By Peter Leitner, Senior Vice President
Pigments are indispensable to the cosmetics industry for creating makeup, lipstick, sunscreen, and soaps. They are also used in the chemical and pharmaceutical industries, and photographic media and limited applicability in food processing, like candy coatings or shells.
Pigments mixing machines must address two requirements: dispersion and particle size reduction. Finding commercial pigment mixing equipment that disperse and eliminate agglomerates, and that can reduce particle size down to 1-5 micron or less is critical for success.
Pigments can be inorganic like metallic oxides, metal powder suspensions, and carbon black, or organic such as animal melanin, vegetable carotene, lakes and toners. Most of our experience is with titanium dioxide, lakes and some iron oxides.
Particle size reduction occurs with a high shear mixer running in a batch operation (such as the Rotosolver), or in a continuous inline operation using the Boston Shearmill. Combining batch mixing with recirculation through an inline device offers the optimal setup.
Pre-mixing ensures that all surfaces are wetted out and agglomerates are broken down. Plus, a good pre-mix drastically reduces the burden put on shearmills downstream to achieve the final particle size. The refractory properties of the materials and the hardness of the particles determine the equipment needed and whether it can be done in one step, but often it's possible to perform both pre-mixing and final milling in one operation.
When pigments are used for making an emulsion of soft to semi-hard particles, either the DynaShear inline disperser or the Rotosolver can be used in a batch mode. Both pigment mixing machines deliver particle size in the 2-4 micron range. Most pigments can be completely processed with our Boston Shearmill configured in a recirculation mode where multiple passes over 10-30 minutes will achieve results down to 1 micron or less.
Many hard particle pigments can be premixed and "milled" to particles in the 4-10 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. Admix recommends lab testing for optimal pigment mixing results. Running both benchtop and 10-100 gallon pilot tests will ensure scale-up success for larger batches or continuous runs.