Aerosol Foams

This invention relates to pressurised shaving foam dispensers of the so-called aerosol type, and more particularly to the formulation of the foamable compositions used therein.

In pressurised shaving foam dispensers of the above-mentioned type, a foamable concentrate, generally an aqueous soap solution, is contained in a dispenser equipped with a dispensing head and valve, and pressurised with a normally gaseous propellant, e.g. a low molecular weight hydrocarbon or hydrocarbon mixture, or a halohydrocarbon or halohydrocarbon mixture. In the container the liquefied propellant forms an emulsion in the foamable concentrate, the emulsion being referred to as an aerosol emulsion. Upon discharge of the emulsion through the dispensing head the volatilization of the dispersed liquid droplets of propellant causes the dispensed concentrate to foam. Depending upon the precise formulation of the concentrate, the dispensed product may range from a dense creamy foam to a light lather.

For the avoidance of doubt, the term "emulsion" will be used throughout this specification to refer to the whole liquid contents of the dispenser, i.e. the foamable concentrate plus liquid phase propellant, and the term "concentrate" will be used to refer to the liquid content of the dispenser, other than the propellant, "liquid" in this context embracing solutions, emulsions and suspensions. In other words, the concentrate itself may be an emulsion or suspension and not necessarily a solution of the foam producing ingredients in a suitable liquid medium, which in the case of the present invention will be water.

Various disclosures have been made of compositions suitable for use in such dispensers, amongst which may be mentioned U.K. Patent Specification No. 838,913 and U.S. Pat. No. 2,655,480. In accordance with the proposals of U.K. Patent Specification No. 838,913 aqueous soap solutions are used in which the quantity of alkali metal ammonium or alkylamine soaps, or soaps of primary or secondary alkanolamines, is kept below 4%, based on the weight of the concentrate, and in which the amount of triethanolamine soap is kept in minor proportion relative to the total soap content. In accordance with U.S. Pat. No. 2,655,480 aqueous soap solutions are also used, the actual concentration varying with the particular soap used. Thus, when triethanolamine stearate is used the concentration may be from 2-30% by weight of the solution and when potassium stearate is used the recommended amount is from 5 to 20%. A generally recommended range for all soap is 5 to 18%.

Yet other aqueous soap solutions are disclosed in U.S. Pat. No. 2,908,650, these being aqueous solutions of alkali metal soaps and soaps of nitrogen bases in specified proportions.

In such prior compositions a variety of additives have been proposed or used to modify or control the properties of the foam or emulsion. For example, U.S. Pat. No. 2,655,480 discloses that water-soluble non-ionic or anionic wetting agents may be added in amounts up to 5 or 6%, based on the weight of the concentrate, to facilitate rinsing of the lather from the face and avoiding oily deposits on the skin. Particular anionic and non-ionic wetting agents mentioned are sodium lauryl sulphate, sodium dodecyl benzene sulphonate, and water-soluble polyoxyethylene ethers of alkyl-substituted phenols. In addition, glycerine may also be added to stabilize the lather. U.K. Patent Specification No. 838,913 discloses the addition of small amounts (1-3%) of water-soluble emulsifiers, e.g. fatty acid alkanolamides. U.K. Pat. No. 838,913 also discloses the addition of water-insoluble fatty acids, fatty alcohols and their ethylene oxide derivatives, to give the lather a creamy character and effect a slight fatting of the skin. In addition, U.K. Pat. No. 838,913 further teaches the addition of relatively high amounts (up to 15%) of water-insoluble free fatty acid to effect stabilization of the lather.

Reference may also be made to the studies reported in J. Soc. Cosmetic Chemists, 17 (1966), pages 801-830 on the effects of the addition of long chain fatty alcohols to aqueous aerosol emulsions based on anionic surfactants, in particular on certain triethanolamine soaps and on sodium lauryl sulphate. In general, the addition of long chain alcohols to these emulsions showed an increase in viscosity and emulsion stability, judged on the time required for phase separation after shaking the aerosol container by hand. Increases were also noted in foam stability and foam stiffness.

Although soap-based aerosol shaving foams have attained a certain degree of popularity, the formulations currently used have certain disadvantages, the foremost of which is the tendency, when used, to form a scum either in the form of hardwater deposits, particularly, of course, when used in hard water areas, or in the form of free fatty acid. This scum, in turn, forms unsightly deposits around the wash basin and, more particularly, on the razor and because of the difficulty of removing these deposits, which are often not removed by simple rinsing, the razor rapidly becomes encrusted.

Soapless aerosol foams based on synthetic surfactants and containing a synthetic surfactant in combination with a long chain fatty acid or alcohol have been described. For example, in Soap and Chemical Specialities, July 1967, pages 70-78 and 162, continued in Soap and Chemical Specialities, August 1967, pages 70-74, 104 and 106, and in J. Soc. Cosmetic Chemists 20, (August 1969) 577-593, Sanders describes a series of studies on aerosol emulsion systems based on certain polyethylene fatty ethers in combination with certain long chain fatty acids and alcohols. Again, increases in emulsion viscosity and stability and increases in foam stability and stiffness were noted. Whilst, since such systems are soap free, the problem of hard water scum does not arise, it has been found that such systems have a particular disadvantage in that they lack storage stability, particularly at moderately elevated temperatures, e.g. 30.degree.-40.degree. C., which in practice may well occur when the products are stored or placed on display, for example, in a shop window exposed to bright sunlight or are used in a hot climate. Under these exposed conditions, compositions containing a synthetic surfactant solution and a long chain fatty alcohol or acid, as described in these articles, undergo an irreversible phase separation, that is to say they cannot be redispersed merely by shaking the aerosol container by hand, with the result that the emulsion no longer foams, or foams inadequately upon discharge from the container. Such products therefore lack the necessary shelf-life. In addition, separated solid phase material may block the valve and discharge apertures and thus further contribute to the malfunction of the container.

In our U.K. Patent Specification No. 1,423,179 and the corresponding German application published as OLS No. P 24 22 937.6 there are disclosed aerosol shaving foam preparations comprising a particular combination of surfactant materials, such preparations having the advantageous properties of not only being free from scum formation when used in hard water, but also having the ability to disperse preformed scums, which result, for example, when the face is washed with ordinary soap under hard water conditions prior to shaving. Furthermore, these preparations are stable at moderately elevated temperatures, e.g. 30.degree.-40.degree. C., for long periods. Broadly speaking, such preparations are based on an aerosol emulsion containing as the surfactant a combination, in particular proportions, of (i) a water-soluble nonionic, anionic or weakly cationic synthetic surfactant, (ii) a water-insoluble long chain fatty alcohol and (iii) an anionic surfactant which is either an alkali metal or alkanolamine soap or an alkyl or alkaryl sulphate, sulphonate or ether sulphate, or an N-acyl sarcosinate. Such compositions therefore contain as essential components two different types of surfactant, both of which are water-soluble or substantially water-soluble (i.e. self dispersing) and a third insoluble ingredient namely the long chain fatty alcohol.

An object of the present invention is to provide stable aerosol foam-forming emulsions having good foam forming properties and which are entirely soap-free. This is in contrast to the compositions disclosed in the aforesaid OLS in which the compositions do preferably contain a soap, albeit in reduced amount. A further object is to provide stable aerosol foam-forming emulsions having good foaming properties and which are scum-free and have scum-dispersing properties when used in hard water.

The present invention is based on the discovery that certain selected nitrogen-containing surfactants, in particular, water-insoluble long chain fatty acid amides, water-insoluble ethylene oxide adducts of long chain fatty acid amides and long chain primary alkylamines, and quaternary ammonium salts of adducts of propylene oxide with low molecular weight secondary amines, when used in combination with a water-insoluble long chain fatty alcohol, particularly tetradecanol (myristyl alcohol) and a third synthetic surfactant give rise to aerosol emulsions of considerable stability even at the moderately elevated temperatures referred to above. In this connection, it should be mentioned that the term "stability" is being used in a somewhat wider sense that that which is normally associated with the phrase "a stable emulsion". Where used in this specification in relation to emulsions, "stable" is to be taken to include not only cases where there is little or no phase separation on standing, but also cases where there may be phase separation when the emulsion is left to stand for any length of time provided that the emulsion can easily be re-established by a few shakes of the hand.

In accordance with this invention there is provided an aerosol foam dispenser comprising a pressurised container equipped with a dispensing head and manually operable valve and containing an aqueous, soap-free, surfactant concentrate, and emulsified or readily emulsifiable therewith, a normally gaseous aerosol propellant in liquid phase, said concentrate consisting essentially of water and:

(i) from 1 to 15% by weight based on the weight of the concentrate, preferably 2 to 10% by weight, of a nitrogen-containing synthetic surfactant selected from:

(a) water-insoluble long chain fatty acid amides and ethylene oxide adducts thereof, being compounds of the formula: ##STR1## where R is C.sub.12 -C.sub.18 alkyl; and n is 0 or an integer of from 1-2 inclusive;

(b) water-insoluble ethylene oxide adducts of long chain primary alkylamines, being adducts of the formula: ##STR2## where R is as above defined and m and n are positive integers whose sum is from 2-9 inclusive; and

(c) quaternary ammonium salts of the formula: ##STR3## where A is (C.sub.3 H.sub.6 O).sub.p H, where p is an integer of from 8-50;

X is an anion, e.g. Cl.sup.- or Br.sup.- ; and

B, c and D are each C.sub.1 -C.sub.3 alkyl;

(ii) from 0.5-6.0% by weight, based on the concentrate, preferably 1-4%, of a long chain fatty alcohol, preferably tetradecanol; and

(iii) from 1-15% by weight based on the concentrate, preferably 4-10% of an additional surfactant compatible with the nitrogen-containing surfactant and being a water-soluble synthetic surfactant having an HLB value in the range 12-40 and comprising, as its hydrophobic part, a straight chain alkyl group of from 12-18 carbon atoms or an alkaryl group containing a straight chain alkyl group of from 5-12 carbon atoms; the weight ratio of components (i) and (iii) together to component (ii) being in the range 0.5:1 to 12:1, preferably 2:1 to 6:1, and the surfactants being such that the HLB value of the total surfactant component (including fatty alcohol) of the concentrate is from 8-18.

The nitrogen-containing surfactants used in this invention are commercially available materials; typical and preferred nitrogen containing surfactants are:

lauric monoethanolamide,

polyoxyethylene (2) tallow amine,

stearamide,

polypropoxyl (8) diethyl methyl ammonium chloride.

Preferred water-soluble synthetic surfactants usable as component (iii) in the present invention are nonionics, in particular alkylene oxide (e.g. ethylene oxide and/or propylene oxide) adducts of long chain fatty alcohols and acids, of polyol esters of long chain fatty acids, and of C.sub.5 -C.sub.12 alkyl phenols. Also suitable are polyol (e.g. sucrose) esters of long chain fatty acids, and ethylene oxide adducts of long chain primary alkylamines containing more than 30 ethylene oxide units. Particularly preferred are polyoxyethylene adducts of long chain alcohols containing from 10-30 ethylene oxide units, nonyl phenoxypolyoxyethylene (50) ethanol, and polyoxyethylene (20) sorbitan monostearate.

Water-soluble anionic, amphoteric and cationic surfactants may also be used as the third component provided that compatibility exists with the nitrogen-containing surfactant. By compatible we mean capable of existing in admixture in aqueous dispersion or solution with the other surfactant components of the system without precipitation or loss of surface activity. Suitable anionic materials include long chain alkyl and alkaryl esters of phosphorus acids, long chain alkyl and alkaryl sulphosuccinates, N-acyl-N-alkyl taurates, beta sulphoethers of long chain fatty acids, long chain alkyl and alkaryl sulphates, sulphonates and ether sulphates, and long-chain N-acyl sarcosinates.

Throughout this specification the expression "long chain" when used in expressions such as "long chain fatty acid", "long chain fatty alcohol", "long chain alkyl" is intended to cover straight chain groups containing from 12-18 carbon atoms, whilst the expression "long chain alkaryl" is intended to cover alkyl-substituted aryl groups comprising a benzene or naphthalene nucleus substituted by a straight chain C.sub.5 -C.sub.12 alkyl substituent. It is also to be understood that, as is customary in referring to surfactants, phrases specifying a carbon atom range, e.g. C.sub.12 -C.sub.18, or a specific number of carbon atoms, e.g. C.sub.12 alkyl, when referring to a surfactant component are intended to cover mixtures of compounds in which the alkyl substituents are predominantly within the stated range, or are predominantly alkyl groups having that particular number of carbon atoms, but which may contain small amounts of other compounds in which the alkyl groups are outside the stated range or which may contain unsaturated, e.g. alkenyl, groups, the reason being, of course, that in practice, such surfactants are frequently obtained from natural products, e.g. coconut oil, which are themselves mixtures of compounds of different chain length, but with one or a small range of chain lengths predominating.

Generally speaking the total solids concentration of the aqueous concentrates used in the present invention will be from 5-30% by weight, preferably 8-20% by weight, based on the weight of the concentrate, but these amounts are not critical.

The propellants used in the compositions used in the present invention are conventional materials e.g. hydrocarbon and hydrocarbon mixtures, e.g. the mixtures of butane, isobutane and propane known commercially as Butane 40, and halohydrocarbons such as dichlorodifluoromethane (12) on its own or mixtures thereof with dichlorotetrafluoroethane (114). Mixtures of hydrocarbon and halohydrocarbon propellants may also be used. The quantity of propellant used will generally be in the range 3-12% by weight of the total emulsion, depending on the propellant used, although the exact amount is by no means critical to this invention. Generally speaking, hydrocarbon propellants such as butane mixtures will be used in amounts at the lower end of the stated range, e.g. 3-7%, whilst halohydrocarbon propellants will be used in amounts at the upper end of the range, e.g. 7-12%. Generally preferred as propellants will be the halohydrocarbons, particularly fluorocarbons, and mixtures thereof with hydrocarbons. Hydrocarbon propellants on their own are less preferred.

Other ingredients such as antioxidants, perfuming agents, stabilizers, viscosity modifiers, humectants, emollients and lubricants, may be included in the compositions of this invention as is conventional in the art, and are embraced by the phrase "consisting essentially of".

Examples of aerosol shaving foam preparations according to the invention are as follows. Each composition was packaged in a conventional pressurised dispenser equipped with conventional discharge valve and foam dispensing head. In every case, a good stiff foam could be dispensed from the nozzle after shaking the dispenser in the hand for a few seconds before opening the valve. This ability was maintained even after the packages had been allowed to stand for prolonged periods of time at temperatures up to 40.degree. C.

Typical foamable aerosol emulsions according to this invention are illustrated in Examples 1-9.