Method and apparatus for spinning bicomponent filaments and products produced therefrom

Abstract: A method and apparatus for spinning bicomponent sheath/core filaments is disclosed. The spinneret assembly for the production of sheath/core bicomponent filaments comprises a distributor (10) having a plurality of spaced core polymer flow passages (17) and multiple sheath polymer flow passages (16), a spinneret (12) having a plurality of spaced core polymer flow passages (22) and multiple sheath polymer flow passages (23), a shim means (11) positioned between said spinneret and said distributor for spacing said spinneret from said distributor and for controlling the sheath polymer flow from the outlet of said distributor sheath polymer flow passages to the inlet of each said spinneret core polymer flow passage separately.

Description: This invention relates to a method and apparatus for spinning bicomponent filaments and the improved products produced therefrom. Further, this invention relates to a method and apparatus for spinning improved bicomponent filaments in concentric or eccentric sheath/core relationships. Bicomponent filaments of the sheath/core configuration are well known and a variety of spinning packs and spinnerets have been employed in the production of such filaments. A conventional spinning assembly involves feeding the sheath-forming material to the spinneret orifices in a direction perpendicular to the orifices, and injecting the core-forming material into the sheath-forming material as it flows into the spinneret orifices. A bicomponent spinning assembly is disclosed in U.S. 4,406,850 whereby molten sheath polymer is issued in ribbon flow into recessed slot-like portions of the top surface of the spinneret positioned between rows of raised spinneret core inlets. U.S. 4,251,200 also discloses a bicomponent spinning assembly comprising a spinneret plate and a distribution plate spaced apart, the distributor plate having an aperture opposite each orifice in the spinneret plate and a plateau-like protrusion extending about the axis common to aperture and the extrusion orifice. Additionally, the assembly includes an orifice plate for restricting the entrance to the orifice. The concentricity of the core and sheath capillaries in the prior art spinning assemblies as described above and in other spinning assemblies is not satisfactory. It is difficult to properly position the distributor plate and the spinneret of the prior art assemblies so that proper alignment of the distributor and flow passages and pressure drop control are obtained so as to produce sheath/core bicomponent fibres of uniform cross section. It is typical of spinning assemblies of the prior art as exemplified by the cited references that the gap between the exit surface of the distributor and the inlet surface of the spinneret is fixed. Thus, if the sheath polymer viscosity varies or the core sheath ratio changes, the pressure drop control in the prior art assemblies is lost. It is necessary to control sheath polymer pressure drop adjacent the spinneret inlet as will be hereafter discussed to obtain bicomponent fibres consistent from filament to filament. Further, in those spinning assemblies where the annular gap between the distributor and spinneret is fixed, polymer pressure is sufficient at times to bow the spinneret away from the distributor thereby opening up the gap and changing the pressure drop. The exit and inlet passages of the distributor and spinneret, respectively, nearest the centre and the source of the sheath polymer will have the widest gaps and those farthest from the centre will have the narrowest gap. Sheath polymer will flow preferentially to the inner passages providing poor bicomponent filament uniformity. WO-A-89/02938 discloses a spin-pack assembly for forming synthetic fibres that comprises supply means for delivering mutually separated, flowable polymers under pressure; permanent and re-useable primary distribution means for delivering the mutually separated polymers to prescribed locations in the assembly; a permanent and reuseable spinneret having an array of multiple spinneret orifices for discharging the synthetic fibres from the spinpack assembly, each spinneret orifice having an inlet hole at its upstream end; and at least one disposable distributor plate positioned between the primary distribution means and the spinneret and having multiple etched distribution flow paths for conducting the mutually separated polymers from the primary distribution means to the said inlet holes in the spinneret. In one embodiment for producing ordinary sheath-core fibres (the spin-pack assembly shown in Figures 11-14 of WO-A-89/02938), each of two flowable polymers is supplied through respective slots in a screen support plate to an apertured metering plate immediately downstream of the screen support plate. Immediately downstream of the metering plate is an intermediate plate having an array of first distribution channels etched therein, said channels terminating in first distribution apertures extending through the intermediate plate. The intermediate plate also has an array of second distribution - channels each terminating in second distribution apertures extending through the said plate. Between the said intermediate plate and the upstream surface of the spinneret there is a final distributor plate having an array of final distribution apertures etched therein. The final distribution apertures are star-shaped, the centre of each such aperture being in register with the inlet of a respective spinneret orifice and the lobes of the star-shaped final distribution aperture extending laterally beyond the rim of the spinneret orifice inlet. The first polymer flows through respective apertures in the metering plate, along the said first distribution channels in the intermediate plate and through the said first distribution apertures, which are in register with respective spinneret orifice inlets. The first (core) polymer thus flows from the first distribution apertures into the spinneret orifice inlets via the central portion of the star-shaped apertures in the final distributor plate. The second polymer flows through its own respective apertures in the metering plate, along the said second distribution channels in the intermediate plate and through the second distribution apertures, the latter being in register with the extremities of the lobes of the star-shaped apertures in the final distributor plate. The second (sheath) polymer then flows along the channels defined by said lobes and into the inlets of the spinneret orifices. The said intermediate plate serves to distribute both of the polymers in the horizontal plane and has to be constructed so as to keep those polymers separated during the distribution. Summary of the Invention By the invention there is provided an improved process and apparatus for the production of improved, bicomponent sheath/core filaments of uniform cross section whereby the spinning pack assembly can be readily adjusted to compensate for changes in sheath polymer viscosity and changes in polymer flux and the sheath polymer flow to each spinneret core polymer flow passage can be controlled separately. In one aspect, the present invention provides a filament spinneret assembly for the production of sheath/core bicomponent filaments which comprises a distributor having a plurality of spaced core polymer flow passages and multiple sheath polymer flow passages; a spinneret having a plurality of spaced spinneret flow passages, and multiple sheath polymer flow passages, each said spinneret flow passage in coaxial alignment with the outlet of the respective core distributor flow passage; core polymer supply means for delivery of pressurized core polymer to the inlet of each said distributor core polymer flow passage; sheath polymer supply means for delivery of pressurized sheath polymer to the inlet of each said sheath polymer flow passage; and a shim means positioned between said spinneret and said distributor for spacing said spinneret from said distributor to form a liquid channel between the distributor and said sheath polymer flow passages of the spinneret and to effect a controlled pressure drop of only the sheath polymer flow from the outlet of said distributor sheath polymer flow passages to the inlet of each said spinneret flow passage separately, wherein said shim means has a shim thickness of from 0.025 to 0.5 mm. In another aspect, the present invention provides a filament spinneret assembly for the production of sheath/core bicomponent filaments which comprises a distributor having a plurality of spaced core polymer flow passages and multiple sheath polymer flow passages; a spinneret having a plurality of spaced spinneret flow passages, each of said spinneret flow passages in coaxial alignment with the outlet of the respective core distributor flow passage, a plurality of recessed sheath polymer flow channels and a plurality of raised buttons each surrounding a respective spinneret flow passage and located between the spinneret flow passage and the sheath channels, wherein each button has a flat top face; core polymer supply means for delivery of pressurized polymer to the inlet of each said distributor core polymer flow passage; sheath polymer supply means for delivery of pressurized sheath polymer to the inlet of each sheath polymer flow channel; and a shim means positioned between said spinneret and said distributor for forming a channel between the top face side of each button of the spinneret and said distributor at each spinneret passage whereby the thickness of the shim effects a controlled pressure drop of the sheath polymer flow through the channel between the top face of each button and the distributor to the inlet of each said spinneret flow passage separately, wherein said shim means has a shim thickness of from 0.025 to 0.5 mm. In a further aspect, the present invention provides a method of melt spinning sheath/core bicomponent filaments comprising passing multiple streams of pressurized molten core polymer from distributor core polymer flow passages into multiple parallel spinneret flow passages in respective axial alignment with said multiple distributor core polymer flow passages, passing pressurized molten sheath polymer from recessed sheath channels into a respective sheath polymer flow channel formed between a shim means and the top face of the spinneret, then the sheath polymer flows through a channel formed by a raised button, shim means and the distributor, then the sheath polymer flows into the spinneret flow passage to form the bicomponent filament. Brief Description of the Drawings Figure 1 is a view in perspective of a spin pack assembly embodiment of the invention. Figure 2 is a vertical section of a multiple passage distributor/shim/spinneret assembly Figure 3 is a vertical section of a distributor/shim/spinneret assembly to produce concentric bicomponent filaments Figure 4 is a vertical section of a distributor/shim/spinneret assembly to produce eccentric bicomponent filaments Figure 5 is a vertical section of a distributor/shim/spinneret assembly to produce bicomponent filaments of non-circular cross-section. Description of Preferred Embodiments Referring to the accompanying drawings and more specifically to Fig. 1, a bicomponent filament spin pack assembly can be fabricated from a distributor 10, a shim 11 and a spinneret 12. Distributor 10 is positioned so as to receive a melt-extruded sheath polymer or a sheath polymer in solution through a channel 13 and a melt-extruded core polymer or core polymer in solution through channel 14. Each of the sheath and core polymers are passed to the respective channels 13 and 14 by conventional melt extrusion, pump and filter means not herein illustrated. The distributor 10 functions to form the core polymer into filaments and to channel the flow of sheath polymer to spinneret 12. The core polymer is pumped through multiple passages 16 to the lower, even surface of distributor 10. Passages 16 can be arranged in any number of rows of columns depending upon their size, the viscosity of the core polymer, the length of passages 16 and the flow characteristics of the particular core polymer. The bottom of each passage 16 is tapered to provide a core filament of the desired diameter. Although not to be limited thereto, the density of passages 16 in distributor 10 when, for example, the core polymer is melted polyethylene terephthalate and the exit passage diameter is in the range from 0.1 millimeter (mm) to 1.0 mm, can be such that each passage utilizes 10 square mm of the spinneret area. Sheath polymer flowing through channel 13 is pumped to passages 17 and through passages 17 to spinneret 12. Although not to be limited thereto, the passages 17 are preferably axially positioned in distributor 10 so that upon exiting passages 17 the sheath polymer will flow radially outwardly toward the inlets of passages 22. A shim 11 is positioned between distributor 10 and spinneret 12 and maintained in fixed relationship to distributor 10 and spinneret 12 by bolts 19 engaging threaded recesses 20 in distributor 10. Distributor 10 and spinneret 12 are relatively positioned by dowel pins 18. In order to overcome bowing and separation of distributor 10 and spinneret 12 which can occur in the operation of conventional spin pack assemblies, a ring of bolts 19 has been positioned in the center of the assembly as shown in figure 2. The shim can be fabricated from a variety of materials such as stainless steel or brass with stainless steel being preferred. The shim can be constructed as a single unit or in two separate inner and outer pieces. The number and positioning of bolts 19 is such as to control deflection, preferably limiting deflection to less than .002 mm. Shim 11 must be of substantially constant thickness, preferably having a variance in thickness of less than .002 mm and the circular openings 21 must be in proper alignment with distributor passages 16 and spinneret passages 22. Shims 11 of different thicknesses, normally ranging from .025 to 0.50 mm, are employed to adjust for changes in sheath polymer viscosity, changes in polymer flux or to change the pressure drop as will be hereafter discussed. The top smooth, even surface of the spinneret 12 is recessed, providing a channel 23 for the flow of sheath polymer to each passage 22. Raised circular portions or buttons 24 surround each passage 22. The raised portions or buttons 24 project upwardly from channel 23 to a height which is equal to the top surface 25 of spinneret 12. The rate of outward flow of sheath polymer through channel 23 and over the buttons 24 to passages 22 is a result of the pressure drop determined by the thickness of shim 11. The pressure drop is inversely proportioned to the third power of the height of the gap 26 between distributor 10 and spinneret 12. Close control of this gap height is effected by shim 11 and maintained by the inner circle of bolts 19. The recess depth of channel 23 is selected so as to provide a low pressure drop (normally 20-50 psi (137.9 - 344.7 kPa)) radially across the top of the spinneret. The shim thickness is selected to normally provide a 100-1000 psi (689.5 - 6895 kPa) pressure drop across the raised buttons 24. As will be evident from the drawings, each passage 22 must be in concentric alignment with its corresponding passage 16. The core polymer flows through passages 16 and passages 22, exiting spinneret 12 as the core of a bicomponent fiber. The sheath polymer flows through passages 17, channel 23 and gap 26 to form a sheath about the filament of core polymer producing the aforementioned bicomponent fiber. The center axis of distributor passage 16 should be within a circle having a radius less than 200 microns, preferably less than 50 microns from the center axis of the spinneret counterbore. The production of concentric bicomponent fibers is further illustrated in Figure 3. Shim 11 is positioned to cause sheath polymer 31 flowing through channel 23, over buttons 24, and through gap 26 into channel 22, forming a concentric sheath about core polymer 30 as shown. The production of eccentric sheath/core fibers is illustrated in Figure 4. The holes in shim 11 are positioned so as to restrict the flow of sheath polymer 33 in the manner illustrated. The eccentric cross section of the formed bicomponent filament is also illustrated in Figure 4. Figure 5 illustrates a spinneret assembly employed to produce sheath/core bicomponent fibers wherein the core has a non-circular cross section. As shown, the core polymer passes through passage 16 of distributor to a core profile shim 36 containing a passage 37 having a Y-shaped cross section. The core polymer flows through core profile shim 36 to passage 22 in the manner previously described. The sheath polymer is transmitted to passage 22 in the previously described manner and a bicomponent fiber having a sheath 39 and core 38 is produced. The bicomponent sheath/core filaments produced by the spinneret assembly of the invention are of uniform cross section from filament to filament. The core and sheath of each filament will have substantially the same cross sectional shape and area. Preferably, the diameter coefficient of variability for the bicomponent fibers of this invention will be less than 2.50% based upon diameter measurements of at least twenty-five simultaneously produced filaments. The coefficient of variability (CV) is determined by: CV = Standard deviation of the filament diameter Mean filament diameter x 100 The eccentricity coefficient of variability for twenty-five simultaneously produced concentric bicomponent filaments of the invention will proferably be less than 1.0%. The eccentricity coefficient variability (ECV) is determined by the following relationship: ECV = Displacement of core center Bicomponent filamenter diameter x 100 Normally, the diameter coefficient of variability for commercially produced sheath/core bicomponent filaments will exceed 4.5% and the eccentricity coefficient of variability for concentric sheath/core bicomponent filaments will exceed 6.00%. The invention will hereafter be described as it relates to the production of sheath/core bicomponent fibers wherein the sheath polymer comprises a melted polyethylene blend as hereafter described and the core polymer comprises a melted polyethylene terephthalate although it will be understood by those skilled in the art that other sheath and core polymers could be employed. A maleic anhydride grafted high density polyethylene was prepared in accordance with the procedure of U.S. 4,684,576, the disclosure of such patent being incorporated herein by reference thereto. The high density polyethylene resin had a melt flow value (MFV) of 25 g/10 min. at 190°C [ASTMD-1238(E)] and a density of 0.955 g/cc (ASTM D 792) before extrusion. After extrusion its MFV measured 15 g/10 min. This product was blended with a linear low density polyethylene resin having an MFV of 18 g/10 min. at 190°C such that the maleic anhydride content of the blend was between 0.09-0.12 weight percent. The polymer blend hereafter employed as the sheath polymer in the following examples had an MFV of 16 g/10 min. at 190°C and a density of 0.932 g/cc. The core polymer of the following examples was a polyethylene terephthalate having an intrinsic viscosity (ASTM D 2857) of 0.645. EXEMPLE I The spinneret assembly of Figure 1 having spinneret hole diameters of C.374 mm was used to spin concentric bicomponent sheath/core filaments with core sheath ratios of 60 : 40 (Run 1), 70 : 30 (Run 2) and 80 : 20 (Run 3) weight percent. The melted sheath polymer was passed to passages 17 at a temperature of 275°C. The melted core polymer was passed to passages 16 at a temperature of 275°C. The throughput per spinneret hole was 0.852, 0.903 and 0.935 g/min, respectively. The bicomponent filaments were quenched with 30°C air and wound up at a speed of 2800 fpm (853.4 m/min). The resulting filaments were then drawn at a draw ratio of 3.0 at 60°C and crimped in a conventional stuffer box. After drawing and heat setting at 90°C, the filaments were cut to 1.5 inch (3.81 cm) fiber lengths and the properties are shown below in Table I. The spinneret assembly of the invention can be employed to produce solution spun bicomponent filaments. By adjusting the pack dimensions and polymer solution viscosities, bicomponent filaments from, for example, cellulose acetate and viscose could be produced. The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms disclosed since those are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the scope of the claims.

Claims: A filament spinneret assembly for the production of sheath/core bicomponent filaments which comprises a distributor (10) having a plurality of spaced core polymer flow passages (16) and multiple sheath polymer flow passages (17); a spinneret (12) having a plurality of spaced spinneret flow passages (22), and multiple sheath polymer flow passages (23), each said spinneret flow passage (22)in coaxial alignment with the outlet of the respective core distributor flow passage (16); core polymer supply means (14) for delivery of pressurized core polymer to the inlet of each said distributor core polymer flow passage (16); sheath polymer supply means (13) for delivery of pressurized sheath polymer to the inlet of each said sheath polymer flow passage (17); and a shim means (11) positioned between said spinneret (12) and said distributor (10) for spacing said spinneret from said distributor to form a liquid channel (26) between the distributor (10) and said sheath polymer flow passages (23) of the spinneret (12) and to effect a controlled pressure drop of only the sheath polymer flow from the outlet of said distributor sheath polymer flow passages (17) to the inlet of each said spinneret flow passage (22) separately, wherein said shim means (11) has a shim thickness of from 0.025 to 0.5 mm. A filament spinneret assembly for the production of sheath/core bicomponent filaments which comprises a distributor (10) having a plurality of spaced core polymer flow passages (16) and multiple sheath polymer flow passages (17); a spinneret (12) having a plurality of spaced spinneret flow passages (22), each of said spinneret flow passages (22) in coaxial alignment with the outlet of the respective core distributor flow passage (16), a plurality of recessed sheath polymer flow channels (23) and a plurality of raised buttons (24) each surrounding a respective spinneret flow passage (22) and located between the spinneret flow passage (22) and the sheath channels (23) wherein each button has a flat top face; core polymer supply means (14) for delivery of pressurized polymer to the inlet of each said distributor core polymer flow passage (16); sheath polymer supply means (13) for delivery of pressurized sheath polymer to the inlet of each said sheath polymer flow channel (17); and a shim means (11) positioned between said spinneret (12) and said distributor (10) for forming a channel (26) between the top face side of each button (24) of the spinneret (12) and said distributor (10) at each spinneret passage (22) whereby the thickness of the shim (11) effects a controlled pressure drop of the sheath polymer flow through the channel (26) between the top face of each button (24) and the distributor (10) to the inlet of each said spinneret flow passage (22) separately, wherein said shim means (11) has a shim thickness of from 0.025 to 0.5 mm. The filament spinneret assembly of claim 1 or 2 wherein said shim means is positioned in a coaxial relationship with the outlet to the said distributor core polymer flow passage. The filament spinneret assembly of claim 1 or 2 wherein said shim means is positioned in an eccentric relationship to the outlet of said distributor core polymer flow passage. The filament spinneret assembly of claim 1, 2 or 3 wherein said shim means has a thickness tolerance of equal to or less than 0.002 mm. The filament spinneret assembly of any preceding claim, which comprises a further shim (36) located immediately adjacent to said distributor (10) and containing a plurality of spaced core polymer flow passages (37) in spaced axial alignment with the plurality of said spaced distributor core polymer flow passages (16), and wherein each of said spaced core polymer flow passages (37) in said further shim (36) has a cross section which is dissimilar to the cross section of each of said distributor core polymer flow passages. A method of melt spinning sheath/core bicomponent filaments comprising passing multiple streams of pressurized molten core polymer from distributor core polymer flow passages into multiple parallel spinneret flow passages in respective axial alignment with said multiple distributor core polymer flow passages, passing pressurized molten sheath polymer from recessed sheath channels into a respective sheath polymer flow channel formed between a shim means and the top face of the spinneret, then the sheath polymer flows through a channel formed by a raised button, shim means and the distributor, then the sheath polymer flows into the spinneret flow passage to form the bicomponent filament. The method of claim 7 wherein each of the bicomponent fibres exiting said spinneret is a concentric sheath/core filament. The method of claim 7 wherein each of the bicomponent fibres exiting said spinneret is an eccentric sheath/core filament. The method of claim 7,8 or 9 wherein said sheath polymer is a polyolefin and said core polymer is a polyester. The method of claim 10 wherein said polyolefin is a blend of a maleic anhydride grafted high density polyethylene and a linear low density polyethylene and said core polymer is polyethylene terephthalate. The method of any of claims 7 to 11, when applied to the simultaneous production of multiple bicomponent sheath/core polymer filaments of uniform cross section. The method of claim 12 wherein the diameter coefficient of variability is less than 2.50%. The method of claim 13 wherein each filament is a concentric sheath/core filament and wherein the eccentric coefficient of variability is less than 1.00%.

Inventors: DAVIES BARRIE LINTON, DAVIES, BARRIE LINTON
Applicants: HOECHST CELANESE CORP, HOECHST CELANESE CORPORATION
Application year: 1990
Main classification: D01D5
IPC codes: D01F8, D01D5