What are the conditions of the cold pad dyeing process?

1 Dyeing mechanism requirements for dyes

1.1 The mechanism of cold pad dyeing is basically the same as that of continuous pad dyeing, and it is also divided into three stages: adsorption, diffusion and fixation. Cold pad dyeing is to expand the fibers through pad dyeing solution without heating, so that the dyes are transferred to the inside of the fibers, so the dyes are required to have good diffusivity and low fiber affinity and directness to ensure the fabric. Even dyeing is helpful to overcome the phenomenon of slight chromatic aberration. Because this process uses a large amount of alkaline agents, in order to take into account the stability of the dye liquor and the reaction speed, it is generally appropriate to select dyes with moderate reactivity.

Vinyl sulfone reactive dyes have moderate reactivity. They are vinyl sulfate compounds, which are soluble in water and do not show any activity in water. They are only active when an alkaline agent is added to form a reactive vinyl sulfone through acid and alkali. Activated dyes react with hydroxyl groups on cellulose to form ether bonds, which not only have high resistance to acid hydrolysis, but also play a major role in improving the fixation rate.

1.2 In the dyeing process, the formation of vinyl sulfone is controlled, so that the dye has sufficient time to diffuse into the fiber, so as to obtain better level dyeing and penetration dyeing effects, so vinyl sulfone type dyes are especially suitable for cold pad dyeing. Specific applicable vinylsulfone dyes include Remazol, domestic KN, Sumitomo Sumitomo, Diamina, and Celmazol. )dye. Others such as monofluoro-s-triazine type include Ciba refined Cibaclone F (Cibacrom F), difluoro-chloropyrimidine type is Clariant Daimian Li R/K (Drimarene), dichloro-s-triazine type There are MX (Procion), domestic X-type dyes, monochloro-s-triazine-type K-type dyes, vinyl sulfone and monochloro-s-triazine-type double-reactive group domestic ME dyes, etc.

(1) Among the reactive dyes, the price of vinyl sulfone type dyes has an absolute advantage. The cost of red, purplish red, brown, navy blue and black dyes in dyeing is 1/3 to 1/5 of other dyes, and the dyes are cold-rolled. Heap staining is preferred.

(2) Cold pad dyeing often requires stacking for several hours to twenty hours (depending on the type of dye) for color-fixing reaction. Commonly used KN vinyl sulfone reactive dyes are prone to hydrolysis with caustic soda. When pH>8, under the condition of 30～35℃, the hydrolysis rate is 0.1% in 5min, 1% in 10min, and 7.7% in 30min.

According to the determination and interpretation of reactive dyes expert Vikstaff, the reaction rate of reactive dyes on fibers exceeds the rate of reaction with water, and the increase of pH has little effect on the reaction rate. great relationship. For example, when the dye absorption rate is 10%, the reaction rate ratio of reactive dyes in fiber and water is 165, and when the dye absorption rate is 90%, the reaction rate ratio is as high as 497. According to this, it can be concluded that the dyes with high dyeing rate are selected, and the small dip tank is used to shorten the mixing time of the dye and the alkali agent in the dyeing tank. rate is also low.

(3) When dyeing and mixing, care should be taken not to mix the dyes with too much difference in the stability time of the alkali bath. If the dye with a stable time of 30min is mixed with the dyestuff of 5min, the disadvantage of color difference is prone to occur.

(4) The CP series reactive dyes of Kehuasu company cold pad heap dyeing. The reactive groups selected for the three primary colors of the CP series are mainly MCT+VS or VS+MCT+VS. The reactive groups are the same in the same group of three primary colors. In the MCT+VS combination, the benzene ring and ethyl ethyl sulfone sulfate are formed, and a conjugated system is at the same level.

(5) It is impossible to achieve instant padding and stacking in mass production. Even if the production is the most normal, it will take more than 7 minutes to fully consume the soaking tank (based on 35L capacity). The padding tank is all exchanged once, at least more than 20 minutes, and some preparations on the machine may be delayed during the initial start-up. The hydrolysis resistance of dyestuffs is a critical factor in order to make the main machine produce conforming to laboratory samples.