Multi-layer papermaker's forming fabric with auxiliary bottom MD yarns

A papermaker's fabric includes a series of repeat units, wherein each of the repeat units includes: a set of top machine direction MD yarns having a first diameter; a set of bottom MD yarns having a second diameter larger than the first diameter; a set of auxiliary bottom MD yarns having the first diameter; 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 and the auxiliary bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns arranged in pairs, wherein at least one of the stitching yarns of the pair interweaves with the top and bottom fabric layers.

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 stretch resistance, 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, in the past the two fabric layers were typically bound together by separate stitching yarns. However, today are more often 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. Pat. No. 4,423,755 to Thompson, and illustrative triple layer fabrics are shown in U.S. Pat. No. 4,501,303 to Osterberg, U.S. Pat. No. 5,152,326 to Vohringer, U.S. Pat. Nos. 5,437,315 and 5,967,195 to Ward, and U.S. Pat. No. 6,745,797 to Troughton.

U.S. Pat. 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. Pat. No. 6,896,009 shows a similar concept with MD stitching yarns.

Efficient drainage of water from a forming fabric can be an issue in papermaking. One solution for efficient drainage is proposed in co-assigned U.S. Pat. No. 8,251,103 to Baumann, the disclosure of which is hereby incorporated herein by reference. Baumann describes the use of engineered channels formed by the interstices in the fabric to provide efficient drainage; the patent proposes the use of a calculated “drainage factor” and a “channel factor” to improve drainage efficiency. It would be desirable to provide additional fabrics that expand on this concept.

SUMMARY

As a first aspect, embodiments of the invention are directed to a papermaker's fabric comprising a series of repeat units, wherein each of the repeat units comprises: a set of top MD yarns having a first diameter; a set of bottom MD yarns having a second diameter larger than the first diameter; a set of auxiliary bottom MD yarns having the first diameter; 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 and the auxiliary bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns arranged in pairs, wherein at least one of the stitching yarns of the pair interweaves with the top and bottom fabric layers.

As a second aspect, embodiments of the invention are directed to a papermaker's fabric comprising a series of repeat units, wherein each of the repeat units comprises: a set of top MD yarns; a set of bottom MD yarns; a set of auxiliary 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 and the auxiliary bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns arranged in pairs, wherein at least one of the stitching yarns of the pair interweaves with the top and bottom fabric layers. Each of the auxiliary bottom MD yarns follows the same weaving sequence with the bottom CMD yarns as an adjacent bottom MD yarn.

As a third aspect, embodiments of the invention are directed to a papermaker's fabric comprising a series of repeat units. Each of the repeat units comprises: a set of top MD yarns; a set of bottom MD yarns; a set of auxiliary 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 and the auxiliary bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns arranged in pairs, wherein at least one of the stitching yarns of the pair interweaves with the top and bottom fabric layers. Each of the auxiliary bottom MD yarns is interwoven with the bottom CMD yarns such that it forms a knuckle under bottom CMD yarns under which the adjacent bottom MD yarns also form knuckles.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter, in which embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the 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 drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity.

In addition, spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Referring now to the figures, a repeat unit of a papermaking forming fabric, designated broadly at100, is shown inFIGS. 1-5.FIG. 1shows the paper side or “top” side of the fabric100, andFIG. 2shows the machine side of the fabric100(i.e., the side facing the papermaking machine, referred to herein also as the “bottom” side of the fabric100).

FIG. 1illustrates the top layer102of the fabric100, which includes twelve top MD yarns1-12, eight top CMD yarns21-28, and eight stitching yarn pairs31a,31b-38a,38b, with a stitching yarn pair being located between adjacent top CMD yarns. The top MD yarns1-12, top CMD yarns21-28and stitching yarn pairs31a,31b-38a,38bare interwoven to form a plain weave surface on the top layer102.

As can be seen inFIGS. 1 and 3, a typical top CMD yarn, such as top CMD yarn21, follows an “over 1/under 1” sequence as it weaves with the top MD yarns1-12. More specifically, top CMD yarn21passes over top MD yarns1,3,5,7,9and11and under top MD yarns2,4,6,8,10and12. Each of the other top CMD yarns22-28follows the same sequence.

As can be seen inFIGS. 1 and 4, corresponding pairs of stitching yarns31a,31b-38a,38binterweave with the top MD yarns and bottom MD yarns in the following pattern. Each of the stitching yarns of the repeat unit can be subdivided into two portions: a fiber support portion which interweaves with the top MD yarns, and a binding portion which passes below the top MD yarns and, in the illustrated embodiment, interweaves with a bottom MD yarn. These are separated at “transitional” top MD yarns, below which one stitching yarn of a pair crosses the other stitching yarn of the pair. The stitching yarns of each pair are interwoven relative to one another such that the fiber support portion of one yarn of the pair is positioned above the binding portion of the other yarn of the pair. The fiber support portion of one stitching yarn of each pair 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 fiber support portion of the other yarn of the pair passes over three other top MD yarns of the repeat unit while passing below two other top MD yarns positioned between those three top MD yarns. Both of the stitching yarns pass below the transitional top MD yarns. Thus, together the stitching yarns of each pair pass over six top MD yarns and under six top MD yarns in an “over 1/under 1” pattern similar to that of the top CMD yarns.

As exemplified inFIG. 4by stitching yarn pair32a,32b, each stitching yarn interweaves with five top MD yarns (passing in alternating fashion over three top MD yarns and under two top MD yarns) and passes under one bottom MD yarn. For example, stitching yarn32apasses over top MD yarns2,4and6and under top MD yarns3and5(and also passes under bottom MD yarn46, as discussed below), while stitching yarn32bpasses over top MD yarns8,10and12and under bottom MD yarns9and11. Thus, together the stitching yarns32a,32b(and each other pair of stitching yarns) form the equivalent of one top CMD yarn that weaves in the “over 1/under 1” sequence followed by the top CMD yarns. As a result, together the top MD yarns1-12, the top CMD yarns21-28, and the portions of the stitching yarns31a,31b-38a,38bthat weave with the top MD yarns form a plain weave surface for the top layer102. Such top surface constructions are well-known (exemplified in, for example, U.S. Pat. No. 5,967,195 to Ward, the disclosure of which is hereby incorporated herein) and need not be described in detail herein.

Referring now toFIG. 2, the machine side of the fabric100includes eight bottom MD yarns41-48, four auxiliary bottom MD yarns42a,44a,46a,48a, and eight bottom CMD yarns51-58that form a bottom layer101. By way of explanation, the auxiliary bottom MD yarns42a,44a,46a,48a(which are similar in size to the top MD yarns1-12and therefore are smaller than the bottom MD yarns41-48) are each paired with a respective bottom MD yarn42,44,46,48and weave in the same pattern as that paired yarn. The bottom MD yarns41-48and the auxiliary bottom MD yarns42a,44a,46a,48aare interwoven with the bottom CMD yarns51-58in an “over 3/under 1/over 3/under 1” sequence (for reference purposes, herein the terms “over” and “under” are used with respect to the paper side of the fabric10being “up” and the machine side being “down”, as is shown inFIGS. 1 and 3-5, with the understanding that in the bottom view ofFIG. 2, yarns seen as passing “over” other yarns actually pass “under” those yarns with the paper side chosen as being “up”). For example, bottom MD yarn44passes over bottom CMD yarns51-53, under bottom CMD yarn54, over bottom CMD yarns55-57and under bottom CMD yarn58. The auxiliary bottom MD yarns42a,44a,46a,48aweave identically to bottom MD yarns42,44,46,48respectively.

Referring now toFIGS. 2 and 5, each bottom MD yarn is offset from its immediate bottom MD yarn neighbors to create a 4-harness broken twill pattern on the bottom surface with the “knuckles” formed by the bottom MD yarns. For example, bottom MD yarn41passes under bottom CMD yarns52and56, bottom MD yarn42passes under bottom CMD yarns53and57, bottom MD yarn43passes under bottom CMD yarns51and55, and bottom MD yarn44passes under bottom CMD yarns54and58. The remaining bottom MD yarns45-48follow a similar offset pattern (seeFIG. 2).

The bottom layer101also includes knuckles formed by the stitching yarns31a,31b-38a,38bunder the bottom MD yarns41-48and auxiliary bottom MD yarns42a,44a,46a,48a. The knuckles form a 4-harness broken twill pattern. As examples, the stitching yarns31a,31bform knuckles under bottom MD yarns41,45, the stitching yarns32a,32bform knuckles under bottom MD yarns42,46(as well as under auxiliary bottom MD yarns42a,46a), the stitching yarns33a,33bform knuckles under bottom MD yarns44,48(as well as under auxiliary bottom MD yarns44a,48a), and the stitching yarns34a,34bform knuckles under bottom MD yarns43,47. A similar pattern is repeated for stitching yarns35a,35b-38a,38b(seeFIGS. 2 and 4).

Those skilled in this art will appreciate that, although the stitching yarns31a,31b-38a,38bare woven with both stitching yarns of the pair both weaving with the top MD yarns and stitching under the bottom MD yarns, in some embodiments only one stitching yarn of the pair may stitch under the bottom MD yarns, with the other stitching yarn of the pair simply routed between the top and bottom MD yarns instead of stitching. This so-called “phantom” stitching yarn is described, for example, in U.S. Pat. No. 7,931,051 to Ward, the disclosure of which is hereby incorporated by reference herein in its entirety.

Turning now toFIGS. 6-10, a repeat unit of a forming fabric according to embodiments of the present invention, designated broadly at200, is illustrated therein. The repeat unit200includes twelve top MD yarns201-212, eight top CMD yarns221-228, four pairs of stitching yarns231a,231b-234a,234b, eight bottom MD yarns241-248, four auxiliary bottom MD yarns241a,243a,245a,247a, and eight bottom CMD yarns251-258. The interweaving of these yarns is described below.

Turning first toFIG. 6, the top surface of the fabric200is shown therein. The top CMD yarns221-228and stitching yarns231a,231b-234a,234bare arranged in an alternating pattern in which two top CMD yarns are followed by a pair of stitching yarns. As exemplified inFIG. 6, top CMD yarns221and222follow stitching yarn pair231a,231b, then stitching yarn pair232a,232bfollows top CMD yarn222. This pattern of “stitching yarn pair/two top CMD yarns” continues throughout the repeat unit.

Each of the top CMD yarns221-228interweaves with the top MD yarns in an “over 1/under 1” sequence. Because two top CMD yarns are positioned between a pair of stitching yarns, they pass over alternating top MD yarns. This pattern is shown inFIG. 8, wherein top CMD yarn222is shown passing over top MD yarns202,204,206,208,210and212, whereas top CMD yarn221is shown passing over top MD yarns201,203,205,207,209and211.

In its fiber support portion, each stitching yarn231a,231b-234a,234bpasses over top MD yarns that the adjacent top CMD yarns pass beneath and under the top MD yarns that the adjacent top CMD yarns pass over. For example, and as shown inFIG. 9, the fiber support portion of stitching yarn232apasses over top MD yarns201,203and205while passing under top MD yarns202and204, and stitching yarn232bpasses over top MD yarns207,209and211while passing below top MD yarns208and210. Both stitching yarns232a,232bpass below the transitional top MD yarns206,212. The remaining stitching yarn pairs weave in a similar manner, although they are offset from adjacent stitching yarn pairs by three top MD yarns. In this manner, the stitching yarns231a,231b-234a,234band the top CMD yarns221-228form a plain weave pattern with the top MD yarns201-212(seeFIG. 6).

Turning now toFIGS. 7 and 10, the bottom surface of the fabric is shown therein. The bottom MD yarns241-248interweave with the bottom CMD yarns251-258in an “over 7/under 1” pattern” (note thatFIG. 7is a bottom view of the fabric200and is opposite the view ofFIG. 6, so the description of the bottom MD yarns passing “over 4” bottom CMD yarns is consistent with the “over” and “under” conventions adopted with respect toFIGS. 6 and 8-10rather than the view seen inFIG. 9). For example, bottom MD yarn241passes over bottom CMD yarns251and252, under bottom CMD yarn253, and over bottom CMD yarns254-258(seeFIG. 10). The remaining bottom MD yarns follow a similar pattern, with each bottom MD yarn being offset from its adjacent bottom MD yarns in a double broken twill pattern.

The auxiliary bottom MD yarns241a,243a,245a,247aare woven with the bottom CMD yarns251-258in either an “over 5/under 1/over 1/under 1” sequence or an “over 2/under 1/over 4/under 1” sequence. Each “under 1” knuckle of the auxiliary bottom MD yarns aligns with the “under 1” knuckles of the bottom MD yarns that sandwich that auxiliary bottom MD yarn. For example, auxiliary bottom MD yarn241aforms knuckles under bottom CMD yarns251,253, which are the same bottom CMD yarns under which bottom MD yarns241,242(located on either side of auxiliary bottom MD yarn241a) form knuckles (seeFIG. 10). The remaining auxiliary bottom MD yarns similarly form knuckles aligned with their neighboring bottom MD yarns.

Also, the binding portion of each of the stitching yarns231a,231b-234a,234bis stitched below two bottom MD yarns, with the stitching yarns of a pair stitching below bottom MD yarns that are separated by two bottom MD yarns. For example, as shown inFIG. 9, stitching yarn232apasses below bottom MD yarns246and247, and stitching yarn232bpasses under bottom MD yarns242,243. Adjacent pairs of stitching yarns are offset from each other by two bottom MD yarns.

Turning now toFIGS. 11-15, a repeat unit of a forming fabric according to embodiments of the present invention, designated broadly at300, is illustrated therein. The repeat unit300includes twelve top MD yarns301-312, six top CMD yarns321-326, four pairs of stitching yarns331a,331b-334a,334b, eight bottom MD yarns341-348, four auxiliary bottom MD yarns342a,344a,346a,348a, and four bottom CMD yarns351-354. The interweaving of these yarns is described below.

Turning first toFIG. 11, the top surface of the fabric300is shown therein. The top CMD yarns321-326and stitching yarns331a,331b-334a,334bare arranged in a pattern in which one top CMD yarn is followed by a pair of stitching yarns, then two top CMD yarns are followed by another pair of stitching yarns. As exemplified inFIG. 11, top CMD yarns321is followed by stitching yarn pair331a,331b, then two top CMD yarns322,323are followed by stitching yarn pair332a,332b. This pattern of “one top CMD yarn/stitching yarn pair/two top CMD yarns/stitching yarn pair” continues throughout the repeat unit.

Each of the top CMD yarns321-326interweaves with the top MD yarns in an “over 1/under 1” sequence. This pattern is shown inFIG. 13, wherein top CMD yarn321is shown passing over top MD yarns301,303,305,307,309,311and under top MD yarns302,304,306,308,310and312.

In its fiber support portion, each stitching yarn331a,331b-334a,334bpasses over top MD yarns that the adjacent top CMD yarns pass beneath and under the top MD yarns that the adjacent top CMD yarns pass over. For example, and as shown inFIG. 14, the fiber support portion of stitching yarn331apasses over top MD yarns302,310and312while passing under top MD yarns301and311, and stitching yarn331bpasses over top MD yarns304,306and308while passing below top MD yarns305and307. Both stitching yarns331a,331bpass below the transitional top MD yarns303,309. The remaining stitching yarn pairs weave in a similar manner, although they are offset from adjacent stitching yarn pairs in a double broken twill pattern. In this manner, the stitching yarns331a,331b-334a,334band the top CMD yarns321-326form a plain weave pattern with the top MD yarns301-312(seeFIG. 11).

Turning now toFIGS. 12 and 15, the bottom surface of the fabric is shown therein. The bottom MD yarns341-348interweave with the bottom CMD yarns351-354in an “over 3/under 1” pattern” (note thatFIG. 12is a bottom view of the fabric300and is opposite the view ofFIG. 11, so the description of the bottom MD yarns passing “over 4” bottom CMD yarns is consistent with the “over” and “under” conventions adopted with respect toFIGS. 11 and 13-15rather than the view seen inFIG. 12). For example, bottom MD yarn342passes over bottom CMD yarns351-353and under bottom CMD yarn354(seeFIG. 15). The remaining bottom MD yarns follow a similar pattern, with each bottom MD yarn being offset from its adjacent bottom MD yarns in a double broken twill pattern.

The auxiliary bottom MD yarns342a,344a,346a,348aare woven with the bottom CMD yarns351-354in an “over 3/under 1” sequence. Each “under 1” knuckle of the auxiliary bottom MD yarns aligns with the “under 1” knuckle of a paired adjacent bottom MD yarn. For example, auxiliary bottom MD yarn342aforms a knuckle under bottom CMD yarns352, which are the same bottom CMD yarn under which paired bottom MD yarn342forms a knuckle (seeFIG. 15). The remaining auxiliary bottom. MD yarns similarly form knuckles aligned with their adjacent bottom MD yarns.

Also, the binding portion of each of the stitching yarns331a,331b-334a,334bis stitched below one bottom MD yarn, with the stitching yarns of a pair stitching below bottom MD yarns that are separated by three bottom MD yarns. For example, as shown inFIG. 14, stitching yarn331apasses below bottom MD yarn348(and auxiliary bottom MD yarn348a), and stitching yarn331bpasses under bottom MD yarn344(and auxiliary bottom MD yarn344a). Adjacent pairs of stitching yarns are offset from each other in a double broken twill pattern.

Those of skill in this art will recognize that the total of six top CMD yarns, four CMD stitching yarn pairs, and four bottom CMD yarns forms a 5:2 ratio of effective top CMD yarns (i.e., number of top CMD yarns+number of stitching yarn pairs) to bottom CMD yarns (i.e., number of bottom CMD yarns). This ratio, which is discussed in, for example, U.S. Pat. No. 8,196,613 to Ward, can provide fabrics with an excellent balance of properties including permeability, fiber support, stability and wear volume. In particular, CMD fiber support may be improved over fabrics with a 2:1 ratio because there are more top CMD yarns per inch. In some embodiments a 5:3 ratio may also be employed.

Those skilled in this art will appreciate that yarns of different sizes may be employed in fabric embodiments of the present invention. For example, the top MD yarns, top CMD yarns, auxiliary bottom MD 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 0.18 and 0.40 mm, and the bottom CMD yarns may have a diameter of between about 0.20 and 0.50 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 from about 20×30 to 30×50 (epcm to ppcm), and the total mesh may vary between about 60×45 to 90×75. More specifically, yarns for the fabrics100,200may be selected as set forth in Table 1:

Parameters of a specific embodiment of the fabric300ofFIGS. 11-15are set forth in Table 2.

The weave patterns of fabrics100,200,300can create engineered drainage channels of the type described in Baumann, supra, and can do so in fabrics with more yarns having the size of top MD yarns (i.e., either top MD yarns or auxiliary bottom MD yarns) than main bottom MD yarns. Doing so can reduce the paper-side MD yarn count relative to the machine-side MD yarn count (while maintaining or increasing the paper-side CMD yarn count), thereby increasing the paper-side open area and reducing the machine-side open area to the extent that the drainage channels become more like as described in Baumann—which can improve fabric drainage. As an example,FIG. 16is a graph showing the flow pressure across the thickness of the fabric. The line labeled “Fabric3” represents the fabric ofFIGS. 11-15and demonstrates reduced drainage pressure on both the paper side and the machine side of the fabric compared to similar prior fabrics. Also, flow velocity is reduced on the paper side of the fabric.

Also, increased paper-side open area without reducing the paper-side CMD yarn count and/or CMD yarn diameters can maintain or improve surface and internal wear. It improves fabric stability and seam strength potential particularly with long float bottom weaves. It can also significantly increase the design flexibility for MD yarns with paper-side to machine-side MD yarn ratios greater than one.

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), polyurethane, 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.

Although each of the embodiments includes 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 bottom surfaces of the fabrics may take other weave patterns, including satin, twill or the like. Also, additional weave patterns with different numbers and ratios of top and bottom MD and CMD yarns may also benefit from the concepts discussed herein. Further, in some embodiments the stitching yarns may be MD stitching yarns rather than CMD stitching yarns.

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.