DE102014107725A1 - Process for the preparation of a structurable multilayer nonwoven and multilayer nonwoven - Google Patents

Abstract

The invention relates to a method for producing a structurable multilayer nonwoven web, in which at least two fiber suspensions are fed in a layered manner to a slanted screen former (1) and dewatered successively via at least one suction zone (3), and the resulting wet laid multilayer nonwoven web hydrodynamically in one of the subsequent processing steps to a nonwoven fabric (30) is solidified, wherein the fiber suspensions essentially have short fibers, and each outer fiber layer of the nonwoven fabric (30) is structurable separately. The invention further relates to a nonwoven comprising at least two layers of short fibers.

Description

The invention relates to a method for producing a structurable multilayer nonwoven in which at least two fiber suspensions are fed to a Schrägsiebformer layered via a headbox and successively dewatered via at least one suction zone, and the resulting wet laid multi-layer nonwoven web hydrodynamically in one of the subsequent processing steps to a nonwoven is solidified according to the preamble of claim 1, as well as a multi-layer nonwoven fabric.

It is known to produce nonwovens with multiple layers of different fibers in order to adapt the product properties to different customer requirements. In particular, in the manufacture of hygiene articles, it is state of the art to make the outer layers of the product so 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 moisture-permeable, without absorbing the moisture itself. In this case, the outer layers may consist of the same fibers, so that a so-called sandwich fleece is formed.

Furthermore, it is known to produce nonwoven webs of several layers of different fibers, wherein in particular the short fibers are used without prior solidification for the inner layers. The outer fibers are always presented loose. They may also be precalendered or preconsolidated with hydroentanglement or may be thermobonded in the thermobonding oven with heated air, in between which are added the short fibers and then hydrodynamically solidified, for example. Thus, it is known to produce a first outer layer of endless spunbond fibers, apply it as a middle layer pulp and cover with a carded web and hydraulically solidify.

It is also known to hydrodynamically solidify a pre-calendered or spunbonded monolayer or multilayer web and to pattern it by means of a structured endless belt or a structured drum. In this case, however, it is assumed that the fibers have a minimum length of> 35-45 mm, otherwise the short fibers are flushed out with the solidification and subsequent structuring and thus the product loses its predetermined properties such as strength or density. In this case, the structuring is possible only over the entire web cross-section by the web receives openings or holes, or the depressions formed by a pattern on a nonwoven surface on the opposite nonwoven surface as an increase.

Another drawback with the conventional production of multi-layer webs with short fibers is that they can be further processed only with low productivity, since the strength between the fibers is too low. Common methods of increasing strength would be the use of fibrillated fiber, binder fibers or binder, which is often undesirable.

The object of the present invention is to provide a process for the production of a multilayer nonwoven in which the outer layers consist of short fibers and the nonwoven fabric can be structured after the hydrodynamic solidification.

The object is achieved by a method for producing a structurable multilayer nonwoven fabric in which at least two fiber suspensions are fed to a Schrägsiebformer layered via a headbox and successively dewatered via at least one suction zone, and hydrodynamically to the resulting wet laid multi-layer nonwoven web in one of the subsequent processing steps a nonwoven is solidified, wherein the fiber suspensions have substantially short fibers, and each outer fiber layer of the nonwoven fabric is structurable separately.

By producing the multilayer nonwoven web by means of a Schrägsiebformers can be dispensed with fibrillated fibers, binder fibers or binder. The strength maintains the nonwoven web by the subsequent hydrodynamic consolidation. By using substantially short fibers in the outer layers, each layer of the nonwoven can be patterned separately.

By Schrägsiebformer whose deducted white water is recycled, separated in the short fibers and fed back to the casserole, can be produced at a cost of almost 100% very cost-effective multilayer nonwoven fabric whose product properties is adjustable by different layers of short fibers.

According to the prior art, sandwich nonwovens could be hydrodynamically consolidated only with long fibers over 35 mm in length, so that the cover layers have a significant strength. With short fibers, a not inconsiderable proportion is flushed out with the water jets, so that the use of materials makes the process more expensive.

It is particularly advantageous that the short fibers have a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm have. Depending on the fiber length, the softness and the grip of the end product can thus be improved. Furthermore, the fiber length has a decisive influence on the structuring, which can be adjusted with shorter fibers with greater accuracy.

The structuring of the nonwoven fabric can be low, so that the embossed or produced by water jetting pattern can arise only by partial displacement of the short fibers of the outer layers. Depending on the pressures used for structuring and the thickness of the outer layers, the underlying layer may still be completely covered by the fibers of the outer layer. However, the structuring of the nonwoven fabric can also lead to a perforation of the outer layers if the embossed pattern or patterns produced by water jets completely penetrates the outer layer, so that the lower or middle fiber layer protrudes due to the displacement of the fibers in the region of the resulting openings occurs.

The invention will be explained in more detail with reference to the accompanying drawings.

1 schematically shows the principle of a Schrägsiebformers;

2 schematically shows the principle of a hydrodynamic solidification plant;

3 shows a textured fleece.

An oblique screen former 1 is below a rotating screen belt 10 arranged. The sieve belt 10 runs around different rollers 12 . 13 . 14 . 15 around and has a sloping section 11 on, which increases in the direction of the screen belt by the angle α. In the area of the sloping section 11 is below the screen belt 10 a drainage box of the Schrägsiebformers 1 arranged on its surface 2 the screen belt 10 supported. Below the rubber 2 is at least one suction zone 3 arranged by means of unillustrated pumps under negative pressure 4 is set. The Schrägsiebformer 1 can have several, in the machine direction of succession arranged suction zones 3 have, which can be acted upon with different pressures or pressures. The vacuum sources may preferably be designed as controllable vacuum pumps.

In this embodiment, over a headbox 8th three superposed fiber suspensions 8.1 . 8.2 and 8.3 on the screen belt 10 given. Each fiber suspension 8.1 . 8.2 and 8.3 In addition to water contains a certain content of solids, which in turn consists of fibers and other additives. Between the fiber suspensions 8.1 . 8.2 . 8.3 are arranged (not shown) lamellae with which the layer thickness of the fiber suspensions can be varied individually or in total. Because the lamellae are the fiber suspensions 8.1 . 8.2 and 8.3 Separate from each other, and are preferably different lengths in the machine direction, they are successively on the Schrägsiebformer 1 dewatered. This is a mixing of the fiber suspensions 8.1 . 8.2 and 8.3 prevents and improves the layer purity of individual layers of pulp. Via the at least one suction zone in conjunction with the controllable vacuum pumps, each layer of a fiber suspension 8.1 . 8.2 and 8.3 be subjected to a separate negative pressure, whereby different mixtures of water with fibers in each fiber suspension can be processed.

In this first embodiment, the fiber suspensions exist 8.1 and 8.3 in the further processing, the outer layers or the cover layer for the middle layer of fiber suspension 8.2 forms, at least partially from short synthetic fibers such as polyester, polyamide or polyolefin. The middle fiber suspension can consist of natural fibers which have a high water retention capacity.

The thickness of the layers is adjustable by the lamellae by the task of fiber suspensions 8.1 . 8.2 and 8.3 over the headbox 8th can be varied. For example, in the case of a sandwich nonwoven, layers of the same thickness can be produced, or the layers can be produced with gradations of, for example, 10%, 80% and 10% thickness. Indirectly, the basis weight of each layer of fibrous material can also be determined 9 to adjust.

The sieve belt 10 , which is permeable to liquids and gases, transports the superposed fiber suspensions 8.1 . 8.2 and 8.3 over the sloping section 11 over the Schrägsiebformer 1 , Due to gravity and negative pressure acting on the fiber suspensions 8.1 . 8.2 . 8.3 acts, the fiber suspensions are dewatered, creating a web of fiber 9 forms with three layers of fibers. That from the fiber suspensions 8.1 . 8.2 . 8.3 withdrawn white water 6 is through a white water drain 7 standing at the suction box 5 is arranged, from the drainage box of Schrägsiebformers 1 away.

Such a multi-layer headbox allows the application of differently composed fiber suspensions in one step on a Formiersieb, which is designed and oriented so that the individual layers of the fiber suspension 8.1 . 8.2 and 8.3 successively applied successively and dehydrated in this order become. The layers of the resulting webs of the pulp lie directly on each other and thus enter into both within each layer and between the layers of compounds that allow the use of short fibers to a high quality and durable product.

In order to adjust the moisture content of the further processing optionally, this first dewatering can be followed by a further reduction of the moisture, for example by pressing. Preferably, the solidification of the sandwich non-woven fabric shown here by a hydrodynamic consolidation by means of water jets, in which the fibers are woven together. Since according to the first embodiment of this invention, in particular synthetic short fibers are to be processed with a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm, a part of these short fibers separates both in Schrägsiebformer 1 as well as in the subsequent hydrodynamic solidification with the wastewater. In order to minimize the loss of short fibers as possible, the white water is provided 6 of the Schrägsiebformers 1 and to treat the wastewater from hydrodynamic solidification and to recycle the short fibers to the headbox.

In a second embodiment, the nonwoven web is also produced in multiple layers, wherein the fibers contained therein have a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm, which are selected alone or in combination of, for example: groundwood, BSKP (bleached long fiber pulp), manila hemp, cotton, china grass, ramie, lyocell or viscose. The aforementioned fibers are natural fibers such as groundwood, NBKP, LBKP, manila hemp, cotton, china grass, ramie, or synthetic fibers made of natural materials such as lyocell or viscose, which can be inexpensively used for high quality end products. The synthetic fibers made of natural fibers are also referred to as artificial fibers, in contrast to synthetic fibers, also called synthetic fibers, which consist of plastic materials. The fleece produced from this short fiber mixture is particularly suitable for biodegradable products for the cosmetics or medical sector for very sensitive applications, where not the softness of the article is in the foreground, but, for example, skin compatibility.

The individual layers of fibers can also be produced from mixtures of fibers, for example 75-85% natural fibers and 25-15% synthetic fibers made of natural materials. The middle layer can also consist of a mixture of pulp with another fiber. Furthermore, it is possible to vary the thickness of the fiber layer, which is particularly due to the subsequent structuring, in which the fibers of at least one cover layer are displaced locally.

In comparison with the prior art, in which synthetic fibers are processed with a length of more than 35 mm, the productivity can be maintained at the same level via the wastewater treatment and thus the return of the fibers. The invention has the advantage that the short fibers can be processed very efficiently, without having to calender the cover layers of, for example, a multilayer nonwoven. Furthermore, the use of fibrillated fibers, binder fibers and binders can be dispensed with, as a result of which the end product is biodegradable, which is necessary in particular for "flushable" products such as cosmetics. The system can be built significantly shorter and cheaper, since it can be dispensed calendering or handling the calendered fibers. The recycling process or the recycling of flushed short fibers can be accomplished with very little effort, since both the Schrägsiebformer 1 as well as the hydrodynamic consolidation already have an integrated water treatment, the only to the treatment 16 and repatriation 17 the short fibers is to expand.

For this purpose, the waste water can be prepared 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 almost complete utilization of the short fibers takes place. Smallest amounts of mixed fibers pose no problem, especially if the fiber layers are designed as a fiber mixture.

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 recycled separately during the aspiration of the liquid.

In 2 is the Schrägsiebformer 1 downstream of a plant for hydroentanglement, in which the three fiber suspensions 8.1 . 8.2 . 8.3 existing pulp 9 via a circulating conveyor belt 20 a drum 21 is supplied. On the outer circumference of the drum 21 can a drum shell 22 be raised. The direction of movement of the pulp 9 and the direction of rotation of the drum 21 are marked with arrows. The feeding belt 20 can with a not shown Be provided nozzle bar for the first solidification or preconsolidation.

The drum 21 is at least one nozzle bar 23 associated, which by means of water jets the pulp 9 solidified and thus a fleece 30 generated. In this embodiment, three are successively on the circumference of the drum 21 arranged nozzle bars 23 provided, each at its bottom a plurality of outlet openings 24 for water jets. With the from the nozzle bars 23 exiting water jets takes place, the loading of the pulp 9 thereby becoming a fleece 30 is solidified. The associated facilities for sucking the water are known in the art and are not shown for clarity. The multi-layer solidified fleece 30 is then subsequently fed to another station, which consists of a rotating drum 25 and a circulating endless belt 26 can exist. The endless band 26 has a structure with openings on the water jets through the outlet openings 28 a nozzle bar 27 incident. This will be the pattern of the endless band 26 transferred to the fleece. Since in this case only the upper layer of the fleece 30 is acted upon by the water jets, only this layer takes the pre-embossed pattern of the endless belt 26 at. The fact that the upper layer consists of very short fibers, these fibers are moved due to the local application of water jets, so that a local volume change is achieved. In the places where the water jets on the fleece 30 are incident, according to the pre-perforated opening of the endless belt 26 The fibers are moved to the places that are not exposed to water jets. The fleece 30 becomes thinner according to the pattern at one point, as the fibers move and thicker at another point, since here move the fibers of the cover layer at least partially and thereby compact. The fleece gets a three-dimensional structure, which was possible in the prior art only with long fibers. The thinner spot arises where the jets of water pass through the perforated opening of the endless belt 26 on the fleece 30 incident. The thicker areas with the increase in volume arise at the through the endless belt 26 covered areas to which the shifted fibers shift. In order that the structuring is incorporated only on an upper fiber layer or cover layer and does not act in the middle or underlying layer, the nozzle bar 27 work with a reduced spray power or with a reduced pressure, which is adjustable between 2 and 80 bar. Depending on the fiber strength and layer thickness, the structuring can thus be adjusted in intensity. Preferably, the spraying power or the pressure of the nozzle bar 27 less than at least one of the previous nozzle bars 23 ,

Depending on the spray rate of the nozzle bar 27 and the layer thickness of the outer layers in multilayer webs, the structuring of the outer layers may be so intense that they are perforated.

Instead of the endless band 26 It is also possible to use a perforated drum or a perforated plate, not shown. Instead of the drum 25 Another band can be used to make the fleece 30 during structuring. Of course, a modification is possible with the both sides of the fleece is structured, even with different patterns.

In the previously described embodiment of 2 becomes the upper layer of the fleece 30 structured. The drum rotates 25 in a clockwise direction, thereby removing the fleece 30 in the area between the drum 25 and the endless band 26 to the right.

In an alternative or supplementary embodiment, the nonwoven runs 30 according to the dashed line of the drum 21 directly to the drum 25 , which then turns counterclockwise while keeping the fleece 30 with the lower layer to the endless belt 26 and the nozzle bar 27 leads, reducing the bottom layer of the fleece 30 is structured. The removal of the fleece 30 then takes place in the area between the endless belt 26 and the drum 21 ,

After the patterning process, the web can be fed to a dryer or another processing station.

The resulting web, which preferably consists of two short-fiber cover layers enclosing, for example, a middle layer of pulp, has a significantly better softness and feel than comparable products whose cover layer consists of long synthetic fibers. According to the first embodiment, the short synthetic fibers may be polyester, which is an extremely inexpensive base material for these products. The cover layers can then absorb moisture, which takes place exclusively via the middle layer, the pulp. Very low-cost nonwovens are produced, for example, for cosmetic products, hygiene articles or wipes which, in contrast to the prior art, have a particularly good hand and excellent surface smoothness due to the short synthetic fibers. According to the second embodiment with the covering layer of short natural fibers or the synthetic fibers of natural materials, biodegradable products are produced for particularly sensitive areas of application in cosmetics or medicine.

In both products, the structuring of a surface or an outer layer is carried out by a local volume change of the layer with short fibers or a change in the spatial arrangement, with which a pattern can be embossed into the nonwoven, which thereby has a high grip. In contrast to the prior art, in which the structuring always relates to the entire nonwoven by forming a deepening structure on one side of the nonwoven on the other side as an increasing structuring, a single cover layer can be specifically structured with it, the second cover layer without Structuring can be performed. Of course, both cover layers can be patterned simultaneously with the same pattern or with a different pattern.

With regard to the fiber used according to the invention, these have a length corresponding to a frequency distribution, according to which 80%, preferably 90% and in particular 95% of the fibers lie in the stated length ranges. For a nonwoven with fibers made of natural fibers, synthetic fibers of natural materials or of synthetic fibers with a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm, thus have 80%, preferably 90% and in particular 95% of the fibers have the aforementioned length.

3 shows a produced according to the method described above fleece 30 , which consists of three layers with short fibers. In the plan view of the upper cover layer are elevations 30a or mass or fiber accumulations recognizable, which arises due to a shift or accumulation of fibers. The wells 30b or mass or fiber reductions correspond to the perforations in the endless belt 30 in which here the jets of the jetbeam 27 impinge and move the fibers sideways, leaving bumps 30a arise. The wells 30b are outlined with sharp lines to better representability, which forms in the final product rather than the area of a transition. As a result, the nonwoven acquires a three-dimensional structure which, in contrast to the prior art, is only possible on one side of the nonwoven, but can also be adjusted selectively on both sides of the nonwoven. In the state of the art with a structured fleece of long fibers, a depression forms on one side of the fleece which forms an elevation on the opposite side. A double-sided same structuring is possible only with great effort.

The embodiments describe a fleece and a process with three layers of fibers, which are particularly suitable for cosmetic or medical products. Basically, it is possible by the manufacturing process to produce multi-layer webs, so from two-ply upwards and to structure one-sided, which is made possible by the use of short fibers.

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

oblique section

12

roller

13

roller

14

roller

15

roller

16

processing

17

return

20

infeed

21

drum

22

drum shell

23

nozzle beam

24

outlet openings

25

drum

26

endless belt

27

nozzle beam

28

outlet openings

30

fleece

30a

deepening

30b

survey

Claims (16)

Process for the preparation of a structurable multi-layer nonwoven in which at least two fiber suspensions are passed over a headbox ( 8th ) layered a Schrägsiebformer ( 1 ) and successively via at least one suction zone ( 3 ), and hydrodynamically forming the resultant wet-laid multilayer nonwoven web in one of the subsequent processing steps to form a nonwoven web (US Pat. 30 ), wherein the fiber suspensions essentially comprise short fibers, and each outer fiber layer of the nonwoven ( 30 ) is structurable separately. A method according to claim 1, characterized in that the short fibers have a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm. A method according to claim 1, characterized in that at least one fiber suspension comprises synthetic short fibers such as polyester, polyamide or polyolefin. A method according to claim 3, characterized in that a further fiber suspension comprises short fibers of natural fibers. A method according to claim 1, characterized in that at least one fiber suspension comprises natural fibers. A method according to claim 5, characterized in that the further fiber suspension comprises synthetic fibers of natural materials. Method according to one of the preceding claims, that the thickness or the basis weight of each fiber layer is adjustable. A method according to claim 1, characterized in that the structuring by means of at least one nozzle bar ( 27 ) and a perforated endless belt ( 26 ) or a perforated drum, in which the short fibers are shifted hydrodynamically. Method according to claim 8, characterized in that the nozzle bar ( 27 ) is operated at a pressure of 2 to 80 bar. Nonwoven, characterized by at least two layers of short fibers, each layer being structurable separately. Nonwoven according to claim 10, characterized in that the short fibers have a length of less than 25 mm, in particular less than 20 mm, preferably less than 15 mm. Nonwoven according to claim 10, characterized in that at least one layer synthetic short fibers such as polyester, polyamide or polyolefin. Nonwoven according to claim 12, characterized in that at least one further layer comprises short fibers of natural fibers. Nonwoven according to claim 10, characterized in that at least one layer comprises short fibers of natural fibers. Nonwoven according to claim 14, characterized in that at least one further layer of short fibers comprises synthetic fibers of natural materials. Nonwoven according to claim 10 to 15, characterized by a production method according to one of claims 1 to 9.

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