1. Perspectives on Supplying Attenuation Grades
of Titanium Dioxide and Zinc Oxide
for Sunscreen Applications
David Schlossman, Yun Shao, Ph.D., Pascal Delrieu, Ph.D.,
Kobo Products Inc.

2. Inorganic UV Filters
Titanium dioxide (TiO2) and zinc oxide (ZnO) pigments are commonly used in personal care products to provide protection against UVA and UV B
They attenuate UV light by absorption and scattering
They are usually surface coated to minimize photo-catalytic activity.
They are typically produced as finer crystals from the same feed stocks and with similar processes as pigmentary grades.

3. Manufacturing Process
The production of TiO2 and ZnO is a two step process :
1. Purification of the raw material
2. Growing of crystals (primary particles) of the desired size
They are two different processes for TiO2, known as sulfate and chloride, and three for ZnO, known as American, French and Wet.
Crystals are grown at high temperatures to the required sizes : 200 nm and above (pigmentary grades) and finer than 200 nm (attenuation grades).
Attenuation grades
Pigmentary grades
10nm nm

4. Surface Treatment of Inorganic UV Filters
M. Kobayashi and al., Cosm & Toil., Vol. 112, No. 6, p83, 1997
* Rate constant of the first order reaction of oxydation of acetalydehyde
It is common industry practice to use surface
treated inorganic UV filters when formulating sunscreens.

5. Optical Properties - TiO2 and ZnO
Absorption
TiO2 : 420 nm (rutile) / 390 nm (anatase)
ZnO : 380 nm (3.24 eV)
Scattering
Refractive Index :
TiO2: ( Rutile) / 2.52 (Anatase)
ZnO: 1.99
Attenuation of UV light is influenced by particle size.
Scattering of visible light (whitening effect) is influenced by particle size and the difference between the refractive index of the pigment and the surrounding media.
Maximum scattering occurs when size equals 1/2 the wavelength and particles are uniformly dispersed (Mie theory).
Wavelength
Particle size

6. Particle Size and Light Scattering
Typical existing form supplied >1 mm UV
Visible
Size reduction
Whitening
Transparent

7. Dispersions of Attenuation Grade TiO2
Comparison of Dispersions and Powders
15 nm TiO2
35 nm TiO2
Dispersion vs Powder
Dispersion vs Powder
*Freeze Fracture TEM (40,000X)
Smaller primary particles are more difficult to disperse :
11/1 ratio of dispersion size to primary particle size for 10 nm TiO2).

8. TiO2 Dispersions in Cyclopentasiloxanenm nm nm nm
10nm TiO2 (110 nm dispersion particle size) makes transparent dispersions for all skin types.
All dispersions diluted in Cyclopentasiloxane (to 20% TiO2)

9. Particle Size and UV attenuation
(1) 308/360 extinction ratio : indication of UVB/UVA balance
(2) 308/524 extinction ratio : indication of transparency

10. Inorganic Sunscreen Formulations
Effect of Particle Size on Attenuation
* Tests were performed by Consumer Product Testing Co. - All testing on 3 people
** FDA method
*** JCIA PPD method (Rating 2-4: +; 4 - 8: ++; : +++).

11. Conclusions
Attenuation grade Titanium Dioxide and Zinc Oxide are produced using the same processes as larger pigmentary grades. They are usually surface coated to minimize their photo-catalytic activity.
TiO2 and ZnO attenuate UV light according to their particle size :
Small primary particle sizes ( nm) are necessary to produce dispersions ( nm) transparent to visible light and efficient against UVB.
ZnO and larger TiO2 ( nm) are more efficient against UVA.
The particle size of pigmentary grades are appropriate to scatter visible light, but they are not efficient at attenuating UV light or effective as sunscreens.