25-10-2012, 04:01 PM
DYEING WITH VAT DYES
[attachment=37134]
Earlier these dyes were dissolved by fermentation in big wooden vessels (vats). Therefore they are called vat dyes.
Most dyes are expensive. Also the application method is expensive.
Generally produce dull shades.
Resistant to reducing agents and so used in discharge printing.
Historically most important class of dye.
Indigo
First member. Obtained 4000-5000yrs
Plant Indigofera tinctoria
2 carboxyl groups are chromophores.
2% of total dye consumption is only of Indigo. It is the single largest dye used today.
Vatting
Amount of reducing agent required is decided by the reduction potential of the dye. (-650 to 100mV)
Hydrose is capable for this.
Hydrose gets reduced very fast as it rects with O2. During dyeing also dye should be in reduced form.
Hence, more hydrose is to be added during dyeing.
Glucose, dextrin or thio urea dioxide can also be added.
Dyeing
Dye bath is set up with blank solution which is 2-3 gpl hydrose and NaOH.
Material is worked in blank dye & then reduced dye is added.
Hydrose & NaOH are added time to time.
Presence of hydrose is checked with vat yellow paper & of NaOH is checked with phenolphthalein paper.
Application procedures
Batch wise method
Semi-continuous method
Continuous Method
Batch wise is done in Jigger or Winch.
Semi-continuous & Continuous method –
Dye applied in pigment form & then reduction
carried out on fabric.
[attachment=37134]
Earlier these dyes were dissolved by fermentation in big wooden vessels (vats). Therefore they are called vat dyes.
Most dyes are expensive. Also the application method is expensive.
Generally produce dull shades.
Resistant to reducing agents and so used in discharge printing.
Historically most important class of dye.
Indigo
First member. Obtained 4000-5000yrs
Plant Indigofera tinctoria
2 carboxyl groups are chromophores.
2% of total dye consumption is only of Indigo. It is the single largest dye used today.
Vatting
Amount of reducing agent required is decided by the reduction potential of the dye. (-650 to 100mV)
Hydrose is capable for this.
Hydrose gets reduced very fast as it rects with O2. During dyeing also dye should be in reduced form.
Hence, more hydrose is to be added during dyeing.
Glucose, dextrin or thio urea dioxide can also be added.
Dyeing
Dye bath is set up with blank solution which is 2-3 gpl hydrose and NaOH.
Material is worked in blank dye & then reduced dye is added.
Hydrose & NaOH are added time to time.
Presence of hydrose is checked with vat yellow paper & of NaOH is checked with phenolphthalein paper.
Application procedures
Batch wise method
Semi-continuous method
Continuous Method
Batch wise is done in Jigger or Winch.
Semi-continuous & Continuous method –
Dye applied in pigment form & then reduction
carried out on fabric.