DE69708459T2 - MICROEMULSIONS AND EMULSIONS WITH CONTINUOUS OIL PHASE, WITH HIGH WATER CONTENT, LOW VISCOSITY AND THEIR USE IN CLEANING APPLICATIONS - Google Patents

Description

Background of the invention

This invention relates to microemulsions and emulsions and their use in various applications.

Microemulsions are well known. Typical components of microemulsions include water, an organic solvent and surfactants. Frequently, microemulsions are used as cleaning formulations. For example, U.S. Patent 4,909,962 describes a clear, single-phase pretreatment composition provided in the form of a microemulsion, solution or gel, which composition is characterized by being infinitely dilutable with water without phase separation. U.S. Patent 5,462,692 describes continuous water microemulsions containing a fragrance as their primary water-insoluble hydrocarbon component. The patent uses tall oil fatty acids, among other components, in formulations suitable as hard surface cleaners. U.S. Patent 5,597,792 describes high water content (water in oil) continuous oil emulsions and microemulsions suitable for cleaning purposes which contain ionic surfactants soluble in an organic solvent phase, such surfactant having an average molecular weight in the range of 350 to 700, preferably greater than 400 and less than 600 excluding the counterion. One of many categories of ionic surfactants briefly described and not exemplified are fatty acid salts.

Other references describe compositions suitable for cleaning applications. In systems described as oil-continuous, the systems have low water contents. While primarily water-continuous systems are described, some of the examples in US Patent 4,909,962 exemplify oil-continuous (water in Oil) systems which have a low water content. It is desirable to find new compositions for such purposes which have high water contents and are oil continuous. Such continuous oil microemulsions are particularly suitable for use as cleaning compositions for the removal of oil and grease.

Summary of the invention

The invention in one respect is a continuous single phase oil microemulsion suitable as a liquid cleaning composition comprising components A, B and C as set out in appended claim 1.

The microemulsion is preferably characterized by being a continuous oil microemulsion and having an electrical conductivity of less than Z microsiemens/centimeter when measured at use temperatures and a viscosity of less than 40 centistokes as measured at use temperatures, where Z is given by the following formula: Z = (1/3)(φw)²σiAimi, where φw is the volume fraction of water in the microemulsion, i is a given electrolyte, Ai is the molar conductivity of the electrolyte i and mi is the molarity of the electrolyte i in the aqueous phase.

In another aspect, this invention is an emulsion which upon standing at 25°C forms at least two phases, wherein one phase is a continuous oil microemulsion comprising components A, B and C as defined in the appended claim 12.

The emulsion is preferably characterized by being a continuous oil emulsion, wherein the emulsion has an electrical conductivity of less than Z microsiemens/centimeter ("uS/cm") as measured at use temperatures and a viscosity of less than 40 centistokes ("cSt") as measured at use temperature, wherein Z is as described above, represented by the following formula: Z = (1/3)(φw)²ΣiAimi, where φW is the volume fraction of water in the microemulsion, i is a given electrolyte, Ai is the molar conductivity of the electrolyte i, and mi is the molarity of the electrolyte i in the aqueous phase.

In yet another aspect, this invention is a bicontinuous or continuous water microemulsion or emulsion which meets all of the criteria set forth above except for the Z value which is perturbable by the addition of salt or a saturated hydrocarbon having a molecular weight of less than about 87 in the compositions described above and which comprises:

A. An organic solvent or a mixture of two or more organic solvents, wherein the organic solvent or mixture of organic solvents is characterized in that it contains not more than 2% by weight of water at 25°C when the organic solvent is saturated with water in the absence of surfactants or other additives; and

B. one or more anionic surfactants which are at least partially soluble in the one or more organic solvents, wherein at least one of the surfactants is a salt of an olefinic or a saturated fatty acid having an average molecular weight in the range of 225 to 365 excluding the counterion group, and wherein the one or more anionic surfactants are present in a total amount of not less than about 0.1% and not more than about 10% by weight based on the total weight of the microemulsion.

In yet another aspect, this invention is a method of cleaning metal having a grease or oil contamination on a surface of the metal, which comprises applying the microemulsion or emulsion described above to the metal having a grease or oil contamination on the surface of the metal to remove at least a portion of the grease or oil contamination from the metal.

The microemulsions and emulsions of this invention find applicability as liquid cleaning compositions for use in metal cleaning, hard surface cleaning, circuit board de-fluxing, automotive cleaning, cold cleaning, dry cleaning, paint removal and fabric cleaning. Furthermore, the microemulsions and emulsions are particularly effective for removing greasy and oily substances. In home and personal care, the compositions of this invention can be used in laundry pretreatments, laundry detergents, coatings, skin cleansers, hair cleansers and conditioning formulations and in aerosol, pump, spray or liquid pesticide formulations. The compositions can also be used in industrial coating and sealing applications such as in adhesives, printing inks, polishes, latexes and as processing solvents. The compositions of this invention can be used in soil treatment processes and water desalination as well as in applications to improve oil recovery and in the provision of acids and other additives for oil wells. The compositions of this invention can be used in pharmaceutical applications such as as vaccine adjuvants, topical drug delivery vehicles and in self-heating compositions. The compositions of this invention can be used as media for producing nanoparticles in ceramic applications as well as in applications for producing catalysts such as zeolites and semiconductors. The compositions of this invention can be used in fuels to solubilize alternative fuel materials such as alcohols. The compositions of this invention can be used to stabilize enzymes, facilitate heterophasic reactions, and increase surface area in reaction medium applications. The compositions of this invention can be used to produce latexes and water-soluble polymers by microemulsion polymerization as well as to produce heterophasic polymers such as self-reinforced plastics and to produce polymer dispersions. It may also be possible to use these formulations to dissolve agricultural pesticides and the like, with the resulting composition to be applied to crops. In addition, the microemulsions and emulsions of this invention can be used in cleaning applications to deliver bleach and enzyme to a formulation such that the bleach only degrades the enzyme to a limited extent. The compositions of this invention can also be used as metalworking fluids, including cutting fluids, forming fluids, quenching fluids and protective fluids, and as power-transmitting hydraulic fluids.

A prominent aspect of this invention is the advantage of forming high water content, low viscosity, and oil continuous compositions using naturally occurring and renewable unsaturated and saturated fatty acid salts at low concentrations to yield products having improved environmental compatibility and electrolyte tolerance over similar water-in-oil ("w/o") microemulsions using sulfonated surfactants.

Microemulsions

As described above, the microemulsions of this invention contain as essential components water, an organic solvent and one or more anionic surfactants. Such microemulsions and emulsions are characterized by being oil-continuous and having a high water content. Microemulsions are generally considered to be compositions in thermodynamic equilibrium having suspended particle sizes in the range of 50 to 1000 angstroms. "Electrolyte" as used herein means all solvated salts in microemulsions or emulsions, including ionic surfactant or added salts such as magnesium sulfate, sodium carbonate and sodium chloride. As used herein, "oil continuous" means compositions, either microemulsions or emulsions, which have an electrical conductivity below Z microsiemens/centimeter, where Z is represented by the following formula: Z = (1/3)(φw)²ΣiAimi, where φw is the volume fraction of water in the composition, i is a given electrolyte, Ai is the molar conductivity of electrolyte i, and mi is the molarity of electrolyte i in the aqueous phase. Therefore, a 0.02 molar composition in an electrolyte having a molar conductivity of 120,000 (microsiemens x liters/centimeter x moles) and a volume fraction of water of 50% has a Z value of 200 and is therefore an oil continuous microemulsion below 200 microsiemens/centimeter (Z). Preferably, the compositions of this invention have an electrical conductivity below 0.5 Z, more preferably below 0.25 Z and most preferably below 0.1 Z. In contrast, bicontinuous compositions are above Z and below 2Z and water-continuous compositions are above 2Z.

In the continuous single phase oil microemulsions, water is present in an amount of not less than 40% and not more than 75% by weight based on the total weight of the microemulsion. Preferably, the microemulsion contains not less than about 45% by weight water. Preferably, the microemulsions contain not more than about 70% water, more preferably not more than about 65% by weight water, and even more preferably not more than about 60% by weight.

In the continuous single phase oil microemulsions an organic solvent or a mixture of two or more organic solvents is used, wherein the organic solvent or mixture of organic solvents is characterized in that it contains no more than 2% by weight of water at 25°C when the organic solvent is saturated with water in the absence of surfactants or other additives. Preferably the organic solvent or mixture of organic solvents contains no more than 1% by weight of water at 25°C when saturated, more preferably no more than 0.5% by weight of water. The water uptake of an organic solvent can be readily determined by water titration, e.g. wherein water is added to one or more organic solvents until turbidity of the solution is observed or an excess water phase forms. The organic solvent or mixture of two or more organic solvents is present in an amount of no less than about 10% and no more than about 60% by weight based on the total weight of the microemulsion. Preferably, the organic solvent or mixture of two or more organic solvents is present in an amount of no more than about 15% by weight, more preferably no more than about 20%, and most preferably no more than about 25% by weight; and preferably no more than about 50% by weight.

Classes of organic solvents that can be used in the practice of this invention include aliphatic alcohols, aliphatic esters, aliphatic Hydrocarbons, chlorinated aliphatic hydrocarbons, aromatic hydrocarbons, aliphatic diesters, aliphatic ketones, and aliphatic ethers. In addition, a solvent may contain two or more of these functional groups, or it may contain combinations of these functional groups. For example, alkylene glycol diethers, alkylene glycol monoethers, and alkylene glycol ether acetates may be used as solvents in the practice of this invention. As used herein, alkylene glycol ethers include dialkylene glycol ethers. The alkylene glycol monoethers and alkylene glycol diethers are particularly suitable for reducing the viscosity of a microemulsion. Preferred classes of organic solvents are the aliphatic hydrocarbons, aromatic hydrocarbons, alkylene glycol monoethers, alkylene glycol diethers, and alkylene glycol ether acetates. More preferred classes of organic solvents are the aliphatic hydrocarbons, alkylene glycol monoethers, and alkylene glycol diethers.

The aliphatic alcohols may be primary, secondary or tertiary. Preferred aliphatic alcohols have 4 to 24 carbon atoms. Representative examples of more preferred aliphatic alcohols include 1-hexanol, isoheptyl alcohol, octanol, 2-ethylhexanol, nonanol, dodecanol, undecanol and decanol.

Preferred aliphatic esters have 4 to 24 carbon atoms. Representative examples of more preferred aliphatic esters include methyl laurate, methyl oleate, hexyl acetates, pentyl acetates, octyl acetates, nonyl acetates and decyl acetates.

The aliphatic hydrocarbons can be linear, branched, cyclic, or combinations thereof. Preferred aliphatic hydrocarbons contain from 3 to 24 carbon atoms, preferably from 6 to 24 carbon atoms. Representative examples of more preferred aliphatic hydrocarbons include alkanes such as liquid propane, butane, pentane, hexane, heptane, octane, decane, dodecane, hexadecane, mineral oils, paraffin oils, decahydronaphthalene, bicyclohexane, cyclohexane, and olefins such as 1-decene, 1-dodecene, octadecene, and hexadecene. Examples of commercially available aliphatic hydrocarbons are Norpar™ 12, 13, and 15 (normal paraffin solvents available from Exxon Corporation), Naphtha SC 140 Petroleum distillate (also from Exxon), IsoparrM G, H, K, L, M and V (isoparaffin solvents, available from Exxon Corporation) and ShellsolTM solvents (Shell Chemical Company).

Preferred chlorinated aliphatic hydrocarbons contain from 1 to 12 carbon atoms, more preferably they contain from 2 to 6 carbon atoms. Representative examples of more preferred chlorinated aliphatic hydrocarbons include methylene chloride, carbon tetrachloride, chloroform, 1,1,1-trichloroethane, perchloroethylene and trichloroethylene.

Preferred aromatic hydrocarbons contain 6 to 24 carbon atoms. Representative examples of more preferred aromatic hydrocarbons include toluene, naphthalene, biphenyl, ethylbenzene, xylene, alkylbenzenes such as dodecylbenzene, octylbenzene and nonylbenzene.

Preferred aliphatic diesters contain 6 to 24 carbon atoms. Representative examples of more preferred aliphatic diesters include dimethyl adipate, dimethyl succinate, dimethyl glutarate, diisobutyl adipate, and diisobutyl maleate.

Preferred aliphatic ketones have 4 to 24 carbon atoms. Representative examples of more preferred aliphatic ketones include methyl ethyl ketone, diethyl ketone, diisobutyl ketone, methyl isobutyl ketone, and methyl hexyl ketone.

Preferred aliphatic ethers have 4 to 24 carbon atoms. Representative examples of more preferred aliphatic ethers include diethyl ether, ethyl propyl ether, hexyl ether, butyl ether, and methyl t-butyl ether.

Preferred alkylene glycol monoethers, dialkylene glycol monoethers, alkylene glycol diethers and alkylene glycol ether acetates include propylene glycol diethers having 5 to 25 carbon atoms, propylene glycol ether acetates having 6 to 25 carbon atoms, propylene glycol monoethers having 7 to 25 carbon atoms, ethylene glycol ether acetates having 6 to 25 carbon atoms, ethylene glycol diethers having 6 to 25 carbon atoms and ethylene glycol monoethers having 8 to 25 Carbon atoms. Representative examples of more preferred solvents within this broad class include propylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol butyl methyl ether, propylene glycol dibutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol butyl methyl ether, dipropylene glycol dibutyl ether; propylene glycol methyl ether acetate, dipropylene glycol methyl ether acetate, propylene glycol butyl ether acetate; propylene glycol monobutyl ether, propylene glycol monohexyl ether, dipropylene glycol monobulyl ether, dipropylene glycol monohexyl ether; ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, diethylene glycol butyl ether acetate; ethylene glycol diethyl ether, ethylene glycol dibutyl ether; ethylene glycol hexyl ether, ethylene glycol octyl ether, ethylene glycol phenyl ether, diethylene glycol hexyl ether, and diethylene glycol octyl ether. Most preferred alkylene glycol monoethers are propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, propylene glycol monopropyl ether and dipropylene glycol monopropyl ether.

In preferred embodiments of the present invention, alkylene glycol monoethers are used in admixture with one or more other organic solvents. The addition of alkylene glycol monoethers facilitates the preparation of microemulsions and low viscosity emulsions. The alkylene glycol monoether is present in an amount of not less than 5 wt% based on the total weight of the microemulsion, preferably not less than about 110 wt%, more preferably not less than about 15 wt%; not more than about 50 wt%, preferably not more than about 40 wt%, and more preferably not more than about 25 wt%. In general, the ratio of glycol ether to total surfactants should be not more than 2 to 1 by weight in both the microemulsions and the emulsions. The alkylene glycol monoether is present in the emulsions containing about 70 to 80% water in an amount of not less than 5% by weight based on the total weight of the emulsion and not more than about 15%.

In the continuous single-phase oil microemulsions, one or more anionic surfactants of specified chemical structure are used, which are at least partially soluble in the one or more organic solvents. The one or more anionic Surfactants are also preferably characterized by having a solubility in the one or more organic solvents greater than in water, and preferably partitioning in the organic solvent in a mixture of water and organic solvent. Preferably, the one or more anionic surfactants are only sparingly soluble in water. The term solubility does not encompass dispersibility or emulsifiability. The one or more anionic surfactants have a molecular weight greater than 225 and less than 365. When two or more anionic surfactants are used, the "molecular weight" as used hereinabove is calculated based on the average of the molecular weights of the two or more anionic surfactants. Often, the naturally occurring fatty acids used to prepare the anionic surfactants are commercially available as mixtures of components of different molecular weights in different degrees of unsaturation and carbon contents.

A preferred class of anionic surfactants are anionic surfactants of the formula (R¹-COO)yM (Formula I) wherein R¹ is an olefinically unsaturated or a saturated alkyl, y is 1 or 2, where M is a cationic counteratom, and where the total number of carbons in R¹ is from 13 to 23. Preferably, R¹ is unsaturated within the alkyl group and is neither alpha, beta-unsaturated nor is the olefinic unsaturation conjugated to the carboxyl group. The molecular weight of an anionic surfactant of the formula I is calculated without the weight of M; i.e., the molecular weight is calculated for R¹-COO⊃min; only.

The anionic surfactants containing M as a counterion can be readily prepared from their acid precursors, where M is hydrogen, such as by reacting the carboxylic acid with a metal hydroxide, including hydroxides of ammonium, lithium, sodium, potassium, magnesium, calcium, etc. The selection of a particular M counterion is not critical so long as the resulting surfactant remains at least partially soluble in the organic solvent, and preferably is only sparingly water soluble, providing anionic surfactants capable of producing the microemulsions and emulsions of this invention. Preferably, M is monovalent and more preferably is selected from sodium, potassium and onium (e.g., quaternary nitrogen as in ammonium, etc.) cations. Preferably, the anionic surfactants have an average molecular weight of at least about 250, more preferably at least about 280, and most preferably at least about 295. Preferably, the anionic surfactants have a molecular weight of no more than 345, and more preferably no more than 340, and most preferably no more than 337 excluding the counterion M.

Examples of specific anionic surfactants useful in the invention are salts of the following olefinic and saturated aliphatic and alicyclic carboxylic acids:

olefinic fatty acids: myristoleic (cis-tetradec-9-enoic) acid; palmitoleic (cis-9-hexadecenoic) acid; linolenic (9,12,15-octadecatriene) acid; linoleic (9, 12 or 13-octadecadienoic) acid; oleic (cis-9-octadecenoic) acid; arachidonic (5,8,11,14-eicosatetraenoic) acid; erucic (cis-13-docosenoic) acid; and unsaturated alicyclic acids containing five carbons: hydnocarpic acid (C₁₆H₂₈O₂); chaulmoogric acid (C₁₆H₃₂O₂); and gorlic acid (C₁₈H₃�0₂O₂); and

saturated fatty acids: myristic (tetradecane-C₁₄H₂₈O₂) acid; palmitic (hexadecane-C₁₆H₃₂O₂) acid; stearic (octadecane-C₁₈H₃�6O₂) acid; eicosanoic (arachidic-C₂�0H₄�0O₂) acid; and docosanoic (behenic-C₂₂H₄₄O₂) acid.

An advantage of using anionic surfactants is that relatively small amounts of the preferred anionic surfactants are required to provide the continuous oil microemulsions and high water content emulsions of this invention. Consequently, the amount of residual anionic surfactant remaining on a surface cleaned with the microemulsions and emulsions is minimal and problems of streaking, etc. are also minimal. An additional advantage is that since the acids are often derivatives of natural products, they are considered to be in some respects more environmentally friendly than typical synthetic anionic surfactants.

Preferably, the preferred anionic surfactants are in the microemulsions in an amount of not less than about 0.5% by weight, and more preferably not less than about 1% by weight. Preferably, the preferred anionic surfactants are present in the microemulsions in an amount of not more than about 6%, and more preferably in an amount of not more than about 5% by weight. Although a carboxylic acid (in addition to its salt) may be present in the formulation, the acid does not act as a surfactant to the extent of the aliphatic alcohol-organic solvents mentioned above. However, the acid acts less efficiently on a weight basis than such an alcohol due to the generally higher molecular weight of the acids.

In the continuous single phase oil microemulsions, the specific carboxylic acid salt surfactant described earlier may be supplemented with other typical anionic sulfonate surfactants of the commonly available sulfonated alkylbenzene/toluene/naphthalene type. For example, those represented by the formula RXB-SO₃M, wherein R is alkyl, · is 1 or 2, B is a divalent radical when · is 1 or a trivalent radical when · is 2 and which is derived from an aromatic radical and wherein M is the same cationic counterion as mentioned earlier and wherein the total carbon number in Rx is from 18 to 30. The molecular weight of a surfactant of the formula RxB-SO₃M is calculated without the molecular weight of the counterion M; ie, the molecular weight is calculated only for RxB-SO₃�min. Such sulfonate surfactants containing M as a counterion can be readily prepared from their precursor sulfonic acid by reacting with a metal hydroxide, including hydroxides of ammonium, lithium, sodium, potassium; magnesium, calcium. The selection of a particular M counterion is not critical so long as the resulting surfactant remains at least partially soluble in the organic solvent and preferably is no more than sparingly water soluble and demonstrates that it is capable of assisting the particular carboxylic acid-derived anionic surfactant in the preparation of the microemulsions and emulsions of this invention. Preferably, M is monovalent. Preferably, B is derived from benzene, toluene or naphthalene. Preferably, the sulfonate surfactants have a molecular weight greater than 400. Preferably, these surfactants have a molecular weight less than 600 and preferably less than 550.

In the continuous single phase microemulsions, one or more nonionic surfactants may also be used to assist or enhance the effectiveness of the anionic surfactants. The one or more nonionic surfactants are used in an amount of from 0 to about 6% by weight based on the total weight of the microemulsion. Preferably, the one or more nonionic surfactants are used in an amount of no more than about 3, more preferably no more than about 2, weight percent. Preferably, the combined weight of the amount of ionic surfactant and nonionic surfactant is no more than about 10, more preferably no more than about 8, weight percent of the microemulsion.

Nonionic surfactants which can be suitably used in this invention include alkylphenol alkoxylates and primary and secondary alcohol alkoxylates, wherein the alkoxylate can be ethoxy, propoxy, butoxy or combinations thereof. Mixtures of alcohol alkoxylates can be used. Preferred nonionic surfactants are alkylphenol ethoxylates and primary and secondary alcohol ethoxylates. The alkylphenol ethoxylates and primary and secondary alcohol ethoxylates are represented by the formula:

R-O-(CH₂CH₂O)n-H

where R is a hydrocarbon having 9 to 24 carbon atoms and n is a number averaging from 1 to 9. Commercially available nonionic surfactants are sold by Shell Chemical Company under the name NeodolTM and by Union Carbide Corporation under the name TergitolTM. Representative examples of preferred commercially available nonionic surfactants include the TergitolTM 15-s series and the NeodolTM 91 or 25 series. Additional representative examples of suitable nonionic surfactants include polyoxyethylated polypropylene glycols, polyoxyethylated polybutylene glycols, polyoxyethylated mercaptans, glyceryl and polyglyceryl esters of natural fatty acids, polyoxyethylenated sorbitol esters, polyoxyethylenated fatty acids, alkanolamides, tertiary acetylene glycols, N-alkyl pyrrolidones and alkyl polyglycosides. More preferred nonionic surfactants used in this invention are secondary alcohol ethoxylates. Representative examples of preferred commercially available secondary alcohol ethoxylates include Tergitol™ 15-s-3, Tergitol™ 15-s-5 and Tergitol™ 15-s-7.

The microemulsions of this invention may further contain other types of surfactants such as amphoteric surfactants having molecular weights above 350, betaines such as N-alkyl betaine including N,N,N-dimethyl-hexyl-amino-(3-propionate) and sulfobetaines such as N,N,N-dimethyl-hexadecylamine-propylenesulfonate.

The conductivity of a microemulsion of this invention is measured at application temperatures since conductivity may vary with temperature as the phase behavior of the microemulsion may also change with temperature. It follows that it is possible to prepare a microemulsion which is not oil continuous and does not fall within the range of this invention at room temperature, but which is oil continuous when heated to a higher application temperature and falls within the range of this invention. Electrical conductivity can be measured using standard techniques and conventional equipment, e.g. using a Fisher Brand Model 326 conductivity meter which has a 1 cm gap between the anode and cathode in the probe. When such a device is used, the probe is simply immersed in the solution, the instrument is allowed to equilibrate and the conductivity value is read on the device. It is understood that the device must be calibrated using standard electrolyte solutions of known conductivity prior to measuring the conductivity of the compositions of this invention.

Microemulsions of this invention have a viscosity of less than 40 centistokes when measured at application temperatures. Viscosity is measured at application temperatures because viscosity can vary with temperature. Consequently, it is possible to prepare a microemulsion which is not within the scope of this invention at room temperature, but which, when heated to higher application temperatures, has a viscosity which falls within the scope of this invention. Preferably, the continuous single phase oil microemulsions have a viscosity of less than 30 centistokes, more preferably less than 20 centistokes, and even more preferably less than 10 centistokes, and most preferably less than about 8 centistokes. An advantage of preferred microemulsions of this invention is that when diluted with up to at least 10 weight percent water or oil, the viscosity of the resulting composition does not increase above 40 centistokes. Viscosity can be measured by well known means using conventional equipment designed for such a purpose. For example, a capillary viscometer such as a Cannon-Fenske capillary viscometer equipped with a size 350 capillary can be used following the procedure of ASTM D 445. Alternatively, a Brookfield Model LVT viscometer with a UL adapter can be used to measure viscosities in centipoise.

Thus, the one or more surfactants are used in an amount effective to form a continuous, single-phase oil microemulsion. This amount will vary depending on the amount and nature of the components in the total microemulsion composition. However, it is equally important that the microemulsions have a high water content, generally above 40% by weight based on the total weight of the composition. Since this is the case, the microemulsions of the invention are characterized by being compositions which are neither bicontinuous nor water-continuous.

A general methodology used to form single phase microemulsion cleaning systems with high water content is as follows: (A) selecting an organic solvent or organic solvent mixture with the desired low water uptake; (B) determining the relationship between surfactant structure (e.g., hydrophilicity) and conductivity, viscosity and phase behavior (e.g., the presence of liquid crystals) of compositions with the desired water, surfactant, organic solvent and additive contents by varying only the surfactant or the surfactant blend composition; (C) The process of steps (A) and (B) may be repeated as needed at multiple concentrations of solvent and surfactant until the amount and types of solvent and surfactant required to produce a single phase oil continuous structure at the desired water content (based on the information generated in step (B)) are determined; (D) determining the viscosity and conductivity of the continuous oil microemulsion; (E) if the viscosity is too high, it can be adjusted by reducing the concentration of the surfactant, by changing the solvent composition (e.g. by increasing the content of oxygenated solvent such as glycol ether or alcohol), by adding a second class of surfactant (e.g. nonionic to an anionic based system) or by adding electrolytes up to 0.6, preferably up to 0.2 wt% (surfactant only) or by changing the ratio of organic solvent to surfactant; (F) if necessary, adjusting the surfactant or surfactant blend composition (repeating steps (B), (C) and (D) with a new formulation) and step (E) to provide a single phase continuous oil microemulsion; and (H) confirming that the viscosity and conductivity of the continuous oil microemulsion are within the scope of this invention. It should be noted that some steps may be omitted or repeated depending on the circumstances.

In general, optimum cleaning performance is obtained when the microemulsion systems are prepared with a minimum amount of surfactant. This results in low residue and lower intrinsic viscosities (in the absence of liquid crystals). To determine the minimum amount of surfactant required, the methodology described above should be repeated at different surfactant levels for a given solvent system and water content. Typically, the minimum surfactant level is defined as the lowest surfactant level at which one can traverse the range from water-continuous to oil-continuous microemulsion structures without generating an excess phase. In practice, it has been found that efficient systems (lowest surfactant contents) can be obtained by using primarily an anionic solvent of the higher molecular weight range specified and then controlling the phase behavior using a second component (either adding small amounts of electrolyte or adjusting the composition of the solvent phase, e.g. by adding the low molecular weight hydrocarbon described below).

Another consideration in determining optimal continuous oil microemulsions is the avoidance of high viscosity regions during the cleaning process. In use, the microemulsions described here can transition from their oil continuous structure through the bicontinuous region to the water continuous one, e.g., by evaporating solvent components, resulting in a new solvent equilibrium; solubilizing soils, which may prefer a water continuous structure; or adding water during a rinse operation. For this reason, the most preferred systems should maintain low viscosities not only in the oil continuous region, but also in the bi- and water continuous regions.

Addition of an electrolyte is an effective method for adjusting phase behavior; however, increasing the electrolyte content reduces the effectiveness of the surfactant. Therefore, the total electrolyte content (excluding surfactants) should be minimized. In another embodiment of the invention, a microemulsion having a conductivity, measured at its application temperature, of greater than its Z number, a bicontinuous or oil-in-water microemulsion comprising the previously mentioned components can be perturbed (also referred to as "titrated" with aqueous sodium carbonate electrolyte) to produce microemulsions. The perturbation is carried out by the incorporation, by weight of the composition, of either up to about 0.5% of an electrolyte as listed above or up to about 20%, preferably up to 10% or less of an aliphatic or alicyclic hydrocarbon having a molecular weight of not more than 100. Typically, the electrolyte selected for this purpose may be one or more of the previously mentioned salts or a soluble polymer electrolyte, e.g. a water-soluble polyacrylic acid or a Polyacrylate salt. The low molecular weight hydrocarbon can be, for example, propane, butane, pentane, hexane, or cyclohexane. In general, the lower the weight of the hydrocarbon, the more effective the perturbation. The use of the electrolyte is described in all examples below, and the effective use of the lower hydrocarbon (cyclohexane) is described in Example 8 (samples E-1 through E-3) and Example 9 (samples H-1 through HA). In Example 13, a number of sample formulations were prepared using the methodology given above until the properties were approximately adjusted by varying the levels and types of the formulation component and Na-Carb electrolyte in samples S-1 through S-5, wherein the w/o microemulsion with a conductivity of less than Z was ultimately produced by the perturbation.

Emulsions

The cleaning emulsions of this invention are well dispersed when adequately mixed; however, upon standing the emulsions form at least two phases, one phase being a continuous oil microemulsion. Typically only two phases form upon standing the emulsions. As used herein, "standing" means standing undisturbed for 7 days at 25°C.

The emulsions of this invention contain water in an amount of greater than 60 wt% and less than 95 wt% based on the total weight of the emulsion. Preferably, the emulsions contain water in an amount of greater than 70 wt%, more preferably greater than 75 wt%; preferably less than 90 wt%, more preferably less than 88 wt%.

The types of organic solvents used in the emulsions of this invention are the same as those described above under the heading Microemulsions, including all classes of solvents, physical characteristics of the solvents, representative examples, and preferred solvents. However, the amount of solvent used in the emulsions of this invention is greater than 4% and less than 40% by weight based on the total weight of the emulsion. Preferably, the amount of solvent used for an emulsion is used, greater than 8 wt%, more preferably greater than 10 wt%; preferably less than 25 wt%, and more preferably less than 15 wt%.

The descriptions of suitable ionic surfactants and nonionic surfactants are the same as those described above under the heading Microemulsions. However, the amount of ionic surfactant used is from about 0.1% to about 5% by weight based on the total weight of the emulsion. Preferably, the amount used is less than 3% by weight.

The definition used above to describe "oil-continuous" compositions is also used to describe the emulsions. Conductivity is measured after stirring and before phase separation occurs at application temperatures since conductivity can vary with temperature as the phase behavior of the emulsion can also change with temperature. It follows that it is possible to prepare an emulsion which is not oil-continuous and does not fall within the scope of this invention at room temperature, but which is oil-continuous when heated to a higher application temperature and falls within the scope of this invention. In addition, the emulsions have a viscosity of less than 40 centistokes as measured at application temperatures. Viscosity is measured at application temperatures since viscosity can vary with temperature. It follows that it is possible to prepare an emulsion which is not within the scope of this invention at room temperature, but which, when heated to a higher application temperature, has a viscosity which falls within the scope of this invention. Preferably, the emulsions have a viscosity of less than 20 centistokes, more preferably less than 10 centistokes.

A generalized methodology used to develop high water content emulsion cleaning systems is as follows: (A) Select an organic solvent or organic solvent mixture with the desired low water uptake; (B) Determine the relationship between the structure of the surfactant (e.g., hydrophilicity) and conductivity of a composition having the desired content of water, surfactant, organic solvent and additives by varying only the surfactant or the mixed composition of surfactants; (C) the process of steps (A) and (B) can be repeated as needed at several concentrations of solvent and surfactant until the amounts and types of solvent and surfactant required to give a continuous oil emulsion structure with a desired water content (based on the information developed in step (B)) are obtained; (D) determining the viscosity, conductivity and water content of the emulsion, stability (time to phase separation) of the continuous oil emulsion; (E) if the viscosity is too high, it can be adjusted by varying the ratio of the surfactant concentration, the ratio of the organic solvent to surfactant or by adding an additional organic solvent such as glycol ether to reduce the viscosity; (F) adjusting the surfactant or surfactant blend composition as needed (repeating steps (B), (C) and (D) with a new formulation from step (E) to provide a continuous oil emulsion; and (H) confirming that the viscosity and conductivity of the continuous oil microemulsion are within the scope of this invention. It should be noted that some steps may be avoided or repeated depending on the circumstances.

Optional

In addition to the required components listed above for microemulsions or emulsions, a variety of optional materials may be added depending on the end use application, the desired physical properties of the microemulsion or emulsion, etc. Thus, various detergent additives, chelating agents (such as tetrasodium ethylenediaminetetraacetate "EDTA"), sequestering agents, suspending agents, fragrances, enzymes (such as lipases and proteases), optical brighteners, preservatives, corrosion inhibitors, phosphating agents, UV absorbers, disinfectants, biologically active compounds such as pesticides, herbicides, fungicides and drugs, fillers and dyes may be included in a microemulsion or emulsion of these invention.

Prior to use, sodium alkyl toluene sulfonates used to supplement the anionic carboxylate surfactant in the preparation of the microemulsions should be treated to remove residual sulfate salts and alkyl toluene disulfonate by extraction of a solution of the surfactant in PnB using aqueous hydrogen peroxide, followed by neutralization using aqueous sodium hydroxide. "PnB" means propylene glycol n-butyl ether (DOWANOLTM PnB, supplied by The Dow Chemical Company), "PnP" means propylene glycol n-propyl ether (DOWANOLTM PnP, supplied by The Dow Chemical Company), "w/o" means continuous oil microemulsions, "o/w" means continuous water microemulsions, Naphtha SC 140 is a commercial petroleum distillate supplied by Exxon Corporation and ExxalTM 7 is a commercial isopheptyl alcohol (5-methylhexanol) also supplied by Exxon.

Sodium erucate ("Na-erucate") is the sodium salt of erucic acid and is prepared in situ by neutralizing erucic acid with 5N aqueous sodium hydroxide solution. Similarly, the other acid salts are prepared by neutralizing their corresponding carboxylic acid with sodium hydroxide or another aqueous alkali metal or alkaline earth metal base, e.g. potassium hydroxide or the like. The term "Na-oleate", "Na-stearate", "Na-linoleate", "Na-palmitate", etc. means the sodium salt of each corresponding carboxylic acid.

The following examples are included for purposes of illustration only and are not to be construed as limiting the scope of the invention or the claims.

Unless otherwise indicated, all parts and percentages are by weight. In all examples, viscosities were determined at 25ºC using ASTM D 445 on a Cannon-Fenske capillary viscometer using a size 350 capillary or on a Brookfield Model LVT viscometer with a UL adapter.

Example 1 Concentrates

A concentrate solution is prepared by mixing 16.2 parts ExxalTM 7 isoheptyl alcohol with 16.2 parts DOWANOLTM PnP propylene glycol n-propyl ether ("PnP") and 41.7 parts DOWANOLTM PnB propylene glycol n-butyl ether ("PnB"), wherein erucic acid is combined and then neutralized with 5N aqueous sodium hydroxide solution to yield 16.2 parts sodium erucate and 9.7 parts water. The result is a stable, clear, single phase solution with low viscosity. This concentrate solution can be perturbed by the addition of electrolyte, water and organic solvent into a resulting w/o microemulsion of the invention.

Example 2 - Water-in-oil microemulsion

A sample of 3.08 parts of the solution prepared as described in Example 1 is mixed with 2.2 parts n-heptane and 4.72 parts deionized water to give a two-phase product with an excess oil phase and a conductivity of 4040 microsiemens/centimeter ("uS/cm") (where Z = 1374) with a total composition of 5 parts Na-erucate, 22 parts heptane, 12.9 parts PnB, 5 parts PnP, 5 parts Exxal 7 and 50.1 parts water. The two-phase product is titrated with a 10% sodium carbonate ("Na-Carb") solution. Upon standing 1 part of the Na Carb solution, dispersed liquid crystals ("LC") form and the resulting sample conductivity drops to 1770 mS/cm (Z = 1475). After a total of 1.25 parts of Na Carb solution is added, a clear, single-phase microemulsion product with 1430 uS/cm conductivity (Z = 1490) is formed and after a total of 1.5 parts of Na Carb solution is added, the resulting clear, bluish, single-phase water/oil microemulsion has a conductivity of 430 uS/cm (Z = 1590) and a viscosity of 9.7 centistokes ("cSt") measured with a Brookfield LVT viscometer with UL adapter.

Example 3 Disturbable microemulsion and W/O microemulsion

In the manner of Example 1, a sample is prepared from the same components in slightly modified proportions by varying the amounts of the two glycol ethers, using 14.9 parts PnB and 3 parts PnP instead. The resulting o/w microemulsion contains LC and has a conductivity of 4250 uS/em (Z = 1375). This is a perturbable microemulsion that can be converted to a w/o microemulsion by adding electrolyte. When mixed with a 10% Na-Carb Solution (the electrolyte) as described in Example 2, the o/w microemulsion is converted into a clear, bluish, low-viscosity single-phase water/oil microemulsion. Addition of 1 part of the Na-Carb solution yields a microemulsion with a conductivity of 530 uS/cm (Z = 1472) and a viscosity of 9.5 cSt.

Example 4 Petroleum-based product and disruptive microemulsion

A sample is prepared in the manner of Example 1 by substituting a petroleum distillate, Naphtha SC 140, obtained from Exxon Chemical, for the previous heptane-based organic solvent. The components of the sample and their respective amounts are: Naphtha SC 140 = 22 parts; PnB = 15 parts, PnP = 3 parts, Exxal 7 = 5 parts, Na erucate = 5 parts, and deionized water (DI water) = 50 parts. The resulting sample is a clear, perturbable single phase o/w microemulsion with a conductivity of 4420 uS/crn (Z = 1459). When this perturbable o/w microemulsion is titrated with 10% Na-Carb solution, the following results are observed: 1 part Na-Carb solution gives a clear, single phase product with a conductivity of 3620 mS/cm (Z = 1547); 1.75 parts Na-Carb solution gives a milky emulsion with excess water phase, which has a conductivity of 1030 uS/cm (Z = 1620) and a viscosity of 11.5 cSt. Then, to this emulsion, an additional amount of the organic solvent Naphtha 5O 140 is added to adjust the water/oil balance to form the desired w/o microemulsion. When a total of 4.76 parts of the Naptha SC 140 has been added, a clear, bluish single phase w/o microemulsion is formed which exhibits a conductivity of 1110 uS/cm (Z = 1370) and a viscosity of 7.5 cSt. It is an excellent grease removal product.

Example 5 Cleaning procedure

The w/o microemulsion with a conductivity of 1110 uS/cm, low viscosity, prepared as described in Example 4 is contacted with steel coupons coated with lithium grease according to the standard Conoco cleaning test. Excellent grease removal and cleaning is observed.

Example 6 d-Limonene based product

In the same manner as the previous examples, a sample is prepared by substituting d-limonene for the heptane previously used. d-limonene is an organic-based solvent component commonly used in a wide range of cleaning products. The sample prepared comprises the following amounts of each respective component: d-limonene = 22 parts, PnB = 14.9 parts, PnP = 3 parts, Exxal 7 = 5 parts and deionized water = 50.1 parts and the resulting o/w microemulsion contains LC and has a conductivity of 4670 uS/cm conductivity (Z = 1527). When the composition is "titrated" with the 10% Na-Carb solution, 0.5 parts Na-Carb solution yields a resulting microemulsion that still contains LC, with a conductivity of 1180 uS/cm conductivity (Z = 1573). Further titration to a total of 1 part Na-Carb solution converts the sample to a clear, single phase w/o microemulsion with 375 mS/cm conductivity (Z = 1613) and a viscosity of 13.5 cSt.

Example 7 Emulsions with high water content

In the same manner as Example 2, a formulation is prepared using: Na erucate = 2.5 parts, heptane = 10.5 parts, PnB = 3.5 parts; PnP = 3.5 parts, deionized water = 80 parts. To this perturbable o/w emulsion containing an excess of the oil phase, varying amounts of the Na carb are added by passing through intermediate bicontinuous formulations until a clear w/o microemulsion with some excess water phase results. Upon stirring, this yields an emulsion having a conductivity of approximately 0.5 Z and a viscosity of 12.5 cSt. The various stages of this preparation are shown graphically in Table 1, Samples A-1 through A-4.

Examples 8-13 Use of other Na-carboxylates as the inorganic surface-active component

In a similar manner to the previous examples, various formulations are prepared using various sodium carboxylic acid salts in place of the Na erucate used in the previous examples. The other components of the formulations are selected from Na-Carb, n-heptane, PnB, 1-hexanol and deionized water and in some formulations cyclohexane. With each different Na-carboxylate, a series of formulations are prepared - the Ratios of the various components are adjusted to achieve the desired properties of conductivity of less than 1 Z and low viscosity. From these series, one can observe how the methodology described in the above teachings is used to prepare and then fine-tune each formulation. The properties of each microemulsion or emulsion formulation can also be observed in these examples. The various formulation compositions and their corresponding resulting physical properties and calculated Z numbers are shown in Tables 2 through 7 below. Table 1 Table 2

1 p.cl. = 1 phase clear

na = not measured

LC = liquid crystals Table 3 Table 4

1 p.cl. = 1 phase clear

na = not measured

LC = liquid crystals Table 5 Table 6

1 p.cl. = 1 phase clear

na = not measured

LC = liquid crystals Table 7

1 p.cl. = 1 phase clear

na = not measured

LC = liquid crystals

Claims (1)

1. A continuous single-phase oil microemulsion comprising: A. Water in an amount of not less than about 40% by weight and not more than about 75% by weight based on the total weight of the microemulsion; 8. an organic solvent or a mixture of two or more organic solvents, wherein the organic solvent or mixture of organic solvents is characterized by containing no more than 2% by weight of water at about 25°C when the organic solvent is saturated with water in the absence of surfactants or other additives, and wherein the organic solvent or mixture of two or more organic solvents is in an amount of no less than about 10% and no more than about 60% by weight based on the total weight of the microemulsion; and C. one or more anionic surfactants which are at least partially soluble in the one or more organic solvents, wherein at least one of the present anionic surfactants is selected from the group of aliphatic and alicyclic carboxylic acid salts represented by the formula (R¹-COO)yM, wherein R¹ is a hydrocarbon group having 14 to 23 carbon atoms and having a molecular weight in the range of 225 to 365 excluding the M group, wherein M is an alkali or alkaline earth metal cation having a valence of 1 or 2 and wherein y is the integer 1 or 2 and wherein the anionic surfactants are present in a total amount of greater than about 0.1% and less than about 10% by weight based on the total weight of the microemulsion. 2. Microemulsion according to claim 1, which is characterized in that it is a continuous oil microemulsion with an electrical conductivity of less than Z microsiemens/centimeter when measured at application temperatures and with a viscosity of less than 40 centistokes when measured at application temperatures, where Z is represented by the following formula: Z = (1/3)(φw)²σiAimi, where φw is the volume fraction of water in the microemulsion, i is a given electrolyte, Ai is the molar conductivity of the electrolyte i and mi is the molarity of the electrolyte 1 in the aqueous phase. 3. The microemulsion of the preceding claims, wherein the one or more organic solvents are an aliphatic alcohol, an aliphatic ester, an aliphatic hydrocarbon, a chlorinated aliphatic hydrocarbon, an aromatic hydrocarbon, an aliphatic diester, an aliphatic ketone, an aliphatic ether, an alkylene glycol monoether, an alkylene glycol diether, an alkylene glycol ether acetate, or combinations thereof. 4. A microemulsion according to any one of the preceding claims, wherein the one or more organic solvents are present in an amount of not less than 30% and not more than 50% by weight. 5. A microemulsion according to any preceding claim, wherein water is present in an amount of not less than 45% and not more than 70% by weight. 6. A microemulsion according to any preceding claim, wherein at least one of the anionic surfactant(s) is an anionic surfactant having a molecular weight of not less than 250 and not more than about 345 without the M counterion. 7. Microemulsion according to claim 6, wherein at least one second anionic surfactant is present having the formula RXB-SO₃M, wherein R is alkyl, · is 1 or 2, B is a divalent radical when · 1 or is a trivalent radical when · is 2 and which is obtained from an aromatic radical and wherein M represents a cationic counterion and wherein the total number of carbons in Rx is from 18 to 30. A microemulsion according to any preceding claim, wherein the electrical conductivity is less than 0.5 Z microsiemens/centimeter. A microemulsion according to any preceding claim, wherein the viscosity is less than 20 centistokes. A microemulsion according to any preceding claim, wherein the electrical conductivity is less than 0.25 Z microemulsions/centimeter. Microemulsion according to one of the preceding claims, wherein at least one organic solvent is an alkylene glycol monoether. Emulsion which forms at least two phases when standing at 25°C, wherein one phase is a continuous oil microemulsion according to any one of the preceding claims, comprising A. Water in an amount of not less than about 60% by weight and not more than about 95% by weight based on the total weight of the emulsion; B. an organic solvent or a mixture of two or more organic solvents, wherein the organic solvent or mixture of organic solvents is characterized in that it contains not more than 2% by weight of water at 25°C when the organic solvent is saturated with water in the absence of surfactants or other additives, and wherein the organic solvent or mixture of two or more organic solvents is in an amount of not less than 4% and not more than 40% by weight based on the total weight of the emulsion; C. one or more anionic surfactants which are at least partially dissolved in the one or more organic solvents are soluble, wherein at least one of the anionic surfactants present is selected from the group of aliphatic and alicyclic carboxylic acid salts represented by the formula (R¹-COO)yM wherein R¹ is a hydrocarbon group having 14 to 23 carbon atoms and having a molecular weight in the range of about 225 to about 365 excluding the M group, wherein M is an alkali or alkaline earth metal cation having a valence of 1 or 2 and wherein y is the integer 1 or 2 and wherein the one or more ionic surfactants are present in a total amount of not less than about 0.1% and not more than about 5% by weight based on the total weight of the emulsion the emulsion being characterized by being a continuous oil emulsion, wherein the emulsion has an electrical conductivity of less than Z microsiemens/centimeter when measured at application temperatures and a viscosity of less than 40 centistokes when measured at application temperatures, wherein Z is as defined above. 13. The emulsion of claim 12, wherein the one or more organic solvents are an aliphatic alcohol, an aliphatic ester, an aliphatic hydrocarbon, a chlorinated aliphatic hydrocarbon, an aromatic hydrocarbon, an aliphatic diester, an aliphatic ketone, an aliphatic ether, an alkylene glycol monoether, an alkylene glycol diether, an alkylene glycol ether acetate, or combinations thereof. 14. An emulsion according to claim 12 or 13, wherein the one or more organic solvents are present in an amount of not less than 8% by weight and not more than 25% by weight. 15. An emulsion according to any one of claims 12 to 14, wherein water is present in an amount of not less than about 70% and not more than about 90% by weight. 16. An emulsion according to any one of claims 12 to 15, wherein the anionic surfactant has a molecular weight of no more than about 345. 17. An emulsion according to any one of claims 12 to 16, wherein the anionic surfactant has a molecular weight of not less than 250. 18. An emulsion according to claim 17, wherein there is at least one additional anionic surfactant of the formula RxB-SO₃M, wherein R is alkyl, · is 1 or 2, B is a divalent radical when · is 1 or a trivalent radical when · is 2 and which is obtained from an aromatic radical and wherein M is a cationic counterion and wherein the total number of carbons in Rx is from 18 to 30. 19. Emulsion according to one of claims 12 to 18, wherein the electrical conductivity is less than 0.5 Z microsiemens/centimeter. 20. An emulsion according to any one of claims 12 to 19, wherein the viscosity is less than 20 centistokes. 21. Emulsion according to any one of claims 12 to 20, wherein the electrical conductivity is less than 0.25 Z microsiemens/centimeter. 22. Emulsion according to one of claims 12 to 21, wherein at least one organic solvent is an alkylene glycol monoether. 23. An emulsion according to any one of claims 12 to 22, wherein water is present in an amount of not less than about 80% and not more than about 90% by weight. 24. Cleaning concentrate which, when diluted with water, can form the microemulsion according to one of claims 1 to 11, comprising: A. an organic solvent or a mixture of two or more organic solvents, wherein the organic solvent or mixture of organic solvents is characterized in that it contains not more than 2% by weight of water at 25ºC when the organic solvent is saturated with water in the absence of surfactants or other additives; and B. one or more anionic surfactants which are at least partially soluble in the one or more organic solvents, wherein at least one of the present anionic surfactants is selected from the group of aliphatic and alicyclic carboxylic acid salts represented by the formula (R¹-COO)yM, wherein R¹ is a hydrocarbon group having 14 to 23 carbon atoms and having a molecular weight in the range of about 225 to about 365 excluding the M group, wherein M is an alkali or alkaline earth metal cation having a valence of 1 or 2 and wherein y is the integer 1 or 2 and wherein the one or more anionic surfactants are present in no less than about 0.1% and no more than about 10% by weight based on the total weight of the microemulsion. 25. Methods for cleaning metal having a greasy or oily soil on a surface of the metal comprising applying the microemulsion of any one of claims 1 to 11 or the emulsion of any one of claims 12 to 23 to the metal having the greasy or oily soil on the surface of the metal to remove at least a portion of the greasy or oily soil from the metal surface. 26. Microemulsion according to claim 1 or emulsion according to claim 12, wherein the carboxylic acid salt without the M group has a molecular weight between 250 and 345, the valence of M being 1 and y being the integer 1. 27. A microemulsion or emulsion according to claim 26, wherein the carboxylic acid from which the salt is derived is selected from erucic, oleic and stearic acid.