Fabric and machine comprising the fabric

Abstract

The invention relates to a fabric, in particular felt, for use in a machine for producing a tissue web, comprising a base structure, which has a textile structure with MD threads, and at least one layer of nonwoven fibers. The invention is characterized in that the MD threads predominantly or as a whole have a diameter ranging between 0.25 mm and 0.45 mm, in particular between 0.3 mm and 0.35 mm, and the thread density of the MD threads is more than 37%, in particular between 37% and 45%. The invention additionally relates to a machine and a method for producing a tissue web using such a fabric.

Description

[0001] The invention relates to a covering for a machine for producing a tissue web according to the preamble of claim 1, as well as a machine and a method for producing a tissue web with such a covering.

[0002] The production of tissue and hygiene papers remains a rapidly growing market. A machine typically used in tissue production is described in EP 3 167 115 B1. Fabrics are described in US 2004 / 094281, EP 1 270 807 A1, and EP 1 184 511. As is generally the case in papermaking, a fiber suspension is applied to a fabric or between two fabrics and dewatered by suction. The fiber web is then further dewatered in a press and subsequently dried thermally. The fiber web is transported into the press on a water-absorbing fabric. The water squeezed from the web is absorbed by the fabric and removed again after the fiber web is removed. This is done, as exemplified in EP 2 602 387 B1, using suction boxes, the so-called Uhle boxes.

[0003] Modern tissue machines operate at very high production speeds, resulting in very short dwell times of the tissue web in the press nip. Therefore, insufficient dewatering of the web in the press is usually the limiting factor preventing an increase in the machine's production speed.

[0004] It is therefore an object of the invention to propose a machine and a method for its operation that ensures improved dewatering of the tissue web.

[0005] Another objective of the invention is to propose a conversion solution for existing systems that can be implemented with little or no effort.

[0006] Another objective of the invention is to propose a covering that enables significantly improved drainage of the tissue web.

[0007] The problems are completely solved by a covering according to the characterizing portion of claim 1, a machine according to claim 7, and a method according to claim 10. Further advantageous features of the embodiment according to the invention are found in the dependent claims.

[0008] With regard to the covering, the problem is solved by a covering, in particular a felt, for use in a machine for producing a tissue web. The covering comprises a base structure which has or consists of a woven textile structure with MD and CD threads. Furthermore, the covering comprises at least one layer of nonwoven fibers. According to the invention, it is provided that the MD threads have a diameter entirely or predominantly between 0.25 mm and 0.45 mm, in particular between 0.3 mm and 0.35 mm, and that the thread density of the MD threads is more than 37%, in particular between 37% and 45%.

[0009] The term "wholly or predominantly" shall be understood to mean that at least 90% of the MD threads, preferably 95%, and in particular all MD threads, have a diameter within the specified range.

[0010] This application uses the term "diameter of a thread". For round threads, this term is well-defined.

[0011] For monofilaments that deviate from a round shape, or for threads twisted from several monofilaments, the diameter of the thread shall be understood to be the diameter of the smallest circle that encloses the cross-section of the thread.

[0012] To determine the thread density of the MD threads, the number of threads per unit length is multiplied by their diameter and the value is expressed as a ratio to the unit length.

[0013] Thus, with 10 threads / cm and a thread diameter of 0.40mm, the thread density is 10 * 0.4mm / 10mm= 40%.

[0014] By combining fine MD threads with a high MD thread density, the base structure can take over some of the functionality otherwise performed by one or more nonwoven layers in the covering, such as pressure distribution. The base structure enables a uniform pressure distribution across the felt, which was previously impossible. Surprisingly, the applicant's trials have shown that coverings, particularly felts with such base structures, can require less nonwoven material. This is not only economically advantageous due to the reduced number of nonwoven layers, but also allows for improved dewatering when used in a tissue machine. For example, with a thinner felt, in addition to Uhle-Box dewatering, nipple dewatering can also be achieved in the press of a tissue machine.

[0015] In embodiments according to the invention, the basic structure is composed of two endless or endlessly constructed layers of fabric, wherein in both layers the MD threads have a diameter entirely or predominantly between 0.25 mm and 0.45 mm, in particular between 0.3 mm and 0.35 mm, and the thread density of the MD threads is more than 37%, in particular between 37% and 45%. This can be a two-layer fabric or two separate layers of fabric.

[0016] In preferred embodiments, the textile structure may be composed of flat woven fabric, with the warp threads of the loom being the MD threads of the fabric. The flat woven fabric may, for example, have a plain weave.

[0017] Advantageously, the textile structure can consist of, or comprise, a woven fabric or a twill weave.

[0018] Round woven fabrics are typically used for the basic structures of coverings.

[0019] These circular fabrics are rotated 90° for installation in the machine. This turns the weft threads of the loom into the MD threads of the warp, and the warp threads into the CD threads.

[0020] An alternative is to use a flat weave.

[0021] In EP0425523 B1, Paul Sudre describes the principle of producing a seam covering using a flat fabric.

[0022] However, it is also possible to use a flat fabric that is the length of the covering to be produced and to join the two ends together. This also creates an endless fabric structure that can be used as a basic structure or as part of one.

[0023] Since the length of warps is generally significantly greater in the machine direction than their width in the CD direction, and the width of the loom is sufficiently large for the width of the machine, the required flat woven fabrics can most easily be produced by weaving a sufficiently long piece, whereby the warp threads then become MD threads in the warp. A 90° rotation, as with circular woven fabrics, is not necessary. This is very advantageous for a warp according to one aspect of the present invention. While the warp threads in a loom can, in principle, be arranged arbitrarily close to one another, two adjacent weft threads are necessarily spaced apart because the warp threads—e.g., in a plain weave—alternate between each pair of weft threads from top to bottom or vice versa.Due to this forced spacing of the weft threads, together with the 90° rotation, such a density of medium-density (MD) threads is not possible, or only with great difficulty, using conventional circular woven fabrics when employing very thin threads. In contrast, with flat woven fabrics, the warp threads serving as MD threads can be arranged arbitrarily close to one another, making it comparatively easy to produce fabrics with the properties described in the invention.

[0024] When using flat fabrics in the basic structure, the flat fabric can advantageously be made endless by joining the end faces. This joining can be achieved, in particular, by welding. Ultrasonic welding and laser welding, especially laser transmission welding, have proven to be suitable welding processes. If necessary, it can be advantageous to join the two end faces using a connecting element. This can, for example, be one or more threads arranged in the CD direction and connected, in particular welded, to the MD threads of the two ends.

[0025] In advantageous embodiments, the basic structure may be composed of two continuous flat woven fabrics. The two fabric loops can then be joined to form a two-layer structure. These two fabric loops can then be connected, for example, by needle-punching with one or more layers of nonwoven fabric. Alternatively or additionally, other joining methods may be used, such as sewing or welding the two layers together.

[0026] The basic structure can consist of a textile structure or include other elements. In particular, the basic structure can contain further textile structures, such as additional fabrics.

[0027] Various materials can be used for the MD threads. Polyamides such as PA 6 and PA 6.6 are suitable, as are other polymers such as PET. If CD threads are present, they can be made from the same or a different polymer.

[0028] It is possible for all MD threads to be identical. However, different types of MD threads can also be used. This allows, for example, the fiber anchorage or dimensional stability to be influenced. Advantageously, MD threads are monofilaments.

[0029] There are also various options when choosing CD threads. In addition to monofilaments, multifilaments or yarns can also be used.

[0030] Suitable yarns can consist of 4 or 6 filaments. The filaments used can have a diameter of 0.15–0.25 mm. For example, 0.2 x 2 x 2 yarns are very suitable.

[0031] In advantageous designs, all CD threads can be made from yarn. All CD threads can be made from the same yarn, or different yarns can be used.

[0032] It can also be advantageous to use both yarns and monofilaments as CD threads. Preferably, around 50% or more of the CD threads are made of yarn.

[0033] In a preferred embodiment, yarns and monofilaments can be alternately used as CD threads. In this case, the proportion of yarns in the CD threads is 50% – or slightly less if, for technical reasons, e.g., to form seam loops, individual CD threads have to be removed.

[0034] In advantageous embodiments, the covering can have one or more layers of nonwoven fabric. The layer(s) can be arranged on the paper side and / or the running side of the covering.

[0035] Preferably, the weight of the covering is between 750 g / m² and 1250 g / m², particularly between 900 g / m² and 1100 g / m². In special cases, weights of up to 1400 g / m² are also possible. This refers to the total weight of the base structure and any nonwoven layers.

[0036] It is very advantageous for the invention if the weight fraction of the nonwoven layers corresponds at most to the weight fraction of the base structure, in particular at most 2 / 3 of the weight fraction of the base structure.

[0037] Typically, in felts used for tissue production, the weight fraction of nonwoven fibers is greater than that of the base structure. Usually, 60% of the total weight consists of nonwoven fibers and 40% of the base structure.

[0038] Since, in the coverings proposed here, the combination of MD thread density and MD thread diameter allows parts of the functionality of the nonwoven layer to be taken over by the base structure, it is possible to reduce the amount of nonwoven fibers. This makes lighter and thinner felts possible.

[0039] In preferred embodiments, the covering can have a thickness of 3.5 mm or less, preferably between 2.5 mm and 3 mm! The thickness is determined under a pressure of 0.1 MPa.

[0040] The relative proportion of nonwoven fibers in the total covering also decreases. Therefore, for example, felts can be used in which the base structure and nonwoven layers each make up 50% of the weight. The base structure can even constitute the larger share of the felt's weight. If 60% of the total weight comes from the base structure and only 40% from the nonwoven fibers, then the weight share of the nonwoven layers corresponds to only 2 / 3 of the weight share of the base structure.

[0041] Over the lifespan of the covering, the nonwoven layers become highly compressed, reducing essential covering properties such as permeability. A lower proportion of nonwoven fibers in the overall covering minimizes these losses due to fiber compression, allowing the covering properties to remain within acceptable limits for a longer period.

[0042] However, it can also be advantageous if the paper side of the covering contains a certain amount of nonwoven fibers. This amount should not be less than 10% of the total weight of the covering. It is also beneficial to use nonwoven fibers with a fineness between 11 and 22 dtex, at least on the paper-contacting top side of the covering.

[0043] The nonwoven fibers can be made of any suitable material, in particular a polyamide, but also an elastomer such as a thermoplastic polyurethane (TPU), melt fibers, two-component fibers or mixtures thereof.

[0044] With regard to the machine, the problem is solved by a machine for producing a tissue web, which includes a press device with at least one press nip. The machine has at least one covering according to one aspect of the invention. During operation of the press device, this covering passes through the at least one press nip together with the tissue web.

[0045] Tissue paper is typically made from wood pulp and is very lightweight. Its basis weight is usually between 15 g / m² and 30 g / m². However, values ​​as low as 10 g / m² or 5 g / m² are also possible, as are papers with more than 30 g / m².

[0046] In advantageous embodiments, the machine includes a so-called CrescentFormer. After initial dewatering in the former, the fiber web can then be transported, usually on a covering such as felt, into a press device, where further dewatering takes place in the press nip.

[0047] Preferably, the press device features a long nip, in particular a shoe nip. Compared to a roller nip, which is also possible, the web's residence time in the nip is longer. This allows for the use of lower press pressures. This is important in the production of tissue papers, as it helps maintain the web's volume, which is a key quality parameter for tissue papers.

[0048] Furthermore, it can be advantageous if the press has a wastewater collector designed to collect water that has been removed from the tissue web in at least one press nip. By using a felt according to one aspect of the invention, the dewatering capacity of the press can be increased—particularly in long nip or shoe presses—by incorporating nip dewatering in addition to the usual Uhle box dewatering. In this process, water (or a water-air mixture) from the tissue web is not only pressed into the fabric but also through it. While the remaining portion of the pressed-out water is transported with the fabric to a downstream Uhle box, this water escapes into the environment as splash water or spray mist after the press nip. It is also possible for splash water to escape forward against the direction of web travel.This portion of the drainage process is referred to as nozzle drainage. To prevent contamination of the press or uncontrolled wetting of the surrounding area, it is advantageous to incorporate one or more drainage traps into the press assembly. These are arranged so that the splash water can be collected and removed.

[0049] By means of the covering according to one aspect of the invention and optionally by the installation of a water catcher, the dewatering performance of the press device can be significantly increased with very little effort, even in existing tissue machines.

[0050] With regard to the method, the problem is solved by a method for producing a tissue web using a machine according to one aspect of the invention.

[0051] Advantageously, it can be provided that part of the dewatering in the pressing device takes place in the form of nipple drainage, and that this dewatered water is collected wholly or partially by a wastewater trap.

[0052] In particular, it may be provided that the nipple drainage accounts for more than 10%, especially between 20% and 50%, of the total drainage volume of the pressing device.

[0053] It is particularly advantageous if the tissue machine is operated at high speeds of more than 1200 m / min, especially more than 1500 m / min or 1800 m / min. Especially at high production speeds, an insufficient dry content after pressing is the limiting factor for increasing production speed. The methods proposed here increase the dry content after pressing, thereby enabling consistently high production speeds.

[0054] The invention will be explained in more detail below using schematic figures that are not to scale.

[0055] Figure 1 shows a tissue machine according to one aspect of the invention.

[0056] Figure 1 Figure 1 shows a tissue machine 1 according to one aspect of the invention. Using this typical design of a tissue machine 1 as an example, aspects of the idea described here will be explained. The invention is not limited to this embodiment. A fiber suspension is applied via a headbox onto a fabric 2, or between a fabric 2 and an outer screen 22. Initial dewatering takes place in a former 20 with the aid of a suction forming roller 21, which is partially enclosed by the fabric 2. The former 20 is in Figure 1It is designed as a crescent former, but other former types are also possible. The resulting fiber mat is then transported, supported by the tensioning device 2, into the press 30. In the Figure 1 The press device 30 is designed as a shoe press 30. The press nip 31 is positioned between the shoe roller 34 and a Yankee cylinder 41. The fabric 2 passes through the press nip 31 together with the tissue web 3. After the press nip, the web 3 continues to run on the surface of the Yankee cylinder 41. A drying hood 42 is arranged on the Yankee cylinder 41. By means of a crepe scraper 43, the web 3 is released from the Yankee cylinder 41 and transported to a winding unit 60. As in Figure 1As shown, a scanner 50 or another suitable measuring device 50 can be provided before the winding 60, with which important parameters of the fiber web 3, such as thickness, moisture content, or basis weight, can be recorded. If the scanner 50 is designed to traverse the web, cross-sectional profiles of these parameters can also be determined.

[0057] The covering 2 of the in Figure 1The machine 1 shown advantageously comprises a covering according to one aspect of the invention. Advantageously, it can comprise a base structure made of a flat woven fabric, in particular a plain weave, which is made endless by joining – e.g., welding – the end faces. The MD threads of this base structure all have a diameter between 0.25 mm and 0.45 mm, in particular between 0.3 mm and 0.35 mm. The thread density of the MD threads is more than 37%, preferably between 37% and 45%, and particularly preferably between 39% and 43%. With a preferred weight of the covering 2 between 750 g / m² and 1250 g / m², in particular between 900 g / m² and 1100 g / m², the nonwoven backing can be reduced to half the weight or less of the covering. Since, according to one aspect of the invention, the basic structure of a covering 2 takes over parts of the function of the nonwoven layers, this covering can be very thin.In contrast to tissue machines 1 known from the prior art, when using such a covering 2 in the press nip 31, particularly in a shoe press nip 31, nip drainage can occur. This results in splashing water or spray mist, which usually occurs after the press nip 31, but can sometimes also occur in front of it. To prevent contamination of the press 30 or uncontrolled wetting of the surrounding area, it is advantageous to provide one or more wastewater traps 33 in the press device 30. Figure 1A wastewater trap 33 is arranged downstream of the pressnip 31. Alternatively or additionally, a wastewater trap 33 can also be provided upstream of the pressnip 31. The wastewater trap(s) 33 collect the portion of the water that has been removed from the web 3 by the pressnip drainage. The remaining portion is stored in the covering 2 and transported away by the pressnip 31. To remove this water from the covering 2, a [missing information] is required in the [missing information]. Figure 1 In the system shown, a suction box 32, a so-called Uhle box 32, is provided between the press nipple 31 and the headbox 10. In a process according to one aspect of the invention, the proportion of nipple dewatering is more than 10%, preferably between 20% and 50% of the total dewatering of the press 30. Reference symbol list

[0058] 1 Tissue machine 2 Fabrication 3 Tissue web 10 Headbox 20 Former 21 Forming roller 22 Outer screen 30 Pressing device 31 Press nip 32 Suction box "Uhle Box" 33 Drainage catcher 34 Shoe roller 40 Drying device 41 Yankee cylinder 42 Hood 43 Crepe scraper 50 Scanner 60 Rewinder

Claims

1. Covering (2), in particular felt (2), for use in a machine (1) for producing a tissue web (3), comprising a base structure consisting of a woven textile structure with MD threads and CD threads, and at least one layer of nonwoven fibres, wherein the MD threads have a diameter of between 0.25 mm and 0.45 mm, wholly or predominantly, in particular between 0.3 mm and 0.35 mm, and the thread density of the MD threads is more than 37%, in particular between 37% and 45%, characterised in that the basic structure is composed of two endless or made-endless fabric layers, wherein in both fabric layers the MD threads have a diameter of between 0.25 mm and 0.45 mm, in particular between 0.3 mm and 0.35 mm, and the thread density of the MD threads is more than 37%, in particular between 37% and 45%, wherein, to determine the thread density of the MD threads, the number of threads per unit length is multiplied by their diameter and the value is set in relation to the unit length, and wherein the term "entirely or predominantly" is to be understood as meaning that at least 90%, preferably 95%, in particular all MD threads have a diameter within the specified range.

2. , according to one of the previous claims, characterised in that the basic structure is constructed from two flat fabrics made endless , wherein the warp threads of the loom provide the MD threads of the and the flat fabric is made endless by connecting the front ends, wherein the connection is made in particular by a welded connection.

3. Covering (2) according to one of the previous claims, characterised in that at least some of the CD threads, in particular 50% or more of the CD threads, are listed as twisted yarn.

4. Covering (2) according to one of the previous claims, characterised in that the covering (2) has a thickness of 3.5 mm or less, in particular between 2.5 mm and 3 mm.

5. Stringing (2) according to one of the previous claims, characterised in that the weight of the stringing is between 750 g / m2 and 1250 g / m2, in particular between 900 g / m2 and 1100 g / m2.

6. Covering (2) according to one of the previous claims, characterised in that the weight proportion of the non-woven layers corresponds at most to the weight proportion of the base structure, in particular at most 2 / 3 of the weight proportion of the base structure.

7. Machine (1) for producing a tissue web (3), comprising a press device (30) with at least one press nip (31), characterised in that the machine (1) has at least one covering (2) according to one of claims 1-6 and the covering (1) passes through the at least one press nip (31) during operation of the press device (30).

8. Machine (1) according to claim 7, characterised in that the press nip (31) is a long nip (31), in particular a shoe nip (31).

9. Machine (1) according to one of claims 7 or 8, characterised in that the pressing device (30) has a waste water collector (33) which is designed to collect splash water which has been removed from the tissue web (3) in the form of nip drainage in the at least one pressing nip (31).

10. Method for producing a tissue web (3), wherein a machine (1) according to one of claims 7 to 9 is used for the production.

11. Method according to claim 10, characterised in that in the pressing device (30), part of the dewatering takes place in the form of nip dewatering, and this dewatered water is collected in whole or in part as splash water by a waste water collector (33).

12. Method according to claim 11, characterised in that the nip dewatering accounts for more than 10%, in particular between 20% and 50%, of the total dewatering amount of the press device (30).

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