Requirements of dyeing mechanism for dyes
1.1.1 The mechanism of cold pad-batch 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-batch dyeing is to expand the fiber through the pad dye solution without heating, so as to transfer the dye to the inside of the fiber. Therefore, the dye is required to have good diffusivity and low fiber affinity and directness to ensure the fabric Even dyeing should help to overcome the slight color difference of the head. Because this process uses a large amount of alkaline agents, in order to take into account the stability of the dye solution and the reaction speed, it is generally appropriate to select dyes with moderate reactivity. Vinyl sulfone reactive dyes have relatively moderate reactivity. They are ethylene sulfate compounds, soluble in water, and do not show any activity in water. Only when alkali agents are added, the reactive vinyl sulfone is formed through acid and alkali. The activated dye reacts with the hydroxyl group on the cellulose to form an ether bond. The ether bond has higher resistance to acid hydrolysis and also plays a major role in improving the fixation rate.
1.1.2 During the dyeing process, control the formation of vinyl sulfone to allow sufficient time for the dye to diffuse into the fiber to obtain a better level and penetrating effect. Therefore, vinyl sulfone dyes are particularly suitable for cold pad-batch dyeing. The specific applicable vinyl sulfone dyes include Dystar Remazol (Remazol), domestic KN type, Japan's Sumitomo Sumifix (Sumifix), Japan's Mitsubishi Diamina (Diamina), Japan's Mitsui Celmazol (Celmazol) )dye. Others such as fluoros-triazine type are Cibacrom F (Cibacrom F), difluoro-chloropyrimidine type are Clariant R/K (Drimarene), dichloro-s-triazine type There are h Neimen Procion 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 reactive dyes, vinyl sulfone dyes have an absolute advantage in price. The cost of red, claret, brown, navy, and black dyes in dyeing is 1/3 to 1/5 of other dyes. This dye is cold pad First choice for dyeing.
②. Cold pad-batch dyeing often requires stacking for several hours to twenty hours (depending on the type of dye) for fixing reaction. Commonly used KN-type vinylsulfone reactive dyes are prone to hydrolysis reaction when using caustic soda. When pH>8, under 30～35℃, the hydrolysis rate is 0.1% in 5min, 1% in 10min, and 7.7% in 30min. According to the measurement and explanation of the reactive dye expert Wikstaff, the reaction speed of reactive dyes on the fiber exceeds the rate of reaction with water. The increase in pH has little effect on the reaction rate. When the hydrolysis rate of the dye is related to the absorption of the dye Great relationship. For example, when the dye absorption rate is 10%, the reaction rate ratio of the reactive dye in the fiber to water is 165, and when the dye absorption rate is 90%, the reaction rate ratio is as high as 497. Based on this, it can be concluded that the use of dyes with high dye uptake and a small immersion tank can shorten the mixing time of the dye and alkali agent in the dye tank. Once the fabric is wound and stacked with the working solution for padding, it will be hydrolyzed. The rate is also very low.
③. When dyeing and mixing, you should be careful not to mix dyes with too big difference in alkali bath stability time. If the dyes with a stabilization time of 30min and dyes with a stabilization time of 5min are mixed together, chromatic aberration is prone to occur.
④ RGB series reactive dyes of cold pad batch dyeing by Tiankun Group. The reactive base selected for the three primary colors of the CP series is 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 conjugate system is at the same level.
⑤ It is impossible for mass production to achieve instant padding and stacking. Even if the production is most normal, the total consumption of the infiltration tank (in 35L capacity) will take more than 7 minutes. However, all the inside of the padding tank should be exchanged once, at least 20 minutes or more, and some preparation work on the machine may delay time during the initial start-up. The hydrolysis resistance of the dye is a key factor in order to make the large-scale machine produce in line with laboratory samples.