Metal Oxide Dispersion
A dispersion contains particles of metal oxide having a median volume particle diameter in the range from 24 to 42 nm which are dispersed in a medium which includes a mixture of at least one polar material having an interfacial tension of less than 30 mNm −1 and at least one non-polar material having an interfacial tension of greater than 30 mNm −1 . The dispersion can be fused in a sunscreen product that exhibits effective UV protection, transparency, and improved skin feel.
1 . A dispersion comprising particles of metal oxide having a median volume particle diameter in the range from 24 to 42 nm, dispersed in a medium which comprises a mixture of at least one polar material having an interfacial tension of less than 30 mNm −1 and at least one non-polar material having an interfacial tension greater than 30 mNm −1 .
2 . A dispersion according to claim 1 wherein the metal oxide particles have a mean crystal size in the range from 4 to 10 nm.
3 . A dispersion according to claim 1 where at least 40% by weight of metal oxide particles have a crystal size within the range 5 to 9 nm.
4 . A dispersion according to claim 1 wherein less than 16% by volume of metal oxide particles have a volume diameter of less than 9 nm below the median volume particle diameter.
5 . A dispersion according to claim 1 wherein less than 30% by volume of metal oxide particles have a volume diameter of less than 5 nm below the median volume particle diameter.
6 . A dispersion according to claim 1 wherein more than 84% by volume of metal oxide particles have a volume diameter of less than 17 nm above the median volume particle diameter.
7 . A dispersion according to claim 1 wherein more than 70% by volume of metal oxide particles have a volume diameter of less than 6 nm above the median volume particle diameter.
8 . A dispersion according to claim 1 wherein the metal oxide particles have an extinction coefficient at 524 nm in the range from 0.4 to 1.2 l/g/cm.
9 . A dispersion according to claim 1 wherein the metal oxide particles have an extinction coefficient at 360 nm in the range from 5 to 11 l/g/cm.
10 . A dispersion according to claim 1 wherein the metal oxide particles have an extinction coefficient at 308 nm in the range from 40 to 52 l/g/cm.
11 . A dispersion according to claim 1 wherein the metal oxide particles have (i) a median volume particle diameter in the range from 29 to 37 nm, and/or (ii) less than 10% by volume of particles having a volume diameter of less than 11 nm below the median volume particle diameter, and/or (iii) less than 16% by volume of particles having a volume diameter of 8 nm below the median volume particle diameter, and/or (iv) less than 30% by volume of particles having a volume diameter of less than 5 nm below the median volume particle diameter, and/or (v) more than 90% by volume of particles having a volume diameter of less than 27 nm above the median volume particle diameter, and/or (vi) more than 84% by volume of particles having a volume diameter of less than 17 nm above the median volume particle diameter, and/or (vii) more than 70% by volume of particles having a volume diameter of less than 6 nm above the median volume particle diameter.
12 . A dispersion according to claim 1 wherein the particles of metal oxide have an extinction coefficient at 524 nm in the range from 0.5 to 1.1 l/g/cm, an extinction coefficient at 450 nm in the range from 1.0 to 2.0 l/g/cm, an extinction coefficient at 360 nm in the range from 6 to 10 l/g/cm, an extinction coefficient at 308 nm in the range from 44 to 48 l/g/cm, a maximum extinction coefficient in the range from 60 to 64 l/g/cm, and a λ(max) in the range from 274 to 282 nm.
13 . A dispersion according to claim 1 wherein the polar material has an interfacial tension in the range from 10 to 25 mNm −1 .
14 . A dispersion according to claim 1 wherein the non-polar material has an interfacial tension in the range form 35 to 45 mNm −1 .
15 . A dispersion according to claim 1 wherein the difference in the interfacial tension of the polar material and the non-polar material is in the range from 13 to 20 mNm −1 .
16 . A dispersion according to claim 1 wherein the ratio of polar to non-polar material is in the range from 30 to 70:30 to 70% by weight.
17 . A dispersion according to claim 1 wherein the polar material is selected from the group consisting of are triethylhexyl triglyceride, C12-15 alkyl benzoate, caprylic/capric triglyceride, isononyl isononanoate, isostearyl neopentanoate, and octyldodecyl neopentanoate.
18 . A dispersion according to claim 1 wherein the non-polar material is selected from the group consisting of isohexadecane, hydrogenated polyisobutene, and squalane.
19 . A dispersion comprising particles of metal oxide having a median volume particle diameter in the range from 24 to 42 nm, dispersed in a medium which comprises a mixture of (i) at least one polar material selected from the group consisting of, C12-15 alkyl benzoate, caprylic/capric triglyceride, cetearyl isononanoate, ethylhexyl isostearate, ethylhexyl palmitate, isononyl isononanoate, isopropyl isostearate, isopropyl myristate, isostearyl isostearate, isostearyl neopentanoate, octyldodecanol, pentaerythrityl tetraisostearate, PPG-15 stearyl ether, triethylhexyl triglyceride, dicaprylyl carbonate, ethylhexyl stearate, helianthus annus (sunflower) seed oil, isopropyl palmitate, and octyldodecyl neopentanoate, and (ii) at least one non-polar material selected from the group consisting of, C13-14 isoparaffin, isohexadecane, paraffinum liquidum (mineral oil), squalane, squalene, hydrogenated polyisobutene, and polydecene.
20 . A sunscreen product formed from a dispersion comprising particles of metal oxide having a median volume particle diameter in the range from 24 to 42 nm, dispersed in a medium which comprises a mixture of at least one polar material having an interfacial tension of less than 30 mNm −1 and at least one non-polar material having an interfacial tension of greater than 30 mNm −1 .
21 . A sunscreen product comprising particles of metal oxide having a median volume particle diameter in the range from 24 to 42 nm, and (i) at least one polar material selected from the group consisting of are triethylhexyl triglyceride, C12-15 alkyl benzoate, caprylic/capric triglyceride, isononyl isononanoate, isostearyl neopentanoate, and octyldodecyl neopentanoate, and (ii) at least one non-polar material selected from the group consisting of isohexadecane, hydrogenated polyisobutene, and squalane.
22 . The use of a dispersion comprising particles of metal oxide having a median volume particle diameter in the range from 24 to 42 nm, dispersed in a medium which comprises a mixture of at least one polar material having an interfacial tension of less than 30 mNm −1 and at least one non-polar material having an interfacial tension of greater than 30 mNm −1 , to produce a sunscreen having improved skin feel.
23 . The use of a dispersion comprising particles of metal oxide having a median volume particle diameter in the range from 24 to 42 nm, dispersed in a medium which comprises a mixture of at least one polar material having an interfacial tension of less than 30 mNm −1 and at least one non-polar material having an interfacial tension of greater than 30 mNm −1 , in the manufacture of a transparent sunscreen having improved skin feel.