United States Patent:  6,106,847

Assignee:  Lancaster Group GmbH (Ludwigshafen, DE)

Filed:  September 5, 1997

The invention relates to a stable multiple phase emulsion of the O₁ /W/O₂ type with high proportions of the primary O₁ /W emulsion. The new emulsions have an emulsifier-free primary oil-in-water phase consisting of a viscoplastic aqueous gel containing the finely distributed inner oil droplets together with a gelling agent, wherein the thixotropic primary oil-in-water phase has a yield point in the range from 20 to 100 Pa and a plastic viscosity of 0.01 to 0.1 Pa.multidot.s and contains at least one lipophilic agent in the primary oil; and a secondary oil phase in which the primary oil-in-water phase is present together with a lipophilic emulsifier; and wherein the proportion of the inner oily phase is from 10 to 35 % by weight relative to the total weight of the emulsion. The higher proportions of the inner oily phase render possible higher proportions of organic sun protection agents with simultaneous avoidance of skin irritations.

DETAILED DESCRIPTION OF THE INVENTION

Following Ross, S. and Morrisson, I. "Colloidal Systems and Interfaces", John Wiley & Sons, New York, Page 17-19, the plastic flow can determined in relation to shear stress and shear rate. The rheogramm of a plastic material describes one that does not flow until sufficient stress is applied. The stress at which the flow begins is called YIELD POINT; at stresses larger than the yield point, the rate of flow is approximately linear with the shearing stress. This yield point is also called yield value.

The plastic viscosity is derived from the slope of the graph line in the rheogramm and can be calculated by the yield point as the experimental result (see also Couarraze, G. and Grossiord, J. L. "Initiation a la Rheology", Lavoisier-Tec&Doc, Paris, 2nd edition, p. 75-78) Yield point of plastic bodies which are also named Bingham or Casson bodies are for example for spraying laquer: low yield point of 0-1 Pa (low plastic viscosity of 0.01-0.1 Pa.multidot.s), paints od ketchup: medium yield point of 5-50 Pa (low plastic viscosity of 0.1-0.5 Pa.multidot.s), ointments: high yield point of 100-1000 Pa (medium to high plastic viscosity of 0.5-5 Pa.multidot.s).

According to the invention the stable O₁ /W/O₂ type multiple phase emulsion consists of a primary oil-in-water phase without emulsifier, in which the inner oil droplets are present in a viscoplastic aqueous gel essentially coalescence-free and finely distributed together with a gelling agent, preferably an amphiphilic polyacrylate block copolymer, wherein the yield point of the viscoplastic gel is in the range from 20 to 100 Pa and their plastic viscosity from 0.01 to 0.1 Pa.multidot.s, and wherein the inner oily phase occupies a proportion of 10 to 35% by weight relative to the total emulsion, and the secondary oil contains at least one lipophilic agent; and a secondary oil phase, in which the primary O/W phase exists together with a lipophilic emulsifier.

For elucidation it must be pointed out that the inner oil droplets (inner oily phase) are constantly incorporated in the primary O₁ /W phase.

In the case of the viscoplastic gel of the invention there were determined for the primary O₁ /W emulsion a medium to high yield point of 20 to 100 Pa. These values were determined by the known Casson equation. The gel structure is very quickly build up, even after a temporary destruction by a large shear rate. This property is called Thixotropie and is essential for the inventive concept.

Suitable as gelling agents for the primary O₁ /W phase are all gelling agents bestowing distinct viscoplastic properties on the aqueous phase and possessing sufficient stabilizing and dispersing characteristics to generate correspondingly small droplets incorporated in finely distributed form in the second stage by the secondary oil phase.

Particularly suitable for this are polyacrylate block colymers with alternating hydrophilic and hydrophobic blocks, particularly Hypan.RTM. hydrogels of the TN type. These hydrogels form a fine three-dimensional net in the aqueous medium which can be reversible degraded by high shear stresses and/or heat. Suitable hydrogels are (CTFA names): Acrylic acid/Acrylonitrogens copolymer such as Hypan.RTM. SA-100H-100H or Hypan.RTM. SR-150H-150H; Ammonium acrylates/Acrylonitrogens copolymer such as Hypan.RTM. SS-201; Polyquaternium-31 such as Hypan.RTM. QT-100 (all produced by Kingston Technology Inc., N. Y., USA).

The amphiphilic polyacrylate block copolymer is responsible herein for both the viscoplastic properties as well as for the good distribution of the inner oil phase in the aqueous gel.

The addition of the Hypan.RTM. TN gels takes place in very small amounts ranging from 0.2 to 0.5% by weight relative to the total mass of the emulsion.

As gelling agent a three-layer clay mineral such as smectite can be used. Suitable above all are synthetic smectites with tri-octahedral coordinated cations prepared from magnesium silicates and alkali cations, for example Smectite SWN.RTM. (from Nikko Chemicals Corp.). The amounts of smectites used are higher than those used for Hypan hydrogels, that means about 1-3% by weight.

With the aid of the gelling agent a thixotropic aqueous gel containing finely distributed oil droplets is obtained and wherein this primary oil-in-water phase has a yield point in the range from 20 to 100 Pa. The yield point can be increased further by addition of polyethylene glycol, e.g. by addition of Glycereth-26 or a polyethylene glycol such as PEG-8.

Moreover essential to the invention is the very low plastic viscosity from 0.01 to 0.1 Pa.multidot.s.

The oil used for the primary oil phase is a normal triglyceride such as vegetable or synthetic oils commonly used in cosmetic formulations. Also included are linear or branched esters of fatty acids and alcohols, esters of fatty acids and glycols such as propylene glycol ester as well as esters of hydroxyfatty acids. Essential for the primary oil is the compatibility with the active agents of the oil phase and the interaction with the polyacrylate block copolymers in order to form a sufficiently thin (low viscosity) primary O₁ /W emulsion which however has a sufficient yield point.

Esters of fatty acids and alcohols of medium chain length have proved particularly advantageous for sun protection preparations such as C₁₂ -C₁₃ Alkyl Octanoate esters used together with organic sun protection agents. Other special esters can be added such as C₁₂ -C₁₃ Alkyl Malate, C₁₂ -C₁₃ Alkyl Lactate and C₁₂ -C₁₃ Alkyl Citrate.

The preferred vegetable oils are avocado oil, rice bran oil, jojoba oil and Babassu oil.

Other esters such as diethylene glycol dioctanoate or diisononanate, propylene glycol dicaprylate, neopentyl glycol diheptanoate etc. can be used.

The primary O₁ /W-emulsion contains at least one lipophilic agent in the primary oil droplets. This agent is preferably a UV-protection agent or a UV-blocking agent such as Octyl Methoxycinnamate, Octyl Salicylate; Homosalate; Menthyl Anthranilate; Octocrylene; Benzophenone-3; Octyl Dimethyl PABA [p-aminobenzoic acid]; 4-Methylbenzilidene Camphor; Butyl Methoxy-Dibenzoyl methane.

The primary (inner) oil phase and also the secondary (outer) oil phase may moreover contain: liposoluble vitamins such as vitamin A esters (Retinol palmitate, acetate); vitamin E such as Tocopherol acetate or Tocopherol linolate; vitamin B₂, vitamin D₆ ; vitamin F;

Anti-inflammatory agents such as Bisabolol, Glycerrethinic acid, Stearyl Glycerrhetinate; polyunsaturated fatty acids or fatty acid esters thereof such as avocado, peanut and borrage oils; jojoba oil and calendula oil etc.; unsaponifiables such as shea butter, avocado, soybean oil etc.; lanolin and lanolin derivatives; emollients such as perhydrosqualene, perfluoropolyethers.

In the aqueous phase certain hydrophilic constituents may be present as humectants such as e.g. glycerol, propylene glycol, different grades of PEG, sorbitol, glucose, maltose etc.; Panthenol or Allantoin; peptides or proteins and their derivatives such as collagen, elastin etc.; water soluble vitamins such as ascorbic acid; preservatives such as chlorohexidine, phenoxyethanol, dimethyl Hydantoin, imidazolidinyl urea.

The secondary or outer oil phase in which the primary oil-in-water emulsion is emulsified as finely distributed droplets is formed by any oil for cosmetic formulations, such as e.g. silicone oil, synthetic fatty acid esters, paraffin oils, waxes such as micro-waxes, beeswax, castor wax or polyethylene wax.

Silicone oil has proved particularly advantageous particularly then if a sun protection preparation is to be produced. Silicone oil is preferred because it does not feel greasy, shows good spreadability on the skin and good water repellence. Linear or cyclic polydimethylsiloxanes such as Cyclomethicone to which further organopolysiloxanes can be added such as Alkyldimethicone, Alkoxydimethicone (Abil.RTM. waxes), or Phenyldimethicone or Phenyltrimethicone can be used.

Other suitable polymers such as silicone acrylates and vinyl silicones or fluorosilicones or perfluoro-polyethers (such as Fomblin.RTM.) as well as silicone gums such as Dow Corning 1401.RTM. and 1403.RTM. can be added to the silicone oils to improve the blocking effect and the ability to form films.

Suitable emulsifiers can be used for the secondary oil phase corresponding to the oils employed. If silicone oils form the secondary oil phase then emulsifiers such as polysiloxane-polycetyl-polyethylene glycol copolymers (CTFA-name: Cetyl Dimethicone Copolyol) e.g. Abil.RTM. EM90 (Goldschmidt), Abil.RTM. WE09 (Goldschmidt), Q2-5200 (Dow Corning) are suitable. To be advantageous the HLB value [hydrophilic-lipophilic balance] of these emulsifiers should not be greater than 8.

Further agents may be contained in the secondary oil phase. Particularly in the case of sun protection preparations sun protection agents may be contained, preferably inorganic mineral pigments such as micronized TiO₂ or ZnO. Other powdery products such as Polyamid-12 (Orgasol.RTM. from Atochem), polymethyl methacrylate (Covabead.RTM. from Wacker) or polymethyl silsesquioxan (Tospearl.RTM. from Kobo, Japan) for improvement of the skin feeling may also be present.

A particularly favorable concept for sun protection preparations consists in detaining organic sun protection agents that can produce irritation effects on the skin in the primary oil phase, and in dispersing the skin compatible inorganic pigments in the secondary oil phase. In this way a preparation is obtained which is particularly skin compatible because of the high proportion of primary oil-in-water phase and the possibility of retaining high proportions of organic sun protection agents in the primary oil phase and thus achieving very high sun protection factors, and which is clearly superior to comparable preparations.

Hitherto unnamed agents, additives and auxiliary substances commonly used in cosmetic and dermatological formulations may also be contained in the preparation according to the invention based on a multiple phase emulsion. Restrictions only exist insofar as these constituents should not disturb the structuring of the multiple phase emulsion. Similarly the viscoplastic characteristic of the primary O₁ /W-emulsion should not be disturbed e.g. by electrolytes which destroy the gel network. Also, the use of hydrophilic emulsifier with HLB values greater than 12 for the outer oil phase would lead to destabilization of the O₁ /W/O₂ emulsion and is thus inexpedient.

In a preferred embodiment in the inner oily phase a micronized mineral pigment such as ZnO, TiO₂, SiO₂, ZrO₂ is present alone or associated with chemical filters. The main advantages as a sun protecting agent are (1) a very good feeling during skin application caused by the silicone nature of the outer layer phase, (2) a better UV sunscreen efficacy for e.g. TiO₂ in an adequate oily phase than organic esters, and the silicone phase is prevented of any interference and (3) attenuation of the whitening effect normally associated with physical UV absorbers when they are dosed at 5% by weight or more in sun products. The range of mineral pigments in a multiple emulsion, e.g. TiO₂ (solid)/Oil/Water/Silicone is betweeen 0.5-8% by weight, referred to the total weight of the emulsion.

The invention also relates to a production process for a stable multiple phase emulsion of the O₁ /W/O₂ type. The process comprises the following steps:

a gelling agent such as a polyacrylate block copolymer is dispersed in an aqueous phase until the formation of a gel;

the aqueous phase and a primary oil phase separated from it are heated to a temperature of maximally 70^oC.;

the primary oil phase is dispersed in the aqueous phase by application of intensive shear stresses at the increased temperature;

the primary O/W-emulsion is subsequently cooled under moderate stirring until a gel formation reoccurs;

the primary O/W-emulsion is dispersed in the secondary oil phase at surroundings temperature under moderate stirring.

The invention also relates to the use of a stable multiple phase emulsion of the O₁ /W/O₂ type as a sun protection preparation or make-up formulation with a primary oil-in-water phase consisting of a viscoplastic gel containing at least one organic UV-absorbant in the oil droplets, and a secondary oil phase of a silicone oil containing one or more inorganic UV-absorbants, wherein the oil proportion in each phase is in the range from 15 to 30% by weight relative to the total weight of the emulsion.

Claim 1 of 16 Claims

1. Stable multiple phase O₁ /W/O₂ emulsion comprising

(a) a primary oil-in-water phase without emulsifier comprising a viscoplastic aqueous gel containing finely distributed oil droplets together with a gelling agent, wherein the thixotropic primary oil-in-water phase has a yield point in the range from 20 to 100 Pa, a plastic viscosity from 0.01 to 0.1 Pa.multidot.s and contains at least one lipophilic agent in the primary oil; and

(b) a secondary oil phase in which the primary oil-in-water phase is present together with a lipophilic emulsifier; and wherein

(c) the proportion of the inner oily phase is 10% to 35% by weight relative to the total weight of the emulsion.

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