Textile chemicals and dyes are either soluble in the dyeing medium or can dissolve into the textile substrate. Some major types of dyes as well as their detail like chemical nature and classes is below.
The direct dyes are one of the most cost-effective groups of dyes used for dyeing cotton and other cellulosic materials. they’re water-soluble and may be applied relatively easily employing a sort of method. These dyes are anionic in nature and have a charge in solution, as do the cellulosic fibers. The addition of common salt (sodium chloride) or Glauber’s salt (sodium sulfate) is typically necessary as well as during dyeing to beat repulsion between the charged dye and therefore the substrate. After absorption into the fiber, these dyes are held to the fiber by hydrogen bonding and/or Van der Waals forces. Supported their leveling properties. Direct dyes are grouped into three main classes:
- Class A: self-leveling dyes
- Class B: dyes with average leveling properties (controlled salt addition improves leveling)
- Class C: dyes with poor leveling properties (controlled salt addition and careful temperature control improves leveling)
Direct dyes usually don’t have excellent wash fastness properties and have a tendency as well as to dissolve from the material on repeated washings. However, Some various after-treatment, including:
- Treatment with cationic agents
- Treatment with copper sulfate
- Treatment with chrome compounds, like salt
- Treatment with combined salt and copper sulfate
- Treatment with formaldehyde
Disperse Dyes – Textile Chemicals
Disperse dyes have extremely low tide solubility and typically utilized in the shape of aqueous dispersions. From an application point of view, disperse dyes are often classified as follows:
Low energy disperse dyes: have a high rate of diffusion; have poor sublimation fastness
Medium energy disperse dyes: have moderate diffusion rate; as well as require heat exhaust dyeing method; have moderate sublimation fastness
High energy disperse dyes: have a low rate of diffusion; require as well as very high dyeing temperature; have excellent sublimation, wet and lightweight fastness properties
The disperse dyes are usually applied in acidic pH. As well as Within the presence of a dispersing agent.
Other dyeing auxiliaries may include a wetter, leveling agent, as well as dyeing carrier.
Reactive Dyes – Textile Chemicals
The reactive dyes constitute the foremost commonly used class of dyes for dyeing cellulosic textiles, due to their good all-round properties, like water solubility, simple application, sort of application methods, availability of various shades, the brightness of color shades, good to excellent wash and lightweight fastness and moderate price. Reactive dyes may have poor fastness to chlorine bleach.
The reactive dyes are further classified consistent with the sort of their reactive groups, giving them different degrees of reactivity. for instance, di chlorotriazine- based dyes are highly reactive and provide good dyeing results at low dyeing temperature, whereas dyes supported trichloro pyrimidine have poor reactivity and provides good color yield only at high dyeing temperatures. Vinyl-sulphone-based dyes have moderate reactivity.
The important process variables for dyeing with reactive dyes by exhaust method include dyeing temperature, type and amount of electrolyte (e. g. common salt or Glauber’s salt), dyeing pH (controlled by type and amount of alkali used) as well as liquor to material ratio and dyeing time. The fixation of reactive dyes as well as on cellulosic fibers takes place through the formation of covalent bonds under alkaline conditions (pH 9−11).
The typical exhaust dyeing procedure involves the exhaustion of the dye onto the substrate with salt addition and temperature control, followed by the addition of alkali for dye fixation as well through covalent bonding. After the dyeing process, any unfixed dye or hydrolyzed dye i. e. the Textile chemicals dye which has reacted.