Title:  Emulsification systems and emulsions

United States Patent:  6,831,107

Issued:  December 14, 2004

Inventors:  Dederen; Christian Joseph (Dorpstraat 144A, Meerbeek, BE B-3078); Wetzel; Thierry (106 Rue Gallait, Brussels, BE B-1030); Serrien; Guido (Duisburgsesteenweg 69, Tervuren, BE B-3080)

Appl. No.:  865296

Filed:  May 29, 2001

Abstract

Personal care or cosmetic oil in water emulsions include an oil emulsifier and a combination of a Xanthan polysaccharide and a polyglucomannan polysaccharide to provide enhanced stability even at low emulsifier stabiliser levels. The emulsifier stabiliser system provides stable emulsions without dominating system rheology, particularly viscosity. Thus, the emulsions can have a low viscosity suitable for formulation as milks or thin lotions, or can be thickened, desirably by thickening agents other than the Xanthan and/or polyglucomannan, to provide emulsion creams or gels. This enables the system to be used very flexibly in end use applications. The emulsifier is desirably a non-ionic emulsifier and particularly is a combination of a low HLB and a high HLB emulsifier and can be formulated with conventional alcohol ethoxylate surfactants or from non-EO surfactants e.g. sucrose ester high HLB surfactants and citrate or sorbitan ester low HLB surfactants.

Description of the Invention

This invention relates to emulsification systems and emulsions and in particular to emulsification systems including emulsifiers and high molecular weight polysaccharide combinations and to emulsions made using such systems as emulsifiers and emulsion stabilisers and particularly to such emulsification systems and emulsions in the form of personal care products such as cosmetic skin creams and milks.

Personal care emulsion products such as creams and milks desirably have a number of properties in combination: stability in manufacture, formulation, storage and use; a viscosity appropriate to the end use; and preferably a desirable body and good skin feel. Body and skin feel are usually assessed subjectively, and although good body and/or skin feel are commonly associated with a non-Newtonian, shear thinning viscosity profile, a shear thinning profile does not guarantee a good body or skin feel. Typical conventional personal care emulsion products use emulsifiers (including emulsion stabilisers) in amounts of about 3 to about 5% by weight of the emulsion. Recently, thickeners have been proposed as emulsion stabilisers and the mechanism of stabilisation when these are used appears to be that the thickener increases the low shear viscosity of the emulsion sufficiently to provide a barrier to emulsion droplet coalescence, probably by limiting the movement of the droplets.

The present invention is based on our discovery that certain combinations of high molecular weight polysaccharides can provide good emulsion stabilisation at levels that do not give high, or even significantly increased, low shear viscosity and that using such combinations, the amount of emulsifier, usually a relatively low molecular weight, often non-ionic, surfactant can be much less than is used conventionally in emulsions, particularly emulsions for personal care products such as cosmetic skin creams and milks.

The present invention accordingly provides a personal care or cosmetic oil in water emulsion which includes as an emulsifier stabiliser system, an emulsifier for the oil and a polysaccharide combination of a Xanthan polysaccharide and a polyglucomannan polysaccharide.

The invention also includes the use of a polysaccharide combination of a Xanthan polysaccharide and a polyglucomannan polysaccharide as an emulsifier stabiliser system in personal care or cosmetic oil in water emulsions. The invention further includes a dry blend emulsifier stabiliser formulation which includes an oil emulsifier and an oil in water emulsion stabiliser which is a polysaccharide combination of a Xanthan polysaccharide and a polyglucomannan polysaccharide.

The polysaccharide combination of a Xanthan polysaccharide and a polyglucomannan polysaccharide may for convenience briefly referred to as a polysaccharide stabiliser.

The combined amount of emulsifier and stabiliser in emulsions of the invention can be much lower than the typical 3 to 5% used in conventional personal care emulsion systems. In particular, in many emulsions of this invention, the amount of emulsifier can be less than about 1.5%, particularly up to about 1%, and the amount of polysaccharide stabiliser can be less than about 0.5%, and sometimes as little as about 0.02%, desirably with the combined amount being less than about 1.5%, particularly up to about 1%. The minimum amount of emulsifier is typically about 0.02% more usually 0.025% by weight of the emulsion (see also below). Accordingly, the invention includes a personal care or cosmetic oil in water emulsion which includes as an emulsifier stabiliser system an emulsifier for the oil in an amount not more than about 1% by weight of the emulsion and a polysaccharide stabiliser in an amount of from about 0.02 to about 0.5% by weight of the emulsion.

Personal care emulsions can be divided by viscosity into milks and lotions, which typically have a low shear viscosity of up to about 10000 mPa.s, and creams which typically have a low shear viscosity of more than about 20000 mPa.s. Typically, milks and lotions have a low shear viscosity of from about 100 to about 10000 mPa.s, more usually from about 500 to about 5000 mPa.s, and typically creams have a low shear viscosity of at least about 30000 mPa.s, particularly from about 30000 to about 80000 mPa.s, although even higher viscosities e.g. up to about 10⁶ mPa.s, may also be used. In this context low shear viscosity refers to viscosity measured at shear rates of about 0.1 to 10 s^-1 as is typically used in Brookfield viscometers. Because for good skin feel, personal care and cosmetic emulsions are usually shear thinning, the measured low shear viscosity is only a general guide to whether the product is a milk (or lotion) or cream.

The present invention includes both milk (and lotion) and cream emulsions and specifically the invention includes a personal care or cosmetic oil in water emulsion milk or lotion having a low shear viscosity of up to about 10000 mPa.s, which includes as an emulsifier stabiliser system an emulsifier for the oil and a polysaccharide stabiliser. The invention further includes a personal care or cosmetic oil in water cream emulsion having a low shear viscosity of more than about 20000 mPa.s, which includes as an emulsifier stabiliser system an emulsifier for the oil and a polysaccharide stabiliser, the emulsion further including thickener components.

Xanthan is a polysaccharide including mannose, glucose and glucuronic acid monomer units and typically the main polymer backbone is polyglucose with 3-unit acetylated side chains including glucose, glucuronic acid, typically present as a mixed potassium, sodium and calcium salt, and mannose residues. Xanthan polymers have a molecular weight typically in the range 1.10⁶ to 5.10⁶ and usually about 2.10⁶ and are typically obtained from bacterial fermentations, particularly of Xanthomannas campestris and related microorganisms. The Xanthan products sold under the Keltrol tradename, particularly the `F` and `T` grades, by Kelco are particularly suitable in this invention.

The polyglucomannan typically has a random glucose/mannose backbone, typically at a molar ratio of glucose to mannose in the range about 1:1.5 to about 1:3, usually about 1:2 with hydroxyl groups on pendent methylol groups randomly acetylated, typically so that there is about one acetyl group per 6 to 20 sugar monomer residues. The molecular weight of useful polyglucomannans can vary within a typical range of from about 2.10⁵ to about 2.10⁶. Suitable materials include vegetable polyglucomannans such as those derived from Konjak. Konjak polyglucomannan, sometimes referred to simply as Konjak or Konjak gum, is particularly effective in this invention and its use as a/the polyglucomannan forms a specific aspect of the invention. Konjak, Amorphophallus konjak, also known as Konjac and Devil's Tongue, is a tuber plant grown in Asia as a food plant. The carbohydrate components of the tuber include Konjak polyglucomannan Naturally occurring Konjak polyglucomannan typically has a molecular weight of about 1.10⁶ to about 2.10⁶, but processing e.g. refining and milling, can reduce the molecular weight.

The emulsions of the invention have aqueous continuous phases and in making the emulsions the polysaccharides will usually be dispersed in water. The particle size of the polysaccharides, especially the polyglucomannan, can be important in achieving good dispersion in water, especially relatively cool, particularly cold (ambient temperature) water. Konjak polyglucomannan is readily dispersible in hot water at concentrations of 0.001 to 0.5% by weight. However, as typically derived from the tuber, Konjak polyglucomannan has a relatively large particle size typically having an average particle size of from about 100 to about 2000 .mu.m. Material with this particle size tends to have relatively poor cold water dispersibility. Milling to lower particle size e.g. from about 50 to about 200 .mu.m, can make the product much more readily cold water dispersible. Cold water dispersibility of Xanthan polymers in the form of their commercially available powders is not usually a problem.

As indicated above Xanthan polymers typically have molecular weights of the order of 2.10⁶. Significant reduction of this molecular weight is generally undesirable as this has an adverse effect on the properties of the Xanthan. For the polyglucomannans, particularly Konjak polyglucomannan, the molecular weight is less important provided that the product is not otherwise substantially chemically degraded. Materials with molecular weights as low as about 2.10⁵, corresponding to notional fragments of about 1/10 of the original polymer, can be effective in the present invention.

The combination of Xanthan and Konjak polysaccharides as the emulsion stabiliser is particularly advantageous and forms a specific aspect of the invention, including the various embodiments described and the invention accordingly includes a personal care or cosmetic oil In water emulsion which includes as an emulsifier stabiliser system an emulsifier for the oil and a polysaccharide combination of a Xanthan polysaccharide and a Konjak polyglucomannan polysaccharide.

Xanthan and polyglucomannan polysaccharides are believed to form complexes which give synergistic thermoreversible gels in aqueous systems (see for example "Biopolymer Mixtures" published by Nottingham University Press [1995], Chapter 14 by V J Morris), but the detailed structure of these complexes have not been definitively established. Similarly other polysaccharide combinations can also give aqueous gels. These properties do not account for the emulsion stabilising effect obtained in this invention, because stable emulsions can be obtained at comparatively low viscosities. This result is remarkable as using other gelling materials such as Tara, Carageenan, Locust bean, Guar and Alginate gums, alone or in combination with Xanthan, we have not been able to combine good emulsion stability with acceptable skin feel and body properties. The results we have obtained suggest that these other gelling materials provide emulsion stabilisation because they provide increased emulsion viscosity. Similarly, the literature reports that in aqueous solution Xanthan typically exists as molecular aggregations sometimes referred to as a dimer. This may explain why we have found that the stabilising effect of the Xanthan/polyglucomannan can be promoted by heating and/or vigorously mixing an aqueous dispersion of the Xanthan and polyglucomannan before emulsifying the oil in the aqueous system (see below). In any event we do not know why we have been able to make very stable emulsions according to the present invention and do not wish to be restricted to any particular "theory" to explain it.

We have found that an improvement in stabilising emulsions can be obtained at weight ratios of Xanthan to polyglucomannan, particularly Konjak polyglucomannan, from about 1:10 to about 10:1, particularly about 4:1 to about 1:4, with more desirable results in the range about 2:1 to about 1:2 and especially about 1:1. This remains the case even when lower molecular weight polyglucomannan is used and the relative constancy of this ratio suggests that when lower molecular weight polyglucomannan is used, the combination formed may include several polyglucomannan molecules for each molecule of Xanthan.

The amount of the polysaccharide stabiliser used will generally be enough to provide an improvement in emulsion stability and more desirably to give adequate emulsion stability. However, the inclusion of amounts of polysaccharide stabiliser significantly in excess of that needed to achieve emulsion stability is undesirable as this can give substantial thickening of the emulsion. Aqueous systems, including emulsions thickened with Xanthan, polyglucomannan or the polysaccharide stabiliser generally have a shear thinning pseudoplastic Theological profile but give slimy and/or stringy products with poor body and/or skin feel that is undesirable in personal care products. These properties represent a significant disincentive to the use of these polysaccharides alone or in combination in personal care and cosmetic emulsions.

The use of even very low concentrations of polysaccharide stabiliser e.g. as low as about 0.01% by weight of the emulsion, can give useful improvements in emulsion stability. In practice, the amount of the polysaccharide stabiliser used will be chosen to give emulsions with extended stability and will generally be at least about 0.02% by weight of the emulsion. The maximum concentration generally used depends on the emulsion system, but is typically about 0.5% by weight of the emulsion. Thus, suitable general concentration ranges are from about 0.02% to about 0.5%, more usually from 0.025 to about 0.25%, particularly up to about 0.2% and especially from 0.025 to 0.15%, by weight of the emulsion. Relatively high concentrations in these ranges may be used e.g. where particularly difficult emulsions are being made including those using very hydrophobic oils, or and especially in cream formulations, or where electrolyte may be present (see below), even though the rheology may not be ideal.

The emulsions made and stabilised according to the invention can have exceptionally high stability even at elevated temperatures e.g. up to about 50^oC. However, the polysaccharide combinations are sensitive to ionic materials which act to destabilise the emulsions. We believe that the presence of ionic materials destabilises the Xanthan/polyglucomannan combination so that it is less available to provide effective emulsion stabilisation. For this reason, ionic materials e.g. acids, bases: and salts including neutral salts, such as organic or inorganic salts, are desirably present only at low concentrations in the emulsions of this invention, or are absent. Generally the concentration of ionic materials will not greater than about 0.05 molar, desirably not more than about 0.02 molar and particularly not more than about 0.01 molar. Similarly, ionic surfactants, including emulsifiers, including anionic, cationic and zwiterionic surfactants are desirably not present at significant concentrations in the emulsions of the invention. Amphoteric surfactants can be used, but usually only under conditions where they do not support charged species and, as this tends to be an environment where amphoteric surfactants are not particularly effective, they are not usually desirably included.

Accordingly, the emulsifier used in the invention is desirably one or more non-ionic emulsifier(s). Suitable emulsifiers include conventional non-ionic oil-in-water emulsifier surfactants such as alkoxylate emulsifiers and surfactants that can be derived from natural materials such as fatty acid esters, ethers, hemi-acetals or acetals of polyhydroxylic compounds or a fatty acid amide which is N-substituted with the residue of a polyhydroxylic compound. The specific nature of the emulsifier surfactant used in any particular instance depends on the type of emulsion being made, particularly whether fatty amphiphilic thickeners are being used, the degree of stability required, the nature of the oil being emulsified and the total desired level of emulsifier/stabiliser system.

The term alkoxylate emulsifier is used to refer to surfactants in which a hydrophobe, usually a hydrocarbyl group, is connected through the residue of a linking group having a reactive hydrogen atom to an oligomeric or polymeric chain of alkylene oxide residues. The hydrocarbyl group is typically a chain, commonly an alkyl chain, containing from 8 to 24, particularly 12 to 22, and usually 14 to 20 carbon atoms. The linking group can be an oxygen atom (hydroxyl group residue); a carboxyl group (fatty acid or ester residue); an amino group (amine group residue); or a carboxyamido (carboxylic amide residue). The alkylene oxide residues are typically residues of ethylene oxide (C₂ H₄ O) or propylene oxide (C₃ H₆ O) or combinations of ethylene and propylene oxide residues. When combinations are used the proportion of ethylene oxide residues will usually be at least about 50 mole % and more usually at least 75 mole %, the remainder being propylene oxide residues. Particularly and desirably, substantially all the residues are ethylene oxide residues. The number of alkylene residues in the emulsifier molecule is desirably from 2 to about 200. At least theoretically, alkyl phenyl ethoxylates could be used, but these are generally not now desired in personal care and cosmetic products for other reasons and are thus not usually used in this invention.

The number of alkylene oxide residues is usually from 2 to 200 per mole of alkoxylate emulsifiers and will vary depending on the balance between hydrophilic and hydrophobic properties desired in the emulsifier (see below). Examples of suitable alkoxylate emulsifiers include alcohol alkoxylates, of the formula (Ia): R¹ --O-(AO)_n --H; a fatty acid alkoxylate of the formula (Ib): R¹ --COO-(AO)_n --R² (plus co-products); a fatty amine alkoxylate of the formula (Ic): R¹ --NR³ -(AO)_n --H; or a fatty amide alkoxylate of the formula (Id); R¹ --NR³ -(AO)_n --H, where each R¹ is independently a C₈ to C₂₄, particularly C₁₂ to ₂₂, hydrocarbyl, particularly alkyl group; R² is a hydrogen atom or a C₁ to C₆ alkyl group; and each R³ is independently a C₁ to C₆ alkyl group or a group (AO)_n --H; each AO is independently an ethylene oxide or propylene oxide group; and the total of the indices n in the molecule is from 2 to 200.

Using alkoxylate emulsifiers, the invention includes a personal care or cosmetic oil in water emulsion, particularly an emulsion having a low shear viscosity of up to about 10000 mPa.s, which includes as an emulsifier stabiliser system an alkoxylate emulsifier for the oil in an amount of from about 0.02 to about 1.5% by weight of the emulsion and a polysaccharide stabiliser in an amount of from about 0.02 to about 0.25% by weight of the emulsion. Further, using high HLB (see also below) alkoxylate emulsifiers, the emulsifier stabiliser system of the invention can be effective at very low levels, and is particularly applicable to low viscosity systems (if only because some materials used to increase emulsion viscosity may require the presence of further emulsifier to disperse them), and accordingly the invention includes a personal care or cosmetic oil in water emulsion, particularly an emulsion having a low shear viscosity of up to about 10000 mPa.s, which Includes as an emulsifier stabiliser system an alkoxylate emulsifier for the oil in an amount of from about 0.02 to about 0.25% by weight of the emulsion and a polysaccharide stabiliser in an amount of from about 0.02 to about 0.25% by weight of the emulsion.

Creams can be made using alkoxylate emulsifiers, but generally the amount of emulsifier will be higher than the minimum to stabilise a milk emulsion. The invention thus includes a personal care or cosmetic oil in water cream emulsion having a low shear viscosity of more than about 20000 mPa.s, which includes as an emulsifier stabiliser system an emulsifier, including an alkoxylate emulsifier, for the oil in an amount of from about 0.25 to about 1.5%, particularly from about 0.5 to about 1%, by weight of the emulsion and a polysaccharide stabiliser in an amount of from about 0.02 to about 0.5%, particularly from about 0.05 to about 0.25, by weight of the emulsion the emulsion further including thickener components.

The emulsifier stabiliser system of the invention is flexible in that emulsifiers that are not derivatives of alkylene oxides can be used. This opens up the possibility of using emulsifier stabiliser systems which are derived entirely from biological, particularly vegetable, source materials. This possibility may be attractive to formulators of personal care products. In this aspect, the invention, therefore, further includes a personal care or cosmetic oil in water emulsion which includes as an emulsifier stabiliser system an emulsifier for the oil, which is a fatty acid ester, ether, hemi-acetal or acetal of a polyhydroxylic compound, or a fatty acid amide which is N-substituted with the residue of a polyhydroxylic compound, especially a saccharide fatty acid ester, and a polysaccharide stabiliser. Sugar (saccharide) esters can be used with advantage in this invention as they can provide very stable emulsions which can entirely avoid using products manufactured using alkylene oxides and can enable the use of emulsifier/stabiliser systems which are derived entirely from "natural" biological source, particularly vegetable source materials.

Particularly useful esters of polyhydroxylic compounds include saccharide esters particularly mono-esters of fatty acids and a sugar, especially sucrose, fructose and/or glucose. Commercially available sugar esters are usually mixtures containing mono-ester, higher esters and sometimes free starting material (sugar). In this invention it is desirable to use sugar esters having a relatively high proportion of mono-ester. Typically the sugar ester used will have a content of mono-ester of at least 50% more usually at least 60% and desirably at least 65%. The proportion may be higher e.g. 70%, 80% or even higher, although products with very high proportions of mono-ester are significantly more expensive and we have not found any particular advantage in using products with more than about 75% mono-ester. Sucrose esters are particularly useful in the invention. Such sugar esters are relatively hydrophilic emulsifiers and less hydrophilic variants can be used in which hydroxyl groups (usually only one) on the saccharide residue are etherified (or acetalated) typically with a C₁ to C₄ alkyl group e.g. a methyl group. Desirable sugar esters may be of the formula (IIa): R¹ --COO-(G)_a, where R¹ is as defined above for alkoxylate emulsifiers; each G is independently a saccharide residue, particularly a glucose, mannose or fructose residue and a is from 1 to about 5, particularly about 2, especially the residue (G)_a is the residue of sucrose or glucose.

Other esters of polyhydroxylic compounds include esters of fatty acids, particularly fatty acids having from 8 to 24, usually 12 to 22, more usually 16 to 20 carbon atoms, and polyols particularly glycerol, or a polyglycerol, or an anhydro-saccharide such as sorbitan. Generally, these materials are desirably also mainly used as the mono-ester. Examples include glycerol mono-laurate, triglycerol mono-stearate and among relatively more hydrophobic emulsifiers glycerol mono-stearate and sorbitan mono-oleate, stearate or laurate. Suitable such esters may be of the formula (IIb): R¹ --COO--R⁴, where R¹ is as defined above for alkoxylate emulsifiers; and R⁴ is a polyhydroxyl hydrocarbyl group, particularly an alkyl group or alkyl ether group containing from 3 to 10 carbon atoms and 2 to 6 hydroxyl groups. Such materials may be used on combination with other e.g. ester emulsifiers as in the blend of (nominally) polyglyceryl stearate and methyl glucoside stearate sold under the trade designation Tego Care 450 by Goldschmidt.

Yet further ester emulsifiers include fatty acid esters of hydroxycarboxylic acids, in particular the products of trans esterification between fatty glycerides, especially mono- and di-glycerides, and polyhydroxy-carboxylic acids. These products are usually described as esters, but are typically mixtures of the starting materials and the trans-esterification products, particularly where the fatty acid residues are esterified to hydroxyl groups on the hydroxycarboxylic acids. In these products, the fatty acid typically has from 8 to 24, usually 12 to 22, more usually 16 to 20 carbon atoms and the hydroxycarboxylic acid is desirably citric acid.

Another type of emulsifier derived from sugars are saccharide hydrocarbyl ethers, hemi-acetals or acetals, commonly known as hydrocarbyl, particularly alkyl, polysaccharides (more properly oligo saccharides), and in particular materials of the formula (IIc): R¹ --O-(G)_a, where R¹ is as defined above for alkoxylate emulsifiers; each G is independently a saccharide residue, particularly a glucose residue and a is from 1 to about 5, particularly from about 1.3 to about 2.5.

A further emulsifier type is of N-substituted fatty acid amides in which the N-substituent is the residue of a polyhydroxylic compound, which is commonly a saccharide residue such as a glucosyl group. This type of emulsifier includes materials of the formula (IId): R¹ --CO--NR⁵ R⁶, where R¹ is as defined above for alkoxylate emulsifiers; R⁵ is a hydrogen atom, a C₁ to C₆ alkyl group or a group of the formula R⁶ ; and R⁶ is a polyhydroxyl hydrocarbyl group, particularly a group containing from 3 to 10 carbon atoms and 2 to 6 hydroxyl groups and is typically a glucosyl residue.

In this aspect the invention includes low viscosity milk emulsions and higher viscosity cream emulsions. Specifically, the invention includes a personal care or cosmetic oil in water emulsion milk having a viscosity of up to about 10000 mPa.s, which includes as an emulsifier stabiliser system an emulsifier for the oil, which is a fatty acid ester, ether, hemi-acetal or acetal of a polyhydroxylic compound, or a fatty acid amide which is N-substituted with the residue of a polyhydroxylic compound, in an amount of from about 0.5 to about 1.5% by weight of the emulsion and a polysaccharide stabiliser in an amount of from about 0.02 to about 0.5% by weight of the emulsion. The invention further specifically includes a personal care or cosmetic oil in water cream emulsion having a viscosity of more than about 20000 mPa.s, which includes as an emulsifier stabiliser system an emulsifier for the oil which is a fatty acid ester, ether, hemi- acetal or acetal of a polyhydroxylic compound or a fatty acid amide which is N-substituted with the residue of a polyhydroxylic compound, in an amount of from about 0.5 to about 1.5% by weight of the emulsion and a polysaccharide stabiliser in an amount of from about 0.02 to about 0.5% by weight of the emulsion, the emulsion further including thickener components.

It can be useful to use a combination of different types of emulsifier and in particular to combine hydrophilic emulsifiers i.e. having a high Hydrophile Lipophile Balance (HLB) e.g. more than about 12, and hydrophobic emulsifiers i.e. having a low HLB e.g. less than about 8, in making the emulsions of the invention. Relatively hydrophilic emulsifiers include alkoxylate emulsifiers with an average of from about 10 to about 100 alkylene oxide, particularly ethylene oxide residues; and non-alkoxylate emulsifiers including sugar mono-esters and polyglycerol mono-esters, hydrocarbyl, especially alkyl, polysaccharides; fatty acid glycerol esters where the fatty acid has 8 to 12 carbon atoms such as glycerol mono-laurate and fatty acid N-sugar amides such as glucamides. Relatively hydrophilic emulsifiers include alkoxylate emulsifiers with an average of from 2 to about 10 alkylene oxide, particularly ethylene oxide residues; glycerol esters where the fatty acid has 14 to 24 carbon atoms such as glycerol mono-stearate, -oleate, or -laurate; and anhydrosaccharide fatty esters such as sorbitan mono-stearate, -oleate, or -laurate.

The amount of emulsifier used is typically from about 0.02 to about 1.5%, more usually from about 0.025 to about 1.2%, particularly from about 0.025 to about 1%, by weight of the emulsion. Where hydrophilic alkoxylate emulsifiers, especially those with HLB greater than about 12, are used it is possible to obtain satisfactory emulsions with very low levels of emulsifier for example from as little as about 0.04 to about 0.1% by weight of the emulsion, and this forms a particular feature of the invention. Higher amounts of such emulsifiers can be used e.g. in the overall range about 0.04 to about 0.8%, particularly about 0.1 to about 0.6%, by weight. Where less hydrophilic alkoxylate emulsifiers are used as the primary emulsifier, the concentration used will typically be higher e.g. in the range from about 0.1 to about 1.5%, more usually from about 0.2 to about 1.2, particularly from about 0.5 to about 1%, by weight of the emulsion. Similarly where non-alkoxylate emulsifiers such as fatty acid esters, ethers, hemi-acetals or acetals of polyhydroxylic compounds, or fatty acid N-(polyhydroxyl residue substituted) amides, are used as the main emulsifier, the amount used will typically be from about 0.2 to about 1 2, more usually from about 0.3 to about 1%, particularly from about 0 4 to 0.8%, by weight of the emulsion.

When a combination of hydrophilic (high HLB e.g. more than about 10) and hydrophobic (low HLB e.g. less than about 8) emulsifiers is used, the amount of hydrophilic emulsifier will typically be in the ranges set out above and the amount of relatively hydrophobic emulsifier will typically be from 0.1 to 1%, particularly from about 0.2 to about 0.8%. In such combinations, the total amount of emulsifier is typically from about 0.5 to 1.5%, particularly from 0.1 to 1%, by weight of the emulsion. The use of combinations of hydrophilic and hydrophobic emulsifier (sometimes called a co-emulsifier) is particularly useful when the oil phase is highly hydrophobic (non-polar) or when the emulsion is thickened by the inclusion of fatty amphiphiles (see below). In such combinations the overall HLB of the emulsifier system will typically be from about 8 to about 12.

We have found that the inclusion of more emulsifier, particularly of a relatively hydrophilic emulsifier, than is needed to provide a suitably small emulsion droplet size, may have a detrimental effect on emulsion stability. Excess of relatively more hydrophobic emulsifiers seems less detrimental to stability and may contribute to a desired emulsion rheology (relatively hydrophobic emulsifiers are chemically fairly similar to fatty amphiphiles such as can be used as thickeners--see below).

It is generally technically possible to freely combine non-ionic emulsifiers of the alkoxylate and non-alkoxylate types described above. Such combinations may be attractive where the emulsifier system includes a hydrophilic alkoxylate emulsifier e.g. using a low HLB non-alkoxylate emulsifier in combination. However, hydrophilic non-alkoxylate emulsifiers, especially sugar mono-ester emulsifiers, are more expensive than typical alkoxylate emulsifiers and will usually be used only when it is desired to have an emulsifier stabiliser system which includes no derivatives of alkylene oxides.

The oil phase used will typically mainly be an emollient oil of the type widely used in personal care or cosmetic products. The emollient can and usually will be an oily material which is liquid at ambient temperature. Alternatively it can be solid at ambient temperature, in which case in bulk it will usually be a waxy solid, provided it is liquid at an elevated temperature at which it can be included in and emulsified in the composition. As is described below manufacture of the composition usually uses temperatures up to about 100^oC. usually about 80^oC. so such solid emollients will have melting temperatures of less than 100^oC. and usually less than 70^oC.

Suitable normally liquid emollient oils include non-polar oils, for example mineral or paraffin, especially isoparaffin, oils, such as that sold by ICI Surfactants as Arlamol HD; or medium polarity oils, for example vegetable glyceride oils such as jojoba oil, animal glyceride oils, such as that sold by ICI Surfactants as Arlamol M812 (caprilic/capric triglyceride), synthetic oils, for example synthetic ester oils, such isopropyl palmitate and those sold by ICI Surfactants as Arlamol IPM and Arlamol DOA, ether oils, particularly of two fatty e.g. C8 to C18 alkyl residues, such as that sold by Henkel as Eutanol G (octyl dodecanol), or silicone oils, such as dimethicone oil such as those sold by Dow Corning as DC200, cyclomethicone oil, or silicones having polyoxyalkylene side chains to improve their hydrophilicity; or highly polar oils including alkoxylate emollients for example fatty alcohol propoxylates such as that sold by ICI Surfactants as Arlamol E (stearyl alcohol 15-propoxylate). Suitable emollient materials that can be solid at ambient temperature but liquid at temperatures typically used to make the compositions of this invention include jojoba wax, tallow and coconut wax/oil. When non-polar oils are used it may be desirable to use relatively high concentrations of emulsifier, particularly high HLB emulsifier, in order to achieve suitably satisfactory emulsification, particularly to obtain small oil droplets.

Mixtures of emollients can and often will be used and in some cases solid emollients may dissolve wholly or partly in liquid emollients or in combination the freezing point of the mixture is suitably low. Where the emollient composition is a solid at ambient temperature, the resulting dispersion may technically not be an emulsion (although in most cases the precise phase of the oily disperse phase cannot readily be determined) but such dispersions behave as if they were true emulsions and the term emulsion is used herein to include such compositions.

The concentration of the oil phase may vary widely. Generally the oil phase concentration will be at least about 1%, and more usually at least about 5%, by weight and in products as used the oil concentration can be as high as about 30%. Certainly we have readily obtained stable emulsions at oil phase content of upwards of 20% by weight. Even higher concentrations are possible, we have made emulsions at up to 80% by weight of oil, and these concentrated emulsions may be used as pre-manufactured concentrates for dilution with other components to make product emulsions.

The polysaccharide stabilisers used in this invention can be used in other contexts as thickeners, but when used as thickeners, although they seem to provide shear thinning properties we have found that they give emulsion products which have a cosmetically poor body and skin feel commonly described as "stringy" and/or "slimy" materials. These properties are undesirable in cosmetics and personal care products, so the inclusion of excess polysaccharide stabiliser or the individual polysaccharides is not usually satisfactory for thickening emulsions e.g. to form creams, for personal care or cosmetic products and is not generally used in this invention.

More desirable ways of rheology modification to make higher viscosity products include the use of materials which build up a network of particles in the continuous water phase. Particularly suitable materials include fatty amphiphiles such as fatty alcohols, fatty acids and waxes. Suitable materials include fatty alcohols, particularly C₈ to C₂₄, especially C₁₄ to C₂₀ fatty alcohols such as stearyl alcohol, e.g. as commercial cetearyl alcohol (a mixture mainly of cetyl and stearyl alcohols); fatty acids, particularly C₈ to C₂₄, especially C₁₄ to C₂₀ fatty acids such as stearic acid; and waxes such as microcrystalline wax such as that sold by Fuller as Lunacera M. The technical boundary between hydrophobic surfactants and fatty amphiphiles is not always clear and the presence of low HLB emulsifiers may contribute to thickening by fatty amphiphiles. Fatty amphiphiles used as thickeners in this invention will commonly be used as mixtures of materials e.g. from a natural source, a distillation cut during manufacture or deliberately blended to give a mixture. The precise mechanism by which fatty amphiphiles contribute to thickening is not fully understood, but they appears to contribute to structure in the aqueous phase.

Other thickeners that can be used include polymeric thickeners such as starches, particularly modified starches, for example modified potato starch, such as that sold by National Starch as Structure Solanace, and modified maize starch such as that sold by National Starch as Structure Zea (hydroxypropyl distarch phosphate); cellulose thickeners such as carboxyalkylcellulose for example carboxymethyl cellulose such as that sold by Hercules as Natrosol 250HHR (hydroxyethyl cellulose), or that sold by FMC as Avicel RC-591 (a mixture of sodium carboxymethylcellulose and microcrystalline cellulose); polysaccharide gums such as Tara, Carrageenan, Guar, Locust Bean, Xanthan and Konjak gums (although with the amounts used may need to be limited to avoid undesirable skin feel and body properties in the emulsion products) and modified gums such as guar hydroxypropyl ether; and synthetic thickeners such as polyacrylic thickeners such as carbomers including the Carbopol resins from Goodrich (although care may be needed with these as they are ionic although they are by weight very effective thickeners and can be used without necessarily making the emulsions unstable).

An important advantage of the invention is that thickened emulsions can be made in which the emulsion is thickened substantially independently of emulsion stabilisation. This affords product formulators much greater freedom in designing cream systems having a desired rheology as compared with the use of thickeners to stabilise emulsions, because the rheology is not restricted by that used in stabilising the emulsion. For reasons which are not clear, using some thickeners, an additive and possibly synergistic effect in thickening emulsions of the invention using the polysaccharide stabiliser has been noted.

When the oil phase components include fatty amphiphiles e.g. included as thickeners, higher concentrations of emulsifier, particularly high HLB emulsifier, and/or the use of combinations of hydrophilic and hydrophobic emulsifiers may need to be used in order to adequately disperse the fatty amphiphile. However, we have achieved satisfactory results using total emulsifier levels not exceeding about 1.5% and usually not more than about 1.2% and particularly desirably so that the total emulsifier polysaccharide stabiliser concentration is not more than about 1%.

The composition of the emulsions of the invention, with regard to the main components, typically fall within the ranges in the tables below.

The emulsions and formulations of this invention are typically near acid/base neutrality--their sensitivity to ionic materials is mentioned above. Moderate deviation from neutrality is possible without losing the stability advantages of the invention. Desirably the pH is from 4 to 9, more desirably 4.5 to 8 and particularly usefully from 6 to 8.

Many other components may be included in the emulsion compositions of the invention to make personal care or cosmetic formulations. These components can be oil soluble, water soluble or non-soluble. Among water soluble components, care may be needed with materials that provide electrolyte to the composition or cause marked shifts in pH (see above). Examples of such materials include:

preservatives such as those based on parabens (alkyl esters of 4-hydroxybenzoic acid), phenoxyethanol, substituted ureas and hydantoin derivatives e.g. those sold commercially under the trade names Germaben II Nipaguard BPX and Nipaguard DMDMH, when used usually in a concentration of from 0.5 to 2% by weight of the emulsion;

perfumes, when used typically at a concentration of from 0.1 to 10% more usually up to about 5% and particularly up to about 2% by weight of the emulsion;

humectants or solvents such as alcohols, polyols such as glycerol and polyethylene glycols, when used typically at a concentration of from 1 to 10% by weight of the emulsion;

sunfilter or sunscreen materials including chemical sunscreens and physical sunscreens including those based on titanium dioxide or zinc oxide; when used typically at from 0.1% to 5% by weight of the emulsion (but noting that physical sunscreen materials are often dispersed using acrylic polyanionic polymers that may tend to destabilise the emulsions because they supply electrolyte);

alpha hydroxy acids such as glycolic, citric, lactic, malic, tartaric acids and their esters;

self-tanning agents such as dihydroxyacetone;

antimicrobial, particularly anti-acne components such as salicylic acid;

Vitamins and their precursors including:

a) Vitamin A e.g. as retinyl palmitate and other tretinoin precursor molecules,

b) Vitamin B e.g. as panthenol and its derivatives,

c) Vitamin C e.g. as ascorbic acid and its derivatives,

d) Vitamin E e.g. as tocopheryl acetate,

e) Vitamin F e.g. as polyunsaturated fatty acid esters such as gamma-linolenic acid esters;

skin care agents such as ceramides either as natural materials or functional mimics of natural ceramides;

phospholipids;

vesicle-containing formulations;

germanium-containing compounds for example that sold by ICI Surfactants as Arlamol GEO;

botanical extracts with beneficial skin care properties;

skin whiteners such as hydroquinone, kojic acid, arbutin and similar materials;

skin repair compounds actives such as Allantoin and similar series;

caffeine and similar compounds;

cooling additives such as menthol or camphor;

insect repellents such as N,N-diethyl-3-methylbenzamide (DEET) and citrus or eucalyptus oils;

essential oils; and

pigments, including microfine pigments, particularly oxides and silicates, e.g. iron oxide, particularly coated iron oxides, and/or titanium dioxide, and ceramic materials such as boron nitride, or other solid components, such as are used in make up and cosmetics, to give suspoemulsions, typically used in an amount of from about 1 to about 15%, but usually at least about 5% and particularly about 10%.

The emulsions of the invention can be formulated either as simple emulsions which may be thickened as is described above or they can be formulated in more complex systems such as suspoemulsions or multiple emulsions. Suspoemulsions include a liquid dispersed phase and a solid dispersed phase. As is mentioned above, the solid can be a pigment e.g. titanium dioxide and/or coloured iron oxides; or a physical sunscreen of a metal oxide such as titanium and/or aluminium and/or zinc oxides, in which case the particles of oxide may be fine enough that they do not scatter visible light (although they will be selected to scatter UV light). The invention therefore includes a suspoemulsion which is an emulsion of the invention additionally including a dispersed solid material, particularly a pigment.

Other forms of more complex system include multiple emulsions in which the dispersed phase of an emulsion has within its droplets a dispersion of droplets of another liquid. There are thus two emulsions a primary or outer emulsion and a secondary or inner emulsion and the phases can be described as primary or outer and secondary or inner external and internal phases. There are thus two internal phases which are commonly referred to as the outer or primary internal phase and the inner or secondary internal phase and two external phases commonly referred to as the outer or primary external phase and the inner or secondary external phase. There are two basic types of multiple emulsion water in oil in water and oil in water in oil. Both types of multiple emulsion can be made using the emulsification stabilisation system of this invention. The invention thus further includes a water in oil in water multiple emulsion in which the primary oil in water emulsion is an emulsion of the invention and an oil in water in oil in which the secondary or inner emulsion is an emulsion of the invention. The secondary internal phase of multiple emulsions can be used to deliver materials which are sensitive to environmental conditions or to materials in the primary external phase.

The emulsions of the invention can be used, as described above, as cosmetic or personal care products in themselves or can be fabricated into such products. In particular they can be used to impregnate tissues particularly paper tissues e.g. to provide cleansing wipes. In this application the emulsion will typically contain a relatively low proportion of oil phase typically from 3 to 15% more usually about 5% by weight of the emulsion. The amount of emulsion impregnated into tissues will depend on the desired properties in the end product, but will typically be from 10 to 100 g.m^-2 of tissue. The tissues will typically have a basis weight of from 30 to 100 g.m^-2. The invention thus includes a cleansing tissue which is impregnated with an emulsion of the invention. Another use for the emulsions of the invention is to remove make up or other cosmetics. We have found that emulsions of the invention are effective in this use and can be broadly as efficient as the neat oil in removing oily make up e.g. mascara, particularly "waterproof mascara". This is a surprising result as the emulsions in this use typically do not contain very high proportions of oil, typical amounts would be from 25 to 50, more usually from 15 to 30% by weight of the emulsion.

The emulsions of the invention can be made by generally conventional emulsification and mixing methods. Typical methods include direct emulsification by first dispersing the emulsifier(s) and polysaccharide stabiliser (either added as separate components or together) in the aqueous phase and then mixing in and emulsifying the oil in the aqueous continuous phase. To ensure formation of the polysaccharide emulsion stabiliser combination it is desirable to either heat she aqueous phase containing the Xanthan and polyglucomannan usually above about 60^oC. e.g. to about 80 to 85^oC., or to subject the aqueous phase to high intensity mixing at lower e.g. about ambient temperature. Vigorous mixing and the use of moderately elevated temperatures can be combined if desired. The heating and/or high intensity mixing can be carried out before, during or after addition of the oil phase.

The emulsions can also be made by inverse emulsification methods, particularly where low HLB emulsifiers are used (typically in combination with high HLB emulsifiers). In such methods, the emulsifier components, usually including the polysaccharide stabiliser, (either added as separate components or together) in the oil phase and aqueous phase is then added and mixed into the oil phase to form a water in oil emulsion. Aqueous phase addition is continued until the system inverts to for an oil in water emulsion. Plainly a substantial amount of aqueous phase will generally be needed to effect inversion and so this method is not likely to be used for high oil phase content emulsions. As described above, to ensure formation of the polysaccharide emulsion stabiliser combination it is desirable to either heat the Xanthan and polyglucomannan in or in contact with the aqueous phase usually above about 60^oC. e.g. to about 80 to 85^oC., or to subject them to high intensity mixing at lower e.g. about ambient temperature. Vigorous mixing and the use of moderately elevated temperatures can be combined if desired. The heating and/or high intensity mixing can be carried out during or after addition of the aqueous phase and before during or after inversion.

Generally we have found that the hot dispersion methods give emulsions that are more stable than those made by the cold dispersion methods, but cold dispersion is very convenient, particularly for formulators and can give good results. Of course where components needing processing at higher temperatures are used e.g. relatively high melting point waxes, hot dispersion may be convenient for this reason. After making the emulsions the disperse phase concentration can readily adjusted by addition of further continuous phase material, usually with gentle mixing. In the context of making the emulsions, vigorous or high intensity mixing refers to mixing at shear rates typically used in emulsification and will usually be at a shear rate of at least about 10⁴ sec^-1.

When relatively high viscosity emulsions are made, water soluble or dispersible thickener components can be included in the aqueous phase suitably after dispersion of the emulsifier and emulsion stabiliser and oil soluble or dispersible thickening components can be dispersed or dissolved in the oil phase and incorporated into the emulsion with the oil.

The invention accordingly includes a method of making an emulsion which includes the steps of

1 dispersing the emulsifier(s) and polysaccharide stabiliser in the aqueous phase,

2 optionally including thickener components in the aqueous phase; and

3 mixing in and emulsifying the oil in the aqueous continuous phase, and in which the aqueous dispersion of the emulsifier(s) and polysaccharide stabiliser is heated to a temperature of at least about 60^oC. and/or is vigorously mixed before or during emulsification of the oil.

The emulsions of the invention can be used in a wide variety of personal care and cosmetic products and the invention includes such products and the use of the emulsions of the invention in such products as specific aspects of the invention. The emulsions of the present invention can be incorporated into both milk and cream products. Examples of such products include cleansing milks and creams; skin moisturising milks and creams; cosmetic remover milks and creams; and sunscreens, usually in milk or sprayable emulsion milk forms.

The emulsifier and emulsion stabiliser components used in the invention can be blended to provide a dry formulation that can be dispersed in water and readily then made into emulsions and as noted previously, this forms an aspect of the invention. Typically these dry formulations include the solid components including the emulsifier and polysaccharide stabiliser. For such formulations it-is useful to use both high HLB and low HLB emulsifiers and optionally to include materials such as milling aids for example sugars, particularly glucose and/or sucrose, which provide relatively hard materials to aid milling and grinding if needed and also act as readily soluble materials aiding subsequent aqueous dispersion of the formulations. Such formulations can be made by dry blending Xanthan and polyglucomannan polysaccharides, emulsifiers and optionally sugar, if desired consolidating the blend e.g. by extrusion, to form pellets and then milling the pellets to a desired particle size.

Desirably the materials are processed at a temperature, typically from 50^oC. to 100^oC., sufficient that one or more of the components typically one or more of the emulsifiers are at least partly melted and can so coat and/or bind the powder components, typically including the polysaccharides. The emulsifier components may desirably be completely melted and the polysaccharides mixed into this melt. This mixing can be carried out using an extruder of a batch mixer and the product can be solidified into flakes or pellets which can, if necessary, be subsequently milled to make more finely divided particles.

The composition of the dry formulation with regard to the main components, typically fall within the ranges in the table below.

Particularly where the dry formulation is intended to be cold dispersible, it (the dry blended product) is desirably a powder having a mean particle size of from about 100 to about 500 .mu.m. To make handling more straightforward e.g. to reduce the risk of powder combustion, the powder desirably contains little or no material having a much lower particle size. In particular, the proportion of particles of size lower than 50 .mu.m is less than 10% (by weight), desirably less than 2%, particularly less than 1%. If cold dispersibility is not an important requirement, the physical form of the dry formulation may be even less finely divided e.g. pastilles, pellets and/or flakes. In such forms the average particle sizes can be significantly larger than with powder e.g. from 0.5 to 5 mm for pastilles and/or pellets and from 0.1 to 1 mm thick and from 2.5 to 10 mm in length and/or width, corresponding to a particle size (measured as the diameter of spheres of equal volume) of ca 1 to ca 6 mm. These larger particle forms form a further aspect of the invention. As for powders the level of fine particles in desirably low, in particular, the proportion of particles of size lower than 50 .mu.m is less than 10% (by weight), desirably less than 2%, particularly less than 1%.

Claim 1 of 43 Claims

What is claimed is:

1. A personal care or cosmetic oil-in-water emulsion in the form of a milk or cream comprising: at least one oil, water; and an emulsifier stabilizer system composed of

(a) from 0.02 to 1.5 by weight of the emulsion of total oil emulsifier component, wherein the oil emulsifier component comprises at least one or more non-ionic emulsifier(s) selected from the group consisting of at least one alkoxylate emulsifiers, fatty acid esters, ethers, hemi-acetals of polyhydroxylic compounds, acetals of polyhydroxylic compounds, and a fatty acids amides which are N-substituted with the residue of a polyhydroxylic compound, and

(b) a polysaccharide combination of a Xanthan polysaccharide and a polyglucomannan polysaccharide which is present from 0.02 to 0.5% by weight of the emulsion.

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