AU701950B2 - UV absorbing compositions - Google Patents

Description

WO 97/17406 PCT/AU96/00697 1 UV ABSORBING COMPOSITIONS The present invention relates to UV absorbing compositions, in particular to UV absorbing composition including a surface modified inorganic oxide dispersed in particulate form.

The invention will be now specifically described in reference to the use of modified zinc oxide as the UV attenuating oxide, however the invention also extends to other inorganic oxides including titanium dioxide and iron oxide.

Zinc oxide scatters some wavelengths of light and absorbs other selected wavelengths of light. It exhibits very strong absorption at wavelengths just short of the visible spectrum. It is a strong UVB absorber at the 210-320 nm wavelength and also at the UVA 320-840 nm wavelength. At wavelengths longer than 370 nm, protection is provided by scattering and at wavelengths shorter than 370 nm, protection is achieved predominantly by absorption. Zinc oxide exhibits a strong semi-conductor absorption in the ultraviolet region. The optimum size of a zinc oxide particle for attenuation of the ultraviolet radiation is less than 0.06 pm for the wavelength range 300 400 nm. Absorption is the dominant mechanism for attenuation of ultraviolet radiation in the wavelength range of 300 400 nm.

Zinc oxide has been used as a white reflective pigment (particles size 1.0 20 pm) and as a UV absorber (particles 0.3 5 pm) for many years. The earliest form of presentation of zinc oxide as a sunscreen agent is a pigmented cream which is used to protect various parts of the exposed body, particularly the nose.

Although this zinc oxide cream has its place, the conspicuous nature of the cream when on the skin reduces its cosmetic appeal significantly. Attempts at turning a disadvantage to advantage has led to recent variations of the zinc oxide cream in which a coloured pigment is used to produce a brightly colour cream such as blue, red, yellow or green cream. Such modifications, although popular particularly with the young, have limited cosmetic appeal to the more general population.

It is highly desirable that the UV attenuating substance be invisible on the skin with any colour variation in the sunscreen formulation being adjusted to achieve a desired cosmetic effect.

WO 97/17406 PCT/AU96/00697 2 To overcome this visual problem and also improve the performance as a sunscreen, zinc oxide with a particle size of 0.1 1.0 pm has been used in order to increase UV absorption and decrease reflectance of light. Moreover zinc oxide with a particle size less than 0.1 pm becomes invisible when rubbed onto the skin. However prior art attempts to use microfine zinc oxide has led to difficulties in formulation. The fine zinc oxide powder is difficult to keep in suspension. The particles irreversibly bond during manufacture, and when formulated into a dispersion, tend to aggregate, agglomerate and then settle out. Prior art sunscreen creams incorporating zinc oxide in this particle size range appear white on the skin, develop a settled out layer which is difficult to disperse. Moreover the prior art formulations tend to develop a clear top layer.

Prior art zinc oxide formulations are also limited in terms of the amount of zinc oxide that could be mixed into the formulation (up to about 10% by weight) which limits the blockout effect of the sunscreen. To disperse the zinc oxide in the formulation, various wetting agents, in combination with anti-settling agents have been used, this effectively decreasing the amount of UV active that can be included in the formulation, adding to the cost of manufacture and increasing the risk of an adverse skin reaction.

When zinc oxide is freshly made into a fine powder by burning fumed zinc metal vapour, oxygen will bond onto the fresh zinc oxide surfaces. This oxygen bonding then prevents any further bonding with hydrogen or oxygen ions when the zinc oxide comes in contact with an ester or alcohol and means that this zinc oxide is prone to agglomeration, aggregation, settling and hence whitening.

Furthermore, freshly made zinc oxide can absorb carbon dioxide which leads to the formation of carbonates on its surface. This absorption of carbon dioxide thus inhibits the UV absorbing properties of the zinc oxide.

We have surprisingly found that it is possible to produce a stable oxide containing product which is less prone to aggregation, agglomeration or settling out to hard layer and where there is some settling, redispersion of the oxide can be achieved easily.

We have found that one or more of the problems attending the prior art may be avoided, or at least partially mitigated, by comminuting, eg intensive WO 97/17406 PCT/AU96/00697 3 milling, the oxide in the presence of a liquid being constituted by or including a component having available hydrogen ion and/or oxygen ion. Accordingly the present invention provides, in one aspect, a process for producing a dispersion of particles of an inorganic oxide selected from zinc oxide, titanium dioxide or iron oxide in a liquid, the process including comminuting the oxide in the presence of the liquid, the liquid being constituted by or including a component having available hydrogen and/or oxygen ions.

Without wishing to limit the invention in any way, it is believed that when zinc oxide crystals are comminuted during the process of the invention, they produce smaller particles with fresh cleavage surfaces, these surfaces when produced by comminution in the liquid, bond to available hydrogen ion and/or oxygen ion to form zinc oxide which is both encapsulated and bonded to a film of the liquid. This gives a very stable product which does not aggregate, agglomerate or settle out to a hard layer.

Preferably the oxide is comminuted to a particle size of less than about pm. More preferably the oxide is not comminuted below a particle size of about 0.025 pm, preferably about 0.04 10 pm. A comminuted particle size of about 0.04 0.1 pm is particularly preferred.

The component containing available hydrogen ion and/or oxygen ion may be a substance or compound having one or more hydroxyl groups or hydrogen groups. Preferably the liquid is selected from one of an alcohol, ester, hydrogenated ester or polymer containing hydroxyl group(s) or hydrogen group(s) or mixtures of two or more of the foregoing.

Examples of suitable liquids may be selected from the group consisting of dioctyl phthalate, glycerol mono-oleate, glycerol mono stearate, isopropyl myristitate, diethyl phthalate, propylene glycol dicaprylate/caprate, glycerol tricaprylate/caprate, methyl laurate, methyl oleate and dioctyl adipate.

Preferably the liquid in which comminution takes place is substantially free of water. More preferably the liquid is free of water.

Comminution of the oxide may be carried out by milling. Milling may be achieved by any suitable method. Milling may be carried out using a ball mill, or other intensive mill such as a bead mill, attritor mill or sigma mixer.

WO 97/17406 PCT/AU96/00697 4 Preferably the process of the invention is carried out by adding the oxide in the particulate form to the liquid whilst milling occurs although the oxide may be combined with the liquid and the mixture milled. The initial particle size of the oxide may be in the range of about 0.1 pm to 10.0 pm.

Preferably the oxide is zinc oxide. The zinc oxide used in the present invention may be crystalline zinc oxide. Amorphous porous zinc oxide is preferred where a very small comminuted particle size is desired as it is easier to mill down.

Preferably comminution occurs at an elevated temperature. The elevated temperature may be in the range of about 500 to 150 0 C. The oxide may added in an amount in the range of about 5% to 95% of the final dispersion.

In a further aspect, the present invention provides a liquid dispersion of an inorganic oxide in particulate form, the oxide selected from zinc oxide, titanium dioxide and iron oxide, wherein the oxide has a particle size in the range of about 0.02 30 pm and wherein the liquid is constituted by or includes a component having an available hydrogen ion, wherein the surfaces of the oxide particles are bonded to the available hydrogen ions and/or oxygen ions.

The oxide dispersion of the invention may be produced by the process of the present invention.

Preferably the oxide is present in the dispersion in an amount of about to 95% by weight. Preferably the oxide is present in an amount of at least about by weight, more preferably greater than about 20% by weight of the dispersion. The surface area of the particulate oxide in the dispersion may be about 6m 2 per gram of oxide to about 50m 2 more preferably about 20 to about 30m 2 /g.

Preferably the liquid component of the dispersion is selected from an alcohol, ester, hydrogenated ester or a polymer containing available hydrogen ion, for example, hydroxyl groups or hydrogen groups or mixtures of one or more thereof.

Preferably the dispersion of the oxide includes oxide in a particle range of about 0.4 to 10 pm, more preferably about 0.04 0.5 pm.

WO 97/17406 PCT/AU96/00697 A zinc oxide powder has a refractive index of 1.9 2 with an oil absorption factor of 32.3. In its natural form, it is one of the whitest-pigments available, however when it is milled to a particle size less than 0.1 pm in the liquid containing available hydrogen ion, it exhibits a distinctive yellow colour. This is believed to be due to scattering of light, similar to the yellow colours in opals which also scatter light with 25 nm crystals.

Preferably the oxide is zinc oxide.

The dispersion of the present invention has a wide range of applications in which its UV absorbent properties may be utilised. In particular, the zinc oxide product of the present invention also has antioxidant properties which also makes it useful in many applications.

The oxide dispersion of the present invention may constitute or be included in topical preparations such as skin care or therapeutic products, cosmetics or hair care products. The dispersion of the invention may be used in coloured cosmetics such as lipsticks, face powders, mascara, eye shadows, blushers etc.

The dispersion may also be included in stick products such as an anti-chap stick.

The present invention provides a sunscreen composition, the composition including a zinc oxide dispersion in accordance with the present invention.

By appropriate selection of the oxide loading in the suspension (for example, about 20% to 30% oxide), the dispersion of the invention may be incorporated into aerosol products. The product of the invention may be incorporated into hair care products to provide UV protection.

The dispersion of the invention also has application in the area of coatings and films. The invention is particularly suitable in instances where a clear finish is required such as in the case of clear lacquers, varnishes and shellacs. In this case, the zinc oxide acts both as a UV absorber and an antioxidant. In the case of a timber coating product, the zinc oxide acts as a UV absorber and by soaking into the timber grain protects the timber product itself.

The dispersion of the invention may be incorporated into latex coating emulsions.

WO 97/17406 PCT/AU96/00697 6 The present invention also finds application in the area of printing inks and is particularly suitable for natural pigmented inks wherein the-oxide may act as an antioxidant and UV absorber.

The product of the invention may also be incorporated into plastic products to use its antioxidants and/or UV absorbing properties. It may be incorporated into addition polymers such as PVC, and polyolefins or condensation polymers such as polyurethanes. The dispersion of the invention may be incorporated in the injection, blow moulding, casting or extrusion stage.

The present invention also has application in paints as a UV absorber and/or antioxidant. The invention also finds particular application in the production automotive finishes such as clear film so as to provide more resistance to scratching and abrasion.

The present invention accordingly extends to the abovementioned compositions or formulations including an oxide dispersion in accordance with the invention.

In order that the invention may be more readily understand, we provide the following non limiting examples.

METHOD

Zinc oxide, titanium dioxide or ion oxide may all be milled in a liquid including a component having available hydrogen ions. Milling may be carried out an intensive mills such as a ball mill, bead mill, attritor mill, edge runner, Z arm or sigma mixer or the like.

Example 1 1220 g zinc oxide 813 g dried tridecanol The tridecanol was loaded into a bead mill with 10 mm PSZ ball. Milling was started and the zinc oxide fed into the mill, continuously at a slow feed rate.

The temperature was allowed to rise to 500C. The zinc oxide was milled for about 12 hours to disperse all the zinc oxide and the particle size was checked against a stand. A dispersion of zinc oxide particles of the size less than 0.2 pm dispersed in tridecanol was produced.

WO 97/17406 PCT/AU96/00697 7 Example 2 1220 g zinc oxide 813 g isopropanol The isopropanol was loaded into a pre mix tank of a bead mill. Zinc oxide was added slowly and continuously. The pre-mix is fed into a bead mill and mixed for six hours and the particle zinc oxide checked against the standard and a dispersion of zinc oxide particles of the size less than about 0.15 pm dispersed in isopropanol was produced.

Example 3 1120 g zinc oxide 813 g glycerol tricaprylate The glycerol tricaprylate and zinc oxide were loaded into a pre mix tank.

The pre mix was mixed and fed into a triple roll mill. The zinc oxide/glycol tricaprylate dispersion was milled until the particle met the standard after three passes.

Example 4 Coated zinc oxide for use in a polyvinyl chloride compmosition was prepared by intensive bead milling of zinc oxide using small bead of 1 mm diameter. Milling was conducted in dioctyl phthalate until a zinc oxide particle size in the range of from 40 to 70 nm was provided. The coated zinc oxide was used in preparing the polyvinyl chloride composition detailed below.

Polyvinyl Chloride Composition Kg PVC Resin K-66 100 Dioctyl Phthalate Lubricant Wax Calcium/Zinc Stabiliser Zinc Oxide encapsulated (coated) milled in DOP WO 97/17406 PCT/AU96/00697 8 The resin mix composition was run on a double roll mil 180°C for 3 minutes to give a clear sheet Example Coated zinc oxide was prepared by ball intensive milling of zinc oxide in the presence of a glycerol tricaprylate/caprate mixed ester. Milling was conducted in an intensive bead mill using bead of 1 mm diameter at 800C until the particle size of about 40-70 nm was provided. The zinc oxide was used in preparing a water based printing varnish detailed below.

Water Based Printing Varnish Kg Joncryl 74 (acrylic polymer resin) Emulsion 32 Jonalec 26 (acrylic polymer resin) Zinc Oxide Coated 3 Butyl Cellosolve 100.0 Mix with high speed mixer Example 6 Coated zinc oxide was prepared by the method described in Example 5 and used to prepare the oil based printing varnish detailed below.

WO 97/17406 PCT/AU96/00697 9 Oil Based Printing Varnish Kg Pentalyn 833 (pentaerythritol ester) Pentalyn 858 (pentaerythritol ester) Micronised PE Wax Micronised PT Wax Long Oil Linseed Alkyd Megasol 52 Solvent (hydrocarbon solvent) 26.5 Zinc Oxide Coated 3 100.0 Mix with high speed mixer The zinc oxide particle size distribution (nm) in an example of a dispersion in accordance with the invention has a number-weighted gaussian analysis (Vesicles) as follows: GAUSSIAN SUMMARY: Mean Diameter 184.8 nm Chi Squared 0.103 Stnd. Deviation 85.6 nm Baseline Adj. 0.000% Coeff. ofVar'n 0.463 Mean Diff. Coeff. 2.32E-08 cm2/s Cumulative Results: of distribution 113.15 nm of distribution 154.51 nm 75% of distribution 211.56 nm 99% of distribution 457.08 nm The distribution may be represented as shown in Figure 1.

Example 7 Sunscreen Lotion WO 97/17406 PCT/AU96/00697 Phase A 60 0 C Mix until dispersed.

Kg Zinc Oxide 150 "Elafac" (glycerol ester) "Minno 21" (dispersing agent) "Bridge 58" (emulsifier) Phase A was prepared by milling in a bead mill using 1 mm beads over a period to provide coated zinc oxide particles of size 100 to 400 nm.

Phase B Blend at 60 0

C.

"Keltanol" Solution (gum suspending agent) 0.3 "Carbopol" 974 (thickener) 0.3 Phased "CA24" Preservative 0.2 Procedure Add Phase B to Phase A. Mix until smooth. Then with Propeller mixer causing vortex add Phase D mix until uniform.

Example 8 Sunscreen Lotion Phase A 40 0 C Mix until disperses.

Kg Cupl Pic (glycerol ester) Minno 21 dispersing 10.0 Titanium dioxide (Micronisers) coated 15.0 Zinc Oxide (Micronisers) coated 12.5 WO 97/17406 PCT/AU96/00697 11 Phase A was prepared by milling the titanium and zinc oxide composition with the ester in a ball mill using beads of size 1 mm diameter to provlde a particle size of 100 to 400 nm.

Phase B 40 0

C

Water 60.3 Phase C Dry blend Veegum 0.70 Keltanol 0.3 Phase D CA24 Preservative 0.2 The sunscreen composition was prepared by adding Phase C to Phase B and mixed until the composition was smooth. With proper mixing (Propeller causing a vortex) Phase A was added and the composition missed until uniform.

Phase D was then added and the resulting composition mixed until uniform.

The sunscreen lotion provides a high level of UV protection without significant whitening of the skin.

Zinc oxide can be used as a protector for light fastness of cheaper and expensive pigments in printing inks and overprint varnishes. Moreover it protects clear varnishes which degrade in the presence of ultraviolet light.

Example 9 Coating Composition The coated zinc oxide prepared in accordance with Example 5 may be incorporated into an acrylic emulsion coating composition for use as a timber finish or other coating application.

The mlling is conducted in the absence of water and the coated zinc oxide mixture is subsequently dispersed in water. The resulting composition may be WO 97/17406 PCT/AU96/00697 12 used in forming an emulsion with acrylic resin or may be incorporated into a preformed acrylic resin emulsion.

Example The zinc oxide single distribution is an example of a dispersion of the invention for use in coating or printing varnish compositions as shown below and is graphically represented in Figure 2.

NUMBER-Weighted NICOMP DISTRIBUTION Analysis (Solid Particles) NICOMP SUMMARY: Peak Number 1: Mean Diameter 80.0 nm Peak Number 2: Mean Diameter 325.1 nm Number: Number: 96.85% 3.15% Mean Diameter 90.4 nm Fit Error 2.737 Residual 12.165 NICOMP SCALE PARAMETERS: Min. Diam.= 30.0nm Plot Size Smoothing 3 Plot Range 100 Run Time 0 Hr 11 Min 15 Sec Count Rate 466 Khz Channel #1 4027.8 K Channel Width 45.0 usec GAUSSIAN SUMMARY: Mean Diameter 165.2 nm Stnd. Deviation 64.8 nm (39.2%) Coeff. of Var'n 0.392 Temperature 20 deg C Viscosity 1.002 cp Index of Ref. 1.333 Chi Squared 4.236 Baseline Adj. 0.000% Mean Diff. Coeff. 1.22E-08 cm2/s

Claims (14)

1. A process for producing a dispersion of particles of an inorganic oxide selected from zinc oxide, titanium dioxide or iron oxide in a liquid, the process including comminuting the oxide in the presence of the liquid to produce smaller particles with fresh cleavage surfaces wherein the liquid is selected from the group consisting of alcohols, esters, hydrogenated esters and polymers containing available hydroxyl group(s) or hydrogen group(s) and wherein the liquid is free of dispersing agent.

2. A process according to claim 1 wherein the liquid selected from the groups consisting of dioctyl phthalate, glycerol mono-oleate, glycerol mono-stearate, isopropy myristate, diethyl phthalate, propylene glycol dicaprylate/caprate, glycerol tricapylate/caprate, methyl laurate, propylene glycol, methyl oleate, dioctyl adipate and mixtures thereof.

3. A process according to claim 1 wherein the inorganic oxide is comminuted to a particle size in the range of less than 10 jm.

4. A process according to claim 1 wherein the inorganic oxide is comminuted to provide a particle size in the range of from 0.04 to 0.1 tm A process according to claim 1 wherein the particles are comminuted in the liquid from a particle size of 0.2 pm to 10.0 p[m to provide a particle size in the range of 0.04 to 0.1 pm.

6. A process according to claim 1 wherein the liquid is substantially free of water.

7. A process according to claim 1 wherein the comminuting is carried out _using a ball mill, bead mill, attritor mill or sigma mixer. AMINl)lE ii;; 14

8. A process according to claim 1 wherein the inorganic oxide is zinc oxide.

9. A process according to claim 1 wherein the comminuting is carried out at a temperature in the range of about 50 to 1500C. A process according to claim 1 wherein the inorganic oxide is added in an amount in the range of 10% to 95% by weight of the final dispersion.

11. A process according to claim 1 wherein the surface area of the particulate inorganic oxide is from about 6m 2 per gram of inorganic oxide to about 50m 2 per gram.

12. Use of the liquid dispersion prepared according to the process of claim 1 in manufacture of a topical preparation for use in skin care, therapeutic treatment, as a cosmetic or as in hair care.

13. A process according to claim 1 wherein a colouring agent is added to the dispersion to provide a cosmetic formulation.

14. Use of a liquid dispersion prepared according to the process of claim 1 in manufacture of a cosmetic selected from lipstick, face powder, mascara, eye shadow or blush. A process according to claim 1 wherein the inorganic oxide is zinc oxide present in an amount of from 20 to 30% by weight of the composition and the dispersion is used in manufacture of a sunscreen.

16. Use of a liquid dispersion prepared according to claim 1 as an additive in a coating or plastics composition. P(71T/AYj 94 bj Ift 0 ~CE~~J)3 CJUL

17. Use according to claim 16 when the coating or plastics composition is clear or semi transparent. AM I.m"