Download Textile Dyeing

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Acid Dye (Anionic Azo dyes)
Acid dye class is a water soluble class of dyes
with anionic properties. The textile acid dyes
are specially effective for protein fibers such as
silk, wool, nylon and modified acrylics.
These are applied from a strongly acidic to
neutral pH bath.
Acid dyes fix to the fibers by means of
• Hydrogen bonding
• Vander waals forces
• Ionic Linkages
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In Azo dyes the uptake rate of the dye is
controlled with the use of sodium chloride.
They are often applied from an acidic solution
in order to intensify the staining.
Note : The acid used in the dye bath is acetic
acid or citric acid.
These dyes have no affinity for cotton
cellulose’s , hence not suitable for cellulosic.
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Mechanism of dyeing with acid dyes
Acid dyes in aqueous solvent, produces a colored
anion, which can be described as follows.
The protein and polyamide fibers produce
cationic sites in water under acidic conditions
and as the acidity of the solution is increased
more cationic sites are produced under these
strongly acidic conditions.
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The above shown bonds have linkages which
are strong enough to break and thus dyeing
produced are fast and efficient in industry point
of view.
Reaction between an acid dye and wool can be
represented by following equation
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When describing the detail in above equation in
Protein fibers contain amino and carboxyl
groups, ionized mostly to NH3+ and COOIn the acid dye bath the carboxylate ions are
converted to undissociated carboxyl groups
owing to the addition of acid HX
It causes the positively charged wool
(H3N+.W.COOH) to take up an equivalent
amount of acid anions X hence build the bond in
between dye molecule and the fiber
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The action of Retarding agents in Acidic
Dye bath
• Electrolyte (Nacl) in the acid dye bath acts as
a retarding agent because of chlorides ions
attracted by the positive sites at the fiber and
in the competition between.
• Addition of acid acts as an exhausting agent ,
because strongly acidic conditions makes
more cationic sites available and thus
available dye anions got combined with these.
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Acid dyes are divided into three groups
based on their differences in
• Affinity
• Based on the leveling properties
• Economy of the dyeing and fastness
properties
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Leveling dyes
• Highest level dyeing properties.
• Quite combinable in trichromatic
shades.
• Relatively small molecule therefore high
migration before fixation.
• Low wet fastness therefore normally not
suited for apparel fabric.
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Milling dyes
• Medium to high wet fastness.
• Some milling dyes have poor light fastness in
pale shades.
• Generally not combinable. Used as self shades
only.
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Metal complex acid dyes
More recent chemistry combined transition
metals with dye precursors to produce metal
complex acid dyes with the highest light
fastness and wet fastness. These dyes are
• Economical.
• Very good light fastness even in pale
shades
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Acid Dye
Structures
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Dye Structures
Acid dyes usually have a sulfo or carboxy group
on the molecule making them soluble in water.
Most acid dyes are related in basic structure to
the following:
Anthraquinone
Many acid dyes are synthesized from chemical
intermediates which form anthraquinone-like
structures as their final state. Many blue dyes
have this structure as their basic shape.
The structure predominates in the levelling class
of acid dye.
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Synthetic dyes are often derived from 9,10anthraquinone, such as alizarin. Important
derivatives
are
1-nitroanthraquinone,
anthraquinone-1-sulfonic
acid,
and
the
dinitroanthraquinone.
From the left:
C.I.Acid Blue 43 an "acid dye" for wool (also called "Acilan Saphirol
SE"),
C.I. Vat Violet 1, which is applied by transfer printing using
sublimation,
a blue colorant commonly used in gasoline, and C.I. Disperse Red 60,
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a so-called vat dye.
Azo dyes
• The structure of azo dyes is based on
azobenzene
• Although Azo dyes are a separate class of
dyesuff mainly used in the dyeing of cotton
(cellulose) fibers.
• Many acid dyes have a similar structure, and
most are red in color.
Yellow azo dye
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Triphenylmethane
• Acid dyes having structures related to
triphenylmethane predominate in the milling
class of dye.
• There are many yellow and green dyes
commercially applied to fibers that are related
to triphenylmethane.
Bromocresol green
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Acid Dyeing
Techniques
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Acid dyeing techniques
Textile Auxiliaries used in acid dyeing
• Leveling agent - for levelness dyeing
• Retarding agent - for inhibiting the dye not
attach to fibers too fast
• Acid - adjust the dyeing condition and
make the fibers to show positive charges
• Water - dyeing media
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Dyeing temperature
The dyeing is generally carried out at boiling
temperature for 30- 60 minutes depending
upon the depth of the shade and dyestuffs
used.
Dyeing leveling agents
In the case dyeing with acid dyes , mainly
cationic agents such as ethoxylated fatty
amines are used as leveling agents.
Heating rates
Heating rate is generally kept 1-30C/Min
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Wool dyeing method with acid
dyes
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Detail about the graph
• At A set bath at 50° with: 2% Formic
Acid (85%) 5% Glaubers Salt
anhydrous
• pH 3.5 to 4.5
• At B add required amount of dye.
• At C add 2% Sulphuric Acid (96%) or
2% Formic Acid (85%).
• Thoroughly rinse after dyeing to
remove loose colour.
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A dyeing cycle for Nylon filament dyeing
A textured yarn
one dye bath. It
nylons 6,6. One
rejects cationic
opposite way
can achieve multicolor effects in
is a combination of two modified
nylon only accepts acid dye and
dye; the other one acts the
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Fastness properties of acid dyes
The wet and light fastness properties of the
acid dyes varies from poor to excellent ,
depending upon the molecular structure of
the dyes.
The fastness properties as per the category
are as follows
Level acid dyes: since these dyes have very
good leveling and migration properties ,and
have a low affinity for the fiber, therefore the
wet fastness properties of this class are
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generally poor.
milling dyes :- These dyes have a medium to
good affinity for the fiber and are generally
applied in a weakly acidic bath, shows
medium to good wet fastness properties.
Metal complex acid dyes :-These dyes have
poor exhaustion properties, therefore
applied under very strong acidic condition ,
exhibit good fastness properties.
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Group Members with their
Contributions
From 061001P – 061015L
including 051055A
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