Recyclable polymer film with improved creasing properties and paper-like appearance, as well as packaging with such a polymer film.

Abstract

Film, in particular wrapping film for food, wherein the film has a density ≤ 1 g / cm³ 3 has and comprises a film-like support comprising a polymer, which has a first and a second surface opposite it, and on each of these surfaces a coating comprising a polymer is arranged, wherein the support has a modulus of elasticity ≥ 300 mPa and at least one of the coatings has a modulus of elasticity ≥ 300 mPa, characterized by the fact that a polymeric intermediate layer is arranged between the film-like carrier and at least one coating, wherein the intermediate layer has a modulus of elasticity. exhibits ≥ 1000 mPa.

Description

[0001] The present invention relates to a film, in particular wrapping film for food, wherein the film has a density ≤ 1g / cm³ 3 The invention comprises a film-like carrier comprising a polymer, which has a first surface and a second surface opposite it, and on each of these surfaces a coating comprising a polymer is arranged. The invention further relates to packaging comprising such a film, in particular wrapping film for food.

[0002] Wrapping films are used to protect and facilitate the handling of a wide variety of food products. Various types of wrapping films are available on the market, differing in their composition to suit different applications and products. These films typically consist of a paper-based backing and a polyolefin layer. Occasionally, metal foils are also used as a layer within this composite. Dairy products, for example, have specific requirements because they spoil particularly quickly and can emit unpleasant odors. Therefore, low permeability to water vapor, light, heat, and aromas is advantageous for wrapping films used for such products.

[0003] Furthermore, the packaging of many products requires that the volume between the product and the packaging be kept as small as possible in order to minimize contact between the product and the atmospheric oxygen contained in that volume.

[0004] Wrapping films are therefore often required to be easy to fold so that they fit snugly against the product, even at the folds, and create little to no space between the product and the packaging. An example of such a film is the wrapping film for butter or cheese. This film should adhere tightly to the surface of the product being wrapped, covering its entire surface. Excessive oxygen could cause the product to become rancid and / or produce the unpleasant odor of butyric acid.

[0005] In the past, these requirements were often met by coating a substrate, such as paper or polymer film, with a metallization, for example an aluminum layer.

[0006] From US patent 2008 / 0299364A1, a multilayer film is known which has at least three layers, namely two outer layers and a core layer. Each outer layer independently contains at least 50 wt.% of an LLDPE component produced with a catalyst having uniform active centers and having a density of less than 940 kg / m³. 3 and 3 to 50 wt.% of an LDPE component. The core layer comprises at least 50 wt.% of a polypropylene component and up to 50 wt.% of an LLDPE component produced with a catalyst having uniform active centers, with a density of less than 940 kg / m³. 3 .

[0007] However, due to their multi-component composition, such wrapping films are difficult to recycle. Furthermore, their density exceeds 1 g / cm³. 3 , so that separation, for example by floating in water, is difficult or even impossible.

[0008] The present invention is therefore based on the objective of providing a film, in particular a wrapping film for food, which is easily recyclable and yet meets the above-mentioned requirements regarding the protection of a product enclosed by such a film.

[0009] This problem is solved by a film according to claim 1 and a packaging according to claim 12. Preferred embodiments are the subject of the dependent claims.

[0010] A film according to the invention, which can in particular be a wrapping film for food, is characterized by having a density ≤ 1g / cm³.3 This results in easy separation of materials with a density > 1g / cm³ during recycling. 3 This is made possible by the film's ability to float in water. Furthermore, a low density has a positive effect on the overall weight of the product wrapped in such packaging, thus reducing transport costs. The transport and handling of the film until the product is packaged is also simplified. It may even be possible to use machines for handling that are not designed for the heavier packaging materials typically used.

[0011] Furthermore, a film according to the invention is characterized by having a film-like carrier comprising a polymer, which has a first surface and a second surface opposite it. A polymer-comprising coating is arranged on each of these surfaces. These coatings, in combination with the carrier, make it possible to adjust the properties of the film according to the respective requirements, for example, those specified by the type of product to be packaged. The coatings can, individually, together, or in combination with other layers, for example, the carrier and / or a bonding layer, ensure properties of the film such as a minimum guaranteed light transmission, air permeability, water vapor permeability, and / or aroma impermeability.

[0012] Surprisingly, it has been found that a film is particularly easy to handle, and therefore especially suitable for wrapping food, when the carrier has a stiffness ≥ 300 mPa and at least one of the coatings also has a stiffness ≥ 300 mPa. The specified stiffness preferably refers to the modulus of elasticity. It has been shown that a film with this stiffness of the carrier and at least one of the coatings can be folded over particularly well. This allows the film to fit very tightly to the product during packaging, even in the area of ​​corners and edges. As a result, the volume between the product and the packaging film, which could potentially be occupied by substances that could damage the product (e.g., gases), can be kept particularly small.

[0013] A particularly advantageous variant of the film has proven to be one in which at least one coating, preferably both coatings, incorporates a filler. Such a filler, or several different fillers, allows the properties of a coating to be tailored to individual needs. For example, a filler can enhance a property of the coating or film selected from a group that includes air permeability, water vapor permeability, aroma impermeability, electromagnetic radiation permeability, light transmission, density, printability, grease resistance, oil resistance, acid resistance, oil tightness, ink absorption, adhesion to a product surface, reflectivity, opacity, flexural stiffness, fracture toughness, torsional stiffness, tear resistance, tensile strength, and solvent resistance.

[0014] The filler preferably comprises an alkali or alkaline earth mineral, more preferably an alkaline earth carbonate, hydrogen carbonate, (hydrogen) sulfate, or (mono- or di-)hydrogen) phosphate, and particularly preferably calcium carbonate. These fillers have proven to be particularly suitable for positively influencing the aforementioned properties. In particular, the optical properties, such as the transmittance for electromagnetic radiation of defined wavelengths (e.g., visible light), the transmittance to certain substances, and the mechanical properties, such as (flexural) stiffness, tear strength, and tensile strength, can be adjusted as desired by these fillers. Alternatively or additionally, such a filler can also serve to adjust the haptic feel as desired and, in particular, to create a paper-like feel.

[0015] The proportion of filler in a coating is preferably in the range of 5% to 80%, more preferably 20% to 60%, and particularly preferably 40% to 50%. These percentages refer to weight percent based on the total mass of the coating. Unless a specific meaning is explicitly stated in the description of the invention, percentages are to be understood as weight percent. The aforementioned proportions of filler in the coating allow for high flexibility of the coating while simultaneously providing good tear resistance and low density. Furthermore, such a filler proportion allows for adjustment of the (barrier) properties of the coating over a wide range without negatively affecting the material properties of the film with regard to its foldability.

[0016] A particularly advantageous design variant has proven to be one in which the coatings on the first and second surfaces of the film-like carrier have an identical composition. Such a variant is not only particularly easy to manufacture but also offers significant benefits in application. For example, when applying a print, the orientation of the film does not need to be considered, as both coatings, due to their identical composition, absorb the ink in the same way. This also results in greater flexibility regarding the orientation relative to the product being packaged, since it is not necessary to ensure that only one side of the film—namely, the one designed for contact with the product—is in contact with it when wrapping.Rather, this design allows the coating on the first surface of the carrier to contact the product in certain sections, while in other areas the coating on the second surface of the carrier makes contact. This results in folding possibilities that were previously impossible, particularly in the corners of a product, thereby reducing the amount of film required to wrap it. This can offer cost advantages.

[0017] According to the invention, a polymeric intermediate layer is arranged between the film-like substrate and at least one coating. This intermediate layer preferably comprises a polyolefin or a polyester. It can, for example, serve to fix the coating to the substrate. Such an intermediate layer can be used to adapt the properties of the film to specific requirements. In particular, it is preferred that a polymeric intermediate layer is arranged between the film-like substrate and both coatings. In this context, "polymeric intermediate layer" is understood to mean a layer comprising a polymer, and preferably having a polymer as its main component. However, non-polymeric additives such as fillers are possible and also preferred for adjusting specific material properties.

[0018] Preferably, the intermediate layer contains a filler, which is preferably selected from the group comprising an alkali mineral, an alkaline earth mineral, an alkaline earth carbonate, an alkaline earth hydrogen carbonate, an alkaline earth sulfate, an alkaline earth hydrogen sulfate, an alkaline earth (mono- or di-)hydrogen phosphate, CaCO3, talc, and silica. These non-polymeric components of the intermediate layer are particularly suitable for positively influencing the properties of the film and, in particular, for keeping its density low. At the same time, the aforementioned additives / fillers enhance the barrier properties of the intermediate layer and thus also of the entire film.

[0019] The proportion of filler in the intermediate layer is preferably in the range of 5% to 80%, more preferably 20% to 60%, and particularly preferably 40% to 50%. These percentages refer to weight percent based on the total mass of the intermediate layer. Unless a specific meaning is explicitly stated in the description of the invention, percentages are to be understood as weight percent. The aforementioned proportions of filler in the intermediate layer allow for high flexibility of the intermediate layer with very good adhesion properties, good barrier properties, and simultaneously low density.

[0020] According to the invention, an intermediate layer has a Young's modulus ≥ 1500 mPa. Preferably, the intermediate layer has a Young's modulus that is a multiple of that of the two adjacent layers. Preferably, the Young's modulus of the intermediate layer is ≥ 1750 mPa, and particularly preferably ≥ 2000 mPa. It has been shown that, despite such a high Young's modulus of the intermediate layer, tight curve radii can be achieved when wrapping a product with the film. This also applies, or even especially so, when the intermediate layer between the film-like substrate and both coatings has the aforementioned bending stiffness. Within the scope of the present invention, the Young's modulus is particularly relevant for the force acting by the film when it is bent. Therefore, the Young's modulus is also referred to as bending stiffness.

[0021] The intermediate layer preferably comprises a transparent polymer. This preferably comprises a cycloolefin copolymer (COC) or a polylactic acid (PLA). Preferably, the cycloolefin copolymer or the polylactic acid forms the main component of the polymer and preferably constitutes a mass fraction of > 70%, more preferably > 80%, further preferably > 90%, and particularly preferably > 95%. The cycloolefin copolymer is preferably formed from monomers comprising at least one, preferably two, monomers of a group comprising norbornene, tetracyclododecene, vinylnorbornene, norbornadiene, ethene, propene, 1-butene, 2-butene, isobutene, and acrylic acid. The polylactic acid is preferably formed from monomers comprising at least one, preferably two, monomers of a group comprising L -Lactic acid, D -Lactic acid and a racemate of the L -Lactic acid and D-Lactic acid is included. These have proven advantageous both in processing and with regard to the properties of the film.

[0022] Due to the molecular structure of the polylactic acid (PLA) component, such an intermediate layer is biodegradable – at least under the conditions prevailing in industrial composting facilities. An intermediate layer comprising PLA is therefore particularly preferred when the biodegradability and / or compostability of the product is desired. Any other components present in the intermediate layer (for example, when using PLA copolymers) are therefore preferably selected in such a way that biodegradability is still ensured.

[0023] A cycloolefin copolymer is particularly preferred when good recyclability is desired. The proportion of the component based on a cycloolefin monomer in the copolymer is preferably in the range of 30% to 100%, preferably ≥ 50%. These percentages refer to weight percent based on the total mass of the copolymer. Since the cycloolefinic component often has a significantly higher molecular weight than the (preferably at least one) other olefinic component of the copolymer, its weight fraction is often considerably larger, even with a 1:1 composition (based on the number of particles). However, the properties of the COC (e.g., its recyclability, optical properties, etc.) can also be positively influenced by the other olefinic component. Depending on its particle fraction and molecular weight, the other olefinic component can therefore also constitute a large weight fraction in the COC.Accordingly, the proportion of the cycloolefin component in the copolymer is preferably ≤ 80%, preferably ≤ 70%, further preferably ≤ 60%, and particularly preferably ≤ 50% (in each case, percent by weight based on the total weight of the interlayer).

[0024] The film-like carrier and / or the coating on the first and / or second surface preferably comprise HDPE, MDPE, and / or LLDPE independently of one another. Polyethylene (PE) is a widely used polyolefin for which recycling processes are established. Therefore, it is preferred that at least some of the substances used in the film can be recovered through these recycling processes. To maximize the recyclable material content, it is preferred that at least two of the aforementioned layers, preferably all three, and especially any additional coatings, comprise PE. It is particularly preferred that at least two of the aforementioned layers, preferably all three, contain no polymers other than PE.

[0025] Preferably, the film-like carrier and / or the coating on the first and / or second surface comprise, independently of one another, preferably HDPE, MDPE, and / or LLDPE with a mineral filler. Even with the established recycling processes mentioned above, a simple separation between mineral fillers and the polymer component is possible. Accordingly, these substances can be easily separated and recycled separately. Therefore, the film's recyclability is not affected if mineral fillers are present in addition to the polymer. As mentioned above, neither the film-like carrier, the coating on the first surface, nor the coating on the second surface contains a polymer other than PE. Since it is irrelevant for most established recycling processes whether mixtures of different polyethylene types are fed in, the PE in different layers can be different from one another.In particular, properties such as the orientation of the polymer chains to each other (for example by stretching), the average molecular weight, the degree of branching and / or the height of the crystalline fraction in the polymer can differ in different layers.

[0026] Preferably, the film-like carrier and / or the coating on the first and / or second surface is stretched / stretched independently or jointly in at least one direction. Stretching / stretching can increase the strength of a layer in one or more directions (for example, by biaxial stretching). The stretching results in one or more high-strength layers and / or a high-strength film. A stretch ratio along at least one direction, preferably in two perpendicular directions, in the range of 1:1.5 to 1:10 has proven particularly advantageous. A stretch ratio along at least one direction, preferably in two perpendicular directions, in the range of 1:2 to 1:5, and especially preferably 1:3 to 1:4, is particularly preferred. In the case of biaxial stretching, the stretch ratio along both directions can be different.Preferably, however, the degree of stretch in both directions lies independently of each other in one of the above-mentioned areas.

[0027] In a preferred embodiment, stretching can be carried out in a stretching frame. The production of the carrier film and / or coating as cast MDO (cast monoaxially oriented film) or, particularly preferably, blast MDO (blown monoaxially oriented film) has also proven suitable and is preferred in some applications. These methods enable production with consistent quality and high throughput.

[0028] Preferably, the film-like carrier and / or the coating on the first and / or second surface and / or the intermediate layer on the first and / or second surface is cavitated. In this process, a cavitating agent is added to the polyolefin before extrusion. After extrusion, the film is stretched in the machine direction and / or transverse direction, causing microcavities to form in the film due to the embedded cavitating agent. This process reduces the film's density. Preferably, one or more of the fillers described above are used as the cavitating agent.

[0029] Preferably, the thickness of a coating or both coatings arranged on the first or second surface differs from the thickness of the film-like carrier. This has proven advantageous for the folding properties of the film when wrapping a product. The folding properties are particularly good when the thickness of the coating or both coatings arranged on the first or second surface is less than that of the film-like carrier. The thickness fraction of the film-like carrier is preferably 40–90% of the total film thickness. Regardless, it is advantageous if the coating arranged on the first and / or second surface independently has a thickness fraction of 5–30% of the total film thickness.With a minimal amount of material and such a thickness ratio between the individual layers, sufficient protection of the product wrapped in such a film can be achieved. Therefore, such films can be produced particularly cost-effectively while meeting specific requirements regarding tear resistance, impermeability, and foldability.

[0030] The filler content in the film is preferably in the range of 5% to 80%, more preferably 20% to 60%, and particularly preferably 40% to 50%. These percentages refer to weight percent based on the total mass of the film. The total filler content can be composed of various fillers. As described above, different fillers are preferred for different layers such as the carrier, intermediate layer, or coating. Accordingly, the total filler content in the film can comprise various fillers. It is preferred that at least one filler in one layer differs from a filler in another layer. By using different fillers in different layers, the film's properties can be tailored even more precisely to the intended application.

[0031] Preferably, the thickness of the entire film is in the range of 20–100 µm, more preferably 30–70 µm, and particularly preferably 40–50 µm. This has proven advantageous for the folding properties of the film when wrapping a product. The folding properties are particularly good when the thickness is not too great, and especially when it is ≤ 100 µm. However, excessively thin film negatively impacts other positive properties, such as tear resistance or puncture resistance. Therefore, a thickness ≥ 20 µm, preferably ≥ 30 µm, and particularly ≥ 40 µm is preferred.

[0032] Puncture resistance has proven to be a suitable criterion for evaluating the mechanical strength of such a film. High puncture resistance ensures that even under point loads, the film remains undamaged and its protective properties for the product are maintained. Therefore, the film preferably has a puncture resistance of ≥ 1.5 N, preferably ≥ 2.5 N, and most preferably ≥ 3 N. Preferably, an intermediate layer containing a cycloolefin copolymer or a polylactide contributes significantly to the puncture resistance of the film. The puncture resistance is determined according to DIN EN ISO 14477.

[0033] Furthermore, tear resistance is a suitable criterion for evaluating the mechanical strength of such a film. High tear resistance is advantageous when handling the film and can, for example, ensure that the film can be removed in one piece when opening the packaging. This also simplifies recycling. Therefore, the film preferably has a tear resistance in the transverse direction (TD) in the range of 5–50 N / mm². 2 preferably 10 - 40 N / mm 2 , preferably 15 - 30 N / mm 2 , particularly preferably 20 - 25 N / mm 2 Additionally or alternatively, the film exhibits a longitudinal tensile strength (MD) in the range of 50–100 N / mm². 2 , preferably 60 - 95 N / mm 2 , preferably 70 - 90 N / mm 2 , particularly preferably 75 - 85 N / mm 2The tensile strength is measured according to ISO 527 or ASTM D882-12. Preferably, the tensile strength in the longitudinal direction (MD) is significantly greater than the tensile strength in the transverse direction (TD), preferably by a factor of 1.2–20, more preferably 2–10, further preferably 2.5–8, particularly preferably 3–4, and especially preferably by about 3.5 (± 0.4, preferably ± 0.2).

[0034] When packaging various products, it is necessary to fold the packaging material to ensure it conforms closely to the product's contours. This is particularly advantageous for solid dairy products such as butter or cheese, as it minimizes the gas volume between the product and the packaging. Therefore, the film preferably has a folding angle in the range of 0°–130°, preferably 50°–90°, and most preferably 70° (± 5°, preferably ± 2°). The folding angle was measured using the following test setup: The film, in DIN A4 format, was laid flat on a work surface at room temperature. Then, one corner was folded inwards by 180°, and the resulting angle of return was measured. The size of the angle depends on the film's foldability. The smaller the angle of return, the better the film's folding properties.

[0035] Another advantageous property of the film was identified as its low water vapor permeability (WVTR). For the aforementioned products, milk and butter, but especially for water-containing or hygroscopic products, a low water vapor permeability of the packaging material is advantageous to protect the product or to permanently prevent water loss through the packaging. This can be ensured when using a film as packaging material if the film has a WVTR of < 6, preferably < 4, particularly preferably < 3 g / m² at 38°C and 90% humidity. 3 × Day. The WVTR measurement is performed according to ISO 15106-2.

[0036] Some products are sensitive to electromagnetic radiation of certain wavelengths, particularly high-energy radiation with a shorter wavelength than visible light. For some products, especially dairy products like butter and cheese, UV light has been identified as particularly detrimental to shelf life. Therefore, preferably at least one layer contains an additive that acts as a UV barrier. This additive is preferably included in the film in addition to a filler, with the filler and additive preferably not being in the same layer, although this is possible in some embodiments. Preferably, an additive acting as a UV barrier is arranged in an inner layer of the film, more preferably in the carrier layer.

[0037] Furthermore, the problem underlying the invention is solved by a packaging that includes a film as described above.

[0038] Such packaging, especially food packaging, comprises a film with a density ≤ 1g / cm³ 3 The packaging comprises a film-like carrier comprising a polymer, which has a first surface and a second surface opposite it, and on each of these surfaces a coating comprising a polymer is arranged. The packaging is further characterized in that the carrier of the film has a stiffness / modulus of elasticity ≥ 300 mPa and at least one of the coatings has a stiffness / modulus of elasticity ≥ 300 mPa. A polymeric intermediate layer is arranged between the film-like carrier and at least one coating, the intermediate layer having a modulus of elasticity ≥ 1000 mPa.

[0039] The advantages described above regarding the film, which can be achieved through the preferred embodiments, also apply analogously to such packaging.

[0040] The applicant reserves the right to claim all features disclosed in the application documents as essential to the invention, provided they are novel individually or in combination compared to the prior art. It is further noted that combinations of features are also described in connection with preferred embodiments, and individual features may also be advantageous on their own. A person skilled in the art will immediately recognize that a particular feature described in combination may be advantageous even without the inclusion of further features. Furthermore, a person skilled in the art will recognize that advantages may also arise from a combination of several separately described features.

Claims

[1] Film, in particular wrapping film for food, the film having a density ≤ 1 g / cm 3 and has a film-like carrier comprising a polymer, which has a first and a second surface opposite thereto and on each of these surfaces a coating comprising a polymer is arranged, wherein the carrier has an E-modulus ≥ 300 mPa and at least one of the coatings has an E-modulus ≥ 300 mPa, characterized by , that a polymeric intermediate layer is arranged between the film-like carrier and at least one coating, wherein the intermediate layer has an E-modulus ≥ 1000 mPa. [2] Film according to claim 1, characterized bythat at least one coating, preferably both coatings, comprises a filler, wherein the filler preferably comprises an alkali or alkaline earth mineral, more preferably an alkaline earth carbonate, hydrogen carbonate, sulfate, hydrogen sulfate, or ((mono-, or di-)hydrogen) phosphate, particularly preferably calcium carbonate. [3] Film according to claim 1 or 2, characterized by , that the coating arranged on the first and the second surface of the film-like carrier have an identical composition. [4] Film according to one of the preceding claims, characterized by that between the film-like carrier and both coatings, a polymeric intermediate layer is arranged, which preferably comprises a polyolefin or a biodegradable polyester. [5] Film according to claim 4, characterized by that the intermediate layer has an elastic modulus ≥ 1500 mPa, preferably ≥ 1750 mPa, particularly preferably ≥ 2000 mPa. [6] Film according to one of claims 4 or 5, characterized by that the intermediate layer comprises a transparent polymer, which preferably comprises a cycloolefin copolymer (COC) or a polylactide (PLA), wherein these preferably form the main component of the intermediate layer and preferably have a mass fraction of > 70%, preferably > 80%, more preferably > 90% and particularly preferably > 95%, wherein the cycloolefin copolymer (COC) is preferably formed from monomers which comprise at least one, preferably two monomers of a group comprising norbornene, tetracyclododecene, vinylnorbornene, norbornadiene, ethene, propene, 1-butene, 2-butene, isobutene and acrylic acid, or the polylactide is preferably formed from monomers which comprise at least one, preferably two monomers of a group comprising L -lactic acid, D -lactic acid and a racemate of L -lactic acid and D -Lactic acid includes... [7] Film according to one of claims 4-6, characterized by that the intermediate layer contains a filler which is preferably selected from a group comprising an alkali mineral, an alkaline earth mineral, an alkaline earth carbonate, an alkaline earth hydrogen carbonate, an alkaline earth sulfate, an alkaline earth hydrogen sulfate, an alkaline earth (mono- or di-)hydrogen) phosphate, CaCO3, talc and silica. [8] Film according to one of the preceding claims, characterized by that the film-like carrier and / or the coating on the first and / or on the second surface independently of one another comprises HDPE, MDPE and / or LLDPE, preferably HDPE, MDPE and / or LLDPE with a mineral filler. [9] Film according to one of the preceding claims, characterized bythat the film-like carrier and / or the coating on the first and / or on the second surface is stretched independently of one another or jointly in at least one direction, and preferably has a degree of stretching in the range of 1:1.5 - 1:10, preferably 1:2 - 1:5, particularly preferably 1:3 - 1:

4. [10] Film according to one of the preceding claims, characterized by that the thickness of a coating arranged on the first or on the second surface or of both coatings is different from the thickness of the film-like carrier and preferably has a smaller thickness, wherein preferably the film-like carrier has a thickness proportion of 40 - 90% based on the total thickness of the film and independently thereof the coating arranged on the first and / or second surface has a thickness proportion of 5 - 30%, in each case based on the total thickness of the film. [11] Film according to one of the preceding claims, characterized bythat the film has a bending angle which is in the range of 0 - 130°, preferably 50 - 90° and particularly preferably 70° ± 5°, preferably ± 2°. [12] Packaging, in particular food packaging, comprising a film with a density ≤ 1g / cm 3 , wherein the film comprises a film-like carrier comprising a polymer, which has a first surface and a second surface opposite thereto and on each of these surfaces a coating comprising a polymer is arranged, wherein the carrier has an E-modulus ≥ 300 mPa and at least one of the coatings has an E-modulus ≥ 300 mPa, characterized by that a polymeric intermediate layer is arranged between the film-like carrier and at least one coating, wherein the intermediate layer has an E-modulus ≥ 1000 mPa.