Metal Oxide Dispersions

Abstract

A dispersion contains particles of metal oxide dispersed in a siloxane fluid and a dispersing agent which is a polysiloxane wherein (i) the polysiloxane contains in the range from 0.1 to 3 carboxyl groups, and (ii) the ratio of non-carboxyl group containing monomer units to carboxyl group containing monomer units in the polysiloxane is in the range from 40 to 150:1. The dispersion is particularly suitable for use as an ingredient in sunscreening cosmetics.

Description

Example 1

86.3 g of cyclomethicone, 11.3 g of polysiloxane containing a carboxyl group (Monasil PCA (trade mark, ex Uniqema)) and 150 g of hydrophobically coated zinc oxide having an average primary particle size of approximately 80 nm (calculated from specific surface area) were mixed together and thoroughly agitated for 15 minutes. The mixture was then passed through a horizontal bead mill operating at approximately 1500 r.p.m. and containing zirconia beads as grinding media. The mixture was passed through the mill and was then returned to the pre-mix vessel and passed through the mill a further three times. The optical characteristics of the resulting dispersion (as determined by UV spectrometry after dilution by a factor of 20,000 using n-octanol) are given in Table 1 below, where λ_max is the wavelength in nm at which maximum attenuation was observed and E_max, E₃₀₈, E₃₆₀ and E₅₂₄ are the observed extinction coefficients in l/g/cm at λ_max, 308 nm, 360 nm and 524 nm respectively,

TABLE 1
λmax	Emax	E308	E360	E524
374	17.0	13.3	14.2	2.8

Example 2

The procedure of Example 1 was repeated except that 66.8 g of cyclomethicone, 10.8 g of Monasil PCA, 2.4 g isostearic acid (Prisorine 3505 (trade mark, ex Uniqema)) and 120 g of uncoated zinc oxide having an average primary particle size of approximately 60 nm were used. The optical characteristics of the resulting dispersion were determined by diluting by a factor of 20,000 in cyclohexane. The results are given in Table 2 below

TABLE 2
λmax	Emax	E308	E360	E524
367	15.6	14.1	14.9	1.3

This dispersion was used to prepare a sunscreen formulation having the following composition;

% by wt.
Phase A
ARLACEL P135 (trade mark, ex Uniqema) 2.0
ARLAMOL HD P135 (trade mark, ex Uniqema) 5.0
ARLAMOL E P135 (trade mark, ex Uniqema) 2.4
Finsolv TN                       4.0
Candelilla Wax                   1.0
Magnesium Stearate               0.7
Zinc oxide dispersion produced in Example 1 14.0
Jojoba Oil                       4.0
Cyclomethicone                   5.6
Parsol MCX                       8.0
Phase B
ATLAS G-2330 (trade mark, ex Uniqema) 3.0
Germaben II                      1.0
Magnesium Sulphate               0.7
D-Panthanol USP                  0.8
Allantoin                        0.2
Demineralised Water              47.6

Procedure

• • (i) Phases A and B were prepared separately and heated to 75-80° C.
  • (ii) Phase B was slowly added to phase A with intensive stirring using a Silverson mixer for two minutes.
  • (iii) The mixture was cooled to 25° C. with intensive stirring.

The Sun Protection Factor for the product was determined using the in vitro method of Diffey and Robson, J. Soc. Cosmet. Chem. Vol. 40, pp 127-133,1989, and a value of 23 was obtained.

The above examples illustrate the improved properties of a dispersion and sunscreen according to the present invention.

Claims

1. A dispersion comprising particles of metal oxide dispersed in a siloxane fluid and a dispersing agent which is a polysiloxane wherein (i) the polysiloxane comprises in the range from 0.1 to 3 carboxyl groups, and (ii) the ratio of non-carboxyl group containing monomer units to carboxyl group containing monomer units in the polysiloxane is in the range from 40 to 150:1.

2. A dispersion according to claim 1 wherein the polysiloxane has a viscosity in the range from 0.2 to 10 Pa·s.

3. A dispersion according to claim 1 wherein the polysiloxane has a molecular weight (number average) in the range from 4,000 to 15,000.

4. A dispersion according to claim 1 wherein the dispersion comprises greater than 30%, more preferably greater than 40%, and particularly greater than 50% by weight of particles of metal oxide.

5. A dispersion according to claim 1 wherein the polysiloxane comprises 0.8 to 2.5 carboxyl groups per molecule.

6. A dispersion according to claim 1 wherein the polysiloxane comprises in the range from 30 to 200 non-carboxyl group containing monomer units.

7. A dispersion according to claim 1 wherein the carboxyl group is attached laterally, preferably only laterally, to the polysiloxane chain.

8. A dispersion according to claim 1 wherein the metal oxide particles are hydrophobic.

9. A dispersion according to any one of the preceding claims claim 1 wherein the siloxane fluid dispersing medium is a cyclic oligomeric dialkylsiloxane, a linear dimethyl-siloxane oligomer and/or polymer, and/or phenyltris(trimethylsiloxy)silane.

10. A method of preparing a dispersion of metal oxide which comprises milling with a particulate grinding medium particles of metal oxide in a siloxane fluid in the presence of a dispersing agent which is a polysiloxane wherein (i) the polysiloxane comprises in the range from 0.1 to 3 carboxyl groups, and (ii) the ratio of non-carboxyl group containing monomer units to carboxyl group containing monomer units in the polysiloxane is in the range from 40 to 150:1.

11. A sunscreen composition comprising particles of metal oxide, a siloxane fluid, and a polysiloxane comprising (i) in the range from 0.1 to 3 carboxyl groups, and (ii) non-carboxyl group containing monomer units to carboxyl group containing monomer units at a ratio in the range from 40 to 150:1.

12. The use of a dispersion comprising particles of metal oxide dispersed in a siloxane fluid and a dispersing agent which is a polysiloxane wherein (i) the polysiloxane comprises in the range from 0.1 to 3 carboxyl groups, and (ii) the ratio of non-carboxyl group containing monomer units to carboxyl group containing monomer units in the polysiloxane is in the range from 40 to 150:1, to form an end-use sunscreen composition.