Suspension / Solution Layering

The most common processing option is to apply the layer from a solution or suspension. Physically the layering process differs not from the coating process, but layers are usually much thicker (60-200 % weight gain) and consist from an active ingredient, whereas the film is formed from some inert material. Very often layering and subsequent filmcoating are two steps of the same process. To achieve very uniform layers the bottom spray method (batch or continuous) should be the processing option of choice. Meanwhile, neutral starter spheres from 100 to 1000µ are available. Average weight gain per processing hour is about 15-20 %, because 80 – 85 % liquid vehicle have to be evaporated. All features of spray coating also apply to suspension and solution layering.