WO2008071965A1

WO2008071965A1 - Aqueous mica suspension

Info

Publication number: WO2008071965A1
Application number: PCT/GB2007/004772
Authority: WO
Inventors: John Hawkins
Original assignee: Chartered Brands Limited
Priority date: 2006-12-14
Filing date: 2007-12-13
Publication date: 2008-06-19
Also published as: WO2008071965A8

Abstract

An aqueous suspension comprising a preferably clear, structured surfactant system and coated mica stably suspended therein, provides personal care formulations, such as shampoos and bubble baths, with a uniquely attractive, lustrous appearance.

Description

AOUEQUS MICA SUSPENSION

The invention relates to aqueous suspensions of coated mica for use in personal care formulations.

"Coated mica" is used herein to refer to artificially coated mica, coated with metal oxides such as iron oxide, titanium oxide, stannic oxide, aluminium oxide and/or silica. Such products are available in a number of different shades, some of which are especially suitable for hair shampoos. The term also includes synthetic, mica-like, pearlescent, mineral flakes such as calcium aluminium borosilicate, which have been coated to give similar effects to coated mica.

Coated mica is one of a large number of lamellar solids, which have found application as opacifiers, to improve the appearance of liquid formulations by masking inhomogeneities. It is known to be capable of imparting an attractive, pearly appearance, or metallic sheen to liquids, but its use in aqueous based formulations has been restricted because it is difficult to suspend in water. Aqueous pearlescent personal care formulations, such as pearl shampoos and bubble baths are therefore normally formulated with glycol stearates, which are self-suspending.

Coated mica is available in a variety of tints that would be suitable for enhancing the appearance of different types of hair, as well as the appearance of shampoos, hair dyes, hair conditioners and other personal care products. The problem of suspending it has therefore received considerable attention.

Attempts to solve the problem of dispersing coated mica in water have generally involved using gums or other polymeric thickeners to raise the viscosity of the liquid medium. These retard, but do not prevent, sedimentation, and at the same time make the composition harder to pour. They do not provide stable suspensions. Hitherto shampoos containing coated mica have been noticeably inhomogeneous and unattractive in appearance. The most commonly used alternative to thickeners, for suspending insoluble solids, is colloidal dispersion. Colloidal dispersions contain particles of about 1 micron or smaller, which are prevented from sedimenting by Brownian motion. Such systems are obviously incapable of dispersing particles, such as mica, whose optical effect depends on their being significantly larger than the maximum size that can be suspended in this way.

We have now discovered that when coated mica is suspended in a structured surfactant system it is possible to obtain homogeneous, stable suspensions, with an especially attractive appearance. We have further discovered that when mica is suspended in clear or translucent, aqueous, structured surfactant systems a stable, homogeneous product with a uniquely attractive appearance is obtained

Structured suspending systems depend on the rheological properties of the suspending medium to immobilise the particles, irrespective of size. This requires the suspending medium to exhibit a yield point, which is higher than the sedimenting or creaming force exerted by the suspended particles, but low enough to enable the medium to flow under externally imposed stresses, such as pouring and stirring, like a normal liquid. The structure reforms sufficiently rapidly to prevent sedimentation, once the agitation caused by the external stress has ceased.

The only structured systems, sufficiently effective to have found widespread application, have been based on aqueous surfactant mesophases.

The term "structured system" as used herein means a composition comprising water, surfactant, any structurants, which may be required to impart suspending properties to the surfactant, and optionally other dissolved matter, which together form a mesophase, or a dispersion of a mesophase in a continuous aqueous medium, and which has the ability to immobilise non-colloidal, water- insoluble particles, while the system is at rest, thereby forming a non-sedimenting, pourable suspension. Three main types of structured system have been employed in practice, all involving an L_α-phase, in which bilayers of surfactant are arranged with the hydrophobic part of the molecule on the interior and the hydrophilic part on the exterior of the bilayer (or vice versa). The bilayers lie side by side, e.g. in a parallel or concentric configuration, sometimes separated by aqueous layers. L_α-phases (also known as G- phases) can usually be identified by their characteristic textures under the polarising microscope and/or by x-ray diffraction, which is often able to detect evidence of lamellar symmetry. Such evidence may comprise first, second and sometimes third order peaks with a d-spacing (2π/Q, where Q is the momentum transfer vector) in a simple integral ratio 1:2:3. Other types of symmetry give different ratios, usually non- integral. The d-spacing of the first peak in the series corresponds to the repeat spacing of the bilayer system.

Most surfactants form an L_α-phase either at ambient or at some higher temperature when mixed with water in certain specific proportions. However such conventional L_α-phases do not usually function as structured suspending systems. Useful quantities of solid render them unpourable and smaller amounts tend to sediment.

The main types of structured system used in practice are based on dispersed lamellar, spherulitic and expanded lamellar phases. Dispersed lamellar phases are two phase systems, in which the surfactant bilayers are arranged as parallel plates to form domains of L_α-phase, which are interspersed with an aqueous phase to form an opaque gel-like system. They are described in EP 0 086 614.

Spherulitic phases comprise well-defined spheroidal bodies, usually referred to in the art as spherulites, in which surfactant bilayers are arranged as concentric shells. The spherulites usually have a diameter in the range 0.1 to 15 microns and are dispersed in an aqueous phase in the manner of a classical emulsion, but interacting to form a structured system. Spherulitic systems are described in more detail in EP 0 151 884. Many structured systems are intermediate between dispersed lamellar and spherulitic, involving both types of structure. Usually systems having a more spherulitic character are preferred because they tend to have lower viscosity. A variant on the spherulitic system comprises prolate or rod shaped bodies sometimes referred to as batonettes. These are normally too viscous to be of practical interest.

Both of the foregoing systems comprise two phases. Their stability depends on the presence of sufficient dispersed phase to pack the system so that the interaction between the spherulites or other dispersed mesophase domains prevents separation. If the amount of dispersed phase is insufficient, e.g. because there is not enough surfactant or because the surfactant is too soluble in the aqueous phase to form sufficient of a mesophase, the system will undergo separation and cannot be used to suspend solids. Such unstable systems are not "structured" for the purpose of this specification.

A third type of structured system comprises an expanded L_α-phase. It differs from the other two types of structured system in being essentially a single phase, and from conventional L_α-phase in having a wider repeat spacing, as indicated by the d-spacing of the first order diffraction peak. Conventional L_α-phases, which typically contain 60 to 75% by weight surfactant, have a repeat spacing of about 4 to 7 nanometers. Attempts to suspend solids in such phases result in stiff pastes which are either non- pourable, unstable or both. Expanded L_α-phases with d-spacing greater than 8, e.g. 10 to 15 nanometers, form when electrolyte is added to aqueous surfactants at concentrations just below those required to form a normal L_α-phase, particularly to surfactants in the H-phase.

The H-phase comprises surfactant molecules arranged to form cylindrical rods of indefinite length. It exhibits hexagonal symmetry and a distinctive texture under the polarising microscope. Typical H-phases have so high a viscosity that they appear to be curdy solids. H-phases near the lower concentration limit (the L_t/H-phase boundary) may be pourable but have a very high viscosity and often a mucous-like appearance. Such systems tend to form expanded L_α-phases particularly readily on addition of sufficient electrolyte.

Expanded L_α-phases are described in more detail in EP 0 530 708. In the absence of suspended matter they are generally translucent, unlike dispersed lamellar or spherulitic phases, which are normally opaque. They are optically anisotropic and have shear-dependent viscosity. In this they differ from Li -phases, which are micellar solutions or microemulsions. Li-phases are clear, optically isotropic and are usually substantially Newtonian. They are unstructured and cannot suspend solids.

Some L_t-phases exhibit small angle x-ray diffraction spectra, which show evidence of hexagonal symmetry and/or exhibit shear dependent viscosity. Such phases usually have concentrations near the Li/H-phase boundary and may form expanded L_α-phases on addition of electrolyte. However in the absence of any such addition of electrolyte they lack the yield point required to provide suspending properties, and are not, therefore, "structured systems" for the purpose of this specification.

Most structured surfactants require the presence of a structurant, as well as surfactant and water in order to form structured systems capable of suspending solids. The term "structurant" is used herein to describe any non-surfactant capable, when dissolved in water, of interacting with surfactant to form or enhance (e.g. increase the yield point of) a structured system. It is typically a surfactant-desolubiliser, e.g. an electrolyte. However, certain relatively hydrophobic surfactants such as isopropylamine alkyl benzene sulphonate can form spherulites in water in the absence of electrolyte. Such surfactants are capable of suspending solids in the absence of any structurant, as described in EP 0414 549.

A problem with the two-phase, especially spherulitic, systems is flocculation of the dispersed surfactant structures. This tends to occur at high surfactant and/or high electrolyte concentration. It can have the effect of making the composition very viscous and/or unstable with the dispersed surfactant separating from the aqueous phase.

Certain amphiphilic polymers have been found to act as deflocculants of structured surfactants. One type of deflocculant polymer exhibits cteniform (comb-shaped) architecture with a hydrophilic backbone and hydrophobic side chains or vice versa. A typical example is a random copolymer of acrylic acid and a fatty alkyl acrylate. Cteniform deflocculants have been described in a large number of patents, for example WO-A-9106622.

WO 01/00788 describes the use of carbohydrates such as sugars and alginates as deflocculants in structured surfactant compositions. The latter comprise surfactant, water and electrolyte in proportions adapted to form flocculated two-phase structured surfactant systems in the absence of the carbohydrate.

The use of deflocculant polymers to prepare clear spherulitic or other dispersed L_α structured systems, by shrinking the spherulites or other L_α domains to a size below the wave length of visible light, has been described in WO 00/63079. The latter also describes the use of sugar to modify the refractive index of the aqueous phase as an alternative means of obtaining clear liquids.

It is known from WO 01/05932 that carbohydrates can interact with surfactants to form suspending structures. Such systems generally exhibit even greater d-spacings than the electrolyte-structured expanded L_α-phases, described in EP 0 530 708. The d- spacings of the sugar-structured systems, described in WO 01/05932, are typically greater than 15nm, and may, for example, be as high as 50nm. Such systems can be obtained in a clear or translucent form by suitable choice of surfactant and carbohydrate concentration.

The invention provides an aqueous suspension comprising: (i) a structured surfactant system; and (ii) coated mica stably suspended therein.

Preferably the structured surfactant system is an optically clear system.

hi the following discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

The surfactant is preferably a mild, high-foam surfactant. It may comprise anionic, amphoteric, zwitterionic, non-ionic and/or cationic surfactants.

A preferred anionic surfactant comprises alkyl ether sulphate, which is preferably the product obtained by ethoxylating a natural fatty or synthetic alcohol with ethylene oxide, optionally stripping any unreacted alcohol, reacting the ethoxylated product with a sulphating agent and neutralising the resulting alkyl ether sulphuric acid with a base. The alcohol has an average of more than 8, preferably more than 10, more preferably more than 12, but less than 30, preferably less than 25, more preferably less than 20, most preferably less than 15 carbon atoms. It is reacted with an average of at least 0.5, preferably more than 1, but less than 60, preferably less than 50, more preferably less than 25, even more preferably less than 15, more preferably still less than 10, most preferably less than 5 ethyleneoxy groups. Alkyl ether sulphates may also comprise alkyl glyceryl sulphates, and random or block copolymerised alkyl ethoxy/propoxy sulphates.

The anionic surfactant may also comprise, e.g. Ci_0-20 e.g. Ci_2-I8 alkyl sulphate, Ci_0-20 alkyl benzene sulphonate or a C_8-2O e.g. C_10-20 aliphatic soap. The soap may be saturated or unsaturated, straight or branched chain. Preferred examples include dodecanoates, myristates, stearates, oleates, linoleates, linolenates, behenates, erucates and palmitates and coconut and tallow soaps. The surfactant may also include other anionic surfactants, such as olefin sulphonates, paraffin sulphonates, taurides, isethionates, ether sulphonates, ether carboxylates, sarcosinates, aliphatic ester sulphonates e.g. alkyl glyceryl sulphonates, sulphosuccinates or sulphosuccinamates.

The cation of any anionic surfactant is typically sodium but may alternatively be potassium, lithium, calcium, magnesium, ammonium, or an alkyl or hydroxyalkyl ammonium having up to 6 aliphatic carbon atoms including ethylammonium, isopropylammonium, monoethanolammonium, diethanolammonium, and triethanolammonium.

Ammonium and ethanolammonium salts are generally more soluble than the sodium salts. Mixtures of the above cations may be used.

The non-ionic surfactants may typically comprise amine oxides, polyglyceryl fatty esters, fatty acid ethoxylates, fatty acid monoalkanolamides, fatty acid dialkanolamides, fatty acid alkanolamide ethoxylates, propylene glycol monoesters, fatty alcohol propoxylates, alcohol ethoxylates, alkyl phenol ethoxylates, fatty amine alkoxylates and fatty acid glyceryl ester ethoxylates. Other non-ionic compounds suitable for inclusion in compositions of the present invention include mixed ethylene oxide/ propylene oxide block copolymers, ethylene glycol monoesters, glyceryl esters, ethoxylated glyceryl esters, alkyl polyglycosides, alkyl sugar esters including alkyl sucrose esters and alkyl oligosaccharide esters, sorbitan esters, ethoxylated sorbitan esters, alkyl capped polyvinyl alcohol and alkyl capped polyvinyl pyrrolidone.

The surfactant preferably comprises an amphoteric or zwitterionic surfactant. The former preferably comprises so-called imidazoline betaines, which are also called amphoacetates, and were traditionally ascribed the zwitterionic formula:

CH₂ CH₂

N ⁴N — CH₂COO^"

R¹ R because they are obtained by reacting sodium chloracetate with an imidazoline. It has been shown, however, that they are actually present, at least predominantly, as the corresponding, amphoteric, linear amidoamines: RCONH CH₂CH₂N CH₂ CH₂OH

CH₂COO-,

usually obtained commercially in admixture with the dicarboxymethylated form:

RCON CH₂CH₂N CH₂CH₂OH

I I

CH₂COO- CH₂COO-

R preferably has at least 8, more preferably at least 10 carbon atoms but less than 25, more preferably less than 22, even more preferably less than 20, most preferably less than 18. Typically R represents a mixture of alkyl and alkenyl groups, obtained, for example, from coconut or palm oil, and having sizes ranging from 8 to 18 carbon atoms, with 12 predominating, or a fraction of such a feedstock, such as lauryl (>90%Ci₂). R may alternatively be a residue derived from a terpene, such as an adduct of acrylic acid with myrcene or α- terpinene.

The zwitterionic surfactant is preferably a betaine, or most preferably a sulphobetaine, which typically has the formula R"R'₂ NCH₂XOH, where X is CO or preferably SO_2, R' is an aliphatic group having 1 to 4 carbon atoms and R" is an aliphatic group having from 8 to 25 carbon atoms, preferably a straight or branched chain alkyl or alkenyl group, or more preferably a group of the formula RCONR' (CH₂),,, where R and R' have the same significance as before, and n is an integer from 2 to 4.

We prefer that R' is a methyl, carboxymethyl, ethyl, hydroxyethyl, carboxyethyl, propyl, isopropyl, hydroxypropyl, carboxypropyl, butyl, isobutyl or hydroxybutyl group.

The surfactant may comprise cationic surfactants such as fatty alkyl trimethylammonium or benzalkonium salts, amidoamines or imidazolines.

According to a preferred embodiment the surfactant comprises a mixture of an amphoteric or zwitterionic surfactant and an alkyl ether sulphate in a proportion of at least 1 : 10 by weight, more preferably at least 1:7, most preferably at least 1:5, but less than 1:1.5, more preferably less than 1:2, still more preferably less than 1:3, most preferably less than 1 :4. The zwitterionic surfactant is preferably a betaine, such as coconut amidopropyl betaine, or a sulphobetaine.

The surfactants preferably have a mean HLB greater than 5.5, more preferably greater than 8, even more preferably greater than 10. More preferably still, for high foaming applications such as shampoos and bubble baths, the HLB is greater than 12, even more preferably greater than 15, most preferably greater than 20. Difficulty may be encountered obtaining stable suspensions with surfactant systems having a mean HLB greater than 60. Preferably the HLB is less than 55, more preferably less than 50, most preferably less than 45.

We generally prefer that the surfactant is present in a total concentration greater than 4% by weight, based on the total weight of the composition, more preferably greater than 5%, still more preferably greater than 8%, most preferably greater than 10%. Preferably the surfactant concentration is less than 20%, more preferably less than 18%, most preferably less than 16% by weight.

In order to obtain a clear suspending system, the structurant preferably comprises a water-soluble carbohydrate, especially a sugar. The sugar is preferably a mono or, more preferably, disaccharide sugar, most preferably sucrose, but could for example be fructose, maltose, glucose or invert sugar. Other sugars, which can be used, include, for example, mannose, ribose, galactose, lactose, allose, altrose, talose, gulose, idose, arabinose, xylose, lyxose, erythrose, threose, acrose, rhamnose, fucose, glyceraldehyde, stachyose, agavose and cellobiose or a tri- or tetra-saccharide.

Preferably the surfactant is stirred into a saturated carbohydrate solution, and if a sufficiently stable suspending system is not obtained, electrolyte is added in small increments until an acceptable yield point is achieved. Usually the total concentration of sugar is greater than 50%, preferably greater than

60%, most preferably greater than 65%, up to saturation.

Where it is desired to use a surfactant of relatively high HLB, such as an ether sulphate with a sugar structurant it is possible to improve the stability by adding an electrolyte as an auxiliary structurant. The electrolyte is typically sodium chloride, but could, for example, alternatively or additionally, be or comprise, sodium carbonate, potassium chloride, sodium phosphate, sodium citrate or any other surfactant desolubilising electrolyte.

The proportion of electrolyte required as an auxiliary structurant generally depends on the amount and HLB of the surfactant, and the concentration of sugar, but typically lies within the range 0 to 15 % by weight, based on the weight of the composition, preferably less than 12%, most preferably less than 11%. Higher HLB surfactants, and lower concentrations of sugar and/or surfactant require higher levels of electrolyte.

Alternatively, especially if a clear system is not required, electrolyte may be used as the principal or sole structurant, typically in amounts between 3% by weight and saturation, depending on the surfactant. For high foaming surfactants suitable for use in shampoos and bubble baths we have found saturated brine is an effective structurant.

Where electrolyte is the sole structurant, very high levels of dissolved electrolyte are often required to structure high foaming surfactants, e.g. greater than 15% by weight, based on the total weight of water, surfactant and dissolved matter, and preferably greater than 20%, more preferably greater than 30%, still more preferably greater than 35%, most preferably greater than 40%. Highly soluble salts such as sodium chloride are obviously required to achieve these levels

Alternatively, or additionally to the use of sugar or salt as the structurant, the high HLB surfactant may be used in conjunction with a surfactant of lower HLB, such as oleic acid or isopropylamine alkylbenzene sulphonate so that the mean value of the surfactant mixture lies within the preferred range for structure formation.

For the purpose of this specification "stable" indicates that the suspended solid does not sediment after six months storage at room temperature. A small amount of bottom separation may be observed, e.g. when using high HLB surfactants, stabilised with electrolyte.

The repeat spacing of the structured surfactant system is preferably greater than 8nm, e.g. greater than IOnm, more preferably greater than 15 nm, still more preferably greater than 20nm, most preferably greater than 30nm, but usually less than lOOnm, preferably less than 70nm, most preferably less than 50nm. The repeat spacing may be too high to resolve using small angle X-ray diffraction, and may in some cases be measurable using light or UV diffraction.

The levels of carbohydrate and/or salt may be sufficiently high to inhibit microbiological growth in the medium and sufficient to act as an effective biodegradable, non-allergenic preservative for the composition.

The proportion of mica is typically at least 0.01, preferably at least 0.05, more preferably at least 0.1, most preferably at least 0.2% by weight of the composition. To avoid excessive cost, and also viscosity, it is preferred that the concentration of mica is less than 5, more preferably less than 2, still more preferably less than 1, most preferably less than 0.5% by weight of the composition.

The mica preferably has a particle size greater than lμm, more preferably greater than 5 μm, most preferably greater than 10 μm, but less than 200 μm, more preferably less than 100 μm, most preferably less than 50 μm.

Aqueous suspensions of the invention may be formulated for use in a variety of personal care applications, including shampoos, hair conditioners, hair dyes, bubble baths, and body glitter. The product may optionally contain other common ingredients of personal cleansers, such as glycerol, essential oils, fragrances, pigments, dyes, emollients, antiseptics and topical medicaments.

The invention will be illustrated by the following examples, in which all proportions are % by weight, based on the weight of the composition, unless stated to the contrary. In each case the balance was water.

EXAMPLE I

The above formulation was prepared by adding the ingredients in the order shown, with gentle stirring to avoid air entrainment, starting with 67% w/w aqueous sugar solution. The sultaine was added as 45% w/w aqueous solution, and the ether sulphate as 70% w/w aqueous solution. In the absence of mica the product was a clear translucent lamellar liquid with a lamellar repeat spacing greater than 40nm.

Samples were prepared using three different tints of oxide-coated mica to give shampoo formulations suitable for blond, brunette and red hair respectively. The shampoos were stable, pourable and had a particularly fine pearly lustre, compared with conventional pearl shampoo based on ethylene glycol stearates as the pearlising agent.

EXAMPLE II

The following body wash formulation was prepared by stirring the ingredients together gently at room temperature.

The product was a clear liquid in the absence of mica. The mica formed a stable suspension with an attractive homogeneous metallic lustre.

EXAMPLE in

The following bubble-bath formulation was prepared by gently stirring the ingredients together at room temperature.

EXAMPLE IV

The following formulation is a "chocolate" bubble bath, prepared by stirring the ingredients together at room temperature.

The composition was a thin, mobile, stable, high-foaming liquid having a rich chocolate colour and a viscosity of 0.4 Ps at 21s^"1. No separation was observed after 1 month at 45^°C, or at laboratory ambient temperature.

Claims

1. An aqueous suspension comprising:

(i) a structured surfactant system; and

(ii) coated mica stably suspended therein.

2. A composition according to claim 1 wherein the structured surfactant is an optically clear system.

3. A composition according to any foregoing claim wherein the surfactant is a high foaming system having a mean HLB greater than 12.

4. A composition according to any foregoing claim, comprising a water-soluble carbohydrate as structurant.

5. A composition according to any foregoing claim comprising an electrolyte as structurant.

6. A composition according to any foregoing claim, wherein the surfactant comprises an alkyl polyethoxy sulphate.

7. A composition according to claim 6 wherein the surfactant additionally comprises an alkanolamide and/or a zwitterionic or amphoteric surfactant.