Why do color spots appear in disperse dyeing

Causes of scattered dyeing spots and spots

There are two kinds of color spots and spots produced by the high temperature and high pressure dyeing machine when dyeing polyester knitted fabrics:

1. The color spots and spots caused by the condensation of dyes can be repaired with a repair agent or stripped and re-dyed;

2. Color spots and stains that are difficult to remove due to the production of oligomers in the fiber.

Cause Analysis

1.Pre-treatment

In many operations, the pre-treatment of polyester dyeing is not paid enough attention, and the inferior degreaser is slightly processed or not processed at all, and the operator suspects improper operation after the dyeing quality problem occurs. In fact, the by-products of polyester in the production of raw materials and the oil in the weaving process are likely to cause dyeing quality problems, such as color patterns, color differences, color spots, stains, etc., so pre-treatment must be carried out before dyeing, and the appropriate selection The degreasing agent is heated to 90°C for 10 minutes and then washed with water.

2. The choice of dyes and auxiliaries

 Improper choice of dye

Generally, when dyeing dark colors, because the dye particles have more chances of thermal collision under high temperature dyeing conditions, the dye molecules are prone to re-agglomeration to produce dye spots and color spots. At the same time, improper use of a large number of fillers used in dyes will also produce stains and color spots.

Improper choice of additives

Poor quality dispersants will condense on the surface of the fabric together with the impurities in the fiber and the dye vat at high temperatures to cause color spots and stains. The mixed use of different ionic additives is prone to conflict and demulsification, which will cause precipitation on the fabric, resulting in color spots and dye spots.

Fabric gram quality and grey fabric capacity

When dyeing in the same dyeing machine, high-gram-quality knitted fabrics are not easy to enter the fiber due to the tight structure, and the gram-mass is 300g/m2. The above knitted fabrics are more prone to dye stains and color spots than sparse and light knitted fabrics of about 200g/m2; when the cylinder gray fabric is too much, it will cause poor operation and produce dye spots and color spots.

Bath ratio

The dyeing bath ratio is small, and the probability of thermal collision of dye particles in the high-temperature and high-pressure dyeing machine is relatively increased, which is easy to produce dye spots and stains.

Measures to prevent color spots and spots

1. Strengthen the pre-dyeing treatment

The grey fabric is treated with 100% NaOH 3% and surface active detergent 1% before dyeing, and treated at 130°C for 60 min, with a bath ratio of 1:10 to 1:15. The pre-dyeing method has a certain corrosive effect on the polyester fiber, but it is extremely beneficial to the removal of oligomers. For polyester filament fabrics, it can reduce "aurora", and for short fibers, it can improve the phenomenon of pilling.

2. Control the dyeing temperature below 120℃, and adopt the appropriate dyeing method with carrier, which can reduce the production of oligomers and obtain the same depth of dyeing.

3. Adding dispersing protective colloid auxiliary agent during dyeing can not only produce leveling effect, but also prevent the precipitation of oligomers on the fabric.

4. After dyeing, the dye liquor will be discharged from the machine rapidly at high temperature. The discharge time is up to 5 minutes. Because the oligomer is evenly distributed in the dye liquor at a temperature of 100～120℃, it is easy to accumulate and precipitate in the dyeing when the temperature is below 100℃. Material. The disadvantage is that some heavy fabrics are prone to wrinkles.

5. Dyeing under alkaline conditions can effectively reduce the formation of oligomers and remove the residual oil on the cloth surface. But the disadvantage is that dyes suitable for dyeing under alkaline conditions must be selected.

6. After dyeing, use reducing agent to clean, then cold, hot, cold, neutralized with acetic acid, and the other is clean with special acid reducing agent, which saves energy and has high efficiency.

7. The bath ratio of high-quality knitted fabric dyeing is above 1:10, and dyeing in an overflow dyeing machine with a thicker feeding tube is selected. If it is restricted by the machine, it must be dyed in a small liquor ratio dyeing machine to appropriately reduce the volume of cloth to ensure the running speed of the fabric.

8. For some dyes that are sensitive to metal ions, such as red 3B (red 60), soft water must be used for production to prevent color spots and stains.