What are the requirements for dyes in reactive printing?
2022-02-11
Coating printing is one of the methods of fabric printing. Unlike dyes, coatings do not have direct properties on fibers and cannot bond with them. They are merely insoluble colored powders, mostly organic compounds, but also include inorganic materials. The principle of 'coloring' the fibers is to use synthetic resins that can create a hard film to fix on the fibers and surface, allowing printing on various fiber fabrics.
Engraving printing means printing on fabric that has been dyed with removable colors in advance, which means that white can attract on black fabric. In direct printing, the back of the fabric does not look good, while the back of engraved printed fabric is a single color.
Reactive printing, as the name suggests, means that our printing dyes are processed through reactive dyeing. The design elements of reactive printing are diverse: plants, flowers, geometric shapes, English letters, and different color blocks are organically combined to showcase different design styles through design techniques. This type of fabric is suitable for a wide range of people and has a long usage time. Reactive printed fabrics have bright colors, good color fastness, a soft feel, can be washed frequently without fading, and can be used as new products for a long time.
Printing is different from dyeing, so reactive dyes suitable for dyeing are not entirely suitable for printing. The dyes suitable for reactive printing mainly have the following requirements.
(1) Low directness, low affinity, and good diffusivity.
If reactive dyes are printed and immediately dried, there will not be a dyeing balance problem like in dyeing, so dyes with low directness, low affinity, and good diffusivity can be used for printing.
If highly direct reactive dyes are used, although it is beneficial for dyeing and increases the chances of reaction between reactive groups and fibers, it makes the hydrolyzed dye difficult to wash off the fabric, leading to unclean white paper, stained fabrics, and reduced color fastness. The greater the affinity, the stronger the printing pollution, and the worse the washability and color fastness.
Using dyes with good diffusivity, during steaming, the dye will transfer from the tent layer to the fibers, helping it penetrate into the fabric.
Unfixed dyes are quickly removed from the fabric during washing.
(2) Good paste stability.
The paste stability of reactive dyes used in reactive printing should be good, meaning that at low temperatures, the reactivity is low, making it easy to control the pulp and printing, with minimal dye hydrolysis. After printing at high temperatures, under the action of alkali agents, it can react with fibers to form covalent bonds. Therefore, low-temperature X-type (Psan MX type) reactive dyes are generally not suitable for printing and are rarely used, while medium-temperature KN type and high-temperature K type are.
(3) No bond breakage phenomenon occurs after reactive printing.
Fabrics with reactive printing should avoid the phenomenon of acid gas breakage during storage as much as possible. Otherwise, the color will change, and color fastness will decrease. Most X-type reactive dyes are prone to keyboard phenomena, easily fading during soap washing and storage, so they are rarely used for printing.
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