indigo dyeing

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INDIGO DYEINGPREPARED BY-RAJDEEP SINGHB-Tech 4th Sem.1CONTENTSIntroduction To Indigo DyeChemical Property And Synthesis Of IndigoWhy Indigo ?Indigo Dyeing BriefingIndigo Dyeing MethodsRecent Developments In Indigo DyeingReferencesIndigo dyeis anorganic compoundwith a distinctive blue colour. Historically, indigo was anatural dyeextracted from plants, and this process was important economically because blue dyes were once rare. Nearly all indigodyeproduced today several thousand tons each year issynthetic. It is the blue ofblue jeans. The primary use for indigo is as a dye for cotton yarn, which is mainly for the production ofdenimclothfor bluejeans. On average, a pair of blue jean trousers requires 3 12 g of indigo.INTRODUCTION

CHEMICAL PROPERTIES INDIGO DYE

Indigo is a dark blue crystalline powder thatsublimesat 390392 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 (max= 613nm).

HEUMANN'S SYNTHESIS OF INDIGOIt involves heatingN-(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.

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.

Its soluble form is not sensitive to water hardness and this allows the dyeing of greige or minimum pretreated cotton.

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

6DIFFERENT INDIGO DYEING METHODS Indigo rope dyeing processIndigo-Slasher-or Sheet-dyeingLoop dye 1 for 6 (continuous dye slashing)Loop dye 1 for 6 with dyemer (continuous mercerization dyeing and sizing).

INDIGO ROPE DYEING WITH SUBSEQUENT SIZING PROCESS

Step 1: Ball WarperStep 2: Rope Dyeing Step 3: Long Chain Beamer Step 4: Sizing 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 overviewINDIGO-SLASHER-OR SHEET-DYEING

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.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.COMPARISION ONSLASHER DYEINGROPE DYEINGRequired SpaceLessMoreMercerizingEasyDifficultManpowerLessMoreDye bathLess capacityMoreYarnCan use Ne 1-30 without major changeCan use Ne 1-16 without major changeFlexibilityFlexibility to produce denim in different colors and small quantitiesLess flexible. Difficult to change colours.CostCost of production is lesser compared to Rope DyeingCost of production is more compared to Sheet DyeingSLASHER DYEING VS ROPE DYEING- A COMPARISON

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.

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.

ContinuedThere 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.

LOOPDYE 1 FOR 6 COMBINED WITH DYEMERPARAMETEREFFECT IN CASE THE REFERRING PARAMETER IS INCREASED,SUPPOSED ALL THE OTHERS ARE KEPT THE SAME1. Indigo concentration-deeper shade-higher degree of penetration-in extreme cases: inferior fastness level2. pH (alkali concentration) -higher degree of penetration -clearer, more reddish shade -increased indigo concentration due to inferior affinity3. Hydrosulphite concentration- higher degree of penetrationclearer, more bluish shade- bronzing shade in absence of hydrosulphite and high indigo concentration4. Temperature- higher degree of penetration- higher indigo concentration due to inferior affinity- higher demand for hydrosulphite- higher demand for caustic sodaIMPORTANT INDIGO DYEING PARAMETERSRECENT DEVELOPMENTS IN INDIGO DYEINGLatest loop dye machines are equipped with nitrogen unitswhich 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.REFERENCES

Indigo-eBook-by-Bluconnection-May-2011

http://en.wikipedia.org/wiki/Indigo_dye

http://www.denimsandjeans.com/denim/manufacturing-process/indigo-dyeing-%E2%80%93-various-methods-explained-and-compared/

http://www.expresstextile.com/20030904/dyeschemicals01.shtml

http://www.denimsandjeans.com/denim/manufacturing-process/indigo-dyeing-with-loop-dyeing-machinery/

http://www.textileworld.com/Articles/2012/March/DyStar_And_RedElec_Start_Sustainable_Indigo_Dyeing.html

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