When the fiber is immersed in a solution at a certain temperature, the dye moves from the water to the fiber, when the amount of the dye in the water decreases gradually. After a period of time, the dye is balanced. The dye that is reduced in water is the dye that moves to the fiber. When the fiber is removed at any time, even if twisted, the dye still remains in the fiber and does not simply make the dye completely out of the fiber. The dye, which combines in the fiber, is called dyeing. If the sponge is immersed in the dye, the dye solution can also enter the sponge, but even if the time is long, the concentration of the dye solution does not change. When the sponge is taken out and twisted, the dye and water are squeezed out from the sponge at the same time, so the sponge is not stained.
(1) the basic dyeing process is based on the view of modern dyeing theory that dyes are able to dye fibers and have certain fastness on the fabric, because there are various gravitational forces between the dye molecules and the fiber molecules, the dyeing principle and the dyeing process of all kinds of dyes, because of the characteristics of the dyes and fibers. There is a great difference and can not be generalized. But in terms of its dyeing process, it can be roughly divided into three basic stages.
1. when the fiber is put into the bath, the dye gradually spreads from solution diffusion to the surface of the fiber. This process is called adsorption. As time goes on, the dye concentration increases gradually, but the dye concentration in the solution decreases gradually, after a period of time, it reaches the equilibrium state. The reverse process of adsorption is desorption, and adsorption and desorption exist simultaneously in the dyeing process.
2. the dye diffused on the surface of the fiber diffused into the fiber until the dye concentration of all parts of the fiber tended to be uniform. Because the concentration of dye adsorbed on the surface of the fiber is greater than that of the dye in the fiber, the dye diffuses from the fiber surface to the inside of the fiber. At this point, the diffusion of the dye destroys the initial adsorption equilibrium, and the dye in the solution will continue to adsorb to the surface of the fiber, and the adsorption and desorption will balance again.
3. fixation is the process of combining dye with fiber, and the way of binding is different with dye and fiber.
The above three stages often exist at the same time in dyeing process and can not be completely separated. It is only in a certain period of time that a process is dominant.
(two) the fixation of dyes in fibers, the fixation of dyes in fibers can be regarded as the process of maintaining dyes on fibers. The principles of fixation between different dyes and different fibers are different. Generally speaking, there are two types of dyes fixed on fibers.
1. pure chemical fixation refers to the chemical reaction between dyes and fibers, and the dye is fixed on fibers.
For example, reactive dyes dyed cellulose fibers, forming ether bond bonds with each other. The general formula is as follows:
DRX+Cell-OH - DR-0-Cell+HX
DRX: reactive dye molecules
X: active group
2. physical and chemical fixation, because of the attraction between the dye and fiber and the formation of hydrogen bonds, make the dye fixed on the fiber. Many dyes that dye cotton, such as direct dyes, sulphur dyes, vat dyes, and so on, all depend on this attraction and are fixed on the fibers.
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