Polyurethane Pigments and Dyes

Polyurethane has excellent dyeability. By adding dye or pigment pastes, polyurethane foam, especially soft polyurethane foam, can be made into brightly colored products.

In addition to providing functional effects through color, coloring polyurethane foam serves the following purposes:

1. Distinction by Color: Different densities and functions of soft polyurethane foam can be identified using various colors and shades. For instance, colors like brown, red, yellow, or black can be used to mask the yellowing of polyurethane, making it less noticeable and reducing the negative impact of the foam's initial white-to-yellow color change.

2. Compatibility of Pigments/Dyes with Polyurethane Foam:

• Ensure pigments or dyes do not react with polyurethane raw materials and lose their coloring effects.
• Evaluate properties such as acid and alkali resistance, oxidation resistance, heat resistance, light resistance, coloring power, water resistance, solvent resistance, and cost.
• Pigments should disperse easily in the components, withstand processing temperatures, minimally impact material properties, and avoid color migration or pigment precipitation.
• The pigment quantity should be adjustable within a wide range.

To enhance convenience and achieve better coloring effects, pigments or dyes are generally pre-dispersed or dissolved in polyether.

Common Pigments for Polyurethane Foam

Advances in Reactive Dyes

Recently, reactive dyes have been developed internationally. For example, Milliken Chemicals in the United States has introduced a series of reactive dyes under the brand name “Reactint.” Unlike conventional pigments dispersed in polyols, these novel dyes are homogeneous liquids.

The new dyes involve grafting dye (or pigment) components onto polyether through reactive processes. The molecular chains containing hydroxyl groups are chemically bonded to chromophores, resulting in distinct colors depending on the chromophore type. This integration of pigments and raw materials ensures ease of use and allows the coloring groups to be incorporated into the polymer network during the polyurethane reaction process. The resulting colors are durable, resistant to migration, and fade-resistant.