WO2007086968A2

WO2007086968A2 - Fiber with release-material sheath for papermaking belts

Info

Publication number: WO2007086968A2
Application number: PCT/US2006/042276
Authority: WO
Inventors: James F. Ii Peterson; Kambiz Damaghi; Pierluigi Cappellini
Original assignee: First Quality Fibers, Llc
Priority date: 2005-11-01
Filing date: 2006-10-27
Publication date: 2007-08-02
Also published as: US20070098984A1; WO2007086968A3

Abstract

Fibers with release-material sheaths, methods and systems for making such fibers papermaking belts incorporating such fibers, and papermaking processes using belts incorporating such fibers are described.

Description

FIBERWITH RELEASE-MATERIAL SHEATH FOR PAPERMAKING BELTS

FIELD OF INVENTION

[0001] The present invention relates to papermaking belts. More particularly, the present invention concerns fibers with release-material sheaths, methods and systems for making such fibers, papermaking belts incorporating such fibers, and papermaking processes using belts incorporating such fibers.

BACKGROUND

[0002] Considerable efforts have been devoted to increasing the efficiency and reducing the costs of making various types of paper, including facial tissue, paper towels, bathroom tissue, and napkins. As part of this effort, there have been numerous attempts to improve the durability and/or release properties of papermaking belts (i.e., the belts and fabrics used during one or more stages of a papermaking process to carry a fibrous web that is being made into paper).

[0003] For example, U.S. patents 6,701,637 and 6,514,382 describe the application of release coatings (e.g., fluoropolymers and silicone release agents) to papermaking belts to reduce the tendency of the fibrous web to stick to the belt. These release coatings, however, are temporary and need to be reapplied, thereby increasing costs.

[0004] To avoid or minimize the use of temporary chemical release agents, WO

03/057977 A2, an international application published under the PCT, describes "papermaking belts and industrial textiles with enhanced surface properties." This application discusses the use of a primer to graft a resin system onto a textile fabric after the surface of the fabric has been sanded. (Belt fabric is typically sanded to increase its surface contact area.) The resin system "provides a number of benefits including the enhancement of hydrophobic properties giving superior paper web sheet release thus eliminating or at least minimizing the need to continuously apply a temporary chemical release agent to the TAD (through-air drying) fabric." [0005] The belts described in WO 03/057977 A2, however, suffer from several deficiencies and shortcomings. The resin may not uniformly cover the fabric, thereby increasing the amount of temporary chemical release agent that needs to be applied to the fabric belt to provide acceptable release properties. Moreover, the use of a primer increases the complexity of the fabrication process.

[0006] In another example, WO 00/51801 describes a transfer fabric that "employs a sheath-core composite yarn which may be heated on one or both surfaces so that the sheath component is melted. Melting produces a support layer which is non-porous or substantially non-porous. The core of each yarn [which has a higher melting temperature than the sheath component] is unaffected by melting and thus becomes embedded in the support layer."

[0007] The belts described in WO 00/51801 also suffer from several deficiencies and shortcomings. The sheath material (e.g., polyurethane) is a tacky substance, not a non- sticking material. Thus, there is no reduction in the amount of temporary chemical release agents that must be repeatedly applied to these belts to provide adequate release properties. [0008] In another example, WO 99/05358 describes "yarns or fibres which have been subjected to plasma treatment." "To provide a water-repellant finish (hydrophobic) the plasma may be created from a siloxane or perfluorocarbon compound." One advantage cited in WO 99/05358 for plasma treatment is that "very small amounts of the raw materials are required (e.g., 30-100 mg per m² fabric)." [0009] The belts described in WO 99/05358 also suffer from several deficiencies and shortcomings. The material deposited on the yarn or fiber by the plasma is so thin (e.g., 30- 100 mg per m² corresponds to 150-500 Angstroms for a material with a density of 2 gm/cm³) that the material will not be durable. Indeed, most or all of the material would be removed from belts made of plasma-treated yarn if the belts were sanded. [0010] Thus, there remains a need for improved papeπnaking belts with better durability and release properties. SUMMARY

[0011] The present invention addresses the needs described above by providing fibers with release-material sheaths, methods and systems for making such fibers, papermaking belts incorporating such fibers, and papermaking processes using belts incorporating such fibers.

[0012] One aspect of the invention involves a fiber for use in a papermaking belt. The fiber includes an inner core and an outer sheath. The outer sheath has a thickness of at least 10 microns prior to sanding, if any, of the fiber, and includes a release material to facilitate the release of a paper web when the paper web is in contact with the fiber.

[0013] Another aspect of the invention involves a method for making a fiber. The method includes forming a fiber core and forming an outer sheath around the fiber core. The outer sheath has a thickness of at least 10 microns prior to sanding, if any, of the fiber, and includes a release material to facilitate the release of a paper web when the paper web is in contact with the fiber.

[0014] Another aspect of the invention involves a papermaking belt that includes a mesh of fibers. At least some of the fibers include an outer sheath integrally formed around an inner core. The outer sheath has a thickness of at least 10 microns prior to sanding, if any, of the belt, and includes a release material to facilitate the release of a fibrous web of paper when the web is in contact with the belt.

[0015] Another aspect of the invention is a method of intermeshing a plurality of fibers to form a papermaking fabric. At least some fibers in the plurality of fibers include an outer sheath integrally formed around an inner core. The outer sheath has a thickness of at least 10 microns prior to sanding, if any, of the fabric, and includes a release material to facilitate the release of a fibrous web of paper when the web is in contact with the fabric.

[0016] Another aspect of the invention is a method of using a papermaking belt to carry a fibrous web in at least one part of a papermaking process. The papermaking belt includes a mesh of fibers. At least some of the fibers include an outer sheath integrally formed around an inner core. The outer sheath has a thickness of at least 10 microns prior to sanding, if any, of the belt, and includes a release material to facilitate the release of a fibrous web of paper when the web is in contact with the belt. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] For a better understanding of the aforementioned aspects of the invention as well as additional aspects and embodiments thereof, reference should be made to the Description of Embodiments below, in conjunction with the following drawings in which like reference numerals refer to corresponding parts throughout the figures.

[0018] FIG. 1 is a schematic diagram illustrating an exemplary system for producing fibers with release-material sheaths.

[0019] FIG. 2 is a schematic diagram illustrating the system of FIG. 1 with additional components for measuring fiber uniformity, cooling fiber in a controlled manner, and winding fiber onto a spool.

[0020] FIG. 3 is a schematic diagram illustrating the spin pack assembly in more detail.

[0021] FIG. 4 is a schematic diagram illustrating multi-purpose blocks 350 A & 350 B and cutaway views of transfer/heating blocks 400 A & 400 B in more detail.

[0022] FIG. 5 is a flow chart illustrating an exemplary process for producing fibers with release-material sheaths.

[0023] FIG. 6 is a schematic diagram illustrating exemplary fiber core cross sections, including (a) circular, (b) corrugated, (c) rectangular, (d) rectangular with rounded corners, and (e) racetrack oval.

DESCRIPTION OF EMBODIMENTS

[0024] This section describes fibers with release-material sheaths, methods and systems for making such fibers, papermaking belts incorporating such fibers, and papermaking processes using belts incorporating such fibers. Reference will be made to certain embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the embodiments, it will be understood that it is not intended to limit the invention to these particular embodiments alone. On the contrary, the invention is intended to cover alternatives, modifications and equivalents that are within the spirit and scope of the invention as defined by the appended claims. [0025] Moreover, in the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these particular details. In other instances, methods, procedures, and components that are well-known to those of ordinary skill in the art are not described in detail to avoid obscuring aspects of the present invention.

[0026] FIG. 1 is a schematic diagram illustrating an exemplary system for producing fibers with release-material sheaths. The system in FIG. 1 includes both "A" components that are used to extrude the core of the fiber and "B" components that are used to continuously extrude the release-material sheath around the core of the fiber. The A and B mechanical components are nearly the same in configuration, with the main difference being the size of the motor/extruder combination. This exemplary system includes: extruder drive assemblies 100 A & 100 B, feed hopper/dryer systems 200 A & 200 B, extruder screw/barrel assemblies 300 A & 300 B, barrel heater bands 310 A & 310 B, multi-purpose blocks 350 A & 350 B, transfer/heating blocks 400 A & 400 B, band heaters 410 A & 410 B for transfer/heating blocks 400 A & 400 B, pump/drive assemblies 500 A & 500 B, pump heater bands 510 A & 510 B, planetary gear pumps 520 A & 520 B, flow distributors 600 A & 600 B, and band heaters 610 A & 610 B for flow distributors 600 A & 600 B.

[0027] FIG. 2 is a schematic diagram illustrating the system of FIG. 1 with additional components for measuring fiber uniformity, cooling fiber in a controlled manner, and winding fiber onto a spool. The additional components include: idler roll 1300, individual product guide 1350, segmented idler roll 1400, quench unit stage 1 1100, quench unit stage 2

1150, quench unit stage 3 1000, segmented drive roll 1200 (with independent controlling motors 1250X for each segment in drive roll 1200), laser micrometer 1900, and winding unit 2000. Winding unit 2000 includes electrically driven high precision draw rolls 2100, accumulator system 2200, and traverse mechanism 2300 for fiber spool 2400.

[0028] In some embodiments, quench unit stage 3 1000 is removed and quench unit stage 1 1100 and quench unit stage 2 1150 are lowered to be closer to spinneret face plate 700. As shown in FIG. 2, in some embodiments, quench units 1000, 1100, and 1150 are stacked on top of each other in the same orientation so that the air flows in the same direction in each quench unit (e.g., right to left in FIG. 2). In other embodiments (not shown), the quench units are stacked in a staggered configuration so that the airflows are in opposite directions in adjacent quench units. For example, the airflow in quench unit stage 1 1100 is right-to-left and the airflow in quench unit stage 2 1150 is left-to-right (with quench unit stage 3 1000 removed). Opposing airflows can help maintain the shape of the fiber.

[0029] In some embodiments, each filament has its own winding unit 2000, which allows for individual adjustment in filament speed. (For clarity, only one winding unit 2000 is shown in FIG. 2.) Multiple winding units 2000 and multiple spinneret inserts 800 allow for the formation of distinct fibers from each of the filament streams. Thus, if desired, a variety of fibers with different shapes and/or sizes can be run concurrently in the extrusion system by varying the spinneret insert(s) 800 and/or the winder 2000 settings. The winding unit accumulator system 2200 provides for continuous operation of the winder even during spool changes through the accumulation of fiber. The traverse mechanism 2300 controls the movement of spool 2400 and is electronically integrated to adjust take-up speed to uniformly wind fiber 1600 onto the spool as the diameter of the fiber accumulated on spool 2400 increases. Traverse mechanism 2300 moves fiber spool 2400 in and out during fiber 1600 uptake onto spool 2400. Additional adjustments are provided for each of the fiber streams produced via the substitution of spinneret inserts 800, e.g., varying the spinneret size and/or geometric shape.

[0030] It will be understood by those of ordinary skill in the art that additional flow distribution channels could be connected with additional extruders to produce multilayered fiber core and/or multilayered release-material sheaths.

[0031] FIG. 3 is a schematic diagram illustrating the spin pack assembly 950 in more detail. Spin pack assembly 950 is typically comprised of a number of sub-blocks, such as: multi-purpose blocks 350 A & 350 B, transfer/heating blocks 400 A & 400 B, filter block 535, flow distributors 600 A & 600 B, band heaters 610 A & 610 B for flow distributors 600 A & 600 B, spinneret face plate 700, spinneret insert(s) 800, spin face heater bands 825, and filtration/polymer integration sub-assembly 850. Filter block 535 contains polymer filters 525. Polymer filters 525 remove any polymer gels present and also remove any potential charred polymer from the extrusion system. Exemplary filter cups are available through the Mott Filter Company (84 Spring Lane, Farmington, CT. 06032) and are capable of removing particles that typically range from 10 to 100 microns in size. Spinneret insert(s) 800 provides for rapid replacement and changeover in spinneret shape(s) and spinneret size(s). As is well- known in the art, polymer integration sub-assembly 850 combines the molten core and sheath materials just prior to co-extrusion so that integrally formed (core + sheath) fiber structures can be produced (e.g., see U.S. Patent 5,533,883, the disclosure of which is hereby incorporated by reference). Co-extrusion promotes adhesion between the core and the release-material sheath so that no primer is needed. [0032] FIG. 4 is a schematic diagram illustrating multi-purpose blocks 350 A & 350

B and cutaway views of transfer/heating blocks 400 A & 400 B in more detail. Multipurpose blocks 350 A & 350 B include burst plugs 353 A & 353 B (pressure safety valves), temperature probes 352 A & 352 B, and pressure transducers 351 A & 351 B. The design of blocks 350 A & 350 B and 400 A & 400 B minimizes resistance to polymer flow and provides feedback on processing parameters (e.g., temperature and pressure). Blocks 400 A & 400 B can be split into two halves for easier cleaning. Transfer blocks 400 A & 400 B also include breaker plates 360 A & 360 B to improve the mixing of melted polymer. FIG. 4 illustrates system components for both the core and the sheath, with each designated by an A or B, respectively. As noted above, it will be understood by those skilled in the art that spin pack assembly 950 could be connected with additional extruders to produce multilayered cores and/or multilayered sheaths.

[0033] The methods described herein can be applied to virtually all core materials and sheath release materials.

[0034] Exemplary core materials include, without limitation, polyester; nylon; polyphenylene sulphide; poly 1,4 cyclohexane dimethylene terephthalate; polyethylene naphthalate; polyetheretherketone; or combinations thereof.

[0035] As used in the specification and claims, a "release material" is a solid fluoropolymer [e.g., polytetrafluoroethylene (PTFE); fluorinated ethylene propylene (FEP) copolymers such as a tetrafluoroethylene hexafluoropropylene copolymer; perfluoroalkoxy (PFA) polymers; ethylene and tetrafluoroethylene (EFTE) copolymers; tetrafluoroethylene hexafluoropropylene vinylidene (THV) copolymers; and polyvinylidene difluoride] that facilitates the release of a paper web from a papermaking belt.

[0036] FIG. 5 is a flow chart illustrating an exemplary process for producing fibers with release-material sheaths. As noted above, the core and sheath extruders operate in an analogous manner, although they may be different in size. [0037] At 5010, pellets of clean and purified core and sheath polymer resins

(polymeric starting materials, typically supplied by commercial resin manufacturers) are fed into feed hopper/dryer systems 200 A & 200 B, respectively. Dryer systems 200 A & 200 B continually dry the polymer resins using compressed air and a heating system. The temperature used in dryer systems 200 A is typically between 100 to 140 ⁰C, with 135 °C being preferred. Moisture is removed from the resins by operating dryer systems 200 A at a dew point of - 40 ⁰C. Dryer system 200 B is not required to operate for all materials. Both dryer systems 200 A & 200 B also have two coalescing filters in series to remove liquid water and oil droplet particles down to 0.01 micron in size. An exemplary dryer system 200 is a Novatec^ta Compressed Air Dryer (Novatec, Inc. 222 E. Thomas Ave., Baltimore Md. 21225, www.novatec.com).

[0038] At 5020, extruder drive assemblies 100 A & 100 B feed the polymers into extruder screw/barrel assemblies 300 A & 300 B, respectively, where the polymers are melted. Extruder drive assemblies 100 A & 100 B are dedicated drive systems that maintain consistent operating RPMs to provide stable pressures during the continuous extrusion processes.

[0039] The gear ratios of the pulleys in extruder drive assemblies 100 A & 100 B can be changed to enable the drive assembly motors to run at a preferred rate of 90-100% of the rated motor speed. A stable motor speed produces a stable screw speed, which, in turn, produces a consistent extrudate pressure. The measured pressure fluctuations are less than 2% during operation at various working pressures. Thus, the precision drives in extruder drive assemblies 100 A & 100 B enable greater extruder control and feeding uniformity of the extrudates.

[0040] In some embodiments, extruder screw/barrel assemblies 300 A & 300 B may be vented to remove volatile contaminants from the melted resins. In some embodiments, the polymers in the extruder assemblies may be blanketed with nitrogen (or inert gas) or subjected to vacuum in order to further reduce resin contamination and to improve the uniformity of the melts.

[0041] At 5030, the feed screws in extruder screw/barrel assemblies 300 A & 300 B move the melted core and sheath polymers through multipurpose blocks 350 A & 350 B and transfer/heating blocks 400 A & 400 B into planetary gear pumps 520 A & 520 B, respectively, in a continuous, uniform manner. Planetary gear pumps 520 A & 520 B are driven by dedicated drive assemblies 500 A & 500 B, respectively. Pumps 520 A & 520 B are single inlet pumps with multiple outlets. In some embodiments, the temperatures for the core and sheath polymers of the fiber are independently controlled and only come together as the fiber is being formed, thereby allowing for core and sheath polymers with different temperatures to be extruded simultaneously.

[0042] At 5040, the melted core and sheath polymers move back into their respective transfer/heating blocks 400 A & 400 B in a continuous, uniform manner. Pumps 520 A & 520 B pressurize the molten polymers as they divide and distribute the flows into independent distribution channels in transfer blocks 400 A & 400 B. For clarity, FIG. 4 shows just one of the independent channels (i.e., channel 450 A) located within transfer/heating block 400 A. Similarly, FIG. 4 shows just one of the independent channels (i.e., channel 450 B) located within transfer/heating block 400 B.

[0043] Channels 450 A and 450 B in blocks 400 A & 400 B, respectively, permit high polymer flow rates with low restriction, thereby reducing shear heating (and concurrent temperature nonuniformities) in the polymer melts. The direction of polymer flow in spin pack assembly 950 can be changed in 90° increments. Thus, extrusion via spin pack assembly 950 can be vertically upward, vertically downward, or horizontal. Heating bands 610 A & 610 B facilitate temperature control (and thus viscosity control) of the molten polymers while passing through spin pack assembly 950. [0044] At 5050, the molten sheath material flows uniformly around the molten core material in polymer integration subassembly 850, just before the molten core and sheath enter spinneret face plate 700. Spinneret face plate 700 is equipped with spinneret inserts 800. Spinneret inserts 800 enable rapid changeover in spinneret hole diameter, shape and the pin length-to-diameter ratio. The spin face heaters 825 control the temperature uniformity of the core and sheath extrudates as they exit the spinneret inserts 800 to form fiber 1600.

[0045] At 5060, the molten polymer core and sheath are co-extruded through spinneret face plate 700. In some embodiments, forcing the molten polymer core through circular openings in spinneret insert(s) 800 forms a fiber core with substantially circular cross-sections. In other embodiments, forcing the molten polymer core through rectangular or other similarly shaped openings in spinneret insert(s) 800 forms a fiber core with substantially flat cross-sections. FIG. 6 is a schematic diagram illustrating exemplary fiber core cross sections, including (a) circular, (b) corrugated, (c) rectangular, (d) rectangular with rounded comers, and (e) racetrack oval. The corrugation shown in FIG. 6(b) applied to a circular cross section can also be applied to other shapes, such as the shapes shown in FIGs. 6(c)-6(e). Co-extruding the molten polymer sheath that has flowed around the molten core material through openings in spinneret insert(s) 800 forms a sheath around the core. Spinneret insert(s) 800 may be changed to allow simultaneous production of different size and/or shaped fibers, thereby adding versatility to the production system.

[0046] In some embodiments, to increase the uniformity of the fiber cross sections, the extrusion in step 5060 is performed in a substantially vertical upward direction, against the force of gravity. [0047] If vertically upward extrusion is used, at the start of the extrusion process, a metal rod or other inert surface makes contact with fiber 1600 exiting spinneret insert 800, and lifts fiber 1600 up through individual product guide 1350, then to idler roll 1300 and onto drive roll 1200. Fiber 1600 is/are then passed over segmented idler roll 1400 and through the rest of the system in the same manner as is commonly done for horizontal or vertically downward extrusion processes. Each segment in idler roll 1400 can spin at a different speed if fiber streams with different dimensions are being extruded simultaneously. Alternatively, each segment in idler roll 1400 can spin at the same speed if fiber streams with the same dimensions are being extruded simultaneously.

[0048] At 5070, fiber 1600 is cooled in a controlled manner. In some embodiments, fiber 1600 is cooled in a two- or three-stage cooling zone system.

[0049] In a two-stage cool with stage 3 quench unit 1000 removed, stage 1 quench unit 1100 is located adjacent to the spinneret face 700 and typically 3.5 inches away from fiber 1600 exiting spinneret insert(s) 800. Stage 1 quench unit 1100 gradually cools fiber 1600 by blowing air over the fibers. Stage 1 quench unit 1100 is typically operated between 0 and 30 ⁰C, with 0 ⁰C being preferred. Fans in stage 1 quench unit 1100 typically operate between 0 and 1750 RPM (corresponding to a measured air velocity of 0 - 493 feet per minute), with 1275 RPM (188 feet per minute) being preferred. Stage 2 quench unit 1150 typically operates at a temperature between 0 and 30 ⁰C, with 0 ⁰C being preferred. Fans in stage 2 quench unit 1150 typically operate between 0 and 1750 RPM (corresponding to a measured air velocity of 0 - 573 feet per minute), with 1300 RPM (192 feet per minute) being preferred. Stage 2 quench unit 1150 is stacked in a staggered configuration with stage 1 quench unit 1100 so that the airflows in quench units 1100 and 1150 are in opposite directions. Stage 2 quench unit 1100 is positioned typically 2 inches away from the centerline of fiber 1600. The staggered configuration allows for more uniform application of cool air to fiber 1600, thereby producing more uniform cooling and preventing curling of the fiber. In some embodiments, the quench system is segmented into discrete chambers around each fiber filament stream to allow for individual control of air temperature and air speed around each individual fiber filament stream.

[0050] In some embodiments, stage 1 1100, stage 2 1150 and stage 3 1000 quench units are stacked directly on top of one another. This embodiment is preferred for round fibers as the "curling" effect is less prevalent. This embodiment also can be segmented to allow for individual control of air temperature and airflow speed for each fiber. Tables 1-6 give exemplary process conditions for the co-extrusion of a fiber with a release-material sheath 1600.

Table 1

Exemplary process conditions for 500 micron diameter polyester fiber (e.g., Dupont 5149 Polyester) with a THV sheath (e.g., Dyneon THV 220G)

Fiber was produced at 8.5 meters per minute. Tensile strength was 8.60 kgf.

Table 2

Exemplary process conditions for 350 micron diameter polyester fiber (e.g., Dupont 5149 Polyester) with a THV sheath (e.g., Dyneon THV 220G)

Fiber was produced at 14.6 meters per minute. Tensile strength was 6.00 kgf.

Table 3

Exemplary process conditions for 500 micron diameter polyester fiber (e.g., Dupont 5149 Polyester) with a THV sheath (e.g., Dyneon THV 815G)

Fiber was produced at 8.4 meters per minute. Tensile strength was 9.44 kgf.

Table 4

Exemplary process conditions for 350 micron diameter polyester fiber (e.g., Dupont 5149 Polyester) with a THV sheath (e.g., Dyneon THV 815G)

Fiber was produced at 14.2 meters per minute. Tensile strength was 5.84 kgf.

Table 5

Exemplary process conditions for 500 micron diameter polyester fiber (e.g., Dupont 5147 Polyester) with a THV sheath (e.g., Dyneon THV 220G)

Fiber was produced at 7.3 meters per minute. Tensile strength was 9.83 kgf.

Table 6

Exemplary process conditions for 350 micron diameter polyester fiber (e.g., Dupont 5149 Polyester) with a FEP sheath (e.g., Dupont FEP 100)

Fiber was produced at 8.3 meters per minute. Tensile strength was 8.60 kgf.

[0051] At 5080, the uniformity of the fiber cross section is measured. In some embodiments, the measurement is done using laser micrometer 1900. An exemplary laser micrometer 1900 is a Beta LaserMike diameter gauge (Beta LaserMike, 8001 Technology

Blvd., Dayton, Ohio 45424, www.betalasermike.comV In some embodiments, to increase the uniformity of the fiber cross section, laser micrometer 1900 can be part of an on-line automatic feedback control system. An automatic feedback system integrated with laser micrometer 1900 can send information used to control a servo-motor system for each fiber filament, thereby controlling size and operation independently for each fiber filament.

[0052] As shown in FIG. 2, at 5090, fiber 1600 is fed to S wrap system 2100 in winding unit 2000 and wound onto fiber spool 2400.

[0053] In addition to the steps described above, after extrusion, fiber 1600 can be drawn (i.e., stretched) by a variety of different methods, including without limitation: (1) spin drawing; (2) spin drawing plus solid-state drawing; and (3) continuous incremental drawing.

[0054] In spin drawing, fiber 1600 are drawn immediately after co-extrusion and wound onto a spool. This drawing method typically provides excellent sheath uniformity with no phase separation between the sheath and the core. This drawing method typically produces fiber with low molecular orientation and moderate strength. [0055] In spin drawing plus solid-state drawing, fiber 1600 is drawn immediately after co-extrusion and wound onto a spool. Fiber 1600 is then unwound from the spool in a secondary process and drawn in the solid state with a large draw ratio. This drawing method typically produces highly oriented fiber with high strength and excellent sheath uniformity. However, phase separation between the core and sheath during the solid-state drawing step may produce defects in fiber 1600.

[0056] In continuous incremental drawing, co-extruded fiber 1600 is continuously drawn by increasing the linear speed of each roll that fiber 1600 passes over. For example, the linear speed of a second roll will be greater than the linear speed of a first roll, thereby drawing the fiber between the second roll and the first roll. This incremental drawing process can be repeated between additional rolls and under different drawing temperatures. This drawing procedure results in a large draw ratio and high molecular orientation without a separate solid-state drawing step. This drawing method typically produces high strength fiber with excellent physical and environmental stability, excellent cross section uniformity, and no phase separation between the sheath and core of fiber 1600.

[0057] Fiber 1600 with a wide range of dimensions can be manufactured. Table 7 presents exemplary dimensional data for 350 micron and 500 micron diameter fibers. In some cases, the standard deviation in fiber cross-section diameter is less than 2 percent of the average fiber cross-section diameter. In some cases, the standard deviation in fiber cross- section diameter is less than 0.5 percent of the average fiber cross-section diameter. The uniformity of the fiber core cross section is essentially the same as the uniformity of the entire (core + sheath) cross section because the sheath thickness is much less than the core thickness. The sheath thickness was typically 10 microns, although greater thicknesses can be used (e.g., to ensure that some release material remains if belts made from the fibers are sanded).

Table 7 Exem lar dimensional data

[0058] A plurality of fibers can be intermeshed to form a papermaking fabric (belt). The intermeshing can be done in a wide variety of ways that are well known in the art, including by weaving, knitting, or coiling. Examples of these methods are described in U.S. Patents 6,352,772; 6,174,825; 5,776,313; and 4,239,065, the disclosures of which are hereby incorporated by reference. In some embodiments, the paper making belt made from the fibers also includes a temporary release material applied to the mesh of fibers. [0059] The papermaking belt can be used to carry a fibrous web in at least one part of a papermaking process. The papermaking can be done in a wide variety of ways that are well known in the art. Examples of papermaking methods are described in U.S. Patents 6,514,382; 6,248,212; 6,139,686; 3,994,771; and 3,825,381, the disclosures of which are hereby incorporated by reference. [0060] The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

Claims

WHAT IS CLAIMED IS:

1. A fiber for use in a papermaking belt, comprising: an inner core and an outer sheath that are integrally formed, wherein the outer sheath: has a thickness of at least 10 microns prior to sanding, if any, of the fiber, and includes a release material with a melting temperature greater than the melting temperature of the inner core to facilitate the release of a paper web when the paper web is in contact with the fiber.

2. A fiber for use in a papermaking belt, comprising: an inner core and an outer sheath, wherein the outer sheath: has a thickness of at least 10 microns prior to sanding, if any, of the fiber, and includes a release material to facilitate the release of a paper web when the paper web is in contact with the fiber.

3. The fiber of claim 2, wherein the core and the outer sheath are integrally formed.

4. The fiber of claim 3, wherein the core and the outer sheath are formed by co- extrusion.

5. The fiber of claim 2, wherein the thickness of the outer sheath is sufficient to allow sanding of the fiber without reaching the inner core.

6. The fiber of claim 2, wherein the release material has a melting temperature greater than the melting temperature of the inner core.

7. The fiber of claim 2, wherein the standard deviation in fiber cross-section diameter is less than 2 percent of the average fiber cross-section diameter.

8. The fiber of claim 2, wherein the standard deviation in fiber cross-section diameter is less than 0.5 percent of the average fiber cross-section diameter.

9. A method of making a fiber, comprising forming a fiber core, and forming an outer sheath around the fiber core, wherein the outer sheath: has a thickness of at least 10 microns prior to sanding, if any, of the fiber, and includes a release material to facilitate the release of a paper web when the paper web is in contact with the fiber.

10. The method of claim 9, wherein the core and the sheath are integrally formed.

11. The method of claim 9, wherein the core and the sheath are formed by coextrusion.

12. The method of claim 9, wherein there is no primer between the core and the sheath.

13. A paper making belt, comprising: a mesh of fibers, wherein at least some of the fibers include an outer sheath integrally formed around an inner core, wherein the outer sheath: has a thickness of at least 10 microns prior to sanding, if any, of the belt, and includes a release material to facilitate the release of a fibrous web of paper when the web is in contact with the belt.

14. The paper making belt of claim 13, further including a temporary release material applied to the mesh of fibers.

15. A method, comprising : intermeshing a plurality of fibers to form a papermaking belt, wherein at least some fibers in the plurality of fibers include an outer sheath integrally formed around an inner core, wherein the outer sheath: has a thickness of at least 10 microns prior to sanding, if any, of the belt, and includes a release material to facilitate the release of a fibrous web of paper when the web is in contact with the belt.

16. The method of claim 15, wherein the intermeshing is done by weaving, knitting, or coiling.

17. A method, comprising: using a papermaking belt to carry a fibrous web in at least one part of a papermaking process, wherein the belt comprises a mesh of fibers, wherein at least some of the fibers include an outer sheath integrally formed around an inner core, wherein the outer sheath: has a thickness of at least 10 microns prior to sanding, if any, of the belt, and includes a release material to facilitate the release of a fibrous web of paper when the web is in contact with the belt.