Analysis of reactive dyes and dyeing technology

Reactive dye is a water-soluble dye containing one or more active groups in the molecule, and react to form a covalent bond with the hydroxyl groups of cellulose fiber and protein fiber and polyamide fiber on the amino under appropriate conditions. The production of reactive dyes is simple, the price is low, the color is bright, the chromatography is complete, and the color fastness is better. Reactive dyes have been developed rapidly since the introduction of commercial dyes in 1956, and new varieties have been emerging. Reactive dyes can be used for dyeing cellulose fiber, protein fiber and polyamide fiber. Dyeing and finishing of silk with reactive dyes not only improves the color fastness of dyed silk, but also makes it more colorful.

Reactive dyes are generally adsorbed, diffused and fixed in three stages, the first two are the upper dyeing stage, and the other is the fixation stage (reactive group in the dye reacts with the fiber in the alkaline condition). Reactive dyes generally have little affinity to fiber, and the dye uptake is low. Therefore, it is necessary to add salt to the dyeing bath. Due to the low rate of direct dyeing of reactive dyes, a large amount of salt can be added to improve the dyeing rate. Therefore, the cost of dyeing is increased and the pollution emission is increased.

In recent years, a number of dye manufacturers have introduced low salt and even salt free reactive dyes. At present, the only defect of reactive dyes is the hydrolysis of dyes. The fixation of reactive dyes should be done under alkaline conditions, and the alkali can also promote reactive dyes to react with water, so that the dyes lose their activity. This is because the hydrolysis of the dye will be adsorbed on the fabric, in the process of washing is not easy to clean.

Reactive dyeing method using dip including one bath one-step and one bath two step process and two bath, one bath method especially one bath one-step dye utilization rate is low, while the two bath method of dye hydrolysis is less, higher utilization rate of dye. Reactive dyes can also be baked. Rolling steaming or baking process of fabric dyeing with reactive dyes, the method can make the direct lower reach leveling effect, and is easy to wash and hydrolyzed dyes. The reactive dyes can also be used in low temperature dyeing or cold rolling process for dyeing fabrics.

In the dyeing process of reactive dyes, the final cleaning process is very important. If the fabric is not clean, it will seriously affect the color fastness of the fabric. In fact, not only will affect the quality of printing and dyeing dye hydrolysis, and storage stability, dye padding liquid or paste stability, thermal dye dissolution process of reactive dye concentration will affect its application performance. The active atoms or groups of the original reactive dyes are replaced by hydroxyl groups, and their diffusion and adsorption properties are similar to those of the original reactive dyes. As a result, it can diffuse into the fiber as well as the reactive dye and absorb it on its surface. In the final stage of alkaline dyeing, reactive dyes for the reaction with water and fiber consumption, the formation of a new balance, which means the distribution of hydrolyzed dyes in the dye bath and fiber with reactive dye in neutral solution is similar to that of the.

At this stage, the fiber also contains a considerable proportion of the chemical binding dye. In general, an average of 70% reactive dyes were fixed, while the remaining 30% were hydrolyzed.

In the actual dyeing system, the main factors affecting the hydrolysis of dyes are: pH value, temperature, dye concentration, electrolyte concentration. Among them, the dyeing bath pH value in cellulose fiber dyeing is not more than l0 ll, the pH value of cellulose fiber all contact hydroxyl has been ionized, and then increase the pH value will only lead to the hydrolysis of dyes. Increased temperature also increased the hydrolysis of reactive dyes. Increasing the concentration of the dye in the solution will cause the dye to condense, thus slowing down the rate of dye hydrolysis.

As the reactive dyes dyed fabric after fixing more or less a considerable part of the hydrolysis of dyes, therefore, the color after washing is particularly important. In order to promote the reaction between dye and fiber, it is necessary to select the appropriate catalyst and water washing process in the process of washing. In addition to the introduction of a number of new water additives, cationic surfactants can also be used for reactive dye dyeing process, it can reduce the production of hydrolyzed dyes stained, such as for reactive dyes, you need to increase the amount of. In reactive dye printing, most of dyes in solid color phase is transferred to the fabric, but a part of the unfixed dyes and colorants in fabric is still on, such as cleaning, will affect the fabric color fastness and handle. In the process of printing after the water, the fabric from the supernatant of the dye will be dipped into the fabric of the white or light colored parts.

Therefore, after printing, not only to remove the water from the fixed parts of the dye, paste and chemical additives, but also to prevent the re staining of the dye to the non printing parts.

The main factors influencing the effect of the reactive dye printing fabric are: the amount of non fixed dye, the washing property of the unfixed dye, and the tendency of the dye. The first factor is mainly related to the preparation of printing paste dyes and auxiliaries. Depends on second factors on dye dissolution and diffusion properties in the specific system and affinity, in general, to increase the solubility and diffusion of dyes, and reduce dye affinity to fiber, after washing is more favorable for printing. Therefore, may adopt the following measures to improve the cleaning efficiency without dye fixation: to reduce the concentration of the dye in the cleaning liquid, increase the fiber and the cleaning solution between the concentration gradient to accelerate diffusion; increase temperature accelerated diffusion; the diffusion has the highest and the lowest fiber affinity dye; use special detergent and chelating agent.

The following measures can avoid the fabric during washing process is not part of printing color: low affinity dyes; prevent water color lotion concentration is too high; the process condition is not conducive to the leveling and dye; by increasing the dyeing rate of process conditions; avoid using the conditions of increasing direct dyes.

                                                                                                                                                       By Emily