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Disperse Dyeing of Polyester Fiber and Its Solution

Sep. 23, 2020

After polyester knitted fabrics are dyed at high temperature and high pressure, the oligomers produced by the aggregation of fibers and dye molecules due to the high oil content of the grey fabric during weaving will cause color stains and seriously affect the quality of the products.

1 Polyester knitted fabric

Polyester is a hydrophobic fiber. The fiber lacks groups that can bind to dyes, and cannot be dyed with water-soluble dyes. It can only be dyed with non-ionic disperse dyes with low molecular weight, no strong ionic water-soluble groups and low solubility. Polyester has a compact structure and is dyed under normal pressure. It is difficult for the dye to diffuse into the fiber to dye the fiber thoroughly. Therefore, high temperature and high pressure dyeing is used.

2 Disperse dyeing

Disperse Dyeing is carried out under high temperature, pressure and humidity. The dye is a granular state with multiple single crystal molecules dispersed in an aqueous solution through a dispersant. Its dyeing rate is very slow within 100°C. Even if dyeing in a boiling dye bath, the dyeing rate and the dyeing percentage are not high, so The pressure must be below 2atm (2.02×105Pa), and the temperature of the dye bath can be increased to 120~130℃. Due to the increase in temperature, the segment of fiber molecules moves violently, resulting in more and larger instantaneous pores. At this time, the dye molecules The diffusion of the dye is also increased, increasing the diffusion rate of the dye into the fiber, and the dyeing rate is accelerated until the dye is exhausted to complete the dyeing.

Due to the low solubility of disperse dyes in water, the dyes in the dyeing liquor need to be dispersed in the dye bath as a suspension through a large amount of dispersant when dyeing polyester fibers. In order to achieve a better dyeing effect. Usually need to add a certain amount of dyeing auxiliaries. The main functions of these dyeing auxiliaries in the dyeing process are: increase the solubility of disperse dyes, promote the adsorption of disperse dyes on the surface of the fiber, plasticize the fiber or increase the degree of swelling, and speed up the disperse dye. The diffusion rate in the fiber improves the dispersion stability of the dye.

Generally, the auxiliaries used in high-temperature and high-pressure dyeing of polyester fibers contain a carrier that plasticizes the fiber, a surface active agent that solubilizes disperse dyes or stabilizes the dye suspension, and other dyeing auxiliaries play a very important role in the dyeing of polyester fibers.

Disperse Dyeing

Disperse Dyeing

3 Types of stains

There are several types of color points:

3.1 Color stains

The color is the same as the dyed color, darker, and the same thing as the print. Most of the things have front and back. Sometimes the stains are stained with dirt, which can be removed. Such color spots and stains account for more than 60% of the total. Most of them appear irregular, ranging in size from mung bean to soybean size, but in severe cases they have large fingernails.

3.2 Black spots

The main focus is on brown, including light brown, light beige, coffee, and dark brown. It is a small color dot the size of black sesame, as if a black oil-based pen has been clicked on the cloth.

3.3 Color points of dyed colors

The color point is darker than in the first case, and it is not too big. Sometimes it can be cut off. Generally, a cylinder of cloth has more on both ends and less in the middle.

These three types can be found when the cloth is out of the dye vat. It came out with a slight repair agent to repair the color, and a serious black.

3.4 Dispersive color points

There is also a black golden spot. The black golden spot does not appear when the cloth is produced. After the cloth is dried in a dryer, there will be golden yellow spots. Such yellow spots can be removed with alkali + degreasing agent. Especially when it is changed to black, it is more likely to appear, and it is scattered on the cloth.

4 Causes of color stains

4.1 Selection of additives

The emulsification stability of the bulking agent is not good, oily matter will precipitate at high temperature, and the dye will condense and appear color points. The oil stains on the fabric have not been cleaned up, and the bulking agent will be released during dyeing to condense the dye. It is recommended to add a high temperature resistant dispersant.

4.2 Uneven chemical materials and defoamers are generated after high temperature generates oil points

The dyestuff is not homogenized and filtered directly into the dyeing machine; when the temperature of the grey fabric in the dyeing vat reaches 80℃, it will foam the hanging cloth, and the defoamer will be produced when the operating temperature is too high.

4.3 Improper control of dyeing heating speed

Some dyes have poor dispersibility and improper dyeing temperature control. Too fast will cause dye points; dispersant or penetrating agent is not resistant to high temperature, resulting in secondary agglomeration of dyes to form dye points; some additives need to be added separately (high solid content) when adding additives, not operating as required The resulting suspension points combine with the dye to form dye points;

Some color points are very small and present in point-like distribution and can only be found by careful observation, and are different from the color of dyed cloth. That's because the dye itself contains insoluble substances, and the dispersion of these dyes is destroyed during the manufacturing process and cannot enter the fiber. This situation mostly occurs in light or brilliant colors; the diffusion effect of red dyes may not be good, and it needs to be solved by adding a diffusing agent.

If a leveling agent is added to the dyeing list, but a dispersing agent is not added, the dispersibility is not enough, the dyes will aggregate, and color spots will be produced. We are Disperse Dyeing supplier, if you are interested in our products, please feel free to contact us.