GENERAL PROPERTIES OF VAT DYES

1
GENERAL PROPERTIES OF VAT DYES

• 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

2
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 1900S

3
CHEMICAL CLASSIFICATION OF VAT DYES

• TWO MAIN CLASSES
• INDIGOID VAT DYES DERIVATIVES OF INDIGO OR
  THIO-INDIGO

4
ANTHRQUININE VAT DYES
5
REDUCTION OF VAT DYE
6
REDUCTION OF VAT DYE

• REDUCING PROPERTY OF SODIUM HYDROSULPHITE
• Na2S2O4 2H2O ? 2 NaHSO3 2H
• REDUCTION OF INDIGO

7
REDUCTION OF VAT DYE
8
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

9
STEPS IN VAT DYEING

• FOUR STEPS
• REDUCTION CONVERSION OF INSOLUBLE FORM TO ITS
  SOLUBLE FORM IN PRESENCE OF STRONG REDUCING AGENT
  AND CAUSTIC SODA (LEUCO VAT DYE)
• DYEING DYEING OF COTTON WITH LEUCO VAT DYE
• OXIDATION OXIDATION OF VAT DYE INSIDE THE FIBRE
  INTO WATER INSOLUBLE FORM (OXIDATION)
• SOAPING SUBSEQUENT TREATMENT OF DYED MATERIAL
  WITH HOT WASHING LIQUOR CONTAINING ANIONIC
  DETERGENT TO OBTAIN BRIGHT SHADES, DYE
  AGGREGATION AND EXTREMELY GOOD FASTNESS
  PROPERTIES

10
CLASSIFICATION ACCORDING TO APPLICATION

• 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

11
RECIPE FOR STOCK VAT

• CLASS DYE QTY CAUSTIC Na2S2O4 water
  Temp. Time
• kg SODA kg litre 0C
  min.
• (32.5) litre
• Iw 1 1.5 0.5 50
  50 10
• In 1 3.0 0.75 50
  60 10
• In special 1 6.0 1.50 100
  60 10

12
DYE BATH ADDITIONS

• Process Iw In In special
• Additions 120 110 15 120
  110 15 120 110 15
• NaOH ml/l 8-10 12-15 18-23 15-20 22-26
  32-40 22-26 32-38 48-58
• 32.5
• Hydro g/l 3-4 5-6.5 8-12 3.5-4.5
  5.5-8 9.5-13 3.5-4.5 5.5-8 9.5-13.5
• NaCl g/l 15-25 15-20 15-20
  --------------------------------------------------
  -----
• Dyeing
• Temp. 0 c 45-50 50-60 50-60

13
DYEING AUXILIARIES

• REDUCING AGENT
• SODIUM HYDROSULPHITE OR SODIUM DITHIONATE
• SENSITIVITY
• 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

14
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

15
DYEING AUXILIARIES

• ALKALI
• 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

16
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

17
EXHAUST DYEING

• BLANK DYE BATH
• CAUSTIC SODA 20 g/l
• HYDRO 15 g/l
• DYEING
• 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.

18
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

19
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
• 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.

20
SEMI-CONTINUOUS METHOD
21
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.

22
PADDING

• 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)
• 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.

23
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.

24
CONTINUOUS METHOD

• 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 -gt RINSE (8 COMPRTMENT OPEN
  SOAPER) ? DRY

25
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

26
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.

27
CONTINUOUS METHOD
28
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

29
INDIGO DYEING

• STOCK VAT
• INDIGO X g/l
• CAUSTIC SODA X g/l
• HYDRO Xg/l
• TEMP. 60OC
• TIME 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.

30
INDIGO DYEING

• CONTINUOUS DYEING RANGE
• TROTMAN P453

31
SOLUBILIZED VAT DYES

• DISULPHURIC ESTERS OF INDIGO OR AQ VAT DYES
• 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

32
GENERAL PROPERTIES

• 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

33
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

34
APPLICATION

• THREE STEPS
• 1. 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

35
DYEING METHODS

• EXHAUST METHOD (JIGGER DYEING)
• PAD-DEVELOP METHOD
• 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

36
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.

37
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
• DRYING THE PADDED FABRIC BEFORE DEVELOPMENT