FOR PRODUCING PRESS FELT

INCORPORATION BY REFERENCE

[0001] The following documents are incorporated herein by reference as if fully set forth: U.S. Provisional Patent Application No. 63/033,495, filed June

2, 2020.

FIELD OF THE INVENTION

[0002] The invention generally concerns seamed and endless woven press felts for use in the manufacture of paper and similar products in a papermaking or like machine. It is particularly concerned with improved batt layer(s).

BACKGROUND OF THE INVENTION [0003] The present invention concerns press felts for use in the press section of papermaking machines. In the manufacture of paper products, a stock slurry consisting of about 1% papermaking fibers and others solids dispersed in about 99% water is delivered at high speed and precision from a headbox slice onto a rapidly moving forming fabric, or between two forming fabrics, in the forming section of a papermaking machine. The stock is subjected to agitation and is dewatered by various means through the forming fabrics, leaving behind a loosely cohesive and wet web of fibers. This web is then transferred to the press section where a further portion of water is removed by mechanical means as the web, supported by one or more press felts, passes through at least one, and usually a series, of press nips where water is essentially squeezed from the nascent sheet and into the press felt. The water is accepted by the press felt and, ideally, does not return to the web. The resulting sheet is then passed to the dryer section which includes a series of rotatable dryer drums, or cans, that are heated by steam. The sheet is directed around and held in contact with the periphery of these drums by one or more dryer fabrics so that the majority of the remaining water is removed by evaporation.

[0004] Press felts play a critical role in the manufacture of paper products.

The known press felts are produced in a wide variety of styles designed to meet the requirements of the papermaking machines on which they are installed, and the paper grades being manufactured. They are generally assembled using a woven or nonwoven base fabric structure into which is needled one and usually multiple layers of a fibrous nonwoven batt. The batt provides a smooth surface upon which the paper product is conveyed, acts as a reservoir to trap water expressed at the press nip, and provides a measure of resiliency to the press felt as it passes through the nip. The base fabrics are typically woven from arrays of machine direction (MD) and cross-machine direction (CD) yarns, which can be monofilament, cabled monofilament, multifilament or similar multicomponent yarns (commonly referred to as “yarns”); they may also be arranged as nonwoven planar arrays. The component yarns are usually comprised of an extruded polymeric resin, typically a polyamide.

[0005] The base fabrics may be of single layer or multilayer construction, or they may be formed from two or more layers which are laminated together. [0006] More recently, multiaxial press felts such as described in US 5,360,656; US 5,268,076; US 5,785,818 and others have gained wider acceptance in the industry. The base fabrics of these press felts are comprised of a plurality of spirally wound and edgewise joined turns of a material strip including at least MD oriented yarns. The material strip is usually a flat woven fabric which is narrower than the width of the intended base fabric of which it is a component; it has also been proposed to use nonwoven arrays of MD yarns as the material strip component. Regardless of whether the component is woven or nonwoven, during assembly each turn of the material strip is directed about two opposing rollers such that its component MD yarns are canted at a small angle that is from about 1° to about 8° to the intended MD of the finished fabric. Each successive turn of the material strip is edgewise bonded to that laid adjacent to it so as to build up a continuous tube-like base fabric of desired width and length. When removed from the assembly rollers and laid flat, the tube has continuous top and bottom surfaces joined at CD oriented fold regions at each of the two opposing ends. The completed multiaxial base fabrics are typically one of a two, three or four layer construction comprising the top and bottom surfaces of the spirally wound continuous tube, and optionally at least one additional flat fabric layer, located either interior to the flattened tube, or on top of one or both exterior surfaces. The assembled base fabric may later be provided with a seam to facilitate their installation on the machine for which it is intended. One and usually multiple layers of a fibrous nonwoven batt are needled to the assembled base fabric.

[0007] A common issue with press felts is shedding of the batt fiber due to wear during use.

[0008] U.S. 6, 712,940 is directed to a paper machine belt, particularly for use in a press and/or dryer section. The belt includes a base layer, a fusible thermoplastic layer in the form of a porous membrane, and a thicker batt layer that is placed over the fusible thermoplastic layer. The whole structure is needled together and the thermoplastic material is then melted during heat setting and expressed through the overlying batt and passes from inside to the outside surface of the fabric through the batt. By varying the heat, pressure, and dwell time, the distribution of fibers can be controlled in order to allow more or less of the fusible material to appear on the surface of the fabric. While this can help to stabilize the batt fibers, there can be issues with uneven distribution of the thermoplastic layer material through the batt, with the uneven distribution causing inconsistent wear and batt retention issues.

[0009] It would be desirable to provide a press felt in which batt shedding is reduced, improving fabric performance and life.

SUMMARY

[0010] According to the disclosure, a press felt is provided that includes a base fabric having an array of MD yarns and an array of CD yarns and having a machine side and a paper support side. The base fabric can be woven or non woven, or a multiaxial construction. At least one paper support side batt layer comprised of batt fibers is located on the paper support side. A non-woven fusible web formed with fusible fibers or strands made from a same material type as at least one paper support side batt layer is applied between at least one of the base fabric and the at least one paper support side batt layer or between paper support side batt layers. The same material type is from the same material family, such as a polyamide, but is not required to be the exact same type of polyamide, such as Nylon 6/6. The fusible fibers or strands of the non- woven fusible web are punched through the base fabric along with the batt fibers during needling of the press felt to provide a uniform distribution through the base fabric and with the at least one paper support side batt. During subsequent heat-setting, the non-woven fusible fibers or strands are melted and the material of the fusible fibers or strands is uniformly distributed through the at least one paper support side batt layer and the base fabric. This uniform distribution of the fusible fiber or strands enhances batt retention uniformly throughout the press felt, improving fabric performance and the life of the press felt. This is due at least in part to the fusible fibers or strands being punched through the base fabric as well as the batt fibers during needling in order to provide the uniform distribution throughout the thickness of the press felt prior to being melted during heat-setting.

[0011] In another aspect, the batt fibers of the at least one paper support side batt layer comprise a polyamide fiber and the fusible fibers or strands are made of a polyamide having a lower melting point than the polyamide fiber of the at least one batt. The use of a same type of material provides improved performance due to the improved bonding between the materials to reduce surface wear and increase felt life through improved batt retention.

[0012] In one arrangement, at least one machine side batt layer is located on the machine side of the base fabric and made of batt fibers of the same material type as the at least one paper support side batt layer. A machine side non-woven fusible web formed with fusible fibers or strands made of the same material type as the at least one machine support side batt layer can also be applied between at least one of the base fabric and the at least one machine support side batt layer or between machine support side batt layers.

[0013] In another aspect, the disclosure provides a method of forming a press felt, the method includes providing a base fabric having a machine side and a paper support side; providing at least one paper support side batt layer comprised of batt fibers located on the paper support side; applying a non-woven fusible web formed with fusible fibers or strands made of a same material type as the at least one paper support side batt layer at least one of between the base fabric and the at least one paper support side batt layer or between paper support side batt layers; punching the fusible fibers or strands of the non-woven fusible web through the base fabric along with the batt fibers during needling of the press felt to provide a uniform distribution of the fusible fibers or strands through the base fabric and with the at least one paper support side batt; and melting the fusible fibers or strands during subsequent heat-setting of the press felt, and uniformly distributing the melted material of the fusible fibers or strands through the at least one paper support side batt layer and the base fabric.

[0014] In one arrangement, the batt fibers of the at least one paper support side batt layer comprising a polyamide fiber and the fusible fibers or strands that are made of a polyamide having a lower melting point than the polyamide fiber of the at least one batt.

[0015] In another aspect, the method further includes providing at least one machine side batt layer located on the machine side of the base fabric and made of batt fibers of the same material type as the at least one paper support side batt layer.

[0016] The method can further include applying a machine side non- woven fusible web formed with fusible fibers or strands made of the same material type as the at least one machine support side batt layer applied at least one of between the base fabric and the at least one machine support side batt layer or between machine support side batt layers..

[0017] Additionally, the method can include tentering the press felt during the heat-setting.

BRIEF DESCRIPTION OF THE DRAWINGS [0018] The foregoing Summary and the following detailed description and claims will be best understood when read in conjunction with the drawings which show the presently preferred embodiments of the invention. In the drawings: [0019] Figure 1 is a schematic view showing an embodiment of a press felt 10 in a disassembled state according to the disclosure.

[0020] Figure 2 is a cross-sectional view of the press felt assembly shown in Figure 1 after needling to join the layers of batt material and the non-woven fusible web together with the base fabric.

[0021] Figures 3A and 3B show the formation of the non-woven fusible web 26 including the creation of fusible fibers or strands 28 from a sheet of fusible material, shown in Figure 3A, as well as the formation of the non-woven fusible web 26 using a webber, as shown in Figure 3B.

[0022] Figure 4 is a flow chart showing a method for constructing a press felt 10 according to a preferred aspect of the present disclosure.

[0023] Figure 5 is a schematic view showing a further embodiment of a press felt 10’ in a disassembled state according to the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0024] Certain terminology is used in the following description for convenience only and is not limiting. The words "top," "bottom," "upper" and "lower" designate directions in the drawings to which reference is made. A reference to a list of items that are cited as "at least one of a, b, or c" (where a, b, and c represent the items being listed) means any single one of the items a, b, or c, or combinations thereof. “A” or “an” refer to one or more of the item noted. “MD” refers to a machine direction in the papermaking machine from the headbox to the dryer section and is the longitudinal direction of the press felt. “CD” refers to the cross-machine direction, or a direction perpendicular to the machine direction in the plane of the fabric. The term “PS” refers to the paper side surface of the fabric, which is the surface upon which the paper product is carried through the papermaking machine. “MS” refers to the machine side of the fabric and is the surface opposite to the PS. Unless otherwise specified, the term “yarn” or “yarns” refers to a continuous length of either single or cabled polymeric monofilaments or multicomponent fiber or fibers such as would be used in the manufacture of the base fabrics of the invention. The term “fiber” or “fibers” refers to relatively small diameter (or other cross-section, such as rectangular) polymeric materials, and in addition to being part of multicomponent yarns, can be used in batt materials; these fibers have a very small dtex (mass in grams per 10,000 meters of fiber). “Orthogonal” or “perpendicular” as used herein with respect to the CD and MD yarns means generally within about 85° to 95° based on the deviation from true perpendicular created by the spiral winding of the MD yarns. The terms “left”, “right”, “up”, “down” are used in relation to the drawings and have the meanings usually assigned. Additional definitions for terms used herein are as follows: [0025] “Press felt base fabric” refers to a woven or nonwoven assembly of yarns provided as an endless structure or continuous loop. The assemblies can take the form of: a) an endless woven structure, b) a modified endless woven structure, c) a flat woven fabric, d) a fabric formed according to a multiaxial assembly process, or e) a nonwoven structure assembled to provide any of the previous assemblies. The present invention is applicable to all of the above. All of the base fabrics, with the possible exception of those which are endless woven, are post processed to provide seam loops formed by the MD oriented component yarns allowing the fabric to be joined and thus rendered endless. These base fabrics provide the finished press felt with the physical properties (strength, void volume, resiliency) necessary for it to survive the rigors of the machine environment in which it will be used, while providing a rugged carrier for the batt fibers.

[0026] PREFERRED EMBODIMENTS

[0027] Referring to Figures 1 and 2, a press felt 10 according to one embodiment of the present disclosure is shown. The press felt 10 includes a base fabric 12, shown as a woven base fabric, including an array of MD yarns 14 and an array of CD yarns 16 that are interwoven together. The base fabric 12 has a machine side (MS) 18 and a paper support side (PS) 20. While the base fabric 12 is shown as a woven assembly, it is within the scope of the invention to use any of the various types of press felt base fabrics discussed above.

[0028] At least one PS batt layer 22A, and in the embodiment disclosed, two PS batt layers 22A, 22B, comprised of batt fibers 24 are located on the PS 20. As shown in Figure 1, a non-woven fusible web 26 formed with fusible fibers or strands 28 made of a same material type as the at least one PS batt layer 22A, 22B is applied between the base fabric 12 and the at least one PS batt layer 22A, 22B. The non-woven fusible web 26 could also be applied between the PS batt layers 22A, 22B, or non-woven fusible webs 26 could be applied between the base fabric 12 and the at least one PS batt layer 22A, 22B and between the PS batt layers 22A, 22B as in the embodiment of the press felt 10’ shown in Fig. 5.

[0029] As shown in the embodiment of Figure 1, preferably the press felt 10 further comprises at least one MS batt layer 30 located on the MS 18 of the base fabric 12 which is made of the same material type as the at least one PS batt layer 22A, 22B.

[0030] Further, as shown in Figure 1, a MS non-woven fusible web 32 formed with the fusible fibers or strands 28 made of the same material type as the at least one MS batt layer 30 can be applied between the base layer fabric 12 and the at least one MS batt layer 30. The non-woven fusible web 32 could also be applied between the MS batt layers 30A, 30B, or non-woven fusible webs 32 could be applied between the base fabric 12 and the at least one MS batt layer 30A, 30B and between the MS batt layers 30A, 30B as in the embodiment of the press felt 10’ shown in Fig. 5. The non-woven fusible web 32 preferably has the same construction as the non-woven fusible web 26.

[0031] The fusible fibers or strands 28 of the non-woven fusible web(s) 26, and preferably also the non-woven fusible web(s) 32 if present, are punched through the base fabric 12 along with the batt fibers 24 (of the PS batt layers 22A, 22B, and the MS batt layer 30 if present) during needling of the press felt 10, 10’ to provide a uniform distribution of the fusible fibers or strands 28 through the base fabric 12 and with the at least one PS batt 22A, 22B, and also the MS batt layer(s) 30, if present. During the subsequent heat setting, these non-woven fusible fibers or strands 28 which are now uniformly distributed throughout the needled press felt 10 are melted and uniformly distributed through the at least one paper support side batt layer 22A, 22B and the base fabric 12, as well as the MS batt layer(s) 30, if present. This provides enhanced batt retention in a more uniform manner across the entire press felt 10, 10’ to prevent shedding of batt fibers 24 due to the fact that the fusible fibers or strands 28 are arranged uniformly and needled punched through the entire press felt 10, 10’ prior to the heat setting process. Further, by providing the non-woven fusible web 26 as a web including fusible fibers or strands 28, this ensures that these fusible fibers or strands 28 can be needle punched through the thickness of the press felt 10, 10’.

[0032] In the preferred embodiment, the at least one PS batt layer 22A,

22B comprises polyamide batt fibers 24 and the fusible fibers or strands 28 used in the non-woven fusible web 26 (as well as 32) are made of a polyamide having a lower melting point than the polyamide batt fibers 24 of the at least one batt 22A, 22B on the paper support side as well as the MS batt layer(s) 30, if present. [0033] Referring to Figures 3A and 3B, one arrangement for producing the non-woven fusible web 26 is shown. In Figure 3A, a sheet of the fusible material 51, preferably a low melt polyamide such as a Copolyamide with a melting temperature of 97°C - 110°C used to form the fusible fibers 28 is feed through a slitting device 52, which can be blades, hot wires, or any other suitable sheet slitter in order to be slit into a plurality of individual fibers or strands. Alternatively, the fusible material can be extruded through a spinneret into multiple fibers. The fibers or strands are chopped into smaller lengths, for example by being fed to a chopping knife 54 which chops the fibers or strands 28 to a desired length, for example, 1-3 inches. These chopped fibers or strands 28 are then used to form the non-woven fusible web 26. As shown in Figure 3B, the chopped fibers or strands 28 may be fed into a webber, which can be for example a Rando webber, which is illustrated only schematically, where the chopped fusible fibers or strands 28 are air laid via an airstream 58 and mixed with an adhesive 60 in order to form the non-woven fusible web 26 which is carried from the webber 56 on a conveyor 62. Other methods for forming the non-woven fusible web can also be used. The non-woven fusible web is then used in connection with the formation of the press felt 10, 10’.

[0034] A method of forming the press felt 10, 10’ is shown in Figure 4 and indicated at 40. The method includes providing a base fabric 12 having a MS 18 and a PS 20, as indicated at 42. Next, at least one PS batt layer 22A, 22B that is comprised of batt fibers 24 is located on the PS 20. This is shown at 44. [0035] Next, a non-woven fusible web 26 formed with fusible fibers or strands 28 as discussed above that are made of a same material type as the at least one PS batt layer 22A, 22B is applied at least one of between the base fabric 12 and the at least one PS batt layer 22A, 22B or between the PS batt layers 22A, 22B.

[0036] At this point, it would also be possible to provide at least one MS batt layer 30 as well as a non-woven fusible web 32 that is located at least one of between the MS batt layer 30 and the base fabric 12 or between the MS batt layers 30A, 30B.

[0037] Next, the fusible fibers or strands 28 of the non-woven fusible web

26, as well as the non-woven fusible web 32, if present, are punched at least one of through the base fabric 12 or the batt layers along with the batt fibers 24 during needling of the press felt 10, 10’ to provide a uniform distribution of the fusible fibers or strands 28 through the base fabric 12 and with the at least one paper support side batt 22A, 22B, as well as the machine side batt layer(s) 30, if present. This is shown at 48.

[0038] The non-woven fusible fibers or strands 28 are then melted during the subsequent heat-setting of the press felt 10, 10’, resulting in the material of the non-woven fusible fibers 28 being uniformly distributed through the at least one PS batt layer 22A, 22B, as well as the base fabric 12, and also the at least one MS batt layer 30, if present. This is shown at 50.

[0039] Additionally, it is preferred that the press felt 10, 10’ is tentered during the heat-setting process in order to maintain the dimensions and stability of the finished press felt 10, 10’.

[0040] While polyamide is a preferred material for both the batt fibers 24 as well as the fusible fibers or strands 28, those skilled in the art will recognize that other materials can be used. However, it is necessary to have the batt fibers 24 as well as the fusible fibers or strands 28 made of a same type of material, such as polyamide as discussed above, because of the improved bonding between the materials to reduce surface wear and increase felt life through improved batt retention.

[0041] Having thus described the present invention in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description of the invention, could be made without altering the inventive concepts and principles embodied therein. It is also to be appreciated that numerous embodiments incorporating only part of the preferred embodiment are possible which do not alter, with respect to those parts, the inventive concepts and principles embodied therein. The present embodiment and optional configurations are therefore to be considered in all respects as exemplary and/or illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all alternate embodiments and changes to this embodiment which come within the meaning and range of equivalency of said claims are therefore to be embraced therein.