Why do polyester choose disperse dyes to dye at 130℃.?

1. Various synthetic fibers have different physical and chemical properties, so the requirements for dyes are also different. Generally speaking, the polarity of the dye, the size and shape of the molecular structure must be compatible with the polarity and physical structure of the fiber. The basic component of polyester is polyethylene terephthalate, which is a high-molecular polymer with good linearity. There are no side chains and side groups on the molecular chain, only ester groups with less polarity. Except for the end groups, There are few hygroscopic centers, so the hygroscopicity is poor.

2. Polyester is a thermoplastic fiber, and its microstructure presents amorphous and crystalline regions, of which the amorphous region accounts for 40%. The structure of the amorphous region is compact, the micro gaps between the fiber molecules are small, and the amorphous region is disperse dyes. It is the main hydrogen bond bonding site, so the resistance of disperse dyes to diffuse into the polyester fiber at room temperature or low temperature is very large, and it is almost impossible to enter the fiber. The Tg (glass transition temperature) of crystalline and oriented polyester increases with the increase of fiber crystallinity. When the polyester is heated to above Tg, the molecular segments inside the amorphous zone move, and the micro gaps between the fiber molecules increase and increase. When a certain temperature is reached, the instantaneous gap formed by the movement of the fiber molecular chain segment will increase, so that the dye molecules can enter the fiber, and the dye uptake rate and dye uptake rate will increase significantly. Due to the tight structure and high Tg of polyester, it needs to be dyed at a higher temperature.

3. In the dyeing process, a type of dye that is dyed in a dispersed state in the dye liquor by means of a dispersant, so it is called disperse dye. The molecular structure of disperse dyes does not contain water-soluble groups, such as sulfonic acid groups, carboxylic acid groups, etc., so it is difficult to dissolve in water and is difficult to ionize in water. It is a non-ionic dye; but there are some polar groups in the molecule, such as hydroxyl Because of the existence of these polar groups, the dye can be dissolved in water in a small amount of monomolecular state at room temperature, and its solubility is equivalent to 0.01% of direct dye. When the temperature is increased, the general solubility will be Increase.

Therefore, the choice of disperse dye for polyester dyeing is determined by the physical and chemical properties of polyester fiber and the characteristics of disperse dyes. The main reason for choosing 130℃ dyeing is the physical and chemical properties of polyester fiber. Secondly, it is related to the solubility of disperse dyes and dyeing equipment. It doesn't matter much.