2. Disperse Dyes
Non-ionic organic coloring substances which are
insoluble in water.
Developed for synthetic fibers which are
hydrophobic.
Disperse dyes were developed because these fibers
were not dyed with any other dye.
Polyester fibers have more crystalline region
which are closely packed (more compact structure).
3. Disperse Dyes
Insoluble in cold water, slightly/partially soluble in
hot water, solubility increases with increase in temp.
Can be dispersed in water.
Disperse dyes are applied in dispersed form that is
why these are called disperse dyes.
Used especially for polyester and acetate rayon.
4. Disperse Dyes
These dyes are Dispersed are converted into fine
particles in the presence of dispersing agent.
In aqueous medium, at high temp, in the presence of
dispersing agent, dye particles are dispersed in water
i.e., converted into fine particles and then retained in
the fiber.
Disperse dyes possess good fastness to washing ,
laundering, light properties.
5. Chemistry of Disperse Dyes
Disperse dyes have the smallest molecules of all the
common dye classes.
A feature of disperse dye molecules is their lack of
polar groups, evidenced by the insolubility of
disperse dye.
Disperse dyes are classified into two groups on the
basis of chemical structure.
Azo Disperse Dyes
Antrhraquinone Disperse Dyes
8. Features of Disperse Dyes
Features:
Good dispersion
Good sublimation
Good levelling (with surfactant or carrier)
Good Satbility (at 130°C)
9. Dyeing with Disperse Dyes
There are two methods of disperse dyeing
Carrier Method
(at 100°C temp.)
High Temperature Method/HT Method
(at 120-130°C temp. without carrier)
10. Dyeing with Disperse Dyes
Disperse dyes are added to water also containing a
surface active agent to form an aqueous dispersion.
Due to their insolubility in water disperse dye
molecules leave the dye liquor as they are more
substantive to the organic fiber than to the inorganic
aqueous dye liquor.
Increase in temp. increases the energy of the dye
molecules and accelerates the dyeing of the textile
fiber.
11. Dyeing with Disperse Dyes
Actually when temp. is increased the dye liquor
swells the fiber to some an extent and force the dye
molecules to penetrate the fiber polymer system
resulting in the penetration of the dye molecules in
the amorphous region of the fiber polymer.
The dyeing results are achieved due to the trapping
of the dye molecules into the fiber polymer as well as
due to hydrogen bond and van der waals’ forces.
12. Dyeing With Disperse Dyes
Polyester fibers are extremely crystalline and
hydrophobic that is why difficult to dye with medium
or dark shades even by dyeing at the boil.
In order to obtain medium to dark shades, carrier
method or high temperature dyeing techniques are
used.
13. Dyeing with Carrier
Due to extremely crystalline and hydrophobic
nature, it is difficult to obtain dark shades by
conventional dyeing methods, even when the dyeing
is carried out at boil of the dye liquor.
Then certain organic compounds were discovered
that assisted the disperse dye molecules to enter the
polyester dyes to enter the polyester fiber polymer
resulting in dark shades.
14. Dyeing with Carrier
Actually carriers enter the polyester fiber and open
(swells which results in easy water diffusion) its
structure so that dye molecules easily penetrate into
it.
Also gives the transportation to the disperse dye
molecules means accelerates the rate of dyeing.
15. Limitations of Carrier Dyeing
High cost of carrier.
Difficult to remove carrier completely from the dyed fabric which
creates odor.
Spotting problems (due to adherence of carrier particles).
Pollution problems.
Carrier (if remain in fabric) adversely affect light fastness properties of
dyed fabrics.
Most of disperse dyes do not exhaust from dye bath to improve heavy
shades.
16. Dyeing at High Temperature
This dyeing is carried out at high temp. (130°C) and
high pressure (0 to 170 kPa) instead of at boil.
Also called high pressure dyeing.
High temp. and pressure causes the polyester fiber to
swell and helps in deep penetration of the disperse
dye molecules into the fiber polymer system.
Eliminates the need of carrier and results in lower
cost and unpleasant odor.
17. Advantages of High Temp. Dyeing
Reduction in dyeing time.
No carrier cost.
Complete penetration of dye molecules in polyester.
Dark and heavy shades easily produced.
Exhaustion of dye molecules is rapidly.
18. Thermofixation Process
High temp. is used in dyeing of polyester fiber under
the name of “Thermosol Process”.
When polyester is heated to high tem. (200-230°C),
it is softened and its internal structure is opened up.
The dye molecules can now diffuse into the fiber very
easily.
The diffusion of the dye molecules takes place with in
few seconds to one minute.
19. Reduction Clearing Process
RC process is simply a washing process in disperse
dyeing for removing unfix dye from the surface of the
textile material after dyeing.
Three substances are used in this process:
Caustic Soda
Sodium Hydrosulphite
Detergent/Soap
Treat the fabric at 60°C for 15 min.
20. Properties of Disperse Dyes
Washing Fastness:
Disperse dyed textile materials show moderate to good
washing fastness (due to partly insolubility of disperse dye
molecules and partly to the hydrophobic nature of the fibers to
which disperse dye are usually applied).
Light Fastness:
Show fair to good light fastness properties (may be attributed
in part to the non-polar nature of the dye molecule which will
not readily attract water molecules and other polar agents that
may have a degrading effect.
