METHOD AND SYSTEM FOR PRODUCING A WET-LAID NON-WOVEN FABRIC WEB

Abstract

A method for producing a wet-laid non-woven fabric web includes: providing a first suspension with natural pulp fibers in a first tank, providing a second suspension with regenerated cellulose fibers in a second tank, combining the first suspension and the second suspension to create a mixture, feeding the mixture to a headbox and dewatering the mixture in the forming section of a machine for producing the wet-laid non-woven fabric web. The second suspension with the regenerated cellulose fibers is conveyed by a volumetric pump, in particular by an eccentric screw pump, from the second tank into the volume flow of the first suspension. Wherein over the entire conveying path between the second tank and the headbox, the second suspension is not conducted through any mixing chest having a stirrer. Furthermore, a corresponding system for carrying out the method is taught.

Description

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a method for producing a wet-laid nonwoven web, which includes the following steps: providing a first suspension containing natural pulp fibers in a first tank, providing a second suspension containing regenerated cellulose fibers in a second tank, combining the first suspension and the second suspension to generate a mixture, supplying the mixture to a headbox, and dewatering the mixture in the forming section of a machine for producing the wet-laid nonwoven web. The invention further relates to a corresponding facility for implementing this method.

A method of this kind and a facility of this kind are already known from the prior art. A wet-laid nonwoven web which is produced from a mixture of natural pulp fibers and regenerated cellulose fibers has the advantages that it can be biodegradable and is able to break down again relatively easily in water. This is significant for enabling the wet-laid nonwoven web to be disposed of in trouble-free fashion even via lavatories. Accordingly, such products are sometimes also called “flushable wipes” and have been enjoying ever greater popularity for what is now a relatively long time.

The term “regenerated cellulose fibers”, also referred to as “regenerated fibers”, is understood to mean fibers which are produced synthetically by spinning from naturally renewable raw materials, more particularly cellulose obtained from wood, by way of a chemical process. Depending on the exact production method, there are different kinds of regenerated fibers, known for example under the following designations: viscose, modal, lyocell, cupro, and acetate. In comparison to the natural pulp fibers, the spun regenerated fibers are very long. The addition of long fibers of such kind is necessary in order to achieve a stable cohesion between the fibers in the fibrous web by waterjet needling or similar processes without it being necessary—as was earlier the usual practice—to employ chemical binders or fusible fibers, which in general lack biodegradability.

It was hitherto customary to mix the different types of fiber with one another in one or more mixing chests arranged one after another. The purpose of the mixing chests is to generate an extremely uniform mixture with precisely defined mixing fractions. Moreover, the mixing chests may also make it possible to turn a discontinuous incoming stream of the various fiber suspensions from the tanks into a continuous outflow of a volume stream to the headbox. Here, between the tanks with the various fiber suspensions and the headbox, water is admixed repeatedly, and so the fiber concentration at the headbox is very low in comparison to the fiber concentration in the tanks. At the headbox, the concentration may typically be only between 1% and 2% by weight. The completed wet-laid nonwoven web may then at the end contain, for example, between 70% and 90% by weight of natural pulp fibers and 10% to 30% by weight of regenerated cellulose fibers, based in each case on the total weight of the nonwoven web.

From the tanks, the highly concentrated fiber suspensions are pumped into the mixing chests, customarily by means of rotary pumps or centrifugal pumps. The mixing chests themselves contain a stirrer, which provides a uniform mixing of the different fiber suspensions. A continually recurring problem here is that the regenerated fibers, owing to their length, become spun in the centrifugal pump and/or in the stirrers of the mixing chest. This then necessitates costly and inconvenient cleaning and gives rise to corresponding production downtimes or outages.

SUMMARY OF THE INVENTION

An object of the present invention is to solve or at least reduce the problem stated above. More particularly, the intention is to provide a method and a facility for producing a wet-laid nonwoven web, with which the regenerated fibers no longer become spun.

This object is achieved through the features of the independent claims. The dependent claims provide advantageous developments of the invention.

With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a wet-laid nonwoven web. The method includes providing a first suspension containing natural pulp fibers in a first tank, providing a second suspension containing regenerated cellulose fibers in a second tank and combining the first suspension and the second suspension to generate a mixture by conveying the second suspension containing the regenerated cellulose fibers from the second tank by means of a volumetric pump into a volume stream of the first suspension, with the second suspension not being passed through any mixing chest having a stirring mechanism over an entire conveying path between the second tank and a headbox. The mixture is then supplied to the headbox. The mixture is then dewatered in a forming section of a machine for producing the wet-laid nonwoven web.

Specifically, the object is achieved by the generic method described at the outset, which in accordance with the invention is distinguished in that the second suspension containing the regenerated cellulose fibers is conveyed from the second tank by means of a volumetric pump, more particularly by means of an eccentric screw pump, into the volume stream of the first suspension, with the second suspension not being passed through any mixing chest containing a stirring mechanism over the entire conveying path between the second tank and the headbox.

The term “volumetric pump” refers to a pump for which the volume flow rate can be adjusted with approximate precision by way of the rotary speed. With the rotary and centrifugal pumps conventionally used, this is not the case, since the pumped volume flow rate is dependent on other factors as well, such as the current fill level in the tank, for example. Particularly preferred in this context are eccentric screw pumps, which according to the brand names of the original licensees are also called Mohno, Moyno or Mono pumps. Their main components are a rotating component, the rotor, and a fixed component, the stator, in which the former performs rotational movement. The rotor, hinged elastically or with articulation on one side, is configured as a kind of circular-thread screw of high pitch, high flight depth, and small core diameter. On the output side, the axial position undergoes oscillation. The hollow stator has an elastic wall, for the same pitch length of the rotor, but a considerably larger core space in an orthogonal axis. As a result, conveying spaces remain between the stator and the rotor, which rotates in the stator and in so doing moves radially, and these spaces move continuously from the input side to the output side. There is no need for valves for delimiting the conveying spaces. The shape of the hollow spaces here is constant, and so the conveying medium is not compressed. The shearing forces which act on the conveyed material here are very small. A particular advantage is that eccentric screw pumps carry out continuous conveying with low pulsation, and even media of high viscosity can be conveyed in a trouble-free manner. Such pumps are available, for example, from the company “Seepex”.

The inventors have determined that this kind of pump not only is superior to the rotary or centrifugal pumps conventionally used in that there is no risk in such pumps of the regenerated fibers becoming spun, but also that this kind of pump also allows the volume flow rate to be set with sufficient precision that they can be used as metering pumps. For the mixing of the second suspension with the first suspension, therefore, it is possible to entirely forgo the conventional mixing chests with stirrers. Instead, the second suspension containing the regenerated fibers can be jetted directly into the volume stream of the first suspension. Because the second suspension containing the regenerated fibers is no longer pumped from the second tank by means of a rotary or centrifugal pump used conventionally, and is not passed through any mixing chest with a stirrer, the aforementioned problems of spinning no longer occur. As a positive side effect, with the solution according to the invention, economies can be made in terms of the construction space for the mixing chests and of the associated costs, particularly the costs of the electrical drive energy for the stirrers in the mixing chests.

In one embodiment of the present invention it is proposed that the first suspension containing the natural pulp fibers is also conveyed from the first tank by means of a volumetric pump, more particularly by means of an eccentric screw pump, into the volume stream of the second suspension, with the first suspension not being passed through any mixing chest containing a stirring mechanism over the entire conveying path between the first tank and the headbox. While it is true that the natural pulp fibers in the first suspension do not tend to become spun, owing to their lower length, it is the case here as well that economies can be made in construction space and costs by virtue of the absence of the mixing chests.

In an alternative embodiment, however, it may also be the case that multiple first suspensions containing natural pulp fibers are provided in multiple first tanks, with the natural pulp fibers in the various first suspensions preferably differing from one another. They may differ from one another, for example, in terms of their fiber length. In this case it may be advantageous if the multiple first suspensions are mixed with one another in at least one mixing chest containing a stirring mechanism before they are conveyed further into the volume stream of the second suspension.

Regenerated fibers, having proven particularly suitable for the production of the wet-laid nonwoven webs are the fibers known as viscose and as lyocell.

In order in particular to enable effective utilization of advantages of the long regenerated fibers for the eco-friendly strengthening of the wet-laid nonwoven web, it is proposed that the nonwoven web undergoes waterjet needling in the machine for producing the wet-laid nonwoven web. As a result, the production process can be specifically configured in such a way that the completed wet-laid nonwoven web is dispersible in water. With regard to the dispersibility and to how it may be determined, reference is made to the disclosure in published European patent application EP2985375A1, corresponding to U.S. Pat. No. 11,214,901.

It is advantageous, moreover, to also allow the completed wet-laid nonwoven web to be disposed of without concern as a “flushable wipe” by way of the lavatory, if all fibers and any further auxiliaries from which the wet-laid nonwoven web is formed are selected such that the completed wet-laid nonwoven web is biodegradable.

According to an additional aspect, the present invention further relates to a facility for producing a wet-laid nonwoven web, which is configured to perform the method of the invention described above, containing: a first tank for a first suspension containing natural pulp fibers, a second tank for a second suspension containing regenerated cellulose fibers, a combining point for combining the first suspension and the second suspension to generate a mixture, a headbox which is charged with the mixture, and a forming section for dewatering the mixture. The facility in accordance with the invention is distinguished in particular in that it further contains a volumetric pump, more particularly an eccentric screw pump, to convey the second suspension containing the regenerated cellulose fibers from the second tank into the volume stream of the first suspension, with the facility being free from a mixing chest containing a stirring mechanism over the entire conveying path for the second suspension from the second tank up to the headbox.

The facility in particular may further contain a waterjet needling apparatus for needling the wet-laid nonwoven web for the advantageous reasons stated above. The forming section is configured preferably as an inclined-wire former. The facility may further comprise a dryer and/or a winder. Otherwise, the developments and advantages applicable to the facility according to the invention are the same as those stated above.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in a method and a system for producing a wet-laid non-woven fabric web, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram of a conventional facility for producing a wet-laid nonwoven web in accordance with the prior art,

FIG. 2 is a block diagram of a first embodiment of a facility of the invention for producing the wet-laid nonwoven web; and

FIG. 3 is a block diagram of a second embodiment of the facility of the invention for producing the wet-laid nonwoven web.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a prior art facility 10′ for producing a wet-laid nonwoven web, where here only the front part up to the a headbox 12′ is represented. For possible configurations of the back part of the facility, up to the rolling function, reference is made, for example, to the observations in the international patent publication WO 2015/000687 A1, which originates from the instant applicant. In this example, only two kinds of fibers are mixed: natural pulp fibers, which are provided in the form of an aqueous suspension in a first tank 14′, and regenerated cellulose fibers, which are provided likewise in the form of an aqueous suspension in a second tank 16′. The two aqueous suspensions are each pumped by means of a conventional rotary or centrifugal pump 18′ to a first mixing chest 20′ having a stirrer 22′. There, the two suspensions, containing the natural pulp fibers and the regenerated cellulose fibers, are mixed with one another for the first time. In general, the first mixing chest 20′ is followed by further mixing chests 20′ with corresponding stirrers 22′ —for example, as shown in FIG. 1, by a second mixing chest 20′ and by a third and final mixing chest 20′, which is also referred to as the machine chest. Water may be added as early as in the chests 20′, to reduce the fiber concentration in the suspension mixture. After the final mixing chest 20′, the mixture may be guided alternatively past or into a preliminary dilution tank 24′. The primary contents of the preliminary dilution tank 24′ are further water. Subsequently, the mixture may be guided again alternatively past or into a white water tank 26′. In the former case, the mixture may be added to the water from the white water tank 26′, either upstream or downstream of a pump 18′. The white water tank 26′ additionally receives the so-called white water from the forming section, this being the water which has passed through a forming wire and is pumped back in the process circuit. Finally, the fiber suspension mixture, heavily diluted with the water from the preliminary dilution tank 24′ and from the white water tank 26′, reaches the headbox 12′, from where it is applied to a forming wire, in a forming section no longer shown here, and is dewatered there, in order to form the actual nonwoven web. This takes place preferably in an inclined-wire former.

With this facility, the problem may occur that the long-regenerated cellulose fibers may become spun in the rotary or centrifugal pump 18′ with which they are pumped out of the second tank 16′, and/or at the stirrer 22′ of one of the mixing chests 20′. This then leads to costly and inconvenient cleaning and gives rise to corresponding production downtimes or outages.

FIG. 2 shows a schematic representation of a front part of the facility 10 for producing a wet-laid nonwoven web, analogous to FIG. 1, but this time of a first embodiment according to the invention. In FIG. 2, the same components have the same reference signs as in FIG. 1, but without a prime. Accordingly, with regard to these components, reference is made to the observations above in relation to FIG. 1.

Differently than in FIG. 1, the facility 10 represented in FIG. 2 has no mixing chests 20′ with stirrers 22′. Moreover, the rotary or centrifugal pumps 18′ which pump the suspension from the first tank 14 and the second tank 16, respectively, were each replaced by a volumetric pump 28, and, to be more precise, by an eccentric screw pump 28. The first suspension containing the natural pulp fibers from the first tank 14 is jetted directly into the conduit which connects the preliminary dilution tank 24 to the white water tank 26, for example upstream of the rotary or centrifugal pump 18 disposed between them. The second suspension containing the regenerated fibers from the second tank 16 is jetted alternatively likewise into the conduit which connects the preliminary dilution tank 24 to the white water tank 26, and/or into the conduit which connects the white water tank 26 to the headbox 12. This jetting may take place either upstream and/or downstream of a respective rotary or centrifugal pump 18. As a result of the extremely high dilution of the suspension mixture with the water from the preliminary dilution tank 24 and/or white water tank 26, the risk here of the regenerated fibers becoming spun is no more than low.

In the volumetric pump 28, provided in accordance with the invention downstream of the second tank, there is likewise virtually no risk of the long regenerated fibers becoming spun, just as there is no longer any risk at the stirrers 22′ of the mixing chests 20′, which in accordance with the invention are done away with entirely in the conveying path of the second suspension from the second tank 16 up to the headbox 12.

Given that with this embodiment there are no mixing chests 20′ with stirrers 22′, a positive side effect possible—relative to the embodiment from FIG. 1 according to the prior art—is that of economizing on construction space and costs, including, in particular, costs for the power to drive the stirrers 22′.

FIG. 3 shows a schematic representation of a front part of a facility for producing a wet-laid nonwoven web, analogous to FIGS. 1 and 2, but this time of a second embodiment according to the invention. In FIG. 3, the same components have the same reference signs as in FIG. 1, but without a prime, and/or the same reference signs as in FIG. 2. Accordingly, with regard to these components, reference is made to the observations above in relation to FIGS. 1 and 2.

Differently than in the first embodiment according to FIG. 2, the second embodiment according to FIG. 3 contains two first tanks 14. Each of the two first tanks 14 is filled with a first suspension containing natural pulp fibers, although the pulp fibers in the two tanks 14 differ from one another. For example, one tank 14 may contain natural pulp fibers of shorter fiber length than the other tank 14.

The first suspensions of both first tanks 14 may be mixed via multiple mixing chests 20 with stirrers 22 substantially in the same way as described above in FIG. 1 with respect to the first suspension and the second suspension. The two first suspensions here may also be pumped from the two first tanks 14 by means of a respective rotary or centrifugal pump 18. For the fibers composed of natural pulp, which are consistently very short by comparison with the regenerated fibers, there is no risk here of them becoming spun. After that, the mixture of the two first suspensions may be guided alternatively into the preliminary dilution tank 24 and/or past it into the connecting conduit between the preliminary dilution tank 24 and the white water tank 26.

It is important for this embodiment that here as well in accordance with the invention, as in the case of the first embodiment according to FIG. 2, the second suspension comprising the regenerated cellulose fibers is conveyed from the second tank 16 into the volume stream of the first suspension by means of a volumetric pump 28, more particularly by means of an eccentric screw pump, with the second suspension not being passed through any mixing chest 20′ containing a stirring mechanism 22′ over the entire conveying path between the second tank 16 and the headbox 12. This reduces the risk of the regenerated fibers becoming spun in the facility 10. The second suspension from the second tank 16 may be routed here in the manner described above in the first exemplary embodiment with regard to FIG. 2.

The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:

• • 10, 10′ facility for producing a wet-laid nonwoven web
  • 12, 12′ headbox
  • 14, 14′ first tank
  • 16, 16′ second tank
  • 18, 18′ rotary or centrifugal pump
  • 20, 20′ mixing chest
  • 22, 22′ stirrer
  • 24, 24′ preliminary dilution tank
  • 26, 26′ white water tank
  • 28 volumetric pump (eccentric screw pump)

Claims

1. A method for producing a wet-laid nonwoven web, which comprises the following steps of: providing a first suspension containing natural pulp fibers in a first tank;providing a second suspension containing regenerated cellulose fibers in a second tank;combining the first suspension and the second suspension to generate a mixture by conveying the second suspension containing the regenerated cellulose fibers from the second tank by means of a volumetric pump into a volume stream of the first suspension, with the second suspension not being passed through any mixing chest having a stirring mechanism over an entire conveying path between the second tank and a headbox;supplying the mixture to the headbox; anddewatering the mixture in a forming section of a machine for producing the wet-laid nonwoven web.

2. The method according to claim 1, which further comprises conveying the first suspension containing the natural pulp fibers from the first tank by means of a further volumetric pump into a volume stream of the second suspension, with the first suspension not being passed through any said mixing chest containing the stirring mechanism over an entire conveying path between the first tank and the headbox.

3. The method according to claim 1, wherein the first suspension is one of a plurality of first suspensions containing the natural pulp fibers disposed in a plurality of first tanks.

4. The method according to claim 3, which further comprises mixing the plurality of first suspensions with one another in at least one mixing chest containing a stirring mechanism before they are conveyed further into a volume stream of the second suspension.

5. The method according to claim 1, wherein the regenerated cellulose fibers contain viscose and/or lyocell.

6. The method according to claim 1, wherein the wet-laid nonwoven web undergoes waterjet needling in the machine for producing the wet-laid nonwoven web.

7. The method according to claim 6, wherein a production operation is configured such that a completed said wet-laid nonwoven web is dispersible in water.

8. The method according to claim 1, wherein all fibers and any further auxiliaries from which the wet-laid nonwoven web is formed are selected such that the wet-laid nonwoven web is biodegradable.

9. The method according to claim 1, wherein the volumetric pump is an eccentric screw pump.

10. The method according to claim 2, wherein the further volumetric pump is an eccentric screw pump.

11. The method according to claim 3, wherein the natural pulp fibers in the first suspensions differ from one another.

12. A facility for producing a wet-laid nonwoven web, the facility comprising: a first tank for a first suspension containing natural pulp fibers;a second tank for a second suspension containing regenerated cellulose fibers;a volumetric pump conveying the second suspension containing the regenerated cellulose fibers from said second tank into a volume stream of the first suspension at a combining point for combining the first suspension and the second suspension to generate a mixture;a headbox being supplied with the mixture, the facility being free from a mixing chest containing a stirring mechanism over an entire conveying path for the second suspension from said second tank up to said headbox; anda forming section for dewatering the mixture.

13. The facility according to claim 12, further comprising a waterjet needling apparatus for needling the wet-laid nonwoven web.

14. The facility according to claim 12, wherein said volumetric pump is an eccentric screw pump.