Dyeing Jeans

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Garment dyeing in denim is mainly categorized in two classes

1- Direct Dyeingdhi colored

2- Reactive Dyeing

Let see it one by one

Direct Dyeing

Direct dyeing some time also referred as Over Dyeing. As reflects in name, this dyeing does not involve much complicated processes. Dye particles penetrate deep in cotton and impose their color on cotton fabric. Dye molecules directly make physical bonds with cotton fiber. Direct dyeing does not involve vigorous conditions like high temperature/pressure. It’s easy to make amendments/improvement. Color fastness is fine to home laundry but cannot sustain for long time. It is low-cost process and very handy to light shades.

Direct Dyes cannot make bonds with polyesters. So in polyester mixed cotton fabric it is difficult to get shades with direct dyes. In this case it is recommended to use greater quantities of dye stuff, color fastening agent and high temperature.     Â

General Recipe Steps

  • Desizing
  • Stone washing  (If Required)
  • Soap Rinsing
  • Bleaching(If Required)
  • Neutralization of Bleach  (If Required)
  • Direct Dyeing  (At high temperature ( About 70 C to 90 C) with some fastening agent like sodium chloride and wetting agent)
  • Softner Application

Additional Applications

 Temperaturedhi colored 2

 It is always recommended to apply dyes in hot bath. High temperature not only increases the penetration of water particles to fabric but also the activity rate of dye particles.

Sodium Chloride

 Sodium chloride or common salt is usually added to dye bath for color fastening. It helps the ionization of water molecules and increases the ability to make bond. Its easy to remove the salt from garment after process with simple rinses. Even then if partial quantities remain in garment it does leave any harm.

Wetting Agent

 It is appropriate some time to add a wetting agent to dye bath. It allows the color particles to penetrate deep in cotton thread and results to good.

Leveling Agents

These are available in market in different brands. It helps to even distribution of dye particles on garment and avoid the dye spots.

Reactive Dyeing

 It involves chemical bonding of dye particles with cotton fabric. Due to its chemical nature it is much more stable as compare to direct dyes. It cannot be removed form fabric with normal physical method.

  Reactive dyeing is a complicated process. The temperature and water level control are very important in this kind of dyeing. All reactive dyes work in alkaline medium, So strong alkalies/bases are used to provide medium. In return, acid is used to neutralize the affect of alkali. Temperature control is very critical in reactive dyeing so washer should be well equipped in this regard.

  Reactive have more capability to resist against conditions. So it is recommended to use reactive dyeing on grey denim. In gray denim no warp of weft is dyed with any of indigo or sulfur or any other dye.

 General Recipe Steps

  • Desizing
  • Stoneing or/and Enzyming  (If Required)
  • Soap Rinsing
  • Bleaching  (If Required)
  • Neutralization of Bleach (If Required)
  • Per Treatment for reactive dyeing
  • Reactive Dyeing

At high temperature (About 70 C to 90 C) with some in alkaline medium

  • Neutralization of Alkalinity
  • Softner Application

Additional Applications

Temperature

  Reactive dyeing is very much concerned with temperature control. During dyeing it is required to rise temperature with a certain gradient between two limits. Usually it is to rise from 40C to 60C in 20 minute and then further treatment on stable temperature of 60C for 20 minute. So a well controlled temperature manipulating equipment is very necessary for this kind of dyeing.

 Soda Ashdhi colored 3

  Soda ash is a moderate alkaline compound. It is used in reactive dyeing bath for maintaining pH level in desired range. Usually it is recommended between pH 8.50 to pH 10 as described in dye literature provided by manufacturer. It helps to make chemical bonds between cotton and dye particle. To check the details of chemical reaction click here.

 Caustic Soda

 Use of caustic soda is very handy in reactive dyeing. It perform two tasks in bath, i.e one is to strengthen the bonds of dye and cotton to improve the dyeing quality and second is to remove the unfixed dye form garment. It is very interesting that at same time it is acting as fixing and de-fixing agent simultaneously. If the unfixed dye is not removed form garment after dyeing process then it will bleed in home laundering and will deposit on other garments, destroying their own shades. To check the details of chemical reaction click here.

 Formic Acid

  Formic acid or some mild (usually organic) acid is used to neutralize the effects of soda ash and caustic soda. It is use in normal temperature in small quantity. It is very important to use the measured quantity of acid only this much to neutralize. If excessive quantity is feed then remaining quantity of acid left in garment can be harmful for human skin. It may adjust the shade of garment usually to reddish look.

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