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how to use disperse dyes
Aug 24, 2018

Because polyester fibers have the characteristics of strong hydrophobicity, high crystallinity and alignment, small fiber gap and difficult to wet and expand, it is difficult to dye polyester fibers in the form of single molecule, so it is necessary to adopt special dyeing methods. There are three dyeing methods: carrier method, high temperature and high pressure method and high temperature hot melt method. These methods make use of different conditions to expand the fiber and increase the interstitial space between the fiber molecules. At the same time, additives are added to improve the diffusion rate of the dye molecules, so that the dye molecules diffuse into the expanded and enlarged interstitial space of the fiber, and the fiber is fixed by intermolecular gravitation and hydrogen bonding to complete the dyeing of polyester fiber. Because the solubility of disperse dyes in water is very low, it depends on adding dyes and dispersants in the solution to form a dye solution. In order to prevent the hydrolysis of disperse dyes and polyester fibers under the action of high temperature and alkali, the dyeing of disperse dyes is usually carried out under weak acid conditions.


1. Carrier staining

Carrier dyeing is carried out under normal pressure. It is the use of some of the dyes and fibers have a direct chemical, when such chemicals into the polyester fiber when dyeing, dye molecules are also carried into the same time, this chemical called carrier or dye carriers.

The principle of polyester dyeing with carriers is that the benzene ring in polyester fiber has a strong intermolecular attraction with the aromatic nucleus in the dye molecule, and the polyester fiber can absorb simple hydrocarbons, phenols and so on. These chemicals become carriers. Because of the interaction between the carrier and the polyester fiber, the molecular structure of the polyester fiber is relaxed, the void of the fiber is enlarged, and the molecules are easy to enter the fiber. At the same time, because the carrier itself can produce direct attraction with the fiber and dye molecules, it can not only help to dissolve the dye, bring the dye monomolecule to the fiber surface, increase the concentration of dye on the fiber surface, but also reduce the surface tension of the fiber, so that the moving dye molecules quickly enter the fiber gap region, and improve the dye content. The rate of diffusion of molecules promotes the combination of dyes and fibers to complete the dyeing step. After dyeing, alkali washing is used to completely remove the carrier. Commonly used carriers are o-phenylphenol, biphenyl, methyl salicylate, etc., because most of them are toxic, harmful to human body, has been rarely used.


2. High temperature and high pressure dyeing

High temperature and high pressure dyeing is carried out under high temperature and pressure. The dyeing rate of dyes is very slow within 100 C. Even in a boiling dyeing bath, the dyeing rate and percentage are not high. Therefore, the dyeing bath temperature can be raised to 120 130 C when the pressure is below 2 ATM (2.02 105 Pa). As the temperature increases, the chain segment of the fiber molecules moves violently, resulting in more instantaneous pores. And the larger the dye molecule, the faster the diffusion of dye molecules, increased the diffusion rate of dye to the fiber, so that the dyeing rate increased until the dye was absorbed and finished dyeing.

High temperature and high pressure dyeing with disperse dyes is an important method, suitable for low temperature dyes with low sublimation fastness and low molecular weight. The dyeing of polyester-cotton blended fabrics with this kind of dyes has good levelness, bright color, good handle and high core penetration. It is suitable for small batch and multi-variety production and is often used for dyeing polyester-cotton blended fabrics.

High temperature and high pressure dyeing with disperse dyes can be carried out on high temperature and high pressure dyeing machine and jet and overflow dyeing machine. It is suitable for deep color. The pH value of dyeing is generally controlled between 5 and 6. Acetic acid and ammonium dihydrogen phosphate are often used to regulate the pH value. In order to maintain the stability of dyeing bath, dispersants and high temperature levelling agents are needed in dyeing fashion.


3. Hot melt dyeing

Hot melt dyeing of polyester/cotton fabrics with disperse dyes is similar to that of padding dyeing. The dyed fabrics are first dried with padding solution and then hot melted. The dyes deposited on the fabrics can diffuse into the fibers in a single molecule form and finish the dyeing of polyester in a very short time under the action of high temperature of 200 C. If polyester-cotton blended fabric, can be hot-melt treatment so that the dye on the cotton in the gas phase or contact transfer to polyester. Hot melt dyeing is the main method of dyeing polyester-cotton blended fabrics. Continuous pad dyeing is the main method with high production efficiency, especially suitable for mass production. The disadvantage of hot-melt dyeing method is that the equipment occupies a large area, at the same time, it has certain restrictions on the use of dyes, and the utilization rate of dyes is lower than that of high temperature and high pressure 


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