Spinneret Assembly

Abstract

A spinneret assembly comprising sandwiched filter block, distribution plates and a spinneret plate is designed to produce a plurality of uniform sheath-core filaments with accurate regulation of sheath thickness without overcrowding extrusion orifices. The flow channels and passages are shaped and interconnected to provide uniform pressure and distribution of the sheath and core polymers across the plurality of extrusion orifices.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for the production of bicomponent filaments and, more particularly, to an improved spinneret assembly for extrusion of sheathcore filaments.

2. Prior Art

Filaments consisting of two or more components are well known in the art and are generally produced by extruding the different components from the spinnerets in side-by-side relationship or in an eccentrically disposed sheath-core arrangement. With the latter type of filament, it has been found difficult to prevent variations in the sheath thickness with the result that product uniformity was less than desirable. U.S. Pat. No. 3,244,785 discloses a process and apparatus which permits more accurate regulation of the sheath thickness and thus produces a more uniform product. While few problems are encountered with this arrangement when the number of filaments extruded from a given spinneret is small, the extrusion of larger numbers of filaments from a single spinneret inhibits equal distribution of the two polymers to the spinneret plate without undesirable crowding of the extrusion orifices.

SUMMARY OF THE INVENTION

The invention comprises sandwiched filter block, upper and lower distribution plates and a spinneret plate. The filter block has two separate filtration cavities in its upper face. One of the filtration cavities is connected via passages in the filter block and the upper distribution plate to recessed areas of the upper surface of the lower distribution plate. The other filtration cavity is connected by flow passages in the filter block and in the upper and lower distribution plates to recessed areas of the lower surface of the lower distribution plate. Said upper and lower recessed areas are connected by core meter passages, each of which terminates at the end of a cylindrical projection. These projections protrude into the central portion of the lower recessed areas and terminate in close proximity to the upper surface of the spinneret plate. The spinneret plate has sheath-core spinneret passages coaxial with the core meter passages which connect the lower surface of the spinneret plate with the lower recessed areas. The spinneret plate additionally has angular sheath spinneret passages which connect the lower recessed areas with the sheath-core spinneret passages at a junction between the upper and lower surfaces of the spinneret plate.

The apparatus of this invention has the advantage of providing a relatively simple arrangement for extruding a considerable number of sheath-core filaments without undue crowding of the spinneret orifices or enlargement of the spinneret assembly. Crowding is obviously undesirable, since it leads to difficulties in proper cooling of the freshly extruded filaments. Enlargement of the assembly is expensive and otherwise undesirable due to space limitations. The inventive juxtaposition of the various polymer flow passages permits desirable spacing of a plurality of orifices while meeting the spinneret requirements for sheath-core spinning and without incurring other problems such as gel formation or improper distribution of the molten polymers.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the spinneret assembly of the instant invention.

FIG. 2 is a view taken along line II -- II of FIG. 1, illustrating the bottom surface of the filter block.

FIG. 3 is a view taken along line III -- III of FIG. 1, illustrating the top portion of the upper distribution plate.

FIG. 4 is a view taken along line IV -- IV of FIG. 1, illustrating the top portion of the lower distribution plate.

FIG. 5 is a view taken along line V -- V of FIG. 1, illustrating the bottom portion of the lower distribution plate.

FIG. 6 is a view taken along line VI -- VI of FIG. 1, illustrating the top surface of the spinneret plate.

FIG. 7 is an illustration, in an alternate embodiment, of the top surface of the upper distribution plate.

FIG. 8 is an illustration, in an alternate embodiment, of the top surface of the lower distribution plate.

FIG. 9 is an illustration, in an alternate embodiment, of the bottom surface of the lower distribution plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the spinneret assembly chosen for purposes of illustration includes a filter block 10 having separate filtration cavities 12,14 from which different viscous polymeric materials are discharged through distribution passages 16,18. Material from cavity 12 passes into groove 20 (see FIG. 2 for the vertical view) in the bottom of the filter block which together with distribution plate 30 forms a flow passage leading to holes 32 (FIG. 3) through which holes the material passes into flow passages 46 and 48 (FIG. 4) and then into upper recessed areas 42, 44. Upper recessed areas 42,44 are closed to form flow channels by the junction of upper distribution plate 30 and lower distribution plate 40. Flow passages 46 and 48 are similarly formed. From recessed areas 42,44 the material passes through core meter holes 50 and then into passages 72 in spinneret plate 70 to form the core of filaments extruded from the spinneret. Meanwhile, another viscous material from filtration cavity 14 passes through passages 18 into groove 22 in the bottom of the filter block which forms together with upper distribution plate 30 a flow passage connecting to holes 34 in plate 30 through which the material passes into holes 62,64 (FIG. 5), which are a continuation of holes 34, in the distribution plate 40, then into flow passages 58,60 which lead into lower recessed areas 54,56. Part of the material in recessed areas 54,56 flows around the core material being jetted from passages 50 and into spinneret passages 72 to form a sheath-core column in passages 72 of spinneret plate 70. Additional material from recessed areas 54,56 passes into angled passages 74 in the spinneret plate and is combined in substantially side-by-side relation with the sheath-core column passing through passages 72.

In another embodiment of the invention, FIGS. 7,8,9 a different arrangement of flow passages is employed between grooves 20,22 in filter block 10 and upper and lower recessed areas 42,44,54,56. Viscous material from groove 20 passes into grooves 33 in the upper surface of upper distribution plate 30a and into flow holes 37 which communicated with upper recessed areas 42a,44a formed by the junction of upper distribution plate 30a and lower distribution plate 40a (either of the plates may be recessed to form areas 42a,44a). From recessed areas 42a,44a the material passes through passages 50a into spinneret passages 72 as in FIG. 1. Material from groove 22 passes through grooves 31 in upper plate 30a into flow holes 35 in the upper plate, thence through flow holes 45 in the lower plate into lower recessed areas 54a,56a. From recessed areas 54a,56a the viscous material flows around the core material being jetted from passages 50a and into passages 72 and 74 of spinneret plate 70 as in FIG. 1.

The spacing between cylindrical projections 52 and the top of spinneret plate 70 is adjusted in relation to the pressure on the polymers and the sizes of the flow passages to control the relative amounts of sheath and core formed in holes 72. The width of projection 52 relative to the diameter of hole 72 is also an important design consideration in regulating the sheath-core distribution in hole 72. The rate of polymer flow through holes 74 will, of course, depend on the diameter and length of the passage, on the polymer viscosity and on the pressure in recessed areas 54,56.

At the juncture of passages 72 and 74 the polymers are combined in an essentially side-by-side relationship and extruded through spinning orifices 76. Formation of sheath-core filaments by first forming a concentric sheath-core column of the polymer in one flow passage and then combining this column with additional sheath material from a second flow passage is disclosed in U.S. Pat. No. 3,244,785. Additional details relative to this procedure may be found therein.

Wider spacing of the flow passages, especially passages 50 and correspondingly passages 72, allows cylindrical projections 52 to have a larger diameter. A projection 52 having a larger diameter creates a longer flow path for the sheath polymer and consequently induces a larger pressure drop across the face of a projection. The result is a smaller percentage variation in sheath thickness when spinning polymer pressure varies.

Recessed areas 42,44 and 54,56 may be tapered from either end toward the center of the assembly to compensate for any temperature gradients in the polymer from the inside to the outside of the assembly as disclosed in U.S. Pat. No. 3,225,383. Suprisingly, however, the spinneret assembly of this invention does not require such tapering.

Grooves 20,22 may be formed by recesses in the filter block as illustrated. However, alternatively they may be formed by appropriate recesses in the top of upper distribution plate 30. Similarly, the upper flow passages can be formed by appropriate recesses in plate 30 rather than in the distribution plate 40 and the lower flow passages by recesses in spinneret plate 70 rather than in plate 40.

The spinneret assembly is, of course, provided with a suitable top plate, and the various elements are bolted or otherwise fastened together, for instance, as disclosed in U.S. Pat. No. 3,262,153.

Various modifications in the shape of the various passages and areas for polymer flow will be apparent to those skilled in the art.

Claims

What is claimed is:

1. A spinneret for production of filaments in an eccentrically disposed sheath core arrangement comprising a filter block, a spinneret plate, and upper and lower distribution plates sandwiched between said filter block and said spinneret plate, said filter block having two separate filtration cavities on its upper face and having two separate flow channels between said filter block and said upper distribution plate, each being connected to a different filtration cavity by a plurality of distribution passages, one flow channel being connected to two upper recessed areas between the upper and lower distribution plates, the other flow channel being connected by holes in the upper distribution plate to two lower recessed areas between the lower distribution plate and the spinneret plate each of said upper recessed areas being connected to a different lower recessed area by two rows of core meter holes each of which terminates at the face of a cylindrical projection in the lower recessed areas, said spinneret plate having four rows of core spinneret passages coaxial with said core meter passages connecting the lower surface of said spinneret plate with said lower recessed areas, said spinneret plate additionally having angular sheath spinneret passages connecting said lower recessed areas with said core spinneret passages at junctions between the upper and lower surfaces of said spinneret plate.

2. The spinneret of claim 1, said filter block having two separate grooves on its lower surface which form said flow channels by the junction of said filter block and said upper distribution plate.

3. The spinneret of claim 1, said upper distribution plate having two separate grooves on its upper surface which form said flow channels by the junction of said filter block and said upper distribution plate.

4. The spinneret of claim 1, said upper recessed areas being in the upper surface of said lower distribution plate.

5. The spinneret of claim 1, said lower recessed areas being in the lower surface of said lower distribution plate.