Method and device for producing a fibrous web

Abstract

The invention relates to a method for producing a fibrous web (3), wherein a first fibre layer (1) of long fibres is provided, wherein a second fibre layer (2) of short fibres is provided, wherein the first fibre layer (1) and the second fibre layer (2) are connected to one another, wherein after connection of the first and the second fibre layer (1, 2), exclusion regions (5) are cut away from the first and the second fibre layer (1, 2), wherein the long fibres of the cut-away exclusion layer (5) are first shortened dry, and therefore they correspond approximately to the length distribution of the short fibres, wherein the dry-comminuted exclusion regions are then dispersed in a pulper (7) and the fibres of the exclusion regions (5) are separated here, wherein the comminuted and dispersed exclusion regions (5) are used as recycling material to produce the fibrous web (3) or a further fibrous web (4) by wet-laying the fibres of the comminuted and dispersed exclusion regions (5). The invention also relates to a device for carrying out the method.

Description

[0001] Method and device for producing a fiber web

[0002] The present invention relates to a method and a device for producing a fiber web, wherein a first fiber layer made of long fibers and a second fiber layer made of short fibers are provided and the first fiber layer and the second fiber layer are bonded to one another.

[0003] Such devices and methods are known from the prior art. For example, EP 4 087 967 A1 discloses a method for producing a fiber web in which a fiber layer of carded long fibers, a so-called C-layer, and a fiber layer of wet-laid cellulose short fibers, a so-called P-layer, are combined to form a fiber web. Fiber webs that contain both carded fibers and fibers laid as fiber pulp are called CP materials. CP stands for "carded pulp." CP materials combine the properties of carded fibers and fibers laid as pulp and are therefore often used in the production of wipes, for example, due to their wet strength, absorbency, and low price.

[0004] The edge areas are particularly problematic in the production of CP materials. Neither the card nor the headbox used to lay the P-layer can be adjusted precisely enough to ensure the desired quality characteristics are maintained right up to the edge of the fiber web. Therefore, the edge areas are typically separated as rejects. The separated material consists of both short fibers and long fibers, which has so far prevented recycling of the separated material. While short fibers can be added back to the pulp and long fibers can be carded again, the composite of short fibers and long fibers proves problematic in both the pulper and the card. Long fibers disrupt the stock preparation process for forming the P-layer because they cannot be separated as desired in the pulper and tend to spun during wet laying.Short fibers are too short to be processed in the carding machine and bring dust and dirt into the carding machine, which can potentially damage the carding machine.

[0005] It is therefore an object of the present invention to provide a method and a device for producing a fiber web, which offer the possibility of recycling waste areas arising during the production of the fiber web.

[0006] This object is achieved by the features of claim 1. According to the invention, a first fiber layer made of long fibers and a second fiber layer made of short fibers are provided, wherein the first fiber layer and the second fiber layer are connected to one another. In particular, it is provided that the long fibers are artificially produced fibers. It is preferably provided that the long fibers have a fiber length between 8 mm and 150 mm, preferably between 15 mm and 60 mm, particularly preferably between 25 mm and 50 mm and in particular between 35 mm and 45 mm. Alternatively, the long fibers can also be continuous filaments, as in the case of spunbond-type threads. It is conceivable that the short fibers comprise natural fibers. In particular, the short fibers can comprise cellulose fibers. It is conceivable that the short fibers comprise recycled fibers, such as waste paper, artificially produced fibers or mixtures thereof.In particular, it is conceivable for the short fibers to have a fiber length between 0.2 mm and 10 mm, preferably between 1 mm and 8 mm, and in particular between 1.6 mm and 5 mm. The cellulose fibers can be, for example, softwood pulp fibers. According to the invention, it is provided that the reject regions are separated from the first and the second fiber layer. In particular, it is provided that the reject regions are separated from the first and the second fiber layer after the first fiber layer has been joined to the second fiber layer. The reject regions can, for example, be edge regions. For this purpose, it is provided that the edge regions are each, for example, 30 mm to 50 mm wide.However, it is also conceivable that the reject areas include areas of the fiber web that cannot be assigned to any or not only one or both edge areas, but, for example, include areas that were produced at the beginning of the production of the fiber web or at the end of the production of the fiber web.

[0007] According to the invention, the fibers of the separated reject areas are first dry-shredded in a shredding step. The long fibers are shortened so that the length distribution of the long fibers approximately corresponds to the length distribution of the short fibers. The dry-shredded reject areas are then dispersed in a pulper in a dissolving step, and the fibers of the reject areas are separated. The shredded and dispersed reject areas are then used as recycling material to produce the fiber web or another fiber web by wet-laying the fibers of the shredded and dispersed reject areas.

[0008] It is conceivable that the reject areas only undergo the shredding and dissolving steps if the proportion of reject areas in the fiber layers exceeds a certain minimum. This ensures that the process is operated profitably, meaning that recycling only occurs when reject areas are generated on a scale that makes it worthwhile to recycle.

[0009] The two-stage recycling process adjusts the fiber lengths of the long fibers to the fiber lengths of the short fibers, so that the material separated with the reject areas can be further used to produce the fiber web or another fiber web. In the shredding step, the length of the fibers in the separated reject areas is first defined. This makes it possible to shorten the long fibers to such an extent that the fibers exhibit an acceptable fiber length distribution after passing through the shredding step. In particular, it is possible to shorten the long fibers to such an extent that they can be wet-laid with a P-layer without spinning. In the subsequent pulping step, the reject areas are dispersed in a pulper, and the fibers of the reject areas are separated.This advantageously makes it possible to return the material separated with the reject areas to the production of the fiber web, thereby providing the second fiber layer. Such a process is significantly more sustainable than a manufacturing process in which the reject areas are discarded. Furthermore, reusing the material reduces costs in the production of the fiber web and saves disposal costs.

[0010] Preferably, the first fiber layer and the second fiber layer are bonded together by hydroentangling. In particular, the hydroentangled fiber layers are dried with a dryer, for example, a through-air dryer, before the reject areas are separated. However, it is also conceivable for the reject areas to be separated between the hydroentangling and the dryer.

[0011] After drying and separating the reject areas, it is preferred that the fiber web is wound up.

[0012] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0013] Optionally, it is provided that the comminution step is preceded by a pre-comminution step. In the pre-comminution step, the reject areas are dry-comminuted. It is conceivable that foreign substances such as cardboard tubes or adhesive tape are removed during this process. Preferably, the pre-comminution step is carried out using a guillotine and / or a knife system and / or a shredder, for example a shaft shredder. It is conceivable that the degree of pre-comminution, i.e. the maximum fiber length after passing through the pre-comminution, is set by adjusting a perforated aperture of a pre-comminution unit. It is conceivable that the perforated aperture is set to 10 mm to 30 mm and preferably to approximately 20 mm. According to a preferred embodiment of the present invention, it is provided that the fibers of the reject areas are defibrated and dry-comminuted in the comminution step.In addition to shortening the long fibers, this also advantageously makes it possible for the recycled fibers to be better bonded to one another and to other fibers during further processing, in particular with hydroentangling. It is conceivable that the comminution step is carried out in a cutting mill. This advantageously makes it possible for the defibration and shortening of the fibers to be carried out in one machine. However, it is also conceivable for the shortening and defibration to take place as separate steps. The fiber length of the fibers after the comminution step can be selected by adjusting the knife assembly and the apertures of the cutting mill. For example, an aperture size of 0.5 mm to 10 mm is conceivable, preferably from 1 mm to 8 mm and particularly preferably from 3 mm to 6 mm.

[0014] According to a further preferred embodiment of the present invention, the fibers are hydrodynamically separated in the pulping step. For this purpose, the dry-comminuted reject areas are mixed with water, and the resulting suspension is set in motion. Dispersion in the pulper preferably takes place as in the production of cellulose pulp. It is conceivable that the suspension in the pulping step has a fiber density of 1% to 10%, and preferably of about 5%. It is conceivable that the pulping step is carried out at a temperature of approximately 30°C to 50°C, and in particular of approximately 40°C. It is preferably provided that the hydrodynamic separation is carried out for 10 minutes to 30 minutes, and in particular 20 minutes.

[0015] To improve the process flow, it is preferably provided that the reject areas undergo a coarse sorting step after the pulping step. During this step, non-dispersed parts of the reject areas are sorted out. This advantageously makes it possible to sort out contaminants and protect the subsequent process from them. In particular, it is provided that the coarse sorting step is carried out using a perforated sorting basket. The perforated sorting basket can be integrated into the pulper. It is conceivable that the coarse sorting step is carried out with a fiber density of the suspension of 1% to 8% and preferably 3.5%. It is also conceivable that the hole diameter of the perforated sorting basket is between 4 mm and 10 mm and in particular 6 mm.

[0016] According to a further preferred embodiment of the present invention, the reject areas undergo an absorption step after the pulping step and preferably after the coarse screening step. In the absorption step, spun fractions from the reject areas are sorted out. Spun fractions, so-called nits, arise during the dry comminution of the fibers in the reject areas. Typically, a pulper is unable to completely dissolve the spun fractions. If the spun fractions enter the fiber web via the recycled material, they lead to a significant reduction in quality. This is avoided by removing the spun fractions in the absorption step. Preferably, the absorption step is carried out using a barrier screen basket. Slotted or perforated screen baskets can be used for this purpose.It is also conceivable that the sorting step is carried out using a dynamic shaker, inclined screens inserted into downdrafts, or cleaners / cone centrifuges. Due to the higher density and hydrodynamically more favorable shape of the spun fibers, these can also be separated by sedimentation in a gravitational field. It is conceivable that a combination of the aforementioned machines or methods is used in the sorting step. It is conceivable that the fiber density of the suspension for sorting out the spun fibers is adjusted to 1% to 5%, and preferably to 2.1% to 3.5%.

[0017] To further improve the recycling rate, it is preferably provided that the spun fibers are dispersed and then returned to the recycling material. For this purpose, it is particularly intended that the spun fibers are mechanically destroyed. This can be done, for example, with a refiner such as a flat, drum or cone refiner, a Dutch refiner or other grinding unit, or a deflaker or disperser. It is important to ensure that the mechanical destruction of the spun fibers results in as little unwanted shortening of the fiber lengths as possible, so that a high proportion of fines is not created. It is conceivable that the spun fibers are only dispersed and then returned to the recycling material if the proportion of spun fibers in the reject areas and / or the proportion of spun fibers in the fiber layers is greater than a further minimum proportion.This ensures that the process is operated even more profitably, meaning that all material is only recycled when it is economically viable.

[0018] In particular, it is provided that the first fiber layer is a carded fiber layer. Preferably, the first fiber layer comprises artificially produced fibers. Furthermore, it is particularly provided that the second fiber layer is wet-laid from a fiber pulp. It is conceivable that the second fiber layer is laid on top of the first fiber layer, i.e. that the fiber web is a CP material. However, it is also conceivable that the first fiber layer is laid on top of the second fiber layer, i.e. that the fiber web is a PC material. It is also conceivable that the fiber web has a plurality of fiber layers with long fibers, in particular a plurality of carded fiber layers. It is likewise conceivable that the fiber web has a plurality of fiber layers with short fibers, in particular a plurality of fiber layers which are wet-laid from a fiber pulp.It is therefore conceivable, for example, that the fiber web is or comprises a CPC material, a PCP material, a CPCP material, a PCPC material, a CCP material, a PPC material, a CPP material, a PCC material, etc.

[0019] According to a further preferred embodiment of the present invention, it is provided that the recycled material is used to produce the fibrous web and that the comminution step and the dissolving step are carried out inline. The recycled material is also fed inline, in particular without storing the recycled material, to provide the second fibrous web. Furthermore, it is preferably provided that the coarse sorting step and / or the sorting step and / or the pre-comminution are carried out inline. For this purpose, it is conceivable that a recycling line for recycling the separated broke areas is arranged along a production line for producing the fibrous web. In this case, the production line preferably has the carding machine, the headbox, the hydroentanglement process, and the dryer. The recycling line preferably has the cutting mill and the pulper.

[0020] A further object for achieving the initially stated problem is a device for producing a fiber web according to the invention. The device comprises a comminution unit for dry comminution of the separated reject areas, preferably a cutting mill. Furthermore, the device comprises a pulper, which is provided for dispersing the dry-comminuted reject areas. In particular, the device comprises the production line and the recycling line.

[0021] The features, details and advantages mentioned above in connection with the method according to the invention also relate to the device according to the invention.

[0022] Further details, features, and advantages of the invention will become apparent from the drawings and the following description of preferred embodiments with reference to the drawings. The drawings merely illustrate exemplary embodiments of the invention, which do not limit the scope of the invention.

[0023] They show:

[0024] Fig. 1 : a schematic view of an apparatus according to an exemplary embodiment of the present invention for carrying out a method according to an exemplary embodiment of the present invention,

[0025] Fig. 2: a schematic view of a device according to a further exemplary embodiment of the present invention for carrying out a method according to a further exemplary embodiment of the present invention and

[0026] Fig. 3: a schematic view of a device according to another exemplary embodiment of the present invention for carrying out a method according to another exemplary embodiment of the present invention. Figures 1, 2, and 3 each show devices 100 according to exemplary embodiments of the present invention for carrying out methods according to exemplary embodiments of the present invention.

[0027] Figure 1 shows a device 100 for producing a fiber web 3. Fiber material consisting of long fibers is transported from a bale opener 10 to a carding machine 11. The long fibers are carded into a first fiber layer 1 by means of the carding machine 11. In the example shown here, the long fibers are artificially produced fibers with a fiber length of approximately 38 mm. After leaving the carding machine 11, the first fiber layer 1 is pre-consolidated in a pre-consolidation unit 12. The pre-consolidation unit 12 can consolidate, for example, using water jets and preferably on a screen belt. For this purpose, hydrodynamic needling or interlacing can be used, which is known to those skilled in the art as hydroentanglement.

[0028] A second fiber layer 2 is placed onto the carded first fiber layer 1 by means of a headbox 20. This is done here using a wet-laying process. The second fiber layer 2 comprises short fibers and is provided as fiber pulp. For this purpose, the short fibers are dispersed in a further pulper 15 to form an aqueous suspension and, if necessary, temporarily stored in a chest 16. A sorter 17 separates components from the aqueous suspension which, for example due to their size, are unsuitable for further feeding into the production process. These separated components are removed from the production process as waste 23. The suspension thus cleaned is, if necessary, temporarily stored in a further chest 18 and then fed to the headbox 20. In the embodiment shown here, the short fibers of the second fiber layer 2 have a fiber length of approximately 2 mm.

[0029] In order to bond the first fiber layer 1 to the second fiber layer 2, the first fiber layer 1 and the second fiber layer 2 undergo hydroentanglement 13. During this process, the fibers of the first fiber layer 1 and the second fiber layer 2 are entangled with one another. Preferably, water is removed from the second fiber layer 2 at the same time, in particular the excess water is filtered off through the first fiber layer 1. For this purpose, the first fiber layer 1 and the second fiber layer 2 can be hydroentangled on a screen belt, with suction boxes arranged below the screen belt to suck off the excess water. However, the hydroentanglement can also take place with the first fiber layer 1 or the second fiber layer 2 lying on a drum.In particular, it is conceivable that a hydroentanglement is initially performed, in which the first fiber layer 1 and / or the second fiber layer 2 rest on a screen belt, followed by a further hydroentanglement, in which the first fiber layer 1 and / or the second fiber layer 2 rests on a drum. The now bonded fiber layers 1, 2 are then dried in a dryer 14.

[0030] It has been shown that, in particular, the edge regions of the fiber web 3 cannot always be produced in satisfactory quality. These reject regions 5 are separated from the fiber web 3 in a separation unit 19. With the separated reject regions 5, valuable material is removed from the production process of the fiber web 3. In order to avoid having to discard the material of the reject regions 5, which contains both long fibers and short fibers, the separated reject regions 5 undergo a recycling process. The separated reject regions 5 are fed to a pre-shredding unit 21. In the pre-shredding unit 21, the separated reject regions 5 are dry-shredded. This can be done, for example, using a guillotine, a knife system, or a shredder. It is conceivable that the fibers of the separated reject regions 5 are shortened to a maximum length of approximately 20 mm.Subsequently, the reject areas 5 are dry-shredded and simultaneously fiberized in a shredding step using a cutting mill 6. The blade assembly and the outlet openings of the cutting mill 6 determine the maximum fiber length of the shredded and fiberized fibers in the reject areas 5.

[0031] From the cutting mill 6, the shredded and defibrated fibers from the reject areas 5 are transported to a pulper 7. In the pulper 7, the shredded and defibrated fibers are mixed with water to form an aqueous suspension and hydrodynamically separated. In the exemplary embodiments shown here, the fiber density of the aqueous suspension is 5%. Typical parameters for this pulping step in the pulper 7 are a temperature of 40°C and a pulping time in the pulper 7 of 20 minutes. After completing the pulping step, the suspension is subjected to coarse screening in the pulper 7. For this purpose, a perforated screening basket 7.1 is provided in the pulper 7. Alternatively, the coarse screening can also be carried out outside the pulper 7. For coarse screening, the fiber density of the aqueous suspension is reduced to approximately 3.5%. With a typical hole diameter of the perforated screening basket 7.1 of 6 mm, non-dispersed fragments can be removed from the suspension.

[0032] From the coarse screening stage, the aqueous suspension is fed to a barrier screen basket 8, where spun fibers are removed from the aqueous suspension in an absorption step. The barrier screen basket 8 is designed here as a slotted screening basket with a slot width of 0.2 mm. Alternative systems for coarse screening include, for example, dynamic shakers, the placement of inclined screens in downdrafts of the suspension, or cone centrifuges. To remove the spun fibers, the fiber density of the aqueous suspension is preferably further reduced, for example, to 2.1%. The absorbed spun fibers are fed as reject to a refiner 9, where the spun fibers are mechanically destroyed. After the spun fibers have been destroyed, the absorbed fibers can be recycled.

[0033] The rejected areas 5 treated in this way can be fed directly to the production process of the fiber web 3 as recycled material 24 by being transported to the further pulper 15 to provide the second fiber layer 2. The recycling process of the rejected areas 5 therefore preferably takes place inline. However, it is also conceivable that the recycling process of the rejected areas 5 does not take place inline, but that the processed rejected areas, after passing through the sorting step and the destruction of the spinning, are first stored in a warehouse 22 as recycled material 24. The fibers of the rejected areas 5 stored in this way can then, for example, be fed to another production process, for example to produce another fiber web 4. Such an embodiment is shown in Figure 2.Except for the feature that the recycling of the fibers from the reject areas 5 does not take place inline in this exemplary embodiment, all details and features already discussed in relation to Figure 1 apply to the exemplary embodiment in Figure 2. The method and device according to the invention are not limited to two-layer fiber webs 3. The method according to the invention relates not only to the production of CP or PC materials, but also, for example, to any desired combinations of different fiber layers with long and short fibers. Figure 3, for example, shows a device 100 and a method according to an exemplary embodiment for producing a fiber web 3 which has a carded first fiber layer 1 with long fibers, a second fiber layer 2 with short fibers, and a carded further first fiber layer 1' with long fibers. In other words, a CPC material is produced here.All details and features discussed in relation to Figure 1 also apply to the exemplary embodiment shown in Figure 3, except for the provision of the further first fiber layer 1' and the lack of pre-shredding. In the exemplary embodiment shown in Figure 3, the dry shredding of the reject areas 5 takes place in the cutting mill 6 without the reject areas 5 being shredded beforehand. To provide the further first fiber web 1', long fibers from a further bale opener 10' are transferred to a further card 11'. The carded long fibers from the further card 11' are pre-consolidated in a further pre-consolidation 12' and deposited as a further first fiber layer 1' on the second fiber layer 2.

[0034] Reference list:

[0035] 1 first fiber layer

[0036] 1' additional first fiber layer

[0037] 2 second fiber layer

[0038] 3 Fibrous tract

[0039] 4 additional fiber tracts

[0040] 5 Committee area

[0041] 6 Cutting mill

[0042] 7 Pulpers

[0043] 7.1 Hole sorting basket

[0044] 8 Barrier sieve basket

[0045] 9 Refiners

[0046] 10 bale openers

[0047] 10' additional bale opener

[0048] 11 teasel

[0049] 11' additional card

[0050] 12 Pre-consolidation

[0051] 12' further pre-consolidation

[0052] 13 Hydroentanglement

[0053] 14 dryers

[0054] 15 more pulpers

[0055] 16 tubs

[0056] 17 sorters

[0057] 18 more vats

[0058] 19 Separation unit

[0059] 20 Headbox

[0060] 21 Pre-shredding

[0061] 22 warehouses

[0062] 23 Waste

[0063] 24 recycled material

[0064] 100 device

Claims

Patent claims:

1. A method for producing a fiber web (3), wherein a first fiber layer (1) made of long fibers is provided, wherein a second fiber layer (2) made of short fibers is provided, wherein the first fiber layer (1) and the second fiber layer (2) are joined together, wherein after the first and second fiber layers (1, 2) have been joined, broke regions (5) are separated from the first and second fiber layers (1, 2), characterized in that the fibers of the separated broke regions (5) are first dry-comminuted in a comminution step, wherein the dry-comminuted broke regions are subsequently dispersed in a pulper (7) in a dissolving step, and the fibers of the broke regions (5) are thereby separated,wherein the shredded and dispersed reject areas (5) are used as recycling material (24) for producing the fiber web (3) or a further fiber web (4) by wet-laying the fibers of the shredded and dispersed reject areas (5).

2. Method according to claim 1, characterized in that the fibers of the reject areas (5) are defibrated in the comminution step, wherein the comminution step is preferably carried out in a cutting mill (6).

3. Method according to one of the preceding claims, characterized in that the fibers are hydrodynamically separated in the dissolving step.

4. Method according to one of the preceding claims, characterized in that the reject areas (5) undergo a coarse sorting step after the dissolving step, wherein non-dispersed parts of the reject areas (5) are sorted out, wherein the coarse sorting step is preferably carried out with a hole sorting basket (7.1), wherein the hole sorting basket (7.1) is particularly preferably in the pulper (7).

5. Method according to one of the preceding claims, characterized in that the reject areas (5) undergo an absorption step after the dissolving step and preferably after the coarse sorting step, wherein spinnings of the reject areas (5) are sorted out, wherein the absorption step is preferably carried out with a barrier sieve basket (8).

6. Method according to claim 5, characterized in that the spinnings are dispersed and then returned to the recycling material (24).

7. Method according to one of the preceding claims, characterized in that the first fiber web (1) is a carded fiber web.

8. Method according to one of the preceding claims, characterized in that the second fiber web (2) is wet-laid from a fiber pulp.

9. Method according to one of the preceding claims, characterized in that the recycled material (24) is used to produce the fiber web (3) and that the comminution step and the dissolving step are carried out inline and that the recycled material (24), in particular without storing the recycled material (24), is fed inline to provide the second fiber web.

10. Device (100) for producing a fiber web (3) according to a method according to one of the preceding claims.

Images