Polyurethane materials have good colorability. By adding polyurethane dyes  or polyurethane pigment pastes, polyurethane products of various colors can be produced, such as colored polyurethane soft foam, elastomer, synthetic leather, etc. These auxiliaries that can color products can be called colorants.
In addition to using colors to provide different visual effects, the dyeing of PU foam products has the following functions:
① Use different colors to distinguish polyurethane flexible foam products with different densities and different functions. Different colors can represent different densities, or represent different types of PU flexible foams, such as flame retardant sponges, antistatic sponges, etc.;
② Brown, red, yellow or black can be used to cover up the yellowing phenomenon of polyurethane, so that the yellowing phenomenon of polyurethane products is not obvious or imperceptible, so as to minimize the negative effect.
There are many varieties of pigments and dyes. Due to the presence of highly reactive NCO groups in the polyurethane reaction system, it is necessary to pay attention to whether there are functional groups or compounds in the pigments and dyes that are easy to react with the polyurethane raw materials (it is easy to lose the coloring effect after the reaction). It is best to choose experimentally whether a pigment is suitable for use in a polyurethane system.
The selection of pigments or dyes generally follows the following principles:
Can be easily dispersed in components;
Can withstand processing temperatures;
The impact on material properties should be as small as possible;
Color shift and pigment precipitation do not occur.
For the convenience of use and better dyeing effect, pigments or dyes are generally dispersed and dissolved in polyether in advance to make color paste. In the production of colorants, wetting and dispersing agents are usually added in order to disperse the powder pigments well.