Uneven dyeing: What causes it?

Introduction: 

Uneven dyeing is the most feared problem during the dyeing process. It not only wastes a lot of fabric but also requires more textile auxiliaries for repair, leading to delayed delivery. This is a major challenge for many dyeing factories.

What forms does uneven dyeing take? It manifests as stripes, wavy stripes, square patterns, and other variations in color depth on the fabric surface. In severe cases, white spots may appear. Minor defects may be difficult to detect with the naked eye, but color differences can be observed after folding.

So, what causes uneven dyeing? What are the reasons?

(1) Causes:

1. Improper operation, knotting during dyeing, power outage during dyeing;

2. Temperature rises too quickly, insufficient holding time;

3. Improper pH adjustment of the dye bath;

4. Incomplete rinsing after boiling and refining, resulting in uneven pH on the fabric surface;

5. Poor dye compatibility;

6. Improper dosage of auxiliaries;

7. Excessive oil content in the greige fabric, not completely removed after boiling and refining;

8. Excessive dyeing amount and length;

9. Dyeing machine operating speed too slow;

10. Blockage in the circulation system, excessively slow flow rate, unsuitable nozzles.

(2) Identification Methods:

1. Severe color difference, partial undyed areas, and stripes are caused by knotting.

2. Irregular rope-like color patterns are caused by excessively high temperature and insufficient holding time.

3. Impure color with small color difference between the front and back is caused by improper dye mixing or insufficient leveling agent dosage. 4. Color differences between different pages are caused by poor boiling effect or excessive storage time of the semi-finished product after boiling.

4. Fabrics that appear colorless after dyeing but show streaks or fading after setting are caused by unclean water after dyeing, insufficient reduction rinsing, or uneven airflow from the setting machine nozzles.

(3) Preventive measures:

1. For semi-finished products after relaxation and boiling, the water quality must be clean, and the pH value of the fabric surface should be controlled between 7 and 7.5. The boiling process must be completed within the shift, and the dyeing process should also be carried out within the same shift.

2. During dyeing, first add dyeing acid (or acetic acid) and run for 5 minutes. Then add dissolved auxiliaries. Adjust the pH value of the dye to 4.5-5, and then dye according to the program sheet or by inputting the required temperature and time parameters into the computer.

3. The processing volume of dyed fabrics should be determined according to different machine types and fabric thicknesses. Generally, the fabric throughput should be controlled within two parameters: firstly, approximately 80% of the original design throughput; and secondly, each cycle time should not exceed 3 minutes.

4. Change nozzles according to fabric thickness and time to prevent knotting caused by nozzles that are too large or unevenly stacked, and to prevent claw marks caused by nozzles that are too small.

5. The selection and suitability of dyes are crucial. It is recommended to mix dyes of the same type. For dyes that dye too quickly, the temperature profile should be adjusted and the amount of leveling agent increased.

6. The selected dispersants and leveling agents must remain stable under high temperature and pressure, have good heat resistance, and avoid generating tar-like compounds.

7. Establish a post-dyeing semi-finished product inspection system to prevent unqualified products from entering the next process and reduce wasted labor time.