Colour Theory, Dyes & Pigments

8/3/2019 Colour Theory, Dyes & Pigments

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Colour theory, Dyes & Pigments

Dr. Nilanjana Bairagi


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What is colour?

Colour is a sensation which occurs when light enters

the eyes.

If a textile material has a particular colour, the textile

material absorbs all the light falling upon it and reflectsonly that particular wavelength of the colour.

A white fabric appears white as it reflects all the light

waves.

Green fabric- reflects light which appears green to theeyes.

Black fabric ?


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Specifying colour

Hue: common name of the colour

Value: Term used to describe lightness, darkness,

tone or shade of the hues.

Chroma: Used to describe the depth of colour;

dullness, brightness, saturation, intensity, vividness or

purity of the colour.


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Dyes & Pigments Dyes are dissolved in whatever solvent is used

(soluble). Pigments are insoluble. Often a pigment is

made by attaching a dye molecule to an insoluble

particle. Dye molecules are comparatively smaller, pigments

are larger in size. it's like comparing a football

(pigment) to say a head of a pin (dye) Pigment

particles are about 1-2 microns in size. (1 micron=1/1000 meter).


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Dyes & Pigments Bonding: Taking the example of dyeing a wood

surface, the dye and the substrate (wood) that is dyed

are chemicals, that have certain features called

functional groups. At the level of molecules thesegroups serve as open pockets of electrostatic charges

(+ or -). The functional group in dyes, serve as a

method for attaching the dye to the wool.

Pigment requires the help of a binder for gluing. As itis an inert substance which is merely suspended in a

carrier/binder .


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Dye molecule Chromophores & Auxochromes

Chromophore: Gives the dye molecule its particular

colour.

Auxochrome:Intensify the hue of the dye moleculess

colour, makes the dye molecule more water soluble

and improves the colour fastness properties of the

dyed or printed fibre.


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Dye molecule Dye molecules are organic molecules

The shape or configuration of the dye moleculedetermines how:

Readily the dye can diffuse through fibresurface;

How deeply the dye molecule will enter thepolymer system of the fibre

How the dye molecule will be able to attachitself and/ or become trapped in the polymersystem of the fibre.


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Dye classification as per application1. Direct dyes (substantive colours)

2. Acid dyes (anionic dyes)

3. Basic dyes (cationic dyes)

4. Disperse dyes5. Mordant dyes

6. Metal-complex dyes

7. Reactive dyes

8. Sulphur dyes9. Vat dyes

10.Azoic dyes


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Dye classification as per applicationClass of dye Fibres which can be dyed

Direct dyes

(substantive colours)

Man-made & natural cellulosic fibres

Acid dyes

(anionic dyes)

Natural protein fibres, nylon fibres

Basic dyes

(cationic dyes)

Acrylic , modacrylic fibres

Disperse dyes Polyester, nylon, acrylic, cellulose acetate


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Class of dye Fibres which can be dyed

Mordant dyes Wool, silk ( natural protein fibres), nylon,&

modacrylic

Metal-complex dyes Wool, silk ( natural protein fibres), & nylon

Reactive dyes

*Covalent bond

formation

Cellulosics & protein fibres ( Natural & man-

made fibres)

Sulphur dyes Natural & man-made cellulosic fibres

Dye classification as per application


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Dye classification as per applicationClass of dye Fibres which can be dyed

Vat dyes Natural and man-made cellulosic fibres

Azoic dyes

(Napthol dyes)

Natural and man-made cellulosic fibres


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Significance of commercial dye names

FORON SCARLET E 2GFL, DRIMAREN BLUE R SPL

FORON- Brand name

SCARLET hue

E : series ( depends on the method of dyeing) 2G: Tone of the hue

F: Brightness

L: Light fastness

G Yellow

R Red

B-Bluish


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General Theory of Dyeing The fibre:

Develop slightly negative surface charge or

potential when immersed in an aqueous

solution.

When the dye molecule & fibre both become

negatively charged they repel one another.

For dyeing the dye molecule has to enter the

fibre structure.


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Dyeing recipe Dye: Shade %

M/L ratio or MLR

Electrolyte

Temperature

Duration

Auxillaries


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Role of water In addition to dissolving the dye, water acts as a

medium through which the dye molecules are

transferred into the fibre.

Heat is necessary

to encourage the dye to leave the water & enter

the fibre, and

also for penetration of the dye into the fibre

Water, assisted by heat also swells the fibre that arehydrophilic, making it more accessible for the dye.


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Heat

Increases the energy of the dye molecule & the rate of

dyeing.

Increases the efficiency of the dye molecules to enter

into the amorphous regions of the fibre.

The heat also swells the fibre, making it easier for the

dye molecule to entre the fibre.


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Role of electrolytes( sod chloride, sod

sulphate) The electrolyte dissociates completely in the water

and increases the dye uptake.

It makes the surface charge of the fibre neutral and

increases the dye uptake when both the dye & thefibre have negative charge.


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Dye auxillaries It includes:

Carriers or swelling agents

Levelling agents

Anti-foaming agents

Dispersing agents

Detergents

Wetting agents


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Levelling agents Addition of levelling agent helps to produce more

uniform colour to the textile fibre.

It slows down the dye uptake of the fibres.

Also termed as retarding agents or retarders.


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Fastness properties Wash-fastness

Light-fastness

Dry-cleaning fastness

Perspiration fastness

Chlorine fastness ( fastness to bleaches containing

chlorine)

Rubbing fastness


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Wash-fastness

The loss of colour during laundering is referred to as the lack of

wash-fastness or bleeding.

It occurs when the dye is held loosely to the fibre and has not

penetrated the fibre structure.

It is tested by using standard methods like : ISO Test 3, ISO Test

2 for wash-fastness.

The grading is given 1-5, where

5 No change in colour ( Excellent wash fastness)

4 slight change in colour 1 Poor wash-fastness


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DYEING MACHINES

Dr. Nilanjana Bairagi


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Dyeing Fibre

Yarn

Fabric - open-width, rope form

Batch wise, continuous

Knitted fabric- tubular form

Garment


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Batch dyeing Machinery for exhaust

dyeing Three types of dyeing machines for batch or exhaust

dyeing are based on machines in which

1. The material moves, but liquor is stationary

Example: jig ( jigger) and winch m/c for fabric dyeing2. The liquor moves, but material is stationary

Example: Hank or package dyeing of yarns and beam

dyeing of fabric

3. Both liquor and the material moves

Example: Jet, Softflow and overflow jet machines for fabrics


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Dyeing machinery Advantages of lower liquor ratio

Decreases water & energy consumption

Decreases volume of waste water

Facilitates rapid dyeing

Increases dye exhaustion


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Jig or Jigger dyeing machine Fabric dyed open width

Fabric traverses from one roll through dyebath-to asecond roller

When the second roller is full, the fabric stops and themotion is reversed.

The procedure is repeated.

Dye liquor is added in portions

A hood prevents the release of steam

Jigs operate at 98-100 C, pressurized jigs operate at140C .

Material to Liquor ratio 1:3-5


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W

inch or Beck dyeing Winch dyeing may be used for dyeing in rope form.

Temperatures upto 98-100 C

Suitable for delicate fabrics to prevent creasing


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Beam dyeing Fabric is wound at open width on to a perforated

stainless steel beam.

Dye liquor is pumped through the multiple layers of

fabric. The fabric winding tension must be low to avoid

stretching.

Mostly used for dyeing thin permeable fabrics of

polyester , nylon MLR 1:10


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S

oft-flow jet dyeing machine Soft-flow jets provide a more gentle mechanical action

on the fabric rope.

The fabric transportation being carried out over a

winch reel followed by soft-flow jet systems. In some machinery the flow is split between two jets

Which exerts low pressure to the fabric


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Pad-batch dyeing

Padding stage

Followed by hot conditions

Used for reactive dyeing


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Continuous dyeing machinery

Continuous dyeing can be carried out by dye

impregnation, fixation, washing off and drying on

ranges.

Woven fabrics at open width, carpet and warp dyeingranges.

Originally designed for economical dyeing.

Polyester cotton blend- first step pad-dry-

thermofixation process. Then reactive dyeing using apad-steam process.


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Garment dyeing machine

Available in 90 to 300 kg.

capacities

An efficient Garment/ Knitwear

Processor &Washer

Carries out desizing, enzyme

silicon wash, bleaching, stoning,

softening, dyeing

Microprocessor - Pneumatics

combines to ensure precise

control oftime, temperature, level, speed,

rotation & process controlFront loaded garmentdyeing machine

Documents

Colour Theory, Dyes & Pigments