• Quality of the dye
• Quality of the dyeing auxiliaries
• Quality of the water being used to dye the material, soft water is preferred
• Condition of the dyeing machine, machines in good condition will be more reliable that machines with broken or missing parts

What are some important points to consider during the determination of a dye recipe for exhaustion dyeing with reactive dyes?

The optimum dyeing temperatures and dyeing conditions for reactive dyes differ according to the type of reactive group involved, so the first thing that must be decided is the type of dye that will be used.

The substantivity to cellulose of reactive dyes is lower than that of direct dyes, but the addition of inorganic salts to the dye bath can raise its substantivity. Usually, Glauber salt is used at a rate of 50g/L, but this rate should be increased in the dyeing of deep shades, and can be reduced with dyes that can be used in low salt dyeing. Inorganic salts can be added incrementally to dye baths for level dyeing, and the preliminary addition of Glauber salt, that is, implementation of a dye bath with this pre-dissolved inorganic salt, can be used for dyes with low primary exhaustion rates and with dyeing machinery that provide effective agitation and circulation in the dye bath.

Alkali is employed to promote the reaction between the dye and the fibre and the important point here is not the type of alkali used but the need for the pH of the bath after addition of the alkali, for example vinyl sulphone dyes require a pH of 11.5 for the reaction with the fibre to occur. Soda ash is easily used as the alkali because it is easily weighed as a powder and easily dissolved in water. Combinations of soda ash and caustic soda (sodium hydroxide) can be used to obtain a pH of 11.5. Because the dyeing rate of reactive dyes depends on a combination of exhaustion through substantivity and fixing through reaction, quantitative adjustments through the control of the dyeing rate by adjusting the rate of temperature increase, as are used for other classes of dyes, are not effective, but adjustments with the incremental addition of inorganic salts or alkalis (pH) are effective. Consequently, isothermal dyeing through the incremental addition of alkali or alkali dosing is used. The specifics of incremental addition and dosing are decided by the agitation efficiency of the dyeing apparatus. To prevent rope marks in the use of piece-dyes, a dye bath lubricant can be used in the bath, and if hard water is used in the dyeing process, a sequestering agent can be added.

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