Screening machines for color pigments and color powders

Color pigments are coloring powdery substances for technical applications. They are used in lacquers, emulsion paints, printing inks, as coating pigments (white pigments) and fillers in the production and finishing of paper, in the coloring of plastics, in artists' paints and crayons, in printing on textiles and in cosmetics. Especially in the case of color pigments for very thin coating layers and high demands on the finished surfaces, the processing of the pigments by screening is essential. 

Sharp separations in the finest particle range without unwanted agglomerates

The decisive factors for the sieving behavior of the color pigments are the bulk properties, such as the crystal structure, crystal modification, particle size and particle size distribution. Particularly for particle sizes smaller than 50 µm, electrostatic gravitational forces between the particles make screening difficult. For particles smaller than 10 µm, additional forces act at the atomic and molecular level (Van der Waals forces), and these forces can no longer be overcome on conventional screening machines. Dispersing the particles therefore requires high acceleration forces directly on the product.

Pigments can also grow together into aggregates via their surfaces. The term agglomerates is used when aggregates are connected via their corners or edges. These disturbing agglomerates must be broken up or reliably separated in the screening process. This is another reason why RHEWUM's directly excited screens offer are the best solution.

The RHEsonox^® screening machine offers an advantageous combination of the vibration features of a linear vibrating screen and a directly excited screening machine. Powerful magnetic vibrating heads enable high-frequency vibrations directly at the screen mesh and thus reliable screening of the color pigments, while the linear motion transports the material. This unique drive combination breaks up agglomerates and achieves much better separation results, especially in the fine particle range, than would be possible with a conventional vibrating screen.

The multi-deck high precision screening machine RHEstack^® is also ideally suited for the screening of color pigments. On horizontally arranged screen decks, the product is screened with unrivaled separation precision. The applied micro-throwing principle exposes the individual particles to a large number of individual throws, which maximizes the separation success.

Wet screening process for colors and pigments

One of the colors used since ancient times is white and one of the oldest white pigments is calcium oxide (CaO, quicklime), which is obtained by burning lime from limestone (CACO3). After slaking quicklime with water to calcium hydroxide (CA(OH)2, slaked lime), wet screening processes are useful for products such as lime slurry or milk of lime to remove impurities. For a protective screening of lime milk, a capacity of more than 20 t/h could already be realized on a RHEhydra^® wet screening machine of the smallest size with a screen mesh of 50 µm. The RHEhydra^® machine type also offers a high-performance alternative to cyclones or filters for colorants in liquids.