This is one of the most important stages for a manufacturer of yarn-dyed fabrics. Divided into several phases, dyeing is the process that transforms grey yarn into coloured yarn by using dyestuffs. Determining factors for dyeing are the uniformity, penetration of the dye and fastness.
Everything starts with scouring, i.e. a hot or cold treatment to eliminate the intrinsic impurities of the fibre which are sometimes caused by subsequent processes.
This is then followed by dyeing which takes place inside an autoclave where a bath in an alkaline environment has already been prepared, containing various products: wetting dyes (to improve the fibre's absorption capacity of a liquid), equalising agents (to achieve colour uniformity on the package) and reducing agents (to activate some chemical processes). The third step is washing and oxidation. Two processes that eliminate the dyestuff in excess that has not been absorbed by the fibre and they make a dye that is water soluble into one that is not.
Soaping is the process that determines the colour wanted by means of a bath at 100°C. The soft application consists in applying synthetic polyethylene waxes to make the yarn more even and reduce the electrostatic charge. Lastly, 50% of the water absorbed by the fibre during dyeing is eliminated in the spinner; The following drying operation - using forced air dryers - allows the correct percentage of humidity to be reached, necessary for the fibre.