EP3597821B1 - Coupling for a machine for producing a sheet of fibrous material - Google Patents

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 a top, a bottom, two side edges and a usable area between the two side edges, the usable area having a plurality of Has through channels which connect the top with the bottom of the substrate. The present invention further relates to a method for producing such a covering.

During the industrial production and/or finishing of fibrous webs, the fibrous web is regularly transported on one or more coverings that rotate endlessly in a machine. For example, in a paper machine, a fibrous suspension from a headbox is first applied to a forming fabric, on which the actual fibrous web is formed by dewatering, which is then transported for further drying on a press felt through a press section and then on a drying fabric through a drying section of the paper machine, before the finished paper web can be rolled up at the end of the paper machine or directly processed or refined. In addition to a few spiral screens, fabrics are still used in practice for these coverings today, ie structures in which warp and weft threads are woven together on a loom. Since this type of production is relatively complex, the idea of producing such coverings in a completely different way, namely by perforating a substrate, has been around for some time. The present invention is also based on this idea. Such a covering, in which the through channels are introduced into the substrate using a laser, was already mentioned in publications in the 1980s and 1990s, for example US 4,446,187 A or. US 5,837,102 A described. Also the printed matter DE 10 2012 210 765 A1 and WO 2014/001217 A1 each show a generic covering.

According to the present invention, the term “substrate” is to be understood as meaning a flat structure generally made of plastic, which per se, ie without the through channels introduced, is essentially impermeable to liquid. Only through the introduction of the through channels does the substrate become fluid-permeable and thus acquires its important ability to drain water from the fibrous suspension or the fibrous 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 connected to one another. The longitudinal ends of the substrate are preferably joined together by welding to make the covering endless. Depending on the intended use, the covering can either consist essentially only of the perforated substrate or have additional layers, such as a fleece layer, for example for producing a press felt. The useful area of the substrate refers to 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 only over a smaller area that is spaced from the side edges.

Particularly when such a covering is used as a forming fabric, it is important that the covering enables good formation during sheet formation. As a rule, a good formation is particularly present when there are no markings on the fibrous web that forms. However, a phenomenon that has long been considered a problem with laser-drilled substrates has been that the material of the substrate remaining between the individual passage channels has prevented uniform drainage of the fibrous suspension across the paper side of the substrate and thus a certain degree of marking has been unavoidable . Only through the teaching in the subsequently published European patent application EP 18168641.1 is described by the applicant, 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 each other, preferably overlap each other. Although the substrate is weakened by the narrow arrangement of the through channels, it has been found that the residual structural stability of the substrate is sufficient for the requirements in the forming section of a paper machine. If immediately adjacent through channels on the paper side of the substrate overlap sufficiently strongly, a topography can be formed on this paper side that essentially resembles the interior of an egg box. In other words, after the through channels have been introduced, 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 essentially only the touching edges that delimit the through channels are on the paper side , as more or less thin webs remain. The peripheral edge forms a contour that does not lie in a 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 drainage can take place, which counteracts the tendency of the covering to mark. The fibers from the fibrous suspension are deposited across the through-channels on the peripheral edges of the same, while the water can flow away through the through-channels. The machine side of the substrate opposite the paper side can still be largely present as a flat surface and thus provide a sufficient contact surface in order to transmit the driving forces from rollers of the paper machine to the substrate without significant slippage.

However, due to the very large open area on the paper side of the substrate, the fibrous suspension can be drained too quickly, at least faster than with the usual laser-drilled substrates in which the individual through channels are spaced apart from one another. However, draining too quickly brings with it certain disadvantages. This is how to become For example, fillers contained in the fibrous suspension and which are intended to remain in the fibrous web are 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 operating the paper machine and to increased wear on the clothing. For these reasons, a moderate to slow drainage performance of the covering is preferable.

It is therefore the object of the present invention to eliminate the disadvantages mentioned above. In particular, the present covering should be easy to produce and have a moderate drainage rate. If the covering according to the invention is used as a forming fabric, a particularly good formation of the fibrous web forming on it should be able to be achieved.

This problem is solved by the features of independent claim 1, relating to a covering according to the invention, and by the features of the independent claim 9, relating to the production of such a covering. Advantageous developments of the invention are the subject of the subclaims.

According to the present invention, the generic covering mentioned at the beginning is characterized 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 greater the roughness, the lower the drainage speed.

As is known to those skilled in the art, the average roughness depth R _z is determined by measuring a defined measuring section on the inner surface of a through-channel in seven Individual measuring sections are divided, with the middle five measuring sections being the same size. The evaluation is only carried out over these five measuring sections, since the Gaussian filter to be used requires half a single measuring section before or after or a fold has a non-negligible inlet and outlet behavior. The difference between the maximum and minimum values is determined for each of these individual measuring sections of the profile. The average value is formed from the five individual roughness depths obtained.

Classically, roughness measurement can be carried out as a tactile measurement of 2D profile sections. Please refer to the standards DIN EN ISO 4287 and 4288. Studies 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 recording of the surface to be examined using 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 in order to determine the average roughness depth R _z , the cut preferably encompassing the central axis of the through-channel whose inner surface 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® . With confocal microscopy, a point on the inner surface is measured using the point-to-point method. The 3D coordinates obtained in this way can then be used to create 2D cutting surfaces, from which 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 in such a way as at the beginning with regard to the subsequently published European patent application EP 18168641.1 described by the applicant. In particular, the through channels can be essentially funnel-shaped. In the sense of the present application, this means that the through channels are starting from from the paper side of the substrate in the thickness direction of the substrate towards a central region which lies between the paper side and the machine side, or between the top and bottom of the substrate, or even up to the machine side, preferably continuously. Although this funnel-shaped taper already slows down the flow velocity in the through-channel, the taper cannot be made arbitrarily strong. If the inlet opening on the paper side or top side of the substrate becomes too large, fibers from the fibrous 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 is too small, the through-channel can quickly become clogged due to flushed-out fillers in the fiber suspension. Therefore, the inventive adjustment of the roughness of the inner surface of the through-channel is of essential importance in optimizing the flow velocity in the through-channel of the substrate.

Since, on the other hand, the dewatering of the fibrous web should not take place too slowly, it is suggested 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, at least if the covering according to the invention is used as a forming fabric of a paper machine, is transferred to the press section and subsequent drying section with excessive residual moisture, which is disadvantageous with regard to the energy consumption of the paper machine.

According to the invention, the substrate is a laser-drilled substrate, with the through channels being introduced into the substrate by means of a laser. It is usually clear from the finished covering how the through channels were introduced into the substrate, for example by punching or by mechanical drilling or by laser drilling. During laser drilling, the substrate material melts and/or sublimates, with some of the evaporated material usually re-precipitating on the substrate as condensate. This leaves characteristic marks 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 passage channels can first be introduced into the individual layers of the laminate, whereby the passage channels of the individual layers can have different diameters, and only then these layers are connected to one another, are not practical, especially since it is not possible to separate the individual layers with the necessary precision so that through channels are reliably formed everywhere that 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 rather 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 :7. If the thickness of the substrate is at least four times as large as the minimum diameter of the through-channel, the effect that the roughness of the inner surface of the through-channel has on the flow velocity in the form of a throttling only comes into effect effectively. However, if the substrate is thinner, the roughness does not lead to a reduction in flow velocity to the same extent. As an approximation, knowledge of pressure losses in perforated plates through which flow can be used can be used. The minimum diameter of a through channel can be described as the minimum distance from one point on the inner surface to an opposite point on the inner surface of the through channel, measured in a plane parallel to the plane of the substrate. The thickness of the substrate refers to the distance between the top and bottom of the substrate. If the top side of the substrate no longer has a smooth surface that lies in one plane after the through channels have been introduced into the substrate, then the highest one is To use the point of the top, i.e. 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 a plane.

The substrate preferably has a thickness between 500µm and 1500µm, more preferably between 600µm and 1200µm and even more preferably between 800µm and 1000µm. The corresponding dimensions of the through channels are 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 4µm, preferably greater than 6µm, more preferably greater than 8µm is not trivial. For example, when laser drilling through channels in a plastic substrate, which is made of PP or PET or PA, for example, without any further precautions, internal surfaces are created that have a noticeably lower average roughness depth R _z . Two concrete ideas are therefore proposed below, with the help of which such a large average roughness depth R _z can be reliably generated. These two ideas can be used alternatively or cumulatively.

The first idea proposed is that the substrate, in addition to a matrix material, also has filler particles, the material of the filler particles being able to be converted into the gas phase slower or faster 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 turbulence thus introduced in the through-channel reduces the flow velocity. In addition to the fillers, the matrix material can also contain other substances and can therefore 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 20µm and 150µm, preferably between 50µm and 100µm, with 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 to 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. “Basic shape” means the shape of the through channels that they 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, that of a straight circular cylinder. Due to the offset at at least one boundary between two adjacent layers, preferably at all boundaries between 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 in which such an offset can be reliably produced in laser-drilled substrates that are formed from a laminate comprising several layers, the corresponding manufacturing process being discussed in more detail below.

In the areas of the through channels between the boundaries of the adjacent layers, the average roughness R _z can be as it usually occurs when laser drilling a substrate without any special precautions. In particular The average roughness depth R _z of 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 within the area of at least one layer can be smaller than 4 μm, preferably smaller than 3 μm, more preferably smaller than 2 μm or even be smaller than 1µm.

According to a further aspect, the present invention relates to a method for producing a previously described covering, wherein at least one through-channel, preferably the majority of all through-channels, more preferably all through-channels in the useful area of the substrate is or are introduced into the substrate by means of a laser.

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 component of the substrate, the material of the filler particles moving slower or faster when irradiated with laser light the gas phase can be transferred as the matrix material.

The substrate can have several layers, with the concentration of the filler particles being different between at least two of these layers. In this way it is possible to adjust the degree of reduction for the drainage of the through channels more finely. 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 cause any undesirable effects upon contact with the fibrous web or machine parts . In other words, only one or more middle layers can have a filler material.

According to the second ideas described above, it is proposed that the substrate is formed from several layers, with the individual layers being connected to one another by means of an auxiliary material, in particular an adhesive layer, with the substrate then being rolled up and unrolled again to introduce the through channels. The adhesive can preferably be a solvent-containing polyester resin. The inventors have found through experiments that it is possible to give the basic shape of the through channels at a boundary between two adjacent layers of the substrate an offset in a direction that lies in the plane of the substrate in a simple and reproducible manner. This is explained by the fact that during laminating and subsequent rolling, internal stresses are introduced into the auxiliary material, in particular adhesive, arranged between two adjacent layers, which are briefly reduced again by the unrolling 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 flow.

In experiments 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 introduced into the substrate using 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 through-channels are each introduced into the substrate by means of a single pulse of the laser. Although more than one pulse could also be used, tests have shown that when multiple pulses are used, the opening angle of the essentially frusto-conical through channels becomes 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 further explained below using schematic and not-to-scale drawings. Show it:

Figures 1 and 2

a device known from the prior art for perforating a substrate using a laser;

Figures 3a - 3c

various well geometries known from the prior art;

Figures 4a and 4b

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

Figures 5a and 5b

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

Figures 1 and 2 show schematically a device 10' known from the prior art or a method for drilling through channels 30' into a substrate 20' using 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'. Like especially in the Figures 3a - 3c As can be seen, passage channels 30' of different shapes can be created with the laser by melting and/or sublimating the material of the substrate 20', which extend in the thickness direction TD of the substrate 20' from the top 22' to the bottom 24'. The substrate 20' consists of a plastic film, which per se, ie before 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 On the other hand, the through-channel 30' has the shape of a truncated cone that tapers from the top 22' to the bottom 24' of the substrate 20'. In Figure 3c the through-channel 30' has an hourglass-shaped shape, i.e. a shape in which the diameter of the through-channel 30', starting from the top 22', initially increases to a central region MR of the substrate 20', which is between the top 22' and the bottom 24 'is arranged, tapers and then widens again starting from the central region MR to the underside 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 large number of passage channels 30' arranged essentially in a checkerboard manner. The laser moves continuously from a 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 covering, for example the finished forming fabric of a paper machine, or it can be further processed. For example, it can be provided with at least one layer of staple fibers in order to be used as a press felt in a paper machine. Or strips of the substrate 20' can be spiraled up in order to be able to achieve larger widths of the covering.

With this method of production and without any special precautions being taken, the respective inner surface 32' of the through-channel 30' is always essentially smooth, 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 top side 22 'of the substrate 20', a smooth wall can have a negative effect, as this results in too rapid drainage of the fibrous web that is transported on the covering will, takes place. The reduction in the drainage speed 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 delimited by a dashed line according to a first exemplary embodiment of the present invention. Figure 4a shows a top 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, where 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 using an adhesive. The substrate essentially consists of a polymer base material. As a special feature in this embodiment, however, filler particles 40, 42 are added to the two middle layers of the substrate 20, with 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. Theoretically, 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 noted that these filler particles are only shown schematically in the figures and not to scale.

Compared to the matrix material of the substrate 20, the filler particles 40 of the first type have the property that they change 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 transition into the melting and/or vapor phase significantly faster or more easily when irradiated with laser light. Therefore, when these filler particles 40 disappear, they leave behind recesses 46 on the inner surface 32 of the laser-drilled through-channel 30 and in this way also 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.

The roughness of the inner surface 32 of the through-channel 30 can be determined via the concentration density of filler particles 40, 42 in the matrix material of the substrate and thus adjust the throttling effect on the flow. 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. In this exemplary embodiment, the two outermost layers of the substrate 20 are free of filler particles 40. 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 or parts of the material to be dewatered Machine when the covering according to the invention is used as intended, but this is not absolutely necessary. Conversely, at least one of the two outermost layers can also specifically contain fillers, particularly when the fillers serve as a separating aid.

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

In the Figures 5a and 5b is a section of a substrate 20 with a through channel 30 shown according to a second embodiment. This shows Figure 5a again a top view of the top 22 of the substrate 20 and Figure 5b a sectional view through the through channel 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, with four layers being present here, the extent of which is essentially the same size in the thickness direction TD. What is special about this embodiment is that the basic shape of the through channel 30, which here essentially corresponds to a truncated cone tapering from the top 22 to the bottom 24 of the substrate 20, has an offset at the respective boundaries between two immediately adjacent layers of the substrate . This offset leads to projections 44 and recesses 46 for the through-channel 30 Through-channel in the intended use of the covering according to the invention through which liquid flows. This introduces turbulence 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 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, however, the average roughness R _z is again significantly lower. If the average roughness depth R _z is also to be increased in these areas, one can, for example, resort to the previously described features of the first exemplary embodiment. 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 when the covering according to the invention is used as intended can be adequately drained.

As the inventors have found, the projections 44 and the recesses 46 can be reliably and reproducibly produced in this embodiment by connecting or laminating the individual layers of the laminate to one another via an adhesive, preferably a solvent-containing polymer resin, then the laminate is rolled up, unrolled again for laser drilling and essentially stretched onto a flat plane in the area of the hole. This effect can be explained by internal stresses in the material, which are briefly released by the heat and force during laser drilling. This effect can be used specifically to increase the roughness in the through-channel 30 and thus to reduce the flow velocity through the through-channel 30.

The present invention comes into effect particularly advantageously when the covering is a forming fabric and when the individual through-channels 30 are placed so closely next to one another that they at least touch, preferably overlap, on the top side 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 different basic shape.

List of reference symbols :

10`

contraption

20', 20

Substrate

22', 22

Top

24', 24

bottom

26'

Page margin

28'

Page margin

30', 30

passage channel

32', 32

Interior surface

40

First grade filler particles

42

Second grade filler particles

44

head Start

46

Jump back

L.B

laser beam

MR

midrange

R

roller

TD

Thickness direction

Claims (10)

1. Fabric 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 region between the two side edges, the useful region having a multiplicity of through channels (30) which connect the upper side (22) to the lower side (24) of the substrate (20), the substrate (20) being a laser-drilled substrate (20), the through channels (30) being made in the substrate (20) by means of a laser,
   characterized in that the inner surface (32) of at least one through channel (30), preferably of the majority of all through channels (30), further preferably of all through channels (30) in the useful region of the substrate (20) has an averaged surface roughness R_z which is greater than 4 µm, preferably greater than 6 µm, further preferably greater than 8 µm.
2. Fabric according to Claim 1,
   characterized in that the averaged surface roughness R_z is smaller than 20 µm, preferably smaller than 15 µm.
3. Fabric according to either of the preceding claims, characterized in that the ratio between the minimum diameter of the through channels (30) and a thickness of the substrate (20) lies between 1:3 and 1:10, preferably between 1:4 and 1:8, further preferably between 1:5 and 1:7.
4. Fabric according to one of the preceding claims, characterized in that, in addition to a matrix material, the substrate (20) comprises, furthermore, filler particles (40, 42), it being possible for the material of the filler particles (40, 42) to be converted into the gas phase more slowly or more rapidly than the matrix material in the case of irradiation with laser light.
5. Fabric according to Claim 4,
   characterized in that the filler particles (40, 42) have a mean diameter between 20 µm and 150 µm, preferably between 50 µm and 100 µm, the filler particles (40, 42) preferably being of substantially spherical configuration.
6. Fabric according to one of the preceding claims, characterized in that the substrate (20) is formed from a plurality of layers, preferably from 2 to 6 layers, further preferably from 3 to 5 layers.
7. Fabric according to Claim 6,
   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 which lies in the plane of the substrate (20).
8. Fabric according to Claim 6 or 7,
   characterized in that the averaged surface roughness R_z of the inner surface (32) of at least one through channel (30), preferably of the majority of all through channels (30), further preferably of all through channels (30) in the useful region of the substrate (20) is within the range of at least one layer of less than 4 µm, preferably less than 3 µm, preferably less than 2 µm or even less than 1 µm.
9. Method for producing a fabric according to one of the preceding claims,

   at least one through channel (30), preferably the majority of all through channels (30), further preferably all through channels (30) in the useful region of the substrate (20) being made in the substrate (20) by means of a layer,

   characterized in that, before the step of the through channels (30) being made, the substrate (20) is formed by filler particles (40, 42) being added to a matrix material which forms the main constituent part of the substrate (20), it being possible for the material of the filler particles (40, 42) to be converted into the gas phase more slowly or more rapidly than the matrix material in the case of irradiation with laser light, the substrate (20) preferably having a plurality of layers, and the concentration of the filler particles (40, 42) being different between at least two of these layers,

   and/or 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 material, in particular an adhesive layer, the substrate (20) subsequently being rolled up and being unrolled again in order to make the through channels (30),

   the substrate (20) preferably being applied to a substantially planar surface, preferably by means of negative pressure, in the region in which the through channels (30) are currently being made in the substrate (20) by means of the laser.
10. Method according to Claim 9,
    characterized in that the through channel (30) or the through channels (30) is/are each made in the substrate (20) by means of a single pulse of the laser.

Images