d US005393461A United States Patent (19) 11 Patent Number: 5,393,461 Fillipova 45 Date of Patent: Feb. 28, 1995 54 PREPARATION OF STABLE AOUEOUS 4,997,864 3/1991 Waters ................................ 523/319 EMULSIONS OF WATER-INSOLUBLE 5,032,390 7/1991 Iwaya et al. .......................... 424/59 5,066,485 11/1991 Brieva et al. .......................... 424/63 PARTICLES 5,091, 188 2/1992 Ahynes ................ ... 424/450 75 Inventor: Irina V. Fillipova, Bethlehem, Pa. 5,171,572 12/1992 Suganuma et al. ...... ... 424/401 73) Assignee: RTD Corporation, Bethlehem, Pa. 5,250,289250,289 10/1993 Boothroydhrowd et al. .................. 424/59/ 21 Appl. No.: 131,448 FOREIGN PATENT DOCUMENTS - a - - 9 22 Filed: Oct. 4, 1993 610397 12/1960219 candCanada ................................ 523/502M 51) Int. Cl. ........................ bo so cosko Primary Examiner-Richard D. Lovering C08K 3/22 57 ABSTRACT 52 U.S. Cl. .................................. 252/314; 106/23 C; A process for preparing an emulsion of water-insoluble 106/472; 252/310; 252/311; 252/312; particles useful in the cosmetic, pharmaceutical, paint 252/315.2; 514/937; 514/938; 514/942; and ink industries comprising: 58 Field of Search 514/952;252/30, 523/502; 311, 312, 523/505 314 treating the water-insoluble particles with a wetting 252/315.2, 514/937,938,942, 952;523/502,505 106/23 C, combiningagent in anthe organic water-insoluble solvent; particles with- an oily- or polymeric substance to obtain an oily suspen 56) References Cited sion; U.S. PATENT DOCUMENTS preparing an aqueous ision of a combination of 2,764,499 9/1956 Porter, Jr. ....................... 252/314 X R. agents; I ti ith the oil 3,133,893 5/1964 Newman ............................. 524/720 combining the aqueous solution with the oily suspen 3,544,500 12/1970 Osmond et al. .. 428/402.24 sion to form an emulsion. 3,580,880 5/1971 Clarke et al. ........................ 524/457 4,421,660 12/1983 Solc nee Hajna ................ 252/62.54 7 Claims, No Drawings 5,393,461 1. 2 b) mixing of 1 to 90% w/w of a finely divided pow PREPARATION OF STABLE AOUEOUS der having 50 to 100 nm particle size distribution EMULSONS OF WATER-INSOLUBLE with the wetting solution to obtain a dispersion; PARTICLES c) mixing the dispersion with of from about 10 to about 99% w/w of an oily/polymeric substance BACKGROUND OF THE INVENTION dissolved in an organic solvent to obtain an oily suspension; Field of the Invention d) preparing an aqueous solution by mixing in water This invention relates to stable aqueous emulsions of of from about 0.1 to about 2.0% w/w of an emulsi water-insoluble particles useful in the cosmetic, phar 1O fying agent selected from the group consisting of a maceutical, paint and ink industries. cationic, nonionic, anionic and zwitterionic surface 2. Reported Developments active agent by stirring for about 30 to 90 minutes The prior art has expended great effort to provide at a temperature of from about 60 to about 70° C. stable emulsions of particulates for various applications to obtain an aqueous solution; in the above-mentioned industries. The main problem 5 e) cooling the aqueous solution to room temperature; encountered with emulsions is inadequate physical sta f) adding from about 20 to about 35% w/w of the bility whereby the particulates flocculate, agglomerate oily/polymeric suspension to from about 65 to and settle-out from the emulsions and become non about 80% w/w of the aqueous solution and mix uniform. ing them for about 20 to 30 minutes at room tem U.S. Pat. No. 3,133,893 discloses pigment particles perature to obtain an aqueous suspension; coated with a polymer for coloring of plastics, resins g) emulsifying the aqueous suspension by using emul and synthetic fibers. The polyner is a thermoplastic, sifying means, such as a sonifier to obtain an emul linear, addition polymer of a compound containing the sion which contains organic solvents used in step polymerizable group of (a); and 25 h) removing the organic solvent by stirring/evapora tion or other means to obtain a final emulsion essen N / tially free of the organic solvent. C The concentration of the final emulsion may be con / N trolled by either varying the percentage of the oily 30 suspension obtained in step (c), added to the aqueous U.S. Pat. No. 3,544,500 discloses a process for encap solution obtained in step (d), or by evaporation of the sulating solid particles for use in insecticides, pharma water from the final emulsion obtained in step (h). ceuticals and powders. The process comprises adsorb DETALED DESCRIPTION OF THE ing a polymer on the surface of the particles and provid 35 ing a stabilizer having an anchor group which become INVENTION associated with the adsorbed polymer on the surface An important requirement in the preparation of the and a pendant hydrophilic component solvated by the emulsion of the present invention is the use of narrow aqueous phase and provides a stabilizing sheath around distribution size particles, namely of from about 50 or the solid particles. less nm to about 100 nm. U.S. Pat. No. 3,580,880 discloses a process for making dispersions of particulate solids by dispersing the partic Water-insoluble Particles ulate solids in a lipophilic or a hydrophilic liquid in the The finely-divided particles used in the present inven presence of a polymeric amphipathic stabilizer which tion should be essentially water-insoluble. Such parti associates with the surface of the particles and provides 45 cles may be inorganic, organic and polymeric particles a solvated steric barrier around the particles. depending on the intended end use of the emulsion. The U.S. Pat. No. 4,421,660 discloses a process for prepar required particle size is achieved by conventional tech ing compositions comprising the steps of: niques, such as by grinding, milling or comminution. emulsifying a hydrophilic emulsion polymerizable Examples of inorganic particles include, but are not 50 limited to zinc oxide, talc, kaolin, mica, titanium diox monomer in an aqueous dispersion of discrete parti ide, zirconium oxide, iron oxides, aluminum hydroxide, cles of an inorganic solid; and aluminum chloride, calcium phosphate, magnesium polymerizing the monomer to coat the discrete parti oxide, aluminum silicate, calcium silicate, titanium diox cles of the inorganic solid. ide, bentonite, asbestine, china clay, calcium carbonate, While the above-listed and similar approaches made 55 magnesium carbonate and dolomite. great strides in satisfying the needs of various industries, Examples of organic and polymeric particles include, they do have some shortcomings including the com but are not limited to, starch, polyamide resin, polyole plexity of the processes and less than the desired stabil fin resins, polystyrene, polystyrene resin, acrylic resin, ity in the products produced thereby. The present in epoxy resin, vinyl resin, vinylidene resin, polyurethane vention intends to provide solutions for these and other resin, natural rubber, synthetic rubber, chitin, chitosan, shortcomings. fibroin, keratin and cellulose. Some of these materials are extensively used in the SUMMARY OF THE INVENTION various industries for various purposes. For example: The present invention provides a process for making zinc oxide is used industing powders, pastes, ointments, an emulsion comprising the steps of: 65 creams and lotions; talc, titanium dioxide and zinc oxide a) preparing a solution of from about 0.01 to about are used in cosmetic powders; titanium dioxide and zinc 5% w/w of a wetting agent in an organic solvent to oxide are used as sunblockers; antimony oxide, red OX obtain a wetting solution; ide, lemon chrone, cobalt blue, metal containing or 5,393,461 3 4 ganic pigments and carbon blacks are used as pigments ethylene oxide wherein the ethylene oxide is present in in the paint and printing industries. equal amounts of from about 30 to 60 moles of ethylene When materials are ground, milled or comminuted to oxide per mole of alcohol; and carboxylic esters formed very small particle size, air is adsorbed onto the surface by the reaction of fatty acids with polyhydric alcohols. of the particles. The adsorbed air prevents or at least greatly reduces the wettability of the particles thereby Other nonionic surfactants include: polyoxyethylene hindering uniform suspensions of the particles in a liquid p-tert-octylphenyl ether and polyoxyethylene mono vehicle. For this reason a wetting agent must be used to hexadecyl ether. replace solid-air interface with a solid liquid interface. Zwitterionic surfactants include N-dodecyl-N,N- In non-aqueous solutions the molecules of a wetting 10 dimethyl betaine. agent are oriented with the hydrophobic group towards Preferred emulsifying agents include: potassium lau the molecules of the nonaqueous solution thereby in rate, sodium dodecyl sulfate, ammonium lauryl sulfate, creasing the hydrophobicity of the solid particles and magnesium laurylsulfate, triethanolamine laurylsulfate, rendering them more wettable. The prior art has uti sulfated castor oil, dialkylglycerylphosphorylcoline, lized aqueous, oily, waxy or volatile organic vehicles 15 sodium lauryl sulfoacetate, sodium dodecyl benzenesul for dispersing solid particles for obtaining the desired fonate, polyoxyethylated lauryl, hexadecyltrime effects in the various end products. While the use of thylammonium bromide or chloride, ethoxylated pa these approaches and materials provided improvements raoctylphenol, 2-ethyl-hexyl alcohol, ethoxylate and in emulsions, the need for further improvements are cetyltrimethyl ammonium persulfate. obvious for those practicing in the cosmetic, paint, 20 The surfactants used as emulsifying agents are prefer pharmaceutical and printing industries. ably used with a co-surfactant. The ratio of surfactant to Wetting Agents co-surfactant should be in the range of 1:1 to 1:3 for best The wetting agents used in an organic solvent in step results.