Nonwoven sheet comprising machine direction oriented fibers

Abstract

The invention relates to a method of manufacturing a nonwoven sheet material comprising a first nonwoven substrate layer and preferably a second nonwoven substrate layer, and a layer of machine direction oriented fibers, the method comprising: providing a first nonwoven substrate layer; preferably, providing a second nonwoven substrate layer; providing machine direction oriented fibers and bonding the resulting fibers to the first nonwoven substrate layer; and bonding the layers together to obtain a nonwoven sheet material. The invention further relates to a nonwoven sheet material prepared by the above-mentioned method, the nonwoven sheet material comprising a first nonwoven substrate layer and preferably a second nonwoven substrate layer, and a layer of machine direction oriented fibers, wherein the layers are bonded together to form a unitary nonwoven sheet material.

Description

[0001] The present invention relates to a nonwoven sheet comprising a nonwoven base layer and a layer of machine-oriented fibers, and a method for manufacturing such a nonwoven sheet.

[0002] The hygiene industry uses nonwoven materials extensively in hygiene products such as baby diapers, adult incontinence products, and feminine hygiene products. Among the various technologies used to manufacture nonwoven materials for the hygiene industry, spunbond technology has become the dominant technology. The basic principle of this technology involves: extruding molten thermoplastic polymer through a spinneret to obtain a web for extruded spun filaments; cooling and drawing (refining) the filaments in a pneumatic device; and depositing the solidified and drawn long fibers onto a breathable, moving web-forming conveyor belt. Before deposition, the fibers pass through a diffuser to cause fiber entanglement and increase orientation in the transverse machine direction. The fact that the diffuser and the fibers exiting it are typically at a much higher speed than the traveling speed of the web-forming conveyor belt contributes to a random fiber distribution, with a large proportion of the fibers also oriented in the transverse machine direction.

[0003] In the foregoing paragraphs and throughout this application, the terms “filament” and “fiber” are distinguished in the context of spunbonding and the novel directional spinning technology further described below. The polymer stream exiting the spinneret is referred to as a “filament.” After the filament is drawn and cooled, the polymer chains within it orient themselves along the length of the filament and gradually crystallize, thereby altering its internal structure. Once the filament has essentially reached its final drawn state, it is referred to as a “fiber” in subsequent stages. Except when describing spunbonding or directional spinning, such as when describing meltblown fibers or staple fibers, only the term “fiber” is used.

[0004] Spunbond technology has been known for over fifty years, as demonstrated by, for example, the disclosure of U.S. Patent 3,855,046 A. Since then, the process has been continuously optimized in many aspects.

[0005] In these areas, there are now higher numbers of finer fibers and better web uniformity. In earlier generations of spunbond processes, 1,000 to 2,000 filaments could be spun per meter in the transverse direction, while in more recent generations, this number has increased to approximately 7,000 to 8,000 filaments, with finer fiber diameters. This evolution necessitates optimization of filament cooling, drawing (thinning), and web formation to enable the production of thinner nonwoven sheets, i.e., lower basis weight (g / m²) for equivalent performance. Performance can be physical properties such as tensile strength and elongation, fabric texture and softness, elasticity, stiffness, or fluid management, with priorities depending on the specific application of the product. Another aspect is the use of bicomponent fiber technology to manufacture crimped fibers, resulting in more fluffy, softer, and more stretchy nonwoven materials. Early research on bicomponent fiber technology is disclosed, for example, in US 5,382,400 A and US 6,454,989B1. For example, subsequent improvements are disclosed in EP 3 246 443 B2, EP 3 246 44 B1, EP 3455 399 B2, and EP 3 521 495 B2. The latter in these references focuses on manufacturing finer crimped fibers to achieve a more uniform web. Another aspect is the production of nonwoven materials comprising fibers made of thermoplastic elastomers with intrinsic elastic elongation. Examples of corresponding technologies include EP 3 715 517 A1, EP 3 867 437 B2, EP 4 180 018 A1, and WO 2023 / 083600 A1.

[0006] As the linear speeds of machines used to produce hygiene products from nonwoven materials continue to increase, a common requirement for any nonwoven material used in such applications is robustness and stability. This requirement conflicts with competitive demands to reduce the production cost of nonwoven materials and to lower basis weight to enhance sustainability, and further solutions are needed despite previous improvements in web uniformity, fiber count, and fiber fineness.

[0007] Woven fabrics (also known as textiles) consist of warp-oriented yarns, which can be single fibers or warp and weft yarns. This contrasts with nonwoven fabrics, in which fibers are distributed roughly randomly in both the machine direction (MD) and the cross-machine direction (CD). Woven fabrics possess unique properties in terms of performance, but their production is relatively expensive and time-consuming because it requires a step-by-step process, including yarn fabrication and subsequent weaving of the fabric with precise control over each warp and weft yarn.

[0008] In view of the above considerations, it is desirable to provide a nonwoven material that incorporates woven fabric elements to enhance performance. Furthermore, it is desirable to provide a method for manufacturing this material that maintains the high speed, high strength, and cost-effectiveness characteristics of spunbond technology.

[0009] In this context, the inventors have considered previously known methods of introducing oriented elements into nonwoven materials. For example, numerous documents, such as US 2004 / 0005835 A1 and US 2021 / 0282979 A1, describe combining nonwoven sheets with potentially pre-stretched elastic filaments to impart elastic elongation properties to nonwoven fabrics. EP 3 974 572 A1 describes the use of in-line extruded elastomeric polymer tapes to form structural elements with a defined MD orientation in stretchable nonwoven materials. EP 2 098 363 B1 describes a process for forming a layered material comprising a nonwoven base layer and layers of substantially parallel, machine-oriented fibers formed by extrusion spinning. This spinning machine does not have a drafting device in the form of a Godet roll or pneumatic device, nor does it have a diffuser. The filaments are stretched under tensile force as they are drawn into the nip points between binder rolls that combine a pre-formed nonwoven base layer with machine-oriented fibers to form a layered material. The fibers are formed of thermoplastic elastomers and remain viscous in these layered combinations, thus stabilizing the layered material without additional bonding. A solution similar to EP 2098 363 B1 is disclosed in WO 2007 / 078344 A1 and EP 0 343 978 A2. As another variation, document WO 2005 / 065932 A1 discloses a concept of elastic machine-oriented fibers bonded to a meltblown base layer. Regarding the manufacture of machine-oriented fibers in a cord extruder, refer to US 5,385,775 A, which discloses the use of an improved meltblown machine in which the fibers are not cooled or stretched. The nozzle end of the meltblown die is arranged close to the web-forming conveyor belt, and the fibers are stretched by the web-forming conveyor belt. A pair of bonding rollers are used to bond machine-oriented fibers to the meltblown substrate.

[0010] Furthermore, the inventors also considered the previously known method of drawing and extruding filaments in spunbond processes using a stretching roller (guide roller) system instead of a pneumatic device. This roller system would be located between the cooling unit and the diffuser. As examples, see DE36 03 814 A1 or DE 41 02 650 A1.

[0011] In view of the aforementioned needs and considerations, the present invention relates to a method for manufacturing a nonwoven sheet comprising a first nonwoven base layer and preferably a second nonwoven base layer, and a layer of machine-oriented fibers, the method comprising: providing a first nonwoven base layer; preferably, providing a second nonwoven base layer; providing machine-oriented fibers and bonding them to the first nonwoven base layer and preferably the second nonwoven base layer; and bonding these layers together to obtain a nonwoven sheet. The invention further relates to a nonwoven sheet manufactured by the method of the invention, comprising a first nonwoven base layer and preferably a second nonwoven base layer, and a layer of machine-oriented fibers, wherein these layers are bonded together to form a monolithic nonwoven sheet.

[0012] Unlike existing technologies such as US 2004 / 0005835 A1 or US 2021 / 0282979 A1, which combine pre-formed filaments with nonwoven sheets, a key aspect of this invention is that the machine-oriented fibers are manufactured online during production and directly bonded to the base layer. This contrasts with methods that pre-form machine-oriented fibers and then unwind these fibers using yarn spools or similar means.

[0013] According to the present invention, machine-oriented fibers are provided by extruding molten thermoplastic polymer through the orifices of a spinneret to obtain a screen for extruded spun filaments, followed by cooling and drawing (refining) of the extruded filaments, and then bonding the resulting machine-oriented fibers with a nonwoven substrate layer in the nip of a pair of bonded rolls or a pair of calender rolls. In embodiments, the machine-oriented fibers pass through a guide roller system on their path from the spinneret to the bonded rolls or calender rolls, meaning that the machine has one or more guide rollers positioned before the bonded rolls or calender rolls. The technique for manufacturing machine-oriented fibers is referred to herein as "directional spinning." In this document, machine-oriented fibers may be synonymously designated as "directionally spun fibers." Unlike conventional spunbond methods, machine-oriented fibers do not entangle in diffusers or similar devices, thus preserving their alignment along the fundamental machine direction and parallelism. Similarly, the filaments do not pass through a pneumatic drawing device that significantly increases the airflow velocity, so that drawing (i.e., stretching and refining) is substantially achieved by increasing the speed of the filaments from the spinneret to the nip of the bonded rolls or calender rolls. Primary cooling of the extruded filament after extrusion from the spinneret is preferably achieved via a process air system, also commonly used in conventional spunbond processes, but with significantly reduced back pressure, thus lowering energy consumption. The airflow still needs to be large enough to ensure cooling / quenching of the molten resin, but not to thin the filament. A baffle plate may be present to guide the airflow in the area between the process air system for primary cooling and the bonding rolls or calendering rolls (or guide rolls if present), but should not significantly increase the airflow velocity. An exhaust system may also be installed to remove cooling air to reduce airflow around the guide rolls.

[0014] In conventional spunbond processes, the maximum airflow velocity during filament stretching is typically at least 800 m / min, and more often above 1000 m / min. In contrast, the directional spinning process described herein preferably uses a maximum airflow velocity of less than 600 m / min, more preferably less than 300 m / min, or even less than 100 m / min. Adjustments within this range depend on factors such as resin yield, melt temperature, desired filament temperature at the binding or calendering rolls and the guide rolls (if present), and factors such as the geometry of the quench chamber and the shape of the guide vanes.

[0015] A guide roller system (if present) may include a single roller, a pair of rollers, a triplet roller, or two or more roller pairs, triplet rollers, or any combination thereof. The guide roller system may also include two or more subsystems arranged spaced apart from each other. These rollers typically have flat or slightly structured surfaces. These rollers are preferably driven and controlled at specific speeds. Especially in the case of a single roller, to generate sufficient contact to perform its function, a minimum wrap angle of ≥30°, more preferably ≥45°, or even ≥60° is preferred. In the case of two or more rollers, different surface speeds can be used for each roller. The temperature of the rollers can be controlled. In a preferred embodiment, the rollers can be cooled to aid in the cooling of the filament. To reduce adhesion tendency, the surface of the rollers may be coated with an inert material such as a fluoropolymer (e.g., polytetrafluoroethylene (PTFE)) or an abrasion-resistant coating such as ceramic or hard chrome.

[0016] The guide roller system enables improved control of the bonded cord of filaments exiting the spinneret. It enhances process stability and allows for step-by-step filament drafting. Specifically, the filaments can be drafted at a first ratio by increasing the filament speed from the speed of the filaments just extruded from the spinneret to the speed of the guide roller system. The cooled filaments can then be further pre-stretched (when elastic) or cold-drawn (when inelastic) at a second ratio by increasing the speed from the speed of the pre-stretch roller system (in a single or multi-step manner) to the speed of the bonded rollers or calendering rollers, thereby forming machine-oriented fibers.

[0017] In an exemplary embodiment, the first ratio (corresponding to the ratio of the guide roller speed to the extruded filament speed) can be 3 to 400, preferably 5 to 300, and more preferably 5 to 250. Due to the gravity of the molten polymer, in order to maintain a higher traction force to overcome the polymer's gravity, the minimum ratio between the filament speed at the spinneret nozzle (the exit speed of the material through the capillary, calculated using the solid density of the polymer material) and the guide roller system is expected to be at least 3, more preferably 5. The second ratio (corresponding to the ratio of the binding roll or calender roll speed to the guide roller speed) can be 1.5 to 10, preferably 1.8 to 9, and more preferably 2 to 8. In the case of multiple guide rollers or multiple spaced-apart guide roller systems, the second ratio is the product of two or more smaller ratios. The maximum achievable draw ratio depends on the polymer type and other process parameters, such as cooling efficiency and the height position of the guide roller system between the spinneret and the web-forming conveyor belt. In absolute terms, the speed at which the machine-oriented fibers bond with the nonwoven substrate can be, for example, from 100 m / min to 1200 m / min, preferably from 120 m / min to 1000 m / min. The speed of the guide roller can be, for example, from 5 m / min to 500 m / min, preferably from 10 m / min to 300 m / min.

[0018] The total distance the filaments / fibers travel between the binding rolls or calendering rolls is preferably at least 100 cm, more preferably at least 200 cm. This provides adequate distance for accommodating the necessary mechanical, step-by-step drafting / stretching, and proper cooling of the machine-oriented fibers before bonding with the nonwoven substrate.

[0019] In one embodiment, the guide roller is mounted such that its distance from the spinneret on one side and from the binding roller or calendering roller on the other side can be adjusted. In this way, the absolute and relative distances traveled during drafting and further drafting / stretching can be adjusted. This achieves more precise control and more flexible adjustment of stretching. In this embodiment, the ratio of the distance from the spinneret to the guide roller system to the distance from the guide roller system to the binding roller or calendering roller is 3:1 to 1:3. The absolute distance of the filament traveling from the spinneret to the guide roller system can be 50 cm to 350 cm, preferably 100 cm to 300 cm. The absolute distance of the machine-oriented fibers traveling from the guide roller system to the binding roller or calendering roller can be 50 cm to 300 cm, preferably 100 cm to 200 cm.

[0020] In one embodiment, the binder roller used to bond the fibers to the nonwoven substrate typically has a flat or slightly structured surface. In one embodiment, the linear pressure applied by the binder roller to the machine-oriented fiber structure and the nonwoven substrate can be from 2 N / mm to 10 N / mm. The surface temperature of one or both binder rollers can be controlled from 20°C to 140°C, preferably from 50°C to 120°C. To reduce adhesion tendency, the surface of one or both binder rollers can be coated with an inert material such as a fluoropolymer (e.g., polytetrafluoroethylene (PTFE), or an abrasion-resistant coating such as ceramic or hard chrome). In a preferred embodiment, regardless of whether calendering rolls are used instead of the bonding rolls already used to bond the fibers to the nonwoven substrate, a bonding step is typically required to obtain a monolithic sheet. For cooled fibers that have already passed through a stretching roll system, relying on the inherent adhesiveness of elastic fibers, as described in EP 2 098 363 B1, is not feasible and will in any case be limited to a specific set of materials. Bonding is also a necessary prerequisite if either or both of the nonwoven substrates are not prefabricated but produced online.

[0021] In a preferred embodiment, bonding includes introducing (imprinting) adhesive points on the sheet by calendering. Typically, a calender includes at least two calender rolls, at least one of which has imprinted protrusions on its surface. Both calender rolls may have independent adhesive protrusions for point-to-point contact, or both rolls may have helical protrusions, again to avoid using the planar full-contact rolls typically used when one roll only has adhesive protrusions, in order to form contact.

[0022] In a preferred embodiment, the machine-oriented fibers obtained by the above-described directional spinning process are bonded to the nonwoven substrate layer at the calendering point. In this embodiment, the pre-bonding of the nonwoven sheet and the corresponding bonding rollers may be omitted from the method and equipment.

[0023] The linear pressure (roll point pressure) between calendering rolls is typically significantly higher than the roll point pressure of the bonding rolls. In embodiments, this roll point pressure can be from 20 N / mm to 100 N / mm. Calendering bonding can be ultrasonic bonding in which ultrasonic vibration is introduced into the embossed protrusions on the surface of the calendering rolls, or thermal bonding in which the embossed protrusions are heated. The bonding points can be arranged in a systematic pattern or randomly distributed. The number of bonding points per square centimeter of sheet can be less than 100, and preferably less than 80, and in another respect, greater than 10, preferably greater than 20. In one embodiment, the total area of ​​the sheet surface occupied by the bonding points is less than 30%, and preferably less than 25%, and in another respect, greater than 4%, preferably greater than 7%. The area of ​​a single point on the sheet can be 0.1 mm². 2 Up to 2 mm 2 .

[0024] Typically, the dot shape can be selected from dot shapes known in the art, such as circular, elliptical, rectangular, rhomboid, or rod-shaped. In embodiments, a preferred variation is a dot in the form of a rod-shaped dot in the transverse machine direction (such as that disclosed in WO 2017 / 148865 A1). Such an adhesive shape allows the nonwoven sheet to achieve high tensile strength in the transverse machine direction, where the tensile strength is not supported by machine-oriented fibers, and without compromising the potential elastic properties of the nonwoven sheet in the machine direction.

[0025] In an embodiment, the method of the present invention does not use adhesive on the base layer or the machine-oriented fibers before bonding the machine-oriented fibers to the base layer. Therefore, the laminate is preferably adhesive-free, at least on the surface of the base layer facing the machine-oriented fibers.

[0026] In one embodiment, the capillary arrangement of the spinneret can be specifically configured to achieve a uniform spacing between machine-oriented fibers. For example, unlike the standard layout in standard spunbond (where capillaries are oriented along parallel machine direction lines), these lines can be tilted relative to the machine direction. For example, the angle can be up to 15°. In one embodiment, the angle can be such that capillaries from different capillary lines do not overlap in position, or that overlap occurs.

[0027] In one embodiment, the capillaries of the spinneret can have a diameter of 0.2 mm to 0.7 mm and an aspect ratio of 1:1 to 5:1.

[0028] The nonwoven substrate layer may individually comprise or consist of one or more spunbond nonwoven layers or meltblown nonwoven layers. The configuration may depend on the intended application. For example, to obtain high flexibility, elongation, and bulk, it is preferable that at least one nonwoven substrate layer comprises or consists of one or more spunbond layers formed of crimped multicomponent fibers. To obtain tensile strength, it is preferable that at least one nonwoven substrate layer comprises or consists of one or more spunbond layers formed of linear monocomponent fibers or symmetrical cross-section bicomponent fibers. To obtain liquid barrier properties, it is preferable that at least one nonwoven substrate layer comprises one or more meltblown layers. Generally, the layer sequence in the nonwoven sheet of the present invention may be, for example, SDS, SSDS, SSDSS, SMDS, SD, or SSD, where S represents a spunbond layer, M represents a meltblown layer, and D represents a machine-oriented spun layer of fibers. In each case, S may be S BiCo or S MoCo S BiCo This refers to a spunbond layer composed of crimped or non-crimped multicomponent fibers, and S MoCo This refers to the spunbond layer of linear single-component fibers.

[0029] There can be more than one step in manufacturing machine-oriented fibers. In other words, the step of providing machine-oriented fibers can be repeated. In terms of layer sequence, this will produce sequences such as SDDS, SDD, SSDD, SDSDS, etc.

[0030] The nonwoven substrate can be a prefabricated nonwoven sheet or formed in-line.

[0031] In the case of spunbond layers, online formation of the substrate layer includes spinning fibers using conventional spunbond processes, including cooling and drawing the filaments in a pneumatic device, passing the drawn and cooled fibers through a diffuser, and depositing the fibers onto a target surface to form a fibrous web. Online formation of a meltblown layer may include meltblown fibers and depositing them onto a target surface. Online formation of a carded layer may include laying a short-fiber carded web onto the target surface in a parallel or cross-laid manner. Regardless of the nature of the nonwoven substrate layer, the target surface can be a moving web-forming conveyor belt or an existing substrate layer when forming the first substrate layer. When forming the second nonwoven substrate layer, the target surface is an existing structure comprising the first nonwoven substrate layer and machine-oriented fibers. The web of the online-formed nonwoven substrate layer is preferably consolidated by passing the structure directly through two consolidation rollers. For details on roller configuration and setup, please refer to the description of the consolidation rollers above.

[0032] The prefabricated nonwoven sheet is already a bonded structure, which is typically manufactured offline and used in the method of the present invention by unwinding from a roll of material and combining it with machine-oriented fibers. For the first nonwoven base layer, the prefabricated layer can be fed together with the machine-oriented fibers into the spool of a bonding roll or calender roll. For the second nonwoven base layer, the prefabricated layer can also be fed together with the machine-oriented fibers into the spool of a bonding roll or calender roll, or combined downstream with a structure comprising the first nonwoven base layer and machine-oriented fibers, for example, downstream of a bonding roll at another pair of bonding rolls or at a bonding station comprising a pair of calender rolls. The prefabricated sheet itself is already a bonded structure, but overall bonding of the sheet of the present invention, comprising the nonwoven base layer and machine-oriented fibers, is still required for the reasons stated above.

[0033] It is feasible to combine the online fabrication of one of the nonwoven substrate layers with the provision of one nonwoven substrate layer as a preformed sheet. In an embodiment, the first nonwoven substrate layer may be provided as a preformed sheet, and the second nonwoven substrate layer may be formed online; or the first nonwoven substrate layer may be formed online, and the second nonwoven substrate layer may be provided as a preformed sheet.

[0034] The machine-oriented fibers can be single-component or bicomponent fibers. The fibers or fiber components can be formed from any polymer suitable for spunbond-related technologies. Polyolefins such as polyethylene (PE), polypropylene (PP), or copolymers including polypropylene (coPP) or polyethylene (coPE), particularly polypropylene (PP), are preferred to achieve the desired product properties. If high strength is desired, polypropylene with a low melt flow rate, such as 2-25 g / 10 min, preferably 3-25 g / 10 min, more preferably 5-25 g / 10 min (ISO 1133, 230°C, 2.16 kg), can be used. If elasticity is desired, thermoplastic elastomers (TPEs), such as styrene-ethylene-butene-styrene (SEBS), can be used. Thermoplastic elastomers can also be blended with other thermoplastic resins, such as polyesters like polyethylene terephthalate (PET) or polylactic acid (PLA).

[0035] If the machine-oriented fibers are bicomponent fibers, the distribution of their components across the fiber's cross-section is preferably symmetrical, i.e., a concentric core-and-shell structure. Symmetrical bicomponent fibers do not crimp, but this allows, for example, when the core of a thermoplastic elastomer is coated with conventional polypropylene, to reduce the fiber's adhesiveness despite its elastic properties; or when the core of a low melt flow rate polypropylene is coated with polyethylene, polypropylene-polyethylene copolymer, or high melt flow rate polypropylene, to improve adhesive properties while maintaining high strength.

[0036] Asymmetric distributions, such as eccentric core-sleeved, side-by-side, or similar structures, can also be used in bicomponent fibers to generate crimp.

[0037] In embodiments, the linear mass density of the machine-oriented fibers can be 300 deniers (g / 9000 m) or less, preferably 200 deniers or less, more preferably 100 deniers or less, and even more preferably 75 deniers or less. Exemplary ranges include 1 to 100 deniers, preferably 10 to 50 deniers, and preferably 20 to 40 deniers. The denier range may vary depending on the type of machine-oriented fiber. For example, elastic fibers may have 30-60 deniers (relaxed, i.e., in a contracted state), while inelastic fibers may have 4-20 deniers. The number of machine-oriented fibers per meter in the transverse machine direction can be 500 or more, preferably 1000 or more, more preferably 2000 or more, or even 4000 or more. Preferred upper limits depend on the application and machine setup and can be 10,000, 8,000, or 6,000 fibers. The number of machine-oriented fibers per meter of sheet in the transverse machine direction (sheet width) given above results in an average fiber center-to-center distance (MDOF) of: no more than 2 mm (CD) for 500 or more fibers, no more than 1 mm (CD) for 1000 or more fibers, no more than 0.5 mm (CD) for 2000 or more fibers, no more than 0.33 mm (CD) for 3000 or more fibers, and no more than 0.25 mm (CD) for 4000 or more fibers. Due to the transverse fiber size, the average gap between fibers will be even smaller. For example, 100 denier fibers typically have a diameter of approximately 0.1 mm; therefore, for such fibers, the average gap between them will be approximately 0.1 mm smaller than the average fiber center-to-center distance.

[0038] The invention includes embodiments in which the filaments pass through a guide roller system before being bonded to the nonwoven base layer in the spools of a pair of binding rollers, or embodiments in which the guide rollers are omitted. The guide rollers can be omitted, particularly when the machine-oriented fibers are inelastic. However, even in this case, the use of a guide roller system is still preferred because it enables cold drawing of the machine-oriented fibers, thereby improving their strength and modulus.

[0039] Further details and advantages of the present invention will be described below with reference to specific embodiments and accompanying drawings. The accompanying drawings show: Figure 1 This is a schematic diagram of a traditional spunbond machine; Figure 2 This is a schematic diagram of one embodiment of the machine used for directional spinning and manufacturing machine-oriented fibers in the method of the present invention; Figure 3 yes Figure 2 The variations differ in the position of the guide roller; Figure 4 yes Figure 2A variant of this design, which features two sets of guide rollers; Figure 5 This is a schematic diagram of another embodiment of the machine used for directional spinning and manufacturing machine-oriented fibers in the method of the present invention; Figure 6 This is a schematic diagram of another embodiment of the machine used for directional spinning and manufacturing machine-oriented fibers in the method of the present invention; Figure 7 This is a graph illustrating the relationship between the speed of the web-forming conveyor belt and the denier number and basis weight of the machine-oriented fibers at a given single-hole polymer output of a spinneret. Figure 8 This is a diagram illustrating the layout of the machine-oriented fiber layers; Figure 9 It is a capillary layout for spinnerets suitable for directional spinning; Figure 10 This is a process setup for manufacturing layered nonwoven sheets according to one embodiment of the present invention; Figure 11 The process setup for manufacturing layered nonwoven sheets according to another embodiment of the present invention; Figure 12 In another embodiment of the present invention, the process setup for manufacturing layered nonwoven sheets is shown. Figure 13 In another embodiment of the present invention, the process setup for manufacturing layered nonwoven sheets is shown. Figure 14 yes Figure 13 A detailed view of a pair of calendering rolls in the setup, where machine-oriented fibers are combined with a base layer; and Figure 15 This is an exemplary stress-strain diagram for polypropylene fibers.

[0040] Figure 1An example of a conventional spunbond machine 10a is shown. A thermoplastic polymer is supplied by a feeding system 11 to an extruder 12, heated, and extruded through a spinneret 13 to form a web of filaments 51a. A ventilation system 14a draws monomer exhaust gas from the spinneret 13, and a process air system 14b (including a pressurization chamber) directs process air to the web of filaments 51a. The process air typically enters through a honeycomb system to achieve good air distribution, stabilize the web of filaments 51a, and promote uniform cooling of all filaments 51a and subsequent drafting. After the process air system 14b, the filaments 51a and process air enter a stretching channel comprising a so-called intermediate channel 15 and so-called SAS plates 16 for drafting and thinning the filaments. In the intermediate channel 15, the air velocity is increased, and the SAS plates 16 have precise positioning and spacing, ensuring uniform airflow across the machine width and thus ensuring equal draw ratios. During drawing and further cooling, the polymer chains within the filament 51a align along the length of the filament and gradually crystallize, increasing the strength of each resulting single fiber. The thus final-stretched long fiber 50a then enters the diffuser 17 (also called the distribution unit). Here, the airflow velocity (and consequently the fiber velocity) is reduced, creating controlled turbulence that evenly distributes the fibers 50a onto the breathable web-forming conveyor belt 20. The combined fiber and airflow exiting the diffuser 17 are guided onto the web-forming conveyor belt 20 for fiber web formation and fibrous web formation. This fiber web is consolidated by a pair of consolidation rollers 18. Process air is drawn away by a suction unit 19 below the web-forming conveyor belt 20. The fiber 50a exits the diffuser 17 at a velocity up to approximately three times the travel speed of the web-forming conveyor belt 20, which contributes to the random distribution of the fibers, with a large proportion of the fibers oriented transversely to the machine direction. In conventional spunbond nonwovens, the single long fiber per meter of fabric length is therefore approximately 3 meters long.

[0041] Figure 2 The diagram illustrates an improved machine 10 used in the method of the present invention for directional spinning and manufacturing machine-oriented (i.e., directional spinning) fibers. As in conventional spunbond processes, a thermoplastic polymer is supplied from a feed system 11 to an extruder 12, heated, and extruded through a spinneret 13 to form a web of filaments 51. Further, as in conventional spunbond processes, a ventilation system 14a extracts monomer exhaust gas from the spinneret 13, and a process air system 14b (including a pressurization chamber) directs process air to the web of filaments 51. In embodiments, the process air system 14b can also be used to remove air from the system (in the figure, this means the arrow at 14b is reversed in direction).

[0042] However, compared to conventional spunbond processes, the cooling air velocity and back pressure are significantly reduced, primarily by omitting components 15 and 16, which are narrowly positioned in conventional setups. An exemplary value is that the cooling airflow is reduced by 50% compared to conventional spunbond processes, while the back pressure is correspondingly reduced by approximately 90%. Since the generation of cooling air accounts for about half of the total energy consumption of conventional spunbond machines (the other half is for polymer melting and yarn drive), this improvement is significant. In other words, directional spinning can reduce energy consumption.

[0043] Furthermore, compared to traditional spunbond processes, the improved machine 10 suitable for directional spinning lacks pneumatic devices (including stretching channels and diffusers), such as... Figure 1 The conventional setup shown. Process air is directly discharged to the environment, and filament 51 is drawn to the nip of guide roller 21 and then further cold-drawn (inelastic fibers) or pre-stretched (elastic fibers) to the nip of binder roller 18, typically along with the web-forming conveyor belt 20 and the nonwoven substrate layer thereon. Deflector plates 22, used to guide airflow in the area between the process air system 14b for primary cooling and guide roller 21, may optionally be present for air guidance, but are arranged so as not to cause a significant increase in process air velocity, preferably below the guide roller system speed and production line speed. This can be illustrated by giving numerical values ​​for the gap / distance between plates 22. The distance between plates 22 can be greater than 80 mm to 500 mm in the machine direction, preferably 150 mm to 350 mm, more preferably 200 mm to 300 mm. In contrast, as Figure 1 In the conventional spunbond setup shown, the distance between the plates defining the intermediate channel 15 and / or between the SAS plates 16 can be from 15 mm to 80 mm in the machine direction.

[0044] Therefore, the filament 51 is achieved by mechanical stretching without the use of pneumatic devices or process air. The resulting fibers 50 are oriented substantially in the machine direction of the web and are arranged substantially parallel to each other.

[0045] The set of guide rollers 21 positioned before the bonding roller 18 allows for improved control of the web of bonded filaments 51 descending from the spinneret 13. The guide rollers 21 are preferably driven and temperature-controlled, and preferably cooled. For example, the surface temperature of the guide rollers can be controlled within the range of 20°C to 80°C. Given a speed ratio between the guide rollers 21 and the bonding roller 18, a higher guide roller temperature within this range can reduce tensile force. Generally, guide roller temperature can be used to control material morphology (such as crystallinity) and tensile force.

[0046] like Figure 3As shown, the position of the guide roller 21 and therefore the distance from which the filament 51 travels from the spinneret 13 to contact the guide roller 21 can be adjusted.

[0047] like Figure 4 As shown, the machine 10 may also include two sets of guide rollers, namely guide roller 21 and guide roller 21a, which are arranged sequentially between the spinneret and the lamination point (e.g., the web forming conveyor belt 20 / bonding roller 18).

[0048] Another embodiment of the improved machine 10 for directional spinning and producing directionally spun fibers in the method of the present invention is as follows: Figure 5 Example in. and Figures 2 to 4 The difference in the improved machine shown is that, Figure 5 The improved machine does not have a guide roller system, and the filament 51 is drawn directly from the spinneret 13 to the bonding roller 18.

[0049] Another embodiment of the improved machine 10 for directional spinning and producing directionally spun fibers in the method of the present invention is as follows: Figure 6 As illustrated below, after the filament 51 leaves the spinneret 13, it is cooled only by cooling air from one side, as shown by the process air system 14b, which exists only on one side. Some process air exits the process from the opposite side, as indicated by the smaller arrow on the right; some process air flows downwards with the fibers. The monomer suction 14a remains constant around the spinneret 13.

[0050] like Figures 2 to 5 In the illustrated setup of the invention, the filament draw ratio and thinning are influenced and controlled by the polymer extrusion rate through the spinneret 13, the speed of the guide roller 21, and / or the speed of the web-forming conveyor belt 20 / binding roller 18. With a constant polymer output per orifice of the spinneret 13, the denier number of the resulting fiber 50 ultimately varies with the speed of the web-forming conveyor belt 20. A higher web-forming conveyor belt speed results in a lower denier number of the resulting fiber; conversely, a lower web-forming conveyor belt speed results in a higher denier number of the resulting fiber. This also applies to the basis weight of the resulting machine-oriented (i.e., directionally spun) fiber 50 layers.

[0051] Figure 7 This correlation is illustrated with an example. As the linear speed (i.e., the speed of the web-forming conveyor belt 20 / binding roller 18) increases, the denier number of the oriented spun fibers decreases. When the polymer output per orifice (i.e., the spinneret) is 0.6 grams per minute (spinneret diameter 0.6 mm, and circular), the denier ranges from 46.0 denier at a linear speed of 117 m / min to 4.6 denier at a linear speed of 1173 m / min. In terms of basis weight, assuming the spinneret includes 5700 orifices per meter in the transverse machine direction, the basis weight of the resulting oriented spun fiber layer (in grams per square meter "gsm" or "g / m²") is...2 The range of denier number (measured) is from 29.2 gsm at 117 m / min to 2.9 gsm at 1173 m / min. (The denier number refers to the denier number measured at the location of the binding roll. For example, if the elastic machine-oriented fibers retract later, the denier number will increase accordingly.)

[0052] The method of this invention provides a highly flexible process that can generate a variety of different fiber denier numbers under different conditions. The distances at which the first and second stretching occur (i.e., the distance between the spinneret and the guide roller system on the one hand, and the distance between the guide roller system and the web forming conveyor belt on the other hand) can be varied and are another parameter that gives the method of this invention great flexibility.

[0053] Figure 8 Examples are shown of the layout of oriented spun fiber layers for different fiber stretch ratios in terms of fiber thickness and open space between parallel fibers.

[0054] Figure 9 This illustrates how the capillary layout of the spinneret can be configured to achieve uniform spacing between oriented spun fibers. The left illustration shows the standard layout for standard spunbond spinning. The capillaries are oriented along lines parallel to the machine direction. The middle and left illustrations show capillary layouts optimized for oriented spinning. Specifically, the capillaries are oriented along parallel lines slightly inclined relative to the machine direction. For example, the angle can be up to 15°. In the middle illustration, the angle is smaller, and capillaries from different capillary lines do not overlap in position. In the right illustration, the angle is larger, and overlap occurs.

[0055] Figure 10 An example of the process setup for implementing the method of the present invention to manufacture a layered nonwoven sheet having an SDS layer sequence in an online production line is illustrated. For this purpose, two spunbond machines 10a and one directional spinning machine 10 are arranged sequentially on a common web-forming conveyor belt. The first conventional spunbond machine 10a (e.g., for manufacturing a fibrous web for forming a first spunbond base layer) is used. Figure 1 Located at the beginning of the production line. Oriented spinning machine 10 (e.g., used to manufacture oriented spun fiber layers) Figure 2 It is located after it in the production line. (This setup can also be achieved using, for example...) Figures 3 to 6 The directional spinning machine shown is used to achieve this). A second conventional spunbond machine 10a (as shown) is used to manufacture a fibrous web for forming a second spunbond substrate layer. Figure 1Located at the end of the production line. In each case, the formed layer is directly bonded by a pair of bonding rollers 18. In the case of the directional spinning machine 10a, the bonding rollers 18 are used to bond the directionally spun fibers with the web used to form the first spunbond base layer, and, where applicable, the directionally spun fibers are further drawn after the guide roller 21 for additional cold drawing (for non-elastic fibers) or pre-stretching (for elastic fibers). The nonwoven base layer formed by the conventional spunbond machine 10a can be formed individually from crimped multicomponent fibers, linear single-component or multicomponent fibers, or different configurations, depending on the product requirements.

[0056] Figure 11 An alternative process setup is illustrated for implementing the method of the present invention to manufacture layered nonwoven fabrics having an SDD layer sequence in an online environment. For this purpose, with Figure 10 Compared to the previous setup, the second traditional spunbond machine was replaced with, for example... Figure 2 The second directional spinning machine 10 (or such as...) Figures 3 to 6 (The directional spinning machine shown).

[0057] Figure 12 This illustrates yet another alternative process setup for implementing the method of the present invention to manufacture layered nonwoven fabrics having an SDS layer sequence. Figure 12 The setup does not include traditional spunbond machines, but only includes, for example, Figure 2 (It can also be as follows) Figures 3 to 6 A directional spinning machine 10 is used, and pre-formed spunbond sheets 40, 41 unwound from corresponding rolls are used as the first and second nonwoven base layers of the sheets. The pre-formed spunbond sheets and the directionally spun fibers formed in the directional spinning machine 10 are combined at the nip point of the bonding roller 18 associated with the directional spinning machine 10. In this embodiment, a web-forming conveyor belt may be absent.

[0058] exist Figures 10 to 12 In any of the embodiments, the combined spunbond base layer and the oriented spun fiber layer are finally bonded together at bonding station 30 by calendering. Bonding is necessary to obtain a monolithic sheet. The calender includes two rolls 31, one of which has embossed protrusions on its surface. The calender roll 31 applies a linear pressure (e.g., 40 N / mm) to the sheet, and the embossed protrusions are heated to promote localized polymer melting and the imprinting of bonding points upon contact.

[0059] In addition, Figures 10 to 12 In any of the embodiments, the product can be placed at a winding station downstream of the bonding station 30. Figures 10 to 12 (Not shown) is wound onto a surface to form a finished roll.

[0060] Figures 10 to 12Combinations of implementation methods (e.g., allowing the manufacture of SDDS or SSDS sheets, or using in-line formation for one of the spunbond substrates and using pre-formed sheets for the other) are feasible and are also included in variations of the invention.

[0061] In one example, directional spinning technology can be used to enhance the tensile strength of nonwoven sheets on their molecular weight (MD).

[0062] like Figures 2 to 4 The embodiments shown, including the guide roller system, are particularly suitable because they allow for the effect that cold drawing of essentially inelastic fibers (such as PP fibers) can increase their tensile strength. To illustrate this effect, Figure 15 The stress-strain diagram of polypropylene (PP) fiber with a linear mass density of 7.25 denier in the unstretched state is shown. Different curves in the figure represent different single tests. As shown, the tensile strength increases significantly with cold stretching and can typically be stretched up to 400% without fiber breakage. In the unstretched state, the force required to stretch the fiber is approximately 3 cN, increasing to approximately three times (9 cN) at 400% stretch, while the fiber denier number decreases to 1.80. The increase in tensile strength is significant at 200-250% elongation with a low risk of fiber breakage. To obtain fabrics with low basis weight and high tensile strength in the machine direction, it is desirable to increase tensile strength while simultaneously reducing linear mass density.

[0063] As an example, an SDS product can be produced, which has two standard polypropylene (PP) spunbond base layers (each layer weighing 5 g / m²). 2 The D layer of machine-oriented polypropylene (PP) fibers (with a basis weight of 2 g / m²) 2 This product can be used in, for example Figure 12 The product is manufactured on the production line shown in the diagram. The polypropylene used has a density of 0.9 g / cm³. 3 The production line speed can reach 600 m / min. To cold-draw the oriented spun fibers to 400% at the guide roller system, the guide roller speed is adjusted to 150 m / min (in the case of multiple rollers, the first roller is used as a reference). 2 g / m 2 The D layer can be composed of different numbers of fibers with different linear mass densities. Options are given in Table 1 below.

[0064] Table 1 Linear mass density [Denier] 2 4 6 8 10 12 Fiber count [fibers / meter (on CD)] 9000 4500 3000 2250 1800 1500 Production volume [kg / hr / m] 72 72 72 72 72 72 Yield [g / min / capillary] 0.13 0.27 0.40 0.53 0.67 0.80 Capillary outlet velocity [cm / min] 52 104 157 209 261 313 Capillary / guide roller speed ratio 287 144 96 72 57 48 Typically, for options with a high fiber count (e.g., 4500 or more), oriented spun fibers are not easily visible to the naked eye in the finished product because of their lower basis weight and smaller fiber spacing.

[0065] In another example, directional spinning technology can be used to impart MD (mesh elasticity) properties to nonwoven sheets.

[0066] In this respect, such as Figures 13 to 14 The illustrated implementation is particularly applicable. This corresponding process setup is used to manufacture layered nonwoven sheets with SDS layer sequences and, especially, high elasticity in the machine direction. Figure 12 The settings are similar. Figure 13 The setup also does not include traditional spunbond machines, but only includes, for example, traditional spunbond machines. Figure 2 The diagram illustrates a directional spinning machine 10, using pre-formed spunbond sheets 40 and 41 unwound from corresponding rolls as the first and second nonwoven base layers of the sheets. In this embodiment, the combination of the pre-formed base layers 40 and 41 with the directionally spun fibers 50 is not performed at the sizing point of the binding roll, but directly at the sizing point of the calendering roll 31. No binding roll or web-forming conveyor belt is present in this embodiment. The guide roller system 21 in this embodiment is illustrated as a single-roller system with an approximately 90° wrap angle, but may also include multiple rollers.

[0067] like Figure 14 As shown, the calendering rolls include a structural roll 31a and a planar roll 31b, which rotate in opposite directions, as indicated by the curved arrow. Rollers 31a and 31b act on the composite sheet with a certain linear pressure (e.g., 40 N / mm), and the embossing protrusions are heated to promote localized polymer melting and the imprinting of bonding points upon contact.

[0068] The speed of the guide roller 21 (exemplified in this embodiment as a single roller system with an encirclement angle of about 90°, but may also include multiple rollers) is less than the speed of the calendering roller 31, so that the oriented spun fibers 50 are spun.

[0069] As described above, this embodiment (including the guide roller system 21 and combining the oriented spun fibers 50 with the base layers 40, 41 in the nip of a pair of calendering rollers 31) is particularly suitable for obtaining nonwoven sheets with elastic properties, especially in the machine direction, in the context of using oriented spun fibers formed from elastic materials (e.g., elastic TPE fibers). In this context, the guide roller 21 operates at a speed lower than that of the calendering rollers 31 to pre-stretch the oriented spun fibers 50, which have been formed and cooled to elasticity at the guide roller 21, such that they are pre-stretched (e.g., ...). Figure 14(Indicated by the opposing arrows on the left side of the middle rollers 31a and 31b), and then retracted after bonding with the base layer at the bonding / calendering station 30. The base layers 40 and 41 can be formed of a stretchable material (such as spunbond material using crimped (asymmetric bicomponent) fibers) or a material with lower stretchability (such as spunbond material using non-crimped (monocomponent or symmetric bicomponent) fibers). In an embodiment, the base layers 40 and 41 can be fed into the calendering rollers without pretension or with a pretension less than that of the oriented spun fibers. In this configuration, the base layers 40 and 41 will be shortened by the retraction force of the elastically oriented spun fibers (e.g., ...). Figure 14 (As indicated by the opposing arrows on the right sides of the middle rollers 31a and 31b), and exhibiting a certain degree of wrinkling, such as Figure 14 As shown. In this context, forming the substrate layers 40, 41 from a material with inherently low stretchability can have the following advantages: obtaining a material that is stretchable in the machine direction but has low stretchability in the transverse machine direction.

[0070] As an example, an SDS product can be produced, which has two spunbond base layers 40 and 41 and a D layer of oriented spun styrene-ethylene-butene-styrene (SEBS) fibers 50 (with a basis weight of 30 g / m²). 2 (Pre-stretched 200%), this product can be used in situations such as Figure 13 Production is carried out on the production line shown. In elastic applications, the oriented spun fiber 50 needs to have a certain minimum basis weight to impart a certain degree of elasticity to the fabric. The production line speed (i.e., the speed of the calendering roller 31) can be 100 m / min. To pre-stretch the oriented spun fiber to 200% at the guide roller system 21, the guide roller speed is adjusted to 50 m / min. 30 g / m 2 The D layer can be composed of different numbers of oriented spun fibers 50 with different linear mass densities. Options are given in Table 2 below.

[0071] Table 2 Linear mass density [Denier] 15 30 45 60 80 100 Fiber count [fibers / meter (on CD)] 18000 9000 6000 4500 3375 2700 Production volume [kg / hr / m] 180 180 180 180 180 180 Yield [g / min / capillary] 0.17 0.33 0.50 0.67 0.89 1.11 Capillary outlet velocity [cm / min] 65 131 196 261 348 435 Capillary / guide roller speed ratio 77 38 26 19 14 11 Typically, options with high fiber counts (e.g., 9000 or more) may be less desirable due to process stability concerns. Medium counts (e.g., 4500) are often preferred because this falls within the standard spinneret range; the exit speed to guide roller speed ratio provides a stable spinning process; and the fiber spacing in directional spinning is sufficiently small to produce a homogeneous product. Two consecutive spinnerets can be used to prepare the DD arrangement, and different settings can be used compared to a single spinneret used for directional spinning.

[0072] The pre-stretched, elastically oriented spun fibers will shrink back after leaving the calender roll 31 and before being wound at station 70. The cooling roll 60 can be used for consolidation and short-range drawing of the reinforcing material. Therefore, the winding speed at station 70 can be lower than the speed of the calender roll 31. On the other hand, this winding speed can be higher than the speed of the guide roll 21. The speed difference between the calender roll 31 and the winding station 70 can be at least 20%, thereby causing the fabric shrinkage and weight gain of layer D to correspondingly reach at least 20%. A suitable winding speed can be determined by measuring the tension of the sheet before winding. A sufficiently low value indicates that the elastic potential of the oriented spun fibers has been fully utilized.

[0073] Of course, such as Figures 13 to 14 The embodiments shown can also be used in the context of non-elastic directional spun fibers, for example, in the cold drawing process described above.

[0074] To improve the uniformity of shrinkage across the entire width of the sheet, the machine may include a series of at least two traction devices positioned between the bonding station 30 and the winding station 70. The distance between adjacent traction devices may be 2 meters or less. Furthermore, for uniform shrinkage, speed control (rather than tension control) of the winding station 70 may be preferred.

[0075] In this embodiment, the sheet with elastically oriented spun fibers is further activated after production. Activation is understood as directional stretching of the sheet. Activation can loosen or weaken the base layer and make it more stretchable. The degree of activation affects the extent to which the final sheet can elastically stretch in the machine direction. One option for activating the sheet includes passing it through a rolling mill comprising a pair of meshing rollers with interlaced transverse ribs and grooves on their surfaces. An alternative option is to use a series of continuous traction devices operating at different speeds. Activation can cause, for example, the sheet to be stretched to 10-300% of its original size, preferably 20-200%, more preferably 50-150%. In terms of time, for example, activation can be carried out at least two days after production, at which point the crystallization process will be substantially complete.

Claims

1. A method for manufacturing a nonwoven sheet, the nonwoven sheet comprising a first nonwoven base layer and preferably a second nonwoven base layer and a layer of machine-oriented fibers, the method comprising: Provide the first nonwoven substrate layer; Preferably, a second nonwoven substrate layer is provided; The machine-oriented fibers are provided by: extruding molten thermoplastic polymer through the holes of a spinneret to obtain a screen for extruded spun filaments, cooling and drawing the filaments, and bonding the resulting machine-oriented fibers with a first nonwoven substrate and preferably a second nonwoven substrate in the nip of a pair of binding rolls or calender rolls. The layers are bonded together to obtain a nonwoven sheet.

2. The method according to claim 1, wherein, The machine-oriented fibers pass through the guide roller system on their path from the spinneret to the bonding roller or the calendering roller.

3. The method according to any of the preceding claims, wherein, The machine-oriented fibers do not pass through a diffuser or pneumatic stretching device located between the spinneret and the binding roll or the calendering roll.

4. The method according to claim 2 or 3, wherein, At least one roller of the guide roller system is driven and controlled at a specific speed and / or cooled.

5. The method according to any one of claims 2 to 4, wherein, The ratio of the distance from the spinneret to the guide roller system to the distance from the guide roller system to the bonding roller or the calendering roller is 3:1 to 1:

3.

6. The method according to any of the preceding claims, wherein, The total distance the filament travels between the spinneret and the bonding roll or the calendering roll is at least 100 cm, more preferably at least 200 cm.

7. The method according to any one of claims 2 to 6, wherein, The ratio of the guide roller speed to the extruded filament speed is 3 to 400, preferably 5 to 300, more preferably 5 to 250; and / or the ratio of the binding roller or calendering roller speed to the guide roller speed is 1.5 to 10, preferably 1.8 to 9, more preferably 2 to 8.

8. The method according to any of the preceding claims, wherein, The bonding includes introducing bonding points in the sheet by calendering, preferably at the slits of a pair of calendering rolls, in which the machine-oriented fibers are bonded to the first nonwoven base layer and preferably the second nonwoven base layer, wherein preferably, the bonding points are shaped as transverse bars.

9. The method according to any of the preceding claims, wherein, The first nonwoven substrate layer and / or the second nonwoven substrate layer are spunbond nonwoven layers.

10. The method according to any of the preceding claims, wherein, The first nonwoven substrate layer and / or the second nonwoven substrate layer are formed in-line.

11. The method according to any of the preceding claims, wherein, The first nonwoven base layer and / or the second nonwoven base layer are provided as pre-fabricated nonwoven sheets, unwound from a material roll and combined with machine-oriented fibers.

12. The method according to any of the preceding claims, wherein, The machine-oriented fibers comprise thermoplastic polyolefins, particularly polyethylene (PE), polypropylene (PP), or copolymers including polypropylene (coPP).

13. The method according to claim 12, wherein, The linear mass density of the machine-oriented fibers is 1 to 50 denier, preferably 2 to 40 denier, and more preferably 4 to 20 denier.

14. The method according to any one of claims 1 to 11, wherein, The machine-oriented fibers contain thermoplastic elastomers (TPEs), particularly thermoplastic olefins (TPE-o), such as, for example, styrene-ethylene-butene-styrene (SEBS).

15. The method according to claim 14, wherein, The linear mass density of the machine-oriented fiber is 10 to 100 denier, preferably 20 to 80 denier, and more preferably 30 to 60 denier.

16. The method according to any of the preceding claims, wherein, The number of machine-oriented fibers per meter length in the transverse machine direction of the sheet is 1,500 to 10,000, preferably 3,000 to 8,000, and more preferably 4,000 to 6,000.

17. A nonwoven sheet prepared by the method according to any preceding claim, comprising a first nonwoven base layer and preferably a second nonwoven base layer and a layer of machine-oriented fibers, wherein the layers are bonded together to form an integral nonwoven sheet.

18. The nonwoven sheet according to claim 17, wherein, The layer sequence in the nonwoven sheet is selected from SDS, SSDS, SSDSS, SMDS, SD, SSD, SDDS, SDD or SSDD, where S represents the spunbond layer, M represents the meltblown layer, and D represents the layer of machine-oriented fibers.

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