The Fixation Of Direct Dyes

The Fixation of Direct Dyes

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Direct dyes refer to dyes that can dissolve directly in water and have high directness to cellulose fibers without the need to use relevant chemical methods to color fibers and other

Production Basic data of The Fixation Of Direct Dyes:

The sulfonic acid group or carboxylic acid group in the direct dye molecule has strong water solubility, and only depends on the van der Waals force and hydrogen bond to be fixed on the fiber. The wet fastness of the dye is low, which is easy to cause fading or staining. The fixation of direct dyes is very important

There are the following two methods for the fixation of direct dyes：

1、 Post-treatment of metal salts

1）The fixation ofdirect dyes mechanism: The dyes and financial ions on the fiber form a stable complex with low water solubility, which improves the wet fastness of the dye.

2）Commonly used metal salts are copper salts, such as copper sulfate, copper acetate, and copper tartrate. Therefore, such dyes are called direct copper salt dyes.

2、Post-treatment of cationic fixing agent

1） The fixation of direct dyes principle: Direct dyes are anionic dyes, When treated with cationic fixing agents, the cationic fixing agents and anionic dyes combine to seal the water-soluble groups to form precipitates, thereby improving the wet fastness of the dyes. It can form a resin film on the surface of the fabric, further seal the dye, increase the smoothness of the fabric, reduce the friction coefficient, reduce the swelling, dissolution, and shedding of the dye during the "wet friction" process, thereby improving soaping, perspiration, water immersion, and friction Color fastness.

2）Common fixing agent used for the fixation of direct dyes

  a. Common type: cationic surfactants, which can block the water-soluble groups of anionic dyes and form lakes on the fibers with the dyes; non-surfactants, improve the washing fastness;

b．Formaldehyde condensate: a resin condensed by dicyandiamide and formaldehyde, which can directly reduce the solubility of the dye on the fiber, and contains formaldehyde.

Polyamine compound: water-soluble resin, formaldehyde-free fixing agent, with a network structure, and ionic bond with the anionic group in the dye to improve the wet fastness. It can be cross-linked with the hydroxyl group in the fiber to further improve the dyeing fastness.

C：Reactive fixing agent: Form salt with dyes, block water-soluble groups to form precipitates, crosslink with amino, amine and hydroxyl groups in fibers and dyes to improve fastness to wet treatment