MXPA01005800A - Stable, constant particle size, aqueous emulsions of nonpolar silanes suitable for use in water repellence applications - Google Patents

Abstract

This invention relates to a stable aqueous silane emulsion with constant particle size. The emulsion comprises a continuous water phase, a discontinuous silane phase, and an emulsifier system. The emulsifier system contains a primary surfactant and a cosurfactant. The primary surfactant functions to prevent coalescence of particles, by steric or ionic repulsion between particles. The cosurfactant prevents diffusion of the silane into the aqueous phase. The combination of primary surfactant and cosurfactant results in an adsorbed inner layer of cosurfactant between the silane and the outer layer of a mixture of both surfactants which contacts the water phase. The combination of primary surfactant and cosurfactant provides a barrier which prevents diffusion of silane into the water phase. A method for preparing the emulsion is also disclosed.

Description

STABLE AQUEOUS EMULSIONS OF NON-POLAR SILICA THAT HAVE CONSTANT PARTICLE SIZE FIELD OF THE INVENTION This invention relates to aqueous silane emulsions which can be used in water repellent applications. More particularly, this invention relates to aqueous silane emulsions which do not separate in phase with aging and which have an average particle size which does not increase significantly with aging.

BACKGROUND OF THE INVENTION In the past, organosilane and organosilicone compounds dissolved in organic solvents have been used to render masonry and other substrates water repellent. For example, U.S. Patent No. 3,772,065 to Seiler discloses a method for making waterproof masonry structures. The method comprises impregnating the masonry structures with an alcoholic or hydrocarbon solution of hydrolyzed alkyltrialkoxysilanes and their lower oligomers. European Patent 0 075 962 to Pühringer discloses an impregnating agent for porous building materials containing tetraalkoxysilanes, alkyltrialkoxysilanes, or aryltrialkoxysilanes, a surfactant, an aliphatic solvent and an optional condensation reaction catalyst. U.S. Patent No. 4,937,104 to Pühringer discloses a process for imparting hydrophobicity to mineral substrates. The process comprises mixing at least one silane, a hydrolysis product of the silane, a condensation product, or combinations thereof, with a surfactant and a water / organic alcohol mixture. The resulting emulsion is applied to a mineral substrate. However, organic solvents such as alcohols and hydrocarbons are flammable, expensive, and have harmful environmental and physiological effects. United States Patent No. RE 33,759 of DePasquale et al., Discloses an aqueous emulsion containing silanes to render masonry surfaces water repellent. The system consists essentially of a hydrolysable silane and oligomers thereof; a surfactant having a hydrophilic-lipophilic balance (HLB) of 4 to 15; and water. The hydrolysable silane has the formula RnSiR '(-n) wherein n is 1 or 2, R is independently selected from hydrocarbon and halogenated hydrocarbon groups of 1 to 20 carbon atoms, and R' is selected from alkoxy groups of 1 to 3. carbon atoms, halide groups, amino groups, and carboxyl groups. The surfactant may be not ionic, amphoteric, ionic, or combinations thereof. The preferred surfactants are SPAN® surfactants having HLB values in the range of 4.3 to 8.6, and TWEEN® 61 and TWEEN® 81, which have HLB values of 9.6 and 10.0, respectively. However, the pH and the particle size of the emulsion are not exposed; neither is the change in particle size exposed over time. The Patents of the United States Nos. 4,877,654 and 4,990,377, both by Wilson et al., Expose aqueous emulsions to render porous substrates water-repellent. The emulsion comprises a hydrolysable silane, an emulsifier with HLB of 1.5 to 20, a buffer and water. The silane has the formula RnSiR'4-n, where R is independently selected from hydrocarbon and halogenated hydrocarbon groups of 1 to 30 carbon atoms; n is 1 or 2, and R 'is an alkoxy group of 1 to 6 carbon atoms, a halide group, an amino group, or a carboxyl group. Nonionic, cationic, anionic and amphoteric emulsifiers are suitable. The emulsion has a pH of 6 to 8. However, the stability and the particle size of the emulsion are not exposed; the change in particle size of the emulsion is not exposed over time. U.S. Patent No. 5,226,954 to Suzuki, discloses a composition of organosilicon comprising a monoalkyltrialkoxysilane and / or a condensate thereof, an emulsifying mixture of an emulsifier anionic and a non-ionic emulsifier and water. The composition is subjected to emulsification to form an emulsion. The "emulsification" as defined herein is achieved when the alkylakoxysilane and the emulsifier are mixed and the resulting top layer is opaque and also where a small amount of water is separated to form a lower layer that is more transparent than the top layer . The '954 Suzuki does not expose the particle size of the emulsion. The '954 Suzuki does not expose the increase in particle size over time. The United States Patent 5No. 746,810 of Suzuki discloses an aqueous emulsion of an alkylalkoxysilane, a surfactant and water. The '810 from Suzuki discloses that the emulsion is stable and has a particle diameter in the range of 2 to 10 micrometers. The '810 from Suzuki defines that "stable" means that after storage, part of the separation within an opaque layer of concentrated silane emulsion and a clear, colorless layer of water is acceptable when the material can easily be re-emulsified. The emulsion has a pH of 7.5 to 9. British Publication GB 2 301 102 A of Toagosei Co., Ltd., discloses an aqueous emulsion prepared by hydrolyzing a silane selected from the group consisting of alkoxysilanes and alkylhalogensilanes when heated in the presence of an acid catalyst and a small amount of water to form a mixture of the silane and its oligomer, and subsequently emulsifying the mixture with water and an emulsifier. The alkoxysilane has the formula RnSiR'4_n, wherein R is independently selected from alkyl groups, substituted alkyl groups, and aryl groups; n is 1 or 2, and R1 is an alkoxy group of 1 to 6 carbon atoms. The emulsifier can be nonionic, anionic or cationic. The particle size of the emulsion is 1 micrometer or smaller. Emulsions prepared according to Toagosei, with particle sizes greater than 1 micrometer tend to be unstable and responsible for phase separation. U.S. Patent No. 5,458,923 and U.S. Patent No. 5,314,533, both to Goebel et al., Disclose aqueous emulsions of organisilicon compounds. The emulsion comprises an alkoxysilane, an ionic surfactant, an organosilicon surfactant and water. The emulsion is stable for weeks at pH from 6 to 9. "Stable" is defined as: 1. an emulsion that has no phase separation without formation of a cream layer; or 2. the emulsion can be obtained by simple agitation without loss of effects, if a layer of cream is present.

However, none of these patents addresses the problem of increasing particle size over time. This is generally due to a process known as Ost ald Maturation in which the low molecular weight emulsified silane compound has a sufficient solubility in water so that it diffuses from smaller particles through the particulate aqueous phase. bigger. This results in a net increase in the average particle size of the emulsion over time. This can lead to inconsistent behavior or performance of the emulsion in commercial use due to changes in the properties of the emulsion with aging. Additionally, when an alkoxysilane is used as the silane compound in the emulsion, over time the alkoxysilane can react when contacted with the phase in water. The alkoxysilane can be subjected to hydrolysis and condensation, thereby forming a siloxane and releasing the alcohol, which can break the emulsion. Therefore, an object of this invention is to provide a means to avoid, or minimize, increasing the particle size of the emulsion with aging; thereby providing the ability to produce stable emulsions of low molecular weight silanes. "Low molecular weight" means a molecular weight (MW) less than 1000.

Increasing size particles will form cream more quickly, according to Stokes' Law for the proportion of cream formation of the particles in an emulsion. Conversely, if the particles are small enough, the speed of random particle movement due to the broian movement will be sufficient to prevent the formation of creams. The use of additives in the silane compound phase or water phase to decrease the density difference between the silane compound and water to almost zero is a technique to minimize creaming. However, this is often undesirable, since it adds to the cost of manufacturing an emulsion and can have deleterious effects on the use of the emulsion in some applications. To reduce the formation of cream, one can increase the viscosity of the aqueous phase with thickeners such as alginates, as described in U.S. Patent No. 5,746,810, or with the use of large amounts of emulsifiers relative to the amount of the interfacial surface area between the oily particles and the aqueous phase. The use of these large amounts of emulsifiers results in the formation of emulsifying structures such as liquid crystals on the particle surface and in the phase which produces a viscous aqueous phase. The use of excessive amounts of emulsifiers is harmful generally for the water repellency properties provided by the silane emulsions. Therefore, another objective of this invention is to produce silane emulsions having small enough particle size so that they do not show significant cream formation and remain essentially stable in silane concentration with aging. For this purpose it is an object of this invention to provide emulsions having an average particle size of less than 10 microns. An emulsion will not change in uniformity due to the formation of cream if the emulsion which is already a cream is so concentrated in oily particles dispersed from the top to the bottom of the container. The maximum packing of rigid spheres of the same diameter is 74% by volume. Therefore, in theory, as the concentration of the silane phase in an emulsion of polydispersed particle size reaches or exceeds this concentration, the emulsion becomes quite viscous and probably does not show uniformity due to the formation of cream, due to that is practically already in a creamy state. Due to the viscous paste-like nature of these emulsions, they are difficult to pump or handle in commercial use. Therefore, a further objective of this invention is to provide silane emulsions Stable with constant particle size that also have low viscosity for easy handling. The emulsions of this invention have silane concentrations of about 65% or less by weight and can be easily handled by both emptying and pumping due to their low viscosity. Therefore, the invention relates to an aqueous silane emulsion and a method for its preparation. The emulsion comprises an alkoxysilane, an emulsifier system consisting essentially of at least two emulsifiers and water. An emulsifier is the primary emulsifier, and a nonionic surfactant having a higher HLB to 13. The second emulsifier is a nonionic co-surfactant, and has an HLB value less than 11. The emulsion has improved stability as emulsion of alkoxysilanes does not show separation in phase with aging. The emulsion has uniformity since the discontinuous phase does not show or minimally show the increase in particle size with aging. The aqueous silane emulsions of the present invention are stable and have constant particle size. "Stable" means that the emulsion does not phase separate into an aqueous layer and a layer of silane (oil) with aging. "Constant" means that the particle size of The emulsion does not increase significantly with aging. Preferably, the particle size does not increase to more than 10% after the emulsion is stored at about 25 ° C for at least 14 days. These emulsions are easily handled by both emptying and pumping due to their low viscosity. Typically, the viscosity of the emulsion is not greater than about 5 square millimeters / sec. However, at silane concentrations greater than 50%, the viscosity of the emulsion will be greater than 5, and may be as high as 1,000 square millimeters / sec. Emulsions with viscosity in the range of 5 to 1,000 square millimeters / s are easily emptied and pumped. In particular, the invention relates to an aqueous silane emulsion comprising: A) a continuous phase comprising water; B) a discontinuous phase comprising at least one non-polar silane, wherein the discontinuous phase forms dispersed particles in the continuous phase; and C) an emulsifier system consisting essentially of (i) a major surfactant, and (ii) a co-surfactant. This emulsion has the advantage that even a low molecular weight silane can be emulsified to form a stable emulsion with constant particle size. However, it does not mean that this invention is limited to non-polar silanes with low molecular weight. This emulsion may contain non-polar silanes having molecular weights greater than 1, 000"Non-polar silane" means that at least one non-polar organofunctional group is attached to the silicon atom. The non-polar silane is preferably a non-polar alkoxysilane. Typically, the amount of non-polar alkoxysilane is from 1 to 65% by weight of the emulsion. When the emulsion will be used in water repellency applications, the amount of non-polar alkoxysilane is from 10 to 60% by weight. However, more dilute emulsions are suitable for some applications (ie, where the amount of the non-polar silane is from 5 to 10% by weight). Suitable non-polar alkoxysilanes have the general formula RnSiR'4-n, wherein each R is independently selected from the group consisting of alkyl, aryl, and substituted aryl groups, R 'is an alkoxy group of 1 to 10 carbon atoms, and n is 1 or 2. R is preferably independently selected from the group consisting of alkyl and aryl groups, and R 'is preferably an alkoxy group of 1 to 5 carbon atoms. However, when the emulsion will be used in water repellency applications, preferably R is independently an alkyl group of 8 to 20 atoms of carbon and R 'has from 1 to 6 carbon atoms. However, alkyl R groups having from 1 to 7 carbon atoms are also suitable for use in this emulsion. Suitable alkylalkoxysilanes and halogenated alkylalkoxysilanes for component (B) are set forth in U.S. Patent No. RE 33,759 to DePasquale et al., Which is incorporated herein by reference for the purpose of disclosing suitable alkoxysilanes. Preferably, the alkylalkoxysilane is selected from the group consisting of isobutyltriethoxysilane, isobutyltrimethoxysilane, n-octyltriethoxysilane and n-octytrimethoxysilane. When the emulsion will be used in water repellency applications, the alkylalkoxysilane is preferably n-octyltriethoxysilane. Suitable halogenated alkylalkoxysilanes include 3,3, 3-trifluoropropyltrimethoxysilane and 6,6,6-trifluoroxytrimethoxysilane. However, this emulsion is advantageous over the emulsion exposed by DePasquale et al., Because the high purity silanes can be emulsified to form stable emulsions having constant particle size. High purity silanes typically contain about 5% by weight or less of impurities. In addition, silanes that have impurity contents as low as 2.50% in weight or less, 0.63% by weight or less, and even 0.1% by weight or less may also be used to form an emulsion according to this invention. "Impurity" means any dimer, trimer or oligomer of the silane; and includes any other siloxane polymer or high molecular weight oil present in the silane. The emulsion of this invention can be produced with a particle size less than 10 microns. Preferably, the particle size is less than 1 micrometer, and more preferably, the particle size is less than 0.5 micrometer. The emulsifier system inhibits the increase in particle size with aging. The emulsifier system comprises a main surfactant and a co-surfactant. The main surfactant prevents the coalescence of the particles by the ionic repulsion between the particles. The co-surfactant prevents diffusion of the silane out of the particle, which may result in Maduration of Ost ald. The amounts of each surfactant in the emulsifier system are sufficient to provide an exterior mixed monolayer that contacts the aqueous phase and a second interior monolayer of essentially water-insoluble co-surfactant. The mixed monolayer is a combination of both surfactants. This bilayer of surfactant it provides a significant barrier to retard or prevent the diffusion of silane out of the particle. The emulsifier system imparts stability and constant particle size to the emulsion. The main surfactant is a nonionic surfactant having an HLB greater than about 13.0, preferably greater than 15.0. The concentration of the main surfactant in the emulsion is 0.5 to 3 molecules per 100 square Angstroms of surface area of the silane particles. However, for very dilute emulsions with a relatively large particle size, where the concentration of the main surfactant becomes low due to these restrictions, it may be necessary to increase this amount by the critical micellar concentration (CMC) of the emulsifier to adjust the amount that could dissolve in the aqueous phase. Suitable nonionic main surfactants are typically selected from the group consisting of ethoxylated octylphenols, esters and ethoxylated fatty oils, ethoxylated alcohols and combinations thereof. Examples of suitable nonionic main surfactants are as follows, with the HLB value in parentheses after the name of the surfactant. Suitable non-ionic major surfactants having an HLB greater than 13.0 are commercially available. For example, you can use surfactants that are solid at room temperature and are exemplified by BRIJ® 700 (18.8), which is a polyoxyethylenetearylether available from ICI Americas Inc. of Wilmington, Delaware; MAPEG® S-40K (17.2), which is a polyoxyethylene monostearate available from PPG / Mazer of Gurnee Illinois; MACOL® SA-40K (17.4), which is a steareth-40 available from PPG / Mazer of Gurnee Illinois; MACOL® SA-40K (15.4) which is a steareth-20 available from PPG / Mazer of Gurnee Illinois; and TERGITOL® 15-S-20 (16.3) which is an ethoxylated secondary alcohol having from 11 to 15 carbon atoms available from Union Carbide Chem. & Plastics Co., Industrial Chemicals Division, Danbury Connecticut. Other suitable nonionic surfactants for the main surfactant include TERGITOL® 15-S-40 (18.0), an ethoxylated alcohol available from Union Carbide Corporation; HETSORB® O-20 (15.0), a laureate of sorbitan available from Herterene Chemical; TWEEN® 80 (15.0), a monoleate of polioxiet ilensorbitan available from ICI Americas Inc., of Wilmington Delaware; APG 325 CS® Glycoside (13.0), an alkyl ether polysaccharide of 9 to 11 carbon atoms available from Henkel Corporation Ambler, Pennsylvania; BRIJ® 35L (16.9), which is polyoxyethylene lauryl ether produced by ICI Surfactant and TRITÓN® X-100 (13.5), TRITÓN® X-305 (17.3) and TRITÓN® X-705 (17.9), all are octylphenols ethoxylates produced by Union Carbide Corporation. BRIJ® 35L is preferred. The co-surfactant must have a HLB less than 11. Examples of some suitable co-surfactants and their HLB values include: ALDO® MS (3.8-3.9), which is glycerol monostearate, and LONZEST® GMO (3.0) which is a ethoxylated fatty ester, which are produced by Lonza Inc., Fairlawn, New Jersey; S-MAZ® 60K (4.7), which is a sorbitan monostearate available from PPG Industries, Gurnee, Illinois; ARLACEL® 60 (4.7), which is a sorbitan stearate available from ICI Americas Inc., Wilmington, Delaware; oleates such as sorbitan monooleate (4.3), sorbitan trioleate (1.8), polyoxyethylene sorbitan monooleate (10.0); ALDO PGHMS® (3.0), which is propylene glycol monostearate available from Lonza Inc., Fairlawn, New Jersey; MAPEG® EGMS (2.9), which is ethylene glycol monostearate available from PPG / Mazer Gurnee, Illinois; HODAG® DGS (4.7), which is diethylene glycol monostearate; ETHOX® SAM-2 (4.9), which is a polyoxyethylene stearyl amine available from Ethox Chemicals Inc., Greenville, South Carolina; MACOL® SA-2 (4.9), which is a polyoxyethylene ester ester available from PPG / MAZER, Gurnee, Illinois; and polyoxyethylene ethers such as BRIJ® 72 (4.9), which is a polyoxyethylene lauryl ether and BRIJ® 52 (4.9), which is a polyoxyethylene cetyl ether, which are available from ICI Americas Inc., SPAN® 20 ( 8.6), that is glycerol monolaurate available from ICI Surfactants; and CALGENE® GML (3.0) which is glycerol monolaurate available from Calgene Chemical, Inc. The sorbitan fatty acid esters having HLB values in the range of 4.3 to 8.6 and polyoxyethylene sorbitan fatty acid esters having values of HLB in the range of 9.6 to 10 are the preferred nonionic surfactants. Preferred sorbitan fatty acid esters having HLB values in the range of 4.3 to 8.6 are commercially available under the trademark SPAN®, produced by ICI Americas; SPAN® 20, a sorbitan monolaurate, has HLB of 8.6, SPAN® 40 has HLB of 6.7, SPAN® 60, a sorbitan monostearate, has HLB 4.7, and SPAN® 80 has HLB of 4.3. Particularly SPAN® 20 is preferred. Polyoxyethylene sorbitan fatty acid esters having HLB values in the range of 9.6 to 10.0 are commercially available under the trademark TWEEN® produced by ICI Americas. In particular, TWEEN® 61 is preferred, which has HLB of 9.6; and TWEEN® 81 which has HLB of 10.0. The concentration of the co-surfactant in the emulsion is from 1.5 to 15, preferably from 4 to 15, molecules per 100 square Angstroms of surface area of silane particles. Higher amounts of surfactant are unnecessary and can lead to instability of the emulsion. The sizes The emulsion particles mentioned above are heavy diameters of "intensity" when measured by dynamic light scattering (photon correlation spectroscopy). A NICOMP® particle sizing instrument was used. The remainder, up to 100% of the aqueous silane emulsion comprises water and any optional component. Typically, the amount of water in the emulsion is from 30 to 99 weight percent. The aqueous silane emulsion may further comprise one or more of the following optional components: (D) a buffer, (E) a biocide, (F) a thickener, (G) a fragrance, (H) a dye, (I) a foaming agent, (J) an antifoaming agent and (K) a mold inhibitor. Component (D) is an optional buffer used to maintain the pH of the aqueous silane emulsion in a desired range. Buffers are typically organic and inorganic acids and bases, including salts thereof. The amount of buffer added to the emulsion is typically from 0.01% to 5% by weight. Suitable dampers are disclosed in U.S. Patent No. 4,877,654, which is incorporated herein by reference in order to describe suitable dampers. When the emulsion will be used in applications for water repellency, the buffer is preferably selected from the group which consists of sodium bicarbonate, sodium benzoate, sodium dibasic phosphate, and a mixture of ammonium hydroxide and acetic acid. Preferably, a buffer is added to the emulsion when a biocide is present, or when the pH of the emulsion is outside the range of 6 to 9. Component (E) is an optional biocide that is typically added in an amount of 0.1. to 5% by weight of the emulsion. Biocides are known in the art and are commercially available. For example, 6-acetoxy-2,4-dimethyl-m-dioxane (GIV-GARD DXN®) sold by Guvaudan Corp. is suitable for this invention. Suitable biocides are described in U.S. Patent No. 4,877,654, which is incorporated herein by reference in order to describe suitable biocides. Component (F) is an optional thickener that moderately increases the viscosity of the aqueous phase. The component (F) can be used to prevent the formation of cream of larger particle size emulsions in this range. The thickener should not affect the stability and particle size of the emulsion. Suitable thickeners are exemplified by water-soluble polymers such as polyacrylic acid and polyacrylic acid salts, alginic acid salt, alginic acid ester, polyvinyl alcohol, polyether, casein, mannan, starch, chitosan, carboxymethylcellulose and methoxymethylcellulose. U.S. Patent No. 5,746,810 is incorporated herein by reference in order to describe suitable thickeners. Thickeners are typically added in an amount of 0.1% to 1% by weight of the emulsion. Component (G) is an optional fragrance. Component (H) is an optional dye. The colorant may be water-based, or it may be an oil-soluble dye. Component (I) is an optional foaming agent. Component (J) is an optional antifoam agent. Component (K) is an optional mold inhibitor. Component (K) is, for example, sodium benzoate. The emulsion of this invention can be used in a wide variety of applications, including water repellency applications. This invention also relates to a method for the substrates to be water repellent. The method comprises impregnating the substrate with the aqueous alkoxysilane emulsion, hydrolyzing and condensing the alkoxysilane. The substrate can be wood, although masonry is preferred. "Masonry" means any porous inorganic substrate, such as building materials. The masonry includes structural ceramics, cements, insulation products, rock and concrete. Suitable substrates are disclosed in U.S. Patent No. 4,877,654 incorporated herein by reference. reference in order to describe suitable substrates. The method for impregnating the substrate with the aqueous alkoxysilane emulsion is not critical. For example, the emulsion can be applied to a surface of the substrate by brush coating, roller coating or spraying. Alternatively, the aqueous alkoxysilane emulsion can be mixed with a composition, such as uncured concrete, and subsequently the composition can be cured to form a substrate having water repellency. The amount of emulsion impregnated in the substrate depends on the porosity and surface conditions of the substrate but typically is in the range of 0.05 to 2.0 Kg / m squared. This invention also relates to a method for preparing the emulsion of the present invention. The method comprises: Emulsifying a composition comprising A) water; B) from 5 to 65% by weight of at least 1 alkoxysilane, wherein the alkoxysilane forms a discontinuous phase of particles dispersed in the water; and C) an emulsifier system consisting essentially of (i) a main surfactant, wherein the main surfactant is a nonionic emulsifier having an HLB greater than 13, and wherein the main surfactant is present in the emulsion at a concentration of 0.5 to 3 molecules per 100 square Angstroms of surface area of the particles and (ii) a co-surfactant, wherein the surfactant is a non-ionic emulsifier having an HLB less than 11, and wherein the co-surfactant is present in the emulsion at a sufficient concentration to provide 1.5 to 15 molecules per 100 square Angstroms of surface area of the particles. The emulsion can be made with a desired particle size of the discontinuous phase (i.e., less than 0.5 micrometer) to obtain the correct range of surfactant coverage on the particles. The particle size can vary when changing the shear conditions such as the pressure by sonolation during the emulsification. For example, if the particle size and the surface coverage is too large, the increasing shear stress or the increasing sonolation pressure can be realized by decreasing the particle size. If the particle surface coverage is too low, i.e. because the particle size is too small, the intensity of the shear stress may be decreased, the additional surfactant may be added, or both as needed. One skilled in the art would recognize how to adjust the particle size and change the shear conditions.

EXAMPLES These examples are intended to illustrate the invention for those skilled in the art and should not be construed as limiting the scope of the invention set forth in the claims. All percentages in these examples are percentages by weight, unless indicated otherwise. For the Finnish of these examples, "n-Otes" means n-octyltriethoxysilane and "i-Btes" means isobutyl triethoxysilane. The nonionic surfactants used are shown by trade name in these examples. BRIJ® 35L is a polyoxyethylene lauryl ether with a HLB of 16.9. TRITÓN® X-100 is an ethoxylated octyl phenol with an HLB of 13.5. TRITÓN® X-305 is an octylphenol ethoxylated with an HLB of 17.3. SPAN® 20 is a sorbitan monolaurate with HLB of 8.6. LONZEST® GMO is an ethoxylated fatty ester with an HLB of 3.0. The equation used to calculate the gamma with (T) which is a number of surfactant molecules per 100 square Angstroms of particle surface area, is shown below: r =% S x D -r (9.96 x 10"3 x M x% silane) wherein S is the weight percentage of the emulsifier in the emulsion, D is the initial particle size (diameter) of the silane particles in nanometers, and M is the molecular weight of the emulsifier.

Reference Example 1 An emulsion of a silane was prepared by mixing 12 parts of water with the main surfactant until the main surfactant was thoroughly mixed with the water. Then 40 parts of the silane were mixed with the co-surfactant and added to the above mixture with water. The resulting mixture was stirred at 2000 RPM with a 3.8 cm (1.5 inch) diameter Cowls blade for 30 minutes. After 30 minutes, an additional 58.3 parts of water were added and the resulting mixture was processed through a 2 stage homogenizer at 7500/1500 psi (51,700 kPa / 10,300 kPa). After homogenizing the mixture, 0.001 part of the sodium bicarbonate was added to the mixture to maintain a pH of about 7.0. The initial particle size of the resulting emulsion was measured by a NICOMP® particle size analyzer. The particle size was presented in nanometers, unless otherwise indicated. Based on the amount of the main surfactant added and the initial particle size, a major surfactant shell was generated per 100 square Angstroms of particle size according to the above formula. Similarly, based on the amount of the co-surfactant and the initial particle size, a co-surfactant coverage per 100 was generated.

Square angstroms of particle size according to the formula above. The particle size of the emulsion was measured after storage at room temperature. When the layer of running water was visually observed on the lower part of the emulsion, stability was judged to have failed. Tables 1 to 3 show the main surfactant and the amount used, the co-surfactant and the amount used, the silane used and the amount of water used. Table 4 shows the coverage of the main surfactant and the co-surfactant and the particle size measured over time for each sample, until the stability of the sample failed.

Comparative Example 1 An emulsion of N-octyltriethoxysilane was prepared by the method of the reference example of Example 1. The surfactants used were the same as those used in the examples of U.S. Patent No. 4,877,654, Wilson et al. . For the purposes of this experiment, it is presumed that TRITÓN® X-305 (HLB = 17.3) will be the main surfactant, and it is presumed that TRITÓN® X-100 (HLB = 13.5) will be the co-surfactant. The amount of TRITON® X-305 was 0.48 parts by weight.

The amount of TRITON® X-100 was 1.12 parts by weight. The resulting emulsion had an initial particle size of 402 nm. Based on the amount of TRITON® X-100 added to the initial particle size, a coverage of 1.8 co-surfactant molecules per 100 square Angstroms of particle size was generated. The emulsion which increased in particle size to a particle size of 1232 nm was measured after 21 days of storage at room temperature. After 21 days, a clear water layer was observed in the lower part of the emulsion and the emulsion was determined to have a failed stability. The formulation for Comparative Sample 1 is in Table 1. Comparative Example 1 shows that unstable emulsions are produced where there is insufficient coverage of co-surfactant in the particles and the co-surfactant has an HLB value greater than 11.

Comparative Example 2 The same procedure used in Reference Example 1 was used to prepare an emulsion, with the exception that isobutyltriethoxysilane was used instead of N-octyltriethoxysilane. It was presumed that TRITÓN® X-305 will be the main surfactant and it was presumed that TRITÓN® X-100 will be the co-surfactant. The amount of TRITON® X-305 was 0.48 parts by weight. The The amount of TRITON® X-100 was 1.12 parts by weight. The resulting emulsion had an initial particle size of 924 nm. Within 24 hours, the particle size of the emulsion increased to 1918 nm. After 24 hours, a clear water layer was observed in the lower part of the emulsion and the emulsion was judged to have failed stability. The formulation for Comparative Sample 2 is in Table 1. Comparative Example 2 shows that unstable emulsions are produced when there is insufficient coverage of co-surfactant on the particles and the co-surfactant has an HLB value greater than 11.

Comparative Example 3 Comparative Sample 3 was prepared by the same method as Reference Example 1, with the exception that the main surfactant was 1.4 parts of BRIJ® 35L. The co-surfactant was 0.59 parts of SAPAN® 20. The emulsion had an initial particle size of 335 nm. Based on the particle size and the amount of SPAN® 20 used, a coverage of 1.4 co-surfactant molecules per 100 square Angstroms of particle size was generated. After 14 days the emulsion had a particle size of 1247 nm and a layer was observed of clear water indicating that the emulsion had a failed stability. The formulation of Comparative Sample 3 is in Table 2.

Comparative Example 4 Comparative Sample 4 was prepared by the same procedure as that of Comparative Example 3, with the exception that only 0.25 parts of SPAN® 20 were added. The resulting emulsion had an initial particle size of 342 nm. Based on the particle size and the amount of SPAN® 20 used, a coverage of 0.62 molecules of co-surfactant per 100 square Angstroms of particle size was generated. After 14 days at room temperature, the emulsion had a particle size of 1619 nm. A layer of clear water was observed in the lower part which indicates that the emulsion had a failed stability. The formulation of Comparative Sample 4 is in Table 2. Comparative Examples 3 and 4 show that when the coverage of the co-surfactant on the particle is insufficient, the emulsions failed in stability after several weeks.

Comparative Example 5 Comparative Sample 5 was prepared by the procedure of Comparative Example 1, with the except that the n-octyltriethoxysilane contained 0.63% by weight of the dimer thereof as an impurity. The resulting emulsion had an initial particle size of 396 nm. After 14 days at room temperature, the particle size was 428 nm. A separation did not occur. The formulation of the Comparative Sample is in Table 5, and the results of the particle size are in Table 6.

Comparative Example 6 Comparative Sample 6 was prepared by the procedure of Comparative Example 1, with the exception that the n-octyltriethoxysilane contained 2.50% by weight of the dimer thereof as an impurity. After 14 days at room temperature, the particle size was 330 nm. A separation did not occur. The formulation of the Comparative Sample 6 is in Table 5, and the results of the particle size are in Table 6. Comparative Example 1, the formulation and the results thereof are included by comparison in Tables 5 and 6, respectively, shows that when used a high purity alkoxysilane (eg, containing 0.1% by weight or less of impurities) without the emulsifier system of this invention, the emulsion has no constant particle size. Comparative Examples 1, 5 and 6 show the effect of the purity of the alkoxysilane on the stability and the particle size. In Comparative Example 1, the n-octyltriethoxysilane contained less than 0.1% by weight impurity and the emulsion was unstable. The particle size was also significantly increased over time. Comparative Examples 1, 5 and 6 show that as the impurity content of the silane increases, the constancy and the particle size of the emulsion also increase.

EXAMPLE 1 Sample 1 was prepared by the same procedure as that of Comparative Example 3, with the exception that 1.0 parts of SPAN® 20 were added. The emulsion had an initial particle size of 392 nm. Based on the initial particle size and the amount of SPAN® 20 used, a coverage of 2.8 co-surfactant molecules per 100 square Angstroms of particle size was generated. After 63 days at room temperature, the average particle size is 437 nm. A separation did not occur. The formulation for Sample 1 is in Table 2. Example 1 shows that the emulsifier system of this invention can be used to produce stable emulsions with constant particle size.

EXAMPLE 2 Sample 2 was prepared by the same procedure as that of Comparative Example 3, with the exception that 2.5 parts of SPAN® 20 were added. The resulting emulsion had an initial particle size of 319 nm. Based on the initial particle size and the amount of SPAN® 20 used, a coverage of 5.8 molecules per 100 square Angstroms of particle size was generated. After 63 days at room temperature, the particle size is 324 nm. No separation occurred. The formulation of Sample 2 is in Table 2. Example 2 shows that the use of the emulsifier system of this invention provides emulsions having particle size which does not increase to more than 10% when stored at about room temperature for 14 minutes. days. In addition, Examples 1 and 2 demonstrate that as the amount of the co-surfactant increases, the rate of change in particle size decreases. The results of Example 2 have been included in Table 6 by comparison. Example 2 and Comparative Example 6 show that the emulsifying system of this emulsion produces an emulsion with constant particle size and stability in comparison with the alkoxysilane emulsions which they have higher impurity contents than those of the alkoxysilanes suitable for use in this invention. Comparative Examples 1 and 6 and Example 2 show that when a pure purity silane is used, the emulsifier system of this invention must be used to produce a stable emulsion with constant particle size.

EXAMPLE 3 Sample 3 was prepared by the same procedure as that of Reference Example 1. The silane was n-octyltriethoxysilane. The main surfactant was 1.4 parts of BRIJ® 35L. The co-surfactant was 2.0 parts of LONZEST® GMO. The resulting emulsion had an initial particle size of 276 nm. After 34 days at room temperature, the particle size is 279 nm. No separation occurred. The formulation of Sample 3 is in Table 3. Example 3 shows that the use of the emulsifier system of this invention provides emulsions having particle size that does not increase to more than 10% when stored at about room temperature for 14 days . Example 3 also demonstrates that different co-surfactants can be used to produce a stable emulsion with constant particle size.

'NR' means unregistered A number in parentheses () indicates the day on which the sample was tested, when it differs from the day in the first line of Table 4 A number in parentheses () indicates the day on which the sample was tested, when it differs from the day in the first line of Table 6

Claims (9)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. An aqueous emulsion comprising: A) a continuous phase comprising water; B) a discontinuous phase comprising at least one non-polar alkoxysilane, wherein the discontinuous phase forms dispersed particles in the continuous phase; and C) an emulsifier system consisting essentially of (i) a main surfactant, wherein the main surfactant is a nonionic emulsifier having an HLB greater than 13, and wherein the main surfactant is present in the emulsion at a concentration of 0.5 to 3 molecules per 100 square Angstroms of surface area of the particles; and (ii) a co-surfactant, wherein the co-surfactant is a non-ionic emulsifier having an HLB of less than 11, and wherein the co-surfactant is present in the emulsion at a concentration sufficient to provide 1.5 to 15. molecules per 100 square Angstroms of surface area of the particles; and wherein the non-polar alkoxysilane contains an impurity in an amount of 2.50% by weight or less.
2. 2. The emulsion according to claim 1, wherein the non-polar alkoxysilane has the general formula RnSiR'4-n, wherein each R is independently selected from the group consisting of alkyl, halogenated alkyl, aryl and substituted aryl groups, R 'is a alkoxy group of 1 to 6 carbon atoms and n is 1 or 2.
3. 3. The emulsion according to claim 1, wherein the concentration of the co-surfactant is sufficient to provide from 4 to 15 molecules of co-surfactant per 100 Angstroms of surface area of the particles.
4. 4. The emulsion according to claim 1, wherein the particles have an average diameter of less than 10 microns.
5. 5. A method for minimizing the particle size increase over time of an emulsion comprising: I) emulsifying a composition comprising A) a continuous phase comprising water; B) a discontinuous phase comprising at least one alkoxysilane wherein the discontinuous phase forms dispersed particles in the water; and C) an emulsifier system consisting essentially of (i) a main surfactant, wherein the main surfactant is a nonionic emulsifier having an HLB greater than 13, and wherein the Main surfactant is present in the emulsion at a concentration of 0.5 to 3 molecules per 100 square Angstroms of surface area of the particles; and (ii) a co-surfactant, wherein the co-surfactant is a non-ionic emulsifier having an HLB of less than 11, and wherein the co-surfactant is present in the emulsion at a concentration sufficient to provide 1.5 to 15 molecules per 100 square Angstroms of surface area of the particles; II) forming an inner adsorbed layer consisting essentially of the co-surfactant between the discontinuous phase and an outer layer consisting essentially of a combination of the main surfactant and the co-surfactant, wherein the outer layer makes contact with the aqueous phase; and wherein the non-polar alkoxysilane contains an impurity in an amount of 2.50% by weight or less.
6. 6. The method according to claim 5, wherein the concentration of co-surfactant is from 4 to 15 molecules per 100 square Angstroms of surface area of the silane particles, thereby minimizing the increase in particle size of said particles. so that the particles do not increase in size to more than 10% after the emulsion is stored at approximately 25 ° C for at least 14 days.
7. 7. A water-repellent composition for masonry, wherein the composition comprises an aqueous silane emulsion comprising: A) a continuous phase comprising water; B) a discontinuous phase comprising at least one alkylalkoxysilane having a molecular weight of less than 1,000; and where the discontinuous phase forms dispersed particles in the continuous phase; and c) an emulsifier system consisting essentially of: i) a main surfactant, wherein the main surfactant is a nonionic emulsifier having an HLB greater than 13 and wherein the main surfactant is present in the emulsion at a concentration of 0.5 to 3 molecules per 100 square Angstroms of surface area of the particles; and ii) a co-surfactant, wherein the co-surfactant is a non-ionic emulsifier having an HLB less than 11 and wherein the co-surfactant is present in the emulsion at a sufficient concentration to provide 1.5 to 15 molecules per 100 square Angstroms of surface area of the particles; D) a buffer, and wherein the non-polar alkoxysilane contains an impurity in an amount of 2.50 weight percent or less.
8. 8. The emulsion according to claim 7, wherein the alkylalkoxysilane has the general formula RnSiR'4-n, wherein R is an alkyl group of 8 to 20 carbon atoms, R 'is an alkoxy group of 1 to 6 carbon atoms and n is 1 or 2.
9. 9. A method for providing a substrate for water repellent masonry comprising: I) impregnating the masonry substrate with an emulsion, wherein the emulsion comprises: A) a continuous phase comprising water; B) a discontinuous phase comprising at least one alkoxysilane having a molecular weight of less than 1,000; wherein the discontinuous phase represents from 5 to 65% by weight of the emulsion and wherein the discontinuous phase forms dispersed particles in the continuous phase; and C) an emulsifier system consisting essentially of (i) a main surfactant, wherein the main surfactant is a nonionic emulsifier having an HLB greater than 13, and wherein the main surfactant is present in the emulsion at a concentration of 0.5 to 3 molecules per 100 square Angstroms of surface area of the particles; and (ii) a co-surfactant, wherein the co-surfactant is a non-ionic emulsifier having an HLB less than 11, and wherein the co-surfactant is present in the emulsion at a sufficient concentration to provide from 1.5 to 15 molecules per 100 square Angstroms of surface area of the particles; and D) a shock absorber; II) hydrolyzing and condensing the alkoxysilane; and wherein the non-polar alkoxysilane contains an impurity in an amount of 2.50% by weight or less.