Patent Application
20070062598
This invention relates generally to woven fabrics, and relates more specifically to woven fabrics for papermakers.
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 rollers. 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 alone or with assistance from one or more suction boxes located on the lower surface (i.e., the “machine side”) of the upper run of the fabric.
After leaving the forming section, the paper web is transferred to a press section of the paper machine, in which 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 on the press felt. The paper is then conveyed to a drier section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.
Typically, papermaker's fabrics are manufactured as endless belts by one of two basic weaving techniques. In the first of these techniques, fabrics are flat woven by a flat weaving process, with their ends being-joined to form an endless belt by any one of a number of well-known joining methods, such as dismantling and reweaving the ends together (commonly known as splicing), or sewing a pin-seamable flap on each end or a special foldback, then reweaving these into pin-seamable loops. 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 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. 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 papermaker's fabric on the papermaking machine, and a direction parallel to the fabric surface and traverse to the direction of travel. 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 and an absence of wire marking are typically important considerations in papermaking, especially for the forming section of the papermaking machine, where the wet web is initially formed. Wire marking is particularly problematic in the formation of fine paper grades, as it can affect a host of paper properties, such as sheet mark, porosity, “see through” and pin holing. Wire marking is typically the result of individual cellulosic fibers being oriented within the paper web such that their ends reside within gaps between the individual threads or yarns of the forming fabric. This problem is generally addressed by providing a permeable fabric structure with a coplanar surface that allows paper fibers to bridge adjacent yarns of the fabric rather than penetrate the gaps between yarns. As used herein, “coplanar” means that the upper extremities of the yarns defining the paper-forming surface are at substantially the same elevation, such that at that level there is presented a substantially “planar” surface. Accordingly, some paper grades, particularly fine paper grades intended for use in quality printing, carbonizing, cigarettes, electrical condensers, and the like, and in some instances tissue paper grades, have typically heretofore been formed on very finely woven or fine wire mesh forming fabrics.
Typically, such finely woven fabrics 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 effect 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 weaves, 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 paper side 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. 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, and U.S. Pat. No. 5,437,315 to Ward.
One particularly desirable type of triple layer fabric is illustrated in U.S. Pat. Nos. 5,967,195 and 6,145,550 to Ward. The fabrics described therein include pairs of stitching yarns between adjacent top CMD yarns that alternately interweave with the top and bottom MD yarns of the fabric. They do so in such a manner that they integrate with and “complete the weave” of the weave pattern of the top MD and top CMD yarns. Such a papermaking surface can provide good fiber support, drainage and interlaminar wear resistance. Alternative fabrics of this type are illustrated in U.S. Pat. No. 5,826,627 to Seabrook et al. These fabrics typically have a plain weave surface (i.e., a surface in which an “over 1/under 1” pattern is followed by both MD and CMD yarns) and are used for fine paper grades. Unfortunately, plain weave fabrics may be susceptible to wear on the papermaking surface, particularly with the top CMD yarns because the single knuckles of a plain weave do not provide a great deal of surface area for wear. Longer CMD floats are typically avoided on the papermaking surface to reduce the tendency for the paper to suffer from diagonal marking.
In some instances, particularly instances in which the paper being made is a tissue paper grade, it may be desirable to produce a forming fabric that has increased wear properties but still provides many of the advantages of a triple layer fabric. A weave pattern that is relatively easily woven on available looms would also be desirable, as would a weave pattern that avoids marking.
The present invention is directed to papermaker's forming fabrics that can provide an adequate papermaking surface for certain grades of paper (such as tissue paper) with increased wear characteristics. As a first aspect, embodiments of the invention are directed to a triple layer papermaker's fabric comprising: a set of top machine direction yarns; a set of top cross machine direction yarns interwoven with the top machine direction yarns to form a top fabric layer; a set of bottom machine direction yarns; a set of bottom cross machine direction yarns interwoven with the bottom machine direction yarns to form a bottom fabric layer; and a plurality of stitching yarns interwoven with the top and bottom fabric layers. The top machine direction yarns, top machine direction yarns, bottom machine direction yarns, bottom cross machine direction yarns, and stitching yarns are interwoven as a series of repeat units. In each of the repeat units, each top cross machine direction yarn forms multiple paper side floats by passing over some of the top machine direction yarns and interweaving beneath a top machine direction yarn on each side of the float, and at least a first of the paper side floats passes over a first number of top machine direction yarns, and at least a second of the paper side floats passes over a second number of top machine direction yarns, and the difference between the first number and the second number is one.
As a second aspect, embodiments of the present invention are directed to a triple layer papermaker's fabric comprising: a set of top machine direction yarns; a set of top cross machine direction yarns interwoven with the top machine direction yarns to form a top fabric layer; a set of bottom machine direction yarns; a set of bottom cross machine direction yarns interwoven with the bottom machine direction yarns to form a bottom fabric layer; and a plurality of stitching yarn pairs interwoven with the top and bottom fabric layers. The top machine direction yarns, top machine direction yarns, bottom machine direction yarns, bottom cross machine direction yarns, and stitching yarns are interwoven as a series of repeat units. In each of the repeat units, each top cross machine direction yarn forms multiple paper side floats by passing over some of the top machine direction yarns and interweaving beneath a top machine direction yarn on each side of the float, the floats being non-uniform for each top cross machine direction yarn. Each stitching yarn pair forms a cross machine direction yarn unit having multiple paper side floats by passing over some of the top machine direction yarns and interweaving beneath a top machine direction yarn on each side of each float, the floats being non-uniform for each cross machine direction yarn unit.
As a third aspect, embodiments of the present invention are directed to a method of forming paper with the above-described fabrics. The method comprises the steps of: providing such a fabric; applying paper stock to the fabric; and removing moisture from the paper stock to form paper. In some embodiments, the paper stock is selected and applied such that the paper formed is tissue paper.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain principles of the invention.
The present invention will now be described more particularly hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. The invention, however, be embodied in many different forms and is not limited to the embodiments set forth herein; rather, these embodiments are provided so that the disclosure will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like components throughout. The dimensions and thicknesses for some components and layers may be exaggerated for clarity.
One aspect of the present invention is directed to triple layer papermaker's forming fabrics that include both a top fabric layer and a bottom fabric layer. These fabrics are “true” triple layer fabrics in that they include sets of MD yarns and CMD yarns that only weave in the top fabric layer, as well as sets of MD yarns and CMD yarns that only weave in the bottom fabric layer. The fabrics also include pairs of adjacent CMD yarns that together replace the equivalent of a single CMD yarn (i.e., they form a “CMD yarn unit”) in the weave pattern on the papermaking surface. These yarns are woven such that when an upper portion of one yarn in the pair is weaving in the top fabric layer so as to complete the weave pattern on the papermaking surface, a lower portion of the second yarn in the pair weaves below the papermaking surface. Throughout the fabric, these yarns trade these positions. The lower portion of at least one of the yarns in the pair also drops down to the bottom fabric layer at one or more points so as to bind the top and bottom fabric layers together. Herein, these yarn pairs are referred to as “stitching yarn pairs” (even in those embodiments in which only one yarn of the pair actually “stitches” with the bottom fabric layer). Individual yarns from these yarn pairs are typically referred to as “stitching yarns.”
Also, as one yarn interlaces with one or more other yarns, the segment of yarn that passes over other yarns is called a “float”. Typically, a float is identified by the number of yarns it passes over; e.g., one yarn passing over two adjacent yarns is a “2-yarn float” (a single yarn float is often also called a “knuckle”).
Referring now to
The top layer 20a is formed with ten top MD yarns sequentially designated at 21-30, ten top CMD yarns sequentially designated at 31-40, and portions of ten stitching yarn pairs designated sequentially at 41a, 41b-50a, 50b. Each top CMD yarn 31-40 interweaves with the top MD yarns 21-30 in an “under 1/over 2/under 1/over 2/under 1/over 3” pattern; thus, the floats formed by the top CMD yarn 31 over the top MD yarns 21-30 are non-uniform (i.e., at least one of the top CMD floats differs in length from the other top CMD floats). The weave pattern is exemplified in
The remaining top CMD yarns 22-30 follow a similar path through the top MD yarns 21-30 (in which they form non-uniform top CMD floats), but each is offset from its adjacent top CMD yarns by two top MD yarns. Thus, top CMD yarn 32 passes over top MD yarns 26, 27, 28 in its “over 3” float, while adjacent top CMD yarn 31 passes over top MD yarns 28, 29, 30 in its “over 3” float. As such, the “over 3” float of top CMD yarn 32 is offset by two top MD yarns from top CMD yarn 31. This offset of two top MD yarns continues with the ensuing top CMD yarns 33-40.
Referring still to
This same “under 1/over 2/under 1/over 2/under 1/over 3” sequence is followed by the other stitching yarn pairs 42a, 42b-50a, 50b, but each is offset by from its adjacent top CMD yarns by one top MD yarn. Thus, for stitching yarn pair 42a, 42b, the “over 3” segment is formed by stitching yarn 42b over top MD yarns 25, 26, 27, whereas for adjacent top CMD yarn 32, the “over 3” segment is formed over top MD yarns 26, 27, 28 (the designations of the stitching yarns herein are such that all of the stitching yarns designated with an “a” form the “over 2/under 1/over 2” segment, and those designated with a “b” form the “over 3” segment).
The afore-described interweaving of the top CMD yarns and the stitching yarns with the top MD yarns forms a pattern in which each top CMD yarn and each top CMD yarn unit (formed by the combination of the upper portions of two stitching yarns of a pair) follows the “under 1/over 2/under 1/over 2/under 1/over 3” sequence, and each adjacent top CMD yarn or top CMD yarn unit is offset from its adjacent CMD yarn unit or top CMD yarn by one top MD yarn. This provides a papermaking surface to the top layer 20a that is entirely filled with yarns forming the “under 1/over 2/under 1/over 2/under 1/over 3” sequence, each offset by one top MD yarn.
It should also be noted that the stitching yarns 41a, 41b-50a, 50b are woven as “reversed picks”. This term refers to the relative positions of the upper portions of adjacent stitching yarn pairs. The presence of reversed picks in a double-pick-stitched triple layer fabric can be established by locating transitional top MD yarns; these are the top MD yarns under which stitching yarns pass when transitioning from the top layer 20a to the bottom layer 20b or vice versa; for example, the transitional top MD yarns for the stitching yarns 41a, 41b are top MD yarns 26 and 30. Once the transitional top MD yarns for each stitching yarn pair are located, the most predominant diagonal (minimum step) formed by their intersection with the stitching yarns is identified (in this instance, the most prominent diagonal would be a diagonal line formed between an intersection K1 of stitching yarns 41a, 41b and top MD yarn 30, an intersection K2 of stitching yarns 42a, 42b and top MD yarn 28, an intersection K3 of stitching yarns 43a, 43b and top MD yarn 26, and so on). The positions of the stitching yarns on-each side of this diagonal relative to each other and to the top CMD yarn between them are examined. If the upper portions of successive stitch yarn pairs on one side of this diagonal are closer to each other (i.e., both are closer to the top CMD yarn between them than their respective paired yarns) in some cases and farther apart in others, then the fabric consists of at least some reversed picks.
To continue with the example above, following the imaginary diagonal line through intersections K1, K2, K3 discussed above, the segments of stitching yarn 41b, 42b that are located on the left side of the diagonal are farther apart from one another than the segments of stitching yarns 41a, 42a (in other words, stitching yarns 41a, 42a are woven directly adjacent top CMD yarn 32, whereas stitching yarns 41b, 42b are not directly adjacent top CMD yarn 32 because stitching yarns 41a, 42a are between them). Moving to the next sets of yarns along the diagonal, the segments of stitching yarns 42b, 43b located on the left side of the diagonal are closer to one another than are the segments of stitching yarns 42a, 43a. Thus, on the left side of the diagonal, the “farther” positions of stitching yarns 41b, 42b reversed to a “closer” position for stitching yarns 42b, 43b. As such, these yarns represent “reversed picks.”
It has been discovered that by reversing the stitching yarns as discussed, marking that may be present on paper produced by the fabric due to the presence of diagonals such as that discussed above can be diminished. Although in the illustrated fabric 20 all of the stitching yarns are “reversed”, those skilled in this art will appreciate that a lower percentage (such as 50, 40, 30, or 25 percent or the like) of the stitching yarn pairs may be reversed.
Referring now to
Each of the stitching yarns 41a, 41b, 50a, 50b also passes below a bottom CMD yarn to stitch the top and bottom layers 20a, 20b together. Referring to
Adjacent stitching yarn pair stitching locations are offset from one another by two bottom MD yarns. Thus, as shown in
In the configuration described herein, it has been determined that the employment of non-uniform top CMD floats can improve the wear properties of the papermaking surface compared to fabrics that have a plain weave surface. The additional float length offered by the “over 2” and “over 3” floats can improve the wear characteristics of the fabric by providing additional CMD surface area for wear. The similarity between the non-uniform floats (i.e., they differ in length by only one yarn) can reduce any marking or other difference in performance that might otherwise occur when floats of different lengths are used. At the same time, the absence of an inordinately long CMD float within a yarn on the papermaking surface can assist in avoiding marking of the paper that might otherwise occur. The presence of 2- and 3-yarn floats on the papermaking surface can provide a sufficiently coplanar surface for some types of paper, particularly tissue paper. The illustrated configuration can be employed with a 20 harness triple layer fabric, which, if it were to have a uniform float repeat for each yarn in a non-plain weave fabric, would be limited to floats of 4 and 9 yarns, each of which is likely to have significant diagonal marking. Thus, if a weaver has a 20 harness loom available, a fabric of the illustrated weave pattern can produce acceptable tissue paper with improved wear properties.
Those skilled in this art will appreciate that the weave pattern may be modified from that illustrated and described. For example, the stitching yarns may be woven as traditional, rather than reversed, picks, and/or one of the stitching yarns may be woven with the bottom layer while the other is not (a so-called “phantom stitch” construction). Also, the stitching yarns may be woven after every two or every three top CMD yarns rather than after every top CMD yarn. Moreover, the stitching yarns may not be present in pairs, but instead may be present as single stitching yarns positioned between adjacent top CMD yarns. Also, the top and bottom CMD yarns may be offset from one another by a different number of top MD yarns.
The bottom layer weave pattern may also be modified in many ways. For example, more or fewer bottom CMD yarns may be included, the stitching yarns may stitch at different locations, and/or the bottom MD and CMD yarns may be woven in different patterns. Exemplary alternative bottom layer weave patterns are shown in U.S. Pat. Nos. 6,244,306; 5,967,195; and 6,253,796, the disclosures of each of which are hereby incorporated herein in their entireties.
Referring now to
The fabric 100 also includes stitching yarn pairs (one of which is illustrated in
Those skilled in this art will appreciate that adjacent top CMD yarns, stitching yarns, and bottom CMD yarns will be offset from one another to form a suitable integrated weave pattern. For example, adjacent top CMD yarns may be offset by two top MD yarns, stitching yarn pairs may be offset from each other by two top MD yarns and from adjacent top CMD yarns by one top MD yarn, and adjacent bottom CMD yarns may be offset from each other by three bottom MD yarns. Other patterns and offsets may also be suitable.
Similar to the fabric embodiments described in connection with
The general concept of non-uniform top CMD floats demonstrated by the fabrics 20 and 100 above can also be utilized in fabrics woven on different numbers of harnesses. For example, a 24 harness fabric embodiment designated broadly at 200 is illustrated in
As another example, a 16 harness fabric embodiment designated broadly at 300 is illustrated in
Each of the embodiments described above may provide improved papermaking surface wear over a plain weave fabric, and may provide improved marking performance over fabrics with longer top CMD floats. As shown in the illustrated embodiments, the non-uniform CMD floats may differ from one another by one top MD yarn (i.e., the floats for a single top CMD yarn will be a combination of 2-yarn floats and 3-yarn floats, or a combination of 1-yarn floats and 2-yarn floats), as this can reduce performance differences in different portions of the fabric and reduce marking of the paper.
The fabrics illustrated and otherwise described and claimed herein may be employed in a variety of applications, including forming fine paper grades, tissue paper, brown paper and newsprint, but may be especially beneficial for tissue paper applications.
The configurations of the individual yarns utilized in the fabrics of the present invention can vary, depending upon the desired properties of the final papermakers' fabric. For example, the yarns may be multifilament yarns, monofilament 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 papermakers' fabric. For example, the yarns may be formed of polypropylene, polyester, nylon, or the like. The skilled artisan should select a yarn material according to the particular application of the final fabric.
Regarding yarn dimensions, the particular size of the yarns is typically governed by the mesh of the papermaking surface. In a typical embodiment of the triple layer fabrics disclosed herein, preferably the diameter of the top MD yarns, the top CMD yarns and the stitching yarns is between about 0.10 and 0.22 mm, the diameter of the bottom MD yarns is between about 0.14 and 0.27 mm, and the diameter of the bottom CMD yarns is between about 0.18 and 0.50 mm. Those of skill in the art will appreciate that yarns having diameters outside the above ranges may be used in certain applications.
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. In particular, paper stock suitable for forming tissue paper may be employed. As the details of how the paper stock is applied to the forming fabric and how moisture is removed from the paperstock is well understood by those of skill in the art, additional details regarding this aspect of the present invention need not be provided herein.
The foregoing embodiments are illustrative of the present invention, and are not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/719,675, filed Sep. 22, 2005, the disclosure of which is hereby incorporated herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60719675 | Sep 2005 | US |
