SURFACE TREATMENT REPELLENT TO WATER WITH ACID ACTIVATION
CROSS REFERENCE TO RELATED APPLICATION This application is a continuation in part of the US Application. Serial No. 08 / 461,464, filed June 5, 1995, which is a continuation in part of the US Application Ser. Serial No. 08 / 363,803, filed on December 27, 1994, now US Pat. No. 5,523,161, which is a continuation in part of the US Application. Serial No. 08 / 220,353, filed March 30, 1994, now abandoned, which is a continuation in part of the US Application Ser. Serial No. 07 / 589,235, filed on September 28, 1990, now US Pat. No. 5,308,705, which is a continuation in part of the US Application. Serial No. 07 / 503,587, filed on April 3, 1990, now US Pat. No. 4,983,459. BACKGROUND Field of the Invention The present invention relates, in general, to the technique of producing a water repellent film on various substrates and, more specifically, to improving the life of water repellent films by activating the substrate with a solution. acid before applying the film. Relevant technique US Pat. No. 4,997,684 to Franz et al. describes a method for obtaining a durable non-wetting surface on glass by contacting the glass with a perfluoroalkylalkylsilane and a fluorinated olefinic compound and heating the glass to produce a durable non-wetting surface. U.S. Pat. No. 5,328,768 to Goodwin describes a technique for producing a durable non-wetting surface on a glass substrate, wherein the surface of the substrate is treated with a silica primer and a perfluoroalkylalkylsilane on the primer layer. The silica primer coat improves the durability of water repellency of the surface. The glass substrate is cleaned with water and a 50/50 volume solution of isopropanol / water before the primer application. U.S. Pat. No. 5,523,162 to Franz et al. discloses a method for producing a durable non-wetting surface on a plastic substrate, which includes treating the plastic substrate with a silica priming layer and a perfluoroalkylalkylsilane. The plastic substrate was cleaned with hexane and then with methanol before the application of the primer. While the previous US patents and US request In the present invention describe durable water repellent films, those skilled in the art can appreciate that it is advantageous and desirable to make available an additional technology to improve the durability of the water repellent surface. COMPENDIUM OF THE INVENTION The present invention relates to a method for improving the durability of water repellent films. The water repellent film used in the practice of the invention is preferably a water repellent composition applied on the substrate, which forms the water repellent film. In the practice of the invention, the durability of the water repellency of the film is improved by activating the substrate with an acid solution before applying the water repellent composition to the substrate.
The acid of the acid solution is preferably hydrochloric acid, sulfuric acid or an organic acid, such as tartaric acid. Other acids described herein can also be used in the practice of the invention. Although it does not limit the invention, the substrate includes glass, metal, plastic, enamels and ceramics. The substrate can be coated or uncoated; for example, the substrate can be coated with one or more inorganic oxide films. DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the durability of a water repellent film; The water repellent film is obtained by applying a water repellent composition on a substrate to form the water repellent film on the substrate. The durability of the water repellent film is enhanced by activating the substrate with an acid solution before applying the water repellent composition. Unless stated otherwise or otherwise made clear by the context of the exhibition, it is to be understood that while the preceding and following disclosures describe the water repellent composition and the acid solution as applied to the substrate itself, it is primarily the surface of the substrate that is affected by the present invention. In addition, unless otherwise indicated or otherwise stated, clear from the context of the disclosure, the term "water repellent composition" as used herein includes: water-repellent compositions applied to the substrate directly, as described above. described in US Pat. No. 4,983,459; water repellent compositions having an integral primer, as described in US Pat. No. 5,523,161; water repellent compositions having a fluorinated olefinic compound, as described in US Pat. No. 5,308,705; or water repellent compositions applied on a discrete primer layer applied to the substrate, as described in US Pat. No. 5,328,768. I. The substrate: The present invention is not limited to any particular substrate surface and may include uncoated glass, metal, plastic, enamel or ceramic substrates. In addition, the method of the present invention can be practiced on coating films or the outermost film of a stack of coating films, including inorganic oxide coating films on glass, metal, plastic, enamel and ceramic substrates. For example, inorganic glass oxide coatings include, but are not limited to, antimony-tin oxide, impure tin oxide, or transition metal oxides. The method of the present invention is also applicable to plastic substrates with a hard coating based on polysiloxane. These coatings of the polysiloxane sol-gel type contain, in general, siloxanes and inorganic oxides which function as a suitable substrate for the deposition of a hydrophobic coating, whose durability is increased by the use of a primer. Metallic substrates include galvanized steel, stainless steel and aluminum. When the substrate can be thermally or chemically treated, for example to increase its structural properties, the glass can be annealed or tempered by chemical or thermal means. In the following discussion, reference may be made to substrate and substrate surface, where reference is made to substrate unless otherwise indicated, the reference to the substrate refers to the substrate surface which may be uncoated or coated with a substrate. one or more movies. II. Possible polishing operation: It has been determined that the durability of water repellency of the water repellent film is prolonged by the method of the present invention, regardless of whether the surface of the substrate is polished prior to acid activation. Although not necessary, the polishing stage before acid activation is recommended. The polishing stage provides two benefits. The first is that it hardens the surface of the substrate. The second is that it partially removes contaminant residues from the substrate surface. Atomic Force Microscopy data has shown that polishing of glass substrates has increased the average hardness of the glass surface from about 0.5 nanometers to about 4 nanometers (measured over an area of 100 square microns). Scratches on the thin surface of up to 10 nanometers deep on the glass substrate have not resulted in any measurable turbidity. This provides more glass surface area for subsequent reaction with water repellent composition. The decontamination of the surface of the substrate can be shown by the contact angle of a drop of water on a freshly polished surface; the smaller the contact angle, the cleaner the substrate surface will be. As will be seen from the following data, polishing does not significantly improve the durability of the water repellent film. However, polishing is recommended to produce a cleaner surface on the substrate before acid activation. Polishing compounds that can be used in the practice of the present invention include, but are not limited to, alumina, ceria, iron oxide, garnet, zirconia, silica, silicon carbide, chromic oxide, diamond or other hard material with a size of Particle small enough not to damage the substrate. Mixtures of these materials are suitable polishing compounds. Preferred polishing compounds include alumina or ceria. The polishing operation is carried out by cleaning the substrate with a pad containing a suspension of the polishing compound. The preferred concentration of the polishing compound in water to form a polishing suspension is in the range of 5 to 30 weight percent. Lower and higher concentrations can be used, but more or less suspension or more or less contact time with the substrate may be necessary to properly polish the substrate. The preferred polishing process includes cleaning the substrate with the polishing suspension until the suspension is no longer pulled from any part of the substrate surface. When the suspension is stripped from a part of the surface of the substrate, it typically does so because the cohesion forces of the suspension are greater than the adhesive strength of the suspension to the substrate. The adhesive forces of the suspension to the substrate increase as a result of the removal of surface impurities from the substrate. The polishing operation removes said impurities, causing the adhesive force of the suspension to the substrate to exceed the cohesive strength of the suspension whereby the suspension is no longer pulled from any part of the substrate. The polishing operation can be carried out by hand or using a motorized equipment, such as an orbital sand sander with a non-abrasive pad that is moistened with the polishing suspension. III. The Water Repellent Composition: The water repellent composition that can be used in the practice of the present invention preferably includes a perfluoroalkylalkylsilane as described in the cross-referenced related applications and in US Pat. No. 4,997,684, No. 5,328,768 and No. 5,523,162, each of which is incorporated herein by reference. Preferred perfluoroalkylalkylsilanes in the practice of the invention have the general formula RmR'nSiX4-m-n, where R is a perfluoroalkylalkyl radical; m is 1, 2 or 3; n is 0, 1 or 2, and m + n is less than 4; R 'is a vinyl or alkyl radical, preferably methyl, ethyl, vinyl or propyl, and X is preferably a radical such as halogen, acyloxy and / or alkoxy. Preferred perfluoroalkyl radicals in perfluoroalkyl-alkyl radicals vary between CF3 and C3oF6 ?, preferably C6F13 to C? 8F37 and, more preferably, C8F? 7 to C? 2F25; the second alkyl moiety of the perfluoroalkylalkyl is preferably a substituted ethyl. R 'is more preferably methyl or ethyl. Preferred radicals for X include chloro, bromo, iodo, methoxy, ethoxy and acetoxy hydrolyzable radicals. Preferred perfluoroalkylalkylsilanes according to the present invention include perfluoroalkylethyltrichlorosilane, perfluoroalkylethyltrimethoxysilane, perfluoroalkylethyltriaketoxysilane, perfluoroalkylethyldiylchlor (methyl) silane and perfluoroalkylethyldiethoxy (methyl) silane. III. . The integral primer layer: The water repellent film that can be used in the practice of the present invention may include a discrete primer layer interposed between the substrate and the water repellent film, as described in one or more of the applications related cross-references and in US Pat. No. 5,328,768 and in US Pat. No. 5,523,162. When a discrete priming layer is selected, the priming layer is first applied onto the substrate prepared according to the invention by application methods including pyrolytic deposition, magnetron spraying or sol-gel condensation reactions. The water repellent composition is then applied on the primer layer. The first, non-limiting layer of the invention may include a silica primer layer. Alternatively, the water repellent film that can be used in the practice of the present invention may include an integral primer that is included in the water repellent composition, also as described in one or more of the cross-referenced related applications and in US Patent No. 5,523,161. The integral, non-limiting primer of the invention may be a hydrolysable silane or siloxane capable of hydrolytic condensation to form silica gel, which functions as an integral primer. Suitable silanes capable of hydrolysis to silica gel have the general formula SiX where X is a hydrolysable radical generally selected from the group of halogens and alkoxy and acyloxy radicals. Preferred silanes are those in which X is preferably chlorine, bromine, iodine, methoxy, ethoxy and acetoxy. Preferred hydrolysable silanes include tetrachlorosilane, tetramethoxysilane and tetraacetoxysilane. Suitable siloxanes have the general formula SiyOzX4? -2z / where X is selected from the group of halogen and alkoxy and acyloxy radicals, and is two or more and z is one or more and 4y-2z is greater than zero. Preferred hydrolysable siloxanes include hexachlorodisiloxane, octachlorotrrisiloxane and higher oligomeric chlorosiloxanes. When the integral primer layer is selected, the water repellent composition is applied to the substrate prepared according to the invention preferably as a solution in an aprotic solvent, preferably an alkane or mixture of alkanes, or a fluorinated solvent. Said solutions can be applied to the substrate by any conventional technique, such as dipping, flow, rubbing or spraying, without the additional step of applying a separate primer layer.
IIIB. The fluorinated olefinic compound: The water-repellent composition that can be used in the practice of the present invention can also optionally include a fluorinated olefinic compound, also as described in the related cross-referenced applications and in US Pat. No. 4,997,684, No. 5,328,768 and 5,523,162, to obtain lubricity and promote dirt repellency of the water repellent surface. A preferred olefinic compound is selected from the group represented by the general formula CmF2m +? CH = CH2, where m is from 1 to 30, preferably from 1 to 16, more preferably from 4 to 10. IV. The acid activation of the present invention: The acid solutions used in the practice of the present invention are selected for their ability to increase the durability of the water repellency of the substrate without damaging the substrate. Although not limiting to the invention, acid solutions that are preferably used in the practice of the invention include solutions of hydrochloric acid, sulfuric acid and organic acids. When organic acid solutions are selected, solutions of strong organic acids are preferred, which include acid solutions having a pH of less than about 5 and, more preferably, less than about 3. Other acids that can be employed in the practice of the invention include phosphoric acid, hydrobromic acid, nitric acid, acetic acid, trifluoroacetic acid and / or citric acid. When the acid is hydrochloric acid, an acid solution of hydrochloric acid dissolved in deionized water can be used, where the concentration of acid is in the range of 0.5-30% by weight of hydrochloric acid, in a deionized water residue; 0.5-20% by weight is acceptable and 0.5-10% by weight is preferred. When the acid is sulfuric acid, an acid solution of sulfuric acid dissolved in deionized water can be used, where the concentration of acid is in the range of 0.5-30% by weight of sulfuric acid dissolved in the rest of deionized water; 0.5-20% by weight is acceptable and 0.5-10% by weight is preferred. When the acid is tartaric acid, an acid solution of tartaric acid dissolved in deionized water can be used, where the acid concentration is in the range of 1-40% by weight of tartaric acid, dissolved in the rest of deionized water and 2-20% by weight is preferred. As can be appreciated, lower and higher acid concentrations are acceptable; however, the use of said concentrations may require more or less activation time on the substrate to improve the durability of the water repellent film. The acid activation of the substrate is carried out by applying the acid solution to the substrate by any conventional technique such as dipping, flow, spraying and, preferably, rubbing. Although a fixed number of passes is not needed, it has been found that rubbing on the substrate approximately six times provides acceptable results. Rubbing is commonly accomplished by applying moderate manual pressure to an acid-resistant absorbent pad containing the acid solution, such as a cotton pad. When the acid solution is volatile and evaporates from the substrate without leaving a residue, the acid is applied to the substrate and allowed to evaporate, after which the water-repellent composition is applied to the substrate. Volatile acid solutions are defined herein as those that are capable of volatilizing at ambient conditions in a short period of time (i.e., in about 10 minutes or less) after application to the substrate. Examples of volatile acid solutions which can be used in the practice of the present invention include hydrochloric, hydrobromic, acetic, nitric and trifluoroacetic acid solutions. When the acid solution is non-volatile, or is volatile but leaves behind a residue after evaporation, the substrate must be washed after the acid activation stage to eliminate the acid solution or its residue. After washing, the substrate is dried and the water repellent composition is applied on the substrate. Non-volatile acid solutions are defined herein as those which are not capable of volatilizing under ambient conditions in a short period of time (i.e., in about 10 minutes or less) after application to the substrate. Examples of non-volatile acids include sulfuric, tartaric, citric and phosphoric acids. Wash solutions may include water or alcohol, with water being preferred. It is thought that, during the acid activation step, the acid solution increases the durability of the water repellent surface by removing contaminating materials from the surface of the substrate and increasing the number of binding sites on the surface of the substrate available for reaction with the water-repellent composition. V. Durability test of the water repellent film: The durability of the water repellent film applied according to the present invention is measured in terms of the ability of the film surface to maintain a contact angle over time in accelerated weather conditions. The greater the degree of contact angle that can be maintained by the sample studied over time or the number of rubbing cycles, the more durable the film and the more water repels the surface. The contact angles mentioned herein are measured by the sessile drop method using a modified captive bubble indicator manufactured by Lord Manufacturing, Inc., equipped with Gaertner Scientific goniometric optics. The surface to be measured is placed in a horizontal position, facing up, in front of a light source. A sessile drop of water is placed on top of the surface in front of the light source, so that the profile of the sessile drop can be visualized and the contact angle can be measured in degrees through the telescope of the goniometer equipped with circular protractor graduation. Simulated atmospheric conditions of the water repellent film are obtained through atmospheric chambers including the Cleveland Condensation Cabin (CCC) and the QUV Meter (products of The Q-Panel Company, Cleveland, OH). The CCC chamber was operated at a vapor temperature of 140 ° F (60 ° C) in an indoor environment that resulted in a constant condensation of water on the test surface. The QUV Meter was operated with 8 hour UV cycles (B313 lamps) at a black panel temperature of 65-70 ° C and 4 hours of condensation humidity at 50 ° C of atmospheric temperature. The abrasion resistance of the water repellent film was measured by the Taber Abrasion Test using the Taber scraper manufactured by Teledyne Taber of North Tonawanda, NY. The Taber Abrasion test consists of rotating a substrate that has to be studied in a horizontal orientation, while a pair of abrasion wheels rotate on the surface. A revolution of the substrate is equal to one cycle. The weight per wheel can vary to increase or decrease the abrasion rate and, for the test of the present invention, 500 grams of weight per wheel was applied. After abrasion, the water repellency in the abrasion track was measured with the previously described sessile water drop method. The abrasion resistance of the water repellent film was measured by means of the Wet Harrow Abrasion Test. In this test, two wiper blades are cycled through the surface of the water repellent film, while water or an abrasive slurry is applied in front of the wiper blades. A cleaned area of approximately 1.5 inches is scraped
(3.8 cm) by 7.5 inches (19.05 cm) for each rubbing during this test, with the result that two such areas are typically scraped onto the substrate in orientation side by side. The blades are typically cycled for 5000 cycles, which result in 20,000 strokes of friction through each scraped area. After abrasion, the water repellency of the water repellent film is measured by the sessile water drop method. The present invention will be better understood thanks to the descriptions of the specific examples that follow. In the following examples, glass coupons were cut from a piece of glass cut from a float glass ribbon formed in a molten tin bath. All the polishing, activating and coating processes described in the following examples were carried out on the tin side of the coupons. EXAMPLE 1 Example 1 shows a comparison between the durability of a water-repellent film formed on a group of glass coupons that were activated by means of an acid solution of hydrochloric acid according to the invention, hereinafter "acid-activated", and the durability of a water repellent film formed on a different group of glass coupons that were not activated by means of an acid solution of the invention. The two groups of glass coupons were each subdivided into four subgroups. Each subgroup activated with acid was paired with a non-activated subgroup with acid and the four pairs of coupon subgroups were then subjected to one of the CCC, QUV, Wet Harrow Abrasion or Taber Abrasion test methods. More specifically, sixteen transparent uncoated float glass glass coupons measuring 2 x 6 x 0.182 inches (5.08 x 15.24 x 0.462 cm) were subjected to the CCC test, 3 x 4 x 0.182 inches (7, 62 x 10.16 x 0.462 cm) for the QUV test, 4 x 16 x 0.090 inches (10.16 x 40.64 x 0.23 cm) for the Wet Harrow Abrasion test and 4 x 4 x 0.090 inches ( 10.16 x 10.16 x 0.23 cm) for the Taber Abrasion test to a heat treatment that simulates the heating cycles used in the bending procedures. This heat treatment consisted in subjecting the glass coupons for approximately 15 minutes at a temperature of 525 to 560 ° C in an electric oven. After the heat treatment, the glass coupons were allowed to slowly cool in air to ambient conditions. After cooling, all 16 glass coupons were polished by hand with a cerium oxide suspension to remove surface impurities. The cerium oxide suspension was formed by mixing a commercial cerium oxide polishing powder with water at a concentration of plus or minus 20% by weight of cerium oxide, the remainder being water. Commercial polishing powders of cerium oxide include Rhodite 19A (average particle size of 3.2 microns) and Rhodox 76 (average particle size of 3.1 microns), both cited as having a purity of 50% of cerium oxide and 90% rare earth oxide, and are supplied by Universal Photonics, Inc. of Hicville, NY. The cerium oxide suspension was applied to the glass coupons with a pad. The polishing continued until the suspension is no longer pulled from any portion of the glass coupon. After polishing, all 16 glass coupons were cleaned with deionized water to remove any residue from the polishing pad or varnish and dried with a paper towel. The 16 coupons were divided into two groups, denominated, for exhibition purposes, as Group A, which included eight glass coupons, and Group B, which included eight coupons. The glass coupons of Group A were subjected to an acid activation with a Normal 1 hydrochloric acid solution (approximately 3.7% by weight). The acid solution was applied by hand using an absorbent pad for 60 seconds. Glass coupons of Group B were not subjected to acid activation. The glass coupons of Groups A and B were then treated twice with a solution of silicon tetrachloride at 0 ° C., 8% by weight in Fluorinert (R) FC-77 (hereinafter, "FC-77"), a perfluorocarbon / perfluoroether solvent product from 3M Corporation of St. Paul, MN. The silicon tetrachloride solution was applied to the glass coupons with an absorbent pad to form a silica priming layer on the glass coupons of Groups A and B. The coupons of Groups A and B were then treated once with a solution of: 1) 2.5% by weight of perfluoroalkyltrichlorosilane (the perfluoroalkyl moieties constituted primarily C6F13 to C? 8F37) and 2) 2.5% by weight of perfluoroalkylethylene (the perfluoroalkyl moieties constituted primarily C6Fi3 to C ? 8F37) in FC-77 to deposit a perfluoroalkylalkyl water-repellent composition on the glass coupons. The coupons from Groups A and B were heated to 150 ° F (65.5 ° C) for about 10 hours to cure the coating and produce a water repellent film on the glass coupons. Excess silanes were removed from the glass surfaces by washing with solvents. The solvent wash was performed with PF-5060 (a perfluorohexane product from 3M Corporation). The coupons were washed with the solvent by rubbing with a paper towel until they were visibly clean. The glass coupons of Group A were then divided again into four subgroups or groups, identified, for exhibition purposes, such as Al Groups (2 coupons), A2 (2 coupons), A3 (2 coupons) and A4 (2 coupons). . Group B glass coupons were similarly divided into Groups Bl (2 coupons), B2 (2 coupons), B3 (2 coupons) and B4 (2 coupons). The glass coupons of Groups Al and Bl were then subjected to atmospheric conditions in the CCC atmospheric cabin as described above. A coupon from Group Bl broke during the sample preparation and was redone before the trial. This resulted in this coupon (and only this coupon) receiving 16 hours less CCC exposure time than indicated in the table below for the rest of the coupons. The glass coupons of Groups A2 and B2 were subjected to atmospheric conditions in the atmospheric cabin QUV-B313 as described above. The glass coupons of Groups A3 and B3 were subjected to the Wet Harrow Abrasion Test. In the present example, the four coupons of Groups A3 and B3 resulted in the formation of eight separate scraped areas. One of the scraped areas on each of the four coupons of Group A3 and Group B3 was scraped for 200 cycles with a suspension of 0.5% by weight of silica precipitated in water. A coupon from Group A3 and a coupon from Group B3 were then selected and the rest of the abrasion area of each of these coupons was scraped for 600 cycles with the same suspension. The abrasion area of the remaining coupon of Group A3 and the remaining coupon of Group B3 not previously selected was then subjected to a test of 5000 cycles using deionized water in place of the suspension. The glass coupons of Groups A4 and B4 were subjected to the Taber Abrasion Test. For all the glass coupons studied in Groups A1-A4 and B1-B4, the water repellency efficiency of the water repellent film was determined by measuring the contact angle of a sessile drop of water placed on the sample, using the Modified captive bubble indicator manufactured by Lord Manufacturing, Inc., as described above. The coupons of Groups A1-A4 and B1-B4 were studied in duplicate. The contact angles of the sessile drop were measured for both glass coupons and the mean of the results was found. The average of the results is shown in the following tables: Table 1 - CCC Angle of contact (°)
Table 2 - QUV-B313 Angle of contact (°)
Table 3 - Wet Harrow Contact Angle (°) Cycles Group B3 Group A3 Without acid With acid 0 124 123 200 112 111 600 112 112 5000 42 97
Table 4 - Taber Scraper Angle of contact (°)
As can be seen from Table 1, in the CCC atmospheric test the glass coupons of Group A1 activated with acid maintained a contact angle of 101 degrees to 1494 hours, while the glass coupons of Group Bl maintained only a contact angle of 59 degrees, which shows a very substantial improvement in the durability and effectiveness of water repellency of acid-activated glass coupons on glass coupons not activated with acid. The Bl Group coupons were not studied beyond 1996 hours of CCC duration. The common test procedure requires discontinuing the test after the contact angle falls below 60 ° or the 3000 test hours are reached. This procedure was followed in general for the data shown in all Tables 1-7. As can be seen from Table 3, in the Wet Harrow Abrasion Test, at 5000 cycles, the glass coupons of Group A3 activated with acid maintained a contact angle of 97 degrees, which greatly exceeded the contact angle of 42. grades of glass coupons not activated with Group B3 acid, which again shows a very substantial improvement in the durability and water repellency efficiency of acid-activated glass coupons over non-activated glass coupons with acid. Similarly, as can be seen from the Table
4, in the Taber Abrasion Test, the contact angle after 150 cycles of the acid-activated Group A4 glass coupons was 83 degrees, while the glass coupons of Group B4 not activated with acid maintained only one contact angle of 75 degrees. The differences in the data of QUV-B313 of Table 2 do not show the substantial improvement obtained for the other tests, but it is considered that the differences in the contact angles are within the normal variations of measurement and are not considered to indicate less durability of the water repellent film within the context of that particular test method. EXAMPLE 2 Example 2 shows a comparison between the durability of a water-repellent film formed on a first group of glass coupons that were not activated with acid, a second group of glass coupons activated with acid with a solution of hydrochloric acid, a third group of glass coupons activated with acid with a solution of sulfuric acid and a third group of acid-activated glass coupons with a solution of tartaric acid. The four groups of glass coupons were studied using the CCC Atmospheric Chamber as described above. Twelve 0.122 inch (0.462 cm) thick transparent uncoated float glass glass coupons measuring 2 inches (5.08 cm) wide and 6 inches (15.24 cm) long were subjected to the same heat treatment as the one described in Example 1. The glass coupons were polished using an orbital sand sander with a polyester felt pad with a suspension of aluminum oxide to remove the impurities. The aluminum oxide suspension was formed by mixing Microgrit (R1 WCA1T (Microgrit is a registered trademark of Micro Abrasives Corp., Westfield, MA) with water at a concentration of approximately 20% .The polishing compound was applied to the coupons of glass using the felt pad and an orbital sand sander until the suspension was no longer ripped from any portion of the glass coupon.After polishing, the glass coupons were cleaned with deionized water and paper towels as in Example 1 The 12 coupons were then divided into four groups, called, for exhibition purposes, such as Groups C, D, E and F, with three coupons in each group. The Group C coupons were not activated with acid. The Group D glass coupons were activated with acid with a Normal 1 hydrochloric acid solution (approximately 3.7% by weight). The Group E glass coupons were activated with acid with a Normal 1 sulfuric acid solution (approximately 4.8% by weight). The glass coupons of Group F were activated with acid with a 10% by weight tartaric acid solution. The acid solutions were applied to the glass coupons by wiping with a cotton pad for 15-30 minutes. The glass coupons of Groups D, E and F were then washed with deionized water and paper towels. The glass coupons of Groups C, D, E and F were then each treated twice with a solution of 0.8% by weight of silicon tetrachloride in FC-77 on an absorbent pad to form a primer layer of silica on the glass coupons. The glass coupons of Groups C, D, E and F were then treated three times each with a solution of: 1) 2.5% by weight of perfluoroalkylethyltri-chlorosilanes (the perfluoroalkyl moieties constituted primarily C6F? 3 to C ? 8F37) and 2) 2.5% by weight of perfluoroalkylethylene (the perfluoroalkyl moieties constituted primarily C6F? 3 to C? 8F3) in FC-77 to deposit a perfluoroalkylalkyl silane water-repellent composition on the glass coupons. The glass coupons of Groups C, D, E and F were then cured at 150 ° F (65.6 ° C) for 8 hours to cure the coating and produce a water repellent film on the glass coupons. Excess silanes were removed from the glass coupons by solvent washing. Solvent washing was carried out with PF-5060 and the coupons were washed with solvent by wiping with a paper towel until visibly clean. The glass coupons of Groups C, D, E and F were subjected to atmospheric conditions in the CCC atmospheric cabin as described above. The water repellency efficiency of the water repellent film was determined by measuring the contact angle of a sessile drop of water as described in Example 1. Each of the coupons of Groups C, D, E and F were prepared in triplicate and the average of the contact angles of each group was found. The average of the results is shown in the following table: Table 5 - CCC Angle of contact (°) Group C Group D Group E Group F
Hours Without acid HCl H2S04 Tartaric 0 114 118 119 120
142 111 116 118 118
312 87 119 120 120
620 72 112 112 113
946 62 94 77 93 1278 56 72 63 67
1588 -. 1588-59 55 57 > can be seen in Table 5, at 1278 hours the contact angle for the acid-activated glass coupons of Groups D, E and F remained much higher, at 72, 63 and 67 degrees, than the angle of Group C coupons not activated with acid, which maintained only a contact angle of 56 degrees after being subjected to atmospheric conditions. EXAMPLE 3 Example 3 shows a comparison of the durability of a water repellent film formed on a first group of glass coupons that were not acid activated with the durability of a water repellent film formed on a second group of glass coupons which were activated with acid with a solution of hydrochloric acid and a third group of glass coupons activated with acid with a solution of tartaric acid. The glass substrate was changed over the previous examples, to show that the superior results of the present invention can be obtained on various glass substrates. Nine glass coupons measuring 0.119 inches (0.30 cm) in thickness of a chemically tempered glass sold by PPG Industries, Inc. of Pittsburgh, PA, HERCULITE (R) II glass measuring 2 inches (5.08) were selected. cm) wide by 6 inches (15.24 cm) in length. Unlike Examples 1 and 2 above, no heat treatment was applied to the glass coupons of Example 3 before polishing. The glass coupons were polished using an orbital sand sander with a polyester felt pad and an aluminum oxide suspension and cleaned with deionized water and a paper towel as described in Example 2.
The glass coupons were divided into three groups, denominated, for exhibition purposes, such as Groups G, H and I, with a content of 3 coupons per group. The Group G glass coupons were not activated with acid. The glass coupons of Group H were activated with acid with a solution of 1 Normal hydrochloric acid as described in the preceding examples. The Group I glass coupons were activated with acid with a 10% by weight tartaric acid solution, as described in the preceding examples. The acid solutions of Groups H and I were rinsed on the coupons for 15-30 seconds. The coupons of Groups H and I were then washed with deionized water as described in the preceding examples. The glass coupons of Groups G, H and I were then treated twice each with a solution of 0.8 wt% silicon tetrachloride in FC-77, as described in the previous examples to form a layer Silica primer on the glass coupons. The glass coupons of Groups G, H and I were then treated three times each with a solution of: 1) 2.5% by weight of perfluoroalkylethyltrotransilanes (the perfluoroalkyl residues constituted prima- rily C6F3 to Ca8F37) and 2) 2.5% by weight of perfluoroalkylathylene (the perfluoroalkyl moieties constituted primarily C6F13 to C? 8F37) in FC-77, as described in the previous examples, to deposit a water-repellent composition on the substrates. of glass. The coupons for Groups G, H and I were cured at 150 ° F
(65.5 ° C) for 8 hours to cure the coating and produce a water repellent film on the glass coupons and excess silanes was removed from the glass surfaces by solvent washing with PF-5060 as described in the previous examples. The coupons of Groups G, H and I were subjected to atmospheric conditions in the CCC atmospheric cabin as described in the previous examples. The effectiveness of water repellency of the water repellent film of the glass coupons of Groups G, H and I was determined by measuring the contact angle of a sessile drop of water as described in the previous examples. While the glass coupons of Groups G, H and I were prepared in triplicate, a coupon treated with Group H HCl was broken before being subjected to atmospheric conditions. Thus, the values given for the glass coupons treated with HCl are the sample means in duplicate, not in triplicate. The values given for Groups G and l are the means of values in triplicate. The average of the results is shown in the following table:
Table 6 CCC
As can be seen from Table 6, at 2310 hours of atmospheric conditions, the non-activated coupons of Group G maintained only a contact angle of 54 degrees, while the acid-activated coupons of Groups H and I maintained angles of contact of 89 and 77 degrees, respectively, showing a considerably higher water repellency after being subjected to atmospheric conditions. EXAMPLE 4 Example 4 shows a comparison of the durability of a water repellent film formed on a first group of glass coupons that were not acid activated with a second group of glass coupons that were activated with a hydrochloric acid solution. In this example, the water repellent composition included an integral primer. The subgroups were selected to obtain a comparison of polished glass coupons versus unpolished glass coupons. None of the glass coupons of Example 4 included a heat treatment before or after coating the glass coupon with the water repellent composition. Twelve 0.182 inch (0.46 cm) thick transparent uncoated float glass glass coupons measuring 2 inches (5.08 cm) wide by 6 inches (15.24 cm) in length were selected. The twelve glass coupons were cleaned with deionized water and a paper towel. The glass coupons were divided into four groups of three coupons each, here described as Groups J, K, L and M. The Group J coupons were not activated with acid or polished. The coupons of Group K were activated with acid with a solution of 1 Normal hydrochloric acid as described in the previous examples, but they were not subjected to a polishing operation. The K glass coupons were then washed with deionized water and dried as described in the previous examples. The Group L coupons were polished as described in the previous examples with a suspension of aluminum oxide as described in the previous examples, but were not activated with acid. The coupons of group M were both polished and activated with acid. The polishing was carried out in the same way as described with respect to the Group L coupons and the acid activation was carried out in the same way as described with respect to the Group K coupons. The glass coupons of Groups J, K, L and M were then treated with a solution of: 1) 0.5% by weight of perfluoroalkyltrichlorosilane (the perfluoroalkyl moieties constituted C8F? 7) and 2) 0.5% by weight of tetrachloride of silicon in Isopar (R1 L, a hydrocarbon solvent produced by Exxon Corporation of Houston, TX, to deposit a water-repellent composition of perfluoroalkylalkylsilane having an integral primer layer on the coupons.) Glass coupons of Groups J, K, L and M were not cured, but were subjected to atmospheric conditions in the CCC atmospheric cabin as described in the previous examples.The water repellency of the water repellent film was measured by the contact angle. of a sessile drop of water as described in the previous examples. The coupons of Groups J, K, L and M were prepared in triplicate and the mean of the contact angles of each group was found. The average of the results appears in the following table: Table 7 - CCC Angle of contact (°) Not polished Polished
As can be seen from Table 7, after 824 hours of atmospheric conditions, the coupons of Groups J and L, without acid activation, maintained a contact angle of only 47 and 46 degrees, respectively, while the coupons activated with acid of Groups K and M maintained respective contact angles of 63 and 64 degrees. The results clearly demonstrate that the acid activated surface used with a water repellent film having integral primer improves the durability of the water repellency of the film. A comparison of the coupons of Group K and Group M shows that, at 824 hours, the buffing operation did not significantly affect the contact angle of the Group M coupons. The above examples are offered to illustrate the present invention. Additional examples were prepared and studied and the previous result is a representative subgroup of all the prepared examples. Various perfluoroalkylalkylsilanes, hydrolyzable silanes, solvents and concentrations can be applied by any conventional technique and can be eventually cured at temperatures suitable for suitable times to obtain durable non-wettable surfaces on a variety of substrates. As can be appreciated, the above description does not limit the invention and was presented to give an appreciation of the invention. The scope of the present invention is defined by the following claims.