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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