Powder Blending in Cosmetics Production

Pigments do not arrive as single particles. They arrive agglomerated, held together tightly enough that tumbling will distribute the agglomerates evenly without ever breaking them, and an evenly distributed agglomerate is still a speck in a pressed powder.

That is the first distinction this industry depends on: distribution and dispersion are different operations. Longer mixing achieves the first and almost nothing of the second.

The second problem is changeover. A shade is assessed visually against a standard, and the tolerance a trained eye applies is tighter than most instrumental limits. A trace of the previous colour in a mixer corner, under a seal or in the discharge valve shifts the next batch, and the shift is noticed by a person rather than by an analysis.

Pigments also travel. Titanium dioxide, iron oxides and organic lakes are fine, light and highly staining, so what escapes the mixer ends up on surfaces, on people and in the next product, with occupational exposure limits that apply to several of them.

Cosmetics manufacturing judges a blend by eye, and the eye resolves a defect that no sampling plan of a reasonable size would catch.

A blend where the pigment is dispersed rather than merely distributed, verified by the way the product is actually assessed: a pressed or applied sample looked at under controlled light.

A mixer and discharge that empty completely and can be brought to visual cleanliness in the changeover time available, because that is the real constraint on shade consistency.

Pigment contained at charging, mixing and discharge, with exposure controlled rather than tolerated.

In food production the deciding figure is the smallest inclusion rate, and a minor ingredient added neat to a full mixer never distributes however long the blend runs.

The dispersion step is specified first and separately. A high shear mixer, a deagglomerator or a hammer mill in the loop breaks agglomerates; the tumbling or ribbon mixer then distributes what the dispersion step produced. Combining the two duties in one gentle machine is the most common reason a shade cannot be hit.

Screening after blending is a routine step rather than a correction. It catches what the dispersion step missed and it catches contamination, and the mesh is chosen so that a failure shows up as a retained quantity rather than as a blocked screen.

Mixer geometry is then chosen for emptying. Complete discharge matters more here than capacity, so a mixer that leaves a heel in a corner is a worse machine than a smaller one that empties clean. Access for visual inspection follows: a shade changeover is signed off by eye, so somebody has to be able to see every internal surface.

Containment is designed around charging, which is where most of the pigment escapes. Enclosed charging, local extraction and a clean down procedure that does not blow powder around are all part of the specification.

• Dispersion and distribution specified as two separate duties with two mechanisms.
• Screening after blending treated as a routine step, with the retained quantity recorded.
• Mixer selected for complete discharge, with no heel left in a corner.
• Internal surfaces visible for inspection, since shade changeover is signed off visually.
• Enclosed charging with local extraction, because charging is where pigment escapes.
• Shade assessed on a pressed or applied sample under controlled light, not on loose powder.

• Shade tolerance and how it is assessed, which is usually visual and therefore stricter than an instrumental limit.
• Pigment agglomerate strength, which decides the dispersion mechanism.
• Changeover frequency between colours, which decides whether cleaning or dedicated contact parts are realistic.
• Complete discharge, since a residual heel is a carryover source that cleaning does not reach.
• Exposure limits for the pigments and the base powders.
• Batch size range, including the smallest quantity the mixer has to blend well.