MULTI-LAYER BLOCKED FILM COMPOSITE

Description

[0001] The invention relates to a polyolefin-based film composite comprising a first monoaxially stretched film layer and a second film layer directly or indirectly bonded to the first film layer. Furthermore, the invention relates to a film packaging comprising a film composite material according to the invention.

[0002] A film composite is a composite material composed of several film layers, combining the advantageous properties of each layer. The film layers are formed from single- or multi-layer plastic films, which are manufactured separately and then bonded together. A laminating adhesive can be used for this purpose.

[0003] Due to their versatility, film composite materials are widely used as packaging materials, for example, in pouch packaging. In the past, the different requirements were specifically addressed by film layers made of different materials: For example, abrasion-resistant and durable film layers made of polyesters, such as polyethylene terephthalate (PET) or biaxially oriented polypropylene (BOPP), were often used as outer layers.

[0004] On the inside, however, layers of easy-melting and viscous polyolefins, such as polyethylene (PE), are often used as so-called "sealing layers." These serve to bond the film laminate / film composite to sealable plastic surfaces, such as similar or dissimilar films and film laminates.

[0005] Additional barrier layers, such as metal foils or metallized plastic films, are often used between the outer and sealing layers. These serve to reduce the permeability of the film composite, particularly to oxygen and / or water vapor.

[0006] However, this diverse mix of different materials poses significant sustainability challenges. Due to the virtually inseparable bond between different plastic materials, pure recycling is impossible. Additional contaminants, such as metallic components, also continue to reduce the recyclability of existing composite materials.

[0007] The invention is therefore based on a so-called "single-material" polymer material that is polyolefin-based. Within the scope of the present invention, this is to be understood as meaning that the film composite (or a single film layer) is made of one or more polymer materials that are predominantly (i.e., at least 50% by weight) composed of one or more polyolefins or their blends or copolymers. This is due to the fact that polyolefins have similar chemical properties and are therefore particularly well suited for recycling together. In particular, the invention relates to a film composite that is based either on polyethylene (PE) or polypropylene (PP). This enables virtually pure recycling.

[0008] From DE 10 2018 132 333 A1 a film composite with an outer layer oriented by stretching and an unstretched sealing layer is known.

[0009] The problem here, however, is that common formulations and structures of polyolefin-based film layers – particularly those made of PE and / or PP – do not yet exhibit equivalent properties to existing outer layers (particularly PET or BOPP) or metal-containing barrier layers. Compared to film layers made of PET, polyamide (PA), or biaxially oriented polypropylene, film layers made of a polyolefin, particularly PE, exhibit lower rigidity and lower thermal dimensional stability. As a result, the film composites formed from these layers can develop waviness when exposed to heat – for example, during a sealing process – which is detrimental to further processing. The resulting end product – for example, a packaging bag – also exhibits increased waviness, which complicates handling and filling and also leads to an unsightly appearance.

[0010] WO 2020 / 159 740 A1 discloses multilayer film composites and relates to the technological background of the invention.

[0011] Against this background, the invention is based on the object of further developing a polyolefin-based film composite such that it exhibits mechanical properties comparable to conventional multi-material composites. By eliminating non-uniform plastics, such as PET, the recyclability of the composite material can be significantly increased. At the same time, the CO2 footprint is also improved, since – in addition to potential material savings – less CO2 is released during the production of, for example, polyethylene than when a comparable amount of a plastic such as polyethylene terephthalate or polyamide is used.

[0012] The subject matter of the invention and the solution to this problem is a film composite according to claim 1 and a film packaging according to claim 11. Preferred embodiments are specified in the dependent subclaims.

[0013] The invention is based on a polyolefin-based film composite with a first stretched film layer and a second film layer directly or indirectly bonded to the first film layer. Based on this, the invention provides that the second film layer is unstretched and has at least two interlocked film layers. By combining these two film layers, the mechanical properties of the film composite can be optimized within the scope of the invention. This allows for improved flexural rigidity of the film composite or film laminate, particularly in so-called single-material structures.

[0014] Both the material webs of the film composite according to the invention and the film packaging produced therefrom (such as film bags) therefore exhibit less waviness and better flatness in practice. Within the scope of the invention, the particularly good stability of a monoaxially stretched first film layer, particularly in the machine direction (MD), is combined with the improved rigidity of a blocked second film layer.

[0015] The stabilization of a blocked film layer is based on the fact that films (especially multi-layer films) often exhibit intrinsic mechanical stresses as a result of solidification and cooling processes during production. These stresses create undesirable waviness in the cooled film web or in the product.

[0016] Within the scope of the invention, this effect is compensated for by blocking two films together. For this purpose, two single- or multi-layer films—preferably in a heated state—are brought into surface contact with two facing film layers, so that they are permanently bonded together. Particularly preferred is a first blocked film layer (first blocking layer) coming into contact with a second blocked film layer (second blocking layer), which have a nearly (at least 95 wt%) identical, preferably completely identical, polymer composition. The identical nature of the polymers guarantees particularly good cohesion.

[0017] Preferably, the first blocking layer is part of a first partial film (first block film) and the second blocking layer is part of a second partial film (second block film), which are blocked together to form the second film layer. The first block film and the second block film particularly preferably have an identical structure with a reversed sequence of the individual film layers. Thus, an identical first block layer and an identical second block layer are in direct contact with one another on the inside to form the blocking. In this preferred embodiment, a particularly smooth and at the same time stable film layer can be produced because the stresses arising in the two block films during production are each directed opposite to one another and of similar magnitude due to the reversed layer structure and therefore cancel each other out.In addition, the mechanical tension between the two interlocked block films increases the stiffness of the film layer and thus of the entire film composite.

[0018] According to a particularly preferred embodiment, the first block film and the second block film are parts of a self-blocked blown film tube. This ensures that the material properties and composition of the first block film and the second block film are always so similar to each other (at least locally) that a consistent force balance can be achieved across the entire film layer. It is also possible to combine the block films during the blown film process. Blocking thus particularly preferably occurs at an elevated temperature, at which the block films can develop strong bonding forces between them.

[0019] The first film layer preferably has a printing layer. This can therefore also be referred to as a "printing layer." The printing layer comprises pigments that can be used to influence the external appearance of the film composite—and thus of a packaging bag made from it. In particular, the first film layer forms a first outer side of the film composite. In addition to the pigments, the printing layer preferably also contains nitrocellulose (NC or cellulose nitrate), polyvinyl butyral (PVB), or polyurethane (PU) as a binder.

[0020] According to a particularly preferred embodiment, the printing layer is arranged on an inner side of the first film layer facing the second film layer. This is also referred to as inner or interlayer printing or counter printing.

[0021] According to a preferred embodiment, the film composite comprises—in addition to the monoaxially stretched first film layer (in particular MDO-PE) and the interlocked, unstretched second film layer—at least one further film layer. This can, for example, assume a further function relative to the first film layer and the second film layer—for example, as a barrier or sealing layer.

[0022] The blocked, unstretched second film layer is preferably arranged on an outer side of the film composite and designed as a sealing layer. The sealing layer comprises at least one low-melting sealing layer, which has a lower melting temperature than the remaining layers, in particular a lower melting temperature than the outermost layer opposite the sealing layer. This can, in particular, be a first layer designed as a printing layer.

[0023] The sealing layer serves to enable the film composite to be bonded together by what is known as heat sealing. This involves localized heating to melt, or at least partially melt, or plasticize the sealing layer. In In this state, it can form a permanent bond—for example, with another film or another (preferably similar) film composite. After cooling again, a solid mechanical bond results.

[0024] The polymer composition of the sealing layer is designed in particular such that when the entire film composite is heated to a specified sealing temperature, the sealing layer is rendered sealable, but the remaining film layers or film plies do not undergo irreversible changes. In particular, it must be ensured that the monoaxially stretched first film layer is not melted or the orientation of the material impaired. The temperature range below such a limit temperature and above the temperature at which the sealing layer becomes sealable (taking into account the sealing time and sealing pressure) is also referred to as the so-called "sealing window." Its limits are largely determined by the composition of the film composite.

[0025] The sealing layer particularly preferably contains a proportion of HDPE of at least 30 wt.%. The HDPE is preferably concentrated in one or more film layers (core layers) or arranged exclusively in the core layers. In particular, the core layers are not arranged on an outer side of the sealing layer, but are covered on the outside by at least one additional film layer. The HDPE contributes to a significant improvement in the mechanical properties. In particular, the strength and rigidity of the film layers can be improved as a result.

[0026] Furthermore, the sealing layer comprises at least one sealing layer with at least 20 wt.% of a PE with a density of no more than 0.905 g / cm3 (in particular ULDPE, VLDPE, and / or VLDPE-m). These are characterized by good meltability.

[0027] Furthermore, the sealing layer preferably contains at least 70 wt.% polyethylene with a density of not more than 0.92 g / cm 3 (LDPE, ULDPE, VLDPE, LLDPE, VLDPE-m and / or LLDPE-m).

[0028] For improved recyclability, the sealing layer consists of at least 70 wt.% homopolymers and α-olefin copolymers. In a particularly preferred variant, the sealing layer contains correspondingly less than 30 wt.% of vinyl or butyl copolymers with limited recyclability, such as EVA.

[0029] Most preferably, the formulation of the sealing layer also contains a PE plastomer. The PE plastomer particularly preferably makes up at least 30 wt.%, in particular between 30 wt.% and 50 wt.% of the sealing layer. Plastomers are very low-density ethylene-α-olefin copolymers that exhibit elastomer-like properties and very good sealing properties. They combine the properties of an elastomer with those of a thermoplastic. Corresponding materials are available under the trade names Exact (Exxon Mobile), Engage (Dow), or Queo (Borealis).

[0030] According to a particularly preferred embodiment, the invention relates to a film composite designed as a "single-material" system with a single dominant polymer type or a few dominant polymers. The film composite is thus particularly well suited for "single-material" recycling.

[0031] Within the scope of the invention, it is also possible for the unstretched, blocked second film layer to be formed internally. In particular, it can be arranged directly adjacent to the first film layer and covered on the side facing away from the first film layer by one or more additional film layers.

[0032] For this purpose, it is preferably provided that all film layers are based either on polyethylene (PE) or polypropylene (PP). This means that within the first film layer, within the second film layer, and optionally within one or more further film layers of the film composite, the sum of the weight fractions of polyethylene or polypropylene and their variants (in particular linear polyethylene, metallocene-catalyzed polyethylene, and its copolymers) is at least 50%, preferably at least 90%, very particularly preferably at least 95%. This ensures that recycling by melting produces a reasonably uniform plastic recyclate with technically usable properties.

[0033] Particularly preferably, the individual film layers are each composed of one or more film layers, each with uniform material properties. According to a particularly preferred embodiment of the invention, each of these individual film layers is based on PE or PP according to the above-mentioned criteria.

[0034] According to a particularly preferred embodiment of the invention, the film composite, preferably all film layers, and most preferably all film layers, are based on polyethylene. Thus, this embodiment variant relates to a "single-material" combination in the strictest sense, which can be recycled by melting to form a virtually ready-to-use plastic recyclate made of multimodal polyethylene. Within the framework of the inventive structure of the film layers, mechanical properties can be achieved that were previously only possible with a combination of different polymer materials.

[0035] According to a preferred embodiment of the invention, the film composite is free of film layers containing oriented polypropylene (OPP) or biaxially oriented polypropylene (BOPP). It is also preferably provided within the scope of the invention that the film composite is free of polyethylene terephthalate (PET), in particular free of any polyester. Reducing or completely eliminating these previously common materials can lead to a reduction in manufacturing costs and, in particular, to a reduction in the carbon dioxide (CO2) generated during production. This is to be welcomed from both an economic and environmental perspective. At the same time, application-appropriate mechanical parameters can be achieved within the framework of the layered and stratified structure according to the invention.

[0036] According to a preferred embodiment, at least one further film layer is designed as a barrier layer. This has at least one film layer designed as a barrier layer. This can, in particular, contain ethylene-vinyl alcohol copolymer (EVOH). Preferably, the barrier layer is formed predominantly, in particular 100%, from EVOH. The EVOH can preferably contain a weight fraction of between 24% and 48%, in particular approximately 32%, ethylene.

[0037] Alternatively, the barrier layer is formed from polyvinyl alcohol (PVOH). Here, too, the barrier layer is predominantly composed of polyvinyl alcohol, i.e., at least 50 wt.%, particularly preferably at least 80 wt.%, and in particular at least 90 wt.%. A PVOH-based barrier layer is preferably formed on an outer side of one of the film layers or as a coating between two adjacent film layers.

[0038] According to a particularly preferred embodiment, the barrier layer has a thickness between 1 µm and 10 µm, preferably between 3 µm and 5 µm, in particular approximately 4 µm. With a corresponding film thickness—relative to a film composite thickness of between approximately 100 µm and 200 µm—impurities in the barrier layer (e.g., made of EVOH) can be easily recycled in a mixture containing predominantly PE, linear PE, PE-m, and / or PP.

[0039] According to a particularly preferred embodiment, several, preferably all, film layers of the film composite comprise at least two interlocked film layers. The advantage of increased stability and reduced tendency to ripple formation created by the use of the interlocked film layer becomes even more apparent when a large number of interlocked film layers are used.

[0040] In a three-layer film composite structure comprising a print layer, a barrier layer, and a sealing layer, within the scope of the invention, at least the sealing layer is preferably formed with two interlocked film layers. However, the outer print layer can preferably also additionally comprise two interlocked film layers. It is also conceivable that, in addition to the sealing layer, only the barrier layer comprises two interlocked layers. Most preferably, each of the print layer, the barrier layer, and the sealing layer each comprise at least two interlocked film layers.

[0041] The thickness of the first layer (especially as a printing layer) is preferably between 20 µm and 50 µm, preferably approximately 30 µm.

[0042] Furthermore, it is preferably provided that the second film layer (in particular as a sealing layer) has a thickness between 60 µm and 250 µm, in particular between 100 µm and 180 µm.

[0043] A third further film layer (in particular as a barrier layer) arranged between the first film layer and the second film layer also preferably has a thickness between 20 µm and 80 µm, in particular between 20 µm and 50 µm.

[0044] Within the scope of the present invention, the film layers of the film composite can be bonded to one another in the usual way. In particular, they are bonded to one another over their entire surface by a laminating adhesive—in this case, one also speaks of a film laminate. The laminating adhesive is preferably PUR-based (polyurethane-based). Within the scope of the invention, film layers of the film composite can also be bonded to one another by thermal lamination or extrusion lamination.

[0045] In other words, the invention also relates to the use of at least one unstretched and blocked film layer in a laminate or film composite in combination with an at least monoaxially stretched second film layer.

[0046] Within the scope of the invention, the following film layer arrangements are particularly preferred: 1.) Unblocked first film layer with machine direction-oriented polyethylene (MDO-PE), multilayer unblocked middle film layer with film layers of PE-EVOH-PE, and a second film layer with blocked PE layers. 2.) Blocked first film layer with machine direction-oriented polyethylene (MDO-PE), multilayer unblocked middle film layer with film layers of PE-EVOH-PE, and a second film layer with blocked PE layers. 3.) Unblocked first film layer with machine direction-oriented polyethylene (MDO-PE), multilayer blocked middle film layer with film layers of PE-EVOH-PE, and a second film layer with blocked PE layers. 4.) Interlocked first film layer with machine-direction-oriented polyethylene (MDO-PE), multilayer interlocked middle film layer with film layers made of PE-EVOH-PE, and a second film layer with interlocked PE layers. The layer sequence of the middle film layers is not limited to a polyethylene layer, an EVOH layer, and another PE layer, but can also include additional repositioned and / or interleaved film layers.

[0047] A further aspect of the invention relates to a film packaging, in particular a packaging bag with an interior space defined by at least one film section. According to the invention, the film section is formed from a film composite as described above. Examples of implementation

[0048] To determine the effectiveness of the present invention, a series of tests were conducted in which a conventional and an improved film material from the prior art were compared with a variant according to the invention. To enable qualitative and quantitative comparison of the film composites, the comparison samples were designed with an identical overall thickness.

[0049] The three comparison films had a three-layer structure with an outer layer (printing layer), a middle barrier layer, and an inner sealing layer. To ensure comparability of the results, the printing layer and the barrier layer of the comparison examples were identical: In the following compositions, the polymer materials from the polyethylene (PE) group used in the tests are to be understood as belonging to the following density classes, according to the usual classification, where the density (unless otherwise stated) is given in grams per cubic centimeter (g / cm3) and the proportions are given as percent by weight (wt.-%): Without additional information, ordinary polyethylene is divided into three density classes: LDPE (low density PE) between 0.915 and 0.927 g / cm 3< , MDPE (medium density PE) with a density between 0.928 and 0.940 g / cm 3< and HDPE (high density PE) with a density range between 0.941 and 0.963 g / cm 3<.

[0050] In the area of ​​linear polyethylenes, a distinction is usually made between ULDPE (ultra low density PE) between 0.860 and 0.899 g / cm 3 , VLDPE (very low density PE) between 0.900 and 0.917 g / cm 3 , LLDPE (linear low density PE) between 0.918 and 0.927 g / cm 3 , LMDPE (linear medium density PE) between 0.928 and 0.940 g / cm 3 , and LHDPE (linear high density PE) between 0.941 and 0.963 g / cm 3 . Linear polyethylenes are ethylene-α-olefin copolymers that are fully miscible with the homopolymers LDPE, MDPE, and HDPE and have very similar properties. Therefore, they do not limit recyclability and can be fully classified as polyethylenes in the sense of a single-material material.

[0051] The metallocene-catalyzed material classes VLDPE-m and LLDPE-m typically have the same density range as their conventional linear counterparts (0.900–0.917 g / cm 3 and 0.918–0.927 g / cm 3 , respectively). Only the medium and heavy metallocene-catalyzed polyethylene classes exhibit a comparatively higher density of 0.928–0.947 g / cm 3 for LMDPE-m and 0.948–0.963 g / cm 3 for LHDPE-m.

[0052] The polyethylene copolymers EVA (ethylene-vinyl acetate), EMA (ethylene-methyl acrylate), EBA (ethylene-butyl acrylate), and EAA (ethylene-acrylic acid) each have densities exceeding 0.92 g / cm³. Copolymers such as COC (cycloolefin copolymers) can be significantly higher, with a density of approximately 1.02 g / cm³. Copolymers containing ethylene can also be classified, at least to a limited extent, as single-component polyethylenes. Nevertheless, they should only be present in small quantities.

[0053] When pursuing a "single-component" strategy, however, foreign polymers without any ethylene content should be avoided. The goal is to use at least 95 wt.% homopolymers and linear copolymers.

[0054] The outer layer of all samples was formed as a three-layer coextrusion film with a first layer (outer layer with a thickness of 7 µm) made of a blend of HDPE and LMDPE. The second core layer had a thickness of 11 µm and was made of a blend of HDPE, LLDPE, and MDPE. The third layer, located inside the film composite and provided with a counterprint, was again made of a blend of HDPE and LMDPE with a thickness of 7 µm. The total density of the outer layer in the exemplary embodiment was 0.94 g / cm³. The outer layer was also monoaxially stretched in the machine direction and thus oriented.

[0055] The barrier layer had a symmetrical five-layer structure with two outer layers (the outer layer and the sealing layer) made of 9 µm polyethylene. These were each followed by two 4 µm adhesion promoter layers of a maleic anhydride-grafted polyethylene copolymer (PE-MAH). Between the two adhesion promoter layers, a 4 µm thick layer of ethylene-vinyl alcohol copolymer (EVOH) with an ethylene content of approximately 32% was formed as an oxygen and grease barrier.

[0056] The three comparison samples differed only in the structure of the sealing layer, which in all three cases had a thickness of 160 µm. 1. Comparison sample (state of the art)

[0057] The first prior art comparison sample had a sealing layer with a three-layer coextruded structure. The first sealing layer, 40 µm thick, comprised a polymer blend of 70% LMDPE with a density of approximately 0.93 g / cm³ and a melt flow index (MFI) of 0.5 g / 10 min and 30% LLDPE with a density of 0.92 g / cm³ and a melt flow index of 1.5 g / 10 min.

[0058] The subsequent second sealing layer had a thickness of 80 µm and was made of the same blend as the first sealing layer. The third sealing layer (the actual sealing layer for bonding with other films or film composites) consisted of 40 µm of a blend of 55% polyethylene plastomer with a density of 0.9 g / cm³ and a melt flow index of 1.4 g / 10 min, 40% ethylene vinyl acetate (EVA) with a vinyl acetate content of 2.5%, a density of 0.924 g / cm³ and a melt flow index of 1.2 g / 10 min, and 5% LDPE with a density of 0.91 g / cm³ and a melt flow index of 2 g / 10 min. This formulation guarantees a low melting temperature, so that targeted melting of the innermost sealing layer can be ensured in the largest possible sealing window without affecting the outer layer of MDOPE. 2. Comparison sample (state of the art)

[0059] In a second, prior-art comparison sample, an improved formulation was used for the sealing film, resulting in improved mechanical properties. The film laminate had an identical outer and barrier layer.

[0060] The sealing layer used in Sample 2 consisted of a three-layer coextrusion film with a first layer (facing the barrier layer) 40 µm thick. This layer was formed from a blend of 70% LMDPE with a density of 0.93 g / cm³ and a melt flow index of 0.5 g / 10 min and 30% LLDPE with a density of 0.92 g / cm³ and a melt flow index of 1.5 g / 10 min. This film layer contributed to the particularly high toughness of the sealing layer and thus of the film composite.

[0061] The first layer was followed by a second 80 µm thick layer made of 100% HDPE with a density of 0.96 g / cm3 and a melt flow index of 0.6 g / 10 min. This core layer of the sealing layer increased the strength and rigidity of the film composite.

[0062] For improved sealing properties, a third layer, also 40 µm thick, was arranged on the inside. This layer consisted of 65% of a PE plastomer with a density of 0.9 g / cm 3< and a melt flow index of 1.4 g / 10 min, 35% of an ethylene-vinyl acetate copolymer with a vinyl acetate content of 2.5 wt.%, a density of 0.924 g / cm 3< and a melt flow index of 1.2 g / 10 min and 5% of an LDPE with a density of 0.91 g / cm 3< and a melt flow index of 2 g / 10 min. 3. Embodiment (invention)

[0063] The sealing layer of the third embodiment according to the invention was formed from an 80 µm thick, three-layer coextrusion blown film, which was interlocked with itself to form a total layer with a thickness of 160 µm. This resulted in a total six-layer structure for the sealing layer according to the invention: The first layer facing the barrier layer—which simultaneously also formed the sixth layer (sealing layer)—was 16 µm thick in the exemplary embodiment and comprised a blend of 65% of a metallocene-catalyzed LLDPE-m with a density of 0.916 g / cm 3 and a melt flow index of 1.0 g / 10 min and 35% of a PE plastomer with a density of 0.9 g / cm 3 and a melt flow index of 1.4 g / 10 min.This material composition also provided a low melting temperature for a particularly large sealing window (temperature range between the melting point of the sealing layer and the melting point of the MDOPE outer layer).

[0064] The second and fifth layers were then applied as 52 µm-thick stabilizing layers, consisting of 60% HDPE with a density of 0.96 g / cm³ and a melt flow index of 0.6 g / 10 min, 25% bimodal LMDPE with a density of 0.93 g / cm³ and a melt flow index of 0.5 g / 10 min, and 15% LLDPE with a density of 0.92 g / cm³ and a melt flow index of 1.2 g / 10 min. The high HDPE content ensured the high strength and rigidity of the entire sealing layer. This effect was further enhanced by the fact that the two stabilizing layers (second and fifth layers) were spaced apart in the middle by the interlocking third and fourth layers. This created a so-called "plywood" effect, which further increased the flexural rigidity.

[0065] The interlocked third and fourth layers were each 12 µm thick and made of 100% ethylene-vinyl acetate copolymer (EVA) with a vinyl acetate content of 18 wt.%. This plastic layer had a density of 0.94 g / cm3 and a melt flow index of 0.5 g / 10 min. The high vinyl acetate content resulted in a particularly sticky plastic melt. This was advantageous because the film bubble collapsed while still warm, so that the facing EVA layers interlocked with each other. This created a particularly intimate bond between the two film layers, which - if at all - can only be distinguished from a single, continuous layer twice as thick under a microscope.

[0066] As an alternative to EVA, a plastomer can also be used as a tackifying blocking agent. Comparative measurements

[0067] The three comparison samples used had an overall identical film composite thickness and identical outer and barrier layers. This allowed the mechanical properties – largely determined by the sealing layer – to be directly and quantitatively compared. For this purpose, various standardized and non-standardized comparison tests were conducted. During the comparative measurements, it was determined that the inventive film composite according to the third sample – with identical thickness – exhibited significantly improved flexural rigidity. The remaining mechanical properties and internal quality tests simultaneously delivered consistently equivalent results.

[0068] In the comparative measurements, the flexural rigidity was first determined according to DIN 53121. At least five samples were measured separately for each of the different samples. The values ​​determined for the flexural rigidity according to the invention are 50% higher than those obtained from samples 1 and 2 taken from the state of the art. This is shown in Table 1 below: Characteristic Test direction Measured value:Minimum / mean / Maximum Unit State of the art invention Pattern 1 Pattern 2 Pattern 3 Bending stiffness MD 440 / 453 / 462 557 / 572 / 617 738 / 749 / 753 mNmm CD 467 / 496 / 522 617 / 639 / 673 713 / 741 / 753

[0069] For quality assurance purposes, other characteristic mechanical properties of the three reference samples were also measured and compared. In a further measurement campaign, the film mechanical properties were determined according to ISO 527-1 from five individual samples each. The results demonstrate overall equivalent and consistent behavior of the inventive film composite compared to the generic reference samples. The results are presented in Table 2 below: Characteristic Test direction Measured value:Minimum / mean / Maximum Unit State of the art invention Pattern 1 Pattern 2 Pattern 3 Tear resistance MD 94 / 97 / 100 101 / 104 / 107 102 / 106 / 109 N / 15mm 27 / 28 / 29 30 / 31 / 32 29 / 31 / 31 N / mm 2 Young's modulus 315 / 322 / 338 447 / 456 / 464 380 / 398 / 418 N / mm 2 Elongation at break 55 / 60 / 70 58 / 64 / 68 61 / 65 / 72 % Tear resistance CD 62 / 67 / 70 63 / 64 / 65 60 / 67 / 74 N15mm 19 / 20 / 20 19 / 19 / 19 17 / 20 / 22 N / mm 2 Young's modulus 319 / 333 / 347 457 / 460 / 464 411 / 425 / 438 N / mm 2 Elongation at break 919 / 985 / 1045 224 / 359 / 556 750 / 910 / 1025 %

[0070] The film composites were also subjected to a puncture resistance test according to DIN 14477. For this purpose, ten individual measurements were performed on finished bags made from the various sample materials, from the inside to the outside – corresponding to a puncture direction from the sealing layer to the outer layer. In this test, the film laminate according to the invention also demonstrated equivalent resistance to the prior art samples. - According to Table 3: Test direction Measured value:Minimum / mean / Maximum Unit State of the art invention Pattern 1 Pattern 2 Pattern 3 Puncture from inside of bag to outside 6,5 / 7,1 / 7,6 7,3 / 7,6 / 8,3 7,1 / 7,6 / 8,1 N

[0071] Furthermore, the applicant also conducted comparative tests in accordance with DIN 55529, with the seals produced in a bag-making system. In a further comparative test, the strength of the seals was compared.

[0072] For this purpose, film bags were first produced from the composite materials to be compared. The tested transverse seal seam in the bottom area of ​​the film bags was joined using permanently heated sealing jaws with a sealing time of 0.7 s. The upper sealing jaw had a temperature of 230 °C and the lower sealing jaw a temperature of 215 °C.

[0073] Strips 15 mm wide and at least 100 mm long were then cut from the finished bags perpendicular to the seams. These samples were clamped by their ends in a tensile testing machine so that the seal was centered between the clamping jaws. The jaw spacing was 50 mm at the beginning of the test procedure. The force required to break the 15 mm seal was then measured in Newtons. As can be seen from Table 4 below, the seal strength of the film composite according to the invention corresponds to the values ​​from the prior art: Seam position Measured value:Minimum / mean / Maximum Unit State of the art invention Pattern1 Pattern 2 Pattern 3 Cross seam 46 / 47 / 49 55 / 59 / 62 49 / 53 / 55 N / 15mm

[0074] The structural integrity of the bags manufactured from the various reference materials was verified in a practical test. For this purpose, the bags were filled with plastic granules. Based on the selected bag format and application, a specified fill volume of 15 kg of dry food was chosen for the reference bags. The bags were each dropped to the ground from a height of 1 m in different orientations. The orientations were chosen so that the filled bags impacted the ground with their front, back, and bottom surfaces. None of the test bags used sustained any damage. In particular, no film parts of the bag were destroyed and no seals were broken.

[0075] The reduced waviness and improved flatness of the material according to the invention were also demonstrated in a direct comparison of the samples. For this purpose, several film packaging bags made from the respective materials were stacked on top of each other. The stack of bags made from the material according to the invention, in the force-free state, achieved a height approximately 50% lower than that of the test bags made from materials 1 or 2.

[0076] The comparative measurements of the exemplary embodiment demonstrate improved mechanical properties of the single-material film composite according to the invention. This can provide an adequate replacement for conventional film composites.

[0077] A conventional multi-material film composite with a 20 µm thick outer layer made of oriented polypropylene (OPP), an intermediate layer of 12 µm made of metallized polyethylene terephthalate (PET-met) and a sealing layer made of polyethylene with a thickness of 140 µm can be used as a benchmark.

[0078] This results in a composite thickness of approximately 172 µm (plus adhesive and printing layers).

[0079] To achieve comparable mechanical properties and a sufficient barrier function, significantly greater layer thicknesses were previously required for "single-material" materials in the state of the art. For example, comparable properties could be achieved with a film composite consisting of 25 µm machine-direction oriented PE (MDOPE), 30 µm metallized PE film (optionally with a coextruded EVOH barrier layer or monoaxially stretched), and a 140 µm PE sealing layer. However, this film composite exhibits a significantly greater total thickness of at least 195 µm – and correspondingly higher material usage and greater environmental impact.

[0080] Due to the improved specific flexural rigidity of the sealing layer according to the invention, its layer thickness can be reduced in the overall composite. Thus, within the scope of the invention, an additional material reduction is possible while maintaining equivalent overall mechanical properties. By combining a 30 µm interlocked MDOPE print layer with a 60 µm interlocked PE-EVOH-PE barrier layer and an 80 µm interlocked barrier layer, equivalent mechanical properties can be achieved with a net total thickness of 170 µm. The teaching of the invention therefore even allows the film composite to be reduced overall compared to multi-material laminates.

[0081] The invention is explained below with reference to a single figure. This shows an embodiment according to sample 3 of the comparative measurements in cross-section.

[0082] The Fig. 1shows a cross section through a polyolefin-based film composite 1 according to the invention. This comprises a first film layer 2 stretched monoaxially in the machine direction (x) and a second film layer 3 indirectly connected to the first film layer 2.

[0083] The first film layer 2 is designed as a printing layer and has a printing layer 4 on the side facing the second film layer 3. This printing layer contains a mixture of a binder and printing pigments.

[0084] Furthermore, the first film layer 2 is formed as a three-layer coextrusion film with a first outer layer 2a made of a blend containing PE-HD and PE-LMD, a core layer 2b made of a blend of PE-HD, LLD, and MD, and an inner layer 2c made of a 7 µm blend of PE-HD and LLD printed by the printing layer 4. The total thickness of the first film layer 2 is 25 µm with a total density of 0.94 g / cm3.

[0085] Between the first film layer 2 and the second film layer 3, a further film layer 5 in the form of a barrier layer is arranged. The barrier layer is designed as a symmetrical five-layer coextrusion film with a 9 µm thick first film layer 5a and fifth film layer 5e made of polyethylene. Adjacent to this are a 4 µm thick adhesion promoter layer as the second film layer 5b and fourth film layer 5d made of maleic anhydride-grafted polyethylene. The core of the barrier layer 5 is formed by a 4 µm thick oxygen and grease barrier made of EVOH with an ethylene content of 32 wt.%. The first film layer 5a and the fifth film layer 5e are each fully laminated to the first layer 2 and the second layer 3, respectively, using a polyurethane-based laminating adhesive layer 6.

[0086] The second film layer 3 is arranged opposite the first film layer 2 on an outer side of the film composite 1 and is designed as a sealing layer. It is formed from a collapsed three-layer coextruded film bubble, resulting in a symmetrical six-layer structure: The first film layer 3a, facing the barrier layer 5, and the sixth film layer 3f of the second film layer 3 are formed from a blend of 65 wt.% PE-LLD-m and 35 wt.% of a PE plastomer with a thickness of 16 µm. The core layers of the sealing layer 3 are formed as the second layer 3b and the fifth layer 3e, 52 µm of a blend of 60 wt.% PE-HD, 25 wt.% of a bimodal PE-LMD, and 15 wt.% of a PE-LLD. The particularly high HDPE content improves the strength and rigidity of the sealing layer 3.

[0087] According to the invention, the second film layer 3 comprises a third film layer 3c and a fourth film layer 3d, which are interlocked according to the invention. The third film layer 3c and the fourth film layer 3d are made of 100 wt.% EVA with a VA content of 18 wt.%. This high VA content improves the adhesive properties, particularly in the heated state at the time of interlocking. The two interlocked EVA layers 3c and 3d each have a thickness of 12 µm – thus a total thickness of 24 µm.

[0088] In the illustrated embodiment, the first film layer 2 has a thickness a of 25 µm. The second film layer 3 has a thickness b of 160 µm. The barrier layer 5, in turn, has a thickness c of 30 µm.

Claims

1. Polyolefin-based film composite (1) comprising a monoaxially stretched first film layer (2) and a second film layer (3) bonded directly or indirectly to the first film layer (2), characterized in that the second film layer (3) is unstretched and comprises at least two film plies (3c, 3d) which are blocked to one another.

2. Film composite (1) according to Claim 1, characterized in that the first film layer (2) comprises a printed layer (4).

3. Film composite (1) according to Claim 1 or 2, characterized by at least one further film layer (5).

4. Film composite (1) according to one of Claims 1 to 3, characterized in that the second film layer (3) is arranged on an outer side of the film composite (1) and is embodied as a sealing layer.

5. Film composite (1) according to Claim 4, characterized in that the sealing layer (3) has a proportion by weight of at least 30% of HDPE.

6. Film composite (1) according to Claim 5, characterized in that the HDPE is arranged exclusively in one or more core plies (3b, 3e).

7. Film composite (1) according to one of Claims 4 to 6, characterized in that the sealing layer (3) comprises at least one sealing ply (3f) comprising at least 20% by weight of polyethylene having a density of not more than 0.905 g / cm3.

8. Film composite (1) according to Claim 7, characterized in that the sealing ply (3f) contains at least 70% by weight of polyethylene with a density of not more than 0.92 g / cm3.

9. Film composite (1) according to Claim 7 or 8, characterized in that the sealing ply (3f) preferably contains at least 30% by weight of a polyethylene plastomer.

10. Film composite (1) according to any one of Claims 1 to 9, characterized in that all the film layers (2, 3, 5) are based on polyethylene (PE).

11. Film composite (1) according to any one of Claims 1 to 9, characterized in that all the film layers (2, 3, 5) are based on polypropylene (PP).

12. Film composite (1) according to any one of Claims 1 to 11, characterized in that a plurality of, preferably all the film layers (2, 3, 5) each comprise at least two film plies (3c, 3d) which are blocked to one another.

13. Film composite (1) according to any one of Claims 1 to 12, characterized in that at least one film layer (5) as a multilayer structure comprises at least one barrier ply (5c), in particular made of ethylene-vinyl alcohol copolymer (EVOH).

14. Film composite (1) according to Claim 13, characterized in that the barrier ply (5c) has a thickness of at most 10 µm, preferably of at most 5 µm.

15. Film composite (1) according to any one of Claims 1 to 14, characterized in that the first film layer (2) has a thickness (a) between 20 µm and 50 µm, preferably between 25 µm and 35 µm, in particular about 30 µm.

16. Film composite (1) according to any one of Claims 1 to 15, characterized in that the second film layer (3) has a thickness (b) of between 60 µm and 200 µm, in particular between 100 µm and 180 µm.

17. Film composite (1) according to any one of Claims 1 to 16, characterized in that the first film layer (2) and the second film layer (3) have a total thickness of between 80 µm and 250 µm, in particular between 120 µm and 200 µm.

18. Packaging bag having an interior space defined by at least one film portion, characterized in that the film portion is formed from a film composite (1) according to any one of Claims 1 to 17.