Disperse dye
The term “disperse dyes” have been applied to organic
coloring substances which are free from ionizing groups. They are of low water
solubility and are suitable for dyeing hydrophobic fibres. The dye has derived
its name for its insoluble acqueous properties and the need to apply it from an
acqueous dispersion. Of all the dyes they are of the smallest molecular size.
They have substantivity for one or more hydrophobic fibres
e.g. Cellulose acetate, nylon, polyester, acrylic and other synthetic fibres
The negative charge on the surface of hydrophobic fibres
like polyester can not be reduced by any names, so non-ionic dyes like disperse
dyes are used which are not influence by that surface charge.
Commercial name of disperse dyes :
Name of dye
|
Manufacturer
|
Contry of origin
|
1. Artisil
|
Sandoz
|
Switzerland
|
2. Cibacel
|
Ciba-seigy
|
Switzerland
|
3. Dispersal
|
ICI
|
UK
|
4. Samaron
|
Hoechst
|
Germany
|
5. SRA
|
British celanese ltd
|
UK
|
6. Setile
|
ACNA
|
Italy
|
Properties of disperse dye :
1) Disperse
dyes are non-ionic dyes. So they are free from ionizing group
2) They
are ready made dyes and are insoluble in water or have very low watr solubility.
Their solubility is at least 0.1gm/lit
3) They
are organic colouring substances which are suitable for dyeing hydrophobic
fibres from colloidal dispersion.
4) Disperse
dyes are used for dyeing man-made , ester-cellulose and synthetic fibres
specially acetic and polyester fibres and sometimes nylon and acrylic fibres.
5) Carrier
or dispersing agent are required for dyeing with disperse dyes.
6) Disperse
dyes have fair to good light fastness with rating about 4-5.
7) The
wash fastness of disperse dyes are moderate to good with rating about 3-4
8) Disperse
dyes have the ability to undergo sublimation that is they can be vaporized
without fastness or wash fastness for sublimation fastnes of disperse dyes the
following cause are responsible
a) Small
molecular size of dye suff
b) No ionic group
c) No
sulphonated group
Sublimation property of disperse dyes are used in transfer
printing. But it is a disadvantageris matter. Because excessive hot ironing or
pressing of disperse dyes/printed material may result in color loss.
9) Of
all dyes stuffs disperse dyes are of the smallest molecular size.the size of
dye molecules are 2-3 nanometre.
10) Generally
dispwrse dyes are derivative of azo, anthraquinone, nitro and quinine group.
11) They
do not undergo any chemical change during dyeing
Classification of disperse dyes:
1) Chemical
classification :
I.
Nitro dyes
Example : dispersal fast yellow A, Serisol yellow 2G
II.
Amino keton dyes :
Example : Gelliton fast green 3B
III.
Anthraquinonoid dyes
Example : duranol violet 2R, duranol brilliant blue G
IV.
Monoazo dyes
Example : cibacel orange 2RD
V.
Diazo
Example : celliton fast yellow 5R,
2) According
to fastness properties :
There are four types:-
i.
Group A : these dyes have excellent dyeing
properties and good fastness. E.g. C.I. disperse Red 5, C.I. disperse Orange 3
ii.
Group B : these dyes are excellent in high
temperature and for carrier dyeing, with moderate fastness. E.g. Disperse
Yellow 1,Disperse Blue.
iii.
Group C : these dyes are moderate for carrier
and high temperature dyeing with higher fastness properties than Group-B dyes. E.g.
C.I disperse Violet 3, Disperse Orange 13.
iv.
Group D : these dyes are of excellent high
fastness to that but poor dyeing properties on carrier dyeing. E.g. Disperse Orange
32, Disperse Yellow 63.
3) According
to energy requirement :
There are three types :-
i.
Low energy dye : these dyes are used to dye with
carrier. For dyeing 77degree C temperature is required. They have extremely
poor resistance to sublimation.
ii.
Medium energy dyes : these dyes are used to dye
mostly in between temperature 104 to 10 degree C which provides better
sublimation fastness than that of low energy dyes.
iii.
High energy dyes : these dyes are used to dye at temperature
above 129 degree C and are suitable for continuous dyeing. They provide good
fastness.
Chemical group present in disperse
dye :
Monoazo dyes – 50%
Anthraquinonoid dyes – 25%
Diazo dyes – 10%
Methane dyes -3%
Styryl dyes - 3%
Acrylene benzimidazol - 3%
Quinonapthalon dyes – 3%
Amino napthyl amide – 1%
Dyeing mechanism of disperse dye
The dyeing of hydrophobic fabric
with disperse dyes may be considered as a process of dye transfer from a
liquire solvent ( water ) to a solid organic solvent(fibre).
Disperse dyes are added to water
with a surface active agent to form an aqueous dispersion. The insolubility of
disperse dyes enablethem to leave the dye liquor as they are more substantive
to the application of that to the dye liquor increases the energy of dye molecules
and accelerates the dyeing of textile fibres.
Heating the dye liquor swell the
fibre to some extent and assists the dye to penetrate the fibre polymer system.
Thus the dye nolecule takes its place in the amorphous regions of the
fibre.withine the fibre polymer system, the dye molecules are held by hydrogen
bonds and van der waals force.
The dyeing is considered to take
place in the following simultaneous steps :-
1)
Diffusion of dye in solid phase, into water by
breaking up into individual molecules. This diffusion depends on dispersibility
and solubility of dyestuff and is aided by the presence of dispersing agent and
increasing temperature.
2)
Adsorption of the dissolved dye from the
solution onto the fibre surface. This dyestuff adsoeption by in the dye bath
and that in the fibre.
3)
Diffusion of the adsorbed dye from the fibre
surface into the interior of the fibre substance towards the centre. In normal
condition, the adsorption rate is always higher than the diffusion rate. Abd this
is the governing step of dyeing.
Carriers:
It has been established that
certain hydrocarbons, phenols, amino-acids, amides, alcohols, esters, ketones,
nitriles etc. Accelerate the rate of dyeing polyester fibres with disperse dyes
from aqueous medium at temperature up to 100 degree C. These dyeing assistants
alter the dispersing properties of the dyes and the physical charactistics of
the fibre so that more dye can be transferred from the dyebath to the fiber. These
are called carriers and are necessary for dyeing polyester fibre at the normal
pressure and temperature below 100 degree C to increase the dyeing rate and to
permit dye migration within the fibre. Level dyeing of disperse dyes depends on
the migration power of dye which is affected by nature and amount of carrier
dyeing time, temperature and the shade.
Some commercial carriers :
Commercial name
|
Manufacturer
|
Chemical class
|
1.
Solvent OP
|
Franco
|
O.-phenyl phenol
|
2.
Tumescal D
|
ICI
|
Diphenyl
|
3.
Palanil carrier-A
|
BASF
|
Aromatic rther
|
4.
Carrier PDC
|
TCC
|
Emulsifiable solvents
|
5.
|
HAR
|
Ester
|
6.
Dilatin TCR
|
Sandoz
|
Chlorinated aromatic compound
|
7.
Involon
|
Ciba-Ceigy
|
|
Factors considered for selecting a
carrier:
i.
High carrier efficiency
ii.
Availablility at low cost
iii.
Little or no effect on light fastness of final
dyeing
iv.
Absence of unpleasant odour
v.
Non-toxicity
vi.
No degration or discolouration of the fibre
vii.
Ease of removal after dyeing
viii.
High stability under dyeing condition
ix.
Compatibility with the dyestuffs
x.
Easw of dispersion in the dyebath
xi.
Low volatility of the carrier including low
volatility in the steam
xii.
Uniform absorption
Application method of disperse dye
:
1) Method
N : Normal dyeing method, dyeing temperature is 80°-100°C
2) Normal NC Method : Method of dyeing
at normal temperature with carriers. Dyeing temperature 80°-100°C
3) Method HT : high temperature dyeing
method, dyeing temperature 105°-140°C
4) Method T : thermal dyeing method,
dyeing temperare 180°-220°C,
continuous method of dyeing.
5) Pad roll method : semi-comtinuous
dyeing method
6) Pad steam method : continuous dyeing
method
Factor considered for
selection a disperse dyeing method :
i.
Available of dyeing mechine.
ii.
Required color effect (dark/medium/light)
iii.
Required color fastness
iv.
Types of material to be dyed.
v.
Cost of dye chemicals and auxiliaries.
vi.
Overall economy of the system.
vii.
Dyeing temperature.
Comparison among high temperature,
carrier and thermosol dyeing method :
Carrier Method
i.
Carrier is required, no thickener is used
ii.
Lower dyeing temperature (80-100°C)
iii.
Less protection is required
iv.
Costly as carrier is used
v.
Less bright shade
vi.
Toxic and unhygienic process
vii.
More shrinkage
viii.
Process is batchwise, so production less
ix.
Removal of carrier difficult and alkali is used
for it
x.
No change in shade
High temperature method
i.
Neither carrier nor thickener is used
ii.
High temperature of dyeing (105-140°C)
iii.
More carefulness is needed
iv.
Not so costly
v.
More bright shade
vi.
Process is batchwise, so production less
vii.
Non toxic and hygienic process
viii.
Less shrinkage
ix.
Not applicable\
x.
No change in shade
Thermosol method :
i.
Carrier is not used,bt thickener is require is
required
ii.
Very high temperature dyeing (180-220°C)
iii.
Very much carefulness is required
iv.
Costly as special machine for dyeing is needed
v.
Very bright shade is required
vi.
Process is continuous, so production higher
vii.
Non-toxic abd hygienic process
viii.
Less shrinkage
ix.
Not applicable
x.
Change in shade
Reduction cleaning :
In case of dark shade dyeing we
have to use more amount of dye and chemicals. But these chemical should be
removed from fabric after dyeing. For this reason a special process is used in
case of disperse dyeing. This cleaning process is called reduction cleaning. By
reduction cleaning surface dye molecule/ unfixed dye molecules are stripped and
this in turn results in leveling. Reduction cleaning also improved the wash
fastness property of textile material.
Disperse dyeing effected by
Temperature :
In case of dyeing with disperse
dye temperature plays an important role.for the swelling of fibre temperature
about 100°C is required
if high temperature dyeing method is applied. Again in case of carrier dyeing
this swelling occurs at 85-90°C
. Incase of thermosol dyeing method if temperature is kept more, fabric is kept
for less time in thermosol unit. Because in higher temperature, less time is
enough for thermofixation of dye. If it is kept for more time at high
temperature dye submation and loss of fabric strength occur.
Again thougt disperse dye is a
water – insoluble dye, its solubility increases with increasing temperature.
Disperse dyeing effected by ph
:
For disperse dyeing the dye bath
should be acidic and ph should be maintained in between 4.5 -5.5 . For
maintaining this ph generally acetic acid is used. We may also use any
mineral acid like H3 PO4 but those are strong
andcostly. So mild acid likeacetic acid is used for controlling ph of the bath. At this ph dye exhaustion is satisfactory. During color
development correct ph should be maintained otherwise fastness will
be inferior and color will be unstable.
Dispersing agent :
Disperse dyes are insoluble in
water and form an aqueous dispersion in water. At first these dye molecules are
formed as large particles and they are made smaller particles by grinding. But as
they are water insoluble, they will give uneven dyeing if they are directly
used in dye bath. So to ensure uniform and trouble- free dyeing the dye should
be present in dye bath in an uniform very fine form and should give an stable
dispersion. This is the reason for which a special chemical is used in dye
bath, named dispersing agent. They should be effective under dyeing conditions.
Stable to hard water, high temperature abd other dyeing assistants.
For example, soa powder, Turky red oil, alkali
sulphates, alkyle arylphonates etc are same surface active agent which are
recommended as dispersing agents in disperse dyeing.
Function of dispersing
agent :
1)
It assists in the process of partical size
reduction of dye.
2)
It enables the dye to be formed in powder form.
3)
It facilitates the reconversion of the powder
into a dispersion, which is required for dyeing.
4)
It maintain the dispersion in a fine form into
dye bat throughout the process.
5)
It increase the solubility of disperse dyes in
water.
6)
It affect on the rate of dyein.