Melt spinning of a blend of a fibre-forming polymer and an immiscible polymer

Description

[0001] This invention relates to the manufacture of synthetic fibres by melt spinning and drawing a high molecular weight, high viscosity, fibre-forming polymer, more particularly polyethylene terephthalate or nylon 66, containing another polymer which is immiscible in a melt of the fibre-forming polymer.

[0002] Recently there have been a number of disclosures relating to the production of melt-spun synthetic fibres from a fibre-forming polymer in which another polymer is added to the fibre-forming polymer before it is spun. The most relevant known to applicant are now discussed.

[0003] Japanese Patent No. 56-118912 (Teijin KK) is concerned with the manufacture of a high strength fibre by melt spinning polyethylene terephthalate containing between 1 and 7 parts by weight % of a bisphenol type polycarbonate. The melt spun fibre is wound up at a speed of 1500 m/minute or less. It is stated that the limiting viscosity of the polyethylene terephthalate used must fall between 0.55 and 0.70. If it falls below 0.55, satisfactory strength and modulus cannot be developed in the fibre. On the other hand, when the limiting viscosity is in excess of 0.70, recognisable improvement in strength becomes insignificant or disappears and there is a tendency for the modulus value to decline as well.

[0004] DE-A-3113717 is concerned with a bristle for brushes consisting of polyethylene terephthalate incorporating between 2 and 25% by weight of a polyolefine, which may be polyethylene or polypropylene or polymer mixture of ethylene and propylene.

[0005] DE-A-2328917 is concerned with a process for producing a composite filament which comprises melt-extruding a mixture of a polyethylene having a melt index of at least 27 and a fibre-forming polyester and withdrawing the extruded filaments from the spinneret at a speed above 2,500 metres per minute.

[0006] In European Patent Application No. 80274 we have described a process of melt spinning a fibre-forming thermoplastic polymer at a minimum wind up speed of 1 kilometre per minute in which, before melt spinning, there is added to the fibre-forming polymer, between 0.1% and 10% by weight of another polymer which is immiscible in a melt of the fibre-forming polymer, such other polymer having an average particle size of between 0.5 and 3 micrometers in the melt with the fibre-forming polymer immediately prior to spinning. The intrinsic viscosity of the polyethylene terephthalate used was 0.63 and the relative viscosity (RV) of the nylon used was 40.

[0007] An advantage of the process described in European Patent Application No. 80274 is that it allows significant productivity gains to be achieved. The effect of blending the immiscible polymer with the fibre-forming polymer is that of wind up speed suppression, i.e. the properties of the spun fibre are those that would be obtained from a fibre which had been spun at a lower wind up speed.

[0008] Nevertheless it would appear from a reading of European Patent Application No. 80274 that the effect of wind up speed suppression cannot be realised at wind up speeds lower than 1 kilometre per minute. However, we have now realised that the effect of wind up speed suppression is really orientation suppression and so, if a sufficiently high molecular weight, i.e. high viscosity, fibre-forming polymer is spun, wind up speed suppression occurs even at wind up speeds below 1 kilometre per minute.

[0009] According to the present invention, therefore, we provide a process of melt spinning a fibre-forming polymer selected from the group consisting of polyethylene terephthalate and nylon 66 in which before melt spinning, there is added to the fibre-forming polymer between 0.1% and 10% by weight of another polymer, but excluding a liquid crystal polymer, which is immiscible in a melt of the fibre-forming polymer, such other polymer having an average particle size less than 3 micrometres in the melt immediately prior to spinning, said immiscible polymer being selected from the group consisting of polyethylene, polypropylene, polyethylene glycol and nylon 66 when the fibre-forming polymer is polyethylene terephthalate and said immiscible polymer being selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and polyethylene glycol, when the fibre-forming polymer is nylon 66 characterised in that the polyethylene terephthalate fibre-forming polymer has an intrinsic viscosity greater than 0.70, the nylon fibre-forming polymer has a relative viscosity greater than 55 and the spun fibre is wound up at a wind up speed less than 1 kilometre/minute.

[0010] In preference, in order to achieve good tensile properties, the additive polymer has an average particle size in the melt of substantially less than 3 micrometres and more preferably of the order of 1 micrometre.

[0011] The intrinsic viscosity of polyethylene terephthalate is measured in ortho-chloro-phenol.

[0012] The relative viscosity of nylon 66 is measured on a 8.4% w/w solution in 90% formic acid compared with the viscosity of 90% formic acid itself.

[0013] By an "immiscible polymer" we mean that at the spinning temperature such a polymer forms a two phase melt with the fibre-forming thermoplastic polymer. Microscopic examination and optical photographs of such a melt show a two phase system in which the immiscible polymer is in the form of circles (indicating spherical particles) dispersed in the continuous, fibre-forming, polymer matrix.

[0014] However we wish the term "an immiscible polymer" to exclude a liquid crystal polymer, i.e. the additive polymers used in the invention do not form an anisotropic melt in the temperature range at which the thermoplastic polymer may be melt spun. This anisotropic condition may form when a liquid crystal polymer is heated or by the application of shear to the polymer, although in the latter case it must persist for a few seconds.

[0015] In the case of nylon 66 the immiscible polymer is selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and polyethylene glycol.

[0016] In the case of polyethylene terephthalate, the immiscible polymer is selected from the group consisting of polyethylene, polypropylene, polyethylene glycol and nylon 66. A preferred immiscible polymer, however, is nylon 66. The extensional viscosity of nylon 66 is such that the molten spheres of the polymer immediately prior to spinning, deform into microfibrils along the spinning threadline.

[0017] We also provide, therefore, melt spun fibres of polyethylene terephthalate made from polymer having an intrinsic viscosity greater than 0.70 containing between 0.1% and 10% by weight of nylon 66 which is present in the melt spun fibres as microfibrils. These microfibrils have an aspect ratio i.e. length/diameter ratio which is very high e.g. typically greater than 50 and such microfibrils will have diameters of about 0.5 micron. It is believed that it is the conversion of the spheres of nylon 66 into microfibrils and the extent of this deformation that produces the change of rheology which is responsible for the orientation suppression and in turn wind up speed suppression which is referred to below.

[0018] A major advantage of the process of the invention is that it allows significant productivity gains to be achieved. The effect of blending the immiscible polymer with the fibre-forming polymer is that of orientation suppression which manifests itself as wind up speed suppression i.e. the properties of the spun fibre are those that would be obtained from fibre which has been spun at a lower wind up speed. As the wind up speed increases in normal spinning, in the absence of an immiscible polymer, the properties of the drawn yarn decrease. Accordingly by lowering the effective wind up speed by the addition of an immiscible polymer (while keeping the actual wind up speed the same) it is possible to achieve improved properties such as a higher modulus which is quite surprising in view of the teaching of Japanese Patent No. 56-118912.

[0019] This is particularly advantageous for industrial fibres because the drawn properties for a specific final extension fall with wind up speed (see H. Brody, J. Macro Sci., Phys, B22, 19 (1983)).

[0020] A particularly useful property of a sewing thread is its modulus, since it has been found that a higher modulus allows faster sewing speeds and gives less puckering of sewn seams. A higher modulus can, of course, be obtained in the normal drawing process by using a higher draw ratio but this is not very desirable since it can lead to a high break level. The present invention achieves this object in a much more convenient and efficient manner.

[0021] The invention will now be described with reference to the following Examples. In all of these Examples the particle size of the additive, i.e. immiscible, polymer was of the order of 1 micrometer.

Example 1

[0022] Polyethylene terephthalate having an intrinsic viscosity (IV) (measured in ortho-chloro-phenol) of 0.73 was dried at 165°C for 4 hours and blended with 3% by weight of Imperial Chemical Industries PLC. SGS grade nylon 66 on a GKN single screw extruder with an L/D ratio of 26:1. The barrel temperature was 290°C and the screw was rotated at 50 rpm. A lace of 2.54 mm (0.1 inch) diameter was extruded into a water bath and then passed to a lace cutter. The average output rate was 100 grams per minute. As a control, polyethylene terephthalate alone was extruded in a similar manner.

[0023] The chips from the lace cutter were then dried at 165°C for 4 hours and made into candles at 240°C for 8 mins. The candles were then spun on a rod spinner. The spinning temperature was 293°C and the throughput per hole was 96 gm/hr/hole into ambient air with no deliberate quenching apparatus, using 35 thou spinneret holes. After cooling, the filaments so formed were wound up at a wind up speed (WUS) of 200 mpm to 1000 mpm without adjustment of spinning rate so that higher speeds yielded finer filaments. The intrinsic viscosity of the control fibre after spinning was 0.70.

[0024] Considerable wind-up suppression was obtained with the blend as demonstrated by higher extensions and lower birefringences. These lower birefringences are an example of orientation suppression, the degree of which depends on the combination of the melt viscosity of the polymer and the WUS.

[0025] The wind up speed suppression produced a potential increase in productivity that can be calculated from the extensibility of the spun filaments as determined on an Instron. The gauge length used was 10 cms and the strain rate was 200% per minute.

[0026] If a spun filament has a percent extension-to-break of E, then the maximum draw ratio to which it can subsequently be subjected is roughly (1+E/100). If a second spun filament has a larger extension-to-break E' then it can be subjected to a larger draw ratio, roughly (1+E'/100). To make drawn filaments of equal decitex d at these maximum draw ratios the spun filaments must therefore have decitexes of d(1+E/100) and d(1+E'/100) respectively. If both filaments are spun at the same speed their production rates are proportional to these decitexes and the percentage increase in productivity of the second filament is

[0027] This is the function listed in Table 1 as the potential increase in productivity.

[0028] It is evident from the table that the degree of wind-up speed or orientation suppression increases considerably with increasing spinning speed.

[0029] At 1000 mpm, the addition of 3% nylon, affords as much as 53% increase in productivity and at 2000 mpm as much as 90% increase in productivity.

Example 2

[0030] This example gives results for other concentrations of nylon and demonstrates that even very small amounts of nylon are very effective in producing orientation suppression. The same blending and spinning conditions were used as in Example 1 except that the spinneret hole used was 15 thou.

Example 3

[0031] This example demonstrates that better tensile properties are obtained at the same WUS by the use of a nylon blend. The improvement shown is in the initial modulus after drawing. The polymers were blended and spun as in Example 1 at 96 g/hr/hole and 800 mpm. They were then drawn to a range of final extensions, using a hot pin at 85°C, a hot plate at 170°C and a draw speed of 20 mpm. A special technique was used on the Instron to measure the initial modulus very precisely. The gauge length was 50 cm, the cross head speed was 5 cm per minute and the chart speed was 100 cm per minute. This gave a load-strain curve which was linear up to 2% strain and from which the initial modulus could be very accurately measured. For a given final extension there was a small scatter of a few percent, and all the results obtained are given in Table 3.

[0032] When smooth curves are drawn through these results, the modulus of the 1 % and 3% nylon blends is about 20% higher than the control at 10% drawn extension. The draw ratio of the control for 10% extension was 3.9, while that of the 1% blend was 4.9, giving a productivity increase of 26%.

Claims

1. A process of melt spinning a fibre-forming polymer selected from the group consisting of polyethylene terephthalate and nylon 66 in which before melt spinning, there is added to the fibre-forming polymer between 0.1% and 10% by weight of another polymer, but excluding a liquid crystal polymer, which is immiscible in a melt of the fibre-forming polymer, such other polymer having an average particle size less than 3 micrometres in the melt immediately prior to spinning, said immiscible polymer being selected from the group consisting of polyethylene, polypropylene, polyethylene glycol and nylon 66 when the fibre-forming polymer is polyethylene terpehthalate and said immiscible polymer being selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and polyethylene glycol when the fibre-forming polymer is nylon 66, characterised in that the polyethylene terpehthalate fibre-forming polymer has an intrinsic viscosity greater than 0.70, the nylon fibre-forming polymer has a relative viscosity greater than 55 and the spun fibre is wound up at a wind up speed less than 1 kilometre/minute.

2. Melt spun fibres of polyethylene terephthalate made in accordance with claim 1.

3. Melt spun fibres of polyethylene terephthalate made in accordance with claim 1 in which the immiscible polymer is nylon 66 which is present in the melt spun fibres as microfibrils having an aspect ratio greater than 50 and diameters of about 0.5 micrometre.

4. Melt spun fibres of nylon 66 made in accordance with claim 1.

Ansprüche

1. Verfahren zum Schmelzspinnen eines faserbildenden Polymers, das aus Polyethylenterephthalat und Nylon-66 ausgewählt ist, bei welchem vor dem Schmelzspinnen dem faserbildenden Polymer zwischen 0,1 und 10 Gew.% eines weiteren Polymers, wobei ein Flüssigkristallpolymer ausgeschlossen ist, zugegeben wird, das mit einer Schmelze des faserbildenden Polymers unmischbar ist, wobei das weitere Polymer unmittelbar vor dem Spinnen in der Schmelze eine durchschnittliche Teilchengröße von weniger als 3 um aufweist und wobei das unmischbare Polymer ausgewählt ist aus Polyethylen, Polypropylen, Polyethylenglycol und Nylon-66, sofern das faserbildende Polymer aus Polyethylenterephthalat besteht, und das unmischbare Polymer ausgewählt ist aus Polyethylen, Polypropylen, Polyethylenterephthalat und Polyethylenglycol, sofern das faserbildende Polymer aus Nylon-66 besteht, dadurch gekennzeichnet, daß das faserbildende Polyethylenterephthalat-Polymer eine intrinsische Viskosität von mehr als 0,70 aufweist, das faserbildende Nylon-Polymer eine relative Viskosität von mehr als 55 aufweist und die gesponnene Faser mit einer Aufspulgeschwindigkeit von weniger als 1 km/min aufgewickelt wird.

2. Schmelzgesponnene Fasern aus Polyethylenterephthalat, welche gemäß Anspruch 1 hergestellt worden sind.

3. Schmelzgesponnene Fasern aus Polyethylenterephthalat, welche gemäß Anspruch 1 hergestellt worden sind, in denen das unmischbare Polymer aus Nylon-66 besteht, welches in den schmelzgesponnenen Fasern in Form von Microfibrillen mit einem Achsenverhältnis von mehr als 50 und mit Durchmessern von ungefähr 0,5 µm vorliegt.

4. Schmelzgesponnene Fasern aus Nylon-66, welche gemäß Anspruch 1 hergestellt worden sind.

Revendications

1. Procédé de filage à état fondu d'un polymère apte à la formation de fibres, choisi dans le groupe comprenant le téréphtalate de polyéthylène et le Nylon 66, dans lequel, avant filage à l'état fondu, il est ajouté au polymère apte à la formation de fibres 0,1% à 10% en poids d'un autre polymère, mais à l'exclusion d'un polymère à cristallinité liquide, qui est non miscible à une masse fondue du polymère apte à la formation de fibres, cet autre polymère ayant un diamètre moyen des particules inférieur à 3 micromètres dans la masse fondue immédiatement avant filage, ledit polymère non miscible étant choisi dans le groupe comprenant le polyéthylène, le polypropylène, le polyéthylèneglycol et le Nylon 66 lorsque le polymère apte à la formation de fibres est le téréphtalate de polyéthylène, et ledit polymère non miscible étant choisi dans le groupe comprenant le polyéthylène, le polypropylène, le téréphtalate de polyéthylène et le polyéthylèneglycol lorsque le polymère apte à la formation de fibres est le Nylon 66, caractérisé en ce que le téréphtalate de polyéthylène constituant le polymère apte à la formation de fibres possède une viscosité intrinsèque supérieure à 0,70, le Nylon consituant le polymère apte à la formation de fibres possède une viscosité relative supérieure à 55 et la fibre filée est enroulée à une vitesse de bobinage inférieure à 1 kilomètre/minute.

2. Fibres de téréphtalate de polyéthylène filées à l'état fondu, produites suivant la revendication 1.

3. Fibres de téréphtalate de polyéthylène filées à l'état fondu produites suivant la revendication 1, dans lesquelles le polymère non miscible est le Nylon 66, qui est présent dans les fibres filées à l'état fondu sous forme de microfibrilles ayant un rapport d'aspect supérieur à 50 et des diamètres d'environ 0,5 micromètre.

4. Fibres de Nylon 66 filées à l'état fondu, produites suivant la revendication 1.