DYEING METHODS OF REACTIVE DYEING

Basic method of reactive dyeing:

Three basic steps are as follows for reactive dyeing of cellulose fibres with reactive dyes:
1. Exhaustion of the reactive dye from an aqueous bath containing common salt or Glauber’s salt normally used in neutral condition.
2. Addition of alkali to promote to further reactive dye uptake and chemical reaction of absorbed reactive dye with the fibers.
3. Dyed material with reactive dye is then rinsed and soaped to remove electrolyte, alkali and unfixed reactive dyes.

Parameters of dye absorption for reactive dyeing:
This is the first dyeing phase, that takes place in the same way as cellulose fibre dyeing with non reactive soluble dyes; in this phase the reactive dye does not decompose, but only diffuses towards the interior of the fibre, where it is absorbed by the cellulosic chains by secondary type forces.

The following dyeing parameters influence the absorption:

(a) Nature of the reactive dye
(b) Liquor ratio of reactive dye bath
(c) Electrolyte concentration in side the dye bath
(d) PH of the liquor
(e) Temperature of the reactive dye bath
(f) Type of the fiber to be dyed with reactive dye
(g) Reactive Dyeing time
(h) Alkali concentration in the liquor

Dyeing method for Reactive dyes: 

1.Discontinuoues method of reactive dyeing
2.Semi continuous method of reactive dyeing
   a) Pad jig reactive dye method
   b) Pad batch reactive dye method
3.Continuoues method of reactive dyeing
  a) Pad steam reactive dye method
  b) Pad thermofixation reactive dye method

CONTINUOUS METHOD OF REACTIVE DYEING:
Reactive Dyeing Process of Pad steam method:

This method is suitable for all types of reactive dyes. Recipe is given below:

Shade	Dyestuff g/l	Migration inhibitor	Soda ash g/l	Salt g/l	Urea g/l
Light	0-10	Small quantity of Na-alginate	5	40-60	150
Medium	10-20	Same	5-10	60-80	150
Heavy	>20	Same	10-20	80	150

Reactive Dyeing Process of pad steam method:
In pad steam method of reactive dyeing in the 1st bowl padding is done with reactive dye solution and urea at a temp of 60-800C. Here urea helps to dissolve the reactive dye completely in water and also to penetrate the reactive dye within the fiber. In some industries Na-alginate is used which act as a migration inhibitor may be add in the 1st bowl and other industries used Na-alginate in a separate bath just after padding with reactive dyes and urea. After padding with reactive dyes, urea and migration inhibitor, the fabric is then added with soda ash and salt at 600C which is known as chemical padding. Then the fabric is passed through the steam chamber at a temp of 100-1020C where it takes 30-60 sec for fixing the reactive dye with the fabric. Then the fabric is subsequently rinsed, soaped at boil and finally washed and dried to complete the dying operation.

Reactive Dying Process of Pad thermofixation method:
Recipe:
Dye – 2% on the weight of material
Soda ash – 1% on the weight of material
Salt – 8% on the weight of material
Urea – 15% on the weight of material
Na-alginate – Little amount

Process of reactive dyeing:
In this method reactive dyestuff, alkali(soda ash), salt, urea and Na-alginate are mixed in the dyebath. The fabric is padded in the padding bath at room temperature. Then the padded fabric is dried in the drying unit. After drying the fabric is treated for 5 minutes at 1600C in a heating chamber for thermofixation. After thermofixation the fabric is rinsed, soaped and rinsed. This method is suitable for moderate reactivity dye.

Semi continuous method of reactive Dyeing:
Pad batch reactive dyeing method:

Recipe:
Dye – 3% on the weight of material
Soda ash – 15 g/l
Salt - 60 g/l
Urea – 150 g/l
Na-alginate – Little amount

Process of reactive dyeing:

The fabric is padded with reactive dye, alkali, salt, urea and Na-alginate at a temp of 20-250 C. The padded fabric in roll form is transferred to a chamber where the temp is 200C and relative humidity is 100%. Four such rolls are prepared at the same time and they are kept at revolving condition so that dyes can not be settled due to centre of gravity at the lower part of the roll causing unevenness. On the basis of reactivity batching is done for 2-4 hours.Then the fabric is rinsed, soaped and rinsed. This method is suitable for high reactivity dye.

Pad-Jig method of reactive dyeing:
Process of dyeing:

In this method of reactive dyeing the fabric is padded with dye liquor in a padding mangle. No alkali and salt is added in this stage of padding. When the fabric is padded with reactive dye it is worked at room temperature. The padded fabric is then transferred to a jigger dyeing m/c. In this machine the dye is developed with the addition of salt and alkali. After the fixation of the dye in the jigger dyeing machine the fabric is rinsed, soaped and rinsed thoroughly. This method is suitable for closely woven fabric and also for fabrics made with hard twisted yarn.

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