Patent Application
20230405978
The present invention relates to barrier-coated paper or cellulose-based substrates and to a method of manufacturing thereof, by dispersion coating of a barrier pre-coating and subsequent vapour deposition coating of a barrier deposition coating. The invention further relates to laminated packaging materials comprising such barrier-coated paper or cellulose-based substrates, in particular intended for liquid carton food packaging, and to such liquid carton packaging containers comprising the laminated packaging material.
Packaging containers of the single use disposable type for liquid foods are often produced from a packaging laminate based on paperboard or carton. One such commonly occurring packaging container is marketed under the trademark Tetra Brik Aseptic® and is principally employed for aseptic packaging of liquid foods such as milk, fruit juices etc, sold for long term ambient storage. The packaging material in this known packaging container is typically a laminate comprising a bulk or core layer, of paper, paperboard or other cellulose-based material, and outer, liquid-tight layers of thermoplastics. In order to render the packaging container gas-tight, in particular oxygen gas-tight, for example for the purpose of aseptic packaging and packaging of milk or fruit juice, the laminate in these packaging containers normally comprises at least one additional layer, most commonly an aluminium foil.
On the inside of the laminate, i.e. the side intended to face the filled food contents of a container produced from the laminate, there is an innermost layer, applied onto the aluminium foil, which innermost, inside layer may be composed of one or several part layers, comprising heat sealable thermoplastic polymers, such as adhesive polymers and/or polyolefins. Also on the outside of the bulk layer, there is an outermost heat sealable polymer layer.
The packaging containers are generally produced by means of modern, high-speed packaging machines of the type that form, fill and seal packages from a web or from prefabricated blanks of packaging material. Packaging containers may thus be produced by reforming a web of the laminated packaging material into a tube by both of the longitudinal edges of the web being united to each other in an overlap joint by welding together the inner- and outermost heat sealable thermoplastic polymer layers. The tube is filled with the intended liquid food product and is thereafter divided into individual packages by repeated transversal seals of the tube at a predetermined distance from each other below the level of the contents in the tube. The packages are separated from the tube by incisions along the transversal seals and are given the desired geometric configuration, normally parallelepipedic, by fold formation along prepared crease lines in the packaging material.
The main advantage of this continuous tube-forming, filling and sealing packaging method concept is that the web may be sterilised continuously just before tube-forming, thus providing for the possibility of an aseptic packaging method, i.e. a method wherein the liquid content to be filled as well as the packaging material itself are reduced from bacteria and the filled packaging container is produced under clean conditions such that the filled package may be stored for a long time even at ambient temperature, without the risk of growth of micro-organisms in the filled product. Another important advantage of the Tetra Brik®-type packaging method is, as stated above, the possibility of continuous high-speed packaging, which has considerable impact on cost efficiency.
Packaging containers for sensitive liquid food, for example milk or juice, can also be produced from sheet-like blanks or prefabricated blanks of the laminated packaging material of the invention. From a tubular blank of the packaging laminate that is folded flat, packages are produced by first of all building the blank up to form an open tubular container capsule, of which one open end is closed off by means of folding and heat-sealing of integral end panels. The thus closed container capsule is filled with the food product in question, e.g. juice, through its open end, which is thereafter closed off by means of further folding and heat-sealing of corresponding integral end panels. An example of a packaging container produced from sheet-like and tubular blanks is the conventional so-called gable-top package. There are also packages of this type which have a moulded top and/or screw cap made of plastic.
A layer of an aluminium foil in the packaging laminate provides gas barrier properties quite superior to most other gas barrier materials. The conventional aluminium-foil based packaging laminate for liquid food aseptic packaging is still the most cost-efficient packaging material, at its level of performance, available on the market today.
Any other material to compete with the foil-based materials must be cost-efficient regarding raw materials, have comparable food preserving properties and have a comparably low complexity in the converting of materials into a finished packaging laminate.
Among the efforts of developing non-aluminium-foil materials for liquid food carton packaging, there is also a general incentive towards developing pre-manufactured films or sheets having high and multiple barrier functionalities, which may replace the aluminium-foil barrier material in the conventional laminated packaging material, or combine several separate barrier layers in the laminated material, and adapt it to conventional processes for lamination and manufacturing.
Preferred types of such alternative, more environmentally sustainable barrier material are barrier-coated paper substrates made by aqueous dispersion coating or vapour deposition coating onto thin paper carrier substrates. There are various aqueous dispersion coating processes and vapour deposition coating processes and material recipes for such coatings, and there is a need for cost-efficient barrier materials of this “non-foil” type, i.e. non-aluminium-foil, having improved properties for use in packaging laminates for liquid food packaging, regarding barrier properties, in particular towards gases, such as oxygen gas.
An earlier patent publication WO2011/003565A1 discloses a non-aluminium-foil packaging material comprising a pre-coated and metallised Kraft paper substrate for the purpose of induction heat sealing. It recommends rather thick coating layers and to include additional nanoclay particles in the pre-coating, and for good gas barrier properties there should also be applied further barrier coating layers in the packaging laminate, such as onto the back side of the paper substrate or onto the bulk paperboard layer. Such further barrier coatings would in this disclosure be needed to complement the rather low barrier properties provided by the metallised Kraft paper.
The earlier patent publication WO2017/089508A1 discloses how further improved barrier properties may be obtained from a metallised paper in a similar packaging laminate, by selecting a paper substrate providing optimal properties. Such a metallised paper substrate provided not only improved barrier properties, but also indicated better stability of the metallised layer for induction heat sealability purposes.
There remains, however, a need for further improved oxygen gas barrier properties from similar barrier-coated paper and other cellulose-based substrates. There remains also a need for improved properties regarding recyclability and sustainability of the materials used.
It is, accordingly, an object of the present invention to provide improved barrier-coated paper or cellulose-based substrates for laminating into packaging materials.
It is also a general object of the invention to provide barrier-coated paper or cellulose-based substrates having good barrier properties as well as improved recyclability and sustainability that fulfil the needs of future sustainable liquid carton laminated packaging materials.
It is a further general object of the invention to provide packaging materials for oxygen-sensitive products, such as non-foil laminated packaging materials for liquid, semi-solid or wet food products, which do not contain aluminium foil but still have good gas and other barrier properties suitable for long-term, aseptic packaging at reasonable cost.
A particular object, is to provide a, relative to aluminium foil barrier materials, cost-efficient, non-foil, paper- or paperboard-based, laminated packaging material, having good gas and water vapour barrier properties, as well as recyclability and a sustainable environmental profile for the purpose of manufacturing packages for long-term, aseptic food storage.
Yet a further object of the invention is to provide a cost-efficient, non-foil, paper- or paperboard-based, mechanically robust and heat-sealable packaging laminate having good gas and water vapour barrier properties and good internal adhesion between its layers, for the purpose of manufacturing aseptic packaging containers for long-term storage of liquid foods at maintained nutritional quality under ambient conditions.
These objects are thus attainable according to the present invention by the barrier-coated paper or cellulose-based substrate, the laminated packaging material, the packaging container and the method of manufacturing the packaging material, as defined in the appended claims.
According to a first aspect of the invention, a barrier-coated cellulose-based substrate, for use as a barrier sheet in a laminated packaging material for liquid food products, comprising a cellulose-based substrate and applied on a first, top side of the cellulose-based substrate a barrier pre-coating, applied by means of dispersion or solution coating, and further onto the barrier pre-coating a barrier deposition coating, the barrier deposition coating being applied by means of a vapour deposition method, wherein the barrier-coated cellulose-based substrate further comprises a base layer pre-coating, which is different from the barrier pre-coating and applied by means of dispersion or solution coating, onto the cellulose-based substrate and positioned directly adjacent and contacting the first, top side of the cellulose-based substrate layer, and positioned beneath the barrier pre-coating, the barrier-coated cellulose-based substrate thus being suitable for providing gas and water vapour barrier properties in such a laminated packaging material and packages made thereof.
In an embodiment, the barrier pre-coating comprises a polymer selected from the group consisting of vinyl alcohol polymers and copolymers, such as from the group consisting of polyvinyl alcohol, PVOH, and ethylene vinyl alcohol, EVOH, and the barrier deposition coating is a vapour deposition coating, such as of a material selected from metals, metal oxides, inorganic oxides and carbon coatings.
In a further embodiment, the barrier deposition coating is a vapour deposition coating selected from the group consisting of an aluminium metallisation coating and aluminium oxide, AlOx, and preferably it is an aluminium metallisation coating.
According to a second aspect of the invention, a laminated packaging material comprising the barrier-coated cellulose-based substrate of the invention is provided. The laminated packaging material may further comprise a first outermost liquid tight, heat sealable polyolefin layer and a second innermost liquid tight, heat sealable polyolefin layer.
For the purpose of carton packaging of liquid food products, the laminated packaging material further may comprise a bulk layer of paper or paperboard or other cellulose-based material, a first outermost liquid tight, heat sealable polyolefin layer, a second innermost liquid tight, heat sealable polyolefin layer and, arranged on the inner side of the bulk layer of paper or paperboard, between the bulk layer and the innermost layer, the barrier-coated cellulose-based substrate.
In a third aspect of the invention there is provided a packaging container comprising the laminated packaging material of the invention, intended for packaging of liquid, semi-solid or wet food. According to an embodiment, the packaging container is manufactured at least partly from the laminated packaging material of the invention, and according to a further embodiment it is in its entirety made of the laminated packaging material.
In a fourth aspect of the invention, a method of manufacturing a barrier-coated cellulose-based substrate is provided, which comprises a first step of providing a cellulose-based substrate as a moving web in a roll to roll system, a second step of applying a first dispersion or solution of a base layer pre-coating composition onto the moving cellulose-based substrate, and subsequently drying the applied base layer pre-coating by forced evaporation, a third step of applying a second dispersion or solution of a barrier pre-coating composition, having different ingredients than the base layer pre-coating composition, onto the base-layer coated moving cellulose-based substrate, and subsequently drying the applied barrier pre-coating by forced evaporation, and a fourth step of further depositing, onto the barrier pre-coating on the moving barrier pre-coated cellulose-based substrate, a barrier deposition coating by a vapour deposition coating operation.
While it has hitherto been assumed that improved gas barrier properties from such barrier-coated papers should be done by sourcing better cellulose-based substrates, inherently by themselves providing gas barrier properties when further laminated to polymer layers, or by coating more polymer having inherent gas barrier properties, in thicker layers, it has recently become better understood that the surface portion of the cellulose-based substrate plays a key role for the optimal performance of subsequently applied coatings that bring the gas barrier properties, such that it may be achieved by adding a further base layer pre-coating onto the surface cellulose-based substrate and subsequently the barrier coatings. What has been seen is that the barrier qualities of the cellulose-based substrate itself do not need to be so high, and the amount of coated gas barrier polymer as a barrier pre-coating may even be reduced. The resulting barrier in a packaging laminate will still be very high, if such a base layer pre-coating is used, although it does not contribute with significant barrier properties itself, i.e. inherent to the base layer material. The base layer pre-coating composition should be selected to provide a homogeneous, even, dense and compatible surface to receive the further dispersion-coated gas barrier pre-coating, which in the next step is to receive a further vapour deposition barrier coating. The material selected for the base layer pre-coating does not need to contribute with inherent gas barrier properties, however.
The base layer pre-coating material advantageously comprises a polymer selected from the group consisting of starch, modified starch and cellulose ethers.
Thus, the barrier-coated cellulose-based substrate obtained by the above method and coating layer configuration, provides improved barrier properties to a laminated packaging material comprising it, and may also impart to it improved recyclability and sustainability profile.
With the term “long-term storage”, used in connection with the present invention, is meant that the packaging container should be able to preserve the qualities of the packed food product, i.e. nutritional value, hygienic safety and taste, at ambient conditions for at least 1 or 2 months, such as at least 3 months, preferably longer, such as 6 months, such as 12 months, or more.
With the term “package integrity”, is generally meant the package tightness, i.e. the resistance to leakage or breakage of a packaging container. The term encompasses the resistance of the package to intrusion of microbes, such as bacteria, dirt, and other substances, that may deteriorate the filled food product and shorten the expected shelf-life of the package.
One main contribution to the integrity of a package from a laminated packaging material is provided by good internal adhesion between adjacent layers of the laminated material. Another contribution comes from the material resistance to defects, such as pinholes, ruptures and the like within each material layer itself, and yet another contribution comes from the strength of the sealing joints, by which the material is sealed together at the formation of a packaging container. Regarding the laminated packaging material itself, the integrity property is thus mainly focused on the adhesion of the respective laminate layers to its adjacent layers, as well as the quality of the individual material layers. Regarding the sealing of the packages, the integrity is mainly focussed on the quality of the sealing joints, which is ensured by well-functioning and robust sealing operations in the filling machines, which in turn is ensured by adequately adapted heat-sealing properties of the laminated packaging material.
The term “liquid or semi-liquid food” generally refers to food products having a flowing content that optionally may contain pieces of food. Dairy and milk, soy, rice, grains and seed drinks, juice, nectar, still drinks, energy drinks, sport drinks, coffee or tea drinks, coconut water, wine, soups, jalapenos, tomatoes, sauce (such as pasta sauce), beans and olive oil are some non-limiting example of food products contemplated.
The term “aseptic” in connection with a packaging material and packaging container refers to conditions where microorganisms are eliminated, in-activated or killed. Examples of microorganisms are bacteria and spores. Generally an aseptic process is used when a product is aseptically packed in a packaging container. For the continued asepticity during the shelf-life of the package, the package integrity properties are of course very important. For long-term shelf-life of a filled food product, it may furthermore be important that he package has barrier properties towards gases and vapours, such as towards oxygen gas, in order to keep its original taste and nutritional value, such as for example its vitamin C content.
With the term “bulk layer” is normally meant the thickest layer or the layer containing the most material in a multilayer laminate, i.e. the layer which is contributing most to the mechanical properties and the dimensional stability of the laminate and of packaging containers folded from the laminate, such as paperboard or carton. It may also mean a layer providing a greater thickness distance in a sandwich structure, which further interacts with stabilising facing layers, which have a higher Young's modulus, on each side of the bulk layer, in order to achieve sufficient such mechanical properties and dimensional stability.
Thickness measurements were performed by Transmission Electronic Microscopy using a Titan 80-300, FEI equipment. Samples may be prepared by ultramicrotomy on an EM UC6 Microtome from Leica.
OTR was measured with Oxtran 2/21 (Mocon) equipment based on coulometric sensors.
The method for determining OTR identified the amount of oxygen per surface and time unit at passing through a material at a defined temperature, a given atmospheric pressure, during a certain time, i.e at an atmosphere of 100% oxygen, during 24 hours.
Water vapour transmission rate (WVTR) measurements were carried out by a Permatran 3/33 (Mocon) instrument (norm: ASTM F1249-13 using a modulated Infrared sensor for relative humidity detection and WVTR measurement) at 38° C. and 90% driving force.
The substrate suitable for barrier-coatings as of the invention is not limited to a certain type of paper, but includes also other cellulose-based substrates, based on any type of native cellulose, fibrous or fibrillar cellulose. The invention is not applicable, however, to substrates from plastics or polymers, such as films made from regenerated cellulose.
It seems so far, that papers or cellulose-based substrates having a surface smoothness of 200 ml/min Bendtsen or below, such as about 150 ml/min or below, on its coating side (“top side” or “print side”), may provide particularly good barrier-coated structures according to the present invention, from an oxygen barrier point of view. It is, however, also perceived that the new combination of pre-coatings and barrier coating of the present invention may improve the barrier properties of more or less any paper substrate beyond what was hitherto believed possible.
To be suitable for the final barrier-coating step by means of a vapour deposition coating process, the substrate needs to be thin, such as 60 g/m2 or below, such as 50 g/m2 or below, preferably 45 g/m2 or below and more preferably 40 g/m2 or below, for reasons of efficiency and production economy and to avoid blistering of the coating, due to air being entrapped in a fibrous, porous cellulose-based substrate. On the other hand, cellulose-based substrates thinner or with a lower grammage than 30 g/m 2 may be mechanically too weak and/or less dimension stable, when they are coated with wet dispersions and subsequently dried, thus exhibiting shrinkage or curling problems. It is thus more preferred to use papers having a grammage of from 30 to 50 g/m2, such as most preferable from 35 to 45 g/m2.
For optimal barrier properties by means of minimal amount of barrier material, it has thus hitherto been seen that a barrier deposition coating, to be coated to nanometer thicknesses only, needs a thin pre-coating from a gas barrier polymer, when to be applied onto a paper or cellulose-based substrate. The best working barrier pre-coating is selected from vinyl alcohol polymers and copolymers, which have inherent gas barrier properties, and which are food safe and environmentally sustainable both regarding recyclability and in industrial coating and lamination processes. Such polymers are water dispersible and/or dissolvable in water and may be applied by means of an aqueous “dispersion coating” process, or a so called “liquid film coating” process. Non-aqueous or only partly aqueous coating compositions, such as those based on alcohols or mixtures of alcohol and water, could also be suitable for achieving the good results from this invention. They would, however, likely be less suitable from environmental sustainability point of view.
Processes suitable for coating of low-dry content polymer dispersion/solution compositions are broadly any suitable wet coating methods, such as gravure roll coating, air spraying, airless spraying, reverse roll coating, wire bar coating, lip coating, air knife coating, curtain flow coating, spray coating, dip coating, and brush coating methods. The experiments for the present invention were performed by means of gravure coating, but it is believed that any of the above liquid film coating methods that would contribute to generate a smooth and even coated surface would be suitable for carrying out the invention.
The preferred barrier pre-coating compositions are thus based on the two most common types of polymers and coplymers suitable for dispersion coating, based on vinyl alcohol monomers, i.e. polyvinyl alcohol (PVOH) and ethylene vinyl alchol (EVOH).
Preferably, the gas barrier polymer is PVOH, because it provides good film formation properties, gas barrier properties, cost efficiency, food compatibility and odour barrier properties.
A PVOH-based gas barrier composition performs best when the PVOH has a degree of saponification of at least 98%, preferably at least 99%, although also PVOH with lower degrees of saponification will provide oxygen barrier properties. On the other hand, EVOH may be advantageous by providing some moisture resistance to the barrier material, since the copolymer comprises ethylene monomer units. The amount is depending on the choice of EVOH grade, but it will be at the expense of some oxygen barrier property inherent from the material, in comparison to PVOH.
Conventional EVOH polymers, are normally intended for extrusion and are not possible to disperse or dissolve in an aqueous medium in order to produce a thin liquid film coated barrier film of 3.5 g/m2 or below. It is believed that EVOH should comprise a rather high amount of vinyl alcohol monomer units to be water-dispersible and that the properties should be as close to those of liquid film coating grades of PVOH as possible. An extruded EVOH layer is thus not an alternative to a liquid film coated EVOH, because it inherently has less similar properties to PVOH than EVOH grades for extrusion coating, and because it cannot be applied at a cost-efficient amount below 4 g/m2 as a single layer by extrusion coating or extrusion lamination.
The barrier pre-coating composition may further comprise from about 1 to about 20 weight %, of an inorganic laminar compound based on dry coating weight, such as exfoliated nanoclay particles, such as bentonite. Thus, the barrier layer may include from about 99 to about 80 weight % of the polymer based on the dry coating weight. An additive, such as a dispersion stabiliser or the like, may also be included in the gas barrier composition, preferably in an amount of not more than about 1 weight % based on the dry coating. The total dry content of the composition is preferably from 5 to 15 weight-%, more preferably from 7 to 12 weight-%.
A further possible additive in the barrier pre-coating composition may be a polymer or compound with functional carboxylic acid groups, in order to improve the water vapour and oxygen barrier properties of a PVOH coating.
Suitably, such polymer with functional carboxylic acid groups is selected from among ethylene acrylic acid copolymer (EAA) and ethylene methacrylic acid copolymers (EMAA) or mixtures thereof. In one embodoment, such a barrier layer mixture may essentially consist of PVOH, EAA and an inorganic laminar compound. The EAA copolymer may be included in the barrier layer in an amount of about 1-20 weight %, based on dry coating weight.
It is believed that some further improved oxygen and water barrier properties may result from an esterification reaction between the PVOH and the EAA at an increased drying temperature, whereby the PVOH is crosslinked by hydrophobic EAA polymer chains, which thereby are built into the structure of the PVOH. Crosslinking can alternatively be induced by the presence of polyvalent compounds, e.g. metal compounds such as metal-oxides. Such mixtures are, however, more expensive because of the cost of the additives and may be less preferred from a recyclability point of view.
Thus, while it is more preferable to use a barrier pre-coating from a pure PVOH or EVOH composition, advantageous gas barrier results may be obtainable also with barrier pre-coatings comprising further additives as described above.
A barrier pre-coating may be applied at a total amount of from 0.1 to 3 g/m2, more preferably from 0.5 to 2 g/m2, dry weight. Below 0.1 g/m2, there will be no gas barrier properties achieved at all, while above 3 g/m2, the pre-coating will not bring cost-efficiency to the packaging laminate, due to high cost of barrier polymers in general and due to high energy cost for evaporating off the liquid. A recognisable level of oxygen barrier is achieved by PVOH at 0.5 g/m2, and above, and a good balance between barrier properties and costs is achieved between 0,5 and 2 g/m2.
In an embodiment, the barrier pre-coating may be applied in two consecutive steps with intermediate drying, as two part-layers. When applied as two part-layers, each layer is suitably applied in amounts from 0.1 to 2 g/m2, preferably from 0.5 to 1.5 g/m2, and allows a higher quality total layer from a lower amount of liquid gas barrier composition. More preferably, the two part-layers are applied at an amount of from 0.5 to 1 g/m2 each.
In an embodiment the barrier pre-coating has been applied by means of dispersion or solution coating at an amount of from 0.5 to 2 g/m2, preferably from 0.5 to 1.5 g/m2, dry weight.
For the unexpected improvement of the invention, the barrier pre-coating shall thus not be coated directly onto the paper or cellulose-based substrate, but shall be preceded by a first base layer pre-coating of a different polymer and composition, to prepare the substrate surface for the barrier pre-coating. It is not perfectly understood why, i.e. what in the physical and/or chemical conditions at the interface between the two pre-coatings is the main factor of the improvement in resulting barrier properties, but it is believed that the particular properties of aqueous starch compositions promote a dense and even base layer top surface for further coating and a compatible adhesion chemistry and wettability for the subsequent application of a polyvinyl alcohol-based barrier pre-coating.
The base layer pre-coating should be coated directly onto, and adjacent, the paper or cellulose-based substrate. The paper allows moisture to migrate outwards through the laminated packaging material, and the base layer pre-coating material also allows such water vapour migration. Thus, there will not be unfavourable entrapment of moisture near the moisture sensitive barrier pre-coating of PVOH or EVOH. Any moisture migrating through the material from the inside liquid food product in the package will simply be further transported via the paper layer and the paperboard bulk layer of the laminated packaging material towards the outside of the packaging container. The cellulose-based substrate and the paperboard bulk layer “breathe away” the humidity from the barrier pre-coating and thus keeps the moisture content within the barrier pre-coating substantially constant over time.
For the above function of smoothening layer, moisture transport and surface comptibility, the base layer pre-coating preferably comprises a polymer selected from the group consisting of starch, modified starch and cellulose ethers. These polysaccharide compounds have similar properties in this connection and will all provide the same advantages.
More specifically, the base layer pre-coating may comprise a material selected from the group consisting of starch, modified starch, methyl cellulose, ethyl cellulose, carboxymethyl cellulose CMC, hydroxy ethyl cellulose HEC, hydroxy propyl cellulose HPC, hydroxypropylmethyl cellulose HPMC and sodium carboxymethyl cellulose NaCMC. These natural, plant-based compounds will the provide optimal desired effects in line with the above, and also regarding ease of recycling and sustainability.
Suitable starch materials, or derivatives of starch, may be oxidised starch, cationic starch and hydroxypropylated starch. Examples of such modified starches are hypochlorite oxidised potato starch (Raisamyl 306 from Raisio), hydroxypropylated corn starch (Cerestar 05773), however also other forms of starch may provide the desired properties in a base layer pre-coating.
Furthermore, since such a base layer pre-coating enables decreasing the amount of the barrier pre-coating, while still achieving the same level of barrier properties, a slightly higher level of sustainability may be reached, since the preferred base layer pre-coating compounds may be more or less entirely of plant-based origin. A base layer pre-coating composition of native starch would for example be 100% plant-based and of 0% fossil origin.
In an embodiment, the total amount applied of the base layer pre-coating and the barrier pre-coating, is from about 1 to about 4 g/m2, preferably from 1.5 to about 3 g/m2, dry weight.
In a further embodiment, the base layer pre-coating has been applied by means of aqueous dispersion or solution coating at an amount of from 0.5 to 2 g/m2, preferably from 0.5 to 1.5 g/m2, dry weight.
The vapour deposited barrier coating to finally be coated onto the barrier pre-coating surface, is applied by means of physical vapour deposition (PVD) or chemical vapour deposition (CVD), for example by plasma enhanced chemical vapour deposition (PECVD).
In an embodiment, the vapour deposition coating is of a material selected from metals, metal oxides, inorganic oxides and carbon coatings.
In a further embodiment, the barrier deposition coating is a vapour deposition coating selected from the group consisting of an aluminium metallisation coating and aluminium oxide, AlOx, and preferably it is an aluminium metallisation coating.
Such thin vapour deposited coating layers are nanometer-thick, i.e. they have a thickness that is most suitably counted in nanometers, for example of from 5 to 500 nm (50 to 5000 Å), such as from 5 to 200 nm, more such as from 5 to 100 nm, such as from 5 to 50 nm.
Generally, below 5 nm the barrier properties may be too low to be useful and above 200 nm, such as above 100 nm, such as above 50 nm, depending on the type of vapour deposition coating, the barrier coating may be less flexible and, thus, more prone to cracking when applied onto a flexible substrate and would also cost more.
In an embodiment, the barrier deposition coating is applied to a thickness of from 10 to 80 nm, such as from 10 to 50 nm, such as from 10 to nm.
One common type of vapour deposition coating, often having some barrier properties, in particular water vapour barrier properties, are so called metallisation coatings, e.g. aluminium metal physical vapour deposition coatings.
Such a vapour deposited layer, substantially consisting of aluminium metal may have a thickness of from 5 to 50 nm, more preferably from 5-40 nm, which corresponds to less than 1% of the aluminium metal material present in an aluminium foil of conventional thickness for packaging, i.e. 6,3 μm. While vapour deposition metal coatings require significantly less metal material, they only provide a low level of oxygen barrier properties, at most, and need to be combined with a further gas barrier material in order to provide a final laminated material with sufficient barrier properties. On the other hand, it may complement a further gas barrier layer, which does not have water vapour barrier properties, but which is rather sensitive to moisture.
Other examples of vapour deposition coatings are aluminium oxide (AlOx, Al2O3) and silicon oxide (SiOx) coatings. Generally, such PVD-coatings are more brittle and less suitable for incorporation into packaging materials by lamination, while metallised layers as an exception do have suitable mechanical properties for lamination material despite being made by PVD.
Normally, an aluminium metallised layer inherently has a thin surface portion consisting of an aluminium oxide due to the nature of the metallisation coating process used.
In an embodiment, such an aluminium metallised layer has been applied to an optical density (OD) of from 1.8 to 2.5, preferably from 1.9 to 2.2. At an optical density lower than 1.8, the barrier properties of the metallised film may be too low. At above 2.5, on the other hand, the metallisation layer becomes brittle, and the thermostability during the metallisation process will be low due to higher heat load when metallising the substrate film during a longer time. The coating quality and adhesion may then be negatively affected. The optical density is measured in production by means of a densitometer, i.e. an instrument (such as from Macbeth, Tobias or similar), which uses the principle of diffuse light transmission. The instrument is suitable for measuring the optical density values of films coated with aluminium metallization. The accuracy and precision of the measurements is high and about +/−0.2 OD and about +/−0.01 OD, respectively, within a measuring range from 0 to 6.60 OD.
In lab measurements, a spectrophotometer may alternatively measure the light transmission over the full visible spectrum (380-800 nm). The optical density is calculated from the light transmission (T) value at 560 nm, according to a formula OD=−log10 (I1/I0) and the values obtained are equally accurate (+/−0.2 OD) and comparable to light transmission densitometer values.
Other coatings may be applied by means of a plasma enhanced chemical vapour deposition method (PECVD), wherein a vapour of a compound is deposited onto the substrate under more or less oxidising circumstances. Silicon oxide coatings (SiOx) may, for example, also be applied by a PECVD process, and may then obtain very good barrier properties under certain coating conditions and gas recipes.
DLC defines a class of amorphous carbon material (diamond-like carbon) that displays some of the typical properties of diamond. Preferably, a hydrocarbon gas, such as e.g. acetylene or methane, is used as process gas in a plasma for producing a coating of amorphous hydrogenated carbon barrier layer applied by a PECVD vacuum process, i.e. a DLC. DLC coatings applied by PECVD under vacuum provide good adhesion to adjacent polymer or adhesive layers in a laminated packaging material. Particularly good adhesion to adjacent polymer layers, are obtained with polyolefins and in particular polyethylene and polyethylene-based co-polymers.
The vapour deposition barrier coating is preferably applied by means of vacuum vapour deposition, but could less preferably be applied also by other methods generally known in the art to have a lower productivity and lower coating quality, such as electroplating or sputtering. The most preferred metal according to the present invention is aluminium, although any other metal capable of being vacuum deposited, electroplated or sputtered may be used according to the invention. Thus, less common metals such as Au, Ag, Cr, Zn, Ti or Cu are less preferred alternative choices. Generally, thin coatings of metal or a mixture of metal and metal oxide provide barrier properties against water vapour and are used when the desired function is to prevent water vapour from migrating into and through the multilayer film or packaging laminate. Preferably, for the purpose of manufacturing food packaging materials, the metal in a metallisation or inorganic metal coating is aluminium (Al).
The barrier coated paper or cellulose-based substrate obtained by the above method, provides excellent low OTR and low WVTR and proves suitable for lamination into a laminated packaging material and further for the fold-forming and sealing operations of such a laminated material into packages.
The laminated packaging material comprising the barrier-coated cellulose-based substrate, further comprises a first outermost protective material layer (22a; 22b) and a second innermost liquid tight, heat sealable material layer (23a; 23b; 23b″). The second innermost liquid tight, heat sealable material layer (23a; 23b; 23b″) may comprise a polyolefin polymer or be made of a polyolefin polymer. The first outermost protective material layer may be transparent, to enable visibility of a printed décor pattern on the outside of the bulk layer. It may also comprise a polyolefin polymer or be made of a polyolefin polymer.
A carton-based laminated packaging material for liquid food packaging may thus comprises a bulk layer of paper or paperboard, a first outermost, protective material layer, a second innermost liquid tight, heat sealable material layer, and, arranged on the inner side of the bulk layer of paper or paperboard, towards the inside of a packaging container made from the packaging material, between the bulk layer and the second innermost liquid tight, heat sealable material layer, said barrier-coated paper or cellulose-based substrate.
The carton-based laminated packaging material may comprise a bulk layer of paper or paperboard, a first outermost liquid tight, heat sealable polyolefin layer, a second innermost liquid tight, heat sealable polyolefin layer and, arranged on the inner side of the bulk layer of paper or paperboard, towards the inside of a packaging container made from the packaging material, between the bulk layer and the innermost layer, said barrier-coated paper or cellulose-based substrate.
A paper or paperboard bulk layer for use in the invention usually has a thickness of from about 100 μm up to about 600 μm, and a surface weight of approximately 100-500 g/m2, preferably about 200-300 g/m2, and may be a conventional paper or paperboard of suitable packaging quality.
For low-cost aseptic, long-term packaging of liquid food, a thinner packaging laminate may be used, having a thinner paper core layer. The packaging containers made from such packaging laminates are not fold-formed and more similar to pillow-shaped flexible pouches. A suitable paper for such pouch-packages usually has a surface weight of from about 50 to about 140 g/m2, preferably from about 70 to about 120 g/m2, more preferably from 70 to about 110 g/m2. As the barrier-coated substrate in this invention in itself may contribute with some stability to the laminated material, the paper layer corresponding to a “bulk” layer may be even thinner, and interact with the barrier cellulose-based substrate ni a sandwich interaction to still produce a laminated packaging material having the desired mechanical properties altogether.
The barrier-coated paper or cellulose-based substrate may be bonded to the bulk layer by an intermediate adhesive, or thermoplastic polymer bonding layer, thus binding the un-coated surface of the barrier-coated paper to the bulk layer. According to an embodiment the bonding layer is a polyolefin layer, such as in particular a layer of a polyethylene-based polyolefin copolymer or blend, including in the majority ethylene monomer units. The bonding layer may be binding the bulk layer to the barrier-coated cellulose-based substrate by melt extrusion laminating the bonding polymer layer between a web of the bulk layer and a web of the cellulose-based substrate, and simultaneously pressing the three layers together while being forwarded through a lamination roller nip, thus providing a laminated structure by extrusion lamination.
In another embodiment, the barrier-coated cellulose-based substrate may be bonded to the bulk layer by wet application of an aqueous dispersion of an adhesive composition comprising an adhesive polymer binder onto one of the web surfaces to be laminated, and pressing the two paper webs together while they are forwarded through a lamination roller nip, thus providing a laminated structure by wet lamination. The moisture of the aqueous adhesive composition is absorbed into the fibrous cellulose network of the two paper layers, and partly evaporating with time, during the subsequent lamination processes. There is thus no need for a forced drying step. The adhesive polymer binder is selected from the group consisting of acrylic polymers and copolymers, starch, cellulose and polysaccharide derivatives, polymers and copolymers of vinyl acetate and vinyl alcohol. For best possible environmental and sustainability profile, adhesive binders originating from plants or non-fossil sources are preferred.
Suitable thermoplastics for the outermost and innermost heat sealable liquid-tight layers are polyolefins such as polyethylene and polypropylene homo- or co-polymers, preferably polyethylenes and more preferably polyethylenes selected from the group consisting of low density polyethylene (LDPE), linear LDPE (LLDPE), single site catalyst metallocene polyethylenes (m-LLDPE) and blends or copolymers thereof. According to an embodiment, the outermost heat sealable and liquid-tight layer is an LDPE, while the innermost heat sealable, liquid-tight layer is a blend composition of m-LLDPE and LDPE for optimal lamination and heat sealing properties.
The same thermoplastic polyolefin-based materials, as listed regarding the outermost and innermost layers, and in particular polyethylenes, are also suitable in bonding layers interior of the laminated material, i.e. between a bulk or core layer, such as paper or paperboard, and a barrier film or sheet. In an embodiment, the thermoplastic bonding layer may be a polyethylene layer, such as a low density polyethylene (LDPE) layer.
In a further embodiment, the second innermost liquid tight, heat sealable polyolefin layer is a pre-manufactured film comprising the same or similar polyolefins, as described above, for improved robustness of the mechanical properties of the packaging material. Due to the manufacturing process in film blowing and film casting operations, and optional subsequent film orientation operation steps, the polymers of such films acquire different properties from what is possible from (co-) extrusion coated polyolefin layers. Such a pre-manufactured polymer film thus contributes to the mechanical robustness of a laminated packaging material and to mechanical strength and package integrity of formed and filled packaging containers from the laminate packaging material.
According to an alternative embodiment, suitable bonding or tie layers in the interior of the laminated material, such as for example between the bulk or core layer and the barrier-coated cellulose-based substrate, or between the outer heat sealable layer and the barrier-coated paper substrate, are also so-called adhesive thermoplastic polymers, such as modified polyolefins, which are mostly based on LDPE or LLDPE co-polymers or, graft co-polymers with functional-group containing monomer units, such as carboxylic or glycidyl functional groups, e.g. (meth)acrylic acid monomers or maleic anhydride (MAH) monomers, (i.e. ethylene acrylic acid copolymer (EAA) or ethylene methacrylic acid copolymer (EMAA)), ethylene-glycidyl(meth)acrylate copolymer (EG(M)A) or MAH-grafted polyethylene (MAH-g-PE). Another example of such modified polymers or adhesive polymers are so called ionomers or ionomer polymers. Preferably, the modified polyolefin is an ethylene acrylic acid copolymer (EAA) or an ethylene methacrylic acid copolymer (EMAA).
A laminated packaging material made according to the above provides good integrity when transformed into filled packaging containers, by good adhesion between the adjacent layers within the laminated construction and by providing good quality of the barrier coating and the barrier pre-coating, each and in combination. Especially, for the packaging of liquids, and wet food, it was an important conclusion that the inter-layer adhesion within the laminated packaging material, as well as the oxygen gas barrier properties, is maintained also under wet packaging conditions.
According to further embodiment, the packaging container formed from the laminated packaging material may be partly sealed, filled with liquid or semi-liquid food and subsequently sealed, by sealing of the packaging material to itself, optionally in combination with a plastic opening or top part of the package.
To conclude, robust and reliable packages for liquid food packaging for long term shelf-life and storage may be obtained by the barrier-coated cellulose-based substrate and the laminated packaging material comprising it, as defined by the invention, thanks to the improved barrier properties provided. The laminated packaging material structure works better for the forming into fold-formed packages, both from the improved adhesion between the substrate and the barrier material coatings and from the improved contribution to gas barrier properties from the barrier-coated substrate itself, which likely also is due to the improved combined cohesion and adhesion of the pre-coatings and barrier coating layers in the barrier-coated cellulose-based substrate.
In the following, preferred embodiments of the invention will be described with reference to the drawings, of which:
Two different paper substrates of the type suitable for greaseproof wrapping were coated with base layer pre-coatings and/or barrier pre-coating layers at small pilot scale, according to what is shown in Table 1, without a further metallised aluminium barrier deposition coating onto the barrier pre-coating. Subsequently the coated paper substrates were laminated into packaging laminate structures as follows:
//outside 12 g/m2 LDPE/Duplex CLC 80 mN, 200 g/m2, paperboard bulk layer/3-4 g/m2 of aqueous PVAc adhesive/barrier pre-coated paper (as listed in Table 1)/6 g/m2 EAA adhesive polymer/22 g/m2 inside heat seal layer of a blend of LDPE and m-LLDPE//
The Duplex CLC paperboard was a clay-coated paperboard of the conventional type, and the m-LLDPE is a metallocene-catalysed linear low density polyethylene. The barrier-coated side of the paper substrate was directed in the laminated structure towards the inside (corresponding to the inside of a packaging container manufactured from the laminated material). The adhesive polymer EAA and the innermost heat-sealable layer were coextrusion coated together onto the barrier-coated paper and the outermost layer of LDPE was extrusion coated onto the outside of the paperboard. The paperboard bulk layer was laminated to the barrier-coated paper by wet lamination with an aqueous adhesive comprising polyvinyl acetate at low amount and without any intermediate drying step.
Oxygen transmission measurements were made with an Oxtran Mocon 2/21 equipment (an equipment based on coulometric sensors) at 23° C. and at 50% and 80% RH (relative humidity), respectively, and the measured values were reported in cc/m2, during 24 hours, at 1 atmosphere of 100% oxygen gas (air at 1 atm having only 20% oxygen gas).
Paper A was a greaseproof paper having a compact, dense surface, from Nordic Paper, identified as “Super Perga® WS Parchment” having a grammage of 38 g/m2.
Paper B was a greaseproof paper from Arjo Wiggins, named “Clearpack”, having a grammage of 46 g/m2.
The papers were measured to have a surface roughness on the top side, i.e. the side to be barrier-coated, of about 200-300 ml/min Bendtsen and of about 150 ml/min Bendtsen, respectively.
The respective papers were thus coated only with base layer pre-coating and/or barrier pre-coating layers according to Table 1, i.e. with dispersion coated pre-coating layers, and then laminated into the same laminated packaging material structure. The pre-coating operations as well as the lamination operations to produce laminated packaging material structures from the pre-coated papers, were made in pilot scale and the oxygen transmission measurements were performed on the resulting packaging materials flat samples.
The barrier papers as listed in Table 1 were thus each laminated uncoated or dispersion-coated (the type of coating methods are generally known by the term “liquid film coating”, applicable for barrier pre-coating of aqueous dispersions or solutions of polymers at low amounts of dry weight onto a substrate) into the standardised laminated packaging material structure above. The base layer pre-coatings and barrier pre-coatings were applied in 1-3 steps as listed, at a dry coating weight of about 1 g/m2 each, with intermediate drying steps in between each coating. Two types of aqueous dispersions and/or solutions were used, i.e. a water-based dispersion of native potato-based starch of the brand Solvicol® from Avebe, and a solution of polyvinyl alcohol, PVOH, from Kuraray having a degree of hydrolysis of at least 98%, i.e. Poval® 6-98. When a starch pre-coating is applied in combination with a PVOH pre-coating for the purpose of forming a barrier-coated paper, the starch coating is applied as a first, base layer pre-coating, which is dried in an in-line dryer equipment and subsequently over-coated with a further, barrier pre-coating of PVOH, further and subsequently dried in an in-line dryer in a second drying step. The dispersions were applied by means of a gravure-coating method in pilot-scale equipment, and the dry content of the aqueous dispersion of the PVOH was about 15 weight-%. The temperature of the substrate surface at each drying operation was regulated to from about 60 to about 80° C.
The dry content and viscosity of the starch dispersion was selected such that the low amount of dry content of the starch may be applied by a gravure coating process, at industrial speed. The base layer pre-coating was applied as a rich, well-adhering, dense and homogenous base pre-coating to enable the subsequent application of an even, low amount of the barrier dispersion pre-coating. The resulting even and smooth surface of the thus dried barrier pre-coating in turn enables the application of a further high-quality vapour deposition coating, being coherent, homogenous without pinholes, and adhering well to the dried barrier pre-coating surface.
Accordingly, the coatings were applied in 2-3 consecutive coating steps, to a dry matter weight of about 1 g/m2 in each coating step, with drying of each applied coating between the coating steps.
It can be concluded from the sample laminated materials comprising the paper substrate pre-coated with base layer and/or pre-coated with barrier coatings in accordance with Table 1, that one or two coatings of starch only improve the oxygen barrier properties to some extent of each of the pre-coated papers in a laminated material, but that the improvement is greater in the case of Paper A, which had a greater initial surface roughness and which exhibited a lower inherent oxygen barrier properties when laminated into the multilayer laminate structure. The pre-coated papers having two or three coatings of the PVOH coating only, have further improved barrier properties than papers having coatings with starch only, partly because starch inherently contributes less by its inherent gas barrier material properties. A significant further improvement was seen, however, when combining the two types of pre-coatings in the order as defined by samples 7 and 14. i.e. a first base layer pre-coating of starch and a second barrier pre-coating of PVOH. Such a further, unexpected improvement of the resulting oxygen barrier of the final laminate was even more notable when Paper B was used, i.e. the paper having greater smoothness and higher inherent barrier properties. Then the OTR of Sample 14 was even further reduced by 50%, compared to samples 12-13, wherein only the higher barrier pre-coating PVOH layers were applied.
Further, similar barrier coating experiments were performed on the two types of papers A and B, in more full-scale production, as listed in samples 7 and 14 in Table 1, and the thus barrier pre-coated papers with a first base layer pre-coating and second barrier pre-coating were metallised and subsequently laminated in the same way into laminated multilayer packaging material structures. The speed of the dispersion coating operations were from 400 to 600 m/min, and the coatings were applied in 2 consecutive coating steps, to a dry matter weight of about 1 g/m2 each, with drying of each applied coating between the coating steps. As in Example 1, the drying was carried out at a substrate surface temperature of from about 60 to about 80° C. In a subsequent, separate coating operation, metallisation barrier coatings were applied onto the barrier pre-coating by physical vapour deposition to an optical density of about 2,0, as measured by a light transmission densitometer, and a thickness of about 40 nm.
Packaging laminate samples were also prepared from the pre-coated paper substrates, not having the metallisation coating of aluminium applied.
The results from this experiment are listed in Table 2.
From the full-scale experiments, we see a further improved oxygen barrier (lower oxygen transmission) in the sample corresponding to sample 7 of Table 1, i.e. from barrier pre-coatings onto Paper A, and to sample 14, i.e. from barrier pre-coatings onto Paper B, by the over-coating of further metallisation coating. See sample 2.3 vs samples 2.5 and 2.6 for Paper A, and samples 2.1 and 2.2 vs sample 2.4, regarding Paper B.
It was not perceived that the coating speed mattered significantly to the resulting OTR measurements, since the amount of the applied dry weight of the coatings was adjusted to approximately 1 g/m2 at each different speed. The different coating operations at industrial speeds such as 400-600 m/min was thus not perceived to pose any problems to the coating quality or efficiency.
As can be seen from the OTR measurements at 80% relative humidity for the laminate samples including also the metallisation coating, the effect of the different contributions from the different paper grades and the possible variations in the metallisation coatings are levelled out and the oxygen barrier results seem to land at the same high level (i.e. the same low OTR values), thanks to the synergy between the combination of the base layer pre-coating and the barrier pre-coating and the metallisation barrier coating. Some differences in the water vapour transmission values were noted and believed due to differences between the quality and thicknesses of the metallised barrier coatings in the different laminate configurations. By comparing the OTR values of the laminate samples with and without the metallization barrier coating onto the barrier pre-coated paper substrate at 80% relative humidity, which is the more realistic environment for a filled, liquid food carton packaging container, there is thus a 4-5 times improvement of the oxygen barrier of the laminated packaging materials having the specific combination of a base layer pre-coating, a barrier pre-coating and a barrier deposition coating.
Laminated packaging materials such as those produced with the configuration of sample 2.3 in Table 2 were further evaluated in limited filling machine trials for forming and filling and sealing into filled packaging. No major problems regarding packaging integrity (i.e. package tightness vs the surrounding environment) and sealability properties were identified during the trials, which therefore were considered successful.
Further, similar barrier paper laminate structures were evaluated in the same trials, with the only difference to the laminate configuration that they had a pre-manufactured blown film of polyethylene on the inside, comprising at least one part-layer with a major proportion of linear low density polyethylene (LLDPE), and thus constituting the innermost heat sealable layer portion applied on the inside of the barrier-coated paper. From the results and perceptions in evaluating the trials, it was concluded that laminate configurations having such a pre-manufactured heat sealable film on the inside would be favourable for further increased robustness of the laminated packaging material.
Further, relating to the attached figures:
In
In
The bulk layer 21a is laminated to the uncoated side of the barrier-coated paper substrate 10, from
The innermost heat sealable layer 23a may consist of one layer or alternatively of two or more part-layers of the same or different kinds of LDPE or LLDPE or blends thereof, and is well adhered to the metallised barrier deposition coating surface 14 of the barrier paper substrate 10, by an intermediate coextruded tie layer, e.g. of ethylene acrylic acid copolymer (EAA) which thus bonds the innermost heat sealable layer(s) to the barrier coated paper substrate 10, in applying the layers together in a single melt coextrusion coating step.
In
The bulk layer 21b is laminated to the barrier-coated paper substrate described in
Thus, the amount of thermoplastic polymer can be significantly reduced in this lamination layer, in comparison to the conventional melt extrusion laminated bonding layer of polyethylene, described in
Alternatively, the innermost heat sealable and liquid-tight layer 23b may consist of a pre-manufactured, blown film, comprising LDPE or LLDPE polymers in any blends thereof, and it may be laminated to the barrier-coated paper substrate, to the surface of its barrier deposition coating, i.e. the aluminium metallisation, by means of an intermediate, melt extrusion laminated bonding layer 24b, comprising a thicker tie layer of EAA than used in
In an alternative embodiment, the pre-manufactured blown film 23b″ is laminated to the metallised coating by means of another wet lamination step, with an aqueous adhesive of an acrylic (co)polymer adhesive layer 24b″, at ambient (cold) temperature, at an amount from 3 to 4 g/m2.
A further embodiment, having all the features as described and a melt extruded bulk layer lamination layer 26a of
A yet further embodiment, wherein the thin, wet, aqueous adhesive dispersion laminated layer 26a of
In
The resulting barrier pre-coated paper substrate web 34a is forwarded to cool off and is wounded onto a reel for intermediate storage and later further vapour deposition coating of a barrier deposition coating 14, onto the barrier pre-coated paper.
As explained in connection to
The resulting paper pre-laminate web 31b is forwarded from an intermediate storage reel, or directly from the lamination station for laminating the paper pre-laminate. The non-laminated side of the bulk layer 21a, 21b, i.e. its print side, is joined at a cooled roller nip 33 to a molten polymer curtain 32 of the LDPE, which is to form the outermost layer 22a; 22b of the laminated material, the LDPE being extruded from an extruder feedblock and die 32b. Subsequently, the paper pre-laminated web, now having the outermost layer 22a;22b coated on its printed side, the outside, passes a second extruder feedblock and die 34b and a lamination nip 35, where a molten polymer curtain 34 is joined and coated onto the other side of the pre-laminate, i.e. on the barrier-coated side of the paper substrate 10; 25a;25b. Thus, the innermost heat sealable layer(s) 23a are coextrusion coated onto the inner side of the paper pre-laminate web, to form the finished laminated packaging material 36, which is finally wound onto a storage reel, not shown.
These two coextrusion steps at lamination roller nips 33 and 35, may alternatively be performed as two consecutive steps in the opposite order.
According to another embodiment, one or both of the outermost layers may instead be applied in a pre-lamination station, where the coextrusion coated layer is first applied to the outside of the (printed) bulk paperboard layer or onto the metallisation coating of the barrier-coated paper substrate, and thereafter the two pre-laminated paper webs may be joined to each other, as described above.
According to a further embodiment, the innermost layers of the heat sealable and liquid-tight thermoplastic layers are applied in the form of a pre-manufactured film, which is laminated to the coated side of the barrier-coated paper substrate 10.
As explained in connection to
As a final remark, the invention is not limited by the embodiments shown and described above, but may be varied within the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20210874.2 | Dec 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/083193 | 11/26/2021 | WO |
