SEBS-based elastic blown film

Abstract

The invention relates to an elastic film (1) having an elastic film layer (3) based on styrene block copolymers, wherein in the event of a multilayer structure formed by coextrusion, the elastic film layer (3) is arranged between partially elastic cover layers (2). The elastic film layer (3) has a proportion of more than 50 wt.% of styrene block copolymers selected from the following substance groups: styrene-butadiene-styrene block copolymers (SBS), styrene-ethylene-butylene-styrene block copolymers (SEBS). The ratio of the MFI (at 200°C and at 5 kg) according to ASTM D1238 of the elastic film layer (3) to the MFI of the partially elastic cover layers (2) is greater than 0.70.

Description

[0001] SEBS-based elastic blown film

[0002] Description

[0003] The invention relates to an elastic film with an elastic film layer based on styrene block copolymers, wherein the elastic film layer is arranged between partially elastic cover layers in a multi-layer structure formed by co-extrusion.

[0004] Elastic, stretchable materials are used in diapers to ensure an optimal fit and leakage protection. These materials are used in various forms: firstly, as a diaper waistband, also known as a "waistband," and secondly, as an elastic closure element called a "back ear" in baby diapers. They are also used as a belt in pull-up diapers.

[0005] To improve wearing comfort, these elements contain elastic components that adapt to the individual body shape thanks to their resilience. To ensure a pleasant feel against the skin, these elastic components, often in the form of films, are combined with textile materials such as nonwovens or fleeces.

[0006] EP 2 024 178 B1 describes a method for producing an elastically stretchable laminate with three layers. The laminate comprises an elastic film and two layers of non-elastic nonwoven fabric. In one variant, a crepe nonwoven fabric is used. A first elastic laminate is bonded to a non-elastic nonwoven layer in a stretched state.

[0007] US Patent 6,531,207 B1 describes a stretchable, elastic strip or tab that serves as a fastening strip for closing garments with a limited lifespan and absorbent disposable items such as diapers and incontinence pads, training pants, diaper inserts, sanitary hygiene products, and similar items. The stretchability is achieved, among other things, by means of differently stretchable areas within a woven layer.

[0008] US Patent 2021 / 0052438 A1 discloses an elastic laminate comprising an elastic film layer and a nonwoven layer, wherein the nonwoven layer is attached to a first surface of the elastic film layer. The laminate has a first elongation zone and a second elongation zone that differ in their elongation properties.

[0009] German patent DE 10 2018 130 054 A1 describes an elastic diaper element comprising an elastic layer and an outer layer made of nonwoven fabric. The diaper element has connection areas between the outer layers and the elastic layer. These connection areas comprise surfaces where there is a positive-locking bond between the nonwoven material of the outer layers and the solidified material of the elastic layer.

[0010] DE 10 2019 104 225 A1 discloses a stretchable diaper element comprising an elastic layer and a nonwoven layer. The elastic element features connection areas between the elastic layer and the nonwoven layer. In the unstretched state of the diaper element, the nonwoven layer is corrugated to provide areas for expansion.

[0011] WO 2021 / 115642 A1 discloses a stretchable diaper element comprising an elastic layer and a nonwoven layer. The elastic element has connection areas between the elastic layer and the nonwoven layer. These connection areas extend in a preferred direction and have discontinuities along their extension. EP 1 316 418 B1 discloses a monoaxially elastic laminate film comprising a core layer of a thermoplastic elastomer and at least one skin layer coextruded with the core layer. The skin layer consists of a thermoplastic polymer with a brittle, strengthened molecular structure that exhibits only minimal stretching under tensile force and can tear seamlessly upon exceeding a predetermined tensile strength.

[0012] US 2018 / 0264163 A1 and WO 2018 169 656 A1 disclose thermoplastic multilayer films and laminates and articles comprising these films, wherein the film comprises at least one inner layer and at least two outer layers, the inner layer comprising a polymer composition comprising approximately 55% to approximately 95% of one or more non-hydrogenated styrene block copolymers, olefin block copolymers or combinations thereof; and each outer layer comprising at least 20% polypropylene and having a thickness of approximately 5% to approximately 15% of the total film thickness, and wherein the film further exhibits a constant force propagation of approximately 20% or less.

[0013] Cast films, also known as cast films, are manufactured through a process called cast film extrusion. In this process, the polymer resin, in the form of granules or pellets, is melted in an extrusion line and forced through a die or slot die to form a continuous film. In cast film extrusion, the molten polymer mass is poured directly onto a cooled roll or mold. Pouring onto a cooled surface allows for rapid cooling of the melt, resulting in a thin film. This process enables precise control over the film's thickness and surface finish.

[0014] Elastic films based on styrene-isoprene-styrene block copolymers (SIS) are typically produced as cast films or blown extrusion films. EP 3 228 291 B1 discloses an elastic film with an elastic film layer based on styrene block copolymer. The elastic film layer is formed without the addition of polystyrene from a first SIS and a second SIS, wherein the first SIS has a styrene content between 10 wt.% and 25 wt.% and a hardness of less than 45 Shore A, and the second SIS has a styrene content between 26 wt.% and 40 wt.% and a hardness of more than 45 Shore A, wherein the ratio of the first SIS to the second SIS is between 6:1 and 2:3, and wherein the elastic film layer is arranged between two partially elastic cover layers in a three-layer structure formed by co-extrusion.

[0015] Elastic films based on styrene-isoprene-styrene block copolymers (SIS) offer advantageous properties such as high elasticity, flexibility, and good resilience. However, SIS-based films can be sensitive to temperature and may release limonene.

[0016] Some people may be allergic to limonene and may develop skin irritation, rashes, or even breathing difficulties. Long-term exposure to limonene can lead to sensitization, meaning that people may become more sensitive to the substance over time.

[0017] The object of the present invention is to provide an elastic film with an elastic film layer that is free of emissions, in particular without the release of limonene. Furthermore, the elastic film should possess the special properties of a blown film. The elastic film should be inexpensive to manufacture and printable in excellent quality. The elastic film should be harmless to health and environmentally sustainable. This object is achieved according to the invention by an elastic film with at least one elastic film layer according to the main claim. Preferred embodiments can be found in the dependent claims, the description, and the drawing.

[0018] According to the invention, the elastic film layer has a proportion of styrene block copolymers of more than 50 wt.% selected from the following material groups: styrene-butadiene-styrene block copolymers (SBS), styrene-ethylene-butylene-styrene block copolymers (SEBS), and the ratio of the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the elastic film layer to the MFI of the partially elastic cover layers is greater than 0.70.

[0019] In one variant of the invention, the elastic film is designed in three layers with an elastic film layer and a surrounding partially elastic cover layer.

[0020] In an alternative version of the invention, the elastic film, in particular the elastic film layer and / or the partially elastic cover layers, can also have several layers.

[0021] Styrene-butadiene-styrene (SBS) is a thermoplastic elastomer. It consists of the monomers styrene and butadiene and is a block copolymer. It exhibits properties of both a plastic and a rubber.

[0022] Styrene-ethylene-butylene-styrene (SEBS) is a thermoplastic elastomer. It is produced by hydrogenating styrene-butadiene-styrene block copolymer (SBS), which improves its thermal stability and resistance. Overall, SEBS contributes to improving the performance and comfort of elastic films by providing elastic, dense, and flexible components. Remarkably, it has been found that an elastic film with an elastic film layer based on either styrene-butadiene-styrene block copolymer (SBS) or styrene-ethylene-butylene-styrene block copolymer (SEBS) can be produced using blown film extrusion. Previously, SBS and SEBS could only be bias-extruded with the help of additives such as plasticizers and processing aids. However, these additives themselves resulted in emissions that were not without concerns for the use of elastic films.

[0023] Surprisingly, it has now been possible to produce an elastic film as a blown film based on styrene-ethylene-butylene-styrene block copolymers (SEBS) that is completely free of additives that cannot be characterized as completely harmless.

[0024] This astonishing and unexpected success was achieved in particular through a special ratio of the MFIs of the elastic film layer to the MFI of the partially elastic cover layers.

[0025] The Melt Flow Index (MFI) is a measure that indicates the flowability of thermoplastic materials under standardized conditions. Specifically, the MFI is measured as the mass of the plastic material, in grams, that flows through a standardized die at a specific temperature and load within a defined time. The unit is given in g / 10 min. The MFI is an important measure of the processability of plastics in various applications, as it provides information about the material's flow properties. The higher the MFI value, the better the plastic flows, and vice versa. According to the invention, the ratio of the MFI (at 200 °C and at 5 kg) of the elastic film layer to the MFI of the partially elastic cover layers, as specified in ASTM D1238, is greater than 0.70.

[0026] For example, the ratio of the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the elastic film layer to the MFI of the partially elastic cover layers is less than 1.80.

[0027] In one variant of the invention, the ratio of the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the elastic film layer to the MFI of the partially elastic cover layers is greater than 0.95 and less than 1.55.

[0028] In another variant of the invention, the ratio of the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the elastic film layer to the MFI of the partially elastic cover layers is greater than 1.00 and less than 1.40.

[0029] In an alternative version of the invention, the ratio of the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the elastic film layer to the MFI of the partially elastic cover layers is greater than 1.1 and less than 1.25.

[0030] For example, the elastic film layer exhibits an MFI (at 200 °C and 5 kg) according to ASTM D1238 of more than 5 g / 10 min and less than 9 g / 10 min. Extrusion can only be achieved through the specific selection and design of the polymer blend in the elastic film layer.

[0031] Surprisingly, for the first time a blown film without questionable additives based on SEBS was produced, achieving the excellent properties of a blown film for an elastic film.

[0032] In one embodiment of the invention, the elastic film layer is formed from a first styrene block copolymer and a second styrene block copolymer. This feature supports both the blown extrusion capability and the advantageous properties of the elastic film.

[0033] For example, the elastic film layer has a first styrene block copolymer of more than 35 wt.%.

[0034] In one variant of the invention, the elastic film layer comprises a second styrene block copolymer of more than 15 wt.%.

[0035] For example, the first styrene block copolymer has a lower styrene content and lower hardness than the second styrene block copolymer.

[0036] In one embodiment, the first styrene block copolymer is designed as a styrene-ethylene-butylene-styrene, wherein the styrene-ethylene-butylene-styrene has a styrene content of less than 16 wt.% and a hardness of less than 60 Shore A.

[0037] For example, the first styrene block copolymer is designed as a styrene-ethylene-butylene-styrene block copolymer, wherein the styrene-ethylene-butylene-styrene block copolymer has a styrene content between 2 and 16 wt.% and a hardness of less than 50 Shore A.

[0038] The first styrene-ethylene-butylene-styrene block copolymer exhibits an MFI (at 200 °C and at 5 kg) of more than 7 g / 10 min and less than 11 g / 10 min, which favors blown extrusion.

[0039] The first styrene-ethylene-butylene-styrene block copolymer, for example, has an MFI (at 200 °C and at 5 kg) of more than 8 g / 10 min and less than 10 g / 10 min. In a variant of the invention, the second styrene block copolymer is designed as a styrene-ethylene-butylene-styrene block copolymer, wherein the styrene-ethylene-butylene-styrene block copolymer has a styrene content of between 2 and 20 wt.% and a hardness of less than 72 Shore A.

[0040] For example, the second styrene block copolymer is designed as a styrene-ethylene-butylene-styrene, wherein the styrene-ethylene-butylene-styrene has a styrene content of more than 16 wt.% and a hardness of more than 60 Shore A.

[0041] The second styrene-ethylene-butylene-styrene block copolymer has an MFI (at 200 °C and at 5 kg) of more than 4 g / 10 min and less than 8 g / 10 min, which advantageously promotes the blown extrusion of the elastic film, especially in combination with the first styrene-ethylene-butylene-styrene block copolymer.

[0042] The second styrene-ethylene-butylene-styrene block copolymer, for example, has an MFI (at 200 °C and at 5 kg) of more than 5 g / 10 min and less than 7 g / 10 min.

[0043] In one embodiment of the invention, the ratio between the first styrene block copolymer and the second styrene block copolymer in the elastic layer is between 3:1 and 1:1.

[0044] The combination of the first styrene-ethylene-butylene-styrene block copolymer and the second styrene-ethylene-butylene-styrene block copolymer in the elastic film results in remarkable product characteristics. The softer and more flexible properties of the first styrene-ethylene-butylene-styrene block copolymer increase wearing comfort, while the higher strength and elasticity of the second styrene-ethylene-butylene-styrene block copolymer ensures a better fit and leakage resistance. In one embodiment of the invention, the elastic film layer contains a proportion of PE-POP, with the PE-POP content being between 10 and 25 wt.%.

[0045] For example, PE-POP has a density of more than 0.85 g / cm³. 3 and of less than 0.89 g / cm³ 3 on.

[0046] For example, PE-POP has an MFI at 200 °C and at 5 kg according to ASTM D1238 of more than 3 g / 10 min and of less than 7.0 g / 10 min.

[0047] The thickness of the elastic film layer was measured according to DIN 53370 and is given as an average value. In one embodiment of the invention, the elastic film layer has a thickness of more than 10 pm, preferably more than 20 pm, particularly more than 30 pm and / or less than 60 pm, preferably less than 50 pm, particularly less than 40 pm. This results in a particularly thin and material-efficient elastic film with excellent mechanical properties.

[0048] Furthermore, the elastic core layer also contains, for example, a proportion of polystyrene, with the proportion of polystyrene ranging between 3 wt.% and 12 wt.%.

[0049] For example, polystyrene has a density of more than 1.02 g / cm³. 3 and of less than 1.06 g / cm³ 3 on.

[0050] For example, polystyrene has an MFI at 200 °C and at 5 kg according to ISO 1133 of more than 8 g / 10 min and of less than 16 g / 10 min.

[0051] Advantageously, the elastic film layer contains no styrene-isoprene-styrene block copolymers. This effectively and reliably prevents the release of limonene. The term "partially elastic" in relation to the partially elastic cover layers refers to a layer whose force under loading and unloading, as well as the ratio of these forces in a hysteresis test, lies between the elastic and inelastic behavior of a film layer. For an elastic film, the force under loading and unloading is identical or nearly identical. For an inelastic film, the ratio of the forces under loading to unloading is greater than three.

[0052] For example, the partially elastic cover layers contain a proportion of polyethylene (PE), preferably LLDPE, wherein the proportion of PE is between 50 and 85 wt.%.

[0053] For example, LLDPE has a density of more than 0.91 g / cm³. 3 and of less than 0.94 g / cm³ 3 on.

[0054] For example, LLDPE has an MFI at 200 °C and at 5 kg according to ASTM D1238 of more than 6.0 g / 10 min and of less than 10.0 g / 10 min.

[0055] In one variant of the invention, the partially elastic cover layers contain a proportion of PE-POP, wherein the proportion of PE-POP is between 1 and 20 wt.%.

[0056] For example, PE-POP has a density of more than 0.85 g / cm³. 3 and of less than 0.89 g / cm³ 3 on.

[0057] For example, PE-POP has an MFI at 200 °C and at 5 kg according to ASTM D1238 of more than 3.0 g / 10 min and of less than 7.0 g / 10 min.

[0058] Polyolefin plastomers (POPs) are a relatively new class of polymers.

[0059] Polyolefin plastomers (POPs) are copolymers of ethylene and octene. Polyolefin plastomers bridge the gap between conventional elastomers and thermoplastics.

[0060] Furthermore, it is planned that the partially elastic cover layers will each have a small thickness of, for example, 1.5 pm and 6 pm, in particular 2 pm and 4 pm.

[0061] In one embodiment of the invention, the partially elastic cover layers contain a proportion of chalk, wherein the proportion of chalk is between 4 and 30 wt.%.

[0062] In one variant of the invention, the chalk consists of CaCOs and has, for example, an organic coating.

[0063] For example, chalk has a mean particle size of more than 0.5 pm and less than 3 pm.

[0064] In one variant of the invention, the chalk has a mean particle size of more than 1.0 pm and less than 2 pm.

[0065] For example, chalk has a density of more than 2.0 g / cm³. 3 and less than 3.2 g / cm³ 3 on.

[0066] For example, the partially elastic cover layers contain a proportion of styrene, with the proportion of styrene being between 5 and 25 wt.%.

[0067] For example, polystyrene has a density of more than 0.95 g / cm³. 3 and of less than 1.1 g / cm³ 3 on.

[0068] For example, polystyrene exhibits a minimum firing index (MFI) at 200 °C and at 5 kg according to ISO 1133 of more than 8 g / 10 min and less than 16 g / 10 min. In coextrusion, the partially elastic cover layers can also limit and stabilize the soft styrene block copolymer.

[0069] The thickness of the elastic film was determined according to DIN 53370 and is given as an average value. For example, the elastic film has a thickness of more than 20 pm, preferably more than 30 pm, particularly more than 35 pm and / or less than 70 pm, preferably less than 60 pm, particularly less than 50 pm.

[0070] In addition to slight elasticity, the elastic laminate should also possess sufficient holding power. This can be ensured by the elastic film and the resulting elastic laminate exhibiting largely elastic properties, allowing a significant portion of the energy expended during stretching to be recovered during contraction.

[0071] The elastic film exhibits the desired mechanical characteristics, particularly due to its design as a blown film.

[0072] In the context of testing the elastic behavior of the elastic film, the terms "first load" and "second load" refer to different phases of the testing process during a tensile test.

[0073] When a tensile force is first applied to an elastic film, it deforms in response to the applied force. The material's initial response to this force is called the "first loading." During this phase, the material typically behaves linearly elastically, meaning that the deformation is proportional to the applied force according to Hooke's Law. In this linear elastic range, the material returns to its original shape after the force is removed, exhibiting reversible deformation. The test speed for the tensile test of the elastic film is 254 mm / min, meaning the sample is loaded at a rate of 254 millimeters per minute.

[0074] When the applied force exceeds a certain threshold, the material can enter a region of nonlinear behavior where the relationship between stress and strain deviates from Hooke's Law. In this region, the material may begin to exhibit plastic deformation or other forms of partially elastic behavior. The force required to induce this nonlinear response is often referred to as the yield strength. Beyond this point, the material may remain plastically deformed until it eventually ruptures. The elastic behavior that the elastic film exhibits after plastic deformation can be described as secondary loading.

[0075] In a hysteresis test in CD, a test piece of elastic film 1 measuring 25 mm in MD and 100 mm in CD was cut. The prepared film piece was then stretched in CD with a chuck spacing of 25 mm and a test speed of 254 mm / min to a chuck spacing of 50 mm (100%) and 100 mm (200%), respectively, and then released back to a chuck spacing of 25 mm. This method is also described in EP 4 122 675 A1.

[0076] In one variant of the invention, the elastic film exhibits a force in CD of more than 1.25 N and less than 2.0 N after activation at a test speed of 254 mm / min and an elongation of 100% at first load.

[0077] For example, after activation, the elastic film exhibits a force in CD of more than 2.05 N and less than 2.75 N at a test speed of 254 mm / min and an elongation of 200% under initial loading. In a variant of the invention, after activation, the elastic film exhibits a restoring force in CD of more than 0.4 N and less than 0.7 N at a test speed of 254 mm / min and an elongation of 50% under unloading after initial and subsequent loading.

[0078] For example, after activation, the elastic film exhibits a force in CD of more than 1.3 N and of less than 1.8 N at a test speed of 254 mm / min and an elongation of 100% at second loading.

[0079] An elastic film with these particularly advantageous mechanical properties with regard to elongation and restoring force is achieved by the special selection of the two styrene-ethylene-butylene-styrene block copolymers and the design as a blown film with at least one elastic film layer surrounded by two thin partially elastic cover layers.

[0080] According to the invention, the elastic film is formed by a process for production by blown extrusion of an elastic film layer from at least one first styrene block copolymer and a second styrene block copolymer with two partially elastic cover layers as coextrusion.

[0081] Surprisingly, through the skillful selection and advantageous design of the composition of the styrene-ethylene-butylene-styrene block copolymers, compounding prior to extrusion could be avoided.

[0082] In this process, the elastic film layer and the two partially elastic cover layers come into full contact after co-extrusion.

[0083] For example, the elastic film is activated directly after extrusion in CD. Various activation methods are known to those skilled in the art, which can be used here, individually or in combination. The elastic film thus formed, with two partially elastic cover layers, can then be rolled up, transported, and unrolled again without clogging due to the stickiness of the elastic film layer based on styrene block copolymers when rolled up.

[0084] Furthermore, the cover layers stabilize the elastic film layer both during the co-extrusion process and in subsequent processing. In subsequent processing, the elastic film can, for example, be rolled and unrolled without excessive stretching, as long as the cover layers remain structurally intact.

[0085] In one embodiment of the invention, the elastic film is bonded to at least one layer of nonwoven material in a form-fitting and / or material-bonded manner to form a laminate. A special manufacturing process for the laminate, consisting of the elastic film and at least one corrugated layer of nonwoven material, allows for the creation of areas with varying degrees of elasticity.

[0086] The connection areas between the elastic film and at least one corrugated nonwoven layer can be created using various methods. In one embodiment of the invention, a pre-solidified elastic film is unwound from a film roll, and a nonwoven layer with defined corrugations is fed into it. The elastic film and the nonwoven layer are joined together by connection areas, which are created by ultrasonic welding. In this process, the corrugated nonwoven material is subjected to external thermal stress.

[0087] In another variant, the bonding areas are created by pressing parts of the nonwoven layer into the molten elastic layer. Alternatively, instead of molten extrusion, a pre-solid elastic layer can be unwound from a film roll and heated using heating rollers to create a bond with the nonwoven.

[0088] In one embodiment of the invention, the nonwoven layer consists of polypropylene. The terms "nonwoven" and "nonwoven" refer to polypropylene, which can be produced from continuous filaments and / or discontinuous fibers without weaving or knitting by processes such as spunbonding, carding, or meltblowing. The nonwoven fabric can comprise one or more layers, each layer potentially containing continuous filaments or discontinuous fibers.

[0089] In one option of the invention, the laminate has a further layer of nonwoven material, so that the elastic film is covered on both sides by a layer of nonwoven material.

[0090] For example, the elastic film is positioned between the two layers of nonwoven fabric. Due to the corrugated design, at least one layer of nonwoven fabric is significantly longer than the elastic film. A second layer of nonwoven fabric improves the feel.

[0091] The second nonwoven layer can consist of either a hydroentangled nonwoven, a carded nonwoven, or a spunbond nonwoven. This second nonwoven layer can be either corrugated or have a flat profile. This gives the laminate a cushion-like effect, the feel of which can be enhanced by the corrugated profile of the nonwoven layer.

[0092] In one embodiment of the invention, the laminate of elastic film and nonwoven material comprises a layer of nonwoven material made from a carded nonwoven fabric. The carded nonwoven fabric used preferably consists of polypropylene fibers and / or mixtures of different fiber types, such as polypropylene / viscose, polypropylene / polyamide, polypropylene / polyester, etc. The carded nonwoven fabric can also consist of polypropylene and / or polyethylene copolymer. Preferably, the specific basis weight of the carded nonwoven fabric is 10 to 40 g / m². 2 , especially between 15 and 25 g / m² 2 The carded nonwoven fabric can be solidified, for example, by means of a calender and / or by exposure to air and / or a water jet.

[0093] Optionally, the laminate includes a nonwoven layer made from a spunbond nonwoven fabric. Spunbond nonwovens are known to be produced at very low basis weights. The spunbond nonwoven used preferably consists of polypropylene fibers and is thermally bonded. Alternatively and / or additionally, the nonwoven layer can also comprise meltblown nonwovens. Ideally, this nonwoven layer has a specific basis weight of more than 4 g / m². 2 , preferably more than 5 g / m² 2 , especially more than 6 g / m² 2 and / or less than 50 g / m² 2 , preferably less than 40 g / m² 2 , especially less than 30 g / m² 2 on.

[0094] Especially when the elastic film has non-elastic cover layers, pre-stretching before bonding with at least one layer of nonwoven material may be useful in the previously described method in order to activate the elastic film by overstretching the cover layers.

[0095] According to the invention, an elastic film is used as the elastic element, wherein the elastic film is formed as a blown film based on styrene-ethylene-butylene-styrene block copolymers (SEBS). The elastic film is free of styrene-isoprene-styrene block copolymers and therefore does not release limonene. Further advantages and features of the invention will become apparent from the description of an exemplary embodiment with reference to a drawing and from the drawing itself.

[0096] This shows

[0097] Fig. 1 shows a schematic structure of the elastic film according to the invention.

[0098] Fig. 2 shows the force-strain behavior in a hysteresis test of the elastic film.

[0099] In Fig. 1, the elastic film 1 is shown with an elastic film layer 3 based on styrene block copolymers, wherein the elastic film layer 3 is arranged between partially elastic cover layers 2 in a multilayer structure formed by coextrusion.

[0100] The thickness of the elastic film 1 was determined according to DIN 53370 and is 40 pm in the illustrated embodiment. The thickness of the partially elastic cover layers 2 is 3 pm each, with the elastic film layer 3 having a thickness of 34 pm.

[0101] In a hysteresis test in CD, an activated piece of elastic film 1 measuring 25 mm in MD and 100 mm in CD was cut. The prepared film piece was stretched in CD with a chuck spacing of 25 mm and a test speed of 254 mm / min to a chuck spacing of 50 mm (100%) and then to 100 mm (200%), and subsequently unloaded back to a chuck spacing of 25 mm. The force-elongation behavior of the film piece before and after activation of the elastic film is shown in Fig. 2. After activation, the elastic film 1 exhibits a force of 2.4 N in CD at a test speed of 254 mm / min and an elongation of 200% at the first loading stage 4.

[0102] The special mechanical properties of the elastic film 1 are particularly evident in a restoring force in CD of 0.45 N at a test speed of 254 mm / min and an elongation of 50 % upon unloading 6 after first loading and second loading.

[0103] Furthermore, after activation, the elastic film 1 exhibits an elasticity in CD of 1.3 N at a test speed of 254 mm / min and an elongation of 100% at second load 5.

[0104] The elastic film 1 before activation exhibits a force in CD of 3.0 N at a test speed of 254 mm / min and an elongation of 50 % at first load 7.

[0105] The elastic film 1, exhibiting these particularly advantageous mechanical properties with regard to elasticity and resilience, is achieved through the specific selection of styrene-ethylene-butylene-styrene block copolymers and its construction as a blown film. The invention of the elastic film is explained below using two exemplary embodiments, without limiting the invention thereto.

[0106] Example 1

[0107] The partially elastic surface layers are formed from the following raw materials:

[0108] The elastic film layer is formed from the following materials: Example 2

[0109] In embodiment 2, the partially elastic cover layers are formed from the following materials:

[0110] In contrast, the elastic film layer differs in the exemplary embodiment.

[0111] 2 of embodiment 1 and is formed from the following materials:

Claims

Patent claims 1. Elastic film (1) with an elastic film layer (3) based on styrene block copolymers, wherein the elastic film layer (3) is arranged between partially elastic cover layers (2) in a multilayer structure formed by coextrusion, characterized in that the elastic film layer (3) has a proportion of styrene block copolymers of more than 50 wt.% selected from the following material groups: styrene-butadiene-styrene block copolymers (SBS), styrene-ethylene-butylene-styrene block copolymers (SEBS), and the ratio of the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the elastic film layer (3) to the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the partially elastic cover layers (2) is greater than 0.

70.

2. Foil according to claim 1, characterized in that the ratio of the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the elastic foil layer (3) to the MFI (at 200 °C and at 5 kg) according to ASTM D1238 of the partially elastic cover layers (2) is less than 1.

80.

3. Film according to claim 1 or 2, characterized in that the elastic film layer (3) has an MFI (at 200 °C and at 5 kg) according to ASTM D1238 shows values ​​of more than 5 g / 10 min and less than 9 g / 10 min.

4. Foil according to one of claims 1 to 3, characterized in that the elastic foil (1) has a force in CD of more than 1.25 N and of less than 2.0 N, with a foil strip of 25 mm width in the MD direction, wherein the foil strip is fixed between the grippers of a test device with a CD spacing of 25 mm, wherein the foil strip is stretched in CD at a speed of 254 mm / min up to an elongation of 100% at first load.

5. Foil according to one of claims 1 to 4, characterized in that the elastic foil (1) exerts a force in CD of more than 2.05 N and of less than 2.75 N, with a foil strip of 25 mm width in the MD direction, wherein the foil strip is fixed between the grippers of a test device with a CD spacing of 25 mm, wherein the foil strip is stretched in CD at a speed of 254 mm / min up to an elongation of 200 % at first load.

6. Foil according to one of claims 1 to 5, characterized in that the elastic foil (1 ) has a restoring force in CD of more than 0.4 N and of less than 0.7 N for a foil strip of 25 mm width in the MD direction, wherein the foil strip is fixed between the grippers of a test device with a CD spacing of 25 mm, wherein the foil strip has a speed of 254 mm / min at an elongation of 50% when unloaded.

7. Film according to one of claims 1 to 6, characterized in that the elastic film layer (3) comprises a first styrene block copolymer of more than 35 wt.% and a second styrene block copolymer of more than 15% by weight.

8. Film according to claim 7, characterized in that the first styrene block copolymer has a lower styrene content and a lower hardness than the second styrene block copolymer.

9. Film according to claim 7 or 8, characterized in that the first styrene block copolymer is designed as a styrene-ethylene-butylene-styrene, wherein the styrene-ethylene-butylene-styrene has a styrene content of less than 16 wt.% and has a hardness of less than 60 Shore A.

10. Film according to one of claims 7 to 9, characterized in that the second styrene block copolymer is designed as a styrene-ethylene-butylene-styrene, wherein the styrene-ethylene-butylene-styrene has a styrene content of more than 16 wt.% and a hardness of more than 60 Shore A.

11. Film according to one of claims 1 to 10, characterized in that the ratio of the proportion of the first styrene block copolymer to the proportion of the second styrene block copolymer in the elastic film layer is between 3:1 and 1:

1.

12. Film according to one of claims 1 to 11, characterized in that the elastic film layer (3) additionally comprises a proportion of polystyrene (PS), wherein the proportion of polystyrene is between 3 wt.% and 12 wt.%.

13. Film according to one of claims 1 to 12, characterized in that the elastic film layer (3) has a proportion of PE-POP, wherein the proportion of PE-POP is between 10 and 25 wt.%.

14. Film according to one of claims 1 to 13, characterized in that the partially elastic cover layers (2) have a proportion of PE-POP, wherein the proportion of PE-POP is between 1 and 20 wt.%.

15. Foil according to one of claims 1 to 14, characterized in that the partially elastic cover layers (2) contain a proportion of chalk, wherein the proportion of chalk is between 4 and 30 wt.%.

16. Film according to any one of claims 1 to 15, characterized in that the partially elastic cover layers (2) contain a proportion of styrene, wherein the proportion of styrene is between 5 and 25 wt.%.

17. Film according to any one of claims 1 to 16, characterized in that the elastic film layer (3) does not contain any proportion of styrene-isoprene-styrene block copolymers.

18. Method for producing elastic film (1) according to any one of claims 1 to 17 comprising at least the following steps: - Bubble extrusion of an elastic film layer (3) with two partially elastic cover layers (2), - Activation of the elastic film (1) in the direction of the CD.

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