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Application of Dyeing Auxiliaries with Different Dyes | Uses of Dyeing Auxiliaries

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Reactive Dyes (Anionic):

They can be dyed on cellulosic fibers. The mechanism is nearly the same as described in direct dyes.

Advantage: high wet fastness due to covalent bonding (Chemical Bonding) between fibers and dyes, easily dyed on fibers.

Disadvantage: Expensive.

Dyeing Conditions:

A. Continuous Process:
1 Pad-dry-bake This is very easy method for cotton or cotton blends fibers.
2 Pad-dry-Pad (Chemical)-Steam This will give brighter and more intense color than method 1.

3 Pad-batch This will put the goods into the dye solution and squeeze with 2 rubber rollers to get rid of excess water and then batch at room temperature for 1-2 days.

B.  Exhaustion Process:  
This method will be used in small factory. Dyeing conditions will be 40-8OoC for 30-90 mm depending to the types and structures of the dyes.

Textile Auxiliaries:
1. Salt - reduce negative charges on the fibers
2. Water - dyeing media.
3. Soda Ash - excite the dye to link with the fibers with covalent bonding. Therefore, it enhances wet fastness
4. Fixing Agent - enhances wet fastness for heavy shade but usually reduce light fastness.

Direct Dyes (Anionic):

They can be dyed directly on cellulosic fibers. Without the presence of salt, when the fibers are immerged in water, it will show anionic charge which repels the dyes. Adding salt into the dye bath, it will reduce anionic on the fibers so the dyes can get closer and adsorb into the fibers.

Advantage: cheap, easily dyed on fibers

Disadvantage: poor wet fastness and some dyes have poor light fastness.

Textile Auxiliaries:
1. Salt - reduce negative charges on the fibers
2. Water - dyeing media
3. Fixing Agent - enhance wet fastness but usually reduce light fastness

Dyeing Conditions:
(Exhaustion): dyeing lOOoC x 30-90 mm fixing 6OoC x 20 mm.
(Continuous) pad --> dry --> steam --> wash --> soap --> dry

Vat Dye (Anionic when soluble):

The dye is named from the container (Vat) that used for rotting the dye with alkali solution. This crucial process will reduce the dye from insoluble to soluble dye (suitable for exhaustion in the cellulosic fibers). Now the manufacturer can synthesize man-made vat dye.

Dyeing Process:
1. Dissolve dye into water (insoluble dye)
2. Vatting process by reducing the insoluble dye in alkali condition. (Soluble dye)
3. Absorb into fibers (soluble dye)
4. After dyeing, oxidize the dye with oxidizing agent (insoluble dye)
5. Wash and soap the goods

Dyeing Conditions:

A. Continuous Process:
1 Pad-dry-Pad (Chemical): The solution of the dye is prepared without adding reducing agent to ensure leveling dyeing. After that, the goods are passed to chemical bath to reduce the dye into soluble dye and fix within the goods. Oxidizing agent is added to the goods and converted to insoluble dyes.
 
2 Pad-oxidize-pad-oxidize (many times): This will put the goods into the dye solution and squeeze with 2 rubber rollers to get rid of excess water, oxidize with the air and then immerse into the dye solution again and again to allow the dye penetrate into the goods.

Textile Auxiliaries:
1. Salt - reduce the negative charges on the fibers
2. Sodium hydroxide - adjusts pH to the dyeing bath and makes the suitable conditions for reducing agent.
3. Sodium hydrosulfite - reducing agent for the vat dyes.
4. Water - dyeing media
5. Oxidizing agents - (Hydrogen peroxide or Acetic acid or Air) oxidize the soluble to insoluble dye

(Sulfur Dye Anionic when soluble) :

The dyeing process has the same process as described in the vat dye except that using Sodium sulfide instead of Sodium hydrosulfide.

Dyes for Synthetic Fiber:

Disperse Dye 
(polyester, nylon, and acetate) (non-ionic): 
The dye is named from less water soluble and normally appeared in dispersion in water. The dye shows no charge due to the groups presented in the dye molecules.

Dyeing Conditions:
1. Insoluble dye in water
2. Less water soluble
3. Water insoluble in polyester fibers 

A. Exhaustion Process:
1 At boil with carrier, this process is suitable for acetate fiber and pale shade polyester fiber dyeing. Carrier is an auxiliary for swollen fiber in order to allow more dyes absorbing in. Now the use of carrier is reduced because it may be a carcinogen. 

2 At l3OoC without carrier with the high temperature, the dyes will be dissolved into smaller molecules and the void in fiber structure will be opened. This will give heavy shade.

B. Continuous Process Pad --> Pre-dry (100oC Thermo fixation (18OoC reduction clearing (RC)

Printing with Disperse Dyes: 
With the sublimation property, the dyes can be printed on paper, place the fabric with a printed paper and then using an iron with high temperature pressed on the paper. The dyes will transfer from paper to polyester fiber. This is called “Transfer Printing”.

Textile Auxiliaries:
1. Dispersing Agent - makes the dye solution stable and disperses in the dye bath.
2. Acid - adjust pH to the suitable condition for the dye bath.
3. Carrier - swell the fiber and dissolve the dye to make the dye getting into fiber.
4. Leveling agent - make more leveling dyeing (some will have adverse effect on slower dyeing)
5. Water - dyeing media

Acid Dye (Anionic):

The dye is called acid because it needs acidic dyeing condition. It can be dyed on protein fibers (silk, wool, and other animal fibers) and on polyamide fibers. Acidic condition will give the fibers showing positive charge. As the negative charge will attach directly to positive charge, and penetrate into the fibers.

Dyeing conditions: l00oC x 30-60 mm

Textile Auxiliaries:
1. Leveling agent - for levelness dyeing.
2. Retarding agent - for inhibiting the dye not attach to fibers too fast.
3. Acid - adjust the dyeing condition and make the fibers to show positive charges.
4. Water - dyeing media.

Basic Dye (Cationic)

The dye shows positive charge. Normally, the dye can be applied on wool, silk and poly-acrylonitrile (acrylic).

Dyeing Conditions:
l00oC x 30-60 mm Dyes Dyeing Condition (pH)
Acid (Wool) 2-4, 4-6, 6-8 (depends on types of dyes)
Acid (Nylon) 4.5-5.5, on types of dyes)
Basic 3.5-4
Direct 7.0
Disperse (Polyester) 5-6
Disperse (Acetate) 6.5-7.0
Disperse (Triacetate) 4.5-6.5
Reactive 7.0

Textile Auxiliaries:
1. Leveling agent - for levelness dyeing.
2. Retarding agent - for inhibiting the dye not attach to fibers too fast.
3. Acid - adjust the dyeing condition and make the fibers to show negative charges.
4. Water - dyeing media. 

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