COLOUR COSMETICS
embed themselves between polymer chains, spacing them to make the film sufficiently flexible in order to avoid cracking or chipping after drying. Dibutylphtalate (DBP) was extensively used as a common plasticiser in nail polish formulations for many decades before recently being banned. Besides nitrocellulose, resins and plasticisers, solvents such as butyl acetate and ethyl acetate are integrated into the formulation to dissolve or create a medium for the formulation and to help the dispersion of nitrocellulose and resins. When applied as a thin coating, these solvents will evaporate quickly to leave behind the pigmented or coloured film. Pigment or effect particles in the nail polish typically need to be suspended, in order to create ‘quasi-stable’ formulations. With this goal in mind, thixotropic agents like bentonite or silica are added to the formulation. The purpose of these ingredients is to suspend or stabilise the pigments in the formulation, which slows down particle sedimentation in the container and allows shear thinning of the formulation during the application phase for a better levelling. Pigmented nail polish represents about 75% of global nail polish market. Choice of pigment or effect particles and their ability to mix well with the solvents and other ingredients is essential to produce a good quality product. Most often, inorganic pigments like titanium dioxide or iron oxides are used to provide an opaque and vivid colour on the surface of the nails. Different effects, like pearly or sparkling effects, can be added by the use of raw materials like mica and bismuth oxychloride. The trend is now to create more artistic or dramatic effects such as metallic shades, crackled look and even animal patterns.
New trend
As already mentioned, solvent-based products containing nitrocellulose dominate the nail polish market today. However these products are facing increased scrutiny because of the solvents they contain and their potential toxicity. Furthermore, the manufacturing of solvent-based nail polish requires special facilities designed to control the hazards of fire and explosion, which is an additional issue for cosmetic producers as well as shipping restrictions. Nail polish manufacturers are slowly shifting toward less toxic formulations, as consumers become conscious of the potential health and environmental impact of these conventional solvent-based nail polishes. The trend for ‘without’ or ‘free of’ has also hit the nail polish industry and it is now possible to find water-based nail polishes
140 PERSONAL CARE April 2012
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■ Solvent based ■ F91-141B based on Sytran PC5620 ■ Water-based Brand 1 ■ Water-based Brand 2 ■ Water-based Brand 3
Figure 1: Drying time evaluation – ASTM D5895-03.
on the market. This new category of nail polish offers a safe and environmentally friendly alternative to the current solvent- based formulations. However, many of the currently available water-based nail polishes are targeted at young girls because of poor performance characteristics.
Therefore Interpolymer has developed a new acrylic polymer dispersion specifically designed to formulate water-based nail polishes. This technology platform was given the acronym SAFE – which means State-of-the-art Acrylate Film-forming Emulsion.
This new acrylic polymer dispersion exhibits excellent initial gloss and gloss retention. The dry-to-touch time is very fast compared to other existing water-based nail polishes. It exhibits excellent water and wear resistance, hardness and adhesion to the nail surface. The SAFE technology eliminates all those concerns with regard to safety hazards, toxicity and VOC issues currently facing solvent-based nail polishes. Moreover the use of this technology allows a safe production process without the use of specialised facilities.
25 20 15 10 5 0 012 24 Figure 2: Film hardness evaluation with time. 36 Dry time (hours) 48 60 72
■ Solvent based ■ F91-141B based on Sytran PC5620 ■ Water-based Brand 2 ■ Water-based Brand 1
Formulations
Clear nail polish formulations were developed with the new acrylic polymer dispersion. Thanks to their aqueous composition these formulations are compatible with other water-based actives and can be promoted in the nail care treatment segment. Marketing claims like hardening, hydration, health, protection could be easily obtained with the addition of water-based actives.
The compositions of four clear nail polish formulations are given in Formulation 1. The basic components of these water- based nail polishes are the same as that of solvent-based formulation. They contain a solvent (water), a film-forming agent and plasticisers. The film-forming agent is the new acrylic polymer dispersion. The polymer dispersion on its own does not form a film but a crystalline powder on drying. Therefore plasticisers are present in the formulation to reduce the Minimum Film Formation Temperature (MFFT) of the final formulation, permitting it to be transformed into a clear, durable film when allowed to dry at room temperature.
Number of oscillations
Drying time (seconds)
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