Causes And Solutions To The "color Stain" Problem

        Color stains are regular, similar in shape and size, or irregular, with shapes and sizes that are not fixed, and are the same color as the dyed fabric. Once this type of defect occurs, it is difficult to repair and has a great impact on the quality of the dyed product, so it must be taken seriously.

Causes

The causes of color stains are roughly the following three aspects.

1. ● The already free dye molecules will recrystallize during the heating (or cooling) process to form new crystals;

2. ●The already free dye molecules will gradually adsorb on the crystal surface of the original dye during the heating (or cooling) process, causing the original dye crystals to grow from small to large;

3. ●The dye particles in the free and semi-free state will directly collide and aggregate into larger dye aggregates without dissolving. These larger dye aggregates are one of the important factors causing color stains.

4. During the color development (or fixation) process of dyeing, strong aggregation forces are generated between dye molecules, causing dye aggregation, which can also cause color stains. Its characteristics are distribution and irregularity.

2. Tarring of dyes 

The so-called tarring of dyes refers to the process in which dye particles and surfactants condense into coal tar-like substances under high temperature conditions. 

The following 4 factors usually cause dye tarring

     ●Poor pretreatment and insufficient purification. The oil agents (lubricants, emulsifiers, antistatic agents, etc. added during the spinning or weaving process) and grease stains (sticky dirt during the processing process) contained in the fabric are not cleaned up and are brought into the dye bath. When dyeing under high temperature conditions, once these water-repellent oil stains come into contact with the dye particles, they adsorb each other, accumulate larger and larger, and finally form a tar-like substance.

    ●When non-ionic auxiliaries or non-ionic and anionic composite auxiliaries (such as refining agents) with a turbidity point lower than the dyeing temperature are used for pre-treatment, if they are not washed clean, they will be brought into the dye bath in large quantities. As the temperature of the dye increases, the non-ionic component gradually loses its water solubility, or separates from the anionic component to form hydrophobic oil particles. At this time, the dye particles in an unstable state in the dye bath facilitate the precipitation of these hydrophobic oil particles. At this time, the dye particles in an unstable state in the dye bath adsorb each other with these hydrophobic oil particles to form a thick colored tar-like substance that adheres to the fabric and produces color stains.

    ●When dyeing with non-ionic and anionic composite auxiliaries such as high-temperature leveling agents, if the dosage is too high (above 2g/L) or mixed with dyes at high concentrations and directly added to a water bath above 90°C, the binding force between the non-ionic component and the anionic component is weak, and the turbidity point of the non-ionic component is not high enough, which often causes the non-ionic component to be freed from the colloid particles of the anionic component and aggregate with the dye to form a tarry substance.

    ●When anionic surfactants such as diffusants are used for dyeing, if the auxiliaries are not well dissolved, the granular dyes and auxiliaries will adsorb each other. Once put into the pot, a viscous paste will form, which will adhere to the fabric and produce color stains.

3. Color lakes stick to fabrics.

During the dyeing process, due to improper operation, foaming of auxiliaries and other factors, the dye liquor often has color lakes floating on the surface. If these color lakes are not treated and are brought to the fabric by the dye liquor foam, it will cause sticky color stains.

Solution

1. Strengthen the pre-treatment of fabrics.

The oil or oily dirt on the fabric has a strong affinity for hydrophobic synthetic fibers such as polyester, so it is not suitable to be washed. Especially during pre-setting, the oily dirt penetrates into the fiber, making washing more difficult. The fabric must be cleaned in the pre-treatment of desizing, scouring, bleaching, etc. When using the refining and cleaning process for some fabrics containing more chemical fibers such as polyester, high-efficiency refining detergents and washing equipment must be used. However, the auxiliaries must be washed clean after cleaning, otherwise it is easy to form tar-like substances with the dye and stain the fabric.

2. Strictly prevent dye coagulation

Commonly used dispersants have a good diffusion and stabilization effect on the dyes in the dye bath during the heating process. However, this diffusion effect often decreases with the increase of temperature, and its levelness (a comprehensive reaction of slow dyeing, migration, and covering) is also poor, and the color is not bright and pure enough.

The following three points must be paid attention to when using high-temperature leveling agents:

Correctly master the operation of chemical materials. The aggregation and association of disperse dyes is directly related to factors such as temperature, concentration, time, and auxiliaries.

Therefore, the following points should be noted when making the chemical:

     ●Use warm water below 50°C to make the chemical, and the temperature must not be too high. For example, the dispersion of S-3GFL is good below 50°C, but serious association precipitation will occur above 80°C.

     ●The amount of water used for chemical making should be as much as possible. If the bath ratio is too small, it will often reduce the dispersion effect of the dye. Practice shows that 1:10~15 is appropriate.

     ●Dispersants or leveling agents should be fully dissolved in warm water, and no granular or paste should exist.

Chemical making should not be too early, and it is best to use it as soon as it is made, otherwise, it will increase the tendency of dyes to associate. Regardless of dyes and auxiliaries, they must be filtered with a sieve before use.

3. Avoid and reduce the generation of lakes as much as possible. 

Chemical making should be carried out according to regulations. You can also add a certain amount of wetting and diffusing agent to help the dyes dissolve evenly and not produce lakes.

If you want to know more about dyeing solutions, please contact: info@tiankunchemical.com