DYEING OF COTTON WITH VAT DYES

Report
GENERAL PROPERTIES OF VAT DYES
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INSOLUBLE IN WATER
CAN NOT BE USED DIRECTLY FOR DYEING
CAN BE CONVERTED TO WATER SOLUBLE FORM
POSSESS AFFINITY TO CELLULOSIC FIBRES
PROCESS OF CONVERTING WATER INSOLUBLE FORM TO
WATER SOLUBLE FORM KNOWN AS VATTING
• INVOLVES TWO STEPS
• REDUCTION OF VAT DYE INTO WEAKLY ACIDIC LEUCO FORM
• SALT FORMATION BY NaOH
• REDUCING AGENT USED IS SODIUM HYDROSULPHITE
Na2S2O4 + 2H2O  2NaHSO3 + 2H
DYEING OF COTTON WITH VAT DYES
PRINCIPLE
• CONVERSION OF WATER INSOLUBLE VAT DYE
INTO ITS SOLUBLE FORM
• DYEING OF COTTON
• RECONVERSION OF SOLUBLE VAT DYE ON FIBRE
INTO PARENT INSOLUBLE FORM
• INDIGO IS ONE OF THE OLDEST NATURAL VAT DYE
• SYNTHETIC INDIGO AND OTHER VAT DYES ARE
MANUFACTURED SINCE EALY 1900’S
CHEMICAL CLASSIFICATION OF VAT
DYES
• TWO MAIN CLASSES
• INDIGOID VAT DYES: DERIVATIVES OF INDIGO OR
THIO-INDIGO
ANTHRQUININE VAT DYES
REDUCTION OF VAT DYE
REDUCTION OF VAT DYE
• REDUCING PROPERTY OF SODIUM HYDROSULPHITE
Na2S2O4 + 2H2O  2 NaHSO3 + 2H
REDUCTION OF INDIGO
REDUCTION OF VAT DYE
AMOUNT OF Na2S2O4 AND NaOH
• STOICHIOMETRICALLY 1 MOLE OF Na2S2O4 AND 2 MOLES OF
NaOH ARE CONSUMED PER ANTHRAQUINONE RING IN DYE
MOLECULE
• IN PRACTCE GREATER AMOUNT OF Na2S2O4 AND NaOH IS
USED
• DECOMPOSITION OF Na2S2O4 BY ATMOSPHERIC OXYGEN
AND DISSOLVED OXYGEN IN WATER AND ENTRAPPED IN
FIBRE
• NEUTRALIZATION OF NaOH BY ACIDIC DECOMPOSITION
PRODUCTS OF Na2S2O4
Na2S2O4 + 2H2O  2NaHSO3 + 2H
NaHSO3 + NaOH  Na2SO3 + 2H2O
• DISSOLVED CO2 IN WATER ALSO CONSUMES SOME ALKALI
• IN PRACTICE AMOUNT OF Na2S2O4 USED IS 2-3 TIMES HIGHER
• AMOUNT OF NaOH USED IS 1.5-2 TIMES HIGHER THAN
NEEDED STOICHIOMETRICALLY
STEPS IN VAT DYEING
1.
FOUR STEPS
REDUCTION: CONVERSION OF INSOLUBLE FORM TO ITS
SOLUBLE FORM IN PRESENCE OF STRONG REDUCING
AGENT AND CAUSTIC SODA (LEUCO VAT DYE)
2.
DYEING: DYEING OF COTTON WITH LEUCO VAT DYE
3.
OXIDATION: OXIDATION OF VAT DYE INSIDE THE FIBRE
INTO WATER INSOLUBLE FORM (OXIDATION)
4.
SOAPING: SUBSEQUENT TREATMENT OF DYED MATERIAL
WITH HOT WASHING LIQUOR CONTAINING ANIONIC
DETERGENT TO OBTAIN BRIGHT SHADES, DYE
AGGREGATION AND EXTREMELY GOOD FASTNESS
PROPERTIES
CLASSIFICATION ACCORDING TO
APPLICATION
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2.
3.
4.
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FOUR GROUPS ACCORDING TO VATTING AND
DYEING CONDITIONS
IK
IW
IN
IN SPECIAL
DYEING STEPS
PREPARATION OF STOCK VAT
DYEING
THE CONDITIONS OF DYEING DEPENDS ON VAT
DYE CLASS USED
RECIPE FOR STOCK VAT
CLASS DYE QTY
kg
Iw
1
In
1
In special
1
CAUSTIC
SODA
(32.5%) litre
1.5
Na2S2O4 water
kg
litre
Temp. Time
0C
min.
0.5
50
50
10
3.0
0.75
50
60
10
6.0
1.50
100
60
10
DYE BATH ADDITIONS
Process
Additions
Iw
1:20 1:10 1:5
In
1:20 1:10
1:5
In special
1:20
1:10
NaOH ml/l 8-10 12-15 18-23 15-20 22-26 32-40 22-26
32.5%
3-4
NaCl g/l
15-25 15-20 15-20 -------------------------------------------------------
45-50
8-12 3.5-4.5 5.5-8 9.5-13 3.5-4.5 5.5-8
48-58
Hydro g/l
Dyeing
Temp. 0 c
5-6.5
32-38
1:5
50-60
50-60
9.5-13.5
DYEING AUXILIARIES
REDUCING AGENT
• SODIUM HYDROSULPHITE OR SODIUM
DITHIONATE
SENSITIVITY
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HYDRO IS SENSITIVE TO ATMOSPHERIC OXYGEN
DECOPOSES DURING VATTING AND DYEING OF VAT DYE
EXCESS MUST ALWAYS BE PRESENT
DECOPOSITION INCREASES WITH
TEMPERATURE
AGITATION OF DYE LIQUOR
EXPOSED SURFACE AREA OF DYE BATH
HYDROSULPHITE DECOMPOSITION
• NEUTRAL MEDIUM
2Na2S2O4 + H2O  Na2S2O3 + 2NaHSO3
• ALKALINE MEDIUM
2Na2S2O4 + 2NaOH  Na2S2O3 + 2Na2SO3 +H2O
• REACTOION WITH ATMOSPHERIC OXYGEN
(ALKALINE MEDIUM)
Na2S2O4 + 2NaOH +O2  Na2SO3 + Na2SO4 +H2O
DYEING AUXILIARIES
ALKALI
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MAINTAIN REDUCED DYE IN WATER SOLUBLE FORM
ALKALI ALSO CONSUMED DURING DYEING BY DYE, REACTION
WITH HYDROSULPHITE, AND ATMOSPHERIC OXYGEN, EXCESS
MUST BE PRESENT
TEST
HYDRO: VAT PAPER, YELLOW PAPER TURNS BLUE
ALKALI: PHENOLPHTHALEIN PAPER, WHITE PAPER TURNS PINK
ELECTROLYTE
MOST COMMON NaCL OR Na2SO4
OTHER AUXILIARIES
WETTING AGENT HELPS IN WETTING OF FABRIC DURING DYEING,
ASSIST DYE PENETRATION
ANIONIC DETERGENT USED DURING SOAPING, FACILITATES
REMOVAL OF SURFACE DYE,
DYE AGGREGATION INSIDE FIBRE
DEVELOP TRUE SHADE AND GOOD FASTNESS PROPERTIES
DYEING OF COTTON FABRIC
EXHAUST DYEING
JIGGER IS THE MOST COMMONLY USED MACHINE FOR EXHAUST
DYEING
STEP 1
VATTING: CONVERSION OF INSOLUBLE FORM TO SOLUBLE FORM
STOCK VAT: REDUCTION IN STRONG CONCENTRATION. CHEMICAL
REACTION INCREASES WITH CONCENTRATION
VAT DYE
X PARTS
HYDRO
2 X PARTS
CAUSTIC SODA
1 X PARTS
WATER
50 X PARTS
TEMPERATURE
50-60OC
TIME
10-15 MIN.
TEST FOR VATTING:
SPOT VATTED DYE SOLUTION ON FILTER PAPER. SPREADING OF
SPOT WITHOUT DEPOSITION OF INSOLUBLE DYE PARTICLES
EXHAUST DYEING
BLANK DYE BATH
CAUSTIC SODA
HYDRO
DYEING
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20 g/l
15 g/l
LOAD THE FABRIC UNIFORMLY WITHOUT CREASES ONTO ONE OF
THE ROLLER OF JIGGER BY PASSAGE THROUGH PLAIN WATER
RUN THE FABRIC (2 ENDS) THROUGH BLANK BATH AT ROOM TEMP.
ADD HALF THE QUANTITY OF STOCK VAT
RUN FOR 2 ENDS
ADD THE REMAINING STOCK VAT
RAISE TEMP SLOWLY TO 60OC
CONTINUE DYEING FOR 45 MIN (8-10 ENDS)
AFTER EACH END CHECK FOR PRESENCE OF HYDRO WITH VAT
PAPER (DYED WITH NAVINON YELLOW 5G) COLOUR CHANGE
YELLOW TO BLUE AND ALKALI WITH PHEOLPHTHALEIN PAPER.
COLOUR CHANGE COLOURLESS TO PINK.
IF FOUND INSUFFICIENT PREDISSOLVE AND ADD TO JIGGER
WHILE STATIONARY.
OXIDATION
• AFTER DYEING DRAIN THE DYEBATH
• RINSE THE FABRIC THROUGH COLD WATER (2ENDS) TO
REMOVE LOOSE DYE AND EXCESS HYDRO AND ALKALI
• CONVERT THE LEUCO VAT DYE TO ITS ORIGINAL OXIDIZED
FORM BY TEATMENT WITH 2 g/l H2O2 AT 40-50OC (4 ENDS)
• RINSE WITH COLD WATER
• SOAPING: ABSOLUTELY ESSENTIAL FOR DEVELOPMENT OF
TRUE SHADE AND BEST FASTNESS PROPERTIES.
• REMOVAL OF SURFACE DYE AND AGGREGATION OF DYE
INSIDE THE FIBRE
• SOAP AT BOIL USING 2 g/l LISSAPOL D (ANIONIC
DETERGENT) AND 2 g/l SODA ASH (4 ENDS)
• RINSE WITH COLD WATER (2 ENDS)
• UNLOAD FROM JIGGER
• DRY
SEMI-CONTINUOUS DYEING
• MANY VAT DYES HAVE STRONG AFFINITY FOR
COTTON
• PENETRATION IN CLOSELY WOVEN FABRIC IS
DIFFICULT
• SEMICONTINUOUS OR CONTINUOUS METHODS
USED
• PIGMENT PAD-DEVELOPMEMNT ON JIGGER
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PAD WITH VAT DYE DISPERSION
DRY
DEVELOP ON JIGGER USING HYDRO AND CAUSTIC SODA
OXIDIZE AND SOAP IN JIGGER
THE METHOD IS USED FOR DYEING TIGHTLY WOVEN
FABRIC LIKE SUITING.
SEMI-CONTINUOUS METHOD
PAD-JIG METHOD
• PREPARATION OF DYE DISPERSION:
• USE ONLY ULTRA FINE VAT DYES
• STIR THE VAT DYE POWDER IN 10-20 TIMES ITS
WEIGHT OF WATER AT 500C WITH HIGH SPEED
STIRRING
• FILTER THE DISPERSION
• MAKE THE TOTAL VOLUME
• ADD WETTING AGENT OR LEVELLING AGENT.
• READY FOR PADDING.
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PADDING
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PADDING
USE WELL SCOURED BLEACHED FABRIC IN DRY STATE
GOOD WETTING OF FABRIC IS ESSENTIAL
SATURATE THE FABRIC WITH DYE DISPERSION
SQUEEZE OUT EXCESS LIQUOR (EXPRESSION 70%)
PADDING MANGLE SPEED 20 M/min.
IF FABRIC IS TOO TIGHT CONSTRUCTION, PAD AT HIGH TEMP (60-700C)
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DRYING
DEVELOPMENT MAY BE DONE IN WET STATE OR AFTER DYRYING
IF WET, DEVELOP WITHOUT DELAY
UNIORM DRYING OF PADDED FABRIC ALONG THE WIDTH AND BACK
AND FACE OF FABRIC IS ESSENTIAL
MACHINE USED EITHER HOT FLUE OR STENTER
HOT CYLINDER DRYING IS NOT ADVISABLE DUE TO BACK TO FACE
DYE MIGRATION.
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DEVELOPMENT ON JIGGER
• SET THE JIGGER BATH WITH REQUIRED AMOUNTS OF
HYDRO AND CAUSTIC SODA.
• ADD SMALL QUANTITY OF PADDING LIQUOR TO THE BLANK
BATH IN JIGGER TO COMPENSATE FOR THE DYE WHICH
BLEEDS OUT FROM FABRIC
• THE DEVELOPMENT IS SIMILAR TO JIGGER DYEING
OPERATION FOLLOWED BY OXIDATION AND SOAPING
TREATMENT.
CONTINUOUS METHOD
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• PAD-STEAM PROCESS
• PRINCIPLE: INCREASE IN RATE OF DYEING WITH
INCREASE IN TEPERATURE.
• DYE REDUCTION ON FABRIC SURFACE
• IMMEDIATE DYE ADSORPTION
• PIGMENT PAD  DRY  CHEMICAL PAD (CAUSTIC
SODA, HYDRO, COMMON SALT)  STEAM (30-60
SEC.)  RINSE  OXIDIZE  SOAP -> RINSE (8
COMPRTMENT OPEN SOAPER)  DRY
CHEMICAL PADDING
• AFTER PIGMENT PADDING AND DRYING, COOL THE FABRIC
TO AVOID DYE REDUCTION IN CHEMICAL PAD TROUGH
• PAD THE FABRIC WITH SOLUTION OF HYDRO AND CAUSTIC
SODA (CHEMICAL PAD LIQUOR)
• THE CONCENTRATION OF HYDRO AND CAUSTIC SODA
DEPENDS ON CONCENTRATION OF DYE ON FABRIC.
• DYE CONC. ON FABRIC
NaOH/Na2S2O4
g/kg
g/l
10
25-30
30
35-50
50
50-70
• 5-10 LITRES OF PIGMENT DISPERSION/100 LITRE OF
CHEMICAL LIQUOR ARE ADDED TO THE BATH
STEAMING
• CHEMICAL PADDED FABRIC IN WET CONDITION
IMMEDIATELY PASSED INTO STEAMER
• STEAM FOR 20-30 SEC. IN SATURATED AIR FREE STEAM
AFTER TREATMENT
• THE FINAL TREATMENTS INVOLVING OXIDATION AND
SOAPING ON 8 COMPARTMENT OPEN SOAPER
• METHOD IS SUITABLE ONLY FOR PALE TO MEDIUM DEPTH
OF SHADES
• THE STEAMER SHOULD BE SITUATED AS CLOSE AS POSSIBLE
TO CHEMICAL PADDING MANGLE, TO MINIMIZE HYDRO
DECOPOSITION IN AIR BEFORE STEAMING.
CONTINUOUS METHOD
DYEING OF COTTON WITH INDIGO
• INDIGO HAS POOR AFFINITY TOWARDS COTTON
• CONVENTIONAL EXHAUST OR CONTINUOUS
METHODS ARE NOT SUITABLE
• SPECIAL METHOD OF MULTIPLE DIP AND NIP (5 DIP
AND 5 NIP) METHOD IS USED IN COMMERCIAL
PRACTICE
• MAJOR APPLICATION FOR DYEING OF COTTON
WARP FOR PRODUCTION OF STONE WASH
DENIM/JEAN FABRIC
INDIGO DYEING
• STOCK VAT
INDIGO
CAUSTIC SODA
HYDRO
TEMP.
TIME
X g/l
X g/l
Xg/l
60OC
15 MIN.
DYEBATH
INDIGO
3 g/l
CAUSTIC SODA
2 g/l
HYDRO
1.5 g/l
WETTING AGENT
1 g/l
DYEING TEMP.
ROOM TEMP.
INDIGO DYEING
• CONTINUOUS DYEING RANGE
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TROTMAN P453
SOLUBILIZED VAT DYES
• DISULPHURIC ESTERS OF INDIGO OR AQ VAT DYES
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LEUCO VAT DYE OBTAINED BY TREATMENT OF VAT DYE WITH
HYDRO
TREAT LEUCO VAT DYE WITH CHLOROSULPHONIC ACID (ClSO3H) IN
PRESENCE OF PYRIDINE AT 60-700C
TREAT THE PRODUCT WITH SLIGHT EXCESS OF Na2CO3 OR NaOH
REMOVE PYRIDINE BY STEAM DISTILLATION
CONCENTRATE TO CRYSTALLIZE OR
SALT OUT WITH NaCl
GENERAL PROPERTIES
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SOLUBILITY
LOW SOLUBILITY, 50 g/l AT 50-600C
SOLUBILITY RANGE IS SUFFICIENT
USED FOR DYEING PALE SHADES
DO NOT DISSOLVE IN BOILING WATER: PREMATURE DYE
OXIDATION
LIGHT SENSITIVITY
SENSITIVE TO SLIGHT IN POWDER AS WELL IN SOLUTION
FORM.
PREMATURE OXIDATION TO INSOLUBLE VAT DYE
EXPOSURE TO LIGHT SHOULD BE AVOIDED
ACTION OF LIGHT CAN BE MINIMIZED BY ADDING SMALL
QUANTITY OF SODA ASH TO DYE SOLUTION
GENERAL PROPERTIES
• SUBSATNTIVITY
• LOW AFFINITY TO COTTON
• GOOD LEVELLING AND PENETRATION ON TIGHTLY WOVEN
FABRIC
• STANDING BATH MAY BE USED
• DYEBATH IS REPLENISHED AFTER DYEING ONE LOT BY DYE
CONCENTRATION EQUIVALENT TO THAT TAKEN BY FABRIC
• EXCELLENT REPRODUCIBILITY OF SHADES
• ADDITION COMMON SALT IMPROVES DYE EXHAUSTION
• DYEING MAY BE CARRIED OUT AT ROOM TEMPERATURE.
• OXIDATION
• CARRIED OUT UNDER ACIDIC CONDITIONS
• H2SO4 + NaNO2, NaNO2 + HCOOH, K2Cr2O7 + H2SO4 ARE
COMMONLY USED
APPLICATION
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THREE STEPS
PADDING OR EXHAUSTION OF DYE FROM SLIGHTLY
ALKALINE OR NEUTRAL SOLUTION
DEVELOPMENT ON FABRIC IN PRESENCE OF OXIDIZING
AGENT NaNO2 + H2SO4 (MOST COMMON) AT ROOM TEMP
OR 50-600C OR EVEN HIGHER DEPENDING ON EASE OF DYE
OXIDATION
AFTER TREATMENT: NEUTRALIZATION, AND SOAPING,
RINSING
DYEING METHODS
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EXHAUST METHOD (JIGGER DYEING)
PAD-DEVELOP METHOD
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JIGGER DYEING
SET DYE BATH WITH 0.5 g/l SODA ASH AND 5-10 g/l NaNO2
DYEING TEMP. ROOM TEMP – 400C
ADD HALF THE QUANTITY OF DISSOLVED DYESTUFF, GIVE ONE END
ADD SECOND REMAINGING DYESTUFF, GIVE ONE END
ADD 10-40 g/l SALT OVER TWO ENDS
EXCESS SALT CONC. PRECIPITTES THE DYE
COMPLETE DYEING IN 4-6 ENDS
DEVELOP THE BATCH ON TO ANOTHER JIGGER IF STANDING BATH
IS TO BE USED.
RUN TWO ENDS THROUGH H2SO4 BATH AT 50-600C
RINSE, SOAP AT BOIL, RINSE
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CONTINUOUS DYEING
• LOW AFFINITY. MOST SUITED FOR CONTINUOUS DYEING
• TYPICAL PAD LIQUOR COMPOSITION
DYE X g/l, Na2CO3 1 g/l, NON-IONIC WETTING AGENT 1 g/l,
NaNO2
10 g/l
• PAD AT ROOM TEMPERATURE
• DEVELOP IN A BATH CONTAINING 10 g/l NaNO2 AND 10 g/l
H2SO4 AT 600 C IN THE 1st COMPARTMENT OF THE 8
COMPARTMENT OPEN SOAPER
• SOMETIMES THE PADDED FABRIC IS DRIED BEFORE
DEVELOPMENT
• INTERMEDIATE DRYING GIVES BETTER COLOUR YIELD
• AFTER ACID DEVELOPMENT GIVE
• COLD RINSE  SODA ASH NEUTRALIZATION  HOT WATER
RINSING  SOAPING AT BOIL  COLD RINSE  DRY.
SEMI-CONTINUOUS DYEING
• PAD THE FABRIC WITH DYE SOLUTION
• DEVELOP ON JIGGER LIKE IN EXHAUST DYEING
• COLD RINSE, SOAP, COLD RINSE
• IMPROVEMENT IN COLOUR YIELD IS OBTAINED BY
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DRYING THE PADDED FABRIC BEFORE DEVELOPMENT

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