How do disperse dyes work?
2022-05-10
Because polyester fiber has the characteristics of strong hydrophobicity, high crystallinity and alignment, small fiber micro-gap and not easy to wet and bulk, it is difficult to make the dye enter the fiber in the form of single molecule to complete the dyeing of polyester, according to the conventional method. Therefore, a special dyeing method is required. The methods used are carrier method, high temperature and high pressure method and high temperature hot melt method. These methods use different conditions to expand the fibers and increase the space between the fiber molecules. At the same time, additives are added to increase the diffusion rate of the dye molecules, so that the dye molecules continue to diffuse into the expanded and enlarged fiber spaces. Intermolecular attraction and hydrogen bond fixation complete the dyeing of polyester. Because the solubility of disperse dyes in water is extremely low, it is necessary to rely on the addition of dyes and dispersants in the solution to form the dye liquor. In order to prevent the hydrolysis of disperse dyes and polyester under the action of high temperature and alkali, the dyeing of disperse dyes often needs to be carried out under weak acid conditions.
1. Vector staining method
The carrier dyeing method is carried out by heating under normal pressure. It uses some chemicals that are direct to dyes and fibers. When such chemicals enter the interior of polyester during dyeing, the dye molecules are also carried in at the same time. This chemical is called carrier or dye carrier.
The principle of using a carrier to dye polyester is that there is a large intermolecular attraction between the benzene ring in the polyester and the aromatic nucleus in the dye molecule, and the polyester can absorb simple hydrocarbons, phenols, etc., and these chemicals become the carrier. Due to the interaction between the carrier and the polyester, the molecular structure of the polyester is relaxed, the fiber gap increases, and the molecules easily enter the fiber. At the same time, because the carrier itself can directly attract the fibers and dye molecules, it can not only help the dye dissolve, bring the dye single molecule to the fiber surface, increase the concentration of the dye on the fiber surface, but also reduce the surface tension of the fiber, so that the moving The dye molecules quickly enter the fiber void area, which improves the diffusivity of the dye molecules and promotes the combination of the dye and the fiber, thereby completing the dyeing step. After dyeing, the carrier is completely removed by alkaline washing. Commonly used carriers are o-phenylphenol, biphenyl, methyl salicylate, etc. Most of them are toxic and harmful to the human body, so they have been rarely used, so here is only a general introduction.
2. High temperature and high pressure dyeing method
The high temperature and high pressure dyeing method is carried out in a humid and hot state under high temperature and pressure. The dyeing rate is very slow within 100℃. Even if it is dyed in a boiling dyebath, the dyeing rate and dyeing percentage are not high, so the pressure must be below 2atm (2.02×105Pa), and the temperature of the dyebath can be increased to 120～130℃, due to the increase of temperature, the segments of fiber molecules move violently, resulting in more and larger transient pores. At this time, the diffusion of dye molecules also increases, which increases the diffusion rate of dyes to the interior of the fiber, making dyeing possible. The rate is increased until the dye is exhausted and the dyeing is completed.
The high temperature and high pressure dyeing method of disperse dyes is an important method, which is suitable for low temperature dyes with low sublimation fastness and small molecular weight. Dyeing with this type of dye has good levelness, bright color, good hand feel, and high degree of fabric penetration. It is suitable for small batch and multi-variety production, and is often used in the dyeing of polyester-cotton blended fabrics.
The high-temperature and high-pressure dyeing of disperse dyes can be carried out on high-temperature and high-pressure jiggers and jet and overflow dyeing machines. It is suitable for dyeing deep and intense colors. The pH value of dyeing is generally controlled at 5-6, and acetic acid and ammonium dihydrogen phosphate are commonly used to adjust the pH value. . In order to keep the dye bath stable, dispersant and high temperature leveling agent should be added when dyeing.
1. Vector staining method
The carrier dyeing method is carried out by heating under normal pressure. It uses some chemicals that are direct to dyes and fibers. When such chemicals enter the interior of polyester during dyeing, the dye molecules are also carried in at the same time. This chemical is called carrier or dye carrier.
The principle of using a carrier to dye polyester is that there is a large intermolecular attraction between the benzene ring in the polyester and the aromatic nucleus in the dye molecule, and the polyester can absorb simple hydrocarbons, phenols, etc., and these chemicals become the carrier. Due to the interaction between the carrier and the polyester, the molecular structure of the polyester is relaxed, the fiber gap increases, and the molecules easily enter the fiber. At the same time, because the carrier itself can directly attract the fibers and dye molecules, it can not only help the dye dissolve, bring the dye single molecule to the fiber surface, increase the concentration of the dye on the fiber surface, but also reduce the surface tension of the fiber, so that the moving The dye molecules quickly enter the fiber void area, which improves the diffusivity of the dye molecules and promotes the combination of the dye and the fiber, thereby completing the dyeing step. After dyeing, the carrier is completely removed by alkaline washing. Commonly used carriers are o-phenylphenol, biphenyl, methyl salicylate, etc. Most of them are toxic and harmful to the human body, so they have been rarely used, so here is only a general introduction.
2. High temperature and high pressure dyeing method
The high temperature and high pressure dyeing method is carried out in a humid and hot state under high temperature and pressure. The dyeing rate is very slow within 100℃. Even if it is dyed in a boiling dyebath, the dyeing rate and dyeing percentage are not high, so the pressure must be below 2atm (2.02×105Pa), and the temperature of the dyebath can be increased to 120～130℃, due to the increase of temperature, the segments of fiber molecules move violently, resulting in more and larger transient pores. At this time, the diffusion of dye molecules also increases, which increases the diffusion rate of dyes to the interior of the fiber, making dyeing possible. The rate is increased until the dye is exhausted and the dyeing is completed.
The high temperature and high pressure dyeing method of disperse dyes is an important method, which is suitable for low temperature dyes with low sublimation fastness and small molecular weight. Dyeing with this type of dye has good levelness, bright color, good hand feel, and high degree of fabric penetration. It is suitable for small batch and multi-variety production, and is often used in the dyeing of polyester-cotton blended fabrics.
The high-temperature and high-pressure dyeing of disperse dyes can be carried out on high-temperature and high-pressure jiggers and jet and overflow dyeing machines. It is suitable for dyeing deep and intense colors. The pH value of dyeing is generally controlled at 5-6, and acetic acid and ammonium dihydrogen phosphate are commonly used to adjust the pH value. . In order to keep the dye bath stable, dispersant and high temperature leveling agent should be added when dyeing.
