Patent Publication Number: US-7219701-B2

Title: Papermaker&#39;s forming fabric with machine direction stitching yarns that form machine side knuckles

Description:
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 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. 
     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&#39; 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&#39;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&#39;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. 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. 6,896,009 and co-pending and co-assigned U.S. patent application Ser. No. 11/207,277, filed Aug. 18, 2005 describe a number of exemplary multi-layer forming fabrics that are “warped-stitched.” In some instances such fabrics may be easier to manufacture than weft-stitched forming fabrics and/or may have desirable performance properties. However, there is still a demand for additional types of warp-stitched fabrics to meet the vast array of papermaking needs. 
     SUMMARY OF THE INVENTION 
     As a first aspect, embodiments of the present invention are directed to a papermaking fabric, comprising a series of repeat units, each of the repeat units including: a set of top MD yarns; a set of top CMD yarns interwoven with the set of top MD yarns; a first set of bottom MD yarns, the first set of bottom MD yarns arranged in pairs; a second set of bottom MD yarns, the second set of bottom MD yarns arranged as single yarns; a set of bottom CMD yarns interwoven with the first and second sets of bottom MD yarns; and a set of pairs of MD stitching yarns interwoven with the top and bottom CMD yarns, each pair of MD stitching yarns sandwiching a respective immediately adjacent bottom MD yarn of the second set. Each of the yarns of a pair of the first set of bottom MD yarns interweaves with the bottom CMD yarns in the same pattern. 
     As a second aspect, embodiments of the present invention are directed to a papermaking fabric, comprising a series of repeat units, each of the repeat units including: a set of top MD yarns; a set of top CMD yarns interwoven with the set of top MD yarns; a first set of bottom MD yarns, the first set of bottom MD yarns arranged in pairs; a second set of bottom MD yarns, the second set of bottom MD yarns arranged as single yarns; a set of bottom CMD yarns interwoven with the first and second sets of bottom MD yarns; and a set of pairs of MD stitching yarns interwoven with the top and bottom CMD yarns, each pair of MD stitching yarns sandwiching a respective immediately adjacent bottom MD yarn of the second set. Each of the yarns of a pair of the first set of bottom MD yarns interweaves with the bottom CMD yarns in the same pattern. Also, each pair of bottom MD yarns of the first set is positioned beneath a top MD yarn. 
     As a third aspect, embodiments of the present invention are direction to a papermaking fabric, comprising a series of repeat units, each of the repeat units including: a set of top machine direction (MD) yarns; a set of top cross machine direction (CMD) yarns interwoven with the set of top MD yarns; a first set of bottom MD yarns, each of the yearns of the first set having a flattened cross-section; a second set of bottom MD yarns, the second set of bottom MD yarns arranged as single yarns; a set of bottom CMD yarns interwoven with the first and second sets of bottom MD yarns; and a set of pairs of MD stitching yarns interwoven with the top and bottom CMD yarns, each pair of MD stitching yarns sandwiching a respective immediately adjacent bottom MD yarn of the second set. 
     As a fourth aspect, embodiments of the present invention are directed to a method of making paper, comprising the steps of: (a) providing a papermaking fabric, the fabric comprising: a set of top MD yarns; a set of top CMD yarns interwoven with the set of top MD yarns; a first set of bottom MD yarns, the first set of bottom MD yarns arranged in pairs; a second set of bottom MD yarns, the second set of bottom MD yarns arranged as single yarns; a set of bottom CMD yarns interwoven with the first and second sets of bottom MD yarns; and a set of pairs of MD stitching yarns interwoven with the top and bottom CMD yarns, each pair of MD stitching yarns sandwiching a respective immediately adjacent bottom MD yarn of the second set; wherein each of the yarns of a pair of the first set of bottom MD yarns interweaves with the bottom CMD yarns in the same pattern; (b) depositing paper stock on the papermaking fabric; and (c) removing moisture from the papermaking stock. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a top view of a repeat unit of a forming fabric according to embodiments of the present invention. 
         FIG. 2  is a bottom view of the repeat unit of the fabric of  FIG. 1 . 
         FIGS. 3A–3F  are section views taken of exemplary machine direction yarns of the fabric of  FIGS. 1 and 2 . 
         FIG. 4  is a top view of a repeat unit of a forming fabric according to other embodiments of the present invention. 
         FIG. 5  is a bottom view of the repeat unit of the fabric of  FIG. 4 . 
         FIGS. 6A–6F  are section views taken of exemplary machine direction yarns of the fabric of  FIGS. 4 and 5 . 
         FIG. 7  is a top view of a repeat unit of a forming fabric according to additional embodiments of the present invention. 
         FIG. 8  is a bottom view of the repeat unit of the fabric of  FIG. 7 . 
         FIGS. 9A–9F  are section views taken of exemplary machine direction yarns of the fabric of  FIGS. 7 and 8 . 
         FIG. 10  is a section view taken of an exemplary top CMD yarn of the fabric of  FIGS. 7 and 8 . 
         FIG. 11  is a section taken of an exemplary top CMD yarn of an alternative fabric embodiment that employs bottom MD yarns that are flattened in cross-section. 
     
    
    
     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. 
     As used herein the expression “and/or” includes any and all combinations of one or more of the associated listed items. 
     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. 
     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. 
     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  FIGS. 1–3F , a repeat unit of a forming fabric according to embodiments of the present invention, designated broadly at  10 , is illustrated therein. The repeat unit  10  includes three top MD yarns  11 – 13 , three pairs of MD stitching yarns  21   a ,  21   b – 23   a ,  23   b , twelve top CMD yarns  31 – 42 , six paired bottom MD yarns  51   a ,  51   b – 53   a ,  53   b , three unpaired bottom MD yarns  61 – 63 , and six bottom CMD yarns  71 – 76 . The interweaving of these yarns is described below. 
     As can be seen in  FIGS. 1 and 3E , each of the top MD yarns  11 – 13  interweaves with the top CMD yarns  31 – 42  in an “over 1/under 1” sequence, in which the top MD yarns  11 – 13  pass over the odd-numbered top CMD yarns  31 ,  33 ,  35 ,  37 ,  39 ,  41  and under the even-numbered top CMD yarns  32 ,  34 ,  36 ,  38 ,  40 ,  42 . 
     As can be seen in  FIG. 1 , each stitching yarn pair  21   a ,  21   b – 23   a ,  23   b  is located between two top MD yarns. As can be seen in  FIGS. 1 ,  3 A and  3 C, each of the stitching yarn pairs  21   a – 23   b  combines to act as a single yarn in completing the plain weave pattern on the top surface of the fabric  10 . More specifically, each of the stitching yarns passes over three even-numbered top CMD yarns, with the stitching yarns designated with an “a” passing over one set of three even-numbered top CMD yarns, and each of the stitching yarns designated with a “b” passing over a set of the remaining three even-numbered top CMD yarns. For example, stitching yarn  21   a  passes over top CMD yarns  36 ,  38  and  40  while passing below top CMD yarns  35 ,  37 ,  39  and  41 , and stitching yarn  21   b  passes over top CMD yarns  42 ,  32  and  34  while passing below top CMD yarns  41 ,  31 ,  33  and  35 . Thus, together stitching yarns  21   a ,  21   b  form a “composite” top MD yarn that follows an overall “over 1/under 1” path relative to the top CMD yarns. The “composite” top MD yarn thusly formed passes over even-numbered top CMD yarns, thereby forming a plain weave pattern with the top MD yarns on the top, or papermaking, surface of the fabric  10 . 
     Each pair of stitching yarns is offset from its neighboring stitching yarn pairs by two top CMD yarns. This can be seen by examination of  FIG. 1 , wherein stitching yarns  21   a ,  21   b  both pass below top CMD yarn  35  as they travel between the top and bottom layers of the fabric  10 . Moving up  FIG. 1  and to stitching yarns  22   a ,  22   b , these yarns both pass below top CMD yarn  33  (which is offset from top CMD yarn  35  by two top CMD yarns) as they travel between the top and bottom layers. 
     The bottom layer of the fabric  10  is illustrated in  FIG. 2 . The bottom layer includes paired bottom MD yarns  51   a ,  51   b – 53   a ,  53   b , unpaired bottom MD yarns  61 – 63 , stitching yarns  21   a ,  21   b – 23   a ,  23   b  and bottom CMD yarns  71 – 76 . The paired bottom MD yarns, which are located beneath a corresponding top MD yarn, interweave as a pair with the bottom CMD yarns in an “over 2/under 1” sequence. For example, referring to  FIGS. 2 ,  3 D and  3 F, bottom MD yarns  51   a ,  51   b  pass over bottom CMD yarns  73 ,  74 , under bottom CMD yarn  75 , over bottom CMD yarns  76 ,  71  and under bottom CMD yarn  72 . Each unpaired bottom MD yarn also follows an “over 2/under 1” sequence as it interweaves with the bottom CMD yarns. For example, unpaired bottom MD yarn  61  passes over bottom CMD yarns  72 ,  73 , under bottom CMD yarn  74 , over bottom CMD yarns  75 ,  76  and under bottom CMD yarn  71  (see  FIGS. 2 and 3B ). 
     The paired bottom MD yarns, which are located beneath a corresponding top MD yarn, interweave as a pair with the bottom CMD yarns in a repeating “over 2/under 1” sequence. For example, referring to  FIGS. 2 ,  3 D and  3 F, bottom MD yarns  51   a ,  51   b  pass over bottom CMD yarns  73 ,  74 , under bottom CMD yarn  75 , over bottom CMD yarns  76 ,  71  and under bottom CMD yarn  72 . Each unpaired bottom MD yarn also follows an “over 2/under 1” sequence as it interweaves with the bottom CMD yarns. For example, unpaired bottom MD yarn  61  passes over bottom CMD yarns  71 ,  72 , under bottom CMD yarn  73 , over bottom CMD yarns  74 ,  75  and under bottom CMD yarn  76  (see  FIGS. 2 and 3B ). 
     Referring again to  FIG. 2 , each pair of stitching yarns sandwiches an unpaired bottom MD yarn (e.g., stitching yarns  21   a ,  21   b  sandwich bottom MD yarn  61 ), and each stitching yarn forms one knuckle under a bottom CMD yarn. As used herein, “knuckle” refers to a portion of one yarn that, in interweaving with other yarns, passes above or below a single other yarn, whereas a “float” refers to a portion of one yarn that passes above or below multiple adjacent yarns. Each knuckle formed by a stitching yarn is positioned beside a knuckle formed by the immediately adjacent unpaired bottom MD yarn, such that each stitching yarn pair and the unpaired bottom MD yarns form pairs of knuckles similar to the paired knuckles of the paired bottom MD yarns. For example, unpaired bottom MD yarn  61  forms knuckles below bottom CMD yarns  71  and  74  (see  FIGS. 3A–3C ). Stitching yarn  21   b  forms a knuckle under bottom CMD yarn  71 , and stitching yarn  21   a  forms a knuckle under bottom CMD yarn  74 . Each pair of paired bottom MD yarns is offset from its neighboring unpaired bottom MD yarn by one bottom CMD yarn. For example, unpaired bottom MD yarn  61  forms a knuckle under bottom CMD yarn  71 , and paired bottom yarns  51   a ,  51   b  form knuckles under bottom CMD yarn  72 . As a result, the pairs of knuckles on the bottom surface form a diagonal thereon. 
     A repeat unit of another fabric according to embodiments of the present invention is designated broadly at  110  and is illustrated in  FIGS. 4–6F . The repeat unit  110  includes four top MD yarns  111 – 114 , four pairs of MD stitching yarns  121   a ,  121   b – 124   a ,  124   b , sixteen top CMD yarns  131 – 146 , eight paired bottom MD yarns  151   a ,  151   b – 154   a ,  154   b , four unpaired bottom MD yarns  161 – 164 , and eight bottom CMD yarns  171 – 178 . The interweaving of these yarns is described below. 
     As can be seen in  FIGS. 4 and 6B , each of the top MD yarns  111 – 114  interweaves with the top CMD yarns  131 – 146  in an “over 1/under 1” sequence, in which the top MD yarns  111 – 114  pass over the odd-numbered top CMD yarns  131 ,  133 ,  135 ,  137 ,  139 ,  141 ,  143 ,  145  and under the even-numbered top CMD yarns  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144 ,  146 . 
     As can be seen in  FIG. 4 , each stitching yarn pair  121   a ,  121   b – 124   a ,  124   b  is located between two top MD yarns. Like the stitching yarns of the fabric  10  described above, and as can be seen in  FIGS. 4 ,  6 D and  6 F, each of the stitching yarn pairs  121   a – 124   b  combines to act as a single yarn in completing the plain weave pattern on the top surface of the fabric  110 . More specifically, each of the stitching yarns passes over four even-numbered top CMD yarns, with the stitching yarns designated with an “a” passing over one set of four even-numbered top CMD yarns, and each of the stitching yarns designated with a “b” passing over a set of the remaining four even-numbered top CMD yarns. For example, stitching yarn  121   a  passes over top CMD yarns  142 ,  144 ,  146 , and  132  while passing below top CMD yarns  141 ,  143 ,  145 ,  131  and  133 , and stitching yarn  121   b  passes over top CMD yarns  134 ,  136 ,  138  and  140  while passing below top CMD yarns  133 ,  135 ,  137 ,  139  and  141 . Together the stitching yarns  121   a ,  121   b  form a composite top MD yarn that follows an overall “over 1/under 1” path while interweaving with the top CMD yarns. The composite top MD yarns formed by the stitching yarns pass over even-numbered top CMD yarns, thereby forming a plain weave pattern with the top MD yarns on the top, or papermaking, surface of the fabric  110 . 
     Each pair of stitching yarns is offset from its neighboring stitching yarn pairs by four top CMD yarns. This can be seen by examination of  FIG. 4 , wherein stitching yarns  121   a ,  121   b  both pass below top CMD yarn  133  as they travel between the top and bottom layers of the fabric  110 . Moving down  FIG. 4  and to stitching yarns  122   a ,  122   b , these yarns both pass below top CMD yarn  137  (which is offset from top CMD yarn  133  by four top CMD yarns) as they travel between the top and bottom layers. 
     The bottom layer of the fabric  110  is illustrated in  FIG. 5 . The bottom layer includes paired bottom MD yarns  151   a ,  151   b – 154   a ,  154   b , unpaired bottom MD yarns  161 – 164 , stitching yarn pairs  121   a ,  121   b – 124   a ,  124   b  and bottom CMD yarns  171 – 178 . The paired bottom MD yarns, which are located beneath a corresponding top MD yarn, interweave as a pair with the bottom CMD yarns in an “over 3/under 1” sequence. For example, referring to  FIGS. 5 ,  6 A and  6 C, bottom MD yarns  151   a ,  151   b  pass over bottom CMD yarns  173 ,  174 ,  175 , under bottom CMD yarn  176 , over bottom CMD yarns  177 ,  178 ,  171  and under bottom CMD yarn  172 . Each unpaired bottom MD yarn also follows an “over 3/under 1” sequence as it interweaves with the bottom CMD yarns. For example, unpaired bottom MD yarn  161  passes over bottom CMD yarns  178 ,  171 ,  172 , under bottom CMD yarn  173 , over bottom CMD yarns  174 ,  175 ,  176  and under bottom CMD yarn  177  (see  FIGS. 5 and 6E ). 
     Referring again to  FIG. 5 , each pair of stitching yarns sandwiches an unpaired bottom MD yarn (e.g. stitching yarns  121   a ,  121   b  sandwich bottom MD yarn  161 ). Each stitching yarn forms one knuckle under a bottom CMD yarn beside a knuckle formed by the immediately adjacent unpaired bottom MD yarn, such that each stitching yarn pair and the unpaired bottom MD yarns form pairs of knuckles similar to the paired knuckles of the paired bottom MD yarns. For example, unpaired bottom MD yarn  161  forms knuckles below bottom CMD yarns  173  and  177  (see  FIG. 6E ). Stitching yarn  121   a  forms a knuckle under bottom CMD yarn  173 , and stitching yarn  121   b  forms a knuckle under bottom CMD yarn  177  (see  FIGS. 6D and 6F ). Each pair of paired bottom MD yarns is offset from its neighboring unpaired bottom MD yarn by one bottom CMD yarn. For example, unpaired bottom MD yarn  161  forms a knuckle under bottom CMD yarn  173 , and paired bottom yarns  151   a ,  151   b  form knuckles under bottom CMD yarn  172 . As a result, the pairs of knuckles on the bottom surface form a diagonal thereon. 
     It can be seen that, in the illustrated embodiment, the paired “a” bottom MD yarns are smaller in diameter than the paired “b” bottom MD yarns. It may be desirable in some embodiments for the “a” yarns to match the diameter of the stitching yarns, such that the paired knuckles of (a) the paired bottom MD yarns and (b) the pair knuckles of the unpaired bottom MD yarns and the stitching yarns are the same dimension. Those skilled in this art will appreciate that, in other embodiments (such as those of  FIGS. 1–3F  and  FIGS. 7–9F ), the paired “a” and “b” bottom MD yarns may be of the same diameter. 
     A repeat unit of a further fabric according to embodiments of the present invention is designated broadly at  210  and is illustrated in  FIGS. 7–9F . The repeat unit  210  includes five top MD yarns  211 – 215 , five pairs of MD stitching yarns  221   a ,  221   b – 225   a ,  225   b , twenty top CMD yarns  231 – 250 , ten paired bottom MD yarns  251   a ,  251   b – 255   a ,  255   b , five unpaired bottom MD yarns  261 – 265 , and ten bottom CMD yarns  271 – 280 . The interweaving of these yarns is described below. 
     As can be seen in  FIGS. 7 and 9B , each of the top MD yarns  211 – 215  interweaves with the top CMD yarns  231 – 250  in an “over 1/under 1” sequence, in which the top MD yarns  211 – 215  pass over the odd-numbered top CMD yarns  231 ,  233 ,  235 ,  237 ,  239 ,  241 ,  243 ,  245 ,  247 ,  249  and under the even-numbered top CMD yarns  232 ,  234 ,  236 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 ,  250 . 
     As can be seen in  FIG. 7 , each stitching yarn pair  221   a ,  221   b – 225   a ,  225   b  is located between two top MD yarns. Like the stitching yarns of the fabrics  10  and  110  described above, and as can be seen in  FIGS. 7 ,  9 D and  9 F, each of the stitching yarn pairs  221   a – 225   b  combines to act as a single yarn in completing the plain weave pattern on the top surface of the fabric  210 . More specifically, each of the stitching yarns passes over five even-numbered top CMD yarns, with the stitching yarns designated with an “a” passing over one set of five even-numbered top CMD yarns, and each of the stitching yarns designated with a “b” passing over a set of the remaining five even-numbered top CMD yarns. For example, stitching yarn  221   a  passes over top CMD yarns  250 ,  232 ,  234 ,  236 , and  238  while passing below top CMD yarns  249 ,  231 ,  233 ,  235 ,  237  and  239 , and stitching yarn  221   b  passes over top CMD yarns  240 ,  242 ,  244 ,  246  and  248  while passing below top CMD yarns  239 ,  241 ,  243 ,  245 ,  247  and  249 . Together the stitching yarns  221   a ,  221   b  form a composite top MD yarn that follows an overall “over 1/under 1” path while interweaving with the top CMD yarns. The composite top MD yarns formed by the stitching yarns pass over even-numbered top CMD yarns, thereby forming a plain weave pattern with the top MD yarns on the top, or papermaking, surface of the fabric  210 . 
     Each pair of stitching yarns is offset from its neighboring stitching yarn pairs by two top CMD yarns. This can be seen by examination of  FIG. 7 , wherein stitching yarns  221   a ,  221   b  both pass below top CMD yarn  239  as they travel between the top and bottom layers of the fabric  210 . Moving down  FIG. 7  and to stitching yarns  222   a ,  222   b , these yarns both pass below top CMD yarn  241  (which is offset from top CMD yarn  239  by two top CMD yarns) as they travel between the top and bottom layers. 
     The bottom layer of the fabric  210  is illustrated in  FIG. 8 . The bottom layer includes paired bottom MD yarns  251   a ,  251   b – 255   a ,  255   b , unpaired bottom MD yarns  261 – 265 , stitching yarn pairs  221   a ,  221   b – 225   a ,  225   b  and bottom CMD yarns  271 – 280 . The paired bottom MD yarns, which are located beneath a corresponding top MD yarn, interweave as a pair with the bottom CMD yarns in an “over 4/under 1” sequence. For example, referring to  FIGS. 7 ,  9 A and  9 C, paired bottom MD yarns  251   a ,  251   b  pass over bottom CMD yarns  271 – 274 , under bottom CMD yarn  275 , over bottom CMD yarns  276 – 279  and under bottom CMD yarn  280 . Each unpaired bottom MD yarn also follows an “over 4/under 1” sequence as it interweaves with the bottom CMD yarns. For example, unpaired bottom MD yarn  261  passes over bottom CMD yarns  271 ,  272 , under bottom CMD yarn  273 , over bottom CMD yarns  274 – 277 , under bottom CMD yarn  278 , and over bottom CMD yarns  279 ,  280  (see  FIGS. 8 and 9E ). 
     Referring again to  FIG. 8 , each pair of stitching yarns sandwiches an unpaired bottom MD yarn (e.g. stitching yarns  221   a ,  221   b  sandwich bottom MD yarn  261 ). Each stitching yarn forms one knuckle under a bottom CMD yarn beside a knuckle formed by the immediately adjacent unpaired bottom MD yarn, such that each stitching yarn pair and the unpaired bottom MD yarns form pairs of knuckles similar to the paired knuckles of the paired bottom MD yarns. For example, unpaired bottom MD yarn  261  forms knuckles below bottom CMD yarns  273  and  278  (see  FIG. 9E ). Stitching yarn  221   b  forms a knuckle under bottom CMD yarn  273 , and stitching yarn  221   a  forms a knuckle under bottom CMD yarn  278  (see  FIGS. 9D and 9F ). 
     Each pair of paired bottom MD yarns is offset from its neighboring paired bottom MD yarns by one bottom CMD yarn. For example, paired bottom MD yarns  251   a ,  251   b  pass under bottom CMD yarn  275 , and paired bottom MD yarns  252   a ,  252   b  pass under bottom CMD yarn  276 , which is offset from bottom CMD yarn  276  by one bottom CMD yarn. Each unpaired bottom MD yarn is also offset from its neighboring unpaired bottom MD yarn by one bottom CMD yarn. For example, unpaired bottom MD yarn  261  forms a knuckle under bottom CMD yarn  273 , and unpaired bottom CMD yarn  262  forms a knuckle under bottom CMD yarn  274 , which is offset from bottom CMD yarn  273  by one bottom CMD yarn. As a result, the pairs of knuckles formed by the paired bottom MD yarns on the bottom surface form one diagonal thereon, and the pairs of knuckles formed by an unpaired bottom MD yarn and a stitching yarn form a second diagonal on the bottom surface. The knuckles formed by the paired bottom MD yarns are offset from the knuckles formed by an unpaired bottom MD yarn and a stitching yarn are offset from each other by two bottom CMD yarns. 
     As can be seen in  FIG. 10 , the paired bottom MD yarns  251   a ,  251   b – 255   a ,  255   b  weave together with the bottom CMD yarns  271 – 280 . As such, in some embodiments the paired bottom MD yarns may be replaced by a single bottom MD yarn of flattened cross-section. This substitution is illustrated in  FIG. 11 , in which the paired bottom MD yarns  251   a ,  251   b – 255   a – 255   b  of the fabric  200  are replaced with bottom MD yarns  351 – 355  in a fabric  300 . The weave pattern of the fabric  300  can be the same as that of the fabric  200 , with the exception that the flattened bottom MD yarns  351 – 355  follow the paths of the pairs of bottom MD yarns  251   a ,  251   b – 255   a ,  255   b  (see exemplary bottom CMD yarn  371  also). A similar substitution of flattened yarns for the paired bottom MD yarns can be made in the other fabric embodiments described herein. Typically, the flattened yarn will have a height similar to that of the bottom MD yarn for which it is substituted and a width similar to that of two bottom MD yarns for which it is substituted. 
     The form of the yarns utilized in fabrics of the present invention can vary, depending upon the desired properties of the final papermaker&#39;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&#39;s fabric. For example, the yarns may be formed of polyester, polyarnide (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 polyarnide are preferred. 
     Fabrics such as those illustrated above can demonstrate improved seam strength compared to similar prior fabrics, which may permit the use of fewer ends for joining the fabric. Also, increases in fabric open area and/or permeability can be achieved. 
     Pursuant to another aspect of the present invention, methods of making paper are provided. Pursuant to these methods, one of the exemplary papermaker&#39;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.