DE69009424T2 - Device and method for spinning bicomponent fibers and products made therewith. - Google Patents

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. <IMAGE>

Description

The invention relates to a method and an apparatus for spinning bicomponent fibers and the improved products produced thereby. Furthermore, the invention relates to a method and an apparatus for spinning improved bicomponent fibers with concentric or eccentric sheath/core relationships.

Bicomponent fibers of sheath/core configuration are well known and a variety of spin packs and spinnerets have been used to make such filaments. A common spinning device involves adding 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 two-component spinning device is disclosed in US 4,406,850, wherein molten sheath polymer flows in ribbon flow into discontinuous slot-like portions of the upper surface of the spinneret disposed between rows of raised spinneret core inlet locations. US 4,251,200 also discloses a two-component spinning device comprising a separate spin plate and a manifold plate, the manifold plate having an opening opposite each opening in the spin plate and a plateau-like projection extending around the axis, the opening and the extrusion opening in common. In addition, the device includes a nozzle opening plate to restrict access to the opening.

The concentric shape of the core and sheath capillaries in the spinning devices according to the prior art as described above and in other spinning devices is not satisfactory. It is difficult to properly position the manifold plate and spinneret of prior art devices to obtain appropriate manifold and flow channel alignment and pressure drop control to produce sheath/core bicomponent fibers of uniform cross-section.

It is typical of prior art spinning devices, as exemplified by the cited references, that the gap between the outlet surface of the manifold and the inlet surface of the spinneret is fixed. Thus, as the sheath polymer viscosity changes or the core/sheath ratio changes, the pressure drop control of the prior art devices is lost. It is necessary to control the sheath polymer pressure drop adjacent the spinneret inlet - as will be discussed later herein - in order to obtain bicomponent fibers that are uniform from filament to filament.

Furthermore, in those spinning devices where the annular gap between the manifold and spinneret is fixed, the polymer pressure is sometimes sufficient to bend the spinneret away from the manifold, thereby opening the gap and changing the pressure drop. The inlet and outlet channels of each manifold and spinneret closest to the center and source of the sheath polymer have the widest spacing and those farthest from the center have the narrowest spacing. Sheath polymer will preferentially flow to the inner channels, thereby providing low bicomponent fiber uniformity.

WO-A-89/02938 discloses a spin-pack apparatus for forming synthetic fibers comprising feed means for delivering mutually separated, flowable polymers under pressure; permanent and reusable primary distribution means for delivering the mutually separated polymers to prescribed locations in the apparatus; a permanent and a reusable spinneret having an array of multiple spinneret orifices for discharging the synthetic fibers from the spin pack device, each spinneret orifice having an inlet hole at its upstream end and at least one available manifold plate disposed between the first manifold device and the spinneret and having multiple etched manifold flow paths for directing the mutually separated polymers from the first manifold device to the inlet holes in the spinneret. In one embodiment for producing conventional sheath/core fibers (the spin pack device shown in Figures 11-14 of WO-A-89/02938), each of the two flowable polymers is fed through respective slots in a metering plate to an open metering plate immediately downstream of the grid support plate. Immediately downstream of the grid support plate is an intermediate plate having an array of first distribution channels etched therein, the channels terminating in first distribution openings extending through the intermediate plate. The intermediate plate also has an array of second distribution channels, all terminating in second distribution openings extending through the intermediate plate. Between the intermediate plate and the upstream surface of the spinneret is an end distribution plate having an array of end distribution openings etched therein. The end distribution openings are star-shaped, the center of each such opening being aligned with the inlet of a respective spinneret orifice and the tines of the star-shaped end distribution orifice extending laterally beyond the edge of the spinneret inlet. The first polymer flows through the respective openings in the metering plate, along the first distribution channels into the intermediate plate, and through the first distribution openings aligned with the respective spinneret orifice inlets. The first (core) polymer thus flows from the first manifold openings into the spinneret orifice inlets via the central part of the star-shaped openings into the final manifold plate. The second polymer flows through its own respective openings in the metering plate, along the second distribution channels into the intermediate plate, and through the second distribution openings, the latter aligned with the extreme ends of the prongs of the star-shaped openings, into the de-distribution plate. The second (shell) polymer then flows along the channels defined by the prongs and into the inlets of the spinneret orifices. The intermediate plate serves to distribute both polymers in the horizontal plane and must be designed to keep these polymers separated from each other during distribution.

Brief description of the invention

The invention provides an improved method and apparatus for producing improved bicomponent sheath/core filaments of uniform cross-section, wherein the spin pack apparatus can be easily adjusted to compensate for changes in sheath polymer viscosity and changes in polymer flow, and wherein the sheath polymer flow to each spinneret core polymer flow channel can be controlled separately.

In one aspect, the present invention provides a filament spinneret apparatus for producing sheath/core bicomponent filaments comprising a manifold having a plurality of separate core polymer flow channels and a plurality of sheath polymer flow channels; a spinneret having a plurality of separate spinneret flow channels and a plurality of sheath polymer flow channels, each spinneret flow channel being coaxially aligned with the outlet of the respective core manifold flow channel; core polymer addition means for adding pressurized core polymer to the inlet of each manifold core polymer flow channel; sheath polymer addition means for adding pressurized sheath polymer to the inlet of each sheath polymer flow channel, and an interface means disposed between the spinneret and the manifold to separate the spinneret from the manifold to form a fluid channel between the manifold and the sheath polymer flow channels of the spinneret and to effect a controlled pressure drop of only the sheath polymer flow from the outlet of the manifold sheath polymer flow channels to the inlet of each of those spinneret flow channels separately, wherein the spacer has a thickness of 0.025 to 0.5 mm.

In another aspect, the present invention provides a filament spinneret apparatus for producing sheath/core bicomponent filaments comprising a manifold having a plurality of separate core polymer flow channels and a plurality of sheath polymer flow channels; a spinneret having a plurality of separate spinneret flow channels, each of the spinneret flow channels being coaxially aligned with the outlet of the respective core manifold flow channel; a plurality of recessed sheath polymer flow channels and a plurality of protruding buttons, each surrounding a corresponding spinneret flow channel and mounted between the spinneret flow channel and the sheath channels, wherein each button has a smooth top surface; core polymer addition means for adding pressurized core polymer to the inlet of each manifold core polymer flow channel; sheath polymer addition means for adding pressurized sheath polymer to the inlet of each manifold sheath polymer flow channel; and a spacer mounted between the spinneret and the manifold to form a channel between the top surface side of each button of the spinneret and the manifold at each spinneret channel, the thickness of the spacer causing a controlled pressure drop of sheath polymer flow through the channel between the top surface of each button and the manifold to the inlet of each of these spinneret flow channels separately, wherein the spacer has a thickness of 0.025 to 0.5 mm.

In another aspect, the present invention provides a method for melt spinning sheath/core bicomponent filaments comprising passing multiple streams of pressurized molten core polymer from manifold core polymer flow channels into multiple parallel spinneret flow channels in respective axial alignment with said multiple manifold core polymer flow channels, passing pressurized molten sheath polymer from recessed sheath channels into a corresponding sheath polymer flow channel formed between a spacer and the top surface of the spinneret; then flowing the sheath polymer through a channel formed by a protruding button, spacer, and the manifold; then flowing the sheath polymer into the spinneret flow channel to form the bicomponent filament.

Short description of the drawings

Figure 1 is a perspective view of a spin-pack device embodiment of the invention,

Figure 2 is a vertical section through a multiple channel manifold/interface/spinneret assembly.

Figure 3 is a vertical section through a manifold/spacer/spinneret device for producing concentric bicomponent filaments.

Figure 4 is a vertical section through a manifold/spacer/spinneret apparatus for producing eccentric bicomponent filaments.

Figure 5 is a vertical section through a manifold/spacer/spinneret apparatus for producing bicomponent filaments with non-circular cross-section.

Description of preferred embodiments

Referring to the accompanying drawings and more specifically to Figure 1, a spin pack device can be made from a manifold 10, an adapter 11 and a spinneret 12. Manifold 10 is arranged to receive a melt-extruded shell polymer or shell polymer in solution through a channel 13 and a melt-extruded core polymer or core polymer in solution through a channel 14. Each of the shell and core polymers is directed to the respective channels 13 and 14 by means of conventional melt extrusion, pump and filter devices, not shown here.

The function of the manifold 10 is to form filaments from the core polymer and to channel the flow of sheath polymer to the spinneret 12. The core polymer is pumped through a plurality of channels 16 to the lower, straight surface of the manifold 10. Channels 16 may be arranged in any number of rows or columns depending on their size, the viscosity of the core polymer, the length of the channels 16, and the flow characteristics of the particular core polymer. The lower end of each channel 16 is tapered to provide a core filament of the desired diameter. Although not so limited, the density of channels 16 in the manifold 10 may, for example, be as high as desired. For example, if the core polymer is molten polyethylene terephthalate and the outlet channel diameter is in the range of 0.1 millimeters (mm) to 1.0 mm, the diameter should be such that each channel occupies 10 mm² of the spinneret area.

Sheath polymer flowing through channel 13 is pumped to channels 17 and through channels 17 to spinneret 12. Although not limited thereto, channels 17 are preferably disposed axially in manifold 10 so that upon exiting channels 17, the sheath polymer will flow radially outward to the inlet openings of channels 22.

An intermediate piece 11 is arranged between manifold 10 and spinneret 12 and is held in fixed position to manifold 10 and spinneret 12 by bolts 19 which comprise spiral recesses 20 in manifold 10. Manifold 10 and spinneret 12 are respectively arranged by dowel pins 18. In order to avoid bending and separation of manifold 10 and spinneret 12 which can occur in the operation of conventional spin-pack devices, a ring of bolts 19 has been arranged in the center of the device as shown in Figure 2. The intermediate piece can be made of a variety of materials such as stainless steel or brass, with stainless steel being preferred. The intermediate piece can be made as a single unit or in the form of two separate inner and outer parts. The number and placement of the bolts 19 to control deflection is such that the deflection is preferably limited to less than 0.002 mm.

Spacer 11 must be of substantially constant thickness, preferably having a thickness variability of less than 0.002 mm, and the annular openings 21 must be in proper alignment with the manifold channels 16 and the spinneret channels 22. Spacers 11 of varying thickness, typically ranging from 0.025 to 0.50 mm, are used to accommodate changes in sheath polymer viscosity, changes in polymer flow, or to vary the pressure drop as will be discussed hereinafter.

The top smooth flat surface of the spinneret 12 is recessed, providing a channel 23 for the flow of sheath polymer to each channel 22. Raised circular members or knobs 24 surround each channel 22. The raised members or knobs 24 extend upwardly from the channel 23 to a height equal to the top surface 25 of the spinneret 12. The rate of outward flow of sheath polymer through channel 23 and over the knobs 24 to the channels 22, results from the pressure drop determined by the thickness of the spacer 11. The pressure drop is inversely proportional to the cube of the height of the gap 26 between manifold 10 and spinneret 12. Precise control of this gap height is effected by spacer 11 and maintained by the inner circle of bolts 19. The recess depth of channel 23 is selected to provide a low pressure drop [typically 137.9-344.7 kPa (20-50 psi)] circularly through the top of the spinneret. The spacer thickness is selected to provide a pressure drop of typically 689.5-6895 kPa (100-1000 psi) through the raised knobs 24.

As can be seen from the drawings, each channel 22 must be in concentric alignment with its respective channel 16. The core polymer flows through channels 16 and 22 and exits the spinneret 12 as the core of a bicomponent fiber. The sheath polymer flows through channels 17, channel 23 and gap 26 to form a sheath around the filament of core polymer, thereby producing the bicomponent fiber mentioned above. The central axis of the distribution channel 16 should lie within a circle having a radius of less than 200 µm, preferably less than 50 µm, from the central axis of the spinneret depression.

The manufacture of concentric bicomponent fibers is further illustrated in Figure 3. Spacer 11 is positioned to cause sheath polymer 31 to flow through channel 23, over buttons 24 and through gap 26 into channel 22, thereby forming a concentric sheath around core polymer 30 as shown.

The manufacture of eccentric sheath/core fibers is shown in Figure 4. The holes in the intermediate piece 11 are arranged in such a way that the flow of sheath polymer 33 is restricted in the manner shown. The eccentric cross section of the formed two-component filament is also shown in Figure 4.

Figure 5 illustrates a spinneret assembly used to make sheath/core bicomponent fibers where the core has a non-circular cross-section. As shown, the core polymer is fed through channel 16 of the manifold to a core profile spacer 36 which contains a channel 37 having a Y-shaped cross-section. The core polymer flows through core profile spacer 36 to channel 22 in the manner described above. The sheath polymer is transferred to channel 22 in the manner described above and a bicomponent fiber having a sheath 39 and core 38 is produced.

The bicomponent sheath/core filaments produced by the spinneret apparatus of the invention are of uniform cross-section from one filament to the next. 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 the invention will be less than 2.50% based on diameter measurements of at least 25 filaments produced simultaneously. The coefficient of variability (CV) is determined by:

CV = standard deviation of filament diameter/mean filament diameter x 100

The eccentricity coefficient of variability for 25 simultaneously produced concentric bicomponent fibers of the invention will preferably be less than 1.0%. The eccentricity coefficient of variability (ECV) is determined by the following relationship:

ECV = core center displacement/two-component filament diameter x 100

Typically, the diameter coefficient of variability for commercially manufactured 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 is described below with respect to the manufacture of sheath/core bicomponent fibers wherein the sheath polymer comprises a molten polyethylene blend - as will be described hereinafter - and the core polymer comprises a molten polyethylene terephthalate, although it will be understood by those skilled in the art that other sheath and core polymers may be used.

A maleic anhydride-grafted high density polyethylene was prepared according to the process of US 4,684,576, the disclosure of which is incorporated herein by reference. The high density polyethylene resin had a melt flow value (MFV) of 25 g/10 min at 190°C [ASTM D-1238(E)] and a density of 0.955 g/cm3 (ASTM D 792) before extrusion. After extrusion, its MFV was 15 g/10 min. This product was blended with a linear low density polyethylene resin having a MFV of 18 g/10 min at 190°C so that the maleic anhydride content of the blend was 0.09-0.12 wt.%. The polymer blend used as the shell polymer in the following examples had an MFV of 16g/10 min at 190 ºC and a density of 0.932 g/cm3. The core polymer of the following examples was a polyethylene terephthalate with an intrinsic viscosity (ASTM D 2857) of 0.645.

example 1

The spinneret device of Figure 1, which has spinneret hole diameters of 0.374 mm, was used to produce concentric bicomponent sheath/core filaments with core/sheath ratios of 60:40 wt.% (batch 1), 70:30 wt.% (batch 2), and 80:20 wt.% (batch 3). The molten shell polymer was fed to channels 17 at a temperature of 275ºC. The molten core polymer was fed to channels 16 at a temperature of 275ºC. The throughput per spinneret hole was 0.852, 0.903, and 0.935 g/min, respectively.

The bicomponent filaments were quenched with air at 30°C and wound at a rate of 853.4 in/min (2800 fpm). 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 into 3.81 cm (1.5 inch) long fibers and the properties are listed in Table I below. Table I Approach Denier per Filament (DPF) ASTM-D-2101-82) Tenacity at Break (ASTM-D-2101-82) % Elongation (ASTM-D-2101-82) Stress at Specified Elongation (10%) (ASTM-D-2101-82) Crimps per cm (inch) (CPI) (ASTM-D-3937-82) Tenacity (ASTM-D-2101-82) % Crimp (ASTM-D-3937-82)

The spinneret device of the invention can be used to produce solution-spun bicomponent filaments. By adjusting the pack sizes and polymer solution viscosities, bicomponent filaments, e.g., cellulose acetate and viscose, could be produced.

The principles, preferred embodiments and operations of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected here is not limited to the particular forms disclosed, since these are to be considered as illustrative rather than restrictive.

Modifications and changes can be made by a person skilled in the art without departing from the scope of the claims.

Claims (14)

1. Filament spinneret apparatus for producing sheath/core bicomponent filaments comprising a manifold (10) having a plurality of separate core polymer flow channels (16) and a plurality of sheath polymer flow channels (17); a spinneret (12) having a plurality of separate spinneret flow channels (22) and a plurality of sheath polymer flow channels (23), each spinneret flow channel (22) being coaxially aligned with the exit of the respective core manifold flow channel (16); core polymer addition means (14) for adding pressurized core polymer to the inlet of each manifold core polymer flow channel (16); Sheath polymer addition means (13) for adding pressurized sheath polymer to the inlet of each sheath polymer flow channel (17); and an intermediate piece (11) mounted between the spinneret (12) and the manifold (10) for isolating the spinneret from the manifold to form a fluid channel (26) between the manifold (10) and the sheath polymer flow channels (23) of the spinneret (12) and for separately causing a controlled pressure drop of only the sheath polymer flow from the outlet of the manifold sheath polymer flow channels (17) to the inlet of each of those spinneret flow channels (22), wherein the intermediate piece (11) has a thickness of 0.025 to 0.5 mm. 2. A filament spinneret apparatus for producing sheath/core bicomponent filaments comprising a manifold (10) having a plurality of separate core polymer flow channels (16) and a plurality of sheath polymer flow channels (17); a spinneret (12) having a plurality of separate spinneret flow channels (22), each of the spinneret flow channels (22) being coaxially aligned with the outlet of the respective core-manifold flow channel (16); a plurality of recessed sheath polymer flow channels (23) and a plurality of protruding buttons (24), each surrounding a corresponding spinneret flow channel (22) and mounted between the spinneret flow channel (22) and the sheath channels (23), wherein each button has a smooth top surface; core polymer addition means (14) for adding pressurized core polymer to the inlet of each prescaler core polymer flow channel (16); sheath polymer addition means (13) for adding pressurized sheath polymer to the inlet of each manifold sheath polymer flow channel (17); and an intermediate piece (11) mounted between the spinneret (12) and the manifold (10) to form a channel (26) between the top surface side of each button (24) of the spinneret (12) and the manifold (10) at each spinneret channel (22), the thickness of the intermediate piece (11) causing a controlled pressure drop of the sheath polymer flow through the channel (26) between the top surface of each button (24) and the manifold (10) to the inlet of each of these spinneret flow channels (22) separately, wherein the intermediate piece (11) has a thickness of 0.025 to 0.5 mm. 3. A filament spinneret apparatus according to claim 1 or 2, wherein the spacer is aligned in a coaxial relationship with the outlet to the manifold core polymer flow channel. 4. A filament spinneret apparatus according to claim 1 or 2, wherein the spacer is oriented in an eccentric relationship to the outlet of the manifold core polymer flow channel. 5. A filament spinneret device according to claim 1, 2 or 3, wherein the spacer has a thickness tolerance of equal to or less than 0.002 mm. 6. Filament spinneret apparatus according to any one of the preceding claims, comprising a further intermediate piece (36) disposed immediately adjacent to the manifold (10) and containing a plurality of separate core polymer flow channels (37) in separate axial alignment with the plurality of separate manifold core polymer flow channels (16), and wherein each of the separate core polymer flow channels (37) in said further intermediate piece (36) has a cross-section dissimilar to the cross-section of each of said manifold core polymer flow channels. 7. A method of melt spinning sheath/core bicomponent filaments comprising passing multiple streams of pressurized molten core polymer from manifold core polymer flow channels into multiple parallel spinneret flow channels in respective axial alignment with said multiple manifold core polymer flow channels, passing pressurized molten sheath polymer from recessed sheath channels into a corresponding sheath polymer flow channel formed between an interface and the top surface of the spinneret; thereafter, the sheath polymer flows through a channel formed by a protruding button, interface and the manifold; then the sheath polymer flows into the spinneret flow channel to form the bicomponent filament. 8. The process of claim 7 wherein each of the bicomponent fibers exiting the spinneret is a concentric sheath/core filament. 9. The process of claim 7 wherein each of the bicomponent fibers exiting the spinneret is an eccentric sheath/core filament. 10. The process of claim 7, 8 or 9, wherein the shell polymer is a polyolefin and the core polymer is a polyester. 11. The process of claim 10 wherein the polyolefin is a blend of a maleic anhydride grafted high density polyethylene and a linear low density polyethylene and the core polymer is polyethylene terephthalate. 12. A process according to any one of claims 7 to 11 when used for the simultaneous production of several bicomponent sheath/core polymer filaments of uniform cross-section. 13. The method of claim 12, wherein the diameter variability coefficient is less than 2.50%. 14. 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%.