Patent Description:
The present invention relates generally to papermaking, and more particularly to fabrics used in papermaking.

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 dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.

Press felts typically include one or more base fabric layers; these can be "flat-woven" and formed after weaving into an endless belt, or can be woven in endless form.

Of course, weaving a fabric of a base layer requires that provision be made for joining it into an endless belt. Such joints should be constructed in such a manner that they are sufficiently strong to withstand the extreme load, temperature, and wear conditions the press felt experiences, yet do not cause the surface of the press felt above the seam to unduly mark the paper. One popular method of joining the base fabric of a press felt is to form loops with machine direction yarns on each end of the base fabric; these loops are often formed over a pin or "pintle" during the weaving process. To form the base fabric into an endless belt, the ends of the fabric are placed adjacent to each other, with each of the loops on one end positioned between two loops on the other end in interdigitating fashion. A "pin" (usually formed of a single monofilament or multiple monofilament strands) is then inserted into all of the loops to join the ends. After the batt layer(s) are needled or otherwise attached to the base layer, the batt layer(s) are cut at the seam location, the pin is removed, and the finished press felt is shipped to a paper mill. Once at the paper mill, the press felt can be installed by placing it onto a paper machine, then inserting another (usually more flexible) monofilament pin or pintle into the loops. Examples of this type of seam are described in <CIT> and <CIT>; <CIT>; <CIT>, and <CIT>.

Base fabrics of press felts have taken a variety of configurations. In one configuration, the "fabric" is actually two separate fabrics that form a total of three layers. The bottom fabric is a double layer fabric that provides the seam loops, with the top fabric being a single layer fabric that is cut after weaving, combination with the bottom fabric, and needling of an overlying batt layer. An exemplary press felt of this configuration is shown in International Patent Application No. <CIT>. One apparent disadvantage of a fabric of this configuration is the need to cut the top fabric layer, which then has loose ends that can impact the manner in which the overlying batt lays over the fabric. A single layer fabric does not have this disadvantage. Prior art showing fabrics with multiple pintles can be seen in <CIT> and <CIT>.

As a first aspect, embodiments of the invention are directed to a fabric for a press felt as defined in claim <NUM> and comprising a plurality of repeat units, each of the repeat units comprising a plurality of cross machine direction (CMD) yarns and a plurality of machine direction (MD) yarns interwoven with the CMD yarns, the MD yarns and CMD yarns being part of a single fabric layer, wherein the machine direction yarns comprise a first set of MD yarns and a second set of MD yarns, wherein the first set of MD yarns include seam loops at their ends that capture a first pintle, and wherein the second set of MD yarns include loops at their ends that capture a second pintle that is positioned above the first pintle.

As a second aspect as defined in claim <NUM>, embodiments of the invention are directed to a method of making a fabric for a press felt for a papermaking machine, comprising:.

The present invention will now be described more fully hereinafter, in which examples for the understanding of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the examples set forth herein. Rather, these are provided so that this disclosure will be thorough and complete. 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. For example, if the device in the figures is turned over, elements described as "under" or "beneath" other elements or features would then be oriented "over" the other elements or features.

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 a papermaking machine, and a direction parallel to the fabric surface and transverse to the direction of travel. Also, both the flat weaving and endless 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.

Referring now to the drawings, a papermaking machine press section, designated broadly at <NUM>, is illustrated in <FIG>. The press section <NUM> includes a press felt <NUM> that is installed upon and conveyed by a set of rollers <NUM>. In its travel, the felt <NUM> passes over a press roll <NUM>. An opposed press roll <NUM> is positioned so that, in conjunction with the felt <NUM> and press roll <NUM>, it forms a nip N between the press rolls <NUM>, <NUM>.

In operation, a paper web P is conveyed from a forming section <NUM> through the nip N formed by the press rollers <NUM>, <NUM>, wherein pressure is applied to the paper web P by the press rolls <NUM>, <NUM>. The pressure forces moisture from the paper web P that is absorbed by the felt <NUM>. As the felt <NUM> is conveyed around its roller set <NUM>, moisture is removed therefrom, and the felt <NUM> is conditioned by one or more suction boxes <NUM>.

<FIG> shows the seam area of a base fabric <NUM> of a prior felt <NUM>, with a portion of the seam <NUM> of the felt <NUM> being shown therein. The fabric <NUM> includes cabled CMD yarns <NUM> interweaving with two different varieties of MD yarns. More specifically, MD yarns <NUM> are monofilament yarns, and MD yarns <NUM> are cabled yarns. The monofilament MD yarns <NUM> alternate with the cabled MD yarns <NUM> in a <NUM>:<NUM> pattern as the MD yarns <NUM>, <NUM> interweave with the CMD yarns <NUM>. The weaving pattern of the MD yarns <NUM>, <NUM> and the CMD yarns <NUM> can be any weave pattern known to those of skill in this art to be appropriate for a base fabric of a press felt and need not be described in detail herein.

As can be seen in <FIG>, the monofilament MD yarns <NUM> are interwoven with the CMD yarns <NUM> such that seam loops 114a are formed as each MD yarn <NUM> "doubles back" on itself to weave with the CMD yarns <NUM>. The seam loops 114a capture a pintle <NUM> or other seaming member within the seam <NUM>. As can be seen in <FIG>, the seam loops 114a formed in one end of the fabric <NUM> interdigitate with the seam loops 114a from the other end of the fabric <NUM> to create space into which the pintle <NUM> can be inserted to form the seam <NUM>.

As can also be seen in <FIG>, as the cabled MD yarns <NUM> interweave with the CMD yarns <NUM>. <NUM>, they do not form seam loops when they "double back" to weave with the CMD yarns <NUM>. Instead, when the cabled yarns <NUM> "double back", they do so by forming a loop around the CMD yarn <NUM> nearest the seam <NUM>. Thus, the ends 116a of the cabled MD yarns <NUM> are routed short of the seam <NUM> and are devoid of seam loops. It can be seen that each end 116a is aligned across the seam <NUM> with a seam loop 114a of a monofilament MD yarn <NUM> that is routed to the seam <NUM> from the opposite side of the seam <NUM>.

Referring still to <FIG>, the press felt <NUM> includes two batt layers: a machine side batt layer <NUM> and a paper side batt layer <NUM>. Illustratively, these batt layers <NUM>, <NUM> are attached to the base fabric layer <NUM> through a needling process, although other attachment techniques, such as heat bonding and adhesives, can also be used with the present invention. The machine side and paper side batt layers <NUM>, <NUM> should be formed of material, such as a synthetic fiber like acrylic, aramid, polyester, or nylon, or a natural fiber such as wool, that assists in wicking water away from the base fabric layer <NUM>. Exemplary materials for the batt layers <NUM>, <NUM> include polyamide, polyester and blends thereof. The weight and thickness of the batt layers <NUM>, <NUM> can vary, although it is typical that the ratio of batt weight to fabric weight is between about <NUM> and <NUM>, with <NUM> being more common. Also, in some embodiments, it may be desirable to have additional batt layers or to omit either or both of the batt layers <NUM>, <NUM>.

The fabric. <NUM>, which is described in detail in <CIT>, can provide performance advantages to the felt <NUM>. The use of the monofilament MD yarns <NUM> can provide a smooth, stable seam, while the inclusion of the cabled MD yarns <NUM> can improve anchoring of the batt fiber. In the past, typically press felts with cabled MD yarns lacked seam loops, as the cabled structure of the yarns was not conducive to forming seam loops that were easily interdigitated and/or filled with a pintle. The use of MD monofilament yarns for seam loops in combination with cabled yarns can enable the felt to achieve both acceptable fiber anchoring and easy installation.

Although these advantages are desirable, a potential shortcoming of the fabric <NUM> can occur when the fabric <NUM> and/or felt <NUM> are under tension, as when the felt <NUM> is installed on a papermaking machine. Tension can cause the ends 116a of the yarns <NUM> to "pull back" the CMD yarn <NUM> nearest the seam <NUM> (labelled as yarn <NUM>' in <FIG>) away from the seam <NUM>. As a result, open areas may form between the ends 116a and the seam <NUM>, which can produce an uneven, inconsistent seam.

This disadvantage can be addressed by a fabric <NUM> according to embodiments of the invention, shown in <FIG>. The fabric <NUM> has a similar weave pattern to the fabric <NUM> discussed above, with monofilament MD yarns <NUM> and cabled MD yarns <NUM> interwoven with CMD yarns <NUM>. However, as shown in <FIG>, the monofilament MD yarns <NUM> are woven such that their ends 214a form loops over a primary pintle <NUM>, and the cabled MD yarns <NUM> are woven such that their ends 216a form loops over a secondary pintle <NUM> that is located above the primary pintle <NUM>. Thus, the ends 216a of the cabled MD yarns <NUM> are positioned some distance from the CMD yarn <NUM> that is nearest the seam <NUM>.

After weaving, the auxiliary pintle <NUM> is removed. Removal of the auxiliary pintle <NUM> results in the ends 216a of the cabled MD yarns <NUM> remaining positioned over the ends 214a of the monofilament MD yarns <NUM> as they are looped over the primary pintle <NUM>.

The fabric <NUM> is then subjected to a heat-setting process. In some embodiments, the heat-setting process involves subjecting the fabric <NUM> to some degree of tension; this tension tends to draw the ends 216a of the cabled MD yarns <NUM> slightly away from the seam <NUM>, to a positon in which the ends 216a are adjacent, and in some instances in contact with and may slightly overlie, the ends 214a of the monofilament MD yarns <NUM> that approach the seam <NUM> from the opposite side of the seam <NUM>. For example, in <FIG>, it can be seen that the end 216a', which approaches the seam <NUM> from the left side of the figure, is adjacent the end 214a', which approaches the seam <NUM> from the right side of the figure. Consequently, the ends 216a of the cabled MD yarns <NUM> can partially or completely fill the gap g that can otherwise form between the ends of the cabled MD yarns and the seam as described above in connection with Patent Publication No. <CIT>, supra.

Typically, after heat-setting, the gap between an end 216a and an adjacent end 214a from the opposite direction is between about -<NUM> to <NUM> (wherein a negative value for the gap g represents the end 216a slightly overlying its adjacent end 214a). In a typical fabric, the primary pintle <NUM> is removed and replaced with a smaller pintle or cable for use; in instances in which the ends 216a overlie their adjacent ends 214a, the use of a lower diameter pintle (e.g., replacing a <NUM>-<NUM> primary pintle <NUM> with a <NUM>-<NUM> pintle), any overlying ends 216a no longer overlie the ends 214a, but instead drop to a position that is in-plane with the ends 214a.

With respect to any of the illustrated or described embodiments, the press felt of the invention may also include one or more batt layers such as those described above in connection with the felt <NUM> and fabric <NUM>.

Although the MD yarns <NUM> are illustrated and described as being cabled monofilament yarns, in some embodiments the MD yarns <NUM> may be cabled or twisted monofilament/multifilament and/or monofilament/card yarn combinations. Also, although the MD yarns <NUM> are illustrated and described as being monofilament yarns, in some embodiments the MD yarns <NUM> may be cabled or twisted monofilament/multifilament and/or monofilament/card yarn combinations. Further, the CMD yarns <NUM> are illustrated and described as being cabled monofilaments, but may in some embodiments be uncabled monofilaments. Other yarn varieties may also be employed.

Yarn sizes and configurations may vary with the desired properties of the press felt. Typical yarn diameters include monofilament MD yarns <NUM> of between about <NUM> and <NUM>. The cabled MD yarns <NUM> are typically formed of two or three yarns cabled together, with the typical diameter of the individual yarns (prior to cabling) being <NUM> to <NUM>. Similarly, the CMD yarns <NUM> are typically formed of two or three monofilament yarns cabled together, with the typical diameter of the individual monofilament yarns being <NUM> to <NUM>.

In one particular embodiment, the fabric <NUM> comprises the following yarns:.

Those skilled in this art will also appreciate that, although the monofilament MD yarns <NUM> and the cabled MD yarns <NUM> are shown in an alternating <NUM>:<NUM> pattern, these yarns may be included in other ratios. For example, there may be <NUM> monofilament MD yarn for every two or three cabled MD yarns, two or three monofilament MD yarns for every cabled MD yarn, three monofilament MD yarns for every two cabled MD yarns, two monofilament MD yarns for every three cabled MD yarns, and the like.

It should also be noted that in some embodiments, the fabric <NUM> is endless woven.

Claim 1:
A fabric (<NUM>) for a press felt (<NUM>), comprising a plurality of repeat units, each of the repeat units comprising a plurality of cross machine direction, CMD, yarns (<NUM>) and a plurality of machine direction, MD, yarns (<NUM>, <NUM>) interwoven with the CMD yarns (<NUM>), the MD yarns (<NUM>, <NUM>) and CMD yarns (<NUM>) being part of a single fabric layer, wherein the machine direction yarns (<NUM>, <NUM>) comprise a first set of MD yarns (<NUM>) and a second set of MD yarns (<NUM>), wherein the first set of MD yarns (<NUM>) include seam loops at their ends (214a) that capture a first pintle (<NUM>), and wherein the second set of MD yarns (<NUM>) include loops at their ends (216a) that capture a second pintle (<NUM>) that is positioned above the first pintle (<NUM>).