Water repellent surface treatment

Abstract: The purpose of the invention is to provide a durable, non-wetting surface on a metal, polymeric or inorganic coated substrate. The construction of the invention is a metal, polymeric or inorganic coated substrate, the surface of which is treated with a perfluoroalkyl alkyl silane and a fluorinated olefin telomer. The remarkable effects of the invention are high water repellancy and high lubricity provided by the perfluoroalkylsilane, which bonds to the substrate surface, and the fluorinated olefin telomer, respectively. The invention encompasses both an article with a surface treated in accordance with the invention, and a method of producing such an article.

Description: The present invention relates generally to the art of surface treatment and, more particularly, to the art of producing a water repellent surface on various polymer substrates. THE PRIOR ART US-A-4,263,371 to Franz teaches a method for reducing the surface energy of a glass article by chemisorption of an organotin compound at a temperature insufficient to thermally decompose the compound. Such compounds as methyltin chloride are shown to increase the contact angle of a drop of water on the surface from 10° for untreated glass to 45 to 90° for various compounds. US-A-4,276,350 to Franz discloses a method for reducing the reactivity of a glass surface by blocking reactive sites such as silanol groups at the glass surface with a molecular layer of fluorocarbon. The method involves absorbing multivalent cations at the glass surface to provide anchoring sites for the chemisorption of otherwise nonreactive fluorocarbons. US-A-4,301,197 to Franz et al. discloses the formation of highly efficient release surfaces on glass substrates by treatment of the glass with poly alkyl hydrogen siloxane. The treated glass surface effectively releases such materials as polycarbonates, acrylics, and polyurethanes contacted in press polishing or laminating processes. US-A-4,529,657 to Franz discloses reducing the surface energy of glass by absorbing multivalent cations such as chromium onto a glass surface, then treating the surface with an aqueous solution of an alkali metal alkylate such as sodium stearate or oleate to bond the long chain paraffinic or olefinic acid anion to the glass surface by ionic bonding of the alkylate anion to the absorbed multivalent cation, thereby rendering the glass surface non-wettable and lubricated. It is the object of the invention to provide durable non-wetting surfaces on polymer substrates. This object is attained by an article comprising a substrate at least a portion of the surface of which is treated with a composition comprising: a. a perfluoroalkyl alkyl silane; and b. a fluorinated olefin telomer, wherein the substrate is a polymer. The solution also includes a method of producing a non-wetting surface on a substrate comprising contacting a surface with a composition comprising a perfluoroalkyl alkyl silane and a fluorinated olefin telomer wherein said substrate is a polymer. Useful substrates are polymers such as cured epoxy resins, polycarbonates, (meth)acrylic polymers and crosslinked polyurethanes. Durable water and dirt repellancy of a substrate surface are provided by applying to the substrate surface a select combination of fluorinated compounds. High water repellancy is provided by perfluoroalkylsilanes which bond to the substrate surface, while high lubricity is provided by addition of fluorinated olefin telomers. DESCRIPTION OF THE PREFERRED EMBODIMENT A perfluoroalkyl alkyl silane is combined with a fluorinated olefin telomer to produce the compositions of the present invention. The silane/olefin composition is preferably employed as a solution, preferably in a fluorinated solvent. The solution of the present invention is applied to a substrate surface by any conventional technique such as dipping, flowing, wiping or spraying. The solvent is evaporated and the composition forms a durable, non-wetting, lubricating surface. Preferred perfluoroalkyl alkyl silanes have the general formula R n R'SiX 4-n , wherein R is a perfluoroalkyl radical, n is preferably 1, R' is an alkyl, preferably ethyl, vinyl or propyl, and X is preferably a radical such as alkyl, halogen, and/or alkoxy. Preferred perfluoroalkyl radicals range from CF₃ to C₃₀F₆₁, preferably C₆ to C₁₆, and most preferably C₈ to C₁₀. R' is preferably ethyl. Preferred radicals for X include chloro, iodo, methyl, methoxy, ethoxy and acetoxy radicals. Preferred perfluoroalkyl ethyl silanes in accordance with the present invention include perfluoroalkyl ethyl-trichlorosilane, perfluoroalkyl ethyl-trimethoxysilane, perfluoroalkyl ethyl-dichloro(methyl)silane and perfluoroalkyl ethyl-diethoxy(methyl)silane. These perfluoroalkyl ethyl silanes appear to react with bonding sites at the substrate surface on a molecular basis. There does not appear to be polymerization or crosslinking. Strong surface bonding of the perfluoroalkyl ethyl silanes produces a substrate surface which exhibits a high contact angle with a drop of water, indicating high water repellancy. The fluorinated olefin telomer, which does not on its own bond to the substrate surface, but which is bonded in combination with the perfluoroalkyl silane, provides lubricity to promote dirt repellancy. The olefin structure provides for crosslinking to produce a durable surface. Preferred olefin telomers have the general formula C m F 2m+1 CH=CH₂ wherein m may range from 1 to 30. The more preferred olefin telomers are a mixture of compounds of the above formula wherein m ranges from 1 to 16, preferably 4 to 10. Suitable solvents include isopropanol, ethanol, hexane, heptane, acetone, toluene and naphtha. Preferred solvents are fluorinated hydrocarbon solvents such as trichlorotrifluoroethane, and methylene chloride, and perfluorinated organic compounds such as perfluorocarbons. Concentrations of about 0.005 to 5, preferably about 0.05 to 2.5, percent of each component are preferred. The solvent is preferably evaporated simply by drying in air at ambient temperature. The composition may be cured by heating the treated surface. A cure cycle of about 200° F. (about 93° C.) for about 30 minutes is suitable. Higher temperatures and shorter heating times may be more efficient. A cure cycle of 2 to 5 minutes at 400 to 500° F. (about 204 to 260° C.) may be preferred, particularly about 3 minutes at about 470° F. (about 243° C.). The contact angles recited herein are measured by the sessile drop method using a modified captive bubble indicator manufactured by Lord Manufacturing, Inc., equipped with Gartner Scientific Goneometer optics. The surface to be measured is placed in a horizontal position, facing upward, in front of a point source light such as a slide projector lamp. A drop of water is placed on top of the surface in front of the light source so that the contours of the sessile drop can be viewed and the contact angle measured through a goneometer telescope equipped with circular protractor graduation. The present invention will be further understood from the descriptions of specific examples which follow. Examples I to III A solution is prepared comprising 2.5 grams of perfluoroalkyl ethyl trichlorosilane and 2.5 grams of fluorinated olefin telomer in 95 grams of Freon TF solvent, available from DuPont. The perfluoroalkyl ethyl trichlorosilane composition comprises a range of perfluoroalkyl radicals CF₃(CF₂) n wherein the average n = 9.0 and the approximate distribution is C₆ = 6 percent, C₈ = 50 percent, C₁₀ = 29 percent, C₁₂ = 11 percent and C₁₄+ = 4 percent. The fluorinated olefin telomer has a similar distribution with C₄ = 4 percent, C₆ = 35 percent, C₈ = 30 percent, C₁₀ = 17 percent, C₁₂ = 8 percent and C₁₄+ = 6 percent. This solution is Treatment A. The above Treatment A solution is applied to the surfaces of steel panels coated with three polymer topcoats used as automotive parts finishes. Another set of polymer coated steel panels is treated with a solution similar to Treatment A except that half of the olefin is replaced with perfluoroiodide CF₃(CF₂) n I wherein n is from about 4 to 14, mostly 6 to 10 in a similar distribution as the silane and olefin. This is Treatment B. The contact angles are compared in the following table. Example Polymer Contact Angle (°) Untreated Treatment A Treatment B I epoxy 75 92 112 II melamine crosslinked polyurethane 73 96 105 III acrylic melamine 74 82 110 The above examples are offered to illustrate the present invention. Various perfluoroalkyl silanes, fluorinated olefin telomers, solvents and concentrations may be applied by any conventional technique, and cured at suitable temperatures for adequate times to provide durable non-wetting surfaces to any of a variety of polymer substrates. The treated substrates of the present invention is especially suitable in automobile and aircraft parts as well as in building components.

Claims: An article comprising a substrate at least a portion of the surface of which is treated with a composition comprising: a. a perfluoroalkyl alkyl silane; and b. a fluorinated olefin telomer, wherein the substrate is a polymer. An article according to Claim 1, wherein said perfluoroalkyl alkyl silane is selected from compounds having the general formula R n R'SiX 4-n , wherein R is a perfluoroalkyl radical, R' is an alkyl radical, n is less than 4, and X is a radical selected from the group consisting of alkyl, halogen, alkoxy and acetoxy radicals. An article according to claim 2, wherein said perfluoroalkyl radical is selected from the group consisting of CF₃ to C₃₀F₆₁. An article according to claim 3, wherein said perfluoroalkyl radical is selected from the group consisting of C₆ to C₁₆. An article according to claim 4, wherein said perfluoroalkyl radical is selected from the group consisting of C₈ to C₁₀. An article according to claim 2, wherein R' is selected from the group consisting of ethyl, vinyl and propyl. An article according to claim 3, wherein X is selected from the group consisting of chloro, iodo, methyl, methoxy, ethoxy and acetoxy. An article according to claim 4, wherein said perfluoroalkyl alkyl silane is selected from the group consisting of perfluoroalkyl ethyl-trichlorosilane, perfluoroalkyl ethyl-trimethoxysilane, perfluoroalkyl ethyl dichloro(ethyl)silane and perfluoroalkyl ethyl-diethoxy(methyl)silane, wherein said fluorinated olefin telomer is selected from the group consisting of C m F 2m+1 CH=CH₂, wherein m is from 1 to 30. An article according to Claim 8, wherein m is from 1 to 16. An article according to Claim 9, wherein m is from 4 to 10. A method of producing a non-wetting surface on a substrate comprising contacting a surface with a composition comprising a perfluoroalkyl alkyl silane and a fluorinated olefin telomer wherein said substrate is a polymer. A method according to claim 11, wherein said perfluoroalkyl alkyl silane is selected from compounds having the general formula R n R'SiX 4-n wherein R is a perfluoroalkyl radical, R' is an alkyl radical, n is less than 4, and X is a radical selected from the group consisting of alkyl, halogen, alkoxy and acetoxy radicals. A method according to claim 12, wherein said perfluoroalkyl radical is selected from the group consisting of CF₃ to C₃₀F₆₁. A method according to claim 13, wherein said perfluoroalkyl radical is selected from the group consisting of C₆ to C₁₆. A method according to claim 14, wherein said perfluoroalkyl radical is selected from the group consisting of C₈ to C₁₀. A method according to claim 12, wherein R' is selected from the group consisting of ethyl, vinyl and propyl. A method according to claim 12, wherein X is selected from the group consisting of chloro, iodo, methyl, methoxy, ethoxy and acetoxy. A method according to claim 17, wherein said perfluoroalkyl alkyl silane is selected from the group consisting of perfluoroalkyl ethyl-trichlorosilane, perfluoroalkyl ethyl-trimethoxysilane, perfluoroalkyl ethyl-dichloro(methyl)silane and perfluoroalkyl ethyl-diethoxy(methyl)silane, wherein said fluorinated olefin telomer is selected from the group consisting of C m F 2m+1 CH=CH₂, wherein m is from 1 to 30. A method according to claim 18, wherein m is from 1 to 16. A method according to claim 19, wherein m is from 4 to 10.

Inventors: FRANZ HELMUT, FRANZ, HELMUT
Applicants: PPG INDUSTRIES INC, PPG INDUSTRIES, INC.
Application year: 1991
Main classification: C09K3
IPC codes: C09D183, C09D5, C03C17, C08J7, C09D127, C09K3