Single counterbore for multiple profile filaments

Abstract: A spinneret plate defines at least one counterbore (40), and within the counterbore, at least one non-round curved capillary. The capillary has a plurality of extending tips, wherein for any one capillary, at least two of the extending tips have a different radius of curvature.

Description: Field of the Invention This invention relates to a spinneret plate according to the preambles of claim 1 and claim 3 and to a process for melt spinning filaments from molten polymers according to the preamble of claim 9 and known, for instance, from document US-A-3 652 753. Background of the Invention In the melt spinning of molten polymers to produce filaments increased efficiency is nearly always a worthwhile goal. One manner of increasing the efficiency of a melt spinning process is to increase the number of fibers which can be produced during a given time period from a single piece of melt spinning machinery. In furtherance of this goal, spinneret plates providing for an increased number of filaments to be extruded therethrough is of value. Another consideration in melt spinning operations is the cross section of the extruded filament. Fibers having novel cross sections may be useful for a variety of different purposes, some of which purposes are readily apparent from the unique cross section and others which remain to be discovered. Fibers of new deniers are also invaluable. Furthermore, new combinations of deniers and cross-sections can result in commercially interesting fibers. For the present purposes, the term "counterbore" refers to the upstream bore in a spinneret plate and its upstream orifice. The term "capillary" refers to the downstream orifice in a spinneret plate and its downstream orifice. The following patents exemplify efforts to modify the melt spinning process and the characteristics of the resulting melt spun filament. In general, the characteristics of only a few classes of spinneret capillaries have been determined with respect to kneeing and for only a few general classes of capillary shapes. U.S. Patent No. 2,838,364 to Smith discloses that cellulosic fibers may be spun in a manner to produce filaments of hollow cross section through a spinneret having a plurality of counterbores each in the shape of a sector of a circle. U.S. Patent No. 3,405,424 to Imobersteg et al. discloses a spinneret for manufacturing hollow synthetic fibers from counterbore groups having at least two laterally opposing star-shaped capillaries. X and Y star shapes are disclosed. Sometimes high pressures on the upstream side of the spinneret plate forces the legs of the star-shaped capillary apart. U.S. Patent No. 3,652,753 as the closest prior art and U.S. Patent No. 3,860,679, both to Shemdin, describe a formula for predicting the appropriate capillary shape to eliminate the phenomenon of kneeing. Kneeing is defined as "when the line of flow of the filament is bent out of the vertical back toward the spinneret face at an angle with respect to the perpendicular to the spinneret face." Kneeing may be so severe that the line of flow actually bends back and touches the spinneret face or it may be only sufficient to cause two or more adjacent filaments to touch and coalesce. The capillaries are generally T-shaped. U.S. Patent No. 3,734,993 to Paliyenko et al. teaches that the effect of kneeing in T-shaped capillaries is reduced if the stems of the T's are arranged such that each stem extends perpendicularly outward (relative to the spinneret die plate) from the cross bar. U.S. Patent No. 3,981,948 to Phillips discloses that kneeing may be used to coalesce individual molten streams. Phillips extrudes individual molten streams through non-round orifices which are dimensioned according to a specified formula The formula assures that the coordinates of the centroid of the square of the velocity profile of the extruding material in the plane perpendicular to the axis of the capillary and the coordinates of the centroid of velocity profile of the extruding material in the plane perpendicular to the axis of the capillary are non-coincident. Conversely, U.S. Patent No. 4,142,850, also to Phillips, describes that certain non-round spinneret capillaries eliminate the kneeing of extruding filaments. The patent applies a formula for configuring the orifices by using the centroid of the square of the velocity profile of the extruding material and the centroid of the velocity profile of the extruding material. When these two parameters are co-incident at each capillary exit, the extruding filaments should not knee. In addition to the foregoing, there are various patents showing that rounded capillaries can be spaced or configured such that their respective extruded streams will merge prior to solidification. U.S. Patent No. 3,924,988 to Hodge shows a spinneret provided with a group of capillaries each defining an arcuate segment and having inwardly tapered enlargements. The particular structure causes a velocity differential to occur in the polymer flow that favors coalescence at the tapered portions to form a single round or rounded hollow filament. U.S. Patent No. 4,407,889 to Gintis et al. shows a method for preparing splittable hollow filaments. These filaments have longitudinal grooves and ridges that are readily split along the grooves. The spinneret used to produce these fibers includes a group of capillaries arranged so that the molten streams issuing therefrom each bulge as they leave the face of the spinneret, causing the streams to coalesce and form the desired hollow filament. In U.S. Patent No. 4,325,765 to Yu et al., high denier non-round filaments are produced by extruding a molten polymer (polyester) through adjacent orifices which are spaced such that the extruded streams merge prior to solidification. This patent addresses the stated problem that markedly non-round cross-sectional filaments having deniers of at least 10 could not be successfully melt spun from polyester polymers at high speeds using the techniques known at that time. In contrast to patents showing the goal of melt stream coalescence, there are also patents directed to spinnerets designed to allow filaments to be extruded in high density without coalescence. One such patent is U.S. Patent No. 4,318,680 to Pfeiffer et al. which shows a spinneret plate having multiple capillaries per counter-bore that effectively melt spins fusion melts of acrylonitrile polymer and water without coalescence. The patent is concerned with round cross-sections. There remains a need for a manner of producing fibers with non-round cross-sections in high density and without coalescence. This goal has, to Applicant's knowledge, been elusive. An object of the present invention is to provide an improved spinneret plate for extruding molten polymers into fibers. Accordingly, the present invention includes a spinneret plate according claim 1 and, in a further embodiment, a spinneret plate according claim 3. A further object of this invention is to provide an improved process for melt spinning filaments from molten polymers. The invention provides also a process therefore according claim 9. Related objects and advantages will be apparent to one ordinarily skilled in the relevant art after reviewing the following description. Description of the Figures FIG. 1 is a portion of a spinneret face showing one cluster of capillaries according to the present invention. FIG. 2 is a cross-section taken along line 2-2 of FIG. 1. FIG. 3 is a photograph representing the filaments produced by Example 1 below. In a first embodiment of the present invention, a spinneret plate allows high density spinning of non-round fiber from a single counterbore. FIG. 1 shows a single cluster 10 of non-round capillaries 11 as they appear from the downstream side of spinneret plate 12. The capillaries shown in FIG. 1 are exemplary of capillaries useful in the spinneret plate of the present invention. Each capillary 11 has three legs 15, 16 and 17. In FIG. 1 these legs are arranged so that four extending tips 20, 21, 22 and 23 are present Furthermore, as illustrated in FIG. 1, each leg is curved to define an arc. It will be understood, however, that it is not essential that every leg of the capillary is curved. For example, leg 15 might be linear. Returning to what is illustrated in FIG. 1, each of the arcs defined by the respective legs has a different origin. It will be understood that the term "origin" as used herein with reference to an arc, refers to the origin of the circle of which the arc is a segment. For example, the origin of the arc defined by leg 15 is near center 25 of cluster 10. Center 25 approximates the longitudinal axis of the counterbore (FIG. 2). The origin of the arc defined by leg 16 is between leg 16 and the closest edge of the next adjacent capillary. The origin of the arc defined by leg 17 is beyond the closest edge of the capillary next adjacent to that leg. As shown in FIG. 1, in addition to having different origins, the arcs also define different radii of curvature. For example, the radius of the arc defined by leg 17 is the longest. The radius of the arc defined by leg 15 is the next longest and the radius of the arc defined by leg 16 is the shortest. Furthermore, according to the depiction in FIG. 1, the origin of each arc defined by a capillary has a unique distance from the center (25) (or longitudinal axis) of the counterbore. Each capillary is preferably about 0.1 mm from its nearest neighbor. Likewise, each cluster 10 is preferably about 10 mm from its nearest neighbor, measured center to center. The dimensions of the spinneret plate itself are without restriction. The plate may be fashioned to a size suitable for the process conditions and the filaments extruded. There are, of course, many considerations when selecting the dimensions of the spinneret plate, counterbores and capillaries. Intercapillary distance depends upon polymer thruput, polymer temperature, polymer flow properties (like melt viscosity and melt elasticity), quenching conditions, the size and shape of the capillary legs (15, 16 and 17) and the mechanical strength of the spinneret design. Concerns in choosing the dimension include obtaining the desired cross section and maintaining the mechanical integrity of the spinneret, i.e., the capillary cluster. Referring to FIG. 1, the cluster of capillaries can be thought of as a disk supported at the five places (ribs) where tips 22 and 23 are closest to their nearest neighbors. The ribs must be able to support the entire orifice disk against the upstream polymer pressure. If the ribs are unable to support the pressure, the disk may rupture. The orifice depth (in the flow direction) and overall dimensions are preferably selected based upon the permissible back pressure. If the rib width is too narrow, the disk could rupture. If the rib is too wide (keeping other dimensions constant), it begins to affect the leg configuration and the polymer stream no longer bends. By increasing the dimensions of the orifice proportionately, the rib can be made much wider. It is notable that, in addition, experience suggests that when the ribs have a width of about 0.10 to 0.11 mm, the polymer streams are expected to merge. This expectation is surprisingly not borne out in the present invention. FIG. 2 is taken along line 2-2 of FIG. 1 and illustrates a cross-section through spinneret plate 12 showing the relationship between counterbore 40 and capillaries 11. It is preferable in constructing the counterbore that entrance cone 42 is two to three times the diameter of back hole 43. Entrance cone 42 is shown with a 90° full angle. In the illustration, back hole 43 has a diameter about 1 mm larger than the diameter of the orifice cluster. Of course, the length of back hole 43 depends upon the spinneret thickness. In the presently preferred embodiment, the back hole is approximately 12 mm. Capillary depth (d) is selected to withstand back pressure (as discussed above). In the presently preferred embodiment, this depth is about 0.7 mm. Turning to a second embodiment of present invention. A method for melt spinning filaments from molten polymers involves extruding molten polymer through a single counterbore which counterbore includes a plurality of separate capillaries. Each capillary produces a non-coalescing independent polymer stream which hardens into an independent non-round filament. A capillary cluster 10 such as that shown in FIG. 1 above, is useful in this method. This method produces fine filaments of lobal cross-sections. For the present purposes, filaments having an undrawn denier between about 3 to about 12 are considered fine. To practice the present process, a spinneret plate 12 (see FIG. 1) may be used in any known melt spinning process. The present invention results in a lobal filament cross-section This filament is extruded by using spinneret plate 12 in the method of the present invention. FIG. 3 illustrates the unique melt spun fiber cross-section that is achieved by extruding molten polymer through the spinneret of the first embodiment (see FIG. 1). The trilobal fiber 30 generally has one lobe which is thicker (or fatter) than the other two. The other two lobes are approximately the same size. As applies to all embodiments, a conventional melt spinning process can be used. The following Example illustrates one such conventional process. A conventional process may be for polyester fibers or polyamide fibers. Other melt-spinnable thermoplastic fibers may also be used. It is also contemplated that other processes and applications will be enhanced when the principles discussed herein are applied. The invention will now be described by referring to the following detailed example. This example is set forth by way of illustration and is not intended to be limiting in scope. Example 1 Nylon 6 chip having a nominal relative viscosity of 2.7 is fed from a hopper to a screw extruder. The extruder melts and pressurizes the polymer to 124,2 bar (1800 psi) at a temperature of 270°C. A Dowtherm • heated distribution line routes the polymer to a spin block while maintaining the polymer temperature. At the spin block, also Dowtherm • heated, the polymer stream is split into four (4) smaller streams, each supplying a separate metering gear pump. The four (4) metered streams, each having a flow rate of 68 grams/min, pass back through the spin block and into the polymer entrance of the four (4) spin packs. The spin pack consists of a filter cavity, sintered metal filtration, spinneret plate, gasket seals and a housing. The spin pack is bolted against the spin block using a seal between the contacting surfaces. The spin pack is located within a heated cavity having only its downstream face exposed. Within the spin pack, the polymer passes through sintered metal filtration before exiting through the spinneret. The spinneret has 14 counterbores as shown in FIG. 2 through which the polymer exits. The multilobal fibers emerging from the face of the spinneret and having the general shape of the fibers shown in FIG. 3, are quenched within the quench cabinet by transverse air flow having a velocity of 36,6 m/min (120 ft/min) and a temperature of 12°C. The filaments pass downward through the quench chimney to the takeup unit. At the takeup unit, an aqueous finish is applied to the filaments by a finish kiss roll. The filaments, now merged into a multifilament yarn, pass over a pair of godets driven at 865 m/min arranged generally in an "S" shaped configuration. The yarns are then wound upon a tube at the winder. The resulting yarn has an undrawn fineness of approximately 80,66 g/1000 m (726 denier), with an elongation of 351%.

Claims: A spinneret plate (12) defining at least one counterbore (40) and, downstream to said counterbore (40), at least one capillary (11) with non-round cross-section having a plurality of legs (15, 16, 17) extending transverse to an extrusion direction of said spinneret plate (12), characterized in that at least two of said legs are curved with different radii of curvature. A spinneret plate of claim 1 wherein, for any one capillary (11), said extending legs (15, 16, 17) define a plurality of intersecting arcs, wherein origins of each of said arcs are separate from each other. A spinneret plate (12) defining at least one counterbore (40) having an axis (25) and, downstream said counterbore (40), at least one curved capillary (11) with non-round cross-section having a plurality of extending legs (15, 16, 17) extending transverse to an extrusion direction of said spinneret plate (12), characterized in that the legs (15, 16, 17) define arcs, wherein the distance between the axis (25) of the counterbore (40) and the origin of the arc defined by each leg (15, 16, 17) is not the same for any two legs. A spinneret plate of claim 2 or 3 wherein each of said capillaries (11) defines three intersecting areas. A spinneret plate of one of claims 1 to 4 wherein each said counterbore (40) includes a plurality of said capillaries (11). A spinneret plate of claim 5 wherein each said counterbore (40) includes five capillaries (11). A spinneret plate of claim 5 wherein adjoining capillaries (11) are about 0.1 mm apart as measured from nearest tips (22; 23) of their respective legs (16; 17). A spinneret plate of one of claims 1 to 7 wherein said plate (12) includes a plurality of counterbores (40). A process for melt spinning filaments from molten polymers, comprising: extruding the molten polymer through a counterbore (40) having an axis (25) and through a plurality of separate capillaries (11) with non-round cross-section downstream to said counterbore (40), each capillary producing an independent polymer stream, characterized by said capillary defining a plurality of intersecting arcs (15, 16, 17), each of the arcs defined by any one capillary extending transverse to an extrusion direction of said molten polymer and being curved with different radii of curvature. A process of claim 9 wherein, for any one capillary, origins of said arcs (15, 16, 17) are separate from each other. A process of claim 9 or 10 wherein adjoining capillaries (11) are about 0.1 mm apart as measured from nearest tips (22; 23) of their respective arcs (16; 17). A process of one of claims 9 to 11 wherein, for any one capillary (11), each of the arcs (15, 16, 17) has a unique distance relative to the axis (25) of the counterbore (40).

Inventors: HODAN JOHN A, HODAN, JOHN A.
Applicants: BASF CORP, BASF CORPORATION
Application year: 1991
Main classification: D01D5
IPC codes: D01D5, D01D4