Dyeing auxiliaries

These auxiliary agents are use to control the dyeing process, depending on their on their chemical composition and type of charge, in order to achieve very special effects on the substrate leather or also in the dye or the dyeing process. The auxiliaries are conveniently classified as anionic, cationic, nonionic, amphotric or special products.
Anionic products
These are mainly neutral salt mixture of aromatic sulphonic acids. In most cases they are used for their leveling effect on cationic dyes.
Cationic products
These are mostly condensation products of urea with formaldehyde or dicyandiamide, ethoxylized fatty amino derivative or conversion products of polyurethanes or protein hydrolizates.
They have a fixing effect and increase the depth of shade of anionic dyes, and a leveling effect on cationic dyes. If used in anionic dyeing excessive amounts should be avoided at all costs because this could cause stripping of the dye instead of a deepening or fixation of the shade. These cationic auxiliaries should be added only to a completely exhausted dye-baths in order to avoid precipitation with the dye. For safety reasons it is recommendable to use a separate intermediate bath and keep the pH value constantly below 4.0.
Nonionic products
These products are mainly ethoxylizing products on the basis of fatty alcohols or nonyl phenols. They promote penetration and levelness of dyes. They should not be used in larger quantities because of their surface-active properties which would give the leather excessive hydrophilicity or wettability.
Amphotric products
These products have both anionic and cationic groups in the molecule. The cationic group is active with low pH values; the anionic group is active with high pH values. Thus it is possible to influence depth of shade, absorption rate, penetration, levelness and exhaustion of the bath by regulation of the pH value.
Special dyeing auxiliaries
These products include penetrators used for spray staining, foams inhibiting agents, resisting agents for drum effect dyeing on one side, thickening agents for dyeing by curtain coater, tray staining or brush staining as well as polyamides to improve light fastness and fastness to migration of metal complex dyes.