Methods of dyeing

Dyeing can be carried out using any one of the following ways:

• Batch-wise dyeing process
• Semi continuous process
• Continuous process

Batch wise Dyeing:

Batch wise dyeing is oldest process of dyeing. It is still very popular as it can be related to changing fashion where colour is one of the predominant factors.  Batch wise process is very useful when small size of lot to be dyed as per the requirement of buyers.  It is some time also referred as exhaust dyeing as the dyeing is exhausted directly on to the fabric using salts. This is because in this process, the dye gets slowly transferred or exhuasted from a comparatively large volume dyebath to the substrate or material that is to be dyed. In the batch wise process any form of materials i.e fibre, yarn , fabric or garments can be dyed.T here are three general types of batch dyeing machines. These are

First type: Textile material is in circulation while dye liquor in dye bath remains stationary.

Second type: In this type, dye liquor in the dyebath gets circulated while material that is being dyed remains stationary, and

Third type:  Here both, liquor in the bath and material to be dyed gets circulated.

Examples of dyeing machines that utilizes batch dyeing process are Winch or Beck, Jet, Jigs, Beam Package dyeing machines etc.

Important processing parameters for dyeing:

Important processing parameters for batch wise dyeing:  Following are the important processing parameters for batch wise dyeing:

Material to liquor ration (MLR): MLR of shall be taken as per the type of machine. For example, in winch dyeing MLR may be 1:20 or more. Means 1 Kg of material you need at least 20 litre of water. If it is a jet dyeing machine then MLR may be 1:10.

Dyeing Temperature: Dyeing temperature plays a crucial role while dyeing. The shade card/colour card should be followed while selecting temperature. For example for polyester dyeing temperature may be 130^oC.

Time Duration of dyeing: Here also shade card should be followed.

Single bath dyeing or double bath: If material is 100% cotton or 100 Polyester and any other fibre then single bath dyeing is carried out. However if there is a blend of fibres which can not be dyed by single class of dye then double bath dyeing is carried. For example if polyester-cotton (p/c) blend to be dyed then first polyester is dyed using disperse dye at 130^oC and then cotton is dyed in the second bath. It is to be noted that in the p/c blend, polyester has to be dyed first and then cotton. If cotton dyed first then during dyeing of polyester at 130^oC, cotton dye would bleed. 

Nature of Dyestuff, auxiliaries: The selection of dye according to the fibre to be dyed is most important. If the dye is not selected according to the fibre, there will be no dyeing and all efforts will go waste. So for cotton, one has to select cotton dyes like reactive dye, vat, sulphur or direct. If polyester then disperse dye should be selected.

The auxiliaries plays an important role while dyeing. For example salts (Sodium chloride of sodium sulhate) are needed to exhaust dye bath in the case of reactive dyeing. If salt is not added, reactive dyes will not exhaust at the optimum. Similarly sodium hydroxide is used as dye fixing agent.

After wash/rinsing: After dyeing it is necessary to wash dyed material other wise colour will bleed during uses of textile material.