Direct dye

Direct dye     click here

Properties of Direct dyes        click here

Classification of direct dyes          click here

Auxiliaries required for dyeing with direct dye       click here

Direct dye:

Direct dyes are anionic dyes having substantivity for all types of cellulose fibres such as cotton, viscose, rayon, cuprmmonium rayon etc. Direct dye have strong affinity towards the fibre which can be applied directly on the fibre and which do not need any assistance. These dyes have an affinity for cellulose and therefore they are also substantive dyes.

Properties of Direct dyes:

        i.            Dirt dyes are soluble in water.

      ii.            These dyes have sodium salt of sulphonic acid or carboxylic acid group present.

    iii.            Cheaper

    iv.            Poor wash fastness rating about 2-3

      v.            Used alkali and neutral medium

    vi.            Various shades are found.

  vii.            They are available.

viii.            Poor light fastness.

Some Trade Name of direct dyes:

Bnd Name	Manufacturer	Country
Benzo, Benzoform	F.Bayer	Germany
Chlorntine, Diphenly	Ciba-gei	Switzerland
Azoform, Chloramine	Sandos A.G.	Switzerland
Indazol	India Checal Industry(ICI)	India

Classification of direct dyes:

A) According to chemical classification:

1)Azo derivatives:

a)      Monoazo:

 Example : Diazoraine scarlet 5B (C.I. Direct Red 14)

b)      Di-azo:

Example : Congo Red ( C.I. Direct Red 28)

c)      Tri-azo:

 Example : Congo Brown R ( C.I. Direct Brown 44)

2) Stilbene derivativesExample : Chrysophenine G ( C.I. Direct Yellow 12 )

3) Thiazol derivatives:

Example : Premuline

4) Triphenodioxazine derivatives:

Example : C.I. Direct Blue 106

5) Phthalocyanine derivatives :

Example : Durazole blue 8G (C.I. Direct Blue 86)

B) Classification of direct dye according to application:

1) Class-A(Self leveling dye)

            i.            Dye migrate well

          ii.            High leveling power

        iii.            They may dye unevenly at first but further boiling will bring about even distribution.

2) Class-B(Salt controllable dye)

          i.            Dyes of poor leveling power

        ii.            ye exhaustion must be brought about by controlled salt addition.

      iii.            If these dyes are not taken up uniformly in the initial stages, it is extremely difficult to correct the unlevelness

3) Class-C(Temperature controllable dye)

          i.            Dyes are not self leveling.

        ii.            Highly sensitive to salt.

      iii.            The exhaustion of this dye is controlled by temperature.

Auxiliaries required for dyeing with direct dye:

·         Wetting agent:

                                  i.            Reduce surface tension water

                                ii.            Helps to penetrate the solution to the fibre.

·         Levelling agent:

                                  i.            To levelness of the dyeing

                                ii.            To ensuring of evenness of the dyes in the fabric

·         Electrolyte:

                                  i.            Helps in dye exhaustion.

                                ii.            NaCl used for deep shade

                              iii.            Na₂SO₄ used for medium shade.

                              iv.            Na₂SO₄.10H₂O used for medium shade.

·         Soda ash or Caustic soda:

                                  i.            Remove solubility of dye

                                ii.            Increase the effectiveness of salt

                              iii.            Increase the brightness of colored materials

                              iv.            To control p^H of the dye bath

                                v.            To strengthen the bond between dye and fibre.