WO2004085740A2

WO2004085740A2 - Warp-stitched multilayer papermaker's fabric

Info

Publication number: WO2004085740A2
Application number: PCT/US2004/007784
Authority: WO
Inventors: Kevin J. Ward
Original assignee: Weavexx Corporation
Priority date: 2003-03-19
Filing date: 2004-03-12
Publication date: 2004-10-07
Also published as: BRPI0408438B1; CN102817268B; CA2519223A1; CN1791719A; CA2519223C; CN102817268A; CN1791719B; KR20060002828A; AU2004223440B2; BRPI0408438A; US7059357B2; US20040182465A1; EP1606450A2; JP4580384B2; JP2006520860A; KR100711991B1; WO2004085740A3; MXPA05009869A; AU2004223440A1; EP1606450B1

Abstract

A warp-stitched multilayer papermaker's fabric has a set of bottom warp yarns, a set of bottom weft yarns, a set of top weft yarns and a set of warp stitching yarn pairs. The bottom warp yarns are interwoven with the bottom weft yarns. The stitching warp yarns interweave with both the bottom weft yarns and the top weft yarns, and are woven such that at locations where the first of the stitching warp yarns in a pair weaves in the top fabric layer, the second stitching warp yarn in the pair drops below the top fabric layer to interweave with one or more bottom weft yarns to bind the top fabric layer and the bottom fabric layer together. The first stitching warp yarn of the stitching warp yarn pair may weave on a first side of one of the bottom warp yarns while the second stitching warp yarn of each stitching yarn pair may weave on the other side of that bottom warp yarn. Each stitching yarn pair may be substantially stacked above a bottom warp yarn. The fabric may further include a set of top warp yarns that interweave with the top weft yarns in the top fabric layer. The set of top warp yarns may be woven from a first warp beam, the set of bottom warp yarns may be woven from a second warp beam and the set of stitching warp yarns may be woven from a third warp beam.

Description

WARP-STITCHED MULTILAYER PAPERMAKER'S FABRICS

FIELD OF THE INVENTION

The present invention relates generally to papermaking, and relates more specifically to multilayer fabrics employed in papermaking.

BACKGROUND OF THE INVENTION

In the conventional fourdrinier papermaking process, a water slurry, or suspension, of cellulosic fibers (known as the paper "stock") is fed onto the top of the upper run of an endless belt of woven wire and/or synthetic material that travels between two or more rolls. The belt, often referred to as a "forming fabric," provides a papermaking surface on the upper surface of its upper run which operates as a filter to separate the cellulosic fibers of the paper stock from the aqueous medium, thereby forming a wet paper web. The aqueous medium drains through mesh openings of the forming fabric, known as drainage holes, by gravity or vacuum located on the lower surface of the upper run (i.e., the "machine side") of the fabric. After leaving the forming section, the paper web is transferred to a press section of the paper machine, where it is passed through the nips of one or more pairs of pressure rollers covered with another fabric, typically referred to as a "press felt." Pressure from the rollers removes additional moisture from the web; the moisture removal is often enhanced by the presence of a "batt" layer of the press felt. The paper is then transferred to a dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.

Typically, papermaker's fabrics are manufactured as endless belts by one of two basic weaving techniques. In the first of these techniques, fabrics are flat woven by a flat weaving process, with their ends being joined to form an endless belt by any one of a number of well-known joining methods, such as dismantling and reweaving the ends together (commonly known as splicing), or sewing on a pin-seamable flap or a special foldback on each end, then reweaving these into pin-seamable loops. A number of auto-joining machines are available, which for certain fabrics may be used to automate at least part of the joining process. In a flat woven papermaker's fabric, the warp yarns extend in the machine direction and the filling yarns extend in the cross machine direction.

In the second basic weaving technique, fabrics are woven directly in the form of a continuous belt with an endless weaving process. In the endless weaving process, the warp yarns extend in the cross machine direction and the filling yarns extend in the machine direction. Both weaving methods described hereinabove are well known in the art, and the term "endless belt" as used herein refers to belts made by either method.

Effective sheet and fiber support are important considerations in papermaking, especially for the forming section of the papermaking machine, where the wet web is initially formed. Additionally, the forming fabrics should exhibit good stability when they are run at high speeds on the papermaking machines, and preferably are highly permeable to reduce the amount of water retained in the web when it is transferred to the press section of the paper machine. In both tissue and fine paper applications (i.e., paper for use in quality printing, carbonizing, cigarettes, electrical condensers, and like) the papermaking surface comprises a very finely woven or fine wire mesh structure.

Typically, finely woven fabrics such as those used in fine paper and tissue applications include at least some relatively small diameter machine direction or cross machine direction yarns. Regrettably, however, such yarns tend to be delicate, leading to a short surface life for the fabric. Moreover, the use of smaller yarns can also adversely affect the mechanical stability of the fabric (especially in terms of skew resistance, narrowing propensity and stiffness), which may negatively impact both the service life and the performance of the fabric.

To combat these problems associated with fine weave fabrics, multi-layer forming fabrics have been developed with fine-mesh yarns on the paper forming surface to facilitate paper formation and coarser-mesh yarns on the machine contact side to provide strength, stability and life potential. For example, fabrics have been constructed which employ one set of machine direction yarns which interweave with two sets of cross machine direction yarns to form a fabric having a fine paper forming surface and a more durable machine side surface. These fabrics form part of a class of fabrics which are generally referred to as "double layer" fabrics. Similarly, fabrics have been constructed which include two sets of machine direction yarns and two sets of cross machine direction yarns that form a fine mesh paperside fabric layer and a separate, coarser machine side fabric layer. In these fabrics, which are part of a class of fabrics generally referred to as "triple layer" fabrics, the two fabric layers are typically bound together by separate stitching yarns. However, they may also be bound together using yarns from one or more of the sets of bottom and top cross machine direction and machine direction yarns. As double and triple layer fabrics include additional sets of yarn as compared to single layer fabrics, these fabrics typically have a higher "caliper" (i.e., they are thicker) than comparable single layer fabrics. An illustrative double layer fabric is shown in U.S. Patent No. 4,423,755 to Thompson, and illustrative triple layer fabrics are shown in U.S. Patent No. 4,501,303 to Osterberg, U.S. Patent No. 5,152,326 to Vohringer, U.S. Patent No. 5,437,315 to Ward and U.S. Patent No. 5,967,195 to Ward. Warp-stitched multilayer fabrics are known in the art. Examples of such fabrics are shown in U.S. Patent No. 5,152,326 to Vohringer, U.S. Patent No. 6,202,705 Bl to Johnson and PCT Patent No. WO 02/00996 Al.

SUMMARY OF THE INVENTION The present invention relates to warp-stitched multilayer papermaker's fabrics that employ weave patterns which can provide one or more of the following advantages: good drainage, increased join strength, reduced weaving time, increased weft yarn counts on the papermaking surface (and hence improved fiber support) and increased fabric modulus. The fabrics of the present invention are particularly useful as papermaker's forming fabrics, although the teachings of the present invention may also be advantageous in certain felt and dryer applications.

Certain embodiments of the present invention are directed to warp-stitched triple layer papermaker's fabrics. In one such embodiment, the warp-stitched triple layer fabric has a set of top warp yams woven from a first warp beam that are interwoven with a set of top weft yarns, and a set of bottom warp yarns woven from a second warp beam that are interwoven with a set of bottom weft yams. The fabric further includes a set of stitching warp yams woven from a third warp beam that interweave with at least some of the top weft yams and with at least some of the bottom weft yams to bind the top fabric layer and the bottom fabric layer together. The stitching warp yams may be woven as stitching warp yam pairs such that at locations in the fabric where the first of the two stitching warp yarns in the pair weaves in the top fabric layer, the second yarn in the pair drops below the top fabric layer so that together the two stitching warp yams in each pair complete the weave in the top fabric layer.

In another embodiment of the present invention, the warp-stitched fabric is a multilayer papermaker's fabric that has a set of bottom warp yarns, a set of bottom weft yarns, a set of top weft yarns and a set of warp stitching yam pairs. The bottom warp yarns are interwoven with the bottom weft yarns. The stitching warp yarns interweave with both the bottom weft yarns and the top weft yams, and are woven such that at locations where the first of the stitching warp yams in a pair weaves in the top fabric layer, the second stitching warp yarn in the pair drops below the top fabric layer to interweave with one or more bottom weft yams to bind the top fabric layer and the bottom fabric layer together. In this embodiment, for each stitching warp yam pair, the first stitching warp yarn of the stitching warp yam pair may weave on a first side of one of the bottom warp yarns while the second stitching warp yam of each stitching yam pair may weave on the other side of that bottom warp yam. The fabrics of this embodiment may further include a set of top warp yams that interweave with the top weft yarns in the top fabric layer.

In additional aspects of the present invention, the papermaker's fabric may include stitching yam pairs that are substantially stacked above a bottom warp yam. The stitching warp yams and/or the top warp yarns may have a smaller diameter than the bottom warp yams. The top weft yams may have a smaller diameter than the bottom weft yams. The papermaking surface may be woven in a plain weave pattern. The machine side surface may be woven such that in each repeat unit of the fabric, each stitching warp yarn passes below the same bottom warp yam as does the bottom warp yam directly adjacent to it. The stitching warp yam may also be woven so that it couples with the bottom warp yarn at locations where the yarns pass below the bottom weft yams so as to form side-by-side machine-side warp direction knuckles. At least some of the top weft yams that the stitching warp yarns pass over immediately before dropping down below the top fabric layer may have a larger diameter and/or a higher modulus than the remainder of the top weft yarns. Additionally, in embodiments which include pairs of stitching warp yams, the two yarns in each pair may cross over different numbers of top weft yarns in each repeat of the fabric. The two yarns in each stitching warp yarn pair may also tend to gravitate toward each other.

Additional aspects of the present invention includes methods of manufacturing warp-stitched triple layer fabrics and methods of using the triple layer papermaker's fabric described herein for making paper.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a top view of the top fabric layer of an embodiment of a 20 harness triple layer forming fabric of the present invention.

Figure 2 is a top view of the bottom fabric layer of the triple layer forming fabric of Figure 1. Figures 3A-3E are section views taken along the lines 3A-3A through 3E-3E of Figure 1.

Figure 4 is a top view of the top fabric layer of an embodiment of a 25 harness triple layer forming fabric of the present invention.

Figure 5 is a top view of the bottom fabric layer of the triple layer forming fabric of Figure 4.

Figures 6A-6E are section views taken along the lines 6A-6A through 6E-6E of Figure 4. Figure 7 is a top view of the top fabric layer of another embodiment of a 25 harness triple layer forming fabric of the present invention.

Figure 8 is a top view of the bottom fabric layer of the triple layer forming fabric of Figure 7. Figures 9A-9E are section views taken along the lines 9A-9A through 9E-9E of Figure 7.

Figures 10A-C are cross-sectional views of selected warp yarns in a fabric constructed according to one aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments or other embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the figures, the dimensions of some components may be exaggerated for clarity.

One aspect of the present invention is directed to "true" warp-stitched triple layer papermaker's fabrics in that they include a set of warp yams and a set of weft yams that only weave in the top layer of the fabric, as well as a set of warp yarns and a set of weft yarns that only weave in the bottom fabric layer. These fabrics also include stitching warp yarns that weave in both the top fabric layer and the bottom fabric layer to bind the layers together. In certain embodiments of the present invention, the stitching warp yams are provided as pairs of two stitching yarns that together replace the equivalent of a single warp yam in the weave pattern on the papermaking surface. These yams are woven such that when one yam in the pair is weaving in the top fabric layer so as to complete the weave pattern on the . papermaking surface, the second yam in the pair weaves below the papermaking surface. Throughout the fabric, the yams in each pair trade these positions. At least one of the yams in the pair also drops down to the bottom fabric layer at one or more points so as to bind the top and bottom fabric layers together. Herein, these yam pairs are referred to as "stitching warp yam pairs."

In certain embodiments of the invention, the "true" warp-stitched triple layer papermaker's fabrics are woven from three separate warp beams. As will be appreciated by those of skill in the art, in manufacturing papermaker's fabrics using a flat weaving process, the warp yarns are fed into the loom off of one or more warp yarn beams (or "warp beams") and the weft yams or "picks" are "thrown" one-by-one by the loom so that they pass in the desired over/under pattern with respect to the warp yams to weave the fabric. The tension on the yams in each warp beam may be independently controlled, and the types of yams provided on each beam (e.g., yarn size, modulus, filament type, etc.) may be varied. By weaving the warp-stitched fabrics of the present invention off of three separate warp beams, at least two distinct advantages may accme.

First, by using three separate warp beams, it is possible to vary the size and/or type of yarn used for (1 ) the top warp yams, (2) the bottom warp yarns and (3) the stitching warp yarns. This may be advantageous because the requirements for yarns that weave in the top layer versus the bottom layer versus both layers may differ. By way of example, in many applications, it may be desirable to use larger, sturdier warp yarns in the bottom fabric layer to provide good stretch resistance and stability. In contrast, finely woven warp yams are often preferred on the papermaking surface as such yams may facilitate providing a highly uniform surface that exhibits good drainage while providing a high degree of fiber support. The stitching warp yams may have their own unique requirements. Through the use of three separate warp beams, the fabric designer can optimize the type and sizes of yams used for the yarns that weave in different parts of the fabric. Second, the use of a separate warp beam for the top, bottom and stitching warp yarns also allows for independent tension control on each type of warp yarn. This tension control may also be used to increase the uniformity of the papermaking surface as variations in tension may impact the degree of the crimp that each type of yarn exhibits on the papermaking surface. Pursuant to another aspect of the present invention, multilayer warp-stitched papermaker's fabrics are provided which include stitching warp yam pairs that are substantially stacked above a bottom warp yam. This aspect of the present invention is best explained with reference to Figures 10A-10C, which are cross-sectional views of a portion of a representative fabric that show the configuration of the warp yams in the fabric.

As shown in Figure 10A, the illustrative fabric sample includes four bottom warp yarns 50-53 that weave exclusively in a bottom fabric layer. The fabric further includes two top warp yams 10-11 that weave exclusively in a top fabric layer. Four stitching warp yams 20, 21, 25, 26 are further provided that weave in both the top fabric layer and the bottom fabric layer. In the view of Figure 10 A, all of the stitching warp yams are weaving adjacent the top fabric layer. As illustrated in the figure, the stitching warp yarns are provided as stitching warp yarn pairs 20, 25 and 21, 26. As shown in Figure 10A, stitching warp yam pair 20, 25 is substantially stacked over a bottom warp yam 51, and stitching warp yam pair 22, 26 is substantially stacked over a bottom warp yam 53.

Figure 10B is another cross-sectional view of the same fabric shown in Figure 10A. In Figure 10B, two of the stitching warp yams 25, 21 are weaving in the bottom fabric layer while the yarns that they are paired with (yams 20 and 26) are weaving in the top fabric layer. Figure 10C is a third cross-sectional view of the same fabric. In Figure 10C, the yams in each stitching yarn pair 20, 25; 21, 26 have traded positions so that yams 25, 21 are weaving in the top fabric layer and yarns 20, 26 are weaving in the bottom fabric layer.

As discussed above, each of the stitching warp yarn pairs 20, 25; 21, 26 are "substantially stacked" over a bottom warp yarn (yarns 51 and 53). By "substantially stacked" it is meant that the stitching warp yams that comprise each pair, at least in locations where they weave in the papermaking surface, are generally located above a bottom warp yam as opposed to being located in the open area falling between two adjacent bottom warp yarns. By weaving the fabric to include such stacked stitching yarn pairs it may be possible to improve the straight-through drainage of the fabric. It will be understood, however, that the stitching warp yams that comprise the stitching warp yam pair will not be stacked over the bottom warp yarn at all locations. This can best be seen in Figures 10B and 10C, which show that at (and about) locations where the stitching warp yarns interlace with the bottom weft yams the stitching warp yarns will weave alongside the bottom warp yams as opposed to being stacked over them.

Pursuant to another aspect of the present invention, the fabric may include stitching warp yarn pairs which are woven so that the two yams in each such pair interlace with the bottom weft yams on opposite sides of a bottom warp yam. This feature of the present invention is illustrated, for example, in Figures 10B and IOC. As shown in Figure 10B, when weaving in the bottom fabric layer, stitching warp yarn 25 weaves on the right side of bottom warp yarn 51. However, as shown in Figure IOC, the stitching warp yam 20 that is paired with stitching warp yam 25 weaves on the left side of bottom warp yam 51 when weaving in the bottom fabric layer. Such a configuration may help facilitate stacking the stitching warp yarn pairs above a bottom warp yarn to improve straight-through drainage. Such a configuration may also facilitate coupling the stitching warp yarns with the bottom warp yarn - which is often a larger, sturdier yarn - at locations where both yams form a machine side warp direction knuckle. As discussed below, such coupling of the yarns may help protect the potentially smaller stitching warp yarn from wear.

An embodiment of the warp-stitched triple layer fabrics of the present invention is illustrated in Figures 1-3 and designated broadly at 100. Figure 1 depicts a top view of the top fabric layer 102 of the triple layer fabric 100 (i.e., a view of the papermaking surface) while Figure 2 depicts a top view of the bottom fabric layer 104 of fabric 100 (i.e., a view of the fabric 100 with the top fabric layer 102 removed). Figures 3A-3E depict the paths of the warp yams 110, 150, 120, 151, 124 that are depicted in Figures 1-2. The triple layer fabric 100 of Figures 1-3 is woven on 20 harnesses. As shown in Figures 1-3, a single repeat of the fabric encompasses 20 warp yams (yams 110-113, 120-127, 150-157) and 24 weft yams (yams 130-145, 160-167). While Figures 1 and 2 only show a single repeat unit of the fabric, those of skill in the art will appreciate that in commercial applications the repeat unit shown in Figures 1 and 2 would be repeated many times, in both the warp and weft directions, to form a large fabric suitable for use on a papermaking machine. As seen in Figure 1, the repeat unit of the top fabric layer 102 includes a set of top layer warp yams 110-113 and a set of top layer weft yarns 130-145 that are interwoven together. The top fabric layer 102 further includes a set of four stitching warp ya pairs 120, 124; 121, 125; 122, 126; 123, 127 that also interweave with the top weft yams 130-145. As shown in Figure 1, a stitching warp yam pair, such as for example, stitching warp yam pair 120, 124, is provided between each pair of adjacent top warp yarns, such as yarns 110-111. Each stitching warp yarn pair (such as pair 120, 124) is woven such that while one of the yarns of the pair (e.g., yam 120) weaves in the top fabric layer 102 to "complete the weave" pattern in the top fabric layer 102, the other of the stitching warp yams (e.g., yam 124) drops down into the bottom fabric layer 104 to bind the top fabric layer 102 and the bottom fabric layer 104 together. In this manner, the stitching warp yam pairs 120, 124; 121, 125; 122, 126; 123, 127 both complete the weave of the top layer fabric 102 and also serve to bind the top and bottom fabric layers 1 2, 104 together.

As shown in Figure 1, the yams comprising the set of top layer weft yams 130-145 are interwoven with the set of top layer warp yarns 110-113 and the stitching warp yarn pairs 120, 124; 121, 125; 122, 126; 123, 127 (each pair of which weaves on the papermaking surface as the equivalent of a single yam) in a lxl or "plain weave" pattern, meaning that each of the top layer weft yams 130-145 alternately pass below one, and then above the next, of the warp yams that at that point are weaving in the papermaking surface. For example, top weft yarn 130 passes below top warp yam 110, above stitching warp yam 120, below top waφ yam 111, above stitching warp yarn 121, below top warp yam 112, above stitching waφ yarn 126, below top waφ yarn 113, and above stitching waφ yam 127. The other top weft yarns 131-145 follow an identical "over one/under one" pattern, although this pattern is offset by one waφ yam for adjacent top layer weft yams 130-145.

Referring now to Figure 2, a repeat unit of the top surface of the bottom fabric layer 104 of the fabric 100 is shown. The repeat unit includes a set of bottom waφ yarns 150-157 which are interwoven with a set of bottom weft yams 160-167. The repeat unit further includes the stitching waφ yarn pairs 120, 124; 121, 125; 122, 126; 123, 127 which are described above. As shown in Figure 2, the stitching waφ yarn pairs 120, 124; 121, 125; 122, 126; 123, 127 are substantially stacked over bottom waφ yams 151, 153, 155, 157, respectively. However, in the vicinity of the locations where one of the stitching waφ yams (e.g., yam 120) interlaces with a bottom weft yam (e.g., yarn 165) the stitching waφ yarn 120 bends so that the yam 120 interlaces with the bottom weft yam 165 adjacent the bottom waφ yam 151 that the stitching waφ yarn 120 otherwise resides above. In this manner, a side-by-side waφ direction knuckle is formed by the bottom waφ yam 151 and the stitching waφ yarn 120 on the machine side surface of the fabric. As shown in Figure 2, the bottom weft yams 160-167 may be constructed using relatively large diameter yams that are well suited to sustain the wear caused by the friction between the machine side surface of the fabric 100 and the papermaking machine during use of the fabric 100. As can also be seen in Figure 2, the weave pattern of fabric 100 provides relatively long weft "floats" on the machine side surface, meaning that, from the viewpoint of Figure 2, the weft ya s pass or "float" below large numbers of adjacent waφ yarns so that the larger, sturdier bottom weft yams 160-167, as opposed to the waφ yams 150-157, 120-127, primarily come into contact with the papermaking machine. The bottom waφ yarns 150-157 may also be constructed using larger diameter yarns than the yarns used for the stitching waφ yarns 120-127 and the top waφ yarns 110-113.

As noted above, in the fabric depicted in Figures 1 and 2, the top fabric layer 102 (pictured in Figure 1) and the bottom fabric layer 104 (pictured in Figure 2) are bound together by the stitching waφ yam pairs 120, 124; 121, 125; 122, 126; 123, 127. In Figure 1, only those portions of the stitching waφ yarns 120-127 which weave with the top fabric layer 102 are depicted. In Figure 2, only those portions of the stitching waφ yams 120-127 which weave with the bottom fabric layer 104 are depicted.

Figures 3A-3E depict the waφ yam paths (for one repeat of the fabric) of waφ yarns 110, 150, 120, 151, 124, respectively, of fabric 100. As shown in Figure 3A the top waφ yam 110 is woven in an "over-one/under-one" pattern with the top weft yams 130-145. The top waφ yarn 110 does not interlace any of the bottom waφ yarns 160-167. Top warp yams 111-113 are woven in the exact same pattern with respect to the top weft yams 130-145 as top waφ yarn 110, and top waφ yarns 111- 113 likewise do not weave in the bottom fabric layer. As shown in Figure 3B, the bottom waφ yam 150 is woven with the bottom weft yams 160-167 in an "over-three/under-one/over-three/under-one" pattern. Specifically, bottom waφ yam 150 passes under bottom weft yam 160, over bottom weft yams 161-163, under bottom weft yam 164, and over bottom weft yams 165-167 in each repeat unit of the fabric. Bottom waφ yarn 154 follows an identical pattern as waφ yarn 150, and bottom waφ yams 152, 156 follow a similar "over-three/under- one/over-three/under-one pattern" weave pattern, although this pattern is offset by two bottom layer weft yams 160-167 as compared to the pattern followed by bottom waφ yarns 150 and 154.

Figure 3C depicts the path for stitching waφ yam 120. As shown in Figure 3C, stitching waφ yam 120 weaves with the top weft yams 130-145 in an "under- one/over-one/under-one/over-one/under-one/over-one/under-nine/over-one" pattem and with the bottom weft yams 160-167 in an "over-seven/under-one" pattern.

Stitching waφ yams 121-123 are woven in the same pattern with the top weft yarns 130-145 and the bottom weft yams 160-167 as is stitching waφ yarn 120, except that each stitching waφ yarn 120-123 is offset by two bottom weft yams (and hence four top weft yams) with respect to the stitching waφ yarns 120-123 adjacent to it. As shown in Figure 3D, the bottom waφ yarn 151 is woven with the bottom weft yarns 160-167 in an "over-three/under-one/over-three/under-one" pattern. Specifically, bottom warp yam 151 passes over bottom weft yam 160, under bottom weft yarn 161, over under bottom weft yams 162-164, under bottom weft yarn 165 and over bottom weft yarns 166-167 in each repeat unit of the fabric. Bottom waφ yarn 155 follows an identical pattern as waφ yam 151, and bottom waφ yarns 153, 157 follow a similar "over-three/under-one/over-three/under-one pattern" weave pattern, although this pattern is offset by two bottom layer weft yams 160-167 as compared to the pattern followed by bottom waφ yarns 151 and 155.

Figure 3E depicts the path for stitching waφ yam 124. As shown in Figure 3E, stitching waφ yarn 124 weaves with the top weft yams 130-145 in an "under- nine/over-one/under-one/over-one/under-one/over-one/under-one/over-one" pattern and with the bottom weft yams 160-167 in an "over-seven/under-one" pattern. Stitching waφ yarns 125-127 are woven in the same pattern with the top weft yams 130-145 and the bottom weft yams 160-167 as is stitching waφ yarn 124, except that each stitching waφ yam 124-127 is offset by two bottom weft yams (and hence four top weft yams) with respect to the stitching waφ yarns 124-127 adjacent to it. In the embodiment of the present invention depicted in Figures 1-3, only 40% of the waφ yams (i.e., 8 out of the 20 waφ yams in each repeat of the fabric) weave in both the top fabric layer 102 and the bottom fabric layer 104. As a result of this configuration, improved "stacking" of the yams running in the waφ direction may be obtained as compared to fabrics such as the fabrics depicted in WO 02/00996 Al (in which all of the waφ yarns stitch with both the top and bottom fabric layers). The stacked waφ yarn arrangement of fabric 100 can provide straight-through drainage - a desired fabric feature in many papermaking applications - as water reaching the top surface of the top fabric layer 102 meets relatively large drainage holes between the yarns that go straight through to the bottom of the bottom fabric layer 104.

Additionally, by having less than 100% of the warp yams weaving in both the top and bottom fabric layers 102, 104, it is generally possible to reduce the yarn mass within the fabric, thereby providing a fabric having increased permeability and a higher void volume than an equivalent fabric formed with 100% of the waφ yams configured as stitching yams. These features are also desirable in numerous papermaking applications.

As can also be seen in Figure 2, one of the bottom waφ yams 150-157 comes together with or "couples" with each of the stitching waφ yarns 120-127 at locations where the stitching waφ yarns pass below a bottom weft yam so as to form a knuckle on the machine side surface. Thus, for example, bottom waφ yarn 151 couples with stitching waφ yarn 120 in the vicinity of bottom weft yarn 165, and couples with stitching waφ yam 124 in the vicinity of bottom weft yarn 161. Often, when two adjacent yams "couple" in this manner persons of skill in the art refer to the two yarns as "pairing" at the locations where the yams come together in the weave. However, to avoid confusion given the references to "stitching waφ yam pairs" herein, the word "couples" will be used to describe situations where two yams come together within the weave.

The coupling arrangement that occurs between the bottom waφ yams 151, 153, 155, 157 and the stitching waφ yams 120-127 may have several beneficial effects in certain fabrics. First, in many fabrics the bottom waφ yams 150-157 will be woven using larger, sturdier yams than the yarns used for the top waφ yarns 110- 113 or the stitching waφ yams 120-127, since smaller diameter yams are usually selected for yarns that weave on the papermaking surface. Thus, by having the stitching waφ yams 120-127 couple with a bottom waφ yam 151, 153, 155, 157 at locations where the stitching waφ yarns 120-127 form a knuckle on the machine side surface, the stitching warp yarns are partially protected from wear by the larger bottom waφ yams that they couple with. This may advantageously extend the life of the fabric, as a potential failure point for a multilayer fabric is wear of the stitching yarns that come in contact with the papermaking machine. Additionally, having two waφ yarns coupled at the locations where the warp yams pass below the bottom weft yarns to form a knuckle on the machine side surface potentially acts to increase the upward force on the bottom weft yarn at that location. This increased upward force helps to "bury" the waφ yarn knuckle on the machine side surface up into the bottom fabric layer 104, which further may help to reduce the machine-induced wear on the bottom waφ yams 151, 153, 155, 157 and the stitching waφ yams 120-127.

Another fabric 200 constructed according to the teachings of the present invention is illustrated in Figures 4-6. Figure 4 depicts a top view of the top fabric layer 202 of the triple layer fabric 200 (i.e., a view of the papermaking surface) while Figure 5 depicts a top view of the bottom fabric layer 204 of fabric 200 (i.e., a view of the fabric 200 with the top fabric layer 202 removed). Figures 6A-6E depict the paths of the waφ yams 210, 250, 220, 251, 225 that are depicted in Figures 4-5. The triple layer fabric 200 of Figures 4-6 is woven on 25 harnesses. As shown in Figures 4-6, a single repeat of the fabric encompasses 25 waφ yams (yams 210-214, 220-229, 250-259) and 30 weft yarns (yams 230-249, 260-269). While Figures 4 and 5 only show a single repeat unit of the fabric, those of skill in the art will appreciate that in commercial applications the repeat unit shown in Figures 4 and 5 would be repeated many times, in both the waφ and weft directions, to form a large fabric suitable for use on a papermaking machine.

As seen in Figure 4, the repeat unit of the top fabric layer 202 includes a set of top layer waφ yarns 210-214 and a set of top layer weft yams 230-249 that are interwoven together. The top fabric layer further includes a set of stitching waφ yam pairs 220, 225; 221, 226; 222, 227; 223, 228, 224, 229 that also interweave with the top weft yams 230-249. As shown in Figure 4, a stitching waφ yarn pair, such as for example, stitching waφ yarn pair 220, 225, is provided between each pair of adjacent top waφ yams, such as yams 210-211. Each stitching waφ yam pair (such as pair 220, 225) is woven such that while one of the yarns of the pair (e.g., yam 220) weaves in the top fabric layer 202 to complete the weave pattern in the top fabric layer 202, the other of the stitching waφ yams (e.g., yam 224) drops down into the bottom fabric layer 204 to bind the top fabric layer 202 and the bottom fabric layer 204 together. In this manner, the stitching waφ yam pairs 220, 225; 221, 226; 222, 227; 223, 228, 224, 229 both complete the weave of the top layer fabric 202 and also serve to bind the top and bottom fabric layers 202, 204 together.

As shown in Figure 4, the yarns comprising the set of top layer weft yarns 230-249 are interwoven with the set of top layer waφ yarns 210-214 and the stitching waφ yam pairs 220, 225; 221, 226; 222, 227; 223, 228, 224, 229 in a plain weave pattern on the papermaking surface. Thus, for example, top weft yam 230 passes below top waφ yam 210, above stitching waφ yarn 225, below top waφ yam 211, above stitching waφ yarn 221, below top waφ yam 212, above stitching waφ yam 222, below top waφ yarn 213, above stitching waφ yam 223, below top waφ yarn 214 and above stitching waφ yam 225. The other top weft yarns 231-249 follow an identical "over one/under one" pattern, although this pattern is offset by one waφ yarn for adjacent top layer weft yams 230-249.

Referring now to Figure 5, a repeat unit of the top surface of the bottom fabric layer 204 of the fabric 200 is shown. The repeat unit includes a set of bottom waφ yams 250-259 which are interwoven with a set of bottom weft yarns 260-269. The repeat unit further includes the stitching waφ yarn pairs 220, 225; 221, 226; 222, 227; 223, 228, 224, 229 which are described above. As shown in Figure 5, the stitching waφ yarn pairs 220, 225; 221, 226; 222, 227; 223, 228, 224, 229 are substantially stacked over bottom waφ yarns 251, 253, 255, 57, 259, respectively. However, in the vicinity of the locations where one of the stitching waφ yams (e.g., yarn 220) interlaces with a bottom weft yam (e.g., yarn 263) the stitching waφ yam 220 bends so that the yarn 220 interlaces with the bottom weft yam 263 adjacent the bottom waφ yarn 251 that the stitching waφ yarn 220 otherwise runs above. In this manner, a side-by-side waφ direction knuckle is formed by the bottom waφ yam 251 and the stitching waφ yarn 220 on the machine side surface of the fabric. As shown best in Figure 5, the bottom weft yams 260-267 may be constructed using relatively large diameter yams that are well suited to sustain the wear caused by the friction between the machine side surface of the fabric 200 and the papermaking machine during use of the fabric 200. As can be seen in Figure 5, the weave pattern of fabric 200 provides relatively long weft "floats" on the machine side surface.

As noted above, in the fabric depicted in Figures 4 and 5, the top fabric layer 202 (pictured in Figure 2) and the bottom fabric layer 204 (pictured in Figure 5) are bound together by the stitching waφ yam pairs 220, 225; 221, 226; 222, 227; 223, 228, 224, 229. In Figure 4, only those portions of the stitching waφ yams 220-229 which weave with the top fabric layer 202 are depicted. In Figure 5, only those portions of the stitching waφ yams 220-229 which weave with the bottom fabric layer 204 are depicted.

Figures 6A-6E depict the paths (for one repeat of the fabric) of waφ yams 210, 250, 220, 251, 224, respectively, of fabric 200. As shown in Figure 6A the top waφ yam 210 is woven in an "over-one/under-one" pattern with the top weft yams 230-249. The top waφ yam 210 does not weave with the bottom fabric layer 204. Top waφ yams 211-214 are woven in the exact same pattern with respect to the top weft yams 230-249 as top waφ yam 210, and top waφ yams 211-214 likewise do not weave in the bottom fabric layer. As shown in Figure 6B, the bottom waφ yam 250 is woven with the bottom weft yams 260-267 in an "over-four/under-one/over-four/under-one" pattern. Specifically, bottom warp yam 250 passes under bottom weft ya 260, over bottom weft yams 261-264, under bottom weft yarn 265, and over bottom weft yams 266-269 in each repeat unit of the fabric. Bottom waφ yarns 252, 254, 256, 258 follow an identical "over-four/under-one/over-four/under-one" pattern, although this pattern is offset by one bottom weft yam 260-269 for adjacent bottom waφ yams 250, 252, 254, 256, 258.

Figure 6C depicts the waφ yarn path for stitching waφ yam 220. As shown in Figure 6C, stitching waφ yarn 220 weaves with the top weft yams 230-249 in an "under-eleven/over-one/under-one/over-one/under-one/over-one/under-one/over- one/under-one/over-one" pattern and with the bottom weft yams 260-269 in an "over- nine/under-one" pattern. Stitching waφ yams 221-224 are woven in the same pattern with the top weft yams 230-249 and the bottom weft yams 260-269 as is stitching waφ yam 220, except that each stitching waφ yam 220-224 is offset by one bottom weft yarn (and hence two top weft yams) with respect to the stitching waφ yarns 220- 224 adjacent to it. As shown in Figure 6D, the bottom waφ yam 251 is woven with the bottom weft yarns 260-269 in an "over-four/under-one/over-four/under-one" pattern. Specifically, bottom warp yam 251 passes over bottom weft yams 260-262, under bottom weft yam 263, over under bottom weft yarns 264-267, under bottom weft yam 268 and over bottom weft yam 269. Bottom waφ yams 253, 255, 257, 259 follow an identical "over-four/under-one/over-four/under-one" pattern, although this pattern is offset by one bottom weft yarn 260-269 for adjacent bottom waφ yams 251, 253, 255, 257, 259.

Figure 6E depicts the waφ yam path for stitching waφ yarn 225. As shown in Figure 6E, stitching waφ yarn 225 weaves with the top weft yams 230-249 in an "under-one/over-one/under-one/over-one/under-one/over-one/under-one/over- one/under-one/over-one/under-ten" pattern and with the bottom weft yarns 260-269 in an "over-nine/under-one" pattern. Stitching waφ yarns 226-229 are woven in the same pattern with the top weft yarns 230-249 and the bottom weft yams 260-269 as is stitching waφ yam 225, except that each stitching waφ yam 225-229 is offset by one bottom weft yams (and hence two top weft yarns) with respect to the stitching waφ yarns 225-229 adjacent to it.

Another fabric 300 constructed according to the teachings of the present invention is illustrated in Figures 7-9. Figure 7 depicts a top view of the top fabric layer 302 of the triple layer fabric 300 (i.e., a view of the papermaking surface) while Figure 8 depicts a top view of the bottom fabric layer 304 of fabric 300 (i.e., a view of the fabric 300 with the top fabric layer 302 removed). Figures 9A-9E depict the paths of the waφ yarns 310, 350, 320, 351, 325 that are depicted in Figures 7-8. The triple layer fabric 300 of Figures 7-9 is woven on 25 harnesses and has a one-to-one "pick" ratio between top weft yams and bottom weft yams (as opposed to the two-to- one pick ratio in the fabrics 100 and 200 described above). As shown in Figures 7-9, a single repeat of the fabric encompasses 25 waφ yarns (yams 310-314, 320-329, 350-359) and 20 weft yarns (yams 360-369). While Figures 7 and 8 only show a single repeat unit of the fabric, those of skill in the art will appreciate that in commercial applications the repeat unit shown in Figures 7 and 8 would be repeated many times, in both the waφ and weft directions, to form a large fabric suitable for use on a papermaking machine. As seen in Figure 7, the repeat unit of the top fabric layer 302 includes a set of top layer waφ yams 310-314 and a set of top layer weft yams 330-339 that are interwoven together. The top fabric layer further includes a set of stitching waφ yam pairs 320, 325; 321, 326; 322, 327; 323, 328, 324, 329 that also interweave with the top weft yams 330-339. As shown in Figure 7, a stitching waφ yam pair, such as for example, stitching waφ yarn pair 320, 325, is provided between each pair of adjacent top waφ yams, such as yams 310-311. Each stitching waφ yarn pair (such as pair 320, 325) is woven such that while one of the yarns of the pair (e.g., yarn 320) weaves in the top fabric layer 302 to complete the weave pattern in the top fabric layer 302, the other of the stitching waφ yams (e.g., yarn 325) drops down into the bottom fabric layer 304 to bind the top fabric layer 302 and the bottom fabric layer 304 together. In this manner, the stitching waφ yam pairs 320, 325; 321, 326; 322, 327; 323, 328, 324, 329 both complete the weave of the top layer fabric 302 and also serve to bind the top and bottom fabric layers 302, 304 together.

As shown in Figure 7, the yams comprising the set of top weft yams 330-339 are interwoven with the set of top layer waφ yams 310-314 and the stitching waφ yarn pairs 320, 325; 321, 326; 322, 327; 323, 328, 324, 329 in a plain weave pattern on the papermaking surface. Thus, for example, top weft yarn 330 passes below top waφ yam 310, above stitching waφ yam 325, below top waφ yam 311, above stitching waφ ya 321, below top waφ yam 312, above stitching waφ yam 327, below top waφ yam 313, above stitching waφ yam 323, below top waφ yarn 314 and above stitching waφ yam 324. The other top weft yarns 331-339 follow an identical "over one/under one" pattern, although this pattern is offset by one waφ yarn for adjacent top layer weft yams 330-339.

Referring now to Figure 8, a repeat unit of the top surface of the bottom fabric layer 304 of the fabric 300 is shown. The repeat unit includes a set of bottom waφ yarns 350-359 which are interwoven with a set of bottom weft yams 360-369. The repeat unit further includes the stitching waφ yarn pairs 320, 325; 321, 326; 322, 327; 323, 328, 324, 329 which are described above. As shown in Figure 8, the stitching waφ yam pairs 320, 325; 321, 326; 322, 327; 323, 328, 324, 329 are substantially stacked over bottom waφ yams 351, 353, 355, 357, 59, respectively. However, in the vicinity of the locations where one of the stitching waφ yams (e.g., yarn 320) interlaces with a bottom weft yam (e.g., yarn 362), the stitching waφ yam 320 bends so that the yarn 320 interlaces with the bottom weft yam 362 adjacent the bottom waφ yarn 351 that the stitching waφ yam 320 otherwise runs above. In this manner, a side-by-side waφ direction knuckle is formed by the bottom waφ yam 351 and the stitching waφ yam 320 on the machine side surface of the fabric. As is also shown in Figure 8, the bottom weft yams 360-369 may be constructed using relatively large diameter yarns that are well suited to sustain the wear caused by the friction between the machine side surface of the fabric 300 and the papermaking machine during use of the fabric 300.

As noted above, in the fabric depicted in Figures 7 and 8, the top fabric layer 302 and the bottom fabric layer 304 are bound together by the stitching waφ yam pairs 320, 325; 321, 326; 322, 327; 323, 328, 324, 329. In Figure 7, only those portions of the stitching waφ yams 320-329 which weave with the top fabric layer 302 are depicted. In Figure 8, only those portions of the stitching waφ yarns 320- 329 which weave with the bottom fabric layer 304 are depicted. Figures 9A-9E depict the waφ yam paths (for one repeat of the fabric) of waφ yams 310, 350, 320, 351, 325, respectively, of fabric 300. As shown in Figure 9A the top waφ yam 310 is woven in an "over-one/under-one" pattern with the top weft yams 330-339. The top waφ yam 310 does not weave with the bottom fabric layer 304. Top waφ yarns 311-314 are woven in the exact same pattern with respect to the top weft yams 330-339 as top waφ yam 310, and top waφ ya s 311-314 likewise do not weave in the bottom fabric layer 304.

As shown in Figure 9B, the bottom waφ yam 350 is woven with the bottom weft yams 360-367 in an "over-four/under-one/over-four/under-one" pattern. Bottom waφ yams 352, 354, 356, 358 follow an identical "over-four/under-one/over- four/under-one" pattern, although this pattern is offset by one bottom weft yam 360- 369 for adjacent bottom waφ yams 350, 352, 354, 356, 358. Figure 9C depicts the waφ yam path for stitching waφ yarn 320. As shown in Figure 9C, stitching waφ yarn 320 weaves with the top weft yams 330-339 in an "under-five/over-one/under-one/over-one/under-one/over-one" pattern and with the bottom weft yarns 360-369 in an over-nine/under-one pattern. Stitching waφ yams 321-324 are woven in the same pattern with the top weft yams 330-339 and the bottom weft yams 360-369 as is stitching waφ yam 320, except that each stitching waφ yam 320-324 is offset by four bottom weft yarns (and hence four top weft yams) with respect to the stitching waφ yams 320-324 adjacent to it.

As shown in Figure 9D, the bottom waφ yam 351 is woven with the bottom weft yams 360-369 in an "over-four/under-one/over-four/under-one" pattern. Bottom waφ yams 353, 355, 357, 359 follow an identical "over-four/under-one/over- four/under-one" pattern, although this pattern is offset by one bottom weft yarn 360- 369 for adjacent bottom waφ yams 351, 353, 355, 357, 359.

Figure 9E depicts the waφ yam path for stitching waφ yam 325. As shown in Figure 9E, stitching waφ yarn 325 weaves with the top weft yarns 330-339 in an "under-one/over-one/under-one/over-one/under-six" pattern and with the bottom weft yarns 360-369 in an "over-nine/under-one" pattern. Stitching waφ yams 326-329 are woven in the same pattern with the top weft yams 330-339 and the bottom weft yarns 360-369 as is stitching waφ yarn 325, except that each stitching waφ yam 325-329 is offset by four bottom weft yams (and hence four top weft yams) with respect to the stitching waφ yams 325-329 adjacent to it.

The principles of the present invention can be extended to a variety of different types of fabrics. For instance, the principles may be employed in fabrics woven on different numbers of harnesses, as shown by the exemplary 20 and 25 harness embodiment fabrics that are pictured and described above. The principles may also be employed with fabrics having various top to bottom weft yarn ratios. Various of the principles may also be employed on any multilayer fabrics, and not just the "true" triple layer fabrics depicted in Figures 1-9.

As noted above, certain embodiments of the present invention are directed to "t e" triple layer fabrics - meaning triple layer fabrics that include (1) a set of waφ yarns and a set of weft yams that each weave exclusively in a top fabric layer, (2) a set of waφ yams and a set of weft yams that each weave exclusively in a bottom fabric layer and (3) stitching waφ yams that stitch the top and bottom fabric layers together. Pursuant to the teachings of the present invention, it will be appreciated that the waφ-stitched tme triple layer fabrics may have improved stacking, increased permeability and higher fiber support as compared to double layer fabrics. Additionally, by using stitching waφ yam pairs that complete the weave in the papermaking surface, it is possible to bind the fabric together at numerous locations, thereby providing a very stable fabric that is resistant to interlayer wear.

Pursuant to another aspect of the present invention, the yarns comprising each stitching waφ yam pair may interlace with the top fabric layer an unequal number of times in each repeat of the fabric. For example, as shown best in Figures 9C and 9E, stitching waφ yarn 320 of fabric 300 interlaces with the top fabric layer 302 three time per repeat while stitching waφ yarn 325 with which yarn 320 is paired only interlaces with the top fabric layer 302 two times per repeat unit of the fabric. This "unequal interlacing" configuration may provide improved performance in certain applications.

Pursuant to another aspect of the present invention, the stitching waφ yams in each stitching waφ yam pair may be woven so that they tend to gravitate toward each other in the weave. This may be accomplished by having the weft yarns exert forces on each stitching waφ yam that urge the stitching waφ yarn in the direction of the other yarn in each stitching waφ yam pair. These forces may facilitate substantially stacking the stitching waφ yams above a bottom waφ yam (except near the points where the stitching waφ yarns interlace with the bottom weft yarns) so as to provide for improved straight-through drainage in the fabric.

As noted above, in certain embodiments of the present invention, the waφ yarns are woven from three separate waφ beams and at least two different sizes of waφ yams may be used. This may provide several potential benefits. For example, in many conventional weft-stitched triple layer fabrics, the weft stitching yams contribute very little to the strength of the join of the fabric (i.e., where the two ends of a flat woven fabric are connected to form the endless belt) as compared to the top weft yarns and the bottom weft yams. In waφ-stitched fabrics such as the fabrics of the present invention, no weft stitching yams are provided so that all of the weft yarns contribute more significantly to the strength of the join. Thus, the fabrics of the present invention may have improved join strength as compared to more conventional triple layer fabrics. Additionally, the fabrics of the present invention may exhibit increased fabric modulus (i.e., the fabric is less prone to stretching and elongation). This feature results from the fact that waφ-stitched multilayer fabrics that include paired stitching waφ yarn pairs tend to have a higher waφ yam count as compared to conventional weft-stitched multilayer fabrics. The fabrics of the present invention also will tend to have reduced weaving time (as the stitching yam pairs are implemented as waφ yams, thus reducing the number of required weft yams). Additionally, implementing the stitching yam pairs as waφ yams helps to reduce the crowding of yams in the fabric in the weft direction, thus allowing for a higher weft yarn count on the papermaking surface per inch, which can improve the level of fiber support provided.

Those of skill in the art will appreciate that numerous modifications can be made to the above described fabrics. By way of example, the yarns that form each stitching waφ yarn pair can be woven in a wide variety of different weave patterns to complete any given weave pattern in the top fabric layer. Thus, for example, in the fabric depicted in Figures 1-3, the stitching waφ yarn pairs are woven so that both yarns in each pair interlace with the top weft yams four times per repeat to complete the plain weave pattern on the papermaking surface. Instead, these yarns could be woven so that (1) one yarn of each pair interlaced five times and the other yarn interlaced three times, (2) one yam of each pair interlaced six times and the other yam interlaced two times or (3) one yam of each pair interlaced seven times and the other yarn interlaced one time per repeat. Additionally, the frequency with which the yams pass in and out of the top fabric layer may also be varied, and the pattern for each stitching waφ yam pair need not be the same. In fact, some stitches may not necessarily interlace with the bottom weft yams. Additionally, a variety of different weave patterns may be employed in the top fabric layer, specifically including 1x2 twill, 2x2 twill, 1x3 and 1x4 twill papermaking surfaces, as well as various derivatives of the above-mentioned weave patterns, including broken twill patterns such as those embodied in 4 or 5 harness satin single layer fabrics, which are known in the art as providing a good papermaking surface. Likewise, the frequency of the stitch points and/or the ratio of top-to-bottom waφ and/or weft yams may be varied. Thus, the scope of the present invention should be construed based on the claims appended hereto, as opposed to the illustrative examples of the claimed fabrics which are provided herein to fully enable those of skill in the ait to practice the claimed invention. Those of skill in the art will likewise appreciate that the stitching waφ yarn pairs need not be included between every adjacent pair of top waφ yams. Instead, a stitching waφ yam pair may be provided after every second, third, fourth or fifth top waφ yam. Additionally, the top waφ yarns themselves could be replaced by stitching waφ yam pairs in certain embodiments of the present invention. Those of skill in the art will also appreciate that the frequency of interlacing can be varied from that shown in the fabrics pictured herein. However, the stitching waφ yams should sufficiently bind the upper and lower fabric layers together to prevent excessive movement between the fabric layers, as such excessive movement could result in inter-layer wear problems. Yet another modification is to vary the positions of the stitching waφ yams that form each stitching waφ yarn pair. For instance, the fabric 100 depicted in Figures 1-3 could be modified so that stitching yam 120 was woven to fall on the right side of bottom waφ yam 151 as those yams are depicted in Figure 2, and stitching waφ yam 124 could be woven to fall on the left side of bottom waφ yam 151. Similar switching of the stitching waφ yarn positions could be done with some or all of the other stitching waφ yam pairs.

Pursuant to another aspect of the present invention, the size and or stiffness of selected of the top weft yarns may be varied to improve fabric performance. As illustrated best in Figure 1, the papermaking surface of certain fabrics made according to the present invention include "transition points" where one of the stitching waφ yams in a stitching waφ yam pair completes its run on the papermaking surface and passes down into the center of the fabric while the second yarn of the stitching warp yam pair emerges from the center of the fabric to start its run on the papermaking surface. An example of such a transition point is the point where stitching waφ yarns 120 and 124 pass under top weft yam 136 in Figure 1. At these transition points the yams of the stitching waφ yam pair enter or exit the fabric at a steeper angle as the yams pass down to, or emerge from, a portion of their n where they weave with the bottom fabric layer 104. This steeper angle may decrease the crimp on the stitching waφ yams at the position where they pass over the last top weft yarn adjacent to the transition point - i.e., where stitching waφ yam 120 passes over top weft yam 135 and where stitching waφ yarn 124 passes over top weft yam 137 - as the stitching waφ yam exerts sufficient force on the top weft yam to pull the top weft yarn slightly farther into the middle of the fabric at this point. Pursuant to the teachings of the present invention, it will be understood that this reduction in the crimp of the stitching waφ ya knuckles adjacent the transition points can be reduced or eliminated by using slightly larger diameter top weft yarns for the top weft yarns that bracket each transition point. In the fabric of Figure 1, this would mean making top weft yams 131, 133, 135, 137, 139, 141, 143, 145 slightly larger than the other top weft yarns. For example, if the top weft yarns 130, 132, 134, 136, 138, 140, 142, 144 are 0.11 millimeters in diameter, then top weft yams 131, 133, 135, 137, 139, 141, 143, 145 may be made 0.13 millimeters in diameter. Instead of modifying the diameter of top weft yarns, one may alternatively use stiffer yams (i.e., yarns having a higher elastic modulus, such as an elastic modulus that is 25 to 50% higher) that will more effectively resist the tendency to be pulled into the fabric adjacent the transition points.

The use of larger diameter and/or higher modulus top weft yarns may also improve the uniformity of the papermaking surface at the transition points themselves. If such yarns are not used, the papermaking surface knuckle formed by the top weft yarn directly over the transition point may be lower than the remainder of the knuckles formed by the top weft yarns because the stitching waφ yarns at that location pass down at a steeper angle and hence provide less support to the top weft yarn. By using larger diameter or higher modulus yarns on the top weft yarn positions that straddle the transition point it is possible to raise the height of the top weft yam that passes over the transition point at the transition point location.

Notably, in the bottom fabric layers 104, 204, 304 of fabrics 100, 200, 300, respectively, the set of bottom waφ yams and the set of bottom weft yams form a machine-side surface having only "single float" waφ knuckles. By a "single float" machine-side waφ knuckle it is meant that when the bottom fabric layer is viewed from the top, no waφ yarn passes under more than one consecutive weft yarn (such that the waφ yam is on the machine-side surface) before passing back to the top surface of the bottom fabric layer. In a preferred embodiment of the triple layer forming fabrics of the present invention, the bottom fabric layer is woven so as to have a machine side surface composed primarily or exclusively of machine side "single float" waφ knuckles.

The fabrics pictured and otherwise described and claimed herein may be employed in a variety of applications, including fine paper grades, tissue paper, brown paper and newsprint, but is especially beneficial for fine paper, newsprint and brown paper applications. The configurations of the individual yams utilized in the fabrics of the present invention can vary, depending upon the desired properties of the final papermakers' fabric. For example, the yarns may be multifilament yams, monofilament yarns, twisted multifilament or monofilament yams, spun yams, or any combination thereof. Also, the materials comprising yarns employed in the fabric of the present invention may be those commonly used in papermakers' fabric. For example, the yarns may be formed of polypropylene, polyester, nylon, or the like. The skilled artisan should select a yarn material according to the particular application of the final fabric. Regarding yarn dimensions, the particular size of the yams is typically governed by the mesh of the papermaking surface. In a typical embodiment of the triple layer fabrics disclosed herein, preferably the diameter of the top weft yarns, the top waφ yarns and the stitching waφ yams is between about 0.10 and 0.22 mm, the diameter of the bottom waφ yarns is between about 0.14 and 0.27 mm, and the diameter of the bottom weft yarns is between about 0.18 and 0.50 mm. Those of skill in the art will appreciate that yams having diameters outside the above ranges may be used in certain applications. In one embodiment of the present invention, the top weft yarns, the top waφ yarns and the stitching waφ yarns have diameters of about 0.13 mm, and the diameter of the bottom waφ yarns is about 0.17 mm. In this embodiment the diameter of the bottom weft yams is between about 0.33 and 0.36 mm. The total top finished end count on this fabric is 34 ends per centimeter. Fabrics employing these yam sizes may be implemented with polyester yams or with a combination of polyester and nylon yams. The fabrics of the present invention have been described herein are flat woven fabrics and hence the waφ yams for these fabrics run in the machine direction (a direction aligned with the direction of travel of the papermakers' fabric on the papermaking machine) when the fabric is used on a papermaking machine and the weft yarns for these fabrics run in the cross machine direction (a direction parallel to the fabric surface and traverse to the direction of travel) when the fabric is used on a papermaking machine. However, those of skill in the art will appreciate that the fabrics of the present invention could also be woven using an endless weaving process. If such endless weaving were used, the waφ yams would run in the cross machine direction and the weft yams would run in the machine direction when the fabric was used on a papermaking machine.

Pursuant to another aspect of the present invention, methods of making triple layer papermaker's fabrics are provided. Pursuant to these methods, the fabrics are woven using three separate waφ beams. Waφ yarns that weave exclusively in the top fabric layer are provided off of the first waφ beam. Waφ yams that weave exclusively in the bottom fabric layer are woven off of the second waφ beam. Waφ yarns that weave in both the top and bottom fabric layers are woven off of the third beam. The waφ yams on the second beam preferably have a larger diameter than the waφ yarns woven off the first beam. Additionally, the waφ yams woven off the third beam may differ from the waφ yarns woven off both the first and second waφ beams, e.g., they might have a lower modulus of elasticity.

Pursuant to another aspect of the present invention, methods of making paper are provided. Pursuant to these methods, one of the exemplary papermaker's forming fabrics described herein is provided, and paper is then made by applying paper stock to the forming fabric and by then removing moisture from the paper stock. As the details of how the paper stock is applied to the forming fabric and how moisture is removed from the paperstock is well understood by those of skill in the art, additional details regarding this aspect of the present invention will not be provided herein.

The foregoing embodiments are illustrative of the present invention, and are not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

THAT WHICH IS CLAIMED:

1. A waφ-stitched triple layer papermaker's fabric having a top fabric layer that has a papermaking surface and a bottom fabric layer that has a machine side surface comprising: a set of top waφ yarns that weave exclusively in the top fabric layer; a set of top weft yarns interwoven with the top warp yams; a set of bottom waφ yarns that weave exclusively in the bottom fabric layer; a set of bottom weft yams interwoven with the bottom waφ yarns; and a set of stitching waφ yams that interweave with at least some of the top weft yarns and with at least some of the bottom weft yarns to bind the top fabric layer and the bottom fabric layer together; wherein the stitching waφ yams are woven as stitching waφ yam pairs such that at locations in the fabric where the first of the two stitching waφ yams in the stitching waφ yarn pair weaves in the top fabric layer, the second of the two stitching waφ yams in the stitching waφ yam pair drops below the top fabric layer so that together the two stitching waφ yams in each stitching waφ yam pair complete the weave in the top fabric layer; and wherein each stitching yam pair is substantially stacked above a bottom warp yarn.

2. The papermaker's fabric of Claim 1, wherein the yarns comprising the set of stitching waφ yams have a smaller diameter than the yarns comprising the set of bottom waφ yarns.

3. The papermaker's fabric of Claim 1 , wherein a stitching- waφ yam pair is provided adjacent each top waφ yarn.

4. The papermaker's fabric of Claim 1 , wherein the top waφ yams, the top weft yarns, and the stitching waφ yarn pairs are woven together to provide a plain weave pattern in the top fabric layer.

5. The papermaker's fabric of Claim 1, wherein each stitching waφ yam couples with one of the bottom waφ yarns at locations where the stitching waφ yams pass below the bottom weft yarns so as to form side-by-side machine-side waφ direction knuckles.

6. The papermaker's fabric of Claim 1 , wherein each bottom waφ yarn passes below exactly two non-adjacent bottom weft yams in each repeat of the fabric.

7. The papermaker's fabric of Claim 1 , wherein the yams comprising the set of top waφ yarns have a smaller diameter than the yams comprising the set of bottom waφ yams.

8. The papermaker's fabric of Claim 2, wherein the ya s comprising the set of stitching waφ yarns differ from the yarns comprising the set of top waφ yams in at least one of the following characteristics: size, modulus or polymer type.

9. The papermaker's fabric of Claim 1, wherein at least some of the top weft yams that the stitching waφ yams of the stitching waφ yarn pairs pass over immediately before dropping down below the top fabric layer have a larger diameter than the remainder of the top weft yarns.

10. The papermaker's fabric of Claim 1 , wherein at least some of the top weft yarns that the stitching waφ yarns of the stitching waφ yarn pairs pass over immediately before dropping down below the top fabric layer have a higher modulus than the remainder of the top weft yarns.

11. The papermaker's fabric of Claim 1 , wherein the two stitching waφ yarns in each pair of stitching waφ yams cross over different numbers of top weft yarns in each repeat of the fabric.

12. The papermaker's fabric of Claim 1, wherein at least some of the bottom waφ yams couple with one of the stitching waφ yams at locations where the bottom waφ yam passes below a bottom weft yarn.

13. The papermaker's fabric of Claim 1 , wherein the stitching waφ yams in each stitching waφ yam pair tend to gravitate toward each other.

14. The papermaker's fabric of Claim 2, wherein the yarns comprising the set of top weft yarns have a smaller diameter than the yams comprising the bottom set of weft yams.

15. The papermaker's fabric of Claim 1, wherein for each stitching waφ yarn pair, the first stitching waφ yam of the stitching waφ yam pair weaves on a first side of one of the bottom waφ yams and the second stitching waφ yam of each stitching yam pair weaves on the other side of the one of the bottom waφ yams.

16. The papermaker's fabric of Claim 1 , wherein the top stitching waφ yarns are woven off a first beam, the bottom stitching waφ yams are woven off of a second beam, and the stitching waφ yarns are woven off of a third beam.

17. The papermaker's fabric of Claim 1 , wherein the papermaker's fabric is a forming fabric.

18. A waφ-stitched multilayer papermaker's fabric comprising: a set of bottom waφ yarns; a set of bottom weft yarns interwoven with the bottom waφ yams to form at least part of a bottom fabric layer having a machine side surface; and a set of top weft yams; a set of stitching waφ yarn pairs that interweave with at least some of the top weft yams to form at least part of a top fabric layer having a papermaking surface and that are woven such that at locations in the fabric where the first of the stitching waφ yarns in the stitching warp yam pair weaves in the top fabric layer, the second of the stitching waφ yarns in the stitching waφ yam pair drops below the top fabric layer to interweave with one or more bottom weft yarns to bind the top fabric layer and the bottom fabric layer together; and wherein for each stitching waφ yam pair, the first stitching waφ yam of the stitching waφ yarn pair weaves on a first side of one of the bottom waφ yams and the second stitching waφ yarn of each stitching yam pair weaves on the other side of the one of the bottom waφ yams.

19. The papermaker's fabric of Claim 18, wherein the fabric further includes a set of top warp yarns that interweave with the top weft yams in the top fabric layer.

20. The papermaker's fabric of Claim 19, wherein a stitching waφ yam pair is provided on each side of each top waφ yarn.

21. The papermaker's fabric of Claim 20, wherein the top waφ yarns, the top weft yarns, and the stitching waφ yam pairs are woven together to provide a plain weave pattern in the top fabric layer.

22. The papermaker's fabric of Claim 18, wherein each stitching waφ yarn couples with one of the bottom waφ yams at locations where the stitching waφ yams pass below the bottom weft yams so as to form side-by-side machine-side waφ direction knuckles.

23. The papermaker's fabric of Claim 20, wherein the yarns comprising the set of stitching waφ yams differ from the yams comprising the set of top waφ yams in at least one of the following characteristics: size, modulus or polymer type.

24. The papermaker's fabric of Claim 20, wherein at least some of the top weft yams that the stitching waφ yams of the stitching waφ yarn pairs pass over immediately before dropping down below the top fabric layer have a larger diameter than the remainder of the top weft yams.

25. The papermaker's fabric of Claim 20, wherein at least some of the top weft yams that the stitching waφ yams of the stitching waφ yam pairs pass over immediately before dropping down below the top fabric layer have a higher modulus than the remainder of the top weft yams.

26. The papermaker's fabric of Claim 18, wherein the two stitching waφ yarns in each pair of stitching waφ yams cross over different numbers of top weft yarns in each repeat of the fabric.

27. The papermaker's fabric of Claim 18, wherein at least some of the bottom waφ yarns couple with one of the stitching waφ yams at locations where the bottom waφ yam passes below a bottom weft yarn.

28. The papermaker's fabric of Claim 18, wherein the yarns comprising the set of top weft yams have a smaller diameter than the yarns comprising the bottom set of weft yarns.

29. The papermaker's fabric of Claim 20, wherein the set of top waφ yams are woven off of a first beam, the set of bottom waφ yarns are woven off of a second beam and the set of stitching waφ yams are woven off of a third beam.

30. The papermaker's fabric of Claim 18, wherein the papermaker's fabric is a forming fabric.

31. A waφ-stitched triple layer papermaker's fabric having a top fabric layer that has a papermaking surface and a bottom fabric layer that has a machine side surface comprising: a set of top waφ yarns woven from a first waφ beam that weave exclusively in the top fabric layer; a set of top weft yarns interwoven with the top warp yarns; a set of bottom waφ yarns woven from a second waφ beam that weave exclusively in the bottom fabric layer; a set of bottom weft yams interwoven with the bottom waφ yams; and a set of stitching waφ yams woven from a third waφ beam that interweave with at least some of the top weft yarns and with at least some of the bottom weft yarns to bind the top fabric layer and the bottom fabric layer together.

32. The papermaker's fabric of Claim 31 , wherein the stitching waφ yarns are woven as stitching waφ yarn pairs such that at locations in the fabric where the first of the two stitching waφ yams in the stitching waφ yam pair weaves in the top fabric layer, the second of the two stitching waφ yarns in the stitching waφ yam pair drops below the top fabric layer so that together the two stitching waφ yarns in each stitching waφ yarn pair complete the weave in the top fabric layer.

33. The papermaker's fabric of Claim 32, wherein a stitching waφ yarn pair is provided adjacent each top waφ yam.

34. The papermaker's fabric of Claim 32, wherein a stitching waφ yam pair is provided on each side of each top waφ yarn.

35. The papermaker's fabric of Claim 34, wherein the top waφ yarns, the top weft yarns, and the stitching waφ yarn pairs are woven together to provide a plain weave pattern in the top fabric layer.

36. The papermaker's fabric of Claim 31 , wherein in each repeat of the fabric each stitching warp yam passes below the same bottom waφ yarn as does the bottom waφ yam directly adjacent to it.

37. The papermaker's fabric of Claim 36, wherein each stitching waφ yam couples with one of the bottom waφ yams at locations where the stitching waφ yams pass below the bottom weft yams so as to form side-by-side machine-side waφ direction knuckles.

38. The papermaker's fabric of Claim 31 , wherein each bottom waφ yam passes below exactly two non-adjacent bottom weft yarns in each repeat of the fabric.

39. The papermaker's fabric of Claim 31 , wherein the yarns comprising the set of top waφ yams have a smaller diameter than the yams comprising the set of bottom waφ yams.

40. The papermaker's fabric of Claim 39, wherein the yarns comprising the set of stitching waφ yams differ from the yams comprising the set of top waφ yarns in at least one of the following characteristics: size, modulus or polymer type.

41. The papermaker's fabric of Claim 32, wherein at least some of the top weft yarns that the stitching waφ yams of the stitching waφ yarn pairs pass over immediately before dropping down below the top fabric layer have a larger diameter than the remainder of the top weft yams.

42. The papermaker's fabric of Claim 32, wherein at least some of the top weft yams that the stitching waφ yams of the stitching waφ yarn pairs pass over immediately before dropping down below the top fabric layer have a higher modulus than the remainder of the top weft yarns.

43. The papermaker's fabric of Claim 31 , wherein all of the yams in the set of top waφ yarns weave over the same top weft yarns.

44. The papermaker's fabric of Claim 43, wherein the top weft yams that the top waφ yams pass over have a smaller diameter than the remainder of the top weft yams.

45. The papermaker's fabric of Claim 43, wherein the top weft yams that the top waφ yams pass over have a lower elastic modulus than the remainder of the top weft yarns.

46. The papermaker's fabric of Claim 31 , wherein the two stitching waφ yarns in each pair of stitching waφ yams cross over different numbers of top weft yarns in each repeat of the fabric.

47. The papermaker's fabric of Claim 32, wherein at least some of the bottom waφ yams couple with one of the stitching waφ yams at locations where the bottom waφ yam passes below a bottom weft yarn.

48. The papermaker's fabric of Claim 32, wherein the stitching waφ yams in each stitching waφ yam pair tend to gravitate toward each other.

49. The papermaker's fabric of Claim 40, wherein the yarns comprising the set of top weft yarns have a smaller diameter than the yams comprising the bottom set of weft yarns.

50. The papermaker's fabric of Claim 32, wherein for each stitching waφ yarn pair, the first stitching waφ yam of the stitching waφ yam pair weaves on a first side of one of the bottom waφ yams and the second stitching waφ yam of each stitching yam pair weaves on the other side of the one of the bottom waφ yarns.

51. The papermaker's fabric of Claim 31 , wherein the papermaker's fabric is a forming fabric.

52. A method of manufacturing a waφ-stitched triple layer papermaker's fabric comprising: providing from a first waφ beam a set of top waφ yams that have a first diameter; providing from a second waφ beam a set of bottom waφ yams that have a diameter that is larger than the first diameter; providing from a third waφ beam a set of stitching waφ yams; interweaving a set of top weft yams with the set of top waφ yams and the set of stitching waφ yams to form a top fabric layer having a papermaking surface; interweaving a set of bottom weft yarns with the set of bottom waφ yarns and the set of stitching waφ yarns to form a bottom fabric layer having a machine side surface; and wherein the stitching waφ yams are woven as stitching waφ yam pairs such that at locations in the fabric where the first of the two stitching waφ yams in the stitching waφ yarn pair weaves in the top fabric layer, the second of the two stitching waφ yams in the stitching waφ yam pair drops below the top fabric layer so that together the two stitching waφ yams in each stitching waφ yarn pair complete the weave in the top fabric layer.

53. The method of Claim 52, wherein each stitching waφ yam pair is woven such that the first stitching waφ yarn of the stitching waφ yarn pair weaves on a first side of one of the bottom waφ yams and the second stitching waφ yarn of each stitching yam pair weaves on the other side of the one of the bottom waφ yams.

54. The method of Claim 52, wherein in each repeat of the fabric each stitching waφ yarn passes below the same bottom waφ yarn as does the bottom waφ yarn directly adjacent to it.

55. The method of Claim 52, wherein the fabric is woven such that each stitching waφ yam couples with one of the bottom waφ yams at locations where the stitching waφ yams pass below the bottom weft yams so as to form side-by-side machine-side waφ direction knuckles.

56. The method of Claim 52, wherein the yams comprising the set of stitching waφ yams differ from the yams comprising the set of top waφ yarns in at least one of the following characteristics: size, modulus or polymer type.

57. The method of Claim 53, wherein the two stitching waφ yams in each pair of stitching waφ yarns cross over different numbers of top weft yarns in each repeat of the fabric.

58. The method of Claim 52, wherein the set of top waφ yarns provided from the first waφ beam are 0.10 to 0.15 mm in diameter, the set of bottom waφ yarns provided from the second waφ beam are 0.15 to 0.21 mm in diameter, and the set of stitching waφ yams provided from the third waφ beam are 0.10 to 0.13 mm in diameter.

59. The method of Claim 52, wherein the set of top waφ yarns provided from the first waφ beam are polyester yarns, the set of bottom waφ yams provided from the second waφ beam are polyester yams that are larger in diameter than the yarns comprising the set of top waφ yams, and the set of stitching waφ yams provided from the third waφ beam are nylon yarns.

60. A machine direction yam stitched triple layer papermaker's fabric having a top fabric layer that has a papermaking surface and a bottom fabric layer that has a machine side surface comprising: a set of top machine direction yarns that weave exclusively in the top fabric layer; a set of top cross machine direction yams interwoven with the top machine direction yams; a set of bottom machine direction yams that weave exclusively in the bottom fabric layer; a set of bottom cross machine direction yarns interwoven with the bottom machine direction yams; and a set of stitching machine direction yarns that interweave with at least some of the top cross machine direction yams and with at least some of the bottom cross machine direction yams to bind the top fabric layer and the bottom fabric layer together; wherein the stitching machine direction yams are woven as stitching machine direction yam pairs such that at locations in the fabric where the first of the two stitching machine direction yams in the stitching machine direction yam pair weaves in the top fabric layer, the second of the two stitching machine direction yams in the stitching machine direction yarn pair drops below the top fabric layer so that together the two stitching machine direction yams in each stitching machine direction yam pair complete the weave in the top fabric layer; and wherein each stitching machine direction yam pair is substantially stacked above a bottom machine direction yam.

61. The papermaker's fabric of Claim 60, wherein the yarns comprising the set of stitching machine direction yarns have a smaller diameter than the yams comprising the set of bottom machine direction yams.

62. The papermaker's fabric of Claim 60, wherein each stitching machine direction yam couples with one of the bottom machine direction yarns at locations where the stitching machine direction yarns pass below the bottom cross machine direction yams so as to form side-by-side machine-side machine direction knuckles.

63. The papermaker's fabric of Claim 60, wherein the two stitching machine direction yams in each pair of stitching machine direction yams cross over different numbers of top cross machine direction yarns in each repeat of the fabric.

64. The papermaker's fabric of Claim 60, wherein at least some of the bottom machine direction yams couple with one of the stitching machine direction yarns at locations where the bottom machine direction yarn passes below a bottom cross machine direction yarn.

65. The papermaker's fabric of Claim 60, wherein for each stitching machine direction yam pair, the first stitching machine direction yarn of the stitching machine direction yarn pair weaves on a first side of one of the bottom machine direction yarns and the second stitching machine direction yarn of each stitching machine direction yam pair weaves on the other side of the one of the bottom machine direction yams.

66. A method of making paper, said method comprising the steps of: (a) a set of bottom waφ yarns; a set of bottom weft yams interwoven with the bottom waφ yarns to form at least part of a bottom fabric layer having a machine side surface; and a set of top waφ yams; a set of stitching waφ yam pairs that interweave with at least some of the top weft yarns to form at least part of a top fabric layer having a papermaking surface and that are woven such that at locations in the fabric where the first of the stitching waφ yarns in the stitching waφ yam pair weaves in the top fabric layer, the second of the stitching waφ yams in the stitching waφ yam pair drops below the top fabric layer to interweave with one or more bottom weft yarns to bind the top fabric layer and the bottom fabric layer together; and wherein for each stitching waφ yarn pair, the first stitching waφ yam of the stitching waφ yarn pair weaves on a first side of one of the bottom waφ yarns and the second stitching waφ yam of each stitching waφ yam pair weaves on the other side of the one of the bottom waφ yarns.

(b) applying paper stock to said papermaker's forming fabric; and (c) removing moisture from said paper stock.

67. The method Claim 66, wherein the yams comprising the set of stitching waφ yams have a smaller diameter than the yams comprising the set of bottom waφ yams.

68. The method of Claim 66, wherein each stitching waφ yarn couples with one of the bottom waφ yams at locations where the stitching waφ yarns pass below the bottom weft yams so as to form side-by-side machine-side waφ direction knuckles.

69. The method of Claim 66, wherein the two stitching waφ yams in each pair of stitching waφ yarns cross over different numbers of top weft yams in each repeat of the fabric.

70. The method of Claim 66, wherein at least some of the bottom waφ yarns couple with one of the stitching waφ yarns at locations where the bottom waφ yarn passes below a bottom weft yam.

71. The method of Claim 66, wherein for each stitching waφ yam pair, the first stitching waφ yam of the stitching waφ yarn pair weaves on a first side of one of the bottom waφ yarns and the second stitching waφ yam of each stitching waφ yam pair weaves on the other side of the one of the bottom waφ yarns.