Abstract:
An apparatus for spinning bicomponent sheath/core filaments such that the filaments are uniformly quenched. 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 holes positioned so that the density of holes is the lowest near the center of the spinneret and increases as radially proceed outward. More specifically, the holes are substantially configured in the shape of a parallelogram in which the sides of the parallelogram are all of equal length. Additionally, the shape of the parallelogram is more flat the further the parallelogram pattern is located from the center of the spinneret. In this manner of positioning the holes, filaments therefrom do not significantly impede quench air from uniformly reaching filaments in the outer rows.

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to a method and apparatus for spinning bicomponent filaments. More particularly, the invention relates to a spinneret used for bicomponent spinning. The spinneret has a plurality of holes wherein the density of holes increase radially outward from the center of the spinneret. 
     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 textile filaments. A conventional spinning assembly involves feeding molten sheath forming material to the spinneret holes, in a direction perpendicular to the holes, and injecting molten core forming material into the sheath-forming material as it flows into the spinneret holes. 
     There are several prior art hole layouts for bicomponent spinnerets. One is providing the same number of holes per row. This configuration is typically used for low hole density/high denier per filament (dpf). Another is a constant hole density wherein there are a different number of holes per row and the hole density is constant by having the hole to hole distance in the same row, and row to row distance, constant. This configuration is typically used for high hole density/low dpf. Both of these configurations have the disadvantage that the hole density is higher towards the center of the spinneret than the outer portion of the spinneret, or remains constant throughout the spinneret. Consequently, quench air radiating outward from the center of the spinneret has difficulty reaching filaments in the outer rows. Filaments in the interior rows are quenched first and, therefore, solidify and crystallize before filaments in the outer rows. This causes a distribution in filament uniformity with spun orientation and filament diameter (dpf) according to which row the filament is in. 
     A distribution of spun yarn orientation is undesirable since this causes broken filaments in the subsequent drawing operation. Thus, when each filament has substantially the same spun orientation, the filaments can be drawn at a high draw ratio without broken filaments. Additionally, by uniformly quenching filaments, conversion is higher, that is, the equipment can be run faster with less stoppage and waste. 
     Accordingly, there is a need for an improved spinneret wherein the density of holes increase radially outwards from the center of the spinneret and are positioned such that filaments are uniformly quenched and have a higher uniformity in spun orientation than prior art devices. 
     SUMMARY OF THE INVENTION 
     The present invention is directed towards a spinneret assembly and method for spinning bicomponent filaments which are substantially uniformly quenched and have a generally uniform spun orientation so that filaments can be drawn with less waste. The spinneret accomplishes this result by arranging spinneret holes in a generally parallelogram pattern having a constant diagonal distance between holes such that the hole density increases in the direction away from the center of the spinneret thereby ensuring that radial quench air uniformly reaches all the filaments. 
     According to the present invention, the spinneret assembly includes a distributor and a spinneret. The distributor is provided with separate flow passages to convey core polymer and sheath polymer to the spinneret. The spinneret is provided with a plurality of bosses, each having a hole, which coaxially align with the distributor core passages for receiving the core polymer. The holes are arranged in increasing density from a center position of the spinneret to an outer edge of the spinneret. 
     According to another aspect of the present invention, the holes are arranged in curvilinear rows and the distance between a hole in one row to a nearest hole in an adjacent row is constant for all such pairs of holes. 
     According to a further aspect of the present invention, the holes in alternative rows are radially aligned. 
     According to still another aspect of the present invention, the distance between succeeding rows decreases radially from a center position to an outer edge of the spinneret. 
     According to another aspect of the present invention, a method is provided for making a bicomponent filament. The method includes providing a distributor having separate flow passages for core polymer and for sheath polymer. A spinneret is provided with bosses and is secured beneath the distributor. Holes are placed in the bosses which extend through the bosses and the spinneret. The holes are coaxially aligned with the core polymer passages. Moreover, the holes are arranged in curvilinear rows and in increasing density in a radial direction from the center of the spinneret to an outer edge of the spinneret. Molten core polymer and molten sheath polymer are supplied to the distributor, forced through respective passages, to the spinneret. The molten core polymer flows through the spinneret holes. The molten sheath polymer flows over the bosses and through the holes forming a sheath about the core polymer. The sheath-core polymer is then substantially uniformly quenched. 
    
    
     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 elevational view, in cross section, of the spin pack assembly of FIG. 1; 
     FIG. 3 is a plan view of a spinneret having holes arranged in a substantially parallelogram pattern having a specific diagonal length; and 
     FIG. 4 is an enlarged sectional view of FIG. 3, of detail section  4 . 
    
    
     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 polymer 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 radially outward directed feed channels  21 , 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 . The radial feed channels  21  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 desired diameter. The outer passages  22  are arranged to coaxially align with spinneret holes  27 . 
     The shim  14  has an 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 a unitary. The unitary shim substantially covers the spinneret and has holes 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 , bosses  37  and an outer rim  38 . The recessed section  36  receives sheath polymer from the distribution inner passages  24 . As shown in FIG. 2, 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 bosses  37  thereby forming pathways  44  between the bosses  37 . The bosses  37  extend upward terminating in a plane common to the top 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  37  to the holes  27  is a result of the pressure drop determined by the shim gap between the distributor  12  and the spinneret  16 . The varying depth of the sloped recessed section pathways  44  is 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  37 . 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 . 
     FIG. 3 shows the layout of the bosses  37  in the spinneret  16 . As shown in FIG. 4, the bosses  37  have holes  27  which are arranged substantially in a parallelogram pattern  48  (shown by dashed lines). That is, the holes form indices substantially of a parallelogram wherein opposed sides are very slightly nonparallel. The parallelogram pattern  48  formed by four adjacent holes in three consecutive rows: one hole (labeled A) in the inner row, two holes (labeled B and C) in the middle row and one hole (labeled D) in the outer row. Lines AB and CD are slightly non-parallel as are lines AC and BC because the holes  27  are positioned along a spiral curve, as indicated, for example, by spiral lines X—X. The substantially parallelogram pattern exist for all groupings of four holes as just described. Moreover, the parallelogram pattern flattens and widens the further the holes are located away from the center of the spinneret  16 . Three sets of dashed lines  48 ,  50 ,  52  are designated to illustrate the parallelogram pattern changing from a narrow to a wide shape. The parallelogram pattern is also defined by a constant diagonal length. The constant diagonal length is the distance between adjacent holes on the same parallelogram, such as for example the distance AB. This distance is the same for adjacent holes in the same parallelogram as it is for all parallelograms throughout the spinneret  16 . 
     The location of the holes  27  is further defined in that they are in circular rows. Each sequential row, from the central hub  34  of the spinneret  16  outward to the outer rim  38 , is positioned closer to the subsequent row than to the preceding row. A comparison of the distance between the innermost two rows A—A, B—B and the distance between the outermost two rows Y—Y, Z—Z illustrates that the distance between rows decrease radially outwards from the center of the spinneret  16 . Moreover, holes from alternating rows are radially aligned from the center of the spinneret  16  as shown by radial line  53  of FIG.  4 . 
     The positioning of the holes  27  results in a spinneret  16  having a hole density, the number of holes per cm 2 , which increases from the central hub  34  to the outer rim  38  of the spinneret  16 . Consequently, quench air is minimally impeded by the curtain of filaments in the inner rows of the spinneret  16  so that all filament rows are uniformly quenched and spun orientation is substantially uniform. The benefit of a spinneret having a constant diagonal hole  27  arrangement is equally applicable to mono-polymer filament production. 
     The bosses  37  preferably are cylindrical and equidistantly spaced from each other. Specifically, the bosses  37  are equidistant along the constant diagonal such that the pathway width between adjacent bosses  37  is the same. Current manufacturing restrictions require a separation of at least one millimeter between adjacent bosses  37 . The present invention incorporates advances in manufacturing techniques such that the bosses  37  can be spaced closer than today&#39;s current limitation. 
     Alternative boss configurations are within the scope of invention so long as the spinneret holes are in the substantially parallelogram pattern. For example, a spiral elongate boss can be used as shown in U.S. patent application Ser. No.09/827,792 to Goodall, McConnell and Hastie filed on Apr. 6, 2001. 
     In use, the distributor  12  receives core and sheath polymer from the manifold  11  through respective inner and outer feed conduits  20 ,  18 . 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 holes  27 . The sheath polymer is pumped to feed channels  21 , then outwardly within the feed channels  21  to the inner passages  24  and therethrough to the recessed section  36  of the spinneret  16 . The pressure drop between the top surface of the boss  37  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 channels  44  and over the bosses  37  to the holes  27 . The recessed section  36  slopes 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 holes  27 , the core polymer flows from the core polymer passages, through the spinneret holes  27 , and exits the spinneret  16  as a core of a bicomponent fiber. The sheath polymer flows through the sheath polymer passages  24 , into the recessed section  36  of the spinneret  16 , over the bosses  37  to form a sheath about the core polymer and exits the holes  27  where it is quenched by air beneath the spinneret  16  (not shown) radiating from the center of the spinneret  16  and forms a bicomponent fiber. Since the filament density increases away from the center of the spinneret  16  the inner filaments do not significantly impede the flow of quench air to the outer filaments, the filaments are more uniformly quenched and have greater uniformity in spun orientation. 
     The spinneret assembly can also be employed to produce a 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, 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.