Behind the inconspicuous little brushes, which can be found in a wide variety of shapes in cosmetic bags around the world, lies a complex production process that begins with the manufacturing of the necessary injection molding tools.
Mascara brushes are available in numerous variations: straight, curved in an S-shape, longer, shorter, with larger or smaller gaps between the hairs. In short: a very individual product that requires equally individual injection molding tools.
The bristles of a mascara brush often have a diameter of less than 0.3 mm at the base and 0.1 mm at the tips. Two tool segments are required for each bristle to enclose the brush. The process becomes particularly challenging with brushes that feature up to 1,000 bristles, which are formed by tiny separation lines. This two-part slider system requires that sliders made from two tool parts precisely replicate each individual bristle of the brush. In order to form these delicate structures, the erosion process must be carried out with the utmost precision; otherwise, burr formation will occur on the brush.
Injection molding tools for mascara brushes are designed to work quickly and efficiently. Our injection molds usually have a 4-cavity design. Four brushes can be produced approximately every 7 seconds – a speed that could not be achieved with the additive process (3D printing). Polypropylene (PP) is often used for the brushes – a flexible and cost-effective plastic.
The 2K sandwich process, a so-called co-injection molding process, is also used for special brushes. In this case, however, this does not mean that a plastic part is molded with an inner and outer layer, but rather that after the first plastic, e.g. TPE for the hairs, the second plastic, e.g. PP for the shaft, is injected using a special nozzle. The result can be a fashionable and functional mascara brush with two different colors for the shaft and hairs.
At RKT, we have been manufacturing tools for the injection molding of mascara brushes for over 20 years. Even though many of our tools are impressively durable – some have been running for 15 years – there is still wear and tear: bearings wear out, guide elements need to be overhauled, slides need to be checked, and so on. Our repair department then takes care of renewing the injection molds. As a rule, molds should be overhauled or replaced after around two to three million cycles.
The development of a new tool is often triggered by a new brush shape. It then takes us around three weeks to design it and a further three months for the tool to be ready for sampling. The mold frame can still be used for new tool inserts – the basic structure remains the same, only the interior is adapted to the bristle design.
Mold making for mascara brushes is extremely complex; there are not many injection molders who take on this task. Behind every mascara brush that is produced with an RKT tool is a great deal of passion for precision.
