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Generic Name
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Colour Index
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Blue FFC
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Blue 71
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T.Blue BL
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Blue 199
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T.Blue G
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Blue 86
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Black NA
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Black 22
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Black VG
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Black 19
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Black OB
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Black 80
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Brown MR
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Brown 2
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Scarlet 4BS
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Red 23
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Properties of DIRECT DYES
:
Direct dyes are usually applied with the addition of electrolyte at or near the
boil in the machines capable of running at atmospheric pressure .But in HTHP dyeing
machines it is carried out at temperatures above the boil in case of pure as well
as blended yarns.
An addition of alkali, usually sodium carbonate, may be made with acid-sensitive
direct dyes and with hard water as well as to enhance the dye solubilisation. When
cellulose is immersed in a solution of a direct dye it absorbs dye from the solution
until equilibrium is attained, and at this stage most of the dye is taken up by
the fibre. The rate of absorption and equilibrium exhaustion vary from dye to dye.
The substantivity of the dye for cellulose is the proportion of the dye absorbed
by the fibre compared with that remaining in the dyebath.
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Types of DIRECT DYES :
(1) Class A – dyes that are self-levelling, i.e. dyes of good migration or leveling
properties.
(2) Class B – dyes that are not self-levelling, but which can be controlled by addition
of salt to give level results; they are described as salt-controllable.
(3) Class C – dyes that are not self-levelling and which are highly sensitive to
salt, the exhaustion of these dyes cannot adequately be controlled by addition of
salt alone and they require additional control by temperature; they are described
as temperature-controllable.
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