Lipstick shear force resistance

  • Mecmesin

Lipstick holds the top spot in the hierarchy of makeup with its ability to completely transform appearance without the help of any other beauty product. One investigation by a beauty magazine concluded that the average consumer applies up to nine pounds of lipstick in their lifetime, so it’s no wonder that so much attention is focused on getting this little tube of oil / wax / colouring agent to perform consistently every time. The result not only needs to look good, with lasting results, but mustn’t bend, crack, crumble or break when applied.

The lipstick ‘bullet’ is formed by blending oils and waxes to create a moulded solid to which a colouring agent is added. Hard waxes give the stick its strength so that it doesn't snap away from the tube every time you use it, while softer waxes help to bind everything together and keep lips conditioned and well moisturised. From a cosmetic point of view the most important ingredient is the dye, pigment or other category of agent which achieves the desired colour; which may impact the physical performance.

It is therefore vital to control the formulation process to achieve a consistent texture that not only feels smooth on the lips but is resilient enough to withstand being applied firmly—irrespective of the shade chosen.

A key method to control the quality and consistency of lipstick is to measure its hardness by shear testing. This involves clamping the lipstick tube in a fixture and applying a cantilever force to push-down on the lipstick itself. The amount of force required to break it determines its hardness whilst how far the lipstick deflects indicates its brittleness. This data aids manufacturers to produce a lipstick which doesn’t snap out of its holder or crack when applied.

Solution

There are 3 distinct probe-types used to test lipsticks, all of which can be used with Mecmesin force testers:

  • Hemisphere-type (to simulate the shape of a lip) and chisel-type for bend tests.
  • ‘Cheese-wire’ to slice through the lipstick crayon.
  • Needle probe to pierce through the top or side of the bullet.

Compressive force is applied to the lipstick at a constant speed by using a motorised tester. Force is measured by a loadcell and data is plotted on a graph, from which calculations are made to determine hardness, brittleness and stiffness.

The peak force indicates the hardness telling you just how much the lipstick can withstand before breaking—usually at the joint with the holder, breaking elsewhere would indicate quality issues with the homogeneity of the material structure.

The amount of deflection of the lipstick at break measures brittleness; with softer lipsticks deflecting further than harder ones. Stiffness is provided by calculating the gradient of the curve when the lipstick is being bent.

Monitoring these key characteristics during production allows manufacturers to identify defects in the process which may produce grainy or flaky lipsticks caused by the presence of unwanted air bubbles or incomplete colourant dispersion. A repeatable test procedure, quantifying the values for acceptable performance, also means in-house test standards can be created to benchmark new formulations. The R&D lab can then report pass/fail results for products created with alternative synthetic, natural, eco-friendly, vegan-approved ingredients that the market demands and those that a regulatory body such as the FDA or EMA demands.

Test equipment

  • MultiTest motorised (plus digital force gauge) or software-controlled test stand
  • Shaped compression probe or knife edge profile bend/shear anvil
  • Custom Lipstick Bend Fixture for bullet testing

See also

Cosmetic packaging pull-off test

A bench-top testing system was required to repeatably test the pull-off force on a variety of cosmetic containers. The system needed to allow a relatively high volume of containers to be tested with the minimum level of training required for users. Mecmesin's solution avoided the risk of damaging the loadcell by excessive torque on tightening the collet grip, and the lipstick barrel was first inserted in the grip and then connected to the gauge by a flexible chain-link.

Food packaging made from thermoformed plastics and intended for freezing, requires testing to ensure optimum functionality when closing and sealing the container. The closing effort of the lid is measured by using a motorised force tester controlled by software together with a custom-designed fixture to hold standard-sized ice cream tubs. In addition the ‘top-load’ crush strength of the container itself can also be tested on the same machine to guarantee it is rigid enough to avoid buckling and spillage when the lid is applied.

Mecmesin develops Combi Cork-i Extraction Tester for leading Scottish whisky

To improve the quality and storage of a premium product, the R&D team at a leading Scottish whisky maker needed to optimise the design of their bottle stoppers. They decided that the strength and performance of their reusable stoppers could be ensured by systematic testing of the characteristics of both portions of the stoppers. Working closely with the R&D team, Mecmesin developed the Combi Cork-i Extraction Tester, an innovative multi-function cork extraction testing system that tests both phases of de-corking synchronously.

  • Jo Webb
  • Product Info
  • English
  • Created 16 Oct 2020
  • Modified 11 Nov 2020
  • Hits 232