Characteristics of Dyes PDF

Characteristics of dyes Prepared by: Ts. Dr. Mohd azlin bin mohd nor / MIAK In order for a colored chemical to serve as a useful dye it should have the following features: Intense color Solubility in water Substantivity to the fiber Durability to wet trea...

Characteristics of dyes Prepared by: Ts. Dr. Mohd azlin bin mohd nor / MIAK In order for a colored chemical to serve as a useful dye it should have the following features: Intense color Solubility in water Substantivity to the fiber Durability to wet treatments Durability to further treatments in production and normal use Safe, easy to handle and reasonable priced  Intense color Bright shades are preferred since duller shades can be made by mixing the brighter ones Small amounts of dyes are sufficient to obtain the desired shades because adding large quantities of chemicals or finishes to textiles may impair their handle, appearance, etc. In practise the increase in weight of fibers by dyeing is between of 0.1% - 3%  Solubility in water Dyes are soluble or dispersible in water – at least some solubility or able to be converted temporarily into a soluble form Water is the vehicle of exhaust dyeing – carries the dyes to the fibers Dyes that form true solutions are in the proper state of single molecules and are ready to be absorbed by the fibers But some soluble dyes tend to form small aggregates (a few molecules grouped together). These aggregates eventually dissociste into single molecules which can then diffuse into fibers  In contrast, disperse dyes are sparingly soluble in water. They require a surfactant (dispersing agent) to form cloudy dispersions. In dispersion, disperse dyes are in the form of extremely fine particles, each consist of hundreds or thousands of molecules grouped together, capable of staying in water for a limited time only. Their solubility increases with increasing temperature  Substantivity to the fiber The affinity that a dye has to a particular fiber is referred to by the dyers as substantivity. This affinity is necessary to drive the dye molecules from the dyebath onto the fibers. The substantivity of a dye to a fiber must be much stronger than its affinity to water. Therefore using dyes with high substantivity will increase the yeild of dyeing.  Durability to wet treatments The dyes must posses the ability to become durable to wet treatments. A high substantivity can sometimes provide sufficient durability of the color to a limited number of mild washings. In many cases, however, an additional after- treatment is needed to obtained the required fastness.  Durability to further treatments in production and normal use Dyes should have fastness to further treatments in production and normal use. For example, durable press finishes usually follow dyeing of cellulose containing fabrics. In this case, the dye should be capable to withstand the low pH and the high temperature of the durable press process. In addition, dyes should have adequate fastness to sunlight, bleaching, perspiration, etc.  Safe, easy to handle and reasonable price Choose a group of dyes that best compromise the properties necessary for the particular textile product.