CN1339073A - High speed melt spinning of fluoropolymer fibers - Google Patents

Abstract

The process and apparatus of the present invention involve melt spinning a high viscosity fluoropolymer into a monofilament or multifilament yarn at high spinning speeds.

Description

High Speed Melt Spinning of Fluoropolymer Fibers

Background of the invention

This invention relates to a method and apparatus for spinning fluoropolymers into monofilament or multifilament yarns at high spinning speeds.

Melt spinning of thermoplastic copolymers based on tetrafluoroethylene is known. However, there remains considerable economic potential to further increase the fiber spinning speed of such high-value polymers. One problem faced by the melt spinning process is that at high shear rates there is progressive melt fracture, which can be seen as the surface of the extruded fibers becomes rougher and rougher. In view of the fact that the critical shear rate at which melt failure begins to appear decreases with the increase of melt viscosity, various measures to reduce melt viscosity have focused on increasing the melt temperature. However, in polymers including tetrafluoroethylene-based thermoplastic copolymers, thermal degradation of the polymer occurs before any significant reduction in melt viscosity is achieved.

Polytetrafluoroethylene (PTFE) homopolymer fibers are also highly valued, especially for their chemical and mechanical properties, such as low coefficient of friction, thermal stability, and chemical inertness. However, processing with melt spinning has proven to be confusing until now. Given that PTFE homopolymer fibers have traditionally been disperse-spun, which involves many steps and complex equipment, finding a way to melt-spin such fibers would be of great economic interest.

The problem of fabricating fibers by melt spinning high viscosity polymers has previously been studied for polyesters. US Patent 3,437,725 describes a spinnerette assembly comprising a top plate, a heater plate and a bottom plate with spacers between the top plate and the heater plate to provide an air gap. Hollow inserts are placed within the top plate, one for each spin hole, extending down to the lower surface of the bottom plate. Molten polymer is fed into the insert for spinning through the spin holes (capillaries). The electric heating head supplies heat to maintain the temperature of the base plate, heating plate and insert base portion at least 60°C above the supplied molten polymer. In Examples, the heated spinning hole temperature of 290 to 430° C. is cited as the polyester spinning conditions. There is no mention of any fluoropolymers or the temperature required to melt spin fluoropolymers at high spin speeds.

Summary of the invention

The present invention provides a process for melt spinning a composition comprising a highly fluorinated thermoplastic polymer or a blend of such polymers, comprising the steps of: making a composition comprising a highly fluorinated thermoplastic polymer or a blend of such polymers The composition is melted to form a molten fluoropolymer composition; the molten fluoropolymer composition is conveyed under pressure to an extrusion die of a melt spinning apparatus; and the molten fluoropolymer composition is passed through the extrusion die. The molten tow is formed by extruding from a die at a temperature of at least 450°C, a shear rate of at least 100 s ^-1 , and a spinning speed of at least 500 m/min.

The present invention also provides a melt spinning method for a composition containing polytetrafluoroethylene homopolymer, comprising the steps of: melting the composition containing polytetrafluoroethylene homopolymer to form a molten polytetrafluoroethylene composition; conveying the molten polytetrafluoroethylene composition under pressure to an extrusion die of a melt spinning apparatus; and extruding the molten polytetrafluoroethylene composition through the extrusion die to form molten strands.

The present invention also provides a melt spinning device, which includes: a spinneret assembly including a filtering means; a spinning plate; an elongated delivery line, and the delivery line is arranged between the filtering means and the spinneret means for heating said elongate transfer line; means for heating said spinnerette; and an elongate annealer disposed below said spinnerette assembly.

Brief description of the drawings

Fig. 1 is a sectional view of a part of a conventional melt spinning apparatus.

Figure 2 is a cross-sectional view of one embodiment of a portion of a melt spinning apparatus of the present invention having an elongated spinnerette.

Figure 3 is a cross-sectional view of one embodiment of a portion of a melt spinning apparatus of the present invention having a short elongated spinnerette.

Figure 4 is a cross-sectional view of one embodiment of a portion of a melt spinning apparatus of the present invention having a short elongated spinneret having heating means in its central cavity and also on its outer surface.

Figure 5 is an exploded cross-sectional view of one embodiment of the melt spinning apparatus of the present invention featuring an elongated transfer line between the pack filter and the spinnerette disc.

Fig. 6 is a cross-sectional view of the assembled melt spinning apparatus of Fig. 5 .

Figure 7 is an exploded cross-sectional view of one embodiment of the melt spinning apparatus of the present invention, featuring another embodiment of the elongated transfer line and spinneret discs.

Fig. 8 is a sectional view of the assembled melt spinning apparatus of Fig. 7 .

Figure 9 is a schematic diagram of one embodiment of the melt spinning apparatus of the present invention.

10A and 10B are cross-sectional views of one embodiment of an annealer used in the present invention. Fig. 10B is a partially enlarged view of Fig. 10A.

Figure 11 is a plot of shear rate (1/s) versus SSF (spinneret draw factor) for the composition of Example 1 at 500°C, where the blackened triangle represents the spinneret draw factor at first filament breakage (SSF), open triangles represent the SSF of the final broken filament. This includes certain denier/strength/velocity/(g/m) data.

Figure 12 is a graph showing the positive effect of temperature on SSF at first broken wire at a constant shear rate. Dots represent SSF at 420°C; squares represent SSF at 460°C; triangles represent SSF at 500°C (see also Example 1).

Figure 13 is a graphical representation of throughput versus solidification distance from the spinneret with and without an annealer, here using a FEP-5100, 30-mil/30-hole spinneret, 3 inch diameter, 41 Foot-long annealer, and spinning plate temperature 380°C (triangle), 430°C (square) and 480°C (dot), where the hollow symbols represent without annealer; black symbols represent annealer.

Figure 14 is a graphical representation of distance from the spinneret (inches) versus yarn temperature with and without slow cooler (black symbols) and 45.4 gpm/6.0 pph , using FEP-5100, 39.4-mil/30-hole spinneret, spinneret temperature 480°C, where the squares represent the yarn temperature when the spinning speed is equal to 400mpm (=m/min); the dots represent when the spinning speed is 500mpm The yarn temperature at ; the triangle represents the yarn temperature at 700 mpm.

Figure 15 is a graph of annealer length (inches) versus initial wire break speed, m/min (mpm). Used: FEP-5100 fluoropolymer, 30 mil/30-hole spinneret, spinneret temperature 480°C, and 44.8 g/min (gpm).

Fig. 16 is a graphical representation of the temperature versus the initial wire breaking speed (mpm) of Example 23, wherein the black circles represent the samples of the present invention, and the squares represent the samples of the comparative example.

A detailed description

The method of the present invention provides the advantages of high temperature spinning while avoiding its associated disadvantages. In the method of the present invention, a composition containing a highly fluorinated thermoplastic polymer or a blend of such polymers is exposed to a temperature in excess of the degradation temperature of the polymer for a time sufficient to cause a decrease in viscosity but not sufficient for the polymer to undergo significant degradation. degradation. In melt spinning, the molten composition experiences the highest shear rate at the instant of transition through an extrusion die, such as a spin hole of a spinneret of a melt spinning apparatus. It is at this point that the molten composition may be heated to a temperature above the degradation temperature of the highly fluorinated polymer in the method of the invention. Due to the high temperatures, high throughput speeds (throughput or throughput rates) can be achieved in the present invention, the residence time of the composition in the extrusion die being kept at extremely short values.

Accordingly, the present invention provides a first method of melt spinning a composition comprising a highly fluorinated thermoplastic polymer or a blend of such polymers, comprising the steps of: blending a composition comprising a highly fluorinated thermoplastic polymer or a blend of such polymers The composition of the blend is melted to form a molten fluoropolymer composition; the molten fluoropolymer composition is conveyed under pressure to an extrusion die of a melt spinning apparatus; and the molten fluoropolymer composition is The molten filaments are formed by extruding through the extrusion die at a temperature of at least 450° C., a shear rate of at least 100 s ⁻¹ , and a spinning speed of at least 500 m/min.

During the melting step, the composition comprising the highly fluorinated thermoplastic polymer or a blend of such polymers is melted. Highly fluorinated thermoplastic polymers that meet the requirements of this first method include homopolymers other than polytetrafluoroethylene (PTFE), such as polyvinylidene fluoride (PVDF) and copolymers, such as tetrafluoroethylene (TFE) with Copolymers prepared from comonomers such as perfluoroolefins such as perfluorovinyl alkyl compounds and perfluoroalkyl vinyl ethers, or blends of such polymers. The term "copolymer", for the purposes of the present invention, is intended to cover polymers comprising 2 or more comonomers in a single polymer. A representative perfluorovinyl alkyl compound is hexafluoropropylene. Representative perfluoroalkyl vinyl ethers are perfluoromethyl vinyl ether (PMVE); perfluoroethyl vinyl ether (PEVE); and perfluoropropyl vinyl ether (PPVE). Preferred highly fluorinated polymers are copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether and copolymers of tetrafluoroethylene and hexafluoropropylene. The most preferred copolymer is TFE and 1-20mol% perfluorovinyl alkyl comonomer, preferably 3-10mol% hexafluoropropylene or 3-10mol% hexafluoropropylene and 0.2-2mol% PEVE or PPVE, and TFE with 0.5-10 mol% perfluoroalkyl vinyl ether, including 0.5-3 mol% PPVE or PEVE copolymer. Also suitable for the practice of the invention are blends of highly fluorinated thermoplastic polymers, including blends of TFE copolymers.

Fluoropolymers suitable for the practice of this invention preferably exhibit a melt flow rate (MFR) of 1 to about 50 g/10 min at 372 °C measurement.

Compositions containing highly fluorinated thermoplastic polymers or blends of such polymers may also contain additives. Such additives may include, for example, pigments and fillers.

In the process of the present invention, a composition comprising a highly fluorinated polymer or a blend of such polymers, as discussed above, is melted to form a molten fluoropolymer composition. Any means known in the art for providing a melt can be used. A representative method may include introducing the fluoropolymer composition into an extruder heated to a temperature sufficient to melt the composition but below the degradation temperature of the highly fluorinated thermoplastic polymer or blend of such polymers. temperature. This temperature depends on the particular polymer used.

Once the composition is in a molten state, it can be conveyed under pressure to an extrusion die, such as a spinneret of a melt spinning apparatus. Means for delivering the composition to an extrusion die are well known in the art and include equipment with plungers or pistons, single or twin screws. In a preferred embodiment of the method of the present invention, an extruder is used to melt and deliver a molten composition suitable for the practice of the present invention to a single or multi-hole filament extrusion die to form a monofilament or multifilament fiber product, respectively. The extruder barrel and screw, as well as the die, are preferably fabricated from corrosion resistant materials, including high nickel corrosion resistant steel alloys such as Hastelloy C276 (Cabot Corporation, Kokomo, IN). A number of suitable extruders are known in the art and are commercially available, including screw and piston types. A metering device such as a gear pump may also be included to facilitate metering of the melt between the screw and the spinneret.

In the process of the present invention, after the molten fluoropolymer composition is delivered to an extrusion die, it is extruded through the capillaries (spinning holes) of the extrusion die, said die being at a temperature of at least 450°C, at least A (melt) shear rate of 100 s-1 and a spinning speed of at least 500 m/min.

The spinning holes of the extrusion die can have any desired cross-sectional shape, but a circular cross-sectional shape is preferred. It has been found that the diameter of the circular cross-section spinning holes suitable for use in the process of the present invention can be in the range of about 0.5 to 4.0 mm, although the practice of the present invention is not limited to this range. The aspect ratio of the spin holes of extrusion dies useful in the present invention is preferably from about 1:1 to about 8:1. Although the arrangement of the holes is not critical, it is preferred that the holes be arranged in one or more concentric circles, with a single circle arrangement being more preferred.

Figure 1 depicts a portion of a conventional melt spinning apparatus for thermoplastic polymers, ie, a spinneret pack 10. The figure shows: an adapter 1 (i.e., a connector), which can be heated by a core heater inserted into the space 9 between the dotted lines along the adapter 1, and means for connecting the fluoropolymer composition delivery and metering means (not represented); Filter cover 2, comprises melt filtration means (or filter material) 3, is typically filter screen; And traditional spinning plate 4, it has panel 5, and panel 5 is arranged on one end of spinning plate 4, The distance from the other end of the spinneret 4 is h. The spinneret 4 is arranged adjacent to the bottom surface 8 of the filter jacket 2 and is fastened together with the filter jacket 2 to the adapter 1 by means of a lock nut 6 . The spin pack 10 is heated by band heaters 7 arranged circumferentially around the lock nut 6 . In FIG. 1 , the spinneret 4 is generally heated by conductive contact with the lock nut 6 .

In the conventional style spinnerette assembly of FIG. 1 , there is no way to heat only the face plate 5 of the spinneret 4 because the spinneret 4 is entirely seated inside the locking ring 6 . Any attempt to overheat face plate 5 will inevitably result in a substantial portion of other areas of spinneret pack 10 being heated to a similar, if slightly lower, temperature. Such undesired heating of areas of the spinneret pack 10 other than face plate 5 to a temperature at or above the degradation temperature of the fluoropolymer composition tends to undesirably result in prolonged exposure of the fluoropolymer composition to elevated temperatures, and In some cases it can lead to excessive degradation of the polymer.

During extrusion of the present invention, the extrusion die is heated to a temperature of at least 450°C. Here, for certain fluoropolymer compositions, the extrusion die may be heated to temperatures greater than about 500°C. Heating to such temperatures without degrading the fluoropolymer composition can be accomplished by thermally insulating the extrusion die from other areas of the melt spinning equipment that may contain the fluoropolymer composition. When the molten fluoropolymer composition begins to pass through the extrusion die, the high temperature of the die induces a rapid decrease in the viscosity of the polymer melt, allowing a high rate of passage through the extrusion die. To avoid thermal degradation, the residence time of the melt at high temperature needs to be reduced. Given that degradation is not only a function of temperature but also of time, it is preferable to keep the residence time as short as possible if the temperature is high. Thus, the present invention provides the highest temperature where high temperature is most beneficial, ie, the extrusion die, such as the capillary walls of the spinneret, ie, within the faceplate of the spinneret. Thus, the extrusion die can remain thermally isolated from other areas of the melt spinning apparatus that may come into contact with the fluoropolymer composition.

The spinneret, or a part thereof including the face plate, can be heated independently of other areas of the spin pack. Any means that provides highly localized heating to temperatures of at least 450°C can be used in the practice of this invention. Such means include coil (wire or coil) heaters, core heaters or strip heaters and devices that heat by radio frequency, conduction, induction or convection, such as induction heaters. Insulation, such as ceramic insulation, may be used to provide offset and thus thermal insulation between the panel and other areas that may come into contact with the fluoropolymer composition. One or more cooling jackets may be used in areas of the spinneret or spinneret pack other than the extrusion die to provide thermal insulation for the extrusion die.

In order to enhance the thermal insulation of the extrusion die, it has now been found that in one embodiment of the invention it is satisfactory to separate the face plate of the spinneret from the body of the spinneret, i.e. The distance h between the two ends of the wire plate. Enlarging the distance in this manner, to become, h' as shown in Figure 2, allows the spinneret face plate to be heated separately from the bulk of the rest of the spinneret pack. Thus, in one embodiment, the face plate of the spinneret of the present invention is spaced a distance h' from the bottom surface of the filter jacket sufficient to allow heating of the face plate of the spinneret alone.

In FIG. 2, a spinneret assembly 20 is shown, comprising an adapter 21 (joint), which is connected to means (not shown) for melting and/or conveying of the fluoropolymer composition; a filter jacket 22, comprising a filter screen 23 and bottom surface 28; Elongated spinneret 24, and it has panel 25, and the latter is arranged on one end of spinnerette 24, and the distance between spinnerette 4 other ends, just the bottom surface 28 of filter cover 2 is h', where h' > h, while the other dimensions of Figs. By virtue of the panel 25 protruding beyond the lock nut 26, the heating means 29 can be used to heat the panel 25 alone, which is then thermally insulated from the rest of the spinneret pack. Heating means 27 , such as strip or spiral heaters, are arranged along the circumference of the locking nut 26 .

FIG. 3 shows an alternative spin pack, as spin pack 30, for use in the present invention. In this embodiment, the lower dimension of the lock nut 26 of FIG. 2 is shortened, eg the lock nut is thinner, see lock nut 36 in FIG. 3 . Here, the body of the elongated spinneret 34 is shortened compared to the length of the spinnerette 24 of FIG. Out of the lock nut 46, the face plate 35 is allowed to be heated by means 39, separate from the illustrated means 37 for heating other areas of the spinneret pack. Also shown are adapters 31 for connection to means (not shown) for melting and/or delivering the fluoropolymer composition; filter jackets 32 and filter means 33; and flow channels 38.

In the above embodiments of the present invention, the molten composition fed into the spinneret can be heated by means arranged on the circumference of the outer wall of the spinneret, so that the temperature of the melt adjacent to the capillary wall is higher than the temperature of the center of the melt . This temperature inhomogeneity effect, highest on the outside and decreasing temperature towards the center of the melt, can cause the extruded strands to bend towards the center of the spinneret. Bending angles in excess of 45° have been observed at high jetting velocities for certain fluoropolymer compositions. A possible consequence of this phenomenon is a reduction in the achievable high-speed filament continuity. To reduce any temperature gradient that exists between the outermost and innermost polymer melts, heating means, such as a core heater, may be introduced into the center of the elongated spinneret 44 within the capillary pores 48, as shown in FIG. 4 Spinneret assembly 40 is shown. Also shown in Figure 4 is an adapter 41 for attachment to fluoropolymer composition melting and/or delivery means (not shown); filter sleeve 42; filter means 43; lock nut 46; heating means 47 and 49; Panel 45.

Another embodiment provided by the present invention is shown in FIGS. 5 and 6 as a spinning pack 50 intended to heat the melt more rapidly, thus passing through a narrow flow channel 62 provided inside the transfer line 58 (relative to FIG. 3 For the flow channel 38), to reduce the volume immediately upstream of the spinneret face plate 55. The residence time is shortened by reducing this volume. Such an embodiment, utilizing the heating means 60, provides an opportunity for creating an intermediate temperature zone during the passage of the composition through the flow path 62 of the delivery line 58. As such, the method of the present invention may further comprise exposing the fluoropolymer composition to a temperature greater than the melt temperature of the fluoropolymer composition but less than the extrusion die temperature, ie, the spinnerette faceplate temperature. As shown, the portion of the transfer line 58 adjacent the filter jacket 52 can be heated by means of heating means 57 arranged around the circumference of the lock nut 56 . The fluoropolymer composition in the flow channel 62 of the delivery pipeline 58 can be preheated to at least one intermediate temperature greater than the melting temperature of the above-mentioned fluoropolymer composition but lower than the temperature of the panel 55 by using the heating means 57 and/or the heating means 60 . Face plate 55 is shown in this embodiment as being individually heated by means of heating means 61 secured within spinnerette sleeve 59 . A transfer line 58 is arranged downstream of the filter jacket 52 and filter means 53, followed, as shown, by a spinneret 54 having the shape of a disc. The spinneret 54 can be removed for cleaning and replacement without dismantling the filter assembly 52 . Also shown is an adapter 51 for connection to fluoropolymer composition melting and/or delivery means (not shown).

Figures 7 and 8 illustrate a spinnerette assembly 70 of the present invention, an embodiment which allows removal of transfer line 78 and which accommodates a larger diameter disc spinneret, such as spinneret 74, than the embodiment shown in Figures 5 and 6 . Spinneret nuts 79 secure the disk spinneret 74 with face plate 75 to the bottom surface 82 of the transfer line 78 . The narrow internal flow passage 83 within the transfer line 78 reduces the volume and residence time of the fluoropolymer composition at elevated temperatures, further reducing the chance of degradation. The transfer line 78 also provides, through its separate heater 80 , a means of gradually increasing the temperature intermediate between the filtering means 73 and the spinneret 74 . At the same time, the transfer line embodiment shown in the figure provides more uniform and faster heat transfer. Another incidental advantage of this embodiment is that the disc spinneret 74 can be removed without removing the filter jacket, and the discs are easy to manufacture. Also show adapter 71 among the figure, be used to be connected on the means (not shown) of fluoropolymer composition melting and/or delivery; Plate 72, a kind of multi-strand distribution channel, provides the support to filtering means 73; Nut 76 , surrounding heating means 77 , cavity 84 disposed between filtering means 73 and delivery line 78 ; and panel 75 .

It is believed that the present invention provides "melt self-lubricating extrusion". The so-called "melt self-lubricating extrusion" means that only the skin layer of the extrudate, that is, the part of the melt that directly contacts the wall of the equipment, is heated to extremely high temperatures by the very hot capillary surface of the die head, causing this Partial melt viscosity is very low while at the same time keeping the bulk of the extrudate at a lower temperature due to short contact or residence times. The considerably reduced viscosity of the skin acts like a thin lubricating film, making the extrusion process a plug flow where the bulk of the extrudate experiences a uniform velocity.

The term "shear rate" as used herein refers to the apparent wall shear rate calculated as 4Q/πR ³ (Q=volume flow rate, R=capillary radius). In the method of the invention, the shear rate is at least 100/s. Under a given configuration and a given temperature, the range of shear rates that can achieve satisfactory fiber melt spinning gradually narrows as the viscosity of the polymer melt increases. This operating range can be extended by increasing the temperature, as this shifts the critical shear rate corresponding to the onset of melt failure towards higher rates, however care must be taken to avoid polymer degradation. The critical temperature/shear rate at which melt fracture occurs, in this case by increasing the throughput rate at a given temperature and die size until the surface is visibly roughened by the naked eye, characterized by a melt extrudate consisting of clear Becomes slightly opaque, marking the onset of melt failure. Further increases in the throughput rate will produce an undesirably rougher surface and poorer spinning performance and performance.

The spinning speed of the inventive method is at least 500m/min, here is determined according to the last roller, therefore, depending on the configuration of the melt spinning equipment, this roller may be a take-up roller (the first roller that contacts the filament bundle) 1 roll or godet) or possibly a winding roll (from which the cake is produced).

It was found in the practice of this invention that both shear rate and SSF have a significant effect on the strength of spun filaments. Strength can be maintained when the shear rate is increased while decreasing the SSF, and vice versa, such as demonstrated in Example 1 and illustrated in FIG. 11 .

The method of the present invention may further comprise shielding the tow. By shielding the tow, the air surrounding the tow will remain warmer than if the tow were exposed to unrestricted ambient air, preventing rapid cooling of the tow. Unrestricted ambient air, especially turbulent air, can result in rapid cooling of the tow, which is undesirable because it may be detrimental to the tow's allowable draw. Thus, shielding the tow allows a higher degree of spinneret draw attenuation to be applied. It has been observed in the present invention that the condition for achieving high SSF in high speed spinning is that the solidification of molten filaments occurs at a distance greater than 50 times the diameter of the extrusion die (spinning hole diameter) (see also Figure 13) . Preferably, the solidification distance is greater than 500 times the diameter of the spin hole. Shielding can be achieved by passing the molten tow through an annealer. The annealer allows a high degree of "spinneret draw" of the molten filament extruded at high speed, thereby increasing the spinning speed. Although the rapid movement of the yarn through the annealer may produce a mild suction, the annealer still provides a relatively static environment that prevents ambient air turbulence, allowing the extremely hot molten tow to partially cool but Rapid cooling is prevented, thereby maintaining the tow above its melting point for a longer distance than a spinnerette without an annealer. This is shown graphically in FIG. 13 . The use of the annealer also maintained the cured yarn at a higher temperature than without the annealer, as shown in Figure 14. In addition, the use of an annealer allows for higher spinning speeds, as shown in Figure 15 (Note: 0-inch means no annealer).

One embodiment of an annealer useful in the present invention is shown in Figures 10A and 10B. As shown, annealer 200 includes inner tube 202, which is an elongated tube disposed concentrically within outer tube 204, which is a slightly larger diameter tube, which may be of substantially the same length. The inner tube 202 may be positioned within the outer tube 204 and protrude from below the outer tube 204 to provide an exit for the molten filaments and create a cylindrical opening 205 at the top of the outer tube 204 . The opening 205 allows air to be drawn into the inner chamber 206 of the inner tube 202 , which air may have been preheated in the annular space between the inner tube 202 and the outer tube 204 . Although no external heat is provided, the annulus 208 can be heated during spinning by thermal radiation from the extruded hot-melt filaments. A top flange 210 , which may have a circumferential lip, sits on top of the outer tube 204 . A mesh tube 212 , preferably composed of a fine mesh wire mesh, such as 20 mesh, may be secured to the top flange 210 and disposed adjacent the inner wall of the inner tube 202 . Mesh tube 212 is inserted axially into inner chamber 206 beyond opening 205, but the mesh tube need not extend the full length of the inner tube. The mesh pipe 212 can also include a second layer of finer meshes, such as 100 meshes, which are fixed on or near the first layer of meshes to reduce the turbulence of incoming air as a whole, and also promote the distribution of air substantially uniformly, so that Air flows radially through the opening 205 into the inner chamber 206 . In the figure, a porous annular spacing plate 214 is also shown, configured between the inner tube 202 and the outer tube 204, and connected to the outer surface of the inner tube 202 or the inner surface of the outer tube 204, which can prevent the inner tube 202 from the outer tube. The role of falling in 204. A fine mesh net 216 may be placed over 214 to disperse and distribute the air blowing upwards and preparing to enter openings 205 . Such spacer plates 214 and 216 are optional. Optional glass ring 220 provides visual inspection of the molten filaments and spinneret face.

The inner and outer tubes of the annealer can be made of materials including metals such as aluminum, or plastics such as Lucite ^(R) . The annealer may stand on its own or be stabilized by other suitable mounting mechanisms which may be affixed to other elements of the melt spinning apparatus or to other materials to keep it stationary.

The process of the invention may also include passing the extrudate in the form of one or more filaments through a quench zone to means for accumulating spun fibers. The quench zone can be at ambient temperature or heated or cooled relative to ambient temperature, depending on the requirements of the particular process configuration used.

Any means for accumulating fibers is suitable for use in the practice of the present invention. Such means include drums, oscillating distributors, or take-up rolls, preferably with traversing means, all of which are known in the art. Other means include continuous spin-drawing fiber chopping or chopping methods for producing staple fiber strands or fibrids. Still other means include, for incorporation of spun-drawn fibers directly into fabric structures or composite structures. One means described below that has been found suitable for embodiments of the present invention is a high speed textile winder, of the type commercially available from Leesona Corporation (Burlington, NC).

Such other means known in the art of fiber spinning for assisting fiber transport may be used if desired. These means include the use of godet rolls (or godet), take-up rolls, exhaust rods, splitters and the like.

Antistatic finishes can be applied to the fibers. Such oiling is well known in the art.

The method of the present invention may also include drawing of the fibers, a relaxation stage, or both. The fiber can be drawn between a take-up roll and a set of drafting rolls. Such drafting is well known in the art as a means for increasing fiber strength and reducing linear density. The take-up rolls may be heated to impart a higher degree of drafting to the fiber, the temperature and degree of drafting being dependent upon the desired final fiber properties. Similar additional steps, as known to those skilled in the art, may also be added to the process of the present invention to relax the fibers.

The present invention also provides a second melt spinning method for a composition containing a polytetrafluoroethylene homopolymer, comprising the steps of: melting the composition containing a polytetrafluoroethylene homopolymer to form a molten polytetrafluoroethylene composition delivering the molten polytetrafluoroethylene composition under pressure to an extrusion die of a melt spinning apparatus; and extruding the molten polytetrafluoroethylene composition through the extrusion die to form molten filaments.

In the melt spinning process of the homopolymer polytetrafluoroethylene (PTFE), preferred PTFE homopolymers are those which exhibit a certain melt flow rate at temperatures below 480°C. Preferred homopolymers include ^Zonyl® fluoroadditives, PTFE granular molding powder grades such as ^Teflon® PTFE TE-6472, and PTFE lubricated paste extrusion resins such as ^Teflon® PTFE 62, all available from DuPont (Wilmington, DE) purchased. The process of the present invention is particularly important for successful PTFE melt processing and fiber spinning due to the extreme temperatures required to exhibit melt flow characteristics near the edge of thermal degradation.

The above first melt spinning process for highly fluorinated thermoplastic compositions and the equipment used therefor are equally applicable to the melt spinning process for polytetrafluoroethylene compositions. However, the same limitations on extrusion die temperature or shear rate or spinning speed that apply in the 1st method may not apply to the current PTFE method. Preferably, the extrusion die temperature is at least 450°C. The spinning speed is preferably at least 50 mpm; more preferably at least 200 mpm; most preferably at least 500 mpm.

The present invention also provides a fiber melt spinning equipment, comprising: a spinneret assembly, which contains filtering means; a spinning plate; and an elongated conveying line, the conveying line is arranged between the filtering means and the spinneret means for heating said elongate transfer line; means for heating said spinnerette; and an elongate annealer disposed below the spinnerette assembly as shown.

Any melt-spun fiber filtration means conventionally used in melt-spinning technology can be used in the present invention. The configuration of the spinneret allows for separate heating of the spinneret face plate, i.e. the portion of the spinneret including the spinhole walls, which surface may comprise a plate separate from other areas of the melt spinning apparatus or the spinneret body inseparable part. The aspect ratio of the spinholes in the spinneret is preferably from about 1:1 to about 8:1. The spin holes of the spinneret are preferably arranged in a pattern such that all holes are heated uniformly. Preferably, the spinning holes are arranged in two concentric circles or one circle. Preferably, the spinnerets are individually removable from the transfer line for easy cleaning and replacement. Likewise, the transfer line is preferably detachable from the filter jacket and spinneret. Means for heating the transfer line and means for heating the spinneret may include band heaters, spiral heaters, or other conduction, convection, or induction heaters known to those skilled in the art.

The elongate annealer, as discussed above and in greater detail in the examples, preferably includes an inner tube and an outer tube, separated by an annular space. Preferably, the inner diameter of the inner tube is between about 3 inches and 8 inches. The elongated annealer may also include a mesh tube disposed adjacent the inner wall of the inner tube and extending downwardly at least a portion of the length of the inner tube. The elongated slow cooler can also include at least one porous plate, arranged in the annular space, extending radially relative to the circumference of the outer tube, and fixed on the outer wall of the inner tube, the outer tube on the inner wall, or on the two pipes.

A net can be placed on or near the above-mentioned perforated plate. Air can enter the annulus of the annealer through openings or ports. The annealer may also include means to measure and control the air flow rate, such as through needle valves or flow meters.

The apparatus of the present invention may also include means for accumulating the spun tow. Any means conventionally known in the art may be used including, but not limited to, take-up rolls, drafting rolls, and winding rolls.

One embodiment of the apparatus of the present invention for melt spinning is shown in FIG. 9 as melt spinning apparatus 100 . Shown is a feed hopper 102 into which the polymer composition is fed, preferably in the form of pellets. These pellets are heated and sent through screw extruder 103 . After the polymer or blend composition is melted, it is sent under pressure to a pump module 104 , through a filter jacket 105 , and a transfer line 106 to a spinneret 107 having a face plate 108 . A glass sleeve 109 allows observation of the molten strand. The molten fluoropolymer composition is extruded through one or more spinholes of faceplate 108 in spinneret 107 to form continuous filaments, which are then directed through elongated annealer 110, where the filaments are shielded from rapid cool down. After leaving the annealer, the spun fiber passes through a take-off guide 111, turns to a guide 116, reaches an oil feed roll 112 for optional oiling, a pair of take-up rolls 113, a pair of draft rolls 114 , and finally the winding roller 115. Additional drafting and even relaxation rollers can be added.

The fibers produced by the method and apparatus of the present invention can be used in textiles. Such textiles can be used in high-performance sports apparel, such as socks. Such fibers can be combined with other fibers in the fabric. PTFE fibers are available as industrial quality yarns for filtration. PTFE fibers can also be chopped for use in dry lubricated bearings.

Example

In the examples, the following polymers were used (all supplied by DuPont, Wilmington, DE):

^Teflon® PFA 340, a copolymer of TFE and perfluoropropyl vinyl ether

Teflon ^® FEP 5100, a copolymer of TFE, hexafluoropropylene and perfluoroethyl vinyl ether

^Zonyl® MP-1300 PTFE

^Teflon® TE-6462 PTFE

^Teflon® PTFE TE-6472, granular molding powder

^Teflon® PTFE 62, lubricated paste extrusion resin

^Zonyl® MP-1600N.PTFE

Unless otherwise noted, the polymer used was ^Teflon® PFA 340.

Example 1

The effects of spinning temperature, shear rate and spinneret draw factor (SSF) on spinning speed and fiber properties were investigated.

Spinning was performed using a 1.0 inch diameter steel single screw extruder to which was attached a spin pump housing (block or pump block) which in turn was attached to a spinneret pack adapter having the following features: The bypass plate replaces the spinning pump. An elongated spinnerette is used, such as that depicted in Figure 2, wherein "h" is equal to 2.0 inches. Use a 30 mil 39-hole spinneret with all of its holes arranged in only one circle to cover low to medium shear rates, such as the shear rate range of about 60/s to about 180/s, while using a 15-mil A 25-hole spinnerette is used to cover moderate to high shear rates, for example in the range of about 350/s to about 1,150/s. A 1 inch high, 1.25 inch internal diameter coil heater (Industrial Heater Co.) was coiled around the bottom 1 inch portion of the elongated spinnerette for separate heating of the spinnerette portion including the faceplate. Traditional take-up rolls are used with Leesona winders.

The temperature profile before the spinneret is: 350°C for the screw extruder; 380°C for feeding the filter from the pump sleeve to the assembly between the extruder and the spinneret. Three spinning operations were carried out using ^Teflon® PFA 340. The spinnerette temperature was set at 420°C, 460°C or 500°C.

In the case of 420°C, melt fracture (M.F.) occurs at a shear rate of about 180/s. At a shear rate of about 90/s, the highest possible spinning speed without melt fracture and with all filaments intact is slightly below 219 mpm. The fiber tenacity at this speed and shear condition was 1.02 gpd (grams per denier). At a shear rate of about 60/s, the highest spinning speed at final filament breakage (tow breakage) was 490 mpm with a fiber tenacity of 1.68 gpd and a denier per filament of 4.0.

At 460°C, the spinnable shear rate increased to slightly below 720/s, after which melt fracture started to occur. At a shear rate of 160/s, the highest measured spinning speed at the first break was 435 mpm, corresponding to a fiber strength of 1.13 gpd. The highest spinning speed at final filament breakage was 850 mpm, also at a shear rate of about 160/s. The highest fiber tenacity spun to final break was 1.61 gpd, corresponding to a spinning speed of 580 mpm and a denier per filament of 2.0.

Figure 11 shows a plot of shear rate versus spinneret draw factor for a 500°C spinneret sample. The black triangles represent the data of the first broken wire, and the open triangles are the data of the final broken wire. At 500°C, the spinnable shear rate was pushed slightly below 1,150/s, after which melt fracture began. At a shear rate equal to about 180/s, the highest spinning speed at first breakage was 933 mpm, and the tenacity of the fiber was equal to 1.04 gpd. The highest spinning speed for final broken filaments was 930 mpm, also at 180/s, and the tenacity at this speed was 1.15 gpd.

It can then be seen that as the spinneret temperature increases from 420°C to 500°C, the achievable spinning speed increases by a factor of 4.3.

At a constant shear rate, temperature has a positive effect on the SSF of the first broken wire, as shown in Figure 12. Blackened circles represent SSF at 420°C; blackened squares represent SSF at 460°C; blackened triangles represent SSF at 500°C. Higher SSF means higher take-up roll speed during spinning for the same throughput rate (ie, throughput) and given spinning hole size.

Unless otherwise noted, in the remaining examples, spinning was carried out using the equipment described above, except that a 1.5 inch diameter corrosion resistant single screw extruder (manufactured by Killion Extruders, Cedar Grove, NJ) was used. The extruder has 3 separate heating zones, designated as "Screw Zones 1, 2 and 3" in the temperature profile below. Secure the extruder to the threaded adapter (threaded sleeve) with a clamping ring so that the two become one piece, then secure the threaded adapter to the spinnerette adapter. The clamping ring is heated with cylindrical rod insertion heaters, while the thread adapter and spinnerette adapter are heated with core heaters. Heat the filter jacket with a band heater. Unless otherwise noted, any transfer lines, if present, as well as the spinning faceplate, were heated with ribbon or helical heaters. Using conventional coiling and winding equipment, including Leesona winders.

Example 2

Spinning was carried out under the following conditions: throughput rate, 1.3 g/min/hole; 30 mil 30 hole elongated spinnerette; jet velocity, 1.9 mpm. The spinning temperature (℃) curve of the equipment is: screw area clamping thread spinning plate assembly 1 2 3 ring adapter adapter filter spinning plate 350 350 350 380 353 480 450 0

The shear rate was 328/s, the maximum spinning speed achieved was 1,100 mpm, and the spinneret draw factor at first filament break (FFB) was 580. The denier, tenacity, elongation and modulus of the spun fibers were 11d/0.76gpd/61%/5.6gpd, respectively.

Example 3

The spinning process was similar to Example 2, except that a 5 foot high conical aluminum annealer was added downstream of the spinneret to shield the molten strands after leaving the spinneret. The slow cooler had a square cross-section, 12 inches square at the top, and tapered downward to a 1.0 inch square at the bottom. The same temperature profile as in Example 2 was used except: thread adapter, 380°C; spinnerette adapter, 470°C; pack filter, 470°C. The shear rate is 328/s. Using the same 1.3g/min/hole throughput as in Example 2 and using the same 30-mil 30-hole elongated spinneret, the maximum spinning speed increased by 35%, or from 385mpm to 1,485mpm, where in FFB The SSF (primary filament breakage) was 782. The denier, tenacity, elongation and modulus of the spun fibers were 9.4d/0.72gpd/76%/5.1gpd, respectively.

Example 4

The spinning process was similar to Examples 2 and 3, except that a different annealer was used. For spinning in this example, a 6 foot 3 inch high free standing Lucete ^(R) annealer with a 12 inch by 12 inch square section was used. The same temperature profile as in Example 3 was used. The shear rate is 328/s. The maximum spinning speed was increased to 1,756mpm, corresponding to an SSF of 924 at the FFB. The spinning speed is 60% higher than that of Example 2 and 18% higher than that of Example 3. The denier, tenacity, elongation and modulus of the spun fibers were 6.0d/1.16gpd/28%/10gpd, respectively.

Example 5

This example uses a spinnerette pack such as that shown in Figure 3, having a short elongated spinnerette. The distance between the lower surface of the filter jacket and the face plate of the spinneret was 1.25 inches. The same temperature profile and the same 6 foot 3 inch Lucite ^(R) annealer as in Example 4 were used. The shear rate is 328/s. The maximum spinning speed achieved was 1,860 mpm and the SSF at FFB was equal to 979. The fiber properties of this high-speed sample were not tested, but under the same conditions, the fiber properties (denier, tenacity, elongation and modulus) of another sample spun at a shear rate equal to 342/s and a spinning speed of 1,701 mpm amount) are respectively: 7.6d/1.01gpd/68%/6.2gpd.

Example 6

Spinning was carried out as in Example 5, except that the short, elongated spinnerette was heated with an induction heating helix wire, and the temperature was changed as follows: module filter, 440°C; spinnerette, 522-531 ℃. The shear rate is 342/s. The maximum spinning speed at FFB is 1,860 mpm. The denier, tenacity, elongation and modulus of the spun fibers were 9.6d/1.06gpd/49%/8.7gpd, respectively.

Example 7

Spinning was carried out as in Example 6, except that the same conical aluminum annealer as in Example 3 was used. A 12 inch clear Lucite ^(R) box was added to the top of the annealer to allow viewing of the filaments. The shear rate is 342/s. The maximum spinning speed at FFB is 1,860 mpm. The denier, tenacity, elongation and modulus of the spun fibers were 9.0d/1.02gpd/54%/7.7gpd, respectively.

Example 8

Spinning was carried out using a spinneret as shown in Figure 4 with a core heater (supplied by Industrial Heater Co., Stratford, CT) in the center of the spinneret and standard band heating on the outside of the spinneret. device. The spinneret length from the bottom of the filter jacket to the face plate of the spinneret was 1.25 inches. The temperature curve used is as follows:

Screw zone clamping ring threaded spindle board component cross -spinning board spinning board 1 2 3 Ender adapter filter center 350 350 380 380 411 410 496 500

The spinnerette used had 26 holes; however, the throughput per hole was maintained the same as in Examples 2-7. Then, the shear rate is about the same, ie, 342/s. The maximum spinning speed is 1,976 mpm corresponding to SSF equal to 1,040. The 6% increase in spinning speed compared to Example 5 was attributed to more uniform heating of the melt along the spinneret. The denier, tenacity, elongation and modulus of the spun fibers were 5.6d/1.09gpd/55%/7.0gpd, respectively.

Another sample spun at a spinneret adapter and pack filter temperature of 400°C and the same spinnerette temperature of 500°C gave a maximum speed of 1,920 mpm with a corresponding SSF equal to 1,010. The fiber strength is high, and the denier, strength, generation and modulus measurements of the fiber are as follows: 5.6d/1.25gpd/54%/8.7gpd.

Example 9

The effectiveness of this embodiment in achieving high spinning speeds was examined using a spinneret assembly such as that shown in Figure 6. A 15 hole 1.0 inch diameter disk spinnerette with 30 mil diameter holes was used. The annealer used was the 6 foot 3 inch Lucite ^(R) annealer used in Example 4 with a band heater to heat the module filter. The length of the transfer line measured from the lower surface of the filter jacket to the spinnerette disc was 3.125 inches.

At a screw speed of 4.0 rpm, the total throughput rate was 20.3 g/min (2.7 lbs/h) or 1.35 g/min/hole. This is essentially the same throughput rate per hole as in the previous example. The spinning speed reached 1,816mpm, and all filaments were intact under the following conditions: screw extruder temperature, all 3 zones were set at 350°C; clamping ring and thread adapter were set at 380°C, corresponding to melt temperature Measured 389°C; spinnerette adapter and pack filter set at 430°C; transfer line set at 470°C; spinneret set at 500°C.

Spinning speed was further improved by lowering spinneret adapter and pack filter temperature and increasing transfer line temperature: spinneret adapter transfer line spinneret max speed performance and pack filter denier/strength/elongation/modulus 430 ℃ 474 ℃ 500 ℃ 1,816MPM 6.5/1.20/45 %/10420 ℃ 471 ℃ 500 ℃ 1,969MPM 5.5/1.24/24 %/12410 ℃ 471 ℃ 500 ℃ 1,965MPM 5.6/1.38/35 %/13400 ℃ 470 ℃ 500 ℃ 500 ℃ 500 ℃ ℃ 1,950mpm 5.8/1.27/32%/12400℃ 480℃ 500℃ 1,994mpm 5.3/1.48/48%/12

The spinning speed reached 1,994 mpm, a 14% improvement over Example 4's spinning speed of 1,756 mpm. The shear rate is 347/s. Fiber strength increased from 1.16 gpd to 1.48 gpd, a 28% improvement. This improvement in strength is due to, in addition to higher speed, less or no polymer degradation.

Several yarn samples were collected at 1,000 mpm to investigate the long-term stability of the spinning process. The spinning continuity of the tow is excellent, allowing winding up to 60min and 105min, both planned for doffing. The properties of denier/strength/elongation and modulus of the fiber are respectively: 11d/0.94～1.01gpd/68～80%/7.5gpd.

One sample, spun at 1,500 mpm for 4 min, had silk properties in terms of denier/tenacity/elongation/modulus: 7.2d/1.20gpd/39%/11gpd, respectively. Another sample, spun at 1,000mpm, drawn 1.4 times on line, at 280°C, the silk properties in terms of denier/strength/elongation/modulus are: 7.6d/1.41gpd/25%/14gpd .

Measurements of air samples collected at the exit of the annealer, above the heated take-up roll along the tow path, and above the take-up roll did not reveal any gas evolution. If there is thermal degradation of the polymer, gas will inevitably be generated. Since the released gas may also be entrapped or dissolved within the fibers, vials were used to collect the fibers at various time intervals and examine their headspace using infrared spectroscopy, gas chromatography/mass spectrometry, and ion chromatography, all of which did not contain Any outgassing. In addition, fiber samples were heated to 200°C in order to release possible dissolved gases, but these were also not detected. This result demonstrates that, in the present invention, no polymer degradation occurs despite the use of temperatures up to 500°C to favor high shear rates, high spinning speeds and high SSF. PFA polymers are easily degraded if kept at a temperature as low as 425°C for more than 1.0 min.

Example 10

The spinning was similar to Example 9, except that about a 1/8 inch induction heating wire coil was wound 2 times around the spinneret faceplate. The temperature profile in the screw extruder up to the screw adapter was maintained at the same level as in Example 9. The shear rate is 347/s. The maximum speed was improved by 3.6% (from 1,994mpm, Example 9) to 2,065mpm, corresponding to SSF equal to 1,087 at FFB. The maximum speed and the performance obtained are given in the table below: Spinneret Adapter Transfer Line Spinneret Maximum Speed Performance Denier/Tenth/Elongation/Die and Assembly Filter Quantity 430°C 470°C 520°C 1,910mpm 6.9/1.04/ 59%/6.5400°C 480°C 525°C 2.065mpm 5.6/1.21/32%/11

Spinning continuity proved to be excellent, at which point the sample was spun at 997 mpm for 90 minutes and was scheduled to doff.

The fiber properties in denier/strength/elongation/modulus etc. are: 10.3d/0.97gpd/68%/3.6gpd, respectively.

Example 11

A spinneret assembly as shown in Figure 8 was used. The diameter of the spin deck was 1.75 inches with 60 holes of 30 mil diameter each. The throughput per hole is 1.35 gpm, which translates to a total throughput of 81 gpm or 10.7 pounds per hour (pph). Based on Example 7, a conical aluminum anneal cooler with a 12 cubic inch Lucite( ^R) box on top was used. The temperature (°C) curve used is: Screw area Clamp ring Thread adapter Spinneret Component pass Conveying tube Spinneret 1 2 3 Distributor Adapter Filter Line 350 350 350 380 380 400 400 477 500

The maximum spinning speed was 1,359 mpm. The shear rate is 347/s. Fiber properties such as denier/strength/elongation/modulus are: 8.0d/1.04gpd/67%/7.1gpd, respectively.

The reduction in spinning speed compared to a 30 hole spinnerette, eg Example 7, is due to the doubling of the total throughput resulting in too high heat retention in the annealer. The annealer was replaced with a larger capacity 6'3" Lucite(R ⁾ box annealer and the maximum velocity was increased to 1,500 mpm. The temperature (°C) profile used is: Screw area Clamp ring Thread adapter Spinneret Component pass Conveyor tube Spinneret 1 2 3 Distributor Adapter Filter Line 350 350 350 380 380 420 420 500 520

Fiber properties such as denier/strength/elongation/modulus are: 7.2d/1.20gpd/48%/9.4gpd, respectively.

In order to reduce the trapping of excess heat inside the annealer, the annealer doors, which run longitudinally and almost surround one side of the annealer, are fully open and covered with air mesh to provide smooth air movement without turbulence. The use of the perforated metal sheet with 3/32 inch diameter holes, center to center spacing 3/16 inch increased the maximum spinning speed to 1,623 mpm, an 8% improvement over the annealer door closed, this example Use a slightly different temperature (℃) curve: screw zone clamping ring threaded spin board component over -convey pipe spinning board 1 2 3 ornament adapter line 350 350 380 380 400 400 520 2020

Fiber properties such as denier/strength/elongation/modulus are: 7.5d/1.18gpd/50%/8.9gpd, respectively.

In the annealer with the front covered by the perforated metal sheet, as mentioned above, a certain degree of non-uniformity in air movement was observed, as there was diffused air in and out of the front, but not on the other 3 sides. Thermocouples placed close to the spinning faceplate showed temperature fluctuations between 368°C and 390°C with a variation of 22°C.

A larger Lucite ^(R) slow cooler was used, measuring 20 inches by 24 inches cross-section, 71.5 inches high, open at the top for the spinneret and open at the bottom for handling the filaments. During spinning, excessive air movement up and down occurred, and the spinning speed was reduced.

Inserts were placed on top of the slow cooler to reduce the 20 inches by 24 inches opening to a 20 inch square. These inserts are tapered downwards so that the yarn falls out. The measured temperature fluctuation is still as high as 25°C, but the actual temperature is significantly lower, from 240°C to 265°C (Note: Although the measured temperature is lower than that in the small annealer, the comparison of the absolute temperature between the two annealers is not clear. Shouldn't be taken too precisely, since the thermocouples don't necessarily sit exactly the same.) The air stability looks calmer. At the same temperature profile, the maximum spinning speed was improved and slightly higher than that recorded by the small annealer: 1,680 mpm. Fiber properties such as denier/strength/elongation/modulus are: 8.2d/0.84gpd/59%/5.9gpd, respectively.

Example 12

In the above annealer design, it is difficult to reach the yarn from the bottom of the annealer in order to feed it into the suction gun and spin up the yarn through all the yarn processing paths to the winder. In addition, the slow cooling of the molten filaments depends entirely on the natural convection of the air, and there is no means of control. The above two problems are solved in the annealer design shown in Figures 10A and 10B. With this slow cooler, it is easy to suck up the yarn at the outlet of the cone bottom. Air from a compressed air source flows between the inner and outer tubes, up through several layers of fine mesh mesh to eliminate eddy currents, and then into the top and blows the molten tow radially. Let the air enter from the lower part of the slow cooler, and use the needle valve to control the air flow rate with a flow meter. The temperature in the inner tube along the top 6 inches was monitored by thermocouples placed every 1 inch. The height of the air inlet damper between the inner and outer tubes is adjustable within the range of 1.0 inches to 4.0 inches. A 1.0" high glass ring provides viewing of the molten filament and spinning faceplate.

Spinning was carried out using a spinneret assembly having a configuration as shown in Figure 8, 30 holes with a diameter of 39.4 mils, and a spin hole aspect ratio of 3.0. Spinning was performed at a throughput of 1.3 gpm and the following temperature profile: screw extruder to pack filter, 350°C; transfer line, 450°C; spinneret, 500°C. The temperature in the slow cooler: 1.0 inches from the spinning plate surface, 268°C; 2.0 inches from the spinning plate surface, 252°C; 6.0 inches from the spinning plate surface, 222°C. Temperature fluctuations were negligible as the variation was only 2°C, compared to the up to 25°C variation observed in the annealer of the previous examples herein. The shear rate is 151/s. The maximum spinning speed achieved was 1,737 mpm. Fiber properties such as denier/strength/elongation/modulus are: 4.2d/1.17gpd/57%/7.8gpd, respectively.

The stability of the spinning system has been confirmed by the fact that at 240°C, the speed of the take-up roll is 702 mpm, and the speed of the take-up roll is drawn 1.4 times on-line, reaching 1,005 mpm for 3.5 hours of silk cake winding, showing excellent spinning continuity. sex. The yarn package (cake) weighed over 20 pounds net and was 2.0 inches thick on a 6.0 inch diameter bobbin. The temperature (℃) curve is: the screw zone clamping ring threaded spinning board component over -convey pipe spinning board 1 2 3 ornament adapter filter line 350 350 350 350 350 448 500

Fiber properties such as denier/strength/elongation/modulus are respectively: 12.6d/0.80gpd/92%/3.8gpd.

Example 13

Spinning was performed as in Example 12, but instead of PFA 340 ^Teflon® FEP 5100 fluoropolymer was used. The temperature (℃) curve is: screw area, clamping ring, thread adapter, spinneret assembly, delivery tube, spinneret 1 2 3 adapter adapter filter line 315 319 325 325 325 325 325 401 480

The temperature used in this example is lower than that of the PFA polymer because FEP is not as stable as PFA. The shear rate is 161/s. The maximum spinning speed achieved was 1,290 mpm. Fiber properties such as denier/strength/elongation/modulus are: 7.3d/1.04gpd/36%/10gpd, respectively.

Example 14

The purpose of this example spinning was to test the stability of the method developed in Example 13 on Teflon(R ⁾ FEP 5100 polymer (spinning). Using the same equipment style as in Examples 12 and 13, excellent spinning continuity was demonstrated, and a silk cake of 3.5 hours was obtained under the same take-up speed of 700 mpm as in Example 12 for PFA polymer. The yarn was drawn off-line at the same draw ratio of 1.4 times, but at a lower drawing temperature of 200°C because the melting point of FEP (260°C) is lower than that of PFA 340 (305°C). The yarn package (mass) was similar to the PFA 340 polymer spun in Example 12. The temperature (°C) profile used was lower than that used in Example 13, i.e.: screw zone clamping ring thread fit spinneret assembly pass transfer tube spinneret 1 2 3 adapter adapter filter line 305 310 315 315 315 315 315 393 480

The shear rate is 163/s. The drawn fiber properties such as denier/strength/elongation/modulus are: 12.2d/0.97gpd/45%/5.8gpd, respectively.

Example 15

PTFE homopolymer spinning: pelletized ^Zonyl® MP-1300 PTFE was used. A pelletized form of the homopolymer was compressed from fine PTFE powder using a pelletizer comprising a 2.0 inch thick male and female die with 1,013 0.257 inch diameter inlaid pins. The powder, which had an original density of about 0.36 g/mL, was compacted into pellets with a diameter of 0.28 inches, a length of 0.50 inches, and a density of 1.58 g/mL under a pressure of 30 tons in the press. The same equipment and 30 hole spinneret as in Example 14 were used. The temperature (°C) profile used is: Screw area Clamp ring Thread adapter Spinneret Component pass Conveyor tube Spinneret 1 2 3 Distributor Adapter Filter Line 400 400 400 400 400 410 410 450 520

The molten tow emerged from the spin faceplate appearing opaque and glistening, indicating some degradation had occurred. However, the tow does not come out of the annealer in a continuous form, but rather in sections. Changing the throughput from 0.17 g/min/hole to 1.33 g/min/hole also failed to produce continuous tow.

After the MP-1300 pellets in the feed hopper were used up, about 200 g of PTFE homopolymer TE-6462 in powder form was added to the hopper and extruded to form long, continuous filaments. The free-falling continuous filament is malleable and can be gently stretched between fingers without interruption. The measured denier of the silk was 349.

Example 16

In order to spin Teflon® ^PTFE TE-6472, the extruder and spinning equipment used in Example 15 are placed in the following high temperature (°C) profile, and PFA 340 is used first to avoid subsequent PTFE homopolymers due to up to 2.5 Degradation due to stagnation during heating up of h: screw zone clamping ring thread fits spinneret assembly through conveying spinneret 1 2 3 distributor adapter filter line 470 470 470 470 470 470 470 450 510

Pressed powder pellets of ^Teflon® PTFE TE-6472, specified as granular molding powder, were added to the extruder after the feed of PFA pellets was exhausted and the screw was allowed to rotate at 14.0 rpm. Six minutes after ^Teflon® PTFE TE-6472 was added, it was found that the component pressure rose rapidly from 204 psi to over 1,000 psi, indicating that ^Teflon® PTFE TE-6472 had reached the component. The screw speed was constantly adjusted and the spinnerette temperature was increased to 550°C to maintain a package pressure of 1,000 psi. Continuous, clear molten strands were extruded but contained air bubbles, indicating thermal degradation, and subsequently solidified to white strands. At 2.0 rpm the throughput was measured to be 7.6 gpd whereas the predicted value was 10.5 gpd. Although the screw speed was maintained at 2.0 rpm, the throughput was found to drop continuously, down to 0.4 gpm, and the continuous strands began to break up into droplets, connected by long (up to 48 inches) and very thin filaments. These very thin filaments look like ethereal spider webs, they are so light that they float in the air. The denier of the filaments between the droplets ranged from less than 0.6 to 18. This clearly shows that PTFE can be melt spun to even very fine filament deniers.

The decrease in throughput was due to an annular blockage at the entrance of the extruder barrel, which effectively prevented the fluoropolymer pellets from being fed. To clear the clog, vacuum out all polymer until the screw is visible. The PFA pellets are then added and pushed out using specially fabricated rectangular plates mounted on 0.5 inch rods the same size as the barrel opening. Turning the screw caused a small amount of PFA pellets to scrape the adhering PTFE compressed powder off the screw surface.

After clearing the ring blockage and refeeding, add the PTFE compressed powder pellets again. Under the conditions of screw speed of 5.0rpm and measured throughput of 9.3gpm, continuous filaments were spun from all 30 holes and taken up by a take-up roll of 30mpm. The excellent spinning continuity lasted for about 15min, and then again An annular blockage occurs, as indicated by a drop in component pressure. This experiment clearly shows that homopolymer PTFE can be melt spun. The temperature (℃) curve is: the screw zone clamping ring threaded spinning plate component transmitted pipe spinning board 1 2 3 ornament adapter line 420 440 485 485 485 495 500

PTFE fiber samples are ductile, can be handled without brittle failure, and can be subjected to tensile tests. Sample Name Tow Denier Strength (g) Strength (gpd) Free Fall 686 36.0 0.05 Free Fall 1,042 71.8 0.0730mpm 332 0 .14.0

Example 17

Spinning was performed on ^Teflon® PTFE 62, which was specified as a lubricated paste extrusion resin. The powder was similarly compacted under 50 tons of pressure into pellets having a diameter, 0.28 inches; a length, 0.52 inches; and a density of about 1.6 g/cc.

Use the same equipment and start-up procedure as Example 16. At a screw speed of 3.8 rpm, Teflon® ^PTFE 62 pellets were added. Feeds were good initially with a measured throughput of 9.9 gpm and a predicted value of 20 gpm. The screw speed was increased to 7.7 rpm. The assembly pressure was found to increase and stabilize at 1,200 psi by reducing the screw speed, indicating good feed conditions. A ring blockage occurs and the component pressure drops. Speeding up the screw speed again to 30rpm loosens the blockage and the assembly pressure rises again. At 10 rpm, the assembly pressure climbed up to 2,150 psi while the continuous tow was pulling at 55 mpm. The spinning continuity lasted for about 5 minutes, and then the ring blockage appeared again.

Example 18

Fibers spun in Examples 16 and 17 were hot drawn in a heated salt bath. The tow was cut to about 1 inch in length and held between 2 pointed tweezers, then drawn while briefly submerged in a salt bath. The drawing temperature is between 330°C and 400°C. The fiber could not be drawn at 320°C. The melting point of PTFE polymer is between 325°C and 342°C, so the fiber is drawn in a molten state. The tow was easily drawn 5.0 to 8.0 times. In cross-polarized light, the tow changes from a bright, non-preferential orientation to a dark blue color along one direction and a magenta-hued red perpendicular to it, indicating preferred molecular orientation along the fiber axis. A drawing temperature of 340°C produced the highest degree of orientation. Drawn yarn with a measured denier equal to 7.7 gave a tenacity of 0.2 gpd.

Example 19

The spinneret pack described in Example 9 and shown in Figure 6 was used to spin ^Teflon® PFA 340, and the spinning conditions normally employed in a conventional spinneret pack style (see Figure 1) where the spinneret could not Heating alone, compared to spinning conditions where the spinnerette and filter assembly are thermally insulated from each other. In this embodiment, thermal insulation is achieved in part by the addition of transfer lines between the lower surface of the module filter and the face of the spinnerette.

Control experiments were carried out using the same spinnerette system but with the spinnerets maintained at the same constant temperature.

Control 1 spinning was done by maintaining the temperature (°C) profile at 350°C as follows: Screw Zone Clamping Ring Thread Adapter Spinneret Assembly Pass Delivery Tube Spinneret 1 2 3 3 Adapter Adapter Filter Line 350 350 350 350 350 350 350 350 350

Throughput was increased until slight melt fracture was observed at 0.178 gpm/hole. The shear rate below this maximum throughput was 45.7/s, and at a jet velocity of 0.26 mpm and an SSF equal to 223, the maximum spinning speed achieved was 58 mpm.

Control 2 spinning was done at a higher temperature profile of 400°C as shown below: Screw Zone Clamping Ring Thread Adapter Spinneret Assembly Pass Delivery Tube Spinneret 1 2 3 Adapter Adapter Filter Line 350 0 350 35 0 350 350 400 400 400

The higher temperature of 400°C allows a higher throughput of 0.370 gpm to be taken before melt failure. At a lower throughput of 0.238 mpm/hole before melt failure, a maximum spinning speed of 206 mpm was achieved. At the highest throughput and melt failure edge, the maximum spinning speed reached was 381 mpm, the shear rate was 95/s, the jet speed was 0.54 mpm, and the SSF was 704.

Use the following temperature (℃) curve: the screw zone clamping ring threaded spinning board component over the conveyor pipe spinning board 1 2 3 ornament adapter line 325 330 335 335 335 335 450 500

Using this temperature profile, the throughput can be increased up to 1.125 gpm/hole, which is equivalent to 3 times that of the comparative example at 400° C., and still no melt fracture occurs. The maximum spinning speed achieved is 1,956 mpm, which is equivalent to 5 times that of the control at 400°C, at this time, the shear rate is 289/s; jet velocity, 1,645 mpm; SSF, 1,189.

The control case of 500°C was not simulated because in the case of a conventional spinneret system the module filter would also have to be heated to a temperature of 500°C as well. When the component filter reaches 500°C, the polymer will be severely degraded due to the too long residence time in the component filter, up to 10.1min. When at 425°C, the polymer will start to degrade in less than 1.3 minutes.

Example 20

The following experiments were carried out to determine at what distance the molten filaments would solidify from the spinneret face. Solidification was judged to have occurred when the transparent molten strands were observed to become opaque with the naked eye. The transition from transparent to opaque can be seen when accelerating to 200mpm by free fall (by gravity). Extrusion of the molten strands was performed with or without an annealing tube. In the case of an annealing tube, a special clear glass annealing tube was used so that it could be observed with the naked eye, and its dimensions were 3.0 inches in diameter by 41 inches in length. The spinnerette used had 30 holes of 30 mil diameter. Teflon ^(R) FEP-5100 polymer was used.

The results plotted in Figure 13 represent: open symbols, data without the annealer; blacked out symbols, with the annealer. The graphs show that the free fall distance increases with increasing total throughput for 3 constant spinnerette temperatures: 380°C (triangle symbols), 430°C (square symbols) and 480°C (dot symbols) . It was shown that the solidification distance increases with the total throughput at a constant spinnerette temperature. It is also shown that the solidification distance increases with the spinneret temperature at the same throughput. It also shows that with slow cooling tube, the solidification distance is about twice as long as without slow cooling tube. Another experiment showed that tow tensioning had the effect of increasing the solidification distance from about 6 inches to about 15 inches with no annealing tubes and a take-up speed equal to 200 mpm. Therefore, the curing distance given in Fig. 13 represents the shortest curing distance.

The following temperature (℃) curve is used: the screw zone clamping ring threaded spinning board component transmitted spinning board 1 2 3 ornament adapter pipeline pipeline 275 285 295 315 315 380 380, 430, 430, 430, 430

480

Example 21

A PTFE homopolymer grade, ^Zonyl® MP-1600N, was melt processed and spun into fibers using the spinneret assembly shown in FIG. The polymer powder was filled in a female mold with 0.25 inch diameter, 0.5 inch high holes and then compacted into approximately 0.1 inch thick discs using pins less than 0.25 inch diameter. About 2 lbs of this flake pellet was produced. Feed the pellets into the screw extruder by hand to just fill the flight profile of the screw to prevent crushing and thus causing sticking screw and ring plugging. The following temperature (°C) profiles were used: Screw area Clamp ring Thread adapter Spinneret Assembly pass Conveyor tube Spinneret 1 2 3 Distributor Adapter Filter Line 380 385 390 390 390 390 390 450 500°C

At a screw speed equal to 1.94 rpm, the throughput was 9.4 g/m, the pack pressure was 238-246 psi, and a 10-hole 30 mil aperture spinneret was used. The shear rate is 242/s. The annealer used in Example 12 and shown in Figures 10A and 10B was used. Ring blockage problems were not encountered. After the pellets are used up, the spinning ends prematurely.

At first, 10 filaments are picked up by hand, passed around the take-up roller and wound once, and then the threading gun is used to guide the yarn all the way to the Leesona winder. The initial spinning speed was 30 mpm and then the speed was gradually increased to a maximum of 202 mpm. Tow denier measurements were performed on 3 types of filaments: 33, 36 and 41. The as-spun filament properties (denier/strength/elongation at break/modulus) measured from 41 denier filaments were: 41 denier/0.05 gpd/1.3%/3.7 gpd.

^Teflon® PTFE 62 was spun using chopped and thin disc pellets to avoid ring plugging. The following temperature (°C) profile is used: Screw area Clamping ring Thread adapter Spinneret Component pass Conveying tube Spinneret 1 2 3 Distributor Adapter Filter Line 440 445 450 450 450 450 450 450 500°C

The feeding of the chopped pellets went fairly smoothly with no clogging. However, wafer pellets end up causing ring plugging problems. Spinning up to 60 mpm, then clogging occurs, the shear rate during spinning ranges from 183/s to 614/s.

Example 22

Pellets of ^Zonyl® MP-1600N PTFE homopolymer powder were prepared similarly to Example 21, using the same spinnerette assembly. The effect of the annealer was studied by spinning with and without the annealer under the conditions of the following temperature profiles. Through a 30 hole spinnerette at a rate of 8.4 g/min/30 mil diameter holes, the shear rate is equal to 72/s. Screw area Clamping ring Thread adapter Spinneret Component delivery tube Spinneret 1 2 3 Distributor Adapter Filter Line 315 330 340 340 340 340 340 400 400℃

Without an annealer. About 15% of these extruded tows could not withstand their own weight in a vertical free fall distance of 5 feet 8 inches. And those tows that can barely be spun can only be spun to the maximum spinning speed of only 15 mpm, and then broken ends occur.

With 48" long slow cooler: All tows are in continuous free fall to the ground. The spinning speed for first filament break (FFB) was 50 mpm; the maximum spinning speed (MSS) achieved was 480 mpm. By increasing the temperature of the transfer line and spinneret from 450°C to 500°C, the FFB was improved to 85 mpm and the MSS was at 250 mpm. The naked eye can see that the tow is thick and thin. Yarn uniformity was found to be improved by introducing room temperature air to the top of the annealer through the annealer jacket. At 250 cfh (cubic feet per hour), the yarn becomes uniform. Under such spinning conditions, the MSS improved to 404 mpm. The filament fiber properties (denier/tenacity/elongation at break/modulus) were 5.8/0.16 gpd/12%/8 gpd.

Example 23

This experiment employed ^Teflon® FEP-5100 as the fluoropolymer composition and demonstrated the superiority of the spinneret thermal insulation. The spinning pack used is shown in Figure 8. The same components are used but all parts are maintained at the same temperature. The temperature (°C) curve used in the comparative example is: the thread of the clamping ring in the screw area is suitable for the spinneret assembly passing through the conveying tube spinneret 1 2 3 distributor adapter filter line 275 300 350 350 350 350 350 350 350 275 350 400 400 400 400 400 400 400 275 350 400 400 450 450 450 450 450

The temperature profile of screw zones 1 and 2 was maintained at a low level until the screw zone 3 or clamping ring reached the test temperature. The degradation was worse if screw zones 1 and 2 were placed at the test temperature. The temperature (℃) curve used in the sample of the present invention is: the screw zone clamping ring threaded spinning board component transmitted pipe spinning board 1 2 3 ornament adapter line 275 295 300 300 300 380 480

The shear rate is: 86/s at 10 gpm; 232/s at 27.2 gpm; 359/s at 42 gpm; 385/s at 45 gpm. As shown in Figure 16, when the spinning temperature was about 480°C, a spinning speed of 1,900 mpm was achieved without any significant degradation. However, the comparative example experienced slight thermal degradation at a spinneret temperature of 400°C, reaching a spinning speed of about 600 mpm, and severe thermal degradation at about 450°C, reaching a spinning speed of 900 mpm.

Claims (31)

1. A process for melt spinning a composition containing a highly fluorinated thermoplastic polymer or a blend of such polymers, comprising the steps of: melting a composition comprising a highly fluorinated thermoplastic polymer or a blend of such polymers to form a molten fluorinated polymer composition; conveying the molten fluorinated polymer composition under pressure to an extrusion die of a melt spinning apparatus; and Extruding the molten fluoropolymer composition through the extrusion die to form molten filaments, the die being at a temperature of at least 450°C, a shear rate of at least 100 s ^-1 , and a spinning speed of at least 500 m/min . 2. The method of claim 1, further comprising shielding the tow. 3. The method of claim 1, further comprising exposing the molten fluoropolymer composition to an intermediate temperature between the melting temperature of the composition and Between temperatures below the extrusion die temperature. 4. The method of claim 1, wherein the melt flow rate of the highly fluorinated polymer at 372°C is between 1 and 50 g/10 min. 5. The method of claim 1, wherein the fluorinated polymer is a copolymer of tetrafluoroethylene and perfluoroolefin. 6. The method of claim 5, wherein the fluorinated polymer is a copolymer of tetrafluoroethylene and hexafluoropropylene. 7. The method of claim 5, wherein the fluorinated polymer is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether. 8. The method of claim 7, wherein the perfluoroalkyl vinyl ether is perfluoromethyl vinyl ether, perfluoroethyl vinyl ether or/and perfluoropropyl vinyl ether. 9. The method of claim 1, wherein the die temperature is at least 500°C. 10. The method of claim 1, wherein the extrusion die and other areas of the apparatus containing the fluoropolymer composition are thermally insulated from each other. 11. The method of claim 1, wherein the spinning speed is at least 1000 m/min. 12. The method of claim 1, wherein the shear rate is at least 500 s ^-1 . 13. The method of claim 1, further comprising drawing the fiber. 14. The method of claim 1, further comprising a relaxation stage. 15. A method for melt spinning of a composition containing polytetrafluoroethylene homopolymer, comprising the following steps: melting a composition comprising polytetrafluoroethylene homopolymer to form a molten polytetrafluoroethylene composition; conveying the molten polytetrafluoroethylene composition under pressure to an extrusion die of a melt spinning apparatus; and The molten polytetrafluoroethylene composition is extruded through the extrusion die to form molten strands. 16. The method of claim 15, wherein the temperature of the extrusion die is at least 450°C. 17. The method of claim 15, wherein the spinning speed is at least 50 mpm. 18. The method of claim 17, wherein the spinning speed is at least 200 mpm. 19. The method of claim 18, wherein the spinning speed is at least 500 mpm. 20. The method of claim 15, further comprising shielding the tow. 21. An equipment for fiber melt spinning, comprising: The spinneret assembly, which includes filter means, spinneret, an elongated delivery line arranged between the filtering means and the spinning between the boards, means for heating said elongate transfer line, means of heating the spinneret; and The elongated slow cooler is arranged under the spinneret assembly. 22. The apparatus of claim 21, wherein the elongated annealer includes an inner tube disposed within an outer tube, said inner tube and said outer tube being separated from each other by an annular space. 23. The apparatus of claim 22, further comprising a mesh tube disposed adjacent the inner wall of the inner tube extending downwardly along at least a portion of the length of the inner tube. 24. The apparatus of claim 22, further comprising at least one perforated plate disposed within said annulus, extending radially relative to the circumference of said outer tube, connected to said inner tube outer wall or said outer tube. on the inner wall of the pipe, or on the two pipes. 25. The apparatus of claim 24, further comprising a mesh placed on or adjacent to at least one perforated plate. 26. The apparatus of claim 21, wherein the elongated annealer further includes means for measuring or controlling the air flow rate. 27. The apparatus of claim 21, wherein the spinneret is removable. 28. The apparatus of claim 21, wherein the delivery line is detachable. 29. The apparatus of claim 21, wherein said means for heating the spinnerette is a conduction heater, a convection heater, or an induction heater. 30. The apparatus of claim 21, wherein the spinneret has a plurality of holes all arranged in a circle. 31. The apparatus of claim 21, further comprising means for accumulating the spun tow.

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