Mdo film for recyclable laminate

Abstract

The invention relates to a monoaxially stretched, transparent film (1) for a recyclable laminate (8) for packaging. The film (1) comprises at least one outer layer (3) and at least one inner layer (6). The at least one outer layer (3) has a higher density than the at least one inner layer (6). The outer layer (3) comprises a mixture of at least two polyethylenes of different density. The polyethylene of higher density in at least one of the outer layers (3) has a density of more than 0.94 g / cm3, and the polyethylene of lower density in at least one of the outer layers (3) has a density of less than 0.94 g / cm3.

Description

[0001] MDO film for recyclable laminate

[0002] Description

[0003] The invention relates to a monoaxially stretched, transparent film for a recyclable laminate, wherein the film comprises at least one outer layer and at least one inner layer.

[0004] Current, commercially available plastic packaging is often film laminates made of different layers that are tailored according to their application and function, such as polyolefins such as polyethylene (PE) and / or polypropylene (PP), often combined with polyethylene terephthalate (PET) and / or polyamide (PA) to achieve the desired physical film properties.

[0005] Polyethylene has proven itself in the production of food packaging films, food bags, stretch films, shrink films, trash can liners, and shipping bags. Conventional blown or cast polyethylene films are often used for flexible packaging as individual wrap or as a laminating film.

[0006] At the same time, the way in which plastics and therefore also packaging films are currently produced and disposed of can also be harmful to the environment under certain circumstances. The consequences range from high CO2 emissions to ocean pollution. To counteract this, the European Union aims to reduce the amount of plastic waste going to landfills as part of its Green Deal. 55% of plastic packaging waste is to be recycled by 2030. To meet the challenges of recycling, packaging design must be made increasingly sustainable. This can be achieved, for example, by implementing more mono-material constructions. The challenge here lies in achieving the very different properties of a package that were previously achieved by combining different plastic layers with different material bases using just one recyclable mono-material construction.

[0007] It has been shown that biaxially oriented polypropylene films and biaxially oriented polyethylene films and cast polypropylene films offer good stiffness and toughness while being able to be made thinner.

[0008] Machine direction orientation gives films good stiffness and optical properties, which are advantageous for applying a printed image. However, if they are strongly oriented in the machine direction, the tear strength of the films can decrease significantly, making printability in modern in-line printing processes with high web speeds problematic. Furthermore, films with high orientation are likely to exhibit fibrillation, which can impair the quality and possibly the appearance of a print.

[0009] EP 3 317 100 B1 discloses a uniaxially oriented film having a first layer comprising a first composition comprising an ethylene-based polymer prepared in the presence of a single-site catalyst, wherein the first composition has a density of 0.935 g / cm 3 up to 0.965 g / cm 3 , a melt index of 0.5 to 6 g / 10 min and a molecular weight distribution of 6.0 or less and a Ziegler-Natta-catalyzed ultra-low density polyethylene having a density of 0.880 g / cm 3 up to 0.912 g / cm 3 , a melt index of 0.5 to 6 g / 10 min and a MWD of 6.0 or less; a second layer comprising at least one polyolefin; and at least one inner layer between the first layer and the second layer comprising a high density polyethylene or a Ziegler-Natta catalyzed ultra-low density polyethylene having a density of 0.880 g / cm 3 up to 0.912 g / cm3 and a melt index of 0.5 to 6 g / 10 min, wherein the film is oriented in the machine direction at a draw ratio of between 4:1 and 10:1 and the film has a 2 percent secant modulus of 590 MPa or more in the machine direction.

[0010] EP 3 481 630 B1 describes a recyclable polyethylene film made of at least 80% polyethylene material and a maximum of 20% compatible polyolefin material, wherein the polyethylene film is less than 40 μm thick and has a central layer made of linear low-density polyethylene and / or linear metallocene low-density polyethylene and two outer layers made of high-density polyethylene which are connected to the central layer and surround the central layer, wherein the HDPE proportion of the polyethylene film makes up at least 60% by volume, preferably at least 70% by volume, very particularly preferably at least 80% by volume, and wherein the polyethylene film is stretched in at least one direction and the two outer layers together are at least three times as thick, preferably at least four times as thick, as the central layer.In order to achieve sufficient heat resistance, polypropylene or cyclo-olefin copolymer must be added to the outer layers of this film, which means that a mono-material construction is no longer possible.

[0011] EP 2 860 031 B1 discloses a machine-direction stretched multilayer film suitable for labels, comprising a core layer and two outer layers sandwiched around the core layer, wherein the core layer comprises a bimodal ethylene / 1-butene / C6-C12 alpha-olefin terpolymer having a density between 926 kg / m 3 up to 950 kg / m 3 and the two outer layers are unimodal HDPE with a density of more than 940 kg / m 3 up to 970 kg / m 3 include.

[0012] WO 2021 / 076 552 A1 discloses a machine direction oriented polyethylene film having a core layer comprising a first ethylene-based polymer having a density of 0.870 g / cm 3 up to 0.920 g / cm3 and a peak melting point of 82 to 126 °C and a weight-related crystallinity of 15 to 30 as well as an outer layer comprising a second ethylene-based polymer with a density of 0.940 g / cm 3 up to 0.965 g / cm 3 and a peak melting point of 130 to 135 °C and a weight-related crystallinity of 30 to 80, and a subcutaneous layer located between and in contact with the core layer and the outer layer, wherein the subcutaneous layer comprises a third ethylene-based polymer having a density of 0.920 g / cm 3 up to 0.950 g / cm 3and a peak melting point of 125 to 130 °C and a crystallinity in weight percent of 40 to 65, with the ratio of the weight percent crystallinity of the core layer to the skin layer being 0.25 to 0.91. In particular, the use of low-density polyethylene, which is used to achieve sufficient toughness in the films, promotes fibrillation at high stretch ratios in the machine direction.

[0013] EP 3390 049 B1 discloses a laminated polyethylene-based film structure with barrier properties, comprising an oriented first film oriented at least in the machine direction with at least one layer A based on polyethylene polymer having a density of 890 to 980 kg / m 3 and optionally at least one layer B of high-density polyethylene (HDPE) with a density of 940 to 970 kg / m 3or medium density polyethylene (MDPE) with a density of 925 to 940 kg / m 3 or a linear low-density polyethylene (LLDPE) with a density of 910 to 950 kg / m 3, wherein the oriented first film is oriented at least in the machine direction at a stretch ratio of 1:1.5 to 1:12 and has a film thickness of 10 to 50 μm after orientation, and wherein the oriented first film is coated by a thin vapor-deposited ceramic or metal barrier layer on a surface of the oriented first film, wherein the oriented first film is laminated with the coated surface to a second film. The polyethylene polymer of layer A is selected from high density polyethylene (HDPE), medium density polyethylene (MDPE), or a linear low density polyethylene (LLDPE), or blends of linear low density polyethylene (LLDPE) with high pressure low density polyethylene (LDPE), or a blend of an ethylene-based plastomer with high pressure low density polyethylene (LDPE).

[0014] High-quality packaging laminates also usually feature an overprint created using a serial printing process, such as gravure or flexographic serial printing. Therefore, PET or PP film webs are often used as the printed film web in such film laminates. Currently, printed film webs with layer thicknesses of only 12 μm are used for this purpose. However, the construction of monolaminates made of polyethylene poses the problem of quality printability at such thin layer thicknesses.

[0015] The object of the present invention is to provide a film for a recyclable laminate that meets the requirements of a monomaterial construction and can ensure good mechanical properties. To this end, the film should be particularly stiff and exhibit sufficient toughness without a tendency to fibrillation. Furthermore, the film should have sufficient heat resistance and be easily recycled. At least one layer of the film or one ply of the laminate should possess the necessary sealing properties. The film should be inexpensive to print with excellent quality. The film should be harmless to health and ecologically sustainable. Furthermore, the film should be odorless.

[0016] This object is achieved according to the invention by a film for a recyclable laminate according to the main claim. Preferred variants can be found in the subclaims, the description, and the drawings.

[0017] According to the invention, at least one outer layer has a higher density than the at least one inner layer. The outer layer comprises a mixture of at least two polyethylenes of different densities, the higher-density polyethylene having a density of more than 0.94 g / cm 3 and the low-density polyethylene has a density of less than 0.94 g / cm 3 has.

[0018] Advantageously, the proportion of higher-density polyethylene in at least one of the outer layers in the mixture is more than 40 wt.%, preferably more than 60 wt.%, in particular more than 80 wt.%, and / or less than 95 wt.%, preferably less than 90 wt.%, in particular less than 85 wt.%. The proportion of higher-density polyethylene imparts excellent rigidity and heat resistance to the film.

[0019] In a particularly advantageous variant of the invention, the proportion of low-density polyethylene in at least one of the outer layers in the mixture is more than 5 wt.%, preferably more than 10 wt.%, in particular more than 15 wt.% and / or less than 60 wt.%, preferably less than 40 wt.%, in particular less than 20 wt.%. The proportion of low-density polyethylene ensures favorable toughness of the film.

[0020] Ideally, the density of the higher density polyethylene is a factor greater than the lower density polyethylene, the value of the factor being more than 1.002, preferably more than 1.005, in particular more than 1.008 and / or less than 1.20, preferably less than 1.15, in particular less than 1.10.

[0021] The flow behavior of polyolefins is described using the melt flow rate according to ISO 1133-1, typically at a temperature of 190 °C for polyethylene and 230 °C for polypropylene under a load of 2.16 kg, 5 kg, or 21.6 kg. A higher melt index correlates with a lower average molecular weight of the polymer. At the same time, the higher the melt index of a polymer, the lower the melt viscosity, which is advantageous for high output from the extrusion line. On the other hand, polymers with a high molecular weight, i.e., a low melt index, are advantageous in terms of mechanical stability, especially tensile strength and toughness.

[0022] For example, the inner or an inner layer is made of a polyethylene whose density according to ISO 1183-1 is more than 0.91 g / cm 3 , preferably more than 0.92 g / cm 3 and / or less than 0.95 g / cm 3, preferably less than 0.94 g / cm 3 and / or whose melt flow rate (at 190 °C at 5 kg) according to ISO 1133-1 is more than 0.1 g / 10 min, preferably more than 1.0 g / 10 min and / or less than 5.0 g / 10 min, preferably less than 3.0 g / 10 min.

[0023] In a variant of the invention, the inner layer is made of a polyethylene whose density according to ISO 1183-1 is 0.937 g / cm 3 amounts.

[0024] Advantageously, the polyethylene of the inner layer has a melt flow rate according to ISO 1133-1 of more than 1.0 g / 10 min, preferably more than 1.5 g / 10 min, in particular more than 1.9 g / 10 min and / or less than 4.0 g / 10 min, preferably less than 3.0 g / 10 min, in particular less than 2.1 g / 10 min at 190 °C and 5 kg. Furthermore, the melt flow rate according to ISO 1133-1 of the polyethylene of the inner layer is more than 20 g / 10 min, preferably more than 30 g / 10 min, in particular more than 40 g / 10 min and / or less than 65 g / 10 min, preferably less than 55 g / 10 min, in particular less than 45 g / 10 min at 190 °C and 21.6 kg. As a result, the polyethylene in the inner layer as well as the entire film achieves high toughness and, at the same time, high stiffness values.

[0025] For example, the polyethylene of the inner layer has a tensile elasticity (TD) of more than 730 MPa, a tensile strength (MD) of more than 60 MPa, and a melting temperature of more than 127 °C. These special physical parameters result in a film that can fulfill the specified task.

[0026] In a variant of the invention, the polyethylene of the inner layer has a bimodal molecular weight distribution.

[0027] In a particularly preferred variant, the film comprises more than one inner layer, preferably more than two inner layers, in particular more than four inner layers, all made of the same polyethylene. This special multi-layer construction gives the film particularly high toughness and rigidity, while at the same time particularly advantageously preventing the formation of fibrils.

[0028] Preferably, the high-density polyethylene has a medium molecular weight and a particularly narrow molecular weight distribution, which leads to good bubble stability and processability. Furthermore, the outer layer(s) exhibit excellent tensile strength and good elongation at break with a low tendency to fibrillation. This allows the film to be printed with particular precision and high quality, as the web tension during printing can be precisely achieved even at high web speeds while maintaining a particularly thin film web.

[0029] Ideally, the higher density polyethylene in at least one of the outer layers is formed from a HDPE whose density is more than 0.942 g / cm 3 , preferably more than 0.944 g / cm 3 and / or less than 0.97 g / cm 3 , preferably less than 0.965 g / cm 3and / or whose melt flow rate (at 190 °C at 21.6 kg) according to ISO 1133-1 is more than 5 g / 10 min, preferably more than 10 g / 10 min and / or less than 25 g / 10 min, preferably less than 20 g / 10 min.

[0030] Ideally, the HDPE in at least one of the outer layers has a melt flow rate according to ISO 1133-1 of more than 1.0 g / 10 min, preferably more than 1.25 g / 10 min, in particular more than 1.5 g / 10 min and / or less than 3.0 g / 10 min, preferably less than 2.0 g / 10 min, in particular less than 1.75 g / 10 min at 190 °C and 5 kg.

[0031] Furthermore, the melt flow rate according to ISO 1133-1 of the HDPE in at least one of the outer layers is more than 11 g / 10 min, preferably more than 13 g / 10 min, in particular more than 15 g / 10 min and / or less than 30 g / 10 min, preferably less than 20 g / 10 min, in particular less than 17 g / 10 min at 190 °C and 21.6 kg.

[0032] For example, the HDPE in at least one of the outer layers has a tensile elasticity of more than 880 MPa, a tensile strength of more than 20 MPa, and a melting temperature of more than 129 °C. These particular physical parameters result in a film that can fulfill the stated task. In an alternative variant of the invention, the HDPE in at least one of the outer layers has a melt flow rate according to ASTM D1238 of more than 0.1 g / 10 min, preferably more than 0.5 g / 10 min, in particular more than 0.8 g / 10 min and / or less than 3.0 g / 10 min, preferably less than 2.0 g / 10 min, in particular less than 1.0 g / 10 min at 190 °C and 2.16 kg. For example, this HDPE has a density of more than 0.961 g / cm 3 according to ASTM D792 and a tensile strength according to Elmendorf of more than 40 g in MD and more than 165 g in TD.

[0033] To ensure better adhesion of a high-quality print, the outer layers of the film are made of a high proportion of HDPE, which, in addition to the small proportion of low-density polyethylene, may also contain a proportion of additives.

[0034] Preferably, the high-density polyethylene has a medium molecular weight and a particularly narrow molecular weight distribution, which leads to good bubble stability and processability. Furthermore, the outer layers exhibit excellent tensile strength and good elongation at break with a low tendency to fibrillation.

[0035] Advantageously, the low-density polyethylene in at least one of the outer layers is formed from a polyethylene whose density is more than 0.91 g / cm 3 , preferably more than 0.92 g / cm 3 and / or less than 0.95 g / cm 3 , preferably less than 0.94 g / cm 3and / or whose melt flow rate (at 190 °C at 5 kg) according to ISO 1133-1 is more than 0.1 g / 10 min, preferably more than 1.0 g / 10 min and / or less than 5.0 g / 10 min, preferably less than 3.0 g / 10 min.

[0036] For example, the low-density polyethylene in at least one of the outer layers is formed from a bimodal polyethylene, preferably from a bimodal terpolymer, in particular from a bimodal ethylene / 1-butene / Ce-Ci2-alpha-olefin terpolymer. The combination of low-molecular-weight, high-density polymer chains and high-molecular-weight, low-density polymer chains results in a combination of stiffness and flexibility in the polyethylene in at least one of the outer layers. This enables an optimal balance between strength, impact resistance, stiffness, and processability of the resulting polyethylene in at least one of the outer layers.

[0037] In a particularly simple embodiment of the invention, the film comprises three layers. The inner layer is preferably made of a polyethylene with a density of, for example, 0.937 g / cm 3 while the two outer layers are made of a polymer mixture of HDPE and polyethylene with a density of, for example, 0.937 g / cm 3 are educated.

[0038] In a particularly advantageous variant of the invention, the film comprises a nine-layer structure. Preferably, three equally thin inner layers made of a polyethylene with a density of, for example, 0.937 g / cm 3 the core of the film, each surrounded by an inner intermediate layer. The inner intermediate layers are ideally also made of polyethylene with a density of, for example, 0.937 g / cm 3formed and approximately twice as thick as the inner layers. An outer intermediate layer is arranged between the inner intermediate layer and the outer layer. The outer intermediate layer is slightly thicker than the inner intermediate layer and preferably consists of a mixture of high- and low-density polyethylene. The outer layer has a thickness that is even slightly greater than the thickness of the outer intermediate layer and also consists of a mixture of high- and low-density polyethylene, with the outer layer additionally containing a small proportion of additives.

[0039] In the nine-layer structure, for example, the thickness of the inner layers is more than 5 pm and / or less than 7 pm before stretching.

[0040] In the nine-layer structure, for example, the thickness of the inner intermediate layers is more than 10 pm and / or less than 15 pm before stretching.

[0041] In a nine-layer structure, the thickness of the outer intermediate layers is, for example, more than 15 μm and / or less than 20 μm before stretching. For example, the outer intermediate layer facing the print is slightly thicker at approximately 19 μm than the outer intermediate layer facing away from the print, at approximately 16 μm.

[0042] In a nine-layer structure, for example, the thickness of the outer layers is more than 15 μm and / or less than 22 μm before stretching. For example, the outer layer facing the printing side is slightly thicker at approximately 20 μm than the outer layer facing away from the printing side, at approximately 17 μm.

[0043] In principle, five- and seven-layer films are also included within the scope of the invention, whereby the mechanical properties can be improved with increasing number of layers. In one variant of the invention, the thickness of the layers increases from the inner layer to the outer layer. This applies to three-layer to nine-layer films. This film design achieves particularly advantageous mechanical properties and thus produces a film that can be printed with high quality.

[0044] In a further variant of the invention, the inner layer is thicker than one of the outer layers, with the inner layer being thicker than one of the outer layers by a factor of more than 1.3, preferably by a factor of more than 1.6, in particular by a factor of more than 1.9. This can be the case, for example, with a three-layer variant of the film.

[0045] The advantageous mechanical properties have so far only been known for films based on a material mix of various thermoplastics. The monomaterial construction according to the invention is characterized by complete and easy recyclability.

[0046] In order to achieve the advantageous mechanical properties, the film is ideally stretched monoaxially in the machine direction by a factor of more than 2.0, preferably by a factor of more than 3.0, in particular by a factor of more than 4.0 and / or by a factor of less than 7.0, preferably by a factor of less than 6.5, in particular by a factor of less than 6.0.

[0047] The film thickness was measured according to DIN 53370 and reported as an average value. Advantageously, the film has a thickness of less than 60 μm, preferably less than 50 μm, in particular less than 40 μm, and / or more than 5 μm, preferably more than 10 μm, in particular more than 15 μm. Thus, the film is designed to be as thin and material-efficient as possible, yet still suitable for applying high-quality printing.

[0048] A frequently used method for printing on film is flexography. This is a direct relief printing process, also known as a web-fed rotary printing process. The flexible printing plates, made of photopolymer or rubber, are used in combination with low-viscosity printing inks. The raised areas of the printing form carry the image. The advantages lie in the cost-effectiveness due to the utilization of a large printing width and high printing speed, as well as the availability of inexpensive printing inks. The printing tools essentially consist of photopolymer printing plates and / or laser-engraved elastomer sleeves. Large print runs can be produced cost-effectively with flexography.

[0049] Preferably, the print is applied directly to an outer layer of the film. The print or overprint can be applied on the side facing away from the packaged goods or as a counterprint between the film and the layer. The overprint can be implemented as a printed motif. In the film sector, the term "print motif" refers to the thematic design element of an overprint. If appropriate, manufacturer-identifying print motifs can also be included in the overprint.

[0050] Preferably, the print is applied to an outer layer of the film using a flexographic printing process, whereby all common printing processes are in principle suitable for this purpose and are expressly included in the invention.

[0051] The special selection of polymers and the three- to nine-layer design result in a particularly thin film that nevertheless exhibits impressive mechanical properties, even in a monomaterial construction. Despite the thin design, the rigidity and toughness, achieved in particular by the polyethylene blend in at least one outer layer, result in excellent printability. In addition, the film is combined with at least one layer to form a packaging laminate, allowing for a wide range of sealing layers that can be sealed at low temperatures.

[0052] In a favorable variant of the invention, the multi-layer structure of the film is symmetrical, whereby the printability of both outer layers can be realized and thus a flexible variation can be made between the printing arrangement on the outside or the counter printing.

[0053] To ensure recyclability and thus also sorting in modern waste separation plants, such as the sink-float process, the density of the film is less than 0.99 g / cm 3 , preferably less than 0.98 g / cm 3 , in particular less than 0.97 g / cm 3 and / or more than 0.60 g / cm 3 , preferably more than 0.70 g / cm 3 , in particular more than 0.80 g / cm 3 .

[0054] The haze value is a measure of the haziness or gloss of transparent films. The method for measuring the haze value is described in the ASTM D 1003 standard and DIN EN ISO 2813. Ideally, the film should have a gloss according to DIN EN ISO 2813 of less than 7%, preferably less than 6%, especially less than 5%. This gives the laminate and film a particularly high-quality appearance.

[0055] Heat sealing is a common method for creating seals and seams in flexible packaging. Adhesive systems are also occasionally used. There are many different types of heat seals. The most common, especially for films, are thermal sealing, bar sealing, and impulse sealing.

[0056] Suitable film layers for heat sealing are LDPE and LLDPE, which can then be sealed with the film to form a laminate. LDPE exhibits better heat sealing properties than LLDPE. It seals at lower temperatures, seals over a wider temperature range, and exhibits better hot tack, largely due to its long-chain branching. Metallocene LLDPE with higher alpha olefins was developed to address this disadvantage of LLDPE. Another approach to achieving the best mix of properties for a specific application is to blend LLDPE and LDPE.

[0057] Thermal sealing uses two heated rods that apply pressure to the films to be sealed while simultaneously conducting heat to the interface, melting the films at those points. This pressure ensures good contact between the films and assists the penetration of the molten, viscous materials at the interface. After sufficient sealing time, the pressure of the rods is released, releasing the films. Therefore, the hot tack of the film material is critical for forming an adequate seal. The full strength of the seal develops as the film material cools, but the initial strength must be sufficient to maintain the integrity of the seal during cooling.

[0058] Sealing bars typically have rounded edges to prevent punctures, and one bar is often provided with an elastic surface to ensure even pressure during sealing. The sealing jaws are usually not flat, but rather serrated, creating a patterned seal. In thermal sealing variants, only one bar is heated and the other is not. Another variant uses heated rollers instead of bars; for example, a bag is sealed as it passes through the rollers.

[0059] To design a film with particularly advantageous sealing properties, at least one outer layer contains a proportion of polypropylene, wherein the proportion is more than 5 wt.%, preferably more than 10 wt.%, in particular more than 15 wt.%, and / or less than 50 wt.%, preferably less than 40 wt.%, in particular less than 30 wt.%. The proportion of polypropylene increases the heat resistance and thus also the temperature at which the film can be sealed without undermining the recyclability of the film.

[0060] Ideally, the layer has a thickness of more than 10 pm, preferably more than 15 pm, in particular more than 20 pm and / or less than 100 pm, preferably less than 80 pm, in particular less than 60 pm. Thus, depending on the application of the film, a thin sealing layer or, for example, a thick sealing layer when enclosing liquids can be realized.

[0061] Advantageously, the layer used to seal the film into a laminate is made of LDPE and / or LLDPE. Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. LDPE has more branches (at about 2% of the carbon atoms) than HDPE, so its intermolecular forces are weaker, its tensile strength is lower, and its elasticity is higher. The side branches mean that the molecules are less densely packed and less crystalline, which is why the density is lower. The production of LLDPE is initiated by transition metal catalysts, particularly Ziegler- or Philips-type catalysts. The actual polymerization process can be carried out either in the solution phase or in gas-phase reactors. Typically, octene is the comonomer in the solution phase, while butene and hexene are copolymerized with ethylene in a gas-phase reactor.LLDPE has higher tensile strength and higher impact and puncture resistance than LDPE. It is very flexible and expands under stress. It can be used to produce thinner films with better resistance to stress cracking. It has good chemical resistance. It has good electrical properties. However, it is not as easy to process as LDPE, has lower gloss, and a narrower heat-sealing range.

[0062] In a particularly advantageous variant of the invention, the film, including the layer, is made entirely of polyethylene. Polyethylene (PE) is a thermoplastic produced by chain polymerization of petrochemically produced ethylene. Polyethylene is semi-crystalline and non-polar. Thus, the film meets the requirements of the Plastics Pact, is based on a monomaterial construction, and is recyclable.

[0063] In an alternative variant of the invention, the film has at least one additional outer layer made of ethylene-vinyl alcohol copolymer (EVOH) and / or polyamide (PA). This additional layer can be formed as an outer layer, to which the print adheres better due to the higher polarity of the outer layer. At the same time, this additional outer layer improves the heat resistance and stiffness of the film. For this purpose, the additional layer made of EVOH and / or PA is particularly thin, so that the fabric content of the overall film is particularly low and the film is considered a monomaterial construction for recycling purposes. In one variant of the invention, the film comprises at least one further outer layer to create a matt film surface.

[0064] For example, the further outer layer does not contain any fillers, whereby the film has a haze value according to ASTM D1003 of more than 65%, preferably more than 75%, in particular more than 85% due to the further outer layer.

[0065] The further outer layer has, for example, a thickness of more than 4 pm and / or less than 10 pm.

[0066] For example, the additional outer layer can be arranged on the side of the film facing away from the print and / or visible from the outside. The matte surface gives the film a favorable appearance.

[0067] In an alternative variant of the invention, at least one of the layers can contain a proportion of LLDPE in order to increase the elasticity and thus also the Elmendorf tear strength of the film.

[0068] According to the invention, the process for producing a film for a recyclable laminate comprises several steps. First, at least two compositions of the polymer components are prepared, which are then extruded into a film with at least three, ideally nine, layers. The polymer blends differ in terms of the outer and inner layers. Advantageously, the film is stretched monoaxially in the machine direction, thereby achieving favorable properties with respect to the total density below 0.99 g / cm 3 , transparency and printability, as well as the stiffness and toughness of the film, are achieved. The film can then be directly printed and laminated with a layer. Ideally, extrusion is carried out as a blown extrusion process, which promotes the development of advantageous film properties, such as stiffness.

[0069] The film is produced by monoaxial stretching with a machine direction orientation, where the film is heated to a temperature slightly below its melting point and stretched in a specific orientation. Stretching can also be performed directly after extrusion, when the film is still at a temperature slightly below its melting point.

[0070] In an advantageous variant of the invention, the film is stretched monoaxially in the machine direction by a factor of more than 2.0, preferably by a factor of more than 3.0, in particular by a factor of more than 4.0 and / or by a factor of less than 7.0, preferably by a factor of less than 6.5, in particular by a factor of less than 6.0. This gives the film advantageous stiffness and favorable transparency, and at the same time, the density of the film has a value of less than 0.99 g / cm 3 .

[0071] According to the invention, the film is used as a recyclable printing carrier film for packaging laminates.

[0072] Further advantages and features of the invention will become apparent from the description of an embodiment with reference to a drawing and from the drawing itself.

[0073] Fig. 1 shows a schematic structure of the film according to the invention in the form of a laminate,

[0074] Fig. 2 shows another variant of the film.

[0075] Fig. 1 shows a schematic structure of the laminate 8, which is formed from the film 1 and the layer 7. A print 2 is arranged directly on an outer layer 3 of the transparent film 1 in the form of a counter print. The print 2 serves to identify the article to be packaged, as well as for visual recognition and to support the brand image of the article brand.

[0076] In this embodiment, the film 1 is designed with nine layers in a symmetrical structure, the respective layer thicknesses of which increase from the inner layer 6 to the outer layer 3. Furthermore, the density of the polymers also increases from the inside to the outside. The inner layer 6 in this embodiment is triple and extremely thin, each approximately 6 μm before stretching, and is made of a polyethylene with a density of 0.937 g / cm 3 and whose melt flow rate (at 190 °C at 5 kg) according to ISO 1133 is 2 g / 10 min.

[0077] Around each of the three inner layers 6 there is an inner intermediate layer 5 which is approximately twice as thick as the inner layer 6 and consists of the polyethylene described above.

[0078] An outer intermediate layer 4 is arranged between the inner intermediate layer 5 and the outer layer 3, with the layer thickness of the outer intermediate layer 4 being somewhat thicker than the inner intermediate layer 5, at approximately 16-19 μm before stretching. The outer intermediate layer 4 consists of a blend of two polyethylenes, with the proportion of higher-density polyethylene in this embodiment being 85 wt.% and the proportion of low-density polyethylene being 15 wt.%.

[0079] The outer layers 3 of the film 1 consist of a 2 wt.% additive content (a highly transparent silica-based anti-blocking and IR filter masterbatch in a PE carrier resin and / or a processing aid to level the melt flowability) and a blend of two polyethylenes, with the higher-density polyethylene content in this embodiment being 83 wt.% and the lower-density polyethylene content being 15 wt.%. The layer thickness of the outer layers 3 is between 17 and 20 μm before stretching.

[0080] In the illustrated embodiment, the higher density polyethylene of the outer layers 3 and the outer intermediate layers 4 is designed as a HDPE, the density of which is 0.946 g / cm 3 and whose melt flow rate (at 190 °C at 5 kg) according to ISO 1133 is 1.6 g / 10 min.

[0081] In the illustrated embodiment, the low-density polyethylene of the outer layers 3 and the outer intermediate layers 4 is designed as a polyethylene whose density is 0.937 g / cm 3 and whose melt flow rate (at 190 °C at 5 kg) according to ISO 1133 is 2 g / 10 min.

[0082] The nine-layer film 1 has a thickness of 119 pm after blow extrusion. After monoaxial stretching by a factor of 5.95, the thickness is 20 pm, with a density of 0.93 g / cm 3 .

[0083] The special selection of polymers and the nine-layer design result in a particularly thin film 1 that nevertheless exhibits convincing mechanical properties, even in a monomaterial construction. Layer 7 is made of LDPE.

[0084] Fig. 2 shows a schematic representation of a further embodiment of the laminate 8, which essentially corresponds to the embodiment in Fig. 1.

[0085] In the embodiment of Fig. 2, the higher density polyethylene of the outer layers 3 and the outer intermediate layers 4 is designed as a HDPE, the density of which is 0.962 g / cm 3 and whose melt flow rate (at 190 °C at 2.16 kg) according to ASTM 1238 is 0.85 g / 10 min.

[0086] Additionally, the film 1 has an optional outer layer 9 formed from an ethylene-vinyl alcohol copolymer (EVOH) layer. In the illustrated embodiment, the thickness of the outer layer 9 after stretching is 4 μm and is formed from a SoarnoL™ from Mitsubishi Chemicals.

Claims

Monoaxially stretched, transparent film (1) for a recyclable laminate (8) for packaging, wherein the film (1) comprises at least one outer layer (3) and at least one inner layer (6), characterized in that the at least one outer layer (3) has a higher density than the at least one inner layer (6), wherein the outer layer (3) comprises a mixture of at least two polyethylenes of different density, wherein the higher density polyethylene in at least one of the outer layers (3) has a density of more than 0.94 g / cm 3 and the low-density polyethylene in at least one of the outer layers (3) has a density of less than 0.94 g / cm 3Film according to claim 1, characterized in that the proportion of higher density polyethylene in at least one of the outer layers (3) in the mixture is more than 40 wt.%, preferably more than 60 wt.%, in particular more than 80 wt.% and / or less than 95 wt.%, preferably less than 90 wt.%, in particular less than 85 wt.%. Film according to claim 1 or 2, characterized in that the proportion of low-density polyethylene in at least one of the outer layers (3) in the mixture is more than 5 wt. %, preferably more than 10 wt. %, in particular more than 15 wt. % and / or less than 60 wt. %, preferably less than 40 wt. %, in particular less than 20 wt. %. Film according to one of claims 1 to 3, characterized in that the density of the higher-density polyethylene in at least one of the outer layers (3) is greater by a factor than the low-density polyethylene in at least one of the outer layers (3), the value of the factor being more than 1.002, preferably more than 1.005, in particular more than 1.008 and / or less than 1.20, preferably less than 1.15, in particular less than 1.10.Film according to one of claims 1 to 4, characterized in that the inner layer (6) is made of a polyethylene whose density is more than 0.91 g / cm. 3 , preferably more than 0.92 g / cm 3 and / or less than 0.95 g / cm 3 , preferably less than 0.94 g / cm 3 and / or whose melt flow rate (at 190 °C at 2.16 kg) according to ASTM D 1238 is more than 0.1 g / 10 min, preferably more than 1.0 g / 10 min and / or less than 5.0 g / 10 min, preferably less than 3.0 g / 10 min. Film according to one of claims 1 to 5, characterized in that the higher density polyethylene in at least one of the outer layers (3) is formed from a HDPE whose density is more than 0.942 g / cm 3 , preferably more than 0.944 g / cm 3 and / or less than 0.97 g / cm 3 , preferably less than 0.965 g / cm 3and / or whose melt flow rate (at 190 °C at 2.16 kg) according to ASTM D 1238 is more than 5 g / 10 min, preferably more than 10 g / 10 min and / or less than 25 g / 10 min, preferably less than 20 g / 10 min. Film according to one of claims 1 to 6, characterized in that the low-density polyethylene in at least one of the outer layers (3) is formed from a polyethylene whose density is more than 0.91 g / cm 3 , preferably more than 0.92 g / cm 3 and / or less than 0.95 g / cm 3 , preferably less than 0.94 g / cm 3 and / or whose Melt flow rate (at 190 °C at 2.16 kg) according to ASTM D 1238 is more than 0.1 g / 10 min, preferably more than 1.0 g / 10 min and / or less than 5.0 g / 10 min, preferably less than 3.0 g / 10 min. Film according to one of claims 1 to 7, characterized in that the low-density polyethylene in at least one of the outer layers (3) is formed from a bimodal polyethylene, preferably from a bimodal terpolymer, in particular from a bimodal ethylene / 1-butene / C6-C12 alpha-olefin terpolymer. Film according to one of claims 1 to 8, characterized in that the thickness of the layers increases from the inner layer (6) to the outer layer (3). Film according to one of claims 1 to 8, characterized in that the inner layer (6) is thicker than one of the outer layers (3), wherein the inner layer (6) is thicker than one of the outer layers (3) by more than a factor of 1.3, preferably by more than a factor of 1.6, in particular by more than a factor of 1.9.Film according to one of claims 1 to 10, characterized in that the film (1) is stretched monoaxially in the machine direction by more than a factor of 2.0, preferably by more than a factor of 3.0, in particular by more than a factor of 4.0 and / or by less than a factor of 7.0, preferably by less than a factor of 6.5, in particular by less than a factor of 6.

0.

12. Film according to one of claims 1 to 11, characterized in that the film (1) has a thickness of less than 60 pm, preferably less than 50 pm, in particular less than 40 pm and / or more than 5 pm, preferably more than 10 pm, in particular more than 15 pm.

13. Film according to one of claims 1 to 12, characterized in that a print (2) is arranged directly on an outer layer (3) of the film (1).

14. Film according to one of claims 1 to 13, characterized in that the multilayer structure of the film (1) is symmetrical.

15. Film according to one of claims 1 to 14, characterized in that the density of the film (1) is less than 0.99 g / cm 3 , preferably less than 0.98 g / cm 3 , in particular less than 0.97 g / cm 3 and / or more than 0.60 g / cm 3 , preferably more than 0.70 g / cm 3 , in particular more than 0.80 g / cm 3 amounts. Film according to one of claims 1 to 15, characterized in that the film (1) has a gloss according to DIN EN ISO 2813 of less than 7%, preferably less than 6%, in particular less than 5%. Film according to one of claims 1 to 16, characterized in that the film (1) has at least one additional outer layer (9) which is made of ethylene-vinyl alcohol copolymer (EVOH) or of polyamide (PA). Film according to one of claims 1 to 17, characterized in that the film (1) comprises at least one further outer layer for producing a matt finish which does not contain any fillers, the film (1) thereby having a haze value of more than 65%, preferably more than 75%, in particular more than 85%. Film according to one of claims 1 to 18, characterized in that the outer layer (3) has a proportion of polypropylene, the proportion being more than 5% by weight, preferably more than 10% by weight.-%, in particular more than 15 wt.% and / or less than 50 wt.%, preferably less than 40 wt.%, in particular less than 30 wt.%.

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