GB2056473A - Silicone Emulsion and Method of Preparation Thereof - Google Patents

Abstract

A high solids content silicon emulsion comprises an anionically stabilized, hydroxyl-endblocked polydiorganosiloxane, amorphous silica, an alkyl tin salt, and optionally an organic amine and additional fillers, and has a solids content of 55 percent by weight or greater and a pH of greater than 9. Drying the emulsion under ambient conditions produces a cured elastomeric product with useful physical properties which make it particularly suitable as a coating for surfaces to be buried in the earth or as non-slumping caulking compounds for building joints. The emulsion can be prepared by emulsifying a diorganosiloxane using an anionic surfactant, adding amorphous silica to the hydroxyl- endblocked polydiorganosiloxane emulsion, adding an alkyl tin salt, and optionally an organic amine and additional fillers. The resulting emulsion yields a cured elastomeric product upon drying without the addition of cross-linking agents.

Description

SPECIFICATION Silicone Emulsions and Method of Preparation Thereof This invention relates to a silicone emulsion and to a method for its preparation.

Emulsions of organopolysiloxanes have been known for many years as described by Hyde etna!. in U.S. Patent No. 2,891,920 issued in 1959. Hyde et a!. considered one of the problems in the organosilicon field was the lack of a good method for preparing stable emulsions of extremely high molecular weight siloxanes having a molecular weight at least high enough to make suitable protective coatings. Although Hyde et al. described a concept for preparing on a commercial scale emulsion of siloxane suitable for protective coating, there are few products available today in the field of emulsions of siloxanes for protective coatings.The primary contribution of Hyde et al. appears to have been a method of polymerizing siloxanes in the emulsified state with strong mineral acids or strong alkaline catalysts which are characterized by their ability to rearrange siloxane bonds. Hyde etna!. state that the emulsion polymerization can be carried out with cationic, nonionic or anionic type dispersing agents, and that it is best to use anionic emulsifying agents for acid catalysts, cationic emulsifying agents for alkaline catalysts, and nonionic emulsifying agents can be used for either acid or alkaline catalysts.

The emulsions prepared by Hyde etna!. are described as extremely stable in that they can stand for years without separation, and can also be centrifuged or diluted without separation. Hyde et a!. also teach that the emulsion can be changed from one type of surfactant system to another after or during polymerization, such as from cationic to anionic or nonionic or vice versa, that anionic systems provide better surface wetting. Hyde etna!. describe their emulsions as useful for release agents and coating compositions. The emulsions are also described as particularly adaptable for the preparation of latex paints, for example, they can be mixed with pigments or other fillers and applied to a surface where the water will evaporate leaving a continuous coating.Although Hyde etna!. teach stability and continuous coating information, they do not teach that stable emulsions can be obtained when additional materials are added such as the pigments and that continuous coatings can be obtained after storage or what the properties of such coatings will be.

Findlay et a!. in U.S. Patent No. 3,294,725 described a method for polymerizing organosiloxanes in emulsion using a surface active sulphonic acid catalyst. Findlay et al. describe this method as a method for preparing stable organopolysiloxane latex emulsions. According to Findlay et a/., the resulting emulsion can be neutralized to a pH near 7 with an alkaline material unless it is desired to remove the polysiioxane from the emulsion. Findlay eft at teach that alkali metal salts of the surface active sulphonic catalyst are useful when additional emulsifying agent is desired, particularly where silica fillers are to be used.The emulsions described by Findlay et a!. are taught as having the same stability expressed by Hyde etna!. and also as having the same utility. Findlay et a/., however, teach that the emulsions either with or without the added filler are quite stable, and for maximum stability of the emulsion, it is desirable to neutralize the acid catalyst in the emulsion with a base to a pH of approximately 7. The neutralization of the acid catalysts can be done either prior to or after the addition of filler. Such systems are taught by Findlay et al. as providing an excellent method of obtaining coatings of tough rubbery siloxane films for release coatings.Findlay eft at describe tough rubbery films obtained from colloidal silica and neutralized emulsions made from polymerized hydroxylated dimethylpolysiloxane reacted with a trialkoxysilane such as methyltrimethoxysilane before emulsification. Findlay et al. do not show the use of fillers with emulsions other than those prepared in this manner with a trialkoxysilane. In one example, Findlay eft awl added a colloidal silica sol which had a pH of 8.5.

Although Find lay etna!. made stable emulsions of organosiloxanes, they apparently did not provide a silicone latex which would be stable on storage and from which a curable polymer could be deposited and which cured to give a tough elastomer because Cekada in U.S. Patent No. 3,355,406 stated that there was still a need in the silicone industry for such a silicone latex. Cekada describes his latexes as useful for many applications including various coating applications. The silicone latexes described in Cekeda are prepared from a colloidal suspension of a curable essentially linear siloxane polymer in water using a suitable dispersing agent. A silsesquioxane in the form of a colloidal suspension, preferably neutral, is added to the polymer in the colloidal state. Cross-linking agents and curing catalysts can be added.Those silicone latexes, according to Cekada, which contain no curing catalyst can be cured by exposing the deposited coating to a suitable radiation source. Cekada teaches that the curing catalysts can be mineral acids, strong bases, dialkyltin diacylates and organic and inorganic peroxides. The cross-linking agents taught by Cekada include alkoxysilanes and methylhydrogenpolysiloxanes. Although Cekada alleges a silicone latex which is stable on storage and from which a curable polymer can be deposited and cured to a tough elastomer, he offered no storage properties for his compositions. Cekada shows neutral latexes, except for one example in which the latex was acidic. In the present invention, a neutral emulsion is not stable on storage and does not cure to an elastomer after storage.

A caulk prepared from cationic emulsions of siloxane block copolymers is described by Butler et al. in U.S. Patent No. 3,817,894. Butler ear as teach that six ingredients are required to prepare the caulk and that the emulsion of the siloxane block polymer is neutralized to a pH of 7 for use in the caulk and that the caulk contain from 20 to 30 parts by weight of cationic surfactant per 300 to 600 parts by weight siloxane copolymer.

It is known in the silicone art that siloxane bonds rearrange in the presence of alkaline materials, particularly alkali metal hydroxides. Such siloxane bond rearrangement can be very useful in the silicone manufacturing for the polymerization of polydiorganosiloxanes from cyclic polydiorganosiloxanes under carefully controlled conditions. However, it is also known that polydiorganosiloxanes under basic conditions in the presence of water can be converted to very low molecular weight species, including monomeric species. It was therefore unexpected that a stable emulsion could be prepared at high pH, stored and still produce an elastomeric coating or film after storage. Under conditions of a pH greater than 9, it would be expected that depolymerization would occur and result in water soluble species which would not give an elastomeric product when the water was removed.As taught by the prior art cited above, the storage stable emulsions are obtained when the emulsion or latex is adjusted to a pH near 7. As taught by the prior art cited above, the curable compositions contain a filler and a tri-functional material to act as a cross-linking site.

A silicone emulsion having a pH of greater than 9 and a solids content of at least 55 percent by weight comprising an anionically stabilized hydroxyl end-blocked polydiorganosiloxane, amorphous silica, an alkyltin salt and optionally an organic amine, produces an elastomeric product when the water is removed under ambient conditions. These emulsions can be prepared as thixotropic coating materials particularly useful as water-proof coatings for surfaces to be buried in the earth or as nonslumping caulking compounds for sealing joints. The emulsions can also contain a thickener, an antifoam, and other fillers. The emulsions can be prepared by emulsifying a hydroxyl endblocked polydiorganosiloxane at high solids content using an anionic surfactant, adding amorphous silica and alkyl tin salt, and adjusting the pH to greater than 9.

This invention relates to an aqueous emulsion suitable to provide an elastomeric product upon removal of the water under ambienttonditions comprising: (A) 100 parts by weight of an anionically stabilized, hydroxyl-endblocked polydiorganosiloxane, present as an oii-in-water emulsion; (B) from 1 to 1 50 parts by weight of amorphous silica; (C) from 0.1 to 1.5 parts by weight of an alkyl tin salt; and (D) from 0 to 200 parts by weight of a filler other than amorphous silica; the silicone emulsion having a pH of greater than 9 and a solids content of at least 55 percent by weight.

The combination of the anionically stabilized, hydroxyl-endblocked polydiorganosiloxane emulsion and the amorphous silica in an emulsion with a pH of greater than 9 can produce a cured elastomeric film upon removal of the water under ambient conditions without the presence of a monoorganotrifunctional silane or siloxane as has been previously used. The alkyl tin salt also present in the composition of this invention imparts practical manufacturing procedures and storage stability to the composition.

The silicone emulsions of this invention can vary in consistency from thixotropic, paint type materials to non-slumping, paste type, caulk materials. The emulsions provide a cured elastomeric film merely by evaporation of the water under ambient conditions.

The high solids content required in the silicone emulsion yields a product which dries without forming voids or cracks as can sometimes be found with products which do not have a high volatile content. The cured elastomeric film possesses a strength and modulus of elasticity such that the cured film is not broken if the substrate is cracked after the film is applied and dried.

The hydroxyl-endblocked polydiorganosiloxanes useful for this invention are those which can be emulsified and which impart elastomeric properties to the product obtained after removal of the water from the emulsion. Such hydroxyl-endblocked polydiorganosiloxanes should have a weight average molecular weight (Mw) of at least 5,000 since hydroxyl-endblocked polydiorganosiloxanes with low Mw do not provide strong elastomeric products. Tensile strengths and elongations at break improve with increasing molecular weight, with reasonable tensile strengths and elongations being obtained above 30,000 Mw and the best tensile strengths and elongations being obtained above 50,000 Mw.

The maximum weight average molecular weight is one which can be emulsified and which will give elastomeric properties to the product obtained after the water is removed from the emulsion. Weight average molecular weights up to about 1,000,000 for the hydroxy-endblocked polydiorganosiloxane are expected to be practical for this invention. The preferred Mw for the hydroxyl-endblocked polydiorganosiloxanes are in the range of 200,000 to 700,000.

The organic radicals of the hydroxyl-endblocked polydiorganosiloxane can be monovalent hydrocarbon radicals containing less than seven carbon atoms per radical and 2-(perfluoroalkyl)ethyl radicals containing less than seven carbon atoms per radical. Examples of monovalent hydrocarbon radicals are methyl, ethyl, propyl, butyl, isopropyl, pentyl, hexyl, vinyl, cyclohexyl and phenyl and examples of 2-(perfluoroalkyl) ethyl radicals are 3,3,3-trifluoropropyl and 2-(perfluorobutyl)ethyl. The preferred hydroxyl-endblocked polydiorganosiloxanes contain organic radicals of which at least 50 percent are methyl.The hydroxyl-endblocked poiydiorganosiloxanes are essentially linear polymers containing two organic groups per silicon atom but may include trace amounts of nonorgano- and/or triorganosiloxy- groups present as impurities of the manufacturing process. The preferred hydroxylendblocked polydiorganosiloxanes are the hydroxyl-endblocked polydimethylsiloxanes.

The most preferred hydroxyl-endblocked polydiorganosiloxanes are those prepared by the method of anionic emulsion polymerization described by Findlay ear as in U.S. Patent No. 3,294,725 which shows the methods of polymerization and the hydroxyl-endblocked polydiorganosiloxane in emulsion.

Another method of preparing hydroxyl endblocked polydiorganosiloxane is described by Hyde et a!. in U.S. Patent No. 2,891,920 which shows the hydroxyl-endblocked polydiorganosiloxanes and their method of preparation. These methods and others are known in the art. The hydroxyl endblocked polydiorganosiloxanes of this invention are those which are anionically stabilized. For the purpose of this invention "anionically stabilized" means that the hydroxyl-endblocked polydiorganosiloxane is stabilized in emulsion with an anionic surfactant. The emulsion is in the form of an oil-in-water emulsion.

Anionic surfactants are preferably the salt of the surface active sulphonic acids used in the emulsion polymerization to form the hydroxyl-endblocked poiydiorganosiloxane as shown in U.S.

Patent 3,294,725 cited above which shows the surface active sulphonic acids and salts thereof. The alkali metal salts of the sulphonic acids are preferred, particularly the sodium salts. The sulphonic acid can be illustrated by aliphatically-subsituted benzenesulphonic acids, aliphatically substituted naphthalene sulphonic acids, aliphatic sulphonic acids, silylalkylsulphonic acids and aliphaticallysubstituted diphenylethersulphonic acids.

One of the advantages of the present invention is the relatively small amount of surfactant or emulsifying agent needed to maintain a stable emulsion. The amount of anionic emulsifying agent can be less than 2 weight percent of the emulsion, wherein this amount can result from the neutralized sulphonic acid wherein the suiphonic acid is used in the emulsion polymerization method for the preparation of the hydroxyl endblocked polydiorganosiloxane.Other anionic emulsifying agents can be used, for example, alkali metal sulphoricinoleates, sulphonated glyceryl esters of fatty acids, salts of sulphonated monovalent alcohol esters, amides of amino sulphonic acid such as the sodium salt of oleyl methyl tauride, sulphonated aromatic hydrocarbon alkali salts such as sodium alpha-naphthalene monosulphonate, condensation products of naphthalene sulphonic acids with formaldehyde, and sulphates such as ammonium lauryl sulphate, triethanol amine lauryl sulphate and sodium lauryl ether sulphate.

Although not specifically required in the present invention, one can optionally include nonionic emulsifying agents in addition to the anionic emulsifying agents. Examples of such nonionic emulsifying agents are saponins, condensation products of fatty acids with ethylene oxide such as dodecyl ether of tetraethylene oxide, condensation products of ethylene oxide and sorbitan trioleate, condensation products of phenolic compounds having side chains with ethylene oxide such as condensation products of ethylene oxide with isododecylphenol, and imine derivatives such as polymerized ethylene imine.

Amorphous silica is a required ingredient in this invention. The silicone emulsion does not yield a cured film upon drying unless amorphous silica is present in the composition. Any of the finely divided amorphous silicas that are capable of being dispersed in the silicone emulsion can be used. The common forms of amorphous silica are colloidal silicas available as colloidal silica dispersions in water and as dry powders of fume silica or precipitated silica and the mined amorphous silicas that are known commercially as diatomaceous earth. It is believed that any amorphous silica in a sufficiently finely divided form is useful in this invention.

One of the embodiments of this invention is a thixotropic paint-type emulsion that has shown usefulness as a coating for waterproofing walls which will be buried underground. A colloidal silica available as a dispersion in water has been shown to be particularly useful in this embodiment. These commercially available colloidal silica dispersions are usually used in a stabilized form, being stabilized with sodium ion, ammonia, or aluminium ion. Aqueous colloidal silica dispersions that have been stabilized with sodium ion are particularly useful for this embodiment of this invention because the pH requirement of this invention can be added by using such a sodium ion stabilized colloidal silica to bring the pH above 9. Colloidal silicas as used herein are those silicas which have particle diameters of from 0.0001 to 0.1 micrometres.Preferably, the particle diameters of the colloidal silicas are from 0.001 to 0.05 micrometres.

Another embodiment of this invention yields a silicone emulsion in the form of an extrudable, non-slump paste. The preferred amorphous silicas for this embodiment are the dry powders, either of the fume, precipitated, or mined varieties. The fume silica is preferred for this embodiment as it produces the desirable thickening effect when added to the polydiorganosiloxane emulsion used. The commercial products are commonly pyrogenic silica produced by the vapour phase pyrolysis of silicon tetrachloride. The fume silica most useful in this invention has a BET specific surface area of greater than 50 m2/g, preferably from 1 50 to 200 m2/g. When this type of fume silica is used as the amorphous silica of the present invention, the emulsion is of a high viscosity so that the emulsion has a thick, paste-like character.When extruded from a storage tube onto a surface, the emulsion adheres without flowing, even when the surface is vertical. This embodiment of the invention is particularly desirable in that it does not tend to "string out" when used as a caulk in a building and is subsequently tooled in a joint as do conventional solvent-based or 100% solids silicone caulks. The precipitated silicas or mined silicas can also be used in this embodiment.

The silicone emulsion of this invention has a continuous aqueous phase in which there are dispersed phases which comprise an anionically stabilized hydroxyl endblocked polydiorganosiloxane and amorphous silica, with an alkyl tin salt also present. For this silicone emulsion to maintain a storage stability and also be curable to an elastomer after the emulsion is stored, the pH of the silicone emulsion must be above 9. The silicone emulsions of this invention which have the best storage stability and still form elastomers at ambient conditions at any point during the storage stable period are those which have a pH in the range of from 10.5 to 11.5.

The silicone emulsions which contain in the dispersed phases the hydroxyl-endblocked polydiorganosiloxane amorphous silica, and alkyl tin salt and have a pH of greater than 9 do not require additional ingredients to obtain an elastomeric product after the water is removed at ambient conditions. However, certain additional ingredients have been found useful in providing certain advantageous characteristics to the silicone emulsion and the elastomeric products obtained therefrom. For example, a thickener can be added to improve the handling characteristics of the silicone emulsion such as thixotropy and structural viscosity.The thickener is useful for increasing the working viscosity of the silicone emulsion to provide a material which can be used to coat a substrate with a film of elastomeric product Such silicone emulsions with thickener permit the application of thicker coats which form thicker elastomeric films. The use of a thickener also permits a broader versatility of the silicone emulsion by allowing one to select the proper and most convenient emulsion consistency for the specific application. Suitable thickeners are available commercially and would be selected for their stability and usability, at pH of 9 and greater Some of the useful thickeners include the classes of cellulose derivatives, alkali salts of polyacrylates and polymethylacrylates, sodium and ammonium salts of carboxylate copolymers and colloidal clays.These and other thickeners can be used but it is advised that a particular thickener be tried on a small scale to determine if it does not adversely effect the storage stability of the emulsion, the formation of the elastomeric product or the resulting properties of this elastomeric product. For the silicone emulsions of this invention, the best thickeners are the sodium salts of polyacryiates.

Another useful ingredient for addition of the silicone emulsions of this invention is a filler other than amorphous silica. Such fillers can be added to provide pigmentation which can be used for example as a colorant as in a paint or an ultraviolet light screening agent. Other fillers can be used as extending fillers which can be used to reduce the cost per unit of the elastomeric product or to make the silicone emulsion useful as a caulking material. Fillers other than amorphous silica permit the emulsion to be manufactured with a high solids content without causing too high a viscosity in the emulsion or without causing too high a modulus in the cured elastomer. The high solids content of the emulsion yields materials which can be dried as thick films or caulks and which do not develop voids or cracks during the drying process.Examples of some fillers other than amorphous silica include carbon blacks, titanium dioxide, clays, aluminium oxide, quartz, calcium carbonate, zinc oxide, mica and various colorant pigments. Titanium dioxide has been found to be particularly useful as an ultraviolet light screening agent. These fillers other than amorphous silica should be finely divided and it may be advantageous to use aqueous dispersion of such fillers if they are commercially obtainable such as aqueous dispersion of carbon black. However, the silicone emulsions of the present invention do not require that these fillers be added in the form of aqueous dispersions. The silicone emulsion readiiy accepts the finely divided fillers in a dry form.

The silicone emulsion of this invention requires a solids content by weight of 55 percent and greater.

For the purposes of this invention the solids content is defined as the non-volatile content of an emulsion. The non-volatile content is determined by placing 2 g of emulsion in an aluminium weighing dish of 50 mm diameter and heating in an air circulating oven for 1 hour at 1 500C. After cooling, the dish is reweighed and the percentage of the original 2 g remaining is determined. This percentage remaining is the percent solids present in the original emulsion.

When the emulsion of this invention is dried, shrinkage takes place. In order to maintain a continuous coating on a substrate, it is necessary to maintain the shrinkage below an amount that causes the coating to rupture during the drying step. The higher the solids content of the emulsion, the less likely the shrinkage will cause rupture to occur. The preferred solids content is in the range from 65 percent to 75 percent by weight.

There are also factors to consider concerning the ratio of hydroxyl-endblocked polydiorganosiloxane to amorphous silica to extending filler. The curing mechanism of the instant invention requires that from 1 to 150 parts by weight of amorphous silica be present per 100 parts by weight of the hydroxyl-endblocked polydiorganosiloxane. The useful upper limit for the amount of amorphous silica will normally be determined by the modulus of the cured elastomer produced when the emulsion is dried. Increasing the amorphous silica content increases the modulus of the resulting elastomer. The modulus is also effected by the physical form of the amorphous silica. The more surface area or the finer the particles, the less required to give a particular level of modulus.

Filler other than amorphous silica is used to raise the total solids content of the emulsion while effecting the modulus to a much lesser degree than the amorphous silica. The amount of these extending fillers used depends upon the type of extending filler chosen, the degree of fineness of the particles, and the properties desired in the final cured elastomer. The optimum amount can easily be determined by simple experimentation. The extending fillers are generally considered to have particle diameters in the range of about 1 to 30 micrometres or surface areas of less than 50 m2/g.

The ratio of hydroxyl-endblocked polydiorganosiloxane to reinforcing amorphous silica to extending filler also effects the modulus. As the amount of filler is raised in relation to the amount of siloxane polymer the modulus raises. At too high a filler loading, the cured product will not be sufficiently elastomeric to function properly.

The dispersed phases required hydroxyl-endblocked polydiorganosiloxane and amorphous silica.

In view of the required pH range of the silicone emulsion, the hydroxyl endblocked polydiorganosiloxane may not contain exclusively silicon-bonded hydroxyi radicals. Some of the hydrogen atoms of the silicon-bonded hydroxyl radicals may be replaced with an alkali metal ion, such as sodium ion; may be complexed with an amine, or may be associated with an emulsifying agent.

Thus, the term "hydroxyl-endblocked polydiorganosiloxane" as used herein covers all the species of terminating groups which may be formed by emulsifying a hydroxyl-endblocked polydiorganosiloxane at a pH of greater than 9.

A preferred method of preparing the silicone emulsions is to emulsify a hydroxyl-endblocked polydiorganosiloxane using an anionic surfactant, add the amorphous silica and then to adjust the pH within the range of 10.5 to 1 1.5 inclusive. A preferred method for emulsifying a hydroxy-endblocked polydiorganosiloxane is to prepare this siloxane polymer by emulsion polymerization as described in U.S. Patent No. 3,294,725, starting with polydiorganocyclosiloxanes. This emulsion polymerization uses an anionic polymerization catalyst and thus the resulting hydroxyl end-blocked polydiorganosiloxane contains an anionic surfactant and it is ready to be used to make the silicone emulsions of this invention. There are other methods of emulsifying a hydroxyl-endblocked polydiorganosiloxane using an anionic surfactant, such as described in U.S. Patent No. 2,891,920.

Although these other methods can be used to emulsify a hydroxyl-endblocked polydiorganosiloxane to provide an anionically stabilized siloxane polymer, they are less convenient inasmuch as additional steps are involved, as well as additional ingredients. The concentration of the hydroxyl-endblocked polydiorganosiloxane in the anionically stabilized emulsion is not critical, however, for convenience, one should use a concentration which is in line with the concentration of the dispersed phase desired in the final silicone emulsion. A minimum useful solids content for the emulsion of the hydroxyiendblocked polydiorganosiloxane is about 40 percent by weight. Emulsions containing 60% by weight polymer have been shown to be useful.

The amorphous silica can be added to the anionically stabilized hydroxyl-endblocked polydiorganosiloxane in the form of a dry powder or as an aqueous dispersion. The best method to add colloidal silica is in the form of a sodium ion-stabilized aqueous dispersion of colloidal silica. There are many such sodium ion-stabilized aqueous dispersions of colloidal silica which are commercially available. These commercial colloidal silicas are usually available in aqueous dispersion having from 1 5 to 50 weight percent colloidal silica and having a pH in the range of 8.5 to 10.5. A preferred method to add fume silica is by simply stirring it into the hydroxyl enblocked polydiorganosiloxane emulsion.

When making a caulk-type material, where the fume silica is most useful, amounts of about 1 to 25 parts by weight of fume silica per 100 parts by weight of polymer can be added without any additional surfactant. Additional filler other than silica is then added to raise the total solids content. As much as 1 50 parts by weight of silica can be used.

After the amorphous silica is added, the pH is adjusted to greater than 9. Silicone emulsions, as described herein, are not storage-stable or do not form an elastomeric product over the entire storage period if the pH is adjusted below 9. The resulting silicone emulsion does not provide a useful elastomeric product when the water is allowed to evaporate at ambient conditions immediately after the emulsion is prepared. However, if this silicone emulsion is stored at room temperature, an elastomeric product can be obtained by removal of the water at room temperature after extended storage periods, such as five months. Such a phenomenon is not understood, but these stored silicone emulsions do provide very desirable elastomeric products. It is commercially undesirable to store the emulsions for such long periods.It has been found that the addition of an alkyl tin salt, preferably a dialkyltindicarboxylate, can be used to reduce the storage time between the preparation of the silicone emulsion and the time an elastomeric product can be obtained from the silicone emulsion by removal of the water under ambient conditions to an acceptable range of one to three days. Such storage times are well within the time required to package and distribute a commercial product. Dialkyltin salts can be used in amounts of from 0.1 to 1.5 parts by weight for each 100 parts by weight of the hydroxylendblocked polydiorganosiloxane, preferably about 0.1 to 1.0 parts by weight for each 100 parts by weight of hydroxyl-endblocked polydiorganosiloxane. Dialkyltincarboxylates, including dibutyltindiacetate, dibutyltindilaurate and dioctyltindilaurate are preferred.The preferred dialkyitindicarboxylate is dioctyltindilaurate. Dibutyltindibromide has also'been found to operable.

The pH of the silicone emulsion prepared as described herein can be adjusted within the defined range by any of a number of methods, such as with a basic compound or an ion exchange means, such as an ion exchange resin. The best methods have been found to be with a basic compound, such as an organic amine, an alkali metal hydroxide or a combination thereof. The organic amines can be primary, secondary or tertiary amines which contain carbon, hydrogen and nitrogen, and can also contain oxygen, and which are water soluble in the amounts required. These organic amines include diethylamine, ethylenediamine, butylamine, hexylamine, morpholine, monoethanolamine, triethylamine and triethanolamine. The preferred organic amine for maximum storage stability is diethylamine.The alkali metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide and cesium hydroxide. The preferred alkali metal hydroxide is sodium hydroxide. The organic amines can be added neat or in aqueous solution. The alkali metal hydroxides are preferably added as an aqueous solution. A combination of diethylamine and sodium hydroxide have been found to be particularly suitable to provide long term storage stability for these silicon emulsions, maintaining the useful elastomeric forming ability, and maintaining useful elastomeric properties in the product obtained after removal of the water at ambient conditions.

The useful upper pH level is determined by practical considerations. The higher the pH, the more corrosive the silicone emulsion becomes so there should not be an excess of basic compound added.

When the pH is above 12 amorphous silica present tends to be dissolved. The system tends to change in pH with time, adjusting to a range of from 10.5 to 1 1.5.

With the proper selection of anionically-stabilized, hydroxyl endblocked polydiorganosiloxane and amorphous silica, the mixing of these two ingredients can automatically adjust the pH within the required range and an additional step of adjusting the pH is not needed. Thus, the mixing of the siloxane and amorphous silica can encompass the step of adjusting the pH. The selection of a hydroxylendblocked polydiorganosiloxane which has a pH of at least 9 and an aqueous dispersion of a colloidal silica which has a pH of at least 9 can provide a silicone emulsion within the scope of this invention without further necessity of adjusting the pH by adding additional ingredients. An aqueous dispersion of a colloidal silica which is sodium ion-stabilized is preferably used as the colloidal silica with a pH above 9.It is not necessary that both the siloxane and colloidal silica have a pH above 9, but the resulting combination would be required to have a pH greater than 9, if not, adjusting the pH would be required as stated above. To obtain the preferred pH range of 10.5 to 1 1.5, it will usually require adjusting the pH after the siloxane polymer and colloidal silica are mixed. For the purpose of this invention, the term "pH" means the electrical potential measured on commercially available glass electrodes designed for this purpose when the glass electrode is immersed in the emulsion. The electrical potential is read from a scale on a commercial instrument in terms of the negative log10 of hydrogen ion activity. The electrode is calibrated with a standard buffer solution which gives a pH of 10.

In the method of preparing the silicone emulsion as described above, frothing can be encountered. It is therefore advantageous to add an antifoaming agent (an antifoam) to control such frothing. A preferred class of antifoams are those based on silicones which are commercially available.

The embodiments of the silicone emulsions as defined above for forming thixotropic emulsions are particularly suitable for coating walls which will be buried underground to render them waterproof.

The thixotropic nature of the coating and the high solids content makes it possible to apply relatively thick coatings, for example of about 1.5 mm thickness, to vertical surfaces in a single coating. The combination of a thick coating and a low modulus coating makes the cured film particularly useful for such application. The coating is elastomeric, forms at temperatures as low as 40C, does not evolve organic solvents which can be irritating to the applicator as well as environmentally unsuitable, and is tough enough to perform in the application. If the substrate, such as a brick or concrete block wall, develops cracks, such as from settling or temperature changes, the coating will bridge the cracks without rupturing, thus preserving a waterproof barrier on the wall.

The embodiments of the silicone emulsions as defined above for forming paste-type compounds are particularly suitable for sealing joints and cracks in building. These materials are elastomeric, form at temperatures as low as 40C, do not evolve organic solvents, and are tough enough to perform in the application. Since the system is a complete system, it can be packaged in a container, ready for use.

When extruded into a joint, it does not flow out of vertical joints. When tooled, the emulsion does not string out as is common with 100% solid type silicone caulks. The cured caulk can have a modulus low enough to allow joint movement without failure of either caulk adhesion to the substrate or of the caulk itself, thus preserving a sealed joint.

Some additional advantages of these silicone emulsions are that relatively small amounts of emulsifying agents are required to maintain stability and as a result the elastomeric product is not loaded with large amount of unreacted ingredients such as the emulsifying agent which can evolve from the elastomeric product, such as blooming, or reduce the strength of the elastomeric product. The elastomeric product forms without curing catalysts or the application of heat or radiation. It was unexpected that a silicone emulsion could produce under ambient conditions an elastomeric product with strong elastic properties from a medium which has such a high pH and still be storage-stable over periods of up to one year or more. Practical silicone emulsions of this invention would be storage stable for at least six months at ambient temperatures.

These silicone emulsions can form elastomeric products by removal of the water under ambient conditions. When the silicone emulsion is spread out to form a coating, the water evaporates to leave a cured silicone elastomer. Silicone emulsion coatings can skin over in about 1 5 minutes becoming tackfree in about one hour and obtaining substantial physical properties in one day and maximum properties in a few days. The curing characteristics can take place in shorter time periods depending upon the film thickness and method of application. It is also expected that heating the silicone emulsions can produce the elastomeric products. It should be understood that this invention is not limited to removal by evaporation of water, other methods of coagulation may be useful.

The following Examples further illustrate the invention.

Example 1 A silicone emulsion was prepared by adding 8.5 parts of an aqueous sodium stabilize colloidal silica having about 20 weight percent SiO2 and a pH at 250C of about 9, to 1 67 parts by weight of an aqueous emulsion (hereinafter referred to as Polymer Emulsion A) having a pH of about 3 and containing about 60 percent by weight of an emulsion polymerized hydroxyl-endblocked polydimethylsiloxane having a weight average molecular weight of about 325,000. Polymer Emulsion A was prepared from 100 parts by weight of linear hydroxyl-endblocked polydimethylsiloxane, 62.5 parts by weight of water, 3.8 parts by weight of sodium laurylsulphate surfactant, and 0.8 part by weight of dodecylbenzenesulphonic acid. Before adding the colloidal silica, Polymer Emulsion A was made basic by adding 2 parts by weight of diethylamine.The remainder of the ingredients were then stirred in, consisting of 0.5 part of an antifoam of 35% solids polydimethylsiloxane/silica mixture: 0.2 part by weight of a tin emulsion containing 50 weight percent dioctyltindilaurate, 9 weight percent of a sodium alkylarylpolyether sulphonate and 41 weight percent water (hereinafter referred to as Tin Emulsion A); 2.5 parts by weight of a carbon black pigment; 0.25 part of propylene glycol; and 75 parts by weight of kaolin clay.

The final emulsion had about 70 percent by weight solids, a viscosity of 0.13 Pa.s (pascal.seconds) as determined by Brookfield viscometer using a No. 3 spindle at 2 rpm, and a pH of 11.3.

Films were prepared from the emulsion by spreading the emulsion over a flat surface and allowing the water to evaporate at room temperature. The dried films had average properties of 0.93 MPa (Mega Pascal) tensile strength, 755 percent elongation at break and a 100 percent tensile modulus of 0.38 MPa.

Example 2 Silicone emulsions were prepared using talc as the extending filler.

a.) An emulsion was prepared by mixing 167 parts by weight of Polymer Emulsion A, 17 parts by weight of the colloidal silica of Example 1,2 parts of diethylamine, 0.5 part of antifoam, 0.25 part of Tin Emulsion A, 2.5 parts of carbon black pigment and 75 parts of talc having particles below 12 micrometres in size with 50 percent by weight being below 1.4 micrometres.

b.) The emulsion of a.) was repeated except the talc used had particles below 30 micrometres with 50 percent by weight below 27 micrometres.

The emulsion had the physical properties shown in Table 1. Films prepared as in Example 1 had the properties shown in Table 1.

Table 1 Emulsion a b Solids, percent 69 69 Viscosity, Pa.s 1.4 2.7 Tensile Strength, MPa 1.1 1.3 Elongation, percent 470 347 Example 3 Silicone emulsions were prepared using different extending fillers.

c.) An emulsion was prepared by mixing 166.5 parts by weight of Polymer Emulsion A, 4 parts by weight of a 50 percent aqueous mixture of diethylamine, 1 part by weight of Tin Emulsion A, 12 parts of a fume silica having a surface area of about 160 m2/g, 80 parts of a finely ground calcined alumina and 3 parts of finely ground titanium dioxide. The emulsion was about 75 weight percent solids.

A film dried to a tack-free surface in about 60 minutes.

d.) A similar emulsion was mixed using 5 parts of the fume silica, 5 parts of the titanium dioxide, and substituting kaolin clay for the calcined alumina. There was also added 0.25 part of monoethanol amine. The emulsion was about 73.6 percent by weight solids.

A film dried to a tack-free surface in 30 minutes.

Films of each emulsion prepared as in Example 1 had the physical properties shown in Table II.

Table II Emulsion c c d Durometer, Shore A 26 30 Tensile Strength, MPa 1.84 1.58 Elongation, Percent 710 650 Tear Strength, kN/m 9.6 9.6 [kN/m=kilonewton per metre.] Example 4 Emulsions were prepared using different levels of the organic tin compound.

Emulsions were prepared by mixing 166.5 parts by weight of Polymer Emulsion A, 4 parts of a 50 percent by weight aqueous diethylamine mixture, 6 parts by weight of the fume silica of Example 3, 80 parts of kaolin clay, 0.25 part of monoethanol amine and x part of Tin Emulsion A. The clay was mixed clay that had been washed and sized to average particle diameters from 0.2 to 20 micrometres.

Samples of each emulsion as shown in Table Ill were stored for the periods shown at room temperature and were then formed into films. After cure of the films for 7 days at room temperature the elongation at break was measured. The amount of Tin Emulsion A and the results are shown in Table Ill.

Additional samples of each emulsion w.ere stored at 500C for the purpose of providing accelerated storage properties. For the purpose of this test, one week at 500C was considered to be equivalent to about 6 months at room temperature and the 2 weeks at 500C was considered to be equivalent to one year. It should be understood, however, that actual room temperature storage properties of the silicone emulsions may be different than those suggested by the 500C accelerated storage test.

Table III Parts rxJ of Tin Emulsion A Storage Time . 0.25 0.5 0.1 1 week at 230C 400 600 600 4weeksat230C 450 450 525 6weeksat230C 400 500 450 2weeksat500C 500 600 350 Example 5 A silicone emulsion was prepared by mixing together 33 parts by weight of a sodium stabilized colloidal silica dispersion containing about 1 5 percent by weight colloidal silica, 1 part of morpholine, 1 67 parts by weight of Polymer Emulsion A, 1 part by weight of Tin Emulsion A, 100 parts by weight of finely divided calcium carbonate, 1 part by weight of antifoam, 6 parts by weight of an acrylic thickener of 60 percent by weight solids, 0.9 parts by weight of a 50 percent by weight sodium hydroxide solution, and 2.5 parts by weight of a black pigment. The completed silicone emulsion had a pH of 11.47, a viscosity of 1 54 Pa.s measured on a Brookfield viscometer using a No. 4 spindle at 2 rpm, a solids content of 67 percent by weight, and a very thixotropic nature. A heavy coating of 1 mm thickness could be applied to a vertical wall without slumping. A film of emulsion, laid out and dried, produced a tensile strength of 2.24 MPa, an elongation of 450 percent, and a tear of 4.2 kN/m.

Example 6 This Example shows the need for evaluating a particular formulation for a particular application.

A silicone emulsion was prepared as described in Example 5, except that only 20 parts by weight of a calcium carbonate were used in place of the 100 parts of Example 5. The amount of thickener was increased to 7 parts by weight, the amount of sodium hydroxide solution was 1.8 parts by weight and an antifoam was used.

This silicone emulsion had a solids content of 56 percent by weight, the pH was 11.5, the viscosity was 1 52 Pa.s with a thixotropic nature. A dried film prepared from the emulsion had a tensile strength of 0.88 MPa, an elongation of 693 percent, a tear strength of 2.6 kN/m and a peal strength when pulled at 1800 from a concrete surface of 3.1 5 kN/m.

The emulsion lost viscosity after 6 to 8 weeks so that it could not have been used after that time to prepare a thick coating on a vertical wall without slumping.

Example 7 A higher solids content sodium-stabilized colloidal silica was used in this Example.

A silicone emulsion was prepared by mixing together 30 parts of a sodium-stabilized coiloidal silica dispersion containing about 50 percent by weight colloidal silica, 1 part of diethylamine, 20 parts by weight of calcium carbonate, 1 67 parts by weight of Polymer Emulsion A, 0.3 part of antifoam, 1 part of Tin Emulsion A, 5 parts of thickener and 2 parts of black pigment. The completed silicone emulsion had a viscosity of 107 Pa.s with a thixotropic nature. The viscosity remained stable on storage. A dried film had a tensile strength of 0.90 MPa, an elongation of 950 percent, and a tear strength of 5.25 kN/m.

Example 8 A series of samples was prepared using as the amorphous silica a fume silica recovered as a byproduct from an aluminum production. The fumed amorphous silica used had a median particle size of 0.4 micrometres with less than 4 percent of the particles being less than 0.1 micron and about 60 percent being less than 0.5 micrometres. The silica had an average surface area of about 21 m2/g. This filler acted as both a reinforcing silica and an extending filler.

A silicone emulsion was prepared by mixing 1 67 parts by weight of Polymer Emulsion A, 4 parts of a 50 percent by weight dispersion of diethylamine in water, x parts of the fumed amorphous silica described above, 0.3 part of antifoam, 1 parts of Tin Emulsion A, y parts of thickener and 2 parts of black pigment. The emulsions were difficult to prepare as the silica did not easily incorporate into the emulsions. The values of x and y in parts by weight, the emulsion properties, and the properties of dried films obtained therefrom are shown in Table IV. All the emulsions were thixotropic and storage stable.

The emulsions made films at high thicknesses (3 mm) without cracking on drying.

Example 9 A silicone emulsion was prepared using a mined amorphous silica. This silica is a natural mined product that has been cleaned and graded for particle size. It typically has a specific gravity of 2.65, a pH of 7, and an average specific surface area of about 1.5 m2/g.

A silicone emulsion was prepared by mixing 167 parts by weight of Polymer Emulsion A, 4 parts by weight of a 50 percent by weight dispersion of diethylamine in water, 100 parts by weight of the silica described above, 0.5 part of antifoam, 1 part of Tin Emulsion A, and 2 parts of acrylic thickener.

The emulsion was very thixotropic with a viscosity of 11 3 Pa.s, and a pH of 11.28 at a solids content of 73 percent by weight. The emulsion could be dried in thick films (1.5 micrometres) with no cracking.

The dried films had a tensile strength of 0.96 MPa and an elongation of 330 percent.

Example 10 A series of silicone emulsions was prepared using different extending fillers to produce emulsions useful as caulking compounds.

The proportions of ingredients used were as shown in Table V. The fumed silica had a surface area in the range of 1 50 to 175 m2/g. The sodium hydroxide used to adjust the pH was a 30 percent solution of sodium hydroxide in water. The thicknener was a 30 percent solution of an acrylic-type thickener in water. In each case the emulsions were prepared by simple mixing of the ingredients. All of these emulsions were of a consistency such that they could be extruded from storage tubes in the form of a bead which would not flow on a vertical surface. All of these emulsions cured on drying at ambient temperatures to yield a cured elastomeric material suitable for use as a caulking compound.

Example 11 A silicone emulsion was prepared without using an amine in the composition.

A composition was prepared using the materials and proportions shown in Example 10, composition 9, except the diethylamine was not added and calcined alumina was used in place of ground quartz.

The finished emulsion was of a consistency that could be extruded from a storage tube in the form of a bead which would not flow on a vertical surface. The emulsion cured on drying at ambient temperature to yield a strong elastomer suitable for use as a caulking compound.

Table IV Solids Viscosity x y % Pa.s pH 25 4 65.6 165 - 50 5 69.5 98 - 100 3 74.8 129 11.1 125 0.5 76.6 140 10.9 Tensile Strength Elongation MPa 0.59 900 0.65 800 1.03 900 1.03 850 Table Composition 1 2 3 4 5 6 7 8 9 10 11 Polymer Emulsion A 167 167 167 167 167 167 167 167 167 167 167 Diethylamine 2 2 2 2 2 2 2 2 1 2 2 Tin Emulsion 2 2 2 2 1 2 1 1 1 1 1 Fumed Silica 15 10 15 12.5 12 10 15 15 12.5 5 30% NaOH 1.5 Thickener 1 Titanium Dioxide 50 3 Calcined Alumina 55 100 175 80 Calcium Carbonate 55 125 150 Ground Silica 100 Diatomaceous Earth 165 Kaolin Clay 75

Claims (14)

Claims

1. An aqueous silicone emulsion capable of providing an elastomeric product upon removal of the water under ambient conditions, the emulsion comprising.

(A) 100 parts by weight of an anionica!ly stabilized, hydroxyl-endblocked polydiorganosiloxane, present as an oil-in-water emulsion; (B) from 1 to 1 50 parts by weight of amorphous silica; and (C) from 0.1 to 1.5 parts by weight of an alkyl tin salt; the silicone emulsion having a pH of greater than 9 and a solids content of 55 percent by weight and greater.

2. An aqueous silicone emulsion according to claim 1, which also comprises; (D) up to 200 parts by weight of a filler other than amorphous silica.

3. An aqueous silicone emulsion according to claim 1 or 2 which also comprises more than 1 part by weight of an organic amine composed of carbon, hydrogen, and nitrogen atoms or carbon, hydrogen, nitrogen and oxygen atoms, the amine being soluble in the amount of water present in the emulsion.

4. An aqueous silicone emulsion according to any of claims 1 to 3, wherein (A) has a solids content of greater than 40 percent by weight, (B) is from 1 to 100 parts by weight, and (C) is from 0.1 to 1.0 part by weight.

5. An aqueous silicone emulsion according to any of claims 2 to 4, which comprises from 25 to 100 parts by weight of component (D).

6. An aqueous silicone emulsion according to any of claims 1 to 5, wherein the alkyl tin salt is a dialkyl tin salt.

7. An aqueous silicone emulsion according to any of claims 1 to 6 wherein the amine is diethylamine, monoethanolamine or morpholine.

8. A method of preparing an aqueous silicone emulsion capable of providing an elastomeric product upon removal of the water under ambient conditions, the method comprising: (I) emulsifying a diorganosiloxane using an anionic surfactant and a sufficient amount of water to provide an emulsion of greater than 40 weight percent solids to yield a hydroxyl-endblocked poiydiorganosiloxane containing emulsion, (li) adding to the emulsion from 1 to 150 parts by weight of amorphous silica, and frdm 0.1 to

1.5 parts of an alkyl tin salt, and (III) controlling the pH of the resulting emulsion to a value greater than 9, the amount of water in (I) being controlled such that the solids content of the final silicone emulsion is at least 55 percent by weight.

9. A method according to claim 8, wherein up to 200 parts by weight of a filler other than amorphous silica are introduced into the emulsion.

10. A method according to claim 8 or 9, wherein up to 3 parts by weight of an organic amine composed of carbon, hydrogen and nitrogen atoms or carbon, hydrogen, nitrogen and oxygen atoms, the amine being soluble in the amount of water present in the emulsion, are introduced into the emulsion.

11. A method according to any of claims 8 to 1 0, wherein in step (I) the emulsion of a hydroxyl endblocked polydiorganosiloxane is prepared by anionic emulsion polymerization of a siloxane selected from polydiorganosiloxane having a viscosity no greater than 0.2 Pa.s at 250C, and mixtures thereof.

12. A method according to any of claims 10 to 12, wherein the pH is controlled in step (II) by the addition of an alkali metal hydroxide.

13. A method according to any of claims 8 to 12 wherein the amorphous silica has an average particle diameter of 0.0001 toO.1 micrometres.

14. A method according to any of claims 8 to 13, wherein the alkyl tin salt is a dialkyl tin carboxylate.

1 5. A method according to any of claims 10 to 14 wherein the pH is controlled in step (III) by the addition of the organic amine.

1 6. An aqueous silicone emulsion substantially as herein described with reference to any of the specific Examples.

1 7. A method of preparing an aqueous silicone emulsion substantially as herein described with reference to any of the specific Examples.

1 8. An aqueous silicone emulsion when prepared by a method according to any of claims 8 to 1 5 and 17.

1 9. A silicone elastomer product obtained by removal of the water from an aqueous silicone emulsion according to any of claims 1 to 7, 16 and 18.