Method for manufacturing an air-laid fibrous web with the aid of a forming screen designed as a perforated film cover

Abstract

The invention relates to a method for producing a fibrous web, in particular a paper web, a board web or a tissue web, from a stock of fibrous material, comprising the following steps: a) treating the stock of fibrous material in an air stream in a low-consistency manner into individual fibers and / or fiber bundles; b) forming the individual fibers and / or fiber bundles in the air stream into a planar fibrous web by means of a dry forming method, wherein the individual fibers and / or fiber bundles are laid down on a forming screen; c) applying up to 30% by weight, preferably up to 20% by weight, further preferably up to 10% by weight, of water and / or a binder to the fibers of the formed fibrous web; d) consolidating the formed fibrous web; wherein the forming screen comprises a perforated film cover (54), preferably consists essentially of a perforated film cover (54), wherein an electrically conductive component (66) is arranged in and / or on the film cover (54). Furthermore, the invention relates to a forming screen and a machine for carrying out the method having such a forming screen.

Description

Technical Field

[0001] This invention relates to a method for manufacturing fiber webs, particularly paper webs, paperboard webs, or thin sheets, from raw materials containing fibrous materials, comprising the following steps:

[0002] a) Processing raw materials containing fibrous materials into single fibers and / or fiber bundles in an airflow with minimal water content;

[0003] b) A single fiber and / or fiber bundle is formed into a planar fiber web in an airflow by a dry forming method, wherein the single fiber and / or fiber bundle is laid on a forming screen.

[0004] c) Apply up to 30% by weight, preferably up to 20% by weight, and more preferably up to 10% by weight of water and / or adhesive to the fibers of the shaped fiber web;

[0005] d) Consolidate the shaped fiber web. Background Technology

[0006] In the past, many fiber webs, particularly paper webs, paperboard webs, or thin sheets, were manufactured almost exclusively using the wet process on an industrial scale, and this remains true today. For this purpose, without using waste paper, bales of pulp are typically dissociated in a pulp bath with a large amount of water to obtain a fiber suspension, which consists of approximately 99% by weight water and only about 1% by weight fiber. The fiber suspension is then applied through a headbox to a forming screen to form the web and undergo pre-dewatering. Subsequently, the fiber web is dewatered or dried under pressure and heat until it can finally be wound and / or otherwise processed. The advantage of the wet process is that hydrogen bonds are formed between the fibers during dewatering or drying, giving the fiber web the necessary strength. However, a disadvantage of this method is that drying the fiber web requires a significant amount of energy. Especially given today's climate change, there is a growing search for alternatives to this classic wet process.

[0007] As an alternative to the wet process, a dry air-laid method is known, for example, from US 4,167,378, in which the fibers are laid out into a fiber web in a substantially dry state. To impart the necessary strength to the fiber web, only a relatively small amount of water (for forming hydrogen bonds) and / or other binders are added. This significantly reduces the energy required for drying. The fibers are typically laid out on a woven forming screen that is air-permeable so that the fibers can be drawn from below the forming screen. Alternatively, an air-permeable spiral mesh can also be used as the forming screen.

[0008] The main challenge of this method lies in reliably conveying the fiber web laid on the forming screen and then transferring it to another processing unit, particularly the consolidation unit, without the fibers undergoing vortexing, localized aggregation, or persistent attachment anywhere. As long as water and / or binders have not been applied to the fibers and the fiber web has been consolidated, there is virtually no cohesion between the fibers. Currently, this remains largely unaffected because dry airflow web forming is primarily used today for manufacturing hygiene products, such as diapers, rather than for paper webs, paperboard webs, or sheet webs, at least not on an industrial scale. However, with increasing fiber material volume and / or production speed, problems, particularly regarding fiber vortexing and / or fiber attachment at the end of the forming screen (where the fiber web should exit the forming screen), are increasingly emerging. Summary of the Invention

[0009] Therefore, the technical problem to be solved by the present invention is to solve or at least alleviate the aforementioned problems from the prior art. In particular, a method and an apparatus are provided that enable the reliable production of high-quality fiber webs, particularly paper webs, paperboard webs, or sheet webs, in a dry air-flow web forming process. This should be achievable on an industrial scale, i.e., a production rate of several metric tons per day, preferably at least one metric ton per hour, wherein the produced fiber webs are preferably wound into rolls at the end of the manufacturing machine.

[0010] This technical problem is solved by the features of the independent claims. The dependent claims describe advantageous extensions of the invention. In particular, according to the first aspect of the invention, this technical problem is solved by a manufacturing method of the same type described at the beginning, characterized in particular by the fact that the forming screen includes a perforated membrane cover, preferably substantially composed of a perforated membrane cover, wherein conductive components are arranged in and / or on the membrane cover.

[0011] The inventors have recognized that perforated membrane covers offer better peeling performance at the end of the conveying path, where the fiber web awaits transfer to the next processing unit, compared to conventional woven screens. This is likely due to the easier retention of fibers at the crossover points of the woven screen. However, this advantage of perforated membrane covers is only fully realized when components are specifically incorporated into or on these covers to resist the establishment of electrostatic forces or to eliminate existing electrostatic forces from previous process steps. The causes and sources of fiber electrostatic charging can be multifaceted. Due to the larger contact area between the perforated membrane covers and the rollers around which they circulate, and possibly other static components such as a vacuum chamber, they generate higher friction compared to woven screens. This friction—unlike wet web forming—can rapidly lead to electrostatic charging, which can have undesirable effects on fiber formation and attachment. Alternatively or additionally, it is also possible that the fibers have already entered the forming head charged from the pipe. They can also continuously change their charge in dry climates due to contact with pipes, other fibers, etc.

[0012] Membrane covers can be essentially composed of a monolithic membrane or can be membrane laminates. Here, the term "membrane" should be understood as a planar structure, typically made of plastic and impermeable to water. Membranes can be manufactured by casting, extrusion, or other processes. Conversely, the term "membrane laminate" should be understood as a structure consisting of multiple layers that are themselves membranes and are planarly connected to each other, particularly without forming cavities, for example, by bonding or welding. The membrane layers can be made of the same or different materials. Furthermore, they can all have the same thickness or different thicknesses. The total thickness of the membrane laminate should be between 0.5 mm and 1.5 mm. Membrane laminates are generally preferred because they have the advantage that the individual layers can be subjected to better biaxial or uniaxial stretching before lamination than a monolithic membrane of the same thickness, thus the membrane laminate can have higher tensile strength relative to a monolithic membrane of the same thickness. Alternatively, the forming screen may also be constructed, for example, from a combination of such a perforated membrane layer and a conventional fabric, in which case the membrane layer is preferably arranged on the side of the forming screen facing the fiber width when used as intended.

[0013] In the context of this invention, paper web should be understood as a web composed of "ordinary" paper, particularly so-called printing and writing paper. The main difference between paper web and paperboard web or thin sheet web lies in the weight per unit area (in g / m²). 2 (Calculated), where the weight per unit area of ​​the paperboard web is higher than that of the paper web, while the weight per unit area of ​​the thinner web is lower than that of the paper web. Specifically, the fiber web can have a weight per unit area of ​​28 g / m². 2 Up to 42g / m 2The thin sheet width. For such a light fiber width, the problem of clean stripping from the forming screen is particularly prominent, thus highlighting the advantages of this invention. Besides varying area weights, paper, paperboard, and sheets often differ from their intended use, particularly in writing, protection, and absorption.

[0014] In the context of this invention, "water-saving processing" means that essentially no water is used to separate the fibers in the raw material into individual fibers, which is significantly different from wet web forming. The raw material can be, for example, pulp in bale form (also known as "bagged pulp") or pulp in "fluff pulp". Alternatively, waste paper can also be considered, for example. Even though the fibers are preferably dissociated only in the airflow in this "water-saving processing", this should not preclude the airflow from being conditioned, in particular its moisture content from being adjusted.

[0015] The forming screen has a fiber web side facing the fiber web and a machine side facing away from the fiber web. Perforations extend from the fiber web side to the machine side, or vice versa, thereby enabling fiber suction. Here, the perforations should be sized such that fibers are prevented from being sucked through the perforations.

[0016] Preferably, water and / or adhesives are not applied to the forming screen, and / or water and / or adhesives are not applied to the fiber web while it is on the forming screen. By providing conductive components in and / or on the membrane cover used as the forming screen, it is unnecessary to apply water and / or adhesives there to conduct away charge or avoid the generation of electrostatic charging. The less water and / or adhesive used, the less energy is required to dry the fiber web.

[0017] Furthermore, it is proposed that the forming screen is designed so flat on the side facing the fiber web that the finished fiber web does not possess any visually identifiable texture originating from the forming screen. This distinguishes the forming screen according to the invention from so-called “textured strips” or the like, which are specifically designed to impose a structuring effect on the fiber web, such as making it more appealing to the touch and / or in appearance. However, the inventors have recognized that using such structured covers as forming screens is disadvantageous because they make it difficult to peel the fiber web from the forming screen, for example, when transferring it to the next cover. Therefore, it is advantageous that the forming screen is constructed as smoothly or flat as possible on its upper side facing the fiber web.

[0018] In one embodiment of the invention, the conductive component can be applied to the membrane cover in the form of a coating. Here, the coating can be conductive or have a resistance significantly lower than the rest of the membrane cover. If the coating is also conductively connected to the base, it can effectively conduct away charge and prevent the establishment of an electric field that could adversely affect fiber orientation and / or adhesion.

[0019] Specifically, the coating can be applied to the diaphragm cover on the side facing the fiber web during specified operation. Alternatively or additionally, the coating can also be applied to the diaphragm cover on the side facing away from the fiber web during specified operation. If corresponding coatings are provided on both sides of the diaphragm cover, these coatings are preferably electrically connected to each other, for example, through the edges of the diaphragm cover. In this way, electrical charge can be guided from the fiber web side of the cover to the machine side, and from there it can then be very easily guided, for example, through conductive guide rollers, into the machine base.

[0020] One particularly preferred embodiment specifies that the coating extends at least partially into the perforations of the membrane cover, preferably forming a conductive connection between the side of the membrane cover facing the fiber web during specified operation and the side of the membrane cover facing away from the fiber web during specified operation.

[0021] Especially when perforation is introduced into the membrane cap using a laser, it is advantageous that the coating is applied to the membrane cap only after perforation, because otherwise the coating might hinder the perforation process due to its different laser absorption rate. Furthermore, coating only after perforation allows the coating to penetrate into the perforation or also cover the walls of the perforation.

[0022] The coating is preferably applied by spraying, similar to painting; however, other methods, such as electroplating and / or sputtering, are also possible.

[0023] The coating may contain or be composed of metallic components. Alternatively, the coating may also contain or be composed of carbon, preferably in the form of graphite or carbon black. Carbon is an excellent electrical conductor. It can also exist, for example, in the form of so-called "carbon nanotubes." However, the concentration of these "carbon nanotubes" must be chosen to be sufficiently high to achieve the desired conductivity.

[0024] However, as an alternative to the coating, conductive components may also be disposed in the plastic material of at least one layer of the membrane cover. For example, carbon black particles or carbon nanotubes may be present in this at least one layer to improve conductivity. Alternatively or additionally, in the case of a membrane composite, the conductive components may also be disposed in at least one adhesive layer between two adjacent layers of the membrane composite.

[0025] Another alternative to the coating specifies that the conductive components can be formed in the form of conductive wires arranged on at least one side of the membrane cover. Preferably, they are arranged on the fiber web side of the membrane cover. For example, these wires can be very fine copper wires, which are fixed, for example, bonded to the fiber web side of the membrane cover.

[0026] Regardless of the exact design of the conductive components, it is advantageous that they are arranged in and / or on the membrane cover such that the first side edge of the forming screen is electrically connected to the second side edge of the forming screen opposite to the first side edge. In this way, charge can be conducted, for example, at the two side edges of the membrane cover, through carbon fiber brushes abutting there, into the machine base. It is not necessary, for example, that the entire fiber web side be designed to be conductive. Instead, it is sufficient that only conductive lines or coated strips are present at specific intervals, extending transversely to the forming screen. In this case, the side edges of the forming screen are preferably designed to be continuously conductive.

[0027] A particularly advantageous extended design provision of the present invention specifies that the conductive components are arranged in and / or on the membrane cover such that multiple conductive strips are generated between the two side edges of the forming screen, preferably in the width direction of the membrane cover, wherein the strips are not conductively connected to each other. Specifically, in this case, the side edges of the forming screen should not be designed to be continuously conductive. The strips can be provided, for example, by conductive wire or by a conductive coating. The advantage of this embodiment is that the circumferentially running forming screen can be in different electrostatic charging or discharging states in different sections, or be electrostatically charged or discharged differently. Specifically, in the front section of the circumferentially running forming screen, where the fibers are laid on the forming screen, electrostatic charging can be allowed to intentionally retain the fibers on the forming screen, while in the rear section of the forming screen, where the fiber web should be transferred from the forming screen to another processing unit, such as a consolidation screen, targeted electrostatic discharge can be induced to avoid or at least reduce attraction between the forming screen and the fiber web due to electrostatic forces at that location. Therefore, the strip should preferably have a width no greater than the length of the transfer zone in which the fiber web is transferred from the forming screen to the subsequent processing unit. Non-conductive insulating strips can be provided between each pair of adjacent conductive strips. The width of the insulating strips can be significantly smaller than the width of the conductive strips. In the transfer zone, for example, a conductive brush can contact the side edge of the forming screen to selectively conduct static charge from the forming screen, for example, into the machine base in this area.

[0028] Perforations can be introduced into the membrane capping material through drilling, particularly laser drilling, and / or punching, and / or hot needle punching. Laser drilling, in particular, allows for the introduction of very fine perforations into the membrane capping material at a high number of perforations per unit area. This results in very uniform fiber aspiration across the surface. In hot needle punching, the membrane is penetrated by a hot needle, where, unlike punching, the membrane material is only displaced and not separated. This results in less or even no waste material being generated in hot needle punching, which is advantageous. Unlike punching, in drilling, particularly laser drilling, and hot needle punching, the wall of the perforation can have an angle not equal to 90° relative to the fiber width side and / or machine side of the forming screen. In particular, the perforation can be tapered.

[0029] Another aspect of the invention relates to a forming screen for manufacturing fibrous webs from a raw material containing fibrous material according to the aforementioned method according to the invention, wherein the forming screen comprises a perforated membrane cover, preferably substantially composed of a perforated membrane cover, and wherein conductive components are arranged in and / or on the membrane cover.

[0030] Another aspect of the invention relates to a machine for manufacturing fibrous webs from raw materials containing fibrous material according to the aforementioned method according to the invention, comprising the aforementioned forming screen according to the invention.

[0031] An advantageous extended design of the invention specifies that the conductive components are arranged in and / or on the membrane cover such that multiple conductive strips are generated, extending between the two side edges of the forming screen, preferably in the width direction of the membrane cover, wherein the strips are not electrically connected to each other, and the machine includes components, particularly conductive brushes, in a transfer zone where the fiber web is transferred from the forming screen to another processing unit, particularly a consolidation screen, said components being designed to cause targeted electrostatic discharge of the forming screen in the transfer zone. Conversely, preferably, the forming screen is not electrostatically discharged in the region upstream of the transfer zone, i.e., in the region where the fibers are laid on the forming screen and the resulting fiber web is conveyed on the forming screen. Thus, the adhesion of the fibers or fiber web to the forming screen can be increased in this region. Attached Figure Description

[0032] The invention will now be described in more detail with the aid of illustrative embodiments. In the accompanying drawings:

[0033] Figure 1 + Figure 2 A method for manufacturing an air-laid fiber web or a machine for performing the method is shown according to the present invention;

[0034] Figure 3 + Figure 4 The fabrication of a membrane cover perforated by a laser is shown;

[0035] Figure 5 The cross-section of a section of the perforated membrane cover is shown, which does not have conductive components;

[0036] Figure 6 As shown Figure 5 The membrane cover shown is of the first type, but with conductive components;

[0037] Figure 7 As shown Figure 5 The membrane cover shown is a second form with conductive components; and

[0038] Figure 8 As shown Figure 5 The membrane cover shown is a third type, but with conductive components. Detailed Implementation

[0039] Figure 1 and Figure 2 The schematic diagram shows a machine 10 for manufacturing dry web fiber webs 14, particularly paper webs, paperboard webs, or thin sheets, according to the method of the present invention.

[0040] Figure 1 The front and middle sections of machine 10 are shown here, in which the following method steps are performed:

[0041] a) Processing the raw material 12 containing fibrous material into single fibers and / or fiber bundles in an airflow with minimal water content;

[0042] b) A single fiber and / or fiber bundle is formed into a planar fiber web 14 in an airflow by a dry forming method, wherein the single fiber and / or fiber bundle is laid on a forming screen 16.

[0043] Figure 2 The middle and rear sections of machine 10 are shown here, in which the following method steps are performed:

[0044] b) A single fiber and / or fiber bundle is formed into a planar fiber web 14 in an airflow by a dry forming method, wherein the single fiber and / or fiber bundle is laid on a forming screen 16.

[0045] c) Apply up to 30% by weight, preferably up to 20% by weight, and more preferably up to 10% by weight of water and / or adhesive to the fibers of the shaped fiber web 14;

[0046] d) Consolidate the shaped fiber width 14.

[0047] To make the illustration clearer, the forming unit in which step b) of method is performed is shown. Figure 1 and Figure 2As shown in the figures, even in this embodiment, the forming unit is actually included only once in machine 10.

[0048] In this embodiment, the fibrous material 12 is preferably in bale form, consisting of multiple stacked pulp boards, for example, from the manufacturer "Mercer Stendal GmbH". The pulp can be NBSK pulp, as it is commonly used in the wet process to manufacture paper webs, paperboard webs, or thin sheets. The bale pulp can have a strength of 600 kg / m³. 3 Up to 1000 kg / m 3 Especially about 920kg / m 3 The density, wherein each pulp board may have a thickness of 1.0 mm to 2.0 mm, particularly about 1.5 mm.

[0049] To perform step a), in this embodiment, the pulp bales may first enter the feed hopper 18, around which a conveyor belt 20 runs. The feed hopper 18 may be designed such that only 1 to 50, preferably 2 to 25, and more preferably 3 to 10 pulp boards are simultaneously supplied to the shredder 22 in a substantially horizontal direction. However, this is not mandatory. The entire bale may also be supplied to the shredder 22 at once, and / or the supply may be carried out without the conveyor belt 20. The shredder 22 includes at least one rotor 24 with protrusions, upstream of which two driven feed rollers are disposed. The shredder 22 produces a large number of fragments 26 from the bales of pulp supplied to it. The fragments 26 produced in the shredder 22 are then preferably supplied to a cleaning device 28 by an airflow. The cleaning device 28 may be, for example, a so-called air classifier. In this device, the fragments 26 are guided into an ascender through which air is blown in from below by a blower 30. The debris 26 is swept and swirled together by the airflow, while impurities 32, such as sand or the like, are separated. These impurities 32 fall downwards against the airflow in the riser due to gravity, where they can exit the riser. Conversely, the debris 26 is carried upwards by the airflow and then enters the cyclone air separator device 34, where the air is separated from the debris. The separated air can, for example, be... Figure 1 As indicated by the arrow, the pulp is returned to fragment 26 before the cleaning device 28. The cleaned fragment 26 falls downward from the cyclone air separator device 34 into the collection container 36. Here, the density of the pulp in the collection container 36 in the form of fragment 26 is preferably at most one-quarter of the density of the pulp in the form of bale pulp before the shredder 22. In other words, the pulp in the form of fragment 26 is preferably present relatively loosely in the collection container 36.

[0050] The continuous stream of fragments 26 can then be supplied from the collection container 36, preferably also via an airflow, to the defiberizing device 40, for which a separate blower 38 can be used. At the defiberizing device, the fragments 26 are defibered into individual fibers during the dry process. Subsequently, the individual fibers enter the air-laid web unit 42 to form a dry-laid fiber web 14. Here, the fiber web 14 is formed on a rotating, permeable forming screen 16, through which it is simultaneously transported away.

[0051] like Figure 2 As shown, the fiber web 14 is then transferred from the forming unit to the consolidation unit, where steps c) and d) of the method are performed. For this purpose, the fiber web 14 is transferred from the forming screen 16 to the consolidation screen 44. The consolidation screen 44 conveys the fiber web 14 through a pressure gap 46 formed by two rollers. Prior to this, the fiber web 14 is wetted by means of nozzles 48, wherein the amount of water and / or adhesive applied is relatively small, particularly less than 15% by weight, preferably less than 10% by weight, and more preferably less than 8% by weight, relative to the weight of the fiber web 14 before wetting. Subsequently, the fiber web 14 is also guided through the dryer 50 and then wound by the winding machine 52. The fiber web 14 is preferably conveyed by the consolidation screen 44 in a suspended manner, for example by means of negative pressure. Furthermore, the wetting of the fiber web 14 by means of nozzles 48 is preferably performed from below. In this way, neither the forming screen 16 nor the consolidation screen 44 is wetted, which significantly reduces the amount of cleaning work, preferably making it completely unnecessary to clean these screens 16 and 44. The consolidation screen 16 and / or at least one of the two rollers forming the pressure gap 46 may have a structure to selectively create localized high-pressure zones in the fiber web 14.

[0052] By applying water and / or adhesive via nozzle 48, combined with pressure applied in pressure gap 46, where the fiber web 14 is preferably also heated, sufficient strength can be imparted to the fiber web 14 so that it can ultimately be wound and further processed without problems, even without the use of large amounts of water and / or relatively large amounts of other reinforcing agents such as melt-bonded fibers or starch, preferably without the use of any other reinforcing agents. Preferably, the amount of water applied is exactly the amount required to form a sufficient number of hydrogen bonds for this purpose. This manufacturing method is particularly energy and water-efficient because only a small amount of water needs to be removed from the fiber web 14 again. Furthermore, the addition of chemical additives, such as melt-bonded fibers, can be omitted, so that the finished fiber web 14 can also be biodegradable or compostable without problems.

[0053] However, in order to reliably operate the entire manufacturing process at high process speeds, particularly at speeds greater than 150 m / min, preferably greater than 250 m / min, and even more preferably greater than 400 m / min, the fiber web 14 needs to be safely and undisturbedly transported from the air-forming unit 42 to the consolidation unit, where it essentially acquires its strength. Here, the fiber web 14 can be imagined as a thin layer of dust until the fiber web is consolidated. This dust layer is held on the forming screen 16 by negative pressure. For this purpose, a ring is arranged in the forming screen 16... Figure 1 and Figure 2 The negative pressure box is not shown, and the forming screen 16 is designed to be permeable.

[0054] According to the invention, a membrane cover 54 is used as the forming screen 16, which is perforated to make it permeable. Figure 3 and Figure 4 This example illustrates how such a membrane cover 54 can be perforated using a laser. For this purpose, a laser beam LB emitted by the laser is aligned with the membrane substrate. The laser is controlled by a controller. Here, the laser drills multiple discrete through-holes or perforations 56 from the laser-facing surface 58 along the thickness direction TD of the membrane cover 54 to the opposite, laser-facing surface.

[0055] During the perforation process, the membrane cap 54, preferably designed as an endless ring, can be used as follows: Figure 4 The tension is shown between two rollers R. For example, perforations 56 can be drilled row by row into the membrane cover 54, starting from the first side edge 60 and moving toward the second side edge 62 opposite to the first side edge 60, using a laser.

[0056] like Figure 5 As shown, the membrane cover 54 is preferably composed substantially of a membrane assembly having multiple layers 64. The layers 64 can be composed of monolithically constructed membranes, which are connected to each other planarly, preferably without cavities, for example, by means of a thin adhesive layer disposed between the membranes. In this embodiment, the membrane assembly comprises four layers 64, all constructed to be substantially the same thickness. For clarity, only two of the perforations 56 shown are indicated by reference numerals.

[0057] The inventors have recognized that, in principle, it is also possible to reliably convey fiber webs 14 at high speeds using a perforated membrane cover 54 as a forming screen 16, where the fiber webs are more easily peeled off from the forming screen 16 than in the case of a conventional woven forming screen. However, it is important to properly control the electrostatic forces that build up in the perforated membrane cover 54 due to friction much stronger than in a conventional woven screen. These forces can adversely affect the fibers laid on the forming screen. For example, the process of fiber peeling off from the forming screen 16 may be adversely affected, and the fibers may persistently accumulate in certain locations as contaminants. For this reason, according to the invention, conductive components 66 are specifically arranged in and / or on the membrane cover to resist the establishment of electrostatic forces between the forming screen 16 and individual fibers and / or fiber bundles, or to eliminate existing electrostatic forces.

[0058] Figure 6 The diagram schematically illustrates a first embodiment of a membrane cover 54 according to the invention, having conductive elements 66. Here, a coating 68 is applied to both sides of the membrane cover 54, forming the conductive elements 66. The coating 68 is designed to be conductive, for example by containing carbon black or graphite. The coating 68 is applied only after the membrane cover 54 is perforated, and therefore also extends into the perforations 56. Specifically, it covers the sidewalls of the perforations 56, thereby establishing a conductive connection between the two sides of the membrane cover 54. The coating 68 is preferably applied by spraying. However, other methods, particularly electroplating and sputtering, are also possible.

[0059] In the context of this invention, "conductive" means having a resistance significantly lower than that of the membrane cap 54, or significantly lower than that of the layer 64 of the membrane composite. Preferably, the resistivity of the conductive component 66 is less than 250 Ohms. cm. Here, the resistivity of the conductive component 66 (in Ohms) The length (in cm) should be understood as the resistance (in Ohms) of the conductive component 66 divided by its length (in cm), and then divided by the reciprocal of its cross-sectional area (in 1 / cm²). 2 The value obtained by calculation.

[0060] Figure 7 The diagram schematically illustrates a second embodiment of the membrane cover 54 according to the invention, having a conductive component 66. In this embodiment, at least one layer 64, exactly one layer 64 in this embodiment, i.e., the uppermost layer 64, is designed to be conductive, for example by containing carbon black or graphite. Therefore, no additional process steps are required, as per [the previous description of the invention]. Figure 6 In this embodiment, a membrane cover 54 is coated after perforation.

[0061] Figure 8The diagram schematically illustrates a third embodiment of the membrane cover 54 according to the invention, having a conductive component 66. Here, conductive wires 70, particularly very small diameter copper wires, are applied, for example, bonded, to one of the two surfaces of the membrane cover 54. Preferably, the wires 70 are so thin and oriented that they do not obscure any perforations 56.

[0062] Regardless of the exact type of conductive component 66 used, it is advantageous if they establish a connection between the two side edges 60, 62 of the membrane cover 54. The side edges 60, 62 may also include conductive components 66, allowing charge to be easily conducted through the side edges 60, 62 into the base of the machine 10.

[0063] Using the method according to the invention, dry-laid fiber webs 14 can be produced at a production speed greater than 400 m / min and / or a width greater than 200 cm, and / or a yield greater than 1 t / h. The fiber webs can particularly be thin sheets with an area weight between 28 g / m². 2 Up to 42g / m 2 between.

[0064] List of reference numerals in the attached diagram:

[0065] 10 machines

[0066] 12 Raw materials containing fibers

[0067] 14 Fiber width

[0068] 16 Forming Screen

[0069] 18 Feeding bin

[0070] 20 Conveyor Belt

[0071] 22. Paper shredder

[0072] 24 rotors

[0073] 26 fragments

[0074] 28 Cleaning equipment

[0075] 30 Blower

[0076] 32 Impurities

[0077] 34 Cyclone Air Separator Device

[0078] 36 Collection Container

[0079] 38. Other blowers

[0080] 40 Fiber Debonding Device

[0081] 42 airflow networking units

[0082] 44 Consolidation sieve

[0083] 46 Pressure gap

[0084] 48 nozzles

[0085] 50 Dryer

[0086] 52 Winding Machine

[0087] 54. Membrane cover

[0088] 56. Perforation

[0089] 58 Surface facing the laser

[0090] 60 First side edge

[0091] 62 Second side edge

[0092] 64th floor

[0093] 66 Conductive components

[0094] 68 Coating

[0095] 70 Conductive wire

[0096] LB laser beam

[0097] R roller

[0098] TD thickness direction

[0099] WD Width Direction

Claims

1. A method for manufacturing a fiber web (14), particularly a paper web, paperboard web, or sheet web, from a raw material (12) containing fibrous material, comprising the following steps: a) Process the raw material (12) containing fibrous material into single fibers and / or fiber bundles in an airflow with minimal water; b) A single fiber and / or fiber bundle is formed into a planar fiber web (14) in an airflow by a dry forming method, wherein the single fiber and / or fiber bundle is laid on a forming screen (16). c) Apply up to 30% by weight, preferably up to 20% by weight, and more preferably up to 10% by weight of water and / or adhesive to the fibers of the shaped fiber web (14); d) Consolidate the shaped fiber web (14); The characteristic feature is that the forming screen (16) includes a perforated membrane cover (54), preferably consisting essentially of a perforated membrane cover (54), wherein conductive components (66) are arranged in and / or on the membrane cover (54).

2. The method according to claim 1, characterized in that, Water and / or adhesives are not applied to the forming screen (16), and / or water and / or adhesives are not applied to the fiber web (14) while the fiber web is on the forming screen (16).

3. The method according to claim 1 or 2, characterized in that, The forming screen (16) is designed to be so flat on the side facing the fiber web (14) that the finished fiber web (14) does not have a texture that is visible to the naked eye and originates from the forming screen (16).

4. The method according to any one of the preceding claims, characterized in that, The conductive component (66) is applied to the membrane cover (54) in the form of a coating (68).

5. The method according to claim 4, characterized in that, The coating (68) is applied to the membrane cover (54) on the side facing the fiber web (14) during operation as specified.

6. The method according to claim 4 or 5, characterized in that, The coating (68) is applied to the membrane cover (54) on the side opposite to the fiber web (14) during operation as specified.

7. The method according to any one of claims 4 to 6, characterized in that, The coating (68) extends at least partially into the perforation (56) of the membrane cover (54), preferably forming a conductive connection between the side of the membrane cover (54) facing the fiber web (14) in the prescribed operation and the side of the membrane cover (54) facing away from the fiber web (14) in the prescribed operation.

8. The method according to any one of claims 4 to 7, characterized in that, The coating (68) is applied to the membrane cover (54) only after perforation, and / or the coating (68) is applied by spraying and / or electroplating and / or sputtering.

9. The method according to any one of claims 4 to 8, characterized in that, The coating (68) contains or is composed of a metallic component, or the coating (68) contains or is composed of carbon, preferably in the form of graphite and / or carbon black.

10. The method according to claims 1 to 3, characterized in that, The conductive component (66) is disposed in at least one layer (64) of the plastic material of the membrane cover (54).

11. The method according to claims 1 to 3, characterized in that, The conductive components (66) are formed in the form of conductive wires (70) arranged on at least one side of the membrane cover (54).

12. The method according to any one of the preceding claims, characterized in that, The conductive component (66) is arranged in and / or on the membrane cover (54) such that the first side edge (60) of the forming screen (16) is electrically connected to the second side edge (62) of the forming screen (16) opposite to the first side edge (60).

13. The method according to any one of the preceding claims, characterized in that, The conductive component (66) is arranged in and / or on the membrane cover (54) such that a plurality of conductive strips are generated between the two side edges (60, 62) of the forming screen (16), preferably in the width direction (WD) of the membrane cover (54), wherein the strips do not have conductive connections to each other.

14. The method according to any one of the preceding claims, characterized in that, The perforation (56) is introduced into the membrane cap (54) by drilling, particularly laser drilling, and / or by punching, and / or by hot needle punching.

15. A forming screen (16) for manufacturing a fiber web (14) from a raw material (12) containing fibrous material according to any one of the preceding claims, characterized in that, The forming screen (16) includes a perforated membrane cover (54), preferably consisting essentially of a perforated membrane cover (54), wherein conductive components (66) are arranged in and / or on the membrane cover (54).

16. A machine (10) for manufacturing a fiber web (14) from a raw material (12) containing fibrous material by any one of claims 1 to 14, comprising the forming screen (16) of claim 15.

17. The machine (10) according to claim 16, characterized in that, The conductive component (66) is arranged in and / or on the membrane cover (54) such that a plurality of conductive strips are generated between the two side edges (60, 62) of the forming screen (16), preferably in the width direction (WD) of the membrane cover (54), wherein the strips are not electrically connected to each other, and the machine includes components, in particular conductive brushes, in the transfer zone in which the fiber web (14) is transferred from the forming screen (16) to another processing unit, in particular a consolidation screen (44), said components being designed to cause targeted electrostatic discharge of the forming screen (16) in the transfer zone.

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