What are the causes of stains and spots on the fabric?

The problem of dyeing defects in oligomers is relatively common, which seriously affects the quality of products, and at the same time, it will contaminate the equipment and be difficult to clean. Here is a summary of the problem:

1. Definition

Oligomer, also known as oligomer, oligomer, short polymer

It is a low-molecular substance with the same chemical structure as polyester fiber and it is a by-product in the polyester spinning process. Generally, polyester contains 1% to 3% of oligomers.

Oligomers are polymers composed of fewer repeating units, and their relative molecular mass is between small molecules and macromolecules. Its English "oligomer" prefix oligo comes from the Greek ολιγος, meaning "some". Most polyester oligomers are cyclic compounds formed by three ethyl terephthalates.

2. Influence

The cloth surface produces color spots and spots; yarn dyeing produces white powder

When the temperature exceeds 120°C, the oligomer can dissolve in the dye bath and crystallize out of the solution, combining with the agglomerated dye. When cooled, it is deposited on the surface of machinery or fabrics to form color spots, color spots and other defects. And disperse dyes are generally kept at 130 ℃ for about 30 minutes to ensure the depth and fastness of dyeing. Therefore, as a solution, the light color can be kept at 120 °C for 30 minutes, and the dark color must be pre-treated before dyeing. In addition, dyeing under alkaline conditions is also an effective method to resolve oligomers.

3. Comprehensive measures

01. Before dyeing the grey fabric, use 100% NaOH 3%. Surface active detergent 1%. Treated at 130 ℃ for 60min, the bath ratio is l:10~l:15. The pre-dyeing treatment method has a certain erosive effect on the polyester fiber, but it is extremely beneficial to the removal of oligomers. For polyester filament fabrics, "Aurora" can be reduced, and short and medium fibers can improve pilling.

02. Control the dyeing temperature below 120 ℃, and adopt the appropriate carrier dyeing method to reduce the production of oligomers and obtain the same dyeing depth.

03. Adding dispersing protective colloid auxiliaries during dyeing can not only produce a leveling effect, but also prevent oligomers from precipitating on the fabric.

04. After dyeing, the dye liquor is quickly discharged out of the machine from high temperature, and the discharge time is at most 5 minutes. Because the oligomers are evenly distributed in the dye solution at a temperature of 100-120 °C, they are easy to accumulate and precipitate on the dyed material when the temperature is below 100 °C, but some heavy fabrics are prone to wrinkles.

05. The use of alkaline conditions for dyeing can effectively reduce the formation of oligomers and remove the residual oil on the cloth surface, but the dyes suitable for alkaline conditions must be selected.

06. Wash with reducing agent after dyeing, add 32.5% (380Be) NaOH 3-5ml/L, hydrosulfite 3-4g/L, treat at 70℃ for 30 min, then wash with cold, hot, cold, neutralize with acetic acid .

4. For yarn white powder

1) The thorough method is the high temperature drainage method

For example, the drain valve is opened immediately after the constant temperature of 130 °C (120 °C is also possible, but it cannot be lower, because 120 °C is the transition point of polyester glass)

2) For factories that cannot discharge liquid at high temperature, Oligomer detergent can be used to replace the detergent in the reduction cleaning process, but the effect is not 100%

After dyeing, wash the tank diligently, and wash the tank once after about 5 tanks of medium and dark colors.

If the current liquid dyeing machine has a lot of white powder, the first priority is to wash the tank.