DYEING OF KNITTED COTTON

FABRIC

DEFINITION

Dyeing is a process of imparting color to the fabric andincrease the aesthetic value of it.

There are many techniques of dyeing both natural fiberand manmade fibers using different types of dye stuffswith different chemistry and method of application.

Among those methods, exhaust dyeing method isvery common for dyeing cotton and cotton blendedknitted fabric.

it is batch dyeing process in which certain weight offabric is dyed in a rope/open width form with a dyemigration or exhaustion from the dye liquor to the fabricwith the help of exhausting chemical either by fabriccirculation only or by both fabric and liquorcirculation.

the dyeing parameters are basically determined by thetype of fiber and the nature of the dyes and chemicalsused.

most commonly reactive dyes and disperse dyes are usedto dye cotton and polyester fibers in exhaust dyeing.

METHODS OF REACTIVE DYEING AND PARAMETERS ON JET

reactive (cotton):

ISOTHERMAL(migration 60°C fixation 60°c)

MIGRATION(migration80°C,fixation60),

TURQUESE DYEING (migration 95°c/80°c,fixation80°c).

machine settings

speed:200-250m/min

nozzle pressure(70%),circulation(70%)

pick up (200%)

cycle time 2 min .

Addition of electrolyte and other chemicals

Electrolytes increase the substantively of reactivedyes, Hence improve the bath exhaustion.

Common salt may reduce the dye staff solubility,therefore, for some dyestuffs which have highermolecular weight like reactive torques(phatalocynic)and blue(like bezactiv blue s –fr150 we use glaubersalt.

It is common to use sequestrates along with thedye to protect dyes stuff coagulation and patchydyeing.

CONTI..

Fixation of reactive dyes is most important part ofdyeing and is achieved at higher PH (10.8-11.5).

Mild alkali (soda ash) or mixed alkali (soda ashand caustic) are use to achieve the alkali PH.

Fixation has to be done with gradual increase of thedye bath PH. Rapid increase in PH result in unleveldyeing

20-30 min progressive dosing 30-45 min holdingtime with out fabric stoppage is recommended forunlevel dyeing.

Conti…

Generally reactive dyeing will take place at differenttemperatures based on the nature of the dyes.

The first group of dyes will be migrated at 60°c abovethis T, there will be hydrolysis. Bifunctional dyes canbe dyed at both 60 and 80 °c and fix at 60 °c.

The other group of dyes migrate at 80 °c, this dyesrelatively have high molecular weight and need highertemperature to migrate and fix at 60 °c.

Turquoise dyes are high molecular dyes and mostlydyed at 95 °c, even though can be done at 80 °c withlonger dyeing time and fix at 80 °c.

DYES AND CHEMICAL PREPARATION

Dye stuff and salt dissolve in hot water. Depending on thenature of the shade, the addition to the machine can be bydosing or transfer (from stock tank or addition tank)

Dye dissolution :80 °C for 5 min with high capacity stirrer.

Salt can be transfer but for sensitive shades it should bedosed in two or three portions in 15 minutes.

Common salt can be transferred to the machine in inpartially soluble state to the machines.

Glaubber salt should not dissolve at temperature lessthan 60⁰c, it forms crystal which will hinder the transferto the machine, but common salt can dissolve at cold.

Stock solution of salt is crucial measure to prevent saltcrystallization.

Conti..

Soda should be dissolved at cold and after dissolution it should be dosed to the machine minimum in thirty minutes.

In machine which don’t have dosing mechanism, 20 % addition of alkali at dye start would be better.

Hot and concentrated dye solution should not beleft unattended for long time.

Urea is used to improve the solubility of reactive sdyes and should not be added to temperature lessthan 50 oc.

Dry salt transfer

Addition tanks

CHECKING POINTS AFTER DYEING.The required shade and pH need to be checked aftersoda holding time.

Small piece of fabric should be washed in hot waterusing soap for 10 mins.

PH after fixation (10.8-11.5).

the above check points help us to make correctionsbefore draining the dye bath.

AFTER TREATMENT PROCESSIt is a process in which fabric neutralization, soaping

and fixing of some dye ruminants on the fabric takesplace .

Add 2 gpl of acetic acid and hold @60⁰c for 10 min.

Add 1 gpl of soap /detergent and hold 98 ⁰c for 10min.(can be done once or twice).

Second neutralizing 0.2 gpl acetic acid for 5 min at cold.

Finally fixing of unfixed dyes left on the fabric forgood wash fastness.(o.5% owf of fixing agent).

Any foaming should be removed before unloadingfabric and the final ph should be neutral.

Finally during unloading good arrangements need tobe done for following processes.

Temperature –time graph of migration

40A

40B

40C

80D

80E

60F

60G

60H

60I

60j

60k

98l

98m

70n

0

20

40

60

80

100

120

Time

TEMP VS TIME TRAPH OF ISOTHERMAL DYEING PROGRAM

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Temprature(⁰c)

Time(min)

TURQUEZE SHADE DYEING GRAPH

0

20

40

60

80

100

120

10 20 30 40 50 60 70 80 90 100 110 120 130 140

TE

MP

RA

TU

RE

IN

⁰C

TIME IN MIN

Settings

Dyes and chemicals used in dyeing

4.4. Chemicals that need special care while using

Acetic acid

Hydrogen peroxide

Urea

Caustic soda

Soda ash

Ammonium sulphate

Sodium hydrosulphite

Sulfuric acid

Sodium sulphate

Necessary safety materials in dye house

Safety shoe,

working cloth,

mouse max,

Eye goggle,

Glove, Apron

Water flasher.

Material safety data sheets.