Polymethylalkylsiloxane emulsions and methods

Abstract: An emulsion and a mixture including water, at least one surfactant and a polymethylalkylsiloxane. The polymethylalkylsiloxane has the formula: wherein R is a methyl radical, a is an integer from one to about three thousand and b is an integer from one to about ten. Also disclosed is a method of rendering a surface repellent to water by treating the surface with an effective amount of the foregoing emulsion. The surface being treated is an organic surface and can be a rubber surface such as wires, cables, the sidewall of a pneumatic tire, footwear, molded goods and coated fabrics. The surface can also be a vinyl surface such as flooring, shower curtains, rain coats, automotive seat upholstery, residential siding and piping.

Description: This invention relates to a method of using an emulsion of water, at least one surfactant and a polymethylalkylsiloxane for the treatment of organic surfaces such as rubber and vinyl. One of the most important commercial applications of rubber is the pneumatic tire. Because of the increased demand for speed and endurance in modern vehicles, it has become necessary to design rubber compounds and build tires with such factors in mind. Tires must be designed to withstand heavy loads and high speeds for prolonged periods of time, and the body of the tire must be capable of withstanding severe shock and must not exhibit excessive heat build-up. In addition to performance, a tire should also have a clean, shiny, appearance. Heavily soiled tires can detract from the appearance of an otherwise expensive vehicle. Most often, soiled surfaces of tires are caused by rain, dirt, road salt, water and snow. Aqueous emulsions of polydimethysiloxane fluids have been applied as a protective coating to many surfaces including rubber, vinyl, plastics, leather and sealed wood surfaces. Some of these surfaces have also been found to have been rendered anti-static for the purpose of repelling dust and dirt. However, when such emulsions are employed as protective coatings in outdoor applications, such as the sidewall of an automobile tire, the polydimethylsiloxane coatings are rapidly removed and rendered ineffective by water which is encountered while driving in rain or snow. In order to restore the appearance of the soiled tire, another and more often, repeated applications of the polydimethylsiloxane emulsion are required. This, of course, is a disadvantage and a time consuming task. Exemplary of such polydimethylsiloxane emulsion coatings are U.S. Patent No. 3,956,174, issued May 11, 1976 and U.S. Patent No. 4,133,921, issued January 9, 1979. In accordance with the method of the present invention, new and improved protective coatings on surfaces such as rubber are provided and frequent reapplication of the coating is not required. The coatings of the present invention are directed to emulsions containing polymethylalkylsiloxanes, rather than polydimethylsiloxanes as in the prior art. Such coatings have been found to possess superior gloss, luster, shine and repellent characteristics, and soiled surfaces may be merely rinsed clean without requiring frequent reapplication of the coating to a tire sidewall, for example. While polymethylalkylsiloxanes as such are not new as evidenced by U.S. Patent No. 4,640,792, issued February 3, 1987, the application according to the invention of emulsions of such compounds to surfaces such as rubber and vinyl as protective coatings is believed to represent a novel advance in the art. This invention relates to a method of rendering a surface repellent to water comprising treating the surface with an effective amount of an emulsion including water, at least one surfactant and a polymethylalkylsiloxane, the polymethylalkylsiloxane having the formula: wherein R is a methyl radical, a is an integer of from one to three thousand and b is an integer of from one to ten. In the more preferred and alternative embodiments of the invention, the surfactant may be a cationic, nonionic or amphoteric surfactant or a mixture thereof. The emulsion includes an amount of water sufficient to provide a transparent mixture. The emulsion may also contain a polyglycol such as ethylene glycol, propylene glycol, butylene glycol, mixtures and copolymers thereof. Ethylene glycol is the most preferred polyglycol. The polymethylalkylsiloxane has a viscosity in the range of from 0.00002 to 0.05 m²/s (twenty to fifty thousand centistokes) measured at 25°C., preferably 0.0002 to 0.003 m²/s (two hundred to three thousand centistokes); with a viscosity of 0.00035 m²/s (three hundred and fifty centistokes) being the most preferred. The integer b in the above formula for the polymethylalkylsiloxane is five in the most preferred embodiment, in which the polymethylalkylsiloxane is polymethyl n -hexylsiloxane. The surface being treated is generally an organic surface and may be a rubber surface such as wires, cables, the sidewall of a pneumatic tire, footwear, molded goods and coated fabrics. The surface may also be a vinyl surface such as flooring; shower curtains; rain coats; automotive convertible tops, vinyl tops, tonneau covers and seat upholstery; residential siding; and piping. These and other features, objects and advantages, of the herein described present invention will become more apparent from a consideration of the following detailed description thereof. In the examples which follow, it will be seen that the surface treatments produced in accordance with the present invention provide a higher luster and require only a single application of the emulsion to the surface, in comparison to conventionally available surface treatment compositions. In fact, following as many as three applications, other types of protective coatings did not provide comparable luster to the surfaces treated in accordance with this invention. Following exposure to water, snow and road salt, the polymethylalkylsiloxane emulsion coatings of the instant invention were unchanged and the surface to which the coating had been applied was washed free of road salt revealing a clean surface of high gloss. Surfaces treated with the protective coatings of the prior art were depleted by exposure and upon rinsing revealed surfaces which were heavily soiled. The increased efficiency of the protective coating of the present invention can be attributed to the fact that alkylmethylsiloxanes possess a more pronounced attraction to organic surfaces than possessed by polydimethylsiloxane fluids. This is believed due to the presence in the molecule of the alkyl group which has great affinity for surfaces such as rubber and vinyl. Hence, the alkylmethylsiloxanes of this invention provide a more permanent surface treatment characteristic than do prior art treatments, with the result that frequent applications of the surface coating are not required. The alkylmethylsiloxanes are not- chemically bonded to the surfaces to which they have been applied, but such coatings remain on the surface for a more extensive period of time because of the greater affinity of the alkyl groups in the molecule for the organic surface. This is of particular significance in outdoor applications where the surfaces are exposed to weathering conditions. While the alkylmethylsiloxanes of the present invention may be prepared in accordance with conventional procedures for the production of dimethylsiloxane materials, the preferred method involves the hydrosilylation of a hydrogenmethylsiloxane with an alpha olefin. For example, hydrosilylation of 1-hexene can be conducted with Me₃SiO(MeHSiO)₃₅SiMe₃ in the presence of a platinum-carbon catalyst. The product is heated and evacuated to remove excess 1-hexene resulting in the production of a polymethylalkylsiloxane which is poly(n-hexyl)methylsiloxane. Emulsions containing the polymethylalkylsiloxanes of the present invention may be prepared by standard emulsion techniques such as those techniques described in U.S. Patent No. 4,620,878, issued November 4, 1986, which is exemplary. While nonionic surfactants are preferred in accordance with the procedures of the present invention, other types of surfactants, especially the nonionic types detailed in the '878 patent, may be employed herein. Other emulsion techniques and surfactants are described in U.S. Patent No. 4,631,273, issued December 23, 1986. The polymethylalkylsiloxanes used to prepare the emulsions in accordance with the present invention are generally of the formula: wherein R is a methyl radical, a is an integer of from one to three thousand and b is an integer of from one to ten. The alkyl group is intended to comprehend ethyl, propyl, butyl, n -pentyl, isopentyl, n -hexyl, n -heptyl, n -octyl, n -nonyl and n -decyl, for example. As will be seen in the following examples, aqueous emulsions of n -hexylmethylsiloxane were applied to two tires of an automobile and to an exterior vinyl wheel cover of the vehicle. The other two tires of the vehicle received an application of a comparative surface treatment which was a coating of ARMOR ALL PROTECTANT. This comparative ARMOR ALL PROTECTANT is an emulsion similar to the emulsion of the present invention, except that the ARMOR ALL PROTECTANT contains polydimethylsiloxane instead of polymethylalkylsiloxane. It was found that the emulsion of the present invention could be spread on the surface of the tire sidewall with a cloth and did not drain from the sidewall surface in excess as did the comparative composition. A single treatment of the emulsion of the present invention produced a continuous high gloss coating on both the rubber and vinyl surfaces treated, however, following three treatments with the comparative product, the other two tires did not exhibit an equivalent high gloss appearance. This procedure was followed with respect to several vehicles and the vehicles were driven and exposed to water, snow and road salt, for three months. The coatings on the several vehicles were also exposed to strong detergents in automatic car wash facilities on an average of six occasions on each vehicle during this period. The coatings on the several vehicles were inspected during and after each wash. This inspection revealed that the tires coated with the comparative product had lost their shiny appearance and did not repel water after the first strong detergent exposure, but that the tires and the vinyl wheel cover treated with the compositions of the present invention continued to show a lustrous appearance and repelled water even after six strong detergent washes. In addition, the dirt and salt were removed from the tires treated with the compositions of the present invention without any abrasive action. In the following examples, TERGITOL® TMN-6 is a trademark of Union Carbide Corporation, New York, New York, and a nonionic surfactant. TRITON® W-30 is also a nonionic surfactant and a trademark of Rohm and Haas Co., Philadelphia, Pennsylvania. The catalyst employed was a platinum-carbon catalyst. EXAMPLE I To 630 g. of 1-hexene and 5.0 g of 0.5% Pt/C catalyst was slowly added 300 g. of [Me₃SiO(HMeSiO)₃₅SiOMe₃]. The reaction was heated to reflux, however, the reaction became exothermic and further heating was not necessary to maintain a reflux of 1-hexene. The mixture was maintained at reflux for 1 hour to complete the hydrosilylation reaction. The mixture was filtered to remove the catalyst and vacuum stripped with heating using a water aspirator and a heating mantle to remove the excess 1-hexene. The product weighed 700 grams and was a clear colorless fluid of n-hexylmethylsiloxane having a viscosity of 0.00035 m²/s (350 centistokes). EXAMPLE II 82.5 g. of distilled water, 28.5 g. of Tergitol® TMN-6 surfactant and 6.4 g. of Triton® W-30 surfactant were weighed into a 1 liter stainless steel beaker. The mixture was stirred at room temperature for several minutes and 450 g. of poly( n -hexylmethylsiloxane) fluid of Example I was slowly poured into this mixture with stirring. After all of the silicone fluid had been added, stirring was continued for an additional 10 minutes. The mixture was homogenized by using a laboratory homogenizer for one pass at 48.26 mPa (7000 psi). To 330 g. of the resulting emulsion was added with stirring, a solution of 0.6 g. of sodium bicarbonate and 1.1 g. of ethylene glycol in 96 g. of distilled water. The mixture was stirred for several minutes until the emulsion was thoroughly diluted and had a uniform appearance. This diluted emulsion contained approximately 60 percent silicone oil as an oil in water, non-ionic emulsion. EXAMPLE III To a portion of the 60 per cent aqueous n -hexylmethylsiloxane emulsion of Example II was added sufficient distilled water to make an emulsion having 20 percent by weight silicone oil. The diluted emulsion was mixed thoroughly and placed in an empty spray container. This emulsion was spray applied to the left front and right rear tires of a 1982 Dodge Van. ARMOR ALL PROTECTANT was spray applied to the right front and left rear tires of the same vehicle. The standard product did not produce the same shiny surface as the n -hexylmethylsiloxane emulsion and three applications were applied to the right front and left rear tires. Even with three applications, the ARMOR ALL PROTECTANT did not produce a coating with the same luster as the coating produced by a single application of the n -hexylmethylsiloxane emulsion. The n-hexylmethylsiloxane aqueous emulsion was spray applied to the vinyl cover of the spare tire in a single application. The n -hexylmethylsiloxane aqueous emulsion was spray applied to all 4 tires of a 1984 Dodge 600 and 1985 Ford Escort and single applications were made. All vehicles were exposed to rain, snow and salt over a period of one week. At the end of this time, the n -hexylmethylsiloxane coated tires and vinyl cover still retained their luster and were readily washed free of salt and dirt. The ARMOR ALL coated tires lost their original less than lustrous appearance. A water rinse did not remove road deposits from these tires. The 1984 Dodge 600 had color matched enamel painted aluminum wheels. The n -hexylmethylsiloxane emulsion was applied to one of these wheels. The other uncoated wheels showed considerable dirt pickup, while the siloxane-coated wheel retained its luster. One application of the n -hexylmethylsiloxane emulsion was also applied to the black vinyl convertible roof of the 1984 Dodge 600 and to the black vinyl convertible roof of a 1969 E-Type Jaguar. This single application rendered the roofs of these vehicles water repellent and minimized dirt pickup for in excess of 6 months. Another observation concerning both of these treated convertible tops was that when exposed to rain, runoff down the painted side of the vehicle did not leave streaks. This is another indication that hexylmethylsiloxane is strongly substantive to the vinyl surface. EXAMPLE IV Example I was repeated and n -hexylmethylsiloxane fluids with a viscosity of 0.001942 m²/s (1942 centistokes) measured at 0°C. and 0.000744 m²/s (744 centistokes) measured at 20°C., were produced. An n -octylmethylsiloxane with a viscosity of 0.000716 m²/s (716 centistokes) measured at 20°C. was also produced. These fluids were emulsified as in Example II and tested as in Example III and performed similarly to the emulsion tested in Example III. It will be apparent from the foregoing that many other variations and modifications may be made in the compounds, compositions, structures, articles 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.

Claims: A method of rendering a surface repellent to water comprising treating the surface with an effective amount of an emulsion including water, at least one surfactant and a polymethylalkylsiloxane, the polymethylalkylsiloxane having the formula: wherein R is a methyl radical, a is an integer of from one to three thousand and b is an integer of from one to ten. A method according to claim 1, in which the emulsion also includes a polyglycol selected from ethylene glycol, propylene glycol, butylene glycol, mixtures and copolymers thereof. A method according to claim 1 or 2, wherein the surface being treated is a rubber surface selected from wires, cables, the sidewall of a pneumatic tire, footwear, molded goods and coated fabrics. A method according to claim 1 or 2, wherein the surface being treated is a vinyl surface selected from flooring; shower curtains; rain coats; automotive vinyl covered hard tops, convertible tops, tonneau covers and seat upholstery; residential siding and piping.

Inventors: LEGROW GARY EDWARD, LILES DONALD TAYLOR, LEGROW, GARY EDWARD, LILES, DONALD TAYLOR
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1990
Main classification: C08J3
IPC codes: C09D183, C08J7, C08J3