1. Dispersion stability of disperse dyes:
The disperse dye is poured into water and then dispersed into fine particles, the particle size distribution is expanded according to the binomial formula, and the average value is 0.5 to 1 micron. The particle size of high-quality commercial dyes is very close, with a high percentage, which can be indicated by the particle size distribution curve. Dyes with poor particle size distribution, with coarse particles of different sizes, also have poor dispersion stability. If the particle size greatly exceeds the average range, recrystallization of tiny particles may occur. Due to the increase in recrystallized large particles, the dye is precipitated and deposited on the wall or fiber of the dyeing machine.
In order to make the fine dye particles into a stable water dispersion, there must be sufficient concentration of boiling dye dispersant in the water. The dye particles are surrounded by the dispersant, so that the dyes are not brought close to each other, preventing mutual aggregation or agglomeration. The charge repulsion of the anions helps to stabilize the dispersion. Commonly used anionic dispersants include natural lignin sulfonates or synthetic naphthalene sulfonic acid-based dispersants: there are other non-ionic dispersants, most of which are alkylphenol polyoxyethylene derivatives, which are specially used for synthetic paste printing.
2. Factors affecting the dispersion stability of disperse dyes:
Impurities in the original dye may adversely affect the dispersion state. The change of dye crystals is also an important factor. Some crystal states are easily dispersed, while others are not easy. During the dyeing process, the crystal state of the dye sometimes changes.
The dye is dispersed in the aqueous solution. Due to the influence of external factors, the stable state of dispersion is destroyed, which may cause the increase of dye crystals, particle aggregation and flocculation.
The difference between aggregation and flocculation is that the former can disappear again, is reversible, and is dispersed by stirring, and the flocculated dye can no longer restore a stable dispersion. The consequences caused by the flocculation of dye particles are: the generation of color points, slow coloration, reduced color, uneven dyeing, and staining in the dyeing tank.
The factors that cause the instability of the dye dispersion are roughly as follows: the quality of the dye is poor, the temperature of the dye is too high, the time is too long, the pump speed is too fast, the pH is low, the auxiliary agent is improper, the fabric is not clean, etc.
3. Test of dispersion stability:
A. Filter paper method:
With 10 g/L disperse dye liquor, add acetic acid to adjust the pH. Take 500 ml with #2 filter paper on a porcelain funnel and observe the fineness of the particles. Another 400 ml was taken in a high-temperature and high-pressure dyeing machine for a blank test, heated to 130°C, kept for 1 hour, cooled down, and then filtered with filter paper to compare the changes in dye particle boiling. The dyeing solution heated at high temperature is filtered, and there is no color point on the paper, indicating good dispersion stability.
B. Colour pet method:
Dye concentration 2.5% (weight to polyester), bath ratio 1:30, add 10% ammonium sulfate 1 ml, adjust to pH 5 with 1% acetic acid, take 10 grams of polyester knitted fabric on the porous wall, and circulate inside and outside the dye liquor In a small prototype of high temperature and high pressure dyeing, the temperature is raised to 130°C at 80°C, kept for 10 minutes, cooled to 100°C, washed with water and dried, and observed for dye condensation on the fabric.
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