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  Particle-stabilised emulsionsUSPTO Application #: 20070281878Title: Particle-stabilised emulsions Abstract: The invention relates to water-in-oil (W/O) or oil-in-water (O/W) emulsions containing an oil phase of at least one water-insoluble constituent; an aqueous phase; pyrogenic silica at the oil-water interface, the pyrogenic silica partially silylated such that non-silylated surface silanol groups remaining are between 95% and 5% of initial silanol groups, the equivalent of 1.7 to 0.1 surface SiOH groups per nm2, a surface energy gamma-s-D of 30 to 80 mJ/m2, and a specific BET surface area between 30 and 500 m2/g; and optionally other substances, such as pigments or preservatives. The inventive emulsions have a mean particle size of the dispersed phase, of between 0.5 μm and 500 μm, and are of low viscosity. (end of abstract) Agent: Brooks Kushman P.C. - Southfield, MI, US Inventors: Torsten Gottschalk-Gaudig, Herbert Barthel, Bernard Paul Binks, Tommy S Horozov USPTO Applicaton #: 20070281878 - Class: 510417000 (USPTO) Related Patent Categories: Cleaning Compositions For Solid Surfaces, Auxiliary Compositions Therefor, Or Processes Of Preparing The Compositions, Cleaning Compositions Or Processes Of Preparing (e.g., Sodium Bisulfate Component, Etc.), Liquid Composition, Plural Immiscible Liquid Phases (e.g., Emulsion, Oily And Aqueous Layers, Etc.) The Patent Description & Claims data below is from USPTO Patent Application 20070281878. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to emulsions of the water-in-oil (W/O) or oil-in-water (O/W) type and the preparation thereof. [0002] Emulsions, either as water-in-oil (W/O) or oil-in-water (O/W) dispersions, are widely used as an application form for coating materials, such as, for example, water-based paints and finishes, as adhesives and sealants, such as, for example, aqueous epoxy or polyurethane systems, as cosmetic formulations, as cleansing agents and disinfectants, in the food industry, for the surface modification of solid or liquid substrates or as reaction media in emulsion polymerization. [0003] In general, the dispersing and stabilization of the disperse phase are effected with the aid of emulsifiers. Cationic, anionic, ampholytic and nonionic emulsifiers are used. Common to the emulsifiers is that they are surface-active substances. That is to say, they preferably accumulate at interfaces, such as, for example, liquid-liquid, liquid-solid or liquid-gas interfaces, and thus reduce the interfacial/surface energy. On application of the emulsion, however, the emulsifiers can also cover the surface of the substrate to be treated and thus greatly change the wetting properties of the surface. This can adversely affect, for example, the adhesion properties of a coating material or of an adhesive joint or seal. Furthermore, the recoatability may be adversely affected. In addition, emulsifiers based on organic molecules are potential hazardous substances when used in pharmaceutical or cosmetic formulations or in foods. [0004] In 1907, Pickering described for the first time the preparation of emulsions which were stabilized only by addition of various solids, such as basic copper sulfates, basic iron sulfates or other metal salts. This type of emulsion is also referred to as "Pickering emulsions". Basic investigations showed that a characteristic of Pickering emulsions is that solid particles are arranged at the interface between the two liquid phases and form a barrier there to the coalescence of the disperse phase. [0005] Frequently, however, such solid-stabilized emulsions as described, for example, in EP 987008 have a high viscosity and/or a great tendency for separation, i.e. for creaming or sedimentation of the disperse phase. [0006] It was an object of the invention to overcome the disadvantages of the prior art, in particular to provide low-viscosity and sedimentation-stable emulsions having a small particle diameter of the disperse phase. [0007] The object is achieved by the invention. [0008] The invention relates to emulsions of the water-in-oil (W/O) or oil-in-water (o/W) type, containing: [0009] an oil phase (phase A), containing one substantially water-insoluble component or optionally a plurality of substantially water-insoluble components, [0010] a water phase (phase B) which may optionally contain further water-soluble components, such as salts or organic compounds, such as alcohols, carboxylic acids or other compounds, [0011] pyrogenic silica which is arranged at the oil-water interface and is partly silylated in a manner such that the content of non-silylated surface silanol groups on the silica surface is from not more than 95% to not less than 5% of the starting silica, equivalent to from 1.7 to 0.1 SiOH groups per nm.sup.2 of silica surface, the dispersion fraction of the surface energy gamma-s-D is from 30 to 80 mJ/m.sup.2 and the specific BET surface area has a value of from 30 to 500 m.sup.2/g, [0012] and optionally further substances, such as pigments or preservatives, [0013] the emulsions having a mean particle size of the disperse phase, i.e. a mean drop diameter, measured by means of laser diffraction, of from 0.5 .mu.m to 500 .mu.m, the emulsions having a low viscosity, low viscosity meaning that the emulsions have relative viscosities .eta..sub.r in the range of from 1 to 10.sup.6, the relative viscosity being defined as the quotient .eta..sub.rel=.eta./.eta..sub.0 of the measured viscosity of the emulsion .eta., measured at 25.degree. C. and a shear rate D=10 s.sup.-1, divided by the viscosity of the pure homogeneous phase .eta..sub.0, [0014] and the relative viscosity .eta..sub.rel of the emulsion obeys the formula .eta..sub.rel=(1-.PHI./0.74).sup.-([.eta.]0.74), .PHI. being the phase volume of the disperse phase and [.eta.] being a form factor which is in a range of from 2.5 to 100 for the emulsions according to the invention. [0015] It was surprising and by no means to be foreseen by the person skilled in the art that low-viscosity and sedimentation-stable emulsions having a small particle diameter of the disperse phase are obtainable by using sinter-aggregated pyrogenic silica as a particulate emulsifier. This is surprising in that sinter-aggregated pyrogenic silica is usually used as a rheological additive for increasing the viscosity of liquid media. [0016] Here, sinter aggregates are secondary structures according to DIN 53206, which are permanent under shear conditions as usually occur on dispersing fillers in liquid media, such as, for example, solvent-containing or solvent-free adhesives or coating materials, i.e. cannot be divided into their primary particles. This can be demonstrated, for example, from TEM images of hardened silica-binder dispersions which have only aggregate structures but no isolated primary particles. [0017] Particulate systems consisting of sinter aggregates are furthermore characterized in that the hydrodynamic equivalent diameter obtained in the particle size determination by means of quasielastic light scattering is at least a factor of 2 greater than the diameter of the primary particles obtainable computationally according to the formula a=6/A.sub.BETd, where A.sub.BET is the specific BET surface area measured by means of nitrogen adsorption according to DIN 66131 and d is the density of the primary particles. [0018] Sinter-aggregated systems are furthermore characterized in that the fractal dimension df of the mass is preferably less than 2.7, where the fractal dimension df is defined as mass being proportional to the radius R to the power df. The fractal dimension of the mass can be determined, for example, by means of small angle X-ray or neutron scattering. [0019] The emulsions according to the invention are preferably substantially free of conventional liquid and solid, purely organic surface-active substances which are not particulate at room temperature and the pressure of the ambient atmosphere, such as nonionic, cationic and anionic emulsifiers. [0020] Here, non-particulate emulsifiers means not particles and colloids but molecules and polymers, following the definition of molecules, polymers, colloids and particles as given in "Dispersionen und Emulsionen [Dispersions and emulsions]", G. Lagaly, O. Schulz, R. Zindel, Steinkopff, Darmstadt 1997, ISBN 3-7985-1087-3, page 14. In general, these organic emulsifiers have a size of less than 1 nm, a molar mass of <10 000 g/mol, a carbon content of >50% by weight, determinable by elemental analysis, and a Mohs' hardness of less than 1. [0021] At the same time, the emulsifiers, of which the emulsions according to the invention are preferably substantially free, generally have a solubility of more than 1% by weight in water at 20.degree. C. and the pressure of the ambient atmosphere, i.e. from 900 to 1100 hPa, in homogeneous or in micellar form. The emulsions according to the invention may contain such surface-active substances up to a maximum concentration of less than 0.1 times, preferably less than 0.01 times, particularly preferably less than 0.001 times, in particular less than 0.0001 times, the critical micelle concentration of these surface-active substances in the water phase; this corresponds to a concentration of these surface-active substances, based on the total weight of the emulsion according to the invention, of less than 10% by weight, preferably less than 2% by weight, particularly preferably less than 1% by weight, in particular 0% by weight. [0022] The emulsion according to the invention contains an oil phase (phase A). Phase A contains one substantially water-insoluble component, optionally a plurality of substantially water-insoluble components. Here, substantially water-insoluble means that the solubility of the components in water alone or as a mixture is less than 10 g/100 g of water, preferably less than 1 g/100 g of water, particularly preferably less than 0.1 g/100 g of water, measured at 20.degree. C. and the pressure of the ambient atmosphere, i.e. from 900 to 1100 hPa. In the case of the emulsion according to the invention, the viscosity of phase A, measured at 20.degree. C. and a shear gradient of 10 s.sup.-1, is from 0.1 to 1 000 000 mPas, preferably from 0.1 to 500 000 mPas, particularly preferably from 0.2 to 100 000 mPas. [0023] In the case of the emulsion according to the invention, the phase A can preferably contain a plurality of components. The individual components may be both substances which are liquid at 20.degree. C. and solids, the total mixture of the individual components having the abovementioned viscosity. Preferably, but not necessarily, a multicomponent phase A is a true solution, i.e. a homogeneous phase in which no further phase interfaces occur. [0024] Examples of substantially water-insoluble components as may be formed by the phase A of an emulsion according to the invention or may be present in it are aliphatic and aromatic hydrocarbons, alcohols, aldehydes, ketones, ethers, esters, amines, carboxylic acids and derivatives thereof, mercaptans, thioethers, oligomeric or polymeric compounds, such as polyolefins, such as polystyrenes, polypropylenes or polyethylenes, saturated or unsaturated polyesters, such as, for example, polycondensates of phthalic acids and 1,2-propanediols or polycocondensates of phthalic acids, 1,2-propanediols and maleic acids, optionally dissolved in reactive diluents, such as styrenes, polyethers, polyepoxides or monomeric or oligomeric precursors thereof, such as alkylene bisglycidyl ethers, such as [0025] bisphenol A-based diglycidyl ethers, such as [0026] with n preferably from 0 to 10, particularly preferably from 0 to 5, [0027] epoxy novolac resins, such as those of the formula [0028] bifunctional epoxy compounds, such as Continue reading... 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