Elastic nonwoven sheets

Abstract

The present invention relates to elastic, stretchable nonwoven sheets comprising a stretchable nonwoven elastic layer and a stretchable facing layer; and to an in-line process for making such sheets.

Description

Technical Field

[0001] The present invention relates to an elastically stretchable nonwoven sheet comprising an elastically stretchable nonwoven elastic layer and a stretchable nonwoven facing layer, and to an in-line method for producing such a sheet. Background Art

[0002] Nonwoven sheets are widely used in the hygiene industry for the mass production of baby diapers and adult incontinence products. However, in many cases, such as creating back ears in open-top diapers or waistbands in diaper pants, elastically stretchable materials are required, and standard nonwoven sheets do not meet this requirement.

[0003] Traditional approaches to addressing the limited elastic stretch of nonwoven sheets involve including an elastic film between the nonwoven layers. The resulting laminate may have good elastic properties, but the elastic film is not breathable, which can cause wearer discomfort. Another approach involves incorporating elastic strands (commonly known as Lycra strands) into the sheet. This approach has the disadvantage of having localized elastic forces, which can also cause wearer discomfort, and the strands are susceptible to breakage during the production process.

[0004] Furthermore, the incorporation of elastic films or strands imparts elasticity to the sheet, but only within the maximum stretchability of the nonwoven material associated with the elastic film or strands. Most conventional nonwoven materials have maximum elongation at break values ​​of approximately 50-80% in the machine direction (MD) and approximately 70-100% in the cross-machine direction (CD) (WSP 110.4), most often even less, meaning they can only be stretched to a very limited extent before breaking. However, for the applications specified above, it is required that the sheet be elastically stretched to 150% of its initial dimensions (i.e., to 250% of its initial dimensions), and this requirement may apply to stretching in either the cross-machine direction or the machine direction, depending on the specific application. For example, for the production of conventional open or tape-type baby diapers, typical production processes require that the material used for the back ears exhibit this magnitude of elastic stretch in the CD. On the other hand, for the production of adult or baby diaper pants, typical production processes require that the elastic materials used therein, such as belts, exhibit this magnitude of elastic stretch in the MD.

[0005] The traditional approach to addressing the limited stretchability of nonwoven materials is to pleat the nonwoven sheet when laminating it to an elastic film or strand. This approach compensates for the nonwoven's inherent lack of extensibility by storing additional material within each pleat. However, the drawback of pleating is the increased material required during production and a higher final product thickness, which results in increased insulation and a more noticeable appearance, leading to a negative consumer impression.

[0006] More recent approaches use inherently elastic stretchable nonwovens. These sheets ultimately consist of a stretchable, but not very elastic, nonwoven facing layer and an elastic nonwoven layer.

[0007] WO 2020 / 187540 A1 discloses an offline process for producing such an elastically stretchable nonwoven sheet. The method involves using a preformed facing layer formed from crimped fibers and depositing elastic fibers thereon during a spunbond process to form a spunbond elastic layer. The sheet is then pre-stretched in a pair of corrugated rollers. The resulting product can be elastically stretched in the CD by 150% or even more of its initial dimensions, a range that meets industry requirements, but its elastic stretch in the MD has proven to be more limited. Offline processes have limited potential for achieving higher MD stretch because the preformed facing layers have been shown to lose considerable stretchability by the second pass through the production line.

[0008] EP 3 715 517 A1 discloses an in-line process for producing elastic, stretchable nonwoven sheets. This method uses a multi-beam spunbond line to produce a sheet comprising a stretchable facing layer formed from crimped fibers and an elastic layer formed from elastic fibers in the same line before calendering, bonding, and pre-stretching the material. The product produced by this process exhibits satisfactory stretchability in the CD but also lacks stretchability in the MD.

[0009] Therefore, the hygiene industry still needs nonwoven sheets with high inherent elastic stretchability in the machine direction. Summary of the Invention

[0010] In this context, the present invention provides an elastically stretchable nonwoven sheet comprising at least two layers of nonwoven material, wherein one layer is an elastically stretchable nonwoven layer comprising spunbond elastic fibers formed from a thermoplastic elastomeric polymer material; and the other layer is a stretchable facing layer comprising spunbond crimped multicomponent fibers; wherein adjacent layers are bonded together by embossed bonding points, and wherein at least one component of the crimped multicomponent fibers is a propylene-α-olefin copolymer material.

[0011] Compared to the nonwoven sheet disclosed in EP 3 715 517 A1, which uses polypropylene as both components of the bicomponent fibers of the facing layer, the use of a propylene-α-olefin copolymer (co-PP) in at least one component of the bicomponent fibers surprisingly results in a significantly increased overall elasticity of the sheet, especially in the machine direction (MD). Specifically, such sheets have achieved a target elongation at break of more than 150%, preferably more than 200%, in the MD direction, when measured according to WSP 100.4.

[0012] The sheet material according to the present invention preferably exhibits an advantageous elastic behavior, especially in the machine direction. Detailed Description of the Invention

[0013] In one embodiment, the permanent set in the machine direction after the first cycle as measured according to ASTM D5459 is less than 15%, preferably less than 10%, and more preferably less than 5%.

[0014] In one embodiment, in the hysteresis curve tested according to ASTM D5459, the area ratio between the rising and falling stress-strain curves in the machine direction of the second cycle, expressed as the ratio of the area under the curve (A) to the total area under the initial rising curve (A+B), % [A / (A+B) x 100], is less than 40%, preferably less than 30%.

[0015] The two or more components of a multicomponent fiber are arranged asymmetrically across the cross-section of the fiber. In a preferred embodiment, the multicomponent fiber is a bicomponent fiber. Side-by-side bicomponent fibers are standard and, in many cases, preferred, but the concept of the present invention is not limited to side-by-side fibers and can also be achieved with other cross-sections, such as an eccentric sheath-core cross-section.

[0016] The nonwoven materials of both the facing layer and the elastic layer are spunbonded nonwoven fabrics, and the nonwoven fabrics are preferably all spunbonded nonwoven fabric sheets.

[0017] The term "α-olefin" has the meaning commonly understood by those skilled in the art. The α-olefin preferably has 1 to 5 carbon atoms, and may be, for example, ethylene, propylene or α-butene.

[0018] The α-olefin that forms the copolymer with propylene is preferably ethylene. In other words, the copolymer is preferably a poly(propylene-ethylene) copolymer. Also preferably, the copolymer is a random copolymer.

[0019] The comonomer content in the propylene-α-olefin copolymer or the ethylene content in the poly(propylene-ethylene) copolymer is preferably ≥ 1 wt.-%, more preferably ≥ 2 wt.-%. As an upper limit, the comonomer content may be ≤ 8 wt.-%, preferably ≤ 6 wt.-%.

[0020] The other component of the crimped multicomponent fiber is preferably a polypropylene homopolymer (PP). Polypropylene homopolymer is understood herein as having a monomer purity greater than 99.5 wt.-%, preferably greater than 99.8 wt.-%, more preferably greater than 99.9 wt.-%.

[0021] Experiments have demonstrated that the use of bicomponent fibers having polypropylene as one component and poly(propylene-ethylene) copolymer as the other component results in a significant increase in MD stretch.

[0022] In another preferred embodiment, the molecular weight distribution (as measured by polydispersity (M)) of the propylene-α-olefin copolymer of the crimped multicomponent fiber is w / M n ) has a broader molecular weight distribution than the other component, preferably the polypropylene homopolymer used as the other component of the bicomponent fiber.

[0023] In terms of specific values, the M w / M n The difference between the two polymers is preferably ≥ 1, more preferably ≥ 2, and most preferably ≥ 3. w / M n The difference between is preferably ≤10, and preferably ≤8. Suitable M w / M n The absolute value of may be in the range of, for example, 2.5 to 7.5 for polypropylene and 4 to 10 for propylene-α-olefin copolymer.

[0024] As a component of a multicomponent fiber, copolymer PP or homopolymer PP can be blended with other polymers or other additives (such as slip aids, filler materials or masterbatches), but the two should account for more than 50% by weight of the corresponding mixture, preferably more than 75% and more preferably more than 90%.

[0025] In the crimped bicomponent fibers, the weight ratio of the copolymerized PP component to the other component, preferably homo-PP, in the bicomponent fibers is preferably 20 / 80 to 80 / 20, more preferably 30 / 70 to 70 / 30, and still more preferably 40 / 60 to 60 / 40.

[0026] The thermoplastic elastomeric material for the elastic fibers 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 2 342 075 A1. Alternatively or additionally, other thermoplastic elastomeric materials, such as, in particular, thermoplastic polyurethanes (TPU) or styrene block copolymers (TPE-s), may be used as a mixture. In one embodiment, the thermoplastic elastomeric material may comprise up to 20 wt. % and preferably up to 10 wt. % of a thermoplastic olefin (e.g., homopolypropylene). Additives such as filters, slip aids, or masterbatches may also be added. In one embodiment, the bicomponent elastic fibers may be formed from two different thermoplastic elastomers, which are arranged, for example, side by side or in a core-sheath configuration.

[0027] The elastic layer and facing layer of the sheet may comprise elastic or bicomponent fibers as defined above and other fibers, but preferably consist of elastic or bicomponent fibers as defined above.

[0028] In one embodiment, the sheet comprises at least one facing layer on both sides of the elastic layer, thus being at least three layers overall.This structure facilitates covering the inherently sticky elastic layer on both sides.

[0029] In various embodiments, additional facing layers may be provided for the first facing layer as described above. The facing layers on different sides of the elastic layer may be the same, but may also be different. For example, one of the nonwoven facing layers may be a spunbond nonwoven layer, and the other nonwoven facing layer may be a different spunbond nonwoven layer or a meltblown nonwoven layer.

[0030] The basis weight of each facing layer may be 5-40g / m 2 Between, preferably 8-30g / m 2 between 10-25 g / m 2 and more preferably between 15-20 g / m 2 The basis weight of the elastic layer can be between 10-140g / m 2 Between, preferably 20-120g / m 2 and more preferably between 25-100 g / m 2 between.

[0031] The sheet material typically comprises a pattern of macroscopic bond points. In a preferred embodiment, the fabric surface is 2 The number of bond points may be less than 100, preferably less than 80, and on the other hand preferably greater than 20. In one embodiment, the localized bond points occupy less than 18% of the total surface area of ​​the fabric, and preferably less than 15%, which means that the bond pattern is preferably relatively open.

[0032] In one embodiment, even though the sheet of the present invention already has inherently high machine direction stretchability, the sheet can be further activated by subjecting it to machine direction pre-stretching, as described in further detail below.

[0033] The present invention also proposes a method for manufacturing an elastic stretchable nonwoven sheet according to the present invention, comprising the following online steps: (a1) spinning crimped multicomponent fibers, wherein at least one component of the crimped multicomponent fibers is a propylene-α-olefin copolymer; and laying them on a moving spinning belt to form a web; (a2) spinning elastic fibers formed from a thermoplastic elastomeric polymer material, and laying them on the surface of the web formed in step (a1) to form another web; and (b) bonding adjacent webs to form an elastic stretchable spunbond nonwoven sheet.

[0034] The spinning of steps (a1) and (a2) involves extruding, quenching, and drawing the fibers in a spunbond machine. The fiber webs formed in steps (a1) and the like are unbonded precursors of the nonwoven materials for the facing layer and elastic layer of the nonwoven sheet, respectively, formed after the bonding step (b).

[0035] The bonding of step (b) is most preferably embossing. Specifically, the bonding may include embossing the bonding points into the sheet, the embossing being achieved by embossing protrusions provided on the surface of at least one calendering roll. Embodiments include ultrasonic bonding, wherein ultrasonic vibrations are introduced into the embossing protrusions. Other embodiments include using thermal bonding at the heated embossing protrusions.

[0036] In a preferred variant, the fabric surface per cm 2 The number of bond points may be less than 100. The localized bond points preferably occupy less than 18% of the total fabric surface area, and more preferably less than 15%, meaning that the bond pattern is relatively open.

[0037] In one embodiment, the method further comprises a step (a3) ​​of spinning additional fibers, preferably crimped multicomponent fibers, most preferably at least one component of the crimped multicomponent fibers being a propylene-α-olefin copolymer, and laying them on the surface of the web formed in step (a2) to form another web. In a variation of this method, a sheet according to a preferred embodiment of the present invention is provided, having a sandwich structure of an elastic layer interposed between two facing layers.

[0038] In one embodiment, the method further comprises pre-compacting the web of the facing layer. Preferably, a pre-compacting step is performed after each respective step, i.e., step (a1) and, if applicable, step (a3). Pre-compacting preferably comprises passing the web through two flat pre-compacting rollers. The applied linear pressure is preferably between 3 and 5 N / mm. The roller temperature may be between 50 and 110°C, more preferably between 60 and 100°C. Due to the inherent stickiness of the fibers formed from thermoplastic elastomer, pre-compacting after step (a2) is not necessary or is not feasible.

[0039] In one embodiment, the method further comprises the step (c) of pre-stretching the sheet in the machine direction.

[0040] For example, machine direction pre-stretch can be effected by pulling the material in the machine direction at different speeds across each set of rollers.

[0041] Another option for achieving machine direction pre-stretching involves mechanically activating the sheet in a milling machine consisting of a pair of interacting rollers whose surfaces include interlocking annular ribs and grooves ("ring rolling") or interlocking transverse ribs and grooves.

[0042] The machine direction pre-stretching of step (c) can be performed in-line, or alternatively can be performed as a separate process.

[0043] During step (c), the degree of machine direction pre-stretching of the sheet can affect the degree of elastic stretching of the final sheet in the machine direction. In one embodiment, during step (c), the sheet is thus pre-stretched in the machine direction. The degree of machine direction pre-stretching can be such that, for example, the sheet is stretched by 40-160%, preferably 60-140%, and more preferably 80-120% of its original dimensions.

[0044] In an alternative embodiment, the process is performed without machine direction pre-stretching. Compared to prior art materials, due to the specific choice of polymers in the bicomponent fibers, machine direction pre-stretching is not even required to achieve suitable machine direction stretch properties.

[0045] The present invention is not limited to two- or three-layer sheets. More than three layers may be present by including additional elastic layers or other facing layers or inelastic layers. Furthermore, within each layer, there may be two or more sub-layers of the same or similar type, formed by separate fiber placement stages during the production process.

[0046] The nonwoven sheet according to the present invention is particularly suitable for use in the manufacture of sanitary products. For example, the nonwoven sheet can be used to manufacture diaper pants that include the sheet as an elastic waist material. The typical production process currently used by the industry for this application requires the material to be able to stretch elastically in the MD.

[0047] Further details and advantages of the present invention will become apparent from the figures and examples described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 : A schematic cross-sectional view of an elastically stretchable nonwoven sheet according to the present invention;

[0049] Figure 2 : An exemplary machine setup for carrying out the method of the invention;

[0050] Figure 3 : Schematic diagram of an apparatus for activating a sheet by stretching it in the machine direction;

[0051] Figure 4 : Running Figure 3 A schematic diagram of the device;

[0052] Figure 5 : MD tensile (stress-strain) curve of the facing spunbond layer alone according to the comparative example configuration;

[0053] Figure 6 : MD tensile (stress-strain) curve of a single facing spunbond layer according to the configuration of the present invention;

[0054] Figure 7 : MD tensile (stress-strain) curve of another separate facing spunbond layer according to the configuration of the present invention;

[0055] Figure 8 : MD tensile (stress-strain) curve of the elastic spunbond nonwoven layer alone;

[0056] Figure 9 : Superimposed MD tensile (stress-strain) curves of a sheet according to the present invention, a separate sheet facing layer, and a separate sheet elastic layer;

[0057] Figure 10 : A schematic diagram of a tensile (stress-strain) graph and subsequent increase and decrease curves of stress-strain cycles, representing the test of ASTM D5459; and

[0058] Figure 11 : Machine direction tensile (stress-strain) graph of sample 5-1 of Example 5, showing the hysteresis curve of the material.

[0059] Figure 1 A schematic cross-section of an elastic, stretchable nonwoven sheet 100 according to the present invention is shown, wherein an elastic nonwoven layer 130 comprising elastic fibers is sandwiched between a first nonwoven facing layer 110 and a second nonwoven facing layer 120 .

[0060] Figure 2 An exemplary machine setup for making an elastically stretchable nonwoven sheet 100 according to the present invention is shown.

[0061] The arrangement comprises a conveyor belt 10 and three spunbond machines 20, 30 and 40 arranged on the conveyor belt.

[0062] In each spunbond machine, molten thermoplastic polymer is extruded through a die orifice. The extruded fiber strands are then quenched and drawn / stretched to form endless fibers, which are then laid down on a conveyor belt 10 or on a web previously deposited on the conveyor belt.

[0063] The first spunbond machine 20 deposits a crimped bicomponent web onto a conveyor belt 10. The two polymer feeds are symbolically represented at the top of the first spunbond machine 20. The intermediate spunbond machine 30 deposits a web formed from a thermoplastic elastomer onto the previously formed web. The final spunbond machine 40 deposits another crimped bicomponent web onto the elastic web. Each spunbond machine 20 and 40 is followed by a pair of pre-compacting rollers 21 and 41, respectively, for pre-compacting the respective webs.

[0064] The pre-compacted web is then calendered in a calendering unit 50 comprising a pair of counter-rotating embossing rolls 51, 52 to form a nonwoven sheet. Calendering is followed by an activation step in an activation unit 60 comprising a pair of counter-rotating activation rolls 61, 62 whose surfaces contain interlocking structural elements, as described in more detail below. At the end of the entire in-line process, the product sheet is collected on a product roll 70.

[0065] Figure 3 An embodiment of activation rollers 61, 62 of an activation unit 60 is shown, which are configured to increase elasticity in the machine direction. Figure 3 The figure is an enlarged cross-section taken along a radial plane perpendicular to the roller axis. Rollers 61 and 62 include a plurality of regularly spaced ribs 63 on their active surfaces, with grooves 65 formed between the ribs. Ribs 63 are oriented in the cross-machine direction and extend axially onto the surfaces of rollers 61 and 62. The width of ribs 63 is indicated by the letter "a," the depth of engagement is indicated by the letter "b," and the distance between adjacent ribs is indicated by the letter "c."

[0066] Figure 4 Shows the running Figure 3 The unit shown. Figure 4 In the figure, from left to right, an unactivated precursor sheet, consisting of two facing layers and an elastic layer sandwiched between them, enters the activation process. The activation process begins when the sheet enters the nip between rollers 61 and 62, and the sheet is locally stretched between intermeshing ribs 63. During this process, the elastic layer stretches due to its elastic properties. Parameters "a," "b," and "c" can be varied as desired, depending on the elongation properties that may be applied and required on the nonwoven sheet.

[0067] In embodiments, it has been demonstrated that the use of a combination of a relatively narrow molecular weight distribution polypropylene homopolymer and a relatively broad molecular weight distribution ethylene-propylene random copolymer in crimped bicomponent fibers, even without activation, can achieve sheets having a significant degree of stretch, such as up to 300%, without breaking in the machine direction. This is sufficient to meet any industry standard and matches the high elongation properties of the elastic nonwoven layer used in the sheets of the present invention, which, in embodiments, can elastically stretch 400-500%.

[0068] The advantageous properties of the sheets of the present invention are demonstrated in the following examples. Example

[0069] Using the materials specified below, multiple spunbond facing layers using side-by-side bicomponent crimped fibers were prepared.

[0070] Table 1: Materials used:

[0071]

[0072] 511A polymer is a polypropylene homopolymer produced by Sabic Company. The molecular weight distribution of this polymer is relatively narrow (M w / M n is 3.8), MFR is 25g / 10min and T m It is 161℃.

[0073] HP552N polymer is a polypropylene homopolymer produced by LyondellBasell. It has a broad molecular weight distribution (M w / M n is 6.8), MFR is 13g / 10min and T m It is 161℃.

[0074] RP248R polymer is a LyondellBasell ethylene-propylene random copolymer with an MFR of 30 g / 10 min and a medium molecular weight distribution (M w / M n is 5.2) and T m It also contains clarifying agents and slip aids.

[0075] QR674K polymer is an ethylene-propylene random copolymer from Sabic, with an MFR of 40 g / 10 min and a broad molecular weight distribution (M w / M n is 8.5) and T m It also contains clarifiers and slip aids.

[0076] As used herein, melt flow rate (MFR) is understood to have been determined according to ISO 1133, conditions 230°C and 2.16 kg.

[0077] The melting temperature (T m ) is understood to have been determined by DSC according to ISO 11357-3.

[0078] The molecular weight average (M w and M n ) and the obtained values ​​of molecular weight distribution (MWD, M w / M n ) is understood to have been determined by GPC in accordance with ISO 16014-1:2003, ISO 16014-2:2003, ISO 16014-4:2003 and ASTM D 6474-12 using the following formula:

[0079]

[0080]

[0081]

[0082] For a constant elution volume interval ΔV i , where A i and M i are the chromatographic peak slice area and the molecular weight (MW) of polyolefins, and the elution volume V i Correlation, where N equals the number of data points obtained from the chromatogram between the integration limits.

[0083] A high-temperature GPC instrument was used, equipped with either a PolymerChar (Valencia, Spain) infrared (IR) detector (IR4 or IR5) or an Agilent Technologies differential refractometer (RI), equipped with 3 Agilent-PLgel Olexis and 1 Agilent-PLgel Olexis guard columns. 1,2,4-Trichlorobenzene (TCB) stabilized with 250 mg / L of 2,6-di-tert-butyl-4-methylphenol was used as the solvent and mobile phase. The chromatographic system was operated at 160°C and a constant flow rate of 1 mL / min. 200 μL of sample solution was injected for each analysis. Data acquisition was performed using Agilent Cirrus software version 3.3 or PolymerChar GPC-IR control software.

[0084] The column set was calibrated using universal calibration (according to ISO 16014-2:2003) using 19 polystyrene (PS) standards with narrow MWD ranging from 0.5 kg / mol to 11,500 kg / mol. The PS standard solutions were dissolved at room temperature for several hours. The conversion of polystyrene peak molecular weights to polyolefin molecular weights was achieved using the Mark Houwink equation and the following Mark Houwink constants:

[0085] K PS =19x10 -3 mL / g,a PS =0.655

[0086] K PE =39x10 -3 mL / g,a PE =0.725

[0087] K PP =19x10 -3 mL / g,a PP =0.725

[0088] A third-order polynomial fit was used to fit the calibration data.

[0089] All samples were prepared in the concentration range of 0.5–1 mg / ml and dissolved at 160°C for 2.5 h.

[0090] Table 2 below shows the properties of individual 20 gsm spunbond facing sheets obtained from these materials.

[0091] Table 2: Achieved performance:

[0092]

[0093] Table 2 (continued): Properties obtained:

[0094]

[0095] *Measured according to WSP120.6

[0096] **Measured according to WSP 100.4

[0097] It is worth noting that no samples were Figures 3 and 4 Activated in the milling machine shown, this sample has a 12% bond area and 24 bond sites / cm 2 Open dot bonding pattern.

[0098] Example 1 is a comparative example. Examples 2-3 are examples of the present invention. The MD tensile (stress-strain) curves of samples 1-3 of the comparative examples are shown in FIG. Figures 5 to 7 Among them Figure 5 and Figure 6 shows a curve of multiple measurements that were subsequently averaged, and Figure 7 Only one averaged curve is shown.

[0099] From the values ​​in Table 2 and Figure 5-7As can be clearly seen from the curves in Figure 2, the MD elongation at break of the facing layer of Example 2 is already significantly higher than that of the facing layer of Comparative Example 1 (the elongation at break increased by approximately 20%, to 188%). The effect becomes even more pronounced with the specifically preferred configuration of the facing layer of Example 3, in which the molecular weight distribution of the Co-PP is broader than that of Example 2, and the MWD difference between PP and Co-PP is even greater than that of Example 2 (the elongation at break increased by approximately 80%, from 188% to 270%). Despite the absence of activation / pre-stretching, the MD elongation at break values ​​of almost 200% (Example 2), not to mention over 250% (Example 3), compared to the comparative example (i.e., Example 1), are quite unique for spunbond materials, where fiber orientation is typically predominantly in the machine direction. It is also noteworthy that, while generally the thickness of the facing layer is somewhat related to the curl level, the facing layers of Examples 2 and 3, despite having the same basis weight, are significantly thinner than the facing layer of Comparative Example 1, indicating that there are apparently other factors besides simple curl level that affect the ability to control the elongation in the machine direction of the spunbond facing layer configured according to the present invention.

[0100] Next, as shown in Example 4, Figure 2 Three sheets according to the present invention (Samples 4-1, 4-2, and 4-3) were produced on the production line shown. The sheets comprised an elastic spunbond layer sandwiched between two facing layers according to the present invention, but were not treated with a milling machine to activate the material (the sheets remained inactive). The layers were prepared and arranged as specified below. Samples 4-1, 4-2, and 4-3 differed only in the basis weight of their layers.

[0101] Table 3: Materials / Structures used in Example 4:

[0102]

[0103] The two facing layers of the sheet of sample 4-1 correspond to the facing layers investigated in a separate manner in Example 3. The bonding mode was as described above for the separate facing layers.

[0104] The elastic layer is made of ExxonMobil's single commercially available TPE-o material Vistamaxx TM 7050FL, a propylene-based thermoplastic elastomeric copolymer with an ethylene content of 13 wt.-% and a melt flow rate of 45 g / 10 min. The bonding mode was also as described above.

[0105] Table 4 below shows the properties obtained for the three samples of Example 4.

[0106] Table 4: Achieved performance:

[0107]

[0108] Table 4 (continued): Properties obtained:

[0109]

[0110] *Measured according to WSP120.6

[0111] **Measured according to WSP 100.4

[0112] As a variation of Example 4, in another Example 5, the same materials as in Example 4 were produced except that they were Figure 3 and Figure 4 The material is pre-stretched and activated in the machine direction in the activation unit 60 shown. Specifically, as the material enters the roller nip of the activation unit 60, the material is pre-stretched 100% in the machine direction (to 200% of its initial length) by varying the translation speed in the production line. In the activation unit, the engagement depth "b" is 2 mm (at a total rib height of 5 mm).

[0113] Table 5 below shows the properties obtained for the three samples of Example 5.

[0114] Table 5: Performance obtained:

[0115]

[0116]

[0117] Table 5 (continued): Properties obtained:

[0118]

[0119] *Measured according to WSP120.6

[0120] **Measured according to WSP 100.4

[0121] In addition to Examples 4 and 5 of the present invention, as Example 6, the elastic layer of Sample 4-1 in Example 4 alone was spun and studied.

[0122] Figure 8 Shown is the MD tensile (stress-strain) curve for a 40 gsm, stand-alone elastic spunbond nonwoven layer of Example 6. The material can elongate significantly in the MD before breaking; specifically, the elongation exceeds 500% at an applied stress of 20-25 N / 50 mm.

[0123] Figure 9Shown are superimposed MD tensile (stress-strain) curves for a sheet according to the present invention, comprising Sample 4-1 of Example 4, a facing layer of Example 3, and an elastic layer of Example 6. It is apparent from the superimposed curves that the facing layer does not restrict the elastic behavior of the elastic layer until the elongation exceeds 300%. The sheet exhibits high elongation and elasticity, meaning that upon relaxation, it retracts to its original state.

[0124] Figure 8 and 9 The curve shown in Figure 7 The curve in is the average curve of multiple measurements.

[0125] Another important parameter of the elastic material herein is the permanent set determined according to ASTM D5459. Permanent set is the increase in length of an elastic material when it fails to recover to its original length after being subjected to the extension specified in the test procedure in ASTM D5459, expressed as a percentage of the initial length. The lower the permanent set percentage, the better the elastic properties of the elastic material.

[0126] Figure 10 A diagram showing a tensile (stress-strain) graph and subsequent stress-strain cycle increase and decrease curves, representing the test according to ASTM D5459. The permanent set value is (AD / AE) x 100.

[0127] Another important parameter is the area ratio between the ascending and descending stress-strain curves in the machine direction of the second cycle in the hysteresis curve tested according to ASTM D5459. This is expressed as the ratio of the area under the curve (A) to the total area under the initial ascending curve (A+B), expressed as % [A / (A+B) x 100]. This is used to calculate the percentage of energy dissipated due to internal friction. When the curves do not align during loading and unloading, as is commonly observed in real-world materials, this indicates a certain amount of energy loss. The lower the percentage, the better the material's elastic properties.

[0128] Figure 11 The stress-strain curves in the machine direction for Sample 5-1 of Example 5, obtained according to ASTM D5459 (first and second cycles), are shown. The hysteresis curves demonstrate that this material possesses very good elastic properties in the machine direction. Specifically, the permanent set value ((AD / AE) x 100) after the first cycle is only 1.28%, while the area between the ascending and descending curves ([A / (A+B)]) in the second cycle is only 24.8%.

Claims

1. An elastically stretchable nonwoven sheet comprising at least three adjacent nonwoven material layers, One of the three layers is a stretchable nonwoven elastic layer comprising spunbond elastic fibers formed from a thermoplastic elastomer polymer material. The other two of the three layers are stretchable facing layers, which include spunbond crimped multicomponent fibers. wherein the sheet comprises a sandwich structure between facing layers on each side of a stretchable nonwoven elastic layer, wherein three adjacent layers are bonded together by localized bonding points which are embossed into the sheet by embossing protrusions provided on the surface of at least one calendering roll, the localized bonding points being heated, or ultrasonic vibrations being introduced into the localized bonding points; wherein each cm 2 The number of bonding points on the sheet surface is higher than 20 and lower than 100, and the local bonding points occupy less than 18% of the total area of ​​the sheet surface. wherein at least one component of said crimped multicomponent fibers is a propylene-α-olefin copolymer material; and one other component of said crimped multicomponent fibers is a polypropylene homopolymer material; and The sheet has an elongation at break in the machine direction greater than 150% when measured according to WSP 100.

4.

2. The sheet of claim 1, wherein the sheet has an elongation at break in the machine direction of greater than 200% when measured according to WSP 100.

4.

3. The sheet of claim 1 or 2, wherein after the first cycle, the sheet has a permanent set in the machine direction of less than 15% as measured according to ASTM D5459.

4. The sheet according to claim 1 or 2, wherein in a hysteresis curve tested according to ASTM D5459, the area ratio between the ascending and descending stress-strain curves in the machine direction of the second cycle, expressed as the ratio of the area under the curve (A) to the total area under the initial ascending curve (A+B), % [A / (A+B) x 100], is less than 40%.

5. The sheet according to claim 1, wherein the propylene-α-olefin copolymer is a poly(propylene-ethylene) random copolymer.

6. The sheet according to claim 5, wherein the propylene-α-olefin copolymer has an ethylene monomer content of 1 to 8 wt%.

7. The sheet according to claim 1 or 2, wherein the molecular weight distribution of the propylene-α-olefin copolymer of the crimped multicomponent fiber is broader than the molecular weight distribution of the other components.

8. The sheet according to claim 1, wherein the molecular weight distribution M of the propylene-α-olefin copolymer and the polypropylene homopolymer is w / M n The difference is 1 to 10.

9. The sheet material of claim 1 or 2, wherein the crimped multicomponent fibers are bicomponent fibers.

10. The sheet of claim 1 or 2, wherein the crimped multicomponent fiber is a bicomponent fiber and the weight ratio of the propylene-α-olefin copolymer to the polypropylene homopolymer is from 20 / 80 to 80 / 20.

11. The sheet material according to claim 1 or 2, wherein the thermoplastic elastomeric polymer material forming the elastic fibers is a thermoplastic polyolefin elastomer.

12. The sheet material according to claim 1 or 2, wherein the sheet material consists of the elastic layers and the facing layer.

13. The sheet material according to claim 1 or 2, wherein the basis weight of each facing layer is 5-40 g / m 2 and / or the basis weight of the elastic layer is between 10-140g / m 2 between.

14. The sheet of claim 3, wherein the sheet has a permanent set in the machine direction of less than 10% after the first cycle as measured according to ASTM D5459.

15. The sheet according to claim 4, wherein in a hysteresis curve tested according to ASTM D5459, the area ratio between the ascending and descending stress-strain curves in the machine direction of the second cycle, expressed as the ratio of the area under the curve (A) to the total area under the initial ascending curve (A+B), % [A / (A+B) x 100], is less than 30%.

16. The sheet material of claim 9, wherein the crimped multicomponent fibers are side-by-side bicomponent fibers.

17. The sheet of claim 11, wherein the thermoplastic polyolefin elastomer comprises a propylene-α-olefin copolymer.

18. A method for producing an elastically stretchable nonwoven sheet according to any one of the preceding claims, said method comprising the following in-line steps: (a1) spinning crimped multicomponent fibers and laying them onto a moving spinning belt to form a web; wherein at least one component of the crimped multicomponent fibers is a propylene-α-olefin copolymer; (a2) spinning elastic fibers formed of a thermoplastic elastomeric polymer material and laying them on the surface of the web formed in step (a1) to form another web; (a3) spinning crimped multicomponent fibers and laying them on the surface of the web formed in step (a2); wherein at least one component of the crimped multicomponent fibers is a propylene-α-olefin copolymer, (b) bonding adjacent webs to form the elastically stretchable spunbond nonwoven sheet; wherein three adjacent layers are bonded together by localized bonding points which are embossed into the sheet by embossing protrusions provided on the surface of at least one calendering roll, the localized bonding points being heated, or ultrasonic vibrations being introduced into the localized bonding points; wherein each cm 2 The number of bonding points on the sheet surface is higher than 20 and lower than 100, and the local bonding points occupy less than 18% of the total area of ​​the sheet surface. wherein at least one component of said crimped multicomponent fibers is a propylene-α-olefin copolymer material; and one other component of said crimped multicomponent fibers is a polypropylene homopolymer material; and The sheet has an elongation at break in the machine direction greater than 150% when measured according to WSP 100.

4.

19. The method according to claim 18, further comprising an online or offline step (c) of pre-stretching the sheet in the machine direction.

20. The method according to claim 19, wherein During step (c), the sheet is pre-stretched in the machine direction by 40-160% of its original dimensions.

21. The method of claim 20, wherein during step (c), the sheet is pre-stretched in the machine direction by 60-140% of its original dimension.

22. The method of claim 20, wherein during step (c), the sheet is pre-stretched in the machine direction by 80-120% of its original dimension.

23. Use of the elastically stretchable nonwoven sheet according to any one of claims 1 to 17 in the manufacture of hygiene articles.

24. The use according to claim 23 in the manufacture of a hygiene article, wherein the hygiene article is a diaper pants, and the diaper pants comprises the elastically stretchable nonwoven sheet as an elastic waist material.

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