INTRODUCTION TO TEXTILE COLORATION

LECTURE-1

By Robel L.

Department of Textile Technology

 COLORATION DEFINED
 Textile coloration refers to the process of imparting color to

textile materials.

DYEING
The whole substrate gets the color
by immersing in to a solution of the
color.

PRINTING

Only certain area of the substrate gets

colored based on design requirement. 3 April 2023 2
 DYES/PIGMENTS
Coloring matters are required to provide the desired color to
textile substrates
 Cosmetics,
 Paper
 Waxes,
 Leather
 Greases
 Fur and hair
 Plastics
 Drugs,

These substances are known as dyestuffs and pigments

 Cont. …
A dye is soluble in the application media and is substantive to the
textile substrate.

They are produced either Chemically

or from plants. • The size of the dye molecules
is smaller than the size of the
pores in the fibre.

A pigment is insoluble & is not substantive to the

textile substrate binding [by adhesive agent].sd

Cont. …
  Some commercial dyes are fine powders; others may be
granular to eliminate dusting problems.
Powdered dyes that easily dust during handling can
quickly contaminate a large area, including the workers.
 Those dyes that are initially pigments, such as vat and disperse dyes,
are also available as aqueous pastes.
 Dyes are also available as liquid solutions or dispersions.
These are ideal for continuous dyeing

Liquid dyes should be

Liquid dye allows the Stable to heating and cooling,
rapid preparation of large Resistant to sedimentation and stratification, and
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volumes of dye solutions. Not contain unsafe co-solvents or additives.
 Colored compounds which are absorbed by the fiber from a solution or
suspension where they are subsequently fixed .

is a group of atoms attached to a

Increase Color chromophore which modifies the ability
of that chromophore to absorb light.
It increases the color of any organic compound.

For example, benzene does not display color as it  Hydroxyl group (−OH),
does not have a chromophore; but nitrobenzene is pale  Amino group (−NH2),
yellow color because of the presence of a nitro group
 Aldehyde group (−CHO),
(−NO2) which acts as a chromophore.
 Methyl Mercaptan group
But p-hydroxynitrobenzene exhibits a deep yellow
(−SCH3)
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color, in which the −OH group acts as an auxochrome.
 color-donating unit

At least five or six conjugated double bonds are

required in the molecular structure for a compound

to be coloured.

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 HISTORICAL DEVELOPMENT OF DYES
Dye development stages Driving forces

Natural dyes Poor substantivity & poor fastness

Use of mordant with natural dyes Long and difficult process

Indigo [Water insoluble pigment] Good fastness but sill long process

First synthetic dye [Mauveine] Affinity for few fibers only & poor light fastness

Acid type azo dyes Acid dyeing of wool and silk

Direct substantive dyes Poor wet/wash fastness

Synthetic indigo vat dye Process difficulty

Fiber reactive dyes Limited substantivity [Hydrophobic fibers]

Disperse dyes For hydrophobic fibers [method of application]

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 CLASSICATION OF DYES
 Scientific classification based on chemical structure
Example: Anthraquinone dyes, Azo dyes etc.

 Technical classification based on dyeing properties

Example: Direct dyes, Acid dyes, Disperse dyes etc.

 Commercial classification based on manufacturers’ aspects

[Brand names based on fastness, method of dyeing and so on]

Example: Indanthrene, Remazol, Procion, etc

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 CLASSIFICATION BASED ON DYEING PROPERTIES

DIRECT DYES BASIC DYES

REACTIVE DYES DISPERSE DYES

VAT DYES MORDANT DYES

AZOIC DYES METAL COMPLEX DYES

OTHER DYES *
ACID DYES
[Sulphur, chrome etc]
 DYE SELECTION

Type of fiber present

Form of textile material & degree of levelness

Fastness properties required

Dyeing method used

Cost & Environment
Availability of machinery

Customer color requirement

 SALIENT FEATURES OF DYEING PROCESS
The stages in dyeing process are:
 Preparation of dye solution [Dye and auxiliary chemicals]

 Application of the dye

 Fixation of the dye DYEING METHODS

 Aftertreatment

BATCH CONTINOUS

EXHAUSTION IMPREGNATION

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 CONTINOUS DYEING
The most economical for production of very large lots of a single color.

Over 50 000 m running for over 8 hours.

Most continuous dyeing processes can be divided into four stages:

1. Dye application by padding;
2. Dye fixation, usually in hot air or steam;
3. Washing-off of unfixed dye and auxiliary chemicals;
4. Drying, usually on steam-heated cylinders.
Cont. …

A pad–thermosol–pad–steam
3 April 2023 continuous dyeing range for cotton/polyester fabrics
16
 Cont. …
Pressure squeezes air out of the
fabric and the solution into it.

The objective of padding is to

impregnate the fabric with a
The material should be well prepared and
solution or dispersion of dyes and
very absorbent because the wetting time
chemicals as uniformly as possibly,
both 3lengthways
April 2023 and side-to-side. in the pad bath may be as short as 0.517s.
 Cont. …

Wet pickup

The minimum wet pick-up is

usually around 55–60% for
cotton/polyester materials, 60–
The greater the applied pressure at the
70% for cotton, and higher for
nip, the smaller the amount of dye
fabrics of the more absorbent
3 April 2023 solution retained by the fabric. 18
viscose.
 BATCH DYEING
 Discontinuous system of dyeing

 The dyebath is allowed to exhaust by providing the necessary condition

 Dye fixation takes place in the dyebath

CIRCULATING LIQUOR IN A STATIONARY MATERIAL

MATERIAL MOVEMENT IN A STATIONARY LIQUOR

CIRCULATION OF BOTH LIQUOR AND MATERIAL

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 AFTERTREATMENT

Washing in detergent at or near the boil [Soaping]

Treatment with chemicals to improve fastness

Application of simple finishing chemicals

 DYEABILITY FACTORS
FIBER CHRACTERISTICS CRYSTALLINITY & HYDROPHILICITY

DYE CHARCTERISTICS STRUCTURE & DIFFUSEABILITY

DYEING CONDITIONS TIME & TEMPERATURE

DYEBATH ADDITIONS SALTS & OTHER AUXILARIES

LIQUOR RATIO TYPE OF MACHINE

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 PROCESS TERMINOLOGIES

EXHAUSION AND FIXATION

 In exhaust dyeing, all the material contacts all the dye liquor and
the fibers absorb the dyes.

 The dye concentration in the bath therefore gradually decreases.

 The degree of dye bath exhaustion as a function of time

describes the rate and extent of the dyeing process

For a single dye, the exhaustion is defined as the mass of dye

taken up by the material divided by the total initial mass of dye
in the bath, but for a bath of constant volume
E % =(Co – Cs)/Co * 100
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 where
CONT. …

amount of dye
3 April 2023transferred from dye-bath to the substrate in the dyeing process.
23
 Dye fixation means the reaction between the dye and fiber molecules.

DEPTH OF SHADE

Paleness or dullness of a given shade

COLOUR YIELD

Shade depth per a given amount of dye

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DYE MIGRATION

Tendency of dye transfer from heavily dyed region

LEVELLING
Uniformity of shade throughout the substrate
Un level dyeing include
 stripiness in either material direction or at random,
 End or edge differences,
 Light and dark patches, and
 skitteriness (closely spaced light and dark regions).

 Poor preparation,
 Faults in the goods
 Problems in the operation of the machine or
 Problems in the dyeing procedure.

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 Fastness to light
Fastness to wet
Fastness to dry rubbing
Fastness to washing
Fastness for perspiration
FASTNESS Fastness for saliva

Resistance to color change or color removal

COMPATIBILITY

Dyes having same or similar rates of dyeing

LIQUOR RATIO Ratio of weight of material to volume of liquor

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 END

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