WO2009094101A2

WO2009094101A2 - Multi-layer papermaker's fabric with long machine side md floats

Info

Publication number: WO2009094101A2
Application number: PCT/US2009/000093
Authority: WO
Inventors: Kevin John Ward; Jason Goins
Original assignee: Weavexx Corporation
Priority date: 2008-01-23
Filing date: 2009-01-08
Publication date: 2009-07-30
Also published as: WO2009094101A3; US7931051B2; US20100147410A1; US20090183795A1

Abstract

A papermaker's fabric includes: a set of top MD yarns; a set of bottom MD yarns; a set of top CMD yarns interwoven with the top MD yarns to form a top fabric layer; a set of bottom CMD yarns interwoven with the bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns that interweave with the top and bottom fabric layers. The top MD yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units. Each of the bottom MD yarns forms a bottom MD float by passing under three or more consecutive bottom CMD yarns.

Description

MULTI-LAYER P APERM AKER' S FORMING FABRIC WITH LONG MACHINE SIDE MD FLOATS

Field of the Invention

This application is directed generally to papermaking, and more specifically to 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 that 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 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. As used herein, the terms machine direction ("MD") and cross machine direction

("CMD") refer, respectively, to a direction aligned with the direction of travel of the papermakers' fabric on the papermaking machine, and a direction parallel to the fabric surface and traverse to the direction of travel. Likewise, directional references to the vertical relationship of the yarns in the fabric (e.g., above, below, top, bottom, beneath, etc.) assume that the papermaking surface of the fabric is the top of the fabric and the machine side surface of the fabric is the bottom of the fabric.

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 now commercially 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 and durability. 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 Nos. 5,437,315 and 5,967,195 to Ward, and U.S. Patent No. 6,745,797 to Troughton.

U.S. Patent No. 5,967,195 to Ward discloses a triple layer fabric in which pairs of stitching yarns extend in the cross machine direction and form part of the papermaking surface, in essence "completing the weave" of the papermaking surface, while also stitching with the bottom layer. The fabrics disclosed in Ward have the same number of top machine direction yarns and bottom machine direction yarns. Such fabrics have proven to provide an excellent papermaking surface (particularly due to the integration of the stitching yarns into the weave of the papermaking surface) and to combat inter-layer wear. U.S. Patent No. 6,896,009 shows a similar concept with MD stitching yarns. However, in some applications (e.g., brown paper), high open area and fiber support may be desirable. Also, the improvement of other performance characteristics, such as wear resistance, may be desirable. Summary of the Invention

As a first aspect, embodiments of the present invention are directed to a papermaker's fabric, comprising: a set of top MD yarns; a set of bottom MD yarns; a set of top CMD yarns interwoven with the top MD yarns to form a top fabric layer; a set of bottom CMD yarns interwoven with the bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns that interweave with the top and bottom fabric layers. The top MD yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units. Each of the bottom MD yarns forms a bottom MD float by passing under three or more consecutive bottom CMD yarns.

As a second aspect, embodiments of the present invention are directed to a papermaker's fabric, comprising: a set of top MD yarns; a set of bottom MD yarns; a set of CMD yarns interwoven with the top MD yarns to form a top fabric layer; and a set of CMD stitching yarn pairs that interweave with the top and bottom fabric layers. The top MD yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units. Each of the bottom MD yarns forms a bottom MD float by passing under three or more consecutive CMD stitching yarn pairs.

As a third aspect, embodiments of the present invention are directed to a papermaker's fabric, comprising: a set of MD stitching yarns, the stitching yarns being arranged in pairs; a set of bottom MD yarns; a set of top CMD yarns interwoven with the MD stitching yarns to form a top fabric layer; and a set of bottom CMD yarns interwoven with the bottom MD yarns to form a bottom fabric layer. The MD stitching yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns, the MD stitching yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units. The MD stitching yarns have a first diameter, the bottom MD yarns have a second diameter, and the first diameter is less than the second diameter.

Brief Description of the Figures Figure 1 is a top view of the top layer of a repeat unit of a fabric according to embodiments of the present invention.

Figure 2 is a top view of the bottom layer of the fabric of Figure 1. Figures 3A and 3B are section views taken along lines 3A--3A and 3B— 3B, respectively, of the fabric of Figures IA and IB showing typical MD yarns.

Figure 4 is a top view of the top layer of a repeat unit of a fabric according to additional embodiments of the present invention. Figure 5 is a top view of the bottom layer of the fabric of Figure 4.

Figures 6A and 6B are section views taken along lines 6A--6A and 6B--6B, respectively, of the fabric of Figure 4 showing typical top and bottom CMD yarns (Figure 6A) and stitching yarns (Figure 6B).

Figure 6C is a section view taken along lines 6C— 6C of Figure 4 showing typical top and bottom MD yarns.

Figure 7 is a top view of the top layer of a repeat unit of a fabric according to embodiments of the present invention.

Figure 8 is a top view of the bottom layer of the fabric of Figure 7.

Figures 9A-9C are section views taken along lines 9A--9A, 9B--9B and 9C--9C, respectively, of the fabric of Figure 7 showing typical stitching yarns and CMD yarns.

Figure 10 is a top view of the top layer of a repeat unit of a fabric according to additional embodiments of the present invention.

Figure 11 is a top view of the bottom layer of the fabric of Figure 10.

Figures 12A-12C are section views taken along lines 12A--12A, 12B--12B and 12C-- 12C, respectively, of the fabric of Figures 10 and 11 showing typical bottom MD yarns (Figure 12A), stitching yarns (Figure 12B) and top MD yarns (Figure 12C).

Detailed Description of Embodiments of the Invention The present invention will be described more particularly hereinafter with reference to the accompanying drawings. The invention is not intended to be limited to the illustrated embodiments; rather, these embodiments are intended to fully and completely disclose the invention to those skilled in this art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity. Well-known functions or constructions may not be described in detail for brevity and/or clarity. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein the expression "and/or" includes any and all combinations of one or more of the associated listed items.

Although the figures below only show single repeat units of the fabrics illustrated therein, those of skill in the art will appreciate that in commercial applications the repeat units shown in the figures would be repeated many times, in both the machine and cross machine directions, to form a large fabric suitable for use on a papermaking machine. Turning now to Figures 1-3B, a repeat unit of a forming fabric according to embodiments of the present invention, designated broadly at 100, is illustrated therein. The repeat unit 100 includes eight MD stitching yarns 101-108, twenty top CMD yarns 111-130, four bottom MD yarns 141-144, and eight bottom CMD yarns 151-158. The interweaving of these yarns is described below. As can be seen in Figures 1 and 3A, the MD stitching yarns 101-108 are disposed in pairs, wherein each pair together interweaves with the top CMD yarns 111-130 in an "over I/under 1" sequence. For example, as can be seen in Figures 1 and 3A, MD stitching yarn 101 follows an "over 1 /under 1" pattern relative to the top CMD yarns to form five consecutive MD knuckles (passing over even-numbered top CMD yarns 116, 118, 120, 122, 124 and below odd- numbered top CMD yarns 117, 119, 121, 123). MD stitching yarn 101 passes below the remaining top CMD yarns. Paired stitching yarn 102 follows an "over I/under 1" pattern relative to the top CMD yarns to form five consecutive MD knuckles (passing over even- numbered top CMD yarns 126, 128, 130, 112, 114 and below top odd-numbered CMD yarns 127, 129, 101, 103). MD stitching yarn 102 passes below the remaining top CMD yarns. Thus, together the stitching yarns 101, 102 pass above all of the even-numbered top CMD yarns and below the odd-numbered top CMD yarns. The remaining MD stitching yarn pairs (i.e., MD stitching yarns 103, 104, MD stitching yarns 105, 106, and MD stitching yarns 107, 108) follow a similar "over 1 /under 1 " sequence with the top CMD yarns, with the result that the MD stitching yarns and the top CMD yarns form a plain weave top, or papermaking, surface.

Turning now to Figure 2 and also to Figure 3A, the MD stitching yarns 101-108 also interweave with the bottom CMD yarns 151-158. Each of the MD stitching yarns 101-108 passes below one bottom CMD yarn, with the MD stitching yarns of each pair together forming "over 3/under 1" pattern. For example, and referring to Figure 3B, MD stitching yarn 101 passes under bottom CMD yarn 151 and over the remaining bottom CMD yarns. MD stitching yarn 102 passes under bottom CMD yarn 155, thus forming the "over 3/under 1 " sequence with the bottom CMD yarns noted above. The remaining MD stitching yarn pairs similarly form an "over 3/under 1 " sequence with the bottom CMD yarns. Each pair of stitching yarns weaves between two adjacent bottom MD yarns.

Referring again to Figure 2 and also to Figure 3B, the bottom MD yarns 141-144 interweave with the bottom CMD yarns in an "under 3/over 1 " sequence that repeats twice within the repeat unit. For example, bottom MD yarn 141 passes below bottom CMD yarns 151-153, above bottom CMD yarn 154, below bottom CMD yarns 155-157, and above bottom CMD yarn 158. The other bottom MD yarns 142-144 follow a similar "under 3/over 1 " pattern relative to the bottom CMD yarns. The result is a series of bottom, or machine, side MD floats formed by the bottom MD yarns that pass below three bottom CMD yarns.

Notably, the MD stitching yarns 101-108 each stitch underneath the bottom CMD yarns in a location where they can be protected by two adjacent bottom MD yarn floats. For example, MD stitching yarns 101, 102 stitch below, respectively, bottom CMD yarns 151, 155. Adjacent bottom MD yarns 141, 144 pass below both of these bottom CMD yarns. As such, the bottom MD floats formed by the bottom MD yarns 141, 144 can protect the MD stitching yarns from wear, which can increase the life of the fabric 100. In addition, it is believed that the presence of the long MD floats (i.e., floats that pass below three or more bottom MD yarns) may reduce drag of the fabric on the paper machine. In many embodiments, the bottom MD yarns comprise monofilament yarns, which tend to have considerable molecular alignment in the axial direction (induced during an extrusion process). In MD yarns, this alignment is substantially parallel with the machine direction. This molecular alignment may reduce drag of the fabric and the power requirement on the paper machine. The MD float and the molecular alignment within the floats may together reduce the wear rate of the fabric on the paper machine.

The materials for an exemplary embodiment of the fabric 100 are described in Table 1, with weaving and performance characteristics of the fabric shown in Table 2.

It can also be seen from Table 1 that, in some embodiments, the MD stitching yarns are of smaller diameter than the bottom MD yarns (a ratio of top MD yarn diameter to bottom MD yarn diameter of between about 0.4 and 0.7 is typical). The use of finer MD stitching yarns can improve the papermaking surface, whereas the use of larger bottom MD yarns can improve wear. The concept can also be applied to fabrics that have CMD stitching. For example, turning now to Figures 4-6C, a repeat unit of another fabric, designated broadly at 200, is illustrated therein. The repeat unit 200 includes ten top MD yarns 201-210, ten top CMD yarns 211-220, ten pairs of CMD stitching yarns 221a, 221b-230a, 230b, ten bottom MD yarns 231- 240, and ten bottom CMD yams 241-250. The interweaving of these yarns is described below. As seen in Figure 4, the top MD yarns 201-210 and the top CMD yarns 211-220 are interwoven such that each top CMD yarn passes over and beneath top MD yarns in an alternating fashion, with each top CMD yarn passing over and under the same top MD yarns. For example, as shown in Figures 4 and 6A, top CMD yarn 211 passes under odd-numbered top MD yarns 201-209 and over even-numbered top MD yarns 202-210.

Still referring to Figure 4 and also to Figure 6B, the top layer of the fabric 200 also includes portions of the CMD stitching yarns 221a-230b, which are positioned in pairs between adjacent top and bottom CMD yarns; there is no bottom CMD yarn below each stitching yarn pair so that space is present for the stitching yarns to stitch. Portions of the stitching yarns 221a-230b interweave with the top MD yarns 201-210 to form, together with the top CMD yarns 211-220, a plain weave pattern in the top surface of the fabric 200. In the illustrated embodiment, a portion of the stitching yarn of each pair designated with an "a" (e^*., 221a, 222a, etc.) interweaves in an alternating fashion with five top MD yarns

(alternately passing over three top MD yarns and under two top MD yarns), and the other stitching yarn of the pair (those designated with a "b") passes over two top MD yarns while passing below a top MD yarn positioned between those two top MD yarns. Thus, together the stitching yarns of a pair pass over each of the odd-numbered top MD yarns 201-209 and pass below each of the even-numbered top MD yarns 202-210 to form an "over 1 /under 1" sequence with the top MD yarns. This arrangement can be seen in Figures 4 and 6B, which shows stitching yarn 211a passing over top CMD yarns 205, 207 and 209 and below top CMD yarns 206 and 208, and further shows stitching yarn 211b passing over top MD yarns 201 and 203 while passing under top CMD yarn 202. The other stitching yarns follow a similar pattern, with adjacent stitching yarn pairs being offset from each other by two top MD yarns. The result is the aforementioned plain weave surface.

Referring now to Figures 5 and 6C, the bottom layer of the repeat unit of the fabric 200 is illustrated therein. Each of the bottom MD and CMD yarns is positioned substantially directly below a corresponding top MD or CMD yarn. The bottom MD yarns are interwoven with the bottom CMD yarns in an "under 4/over 1 " pattern that is repeated twice within the repeat unit. For example, as shown in Figure 6C, bottom MD yarn 231 passes below bottom CMD yarns 244-247, above bottom CMD yarn 248, below bottom CMD yarns 249, 250, 241, 242 and above bottom CMD yarn 243. The other bottom MD yarns follow a similar "over 4/under I/over 4/under 1" weave pattern, but are offset from their adjacent bottom MD yarns by two bottom CMD yarns. The long bottom MD floats formed by the bottom MD yarns can impart reduced drag and, consequently, improved wear resistance in the manner discussed above with respect to the fabric 100 shown in Figures 1-3B.

In addition, each of the stitching yarns 221a-230b passes below one of the bottom MD yarns to form a bottom knuckle, with the bottom knuckles of the stitching yarns of a pair being separated by five bottom MD yarns. For example, and as shown in Figure 6B, stitching yarn 221a passes below bottom MD yarn 232, and stitching yarn 221b passes below bottom MD yarn 237. As is the case with the portions of the stitching yarns that interweave with the top MD yarns, the portions of the stitching yarns that interweave with the bottom MD yarns are also separated from each other by two bottom MD yarns. Notably, the stitching points of the stitching yarns are located immediately adjacent the bottom knuckles formed by the bottom CMD yarns as they pass below a bottom MD yarn. For example, as best seen in Figures 5, 6A and 6B, both stitching yarn 211a and immediately adjacent bottom CMD yarn 241 pass below bottom MD yarn 232, and both stitching yarn 221b and bottom CMD yarn 241 pass below bottom MD yarn 237. As such, the stitching yarns are protected from wear by the presence of the bottom CMD knuckle formed by the adjacent bottom CMD yarn.

It can also be seen in Figures 4 and 5 that the stitching yarns are interwoven with the top and bottom MD yarns as "reversed picks." This concept is described in detail in U.S. Patent No. 5,967,195 to Ward and need not be discussed further herein. Those skilled in this art will appreciate that, although the illustrated reversed picks configuration is preferred, the present invention may also be employed with non-reversed picks fabrics.

As another example of a CMD-stitched fabric, a repeat unit of another fabric, designated broadly at 300, is illustrated in Figures 7-9C. The repeat unit 300 includes four top MD yarns 301-304, four top CMD yarns 311-314, four pairs of CMD stitching yarns 321, 321b-324a, 324b, and four bottom MD yarns 331-334. The interweaving of these yarns is discussed in greater detail below. Looking first at Figures 7 and 9C, the top MD yarns and top CMD yarns interweave such that the top CMD yarns 311-314 pass under each of the odd-numbered top MD yarns 301, 303 and over each of the even-numbered top MD yarns 302, 304. For example, as shown in Figures 7 and 9C, top CMD yarn 311 passes under odd-numbered top MD yarns 301, 303 and over even-numbered top MD yarns 302, 304 to form an "over I/under 1" pattern. The remaining top CMD yarns follow a similar pattern with respect to the top MD yarns.

Turning now to Figures 7, 9A and 9B, the stitching yarn pairs 321a, 321b-324a, 324b interweave with the top MD yarns such that one of the stitching yarns (the yarns with an "a" designation) passes over one of the odd-numbered top MD yarns and under the other top MD yarns. For example, as shown in Figure 9 A, the stitching yarn 321a passes over the top MD yarn 303 and under the other top MD yarns. The stitching yarn of a pair with a "b" designation passes over the odd-numbered stitching yarn in the repeat unit that the "a" yarn does not; for example, the stitching yarn 321b passes over top MD yarn 301 and under the remaining top MD yarns (Figure 9B). Thus, together the stitching yarns 321a, 321b follow an "over 1 /under 1 " sequence with respect to the top MD yarns. As such, the top MD yarns, the top CMD yarns, and the stitching yarns combine to form a plain weave papermaking surface.

Referring now to Figure 8, 9A and 9B, each of the "b" stitching yarns passes below one of the bottom MD yarns 331-334; however, the "a" stitching yarns do not (i.e., they are so-called "phantom" stitching yarns). For example, stitching yarn 321a does not pass below any of the bottom MD yarns, but stitching yarn 321b passes below bottom MD yarn 332 (see Figures 9A and 9B). The remaining stitching yarn pairs follow a similar pattern. The result is that each of the bottom MD yarns 331-334 forms an "under 3/over 1 " pattern with the "b" stitching yarns, with the result that the bottom MD yarns form long MD floats (in this case, floats that are three CMD yarns in length) on the bottom surface of the fabric (see Figure 8).

It should also be noted in Figures 9A-9C that the bottom MD yarns are staggered relative to the top MD yarns; in other words, the bottom MD yarns are not positioned directly beneath the top MD yarns, but are positioned directly below the space between adjacent top MD yarns.

Another example of a fabric that is MD-stitched is shown in Figures 10-12C, wherein a repeat unit of another forming fabric according to embodiments of the present invention, designated broadly at 400, is illustrated. The repeat unit 400 includes four top MD yarns 401- 404, eight MD stitching MD yarns 411a, 411b-414a, 414b, thirty top CMD yarns 421-450, and twelve bottom MD yarns 451-462, and twelve bottom CMD yarns 471-482. The interweaving of these yarns is described below. As can be seen in Figures 10 and 12C, each of the top MD yarns 401-404 interweaves with the top CMD yarns 421-450 in an "over I/under 1 " sequence, in which the top MD yarns 401-404 pass under the odd-numbered top CMD yarns 421-449 and over the even-numbered top CMD yarns 422-450. As an example, and as shown in Figure 12C, top MD yarn 401 passes over even-numbered top CMD yarns 422-450 and under odd-numbered top CMD yarns 421- 449. This pattern is repeated for the remainder of the top MD yarns 402-404.

Referring now to Figures 10 and 12B, the MD stitching yarns 411a, 411b-414a, 414b are disposed in pairs, wherein each pair together interweaves with the top CMD yarns 421-450 in an "over I/under 1" sequence. For example, as can be seen in Figures 10 and 12B, MD stitching yarn 411a follows an "over I/under 1" pattern relative to the top CMD yarns to form seven consecutive MD knuckles (passing over odd-numbered top CMD yarns 421-433 and below even-numbered top CMD yarns 422-432). MD stitching yarn 411a passes below the remaining top CMD yarns 434-450. Paired stitching yarn 411b follows an "over 1 /under 1" pattern relative to the top CMD yarns to form eight consecutive MD knuckles (passing over odd-numbered top CMD yarns 435-449) and below even-numbered top CMD yarns 436-448). MD stitching yarn 411b passes below the remaining top CMD yarns. Thus, together the MD stitching yarns 411a, 411b follow an "over I/under 1" pattern relative to the top CMD yarns. The remaining MD stitching yarn pairs (i.e., MD stitching yarns 412a, 412b, MD stitching yarns 413a, 413b, and MD stitching yarns 414a, 414b) follow a similar "over I/under 1" sequence with the top CMD yarns. As a result, the top MD yarns, top CMD yarns, and stitching yarns combine to form a plain weave surface.

Turning now to Figure 11 and also to Figure 12, the MD stitching yarns 411a-414b also interweave with the bottom CMD yarns 471-482. Each of the MD stitching yarns 411a-414b passes below one bottom CMD yarn, with the MD stitching yarns of each pair together forming "over 5/under 1" pattern. For example, and referring to Figure 12B, MD stitching yarn 411a passes under bottom CMD yarn 479 and over the remaining bottom CMD yarns. MD stitching yarn 411b passes under bottom CMD yarn 473, thus combining with MD stitching yam 411a to form the "over 5/under 1 " sequence with the bottom CMD yarns noted above. The remaining MD stitching yarn pairs similarly form an "over 5/under 1 " sequence with the bottom CMD yarns.

Referring again to Figure 11 and also to Figure 12A, the bottom MD yarns 451-462 interweave with the bottom CMD yarns in an "under 5/over 1 " sequence that repeats twice within the repeat unit. For example, bottom MD yarn 451 passes below bottom CMD yarns 471-475, above bottom CMD yarn 476, below bottom CMD yarns 477-481, and above bottom CMD yarn 482. The other bottom MD yarns 452-462 follow a similar "under 5/over 1" pattern relative to the bottom CMD yarns. Thus, the bottom MD yarns form long MD floats (in this instance under five bottom CMD yarns) that may have the same drag reduction and wear resistance discussed above.

Also, each of the stitching locations is positioned under a bottom CMD yarn that the adjacent bottom MD yarns do not pass under. As such, the stitching locations can be protected as described above.

The form of the yarns utilized in fabrics of the present invention can vary, depending upon the desired properties of the final papermaker's fabric. For example, the yarns may be monofilament yarns, flattened monofilament yarns as described above, multifilament yarns, twisted multifilament or monofilament yarns, spun yarns, or any combination thereof. Also, the materials comprising yarns employed in the fabric of the present invention may be those commonly used in papermaker's fabric. For example, the yarns may be formed of polyester, polyamide (nylon), polypropylene, aramid, or the like. The skilled artisan should select a yarn material according to the particular application of the final fabric. In particular, round monofilament yarns formed of polyester or polyamide may be suitable, and, as noted, the use of monofilament yarns as bottom MD yarns may be particularly suitable. Those skilled in this art will appreciate that yarns of different sizes may be employed in fabric embodiments of the present invention. As noted above, in embodiments that include both top and bottom MD yarns, the top MD yarns may be of a smaller diameter than the bottom MD yarns. For example, the top MD yarns, top CMD yarns, and stitching yarns may have a diameter of between about 0.10 and 0.20 mm, the bottom MD yarns may have a diameter of between about 0.15 and 0.25 mm, and the bottom CMD yarns may have a diameter of between about 0.20 and 0.30 mm. The mesh of fabrics according to embodiments of the present invention may also vary. For example, the mesh of the top surface may vary between about 20 x 30 to 30 x 50 (epcm to ppcm), and the total mesh may vary between about 60 x 45 to 90 x 75.

In addition, the numbers of different types of yarns relative to other types of yarns may vary. For example, in some of the embodiments shown, the ratio of top MD yarns to bottom MD yarns is 1 : 1 ; in others, the ratio of "effective" top MD yarns (i.e. , the number of top MD yarns plus the number of MD stitching yarn pairs) to bottom MD yarns is 1 :1 or 2:3, but other ratios may also be employed. In some embodiments, the number of top CMD yarns to bottom CMD yarns is 1 : 1 ; in others, the number of "effective" top CMD yarns (/. e. , the number of top CMD yarns plus the number of CMD stitching yarn pairs) is 2:1; and in other embodiments, the ratio of top CMD yarns to bottom CMD yarns is 5:2; however, other ratios may also be employed.

Finally, although each of the embodiments include a plain weave top surface, other embodiments may include a top surface having a different weave pattern, including twill, satin, or the like. In addition, the long MD float bottom surfaces of the fabrics may take other weave patterns, including satin, twill or the like.

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 paper stock is well understood by those of skill in the art, additional details regarding this aspect of the present invention need not be provided herein.

The foregoing embodiments are illustrative of the present invention, and are not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

That Which is Claimed is:

1. A papermaker's fabric, comprising: a set of top machine direction (MD) yarns; a set of bottom MD yarns; a set of top cross machine direction (CMD) yarns interwoven with the top MD yarns to form a top fabric layer; a set of bottom CMD yarns interwoven with the bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns that interweave with the top and bottom fabric layers; wherein the top MD yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units; wherein each of the bottom MD yarns forms a bottom MD float by passing under three or more consecutive bottom CMD yarns.

2. The papermaker's fabric defined in Claim 1, wherein the bottom MD floats pass under between three and five consecutive bottom CMD yarns.

3. The papermaker's fabric defined in Claim 1, wherein the bottom MD yarns comprise monofilament yarns.

4. The papermaker's fabric defined in Claim 1 , wherein the stitching yarns are arranged in pairs.

5. The papermaker's fabric defined in Claim 4, wherein the stitching yarn pairs comprise MD stitching yarns.

6. The papermaker's fabric defined in Claim 4, wherein the stitching yarn pairs comprise CMD stitching yarns.

7. The papermaker's fabric defined in Claim 1, wherein the top MD yarns, the top CMD yarns, and the stitching yarns combine in the top fabric layer to form a plain weave top surface.

8. The papermaker's fabric defined in Claim 1, wherein each of the MD yarns of the top layer is also a stitching yarn.

9. The papermaker's fabric defined in Claim 4, wherein one of the stitching yarns of each pair is a phantom stitching yarn.

10. The papermaker's fabric defined in Claim 5, wherein each of the stitching yarns stitches below a bottom CMD yarn that is one of the consecutive yarns that each of the adjacent bottom MD yarn passes under in forming the bottom MD float.

11. The papermaker's fabric defined in Claim 6, wherein each of the stitching yarns stitches under a bottom MD yarn that an adjacent bottom CMD yarn also passes under.

12. The papermaker's fabric defined in Claim 1 , wherein the top MD yarns have a first diameter, the bottom MD yarns have a second diameter, and the first diameter is smaller than the second diameter.

13. The papermaker's fabric defined in Claim 8, wherein the ratio of MD stitching yarn pairs to bottom MD yarns is 1 : 1.

14. The papermaker's fabric defined in Claim 5, wherein the ratio of top MD yarns and stitching yarn pairs to bottom MD yarns is 2:3.

15. The papermaker's fabric defined in Claim 5, wherein the ratio of top CMD yarns to bottom CMD yarns is 5:2.

16. The papermaker's fabric defined in Claim 6, wherein the ratio of top CMD yarns to bottom CMD yarns is 1 : 1.

17. A papermaker's fabric, comprising: a set of top machine direction (MD) yarns; a set of bottom MD yarns; a set of cross machine direction (CMD) yarns interwoven with the top MD yarns to form a top fabric layer; a set of CMD stitching yarn pairs that interweave with the top and bottom fabric layers; wherein the top MD yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units; wherein each of the bottom MD yarns forms a bottom MD float by passing under three or more consecutive CMD stitching yarn pairs.

18. The papermaker's fabric defined in Claim 17, wherein the bottom MD yarns comprise monofilament yarns.

19. The papermaker's fabric defined in Claim 17, wherein the top MD yarns, the top CMD yarns, and the stitching yarns combine in the top fabric layer to form a plain weave top surface.

20. The papermaker's fabric defined in Claim 17, wherein one of the CMD stitching yarns of each pair is a phantom stitching yarn.

21. The papermaker's fabric defined in Claim 17, wherein the ratio of top MD yarns to bottom MD yarns is 1 : 1.

22. A papermaker's fabric, comprising: a set of machine direction (MD) stitching yarns, the stitching yarns being arranged in pairs; a set of bottom MD yarns; a set of top cross machine direction (CMD) yarns interwoven with the MD stitching yarns to form a top fabric layer; and a set of bottom CMD yarns interwoven with the bottom MD yarns to form a bottom fabric layer; wherein the MD stitching yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns, the MD stitching yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units; and wherein the MD stitching yarns have a first diameter, the bottom MD yarns have a second diameter, and the first diameter is less than the second diameter.

23. The papermaker's fabric defined in Claim 22, wherein the ratio of the first diameter to the second diameter is between about 0.4 and 0.7.