1.Dye-fixing agent theory.
The basic principle is the covering theory, fixing agent is polymer, containing many sulfonic group with nylon fiber end amino bonded, forming a net structure, coated with dye, the color fastness to washing can be guaranteed and improve.

2.Dye-fixing condition
In general, dye-fixing agent is as follows:
Temp：70-80 ℃
PH：4.0-4.5
Time：20-30 min.

Both the higher and lower temperature have negative influence on the dye-fixing effect. When the temperature is too low, the dye fixing agent can not be absorbed completely. When the temperature is too high, the dye-fixing agent penetrate too much to the inner of fiber and the covering effect will affected.  So  both of them will effect the result.

3.The reason for nylon color fixing spot
The dyeing Nylon color fixing spot usually be caused by the following reasons:
(1)the excessive hardness (Ca++, Mg++)of water

(2)the weak cationic auxiliary residue on the fabric

(3)the influence of acid

(4)the high shear spitting from dyeing machine(such as Jet dyeing machine)


4.Improvement strategy
(1) Add water ameliorant to improve the hardness of the water.

(2) Choose weak cationic levelling agent or the combining levelling agent of anionic and Ionic belling agent to avoid the agglutination sediment of levelling and dye-fixing agent.

(3) Add little AVOLAN IS to ensure the residue of levelling agent is lowest.

(4) In order to avoid the agglutination and sediment of the dye-fixing agent and high concentrated acid, we can dilute the acid with water and slowly poor into it.

(5) Another methods is choosing dye-fixing agent that do not need to combine with acid, which can not just avoid the desperation and save the operation time.

5. For some high shearing force dye, such as, Jet dyeing machine, we recommend some non-activated shearing dye-fixing agent.