Process for thickening aqueous solutions

The viscosity of cosmetic cleansing composition is increased by admixing with such compositions an effective amount of a thickener comprising an alpha-acetamido-fatty acid soap.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention concerns the field of thickeners for cosmetic cleansing 
agents. 
2. Description of the Related Art 
Because cosmetic cleansing agents are often applied to vertical or 
otherwise non-level surfaces, it is considered advantageous for the 
formulation to have an increased viscosity so as to inhibit the propensity 
of the composition to flow. There are a variety of methods known to 
thicken compositions containing anionic surfactants. See Surfactants In 
Cosmetics, Vol. 16 of Surfactant Science Series, M. M. Rieger, Ed., Marcel 
Dekker 1985, Chap. 9, pp. 251-292, for a discussion of related topics. 
U.S. Pat. No. 3,954,660 to Kennedy, et al. proposes increasing the 
viscosity of anionic surfactant slurries by admixing with such slurries an 
effective amount of an additive selected from the group consisting of 
dialkyl ethers, alkoxyethoxyethanols and tertiary amines having the 
general formula R.sub.3 N, wherein R is an alkyl group containing from 2 
to 4 carbon atoms. 
Polymeric thickeners are known to capitalize on the hydration and swelling 
properties of high molecular weight polymers and the chain extension and 
hydrogen-bonding of polymer units to achieve an increase in viscosity. 
European Pat. Nos. 132,961 and 133,345 disclose liquid soap compositions 
containing a water-soluble polymer selected from the group consisting of 
hydroxyethyl cellulose and hydroxypropyl guar. A quaternary 
nitrogen-containing cellulose ether thickening agent is disclosed as 
useful in the production of mild thickened liquid shampoo compositions in 
U.S. Pat. No. 3,962,418 to Birkofer. 
Electrolytes such as sodium and ammonium chloride, by increasing the size 
of the surfactant micelles, are known to raise the viscosity of surfactant 
formulations. Long-chain lipophiles having a hydrophilic end-group such as 
alkanolamides, betaines and amine oxides are also known to increase 
viscosity by enlarging micelles. U.S. Pat. No. 4,375,421 to Rubin, et al. 
discloses solutions containing alkylamido betaines and certain 
water-soluble inorganic and organic salts. These salts have a 
viscosity-building effect on aqueous compositions containing alkylamido 
betaines in the presence of anionic surfactants. U.S. Pat. No. 4,490,355 
to Desai teaches that a mixture of cocoamidopropyl betaine and 
oleamidopropyl betaine improves the thickening and foam boosting 
properties in hair and skin care formulations. 
The viscosity enhancing effect of different amides on a 15% active 
monoethanolamine-lauryl sufate and a 15% active sodium laureth-2 sulfate 
has been reported. B. R. Donaldson and E. T. Messenger, Int. J. Cosm. Sci. 
1:71-90 (1979). In a different report, cocamide MEA was found to be an 
effective thickener. G. Felletschin, Tensile Detergents 7:16-18 (1970). 
Further, U.K. Patent Application No. GB 2 143 841A discloses the use of a 
variety of thickeners, including long-chain (C.sub.12 -C.sub.18) fatty 
acid amides, as useful in thickened aqueous surfactant compositions. 
It has also been proposed to thicken shampoos by combining two surfactants, 
one being a nonionic surfactant typified by dibasic and tribasic acid 
reaction products of alkoxylated polyol fatty esters and another being of 
a different type such as an amphoteric/anionic surfactant. U.S. Pat. No. 
4,261,851 to Duke reports that the nonionic surfactant has a thickening 
effect on the composition. 
Applicant has discovered that alpha-acetamido-fatty acid soaps having the 
general formula: 
##STR1## 
wherein R is a hydrocarbon group containing from 10-20 carbon atoms and M 
is a cation, display much greater thickening power than the thickeners of 
the prior art. These thickeners have been found to raise the viscosity of 
anionic surfactant formulations by increasing the size of the surfactants 
micelles. U.S. Pat. No. 4,404,109 to Tellier, et al. discloses a 
surfactant having the formula: 
##STR2## 
wherein R and R' are hydrocarbon groups and M is an alkali metal cation, 
as useful for the production of micro-emulsions in the presence of aqueous 
saline solutions in the assisted recovery of crude oil. Tellier, et al. 
describes a process that prepares a micro-emulsion of hydrocarbon and 
water containing a surfactant having the formula described above and a 
"cosurfactant," defined in the specification, examples and claims as a 
primary alcohol. Although it is stated that other surface-active co-agents 
may be used, no definition other than "the various alcohols" is provided. 
SUMMARY OF THE INVENTION 
The invention is a process for thickening an aqueous solution containing an 
anionic surfactant selected from the group consisting of alkyl sulfates, 
alkyl ether sulfates, alkyl benzene sulfonates and olefin sulfonates 
comprising the addition to the solution of an alpha-acetamido-fatty acid 
soap having the general formula: 
##STR3## 
wherein R is a hydrocarbon group containing from 10-20 carbon atoms and M 
is a cation. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Alpha-acetamido-fatty acid soaps are found to be effective thickeners for 
anionic surfactants in aqueous solution. The thickened blends are suitable 
for hair and body shampoos, pet shampoos, skin cleansers and light duty 
detergents. The amido acid soaps of this invention display superiority 
over thickening agents most commonly used in such compositions, giving 
blends with much higher viscosities. 
The alpha-acetamido-fatty acid soaps used to thicken these compositions 
have the following general formula: 
##STR4## 
wherein R is a hydrocarbon group containing from 10-20 carbon atoms, 
preferably from 10-14 carbon atoms, and M is a cation, preferably selected 
from the group consisting of sodium, potassium, magnesium, calcium, 
ammonium, ethanolammonium and propanolammonium cations. It is especially 
preferred that M is a sodium cation. It is also preferred that the amount 
of the alpha-acetamido-fatty acid soap present in the composition is from 
about 1 to about 25 wt. % of the total active ingredients. It is 
especially preferred that the amount of alpha-acetamido-fatty acid soap 
present is from about 0.5 to about 5 wt. % of the thickened composition. 
The alpha-acetamido-fatty acid soaps are prepared by neutralizing or partly 
neutralizing the respective amido acids with bases such as NaOH, KOH, 
Mg(OH).sub.2, Ca(OH).sub.2` NH.sub.3, an ethanolamine or propanolamine. 
The amido acids may be produced from alpha olefins by carbonylation in the 
presence of acetamide and excess CO. The carbonylation of olefinically 
unsaturated compounds by reacting the olefins with carbon monoxide and a 
hydroxylic compound at an elevated temperature and pressure in the 
presence of certain metal-containing catalysts to produce carboxylic acids 
and derivatives of carboxylic acids is well known in the art. See, for 
example, U.S. Pat. Nos. 3,887,595; 4,245,115 and 4,258,206. 
The concentrations of the other principal ingredients of this invention may 
vary. The concentration of the anionic surfactant is preferably from about 
5 to about 50 wt. % of the thickened composition. Suitable anionic 
surfactants include alkyl sulfates, alkyl ether sulfates, alkyl benzene 
sulfonates and olefin sulfonates. It is preferred that the anionic 
surfactant is an alpha olefin sulfonate containing from 10 to 16 carbon 
atoms, or a mixture thereof. Further, a portion of the anionic surfactant 
may be replaced with a combination of anionic, amphoteric and nonionic 
surfactants. Water is typically the vehicle for liquid based soaps and 
preferably is present up to about 90 wt. %. Further, it is preferable that 
an inorganic salt (sodium chloride is especially preferred) be present, up 
to about 5 wt. %, to aid thickening. 
In addition to the components mentioned, the composition may also contain 
conventional additives such as lathering agents, opacifying agents, 
conditioning agents, chelating agents, stabilizers, preservatives, 
colorants, fragrances and others known in the art.