What are Dyes?

Dyes are coloured substances that possess a great affinity to the substrate to which they are applied. The colouration process is carried out in the aqueous solution where they require mordant to enhance the functioning of dyes on fiber. One such example of dye is Azobenzene.

Properties of Dyes

1. Dyes molecules are initially available in their coloured state.

2. They possess a chromophore group, which reacts as a colour-bearing group.

3. They are water-soluble and a solution can be prepared by dissolving them in water.

4. Must hold the power of entering dyestuff to fiber from dye bath.

5. Excellent fastness properties i.e. colourfastness to light, wash, rubbing, etc.

What are Pigments?

The objective of pigment is the same as dyes i.e. to impart colour to fibers. However, pigment changes the colour of reflected or transmitted light as a result of the wavelength in which a material emits light. Quinacridone, Dioxazine are some of the well-known pigments.

Properties of Pigments

1. They are water-insoluble.

2. They are available in both organic and inorganic in nature.

3. Their size ranges from 1-2µ.

4. Should possess excellent covering and mixing properties.

5. Should hold good resistance to solvent.

Different Types of Dyes

Acid Dyes

These are water-soluble anionic dyes that are applied to fibers such as silk, wool, nylon, and modified acrylic fibers using neutral to acid dye baths. The fiber attachment is attributed partly to salt formation between dyes anionic groups and fiber cationic groups. Acid dyes are not suitable for cellulose fibers but are widely used for synthetic food colours.

Basic Dyes

These are water-soluble cationic dyes and are applied to acrylic fibers, wool, and silk. Acetic dyes are added into the dyebath to help the uptake of the dye onto the fiber. Basic dyes are also endorsed for the colouration of paper.

Direct Dyes

Direct dyeing is the colouration process carried out in a neutral or slightly alkaline dye bath, at a temperature near the boiling point, by adding either sodium chloride or sodium sulfate, or sodium carbonate. Direct dyes are best suited for cotton, paper, leather, wool, silk, and nylon. These dyes are used as PH indicators and biological stains.

Vat Dyes

These water-insoluble dyes are incapable of dyeing fibers directly. However, reduction in alkaline liquor produces the water-soluble alkali metal salt of the vat dyes, i.e. in the leuco form, and holds the affinity for the textile fiber. Subsequent oxidation reforms the original insoluble dye. This is why the colour of denim comes from indigo that is the original vat dye.

Reactive Dyes

They utilize a chromophore attached to a substituent that holds the capacity to directly react with the fiber substrate. Covalent bonds that attach reactive dyes with natural fiber make them among the most permanent of dyes. “Cold” reactive dyes like Procion MX, Cibacron F, and Drimarene K are easy to apply at room temperature.

Disperse Dyes

These were initially developed for dyeing cellulose acetate and water-soluble. These dyes are finely grounded in the presence of dispersing agents and sold in the form of a paste, or spray died or powder. In some exceptional cases, a dyeing temperature of 130°C (266°F) is required, and a pressurized dye bath is used. Its fine particle size gives a large surface area that aids dissolution to allow uptake by the fiber. The dyeing rate also depends on the choice of dispersing agent used during the grinding.

Sulphur Dyes

These dyes consist of two-part that are widely used to dye cotton with dark colours. The primary bath imparts a yellow or pale chartreuse colour, that is after being treated with a sulphur compound, produce the dark black we are familiar with in socks, for instance, Sulphur Black 1 is the largest selling dye.

Veeraco Colourants Private Limited is a top dyes and pigments manufacturer in India, provide all kinds of dyes and pigments.

You may also read:

Types Of Dyes Used In Textile Industry

What Are Dyes And Pigments?