Mineral UV filters meet the challenge

Fulfilling the promise of mineral UV filters

It’s not surprising that more sun care formulations are turning to mineral UV filters, i.e., zinc oxide (ZnO) and titanium dioxide (TiO2). These minerals are a more natural alternative to traditional chemical sunscreens that provide broad-spectrum protection. TiO2 is most often used for UVB protection (290–320nm), but also provides significant UVA (320–400nm) protection. ZnO is less effective than TiO2 for UVB protection, but is usually more effective in the long wavelength UVA part of the spectrum. As desirable as mineral UV filters are, there are some definite challenges in integrating them into a successful formulation.

Aesthetic challenges

Consumers may seek out personal care products that are more natural, but they are not willing to sacrifice aesthetics. There has been a shift in consumer expectations from function and efficacy benefits to sensory and emotional benefits. To ensure that their products meet these demands, manufacturers are increasingly using a variety of scientific methods to measure consumer responses to products based on the senses of sight, smell, touch, taste and hearing3.

This same attention to consumers’ sensory reactions in other personal care products is evident in the sun care market as well. Consumers now assume that sun care products are effective, but they also want products that spread smoothly, feel good on the skin, dry smoothly, do not cause whitening and make them feel good and happy.

Achieving these desirable sensory characteristics with a mineral UV filter can be challenging, but essential for a successful product. After all, the most effective sunscreen product is one that consumers will actually use on a regular basis.

Advanced technology for improved performance

Tightening particle size distribution and restricting the formation of agglomerates by coating the mineral particles improve the effectiveness of formulations by increasing the amount of light that is reflected and refracted away from the skin. 

In addition, the aesthetics of the formulation are enhanced as perceptible particulates are eliminated. The feeling of grittiness and tackiness is reduced and flowability is improved, leaving consumers with a pleasant experience and skin feel. And last but not least skin whitening is reduced. 

Putting UV mineral filters in a concentrated form in a dispersant not only eliminates the need to work with powdered minerals, it also improves and tightens overall particle size distribution. This is essential since particle size distribution directly affects both the aesthetics and efficacy of a sun care product formulation. This tendency to form agglomerates appears in both TiO2 and ZnO formulations, although the issue is more severe in TiO2 formulations.

One successful way of tightening overall particle size distribution is to coat the mineral particles. An effective coating system consists of silica moieties (derived primarily from tetraorthosilicate), alkyl groups (derived from triethoxycaprylylsilane) and polydimethylsiloxane (derived from dimethiconol).

This combination forms a complete coating that surrounds the mineral particles and eliminates gaps. Chemical interactions with the particles are virtually eliminated and the particles no longer form clumps, but rather slide right over each other.

For example,Hallstar’s zinc and titanium oxide dispersions (HallBrite EZ-FLO ZDX, EZ-FLO ZDX Plus, EZ-FLO TDX, and EZ-FLO TDX Plus) feature proprietary and patented coating systems that eliminate agglomeration and create a smooth lotion consistency while also outperforming the competition on whiteness reduction. At the same time, these dispersions maintain safe, high-performing broad-spectrum protection without the synthetic sunscreens many consumers want to avoid (though the dispersions also work well with Avobenzone). With the addition of Hallstar’s SolaStay S1, one of the most powerful photostabilisers on the market, these products promote exceptional stability. Its triple advantage for beauty and personal care companies comprises efficacy, aesthetics and natural ingredients (see fig. 1).

Using coated titanium dioxide particles in a concentrated solution dramatically reduces whitening compared to traditional formulations (see fig. 2*).

Improving photostability

To mitigate the photocatalytic and oxygen species-generating activities of TiO2 and ZnO formulations, adding a photostabiliser, such as ethylexyl methoxycrylene, can improve stability and reduce harmful reaction upon exposure to sunlight. In addition, instead of a more traditional solvent of C12-15 Alkyl Benzoate, adding butyloctyl salicylate to the solvent system will increase the polarity of the overall oil-phase. This further improves the photostability of the formulation, as well as improving aesthetics by imparting an elegant, moisturising feel to the skin from an odourless, colourless, non-irritating liquid, (see fig. 3a).

Compared to competitive products A and B, both HallBrite EZ-FLO TDX and TDX Plus show superior absorption in the UV range (UVB-UVA) by reducing particle conglomeration through the patented coating system and unique dispersion system. This is further exhibited in the technology’s transmittance data (see fig. 3b) where both ingredients show lower transmission of light. TiO2 particles typically work by reflecting light energy, and the ability for the TDX series to reduce light transmission ultimately leads to higher w/w SPF and PFA results in customers’ formulas.