Coloring agents can be either; pigments or dyes. Pigments are not soluble in the medium in which they have to be incorporated, while on the other hand, during their application dyes dissolve, which makes them lose their particulate or crystalline structure, during the process.
Therefore the difference between these two types of colorants is not on the basis of their chemical composition, but it is actually due to their physical characteristic.
Many industries make use of dyes for printing and surface coating. Because they are used in the printing industry too, they demand a high degree of transparency for manufacturing colored films and metal foils. They are also used for giving a flamboyant finish in the painting industry, and it is also used for staining woods and several other applications.
Because of the advancement in the resin technology, these colorants are now also being utilized for specific automotive finish purposes. This is because of their advanced properties in terms of transparency and color.
These colorants are also used for mass coloring of thermoplastic during glass transition state at normal temperatures. The ones that are selected for the purpose of coloring polymers are soluble in those substrates.
There are three major categories in which these colorants are divided. Those three categories are; basic, fat soluble and metal complex.
Basic Dyes- are cationic and are soluble in solvents like glycol, water and alcohol. They are majorly used in the printing ink industry, with agents like tannic acid to manufacture bright and clean shades. However, their usefulness becomes limited due to poor lightfastness.
Fat Soluble Dyes- includes metal free azo, anthraquinone and nonionic dyes. These are soluble in less polar solvents like aliphatic hydrocarbons and aromatic. Azo dye is used for coloring styrene polymers, while anthraquinone dyes are used widely for coloring fibers and plastic.
Metal-Complex Dyes- are cobalt and anionic chromium complex of azo dyes. Substituted soluble phthalocyanines are a part of this category. They are soluble in esters, ketones, alcohol, and glycolethers.
A solvent dye– is soluble in organic solvents. They are used for coloring hydrocarbon fuels, lubricants, waxes, plastics, organic solvents and nonpolar materials based on hydrocarbon. They have nonpolar or slightly polar molecules, and don’t go through the process of ionization. They have poor to good lightfastness. These colorants are not soluble in water.