Texture Analysis in the Nailcare Industry: 2: Nail polish drying time

Nail polish has been developed to have a faster drying time with brands claiming “dry in 60 seconds” or “quickdry”. 

However, smudging a manicure is still a common complaint. There are also difficulties accelerating the drying time of more natural polishes containing fewer volatile solvents. New products must be tested for this in a consistent way.

A Nail Polish Adhesion Rig (Community Registered Design - Figure 1) and method have been developed to provide the solution to this assessment requirement. During the polish drying time test, a channel 20cm long is filled with polish to a specific depth and wiped level using a glass rod. At this point a timer within the Exponent software test sequence is started. 

Figure 1: Nail Polish Adhesion Rig

This channel is seated on top of the Adhesive Indexing System that has ten detents and so ten test sites are available by simply sliding the platform along. A 1 inch detented ball probe is used for the tests, which can be turned to allow a clean test site without replacing the probe or the requirement to clean and dry the test probe between tests. This is used to perform an adhesive test at the first test site. A specific force is held for 5 seconds to allow a bond to form. 

The probe is then quickly withdrawn, breaking the nail polish bonds and the force to do this is measured. The channel is moved along to the next site and the test repeated. A set of ten tests are performed in this way with pre-set time delays between the tests (Figure 2a). Tests are performed over the whole drying period of the polish.

Figure 2a: Ten adhesive tests of a polish sample
changing from liquid to solid as it cures
over a period of 40 minutes

Several measurements can be made from the force-time graph (Figure 2b):

i) The maximum force needed to withdraw the probe from the sample is a measure of the strength of the bond or the adhesiveness/stickiness of the polish. The initial wet polish has a very low adhesive force. As time passes the stickiness increases until it peaks, then drops off. After the highest adhesive force cycle is obtained the polish is usually ‘touch dry’.

ii) Softness is defined as the time the probe takes to sink into the surface of the polish before the force reaches 5g. The softness decreases with drying time until it reaches a plateau, at which point the polish is touch dry.

Figure 2b: Zoomed in section of
one adhesion cycle explaining
parameters of interest

iii) Stringiness is the time period over which the probe remains adhered to the polish. If the polish and probe immediately lose contact after the probe has withdrawn, the polish is not stringy. A stringy sample will leave a force on the probe for a longer time.

The series of adhesion tests is automated by a unique test sequence developed in Exponent software, with parameters such as the delay between tests, the number of repeats, applied force and holding time adjusted by the user if necessary. Additionally, an analysis macro is available to measure the above three properties across all repeats at the press of a button.

Figure 3: Comparison of softness, stickiness and stringiness of two polish samples. 

Figure 3 shows graphs of these properties for two samples. The purple gel sample is more desirable than the pink polish in every case as it dries more quickly and with less tack force. It is also initially harder and so will be less prone to initial film damage when a wet layer of polish remains underneath the touch dry surface.

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We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.
For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

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