Vat Dyessss

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7

VAT DYES

Except Deep Red

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Introduction1

Chemical Structure of Vat Dyes2

Dyeing Structure of Vat Dyes3

Method of Dyeing4

Treatments After Exhaustion of Vat Dyes5

Overview

Semi and Fully Continuous Method6

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Wet on Wet Process7

Fixation Process8

Package Dyeing9

Dyeing of Knit Goods10

Correction of Faulty Dyeing11

Overview

Indigo Dyeing for Denim12

Solublised VAT Dyes137/2/2008 33


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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)

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the vat dyes areextensively used for

dyeing yarnTHIS CLOTH can

undergo thepretreatment

processes like7/2/2008 55


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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.

q VATTING: In order to apply cellulosic Fibers

q VAT PIGMENTS are made water soluble by reducing to

HYDROQUINONE Forms in an alkaline media.This process Known as

Vatting.

q 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.

v PRESENT VATTTING CHEMICALS ARE:

v Sodium Hydroxide7/2/2008 66


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v PRESENT VATTTING / REDUCING CHEMICALS ARE:

v Sodium Hydroxide

v Sodium Dithionate(Na2 S2 O4) a strong reducing agent one with

high reduction potential.

v Commonly termed in Industry as Sodium Hydro Sulphite or Simply

HYDROS.

v Sodium Dithionate reduces the KETO GROUPS into the ENOL Form

v Sodium Hydroxide forms sodium salts of the ENOL to make the

DYES WATER SOLUBLE.

v Caustic Soda Also NEUTRALISE THE ACIDIC Decomposition products

of the reducing agent DITHIONITE produced during vatting and

Dyeing.

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v PRESENT VATTTING / REDUCING CHEMICALS ARE:

v 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.

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L OH


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v Around 1900 Rene Bohn in GERMANY

v accidently prepared a blue dye from ANTHRAscene,

which he named as an INDANthrene dye. Soon after

this breakthrough

v Bohn and his Coworkers synthesize many other

VAT DYES.

v THE VAT DYES ARE OFTEN CLASSIFIED AS:

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v Sodium Salts (Nacl) of the Reduced or Leuco VAT

Dyes behave like:

v Direct dyes

v As for as adsorption on the cellulose fibres is

concerned

v But the ANTHRAquinone derivatives have

v High intrinsic substantivity

v In spite of lack of linearity and

v Hydrogen bonding groups attributed

to the molecular complexity

And CO-PLANARITY of the VAT

dyes.

As a High Concentration of SODIUM IONS from

Caustic Soda(NaoH) and Sodium Dithionate(Na2S2O4)7/2/2008 1010


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v After the adsorption of the LEUCO DYES

v AN OXIDIZING AGENT IS ADDED TO THE BATH

v That regenerates the VAT PIGMENT inside the fibres.

v Finally, to achieve full fastness properties and to

develop the proper shade, the dyed goods are THOROUGHL

Y SOAPED AT

BOIL.

v VAT dyes three main classes for APPLICATION

PUPOSES.

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Where I stands for Indanthrene and N for NormalIn their Leuco forms Have High substantively for the cellulosicfibres.These needs High Alkalinity for DissolutionAnd are dyed at about 75o c.

Where I stands for Indanthrene and W for WarmIn their MODERATE substantivity for cellulosic fibres.These needs MEDIUM Alkalinity for DissolutionAnd are dyed at about 45o c TO 75o c.Needs Electrolytes for complete EXHAUSTION of the dye.


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Where I stands for Indanthrene and K for KALT / COLDHave LOW substantivity for the cellulosic fibres.These needs moderate Alkalinity for DissolutionAnd are dyed at low temperature about 20o c to 30o c..Needs in a Higher concentration Electrolytes than class II forcomplete EXHAUSTION of the dye.

Dyes of the IK Group other than the Indigo, are Not much usednow a days.Some vat dyes like BLACKS do NOT into the above mentionedthree groups and are dyed by a special method


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v 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.

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v REDUCED VAT DYEING:

v This process is applicable for

Batch wise dyeing WOVEN and KNIT fabrics

Also for YARNs in hank or package form.

REDUCTION OF the dye is faster in the STOCK VAT

BECAUSE

Concentration of the dye and reducing chemicals is

higher than LONG BATH.

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The dye is first reduced intoSOLUBLE FORM.In the bath(long liquor)Or in the stock vat

Beforebringing it incontact with

substrate


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v REDUCED VAT DYEING:

v THE MORE Difficult to reduced CLASS I dyes:

v Vatted by the STOCK VAT method.

This dispersion at optimum temperature

Stirred for 10 minutes. When reduction is COMPLETE.

SOFT WATER must for dissolving and as far as

dyeing. D ein in HARD WATER causes reci itation7/2/2008 1616

Dye is pasted

with thedispersingagent. And soft

water

And then the required quantitiesof

Caustic Soda(NaoH)And

DI-THIONATE(S2O4)Are added as per manufacturer

literature.


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WETTING AGENT WETTING AGENT

CAUSTIC SODA CAUSTIC SODA

Goods are thoroughly wetted in itbefore reduced dye.

Goods are thoroughly wetted in itbefore reduced dye.

Concentration of the Concentration of the

THE DYE BATH is set with


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v THE FOLLOWING TABLE WILL GIVE A

v GENERAL IDEA OF CONCENTRATION

v OF rducing and exhausation chemicalsrequired inthe bath at a liquor ratio of 10:1

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v For the Class I dyes,

a nonionic retarding agent (ALKO-Xylated type)

v Is often added that forms a complex with the

REDUCED dye and release it gradually as the bath is

exhausted,

v addition of the Retarding or LEVELLING agent ismore necessary

When dyeing mercerized COTTON, Regenerated

RAYON

And for PALE SHADES

And also in LOW LIQUOR ratios.

v These LEVELLING Agent reduce the ultimate dye-

uptake slightly,

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During DYEING

Desired Excess Checked With

Metering Devices


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v Some Dyes during dyeing

OVER REDUCED

Their SHADES becomes LIGHTER or evenALTERED.

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THIS is checked by adding RADOX BUFFOERS

Like

SODI

U

Like SODIUM NITRITE

O

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p

Or by replacing part of


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Dyeing is started at temperature of 20o C.

Which is gradually raised to the optimum.

Dyes of IN and IW groups temperature

can be raised to 80o 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 BATH7/2/2008 2222

T A O


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AFTER EXHAUSTION OF THE VAT DYES

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The

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And

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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 PENETRATION

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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.

q The latter is added for quick wetting of thefabric.

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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.7/2/2008 3030


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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 Agent7/2/2008 3131


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3. DEVELOPMENT: CONTINUOUS PROCESS

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Drie

dandCoolP

ig

Dried and CoolPigment PADDEDFABRIC is

Also 1-2 G/L WETTINGAGENT ------- 0-30 G/L

40 to 80 ml / l30% Caustic SodaSolution------

THE CONCENTRATIONOF THE CHEMICALS

DEPENDING ON 30 40 ml/l PIGMNET

PADDING LIQUOR PICKUP 70 -80%

maintained atTemperature

S

T

EA

M

E

R

STEAME

R

THE FABRIC IS THEN IMEDIATELY ENTERINTO STEAMER

Temp of water seal should be keptlow(below 40

Steam should be free of air and water

droplets and its temp should 102----105----

I

nInSom Dithionate


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OXIDATION AND SOAPING

In the Continuous Process,

In a WASHING RANGE

In which fabric is treated in the following different sequences:

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1&2

3&4

5&6


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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 fibersand so difficult to strip off the dyed goods.

LEVELLING OUT

PARTIAL STRIPING

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Vat Dyessss