Acid Wash Process on Denim Garments

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Last Updated on 28/01/2022

Acid Wash:
Actually, the term ‘acid wash’ is a misleading term because mineral acids are not used for this process. During acid wash on denim, pumice stones are used. By the action of pumice stones, irregular fading affect is developed on the heavy garments like denim, thick canvas/twill, and sweater. The pumice stones act a brushing action on the garment fabric surface. The area where more brushing action takes place there more discolor or fading affect is developed and the area where less brushing action takes place less brushing action and takes place less fading affect will be developed. The multi-layer fabric areas like –collar, calf, pocket, placket, side seam etc area will be brushed more than the single layer areas. As a result irregular fading affect will be developed on the garments fabric surface. Thus in this way fading affect may be developed on the denim garments by acid wash technique.

acid wash jeans
Fig: Acid wash jeans

In acid wash on denim, pumice stones are soaked in a strong oxidizing agent such as sodium hypochlorite or potassium permanganate, the excess liquor is removed. This can be accomplished by placing stones in net or mesh fabric before soaking. Then the stones can be removed and the excess liquor drained off. Another alternative is to place the stones in a rotary tumble machine along with ‘waste’ fabric and tumbling for several minutes to remove the excess solution. Another alternative is to use presoaked stones. There are many shapes, varying levels of chemicals and other additives which produce different effects. After soaking the stones, stones and denim garments are put into the machine for tumbling for 10–30 min or until the desired effects are achieved. Results are dependent upon dyestuff, fabric, concentration of chemicals, stones and equipment. In some cases, the stones can be reused for another load before resoaking, depending upon their porosity. It is advantageous to remove the denim garments from the machine and transfer them to another machine for washing to minimize the number of machines used for acid washing.

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After getting the desired effect, the machine is filled with water for rinsing for 5 min to remove the stone dust. If potassium permanganate is used, manganese dioxide gets formed (a brown/orange color) and must be removed by rinsing with oxalic acid. In the case of sodium hypochlorite, a reduction process, anticolor with a reducing agent (e.g. sodium bisulphite) is used for removing the residual chlorine.

In acid washing, the addition of water is not required. The color contrast after tumbling can be further enhanced by a subsequent optical brightening process. Soft stones that dust off easily are more suitable for this process.

Objects of Acid Wash on Denim:

  1. To produce irregular fading effects or old looking effect.
  2. For soft feeling to wear the garments i.e. to improve softness.
  3. To achieve the buyer washing standard.
  4. To increase rubbing fastness.

Step by Step Working Process of Acid Wash:
A processor Acid wash of 60 kg batch of Denim Trouser as mentioned below:-

First Step: Pretreatment/Desizing.

  • Add water @ L : R = 1 : 10 ………….. 600 litres.
  • Start Machine.
  • Add desizing agent @ 1 gm/litre ……………..600 Gms.
  • Add detergent @ 1 gm/litre …………………… 600 Gms.
  • Temperature……………………….. 60°C.
  • Time……………………… 20 mts.
  • Drop the liquor.
  • Rinse one for 3 minutes (cold).

Second Step: Hot wash

  • Add water @ L: R = 1: 10………….. 600 litres.
  • Temperature……………………….. 60°C.
  • Time……………………… 5 mts.
  • Drop the liquor.
  • Here hot wash is used to remove the adhering materials from the garment surface.
  • Unload the garments from the washing m/c in the trolley.
  • Load the pre treated garments in the dryer machine.
  • Dry the garment completely and unload the garments.
  • The pumice stones used for acid wash need to pre-treat in the following chemical solution:
  • Water ………………… 100 L
  • Potassium per manganate………….. 1000 Gms.
  • Phosphoric Acid…………………………. 250 Gms.
  • Stir the solution in a stainless steel tub with dry pumice stone.
  • Soak the stones with the chemical solution ……… 10 –15 minutes.
  • The stones will pick up the solution. Then the soaked stones are dried in the open air for………….. 2 to 3 hrs.
  • Then pretreated garment 30 –40 kg per batch load in the dry washing machine.
  • Load the per-treated stones (about 50 kg) in washing machine.
  • Start machine running for each batch …………………… 7 to 10 mts.
  • Stop machine running.
  • Unload the treated garment separately. Pumice stones with P.P. solution hit on garment surface as a result fading will be developed.
  • Then load the stones treated garment in another washing machine.

Third Step: Wash for Cleaning

  • Batch wt………………………….. 70 kg.
  • Add water @ L: R = 1: 8………….. 560 litres.
  • Add detergent @ 1 gm/litre ………….560 Gms.
  • Temperature……………………….. 40°C -50°C.
  • Time …………………………….10 mts.
  • Drop the liquor.
  • Here detergent is used to remove the breaking stone dust and chemicals from the garment surface.

Fourth Step: Whitening/Neutralization

  • Add water @ L: R = 1: 8………….. 560 litres.
  • Machine running.
  • Add Metabisulphite @ 5 gm/litre….. 2800 Gms.
  • Cold temperature.
  • Time 5 mts.
  • Drop the liquor.

Fifth Step: Soft Wash

  • Add water @ L: R = 1: 7………….. 490 litres.
  • Machine running.
  • Add Acetic acid @ 0.6 gm/litre ………………… 294 Gms.
  • Add Softner @ 1 gm/litre …………………… 490 Gms.
  • Then unload the garments.

Sixth Step: Hydro Extractor Machine
Hydro extractor machine to remove excess water from the garments.

Seventh Step: Dryer Machine.
After hydro extraction the garments are sent to drying machine for complete drying.

Eighth Step: Quality and Delivery.
After drying the garments go to quality checking and rectify washing fault and then good one delivery.

Precautions:
During acid washing, the workers should wear masks and aprons. The operator should use protective rubber gloves and safety glasses.

Other precautions of denim acid wash is point-out below:

  1. Maintain the stock solution properly constant when comes socking the stone.
  2. No water licks age in to the machine when treated pumice stone and garments in to the machine.
  3. Not excess load the garments in the Acid wash processing.
  4. Add some new stone after finishing on batch to maintain the volume for 2nd batch. It is a mater of experience.

Pollution by acid wash:
Acid wash uses both pumice stone and chemicals (sodium hypochlorite or potassium permanganate) for washing. It does not require water but leads to pollution. Using a smaller amount of stones does not give the expected look (bleaching effect) and use of more stones damages the fabric and accessories and the machine itself. The acid damages the washing machine and the metal accessories used in the jeans. The effluent contains pumice dust and residual manganese, which are hazardous, and also cotton fiber dust as a result of abrasion caused by pumice stones. Acid-washed jeans have a tendency to yellow upon repeated use.

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