High temperature levelling agent, soluble in water and general organic solvents, has excellent dye dispersibility, early retarding property and can be used with dyes at the same time.

The performance of high temperature levelling agent is mainly measured by three indexes: retarding, dispersivity and migration. Retarding refers to dyeing rate, or dyeing speed. The faster the dyeing speed is, the easier the fabric is uneven. While it shouldn’t completely prevent the fabric from being colored, which will affect the final dyeing rate. Dispersivity is the ability to distribute dyes evenly in water bath so that the dye can be evenly absorbed by fiber or fabric. Migration refers to the transfer of disperse dyes to the lower concentration of the dye through levelling agent.
 
High temperature and high pressure dyeing is an important dyeing method of polyester fiber. On the one hand, because of dyeing properties of polyester fiber, it has basic requirements for high temperature levelling agent. On the other hand, due to the differences between polyester fiber semi-finished products, it has corresponding personalized requirements for high temperature levelling agent.
Therefore, except for the basic properties such as retarding and transfection in 130 ℃ high temperature conditions, high temperature leveling agent for polyester dyeing also should have special properties in accordance with the characteristics of all kinds of semi-finished products dyeing polyester fiber. 

The basic properties of high temperature levelling agent for polyester dyeing

Hydrophobic disperse dyes are suitable for the dyeing of hydrophobic dacron fibers, but the hydrophobic property can lead to low water solubility, which can cause difficulties in dyeing process with water as medium. For this disperse dye, the mixture of the dispersant, which is not less than the proportion of the dye, can be used to improve the solubility of the dye, and the general dye: filler = 1:1 ~ 1.5. Adding high temperature leveling agent in dye solution can further promote  suspended diffusion state of disperse dye particles and maintain stability of dye molecules uniform distribution, so it can play a secondary and supplementary role in dye solubility. It is especially important to dye light color. Because dyeing light color need less dyes which means less dispersing agent in dyes, so adding high temperature leveling agent can assist in dissolving dye.

In general, the retarding function of the levelling agent is the key to dyeing evenly. However, in the case of dispersing dyes dyeing polyester fiber, the levelling agent needs to have strong migration performance. Because in this process, chemical reactions do not happen, just dye disperse on polyester fiber. But the polyester fiber compact structure and extremely fine shape and surface characteristics such as crystal layer block the diffusion of disperse dye. The migration performance of levelling agent can make up for the inadequacy of retarding performance in this aspect, especially after 130 ℃ heat preservation stage of dyeing. At this time, dyes in the dyeing bath mostly have been on fiber, retarding function has been basically completed, so migration function at this stage is the key, it will further promote and guarantee the effect of fabric overall leveling.