Disperse Dyes

Chemical Nature

These are nonionic in nature.Disperse dyes are characterized by the absence of solubilizing groups and low molecular weight. From a chemical point of view more than 50 % of disperse dyes are simple azo compounds, about 25 % are anthraquinones and the rest are methine, nitro and naphthoquinone dyes.

General properties
Disperse dyes are supplied as powder and liquid products. Powder dyes contain 40 - 60 % of dispersing agents, while in liquid formulations the content of these substances is in the range of 10 - 30 %. Formaldehyde condensation products and ligninsulphonates are widely used for this purpose.
Classes of Disperse dyes
1.Low Energy(E type):-These dyes have low molecular weight ,low polarity , high dyeing rate and low sublimation fastness.
2.Medium Energy(SE type):- These dyes have moderate molecular weight, moderate polarity,moderate dyeing rate and moderate sublimation fastness.
3.High Energy(S type):- These dyes have high molecular weight ,high polarity , low dyeing rate and high sublimation.
Applicability
Disperse dyes are used mainly for polyester, but also for cellulose (acetate and triacetate), polyamide and acrylic fibres.
Dyeing Mechanism

The dye-fibre affinity is the result of different types of interactions:

· hydrogen bonds

· dipole-dipole interactions

· Van der Waals forces.

Disperse dyes have hydrogen atoms in their molecule, which are capable of forming hydrogen bonds with oxygen and nitrogen atoms on the fiber.

Dipole-dipole interactions result from the asymmetrical structure of the dye molecules, which makes possible electrostatic interactions between dipoles on the dye molecules and polarized bonds on the fiber.

Van der Waals forces take effect when the molecules of the fibre and colourant are aligned and close to each other. These forces are very important in polyester fibres because they can take effect between the aromatic groups of the fibre and those of the colourant.

Chemicals and auxiliaries required in disperse dyeing

pH buffers

Levelling and retarding agents see leveling agents

Dispersing agents

carreers

Reducing agents for reduction clearing

Important Dyeing Parameters

1.Pretreatment process.

2.Dye solubility ,dye dissolution, and dye selection.

3.Material to liquor ratio.

4.pH and Dyeing temperature.

5.Dyeing duration.

6.Leveling and retarding agents.

7.Dispersing agents.

8.Removal of excess dyes from the fibers.

9.Oligomers  and their removal.

10.Reduction clearing.

11.Soaping treatment.

12.Use of dyeing career.

FACTORS I N SELECTING DYES FOR POLYESTER
1.Economy
2.Fastness levels required.

3.Level Dyeing or Barre control.
4.Stability at high temperature.
5.Dispersion Stability (in package dyeing)

Fastness Properties(on polyester)
Light fastness:-Fastness to light is generally quite good.
Washing Fastness:-Fastness to washing is highly dependent on the fiber. In particular, in polyamides and acrylics they are used mostly for pastel shades because in dark shades they have limited build-up properties and poor wash fastness.
Sublimation Fastness
Depend upon the class of disperse dyes.
Crocking fastness

Good
Fastness to dryclean
Good
Fastness to Chemicals wash
The dyes may fade and loose color value if subjected to Chlorine bleaches in acidic medium.
An introduction to disperse dyes
All about Manufacturing of Disperse Dyes
Dyeing of Polyester -1
Dyeing of polyester -2
Dyeing of Polyester -3
Dyeing of Polyester -4
Dyeing of Polyester -5
Dyeing Procedure of disperse dyes