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Today's Topic: Pigments
Presented by: Peter Leitner, VP Sales

Pigments present a different challenge for mixing engineers, as the two principle requirements are dispersion and particle size reduction. The ability to reduce the pigment to a very small 1 to 5 micron particle size or less is critical for success. Pigments are indispensable to the cosmetics (makeup,lipstick, sunscreen, soaps) and paint industry, with major application also in pharmaceuticals and photographic media and limited applicability on food processing (perhaps candy coatings or shells). Pigments may be inorganic (metallic oxides, metal powder suspensions, carbon black), and organic (animal melanin or vegetable carotene, lakes and toners). Most of our experience is with titanium dioxide, lakes and some iron oxides. Particle size reduction can occur with a high shear mixer running in a batch operation, or in a continuous operation using in-line high shear mixers, shearpumps, or shearmills. A combination of the two, that is batch mixing combined with recirculation through an in-line device offers the best setup. Pre-mixing will always be helpful to insure that all surfaces are wetted out and agglomerates are broken down. A very good pre-mix can drastically reduce the burden put on shearpumps or mills downstream to achieve the final particle size. It is possible to perform both the pre-mixing and final milling stages in one operation. The refractory properties of the materials and the hardness of the particles will determine the equipment necessary, and whether it can be done in one step.

Where pigments are used for making an emulsion of mostly soft to semi-hard particles, either the DynaShear^® can be used as an inline high shear continuous mixer or the Rotosolver^® can be used in a batch mode. Both machines will deliver particle sizes for this application in the 2 to 4 micron range. Most pigments can be completely processed with our Boston Shearpump^® set up in a recirculation mode where multiple passes over 10 to 30 minutes will achieve the desired result (down to 1 micron or less). Many hard particle pigments, however, can be premixed and "milled" to particles in the 4 to 10 micron range in a batch reactor alone using our Rotosolver^® or Rotostat^® set at a high tip speed, eliminating the need for further downstream refinement. As with many applications, we highly recommend a factory test when dealing with pigments. Running both benchtop and 10 to 100 gallon pilot tests will insure success of the full-scale larger batches or continuous runs.

Bring us your mixing challenges, and we will recommend creative solutions... Please call our applications engineers at 800-466-2369 or email us at mixing@admix.com.

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