How To Get Rid of Agglomerations in Cosmetics

From the lab at Torrey Hills Technologies


Cosmetic Overview

Cosmetics are broadly classified into basic types such as lotions, creams, foundations, lipsticks, rouges, eyeliners, mascaras, eye shadows, eyebrow pencils etc.. The cosmetic should exhibit aesthetic qualities such as the color, which can be either a transparent or opaque and shouldn’t deteriorate in quality over time. 

The Makeup of Makeup
Makeup composition mainly includes pigment, fatty binder, and filler. Cosmetic products must be homogeneous and stable during the application. Basically, the pigment raw material has a relatively large and irregular particle. The pigment is usually ground in a ball mill to reduce the pigment particle size. In this step, the pigment can go down to about 10-15 microns. However, a reagglomeration of the various particles is observed after the above grinding and drying. Due to the agglomeration, the compositions are visually unappealing, often unstable, and cover poorly. Therefore, pigments and other ingredients in the cosmetic need to be further ground through a milling apparatus to form a homogeneous and finely dispersed paste the ideal pigment particle size should be in 10-30 nm.

Dispersion

There are many different ways to mix raw cosmetic material, such as Sand Mills, Colloid Mills, and Three Roll Mills. Each works differently but all subject the mixture to sheer force.

Sand Mills

Sand Mills are vertical cylinders filled with grinding media, operate on the principle that small mill media stir rapidly in the presence of the pigment slurry. Dispersion takes place as a result of pigment shearing as it rises through shaft impeller. Dispersion of the pigment depends strongly on the media size. Therefore, the use of sand mills makes it difficult to decrease the particle size to the nano range.

Colloid mill

The Colloid mill uses stone grinding discs. The upper stone is stationary and the lower stone is rotating fast at speeds up to 3600 revs per minute. The low viscosity slurry is fed into the center of the static top stone by gravity and is passed between the two stones by centrifugal force, where it is subjected to extreme turbulence and shear forces to affect the dispersion. Colloid mill can reach the very fine particle size but with a limitation on the size of batch material since it is small. 

Three-Roll Mills

Three-roll mill consists of three rollers which are made from chilled steel or granite, run parallel to each other, and each one rotates at a different speed. Additionally, each contact face passes in the opposite direction to the adjacent roller. The gap between them, called the nip, can be adjusted. The mill base is fed into the nip between rollers one and two and the final product is taken from roller three by means of a scraper bar. Among these mills, the three-roll mill is preferred since all paste compositions are subject to the sheer force when they go through the gap. Therefore, the more homogenous structure can be reached by this process. The particle size could go down to nanosize range. The gap between the rolls may be adjusted to control the fines of dispersion. The loading capacity could be easily adjusted through the machine design.

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