dyeing techniques

Prithwiraj Mal, Assistant Professor, NIFT Hyderabad

DYEING

Why Textiles are Coloured ??

Objectives

Make textiles attractive for aesthetic appeal

Functional application

Camouflage fabrics for military

Fluorescent jackets for road repairing personals

Life would be dull without colour


Defining a Colour

Three terms are generally used to define a colour

Hue

Value

Chroma


Hue

This is the term to define the colour

Example: Pink, Red, Blue etc.

Value

This is the term used to define the lightness, darkness, tone or shades of the colour

Example: If a colour have a low value that means the colour is light and vice – versa

Chroma

This term is used to indicate the depth (i.e. the brightness/dullness, intensity) of the

colour

A colour of high chroma value will be very bright


Relationship between Hue, Value and Chroma

Weaker

Duller

Brighter

Stronger

Hue

Value

Chroma Prithwiraj Mal, Assistant Professor, NIFT Hyderabad

Colouring Material

Dyestuffs Pigments

Synthetic Dyes Natural Dyes

Water Soluble Water Insoluble

Dyes

Vat Dye

Disperse Dye

Sulphur Dye

Reactive Dyes

Direct Dyes

Acid Dyes

Basic Dyes

Ingrain Dyes

Mineral

Oxidation

Colours

Azo Dye


SUBSTANCES USED FOR COLOURING

Dye

Water soluble

Certain dyes are attracted to certain fibre types

Pigments

Not water soluble

Have no affection for any type of fibre

Used mainly for printing or mass-colouration of synthetic fibers

The constituents of dye

Dye particles contains two portion

Chromophores or colour bearing group

Auxochrome or colour helping group

The chromophores decides the hue or colour of a dye molecule

The auxochrome intensify the hue of the colour, makes the dye

molecule water soluble, improves its fastness properties etc.

DYE AUXILIARIES

Dyeing assistants or auxiliaries are the chemicals that facilitates the

production of required shades of dyeing

Water

Acid/ Alkali

Carrier

Water Softening Agent

Exhausting Agent

Dispersing Agent

Levelling Agent

Retarding Agent

MECHANISM OF DYEING

Mechanism of Dyeing

Adsorption of dyestuff on fibre surface

Diffusion of the dyestuff through the internal structure of the fibre

Fixation of dye molecule

Adsorption

Dye molecules move towards the fiber

Get adsorbed on the fibre surface

Penetration

Adsorbed dye molecule enter the fibre structure

Gradually penetrate or ‘diffuse’ in the structure

Rate of penetration depends upon the molecular structure of the

dye and dyeing condition

Greater the penetration of dye in the fibre, better and brighter is

the dyeing

Cross section of fibre with poor dyeing penetration

Cross section of fibre with good penetration

FIXATION

The final step where the dye molecules find suitable locations,

where they get fixed or ‘anchored’

Stages of Dyeing


Stages of Dyeing


Fibre Stage

Yarn Stage

Fabric Stage

Product Stage / Garment Stage

FIBRE STAGE


Fibres are dyed before yarn spinning.

Stock dyeing is adding colour loose fibres before yarn spinning

Top dyeing is dyeing of wool fibres in between spinning process.

Tops, the loose ropes of wool from combing, are wound into balls,

are placed on a perforated spindles, and is enclosed in a tank. The dye

is then pmped back and forth through the wool.

Coloured are also added to the spinning solution before the fibre

formation. This is known as mass colouration or dope dyeing or

solution dyeing

YARN STAGE


Yarns can be dyed in the following forms

Skein or hank – Known as skein dyeing or hank dyeing

Package or cone – Known as package dyeing or cone dyeing

Yarn dyeing is less costly than fibre dyeing but more

costly than fabric or product dyeing

FABRIC STAGE


Fabrics are dyed. Also known as piece dyeing.

Piece dyeing normally produce solid colour fabric. Multiple

colour patterns are also possible

Cross Dyeing

Union Dyeing

Cost is comparatively less. Also colour decission can be

delayed so that quick adjustment to the fashion trends are

possible.

FABRIC STAGE


Cross Dyeing

Cross dyeing is a fabric made from different generic groups are

dyed with different dyes.

An example is a fabric made of wool warp and cotton filling

dyed with red acid dye and blue direct dye respectively. In this

example the warp would be red and the filling blue.

FABRIC STAGE


Union Dyeing

Union dyeing is a type of piece dyeing of fabrics made with

fibres from different groups. Unlike cross dyeing, union dyeing

produces a finished fabric in a solid colour

PRODUCT / GARMENT STAGE


Final product or garment is dyed

Great care must be taken in handling the materials and in dyeing to

produce a level, uniform colour throughout the product.

Product dyeing is important in the apparel and furnishing industries

when quick response to retail and consumer demands

METHODS OF DYEING


Methods of Dyeing


Method entirely depends on type of material (fibre, yarn –

skein or cone, fabric – woven, knitted), fibre content, dyeing

time etc.

Generally three basic methods are used

Textile is circulated in a dye bath

Dye bath is circulated around the textile

Both textile and dye bath are circulated together

Batch Dyeing


Also known as exhaust method

The textile is circulated through the dye bath

Used for any type of textile (fibre, yarn, fabric)

Mainly used for small lots

Types

Jet Dyeing

Jig Dyeing

Beam Dyeing

Winch Dyeing

JIG Dyeing


Fabric is dyed in open width form under

tension

Batchwise process of dyeing fabric

The fabric is circulated through the dye bath

Fabric is fed to the dye bath from a fabric roll

and is rolled back to the other roll. Both the

rolls are placed above the dye bath

Fabric that may crease in rope form are dyed

WINCH Dyeing



Fabric is dyed in rope form with minimum

tension

Applicable for delicate fabrics (lightweight

fabrics, knitted fabrics etc.)

Fabric is circulated through the dye liquor

The fabric in a loose rope sewn together at the

ends, is lifted in and out of the dye bath by a reel

/ winch.

Causes creasing and distortion of some fabric

during dyeing in rope form

JET Dyeing



Fabric is dyed in rope form with less

tension

Involves vigorous agitation of the dye bath

and the textile

Because of its rapid speed, fabric wrinkling

is minimum

CONTINIOUS DYEING


Continuous machines, called ranges, are used for large fabric lots

Ranges include compartments for wetting – out, dyeing, after treatment,

washing and rinsing

Both yarns and fabrics can be dyed using continuous ranges

Yarns are dyed in yarn sheet form (Ex: Warp sheet dyeing for denims)

Dye Liquor

Pad Dyeing


Mainly used for continuous process of

dyeing

Fabric is run through the dye bath in open

width form between squeeze or nip rollers

that force the dye into the fabric with

pressure

Subsequent Drying and Steaming helps the

dye to fix with the fibres

PACKAGE Dyeing


Both yarn and fabric can be dyed in a package form

The dye bath is forced through the textile

Yarn package dyeing

Yarn is wound on a perforated core of stainless steel or plastic in a pressurized machine.

The dyes are pressurized inwards and outwards through the package. Liquor ratios are high

to ensure uniform dyeing

Fabric package dyeing

Also known as beam dyeing

The fabric is wound on perforated beam in a pressurized machine. The dye liquor is

pressurized inwards and outwards through the package. Liquor ratios are high to ensure

uniform dyeing

dyeing techniques

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