(1) Physical properties of disperse dyes:
Wetting, dispersibility, particle fineness, dispersion stability, etc. These properties will affect the preparation of the dye solution and are the main factors for the formation of dyeing spots.
(2) High temperature dispersion stability of disperse dyes:
Represents the dispersing, agglomerating or decomposing state of dyes during high-temperature and high-pressure dyeing, and is the main cause for the formation of dye spots, floating color on the surface, and contamination of the cylinder.
(3) High temperature dyeability:
i. Coverage: Polyester fibers have undergone various heat treatments during the manufacturing process, resulting in uneven physical structures such as fiber crystallinity, distribution and molecular orientation, resulting in differences in dye uptake, resulting in so-called stripes, warp Shadow. (The property of covering the dyed flowers due to uneven fiber structure is called hiding.)
ii. Dyeing migration: It refers to the migration of dyes between fibers due to raising the temperature or adding auxiliaries after the dyes are dyed on the fibers. Dyes with good migration properties are easier to obtain level dyeing, so good or bad migration is an important factor for level dyeing. Generally, E-type disperse dyes have good dyeing properties, while S-type disperse dyes have poor dyeing properties.
iii. Dyeing rate:
The dyeing process of disperse dyes on polyester fibers is divided into three stages:
a. Disperse dyes diffuse to the fiber surface in a dispersed state or a slightly melted state and a dissolved state.
b. Disperse dyes are adsorbed on the surface of polyester fibers.
c. Disperse dyes diffuse into the polyester fiber.
Therefore, the high-temperature dyeing speed of disperse dyes has a complex relationship with the solubility, adsorption and diffusivity of the dye. In order to obtain a good leveling effect, the dyeing rate of the dye with a large dyeing rate should be selected. dyes with similar dyeing speed (that is, good compatibility) should be selected during color matching.
iv. Promotion rate:
When dyeing dark colors, dyes with high lift rate should be selected, otherwise the utilization rate of dyes will not be high.
(4) Adaptability to process factors:
i. Selection of dyeing auxiliaries: In the dyeing process, in order to improve the dyeing performance of dyes, dyeing auxiliaries are usually added. The auxiliaries use anionic and non-anionic leveling agents, and the dosage is 0.5g/L-1.0g /L, if the dosage is too high, the dispersibility at high temperature will decrease.
ii. Selection of dyeing bath ratio: In high temperature and high pressure dyeing, the change of bath ratio will affect the dyeing rate, especially the coverage. The dyes with good migration, high solubility, and high affinity for water have a large dependence on the liquor ratio, and should be strictly controlled to prevent batch difference.
iii. Selection of pH value of dyeing bath: water for dyeing, auxiliaries, alkali agent left in fabric pretreatment and auxiliaries added during dye manufacture all have a certain influence on pH value. Too high pH value will cause some disperse dyes. The discoloration is caused by the hydrolysis of the molecular structure, and the pH is generally controlled between 4.5-5.5.
iv. Selection of dyeing water:
If hard water is used or metal ions Ca2+, Fe3+, Fe2+, etc. are mixed into the dyeing liquid, the color of the dyeing material will be dull, so the hardness of the dyeing water is controlled within 100PPM.
(5) The choice of temperature during high temperature and high pressure dyeing:
When disperse dyes are dyed at high temperature and high pressure, the temperature is generally controlled at 130°C. Dyes with low temperature sensitivity, such as E type or SE type, although the temperature changes greatly, then their dye uptake changes very little, so not only good dyeing reproducibility can be obtained, but also better leveling dyeing can be obtained Effect. The dyeing temperature should be strictly controlled in addition to the heating process and heat preservation, and attention should also be paid to the cooling process, otherwise it will easily lead to batch differences. For this reason, dyes with more consistent temperature sensitivity should be selected when color matching, especially when color matching of different types of dyes.