Reactive Dyes for Printing

Reactive dyes maintain an important position in dyes for cellulose fiber printing. The selection of such dyes should pay attention to three aspects: lifting power, compatibility and easy washing. The lifting force is printed with different dye concentrations to obtain different depths. After reaching a maximum concentration, the apparent printing depth is no longer significantly improved. The linear part of the curve below this concentration is the best use range.

The compatibility of dyes is an important feature of print reproducibility. The compatibility of the mixed dyes depends on the sensitivity of the dyes to the steaming state. Even if the steaming temperature and humidity change, whether the color change will be caused by the difference in the amount of color supplied. It also depends on the sensitivity of the dye to changes in the amount of alkali and urea.

The ease of washing of dyes is determined by the fixation rate and re-staining properties of the dyes. Therefore, reactive dyes with high fixation rate, low affinity and high diffusivity should be used for printing.

In addition, it has higher solubility (>100g/1) at room temperature, which is convenient for the preparation of dark-colored printing pastes, as well as higher fastness to sunlight and washing.

Domestic and foreign dye companies have a set of P-type (Priming) special dyes for printing, which are used by printing factories according to the above requirements. Domestic companies such as Wonder Company, Jinji Company, and Longsheng Company provide P-type reactive dyes, but for the sake of confidentiality, the "Dye Index" number is not provided. The P-type reactive dyes of famous foreign dye companies, in addition to the trade name, also have the reference C.I. number. It is a pity that the C.I. structure number and molecular structural formula can be found only for the disclosed trichromatic dyes, but most of the dyes have the C.I. number, but no C.I. structure number. It shows that the molecular structural formula of reactive dyes for printing cannot be disclosed so far.

It can be known from the molecular structural formula that, except C.I. Reactive Blue 21 is vinyl sulfone type and C.I. Reactive Green 19 is bis-chloro-s-triazine, all are mono-chloro-s-triazine, namely K-type reactive dyes. The biggest disadvantage of this type of dye is that the fixation rate is very low, only 50%~60%, and C.I. reactive blue 14, 15 is only about 40%. However, the difference between the dye uptake rate and the fixation rate is large, resulting in a lot of floating color, which is difficult to wash and affects mutual staining and whitening. Although the linker imino was changed to an alkylamino. Due to the steric hindrance of the alkyl group (methyl or ethyl), the coplanarity between the precursor and the s-triazine active group is destroyed, and the directness of the dye is reduced, which is beneficial to the easy washing of the hydrolyzed dye.

Among them, C.I. Active Green 19 is bis-monochloro-s-triazine, and the color fixing rate reaches 80%, which is beneficial to the washing of floating color. In fact, in the 1980s, Shanghai Dyeing and Chemical Plant No. 8 created dual reactive groups of vinylsulfone group and monochloro-s-triazine, namely M-type reactive dyes for printing. Therefore, the new reactive dyes for printing can also be dual reactive groups. The linking group is an alkylamino group, and the fixation rate, lifting power and easy washing can be improved.