Reactive dyes have the same printing process as other dyes. After printing, they need to be steamed to fix or develop color. Therefore, the steamer is one of the main equipment for printing.
Depending on the type of fabric, commonly used steaming machines include reduction steaming machines and high-temperature bottomless steaming machines. Here, combined with the short-process wet steaming process of reactive dyes, we first briefly introduce the high-temperature and high-pressure bottomless steaming machines. introduce.
1. High temperature and high pressure bottomless steamer
As shown in Figure 3-7 This is a schematic diagram of a high-temperature bottomless steamer:
The steaming machine is characterized by a bottomless steaming box. The steaming temperature is around 100℃, the superheated steam temperature can reach 180℃, and the steam pressure is 784kPa (8kgf/cm2), which is suitable for steaming chemical fiber fabrics. There are equipment for extracting waste moisture on both sides of the lower part of the steamer. There is no air or water droplets in the steamer.
Due to the rotation of the guide roller, the fabric forms a long ring without tension and is suspended in the steamer. The bottomless steamer is composed of a sandwich top and a sandwich wall welded by multi-faceted flat plates. The saturated steam is generated from the heated sandwich wall and injected from top to bottom from the angle. The excess steam comes from the suction pipes on both sides of the bottom and the waste. The moisture is discharged together. The hanging situation of the fabric in the bottomless steamer is shown in Figure 3-8.
2. Mechanism of wet short steaming process of reactive dyes
The wet short steaming process of reactive dyes is On the premise of selecting appropriate dyes and color-fixing alkali agents, special steaming equipment is used to heat the fabric as quickly as possible. After the moisture on the fabric quickly drops from 60% to 70% to an appropriate level, wet steaming or steaming is performed. , making the dye fix quickly.
The wet short steaming process quickly reduces the moisture content of cotton fabrics to about 30%. When the viscose fabrics drop to about 35%, the moisture on the fabrics is basically bound water and There is chemically bound water and very little free water, so at this time, it can not only ensure that the pores in the fiber are filled with water, but also facilitate the dissolution, diffusion and adsorption and fixation of the dye in the pores, and reduce the amount of hydrolyzed dye.
The short-process wet steaming process of reactive dyes uses a far-infrared radiator installed at the entrance of the reaction steamer to preheat the wet fabric impregnated with the dyeing liquid, so that the fabric can quickly Ground temperature rises, and is heated for 2 to 3 minutes by a mixture of a small amount of steam and dry hot air in the reaction box to achieve the purpose of color fixation.
3. Advantages of the short-flow wet steaming process for reactive dyes
The new wet-short steaming process and Compared with the traditional process, the color giving rate of reactive dyes can be improved, and the fabric can be fully penetrated to obtain uniform color.
According to relevant data, the color yield of the conventional baking process of reactive dyes is about 70% of that of the conventional steaming process, while the color yield of the wet short steaming process is higher than that of the conventional steaming process. The color yield of the steaming process is 10%-20% higher. Therefore, the wet short steaming process has the advantages of short process, high color fixation rate, bright color, good reproducibility, energy saving, and dye saving.
4. Short-process steaming process of reactive dyes
In order to quickly remove moisture from the fabric To evaporate and maintain it at a suitable level, in addition to supplying normal pressure saturated steam, the wet short steaming steamer also needs to have additional equipment to quickly heat up the steam.
It often uses steam/air mixed gas or high-temperature superheated steam as the heating medium. The former steaming temperature is 120~130℃ and the time is 2~3min; the latter steaming temperature At around 180°C, the time is only 20~75s, and the fixation rate under this condition is relatively high.
5. Issues that should be paid attention to in the short-flow steaming process of reactive dyes
(1) Selection Suitable dyes and corresponding steaming and baking temperatures. There are many kinds of reactive dyes suitable for wet short steaming process. Lower temperature steaming and baking is suitable for reactive dyes with strong reactivity, such as dichloro-s-triazine and fluorochloropyrimidines; high-temperature steaming and baking is suitable for dyes with slightly lower reactivity, including commonly used dual-reactive dyes.
(2) Choose a suitable fixing agent. Regardless of the type of dye, it is required that when the moisture content of the wet fabric is high during steaming, the dye will not undergo a large amount of hydrolysis, and a rapid color fixation reaction will occur only after reaching a sufficiently high temperature.
Therefore, a weakly alkaline alkali agent should be used to fix the color, or the alkaline agent should not be strong when the moisture content of the fabric is high. Alkali agents that meet this requirement include baking soda or soda ash mixed with some alkali agents. If low-alkali or neutral color fixing is performed, the effect will be better. Studies have found that using neutral fixing agents to fix colors has good color fixing effects whether at 120~130℃ or around 180℃. </p
