2. CONTENTS
Introduction To Indigo Dye
Chemical Property And Synthesis Of Indigo
Why Indigo ?
Indigo Dyeing Briefing
Indigo Dyeing Methods
Recent Developments In Indigo Dyeing
References
3. Indigo dye is an organic compound with a
distinctive blue colour. Historically, indigo
was a natural dye extracted from plants, and
this process was important economically
because blue dyes were once rare. Nearly all
indigo dye produced today several thousand
tons each year is synthetic. It is the blue
of blue jeans. The primary use for indigo is
as a dye for cotton yarn, which is mainly for
the production of denim cloth for blue jeans.
On average, a pair of blue jean trousers
requires 3 – 12 g of indigo.
INTRODUCTION
4. CHEMICAL PROPERTIES INDIGO DYE
Indigo is a dark blue crystalline powder that sublimes at 390–392 °C.
It is insoluble in water, alcohol or ether but soluble in DMSO, chloroform,
nitrobenzene, and concentrated sulfuric acid.
The chemical formula of indigo is C16H10N2O2.
The molecule absorbs light in the orange part of the spectrum (λmax = 613 nm).
HEUMANN'S SYNTHESIS OF INDIGO
It involves heating N-(2-carboxyphenyl)glycine to 200 °C in an inert atmosphere with
sodium hydroxide. Indoxyl-2-carboxylic acid is generated.This material readily
decarboxylates to give indoxyl, which oxidizes in air to form indigo.
5. WHY INDIGO ?
•It supplies favoured shades from black to navy to sky blue.
• Pleasant colour shade.
•Possibility to dye cotton in cold dye bath.
•Competitive in price.
•Gives acceptable colour fastness and the exceptional advantage by
repeated washing of fading colour, to keep the colour shade that always a
clear, pleasant blue shade result.
•It’s soluble form is not sensitive to water hardness and this allows the
dyeing of greige or minimum pretreated cotton.
6. The warp yarn in denim jeans is traditionally dyed with INDIGO,
whereas the weft yarn is white.
In indigo dyeing there is symbolic built-up of dye stuff on the yarn
according to the multi-deep process. Indigo sticks to the surface of the
cotton yarn, resulting in a blue surface, while the interior of the yarn
will remains white.
INDIGO DYEING
7. DIFFERENT INDIGO DYEING METHODS
Indigo rope dyeing process
Indigo-Slasher-or Sheet-dyeing
Loop dye 1 for 6 (continuous dye slashing)
Loop dye 1 for 6 with dyemer (continuous
mercerization dyeing and sizing).
8. INDIGO ROPE DYEING WITH SUBSEQUENT SIZING PROCESS
Step 1: Ball Warper
Step 2: Rope Dyeing
Step 3: Long Chain Beamer
Step 4: Sizing
9. Yarn from the ring spinning machine is wound into suitable package,assembled into a
rope and wound into a ball.
Usually 18 – 24 ropes are simultaneously processed.
Prior to dyeing, the ropes are boiled out and treated with caustic-soda and wetting agent.
The ropes are immersed into the dye-bath.
Immersion time 30 – 60 seconds .
Oxidation time 60 – 180 seconds for uniform dyeing.
For deep shade 5 – 6 times the ropes are immersed in a sequence of dye boxes.
After dyeing and oxidation range the ropes are guided through 2 or 3 washing boxes to
wash off excessive dye.
They are dried in a series of cans and deposited into large coilers.
After this rebeaming and opening of the ropes takes place for sizing operation.
Processing -An overview…………
11. Processing of single sheet slasher dyeing……..
In continuous slasher dyeing and sizing back beams are used.
Here the total number of ends required for a weavers beam are dyed, dried, sized
and dried simultaneously.
Number of ends are pretreated (washed),dyed in 4 dye boxes and oxidized, no
softener are used in the last wash box.
The squeezing effect here is lower and therefore the danger of streakiness and
shade variation from centre to out side is also higher.
The immersion time in the dye boxes is approx. 10 – 15 seconds
Time for oxidation 30 – 60 second.
This system allows the installation of less expensive dye range and less additional
preparatory machinery.
12. In this system dyeing, sizing is done in 2 operations.
The main reason for dyeing of 2 sheet simultaneously is that it gives more even
dyed sheet .
These beams are dyed, oxidized and dried.
These beams are transported to the sizing machine and the yarn sheet sized in
double size boxes.
Immersion time and oxidation time is the same as with continuous slasher
dyeing.
With double sheet dyeing the linear warp thread density is doubled which have
following additions:
• Squeezing effect is increased.
• An even squeezing over the whole width is achieved.
•There is no colour strips formation, streakiness or shading in the finished fabric.
•The production out put of the dyeing is increased by 75%.
Processing of double sheet dyeing…….
13. COMPARISION ON SLASHER DYEING ROPE DYEING
Required Space Less More
Mercerizing Easy Difficult
Manpower Less More
Dye bath Less capacity More
Yarn Can use Ne 1-30 without major
change
Can use Ne 1-16 without
major change
Flexibility Flexibility to produce denim in
different colors and small
quantities
Less flexible. Difficult to
change colours.
Cost Cost of production is lesser
compared to Rope Dyeing
Cost of production is more
compared to Sheet Dyeing
SLASHER DYEING VS ROPE DYEING- A COMPARISON
14. LOOP DYE 1 FOR 6 (CONTINUOUS DYE SLASHING)
In this system 10 – 16 warper beams with the total number of ends required for the
weaver beams are used.
The warper beams are placed in a moveable warp creel of which one can be loaded
while other one set is in rotation.
The yarn sheet is guided to the soaking bath through a feed-in system
The soaking bath has the task to prepare the yarn for the following dyeing operation.
15. There is only a single Indigo dye box through which the yarn passes 4-5 times.
The yarn sheet after having been immersed into a single indigo dye instead of
moving forward runs into a long loop where oxidation takes place.
One of the advantages is ideal, utilization of hydrosulphite through squeezing 4 – 6
layers simultaneously and oxidation of yarn in a comparatively long oxidation loop.
After the oxidation the yarn sheet is guided through 2 washing boxes ,finally on to a
series of drying cans.
After that yarn is immersed into size boxes, dried and wound onto a weavers beam.
Continued………
16. There is growing demand for dark shades specially dark marine blue for super
blue denims.
For this new indigo dyeing ranges which have increased the number of dye boxes
between 8-15 with corresponding oxidation ranges.
In some cases hydroxyaceton is used which gives a darker shade with the desire
greenish touch .
In order to achieve ring dyeing, mercerized yarn has also been used. Mercerizing
gives an optical blue effect and superior colour fastness and behaviour in washing.
Mercerizing is very costly, therefore new ways in continuous mercerizing and indigo
dyeing was found.And so dyemer was introduced.
DYEMER
The dyemer range is integrated. For impregnation;padder for hot caustic solution is
placed after the heating system . The yarn is guided over cold cylinders and with an
adjustable roller the tension of the yarn sheet can be adjusted according to the
required tension prior to the scouring in 2 more boxes.
After having passed this, the yarn sheet is immersed into the dye box and the same
process as with the loop dye method is repeated.
LOOP DYE 1 FOR 6 COMBINED WITH DYEMER
17. PARAMETER EFFECT IN CASE THE REFERRING PARAMETER IS
INCREASED,SUPPOSED ALL THE OTHERS ARE KEPT THE
SAME
1. Indigo concentration -deeper shade
-higher degree of penetration
-in extreme cases: inferior fastness level
2. pH
(alkali concentration)
-higher degree of penetration
-clearer, more reddish shade
-increased indigo concentration due to inferior affinity
3. Hydrosulphite
concentration
- higher degree of penetration
-clearer, more bluish shade
-- bronzing shade in absence of hydrosulphite and high indigo
concentration
4. Temperature - higher degree of penetration
- higher indigo concentration due to inferior affinity
- higher demand for hydrosulphite
- higher demand for caustic soda
IMPORTANT INDIGO DYEING PARAMETERS
18. RECENT DEVELOPMENTS IN INDIGO DYEING
Latest loop dye machines are equipped with nitrogen units which use
nitrogen gas as protective blanket over the surface of the Indigo dye. The
nitrogen gas prevents oxygen in the air from attacking sodium hydrosulphite
resulting in more consistent dyeing and reducing consumption of
hydrosulphite,which lowers the costs and pollution. There are other claimed
advantages such as higher speeds and darker Indigo colour.
DyStar and RedElec in regard of global awareness of environmental issues
have decided to use join forces to develop electrochemical dyeing of Indigo, a
sustainable solution that will eliminate harmful substances in dyeing and waste
water. The team will use its patented products, DyStar Indigo® Vat 40%
Solution and RedElec's electrochemical technologies, throughout the
development process.
