Biliquid foams consist of a water-insoluble liquid "bubble" (or "globule" or "internal phase") trapped within a film of an aqueous surfactant-containing solution ("external" or "continuous phase"). Biliquid foams have very small "bubbles" (e.g., of a diameter in the order of a micron or even a submicron). The foams have been recognized for use in cleaning generally because such bubbles are said to be stable and to have a relatively large surface/volume ratio.
U.S. Pat. No. 4,486,333 issued Dec. 4, 1984 to Sebba discloses and claims a method for preparing such a biliquid foam composition of the polyaphron type (Col. 1, lines 35-47) for use inter alia in cleaning (Col. 6, lines 31-41) or in making dispersions from concentrates of emulsified liquids (Col. 6 lines 23-31) to be used, e.g., in solvent extraction. The '333 polyaprhons have globules of 0.1-10 microns and a PVR (phase volume ratio, i.e., ratio of volume of discontinuous phase to volume of lamellar continuous phase) of up to about 50.
First, according to '333, an ordinary gas foam is prepared using water and/or another hydrogen-bonded liquid such as an alcohol or glycol and a water-soluble surfactant; intermittently, a limited amount of a nonpolar water-immiscible liquid is added and the mixture is agitated to cause the nonpolar liquid to spread on the foam surface and to form noncoalescing globules of nonpolar liquid dispersed in a continuous phase of hydrogen-bonded liquid. Each globule is encapsulated in a double-surfaced film of surfactant and water. The nonpolar liquid and the surfactant are said to be selected to have a spreading coefficient greater than or equal to zero to permit the nonpolar liquid to initially spread as a thin sheet on the surfactant-containing aqueous lamellae and then to break up into fragments and globules (of 0.1-10 micron size) (Col. 2, lines 55-68).
The total amount of nonpolar liquid thus encapsulated is between 40 and 98% by volume of the entire composition and the PVR is at least 1.5 and up to 49 ('333, claim 1).
The surfactant in '333 can be any anionic, cationic or nonionic surfactant that would produce a good foam (as long as it fulfills the above spreading coefficient relationship) and it is used in an amount preferably at least about 0.3% by weight of the water (Col. 4, lines 26-32).
The '333 nonpolar liquid also preferably contains a small (up to 5% by weight) quantity of a soluble nonionic surfactant that permits the nonpolar liquid to spread on the aqueous film (Col. 4, lines 50-62).
The '333 invention suffers from the disadvantage that it is difficult to prepare. Also, there is no attempt to tailor a particular polyaphron to a given cleaning task other than as a fuel additive and as a foaming gel although cosmetic applications are alluded to. See, e.g., '333 Example 4.
U.S. Pat. No. 4,606,913 issued to Aronson on Aug. 19, 1986 also concerns high-internal phase emulsions (i.e., emulsions in which the internal phase constitutes 74-75% of the total volume) (Col. 1, lines 9-16). Use in industrial cleaning applications is disclosed (Col. 1, line 30).
The '913 patent recognizes that choice of the emulsifier affects the stability of these emulsions and further proposes the incorporation of "an electrolyte" in the emulsion, particularly in the aqueous phase to improve stability. Although any type of electrolyte is said to be suitable and trivalent inorganic salts are said to be preferred, only magnesium sulfate and potassium sulfate are claimed (Col. 9, line 9; Col. 10, line 60).
The emulsifiers generally named in the '913 patent are conventional, generally nonionic, emulsifiers usually having an HLB (hydrophilic to lyophilic balance) between 1 and 7 and are said to include combinations of sorbitan trioleates; mono- and multi-phosphoric esters of oleic acid; polyoxyethylene sorbitol hexastearates, ethylene glycol fatty acid esters, glycerol mono-180 stearates, and sorbitan monooleates; polyoxyethylene 2-oleyl ethers, glycerol/fatty alcohol ethers, esters of polyalcohols, polyethoxylated 2-oleyl alcohols, synthetic primary alcohol ethylene oxide condensates; and mono- and diglycerides of fat-forming fatty acids (Col. 5, lines 34-67). Emulsifiers are said to be present at 5-30% by weight of the external phase.
The '913 emulsions are said to be prepared by incorporating the emulsifier in the oil phase and the electrolyte in the aqueous phase and adding the aqueous phase to the oil phase in small aliquots (not more than 15% of the total oil phase at a time).
U.S. Pat. No. 3,976,582 issued to Douglas on Aug. 24, 1976 discloses a method for making and stabilizing micellar systems including microemulsions having maximum zeta potential for optimizing the recovery of petroleum from shale rock and other subterraneous formations and minimizing the undesirable adsorption of surfactant or rock formations.
The micellar systems are said to be made in accordance with known techniques. They comprise 5-20% surfactants (which can be anionic or cationic), 5-60% hydrocarbon solvent, 10-60% electrolyte-containing water and 1-3.5% "co-surfactant". Cosurfactants are co-solubilizers i.e., semipolar organic compounds, preferably alcohols.
The '582 invention involves measuring the zeta potential of a range of micellar systems (varying in aqueous phase content) (the zeta potential is normalized to account for differences in electric conductivity) and selecting as optimum those compositions that have a maximum or near maximum systemic zeta potential.
U.S. Pat. No. 4,542,745 discloses an oil-in-water emulsion for use in medical ultrasonic probes containing as the aqueous phase water and alcohol, glycerol or lower alkylene glycol. The oil phase is silicone fluid and is in droplets of 0.15 microns to 1.5 microns in diameter.
U.S. Pat. No. 3,813,345 issued to Urton on May 28, 1974 is directed to a method for reducing the micelle size of an oil-in-water emulsion (wherein the oil phase contains an organic solvent, a surfactant and an unsaturated organic compound soluble in the solvent and the aqueous phase in water) by adding to such an emulsion a water-soluble resin with a high number of positive-ion accepting sites and equilibrating this resin with a positive ion donor to cause it to have the same sign of (surface) charge (positive or negative) as the micelles, thereby causing further subdivision of the micelles. The disclosed use for such micellar systems is in insecticide preparations.
U.S. Pat. No. 4,472,291 issued to Rosano on Sep. 18, 1984 discloses viscous oil-in-water microemulsions containing a surfactant, a co-surfactant (emulsifier) and a secondary surfactant which has the property of increasing the viscosity of the microemulsion. The stated uses of such microemulsions include hard surface cleaners, shampoos, lotions, salves or creams, car waxes, window cleaners, anti-rust formulations and floor polishes (col. 5, lines 35-40).
U.S. Pat. No. 4,592,859 issued to Smith-Johannsen on Jun. 3, 1986 is directed to stable suspensions of oil and water in which the droplets of the discontinuous phase are surrounded by colloidal particles having a zeta potential within the range of +18 to -18 mV. The suspensions are prepared by adding to water a combination of surfactants (anionic and cationic) which form colloidal particles with the requisite zeta potential. The oil phase is then added. Disclosed uses include cleaning and polishing compositions, paints, varnishes, impregnants for porous surfaces, cosmetics, cement additives, industrial oils and waxes. Pharmaceutical and agricultural uses are also mentioned.
All of the foregoing prior art systems entail complicated and time-consuming formulation methods, and/or are not suitable for industrial cleaning applications. They require special equipment and/or calculations and/or sophisticated additives (such as water soluble resins or electrolytes) as well as specific methods of addition of the dispersed phase to achieve the necessary stability and/or globule configuration (size and type of the dispersed phase). As a result, the prior art systems are expensive and, most important, their use is confined to specialty applications and they lack the versatility necessary for an industrial-type cleaning composition.