Denim is a quality product and is multipurpose it can be used as a garment and clothing as well as package or covering. It’s a diverse material with multiple types each with a unique quality. Denim has a lot of scopes and if used consciously can create a great scope for humanity. One of the best ways to shop in a sustainable way is to do so within the circular economy, prolonging the life of garments and keeping them out of landfills that much longer. Also since denim is a durable fabric hence, we can easily upcycle denim.
Finishing of Elastic Denim Fabric
The elastic denim fabric has already established itself in the denim industry with growing market shares. Many premium denim brands employ modern stretch denim. These articles today have a more natural appearance and are no longer as glossy. These articles require a few treatment steps more than for normal classic denim finishing. The finishing process is therefore slightly more costly, but the prices that can be achieved are also somewhat better than for the classic denim fabric.
Apart from elastic texturized polyester — expand from Trevira, for example — with approximately 20 per cent stretch, yarns of elastane fibres with approximately 40 per cent stretch are frequently used to maintain the form stability and to improve the wearing comfort. Of the elastane fibres Dorlastan®, Lycra®, Linel®, Glospun®, Roicka® and Teplon®, may be used in denim. From molecular structure, elastane is a fibre with a polyurethane hard segment and a polyether or polyester soft segment, whereby the soft segment is responsible for the properties of the fibre.
As a large number of these fibre types are encountered, it is essential to observe the information provided by the respective fibre producers with respect to controlled shrinkage and proper fibre fixing. The producer should be consulted on the deviation ranges of the elastane fibres to be used in order to create optimum conditions for finishing. When selecting the finishing parameters — pH value, treatment time and mechanical influence — care must be taken from the point of view of the elastane fibres that the intended finished product data of the article are not impaired. For denim articles, cotton blends with different percentages of elastane are used.
The Behavior of Weft-Elastic Denim Fabric
A classic denim fabric without elastane content normally has a greige width of 157 to 159 cm. The washing tests on such articles show on average a shrinkage of -15 per cent in the warp direction and -6 per cent in the weft direction.
The weft-elastic denim fabric with elastane content may have a greige width of 180 cm and also shrinks during the washing test on average by -15 per cent in the warp direction, but by -34 per cent in the weft direction. This means that the fabric still had a width of approximately 119 cm after washing. And that with a desired finished width of 151 cm. The weft-elastic denim fabric therefore always has to be stabilized. To stabilize the fabric is heat-set in order to achieve:
- The desired stretch;
- The desired weight per square meter;
- A desired finished width;
- A desired improvement in the dimensional stability; and
- To avoid cold creep shrinkage.
Fixing ranges at 180 to 200°C lie in the order of 15 to 60 second dwell time. The fibre manufacturer’s recommendations have to be observed here. Within this range, the fabric reacts under optimum conditions. The times cited in this article are empirical values from the respective finishers.
The Discontinuous Finishing Method for Weft-Elastic Denim Fabric
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Manufacturing process of Denim Fabrics
After singeing, the weft-elastic denim greige cloth with a 180 cm fabric width undergoes hot washing on a washing machine where the fabric is washed and the majority of the size is removed. The fabric is then pre-dried, padded — liquor application — and then dried and fixed on a stenter with drying and fixing temperature of 190°C, stenter width 152 cm. The third finishing step is the compressive shrinkage process. The fabric to be shrunk is sprayed with water, passed over a steaming drum, skewed on a weft straightener and then fed to the rubber calendar with a defined rubber blanket pressure before finally being dried on the felt calendar. Instead of the spray system, the Matex ECO-Applicator can also be used for a selective moisture application. The fabric width before the rubber calendar is 150 cm; the fabric width after the felt calendar is also 150 cm.
The washed shrinkage values after treatment showed a residual shrinkage in the warp direction of -1 per cent and residual shrinkage in the weft direction of -1.5 per cent, thus falling within the range of the international standards required by Levis, Lee, Wrangler, Maverick, Mustang and General, for example. These respectable residual shrinkage values are achieved in three separate finishing steps.
The Fully Continuous Finishing Method for Classic and Elastic Denim Fabrics
The most modern, most ecological and most economical denim range version is shown below.
This range allows fabric webs of 100-per cent cotton and of cotton blends with elastane to be finished. Different setting parameters are selected, depending on the quality. After unrolling, the grey fabric is cleaned and singed. In the following washing compartments, the fabric is partly de-sized and the first shrinkage in the length and width of the fabric web takes place. Other processes can also be integrated, depending on the number of washing compartments.
A high-performance squeezing unit optimally dewaters the fabric web for a wet-in-wet process. Minimal amounts of finishing liquor are applied with the ECO-Applicator. A concentration check of the finishing liquor, as is necessary with the wet-in-wet process with two padders, can be eliminated here. When using the ECO-Applicator, the finishing liquor is not diluted. The fabric is then pre-dried in the cylinder drier unit. Residual drying, stretching and skewing are performed on the Thermo Stretch stretcher and weft straightener.
The fabric is thereby carefully stretched in stages by passing it over rollers while skewing and stretching in small steps. The process takes place in a defined temperature and moist climate and achieves better fabric appearances. Compared with the conventional denim stretching technique this means: Significantly lower stretching forces, less fabric tension, better ‘look and feel’, Higher production speed and simpler residual moisture control. The fabric width, skew and number of filling threads are monitored by a special camera as mentioned above and the measured values are converted into corresponding control pulses for the range control.
The stenter with upline Matex ECO-Applicator and a coating range is then used either for finishing, drying of the coating or surface stabilization (fixing), depending on the article. The machine settings depend on the process to be employed. The fabric arrives at the range for the compressive shrinking process with a controlled residual moisture content or with moisture application using the Matex ECO-Applicator. Two rubber calenders and two felt calenders ensure a high production speed with gentle use of the rubber blanket and effective energy consumption. Two rubber calenders and two felt calenders are required to produce denim of 14.5 oz/yd² with 1 to 2-per cent residual shrinkage at speeds of at least 70 m/min.
The Thermo Stretch stretcher is a modified hot flue with reinforced and adjustable rolls with a diameter of 180 millimetres (mm). The stretcher can be heated and the fabric moisture at the exit is regulated to suit the shrinkage process. With their differently controlled speeds V1 and V2, the two tension rolls determine the longitudinal tension in the fabric, and hence the reduction in width monitored and controlled by the Pleva SD 1 camera. The camera also measures the weft thread position, and monitors and controls the skew by skewing on side of the roll package in the Thermo Stretch stretcher. Low-tension guidance of the fabric during rolling is important for the end of the process.