Abstract:
An apparatus and method for spinning hollow bicomponent filaments. The apparatus includes a distributor, a spinneret having holes and a shim having openings fixed between the distributor plate and the spinneret. The distributor supplies a first polymer having an MV to a first part of the spinneret holes and a second polymer having a lower MV to a recessed section of the spinneret. The shim openings are positioned above the spinneret holes and extend away from the first part of the holes to allow the second polymer to flow from the recessed section, through the shim openings, to a second part of the spinneret holes. The two polymers travel along the opposed first and second parts of the holes until exiting the spinneret through respective asymmetric C-shaped apertures. The apertures are sized so that hydraulic split does not occur between the polymers and consequently potential filament kneeing is obviated. Upon exiting the apertures, the polymers self-join to form hollow filaments and are quenched. Since the polymers have different MV properties, the filaments self-crimp into a spiral configuration.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1) Field of the Invention  
           [0002]    The present invention relates to a method and apparatus for spinning hollow bicomponent filaments. More particularly, the invention relates to using a spinneret and a shim for hollow bicomponent filament spinning. More particularly still, the spinneret has a plurality of capillaries having asymmetric apertures, and the shim has a plurality of fan shaped openings.  
           [0003]    2) Prior Art  
           [0004]    Mono-component filaments are well-known and a variety of spinning packs and spinnerets have been employed in the production of hollow filaments. A conventional mono-filament spinning assembly involves feeding polymer through spinneret holes then forcing the polymer through apertures at the bottom of the hole to form a hollow filament. Subsequently, the filament can be mechanically crimped to provide additional bulk.  
           [0005]    Spinning packs are also well-known for the production of bicomponent filaments having side/side and sheath/core configurations. A conventional bicomponent spin pack assembly involves feeding molten sheath forming material to 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.  
           [0006]    Traditionally, use of bicomponent polymers to produce hollow filaments has been impeded by kneeing of the filament. For bicomponent hollow filament production, the polymers must first be fed to opposed parts of the spinneret hole and through opposed apertures in a bottom of the spinneret hole. Since the polymers have different melt viscosities (hereinafter MV) there is more resistance to the higher MV in going through its designated aperture than for the lower MV in going through its designated aperture. The difference in MV causes a hydraulic split where the higher MV polymer partially splits to egress the aperture designated for the lower MV polymer. The lower MV polymer, forced to egress a reduced aperture area, exits at a higher velocity causing the filament to “knee”, that is veer substantially from a linear direction. Kneeing causes operational problems with the spin pack such as difficulty in extruding the filaments and increased filament breakage.  
           [0007]    Accordingly, there is a need for an improved spin pack assembly wherein a hollow bicomponent filament can be produced without excessive kneeing. Additionally, there is a need for an improved shim for directing one polymer to a designated part of the spinneret hole. Further there is a need for improved spinneret openings each having apertures configured in the capillary to eliminate hydraulic split of the polymers. Lastly, there is a need for a self-crimping hollow bicomponent filament.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed towards a spin pack assembly and method for spinning hollow bicomponent filaments which do not knee and are self-crimping. Since each polymer has different properties, and in particular substantially different shrinkage rates, the bicomponent filaments will self-crimp in spiral after being drawn and heated. The spiral crimp bicomponent filaments have substantial bulk suitable for use in fiberfill for sleeping bags, winter quilted clothing and other similar applications requiring a high thermal insulation “R” value.  
           [0009]    The spin pack assembly forms hollow self-crimping filaments by utilizing a unique shim and a spinneret having openings with asymmetric apertures to separately handle at least two polymer streams. Upon exiting the apertures, the polymer streams join to form self-crimping hollow filaments. The shim is provided with a plurality of openings which direct a first polymer to a first part of the spinneret holes while restricting the first polymer from a remaining part of the holes. Distributor holes offset from the holes in the spinneret, deliver a second polymer to the opposed remaining part of the spinneret holes. The polymers are then forced through separate apertures provided in a lower section of the spinneret holes. The apertures are configured to avoid hydraulic split of the polymers and accordingly avoid kneeing of the resulting hollow bicomponent filament.  
           [0010]    In the broadest sense, the present invention also is directed towards a spin pack assembly comprising a distributor having outer flow passages for the flow of a first polymer and an inner polymer flow passage for the flow of a second polymer, and a spinneret secured relative to the distributor and communicating with the distributor to receive the first and second polymers. The spinneret has a top face directed towards the distributor, an opposed bottom face and a plurality of holes extending from the top face to the bottom face. The holes have a lower section which is provided with a plurality of apertures. Each of the apertures communicate with substantially only the inner flow passage or at least one of the outer flow passages.  
           [0011]    In the broadest sense, the present invention also is directed towards a spin pack assembly comprising a distributor having outer flow passages for the flow of a first polymer and an inner polymer flow passage for the flow of a second polymer, and a spinneret secured relative to the distributor and communicating with the distributor to receive the first and second polymers. The spinneret has a top face directed towards the distributor, an opposed bottom face and a plurality of holes extending from the top face to the bottom face. The holes have a lower section which is provided with a plurality of apertures in which substantially only one of the first or second polymers egresses any one of the apertures. The first and second polymers flowing through the apertures are capable of forming hollow filaments due to the configuration of the apertures.  
           [0012]    An object of the present invention is to configure the spinneret apertures with different cross-sectional areas.  
           [0013]    Another object of the present invention is to limit the apertures to two C-shaped apertures.  
           [0014]    Still another object of the present invention is to provide a shim secured between the distributor and the spinneret. The shim is provided with a plurality of openings having a first portion and a second portion. The first portion is positioned between a bottom section of the distributor outer flow passages and the spinneret holes to form a continuous path therebetween. The second portion extends from the first portion in a direction away from a first part of the holes to form a continuous course for polymers to flow from the spinneret, through the second portion, to a remaining part of the holes which is opposed to the first part.  
           [0015]    A further object of the invention is to configure the first portion in circular shape and the second portion in block-arc shape. Additionally, the first portion is coaxial with the holes, and the second portion spans an arc of about 120 degrees.  
           [0016]    A still further object of the present invention is to provide the distributor outer flow passages with a bottom section which is offset from the spinneret holes such that if the bottom sections were extended, the bottom sections would be positioned within the first part of the respective spinneret hole.  
           [0017]    In the broadest sense, the present invention is directed towards a method for producing hollow bicomponent filaments. The method includes providing a distributor having a plurality of outer polymer flow passages which have a bottom section, and an inner flow passage. A spinneret, secured relative to the distributor and having a top face directed towards the distributor and an opposed bottom face, is also provided. Holes are provided in the spinneret which extend from the top face to the bottom face. The holes have a first part, a remaining part, and a lower section having a plurality of apertures. The holes are axially offset from the bottom sections such that the bottom sections would be positioned within the first parts if extended. A source for a first polymer and a source for a second polymer are provided. The first polymer is forced through the outer flow passages, through the first part of the holes and through any of the apertures positioned on the first part of the spinneret holes. The second polymer is forced through the inner flow passages, through the remaining part of the holes and through any of the apertures positioned in the remaining part of the spinneret holes. Upon exiting the apertures, the polymers form into filaments which are quenched. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    These and further features of the present invention will be apparent with reference to the following description and drawings, wherein:  
         [0019]    [0019]FIG. 1 is a fragmented perspective view of a spin pack assembly according to the preferred embodiment of the invention;  
         [0020]    [0020]FIG. 2 is a fragmented elevational view, in cross section, of the spin pack assembly of FIG. 1;  
         [0021]    [0021]FIG. 3 is an enlarged fragmented elevational view, in cross section, of an outer distributor passage and a spinneret hole taken through section  3 - 3  of FIG. 2, and having an enlarged hollow filament, shown in cross section, extending from the spinneret hole;  
         [0022]    [0022]FIG. 4 is a plan view of a shim having openings;  
         [0023]    [0023]FIG. 5 is an enlarged fragmented plan view of a shim intermediate opening positioned over a spinneret hole having apertures, taken through detail  5 - 5  of FIG. 1;  
         [0024]    [0024]FIG. 6 is another embodiment of the spinneret hole shown in FIG. 5, having apertures of an alternative configuration, and with the shim removed; and  
         [0025]    [0025]FIG. 7 is a further embodiment of a spinneret hole shown in FIG. 5 having apertures of a further alternative configuration and with the shim removed. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    [0026]FIGS. 1 and 2 illustrate a spin pack assembly  10  according to the present invention. The spin pack assembly  10  is configured in a stack and includes from top to bottom: a supply manifold  11 , a distributor  12  fixed beneath the manifold  11 , a shim  14  fixed beneath the distributor  12 , and a spinneret  16  fixed beneath the shim  14 . The distributor  12 , shim  14  and spinneret  16  are provided with co-axial openings or threaded openings for receiving inner and outer rings of threaded bolts  20 ,  22 . The rings of bolts  20 ,  22  secure the distributor  12 , shim  14  and spinneret  16  together to overcome bowing and separation of the components. Additionally, the distributor  12 , shim  14  and spinneret  16  are relatively positioned by a central dowel  24  in the center of the spin pack assembly and by outer dowel  26  interposed along the outer ring of bolts  22 . The spin pack assembly  10  components are manufactured from a high strength material such as, for example, stainless steel.  
         [0027]    First and second polymers are forced through the spin pack assembly  10  generally in the top to bottom fashion that the components are arranged. The polymers can be any spinnable polymer such as, for example, polyolefin, polyester or nylon.  
         [0028]    The manifold  11  forces a first molten polymer and a second molten polymer via conventional pump and filter means (not herein illustrated) through respective outer and inner feed conduits  28 ,  30  to the distributor  12 . The distributor  12  is provided with radial outward directed feed channels  32  in the top surface of the distributor  12 , an annular channel  34  formed in the bottom surface of the distributor  12 , and inner passages  36  which connect the feed channels  32  to the annular channel  34 . The annular channel  34  disburses the second polymer to the shim  14  in a circular ring pattern. The shim  14  is provided with inner openings  38 , arranged in a circular ring pattern which coincides with the annular channel  34 , to allow passage of the second polymer from the annular channel  34  to a recessed section  40  of the spinneret  16 .  
         [0029]    As shown in FIGS. 2 and 3, the distributor  12  also includes outer passages  42  which provide passage for the first polymer from the manifold  11 , through the distributor  12 , to the shim  14  and the spinneret  16  positioned therebeneath. The outer passages  42  have an upper counterbore  50  and a lower tapered bottom  52 . The tapered bottoms  52  are positioned immediately above intermediate openings  54  provided in the shim  14 .  
         [0030]    Particularly illustrated in FIG. 3, the tapered bottoms  52  are also spaced above, and axially offset from, corresponding spinneret holes  56 . The tapered bottoms  52 , intermediate openings  54 , and spinneret holes  56  are related such that that if the tapered bottoms  52  were extended they would pass through the intermediate openings  54  and into a first part  60  of the spinneret holes  56 . That is, a passage (indicated by arrow W) guides the first polymer from the tapered bottoms  52  to the first part  60  of the spinneret holes  56 . Accordingly, the first polymer does not flow co-axial with a longitudinal center-line of the holes  56 . Preferably, the first part  60  is the part of the holes  56  radially closest to the center of the spinneret  16  (arrow X points towards the center of the spinneret) to maximize the property difference in the first and second polymers during quenching, as discussed below.  
         [0031]    As illustrated in FIGS. 1 and 2, the spinneret  16  includes a central hub  62 , an outer rim  64  and the interposed recessed section  40 . Cylindrical bosses  66 , each provided with the co-axial spinneret hole  56 , vertically extend from the recessed section  40  and terminate in a plane common with a top surface of the outer rim  64  and the central hub  62 . The recessed section  40  defines a volume between the central hub  62  and the rim  64  for conveyance of the second polymer which is received by the spinneret  16  from the inner passages  36 . The recessed section  40  is preferably deeper nearer the central hub  62  and shallower near the outer rim  64  to maintain the second polymer under constant pressure. The second polymer flows within the recessed section  40  between the bosses  66  and is confined between the central hub  62  and outer rim  64 .  
         [0032]    The shim  14  is unitary, has a uniform thickness, and slightly separates the distributor  12  from the spinneret  16 . Various openings in the shim  14  are shown in FIG. 4 and include respective openings  67 ,  68 ,  69 ,  70 , for receiving the inner and outer ring of bolts  20 ,  22  and the central and outer dowels  24 ,  26 . The shim  14  is also provided with the inner openings  38  and the intermediate openings  54  to direct passage of polymers. The shim  14  sets in the plane common with the terminal ends of the bosses  66  and is flush against the bosses  66  to restrict polymer from entering the spinneret holes  56  except via the intermediate openings  54 , as shown in FIGS. 2, 3 and  5 .  
         [0033]    As illustrated in FIG. 3, the intermediate openings  54  are configured to allow unrestricted passage (arrow W) of the first polymer directly from the distributor  12  to the first part  60  of the spinneret holes  56 . Additionally, the intermediate openings  54  allow passage of the second polymer along a continuous course (indicated by arrow Y) to a remaining part  70  of the spinneret holes  56  opposed to the first part  60 .  
         [0034]    Although different intermediate opening  54  configurations can be used, the preferred formation, shown in FIGS. 4 and 5, consist of a circular section  72  contiguous with a block-arc section  74 . FIG. 5 illustrates that the circular sections  72  are co-axial with, and substantially the same size as, the spinneret holes  56 . The block-arc sections  74  extend from the circular section  72  in a direction away from the first part  60  of the spinneret holes  56  and terminate beyond the corresponding boss  66 . As shown in FIG. 3, the continuous course (arrow Y) for the second polymer is provided from the recessed section  40 , through the block-arc section  74 , over the boss  66 , and thereafter past circular section  72  to the remaining part  70  of the hole  56 . To obviate the second polymer from being trapped in dead-space near the rim  64  of the spinneret  16 , the block-arc section  74 , and consequently the continuous course (Y), is preferably oriented at a part of the hole  56  radially furthest from the center of the spinneret  16 .  
         [0035]    Per FIG. 5, the block-arc section  74  spans in an arc  80  in the range of about 90 degrees to about 180 degrees, and preferably approximately 120 degrees. As a further alternative, the block-arc section  74  can be partitioned, such as for example, by having a first block-arc section and a second block-arc section each spanning about 60 degrees with a land therebetween (not shown).  
         [0036]    As shown in FIG. 3, the spinneret holes  56  are co-axial with the bosses  66  and extend from a top face  82  to a bottom face  84  through the spinneret  16 . The holes  56  have a counterbore top section  86 , a tapered transition section  88  and a lower section  90 . The lower section  90  includes opposed first and second apertures  92 ,  94  (more clearly shown in FIG. 5) extending from an intermediate surface  96  of the hole  56  to the bottom face  84  of the spinneret  16 .  
         [0037]    In an embodiment, FIG. 5 shows the first aperture  92  positioned in the first part  60  of the hole  56  and the second aperture  94  positioned in the opposed remaining part  70  of the hole  56 . The apertures  92 ,  94  are shaped as ½ of a circular annulus. That is, each aperture  92 ,  94  extends 180 degrees in an elongate arc. A pair of opposed lands  97  space the apertures  92 ,  94  apart and integrally join a center core  98  with the spinneret  16 . The apertures  92 ,  94 , taken with the lands  97 , form a slightly elongated circular annulus. Stated another way, if the apertures  92 ,  94  were positioned end-to-end, they would form a circular annulus. The lands  97  are as narrow as possible so that the first and second polymers will join together after exiting the respective apertures  92 ,  94  while balancing the need to maintain the integrity of the center core  98 .  
         [0038]    Although configuring each aperture as ½ of a circular annulus is preferred, other configurations are also acceptable such as accurate, semi-circular, oval and even linear. Apertures which are generally semi-circular are defined as being C-shaped.  
         [0039]    The apertures  92 ,  94  are further characterized as being asymmetric, that is, each having a different cross-sectional area. The first aperture  92  has a greater cross-sectional area than the second aperture  94 , and in particular, the first aperture  92  is wider than the second aperture  94 . The cross-sectional areas are derived according to the MV ratio of the polymers so that hydraulic split is avoided. Accordingly, substantially only one polymer egresses from any one aperture. That is, each aperture communicates with substantially only the inner passages  36  or one of the outer passages  42  so that any hydraulic split is sufficiently de minimis and virtually no kneeing of the resulting filament occurs. For example when using PET, the asymmetric apertures  92 ,  94  can be configured to enable spinning of polymer at intrinsic viscosity (hereinafter “IV”) combinations such as 0.5/0.67 IV, 0.63/0.8 IV and 0.55/0.8 IV without hydraulic split. Each aperture configuration is prefixed on providing a larger aggregate cross-sectional area for the higher IV polymer than the lower IV polymer, based upon the IV ratio of the polymers, to avoid hydraulic split.  
         [0040]    Alternative aperture configurations are illustrated by FIGS. 6 and 7. The alternative embodiments have the same spinneret  16 , boss  66  and hole  56  arrangement as discussed above, but with a different aperture configuration. Also, by increasing the number of lands, the center core is further maintained against failure of lands due to stress from hydraulic pressures of the polymers.  
         [0041]    In particular, FIG. 6 shows an alternative aperture configuration including first and second apertures  100 ,  102  which have a larger cross-sectional area in aggregate than a third aperture  104 . The apertures  100 ,  102 ,  104  are separated by respective lands  106 ,  108 ,  110  and define a center core  111  therebetween. The first polymer is directed through the first and second apertures  100 ,  102  and the second polymer through the third aperture  104 .  
         [0042]    Similarly, FIG. 7 shows four apertures  120 ,  122 ,  124 ,  126 , separated by lands  128 ,  130 ,  132 ,  134 , and defining a center core  135 . The first and second apertures  120 ,  122 , in aggregate, have a larger cross-sectional area than the combined third and fourth apertures  124 ,  126 . The higher MV first polymer is directed through the first and second apertures  120 ,  122 , while the lower MV second polymer is directed through the third and fourth apertures  124 ,  126 .  
         [0043]    As a further alternative, the apertures could be configured as three or more semicircular apertures equally spaced in a circular pattern. Additionally, each aperture could be of equal cross-section or have different cross-sectional areas. Likewise, linear apertures could be positioned in the shape of a triangle with the apertures having equal or different cross-sectional areas. In each case, the total cross-sectional area through which each polymer flows is based on the MV ratio of the polymers to avoid hydraulic split. Accordingly, where the apertures have the same cross-section, a greater number of apertures will be designated for handling the higher MV polymer than for the lower MV polymer. The myriad of possible aperture configurations is not limited by the embodiments illustrated or described herein.  
         [0044]    In operation, the distributor  12  receives the first and second polymers from the manifold  11  through the respective outer and inner feed conduits  28 ,  30  and directs the polymers through the shim  14  to the spinneret  16 , as shown in FIGS. 1 and 2. The first polymer is pumped through the outer passages  42 , through the intermediate shim openings  54 , and thereafter is received by the first part of the spinneret holes  56 , as indicated by arrow (W) of FIG. 3. Per FIGS. 1 and 2, the second polymer is pumped to the feed channels  32 , outwardly within the feed channels  32  to the inner passages  36 , and thereafter through the inner shim openings  38  to the recessed section  40  of the spinneret  16 . The pressure drop between the top surface of the bosses  66  and the bottom surface of the distributor  12 , and the pressure drop between the sloping recessed section  40  and the bottom surface of the shim  14  create an overall pressure drop forcing the second polymer through the recessed section  40 , through the block-arc shim sections  74 , and over the bosses  66  to the remaining part  70  of the holes  56 , as illustrated by arrow (Y) of FIG. 3.  
         [0045]    In regards to FIGS. 3 and 5, the first polymer flows through the first part  60  of the holes  56  and the second polymer flows through the remaining part  70  of the holes  56 . The higher MV first polymer is fed through the larger first apertures  92  positioned on the first part  60  of the holes  56 , while the lower MV second polymer is fed through the smaller second apertures  94  positioned on the remaining part  70  of the holes  56 , to avoid hydraulic split. Since the lands  97  minimally space the apertures  92 ,  94  apart, the terminal sides  140  of the molten polymers join after exiting the apertures  92 ,  94  to form a hollow filament  142  (shown in cross-section in FIG. 3). Upon exiting the apertures  92 ,  94 , the hollow filament  142  is quenched. The quenching can be by any suitable manner, with radial quenching emanating from the center of the spinneret  16  preferred. Preferably also, the larger first apertures  92  are positioned radially closer to the center of the spinneret  16  than the corresponding smaller second apertures  94 . Consequently, with radial quenching, the polymer having a higher MV is quenched at a slightly greater rate than the lower MV polymer so that the property differences between the polymers are maximized.  
         [0046]    Although a composition of 50% for each polymer is ideal, the lower MV polymer generally constitutes about 30% to 50% of the filament with a typical amount of about 40%.  
         [0047]    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 include all changes and modifications coming within the spirit and terms of the claims appended hereto.