Lecture 6 dyeing of cotton with vat and sulphur dyes

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Lecture 6 dyeing of cotton with vat and sulphur dyes

  1. 1. DYEING OF COTTTON WITH VAT DYES R.B.CHAVAN Department of Textile Technology Indian Institute of Technology Hauz-Khas, New Delhi 110016 E-mail rbchavan@hotmail.com
  2. 2. GENERAL PROPERTIES OF VAT DYES <ul><li>INSOLUBLE IN WATER </li></ul><ul><li>CAN NOT BE USED DIRECTLY FOR DYEING </li></ul><ul><li>CAN BE CONVERTED TO WATER SOLUBLE FORM BY REDUCTION </li></ul><ul><li>POSSESS AFFINITY TO CELLULOSIC FIBRES </li></ul><ul><li>PROCESS OF CONVERTING WATER INSOLUBLE FORM TO WATER SOLUBLE FORM KNOWN AS VATTING </li></ul><ul><li>INVOLVES TWO STEPS </li></ul><ul><li>REDUCTION OF VAT DYE INTO WEAKLY ACIDIC LEUCO FORM </li></ul><ul><li>SALT FORMATION BY NaOH </li></ul><ul><li>REDUCING AGENT USED IS SODIUM HYDROSULPHITE </li></ul><ul><li>Na2S2O4 + 2H2O  2NaHSO3 + 2H </li></ul>
  3. 3. CHEMICAL CLASSIFICATION OF VAT DYES <ul><li>TWO MAIN CLASSES </li></ul><ul><li>INDIGOID VAT DYES: DERIVATIVES OF INDIGO OR THIO-INDIGO </li></ul>ANTHRQUININE VAT DYES
  4. 4. REDUCTION OF VAT DYE
  5. 5. <ul><li>REDUCTION OF INDIGO </li></ul>
  6. 6. STEPS IN VAT DYEING <ul><li>FOUR STEPS </li></ul><ul><li>REDUCTION: CONVERSION OF INSOLUBLE FORM TO ITS SOLUBLE FORM IN PRESENCE OF STRONG REDUCING AGENT AND CAUSTIC SODA (LEUCO VAT DYE) </li></ul><ul><li>DYEING: DYEING OF COTTON WITH LEUCO VAT DYE </li></ul><ul><li>OXIDATION: OXIDATION OF VAT DYE INSIDE THE FIBRE INTO WATER INSOLUBLE FORM (OXIDATION) </li></ul><ul><li>SOAPING: SUBSEQUENT TREATMENT OF DYED MATERIAL WITH HOT WASHING LIQUOR CONTAINING ANIONIC DETERGENT TO OBTAIN BRIGHT SHADES, DYE AGGREGATION AND EXTREMELY GOOD FASTNESS PROPERTIES </li></ul>
  7. 7. CLASSIFICATION ACCORDING TO APPLICATION <ul><li> FOUR GROUPS ACCORDING TO VATTING AND DYEING CONDITIONS </li></ul><ul><li>IK </li></ul><ul><li>IW </li></ul><ul><li>IN </li></ul><ul><li>IN SPECIAL </li></ul><ul><li>DYEING STEPS </li></ul><ul><li>PREPARATION OF STOCK VAT </li></ul><ul><li>DYEING </li></ul><ul><li>THE CONDITIONS OF DYEING DEPENDS ON VAT DYE CLASS USED </li></ul>
  8. 8. DYEING OF COTTON FABRIC <ul><li>EXHAUST DYEING </li></ul><ul><li>JIGGER IS THE MOST COMMONLY USED MACHINE FOR EXHAUST DYEING </li></ul><ul><li>STEP 1 </li></ul><ul><li>VATTING: CONVERSION OF INSOLUBLE FORM TO SOLUBLE FORM </li></ul><ul><li>STOCK VAT: REDUCTION IN STRONG CONCENTRATION. CHEMICAL REACTION INCREASES WITH CONCENTRATION </li></ul><ul><li>VAT DYE X PARTS </li></ul><ul><li>HYDRO 2 X PARTS </li></ul><ul><li>CAUSTIC SODA 1 X PARTS </li></ul><ul><li>WATER 50 X PARTS </li></ul><ul><li>TEMPERATURE 50-60 O C </li></ul><ul><li>TIME 10-15 MIN. </li></ul><ul><li>TEST FOR VATTING: </li></ul><ul><li>SPOT VATTED DYE SOLUTION ON FILTER PAPER. SPREADING OF SPOT WITHOUT DEPOSITION OF INSOLUBLE DYE PARTICLES </li></ul><ul><li> </li></ul>
  9. 9. EXHAUST DYEING <ul><li>BLANK DYE BATH </li></ul><ul><li>CAUSTIC SODA 20 g/l </li></ul><ul><li>HYDRO 15 g/l </li></ul><ul><li>DYEING </li></ul><ul><li>LOAD THE FABRIC UNIFORMLY WITHOUT CREASES ONTO ONE OF THE ROLLER OF JIGGER BY PASSAGE THROUGH PLAIN WATER </li></ul><ul><li>RUN THE FABRIC (2 ENDS) THROUGH BLANK BATH AT ROOM TEMP. </li></ul><ul><li>ADD HALF THE QUANTITY OF STOCK VAT </li></ul><ul><li>RUN FOR 2 ENDS </li></ul><ul><li>ADD THE REMAINING STOCK VAT </li></ul><ul><li>RAISE TEMP SLOWLY TO 60 O C </li></ul><ul><li>CONTINUE DYEING FOR 45 MIN (8-10 ENDS) </li></ul><ul><li>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. </li></ul><ul><li>IF FOUND INSUFFICIENT PREDISSOLVE AND ADD TO JIGGER WHILE STATIONARY. </li></ul>
  10. 10. OXIDATION <ul><li>AFTER DYEING DRAIN THE DYEBATH </li></ul><ul><li>RINSE THE FABRIC THROUGH COLD WATER (2ENDS) TO REMOVE LOOSE DYE AND EXCESS HYDRO AND ALKALI </li></ul><ul><li>CONVERT THE LEUCO VAT DYE TO ITS ORIGINAL OXIDIZED FORM BY TEATMENT WITH 2 g/l H2O2 AT 40-50 O C (4 ENDS) </li></ul><ul><li>RINSE WITH COLD WATER </li></ul><ul><li>SOAPING: ABSOLUTELY ESSENTIAL FOR DEVELOPMENT OF TRUE SHADE AND BEST FASTNESS PROPERTIES. </li></ul><ul><li>REMOVAL OF SURFACE DYE AND AGGREGATION OF DYE INSIDE THE FIBRE </li></ul><ul><li>SOAP AT BOIL USING 2 g/l LISSAPOL D (ANIONIC DETERGENT) AND 2 g/l SODA ASH (4 ENDS) </li></ul><ul><li>RINSE WITH COLD WATER (2 ENDS) </li></ul><ul><li>UNLOAD FROM JIGGER </li></ul><ul><li>DRY </li></ul>
  11. 11. SEMI-CONTINUOUS DYEING <ul><li>MANY VAT DYES HAVE STRONG AFFINITY FOR COTTON </li></ul><ul><li>PENETRATION IN CLOSELY WOVEN FABRIC IS DIFFICULT </li></ul><ul><li>SEMICONTINUOUS OR CONTINUOUS METHODS USED </li></ul><ul><li>PIGMENT PAD-DEVELOPMEMNT ON JIGGER </li></ul><ul><li>PAD WITH VAT DYE DISPERSION </li></ul><ul><li>DRY </li></ul><ul><li>DEVELOP ON JIGGER USING HYDRO AND CAUSTIC SODA </li></ul><ul><li>OXIDIZE AND SOAP IN JIGGER </li></ul><ul><li>THE METHOD IS USED FOR DYEING TIGHTLY WOVEN FABRIC LIKE SUITING. </li></ul>
  12. 12. SEMI-CONTINUOUS METHOD
  13. 13. PAD-JIG METHOD <ul><li>PREPARATION OF DYE DISPERSION: </li></ul><ul><li>USE ONLY ULTRA FINE VAT DYES </li></ul><ul><li>STIR THE VAT DYE POWDER IN 10-20 TIMES ITS WEIGHT OF WATER AT 50 0 C WITH HIGH SPEED STIRRING </li></ul><ul><li>FILTER THE DISPERSION </li></ul><ul><li>MAKE THE TOTAL VOLUME </li></ul><ul><li>ADD WETTING AGENT OR LEVELLING AGENT. </li></ul><ul><li>READY FOR PADDING. </li></ul>
  14. 14. PADDING <ul><li>PADDING </li></ul><ul><li>USE WELL SCOURED BLEACHED FABRIC IN DRY STATE </li></ul><ul><li>GOOD WETTING OF FABRIC IS ESSENTIAL </li></ul><ul><li>SATURATE THE FABRIC WITH DYE DISPERSION </li></ul><ul><li>SQUEEZE OUT EXCESS LIQUOR (EXPRESSION 70%) </li></ul><ul><li>PADDING MANGLE SPEED 20 M/min. </li></ul><ul><li>IF FABRIC IS TOO TIGHT CONSTRUCTION, PAD AT HIGH TEMP (60-70 0 C) </li></ul><ul><li>DRYING </li></ul><ul><li>DEVELOPMENT MAY BE DONE IN WET STATE OR AFTER DYRYING </li></ul><ul><li>IF WET, DEVELOP WITHOUT DELAY </li></ul><ul><li>UNIORM DRYING OF PADDED FABRIC ALONG THE WIDTH AND BACK AND FACE OF FABRIC IS ESSENTIAL </li></ul><ul><li>MACHINE USED EITHER HOT FLUE OR STENTER </li></ul><ul><li>HOT CYLINDER DRYING IS NOT ADVISABLE DUE TO BACK TO FACE DYE MIGRATION. </li></ul>
  15. 15. DEVELOPMENT ON JIGGER <ul><li>SET THE JIGGER BATH WITH REQUIRED AMOUNTS OF HYDRO AND CAUSTIC SODA. </li></ul><ul><li>ADD SMALL QUANTITY OF PADDING LIQUOR TO THE BLANK BATH IN JIGGER TO COMPENSATE FOR THE DYE WHICH BLEEDS OUT FROM FABRIC </li></ul><ul><li>THE DEVELOPMENT IS SIMILAR TO JIGGER DYEING OPERATION FOLLOWED BY OXIDATION AND SOAPING TREATMENT. </li></ul>
  16. 16. CONTINUOUS METHOD <ul><li>PAD-STEAM PROCESS </li></ul><ul><li>PRINCIPLE: INCREASE IN RATE OF DYEING WITH INCREASE IN TEPERATURE. </li></ul><ul><li>DYE REDUCTION ON FABRIC SURFACE </li></ul><ul><li>IMMEDIATE DYE ADSORPTION </li></ul><ul><li>PIGMENT PAD  DRY  CHEMICAL PAD (CAUSTIC SODA, HYDRO, COMMON SALT)  STEAM (30-60 SEC.)  RINSE  OXIDIZE  SOAP -> RINSE (8 COMPRTMENT OPEN SOAPER)  DRY </li></ul>
  17. 17. CHEMICAL PADDING <ul><li>AFTER PIGMENT PADDING AND DRYING, COOL THE FABRIC TO AVOID DYE REDUCTION IN CHEMICAL PAD TROUGH </li></ul><ul><li>PAD THE FABRIC WITH SOLUTION OF HYDRO AND CAUSTIC SODA (CHEMICAL PAD LIQUOR) </li></ul><ul><li>THE CONCENTRATION OF HYDRO AND CAUSTIC SODA DEPENDS ON CONCENTRATION OF DYE ON FABRIC. </li></ul><ul><li>DYE CONC. ON FABRIC NaOH/Na2S2O4 </li></ul><ul><li>g/kg g/l </li></ul><ul><li>10 25-30 </li></ul><ul><li>30 35-50 </li></ul><ul><li>50 50-70 </li></ul><ul><li>5-10 LITRES OF PIGMENT DISPERSION/100 LITRE OF CHEMICAL LIQUOR ARE ADDED TO THE BATH </li></ul>
  18. 18. STEAMING <ul><li>CHEMICAL PADDED FABRIC IN WET CONDITION IMMEDIATELY PASSED INTO STEAMER </li></ul><ul><li>STEAM FOR 20-30 SEC. IN SATURATED AIR FREE STEAM </li></ul><ul><li>AFTER TREATMENT </li></ul><ul><li>THE FINAL TREATMENTS INVOLVING OXIDATION AND SOAPING ON 8 COMPARTMENT OPEN SOAPER </li></ul><ul><li>METHOD IS SUITABLE ONLY FOR PALE TO MEDIUM DEPTH OF SHADES </li></ul><ul><li>THE STEAMER SHOULD BE SITUATED AS CLOSE AS POSSIBLE TO CHEMICAL PADDING MANGLE, TO MINIMIZE HYDRO DECOPOSITION IN AIR BEFORE STEAMING. </li></ul>
  19. 19. CONTINUOUS METHOD
  20. 20. DYEING OF COTTON WITH INDIGO <ul><li>INDIGO HAS POOR AFFINITY TOWARDS COTTON </li></ul><ul><li>CONVENTIONAL EXHAUST OR CONTINUOUS METHODS ARE NOT SUITABLE </li></ul><ul><li>SPECIAL METHOD OF MULTIPLE DIP AND NIP (5 DIP AND 5 NIP) METHOD IS USED IN COMMERCIAL PRACTICE </li></ul><ul><li>MAJOR APPLICATION FOR DYEING OF COTTON WARP FOR PRODUCTION OF STONE WASH DENIM/JEAN FABRIC </li></ul>
  21. 21. INDIGO DYEING <ul><li>STOCK VAT </li></ul><ul><li>INDIGO X g/l </li></ul><ul><li>CAUSTIC SODA X g/l </li></ul><ul><li>HYDRO Xg/l </li></ul><ul><li>TEMP. 60 O C </li></ul><ul><li>TIME 15 MIN. </li></ul><ul><li>DYEBATH </li></ul><ul><li>INDIGO 3 g/l </li></ul><ul><li>CAUSTIC SODA 2 g/l </li></ul><ul><li>HYDRO 1.5 g/l </li></ul><ul><li>WETTING AGENT 1 g/l </li></ul><ul><li>DYEING TEMP. ROOM TEMP. </li></ul>
  22. 22. INDIGO DYEING <ul><li>CONTINUOUS DYEING RANGE </li></ul><ul><li>TROTMAN P453 </li></ul>
  23. 23. SOLUBILIZED VAT DYES <ul><li>DISULPHURIC ESTERS OF INDIGO OR AQ VAT DYES </li></ul><ul><li>LEUCO VAT DYE OBTAINED BY TREATMENT OF VAT DYE WITH HYDRO </li></ul><ul><li>TREAT LEUCO VAT DYE WITH CHLOROSULPHONIC ACID (ClSO3H) IN PRESENCE OF PYRIDINE AT 60-70 0 C </li></ul><ul><li>TREAT THE PRODUCT WITH SLIGHT EXCESS OF Na2CO3 OR NaOH </li></ul><ul><li>REMOVE PYRIDINE BY STEAM DISTILLATION </li></ul><ul><li>CONCENTRATE TO CRYSTALLIZE OR </li></ul><ul><li>SALT OUT WITH NaCl </li></ul>
  24. 24. GENERAL PROPERTIES <ul><li>SOLUBILITY </li></ul><ul><li>LOW SOLUBILITY, 50 g/l AT 50-60 0 C </li></ul><ul><li>SOLUBILITY RANGE IS SUFFICIENT </li></ul><ul><li>USED FOR DYEING PALE SHADES </li></ul><ul><li>DO NOT DISSOLVE IN BOILING WATER: PREMATURE DYE OXIDATION </li></ul><ul><li>LIGHT SENSITIVITY </li></ul><ul><li>SENSITIVE TO SLIGHT IN POWDER AS WELL IN SOLUTION FORM. </li></ul><ul><li>PREMATURE OXIDATION TO INSOLUBLE VAT DYE </li></ul><ul><li>EXPOSURE TO LIGHT SHOULD BE AVOIDED </li></ul><ul><li>ACTION OF LIGHT CAN BE MINIMIZED BY ADDING SMALL QUANTITY OF SODA ASH TO DYE SOLUTION </li></ul><ul><li> </li></ul>
  25. 25. GENERAL PROPERTIES <ul><li>SOLUBILITY </li></ul><ul><li>LOW SOLUBILITY, 50 g/l AT 50-60 0 C </li></ul><ul><li>SOLUBILITY RANGE IS SUFFICIENT </li></ul><ul><li>USED FOR DYEING PALE SHADES </li></ul><ul><li>DO NOT DISSOLVE IN BOILING WATER: PREMATURE DYE OXIDATION </li></ul><ul><li>LIGHT SENSITIVITY </li></ul><ul><li>SENSITIVE TO SLIGHT IN POWDER AS WELL IN SOLUTION FORM. </li></ul><ul><li>PREMATURE OXIDATION TO INSOLUBLE VAT DYE </li></ul><ul><li>EXPOSURE TO LIGHT SHOULD BE AVOIDED </li></ul><ul><li>ACTION OF LIGHT CAN BE MINIMIZED BY ADDING SMALL QUANTITY OF SODA ASH TO DYE SOLUTION </li></ul><ul><li> </li></ul>

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