through the entire thickness of the film, with EVOH on the low moisture side, are calculated for the films from Example 6 and Comparative Example 6 and are shown graphically in Fig. 13. Curve "D" in fig. 13 represents the films from example 6. Curve "E" represents the films from comparative example 6. As can be seen from this, both films have an excellent oxygen barrier of approx. 0.2-0.3 with low humidity. And, while both curves rise with increasing humidity, curve "D" rises much less than curve "E", indicating that the film of Example 6 is much less sensitive to increasing humidity. At 100$ relative humidity, the film from example 6 has an OTR of approx. 1.6, while the film from comparison example 6 is approximately 18.

The extent to which the objectives of the invention are achieved depends somewhat on the choice of the VDC and EVOH copolymers, on the thicknesses of the many layers and the humidity to which the film is exposed. Thus, the OTR of the selected EVOH layer should be less, at 0$ R.H., preferably at 50$, than the OTR of the layer of the selected VDC copolymer. Representative OTRs for films that are 0.025 mm thick are shown in Fig. 11, both for EVOH, varying ethylene content, and for different VDC copolymers. By selecting a particular combination of EVOH and VDC copolymers, along with specifying appropriate corresponding layer thicknesses, where the OTR of the EVOH layer at lower humidity is less than the OTR of the selected VDC layer, improved OTR is achieved in the film compared to a similar film using VDC with low moisture, and with a similar film using EVOH with high moisture. The layer thicknesses that are actually achieved by extrusion are, of course and something that is conventionally known, only the approximation of the desired thicknesses, the accuracy being limited to the accuracy possibilities of the equipment used for the film production. The greater the difference between the OTRs of the EVOH and VDC layers, and the greater the humidity range over which there is a difference, the greater the benefits of combining the EVOH and VDC layers in the same film. Thus, it is preferred to select a combination of EVOH and VDC copolymers, and layer thicknesses, where the OTR of the EVOH layer is less than the OTR of the VDC layer over a range of 0$ R.H. to at least $25 R.H., preferably 0 to at least $50 R.H. For use with VDC-MA, the EVOH layer must therefore generally have an ethylene content of less than approx. 40$, where the EVOH and VDC layer thicknesses are the same. EVOH with 40$, or even 44$ ethylene content, as can be seen from fig. 11, can still benefit from a film if it is combined with VDC-VC as the VDC layer, or if it is used 1 layer thicknesses greater than the thickness of the corresponding VDC layer, since OTR is a function not only of the polymer composition, but also of the layer thickness.

However, since the VDC copolymer governs the maximum OTR of the film, at high humidity, EVOH can be selected without concern for OTR at high humidity. Instead, more consideration must be given to the OTR for the EVOH mixture at low humidity, where the OTR for EVOH is more decisive for the film's OTR. Thus, preferred EVOH extrudable mixtures with a lower ethylene content such as e.g. 28-32$ ethylene, which provides lower OTR at low humidity. The good oxygen barrier properties of EVOH are typically regulatory at lower humidity, while the higher, but less moisture sensitive, oxygen barrier property of the VDC copolymer is regulatory at higher humidity. Since the highest oxygen transfer rate of a film is generally governed by the oxygen transfer rate of the VDC copolymer, it is usually advantageous to select a VDC copolymer with a relatively low oxygen transfer rate. Among the commercially available VDC copolymers, those having the methyl acrylate comonomer are generally better than those comprising the vinyl chloride comonomer, as can be seen from fig. 11. The copolymer prepared with methyl acrylate as comonomer is therefore preferred in films and packages according to the invention where the oxygen transfer rate is a factor in choosing the VDC copolymer.

Thus, the invention provides new films and gaskets with excellent oxygen barrier and reduced sensitivity of the oxygen barrier to moisture, as well as methods of making the films. The person skilled in the art will see that certain modifications can be made in the mixtures and structuring of the films and packs according to the invention, and the methods for its production, without deviating from the scope of the present invention.

And while the invention has been described above in connection with its preferred embodiments, it is to be understood that various rearrangements, modifications and changes may be made to the invention, and all such arrangements, modifications and changes are intended to be within the scope of the accompanying claims.

Claims (45)

1. Multi-layer, polymer film, characterized in that it comprises: (a) a first layer (112, 212, 312, 412, 512, 612) of an ethylene vinyl alcohol copolymer, (b) a second layer (114, 214, 314, 414, 514, 614) of a vinylidene chloride copolymer, and (c) a third adhesive layer (216, 316, 416, 516, 616) between said first and second layers (112, etc; 114, etc.) and which provides adhesion with at least one of said first and second layers of at least 39, 4 g per cm width formwork strength, the composition of said third adhesive layer (216, etc.) being selected from ethylene vinyl acetate copolymer with more than 15% vinyl acetate, mixtures and copolymers of polypropylene and ethylene vinyl acetate copolymer with more than 15% vinyl acetate, mixtures and copolymers of polypropylene and ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer , anhydride-modified polypropylene and anhydride-modified ethylene vinyl acetate copolymer, and preferably selected from ethylene vinyl acetate copolymers comprising approx. 18 to approx. 35$ vinyl acetate copolymer, anhydride modified ethylene vinyl acetate copolymer and anhydride modified polypropylene, wherein the ratio between increasing water vapor transfer rate between said first layer (112, etc.) of ethylene vinyl alcohol copolymer and the outer surface of said film through said vinylidene chloride copolymer layer (114, etc.) and the water vapor transfer rate between said first layer and the second surface of said film is not more than approx. 0.25/1. 2. Multi-layer, polymeric film, according to claim 1, characterized in that it comprises a fourth sealing layer (318, 418, 518, 618), the second layer (314, etc.) of vinylidene chloride copolymer between the third layer (316, etc.) and the fourth, the sealing layer. 3. Multi-layer, polymer film according to claim 2, characterized in that the composition of the sealing layer (318, 418, 518, 618) is selected from linear low-density polyethylene, polypropylene polymers and copolymers, and polyethylene with a resin density of at least 0.940. 4. Multi-layer, polymeric film according to claim 2 or 3, characterized in that it comprises a fifth adhesive layer (420, 520) between the second layer (414, etc.) of vinylidene chloride copolymer and the fourth sealing layer (418, etc.), the composition of the fifth layer (420, 520) is selected from ethylene vinyl acetate copolymer with more than approx. 15$ vinyl acetate, mixtures and copolymers of polypropylene and ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, anhydride modified polypropylene and anhydride modified ethylene vinyl acetate copolymer. 5. Multi-layer, polymer film, characterized in that it comprises in sequence: (a) a first layer (412, 512) comprising ethylene vinyl alcohol copolymer; (b) a second layer (416, 516) comprising an ethylene vinyl acetate copolymer having more than about 15$ vinyl acetate ; (c) a third layer (414, 514) comprising a vinylidene chloride copolymer; (d) a fourth layer (420, 520) comprising an ethylene vinyl acetate copolymer having more than about 15$ vinyl acetate; and (e) a fifth layer (418, 518) comprising linear low density polyethylene. 6. Multi-layer, polymer film, characterized in that it comprises in sequence: (a) a first layer (412, 512) comprising ethylene vinyl alcohol copolymer; (h) a second layer (416, 516) comprising an anhydride-modified polypropylene or an anhydride-modified ethylene vinyl acetate copolymer; (c) a third layer (414, 514) comprising a vinylidene chloride copolymer; (d) a fourth layer (420, 520) comprising an anhydride-modified polypropylene or an anhydride-modified ethylene vinyl acetate copolymer; and (e) a fifth layer based on polypropylene or linear low density polyethylene. 7. Multi-layer, polymeric film according to claim 1 or 2, characterized in that the third adhesive layer (216, etc.) is in surface-to-surface contact with both the first (112, etc.) and second (114, etc.) layers , thereby binding them to each other. 8. Multilayer, polymeric film according to any one of claims 1-7, characterized in that the vinylidene chloride copolymer is vinylidene chloride methacrylate copolymer. 9. Multi-layer, polymeric film, characterized in that it comprises a first extruded layer (112, 212, 312, 412, 512, 612) of ethylene vinyl alcohol copolymer, a second layer (114, 214, 314, 414, 514, 614) of a vinylidene chloride copolymer and a third layer (216, 316, 416, 516, 616) of an adhesive polymer, said second second and third layers both being co-extruded with said first layer of ethylene vinyl alcohol copolymer, said third adhesive layer being bonded to both the first and second layer with a peel strength of at least 39.4 g/cm width, and wherein the vinylidene chloride copolymer is vinylidene chloride methyl acrylate or vinylidene chloride vinyl chloride. 10. Multi-layer, polymeric film according to claim 9, characterized in that the first layer (112, etc.) of ethylene vinyl alcohol copolymer has a growing oxygen transfer rate at 0$ relative humidity which is less than the corresponding growing oxygen transfer rate for the second layer (114, etc.) of vinylidene chloride copolymer at 0$ relative humidity. 11. Multi-layer, polymeric film according to claim 10, characterized in that the increasing oxygen transfer rate for the ethylene vinyl alcohol copolymer layer (112, etc.) at 50$ relative humidity is less than the corresponding increasing oxygen transfer rate for the vinylidene chloride copolymer layer at 50$ relative humidity. 12. Multilayer film according to any one of claims 1-11, characterized in that the ratio of increasing water vapor transfer rate between the first layer (112, etc.) of ethylene vinyl alcohol copolymer and an outer surface of said film through said vinylidene chloride copolymer layer (114 , etc), and the water vapor transmission rate between said first layer and the second surface of said film is not more than 0.25/1. 13. Multi-layer, polymer film, characterized in that it comprises: (a) a first layer (612) of ethylene vinyl alcohol polymer; (b) a second layer (614) of a vinylidene chloride copolymer; (c) a third, heat-sealable layer (618), said first layer (612) of ethylene vinyl alcohol copolymer being between said second layer (614) of vinylidene chloride copolymer and the heat-sealable layer (618); and the ratio between the increasing water vapor transfer rate between the layer of ethylene vinyl alcohol copolymer and a surface of said film, through said vinylidene chloride copolymer layer, and the water vapor transfer rate between the first layer and the second surface of the film is not more than about 0.25/1. 14. Multi-layer, polymeric film according to claim 13, characterized in that the composition of the heat-sealable layer (618) is selected from polypropylene, low density polyethylene, medium density polyethylene, ethylene vinyl acetate copolymer and ionomers. 15. Packing, characterized in that it is produced from a film according to any one of claims 1-12. 16. Seal made with a film according to claim 13 or claim 14, characterized in that the third sealing layer is placed against the inside of the seal. 17. A package made with a film according to claim 1, 2 or 3, characterized in that the packaging material comprising said said film (1010) delimits an enclosed space (1045) inside the package (1044) separated from the surroundings outside the packages, one of said enclosed spaces and said surroundings have a lower humidity, thereby comprising a low humidity side and another comprising a high humidity side, in which the barrier against moisture transfer between the ethylene vinyl alcohol copolymer (e.g. 112) and the low humidity side is significantly less than the barrier against moisture transfer between the ethylene vinyl alcohol copolymer and the high humidity side. 18. Packing according to claim 17, characterized in that the composition of the third layer of the film (116, etc.) is selected from ethylene vinyl acetate copolymers comprising approx. 18 to c. 35$ vinyl acetate, anhydride modified ethylene vinyl acetate copolymer and anhydride modified polypropylene. 19. Gasket according to claim 17, which when dependent on claim 2 or 3, is further characterized by a fifth adhesive layer (420, 520) between the second layer (414, 514) of vinylidene chloride copolymer and the fourth sealing layer (418, 518) , the composition of the fifth layer (420, 520) being selected from ethylene vinyl acetate copolymer with more than approx. 15$ vinyl acetate, mixtures and copolymers of polypropylene and ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, anhydride-modified polypropylene and anhydride-modified ethylene vinyl acetate copolymer . 20. A package produced using a film according to claim 5, 6, 7 or 8, characterized in that the packaging material comprising said film (1010) delimits an enclosed space (1045) inside the package (1044), separated from the surroundings outside the package, one of said enclosed spaces and said environment having a lower humidity, thereby comprising a low humidity side, and the other comprising a high humidity side, wherein the barrier against moisture transfer between the ethylene vinyl alcohol copolymer (e.g. 412, 512) and the low humidity side is significantly less than the barrier against moisture transfer between the ethylene vinyl alcohol copolymer and the high humidity side. 21. Gasket according to claim 17 or 18, characterized in that the third adhesive layer (e.g. 216) is in surface-to-surface contact with both the first and second layers (e.g. 212, 214), and thereby binds said first and second layers to each other. 22. Gasket according to claim 17 or 21, characterized in that it comprises a fourth sealing layer (e.g. 318) in the film, the second layer (314) of vinylidene chloride copolymer being between the third layer (316) and the fourth the sealing layer (318). 23. Method for producing a multi-layer, polymeric film, characterized by (a) a first mixture comprising ethylene vinyl alcohol copolymer is processed in a first extruder (726) thereby forming a first melt stream (844); (b) a second composition comprising a vinylidene chloride copolymer, such as vinylidene chloride-vinyl chloride copolymer or vinylidene chloride-methyl acrylate copolymer is processed in a second extruder (728) thereby producing a second melt stream (840); (c) a polymeric composition which in the molten state can be bonded directly to a surface of at least one of the first and second compositions to provide in the solid state a peel strength of at least 39.4 g/cm 1 of the contact surface is processed in a third extruder ( 729), whereby a third melt stream (842) is produced; (d) the first, second and third melt streams (844, 840, 842) are fed into a coextrusion die (838); (e) the first and second melt streams are combined with said third melt stream (842) between the first and second melt streams (844, 842); (f) the combined melt streams are processed to obtain a multilayer film in the die (838) and the multilayer film (810) is extruded from the die; and (g) cooling the coextruded film (810). 24. Method for producing a film, characterized by (a) first and second mixtures of ethylene vinyl alcohol copolymer and vinylidene chloride copolymer, respectively, and respective first and second thicknesses of respective first and second layers to be prepared from the first and second mixtures, are selected such that the increasing oxygen transfer rate of said first layer of ethylene vinyl alcohol copolymer at 0% relative humidity is less than the increasing oxygen transfer rate of said second layer of vinylidene chloride copolymer at 0$ relative humidity; and (b) film with said first and second layers (eg 112, 114) having approximately said first and second thicknesses and made from said first and second mixtures is prepared. 25. Method for producing a film according to claim 24, characterized in that the film production step comprises coextrusion of the first and second layers of ethylene vinyl alcohol copolymer and vinylidene chloride copolymer. 26. Method for producing a film, characterized in that an extrudable mixture of ethylene vinyl acetate copolymer containing more than 15% vinyl acetate, mixtures and copolymers of polypropylene and ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, anhydride-modified polypropylene and anhydride-modified ethylene vinyl acetate copolymer and the selected extrudable adhesive is selected as the adhesive is coextruded with said first and second layers (112, 114) as a third layer (116) between said first and second layers (112, 114). 27. Method for producing a film according to any one of claims 24-26, characterized in that the film is structured so that the relationship between the increasing water vapor transfer rate between the first layer (e.g. 112) of ethylene vinyl alcohol copolymer and the outer surface of the film via the vinylidene chloride copolymer layer (eg 114) and the water vapor transfer rate between the first layer and the second surface of the film is not more than 0.25/1. 28. Method for producing a packaged product, characterized by (a) a multilayer polymeric film (810) with a first layer (812) comprising an ethylene vinyl alcohol copolymer, a second layer (814) comprising a vinylidene chloride copolymer, such as vinylidene chloride methyl acrylate copolymer, and a third, intermediate bonding layer (816) between said first and second layers is produced, e.g. by coextrusion, the ratio between increasing water vapor transfer rate between the first layer (812) of ethylene vinyl alcohol copolymer and an outer surface of said film through the vinylidene chloride copolymer layer (814) and the water vapor transfer rate between the first layer and the second surface of the film is no more than about 0.25/1; (b) the film (810) is made into a container packing (942, 1044), the film being arranged for greater, increasing water vapor transfer rate from the leading layer outward from the packing than inward from the packing, and a product that provides moisture inside the packing is placed in the container; and (c) the container seal is closed and sealed; wherein the layer (814) of vinylidene chloride copolymer acts as a moisture barrier to protect the ethylene vinyl alcohol copolymer from moisture inside the package, and wherein moisture in the ethylene vinyl alcohol copolymer layer (812) and between the ethylene vinyl alcohol copolymer and the outer surface of the package is transferred to said outer surface faster than moisture is transferred from the inside of the package to the ethylene vinyl alcohol copolymer layer, so that the moisture content in the ethylene vinyl alcohol copolymer layer reflects the ambient humidity outside the package. 29. Method according to claim 24, characterized in that the film production step comprises coextrusion of the first, second and third layers (812, 814, 816). 30. Method according to claim 28 or 29, characterized in that the third adhesive layer (816) is selected to provide adhesion to at least one of the first and second layers (812, 814) of at least 39.4 g/cm width peel strength, and is selected from ethylene vinyl acetate copolymer with more than 15% vinyl acetate, blends and copolymers of polypropylene and ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, anhydride modified ethylene vinyl acetate copolymer and anhydride modified polypropylene. 31. Method according to any one of claims 28-30, characterized by the further steps of treating the container packing in a high humidity environment, and then returning it to a lower humidity environment, whereby the film absorbs moisture from the high humidity environment and then emitting moisture between the ethylene vinyl alcohol copolymer and the outer surface to the lower humidity environment, so that the oxygen barrier quality of said ethylene vinyl alcohol copolymer is reduced when the film absorbs moisture, and is restored when said film emits moisture to the lower humidity environment. 32. Procedure for wrapping a product, characterized by: (a) a packaging container (942, 1044) having a multilayer packaging sheet material (810) having a first layer (e.g., 112, 812) comprising ethylene vinyl alcohol copolymer, and a second layer (114, 814) comprising vinylidene chloride copolymer is prepared, the sheet material being arranged for greater water vapor transfer rate from the first layer outwards from the container than inwards into the container, (b) a product that provides moisture inside the package is placed in the container (942, 1044); (c) the container is closed and sealed, (d) the closed and sealed container (942, 1044) is processed in a high humidity environment, wherein the sheet material (810) absorbs moisture from the high humidity environment, thereby reducing the instantaneous effective oxygen barrier property of the ethylene vinyl alcohol copolymer, and (e) the closed and sealed container (942, 1044) is then returned to a lower humidity environment, wherein the sheet material (810) releases moisture between the ethylene vinyl alcohol copolymer and the lower humidity environment, and the ethylene vinyl alcohol copolymer oxygen barrier is correspondingly restored. 33. Packing made with a wrapping sheet material, characterized in that the wrapping material (1010) delimits an enclosed space (1045) inside the packing (1044) separated from the environment outside the package, the wrapper sheet material (1010) comprising a first layer (e.g. 112, 812) of ethylene vinyl alcohol copolymer and a second layer (e.g. 114, 814) of vinylidene chloride copolymer, e.g. vinylidene chloride methyl acrylate copolymer, one of the enclosed space (1045) and the surroundings having a lower humidity, and thereby comprising a low humidity side, than the other of the enclosed space and the surroundings, comprising a high humidity side, wherein the barrier against moisture transfer between the ethylene vinyl alcohol copolymer and the low humidity side is significantly less than the barrier to moisture transfer between the ethylene vinyl alcohol copolymer and the high humidity side. 34. A gasket according to claim 33, characterized in that the moisture vapor transfer rate ratio between (i) the ethylene vinyl alcohol copolymer and said high humidity side and (ii) the ethylene vinyl alcohol copolymer and the low humidity side is not more than 0.25/1. 35. Package according to claim 33 or 34, characterized in that it comprises a third, heat-sealable layer (e.g. 818) which is placed on the inner surface of the wrapping sheet material (810), the third, heat-sealable layer being selected from polypropylene , low density polyethylene, medium density polyethylene, ethylene vinyl acetate copolymer and ionomers. 36. Package according to any one of claims 33 to 35, characterized in that the wrapping sheet material (810) comprises coextruded material of the first and second layers (812, 814). 37. Gasket according to claim 36, characterized in that it comprises adhesives (e.g. 116, 816) which bind the first and second layers to each other with a peel strength of at least approx. 39.4 g/cm width. 38. A gasket according to any one of claims 33-37, characterized in that the increasing oxygen transfer rate of the first layer (e.g. 112, 812) of ethylene vinyl alcohol copolymer at 50% relative humidity is less than the increasing oxygen transfer rate of the second layer (eg, 114, 814) of vinylidene chloride copolymer at 50% relative humidity. 39. Wrapping system, characterized in that it comprises a multi-layer wrapping material (812) and a product in the wrapping system, the wrapping material comprising a first layer (812) comprising ethylene vinyl alcohol copolymer, a second layer (814) comprising vinylidene chloride copolymer placed between the first layer (812) and the product, and an environment on the outside of the wrapping material with a lower humidity than the humidity on the inside of the package, the ratio of the increasing water vapor transfer rate between the first layer (812) of ethylene vinyl alcohol copolymer and the outer surface of the film through the vinylidene chloride copolymer layer (814) and the water vapor transfer rate between the first 46. Wrapping paper according to any one of claims 39-45, characterized in that the vinylidene chloride copolymer comprises vinylidene chloride vinyl chloride copolymer or vinylidene chloride methyl acrylate copolymer. layer and the second surface of the film is not more than 0.25/1. 40. Wrapping system according to claim 339, characterized in that there is a third binding layer (816) between the first and second layers. 41. Packaging system according to claim 40, kara k-.' characterized in that it comprises a fourth heat-r sealable layer (818) between the product and the second? layer (814) and a fifth layer (820), comprising a second bonding layer, between the second layer (14) and the fourth heat-sealable layer (818). 42. Wrapping system according to claim 40 or 41, characterized in that the fourth layer (818) comprises linear low-density polyethylene and the fifth layer (820) comprises ethylene vinyl acetate copolymer. 43. Wrapping system according to claim 40 or 41, characterized in that the fourth layer (818) comprises a propylene-based polymer mixture and said fifth layer comprises an anhydride-modified propylene-based polymer mixture. 44. Wrapping system according to any one of claims 39 to 42, characterized in that the third and fifth binding layers (816, 820) comprise anhydride-modified ethylene vinyl acetate and the fourth heat-sealable layer (818) comprises linear low-density polyethylene. 45. Wrapping system according to any one of claims 39 to 44, characterized in that the film is a coextruded, thermoplastic multilayer film (810). 1