GB1594099A - Synthetic hollow filaments - Google Patents

Description

IMPROVEMENTS IN SYNTHETIC HOLLOW FILAMENTS (71) We, PLASTICISERS LIMITED, a British company, of Old Mills, Drighlington, Near Bradford, Yorkshire, BD11 lBY, England, do hereby delare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to improvements in synthetic filaments especially hollow filaments.

It is an object of the invention to provide hollow synthetic filaments having bulk, which retain their bulk at high draw ratios and which will also retain their bulk under lateral compressive forces.

According to the invention a synthetic filament is provided which has a crosssection composed of at least three elongated branches, the inner ends of the branches being integral with one another throughout the length of the filament and the outer end of each of said branches along the length of the filament being so disposed as to define with an adjacent branch a continuous lon gitudinal hollow lobe along the length of the filament, the number of hollow lobes thus defined being equal to the number of branches. Each outer end of each branch may over intermittent portions along the length of the filament be integral with the said adjacent branch but preferably each outer end of each branch is integral with the said adjacent branch over the whole length of the filament.Filaments having a plurality of such continuous longitudinal hollow spaces along their lengths are herein termed multihollow-lobed filaments. The ratio of length to thickness in each branch should be at least 5 to 1 and is preferably 11.5 to 1 with a thickness of 0.2 mm.

Preferably the filaments have four branches i.e. are quadri-hollow-lobed filaments and are composed of propylene homopolymers or copolymers e.g. with a minor proportion of ethylene.

The filaments may be produced by meltextrusion through a spinneret, the orifice having a configuration corresponding to the cross-section of the filament to be formed except that the outer end of each branch must of necessity be spaced from the adjacent branch with which is defines a hollow space. The viscosity of the melt and the rate of extrusion are chosen such that the crosssection of the filament is maintained during the period between extrusion from the spinneret and subsequent solidification of the filament, the outer end of each of the branches preferably becoming integral with its adjacent branch during this period. In the most preferred embodiment all the defined continuous longitudinal hollow spaces are totally enclosed throughout the length of each filament.When such filaments are stretched (i.e. longitudinally oriented) the outer ends of the cross-sectional branches may break away from their adjacent crosssectional branches along a part or along several parts of the length of each filament so that the outer ends of the cross-sectional branches are only intermittently integral with an adjacent branch along the length of the filament. The cross-section may thus vary along the length of the filament from that in which all the said hollow spaces are totally enclosed to that in which some or all the said hollow spaces are partially open. For a given orifice the thickness of the cross-sectional branches will depend principally on the rate of take off from the dyehead of the extrusion equipment and on the viscosity of the melt.

The cross-section of the filaments of the invention enables high bulk to be achieved which is retained on drawing and which withstands lateral pressure. Multibranch filaments of the prior art did not have good bulk properties particularly under lateral pressure or when crushed together since the branches of adjacent filaments tended to stack one alongside the other.

In the drawing accompanying the specification: Fig. 1 is a diagramatic illustration of a dieorifice for producing a filament of the invention with three branches.

Fig. 2 is a diagramatic illustration of a dieorifice for producing the preferred filament of the invention having four branches.

Fig. 3 is a diagramatic illustration of a die orifice for producing a filament of this invention having five branches.

Referring to Fig. 2 of the drawings a dieorifice has four branches 1, 2, 3 and 4 all of which are segments of different annular rings, the inner ends of the segments being integral at 5 and the outer end of each branch terminating immediately adjacent to but spaced from an adjacent branch, the space between being indicated in the drawing by the letter "d". The thickness of each branch is determined by the difference in the diameter P) of the circles defining the inner and outer faces of the branches.

Referring to Figs. 1 and 3 similar considerations apply except that in Fig. 1 there are only three branches and in Fig. 3 there are five branches.

The invention will be further described by reference to the following Examples which are purely illustrative.

Example I A 1" extruder fitted with 3 heating zones was charged with general purpose, medium flow polypropylene homopolymer designed for extrusion and blowing and having a nominal melt flow index of 4.0 (sold under Imperial Chemical Industries under the name Propathene Reg. Trade Mark grade GWE 28) melt flow index of 3.5 and was extruded with a temperature profile of 220/240/260"C. The extruder in question was fitted with a filament extrusion die-head in which there were 9 orifices having the configuration of Fig. 2 of the drawing in which P)1 was 1.3 mm, 2 was 0.91 mm and d was 0.1 mm. The multi-branched filaments which emerged from the die-plate were cooled by blowing cold air across them and were pulled away by a pair of Godet rollers.

The draw-down imposed on the multibranch filaments by these Godet rollers caused the free edge of each branch to merge with the adjacent branch whilst their surfaces were still molten such that they were welded into a continuous filaments each of which had four separate longitudinal continuous and enclosed air containing ducts running through them. Premature welding usually caused by too small a value for "d" must be avoided as this can cause a vacuum to form in the duct which collapses the filament.

The filaments were then stretched over a hot roller with a stretching ratio of 10:1 and the resultant stretched filaments were taken up and wound on a collecting bobbin.

The process described above was repeated several times using a variety of linear speeds and stretching ratios to produce fibres which ranged in individual denier from 15 up to 250. In each case the resultant filaments were cut and their cross-section examined under a stereo microscope fitted with a Polaroid Rg. Trade Mark camera. In all cases it was observed that the filament produced was a quadri-hollow-lobed filament in which all four branches of the cross-section were integrally joined at their inner ends and the outer ends of which branches were integral with and adjacent branch whereby to define a hollow space, the hollow spaces being equal in number to the number of branches.

The above process was repeated using the following polymers which have a wide range of melt indices. In all cases multi-hollowlobed filaments resulted.

It was, however, found that co-polymers of ethylene and propylene produced fibres where the welding of the segments appeared to be stronger and more resistant to breaking when heavily crushed. Compared to a circular tubular hollow filament extruded from 3 segments, the quadri-lobed tubular filaments were found to possess considerably superior resistance to crushing effects and were found not to collapse readlly under load. Circular tubular filaments having only one central hollow were found to have poor resistance to crushing and a tendancy to collapse under load.

List of polymers used: 1. General purpose medium flow extrusion type propylene copolymer of melt flow index 4.0 (ICI grade GWE 105).

2. General purpose medium flow injection moulding type propylene copolymer of melt flow index 4.0 (ICI grade GWM 101).

3. General purpose medium flow injection moulding type propylene copolymer of melt flow index 1.5 (ICI grade GWM 201).

4. Long term heat endurance medium flow injection moulding type propylene copolymer of melt flow index 4.0 (ICI grade HWM 107).

5. General purpose easy flow polypropylene homopolymer of the injection moulding type, having a melt flow index of 15.0 (ICI grade GYM 45).

6. General purpose easy flow injection moulding type propylene copolymer of melt flow index 9.0 (ICI grade GYM 202).

7. General purpose medium flow injection moulding type of propylene copolymer having a melt flow index at 1.5 (ICI grade GWM 203).

8. General purpose low to medium flow extrusion type propylene copolymer of melt flow index 0.8 (ICI grade GSE 108).

Propylene homo and copolymers having very low melt flow indices e.g. less than about 0.8 were not found to be useful in the method of the invention since they were too stiff even at high extrusion temperatures and tended to shear when stressed rather than elongate at the die-face.

Example 2 A 29" extruder was fitted with a die-head which would accommodate a die-plate with the dimensions of 19.1" long x 1.25" wide having 1,000 orifices identical to that of Example 1. The extruder was charged successively with the polymers of the list set forth in Example 1 under the same process conditions. In all cases despite the large number of fibres extruded simultaneously by this method no difficulties were experienced in the working of the equipment and satisfactory quadri-hollow-lobed filaments were produced in each case. The linear speed and stretching ratios were varied as in Example 1 and successfully gave fibres which ranged in individual denier from 15 up to 250.

This confirmed that the process of the invention could be carried out on commercial sized equipment on a commercially viable basis.

Example 3 A circular spinnerette of 34" diameter was removed from the die-head of a conventional monofilament casting line and replaced with a spinnerette having 32 orifices, having the cross-sectional shape and dimensions defined in Example 1.

The filaments emerging from the die-plate were cast into a water chilling bath, the water level of which was 1" below the die-plate. The line was operated with a first Godet speed of 30 ft. per minute and a second Godet speed of 300 ft. per minute, giving a stretching ratio between the 2 Godets of 10:1.

The equipment was charged successively with polymers set forth in the list of Example 1 and satsifactory quadri-hollow-lobed filaments were produced in each instance. Of the above polymers GWE 105 and GWM 203 gave the best results in that crushing did not produce any breaking away of the outer ends of the cross-sectional branches. In the case of GWE 105 and GWM 203 the denier of the final drawn filament was 350 and had a tenacity of 4.4 grammes per denier and an elongation of 14%. The draw ratio was then increased to 12:1 with the consequence that the tenacity for these polymers was increased to 5 grammes per denier and the elongation reduced to 12%. The filaments were very suitable for use in textile applications and as tying materials if they were twisted or alternatively if they were spirally bound together with another polymer material.

WH T WE CLAIM IS: 1. A synthetic filament composed of synthetic plastics material having a crosssection composed of at least three elongated branches, the inner ends of the branches being integral with one another throughout the length of the filament and the outer end of each of said branches along the length of the filament being so disposed as to define with an adjacent branch a continuous longitudinal hollow lobe along the length of the filament, the number of such hollow lobes thus defined being equal to the number of branches.

2. A synthetic filament as claimed in claim 1, in which the outer end of each branch is integral with said adjacent branch over the whole length of the filament.

3. A synthetic filament as claimed in claim 1, in which the outer end of each branch is integral with said adjacent branch only over intermittent portions along the length of the filament.

4. A synthetic filament as claimed in claim 1, 2 or 3 in which the ratio of cross sectional length to cross-sectional thickness of each branch is at least 5:1.

5. A synthetic filament as claimed in any of claims 1 to 3 in which the ratio of cross sectional length to cross-sectional thickness of each branch is essentially 12.5 to 1.

6. A synthetic filament as claimed in any of claims 1 to 5 in which the synthetic plastics material is polypropylene.

7. A synthetic filament as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings and described in any one of Examples 1 to 3.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. Example 1. The extruder was charged successively with the polymers of the list set forth in Example 1 under the same process conditions. In all cases despite the large number of fibres extruded simultaneously by this method no difficulties were experienced in the working of the equipment and satisfactory quadri-hollow-lobed filaments were produced in each case. The linear speed and stretching ratios were varied as in Example 1 and successfully gave fibres which ranged in individual denier from 15 up to 250. This confirmed that the process of the invention could be carried out on commercial sized equipment on a commercially viable basis. Example 3 A circular spinnerette of 34" diameter was removed from the die-head of a conventional monofilament casting line and replaced with a spinnerette having 32 orifices, having the cross-sectional shape and dimensions defined in Example 1. The filaments emerging from the die-plate were cast into a water chilling bath, the water level of which was 1" below the die-plate. The line was operated with a first Godet speed of 30 ft. per minute and a second Godet speed of 300 ft. per minute, giving a stretching ratio between the 2 Godets of 10:1. The equipment was charged successively with polymers set forth in the list of Example 1 and satsifactory quadri-hollow-lobed filaments were produced in each instance. Of the above polymers GWE 105 and GWM 203 gave the best results in that crushing did not produce any breaking away of the outer ends of the cross-sectional branches. In the case of GWE 105 and GWM 203 the denier of the final drawn filament was 350 and had a tenacity of 4.4 grammes per denier and an elongation of 14%. The draw ratio was then increased to 12:1 with the consequence that the tenacity for these polymers was increased to 5 grammes per denier and the elongation reduced to 12%. The filaments were very suitable for use in textile applications and as tying materials if they were twisted or alternatively if they were spirally bound together with another polymer material. WH T WE CLAIM IS:

1. A synthetic filament composed of synthetic plastics material having a crosssection composed of at least three elongated branches, the inner ends of the branches being integral with one another throughout the length of the filament and the outer end of each of said branches along the length of the filament being so disposed as to define with an adjacent branch a continuous longitudinal hollow lobe along the length of the filament, the number of such hollow lobes thus defined being equal to the number of branches.

2. A synthetic filament as claimed in claim 1, in which the outer end of each branch is integral with said adjacent branch over the whole length of the filament.

3. A synthetic filament as claimed in claim 1, in which the outer end of each branch is integral with said adjacent branch only over intermittent portions along the length of the filament.

4. A synthetic filament as claimed in claim 1, 2 or 3 in which the ratio of cross sectional length to cross-sectional thickness of each branch is at least 5:1.

5. A synthetic filament as claimed in any of claims 1 to 3 in which the ratio of cross sectional length to cross-sectional thickness of each branch is essentially 12.5 to 1.

6. A synthetic filament as claimed in any of claims 1 to 5 in which the synthetic plastics material is polypropylene.

7. A synthetic filament as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings and described in any one of Examples 1 to 3.