What are right practices of Continuous and Semi Continuous process of woven cotton fabric, from preparation to reactive dyeing?

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What are right practices of Continuous and Semi Continuous process of woven cotton fabric, from preparation to reactive dyeing? What are reasons for the following problems and how they can be taken care of?

Problems:

1. Tailing
2. C/S variation (Center to selvedge)
3. Back to Face variation
4. Lot to Lot variation
5. Specks and spots in dyeing.

Continuous Processing of Cotton woven fabric: A general process sequence may be as below:

PRETREATMENT PART:

1. Singe & Desize (Semi Continuous process)
2. Scouring or Boiling
3. Peroxide Bleaching
4. Neutralization
5. Drying
6. Mercerising and washing off to a pH of 6
7. Neutralizing
8. Drying
9. Ready For Dyeing (RFD stage).

1. Singeing & Desizing:
1. Recipe: Bactosol HC   = 5 g/l
2. Common Salt              = 5 g/l
3. Wetting Agent (100%)= 3 g/l

                                                               i.      Do cold padding with the above chemicals, batch, and keep rotating the batch for 8 hours;

                                                             ii.      Desize washing in 4 compartments @ 90mts/minute speed.

2. Bleaching (Continuous Process)-
1.  Caustic Impregnation: 

                                                               i.      Recipe:

1.      Caustic Soda       = 70gram/liter

2.      Lissopal D paste = 10 gram/liter

a.       4 dips – 1 nip @ 90 mtrs/minute speed.

b.      Steaming @ 105°C for 45 minutes in the steaming chamber.

c.       Cold Wash in 2 compartments (4 dips – 1 nip) x 2

2. J-BOX Bleaching optional

                                                               i.      Recipe:

1.      Sodium Hypochlorite = 2 g/l Avl Cl₂

2.      Dwell time in J box – 30 to 45 minutes at room temp.

3.      No washing

3. Peroxide Impregnation:

                                                               i.      Recipe:

1.      Hydrogen Peroxide(50%)  = 3 ml/liter

2.      Stabilizer                          = 0.5 gram/liter

a.       4 Dips – 1 Nip at cold.

b.      Steam in Peroxide Steamer for 45 minutes.

3.      Washing in 5 compartments with each 4 dip and 1 nip.

4.      Dry and batch on A frame roller.

3. Mercerisation: (Chainless Merceriser)

                                                               i.      Recipe:

1.      Caustic Soda  = 280 to 300 gpl

2.      Permenol N = 10 g/l

a.       Cold Padding Speed:

                                                                                                                                       i.      Bleached Fabric = 25 mtrs/minute

                                                                                                                                     ii.      Grey Fabric        = 15 mtrs/minute

                                                                                                                                    iii.      Scoured Fabric   =  20 mtrs/minute

b.      Mangle Pressure: 3.2 to 4 kg/cm²

c.       Liquor Pickup : 110%

d.      Recuperation:

                                                                                                                                       i.      1^st compartment – strength = 8 to 27 gpl

                                                                                                                                     ii.      1^st compartment – temp = 90 to 95°C

                                                                                                                                    iii.      2^nd compartment – strength = 1.6 to 6.4 gpl

                                                                                                                                   iv.      2^nd compartment – temp = 65 to 95°C

e.       Wash Tanks:

                                                                                                                                       i.      Tank 1 – 50 to 55°C

                                                                                                                                     ii.      Tank 2 – Acetic Acid Neutralizing

                                                                                                                                    iii.      Tank 3 – 60 to 70°C

                                                                                                                                   iv.      Wetting Agent room temp

f.        Final fabric pH – 5.5.to 6.0

g.       Drying:

                                                                                                                                       i.      Fabric is dried in cylinder or stenter and batched as RFD.

4. Continuous Dyeing Method for 100% Cellulose:
1. There are 3 methods:

                                                              i.      Pad – Dry – Chemical Pad – Steam

1.      Dye Liquor Preparation & recipe:

a.       Cotfix Dyestuff            =   x  grams/liter

b.      Wetting Agent             = 2-3 gram/liter

c.       Antimigartion agent     = 8-10 gram/liter

d.      Mild Oxidizing Agent  = 5-10 gram/liter

2.      Padding Temperature should be < 35°C

3.      Liquor Pick up%     = 60 to 80

4.      Chemical Pad Recipe:

5.      Chemical Padding Temperature < 35°C

6.      Liquor Pickup                            70 to 80%

7.      Steaming                                    45-90 seconds with     

                                  Saturated steam                                      (101 to 105°) the steam should be free

                                                          from acid.

                                                             ii.      Pad-Dry-Steam:

1.      This is carried out on a padding mangle attached with either Hot Flue or Flow Dried. To fix the dyestuff, the dried material is steamed in the normal continuous steamer for 4 to 7 minutes at 100 to 103°C.

2.      PAD LIQUOR PREPARATION for VS dyes:

3.      Take all the precautions and conditions mentioned for Pad –Dry-Chemical Pad-Steam.

                                                            iii.      Pad-Dry-Thermo fix Process:

1.      Here again there are 2 processes:

a.       Soda Ash Method

b.      Sodium Bicarbonate Method

PAD LIQUOR PREPARATION for VS dyes

The material is padded in the above liquor at room temperature, dried & thermo fixed as follows:

5. After treatment:
1. Overflow Cold wash in soapers 4 dip 1 nip in 2 compartments
2. Neutralization with Acetic Acid in the soaped at cold with 2 ~3 g/l Acetic acid.
3. Hot wash in one compartment (soaper) @ 80° , 4 dip 1 nip in
4. Soaping with 2 g/l of soaping agent (Sandopur RSK) at 90°C
5. 2^nd soaping with 1 g/l soaping agent (Sandopur RSK) at 90°C
6. Hot Wash
7. Hot Wash
8. Cold Wash
9. Acetic Acid Treatment 1 g/l or Formic Acid treatment 0.5 g/l
10. Squeezed on the last mangle and either plaited or wound on a batcher and taken for drying.

 

Possible Faults that may occur during the above process and check points/rectification:

1.            Tailing: The Alkalinity in the mercerized fabric would be un-uniform ranging from 0.25 to 1 and above gram/liter due to inefficient recuperation. That means more and more alkalinity would be carried over on the mercerized cloth and that can be checked in lab by titration. Any variation in the alkalinity of the mercerized fabric can show up through the length by the dye affinity difference and that is tailing.

a.       Check Point:

                                                                                                                                       i.      Alkalinity of the mercerized cloth has to be quantitatively checked in the lab at intervals of 500 meters. It must be uniform.

2.            C/S Variation – may arise due to

a.                   Desizing – Expression of the squeezing mangle is to be checked at frequent intervals.

b.                  Caustic Impregnation - Expression of the squeezing mangle is to be checked at frequent intervals.

c.                   Peroxide Bleaching:

                                                                                                                                       i.      Steam Pressure

                                                                                                                                     ii.      Steam Temperature

                                                                                                                                    iii.      Time duration of the steaming are to be controlled.

                                                             ii.      Mercerising – Impregnation Mangle expression has to be checked.

1.      Recuperator Efficiency has to be checked at every 1000 meters.

2.      Final Alkalinity of the mercerized fabric should be less than 0.25 g/l of caustic.

3.      Soaper washing – Acid for neutralization should be prepared in volume and should be fed in to the neutralization tank continuously. 

4.       To counter check, the fabric absorbency may be checked in the center and the two selvedges at regular intervals.

3.          Face to back variation

a.       Mangle Expression in the dye padding should be 70% and chemical padding should be 80%.

b.      Thermosol temperature difference between faces may result in migration of dyestuff.

c.       In a 2 dip 2 nip mangles, if the expression of both the mangle are not identical, then back to face variation is possible at any stage, dyeing, finishing etc.

d.      In stenters, if the hot air blowers are not functioning, there may be face to back variation.

e.       In jigger dyeing machine, out of the two bottom rollers, one is not rotating properly then back to face variation is possible.

4.      Specky Dyeing:

a.       Improper dissolution of dyestuff:

                                                                       i.      The quantity of the dyestuff is to be pasted, say for 1 kg of dyestuff, 5 liters of soft water should be used for pasting. Then 1 kg of urea is dissolved in 5 liters of water and this solution is added in the paste and stirred well to make a uniform lump less slurry. About 40 liters of hot water at 85°C is added to the slurry which is kept under a high speed stirrer. The hot water should be added slowly to the rotating vertex of the dye slurry. The filter this dissolved dyestuff through a fine gauze.

                                                                     ii.      Temperature of dissolution:

1.      M-Brand        = 50°C

2.      V.S                = 80°C

3.      ME, XL, HE = 80°C.

                                                                    iii.      The dissolved dyestuff may be spotted on a filter paper  - a uniform circle shows proper dissolution.