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  1. 1. VAT DYES Except Deep Red 7/2/2008 1
  2. 2. Overview 1 Introduction 2 Chemical Structure of Vat Dyes 3 Dyeing Structure of Vat Dyes 4 Method of Dyeing 5 Treatments After Exhaustion of Vat Dyes 6 Semi and Fully Continuous Method7/2/2008 2
  3. 3. Overview 7 Wet on Wet Process 8 Fixation Process 9 Package Dyeing 10 Dyeing of Knit Goods 11 Correction of Faulty Dyeing 12 Indigo Dyeing for Denim 13 Solublised VAT Dyes7/2/2008 3
  4. 4. 1 Introduction  Dyeing produced with the vat dyes have the highest overall fastness properties. All of these dyes have good fastness against Wet treatments Crocking Light fastness in the region of 6 to 7. The vat dyes can also withstand oxidizing agents like Hydrogen peroxide (H202) Sodium Chloride (NaCl) Hypochlorite (--OCl)7/2/2008 4
  5. 5. 1 Introduction  the vat dyes are extensively used for dyeing yarn THIS CLOTH can undergo the pretreatment processes like Alkali Boiling Bleaching Mercerizing Without any damage to the dyed yarn. After the introduction of hydrogen peroxide - tolerant reactive dyes Yarn dyeing has been taken over by the reactive dyes. Because reactive dyes less expensive , easier to apply. Vat dyes are still popular on account of the all round high fastness properties. VAT DYES ARE COMMONLY USED FOR: Superior Quality Shirting Material Military Uniforms Furnishings, Curtain, Toweling etc.7/2/2008 5
  6. 6. 1 Introduction  there are about 60 vat dyes in the market That cover the entire Gamut(range) of shades except Deep Red Colors . VAT DYES ARE ESSENTIALLY Insoluble Polycyclic Aromatic Compound: Containing Two or more pair of QUINONE GROUPS Indigo and Tyrian Purple belongs to this family. VATTING: In order to apply cellulosic Fibers VAT PIGMENTS are made water soluble by reducing to HYDROQUINONE Forms in an alkaline media.This process Known as Vatting. Vatting Term referring to a historical link with the vegetable Indigo Dye that used to reduced in WOODEN VATS with natural reducing agents like sugar. PRESENT VATTTING CHEMICALS ARE: Sodium Hydroxide Sodium Dithionate(Na 2 S2 O4) a strong reducing agent one with high reduction potential. Commonly termed in Industry as Sodium Hydro Sulphite or Simply HYDROS. Sodium Dithionate reduces the KETO GROUPS into the ENOL Form Sodium Hydroxide forms sodium salts of the ENOL to make the DYES WATER SOLUBLE.7/2/2008 6
  7. 7. 1 Introduction PRESENT VATTTING / REDUCING CHEMICALS ARE: Sodium Hydroxide Sodium Dithionate(Na2 S2 O4) a strong reducing agent one with high reduction potential. Commonly termed in Industry as Sodium Hydro Sulphite or Simply HYDROS. Sodium Dithionate reduces the KETO GROUPS into the ENOL Form SodiumHydroxide forms sodium salts of the ENOL to make the DYES WATER SOLUBLE. Caustic Soda Also NEUTRALISE THE ACIDIC Decomposition products of the reducing agent ‗DITHIONITE‘ produced during vatting and Dyeing.7/2/2008 7
  8. 8. 1 Introduction PRESENT VATTTING / REDUCING CHEMICALS ARE: Quantity of Reducing Agent Depend upon No. of KETO groups Present in the Dye Molecule To the extent/ amount of exposure or the dye bath to AIR. Reduction is Accompanied by Change in Color that is due to alteration in the conjugation of DOUBLE BONDS. The reduced indigo has a PALE SHADE and so it was called the LEUCO(white) dye.7/2/2008 8
  9. 9. 2 Chemical Structure of VAT Dyes Around 1900 Rene Bohn in GERMANY accidentlyprepared a blue dye from ANTHRAscene, which he named as an INDANthrene dye. Soon after this breakthrough Bohn and his Coworkers synthesize many other VAT DYES. THE VAT DYES ARE OFTEN CLASSIFIED AS: • Includes the HYDRONE •Majority of vat dyes•Low substantive to BLUES that are type of belongs to this group. cellulose HYBRIDS of sulphur •Having a more complex •Often used as substitute structure. of Indigo •Posses high affinity. •Low substantive to •Better all- around cellulose fastness properties than other two groups.INDIgoid Thio-INDIgoid AnthraQuinonOid 7/2/2008 9
  10. 10. 3 DYEING Structure of VAT Dyes Sodium Salts (Nacl) of the Reduced or Leuco VAT Dyes behave like: Direct dyes As for as adsorption on the cellulose fibres is concerned But the ANTHRAquinone derivatives have High intrinsic substantivity In spite of lack of linearity and Hydrogen bonding groups attributed to the mo le cular co mple x ity And CO -PLANAR IT Y o f the VAT dye s. As a High Concentration of SODIUM IONS from Caustic Soda( NaoH) and Sodium Dithionate(Na2 S2O4) Already exist in the Reduced Bath. The VAT dye tend to have HIGH RATE of adsorption And EXHAUSTION in the initial stage of Application. The RAPID ADSORPTION of dye in the first few minutes: Technically termed as ―HIGH STRIKE‖ value. This tendency require a careful attention as well as ADDITION of RETADING agents to obtained level dyeing.7/2/2008 10
  11. 11. 3 DYEING Structure of VAT Dyes After the adsorption of the LEUCO DYES AN OXIDIZING AGENT IS ADDED TO THE BATH That regenerates the VAT PIGMENT inside the fibres. Finally,to achieve full fastness properties and to develop the proper shade, the dyed goods are THOROUGHLY SOAPED AT BOIL. VAT dyes three main classes for APPLICATION PUPOSES. CLASS I or IN CLASS II or IW CLASS III or IK7/2/2008 11
  12. 12. 3 DYEING Structure of VAT Dyes CLASS I or IN Where I stands for Indanthrene and N for Normal In their Leuco forms Have High substantively for the cellulosic fibres. These needs High Alkalinity for Dissolution And are dyed at about 75o c. CLASS II or IW Where I stands for Indanthrene and W for Warm In their MODERATE substantivity for cellulosic fibres. These needs MEDIUM Alkalinity for Dissolution And are dyed at about 45o c TO 75o c. Needs Electrolytes for complete EXHAUSTION of the dye.7/2/2008 12
  13. 13. 3 DYEING Structure of VAT Dyes CLASS III or IK Where I stands for Indanthrene and K for KALT / COLD Have LOW substantivity for the cellulosic fibres. These needs moderate Alkalinity for Dissolution And are dyed at low temperature about 20o c to 30o c.. Needs in a Higher concentration Electrolytes than class II for complete EXHAUSTION of the dye. Dyes of the IK Group other than the Indigo, are Not much used now a days. Some vat dyes like BLACKS do NOT into the above mentioned three groups and are dyed by a special method7/2/2008 13
  14. 14. 4 METHOD DYEING In Batch dyeing of fabric, VAT dyes are normally applied in the Reduced in a JIGGER. For continuous processes, Fabric is PADDED in stable dispersion of very finely divided vat pigments often termed as MICRO- DISPERSIONS. After drying the dye padded fabric, it is reacted with an ALKALINE REDUCING SOLUTION in a padder to VAT PIGMENT into water-soluble LEUCO FORM LEUCO FORM diffuses into the fibre.7/2/2008 14
  15. 15. 4 METHOD DYEING REDUCED VAT DYEING: This process is applicable for Batch wise dyeing WOVEN and KNIT fabrics Also for YARNs in hank or package form. The dye is first reduced into Before SOLUBLE FORM. bringing it in In the bath(long liquor) contact with Or in the stock vat substrate REDUCTION OF the dye is faster in the STOCK VAT BECAUSE Concentration of the dye and reducing chemicals is higher than LONG BATH.7/2/2008 15
  16. 16. 4 METHOD DYEING REDUCED VAT DYEING: THE MORE Difficult to reduced CLASS I dyes: Vatted by the STOCK VAT method. Dye is pasted And then the required quantities of with the Caustic Soda(NaoH) dispersing agent. And And soft water DI-THIONATE(S2O4) Are added as per manufacturer literature. This dispersion at optimum temperature Stirred for 10 minutes. When reduction is COMPLETE. SOFT WATER must for dissolving and as far as dyeing. Dyeing in HARD WATER causes precipitation (useless product) COUNTER THIS PROBLEM by use of SQUEStering AGENT.7/2/2008 16
  17. 17. 4 METHOD DYEING REDUCED VAT DYEING: CAUSTIC SODA WETTING AGENT & HYDROS(dithionate) THE DYE BATH is set with Concentration of the castic Goods are thoroughly and hydros depend upon wetted in it before reduced class of dye and the liquor dye. Ratio and literature of mfr should be consulted.7/2/2008 17
  18. 18. 4 METHOD DYEING REDUCED VAT DYEING THE FOLLOWING TABLE WILL GIVE A GENERAL IDEA OF CONCENTRATION OF rducing and exhausation chemicalsrequired in the bath at a liquor ratio of 10:1 DYE Caustic soda Hydros (g/l) Sod.Sulphate GROUP (g/l) (g/l) IN 8.8 5.0 NIL IW 4.8 4.0 12.0 IK 3.6 3.0 12.07/2/2008 18
  19. 19. 4 METHOD DYEING REDUCED VAT DYEING For the Class I dyes, a nonionic retarding agent (ALKO-Xylated type) Isoften added that forms a complex with the REDUCED dye and release it gradually as the bath is exhausted,  addition of the Retarding or LEVELLING agent is more necessary When dyeing mercerized COTTON, Regenerated RAYON And for PALE SHADES And also in LOW LIQUOR ratios. These LEVELLING Agent reduce the ultimate dye - uptake slightly,7/2/2008 19
  20. 20. 4 METHOD DYEING REDUCED VAT DYEING •Dithionate •Keeps on oxidizing due to contact with air. •And their oxidation products During DYEING •Being acidic •Neutralize Caustic Soda • IF concentration of ALKALI falls below the certain LEVEL • The ACID LEUCO is formed, that PRECIPITATE cause a Weaker SHADE with Lower Fastness To RUBBING. • Phenol-Ph-Thalein • Yellow Papers (carries a yellow VAT Dye – Deep BLUE when Leuco state ) • If the PAPER turn BLUE (Adequate Quantity of DITHIONATE in the Bath)Desired ExcessChecked With •That may automatically control INPUTS OF REDUCING CHEMICALS into the DYEBATH. Metering •These have improve level of REPORODUCEABILITY OF THE SHADE. Devices 7/2/2008 20
  21. 21. 4 METHOD DYEING REDUCED VAT DYEING Some Dyes during dyeing  OVER – REDUCED Their SHADES becomes LIGHTER or even ALTERED. THIS is checked by adding RADOX BUFFOERS  Like SODIUM NITRITE Or by replacing part of DiThionate with GLUCOSE7/2/2008 21
  22. 22. 4 METHOD DYEING REDUCED VAT DYEING Dyeing is started at temperature of 20 o C. Which is gradually raised to the optimum. Dyes of IN and IW groups temperature can be raised to 80 o C The Dyeing Continued for 45 TO 60 minutes. ELECTROLYTE is added in portions about 20 Minutes After the dye Liquor reaches the MAXimum Temperature. In case or CLASS III ELECTROLYTE added at beginning And dyeing is carried out in a cooling BATH after attaining TEMP of 45 o C. However SPECIAL REDUCING AGENTS of the HYDROXY- Alkyl-Sulphinate type may have to be used that can withstand decomposition at these HIGH Temperature.7/2/2008 22
  23. 23. 5 TREATMENTS AFTER EXHAUSTION OF DYES AFTER EXHAUSTION OF THE VAT DYES• The substrate is •And REDUCING OXIDATION IS usually first washed CHEMICALS before FOLLOWED BY: free of ALKALI regeneration of the SOAPING: to remove DYE PIGMENTS inside the pigments sticking the fibers by oxidation. to the surface layers of the dyed material.Rinsing OXIDATION SOAPING 7/2/2008 23
  27. 27. 5 TREATMENTS AFTER EXHAUSTION OF DYES AFTER EXHAUSTION OF THE VAT DYES•AFTER OXIDATION, THE PIGMENT IS IN MOLECULAR FORM AND IS loosely held in between the cellulose molecules.•DURING THE SOAPING the dye molecules , under the influence of HEAT and lubrication by the detergent, migrate and come close to one an other to form SUBMICROSCOPIC CRYSTALS in the fissure/gap of the fiber.•Crystals have different absorption spectra so true solid shade produced after soaping.•Crystallization process increase SIZE OF THE DYE PARTICLE. Increased wet fastness.•Detergent 1 – 2 g/l•Sodium Carbonate 2 g/l•Boils for 30 minutes•Then rinsed hot and cold followed this. SOAPING 7/2/2008 27
  28. 28. 6 Semi and Fully Continuous Dyeing Method THE PRINCIPLE OF THIS TECHNIQUE TO pad the well prepared fabric With a very fine dispersion (PARTICLE SIZE 0.5 – 1 um) of VAT PIGMENT. Then to convert the absorb pigment into LUECO FORM This is followed by OXIDATION SOAPING in a Washing Range The MAIN ADVANTAGE of this process over the reduced -VAT method are as under. A) HIGH PRODUCTIVITY B) BETTER LEVELLING C) GOOD PENETRATION7/2/2008 28
  29. 29. 6 Semi and Fully Continuous Dyeing Method Different steps involve in the APPLICATION are: 1. PADDING: Padder should be mechanically perfect And exert even pressure throughout the Width of the fabric. The pigment dispersion normally contains  a migration inhibitor and a wetting agent. The latter is added for quick wetting of the fabric.7/2/2008 29
  30. 30. 6 Semi and Fully Continuous Dyeing Method Different steps involve in the APPLICATION are: 2. DRYING: It is not necessary for Light Shades But it HELPS IN LEVELLING and improving colour yield. It may be done at  Combination of INFRA- RED  HOT FLUE or  CYLINDER DRYER  Incase the cylinder are used  The IR-predryer is must  First few cylinder Teflon Coated as to reduce staining.  Temp 100 o C first few cylinders to minimize Migration and two sided effect.7/2/2008 30
  31. 31. 6 Semi and Fully Continuous Dyeing Method Different steps involve in the APPLICATION are: 3. DEVELOPMENT: Method are used for both Development of the DYE PIGMENT:  BOTH the batch and continuous.  In the BATCH PROCESS  Reduction and  Adsorption Of the dye can be carried out on a Jigger.  DONE in the reduced dyeing method, after ADDING  Alkali and Reducing Agent  IF variation in SHADE due to BLEEDING in not totally eliminated  In the CHEMICAL PADDER 5 – 10 % of the bath is made7/2/2008 with the pad liquor 31
  32. 32. 6 Semi and Fully Continuous Dyeing Method Different steps involve in the APPLICATION are: 3. DEVELOPMENT: CONTINUOUS PROCESS Dried and Cool Pigment PADDED FABRIC is • Padded in solution containing • 40 to 80 ml / l 30% Caustic Soda Solution------And 15 to 40 g / l Dithionate in COLD • Also 1-2 G/L WETTING AGENT ------- 0-30 G/L Glauber‘s Salt • 30 – 40 ml/l PIGMNET PADDING LIQUOR • PICKUP 70 -80% maintained at Temperature 20-30oC • THE CONCENTRATION OF THE CHEMICALS DEPENDING ON THE DEPTH OF SHADE STEAMER • THE FABRIC IS THEN IMEDIATELY ENTER INTO STEAMER • For 20 ---- 40 SECONDS for reduction, sublimation of the dye and its diffusion into fiber. • Steam should be free of air and water droplets and its temp should 102----105oC. • Temp of water seal should be kept low(below 40oC) other wise it becomes a reducing DYEBATH. • Brief Airing passage may follow after steaming to complete exhaustion and partial oxidation of dye. In Some Cases • Dithionate is REPLACED with7/2/2008 • More stable SODIUM SULPOXY LATE FORMALdehyde (Na HSO2..CH2O) 32
  33. 33. 6 Semi and Fully Continuous Dyeing Method OXIDATION AND SOAPING In the Continuous Process,  In a WASHING RANGE  In which fabric is treated in the following different sequences: • Cold Water • Warm water at 40OC 1&2 • Hydrogen Peroxide (50%) 1—3 ml/l Plus 1 to 2 ml/l acetic acid in 2 cisterns 3&4 • RINSING at 60oC. • Soaping in 2 cisterns with 2 g/l of a Detergent and 2g/l sodium carbonate 5&6 • Rinsing at 60oC…….80oC. 7/2/2008 33
  34. 34. 7 CORRECTION OF FAULTY DEING  Fauls are usually corrected by  Levelling Out  Partial Stripping or Cross Dyeing  However kept in mind LEUCO VATS have a very high affinity with cotton fibers and so difficult to strip off the dyed goods. •Defective material treated in a Blank bath containing 10-20 ml/l Caustic Soda(30%) •50 – 100 G/L dithionate •1-2 g/l wetting /and Dispersing Agent •At 70-80OC for about 30 minutesLEVELLING •After this color removal treatment (15% of the original dye is used is ADDED) and the normal dyeing and OUT oxidation is carried out. •SIMILAR TO THE LEVELLING OUT BUT ADDITION OF DYE complexing agent •2-3 G/L poly vinyl pyrol idine (PVP) •COMPUND FORMS A STABLE COMPLEX with the Reduced dye •Does not allow to exhaustion on the fibrePARTIALSTRIPING 7/2/2008 34