IE902617A1 - "Apparatus and method for the spinning of core/sheath fibres" - Google Patents

Abstract

In the apparatus for spinning core/skin fibres consisting of various fibre-forming materials, a preplate (16) is arranged between a distributor plate (14) and a spinneret plate (12). Nozzle capillaries (18) having prechannels (20) are formed in the spinneret plate (12). The materials for the skin and the core of a fibre are fed to the spinneret plate via an annular channel (28) and a feed channel (32), approximately concentric with this, which are formed in the preplate (16). The annular channel (28) is connected via at least one feed channel (30) to at least one guide channel (24) and the central channel (32) for the core material is connected via at least one feed channel (34) to at least one guide channel (26) in the distributor plate (14). By means of the arrangement of a preplate having channels formed therein for the core material and skin material of the fibres, on the one hand high-quality fibres with exact geometries can be produced and on the other hand the number of nozzle capillaries per unit area can be increased to more than 10 per cm<2>, since a compact formation of the channels in the preplate (16) is possible. <IMAGE>

Description

BACKGROUND OF THE INVENTION Core/sheath fibers and yarns are well known in the existing prior art. They comprise at least two fiberforming materials, usually polymers of different types and/or of different properties. At least one of the polymers forms the core of the finished fiber, while at least one other forms the sheath. It is a goal of the prior art to produce perfectly concentric structures, which constitute superior products.

Such fibers have substantial advantages. lor •J example, by appropriately selecting the materials of which the core and sheath are made, the overall mechanical properties of the fiber may be varied widely. One set of properties is found in the sheath, while another set of properties results from the core. .. ..- i " l:or example, flame m s i 5 t a nc c can be imparted to the core by die use of certain auoitives; at tbc same time, the sheath can be selected foi its slienf'ih or load carrying properties. Similarly, complementary libeis of this type can be used to prepare filter materials. Also, contrasting properties can be provided where needed.

However, if thin fibers to be spun into yarn are desired, the previously known equipment for doing so was highly complex and awkward to use. Due to the separate supply lines necessary to bring the plurality of fiber-forming materials to each die capillary (of a plurality of die capillaries) in order to form filaments, the devices comprise a large number of complicated individual parts which are expensive to produce.

Moreover, dismantling, cleaning, and servicing such devices becomes a delicate and time consuming operation.

In one previously known pack, the core polymer is introduced through tubular members which extend into the material forming the sheath. In order to accomplish this, the pack is made up of an upper distributor and a lower spinneret plate. The latter contains die capillaries having very small diameters. At the same time, the entry channels are relatively wide in order to receive the core tubes. The device is set up so that all of the tubes are as concentric as they can be to the entry channel of, the die. - 2 IE 902617 However, this device suffers from a number of serious disadvantages. Most importantly, it is no I possible to get more than four die capillaries per square centimeter of die area. Furthermore, the delicate nature of the fine tubes presents serious problems in dismantling, cleaning, and reinsta 1 lation . A further serious problem resides in the positioning of the core tubes. Due to the fragility of these tubes, cleaning and servicing of the pack virtually precludes maintaining the bore tubes precisely concentric during the life oi the devices, without the necessity of extreme care and adjustment.

When the above maladjustment occurs, and corc/sheath fibers having substantial differences in viscosity between the core and the sheath arc being produced, a substantial proportion of the individual fibers will exhibit pronounced kneeling and have a tendency to stick to the spinneret plate, thus interrupting production. Kneeling occurs when two 1iher-forming materials each occupy a certain proportion of the total cross section of flow and both are subjected to the same pressure conditions. This will force time into different flow behaviors resulting from the different viscosities; the lower viscosity component will flow more rapidly so that the cross section of its flow will be reduced. -3IE 902617 After extrusion t rum the die capillary, the speeds ol flow of the sheath and ton: are matched once again. Thus, the two materials again occupy the original proportion of the total cross section dictated by their respective volumes. However, due to normal inertia of the fiber, there is a delay before the matching of speeds occurs. Therefore, the low vi’seusity component is still moving taster than the high viscosity component after the fiber passes through the die orifice. In sucii a case, if ) the components are not precisely concentric, the fiber will knee L as a result.

The problem of precisely centering the various channels with respect to each other is a serious one.

There are many factors which cause unpredictable variations, even alter the devices have been manufactured. Obviously, there are the ever-present unavoidable production tolerances, both as to the location of the centers of the channels and the positions of the receiving bores for the locating pins on the elements of packs.

Moreover, even if the pack is properly set when new, it can easily become misaligned due to the necessary servicing during its life. The necessary disassembly, cleaning, reassembly, adjustment, etc. all provide b opportunities for misalignment. As a result, it becomes difficult (and hence expensive) to provide and maintain devices which will produce fine fibers in coro/sheath form - 4 IE 902617 If the production cost tor such fibers arc to remain within ccouomicaj1y acceptable limits, extremely close tolerances simply cannot be used. Since a large number of die capillaries are necessary, allowance must be made for the substantial portion which will exhibit the variations due to tolerance aqd handling. Extensive spinning tests have corroborated this.

One attempted solution has been to guide the core tubes into the channel openings by suitable elements.

Those which arc star-shaped have frequently been used. However, it is not possible to obtain a high die capillary density and the costs and complications of such devices (particularly during cleaning and reassembly) render them unsatisfactory.

In U.S. Patent 4,052,146, there is disclosed a device wherein the annular cavities (which form the sheath) are offset vertically from each other so that they can be partially interleaved. The annular channels which form the sheath are flat and arranged around the extension of the die channels. However, the external diameters thereof limit the capillary density which can be obtained, even if the annular channels are offset in height and overlapping. Even with this arrangement, however, the density of the die capillaries achieved is still only less than three per square centimeter.

I ii European Application 2 84 , 784, the core tubes arc replaced by lamellas which are fixed together and traverse entire rows oi the inlet openings. This assists in alleviating some ol the foregoing problems; however, misalignment oi the co re - ι ο π» i ng and shea t h-lorming elements still occurs because ol unavoidable manufacturing tolerances. The cylindrical side channels require greater volume than the usual spinning channels and the separate polymer feeds may result in differences in the thickness of the sheath. This, of course, will produce the kneeling effect previously described herein. Moreover, all of the known devices, because of the high precision necessary in their manufacture, are relatively expensive.

DESCRIPTION UF THF. PRESENT INVENTION It is, therefore, among the objects of the present invention to provide an pack which permits the spinning of core/sheath tibers from at least two different molten or dissolved polymers having differing properties, e.g. viscosities. It is also among the objects of this : invention to provide such a pack which will produce concentric fibers of this type with precision. It is further among the objects ol this invention to provide a device wherein there is a high density of die capillaries per square centimeter of spinneret, area under the same ) production conditions as are currently used for single component fibers. It is still further among the objects of the present invention to provide a device which can be used with existing, equipment. - 6 IE 902617 The known basic packs fur the production o£ hili 111 -componeiit fibers are arranged side-by-side and consist of a distributor and a spinneret plate. The fibers arc spun from mol ten or dissolved materials, preferably synthetic polymers, and have cross sectional structures formed trout at least two polymers having different properties. In accordance with the present invention, a thin separating plate is located between the distributor and the spinneret plate and the polymers used are guided through the separating plate in independent streams. Thereafter, the streams enter the exit channel in the spinneret plate which may have an enlarged entry diameter at its upstream end.

The laminar streams do not mix and Lite composite core/sheath fiber is produced when the streams exit the spinneret plate through the die capillary. The die openings are frequently circular, but need not be so. The fiber can be hollow if desired; one way of producing this is to make the core in the form of an annulus having a diameter smaller than that ot the outer annulus. ΡΠΤΑίΙ.Πη ObSCR 1 ΡΤΙϋΝ Ob' THE INVENTION The present invention comprises an pack for spinning core/sheath fibers from the plurality of fiber-forming materials. The pack, broadly includes a spinneret plate, a separating plate superposed thereon, and a distributor located on the separating plate. The distributor lias a first conduit which receives a first - 7 IE 902617 polymeric material ano a second conduit which receives a second polymeric material. These materials are conveyed by their respective conduits in first and second streams to the separating plate.

This plate comprises the core cavity and an annulus surrounding it. There· is a sheath channel which fluidly connects the first, conduit with the annulus and a core channel correspondingly which fluidly connects the second conduit and the core cavity.

Thus, che two streams flow through the separating plate to the spinneret plate. Ί lie latter contains an exit channel which leads to the die capillary at the downstream end thereof. The annulus and cure cavity feed into this channel so that the streams are joined at this point, but do not mix. As previously indicated, the entry diameter of the exit channel must be at least as large as the diameter of the annulus. I:, is, of course, preferable that the entry diameter be larger than the diameter of the annulus in order to allow for variations in the alignment of the plates. It is also preferred that the exit channel have an intermediate section which has a diameter smaller than the entry diameter, but largei than the diameter of the die capillary.

BRIEF DESCRIPTION Ol· TIIE_ URA]. I NGS In the accompanying drawings, constituting a part hereof, in which like reference· characters indicate like parts, l-igure 1 is a section through the lirst ciabodimcnl of the pack of the present i nven tion; Figures 2, 4, 6, f, 8 are views similar to that of figure 1 showing additional embodiments of the present invention; figures 3 , , 7, 5 9 arc cross sections of libers produced by the packs of figures 2, 4, 6, and 8, respectively; Figure 10 is a cross section of a separating plate and the tool useu to produce the annular channe1; and Figures 11 to 14 arc schematic plan views of various embodiments of separating plates.

Referring first to figure 1, there is provided pack 1 comprising distributor /, separating plate 3, and spinneret plate 4. Distributor 2 consists of sheath feed and core feed ΰ. Sepa ra t i nj; 1 y ! (: 3 i s provided with sheath channel 9 which, at its υ ρ pe r end , is open to shea th feed 5 and, at its 1 o w ei end , i s conuected t o annulus 7. Correspondingly, core channel 10 connects core feed 6 with core cavity ,8. - 9 IE 902617 Spinneret plate Ί contains exit channel 12 which comprises entry 13, section ! «I, and die capillary 11. As can be seen in figure 1, the diameter ol entry 13 is greater than that of any por t ion of exit channel 12 a n d also exceeds the diameter of annulus 7. The latter is an important feature of the present invention, since it k permits substantial inaccuracy in the alignment of separating plate 3 (and hence annulus 7 and core cavity 8) and spinneret plate 4. Thus, even though separating plate 3 is out of alignment with spinneret plate 4 by an amount 16, the diameter of entry 13 is sufficient to receive the entire polymer stream from annulus 7. The conical shape preserves the concentricity of the finished product. Moreover, this configuration can even accept non concentricity of core cavity 8 and annulus 7.

In operation, a first polymeric material is led into sheath feed 5 and a second polymeric material is fed into core feed 6. The streams formed thereby arc conveyed through sheath channel 9 and core channel 10 to the annulus 7 and core cavity 8, respectively. They exit therefrom into entry 13 of exit channel 12, flow through wide section 14 and are extruded from die capillary 11.

The misalignment which has been shown in figure 1 is equally applicable to all embodiments of the present invention. However, for simplicity, this has not been illustrated in any ol the remaining figures.

Figure 2 shows a second embodiment of the present' invention. It is substantially similar to that of Figure 1, except that there are two sheath channels 9, whereby the material in sheath fcco 5 is conveyed to annulus 7 at two points, preferably d i arne t r i ca 11 y opposite each other.

This can be usea to etiect superior flow in annulus 7 if • » desired. Otherwise, it is the same as the first embodiment. Fiber 19 (sec Figure .3), which is produced by the packs of Figures 1 or i, comprises sheath 17 and core 18.

A third embodiment is shown in Figure 4. It is substantially the same as the previous embodiments except that core cavity 8 extends through the entire thickness of separating plate 3 and both sheath iced S and core teed 0 are open thereto. Thus, fiber 19 (see Figure 5), which is produced by this embodiment, comprises sheath 17, core 18, and arc 20. in essence, core 18 is of semi-circular cross section, and fiber 19 is really half solid fiber and half corc/shcath fiber.

A fourth embodiment of the present invention is shown in Figure 6. In this embodiment, there arc two sheath feeds 5 and a single core feed 6. This permits the Jormation of fiber 19 (Figure 7) wherein sheath 17 comprises first arc 20 and second arc 21 of different materials. Λ fifth embodiment, which is essentially a reversal of the fourth embodiment, is shown in Figure 8. -11IE 902617 Here, there arc two core feeds 6 and a single sheath feed . As is shown in Figure 9, fiber 19 resulting therefrom comprises sheath 17 and a core composed of fiisl semi-circle LT and second sens i · c. i rc 1 e 23. These can he of different materials.

The preferred method of producing separating plate 3 is shown in Figure 10. Rotary tool 24 is provided with teeth 2S. These grind out annulus 7 in separating plate 3. As a result, annulus 7 is of constant thickness throughout its periphery and variation thereof (which is greatly to be avoided) is substantially eliminated.

Figure 11 is directed to the embodimcni of Figure 6. Sheath channels 9, core channel 10, as well as annulus 7 and core cavity 8 are all visible. Figure 12 is the corresponding view of separating plate 3 of Figure 2, Figure 13 corresponds to Figure 1, and Figure 14 shows the embodiment of Figure 8.

One of the advantages of the present invention is that it permits the easy conversion of existing packs to those of the present invention. It is only necessary to disassemble the distributor and spinneret plate, insert the separating plate of the present invention, and reassemble the pack.

In producing the separating plate of the present invention, it has been found advantageous to use a rotary tool in order to cut the annulus. The specific method of accomplishing this is not critical, although the use of a toothed tool or an erosion electrode has been found satisfactory. bun to the rotary method of manufacturing, tiie annulus is precisely concentric with the core cavity anu is of constant thickness around its entire periphery.

Because of the foregoing accuracy, it is possible to produce fibers with very precise concentric cross sections, even though there are variations in spacing resulting from unavoidable manufacturing tolerances. Moreover, the die capillaries can be located much closer together than would be possible using the packs of the prior art. In addition, the precision possible with the present invention eliminates ur minimizes the undesirable kneeling of the spun fibers as they exit the die capillary. Finally, the present invention is able to achieve higher throughputs (even exceeding two kilograms per minute) while maintaining excellent quality.

As a result of substantial experimentation with the present device, a number of phenomena were observed. The centering of the core is substantially dependent on the constancy of the width ot the annular channel. Therefore, precise alignment of the core and sheath producing elements of the pack is not necessary. It is only required that no portion oi the annulus be outside the entry portion of the exit channel in the spinneret plate. Thus, if this portion ol. the exit channel has a diameter substantially latgcr than that ol the annulus, considerable variation can be tolerated without impairing the concentricity of the finished product. - 13 IE 902617 As a matter of fact, even eccentricity oi core channel inside tire annulus does not aiieci. the cross section of the fiber, provided only that the channel walls do not intercept. In similar fashion, the type and position of the entrance of the channels does not, within wide limits, affect the fiber cross section. Thus, the closeness of the die capillaries is limited only by the diameter of the exit channel and the requirements lor strength of the elements of the pack. The remaining portions of the present invention require virtually no space which extends beyond the enlarged entry diameter of tiie exit channel; as a result, it is possible to achieve in excess of ten die capillaries per square centimeter of spinneret plate.

The present invention avoids small delicate parts, and provides compact components wherein the various channels needed to shape the fiber cross section are within the device, so that no vulnerable parts project therefrom. Moreover, the components arc planar and are superposed so that no complex interconnections are required. Simple locating pins and complementary bores arc satisfactory for this purpose. As a result oi the foregoing, the devices of the present invention are strong and can withstand the necessary dismantling, cleaning, and reassembly.

In summary, the device of the present invention provides great flexibility in installation, removal, and use. For example, a hollow fiber may be produced by - 14 IE 902617 simply making Lin..· core annular in cross section. Such oilier and furthei mod i i t c a t i oils of.' the present invention may be made without departing from the scope or spirit thereof. Although, only a limited number of specific embodiments of the present invention have been expressly described, it is, nonetheless , to be broadly construed and not to be limited except by the character of the claims appended hereto.

Claims (14)

1. I CLAIM

1. A pack for spinning a co re/sheath fiber from a plurality of f iber-ί ormiitg ma tcrials , said pack comprising a distributor, a spinneret plate, and a separating plate therebetween, said distributor having at least one first conduit and at least one second conduit, said first conduit adapted to convey a first material in a first stream in a downstream direction, and said second conduit adapted to convey a second material in a second stream in said downstream direction, said separating plate comprising a core cavity, an annulus, having an annulai diameter and surrounding said cavity, a sheath channel fluidly connecting said first conduit and said annulus, and a core channel fluidly connecting said second conduit and said cavity, said spinneret plate comprising an exit channel having a die capillary at its downstream end and being fluidly connected to said annulus and said core cavity at its upstream end, said die capillary having a die diameter, said entry channel having an entry having an entry diameter at least equal to said annular diameter, said entry located at or adjacent said upstream end, whereby said first stream surrounds said second stream and both arc cxtriiacd through said die capillary as said fiber. - 16 IE 902617

2. The pack of Claim 1 wherein said annulus comprises an annular channel having a substantiaiiy constant width.

3. The pack of Claim 2 wherein said entry diameter is larger than said annular diameter. 1 . The pack of Claim 2 wherein said exit channel further comprises a section having a section diameter smaller than said entry diameter, larger than said die diameter, and located between said upstream end and said die capillary.

4. 5. The pack of Claim 2 wherein there is a plurality of sheath channels.

5. 6. The pack of Claim 4 wherein there are two sheath channels.

6. 7. The pack of Claim 2 wherein there is a plurality of core channels.

7. 8. The pack of Claim 6 wherein there are two said core channels.

8. 9. The pack of Claim 2 wherein there is a third conduit adapted to convey a third material in a third stream in said downstream direction, said core cavity or said annulus being fluidly connected to said third conduit by said sheath channel or said core channel. - 17 IE 902617 It). The pack ol Claim y wherein said third conduit is connected to said sheath channel.

9. 11. The pack of Claim 9 wherein said third conduit is connected to said core channel . »

10. 12 . The pack oi Claim 2 wherein said die capillary is non-circular.

11. 13. The pack of Claim 2 wherein said die capillary is substantially circular. Id. The pack of Claim 2 wherein said separating plate further comprises at least one locating pin normal to said plate or said distributor, a complementary recess in said distributor or said plate adapted to receive said pin, whereby said separating plate is secured to said distributor. 13. The pack of Claim 2 wherein there arc at least 1(J said die capillaries per square centimeter. IΟ, Tho pack ol Claim 2 wherein said first material and said second material have different viscosities. 1 . The pack of Claim 2 wherein at least one of said ίiher-forming materials is in solution. 18 IE 902617

12. 18. A pack lor spinning hollow libers from at least one £iber-forming material, said pack comprising a distributor, a spinneret plate, and a separating plate tberebe tween, said distributor having a conduit adapted to convey said material in a stream in a downstream direction, said separating plate comprising an annulus having an annular diameter, a sheath channel fluidly connecting said conduit anti said annulus, and an annular core cavity, a spinneret plate comprising an exit channel with a die capillary at its downstream end, said channel being fluidly connected to said annulus and said annular core cavity at its upstream end, said die capillary having a die diameter, whereby said stream is extruded through said die capillary to form said hollow fiber. ly. A pack for spinning a core/sheath fiber from a plurality of f i her-f uniting materials, said pack comprising a distributor, a spinneret plate, and a separating plate therebetween, -

13. 19 IE 902617 said distributor having at least one first conduit and at. least one second conduit, said first conduit adapted to convey a first material in a first stream in a downstream direction, and said second conduit adapted to convey a second material in a second stream in said downstream direction, » said separating plate comprising a core cavity; an annulus having an annular diameter, a substantially constant width, and surrounding said cavity; a sheath channel fluidly connecting said first conduit and said annulus’, and a core channel fluidly connecting said second conduit and said cavity, said spinneret plate comprising an exit channel having a circular cross section die capillary at its downstream end and being fluidly connected to said annulus and said core cavity at its upstream end, said die capillary having a die diameter, an entry channel having an entry having an entry diameter greater than said annular diameter, said entry located at or adjacenL said upstream end, said exit channel having a section with a section diameter smaller than said entry diameter, larger than said die diameter, and located between said upstream end and said die capillary , whereby said first stream surrounds said second stream and both arc extruded through said die capillary as said fiber. - 20 IE 902617

14. 20. The pack of any of the preceding claims, substantially as described herein with reference to one or more of the accompanying drawings.