The invention relates to aqueous cleansing compositions. In particular, the invention is concerned with aqueous cleansing compositions suitable for cleaning human skin and hair, which comprise a combination of certain specific long-chain and short-chain surfactants. The compositions are not only very mild but also show an excellent lather performance.
In the recent past it has become more and more important for consumers that aqueous cleansing compositions are high foaming as well as mild. These combined properties are especially useful if the cleansing compositions are to be topically applied to human skin and hair. Consequently, efforts have been made to provide washing products, such as hair shampoos, shower gels and facial wash foams, showing these two properties. The major problem to provide such products resides in the fact that both properties tend to be mutually incompatible. While high lathering surfactants are generally very harsh, mild surfactants tend to give insufficient lather.
In the past attempts have been made to overcome these problems by combining harsh surfactants generating sufficient lather with very mild co-surfactants.
U.S. Pat. No. 3,728,447 (C J Patterson) discloses hair shampoo compositions containing fatty acid lactylates or glycolates while the cleaning actions of these shampoos is satisfactory the foam remains minimal. In order to achieve higher foaming action it is described to incorporate booster surfactants, such as sodium lauryl sulphate or triethanol amine lauryl sulphate, in the shampoo compositions. However, these booster surfactants are causing a high degree of irritancy when applied on human skin.
WO 91/09923 describes compositions comprising an ultra mild surfactant and a foam enhancer. The ultra mild surfactant is an alkyl glyceryl ether sulfonate (AGS) which has a hydrophobic group containing a linear alkyl chain containing from about 7 to 9 carbon atoms. Conventional foam boosters such as amine oxides and water soluble halide salts are added to improve lather creaminess, volume and stability.
EP-A-224 796 (Kao) describes a detergent composition comprising (a) a phosphate surfactant and (b) an acyl lactylate having an acyl group containing 12 to 18 carbon atoms. Specific examples for such combinations are mixtures of lauryl phosphate and stearoyl lactylate, isostearoyl lactylate and lauroyl lactylate, respectively.
U.S. Pat. No. 4,761,279 (Eastman Kodak) discloses shaving cream formulations comprising salts of C14-C22 acyl lactylates, saturated monoglycerides, propylene glycol monoesters and humectants.
It has now been discovered that a combination of specific short-chain surfactants with specific long-chain surfactants provides mild cleansing compositions with the added attribute that by using these compositions a high degree of lather is generated. Unexpectedly, these properties have been achieved by combining very mild surfactants, which on application on their own give unsatisfactory lather in terns of foam volume. The synergistic effect obtained by combining the specific short-chain and the specific long-chain surfactant is described later herein.
Accordingly, the invention provides an aqueous cleansing composition, which comprises:
(a) a short-chain anionic surfactant chosen from C6-C9 alkyl ether sulphates, C8-C11 acyl lactylates, C6-C9 acyl methyl taurates, C6-C9 acyl isethionates, C6-C11 fatty acid soaps. C6-C9 alkyl sulphates, C6-C11 acyl sarcosinates, C6-C9 alkyl sulphosuccinates, C6-C9 alkyl ether sulphosuccinates, or mixtures thereof;
(b) a long-chain anionic surfactant chosen from C13-C18 alkyl ether sulphates, C13-C18 acyl lactylates, C13-C16 acyl methyl taurates, C13-C15 acyl isethionates, C13-C16 alkyl sulphates, C13-C16 acyl sarcosinates, C13-C16 alkyl sulphosuccinates, C13-C16 alkyl ether sulphosuccinates, or mixtures thereof;
(c) optionally, a medium-chain anionic surfactant chosen from C10-C12 alkyl ether sulphates, C12 acyl lactylates, C10-C12 acyl methyl taurates, C10-C12 acyl sethionates, C10-C12 alkyl sulphates, C12 acyl sarcosinates, C10-C12 alkyl sulphosuccinates, C10-C12 alkyl ether sulphosuccinates, or mixtures thereof,
(d) water;
wherein
(i) at least one of the surfactants (a) and (b) is selected from the group consisting of the acyl lactylates, the acyl sarcosinates, the acyl methyl taurates, the alkyl ether sulphates and the acyl isethionates; or the short-chain anionic surfactant (a) is a C6-C11 fatty acid soap;
(ii) if surfactant (c) is present, then the surfactants (a), (b) and (c) are present in an amount such that the weight ratio of (c):[(a)+(b)] is less than 1:1.
Short-chain anionic surfactant (a)
The aqueous cleansing composition according to the invention comprises from 0.1 to 36% by weight of a short-chain surfactant chosen from C6-C9 alkyl ether sulphates, C8-C11 acyl lactylates, C6-C9 acyl methyl taurates, C6-C9 acyl isethionates, C6-C11 fatty acid soaps, C6-C9 alkyl sulphates, C6-C11 acyl sarcosinates, C6-C9 alkyl sulphosuccinates, C6-C9 alkyl ether sulphosuccinates, or mixtures thereof.
It is preferred to use the short-chain anionic surfactant (a) in amounts of from 0.5 to 20% preferably from 1 to 10% by weight in the cleansing composition according to the invention.
Long-chain anionic surfactant (b)
The aqueous cleansing composition according to the invention comprises from 0.1 to 36% by weight of a long-chain surfactant chosen from chosen from C13-C18 alkyl ether sulphates, C13-C18 acyl lactylates, C13-C16 acyl methyl taurates, C13-C15 acyl isethionates, C13-C16 alkyl sulphates, C13-C16 acyl sarcosinates, C13-C16 alkyl sulphosuccinates, C13-C16 alkyl ether sulphosuccinates, or mixtures thereof.
It is preferred to use the long-chain anionic surfactant (b) in amounts of from 0.5 to 20%, preferably from 1 to 10%, by weight in the cleansing composition.
Combination of short-chain surfactants (a) and long-chain surfactants (b)
The aforementioned short-chain surfactants and long-chain surfactants are combined in such a way so that at least one is chosen from the group consisting of the acyl lactylates, the acyl sarcosinates, the acyl methyl taurates, the alkyl ether sulphates, the acyl isethionates and the C6-C11 fatty acid soaps, as specified above.
This means that:
a C6-C9 alkyl ether sulphate is present as short chain surfactant or a C13-C18 alkyl ether sulphate is present as long chain surfactant, or:
a C8-C11 acyl lactylate is present as short-chain surfactant or a C13-C18 acyl lactylate is present as long-chain surfactant, or:
a C6-C9 acyl methyl taurate is present as short chain surfactant or a C11-C16 acyl methyl taurate is present as long chain surfactant, or:
a C6-C9 acyl isethionate is present as short chain surfactant or a C13-C15 acyl isethionate is present as long chain surfactant, or:
a C6-C11 acyl sarcosinate is present as short chain surfactant or a C13-C16 acyl sarcosinate is present as long chain surfactant; or
a C6-C11 fatty acid soap is present as short chain surfactant.
Surprisingly, it is not essential for the purposes of the invention that both types of surfactants, long and short-chain, are chosen from the same homologous series of surfactants.
The weight ratio of the short-chain surfactant (a) to the long chain surfactant (b) is preferably in the range of 1:10 to 10:1, more preferably 1:3 to 6:1 and most preferably 1:1 to 3:1.
Medium-chain anionic surfactant
The cleansing composition according to the invention optionally comprises a medium-chain anionic surfactant (c) chosen from C10-C12 alkyl ether sulphates, C12 acyl lactylates, C10-C12 acyl methyl taurates, C10-C12 acyl isethionates, C10-C12 alkyl sulphates, C12 acyl sarcosinates, C10-C12 alkyl sulphosuccinates, C10-C12 alkyl ether sulphosuccinates, or mixtures thereof.
Within each homologous series of surfactants, it has been found that the above mentioned medium-chain anionic surfactants (c) are the species which, of the particular series, generate the highest degree of lather according to the foam test, described herebelow. These medium-chain surfactants, on the other hand, have been found in general to be the most irritant surfactant within their respective homologous series. The medium-chain surfactant (c) exists for every homologous series of surfactants and its specific chain length or chain-length range can be determined by the foam test described herebelow.
For example, according to the foam test described below, the C12 acyl sarcosinate, recited above as one of the medium-chain anionic surfactants (c), is the medium-chain length acyl sarcosinate. It is thus the one acyl sarcosinate generating the highest degree of lather, and is also the most irritant surfactant within the homologous series of acyl sarcosinates.
It is essential for the purposes of the present invention that the short-chain anionic surfactant (a), the long-chain anionic surfactant (b) and the medium-chain anionic surfactant (c) are present in amounts such that the weight ratio of (c):(a)+(b) is less than 1:1.
The amounts of the surfactants (a), (b) and (c) are preferably chosen so that the weight ratio of (c):(a)+(b) is less than 1:1.5 and more preferred less than 1:2. It is, however, most preferred that no medium-chain surfactant (c) is present in compositions according to the invention.
According to the teaching of the prior art high foaming compositions can only be obtained by using high foaming surfactants, in particular medium-chain surfactants, simultaneously having the disadvantage of being very skin irritant compounds. In contrast to this teaching, the present invention provides extremely mild and high lathering aqueous cleansing compositions by using very mild surfactants which when used singly do not give sufficient foam. It is surprising that by use of mild and low foaming surfactants compositions can be provided having about the same foaming properties but not the undesired skin irritancy as the medium-chain surfactant.
Water
The composition according to the invention comprises water in an amount of from 60 to 99%, preferably 96 to 70%, most preferably 92 to 78% by weight based on total weight of the composition.
Use of the composition
The invention also provides the use as a cleanser for human skin and hair of an aqueous composition which comprises:
(a) a short-chain anionic surfactant chosen from C6-C9 alkyl ether sulphates, C8-C11 acyl lactylates, C6-C9 acyl methyl taurates, C6-C9 acyl isethionates, C6-C11 fatty acid soaps, C6-C9 alkyl sulphates, C6-C11 acyl sarcosinates, C6-C9 alkyl sulphosuccinates, C6-C9 alkyl ether sulphosuccinates, or mixtures thereof;
(b) a long-chain anionic surfactant chosen from C13-C18 alkyl ether sulphates, C13-C18 acyl lactylates, C13-C16 acyl methyl taurates, C13-C15 acyl isethionates, C13-C16 alkyl sulphates, C13-C16 acyl sarcosinates, C13-C16 alkyl sulphosuccinates, C13-C16 alkyl ether sulphosuccinates, or mixtures thereof;
(c) optionally, a medium-chain anionic surfactant chosen from C10-C12 alkyl ether sulphates, C12 acyl lactylates, C10-C12 acyl methyl taurates, C10-C12 acyl isethionates, C10-C12 alkyl sulphates, C12 acyl sarcosinates, C10-C12 alkyl sulphosuccinates, C10-C12 alkyl ether sulphosuccinates, or mixtures thereof, and
(d) water;
wherein (i) at least one of the surfactants (a) and (b) is selected from the group consisting of the acyl lactylates, the acyl sarcosinates, the acyl methyl taurates, the alkyl ether sulphates and the acyl isethionates, or the short-chain anionic surfactant (a) is a C6-C11 fatty acid soap;
(ii) if surfactant (c) is present, then the surfactants (a), (b) and (c) are present in an amount such that the weight ratio of (c):[(a)+(b)] is less than 1:1.
Compositions of the invention may be formulated for washing the hair or skin, for example, hair shampoos; rinse-off hair care products; bath or shower gels; and facial washing compositions.
Preferably the compositions according to the invention will also include a cosurfactant. The cosurfactant can be selected from any known surfactant suitable for topical application to the human body and is selected from nonionic, zwitterionic and cationic surfactants and mixtures thereof. Mild surfactants, ie. surfactants which do not damage the stratum corneum, the outer layer of skin, are particularly preferred.
Suitable nonionic surface active agents include alkyl polysaccharides, lactobionamides, ethyleneglycol esters, glycerol monoethers, polyhydroxyamides (glucamide), primary and secondary alcohol ethoxylates, especially the C8-20 aliphatic alcohols ethoxylated with an average of from 1 to 20 moles of ethylene oxide per mole of alcohol.
Preferred zwitterionic detergents are those which have an alkyl or alkenyl group of 7 to 18 carbon atoms and comply with an overall structural formula: 
where R1 is alkyl or alkenyl of 7 to 18 carbon atoms R2 and R3 are each independently alkyl, hydroxyalkyl or carboxyalkyl of 1 to 3 carbon atoms
m is 2 to 4
n is 0 or 1
X is alkylene of 1 to 3 carbon atoms optionally substituted with hydroxyl, and
Y is xe2x80x94CO2xe2x88x92 or xe2x80x94SO3xe2x88x92
Zwitterionic detergents within the above general formula include simple betaines of formula: 
and amido betaines of formula: 
where m is 2 or 3.
In both formulae R1, R2 and R3 are as defined previously. R1 may, in particular, be a mixture of C12 and C14 alkyl groups derived from coconut so that at least half, preferably at least three quarters of the groups R1 have 10 to 14 carbon atoms. R2 and R3 are preferably methyl.
A further possibility is a sulphobetaine of formula: 
where m is 2 or 3, or variants of these in which xe2x80x94(CH2)3SO3xe2x88x92 is replaced by 
R1, R2 and R3 in these formulae are as defined previously.
The compositions of the invention may comprise a structurant, i.e. a material added to increase the viscosity at low shear, such as less than 1 sxe2x88x921. Suitable materials include swelling clays, for example laponite; fatty acids and derivatives thereof and, in particular, fatty acid monoglyceride polyglycol ethers cross-linked polyacrylates such as Carbopol (TM) (polymers available from Goodrich); acrylates and copolymers thereof, polyvinylpyrrolidone and copolymers thereof; polyethylene imines; salts such as sodium chloride and ammonium sulphate; sucrose esters; gellants; and mixtures thereof.
Of the clays, particularly preferred are synthetic hectorite (laponite) clay used in conjunction with an electrolyte salt capable of causing the clay to thicken. Suitable electrolytes include alkali and alkaline earth salts such as halides, ammonium slats and sulphates.
The compositions according to the invention may also comprise a thickening agent, ie a material which maintains the viscosity of the composition as the shear rate thereof is increased during use. Suitable materials include cross-linked polyacrylates such as Carbopol (TM) (polymers available from Goodrich); fatty acids and derivatives particular, fatty acid monoglyceride gums including alginates, guar, derivatives including hydroxy methyl cellulose and hydroxypropyl and propylene glycol oleates; salts and ammonium sulphate; glycerol mixtures thereof.
structurants and thickeners are given in Ingredient Dictionary, Fifth by CTFA (The Cosmetic, Toiletry and incorporated herein by reference.
Examples of other adjuncts which may be added to the compositions of the invention include opacifiers; preservatives such as para-hydroxy benzoate esters; antimicrobials such as antioxidants such as butyl hydroxy toulene; bactericides; humectants such as glycerol and sorbitol; waxes; plant extracts such as Aloe Vera, witch hazel and elderflower; colourants; and perfumes.