Disperse Dyes Disperse Dyes

Disperse Dyes

Non-ionic organic coloring substances which are insoluble in water.

Developed for synthetic fibers which are hydrophobic.

Disperse dyes were developed because these fibers were not dyed with any other dye.

Polyester fibers have more crystalline region which are closely packed (more compact structure).

On the other hand disperse dye molecule size is smaller, that is why disperse dyes are used for these fibers.

Disperse Dyes

Insoluble in cold water, slightly/partially soluble in hot water, solubility increases with increase in temp.

Can be dispersed in water.

Disperse dyes are applied in dispersed form that is why these are called disperse dyes.

Used especially for polyester and acetate rayon.

Disperse Dyes

These dyes are Dispersed are converted into fine particles in the presence of dispersing agent.

In aqueous medium, at high temp, in the presence of dispersing agent, dye particles are dispersed in water i.e., converted into fine particles and then retained in the fiber.

Disperse dyes possess good fastness to washing , laundering, light properties.

Chemistry of Disperse Dyes

Disperse dyes have the smallest molecules of all the common dye classes.

A feature of disperse dye molecules is their lack of polar groups, evidenced by the insolubility of disperse dye.

Disperse dyes are classified into two groups on the basis of chemical structure. Azo Disperse Dyes Antrhraquinone Disperse Dyes

Azo Disperse Dyes

Anthraquinone Disperse Dyes

Features of Disperse Dyes

Features:

Good dispersion Good sublimation Good levelling (with surfactant or carrier) Good Satbility (at 130°C)

Dyeing with Disperse Dyes

There are two methods of disperse dyeing

Carrier Method (at 100°C temp.)

High Temperature Method/HT Method (at 120-130°C temp. without carrier)

Dyeing with Disperse Dyes

Disperse dyes are added to water also containing a surface active agent to form an aqueous dispersion.

Due to their insolubility in water disperse dye molecules leave the dye liquor as they are more substantive to the organic fiber than to the inorganic aqueous dye liquor.

Increase in temp. increases the energy of the dye molecules and accelerates the dyeing of the textile fiber.

Dyeing with Disperse Dyes

Actually when temp. is increased the dye liquor swells the fiber to some an extent and force the dye molecules to penetrate the fiber polymer system resulting in the penetration of the dye molecules in the amorphous region of the fiber polymer.

The dyeing results are achieved due to the trapping of the dye molecules into the fiber polymer as well as due to hydrogen bond and van der waals’ forces.

Dyeing With Disperse Dyes

Polyester fibers are extremely crystalline and hydrophobic that is why difficult to dye with medium or dark shades even by dyeing at the boil.

In order to obtain medium to dark shades, carrier method or high temperature dyeing techniques are used.

Dyeing with Carrier

Due to extremely crystalline and hydrophobic nature, it is difficult to obtain dark shades by conventional dyeing methods, even when the dyeing is carried out at boil of the dye liquor.

Then certain organic compounds were discovered that assisted the disperse dye molecules to enter the polyester dyes to enter the polyester fiber polymer resulting in dark shades.

Dyeing with Carrier

Actually carriers enter the polyester fiber and open (swells which results in easy water diffusion) its structure so that dye molecules easily penetrate into it.

Also gives the transportation to the disperse dye molecules means accelerates the rate of dyeing.

Limitations of Carrier Dyeing

High cost of carrier.

Difficult to remove carrier completely from the dyed fabric which creates odor.

Spotting problems (due to adherence of carrier particles).

Pollution problems.

Carrier (if remain in fabric) adversely affect light fastness properties of dyed fabrics.

Most of disperse dyes do not exhaust from dye bath to improve heavy shades.

Dyeing at High Temperature

This dyeing is carried out at high temp. (130°C) and high pressure (0 to 170 kPa) instead of at boil.

Also called high pressure dyeing.

High temp. and pressure causes the polyester fiber to swell and helps in deep penetration of the disperse dye molecules into the fiber polymer system.

Eliminates the need of carrier and results in lower cost and unpleasant odor.

Advantages of High Temp. Dyeing

Reduction in dyeing time.

No carrier cost.

Complete penetration of dye molecules in polyester.

Dark and heavy shades easily produced.

Exhaustion of dye molecules is rapidly.

Thermofixation Process

High temp. is used in dyeing of polyester fiber under the name of “Thermosol Process”.

When polyester is heated to high tem. (200-230°C), it is softened and its internal structure is opened up.

The dye molecules can now diffuse into the fiber very easily.

The diffusion of the dye molecules takes place with in few seconds to one minute.

Reduction Clearing Process

RC process is simply a washing process in disperse dyeing for removing unfix dye from the surface of the textile material after dyeing.

Three substances are used in this process: Caustic Soda Sodium Hydrosulphite Detergent/Soap

Treat the fabric at 60°C for 15 min.

Properties of Disperse Dyes

Washing Fastness: Disperse dyed textile materials show moderate to good

washing fastness (due to partly insolubility of disperse dye molecules and partly to the hydrophobic nature of the fibers to which disperse dye are usually applied).

Light Fastness: Show fair to good light fastness properties (may be

attributed in part to the non-polar nature of the dye molecule which will not readily attract water molecules and other polar agents that may have a degrading effect.