Field of the Invention

This invention relates to a process for producing plastic containers or containers being partly composed of plastics as well as other materials, e.g. cardboard having a scratch and moisture resistant barrier coating against oxygen or carbon dioxide as well as improved tamper resistance. Background of the Invention

Plastic containers for food and beverages from polyethylene terephthalate (PET), polypropylene (PP) or polyethylene (PE) as well as combinations of aforementioned plastics with e.g. cardboard are long known. Whereas single plastic containers are mostly produced in stretch blow molding processes plastic / cardboard combination containers are assembled employing prefabricated parts. The term combination-container is subsequently used in this document referring to such containers consisting of plastic as well as other materials, e.g. cardboard, or multilayer cardboard/aluminium/cardboard or other suitable combinations.

It is also known to apply a barrier coating on such containers in order to reduce the permeation of gases, especially oxygen or carbon dioxide into or out of the container, thereby improving the shelf life of the packed goods. In case of the combination containers, the plastic parts may either be pre- coated offline prior to assembly or be coated as a final step after assembly of the container and its filling. For example, EP 2431409, EP 2532600, WO 03/037969 Al , GB 879595, GB 2337470, WO 2004/089624, DE 10153210 and DE 10207592 Al describe the use of polyvinyl alcohol as gas barrier on PET bottles with an additional top coat comprising polyvinyl butyral to improve the water resistance of the barrier coating. Such multilayer coatings show a good barrier performance against oxygen and carbon dioxide, scratch resistance and are recyclable after mechanically destroying the top layer due the to the water solubility of the barrier coating.

The gas barrier disclosed in the prior art consists of or comprises polyvinyl alcohol (PVA) . PVA is a polymer obtained by hydrolysis of polyvinyl acetate and contains vinyl alcohol and vinyl acetate subunits. Depending on the amount of vinyl acetate subunits, PVA is more or less soluble in water. Therefore, coatings comprising PVA have certain moisture sensitivities and can deteriorate under humid conditions, which has a negative impact on the overall gas barrier properties of the coating.

In this respect, JP 11349713 proposes a polyvinyl alcohol/polyvinyl acetal/ethylene terpolymer as gas barrier coating of PET substrates. The gas barrier coating according to JP 11349713 is applied directly on the PET surface, which makes the coating vulnerable to mechanical and moisture impact and does not provide sufficient adhesion on the substrate.

Object of the invention was to improve the gas barrier coating of the containers known from the prior art.

The known barrier coating for plastic containers / combination containers suffers from the drawback that either the outer thread is coated, which is then impaired by opening and closing the combination container / container with a cap or that the coating is placed on the inside of the combination container / container, with the danger of food contact.

Object of the invention The present invention relates to a process for producing a plastic container or a preform thereof or a combination container with a barrier coating comprising the steps a) applying at least one coating layer of a first polyvinyl acetal on at least a part of the plastic container or the plastic part in the combination container, respectively; b) applying at least one coating layer of a polymer comprising vinyl alcohol repeating units (PVX) on the first polyvinyl acetal layer; c) applying at least one top coating layer of a second polyvinyl acetal on the PVX layer, characterized in that the plastic container or the preform thereof or the plastic part in the combination container, respectively, comprises an inside thread for a cap having an outside thread and that the barrier coating is provided on the complete outside surface of the container or the preform or the plastic part in the combination container, respectively.

Applying the screw thread to the inside enables the container or the plastic part in the combination container, respectively, to be coated without affecting the performance of the thread . The barrier is applied on a flat surface resulting in perfect barrier performance. The thread remains as produced, including being gas and liquid tight. A coated thread could perform negatively as abrasion of the coating material due to mechanical force while screwing and unscrewing the container generating rubbed-off parts could occur. This rupped-off material may either contaminate the goods or may be accidentally consumed. In addition it may hinder the re-use of the thread while being entrapped in it.

Fig 1 shows a preform coated according to the prior art. The coating does not fully encapsulate the contents with barrier, and is likely to crack when the bottle cap is secured or opened. Fig.2 shows the coating process of the invention. The coating covers the whole surface of the container and there is no risk of damaging the coating when the bottle bottle cap is secured or opened.

The coating acting at the same time acts as a seal to avoid tampering. Once the container was opened it would be identified as being pre-opened as the coating breaks.

The first layer of polyvinyl acetal provided in step a) serves as base coating for the subsequent added barrier coating of PVX. The first base coating of polyvinyl acetal has strong adherence to the plastic material of the container and provides support for the PVX layer provided in step b) and the top coating layer of polyvinyl acetal provided in step c) .

The polymer comprising vinylalcohol repeating units (PVX) can be polyvinyl alcohol i.e. a vinylalcohol/vinylacetate copolymer comprising vinyl alcohol and vinyl actetate repeating units and/or a vinylalcohol/vinylacetate/ethylene terpolymer.

Since PVX adheres very well on polyvinyl acetal and vice versa, the subsequent added layers are likewise mechanical stable and result in a mechanically stable overall coating after the final shaping process of the container. PVX reduces the gas permeability (especially O ₂ and CO ₂ ) of the substrate significantly, thereby improving the shelf-life of packed foods, soft drinks or beer.

The barrier coating comprising the layers manufactured in steps a, b and c) is applied on the complete outside surface of the containers or the plastic part in the combination container, respectively. In another embodiment of the invention, the barrier coating may be applied to the outside and at least a part of the inside of the plastic container or a preform thereof or the plastic part in the combination container, respectively.

The term "at least a part of the inside of the container" refers to any part of the container where the gas barrier of the plastic material shall be improved by the method of the invention. In one variant of the invention, the entire outer or inner surface of the container is coated. In another variant, only the parts of the container are coated which have a lower gas barrier as other parts, e.g. the plastic part in the combination container where the other component may already provide sufficient barrier performance.

It is within the invention to coat additional the cap of a container. To improve the overall gas barrier and the shelf life of the packed good, it is sufficient to provide the lid with a barrier coating of the present invention.

In the process according to the invention, the plastic container or the plastic part in the combination container, respectively, is optionally prior to step a) pre-treated by chemical roughening, oxyfluorination, corona, electron beam or flame treatment.

The plastic material is optionally pre-treated or activated on the inside and/or outside, for example with corona, electronic beam or plasma.

Mechanical roughening can be achieved by a sandblast process, wherein the inside and/or outside surface of the container is provided with a roughness Rz of at least 100 um, preferably 200 μπι.

Preferably the pre-treatment or activation of at least a part of the surface of the plastic material results in an increase of the surface energy of the treated part of the plastic material of at least 25%, more preferably of at least 50%, based on the surface energy prior to treatment.

Untreated PET shows a surface energy of 30-45 mJ/m ² . Accordingly, if the plastic material consists of PET, surface energy after pre-treatment should be at least 50 mJ/m ² , preferable at least 55 mJ/m ² and especially at least 60 mJ/m ² , the upper range being 150 mJ/m ² .

Untreated PP has a surface energy of 25-35 mJ/m ² . Accordingly, if the plastic material consists of PP, surface energy after pre-treatment should be at least 45 mJ/m ² , preferable at least 50 mJ/m ² and especially at least 55 mJ/m ² , the upper range being 150 mJ/m ² . The surface energy is measured according the manual of Accu Dyne Test™ Marker Pens.

Oxyfluorination is described in detail for example in WO2004/089624 or US 5,900,321. The pre-treatment by oxyfluorination according to this invention may be conducted by exposing at least a part of the surface of the plastic material to a fluorine-containing gas mixture containing 0.01% to 5 % by volume fluorine and optionally inert gases like nitrogen or air, or an additional reactive species such as chlorine or oxygen. Oxyfluorination for this invention may take place at a pressure of 10 - 10000 kPa, preferably 100 - 5000 kPa at a temperature of 10 — 90°C with a time of exposure of 1 to 60 minutes . Pre-treatment can enhance the adherence of the layers to the substrate. However, pre-treatment is an additional process step and the method of the invention provides in most cases mechanical stable coating layers which can be stretch-blown without cracks or delamination without pre-treatment. Accordingly, the present process can be performed in that the at least one coating layer of a first polyvinyl acetal is applied on the plastic container or the plastic part in the combination container, respectively without pre-treatment.

Optionally after cleaning and pre-treatment, the first (base) layer of polyvinyl acetal is applied to the container or the plastic part in the combination container, respectively, or the lid.

For the first and second coating, polyvinyl acetal as the reaction product of polyvinyl alcohol with one or more aldehydes like formaldehyde, acetaldehyde, n-Butyraldehyde or iso-Butyraldehyde is used.

Suitable first and second polyvinyl acetal can be selected independently from the group consisting of polyvinyl (n) utyral, polyvinyl ( iso ) butyral , polyvinyl acetyl-co- (n)butyral, crosslinked polyvinyl (n) butyral, crosslinked polyvinyl ( iso ) butyral , Vinylalcohol/vinylacetate/ethylene terpolymer- (n) butyral , Vinylalcohol/vinylacetate/ethylene terpolymer-acetyl-co- (n) butyral .

The acetalisation degree of the first and second polyvinyl acetal can be the same or different, but should be between 70 and 90 mol%, the polyvinyl alcohol content between 8 and 30 mol% . Preferable, the first polyvinyl actetal has a viscosity of 10 to 70 m*Pas and/or second polyvinyl actetal has a viscosity of 50 to 500 m*Pas . Viscosity of polyvinyl actetal is measured in a solution of 10 % by Wght in ethanol containing 5 Wght . % water at 20 °C

The polyvinyl acetal is applied on the surface of the container or the plastic part in the combination container, respectively, and/or the polyvinyl alcohol layer as solution in an organic solvent, for example as solution in methyl ethyl ketone (MEK) , methanol, acetone or ethanol for example by dip-coating, flowing or spraying. The concentration of the coating solution is preferable between 5 and 25% by Weight. The base layer from polyvinyl acetal thus applied may have a thickness of 0,01 to 5 μπι.

Superfluous coating material may be removed by spinning of the plastic material. The coating is dried at room temperature for 4-8 hours (overnight) or at elevated temperature in an oven with temperatures between 30 and 60 °C for 0,5 to 2 hours. With the aid of appropriate machinery like conveyors with heaters, fast drying/curing is obtained in 15-30 sec. After the first polyvinyl acetal layer is applied to at least a part of the container, the plastic material is coated with PVX as barrier coating on the first layer of polyvinyl acetal.

Preferably, the PVX has a degree of saponification/hydrolysation of 80 to 99 Mol%, preferable of 90 to 99 Mol%. The PVX layer does not contain a plasticizer except some traces of moisture originating from the coating process. The PVX used in the present invention has a preferable a content of ethylene groups of 1 to 20 mol%, more preferred between 3 and 10 Mol%. The degree of polymerisation is between 200 and 5000, preferable between 400 and 3000 or 700 and 1000.

Preferable, the PVX has a viscosity of 10 - 100 m*Pas

Viscosity of the PVX is measured in a solution of 10 % by ght in water at 20°C.

The coating layer from PVX may have a thickness of 0.01 to 5 μπι. Preferable, the PVX is applied as aqueous solution, for example by dip-coating, flowing or spraying. The concentration of the coating solution is preferable between 5 and 25% by weight .

Again, superfluous coating material may be removed by spinning of the plastic material. The barrier-coated plastic material is dried to remove essential all water at ambient temperature of 10 to 90°C, preferable 10 - 50 °C optionally at reduced pressure and then subjected to the protective top-coating with the second polyvinyl acetal.

First and second polyvinyl acetals may be different or identical polymers. The process of coating and drying of the first and second layer of polyvinyl acetal may be different or identical. In order to reduce the complexity of the process it is preferred to utilize identical polyvinyl acetals and methods for both steps a) and c) .

The barrier coating of steps a, b) and c) can be applied on at least a part of the outside or the inside of the plastic container or the plastic part in the combination container, respectively. It is furthermore possible to apply the barrier coating of steps a, b) and c) on at least a part of the inside and at least a part of the outside of the plastic container or the plastic part in the combination container, respectively.

It is possible to incorporate dyes or pigments in the barrier coating, the base and/or the protective top coating. Suitable pigments are for example Si0 ₂ , A1 ₂ 0 ₃ , or Ti0 ₂ , as dyes "Rhenol"- type dyes from Clariant can be used. The concentration of dyes or pigments in each layer can range from 0.01 to 5 Wght%, based on the polymer.

Subsequent to coating and drying according to the steps a, b, c, the plastic material may be final shaped into a container by a blow-forming process a blowing process like stretch blowing or injection stretch blow moulding. The optional step d) may be performed prior or after the blowing process.

The plastic material to be coated with the process of the invention may comprise or consist of polymers selected from the group PET, PP, PE (polyethylene) and COC (cyclic olefin copolymer .

The plastic material may have any two or three dimensional shape like film or a container or a part of a container. The coating may also be applied on a first shaped body (preform) which is then formed into the container. "Preform" as used in this application is not limited to any shaped body, especially not to preforms of a bottle and may characterize any first shaped body which is used to produce the final container by another shaping process. Preferable, shaping the preform is performed by a blowing process like stretch blowing or injection stretch blow moulding .

The containers or the plastic part in the combination container, respectively, coated by the process of the invention may be used for food, or beverages, drugs, spices, coffee, tea or chemicals. The container may have a shape selected from the group consisting of capsules, blister packages, sachets, envelopes, jerry cans, bottles, jars and lids thereof.

The advantage of the process according to the invention is that the coating is flexible enough to survive a stretch blow process, yet mechanically and chemically stable enough to protect packed goods. Smooth non-obstracted preform shapes allow good access for surface treatment and uniform coating. Side bottle grooves, curved-in bottom and side panels are difficult to reach areas for plasma surface treatment, easy to melt and result in coating uneven distribution with accumulation in the grooves and panel corners