Dyeing Cationic Dyeable Polyester (CDP) with Cationic Dyes By Michael Hilton

This article is contributed by Michael Hilton

Cationic Dyeable Polyester is a special Polyester fiber which has undergone a change during polymerization. They were built of molecules of 5 - sulphophthalic acid, to generate anionic sites that the fibers of normal PET not have. Having anionic groups it can also be dyed with cationic dyes with results of high brilliance. However, these fibers can be dyed with disperse dyes. Compared to ionic dyes, disperse dyes have smaller molecular extinction coefficients and lower build-up property, so these dyes cannot give bright and deep colors. This type of fibers were born also to lower the Tg (glass transition temperature) of the polymer, 10 ° C lower than normal Polyester fibers, so to obtain a more segmental mobility and open polymer structure. Resulting in increased rate of diffusion of the dye in the fiber at a lower temperature. Tg Range (70 – 85°C). This modified polymer is also more easily hydrolised and more sensitive to heat setting before dyeing at a maximum temperature of 180°C.

Example 

scouring and dyeing exhausted process in Overflow – Jet Machine (Liquor ratio - 1:10 – 1:20) :

Scouring:

Continuous washing cold for 10 min 

drain well (for water soluble oils)

Fill with water 30 ° - 35°C

0,5 g/l Antifoam (preferably non-silicone) alone

1 g/l Detergent non – ionic

0,5 g/l Caustic Soda 36° Bè

Raise to 80°C quickly and hold for 20 – 25 min

Drain well 

washing cold for 10 min 

and after starting in dyeing

Dyeing with Cationic dyes

Follow the Graph below :

The dyebath is set at 60°C - introduce order

0,5 g/l Antifoam (alone)

6 g/l Sodium sulphate (only dyeing at 120°C) (1)

1 g/l Dispersant non-ionic

X g/l Acetic Acid pH = 4,5

X % Levelling – Carrier anionic (only dyeing at 98°C)

X% Cationic dyes (dissolved at 60°C with 1 g / l of acetic acid) - (introduce preferably dosed curve progressive Sen +)

Then raise to 70°C - after to 85°C at 0,5°C / min (while the fiber is softening) and hold for 10 min, after raise to 120° (or 98°C) at 0,6°C / min – hold for 30 – 60 min (depends on the depth of the color) 

then cool to 70°C at 0,5°C / min and check the color.

Please note that sodium sulphate (Na +), being very stable at high temperatures, is the protector of te anionic sites sensitive to the acid at 120 °C.

After dyeing, the dyed samples were rinsed and washed with 2 g/l of non-ionic detergent at 60 – 70°C.

Light fastness: moderate to good

Washfastness: good to excellent

Rubbingfastness: good

Excellent resistance to sublimation on wet

No fouling of lycra mixed