Upload
adane-nega
View
1.433
Download
17
Tags:
Embed Size (px)
Citation preview
DYEING OF COTTTON WITH VAT DYES
R.B.CHAVAN
Department of Textile Technology
Indian Institute of Technology
Hauz-Khas, New Delhi 110016
E-mail [email protected]
GENERAL PROPERTIES OF VAT DYES• INSOLUBLE IN WATER• CAN NOT BE USED DIRECTLY FOR DYEING• CAN BE CONVERTED TO WATER SOLUBLE FORM BY
REDUCTION • 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
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 INDIGO
STEPS IN VAT DYEING
FOUR STEPS
1. 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
FOUR GROUPS ACCORDING TO VATTING AND DYEING CONDITIONS
1. IK 2. IW 3. IN 4. IN SPECIAL
DYEING STEPS• PREPARATION OF STOCK VAT• DYEING• THE CONDITIONS OF DYEING DEPENDS ON VAT
DYE CLASS USED
DYEING OF COTTON FABRIC
EXHAUST DYEING
JIGGER IS THE MOST COMMONLY USED MACHINE FOR EXHAUST DYEINGSTEP 1VATTING: CONVERSION OF INSOLUBLE FORM TO SOLUBLE FORMSTOCK VAT: REDUCTION IN STRONG CONCENTRATION. CHEMICAL REACTION INCREASES WITH CONCENTRATIONVAT DYE X PARTSHYDRO 2 X PARTSCAUSTIC SODA 1 X PARTSWATER 50 X PARTSTEMPERATURE 50-60OCTIME 10-15 MIN.
TEST FOR VATTING: SPOT VATTED DYE SOLUTION ON FILTER PAPER. SPREADING OF SPOT WITHOUT DEPOSITION OF INSOLUBLE DYE PARTICLES
EXHAUST DYEINGBLANK DYE BATHCAUSTIC SODA 20 g/lHYDRO 15 g/lDYEING
• 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• 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.
•
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.
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
• 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 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.
INDIGO DYEING
• CONTINUOUS DYEING RANGE• TROTMAN P453
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
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
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