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» Metal-Complex Dyes
Metal complex dyes are premetalised dyes that show great affinity
towards protein fibres. In this dye one or two dye molecules are coordinated
with a metal ion. The dye molecule is typically a monoazo structure
containing additional groups such as hydroxyl, carboxyl or amino, which are
capable of forming a strong co-ordination complexes with transition metal
ions such as chromium, cobalt, nickel and copper.
The following table shows a comparison between 1:1 metal-complex and 1:2
metal complex dye:
|1:2 metal complex
Metal-complex dyes belong to numerous application classes of dyes. For
example, they are found among direct, acid, and reactive dyes. When applied
in the dyeing processes, metal-complex dyes are used in pH conditions that
is regulated by user class and the type of fibre type (wool, polyamide,
etc). The pH levels for wool typically ranges from:
- Strongly acidic (ranging from 1.8 - 4 for 1:1 metal-complex dyes)
- Moderately acidic neutral (ranging from 4 - 7 for 1:2 metal-complex
Types of Metal Complex Dyes
The classification of metal complex dyes is dyes
is based on the basis of number of dye molecules which are complexed with
one metal ion
1:1 metal complex dyes: In 1:1 metal complex dyes one metal ion is
complexed with one dye molecule.
1:2 metal complex dyes: In 1:2 metal complex dyes there are two dye
molecules which are complexed with one metal atom.
Features of Metal Complex Dyes
- Medium washing fastness.
- Excellent, light-fastness.
- Shows very good level dyeing and penetration characteristics.
- Can cover up for the irregularities in the substrates.
Application of Metal Complex Dyes
Metal Complex Dyes is using for a variety of
applications like wood stains, leather finishing, stationery printing inks,
inks, coloring for metals, plastic etc. As this dye is classified into two
categories and both have different applications.
1:1 metal complex dyes:-
These dyes have good leveling and penetration properties and are
particularly suitable for application on carbonized wool. These dyes are
applied under a strongly acidic bath at a pH of 1.8 2.5 with sulfuric
acid or at a pH of 3-4 with formic acid, therefore these are not suitable
for the blends having cotton component. Glauber salt is used as exhausting
agent and organic leveling agents are used to
1:2 metal complex dyes:-
These dyes are subdivided into two subgroups based on the solubilising
groups present in the dye molecule, these dyes shows moderate migration
properties on nylon but very good overall fastness properties, because metal
complex dyes not only attach to nylon with ionic linkages, but also with
coordinate bonds. The two subgroups are:
- Weakly polar dyes
- Strongly polar dyes