The dyeing of textile products

Most textile fibers have a rather dull natural color, but finished fabrics must be presented in an attractive range of colors. Up until about a century ago, the dyes used in the textile industry were only of plant origin, but since 1856, when William Henry Perkin prepared the first dye bath, hundreds of thousands of artificial dyes have been discovered and experimented with. Currently, there are about 4000 commercially available. To give fabric a unique and uniform color, the dyeing process is followed, while to give the fabric multiple colors, the printing process is followed. Fibers that are not yet spun are colored by immersing them in a perforated container, into which the dyeing liquid is introduced, while skeins of yarn are aligned suspended in a container where the liquid circulates. Woven fabrics are colored in a dyeing apparatus that unfolds the fabric and moves it back and forth in the liquid. This method is suitable for woven fabrics, but not for knitted ones, which would stretch too much under the strain. Knitted fabrics are generally colored by means of a dyeing machine, in which a winch lifts the fabric out of the dyeing liquid, and then immerses it again. The fabric will remain loose at the bottom of the bath until the winch pulls it out again. A fabric can also be colored by first passing it through a dyeing liquid, then under the action of rollers that squeeze out the excess liquid, and finally passing it over heated cylinders or subjecting it to steam in a closed chamber. All the dyeing processes we have briefly described so far take place at or near boiling point, because heat fixes the dyes in the fibers and makes the color wash-resistant. Recently, reactive dyes have been discovered that chemically combine with fibers at room temperature, producing colors that are perfectly wash-resistant. Multi-colored fabrics are produced either by means of a roller printing machine or by means of a printing screen (a modification of stenciling). The very high cost of roller printing equipment makes the first of the aforementioned methods convenient only for large quantities of material; the second method is used for smaller quantities, about a thousand meters. In a roller printing machine, the fabric runs along a large rotating horizontal cylinder, equipped with a certain number of printing rollers, one for each color to be printed: on each roller are engraved those parts of the pattern that are to be printed in a particular color, and each roller has its own supply of printing paste, a dense mixture of gum and color; as the fabric passes around the cylinder, each roller imprints its part of the pattern. The fabric is then steam-heated from 100 to 102 °C (to fix the color) and thoroughly washed (to remove the gum). If we want to print a multi-color design on a dark background, there are two ways to proceed. The entire fabric can be dyed dark, and in this case it will be necessary to add to the printing pastes some substance that does not affect the dyes but is able to destroy (or discharge) the dye used to create the dark background (this system is called discharge printing), or the other system can be adopted, which is to print the multi-color design on a white fabric, and then apply the dark background at a later stage. Since the printing pastes contain a substance that resists the fixing of the dye used for the background color, the printed design will not be damaged (this process is called resist printing). If a printing screen is used, the fabric is laid flat on a table and the color design is applied by means of silk or metal mesh screens. The fabric is then subjected to steam treatment and washing. florencecashmereyarn.com