Method and system for producing a wet-laid non-woven fabric web

Abstract

The invention relates to a method for producing a wet-laid non-woven fabric web, comprising the following steps: providing a first suspension with natural pulp fibres in a first tank (14), providing a second suspension with regenerated cellulose fibres in a second tank (16), combining the first suspension and the second suspension to create a mixture, feeding the mixture to a headbox (12) and dewatering the mixture in the forming section of a machine for producing the wet-laid non-woven fabric web, wherein the second suspension with the regenerated cellulose fibres is conveyed by means of a volumetric pump (28), in particular by means of an eccentric screw pump (28), from the second tank (16) into the volume flow of the first suspension, wherein over the entire conveying path between the second tank (16) and the headbox (12) the second suspension is not conducted through any mixing chest comprising a stirrer. The invention further relates to a corresponding system for carrying out said method.

Description

[0001] Process and plant for producing a wet-laid nonwoven web

[0002] The invention relates to a method for producing a wet-laid nonwoven web, comprising the following steps: providing a first suspension containing natural cellulose 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 produce a mixture, feeding the mixture to a headbox, and dewatering the mixture in the forming section of a machine for producing the wet-laid nonwoven web. Furthermore, the invention relates to a corresponding system for carrying out this method.

[0003] Such a process or system is already known from the state of the art. A wet-laid nonwoven web, made from a blend of natural pulp fibers and regenerated cellulose fibers, has the advantage of being biodegradable and relatively easy to dissolve in water. This is important for the wet-laid nonwoven web to be easily disposed of, even via toilets. Such products are therefore sometimes called "flushable wipes" and have been enjoying increasing popularity for some time now.

[0004] The term "regenerated cellulose fibers," also known as "regenerated fibers," refers to fibers that are artificially produced from naturally renewable raw materials, particularly cellulose derived from wood, through a chemical process by spinning. Depending on the exact manufacturing process, different types of regenerated fibers are produced, known, for example, under the names: viscose, modal, lyocell, cupro, and acetate. Compared to natural cellulose fibers, the spun regenerated fibers are very long. The addition of such long fibers is necessary to achieve stable cohesion between the fibers in the fibrous web through waterjet needling or similar processes, without having to resort to chemical binders or melt fibers, which are generally not biodegradable, as was previously common.Until now, it was common practice to mix the various fiber types in one or more consecutively arranged mixing chests. The mixing chests serve to create the most homogeneous mixture possible with precisely defined mixing proportions. Furthermore, the mixing chests can also make it possible to achieve a continuous volume flow outflow to the headbox with a discontinuous inflow of the various fiber suspensions from the tanks. Water is repeatedly added between the tanks containing the various fiber suspensions and the headbox, so that the fiber concentration at the headbox is very low compared to the fiber concentration in the tanks. It can typically be only between 1 and 2 wt.% at the headbox.The finished wet-laid nonwoven web can then, for example, contain between 70 and 90 wt% natural cellulose fibers and 10 to 30 wt% regenerated cellulose fibers, each based on the total weight of the nonwoven web.

[0005] The highly concentrated fiber suspensions are typically pumped from the tanks into the mixing vats using rotary or centrifugal pumps. The mixing vats themselves contain a stirrer that ensures the homogeneous mixing of the various fiber suspensions. A recurring problem is that the regenerated fibers, due to their length, become entangled in the centrifugal pump and / or the stirrers of the mixing vat. This requires extensive cleaning and causes production downtimes or disruptions.

[0006] The object of the present invention is to solve or at least mitigate the aforementioned problem. In particular, a method and a system for producing a wet-laid nonwoven web are to be provided in which spinning of the regenerated fibers no longer occurs.

[0007] This object is achieved by the features of the independent claims. The dependent claims relate to advantageous developments of the invention. Specifically, the object is achieved by the generic method described above, which is characterized according to the invention in that the second suspension containing the regenerated cellulose fibers is conveyed from the second tank into the volume flow of the first suspension by means of a volumetric pump, in particular by means of an eccentric screw pump, wherein the second suspension is not guided through a mixing chest comprising an agitator along the entire conveying path between the second tank and the headbox.

[0008] The term "volumetric pump" refers to a pump in which the volumetric flow rate can be adjusted almost precisely via the speed. This is not the case with conventional rotary or centrifugal pumps, as the pumped volumetric flow rate also depends on other factors, such as the current fill level in the tank. Progressing cavity pumps, also known as Mohno, Moyno, or Mono pumps after the trademarks of the original licensees, are particularly preferred. Their main components are a rotating part, the rotor, and a stationary part, the stator, within which the former rotates. The rotor, which is articulated or elastically linked at one end, is designed as a type of round-thread screw with a large pitch, large flight depth, and small core diameter. The axis position oscillates on the output side.The hollow stator has an elastic wall with the same pitch length as the rotor, but a significantly larger core space along an orthogonal axis. This creates pumping chambers between the stator and the rotating, radially moving rotor, which move continuously from the inlet to the outlet side. Valves to restrict the pumping chambers are not required. The shape of the cavities remains constant, so the pumped medium is not compressed. The shear forces acting on the pumped material are very small. A particular advantage is that progressive cavity pumps pump continuously and with little pulsation, and can even pump highly viscous media without any problems. Such pumps are offered, for example, by the company "Seepex".

[0009] The inventors have discovered that this type of pump is not only superior to conventionally used rotary or centrifugal pumps in that there is no risk of spinning the regenerated fibers, but that this type of pump also allows such fine adjustment of the volume flow that it can be used as dosing pumps. Thus, the conventional mixing tubs with stirrers for mixing the second suspension with the first suspension can be completely dispensed with. Instead, the second suspension containing the regenerated fibers can be injected directly into the volume flow of the first suspension. Because the second suspension containing the regenerated fibers is no longer pumped from the second tank using a conventionally used rotary or centrifugal pump and is not passed through a mixing tub with a stirrer, the spinning problems mentioned above no longer arise.As a positive side effect, the solution according to the invention can save the installation space for the mixing vats and the associated costs, in particular the costs for the electrical drive energy of the stirrers in the mixing vats.

[0010] In one embodiment of the present invention, it is proposed that the first suspension containing the natural pulp fibers be conveyed from the first tank into the volume flow of the second suspension by means of a volumetric pump, in particular by means of an eccentric screw pump, wherein the first suspension is not guided through a mixing chest comprising an agitator along the entire conveying path between the first tank and the headbox. Although the natural pulp fibers in the first suspension do not tend to spin due to their shorter length, here too, space and costs can be saved by omitting the mixing chests.

[0011] However, in an alternative embodiment, it may also be provided that several first suspensions with natural pulp fibers are provided in several first tanks, wherein the natural pulp fibers in the various first suspensions preferably differ from one another. For example, they may differ from one another in terms of their fiber length. In this case, it may be advantageous if the several first suspensions are mixed together in at least one mixing vat comprising an agitator before being conveyed further into the volume flow of the second suspension.

[0012] The regenerated fibers known as viscose and lyocell have proven particularly suitable for the production of wet-laid nonwoven webs.

[0013] In particular, in order to effectively utilize the advantages of long regenerated fibers for the environmentally friendly strengthening of the wet-laid nonwoven web, it is proposed that the nonwoven web be water-jet needled in the machine used to produce the wet-laid nonwoven web. This allows the manufacturing process to be specifically designed so that the finished wet-laid nonwoven web is dispersible in water. Regarding dispersibility and how it can be determined, reference is made to the disclosure of document EP2985375A1.

[0014] In addition, in order to be able to safely dispose of the finished wet-laid nonwoven web as a “flushable wipe” via the toilet, it is advantageous if all fibers and any other auxiliary materials from which the wet-laid nonwoven web is formed are selected in such a way that the finished wet-laid nonwoven web is biodegradable.

[0015] According to a further aspect, the present invention further relates to a plant for producing a wet-laid nonwoven web, which is designed to carry out the above-described method according to the invention, comprising: a first tank for a first suspension with natural pulp fibers, a second tank for a second suspension with regenerated cellulose fibers, a merging point for merging the first suspension and the second suspension to produce a mixture, a headbox which is fed with the mixture, and a forming section for dewatering the mixture, wherein the plant is particularly characterized according to the invention in that it further comprises a volumetric pump, in particular an eccentric screw pump, to convey the second suspension with the regenerated cellulose fibers from the second tank into the volume flow of the first suspension,wherein the installation is free of a mixing vat comprising an agitator along the entire conveying path of the second suspension from the second tank to the headbox.

[0016] In particular, the system may further comprise a water jet needling device for needling the wet-laid nonwoven web for the advantageous reasons mentioned above. The forming section is preferably designed as an inclined wire former. Furthermore, the system may comprise a dryer and / or a winder. Furthermore, the above-mentioned developments and advantages also apply to the system according to the invention.

[0017] The present invention and further advantages thereof are explained in more detail below using merely schematically illustrated embodiments. In the drawings: Fig. 1 shows a conventional system for producing a wet-laid nonwoven web according to the prior art,

[0018] Fig. 2 shows a first embodiment of a plant according to the invention for producing a wet-laid nonwoven web, and

[0019] Fig. 3 shows a second embodiment of a plant according to the invention for producing a wet-laid nonwoven web.

[0020] Figure 1 shows a conventional system 10' known from the prior art for producing a wet-laid nonwoven web, wherein only the front part up to the headbox 12' is shown here. With regard to possible configurations of the rear part of the system up to the reel, reference is made, for example, to the explanations in the document WO 2015 / 000687 A1 from the applicant's company. In this example, only two types of fibers are mixed: namely natural pulp fibers, which are provided in the form of an aqueous suspension in a first tank 14', and regenerated cellulose fibers, which are also provided 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' with a stirrer 22'.There, the two suspensions containing the natural pulp fibers and the regenerated cellulose fibers are mixed together for the first time. This first mixing vat 20' is usually followed by further mixing vats 20' with corresponding stirrers 22', for example, as shown in Figure 1, a second mixing vat 20' and a third and final mixing vat 20', which is also referred to as the machine vat. Water can already be added to the vats 20' to reduce the fiber concentration in the suspension mixture. After the last mixing vat 20', the mixture can be passed either into or past a pre-dilution tank 24'. The pre-dilution tank 24' primarily contains water. The mixture can then be passed again into or past a white water tank 26'. In the latter case, the mixture can be added to the water from the white water tank 26' either before or after a pump 18'.The so-called white water tank 26', also called the "white water tank," also receives the so-called white water from the forming section, i.e., the water that has passed through a forming fabric and is pumped back into the process cycle. Finally, the fiber suspension mixture, highly diluted by the water from the pre-dilution tank 24' and the white water tank 26', reaches the headbox 12', from where it is applied to a forming fabric in a forming section (not shown here) to form the actual nonwoven web, where it is dewatered. This preferably takes place in an inclined wire former.

[0021] With this system, the problem can arise that the long regenerated cellulose fibers can spin together in the rotary or centrifugal pump 18', which pumps them out of the second tank 16', and / or at the agitator 22' of one of the mixing chests 20'. This then leads to complex cleaning and causes corresponding production downtimes or failures.

[0022] Figure 2 shows a schematic representation of a front part of a system 10 for producing a wet-laid nonwoven web, analogous to Figure 1, but this time of a first embodiment according to the invention. The same components in Figure 2 have the same reference numerals as in Figure 1, but without a prime. Regarding these components, please refer to the explanations above for Figure 1.

[0023] Unlike Figure 1, the system 10 shown in Figure 2 does not have mixing vats 20' with stirrers 22'. Furthermore, the rotary and 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 more precisely, by an eccentric screw pump 28. The first suspension with the natural pulp fibers from the first tank 14 is injected directly into the line that connects the pre-dilution tank 24 with the white water tank 26, for example upstream of the rotary or centrifugal pump 18 arranged therebetween. The second suspension with the regenerated fibers from the second tank 16 is optionally also injected into the line that connects the pre-dilution tank 24 with the white water tank 26 and / or into the line that connects the white water tank 26 with the headbox 12. The injection can take place either upstream and / or downstream of a respective rotary or centrifugal pump.Centrifugal pump 18. Due to the extremely strong dilution of the suspension mixture with the water from the pre-dilution tank 24 and / or white water tank 26, the risk of spinning of the regenerated fibers is now minimal. In the volumetric pump 28 provided according to the invention downstream of the second tank, there is also virtually no risk of spinning of the long regenerated fibers, just as there is no longer any risk at the agitators 22' of the mixing chests 20', which are completely dispensed with according to the invention in the conveying path from the second suspension from the second tank 16 to the headbox 12.

[0024] By not providing mixing tubs 20' with stirrers 22' in this embodiment, as a positive side effect - compared to the embodiment of Figure 1 according to the prior art - installation space and costs can be saved, in particular also costs for the electricity to drive the stirrers 22'.

[0025] Figure 3 shows a schematic representation of a front part of a system for producing a wet-laid nonwoven web, analogous to Figures 1 and 2, but this time of a second embodiment according to the invention. The same components in Figure 3 have the same reference numerals as in Figure 1, but without a prime, or the same reference numerals as in Figure 2. Regarding these components, please refer to the explanations above for Figures 1 and 2.

[0026] Unlike the first embodiment shown in Figure 2, the second embodiment shown in Figure 3 has two first tanks 14. Each of the two first tanks 14 is filled with a first suspension of natural pulp fibers, but the pulp fibers in the two tanks 14 differ from each other. For example, one tank 14 may contain natural pulp fibers of shorter fiber length than the other tank 14.

[0027] The first suspensions from both first tanks 14 can be mixed via several mixing vats 20 with stirrers 22 essentially in the same way as described above in Figure 1 with regard to the first suspension and the second suspension. The two first suspensions can also be pumped from the two first tanks 14 by means of a respective rotary or centrifugal pump 18. There is no risk of spinning for the natural pulp fibers, which are always very short compared to the regenerated fibers. The mixture of the two first suspensions can then be directed either into the pre-dilution tank 24 and / or past it into the connecting line between the pre-dilution tank 24 and the white water tank 26.

[0028] What is important in this embodiment is that, according to the invention, as in the first embodiment according to Figure 2, the second suspension with the regenerated cellulose fibers is conveyed from the second tank 16 into the volume flow of the first suspension by means of a volumetric pump 28, in particular by means of an eccentric screw pump, wherein the second suspension is not guided through a mixing chest 20' comprising an agitator 22' along the entire conveying path between the second tank 16 and the headbox 12. This reduces the risk of spinning of the regenerated fibers in the system 10. The second suspension from the second tank 16 can be guided as described above in the first embodiment with regard to Figure 2.

[0029] List of reference symbols

[0030] 10, 10' Plant for the production of a wet-laid nonwoven web

[0031] 12, 12' headbox

[0032] 14, 14' first tank

[0033] 16, 16' second tank

[0034] 18, 18' rotary or centrifugal pump

[0035] 20, 20' mixing tub

[0036] 22, 22' stirrer

[0037] 24, 24' pre-dilution tank

[0038] 26, 26' white water tank

[0039] 28 volumetric pump (eccentric screw pump)

Claims

1 . A method for producing a wet-laid nonwoven web, comprising the following steps: Providing a first suspension with natural pulp fibers in a first tank (14), Providing a second suspension with regenerated cellulose fibers in a second tank (16), combining the first suspension and the second suspension to produce a mixture, Feeding the mixture to a headbox (12) and dewatering the mixture in the forming section of a machine for producing the wet-laid nonwoven web, characterized in that the second suspension with the regenerated cellulose fibers is conveyed from the second tank (16) into the volume flow of the first suspension by means of a volumetric pump (28), in particular by means of an eccentric screw pump (28), wherein the second suspension is not guided through a mixing chest (20') comprising an agitator (22') on the entire conveying path between the second tank (16) and the headbox (12).

2. Method according to claim 1, characterized in that the first suspension with the natural cellulose fibers is also conveyed from the first tank (14) into the volume flow of the second suspension by means of a volumetric pump (28), in particular by means of an eccentric screw pump (28), wherein the first suspension is not guided through a mixing chest (20') comprising an agitator (22') on the entire conveying path between the first tank (14) and the headbox (12).

3. Method according to claim 1, characterized in that a plurality of first suspensions with natural pulp fibers are provided in a plurality of first tanks (12), wherein preferably the natural pulp fibers in the various first suspensions differ from one another.

4. Method according to claim 2, characterized in that the plurality of first suspensions are mixed with one another in at least one mixing vat (20) comprising an agitator (22) before they are further conveyed into the volume flow of the second suspension.

5. Process according to one of the preceding claims, characterized in that the regenerated cellulose fibers comprise or consist of viscose and / or lyocell.

6. Method according to one of the preceding claims, characterized in that in the machine for producing the wet-laid nonwoven web, water jet needling of the nonwoven web takes place.

7. The method according to claim 6, characterized in that the manufacturing process is designed such that the finished wet-laid nonwoven web is dispersible in water.

8. A method according to any one of the preceding claims, characterized in that all fibers and any other auxiliary materials from which the wet-laid nonwoven web is formed are selected such that the finished wet-laid nonwoven web is biodegradable.

9. Plant (10) for producing a wet-laid nonwoven web, which is designed to carry out the method according to one of the preceding claims, comprising: a first tank (14) for a first suspension with natural cellulose fibers, a second tank (16) for a second suspension with regenerated cellulose fibers, a merging point for merging the first suspension and the second suspension to produce a mixture, a headbox (12) which is fed with the mixture, and a forming section for dewatering the mixture, characterized in that the system (10) further comprises a volumetric pump (28), in particular an eccentric screw pump (28), for conveying the second suspension with the regenerated cellulose fibers from the second tank (16) into the volume flow of the first suspension, wherein the system (10) is free of a mixing chest (20') comprising an agitator (22') along the entire conveying path of the second suspension from the second tank (16) to the headbox (12).

10. System (10) according to claim 9, characterized in that it further comprises a water jet needling device for needling the wet-laid nonwoven web.

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