What Is Migration Of Color And Why Should It Be Minimized
Dye migration refers to the replacement of a compound within the material or from one material to another by diffusion at the molecular level. In other words, the compounds are able to make their way through the material to the new site, however far away that may be. Compounds are sometimes obliged to cross several materials or layers of differing natures before arriving at their end destination.
Non-fixed compounds do not have strong links with their environments. The fitting of a compound within its environment is determined by its ability to merge into the environment or fix to it.
Materials can be either donors or acceptors depending on what they are in contact with. The carriers that run the most are solvents, resins, and fat liquors. Humidity can also play the role of a carrier when it comes to water soluble and water absorbent compounds, except when they play the role of accelerating the process. The accelerators of migration are essentially heat and humidity.
The most common migrations:
- Dye migration from one material to another.
- Dye migration within the same material without distinction.
- Dye migration between different layers of the same material.
- Dye rising to the surface.
In the footwear industry, the occurrence of dye migration has become apparent through cases of dyes migrating from open pore leathers such as suede and nubuck leathers into light-colored outsole materials, primarily PVC and TR soles, which leads to discoloration.
In cases of dye migration it is not uncommon to observe that the bleeding color hue bears no resemblance to the original hue of the leather. The reason for this occurrence is the actual color consists of a blend of dyes. If one of the dyes is not fast to migration, then it can cause discoloration. This explains why, for example, a black leather can color another material green or red, or a green leather can be responsible for a brown discoloration. The intensity of the discoloration depends upon the concentration of the dye in the material. Such discolorations are observed most frequently in footwear made of suede or nubuck leather. These leathers are mostly through dyed, which requires a considerably greater quantity of dye than surface coloring. It may happen that a substantial proportion of the dye used is not bound to the leather fibers and thus constitutes a greater risk of migration.
With a goal in mind of producing a color in leather that will have little to no migration of dye, we have to take a look at the affinity of the dyes and their properties. Then select dyes with similar properties which will be suitable for shade combination since the tendency of each dye to exhaust is similar to other components especially in terms of the amount of color deposited during the critical phase of dyeing.
The pretreatments before dyeing the leather, in this case re-tannage, have a direct and pronounced effect on the shade. You also need to remember that some resins and fatliquors migrate and are capable of taking some of the dye with them. This shows that the pretreatment products used interact with the tanned collagen and the combination of pretreatment molecules and tanned collagen interact with the dye to produce a variety shades.
In conclusion, we must develop a re-tan formula that will minimize the migration of color. Also we must select dyes with similar properties. The dyes must have level dyeing properties, light fastness, dry cleaning fastness, and excellent migration into PVC. Dyes with these properties offer the most reliable means of coloring high quality leather. If you have further questions, please click the picture below for assistance from the FSW technical team.