Method and installation for producing a two-layer nonwoven

Abstract

The invention relates to a method and an installation for producing a two-layer nonwoven, wherein a supply unit (2) is used to supply synthetic staple fibers (2a) to a carding machine (3) for cleaning and aligning purposes, and the card web (3a) exiting the carding machine (3) is consolidated in a first consolidation process in order to form a nonwoven (4a) and is deposited on a circulating belt (5). Further along the material transport direction, short wetlaid fibers (6a) are deposited on the upper face of the nonwoven (4a) by means of a second supply unit (6) such that a two-layer nonwoven (9) is produced, the individual layers (4a, 6a) being connected together and dried in a second subsequent consolidation process.

Description

[0001] Title: Process and plant for producing a two-layer nonwoven

[0002] Description

[0003] The invention relates to a method and a plant for producing a two-layer nonwoven according to the preamble of claims 1 and 11. Furthermore, the invention relates to a two-layer nonwoven.

[0004] In hygiene and cosmetic products, the nonwoven insert is often made up of multiple layers, with each layer serving a different purpose. It is advantageous if the fluid-absorbing layer is bonded to a carrier layer but the fibers do not mix to improve fluid drainage or storage. Since the fluid-absorbing layer is often made from short fibers such as cellulose, which have insufficient bonding with each other, a high proportion of these short fibers are washed out when the two layers are subsequently bonded together using water jets. The fluid-absorbing layer, in turn, is not designed to quickly and evenly distribute the fluid it absorbs. For this purpose, the carrier layer acts as a distribution layer to evenly distribute the fluid into the absorption layer, also known as the ADL (Acquisition Distribution Layer).The fibers of this carrier or distribution layer therefore have only a low liquid absorption capacity and are often made of continuous plastic fibers that are further processed into staple fibers. According to the current state of the art, the liquid-absorbing layer and the distribution layer are not manufactured in an integrated, single-stage plant concept, but rather separately in a two-stage process and then bonded together. In the known single-stage processes, a high proportion of the fibers are washed out of the distribution layer when the layers are bonded together, as the necessary basic strength is lacking.

[0005] EP4199872 A2 describes a comparable product in which the absorbent layer consists of cross-linked cellulose fibers, which restricts the process too much to a single raw material. The use of a variety of absorbent fibers, which can also consist of recycled fibers or fiber blends, is advantageous.

[0006] According to the state of the art, it is known to apply a layer of loose short fibers to a carded PET nonwoven, which is applied from a meltblown system, a wetlaid system, or some other method. Both layers are bonded using hydroentanglement. The disadvantage is that hydroentanglement can cause the PET carrier nonwoven to blur, thus flushing out a high proportion of fibers. If a bonded nonwoven is used for the carrier or distribution layer, it must currently be supplied from a second system, which makes the process inflexible. This requires an unwinding station instead of the carding machine and the first bonding device, which shortens the system but does not make it more flexible.

[0007] The object of the invention is the production of a two-layer nonwoven fabric with a first layer of a pre-consolidated carded nonwoven fabric made of synthetic fibers as a carrier or distribution layer, and a second layer of short fibers with high liquid absorption as an absorption layer in a one-step process.

[0008] The invention is achieved by a method according to claim 1, a system according to claim 11 and by a two-layer nonwoven according to claim 16.

[0009] The inventive method for producing a two-layer nonwoven fabric provides a first feed unit for synthetic staple fibers to a carding machine, which are cleaned and aligned in the carding machine. The fiber web emerging from the carding machine is consolidated into a nonwoven fabric in a first consolidation step and deposited on a circulating belt. Further in the material transport direction, wet-laid short fibers are deposited on the upper side of the nonwoven fabric by means of a second feed unit, creating a two-layer nonwoven fabric in which the individual layers are bonded together and dried in a second subsequent consolidation step. This produces a multilayer ADL in a single-step process with pre-consolidated carded synthetic staple fibers as the carrier or distribution layer and a wet-laid pulp, modified pulp, or pulp-fiber blend as the absorption layer.

[0010] The first bonding step can be thermal bonding, in which the synthetic fibers are bonded using bicomponents mixed in as binders. Thermal bonding prevents the synthetic fibers from washing out, which would inevitably occur with hydroentanglement. At the same time, high strength is achieved for the carrier or distribution layer onto which the liquid-absorbing layer is applied.

[0011] Because the synthetic fibers are at least partially hollow fibers, with the hollow space amounting to between 5 and 20% of the cross-section, the basis weight can be ensured while maintaining sufficient stability. The synthetic fibers preferably have a fiber length of 20 to 50 mm with a fiber density of 4 to 10 dtex. This creates a layer of carded nonwoven fabric with high water permeability.

[0012] Because the nonwoven fabric made of synthetic staple fibers has a basis weight of 20 to 60 g / m 2 the carrier or distribution layer can be made very easily.

[0013] The wet-laid fibers have a fiber length of 1 to 12 mm, so that a variety of different natural or synthetic fibers can be processed.

[0014] The wet-laid fibers can consist entirely of pulp or other natural fibers, or of secondary fibers, recycled fibers or regenerated fibers, so that a biodegradable fiber layer can be produced.

[0015] Alternatively, the wet-laid fibers can consist of a blend of fibers with a high proportion of pulp and a smaller proportion of short synthetic fibers such as polyester, polyamide, polyolefin, polypropylene, viscose, or lyocell. This blend of fiber types can improve the feel and comfort of this layer. If this absorbent layer is to be covered with another layer, the addition of short synthetic fibers can improve the bond to the additional covering layer.

[0016] Preferably, the layer of wet-laid fibers applied to the nonwoven fabric has a basis weight of 30 to 100 g / m 2 This means that the absorbent layer has a higher surface weight than the carrier layer and can therefore absorb a large amount of moisture.

[0017] The second consolidation, which joins the two layers of fibers, can be performed by hydroentanglement, which is operated at a pressure of 20 to 200 bar.2

[0018] The plant according to the invention for producing a two-layer nonwoven, which is operated according to the method described above, comprises a first feed unit designed to feed synthetic fibers to a downstream carding machine. Downstream of the carding machine in the material transport direction, there is a first consolidation unit designed to consolidate the fiber web of the carding machine into a nonwoven, wherein the formed nonwoven is deposited on a circulating belt. The circulating belt is arranged below a second feed unit for short fibers, such that the second feed unit is designed to deposit the short fibers on the upper side of the nonwoven. This creates a two-layer nonwoven, which is bonded together in a subsequent second consolidation unit, as well as a dryer and winder arranged downstream in the material transport direction.The system according to the invention is designed to produce a multilayer ADL with pre-consolidated carded synthetic staple fibers as a carrier or distribution layer and a wet-laid pulp, modified pulp or pulp-fiber mixture as an absorption layer in a one-step process.

[0019] The first consolidation step can be performed by hydroentanglement. This allows a carrier or distribution layer to be produced from a single or multiple fiber components that do not contain any binders or bicomponent fibers.

[0020] Alternatively, the first bonding step can be performed by thermal bonding. For this purpose, a small proportion of bicomponent fibers with a lower melting point are mixed into the fibers (main components) of the carrier or distribution layer, so that the fibers of the main component acquire their structure during thermal bonding. The bicomponent fibers thus create the bond between the fibers of the main component.

[0021] Preferably, the initial consolidation takes the form of calender rolls or thermal bonders. Calender rolls can simultaneously compact and further align the fibers. The thermal bonder has the advantage of high throughput speed, thus achieving high plant productivity.

[0022] The second fiber feed unit can be designed as an inclined wire former or a round wire former, which produces a layer of fibers using a wet-laid process. An inclined wire former has the advantage that the fiber layer can be constructed from one or more layers, with each layer containing a different fiber or fiber blend. The inclined wire former is used for high basis weights and large line widths. Alternatively, a secondary headbox can also be used.

[0023] The use of a cylinder former, in contrast to the classic inclined-wire former, offers the advantage of being more compact and less expensive, consuming less water, and the entire system, including pumps, piping, etc., is smaller and more compact, making it significantly cheaper to operate. Compared to an airlaid system, the cylinder former has the advantage of allowing the wet-laid fibers to be further processed with two smooth or flat surfaces. Due to the smoothed surfaces, a very even material distribution and a very uniform basis weight are achieved, particularly with light and thin wet-laid fibers, which cannot be achieved with other processes (airlaid, meltblown). The use of a cylinder former is particularly advantageous for thin and light layers of wet-laid fibers with a basis weight of 10 to 50 g / m². 2, where uneven thickness has a particularly significant impact. In particular, the processing of pulp fibers cannot be achieved with this level of uniformity using an airlaid system. A further advantage of the cylinder former compared to an airlaid or meltblown system is the wide variety of fibers or fiber blends that can be processed, in terms of length and fiber type. The use of secondary fibers, recycled fibers, and regenerated fibers is particularly advantageous for producing a biodegradable nonwoven, which cannot be processed using an airlaid system.

[0024] The two-layer nonwoven according to the invention comprises a first layer of nonwoven as a carrier or distribution layer and a second layer of short wet-laid fibers as an absorption layer for liquids. The two-layer nonwoven is produced in a single-step process and has a basis weight of 50–160 g / m². 2wherein the first layer consists of synthetic staple fibers with at least 90% by weight PET, and the second layer consists of short wet-laid natural fibers or a mixture of short wet-laid natural fibers with synthetic fibers.

[0025] Further measures improving the invention are described in more detail below together with the description of a preferred embodiment of the invention with reference to the figure.

[0026] It shows:

[0027] Figure 1: A layout of the system according to the invention.

[0028] Figure 1 shows a layout of the system 1 according to the invention, in which fibers 2a are fed to a carding machine 3 by means of a first feed unit 2. In the carding machine 3, the fibers 2a are cleaned and aligned to form a fiber web 3a, which is then consolidated into a nonwoven 4a by means of a first consolidation process. In this exemplary embodiment, the first consolidation process is designed as a thermobonder 4. However, it can also be designed as a calender or hydroentanglement process. The nonwoven 4a is guided from the first consolidation process, here the thermobonder 4, onto a circulating belt 5, which is arranged below a second feed unit 6 for short fibers 6a. The short fibers 6a are deposited on the nonwoven 4a, and both layers are bonded together to form a two-layer nonwoven 9 by means of a bonding station, which can be designed as a hydroentanglement process 7. The two-layer fleece can then be dried in a dryer 10 and wound up by means of a winder 11.

[0029] The fibers 2a fed to the carding machine 3 are synthetic fibers made of plastic, which can be formed at least partially or completely as hollow fibers with one or more cavities. The hollow fibers preferably have a concentric or eccentric cavity across the cross-section, with the cavity amounting to between 5% and 20% of the cross-section. A fiber with multiple cavities or a cavity with a cross-section exceeding 20% ​​usually has reduced stability. This allows a lighter carrier fleece to be produced with the same strength while maintaining the same fiber cross-section. The fiber length is preferably 20-50 mm with 4-10 dtex.

[0030] Depending on the first consolidation device downstream of the carding machine 3, the synthetic fibers can comprise at least a high proportion of at least 90% by weight of polyethylene terephthalate (PET), which is processed from a continuous filament into staple fibers. In addition to the main component, which is preferably PET, the plastic fibers can comprise bicomponent fibers consisting of a small proportion of polypropylene (PP), polyethylene (PE), or other plastic. The decisive factor for the second component is its lower melting point compared to the main component, as the bicomponent can serve as a binder for consolidating the main component. The fiber length of the main component is preferably 20-50 mm with 4-10 dtex. The bicomponent fiber can preferably have a thickness of 1.7 dtex.

[0031] The fibers 2a are cleaned, prepared, and aligned in a carding machine 3 to form a fiber web 3a, which undergoes a first consolidation after the carding machine 3. The consolidation can be implemented as a hydroentanglement or as a thermal process such as calendering or thermal bonding, which is illustrated in Figure 1 by way of example with a thermal bonder 4. In a thermal consolidation process, a bicomponent with a reduced melting point is mixed into the main component of the fibers 2a, which takes over the initial bonding of the main component fiber. In a heat-neutral consolidation process, the fibers 2a can consist entirely of a single material component.

[0032] After the initial consolidation of the fiber web 3a from the carding machine 3, the nonwoven fabric 4a, which forms the carrier or distribution layer of the hygiene product, is deposited on a circulating belt 5. The nonwoven fabric 4a thus has a basic strength with a significantly higher strength in the longitudinal direction than in the transverse direction. For example, the nonwoven fabric can have a longitudinal strength of 70N (md) and a transverse strength of 9N (cd). This ensures that the individual fibers of the nonwoven fabric 4a no longer become blurred or washed out during the subsequent consolidation by means of water jets. The basis weight of the consolidated carrier or distribution layer can be 20 to 60 g / m 2 be.

[0033] A second feed unit 6 is arranged above the circulating belt, with which short fibers for the absorbent layer are applied to the nonwoven 4a. The second feed unit 6 can preferably be designed as a cylinder former or inclined wire former, in which a layer of fibers is produced in a wet process. Alternatively, a secondary headbox can also be used. The wire former has the advantage that the layer of fibers can consist of one or more layers, each of which has a different fiber mixture. In contrast to other processes (inclined wire former, airlaid, meltblown), the use of the cylinder former offers the advantage that the wet-laid short fibers 6a can be further processed with two smooth or flat surfaces. Due to the smoothed surfaces, a uniform material distribution orA uniform basis weight is achieved that cannot be achieved with other processes (airlaid, meltblown). The advantage of the cylinder former over the traditional inclined-wire former is its compactness and low investment and operating costs. In contrast, the application of short fibers using airlaid has the disadvantage that the short fibers can only be water-jet-needled with increased effort, e.g., using binding agents, making it very difficult to produce a biodegradable product.

[0034] The fibers 6a to be applied can consist at least partially of short fibers with a fiber length of 1 to 3 mm, preferably 1 to 12 mm, such as 100% pulp or other natural fibers that have a high water retention capacity and are preferably biodegradable. The use of secondary fibers, recycled fibers, or regenerated fibers is also possible and advantageous, as these are biodegradable. The fibers 6a to be applied can consist of a mixture of fibers with a high proportion of pulp and a smaller proportion of short synthetic fibers with a fiber length of 1 to 3 mm, preferably 1 to 12 mm, such as polyester, polyamide, polyolefin, polypropylene, viscose, or lyocell. The basis weight of the layer of short fibers 6a can preferably be 30 to 100 g / m 2 be.

[0035] The subsequent hydroentanglement process 7 can be operated in one or more stages at a pressure of 20 - 200 bar, whereby a suction device 8 can be arranged below the circulating belt 5 to suck away the water from the hydroentanglement process 7. The first consolidation of the fiber web 3a in the first consolidation device has the advantage that the staple fibers 2a are not washed out in the hydroentanglement process 7. The consolidated two-layer web 9 then passes through a dryer 10, which can be designed as a drum dryer or belt dryer. After drying 10, the two-layer web 9 can be wound onto a winder 11 or directly processed further in subsequent system components.

[0036] An advantage of the inventive method and the associated system lies in the production of a multilayer ADL with pre-consolidated carded PET fibers as the carrier or distribution layer and a wet-laid pulp, modified pulp, or pulp-fiber blend as the absorption layer in a single-step process. The layer of fibers (2a) can be prepared with bicomponent fibers, so that a carded nonwoven (4a) is created by thermal bonding, onto which the layer of short fibers is applied, and both layers are bonded together without any fiber flushing. Reference numerals

[0037] 1 system

[0038] 2 first feed unit

[0039] 2a Fibers

[0040] 3 junk

[0041] 3a Fiber pile

[0042] 4 thermal bonders

[0043] 4a fleece

[0044] 5 volumes

[0045] 6 second feed unit

[0046] 6a short fibers

[0047] 7 Hydroentanglement

[0048] 8 Extraction

[0049] 9 two-layer fleece

[0050] 10 dryers

[0051] 11 winders

Claims

Patent claims 1. A method for producing a two-layer nonwoven fabric (9), in which synthetic staple fibers (2a) are fed to a carding machine (3) for cleaning and alignment by means of a first feed unit (2), and the fiber web (3a) running out of the carding machine (3) is consolidated into a nonwoven fabric (4a) in a first consolidation and laid down on a circulating belt (5), and further in the material transport direction short wet-laid fibers (6a) are laid down on the upper side of the nonwoven fabric (4a) by means of a second feed unit (6), so that a two-layer nonwoven fabric (9) is produced, in which the individual layers (4a, 6a) are bonded to one another and dried in a second subsequent consolidation.

2. Method according to claim 1, characterized in that the first consolidation is carried out as a thermal consolidation, in which the synthetic fibers are consolidated by means of admixed bicomponents as binders.

3. Method according to claim 1, characterized in that the synthetic fibers (2a) are at least partially formed as hollow fibers, the hollow space being between 5-20% of the cross section.

4. Method according to one of claims 1 to 3, characterized in that the synthetic fibers (2a) have a fiber length of 20-50mm with 4-10dtex.

5. Method according to claim 1, characterized in that the nonwoven fabric (4a) made of synthetic staple fibers has a basis weight of 20 to 60 g / m 2 has.

6. Method according to claim 1, characterized in that the wet-laid fibers (6a) have a fiber length of 1 to 12 mm.

7. Method according to claim 1, characterized in that the wet-laid fibers (6a) consist entirely of pulp or other natural fibers, or of secondary fibers, recycled fibers or regenerated fibers.

8. Method according to claim 1, characterized in that the wet-laid fibers (6a) consist of a mixture of fibers with a high proportion of pulp and a smaller proportion of short synthetic fibers such as polyester, polyamide, polyolefin, polypropylene or viscose or lyocell.

9. Method according to claim 1, characterized in that the layer of wet-laid fibers (6a) applied to the nonwoven (4a) has a basis weight of 30 to 100 g / m 2 has. io 10. The method according to claim 1, characterized in that the second consolidation of the individual layers (4a, 6a) comprises a water jet consolidation (7) which is operated at a pressure of 20 to 200 bar.

11. Plant for producing a two-layer nonwoven fabric, which is operated according to the method of claims 1 to 10, comprising a first feed unit (2) which is designed to feed synthetic fibers (2a) to a downstream carding machine (3), further comprising a first consolidation unit which is designed to consolidate the fiber web (3a) of the carding machine (3) into a nonwoven fabric (4a), wherein the formed nonwoven fabric (4a) is laid down on a circulating belt (5), and the circulating belt (5) is arranged below a second feed unit (6) for short fibers (6a), so that the second feed unit (6) is designed to lay short wet-laid fibers (6a) on the upper side of the nonwoven fabric (4a), so that a two-layer nonwoven fabric (9) is created, which is joined together in a subsequent second consolidation unit, and with a dryer (10) and winder (11) arranged downstream in the material transport direction.

12. Plant according to claim 11, characterized in that the first consolidation is designed as a water jet consolidation.

13. Plant according to claim 11, characterized in that the first solidification is designed as thermal solidification.

14. Plant according to claim 13, characterized in that the first consolidation is designed as calender rolls or thermobonder (4).

15. Plant according to claim 11, characterized in that the second feed unit (6) is designed as a round wire former, inclined wire former or secondary headbox.

16. Two-layer nonwoven fabric, in which a first layer of nonwoven fabric (4a) is designed as a carrier or distribution layer and a second layer of short wet-laid fibers (6a) is designed as an absorption layer for liquids, produced in a one-step process according to one of claims 1 to 10, with a basis weight of 50 - 160 g / m 2, wherein the first layer consists of synthetic staple fibers (2a) with at least 90 wt% PET, and the second layer consists of short wet-laid natural fibers (6a) or a mixture of short wet-laid natural fibers with synthetic fibers.

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