Development Of Reactive Dyeing Technology
Development Of Reactive Dyeing Technology
In recent years, the new dyeing process of reactive dyeing has developed rapidly. The current reactive dyeing processes include: reactive dye pad dyeing and short steaming dyeing, reactive dye dip dyeing short process, reactive dye low temperature and cold pad batch dyeing, and neutral fixing agent dyeing , Reactive dye low-salt and salt-free dyeing, use "substitute salt" reactive dye low-salt dyeing, reactive dye low-alkali and neutral dyeing.
1.Reactive dye pad dyeing and wet short steam dyeing. Pad dyeing is one of the important dyeing methods of reactive dyes. However, after the fabric is impregnated with the pad dye solution, intermediate drying is required to facilitate subsequent steaming, or to increase the processing speed during baking and fixing. And reduce the dye hydrolysis, and obtain high fixation rate and color fastness. Intermediate drying will bring many problems: energy consumption, a large amount of heat energy is consumed when drying wet fabrics to evaporate water; dyes are prone to migration during drying, resulting in color difference and reduced color fastness, and dyeing reproducibility is also poor ; Drying after dipping the dyeing solution not only adds a processing procedure and is inconvenient to manage, but also when the dry fabric is steamed, the dyes and chemicals must absorb water to dissolve again. Dry fabric will emit heat when it absorbs moisture, resulting in overheating, which is detrimental to dyeing and fixing. Therefore, steaming is a long-term goal that people pursue. It is very difficult to steam dyed fabrics. Firstly, the wet fabric is directly steamed. Because the moisture absorbs heat and evaporates, the fabric heating rate is slowed down, which prolongs the steaming and fixing time; secondly, the fabric contains a lot of moisture (usually the liquid rate after padding is 60% to 70% ), in the process of steaming and heating, the reactive dyes on the fabric will undergo a large amount of hydrolysis, which reduces the fixation rate and color fastness. The moisture on the fabric has many states, which can be roughly divided into two categories: the fiber absorbed water and the free water on the fabric. The chemically bound water that absorbs the water (mainly bonded to the fiber molecular chain through hydrogen bonds) is also called unfreeze water (its freezing point is much lower than 0°C). This part of the water content is not much, and the probability of reaction with dyes is also less, because It cannot move freely. A considerable part of the absorbed water is in the fiber pores. The fiber pores are very thin. This part of the water is not easy to flow freely, so it is also called bound water. Its reaction rate with dyes is also low. Although part of the free water outside the fiber is in the inter-fiber capillary and is not easy to flow due to the capillary effect, most of it can flow freely. The water in these two states outside the fiber is easy to react with the dye. When the dye is high, it is required that the dye does not undergo a large amount of hydrolysis, and the fast fixation reaction occurs after reaching a sufficiently high temperature. For this reason, the alkali agent suitable for use should be weaker, or the alkalinity should not be strong when the moisture content of the fabric is high (including the mixed alkali of baking soda or soda ash and some alkali agents), if low alkali or neutral fixation is performed The effect will be better. Studies have found that the use of neutral fixing agent to fix the color has a good effect at 120～130℃ or 180℃.
2.Short reactive dye dip dyeing process shortens the reactive dye dyeing process, improves production efficiency, saves energy, saves water, and reduces sewage discharge. Wet short steam dyeing is a short process dyeing process of pad dyeing. The short-flow dyeing process of dip dyeing is also the focus of research in recent years, improving equipment, shortening the dyeing time, and more importantly, reasonable control of the dyeing process, and automatic computer control can shorten the dyeing, fixing and washing time. In recent years, many dye production companies have developed reactive dye rapid dyeing processes in order to promote their products. The basis of the fast dyeing process is to select dyes reasonably according to their characteristics, and to shorten the entire dyeing time under the premise of ensuring good leveling and reproducibility. Take controlled metering and continuous addition, which can shorten the time. Greatly save dyes, alkalis and salt, and reduce sewage discharge. Some processes also automatically control the washing after dyeing to further save water and reduce sewage. Some dye or equipment manufacturers have also developed a variety of dedicated controlled dyeing software.
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