Polyester fabrics are widely used in various textile and clothing fabrics due to their high strength, good elasticity, excellent wear resistance, good dimensional stability, and good wrinkle resistance. Disperse dyes have a small molecular weight and are slightly soluble in water, making them ideal dyes for polyester fabrics. Disperse dyes are commonly used to dye polyester, and there are three methods: hot melt dyeing, high-temperature and high-pressure dyeing, and carrier dyeing. The method we commonly use now is high-temperature and high-pressure dyeing. In order to prevent dyeing defects such as color spots and spots during the dyeing process, we must pay attention to the following aspects:
1、 Selection of dyes
Disperse dyes are difficult to dye polyester fibers at low or normal temperatures, and only when the glass transition temperature of polyester is exceeded, the dye quickly dyes.
If the initial dyeing rates of several selected color matching dyes differ too much, it is easy to form local competitive dyeing at this time and cause color distortion. So when choosing dyes, the initial dye uptake of several color matching dyes should be similar.
If the selected dye has a high initial dye uptake rate, it can also easily cause color distortion. In general, when dyeing polyester with dispersed materials, dyes with similar initial dyeing rates, slow initial dyeing rates, good quality, and similar color compatibility should be selected. Using E-type for light colors, SE type for medium colors, and XF or SF type for dark colors can basically meet the requirements of deep, medium, and light dyeing of polyester, and the effect is good.
2、 Selection of additives
Due to the dyeing characteristics of polyester fibers, they have basic requirements for high-temperature leveling agents; On the other hand, due to the differences in variety and specifications of polyester fiber semi-finished products, there are corresponding personalized requirements for high-temperature leveling agents. Therefore, high-temperature leveling agents for polyester dyeing should not only have basic properties such as slow dyeing and transfer dyeing under high temperature conditions of 130 ℃, but also have specialized properties that meet the dyeing characteristics of various semi-finished polyester fibers.
3、 Control of heating rate
The heating rate is also an important factor in the formation of color spots. After reaching the glass transition temperature of polyester, if the heating is too fast, the dye will quickly dye onto the fiber, forming localized dye spots and color blocks. If the initial dye uptake rate is high, the color spots will be more severe. So, in the process of dyeing and heating up, it can be divided into three stages and controlled by different heating rates. The first stage is to raise the temperature from room temperature to 75 ℃. During this stage, the dispersed dye will hardly dye the fibers, and a faster heating rate of 2-3 ℃ can be used. The second stage is from 75-110 ℃, which is the fastest stage for dye dyeing, and slow heating should be used, preferably controlled at 0.8-1 ℃. The third stage is from 110-130 ℃, during which the dye dyeing will be exhausted, and a heating rate of 1.5-2 ℃ can be used.

4、 Other factors
For example, factors such as chemical composition, fabric capacity, bath ratio, pH value, cleanliness of the fabric, appropriate overflow speed, and fabric running speed also have a certain impact on the production of color spots. Dispersed dyes are generally treated with 40 ℃ warm water, stirred evenly, filtered, and then injected into the dyeing tank; It is best not to exceed the maximum fabric capacity of the dyeing tank in terms of the dyeing amount; A bath ratio of 1:8-12 is more suitable; The pH value should be controlled between 4-4.5; When dyeing, it is required that the fabric surface be clean and the pH value be neutral; In addition, it is necessary to adjust the running speed of the fabric in the cylinder to regulate the overflow speed reasonably.
Finally, if slight color spots are found after dyeing, a certain amount of repair agent can be added and transferred for color correction.