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HISTORY
•One of the oldest dyes used for thousands of years.•Used in mummy cloths in ancient Egypt. •Before the synthetic dyes were developed in the 19th century indigo dyes were produced from plants.•Woad was cultivated for indigo production in Europe in the middle ages and brought immense wealth to the woad traders. •Woad disappeared entirely in the beginning of the 20th century with the appearance of synthetic indigo to the markets in India and Java.•The BASF started the production of synthetic vat dyes in 1897.
INDIGOFERA PLANTINDIGOFERA PLANT33
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WHY NAMED VAT ?
•The name Vat was derived from the large wooden vessel from which vat dyes were first applied.
•The process "reduces" the vat dye, changing it from water insoluble to soluble form. In this state, it dissolves in an alkaline solution. This process is called “VATTING”
•Finally oxidation is done for final color generation.
•It can be used to dye any natural fibre and also protein fibres like wool.
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VAT DYED PRODUCT ?
•Vat dyed product is very popular & covers a big fashion market on all over the world.•Garments are faded gradually specially on those location which faces frequent friction like elbow, knee, whisker etc. that now a days includes an extra value in fashion market.•Denim or jeans pants, shirt, jacket, coat, overcoat, scarf, covering items, shoes etc.
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PROPERTIES OF VAT DYESPROPERTIES OF VAT DYES Natural coloring dyes. Water insoluble and cannot be applied directly on textile material. Vatting process is needed for making the insoluble vat dyes into
soluble form. Vatting is done in alkaline condition. Final color is developed by the oxidation process. Mainly used for cellulosic fibre but in application of protein fibre,
pH should be controlled. Color fastness to wash is very good. Color fastness to light is also very good. Color fastness to rubbing is poor. Wide range of shade can be produced. Dye is costly.
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CLASSIFICATION OF VAT DYESCLASSIFICATION OF VAT DYES Divided into two main classes on the basis of chemical structure.
A. The Indigoid vat dyes which are derivatives of Indigotin or Thio-indigo.
Fig : Indigotin (left) & Thioindigo (right) structure B. Anthraquinone vat dyes which are derives from anthraquinone
Fig 3: Anthraquinone structure
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CLASSIFICATION OF VAT DYESCLASSIFICATION OF VAT DYES
Can also be classified into four main classes on the basis of application.
A. IN (Indanthrene Normal)B. IW (Indanthrene warm)C. IK (Indanthrene cold)D. IN special
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TRADE NAME OF VAT DYESName of Vat Dyes Country
Artex Vat India
Meta Vat India
Calcoloid U.S.A
Cibanone Switzerland
Caledon U.K.
Paradone U.K.
Indanthren Germany
Tina Switzerland
Novasol Blue RS MD Switzerland
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MECHANISM OF VAT DYEING
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STEPS OF VAT DYEING
Step – 1 (Vatting): Vatting is a process developed for reducing the vat dye unto soluble “leuco form”.
Step – 2 (Dyeing): The predetermined amount of cotton goods is dyed with water soluble leuco vat dyes.
Step – 3 (Oxidation): The exhausted dyes are then oxidized to convert it to insoluble form into the fibre.
Step – 4 (Aftertreatment): Normally detergent & soda ash are used for soap wash.
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VAT DYEING PROCESSES
Three processes of vat dyeing.
Dis-continuous processSemi-continuous processContinuous process
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SAMPLE CALCULATIONShade% Oxidation process Type & number of sample
Woven Knit
1% shade blue
with air 1 1with Na-perborate 1 1with Hydrogen peroxide 1 1with Potassium dichromate 1 1
2% shade blue
with air 1 1with Na-perborate 1 1with Hydrogen peroxide 1 1with Potassium dichromate 1 1
1% shade yellow
with air 1 1with Na-perborate 1 1with Hydrogen peroxide 1 1with Potassium dichromate 1 1
2% shade yellow
with air 1 1with Na-perborate 1 1with Hydrogen peroxide 1 1with Potassium dichromate 1 1
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Total number of sample for knit is 16 & for woven is 16 = 32
MATERIAL & EQUIPMENT FABRIC
a. Knit fabricb. Woven fabric
EQUIPMENT: a. Beaker.b. Stirring rod.c. Stand.d. Gas burner.e. Match box.f. Measuring tube.g. Scissor.h. PH paper.i. Weight meter.j. Thermometer.k. Lid of dye bath
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DYESTUFF & CHEMECALS USED
Dye 1: NOVASOL BLUE RS md Dye 2: YELLOW 5G md Common salt (NaCl) Caustic soda (NaOH) Hydrose Oxidizing agents. Acetic acid
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CONTROL PARAMETERS OF VAT DYEING pH of vatting Liquor ratio Amount of Hydrose Temperature & time of vatting Rate of heating Rate of cooling Way of oxidation or fixation Restricted air contact during dyeing. Level of scouring & bleaching Manual work Common chemicals (Salt, Alkali) Auxiliaries
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PRETREATMENT(SCOURING & BLEACHING)
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SCOURING & BLEACHING RECIPE
Hydrogen peroxide 35% (H2O2) : 5% on the weight of fabric Caustic soda (NaOH) : 4% on the weight of fabric Soda ash (Na2CO3) : 3% on the weight of fabric Wetting agent : 1% on the weight of fabric Stabilizer (sodium silicate) : 2% on the weight of fabric pH : 10.5 – 11 M:L : 1:30 (for open bath) Temperature x Time : 100˚C x 1hr
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DROP TEST TO ASSESS SCOURING
In a pipette, solution of direct red (Congo red) solution is taken and dropped on the scoured fabric. Standard time for the absorption of one drop of solution is up to 1 second
2020
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