Abstract:
An apparatus to increase the orifice density in a spinneret by using an elongate boss having a plurality of orifices. The apparatus is for spinning bicomponent sheath/core filaments. The apparatus includes a distributor plate, and spinneret and a shim position between the distributor plate and the spinneret. The spinneret includes a plurality of elongate bosses spaced apart by channels. Each boss having a plurality of orifices of which the distance between the orifices are restricted only by manufacturing tolerances.

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to a method and apparatus for spinning bicomponent filaments in a sheath/core polymer configuration. More particularly, the invention relates to a spinneret, used for bicomponent spinning, having a plurality of orifices in a boss. 
     2) Description of Prior Art 
     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 molten sheath forming material to the spinneret orifices, in a direction perpendicular to the orifices, and injecting molten core forming material into the sheath-forming material as it flows into the spinneret orifices. 
     As disclosed in U.S. Pat. No. 5,505,889 to Davies, prior art bicomponent spinnerets provide one orifice per boss. Boss spacing, and consequently orifice density, is restricted by a manufacturing requirement of one millimeter spacing between adjacent bosses. An increased orifice density yields a corresponding increase in the number of filaments produced. Accordingly, there is a need for an improved spinneret with an increased orifice density. 
     SUMMARY OF THE INVENTION 
     The present invention is directed towards a spinneret assembly and method for spinning bicomponent filaments. According to the present invention, the spinneret assembly includes a distributor and a spinneret. The distributor is provided with inner openings near the center of the distributor and with outer openings further from the center. The inner openings convey molten sheath polymer to the spinneret and the outer openings convey molten core polymer to the spinneret. The spinneret is provided with an integral boss having a plurality of orifices for receiving core polymer which coaxially align with the distributor outer openings for receiving core polymer. By providing the spinneret with an integral boss having multiple orifices, orifice density is increased over prior art spinnerets which contain one orifice per boss. Orifices on the same boss can be manufactured closer to each other than orifices on adjacent bosses. The spinneret is also provided with a plurality of openings and recessed pathways adjacent to the boss for conveying sheath polymer to the orifices. 
     According to another aspect of the present invention, the bosses are curvilinear. Still further aspects of the present invention include spiral, semi-circular or linear bosses. 
     According to another aspect of the present invention, a method is provided for making a bicomponent filament. The method includes providing a distributor having an inner flow passage and outer flow passages, providing a spinneret beneath the distributor having a plurality of bosses which have a plurality of orifices aligning with the outer flow passages, forcing core polymer through the outer flow passages and the spinneret openings, forcing sheath polymer through the inner flow passage and onto recessed pathways provided adjacent to the boss, and forcing the sheath polymer through the recessed pathways, over the bosses, then through the spinneret openings to form a sheath about the core polymer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and further features of the present invention will be apparent with reference to the following description and drawings, wherein: 
     FIG. 1 is a fragmented perspective view of a spin pack assembly according to the preferred embodiment of the invention; 
     FIG. 2 is a fragmented view, in cross section, of the spin pack assembly of FIG. 1; 
     FIG. 3 is a fragmented plan view of a spinneret having elongate spiral bosses; 
     FIG. 4 is a fragmented plan view of a spinneret having elongate semi-circular bosses; and 
     FIG. 5 is a fragmented plan view of a spinneret having elongate radial bosses. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 illustrate a spin pack assembly  10  according to the present invention. The spin pack assembly  10  includes a supply manifold  11 , a distributor  12 , a shim  14  and a spinneret  16 . The manifold  11  delivers molten sheath polymer and molten core polyester through respective feed conduits  18 ,  20  to the distributor  12 . The sheath and core polymers can be any melt spinnable polymer such as, for example, polyolefin, polyester or nylon. The sheath and core polymers are passed to the respective feed conduits  18 ,  20  by conventional pump and filter means not herein illustrated. The distributor  12  is positioned beneath the manifold  11  to receive the sheath and core polymers. 
     The distributor  12  includes outer passages  22  to form the core polymer into filaments and inner passages  24  to convey the flow of sheath polymer to the spinneret  16 . Radial feed channels can be provided about the center of the distributor  12  to direct sheath polymer from the feed conduit  18  to the inner passages  24 . The inner passages  24  can be vertical or can be slanted as necessary to avoid obstructions such as bolts. The outer passages  22  have an upper counterbore  25  and a lower tapered bottom  26  to provide a core filament of the desired diameter. The outer passages  22  are arranged to coaxially align with spinneret orifices  27 . 
     The shim  14  has a substantially uniform thickness and is positioned between, and slightly separates, the distributor  12  and the spinneret  16 . Preferably the shim  14  is constructed with a separate inner and outer section. The inner and outer shim  14  sections are maintained in fixed relationship to the distributor  12  and spinneret  16  by a respective ring of inner and outer bolts  29 ,  30  engaging threaded recesses in the distributor  12 . The bolts  29 ,  30  also overcome bowing and separation of the distributor  12  and spinneret  16 . The distributor  12  and spinneret  16  are relatively positioned by a central dowel pin  32  in the center of the spin pack  10  and outer dowel pins  33  interspersed along the outer ring of bolts  30 . Alternatively, the shim can be unitary. The unitary shim substantially covers the spinneret and has openings provided in alignment with distributor passages  22 ,  24  and spinneret orifices  27 . The shim  14  can be manufactured from a variety of materials such as stainless steel or brass. The thickness of the shim  14  is selected according to a variety of operating parameters such as the sheath polymer viscosity and desired pressure drop across the top of the spinneret  16 . 
     The spinneret  16  includes a central hub  34 , a recessed section  36  and an outer rim  38 . The central hub  34  preferably is provided with radially outward directed feed channels  40  for conveying the sheath polymer to the recessed section  36  of the spinneret  16 . The recessed section  36  is preferably sloped upwards from the central hub  34  to the outer rim  38  to maintain the sheath polymer under constant pressure. The recessed section  36  is provided with vertically extending elongate bosses  42  thereby forming pathways  44  between the bosses  42 . The bosses  42  extend upward terminating in a plane common to the upper surface of the outer rim  38  and the central hub  34 . The rate of outward flow of sheath polymer through the pathways  44  and over the bosses  42  to the orifices  27  is a result of the pressure drop determined by the shim gap between the distributor  12  and the spinneret  16 . The depth of the pathways  44  are selected to provide a low pressure drop radially across the top of the spinneret  16 , and the shim  14  thickness is selected to provide a higher pressure drop across the bosses  42 . The outer rim  38  forms an outer boundary restricting the sheath polymer and includes the outer rings of bolts  30  joining the distributor  12 , shim  14  and spinneret  16 . 
     As illustrated by FIGS. 3,  4  and  5 , but not exclusive thereof, the elongate bosses  42  can be provided in a myriad of configurations such as spiral, semi-circular and radial, respectively. Each spiral shaped boss  42  is shaped as being wound around a fixed datum point at a continuously increasing or decreasing distance from the datum point. Each semi-circular boss  42  is shaped as arcing about a fixed datum point. Each radial boss  42  linearly extends from a center point of the spinneret  16 . Other linear and curvilinear configurations for bosses  42  are within the scope of the invention. 
     Each elongate boss  42  has the same configuration and preferably has a uniform width, and preferably each pathway  44  has the same configuration and has a varying width. Alternatively, each pathway width can be uniform. Current manufacturing restrictions require a separation of at least one millimeter between adjacent bosses  42 . The present invention incorporates advances in manufacturing techniques such that the bosses  42  can be spaced closer than today&#39;s current limitation. In each case, the bosses  42  contain a plurality of orifices  27  along a centerline  46  of the boss  42 . A minimum distance is required between the edge of each orifice  27  and the side of the boss  42  for sufficient pressure drop. The distance between adjacent orifices on the same boss  42  is restricted only by current manufacturing techniques, and therefore, orifices need only be spaced apart such that one orifice does not breach another orifice. As shown in FIG. 2, each orifice  27  has a counterbore  48  top portion and a narrower capillary  50  bottom portion to provide a filament of desired diameter. Since a plurality of orifices  27  are provided in each boss  42 , a higher density of orifices  27  can be provided than prior art spinnerets  16  which contain one orifice  27  per boss  42 . Consequently, a greater number of filaments can be produced per unit area of spinneret  16 . 
     In use, the distributor  12  forms the core polymer into filaments and directs the flow of sheath polymer to the spinneret  16 . The core polymer is pumped to, then through, the outer passages  22  and is received by the spinneret orifices  27 . The sheath polymer is pumped through the inner passages  24  to the central hub  34  of the spinneret  16 . The sheath polymer flows outwardly in the feed channels  40  to the recessed section  36  of the spinneret  16 . The pressure drop between the top surface of the boss  42  and the bottom surface of the distributor  12 , and the pressure drop between the channels and the bottom of the distributor creates an overall pressure drop forcing the sheath polymer through the pathways  44  and over the bosses  42  to the orifices  27 . The pathways  44  slope upward toward the outer rim  38  to compensate for the reduced volume of sheath polymer, and maintain uniform pressure for even flow. 
     Since the distributor outer passages  22  are in coaxial alignment with the corresponding orifices  27 , the core polymer flows from the outer passages, through the spinneret orifices  27 , and exits the spinneret  16  as a core of a bicomponent fiber. The sheath polymer flows through the inner passages  24 , outwardly through the feed channels  40 , into the recessed section  36  of the spinneret  16 , over the bosses  42  to form a sheath about the core polymer and exits the orifices  27  where it is cooled and forms as a bicomponent fiber. 
     The spinneret assembly can also be employed to produce sheath core bicomponent fibers where the core has a non-circular cross section. Examples of non-circular cross sections are shown in U.S. Pat. No. 5,256,050 to Davies and are herein incorporated by reference. 
     Although particular embodiments of the invention have been described in detail, it will be understood that the invention is not limited correspondingly in scope, but includes all changes and modifications coming within the spirit and terms of the claims appended hereto.