EP3597821A1 - Coupling for a machine for producing a sheet of fibrous material - Google Patents

Abstract

The present invention relates to a covering for a machine for producing a fibrous web, in particular a paper, cardboard or tissue web, comprising a substrate (20) with an upper side (22), a lower side (24), two side edges and a useful area between the two side edges, the useful area having a multiplicity of through channels (30) which connect the top side (22) to the bottom side (24) of the substrate (20). The inner surface (32) of at least one through channel (30), preferably of the majority of all through channels (30), more preferably of all through channels (30) in the useful area of the substrate (20), has an average roughness depth Rz which is greater than 4 μm , preferably larger than 6 µm, more preferably larger than 8 µm. The present invention further relates to a method for producing such a covering by means of a laser.

Description

The present invention relates to a covering for a machine for producing a fibrous web, in particular a paper, cardboard or tissue web, comprising a substrate with an upper side, a lower side, two side edges and a useful area between the two side edges, the useful area being a multiplicity of Has through channels that connect the top with the bottom of the substrate. The present invention further relates to a method for producing such a covering.

In the industrial production and / or refinement of fibrous webs, the fibrous web is regularly transported on one or more clothing (s) that circulate endlessly in a machine. For example, in a paper machine, a fiber suspension from a headbox is first applied to a forming wire, on which the actual fiber web is formed by dewatering, which is then transported through a press section for further drying on a press felt and then through a dryer section of the paper machine on a drying wire, before the finished paper web can be rolled up at the end of the paper machine or processed or refined directly. In practice, in addition to a few spiral sieves, fabrics are mostly used for these coverings, ie structures in which warp and weft threads are interwoven on a loom. Since this type of production is relatively complex, there has been an idea for quite some time to produce such coverings in a completely different way, namely by perforating a substrate. The present invention is also based on this idea. Such a covering, in which the through-channels are introduced into the substrate by means of a laser, was already described in the publications in the 1980s and 1990s, for example US 4,446,187 A respectively. US 5,837,102 A described.

According to the present invention, the term “substrate” is to be understood to mean a sheet-like structure which is generally made of plastic and which, per se, ie without the through-channels introduced, is initially essentially impermeable to liquids. It is only through the introduction of the through-channels that the substrate becomes fluid-permeable and thus acquires its important ability to be able to remove water from the fiber suspension or the fiber web. The substrate can essentially be a monolithic plastic film, for example produced by extrusion or casting, or alternatively a laminate which comprises several layers. These layers can, for example, be co-extruded or they can be produced completely separately from one another and only then joined together. The longitudinal ends of the substrate are preferably connected to one another by welding in order to make the clothing endless. Depending on the intended use, the covering can either consist essentially of only the perforated substrate or have further layers, such as a nonwoven layer, for example for the production of a press felt.

The useful area of the substrate denotes the area on which the fibrous web is actually formed and / or transported. The useful area can extend over the entire width of the substrate or else only over a smaller area that is spaced from the side edges.

In particular, when such a covering is used as a forming fabric, it is important that the covering enables good formation during sheet formation. A good formation is usually present in particular when there are no markings in the fibrous web that forms. However, a phenomenon of laser-drilled substrates that has long been regarded as a problem has been that the material of the substrate remaining between the individual through-channels has prevented uniform dewatering of the fiber suspension over the paper side of the substrate, and a certain degree of marking has therefore been inevitable , Only through the teaching in the post-published European patent applications EP18168641.1 and EP18168641.1 the applicant, the disclosure of which is hereby fully incorporated by reference this problem could be solved. According to this teaching, essentially funnel-shaped through channels are arranged so closely next to one another in the substrate that immediately adjacent through channels on the paper side of the substrate at least touch, preferably overlap one another. Although the substrate is weakened by the close arrangement of the through channels, it has been found that the structural residual stability of the substrate is sufficient for the requirements in the forming section of a paper machine. If immediately adjacent through channels overlap sufficiently on the paper side of the substrate, a topography can be formed on this paper side which essentially resembles the inside of an egg box. In other words, after the introduction of the through-channels, in particular by means of a laser, the originally smooth surface on the paper side of the substrate has completely, or at least almost completely, disappeared, so that on the paper side essentially only the contacting edges that delimit the through-channels , as more or less thin webs remain. The peripheral edge forms a contour that is not in one plane. In this way, a very large open area for the fiber suspension can be provided on the paper side of the substrate, so that extremely uniform dewatering can take place, which counteracts the tendency of the fabric to mark. The fiber from the fiber suspension is deposited over the through-channels on the peripheral edges of the same, while the water can flow through the through-channels. The machine side of the substrate opposite the paper side can still be present largely as a flat surface and thus provide a sufficient contact surface in order to transmit the driving forces of rollers of the paper machine to the substrate without any significant slippage.

Due to the very large open area on the paper side of the substrate, however, the fiber suspension can be drained too quickly, or at least faster than the usual laser-drilled substrates, in which the individual through-channels are spaced apart. However, draining too quickly has certain disadvantages. So become Example fillers contained in the fibrous suspension, which are to remain in the fibrous web, washed out excessively, which in turn is detrimental to the quality of the formation. Furthermore, it can happen that the forming fabric runs dry very quickly, which leads to an increased energy requirement for the operation of the paper machine and to increased wear during the clothing. For these reasons, a moderate to slow drainage rate of the fabric is preferred.

It is therefore an object of the present invention to remedy the disadvantages mentioned above. In particular, the present covering should be easy to manufacture and have a moderate drainage rate. If the fabric according to the invention is used as a forming fabric, it should be possible to achieve a particularly good formation of the fibrous web formed on it.

This object is achieved by the features of independent claim 1, relating to a covering according to the invention, and by the features of independent claim 10, relating to the manufacture of such a covering. Advantageous developments of the invention are the subject of the dependent claims.

The generic covering mentioned at the outset is distinguished according to the present invention in that the inner surface of at least one through channel, preferably of the majority of all through channels, more preferably of all through channels in the useful area of the substrate, has an average roughness depth R _z which is greater than 4 μm , preferably larger than 6 µm, more preferably larger than 8 µm. Studies have shown that the roughness of the inner surface of the through channels has a noticeable influence on the drainage speed of the fibrous web. In principle, the following applies: the greater the roughness, the lower the drainage rate.

As is known to the person skilled in the art, the average roughness depth R _{z is} determined by dividing a defined measuring section on the inner surface of a through channel into seven Individual measuring sections are divided, the middle five measuring sections being the same size. The evaluation is carried out only over these five measuring sections, since the Gaussian filter to be used requires half a single measuring section before or after the run, or because a convolution has a not negligible inflow and outflow behavior. The difference between the maximum and minimum value is determined from each of these individual measuring sections of the profile. The mean value is formed from the five individual roughness depths thus obtained.

Classically, the roughness measurement can be carried out as a tactile measurement of 2D profile cuts. Please refer to the standards DIN EN ISO 4287 and 4288. Investigations commissioned by the applicant have shown that the average roughness depth R _{z of} the inner surface of a through-channel of laser-drilled substrates can be determined more easily by 3D detection of the area to be examined by means of optical measurement technology. In this context, reference is made to the DIN EN ISO 25178 standard. Specifically, it is proposed to first cut open the substrate to determine the average roughness depth R _z , the cut preferably comprising the central axis of the through-channel, the inner surface of which is to be examined. The inner surface is then measured three-dimensionally using a suitable optical device, such as the DCM 3D confocal microscope from Leica®. Confocal microscopy uses a point-to-point method to measure a particular point on the inner surface. The 3D coordinates obtained in this way can then be used to lay 2D cut surfaces, from which in turn height profiles and roughness values can be obtained.

The covering according to the invention is preferably a forming fabric, or is used as such. Furthermore, the through channels can advantageously have a shape and be arranged in the substrate, as at the beginning with regard to the subsequently published European patent applications EP18168641.1 and EP18168641.1 described by the applicant. In particular, the through channels can be essentially funnel-shaped. For the purposes of the present application, this means that the through-channels start out from the paper side of the substrate in the thickness direction of the substrate to a central region which lies between the paper side and the machine side, or between the top and bottom of the substrate, or even tapered, preferably continuously, to the machine side. Although this funnel-shaped tapering already slows the flow velocity in the through-channel, the tapering cannot be made to any degree. If the inlet opening on the paper side or top side of the substrate becomes too large, fibers from the fiber suspension that are to be retained by the substrate can be sucked into the through-channel. If the outlet opening of the through-channel on the machine side or underside of the substrate becomes too small, the through-channel can quickly become blocked by fillers in the fiber suspension that have been flushed out. Therefore, the adjustment according to the invention of the roughness of the inner surface of the through-channel is of essential importance when optimizing the flow velocity in the through-channel of the substrate.

On the other hand, since the dewatering of the fibrous web should not take place too slowly, it is proposed that the average roughness depth R _{z is} less than 20 µm, preferably less than 15 µm. If the dewatering is too slow, the fibrous web is transferred to the press section and subsequent drying section with excessive residual moisture, at least when the fabric according to the invention is used as a forming wire of a paper machine, which is disadvantageous with regard to the energy consumption of the paper machine.

It is further proposed that the substrate is a laser-drilled substrate, the through-channels being introduced into the substrate by means of a laser. The finished covering can generally be clearly seen in which way the through-channels were introduced into the substrate, for example by punching or by mechanical drilling or by laser drilling. Laser drilling results in melting and / or sublimation of the substrate material, with part of the vaporized material usually being deposited on the substrate again as condensate. This leaves characteristic traces in the borehole and around the borehole. If the substrate of the covering according to the invention is a laminate which consists of more than one layer, the term “laser-drilled” substrate means that the finished laminate has been perforated with a laser. Ideas according to which through-channels can first be introduced into the individual layers of the laminate, the through-channels of the individual layers having different diameters, and only then connecting these layers to one another, are not practical, particularly since the individual layers cannot be used to cover with the necessary accuracy so that through-channels can be reliably formed everywhere, which connect the top with the bottom of the finished substrate. In this respect, such embodiments are explicitly not to be understood as "laser-drilled substrates" in the sense of the present invention, but at most the individual layer in such a laminate could be understood as a "laser-drilled substrate".

An advantageous development of the invention provides that the ratio between a minimum diameter of the through channels and a thickness of the substrate is between 1: 3 and 1:10, preferably between 1: 4 and 1: 8, more preferably between 1: 5 and 1 : 7th If the thickness of the substrate is at least four times the minimum diameter of the through-channel, then the effect which the roughness of the inner surface of the through-channel exerts on the flow velocity in the form of a throttling only becomes effective. With smaller thicknesses of the substrate, however, the roughness does not lead to the same reduction in the flow rate. As an approximation, the knowledge of pressure losses in the case of perforated plates with flow can be used. The minimum diameter of a through channel can be described as the minimum distance from a point of the inner surface to an opposite point of the inner surface of the through channel, measuring in a plane parallel to the plane of the substrate. The thickness of the substrate denotes the distance between the top and bottom of the substrate. If the top of the substrate no longer has a smooth surface lying in one plane after the through-channels have been introduced into the substrate, the highest is To draw the point of the top, that is the point that is the greatest distance from the bottom of the substrate, it being assumed that the bottom of the substrate still has an essentially smooth surface that lies in one plane.

The substrate preferably has a thickness between 500 µm and 1500 µm, more preferably between 600 µm and 1200 µm and even more preferably between 800 µm and 1000 µm. The corresponding dimension of the through channels is then based on these values.

Providing the inner surface of a through-channel according to the present invention with an average roughness depth R _z , which is greater than 4 µm, preferably greater than 6 µm, more preferably greater than 8 µm, is not trivial. For example, laser drilling of through-channels in a plastic substrate, which is formed, for example, from PP or PET or PA, produces internal surfaces without a further precaution, which have a noticeably lower average roughness depth R _z . Two concrete ideas are therefore proposed below, with the aid of which such a large average roughness depth R _z can be reliably generated. These two ideas can be used alternatively or cumulatively.

As a first idea, it is proposed that the substrate also have filler particles in addition to a matrix material, the material of the filler particles being able to be converted into the gas phase more slowly or more quickly than the matrix material when irradiated with laser light. In this way it is possible to provide the inner surface of a laser-drilled through-channel with projections and / or recesses which act as a kind of "turbulence generator" for the liquid flowing through the through-channel. The flow velocity is reduced by the turbulence introduced in the through-channel. In addition to the fillers, the matrix material can also contain other substances and can thus be designed, for example, as a composite material.

In a further development of this first idea, it is proposed that the filler particles have an average diameter between 20 µm and 150 µm, preferably between 50 µm and 100 µm, the filler particles preferably being essentially spherical.

As already described above, the substrate can be a laminate formed from several layers. In particular, the substrate can be formed from several layers, preferably from 2 to 6 layers, more preferably from 3 to 5 layers. By using several thin layers instead of a single thick layer, it is possible to bring higher tensile strengths into the substrate, since individual thinner layers can be stretched more (bi-) axially than a single thick layer.

In this case, according to the second concrete idea, the desired roughness can be achieved if a basic shape of the through channels at a boundary between two adjacent layers of the substrate has an offset in a direction that lies in the plane of the substrate. The offset acts as a turbulence generator for the flow in the through channel. The "basic shape" is to be understood as the shape of the through-channels that these would have without the offset. The basic shape can, for example, essentially correspond to the geometric shape of a truncated cone or, in extreme cases, also that of a straight circular cylinder. By displacing at least one boundary between two adjacent layers, preferably at all boundaries between each two adjacent layers, this basic shape is disturbed by the corresponding offset. It is to the credit of the inventors that they have found a way how such an offset can be reliably produced in the case of laser-drilled substrates which are formed from a laminate comprising several layers, the corresponding production method being discussed in more detail below.

In the areas of the through channels between the boundaries to the adjacent layers, the average roughness depth R _z can be as it usually occurs when laser drilling a substrate without special precautions. In particular the average roughness depth R _{z of} the inner surface of at least one through channel, preferably from the majority of all through channels, more preferably from all through channels in the useful area of the substrate, within the area of at least one layer less than 4 μm, preferably less than 3 μm, more preferably less than 2 μm or can even be smaller than 1 µm.

According to a further aspect, the present invention relates to a method for producing a fabric described above, the method being characterized in that at least one through channel, preferably the majority of all through channels, more preferably all of the through channels in the useful area of the substrate are introduced into the substrate by means of a laser will or will.

The advantages of the invention described with regard to the covering according to the invention also apply to the manufacturing method according to the invention and vice versa.

According to the first idea described above, it is proposed that, before the step of introducing the through channels, the substrate is formed by adding filler particles to a matrix material which forms the main constituent of the substrate, the material of the filler particles being irradiated more slowly or faster when irradiated with laser light the gas phase can be converted as the matrix material.

The substrate can have several layers, the concentration of the filler particles being different between at least two of these layers. In this way, it is possible to fine-tune the degree of reduction for the drainage of the through channels. Furthermore, the outermost layer of the substrate on the top or paper side and / or the outermost layer of the substrate on the bottom or machine side can be free of filler particles in order not to have any undesirable effects on contact with the fibrous web or To effect machine parts. In other words, only one or more middle layer (s) can have a filler material.

According to the second ideas described above, it is proposed that the substrate be formed from a plurality of layers, the individual layers being connected to one another by means of an auxiliary, in particular an adhesive layer, the substrate then being rolled up and unrolled again for the introduction of the through-channels. The adhesive can preferably be a solvent-containing polyester resin. The inventors have found by means of experiments that it is possible in this way to give the basic shape of the through channels at a boundary between two adjacent layers of the substrate a simple and reproducible offset in a direction which lies in the plane of the substrate. This is explained by the fact that during lamination and subsequent rolling up, residual stresses are introduced into the auxiliary material, in particular adhesive, arranged between two adjacent layers, which are briefly reduced again by the rolling and the heat input during laser drilling. The projections and recesses thus created for the flow in the through-channel lead to an increase in the average roughness depth R _{z of} the inner surface of the through-channel. They serve as turbulence generators for the flow and thus lead to the desired throttling of the same.

In tests, it has proven to be advantageous if the substrate is applied to an essentially flat surface in the area in which the through-channels are being introduced into the substrate by means of the laser, preferably by means of negative pressure. For example, a so-called vacuum table can be used for this.

Furthermore, it is preferred if the through channel or channels are respectively introduced into the substrate by means of a single pulse of the laser. Although more than one pulse could be used, tests have shown that when using several pulses the opening angle of the Essentially frustoconical through-channels become very large, which can be disadvantageous with regard to the structural stability of the finished product.

Figur 1 und 2

eine aus dem Stand der Technik bekannte Vorrichtung zum Perforieren eines Substrats mittels eines Lasers;

Figuren 3a - 3c

verschiedene aus dem Stand der Technik bekannte Bohrlochgeometrien;

Figur 4a und 4b

eine erste Ausführungsform eines Durchgangskanals in einer erfindungsgemäßen Bespannung;

Figur 5a und 5b

eine zweite Ausführungsform eines Durchgangskanals in einer erfindungsgemäßen Bespannung.

The invention is explained in more detail below with the aid of schematic drawings which are not to scale. Show it:

Figure 1 and 2

a device known from the prior art for perforating a substrate by means of a laser;

Figures 3a - 3c

various borehole geometries known from the prior art;

Figure 4a and 4b

a first embodiment of a through-channel in a covering according to the invention;

Figure 5a and 5b

a second embodiment of a through-channel in a covering according to the invention.

Figures 1 and 2 schematically show a device 10 'known from the prior art or a method for drilling through channels 30' into a substrate 20 'by means of a laser. The laser is controlled by a computer or controller. It sends a laser beam LB perpendicular to the top 22 'of the substrate 20'. As especially in the Figures 3a - 3c It can be seen that through-channels 30 'of different shapes can be produced with the laser by melting and / or sublimation of the material of the substrate 20', which extend in the thickness direction TD of the substrate 20 'from the upper side 22' to the lower side 24 '. The substrate 20 'consists of a plastic film, which per se, ie before the perforation by the laser, is initially impermeable to liquids. In Figure 3a the through-channel 30 'has the shape of a straight circular cylinder. In Figure 3b the through-channel 30 ', on the other hand, has the shape of a truncated cone tapering from the top 22' to the bottom 24 'of the substrate 20'. In Figure 3c the passage channel 30 'has an hourglass-shaped shape, that is to say a shape in which the diameter of the passage channel 30', starting from the upper side 22 ', initially changes to a central region MR of the substrate 20' which is between the upper side 22 'and the Bottom 24 'is arranged, tapered and then widening outgoing from the central region MR to the bottom 24' of the substrate.

Figure 2 shows how an endless substrate 20 ', stretched over two rollers R, is perforated by means of the laser with a multiplicity of through channels 30' arranged essentially in the manner of a chessboard. The laser moves continuously from one side edge 26 'to the side edge 28' of the substrate 20 'opposite in the width direction WD and back or vice versa in order to drill the through channels 30'. The through channels 30 'can be evenly distributed over the entire width, or the perforated, usable area of the substrate 20' is narrower, depending on the desired application. The substrate 20 'can already represent the finished fabric, for example the finished forming fabric of a paper machine, or it can be processed further. For example, it can also be provided with at least one layer of staple fibers in order to be used as press felt in a paper machine. Or tracks of the substrate 20 'can be spiraled in order to be able to achieve larger widths of the covering.

The respective inner surface 32 'of the through-channel 30' is always essentially smooth with this method of manufacture and without any special precautions being taken, ie has an average roughness depth R _z of well below 4 µm. In particular, if the through-channels are arranged so close to one another that they touch or even overlap on the upper side 22 'of the substrate 20', a smooth wall can have a negative effect, since this results in too rapid dewatering of the fibrous web that transports the fabric is done. The reduction in the dewatering rate is achieved according to the invention by specifically increasing the roughness of the inner surface 32 of the through-channel 30.

The Figures 4a and 4b show a section of a substrate 20 with a single through channel 30, which is delimited by a dashed line, according to a first exemplary embodiment of the present invention. Figure 4a shows a plan view of the top 22 of the substrate 20, whereas Figure 4b a Sectional view along the section plane IVb - IVb Figure 4a shows. In this exemplary embodiment, the substrate 20 is a laminate formed from four layers, wherein the individual layers can all have essentially the same thickness, ie the same dimension in the thickness direction TD. The individual layers can be connected to one another with an adhesive. The substrate consists essentially of a polymer base material. As a special feature, however, filler particles 40, 42 are added to the two middle layers of the substrate 20 in this embodiment, the one of the two middle layers exclusively containing filler particles 40 of a first type and the other of the two middle layers exclusively containing filler particles 42 of a second type different from the first can have. In theory, however, both layers could also have the same type of filler particles 40, 42 or both types of filler particles 40, 42. It should be pointed out that these filler particles are only shown schematically and not to scale in the figures.

Compared to the matrix material of the substrate 20, the filler particles 40 of the first type have the property that they pass into the melting and / or vapor phase less quickly or not at all when irradiated with laser light. Therefore, these filler particles 40 remain as projections 44 on the inner surface 32 of the laser-drilled through-channel 30 and thus cause turbulence in the flow of the fluid which flows through the through-channels 30 when the covering according to the invention is used as intended.

Compared to the matrix material of the substrate 20, the filler particles 42 of the second type have the property that they pass into the melting and / or vapor phase significantly faster or easier when irradiated with laser light. Therefore, these filler particles 40 leave recesses 46 on the inner surface 32 of the laser-drilled through channel 30 when they disappear and in this way likewise provide turbulence in the flow of the fluid which flows through the through channels 30 when the covering according to the invention is used as intended.

The roughness of the inner surface 32 of the through-channel 30 and thus the throttling effect on the flow can be adjusted via the concentration density of filler particles 40, 42 in the matrix material of the substrate. The average roughness depth R _{z of} the inner surface 32 of the through-channel 30 is increased according to the invention to over 4 µm, preferably over 6 µm, more preferably over 8 µm. The two outermost layers of the substrate 20 are free of filler particles 40 in this exemplary embodiment. 42. This is advantageous in order to prevent the filler particles from having an undesirable effect when they come into direct contact with the fibrous web to be dewatered or parts of it Machine when using the fabric according to the invention as intended, but this is not absolutely necessary. Conversely, however, at least one of the two outermost layers can also specifically contain fillers, namely in particular when the fillers serve as a separation aid.

It should be noted that the filler particles 40, 42 shown here have an essentially spherical basic shape. However, this is also not absolutely necessary.

In the Figures 5a and 5b A portion of a substrate 20 is shown with a through channel 30 according to a second embodiment. It shows Figure 5a again a top view of the top 22 of the substrate 20 and Figure 5b a sectional view through the passage 30 along the section plane V - V in Figure 5a , The special features of this second embodiment can be used alternatively or cumulatively to the special features of the first embodiment.

In this example too, the substrate 20 is formed as a multi-layer laminate, four layers being present here, the extent of which in the thickness direction TD is essentially the same. The special feature of this embodiment is that the basic shape of the through-channel 30, which here essentially corresponds to a truncated cone tapering from the upper side 22 to the lower side 24 of the substrate 20, directly at the respective boundaries between two adjacent layers of the substrate have an offset. This offset leads in the through-channel 30 to projections 44 and recesses 46 for the liquid flowing through the through-channel in the intended use of the covering according to the invention. As a result, turbulence is introduced into the liquid, which reduces the flow velocity in the through-channel 30. The projections 44 and the recesses 46 ensure that the average roughness depth R _{z of} the inner surface 32 of the through-channel is greater than 4 μm, preferably greater than 6 μm, more preferably greater than 8 μm. In the area between two adjacent layer boundaries, on the other hand, the average roughness depth R _z is again significantly lower. If the average roughness depth R _{z is} also to be increased in these areas, the features of the first exemplary embodiment described above can be used, for example. However, care must be taken to ensure that the flow velocity in the through-channel 30 is not throttled too much, so that the fibrous web transported on the substrate in the intended use of the covering according to the invention can be adequately dewatered.

As the inventors have found, the protrusions 44 and the recesses 46 in this embodiment can be produced reliably and reproducibly by connecting or laminating the individual layers of the laminate together using an adhesive, preferably a solvent-containing polymer resin, followed by the laminate is rolled up, unrolled again for laser drilling and essentially clamped on a flat plane in the area of the hole. This effect can be explained with internal stresses in the material, which are released for a short time due to the heat and force of laser drilling. This effect can be used in a targeted manner in order to increase the roughness in the through-channel 30 and thus to reduce the flow velocity through the through-channel 30.

The present invention has a particularly advantageous effect when the covering is a forming fabric and when the individual through channels 30 are so are placed close to one another so that they at least touch, preferably overlap, on the top 22 or paper side, as described at the beginning.

In the two exemplary embodiments of the present invention shown here, the basic shape of the through-channel 30 is always essentially frustoconical. However, this is not mandatory. In practice, the through channels 30 can also have a more or less strongly deviating basic shape.

LIST OF REFERENCE NUMBERS

10 '

contraption

20 ', 20

substratum

22 ', 22

top

24 ', 24

bottom

26 '

margin

28 '

margin

30 ', 30

Through channel

32 ', 32

inner surface

40

First-class filler particles

42

Filler particles of the second type

44

head Start

46

return

LB

laser beam

MR

mid-range

R

roller

TD

thickness direction

Claims (15)

Covering for a machine for producing a fibrous web, in particular a paper, cardboard or tissue web, comprising a substrate (20) with an upper side (22), a lower side (24), two side edges and a useful area between the two side edges, the Usable area has a plurality of through channels (30) which connect the top (22) to the bottom (24) of the substrate (20),
characterized in that the inner surface (32) of at least one through channel (30), preferably of the majority of all through channels (30), more preferably of all through channels (30) in the useful area of the substrate (20) has an average roughness depth R _z , which is larger than 4 µm, preferably larger than 6 µm, more preferably larger than 8 µm. Covering according to claim 1,
characterized in that the average roughness depth R _{z is} less than 20 µm, preferably less than 15 µm. Covering according to claim 1 or 2,
characterized in that the substrate (20) is a laser-drilled substrate (20), the through-channels (30) being introduced into the substrate (20) by means of a laser. Covering according to one of the preceding claims,
characterized in that the ratio between a minimum diameter of the through channels (30) and a thickness of the substrate (20) is between 1: 3 and 1:10, preferably between 1: 4 and 1: 8, more preferably between 1: 5 and 1. 7 Covering according to one of the preceding claims,
characterized in that the substrate (20) also has filler particles (40, 42) in addition to a matrix material, the material of the filler particles (40, 42) being able to be converted into the gas phase more slowly or more quickly than the matrix material when irradiated with laser light. Covering according to claim 5,
characterized in that the filler particles (40, 42) have an average diameter between 20 µm and 150 µm, preferably between 50 µm and 100 µm, the filler particles (40, 42) preferably being essentially spherical. Covering according to one of the preceding claims,
characterized in that the substrate (20) is formed from several layers, preferably from 2 to 6 layers, more preferably from 3 to 5 layers. Covering according to claim 7,
characterized in that a basic shape of the through channels (30) at a boundary between two adjacent layers of the substrate (20) has an offset in a direction lying in the plane of the substrate (20). Covering according to claim 7 or 8,
characterized in that the average roughness depth R _{z of} the inner surface (32) of at least one through channel (30), preferably of the majority of all through channels (30), more preferably of all through channels (30) in the useful area of the substrate (20) within the area at least one layer is smaller than 4 µm, preferably smaller than 3 µm, more preferably smaller than 2 µm or even smaller than 1 µm. Method for producing a covering according to one of the preceding claims,
characterized in that at least one through channel (30), preferably the majority of all through channels (30), more preferably all through channels (30) in the useful area of the substrate (20) is or are introduced into the substrate (20) by means of a laser. A method according to claim 10,
characterized in that before the step of introducing the through channels (30) the substrate (20) is formed by adding filler particles (40, 42) to a matrix material which forms the main component of the substrate (20), the material of the filler particles (40, 42) can be converted into the gas phase more slowly or more quickly than the matrix material when irradiated with laser light. A method according to claim 11,
characterized in that the substrate (20) has a plurality of layers, the concentration of the filler particles (40, 42) being different between at least two of these layers. Method according to one of claims 10 to 12,
characterized in that the substrate (20) is formed from a plurality of layers, the individual layers being connected to one another by means of an auxiliary, in particular an adhesive layer, the substrate (20) then being rolled up and unrolled again for introducing the through-channels (30) becomes. A method according to claim 13,
characterized in that the substrate (20) is applied to an essentially flat surface in the area in which the through-channels (30) are being introduced into the substrate (20) by means of the laser, preferably by means of negative pressure. Method according to one of claims 10 to 14,
characterized in that the through-channel (30) or the through-channels (30) are introduced into the substrate (20) by means of a single pulse of the laser.

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