Recyclable paper-based packaging material with high barrier properties against water vapor and oxygen

Abstract

To provide a recyclable, easily-manufacturable paper-based packaging laminate with high barrier properties against water vapor, oxygen, and / or aroma.SOLUTION: A barrier film (3) includes at least one base layer, a bonding layer, and a barrier layer. The bonding layer is disposed between the base layer and the barrier layer. The base layer has a polyethylene or polypropylene content of at least 60 wt.% and is mainly composed of polyethylene or polypropylene. At least one base layer of the barrier film (3) is stretched. The ratio of a paper layer (2) is between 50 wt.% and 90 wt.% of a paper packaging laminate (1). The barrier film (3) is bonded to the paper layer (2) by using a hydrophilic adhesive layer (9).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention is directed to a composition comprising a polymer having a molecular weight of 30 to 360 g / m 2 The present invention relates to a recyclable paper packaging laminate comprising a paper layer using paper having a basis weight of up to 1000 g / m2 and a barrier film bonded to the paper layer, which not only has recyclability but also high oxygen, water vapor and / or aroma barrier properties. [Background technology]

[0002] In the packaging industry, paper packaging laminates are used, which have different properties depending on the application. These paper packaging laminates are usually laminated with multi-layer plastic films produced by extrusion, coextrusion (in both cases, either flat film or blown film) or lamination (bonding of the individual layers with lamination adhesives), as well as combinations thereof. Paper packaging laminates can also incorporate layers that are not made of plastic, such as aluminum or even other paper layers. The paper packaging laminates usually also have an outer sealing layer, so that they can be processed by heat sealing into the desired packaging, such as bags, sacks, paper bags, etc.

[0003] One of the typical requirements for paper packaging laminates is a barrier function against water vapor, oxygen and aroma substances. For that purpose, paper packaging laminates generally contain a barrier layer made of aluminum or a suitable barrier polymer, such as ethylene-vinyl alcohol-copolymer (EVOH) or polyamide (PA).

[0004] Similarly, paper packaging laminates usually also contain a sealing layer to enable them to be converted into packaging materials by heat sealing. The sealing layer is typically made of a polyolefin, usually polypropylene (PP) or polyethylene (PE) of various densities such as LLDPE, LDPE, MDPE or HDPE (including blends or multi-layers with the same or different types).

[0005] Additional layers may also be included to impart desired properties to the paper packaging laminate, such as toughness, stiffness, tear resistance, etc.

[0006] In order for the paper packaging laminate to be easy to process, it should of course not warp or curl up (so-called curling) during processing, for which reason a symmetrical layer structure is usually used in laminated plastic films.

[0007] It is further known to change the properties of paper packaging laminates by uniaxial or biaxial orientation of the plastic layers of the paper packaging laminate. Such orientation can be achieved by the extrusion process, for example in a multiple bubble process, or only after the extrusion process by stretching the plastic film in the machine direction (longitudinal direction of the paper packaging laminate) and / or in the transverse direction (perpendicular to the longitudinal direction). This orientation of the plastic film can improve, among other things, the stiffness, tensile strength and toughness.

[0008] However, it should be mentioned here that in blown and flat film extrusion, the extrusion gap (1.5-2.5 mm for blown film) or the extrusion die gap is clearly larger than the final thickness of the extruded film (typically 10-200 μm). For this, the extruded melt is stretched at a temperature clearly above the melting point of the extruded polymer, whereby the final thickness is obtained. In blown film extrusion, the melt is typically stretched, for example, by a factor of about 2-3 in the transverse direction (the so-called blow-up ratio) and by a factor of 1:10-1:100 in the longitudinal direction (the so-called draw-off ratio). However, the stretching during extrusion cannot be compared with the stretching of plastic films, since the stretching is usually carried out at a temperature slightly below the melting point of the polymer (typically 5° C. to 20° C. below), in order to permanently align the disordered polymer and partially crystalline regions in the stretching direction by stretching. In so-called MDO stretching (machine direction only stretching) a stretching gap (spacing of the rolls) of 40 to 100 mm is usually processed. In biaxial stretching, stretching in the transverse direction is then carried out in a heated oven.

[0009] Especially for ecological reasons, paper is often used as a packaging material, because it has good recyclability. However, due to the usual requirements for packaging materials, such as a barrier function against water vapor, oxygen and / or aromas, or sealing properties for producing packaging materials, paper cannot be used as a packaging material by itself, because paper alone does not have significant barrier properties. Therefore, in the field of flexible packaging materials, paper is usually combined with other layers, such as layers made of plastic or metal, to meet the barrier requirements. However, such paper packaging laminates, such as the widely used paper / aluminum / polyethylene structures, are usually difficult to recycle or cannot be recycled at all due to the materials used.

[0010] Recently, more and more paper packaging with only thin barrier and sealing layers are coming onto the market, so that the foreign components / impurities permitted in paper recycling according to EN643.1 do not exceed a maximum of 5% of the total weight of the packaging as specified therein, see for example "Design Tips for Recycling" by the Condederation of Paper Industry (CPI), www.wrap.org.uk / packaging.

[0011] It should also be noted that some coating materials, such as silicones and waxes, as well as some colorants, are considered hazardous to the recycling process, even at less than 5%.

[0012] WO2013 / 086950A1 (Patent Document 1) discloses a recyclable laminate using a "water-dispersible ionomer (WPI)" as adhesive, by means of which a thermoplastic material is bonded to a base material consisting of paper or aluminum. Although the laminate is recyclable because the paper layer and the thermoplastic material can be separated via the WPI, the recycling step requires high water temperatures, especially 80°C, and an action time of especially 1 hour.

[0013] EP 3194164 B1 describes a laminated structure for food products with paper as material layer, aluminum as gas barrier layer and a polymer layer as laminate material, where improved environmental compatibility is addressed, in particular by omitting ozone treatment during the surface treatment of the polymer. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] WO2013 / 086950A1 [Patent Document 2] EP3194164B1 Summary of the Invention [Problem to be solved by the invention]

[0015] One of the objectives of the present invention is to provide a recycle-friendly paper packaging laminate made of paper that has high barrier properties against water vapor, oxygen and / or aromas, which can be easily produced and is well recyclable. [Means for solving the problem]

[0016] The above problem is that the barrier film is at least one substrate layer, an adhesive layer, and a barrier layer, wherein the adhesive layer is disposed between the substrate layer and the barrier layer; the substrate layer is composed predominantly of polyethylene or polypropylene, with a polyethylene or polypropylene proportion of at least 60% by weight, preferably at least 70% by weight and very particularly preferably at least 80% by weight of the substrate layer 4, At least said at least one substrate layer of the barrier film is stretched, the proportion of the paper layer is between 50% and 90% by weight of the paper packaging laminate, preferably between 70% and 90% by weight, and the barrier film is bonded to the paper layer by means of a hydrophilic adhesive layer, whereby the paper layer is not coated on the side facing the barrier film; The problem is solved by the above-mentioned. Thereby, the function of (high) barrier and recyclability is achieved with a polyolefin content (PE or PP) of 10 to 50% by weight, in particular 10 to 30% by weight, i.e. a significantly higher polyolefin content than previously considered necessary, and a predominant paper content in the paper packaging laminate. In this way, a recyclable paper packaging material can be produced that still has a high barrier effect against water vapor, oxygen and / or aromas.

[0017] The barrier film can be designed asymmetrically with a substrate layer that is bonded to the barrier layer via a bonding layer. Asymmetric barrier films can be designed thinner, which allows the proportion of polymer in the paper packaging laminate to be reduced. In this case, the barrier layer is preferably arranged on the paper layer side and bonded to the paper layer via an adhesive layer.

[0018] Alternatively, the barrier film can be designed symmetrically with a barrier layer bonded to a substrate layer on both sides using a bonding layer, one of the substrate layers being bonded to a paper layer via an adhesive layer. Symmetric barrier films can be processed more easily because they are less prone to curling. Similarly, the barrier layer in a symmetrical structure is better protected.

[0019] The barrier layer can be designed as a barrier coating in the form of a metallization or a silicon oxide or aluminum oxide coating, or as a layer made of a barrier polymer, preferably a polyamide or an ethylene-vinyl alcohol copolymer. Additionally, in order to further increase the barrier effect, a barrier coating in the form of a metallization or a silicon oxide or aluminum oxide coating can also be applied to the layer made of a barrier polymer. This makes it possible to very well adapt the barrier effect to the individual barrier requirements of the paper packaging laminate.

[0020] Preferably, the barrier film is stretched. This can be achieved, for example, by coextrusion of the barrier film as a whole and then stretching it. Additionally, stretching the barrier polymer can also enhance its barrier action.

[0021] For many packaging applications a sealing layer is necessary, which can be bonded to a barrier film on the side opposite the paper layer. In order to increase the recyclability of the paper packaging laminate, it is advantageous when the sealing layer consists of PE if the substrate layer mainly consists of PE, or when the substrate layer mainly consists of PP, the sealing layer consists of PP. This allows the production of paper packaging laminates with a particularly pure polymer content, which is advantageous for recyclability.

[0022] Advantageously, the sealing layer is likewise stretched, which on the one hand allows the thickness of the sealing layer to be reduced, and on the other hand allows it to be coextruded and stretched together with the barrier film, which simplifies production.

[0023] The invention will be explained in more detail below in relation to Figures 1 to 3 which show exemplary, schematic and non-limiting advantageous embodiments of the invention. [Brief description of the drawings]

[0024] [Figure 1] 1 shows a first embodiment of a paper packaging laminate according to the present invention. [Diagram 2] 1 shows one design of an asymmetric barrier film. [Diagram 3] 1 shows one symmetric barrier film design. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Figure 1 shows a paper packaging laminate 1 according to the invention comprising a paper layer 2 and a barrier film 3 joined thereto, which provides the required barrier action against water vapour, oxygen and / or aromas. The paper packaging laminate 1 can be provided with a sealing layer 7 on the side opposite the paper layer 2. The paper layer 2 is joined to the barrier film 3 by means of an adhesive layer 9 consisting of a hydrophilic laminating adhesive. A typical thickness of the paper packaging laminate 1 is between 50 μm and 150 μm.

[0026] The individual layers of the paper packaging laminate 1 are described in more detail below.

[0027] The paper layer 2 is 30 to 360 g / m 2 Basis weight, especially for flexible packaging materials, 30-100 g / m 2 The paper is, as is known, produced from fibrous materials, such as cellulose, wood pulp or recycled paper. In the sense of the present application, Pergamin paper is also understood as paper.

[0028] The paper layer is uncoated at least on one side (the side facing the barrier film 3 in the paper packaging laminate 1). Uncoated means that the paper is substantially uncoated on said side, in particular that no plastic material capable of penetrating into the paper and penetrating and bonding with the paper fibres has been applied onto the paper. Such a plastic coating would be a coating layer inseparably joined to the paper layer on this side. In particular, said side is therefore not coated with, for example, a barrier paint, a sealing paint or other paint, nor is it extrusion coated with a plastic layer. In contrast, layers of layered silicates or minerals (clay coatings), which are often applied in the paper industry, can be present at all, since these do not normally prevent the recycling of the paper.

[0029] In the paper packaging laminate 1, the lamination adhesive used in the adhesive layer 9 is hydrophilic. A hydrophilic lamination adhesive has a strong interaction with water and is usually (but not necessarily) also water-soluble. A hydrophilic lamination adhesive used in the paper packaging laminate 1 according to the invention loses its adhesiveness with water based on a chemical mechanism, e.g. the rupture of hydrogen bonds or the lamination adhesive dissolves in water.

[0030] Hydrophilic lamination adhesives can be made based on starch, sugar derivatives, cellulose, amino resins, (poly)acrylates, polyvinyl alcohol (PVOH), polyvinyl acetate, polyacrylic acid, maleic acid modified ethylene copolymers, methylcellulose, carboxymethylcellulose, carboxy-functional polyesters, polyethylene-succinate, polybutylene-succinate, ionomers or hydrophilic polyurethanes.

[0031] Similarly, hydrophilic lamination adhesives for extrusion lamination can be used, including (but not limited to) ethylene copolymers with polar group-containing comonomers, such as ethylene-vinyl acetate copolymer (EVA), ethylene-butyl acrylate (EBA), ethylene-acrylic acid copolymer (EAA), or maleic anhydride grafted polyethylene / polypropylene (PE-G-Mah, PP-G-Mah).

[0032] The lamination adhesive is naturally selected such that sufficient adhesion is achieved between the paper layer 2 and the barrier film 3 to prevent undesired delamination of the paper packaging laminate 1 during use. By means of the adhesive layer 9, an adhesion between the paper layer 2 and the barrier film 3 of at least 1 N / 15 mm, preferably at least 1.5 N / 15 mm, should be achieved.

[0033] The adhesion is determined by a peel test. In the peel test, a test strip of the paper packaging laminate 1 is pulled away from each other at the free ends of the paper layer 2 and the barrier film 3. These free ends are clamped in a tensile tester and pulled away from each other at a defined peel angle (for example 90°), and the force is measured. If the test strip is 15 mm wide, the adhesion value is given by xN / 15 mm. In this case, the adhesion value is an approximately constant peel value (peel value), not a maximum initial peel value that occurs as a force peak at the beginning of the peel test. Generally, to determine the adhesion, several peel tests are performed, and the actual adhesion value is determined as an average value from the individual measurements. The peel test is performed, for example, according to ASTM standard F904.

[0034] Since paper is used in the paper packaging laminate 1, a liquid lamination adhesive, in particular a lamination adhesive dissolved in water or a suitable solvent, can be used to form the adhesive layer 9 between the paper layer 2 and the barrier film 3. After applying the liquid lamination adhesive and combining the paper layer 2 and the barrier layer 3, the lamination adhesive is dried, during which water or the solvent can diffuse into the paper. After drying, an adhesive layer 9 remains, with a bond being formed between the paper layer 2 and the barrier film 3. However, non-liquid lamination adhesives can also be used to form the adhesive layer 9, as long as they are hydrophilic.

[0035] Likewise, extrusion lamination methods are also conceivable, in which a molten lamination adhesive is extruded in the molten state at high temperatures above 180° C. onto the paper layer 2 or onto the barrier film 2 or onto both, and then the paper layer 2 and the barrier film 3 are brought together. After curing of the lamination adhesive, it forms an adhesive layer 9.

[0036] The barrier film 3 is composed of at least one oriented substrate layer 4, mainly made of polyethylene (PE) or mainly made of polypropylene (PP), a bonding layer 5 and a barrier layer 6 (Figure 2). The thickness of the barrier film 3 is typically from 10 to 40 μm.

[0037] The barrier film 3 can be designed asymmetrically (as shown in FIG. 2) with a substrate layer 4, a barrier layer 6 and an adhesive layer 5 arranged therebetween, in which case the adhesive layer 5 is directly bonded to the substrate layer 4 and to the barrier layer 6. In the case of an asymmetric barrier film 3, the barrier layer 6 is preferably arranged on the side of the paper layer 2 in the paper packaging laminate 1 and is directly bonded to the uncoated side of the paper layer 2, but also to the side of the sealing layer 7, by means of an adhesive layer 9. However, the barrier film 3 can also be designed symmetrically (as shown in FIG. 3). In this case, the barrier layer 6 would be bonded on both sides thereof, respectively to substrate layers 4 (which may be different), respectively via adhesive layers 5. In a symmetrical design, the uncoated side of the paper layer 2 is directly bonded to one substrate layer 4 of the barrier film 3 via an adhesive layer 9.

[0038] In one possible embodiment, the barrier layer 6 is a barrier coating applied to the bonding layer 5 in the form of a metallization, for example with aluminum, or a coating made of silicon oxide (SiOx) or aluminum oxide (AlOx). This embodiment is preferably used in the case of asymmetric barrier films 3. This barrier coating results in a thin barrier layer 6 of only a few nanometers (typically about 10 to 50 nm) on the bonding layer 5. The metallization can be carried out, for example, by known vacuum metallization. The SiOx or AlOx coating can be applied, for example, by chemical vapor deposition or vacuum evaporation. Of course, other methods for producing the barrier coating are also possible. The barrier coating can additionally be covered with a protective paint as a protection against microcracking, which could impair the barrier function. With such a barrier coating, a barrier layer of 2 cm 3 / m 2 Low oxygen transmission rate (OTR) of less than 3 cm / d (23°C, 75% relative humidity, both sides) and 3 / m 2It is possible to achieve a low water vapour transmission rate (WVTR) of less than 1 / d (38° C., 90% relative humidity, double-sided), where d represents a day, i.e., 24 hours.

[0039] In yet another possible embodiment, the barrier layer 6 is a layer of a barrier polymer (used in both asymmetric and symmetric barrier films 3), i.e. a layer of a polymer having sufficient barrier properties, in particular against oxygen and / or aromas. The barrier polymer is preferably a polyamide (PA) or an ethylene-vinyl alcohol copolymer (EVOH). Preferably, EVOH is used as the barrier polymer. The barrier polymer has a thickness of at most 20%, preferably from 5 to 10%, of the total thickness of the barrier film 3, i.e. for example at most 2 to 8 μm, in the case of a barrier film having a thickness of 10 to 40 μm. The use of a barrier polymer as the barrier layer 6 not only makes it possible to achieve a low water vapor transmission rate (similar to or better than those described above), but also a high water vapor transmission rate of at least 2 cm. 3 / m 2 A low oxygen transmission rate (OTR) of less than 1 / d (23°C, 75% relative humidity, both sides) and a high aroma barrier can also be achieved. There is no objective measure for the aroma barrier, and the performance as an aroma barrier is subjectively determined by odor testing.

[0040] If a barrier layer 6 made of a barrier polymer is provided in the barrier film 3, the barrier layer 6 can additionally be coated with a barrier coating, in the asymmetric or symmetric barrier film 3, in particular with a metal coating, for example with aluminum, or with aluminum oxide or silicon oxide, thereby making it possible to further increase the barrier effect of the barrier film 3, in particular to further reduce the OTR and WVTR, i.e., to within 1 cm 3 / m 2 / d. In this embodiment, the barrier coating may also be additionally covered with a protective paint.

[0041] The substrate layer 4 is mainly produced from polyethylene (PE) or polypropylene (PP), with a polyethylene or polypropylene proportion of at least 60% by weight, preferably at least 70% by weight, very particularly preferably at least 80% by weight of the substrate layer 4, respectively. The higher the polyethylene or polypropylene proportion (i.e. the purer the substrate layer 4), the better the recyclability. The thickness of the substrate layer 4 is preferably from 5 to 35 μm, in which case substrate layers 4 of different thicknesses and / or differently constructed can also be used in symmetrical barrier films 3. However, in symmetrical constructions, both substrate layers 4 are preferably designed with PE or PP as the same main component. The substrate layers 4 can be supplemented with customary additives (e.g. slip agents, antiblocking agents, fillers, etc.). Different polyethylene or polypropylene species can also be used in the substrate layers 4, respectively, as mixtures or coextrusions. Similarly, the substrate layers 4 can comprise, in addition to the respective main components PE or PP, respectively, polyolefin materials that are compatible therewith.

[0042] The polyethylene type of the base layer 4 is, for example, HDPE (0.94 to 0.97 g / cm 3 0.915-0.935g / cm2), MDPE (medium density polyethylene), LDPE (0.915-0.935g / cm2) 3 Low density polyethylene (LLDPE) with a density between 0.87 and 0.94 g / cm 3 Considerations include linear low density polyethylene (mLLDPE) or mLLDPE (linear low density metallocene polyethylene) having a density between 1000 and 10000 mm. Preferably, HDPE or MDPE is used. As polypropylene species for the substrate layer 4, for example atactic, syndiotactic or isotactic PP come into consideration.

[0043] As PE-compatible polyolefin materials, basically any type of polyethylene comes into consideration, in particular ethylene copolymers, such as ethylene-vinyl acetate copolymer (EVA), methacrylic acid ethyl ester (EMA), ethylene / acrylic acid copolymer (MAA) or ethylene-butyl acrylate copolymer (EBA). Likewise, polypropylene (PP) or cycloolefin copolymers (COC) can be used as PE-compatible polyolefin materials to the extent of up to 20% by volume. In the case of PP, preferably polypropylene random copolymers with ethylene as comonomer (usually 5-15%), ethylene-containing polypropylene copolymers or polypropylene homopolymers are used, which are fully compatible with linear PE types, such as mLLDPE, LLDPE or HDPE, in order to achieve at least limited recyclability.

[0044] As PP-compatible polyolefin materials, PP copolymers, such as random and block copolymers, come into consideration. The addition of up to 20% polyethylene likewise does not significantly impair recyclability.

[0045] If a PE- or PP-compatible polyolefin material is contained in the substrate layer 4, then in order to improve recyclability, the proportion of the main components polyethylene (PE) or polypropylene (PP) in the substrate layer 4 is preferably at least 60% by weight (based on the substrate layer 4), preferably at least 70% by weight, very particularly preferably at least 80% by weight. In this case, the PE or PP and the respectively compatible polyolefin material can be present in the substrate layer 4 as a mixture.

[0046] However, the substrate layer 4 may also be constructed in a multi-layer (extruded or coextruded) configuration, comprising one (or more) PE or PP layer(s) and one (or more) layer(s) of a compatible polyolefin material.

[0047] A cavity former can also be added to the main component PE or PP of the substrate layer 4, the cavity former being added in an amount of 5 to 30% by weight, preferably 15 to 25% by weight, of the substrate layer 4. Possible cavity formers are polymers that are incompatible with PE or PP (i.e. polymers that remain isolated in the PE or PP matrix), such as polyamides (PA), polyesters (e.g. PET or PBT), polylactides (PLA). It is also possible to use, in particular, mineral cavity formers, such as calcium carbonate or mica. The cavity formers are usually present as fine powders, which are embedded in the PE or PP matrix as a masterbatch and mixed with the PE or PP granules before extrusion.

[0048] If a voided PE or PP layer is used in the substrate layer 4, it is preferably surrounded on one or both sides by a non-voided PE or PP layer. One possible structure of the substrate layer 4 of the laminate layer 3 would be, for example, a voided PE layer bonded (for example co-extruded) on one side with a non-voided PE layer. In this case, the voided PE layer is on the paper layer 2 side in the paper packaging laminate 1. Another preferred structure of the substrate layer 4 would be, for example, a voided PE layer bonded (for example co-extruded) on both sides with a non-voided PE layer. There is also such a structure with PP as the main component in the substrate layer 4. The use of a voided layer in the substrate layer 4 can also improve the sealing properties of the paper packaging laminate 1.

[0049] The sum of PE or PP, cavity former, any additives present and possible compatible polyolefin materials in the substrate layer 4 can of course only add up to 100% by weight. In this case, the proportion of the main component polyethylene or polypropylene is important and the other proportions must be adjusted accordingly.

[0050] At least the substrate layer 4 in the barrier film 3 is stretched in one or two directions, i.e. in the machine direction (MDO) (usually the longitudinal or extrusion direction) and / or in the transverse direction (TDO) (rotated 90° to the machine direction). If a barrier polymer is used as the barrier layer 6 in the barrier film 3, the entire barrier film is preferably stretched. If the bonding layer 5 or the barrier layer 6 is coated, it is stretched before coating. In this case, the stretch ratios in the machine direction and the transverse direction do not have to be the same. In this case, the stretch ratio in the machine direction is preferably at least 4:1 to 8:1. In this case, the stretch ratio in the transverse direction is preferably at least 5:1 to 10:1. Unidirectional MDO stretching is preferred, since unidirectional stretching is simpler than bidirectional stretching.

[0051] By stretching the barrier film 3, or at least the substrate layer 4 of the barrier film 3, the weight proportion of polyolefin (PE or PP) in the paper packaging laminate 1 can be kept low, since only by this stretching can a thin but still stiff film be produced.

[0052] As is known, the orientation of a barrier polymer can significantly increase its barrier properties. By orientation of the barrier polymer, barrier values ​​that are approximately 3 to 4 times higher than for the same unoriented barrier polymer can be achieved, which allows the use of less expensive barrier polymers while still maintaining the same barrier properties. This allows the cost of the paper packaging laminate 1 to be significantly reduced.

[0053] The adhesive layer 5 is used to bond the barrier layer 6 and the substrate layer 4. In this case, sufficient adhesion should be achieved, in particular to prevent undesired delamination of the barrier film 3. Suitable polar adhesive layers 5 preferably consist of polymers with increased polarity, for example polyolefins modified with maleic anhydride (e.g. PE or PP), polymers based on ethylene-vinyl acetate copolymers (EVA), ethylene / acrylic acid copolymers (EAA), ethylene-butyl acrylate (EBA) or similar polyolefin copolymers. The material of the adhesive layer 5 is preferably selected to match the main components of the substrate layer 4. The thickness of the adhesive layer 5 is at most 10% of the total thickness of the barrier film 3, for example from 1 to 5 μm when the thickness of the barrier film 3 is from 10 to 40 μm.

[0054] The sealing layer 7 is preferably polyethylene, for example LLDPE, LDPE, MDPE or HDPE, if the main component of the substrate layer 4 is PE. Just like in the case of a multi-layer sealing layer 7 of the same or different PE types, a mixture of different PE types in the sealing layer 7 is also conceivable. If the main component of the substrate layer 4 is polypropylene, the sealing layer 7 is preferably polypropylene, for example unoriented PP (CPP). In this case too, the sealing layer 7 can be a mixture of different PPs and / or can be constructed in a multi-layered manner. The thickness of the sealing layer 7 should be as thin as possible in the sense of improved recyclability, in particular less than 50 μm, in particular less than 30 μm.

[0055] If necessary, an adhesive layer 8, e.g. as described above (suggested in FIG. 3), may also be provided between the barrier film 3 and the sealing layer 7 to improve adhesion.

[0056] In order for the paper packaging laminate 1 to be well recyclable, the polymer components of the paper packaging laminate 1 (essentially the barrier film 3 and, if present, the sealing layer 7) should account for between 10% and 50% by weight of the paper packaging laminate 1, preferably at most 30% by weight, particularly preferably at most 20% by weight. The paper packaging laminate 1 according to the invention therefore follows a different approach from the recommendations in the prior art, which require that the polymer proportion be kept below 5% by weight. Nevertheless, in order to achieve good recyclability, the paper layer 2 is not coated on the barrier film 3 side and is joined to the barrier film 3 by means of a hydrophilic adhesive layer 9.

[0057] If the paper packaging laminates 1 are to be recycled, they are usually softened by immersion in water at a defined water temperature and for a defined time after mechanical attenuation (pulping process). Due to the properties of the paper packaging laminate 1 according to the invention, the paper layer 2 peels off from the barrier film 3 during the pulping process in recycling with all layers and potential impurities of the paper recycling. The hydrophilic adhesive layer 9 reacts with water during the pulping process and in the process loses its adhesive properties or dissolves completely in water, so that the paper layer 2 is separated from the barrier film 3. The paper layer 2 can therefore dissolve in water to form pulp, from which recycled paper can be produced again. For recycling the paper packaging laminate 1, it is advantageous when the adhesive layer 9 loses its adhesive properties or dissolves sufficiently at a water temperature of 40° C. within a maximum of 20 minutes, preferably within a maximum of 10 minutes, particularly preferably within a maximum of 5 minutes, so that the paper layer 2 and the barrier film 3 with the sealing layer 7 are easily separated.

[0058] The metal coating (if present) remains on the peeled barrier film 3 after separation during the pulping process during paper recycling and therefore does not result in darkening of the recycled paper that would inevitably occur when a paper surface is barrier metal coated.

[0059] The barrier film 3 (possibly with sealing layer 7) separated from the paper layer 2 during paper recycling can be fed to a further recycling process in order to allow the polyolefin contained therein (main component PE or PP) to be reused. Due to the purest possible design of the barrier film 3 and of the sealing layer 7 with either the main component PE or PP and materials compatible therewith, the barrier film 3, optionally also with the sealing layer 7, can be reused simply and cost-effectively in mechanical recycling using conventional methods. If the barrier layer 6 in the barrier film 3 is thin, the recycle suitability of the polyolefin stream coming out of the pulp of the paper recycling is not impaired.

[0060] The barrier film 3 is advantageously formed by coextrusion, since this allows a particularly simple and cost-effective production. Preferably, the known blown film or flat film extrusion methods are used. In this case, the individual layers of the previously described symmetric or asymmetric layer structure of the barrier film 3, i.e. the substrate layer(s) 4 and the bonding layer(s) 5, optionally the barrier layer 6 consisting of a barrier polymer, except for any coatings that may be present, are preferably coextruded in one step. After coextrusion, this laminate is stretched in one or two directions. After this stretching, a further barrier coating can also be applied as a barrier layer 6 on the bonding layer 5 or on the barrier polymer of the barrier layer 6.

[0061] The barrier film 3 can also be co-extruded with the sealing layer 7 in one step. In this case, the sealing layer 7 is also stretched together with the barrier film 3. Alternatively, the sealing layer 7 can be joined to the stretched barrier film 3 by extrusion lamination (extrusion of the sealing layer 7 onto the barrier film 3) or in a lamination process (joining the barrier film 3 and the sealing layer 7 with a lamination adhesive). A stretched sealing layer 7 can also be used during lamination of the sealing layer 7.

[0062] Particularly preferably, the sealing layer 7 is directly integrated into the barrier film 3, for example by coextrusion, when it is formed on the barrier film 3 on the side opposite the barrier layer 6. This allows the sealing layer 7 to be designed thinner and the total proportion of polymer in the paper packaging laminate 1 to be smaller, as compared to a sealing layer 7 that is applied later. Apart from this, this simplifies production.

[0063] In this case, the stretching of the barrier film 3 (optionally with the sealing layer 7) can take place in-line (i.e. directly after coextrusion) or off-line (i.e. at a later time point following coextrusion). In this case, in the case of bidirectional stretching, it is equally conceivable to stretch first in the machine direction and then in the transverse direction or simultaneously in both directions. This stretching is typically carried out at a temperature about 10° C. to 30° C. lower, typically about 20° C. lower (for HDPE, approximately 128° C. to 130° C.), than the lowest melting temperature of the plastic in the barrier film 3 or in the optional sealing layer 7. This stretching is in any case carried out before the optional coating of the barrier layer 6 and / or the bonding layer 5.

[0064] In the case of a hollowed PE or PP in the base layer 4, microcavities are formed in the PE or PP by the unidirectional or bidirectional stretching due to a cavity-forming agent, as is known in the art. The microcavities then increase the density of the base layer 4 to between 0.4 and 0.85 g / cm. 3 It has been confirmed that the value of .gtoreq..times ...

[0065] The paper layer 2 is laminated with a barrier layer 3, optionally provided with a sealing layer 7. For this purpose, a hydrophilic lamination adhesive can be applied in liquid form, either on the paper layer 2 or on the barrier film 2 or on both, e.g. by roller or print application or by spraying. The paper layer 2 and the barrier film 3 are then pressed together, e.g. between two rollers, to produce the paper packaging laminate 1. If necessary, the lamination adhesive can then be dried, e.g. by passing through a heat tunnel, for the formation of an adhesive layer 9.

[0066] Alternatively, the paper layer 2 and the stretched barrier film 3 can be joined using a suitable lamination adhesive using an extrusion lamination process in which a molten lamination adhesive is extruded onto the paper layer 2 or onto the barrier film 3 or onto both, and the paper layer 2 and the barrier film 3 are then pressed together, for example between two rollers, to produce the paper packaging laminate 1. The lamination adhesive can then be cooled, which can usually be assisted by chilled rollers.

[0067] The sealing layer 7 of the paper packaging laminate 1 may be laminated either after the paper layer 2 and the barrier film 3 have been laminated.

[0068] In an exemplary embodiment, a barrier film 3 having a thickness of 10 to 40 μm is used with a substrate layer 4 containing PE (the proportion of PE is at least 60% by weight), preferably HDPE, as the main component, which accounts for at least 60% of the thickness of the stretched barrier film 3. As the bonding layer 5, a polar PE or PP material (depending on the main component of the substrate layer 4) is used. A barrier layer 6 made of EVOH (barrier polymer) is bonded to this bonding layer 5. The barrier film 3 is coextruded and then stretched in one or two directions. Additionally, the barrier polymer may be coated with a barrier coating (metallized, SiOx or AlOx) after stretching. In an alternative embodiment, a barrier coating is applied onto the stretched substrate layer 4 with the bonding layer 5. The at least partially stretched barrier film 3 is bonded to the paper layer 2 with an adhesive layer 9 made of a hydrophilic laminating adhesive. Additionally, the paper packaging laminate 1 may comprise, on the side opposite the paper layer, a sealing layer 7 made of a PE material.

Claims

1. 30 to 360 g / m ２ A recyclable paper packaging laminate comprising a paper layer (2) using paper having a basis weight of up to 100 g / m2 and a barrier film (3) bonded thereto, The barrier film (3) comprises at least one substrate layer (4), an adhesive layer (5) and a barrier layer (6), wherein the adhesive layer (5) is disposed between the substrate layer (4) and the barrier layer (6); the substrate layer (4) is predominantly composed of polyethylene or polypropylene, with a polyethylene or polypropylene proportion of at least 60% by weight, preferably at least 70% by weight and very particularly preferably at least 80% by weight of the substrate layer (4); At least said at least one substrate layer (4) of the barrier film (3) is stretched; the proportion of the paper layer (2) is between 50% and 90% by weight of the paper packaging laminate (1), preferably between 70% and 90% by weight; and The barrier film (3) is bonded to the paper layer (2) using a hydrophilic adhesive layer (9), provided that the paper layer (2) is not coated on the barrier film (3) side. A recyclable paper packaging laminate, characterized by:

2. 2. The recyclable paper packaging laminate according to claim 1, characterized in that the barrier film (3) is asymmetrically designed with a substrate layer (4) joined to a barrier layer (6) via a joining layer (5).

3. 3. The recyclable paper packaging laminate according to claim 2, characterized in that the barrier layer (6) is arranged on the paper layer (2) side and is joined to the paper layer (2) via an adhesive layer (9).

4. 2. The recyclable paper packaging laminate according to claim 1, characterized in that the barrier film (3) is designed symmetrically with barrier layers (6) which are joined on both sides to substrate layers (4) via respective joining layers (5) and one of these substrate layers (4) is joined to the paper layer (2) via an adhesive layer (9).

5. 5. Recyclable paper packaging laminate according to claim 1, characterized in that the barrier layer (6) is formed as a barrier coating in the form of a metallization or in the form of a silicon oxide or aluminum oxide coating.

6. 5. Recyclable paper packaging laminate according to any one of claims 1 to 4, characterized in that the barrier layer (6) is formed as a layer of a barrier polymer, preferably a polyamide or an ethylene-vinyl alcohol copolymer.

7. 7. A recyclable paper packaging laminate according to claim 6, characterised in that a barrier coating in the form of a metallisation or in the form of a silicon oxide or aluminium oxide coating is provided on the layer of barrier polymer.

8. 7. Recyclable paper packaging laminate according to claim 6, characterised in that the barrier film (3) is oriented.

9. 9. Recyclable paper packaging laminate according to any one of claims 1 to 8, characterized in that the barrier film (3) is joined to a sealing layer (7) on the side opposite the paper layer (2).

10. 10. The recyclable paper packaging laminate according to claim 9, characterized in that the sealing layer (7) consists of polyethylene when the base layer (4) mainly consists of polyethylene or the sealing layer (7) consists of polypropylene when the base layer (4) mainly consists of polypropylene.

11. Recyclable paper packaging laminate according to claim 9 or 10, characterised in that the sealing layer (7) is oriented.

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