The poor water solubility of disperse dyes is almost entirely dependent on the dispersant that coats them to form hydrophilic dye colloidal particles before dispersing the dispersant in water. However, during the dyeing process, due to the shear force of the dyeing solution and the high temperature of the dye colloidal particles, the "binding energy" between the dye and the dispersant will gradually decrease, and even a part of them will be destroyed. The repulsive force of water will gather each other, making the tiny dye crystal particles gradually larger. The lighter ones will reduce the brightness of the color and the fastness of dyeing. If the aggregation is serious, it will gather with the polyester oligomers and suspended solids in the dyeing liquor to form a tar-like substance, which adheres to the fabric and forms a tar spot that cannot be eliminated.
In order to solve such problems, in addition to choosing dyes with low aggregation tendency, the most important method is to add a high-temperature dispersion leveling agent during the dyeing process. There are three types of dispersing and leveling agents commonly used in the market.
1. Anionic dispersion leveling agent
This type of dispersion leveling agent usually has two disadvantages. First, the "binding energy" between it and the dye grains is low. Therefore, the dispersion ability is better at low temperatures. However, with the increase of temperature and the intensification of thermal movement, the originally formed dyed colloidal particles are easily broken and lose dispersion stability. Second, the adsorption of dyes lacks slow dyeing effect, and it also lacks promotion effect on interface migration.
2. Non-ionic dispersion leveling agent
This type of dispersing leveling agent, due to the lack of repulsive force of the same charge in the outer layer of the colloidal particles formed with the dye, is not as good as the anionic leveling agent, but because it can combine with the dye to form an unstable polymer It releases slowly during the dyeing process, so this type of dispersing and leveling agent has both dispersion stabilization and slow dyeing and migration functions. However, when the amount is too large, the color of the fabric will be affected, and the color will be low.
3. Anionic/non-composite dispersion leveling agent
This kind of dispersing and leveling agent is a compound of anionic and non-ionic surfactant. Has a good synergistic effect. Since the colloidal particles formed by the two and the dye have an electric double layer, the protection effect on the dye crystal particles is stronger and the dispersion liquid is more stable. It also has better slow dyeing and migration functions, and has a relatively small impact on dye uptake.
Obviously, it is better to use anionic/nonionic high-temperature dispersion leveling agent.