Unlike many other types of dyes, disperse dyes are far less water soluble. This means that disperse dyes, by themselves, do not dissolve easily in water. That said, disperse dyes are most commonly utilized with dye bath solutions. In order to make these dye bath solutions function properly, dispersing agents are utilized to increase the water solubility of the dye (hence the name “disperse dyes”).
In addition to being used in conjunction with a dispersing agent, disperse dyes achieve the best results when the dying process takes place at high temperatures. At lower temperatures, while disperse dyes may result in uneven and less vibrant colors, at higher temperatures (around 120 to 130°C), disperse dyes produce evenly distributed and bold colors.
Due to their chemical properties and the behavior explained above, disperse dyes are commonly used to dye polyester fibers (and other related materials such as nylon). Most forms of polyester are hydrophobic and lack ionic properties, which makes them nearly impossible to color with anything other than disperse dyes. Additionally, at regular temperatures, even when submerged in a dye bath, polyester fibers do not swell, making it difficult for dye molecules to interact with the material. Even at the boiling temperature—100°C —the dyeing of polyester is problematic. For this reason, when dyeing polyester, disperse dyes are used in dye bath solutions at temperatures around 20 to 30 degrees higher than the boiling point of the dye bath solution. At these elevated temperatures required to color polyester, disperse dyes are known to maintain their molecular integrity.
For the same reasons that disperse dyes are used to dye polyester, they are also used to dye other synthetic materials that are nonionic. The fact that disperse dyes possess no cationic or anionic tendencies is perhaps the most classifiable characteristic of disperse dyes.