EP0080273A2

EP0080273A2 - Bulked polyester fibre

Info

Publication number: EP0080273A2
Application number: EP82305736A
Authority: EP
Inventors: Harry Brody
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1981-11-23
Filing date: 1982-10-28
Publication date: 1983-06-01
Also published as: EP0080273A3; AU9061682A; ES517564A0; ES8402030A1

Abstract

A bulked fibre of fibre-forming polyester, for example polyethylene terephthalate, containing between 0,1% and 10% by weight of either an immiscible polymer or a liquid crystal polymer and a process for producing such bulked fibre.

Description

This invention relates to an improved bulked fibre of a polyester and to methods of producing such a fibre.
In our UK patent application No 8132250 we have described how self bulking filaments having a rectangular, ie tape, section may be produced by forming the yarn as a plurality of side by side heterofilaments from two different fibre-forming polymers such as polyethylene terephthalate and a copolymer of polyethylene terephthalate and polyethylene isophthalate. In the described yarn, a shrinkage differential exists across the filaments and this causes spontaneous bulking of the filaments.
Also in European patent application No 81302121.9 we have described a process of melt spinning a fibre-forming thermoplastic polymer such as polyethylene terephthalate in which there is added to the thermoplastic polymer a small proportion of a liquid crystal polymer and the polymers are then melt spun together in intimate mixture at a minimum wind up speed of 1 kilometre per minute. A feature of the process is that there is wind-up speed suppression ie the properties of the spun fibre are those that would be obtained from a fibre spun at a lower wind-up speed in the absence of the liquid crystal polymer.
Furthermore in UK patent application No 8135250 we have described how the addition of an immiscible polymer to a fibre-forming polymer such as polyethylene terephthalate also produces wind-up speed suppression.
We have now found that blends of a fibre-forming polyester and either an immiscible polymer or a liquid crystal polymer, when spun at certain high speeds, produce a fibre which bulks spontaneously when heated.
According to the present invention we provide a bulked fibre of a fibre-forming polyester containing between 0.1% and 10% by weight of either an immiscible polymer or a liquid crystal polymer.
We also provide a process of producing a bulked fibre camprising melt spinning a fibre-forming polyester to which has been added between 0.1% and 10% by weight of either an immiscible polymer or a liquid crystal polymer, taking up the spun fibre at a minimm wind-up speed of 1 kilometre per minute and heating the spun yarn to a temperature at which the yarn bulks spontaneously.
The process of the invention is suited to the more common fibre-forming polyesters. It is particularly suitable for producing fibres from those melt-spinnable polyesters based on polyethylene terephthalate and cantaining at least 85 mol percent ethylene terephthalate and preferably at least 90 mol percent ethylene terephthalate. A particularly preferred polyester is polyethylene terephthalate. Alternatively during preparation of the polyester, minor amounts of one or more ester-forming ingredients other than ethylene glycol or terephthalic acid or its derivatives may.be copolymerised. For instance, the melt spinnable polyester may contain 85 to 100 mol percent (preferably 90-100 mol percent) ethylene terephthalate structural units and 0-15 mol percent (preferably 0-10 mol percent) copolymerised ester units other than ethylene terephthalate. Illustrative examples of other ester-forming ingredients which may be copolymerised with ethylene terephthalate include glycols such as diethylene glycol, tetramethylene glycol, hexamethylene glycol and dicarboxylic acids such as hexahydro terephthalic acid, benzoic acid, adipic acid, sebacic acid, azelaic acid.
In general any known liquid crystal polymer can be chosen for addition to the fibre-forming polyester provided that it can be processed in the same melt temperature raage as the polyester and provided that it does not react chemically with the polyester to cause significant degradation of the polyester during melt processing.
Suitable liquid crystal polymers for blending with polyethylene terephthalate are copoly chloro 1,4 phenylene ethylene dioxy 4,4' dibenzoate/terephthalate (CLOTE) and a copolymer of o-oxy-2-naphthoyl and p oxybenzoyl moieties in the molar proportion 27%/73% (CO).
Also, in general, any immiscible polymer may be added to the fibre-forming polyester provided that it can be processed in the same temperature range as the polyester and that it does not cause undue degradation of the polyester during melt processing. By "immiscible polymer" we mean that at the spinning temperature such a polymer forms with the fibre-forming polyester, a two phase melt. 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.
Suitable immiscible polymers are polyolefines, such as polyethylene and polypropylene; condensation polymers such as polyamides, and copolyamides, for example polyepsilon - caproamide, polyhexamethylene adipamide and the like; and polyethylene glycol.
The effect of adding a small proportion of an immiscible polymer or a liquid crystal polymer to a fibre-forming polyester is to produce wind-up speed suppression in the fibres as they are being spun ie the. properties of the spun fibre are those that would be obtained from a fibre spun at lower wind-up speed in the absence of the added polymer.
The property which is of particular interest is spun yarn boiling water shrinkage (SYS) which, for a fibre-foxming polyester, is governed by the wind-up speed, the S1S/wind-up speed curve having an inverted 'U' shape. We have found that the effect of the added polymer is to displace the SYS/wind-up speed curve (to the right) together with some change of scale. Variability results in different parts of the spun fibre having a different equivalent lower wind up speed and therefore different shrinkages. On account of this the fibre bulks spontaneously when heated.
Another feature of this variability is that the spun fibres have a rough surface, similar in some respects to natural fibres, which offers advantages from a 'bandle' point of view.
It will be realised, however, that variability within the spun fibre is probably undesirable in order to achieve satisfactory tensile properties. Accordingly it is necessary that the actual proportion of added polymer used is such that adequate bulk can be achieved without the loss of acceptable tensile properties.
The invention will now be described with reference to the following Examples.
In these Examples the polymers whichare blended with the fibre-forming polymers have a melt viscosity at the spinning temperature which is much lower than the melt viscosity of the fibre-forming polymer at the spinning temperature by which we mean that the melt viscosity of the added polymer is less than 25% of the fibre-forming polymer. However it should be understood that this invention is not limited to the use of such low melt viscosity additives.

EXAMPLE 1

A commercial grade of polyethylene, Alkathene Grade 23, was blended with a commercial grade of polyethylene terephthalate. The polyethylene had a melt flow index of 200 and a melt viscosity of 12 Ns/m² at 10⁴ N/m² and 280°C. The polyethylene terephthalate had a melt viscosity of 320 Ns/m² at 10⁴ N/m² and 280°C.
3% by weight of the polyethylene was compounded with the polyethylene terephthalate in an MPM single screw extruder with a 32:1 L/D ratio operating at 40 rpm with a feed zone at 230°C, barrel temperatures at 280°C, 270°C, 265°C and 275°C and die temperature 250°C, extruding 3/8 inch diameter lace which was water quenched and cut. This blend polymer was melt spun in a rod spinner through a spinneret having 5 holes, each being of 15 thou diameter, at 40 gms/hr/hole with no deliberate queaching. After cooling, the filaments so formed were wound up at wind-up speeds of from 1 to 5 kilometres per minute without adjustment of spinning rate so that the higher wind up speeds yielded finer filaments. The extrusion temperature was 300°C.
The spun fibres were immersed in boiling water for a few seconds. Spontaneous self bulking occurred. The relationship between degree of bulk and wind up speed is given in Table 1.
As a control the Example was repeated without, the immiscible additive. The filaments produced did not possess self-bulking properties.

EXAMPLE 2

This example is designed to show that the thermal history and temperature of the threadline contribute significantly to the bulk which can be obtained in the spun fibre. The degree of self-bulking is increased by factors which produce a colder threadline, such as lower extrusion temperature, reduced throughput per spinneret hole and the use of quench air. The colder threadline actiates the polyethylene, presumably by increasing the net viscosity ratio of the polyethylene terephthalate to the polyethylene.
A laboratory melt spinner was used with a spinneret having 5 holes each of 9 thou diameter. The wind-up speed was kept constant at 4 kilometres per minute. Otherwise the example was identical to Example 1.
The results are shown in Table 2.
In the above Examples spontaneous bulking of the fibres has been achieved by immersing the spun fibre in boiling water. Alternatively however bulking might equally well have been achieved by some other means which involves heating the spun fibre while under no or low tension for example a hot jet bulking technique. As a further alternative the spun fibre yarn may be knitted or woven into a fabric which is then heated, for example by immersion in boiling water, to produce bulk in the fibre yarns.
It should also be understood that the spun yarns of the invention may be drawn under tension in a conventional manner before they are bulked. On the other hand if the draw ratio exceeds a certain value, the self bulking capacity of the drawn yarns will be diminished.

EXAMPLE 3

1% by weight of a polymer capable of forming an anisotropic melt in the temperature range at which the polyethylene terephthalate is melt spun was blended with polyethylene terephthalate. The polymer added was C0, a copolymer of 6-oxy-2-naphthoyl and p-ox^ybenzoyl moieties in the molar proportion 27/73, prepared according to Example V of US 4 161 470. It was blended on a BETOL single screw extruder at 275°C, operating at a screw speed of 50 rpm. The extruder screw had a 30:1 L/D ratio. The lace was water quenched and then cut with a lace cutter.
This blend polymer was melt spun in a rod spinner through a spinneret having 3 holes, each being of 9 thou diameter, at 96 gms/hr/hole, with no deliberate quenching. The extrusion temperature was 300°C.
The spun fibres were immersed in. boiling water for a few seconds. Spontaneous self bulking occurred. The relationship between average degree of bulk and wind up speed is given in Table 3. The degree of bulk was variable, and the amplitude of the most highly bulked, very high frequency sections was very low, of the order of a few fibre diameters.

Claims

1. A bulked fibre of a fibre-forming polyester characterised in that it contains between 0.1% and 10% by weight of either an immiscible polymer or a liquid crystal polymer.

2. A bulked fibre of polyethylene terephthalate as claimed in Claim 1.

3. A bulked fibre of polyethylene terephthalate as claimed in Claim 1 further characterised in that the additive polymer is polyethylene.

4. A bulked fibre of polyethylene terephthalate as claimed in Claim 1 further characterised in that the additive polymer is a copolymer of 6-oxy-2-naphthoyl and p-oxybenzoyl moieties.

5. A process of producing a bulked fibre comprising melt spinning a fibre-formiag polyester to which has been added between 0.1 and 10% by weight of either an immiscible polymer or a liquid crystal polymer, taking up the spun fibre at a minimum wind-up speed of 1 kilometre per minute and heating the spun yarn to a temperature at which the yarn bulks spontaneously.

6. A process as claimed in Claim 5 characterised in that the spun fibre is heated by immersion in boiling water.

7. A process as claimed in Claim 5 characterised in that the spun fibre is heated while under no or low tension by a hot jet bulking technique.