WO2000073545A1

WO2000073545A1 - Cooling device for cooling synthetic filaments

Info

Publication number: WO2000073545A1
Application number: PCT/NL2000/000351
Authority: WO
Inventors: Michael Maria Thomas Nuyten
Original assignee: Stork Screens BV
Current assignee: Stork Screens BV
Priority date: 1999-05-28
Filing date: 2000-05-22
Publication date: 2000-12-07
Anticipated expiration: 2001-11-28
Also published as: US20020090407A1; NL1012184C2; AU4956600A; CN1210447C; CN1353780A; CA2375541A1; DE19962398A1

Abstract

In a cooling device for cooling synthetic filaments using a cooling medium, in particular for use in the spinning of multifilaments, at least one cooling shaft (21), through which the filaments are passed, is arranged between an entry and exit for filaments. According to the invention, the cooling shaft (21) comprises a seamless, electroformed support (22) with passage-openings (23) which are separated by dykes, with the result that a uniform flow profile of the cooling medium is obtained in the cooling shaft (21) and the filaments are subjected to a uniform cooling treatment.

Description

Cooling device for cooling synthetic filaments

The present invention relates to a cooling device for cooling synthetic filaments, in particular for use in the spinning of (multi) filaments, which device comprises a housing with at least one inlet and at least one outlet for a cooling medium, and an entry for filaments which are to be cooled and an exit for cooled filaments, at least one cooling shaft being arranged between the entry and the exit, through which shaft the filaments are passed, and which cooling shaft is provided with openings allowing cooling medium to pass through. A cooling device of this nature is generally known in the art. Three different basic methods are used for the production of fibres or filaments, namely melt spinning, dry spinning and wet spinning, although there are many variations and combinations of these basic methods. It should, incidentally, be noted here that in the present application the term "spinning" is used in the broadest sense, namely that of the production of filaments, and is not limited to the production of filaments from staple fibres.

During melt spinning, a polymer is heated to a temperature above its melting point, and the molten polymer is extruded through a spinneret. A spinneret is a die with a large number of capillaries, the diameter and shape of which may vary. The jets of molten polymer which emerge from the capillaries are passed through a cooling zone, where the jet of polymer solidifies, resulting in the formation of a continuous filament. During dry spinning, the polymer is dissolved in a suitable solvent, and the solution thus obtained is extruded under pressure through a spinneret. The jets of polymer solution are passed into a heating zone, where the solvent evaporates from the polymer and the filament solidifies. During wet spinning, the polymer is likewise dissolved in a suitable solvent, and the solution thus obtained is extruded through a spinneret, which spinneret is submerged in a so-called coagulation bath. Precipitation or chemical regeneration of the polymer in the form of a filament takes place in this coagulation bath. The filaments thus obtained often have to undergo further treatments such as hot or cold stretching, twisting and texturing in order to obtain (multi) filaments having the desired properties for the intended end use.

In the case of melt spinning, either of monofilaments or of multifilaments, the cooling after the extrusion step is of essential importance, since the uniformity of cooling has a direct influence on the physical parameters of the filaments, such as the uniformity of the thickness of the filaments or the dyeability. In general, it is assumed that variations in these properties in the longitudinal direction of the filament and between different filaments are caused by a non-laminar or turbulent flow of the cooling medium, usually cooling air. In the cooling zone, the molten filaments have to be cooled to below the melting point of the polymer before the filaments are able to come into contact with one another or with components of a device used for the production, such as guides.

In order to expose the molten and extruded filaments to a cooling-air treatment which is as uniform as possible, all kinds of expensive cooling systems and methods have been devised, requiring complex air-distribution, control and homogenization devices in order to direct the turbulent cooling air and to be able to feed it in laminar form.

In a system which is known in the art, use is made of a cooling shaft, at least part of which is provided with openings allowing the cooling medium to pass through. A cooling shaft of this nature is arranged, optionally directly, beneath one or more spinnerets of a spinning device and may optionally be operated with forced feed and/or discharge of cooling air. Examples of systems of this nature are described in DE-A-42 20 915, DE-A-42 23 198 and O-A-93/19229. In the cooling systems for cooling (multi) filaments which are known from these publications, a cooling shaft which is generally composed of a screen cloth or a tube which is perforated with holes and slots is used. More specifically, as examples of a cooling shaft of this nature WO-A-93/19229 mentions a metal screen, in which case relatively large holes are arranged close together over the entire surface, and a perforated shaft which is provided with perforations over its entire surface. The holes have a diameter of 1-5 mm, with a maximum passage of 50%. In Example 1 of this document, a screen cylinder with a mesh density of 600/cm² is used. In the cooling system according to DE-A-42 20 915, a cooling shaft which is composed of a screen cloth or a cooling shaft whose walls are perforated with small holes and slots is used. The cooling shaft according to DE-A-42 23 198 is designed in the same way as that described in DE-A-42 20 915. The shape of the cross section of the cooling shaft is adapted to the form of the spinneret arrangement . In the case of the spinning of multifilaments, each filament bundle is preferably surrounded by a cooling shaft . If a cooling shaft is made from screen material, it is necessary for this screen material to be supported at various locations, and the ends have to be attached to one another, for example via a weld seam. This need for supporting measures and joints means that "dead" zones may form in the cooling shaft, and local heating of the virtually stationary cooling air in dead zones of this nature - since heat is transferred from the hot filaments to the cooling air - interferes with the desired stable (laminar) flow of the cooling air. Consequently, the filaments are not subjected to a uniform cooling treatment, which may give rise to variations in the physical properties of the product. With a cooling shaft with large perforations, the risk of disruption to the desired laminar flow profile is also present, partly because the speed of movement of the filaments exerts a sucking action on the cooling air. The object of the present invention is to at least partially eliminate the above drawbacks and, in particular, to provide a cooling shaft in which the risk of dead zones occurring is reduced further.

In the cooling device of the type described above according to the invention, the cooling shaft comprises a seamless, electroformed support with passage-openings which are separated by dykes. According to the invention, the cooling shaft is produced without a seam by means of electroforming. During operation, a cooling shaft of this nature will be less susceptible to the formation of dead zones, with the result that the cooling treatment can be carried out more uniformly and thus a more uniform distribution of the properties in the filaments can be obtained. Furthermore, an electroformed cooling shaft of this nature is sufficiently strong and resistant to bending, so that further supporting measures are not required.

For the electroforming of the cooling shaft, a die is used in which a system of electrical conductors which delimit isolating islands is provided. The electrical conductors define the dykes which are to be formed, and the isolating islands define the passage-openings which are to be formed. In an electrolysis bath, metal is electrodeposited on the electrical conductors to a desired thickness, after which the product thus obtained is removed from the die. On the other hand, it is possible in the same way firstly to deposit a base skeleton of the cooling shaft on the die, which is allowed to grow further after it has been removed. In general, dies which are circular in cross section are used, so that the electroformed cooling shaft is also circular in cross section. Other shapes, such as oval or rectangular, are also possible, however. The number of openings per unit surface area can be selected as a function of the desired application, the type of polymer also being important. The length of the cooling shaft is kept as short as possible, so that the overall spinning device, of which the cooling device according to the invention forms part, can be kept relatively compact. It has been found that cooling shafts with lengths of the order of magnitude of from 20 mm to 50 mm and mesh numbers of approximately 50 to 100, in particular 60 or 70 mesh for a passage of 10 or 16% respectively, in practice function successfully for numerous applications. The thickness of an electroformed cooling shaft of this nature is usually of the order of magnitude of 100 micrometres, although both thinner and thicker cooling shafts may be used. The shape and dimensions of the cross section of the cooling shaft are adapted to the dimensions and shape of the spinneret. Preferably, the seamless, electroformed support is made from nickel, with the result that a cooling shaft with a long service life is obtained.

In a preferred embodiment of the cooling shaft according to the invention, the passage-openings which are separated by dykes are arranged in a regular pattern. Depending on the particular application, the seamless, electroformed support may comprise a first zone in which there are passage-openings separated by dykes, and a second zone without passage-openings, which adjoins the first zone, as is already known per se from the prior art. In another embodiment, an uninterrupted sleeve is arranged displaceably inside the seamless, electroformed support. This sleeve without openings is used to seal off some of the passage- openings in the electroformed support, so that the amount of cooling air and the location where cooling air enters can be adjusted by the displacement of the sleeve in the seamless electroformed support.

The invention also relates to a seamless, electroformed support with passage-openings which are separated by dykes, which is suitable for use in the cooling device according to the invention.

The invention also relates to a device for producing synthetic filaments in which a cooling device according to the invention is used, as defined in claim 7 et seq. According to a preferred embodiment of the invention, the extrusion head of the extrusion device used is connected to the entry to the cooling device, and more preferably each spinneret from which monofilaments which are combined to a filament bundle emerge is connected to a cooling shaft of the cooling device. According to a further preferred embodiment of the device for producing synthetic filaments according to the invention, the cooling device used has two outlets for cooling medium, one of which is arranged in the vicinity of the entry end of the cooling shaft and the other of which is arranged in the vicinity of its exit end. In this way, the cooling air supplied is discharged partially in cocurrent and partially in countercurrent with respect to the path of the filaments. Such a direction of the air flow promotes the uniformity of the cooling treatment.

The invention is explained below with reference to the drawing, in which:

Fig. 1 diagrammatically depicts melt spinning; and Fig. 2 diagrammatically depicts an embodiment of a cooling device according to the invention.

Fig. 1 shows a diagram for the melt spinning of a polymer, such as PET, during which process PET granules and, if desired, additives are fed via a hopper 1 to a screw-type extruder 2, in which the polymer is melted and then extruded. The extruded polymer is fed to a spinneret 6 via a metering pump 3, mixing device 4 and filter 5. The spinneret 6 is provided with a plurality of capillaries, out of which separate jets 7 of molten polymer are forced. The jets 7 of molten polymer are cooled using cooling air

(indicated by arrows) in a manner which is to be described in more detail; if desired, additives may be applied at the end of the cooling operation, such as a lubricant, after which the filaments which have been cooled separately in this way are combined to form a multifilament and are wound up for further processing. Further processing of this nature may, for example, comprise the stretching of the yarn in order to obtain the desired orientation in the yarns, and texturing.

Fig. 2 shows part of an embodiment of a cooling device according to the invention. A cooling device of this nature comprises a closed housing (not shown) in order to limit disruption to the cooling process caused by variation in environmental factors as far as possible. The housing is provided with an inlet and an outlet for a cooling medium and an entry and an exit for filaments. A cooling shaft 21, which comprises a cylindrical, thin-walled support 22 which is provided with a regular pattern of passage- openings 23, is arranged in the housing. The support 22 having passage-openings 23 is produced by means of electroforming as has already been explained above. In the situation shown, the top side of the cooling shaft 21 bears against a spinneret 6 with capillaries 24, but if desired it may be arranged at a distance therefrom so that a relatively large amount of cooling air can cool the filaments directly beneath the spinneret 6. A thin-walled, tightly fitting, cylindrical sleeve 25 is arranged displaceably inside the cylindrical support 22. The cylindrical sleeve 25, which does not comprise any openings in its wall, is provided with a base 26 with a passage 27 for cooled filaments.

Claims

1. Cooling device for cooling synthetic filaments (7), in particular for use in the spinning of multifilaments, which device comprises a housing with at least one inlet and at least one outlet for a cooling medium, and an entry for filaments which are to be cooled and an exit for cooled filaments, at least one cooling shaft (21) being arranged between the entry and the exit, through which shaft the filaments (7) are passed, and which cooling shaft (21) is provided with openings allowing cooling medium to pass through, characterized in that the cooling shaft (21) comprises a seamless, electroformed support (22) with passage-openings (23) which are separated by dykes.

2. Cooling device according to claim 1, characterized in that the seamless, electroformed support (22) is made from nickel.

3. Cooling device according to one of the preceding claims, characterized in that the passage-openings (23) which are separated by dykes are arranged in a regular pattern.

4. Cooling device according to one of the preceding claims, characterized in that the seamless, electroformed support comprises a first zone in which there are passage-openings separated by dykes, and a second, uninterrupted zone which adjoins the first zone.

5. Cooling device according to one of the preceding claims 1-3, characterized in that a displaceable sleeve (25) is arranged inside the seamless, electroformed support (22) .

6. Seamless, electroformed support (22) with passage-openings (23) which are separated by dykes, suitable for use as a cooling shaft (21) in the cooling device according to one of the preceding claims.

7. Device for the production of synthetic filaments, in particular for the spinning of multifilaments, which device comprises an extrusion device for the extrusion of a molten polymer mass through openings in an extrusion head, and a cooling device for cooling extruded filaments, characterized in that the cooling device is a cooling device according to one of the preceding claims 1-5.

8. Device according to claim 7, characterized in that the extrusion head is connected to the entry to the cooling device.

9. Device according to claim 6 or 7, characterized in that the extrusion head comprises one or more spinnerets (6) each spinneret (6) being connected to a cooling shaft (21) of the cooling device.

10. Device according to one of the preceding claims, characterized in that the cooling device comprises two outlets for cooling medium, one of which is arranged in the vicinity of the entry end of the cooling shaft and the other of which is arranged in the vicinity of the exit end of the cooling shaft.