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Properties of metal complex dyes
Metal complex dyes are premetalised dyes, in which one or two dye molecules are co-ordinated 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.
Fastness:
The metal complex dyes exhibit good fastness towards exposure to light, however the wet fastness properties are moderate, particularly in darker shades. However the fastness is also depends upon the fiber type and dye type.
Solubility:
These are water soluble dyes.
Application:
These dyes are applied from neutral, weakly acidic to a very strongly bath depending upon the dye sub class.
Applicability:
These dyes are suitable for dyeing of wool, silk, polyamides and leather.
1:1 metal complex 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, there fore these are not suitable for the blends having cotton component.
1:2 metal complex dyes exhibit excellent light and wet fastness properties with excellent penetrating power. These dyes are solubilised by the inherent anionicity of the complex or containing non ionic, hydrophilic substitutes such as methylsulphone. Weakly polar dyes are applied in the range of pH 4-7 adjusted with acetic acid in the presence of ammonium acetate.
