Types of Dyeing

Three  Basic Approaches of Dyeing

Textile dyeing can be carried out by three basic approaches.They are batch dyeing, continuous dyeing and semi-continuous dyeing. The type of process used depends on several factors including the type of materials and the quality requirements for the dyed fabric . In these cases, the dye is mixed with water, which acts as a solvent vehicle for the dye and as a swelling agent for the fiber.

Batch dyeing

Batch process is the most common method to dye textile materials. Batch dyeing is sometimes called exhaust dyeing because the dye moves from the dyebath liquor onto the fiber in a set time. During that time, it diffuses or migrates into the interior of the fiber and is fixed. The dye liquor, with initial high dye content, becomes gradually exhausted while the dye accumulates in the fiber.

The dyes preferred for exhaust dyeing are those with a high affinity for the fiber, Exhaust dyeing is done with a given liquor ratio. The batch dyeing of textiles can be undertaken in a range of different textile forms, some of these are loose stock(fibers), yarns, piece goods (fabric) and garments, The dyeing machines may include winch, jet, jig and beam dyeing machines in what we call batch dyeing. Small to medium sized batches can be processed using this method.

Continuous dyeing and padding

Continuous dyeing is most economic for production of very large lots of a single colour. Woven fabrics of cotton and polyester and their blend are predominantly used in continuous dyeing. Knitted fabrics are rarely dyed by this way, because they undergo considerable elongation when being under tension.

Most continuous dyeing processes can be divided into four stages:

1) Dye application by padding.

2) Dye fixation, usually in hot air or steam.

3) Washing-off of unfixed dye and anxiliary chemicals.

4) Drying, usually on infrared dryer or steam-heated cylinders.

Semi-continuous dyeing

The material may be padded with the dye solution on a mangle and finished off on a jig(pad/batch method). Pad-batch method is carried out in following phases:

1) Dye and alkali padding

2) Cold- rolled fabric resting stage.

3) Continuous washing and soaping in a series of tanks.