Patent Publication Number: US-9416465-B2

Title: Process for making a high heat polymer fiber

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a process for making fiber from a high heat polymer. More specifically, the present invention relates to fiber spun from a polymer having a melt temperature that ranges from about 180° C. to 500° C. 
     BACKGROUND OF THE INVENTION 
     High melting temperature polymers, such as polyimide polymers having a glass transition temperature that can range from about 180° C. to about 450° C. have found utility in a variety of applications because of their currently extreme physical properties in addition to their heat resistant properties. For example, polyetherimides, available from General Electric Company under the ULTEM® trademark have high glass transition temperatures, are ductile, flame resistant and generate low amounts of smoke while still having good chemical resistivity. These polymers have found wide use in shaped articles, sheet materials, and coatings for use in challenging physical environments such as aerospace applications. 
     Despite their high processing temperatures, high performance polymers, such as polyetherimides can be made into fibers, however, they require higher processing temperatures not generally used for processing other polymeric fibers. These processing conditions often lead to unexpected and difficult processing issues in the commercial manufacture of articles. 
     In a conventional system for making polymer fiber, polymer resin is extruded in an extruder and passed through a spinneret containing a plurality of hole openings to form a fiber bundle which is cooled, and drawn to a spool or coil. High performance polymers, such as polyetherimides, require higher processing temperatures not generally used for processing other polymeric fibers. These processing conditions often lead to unexpected and difficult processing issues in the commercial manufacture of articles and fiber. In addition, the output production rate of fibers generated from materials having high melt temperature or high glass transition temperatures are typically low, which limits on the cost-effectiveness for these materials in a variety of product applications. There is therefore a continuing need in the art to develop processes for high heat materials being used to make fibers. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment, a process for producing polymer fiber includes melting a polymer having a melt temperature that ranges from about 180° C. to about 450° C. to produce a molten polymer, passing the molten polymer through a spinneret comprising a plurality of hole openings to produce a fiber bundle, and contacting the fiber bundle with a cooling medium having a substantially uniform flow distribution across a bundle width of the fiber bundle as it emerges from the spinneret, where the cooling medium has a temperature that ranges from about 0° C. to about 80° C. 
     In another embodiment the process for producing polymer fiber includes cooling the fiber bundle by directing the cooling medium toward the fiber bundle through a cooling zone as it contacts the fiber bundle, and wherein the width of the cooling zone is up to about 10% greater than the size of the bundle width. 
     In yet another embodiment the process for producing polymer fiber includes melting a polymer having a melt temperature that ranges from about 180° C. to about 450° C. to produce a molten polymer, passing the molten polymer through a spinneret comprising a plurality of hole openings to produce a fiber bundle comprising a cross-sectional first region and a cross-sectional second region, the cross-sectional second region having a fiber density that is less than fiber density of the cross-sectional first region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various embodiments of the present invention can be understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Also, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic illustration of spinning apparatus according to an embodiment of the invention; and 
         FIG. 2  is a cross-sectional view taken along lines  2 - 2  of the spinning apparatus of  FIG. 1  through the fiber bundle below the spinneret, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the present invention the term “Denier” refers to a unit of fineness of silk and some artificial fibers such as nylon equal to one gram per 9,000 meters of yarn. 
     For purposes of the present invention, the term “polymer” is meant to include oligomers, homopolymers and copolymers. 
     For purposes of the present invention the term “polyetherimide” refers to a polymer containing monomer units which comprise both a ether and an imide group. 
     An ether group is well known in the art and consists of an oxygen atom single bonded to two different carbon atoms. An imide group is a nitrogen containing acid having two double bonds. 
     The term “remove”, “removed” and “removing” all refer to the removal of foreign particulate matter from the polymer with which fiber is to be made. 
     “Filter screen” refers to a woven metal mesh, or gauze, with a specified number of holes per unit area used as a filter. Sintered metal powder or fibers can also be used. The screen mesh may be composed of a square weave or a weave with parallel diagonal lines, sometimes called “Dutch Twill”. These screens are generally classified by their mesh number and open area. 
     “Filter pack” or “screen pack” is a combination of two or more layers of screens or gauze for use in filtering a polymer. For example, a screen pack may be made from an assembly of a 20 mesh, 60 mesh, 100 mesh, 60 mesh and 20-mesh gauzes (designated as 20/60/100/60/20). 
     “Foreign Particulate Matter” refers to contamination in the extrusion melt stream by extraneous materials (metal, paper, wood, dust, etc.), non-polymeric material which can adversely effect the optimal performance of the fiber and/or the fiber making process according to the present invention. For example, in many high Tg polymers, organic material exposed to the high reaction or processing temperatures, required for making and/or using these polymers can be turned to black specs of carbonized polymer of various sizes. These specs can cause one or more holes in the spinneret to become blocked and cause pressure changes on the inside surface of the spinneret. Such pressure changes adversely affect the speed, volume and quality of fiber. Moreover, if such specs make it through the spinneret, they can become embedded in the fiber, and cause the fiber to have an area of inferior performance, such as a weak spot. Other foreign matter can come from reaction vessels, conduit pipe, shipping packages, unreacted reactants, gels, pre-polymer, process by-products, etc. 
     The term “rectifier” refers to a device to uniformly diffuse a cooling medium around the fiber bundle emerging from the spinneret. 
     The term “cooling zone” refers to the cross-sectional area along which the cooling medium is directed toward the fiber bundle that emerges from the spinneret. 
     The term “substantially uniform flow distribution” refers to the volumetric flow rate of cooling medium across a defined area. 
     The term “substantially even cooling rate” refers to the substantially even cooling of the individual fibers within the fiber bundle relative to one another. 
     The term “fiber density” refers to area taken up by the diameter of the fibers of a given region of the fiber bundle relative to the area of the fiber bundle as it emerges from the spinneret. The fiber density of a cross-sectional region of the fiber bundle is the summation of the cross-sectional areas of the fibers in the region divided by the cross-sectional area of the region. 
     The present invention relates to a process that converts high melting temperature polyimide polymer to fiber having desirable physical and mechanical properties at an improved output rate. It has been found that the production of high melting temperature polymers can be improved by employing heat-management techniques according to the various embodiments described herein. 
     In one embodiment, process for producing polymer fiber includes melting a polymer having a melt temperature that ranges from about 180° C. to about 450° C. to produce a molten polymer, passing the molten polymer through a spinneret comprising a plurality of hole openings to produce a fiber bundle, and contacting the fiber bundle with a cooling medium having a substantially uniform flow distribution across a bundle width of the fiber bundle as it emerges from the spinneret, where the cooling medium has a temperature that ranges from about 0° C. to about 80° C. The polymer can have a melt temperature that ranges from about 180° C. to about 500° C., in another embodiment from about 180° C. to about 470° C., in another embodiment from about 200° C. to about 450° C., and in yet another embodiment from about 300° C. to about 425° C. 
       FIG. 1  is a schematic showing spinning apparatus  10  generally used in a process for producing fiber according to an embodiment of the present invention. Molten polymer flows from an extruder  12 , into a metering pump  14  and then flows through a pack top  16  having at least one channel (not shown) that leads to a filter  18  to remove foreign particulate matter before the material flows through the spinneret  20  having holes  22 , to form a fiber bundle  30  made up of a plurality of individual polymer fibers or filaments. The number of individual fibers in the fiber bundle  30  can depend upon several factors relating to the design of the spinneret  20 , such as, for example the hole pattern, the number of holes  22  and sizes of holes  22 , and the size and geometric shape of the spinneret to accommodate the holes. For example, there may be anywhere from twenty to several thousand holes in a typical spinneret  20 , depending on whether a textile filament, industrial filament, or textile staple is being produced. 
     The fiber bundle  30  is quenched by quench system  32  which includes a gaseous cooling medium  33 , a source  34  that produces the cooling medium, such as for example a motorized fan, and a rectifier  36  through which the cooling medium flows on its path toward the fiber bundle  30 . Rectifiers  36  are commonly made from perforated mesh, for example metal or high temperature plastic, or a permeable foam material to provide a uniform velocity distribution across the path of the fiber bundle  30  extruded from the spinneret  20 . The rectifier  36  has a predetermined length, L, that defines the length of a cooling zone. The cooling medium flows in a direction represented by arrow  37  and shown, for example, in a direction that is transverse to the path of travel of the fiber bundle  30  which is indicated by arrow  38 . 
     Beyond the quench system  32 , the fiber bundle  30  is then further processed through a convergence guide  40  and are then drawn by at least one roll, or godet, for example rolls  42 ,  44 ,  46  and  48  and wound on a bobbin or spool  50 . Optionally, the process for producing fiber can include a finishing step in which a finish can be applied via a finish applicator (not shown) before the fiber bundle reaches the convergence guide  40 . 
       FIG. 2  is a cross-sectional illustration taken along the lines  2 - 2  of the spinning apparatus  10  of  FIG. 1  and through fiber bundle  30  with a view toward the spinneret  20 , according to an embodiment of the invention. As shown, quench system  32  further includes opposing sidewalls  60  and  62  which extend outward from the rectifier  36  alongside the fiber bundle  30  and which contain the flow of cooling medium  33  which flows through the rectifier  36 . As shown, sidewalls  60  and  62  span a width W 2  that is greater than the width W F  of the fiber bundle  30 , however, in alternative embodiments, sidewalls  60  and  62  can also span a width W 2  that is approximately equal to the width W F  of the fiber bundle  30 , or one of several widths between W 2  and W F . In an embodiment in which the distance between sidewalls  60  and  62  is greater that the transverse width W F  of the fiber bundle  30 , as shown in  FIG. 2 , sidewalls  60  and  62  can optionally include a first and a second flow guide  64  and  66 , respectively, which allow the cooling medium  33  to be directed toward the fiber bundle  30  through a cooling zone having a width W 1 . 
     As shown in  FIG. 2  the width of the cooling zone is substantially equal to the width W F  of the fiber bundle  30  as it exits the spinneret  20 . Flow guides  64 ,  66 , span a width W 1  which is less than the width W 2  of sidewalls  60 ,  62  to help prevent the cooling medium  33  from moving around the fiber bundle  30 , thereby causing uneven flow of cooling medium  33  across the transverse width W F  of the fiber bundle  30 . The flow guides  64 ,  66 , help thermally manage the flow of cooling medium across the fiber bundle  30  so that all fibers emerging from the spinneret  20  are cooled at a substantially uniform rate. That is, according to an embodiment of the present invention, the process for making polymer fiber includes contacting the fiber bundle with a cooling medium having a substantially uniform flow distribution across a bundle width of the fiber bundle as it emerges from the spinneret. Although the cooling medium exiting the source may have a constant velocity along the cooling zone, the process provides for a contacting the fiber bundle with a substantially uniform flow distribution across the width W F  of the fiber bundle so that the volumetric flow rate of the cooling medium is substantially uniform and the fibers are cooled at a substantially even cooling rate. 
     In alternative embodiments, sidewalls  60  and  62 , or flow guides  64  and  66  can be separated by a distance that extends slightly beyond, or short of, the transverse width W F  of the fiber bundle  30 , however, it has been found that if the cooling medium  33  is directed across a width that is substantially greater or substantially less than the transverse width W F , then the polymer filaments can be under-cooled or over-cooled and can break from the fiber bundle  30  thereby decreasing the production output rate of the fiber. That the fibers do not break or drop away from the fiber bundle along the cooling zone due to overcooling or undercooling, is an indication that the fibers are cooled at a substantially even cooling rate. The individual fibers within the fiber bundle cool within a temperature range that prevents the individual fibers from breaking due to overcooling and undercooling. As mentioned above, it is possible that the sidewalls  64  and  66  span a width W 2  that is approximately equal to the width W F  of the fiber bundle  30  and no flow guides extending from the sidewalls are present. Accordingly, in an example embodiment the process for producing fiber includes directing the cooling medium through a cooling zone as the cooling medium contacts the fiber bundle, where the width of the cooling zone W 1  is up to about 20%, in another embodiment up to about 10%, in yet another embodiment up to about 5% greater than the width W F  of the fiber bundle, and in still yet another embodiment is substantially equal to the width W F  of the fiber bundle  30 , and all ranges therebetween. 
     Thermal management of the high temperature polymer fibers of fiber bundle  30  exiting the spinneret  20  can be achieved by various arrangements of the pattern of holes of the spinneret  20  and the resulting pattern formed by the individual fibers of the fiber bundle  30 . The cross-sectional pattern of fiber bundle  30  shown in  FIG. 2  substantially reflects the pattern of the holes  22  ( FIG. 1 ) of the spinneret  20  through which the fiber bundle  30  is formed. Fiber bundle  30  has a cross-sectional first region  70  and a cross-sectional second region  72 , in which the fiber density of the first region  70  is greater than the fiber density of the second region  72 . It has been found that in a process for producing fiber, a spinneret  20  having at least two regions each of which has a different hole density and which produces a fiber bundle  30  having at least two cross-sectional regions of different polymer fiber density, results in improved productivity of the fiber. 
     The hole density of a particular region of the spinneret  20  is herein defined as the ratio of the open area of the holes of the region divided by the area of the region. The fiber density of a particular region is herein defined as the cross-sectional area of the fibers in the region divided by the cross-sectional area of the region. 
     In the example embodiment of  FIG. 2 , fiber bundle  30  has a cross-sectional first region  70  that surrounds a cross-sectional second region  72 , and the fiber density of the first region  70  is greater than the fiber density of the cross-sectional second region  72 . The fiber density of the cross-sectional second region of fiber bundle  30  is determined by the hole pattern of a second portion of the spinneret  20  (not shown) and opposite the cross-sectional second region of the fiber bundle  30 , having a hole density that is less than the hole density of the first portion of the spinneret  20 . The fiber density of the cross-sectional second region  72 , as shown in  FIG. 2 , is substantially zero, however, the fiber density of the second region  72  can be any fiber density that is less than the fiber density of the first region  70 . For example, the cross-sectional second region  72  of fiber bundle  30  can have a sparse arrangement of fibers relative to the cross-sectional first region  70  of the fiber bundle  30 . The region that has a relatively lower polymer filament density can reduce the heat build-up within the fiber bundle  30 , has been found to promote substantially even cooling of the fibers and result in increased productivity for the process of producing the fiber. The individual fibers of the cross-sectional first region  70  are shown as equally spaced apart, however, the filaments of cross-sectional first and second regions  70  and  72  may each be evenly spaced apart or irregularly spaced apart. 
     The area of the cross-sectional second region  72  can be less than the area of the cross-sectional first region  70 , in another embodiment, the cross-sectional second region is at least about 5% of the area of the cross-sectional first region, in another embodiment from about 5% to about 50% of the area of the cross-sectional first region, in yet another embodiment from about 10% to about 20% of the area of the cross-sectional first region, and all ranges therebetween. The fiber density of the cross-sectional second region  72  is less than about 90% of the fiber density of the cross-sectional first region  70 , in another embodiment less than about 50%, in another embodiment less than about 25%, and in yet another embodiment, the fiber density of the second region is substantially zero. 
     In another embodiment, the fiber bundle  30  can include a cross-sectional third region  74  that is surrounded by the cross-sectional first region  70 , and having a fiber density that is less than the fiber density of the first region  70 . The fiber density of the third region is determined by a third portion of the spinneret  20  (not shown) having a hole density that is less than the hole density of the first portion of the spinneret  20 . In the example embodiment shown in  FIG. 2 , the fiber density of the third region  74 , like the second region  72 , is substantially zero, however, the fiber density of the third region  74  can be any fiber density that is less than the fiber density of the first region  70 . For example, the cross-sectional third region  74  is at least about 5% of the area of the cross-sectional first region  70 , in another embodiment from about 5% to about 50% of the area of the cross-sectional first region, in yet another embodiment from about 10% to about 20% of the area of the cross-sectional first region, and all ranges therebetween. The fiber density of the cross-sectional third region  74  is less than about 90% of the fiber density of the cross-sectional first region  70 , in another embodiment less than about 50%, in another embodiment less than about 25%, and in yet another embodiment, the fiber density of the third region is substantially zero. Moreover, the fiber bundle  30  can include additional regions (not shown) having varying fiber density. For example, each of these additional regions can be surrounded by the first region  70  and can have a fiber density that is less than the fiber density of the first region. 
     The fiber density of the third region can be the same or different than the fiber density of the second region  72 . In one embodiment, the fiber density of each of the second region  72  and third region  74  of the fiber bundle  30  can be about 95% or less, in another embodiment about 80% or less, and in yet another embodiment about 50% or less than the fiber density of the first region  70 . In another embodiment, the fiber density of each of the second region  72  and the third region  74  can range from about 20% to about 95%, in another embodiment from abut 20% to about 80%, and in yet another embodiment from about 30% to about 70% of the fiber density of the first region  70 . 
     The cross-sectional second region  72  and third region  74  are shown to be substantially circular in shape, as determined by a hole pattern of the spinneret  20  which is substantially circular in shape, however, these regions can be one of many various shapes, for example, rectangular, triangular, etc., and the shape of the second region  72  can be different than the shape of the third region  74 . 
     Thermal management of the high heat generated by the polymer passing through the spinneret  20  to form a fiber bundle  30  according to the embodiments described above promotes uniform flow of cooling medium across the fiber bundle  30  to substantially equilibrate the cooling rate of each of the individual fibers within the fiber bundle. The embodiment shown in  FIG. 2  shows a spinning apparatus  10  for a process in which the cooling medium is directed by sidewalls  60  and  62  or protrusions  64  and  66 , as described above, or the spinneret includes at least two regions of different hole density to produce a fiber bundle  30  having at least two regions of different fiber density. However either of the above-described thermal management techniques may be employed separately depending upon the desired output rate of the fiber as well as several other factors pertaining to the polymer, for example, the melt index, the melt temperature, as can be determined by one of ordinary skill in the art. 
     The fiber bundle exiting the spinneret can be cooled with a cooling medium having a temperature that ranges from about 0° C. to about 80° C. to produce fibers depending on the particular composition of polymer comprising polyetherimide. In another embodiment, the cooling medium has a temperature that ranges from about 0° C. to about 40° C., and in yet another embodiment, the cooling medium has a temperature that ranges from about 10° C. to about 24° C. The cooling medium can be a liquid, for example water, or a gas, for example air. The cooling medium can be directed toward the fiber bundle as it emerges from the spinneret, and can have at a substantially uniform velocity distribution. For example the gaseous cooling medium directed toward the fiber bundle ranges from abut 0.01 to about 20 meters per second, in another embodiment from about 0.01 to about 10 meters per second, in yet another embodiment from about 0.05 to about 5 meters per second, and all ranges therebetween. Velocities which are too high can cause fibers to break, depending upon the composition of the polymer and the diameter of the fiber, for example. 
     Productivity output rates of fiber from at least about 100 meters/minute up to and including 7500 meters/minute can be achieved. In another embodiment, the output rates can range from about 100 meters/minute to about 5,000 meters/minute, in another embodiment from about 500 meters/minute to about 5,000 meters/minute. In still yet another embodiment, the output rates of fiber can range from about 750 meters/minute up to and including about 4000 meters/minute. 
     The size of the holes in the spinneret are directly related to the size of the fiber exiting from the spinneret. The spinneret can have a variety of number of holes depending on the volume, denier, commercial requirement or end properties of the fiber to be produced. For example, the spinneret can have from about 1 (to produce very thick, i.e. 2.00 mm fibers) to about 3000 holes, or in another embodiment from about 30 to about 1000 holes. In yet another embodiment, the number of holes can range from about 60 to about 850, alternatively from about 100 to about 800 holes, and for example from about 400 to about 700 holes, and all ranges therebetween. 
     The spinneret holes can be of any diameter that will produce a desired denier fiber. Diameters can range from 0.001 mm up to about 3 cm, in another embodiment from about 0.1 mm up to about 1 cm, and for example can range from about 0.3 mm up to about 5 mm. In many circumstances, the diameter of the spinneret hole will be directly related to the denier of the fiber to be produced. For example, a spinneret hole diameter of from 0.45 mm to 0.6 mm will produce a fiber from about 2 to 4 denier using ULTEM® 9011, a commercially available PEI from GE Plastics, Pittsfield, Mass., USA. 
     The thickness of the fiber according to the present invention is preferably between 0.1 and 100,000 dpf (denier per filament), or, in another embodiment, from about 0.1 dpf to about 100 dpf, in another embodiment from about 0.1 dpf to about 50.0 dpf, and in yet another embodiment from about 0.25 dpf to about 10.0 dpf, or still yet further from about 0.25 dpf to about 1.0 dpf. In accordance with an embodiment of the present invention, a polymer fiber may range from about 1 dpf to about 20 dpf, in another embodiment, less than about 10 dpf, for example 2 dpf, 4 dpf, and 6 dpf. Depending on the end use of the fiber, other dimensional characteristics may also be employed to describe the fibers according to the present invention. For example, dyed fibers also include those from 0.01 dpf through 50,000 dpf, or for example, 0.1 dpf to about 100 dpf. 
     The fiber may also be measured characterized in terms of its diameter which can range from about 0.00001 mm to about 2 mm, for example from about 0.0001 mm to about 0.5 mm, and as another example, from about 0.005 mm to about 0.5 mm, and still yet in another example from about 0.005 mm to about 0.095 mm. The skilled artisan will appreciate that these ranges include different breadths depending on the spinneret hole measurements and the use of the fiber and that the present invention is intended to encompass the entire range of sizes of polyetherimide fiber. 
     The produced fiber may be either of a continuous filament shape or cut into a short staple fiber shape (for example, staple yarn sizes can be 2.25/2 and 10/1 English cotton count; which equates to deniers of 4703 and 532 respectively), including those uniform or irregular in thickness in the lengthwise direction, the cross-sectional shape of which may be circular, triangular, polygonal, multi-lobal or indefinite, including an L-shape, a T-shape, a Y-shape, a W-shape, an octagonal lobal shape, a flat shape and a dog-bone shape. The fiber according to the present invention may be either solid or hollow. 
     The polymer fibers comprising polyetherimide described herein have a tenacity of at least about 0.5 g/denier, in another embodiment from about 0.5 g/denier to about 50 g/denier, in yet another embodiment from about 1 g/denier to about 7 g/denier, and in still yet another embodiment from about 1 g/denier to about 3.5 g/denier, as tested according to ASTM-02256-97. The polymer fibers comprising polyetherimide described herein have an elongation at break of at least about 10%, in another embodiment from about 10% to about 50%, in yet another embodiment from about 10% to about 30%, and in still yet another embodiment at least about 30%, as tested according to ASTM-02256-97. The measured elongation varies as a function of the draw ratio of the rollers, where a relatively higher draw ratio results in a relatively lower elongation. 
     Any final fiber produced according to the claimed invention, may be included in a multifilament yarn including, in addition to, one or more fibers comprising a polyetherimide, other synthetic, organic, inorganic or natural fibers. Other fibers which may be blended with one or more polyetherimide fibers are selected from synthetic fibers selected from the group consisting of nylons, acrylic, modacrylic, PBI, polyesters, polypropylene, polyethylene, latex, PET, PI, polyesters, spandex, sulfar, vivyon, NOMEX, carbon, aramid, ceramic, metal, glass, etc., and mixtures thereof. Natural fibers including but not limited to cellulosic fibers, e.g., cotton, rayon, linen, poly/cotton blends, Tencel, and mixtures thereof, proteinaceous fibers, e.g., silk, wool, related mammalian fibers, and mixtures thereof, long vegetable fibers, e.g., jute, flax, ramie, coir, kapok, sisal, henequen, abaca, hemp, sunn, and mixtures thereof, and natural material in the form or fibers including asbestos, for example. 
     The fiber may be converted to a yarn form according to any method known in the art, such as a spun yarn manufactured from a ring spinning frame or an open end spinning frame, a filament yarn having a single fiber thickness in a range from 0.001 inch to 0.35 inch (including an ultra-fine, yarn), a soft or hard twisted yarn, a mixed fiber yarn, a false-twist textured yarn (including a draw-false twist textured yarn of POY) or an air jet textured yarn. In this regard, the mixed fiber yarns according to the present invention may be made through such well known processes as fiber-mixing means, such as a mixed-spinning process (including a ciro-spun or a ciro-fil), an entanglement mixing process (wherein yarns having various shrinkages are mixed together), a mixed-twisting process, a composite false-twist process (including an elongation-difference-false-twist process) or a two-feed air jet texturing process. 
     The high heat polymer, for example polyetherimide, may undergo at least one of several various processes to remove foreign particulate matter of many sizes. The skilled artisan will appreciate that a wide range of methods and apparatus are known in the art and that depending on the size of the particulate matter as well as the end use of the fiber, there will be a variety of different ways of producing a polyimide-containing product that is substantially free of foreign particulate matter. A removal process to remove at least a portion of one or more types of foreign particulate matter to produce a “purified” polymer, where the purified polymer is defined herein as having a reduced concentration of foreign particulate matter. 
     Known processes for the removing foreign particulate matter from materials include, but are not limited to, for example, a filtration process, an irradiation process, a heating process, a cooling process, a pressurization process, a depressurization process, a chemical addition process, adsorption process, precipitation process, a phase transfer process, and combinations thereof, for at least one of separating, destroying, and converting the foreign particulate matter to remove it. As a specific example of a combined process, the polyetherimide polymer can be dissolved in solvent to a liquid, which is then filtered and then re-solidified to a polymer that is substantially free of foreign particulate matter. 
     The polymer fiber comprising polyetherimide, according to an embodiment of the present invention, is substantially free of foreign particulate matter greater than about 100 μm in size, in another embodiment greater than about 75 μm in size, in another embodiment, greater than about 50 μm in size, and yet in another embodiment, greater than about 25 μm in size, and in still yet another embodiment, greater than about 10 μm. In another embodiment of the present invention, the fiber is substantially free of foreign particulate matter having a size greater than or equal to about 85% of the diameter of the fiber, in another embodiment greater than or equal to about 50% of the diameter of the fiber, in another embodiment greater than or equal to 25% of the diameter of the fiber, and in yet another embodiment greater than or equal to 10% of the diameter of the fiber. 
     As described above with respect to  FIG. 1 , the polymer can be filtered to remove foreign objects. The polymer can be filtered prior to processing into a fiber to remove any particulate matter that may effect any parameter of commercial scale fiber manufacturing process, including speed, volume and quality of fiber produced. The polymer may be filtered to remove particulate matter of any size. The skilled artisan will appreciate that a wide range of methods and apparatus are known in the art and that depending on the size of the particulate matter as well as the end use of the fiber, there will be a variety of different ways of producing a filtered polyimide product. 
     In one embodiment, the process for making fiber includes filtering the polymer to remove foreign particulate matter so that the polymer is substantially free of foreign particulate matter. The polymer can be filtered prior to processing into a fiber to remove any particulate matter that may effect any parameter of commercial scale fiber manufacturing process, including speed, volume and quality of fiber produced. For example, the polymer used in the fiber of the present invention can be filtered prior to passing the molten polymer through the spinneret, and in another embodiment the polymer comprising polyetherimide can be filtered before or after melting the polymer in the production of fiber. 
     The skilled artisan will appreciate the multitude of different ways for filtering the polymers of the present invention to allow for the commercial production of the novel fibers of the present invention. The polymer can be filtered at any time prior to, or during the production of the fibers using a variety of apparatus and techniques known in the art. 
     Filtering the polymer prior to the exit of the polymer from the spinneret or diehead, has the additional advantage of changing the pressure on the polymer (as opposed to fiber) side of spinneret or die head. The pressure on the inside surface of the spinneret can be manipulated to be uniform and constant such that output and quality are maintained for extended periods allowing for long production runs. The pressure on the inside of the spinneret can be maintained at any pressure greater than zero to about 3,000 psi, in another embodiment from about 50 psi to about 1000 psi, in yet another embodiment from about 400 psi to about 800 psi, and in yet another embodiment from about 500 psi to about 600 psi. Depending on the number of holes in the spinneret, this pressure will be distributed among the holes. In another embodiment of the present invention, the pressure will be evenly distributed and the pressure per hole of the spinneret will be approximately 1 psi/hole. 
     The fiber according to various embodiments of the present invention may be made exclusively of one polyetherimide or may comprise a blend of two or more polymers including a second polyetherimide. Alternatively, polyetherimide co-polymers may be used to make the fibers of the present invention. Fibers of the present invention can also be manufactured from blends of polyimides and polyetherimides with other polymers. The skilled artisan will appreciate the number of polymers currently marketed and that any polymer can be used in association with the present invention that will meet the end use requirements for the fiber. 
     Similarly, different polyimides and polyetherimides will have different properties and the skilled artisan will appreciate the desirability of blending one or more of the polyimides and/or polyetherimide polymers with another polymers, for example, crystalline or amorphous polymers, or both, to improve the fiber making process or fiber properties of a polymer fiber according to the present invention. The polymer fibers herein can include polymer compositions comprising from about 1% to about 99% of a polymer or polymers different than polyetherimide, and from about 99% to about 1% polyetherimide polymer, and all ranges therebetween. For example, in one embodiment the polymer fiber comprises at least about 50% polyetherimide, in another embodiment, at least about 75% polyetherimide, in yet another embodiment at least about 95% polyetherimide, and still yet another embodiment at least about 99% polyetherimide. 
     The fiber can include one or more polyetherimides. Thermoplastic polyimides have the general formula (1): 
                         
wherein a is more than 1, typically about 10 to about 1,000 or more, or more specifically about 10 to about 500; and wherein V is a tetravalent linker without limitation, as long as the linker does not impede synthesis or use of the polyimide. Suitable linkers include but are not limited to: (a) substituted or unsubstituted, saturated, unsaturated or aromatic monocyclic and polycyclic groups having about 5 to about 50 carbon atoms, (b) substituted or unsubstituted, linear or branched, saturated or unsaturated alkyl groups having 1 to about 30 carbon atoms; or combinations comprising at least one of the foregoing. Suitable substitutions and/or linkers include, but are not limited to, ethers, epoxides, amides, esters, and combinations comprising at least one of the foregoing. At least a portion of the linkers V contain a portion derived from a bisphenol. Desirably linkers include but are not limited to tetravalent aromatic radicals of structures (2)
 
                         
wherein W is a divalent moiety including —O—, —S—, —C(O)—, —SO 2 —, —SO—, —C y H 2y — (y being an integer from 1 to 5), and halogenated derivatives thereof, including perfluoroalkylene groups, or a group of the formula —O—Z—O— wherein the divalent bonds of the —O— or the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, or the 4,4′ positions, and wherein Z includes, but is not limited, to divalent radicals of formulas 3.
 
                         
wherein Q includes but is not limited to a divalent moiety including —O—, —S—, —C(O)—, —SO 2 —, —SO—, —C y H 2y — (y being an integer from 1 to 5), and halogenated derivatives thereof, including perfluoroalkylene groups.
 
     R in formula (1) includes but is not limited to substituted or unsubstituted divalent organic radicals such as: (a) aromatic hydrocarbon radicals having about 6 to about 20 carbon atoms and halogenated derivatives thereof, (b) straight or branched chain alkylene radicals having about 2 to about 20 carbon atoms; (c) cycloalkylene radicals having about 3 to about 20 carbon atoms, or (d) divalent radicals of the general formula (4) 
                         
wherein Q includes but is not limited to a divalent moiety including —O—, —S—, —C(O)—, —SO 2 —, —SO—, —C y H 2y — (y being an integer from 1 to 5), and halogenated derivatives thereof, including perfluoroalkylene groups.
 
     Exemplary classes of polyimides include polyamidimides and polyetherimides, particularly those polyetherimides which are melt processable, such as those whose preparation and properties are described in U.S. Pat. Nos. 3,803,085 and 3,905,942. 
     Exemplary polyetherimide resins comprise more than 1, typically about 10 to about 1,000, or more specifically, about 10 to about 500 structural units, of the formula (5) 
                         
wherein T is —O— or a group of the formula —O—Z—O— wherein the divalent bonds of the —O— or the —O—Z—O— group are in the 3,3′, 3,4′, 4,3′, or the 4,4′ positions, and wherein Z includes, but is not limited, to divalent radicals of formula 10 as defined above.
 
     In one embodiment, the polyetherimide may be a copolymer which, in addition to the etherimide units described above, further contains polyimide structural units of the formula (6) 
                         
wherein R is as previously defined for formula (1) and M includes, but is not limited to, radicals of formulas (7).
 
     
       
         
         
             
             
         
       
     
     The polyetherimide can be prepared by various methods, including, but not limited to, the reaction of an aromatic bis(ether anhydride) of the formula (8) 
                         
with an organic diamine of the formula (9)
 
H 2 N—R—NH 2   (9)
 
wherein R and T are defined in relation to formulas (1) and (5).
 
     Examples of specific aromatic bis(ether anhydride)s and organic diamines are disclosed, for example, in U.S. Pat. Nos. 3,972,902 and 4,455,410. Illustrative examples of aromatic bis(ether anhydride)s of formula (8) include:
     2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride;   4,4′-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride;   4,4′-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride;   4,4′-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride;   4,4′-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride;   2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride;   4,4′-bis(2,3-dicarboxyphenoxy)diphenyl ether dianhydride;   4,4′-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride;   4,4′-bis(2,3-dicarboxyphenoxy)benzophenone dianhydride;   4,4′-bis(2,3-dicarboxyphenoxy)diphenyl sulfone dianhydride;   4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl-2,2-propane dianhydride;   4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl ether dianhydride;   4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride;   4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)benzophenone dianhydride; and,   4-(2,3-dicarboxyphenoxy)-4′-(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride,   as well as various mixtures comprising at least one of the foregoing.   

     The bis(ether anhydride)s can be prepared by the hydrolysis, followed by dehydration, of the reaction product of a nitro substituted phenyl dinitrile with a metal salt of a bisphenol compound (e.g., BPA) in the presence of a dipolar, aprotic solvent. An exemplary class of aromatic bis(ether anhydride)s included by formula (15) above includes, but is not limited to, compounds wherein T is of the formula (10): 
                         
and the ether linkages, for example, are in the 3,3′, 3,4′, 4,3′, or 4,4′ positions, and mixtures comprising at least one of the foregoing, and where Q is as defined above.
 
     Any diamino compound may be employed. Examples of suitable compounds are: ethylenediamine, propylenediamine, trimethylenediamine, diethylenetriamine, triethylenetetramine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 1,12-dodecanediamine, 1,18-octadecanediamine, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 4-methylnonamethylenediamine, 5-methylnonamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 2,2-dimethylpropylenediamine, N-methyl-bis(3-aminopropyl) amine, 3-methoxyhexamethylenediamine, 1,2-bis(3-aminopropoxy) ethane, bis(3-aminopropyl) sulfide, 1,4-cyclohexanediamine, bis-(4-aminocyclohexyl) methane, m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, m-xylylenediamine, p-xylylenediamine, 2-methyl-4,6-diethyl-1,3-phenylene-diamine, 5-methyl-4,6-diethyl-1,3-phenylene-diamine, benzidine, 3,3′-dimethylbenzidine, 3,3′-dimethoxybenzidine, 1,5-diaminonaphthalene, bis(4-aminophenyl) methane, bis(2-chloro-4-amino-3,5-diethylphenyl) methane, bis(4-aminophenyl) propane, 2,4-bis(b-amino-t-butyl) toluene, bis(p-b-amino-t-butylphenyl) ether, bis(p-b-methyl-o-aminophenyl) benzene, bis(p-b-methyl-o-aminopentyl) benzene, 1,3-diamino-4-isopropylbenzene, bis(4-aminophenyl) sulfide, bis(4-aminophenyl) sulfone, bis(4-aminophenyl) ether and 1,3-bis(3-aminopropyl) tetramethyldisiloxane. Mixtures of these compounds may also be present. Desirably, the diamino compounds are aromatic diamines, especially m- and p-phenylenediamine and mixtures comprising at least one of the foregoing. 
     In one embodiment, the polyetherimide resin comprises structural units according to formula 6 wherein each R is independently p-phenylene or m-phenylene or a mixture comprising at least one of the foregoing and T is a divalent radical of the formula (11) 
     
       
         
         
             
             
         
       
     
     Included among the many methods of making the polyimides, particularly polyetherimides, are those disclosed in U.S. Pat. Nos. 3,847,867; 3,850,885; 3,852,242; 3,855,178; 3,983,093; and, 4,443,591. 
     The reactions can be carried out employing solvents, e.g., o-dichlorobenzene, m-cresol/toluene and the like, to effect a reaction between the anhydride of formula (8) and the diamine of formula (9), at temperatures of about 100° C. to about 250° C. Alternatively, the polyetherimide can be prepared by melt polymerization of aromatic bis(ether anhydride)s (8) and diamines (9) by heating a mixture of the starting materials to elevated temperatures with concurrent stirring. Generally, melt polymerizations employ temperatures of about 200° C. to about 400° C. Chain stoppers and branching agents may also be employed in the reaction. 
     When polyetherimide/polyimide copolymers are employed, a dianhydride, such as pyromellitic anhydride, is used in combination with the bis(ether anhydride). The polyetherimide resins can optionally be prepared from reaction of an aromatic bis(ether anhydride) with an organic diamine in which the diamine is present in the reaction mixture at less than or equal to about 0.2 molar excess. Under such conditions the polyetherimide resin may have less than or equal to about 15 microequivalents per gram (μeq/g) acid titratable groups, or, more specifically less than or equal about 10 μeq/g acid titratable groups, as shown by titration with chloroform solution with a solution of 33 weight percent (wt %) hydrobromic acid in glacial acetic acid. Acid-titratable groups are essentially due to amine end-groups in the polyetherimide resin. 
     One route for the synthesis of polyetherimides proceeds through a bis(4-halophthalimide) having the following structure (12): 
                         
wherein R is as described above and X is a halogen. The bis(4-halophthalimide) wherein R is a 1,3-phenyl group (13) is particularly useful.
 
     
       
         
         
             
             
         
       
     
     Bis(halophthalimide)s (12) and (13) are typically formed by the condensation of amines, e.g., 1,3-diaminobenzene with anhydrides, e.g., 4-halophthalic anhydride (14): 
                         
Polyetherimides may be synthesized by the reaction of the bis(halophthalimide) with an alkali metal salt of a bisphenol such as bisphenol A or a combination of an alkali metal salt of a bisphenol and an alkali metal salt of another dihydroxy substituted aromatic hydrocarbon in the presence or absence of phase transfer catalyst. Suitable phase transfer catalysts are disclosed in U.S. Pat. No. 5,229,482. Suitable dihydroxy substituted aromatic hydrocarbons include those having the formula (15)
 
OH-A 2 -OH  (15)
 
wherein A 2  is a divalent aromatic hydrocarbon radical. Suitable A 2  radicals include m-phenylene, p-phenylene, 4,4′-biphenylene, and similar radicals.
 
Representative polyetherimides are those produced under the ULTEM® trademark, including, but not limited to ULTEM® 1000 (number average molecular weight (Mn) 21,000 g/mole; Mw 54,000 g/mole; dispersity 2.5), ULTEM® 1010 (Mn 19,000 g/mole; Mw 47,000 g/mole; dispersity 2.5) and ULTEM® 9011 (Mn 19,000 g/mole; Mw 47,000 g/mole; dispersity 2.5) resin by GE plastics, Pittsfield, Mass., in the United States of America. ULTEM® type polyetherimides are described in detail in U.S. Pat. Nos. 3,847,867; 4,650,850; 4,794,157; 4,855,391; 4,820,781; and, 4,816,527, which are hereby incorporated by reference herein in their entirety as though set forth in full.
 
     The polyetherimide resin can have a weight average molecular weight (Mw) of about 1,000 to about 1,000,000 grams per mole (g/mole), more specifically a Mw of about 5,000 g/mole to about 500,000 g/mole, and still more specifically from about 10,000 g/mole to about 75,000 g/mole as measured by gel permeation chromatography, using a polystyrene standard. 
     Viscosity data for polyetherimides useful as fibers according to the present invention is calculated according to the equation: melt flow index (MFI)×10=melt flow rate (MFR) according to ASTM D1238 (volume 08/2001) with the test run at 337° and 6.6 kgf Some of that melt flow rate is provided below:
         ULTEM® 9011: MFR 16-20 g/10 min   ULTEM® 1040: MFR 50-111 g/10 min   ULTEM® 1010: MFR 16-20 g/10 min   ULTEM® 1000: MFR 7-11 g/10 min       

     The melt index of the polymer comprising polyetherimide and as measured according to ASTM 1238 can range from about 0.5 to about 12, in another embodiment from about 1 to about 8, in another embodiment, from about 1.5 to about 2.5, and in yet another embodiment, from about 1.8 to about 2.2, and all ranges therebetween. The melt index range will depend on the composition of the polymer comprising polyetherimide and should not be too low as to be too viscous for uniformly passing through the holes of the spinneret, and should not be to high so as to lose melt strength or compromise the physical properties of the fiber produced, a as can be determined by one of ordinary skill in the art. 
     Typical drying conditions for drying the polymer having a melt temperature that ranges between 180° C. and 500° C. are well within the knowledge of the skilled artisan. For example, polyetherimide polymer is dried by heating the polymer to about 300° C. for about four to twelve hours. Drying may be achieved at an extruder before it enters the extruder barrel to be melted. 
     As described above, the scope of the present inventions is intended to cover fibers manufactured from blends of polyimides and polyetherimides with other polymers. The skilled artisan will appreciate the number of polymers currently marketed and that any polymer can be used in association with the present invention that will meet the end use requirements for the fiber. Similarly, different polyimides and polyetherimides will have different properties and the skilled artisan will appreciate the desirability of blending one or more of the polyimides and/or polyetherimide of the present invention with another polymer to improve the fiber making or fiber properties of any polymer to be blended. 
     Amounts of adjunct ingredients effective to impart, or improve a desirable fiber property such as, brightness of color, strength, cleanability, flame retardance, colorfastness, or dyability. For example, one or more ingredients from the following classes of ingredients may be added to the fiber: perfume, odor control agent, antimicrobial active and/or preservative, surfactant, optical brightener, antioxidant, chelating agent including aminocarboxylate chelating agent, antistatic agent, dye transfer inhibiting agent, fabric softening active, and/or static control agent. 
     The final fiber produced according to the example embodiments of the present invention described above can have a variety of properties depending on the polymer, and if polyetherimide then the type of polyetherimide, the processing conditions, and the desired end use. For example, as a general observation at the time of the filing of the present invention, and without intending to be bound in any way, as the melt index of polyethrimide increases, the tenacity trends downward. 
     EXAMPLES 
     The following examples are included to provide additional guidance to those skilled in the art of practicing the claimed invention. These examples are provided as representative of the work and contribute to the teaching of the present invention. Accordingly, these examples are not intended to limit the scope of the present invention in any way.
         Experimental runs were conducted to evaluate the feasibility of producing polyetherimide fiber at a higher output rate and to observe the impact of changes in the various processing. Polyetherimide resin, specifically, ULTEM® 9011 in the form of pellets, available from GE Plastics, Pittsfield, Mass., and which had melt index of approximately 1.8 to 2.2 were dried at 300° C. for at about 12 hours prior to extrusion. The pellets were fed at a feed rate of 1 to 10 Kg/hr through a one-inch (1″) single screw extruder (L/D=24/1) and the actual melt temperature of the polymer ranged between about 340° C. and about 400° C. The pellets were fed at a feed rates of 1 to 10 Kg/hr through a one inch (1″) single screw extruder (L/D=24/1). The actual melt temperature of the polymers ranged between about 340° C. and about 400° C. The polyetherimide was extruded through a metering pump, a pack top, and then was filtered before the molten polymer flowed through the holes of the spinneret to produce fiber. The smallest screen hole sizes of the screen pack were approximately 25 microns. In the four examples described below polyetherimide fibers were produced at an output rate of up to about 80 pounds/hour depending upon the denier of the fiber produced. The fiber bundle exiting the spinneret were quenched by air which had velocity range of 0.1 to 10 meters per second. Various changes were made to the cooling conditions as described below. The range of processing parameters that were used to produce polyetherimide fiber wound onto coils is summarized in Table I below.       

     
       
         
           
               
               
               
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                   
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Material 
                   
                 ULTEM ® 
                 ULTEM ® 
                 ULTEM ® 
                 ULTEM ® 
               
               
                   
                   
                 9011 
                 9011 
                 9011 
                 9011 
               
               
                 Color 
                   
                 100 
                 100 
                 100 
                 100 
               
               
                 Lot 
                   
                 A 
                 A 
                 B 
                 C 
               
               
                 denier per filament 
                   
                 — 
                 — 
                 — 
                 7.8 
               
               
                 Spinneret hole dia. 
                 mm 
                 0.7 
                 0.45 
                 0.45 
                 0.45 
               
               
                 Holes/spinneret 
                   
                 637 
                 637 
                 637 
                 ~570(637)* 
               
               
                 Extruder Drive 
                 % 
                 50 
                 50 
                 40-56 
                 80 
               
               
                 Pressure 
                 psi 
                 1600 
                 1600 
                 1600 
                 1600 
               
               
                 Zone 1 
                 ° C. 
                 350 
                 350 
                 350 
                 350 
               
               
                 Zone 2 
                 ° C. 
                 354 
                 354 
                 370 
                 360 
               
               
                 Zone 3 
                 ° C. 
                 377 
                 377 
                 407 
                 397 
               
               
                 Head T 
                 ° C. 
                 350-390 
                 380 
                 410 
                 410 
               
               
                 Melt T 
                 ° C. 
                 350-390 
                 380 
                 402-405 
                 401 
               
               
                 R&amp;L Melt Pumps 
                 rpm 
                 25 
                 25-27 
                 12-21 
                 30 
               
               
                 Head Pressure 
                 psi 
                 — 
                 600 
                 350 
                 630 
               
               
                 Quench T 
                 ° C. 
                 11-13 
                 11 
                 10-23 
                 12 
               
               
                 Quench Velocity (blower) 
                 rpm 
                  750-1282 
                 805 
                   412-900+ 
                 1000 
               
               
                 Room T 
                 ° C. 
                 18-23 
                 18 
                 20-23 
                 25.5 
               
               
                 Godets Roll T 1 
                 ° C. 
                 40 
                 120 
                 100-150 
                 133 
               
               
                 Roll Speed 1 
                 rpm 
                 19-24 
                 15.9 
                 12-25 
                 25.2 
               
               
                 Draw Ratio 
                 % 
                 0 
                 0 
                 0 
                 31 
               
               
                   
               
               
                 *~70 holes of 637 were plugged, resulting in ~577 filaments 
               
            
           
         
       
     
     Example 1 
     Polyetherimide fibers were produced using a spinneret having 637 holes of a diameter of 0.7 millimeters per the processing conditions described in Table I. Quench air was blown through a rectifier to evenly distribute the airflow directed to the fiber bundle. The airflow and contained by sidewalls extending from the rectifier such that the width between the sidewalls (40 cm) was greater than width of the fiber bundle (25 cm) exiting the spinneret. The process conditions caused random fibers to solidify, break away, and drop from the bundle along the air flow-front interface (i.e. leading edge) areas of the fiber bundle. 
     Example 2 
     Polyetherimide fibers were produced using a spinneret again having 637 holes of a diameter of 0.45 millimeters and otherwise similar extrusion conditions as in Example 1 and as listed under Ex. 2 of Table I. In addition, cardboard baffles, or protrusions, were attached to the sidewalls which ran parallel to the flow of the fiber bundle and which extended outward from the rectifier. The baffles extended from the sidewalls such that the distance between the sidewalls was approximately equal to the distance between the edges of the spinneret, and the baffles were positioned laterally between the rectifier and the spinneret. Improvements were made over Example 1 in that a fewer number of strands were dropped. 
     Example 3 
     Polyetherimide fibers were produced with a spinneret that had 637 holes with diameter of 0.45 millimeters and otherwise similar extrusion conditions as in the examples above and as listed under Ex. 3 of Table I. The screen pack was changed in an attempt to increase the back pressure of flow through the spinneret. The filter screens were changed to a fine screen pack which included a screen having holes of approximately 15 microns (screen pack configuration 20/60/325/200×400). The spinneret was also modified to plug holes in the front corners where the fibers were dropped. In addition, to facilitate cooling, a vacuum was introduced and mounted opposite the quench air entrance to increase the cross-flow of air through the fibers. The finer screen pack caused a buildup to be produced on the face of the spinneret possibly as a result of shear degradation of the polyetherimide polymer. The build-up accumulated around the perimeter of the holes and the build-up grabbed the fibers and caused the fibers to curl and break. The vacuum appeared to improve the cooling to a point at which the suction of air at high speeds caused fibers to drop and/or caused fibers that were otherwise broken to be pulled toward the vacuum while interrupting the flow of neighboring filaments. 
     Example 4 
     Polyetherimide fibers were produced according to the extrusion conditions listed under Ex. 4 of Table I. The same spinneret sized for 637 holes with diameter of 0.45 millimeters as described above with regard to Examples 2 and 3 was used, however 70 holes of the spinneret holes were plugged in a configuration that formed two substantially circular areas as shown and described in  FIG. 2  above. The baffles which extended from the sidewalls and aligned with the edges of the spinneret as described in Example 2 moved to a different lateral position such that they approximately aligned with air flow-front interface (i.e. leading edge) of the fiber bundle as shown in  FIG. 2 . These changes improved the fiber processing, and fiber was wound on the spool for 10 minutes. 
     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.