Fastness properties of the Reactive dyes on cellulosic fibres

·       Fastness properties of the Reactive dyes on cellulosic fibres :

In general, reactive dyes on cellulosic fibres give dyeing with good to very fastness to washing and other wet processes. Apparent inferior fastness to washing is usually because of incomplete removal of unreacted and hydrolysed dye from the material by washing after dyeing.

The presence of unfixed dye can easily be tested for by hot pressing a wet sample of the dyeing sandwiched between two pieces of dry white cotton. Colour transfer to the white material indicates the presences of unfixed dye in the dyeing. It is more likely to be a problem for deep dyeing. The use of reactive dye is growing rapidly, faster than for any other dye application class. This is because these dyes also give dyeing of moderate to good light fastness, allow relatively simple and diverse dyeing methods and are available in a range of bright colours. In particular, the fastness to bleaching by chlorine, and to a lesser extent by peroxides present in modern household detergents is often only moderate.

Pad steam method

Pad steam method:

 

Steps:

1)    Fabric is first padded in a padder with the dye.

2)    It is then passed through between two squeezing roller in a dryer. Drying should be done slowly; otherwise precipitation of dye due to quick removal of water may take place leading to lower color value.

3)    After coming out from dryer fabric is padded in a padder containing salt and alkali. Due to salt exhaustion of dye takes place and due to alkali fixation occurs.

4)    Fabric then passed through a steamer where it is kept for 15-19 second. Due to high temperature here fixation rate increases.

5)    In this step fabric is washed in a washing machine to remove the unfixed dye.

Pad dry method

Pad dry method:

Steps:

1)    Fabric is first padded in a padder with reactive dye in presence of an alkali.

2)    Padded fabric is then passed through a squeezing roller into a dryer. As a dryer cylinder, stenter etc may be used. During drying due to higher temperature fixation of dye in fibre increases and at the same time water is removed by evaporation. 

3)    After drying fabric is washed in a washing machine to remove unfixed dye.

Different methods of reactive dye application: Pad-batch method

Different methods of reactive dye application:

1)    Pad-batch method.

Pad batch processes are of two types-

a)    Pad (alkali)-batch (cold) process.

b)    Pad (alkali)-batch (warm or hot) process.

2)    Pad dry method

3)    Pad steam method.

1)    Pad-batch method.

a.     Pad (alkali)-batch (cold) process.

Steps:

1)    The fabric is first padded in a padding mangle with reactive dye in presence of an alkali.

2)    The padded fabric is rolled in a batch and the batches are wrapped by polyethylene sheets and stored in wet condition for 1-24 hours at 200-300C in a room.

3)    During the storage period, the rolls may be kept slowly rotating to prevent seepage of the dye liquor.

4)    After storing time is finished fabric is washed in a rope washing machine to remove the unfixed dye from fabric surface.