Barrier-coated cellulose substrate for laminated packaging materials

Abstract

A laminate packaging material (10a) for packaging liquid or semi-liquid food products comprises: a bulk layer (11) made of cellulosic material, preferably paper or paperboard; a first outermost liquid-tight, heat-sealable thermoplastic layer (12) arranged outside the bulk layer and constituting the exterior of the package formed from the packaging material; a second, innermost liquid-tight, heat-sealable thermoplastic layer (13) placed inside the bulk layer so as to be in direct contact with the filled food product; a barrier layer (14) comprising a barrier substrate layer (14b) coated with a physical vapor deposition (PVD) barrier coating comprising partially oxidized aluminum, the barrier coating having a thickness of 8-40 nm and a transmittance of 20-60%, the barrier layer being laminated between the bulk layer and a second, innermost liquid-tight, heat-sealable thermoplastic layer.

Description

[Technical Field]

[0001] The present invention relates to a laminate packaging material.

[0002] Furthermore, the present invention relates to a method for producing a laminate packaging material, a packaging container including the laminate packaging material, and a method for producing a packaging container. [Background technology]

[0003] Single-serve packaging for liquid foods is often manufactured from paperboard or carton-based packaging laminates. One such commonly used packaging is sold under the trademark "Tetra Brik Aseptic" (registered trademark) and is primarily used for the aseptic packaging of liquid foods, such as milk and fruit juice, that are sold for extended shelf life. The packaging material of this known packaging is a laminate including a bulk or core layer of paper or paperboard and an outer liquid-tight layer of thermoplastic plastic. To make the packaging gas-tight, particularly oxygen-tight, for purposes such as aseptic packaging or packaging of milk or fruit juice, the laminates of these packaging usually include at least one additional layer, most commonly aluminum foil.

[0004] On the inside of the laminate, i.e., the side of the container made from the laminate intended to face the filled food contents, there is an innermost layer coated on the aluminum foil, which innermost layer comprises one or more sub-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.

[0005] Packaging containers are typically produced by modern high-speed packaging machines that form, fill, and seal packages from webs of packaging material or prefabricated blanks. Packaging containers can be produced by joining the longitudinal edges of a web of laminate packaging material together at overlapping joints by welding together inner and outer heat-sealable thermoplastic polymer layers, converting the web 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 predetermined distances from each other below the level of the contents within 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 scoring the packaging material along pre-prepared crease lines.

[0006] The main advantage of this continuous tube forming, filling and sealing packaging 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 produced under clean conditions in which the filled liquid contents and the packaging material itself are reduced in bacteria, there is no risk of microbial growth in the filled product, and the filled packages can be stored for long periods, even at ambient temperatures. Another important advantage of Tetra Brik® type packaging processes is that, as mentioned above, continuous high-speed packaging is possible, which has a significant impact on cost efficiency.

[0007] Packaging containers for sensitive liquid foods, such as milk or juice, can be manufactured from sheet blanks or pre-assembled blanks of the laminate packaging material of the present invention. Packages are manufactured from flat-folded tubular blanks of the packaging laminate by first assembling the blanks to form an open tubular container capsule, and then closing one open end of the tubular container capsule by folding and heat-sealing an integral end panel. The closed container capsule is then filled with a food product, such as juice, through the other open end, and then closed by further folding and heat-sealing the corresponding integral end panel. Examples of packaging containers manufactured from sheet and tubular blanks include conventional gable-top packages. These types of packages also include those with molded plastic tops and / or screw caps.

[0008] The aluminum foil (also called Alufoil) layer of packaging laminates provides significantly better gas barrier properties than other gas barrier materials. At their performance levels, traditional aluminum foil-based packaging laminates for aseptic packaging of liquid foods are the most cost-effective packaging materials available on the market today. Summary of the Invention [Problem to be solved by the invention]

[0009] Other materials that compete with aluminum 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.

[0010] In an effort to develop non-aluminum foil materials for liquid food carton packaging, it would be desirable to develop pre-manufactured films or sheets with high levels of multi-barrier functionality (i.e., oxygen and gas barrier properties as well as water vapor, chemical and / or aroma barrier properties) to replace conventional aluminum foil barrier materials, and to make such films or sheets compatible with conventional aluminum foil processes for lamination and manufacturing. Such films or sheets may be barrier coated, for example, by vapor deposition coating.

[0011] Such barrier films typically have at least one drawback compared to conventional aluminum foil when used in liquid paperboard packaging for liquid foods. One significant drawback is the high cost and / or complex manufacturing process of such barrier films. Another drawback is that when converted into laminated packaging materials, the lamination process becomes complicated, making them unable to directly replace aluminum foil.

[0012] One type of vapor-deposited coating that often has some barrier properties, particularly water vapor barrier properties, is the so-called metallized coating, for example an aluminum metal physical vapor deposition (PVD) coating.

[0013] Such vapor-deposited layers, consisting essentially of aluminum metal, may have a thickness of 10-30 nm, which corresponds to less than 1% of the aluminum metal material present in conventional thicknesses of aluminum foil for packaging, i.e., 6.3 μm. While vapor-deposited metal coatings require little metal material, they have a lower level of oxygen barrier and may need to be combined with additional gas barrier materials to provide a final laminate material with sufficient barrier properties. On the other hand, they may complement additional gas barrier layers and provide good water vapor barrier properties. Pure aluminum coatings have a metallic appearance that makes them visually indistinguishable from foil-based packaging materials.

[0014] Other examples of vapor-deposited coatings are aluminum oxide (AlOx, Al2O3) and silicon oxide (SiOx) coatings. Such coatings may also be applied by physical vapor deposition. Aluminum oxide (AlOx) coatings are transparent and have good oxygen barrier properties. However, the coatings are very brittle. AlOx coatings are disclosed, for example, in the applicant's WO 2009 / 112255.

[0015] Other coatings may be applied by plasma-enhanced chemical vapor deposition (PECVD), in which vapors of compounds are deposited on a substrate in a more or less oxidizing environment. For example, silicon oxide coatings (SiOx) may be applied by a PECVD process.

[0016] EP 437946 to Bowater Packaging Limited discloses a web material for producing microwave-safe pouches for packaging oxygen- and / or moisture-sensitive substances. The material comprises a web substrate coated with a coating consisting of a uniform mixture of metal and metal oxide, with the amount of metal being low so that the coated substrate is microwave-transparent. The material is produced by a reactive evaporation process, in which a controlled amount of oxygen-containing gas is introduced into a stream of evaporating metal, causing the mixture to deposit on the substrate. The material is formed into a pouch. In an example, the coating weight is about 0.1 g / m. 2 For microwaveable products, the maximum final optical density of the coating is listed as 0.25, which corresponds to a minimum transmission of 56%. [Means for solving the problem]

[0017] According to a first aspect of the present invention, there is provided a laminate packaging material for packaging liquid or semi-liquid food products, the laminate packaging material comprising: a bulk layer made of a cellulosic material, preferably paper or paperboard; - a first outermost liquid-tight heat-sealable thermoplastic layer disposed outside the bulk layer and constituting the exterior of a package formed from the packaging material; - a second, innermost liquid-tight, heat-sealable thermoplastic layer disposed inside the bulk layer and in direct contact with the filled food product; a barrier layer comprising a barrier substrate layer coated with a physical vapor deposition (PVD) barrier coating comprising partially oxidized aluminum; The barrier coating has a thickness of 8-40 nm and a transmittance of 20-60%, and the barrier layer is laminated between the bulk layer and a second, innermost liquid-tight, heat-sealable thermoplastic layer.

[0018] According to a second aspect, there is provided a method for producing the laminate packaging material of the present invention. The method for producing the laminate packaging material of the present invention is the method for producing the laminate packaging material described above, comprising: - laminating a barrier layer inside the bulk layer; - applying a first outermost liquid-tight heat-sealable thermoplastic layer to the exterior of the bulk layer and a second innermost liquid-tight heat-sealable thermoplastic layer to the interior of the barrier layer; in any order.

[0019] According to a third aspect, there is provided a packaging container for liquid or semi-liquid food, comprising the laminate packaging material described above.

[0020] According to a fourth aspect, there is provided a method of forming a packaging container as described above, the method comprising folding a laminate packaging material.

[0021] (Detailed explanation) The laminate packaging material of the present invention comprises a barrier substrate layer, which comprises a barrier layer and a partial aluminum oxide barrier coating on the barrier substrate layer.

[0022] The barrier coating is applied to the surface of the barrier substrate layer by physical vapor deposition (PVD) involving reactive evaporation. The reactants are aluminum and oxygen, which are supplied to the PVD process in the appropriate ratio so that the aluminum is only partially oxidized. A PVD apparatus (also referred to herein as a plant) with a coating zone is used.

[0023] Aluminum is preferably supplied to the PVD process in the coating zone by a wire feed. However, other methods of supplying aluminum, such as pans, are also possible. This has the advantage of reducing maintenance costs. This is called induction evaporation. As a further alternative, an electron beam gun can be used to evaporate an aluminum slab placed in a cooled crucible. High-energy bombardment heats the aluminum source to a temperature where it melts and vaporizes. Electron beam evaporation is primarily used for ceramic coating, but can also be used for metallization.

[0024] Oxygen is supplied to the PVD process in the coating zone as a gas, preferably via an injection nozzle.

[0025] Preferably, plasma-enhanced reactive evaporation of aluminum in combination with oxygen is used, in which case the use of a mixture of oxygen and a noble gas (e.g., argon) helps to stabilize the plasma discharge and / or improve the coating density.

[0026] The partially oxidized aluminum has an overall stoichiometry between Al and Al2O3. Preferably, the partially oxidized aluminum comprises a ceramic-metal (cer-met) composite of aluminum particles and Al2O3. The aluminum particles can be visualized by TEM, as described in the Examples below.

[0027] Without wishing to be bound by theory, the inventors believe that the growth of aluminum clusters into TEM visible particles is influenced not only by the aluminum to oxygen ratio in the reactive deposition PVD process, but also by process parameters such as coating line speed (higher coating line speeds are expected to result in smaller particles).

[0028] Additionally, performing reactive evaporation in the presence of a plasma (ie, plasma-assisted reactive evaporation) is believed to affect particle size growth by producing smaller particles.

[0029] The coating thickness is in the range of 8 (or 10) to 40 nm. A preferred coating thickness is 15 nm or more and / or 30 nm or less (more preferably 25 nm or less). If the coating thickness is too thin, defects such as pinholes may occur, which may reduce the oxygen barrier properties. If the coating thickness is too thick, the coating may become brittle, and cracks may occur when the barrier layer is subjected to mechanical treatments such as extrusion coating or folding. Such cracks also lead to a reduction in the oxygen barrier properties.

[0030] However, when the barrier substrate layer is a polyolefin, the thickness of the barrier coating is preferably 15 nm or less, since polyolefin is a soft polymer and therefore a barrier coating formed on a polyolefin substrate layer is particularly susceptible to cracking.

[0031] Preferably, the barrier coating has a non-metallic appearance. The coating is typically gray or brown. Coatings with a final transmittance of less than 20% have been found to have a metallic appearance, which is undesirable. Coatings with a transmittance greater than 20% have not had a metallic appearance after lamination, especially when unbleached board is used as the bulk layer. Preferably, the transmittance of the barrier layer is 25-60%, more preferably 30-60%. A transmittance greater than 60% results in poor oxygen barrier properties.

[0032] The barrier substrate layer may comprise a polymeric film or a cellulosic material.

[0033] A typical thickness of the polymeric film barrier substrate layer is from 6 to 30 μm, for example from 8 to 20 μm, such as 12 μm.

[0034] The polymeric film barrier substrate layer is preferably a prefabricated oriented film, such as a blown film or a cast-oriented film. Both types of prefabricated films are produced by extruding a molten composition into a sheet and then stretching it into a fairly thin but stable film. This prevents the film from shrinking or deteriorating due to environmental changes or aging. The orientation of the film can be uniaxial, i.e., in the machine direction, or biaxial, in both the machine direction (MD) and the cross direction (CD).

[0035] The polymeric film barrier substrate layer is preferably a polyester or polyolefin.

[0036] The polyester is preferably polyethylene terephthalate (PET). Monoaxially oriented PET (MOPET) and biaxially oriented PET (BOPET) are particularly preferred. Mitsubishi RNK12.0 2 is an example of a suitable BOPET film having a thickness of 12 μm.

[0037] Polyethylene (PE, eg HDPE, MDPE and / or LLDPE, and optionally films containing small amounts of LDPE) and polypropylene (PP, eg BOPP) are preferred polyolefins.

[0038] Films are designed according to their end use and their components (polymer grades) are selected to meet specific requirements such as mechanical performance, sealability, printability, coating acceptance, puncture resistance, and / or tear strength.

[0039] A suitable film design will contain at least three layers (and in some cases up to five), with one specific PE layer in the core to ensure stiffness and thermal stability, and other grades selected to provide enhanced coating receptive layers or sealants.

[0040] Suitable film materials include the base polymer films described on pages 17-19 of WO2009 / 112255.

[0041] When the barrier substrate layer comprises a cellulosic material, it is preferably paper, for example of the type described in WO 2022 / 117462. Preferably, the paper is thin, for example 30-60 g / m 2 (gsm) and high density, e.g. at least 900 kg / m 3 Preferably, the paper is pre-coated, for example with starch and / or PVOH, to give it a smooth surface.

[0042] Improved adhesion and gas barrier properties can be partially achieved by ion bombardment in a surface treatment process to activate the surface before coating. Such surface activation treatments include corona, plasma, atmospheric plasma during film production, and in-line plasma pretreatment before the coating process. Such processes are described in US8048532B2, US10569515b2, and WO2020155795a1. Therefore, the surface of the barrier substrate layer to be PVD-coated is preferably pretreated with plasma and / or corona. Corona treatment is typically performed during film production. Plasma pretreatment may use oxygen, nitrogen, argon, and / or neon plasma; oxygen / argon and neon / argon are examples of suitable plasma mixtures. The plasma may be triggered by alternating or direct current. Pretreatment is particularly important for polyolefin films.

[0043] It has also been found that similar improvements can be achieved by post-treating the barrier-coated substrate layer with a plasma after the barrier coating has been applied. Post-treatment is useful for oxidizing the surface of the coating and / or removing aluminum hydroxide from the surface of the coating, which can cause poor adhesion to adjacent layers. Post-treatment using nitrogen mixed with the plasma gas is preferred.

[0044] To ensure the best possible results in terms of OTR and adhesion, films may be both pre-treated and post-treated. The pre-treatment and post-treatment may be the same or different. Barrier-coated films may alternatively be post-treated only, with similar improvements.

[0045] Pre- and post-treatment of the surfaces of the film substrate and the barrier coating, respectively, may be carried out in the same PVD apparatus as the barrier coating itself, using different (or the same) gas compositions in pre-plasma and / or post-plasma zones. Each such zone preferably has a different pressure than the coating zone and is separated from the coating zone by a suitable arrangement. Plasma treatment may be carried out by magnetron plasma or inductively coupled plasma arrangements.

[0046] Surface treatments may be performed in separate plasma chambers of the device. These are very short duration plasma treatments, lasting only a few milliseconds on the surface.

[0047] Preferably, the barrier coating of the barrier layer is adjacent to the bulk layer, but the barrier layer may be oriented in either direction when laminated to the packaging material. The uncoated side of the barrier substrate layer may be laminated to the polyolefin layer via an adjacent adhesive layer of a primer or adhesion-promoting layer to improve adhesion between the layers in the laminate.

[0048] The laminate packaging material further comprises a first outermost liquid-tight heat-sealable polyolefin layer and a second innermost liquid-tight heat-sealable polyolefin layer. 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), single-site catalyst metallocene polyethylene (m-LLDPE or mPE), and blends or copolymers thereof. According to a preferred embodiment, the outermost heat-sealable liquid-tight layer is LDPE, and the innermost heat-sealable liquid-tight layer is a blend composition of m-LLDPE and LDPE to obtain optimal lamination and heat-sealing properties.

[0049] The thickness of the innermost heat-sealable layer is 15 to 45 g / m 2 , for example, 25 to 35 g / m 2 The thickness of the outermost heat-sealable layer may be 10 to 20 g / m 2 Thicknesses vary depending on the type of polymer used as the sealant and the integrity requirements. Typically, m-LLDPE can be downgauged up to 50% compared to LDPE.

[0050] The bulk layer of cellulosic material is typically 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 packaging container folded from the laminate. Typically, the bulk layer comprises paper, paperboard, or carton. Preferably, the bulk layer has a bending strength of 320 mN. The bulk layer may also be a layer that provides a larger thickness distance in the sandwich structure, further interacting with stabilizing facing layers with higher Young's moduli on both sides of the bulk layer to achieve sufficient mechanical properties and dimensional stability. The barrier substrate layer may be such a stabilizing facing layer, especially in the case of paper.

[0051] The paper or paperboard bulk layer used in the present invention typically has a thickness of from about 100 μm to about 600 μm and a weight of from about 100 to 500 g / m 2 , preferably about 200 to 300 g / m 2 The packaging laminate may be conventional paper or paperboard of suitable packaging quality, having a surface weight of about 1000 g / m². For low-cost, aseptic, long-term packaging of liquid foods, thinner packaging laminates with thinner paper core layers may be used. Packages made from such packaging laminates are not collapsible, but rather resemble pillow-shaped flexible pouches, as further described below in connection with Figure 5b. Paper suitable for such pouch packages is typically 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 has a surface weight of

[0052] The barrier layer may be bonded to the bulk layer by an intermediate adhesive, or a thermoplastic polymer adhesive layer, or a so-called laminating layer, thus bonding the barrier layer to the inner surface of the bulk layer (the inner surface being the direction toward the interior of a packaging container made from the material). The bonding / laminating layer may be a polyolefin layer or a layer of a polyethylene-based polyolefin copolymer or polyethylene blend containing a majority of ethylene monomer units. Preferably, the bulk layer is bonded to the barrier layer by melt-extrusion laminating the bonding polymer layer between the bulk layer web and the barrier layer web and simultaneously pressing the three material layers together while advancing them through a lamination roller nip, thus providing a laminate structure, i.e., by extrusion laminating the bulk layer to the barrier layer.

[0053] The same thermoplastic polyolefin-based materials, particularly polyethylene, listed for the outermost and innermost layers may be suitable for the adhesive layer within the laminate material, i.e., between the bulk layer, such as paper or paperboard, and the barrier layer. In one embodiment, the thermoplastic adhesive layer may be a polyethylene layer, such as a low-density polyethylene (LDPE) layer.

[0054] The packaging container is preferably of the type described below in connection with Figure 5. The packaging container may be made partly or entirely from a laminate packaging material.

[0055] Folding of the laminate packaging material and other steps to form the package include mechanical manipulation of the barrier layer.

[0056] The packaging container is formed from laminated packaging material, partially sealed, filled with a liquid or semi-liquid food product, and then finally sealed completely by sealing the packaging material itself, and optionally in combination with a plastic opening or package top.

[0057] Preferably, the laminate packaging material has an oxygen transmission rate of 5 cm , especially when BOPET is used as the barrier substrate layer. 3 / m 2 / 24h / atm or less, preferably 2cm 3 / m 2 / 24h / atm is less than.

[0058] (definition) In the context of the present invention, the term "long-term shelf life" means that the packaging container is capable of preserving the quality of the packaged food, i.e., nutritional value, hygienic safety and taste, for at least 1-2 months, such as at least 3 months, preferably 6 months, such as 12 months or more, under ambient temperature conditions.

[0059] The term "package integrity" generally refers to the tightness of the package, i.e., the resistance of the package to leakage or breakage. More specifically, it defines the resistance of the package to the ingress of microorganisms such as bacteria, dirt, and other substances that may deteriorate the food product contained therein and shorten the expected shelf life of the package.

[0060] "Liquid or semi-liquid food" generally refers to food that is flowable and optionally contains food particles. Viscous foods are also included. Non-limiting examples of contemplated foods include dairy products, milk, soy, rice, grain, seed drinks, fruit juice, nectar, carbonated drinks, energy drinks, sports drinks, coffee or tea drinks, coconut water, wine, soups, purees, jalapeños, tomatoes, sauces (such as pasta sauce), legumes, olive oil, etc.

[0061] The term "sterility" in relation to packaging materials and containers refers to a condition in which microorganisms are removed, inactivated, or killed. Examples of microorganisms include bacteria and spores. Aseptic processes are generally used when products are aseptically packaged in packaging containers. The integrity characteristics of the package are crucial to maintaining sterility throughout the package's shelf life. For the long-term storage of the packaged food, and to preserve the original taste and nutritional value, e.g., vitamin C content, it is important that the package have barrier properties against gases and vapors, such as oxygen gas.

[0062] Measurement method

[0063] Transmission electron microscope (TEM) and thickness Barrier layer thickness measurements were performed using a transmission electron microscope (TEM) with a Titan 80-300 microscope (FEI). Samples were prepared by ultramicrotomy using a Leica EM UC6 microtome. Each barrier layer was embedded in an epoxy resin (EpoFix-Struers) that polymerizes for several hours at room temperature. Lateral cuts (60 nm thick sections) were made in the resin blocks using a diamond knife at room temperature using an ultramicrotome. TEM images were taken at 300 kV using a contrast diaphragm (40 μm). Barrier coating thickness measurements were performed using DigitalMicrograph software.

[0064] Oxygen permeability OTR is the amount of oxygen per unit of surface and time that passes through a material at a defined temperature and relative humidity, a given atmospheric pressure, and a defined oxygen partial pressure.

[0065] The OTR of the barrier layer was measured in a 100% oxygen atmosphere (1 atmosphere (atm) oxygen) according to ASTM D3985-05. The OTR of the laminate was measured in a 20% oxygen atmosphere (0.2 atmospheres oxygen, i.e., in air) according to ASTM F1927-14. The OTR of the package was measured in a 20% oxygen atmosphere using an Oxtran 2 / 21 instrument based on a coulometric sensor according to ASTM F1927-14 and ASTM F1307-14. ASTM F1927-14 was used for measurements under controlled climatic conditions on both flat samples and packages. All OTR measurements were performed under climatic conditions of 23°C and 50% relative humidity (RH).

[0066] Crack generation strain The cracking strain of the barrier layer was determined by measuring the OTR under strain. This was performed at 23°C and 50% RH using a combination of the ASTM D3985 OTR measurement method (described above) and the ASTM D882 method for measuring the tensile properties of plastic sheets. The OTR was measured while the barrier layer was under a constant strain, which was increased in steps (e.g., 0.1%) without relaxation between measurements. Smaller steps resulted in better measurement accuracy. At a certain strain value, a significant increase in OTR was observed, indicating the onset of cracking in the barrier coating. This was the cracking strain.

[0067] Transmittance The optical density is measured during the manufacturing process using a densitometer (Macbeth, Tobias, etc.) that utilizes the principle of diffuse light transmission. This instrument is suitable for measuring the optical density value of coated films. The measurement accuracy and precision of aluminum-coated films are high, and can be approximately ±0.2 OD and ±0.01 OD, respectively, within the measurement range of 0 to 6.60 OD.

[0068] Alternatively, laboratory measurements can be performed using a spectrophotometer to measure light transmittance across the entire visible spectrum (380-800 nm). Optical density is calculated from the light transmittance (T) value at 560 nm according to the following OD formula, and the resulting values ​​are comparable in accuracy to those obtained using a light transmittance densitometer:

[0069] The transmittance has the following relationship with the optical density:

[0070] T=10 -OD %T=100xT OD=-logT OD=Optical Density T=Transmission

[0071] Here, transmittance T is defined as I1 / I0, where I1 = transmitted light ("output") and I0 = incident light ("input"). Therefore, OD = -log 10 (I1 / I0).

[0072] The permeability values ​​relate to the final value of the barrier coating after stabilization in air unless otherwise stated. The in-line permeability values ​​of the barrier coating during the coating process are those measured in the examples.

[0073] Gelbo Flexing Gelboflex was performed according to ASTM F392. The flexing action is a combination of torsional and horizontal (compression) actions that repeatedly twist and crush the film.

[0074] X-ray photoelectron spectroscopy (XPS) XPS was performed on the barrier layer using a NOVA-KRATOS instrument under the following analytical conditions: X-ray source: monochromated Al Kα 225 watts for both survey and elemental spectra Analysis area: 300 x 700 μm at grazing detection 2 Detection angle: Normal detection (θ=0°) Analysis depth: less than 10 nm

[0075] ( DESCRIPTION OF THE PREFERRED EMBODIMENT ) Preferred embodiments of the present invention will now be described with reference to the drawings. [Brief explanation of the drawings]

[0076] [Figure 1] 1 is a schematic cross-sectional view of a laminate packaging material according to a preferred embodiment of the present invention. [Figure 2] 2 is a schematic diagram of a plant for PVD partial aluminum oxide barrier coatings onto barrier substrate layers for use with the material of FIG. 1. [Figure 3] FIG. 2 is a schematic diagram of a plant for plasma surface pretreatment of barrier substrate layers for use in the material of FIG. 1. [Figure 4] FIG. 2 is a diagram schematically illustrating a method for producing the laminate packaging material of FIG. [Figure 5a] 2 is a diagram showing a typical example of a packaging container manufactured from the laminate packaging material of FIG. 1. FIG. [Figure 5b] 2 is a diagram showing a typical example of a packaging container manufactured from the laminate packaging material of FIG. 1. FIG. [Figure 5c] 2 is a diagram showing a typical example of a packaging container manufactured from the laminate packaging material of FIG. 1. FIG. [Figure 5d] 2 is a diagram showing a typical example of a packaging container manufactured from the laminate packaging material of FIG. 1. FIG. [Figure 6]FIG. 6 illustrates how the packaging container of FIG. 5 is manufactured from packaging laminate in a continuous roll-fed form-fill-seal process. [Figure 7] 1 is a TEM image of a barrier coating 3a of an example. [Figure 8] FIG. 1 is a diagram showing the oxygen permeability of the barrier layer of an example. [Figure 9] FIG. 10 is a diagram showing the oxygen permeability of the barrier layer of the example after Gelboflex. [Figure 10(a)] 1 is a graph showing the oxygen permeability versus strain of a BOPET-based barrier layer of an example, showing the strain value at which cracks occur. [Figure 10(b)] 1 is a graph showing the oxygen permeability versus strain of the MOPET-based barrier layer of an example, showing the strain value at which cracks occur. [Figure 11] FIG. 1 is a diagram showing the oxygen permeability of the barrier layer and packaging laminate of the examples. [Figure 12] FIG. 10 is a diagram showing the oxygen permeability of the package of the example. DETAILED DESCRIPTION OF THE INVENTION

[0077] FIG. 1 shows a preferred embodiment of a laminate packaging material 10a (also referred to herein as a packaging laminate) for liquid carton packaging of the present invention. This laminate material comprises a bulk layer 11 of paperboard and a liquid-tight, heat-sealable outer layer 12 of polyolefin applied to the outside of the bulk layer 11, with this outer layer 12 facing the outside of a packaging container manufactured from the packaging laminate. The polyolefin of outer layer 12 is a conventional heat-sealable low-density polyethylene (LDPE). An innermost liquid-tight, heat-sealable layer 13 is positioned opposite the bulk layer 11, i.e., layer 13 is in direct contact with the packaged product. This innermost heat-sealable layer 13 forms a very strong seal for a liquid packaging container made from the laminate packaging material and comprises m-LLDPE.

[0078] The bulk layer 11 is laminated to a barrier layer 14 (also referred to herein as a barrier film) formed from an oriented BOPET film barrier substrate layer 14b coated with a PVD barrier coating 14a comprising partially oxidized aluminum. The coating 14a is applied by PVD by reactive evaporation to a thickness of approximately 15 nm. The morphology of the partially oxidized aluminum is described in more detail in the examples below.

[0079] 2 is a perspective view of an example of a plant 20a for PVD deposition of a coating 14a on a polymer film barrier substrate layer 14b; 24b-c. The thin film substrate 14b; 24b-c is subjected to sequential depositions on the coating-receiving side to form the coated barrier layer 14 of the present invention. Aluminum vapor is supplied from a solid piece aluminum evaporation source 21. Aluminum evaporation is thermal and occurs when an aluminum wire contacts a hot surface (heated to 1500-1700°C by Joule heating) containing boron nitride.

[0080] A limited amount of oxygen is introduced into the chamber through an injection nozzle, where reactive evaporation occurs between the aluminum and the oxygen.

[0081] Before the PVD coating begins, the surface of the polymer film barrier substrate layer 14b is briefly pre-treated with plasma to functionalize and clean the surface, making it more susceptible to the coating and strengthening the bond between the coating and the substrate.

[0082] 3 is a perspective view of an example of a plant for plasma surface pretreatment of polymeric film barrier substrate layers. A film substrate 44 is exposed on one surface to an oxygen-argon plasma in a plasma reaction zone 50 formed in the space between a magnetron electrode 45 and a cooled film transport drum 46, which also functions as an electrode, while the film is transported by the rotating drum along the periphery of the drum through the plasma reaction zone. The plasma is applied as a surface treatment only.

[0083] Post-treatment is also performed to remove aluminum hydroxide and oxidize the surface of the coating 14a.

[0084] Returning to the structure shown in Figure 1, a first outer side of barrier layer 14 is laminated to bulk layer 11 by an intermediate adhesive layer 15 of LDPE. An innermost heat-sealable layer 13 comprising m-LLDPE is adhered to barrier layer 14 by a layer 16 of LDPE and, optionally, an adhesive polymer such as a polyolefin having functional polar groups to enhance adhesion to adjacent layers.

[0085] 4 shows a lamination process 30 for producing the laminated packaging material 10a of FIG. 1, in which a bulk layer 11 is laminated to a barrier layer 14 by extruding adjacent bonding layers of LDPE 15; 34 from an extrusion station 35 and pressing them together in a roller nip 36. The barrier layer 14, as described above, has a barrier coating 14a pre-applied to one side of the substrate layer, which side faces the bulk layer 11 as shown in FIG. 1. The laminated paper bulk layer and barrier layer then pass through a second extruder feedblock 37-2 and lamination nip 37, where an outermost heat-sealable layer of LDPE 12; 37-3 is coated onto the outside of the paper layer. Furthermore, the laminate including the outermost heat-sealable polymer layer 12; 37-3 passes through a third extruder feedblock 38-2 and a lamination nip 38, where an innermost heat-sealable polymer layer 13; 38-3 is coated onto the barrier layer side of the paper-film laminate coming from 37. Alternatively, this latter step may be carried out before lamination at 37, advantageously to protect the inner barrier layer 14 as soon as possible; according to another alternative embodiment, lamination of the outermost layer 37 to the paperboard may be carried out before lamination at 36. The finished packaging laminate 39 is finally wound up on a storage reel, not shown.

[0086] FIG. 5a shows an embodiment of a packaging container (also referred to herein as a package) 50a made from a packaging laminate 10a according to the present invention. This packaging container is particularly suitable for beverages, sauces, soups, and the like. Typically, such packages have a volume of approximately 100 to 1000 mL. The packaging container may be any shape, but is preferably brick-shaped, with longitudinal seals 51a and lateral seals 52a, and optionally an opening device 53. In another embodiment (not shown), the packaging container may be wedge-shaped. To achieve this "wedge" shape, only the bottom of the package is folded over, with the bottom lateral heat seal hidden beneath triangular corner flaps that are folded and sealed to the bottom of the package. The top lateral seal remains unfolded. In this way, the folded packaging container remains dimensionally stable and easy to handle when placed on a grocery store shelf, table, or similar.

[0087] Figure 5b shows an alternative preferred example of a packaging container 50b made from an alternative packaging laminate according to the present invention. This alternative packaging laminate is thinner due to having a thinner paper bulk layer, and therefore does not have sufficient dimensional stability to form a parallelepiped or wedge-shaped packaging container, and does not fold after transverse seal 52b. Therefore, it remains a pillow-like pouch-like container and is sold and distributed in this form.

[0088] Figure 5c shows a gable-top package 50c that is folded and formed from a pre-cut sheet or blank of laminate packaging material that includes a bulk layer of paperboard and a durable barrier layer of the present invention. Alternatively, flat-top packages may be formed from similar blank materials.

[0089] 5d shows a bottle-shaped package 50d that combines a sleeve 54 formed from a pre-cut blank of the laminate packaging material of the present invention with an opening device, such as a screw cap, and a top portion 55 formed by injection molding plastic. Packages of this type are sold, for example, under the trade names Tetra Top® and Tetra Evero®. These specialized packages are formed by attaching a molded top portion 55 with an opening device in a closed state to a tubular sleeve 54 of laminate packaging material, sterilizing the resulting bottle-top capsule, filling it with a food product, and finally folding and sealing the bottom of the package.

[0090] 6 illustrates the form-fill-seal principle described at the beginning of this application, i.e., a web of packaging material is formed into a tube 61 by joining the longitudinal edges 62 of the web together at overlap joints 63. The tube is filled (at 64) with the desired liquid food product and divided into individual packages by repeating transverse seals 65 of the tube at predetermined distances from each other below the level of the fill contents in the tube. Packages 66 are separated by the transverse seal incisions and are given the desired geometric shape by folding along prepared creases in the material.

[0091] ( Example ) A series of barrier layers 14 were produced by vapor coating a barrier substrate layer 14b. The barrier layers were included in a packaging laminate and formed into a package as described below.

[0092] The barrier substrate layer used polymer films of BOPET (Mitsubishi Prime Films, BOPET RNK12-2DF) and MOPET (developed in-house).

[0093] The barrier substrate layer was subjected to plasma pretreatment as described in connection with Figure 3. Direct current was used.

[0094] The partially oxidized aluminum barrier coating 14a was applied by PVD via reactive evaporation of aluminum and oxygen, as described in connection with Figure 2. The film substrate web was 1900 mm wide and was coated at a nominal speed of 7.8 m / s. Oxygen was injected into the evaporation zone at various flow rates to provide an atmosphere containing different ratios of evaporated oxygen and aluminum. The test coatings were formed with a lower oxygen / aluminum ratio than the control coating.

[0095] The amounts of oxygen and aluminum were varied as shown in Table 1 ("sccm" = standard cubic centimeter gas volume flow rate).

[0096] [Table 1]

[0097] The barrier layers were used to prepare packaging laminates. The laminate construction was as shown in Figure 1 above, and the laminates were prepared according to the method described in Figure 4. Thus, all laminates produced had the same basic construction, and, unless otherwise noted, were formed from the same polymer and paperboard materials and laminated together in the same manner.

[0098] / LDPE(12g / m 2 ) Outermost layer: Unbleached paperboard / LDPE (20g / m) with optional adhesive 2 ) / Barrier coating / 12 μm thick MOPET or BOPET film substrate / [LDPE (12 g / m 2 ) / m-LLDPE(13g / m 2 ) or adhesive (6g / m 2 ) / m-LLDPE(19g / m 2 )] /

[0099] The laminate was formed into a cubic package using a TETRA PAK A3 Flex / TBA1000 packaging machine with ultrasonic sealing.

[0100] Barrier layers, laminates and packaging were evaluated.

[0101] TEM images TEM images of the barrier coatings were obtained. As shown in Table 1, dark particles were visible in some, but not all, coatings. Particles were visible in coatings 3a (shown in Figure 7), 4a, and 2b. In coating 3b, a granular structure was visible under TEM. Control coatings 1a, 1b, and coating 2a did not show any dark particles.

[0102] While not wishing to be bound by this theory, the inventors believe that the dark particles are particles of aluminum metal dispersed in aluminum oxide, Al2O3, and that the coating is a ceramic-metal (ceram-met) composite. At low levels of aluminum metal, particles are present but too small to be visible by TEM.

[0103] XPS analysis XPS analysis of the three MOPET-based samples 1b, 2b, and 3b showed that the surface composition of the barrier layer coating was Al2O3.

[0104] Thickness The coating thickness was measured by TEM and is shown in Table 1. The coating thickness ranged from 10.3 to 28.9 nm.

[0105] Coating transmittance The transmittance values ​​of the coatings were measured online during coating formation and are shown in Table 1.

[0106] The transmittance values ​​increased after coating, likely due to further oxidation and stabilization of the coating during post-treatment and in air thereafter. An increase of 5-7 percentage points (30-40% of the initial value for lower initial transmittance values) was typical. Therefore, the values ​​shown in Table 1 increased for each coating to a final stable value that was 5-7 percentage points higher.

[0107] Oxygen permeability of the barrier layer FIG. 8 shows the OTR of the barrier layer at 23° C. and 50% RH.

[0108] That is, the OTR of BOPET-based barrier layers is 1a (control, labeled "BOPET AlOx(std)") > 2a > 3a > 4a, and the OTR of MOPET-based barrier layers is 1b (control, labeled "MOPET AlOx(std)") > 2b > 3b. A low OTR is desirable.

[0109] Coatings 3a, 4a, 2b and 3b have an OTR of 3 cm 3 / (m 2 The OTR for coatings 2b and 3b (on MOPET) is less than 2 cm. 3 / (m 2 0.24h.1atm), which is even more desirable.

[0110] Figure 9 shows the OTR (23°C, 50% RH) of the barrier layer after 0, 10, and 50 cycles of Gelbo flex. It can be seen that the good initial OTR performance of the partially oxidized aluminum coating is maintained even after Gelbo flex. This indicates that this coating has better mechanical properties and is less brittle than standard AlOx coatings. Coating 4a is thicker and has less embedded aluminum (25% transmittance compared to 18%), making the coating more brittle.

[0111] Crack generation strain Figure 10 shows the crack initiation strain for (a) a BOPET-based barrier layer and (b) a MOPET-based barrier layer. The crack initiation strain is the strain at which the OTR (23°C, 50% RH) begins to increase sharply. A large crack initiation strain indicates good mechanical properties and crack resistance.

[0112] The crack initiation strain for BOPET-based barrier layers increased in the order 1a (control, denoted as A1) < 2a (A2) < 3a (A3) < 4a (A4).For BOPET-based films, films 2b (A2) and 3b (A3) also showed better results than the control (1b / A1).

[0113] Oxygen permeability of laminate FIG. 11 shows the OTR (23° C., 50% RH) of a BOPET-based laminate ("packaging material").

[0114] Again, it can be seen that lowering the oxygen ratio of the coating reduces the OTR, with the control 1a (labeled "BOPET AlOx(std)") having a higher OTR than 4a.

[0115] Furthermore, the OTR of the 4a packaging material is similar to that of the barrier layer, indicating that the barrier layer maintains good properties even after extrusion lamination.

[0116] Oxygen permeability of the package FIG. 12 shows the OTR (at 23° C. and 50% RH) of a package ("packaging material") formed from the laminate.

[0117] Here again, it can be seen that lowering the oxygen ratio of the coating reduces the OTR. For MOPET and BOPET, the standard AlOx coating exhibited a higher OTR than the modified (Mod) AlOx coating.

[0118] exterior The appearance of the test coatings was assessed visually and the coatings were usually gray, brown, dark brown, or bluish in color, although in one case the coating was purple in color.

[0119] Coatings with a final transmittance of less than 20% were found to have a metallic appearance. Coatings with a transmittance higher than 20% did not exhibit a metallic appearance after lamination, especially when unbleached boards were used.

[0120] Without wishing to be bound by theory, the inventors believe that the appearance of the coating depends on both the thickness of the coating and the size of the aluminum particles.

[0121] Conclusion of the working example The example coatings had several advantages. - The appearance of the coating, especially after lamination, is non-metallic and visually distinct from metals and metallized films. This can be important in meeting market needs. For example, the Japanese market requires a barrier layer that is non-metallic in appearance to enable packaging recycling. The coating provided effective barrier properties, as indicated by the OTR. The good OTR was maintained when the barrier layer was processed into a laminate (including extrusion coating) and when the laminate was molded into a package. The good OTR was also maintained after Gelboflex testing. The crack initiation strain was large. Thus, the coating exhibited superior mechanical properties to conventional AlOx coatings, which tend to be brittle. While not wishing to be bound by theory, the inventors believe that the cermet structure containing aluminum particles contributes to the good mechanical properties of the test coating by reducing brittleness. The coating is promising as a barrier layer for use in liquid packaging laminates (including those intended for long-term, sterile, ambient storage), where crack resistance is critical. The thin coating thickness contributes to the good mechanical properties. Thicker coatings used in the prior art, such as those in EP437946 (which are approximately 5-7 times thicker than the coating in this example), are likely to be more brittle. - It can be applied faster than PECVD coating using standard PVD equipment, and the thinner coating allows for increased coating speeds, making it a low-cost, scalable option. - The coating uses less metal than conventional aluminum foil, making the laminate material easier to recycle and producing less carbon dioxide during the manufacturing process. Furthermore, the PE used in the various layers can be bio-based. This makes the laminate more sustainable. - The coating can be heated in a microwave.

[0122] 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 claims.

Claims

1. A laminate packaging material (10a) for packaging liquid or semi-liquid food products, A bulk layer (11) containing cellulose-based material, A first outermost liquid-tight, heat-sealable thermoplastic layer (12) is disposed outside the bulk layer and constitutes the outer surface of the package formed from the packaging material, A second innermost liquid-tight, heat-sealable thermoplastic layer (13) is positioned inside the bulk layer so as to be in direct contact with the filled food, A barrier layer (14) comprising a barrier substrate layer (14b) coated with a physically vapor-deposited (PVD) barrier coating containing partially oxidized aluminum, The barrier coating has a thickness of 8 to 40 nm and a transmittance of 20 to 60% when measured with a spectrophotometer at wavelengths across the visible spectrum, and after the barrier coating is stabilized in air, the barrier layer is laminated between the bulk layer and the second innermost liquid-tight, heat-sealable thermoplastic layer. Laminate packaging material (10a).

2. The partially oxidized aluminum consists of aluminum particles and Al ２ O ３ Including a ceramic-metal composite, The laminate packaging material according to claim 1.

3. The barrier coating has a non-metallic appearance. The laminate packaging material according to claim 1.

4. The barrier substrate layer includes a polymer film or a cellulose-based material. The laminate packaging material according to claim 1.

5. The polymer film is a polyolefin film or a polyester film. The laminate packaging material according to claim 4.

6. The polymer film is a pre-manufactured uniaxial or biaxially oriented film. The laminate packaging material according to claim 5.

7. The polymer film is a uniaxially oriented polyethylene terephthalate (MOPET) film or a biaxially oriented polyethylene terephthalate (BOPET) film. The laminate packaging material according to claim 6.

8. The barrier substrate layer is a paper layer. The laminate packaging material according to claim 4.

9. The surface of the barrier substrate layer to be coated with PVD is pretreated during film manufacturing by in-line plasma pretreatment and / or corona, plasma, or atmospheric pressure plasma. The laminate packaging material according to claim 1.

10. The barrier coating is post-treated by plasma treatment. The laminate packaging material according to claim 1.

11. The PVD barrier coating is applied by plasma-assisted reactive evaporation. The laminate packaging material according to claim 1.

12. A method for producing a laminate packaging material according to claim 1, This method is The steps include: laminating the barrier layer inside the bulk layer (11), The steps include: applying a first outermost liquid-tight, heat-sealable thermoplastic resin layer (12) to the outside of the bulk layer, and applying a second innermost liquid-tight, heat-sealable thermoplastic resin layer (13) to the inside of the barrier layer (14); Includes in any order method.

13. The barrier layer is laminated to the bulk layer by melting (co)extruding (35) an adjacent laminate layer (15) of a thermoplastic polymer between the bulk layer and the barrier layer, and then applying pressure with a laminating roller nip. The method according to claim 12.

14. A laminate packaging material (10a) according to claim 1, Packaging containers for liquid or semi-liquid foods (50a; 50b; 50c; 50d).

15. A method for forming a packaging container (50a; 50b; 50c; 50d) according to claim 14, comprising the step of folding a laminate packaging material (10a).

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