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Coloring of Casting Polyurethane

Views: 45 Update date: Feb 23,2021

CPU coloring

  Adding coloring agent to polyurethane cast elastomer can make colorful products. In addition to giving people intuitive enjoyment, it can also play a role in shielding the darkening of color quality caused by the use of oligomer polyols and aromatic diisocyanates. The colorant can be dispersed in the chain extender, oligomer polyol or prepolymer, and the addition amount can be from a few percent to five ten thousandths or less, depending on the variety, concentration and quality of the colorant. In order to facilitate the dispersion, the colorant used in the castable polyurethane elastomer is generally processed into a paste-like color, sometimes also called a paste-like color or color paste. The color paste is mainly a dispersion system composed of three components: organic pigments, carriers and additives. The production process includes soaking, pre-dispersion, sanding or three-roll grinding, filtering and testing. Generally, the fineness of the color paste is required to be below 10μm, and the imported color paste is generally controlled below 2μm. Due to the different components of the color paste, the product can be transparent or opaque. The choice of materials is also very particular when making color pastes. Some color pastes used for polyurethane foam are not suitable for castable polyurethane elastomers, which will cause difficulty in process operation and even decline in physical properties. The reason is that the color paste contains reactive groups that react with isocyanate.


  The ideal colorant should have the following conditions.

Bright colors and strong tinting power.

Low price, non-toxic and odorless.

Good dispersibility, can be evenly dispersed in the CPU, without agglomeration.

No effect on the processing performance and physical performance of the CPU.

Good heat resistance, good thermal stability at the processing temperature and maximum use temperature of the CPU, no discoloration, no decomposition, and long-term heat resistance. •Solvent resistance, good chemical stability and light stability. • The colorant has good storage stability, for example, the colorant does not aggregate and flocculate during storage. The colorants used in the CPU include inorganic colorants and organic colorants.


  Commonly used are: titanium dioxide, carbon black, iron oxide red, cadmium mercury red, cadmium selenide, ultramarine red, chrome orange bisazo orange, isoindolinone, chrome yellow, cadmium yellow, reduced yellow, chrome oxide green , Phthalocyanine Green, Manganese Blue, Phthalocyanine Blue, Manganese Violet and Diazine Violet etc.

Usually, the color paste will change color due to heat, but the degree is different. Therefore, for high-temperature vulcanized CPU systems, the color paste should be dispersed in the prepolymer. If the pouring machine is used for operation, the color paste can be directly injected into the mixing chamber through the color paste metering system, which is convenient and quick, avoids the trouble of dispersion, and the dispersion is more uniform.

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