1. Explain the dyeing of polyester fabric with disperse dyes using HTHP method with neat diagram.The dyeing of polyester with disperse dyes at the boil is slow because of the low rate of diffusion of the dyes into the fibre. The activation energy for diffusion is quite high and raising the dyeing temperature from 100 to 130 °C considerably increases the rate of dye diffusion. Dyeing at this higher temperature under pressure, without a carrier, considerably increases the rate of dyeing and gives better coverage of filament irregularities because of the improved migration of the dyes. Dyeing is then also possible using higher molecular weight dyes, whose rates of diffusion at 100 °C are unacceptable. This permits production of dyeing with better fastness to light and to sublimation during permanent pleating. For those fabrics and yarns that lose bulk when dyed at 130 °C, dyeing at a lower temperature (110–120 °C) in the presence of some carrier is preferred.

Step involved Process:1. Preparation fabric2. Preparation of dye solution3. Preparation machine4. Dyeing 5. Rinsing 6. Reduction clearing7. Rinsing 8. Hydro extractor 9. Drying

1. Preparation fabricTo make fabric whiteTo make the fabric is better wettablity due to remove the natural coluring matters.

2. Preparation of dye solution Take the required quantity of dye stuff and dispersing agent based on the shade

percentage and weight of the material Add few drops of water and make the paste Add remaining amount of water and dissolving dyestuff with stirring at 50ºC

Recipe:Disperse dyes - x %Dispersing agent - 1gplTemperature - 50ºCTime - 30 mins

Role of dispersing agent:

i. To disperse the dyesii. To reduce the molecule size of dyes

iii. To facilitate for easily dissolve in waterRole of temperature:

i. To dissolve the dyes in water3. Preparation machine

To clean the machine with water and load the fabric

Add the water with wetting agent depends ML ratio 1:5 to 1:10

Fabric is free run at water for 10 – 20 mins to make the fabric for wet condition and release the air

4. Dyeing Recipe

Dyes – depends on shade percentageWetting agent – 0.5gplAcetic acid – enough to get pH - 5 to 6Leveling agents – 0.5 to 1gpl (optional)

Temp Initial - 50 ºCFinal - 135 ºC

Time – 50 minspH - 5 to 6

The dye bath is set at 50 ºC with dispersing agent and leveling agents

Then add the acetic acid for adjust the pH of the dye bath is 5 to 6

The fabric is run at 15 mins at 50 ºC for this solution

The first portion of dye solution is added and run at 20 mins

Then add second portion of dye solution and raise temperature 90º C

Raise the temperature 90º C to 110º C at very slow rate of 0.5º C per minutes

Raise the temperature further for 135ºC at same rate

Dyeing is continue with 30-45 mins for this conditions

After dyeing, once again reduce the dye bath temperature 135º C to 90º C for settle fabric to

Original state and dye with 15 mins for this temperature.

5. Rinsing The dyed fabric rinsed with hot water for 10 mins in two times

6. Reduction clearing The dyed fabric treats with caustic soda (NaOH) and Hydrose (sodium hydrosulphite) at 60º C for 20 – 30 minutes. This treatment is to remove the any unfixed dye from the fabric

Caustic soda (NaOH) : 1 gplHydrose : 1 gpl(Sodium Hydrosulphite)Temp : 60ºCTime : 20-30 mins

7. Rinsing The dyed fabric rinsed with hot water for 10 mins Followed with cold water for 10 mins

8. Hydro extractor To remove the water from dyed material with help of hydro extractorTo facilitate to drying

9. Drying To dry the fabric with dryer or sun light.