Post on 02-Jun-2018
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Pad Dyeing with Reactive Dyes
Dr. Tanveer HussainDean Faculty of Engineering & Technology
National Textile University Faisalabad.
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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
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CIBACRON C Dyes
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Dye solubility in the presence of alkali
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Dye solubility in the presence of alkali
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Bath stability in pad-batch
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Stability vs. bath pH
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Dye affinity & pad dyeing
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Padding
X g/l dyes
1 g/l wetting agent
2 g/l sequestring agent
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Pad batch process
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Kuesters Contidos System
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Batching
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Changing pH during batching
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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
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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
2 g/l sequestering 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
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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
2 g/l sequestering 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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Pad humidity-fix process - Econtrol
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Pad humidity-fix process - Econtrol
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)
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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
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Effect of washing temperature
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Effect of washing time
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Washing-off profile
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Washing-off profile
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Setting-up washing-off conditions
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