Semi continuous process:

Pad-Batch dyeing is one of the best example of semi continuous process. Pad-batch dyeing is a cold method used for dyeing cellulosics (mainly 100-percent cotton and polyester/cotton blends) material.

With this process one can achieve large reductions in pollution, energy requirements, and costs.

The basic technique is to saturate the prepared fabric with a premixed dye liquor and pass it through a padder (Set of Squeeze rollers), which forces the dyestuff inside the fabric for greater penetration while removing excess dye solution. The fabric is then stored, or batched, on rolls or in boxes for 4 to 12 hours. Typically, the batches are covered with a plastic film to prevent carbon dioxide absorption and water evaporation. While in batching, the dyestuff reacts with and penetrates the fabric, resulting in even, consistent color. After the reaction is complete, the fabric is washed.

Pad-batch dyeing offers several advantages over conventional dyeing processes:

• No salt or chemical specialty agents are needed. Eliminating these chemicals reduces waste as well as chemical and wastewater treatment costs.

• More efficient use of dye leaves less color in the wastewater and reduces water and energy consumption. 

 • Dye quality is more consistent. Compared with rope dyeing, pad-batch dyeing can attain more even color absorbency, greater colorfastness, and much lower defect levels (when the fabric is correctly prepared). High-reactivity dyes used in pad-batch dyeing have rapid fixation and stability, resulting in shade reliability and repeatability. With highly reactive dyes, cleanup is easy and frequent shade changes present little problem.

• Pad-batch dyeing can be used on wovens or knits in many constructions. 

• Pad-batch dyeing requires a low capital investment and offers overall cost savings, in dyes, chemicals, labor, water, and other areas.