DE102018114634A1 - Process for producing a wet laid nonwoven web and multilayer fibrous web - Google Patents

Abstract

The invention relates to a method for producing a wet-laid nonwoven web, in which a plurality of fiber suspensions (8.1, 8.2, 8.3) layered via a headbox (8) are fed to an inclined screen former (1) and are successively 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 from 2 to 20 mm, and that the medium fiber suspension (8.2) has fibers of at least 50% by weight from a natural material or natural fibers, the fiber material (9) being hydrodynamically consolidated in one of the subsequent processing steps a multi-layer fiber 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 a corresponding 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, for example, to produce a first outer layer from endless spunbond fibers, to apply pulp thereon as a middle layer and to cover it with a carding fleece and to 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.

In the EP 0992338 B1 describes the production of a sandwich fleece, in which pulp is embedded between carded fibers and hydrodynamically needled as a middle layer. 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.

The 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. In the case of multi-layer products, the outer layer of which should consist of short fibers, on the one hand an elaborate 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 consist at least partially 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, which significantly increase the softness, feel and bulk of the product and at the same time due to the use of synthetic fibers reduce the manufacturing costs of the product.

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.

1 shows schematically the principle of an inclined screen former.

An inclined screen former 1 is below a rotating sieve belt 10 arranged. The sieve belt 10 runs around different rollers 12 . 13 . 14 . 15 around and has a sloping section 11 that increases in the running direction of the sieve belt by the angle α. In the area of the sloping section 11 is below the sieve belt 10 the inclined screen former 1 arranged on its surface 2 the sieve belt 10 supported. Below the topping 2 is at least a suction zone 3 arranged by means of pumps, not shown, under vacuum 4 is set. The inclined screen former 1 can have multiple suction zones 3 have different pressures or negative pressures applied to them. The vacuum sources can preferably be designed as controllable / adjustable vacuum pumps.

In this embodiment, a headbox 8th three fiber suspensions arranged one above the other 8.1 . 8.2 and 8.3 on the sieve belt 10 given. Any fiber suspension 8.1 . 8.2 and 8.3 In addition to water, it contains a certain amount of solid matter, which in turn consists of fibers and other additives. Between the fiber suspensions 8.1 . 8.2 . 8.3 lamellae, not shown, are arranged with which the layer thickness of the fiber suspensions can be varied individually or in total. Because the lamellae the fiber suspensions 8.1 . 8.2 and 8.3 separate from each other, they are placed one after the other on the inclined screen former 1 dewatered. This will mix the fiber suspensions 8.1 . 8.2 and 8.3 prevents and improves the layer cleanliness of the individual layers of fiber. Via the at least one suction zone in connection with the controllable vacuum pumps, each layer of a fiber suspension can 8.1 . 8.2 and 8.3 exposed to a separate vacuum, which allows different mixtures of water with fibers to be processed in each fiber suspension.

In this embodiment, the fiber suspensions exist 8.1 and 8.3 which, during further processing, the outer layers or the top layer for the middle layer of fiber suspension 8.2 forms, at least partially from short synthetic fibers such as polyester, polyamide, polyolefin or from regenerated fibers from 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 the slats by giving up the fiber suspensions 8.1 . 8.2 and 8.3 over the headbox 8th can be varied. 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 can also be measured indirectly 9 to adjust.

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

Such a multi-layer headbox allows the application of differently composed fiber suspensions in one work step to a forming wire, which is designed and oriented so that the individual layers of the fiber suspension 8.1 . 8.2 and 8.3 successively applied and drained in this order. The layers of the then resulting webs of the fiber material lie directly on top of one another 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 woven together. Below the consolidation 20 can suction 21 be arranged. The consolidation 20 can be designed with a water pressure of 60 - 150 bar. Before solidification 20 can be pre-consolidation 18 with suction 19 can be arranged with a lower pressure of 30 to 60 bar water jets on the fiber 9 injected and pre-compacted or pre-consolidated. 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 as in the subsequent hydrodynamic consolidation with the wastewater. In order to minimize the loss of short fibers as much as possible, the white water is provided 6 of the inclined screen former 1 as well as treating the wastewater from the hydrodynamic consolidation and returning the short fibers 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 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 the flushed-out short fibers can be accomplished with very little effort, since both the inclined screen former 1 as well as the hydrodynamic consolidation already have an integrated water treatment, which is only for the treatment 16 and repatriation 17 the short fibers are to be expanded.

For this purpose, the waste water 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 become the headbox 8th fed again, so that an almost complete utilization of the short synthetic fibers takes place. 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 be done by adding 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 not absorb any moisture, which takes place exclusively via 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.

LIST OF REFERENCE NUMBERS

1

Schrägsiebformer

2

covering

3

suction zone

4

vacuum

5

suction box

6

white water

7

Siebwasserablauf

8th

headbox

8.1

fiber suspension

8.2

fiber suspension

8.3

fiber suspension

9

fiber

10

screen belt

11

sloping section

12

roller

13

roller

14

roller

15

roller

16

processing

17

return

18

presolidification

19

suction

20

consolidation

21

suction

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 0992338 B1 [0004]
• EP 1266058 B1 [0005]

Claims (10)

Process for the production of 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 successively dewatered via at least one suction zone (3), the outer layers of the resulting Fibers (9), which are formed from the fiber suspensions (8.1) and (8.3), at least partially 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 middle fiber suspension (8.2) has fibers of at least 50% by weight made from a natural material or natural fibers, the fiber material (9) being hydrodynamically consolidated in one of the subsequent processing steps. Procedure according to Claim 1 , characterized in that the white water (6) drawn off via the suction zone (3) is fed to a treatment (16) by means of which the short synthetic fibers are separated and fed back to the casserole (8). Procedure 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). Procedure according to Claim 1 , characterized in that the short synthetic fibers have a fiber length of 4 to 15 mm, preferably of 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 fiber 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. Multi-layer fiber web after Claim 7 , characterized in that the outer layers have a fiber length of 4 to 15 mm, preferably of 8 to 12 mm. Multi-layer fiber web after Claim 7 , characterized in that the outer layers have only short synthetic fibers. Multi-layer fiber web according to one of the 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 secondary fibers.

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