• Factors related to dyeing conditions
  
  
  • Dye concentration
  • Characteristics and amount of dyeing auxiliaries (dispersant, leveling agent, carrier etc.)
  • Dye bath pH
  • Quality of water used in dyeing
  • Dyeing temperature (temperature raising conditions, simmering temperature etc.)
  • Dyeing time
  • Volume of substrate in the dye bath
  • Dye bath circulation efficiency

 

Dye bath pH

90 per cent of disperse dyes are azo dyes, which decrease in the presence of alkaline pH; thus reducing the shade depth. Hence, acidic pH is very important to maintain in dye bath.

Time

Prolonged boiling or high temperature increases the particle size of the disperse dye through agglomeration of dye crystals. High agglomeration causes irreversible precipitation of the dye. Hence, to minimise the aggregation tendency, proper selection and control of dispersing agent and additives is essential.

Machine

Package or beam dyeing machines are strictly discouraged for polyester dyeing. A variety of jet dyeing machines-including the soft flow type and low liquor ratio type over flow units-are more or less suitable for dyeing polyester.

The chances of uneven dyeing can be removed by using high rate liquor circulation. Polyester fabrics are structured with a large number of small interstices which make it extremely difficult to wash out any unfixed dye and chemicals completely. Therefore the dyeing machine used should also have an efficient washing system.

The latest machines handle a wide range of fabrics including PET micro fibre fabrics. This machine helps maintain the quality associated with level dyeing of PET. In this machine, a new air jet attachment has been introduced to provide a solution to reduce the variation in dyeing. This newer jet dyeing machine with air jet attachment is especially good for dyeing the pure synthetic polyester fabrics at a low liquor ratio of 1:3

Skitteriness

Skitteriness occurs due to the differential dye uptake by the fibres in the fabric. Often one cannot dye two components in a fibre blended fabric in exactly the same shade if one of the fibres is highly lustrous while the other is devoid of luster.

Remedies include:

• In piece dyeing, ensure that polyester of different deniers is not mixed together at any stage. The skittery could be due to mixing of polyester fibres of different deniers between 1.2-1.5 deniers.