BACKGROUND OF THE INVENTION Packages for pourable food products need to have oxygen barrier proper- ties in order for the filled and unopened packages to be able to be stored. The required shelf-life and the degree of oxygen barrier needed depends on the type of food product, the type of packaging material, the type of package, the type of opening on the package etc. , and also on aspects such as if the package is aseptic and intended for ambient storage or if is not aseptic and thus intended for chilled storage, e. g. In all cases, some degree of oxygen barrier is needed.

Hitherto, it has been common to provide the packaging material, having a <BR> <BR> polymeric or fibre based core material e. g. , with a barrier layer, already before the package is formed from the packaging material. For example, a packaging material having a fibre based core layer and intended for juice packages, has been laminated with an oxygen barrier layer consisting of aluminium foil. Other packaging laminates, intended for pourable food products less sensitive to oxygen than juice, have been suggested to be provided with an oxygen barrier layer by e. g. extrusion or dispersion coating with a polymer that has oxygen barrier properties, such as e. g. a polymer having functional hydroxyl groups, like polyvinyl alcohol or ethylene vinyl alcohol, optionally mixed with a polymer having functional carboxyl groups, like ethylene acrylic acid copolymers (EAA) or ethylene methacrylic acid copolymers (EMAA).

In WO 01/17771 and WO 01/17774, showing dispersion coatings coated onto a carrier layer which is subsequently laminated to the core layer of the packaging material, it has also been shown that the oxygen barrier properties of the dispersion coating can be further enhanced by the incorporation of nano- scale clay particles.

In WO 00/40404, there has been described a thermoplastic film, intended for the packaging of food products, such as wrapping the same in a transparent film, but not intended for the production of dimension stable packages for pourable food. The film described in WO 00/40404 has a coating on at least one surface thereof, which coating comprises a polymeric binder and an additive comprising nano-scale particles. It is stated that the nano-scale particles preferably comprise 5 to 20 weight percent of the additive and that the additive comprises 40 to 90 weight percent of the coating.

One problem of providing the packaging material with an oxygen barrier layer before forming the package is that it is hard or even impossible to control the barrier effect on different parts of the package. For example, an increased need for an oxygen barrier at the seals of the package is difficult to achieve without affecting the rest of the package. Also, due to the overlapping nature of conventional seals in a fibre based packaging laminate, a barrier layer in the laminate may not give the desired barrier properties at the overlap of the same.

Moreover, any functional details, such as plastic details or opening devices, pre- applied onto the packaging material or even applied onto the final package, will not exhibit the same oxygen barrier properties as the rest of the material. This is a problem especially in connection with opening devices on aseptic, i. e. sterilised, packages for oxygen sensitive food products such as fruit or vegetable juices e. g.

Some package types may also be built up from different parts of different mate- rials, one example being a package that has side walls and a bottom of a fibre based packaging laminate but a top which is made of plastics (Tetra TopO). In this case, it may be difficult to achieve the same or essentially the same oxygen barrier properties on all parts of the package.

One type of opening device that poses a special problem in connection with oxygen barrier properties is a pre-applied, direct injection moulded, plastic cap, especially on an aseptic package. By"pre-applied"means that it is applied onto the finished packaging laminate before the packaging laminate is formed into a package, filled with the pourable food product and sealed. If the package is aseptic, the packaging laminate including the pre-applied opening device is sterilised before the form-fill-and-seal operation, usually by peroxide. The aim of achieving such oxygen barrier properties is rendered extra difficult by the fact that any barrier layer created on the cap at its moulding or in connection therewith, must be able to withstand the sterilisation treatment.

Though it might be possible to provide a plastic cap with barrier properties by producing it from a polymer blend, this has a severe impact on mechanical and sealing properties. Another option might be to incorporate an oxygen

scavenger in the plastic but this can also influence the mechanical properties and also the oxygen scavenger has to be approved for food packages and it has to be able to function properly under the conditions of the cap. To our knowledge, no known technique exist which is able to give barrier and at the same time acceptable sealing and mechanical properties in the cap.

DESCRIPTION OF THE INVENTION The present invention aims at presenting a method of providing a package for pourable food products with an oxygen barrier, by which method the above problems are overcome or at least decreased. Specifically, the method according to the invention aims at presenting a method by which selected parts of a package can be provided with an oxygen barrier, independent of any oxygen barrier properties on other parts of the package. Moreover, the method according to the invention aims at presenting a method by which details, especially plastic details, such as opening devices, tops etc, on a package can be provided with an oxygen barrier. The invention should be able to provide such barrier properties without influencing the mechanical and sealing properties. According to one aspect of the invention, this is to be achieved also in case the packaging material, including any plastic details, is to be sterilised before forming and filling of the package.

The invention also aims at presenting the package thus obtained.

These and other objectives are achieved by the method according to the invention, as described in the claims.

It has now been found that surprisingly good oxygen barrier properties can be achieved in a package by post-applying a liquid oxygen barrier composition comprising a polymer dispersion or solution, as a coating, onto the entire or a selected part of an outside surface of the package. By"post-applying"is meant that the coating is applied onto the finished package, preferably even after filling and sealing of the same.

According to one aspect of the invention, said oxygen barrier composition is applied by a method in the group that consists of spraying, douching, atomising, brushing and immersion of the selected part of the package. In a commercial application, the coating can be applied by spraying by one, two or <BR> <BR> more spray nozzles e. g. , at rates of thousands of packages per hour, for example 4000-8000 packages per hour.

According to another aspect of the invention, said oxygen barrier composition is applied at a coating thickness of 1-50, um, preferably 1-40, um,

even more preferred 1-30, um, even more preferred 1-20, um, even more preferred 5-20, um and most preferred 10-15, um, measured at dry state.

The package is preferably formed mainly of a fibre based packaging laminate but applications are conceivable also in cases where the package is formed mainly of a polymeric packaging material. Also, combinations are conceivable, such as for example a package that has side walls and a bottom of a fibre based packaging laminate but a top that is polymer based (such as Tetra Top@ e. g.) If only a selected part of the package is coated according to the method according to the invention, this selected part of the package is preferably a part in the group that consists of a seal, an opening device, a plastic detail on the package and a plastic part of the package, such as a plastic top e. g. In an especially preferred embodiment of the invention, the oxygen barrier composition is applied onto the outside of a direct injection moulded opening device (cap), in order to provide the cap with oxygen barrier properties. Here, the outer surface post-applying of the oxygen barrier coating beneficially means that the packaging laminate, including intermittently arranged caps, can be sterilised already before applying the oxygen barrier coating onto the caps, whereby the coating need not be resistant to the sterilising agent. According to this embodiment of the invention, the method includes the steps of: (a) injection moulding plastic opening devices in opening holes on a packaging material web, (b) forming the packaging material web to a tube while sealing its longitudinal edges to each other and filling the tube with a pourable food product, (c) intermittently sealing the tube in transversal seals and cutting the tube in the transversal seals to form cushions, (d) folding the cushions to form dimension stabile packages, each having one plastic opening device, where after said liquid oxygen barrier composition is applied onto the outside of said opening devices in a step (e).

Optionally, the packaging material web including the plastic opening devices is sterilised, preferably by a liquid sterilising agent and even more preferred by peroxide, in a step (f), between steps (a) and (b).

After the application of the coating in step (e) the coating is preferably forcibly dried, preferably by hot air treatment, IR treatment, UV treatment or electron beam treatment of the coating, in a step (g).

According to an alternative embodiment of the invention, the method includes the steps of : (a) forming a blank of the packaging material into a tubular packaging capsule, while sealing its longitudinal edges to each other, (b) moulding a top of plastics, including a device for opening of the filled package, to one end of the tubular capsule, (c) filling the capsule with a pourable food product, (d) folding the other end of the capsule into a bottom fold and sealing the fold, where after said liquid oxygen barrier composition is applied onto the outside of said opening devices in a step (e).

Optionally, the packaging material capsule and the moulded plastic top including the opening device is sterilised in a step (f), between steps (b) and (c), preferably by a gaseous sterilising agent alone or in combination with irradiation sterilisation, more preferably by gaseous hydrogen peroxide in combination with UV irradiation.

According to one aspect of the invention, said polymer dispersion or solution is based on a polymer that has functional hydroxyl groups or functional carboxylic groups. Preferably, said polymer dispersion or solution is based on a polymer in the group that consists of ethylene acrylic acid copolymer, ethylene methacrylic acid copolymer, ethylene vinyl acetate copolymer, ethylene vinyl alcohol copolymer, modified ethylene copolymer, styrene copolymers and combinations thereof.

Moreover, it is preferred that said oxygen barrier composition also comprises nano-scale particles, preferably particles in the group that consists of clay particles and silica particles, and combinations thereof.

It is also conceivable to use a UV-EB (electron beam) curable resin.

Surprisingly, it has been found that polymers conventionally used only as adhesives or used in combination with other polymers having barrier properties per se, can provide a coating with surprisingly good barrier properties on their own, when combined with nano-scale particles, i. e. in a solution or dispersion which is essentially without any polymer having oxygen barrier properties per se.

Preferred examples of such polymers are polymers having functional carboxylic groups, such as ethylene acrylic acid copolymer and ethylene methacrylic acid copolymer.

Nano-scale particles may be present in the oxygen barrier composition at contents of at least 20 weight %, preferably at least 30 weight % and even more

preferred at least 40 weight %, but 60 weight %, more preferred 55 weight % and even more preferred 50 weight % at the most, as calculated on dry matter and the remainder essentially being said polymer.

According to one aspect of the invention, said nano-scale particles are clay particles, in which case said liquid barrier composition exhibits a dry content of 2- 20 weight %, preferably 3-16 weight % and even more preferred 5-12 weight % of nano-scale clay particles and polymer. The nano-scale clay particles can include minerals in the group that consists of kaolinite, antigorite, smectite, vermiculite or mica. Specifically, laponite, kaolinite, dickite, nacrite, halloysite, antigorite, chryso- lite, pyrophyllite, montmorillonite, hectorite, sodium tetrasilicic mica, sodium taeniolite, commonmica, margarite, vermiculite, phlogophite, xanthophyllite and the like may be mentioned as suitable clay minerals.

The nano-scale clay particles should have an average widest dimension of at least 0. 2, um, even more preferred 0. 4, um and most preferred 0. 6, um but 9, um, preferably 8, um and even more preferred 7, um at the most, and a smallest dimension in the nano-scale range, i. e. 100 nm at the most and preferably 10 nm at the most, usually about 1 nm. The size ranges refer to single clay platelets, i. e. not taking into account that the platelets may form stacks.

It has been found in connection with the development of the invention, that surprisingly good oxygen barrier properties are achieved when there is made use of aluminium magnesium silicate hydrate particles, preferably having an average widest dimension of at least 0. 2, um, even more preferred 0. 4, um and most preferred 0. 6, um, but 5, um, preferably 4, um and even more preferred 3, um at the most and a smallest dimension in the nano-scale range, or synthetic tetrasilisic fluoromica particles, preferably having an average widest dimension of at least 4 , um, even more preferred 5, um and most preferred 6, um, but 9, um, preferably 8 , um and even more preferred 7, um at the most, and a smallest dimension in the nano-scale range.

It has also been found in connection with the development of the invention, that surprisingly good oxygen barrier properties are achieved when there is made use of colloidal silica particles, exhibiting a particle size of 3-150 nm, preferably 4- 100 nm and even more preferred 5-70 nm, which particles are preferably amor- phous and/or spherical. The use of colloidal silica particles moreover has the advantage that the liquid barrier composition may be applied at a dry content of 15-40 weight %, preferably 20-35 weight % and even more preferred 24-31 weight %, whereby the demand on forcible drying is decreased.

Optionally, the composition may also comprise an additive for increasing the resistance to scratching of the coating. Alternatively, or in combination, the coating may be treated to exhibit increased resistance to scratching.

According to a preferred embodiment of the invention, the post-applied oxygen barrier coating according to the invention is applied in two or more steps, preferably three or more steps, to form a coating that comprises two or more, preferably three or more part layers. Between each coating step, the resulting coating is dried or cured, preferably by a treatment in the group that consists of hot air treatment, IR treatment, UV treatment or electron beam treatment of the coating or any combination of such treatments. Treatments such as UV or electron beam treatments will also result in a sterilisation taking place.

It has been found that the stepwise coating allows for a relatively thick, but still uniform coating, that is uniformly dried/cured throughout its thickness.

According to another preferred embodiment of the invention, it has been found that the wetting and adhesion is surprisingly improved if a first part coating, in direct contact with the object to be provided with an oxygen barrier, is com- posed of a coating polymer dispersion or solution, that is essentially free from any nano-scale particles. The second part coating should then preferably be com- posed of a coating polymer dispersion or solution, but including nano-scale particles, to provide for the oxygen barrier effect. Finally, a third part coating is applied, that again is preferably composed of a coating polymer dispersion or solution, that is essentially free from any nano-scale particles. This final and outermost part coating layer serves as a protection against moist and scratching etc. The first, second and third part coatings are preferably based on the same type of polymer dispersion or solution, of the same or different qualities. Between each coating step, the resulting coating is dried or cured, preferably by a treatment in the group that consists of hot air treatment, IR treatment, UV treatment or electron beam treatment of the coating or any combination of such treatments. Optionally, the coating is forcibly dried between the different coating steps and cured at the end, when all part coatings have been applied. It is also conceivable that the first, second and/or third part coatings, preferably the second part coating comprising nano-scale particles, are applied in two or more steps, with intermediate drying or curing.

The coating may have a total coating thickness of 1-50, um, preferably 1-40 , um, even more preferred 1-30, um, even more preferred 1-20/im, even more preferred 5-20, um and most preferred 10-15, um, measured at dry state. Part coatings, if several coating steps are used, suitably have a thickness of 1-20, um,

even more preferred 1-10, um, even more preferred 1-5, um and most preferred 1- 3, um, measured at dry state.

DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in detail with reference to a preferred embodiment and to the drawings, of which: Fig. 1 is showing a flow chart of a production line according to a preferred embodiment of the invention, Fig. 2 is showing a first package including an opening device, as produced in the process line of Fig. 1, Fig. 3 is showing a second fibre based package including a polymeric top.

In the flow chart of Fig. 1, the box 1 symbolises apparatus for intermittently pre-applying opening devices onto a packaging laminate web, at pre-made opening holes in the web, in a step (a). Known apparatuses 1 of this kind com- prise apparatuses for direct injection moulding of a polymeric cap including a pouring rim and an optionally hinged lid for opening and closing the opening device e. g. If the package including the opening device is aseptic, the sterility is broken at the first opening of the opening device, as the lid is severed from the rim.

In step (f), the packaging laminate web, including the opening devices, is passed through sterilising equipment 2, where it is sterilised by liquid or vaporised peroxide e. g.

In steps (b), (c), (d) the packaging laminate web is formed, filled and sealed in form-fill-seal equipment 3 of conventional type, to produce brick or tetrahedron shaped packages 20, each having one opening device 30 and longitudinal and transversal seals 40a and 40b, respectively, as shown in detail in Fig. 2.

In step (e), the packages are passed through an apparatus 4 for post- application of a liquid oxygen barrier composition comprising a polymer dis- persion or solution, at least onto the outside of the opening device 30 and/or the seals 40a, 40b of the package, or onto the entire outside of the package. The apparatus 4 could comprise any suitable means for applying the dispersion or solution, such as one or more spray guns, atomising means, a bath for immersion of the package or part of the package, douching means, brushing means etc.

After step (e), the post-applied coating is dried or cured in a step (g) in a drying or curing apparatus 5, which for example may comprise means for hot air treatment, IR treatment, UV treatment or electron beam treatment of the coating.

Fig. 3 is showing one example of a package 50 of the Tetra Top@ type, having a bottom and side walls 54 of a fibre based packaging laminate with a longitudinal seal 53 and a bottom seal (not shown). The top is a polymeric top 51 including an opening device 52. A post-applied oxygen barrier coating according to the invention coats the top 51 including the opening device 52. Many other types of opening devices can be contemplated, e. g. a screw cap.

EXAMPLES In the experimental series, the following polymers and nano-scale particles were tested: Nanoclay (Montmorillonite) Reference : Cloisite-Na (Southern Clay Products, Inc., Texas, USA), 3 % dispersion in water, size 200-1000 nm, CEC: 92 meq/100g.

KunipiaF (Aluminium Magnesium Silicate Hydrate; Kunimine Industries Co. , Ltd., Tokyo, Japan), 3 % dispersion in water, size 0.6-3 Rm, CEC 119 meq/100g.

Nanoclay (Synthetic) Somasif ME-100 (Synthetic Swellable Tetrasilisic Fluoromica ; CO-OP Chemical <BR> <BR> Co. , Ltd. , Tokyo, Japan), 8 % dispersion in water, size 6-7, um, CEC 120<BR> meq/1 OOg.<BR> <P>Colloidal Silica (SiO) : Bindzil 40/170 (Eka Chemicals, Bohus, Sweden), 40 % dispersion in water, size 20 nm.

Bindzil 30/220 NH3 (Eka Chemicals, Bohus, Sweden), 30 % dispersion in water, size 15 nm.

Polymeric binders : Epotal 2343, (Ethylene Acrylic Acid copolymer, BASF, Germany)

Barritech YP2, (Ethylene Acrylic Acid copolymer, BimKemi, Sweden) Example 1 Dispersions of EAA copolymer and nano-scale particles were mixed together. The resulting dispersions were applied on OPET film (Melinex 800, DuPont, 36, um) in a Hirano lab coater (1 m/min) and dried at 150 °C. Coating thickness was 5, um dry. Table 1 is showing the resulting oxygen barriers of the coating (barrier effect of the OPET film taken out of account).

Table 1 Sample Filler/Binder, % RH Coat oxygen % transmission, cc/m2/24h/5Zm P=1 atm CloisiteNa/epotal 40/60 50 No barrier reference KunipiaF/epotal 40/60 0 99 KunipiaF/epotal 40/60 50 159 KunipiaF/epotal 40/60 100 420 KunipiaF/YP2 40/60 50 111 Somasif/epotal 40/60 0 62 Somasif/epotal 40/60 50 62 Somasif/epotal 40/60 100 120 Bindzil/epotal 40/60 50 419 (40/170) Bindzil/epotal 50/50 50 648 (40/170) Bindzil/epotal 60/40 50 No barrier (40/170) Bindzil/epotal 40/60 50 No barrier (30/220) Bindzil/epotal 50/50 50 648 (30/220) Bindzil/epotal 60/40 50 1332 (30/220)

For a comparison, the barriers shown in Table 2 of WO 00/40404 have been calculated in the same unit as used in Table 1 above: Table 2 Film Coat oxygen Coat oxygen transmission in transmission in cc/645, 2cm2/24h/cc/m2/24h/5, um 0.00254cm SC96-034 95 31166 SC96-035 78 16333 SC96-036 46 5731 SC96-037 28 2841 SC96-038 9 764 It can be concluded that the results according to the present invention are surprisingly much better than the results achieved in WO 00/40404 for similar dispersions when using the preferred nano-scale particles according to the present invention.

Moreover, it can be concluded that the oxygen barrier of a dispersion including Somasif ME-100 particles seems to be less affected by increased humidity, at least up to 50 % RH, which is a major advantage in the present application of the barrier.

Example 2 Oxygen transmission was measured per package, for six 1000 ml, aseptic, brick shaped packages (Tetra Brio) formed from a packaging laminate including aluminium foil as oxygen barrier and provided with one direct injection moulded opening device (cap) per package. Thereafter, the caps were coated with oxygen barrier by airbrush and dried in a heating cabinet at 90°C for approximately 1-5 minutes. The coating had a thickness of 5-10 um. After testing the oxygen transmission of the packages having coated caps, the caps were subjected to tap water washing for 4 hours, where after the remaining oxygen barrier was tested again. Table 3 shows the results after coating and after washing of the coated caps as per cent improvement. Oxygen transmission was measured as

cc/package/24h, 50% RH, p=0.21 atm, average for seven packages. The improvement was calculated as Improvement = 100-100 x (OTRcc-OTRref)/ (OTRc-OTRref), where OTRref = Oxygen Transmission for the package without cap OTRc = Oxygen Transmission for the package having an uncoated cap OTRcc= Oxygen Transmission for the package having a coated cap (and washed if so) Table 3 Coat Filler/Binder, Improvement improvement % OTR, coat, % OTR, coat + wash, % KunipiaF/epotal 40/60 46. 3 44. 3 Example 3 Oxygen transmission was measured per package, for Tetra Tope packages construed in essence according to Fig. 3. The polymeric (LDPE) top was coated with three part coatings, with intermediate drying in between: 1. Pure ethylene acrylic acid copolymer, 2. Ethylene acrylic acid copolymer comprising nano-scale clay particles, 3. Pure ethylene acrylic acid copolymer.

It was found that the first part coating layer provided for a good wetting and a good adhesion on the polymeric top that was coated. The second part coating provided for improved oxygen barrier properties, but the coating had a milky look even after drying and did not withstand water and scratching. However, when the third part layer was applied and dried, it was surprisingly found that the entire coating became clear and that it was able to withstand moist and scratching.

The oxygen barrier transmission was reduced from 0.30 cm3/m2 and 24 h (uncoated reference) to 0.12-0. 15 cm3/m2 and 24 h, thanks to the three part coating, at the conditions 0.21 atm, 23 °C and 50 % RH.