When the dyeing defect is caused by the uneven absorption of the leuco vat dye by the textile material, the correction of this defect becomes necessary. If these uneven defects are not obvious, the corrective method is to evenly distribute the color, including in a bath containing sodium hydroxide and sodium hydroxide, at a relatively high temperature, the dye on the material Restore again. In the presence of certain leveling agents used as retarders in vat-like dyeing, the degree of leveling obtained depends on the type of dye, the type of dyeing material, and the concentration of the leveling agent used. Usually. Increase the leveling agent, increase the degree of peeling, although this is different with the dye. During this process, partial peeling occurs, and most of the peeling dye remains in the bath. Therefore, it is necessary to re-dye from a fresh bath containing the newly-distributed dye amount of the reduced chromatin body to obtain the desired color and luster.
From the perspective of peeling, vat dyes can be divided into three categories.
1. Those dyes, for which leveling agents such as Dipersol VL mainly have a stripping effect, and the dyes removed from the fiber remain in the solution.
2. Those dyes have a stripping effect on the leveling agent. However, the removed dyes may partially re-dye the fibers.
3. Those dyes mainly have level dyeing effect on the auxiliary agent, and almost all the removed dyes are re-dyed to the fiber.
When all peeling is required, Lissoamine V (I.c.I.) can be used in a bath of sodium hydroxide-sodium hydroxide. This stripping agent is described as a cationic active compound. Some vat dyes are completely removed by using this reagent, almost giving a white material. In other cases, considerable peeling occurs, leaving a light swirling color. Re-dyeing on this can be done satisfactorily. Lissolamine V has no harmful effect on fibrous fibers.
The aqueous solution of polyvinylpyrrolidine (PVP) has a strong affinity for leuco vat dyes. This combination, between PVP and leuco vat dye, leads to the formation of a very stable cation-anion complex. In this way, there is no simple way to disassemble the complex and it is impossible to remove the dye. Restained. PVP is sold under different trade names, such as Albigen A (BASF). It is light yellow (or colorless), weak cationic liquid (with 30% active material specified), or light yellow or white powder. And it is stable to hard water, acid, alkali, etc. usually encountered in textile processing. When PVP is used in a stripping bath containing sodium hydroxide and sodium hydroxide, it can reduce the stripping duration and increase the bath temperature, which has a significant effect. It is controlled by the following factors:
a) The resistance of the dye to peeling;
b) Sensitivity of leuco dye to high temperature;
c) Depth of color.
When the dark color is peeled off, the amount of PVP may have to be increased, but it should not exceed 3 g/L (30% of the active compound). If a higher amount is used, the PVP dye complex will precipitate and deposit on the fiber.