Elastic nonwoven fabric

Abstract

The present invention relates to nonwoven sheets that have the ability to elastically stretch to a large extent in the machine direction while exhibiting low extensibility in the cross machine direction. The present invention also relates to a method for making such sheets.

Description

[Technical field]

[0001] The present invention relates to nonwoven sheets that have the ability to elastically stretch to a large extent in the machine direction while exhibiting low extensibility in the cross machine direction. The present invention also relates to a method for making such sheets. [Background technology]

[0002] Nonwoven sheets are used extensively in the hygiene industry as materials for making baby diapers and adult incontinence products. In many cases, for example to make the back ears of open diapers or the waist belt of diaper pants, elastically stretchable materials are required, and standard nonwoven sheets do not meet this requirement.

[0003] Traditional methods for preparing elastically stretchable materials based on nonwovens generally involve pleating a nonwoven fabric with an elastically stretchable material such as Lycra yarn. A more modern approach aims to combine an elastically stretchable nonwoven sheet containing fibers made of a thermoplastic elastomer material with a stretchable but non-elastic facing layer to prepare a nonwoven sheet with an inherent property of elastically stretching ability. Examples include the nonwoven sheets disclosed in WO2020 / 187540 A1 or EP3715517 A1. Summary of the Invention [Problem to be solved by the invention]

[0004] In a typical manufacturing process for diaper pants for adults or babies, the circumferential direction of the diaper is usually the machine direction (MD) of the nonwoven sheet used, and the top-to-bottom direction of the diaper is usually the cross-machine direction (CD) of the nonwoven sheet used. In such a case, it is advantageous for the material to exhibit a large degree of elastic extensibility in the machine direction, allowing the diaper pants to elastically stretch in the circumferential direction for a good fit, while exhibiting low extensibility in the cross-machine direction to prevent excessive stretching when pulling up the diaper. This requirement conflicts with the fact that in spunbond nonwoven sheets, which are currently the industry standard for some diaper materials and applications, the average fiber direction is in the machine direction, which usually results in lower extensibility in the machine direction than in the cross-machine direction.

[0005] Therefore, there is a need in the hygiene industry for nonwoven sheets that have inherent properties that allow for high stretch in the machine direction, while at the same time reducing stretch in the cross machine direction. [Means for solving the problem]

[0006] In this context, the present invention relates to a method for making an elastically stretchable multilayer nonwoven sheet in the machine direction, the method comprising the steps of providing an elastically stretchable nonwoven sheet comprising at least two layers of nonwoven material, where one layer is an elastically stretchable nonwoven comprising spunbond elastic fibers of a thermoplastic elastomeric polymer material and one layer is a stretchable decorative layer comprising spunbond crimped multicomponent fibers, and providing an elastically stretchable nonwoven sheet having an elongation at break less than the elastically stretchable nonwoven sheet in at least the cross machine direction. and co-feeding the elastically stretchable nonwoven sheet and the low stretch nonwoven sheet to a bonding station where the sheets are melt bonded together in a predetermined pattern, the elastically stretchable nonwoven sheet being fed to the bonding station under machine direction pretension and pre-stretched in the machine direction, while the low CD stretch nonwoven sheet is fed to the bonding station with no pretension or under a pretension that results in a machine direction pre-stretch that is less than the machine direction pre-stretch of the elastically stretchable nonwoven sheet.

[0007] The degree of pre-stretching in the machine direction of the elastically stretchable nonwoven sheet may be such that it is stretched 40-160%, preferably 60-140%, more preferably 80-120% of its original dimension.

[0008] Preferably, in terms of absolute force and regardless of the resulting pre-stretch, the pre-tension in the low-stretch nonwoven sheet in the machine direction is less than the pre-tension in the elastically stretchable nonwoven sheet in the machine direction, if any. The degree of pre-tension and pre-stretch in the sheets simultaneously fed to the bonding station, both absolute and relative, depends on the type of sheets and the type of bonding station, including the variations discussed below. In any case, however, the method of the invention results in a configuration in which the resulting contraction in the multi-layer sheet, this contraction caused by the elastically stretchable nonwoven sheet, causes the contraction of the low-stretch nonwoven sheet between the bonding points. As a result, a pattern with pleats and other repetitive structural changes are created, which is the reason for the accumulation that allows unopposed stretching in the machine direction, at least to the extent of the previous contraction. On the other hand, there is no such accumulation in the cross-machine direction, so that the resulting multi-layer sheet is largely elastically stretchable in the machine direction, while showing low extensibility in the cross-machine direction.

[0009] The term "low elongation" used herein to characterize a nonwoven sheet co-fed with an elastically stretchable nonwoven sheet is not intended to specify a specific absolute elongation value. In general, the elasticity and elongation at break of the nonwoven sheet is preferably lower in the machine direction and preferably also in the cross-machine direction than the elastically stretchable nonwoven sheet. In absolute terms, the elongation at break of the fed sheet alone may be less than 150%, preferably less than 100%, in both the machine direction and the cross-machine direction, as measured according to WSP 110.4. The tensile strength in the machine direction is greater than 15 N / 50mm, preferably greater than 20 N / 50mm, and the tensile strength in the cross-machine direction is greater than 5 N / 50mm, preferably greater than 10 N / 50mm.

[0010] In a preferred embodiment, the elastically stretchable nonwoven sheet and the low elongation nonwoven sheet are co-fed to the bonding station under different pre-stretches, preferably pre-bonded by a pattern of melt bond points.

[0011] Preferably, the low elongation nonwoven sheet is a spunbond sheet or comprises at least a layer of a spunbond sheet. More preferably, the low elongation nonwoven sheet is a spunbond sheet made of non-crimped monocomponent fibers. The preferred material of which these fibers are made is polypropylene, but it can also be implemented using polypropylene copolymers (co-PP), such as poly(propylene-ethylene) copolymers (co-PP), or polyethylene (PE).

[0012] The crimped multicomponent fibers of the elastically stretchable decorative layer of the elastically stretchable nonwoven sheet may be bicomponent fibers having any asymmetric cross-sectional distribution, preferably side-by-side fibers, but may also be eccentric core-sheath or other known configurations.

[0013] In one embodiment, the components of the bicomponent fiber are both polypropylenes, and the polypropylenes differ from each other in properties such that the resulting fiber is crimped. A decorative layer comprising crimped bicomponent fibers of polypropylene-polypropylene construction is used, for example, in the sheeting of EP 3715517 A1.

[0014] In another embodiment, at least one of the components of the crimped multicomponent fiber is a polypropylene-α-olefin copolymer material (co-PP). This has been found to potentially lead to an increase in the overall elasticity of the sheet, especially in the machine direction (MD). The α-olefin that constitutes the copolymer together with propylene is preferably ethylene. In other words, the copolymer is preferably a poly(propylene-ethylene) copolymer. The copolymer is also preferably a random copolymer. The other of the components of the crimped multicomponent fiber is preferably a polypropylene homopolymer (PP). The co-PP or homo-PP components of such multicomponent fibers may be blended with additional polymers or other additives such as slip agents, fiber materials, paints or pigments, but should represent more than 50%, preferably more than 75%, and more preferably more than 90% of the corresponding composition.

[0015] In crimped bicomponent fibers, the ratio of one component to the other is preferably between 20 / 80 and 80 / 20, more preferably between 30 / 70 and 70 / 30, and even more preferably between 40 / 60 and 60 / 40.

[0016] The elastic fibers in the elastically stretchable layer of the elastically stretchable nonwoven sheet may comprise a thermoplastic polyolefin elastomer (TPE-o), preferably a thermoplastic polyolefin elastomer comprising a propylene-α-olefin copolymer. Suitable TPE-o materials for use in the context of the present invention are disclosed in EP 2342075 A1. Alternatively or additionally, i.e. as a mixture, other thermoplastic elastomer materials may be used, in particular thermoplastic polyurethanes (TPU) or styrene block copolymers (TPE-s). In one embodiment, up to 20% by weight, preferably up to 10% by weight, of a thermoplastic olefin, such as homopolypropylene, may be included in the thermoplastic elastomer material alongside the thermoplastic elastomer. In one embodiment, the bicomponent elastic fibers may be made of two different thermoplastic elastomers and may have a side-by-side or core-sheath configuration.

[0017] In one embodiment, the elastically stretchable nonwoven sheet comprises at least one decorative layer on either side of the elastic layer, making a total of at least three layers. This configuration can be useful for covering on both sides the elastic layer, which has inherent properties of being sticky and tends to be difficult to handle during the manufacturing process when exposed. Additional decorative layers may be provided on the first decorative layer as described above. The decorative layers on different sides of the elastic layer may be the same or different. For example, one of the nonwoven decorative layers is a spunbond nonwoven and the other nonwoven decorative layer is a different spunbond or meltblown nonwoven.

[0018] In another embodiment, the elastic layer of the elastically stretchable nonwoven sheet is exposed on the side facing the low elongation nonwoven sheet and is directly adjacent to the low elongation nonwoven sheet after the sheets are joined together at the bonding station, which has the advantage of having fewer overall layers.

[0019] The layers as defined above are elastic and preferably consist of the defined fibers, although they may also comprise monocomponent or bicomponent fibers as defined above in addition to other fibers.

[0020] The pre-stretching of the elastically stretchable nonwoven sheet may be adjusted, for example, by nip rolls arranged before the bonding station and, optionally, after the bonding station, which allow the translation speed of the sheet to be adjusted.

[0021] The bonding station comprises at least a calender roll with embossing projections on its surface. In an embodiment, ultrasonic bonding is used, where ultrasonic waves are introduced into the embossing projections. In another embodiment, thermal bonding is used, where the embossing projections are heated. In an embodiment, the sheet is fed into a gap between two counter-rotating rolls, at least one of which is a calender roll.

[0022] A particular embodiment of the bonding station comprises a pair of interacting rolls having transverse interlocking ribs and grooves on their surfaces, and embossed projections disposed along the rib crests and / or grooves on at least one of the rolls. The interlocking ribs and grooves further localize the machine direction pre-stretch in the multiple layers. Bonding the sheets together in this manner enhances the effect of the differential pre-tension discussed above.

[0023] In view of the background discussed above, the present invention further relates to a machine direction elastically stretchable multilayer nonwoven sheet comprising at least three layers of nonwoven material, a first layer comprising spunbond elastic fibers of a thermoplastic elastomeric polymer material, a second layer comprising spunbond crimped multicomponent fibers, the layers of the sheet being melt bonded with a pattern of bond points, and a third layer being contracted between the bond points and exhibiting a pleated pattern and / or varying structure that repeats in the machine direction.

[0024] By the process of the invention a fabric can be obtained, the preferred embodiment of each layer being taken from the description of the process of the invention given above.

[0025] Preferably, the multilayer sheet has a breaking elongation in the machine direction greater than 100%, preferably greater than 150%, measured according to WSP 110.4, and preferably has a breaking elongation in the cross machine direction less than 100%, measured according to WSP 110.4.

[0026] In one embodiment, the multi-layer nonwoven sheet may have a breaking elongation in the machine direction greater than the breaking elongation in the cross-machine direction, measured according to WSP 110.4.

[0027] The cross machine direction tensile strength of the multilayer sheet, measured according to WSP 110.4, is preferably greater than 10 N / 50 mm, more preferably greater than 15 N / 50 mm. The CD (at break) tensile strength of the third layer is determined to a large extent by the tensile strength of the third layer, which, considered by itself, preferably has a higher cross machine direction tensile strength compared to the first or second layers.

[0028] The basis weight of the second layer and, more generally, the decorative layer formed by the respective crimped fibers in the fabric (in the elastically stretchable nonwoven sheet in the multi-layer sheet) is 5-40 g / m 2 Between 8 and 30 g / m 2 Between 10 and 25 g / m 2 Between 15 and 20 g / m 2 It may be between.

[0029] If more than one decorative layer formed by crimped fibers is present in the fabric, they may be of the same basis weight or one may be of a smaller basis weight than the other. The different basis weight embodiment is preferred because the decorative layer in the three-layer elastically stretchable nonwoven sheet only serves the function of protecting the sticky elastic layer before the stretchable sheet is laminated to the low elongation nonwoven sheet.

[0030] The basis weight of the first (elastic) layer is preferably 10-150 g / m 2 Between 20 and 120 g / m 2 between 25 and 100 g / m 2 It may be between.

[0031] The basis weight of the third (low elongation nonwoven) layer is preferably 5-50 g / m 2 Between 8 and 30 g / m 2 between 10 and 25 g / m 2 It may be between.

[0032] The nonwoven sheet of the present invention is particularly suitable for the manufacture of hygiene products. For example, the nonwoven sheet can be used to manufacture diaper pants, using the sheet as an elastic waist material. Typical manufacturing processes currently practiced in this application area of ​​the industry require materials that are elastically stretchable in the MD.

[0033] Further details and advantages of the invention will become apparent from the figures and examples described below. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a manufacturing layout showing how nonwoven sheets are typically used in the manufacture of pant-type diapers. [Diagram 2] 1 is a pant-type diaper showing the machine and cross machine directions of the nonwoven belt material. [Diagram 3] 1 is a machine arrangement for carrying out the method of the first example of the invention; [Figure 4] FIG. 13 is a schematic diagram of an activation unit for additional prestretching and simultaneous bonding of co-fed laminates. [Diagram 5] 5 is a photograph showing the rib crest line of the roll shown diagrammatically in FIG. 4. [Figure 6] FIG. 5 is a schematic diagram of the activation unit of FIG. 4 in operation. [Figure 7] 4 is a machine arrangement for carrying out the method of the second example of the invention; [Figure 8] FIG. 1 illustrates the change in structure in a three-layer elastically stretchable nonwoven sheet when machine direction pretension is applied. [Figure 9] FIG. 1 illustrates an embodiment of a multi-layer nonwoven fabric based on three layers of elastically stretchable nonwoven sheets. [Figure 10] FIG. 1 illustrates an embodiment of a multi-layer nonwoven fabric based on two layers of elastically stretchable nonwoven sheets. [Figure 11] 1 is a hysteresis curve in a machine direction tension (stress-strain) diagram recorded for the laminate material in the first example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] 1 and 2 illustrate why in the manufacture of pant diapers it is preferable to have a sheet that has elastic properties in the machine direction and relatively little elongation in the cross machine direction.

[0036] Specifically, Figure 1 is a manufacturing layout showing how nonwoven sheets are typically used in the industrial manufacture of pant diapers. The diaper belt of the diaper, which originates from the material, can be seen to be oriented in the machine direction.

[0037] A pants-type diaper should have elasticity in the belt area to be comfortable to wear, and at the same time, should be dimensionally stable in the vertical direction to be easy to put on. Therefore, a nonwoven fabric optimized for this requirement should have good elastic properties in the machine direction, but relatively little elasticity and elongation in the cross-machine direction, and the elongation in the cross-machine direction should be low enough to withstand the force required to pull the diaper up to put it in the correct position.

[0038] The cross machine direction of the nonwoven belt material and the corresponding machine direction of a pant diaper are shown in FIG.

[0039] FIG. 3 shows an exemplary machine layout for carrying out the method of the present invention in a first example, where an elastically stretchable nonwoven sheet is laminated to a standard spunbond nonwoven sheet (also known as a low elongation nonwoven sheet), and the lamination process is carried out without adding any adhesive or adhesive.

[0040] During the process, the elastically stretchable nonwoven sheet 10 is unwound for the process at station 910, its speed being controlled by a pair of nip rolls 920. A standard (low elongation) spunbond nonwoven sheet 20 is unwound at station 930 and co-fed to an activation and bonding step at bonding station 940, which is described in more detail below in Figures 4-6. Upon leaving station 940, the material is relaxed and processed through so-called banana or separator rolls at station 960 to control the web path and ensure no wrinkles. The resulting multi-layer sheet 30 is then wound into a finished laminate roll at station 970.

[0041] Figures 4-6 show one embodiment of the bonding station 940 used in the example of Figure 3, configured as an activation unit for additional pre-stretching and simultaneous bonding of co-fed sheets. The unit includes two counter-rotating activation rolls 51, 52 configured to additionally stretch the co-fed sheets in the machine direction and bond them in a stretched state.

[0042] 4 is an enlarged cross-section taken along a radial plane perpendicular to the roll axis. As can be seen from this figure, both rolls 51 and 52 have regularly spaced ribs 53 on their working surfaces with grooves 54 formed therebetween. The ribs 53 in this embodiment are oriented in the cross machine direction and extend axially on the surfaces of rolls 51 and 52.

[0043] The width "a" of the ribs 53, the depth of interlocking "b" and the distance "c" between adjacent ribs 53 control the degree of pre-stretch in the machine direction upon activation.

[0044] At the top line of the ribs 53 of both rolls 51 and 52, a row of embossed projections 59 is provided to stretch and bond the co-fed sheets together, in other words, to simultaneously bond the co-fed sheets together while additionally stretching and activating them.

[0045] Figure 5 shows a photograph of the top line of ribs 53 on activation rolls 51, 52 shown diagrammatically in Figure 4. Ribs 53 are provided with embossed projections 59 on the top line.

[0046] Figure 6 shows the operation of the unit shown in Figure 4. From left to right in Figure 6, multiple sheets (shown as one sheet in the figure) fed simultaneously enter a combined activation and bonding process. As the sheets enter the nip of the two rolls 51, 52, the activation process is initiated by the interlocking ribs 53. The increasing interlocking of the ribs 53 into the grooves 54 causes progressively increasing localized stretching until a central position where the ribs 53 and grooves 54 are fully interlocked.

[0047] At the point of maximum meshing at the center position of the two rolls 51, 52, the embossed protrusions 59 on the ribs 53 of one roll (here, roll 51) contact the bottom of the opposing grooves 54 in the opposing roll (here, roll 52), forming a row of bond points along the top line of the ribs 53, i.e., the stripe-shaped high-density region A of the simultaneously fed sheets.

[0048] As the material exits station 940, the elastic fibers in the elastic layers of the elastically stretchable nonwoven sheet contract, restoring the material to its original elongation. The portions of the standard (low stretch) spunbond nonwoven sheet 20 that are not bonded to the elastically stretchable nonwoven sheet 10 at bond points will be pleated, wrinkled or compressed during this relaxation step by the fibers restrained within the sheet, and will retain their original low extensibility in the cross machine direction while retaining the ability to re-stretch into the machine configuration to the same extent as they were pre-stretched at station 940.

[0049] 3, at station 930, the speed of the elastically stretchable nonwoven sheet 10 before entering bonding station 940 is controlled and adjusted to be lower than the speed of the activation rolls at station 940, and thus lower than the speed of a standard (low elongation) nonwoven sheet 20 before entering bonding station 940, which is equivalent to the speed of the rolls at station 940. By running the elastically stretchable nonwoven sheet 10 at a lower speed, it enters station 940 in a pre-stretched state, and is further stretched and activated by the positioning of the rolls at station 940 to an elongation of up to 200% or more.

[0050] The activation rolls at station 940 are heated to a temperature suitable to form a bond between the elastically stretchable nonwoven sheet 10 and the standard (low elongation) nonwoven sheet 20. Typical temperatures range from 50° C. to 145° C., preferably 60° C. to 70° C. The temperatures at the bottom and top of the rolls may be different from each other.

[0051] Figure 7 shows a machine arrangement for carrying out the method of the invention in a second example. This arrangement is very similar to Figure 3, but differs only in the configuration of station 950, which comprises only one embossing roll 951 with an embossing pin on its surface and an ultrasonic welding tool, more specifically a sonotrode 952, arranged at a small distance above it. The co-fed sheets are guided, preferably slightly curved, onto roll 951 and pass through the gap between roll 951 and sonotrode 952, resting on roll 951.

[0052] Ultrasonic welding is well known in principle: the thermoplastic fibres of the sheet are activated by mechanical vibrations generated by sonotrode 952, leading to their melting and bonding in a pre-determined pattern following bonding pins on the surface of roll 951. The bonding pins focus the energy and therefore precisely define the weld points.

[0053] The machine arrangement of FIG. 7 provides somewhat less pre-stretching than the machine arrangement of FIG.

[0054] The nip pressure at stations 940 and 950 mentioned above in any example may be 5-100 N / mm and the embossing projections may occupy 8-20% of the bond area. 2 to 2 mm 2 and may have a rectangular, circular, oval or other shape.

[0055] Figure 8 is a diagram illustrating the change in structure when a three-layer elastically stretchable nonwoven sheet 10 is pre-tensioned in the machine direction. The sheet comprises two decorative layers 11 and 13 on either side of an elastic layer 12. The decorative layers 11 and 13 can each be a spunbond fabric formed from crimped fibers, which makes the sheet softer and more stretchable than a standard spunbond nonwoven sheet formed from non-crimped fibers. The elastic layer 12 is a spunbond nonwoven fabric made from elastic fibers made of a thermoplastic elastomeric polymer material.

[0056] The top diagram of Figure 8 shows the sheet 10 in an unstretched state. If a longitudinal force F is applied (middle diagram of Figure 8), which can be accomplished, for example, by slowing down the speed at which the fabric is fed to the bonding station 950 in the machine configuration of Figure 7, the fabric will be stretched in the machine direction (bottom diagram of Figure 8). When the force is removed, the fabric will automatically return to its original length due to the action of the elastic layer 12 (top diagram of Figure 8).

[0057] If an additional layer were to be joined to sheet 10 in the stretched state of the bottom diagram of Figure 8 in the form of a standard (low elongation) nonwoven layer 20, and if the combined multilayer sheet 30 were allowed to relax and return to its original shape, the layer returning to sheet 10 would contract in the machine direction between the bond points. This would result in pleated patterns and other repeating structural changes, explaining the accumulation that allows for some unopposed stretch in the machine direction, at least to the extent that it did before shrinkage. On the other hand, there would be no such accumulation in the cross machine direction, so the layer returning to sheet 10 would remain in its original (low) extensibility.

[0058] Figures 9 and 10 show the multilayer sheet 30 in its final relaxed state, with Figure 9 showing an embodiment of the multilayer nonwoven sheet 30 based on a three-layer elastically stretchable nonwoven sheet 20 including two decorative layers 11 and 13 and an elastic layer 12, and Figure 10 showing a multilayer nonwoven sheet 30 based on a two-layer elastically stretchable nonwoven sheet including only one decorative layer 11 and in which the elastic layer 12 is directly adjacent to the standard (low elongation) layer 10.

[0059] (Example 1) The following example illustrates the manufacture of a four-ply fabric according to the invention in an apparatus as shown diagrammatically in FIG.

[0060] A three-layer elastically stretchable nonwoven sheet 10, shown diagrammatically in FIG. 8, in which a spunbond elastic layer 11 is sandwiched between two spunbond decorative layers 12 and 13 made of crimped bicomponent fibers, is co-fed with a standard low stretch spunbond fabric 20 made of non-crimped monocomponent fibers to an activation and bonding combination unit 940.

[0061] During feeding, the elastically stretchable nonwoven sheet 10 is pre-stretched to 100% of its original length because the speed entering the nip of the rollers in unit 940 is 22 m / min, while the rollers are running at 44 m / min. The standard low stretch spunbond fabric 20 is fed at 44 m / min. The depth of engagement "b" in unit 940 is 5 mm (5 mm total rib height, which allows the bond points of the crest lines to engage with the other roller surface).

[0062] The settings for sheet 10 are shown in Table 1 below.

[0063] [Table 1] The 511A polymer is a polypropylene homopolymer from Sabic with a narrow molecular weight distribution (Mw / Mn of 3.8), a MFR of 25 g / 10 min and a Tm of 161°C.

[0064] The QR674K polymer is an ethylene-propylene random copolymer from Sabic with a MER of 40 g / 10 min, a broad molecular weight distribution (Mw / Mn of 8.5) and a Tm of 150° C. This polymer also contains a clarifier and a slip agent.

[0065] The elastic layer was composed of a single commercially available TPE-o material, ExxonMobil's Vistamaxx® 7050FL, which is a propylene-based thermoplastic elastomer copolymer with an ethylene content of 13 w% and a melt flow rate of 45 g / 10 min.

[0066] The bond pattern for sheet 10 is an open dot bond pattern with 24 bond sites per square centimeter for a bond area of ​​12%.

[0067] The measured properties of the sheet 10 are shown in Table 2 below.

[0068] [Table 2] *Measured with WSP120.6 **Measured with WSP100.4 Sheet 20 is a commercially available standard spunbond nonwoven material made of monocomponent PP fibers, with the trade name A10150KW, from Fibertex Personal Care A / S. The technical data is summarized in Table 3 below.

[0069] [Table 3] *Measured with WSP120.6 **Measured with WSP100.4 The CD breaking strength and elongation obtained after laminating the sheets 10 and 20 cannot be smaller (strength) or higher (elongation) than the respective values ​​of the sheet 20 alone. However, such (desired) limitations in the cross machine direction do not impede the laminate from performing favorably in terms of MD elongation and elasticity. This has been confirmed experimentally. Specifically, the measurement data for the obtained sheet 30 are summarized in Table 4 below.

[0070] [Table 4] *Measured with WSP120.6 **Measured with WSP100.4 11 shows the hysteresis curve in the machine direction tensile (stress-strain) diagram measured on a sheet of laminate material 30, according to the standard method of measurement of ASTM D5459. From this curve, two parameters of the elastic behavior in the machine direction can be identified.

[0071] The first parameter is permanent set, defined as the increase in length of an elastic material that cannot return to its original length after being stretched as specified in the ASTM D5459 test procedure, expressed as a percentage of the original length. The lower the percentage of permanent set, the better the elastic properties of the elastic material.

[0072] The second parameter is the area between the increase and decrease of the stress-strain curves of the hysteresis plot of the second cycle of the ASTM D5459 test, which is expressed by the relative magnitude of the area between the curves (A) to the area under the first increase curve (A+B), and is expressed as %[A / (A+B)×100]. If the plots do not match during the increase and decrease of the load, as is usually observed for real-world materials, it means that some energy has been lost. The smaller the %, the better the elastic properties of the material.

[0073] For the material tested, the permanent deformation after the first cycle was measured to be less than 5% from the hysteresis plot shown in Figure 11, and the area between the increasing and decreasing curves on the second cycle was measured to be 26.7%, which are very good values.

Claims

1. 1. A method for producing a machine direction elastically stretchable multilayer nonwoven fabric sheet, comprising: Providing an elastically stretchable nonwoven sheet comprising at least two layers of a nonwoven sheet, one layer being an elastically stretchable nonwoven comprising spunbond elastic fibers of a thermoplastic elastomeric polymer material and one layer being a stretchable facing layer comprising spunbond crimped multicomponent fibers; providing a low elongation nonwoven sheet having a breaking elongation less than that of the elastically stretchable nonwoven fabric in at least the cross machine direction; and co-feeding the elastically stretchable nonwoven sheet and the low stretch nonwoven sheet to a bonding station where the sheets are melt bonded together in a predetermined pattern, the elastically stretchable nonwoven sheet being fed to the bonding station under machine direction pretension and therefore pre-stretched in the machine direction, while the low stretch nonwoven sheet is fed to the bonding station without pretension or under a pretension that results in a machine direction pre-stretch that is less than the machine direction pre-stretch in the elastically stretchable nonwoven sheet.

2. 10. The method of claim 1 , The method of the present invention, wherein the elastically stretchable nonwoven sheet is pre-stretched in the machine direction by 40-160%, preferably 60-140%, more preferably 80-120% of its original dimensions.

3. 2. The method of claim 1 , The method wherein the elastically stretchable nonwoven sheet and the low elongation nonwoven sheet which are co-fed to the bonding station are pre-bonded, preferably by a pattern of melt bond points.

4. 10. The method of claim 1 , The method of claim 1, wherein said low elongation nonwoven sheet is a spunbond sheet, preferably comprised of non-crimped monocomponent fibers.

5. 10. The method of claim 1 , The method wherein the components of said crimped multicomponent fiber are all polypropylene.

6. 10. The method of claim 1 , one of the components of the crimped multicomponent fiber is a propylene-α-olefin copolymer material (co-PP), preferably a poly(propylene-ethylene) copolymer; The method of claim 1, wherein at least one other component of the crimped multicomponent fiber is a polypropylene homopolymer (PP).

7. 10. The method of claim 1 , The method, wherein the elastic fibers of the elastically stretchable layer comprise a thermoplastic polyolefin elastomer (TPE-o), preferably a thermoplastic polyolefin elastomer comprising a propylene-α-olefin copolymer.

8. 10. The method of claim 1 , The method of claim 1, wherein the elastically stretchable nonwoven sheet comprises at least one decorative layer on either side of the elastically stretchable nonwoven.

9. 10. The method of claim 1 , The method of claim 1, wherein the elastically stretchable nonwoven sheet has an exposed side facing the low elongation nonwoven sheet and is positioned directly adjacent to the low elongation nonwoven sheet after the sheets are bonded together at the bonding station.

10. 10. The method of claim 1 , The method of claim 1, wherein the pre-stretch in the elastically stretchable nonwoven sheet is adjusted by adjusting the translation speed of a nip roll.

11. 10. The method of claim 1 , The method wherein the bonding station comprises at least one calender roll having embossed projections on a surface thereof, the calender roll being heated or ultrasonically vibrated.

12. 10. The method of claim 1 , The bonding station comprises a pair of interacting rolls having surfaces with interlocking transverse ribs and grooves, and embossing projections disposed along the crests of the ribs and / or along the grooves of at least one of the rolls.

13. A multi-layer nonwoven sheet elastically stretchable in the machine direction, at least three layers of nonwoven material; the first layer comprises spunbond elastic fibers made of a thermoplastic elastomeric polymer material; the second layer comprises spunbond crimped multicomponent fibers; each layer of the sheet is melt bonded with a pattern of bond points; and The third layer is a multi-layer nonwoven sheet that is contracted between bond points and exhibits a pleated pattern and / or other structural variations that repeat in the machine direction.

14. The multilayer nonwoven fabric sheet according to claim 13, The multi-layer nonwoven sheet has a breaking elongation in the machine direction of greater than 100%, preferably greater than 150%, measured according to WSP 110.4; and / or The multi-layer nonwoven sheet has a breaking elongation in the cross machine direction of less than 100% as measured according to WSP 110.4, and / or The multilayer nonwoven sheet may have a breaking elongation in the machine direction greater than its breaking elongation in the cross-machine direction, also measured according to WSP 110.

4.

15. Use of the multi-layer nonwoven fabric sheet according to claim 13 or 14 in the manufacture of hygiene products, preferably in the manufacture of diaper pants.

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