pad dyeing with reactive dyes-libre

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Pad Dyeing with Reactive Dyes

Dr. Tanveer HussainDean Faculty of Engineering & Technology

National Textile University Faisalabad.

4/20/2012 Dr. Tanveer Hussain 1

Pad dyeing methods with reactive dyes



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Reactive dye requirements for pad dyeing

Powder and liquid dyes Excellent solubility

Excellent bath stability

Low-to-medium substantivity, good compatibility

Good diffusion and levelling properties

Similar reactivity and rapid fixation

Unaffected by fixation time variations

High degree of fixation

Excellent washing-off properties Good fastness level


CIBACRON C Dyes



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Dye solubility in the presence of alkali


Dye solubility in the presence of alkali



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Bath stability in pad-batch


Stability vs. bath pH



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Dye affinity & pad dyeing


Padding

X g/l dyes

1 g/l wetting agent

2 g/l sequestring agent


Pad batch process


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Kuesters Contidos System


Batching



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Changing pH during batching


Merits & demerits of pad batch method

Merits

Modest investment layout

Suitable for small and fairly largebatches

Very simple working conditions

Limited manpower required

Low energy consumption

Lower water consumption thanexhaust dyeing

Good penetration and leveldyeing

Good reproducibility

Suitable for dyeing knitgoods

Demerits

Batch process

Higher dye consumption

than pad-dry-pad-steam

Moderate coverage of dead

and immature cotton



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Pad-dry-pad-steam process

Dye Pad X g/l dye

1 g/l wetting agent

2 g/l sequestering agent

5-10 g/l migration inhibitor

IR pre-drying To residual 30-35% moisture content

Drying 120C

Chemical Pad 250 g/l salt

15 ml/l Caustic Soda (36Be)

Steaming 60 seconds with saturated steam

Washing-off


Pad-dry-pad-steam process

Merits

Economical process for largeproduction runs

Still economical for fairlysmall runs (>5000m) onmodern equipment

High colour yield Very good appearance of the

dyed fabric

Good reproducibility

No detrimental influence onlight and/or chlorine fastness

Demerits

Shade changes are time

consuming

Less suitable for dyeing

fabrics prone to migration

problems or difficult to dry(pile fabrics)



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Pad-steam process

Dye Pad X g/l dye

1 g/l wetting agent


3 g/l thickener/migration inhibitor

60-90 g/l salt

10-30 g/l soda ash

Steaming

60-90 seconds in saturated steam Washing-off


Pad-steam process

Merits

Continuous method mainlyused for dyeing fabrics withhigh liquor retention, such asterry fabrics and corduroy,because no intermediatedrying is required

No migration problems Reduced energy costs

Good appearance of the dyedfabrics

No detrimental influence onfastness

Demerits

Higher amounts of dye arerequired to produce deepshades compared to thepad-batch or pad-dry-pad-steam processes

Worthwhile for dyeingdeep shades when thehigher dye costs are at leastbalanced by savings inenergy and gains inproductivity



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Pad humidity-fix process - Econtrol

Dye Pad X g/l dye

1 g/l wetting agent


5-10 g/l migration inhibitor

20 g/l soda ash

Y ml/l caustic soda (36Be)

Drying/fixation

2-3 minutes at 120-130C, 25% RH (depending onfabric weight)

Washing-off





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Merits

Low chemical and auxiliaryrequirements

Suitable for dyeing viscose andcellulosic blends

Good colour yield

Good appearance of the dyedfabric

No need for a chemical pad

liquor or steamer No detrimental influence on

fastness (light or chlorine)

Demerits

Lower fixation level whencompared to pad-batch or pad-dry-pad-steam

For heavy weight fabrics IR pre-drying is necessary to controlmigration and prevent surfacedyeing

Controlling the chamber climatecan be problematic, especiallywhen processing a mixture ofdifferent fabric qualities

Lab shade matching requiresspecialist equipment (e.g.universal steamer, type DH/DHefrom Mathis AG)


Continuous washing-off reactive dyes

Best washing conditions:

When substantivity of the dye is as low as possible

When diffusion rate as high as possible

Phase 1: Dilution or exchange

Removal of unfixed dye, alkali, auxiliaries & alkali

residues from the fabric surface. Influenced by:

The number of bath changes.

The amount of water.

Turbulence, running speed and bath circulation.



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Continuous washing-off reactive dyes

Phase 2: Diffusion and desorption

Removal of unfixed dye, chemicals and alkali

residues from inside the fibre.

Influenced by:

Amount of unfixed dye and electrolyte content

Substantivity and diffusion rate of the unfixed dye

Time & Temperature

Liquor ratio (number of wash baths, turbulence)

Phase 3: Dilution & removal of diffused out dye


Effect of washing temperature



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Effect of washing time


Washing-off profile



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Washing-off profile


Setting-up washing-off conditions


pad dyeing with reactive dyes-libre

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