IE71668B1 - 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

The present invention is directed lo an apparatus lor the spinning of corc/sheath fibers from various liberforming materials. It. is particularly characterized by permitting a high concentration ol fibers in a small area.

) BACKGROUND OF THE INVENTION Core/shcath libers 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 '·) example, by appropriately selecting the fhaterials 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. 71668For example, flame resistance can be j impart cd to the core by the use of certain aoditives; a I the same time, the sheath can be selected for its strength or load carrying properties. Similarly, complementary libers of this type can be used to prepare filler 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 (ol 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 lowcr spinneret plate. The latter contains die capillaries having very small diameters. At the same time, Lite 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 However, Lliis device suffers from a number of serious disadvantages. Most importanliy, it is not 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 reinstallation. Λ 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 of 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 iiber-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 them into different flow behaviors resulting from the different viscosities; the lower viscosity component will ilov more rapidly so thaL the cross section of its flow will be reduced. -3After extrusion 1 rul:: the die capillary, the speeds of flow of the sheath and coin are matched once again. Thus, the t-wo 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 viscosity component is still moving taster than the high viscosity component after the fiber passes through the die orifice. In such a case, if the components are not precisely concentric, the fiber will kneel 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 after the devices have been manufactured. Obyiously, there are the ever-present unavoidable production tolerances, both as to the location of the ccnLers 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 opportunities for misalignment. As a result, it becomes difficult (and hence expensive) to provide and maintain devices which will produce fine fibers in core/sheath form - 4 If die production cost lot such fibers arc to remain within economically 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 and handling. Extensive spinning tests have corroborated this.

One attempted solution has been to guide the core tubes into the channel openings hy 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 l!.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 und 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 ol' the die capillaries achieved is still only less than three per square centimeter.

In European Application 284,784, the core tubes are replaced by lainellas which are fixed together and traverse entire rows oi the inlet openings. This assists in alleviating some ol the loiegoing problems; however, misalignment ot the core-iorming and sheath-forming elements still occurs because of 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.

BRIEF DESCRIPTION OF THE PRESENT INVENTION It is, therefore, among the objects of the present invention to provide an pack which permits the spinning of core/sheath libers 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 of 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 The known basic packs lor the production of mulli-component libers are arranged side-by-side and consist of a distributor and a spinneret plate. The fibers arc spun from molLen or dissolved materials, preferably synthetic polymers, and have cross sectional structures formed from at least two polymers having different properties. In accordance with the present invention, a tbin 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 cuter 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 the 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 oL the outer annulus. ΡΕΤΑΙΙ.ΠΡ DbSCK 1PTION Ol·' 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 has a first conduit which receives a first - 7 polymeric material and 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, the two streams flow through the separating plate to the spinneret plate. Ihe latter contains an exit channel which leads to the die capillary at the downstream end thereof. The annulus and core cavity iced 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. It. is, of course, preferable that the entry diameter be larger than the diameter of the annulus in order to allow lor variations in the alignment of the plates. It is also preferred that the exit channel have an intermediate section whii.li has a diameter smaller than the entry diameter, but larger than the diameter* of Lhe die capillary. ·«> BRI lib DESCRIPTION Ob TJ1L_ ΒΚΛίϊ lhGJi In the accompanying drawings, constituting a part hereof, in which like reference characters indicate like parts, - 8 Figure 1 is a section through the first embodiment of the pack of (lie present invent ion; Figures 2, 4, 6, ξ 8 are views similar to that of Figure J 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, ύ, and 8, respectively; Figure 1(1 is a cross section of a separating plate and tiie tool useo to produce the annular channel; and Figures 11 to 14 arc schematic plan views of various embodiments ot separating plates.

Referring first to Figure 1, there is provided pack 1 comprising distributor Z, separating plate 3, and Spinneret plate 4, Distributor 2 consists of sheath feed 5 and core feed 0. Separating plate 3 is provided with sheath channel 9 which, at its upper end, is open to sheath feed 5 and, at its lower end, is connected to annulus 7. Correspondingly, core channel 10 connects core feed 6 with core cavity 8. - 9 Spinneret plate 4 con la ins exit channel 12 which comprises entry 13, section 14, and die capillary 11. As can be seen in Figure I, the diameter oi entry 13 is greater than that of any portion of exit channel 12 and also exceeds the diameter of annulus 7. The latter is an important feature of the present invention, since it 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 spiuneret 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 fed into sheath feed 5 and a second polymeric material is fed into core feed 0. 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 Jias Been shown in Jig lire 1 is equally applicable to all embodiments of the present invention. However, for simplicity, tliis Jias not been illustrated in any ol the remaining figures. - 10 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 feco 5 is conveyed to annulus 7 at two points, preferably diametrically opposite each other. This can be used to effect 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 2, 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 5 and core feed 6 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, cote 18 is of semi-circular cross section, and fiber 19 is really half solid fiber and half corc/sbcath fiber.

A fourth embodiment of the present invention is shown in Figure 6. In this embodiment, there are two sheath feeds 5 and a single core feed 6. This permits the formation of liber 19 (Figure 7) wherein sheath 17 comprises first arc 20 and second arc 21 of different materials. A fifth embodiment, which is essentially a reversal of the fourth embodiment, is shown in Figure 8.

-III <.· Here, there arc two core feeds 0 and a single sheath feed . As is shown in Figure 9, fiber 19 resulting therefrom comprises sheath 17 and a core composed of first semi-circle 22 and second semi-circle 23. These tan be of different materials.

The preferred metbod of producing separating plate 3 is shown in Figure 10. Rotary tool 24 is provided with teeth 25. 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 embodiment 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 bas been found advantageous to use a rotary tool in order to c:ut the annulus. The specific method of accomplishing this is not critical, although the use of a - 12 toothed tool or an erosion electrode has been found satisfactory, hue to the rotary method of manufacturing, the annulus is precisely concentric with die 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 witli the present invention eliminates or minimizes the undesirable kneeling of the spun fibers as they exit the die capillary. Finally, the present invention is able co 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 wiut.li of 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 ol the annulus be outside the entry portion of the exit channel in the spinneret plate. Titus, if this portion of the exit channel lias a diameter substantially latger than that of the annulus, considerable variation can be tolerated without impairing the concentricity ol Lite finished product. - 13 As a matter of fact, even eccentricity ol core channel inside the annulus does not affect the cross section of the fiber, provided only that the channel wails 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 for 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 the exit channel; as a result, it is possible to achieve in excess of ton 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 arc within the device, so that no vulnerable parts project therefrom. Moreover, the components are planar and are superposed so that no complex interconnections are required. Simple locating pins and complementary bores are satisfactory for this purpose. As a result of the foregoing, the devices of the present invention arc 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. l;or example, a hollow fiber may be produced by - 14 simply making ihe core annular in cross section. Such other and further modifications 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 (13)

1. Apparatus for the spinning of core-sheath fibres from at least two different molten or dissolved polymers having the same or different viscosity, comprising a spinneret plate (12) having a number of capillaries (18) and enlarged preliminary channels (20, 22) opposite them, a distributor plate (14) having a number of guide channels (24, 26) for the divided supply of the corresponding number of materials for spinning, in combination, a preliminary plate (16) arranged between the distributor plate (14) and the spinneret plate (12), which contains an annular channel (20, 22), which for its part surrounds a central channel (32), wherein each annular channel (28) is connected by at least one supply channel (20) to the guide channel (24) lying thereabove, to which the sheath-forming material is introduced, and wherein each central channel (32) is connected by at least one supply channel (34) to the guide channel (26) lying thereabove, to which the core-forming material is introduced, characterised in that the width of the annular channel (28) is constant over its whole periphery, that the outer cross-section of the annular channel (28) is smaller than that of the corresponding inlet opening (22) in the preliminary channel (20).

2. Apparatus according to claim 1, characterised in that the preliminary channels (20) in the spinneret plate (12) have conicallybroadened inlet openings (22).

3. Apparatus according to claims 1 to 2, wherein the guide channel (24) for sheath material is connected via at least two supply channels (42) in the preliminary plate (40) with the annular channel (44).

4. Apparatus according to claims 1 to 3, wherein the central channel (66) extends through the whole preliminary plate (60) and is there open to both guide channels (24, 26).

5. Apparatus according to claims 1 to 4, wherein the distributor plate (82) is provided with three guide channels (86 , 88 , 90) for three different materials, which are each connected with one of three supply channels (94, 96, 100) in the preliminary plate (84). - 17

6. Apparatus according to claim 5, wherein the annular channel (92) with two supply channels (94, 96) in the preliminary plate (84) is connected with two guide channels (86, 90) in the distributor plate (82).

7. Apparatus according to claim 5, wherein the central channel (136, 216) is connected with two supply channels (138, 140, 218, 220) in the distributor plate (124).

8. Apparatus according to one of claims 1 to 7, characterised in that channels (28, 32) are provided in the preliminary plate (16) for at least ten capillaries (18) per cm die area.

9. Apparatus according to one of claims 1 to 8, characterised in that the preliminary plate (16) is a thin plate which is planar on both sides, is fixed by locating pins and has no teeth.

10. Apparatus according to one of claims 1 to 9, characterised in that the spinneret (12) is provided with capillaries (18) which are adapted for the spinning of non-circular fibres and/or those having a hollow space.

11. A process for the preparation of core-sheath fibres comprising at least two different fibre-forming materials having the same or different viscosity, by using the apparatus according to one of the preceding claims.

12. Apparatus according to one of the preceding claims comprising a spinneret plate (12) for the spinning of multi-component fibres of the side-by-side type, and a distributor plate (14), characterised in that this is adapted to a spinning apparatus for core-sheath fibres by interposing a preliminary plate (16) between spinneret plate (12) and distributor plate (14).

13. Apparatus for the spinning of core/sheath fibres according to any of the preceding claims and substantially as described herein with reference to and as shown in the accompanying drawings.