Metal oxide composition
A composition comprises a non-ionic surfactant and hydrophobic particles of metal oxide having the mean length of the primary particles in the range from 50 to 90 nm, the mean width of the primary particles in the range from 5 to 20 nm, and the median volume particle diameter of the secondary particles is less than 45 nm. The composition is particularly suitable for use in aqueous media, and can be used in a sunscreen product that exhibits both effective UV protection and improved transparency.
1. An aqueous dispersion, comprising:
i) at least one non-ionic surfactant having an HLB value in the range from 5 to 20; and
ii) hydrophobic particles of metal oxide having:
a) primary particles having a mean length in the range from 50 to 90 nm and a mean width in the range from 5 to 20 nm;
b) secondary particles, comprising clusters or agglomerates of the primary particles, having a median particle volume diameter of less than 45 nm;
c) an extinction coefficient at 524 nm (E 524 ) of less than 2.0 l/g/cm; and
d) an extinction coefficient at 308 nm (E 308 ) of greater than 30 l/g/cm.
2. The aqueous dispersion of claim 1 , wherein the hydrophobic particles of metal oxide further comprise an extinction coefficient at 450 nm (E 450 ) of less than 3.0 l/g/cm, an extinction coefficient at 360 nm (E 360 ) of greater than 3 l/g/cm, a maximum extinction coefficient E(max) of greater than 45 l/g/cm, and a λ(max) in the range from 260 to 290 nm.
3. A sunscreen product formed from the aqueous dispersion of claim 1 .
4. The aqueous dispersion of claim 1 , wherein the primary particles of metal oxide have a mean length in the range from 55 to 77 nm.
5. The aqueous dispersion of claim 1 , wherein the primary particles of metal oxide have a mean width in the range from 8 to 19 nm.
6. The aqueous dispersion of claim 4 , wherein at least 60% by number of the primary particles have a length in the range from 55 to 77 nm and/or at least 60% by number of the primary particles have a width in the range from 8 to 19 nm.
7. The aqueous dispersion of claim 1 , wherein the median particle volume diameter of the primary particles of metal oxide is in the range from 25 to 31 nm.
8. The aqueous dispersion of claim 1 , wherein the median particle volume diameter of the secondary particles of metal oxide is in the range from 22 to 30 nm.
9. The aqueous dispersion of claim 1 , wherein no more than 16% by volume of the secondary particles of metal oxide have a volume diameter of less than 20 nm.
10. The aqueous dispersion of claim 1 , wherein more than 84% by volume of the secondary particles of metal oxide have a volume diameter of less than 40 nm.
11. The aqueous dispersion of claim 1 , wherein the particles of metal oxide comprise an organic water repellant coating.
12. The aqueous dispersion of claim 1 , wherein the metal oxide particles comprise (i) in the range from 65% to 95% by weight of titanium dioxide, (ii) in the range from 2% to 12% by weight of inorganic coating, and (iii) in the range from 4% to 18% by weight of organic coating, all with respect to the total weight of the particles.
13. The aqueous dispersion of claim 1 , wherein the at least one non-ionic surfactant has a molecular weight in the range from 200 to 1500.
14. The aqueous dispersion of claim 1 , further comprising a mixture of two non-ionic surfactants which differ in molecular weight by an amount in the range from 250 to 700.
15. The aqueous dispersion of claim 1 , wherein the aqueous dispersion comprises at least 35% by weight of metal oxide particles.
16. The aqueous dispersion of claim 1 , wherein the particles of metal oxide have an extinction coefficient at 524 nm (E 524 ) of less than 1.5 l/g/cm.
17. The aqueous dispersion of claim 2 , wherein the particles of metal oxide have an extinction coefficient at 524 nm (E 524 ) in the range from 0.1 to 1.0 l/g/cm, an extinction coefficient at 450 nm (E 450 ) in the range from 0.3 to 1.7 l/g/cm, an extinction coefficient at 360 nm (E 360 ) in the range from 5 to 10 l/g/cm, an extinction coefficient at 308 nm (E 308 ) in the range from 40 to 60 l/g/cm, a maximum extinction coefficient E(max) in the range from 55 to 75 l/g/cm, and a λ(max) in the range from 260 to 290 nm.
18. The aqueous dispersion of claim 1 , wherein the particles of metal oxide particles have a photogreying index in the range from 1 to 10.
19. The aqueous dispersion of claim 1 , having a change in whiteness ΔL of less than 3.
20. The aqueous dispersion of claim 1 , having a whiteness index in the range from 10% to 80%.
21. The aqueous dispersion of claim 1 , having a Sun Protection Factor (SPF) of greater than 15.
22. The aqueous dispersion of claim 1 , which is transparent when applied to the skin.
23. The aqueous dispersion of claim 1 , wherein the aqueous dispersion comprises at least 40% by weight of metal oxide particles.
24. The aqueous dispersion of claim 1 , wherein the at least one non-ionic surfactant has a HHB value in the range from 7 to 18.
25. The sunscreen product of claim 3 , wherein the at least one non-ionic surfactant has a HLB value in the range from 7 to 18.
26. The aqueous dispersion of claim 1 , wherein the concentration of the at least one non-ionic surfactant is 5 to 50% by weight, calculated with respect to the weight of the metal oxide particles.