A method of making a filamentary structure comprising a spiral thermoplastic core filament disposed within a thermoplastic sheath component is provided. The method involves extruding together from an extrusion die filaments forming the core filament and the sheath component, with the core filament being extruded at a faster rate than the sheath component which causes the core filament to spiral, and cooling the extrudates to form a unitary structure. A plurality of the filamentary structures may be extruded side-by-side so that their sheath components are joined together to form a fabric structure.
This invention is concerned with the extrusion of thermoplastic polymers to form a novel filamentary structure.
According to the invention, a filamentary structure comprises a spiral thermoplastic core filament disposed within a thermoplastic sheath component which is joined to the succesive turns of the spiral core filament.
The sheath component is preferably a cage formed by at least three thermoplastic filaments each of which is joined to the successive turns of the spiral core filament. Alternatively, the sheath component may comprise a tube.
The invention includes a process for making such a filamentary structure comprising feeding molten thermoplastic polymer to a stationary one-piece extrusion die having an inner jet hole ringed by outer jet holes, extruding the polymer through the inner die hole at a greater velocity than polymer is extruded through the outer die holes to form a spiral extrudate disposed within an extruded sheath component to which its successive turns are adhered, and cooling the extrudates to solidify them to a unitary structure.
The thermoplastic polymer may be any which can be melt spun into filaments including polyamides, polyesters and polyolefins. The polymer extruded through the inner die hole to form the spiral core may be the same as or different from the polymer extruded through the outer die holes to form the sheath component. Preferably it is the same in order to simplify spinning and ensure good adherence between the turns of the spiral core filament and the sheath component.
An elastic filamentary structure may be formed by making the spiral core filament from a non-elastomeric polymer and the sheath component from an elastomeric polymer.
The polymer extruded through the inner die hole is required to have a greater velocity than that flowing through the outer die holes in order that it will take up the desired spiral form. With a common supply of molten polymer, this greater velocity may be achieved by having the inner die hole of greater cross-sectional area and/or of shorter capillary length than each of the outer die holes. Preferably it is of greater cross-sectional area for two reasons: the first being that in the most desirable filamentary structure of the invention the cage filaments which comprise the sheath component are of smaller cross-sectional area than the spiral core filament; and the second being that jets having holes of a common capillary length are much easier to make.
The sizes and cross-sectional shapes of the die holes determine the size and shape of the filaments extruded through them. The preferred shape is circular, particularly for the inner die hole. For a given spacing between the inner die hole and the outer die holes, the pitch of the spiral core filament is determined by the relative polymer velocities through the inner and outer holes. That is, the pitch reduces as the velocity differential increases.
Preferably, the axes of the inner and outer die holes are all parallel to one another so that, in the embodiment where the sheath component comprises a cage of filaments, these filaments are in substantially parallel alignment with the axis of the spiral core filament.
The diameter of the spiral of the core filament is determined by the sheath component which holds it in place and which stabilises it by adhering to its successive turns. When the sheath component comprises a cage of filaments it has been found that it is necessary to have at least three cage filaments for this purpose otherwise the core filament `breaks out` and is uncontrolled. Preferably each cage filament is spaced apart from its adjacent cage filaments by substantially equal distances. This may be arranged by using a spinning jet with a central inner jet hole ringed by at least three outer die holes pitched at substantially equal angles to and substantially equidistant from the central inner die hole.
The number of cage filaments can be increased to any desired number commensurate with the dictates of jet geometry. In the limit, each outer die hole is positioned sufficiently closely to its adjacent outer die holes that because of die swell the extruded cage filaments merge to form a tube. The outer die holes are preferably of circular cross-section, although other suitable cross-sections may be used, for example arcuate slots which may be used to produce a tube as described.
The extruded structure may be cooled in air to solidify it, but it is preferred to stabilise it more quickly by quenching it in a liquid bath which is conveniently water.
The filamentary structure of the invention may be used as yarn, core or twine, or as a reinforcement for a tube. In the embodiments described where the sheath component comprises a tube, it constitutes a reinforced tube itself. It may also be used to construct an abrasive pad such as a pan scrub.
The invention includes a fabric structure comprising a plurality of filamentary structures according to the invention joined to each other with the axes of the spiral filaments in substantially parallel relation. This fabric structure may be produced directly by extrusion using a bank of adjacent sets of die holes from which adjacent filament structures are extruded. These merge and become adhered so that after being cooled to solidify them, they remain joined as a unitary fabric structure. The component filamentary structures may be arranged in a planar array by a corresponding arrangement of the adjacent sets of die holes, to produce a planar fabric structure. Three-dimensional fabric structures may be made using appropriate groupings of the sets of die holes from which the component filamentary structures are extruded.
The fabric structure of the invention has a variety of uses including use as drainage, earth-support and other civil engineering fabrics, and as matting such as door mats.
In the embodiment of the invention where the sheath component comprises a cage of filaments, limited stretching of the filamentary structure produces elongation of the cage filaments between the successive points of adherence, with the result that after removal of the stretching forces and contraction of the spiral core, the cage filaments balloon out between the adherence points giving an expanded structure.
Greater stretching causes the cage filaments to break between the points where they are joined to the spiral core filament, close to those points, to produce a modified filamentary structure which is a further aspect of the invention. The broken cage filaments constitute fibrils which are substantially uniform in length, with the majority of the fibrils being raked in a common direction.
The modified filamentary structure has decorative qualities and may be used as fancy yarn, or twine, especially if coloured. The rake of the fibrils gives it a particularly distinctive appearance and also imparts good knot-tying properties. The roughness of the fibrils, particularly at the adherence points, gives the product abrasive properties making it suitable for the construction of scouring pads, for example.
The invention is illustrated by the accompanying drawings in which:
FIG. 1 is a plan of the face of a one-piece stationary extrusion die suitable for use in the process of the invention,
FIG. 2 is a cross-section on the line II . . . II of FIG. 1,
FIG. 3 is an elevation of a filamentary structure in accordance with the invention,
FIG. 4 is an elevation of a modified filamentary structure formed by stretching the structure of FIG. 3,
FIG. 5 is a sectional elevation of another filamentary structure in accordance with the invention,
FIG. 6 is a plan, on an enlarged scale, of the face of an extrusion die suitable for spinning the filamentary structure shown in FIG. 5,
FIG. 7 is an elevation of the structure of FIG. 3 after being partially stretched,
FIG. 8 is an elevation of a fabric structure in accordance with the invention,
FIG. 9 is a plan, on an enlarged scale, of the face of a die suitable for spinning the fabric structure shown in FIG. 8, and
FIG. 10 is a diagram of apparatus for spinning a filamentary structure in accordance with the invention.
Referring to FIGS. 1 and 2, a spinning jet 1 has a circular die face 2 in which are drilled an inner die hole 3 encircled by a ring of four outer die holes 4. The die holes have the same capillary length and the inner die hole is shown as about twice the diameter of the outer die holes.
FIG. 3 shows a filamentary structure 5 spun from a die similar to that shown in FIGS. 1 and 2, but comprising eight outer die holes instead of four. The filamentary structure 5 comprises a spiral core filament 6 held within a cage of eight finer filaments 7 which are joined to the successive turns of the spiral core filament at points 8.
FIG. 4 shows a modified filamentary structure 9 produced by stretching the structure 5, whereby the cage filaments 7 have broken close to the points 8. The resulting fibrils 10 are regularly spaced and uniform in length. As shown they are raked in a common direction. The points at which they are joined to the core filament 6 lie on a generally spiral path around the core filament.
The filamentary structure 11 shown in FIG. 5 comprises a spiral core filament 12 held within a tubular sheath 13 which is joined to the successive turns of the spiral core filament at points 14. The structure 11 may be spun from a die of the type shown in FIG. 6 in which the die 15 has a central inner die hole 16 ringed by two outer die holes 17 in the form of two arcuate slots. The extrudates from the outer die holes merge below the die to form a tube enclosing the spiral core filament formed from the higher velocity extrudate from the inner die hole.
FIG. 7 shows a filamentary structure of the type shown in FIG. 3 after being stretched to a degree which elongates the cage filaments without breaking them. On being allowed to relax, the spiral core filament 18 contracts and causes the elongated cage filaments 19 to balloon out as shown to produce an expanded filamentary structure 20.
The fabric structure 21 shown in FIG. 8 comprises three filamentary structures of the type shown in FIG. 3 with the axes of their spiral core filaments 22 parallel and adjacent cage filaments 23 fused together. This fabric structure may be produced by a die of the type shown in FIG. 9 which has a rectangular die face 24 with three sets 25 of die holes lying adjacent to each other in a line. Each set 25 comprises an inner die hole 26 ringed by eight outer die holes 27 of smaller diameter. The cage filaments extruded from the adjacent pairs of outer die holes 28, 29 and 30, 31, respectively, merge below the jet face to join the extruded filamentary structures together as a fabric.
The number of sets of die holes may be extended beyond three to produce wider fabric structures, and may also be grouped other than in line, for example as a grid, to provide three-dimensional fabric structures.
In FIG. 10, the apparatus shown diagrammatically comprises an extrusion die 32 from which a filamentary structure 33 according to the invention is extruded downwardly into a water quench bath 34. The solidified structure is withdrawn from the die by driven rollers 35 is a `clover leaf` formation and located below the surface of the bath. The structure is withdrawn from the bath by a godet 36 and, if desired, stretched between the godet 36 and a further godet 37 to produce a structure as shown in FIG. 4 or FIG. 6 depending upon the degree of stretch.
The invention is illustrated by the following Examples:
Examples 1 to 6
Nylon 6 polymer was melted and extruded through various spinning jets as shown in FIGS. 1 and 2 of the drawings, some with four outer die holes and some with eight outer jet holes with variations also in the pitch circle diameter (PCD) of the outer die holes. The extrudates were quenched in a water bath at room temperature and collected either by free fall or by nip rollers. Samples were taken and stretched at two different percentage stretches, one simply to bulk the product and the other a greater stretch to break the cage filaments and produce the modified filamentary structure.
The following die dimensions and process conditions were common to all six Examples. Other conditions which varied between Examples and the product properties are shown in the succeeding Table.
TABLE
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Inner die hole diameter
350 .mu.m
Outer die hole diameter
175 .mu.m
Capillary length of all die holes
437 .mu.m
Head temperature of die
260.degree. C.
Polymer throughput 13.46 g/min.
Example 1 2 3 4 5 6
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Number of outer
8 8 4 4 8 8
die holes
PCD of outer
844 844 900 900 1000 1000
die holes (.mu.m)
Distance from die
1.5 10 1.5 10 1.5 10
face to quench
bath (cm)
Take-up speed
13.3 Free 17.7 Free 12 Free
m/min Fall Fall Fall
Diameter of 0.18 0.21 0.20 0.25 0.21 0.23
extrudate (cm)
Diameter of spiral
0.07 0.07 0.07 0.07 0.07 0.07
core filament (cm)
Pitch of spiral
0.21 0.17 0.31 0.30 0.22 0.21
(cm)
Direction of spiral
acw acw cw acw cw cw
(cw or acw)*
Diameter of cage
0.02 0.025 0.02 0.020 0.025
0.025
filaments (cm) to to
0.030 0.028
Weight/unit length
0.973 1.311 0.760
0.886 1.210
1.260
of extrudate (g/m)
Stretch to bulk
120 130 100 110 130 120
(percent)
Stretch to break
425 400 500 520 420 410
(percent)
Percentage of
fibrils raked
towards die 95 70 95 95 90 95
away from die
5 30 5 5 10 5
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*cw = clockwise
acw = anticlockwise
