COMPOSITE NON-WOVEN FABRIC AND METHOD FOR PRODUCING A COMPOSITE NON-WOVEN FABRIC

Description

[0001] The present invention relates to a composite nonwoven fabric comprising at least a spunbond nonwoven having randomly laid and substantially endless regenerated cellulosic filaments, and a layer of bio-based biodegradable short fibers.

[0002] Furthermore, the invention relates to a method for producing a composite nonwoven fabric in which a cellulosic spinning mass is extruded into filaments through a plurality of nozzle holes of at least one spinning nozzle and the filaments are each stretched in the extrusion direction, wherein the filaments are laid down in a tangled position on a perforated conveying device to form a spunbond nonwoven, and in which short fibers are added to the spunbond nonwoven to form the composite nonwoven.

[0003] Furthermore, the invention relates to a system for carrying out a process for producing a composite nonwoven fabric. State of the art

[0004] The production of spunbond nonwovens is known from the prior art, using both spunbond and meltblown processes. In the spunbond process (e.g., GB 2 114 052 A or EP 3 088 585 A1), the filaments are extruded through a die and drawn off and stretched by a drawing unit below. In the meltblown process (e.g., US 5,080,569 A, US 4,380,570 A, or US 5,695,377 A), the extruded filaments are drawn and stretched by hot, high-speed process air as they exit the die. In both technologies, the filaments are laid down in a random orientation on a storage surface, such as a perforated conveyor belt, to form a nonwoven fabric, transported to post-processing steps, and finally wound into rolls.

[0005] Spunbond nonwovens produced from polymer melts using the aforementioned methods can be manufactured with very low basis weights in the range of up to 10 g / m² and high tensile strengths. However, such nonwovens generally exhibit insufficient absorption properties for applications where absorbency is important. Furthermore, these nonwovens are poorly biodegradable, if at all.

[0006] In contrast, wet lay-up processes for the production of nonwovens with high absorbency are known from the prior art (US 4,755,421, WO 2015 / 000687, US 4,166,001), in which a low-concentration cellulose suspension is prepared and applied on a conveyor belt. However, such nonwovens suffer from low tensile and abrasion strength. The mechanical properties of these products can be partially improved by the use of synthetic binders and adhesives, which in turn has a negative impact on biodegradability.

[0007] A large market for nonwovens lies in applications for wipes used in medicine, hygiene, cosmetics, industry, and households. However, wipes, especially pre-moistened wipes, must meet high standards of tensile strength and absorbency to ensure a reliable product. To mechanically reinforce wet-laid nonwovens, synthetic binders and short-cut fibers based on polyethylene, polypropylene, or polyester are added to the processing suspensions, as described in US 2004 / 0013859. Nonwovens produced using such methods exhibit poor or incomplete biodegradability due to their synthetic fiber content.

[0008] To combine the mechanical stability of spunbond nonwovens with the absorbent properties of cellulose, a process was described in EP 0 333 211 in which a synthetic, in particular polyester- or polyolefin-based, meltblown nonwoven product is hydrodynamically bonded to cellulosic staple fibers or to a layer of wet-laid cellulose. Further developments of this process (US 5,284,703, US 5,587,225, US 2009 / 0233049) allow the production of a wider range of products, in particular a more affordable mass-market product for the wipes market. For example, these processes can combine a modified airlay process with meltblown technology to produce an absorbent nonwoven product in which cellulose fibers are homogeneously distributed over a synthetic polyolefin fiber matrix. However, such products also suffer from incomplete biodegradability.

[0009] From today's ecological perspective, the combination of petroleum-based staple fibers and petroleum-based spunbond nonwovens, such as those made of polyester or polypropylene, with cellulose is problematic. Products manufactured specifically for the mass market that contain petroleum-based fibers or filaments are neither fully biodegradable nor are there suitable recycling methods for them. Composite nonwovens made of plastic and cellulose are sold worldwide and, after a single use, end up in landfills, rivers, or the oceans. This process generates microplastics, which enter the food chain, and whose full impact on life is not yet known. Even during the initial use phase of these products, significant amounts of microplastics are generated – as demonstrated by abrasion tests and subsequent microscopic examination, which reveal clear signs of material abrasion and fiber breakage.

[0010] Methods for producing nonwovens without plastic content or chemical binders are known from the prior art (WO 2012 / 090130). In this process, a layer of wet-bonded cellulose is bonded to a second nonwoven layer of regenerated cellulose fibers or cellulose filaments using water jet bonding. However, the described process is very complex due to the process control, as the spunbond rolls must be unwound and guided via deflection rollers to the already produced wet-bonded cellulose layer. It is noted that the cellulosic spunbond can also be produced continuously, as with conventional spunbond processes, and bonded to the wet-bonded cellulose layer via deflection rollers and then hydraulically bonded. However, how the production of the cellulosic spunbond layer is to be carried out and what the necessary equipment for this is to look like is not described.Also not addressed is the material and bonding density of the spunbond component, which is explicitly described in the previously cited prior art (EP 0 333 211, US 5,284,703, US 5,587,225) and presented as critical to success, the incorrect setting of which leads to insufficient penetration or weak anchoring of the cellulose fibers in the spunbond and thus to poor layer cohesion.

[0011] Another manufacturing process, in which a plastic-based spunbond process is directly combined with a wet lay-up process, is known from US 7,432,219. However, this is also a non-biodegradable and therefore not sustainable solution.

[0012] From US patent 4,523,350, it is further known that cellulosic staple fibers can be processed into a fiber nap using a carding machine and then into a nonwoven fabric using a bonding machine. However, such processes and systems are significantly inferior to spunbond and wetlay systems in terms of production capacity due to their lower production speeds. Cellulosic staple fibers are dried and pressed into bales during their production, then mechanically opened in the subsequent nonwoven fabric production process, rewetted by jet bonding, and finally dried again as a nonwoven. From the perspective of global energy conservation, such a process is questionable.In order to reduce raw material and drying costs and thus be able to produce competitive nonwoven products for the mass market such as baby wipes or hygiene wipes, carded nonwovens are usually made from a mixture of polyester and viscose fibers, and due to the proportion of petroleum-based fibers, they contribute to the global microplastic problem because of their lack of biodegradability.

[0013] It is also known from the prior art to produce cellulosic spunbond nonwovens according to the spunbond technology (e.g., US 8,366,988 A) and according to the meltblown technology (e.g., US 6,358,461 A and US 6,306,334 A). In these processes, a lyocell spinning mass is extruded and drawn according to the known spunbond or meltblown methods.

[0014] Before being laid down to form a nonwoven fabric, the filaments are additionally exposed to a coagulant to regenerate the cellulose and produce dimensionally stable filaments. The wet filaments are then laid down in a random orientation as a nonwoven. However, these processes have little in common with the thermoplastic spunbond or meltblown production of nonwovens using the classic spunbond or meltblown processes described earlier. Since the lyocell spinning mass is a solution with a cellulose content of 7-14%, a significantly larger amount of solvent is extruded during spunbond nonwoven production, in addition to the fiber-forming cellulose. This solvent is then extracted from the nonwoven and recovered in a subsequent washing process.The specific compressed air consumption of all lyocell-based spunbond processes is significantly higher than that of spunbond processes based on thermoplastic melts due to the greatly reduced solids content. To achieve productivity comparable to thermoplastic spunbond processes, considerably larger mass flows must be moved and processed into a spunbond using more air and energy. While the increased energy consumption makes such products suitable for specialized applications in filtration, hygiene, or high-priced wipes due to their very fine fiber diameter, they hardly meet the demand for an affordable, purely cellulosic, and biodegradable nonwoven fabric for mass markets such as baby wipes, household wipes, hygiene products, and industrial applications.

[0015] WO 2018 / 184048 discloses a process for producing a composite nonwoven fabric comprising a spunbond nonwoven consisting of endless regenerated cellulosic filaments and a layer of cellulose short fibers.

[0016] The current state of the art therefore does not offer a satisfactory solution for producing a biodegradable, inexpensive nonwoven fabric with good tensile strength, absorption and cleaning properties, as well as a haptic feel adapted to the intended application. Disclosure of the invention

[0017] The present invention therefore aims to provide a completely biodegradable composite nonwoven fabric of the type mentioned above, which has high stability and tensile strength as well as good absorption and haptic properties and can also be manufactured cost-effectively.

[0018] The invention solves the stated problem by providing the composite nonwoven fabric with at least one mixing zone in which the filaments of the spunbond nonwoven and the short fibers are physically bonded together. The composite nonwoven fabric is defined as in claim 14.

[0019] It has surprisingly been found that by incorporating a mixing zone into the composite nonwoven fabric, a particularly reliable and durable bond between the spunbond and the short fibers can be created. This is especially true even when no additional binders are used to bond the filaments of the spunbond and the short fibers. In the mixing zone, the filaments of the spunbond and the short fibers are physically mixed and can thus be physically bonded together, particularly without the presence of a binder. The physical bond between the filaments of the spunbond and the short fibers can be formed, at least partially, by hydrogen bonds, mechanical interlocking or entanglement, frictional forces, or similar mechanisms.This allows a materially bonded connection to form between the spunbond nonwoven and the short fibers, which in particular cannot be undone without causing damage.

[0020] The physical mixing between spunbond and short fibers can be achieved, for example, by applying a suspension of short fibers to the spunbond in its never-dried state, thereby enabling mutual penetration of the filaments of the spunbond and the short fibers and creating the mixing zone.

[0021] The composite nonwoven fabric according to the invention is thus a purely bio-based and completely biodegradable nonwoven. The invention can therefore contribute to preventing environmental pollution. Furthermore, the composite nonwoven exhibits high strength values ​​due to the physical mixing or bonding between the spunbond nonwoven and the short fibers, since the spunbond nonwoven – which typically has very high strength values ​​– stabilizes the layer of short fibers. Surprisingly, this stabilization can also be achieved without negatively affecting the feel of the composite nonwoven. While composite nonwovens containing binders typically exhibit high stiffness, the composite nonwoven fabric according to the invention yields a softer and more flexible composite nonwoven compared to the prior art.The purely bio-based and completely biodegradable composite nonwoven fabric also has a high absorption capacity and can be produced in a resource-saving manner.

[0022] For the purposes of this invention, bio-based fibers are defined as natural fibers as well as bio-based plastic fibers produced from renewable raw materials. These are to be distinguished only from biodegradable plastic fibers, which are not of biogenic origin and may be produced from petroleum-based raw materials. The term "bio-based fibers" within the scope of this invention specifically excludes the presence of petroleum-based components in these fibers.

[0023] In the context of this invention, biodegradable fibers are understood to be, in the case of plastic fibers, fibers that are considered fully compostable according to the guidelines for biodegradable plastics in the European standard EN 13432.

[0024] If the short fibers are cellulosic short fibers, the composite nonwoven fabric according to the invention, in its absolutely dry ("atro") state (i.e., free of water), can have a cellulose content of at least 93 wt.%, depending on the cellulosic short fiber used. The remaining content can consist of substances naturally occurring in cellulose, such as lignins, as well as unavoidable impurities. Such a composite nonwoven fabric exhibits very good and complete biodegradability. Preferably, the absolutely dry composite nonwoven fabric can have a cellulose content of at least 95 wt.%, and particularly preferably at least 97 wt.%.

[0025] Advantageously, the composite nonwoven fabric can contain between 10 wt.% and 99 wt.% of cellulosic filaments of the spunbond and between 1 wt.% and 90 wt.% of short fibers. The composition according to the invention ensures, in particular, a composite nonwoven fabric with good cohesion between filaments and short fibers, and thus high strength. Preferably, the composite nonwoven fabric contains between 15 wt.% and 95 wt.%, particularly preferably between 20 wt.% and 90 wt.%, of cellulosic filaments and between 5 wt.% and 85 wt.%, particularly preferably between 10 wt.% and 80 wt.%, of short fibers.

[0026] A composite nonwoven fabric with a particularly advantageous feel, high softness, and flexibility can be provided if the composite nonwoven fabric is essentially free of binders not naturally occurring in wood, especially synthetic ones. Such binder-free composite nonwoven fabrics according to the invention can be particularly well suited for a variety of applications, such as skin-friendly hygiene products. Composite nonwoven fabrics containing binders, on the other hand, can exhibit very high stiffness and low softness, which limits the range of applications for such products.

[0027] All types of cellulosic short-cut fibers, such as natural cellulose fibers, viscose, modal, lyocell, or cupro fibers, as well as chemically modified cellulose fibers, can be used as bio-based, biodegradable short fibers for the composite nonwoven fabric according to the invention. Furthermore, all types of fibers from wood-containing pulps, such as mechanically pulped pulps or groundwood, e.g., MP (mechanical pulp), TMP (thermo-mechanical pulp), CTMP (chemo-thermo-mechanical pulp), etc., are suitable as short fibers. In addition, the short fibers can consist of all types of fibers from wood-free pulps, such as chemically pulped CP (chemical pulp) produced using sulfite, sulfate, or other processes. Furthermore, all types of cellulose obtained from wood or other plants, such as grasses, bamboo, algae, cotton or cotton linters, hemp, flax, starch-based fibers, etc., are also possible as short fibers.Furthermore, all types of cellulose produced from recycled textiles or nonwovens, or recycled cellulosic fibers as short fibers, can also be used.

[0028] Alternatively, starch fibers are also suitable as bio-based, biodegradable short fibers for the composite nonwoven fabric according to the invention.

[0029] A particularly homogeneous composite nonwoven fabric can be created if the short fibers have a length between 0.5 mm and 15 mm. Shorter fibers cannot be reliably retained in the composite nonwoven fabric, while longer fibers can lead to inhomogeneous products. A length of the short fibers between 1 and 12 mm is particularly preferred.

[0030] Furthermore, the composite nonwoven fabric can contain non-fibrous functional additives, such as activated carbon, superabsorbents, particulate colorants and fillers (clays, ground nonwoven or wood waste), etc. This allows the composite nonwoven fabric to be endowed with certain additional properties, such as high water absorption capacity, etc.

[0031] Furthermore, the nonwoven fabric can be treated before or after drying with additives that modify product properties or facilitate processing, such as antistatic agents or other additives.

[0032] The nonwoven fabric according to the invention is obtainable by a method according to claim 1. If the nonwoven fabric is produced according to the method according to claim 1, the special properties of the nonwoven fabric result from the process steps as described below.

[0033] The invention also aims to provide a simple and reliable method of the type mentioned at the outset for the production of a composite nonwoven fabric according to claim 14.

[0034] The problem is solved with regard to the process by applying the short fibers to the filaments of the spunbond nonwoven fabric in a state that has never been dried.

[0035] In this process, a cellulosic spinning mass is extruded into filaments through a multitude of die holes in at least one spinneret, and the filaments are then stretched in the extrusion direction. The filaments are laid down in a tangled position on a perforated conveyor to form a spunbond nonwoven fabric. Short fibers are added to the spunbond nonwoven fabric in a further step to create the composite nonwoven.

[0036] Surprisingly, it has been shown that a composite nonwoven fabric according to the invention with a mixing zone between the filaments of the spunbond nonwoven and the short fibers can be created if the spunbond nonwoven is exposed to the short fibers while still undried, i.e., while the filaments of the spunbond nonwoven are still highly swollen. Due to the softness and deformability of the undried spunbond nonwoven, as well as the weak bonds between the filaments within it, mutual interpenetration of the filaments of the spunbond nonwoven and the short fibers can occur, thus creating the mixing zone in the composite nonwoven fabric.In a subsequent drying process, hydrogen bonds can form between the spunbond filaments and the short fibers, ensuring the strong cohesion and high strength of the composite nonwoven, which, conversely, would not be possible with composite nonwovens made of thermoplastic nonwovens and cellulose fibers (as described, for example, in WO 2012 / 090130).

[0037] This process makes it possible to obtain a fully biodegradable composite nonwoven fabric with basis weights above 10 g / m². Depending on the positioning of the short fiber feed and the parameters of any additional water jet bonding, composite nonwoven fabrics can be obtained in which either the process-related layer structure is still recognizable or the added short fibers are homogeneously distributed throughout the thickness of the composite nonwoven fabric.

[0038] A particularly simple and reliable method for producing the composite nonwoven fabric can be provided if the filaments of the spunbond nonwoven are exposed to a suspension of short fibers while still dry. The short fibers can be easily suspended in an aqueous transport medium, especially an aqueous solution or water, and thus applied to the formed spunbond nonwoven in a technically straightforward manner.

[0039] Preferably, the suspension contains between 0.01 wt.% and 2.00 wt.% short fibers. This prevents transport problems with the suspension, particularly clogging of lines or nozzles. Furthermore, it has been found that impregnating the spunbond with such a small amount of short fibers is sufficient to guarantee the desired loading of the spunbond with a defined quantity of short fibers. The reliability of the process can thus be further increased.

[0040] The filaments of the spunbond nonwoven fabric can advantageously be impregnated with a suspension of short fibers during washing. This allows the short fibers to be suspended directly in the washing solution or water, or the suspension to be used as the washing solution itself. This enables the impregnation of the spunbond nonwoven fabric with short fibers to be integrated into a standard spunbond nonwoven washing line. This results in a particularly economical process.

[0041] Alternatively or in addition to the washing process described above, the filaments of the spunbond can also be treated with the suspension during the spunbond formation process. For example, the suspension can be applied directly to the freshly formed spunbond or to the freshly extruded filaments.

[0042] A particularly simple and versatile method for producing the composite nonwoven fabric can be achieved by exposing the filaments of the spunbond nonwoven, while they are still dry, to an airflow containing short fibers. Providing this airflow allows for a simple, homogeneous distribution of the short fibers. Furthermore, the airflow containing the short fibers can be reliably introduced at many points in the process, resulting in exceptionally easy handling.

[0043] After extrusion from the spinneret, the filaments can be subjected to a drawing air stream for stretching. Short fibers can simply be added to this stretching air stream to impregnate the filaments of the still-undried spunbond. This process can therefore be implemented technically easily and without expensive modifications in an existing cellulose spunbond production line.

[0044] After the filaments are coated with the short fibers, the composite nonwoven can undergo at least one further treatment step. This can involve, for example, washing the composite nonwoven to remove solvents from the cellulosic spunbond.

[0045] Furthermore, the composite nonwoven can undergo water jet bonding in a treatment step, in which it is additionally bonded by (high-pressure) water jets. Water jet bonding can also help to increase the physical mixing between the filaments of the composite nonwoven and the short fibers in the mixing area, thus improving the integrity of the composite nonwoven.

[0046] Furthermore, the composite nonwoven fabric can be subjected to waterjet embossing or waterjet perforation in a single treatment step. This allows patterns, three-dimensional structures, and perforations to be introduced into the composite nonwoven fabric.

[0047] After washing or water jet bonding, the composite nonwoven fabric can be subjected to further drying in a treatment step to remove residual moisture from the composite nonwoven fabric.

[0048] In an optional treatment step, the composite nonwoven fabric can also be subjected to a crepe process, which gives the composite nonwoven fabric a crepe structure.

[0049] A reliable process for producing a multilayer composite nonwoven fabric is achieved when the cellulosic spinning mass is extruded into filaments through a multitude of die holes in at least one second spinneret, and the filaments are then stretched in the extrusion direction. The filaments from the second spinneret are laid down in a random arrangement on the conveying device above the spunbonded nonwoven fabric, which already contains the short fibers, to form a second spunbond nonwoven within the composite fabric. In this way, a second cellulosic spunbond nonwoven is deposited above the already formed first spunbond nonwoven fabric, which has already been impregnated with the short fibers and forms a blending zone with them.

[0050] The second cellulosic spunbond is applied directly to the short fiber layer, thus forming a purely physical bond with it. Preferably, the second cellulosic spunbond can have different internal and structural properties than the first spunbond, in particular a different basis weight, different air permeability, different filament diameters, etc.

[0051] On the second cellulosic spunbond, a second layer of short fibers can be applied while still dry. This layer forms a second mixing zone with the second spunbond, in which the filaments of the second spunbond are physically mixed with the short fibers of the second layer. Reference is made to the description above. The short fibers of the second layer can also differ from those of the first layer, thus enabling the production of a composite nonwoven fabric with a particularly versatile range of applications.

[0052] In the same way as previously described for the second spunbond and the second layer of short fibers, third and further cellulosic spunbonds or layers of short fibers can also be applied to the already formed composite nonwoven.

[0053] The process according to the invention can be used particularly advantageously for the production of a composite nonwoven fabric with a cellulosic spunbond made from lyocell spunbond. Lyocell spunbond is a solution of cellulose in a direct solvent.

[0054] The direct solvent may preferably be a tertiary amine oxide, preferably N-methylmorpholine N-oxide (NMMO) in aqueous solution, or an ionic liquid in which cellulose can be dissolved without chemical derivatization.

[0055] The cellulose content in the spinning mass can be between 4% and 17%, preferably between 5% and 15%, and particularly preferably between 6% and 14%.

[0056] The internal structure of the spunbond nonwoven can also be reliably controlled if the filaments extruded from the spinneret are at least partially coagulated. For this purpose, the filaments can preferably be treated with a water-based coagulation fluid, which is preferably applied to the filaments in the form of liquid, gas, mist, vapor, etc.

[0057] If NMMO is used as a direct solvent in the lyocell spinning mass, the coagulation fluid can be a mixture of fully demineralized water and 0 wt.% to 40 wt.% NMMO, preferably 10 wt.% to 30 wt.% NMMO, and particularly preferably 15 wt.% to 25 wt.% NMMO. This allows for particularly reliable coagulation of the extruded filaments.

[0058] The process according to the invention can be carried out by an apparatus for producing a composite nonwoven fabric, the apparatus comprising: a spinning mass production unit for producing a cellulosic spinning mass, at least two spunbond lines for producing the cellulosic spunbond from the spinning mass, each spunbond line comprising at least one spinneret for extruding the spinning mass into filaments, at least one coagulation system for at least partial coagulation of the filaments, and a conveying device for depositing the filaments and forming the spunbond, a washing unit, optionally a water jet bonding unit, a dryer, optionally a creping unit, and a winder. Furthermore, according to the invention, the apparatus comprises a wet lay-up unit or a dry lay-up unit for impregnating the cellulosic spunbond with short fibers, wherein the wet lay-up unit or the dry lay-up unit is a wet lay-up unit or a dry lay-up unit, respectively.The drying device for the short fibers is provided between two spunbond nonwovens. Brief description of the characters

[0059] Preferred embodiments of the invention are described in more detail below with reference to the drawings. They show: Fig. 1 a schematic representation of a method for producing a composite nonwoven fabric (not according to the invention), Fig. 2 a schematic representation of the method according to the invention for producing a composite nonwoven fabric according to a first embodiment, Fig. 3 a schematic representation of the method according to the invention for producing a composite nonwoven fabric according to a second embodiment, Fig. 4 an electron microscope image of a first composite nonwoven fabric (not according to the invention) and, Fig. 5 an electron microscope image of a second composite nonwoven fabric (not according to the invention). Ways to implement the invention

[0060] Fig. 1Figure 1 shows a process 100 for producing a composite nonwoven fabric 1 and an apparatus 200 for carrying out the process 100 according to an embodiment of the disclosure. In a first process step, a spinning mass 2 is produced from a cellulosic raw material and fed to a spinneret 3 of the apparatus 200. The cellulosic raw material for producing the spinning mass 2, which is not shown in detail in the figures, can be a pulp suitable for producing lyocell fibers from wood or other plant-based raw materials. However, it is also conceivable that the cellulosic raw material consists at least partially of production waste from spunbond nonwoven production or recycled textiles. The spinning mass 2 is a solution of cellulose in NMMO and water, wherein the cellulose content in the spinning mass 2 is between 3 wt.% and 17 wt.%.

[0061] In the next step, the spinning mass 2 is extruded through a multitude of nozzle holes in the spinning nozzle 3 to form filaments 4. The extruded filaments 4 are then accelerated and stretched in a drawing air stream in the extrusion direction, although this process is not shown in detail in the figures.

[0062] In one embodiment, the drawing airflow can exit between the nozzle holes of the spinneret 3. In another embodiment, the drawing airflow can alternatively exit around the nozzle holes. This is not shown in detail in the figures. Such spinnerets 3 with drawing devices for generating a drawing airflow are known from the prior art (US 3,825,380 A, US 4,380,570 A, WO 2019 / 068764 A1).

[0063] In the preferred embodiment shown, the extruded and stretched filaments 4 are also treated with a coagulant from a coagulation device 5. This coagulant is generally water or an aqueous solution in the form of liquid, mist, or vapor. Contact of the filaments 4 with the coagulant at least partially coagulates or regenerates them, which in particular reduces adhesion between the individual extruded filaments 4.

[0064] The stretched and at least partially coagulated filaments 4 are then deposited in a tangled position on the tray 6 of a conveying device 7 to form a cellulosic spunbond nonwoven 8.

[0065] After forming, the spunbond nonwoven fabric 8 is conveyed via conveyor belt 9 through a washing unit 10, in which it is washed to remove residues of the solvent, namely the NMMO contained in the spinning mass 2. In a preferred embodiment, the washing unit 10 is a multi-stage countercurrent washing unit with several washing stages 11, wherein fresh washing solution 12 is supplied to the last stage and the increasingly used washing solution of a washing stage 11 is passed on to the preceding washing stage 11.

[0066] After washing 10, the spunbond nonwoven fabric 8 is passed through a wet-setting unit 13, in which the never-dried spunbond nonwoven fabric 8 is impregnated with cellulosic short fibers 14. The short fibers 14 are present in a suspension 15, and the suspension 15 is applied or sprayed onto the spunbond nonwoven fabric 8. The suspension 15 has a short fiber content of between 0.01 and 2.00 wt.%. By providing a separate wet-setting unit 13 in the process 100 or the device 200, independent operation of the short fiber feed from the surrounding spunbond production can be ensured.

[0067] During the application of the suspension 15 containing the short fibers 14 to the never-dried spunbond nonwoven fabric 8, a layer of short fibers 14 is formed over the nonwoven fabric 8, thereby creating the composite nonwoven fabric 1. A mixing zone also forms within the composite nonwoven fabric, in which the filaments of the nonwoven fabric 8 and the short fibers 14 are mixed purely physically and therefore hold together without any chemical bond. Following the wet lay-up unit 13, the composite nonwoven fabric 1 is then subjected to water jet bonding 16 in a subsequent step. During this water jet bonding 16, a further bond is created between the nonwoven fabric 8 and the layer of short fibers 14, whereby the physical bonds between the filaments of the nonwoven fabric 8 and the short fibers 14 are further strengthened by mixing, in particular by interlocking, entanglement, static friction, etc.

[0068] To finally remove the remaining moisture from the composite nonwoven fabric 1 and obtain a composite nonwoven fabric 1 ready for packaging, the composite nonwoven fabric 1 is subjected to drying 17 following water jet bonding 16.

[0069] Finally, the process 200 is completed by optionally winding 18 and / or packaging the finished composite nonwoven fabric 1.

[0070] In Fig. 2 A first embodiment of the method 101 or the device 201 according to the invention is shown. In contrast to the one described in Fig. 1In the illustrated embodiment, the suspension 15 containing the short fibers 14 is not fed to a separate wet lay-up device 13. Instead, the short fibers 14 are added to the washing solution 12 at least to one washing stage 11, preferably the last washing stage 11, of the laundry 10 in such a way that the spunbond nonwoven 8 is simultaneously washed and impregnated with the short fibers 14 during washing 10. Regarding the other features, reference is made to the descriptions in [reference to be added]. Fig. 1 referred.

[0071] This represents the technically simplest and also the most economical embodiment of the invention, since only the washing 10 of an existing spunbond nonwovens plant needs to be converted in such a way that one or more of the existing washing stages 11, in addition to their original function of homogeneous distribution and application of the washing solution 12, also serve to impregnate the spunbond nonwovens 8 with suspensions 15 made of short fibers 14.

[0072] The suspension 15 contains short fibers 14 in the concentration range between 0.01 wt% and 2.00 wt% and fiber lengths from 0.5 mm to 20 mm. In another embodiment, which is not shown in the figures, the short fibers 14 can also be mechanically fibrillated fibers or cellulose fibers, in which case a refiner is additionally required for fibrillating the short fibers.

[0073] The suspension 15 is preferably formed by suspending the short fibers 14 in fresh water. Preferably, the suspension 15 is applied to the spunbond nonwoven 8 only in the last two washing stages 11 in order to minimize any shift in the solvent concentration distribution in the washing solution throughout the entire wash 10 and thus avoid, as far as possible, additional technical requirements and increased operating costs associated with the treatment or concentration of the solvent-containing wash water. Furthermore, by adding the suspension 15 to the wash 10, the amount of washing solution 12 required in the wash 10 can be reduced accordingly.

[0074] In another version, which is in Fig. 2As shown in the dashed line, a second spinneret 23 can be provided after the first spinneret 3, through which the spinning mass 2 is also extruded into filaments 24. The filaments 24 are then deposited on the conveyor 7 above the first spunbond 8 to form a second spunbond.

[0075] The suspension 15 containing short fibers 14 is applied to the first spunbond 8 between the first spinneret 3 and the second spinneret 23 to create the layer of short fibers 14. The second spunbond is then laid directly onto the layer of short fibers 14, forming a multilayer composite nonwoven fabric 1 with several cellulosic spunbonds 8 and short fibers 14. Optionally, the composite nonwoven fabric 1 can be further treated with short fibers 14 during washing 10, as described above.

[0076] In another embodiment, the multilayer composite nonwoven 1 is treated in the subsequent water jet bonding 16 in such a way that the layer structure of alternating spunbond nonwovens 8 and short fibers 14 can be largely rendered unrecognizable, thus creating an even more extensive mixing area in the composite nonwoven 1.

[0077] For all of the aforementioned embodiments of the inventive method 100, 101, significant savings in energy and fresh water requirements result compared to the prior art, since a) already moist, never dried spunbond nonwoven 8 is used and no already dried substrate is re-wetted by the addition of the short fibers 14 in the form of a suspension 15, b) the added, wet short fibers 14 introduce less water per unit mass of cellulose into the still moist nonwoven product than an equivalent amount of undried cellulosic spunbond nonwoven, c) the requirement of washing solution 12 in the washing 10 can be reduced by the amount of water supplied as suspension 15, and d) the wastewater from a water jet bonding 16 can be used as fresh water for the washing 10 or for the production of the suspension 15.

[0078] Furthermore, in another embodiment, the equipment required for process 101 can be further simplified by performing the water jet bonding 16 together with the washing 10 on the conveyor belt 9. The latter can also have a three-dimensional embossed structure that can be transferred to the spunbond nonwoven fabric by the water jet treatment.

[0079] In Fig. 3 A second embodiment of the inventive method 102 and the device 202 is shown. In this embodiment, the short fibers 14 are, in contrast to those in the Fig. 1 and 2 In the illustrated embodiments, the suspension 15 is not applied to the spunbond nonwoven 8, but rather, using Airlay technology, it is applied to the spunbond nonwoven 8 in the form of an airflow 26. Regarding the further features of the process 102, reference is made to the descriptions of the Fig. 1 and 2 referred.

[0080] The supply of the airflow 26 containing short fibers 14 to the spunbond 8 can take place between two spinnerets 3, 23 as well as before, during and / or after washing 10.

[0081] In order to enable a homogeneous distribution of the short fibers 14 in the airflow 26 and to transport the short fibers 14 to the point of application, special units for opening the fibers and for transporting the short fibers 14 are provided, which, however, have not been shown in detail in the figures.

[0082] In another embodiment, not shown in detail in the figures, the short fibers 14 can also be fed directly to the drawing devices in the spinnerets 3, 23 and thus laid directly onto the filaments 4 of the spunbond 8 by the drawing airflow. The short fibers 14 are thereby directly mixed with the filaments 4 in the spunbond, creating a mixing zone extending over the entire thickness of the composite nonwoven 1. For this purpose, in one embodiment, a secondary airflow containing the short fibers 14 can be introduced below the spinnerets 3, 23, where it is combined with the drawing airflow to impregnate the filaments 4 with the short fibers 14.

[0083] In a further embodiment of the disclosure, which is not according to the invention, a multilayer spunbond nonwoven 8 is produced by two spinnerets 3, 23 arranged one behind the other, but is separated back into the two spunbond layers before the short fibers 14 are applied, with the short fibers 14 then being introduced between the two spunbond layers – either as a suspension 15 or dry in an air stream 26. Afterwards, the two spunbond layers are joined again and the resulting composite nonwoven 1 is bonded by a water jet bonding process 16.

[0084] In order to ensure the complete biodegradability of the composite nonwovens 1 according to the invention, the cellulosic short fibers introduced by means of the embodiment variants described above consist exclusively of the material classes of industrially produced pulps, pulps recovered from recycling processes, cellulosic short-cut fibers, cellulosic natural fibers or of all conceivable combinations of these material groups.

[0085] In the Figs. 4 and 5 Electron microscope images of composite nonwovens are shown 51, 61.

[0086] Fig. 4 Figure 1 shows a composite nonwoven fabric 51 in which a limited mixing zone 56 is formed between a layer 52 of short fibers 53 (in this case, cellulose fibers) and a cellulosic spunbond nonwoven 54 (lyocell spunbond nonwoven). In the mixing zone 56, the filaments 55 of the spunbond nonwoven 54 are physically mixed with the short fibers 53.

[0087] Fig. 5 Figure 1 shows a composite nonwoven fabric 61 which no longer exhibits a recognizable layer structure. Here, the cellulosic spunbond nonwoven fabric 64 (lyocell spunbond nonwoven) essentially completely penetrates the layer 62 of short fibers 63 (cellulose fibers). The mixing zone 66 thus extends over the entire thickness of the composite nonwoven fabric 61. The short fibers 63 are therefore homogeneously distributed throughout the composite nonwoven fabric 61. Examples (not according to the invention)

[0088] The following section illustrates the advantages of revelation using several examples.

[0089] The following measurement methods were used to determine various parameters of the produced composite nonwovens: basis weight

[0090] The basis weight indicates the mass of the composite nonwoven fabric per unit area. The basis weight is determined according to the standard NWSP 130.1.R0 (15). Tensile strength / elongation

[0091] The tensile strength values ​​indicate the robustness of the wipe during wiping and when removed from the packaging. Higher tensile strength therefore results in greater resistance to damage under tensile stress. Low elongation is helpful when removing the wipes from the packaging and helps maintain a good grip on the wiper hand. Tensile strength and elongation are determined according to DIN EN 29073 Part 3 / ISO 9073-3 (1992 version). Wicking

[0092] The wicking test provides information about the distribution rate of a liquid or lotion across the nonwoven fabric surface in both machine and cross directions. The values ​​given below refer to water wicking heights in the nonwoven fabric over a period of 300 seconds. The wicking height is determined according to NWSP 010.1.R0 (15). Fleece conditioning

[0093] Before each measurement, the samples were conditioned at 23 °C (± 2 °C) and 50 % (± 5 %) relative humidity for a period of 24 h. Electron microscopy

[0094] The electron microscopy images were acquired using a Thermo Fisher Quanta 450 (5kV, Spot 3, WD10, EDT) or Thermo Fisher Scientific Phenom ProX instrument. Site selection was randomized.

[0095] The composite nonwovens described below were produced according to the inventive process by generating single-layer lyocell spunbond nonwovens with basis weights of 20-45 g / m² and loading them with a 0.8-1.5% cellulose suspension using an additional wet-laying device during washing. The composite nonwoven was then treated by water jet bonding using three pressure stages (with pressures between 40 bar and 100 bar), dried to a final moisture content of less than 10%, and obtained as rolls with basis weights of 30-80 g / m². The nozzle strips used in the water jet bonding process had a single-row hole pattern with hole diameters of 0.12 mm and a hole spacing of 13 holes / cm.

[0096] The detailed parameters of the tests carried out and the measured properties of the associated composite nonwovens are shown below in Table 1. Table 1: Test parameters and product properties Example / Product 1 2 3 4 5 Basis weight of the substrate [g / m²< ] 45 20 20 20 20 Solid content of the suspension [%] 0,5 0,7 0,8 1,0 1,2 Water jet hardening pressure p1 [bar] 40 70 40 40 40 Water jet hardening pressure p2 [bar] 40 80 40 40 40 Water jet hardening pressure p3 [bar] 60 100 70 40 40 Basis weight of the final product [g / m²< ] 70 45 45 45 60 Tensile strength (dry, MD) [N / 5cm] 45 16 30 33 40 Tensile strength (dry, CD) [N / 5cm] 18 7 10 12 15 Tensile strength (wet, MD) [N / 5cm] 14 6 10 11 8 Tensile strength (wet, CD) [N / 5cm] 6 3 5 5 5 Elongation (dry, MD) [% / 5cm] 4 4 4 4 4 Elongation (dry, CD) [% / 5cm] 7 7 7 7 7 Elongation (wet, MD) [% / 5cm] 14 8 8 8 8 Stretch (wet, CD) [% / 5cm] 27 28 18 20 25 Wicking MD [mm] 146 161 149 150 152 Wicking CD [mm] 122 139 132 131 133

[0097] In parallel with the composite nonwovens produced according to the invention, a commercially available composite nonwoven based on a polypropylene nonwoven substrate with incorporated cellulose and a total basis weight of 45 g / m² was investigated with regard to its mechanical properties. With dry tensile strengths of 33 N / 5 cm in the machine direction (MD) and 13 N / 5 cm in the transverse direction (CD), the commercial product exhibits dry strengths comparable to those of the example product 4 listed in Table 1. The strength values ​​provide information about the robustness of the wipe during wiping processes and removal from the packaging, whereby the composite nonwovens produced according to the invention do not require the use of a synthetic carrier nonwoven. In contrast, exclusively wet-laid paper products of comparable basis weight show lower wet tensile strengths of 4–8 N / 5 cm, which are hardly sufficient for the usual use as a wet wipe.

[0098] The previously mentioned, commercially available composite nonwoven fabric, based on a polypropylene nonwoven substrate with incorporated cellulose at a total basis weight of 45 g / m², was also investigated with regard to its liquid absorption capacity: According to the wicking test, significantly lower rise heights of 94 mm in MD and 73 mm in CD were measured, which gives the product according to the invention clear advantages with regard to its loading speed with lotions in conversion processes to commercial wet wipes, i.e. the dry roll material absorbs the lotion much faster during the loading process and the homogeneously distributed liquid within the closed wipe packs shows the formation of a loading gradient due to the weight-related settling of the liquid much more slowly.

Claims

1. Method for producing a composite nonwoven fabric (1) comprising at least one spunbond (8, 54, 64) comprising tangled and essentially endless regenerated cellulosic filaments (4, 55, 65) and at least one layer (52, 62) of bio-based biodegradable short fibres (14, 53, 63), wherein the composite nonwoven fabric (1, 41, 61) has at least one mixing zone (56, 66) in which the filaments (4, 55, 65) of the spunbonded fabric (8, 54, 64) and the short fibres (14, 53, 65) are physically bonded to one another, in which a cellulose-containing spinning mass (2) is extruded through a plurality of nozzle holes of at least one first spinneret (3) to form filaments (4) and through a plurality of nozzle holes of at least one second spinneret (23) to form filaments (24), and the filaments (4, 24) are each stretched in the extrusion direction, wherein the filaments (4) of the first spinneret (3) are being deposited in a tangled state on a perforated conveyor device (7) to form a first spunbond nonwoven fabric (8), and in which, to form the composite nonwoven fabric (1), short fibres (14) are added to the first spunbond nonwoven fabric (8) in a state in which it has never been dried, and the filaments (24) of the second spinneret (23) are added to the short fibres (14) to form a second spunbond nonwoven fabric (10), and in which the filaments (4) of the first spinneret (3) are stretched in the extrusion direction to form a first spun (8) in the undried state, and wherein the filaments (24) of the second spinneret (23) are deposited in a tangled state in the composite nonwoven fabric in the composite nonwoven fabric above the first spunbonded fabric (8) supplied with the short fibres on the conveyor device to form a second spunbonded fabric.

2. Method according to claim 1, characterised in that the filaments (4) of the first spunbonded fabric (8) are fed, in a state which has never been dried, with a suspension (15) of the short fibres (14).

3. Method according to claim 2, characterised in that the suspension (15) contains between 0.01% by weight and 2.00% by weight of short fibres (14).

4. Method according to one of claims 2 to 3, characterised in that the filaments (4) of the spunbonded fabric (8) are exposed to the suspension (15) during the formation of the spunbonded fabric (8).

5. Method according to one of claims 1 to 4, characterised in that the filaments (4) of the spunbonded fabric (8) are exposed to an air stream (26) containing the short fibres (14) while in a state which has never been dried.

6. Method according to one of claims 1 to 5, characterised in that the composite nonwoven fabric (1) is subjected to at least one treatment step after the filaments (4) have been impregnated with the short fibres (14), wherein the treatment step is selected from the group, consisting of: a water jet consolidation (16), a water jet embossing, a water jet perforation, a washing process (10) and a drying process (17).

7. Method according to one of claims 1 to 6, characterised in that the spinning mass (2) is a solution of cellulose in a direct solvent, in particular a tertiary amine oxide.

8. Method according to one of claims 1 to 7, characterised in that the filaments (4) get at least partially coagulated after extrusion from the at least one spinneret (3).

9. Process according to one of the preceding claims, characterised in that the short fibres (14, 53, 63) are cellulosic short fibres (14, 53, 63) and the composite nonwoven fabric (1, 51, 61) has a cellulose content of at least 93% by weight, in particular at least 95% by weight, preferably at least 97% by weight, in the absolutely dry state.

10. Method according to one of the preceding claims, characterised in that the composite nonwoven fabric (1, 51, 61) contains between 10 wt.% and 99 wt.%, in particular between 15 wt.% and 95 wt.%, preferably between 20 wt.% and 90 wt.%, of cellulosic filaments (4, 55, 65) of the spunbonded nonwoven fabric (8, 54, 64) and between 1 wt.% and 90 wt.%, in particular between 5 wt.% and 85 wt.%, preferably between 10 wt.% and 80 wt%, of short fibres (14, 53, 63).

11. Method according to one of the preceding claims, characterised in that the composite nonwoven fabric (1, 51, 61) is essentially free of binding agents not naturally occurring in wood.

12. Method according to one of the preceding claims, characterised in that the short fibres (14, 53, 63) are selected from the group comprising: natural cellulose fibres, pulp fibres, viscose, modal, cupro and lyocell fibres, chemically modified cellulose fibres, recycled cellulose fibres, starch fibres.

13. Method according to one of the preceding claims, characterised in that the short fibres (14, 53, 63) have a length between 0.5 mm and 15 mm, in particular between 1 and 12 mm.

14. Composite nonwoven fabric comprising at least two spunbonded nonwovens (8, 54, 64) which comprise regenerated cellulosic filaments (4, 55, 65) laid in a tangled arrangement and are essentially endless, and at least one layer (52, 62) of bio-based biodegradable short fibres (14, 53, 63), characterised in that the composite nonwoven fabric (1, 51, 61) can be obtained by a method (100, 101, 102) according to claim 1.

15. Plant for carrying out a process according to claim 1, comprising a spinning mass production for producing a cellulosic spinning mass, at least two spunbond plants for producing the cellulosic spunbond from the spinning mass, each spunbond plant comprising at least one spinneret (3, 23) for extruding the spinning mass into filaments (4, 24), at least one coagulation system for at least partial coagulation of the filaments and a conveyor device for depositing the filaments and forming the spunbond, a washing unit, optionally a water jet consolidation unit, a dryer, optionally a creping device and a winder, characterised in that the device has a wet laying device or a dry laying device for applying short fibres to the cellulosic spunbonded fabric, wherein the wet laying device or the dry laying device for the short fibres is provided between two spunbonded fabric systems.