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Cationic Dyes are those dyes which are parted and
give colored positively charged ions, when they are mixed in aqueous
solution.
 Some
common features of Cationic Dyes |
- Having intensive bonding capability.
- Molecular structure is in planar form.
- Positively charged surface groups are stronger over the
negatively charged surface groups.
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Composition
of Cationic Dyes |
In the Color Index scheme, cationic direct dyes
are classified along with Basic Dyes.
In a Direct dye molecule, the chain of conjugation almost always
contains two or more aromatic groups.
The word "Direct" implies that the dye has an adequate
molecular size so that it has a strong preference to remain on surfaces.
In other words, the user can add it "directly," without a
fixative or mordant, as it will remain sticked to the surface. Cationic
Direct dyes have particularly high affinity for anionic surfaces due to
presence of cationic amine groups.
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Functions
of Cationic Dyes |
- Cationic direct dyes can be very valuable where (a) the
effluent water has to be colorless, or (b) where a high frequency of
production changes between different colored products that provides
an incentive for keeping the white water free of residual dye.
- Cationic direct dyes tend to irreversible stain i.e. the
first surfaces with which they come into contact. The speckled
appearance of paper products is due to this fact. Users may use
adequate dilution and add the dye at a point of good agitation if
they want to avoid it.
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Advisable measures
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- Cationic direct dye should not be added to white water,
since it will stain the non-retained fines.
- It should never be added in a chest as it will stain the
fibers that happen to be near to the point of addition.
- Strongly avoid direct contact between a Cationic Direct dye
solution and streams of highly anionic additives. e.g., a
mixture of Cationic Direct dye and traditional(anionic) direct
dye produces an insoluble tar.
- Instead of adding concentrate CD dye directly to the process,
the stream is combined with a relatively large amount of pure
water without any fibers or fines. The dilution ratio is not
critical.
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