Method and felt

Abstract

The invention relates to a method for producing a felt, in particular a press felt for a paper machine, and to an associated felt, the method comprising the following steps: a. providing a base structure, in particular a woven base structure, b. arranging at least one first nonwoven layer on one side of the base structure, c. needle-punching the first nonwoven layer to the base structure, forming a nonwoven support, wherein the needle-punching operation is performed by means of water jet needling, wherein the needle-punching operation is performed until the material density of the nonwoven support is at least 60%, in particular between 70% and 90%.

Description

[0001] Process and felt

[0002] The invention relates to a method for producing a felt, in particular a press felt for a paper machine according to the preamble of claim 1, and to an associated felt.

[0003] In the production of felts, especially press felts for paper machines, it is common practice to provide a base structure with a layer of nonwoven fibers. The base structure is usually a woven base structure.

[0004] For attachment, the nonwoven fibers are arranged on the base structure and attached to it by needling. This mechanical needling of nonwoven fibers has long been known and is described, for example, in EP 0 480 868 B1.

[0005] Mechanical needling uses special needles, described, for example, in documents EP1069224 A1 or DE102004037716 A1, which are used in large numbers in so-called needle boards. Such needle boards are shown as an example in EP1953287 A1.

[0006] Although the needling process has been proven successful for decades, it does have several disadvantages. Firstly, these needles wear out with continued use and must be replaced. This, in addition to the costs, leads to extended downtime of production facilities.

[0007] Another disadvantage is that needling causes a certain amount of damage to the nonwoven fibers. The more deeply the felt is needled, the more noticeable this damage becomes. This can lead to the technologically desired greater densification of the nonwoven layer not being achieved, as the damage to the fibers caused by the needles is no longer within the tolerable range. The surface of the felt is also influenced to some extent by needling. So-called "needle craters" can often be observed where the fibers have been pierced into the structure. This can lead to an inhomogeneous paper side of the felt and uneven drainage or even to undesirable influences on the paper surface.

[0008] Finally, needling also limits the thickness of nonwoven fibers that can be used for felt.

[0009] To avoid these disadvantages, some attempts have been made to dispense with the mechanical needling process and instead use water jet needling, which is known from nonwoven fabric production.

[0010] Patent applications DE102009024057 A1 and WO12098223 A1 describe processes for this purpose. However, these processes have not yet been widely adopted in the production of press felts. One of the reasons for this is certainly the fact that the application of heavier nonwoven layers, e.g., 500 g / m 2 and more, is only possible with difficulty.

[0011] The object of the invention is to propose an alternative method for attaching the nonwoven layer and a corresponding felt that overcomes the problems known from the prior art. In particular, the object of the invention is to propose a novel felt that has not been efficiently manufactured to date.

[0012] The object is achieved according to the invention by an embodiment according to the independent claims. Further advantageous embodiments of the present invention can be found in the subclaims.

[0013] With regard to the method, the object is achieved by a method for producing a felt, in particular a press felt for a paper machine, the method comprising the following steps: a. Providing a base structure, in particular a woven base structure b. Arranging at least one first nonwoven layer on one side of the base structure c. Needling the first nonwoven layer to the base structure to form a nonwoven overlay.

[0014] It is provided that the needling is carried out by means of water jet needling, and that either the needling is carried out until the material density of the nonwoven layer is at least 40% or at least 50%, preferably at least 60%, in particular between 70% and 90% and / or that at least a part of the nonwoven layer, in particular at least 10% by weight or at least 20% by weight of the nonwoven layer, consists of splittable fibers, wherein the water jet needling is set such that a part of the splittable fibers is split in step c. by the water jet needling.

[0015] Waterjet needling of a nonwoven fabric can be achieved using a nozzle bar, which has a strip of nozzles with outlet openings, usually arranged in two or more parallel rows. Accordingly, the water jets are arranged in two or more parallel rows and act on the nonwoven fabric. The outlet openings, and thus the emerging water jets, are advantageously arranged offset from one another. The water jets usually emerge as continuous jets, but can also be pulsed.

[0016] For needling, the base structure, together with the arranged nonwoven fabric, is moved relative to the nozzle bar. This can be done either by moving the base structure with a fixed nozzle bar, or by moving the nozzle bar with a fixed base structure. Alternatively, both the nozzle bar and the base structure can move.

[0017] The inventors recognized that the targeted use of waterjet needling allows for the production of felts with highly advantageous properties that cannot be achieved, or are not cost-effective, with conventional needling. One of the felt properties that can be adjusted very precisely and over a very wide range using waterjet needling is the material density in the fleece layer.

[0018] The specification of [xx%] material density refers to the fact that xx% of the volume of the nonwoven overlay consists of the nonwoven fiber material and, if applicable, other solid components of the nonwoven overlay, while the remaining (100-xx)% is formed by cavities ("void volume"). The material density / void volume can be determined using known methods. Mercury porosimetry, for example, is suitable. Alternatively, the void volume can be determined using a p-CT scan.

[0019] To determine the material density, the sample is subjected to a pressure of 5 MPa. It has been shown that determining the material density under this pressure very accurately reflects the conditions that occur in a felt that has been running in the machine for some time.

[0020] To increase the material density in the nonwoven layer to values ​​of 60% or more, the nonwoven fibers must be densified through long and intensive needling. If this is achieved through mechanical needling, surface defects due to mechanical damage to the fibers increase significantly. Such material densities are almost impossible to achieve using conventional methods and are generally only possible with felts where the surface quality is not particularly relevant to the product being manufactured. The inventors recognized that if this densification is achieved entirely or at least partially through waterjet needling, these defects will not occur. In this way, felts with properties that would not be possible with purely mechanical needling can be produced.

[0021] Furthermore, the inventors have recognized that it is possible for at least a portion of the nonwoven layer, in particular at least 10% by weight or at least 20% by weight of the nonwoven layer, to consist of splittable fibers, wherein the water jet needling is or can be adjusted such that a portion of the splittable fibers is split by the water jet needling in step c.

[0022] Splittable fibers are known per se and are described, for example, in documents WO03054272 A1 and US6410139 BA. These fibers are composed of several components that can be separated from one another under the application of appropriate force. Until now, such fibers have not been used on a large scale in press felts because splitting the fibers is very laborious. During the mechanical needling process, even with a high energy input, the fibers are not completely split. Instead, the fibers are increasingly damaged and shortened by the needles.

[0023] Surprisingly, it has been shown that water jet needling is capable of not only securing such splittable fibers but also splitting them. This can be particularly advantageous if the splittable fibers become thinner as a result of splitting. Thus, in advantageous embodiments, the linear density of the nonwoven fibers in the nonwoven layer before water jet needling is at least 11 dtex, preferably at least 22 dtex, while the minimum linear density after water jet needling is less than 11 dtex, in particular 6 dtex or less. Fibers with 11 dtex or less can be referred to as fine fibers.

[0024] Fibers with a low linear density are highly desirable in the nonwoven fabric layer, especially in the paper-contacting surface, as they make the felt surface smoother and reduce the tendency of the felt to mark. However, processing such thin fibers is not easy. Carding these fibers, in particular, is challenging and requires special care.

[0025] Combining splittable fibers with waterjet needling provides a very elegant solution. Processing, especially carding, takes place with the still unsplit, and thus thicker, fibers. This is comparatively easy. Waterjet needling then splits these fibers completely or at least partially. Thus, the desired thinner fibers are found in the finished nonwoven layer. Furthermore, this advantageous effect can be achieved without an additional processing step.

[0026] The splittable fibers can be provided in all nonwoven layers (the first nonwoven layer and all subsequent nonwoven layers) of the nonwoven overlay. Alternatively, the splittable fibers can be provided in only some or only one nonwoven layer. This allows the resulting fine fibers to be positioned at the desired positions in the nonwoven overlay. It can be particularly advantageous if the splittable fibers are incorporated in the nonwoven layer, which will later provide the paper-contacting surface of the felt.

[0027] Each of these features (high material density or splittable fibers) represents an inventive idea in itself.

[0028] In particular, it is also possible to implement both features together. This makes it possible to produce felts with a nonwoven material density of at least 60%, especially between 70% and 90%, in which a significant portion of the nonwoven fibers consists of fine fibers produced from split fibers by waterjet needling.

[0029] In processes within the scope of this invention, it is possible for one or more additional nonwoven layers to be arranged in step b., and for the additional nonwoven layer(s) to be needled to the base structure together with the first nonwoven layer by means of water jet needling to form a nonwoven overlay in step c. Here, too, needling can be continued until the material density of the nonwoven overlay is at least 60%, in particular between 70% and 90%. (The material density is determined using a sample subjected to a pressure of 5 MPa.)

[0030] For the purposes of this application, the term "fleece overlay" refers to the entire fiber fleece attached to one or both sides of the felt. This fleece overlay can, in turn, be constructed from several "fleece layers." Such fleece layers can be available as rolls or in another suitable form.

[0031] If multiple nonwoven layers are used, the additional nonwoven layers can be arranged on a previous nonwoven layer or on the second side of the base structure. A structure consisting of multiple nonwoven layers can be advantageous, for example, for applying a larger quantity of nonwoven fibers to a felt than is reasonably possible with a single nonwoven layer. Alternatively or additionally, the nonwoven fibers of the various nonwoven layers can be different, for example, in material or titer. In this way, the nonwoven overlay can be adapted to the requirements of the felt by selecting and arranging the individual nonwoven layers.

[0032] Woven base structures are preferably used as the base structure. These can be endless fabric loops or fabric loops made endless by means of a seam—for example, a pintle seam. In advantageous embodiments, this base structure can be constructed from simple flat fabrics, as described, for example, in EP 0 425 523 B1 or EP2788546 B1.

[0033] Alternatively or additionally, the base structure can also contain or consist of layers of threads. One possible embodiment of such a base structure is described, for example, in WO23110220 A1. Other textile fabrics, such as knitted or spacer fabrics, can also be present in the base structure.

[0034] The nonwoven overlay may also contain coarse nonwoven fibers with a linear density of at least 67 dtex, especially 100 dtex and above. Even higher linear density of 200 dtex, 250 dtex, 300 dtex, or 400 dtex are also possible.

[0035] A total of at least 50 g / m 2 preferably at least 100 g / m 2 , especially on coarse fleece fibers in the fleece layer.

[0036] These coarse nonwoven fibers can be provided in a single nonwoven layer or in multiple nonwoven layers. In particular, it can be provided, for example, that at least one nonwoven layer consists of more than 50%, in particular entirely, of such coarse nonwoven fibers.

[0037] A total of at least 50 g / m 2 preferably at least 100 g / m 2 of coarse fleece fibers in the fleece layer.

[0038] Alternatively or additionally, it can be provided that at least one nonwoven layer consists of more than 50%, in particular entirely, of coarse nonwoven fibers with a titer of at least 67 dtex, in particular 100 dtex and more. Even higher titers of 200 dtex, 250 dtex, 300 dtex, or 400 dtex are also possible. For each individual fiber type and thickness, at least 50 g / m 2 preferably at least 100 g / m 2 in the fleece layer or even in a single fleece layer.

[0039] Such thick nonwoven fibers cannot be needled, or only very poorly, using conventional mechanical needling. The needles damage the thick fibers. However, since a significant portion of the needling is done using waterjet needling, these fibers can also be used.

[0040] It has proven advantageous if, in step c., the water jets are operated at a pressure of maximum 400 bar, preferably between 20 bar and 250 bar.

[0041] The speed at which the web is moved through the water jet needling unit is also a control variable for the needling. In water jet needling, speeds of 400 m / min are quite common. However, the speed can be increased depending on the application, so that speeds of 600 m / min and more are also possible. In the applications described here, however, lower speeds can also be advantageous, especially when thicker fibers and larger application quantities are to be used. For example, speeds of 100 m / min or less, in particular 50 m / min, 30 m / min, 20 m / min, 10 m / min, 5 m / min or less can be advantageous in individual cases. In methods according to aspects of the present invention, it can be advantageous if mechanical needling is provided between steps b. and c. - i.e. before the water jet needling.Through this mechanical needling, for example, a nonwoven layer can be attached to the base structure, which can then be completed by waterjet needling. In particular, increasing the material density and / or splitting the splittable fibers is still achieved by waterjet needling.

[0042] The defects known from classical mechanical needling, such as damage to the nonwoven fibres due to excessive needling, can also be largely avoided in this combined process.

[0043] Furthermore, a felt, in particular a press felt for a paper machine, comprising a base structure, in particular a woven base structure, and a nonwoven overlay which is at least partially attached to the base structure by means of water jet needling is proposed.

[0044] The felt is characterized in that the material density of the nonwoven layer is at least 60%, in particular between 70% and 90%, and / or a significant part of the nonwoven fibers, in particular at least 20% by weight of the first nonwoven layer, consist of fine fibers which have been produced from splittable fibers by water jet needling.

[0045] The feature that the nonwoven layer is at least partially attached to the base structure by means of water jet needling should be understood to mean that a mechanical needling step can also be provided during needling, but that at least part of the needling is carried out by water jet needling.

[0046] In particular, it can be provided that the weight of the fleece layer is between 300 g / m 2 and 3000 g / m 2 , especially between 400 g / m 2 and 1600 g / m 2It can be provided that the nonwoven fibers of the nonwoven layer have a titer of between 1 dtex and 400 dtex, in particular between 5 dtex and 250 dtex. In particular, it can be provided that at least one nonwoven layer consists of more than 50%, in particular completely, of coarse nonwoven fibers with a titer of at least 67 dtex, in particular 100 dtex and more. Even larger titers of 200 dtex, 250 dtex, 300 dtex or 400 dtex are also possible. For each individual fiber type and thickness, at least 50 g / m 2 preferably at least 100 g / m 2 in the fleece layer or even in a single fleece layer.

[0047] Such thick nonwoven fibers cannot be needled, or only very poorly, using conventional mechanical needling. The needles damage the thick fibers. However, since a significant portion of the needling is done using waterjet needling, these fibers can also be used.

[0048] The invention is further explained below with reference to the figures.

[0049] Figure 1 shows a needling device for a method according to one aspect of the present invention

[0050] Figure 2 shows a pCT image of a felt

[0051] Figures 3a to 3c show material densities determined using pCT images. (Caliper values ​​in mm)

[0052] Figure 1 shows a needling device 10 for carrying out a method for producing a felt according to one aspect of the present invention. A series of rollers 6 are provided for guiding a material web 1, 3. Some of these rollers 6 can be provided with drives. The basic structure 1 can initially be inserted into the needling device 10 as the material web. During the process, this is converted into a basic structure with a fleece layer 3 or a finished press felt. In this embodiment, the arrangement of the first fleece layer 2 on the basic structure 1 is carried out, for example, by unwinding the first fleece layer 2 from a roll and depositing it on the basic structure 1 by means of a feed roller 9. However, the arrangement can also be implemented in other ways. After the arrangement of the first fleece layer 2, a mechanical needling unit 4 is provided in the needling device 10 shown here.This serves to needling the first nonwoven layer 2 to the base structure 1 in a first needling operation. This mechanical needling attaches the first nonwoven layer 2 to the base structure 1. Such mechanical needling or mechanical needling unit 4 is not necessary for methods according to the present invention, but can nevertheless be advantageous.

[0053] The base structure with the resulting nonwoven layer 3 is then guided directly or via additional guide rollers 6 to a water jet needling unit 5. There, the first nonwoven layer 2 is further needled to the base structure 1 in a second needling process. The water jets can be operated at a pressure of up to 400 bar, preferably between 20 bar and 250 bar.

[0054] In addition to the water jet nozzles, the water jet needling unit 5 can also have a support element 7 for supporting the material web during needling.

[0055] In the needling device 10 in Figure 1, a further nonwoven layer 2b is arranged after the first nonwoven layer 2. The further nonwoven layer 2b is arranged on the first nonwoven layer 2 before the mechanical needling unit 4 and is then needled together with it. It is also possible to use more than two nonwoven layers 2, 2b.

[0056] Needling, in particular water jet needling, can be carried out until the material density of the nonwoven layer is at least 60%, in particular between 70% and 90%.

[0057] Alternatively or additionally, at least a portion of the nonwoven layer, in particular at least 10% by weight of the nonwoven layer, can consist of splittable fibers, wherein the water jet needling is adjusted such that a portion of the splittable fibers is split by the water jet needling in step c. In this case, the splittable fibers can be provided in all nonwoven layers 2, 2b. Alternatively, the splittable fibers can also be provided in only a few or only one nonwoven layer 2, 2b. This allows the resulting fine fibers to be positioned specifically at desired positions in the nonwoven layer.

[0058] Figure 2 shows an example of a PCT image of a felt structure. The image has been processed so that solid structures are shown in white, while the voids are black. The clearly visible large circles in the center originate from the filaments of the basic structure 1 , while the thinner structures are from the nonwoven fibers. The material density across the thickness of the felt can be easily determined on the basis of such images by image analysis using the ratio of black to white. To obtain a reproducible measurement, several such sections of a felt sample should be analyzed, and the mean value of these measurements taken as the value for the material density.

[0059] Figures 3a, 3b, and 3c show exemplary material densities determined from pCT images as shown in Figure 2. Measurements are taken from the paper-contacting felt surface ("0 mm") downwards.

[0060] Figure 3a shows the material density in the same, new felt, measured at different pressures. Curve K1 was determined at 5 MPa, while curve K2 was determined at 0.1 MPa. This clearly shows that the felt is compressed by the applied pressure. Thus, the felt at 5 MPa has a caliper of only 2.5 mm, while the felt measured at 0.1 MPa is significantly thicker at around 3.5 mm. This compression naturally entails a change in the material density, as the unchanged felt mass is now distributed over a smaller volume.

[0061] Figure 3b again shows curve K1, but this time together with the material density K3 of a felt that has already been used in a paper machine for some time. This curve K3 was determined at a pressure of 0.1 MPa. It is clearly visible that these two curves K1 and K3 are very similar. For this reason, the material density measurements in the context of the present invention are carried out at a pressure of 5 MPa, as this very accurately reflects the situation of a felt in production after a certain run-in period. A striking feature of all material density curves are the two "humps" approximately in the middle of the felt thickness. These arise from the influence of the base fabric, which is also measured when determining the material density. Within the framework of the ideas described here, however, the material density of the fleece layer is relevant.

[0062] One way to determine the material density of the fleece layer is to measure the height of the fleece layer and only look at this area of ​​the material density curves.

[0063] Alternatively, image analysis can be used again. As shown in Figure 2, the filaments of basic structure 1 are clearly visible as thick threads in the PCT images. Curve K4 in Figure 3c shows the material density generated solely by these filaments of basic structure 1. Subtracting curve K4 from curve K1 yields curve Delta, which represents the material distribution of the nonwoven fibers of the nonwoven overlay.

[0064] Points S1 and S2 indicate the points where the K1 and Delta curves begin to diverge. This is where the basic structure begins. Therefore, to determine the material density of the fleece overlay, only the area from the outer edges to the separation points S1 / S2 should be considered.

[0065] In the example of Figure 3c, this results in a material density of ~ 57% on the top side and ~ 58% on the bottom side of the felt.

[0066] List of reference symbols

[0067] 1 Basic structure

[0068] 2 first fleece layer 2b further fleece layer

[0069] 3 Basic structure with fleece layer

[0070] 4 mechanical needling unit

[0071] 5 Water jet needling unit

[0072] 6 Guide roller 7 Support element

[0073] 9 Feed roller

[0074] 10 needling device

[0075] K1 Material density of new felt at 5 MPa

[0076] K2 Material density of new felt at 0.1 MPa K3 Material density of used felt at 0.1 MPa K4 Material density of covering at 5 MPa

[0077] Delta difference K1 - K4

Claims

Patent claims 1 . A method for producing a felt, in particular a press felt for a paper machine, the method comprising the following steps: a. Providing a base structure (1), in particular a woven base structure (1) b. Arranging at least one first nonwoven layer (2) on one side of the base structure (1) c. Needling the first nonwoven layer (2) to the base structure (1) to form a nonwoven layer, wherein the needling is carried out by means of water jet needling, wherein the needling is carried out until the material density of the nonwoven layer is at least 40%, preferably at least 60%, in particular between 70% and 90% 2. Method according to claim 1, characterized in that in step b. one or more further nonwoven layers (2b) are arranged, and the further nonwoven layer or the further nonwoven layers (2b) together with the first nonwoven layer are needled to the basic structure (1) by means of water jet needling to form a nonwoven overlay in step c., wherein the needling is carried out until the material density of the nonwoven overlay is at least 60%, in particular between 70% and 90%.

3. Method according to one of the preceding claims, characterized in that at least one nonwoven layer consists of more than 50%, in particular completely, of coarse nonwoven fibers with a titre of at least 67 dtex, in particular 100 dtex and more.

4. Method according to one of the preceding claims, characterized in that the nonwoven fibers of the nonwoven layer have a linear density of maximum 400 dtex, in particular less than 250 dtex.

5. Method according to one of the preceding claims, characterized in that in step c. the water jets are operated at a maximum pressure of 400 bar, preferably between 20 bar and 250 bar.

6. Method according to one of the preceding claims, characterized in that at least a part of the nonwoven layer, in particular at least 10% by weight of the nonwoven layer consists of splittable fibers, wherein the water jet needling is adjusted such that a part of the splittable fibers is split in step c. by the water jet needling and the titer of the nonwoven fibers in the nonwoven layer before the water jet needling is at least 11 dtex, preferably at least 22 dtex, while the minimum titer after the water jet needling is less than 11 dtex, in particular 6 dtex or less.

7. Method according to one of the preceding claims, characterized in that mechanical needling is provided between steps b. and c.

8. Method according to one of the preceding claims, characterized in that the water jet needling in step c. is not carried out uniformly across the width direction of the felt, so that in particular the material density of the nonwoven layer varies in the width direction of the felt.

9. Felt, in particular press felt for a paper machine, comprising a base structure (1), in particular a woven base structure (1), and a nonwoven overlay which is at least partially attached to the base structure (1) by means of water jet needling, characterized in that the material density of the nonwoven overlay is at least 60%, in particular between 70% and 90%, and / or a significant portion of the nonwoven fibers, in particular at least 20% by weight of the first nonwoven layer, consists of fine fibers produced from splittable fibers by water jet needling 10. Felt according to claim 9, characterized in that the weight of the fleece layer is between 300 g / m 2 and 3000 g / m 2 , especially between 400 g / m 2 and 1600 g / m 2 amounts.

11. Felt according to one of claims 9 or 10, characterized in that the nonwoven fibers of the nonwoven layer have a titre of between 1 dtex and 400 dtex, in particular between 5 dtex and 250 dtex.

Images