Disperse dyes
Disperse dyes are small polar molecules, usually
containing anthraquinones or azo groups that do not charge the cationic or
anionic groups within the structure. It should be dissolved in a small amount
of water and spread on the dye with the help of a surfactant. As a small amount
of dissolved dye is scattered in the fiber, the excess dye dispersed in the
solution dissolves until the dye is almost completely exhausted in the dyed
fiber. The lightfastness and wash fastness of these dyes are generally good but
there has been a problem with fume fading from some of the dispersed dyes.
It is non-ionic, water-insoluble, and does not react
chemically with nylon. Dyeing occurs regardless of the −COOH or −NH2 group, but
the dyes are held by the van der Wales balls and H-bonds by the fan.
Disperse dyes are supplied as a powder and liquid
form products. Powder dyes contain 40-60% dispersing agents but liquid formulas
contain between 10-30%. Formaldehyde concentration products and lignin
sulfonates are widely used for this purpose. Some dispersed dyes contain organic
halogen, but they are not expected to be found in equal amounts after treatment
with unclean water due to their active composition.
Characteristics of disperse dyes
i.
Disperse dyes are molecularly dispersed in the liquor at the time of dyeing.
ii.
It is very less soluble in water which makes fine dispersion.
iii.
It crystalline material with a high melting point (>150°C).
iv.
The saturation level of pure disperse dyes in the fiber is relatively high.
v.
It has fair to good lightfastness and a lightfastness rating of 4-5.
vi.
Washing fastness is moderate to good, rating of 3-4.
vii.
Its good sublimation power due to its stable electron arrangement.
viii.
Disperse dyes are non-ionic in nature.
ix.
The color will fade due to heat application on dispersed dye.
x.
In the presence of nitrous oxide, textile material dyed with certain blue and
violet disperse dyes with anthraquinone dye structure will be faded.
xi.
It is used for dyeing hydrophobic thermoplastic fibers including nylon,
polyester, acrylic, and other synthetics.
xii.
The general structure of dispersed dyes is small and planar, and it contains polar
functional groups like hydroxyalkyl, –NO2, and –CN.
xiii. It is characterized
by the absence of solubilizing groups and low molecular weight.
xiv. The good
migration properties of disperse dyes result in problem-free level dyeing.
xv.
The zeta potential of commonly used disperse dyes ranges from − 30 to -80 mV.
xvi.
These dyes have a bulk density of 0.4–0.6, a pH value of 7.0–9.0 (10 g/L water)
xvii.
It is usually containing anthraquinone or azo groups which do not have charged
cationic or anionic groups within the structure.
xviii.
It is unsuitable for human skin because of the allergic effect.
xix.
It is known that this kind of sensitive dispersed dye is still used in items
such as stockings and tights, socks, leggings, blouses, and underwear.
xx. It does not require any specific fixing agent because the dyes become
substantive to the fibers through phase changes initiated by temperature.
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