Poor reproducibility and fastness are usually problems in polyester/polyurethane conjugated fabric dyeing.

It is necessary to remove the disperse dyestuff fixed to polyurethane in order to improve fastness in polyester/polyurethane dyeing. This sort of staining occurs so often that reducing and alkali agents, which can remove stains comparatively well, are used. Dischargeable dyestuffs are frequently used as well.

However, when dischargeable dyestuffs are used for dyeing, there are a few disadvantages, i.e. (1) poor color reproducibility and (2) poor fastness. In most cases the phenomena below will follow:

1. Conditional dependency (temperature dependency and pH dependency) in dyeing is high. In other words, the dyeing properties change depending on pH and temperatures.
2. Disperse dyestuff easily re-bleeds during heat setting after reduction clearing. Fastness decreases even though stains are removed.

In the case of dyeing polyester/polyurethane blended fabric with disperse dyestuff, most of the dyestuff fixes to the polyurethane when raising the temperature to about 100°C. This is what we call, "staining". When the temperatures range from 100-120°C, the disperse dyestuff fixed to the polyurethane gradually migrates to the polyester fiber.

The following procedures should be taken into consideration in order to prevent problems in the case of dyeing polyester/polyurethane blended fabric:

(a) Inhibiting disperse dyestuff staining on polyurethane so that the dyestuff can effectively fix to the polyester.
(b) Using disperse dyestuffs with good reproducibility and fastness
(c) Effectively removing the disperse dyestuff which has stained polyurethane through reduction clearing.

It is also necessary to consider polyester dyeing at 110°C, which Toru Takagishi, PhD. from Osaka Prefecture University has suggested.

Dyeing polyester/polyurethane blended materials can be improved based on the 3 major methods listed in the following table. Dyeing was carried out at 120°C.