Polyester fibers have a compact structure, and it is usually difficult for dyes to diffuse and penetrate into their fibers. Therefore, carrier dyeing and high-temperature high-pressure dyeing are often used. The carrier method is generally applied to the dyeing of wool polyester blended yarn and its fabrics, while polyester dyeing mostly uses high-temperature and high-pressure methods; Various dyeing defects often appear in high-temperature and high-pressure dyeing. Summarize some possible causes and solutions through production practice for reference.

There are two main types of defects in polyester dyeing: dyeing uneven and lots defects.

01

Dyeing uneven

There are many types and forms, and there are also many reasons.

  1. White dots

There are white spots on the dyed polyester fabric, which are caused by the absence of coloring or coloring at the white spots.

The reasons that affect the non coloring and non coloring of polyester are:

(1) The alkaline agents or wool oil added to polyester fabrics during spinning and weaving are uneven;

(2) Polyester fabrics are stained with oil or other stains during handling or other processes before dyeing.

  1. Dot patterns and colors

Dye particles appear on polyester fabrics after dyeing.

The reason for the occurrence is:

(1) From the perspective of raw materials, polyester contains a certain amount of low molecular weight polymers (with a content of 0.2~0.3%), which will precipitate from the fibers during dyeing. The amount of precipitation increases with the increase of temperature and time; It is slightly soluble in water and dispersed in the dyeing bath at high temperatures of 120 ℃. At 80 ℃, it will condense and adhere to the fibers to form crystals, producing colored spots.

Solution:

Add an appropriate amount of dispersant to the dyeing solution to maintain the dispersion of oligomers. After dyeing is completed, the dye solution must be cooled to 80 ° C before being discharged. Rinse with hot water above 80 ° C instead of cold water.

(2) From the analysis of dyes, some dispersed dyes have poor dispersion stability. If the dyeing solution temperature is high, condensation will occur. The dyes cannot enter the fibers and can only adhere to the surface of the fibers, resulting in staining spots and spots.

To solve this problem, it is necessary to choose dyes with good dispersibility or add dispersants with good high temperature resistance and stability, so that the dyes form dispersed small particles in the dyeing bath, thereby preventing the aggregation of dye particles. It is worth noting that when using dispersants, the influence of their dosage on the color yield should be considered. When dyeing light colors, the amount of dye used is small, and more dispersants should be added; When dyeing dark colors, it can be added less or not.

(3) From the analysis of dyeing water, some dispersed dyes are more sensitive to dyeing water, especially in water with higher hardness. Dye molecules combine with calcium and magnesium ions in water to form insoluble substances that accumulate on polyester fabrics, forming color stains.

(4) From an operational perspective, the most likely reason is uneven chemical composition. Due to the low solubility of dispersed dyes, they need to be thoroughly dissolved into a molecular dispersed state through pulping to prevent aggregation on the fiber surface and facilitate internal permeation and diffusion. Practice has shown that the dye is stirred into a paste using water several times that of the dye. This means that the ratio of the feed to water should be increased, and then heated and hydrated, stirring for 10-15 minutes. At the same time, additives are added to accelerate the dispersion and dissolution of the dye, acid is added to adjust the pH value, and the dyeing tank is heated to 50-60 ℃. The dye is added quantitatively to make it flow evenly, and after running for about 10 minutes, the temperature is raised. This way, the dye will not form crystalline particles on the surface of the fiber due to insufficient chemical material and dye flowers.

(5) From the perspective of equipment analysis, it may be due to malfunction of the dyeing liquid circulation system in the dyeing tank or other factors that cannot achieve normal dyeing liquid circulation, uneven distribution of dyes in the dyeing bath, or uneven fiber absorption caused by “firewood and cloth wrapping” during the dyeing process. Therefore, it is necessary to regularly inspect the equipment and report for repair in a timely manner; Properly operate the dyeing machine to ensure its normal operation.

  1. Striped flowers

After dyeing, the polyester fabric shows a series of color patterns.

The reasons are as follows:

(1) From the perspective of raw materials, the quality of polyester is poor, and it is necessary to use better leveling agents to overcome this. In addition, it is also possible that polyester fabrics may become moldy due to rain or moisture during transportation and storage, which can affect coloring and cause color spots. Therefore, it is important to pay attention to the ventilation of the raw materials. Due to the low moisture absorption of polyester, this situation rarely occurs.

(2) From the analysis of dyes, some dyes have poor solubility, which affects dyeing and produces color patterns. At this point, it is necessary to choose a dye with good color compatibility for re sampling.

(3) From a process perspective, in terms of heating rate, polyester fabrics tend to color slower when their glass transition temperature is below 80 ° C; After exceeding 80 ℃, the coloring speed increases rapidly. If the temperature rises too quickly at this time, it is easy to dye the flowers, so it is necessary to slow down the heating rate appropriately at 80-130 ℃. The empirical data is 1 ℃/min in the range of 80-100 ° C and 1-1.5 ℃/min in the range of 100-130 ° C.

In terms of insulation time, under the condition of not damaging the fibers, the insulation time must be sufficient, generally 45-60 minutes, to ensure uniform penetration and fixation of the dye. Furthermore, under high temperature conditions, the dyeing rate is particularly sensitive to temperature differences, especially for sensitive colors. If there is a temperature difference in the entire dyeing solution, it is easy to cause dyeing flowers. So during the high-temperature insulation stage, it is necessary to ensure even dyeing. If quality problems are often found in certain colors during production, it is recommended to implement segmented insulation in the production process to ensure sufficient even dyeing. It should be noted that the selection and dosage of additives are also important for the uniformity of dyeing. Under the condition of not affecting the color depth, additives should be used reasonably to achieve the goal of uniform dyeing.

(4) From an operational perspective, if employees do not follow the process and do not grasp the heating rate and insulation time well, it may cause dyeing flowers. So it is necessary to strictly operate the process, eliminate human factors, and improve the quality of dyeing.

(5) From the perspective of equipment analysis, factors such as damaged circulation pumps, slipping belts, and malfunctioning flow valve controls can all cause quality defects. So, it is necessary to regularly inspect and maintain the equipment to ensure its good operating condition.

02

Cylinder difference

The main reasons for cylinder difference are two factors: human factors and equipment factors.

  1. Human factors

As long as employees operate carefully, it can be avoided to a certain extent.

The main reasons are as follows:

(1) Inaccurate weighing of dyes;

(2) Inconsistent process operations, unstable pH control, and some dyes are sensitive to pH, which can easily cause cylinder differences when the pH deviation is large; Inconsistent heating rate and insulation time.

(3) The bath ratio is inconsistent, and the size of the bath ratio has a significant impact on the color depth.

  1. Equipment factors

The high temperature and high pressure dyeing method has a high pressure, which is caused by equipment malfunction. So, it is necessary to conduct more cyclic inspections on the equipment and promptly report any hidden dangers for repair.

03

afterword

In summary, the causes of quality defects in production are complex and require actual investigation and analysis as well as process investigation to accurately identify the root cause of the problem, identify the true problem, and make timely improvements to ensure dyeing quality.

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