press felt

Abstract

The invention relates to a press felt for a machine for manufacturing a fibrous web, comprising a woven base structure and a nonwoven cover layer fixed on the base structure, wherein the base structure has a first fabric layer and a second fabric layer, wherein at least the first fabric layer has longitudinal yarns and transverse yarns which intersect at intersection positions, wherein the longitudinal yarns and the transverse yarns of the first fabric layer are materially connected to one another, in particular welded to one another, at at least 5% of the intersection positions, in particular at at least 10% of the intersection positions.

Description

Technical Field

[0001] This invention relates to a press felt for a machine used to manufacture fiber webs. Background Technology

[0002] In the manufacture of paper or paperboard, press felt, a type of paper machine wire mat, is used to transport and dewater the fiber web within the press section. The main components of this felt are a load-bearing base structure and a nonwoven layer, which is typically sewn together with the base structure. In most cases, the fabric is used for the base structure.

[0003] To increase the volume for absorbing liquid and also to increase strength, the load-bearing base structure can have multiple overlapping layers of fabric. For example, felts with such a base structure are described in patent documents EP 0 425 523 or EP 0 672 784 81. Similarly, multiple layers of nonwoven fibers with different fiber fineness can also be provided, as described in patent document EP 2160495 B1.

[0004] During operation, the press felt is subjected to repeated loading in one or more press zones. In the press zones, the felt is compressed, and after passing through the press zones, the felt expands again to essentially its original thickness. Because this process occurs very frequently, the felt is compacted after a short time. The prior art explains this as the compression of the nonwoven layers. Compaction of the woven layers also occurs as a layer with reduced permeability is formed. Important properties of the felt, such as permeability, are thus altered. To compensate for this, it is known from patent document EP2 678 472, for example, to provide a particularly fine nonwoven layer that is worn away during the operation of the felt. By wearing away the fine nonwoven fibers, the permeability of the felt increases, while simultaneously, the permeability decreases through compaction. While this achieves substantially constant permeability of the felt, the use of a “sacrificial nonwoven layer” introduces additional costs and expenses. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to propose a press felt in which the tendency to compact is reduced. Another technical problem to be solved by the present invention is to propose a felt that provides a large volume for liquid absorption.

[0006] This invention proposes a press felt for a machine used to manufacture fiber webs, comprising a woven base structure and a nonwoven overlay fixed to the base structure, wherein the base structure has a first fabric layer and a second fabric layer. According to the invention, at least the first fabric layer has longitudinal and transverse yarns crossing at intersections, wherein the longitudinal and transverse yarns of the first fabric layer are welded together at at least 5% of the intersections, particularly at at least 10% of the intersections.

[0007] In this context, the terms "longitudinal yarn" and "MD yarn" are synonyms, as are "transverse yarn" and "CD yarn".

[0008] As described above, a base structure with multiple fabric layers is advantageous in providing a large volume for liquid absorption (“Void Volume”). However, it also indicates that such a felt has a relatively high tendency to compact. The inventors recognize that this compaction effect is partly due to the different fabric layers being partially pressed into each other by the load in the compression zone. This is facilitated or reinforced by the fact that the yarns of the fabric are somewhat movable. With the continuous load in the compression zone, the individual MD or CD yarns move, causing the yarns of one layer to be pressed into the gaps between the yarns of another layer, which increases the compaction of the felt and also reduces its permeability.

[0009] To prevent, or at least greatly reduce, this inventor proposes that, at least in the first fabric layer, a portion of the longitudinal and transverse yarns that cross at the crossing points be welded together. It is advantageous that the longitudinal and transverse yarns of the first fabric layer are materially connected, particularly welded, to each other at at least 5% of the crossing points, and especially at at least 10% of the crossing points. This prevents or hinders yarn movement and suppresses the aforementioned compaction effect.

[0010] As the proportion of welded intersections increases, for example to 15%, 20%, 25%, 30%, 35%, 40% or more, the fixation of the yarns and the inhibition of movement also increase. However, this also increases the rigidity or strength of the base structure and therefore the entire felt. This is usually only possible or desirable to a certain extent. Therefore, it is generally advantageous for the longitudinal and transverse yarns of the first fabric layer to be welded together at less than 60%, especially less than 50%, of the intersections.

[0011] If the second fabric layer also has longitudinal and transverse yarns crossing at intersection points, wherein at at least 5% of the intersection points, particularly at at least 10% of the intersection points, the longitudinal and transverse yarns of the second fabric layer are connected to each other in a cooperative manner, particularly welded together, the advantageous effects of the invention can be enhanced. This further reduces the mutual movement of the yarns in the two layers. It is also applicable in the second layer that as the proportion of welded intersection points increases, for example to 15%, 20%, 25%, 30%, 35%, 40% or more, the fixation of the yarns and the suppression of movement also increase, and it is generally advantageous that the longitudinal and transverse yarns of the second fabric layer are welded together at less than 60%, particularly less than 50% of the intersection points.

[0012] Even though in most of the examples described the base structure has exactly two fabric layers, it is also possible to specify a design in which the base structure also includes one or more layers, especially one or more additional fabric layers.

[0013] The connection of materials at the intersection can be achieved in different ways.

[0014] For example, bicomponent fibers (“BiCo fibers”) can be used. Bicomponent fibers consist of two parts, for example, a core and a sheath. These two polymers have different softening or melting temperatures. The core has a higher melting temperature than the sheath, allowing the sheath to melt under certain temperature shocks, thereby forming connection points between the corresponding core fibers in the current matrix mixture.

[0015] As an alternative, the MD and CD yarns can be joined together by welding. Different methods, such as ultrasonic welding or transmission welding, can be used to create the welded joint.

[0016] Near-infrared transmission welding is considered particularly advantageous. Commonly used polyamide yarns are essentially transparent to light in the near-infrared range between approximately 780 nm and 1100 nm.

[0017] It can now be advantageously specified that at least some of the warp and / or transverse yarns of the first and / or second layers completely or substantially absorb laser light with wavelengths between 780 nm and 1100 nm. (Absorption exceeding 30%, especially exceeding 40%, of the corresponding light is considered substantially absorbed. Such yarn is referred to below as absorbing yarn.) When the fabric is properly irradiated with light from this wavelength range, the light penetrates the non-absorbing yarn relatively unimpeded and is absorbed by the absorbing yarn. This heats the contact point of the two yarns to achieve welding.

[0018] Advantageously, the absorbent yarn can be made of the same polymer as other yarns, with additional absorbent additives added. This allows for particularly durable welding. Alternatively, compatible polymers, such as polyamide 6 and polyamide 6.6, can be used instead of the same polymer.

[0019] Alternatively, quasi-synchronous welding methods can be used to produce spot welds. In this case, the use of absorbent can be partially omitted.

[0020] By selectively irradiating the selected contact areas / intersections, only these contact areas / intersections can be welded.

[0021] For example, this selective illumination can be performed in the form of regular patterns, such as straight lines, wavy lines, dotted patterns, etc. The width of these lines or the diameter of the dots can be selected to be so large that multiple intersections, especially 2, 3, 4, 5 or more intersections, are covered.

[0022] For the desired effect, the intersections of the material-matched connections are not only located in parts of the netting, such as the seam areas, but also distributed across the entire surface of the netting, especially evenly distributed across the entire surface of the netting.

[0023] This uniform distribution can be achieved, for example, by weaving the absorbent yarn as a CD yarn or also as an MD yarn in a fixed, predetermined pattern. For example, it can be specified that every 10th CD yarn is an absorbent yarn. This results in a relatively small number of connection points. If every 4th CD yarn, every 2nd CD yarn, or even every CD yarn is woven in as an absorbent yarn, the number of feasible connection points increases.

[0024] Similarly, BiCo yarn can also be woven in according to the above pattern.

[0025] There is a great deal of freedom in the fabric layers described herein. Here are some examples:

[0026] • The fabric can be a plain weave fabric.

[0027] • Fabrics can be processed during the roll-to-roll process. In particular, fabrics with material-fitting connections can be produced as roll products and then cut accordingly when manufacturing actual felt.

[0028] • The fabric can be a plain weave fabric welded into a continuous (or endless) strip.

[0029] • Fabrics can be woven continuously (or without end).

[0030] • The fabric may have seam connections, preferably with insert seams.

[0031] • The fabric can be single-layered or multi-layered.

[0032] • The fabric can be woven from monofilament and / or multifilament and / or twisted yarn.

[0033] These fabrics can also be gauze fabrics.

[0034] In a highly advantageous design, it can be specified that at each intersection where the longitudinal and transverse yarns are connected to each other in the first and / or second fabric layers, there is no material connection at adjacent intersections.

[0035] Adjacent intersections are understood here as four intersections that are directly adjacent in both the longitudinal and transverse directions.

[0036] The arrangement of material fits, especially welding, is advantageous because it allows for good fixation of the yarn. However, even with a relatively high proportion of material fits at the intersections (e.g., 30%, 40%, or 50%), the increase in structural rigidity is still tolerable.

[0037] This fabric layer is also easy to manufacture. For example, a fabric made with a plain weave or plain knit structure can be used as the first fabric layer. For the fabric, the longitudinal yarns can be transparent to light of a specific wavelength, while the transverse yarns completely or partially absorb this wavelength. The joining of the materials can then be achieved by welding using light transmission of this wavelength.

[0038] If light of this wavelength, such as a laser, is shone on the fabric from one side, intersections will appear where the transparent yarn lies on the absorbing yarn. At these intersections, the light passes through the transparent yarn and is absorbed by the absorbing yarn, thus creating a bond at the contact point through heat and material mating.

[0039] However, due to the plain knit or plain weave structure, at the four adjacent intersections, the absorbent yarn lies on top of the transparent yarn. Therefore, the absorbent yarn is only heated on its upper side, not at the contact point. Consequently, there is no material bonding at these intersections.

[0040] If the entire fabric is irradiated with a laser using this method, approximately 50% of the cross-sections will be welded together.

[0041] However, it is also feasible to irradiate only a portion of the fabric with a laser, thereby obtaining a smaller proportion of the cross positions of the connections. Attached Figure Description

[0042] Other advantageous designs of the invention are illustrated with reference to the accompanying drawings and embodiments. The mentioned features can be advantageously implemented not only in the shown combinations, but also individually combined with each other. The drawings show in detail:

[0043] Figure 1 This illustrates a fabric layer for press felt according to one aspect of the invention.

[0044] Figure 2a , 2b 2c illustrates the process of suppressing compaction by means of a design according to the present invention.

[0045] Figure 3 A press felt according to one aspect of the invention is shown.

[0046] The accompanying drawings will be described in detail below. Detailed Implementation

[0047] Figure 1A fabric layer is shown, which, according to one aspect of the invention, can be used as a first fabric layer 1 or a second fabric layer 2 in a press felt. A plain weave structure composed of intersecting longitudinal yarns 3 and transverse yarns 4 is shown. Some of the transverse yarns 6 are designed here as absorbent yarns 6. Figure 1 In the example shown, every second transverse yarn 4 is designed as an absorbing yarn 6. The remaining yarns 3 and 4 are made of a material such as polyamide, which is completely or substantially transparent to light in the near-infrared range. For example, the absorbing yarn 6 can be composed of the same polymer, with absorbent additives incorporated. If the intersection 5 is irradiated with light of the wavelength range absorbed by the absorbing yarn 6, for example by means of a corresponding near-infrared laser, the light penetrates through the non-absorbing longitudinal yarns 3 to the absorbing yarn 6. They are heated primarily at the contact point of the two yarns, thereby creating a welded connection between the two yarns.

[0048] At this or all of these intersections, 5 can be welded, or only a portion of them can be welded.

[0049] It is important to note that, for Figure 1 At some of the cross locations, the absorbent yarn 6 extends above the longitudinal yarn 3. If it is desired to also form a material fit connection at these cross locations, it is advantageous to irradiate the fabric from the opposite side.

[0050] If only one side is irradiated, then Figure 1 The fabric shown also constitutes a design in which, at each intersection 5 where the longitudinal yarns 3 and transverse yarns 4 are connected to each other in a material-matching manner, there is no material-matching connection at adjacent intersection 5.

[0051] In these fabric layers 1 and 2, the movement of the longitudinal yarn 3 in the transverse direction and the movement of the transverse yarn 4 in the longitudinal direction are both hindered or prevented.

[0052] Figure 2a , 2b Figure 2c schematically illustrates the characteristics of a press felt under load, in which there are no interlocking points 5 between the fabric layers 1 and 2. The press felt here has a first fabric layer 1 and a second fabric layer 2, which together provide the basic structure of the felt. A nonwoven overlay 7 is provided on the first fabric layer 1. For simplicity, only the warp yarns 3.1 and 3.2 of fabric layers 1 and 2 are shown. In the felt shown here, the first fabric layer 1 and the second fabric layer 2 are different, for example, shown by the different diameters of the warp yarns 3.1 of the first layer 1 and the warp yarns 3.2 of the second layer 2. However, the two layers 1 and 2 can also be of the same fabric type, especially since they can be formed by folding and stacking single pieces of fabric, as described in patent document EP 0 425 523.

[0053] Figure 2a This shows a felt without external load. (Example) Figure 2b As shown, for example, a load is applied to the felt when passing through the pressing zone. The second fabric layer 2 is thus pressed upward onto the first fabric layer. This generates a transverse shear force on the longitudinal yarns 3.1, 3.2, which is more advantageous due to the circular shape of the yarns.

[0054] Then, Figure 2c The compressed form of the felt is shown. On one hand, the nonwoven covering 7 is compressed by an external load. On the other hand, the longitudinal yarns 3.1 and 3.2 also move laterally, causing the two fabric layers 1 and 2 to partially press into each other. As a result, the "Void Volume" of one fabric layer 1 and 2 for liquid absorption is partially filled by the yarns of the other fabric layer 2 and 1, and is no longer available for liquid absorption.

[0055] Figure 3 and Figure 2c The only difference is that the felt is constructed according to one aspect of the invention. That is, particularly at at least 5% of the cross positions 5, and particularly at at least 10% of the cross positions 5, the longitudinal yarns 3.1 and transverse yarns 4 of the first fabric layer 1 are materially connected to each other, and particularly welded to each other. Furthermore, it can be specified that at at least 5% of the cross positions 5, and particularly at at least 10% of the cross positions 5, the longitudinal yarns 3.2 and transverse yarns 4 of the second fabric layer 2 are materially connected to each other, and particularly welded to each other.

[0056] Here, the nonwoven overlay 7 is also compressed. However, the longitudinal yarns 3.1 and 3.2 cannot shift laterally. The lateral force is absorbed by the material fit at the intersection 5. This prevents or at least reduces the penetration of the first fabric layer 1 and the second fabric layer 2. The volume of fabric layers 1 and 2 for liquid absorption is hardly reduced by the penetration of yarns 3 and 4 from the other fabric layer 2 and 1, and therefore can still be used for liquid absorption.

[0057] List of reference numerals in the attached diagram:

[0058] 1 First fabric layer

[0059] 2 Second fabric layer

[0060] 3 longitudinal yarns

[0061] 3.1 Longitudinal yarn

[0062] 3.2 Longitudinal yarn

[0063] 4 horizontal yarns

[0064] 5 intersections

[0065] 6 Absorbent Yarn

[0066] 7 Non-woven coating

Claims

1. A press felt for a machine used to manufacture fiber webs, comprising a woven base structure and a nonwoven covering (7) fixed to said base structure, wherein, The basic structure has a first fabric layer (1) and a second fabric layer (2), characterized in that at least the first fabric layer (1) has longitudinal yarns and transverse yarns (4) intersecting at intersection positions (5), wherein the longitudinal yarns and transverse yarns (4) of the first fabric layer (1) are materially connected to each other at at least 5% of the intersection positions (5), wherein the materially connected intersection positions (5) are not only located in local areas of the press felt, but also distributed across the entire surface of the press felt, and wherein the longitudinal yarns and transverse yarns (4) of the first fabric layer (1) are welded to each other at less than 60% of the intersection positions (5).

2. The press felt according to claim 1, characterized in that, The longitudinal yarns and transverse yarns (4) of the first fabric layer (1) are welded together at less than 50% of the intersection position (5).

3. The press felt according to claim 1 or 2, characterized in that, The second fabric layer (2) also has longitudinal yarns and transverse yarns (4) that intersect at the crossing position (5), wherein the longitudinal yarns and transverse yarns (4) of the second fabric layer (2) are connected to each other at at least 5% of the crossing positions (5).

4. The press felt according to claim 1 or 2, characterized in that, The infrastructure also includes additional layers.

5. The press felt according to claim 1, characterized in that, At least a portion of the longitudinal yarns and / or transverse yarns (4) of the first fabric layer (1) are absorbing yarns (6) that completely or largely absorb laser light with wavelengths in the range between 780 nm and 1100 nm.

6. The press felt according to claim 5, characterized in that, At least every 10th transverse yarn (4) is an absorbent yarn (6).

7. The press felt according to claim 5 or 6, characterized in that, At least every 10th longitudinal yarn is an absorbent yarn (6).

8. The press felt according to claim 1 or 2, characterized in that, At the cross positions (5) in the first fabric layer (1) and / or the second fabric layer (2) where each longitudinal yarn and transverse yarn (4) is materially connected to each other, there is no material connection at adjacent cross positions (5).

9. The press felt according to claim 1 or 2, characterized in that, The cross positions (5) of the material-fitted connection are not only located in the seam area, but are also evenly distributed across the entire surface of the press felt.

10. The press felt according to claim 1, characterized in that, The longitudinal yarns and transverse yarns (4) of the first fabric layer (1) are connected to each other in a material-fitting manner at at least 10% of the crossing positions (5).

11. The press felt according to claim 3, characterized in that, The longitudinal yarns and transverse yarns (4) of the second fabric layer (2) are welded together at at least 10% of the intersection positions (5).

12. The press felt according to claim 4, characterized in that, The other layer is a fabric layer.

13. The press felt according to claim 5, characterized in that, At least every fourth transverse yarn (4) is an absorbent yarn (6).

14. The press felt according to claim 5, characterized in that, Every second transverse yarn (4) is an absorbent yarn (6).

15. The press felt according to claim 5 or 6, characterized in that, At least every fourth longitudinal yarn is an absorbent yarn (6).

16. The press felt according to claim 5 or 6, characterized in that, The second longitudinal yarn is an absorbent yarn (6).

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