Method for producing a barrier-coated cellulose-based substrate, laminated packaging material and packaging container containing the produced cellulose-based substrate

Abstract

The present invention relates to an industrially feasible and optimized process for producing high quality gas barrier coated cellulose-based substrates (10a; 10b; 25a; 25b; 25c).The present invention further relates to laminated packaging materials (20a; 20b; 20c) comprising the barrier coated cellulose-based substrates (10a; 10b) for packaging oxygen sensitive products and to packaging containers comprising the laminated packaging materials.

Description

[Technical field]

[0001] The present invention relates to an industrial process for the production of barrier-coated paper or cellulose-based substrates for packaging oxygen-sensitive products such as food, and further to a laminated packaging material made of the barrier-coated paper or cellulose-based substrate thus produced for packaging oxygen-sensitive products such as liquid or semi-liquid foods, and to a packaging container made of the laminated packaging material. [Background technology]

[0002] Single-use packages for liquid foods are often manufactured from paperboard or carton-based packaging laminates. One such commonly used package is sold under the trademark "Tetra Brik Aseptic" and is primarily employed for the aseptic packaging of liquid foods such as milk, fruit juices, etc., sold for long-term ambient storage. The packaging material of this known package is usually a laminate comprising a bulk or core layer of paper, paperboard or other cellulose-based material and a liquid-tight outer layer of thermoplastic. To make the package gas-tight, and in particular oxygen-tight, for the purposes of aseptic packaging or packaging of, for example, milk or fruit juice, these laminates usually comprise at least one additional layer, most commonly aluminum foil.

[0003] On the inside of the laminate, i.e. the side intended to face the filled food contents of a container made from the laminate, there is an innermost layer applied onto the aluminum foil, which innermost layer comprises one or more partial layers comprising adhesive polymers and / or heat-sealable thermoplastic polymers such as polyolefins, and, outside the bulk layer, there is an outermost heat-sealable polymer layer.

[0004] Packaging containers are generally produced by modern high-speed packaging machines of the type that form, fill and seal packages from webs of packaging material or prefabricated blanks. The packaging containers are produced by joining the longitudinal edges of a web of laminate packaging material together at overlap joints by welding together the inner and outer heat-sealable thermoplastic polymer layers, converting it into a tube. The tube is filled with the desired liquid food product and then divided into individual packages by repeatedly transversely sealing 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 scoring along the transverse seals and formed into the desired geometric shape, usually a parallelepiped, by creating creases in the packaging material along pre-prepared crease lines. Each package may be equipped with an opening device, such as a screw cork, before or after filling, forming and sealing the container.

[0005] The main advantage of this continuous tube forming, filling and sealing packaging process concept is that the web can be continuously sterilized just before tube formation, offering the possibility of an aseptic packaging process, i.e. a process in which the liquid contents to be filled and the packaging material itself are reduced from bacteria and the filled packaging containers are produced under clean conditions so that they can be stored for long periods even at ambient temperature without risk of microbial growth in the filled product. Another important advantage of Tetra Brik® type packaging processes is that they allow continuous high speed packaging, which, as mentioned above, has a great impact on cost efficiency.

[0006] Packaging containers for sensitive liquid foods, such as milk and juice, can also be produced from sheet blanks or preassembled blanks of the laminate packaging material of the invention. Packages are produced from flat-folded tubular blanks of the packaging laminate by first assembling the blanks to form an open tubular container capsule, one open end of which is closed by folding and heat sealing an integral end panel. The container capsule thus closed is filled from the other open end with a food product, such as juice, and is then closed by further folding and heat sealing the corresponding integral end panel. Examples of packaging containers produced from sheet and tubular blanks are the conventional so-called gable top packages. Packages of this type can also be provided with a molded plastic top and / or a screw cap.

[0007] The aluminum foil layer of the packaging laminate provides a gas barrier that is significantly superior to other gas barrier materials. Conventional aluminum foil-based packaging laminates for aseptic packaging of liquid foods have inherent barrier properties against water vapor, light, aromas, flavors, and even acidic substances, and at their performance level, are the most cost-effective packaging materials available on the market. Furthermore, the aluminum foil allows for heat sealing or heating of the laminate material by induction within the aluminum foil.

[0008] Other materials that compete with foil-based materials need to be cost-effective in terms of raw materials, have comparable food preservation properties, and require relatively low complexity in converting the material into the finished packaging laminate.

[0009] In the effort to develop non-aluminum foil materials for liquid food carton packaging, there is an incentive to develop prefabricated films or sheets with high or multiple barrier properties that can replace aluminum foil barrier materials in traditional laminate packaging materials or combine multiple separate barrier layers in laminate materials and be compatible with traditional processes for lamination and manufacturing.

[0010] A preferred type of such alternative, more environmentally sustainable barrier material is a barrier coated paper substrate made by aqueous dispersion coating or vapor deposition coating onto a thin paper carrier substrate. Although there are various aqueous dispersion coating processes, vapor deposition coating processes and material recipes for such coatings, there is a need for a "non-foil" type, i.e., non-aluminum foil, cost-effective barrier material with improved barrier properties, especially against gases such as oxygen gas, for use in packaging laminates for liquid food packaging.

[0011] Patent publication WO2011 / 003565A1 discloses a non-aluminum foil packaging material comprising a precoated metallized paper or cellulose-based substrate for induction heat sealing, and recommends providing a further barrier coating layer on the packaging laminate, such as on the backside of the paper substrate or on a paperboard bulk layer, to obtain good gas barrier properties.

[0012] Patent publication WO2017 / 089508A1 discloses that further improved barrier properties can be obtained in a similar manner from metallized paper by selecting a paper substrate that provides optimal properties in a similar packaging laminate. Such metallized paper substrates not only provide improved barrier properties but also exhibit better stability of the metallized layer for induction heat sealing purposes.

[0013] However, there remains a need for robust, industrially viable coating processes, i.e. operating at high coating line speeds, to provide optimal and reliable oxygen gas barrier properties for a selected range of paper and cellulose-based substrates. There is also a need for improvements in the recyclability and sustainability of the materials used in general, aiming to reduce the amount of material and the number of different materials used. Summary of the Invention [Problem to be solved by the invention]

[0014] It is therefore a general object of the present invention to provide an industrially viable process for the rapid and robust production of barrier-coated paper or cellulose-based substrates suitable as gas barrier materials in the packaging of oxygen-sensitive products, such as food products, in particular liquid or semi-liquid or moist foods, for use in future sustainable non-aluminium foil-based ("non-foil") laminate packaging materials produced for the packaging of oxygen-sensitive products.

[0015] It is also a general object of the present invention to provide an industrially viable method for the rapid and robust production of barrier-coated paper or cellulose-based substrates with good gas barrier properties and improved recyclability and sustainability, i.e. to meet the need for future sustainable packaging materials for packaging oxygen-sensitive products.

[0016] A more specific object is to provide an industrially viable and robust method for producing barrier coated paper or cellulose based substrates suitable for use in non-foil laminate packaging materials and packaging containers for liquid, semi-liquid or viscous foods, allowing long term sterile storage under ambient conditions.

[0017] A further object is to provide a paper or paperboard based laminate packaging material for packaging and wrapping oxygen sensitive products such as food, which is more cost effective and reliable than aluminium foil barrier materials, has good gas barrier properties and optionally water vapour barrier properties, is easily recyclable and is environmentally sustainable.

[0018] It is a further object of the present invention to provide a cost-effective, non-foil, paper- or paperboard-based, heat-sealable packaging laminate with reliable gas and water vapour barrier properties, with nutritional quality maintained under ambient conditions, for the production of aseptic packaging containers for the long-term storage of liquid, semi-liquid or viscous foods.

[0019] These objects are therefore attainable according to the present invention by a barrier-coated paper or cellulose-based substrate, a laminate packaging material and a method for producing a packaging container as defined in the appended claims. [Means for solving the problem]

[0020] According to a first aspect of the present invention there is provided a method for producing a barrier coated cellulose-based substrate for packaging oxygen sensitive products, the method comprising the steps of conveying a web of paper or cellulose-based substrate at a line speed of at least 300 m / min; The cellulose-based web has a basis weight of 30 to 70 g / m2, measured according to ISO 536:2012. 2 and a density between 800 and 1400 kg / m, measured according to ISO 534:2011 3 and the surface of the upper side of the paper or cellulose-based substrate has a Bendtsen roughness value of less than 130 ml / min, measured according to ISO 8791:4, and a Cobb 60 of less than 30 g / m, measured according to ISO 535. 2 is as follows: providing an aqueous solution of a gas barrier polymer selected from vinyl alcohol polymer, PVOH, ethylene vinyl alcohol copolymer, EVOH, and modified PVOH and EVOH polymer, the aqueous solution having a solid content of 5 to 15 wt % and a viscosity of 10 to 120 mPa s; Dry weight: 0.5-2g / m 2 applying said aqueous gas barrier polymer solution by roll coating onto a top surface of a web of paper or cellulose-based substrate to provide a uniform coating in an amount of drying the water gas barrier polymer coating applied in the previous step while maintaining the surface temperature of the web substrate at a constant temperature of less than 60°C to 95°C; The steps of applying the aqueous gas barrier polymer solution and then drying the applied aqueous gas barrier polymer coating are repeated at least once, and optionally the thus obtained coated and dried web substrate is further coated with a nanometer thick barrier vapor deposition coating of metal and / or metal oxide by physical vapor deposition, thus obtaining a barrier coated paper or cellulose based substrate having minimal defects in the gas barrier coating and, optionally, in the vapor deposition coating of metal and / or metal oxide.

[0021] In one embodiment, the roll coating process is a gravure coating process, such as a reverse gravure coating process.

[0022] The aqueous solution of PVOH or EVOH may have a solids content of 7 to 13% by weight, such as 9 to 13% by weight, for example 10 to 12.5% ​​by weight.

[0023] The steps of applying an aqueous solution of a gas barrier polymer and then drying the applied water-gas barrier polymer coating are such that each coating step has a dry weight of 0.5 to 1 g / m 2 This has been found to work best in high speed processes, i.e. it allows a thin, uniform coating with few mistakes and defects to be applied, with correspondingly sufficient oxygen barrier properties, and allows the coating to be carefully dried, including avoiding the formation of defects in the coating during the drying step, and fast enough for the high speed of the coating line. At the same time, for a paper substrate of selected quality, a wet, thinly applied coating of the aqueous gas barrier polymer solution will level out the roughness of the substrate surface, while retaining the cohesive properties of the coating, without being destroyed or partially absorbed into the substrate surface, resulting in a coherent, uniform barrier coating layer before drying.

[0024] In a preferred embodiment, the surface temperature of the web substrate is consistently kept below 85°C, such as below 80°C, during each drying step.

[0025] The optional vapor deposition coating may be a metallized coating of aluminum, a coating of aluminum oxide, or a mixed coating of aluminum and aluminum oxide.

[0026] According to a second aspect of the present invention there is provided a laminate packaging material comprising a barrier coated cellulose-based substrate produced by the method of the first aspect and further comprising a first outermost protective material layer and a second innermost liquid-tight heat-sealable material layer, the laminate packaging material having a thickness of less than 0.5 cm as measured in accordance with ASTM F 1927-14. 3 / m 2 , 24h, 0.2 atm oxygen, 50% RH or less, measured according to ASTM F 1927-14, the oxygen barrier properties thus measured being provided solely by the coating material of the first embodiment.

[0027] The first, outermost protective material layer may be a thin layer of polymer whose purpose is to protect the paper or paperboard based laminate packaging material from dirt and moisture in the external environment of the sealed packaging container, i.e. on the side facing the outside of the packaging container produced from the packaging laminate.

[0028] The second, innermost liquid-tight heat-sealable layer of material may comprise a layer of a thermoplastic polymer that is readily heat-sealable by available heat sealing methods such as induction heat sealing, ultrasonic heat sealing, or simply contact heat sealing, and is positioned on the barrier-coated side of the barrier-coated paper or cellulose-based substrate so as to face the inside of a packaging container made from the packaging laminate, i.e., so as to be in direct contact with the packaged food.

[0029] The second, innermost liquid-tight, heat-sealable material layer may comprise a polyolefin polymer, for example, a polyethylene from the low density range, such as selected from the group consisting of LDPE, LLDPE, m-LLDPE, and blends of two or more thereof.

[0030] According to one embodiment, both the first, outermost, protective material layer and the second, innermost, liquid-tight, heat-sealable material layer may comprise polyolefin polymers, such as polyethylene polymers of the same or different types.

[0031] For the purpose of carton packaging of oxygen-sensitive products such as liquid or semi-liquid or viscous foods, the laminate packaging material may further comprise a bulk layer of paper or paperboard or other cellulosic material, disposed inside the bulk layer of paper or paperboard between the bulk layer and a second, innermost, liquid-tight, heat-sealable material layer, thus comprising a barrier-coated cellulose-based substrate. The bulk layer contributes to the bending stiffness of the laminate packaging material and may also contribute to the dimensional stability of the folded and molded packaging containers used therewith, for example to withstand the high forces caused by the movement during distribution and handling of the package contents of oxygen-sensitive liquid or viscous products.

[0032] In one embodiment, for such liquid carton packaging purposes, the second, innermost liquid-tight, heat-sealable polyolefin layer is a prefabricated polyolefin film, such as, for example, a cast biaxially oriented polyethylene film with at least one layer having a majority of LLDPE polymer, to improve the robustness of the mechanical properties of the laminate packaging material.

[0033] In a third aspect of the present invention, there is provided a packaging container comprising the laminate packaging material of the second aspect. According to an embodiment, the packaging container is at least partially manufactured from the laminate packaging material of the present invention, and according to a further embodiment, the entire packaging container is manufactured from the laminate packaging material.

[0034] While it has been thought in the past that improving the gas barrier properties of such barrier coated cellulose based substrates was achieved by sourcing better papers or substrates that, when further laminated to a polymer layer, inherently provide gas barrier properties in themselves, or by applying thicker coatings of polymers that have inherent gas barrier properties, it is now better understood that the surface portion of the paper or cellulose based substrate plays a key role in the optimal performance of the subsequently applied coatings and provides the gas barrier properties, together with an optimized method for applying the barrier coating with high reliability of quality, i.e. without defects or thickness variations, under industrially feasible conditions and with minimal consumption of barrier material. Industrially feasible conditions mean that it must be possible to apply a good barrier coating at high speeds, resulting in low or reasonably balanced costs.

[0035] What has become clear is that the barrier properties of the cellulose-based substrate itself do not need to be high, and that high-quality coated paper and cellulose-based substrates can be produced economically even if the amount of gas barrier polymer applied as a barrier precoat is minimized under certain conditions.

[0036] By using a barrier-coated cellulose-based substrate as described above and producing it by the method of the present invention, it is possible to impart good gas barrier properties to laminated packaging materials and packaging containers using the same on an industrial scale, and by increasing the content of cellulose fibers that can be easily repulped, it is possible to impart improved repulpability and recyclability, i.e., improved sustainability.

[0037] Generally, the use of cellulose-based substrates in laminate materials and packaging provides a high percentage of fiber content that is renewable, i.e., of non-fossil origin, recyclable, biodegradable, and allows old materials to be recycled into the production of new materials. Furthermore, the use of paper or cellulose-based substrates as "surface layers" in sandwich constructions allows the use of bulk materials with lower bending stiffness, lower fiber quality, cheaper, or lower density and fiber usage by laminating such surface layers on both sides of the bulk layer.

[0038] Thus, the gas barrier coated cellulose-based substrate obtained by the method of the first aspect may impart improved barrier properties to laminate packaging materials containing it, and may also impart a better recyclability and sustainability profile, depending on the resulting material layer configuration.

[0039] (Detailed Description) The term "long-term storage" as used in the context of the present invention means that the packaging container is capable of preserving the quality, i.e. nutritional value, hygienic safety and taste, of the packaged food at ambient temperature conditions for at least 1 or 2 months, such as at least 3 months, preferably 6 months, such as 12 months or more.

[0040] The term "package integrity" generally refers to the tightness of the package, i.e., the resistance of the packaging container to leakage or breakage. The term encompasses the resistance of the package to the ingress of bacteria, dirt, and other microorganisms that may deteriorate the food contained therein and shorten the expected shelf life of the package.

[0041] One major contribution to the integrity of a laminate packaging material comes from good internal adhesion between adjacent layers of the laminate material. Another contribution comes from the resistance of the material to defects such as pinholes, ruptures, etc. in each material layer itself, and yet another contribution comes from the strength of the seal joints where the material is sealed when the package is formed. Thus, with respect to the integrity of the laminate packaging material itself, the focus is primarily on the adhesion of each laminate layer to its adjacent layers as well as the quality of the individual material layers. With respect to the sealing of the package, the focus is primarily on the quality of the seal joints, which is ensured by a well-functioning and robust heat-sealing operation in the filling machine, and further by the properly adapted heat-sealing properties of the laminate packaging material.

[0042] The term "liquid, semi-liquid or viscous food" generally refers to food that contains flowable contents and optionally solids. Non-limiting examples of contemplated foods include dairy products, milk, soy, rice, grain, seed drinks, juices, nectars, soft drinks, energy drinks, sports drinks, coffee or tea drinks, coconut water, wine, soup, crushed tomatoes, sauces (such as pasta sauces), legumes, olive oil, etc.

[0043] Other examples of oxygen-sensitive foods that can be packaged and protected with the laminate packaging materials of the present disclosure include, for example, dry foods and / or fatty foods.

[0044] The term "sterile" in relation to packaging materials and containers refers to a state in which microorganisms have been removed, inactivated, or killed. Examples of microorganisms include bacteria and spores. Generally, when a product is filled aseptically into a packaging container, an aseptic process is used. In order to maintain the sterility during the shelf life of the packaging container, the integrity properties of the package are very important. For the long-term storage of the filled food, and also to preserve the original taste and nutritional value, e.g., vitamin C content, it is important to have a barrier property against gases such as oxygen gas and vapors.

[0045] The term "bulk layer" usually refers to the thickest layer or the layer containing the most material in a multi-layer laminate, i.e. the layer that contributes most to the mechanical properties and dimensional stability of the laminate and the structural stability of the packaging container folded from the laminate, e.g. paper, paperboard or carton. It can also refer to the layer that provides a larger thickness distance in the sandwich structure, which further interacts with stabilizing surface layers with higher Young's modulus on both sides of the bulk layer to achieve sufficient structural stability of the formed packaging container and to achieve structural stability of the formed packaging container.

[0046] OTR was measured on a coulometric sensor-based Oxtran 2 / 21 (Mocon) instrument according to ASTM F1927-14.

[0047] The method for measuring OTR is to determine the amount of oxygen per surface and time unit that passes through a material at a defined temperature, at a given atmospheric pressure, for a fixed period of time, i.e., 20 atmospheres, or 100% oxygen atmosphere expressed as 0.2 atmospheres or 1 atmosphere (oxygen), over a 24-hour period.

[0048] Substrates suitable for the method of the present invention are not limited to any particular type of paper or cellulose, but include any kind of natural cellulose, other cellulose-based substrates based on fibrous or fibrillar cellulose, but the present invention is not applicable to substrates made from plastics or polymers, such as films made from regenerated cellulose.

[0049] a surface smoothness measured according to ISO 8791:4 of 130 ml / min Bendtsen or less, such as 120 ml / min or less, for example 100 ml / min or less, such as 80 ml / min or less, for example 50 ml / min or less, such as 30 ml / min or less, for example 25 ml / min or less, and a Cobb 60 surface water absorption of its coated side (the "top side" or "printed side") of 30 g / m2 measured according to ISO 535:2014. 2The following paper or cellulose-based substrates may perform well in the method for producing a barrier-coated structure according to the invention to produce such a structure under industrially feasible conditions. It is recognized that the combination of process steps carried out at high coating line speeds, as enumerated for coating and producing the barrier-coated cellulose-based substrate of the invention, may improve the barrier properties of different paper substrates, as long as the substrate meets a selected set of characteristic parameters. If the surface roughness, measured by Bendtsen value (ml / min), is too high, the surface of the cellulose-based material will have "valleys" and "peaks", and a thin wet coating of an aqueous solution of a gas-barrier polymer will not be able to fill and level the "valleys" and will not be able to cover the "peaks". As a result, the applied and dried coating of the gas-barrier polymer will not be able to completely cover the surface, resulting in defects detectable by dye staining methods through which oxygen gas molecules may easily permeate. Thus, the contribution of the gas barrier properties due to such defective and insufficient barrier coating will be significantly reduced. Naturally, if the substrate surface is rough, a larger amount of polymer coating will be applied, and it is also possible to apply it at a lower coating line speed. However, when the coating speed is high, there are limitations to the amount of aqueous coating that can be applied, the amount of water that evaporates during the drying operation, and the viscosity and solids content of the aqueous gas barrier polymer solution.

[0050] In one embodiment, a surface roughness of less than 120 ml / min Bendtsen is required, such as 100 ml / min or less, such as 80 ml / min or less, such as 50 ml / min or less, such as 30 ml / min or less, such as 25 ml / min or less. Below 30 ml / min, the substrate surface is practically smooth and has a surface roughness of less than 0.5 g / m 2 Even a thin coating of PVOH can be applied to completely cover and coat a surface.

[0051] The Cobb 60 method according to ISO 535:2014 measures the water absorption of cellulose-based substrates under standardized conditions and in a sense measures the "coverability" of the cellulose-based substrate surface, i.e. its ability to be coated with an aqueous gas barrier polymer composition. If the surface absorbs too much solution before drying, the thinly applied wet coating will break down and will no longer be able to form a continuous coating of gas barrier polymer. Thus, a Cobb 60 value of 30 g / m 2 Less than, for example, 28 g / m 2 Less than 25 g / m 2 It is important that it is less than the following:

[0052] The surface of the upper surface of the cellulose-based substrate has a Bendtsen roughness value of less than 30 ml / min and a surface roughness of less than 25 g / m 2 The following Cobb 60 absorption values ​​may be exhibited:

[0053] To be suitable for the final barrier coating step by the vapor deposition coating process, the cellulose-based substrate must be thin, between 30 and 70 g / m2 measured according to ISO 536:12. 2 , for example 30-60g / m 2 , for example 35-50g / m 2 , for example 35-45g / m 2 and 800 kg / m 3 ~1400 kg / m 3 , e.g. 900~1400kg / m 3 , e.g. 950~1400kg / m 3 For reasons of efficiency and production economy, and to avoid blistering of the coating due to air entrapment in the fibrous, porous cellulose-based substrate during coating and drying operations, a cellulose-based substrate with high density, low weight and low thickness is required. 2 Cellulosic-based substrates of less than this basis weight, when coated with a wet dispersion and then dried, can become mechanically weaker and have reduced dimensional stability, resulting in shrinkage and curl problems.

[0054] Therefore, the basis weight is 30 to 50 g / m 2 , and most preferably 35 to 45 g / m 2 and its density is 900kg / m 3 ~1400kg / m 3 It is more preferred to use a cellulose-based substrate in which

[0055] The thickness of the cellulose-based substrate may be 35-65 μm, such as 35-60 μm, for example 35-50 μm, for example 35-45 μm. In some applications, such as liquid-tight packaging of wet or liquid or viscous products, it is also advantageous to use a high density paper substrate that is as thin as possible, because less polymer is needed in the adjacent liquid-tight or heat-sealable layers while still maintaining the integrity of the package and its heat seals.

[0056] In one embodiment, the surface of the top surface of the paper-based or cellulose-based substrate exhibits a Gurley porosity value according to Tappi T460 om-2 of more than 1000 s / dl, for example more than 2000 s / dl. The advantage of a surface with low porosity is that less of the aqueous solution of the gas barrier polymer is absorbed into the cellulose-based substrate. Since each coating of the aqueous solution of the gas barrier polymer is very thin, this is important for the internal coherence of the coating and for the ability of the coating to form a smooth and uniform surface on which further coatings or layers can be formed.

[0057] Therefore, for a cellulose-based substrate suitable for coating with a thin coating of an aqueous composition of oxygen barrier polymer, the number and size of pores in the substrate should preferably be significantly reduced. The pulp used to manufacture the substrate is extensively refined to increase the degree of fiber bonding, resulting in a reduction in porosity. Greaseproof paper is produced by such extensive refinement and has a sufficiently low porosity to provide a grease barrier. It has therefore been thought that greaseproof paper could potentially be used as a substrate or carrier for gas barrier coatings. However, the resulting pulp has a high resistance to dewatering, requires long stock dewatering times, is costly to manufacture, and is undesirable for repulping or recycling. The same can be said for parchment paper. In the manufacture of parchment paper, the fibers are gelled by passing through a bath of sulfuric acid, which makes the fibers less easily dewatered and pulped, and also makes the parchment paper undesirably brittle.

[0058] According to one embodiment, the cellulose-based substrate for use in the present invention may be formed from cellulose fibers containing at least 50% by dry weight of a chemical pulp, such as kraft or sulfite pulp. Sulfate or sulfite pulp is used to obtain a paper that is strong enough for downstream processes such as coating on high speed lines, as well as lamination and final packaging uses.

[0059] Sulfate / kraft pulps are preferred because they are widely produced in large quantities and have the advantage of improved repulping in recycling and general dewatering of the fibers. Sulfite fibers usually have a high proportion of refined fibers, which may have some adverse effects depending on the proportion and degree of refinement. According to one embodiment of the present invention, kraft pulp is preferred.

[0060] The cellulose-based substrate may be formed from cellulose fibres consisting of 35-100%, such as 35-80%, such as 40-70%, softwood pulp, by dry weight of the pulp used to form the high density paper, the remaining portion of the pulp composition may comprise hardwood fibres and minor amounts of other fibres.

[0061] The advantage of including softwood pulp is improved runnability on the paper machine and increased strength / toughness properties of the resulting paper. A relatively high percentage of softwood pulp allows the cellulose-based substrate to be dense enough without causing problems in dewatering during substrate production, allowing for repulping in recycling operations. The degree of fineness of the fiber composition is further selected to promote both dewatering and repulping capabilities while at the same time promoting the formation of a dense paper with low porosity.

[0062] Thus, although there are some base papers that have intrinsically good oxygen barrier properties, they are less preferred as final materials for other reasons, such as poor recyclability (repulpability), and a significant contribution to the oxygen barrier properties is required from coating materials that are applied to the substrate surface and that bond well to and interact well with the substrate surface.

[0063] To have good mechanical properties for coating at high coating line speeds, such as above 300 m / min, e.g., above 400 m / min, the cellulose-based substrate may have a tensile strength of 3-6 KN / m in MD (machine direction) and 1.5-3.5 KN / m in CD (cross direction). In the present disclosure, the tensile strength is measured according to ISO 1924-3:2005. Thus, a higher tensile strength may indicate a useful paper substrate to withstand web handling forces during coating and lamination operations.

[0064] The cellulose-based substrate may further have a tensile strain in the machine direction of 1.4 to 3.5% and in the CD of 2.1 to 6.0%.

[0065] The cellulose-based substrate also has a mechanical strength of 35 to 90 J / m 2 , 37~140J / m in CD direction 2 The tensile energy may be

[0066] Additionally, the elastic modulus (E Modulus) of the cellulose-based substrate may be between 9500 and 12500 MPa in MD and between 4000 and 7000 MPa in CD.

[0067] Preferably, beneficial barrier and recyclability properties are obtained without sacrificing tensile strength or other mechanical properties.

[0068] It has long been known that in order to provide good gas barrier properties from small amounts of barrier coating material, vapor deposition coatings applied to thicknesses of only nanometers require a thin, defect-free pre-coating of a gas barrier polymer to be applied first onto the paper or cellulose-based substrate to provide additional barrier properties. Such barrier pre-coatings are most effectively selected from vinyl alcohol polymers and copolymers. Such polymers have inherent gas barrier properties, are food safe, recyclable, and are environmentally sustainable in industrial coating and lamination processes. Such polymers are water-dispersible and / or soluble in water and are applied by aqueous "dispersion coating" processes or by so-called "liquid film coating" processes.

[0069] The industrially viable, i.e. high-speed, method suitable for coating the aqueous gas barrier polymer composition of the present invention is any suitable wet roll coating method, such as rotogravure roll coating, smooth roll coating, reverse roll coating or gravure coating in the broad sense. In an advantageous embodiment of the method of the present invention, the aqueous gas barrier polymer composition is applied by reverse gravure coating. The reverse gravure coating method has been shown to make it easier to smooth the coated surface, compared to the forward gravure coating method, which functions as a printing method on the surface of the gas barrier polymer rather than a full coating method.

[0070] Thus, the gas barrier polymer of the aqueous coating composition may be a polymer or copolymer based on vinyl alcohol monomers, such as selected from polyvinyl alcohol (PVOH), ethylene vinyl alcohol copolymers (EVOH), and modified PVOH and EVOH copolymers capable of forming aqueous solutions, such polymers optionally modified, for example, by the addition of carboxyl functional groups.

[0071] In one embodiment, the water soluble gas barrier polymer is PVOH, such as Kuraray's Poval® type PVOH, which provides good film forming properties, gas barrier properties, cost efficiency, food compatibility, and odor barrier properties.

[0072] In another embodiment, the gas barrier polymer is a water-soluble EVOH with a low content of ethylene monomer, such as Kuraray's Exceval® type EVOH. The advantage of using EVOH polymer as a gas barrier material is that the ethylene content supports resistance to humidity, so that oxygen barrier properties are better maintained even at high relative humidity, such as 80% RH. This is particularly relevant for packaging oxygen-sensitive liquids, such as carton laminate packaging for liquid foods.

[0073] Conventional EVOH polymers are typically extrusion grade and have a density of 4 g / m2 It was not possible to disperse or dissolve in aqueous media to produce thin liquid film coating barrier films below 4 g / m2. Water-soluble EVOH has a higher amount of vinyl alcohol monomer units due to its water dispersibility, and has properties as close as possible to liquid film coating grades of PVOH. On the other hand, extruded EVOH layers are inherently less similar to PVOH than EVOH grades for dispersion / solution coating, and can only be applied by melt extrusion coating or melt extrusion lamination as a single layer at a thickness of 4 g / m2. 2 It is not a replacement for liquid film coating EVOH as it cannot be applied in cost-effective amounts.

[0074] PVOH-based gas barrier compositions perform best when the PVOH has a degree of saponification of at least 98 mol%, for example at least 99 mol%, although PVOH with lower degrees of saponification also exhibit oxygen barrier properties. The most advantageous quality and grade of PVOH for the process of the present invention is Poval® 6-98.

[0075] In a further embodiment, the PVOH is Poval® 15-99.

[0076] In yet another embodiment, the PVOH may be Poval® 6-96, although this grade may provide a somewhat lower oxygen barrier.

[0077] Suitable EVOH grades for coating with the method of the present invention include Exceval® 4104 AQ, which has similar coatability to Poval® 6-98, and Exceval® HR-3010, which has similar coatability to Poval® 15-99.

[0078] The solid content of the water-soluble gas barrier polymer is preferably 5-15 wt% so as to be suitable for roll coating application, and can be adjusted to a suitable solid content depending on the selection of EVOH or PVOH and the coating speed. The solid content in the method of the present invention is more preferably 7-13 wt%, for example 9-13 wt%, for example preferably 10-12.5 wt%. At the above solid content of 10%, it has been demonstrated that the best quality PVOH coating, i.e. a uniform, smooth and substantially free of coating defects, can be obtained by reverse gravure coating. More specifically, in combination with PVOH grade Poval® 6-98, better results have been obtained at high coating line speeds of 300 m / min or more, for example 400 m / min or more, for example 600 m / min or more.

[0079] The viscosity of the aqueous gas barrier polymer solution to be coated is preferably 10-120 mPa·s, for example 50-100 mPa·s, which allows optimal pick-up of the gas barrier solution by the gravure roller and further transfer to the substrate surface at high line coating speeds of 300 m / min or more, for example 400 m / min or more, for example 600 m / min or more.

[0080] The barrier pre-coating composition may further comprise a low amount, such as about 1 to about 10 weight percent of an inorganic layered compound, such as calcium carbonate, CaCO3, talc, or exfoliated nanoclay particles, such as bentonite, based on the dry coating weight. In such a case, the barrier layer may comprise about 99 to about 90 weight percent of the polymer, based on the dry coating weight.

[0081] Additives such as dispersion stabilizers may also be included in the gas barrier composition, preferably in an amount of about 1% by weight or less based on the dry coating. The total dry content of the composition is preferably 5-15% by weight, more preferably 7-12% by weight.

[0082] Further possible additives in the barrier pre-coating composition can be polymers or compounds with functional carboxylic acid groups to improve the water vapor and oxygen barrier properties of the PVOH coating. Suitably, such polymers with functional carboxylic acid groups are selected from among ethylene acrylic acid copolymers (EAA) and ethylene methacrylic acid copolymers (EMAA) or mixtures thereof. In one embodiment, such a barrier layer mixture can essentially comprise PVOH, EAA and inorganic layered compounds. The EAA copolymer can be included in the barrier layer in an amount of about 1-20 wt%, such as 1-15 wt%, such as 1-10 wt%, based on the dry coating weight.

[0083] It is believed that increasing the drying temperature leads to an esterification reaction between PVOH and EAA, and the PVOH is crosslinked by the hydrophobic EAA polymer chains and incorporated into the structure of the PVOH, further improving the oxygen and water barrier properties. Crosslinking can also be induced by the presence of polyvalent compounds, e.g. metal compounds such as metal oxides. However, such mixtures are more expensive due to the cost of additives and are not preferred from the standpoint of recyclability.

[0084] Therefore, it is more preferred to use a barrier pre-coating consisting of a pure PVOH or EVOH composition, although advantageous results can also be obtained with gas barrier coatings containing further additives as described above.

[0085] In one embodiment, an aqueous solution of a vinyl alcohol (co)polymer, such as PVOH or EVOH, may, for example, comprise a low amount of n-octanol, such as 0.01-0.1 wt %, as an antifoam additive.

[0086] The gas barrier polymer aqueous solution has a dry weight of 0.5 to 2 g / m 2 The coating is applied uniformly to the top surface of a web of paper or cellulose-based substrate by roll coating to provide a coating of 0.5 g / m 2 If the thickness is less than 2g / m, the gas barrier properties are insufficient. 2Above 0.5 g / m2, coating is not cost-effective for packaging laminates due to the high energy costs and short time to evaporate the liquid (due to high coating line speeds). 2 These PVOHs achieve appreciable oxygen barrier properties, ranging from 0.5 to 2 g / m 2 This coating layer provides a good balance between barrier properties, coating layer quality, and cost. In many cases, a thicker coating of the gas barrier polymer is desired, so at least one additional coating step is added after the first coating layer has dried.

[0087] In the method of the present invention, the gas barrier coating is applied in at least two successive steps with intermediate drying as at least two partial layers. When applied as two partial layers, each layer preferably has a dry weight of 0.5 to 2 g / m 2 , for example 0.5 to 1.5 g / m 2 , for example, preferably 0.5 to 1 g / m 2 0.5-1 g / m2, resulting in a higher quality overall layer from a smaller amount of liquid gas barrier composition. Most preferably, the two partial layers of PVOH are applied in an amount of 0.5-1 g / m2 each. 2 is applied in an amount of

[0088] The amount of wet coating applied is about 10 times the solid target coating applied and dried, and therefore the amount of applied wet coating of PVOH is about 5 to about 20 g / m 2 , for example, about 5 to about 10 g / m 2 and at high coating speeds, a significant amount of water needs to be evaporated in the drying step, as water can interfere with later steps in the coating process and cause defects in the applied barrier coating, thus compromising the coating quality and ultimately reducing the oxygen barrier properties provided by the barrier coated substrate.

[0089] The aqueous solution composition of the gas barrier polymer may be applied by heating at a temperature of 60 to 70° C. By heating to such a warm temperature, the risk of bubbles forming during coating is reduced.

[0090] To further reduce the formation of bubbles or foam in the aqueous gas barrier polymer solution, an antifoam additive can be added. The preferred antifoam agent is n-octanol, which is food safe and has been shown to be effective at lower dosages than the other test agents, e.g., 0.01-0.1% by weight of the solution, e.g., about 0.05% by weight. The other test agents degrade the PVOH and increase the OTR of the applied and dried PVOH coating.

[0091] According to the method of the present invention, it is very important that the wet coating of the aqueous gas barrier polymer solution is dried consistently only at low temperatures, since it is very thin and can be damaged by the application of too strong heat.

[0092] The drying step may be carried out by a hot air dryer, whereby the water evaporates and is blown off the surface of the substrate by air convection. The temperature of the substrate is kept constant during its passage through the dryer at a temperature between 60°C and 95°C or less, such as between 65°C and 90°C or less, such as between 70°C and 90°C or less, such as between 70°C and 85°C, such as between 70°C and 80°C. Drying may be partially assisted by radiant heat from infrared IR lamps in combination with hot air convection drying if necessary at high line speeds.

[0093] The more water added by the wet applied coating, the more it must be evaporated in the dryer at high line speeds. Only 1-2 g / m 2There is a balance between how high the solids concentration of the aqueous coating needs to be to reach a dry, thin coating of 100%. The drying rate must not be too fast, as there is a risk of skin formation, nor too slow, as absorption into the paper would be too high, resulting in a low surface film thickness or the coating breaking down (creating defects). Thus, water evaporation should be controlled to prevent the substrate surface from getting too hot and causing a skin to form.

[0094] Such a balanced setup may be unique for each coating line / paper / coating combination.

[0095] Preferably, the method of the present invention comprises depositing a barrier coating by physical vapor deposition (PVD) onto an initially applied gas barrier pre-coating obtained from a dried aqueous gas barrier polymer solution.

[0096] Such physical vapor deposition coatings may be composed of materials selected from metals, metal oxides, and inorganic oxides.

[0097] In the method of the present invention, the barrier deposition coating is selected from the group consisting of aluminum metallized coatings, aluminum oxide AlOx, and mixed aluminum and AlOx coatings, preferably aluminum metallized coatings.

[0098] Such thin vapor-deposited coating layers are nanometer thick, i.e. most preferably have a thickness countable in nanometers, for example 5-500 nm (50-5000 Å), for example 5-200 nm, more preferably 5-100 nm, for example 5-50 nm.

[0099] Generally, below 5 nm the barrier properties may be too low to be useful, and above 200 nm, e.g. above 100 nm, e.g. above 50 nm, depending on the quality of the vapor deposition coating, the barrier coating may be inflexible and prone to cracking when applied to flexible substrates, and the vapor deposition coating rate may be slower, increasing costs.

[0100] In one embodiment, the barrier deposition coating is applied to a thickness of 10 to 80 nm, such as 10 to 50 nm, for example 10 to 45 nm.

[0101] The vapor-deposited layer, consisting essentially of aluminum metal, may therefore have a thickness of 5-50 nm, more preferably 5-40 nm. This corresponds to less than 1% of the aluminum metal material present in aluminum foils of conventional thickness for packaging, i.e. 6.3 μm. Vapor-deposited metal coatings, while requiring significantly less metal material, provide at best only low levels of oxygen barrier properties and must be combined with further gas barrier materials to provide a final laminate material with sufficient barrier properties. On the other hand, they can also be supplemented with gas barrier layers such as PVOH or EVOH, which do not provide water vapor barrier properties and are rather sensitive to moisture.

[0102] Other examples of vapor-deposited coatings are aluminum oxide (AlOx, Al2O3) and silicon oxide (SiOx) coatings. In general, such PVD coatings are more brittle and may not be suitable for incorporation into packaging materials by lamination. On the other hand, metallized layers, although made by PVD, can obtain mechanical properties more suitable for laminate materials.

[0103] Typically, aluminum metallization layers have a thin surface portion that consists essentially of aluminum oxide due to the nature of the metallization coating process used.

[0104] For the PVD coating process to function optimally, the moisture content of the paper or cellulose-based substrate should be kept between 4-8%. If the paper substrate becomes too dry, the longitudinal edges may curl towards each other, causing problems in coating and handling in the process of the present invention. On the other hand, if the moisture content becomes too high, the deposition coating operation may not function properly and a high quality coating may not be obtained.

[0105] In one embodiment, the aluminum vapor deposition layer is applied to have an optical density (OD) of 1.8 or more, for example, 1.8 to 3.5, for example, 2.0 to 3.0, preferably 2.1 to 2.6. If the optical density is less than 1.8, the barrier properties of the metallized film may be too low.

[0106] The optical density is measured using a densitometer (Macbeth, Tobias, etc.) that uses the principle of diffuse light transmission. This instrument is suitable for measuring the optical density value of aluminum metallized films. The measurement precision and accuracy are high, about ±0.2 OD and about ±0.01 OD, respectively, within the measurement range of 0~6.60 OD.

[0107] Alternatively, laboratory measurements may be performed using a spectrophotometer to measure the light transmittance over the entire visible spectrum (380-800 nm). The optical density can be calculated from the light transmittance (T) value at 560 nm as follows: OD = -log 10 (I / I 10 The calculated value has the same accuracy (±0.2 OD) as that of a light transmittance densitometer.

[0108] Generally, thin coatings of metals or mixtures of metals and metal oxides are used to provide barrier properties to water vapor and prevent water vapor from migrating into and through multilayer films or packaging laminates. Preferably, for the purposes of producing food packaging materials, the metal of the metallized or inorganic metal coating is aluminum (Al).

[0109] The barrier coated paper or cellulose based substrate obtained according to the method of the present invention provides excellent low OTR and low WVTR and proves suitable for lamination into laminate packaging materials and further creasing and sealing such laminate materials into packages.

[0110] A high quality dispersion coating is important and necessary to achieve a high quality subsequent deposition coating, especially when the deposition coating is a metallized coating for high frequency induction heat sealing.

[0111] The laminate packaging material comprising the barrier-coated cellulose-based substrate further comprises a first outermost protective material layer and a second innermost liquid-tight heat-sealable material layer. The second innermost liquid-tight heat-sealable material layer may be made of or comprise a thermoplastic polymer such as a polyolefin polymer. The first outermost protective material layer may be transparent to allow the decorative pattern printed on the outside of the bulk layer to be visible. It may also be made of or comprise a thermoplastic polymer such as a polyolefin polymer.

[0112] The carton-based laminate packaging material for liquid food packaging may further comprise a bulk layer of paper or paperboard, a first outermost protective material layer, a second innermost liquid-tight, heat-sealable material layer, and a barrier-coated paper or cellulose-based substrate disposed inside the bulk layer of paper or paperboard, toward 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.

[0113] In one embodiment, a carton-based laminate packaging material may thus be composed of a bulk layer of paper or paperboard, a first, outermost liquid-tight, heat-sealable polyolefin layer, and a second, innermost liquid-tight, heat-sealable polyolefin layer, said barrier-coated paper or cellulose-based substrate disposed inwardly 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.

[0114] The barrier coated side of the barrier coated paper or cellulose-based substrate is thus oriented toward the second, innermost liquid-tight, heat-sealable layer, and thus the metallized barrier coating is adjacent to the innermost liquid-tight, heat-sealable material layer or layers.

[0115] The paper or paperboard bulk layer used in the present invention typically has a thickness of about 100 μm to about 600 μm and a surface weight of about 100 to 500 g / m 2 , preferably about 200 to 300 g / m 2 and may be any conventional paper or paperboard of suitable packaging quality.

[0116] For low-cost, long-term, aseptic packaging of liquid foods, thinner packaging laminates with thinner paper core layers can be used. Packages made from such packaging laminates are more like pillow-shaped flexible pouches rather than collapsible. Papers suitable for pouch packaging typically have a surface weight of about 50 to about 140 g / m2. 2 , preferably about 70 to about 120 g / m 2 , more preferably about 70 to about 110 g / m 2 Since the barrier-coated paper or cellulose-based substrate of the method of the present invention may itself contribute some stability to the laminate material, the paper layer representing the "bulk" layer may be thinner and interact in a sandwich manner with the barrier-coated cellulose-based substrate to produce a laminate packaging material that also has the desired mechanical properties.

[0117] The barrier coated paper or cellulose-based substrate may be bonded to the bulk layer by an intermediate adhesive, or a thermoplastic polymeric bonding layer, which bonds the uncoated surface of the barrier coated paper to the bulk layer. According to one embodiment, the bonding layer may be a polyolefin layer, such as a layer of a polyethylene-based polyolefin copolymer or blend, particularly one containing a majority of ethylene monomer units. The bonding layer may be bonded 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 advancing through a lamination roller nip, thereby providing a laminate structure by extrusion lamination.

[0118] In another embodiment, the barrier coated cellulose-based substrate may be adhered to the bulk layer by wet applying an aqueous dispersion of an adhesive composition containing an adhesive polymer binder to one of the web surfaces to be laminated and pressing the two paper webs together while advancing them through a lamination roller nip, thereby providing a laminate structure by wet lamination. The moisture of the aqueous adhesive composition is absorbed into the fibrous cellulose network of the two cellulosic layers and partially evaporates over time during the subsequent lamination process. Thus, no forced drying step is required.

[0119] The aqueous adhesive polymeric binder may be 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 the best environmental and sustainability profile, adhesive binders derived from plants or non-fossil sources are preferred.

[0120] Suitable thermoplastics for the outermost and innermost heat-sealable liquid-tight layers are polyolefins such as homopolymers or copolymers of polyethylene and polypropylene, preferably polyethylene, more preferably polyethylene selected from the group consisting of low density polyethylene (LDPE), linear LDPE (LLDPE), metallocene catalyzed linear low density polyethylene (m-LLDPE) and blends or copolymers thereof. According to one embodiment, the first outermost protective and liquid-tight layer is LDPE and the second innermost heat-sealable liquid-tight layer is a blend composition of m-LLDPE and LDPE for optimal lamination and heat sealing properties.

[0121] The same thermoplastic polyolefin-based materials, particularly polyethylene, listed for the first outermost and second innermost layers are also suitable as adhesive layers within the laminate material, i.e., between a bulk or core layer, such as paper or paperboard, and a barrier film or sheet. In one embodiment, the thermoplastic inner bonding layer can be a polyolefin layer, e.g., a polyethylene layer, such as a low density polyethylene (LDPE) layer.

[0122] In a further embodiment, the second innermost liquid-tight heat-sealable polyolefin layer is a prefabricated film of the same or similar polyolefins as described above, i.e. LDPE, LLDPE and / or m-LLDPE, for example a biaxially oriented film with at least one layer dominated by LLDPE polymer, in order to improve the robustness of the mechanical properties of the packaging material. Due to the manufacturing process in film blowing and film casting operations, and optionally the subsequent film orientation operation step, the polymer of such a film acquires properties different from those possible from the (co)extrusion coated polyolefin layers. Such prefabricated, preferably oriented, polymer films can contribute to the mechanical robustness of the laminate packaging material and to the mechanical strength and packaging integrity of the packaging containers formed and filled from the laminate packaging material.

[0123] According to alternative embodiments, suitable adhesive or tie layers in the interior of the laminate material, for example between a bulk or core layer and a barrier-coated cellulose-based substrate, or between an outer heat-sealable layer and a barrier-coated paper substrate, may be so-called adhesive thermoplastic polymers, for example modified polyolefins, mainly based on LDPE or LLDPE copolymers, or graft copolymers with functional group-containing monomer units, such as carboxyl or glycidyl functional groups, for example (meth)acrylic acid monomers or maleic anhydride monomers (i.e. ethylene acrylic acid copolymers (EAA) or ethylene methacrylic acid copolymers (MAH)). For example, (meth)acrylic acid monomers or maleic anhydride (MAH) monomers (i.e. ethylene acrylic acid copolymers (EAA) or ethylene methacrylic acid copolymers (EMAA)), ethylene-glycidyl (meth)acrylate copolymers (EG(M)A) or MAH-grafted polyethylene (MAH-g-PE). Another example of such modified or adhesive polymers are so-called ionomers or ionomeric polymers. Preferably, the modified polyolefin is an ethylene acrylic acid copolymer (EAA) or an ethylene methacrylic acid copolymer (EMAA).

[0124] The application of a further vapor deposition coating to the gas barrier coated cellulose-based substrate imparts water vapor barrier properties to the barrier coated substrate, so that it is typically not necessary to add further layers of gas or water vapor barrier material to the overall laminate structure of the packaging material for liquid carton packaging.

[0125] However, in another embodiment, the gas barrier coated cellulose-based substrate, i.e., the substrate coated only with the aqueous gas barrier solution, may be laminated to a further water vapor barrier material by an adjacent adhesive layer instead of being directly coated with a water vapor barrier material. Thus, the gas barrier coated paper substrate may be adhered with its barrier coated side to a prefabricated polymer film having a metal or metal oxide vapor deposition coating. Thus, the vapor deposition coated side of the prefabricated film is bonded towards the gas barrier coated paper substrate. The adhesive layer may be a polymer or binder applied by melt extrusion lamination or wet adhesive lamination as described above. The prefabricated film polymer substrate may further comprise a heat sealable polymer layer on its opposite side, which may participate in the heat sealing operation of the laminate packaging material. Alternatively, a separately applied heat sealable polymer may further be coated on the inside of the prefabricated film to form a second innermost liquid-tight heat sealable layer of the laminate packaging material. In this manner, a separately produced barrier-coated base paper and a barrier-coated pre-manufactured polymer film can be combined into a laminated packaging material, which also functions effectively to protect oxygen-sensitive products from high exposure to oxygen under high humidity conditions, such as 80-90% relative humidity in the laminated packaging material.

[0126] The laminate packaging material may, according to different specific embodiments, have a pre-manufactured polymeric film substrate laminated to the inside of the barrier-coated paper substrate, i.e., on the side of the paper substrate opposite to that laminated to the bulk layer, where the polymer composition of the pre-manufactured polymeric film, instead of being vapor-deposited with a metal or metal oxide coating, also includes an inorganic layered compound to impart vapor barrier properties to the pre-manufactured polymeric film. Such a filled polymeric film can protect the gas barrier coating on the barrier-coated paper even under conditions of high moisture content in the material (such as packaging for oxygen-sensitive liquid products).

[0127] For best oxygen and water vapor barrier properties, it is most advantageous and preferred to directly vapor-deposition coat the gas barrier polymer coating with a metal or metal oxide coating.

[0128] The laminate packaging material produced according to the above provides good adhesion and interaction between adjacent layers in the laminate structure, and good quality of the gas barrier coating and the vapor deposition barrier coating, thereby providing good integrity when transformed into a filled packaging container. An important conclusion, especially in packaging for liquids and wet foods, is that the interlayer adhesion within the laminate packaging material, as well as the oxygen gas barrier properties, can be maintained even under wet packaging conditions.

[0129] According to further embodiments, packaging containers formed from the laminated packaging material may be partially sealed, filled with a liquid or semi-liquid food product, and then sealed by sealing the packaging material itself, optionally in combination with a plastic opening or package top.

[0130] In conclusion, the improved barrier properties provided by the barrier coated cellulose-based substrates defined by the present invention and laminate packaging materials comprising same result in robust and reliable packages for shelf-stable liquid food packaging. The laminate packaging material structure performs better for forming into a folded and formed package due to both the improved adhesion between the substrate and the barrier material coating and the improved contribution to gas barrier properties from the barrier coated substrate itself.

[0131] ( Examples and Description of the Preferred Embodiments Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. [Brief description of the drawings]

[0132] [Figure 1a] FIG. 1 is a schematic cross-sectional view of an example of a gas barrier coated cellulose-based substrate produced by a method according to the present invention. [Figure 1b] FIG. 2 shows a schematic representation of a further example of a gas- and water-vapor-barrier coated cellulose-based substrate produced by a method according to the invention. [Figure 2a] FIG. 1b is a schematic cross-sectional view of a laminated packaging material comprising the barrier-coated cellulose-based substrate of FIG. 1a. [Figure 2b] FIG. 1b is a schematic cross-sectional view of a laminate packaging material comprising the barrier-coated cellulose-based substrate of FIG. [Figure 2c] FIG. 1c shows a further laminate packaging material comprising the barrier-coated cellulose-based substrate of FIG. [Figure 3a] FIG. 1 is a schematic diagram showing a method for dispersion coating a gas barrier coating composition onto a cellulose-based substrate. [Figure 3b] FIG. 2 is a schematic diagram illustrating a method for melt (co)extrusion coating a layer of a thermoplastic heat-sealable liquid-tight polymer onto a web substrate to form the innermost and outermost layers of the packaging laminate of the present invention. [Figure 4] FIG. 1 is a perspective view of a plant for physical vapor deposition (PVD) coating a web substrate using solid metal evaporation flakes. [Figure 5a] FIG. 2 is a diagram showing a typical example of a packaging container manufactured from a laminate packaging material according to the present invention. [Figure 5b] FIG. 2 is a diagram showing a typical example of a packaging container manufactured from a laminate packaging material according to the present invention. [Figure 5c] FIG. 2 is a diagram showing a typical example of a packaging container manufactured from a laminate packaging material according to the present invention. [Figure 6] FIG. 1 illustrates the principle of how packaging containers are produced from packaging laminates in a continuous, roll-fed, form, fill and seal process. [Figure 7a] 1 shows the quality results of wet-applied water gas barrier coatings from comparative coating tests. [Figure 7b] 1 shows the quality results of wet-applied water gas barrier coatings from comparative coating tests. [Figure 7c] 1 shows the quality results of wet-applied water gas barrier coatings from comparative coating tests. [Figure 7d] 1 shows the quality results of wet-applied water gas barrier coatings from comparative coating tests. [Figure 7e] 1 shows the quality results of wet-applied water gas barrier coatings from comparative coating tests. [Figure 7f] 1 shows the quality results of wet-applied water gas barrier coatings from comparative coating tests. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0133] Working Example Various paper substrates were coated with PVOH aqueous solutions under various conditions at high line speeds of 300 m / min or more, e.g., 400 m / min to 600 m / min, to verify that uniform, defect-free coatings could be achieved with the aim of imparting reliable oxygen gas barrier properties to paper substrates under industrially viable manufacturing conditions. While this was possible in preliminary coating experiments at pilot and lab scales, significant problems arose when scaled up to industrial speeds.

[0134] At industrial line speeds, two main interrelated problems arose. First, increasing the line speed in the drying step with hot air convection dryers did not allow enough time for the evaporation of the large amount of water applied by the aqueous wet coating composition. As a result, the moisture content in the gas barrier coated substrate could become too high, such as over 8% by weight, which could cause problems in subsequent operations involving high temperatures, such as deposition coating and other heat lamination processes. Second, as the line speed through the dryer increases, the temperature of the drying operation also needs to be increased, which translates into higher heat loads on the wet applied coating and higher temperatures on the paper substrate, which overall promotes the formation of coating defects such as coating skin formation, bubbling, pinholes, and inhomogeneous and inconsistent material in the coating. It was therefore important to balance the effects of the coating and manufacturing process variations and identify robust settings and parameters that would work for water-gas barrier coatings on high speed coating lines.

[0135] During the experiments, several underlying causes of defect formation at high speed lines were identified. The applied wet coating must, on the one hand, not be too thick or heavy, and on the other hand, cover the substrate surface well to allow the formation of a uniform, defect-free dry coating. The surface properties of the paper substrate support or hinder the formation of an oxygen-tight dry polymer coating of PVOH or EVOH from a thinly applied aqueous polymer solution. Rough and highly absorbent substrate surfaces require high wet coating application rates, which are contrary to the desire for coating at high speed lines. Higher amounts of applied water, and the associated higher moisture content in the structure, further adversely affect the ability of the paper substrate to be subsequently coated and / or laminated. The need for higher line speeds, together with the increased need for more severe temperatures acting on the coated substrate, hinder the drying operation. High temperatures have a negative effect on both the paper substrate and the coating. As a result, it was concluded that in general high speed coating is better suited to paper substrates with high density and smooth surfaces. Furthermore, the basis weight of the paper should be as low as possible, as long as the web has sufficient mechanical strength. A lower basis weight for the paper substrate has positive effects on subsequent vapor deposition coating steps and on laminate materials later in the value chain, for example when folded into packaging, resulting in less distortion.

[0136] ( Example 1) Three high density paper substrates were coated with a gas barrier coating layer of PVOH using different process parameters and compared with the results of coating in a similar manner. A web of paper substrate was coated on top of each at a speed of about 400 m / min. A first wet coating of an aqueous solution of PVOH Poval® 6-98, having a solids content of about 10% by weight and a viscosity of about 50 mPa·s, was applied by reverse gravure coating at a rate of about 8 g / m2, as measured gravimetrically. 2The wet-coated substrate was then sent to a drying station where hot air was applied to the wet substrate to evaporate the water, and the temperature of the drying tunnel and air was carefully regulated so that the temperature of the substrate surface was kept below 85-90°C. After drying in this way, the coating thickness was 0.8 g / m 2 A second coating of the same weight was applied over the dried first coating in the same manner and then dried to give a dry weight of 1.6 g / m2 together with the first coating. 2 This provided a perfect gas barrier coating of PVOH.

[0137] The PVOH coatings of (Table 1) were applied under optimized coating conditions as defined in claim 1 attached hereto.

[0138] At the same time, the moisture content of the paper substrate was controlled by a drying operation to be within 4-8% by weight so that the next step of the aluminum metallization coating by physical vapor deposition could be performed without glitches or defects. For the papers tested, it was found that when the moisture content was below 4% by weight, the paper substrate had a tendency to "curl", i.e., to roll up in the cross web direction, and the machine direction web tended to form a paper tube.

[0139] The uniform, smooth surface of the dried gas barrier coating in this manner allows for a higher quality vapor deposition coating that is coherent, homogeneous and pinhole-free, and adheres well to the dried gas barrier coating surface.

[0140] Thus, a thin aluminum coating was applied to the surface of the second PVOH coating by passing through a PVD metallizer to a thickness of about 50 nm and an optical density of about 2.5 as measured by a light transmission densitometer.

[0141] The barrier coated paper substrate was then laminated to the same packaging laminate construction according to the following procedure. / / Outer layer 12g / m 2LDPE / Duplex CLC 80mN, Paperboard bulk layer / 20g / m 2 LDPE / barrier coated paper substrate (as listed in Table 1) / 6g / m 2 EAA adhesive polymer / 13~20g / m 2 LDPE / 17gsm LLDPE film / /

[0142] [Table 1]

[0143] Duplex CLC board is a conventional clay-coated board in which the innermost liquid-tight, heat-sealable layer was made from a prefabricated cast biaxially oriented film with at least one layer of predominantly linear low density polyethylene (LLDPE). The barrier-coated side of the paper substrate was oriented toward the inside in the laminate structure (corresponding to the inside of a package manufactured from the laminate material). The paperboard bulk layer was laminated to the barrier-coated paper by melt-extrusion laminating LDPE polymer between the paperboard bulk layer and the two webs of barrier-coated paper substrate to be joined in a chilled laminating roller nip. A layer of adhesive polymer EAA and LDPE adjacent the inside was coextrusion laminated between the barrier-coated paper and the innermost prefabricated film comprising LLDPE. An outermost layer of LDPE, which is oriented toward the outside of the laminate and the package made therefrom, was extrusion coated onto the outside of the paperboard.

[0144] Oxygen permeability measurements were made using an Oxtran Mocon 2 / 21 instrument (a coulometric sensor-based instrument) at 23°C, 50% and 80% RH (relative humidity) and measurements are reported in cc / m2 over 24 hours in 0.2 atm oxygen gas (i.e. 1 atm air). 2 Reported in units of

[0145] Paper A has a smooth surface and is approximately 40 g / m 2 and has a Cobb 60 absorption value of 22 g / m 2It was a high density calendar paper with good coatability and a fairly low viscosity.

[0146] Paper B was a fairly dense, low-porosity paper with a density of 1055 and a basis weight of about 45, and also had a smooth, non-absorbent surface, suitable for coating with the aqueous polymer solution.

[0147] Paper C was a much less porous and less smooth paper with a similar density to Paper A. It was composed of highly refined fibres and fibrils, with the pores between the long fibres being filled with smaller cellulose components. This unfortunately made the paper brittle and unsuitable for use in flexible laminates for folding carton packaging. Paper C, despite its high density, had a high Cobb 60 absorption value and a less smooth surface than Papers A and B.

[0148] All of the paper substrates A to C were calendered to give them higher density and surface smoothness.

[0149] For comparison, we coated Paper D, a more porous and less dense paper substrate, but still with a fairly smooth surface of the glassine type, so that finer cellulose fibers and fibrils are also involved in “closing” its upper surface.

[0150] From the above coating and lamination tests, it was concluded that for paper substrates with high surface roughness such as that for Paper C, a larger coating amount needs to be applied to form a gas barrier coating from the PVOH aqueous solution of uniform thickness without defects and further reduce the oxygen transmission rate. Thus, this test showed that OTR does not significantly improve the oxygen barrier property. On the other hand, Paper C had a very high intrinsic oxygen barrier property, i.e., a low OTR, when laminated to the same laminate structure in the same way without the barrier coating. This intrinsic barrier property of Paper C is obtained by a combination of cellulose fibrils and fines filling the fiber structure and the paper being supercalendered, resulting in a very dense paper with a very low porosity. In previous pilot laboratory tests, Paper C had a gas barrier of 0.2 cc / m2 at 23°C, 0.2 atm, and 50% RH. 2 It was confirmed that it was possible to coat paper to very low total gas barrier values, such as 1.6 g / m2 for 24 h, but industrial tests confirmed that such low values ​​could not be reached at industrial speeds, i.e. 400 m / min and 600 m / min, and that to reach the lowest possible OTR a starch pre-coating was first required before applying the PVOH gas barrier coating. From these tests it was concluded that the surface of Paper C was too rough and required an additional smoothing pre-coating; in this example it was only 1.6 g / m2. 2 It was shown that a thin coating of PVOH of 100% does not result in a robust and reliable coating without defects. The oxygen transmission rate remained at the same level as for uncoated Paper C. In any case, Paper C was not selected due to other disadvantages, such as less suitable mechanical and recycling properties, derived from the high content of highly refined cellulose components. It was also previously concluded that for paper substrates with a high surface roughness to be coated, it is better to first smooth the surface by pre-coating with a smoothing substance, e.g. starch, which has much lower or no intrinsic gas barrier properties.

[0151] Previous studies have concluded that when coated papers with good barrier properties are measured at 50% RH, laminates using only PVOH coated paper have OTR values ​​less than two times higher than those using PVOH coated paper that has been further metallized. Also, OTR measurements at 80% RH for laminate samples containing metallized coatings have shown that, as long as the coating quality is good, the effects of different paper grades are leveled out and the oxygen barrier results remain at the same high level (i.e., approximately the same low OTR value). On the other hand, when the OTR of the same packaging laminate using only PVOH coated paper substrate is measured at 50% RH and 80% RH, the moisture sensitivity of the gas barrier polymers (PVOH, EVOH, starch, etc.) increases the OTR by a factor of 4-10 at 80% RH (0.2 atm oxygen, 23 degrees Celsius).

[0152] Table 1 further shows how the quality of the gas barrier polymer coating was ranked for the different papers based on an internal test method for detecting defects in the barrier coating after a second aqueous coating and subsequent drying step. The virtually defect-free polymer barrier coating ensured a further defect-free or even defect-free aluminum metallized coating by a subsequent optional physical vapor deposition coating step. The quality of the aluminum metallized coating was evaluated by observing its surface with a SEM microscope and measuring the final oxygen transmission rate (OTR) values ​​obtained for the laminated materials.

[0153] ( Example 2 ) FIG. 7 shows the evaluation of the effect of the method steps and coating conditions in the coating method of the present invention. The parameters compared in this example were the maximum temperature of the cellulose-based substrate surface during the drying operation and the solids content of the aqueous gas barrier solution composition. The defects in the PVOH coating were visualized by applying a solvent-based (non-aqueous) colorant composition, which showed defects where the PVOH coating was damaged. Such defects were clearly visible to the naked eye because the colorant solution penetrated through the holes in the PVOH coating, reached the surface of the paperboard and colored in dots or blots. The colorant composition includes a solvent, a non-ionic surfactant, and an oil-soluble organic red dye. The test samples were dried, cleaned, and free of interfering substances (fats, grease, etc.). The colorant solution was applied to the application surface of the paper substrate, completely covering the sample area, and then left for about 10 minutes. Afterwards, the traces of the defects thus colored were inspected and counted / estimated.

[0154] Figure 7 shows an example of the evaluation of a series of comparative coating tests at a coating line speed of 400 m / min, varying the maximum drying temperature on the substrate surface and only the solids content of the aqueous PVOH solution, to show the effect of these features on the quality of the applied PVOH coating. For the paper substrate samples tested in this way, an aqueous PVOH solution (Poval® 6-98) was applied at 0.8 g / m 2 After two-step coating with aqueous PVOH solutions of 1000g each and drying after each coating, photographs were taken at different maximum surface temperatures. Typically, the maximum surface temperature is reached at the end of each drying operation, i.e., at the end of the drying step for each drying zone.

[0155] Therefore, in the coating method of Figure 7a, the temperature of the substrate surface never exceeded 60°C and the solid content of PVOH was set to 10 wt%. As shown in Figure 7a, a nicely coated surface was obtained with only a few color spots resulting from the stain test, indicating small holes in the dried coating where the stain solution had passed through to stain the coated paperboard surface. However, the moisture content of the coated paper substrate was quite high and was at the limit suitable for the next step of the option of metallization by PVD coating.

[0156] Similarly, the PVOH solution had the same composition and solids content for the coating methods performed on the coated papers shown in Figures 7b to 7e by increasing the maximum drying temperature on the substrate surface, whereas in Figure 7f the solids content was increased while keeping the maximum temperature constant compared to the coating operation in Figure 7e.

[0157] Thus, in Figure 7b, the drying temperature was increased to a maximum of 70°C, which resulted in a decrease in moisture content while still showing a low number of defect indications. In the method of Figure 7c, the maximum temperature was kept below 80°C, which still showed a low number of defect indications, but the moisture content of the paper substrate was reduced to a more favorable 4.5%.

[0158] Moreover, in the method related to Fig. 7d, the maximum temperature on the paper substrate surface was increased to 90 °C, and the number of defects was also very low. The increase in drying temperature reduced the moisture content of the paper to 3.9 wt%, which was the lower limit at which the paper substrate tended to curl, i.e., roll up in the MD.

[0159] In the method related to Figure 7e and Figure 7f, the temperature was kept slightly below the too high surface temperature of 115 °C, which resulted in a significant increase in defects in both coating samples. The coating sample in Figure 7f was the worst and also had a high solids content of 12.5% ​​in the PVOH coating solution. Meanwhile, the coating sample in Figure 7e was slightly better, but still unacceptable as a gas barrier coating. Additionally, samples Figure 7e and Figure 7f caused the paper substrate to dry and curl.

[0160] Thus, it was found that the maximum temperature should not exceed 95°C in order to balance the moisture content of the barrier coated paper substrate, and if such drying conditions could be maintained, few defects would be obtained. A maximum drying temperature of just under 80-90°C seemed optimal to keep the moisture content in the substrate low, but in balance, with as few defects as possible. All the coated samples related to Figures 7a, 7b, 7c and 7d had very few defects, i.e., within 1 dm 2 There were less than 10 colored dots per sheet. For the coated paper in Figure 7e and Figure 7f, the moisture content was too low and curling of the paper was observed. The results obtained with the method in Figure 7e and Figure 7f were considered unacceptable with rank 4 being "very poor" compared to the ranks in (Table 1).

[0161] It should be noted that generally, what is seen as a few or many dots or defect indications is a failure of the oxygen barrier coating, regardless of the material used, i.e., each color dot or spot represents a point of oxygen penetration through the coating and the barrier coated cellulose-based substrate.

[0162] Table 1 further shows the ranking of the paper substrates with regard to their recyclability, i.e. their repulpability. The repulpability was tested by the Valmet repulping method on a Valmet pulper HD400. This method involves cutting 0.5 kg of air-dried paper substrate into pieces of 0.04 x 0.10 m and repulping them with 15 liters of water in a Valmet pulper at 42°C and a rotation speed of 50 Hz for 7.5 minutes. The dewatering ability of the pulped samples, the appearance and feel of the cellulose remaining in the filter were investigated. The repulpability was evaluated from the appearance of the pulp and the handsheets.

[0163] Paper A was well repulped, with almost no paper debris in the pulp or handsheets. Fiber clumps were observed in the handsheets, which is evidence of long fibers. Long fibers are excellent in terms of recyclability.

[0164] Paper C was completely repulped. The pulp was thicker than the other varieties, and no large pieces of paper were found in the pulp. The amount of short fibers was high from the beginning, and the fibers after repulping were very refined. The refined fibers and fines clogged the filters in the sheet making machine, which made it very slow to produce handsheets.

[0165] Paper D showed relatively poor repulping results. Paper chips were found in both the pulp and the handsheet. The handsheet contained more short fibers than the other papers.

[0166] The internal relative rankings between the samples were assigned in the order of 1 to 4. As a result, Papers C and D turned out to be not as good as expected, even though they were selected for this characteristic.

[0167] Laminated packaging materials as produced in the configuration described above in connection with Table 1 were further evaluated in limited filler testing for forming, filling and sealing into filled packages. During testing, no significant issues were identified with respect to package integrity (i.e., tightness of the package to the surrounding environment) and sealability characteristics, and therefore the testing was deemed successful.

[0168] It was further concluded that a laminate construction having a prefabricated heat-sealable film on the inside of a barrier-coated paper substrate is advantageous in terms of the mechanical robustness of the laminate packaging material and the packaging containers produced therefrom by heat sealing.

[0169] Further, with respect to the accompanying drawings: An example of a barrier coated cellulose-based substrate 10a produced by the method of the present invention is shown in cross-section in Figure 1a. The cellulose-based substrate 11 has a surface area of ​​900 kg / m 3 Density of over 40g / m 2 grammage, a top surface roughness Bentsen value of less than 30 ml / min, and 25 g / m 2The paper has a Cobb 60 value of less than 0.25 and is provided with a first gas barrier coating 12a of PVOH, which is Poval® 6-98 from Kuraray Co., which is applied in the form of an aqueous solution by reverse gravure coating and then baked at 80-85°C to evaporate the water from the wet coating. The resulting PVOH gas barrier coating has a dry weight of about 0.8 g / m 2 The paper substrate was then coated with a second gas barrier coating 12b of the same PVOH solution, Poval® 6-98 from Kuraray, on the dried surface of the first gas barrier coating 12a. The gas barrier coating layer 12b was similarly coated and dried, with the dry weight of the second PVOH gas barrier coating also being about 0.8 g / m2. 2 . At least a further layer or coating 13 of a protective polymer is optionally applied on the second coating layer 12b of PVOH, since the gas barrier coating of PVOH is sensitive to moisture, dirt and liquids. The further layer or coating 13 may be a thermoplastic polymer, such as a polyolefin, such as LPDE. Such a further layer is usually necessary to measure the oxygen transmission rate of the barrier-coated cellulose-based substrate, to cover defects such as pinholes in the first PVOH coating. The idea here is that since the coating has no or only minor defects, it should not actually be necessary to provide a further layer of polymer on the barrier coating. In any case, the further polymer layer or coating itself does not have inherent oxygen barrier properties and therefore does not further contribute to the measured oxygen transmission rate value. The further layer or coating 18 of the protective polymer may be of the same or different type as the coating or layer 13, and may optionally be applied on the opposite side of the cellulose-based substrate. As a result, a simple laminate material 10a can be obtained by simply adding the outermost protective polymer layers 13 and 18 to the barrier-coated cellulose-based substrate.

[0170] In Fig. 1b, a further example of a barrier-coated cellulose-based substrate 10b produced by the method of the present invention is shown in cross section. The same PVOH first and second gas barrier coatings are applied on the same cellulose-based substrate 11 in the same manner as described above in relation to Fig. 1a. The thus gas-barrier-coated cellulose-based substrate is then vapor-coated on the dry surface of the second gas barrier coating 12b with an aluminum vapor-deposition coating 14, i.e., an aluminum vapor-deposition layer, applied by physical vapor deposition to an optical density of about 2 and a thickness of about 40 nm. Optionally, at least a further layer or coating 13 of a protective polymer is applied on the metallized coating layer of aluminum 14 in a manner similar to that described above in Fig. 1a. The further layer or coating 13 may be a thermoplastic polymer, such as a polyolefin, such as LPDE. A further layer or coating 18 of a protective polymer may be of the same or different type as the coating or layer 13 and may also be applied on the other side of the cellulose-based substrate (not shown). As a result, a simple laminate material 10b can be obtained by simply adding outermost protective polymer layers 13 and 18 (not shown) to the barrier coated cellulose-based substrate.

[0171] In Fig. 2a, a laminated packaging material 20a for packaging oxygen sensitive products, such as for liquid carton packaging, is shown, which comprises a barrier coated cellulose-based substrate 25a (10b in Fig. 1b) produced by the method of the present invention. The laminated material has a bending force of 80mN and a strength of about 200g / m 2The packaging laminate further comprises a bulk layer 21a of paperboard having a basis weight of 100 g / m2 and an outermost protective layer, for example a liquid-tight, heat-sealable polymer layer 22a, applied to the outside of the bulk layer 21a, which is directed towards the outside of the packaging container produced from the packaging laminate. This layer 22a is transparent to allow a printed decorative pattern 27a printed on the bulk layer of paper or paperboard to be seen on the outside. This allows the printed pattern to inform the contents of the package, the packaging brand and other information targeted to consumers in retail establishments and food stores. The polymer of the outermost layer 22a may be a polyolefin such as a conventional low density polyethylene (LDPE) of heat-sealable quality, but may also include further similar polymers including LLDPE. The application weight is about 12 g / m2. 2 The innermost liquid-tight heat-sealable layer 23a is located opposite the bulk layer 21a, this layer being directed towards the inside of the packaging container produced from the packaging laminate. It will form a strong transverse heat seal of the liquid packaging container produced from the laminate packaging material. The innermost heat-sealable layer 23a thus comprises one or more combinations of polyethylenes selected from the group consisting of LDPE, linear low density polyethylene (LLDPE) and LLDPE produced by polymerizing ethylene monomers with C4-C8, more preferably C6-C8, α-olefin alkylene monomers in the presence of a metallocene catalyst, the so-called metallocene-LLDPE (m-LLDPE). It has a density of about 22 g / m 2 It is.

[0172] The bulk layer 21a is laminated to the uncoated side, i.e. 25a, of the barrier coated paper substrate 10b from Fig. 1b by an intermediate bonding layer 26a of low density polyethylene (LDPE). The intermediate bonding layer 26a is formed by melt extrusion as a thin molten curtain of polymer between the two paper webs, so that the bulk layer and the barrier coated paper substrate are laminated together when all three layers pass through a chilled press roller nip. The thickness of the intermediate bonding layer 26a is 12-18 μm, e.g. 12-15 μm.

[0173] The innermost heat-sealable layer 23a may consist of one layer or may comprise two or more partial layers of the same or different types of LDPE or LLDPE or blends thereof, with a density of several g / m 2 , for example 4 to 7 g / m 2 The innermost heat sealable layer is well adhered to the metallized barrier deposition coated surface 14 of the barrier coated paper substrate 10b by an intermediate coextrusion tie layer 24a, for example of ethylene acrylic acid copolymer (EAA), which bonds the innermost heat sealable layer to the barrier coated paper substrate 10b when the layers are applied together in a single melt coextrusion coating step.

[0174] 2b shows another embodiment of a laminate packaging material 20b comprising a barrier-coated cellulose-based substrate 25b produced by the method of the present invention. The laminate material has a bending force of 80mN and a compressibility of about 200g / m 2 and an outer liquid-tight, heat-sealable layer 22b of polyolefin applied to the outside of bulk layer 21b, which layer will face the outside of a package produced from the packaging laminate. The polyolefin of outer layer 22b is a conventional low density polyethylene (LDPE) of heat-sealable quality, having a basis weight of 12 g / m 2 100%, but may comprise further similar polymers including LLDPE. The innermost liquid-tight heat-sealable layer 23b is disposed opposite the bulk layer 21b, this layer being directed towards the inside of a packaging container made from the packaging laminate. The innermost heat-sealable layer 23b, which forms a strong heat seal for a liquid packaging container made from the laminate packaging material, comprises one or more combinations of polyethylenes selected from the group consisting of LDPE, linear low density polyethylene (LLDPE), and LLDPE made by polymerizing ethylene monomers with C4-C8, more preferably C6-C8, α-olefin alkylene monomers in the presence of a metallocene catalyst, so-called metallocene-LLDPE (m-LLDPE).

[0175] The bulk layer 21b is laminated to the barrier-coated paper substrate 25b, i.e. 10b, described in Fig. 1b, by wet lamination with an intermediate adhesive layer 26b, a thin layer of adhesive polymer, obtained by applying an aqueous dispersion of polyvinyl acetate adhesive to one of the surfaces to be bonded to each other and then pressing them together in a roller nip. This lamination step is carried out in an efficient cold or ambient lamination step at industrial speeds, without energy-consuming drying operations required to promote the evaporation of water. The dry coating weight of the intermediate adhesive layer 26b is 3-4 g / m 2 This means that only the addition of water is required and no drying or evaporation is required.

[0176] Thus, the amount of thermoplastic polymer in this laminate layer can be significantly reduced as compared to the conventional polyethylene melt extruded laminate adhesive layer 26a described in Figure 2a.

[0177] According to a preferred embodiment, the innermost heat-sealable liquid-tight layer 23b comprises a prefabricated oriented film comprising at least one partial layer with a major proportion of linear low density polyethylene (LLDPE), which may further comprise a portion of LDPE.

[0178] The prefabricated film is laminated to the vapor-deposited barrier coating surface, i.e., the aluminum metallization surface, of the barrier-coated paper substrate by means of an intermediate melt-extruded laminate tie layer portion comprising an EAA tie layer, also used in the laminate of FIG. 2a, and / or an LDPE tie layer 24b having a thickness of 12-20 μm, e.g. 12-18 μm.

[0179] In an alternative embodiment, the pre-manufactured film 23b' is laminated by a separate wet lamination step with a water-based adhesive of acrylic (co)polymer adhesive layer 24b' at ambient (low) temperature with a thickness of 3-4 g / m 2 may be laminated to the metallized coating in an amount of

[0180] Further embodiments are also disclosed herein which have all of the described features and combine them with the features of an innermost heat sealable film configuration 23, 23b' having the melt extruded bulk layer lamination layer 26a of FIG. 2a, but which is instead applied by either melt extrusion lamination means with layer 24b, or by wet lamination means 24b' with a water-based adhesive, as described in connection with FIG. 2b.

[0181] Yet another embodiment combining a thin wet water-based adhesive dispersion laminate layer 26b of FIG. 2b with conventional melt coextrusion coated inner layers 24a and 23a is also contemplated and disclosed herein.

[0182] In Fig. 2c, a further embodiment of a laminate packaging material 20c is shown, which comprises a barrier-coated cellulose-based substrate 25c produced by the method of the present invention, i.e., 10a according to Fig. 1a. Such a gas-barrier-coated cellulose-based substrate is not further coated with a vapor-deposited water vapor barrier layer, but instead, in a laminate packaging material, the barrier-coated cellulose-based substrate can be complemented by laminating, on its inner side, a vapor-deposited coated pre-manufactured polymer film 28c. Thus, the laminate packaging material 20c has the same types of layers as the corresponding layers in Fig. 2a or 2b described above, i.e., a bulk layer of paperboard 21c, an outermost protective polymer layer 22c, and an inner laminate layer 26c.

[0183] The prefabricated polymer film 28c comprises a polymer film substrate 28a and a vapor deposition coating of aluminum metallized and / or aluminum oxide. This prefabricated vapor deposition coated film 28c is laminated to the gas barrier coated cellulose-based substrate 25c by an intermediate bonding layer 29c, such as a melt extrusion laminate layer. The prefabricated polymer film may comprise a heat sealable layer for the innermost surface of the laminate material 20c. Alternatively, further inner layers 23c, 24c are melt coextrusion coated onto the inside of the prefabricated film 28c.

[0184] In FIG. 3a, an aqueous dispersion coating process 30a is shown, which can be used to apply the aqueous composition of the gas barrier polymer coating layers 12a and 12b. A paper substrate web 31a (e.g., cellulose-based substrate 11 in FIG. 1a and FIG. 1b) is fed to a dispersion coating station 32a, where the aqueous composition is applied by rollers to the top surface of the substrate. When the two sides of the substrate have different surfaces, there is usually one side that is suitable for receiving a coating or a printed decorative pattern, and therefore this is the side that is coated for the present invention (this side is called the top or printed side). Since the composition has an aqueous content of 80-99% by weight, there is a large amount of water present on the wet coated substrate, which is dried and evaporated by heat to form a continuous coating that is homogeneous and has uniform quality in terms of barrier and surface properties, i.e. uniformity and low occurrence of defects. Drying is performed by a hot air dryer 33a, which evaporates and removes water from the substrate surface. The temperature of the substrate surface as it passes through the dryer is consistently maintained below 95°C, such as between 60 and 95°C, such as between 70 and 90°C, such as between 80 and 90°C, such as below about 85°C.

[0185] The resulting gas barrier coated paper substrate web 34a is cooled and wound onto reels for intermediate storage. Optionally, at a next or subsequent stage, the thus coated web may be sent to a further coating process for physical vapor deposition coating of the barrier vapor deposition coating 14 onto the gas barrier coated paper.

[0186] FIG. 3b illustrates the process of the final lamination step in the manufacture of the packaging laminate 20a, 20b or 20c of FIGS. 2a, 2b and 2c, respectively, after a bulk layer 21a, 21b, 21c has first been laminated to the barrier coated cellulose-based substrate 10a of FIG. 1a (i.e., 25a or 25b of FIGS. 2a and 2b), or to the barrier coated substrate 10b of FIG. 1b (25c).

[0187] As explained in connection with Figures 2a and 2b, the bulk layer paperboard 21a; 21b can be laminated to the barrier coated paper substrate 10a; 25a; 25b by wet cold water-based adhesive lamination or by melt extrusion lamination. The wet lamination adhesive may be applied as explained in Figure 3a in connection with dispersion coating, and lamination is performed by simply pressing the surfaces to be joined together without forcing the adhesive composition to dry. The main method of melt extrusion lamination is as shown in Figure 3b below.

[0188] The resulting paper prelaminate web 31b is transported from an intermediate storage reel or directly from a lamination station for laminating the bulk layer prelaminate to a barrier-coated cellulosic substrate. The non-laminate side, i.e. the printed side, of the bulk layer 21a; 21b is melt extrusion coated in a cooled roller nip 33 by bonding with a molten polymer curtain 32 of LDPE forming the outermost layer 22a; 22b of the laminate material, the LDPE being extruded from an extruder feedblock and tie layer 32b. The prelaminate bulk paper web with the outermost layer 22a; 22b coated on the printed side, i.e. on the outside, then passes through a second extruder feedblock and tie layer 34b and a lamination nip 35 where the molten polymer curtain 34 is bonded and coated on the other side of the prelaminate, i.e. the barrier-coated side of the paper substrate 10; 25a; 25b. Thus, the innermost heat-sealable layer 23a, optionally together with a tie layer of adhesive polymer having functional groups to enhance its adhesive ability with adjacent layers, is coextrusion coated onto the inside of the paper prelaminate web to finally form the laminate wrapper 20a;36, which is wound up onto a storage reel (not shown).

[0189] These two co-extrusion steps in the lamination roller nips 33 and 35 may alternatively be performed as two successive steps in the reverse order.

[0190] According to another embodiment, one or both of the outermost layers can instead be applied in separate pre-lamination stations, in which case a co-extrusion coating layer is first applied to the outside of the (printed) bulk paperboard layer and then applied onto the metallized coating of the barrier coated paper substrate, and finally, the two pre-lamination paper webs are then laminated together as described above.

[0191] According to another embodiment, the innermost layer of the heat-sealable, liquid-tight thermoplastic resin layer is applied in the form of a pre-fabricated film that is laminated to the coated surface of the barrier-coated paper substrate 10a; 10b; 25a, 25b.

[0192] As described in relation to Figures 2a and 2b, such an innermost layer 23a; 23b, 23b' may be laminated to the barrier-coated paper substrate 10a by a melt extrusion lamination method or by a wet cold water-based adhesive lamination method.

[0193] FIG. 4 is a perspective view of an example of a physical vapor deposition (PVD) plant for, for example, aluminium metal coating onto a web substrate of the invention. A gas barrier coated paper substrate 44 is passed through a deposition chamber and on its gas barrier coated side is subjected to continuous deposition 40 of evaporated aluminium to form a metallised layer of aluminium, or to a mixture of oxygen and aluminium vapour to form a vapour deposition coating of aluminium oxide. The coating is applied to a thickness of 5-100 nm, preferably 10-50 nm, forming the barrier coated paper 43 of the invention. The aluminium vapour is formed by ion bombardment of a solid piece of aluminium 41 onto an evaporation source. In the case of aluminium oxide coating, oxygen gas may be injected into the plasma chamber through an inlet port.

[0194] FIG. 5a shows an embodiment of a packaging container 50a made from a packaging laminate according to the invention. This packaging container is particularly suitable for beverages, sauces, soups, etc. Typically, such packaging containers have a volume of about 100-1000 ml. It may be of any shape, but is preferably brick-shaped, with vertical and horizontal seals 51a and 52a, respectively, and optionally an opening device 53. In another embodiment, not shown, the packaging container may be wedge-shaped. To obtain such a "wedge shape", only the bottom of the package is folded, and the bottom horizontal heat seal is formed to be hidden under a triangular corner flap that is folded and sealed against the bottom of the package. The top horizontal seal remains unfolded. In this way, the packaging container, only partially folded, remains easy to handle and dimensionally stable enough to be placed on a shelf in a food store or on a flat surface.

[0195] Figure 5b shows an alternative packaging container 50b made from an alternative packaging laminate according to the invention, which is not dimensionally stable enough to form a parallelepiped or wedge shaped package due to the thin paper bulk layer, and no creases are formed after transverse seal 52b, and the package remains a pillow-like bag, and is sold and distributed in this form.

[0196] Figure 5c shows a gable-top package 50c that is folded and formed from a pre-cut sheet or blank of a laminate packaging material comprising a bulk layer of paperboard and a barrier-coated paper substrate of the present invention. Flat-top packages may also be formed from similar blank materials.

[0197] Fig. 5d shows a bottle-like package 50d, which is a combination of a sleeve 54 formed from a pre-cut blank of the laminate packaging material of the present invention and a top 55 formed by injection molding of plastic in combination with an opening device such as a screw cork. Packages of this kind are sold, for example, under the trade names Tetra Top® and Tetra Evero®. These special packages are formed by fitting a molded top 55 with an opening device in a closed state to a cylindrical sleeve 54 of laminate packaging material, sterilizing the bottle-top capsule thus formed, filling it with food, and finally folding and sealing the bottom of the package.

[0198] 6 illustrates the principle described at the beginning of this application: a web of packaging material is formed into a tube 61 by overlapping the longitudinal ends 62, 62' of the web and heat sealing them together to form an overlap joint 63. The tube is continuously filled 64 with the liquid food product to be filled and divided into individual filled packages by repeating double transverse sealing 65 of the tube at predetermined intervals below the level of the filled contents in the tube. The packages 66 are separated by cutting between the double transverse seals (top and bottom seals) and finally formed into the desired geometric shape by forming folds along crease lines prepared in the material.

[0199] Finally, it should be noted that the present invention is not limited to the embodiments shown and described above, but may be modified within the scope of the appended claims.

Claims

1. 1. A method for producing a barrier coated paper or cellulose-based substrate (10a; 10b) for packaging oxygen-sensitive products, said method comprising the steps of: a) conveying a web of paper or cellulose-based substrate at a line speed of 300 m / min or greater; The paper or cellulose-based substrate web has a basis weight of 30 to 70 g / m2 measured in accordance with ISO 536:2012. ２ and a density measured in accordance with ISO 534:2021 of 800 to 1400 kg / m ３ and the surface of the upper side of the paper or cellulose-based substrate has a Bendsen roughness value measured according to ISO 8791:4 of less than 130 ml / min and a Cobb value 60 measured according to ISO 535 of less than 30 g / m ２ is as follows: b) providing an aqueous gas barrier polymer solution selected from vinyl alcohol polymers, PVOH, ethylene vinyl alcohol copolymers, EVOH, and modified PVOH and EVOH polymers, having a solids content of 5 to 15 wt. % and a viscosity of 10 to 120 mPa·s; c) 0.5 to 2 g / m2 in dry weight ２ applying said aqueous gas barrier polymer solution to the top surface of a web of paper or cellulose-based substrate by a roll coating method to provide a uniform coating in an amount of d) drying the water-gas barrier polymer coating applied in step c) while maintaining the temperature of the web substrate surface at 60°C to less than 95°C; e) repeating steps c) and d) at least once; and f) optionally further coating the dried web substrate coated with the aqueous gas barrier polymer solution obtained in step e) with a nanometer-thick barrier vapor deposition coating of a metal and / or metal oxide by physical vapor deposition; resulting in a barrier-coated paper or cellulose-based substrate having minimal defects in the gas barrier coating and the metal and / or metal oxide vapor-deposited coating. method.

2. The roll coating method is a gravure rotation coating method such as a reverse gravure coating method. The method of claim 1.

3. The aqueous solution of PVOH or EVOH has a solids content of 7 to 13 wt. %. The method of claim 1.

4. The aqueous solution of PVOH or EVOH has a viscosity of 50 to 100 mPa s. The method of claim 1.

5. the surface of the upper surface of the paper-based or cellulose-based substrate exhibits a Bendtsen roughness value of less than 120 ml / min; The method of claim 1.

6. The surface of the upper surface of the paper or cellulose-based substrate has a Bendtsen roughness value of less than 30 ml / min and a roughness of less than 25 g / m ２ The following Cobb 60 absorption values ​​are shown: The method of claim 1.

7. The steps c) and d) are repeated once in step e), and in each coating step, a coating weight of 0.5 to 1 g / m2 is applied. ２ The coating is applied in an amount of The method of claim 1.

8. In step d), the temperature of the surface of the web substrate is maintained at 65°C to less than 95°C. The method of claim 1.

9. the barrier vapor deposition coating (14) is an aluminum metallized coating, the coating being applied to have an optical density OD of 1.8 or greater; The method of claim 1.

10. -9+ the surface of the upper side of the paper or cellulose-based substrate exhibits a Gurley porosity value of greater than 1000 s / d1 according to Tappi T460 om-2; The method of claim 1.

11. The paper or cellulose-based substrate web has a thickness of 30 to 60 g / m ２ having a basis weight of The method of claim 1.

12. The gas barrier polymer is selected from the group consisting of PVOH types having a saponification degree of at least 98 mol%. The method of claim 1.

13. 20a; 20b; 20c) comprising a barrier-coated cellulose-based substrate (11-12; 11-12-14; 25a; 25b; 25c) produced by the method of claim 1, a first outermost protective material layer (22a, 22b; 22c); a second, innermost liquid-tight, heat-sealable material layer (23a; 23b; 23b'; 23c); The laminate packaging material has an oxygen transmission rate of 0.5 cm when measured according to ASTM F1927-14. ３ / m ２ , 24 hours, 0.2 atmospheres oxygen, 50% RH or less oxygen transmission rate, the oxygen barrier is provided by the barrier-coated paper or cellulose-based substrate when laminated; Laminated packaging material (10a; 10b; 20a; 20b; 20c).

14. the second, innermost liquid-tight, heat-sealable material layer (23a; 23b; 23b'; 23c) is selected from the group consisting of thermoplastic polymers, such as polyolefin polymers, such as polyethylene from the low density range, such as LDPE, LLDPE, m-LLDPE, and any blend of two or more thereof, The laminate packaging material of claim 13.

15. wherein both the first outermost protective material layer (22a; 22b; 22c) and the second innermost liquid-tight heat-sealable material layer (23a; 23b; 23b'; 23c) comprise a thermoplastic polymer, such as a polyolefin polymer, such as polyethylene; The laminate packaging material of claim 13.

16. a bulk layer (21 a; 21 b; 21 c) of said paper or paperboard or other cellulosic material; and said barrier coated cellulose-based substrate (10 a; 10 b; 25 a; 25 b; 25 c) disposed inside said bulk layer of paper or paperboard and between said bulk layer and said second, innermost liquid-tight, heat-sealable material layer (23 a; 23 b; 23 b'; 23 c), The laminate packaging material of claim 13.

17. the barrier-coated cellulose-based substrates (10a; 10b; 25a; 25b; 25c) are bonded together by an intermediate tie layer (26a; 26b, 26c) comprising an adhesive from an aqueous composition comprising a binder selected from the group consisting of acrylic polymers and copolymers, starch, cellulose and polysaccharide derivatives, polymers and copolymers of vinyl acetate and / or vinyl alcohol, 17. The laminate packaging material of claim 16.

18. the second, innermost liquid-tight, heat-sealable polyolefin layer (23a; 23b; 23b'; 23c) is a pre-fabricated polyolefin film, such as a biaxially oriented polyethylene film comprising at least one layer having a majority of LLDPE polymer to improve the robustness of the mechanical properties of the laminate packaging material; The laminate packaging material of claim 14.

19. A packaging container (50a; 50b; 50c; 50d) comprising the laminate packaging material of claim 13.

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