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.