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 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.

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. Generally, the flat-woven process is preferred, as it is

typically less expensive and more versatile than the endless weaving process.

Also, in many instances the felt is cut widthwise and reattached to simplify installation on a paper machine, in which case some of the advantages of endless weaving (such as the absence of a seam in the fabric) are lost.

Of course, flat weaving a fabric of a base layer requires that provision be made for joining it into endless belts. 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. To form the flat-woven 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 mutilfilament polymeric fiber 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) multifilament pin into the loops. Examples of this type of seam are described in U. S. Patent Nos. 4, 764,417 and 4,737,241 to Gulya and 4,601,785 to Lilja et al., the disclosures of which are hereby incorporated herein by reference in their entireties.

In some press felts, the base fabric layer itself contains multiple fabric layers (i. e., is a"laminated"base layer). For example, a felt may contain a "duplex"fabric (i. e., a fabric having upper and lower sets of machine direction yarns interwoven with at least one set of cross machine direction yarns-also known as a"double layer"fabric) as well as a finer mesh single layer fabric (i. e., a fabric having only one set each of machine direction yarns and cross machine direction yarns). This combination provides a good balance of strength and durability to the felt with relatively little marking. Typically, the felt is constructed by flat weaving the duplex fabric, endless weaving the single layer fabric, joining

the duplex fabric with a pin as described above, overlaying the single layer fabric over the duplex fabric, needling both fabric layers with batt to form machine side and paper side batt layers, removing the pin from the double layer fabric and cutting the batt layers and the single layer fabric at the seam to form a flat structure. Once at the paper mill, the felt is installed on the papermaking machine by inserting a new, more flexible pin into the duplex fabric layer.

This press felt construction has at least one significant shortcoming.

When the single layer fabric is cut, its yarns, particularly its cross machine direction yarns, tend to fray somewhat at the cut. Thus, when the felt is installed and operated on the paper machine, the frayed ends of the finer mesh single layer fabric can interfere with the manner in which the cut portion of the batt layer (which is often a flap of batt layer material) overlays the base fabric. As such, paper formed with such a felt can have an inconsistent appearance and be more susceptible to breaking on the paper machine due to the presence of the seam of the felt.

Summarv of the Invention In view of the foregoing, it is an object of the present invention to provide a press felt having a laminated base fabric with a reduced tendency for the fraying of yarns at the base fabric seam.

It is also an object of the present invention to provide such a press felt at a relatively low cost.

It is a further object of the present invention to provide a method for constructing such a press felt.

These and other objects are satisfied by the present invention, which is directed to a press felt having a laminated base fabric layer wherein one of the fabrics of the base fabric layer is joined via a pin seam as described hereinabove, and another of the fabrics of the base fabric layer includes a band of"low melt" material positioned over the pin seam. The papermaker's press felt of the present invention includes a base fabric layer (preferably sandwiched between a paper side batt layer and a machine side batt layer) comprising a first fabric and a second

fabric. The first fabric includes machine direction yarns and cross machine direction yarns interwoven with the machine direction yarns, wherein the first fabric has first and second ends with loops. The loops of the first end are interdigitated with the loops of the second end and receive a pin to form the first fabric into an endless belt having a seam. The second fabric is formed into an endless belt overlying the first fabric and includes machine direction yarns and cross machine direction yarns interwoven with the machine direction yarns. A set of the cross machine direction yarns is formed of a low melt material and forms a low melt band that traverses the fabric. The low melt band is positioned to overlie the seam of the first fabric. The low melt yarns, particularly after a finishing heat treatment, have a lower tendency to fray after cutting; thus, they are less likely to interfere with a cut seam in adjacent portions of attached batt layers.

Such a fabric can be constructed by a method of the present invention, which comprises the following steps. The machine direction yarns and cross machine direction yarns of the first fabric are interwoven such that the ends of the fabric have the aforementioned loops. The loops are then positioned in interdigitated relationship, and a pin is inserted into the loops to form a seam that joins the first and second ends of the first fabric, thereby forming the first fabric into an endless belt. The machine direction yarns and cross machine direction yarns of the second fabric are then interwoven (preferably through a flat weaving process) such that cross machine direction yarns formed of a low melt material forms a low melt band that traverses said fabric. The second fabric is attached to the first fabric such that the low melt band of the second fabric overlies the seam of the first fabric to form a laminated base fabric layer. After any batt layers are attached, the low melt band is heated to cause the low melt material to soften. A seam is then cut through the low melt band and any batt layers that correspond to the seam of the first fabric.

Brief Description of the Drawings Figure 1 is a schematic illustration of the press section of a paper machine employing a press felt of the present invention.

Figure 2 is an enlarged partial cutaway perspective view of the press felt of Figure 1.

Figure 3 is a greatly enlarged side section view of the press felt of Figure 1.

Figure 4A is a greatly enlarged partial perspective view of the pin seam of the press felt of Figure 1 in a joined condition.

Figure 4B is an enlarged partial perspective view of the pin seam of Figure 4A in an unjoined position.

Figure 5 is a schematic representation of a process for constructing the press felt of Figure 1.

Detailed Description of the Invention The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown and described. This invention may, however, be embodied in many 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. Like numbers refer to like components throughout. Components and layers may be exaggerated for clarity.

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 10, is illustrated in Figure 1. The press section 10 includes a press felt 14 that is installed upon and conveyed by a set of rollers 12.

In its travel, the felt 14 travels over a press roll 15. An opposed press roll 17 is positioned to, in conjunction with the felt 14 and press roll 15, form a N between the press rolls 15.

In operation, a paper web P is conveyed from a forming section 16 through the nip N formed by the press rollers 15,17, wherein pressure is applied to the paper web P by the press rolls 15,17. The pressure forces moisture from the paper web P that is absorbed by the felt 14. As the felt 14 is conveyed around its roller set 12, moisture is removed therefrom, and the felt 14 is conditioned by one or more suction boxes 20.

Figures 2 and 3 illustrate an enlarged section of the felt 14. As can be seen in Figure 2, the felt 14 includes a laminated base fabric layer 22 which comprises two separate fabrics: namely, a lower fabric layer comprising a duplex fabric 24 and an upper fabric layer comprising a single layer fabric 36. The duplex fabric 24 includes two sets of machine direction yarns 26 and one set of cross machine direction yarns 28 interwoven with the machine direction yams 26. The duplex fabric 24 is woven in a flat weave process; thus, in a flat condition, the duplex fabric 24 has two free ends 29a, 29b, one of which (29a) includes loops 30 (formed by machine direction yarns 26), and the other of which (29b) includes loops 32 formed by machine direction yams 26. When the duplex fabric 24 is in an endless condition such as that illustrated in Figures 2 and 3, the loops 30,32 are positioned in interdigitated fashion, and a pin 34 is inserted through the loops 30, 32 to join the ends 29a, 29b of the duplex fabric 24 (see Figures 4A and 4B).

Those skilled in this art will recognize that other types of fabrics can be employed as the lower fabric layer of the base fabric layer 22 in the manner of the duplex fabric 24, including single layer fabrics, other duplex fabrics, and triplex fabrics (i. e., those having two sets of machine direction yams and two sets of cross machine direction yarns). Virtually any weave pattern known to those skilled in this art, such as the illustrated plain weave, twills, satins, and the like, can be used

for this fabric layer. The lower fabric layer will typically, but not always, have a mesh that is somewhat more coarse than that of the upper fabric layer; it is preferred that the mesh of the lower fabric layer be between about 30 to 50 machine direction yarns and 50 to 100 cross machine direction yams per inch. The lower fabric layer should have the aforementioned loops 30,32 at its ends 29a, 29b to enable it to be joined into an endless belt with the pin. The construction of the loops 30,32 and pin 34 are known to those skilled in this art and need not be described in detail herein; exemplary loop and pin constructions are described in U. S. Patent Nos. 4,737,241 and 4,764,417 to Gulya.

Still referring to Figures 2 and 3, the single layer fabric 36 comprises machine direction yarns 38 interwoven with cross machine direction yarns 40 in a plain weave pattern. The single layer fabric 36 includes a low melt band 42 that traverses the width of the single layer fabric 36 over an area approximately six inches in length. The low melt band 42 includes low melt cross machine direction yams 44 that differ in material composition from the remaining cross machine direction yarns. As used herein, the term"low melt"means that the yarns have a lower melting point than at least the machine direction yarns of the lower fabric layer, and in many instances than the other yarns of both the upper and lower fabric layers. The melting point of the low melt yarns should be at least 25°C lower than that of the machine direction yarns of the lower fabric layer.

Exemplary low melt materials to be employed as cross machine direction yarns 44 in the low melt band 42 include nylons (including nylon 6, nylon 66, nylon 610, nylon 612 and nylon 12, and blends and copolymers thereof), polyesters and copolymers thereof and polypropylene and copolymers thereof.

Those skilled in this art will recognize that other types of fabrics can be employed as the upper fabric layer of the base fabric layer 22 in the manner of the single layer fabric 36, including other single layer fabrics, duplex fabrics, and triplex fabrics. Virtually any weave pattern known to those skilled in this art, such as the illustrated plain weave, twills, satins, and the like, can be used for this fabric layer. The mesh of the upper fabric layer may vary from between about 16 to 100 machine direction yams and 16 to 100 cross machine direction yarns per inch, but

typically the mesh will be somewhat finer than that of the lower fabric layer.

Those skilled in this art will also recognize that, although it is preferred for cost reasons to employ low melt yarns 44 as cross machine direction yarns in the low melt band 42 only, low melt yams can also be used as the machine direction yarns and/or the remaining cross machine direction yams of the upper fabric layer, or even as the cross machine direction yarns of the lower fabric layer.

Preferably, the single layer fabric 36 is woven in a flat weaving process that produces a fabric with two free ends. The single layer 36 is formed into an endless belt through a joining process such as heat welding, which forms a weld line 46, although other methods of joining known in the art may also be employed.

The form of the yarns employed in the lower and upper fabric layers of the base fabric layer 24 can vary, depending upon the desired properties of the final press felt. For example, the yarns may be multifilament yarns, monofilament yams, twisted or cabled multifilament or monofilament yarns, spun yarns, or any combination thereof. Also, the materials from which the yarns employed in the fabric layers are formed may be those commonly used in press felts, such as nylon, cotton, wool, polypropylene, polyester, aramid, polyamide, or the like, and blends and combinations thereof.

The felt 14 also includes two batt layers: a machine side batt layer 50 and a paper side batt layer 52. Illustratively and preferably, these batt layers 50, 52 are attached to the base fabric layer 22 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 50,52 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 22. Preferred materials for the batt layers 50,52 include polyamide, polyester and blends thereof. The weight and thickness of the batt layers 50,52 can vary, although it is preferably that the ratio of batt weight to fabric weight is about between about 0.5 and 2.0, with 1.0 being more preferred.

Also, in some embodiments, it may be desirable to have additional batt layers or to

omit either or both of the batt layers 50,52.

Notably, the felt 14 includes a seam cut 48. The seam cut 48 extends through the paper side batt layer 52, the single layer fabric 36, and the machine side batt layer 50. Illustratively and preferably, the seam cut 48 is made at an angle of between about 30 and 90 degrees to the plane of the base fabric layer 22, and a flap 52a is formed by loosening the portion of the paper side batt layer 52 adjacent the seam cut 48. This process is described in detail in the aforementioned U. S. Patents to Gulya and Lilja. Of course, no cut is necessary for the duplex fabric 24, as the pin 34 can simply be removed to enable the ends 29a, 29b of the duplex fabric 24 to be separated.

Figure 5 illustrates an exemplary manufacturing process for the felt 14. Initially, the duplex fabric 24 is flat woven such that machine direction loops 30,32 are created on the ends 29a, 29b. A pin 60 (which is typically larger and less flexible than the pin 34 described above) is inserted through the loops 30,32 (as they are interdigitated) to join them and thereby form the duplex fabric 24 into an endless belt. Separately, the single layer fabric 36 is woven in a flat weaving process. The single layer fabric 36 is formed into an endless belt with a heat welding process, such as one that employs heat or ultrasonic radiation. The single layer fabric 36 is then positioned to overlie the duplex fabric 24 such that the low melt band 42 overlies the pin 34, and the machine side and paper side batt layers 50,52 are needled to the base fabric layer 22.

Once the batt layers 50,52 have been added, the entire felt 14 is then heat treated at a temperature sufficient to cause softening of the yarns 44 of the low melt band 42 without unduly softening the other yarns of the base fabric 22, and in particular the machine direction yarns 26. Typically, the heat treatment is carried out at a temperature of between about 130° to 200° C. The pin 60 is then removed, and the seam cut 48 is formed with blades or other cutting devices through the machine side and paper side batt layers 50,52 and the single layer fabric 36. The felt 14 can then be shipped in its flat form to a paper mill, where the pin 34 can be inserted into the machine direction loops 30,32 as the felt 14 is installed on the upper rolls 12.

Importantly, when the seam cut 48 is made, the yarns of the single layer fabric 36, and in particular the cross machine direction yarns 38 have a far lower tendency to fray than the fabrics of prior art felts. This reduced fraying is the result of the inclusion of the low melt cross machine direction yarns 44 and the low melt band 42. As described, during the heat treatment of the felt 14, the softening of the low melt cross machine direction yarns 44 causes the agglomeration of the cross machine yams 44, the machine direction yarns 38 and the fibers of the paper side batt layer 52. As a result, the flap 52a adjacent to the seam cut 48 lays much more uniformly than has been the case in prior art fabrics.

The invention will now be more particularly described in the following non-limiting example.

EXAMPLE A press felt was constructed according to the following parameters

MD yarns CMD yams Mesh Base Fabric Layer Size Material Size Materials (inches) (inches) Duplex Layer 0.040 Nylon 0.040 Nylon 40x80 Single Layer 0.08x4 Cabled 0.080 Nylon 32x12 nylon Low Belt Band------0. 080 Nylon 32x12 copolymer Batt Layers Material Weight (glm2) Machine Side Nylon staple 150 Paper Side Nylon staple 780

Heat Treatment: 3 minutes at 175°C.

The resulting press felt successfully produced linerboard paper.

The foregoing is illustrative of the present invention and is 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. In the claims, means- plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.