GB2105641A - Manufacture of filamentary polymer tow - Google Patents

Abstract

A method and apparatus for the manufacture of filamentary polymer tow by melt spinning in which molten orientable polymer is extruded through a spinnerette plate to produce molten filaments which are cooled to solidify them and draw off at a rate sufficient to cause the required orientation of the filaments, said orientation being the sole orientation step in the process. Usually, (e.g. for use in cigarette filters) the filaments will be crimped after orientation. Thus, the filaments may be drawn off as aforesaid by draw off rollers and fed from the rollers to texturising equipment (preferably a stuffer box crimper) without further orientation, or the filaments may be drawn off as aforesaid directly by the texturising equipment or the filaments may be drawn off as aforesaid through a constant tension device (e.g. dancing arm) and thence into texturising equipment. Directly drawn filaments may be steam treated prior to texturing.

Description

SPECIFICATION Manufacture of filamentary polymer tow This invention is concerned with the manufacture of filamentary tow from orientable polymer.

In conventional melt spinning processes, orientable polymer granules are fed into an extruder where they are melted and the resultant melt forced through a filtration/metering system and thence through a spinnerette plate (i.e. a plate have a plurality of holes) yielding a plurality of molten filament streams. The molten filaments so produced are cooled (quenched) by an air stream of an intensity sufficient to cool the filaments but not so great that the filaments stick together.

Alternatively, the filaments may be cooled by passage through water or other convenient fluids sometimes containing spin finish or other additives acting as processing aids. Usually the air cooled filaments are drawn over a rotating lick roller system where a spin finish chemical is applied to the filaments and the drawing force is provided by a stand of rotating rolls acting as a capstan. Draw down (i.e. reduction in crosssectional area) of the filaments occurs between issuing of the molten filaments from the spinnerette plate and freezing of the filaments due to impingement of the cooling air stream. This draw down is called "melt drawdown".In the accompanying drawing of conventional apparatus, granules of orientable polymer are fed into the extruder (1). Molten polymer passes from the extruder through heated pipes, through a filter mechanism located in the spin beam and through melt metering pumps (2) which meter the melt to one or more spinnerette plates. Melt issues from the spinnerette plates in the form of multifilaments which are pulled away from the plates by a slow haul off stand of rollers (3) and in the process the filaments are treated with a spin finish by lick units (4) and are cooled by a stream of air (5).In order to achieve required filament size and properties in conventional spinning operations, the filaments are subjected to an orientation step involving heating the filaments in an oven, by hot air or steam or over a heated metal plate, or heated rollers (6) and stretching them by using a fast haul off stand of rollers (7) rotating at a higher speed than the rollers (3). The normal ratio of speeds of rollers (3) to rollers (7) is in the range 1 to 2 to 1 to 8. Following this orientation step the filaments may be crimped and packaged.

It is the basis of the present invention that it has been found that filaments exhibiting the desired properties may be manufactured by omitting the orientation step mentioned above and that simply by taking filaments orientated directly from the spinnerette plates filaments of acceptable properties may be obtained.

The invention provides a method and apparatus for the manufacture of filamentary.. polymer tow by melt spinning in which molten orieiiable polymer is extruded through a spinnerette plate to produce molten filaments which are cooled to solidify them and drawn off at a rate sufficient to cause the required orientation of the filaments, said orientation being the sole orientation step in the process.

Usually, (e.g. for use in cigarette filters) the filaments will be crimped after orientation. Thus, in accordance with the present invention, the filaments may be drawn off as aforesaid by draw off rollers and fed from the rollers to texturisiny equipment (preferably a stuffer box crimper) without further orientation, or the filaments may be drawn off as aforesaid directly by the texturising equipment or the filaments may be drawn off as aforesaid through a constant tension device (e.g. dancing arm) and thence into texturising equipment. Directly drawn filaments may be steam treated prior to texturing.

Apparatus required to manufacture filaments according to the invention may comprise a polymer chip feeding system to an extruder associated with a spinning beam comprising filter mechanism, melt metering pumps and spinnerette plates. The diameter of the holes in the spinnerette plates is smaller than normally associated with a given filament diameter where the conventional two stage drawn down system is employed. Filaments are drawn away from the spinnerette plates by means of a fast haul off stand of rollers and thence fed into a texturising device (preferably a stuffer box crimper) and packaging system or are drawn away from the spinnerette plate by means of a texturising device (e.g. stuffer box crimper) and thence fed to a packaging system.

Advantages provided by the present invention are that the capital cost of the manufacturing plant required is smaller and improved processing characteristics are obtained, i.e. there is no filament breakage at the second orientation stage (i.e. in an orientation chamber (oven 6)) and the necessity of applying spin finish chemicals to assist processing may be avoided. This is an advantage where this type of chemical might prove a toxicological hazard or affect the taste e.g. in the manufacture of cigarette filter tow.

The preferred filament denier range for filaments making up suitable tows is 1.5 to 1 5 and preferably 2.5 to 5.0 denier and the preferred total tow denier range is 25,000 to 45,000 denier.

The polymer used in the manufacturing operation may be a polypropylene homopolymer or copolymer of propylene and ethylene e.g. of melt index (230C 2.16 kgf) 12-40 g/1 0 mins, 20 g/1 0 mins being a typical example. However, other orientable polymers may be used (e.g.

polyethylenes, polyamides or polyesters). If desired, combinations of like or unlike polymers may be used, for example, to produce coextruded filaments with an annular sheath of a filament made from one polymer (e.g. polyethylene) and with a core of a filament made from another polymer (e.g. polypropylene).

For conventional cigarette filter tow, pigmentation of the filaments is necessary; any of or combinations of methods (a) to (c) below may be used; the pigment(s) employed would be titanium dioxide, calcium carbonate, silica or a combination of these.

a) using "mass coloured" compound (i.e. the feedstock polymer pigmented) b) using a masterbatch (i.e. adding to the feedstock polymer a proportion of highly pigmented polymer and blending the two to obtain a coherent mix) c) using a liquid "carrier" system in which the pigment(s) is suspended or dissolved and pumping this liquid into the feedstock polymer before or during extrusion (i.e. into the melt).

The spinnerette plates to manufacture the filaments may typically have 15,000 orifices each, though the number of orifices may vary in the range 250-25,000 depending upon the speed of offtake. In the present invention the spinnerette plates would preferably possess about 15,000 orifices each.

Orifice shape may typically be circular, pentalobal, I or preferably Y section. Hollow filaments may also be manufactured from orifices having non interconnecting slots arranged peripherally around arcs of circles of diameter 2 mm. In conventional spin processes a circular orifice to give the required filaments would typically have a diameter in the range 0.35 to 0.7 mm, whilst the equivalent orifice diameter to give suitable filaments by the present invention would be in the range 0.10 to 0.5 mm, preferably 0.432 mm. A Y section hole profile would be 0.56 mm x 0.18 mm with an aspect ratio of approximately 3:1 (i.e. ratio of leg length to width).

There are two types of conventional spinning processes both involving the two stage draw principle outlined. In type A processes the number of orifices in the spinnerette plate is relatively small (circa 200-500 holes) and filaments are produced from the spinnerette at high speed (circa 1000-3000 m/min). Groups of these filaments are collected together in a second operation until the required number is achieved (say 15,000) and then these filaments are subjected to the second draw stage, followed by crimping, packaging etc.

In type B processes, the number of orifices in the spinnerette plate is large (circa 15000) and the filaments are drawn from the plate at comparatively slow speed (circa 10-50 m/min) and then (as an in-line operation) subjected to the second draw stage followed by texturing, packaging etc.

In both processes the outgoing line speed (i.e.

after secondary draw) is usually circa 1 50 m/min to 300 m/min. This speed limitation is imposed by the speed at which conventional stuffer box crimping machines will operate.

In the present invention individual spinnerette plates will as mentioned above preferably have about 1 5000 orifices each, these orifices being smaller than those associated with the conventional spin (ass) processes as previously described. Preferably, the rate of draw off can be in the range 50 to 200 m/min and desired throughput of material achieved by having the appropriate number of spinnerette plates located within the spin beam.

EXAMPLES 1) A filamentary tow was produced according to the invention from a spinnerette plate having 10,400 orifices, orifice .0432 mm (circular) Draw down was 322:1 and filaments were pulled away from the die at 52 m/min. After texturing and processing of the tow on conventional cigarette filter rod making machinery it was found that a 120 mm long filter rod gave a pressure drop between the ends of 360mm water gauge at a flow rate of 17.5 ml/sec.

2) Filaments made as in example (1) were steam treated prior to texturing. The resulting tow gave cigarette filter rods having a pressure drop between ends of 280 mm water gauge at a flow rate of 1 7.5 ml/sec., rod length being 120 mm.

Filament denier was 3.85 denier and draw down effected from the spinnerette plate was 312:1.

Claims (21)

1. A method for the manufacture of filamentary polymer tow by melt spinning in which molten orientable polymer is extruded through a spinnerette plate to produce molten filaments which are cooled to solidify them and drawn off at a rate sufficient to cause the required orientation of the filaments, said orientation being the sole orientation step in the process.

2. A method according to claim 1 in which the filaments are crimped after orientation.

3. A method according to claim 1 or 2 in which the filaments are drawn off by draw off rollers and fed from the rollers to texturising equipment without further orientation.

4. A method according to claim 1 or 2 in which the filaments are drawn off directly by texturising equipment.

5. A method according to any preceding claim in which the filaments are drawn off through a constant tension device and thence into texturising equipment.

6. A method according to any of claims 3, 4 or 5 in which the filaments are steam treated before entering the texturising machine.

7. A method according to any preceding claim in which the tow has a filament denier range of 1.5 to 1 5.

8. A method according to claim 7 in which the filament denier range is 2.5 to 5.0.

9. A method according to claim 7 or 8 in which the total tow denier range is 25,000 to 45,000 denier.

10. A method according to any preceding claim in which the polymer comprises a polypropylene homopolymer or copolymer of propylene and ethylene.

11. A method according to any preceding claim in which each spinnerette plate has about 15,000 orifices.

1 2. A method according to any preceding claim in which each orifice has a diameter of 0.10 to 0.5 mm in the case of a circular orifice or an equivalent area in the case of a non-circular orifice.

1 3. A method according to claim 12 in which the orifice diameter is 0.432 mm.

14. A method according to any preceding claim in which the rate of draw off is in the range 50 to 200 m/min.

1 5. Apparatus for carrying out the method according to any preceding claim comprising an extruder for said polymer, at least one spinnerette plate through which molten polymer from said extruder can be extruded to produce molten filaments, means for cooling the molten filaments to solidify them, and means for drawing off the filaments from the spinnerette plate at a rate sufficient to cause the required orientation of the filaments, said means for drawing off the filaments from the spinnerette plate causing the sole orientation step in the apparatus.

16. Apparatus according to claim 1 5 in which said drawing off means comprises draw off rollers from which the filaments are fed to texturising equipment without further orientation.

1 7. Apparatus according to claim 1 5 in which said drawing off means comprises texturising equipment for drawing off the filaments directly.

18. Apparatus according to any of claims 1 5 to 1 7 comprising a constant tension device through which filaments are drawn off and from which they pass to a texturising machine.

19. Apparatus according to any of claims 1 6 to 1 8 in which means are provided for steam treating the filaments prior to texturising.

20. A method for the manufacture of filamentary polymer tow as claimed in claim 1 and substantially as hereinbefore described.

21. Apparatus for the manufacture of filamentary polymer tow as claimed in claim 1 5 and substantially as hereinbefore described.