Press fabrics for paper machines

Abstract: A press fabric for use on the press section of a paper machine has a multilayer structure, and is woven according to techniques normally applied in the weaving of forming fabrics. The press fabric is woven from at least one system of warp yarns (24) and two or more layers (10,14,18) of weft yarns (12,16,20,22), with the yarn sizes and weave patterns chosen with a view toward providing the resulting press fabric with a fine paper-contacting surface, and ample void volume. One layer (14) of the two or more layers of weft yarns includes, or is entirely composed of, multicomponent yarns (16) having a plurality of load-bearing members. The multicomponent yarns (16) may be multifilament or multistrand yarns composed of fine filaments, or may be polyurethane-coated monofilament yarns, and provide the press fabrics with a compressible and resilient structure. The multifilament or multistrand yarns may also be polyurethane-coated.

Description: The present invention relates to a press fabric for use on the press section of a paper machine. The press section of a paper machine generally includes at least one press designed to remove water from a fibrous web, which is a nascent paper sheet. Each such press includes a press nip, which is a region of elevated compression to squeeze water from the fibrous web. The press nip itself may be formed between two adjacent press rolls. Alternatively, according to a more modern press design, the press nip may be formed between a press roll and an arcuate pressure shoe having a cylindrically concave surface of radius substantially equal to that of the press roll. A press nip formed in this manner is several times longer, in the machine, or longitudinal, direction than one formed between two press rolls and is commonly referred to as an extended nip press. Those in the papermaking industry are continually seeking ways to provide a quality paper product more efficiently and economically. In particular, paper manufacturers are continually striving to reduce the energy costs which accompany paper production. These costs arise because steam is normally provided to heat, from within, the series of rotatable dryer cylinders which make up the dryer section, a final stage in a paper machine. It is in the dryer section that the water remaining in the fibrous web, upon its exit from the press section, is removed by evaporation by passing the web around each in a series of dryer cylinders. The less water that remains in the fibrous web leaving the press section, the less water will have to be removed by evaporation in the dryer section, and, as a consequence, the lower will be the costs associated with the production of steam for that section. The present invention is directed to this need to remove more water from the fibrous web in the press section, thereby leaving less to be removed in the dryer section. As previously noted, water is removed from the fibrous web in the press section by passing the web through at least one press nip. More particularly, the fibrous web passes through the nip in conjunction with at least one press fabric, which supports it in its still fragile condition, and which accepts the water squeezed therefrom in the nip. Commonly, the fibrous web passes through the press nip sandwiched between two such press fabrics. It is a goal, then, of the present invention, to bring about an increase in the amount of water removed from the fibrous web in the press section by increasing the water-handling ability of the press fabrics used thereon. It is a further goal to increase the water-handling ability of the press fabrics to such a degree that the speed of the paper machine may be increased without sacrificing the structural integrity or degree of dryness of the fibrous web leaving the press section en route to the dryer section. GB 1 220 531 discloses a machine cloth for use in the wet pressing compartment of a papermaking machine comprising an upper weft layer formed of yarns of staple fibres and/or wool or multifilament yarns or blends thereof, and a lower weft layer of monofilament yarns, interwoven with warp monofilament yarns. An intermediate weft layer of similar construction to the upper weft layer may also be present. GB 1 207 446 discloses a dryer felt for a papermaking machine comprising two layers of cross-wise monofilament yarns interwoven with monofilament warp yarns, there being provided an additional intermediate layer of soft spun polyester staple fibres to restrict air flow through the fabric. EP-A-0 098 612 describes a press felt comprising an open-mesh base fabric woven of a plurality of synthetic filaments extending in the lateral and longitudinal directions, and at least one batt of staple fibres needled thereto, at least some of the filaments in the lateral direction being monofilaments having a flattened cross-section. The base fabric preferably has a duplex weave structure with upper layer multifilament wefts and lower layer monofilament wefts, interwoven with monofilament warp yarns. The present invention provides a press fabric for the press section of a papermachine, said press fabric having a multilayer, compressible, resilient structure, said press fabric comprising: three layers of weft yarns, only one of said three layers comprising multicomponent yarns, said multicomponent yarns each having a plurality of load-bearing members, the or any remaining weft yarns in all of said three layers being monofilament yarns, said three layers of weft yarns being a top layer, a middle layer and a bottom layer, the weft yarns in said bottom layer comprising monofilament yarns of greater diameter than monofilament yarns in any other one of said three layers; and, a first system of warp yarns, said warp yarns being monofilament yarns, said warp yarns of said first system being interwoven with said weft yarns of said three layers of weft yarns in a repeating pattern, so that said press fabric may be provided with an extremely fine paper-contacting surface, an open non-paper-contacting surface, and a structure having adequate void volume to store water pressed from a paper sheet. The press fabric may be woven endless. The press fabric may also be open-ended and seamable into closed form with a pintle. Further, the press fabric may be woven open-ended and joined into endless form with a woven marking-free seam prior to installation on a papermachine. The present invention also provides a papermaking machine provided with a press fabric as described above. The present invention relates to a press fabric manufactured according to the techniques used to weave forming fabrics, and which has an extremely fine surface formed predominantly by fine monofilament or multicomponent yarns. Described in broad terms, the fabric has three woven layers formed by weaving at least one system of fine monofilament warp yarns with three layers of weft yarns, one of which comprises a multicomponent yarn having a plurality of load-bearing members. The multicomponent yarn may be a multifilament or multistrand yarn, whose individual components are fine filaments, or it may be a polyurethane-coated monofilament yarn. The multistrand yarn may be described as and understood to be an untwisted multifilament yarn. The multifilament or multistrand yarns may also be polyurethane-coated. The press fabric has a compressible, yet resilient, structure having an extremely fine paper-contacting surface with a high contact area, and an open backside to provide sufficient void volume and the desired increased water-handling ability. The press fabric may be woven endless or it may be woven open-ended and joined into endless form with a woven seam, or manufactured open-ended so as to be pintle-seamed during installation on the paper machine. Further, the press fabrics may be used on the press section of a paper machine as woven, that is, as a base fabric alone, or, following weaving, may be coated with a polymeric resin material, or may be laminated with a polymeric resin foam or other non-woven material, or, needled with a batt of fibrous material, on the paper-contacting surface thereof. Lamination, coating and needling all have application on the present woven press fabric. While the woven press fabric itself may be used on many press positions, it would not be suitable for all press types. On some suction-type presses, such as pickup positions, it is necessary to provide a press fabric with lower void volume and permeability than is possible with only the woven press fabric. The three above-mentioned methods of applying additional material each enable the press fabric to generate a pressure drop sufficient to facilitate dewatering. The methods also provide the press fabric with increased compression and energy absorbing characteristics. Various press fabrics embodying the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a longitudinal cross-section through a press fabric that forms a first embodiment of the present invention, wherein said cross-section has been taken through the press fabric along a line corresponding to line I-I in Figure 2; Figure 2 is a weave chart showing the relationship of the warp and weft yarns of the embodiment according to Figure 1; Figure 3 is a longitudinal cross-section of a second embodiment of the present invention, wherein said cross-section has been taken through the press fabric along a line corresponding to line III-III in Figure 4; Figure 4 is a weave chart showing the relationship of the warp and weft yarns of the embodiment according to Figure 3; Figure 5 is a longitudinal cross-section of a third embodiment of the present invention, wherein said cross-section has been taken through the press fabric along a line corresponding to line V-V in Figure 6; Figure 6 is a weave chart showing the relationship of the warp and weft yarns of the embodiments according to Figures 5 and 7; Figure 7 is a longitudinal cross-section of a fourth embodiment of the present invention, wherein said cross-section has been taken through the press fabric along a line corresponding to line V-V in Figure 6; Figure 8 is a longitudinal cross-section of a fifth embodiment of the present invention, wherein said cross-section has been taken through the press fabric along a line corresponding to line VIII-VIII in Figure 9; Figure 9 is a weave chart showing the relationship of the warp and weft yarns of the embodiment according to Figure 8; Figure 10 is a longitudinal cross-section of a sixth embodiment of the present invention, wherein said cross-section has been taken through the press fabric along a line corresponding to line X-X in Figure 11; Figure 11 is a weave chart showing the relationship of the warp and weft yarns of the embodiment according to Figure 10; Figure 12 is a longitudinal cross-section of the fourth embodiment of the present invention, previously shown in Figure 7, having a coating of a polymeric resin material on the top, or paper-contacting, layer; Figure 13 is a longitudinal cross-section of the fourth embodiment of the present invention, having a layer of polymeric resin foam on the top, or paper-contacting, layer; and, Figure 14 is a longitudinal cross-section of the fourth embodiment of the present invention, having a batt of fibrous material needled into the top, or paper-coating, layer. Before describing in detail several press fabrics embodying the present invention, as depicted in the figures identified above, some general comments, applicable to all embodiments, are appropriate. The press fabrics are multi-layered structures woven from at least one system of fine monofilament warp yarns and three layers of weft yarns. One of the three layers of weft yarns includes, or is entirely composed of, multicomponent yarns having a plurality of load-bearing members. These yarns provide the press fabrics of the invention with a compressible, yet resilient, structure. The so-called multicomponent layer may be any one of the three weft layers. It is a general characteristic of embodiments of the present invention that a layer containing all,or in part, multicomponent yarns, is captured, or interwoven with, the monofilament yarns. An example of the multicomponent yarns included in the multicomponent layer is a multifilament yarn comprising eight strands of 0.10 mm (4 mil) filament twisted together, as set forth in the examples to follow hereinbelow. The multicomponent yarn includes a plurality of load-bearing members, as does this eight-stranded multifilament yarn. Broadly stated, the multicomponent yarn may be a multifilament or multistrand yarn, whose individual components are fine filaments, or it may be a polyurethane-coated monofilament yarn. A multistrand yarn may be considered to be equivalent to an untwisted multifilament yarn. The multifilament or multistrand yarns may also be polyurethane-coated. The monofilament warp yarns may be either polyamide or polyester yarns. It is highly desirable that the monofilament weft, or shute, yarns, and the multicomponent weft yarns, exclusive of any polyurethane coating, all be polyamide yarns so as to avoid or reduce problems that would be otherwise encountered during the installation of the fabric on a paper machine. Polyamide material is preferred over polyester in being less prone to fibrillation as a result of press nip compressions, and less prone to damage during needling. The polyamide weft yarn also leaves the fabric less stiff, and less likely to be creased during installation. As a consequence, the press fabrics of the present invention will be woven predominantly from polyamide yarns, although other types of yarns with the same or similar properties may also be used. In all the illustrated embodiments, the use of larger diameter yarns in the weft layers below the paper-contacting surface, together with the weave patterns chosen, provide the press fabrics with open back, or machine, sides and sufficient void volume to accept increased quantities of water from the fibrous web. Having made the preceding general introductory comments, several embodiments of the present invention will now be considered separately and in detail below. Embodiment 1 A first embodiment of the present invention is illustrated in longitudinal cross section in Figure 1. Here, and in all subsequent figures showing cross sections of embodiments of the present invention, the amount of separation between the yarns-and layers of the fabric has been greatly exaggerated for the sake of clarity. In an actual fabric, weft yarns in each layer, and adjacent layers themselves, would be in substantial contact with one another, except for the spaces brought about therebetween by the interweaving of warp yarns between the layers. This interweaving gives rise to spaces within the fabric for the passage and temporary storage of water. With more particular reference now to Figure 1, the press fabric shown there in cross-section comprises three layers of weft yarns interwoven with one system of warp yarns. The bottom layer 10 comprises monofilament yarns 12. The middle layer 14 comprises multifilament yarns 16. The top, or paper-contacting, layer 18 comprises monofilament yarns 20, 22, which alternate with one another and which are of different cross-sectional diameters. Monofilament yarns 20 of the top layer 18, multifilament yarns 16 of the middle layer 14, and monofilament yarns 12 of the bottom layer 10 are in a vertically stacked relationship with one another through the thickness of the fabric, and therefore are provided in equal numbers on each layer. Monofilament yarns 22 of the top layer 18 alternate with monofilament yarns 20, providing the top layer 18 with twice as many weft yarns as the middle layer 14 or the bottom layer 10. The fabric is woven in an 8-shed weave as illustrated in Figure 1 by characteristic warp yarn 24. In any given repeat of the weave pattern, a warp yarn 24 passes over three consecutive weft yarns 20 of the top layer 18, then passes obliquely downward through the middle layer 14 between the following two multifilament yarns 16 thereof, and under the third monofilament yarn 12 of the bottom layer 10, then passes obliquely upward through the middle layer 14 between the following two multifilament yarns 16 thereof to finally weave over the next monofilament yarn 20 of the top layer 18 to repeat the pattern. Figure 2 is a weave chart for the embodiment shown in Figure 1, which is a cross-sectional view taken along line I-I of Fig. 2. In this, and all subsequent, weave charts, the letter "X" indicates that the warp yarn, represented by the columns in the chart, crosses over the weft yarn, represented by the rows in the chart. A dot "." indicates that the warp yarn passes under the weft yarn with which it is crossed. Where it may happen to appear in subsequent weave charts in the present specification, the letter "o" indicates that the warp yarn weaves under a weft yarn in the bottommost layer of the fabric. As a specific example, the fabric shown in Figure 1 may be woven according to the weave chart shown in Figure 2 with yarns selected as follows: weft monofilament yarns 12 .22mm polyamide weft multifilament yarns 16 8x.10mm polyamide weft monofilament yarns 20 .17mm polyamide weft monofilament yarns 22 .12mm polyamide warp monofilament yarns 24 .17mm polyester (56 ends/cm) The flat weaving of the fabrics of the present invention with 56 ends/cm may be regarded as typical. Actually, the warp density falls in a range from a minimum of 40 ends/cm to a maximum of 70 ends/cm. Other yarn densities would apply if the fabrics are woven endless. As may be observed, the top, or paper-contacting, layer 18 of this embodiment is of fine monofilament yarns, and provides an extremely fine surface with high contact area. Embodiment 2 A second embodiment of the present invention is substantially the same as the first embodiment, and is illustrated in longitudinal cross section in Figure 3. Again, the press fabric shown comprises three layers of weft yarns interwoven with one system of warp yarns. The bottom layer 30 comprises monofilament yarns 32. The middle layer 34 comprises multifilament yarns 36. The top, or paper-contacting, layer 38 comprises monofilament yarns 40, 42, which alternate with one another and which are of different cross-sectional diameters. Monofilament yarns 40 of the top layer 38, multifilament yarns 36 of the middle layer 34, and monofilament yarns 32 of the bottom layer 30 are in a vertically stacked relationship with one another through the thickness of the fabric, and therefore are provided in equal numbers on each layer. Monofilament yarns 42 of the top layer 38 alternate with monofilament yarns 40, providing the top layer 38 with twice as many weft yarns as the middle layer 34 or the bottom layer 30. The fabric is again woven in an 8-shed weave as illustrated in Figure 3 by characteristic warp yarn 44. In any given repeat of the weave pattern, warp yarn 44 passes over two consecutive weft yarns 40 of the top layer 38, then passes obliquely downward through the middle layer 34 between the following two multifilament yarns 36 thereof, under the third monofilament yarn 32 of the bottom layer 30, over and under the next two monofilament yarns 32 of the bottom layer 30, then passes obliquely upward through the middle layer 34 between the following two multifilament yarns 36 thereof to finally weave over the monofilament yarn 40 of the top layer 38 directly over the second of the last two multifilament yarns 36 to repeat the pattern. Figure 4 is a weave chart for the embodiment shown in Figure 3, which is a cross-sectional view taken along line III-III thereof. As a specific example, the fabric shown in Figure 3 may be woven according to the weave chart shown in Figure 4 with yarns selected as follows: weft monofilament yarns 32 .30mm polyamide weft multifilament yarns 36 8x.10mm polyamide weft monofilament yarns 40 .17mm polyamide weft monofilament yarns 42 .12mm polyamide warp monofilament yarns 44 .17mm polyester (56 ends/cm) Again, in this second embodiment, the top, or paper-contacting, layer 38 is of fine monofilament yarns, and provides an extremely fine surface with high contact area. Embodiment 3 A third embodiment of the present invention is illustrated in longitudinal cross-section in Figure 5. The press fabric shown there in cross-section comprises three layers of weft yarns interwoven with two systems of warp yarns. The bottom layer 50 comprises monofilament yarns 52. The middle layer 54 comprises monofilament yarns 56. The top, or paper-contacting, layer 58 comprises multifilament yarns 60. Multifilament yarns 60 of the top layer 58, monofilament yarns 56 of the middle layer 54, and monofilament yarns 52 of the bottom layer 50 are in a vertically stacked relationship with one another through the thickness of the fabric and therefore are provided in equal numbers on each layer. The fabric is woven in an 8-shed weave as illustrated in Figure 5 with two systems of warp yarns. A top system of warp yarns, one of which is warp yarn 62 in Figure 5, interweaves with multifilament yarns 60 of the top layer 58 in what may be described as a plain weave modified to the extent that each warp yarn 62 weaves under every eighth monofilament yarn 56 of the middle layer 54 in a repeating pattern to bind the top layer 58 to the middle layer 54. A bottom system of warp yarns, one of which is warp yarn 64 in Figure 5, interweaves with monofilament yarns 56 of the middle layer 54 and monofilament yarns 52 of the bottom layer 50 in what may be characterized as a duplex weave. In any given repeat of the weave pattern, warp yarn 64 passes over two consecutive weft yarns 56 of the middle layer 54, then passes obliquely downward between the next stacked pair of weft yarn 56 of the middle layer 54 and weft yarn 52 of the bottom layer 50, weaves under the next weft yarn 52 of the bottom layer 50, over the next two weft yarns 52 and under the next weft yarn 52, and then, finally, obliquely upward between the following stacked pair of weft yarn 56 and weft yarn 52 to weave over the next weft yarn 56, beginning the pattern anew. Figure 6 is a weave chart for the embodiment shown in Figure 5, which is a cross-sectional view taken along line V-V thereof. Column 1 in the weave chart shown in Figure 6 indicates the pattern for warp yarn 62 in Figure 5. Generally, the odd-numbered columns indicate the patterns for the top system of warp yarns, while the even-numbered columns do so for the bottom system of warp yarns. One of these latter warp yarns, warp yarn 64 in Figure 5, is indicated by column 2 in Figure 6. As noted earlier, the letters "o" in the even-numbered columns indicate those points where the warp yarns of the bottom layer, such as warp yarn 64, weave under a weft yarn 52 of the bottom layer 50. As a specific example, the fabric shown in Figure 5 may be woven according to the weave chart shown in Figure 6 with yarns selected as follows: weft monofilament yarns 52 .22mm polyamide weft monofilament yarns 56 .17mm polyamide weft multifilament yarns 60 8x.10mm polyamide warp monofilament yarns 62 .17mm polyester warp monofilament yarns 64 .17mm polyester (56 ends/cm total) As may be observed, the top, or paper-contacting, layer 58 of this embodiment may be characterized in that each weft yarn 60 is a multifilament yarn 60. Embodiment 4 A fourth embodiment of the present invention is illustrated in longitudinal cross-section in Figure 7. This fourth embodiment is identical to the third embodiment, except that the layer of multifilament weft yarns is the middle layer rather than the top layer. The press fabric shown in cross-section in Figure 7 again comprises three layers of weft yarns interwoven with two systems of warp yarns. The bottom layer 70 comprises monofilament yarns 72. The middle layer 74 comprises multifilament yarns 76. The top, or paper-contacting, layer 78 comprises monofilament yarns 80. Monofilament yarns 80 of the top layer 78, multifilament yarns 76 of the middle layer 74, and monofilament yarns 72 of the bottom layer 70 are again in a vertically stacked relationship with one another through the thickness of the fabric and therefore are provided in equal numbers on each layer. The fabric is woven in an 8-shed weave as illustrated in Figure 7 with two systems of warp yarns. One may readily observe that the weave pattern for the fabric shown in Figure 7 is the same as that for the fabric shown in Figure 5. Accordingly, the top system of warp yarns, one of which is warp yarn 82 in Figure 7, and the bottom system of warp yarns, one of which is warp 84, weave in patterns identical to those previously described for the warp yarns of the third embodiment of the present invention. It follows that Figure 6 is also the weave chart for the embodiment shown in Figure 7, which is again a cross-sectional view taken along line V-V thereof. As a specific example, the fabric shown in Figure 7 may be woven according to the weave chart shown in Figure 6 with yarns selected as follows: weft monofilament yarns 72 0.22mm polyamide weft multifilament yarns 76 8x.10mm polyamide weft monofilament yarns 80 0.17mm polyamide warp monofilament yarns 82 0.17mm polyester warp monofilament yarns 84 0.17mm polyester (56 ends/cm total) As may be observed, the multifilament weft yarns in this fourth embodiment are in the middle layer, and are used to bind the top layer to the middle layer. Embodiment 5 A fifth embodiment of the present invention is illustrated in longitudinal cross-section in Figure 8. The press fabric shown there comprises three layers of weft yarns interwoven with two systems of warp yarns. The bottom layer 90 comprises monofilament yarns 92. The middle layer 94 comprises multifilament yarns 96 and monofilament yarns 98, which alternate with one another. The top, or paper-contacting, layer 100 comprises monofilament yarns 102. Monofilament yarns 102 of the top layer 100 multifilament yarns 96 and monofilament yarns 98 of the middle layer 94, and monofilament yarns 92 of the bottom layer 90 are in a vertically stacked relationship with one another through the thickness of the fabric, and therefore are provided in equal numbers on each layer. The middle layer 94 is half multifilament yarns 96 and half monofilament yarns 98, which alternate with one another as previously stated. The total number of weft yarns in middle layer 94 is the same as that in the bottom layer 90 and in the top layer 100. The fabric is woven in an 8-shed weave as illustrated in Figure 8 with two systems of warp yarns. A top system of warp yarns, one of which is warp yarn 104 in Figure 8 interweaves with monofilament yarns 102 of the top layer 100 in what may be described as a plain weave, modified to the extent that each warp yarn 104 weaves under every other monofilament yarn 98 of the middle layer 94 in a repeating pattern to bind the top layer 100 to the middle layer 94. Generally stated, the warp yarns of the top system in this fifth embodiment bind only with the monofilament yarns in the middle layer to join the top and middle layers, and do not bind with the multifilament yarns of the middle layer. In comparison to the embodiments shown in Figures 5 and 7, the top layer 100 is bound to the middle layer 94 at twice as many points in this fifth embodiment. A bottom system of warp yarns, one of which is warp yarn 106 in Figure 8 interweaves with multifilament yarns 96 and monofilament yarns 98 of the middle layer 94 and with monofilament yarns 92 of the bottom layer 90 in what may be characterized as a duplex weave. Warp yarn 106, and all other warp yarns in the bottom system of warp yarns of this embodiment, weave in a pattern identical to that previously described for the warp yarns of the bottom systems of the third and fourth embodiments. Figure 9 is a weave chart for the embodiment shown in Figure 8, which is cross-sectional view taken along line VIII-VIII thereof. Column 1 in the weave chart shown in Figure 9 indicates the pattern for warp yarn 104 in Figure 8. As was the case with Figure 6, the odd-numbered columns in Figure 9 indicate the patterns for the top system of warp yarns, while the even-numbered columns do so for the bottom system of warp yarns. One of these latter yarns, warp yarn 106 in Figure 8, is indicated by column 2 in Figure 9. As a specific example, the fabric shown in Figure 8 may be woven according to the weave chart shown in Figure 9 with yarns selected as follows: weft monofilament yarns 92 0.22mm polyamide weft multifilament yarns 96 8x.10mm polyamide weft monofilament yarns 98 0.15mm polyamide weft monofilament yarns 102 0.17mm polyamide warp monofilament yarns 104 0.17mm polyester warp monofilament yarns 106 0.17mm polyester (56 ends/cm total) Embodiment 6 A sixth embodiment of the present invention is illustrated in longitudinal cross-section in Figure 10. The press fabric shown there comprises three layers of weft yarns interwoven with one system of warp yarns. The bottom layer 110 comprises monofilament yarns 112. The middle layer 114 comprises multifilament yarns 116. The top, or paper-contacting, layer 118 comprises monofilament yarns 120. Monofilament yarns 120 of the top layer 118 and monofilament yarns 112 of the bottom layer 110 are in a vertically stacked relationship with one another through the thickness of the fabric, and therefore are provided in equal numbers on each of these two layers. Multifilament yarns 116 of the middle layer 114 are positioned in a staggered fashion substantially half way between each vertically stacked pair of monofilament yarns 120 of the top layer 118 and monofilament yarns 112 of the bottom layer 110. The fabric is woven in a 5-shed weave as illustrated in Figure 10 by characteristic warp yarn 122. In any given repeat of the weave pattern, warp yarn 122 passes over one weft yarn 120 of the top layer 118, then passes obliquely downward through the middle layer 114 to weave under the second monofilament yarn 112 of the bottom layer 110, then passes obliquely upward again through the middle layer 114 to weave over the third monofilament yarn 120 of the top layer 118 to repeat the pattern. In short, warp yarn 122 weaves over every fifth weft yarn 120 of the top layer 118 and under every fifth weft yarn 112 of the bottom layer 110. Figure 11 is a weave chart for the embodiment shown in Figure 10, which is a cross-sectional view taken along line X-X thereof. As before, the letters "o" indicate those points where a warp yarn weaves under a weft yarn 112 of the bottom layer 110. As a specific example, the fabric shown in Figure 10 may be woven according to the weave chart shown in Figure 11 with yarns selected as follows: weft monofilament yarns 120 0.20mm polyamide weft multifilament yarns 116 8x.10mm polyamide weft monofilament yarns 112 0.25mm polyamide warp monofilament yarns 122 0.20mm polyester (28 ends/cm) Figures 12 through 14, for the purpose of illustration, show longitudinal cross-sections of the fourth embodiment of the present invention, previously shown in Figure 7, wherein the top, or paper-contacting, layer 78 has been modified by coating, lamination or needling. Specifically, in Figure 12, the top layer 78 has been coated with a layer 150 of polymeric resin particles 152, which may be obtained by chopping sheets of polyurethane into small particles of a substantially uniform size. The polymeric resin particles 152 are then applied to the top layer 78 in a layer 150 of uniform thickness, and secured thereto by exposure to an infra-red heat source. In Figure 13, a layer 160 of polymeric resin foam 162 is attached to the top, or paper-contacting, layer 78. In place of polymeric resin foam 162, other non-woven materials could be attached to the top layer 78 in a similar manner. Figure 14 depicts the embodiment of Figure 7 wherein a layer 170 of fibrous batt 172 has been needled into the top layer 78 in a manner well known in the art. As would be immediately apparent to one skilled in the art, it is possible to weave variations of the fabrics described above. A fabric could, for example, be produced with a structure inbetween those of the fourth and fifth embodiments, the fabric having a middle layer wherein two thirds of the weft yarn are multifilament yarns. In such a case, every third yarn of the middle layer could be a monofilament yarn used to bind the top layer of the fabric to the middle layer.

Claims: A press fabric for the press section of a papermachine, said press fabric having a multilayer, compressible, resilient structure, said press fabric comprising: three layers of weft yarns, only one of said three layers comprising multicomponent yarns, said multicomponent yarns each having a plurality of load-bearing members, the or any remaining weft yarns in all of said three layers being monofilament yarns, said three layers of weft yarns being a top layer, a middle layer and a bottom layer, the weft yarns in said bottom layer comprising monofilament yarns of greater diameter than monofilament yarns in any other one of said three layers; and, a first system of warp yarns, said warp yarns being monofilament yarns, said warp yarns of said first system being interwoven with said weft yarns of said three layers of weft yarns in a repeating pattern, so that said press fabric may be provided with an extremely fine paper-contacting surface, an open non-paper-contacting surface, and a structure having adequate void volume to store water pressed from a paper sheet. A press fabric as claimed in claim 1, wherein the monofilament weft yarns and/or the multicomponent weft yarns are polyamide yarns. A press fabric as claimed in claim 1 or claim 2, wherein the warp yarns of the first system and/or of any second warp system, if present, are polyester or polyamide yarns. A press fabric as claimed in any one of the preceding claims, wherein the multicomponent yarns are multifilament or multistrand yarns, optionally polyurethane-coated. A press fabric as claimed in any one of claims 1 to 3, wherein the multicomponent yarns are polyurethane-coated monofilament yarns. A press fabric as claimed in any one of the preceding claims further comprising a coating of a polymeric resin material on the paper-contacting surface. A press fabric as claimed in any one of claims 1 to 5 further comprising a layer of polymeric resin foam or other non-woven material secured to the paper-contacting surface. A press fabric as claimed in any one of claims 1 to 5 further comprising a batt of fibrous material needled into the paper-contacting surface. A press fabric as claimed in any one of claims 1 to 8, wherein said weft yarns of said top layer of weft yarns are all multifilament yarns. A press fabric as claimed in any one of claims 1 to 8, wherein said weft yarns of said top layer of weft yarns include multifilament yarns and monofilament yarns. A press fabric as claimed in any one of claims 1 to 8, wherein said weft yarns of said middle layer of weft yarns are all multifilament yarns. A press fabric as claimed in any one of claims 1 to 8, wherein said weft yarns of said middle layer of weft yarns include multifilament yarns and monofilament yarns. A press fabric as claimed in any one of claims 1 to 12, wherein the numbers of weft yarns in each of said top, middle and bottom layers of weft yarns are equal or there are twice as many weft yarns in the top layer of weft yarns as in the middle layer of weft yarns. A press fabric as claimed in any one of claims 1 to 12, wherein the weft yarns in either all three layers or only in the top and bottom layers are in a vertically stacked relationship. A press fabric as claimed in any one of claims 1 to 14 further comprising a second system of monofilament warp yarns, wherein the warp yarns of the first system weave with the weft yarns of the top layer in a repeating pattern and bind the top layer to the middle layer by weaving with selected weft yarns of the middle layer, and wherein the warp yarns of the second system weave with the weft yarns of the middle layer and the weft yarns of the bottom layer in a repeating pattern to form a duplex weave therebetween. A press fabric as claimed in claim 15, wherein the weft yarns of the middle layer of weft yarns include multifilament yarns and monofilament yarns and wherein the warp yarns of the first system weave with selected monofilament weft yarns of the middle layer when binding the top layer to it. A papermaking machine provided with a press fabric as claimed in any one of the preceding claims.

Inventors: DAM EBO E, FITZPATRICK KEITH, MCCARTHY WILLIAM M, VAN BERGEN WIL F, DAM, EBO E., FITZPATRICK, KEITH, MCCARTHY, WILLIAM M., VAN BERGEN, WIL F.
Applicants: ALBANY INT CORP, ALBANY INTERNATIONAL CORP.
Application year: 1992
Main classification: D21F1
IPC codes: D21F7, D21F1