Bright, dull, subtle, loudthe choices of colours vary, but it is certain that these choices give character to the clothing. It is for this purpose that the dyeing of yarn or fabric is extremely important. There are various varieties of dyes available as per processes, type of yarn and cost of dyeing. The natural fibres like cotton, silk, wool are enable to dissolve more readily in water, following which direct, acid, sulphur or vat dyeing can be used. In case of manmade fibres, which have difficulty in absorbing water, special category of dyes that are almost insoluble in water is used. These dyes are known acetic dyes or disperse dyes. The chief characteristics of disperse dyes include low solubility in water, the colloidal dispersion property is applied and dispersion dyes are non-ionic dyes so they are free from ionizing.
Disperse dyes are often classified as per the rate of dyeing, molecular size and colour fastness. There are low energy disperse dyes, medium energy disperse dyes and high energy dyes. The disperse dyes that involve the compound colours i.e. the mixture of two colours together, can create some problems. However, with rising standards of technology, these problems can easily be controlled. The general properties that disperse dyeing incorporate are the solubility factor, which means that disperse dyes are almost insoluble or only slightly soluble in water. These dyes dissolve in organic solvents like benzene, toluene etc. Another property is fastness to washing. The fabric with disperse dyes show average to good washing fastness. Most of the disperse dyes are very fast to washing. The minimum light fastness rating of disperse dyes is between 4-5. Also, the constant electronic arrangement of disperse dyes imparts decent sublime ability. It is also observed that fabrics that are dyed with blue and violet disperse dyes containing anthraquinone structure become dull when they come in contact of nitrous oxide. Electric heating or open gas fire can be held culpable for producing nitrous oxide.
There are several colours available under disperse dyes category and these colours are reported to have average to good fastening on polyester fibres. Lack of smoothness or evenness in filament texturising or heat setting can lead to higher dyeing temperatures. In case of black disperse dyes, a mixture of faded yellow, red and blue dyes is used.
The use of dispersion dyes is fairly on a large scale, as fibres like polyester, nylon, polyester blends and other synthetic textiles. With recent development in medical science, disperse dyes are often blamed for allergic reactions on skin in some patients. The most common source of disperse dyes is black or navy blue acetate liners of dress clothing. The dark coloured polyester or velour fabric and in some cases even the light coloured products including diapers for children contain disperse dyes. In weighing against the acetate and polyester, disperse dyes fasten on nylon very easily. Following this in some cases, people can contact skin reactions from nylon stockings or tights, as these too contain disperse dyes. The options available with customers who have allergic reaction to dispersion dyes is to avoid wearing polyester or nylon fabrics or soaking the fabric in water prior to wearing it can ensure that excessive dye is washed out. These apart, as sweating can result in release of dye, so dark coloured synthetic exercise garments should be avoided at all costs. In EU certain dispersion dyes are banned following allergic reactions that they can cause.
The disperse dyes have also been held culpable for not being environment friendly, following which, newer methods are being developed to make the dyes more eco-friendly. There have some specific changes in production of disperse dyes and today the textile units are ensuring that the disperse dyes are free from synthetic surfactants. There have been researches that show use of liposomes as supplementary dispersing agent in order to shun accumulation of the molecules in dye when treated at high temperatures. It also improves the dispersion.
Use of liposomed disperse dye formulations that are completely free of synthetic surfactants and display higher dispersing effect, thus increasing dye uptake into the polyester fiber is on rise. The liposomic disperse dyes permit the reduction in deposition of disperse dyes in the dyeing conditions and also increases the stability. The increase of dye dispersion during dyeing or printing process increases its absorption onto the fabric. The dye exhaustion and colour fastness also increase substantially with liposomed disperse dye formulations. The best aspect of liposomed disperse dye formulations is that it is easy on environment, which is one of the most important factors for the textile units of modern times. The biodegradability in residual dyeing liquor increases with liposomed application and there is decent amount of reduction in conductivity and chemical oxygen demand in wasting waters (more than 1000 units). These features allow reducing waste dye bath with environmental benefits.
Use of disperse dyes cannot be avoided, as synthetic fibres are largely used by the garment factories. In such a scenario, the innovations and researches to make disperse dyes better in terms of environment and applicability is the best available option with the textile sector.