Recent developments in the field of texturing technologies

Texturing process applied to impart additional value and quality to synthetic filament yarns creates crimps, curls and loops and like features that natural fibres possess by nature, says Prof Dr Ali Demir

Texturing process as applied to most of the filament yarns are today well accepted by the textile industry. The following technologies are the majors techniques for the purpose of texturing:

• False-twist texturing
• Texturing by a cold air-jet
• Texturing by a hot air-jet and a stuffer box
• Other marginal techniques.

There have been many developments in the above mentioned technologies during the last decade when the demand for synthetic filament yarns have especially increased. These developments may be grouped in the following areas: higher texturing speeds for better economics, quality monitoring and control systems for better quality, and systems for the production of fancy textured yarns.

This paper will present the details of these developments and also introduce the most recent crimp formation techniques entitled 'self-crimped filament yarn spinning'. It is believed that these recent techniques will have a tremendous potential for the future.

Texturing-technology basics

The purpose of texturing is to impart permanent crimps, curls and/or loops to flat filaments in order to improve the use of these monotonous one-dimensional structures. Depending on the material of the filament, texturing is achieved by thermo-mechanical as well as pure-mechanical techniques. The false-twist texturing and BCF technologies dominate the thermo-mechanical techniques whereas the air-jet texturing solely represent the pure-mechanical texturing.

False-twist texturing technology

The helicular, i.e., three-dimensional, crimps are created by the simultaneous effects of false-twisting and heat-setting. As soon as the twisted structure is untwisted by the nature of false-twisting effect, the filaments obtain the crimped geometry. At the current state of development, the false-twist texturing is achieved at around 800-1200 m/min (depending on the polymer and yarn count) using POY as feed material which is also drawn simultaneously. The process economics have, for long, been requiring the integration of the spinning and texturing processes. The first ever prototype of this approach was on display.

• Integration of the false-twist texturing with spinning

  The Swiss company RETECH has been working on the development of a false-twist texturing using rotating heated cylinders instead of conventional texturing heater. They have developed and marketed a machine, named as TEX2000, which is claimed to run at 2000 m/min. With the encouragement of this technology, Retech has extended the application area of this machine to the integration with POY spinning process. Working with a Italian POY spinning equipment manufacturer, certain integration seemed to have been achieved. The process is currently successful, on PP spin-draw-texturing due to much forgiving nature of PP polymer.

• Fancy effects created by the false-twist texturing

  Despite the fact that, the false-twist texturing creates crimps to impart natural feel and stretch to synthetic filament yarns, it lacs natural appearance due to monotonous geometry. In order to break up this monotonous look, certain effects are imparted to the false-twist textured yarns during the process by the following techniques:

• Hot pin for colour variation

  The major portion of drawing is done on an additional draw zone equipped with a hot-pin or hot-shoe before the texturing process. Since the hot-pin imparts irregular and repetitive action on the filaments, the textured yarn obtains light and dark coloured sections when dyed. By varying the draw ratio, hot-pin temperature as well as the yarn speed, various affects are created. Especialy at low yarn speeds such as 200 m/min, the effecs are so pleasant that the textured yarn gets a high value in the market.

• Thick-and-thin yarn

  When the draw ratio is reduced to its lowest possible level whilst the twist insertion, D/Y ratio, rate is increased to its maximum possible level, the textured yarn gets a continuous state of surging where yarn obtains thick and thin places all over the yarn. Despite the fact that, this effect is not a permanent feature, it stays on the yarn under the tensions applied in weaving. Therefore, the woven fabric achieves a linen-like appearance.

• Elastan covering during texturing

  The modern fashion life requires the lightest possible garment with freedom of movement. This two contradicting requirements are best compromised by the stretch garments be it underwear, swimwear or outerwear. The traditional textile fibres do not have the necessary stretching power. Yet, the modern polymeric fibre elastan offers this flexibility with one small drawback. That is the biting effect on bare skin. Due to this peculiar effect, the elastan fibres have to be covered with traditional fibres. The covering may be achieved before or during fabric formation. The twist covering is very well known due to its huge costs emanating from the high twist requirement.

  The economical alternative has been developed as air-jet covering using the intermingling process. Nevertheless, increasing economical pressures as well as improved intermingling jets, it is now possible to integrate the elastan covering during the texturing operation.

  With the addition of elastan feeding equipment to the texturing machines, it is becoming a standard feature especially for PA texturing operation where PA is widely used to cover the elastan for all purposes ranging from ladies hosiery to ladies suitings. Moreover, PET textured yarn is also widely used to cover elastan for mens' stretch suiting as well as home textiles for excellent drape properties of elastan covered yarns.

Bulked continuous filament (BDF) technology

The traditional area of application for the BCF yarns is the floor covering. However, the current developments resulting in higher speeds and lower yarn counts, tend to make these yarns to be employed in the traditional textile uses such as upholstery as well as outerwear. Despite the usual filament dpf of 10-15 denier for the BCF yarns, the recently developed BCF texturing jets are able to handle fine filaments as low as 3-5 denier. The completed spin-draw-texturing is fully achieved with the BCF process. Nevertheless, it is only limited to PA and PP polymers as PET requires more time for necessary heat transfer to the core of the filaments. Today, PA6 or PA6.6 filament BCF yarns at 600 dtex are produced at 3500 m/min winding speeds. Due to the inherent low molecular weight and adverse molecular weight distribution, the PP BCF yarns at 900 dtex can only be produced at 3000 m/min.

Air-jet texturing technology

In comparison with the false-twist texturing or BCF yarn production, the process speeds of air-jet texturing is still regarded as low speed at 500-600 m/min levels. However, the development efforts of Heberlein, the pioneering jet developer for the air-jet texturing process, have been constantly focused on higher process speeds. The latest developed jets have been claimed to process at 800 m/min with 150 dtex yarns. Since the wetting of filaments before they are ed into the texturing jets is an inevitable process requirement, it entails the washing off the spin finish and hence blockage of yarn path with spin finish residues. Especially extreme working conditions such as cold/hot ambient, higher speeds as well as long process runs, this poses an immense quality assurance problems. In order to avoid such surprises, Heberlein has developed a novel jet that rotates during the process. The rotating action of the jet creates a self cleaning action for longer runs.

Future trends

Due to tremendous economical as well as ecological (low or no noise emission) advantages, it is firmly believed that the future developments will be focused around the creating texturing effect by means of self-crimping. However, for some in the near future, the conventional texturing technologies will further be developed for better economics, higher process speeds and fancy texturing effects, and for better quality, on-line quality monitoring sensors and systems.

(The author is with Istanbul Technical University, Department of Textile Engineering, 80190-Gumussuyu-Taksim-Istanbul, Turkey)