Particulate metal oxide
A particulate metal oxide having a 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 metal oxide can be used in a sunscreen product that exhibits both effective UV protection and improved transparency.
1. A particulate metal oxide, optionally hydrophobic, having an extinction coefficient at 524 nm (E 524 ) in the range from 0.2 to 0.7 l/g/cm, an extinction coefficient at 450 nm (E 450 ) in the range from 0.5 to 1.5 l/g/cm, an extinction coefficient at 360 nm (E 360 ) in the range from 5 to 8 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 45 to 75 l/g/cm, and a λ(max) in the range from 260 to 290 nm, wherein the extinction coefficient E, is calculated from the equation A=E.c.l, where A=absorbance, E=extinction coefficient in liters per gram per cm and l=path length in cm, for a sample of the particulate metal oxide at a dilution of 1:20,000 in a spectrophotometer at a path length of 1 cm.
2. The particulate metal oxide according to claim 1 having a photogreying index in the range from 1 to 10.
3. A coated particulate metal oxide having an extinction coefficient at 524 nm (E 524 ) of in the range from 0.1 to 1.0 l/g/cm, an extinction coefficient at 450 nm (E 450 ) in the range from 0.1 to 2.0 l/g/cm, an extinction coefficient at 360 nm (E 360 ) in the range from 4 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 45 to 75 l/g/cm, and a λ(max) in the range from 260 to 290 nm, wherein the extinction coefficient E, is calculated from the equation A=E.c.l, where A=absorbance, E=extinction coefficient in liters per gram per cm, c=concentration in grams per liter, l=path length in cm, for a sample of the particulate metal oxide at a concentration of 0.025 g/l in a spectrophotometer at a path length of 1 cm.
4. The coated particulate metal oxide according to claim 3 having an extinction coefficient at 524 nm (E 524 ) in the range from 0.2 to 0.7 l/g/cm.
5. The coated particulate metal oxide according to claim 3 having an extinction coefficient at 450 nm (E 450 ) in the range from 0.5 to 2.0 l/g/cm.
6. The coated particulate metal oxide according to claim 3 having an extinction coefficient at 360 nm (E 360 ) in the range from 5 to 8 l/g/cm.
7. The coated particulate metal oxide according to claim 3 having an extinction coefficient at 308 nm (E 308 ) in the range from 45 to 55 l/g/cm.
8. The coated particulate metal oxide according to claim 3 having a maximum extinction coefficient E(max) in the range from 50 to 70 l/g/cm.
9. The coated particulate metal oxide according to claim 3 having a λ(max) in the range from 265 to 285 nm.
10. The coated particulate metal oxide according to claim 9 having a λ(max) in the range from 270 to 280 nm.
11. The coated particulate metal oxide according to claim 3 wherein the mean length of the primary particles of the metal oxide is in the range from 50 to 90 nm, the mean width of the primary particles is in the range from 5 to 20 nm, and the median particle volume diameter of the particulate is less than 45 nm.
12. The coated particulate metal oxide according to claim 11 wherein the primary particles have a mean length in the range from 55 to 85 nm and a mean width in the range from 8 to 19 nm.
13. The coated particulate metal oxide according to claim 12 wherein at least 70% of the primary particles have a length in the range from 55 to 85 nm.
14. The coated particulate metal oxide according to claim 13 wherein at least 70% of the primary particles have a length in the range from 60 to 80 nm.
15. The coated particulate metal oxide according to claim 11 wherein the median particle volume diameter of the particulate is in the range from 25 to 35 nm.
16. The coated particulate metal oxide according to claim 15 wherein the median particle volume diameter of the particulate is in the range from 27 to 33 nm.
17. The coated particulate metal oxide according to claim 11 wherein the median particle volume diameter of the particulate is in the range from 30 to 40 nm.
18. The coated particulate metal oxide according to claim 17 wherein the median particle volume diameter of the particulate is in the range from 32 to 38 nm.
19. The coated particulate metal oxide according to claim 18 wherein the median particle volume diameter of the particulate is in the range from 33 to 37 nm.
20. The coated particulate metal oxide according to claim 11 wherein no more than 16% by volume of the particulate has a volume diameter of less than 20 nm.
21. The coated particulate metal oxide according to claim 20 wherein no more than 16% by volume of the particulate has a volume diameter of less than 24 nm.
22. The coated particulate metal oxide according to claim 11 wherein more than 84% by volume of the particulate has a volume diameter of less than 70 nm.
23. The coated particulate metal oxide according to claim 22 wherein more than 84% by volume of the particulate has a volume diameter of less than 60 nm.
24. The coated particulate metal oxide according to claim 23 wherein more than 84% by volume of the particulate has a volume diameter of less than 50 nm.
25. The coated particulate metal oxide according to claim 3 wherein the median particle volume diameter of the particulate is less than 45 nm, no more than 16% by volume of the particulate has a volume diameter of less than 20 nm, and more than 84% by volume of the particulate has a volume diameter of less than 50 nm.
26. The coated particulate metal oxide according to claim 3 wherein the particulate is hydrophobic.
27. The coated particulate metal oxide according to claim 26 wherein the particles comprise an organic water repellant coating.
28. The coated particulate metal oxide according to claim 3 wherein the particles comprise (i) 65% to 95% by weight of titanium dioxide, (ii) 2% to 12% by weight of inorganic coating, and (iii) 4% to 18% by weight of organic coating, relative to the weight of the particles.
29. The coated particulate metal oxide according to claim 3 wherein the mean length of the primary particles is in the range from 55 to 85 nm, the mean width of the primary particles is in the range from 8 to 19 nm, and at least 70% of the primary particles have a length in the range from 55 to 85 nm.
30. The coated particulate metal oxide according to claim 3 wherein the median particle volume diameter of the particulate is in the range from 32 to 38 nm, no more than 16% by volume of the particulate has a volume diameter of less than 24 nm, and more than 84% by volume of the particulate has a volume diameter of less than 60 nm.
31. The coated particulate metal oxide according to claim 3 having a photogreying index in the range from 1 to 10.
32. The coated particulate metal oxide according to claim 3 which when incorporated into a sunscreen product is transparent when applied to the skin and has a change in whiteness ΔL in the range from 0.5 to 2.5.
33. The coated particulate metal oxide according to claim 3 which when incorporated into a sunscreen product has a whiteness index in the range from 10% to 80%.
34. The coated particulate metal oxide according to claim 3 comprising titanium dioxide particles.
35. The coated particulate metal oxide according to claim 3 wherein the particles are coated with an inorganic coating comprising alumina.
36. The coated particulate metal oxide according to claim 35 wherein the particles are further coated with an organic coating which comprises fatty acid and/or salts thereof.
37. The coated particulate metal oxide according to claim 3 wherein the particles are coated with an organic coating which comprises fatty acid and/or salts thereof.
38. A hydrophobically coated particulate metal oxide having an extinction coefficient at 524 nm (E 524 ) of less than 2.0 l/g/cm, an extinction coefficient at 450 nm (E 450 ) in the range from 0.1 to 2.0 l/g/cm, an extinction coefficient at 360 nm (E 360 ) in the range from 4 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 45 to 75 l/g/cm, and a λ(max) in the range from 260 to 290 nm, wherein the extinction coefficient E, is calculated from the equation A=E.c.l, where A=absorbance, E=extinction coefficient in liters per gram per cm, c=concentration in grams per liter, l=path length in cm, for a sample of the particulate metal oxide at a concentration of 0.025 g/l in a spectrophotometer at a path length of 1 cm.
39. A coated particulate metal oxide having an extinction coefficient at 524 nm (E 524 ) of 0.5 to 1.0 l/g/cm, an extinction coefficient at 450 nm (E 450 ) in the range from 1.5 to 2.0 l/g/cm, an extinction coefficient at 360 nm (E 360 ) in the range from 7 to 10 l/g/cm, an extinction coefficient at 308 nm (E 308 ) in the range from 40 to 55 l/g/cm, a maximum extinction coefficient E(max) in the range from 55 to 70 l/g/cm, and a % (max) in the range from 265 to 285 nm, wherein the extinction coefficient E, is calculated from the equation A=E.c.l, where A=absorbance, E=extinction coefficient in liters per gram per cm, c=concentration in grams per liter, l=path length in cm, for a sample of the particulate metal oxide at a concentration of 0.025 g/l in a spectrophotometer at a path length of 1 cm.
40. The coated particulate metal oxide of claim 37 wherein said λ(max) is in the range of from 268 to 280 nm.
41. A dispersion comprising a dispersing medium, a dispersing agent and a coated particulate metal oxide, wherein said coated particulate metal oxide has an extinction coefficient at 524 nm (E 524 ) of in the range from 0.1 to 1.0 l/g/cm, an extinction coefficient at 450 nm (E 450 ) in the range from 0.1 to 2.0 l/g/cm, an extinction coefficient at 360 nm (E 360 ) in the range from 4 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 45 to 75 l/g/cm, and a λ(max) in the range from 260 to 290 nm, wherein the extinction coefficient E, is calculated from the equation A=E.c.l, where A=absorbance, E=extinction coefficient in liters per gram per cm, c=concentration in grams per liter, l=path length in cm, for a sample of the particulate metal oxide at a concentration of 0.025 g/l in a spectrophotometer at a path length of 1 cm.
42. A sunscreen comprising a hydrophobically coated particulate metal oxide, wherein said coated particulate metal oxide has an extinction coefficient at 524 nm (E 524 ) of less than 2.0 l/g/cm, an extinction coefficient at 450 nm (E 450 ) in the range from 0.1 to 2.0 l/g/cm, an extinction coefficient at 360 nm (E 360 ) in the range from 4 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 45 to 75 l/g/cm, and a λ(max) in the range from 260 to 290 nm, wherein the extinction coefficient E, is calculated from the equation A=E.c.l, where A=absorbance, E=extinction coefficient in liters per gram per cm, c=concentration in grams per liter, l=path length in cm, for a sample of the particulate metal oxide at a concentration of 0.025 g/l in a spectrophotometer at a path length of 1 cm.
43. The hydrophobically coated particulate metal oxide of claim 38 wherein said extinction coefficient at 524 nm (E 524 ) is less than 1.2 l/g/cm.