Method and machine for producing a dried fibrous web

Abstract

The invention relates to machine (1) and a corresponding method for producing a dry-air laid fibrous web (309). The machine (1) comprises: a) a raw material processing plant for the low-water processing of cellulose-containing fibers (200) into single fibers and / or fiber bundles (209); b) a dry forming device (4) for dry forming of the individual fibers and / or fiber bundles (209) in an air stream to form a planar fiber fabric (300) on a forming belt (40); c) an application device (71) for applying a fluid, preferably water and / or a water-additive mixture, to the fiber fabric (300); d) a consolidation device (8) for consolidating the planar fiber fabric (300) by applying pressure in a press gap (80) when the fiber fabric (300) is guided through the press gap (80) on a press belt (41); and furthermore a transfer area (100) which is configured to transfer the fiber fabric (300) from the forming belt (40) to the press belt (41), wherein the forming belt (40) and the press belt (41) in the transfer area (100) are both guided substantially parallel to a displacement direction over a length (110) of at least 50 mm and at most 1,000 mm.

Description

[0001] The invention relates to a method for producing a fibrous web, preferably a tissue, paper or cardboard web or a nonwoven web, in particular a tissue web with a basis weight of 28g / m². 2 up to 42g / m² 2 , comprising the following steps: a) low-water raw material processing of cellulose-containing fibers into individual fibers and / or fiber bundles; b) Forming the individual fibers and / or fiber bundles in an air stream to form a flat fiber fabric on a forming belt by a dry forming process; c) Application of a fluid, preferably water and / or a water-additive mixture, to the fiber fabric; d) Consolidation of the planar fiber fabric by applying pressure in a press gap, wherein the fiber fabric is guided through the press gap on a press belt; wherein the fiber fabric is transferred from the forming belt to the press belt in a transfer area, wherein a fiber fabric-carrying section of the forming belt is guided at its end over a final forming belt deflection roller and a fiber fabric-carrying section of the press belt is guided at its beginning over a first press belt deflection roller. The invention further relates to a machine for carrying out the manufacturing process according to the invention.

[0002] It should be noted here that in mechanical engineering, the term "Trum" regularly refers to a part or branch of a rotating component. In particular, the terms "loaded run" and "slack run" for belts that transmit tensile forces are common in mechanical engineering. For the purposes of the present invention, the term "Trum" is used specifically to describe the section of a covering or belt that transports the fiber fabric.

[0003] Many fibrous webs, especially paper, cardboard, or tissue, were and still are produced almost exclusively using the wet process on an industrial scale. For this process, unless recycled paper is used, baled pulp is typically dissolved in large quantities of water in a vat, resulting in a fiber suspension consisting of approximately 99% water and only about 1% fiber by weight. This fiber suspension is then applied to a forming wire via a headbox to form sheets. The resulting fibrous web is subsequently dewatered or dried by pressure and heat until it can be wound up or otherwise processed. The wet process has the advantage that hydrogen bonds form between the individual fibers during dewatering or drying, giving the fibrous web the necessary strength.However, a disadvantage of this process is that drying the fiber web requires large amounts of energy. Especially in light of current climate change, there is therefore an intensive search for alternatives to this traditional wet process.

[0004] As an alternative to the wet process, the dry air lay-up process is already known, in which fibers are laid down into a fiber web in a largely dry state. To give the fiber web the necessary strength, only relatively small amounts of water (for the formation of hydrogen bonds) and / or other binders are added. This results in significantly less energy being required for drying. One challenge with this process is achieving good formation and uniform fiber distribution. Unlike in suspension, dry fibers tend to form undesirable clumps. Therefore, precise fiber separation is extremely important. For this reason, so-called "fluff pulp" is generally used for the dry air lay-up process.This refers to pulp that has been pre-treated so that the individual fibers already have fewer and / or weaker bonds to each other. This makes the pulp more voluminous, more absorbent, and better suited for the dry air layup process. However, fluff pulp, which is usually produced in rolls, is much more expensive than ordinary baled pulp, as is typically used in the paper industry. Therefore, the dry air layup process is currently used primarily only for the production of sanitary products, such as diapers, and not for the production of paper, cardboard, or tissue webs, at least not on an industrial scale. For such an industrial level, the use of fluff pulp would be uneconomical, despite currently high energy costs.

[0005] The embodiment according to Fig. Document 3 in publication WO 2019 / 137667 A1 already discloses a generic process, described at the outset, for producing a dried fibrous web. The last forming belt deflection roller is positioned almost directly below the first press belt deflection roller, so that the transfer area is correspondingly short, in particular linear in the transverse direction of the machine. In the transfer area, the fiber layer, which has been transported on the forming belt essentially in a horizontal direction, is transferred to the press belt, which transports the fiber layer further in an oblique upward direction.

[0006] It has been found that with this plant configuration known from the prior art, increasing the production speed to an industrial level can lead to a qualitative deterioration of the fiber web, especially with regard to the formation, but also with regard to basis weight profiling in the machine and / or machine transverse direction, as well as feel behavior and appearance.

[0007] It is therefore an object of the present invention to provide a method and a machine for producing a dried fibrous web, in particular a tissue web, with which the problems described above can be solved or at least reduced. In particular, it should make it possible to achieve high quality even at industrial production speeds.

[0008] "At an industrial level" means a high, continuous production speed of 150 m / min or greater, in particular 250 m / min or greater, and preferably 400 m / min or greater. Furthermore, at an industrial level, the width of the continuously produced fibrous web is preferably 0.5 m or greater, more preferably 1 m or greater, in particular 2.3 m or greater, but generally 10 m or less.

[0009] To differentiate between the manufactured fiber webs, for example a tissue, paper or cardboard web on the one hand and a non-woven web on the other, the following distinction is made, which is based on fiber length, density and fiber bonding type: A fibrous web with predominantly medium fiber lengths, shorter than the fiber lengths of nonwoven webs, of less than or equal to 5 mm, in particular less than or equal to 4 mm, preferably less than or equal to 3 mm, predominantly bonded by hydrogen bonds and with a bulk density of greater than or equal to 0.4 g / cm³, is placed under a tissue, paper or cardboard web. 3 Understood. The fibers used in a tissue, paper or cardboard web are additionally characterized by having a slenderness ratio of fiber length to fiber diameter of less than or equal to 200, in particular less than or equal to 150, preferably less than or equal to 100.

[0010] A nonwoven web, which also consists primarily of fibers, is defined—as a key distinction from tissue, paper, or cardboard webs—by having a fiber content of at least 30% consisting of very long fibers with an average fiber length of more than 5 mm, or continuous fibers, which determine the nonwoven characteristics. Furthermore, a fiber-to-diameter ratio of greater than or equal to 300 is targeted for a nonwoven web. The remaining fiber content of a nonwoven web can be of a different composition, and the bulk density should be below 0.40 g / cm³. 3 to classify a fibrous web as a nonwoven fabric.

[0011] The problem described above is solved by the features of the independent claims. The dependent claims relate to advantageous embodiments of the present invention.

[0012] In particular, the problem is solved by the generic manufacturing process described above, which is characterized in particular by the fact that in the transfer area the forming belt and the press belt are both guided essentially parallel to a displacement direction over a length of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm, wherein the length is defined as the distance, measured in the displacement direction, between the axis of rotation of the first press belt deflection roller and the axis of rotation of the last forming belt deflection roller.

[0013] The inventors recognized that the quality problems observed when production speed was increased could be reduced if the transfer area was sufficiently long and the forming belt and the pressure belt were guided essentially parallel to each other or to the direction of displacement within the transfer area. "Essentially parallel" in the context of the present invention means that any angular deviation, if measurable at all, should be very small, in particular less than 5°, preferably less than 3°, and even more preferably less than 1°. The inventors explain this as follows: The fiber fabric transported on the forming belt has a very low tensile strength.To prevent any deterioration in the quality of the fiber fabric, a "gentle" transfer appears to be important, allowing the fiber fabric sufficient time to detach from the forming belt and adhere to the pressing belt. This then necessitates a longer transfer area when production speed is increased. However, extending the transfer area beyond 1,000 mm has not demonstrated any further advantages. The increased space requirement of a further extension only results in disadvantages.

[0014] The advantages of the present invention are particularly evident when the speed at which the fiber fabric is guided through the transfer area is greater than or equal to 150 m / min, particularly greater than or equal to 250 m / min, and preferably greater than or equal to 400 m / min. The advantages of the present invention are also particularly evident when the moisture content of the fiber fabric to be transferred in the transfer area is less than 20%. In such cases, the transfer process is particularly critical.

[0015] Furthermore, to further counteract deterioration of the fiber layup at high production speeds, it has proven particularly advantageous if, in the transfer area, the forming belt maintains a distance from the pressing belt that is no greater than the thickness of the fiber layup immediately before the transfer area. The thickness of the fiber layup immediately before the transfer area can, for example, range from 0.3 mm to 10 mm. In this way, the fiber layup is supported by both belts simultaneously along the entire length of the transfer area. The fiber layup experiences no significant change in its direction of movement throughout the entire transfer area and has sufficient time to detach smoothly from the forming belt and adhere to the pressing belt.

[0016] To facilitate detachment from the forming belt and attachment to the pressing belt, the first pressing belt deflection roller can be vacuum-assisted. However, this is not mandatory. The last forming belt deflection roller, on the other hand, should be vacuum-assisted. For this purpose, both the forming belt and the pressing belt should be air-permeable. Additional vacuum devices, such as suction boxes, can also be provided behind the first pressing belt deflection roller in the screen loop of the pressing belt to attach and hold the fiber layup to the pressing belt. Preferably, the intensity of the vacuum in the transfer area increases in the direction of displacement. The applied vacuum from the vacuum devices is preferably between 1 mbar and 10 mbar.

[0017] In an advantageous embodiment of the present invention, the fiber fabric, after leaving the transfer area, is preferably suspended overhead, and is guided to the press gap, in particular by means of vacuum means provided in the loop of the press belt, in order to then be guided through the press gap together with the press belt.

[0018] The fluid from step c) can be applied to the fiber fabric after it leaves the transfer area and before reaching the press gap. If this fluid is applied to the fiber fabric shortly before reaching the press gap, the water has less time to penetrate the interior of the fibers, so that more free water is available to form hydrogen bonds between the fibers in the press gap.

[0019] Furthermore, the press belt can be designed to provide the fiber fabric in the press gap with a multitude of high-pressure and low-pressure zones, thereby increasing the strength of the fiber fabric. Preferably, the high-pressure and low-pressure zones are dimensioned such that they form a structure visible to the naked eye within the fiber fabric. This offers the possibility of achieving good strength of the fiber web while simultaneously maintaining good feel and absorbency.

[0020] The concept of a "gentle" transfer is not only applicable to the transfer area between the forming belt and the pressing belt, even though it is of particular importance there due to the low strength of the fiber fabric, but it can also be advantageously applied at other points where the fiber fabric is transferred from one belt to another. In particular, the fiber fabric can be transferred from the pressing belt to a connecting belt in a further transfer area, wherein the fiber fabric-carrying section of the pressing belt is guided at its end over a final pressing belt deflection roller, and a fiber fabric-carrying section of the connecting belt is guided at its beginning over a first connecting belt deflection roller, wherein in the further transfer area the pressing belt and the connecting belt both run essentially parallel to a further displacement direction over a length of at least 50 mm and at most 1 mm.000mm, preferably at least 100mm and at most 800mm, and wherein the length is defined as the distance, measured in the further displacement direction, between the axis of rotation of the first connecting belt deflection roller and the axis of rotation of the last press belt deflection roller.

[0021] The connecting belt can be a drying screen on which the fiber fabric is guided through a drying device, in particular a flow-through dryer.

[0022] An advantageous embodiment of the present invention provides that the fiber web is dried by an electrically operated drying device, in particular a purely electrically operated flow-through dryer. Instead of using a conventional steam- or gas-heated drying device, the electricity for operating the drying device can be obtained from renewable sources, such as wind power or solar panels, thus further reducing the CO2 footprint for the production of the fiber web compared to conventional methods.

[0023] Another aspect of the present invention relates to a machine for producing a fibrous web, preferably a tissue, paper or cardboard web or a nonwoven web, in particular a tissue web with a basis weight of 28g / m². 2 up to 42g / m² 2 , comprehensive: a) a raw material processing plant for the low-water processing of cellulose-containing fibers into individual fibers and / or fiber bundles; b) a dry forming device for dry forming of individual fibers and / or fiber bundles in an air stream to form a flat fiber fabric on a forming belt; c) an application device for applying a fluid, preferably water and / or a water-additive mixture, to the fiber fabric; d) a consolidation device for consolidating the planar fiber fabric by applying pressure in a press gap when the fiber fabric is guided through the press gap on a press belt; and furthermore a transfer area configured to transfer the fiber fabric from the forming belt to the press belt, wherein a fiber fabric-carrying section of the forming belt is guided at its end over a final forming belt deflection roller and a fiber fabric-carrying section of the press belt is guided at its beginning over a first press belt deflection roller, wherein the transfer area is configured so that the forming belt and the press belt are both substantially parallel to a displacement direction over a length of at least 50 mm and at most 1.000mm, preferably at least 100mm and at most 800mm, wherein the length is defined as the distance, measured in the direction of displacement, between the axis of rotation of the first press belt deflection roller and the axis of rotation of the last forming belt deflection roller.

[0024] The advantageous further developments previously described for the method according to the invention also apply analogously to the machine according to the invention.

[0025] For the purposes of the present invention, the term "low-water" raw material processing also includes the processing of the raw material entirely without the targeted addition of water and / or other liquids.

[0026] The invention expressly extends to embodiments which are not given by combinations of features from explicit cross-references of the claims, whereby the disclosed features of the invention can be combined arbitrarily with one another - insofar as this is technically sensible.

[0027] Further features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawing.

[0028] The invention will be explained below with reference to the following figures. Fig. Figure 1 shows a schematic representation of a raw material processing plant 2 for the low-water processing of cellulose-containing fibers 200; Fig. Figure 2 shows a schematic representation of a fiber web plant 3 for the production of a dry-formed fiber web 309.

[0029] To clarify the individual directions, a higher-level Cartesian coordinate system is used in the figures. The x-direction corresponds to a longitudinal extent, also known as the machine direction (MD). The y-direction corresponds to a direction orthogonal to the machine direction (MD) and is also known as the cross-direction (CD). The z-direction corresponds to the vertical direction.

[0030] The Fig. 1 and Fig. Figure 2 shows a schematic representation of a possible embodiment of the manufacturing process or the manufacturing machine 1 according to the invention.

[0031] The Fig. Figure 1 schematically represents a possible embodiment of a low-water processing plant, or a low-water raw material processing plant 2, in which the individual fibers and / or fiber bundles 209 are produced, for example, from fiber-containing recycled material and / or from virgin fiber pulp as bales 200, by comminution devices 221, 222, 223 and / or fiberizing devices 222, 223. The individual fibers and / or fiber bundles 209 are transported in an airflow after successful comminution or fiberizing. Specifically, the air / fiber mixture is conveyed via one or more distribution channels to a [missing information - likely a specific component or system]. Fig. 2 dry forming device 4 of a fiber web plant 3 for the production of a dry formed fiber web 309.

[0032] It is also conceivable to have several raw material preparation plants 2 in parallel, which can supply a single fiber web plant 3. This is advantageous if a raw material preparation plant 2 alone cannot produce the required quantity of individual fibers and / or fiber bundles 209, or if different types of cellulose-containing fibers 200 are used as raw material, for example for a multi-layer fiber web 309.

[0033] The low-water processing method makes a crucial contribution to the quality and properties of the produced dry-formed fiber web 309, as well as to the overall economic and energy efficiency of the manufacturing process. For example, one challenge is transforming a discontinuous process into a continuous one, aiming for very high production volumes of several thousand tons of finished fiber web 309 per year. These high production volumes mean that the available raw material should ideally be stored as compactly as possible to minimize storage requirements. An important aspect of low-water raw material processing is that the required volume of processed raw material increases steadily until final processing in the fiber web plant 3.The increase in volume can typically range from a factor of 30,000 to 50,000 between that of virgin pulp in bales 200 and that of individual fibers and / or fiber bundles 209 dissolved in the airflow. This allows storage or intermediate storage in a storage facility 240 in the raw material processing plant 2 to be kept to a minimum and / or only required at the crucial processing steps.

[0034] Another aspect for the overall balance is to keep the availability of the supplied raw materials high and the costs low. For example, virgin fiber pulp can be delivered not only in bales but also in the form of more expensive and voluminous rolls. A bale typically consists of several sheets or strips of virgin fiber pulp.

[0035] In everyday language, the widespread use of virgin pulp in roll form for end products has led to the term "fluff pulp" ("fluff pulp" or "cellulose wadding") becoming synonymous with virgin pulp from rolls. However, this is incorrect, as only shredding the rolls can produce a loosened fluff pulp.

[0036] Typically, with virgin pulp in roll form, a large part of the raw material preparation for the manufactured fiber web is already integrated into the virgin pulp production process. This makes production more complex and costly. Generally, the mass distribution in rolls is subject to lower tolerances compared to bales. This is advantageous for the known, simplified fiber web production process, ensuring a continuous mass flow.

[0037] Furthermore, the composition of the pulp in the roll stock can already be tailored to the final fiber web to be produced, using additives. For example, additives such as debonding agents are typically already mixed into the roll stock. These facilitate the separation of the fibers and counteract fiber recombination during the subsequent manufacturing process. This is usually not the case with baled pulp, or is reduced to a minimum.

[0038] Fresh pulp in bale and roll form typically has similar material density values ​​of around 600 - 960 kg / m³. 3However, due to its cylindrical shape, a roll typically requires up to 30% more storage space for the same quantity of virgin pulp compared to a bale, which is essentially cubic. Virgin pulp in bale form is therefore characterized by a smaller storage volume and a higher fiber concentration per cubic meter of storage space compared to roll form. The lower volume of bales allows for optimized transport and storage. This is particularly important when processing large quantities, especially several tons per day, to ensure competitive production.

[0039] A coupling of the two manufacturing processes of the low-water raw material preparation 2 and the fiber web plant 3 is an important component for the production of high-quality fiber webs 309, both of which can be coordinated, controlled and / or regulated via a higher-level control and / or regulation device 60.

[0040] The low-water raw material preparation process or raw material preparation plant 2 is characterized by a multi-stage comminution of the discontinuously fed raw material, whereby at the end of the low-water raw material preparation process 2, an airflow containing dispersed individual fibers and / or fiber bundles 209, tailored to the subsequent fiber web plant 3, can be continuously provided. The low-water raw material preparation process or raw material preparation plant 2 and the subsequent fiber web plant 3 are preferably free of an intermediate storage of the individual fibers 209 between plants 2 and 3 and are thus made available to the fiber web plant 3 on demand.

[0041] The general term "raw material" is used for cellulose-containing fibers 200, preferably virgin fiber pulp in bales 200 and / or recycled fibers. The recycled fibers can originate from the fiber web plant 3 itself as high-quality recycled virgin fiber pulp and / or it can be provided that recycled material from waste paper is used to further improve the overall efficiency of the manufacturing process.

[0042] The discontinuously supplied raw material is typically fed as bales 200 via a conveyor belt 220 to a first shredding device 221. The first shredding device 221, preferably a first shredder 221, is designed such that it can perform a first shredding of the bales 200 into coarse chips, shreds or chips 201.

[0043] For example, a bale of 200 mm virgin fiber pulp can consist of numerous stacked 200 mm pulp sheets. This pulp is NBSK pulp, typically used for wet-process paper, board, or tissue production. The starting material can have a density of approximately 920 kg / m³. 3 The individual cellulose sheets have a thickness of approximately 1.5 mm. One to five of these cellulose sheets are always fed simultaneously in a substantially horizontal direction to a first comminution device 221, preferably a shredder 221.

[0044] The chips 201 are then fed into a cleaning device 230, where any unwanted components, so-called "rejects," such as metals, contaminants, and / or packaging residues, that may still be contained in the chips 201 can be filtered out. After passing through the cleaning device 230, which may be, for example, a cyclone separator, the chips 201 are available as cleaned chips 202.

[0045] These cleaned chips 202 are ideally temporarily stored in a larger storage unit 240, preferably in the form of a silo. Advantageously, this is the only larger storage unit 240 in the entire raw material processing plant 2. The term "single larger storage unit 240" refers to the fact that, due to the design of the individual components of the raw material processing plant 2, there may be smaller micro-storage units, which, however, are not suitable for supplying the process for several minutes. Advantageously, the storage unit 240 is located immediately after the cleaning of the chips 201, thus minimizing the increase in volume.The storage unit 240 can have a maximum capacity of 30 minutes or more, in particular 60 minutes or more, preferably 90 minutes or more, and 120 minutes or less than, of the production time of the fiber web system 3. The size of the storage unit 240 depends on the desired basis weight and width of the fiber web 309, as well as on the production speed of the fiber web system 3. The design of the storage unit 240 is preferably geometrically optimized to enable compact, low-air, volume-optimized storage of the cleaned chips 202.

[0046] Optionally, a conditioning device 260 or a conditioning process can be provided for the cleaned chips 202 after the cleaning of the chips 201 and before the memory 240. During conditioning, a small amount of moisture can be added to the cleaned chips 202, for example, to minimize or prevent dust formation and / or electrostatic charging. However, the amount of moisture applied should be kept as low as possible to avoid negatively impacting the overall energy balance. Additives can also be added during conditioning.

[0047] The storage unit 240 is preferably designed as a vertical storage silo 240, wherein the cleaned chips 202 can be easily compressed by their own weight. Furthermore, at least one discharge device 241 is provided in the storage unit 240, which enables continuous discharge of the cleaned chips 202.

[0048] To assist in the discharge of the cleaned chips 202 from the memory 240, a first airflow 90 is added directly at the outlet of the memory 240, so that the cleaned chips 202 can be distributed and mixed in the first airflow 90 and thus be transported very easily to the second shredding device 222.

[0049] In one embodiment, preferably, reject material from the fiber web system 3 can be added to the cleaned chips 202. This reject material can, for example, be edge trimming 50 or edge extraction 50, in which fibers from a fiber layup 300 are extracted at the edge after a dry forming device 4. Furthermore, uncollected individual fibers and / or fiber bundles 209 filtered from the ambient air can also be added back in as recycled material before the second comminution device 222. It is particularly advantageous if the recycled material does not yet contain any additives and thus meets the specified quality requirements without further processing steps.

[0050] The second comminution device 222, or first fiberizing device 222, is preferably designed as a first hammer mill 222, in which the cleaned chips 202 are comminuted or fiberized until individual fibers with isolated nodes 205 are formed. These fibers can then pass through a filter device included in the second comminution device 222. The discharge of the individual fibers 205 from the second comminution device 222 is supported by the supply of an airflow 90 downstream of the second comminution device 222, and their transport to the next processing station is carried out. The individual fibers with isolated nodes 205B are highly dispersed in the supplied airflow 90.

[0051] The individual fibers with isolated nodes 205B can be further processed in a fiber processing device 250 to form a continuous mass flow of fibers 206, to which a further air flow 90 is subsequently added and the continuous mass flow of fibers 206 becomes a high-resolution, continuous mass flow of a fiber-air mixture 207.

[0052] The high-resolution, continuous mass flow of a fiber-air mixture 207 is fed directly to the third comminution device 223, or second fiberizing device 223, which is preferably designed as a second hammer mill 223. The third comminution device 223 comminsues or fiberizes the high-resolution, continuous mass flow of a fiber-air mixture 207 until essentially only individual fibers 208 remain, preferably free of knots or with only a small proportion of knots, which can then pass through a filter device included in the third comminution device 223.

[0053] To further reduce the single-fiber concentration, another airflow 90 can then be added. Alternatively or additionally, for example, exhaust air from the vacuum boxes 32 included in the fiber web system 3 can be added for web stabilization (see also Fig. 2), before the high-resolution individual fibers 209, essentially free of knots, are precisely dosed and continuously fed via a distribution system or distribution channels of the fiber web system 3.

[0054] The individual fibers and / or fiber bundles 209 transported by the airflow are, as in the Fig. 2 shown, further fed to a dry forming device 4 of the fiber web system 3 and distributed as evenly as possible transversely to the machine direction MD or in the transverse direction CD of the fiber web system 3.

[0055] Following the dry forming device 4, at least two application devices 7 are provided, which apply a fluid, preferably water or a water-additive mixture, to the fiber fabric 300 or the consolidated fiber fabric 305. The at least two application devices 7 are configured as a first application device 71 and at least one last application device 72, 73. In the Fig. In the embodiment shown in Figure 2, three application devices 7 are arranged, with a second application device 72 additionally arranged between the first 71 and the last 73.

[0056] Furthermore, at least one consolidation device 8 is provided after the dry forming device 4, which can consolidate the fiber fabric 300. In the Fig. In the embodiment shown in Figure 2, two consolidation devices 8 are arranged. Preferably, at least one consolidation device 8 is designed such that, in addition to consolidation of the fiber layup, it can also structure and / or heat it. The structuring by the consolidation device 8 is particularly useful for producing a tissue web with low- and high-pressure zones, preferably a tissue web with a basis weight of 28 g / m². 2 up to 42g / m² 2 , important.

[0057] To complete the continuously produced fiber web 309, a web-width winding unit 12 is arranged at the end of the fiber web system 3.

[0058] Preferably, at least one drying device 10 is further included in the fiber web system 3. It is advantageous if the at least one drying device 10 is arranged downstream of the application devices 7 in order to dry the fiber web 309 onto which the fluid has been applied. Preferably, the at least one drying device 10 is arranged upstream of the winding unit 12 of the finished fiber web 309, which is also included in the fiber web system 3.

[0059] The dry forming step in the dry forming device 4 can be controlled and / or regulated by at least one included control and / or regulating means, wherein the individual fibers and / or fiber bundles 209 in the dry forming device 4 are laid down, preferably partially by the force of gravity, onto a circulating, preferably permeable, forming belt 40 and form a fiber fabric 300, preferably still substantially unconsolidated.

[0060] Furthermore, the dry forming device 4 can include a suction device 30 which supports the laying of the individual fibers 209 on a permeable forming belt 40, and can also influence this process as a control and / or regulating means.

[0061] Preferably, the fiber layup 300 is measured with respect to its mass distribution by at least one encompassed measuring device 61, preferably a mass measuring device extending in the transverse direction CD, wherein the measuring signal can act as a control variable, preferably via the higher-level control and / or regulating device 60, on the supply of the individual fibers without knots 209 from the raw material preparation plant 2 and / or on the suction device 30.

[0062] The air 39 extracted by the suction device 30 may contain a certain quantity of individual fibers 209. Therefore, it is advantageous if a large proportion, preferably up to 95%, of the air extracted by the suction device 30 is returned directly to the dry forming device 4 as a recirculation circuit. This makes it possible to further break down the continuously added individual fibers 209 in order to achieve good formation on the forming belt 40, while the extracted individual fibers can be immediately returned to the corresponding production step.

[0063] In one embodiment, an extraction device extending in the transverse direction CD of the machine can extract excess fibers in the z-direction (thickness) from the surface of the first fiber layup 300 after it has left the dry forming device 4, thus achieving a homogeneous thickness distribution of the fiber layup 300 in both the CD and MD directions. This process can be selectively influenced by the at least one measuring device 61, preferably supported by the higher-level control and / or regulating device 60.

[0064] Alternatively, the extraction device can also be designed as an edge trimming device 50 or edge extraction device 50, wherein fibers are preferably selectively extracted from the edge regions of the fiber web 300 emerging from the dry forming device 4 and which is not yet solidified. It has been found that the edge regions often exhibit very strong variations in thickness compared to the main or central region of the fiber web 300. Advantageously, the edge strip extraction allows fresh fibers, free of chemicals, to be fed directly back into the raw material preparation plant 2 immediately after the dry forming device 4, which has a positive effect on the overall efficiency of the manufacturing process. This also enables the production of a clean edge on the fiber web 309.

[0065] As in Fig. As shown in Figure 2, the fiber fabric 300 deposited in the dry forming device 4 can pass through a pre-solidification device 83 before the first application device 71, in which the still unsolidified fiber fabric 300 receives a first, full-surface pre-solidification or pre-compacting over the entire transverse direction CD.

[0066] The application devices 71, 72, 73 are preferably designed as nozzle applicators which can spray a fluid in the form of a spray jet consisting of individual small fluid droplets onto the fiber fabric 300, 305. Alternatively, the application devices can also be designed such that the fluid is applied in the form of foam, mist or vapor.

[0067] Alternatively, a curtain applicator or a roller applicator can be provided, wherein the roller applicator is advantageously integrated into one of the consolidation devices 8 and is coated with a fluid via an applicator, e.g. a press roller 81, which is then transferred to the fiber fabric 300 in a subsequent press gap 80.

[0068] Immediately before being wound up 12, the fibrous web 309 is guided through a dryer 10, preferably electrically operated. The properties of the fibrous web 309 with regard to its thickness, feel, and absorbency can be advantageously maintained by means of a non-contact dryer 10. The non-contact dryer 10 can, for example, be designed as a hot air dryer 10, a flow-through drying hood, or a TAD dryer. Alternatively or additionally, the dryer 10 can also be equipped with infrared elements.

[0069] Due to the small amounts of moisture used in the manufacturing process, the length of the dryer unit 10 can be kept very compact compared to the usual drying sections from wet lay-up processes. This allows the overall length of the fiber web plant 3 and infrastructure costs to be kept low.

[0070] Furthermore, at least one additional heating step of the laid fiber fabric 300 can also be provided upstream of the dryer 10. This additional heating step can, for example, be integrated into a consolidation device 8 by heating, for instance, a press roller 81 provided for consolidation and / or a pressing element 82 arranged opposite it. Heating below 250°C, in particular less than or equal to 100°C, preferably less than or equal to 80°C, is advantageous because the heating supports the penetration depth and distribution of a fluid, preferably water, applied in a first application step 71 within the fiber fabric 300, leading to more efficient consolidation and / or structuring. The temperature specifications refer to the temperature of the heating elements used. The temperature introduced into the fiber web or the fiber fabric can be lower.

[0071] In the case of structuring, the press roller 81 is preferably designed with a surface structure.

[0072] The first application device 71 is preferably arranged directly upstream of the solidification device 8, which follows the pre-solidification device 83. Furthermore, the first application device 71 applies a fluid, preferably ordinary water, i.e., water that is free of artificial or chemical additives.

[0073] Alternatively, the first application device 71 can be configured to apply a different fluid, preferably a water-additive mixture. If a water-additive mixture is applied to the fiber web 300 before consolidation 8, the additive is selected from the group of dry-strength agents, for example, starch, to increase the strength of the produced fiber web 309 in its dry state. Dry-strength agents are suitable for application prior to consolidation because they exhibit a lower tendency to stick compared to adhesives or wet-strength agents.

[0074] The application devices 71, 72, 73 are designed such that the fiber fabric 300 can be wetted over its entire surface with the fluid. "Over its entire surface" means that the fluid is applied substantially uniformly over the entire width or over the entire transverse direction CD of the fiber fabric. In the first, second, and third application devices 71, 72, 73, a vacuum box 31 can be arranged on the side of the fiber fabric 300 opposite the side to be wetted. This vacuum box draws ambient air through the fiber fabric 300 and through a permeable support element supporting the fiber fabric 300, preferably a pressure belt 41 and / or a drying screen 42, each having a direction of travel 22.This makes it advantageously possible, for example, to influence the penetration depth of the applied fluid into the fiber fabric 300 and / or a quantity distribution in the machine direction MD or machine transverse direction CD during the application of a fluid.

[0075] Optionally, at least one moisture measuring device 63 and / or a measuring device for monitoring the fluid application may be provided. Preferably, the at least one moisture measuring device 63 is arranged such that it can measure before and / or after the heating device 10.

[0076] It is also conceivable to provide a moisture measuring device 63 immediately after each application device 71, 72, 73. The moisture measuring device 63 can be stationary or traversing in the machine transverse direction CD. Furthermore, the moisture measuring device 63 can also be suitable for measuring other fiber web properties, such as mass, thickness, formation, opacity, or the like.

[0077] After passing through the pre-consolidation unit 83, the fiber fabric 300 is transported on the conveying section of the forming belt 40 to a transfer area 100. The transfer area 100 serves to transfer the fiber fabric 300 from the forming belt 40 to the pressing belt 41. According to the invention, this transfer is particularly gentle, so that even at high production speeds no qualitative impairment of the fiber fabric 300 occurs. For this purpose, the forming belt 40 and the pressing belt 41 are both guided essentially parallel to a displacement direction. In the exemplary embodiment, the displacement direction corresponds to the Fig. 2 of the machine direction MD. According to the invention, the transfer area 100 has a certain length 110, namely a length of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm. The length 110 of the transfer area 100 is defined as the distance, measured in the displacement direction or in the machine direction, between the axis of rotation of a first press belt deflection roller 105 and a last forming belt deflection roller 106. The first press belt deflection roller 105 is the deflection roller in the screen loop of the press belt 41, which is arranged at the beginning of the conveying section of the press belt 41. The last forming belt deflection roller 106, on the other hand, is the deflection roller in the screen loop of the forming belt 40, which is arranged at the end of the conveying section of the forming belt 40.By guiding the two belts 40, 41 parallel over the corresponding length 110, the still very sensitive fiber fabric 300 is given sufficient time, even at high production speeds, in particular at production speeds of greater than or equal to 150m / min, preferably greater than or equal to 250m / min, and more preferably greater than or equal to 400m / min, to gently detach itself from the forming belt 40 and attach itself to the press belt 41.

[0078] It is further advantageous if the forming belt 40 in the transfer area 100 has a distance from the press belt 41 that is no greater than the thickness of the fiber layup 300, measured immediately in front of the transfer area 100. The distance between the two belts 40, 41 can be determined or adjusted via a distance 112 measured in a direction orthogonal to the displacement direction or in the z-direction between the axis of rotation of the first press belt deflection roller 105 and the axis of rotation of the last forming belt deflection roller 106. The distance between the two belts 40, 41 in the transfer area 100 essentially corresponds to the distance between the axis of rotation of the first press belt deflection roller 105 and the axis of rotation of the last forming belt deflection roller 106, minus the radius of the first press belt deflection roller 105, the radius of the last forming belt deflection roller 106, the thickness of the forming belt 40 and the thickness of the press belt 41.The press belt 41 is preferably designed to provide the fiber fabric 300 in the subsequent press gap 80 between the press roller 81 and the press element 82 with a plurality of high-pressure and low-pressure zones, thereby increasing the strength of the fiber fabric 300. The high-pressure and low-pressure zones should be dimensioned such that they form a structure visible to the naked eye in the fiber fabric 300. In such a case, the press belt 41 includes protrusions on its upper surface facing the fiber fabric 300 to form the high-pressure zones. However, the height of these protrusions should be disregarded when determining the "thickness of the press belt 41".

[0079] Such a distance between the two belts 40, 41 in the transfer area 100 prevents the fiber fabric 300 in the transfer area 100 from undergoing any significant change in its direction of movement, which corresponds to the displacement direction or the machine direction MD. This also contributes to ensuring that no impairment of the quality of the fiber fabric 300 occurs at high production speeds.

[0080] The first press belt deflection roller 105 is preferably vacuum-operated to enable the "gentle" transfer of the fiber fabric 300 to begin immediately at the start of the transfer section 100. Several vacuum boxes 32 or other vacuum devices can be arranged in the screen loop of the press belt 41 behind the first press belt deflection roller 105 to continue the transfer of the fiber fabric 300 over the entire length 110 of the transfer section 100 and to hold the fiber fabric upside down on the conveying section of the press belt 41 even after the transfer section 100.

[0081] The last forming belt deflection roller 106 is preferably non-vacuum-controlled, and the screen loop of the forming belt 40, at least in the transfer area 100, preferably also lacks vacuum boxes or other negative pressure devices to prevent the fiber fabric 300, which is to detach from the forming belt 40 in the transfer area 100, from being held against it. The first press belt deflection roller 105 can be vacuum-controlled if required.

[0082] At the end of the conveying section of the press belt 41, the fiber fabric 305, which has meanwhile been compacted by the press gap 80, is transferred in a further transfer section 120 from the press belt 41 to a connecting belt, namely, in the present embodiment, to the drying screen 42. The second transfer section 120 is preferably designed analogously to the transfer section 100. Although the fiber fabric 305 exhibits a significantly greater strength after the press gap 80 than before the press gap 80, the principle of "gentle transfer" has also proven advantageous for the quality of the final fiber web 309 at this point.

[0083] After passing through the press gap 80, the fiber fabric 300 is transported overhead on the conveying section of the press belt 41 to the further transfer area 120. The further transfer area 120 serves to transfer the fiber fabric 305 from the press belt 41 to the drying screen 42. For this purpose, the press belt 41 and the drying screen 42 are both guided essentially parallel to a further displacement direction. In the exemplary embodiment, this further displacement direction corresponds to the Fig.2 also in the machine direction MD. The further transfer section 120 has a certain length 130, namely a length of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm. The length 130 of the further transfer section 120 is defined as the distance, measured in the further transfer direction or in the machine direction, between the axis of rotation of a first connecting belt deflection roller 125 and a last press belt deflection roller 126. The first connecting belt deflection roller 125 is the deflection roller in the screen loop of the connecting belt, or here the drying screen 42, which is arranged at the beginning of the conveying section of the drying screen 42. The last press belt deflection roller 126, on the other hand, is the deflection roller in the screen loop of the press belt 41, which is arranged at the end of the conveying section of the press belt 41.By guiding the two belts 41, 42 in parallel over the corresponding length 130, the fiber fabric 305 is given enough time, even at high production speeds, to gently detach itself from the press belt 41 and attach itself to the connecting belt, or in this case to the drying screen 42. Reference symbol list 1 machine 2 Raw material processing plant 3 Fiber web plant 4 Dry forming device 7 Application device 8 Solidification device 10 Dryer device 12 Roll-up 22 Direction of travel 30 Suction device of the dry forming device 31 Vacuum Box - Application Device 32 vacuum boxes 39 extracted air 40 support element, forming belt 41 Support element, press band 42 Support element, drying sieve 50 Edge trimming (edge ​​suction) 60 Control and / or regulating device 61 Measuring device 63 Moisture measuring device 71 first application device 72 second application device 73 third application device 80 Press gap 81 Press roller 82 Press element 83 Pre-solidification device 90 airflow 100 Transfer area 105 first press belt deflection roller 106 last forming belt deflection roller 110 Length Transfer area 112 Distance between rotation axes of the first press belt deflection roller and the last forming belt deflection roller 120 additional transfer area 125 first connecting belt deflection roller 126 last press belt deflection roller 130 Length of further transfer area 200 cellulose-containing fibers (bales) 201 shredded baled goods, chips 202 cleaned chips 205 individual fibers with scattered nodes or frayed chips 205B single fibers with isolated nodes or fiberized chips, high resolution in a fiber-air mixture 206 continuous mass flow of fibers 207 continuous mass flow of fibers, high resolution in a fiber-air mixture 208 individual fibers essentially free of knots 209 single fibers and / or fiber bundles 220 Conveyor belt 221 first shredding device (shredder) 222 second comminution device, preferably a fiberizing device, in particular a first hammer mill 223 third comminution device, preferably a fiberizing device, in particular a second hammer mill 230 Cleaning device 240 storage 241 Discharge device 250 fiber processing device 260 Conditioning device 300 fiber layups after dry forming device 305 reinforced fiber fabric 309 Fibre web MD Machine direction CD machine transverse direction z Vertical direction QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2019 / 137667 A1

[0005]

Claims

[1] Method for producing a fibrous web (309), preferably a tissue, paper or cardboard web or a nonwoven web, in particular a tissue web with a basis weight of 28g / m² 2 up to 42g / m² 2 , comprising the following steps: a) low-water raw material processing of cellulose-containing fibers (200) into single fibers and / or fiber bundles (209); b) Forming the individual fibers and / or fiber bundles (209) in an air stream to form a planar fiber fabric (300) on a forming belt (40) by a dry forming process; c) Application of a fluid, preferably water and / or a water-additive mixture, to the fiber fabric (300); d) Consolidating the planar fiber fabric (300) by applying pressure in a press gap (80), wherein the fiber fabric (300) is guided through the press gap (80) on a press belt (41); wherein the fiber fabric (300) is transferred from the forming belt (40) to the pressing belt (41) in a transfer area (100), wherein a fiber fabric (300) transporting section of the forming belt (40) is guided at its end over a final forming belt deflection roller (106) and a fiber fabric (300) transporting section of the press belt (41) is guided at its beginning over a first press belt deflection roller (105), characterized by , that in the transfer area (100) the forming belt (40) and the pressing belt (41) are both guided substantially parallel to a displacement direction over a length (110) of at least 50mm and at most 1,000mm, preferably of at least 100mm and at most 800mm, where the length (110) is defined as the distance, measured in the direction of displacement, between the axis of rotation of the first press belt deflection roller (105) and the axis of rotation of the last forming belt deflection roller (106). [2] Method according to claim 1, characterized by , that the speed at which the fiber layup (300) is guided through the transfer area (100) is greater than or equal to 150m / min, in particular greater than or equal to 250m / min, preferably greater than or equal to 400m / min. [3] Method according to claim 1 or 2, characterized by , that in the transfer area (100) the forming belt (40) has a distance to the pressing belt (41) which is not greater than the thickness of the fiber fabric (300) immediately in front of the transfer area (100). [4] Method according to any one of the preceding claims, characterized by , that the fiber fabric (300) after leaving the transfer area (100), preferably hanging overhead, is guided to the press gap (80) by means of vacuum means (31, 32) provided in the loop of the press belt (41), in order to then be guided through the press gap (80) together with the press belt (41). [5] Method according to claim 4, characterized by, that the fluid from step c) is applied to the fiber fabric (300) after leaving the transfer area (100) and before reaching the press gap (80). [6] Method according to claim 4 or 5, characterized by , that the press belt (41) is designed to provide the fiber fabric (300) in the press gap (80) with a plurality of high-pressure and low-pressure zones and thus increase the strength of the fiber fabric (300), wherein preferably the high-pressure and low-pressure zones are dimensioned such that they form a structure visible to the naked eye in the fiber fabric (300). [7] Method according to any one of the preceding claims, characterized by , that the fiber fabric (300) is transferred from the press belt (41) to a connecting belt in a further transfer area (120), wherein the fiber fabric (305) transporting section of the press belt (41) is guided at its end over a final press belt deflection roller (126), and a fiber fabric (305) transporting section of the connecting belt is guided at its beginning over a first connecting belt deflection roller (125), wherein in the further transfer area (120) the press belt (41) and the connecting belt are both guided substantially parallel to a further displacement direction over a length (130) of at least 50mm and at most 1,000mm, preferably of at least 100mm and at most 800mm, wherein the length (130) is defined as the distance, measured in the further displacement direction, between the axis of rotation of the first connecting belt deflection roller (125) and the axis of rotation of the last press belt deflection roller (126). [8] Method according to claim 7, characterized by, that the connecting belt is a drying screen (42) on which the fiber fabric (305) is guided through a drying device (10), in particular a flow-through dryer (10). [9] Method according to any one of the preceding claims, characterized by , that the fiber fabric (305) is dried by an electrically operated drying device (10), in particular a purely electrically operated flow dryer (10). [10] Machine (1) for producing a fibrous web (309), preferably a tissue, paper or cardboard web or a nonwoven web, in particular a tissue web with a basis weight of 28g / m² 2 up to 42g / m² 2 , comprehensive: a) a raw material processing plant (2) for the low-water processing of cellulose-containing fibers (200) into single fibers and / or fiber bundles (209); b) a dry forming device (4) for dry forming of the individual fibers and / or fiber bundles (209) in an air stream to form a planar fiber fabric (300) on a forming belt (40); c) an application device (71) for applying a fluid, preferably water and / or a water-additive mixture, to the fiber fabric (300); d) a consolidation device (8) for consolidating the planar fiber fabric (300) by applying pressure in a press gap (80) when the fiber fabric (300) is guided through the press gap (80) on a press belt (41); and furthermore a transfer area (100) which is configured to transfer the fiber fabric (300) from the forming belt (40) to the pressing belt (41), wherein a fiber fabric transporting section of the forming belt (40) is guided at its end over a final forming belt deflection roller (106) and a fiber fabric transporting section of the pressing belt (41) is guided at its beginning over a first pressing belt deflection roller (105), characterized by , that the transfer area (100) is designed to guide the forming belt (40) and the pressing belt (41) both substantially parallel to a displacement direction over a length (110) of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm, where the length (110) is defined as the distance, measured in the direction of displacement, between the axis of rotation of the first press belt deflection roller (105) and the axis of rotation of the last forming belt deflection roller (106).

Images