Summer prcoessing problems & solutions
Drying up of water sources such as ponds, lakes and even dams are taking place during this season due to the high temperature rises we experience year after year.
The drying makes the water sources to acquire high TDS levels and increased levels of hardness. Even river water during this season used to have higher levels of TDS and hardness.
This hardness and TDS impart so many dyeing and bleaching problems.
The white precipitate of hardness that occur on the fabric or yarn during alkaline treatments such as scouring, bleaching and dyeing produces various quality oriented problems such as dusting, un level dyeing, low colour yield, less brightness, lower whiteness levels, poor rubbing fastness and nil reproducibility of batches.
So be cautious during this season and try to use good quality of water by increasing your water-softening-plant capacity or by judicial inclusion of a good sequestering agent in the alkaline treatment baths.
Some Useful Tips :
1.A good pretreatment always results in good results. A thorough scouring, bleaching and neutralization of fabric and a good absorbency are essential criterions for a good pretreatment. The RFD (Ready For Dyeing) stage fabric/yarn should be uniformly white, absorbent and free from residual alkali, chlorine, Hydrogen peroxide.
2. The dyeing starting may be done at a pH between 5.5 and 6.5.
3. No mixture of classes of dyes should be done viz., Cold brands & Hot brands or Vinyl-sulphones (V.S) and Bifunctional (ME) or High Exhaust (HE) and Bifunctional (ME) and so on.
3. Avoid using Calcium hypochlorite for bleaching. Better use Sodium hypochlorite. Use appropriate anti-chlor treatments to remove the residual chlorine from the fabric. Check for residual chlorine using special indicator solutions available in the market or with an acidified Potassium Iodide solution. Thorough washing is essential to remove the remaining anti-chlor chemical from the fabric.
4. While dyeing pale and critical shades, after peroxide bleaching, proper peroxide killer should be used to remove all the residual peroxide from the fabric. All blues and turquoise blues are very sensitive and prone to get oxidized leaving behind colorless chromospheres.
5. All dark shades should be soaped thoroughly using a neutral soaping agent.
6. After dyeing run a cold wash followed by neutralization and two or three warm washes to remove the salt from the fabric. If soaping is attempted without removing the salt, a partial stripping will take place resulting in poor dept
7. No cationic fixing treatment is necessary if good soaping and proper washings are carried out in good quality water.
8. The tonal changes during compacting in the case of knits, take place mainly due to the destruction of chromospheres of the dye molecule by the fixing agents used. So avoid using cationic urea formaldehyde or melamine formaldehyde fixing agents. A simple softening treatment with a good silicone softener yields good softness and crocking fastness.
9. Make proper selection of dyestuff mixture, according to the shade, depth, machine availability, environmental shortfalls etc and lastly by economy.
Precautions in dyestuff dissolution:
There are so many simple but important hints that would be floating among the experienced dyeing managers. Those pivotal points can be shared among the audience here to benefit your colleagues.
The dissolving and careful dispensing of dyestuff is a crucial step, which determine the colour yield, repeatability and lab to bulk reproducibility.
For a tri-chromatic combination, the individual dyestuff in the combination should be weighed and put into separate three containers. Each dye should be dissolved separately using 1:15 M: L ratio i.e., for 1 kg of dye 15 liters of water should be used. First the dye should be thoroughly pasted into a uniform colloidal mass with a little cold water. Then dilute with hot water (80°C ) while continuously stirring.
Filter through fine bolting cloth and the mix the three dye solutions.
Do not add urea directly to the solid dye powder. If a large quantity of dyestuff is dissolved, add 1/10th by weight of urea, to improve dissolution.
Turq Blue H2GP and Turq Blue G should be dissolved only with warm water ( temperature should not be more than 60°C; otherwise very hot water would produce lumps and oil like products separation may occur). This oily mass would create turq blue dark speck marks here and there.
Turquoise Blue G and Turquoise Blue H2GP combinations:
Do not use non-ionic detergents, wetting agents, dispersing agent in the pretreatment of fabric.
Similarly do not use non-ionic products during dyeing.
Use of sequestering agents do not have any detrimental effect on the dyeing of metal complex dyestuffs like Turquoise Blue G, Turquoise Blue H2GP or Blue R spl. A neutral to alkaline pH stable sequestering agents are preferable.
Do not use common salt or vacuum salt. Use only Glauber’s salt.
Do not use Caustic Soda for fixation.
Use of TSP (Tri Sodium Phosphate) in place of Soda Ash gives better color yield and fastness.
Better color yield and fixation is obtained only at 85°C. While dyeing combinations with vinyl-sulphone, dye at 60°C for ½ to ¾ hour and then raise the temp to 85°C and dye for another ½ hour to fix the turquoise blue.
While dyeing pale shades using these dyes, take care to eliminate the residual peroxide, which will result in uneven dyeing.
Ensure thorough soaping before doing any cationic fixing treatment.
Do not unload the batch from the machine if proper cationic fixing is not done. Sometimes the unfixed residual dyes that migrate with water may form drip marks on the fabric.
Refer: Turquise Blue Dyeing Procedure:
Sampling/Shading/Addition of Dyes during dyeing:
1. Do not compare any sample taken just after the addition of salt against the standard shade. This will mislead you.
2. Take sample, 30 minutes after the addition of soda for light & medium shades and 45 minutes for dark and very dark shades.
3. Wash Cold- ½ minute
4. Wash Hot – 60°C- ½ minute
5. Neutralize – cold- ½ minute with 1 g/l acetic acid.
6. Neutral soap – boil – ½ minute
7. Neutral soap – boil – ½ minute
8. For dark and very dark shades, do 6 soaps of ½ minute duration.
9. Cold wash.
10. Check shade.
11. If shade is not matching, and if you want to make 10 or 20 or 30% addition in total, drain the running bath up to ½ volume, refill with fresh water, then add the required dye (pre-dissolved, filtered) in two portions, continue dyeing for another ½ hour. Do not make any addition of salt or soda into the bath.
After dyeing is over, drain the bath.
Do one cold wash – no running bath.
Do one hot wash -- 60°C – 10 minutes.
Do neutralization with 1 to 2 g/l of Acetic Acid.
Do one cold wash.
Neutral soap 0.5 to 1.0 g/l at 80 to 90°C for 15 minutes.
Hot wash at 80°C – 10 minutes.
Cold wash – 10 minutes.
Softening treatment with some non-ionic softener.
Fabric Faults Created During Dyeing - With Respect to Soft Flow Dying:
Cockling: using a larger diameter nozzle, increasing the liquor ratio and reducing the fabric speed can generally eliminate Cockling or Dimpling of the fabric. However in the case of heat sensitive or thermoplastic fabrics, care should be taken to arrive at a “compromise speed�?. As running the material at too low a speed during cooling, will also cause cockling.
Crack, Rope and Running marks: Running marks are frequently related to material’s construction, and are caused by poor opening of the fabric rope. They can be avoided by either presetting or pre-relaxation of the fabric before dyeing.
Running and crack marks can also be a result of incorrect process procedures.
A high fabric speed, combined with slower rates of rinse and cooling will often correct the problem.
Reducing the machine load and running at a slightly higher nozzle pressure, or using the next largest available nozzle size, may also help.
Cloudy Dyeing: Inadequate pretreatment is the reason. Check your pretreatment cycle.
Too much foam in the dye-bath: Use de-foamers.
Pale areas: Inadequate pretreatment.
Deviation of shade: Dye sensitivity to hydrolysis, reduction, electrolyte concentration – to check all these parameters. Select dyes carefully. Pay attention to stability of dye to the electrolytes (salt), dye sensitivity to metal ions in the dye-bath (use suitable sequestering agents).
Precipitation in the Dye-bath: Pay attention to chemicals in the dye-bath