Elastic film, nonwoven member, and sanitary article

Abstract

To provide an elastic film having enhanced elastic behavior and featuring a cost-effective and resource-efficient design.SOLUTION: The present invention relates to an elastic film (3) having an elastic film layer (6) and at least one first non-elastic cover layer (4, 5) co-extruded with the elastic film layer, wherein the elastic film layer (6) is formed from a polymer mixture comprising a first polymer component A and a second polymer component B, the first polymer component being a polyolefin or a polyolefin mixture. In the present invention, the second polymer component B is a styrene block copolymer present in an amount of 28 wt.% to 60 wt.% in the polymer mixture, and the polymer mixture contains less than 1 wt.% of inorganic residual components and less than 5 wt.% of organic residual components.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an elastic film having an elastic film layer and at least one first non-elastic cover layer coextruded with the elastic film layer.

[0002] Such elastic films are typically used to produce elastic laminates. Such laminates are particularly suitable for disposable hygiene products, such as disposable diapers, disposable pants, or adult disposable incontinence products. These products require, on the one hand, a simple, low-cost, and resource-saving construction, and, on the other hand, a good and reliable fit. The elastic laminates can be used to form elastic regions, such as diaper ears, waistbands, etc. They can also be used for specific medical applications, such as bandages or heating belts. When diapers are specifically mentioned below, this application should be considered merely as an example. [Background technology]

[0003] Diapers, particularly baby diapers, are manufactured as disposable mass-produced items, which results in particularly high demands on efficient material utilization and low manufacturing costs.

[0004] However, at the same time, a high level of functionality is also required to ensure a high level of safety and reliable protection for the wearer under all conditions of use: for example, disposable diapers must accommodate and contain large amounts of body waste overnight and must be equipped with elastic elements and sections for sealing around the waist and legs of the user.

[0005] To form elastic side sections, in particular diaper closures at the sides, elastic laminates are known which have nonwoven layers on their opposing outer sides and an elastic film therebetween as a core, which in the prior art can be formed, for example, by an integral elastic film or by elastic strands.

[0006] The elastic film is therefore important for the elastic behavior of the laminate, and is formed by a process known as a coextruded multilayer composite. The elastic film thus has at least one cover layer made of a non-elastic material, where the elasticity of the film is achieved through the adjacent elastic film layer. The non-elastic cover layer ensures that the coextruded materials do not block each other during manufacturing, thereby making the elastic film much easier to handle.

[0007] Furthermore, the non-elastic cover layer also contributes to maintaining web tension. It should be noted that, while films are typically transported along the machine direction (MD) during manufacturing and processing, web tension must be applied to transport an elastic film in the machine direction. If the elastic film were formed only over the elastic film layer, this web tension would at least partially lengthen the material, making processing more difficult. To still utilize the elasticity of the elastic film layer, the entire film must be stretched, particularly in the machine direction. This thins the cover layer, causing it to wrinkle when unwound. Depending on the brittleness or extensibility of the cover layer, it may also rupture alternatively or additionally. Therefore, stretching the film reveals the elastic behavior of the elastic film layer. This step is also typically referred to as activation, since stretching activates the elastic behavior of the elastic film.

[0008] The elastic behavior is essentially determined by the elastomer material used, and the prior art has known the use of polyolefin elastomers (POE). Such elastomers have the advantage of allowing particularly good bonding to outer layers, especially nonwoven outer layers, during the laminate manufacturing process. In practice today, this bonding is often achieved by ultrasonic welding, in which nonwoven layers are bonded to each other on or through an elastic film by applying ultrasonic energy. Here, polyolefin elastomers have very good inherent strength in the stretched state, which makes the elastic film particularly resistant to tearing, for example, during ultrasonic bonding in the stretched state.

[0009] Alternatively, elastic film layers made of styrene block copolymers (SBC) have also proven particularly suitable in practice, as they have better elastic properties than elastic film layers based on polyolefin elastomers. However, at the same time, they also have lower intrinsic strength. Against this background, elastic films formed from a polymer blend having a first polymer component A and a second polymer component B, where the first polymer component is a polyolefin, in particular an elastomeric polyolefin, or a polyolefin blend, have proven particularly advantageous in practice.

[0010] For example, EP3126140B1 (Patent Document 1) proposes a multilayer elastic film in which an elastomeric film layer is disposed between two inelastic cover layers. Here, the elastic film layer consists essentially of an elastomeric polyolefin and may contain up to 30% of a second polymer component B, which is mainly styrene-ethylene-butylene-styrene (SEBS). In addition, a certain amount of inorganic particles, such as clay, may also be included. This improves the strength of the elastic film layer, resulting in higher breaking strength at a lower elongation at break.

[0011] EP 4032703 A1 also discloses a multilayer assembly made of an inelastic outer layer and an elastic core layer, the latter containing a polyolefin and a styrene block copolymer. Furthermore, a proportion of up to 20% of a softener is permitted, particularly oils. Such a softener makes the film softer and more flexible.

[0012] Although the elastic films known so far have basically demonstrated their usefulness, for example, when a compromise is made between good elastic behavior on the one hand and good processability on the other hand, the films formed therefrom and the elastic laminates formed therefrom have unfavorable elastic behavior, especially under dynamic loads. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] EP3126140B1 [Patent Document 2] EP4032703A1 Summary of the Invention [Problem to be solved by the invention]

[0014] Against this background, the present invention is based on the problem of providing an elastic film that is characterized by improved elastic behavior as well as a low-cost, resource-saving design. At the same time, the process behavior of the film during production should also be improved. [Means for solving the problem]

[0015] The object and solution to this problem is an elastic film according to claim 1. It therefore comprises, in addition to a first polymer component A which is a polyolefin, in particular a polyolefin elastomer, a second polymer component B. This second polymer component B is a styrene block copolymer present in the polymer mixture in an amount of 28% to 60% by weight, the polymer mixture containing less than 1% by weight of inorganic and less than 5% by weight of organic residual components.

[0016] The present invention is based on the finding that particularly good elastic behavior can be achieved by using a relatively high proportion of styrene block copolymer while simultaneously reducing the remaining components. Thus, by increasing the second polymer component, the organic and inorganic remaining components can essentially be omitted, resulting in a second polymer mixture essentially consisting exclusively of polyolefin and styrene block copolymer. This allows for the formation of an elastic film characterized by a particularly low cracking tendency. This property is particularly important for the further processing of the film, for example, into laminates. Especially during ultrasonic welding, the film melts, thins, or breaks at certain points, risking the formation of cracks in the elastic film starting from the joint. Therefore, a low cracking tendency of the film is advantageous. Furthermore, the film can also be pre-stretched or activated significantly more vigorously before further processing.

[0017] An alternative or additional solution further provides that, starting from an elastic film layer and at least one first non-elastic cover layer coextruded with the elastic film layer, the elastic recovery value (ERV) after 300% activation is greater than 0.4, particularly in the machine direction.

[0018] This elastic recovery value can be determined based on a hysteresis measurement of the film. Measurements are typically performed using the so-called three-cycle hysteresis method, in which an elastic film sample with a sample width of 25.4 mm and a grip distance of 25.4 mm is pre-stretched to 300% in the first overstretching cycle. This initial overstretching is also referred to as activation within the scope of the present invention, since it thins or wrinkles the inelastic cover layer, thereby revealing the elastic behavior of the elastic film layer. Essentially, immediately after this first cycle, the film can have an elastic recovery value of at least 0.4. However, preferably, two further cycles are subsequently performed, and the elastic recovery value is determined based on hysteresis only after the third cycle. For these second and third cycles, the now pre-stretched sample of elastic film is remounted, taking into account the plastic deformation and resulting elongation of the sample that occurred within the first cycle. After reloading the sample, it is stretched to 120% in the second and third cycles, with the film being held in a relaxed state for 60 seconds between each cycle. In contrast, the film is held in a stretched state for 30 seconds. The test speed is 500 mm / min. After each cycle, a hysteresis curve can be determined, in which the force required for stretching is plotted against the stretch, where the stretch is usually expressed as a percentage and is referenced to the original length of the sample. Here, 100% stretch corresponds to twice the original length of the sample. At 0% stretch, the sample returns to its original length, so that only elastic behavior can be observed.

[0019] Based on such a hysteresis curve, it can be determined that the force required for stretching is greater than the force released during relaxation. Therefore, the so-called load curve lies above the relaxation curve. This behavior is also called viscoelastic behavior because part of the energy required for stretching is dissipated by internal processes within the film and is not available for relaxation. This difference between the load curve and the relaxation curve is also called loss energy and can be expressed by the so-called elastic recovery value (ERV). Here, the elastic recovery value represents the ratio of the area under the relaxation curve to the area under the load curve. Therefore, although an ERV value of up to 1 can be achieved, such a value is only theoretically achievable and represents ideal elastic behavior.

[0020] Within the scope of the present invention, it is now possible to achieve an elastic recovery value of at least 0.4, particularly 0.45, and thus at least 40% of the energy introduced for stretching can be used during relaxation. This allows, for example, in the case of diapers, the material to return to its original state as quickly as possible under dynamic load, thereby more quickly compensating for movements, for example, in babies. At the same time, it is ensured that the material applies sufficient force to adjacent body parts as quickly as possible, even during movement, thereby ensuring a particularly good seal.

[0021] Although an amount of second polymer component B of 28 to 60 wt. % may be sufficient, in preferred embodiments the second polymer component B is present in an amount of 30 to 55 wt. %, particularly preferably 32 to 50 wt. %.

[0022] The present invention is particularly characterized by providing a polymer mixture having a first and a second polymer component, wherein the second polymer component is a styrene block copolymer. The styrene block copolymer can be a styrene-isoprene-styrene block copolymer (SIS), a styrene-butadiene-styrene block copolymer (SBS), a styrene-ethylene-butylene-styrene (SEBS), or a styrene-ethylene / propylene-styrene block copolymer (SEPS). Styrene-ethylene-propylene-styrene block copolymer (SEEPS) is particularly preferred as the styrene block copolymer. SEEPS is particularly well mixed with the first polymer component A (which is particularly a polyolefin or polyolefin blend), so that no additional auxiliary substances are required to achieve compatibility. Against this background, the two main components can be directly mixed during extrusion, thereby significantly reducing the use of residual components, especially organic residual components. SEEPS is sold, for example, by Kuraray under the trade name Septon.

[0023] In a further embodiment of the present invention, the first polymer component A contains or is composed of a polyolefin elastomer (POE). Similar to styrene block copolymers, these elastomers also belong to the thermoplastic elastomers, which can be plastically deformed by applying heat, making them suitable for extrusion processing, for example. At the same time, they always contain two phases, the hard phase responsible for melting and the soft phase responsible for elastomeric properties. Corresponding polyolefin elastomers are also sold, for example, by Exxon under the trade name Vistamaxx or by Dow Chemical under the trade name Infuse.

[0024] In a further embodiment of the present invention, the first polymer component A is a polyolefin blend of a first polyolefin and a second polyolefin, wherein the weight ratio of the first polyolefin to the second polyolefin is between 1:3 and 2:3. In particular, the polyolefin blend consists solely of the first and second polyolefins. Furthermore, at least the first and / or second polyolefins are formed as polyolefin elastomers.

[0025] In a further embodiment of the present invention, a second non-elastic cover layer is co-extruded with the elastic film layer and disposed between the first and second cover layers. Thus, a kind of sandwich composite is formed in which the elastic film layer acts as a core layer and is surrounded by the two non-elastic cover layers. While the two non-elastic cover layers can be produced by fundamentally different methods, they preferably have substantially the same construction. In particular, the two cover layers can have the same thickness and / or the same material composition.

[0026] In a particularly preferred embodiment, the ratio of the thickness of the elastic film layer to the thickness of the first and / or second cover layer, respectively, is 6:1 to 15:1, in particular 7:1 to 12:1. The present invention is therefore characterized by very thin cover layers. It should be noted that in each case, the elastic behavior of the film is essentially determined by the ratio of the elastic film layer to the non-elastic cover layer. As the ratio increases, the overall elastic performance of the resulting elastic film also increases. Therefore, a relatively thin non-elastic cover layer results in a particularly good elastic behavior of the film.

[0027] In particular, the first and / or second cover layer has a thickness of 1 μm to 5 μm, preferably 1.5 μm to 4 μm, particularly preferably 2 μm to 3.5 μm. In contrast, the elastic film layer has a thickness of 15 to 43 μm, preferably 17 to 30 μm, particularly preferably 20 to 26 μm. The total thickness of the elastic film is preferably 17 to 45 μm, particularly preferably 20 to 36 μm, and very particularly preferably 24 to 33 μm.

[0028] According to a preferred embodiment, the first and / or second cover layer is formed from a polyolefin as the main component. Main component here means that the polyolefin is present in the corresponding first or second cover layer in a proportion of at least 30% by weight. Particularly preferably, the polyolefin is present in the respective first and / or second cover layer in an amount of at least 45% by weight, particularly preferably at least 60% by weight. A range of 45 to 70% by weight is particularly preferred. The remaining components can be organic or inorganic. In particular, the remaining components are additives, such as stabilizers, processing aids, lubricants, and / or antiblocking agents. For example, the remaining components can comprise or consist of talc. The proportion of the remaining components can be 6 to 18% by weight, based on the composition of each cover layer. Preferably, the proportion of talc is 3 to 15% by weight, particularly preferably 5 to 10% by weight, based on the composition of each cover layer.

[0029] According to a particularly preferred embodiment of the present invention, the polyolefin of the first and / or second cover layer is polyethylene or polypropylene. In the case of polyethylene, this is in particular low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE). LLDPE has been found to be particularly advantageous. The polypropylene can be, for example, a homopolymer or copolymer. Also preferred in this context are mixtures of polyethylene, in particular linear low-density polyethylene, with polypropylene, where the proportion of polypropylene can be 30 to 60% by weight, based on the polyolefin component, and / or the proportion of polyethylene can be 30 to 60% by weight. The proportion of the remaining components, in particular talc, can be 15 to 25% based on the proportion of polypropylene. Furthermore, the film can also advantageously be relatively thin overall, resulting in material savings compared to comparable solutions from a sustainability perspective.

[0030] As already explained above, inventive embodiments of the present invention, the elastic recovery value (ERV) after 300% activation exceeds 0.4, in particular exceeds 0.45. The activation is particularly carried out by overstretching the inelastic cover layer in the machine direction (MD), and this elastic recovery value can be achieved particularly by using a polymer blend of a polyolefin elastomer and a styrene block copolymer, in particular SEEPS, in the elastic film layer. A high elastic recovery value allows the elastic film to return to its original state particularly quickly and with relatively high force after stretching, thereby providing a particularly comfortable fit.

[0031] In addition to assessing the elastic recovery value, the so-called permanent set is also important, which provides information on how the elastic film continues to stretch after the initial activation. For this purpose, the permanent set is usually determined based on two consecutive cycles in which the elastic film is stretched by 300% without being reloaded each time. In the first cycle, the stretching is carried out to 300% at a test speed of 500 mm / min. The film is then held in the stretched state for 30 seconds, then released, and held in a relaxed state for another 60 seconds. Subsequently, it is again stretched by 300% at a test speed of 500 mm / min. The film used for the measurement corresponds in terms of its dimensions to the film also used for the hysteresis measurement. It therefore has a sample width and grip distance of 25.4 mm. The grip distance is then compared with the corresponding stretched sample, and the difference in length based on the original grip distance is defined as the permanent set. For example, if a sample has a length of 50.8 mm after the corresponding stretch, this corresponds to a permanent set of 100%.

[0032] Based on this measurement, after 300% activation, especially after two 300% activations, the permanent strain is preferably less than 40%, particularly preferably less than 35%, very particularly preferably less than 30%.Therefore, an elastic film is provided that has high elastic recovery value on the one hand and at the same time has low permanent strain.Therefore, compared with known films, under the same permanent strain, it can generate higher recovery force or need lower permanent strain to achieve required recovery value.

[0033] In this context, a solution having an independent meaning of the present invention is that, in particular for general films, the second polymer component B is a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) and the permanent deformation after 300% activation is less than 40%, particularly preferably less than 35%, very particularly preferably less than 30%.

[0034] This allows for the provision of an elastic film that can be produced with a particularly thin cover layer. It should be noted here that layer thickness is typically limited by extrusion techniques, and therefore, arbitrarily thin cover layers cannot be produced. However, in the present invention, the elastic film can be activated not only in the machine direction (MD) but also in the cross direction (CD). However, this activation in the cross direction is not primarily used to form a film that can be stretched in the cross direction. Rather, this activation thins the cover layer material, while the low permanent set ensures that this thinning does not substantially affect the elastic film layer. This shifts the thickness ratio between the individual layers more in favor of the elastic film layer, thereby further improving the elastic performance of the film. For example, it is even possible to produce a cover layer that has a thickness of less than 1 μm, at least in part.

[0035] The above-mentioned elastic recovery values ​​can be achieved by minimizing the difference between the area under the load curve and the area under the relaxation curve at 120% elongation after 300% activation, in particular by appropriate material selection and composition based on hysteresis measurements, in particular by a difference of less than 90 N / inch%, particularly preferably less than 80 N / inch%, very particularly preferably less than 70 N / inch%.

[0036] According to a preferred embodiment, the coefficient of friction of the film according to ISO8295 is 0.2 to 0.6.

[0037] The present invention also provides an elastic laminate having at least one cover layer made of a nonwoven fabric and an elastic film of the present invention bonded to the cover layer. Typically, during manufacturing, the cover layer and the elastic film are provided via separate nonwoven and film webs, which are then bonded to each other to form the corresponding laminate. In particular, the elastic film is disposed between and bonded to two nonwoven cover layers. The elastic film thus forms the elastic core of the elastic laminate. The nonwoven cover layer provides a soft, comfortable, textile-like surface, while at the same time allowing the laminate to be manufactured at low cost. The elastic film ensures elastic recovery properties for a secure fit and good seal of the sanitary article made therefrom.

[0038] Various approaches are known for producing such laminates: for example, a prefabricated elastic film and at least one prefabricated cover layer made of a nonwoven fabric can be bonded together substantially tension-free using pressure and temperature, adhesives, or ultrasonic welding, resulting in, among other things, a pattern of bonded and unbonded areas.

[0039] However, in many cases, during the manufacturing process, the elastic film or the laminate formed therefrom is activated, so that the film is stretched across the laminate in the desired stretching direction.In particular, the elastic film is stretched at least in the machine direction (MD) before being bonded to at least one cover layer.This can be done, for example, by using two roller devices arranged in succession and operating at an increasing speed.Therefore, a greater web tension is generated between these two roller devices, which leads to the desired activation of the film.The elastic film can then be bonded to at least one cover layer in a stretched state by the above-mentioned bonding method.This process is also generally called stretch bonding.

[0040] In another known method, an elastic film is first preactivated, for example by a ring roller, and cut into two strips. Both strips are then introduced into an associated stretching unit with an inclined disk (spreader) and subjected to this stretching unit when the two mutually inclined disks have a minimum distance. Subsequently, the inclination of the disks causes stretching of the elastic strips in the cross direction (CD), and the elastic film strips are held at their edges by a vacuum and introduced by the spreader.

[0041] After the first nonwoven web is guided over the central roller, the first elastic strip is subsequently applied from the spreader and held in place by vacuum. The second elastic strip is then similarly moved in parallel, placed on top, and held in place. After both elastic strips are positioned parallel to the first nonwoven web, the second nonwoven web can then be placed on top. Ultrasonic welding then follows.

[0042] Alternatively, the elastic film can be bonded to the cover layer(s) in an activated but unstretched state. The laminate can then be subsequently activated, for example, in the transverse direction to the machine direction. In this regard, the laminate can be stretched, for example, using ring rollers. The corrugated or zigzag path of the nip of the interlocking ring rollers stretches the introduced material in the transverse direction, thereby overstretching, permanently deforming, and possibly partially destroying the stretchable but non-elastic nonwoven cover layer.

[0043] The manufacturing process described above is merely exemplary, and other bonding configurations and manufacturing processes for the laminate of the elastic film and cover layer are of course possible.

[0044] Furthermore, it is not necessary for the elastic film to be adjacent to at least one cover layer(s) over the entire surface. It is also conceivable that the elastic film is only partially disposed in sections between the nonwoven webs, especially in the case of embodiments with two outer cover layers. For example, these sections can be a plurality of strands spaced apart laterally, with the cover layers being directly bonded to each other between each strand, rather than via the elastic film. Therefore, in such embodiments, elasticity is provided only in the sections of the elastic laminate. In this case, it is sufficient for the cover layer to be activated only in the areas where the elastic film is also disposed.

[0045] The subject of the present invention is also a sanitary article comprising the elastic laminate of the present invention, in particular an elastic waistband, an elastic sealing element or other elastic element of a diaper.

[0046] In the following, the invention will be explained in more detail by means of illustrative examples. The figures show: [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 1 shows an exemplary structure of an elastic film according to the present invention. [Figure 2A] 2A, 2B, 2C, and 2D show hysteresis curves for two exemplary films and for two comparative examples from the prior art. [Figure 2B] 2A, 2B, 2C, and 2D show hysteresis curves for two exemplary films and for two comparative examples from the prior art. [Figure 2C] 2A, 2B, 2C, and 2D show hysteresis curves for two exemplary films and for two comparative examples from the prior art. [Figure 2D] 2A, 2B, 2C, and 2D show hysteresis curves for two exemplary films and for two comparative examples from the prior art. [Figure 3] FIG. 3 shows, in a schematic diagram, a method for making the elastic laminate of the present invention.

[0048] 1 shows an elastic laminate of the present invention, made from a nonwoven fabric, having an upper first cover layer 1 and a second lower cover layer 2 surrounding an elastic film 3 formed as a core layer. Such elastic laminates are particularly used in hygiene products, because the outer cover layers 1, 2 provide a comfortable soft surface, while the inner elastic film 3 can exhibit recovery behavior.

[0049] The cover layers 1, 2 can be bonded to the elastic film 3 in various ways, particularly by adhesive or ultrasonic welding. In the case of ultrasonic welding, bonding occurs at multiple bond points (not shown in more detail in FIG. 1 ), where the cover layers 1, 2 are bonded to each other either directly through the elastic film 3 or via the elastic film 3. Because the elastic film 3 is typically bonded to the cover layers 1, 2 under tension, holes are formed in the elastic film 3 at the bond points during the ultrasonic welding process, which allows for particularly good breathability through the laminate. However, these holes also represent weak points in the film 3, because cracks can form in the film 3 from these holes. The elastic film 3 used within the elastic laminate of the present invention has a very low tendency to crack and can be bonded to the cover layers 1, 2 under particularly high tension.

[0050] The elastic film 3 is a multilayer coextruded film, the individual layers of which are more clearly shown in cross section, particularly in the detailed drawing. As shown there, the elastic film 3 has first and second inelastic cover layers 4, 5, which surround a core elastic film layer 6. The elastic behavior of the elastic film 3 and of the entire elastic laminate is therefore determined by the elastic film layer 6, which is already clear from FIG. 1 , since the elastic film 3 comprises relatively thin inelastic cover layers 4, 5, the elastic behavior of the entire elastic film 3 is determined crucially by the elastic film layer 6.

[0051] Since the laminate according to the present invention is intended to be used, inter alia, in sanitary articles such as diapers, it is very important here that the laminate, and therefore also the elastic film 3 used, have good recovery behavior. It should be noted here that even when such a laminate is subjected to dynamic load, it must always be ensured that the sanitary article made from the laminate seals the gaps and at the same time adheres to the corresponding body part with high wearing comfort, for example to prevent leakage of body waste. However, in practice, known elastic films 3 often exhibit a strongly pronounced viscoelastic behavior. This means that the energy required for stretching is often significantly higher than the energy released during relaxation. This energy loss leads to a damping of the elastic properties, so that, for example, when the corresponding sanitary article is subjected to load, the material deforms, but does not adhere to the corresponding body part sufficiently quickly and with sufficient sealing force when unloaded.

[0052] Here, the elastic film 3 according to the invention has an elastic recovery value (ERV) of greater than 0.4, preferably greater than 0.45, after 300% activation. This elastic recovery value compares the energy released with the energy required for stretching at 120% elongation. An elastic recovery value of 1 represents an ideal rubber, but in reality, dissipation effects result in energy losses, so this value is of course not achievable in practice. Here, the elastic film 3 according to the invention is able to utilize at least 40% or more of the energy required for stretching for recovery, thereby achieving a significant improvement compared to solutions already known from the prior art.

[0053] To achieve such high elastic recovery values, the elastic film layer 6 can be formed from a polymer blend having a first polymer component A and a second polymer component B. The first polymer component A is a polyolefin, particularly a polyolefin elastomer, and the second polymer component B is a styrene block copolymer. Styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS) have been found to be particularly advantageous, with the polymer component B present in the polymer blend in an amount of 32% to 55% by weight. Furthermore, the present invention also provides for the elastic film layer 6 to be formed exclusively from the first and second polymer components, resulting in zero or only trace amounts of residual components present in the elastic film layer 6. In particular, inorganic residual components comprise less than 1% by weight, and organic residual components comprise less than 5% by weight within the polymer blend. SEEPS is particularly important as the second polymer component B because it is highly miscible with polyolefin elastomers, eliminating the need for additional processing aids. The reduction of the residual component provides a polymer mixture formed solely from elastic components, whereby the elastic film layer 6 as well as the film 3 and laminate have particularly good recovery behavior.

[0054] Table 1 shows four different elastic films 3. Films 1 and 2 are formed solely from polyolefin elastomer in the elastic film layer 6 by known methods. Film 3, on the other hand, has 41% by weight of styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) and 59% by weight of polyolefin elastomer in the elastic film layer 6. Film 4 has 45% by weight of styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) and 55% by weight of polyolefin elastomer in the elastic film layer 6. Furthermore, Film 4 was activated in the cross direction (CD), thereby thinning the non-elastic cover layers 4 and 5. As a result, 82% of the film's thickness is defined by the elastic film layer 6, whereas in Films 1 through 3, the elastic film layer 6 accounts for only 80% of the thickness of Film 3.

[0055] [Table 1]

[0056] The exact construction of films 1 and 2 is shown in Tables 2 and 3, and the construction of films 3 and 4 in Tables 4 and 5, where the composition of cover layer 4 is the same for films 3 and 4, with the essential difference being the elastic film layer 6. Furthermore, film 4 also has slightly thinner cover layers 4, 5 than films 1-3.

[0057] [Table 2]

[0058] [Table 3]

[0059] [Table 4]

[0060] [Table 5]

[0061] As can be seen from Tables 2-5, the inelastic cover layers 4 and 5 consist essentially of polyolefin. As shown in Tables 4 and 5, films 3 and 4 are polyolefin blends of 55% linear low-density polyethylene (LLDPE) and 35% by weight polypropylene. As shown in Tables 2 and 3, films 1 and 2 use a slightly lower proportion of linear low-density polyethylene. In this regard, the outer layer contains 10% low-density polyethylene. It has been found that a higher proportion of linear low-density polyethylene (LLDPE) is advantageous in terms of the extensibility of the thin outer layer. It is also believed that the LLDPE of films 3 and 4 has a higher degree of molecular branching, which is advantageous because it allows for the formation of a uniformly thin outer layer that can be easily stretched during the extrusion process for subsequent film activation.

[0062] In the examples, a polymer from Exxon was used as linear low density polyethylene. This material has a density of 0.936 g / cm 3 and a melt index (MFI) of 5.0 g / 10 N (190°C / 2.16 kg). It is an ethylene-butene copolymer with a melting point of 125°C and a flexural modulus of 470 MPa.

[0063] As polypropylene, 0.910 g / cm 3 Polypropylene having a density of 1000 MPa and a melt flow rate (MFR) of 26 g / 10 n (230°C / 2.16 kg) was used. The melting point of the polypropylene was 161°C.

[0064] Low-density polyethylene (LDPE) for films 1 and 2: 0.919 g / cm 3 An ethylene-octene copolymer having a density of 1000 MPa and a melt index (MFI) of 6 g / 10 n (230° C. / 2.16 kg) was used.

[0065] In addition to the two polyolefin components, talc and processing additives were also used in the polymer mixture. Both cover layers 4, 5 were formed in the same way.

[0066] For elastic film layer 6, Vistamaxx 6102 was used as the polyolefin elastomer in all four films. The material had a density of 0.862 g / cm 3 and a melt index (MFI) of 1.4 g / 10n (190°C / 2.16 kg) and 3.0 g / 10b (230°C / 2.16 kg). The hardness is 67 Shore A. The ethylene content is 16% and the flexural modulus is 14 MPa.

[0067] The polymer Septon F4902 from Kuraray was used as a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS). It is a hydrogenated triblock copolymer containing styrene, isoprene, and butadiene. The material has a density of 0.9 g / cm. 3 It has a density of 1.0g / 10n, a melt index (MFI) (200°C / 5kg) of 2.9g / 10n and a Shore A hardness of 56.

[0068] All films were produced by cast coextrusion. Of course, it is also possible within the scope of the present invention to produce films by blown film techniques.

[0069] After production, four films were subjected to hysteresis measurements using three cycles of hysteresis, as well as permanent set measurements. For the hysteresis measurements, samples with a width of 25.4 mm and a grip distance of 25.4 mm were stretched 300% at a test speed of 500 mm / min and held in the stretched state for 30 seconds. The films were then relaxed and held in the relaxed state for 60 seconds. After reloading the samples, they were stretched to 120% and then held in the stretched state for 30 seconds. After relaxation and a further 60-second hold time, a further stretch of 120% and subsequent relaxation were performed.

[0070] Figures 2A, 2B, 2C, and 2D show the force course during extension of the corresponding samples for all four listed films, where Figure 2A shows the hysteresis curve for Film 1, Figure 2B shows the hysteresis curve for Film 2, Figure 2C shows the hysteresis curve for Film 3, and Figure 2D shows the hysteresis curve for Film 4. All hysteresis curves were recorded during the third cycle of the hysteresis measurement.

[0071] As can be seen from Figures 2A, 2B, 2C, and 2D, an upper loading curve L and a lower unloading curve U are given for all measurements. Here, the loading curve L represents the force required to stretch the sample 120°, and the unloading curve U shows the force released during the unloading process. The hysteresis curves therefore show that the initially introduced energy cannot be fully utilized during unloading due to dissipation effects between tension and relaxation. This lost energy can be quantified, in particular, by the so-called elastic recovery value (ERV). This is done by comparing the areas under the loading curve L and the unloading curve U, as shown in Figure 2A.

[0072] The area under the unloading curve 7 and the area under the unloading curve 8 are shown in Figure 2A, but can of course be plotted for all other films. Furthermore, the area under the unloading curve 8 is divided by the area under the loading curve 7, so that, theoretically, a maximum value of 1 is achieved.

[0073] Furthermore, the elastic recovery values ​​are shown in Table 6. Overall, it is clear that significantly higher elastic recovery values ​​of more than 0.4 are achievable with the elastic film 3 of the present invention compared to films 1 and 2 known from the prior art. In particular, film 4 results in an elastic recovery value of 0.49, so that almost half of the energy required for stretching can be released and utilized again during the unloading process.

[0074] [Table 6]

[0075] This positive effect is also evident in a visual comparison of the hysteresis curves, in particular the difference area 9 between the load curve L and the unload curve U being significantly smaller in the inventive film 3 according to Figures 2C and 2D than in the comparative example according to Figures 2A and 2B. These differences are quantitatively described in Table 7, which reveals that the load curve L and the unload curve U are clearly closer to each other, especially in the case of film 4, where a value of 49.5 N / inch% is possible, while the value for the comparative example is substantially around 100 N / inch.

[0076] [Table 7]

[0077] In addition to the elastic recovery value (ERV), the permanent set is significantly improved with inventive film 3. The permanent set values ​​are shown in Table 8 below, where the permanent set after two stretches of 300% is 22.6% for film 4, more than double the permanent set for the comparative example.

[0078] [Table 8]

[0079] Furthermore, Table 9 below shows the mechanical properties of the different films and it is clear that despite the improved elastic properties, no deterioration in mechanical properties is expected.

[0080] [Table 9]

[0081] 3 exemplarily illustrates a manufacturing method for producing a laminate web 10 having the structure shown in FIG. 1. For this purpose, the cover layers 1, 2 and the elastic film 3 are guided in the form of a web along the machine direction (MD), and the elastic film 3 is activated in the machine direction (MD) in an activation unit 11 before being bonded to the cover layers 1, 2. This is done via two roller devices 12, 13 rotating at different rotation speeds, with the roller device 13 having a higher rotation speed than the roller device 12, so that the elastic film 3 is appropriately stretched between these roller devices 12, 13. Next, bonding to the cover layers 1, 2 is carried out in an ultrasonic welding device 13 in a stretched state.

Claims

1. An elastic film (3) having an elastic film layer (6) and at least one first inelastic cover layer (4, 5) coextruded with said elastic film layer, said elastic film layer (6) being formed from a polymer blend including a first polymer component A and a second polymer component B, said first polymer component being a polyolefin or a polyolefin blend; The elastic film (3), wherein the second polymer component B is a styrene block copolymer present in the polymer mixture in an amount of 28% to 60% by weight, and the polymer mixture contains less than 1% by weight of an inorganic residual component and less than 5% by weight of an organic residual component.

2. 2. The elastic film (3) of claim 1, characterized in that the second polymer component is present in the polymer mixture in an amount of 30% to 55% by weight.

3. Elastic film (3) according to claim 1 or 2, characterized in that the second polymer component B is a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

4. 4. The elastic film (3) according to any one of claims 1 to 3, characterized in that the first polymer component A is a polyolefin blend of a first polyolefin and a second polyolefin, the ratio between the weight proportion of the first polyolefin and the weight proportion of the second polyolefin being 1:3 to 2:

3.

5. Elastic film (3) according to any one of claims 1 to 4, characterized in that the first polymer component A comprises or consists of a polyolefin elastomer.

6. 6. The elastic film (3) according to any one of claims 1 to 5, characterized in that a second inelastic cover layer (4, 5) is coextruded with the elastic film layer (6), the elastic film layer (6) being disposed between the first and second cover layers (4, 5).

7. 7. The elastic film (3) according to any one of claims 1 to 6, characterized in that the ratio between the thickness of the elastic film layer (6) and the thickness of the first and / or second cover layer (4, 5), respectively, is between 6:1 and 15:

1.

8. Elastic film (3) according to any one of claims 1 to 7, characterized in that the first and / or second cover layer (4, 5) is / are formed from a polyolefin as the main component.

9. 9. The elastic film (3) according to claim 8, characterized in that the first and / or second cover layer (4, 5) each comprises linear low density polyethylene (LLDPE) in a proportion of at least 40% by weight.

10. Elastic film (3) according to any one of claims 1 to 9, characterized in that the first and / or second cover layer (4, 5) comprises a filler.

11. An elastic film (3) comprising an elastic film layer (6) and at least one first inelastic cover layer (4, 5) coextruded with said elastic film layer, in particular an elastic film (3) according to any one of claims 1 to 10, in which in particular said elastic film layer (6) is formed from a polymer blend comprising a first polymer component A and a second polymer component B, said first polymer component being a polyolefin or a polyolefin blend, The elastic film (3), in particular the elastic film (3) according to any one of claims 1 to 10, characterized in that it has an Elastic Recovery Value (ERV) after 300% activation of more than 0.

4.

12. An elastic film (3) comprising an elastic film layer (6) and at least one first inelastic cover layer (4, 5) coextruded with said elastic film layer, in particular an elastic film (3) according to any one of claims 1 to 11, in particular wherein said elastic film layer (6) is formed from a polymer blend comprising a first polymer component A and a second polymer component B, said first polymer component being a polyolefin or a polyolefin blend, The elastic film (3), in particular the elastic film (3) according to any one of claims 1 to 11, characterized in that the second polymer component B is a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) and has a permanent set after 300% activation of less than 40%.

13. 13. The elastic film (3) according to any one of claims 1 to 12, characterized in that the difference area (9) between the area under the load curve (L) and the area under the unload curve (U) at 120% elongation after 300% activation is less than 90 N / inch%.

15. An elastic laminate comprising at least one cover layer (1, 2) made of nonwoven fabric and, joined thereto, an elastic film (3) according to any one of claims 1 to 14.

16. 16. Elastic laminate according to claim 15, characterized in that the elastic film (3) is arranged between and joined to two cover layers (1, 2) made of nonwoven fabric.

17. 17. Elastic laminate according to claim 15 or 16, characterized in that the elastic film (3) is joined to the at least one cover layer (1, 2) by ultrasonic welding.

18. Elastic laminate according to any one of claims 15 to 17, characterized in that the elastic film (3) in the activated state is joined to the at least one cover layer (1, 2).

19. A sanitary article made from the elastic laminate according to any one of claims 1 to 18.

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