Aqueous Silane Water Repellent Compositions

This invention relates to a water repellent composition which is in the form of an aqueous solution containing a alkyltrialkoxysilane and a water soluble silane coupling agent. The aqueous solution is applied to the surfaces to be treated and the aqueous solution contains a certain predetermined mole ratio of the alkyltrialkoxysilane and water soluble silane coupling agent.

Water resistance is an important factor for many surfaces such as in concrete and masonry construction. This is because moisture movement in concrete causes or contributes to problems such as expansion, shrinkage, cracking, staining, mildew, lowered resistance to freezing and thawing, chemical attack, corrosion of reinforcing steel, and damage to structures from settling. Because of these problems, various techniques have been used to render concrete water resistant. Some of these methods include the surface treatment of concrete structures with water repellents. Water repellents that have been used in the past are oils, waxes, soaps, resins and organosilicon compounds, and they have been applied to the masonry surfaces by brush, roller, air spray, or airless spray techniques. One of the most prevalent category of repellent that has been sued is organosilicon compounds, and such compounds in organic solvents have been found to be useful for brick, concrete, stucco, or terrazo surfaces.

It is not new in the art to employ organosilicon compounds for the treatment of masonry surfaces in order to render such surfaces water repellent. For example, in U.S. Pat. No. 3,772,065, issued Nov. 13, 1973, there is disclosed an impregnant which is an alcohol or hydrocarbon solution of alkyltrialkoxysilanes or oligomers thereof. In U.S. Pat. No. 3,849,357, issued Nov. 19, 1974, a composition is described which is a mixture of a water base paint, and the reaction product of an alkyltrialkoxysilane, and alkylorthosilicate, and water. U.S. Pat. Nos. 3,389,206, issued Apr. 22, 1975, and 4,002,800, issued Jan. 11, 1977, there is disclosed a solution containing an alcohol or hydrocarbon solvent, an alkyltrialkoxysilane, and an additive. The additive is either an organofunctional silane such as aminopropyltriethoxysilane or an alcoholate such as butyl titanate. U.S. Pat. No. 3,914,476, issued Oct. 21, 1975, refers to an aqueous solutions containing an alkali metal organosiliconate, and an aqueous soluble carbonate or bicarbonate. In U.S. Pat. No. 3,955,985, issued May 11, 1976, an aqueous solution is described containing an alkali metal organosiliconate, a miscible alcohol or ketone, and an organic complexing or chelating agent such as nitrilotriacetic acid.

U.S. Pat. No. 3,956,5709, issued May 11, 1976, applies an aqueous solution of an alkali metal propylsiliconate. Surfaces are contacted with water followed by treatment with a mixture of calcium hydroxide and butyltrimethoxysilane in ethyl alcohol in U.S. Pat. No. 4,073,972, issued Feb. 14, 1978. In U.S. Pat. No. 4,076,868, issued Feb. 28, 1978, there is applied a solvent solution thickened with a filler, and containing either (i) a polysiloxane having a viscosity less than 1000 cs, (ii) an alkyltrialkoxysilane, or (iii) an alkali metal hydrocarbon siliconate. U.S. Pat. No. 4,102,703, issued July 25, 1978, forms a stable suspension of hydrophobed metal oxides in ethylene glycol, and applies the suspension to masonry. Hydrophobing is accomplished with either (i) organohalosilanes, (ii) organosilylamines, (iii) cyclic organosilazanes, (iv) organocyclosiloxanes, (v) polyorganosiloxanes, (vi) alkylhydrogen silicone oils, or (vii) hydroxy endblocked polyorganosiloxanes.

In U.S. Pat. No. 4,209,432, issued June 24, 1980, the patentee applies a solvent solution containing a filler such as fume silica, and containing either (i) an organosiloxane having more than ten silicon atoms per molecule, (ii) an alkyltrialkoxysilane, (iii) the reaction product of a silane and ethylene glycol, or (iv) an alkali metal hydrocarbon siliconate. U.S. Pat. No. 4,273,813, issued June 16, 1981, employs a coating of an emulsion of an anionically stabilized hydroxy endblocked polydiorgano-siloxane, amorphous silica, and an organic tin salt. In U.S. Pat. No. 4,342,796, issued Aug. 3, 1982, the patentee dries the surface to be treated applies an alkyltrialkoxysilane to the dried surface, allows the silane to migrate into the surface, and applies water to the treated surface. U.S. Pat. No. 4,352,894, issued Oct. 5, 1982, applies an aqueous solution of an alkylsilanol prepared from propyltrimethoxysilane. A coating of a moisture curable urethane resin and an alkylpolysiloxane or hydroxyalkyl polysiloxane such as 2-ethyl-hexyl polysiloxane, stearyl polysiloxane, or hydroxyethyl polysiloxane, is disclosed in U.S. Pat. No. 4,413,102, issued Nov. 1, 1982. In U.S. Pat. No. 4,433,013, issued Feb. 21, 1984, there is applied an emulsion of an alkytrialkoxysilane including a deactivatable surfactant such as a fatty acid ester or silica ester. After the emulsion is applied, the surfactant is deactivated with water containing an alkaline or acid substance. U.S. Pat. No. 4,478,911, issued Oct. 23, 1984, relates to a coating which includes an alkyltrialkoxysilane, water, an organic solvent, and a catalyst such as an organic amine. In U.S. Pat. No. 4,486,476, issued Dec. 4, 1984, the patentee impregnates with a water immiscible solvent such as naphtha containing a mixture of a methyl-ethoxysiloxane having an ethoxy content of 12 percent and a methyl-ethoxysiloxane having an ethoxy content of 43 percent.

U.S. Pat. No. 4,631,207, issued Dec. 23, 1986, employs a solvent such as a glycol ether containing the reaction product of octamethylcyclotetrasiloxane and N-(2-aminoethyl)-3-aminopropyl dimethoxy-methylsilane. Reexamined U.S. Pat. No. B1 4,648,904, issued Mar. 10, 1987, is direct to an emulsion of an alkyltrialkoxysilane, an emulsifier having a HLB value of 2-20, and water. A solution containing an alkylalkoxy polysiloxane resin is applied to masonry in U.S. Pat. No. 4,717,599, issued Jan. 5, 1988. An oily composition or emulsion is disclosed in U.S. Pat. No. 4,741,773, issued May 3, 1988, containing a mixture of a silicone oil with either a nonvolatile paraffinic oil such as turbine oil or a nonvolatile low molecular weight hydrocarbon resin such as polybutene. In U.S. Pat. No. 4,753,977, issued June 28, 1988, the reacting composition includes an organopolysiloxane resin, an alkylalkoxy polysiloxane resin, and a condensation catalyst. A sealer including a hydroxysubstituted polyorganosiloxane and a mixture containing (i) an aromatic solvent such as toluene, (ii) a chlorinated solvent such as trichloroethane, and (iii) an aliphatic solvent such as heptane, is taught in U.S. Pat. No. 4,786,531, issued Nov. 22, 1981.

In U.S. Pat. No. 4,846,886, issued July 11, 1989, and in U.S. Pat. No. 4,874,431, issued Oct. 17, 1989, the patentees apply a combination of (i) a carrier such as an alcohol, glycol ether, or mineral spirits, (ii) a metal salt catalyst, (iii) an alkylalkoxysilane, and (iv) a beading agent such as a fluorosilicone fluid, a polydimethylsiloxane fluid, a room temperature curable silicone rubber, an amine salt functional siloxane copolymer, or trimethylsilyl endcapped polysilicate. A buffered aqueous silane emulsion is disclosed in U.S. Pat. No. 4,877,654, issued Oct. 31, 1989, and U.S. Pat. No. 4,889,747, issued Dec. 26, 1989, containing a hydrolyzable silane, an emulsifier with an HLB value of 1.5-20, water, and a buffering agent.

Of particular relevance to the present invention are U.S. Pat. Nos. 3,879,206, and 4,002,800, noted above, each of which teach an alkyltrialkoxysilane such as butyltrimethoxysilane in combination with an additive such as aminoethylaminopropyltriethoxysilane. However, the combination is applied in a solvent such as ethanol rather than in the form of an aqueous solution as in the present invention. While U.S. Pat. No. 4,478,911, also noted above, includes an alkyltrialkoxysilane combined with an amine, the amine is an organic amine rather than an aminofunctional silane as in the present invention. Both U.S. Pat. Nos. 4,846,886, and 4,874,431, noted previously, teach an alkylalkoxysilane and a beading agent which can be a material such as an aminofunctional silane of the formula H.sub.2 HCH.sub.2 CH.sub.2 NH(CH.sub.2).sub.3 SI(OMe).sub.3, however, the combination is applied in a carrier other than water such as an alcohol, glycol ether, or mineral spirits, and no aqueous solution is formed as in the present invention.

Thus, there are significant differences between what it taught in accordance with the concept of the present invention and what is disclosed in the prior art as evidenced by the several patents noted and discussed above.

This invention is directed to a composition which is an aqueous solution of a water soluble silane coupling agent and an alkyltrialkoxysilane, wherein the alkyltri-alkoxysilane is selected from the group consisting of alkyltrialkoxysilanes with C.sub.1 to C.sub.6 alkyl groups on silicon and a blend of alkyltrialkoxysilanes each with C.sub.1 to C.sub.6 alkyl groups on silicon.

In the most preferred embodiment of the invention, it has been found that the alkyltrialkoxyrsilane and the silane coupling agent should be present in the aqueous solution in the mole ratio of between about 0.5:1 to about 3.0:1 preferably 1.5:1.0 to about 2.0:1.0, in order to provide stable solutions. Aqueous solutions containing the alkyltrialkoxysilane and the silane coupling agent in mole ratios substantially beyond the range noted above are not entirely satisfactory, and in fact have been found to form gels.

The alkyltrialkoxysilane and the silane coupling agent are also preferably present in the aqueous solution at a level of about two to about forty percent by weight based on the weight of the aqueous solution. More particularly, and preferably the alkyltrialkoxysilane and the silane coupling agent are present in the aqueous solutions at a level of about 2.5-20.0 percent by weight based on the weight of the aqueous solution.

The most preferred of the alkyltrialkoxysilanes are either methyltrimethoxysilane and isobutyltrimethoxy-silane, and blends thereof. In the case of the silane coupling agent, the most preferred category is the aminofunctional silane coupling agent of which N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is a prime example. Other categories of silane coupling agents may be employed, however, such as quaternary ammonium functional silane coupling agents and other water soluble silane coupling agents.

The invention is further directed to a method of treating a surface in order to render the surface water repellent by applying to the surface to be treated an aqueous solutions of a silane coupling agent and a alkyltrialkoxysilane as defined previously.

The invention is also directed to a method of producing on a substrate a water shedding surface coating by applying to the substrate a composition in the form of an aqueous solution for producing on the surface of the substrate a durable water shedding surface coating.

It is therefore an object of the present invention to chemically fix a water-repelling agent to a substrate such as wood, concrete, limestone, and natural stone, in order to improve its resistance to the absorption of water, as well as to impart to the surface thereof the ability to shed surface water.

It is a further object of the present invention to increase the density of a silicone matrix within a substrate such as wood, concrete, limestone, and stone, in order to render the substrate water resistant, and at the same time provide it with the property of shedding surface waters.

It is also an object of the present invention to provide a penetrating water repellent composition for substrates such as wood, concrete and limestone as well as other non-reactive masonry surfaces in which the repellent not only renders the substrate resistant to water penetration but in addition hinders the ingress of water at the surface.

These and other objects, features, and advantages of the herein described invention will become more apparent from a consideration of the following detailed description thereof.

Water repellents including alkylalkoxysilanes impart water repellent properties to such porous substrates as wood, concrete, mortar, and stone. Such repellents function in this fashion because of the fact that they penetrate into the masonry for example prior to the time that they are transformed into immobile resinous materials. However, due to the penetration of the repellent into the porous substrate, the repellent does not leave behind much of a layer on the porous substrate. As a result the repellent, though effective to render the substrate water resistant, fails nevertheless to provide the substrate with coatings of any significant durability. The compositions disclosed herein are intended to overcome this deficiency and there can be achieved a good degree of water shedding function of a wood or masonry structure because of deposition on the surface, in addition to the penetration of the repellent formulation to provide a deep section water barrier to water migration within the substrate itself.

The penetrating water repellents of the present invention have particular application to the highway industry where water resistance is required for bridge decks, roads, and parking garages. In addition, such compositions are applicable especially to the building industry which makes use of materials for walls such as natural stones, which are porous and contain neutral mineral components including, for example, limestone, marble, and granite. These heretofore difficult to treat building materials can be effectively rendered water resistant with the compositions of the present invention. While the highway industry applications of the formulations will be primarily concrete, the building industry applications of the formulations can range from wood, brick, natural stone, as noted above, cinder block, and stucco.

Generally, concrete, brick, and stucco, may be treated with a alkylalkoxysilane rendering the substrate water resistant. The latent alkalinity of such substrates promotes the hydrolysis and condensation of the silane into a resinous silicone matrix being permanently formed and deposited within the interior of the concrete, brick, or stucco substrate. Natural stone, such as limestone, is an exception in that it is relatively neutral and possesses no latent catalytic activity. As a consequence, the silane will not convert to a silicone as rapidly, nor will it affix itself to the calcareous interior surfaces of the substrate. The result is that there is provided very little or no water repellency or resistance to water absorption. This lack of reactivity of limestone is particularly noticeable when limestone aggregate is employed as a constituent in the preparation of concrete. In such instance, water readily penetrates along the interfacial boundaries between the concrete and the course limestone aggregate. Since the silane-based repellent does not adhere to the limestone, those portions of the concrete adjacent the aggregate are not rendered water resistant whereas the remainder of the concrete substrate is treated successfully. The water takes the path of least resistance in to the mass of concrete, therefore, migrating along the side or through the aggregate of limestone particles. It is for these types of situations that the compositions of the present invention are particularly useful along with their capacity to shed water at the surface of the substrate.

The water repellent compositions of the present invention including their capability of water shedding have wide application including for example wood and concrete articles such as precast products, blocks, brick, pipe, prestressed products, structural concrete, and highway surfacing; floor and wall tiles, roofing tile, and structural tiles; Portland cement concrete containing coarse limestone aggregate as footings, poured foundations, paving, steps, curbs; structural products; molded, reinforced and prestressed concrete products such as blocks, bricks, pipes, panels, and beams; exterior and interior plaster; stucco; and terrazo.

A major advantage of the repellent compositions of the present invention is that the compositions are capable of being formulated into an aqueous solution which complies with various state and federal regulations regarding volatile organic content (VOC). These regulations generally prohibit a volatile organic content for an architectural coating which is in excess of about four hundred grams per liter. Prior art solvent base alkoxysilanes liberate alcohol which is a volatile organic compound.

Accordingly, a penetrant can be formulated with the compositions of the present invention which complies with the volatile organic content regulations. Thus, a penetrant in accordance with the present invention will have a volatile organic content generally less than about four hundred grams per liter. In contrast, the equivalent penetrants of the prior art which contain alkoxysilanes such as isobutyltrimethoxysilane have volatile organic contents of the order of magnitude of about 650-700 grams per liter.

Conventional silane coupling agents are well known in the art for bonding resins to fillers and substrates. Typically as part of the process of producing composite materials, reinforcing fillers are treated with silane coupling agents before being introduced into the uncured resin. The silane coupling agents form a coating on the filler, and the coating interacts with the resin, either chemically or through the formation of interpenetrating polymer networks, to form a strong cohesive bond between the resin and filler. A significant benefit of silane coupling agents is the added hydrolytic stability they provide composite materials.

Various conventional highly water soluble silane coupling agents can be used in the present invention. Generally silane coupling agents are of the formula

where A is a monovalent organic radical, Y is a hydrolyzable radical, and n is 1, 2, or 3 (most preferably 3). A can be various types of organic radical including alkyl or aryl radicals. Y radicals hydrolyze in the presence of water and include acetoxy radicals, alkoxy radicals with 1 to 6 carbon atoms, and alkylalkoxy radicals with 2 to 8 carbon atoms.

Specific silane coupling agents within the scope of the present invention include N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(aminoethylaminomethyl)phenyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltris(2-ethylhexoxy)-silane, 3-aminopropyltrimethoxysilane, trimethoxysilyl-propyldiethylenetriamine, bis(2-hydroxyethyl)-3-aminopropyltrimethoxysilane, 2-methacryloxyethyldimethyl-[3-trimethoxysilylpropyl] ammonium chloride, methyltrimethoxysilane, ethyltrimethoxy-silane, propyltrimethoxysilane, and isobutyltrimethoxy-silane.

In particular, the most preferred silane coupling agents include N-(2-aminoethyl)-3-aminopropyltrimethoxy-silane, 3-aminopropyltrimethoxysilane, and the quaternary ammonium functional silanes. The most preferred silane coupling agents are commercially available. The other silane coupling agents are available commercially, or their preparation is known in the art.

The following examples illustrate the concepts of the present invention.

Into a container was placed two moles of methyltrimethoxysilane, one mole of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 2.4 moles of water. The contents of the container were mixed and stripped to sixty degrees Centigrade under an aspirator. Ten percent by weight aqueous silane solutions were prepared from the residue.

Into a container was placed a mixture containing isopropyltrimethoxysilane, methyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, in a mole ratio of 1.5:1.5:2.0. The contents of the container and four moles of water were mixed and stripped to sixty degrees Centigrade under an aspirator. Ten percent by weight aqueous silane solutions were prepared from the residue cohydrolyzate oligomer.

The aqueous silane solution in Examples I and II were tested for water repellency. Test pieces of concrete, red brick, gypsum board, and gypsum plaster, were soaked in the ten percent aqueous silane solutions of Examples I and II for thirty minutes and air dried for two to three days to obtain a constant weight. The test pieces were soaked in water at room temperature for one hour, and were weighed in order to determine any increase in weight. The test pieces were air dried for one day and again weighed in order to determine the recovery of the test pieces to the dry state. The results of these tests are set forth in Table I. A tap water control was employed.

Various additional aqueous silane solutions were prepared in accordance with the procedures of Examples I and II and were tested for water exclusion employing limestone, sandstone, cement block, and concrete block, test pieces. The test solutions contained twenty weight percent of active ingredient. The test pieces were soaked in the twenty percent aqueous silane solution for thirty seconds and air dried for twenty-four hours. The tests pieces were immersed in water in the case of the limestone and sandstone test pieces, and in a fifteen percent salt solution in the case of the cement and concrete block test pieces. The time of immersion varied from twenty-four hours to twenty-one days. The results of these tests are shown in Table II at representative immersions times of six, twelve, and eighteen days, respectively. THOMPSON'S WATER SEAL is included in Table II for comparison purposes. In Table II, the solutions are in a mole ratio of 1:1 unless otherwise indicated. IPTMS denotes isopropyltrimethoxysilane. MTMS denotes methyltrimethoxysilane. AFS indicates the aminofunctional silane coupling agent N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. IBTMS indicates isobutyltrimethoxysilane.

The silane coupling agents employed in accordance with the present invention should be highly water soluble silane coupling agents or hydrolyzed aqueous solutions thereof, as noted hereinbefore, and exemplary of such materials are: ##STR1##

The following example illustrates a method of preparing treatment solutions in accordance with the present invention containing one such silane coupling agent.

To a 3:1 mole mixture of CH.sub.3 Si(OCH.sub.3).sub.3 and ##STR2## as a fifty percent solution in methanol, was added 3.2 moles of water. After one day, the partial cohydrolyzate was found to be completely soluble in water. Excess methanol was stripped from the product to obtain an oily residue that was also completely soluble in water. The residue generated less than four-hundred parts of methanol by hydrolysis of the methoxy groups per one thousand parts of product. It was found that films deposited from water were water repellent when dried.

The term substrate as used herein is intended to encompass concrete and masonry products and surfaces, textiles, paper and paperboard, leather products, and cellulosic materials. Some exemplary leather products are garments, shoes, and boots. Textiles include awnings, tents, tarpaulins, rainwear, covers, slickers, canvas, asbestos, fiberglass, natural fibers, peat moss, natural and synthetic yarns, woven and non-woven materials, carpets, and carpet fibers. Cellulosic materials contemplated herein for treatment may include wood, wood products, fiberboard, cedar, redwood, firs, plywood, and structural timbers. Concrete and masonry substrates which may be treated vary and are intended to include any product or surface of heavy and light-weight concrete, gypsum, concrete blocks, cinder blocks, soft mud bricks, sand lime bricks, drain tiles, ceramic tiles, sandstone, plaster, clay bricks, natural stones and rocks, roofing tiles, calcium silicate bricks, asbestos cement, slag stones and bricks, stucco, limestone, macadam, marble, mortar, terrazzo, clinker, pumice, terra cotta, porcelain, adobe, coral, dolomite, and asphalt. Non-cementitious substrates may also be treated in accordance with the present invention including perlite, cellular glass, vermiculite, mica, and diatomaceous earth.

Treatment of substrates at various concentrations including lower levels of about 2.5 percent by weight of the aqueous silane solutions of the present invention are set forth below.

Aqueous silane test solutions indicated in Table II as IBTMS/MTMS/AFS were prepared at concentration levels of twenty, ten, five, and 2.5 weight percent. These solutions were evaluated on two by two inch cement blocks. The blocks were treated with the test solutions by immersion in the treatment solution for ten seconds followed by curing for forty-eight hours. The cubes were weighed and immersed upside down in one-quarter inch of water for seventy-two hours. The percent water absorbed was calculated based on the weight of the dry treated cube. Percent water absorbed was computed as being (B/A -1) times 100 where A is the weight of the treated cube before immersion and B is the weight of the treated cube after immersion. The results are shown in Table III which includes a tap water control and a comparison with THOMPSON'S WATER SEAL.

Aqueous silane test solutions indicated in Table II as IBTMS/MTMS/AFS were prepared at concentration levels of twenty, five, and 2.5 weight percent. These solutions were evaluated on two by four by twelve inch straight grained knot-free kiln dried pine sapwood test boards. The test solution was brushed on each board and excess solution allowed to drain. The treated boards were air dried for seven days at fifty percent relative humidity and at room temperature. The boards were weighed. The dried weighed boards were allowed to float in tap water for fifteen minutes on each side. This floating procedure was repeated a second time. Excess water was drained from the boards and the boards were weighed. Percent water repellent effectiveness (WRE) was calculated as [(A-B)-(C-D)]/100(A-B), where A is the weight of the untreated board after water contact in grams, B is the weight of the untreated board before water contact in grams, C is the weight of the treated board after water contact in grams, and D is the weight of the treated board before water contact in grams. The results are shown in Table IV which includes a comparison with THOMPSON'S WATER SEAL.

It will be apparent from the foregoing that many other variations and modifications may be made in the compounds, compositions, structures, and methods described herein, without departing substantially from the essential features and concepts of the present invention. Accordingly, it should be clearly understood that the forms of the invention described herein are exemplary only and are not intended as limitations on the scope of the present invention as defined in the appended claims.