Cold Pad Batch Method of Reactive dyeing

COLD PAD BATCH dyeing is a more environmentally sound and higher quality dyeing
method for woven and knitted cotton/viscose fibers. The process removes salt from the
effuent, reduces the use of water, energy, reduces the volume of effluent and occupies less
space on the production floor.
Benefits of CPB dyeing can be summarized as follows;

  • Relatively low cost of equipment
  • Less surface area
  • Low amount of effluent
  • No salt residue in effluent water
  • Conventional exhaust dyeing system emits up to 1 kg salt per kg of fabric
  • Low steam consumption, 50 percent less
  • Low electricity requirement, 30 - 40 % less
  • Improved fabric quality
  • Reduced labot cost
POINTS TO BE CONSIDERED
Machinery and Production Area, Laboratory
  • Padding cylinders should be horizontally mounted.
  • Padding trough should have small volume of 15 - 25 liters.
  • For the cooling front and back side of entering fabric, two water cooled cylinder should be available
  • Padding trough should be clad in a cooling jacket to maintain a constant liquor temperature. Ideal temperature is around 22 - 23 °C
  • Lab. padder should be also horizontal and liquor should be placed between the nips of cylinders.
  • Dyed lab. samples should be kept at the same temperature of production dwelling area
  • Dwelling area should be air conditioned and kept 3 - 5 °C above padder temp.
  • Lab. padder and batching area should be away from sun shine, air current, chemical fumes.
  • Dye/alkali supplying pump should run always at 4/1 ratio and be checked regularly.
  • Batch rotation should be around 5 - 10 rpm.

FABRIC

  • Fabrics should be uniformly bleached, and if possible mercerized.
  • Absorbency should be high and be same along width of fabric.
  • Fabric should be uniformly dried and cooled down prior to padding.
  • Fabric stitching should not be overlapped.
DYE
  • Dyes should have high solubility at room temperature water.
  • Dyes should have similar substantivity in order to prevent tailing.
  • Dyes should have similar reactivity to obtain excellent reproducibility
  • Dyes should have higher alkali stability to prevent hydrolyzation.

CHEMICALS
Alkali Resistant Penetrator: For uniform absorbtion of dye along with fabric, a
powerful, foamless, alkali resistant penetrator is required. Usage amount is 1 - 3 g/L. It should be silicon
antifoam free.
Sequestering Agent: In order to diminish calcium and silicate deposition on the fabric
and cylinders, a strong sequestering and dispersing chemical is required. Application amount is 1 - 3 g/L.
Anti-clogging Agent: In order to prevent agglomeration of dyes and hence dye spot problem,
an Anto Clogging Agent is added into the dye solution. Recommended amount is 5 g/L. In case of
Turquoise combinations, 10 g/L is advised.
SILICATE: Silicate is used as hydrolytic stabilizer of dyes in alkaline medium with
NaOH. Normally 50 ml or 95 ml is used but in tropical conditions 110 ml is preferred. Silicate
gravity is 38 - 40 Bé. By increasing dosage amount, stability is promoted but fabric hardness
and silicate sedimentation on cylinders is inevitable.

Recipe :

  • NaOH
  • SILICATE
  • DYE x g/L
  • Penetrator 2-3 g/L
  • Sequestering agent 1-3 g/L
  • Anti Clogging Agent 5-10 g/L

DWELLING TIME
Batching area should be conditioned kept at 3 - 5 °C above the padder temperature.
Dwelling time varies according to the chemical reaction group of dye.

Dye Group Batching Time
Black Dyes 6-8 hrs
Vinyl sulphone dyes
12 hrs
Brill Blue R spl 12 hrs
BIFUNCTIONAL DYES 12 - 16 hrs
Grey HFL 24 hrs
Turquoise Blue 24 hrs

 

 

 

 

 

 

Extension of dwelling time has no effect on the tone or yield of VS dyes.

WASHING
For efficient washing of CPB dyed fabrics, 7 - 8 chamber washing tank is sufficient. In
the first 2 - 3 tank, excess amount water is used, to remove silicate and drop the pH to
8 - 8,5. Temperature in these tanks should not be above, 50 °C. If pH does not drop or
washing machine is short, it is wiser to wash rest of the chambers at 50 °C and in the second
pass at boiling temperature.
1. Chamber 50 °C
2. Chamber 50 °C
3. Chamber 50 °C pH 8 - 8,5
4. Chamber 98 °C No foam soaping agent 4-5 gpl
5. Chamber 95 °C
6. Chamber 98 °C
7. Chamber 70 °C
8. Chamber 40 °C