WO2019243109A1 - Method for producing a wet-laid nonwoven fabric web, and multilayer fiber web - Google Patents

Abstract

The invention relates to a method for producing a wet-laid nonwoven fabric web, wherein multiple fiber suspensions (8.1, 8.2, 8.3) are supplied to an inclined screen former (1) in a layered manner via a headbox (8) and are successively dewatered via at least one suction zone (3), wherein the outer layers of the resulting fiber material (9) made of the fiber suspensions (8.1) and (8.3) have at least partly short synthetic fibers, such as those made of polyester, polyamide, polyolefin, or regenerated fibers made from natural raw products for example, such as lyocell or viscose with a fiber length of 2 to 20 mm, and the central fiber suspension (8.2) has fibers made of up to at least 50 wt.% of a natural material or natural fibers, wherein the fiber material (9) is hydrodynamically solidified in one of the following processing steps. The invention additionally relates to a multilayer fiber web.

Description

 Title: Process for making a wet-laid

 Nonwoven web and multilayer fibrous web

 description

The invention relates to a method for producing a wet-laid nonwoven web according to the preamble of claim 1, and a multilayer fibrous web.

It is known to produce nonwovens with several layers of different fibers in order to adapt the product properties to different customer requirements. In the manufacture of hygiene articles in particular, it is state of the art to design the outer layers of the product in such a way that the inner layer with the high moisture absorption capacity is kept stable. For this purpose, the outer layers must have an appropriate strength and at the same time be permeable to moisture without absorbing the moisture itself. The outer layers can consist of the same fibers, so that a so-called sandwich fleece is created.

It is also known to produce nonwoven webs from several layers of different fibers, the short fibers in particular being used for the inner layers without prior consolidation. For reasons of strength, the outer fibers are usually introduced into the manufacturing process by pre-calendering or as a prepared fleece, the short fibers are added in between and the whole is then, for example, hydrodynamically consolidated. It is known to produce a first outer layer from endless spunbond fibers, to apply pulp thereon as a middle layer and with one Cover carding fleece and consolidate it hydraulically. The disadvantage is that the individual layers of different fibers must have a minimum basis weight so that they can be processed in the process without damage. EP 0992338 B1 describes the production of a sandwich fleece in which pulp is embedded between carded fibers as the middle layer and needled hydrodynamically. The plant for the production of this sandwich fleece is very expensive and complex, since either a card is required for the preparation of the carded fibers for the two outer layers, or an unwinding station for a prepared fleece. It is not possible to process the different fibers in one production step. Another disadvantage is that only long fibers> 35-45 mm fiber length are provided for the outer layers, their availability as a raw material is limited and expensive. The end product according to the process described here is a multi-layer fleece.

EP 1266058 B1 describes a method for producing a composite fleece for the absorption and storage of liquids. An outer layer of the fleece consists of a solidified carded fleece onto which a middle layer of cellulose, for example wood pulp fibers, is applied. Both layers of fleece are hydrodynamically consolidated, then dried and then calendered again. In a second embodiment, a second pre-consolidated and pre-calendered fleece is placed on the pulp layer and all three layers are bonded together.

The disadvantage is that short fibers, which enable high-quality products in terms of feel, texture, softness, bulk etc., have major disadvantages in terms of processability. For multi-layer products, the outer layer of which should consist of short fibers On the one hand, extensive preparation is necessary, and on the other hand, these can only be processed with low productivity. Another disadvantage is that a certain basis weight for the individual layers of fleece cannot be undershot in order to process it without damage in the system.

The object of the present invention is to create a method for producing multilayer nonwoven, in which the outer layers at least partially consist of short synthetic fibers.

The object is achieved by a process for producing a wet-laid nonwoven web, in which a plurality of fiber suspensions, layered via a headbox, are fed to an inclined screen former and successively dewatered via at least one suction zone, the outer layers of the resulting fibrous material, which are formed from the fiber suspensions, at least sometimes have short synthetic fibers such as polyester, polyamide, polyolefin or regenerated fibers from natural raw materials such as lyocell or viscose with a fiber length of 2 to 20 mm, and that the medium fiber suspension fibers at least 50 wt .-% of a natural material or natural fibers have, and the fibrous material is hydrodynamically consolidated in one of the subsequent processing steps.

In contrast to multi-layer nonwoven products, these multi-layer nonwoven products already show greater cohesion between the individual layers in the first manufacturing step. In particular, thin and light layers with a basis weight of 4-5 g / m ² can be processed in this way.

The resulting multi-layer fleece has short synthetic fibers in the top layers that reflect the softness, feel and bulk of the Increase product significantly while reducing the manufacturing costs of the product due to the use of synthetic fibers.

It is possible that the white water drawn off via the suction zone is fed to a treatment by means of which the short synthetic fibers are separated and fed back to the casserole. With a material use of almost 100%, a sandwich fleece can be produced very cost-effectively, which is extremely soft and has a good grip.

In a further advantageous embodiment, the short synthetic fibers which have been flushed out of the hydrodynamic consolidation are fed back into the headbox of the inclined screen former. According to the state of the art, sandwich nonwovens could only be hydrodynamically consolidated with long fibers over 35 mm in length, so that the cover layers have a notable strength. In the case of short fibers, a not inconsiderable proportion is washed out with the water jets, so that the use of materials makes the process more expensive.

It is particularly advantageous that the short synthetic fibers have a fiber length of 4 to 15 mm, preferably 8 to 12 mm. Depending on the fiber length, the softness and feel of the end product can be improved.

The process enables very inexpensive products compared to the prior art, since the short synthetic fibers consist, for example, of polyester, polyamide, polyolefin or of regenerated fibers from natural raw materials such as lyocell or viscose. The middle fiber suspension preferably has at least 50% by weight pulp, whereas the remaining fibers consist of viscose and / or PET and / or of secondary fibers, such as waste paper. A further improvement is achieved if the middle fiber suspension has at least 80% by weight pulp and the remaining fibers consist of viscose and / or PET and / or of secondary fibers. In particular, cosmetic products, hygiene articles or wipes with a high water retention capacity can be produced from the multi-layer fiber web in which the middle fiber suspension has fibers made from a natural material or natural fibers. The high fiber content in the middle layer, which consists of pulp, ensures good absorption of liquids. The variation in the amount of pulp is influenced by the planned use as a hygiene or cosmetic product.

The multilayer fibrous web produced by the method according to the invention is characterized in that the outer layers have at least partially short synthetic fibers such as polyester, polyamide, polyolefin or regenerated fibers from natural raw materials such as lyocell or viscose with a fiber length of 2 to 20 mm, and that the middle fiber layer has fibers of at least 50% by weight from a natural material or natural fibers. The product made from this fibrous web has a particularly high softness and good grip due to the proportion of short fibers in the outer layers. The product has a higher strength than comparable products made from individual layers of fibers that are consolidated with each other, since the wet-laid fiber suspension already creates a high degree of cohesion between the fiber layers in the manufacturing process. Another advantage is that the individual fiber layers can be processed with a differently thin basis weight, which with carded fibers or fibers from a unwound fleece is not possible in this low weight in a reliable manner. The outer layers preferably have a fiber length of 4 to 15 mm, preferably 8 to 12 mm. The handle of the end product can be changed over the fiber length.

The use of only short synthetic fibers for the outer layers enables the use of inexpensive raw materials.

The fact that the middle fiber layer has at least 50% by weight pulp and the remaining fibers consist of viscose and / or PET and / or secondary fibers can also reduce the manufacturing costs, since recycled secondary fibers such as waste paper stock in particular are very inexpensive ,

The invention is explained in more detail with reference to the accompanying drawing.

Fig. 1 shows schematically the principle of an inclined screen former.

An inclined screen former 1 is arranged below a rotating screen belt 10. The sieve belt 10 runs around different rollers 12, 13, 14, 15 and has an inclined section 11 which increases in the running direction of the sieve belt by the angle a. In the area of the inclined section 11, the inclined sieve former 1 is arranged below the sieve belt 10, on the covering 2 of which the sieve belt 10 is supported. At least one suction zone 3 is arranged below the covering 2 and is placed under suppressor 4 by means of pumps (not shown). The

Inclined screen former 1 can have a plurality of suction zones 3 which are subjected to different pressures or negative pressures. The vacuum sources can preferably be designed as controllable / adjustable vacuum pumps. In this exemplary embodiment, three fiber suspensions 8.1, 8.2 and 8.3 arranged one above the other are placed on the sieve belt 10 via a headbox 8. In addition to water, each fiber suspension 8.1, 8.2 and 8.3 contains a certain amount of solid, which in turn consists of fibers and other additives. Slats, not shown, are arranged between the fiber suspensions 8.1, 8.2, 8.3, with which the layer thickness of the fiber suspensions can be varied individually or in total. Since the lamellae separate the fiber suspensions 8.1, 8.2 and 8.3 from one another, these are successively dewatered on the inclined screen former 1. This prevents mixing of the fiber suspensions 8.1, 8.2 and 8.3 and improves the layer purity of the individual layers of fibrous material. Each layer of a fiber suspension 8.1, 8.2 and 8.3 can be exposed to a separate suppressor via the at least one suction zone in connection with the controllable / adjustable vacuum pumps, with which different mixtures of water with fibers can be processed in each fiber suspension.

In this exemplary embodiment, the fiber suspensions 8.1 and 8.3, which form the outer layers or the cover layer for the middle layer of fiber suspension 8.2 during further processing, at least partially consist of short synthetic fibers such as, for example, polyester, polyamide, polyolefin or regenerated fibers made of natural Raw materials such as lyocell or viscose. The medium fiber suspension can consist of natural fibers that have a high water retention capacity.

The thickness of the layers can be adjusted by means of the lamellae, in that the task of the fiber suspensions 8.1, 8.2 and 8.3 can be varied via the headbox 8. In the case of a sandwich fleece, for example, layers of the same thickness can be produced, or the layers can be produced with a gradation of, for example, 10%, 80% and 10% thickness. The basis weight of each layer of fibrous material 9 can also be adjusted indirectly.

The sieve belt 10, which is permeable to liquids and gases, transports the fiber suspensions 8.1, 8.2 and 8.3 arranged one above the other via the inclined section 11 via the inclined sieve former 1. Due to the gravity and the negative pressure which acts on the fiber suspensions 8.1, 8.2, 8.3, the fiber suspensions are dewatered, whereby a web of fiber 9 with three layers of fibers is formed. The white water 6 drawn off from the fiber suspensions 8.1, 8.2, 8.3 is removed from the inclined screen former 1 through a white water drain 7 which is arranged on the suction box 5.

Such a multi-layer headbox allows the application of differently composed fiber suspensions in one work step to a forming screen, which is designed and oriented in this way is that the individual layers of fiber suspension 8.1, 8.2 and 8.3 are successively applied one after the other and dewatered in this order. The layers of the then resulting webs of fiber material lie directly on top of each other and thus form connections both within each layer and between the layers, which enable the use of short fibers to form a high-quality and durable product.

In order to adjust the moisture content for further processing if necessary, this first dewatering can be followed by a further reduction in moisture, for example by pressing. The sandwich fleece shown here is preferably consolidated by hydrodynamic consolidation 20 by means of water jets, in which the fibers are interwoven. A suction device 21 can be arranged below the solidification 20. The solidification 20 can be designed with a water pressure of 60-150 bar. Before the solidification 20, a pre-consolidation 18 with a suction 19 can be arranged, which sprays water jets onto the fibrous material 9 at a lower pressure of 30 to 60 bar and pre-compresses or pre-consolidated it. Since according to this invention in particular synthetic short fibers with a length of 2-20 mm, preferably 4-12 mm are to be processed, some of these short fibers are separated both in the inclined screen former 1 and in the subsequent hydrodynamic consolidation with the waste water. In order to minimize the loss of short fibers as much as possible, it is provided that the white water 6 of the inclined screen former 1 and the waste water from the hydrodynamic consolidation are treated and the short fibers are returned to the headbox. In comparison with the prior art, in which synthetic fibers with a length of more than 35 mm are processed, the wastewater treatment and thus the recycling of the fibers can keep productivity at the same level. The invention has the The advantage that synthetic short fibers can be processed very efficiently without the cover layers of a multi-layer fleece, for example, having to be calendered. The system can be set up much shorter and cheaper, since there is no need for calendering or handling with the calendered fibers. The return process or the recycling of the flushed-out short fibers can be accomplished with very little effort, since both the inclined screen former 1 and the hydrodynamic consolidation already have an integrated water treatment system, which can only be expanded by the treatment 16 and recycling 17 of the short fibers.

For this purpose, the wastewater can be treated in a fractionator, in which the short fibers of the outer layers are separated from the long fibers of the inner or middle layer. The short fibers are fed back into the headbox 8 so that the short synthetic fibers are almost completely utilized. The smallest amounts of mixed fibers are not a problem, especially not if the fiber layers are designed as a fiber mixture.

A further separate preparation of the fibers can take place in that each layer of fiber suspension 8.1, 8.2, 8.3 has its own suction zone, so that the fibers can be returned separately when the liquid is sucked off.

The resulting fleece, which preferably consists of two outer layers with short synthetic fibers, which for example enclose a middle layer of pulp or a fiber mixture with pulp, has a significantly better softness and feel than comparable products, the outer layer of which consist of long synthetic fibers. In this embodiment, the short synthetic fibers can be made of polyester, which is an extremely inexpensive base material for these products. The cover layers can then no moisture record what happens exclusively through the middle layer, the pulp. Very inexpensive nonwovens are produced, for example for cosmetic products, hygiene articles or wipes, which, in contrast to the prior art, have a particularly good grip due to the short synthetic fibers.

In contrast to the prior art, the fleece produced according to the invention is a multi-layer fleece, not a multi-layer fleece, in which individual layers are fed to the production line and connected to one another. This has the advantage that the individual layers can have very different and low basis weights, which cannot be handled by a pre-processed and unwound fleece. The manufacturing process with the wet-laid nonwoven layers of the individual fiber suspensions results in a minimum strength between the individual nonwoven layers, which can be further processed by means of hydroentangling, although the layers with the short fibers are on the outside.

reference numeral

1 inclined screen former

2 topping

3 suction zone

 4 suppress

5 suction box

6 white water

7 White water drain 8 Headbox

8.1 Fiber suspension

8.2 fiber suspension

8.3 fiber suspension

9 pulp 10 mesh belt

 11 sloping section

12 roller

 13 roller

 14 roller

15 roller

 16 Preparation

17 return

18 pre-consolidation

19 suction 20 solidification

21 suction

Claims

claims 1. A process for producing a wet-laid nonwoven web, in which several fiber suspensions (8.1, 8.2, 8.3) are layered over a headbox (8) and fed to an inclined screen former (1) and are gradually dewatered via at least one suction zone (3), the outer layers of the resulting fiber (9), which are formed from the fiber suspensions (8.1) and (8.3), at least partially short synthetic fibers such as polyester, polyamide, polyolefin or regenerated fibers from natural raw materials such as Lyocell or viscose with a fiber length of 2 to 20 mm, and that the middle fiber suspension (8.2) has fibers of at least 50% by weight of a natural material or natural fibers, the fiber material (9) being hydrodynamically consolidated in one of the subsequent processing steps. 2. The method according to claim 1, characterized in that the white water (6) drawn off via the suction zone (3) is fed to a preparation (16) by means of which the short synthetic fibers are separated and fed back to the casserole (8). 3. The method according to claim 2, characterized in that the wastewater arising in the hydrodynamic consolidation is fed to the treatment (16) by means of which the short synthetic fibers are separated and fed back to the casserole (8). 4. The method according to claim 1, characterized in that the short synthetic fibers have a fiber length of 4 to 15 mm, preferably from 8 to 12 mm. Method according to one of the preceding claims, characterized in that the middle fiber suspension (8.2) has at least 50% by weight pulp and the remaining fibers consist of viscose and / or PET and / or of secondary fibers. Method according to one of the preceding claims, characterized in that the middle fiber suspension (8.2) has at least 80% by weight pulp, and the remaining fibers consist of viscose and / or PET and / or of secondary fibers. Multilayer fibrous web, produced according to one of the preceding claims, characterized in that the outer layers have at least partially short synthetic fibers such as polyester, polyamide, polyolefin or regenerated fibers from natural raw materials such as lyocell or viscose with a fiber length of 2 to 20 mm, and that the middle fiber layer has fibers of at least 50% by weight made of a natural material or natural fibers. 8. Multi-layer fiber web according to claim 7, characterized in that the outer layers have a fiber length of 4 to 15 mm, preferably of 8 to 12 mm. 9. Multi-layer fiber web according to claim 7, characterized in that the outer layers have only short synthetic fibers. 10. Multi-layer fiber web according to one of claims 7 to 9, characterized in that the middle fiber layer has at least 50 wt .-% pulp and the remaining fibers consist of viscose and / or PET and / or of secondary fibers.