This invention relates to novel aqueous surfactant compositions, particularly to surfactant compositions of alkyl phosphate ester salts and amphoteric surfactants. More particularly, this invention relates to essentially non-irritating aqueous surfactant compositions containing alkyl phosphate ester salts having a high monoalkyl phosphate content and amphoteric surfactants.
A wide variety of surfactants and mixtures of surfactants are known for many industrial, commercial and domestic applications. In these uses, there is often a need for the surfactant to be in a pumpable or fluid form for addition to formulations requiring the surfactant since such form enables one to save costs in handling and storing of the composition, as well as ease and convenience in formulating products therewith. Additionally, for numerous reasons, such as formulation flexibility, transportation and storage costs, it is desirable for the surfactant to be available in such pumpable compositions in as high a concentration or proportion of surfactant or active ingredient as possible.
The superior performance of fatty alcohol-based anionic phosphate esters of high monoalkyl phosphate ester content relative to dialkyl phosphate ester content, especially at a ratio of at least 80:20 or more, has long been recognized, especially for their mildness, detergency and foaming properties, and particularly for use in cosmetic or personal care products like shampoos, conditioners and body cleansers. See U.S. Pat. No. 4,139,485 to G. Imokawa et al., issued Feb. 13, 1979. Their usefulness in the latter products is due, at least in part, to their ability to produce high detergency with low skin irritancy compared to other surfactants, such as alkyl sulphates, alkyl ether sulphates, polyoxyethylene alkyl sulphates, alkyl benzene sulphonates and the like. Moreover, such fatty alcohol-based anionic phosphate ester surfactants of high monoalkyl ester content provide surfactants that evidence an excellent balance of properties. For example, as the monoalkyl phosphate content increases relative to the dialkyl phosphate content, the solubility, foaming ability and detergency increase. Additionally, the increase in monoalkyl phosphate content reduces the skin irritancy effect.
The novel aqueous surfactant compositions of this invention consist essentially of alkyl phosphate ester salts high in monoalkyl phosphate content and an amphoteric surfactant, wherein said composition is essentially free of compounds having a tetra-alkyl ammonium moiety. This invention also provides aqueous compositions which are comprised of an alkyl phosphate ester salt surfactant composition in which the monoalkyl phosphate (1) and dialkyl phosphate (2) are present in a molar ratio of equal to or greater than 50:50, and an amphoteric surfactant. The amphoteric surfactants useful in this invention do not contain a tetra-alkyl ammonium moiety.
xe2x80x9cAlkyl phosphate ester saltsxe2x80x9d is meant to include alkylether phosphate ester salts (i.e. polyoxyalkylene derivatives of the alkanol(s) from which they are derived) as well as non-alkoxylated derivatives. Preferred alkyl phosphate ester salts are mixtures of compounds having the formula (1) and (2): 
wherein R1 and R2 are individually C8-C22 linear or branched saturated or unsaturated hydrocarbons, m and n are individually integers from 2 to 4, w, x, y and z are individually integers from 0 to 20 and M is individually hydrogen, an alkali metal, amine or alkanolamine.