Paper Machine Clothing and Method of Producing the Same

This application claims the priority, under 35 U.S.C. § 119, of European Patent Application EP 24164765.0, filed Mar. 20, 2024; the prior application is herewith incorporated by reference in its entirety.

The present invention pertains to a paper machine clothing comprising a substrate with an upper side, a lower side, two lateral edges and an usable region between the two lateral edges. The usable region is formed with a plurality of through-channels extending through the substrate and connecting the upper side with the lower side. Another aspect of the present invention concerns a method of producing such a paper machine clothing.

In the context of the present invention the term “paper machine clothing,” abbreviated “PMC,” refers to any kind of a rotating clothing used to transport a nascent or already formed fiber web in a machine that is designed to continuously produce and/or finish a fiber web, such as paper, tissue or board material. For historical reasons, PMC is sometimes also called wire, felt or fabric. In particular, PMC can be a forming wire or a dryer fabric or a press felt, depending on its intended use in the corresponding machine. Furthermore, in the sense of the present invention the term PMC may also refer to any kind of clothing used in the wet and/or dry production of fibrous nonwovens.

The term “substrate” in the context of the present invention refers to some kind of foil material made of plastic. The substrate itself is usually impermeable to water, so that through-channels are needed to obtain a desired permeability, e.g., for dewatering the nascent fiber web or further drying the already formed fiber web. The substrate can be formed monolithic or comprise several layers that might be co-extruded or produced separately and laminated together afterwards. After joining the longitudinal ends of the substrate to each other, e.g. by laser welding, to obtain some kind of an endless belt, the perforated substrate may already represent the final product, for example a forming wire. For other applications, further steps might be necessary to produce the final PMC, such as permanently attaching fibers thereto to form a press felt. Furthermore, the substrate may comprise a reinforcing structure, such as yarns, that may be imbedded therein. After joining the longitudinal ends of the substrate to each other, the “upper side” of the substrate shall be the radially outer side, sometimes also referred to as “paper side.” The “lower side” of the substrate shall be the radially inner side, sometimes also referred to as “machine side.”

The idea of producing a PMC from a substrate that is perforated, especially by using a laser, has already been known in the prior art for quite some time. It was described, for example, in the 1980's and 1990's in U.S. Pat. Nos. 4,541,895 and 5,837,102, respectively. The content of these documents is hereby incorporated by reference.

illustrates the processes of perforating a substrate via laser drilling according to U.S. Pat. No. 5,837,102.only shows a portion of a substrateused to produce a PMC forming fabric. The substratehas a first surfaceand an opposite second surface that is not shown in the figure. Even though the first surfacemay be embossed it can be considered as being substantially plane and parallel to the second surface. The substrateis perforated using a laser beam LB from a laser that is connected to a controller so as to drill a plurality of discrete through-channelsinto the substrate. The through-channelsconnect the side of the first surfacewith the side of the opposite second surface of the substrate. The through-channelsextend in the thickness direction TD of the substrate, i.e., perpendicular to the first surfaceand the second surface.

In the sense of the present invention the term “usable region” refers to a region of the PMC that is actually used for the production and/or finishing of the fiber web. The usable region may span the entire width of the PMC, i.e., it may reach from one lateral edge to the other lateral edge thereof. Alternatively, the usable region may refer only to a region that is located between the two lateral edges and is spaced apart from the two lateral edges. In the latter case, the PMC may have a different configuration, such as permeability and thickness, outside the usable region compared to the usable region.

A pertinent paper machine clothing is known, for example, from the disclosure of U.S. Pat. No. 4,446,187 and German published patent application DE 10 2010 040 089 A1, which are hereby incorporated by reference.are based on the disclosure of U.S. Pat. No. 4,446,187.

shows a substratethat is placed under tension between two rollers R. The substratehas a radially outer, first surfaceand an opposite, radially inner, second surface, as can be seen in. The first surfaceand the second surfaceare planar and parallel to each other. The thickness direction TD is oriented perpendicular to the first surfaceand the second surface. The substratefurther comprises a first lateral edgeand a second lateral edge. In this example, the usable region of the substrateextends in width direction WD of the substratethe full way from the first lateral edgeto the second lateral edge. In the usable region the substrateis perforated by a laser that is drilling a plurality of discrete through-channelsinto the substrate. As indicated inthe laser first makes the through-channelsclose to the first lateral edgein a first row and continues moving across the substrateto the through-channelclose to the second lateral edgeat the end of the same row. Thereafter, the laser is displaced by one row to make another through-channelclose to the first lateral edgein a next row.

show different possible configurations of the through-channels. Inthe through-channel is cylindrical having the same cross sectional area at any location along the thickness direction TD of the substrate. Inthe through-channelis conical wherein the cross sectional area of the through-channelclose to the first surfaceis larger than the cross sectional area of the through-channelclose to the second surface. Inthe through-channelis neither cylindrical nor conical. Instead it resembles a hyperboloid having a cross sectional area that is also always circular, like in the previous two examples, but the radius of this circle is first decreasing in thickness direction TD from the first surfaceto a middle region MR of the substratesituated in the thickness direction TD between the first surfaceand the second surface, and is then increasing again when further going from the middle region MR of the substrateto the second surface.

Furthermore, U.S. Pat. Nos. 11,060,241 B2 and 11,608,594 B2, and their counterpart European patent EP 3 561 176 B1, the content of which is hereby incorporated by reference, also disclose a pertinent paper machine clothing. The followingare based on the disclosures of those documents.

shows a section of a substratewhich section is indicated by a dashed square. The substratecomprises a first surfaceand an opposite second surface(see), wherein the first surfaceand the second surfaceare substantially planar and parallel to each other.

A single through-channelis provided in the center of the section of the substrate.shows a cross sectional view which is taken through the through-channelalong line A-A or line B-B of. As can be seen from, the through-channelextends through the substratein its thickness direction TD along a central axis CA of the through-channel, the central axis CA being indicated by a dashed line in. Thus, the through-channelconnects the first surfacewith the second surfaceof the substrate. The through-channelis substantially funnel shaped with a cross sectional area becoming continuously smaller when going in the thickness direction TD from the first surfaceto the second surface. The cross-sectional area of a through-channelis obtained by cutting the through-channelwith a plane that is oriented perpendicular to the thickness direction TD of the substrate. In this embodiment the shape of the cross-sectional area of the through-channelis always circular, no matter at which height level of the substrate the cross sectional area is taken.

The through-channelhas a circular upper rimwhere a side wall of the through-channelends and the flat first surfacebegins. The circular upper rimhas a diameter A, as shown in. Furthermore, the through-channelhas a circular lower rimwhere the side wall of the through-channelends and the flat second surfacebegins. The circular lower rimhas a diameter a, as also shown in. Diameter A of the upper rim is larger than diameter a of the lower rim.

According to the teaching of European patent EP 3 561 176 B1 (and U.S. Pat. Nos. 11,060,241 B2, 11,608,594 B2), to improve fiber retention, permeability and the degree of marking compared to previously known paper machine clothings, several of such non-cylindrical through-channels are arranged in such a close relationship that they partially overlap each other in the substrate. An example of such an arrangement for the through-channels is shown in. To be more precise, nine corresponding through-channelsarranged in a checkered pattern are shown in this figure. The term “checkered pattern” means that all through-channels have the same distance to all their neighboring through-channels and all through-channels are arranged in rows that are oriented perpendicular to each other. The through-channelseach have a respective lower rim. Furthermore, for the sake of clarity, also the corresponding upper rimsof the through-channelsare shown, even though these upper rimsdo not exist anymore as such in the final product. Instead, in the final product, i.e., in the finally perforated substrate, through-channelsare formed having a respective upper rimthat is at least partially delimited by the upper rimof a neighboring through-channel. As shown in, the originally existing flat or planar first surfaceof the substratehas almost completely disappeared after the perforation of the substratein the usable region UR thereof. In alternative embodiments it may have completely disappeared. One reason for the complete disappearance of the originally flat first surfaceof the substratecould be that the distance between the through-channelsis chosen even smaller than shown in. An additional or alternative reason for the complete disappearance of the originally flat first surfaceof the substratecould be that the through-channelshave been laser-drilled and that the material of the substratethat has been evaporated by the energy of the laser at least partially condensates again on the first surface, thus forming some kind of hill or ridge thereon. Therefore, the upper rimof a corresponding through-channeldoes not necessarily extend within a plane but is rather a closed line that extends three-dimensionally. It should be noted that the upper rimof the through-channelmay extend partially below the originally flat first surfaceof the substrateand/or extend partially above the originally flat first surfaceof the substrate.

represents a view similar to the one shown inbut now with several neighboring through-channelsformed in the substrateof the final product. Ina location (see reference sign) of the upper rimof the through-channelis shown that represents an absolute minimum of the upper rim. In other words, the upper rimhas the largest distance to the originally flat first surfaceof the substratewhich surfaceis indicated by a dotted line in. The surface of the substratehas a saddle point at this location of the upper rim.

shows a section of a substratesimilar to the one shown inabove, with the difference that the through-channelsare arranged in a non-checkered pattern. While ineach through-channelhas eight neighboring other through-channelswherein the distance to four of these eight neighboring through-channelsis larger than the distance to the remaining four neighboring through-channels, in, each through-channelhas six neighboring other through-channels wherein the distance to all these neighboring through-channelsis substantially the same. These six neighboring through-channelsare arranged in a honeycomb pattern around a corresponding through-channelin the middle thereof. In other words, EP3561176B1 discloses the arrangement of through-channelsin the shape of regular hexagons, as shown in, wherein each regular hexagon has one through-channelin its geometrical center, as shown in. Each through-channelhas the same distance to all other directly neighboring through-channels. The distance of two neighboring through-channelsshall be understood as the distance of their respective central axes CA. Connecting the axes CA of three directly neighboring through-channelsgives an equilateral triangle. With the honeycomb arrangement of, the density of through-channelsin the final substratecan be increased, as well as the open area on the upper side of the substrate, compared to the checkered pattern arrangement of.

Even though the arrangements of the through-channelsshown inare very well in terms of uniformity of dewatering, there is still room for improvements in terms of strength of the paper machine clothing. In practice, the paper machine clothing often must stand high tensile forces at elevated temperatures. This is particularly true for the machine direction of the paper machine clothing.

It will be understood by those of skill in the art, the term “machine direction” (MD) refers to the longitudinal direction of the PMC, i.e., the direction of transportation of the fiber web or the fibrous nonwoven when the PMC is installed in a corresponding machine, whereas the term “cross machine direction” (CMD) refers to a direction within the plane of the PMC that is perpendicular to the machine direction.

Thus, it is an object of the present invention to provide a paper machine clothing with improved characteristics compared to the known paper machine clothing, thereby enabling a fiber web of very high quality to be produced while at the same time providing a relatively high tensile strength.

With the above and other objects in view there is provided, in accordance with the invention, a paper machine clothing, comprising:

In other words, according to the invention, a paper machine clothing as initially described above is provided wherein at least one of the plurality of through-channels has exactly six directly neighboring through-channels of the plurality of through-channels surrounding it as a central through-channel in the shape of an irregular hexagon.

By arranging the six directly neighboring through-channels in the shape of an irregular hexagon around the central through-channel it is possible to still have a relatively large open area of the paper machine clothing, e.g. an open area that is substantially the same as in the example shown inwith the checkered pattern arrangement, while at the same time providing the paper machine clothing with an improved tensile strength, especially in its machine direction, compared to the example ofand also to the example with the honeycomb arrangement of. The shape of an irregular hexagon is not an intuitive choice for a person skilled in the art because it automatically leads to an irregularity of dewatering. However, the inventors surprisingly found out that—at least in certain ranges—such irregularity is unproblematic not leading to visible markings or the like of the fiber web that is transported on the paper machine clothing according to the present invention. The advantages of gaining more tensile strength make it worth the switch from a traditional checkered pattern (like a chess board) or from a honeycomb pattern, i.e., a pattern of regular hexagons, to a pattern of irregular hexagons. It is the merit of the inventors to have found out that with the present invention it is possible to impart anisotropic properties to the substrate in a beneficial way.

In the sense of the present invention the term “neighboring” could be replaced by the term “adjacent,” meaning that there is no other through-channel placed between two neighboring or adjacent through-channels.

In a preferred embodiment of the present invention, two of the six surrounding through-channels that are located on opposite sides of the central through-channel each have a first distance from the central through-channel, whereas the remaining four through-channels of the six surrounding through-channels each have a second distance from the central through-channel, wherein the second distance differs from the first distance. In particular, the second distance can be larger than the first distance. To be more specific, the second distance can be more than 1.05 times, preferably more than 1.10 times, the first distance and/or the second distance can be less than 1.25 times, preferably less than 1.13 times, the first distance. Thus, the second distance can be for example between 1.10 and 1.13 times the first distance. The first distance and the second distance should be understood each as a substantially constant values, meaning that the corresponding values have only a small tolerance of less than 5%, preferably by less than 3%, even more preferably by less than 1%.

To improve the tensile strength of the paper machine clothing especially in its machine direction it is advantageous if the two opposite through-channels each having the first (smaller) distance from the central through-channel are substantially aligned parallel to the two lateral edges of the paper machine clothing.

To improve the tensile strength of the paper machine clothing efficiently, it is advantageous if at least one, preferably more than one, more preferably all, of the six surrounding through-channels is or are itself or themselves surrounded by exactly six directly neighboring through-channels of the plurality of through-channels. In other words, the complete usable region of the paper machine clothing, maybe apart from the lateral sides of the usable region, can have the same pattern of irregular hexagons.

Expressed differently, at least half, preferably at least 90%, more preferably substantially all, of the plurality of through-channels in the usable region can have exactly six directly neighboring through-channels of the plurality of through-channels surrounding it as a central through-channel in the shape of an irregular hexagon.

For the reasons described in detail in the above-referenced document EP 3 561 176 B1, it is very beneficial if the through-channels are non-cylindrical with a cross sectional area becoming smaller when going in a thickness direction of the substrate from the upper side to a middle region of the substrate between the upper side and the lower side and if an upper rim of the central through-channel directly contacts an upper rim of at least two, preferably to all six, of the six surrounding through-channels.

The term “cross sectional area” of a through-channel in the sense of the present invention refers to an area of the through-channel that is obtained by cutting the through-channel with a plane that is perpendicular to the thickness direction of the substrate.

The term “non-cylindrical” in the sense of the present invention means that there are at least two different cross-sectional areas of a through-channel. For example, in the case of a non-cylindrical through-channel that is substantially conical, a cross sectional area taken at a first plane perpendicular to the thickness direction of the substrate may be substantially circular having a first radius, whereas another cross sectional area taken at a second plane perpendicular to the thickness direction of the substrate may be also substantially circular but having a second radius that differs from the first radius.

In the sense of the present invention the term “upper rim” of a through-channel refers to the rim of the through-channel on the upper side of the substrate. The rim itself may be defined as a closed line where the sidewall of the through-channel ends. In view of the previously described examples of the prior art with through-channels that are sufficiently spaced apart from each other to not overlap each other, the upper rim can be easily identified, always being completely surrounded by the first surface(see). To be more specific, in these examples, the upper rim is always a circular line lying within the plane of the first surfaceof the substrate. In contrast, according to this preferred embodiment of present invention, the upper rim of a through-channel may not lie within a plane. This is particularly true when two neighboring through-channels partially “intersect” or “overlap” each other on the upper side of the substrate. The upper rim may then partially be surrounded or defined by portions of the still existing first surface of the substrate and partially by the sidewall of at least one neighboring through-channel. As an alternative, the upper rim of a through-channel may be even completely surrounded or defined by the respective upper rims of the neighboring trough-channels. In the latter case, the original first surface of the substrate, i.e., the surface that was substantially plane and parallel to the second surface of the substrate before the perforation of the substrate, may have been completely lost in the usable region of the substrate. The topography of the substrate after the perforation process may somehow resemble the topography of an egg box.

According to one embodiment of the present invention, the cross sectional area of at least one through-channel, preferably of all through-channels, of the plurality of through-channels in the usable region of the substrate may continuously decrease when going in the thickness direction of the substrate from the upper side to the lower side of the substrate.

Especially when the paper machine clothing is used as forming fabric a good dewatering capability is key for obtaining a fiber web of high quality and with a good formation. Therefore, it is proposed that less than 20%, preferably less than 10%, and more preferably less than 5%, of a surface on the upper side of the substrate is flat and substantially orthogonal to the thickness direction of the substrate. In other words, it is preferred if hardly any portion of the original first surface of the substrate, that was existing before the perforation process, is left after the perforation process.

In contrast to the first surface, with respect to the second surface of the substrate, it is advantageous, if between 70% and 90%, preferably between 75% and 85%, and more preferably about 80%, of a surface on the lower side of the substrate is flat and substantially orthogonal to the thickness direction of the substrate. Such a result can be achieved if the cross sectional area of the through-channels is smaller on the lower side of the substrate compared to the upper side of the substrate. For example, the through-channels may be substantially funnel-shaped tapering to the lower side of the substrate.

According to another aspect, the present invention also refers to a method of producing the paper machine clothing as previously described comprising the following steps: providing a substrate having a first surface and a second surface, wherein the first surface and the second surface are preferably planar and parallel to each other; and forming a plurality of through-channels into a usable region of the substrate, wherein at least one of the plurality of through-channels has exactly six directly neighboring through-channels of the plurality of through-channels surrounding it as a central through-channel in the shape of an irregular hexagon.

According to one embodiment of the present invention it is proposed that at least some, preferably all, of the plurality of through-channels that are neighboring each other are formed at such a close distance that they partially overlap each other.

Furthermore, it is proposed that, when all the through-channels have been formed into the usable region of the substrate, at least one of the first surface and the second surface in the usable region has disappeared by at least 90%, preferably by 100%. As result the finally drilled substrate has none or hardly any opposite surface portions that are planar and parallel to each other. Preferably the substrate, before it is perforated, has a caliper in its usable region between 0.5 mm and 1.5 mm and even more preferable between 0.8 mm and 1.2 mm. After perforating the substrate in its usable region, the caliper thereof may be different. In some embodiments the caliper of the perforated substrate may be smaller compared to the substrate before perforation. This may be particularly true when at least one of the first surface and the second surface in the usable region has completely disappeared. However, in other embodiments, the caliper of the perforated substrate may be even greater compared to the substrate before perforation. This can happen if part of the material that is evaporated e.g. by means of a laser condensates again, thereby forming some kind of hills or ridges. Anyway, as previously mentioned, the topography of the substrate after the perforation process may somehow resemble the topography of an egg box.

Preferably the plurality of through-channels is formed into the substrate by using a laser, wherein preferably cold air is blown onto the substrate during the step of forming the through-channels into the substrate. The cold air inhibits overheating and damaging of the substrate material, which is particularly important for the material region between two neighboring through-channels when the laser is advancing form the first of the two through-channels to the second one.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in a paper machine clothing and method of producing the same, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection withof the accompanying drawings. It will be understood that the illustrations are not due to scale.

shows a comparative example, not forming part of the present invention, with a section of a substratehaving a plurality of through-channelsthat are arranged in a checkered pattern. Thus, this comparative example substantially corresponds to the prior art example of. However, for the sake of simplicity, the through-channelsinare shown as cylindrical through-channels instead of non-cylindrical, in particular funnel-shaped through-channels partially overlapping each other. Nevertheless, the through-channelsofcould also be funnel-shaped, particularly overlapping each other like in.

shows an enlarged view of four through-channels fromthat form a square. The upper left through-channelhas a directly neighboring through-channelon its right side in, which neighboring through-channelis located at a first distance d. Furthermore, the upper left through-channelhas a directly neighboring through-channelon its lower side in, which neighboring through-channelis also located at the first distance d.

shows an example according to the present invention, with a section of a substratehaving a plurality of through-channelsthat are arranged in the shape of hexagons. Thus, this inventive example is similar to the prior art example of. Again, for the sake of simplicity, the through-channelsinare shown as cylindrical through-channels instead of non-cylindrical, in particular funnel-shaped through-channels that partially overlap each other. Nevertheless, the through-channelsofcould also be funnel-shaped, particularly overlapping each other like in.

More importantly, the inventive example ofdiffers from the prior art example ofin thatshows a pattern of irregular hexagons instead of regular hexagons. This pattern could be simply created by taking the checkered pattern of the comparative example ofand by shifting every second column of through-channelsupwards or downwards by half of the first distance d. The distance between the columns of through-channelsstays constant, i.e., the first distance d. Doing so, the open area in the section of the substrateshown inis the same. However, the tensile strength of the paper machine clothing is raised in the inventive example ofcompared to the comparative example of. This applies for the direction to which every second column of through-channelswas shifted, i.e., for the up-down-direction in. If this direction substantially corresponds to the machine direction of the paper machine clothing, the paper machine clothing can better stand the higher tensile forces that are typically applied to the paper machine clothing in that direction.

shows an enlarged view of four through-channelsfromthat form a parallelogram but not a square. The upper left through-channelhas a directly neighboring through-channelon its upper right side in, which neighboring through-channelis located at a second distance d. Furthermore, the upper left through-channelhas a directly neighboring through-channelon its lower side in, which neighboring through-channelis located at the first distance d(like in the comparative example of). The second distance dis larger than the first distance d. To be more precise, in this exemplary embodiment the second distance dis about 1.12 times (square root of 1.25) the first distance d. In other words, the second distance dis about 12% larger than the first distance d.

Note: The distance between two through-channelsis defined as the distance between their respective central axes CA.

Even though 12% does not seem to be a lot, there is significantly more material of the substrate(e.g. more than twice) between two directly neighboring columns of through-channelsalong the line of the second distance d, compared to the comparative example according toalong the line of the first distance dthere. This results in a much higher tensile strength of the paper machine clothing according to the present invention compared to the examples known from the prior art.

The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: