Agglomeration of Dyes
Due to the direct collision of dye molecules, larger dye aggregates (or dye associations) are aggregated. These larger dye aggregates are deposited on the fabric during the dyeing process, resulting in color stains.
When dyeing: the free dye molecules will recrystallize during the heating (or cooling) process to form new crystal grains; the free dye molecules will gradually adsorb on the crystal surface of the original dye during the heating (or cooling) process. The original dye crystals are changed from small to large; the dye particles in the free and semi-free state will directly collide and aggregate into larger dye aggregates without being dissolved. These larger dye aggregates are one of the important factors causing stains. In the process of color development (or color fixation) of dyeing, strong polymerization force is generated between the dye molecules, which causes the dye to aggregate and also causes color stains. Its characteristics are distributed and irregular.
Tarification of Dyes
The so-called taring of dyes refers to the process of agglomeration of dye particles and surfactants into coal tar-like substances under high temperature conditions.
There are usually four factors that cause dye taring:
① Poor pretreatment and insufficient purification. The oils (additional lubricants, emulsifiers, antistatic agents, etc.) and grease (sticky stains during processing) contained on the fabrics are not cleaned and brought into the dye bath under high temperature conditions. During dyeing, once these water-repellent oil stains come into contact with the dye particles, they will adsorb to each other, the accumulation will increase, and finally a tar-like substance will be formed.
② When using non-ionic auxiliaries or non-ionic and anionic composite auxiliaries (such as refining agents) with cloud point lower than the dyeing temperature as pretreatment, if the washing is not clean, it will be brought into the dye bath in large quantities. When 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 that are in an unstable state in the dye bath will adsorb with these hydrophobic oil particles to form a thick colored tar-like substance, which adheres to the fabric and produces color stains.
③ When using non-ionic and anionic composite auxiliaries such as high-temperature leveling agent for dyeing, if the dosage is too high (above 2g/L) or mixed with dyes in high concentration, and directly added to the water bath above 90 ℃, due to the non-ionic The binding force between the component and the anionic component is weak, and the cloud point of the non-ionic component is not high enough, which often causes the non-ionic component to be freed from the colloidal particles of the anionic component and aggregate with the dye to form a tared substance.
④ When anionic surfactants such as diffusing agents are used for dyeing, if the auxiliary agent is poorly dissolved, the granular dye and auxiliary agent will be adsorbed to each other. Once put into the pot, it will form a viscous paste and adhere to the fabric. resulting in stains.
Fouling of the fabric by the lake
During the dyeing process, due to factors such as improper operation and foaming of auxiliary agents, the dyeing liquid often has color lakes floating on the surface. If these lakes are not treated, they will be brought to the fabric by the dyeing liquid foam, which will cause sticky stains. stains.