Transparent hydrophobic coating materials with improved durability and methods of making same

Abstract

Durable, transparent, inorganic-organic hybrid hydrophobic coating materials for glass, metal or plastic substrates are provided. The coating materials are generally an acid catalyzed condensation reaction product comprised of an organic polymeric silane (e.g., a polyol functionalized with a silane through a urethane linkage or a polyamine functionalized with a silane through a urea linkage, such as isocyanatopropyltrimethoxysilane or isocyanatopropyltriethoxysilane), an inorganic metal alkoxide (e.g., silicon alkoxides such as tetraethoxysilane or tetramethoxysilane) and a fluorinated silane (e.g., (3,3,3-trifluoropropyl)trimethoxysilane or nonafluorohexyltrimethoxysilane).

Claims

1. A hydrophobic coating material which comprises an acid catalyzed condensation reaction product comprised of: an organic polymeric silane selected from the group consisting of polycaprolactone polyols having 2 to 4 hydroxyl groups reacted with an isocyanate-terminated silane and polyurea silanes; an inorganic metal alkoxide; and a fluorinated silane.

2. The hydrophobic coating material according to claim 1, wherein the polycaprolactone polyol has a molecular weight between 50 and 10,000 g/mol.

3. The hydrophobic coating material according to claim 1, wherein the polyurea silane is a reaction product of an amine having at least two primary or secondary amine groups with an isocyanate-terminated silane.

4. The hydrophobic coating material according to claim 3, wherein the polyurea silane is reaction product of diethylenetriamine with an isocyanate-terminated silane.

5. The hydrophobic coating material according to claim 4, wherein metal alkoxide comprises at least one hydrolyzable compound having at least one silane group represented by the formula Si(R1)x(R2)4-x per molecule, wherein R1 represents a C1-C8 alkyl group, an epoxide group, a vinyl group, an acrylic group, R2 represents a hydrolyzable alkoxy group or halide group, and x is 0, 1, 2 or 3.

6. The hydrophobic coating material according to claim 5, wherein the fluorinated silane is a compound having the formula Rf1Si(R1)x(R2)3-x where Rf1 represents a fully or partially perfluorinated segment, R1 represents an alkyl group, represents a hydrolyzable alkoxy group or halide group, and x is 0, 1 or 2.

7. The hydrophobic coating material according to claim 1, wherein the fluorinated silane is a bis-silane terminated polyfluoropolyether or a fluoro-terminated silane.

8. The hydrophobic coating material according to claim 1, wherein the fluorinated silane is (3,3,3-trifluoropropyl)trimethoxysilane or nonafluorohexyltrimethoxysilane.

9. The hydrophobic coating material according to claim 1, wherein the organic polymeric silane and the inorganic metal alkoxide are present in a weight ratio of between about 1:10 to about 10:1.

10. The hydrophobic coating material according to claim 9, wherein the fluorinated silane is present in an amount between about 0.0001 to 1 wt. %.

11. The coated substrate according to claim 10, wherein the substrate is a glass substrate, polymeric substrate or metal substrate.

12. The coated substrate according to claim 10, wherein the coating is cured.

13. A coated substrate which comprises a substrate and a coating on the substrate, wherein the coating is comprised of the hydrophobic coating material according to claim 1.

14. A method of making a hydrophobic coating material which comprises reacting under acid-catalyzed hydrolysis condensation reaction conditions a reaction mixture comprising: an organic polymeric silane selected from the group consisting of polycaprolactone polyols having 2 to 4 hydroxyl groups reacted with an isocyanate-terminated silane and polyurea silanes; an inorganic metal alkoxide; and a fluorinated silane.

15. The method according to claim 14, wherein the polycaprolactone polyol has a molecular weight between 50 and 10,000 g/mol.

16. The method according to claim 14, wherein the polyurea silane is a reaction product of an amine having at least two primary or secondary amine groups with an isocyanate-terminated silane.

17. The method according to claim 16, wherein the polyurea silane is a reaction product of diethylenetriamine with an isocyanate terminated silane.

18. The method according to claim 17, wherein metal alkoxide comprises at least one hydrolyzable compound having at least one silane group represented by the formula Si(R1)x(R2)4-x per molecule, wherein R1 represents a C1-C8 alkyl group, an epoxide group, a vinyl group, an acrylic group, R2 represents a hydrolyzable alkoxy group or halide group, and x is 0, 1, 2 or 3.

19. The method according to claim 18, wherein the fluorinated silane is a compound having the formula Rf1Si(R1)x(R2)3-x where Rf1 represents a fully or partially perfluorinated segment, R1 represents an alkyl group, a hydrolyzable alkoxy group or halide group, and x is 0, 1 or 2.

20. The method according to claim 14, wherein the fluorinated silane is a bis-silane terminated polyfluoropolyether or a fluoro-terminated silane.

21. The method according to claim 14, wherein the fluorinated silane is (3,3,3-trifluoropropyl)trimethoxysilane or nonafluorohexyltrimethoxysilane.

22. The method according to claim 14, wherein the organic polymeric silane and the inorganic metal alkoxide are present in a weight ratio of between about 1:10 to about 10:1.

23. The method according to claim 22, wherein the fluorinated silane is present in an amount between about 0.0001 to 1 wt. %.

24. The method according to claim 14, which comprises conducting the reaction in the presence of an aqueous acid catalyst in an amount sufficient to achieve a pH of the reaction mixture of below 5.

25. The method according to claim 24, wherein the pH of the reaction mixture is between about 2 to about 4.

26. The method according to claim 24, wherein the acid catalyst is a mineral acid or an organic acid.

27. The method according to claim 26, wherein the acid catalyst is selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and acetic acid.

Description

DETAILED DESCRIPTION

(1) As noted above the durable, transparent, inorganic-organic hybrid hydrophobic coating materials for glass, metal or plastic substrates according to the embodiments described herein is generally an acid catalyzed condensation reaction product comprised of an organic polymeric silane, an inorganic metal alkoxide and a fluorinated silane.

(2) A. Organic Polymeric Silane

(3) The organic polymeric silane component of the coating material will necessarily include either a polyol (including but not limited to diols, triols, tetraols, pentols, and the like) which is silane functionalized with a metal alkoxide (e.g., an isocyanate terminated silane) through a urethane linkage or a polyamine which is silane functionalized with a metal alkoxide through a urea linkage. The reaction between the polyol and the isocyanate-terminated silane may be catalyzed using a tin catalyst such as dibutyltindilaurate. Other polyols, such as those derived from polyester, polyether, polycarbonate, and the like may also be used.

(4) In preferred embodiments, the polyol or polyamine is silane-functionalized with isocyanatopropyltrimethoxysilane or isocyanatopropyltriethoxysilane through urethane or urea linkages, respectively.

(5) The polyurethane silane can be produced from a wide range of molecular, oligomeric, or polymeric polyether or polyester based polyols possessing at least 2 hydroxyls, preferably 3 or 4 hydroxyls. Polyols with molecular weights between 50 and 10,000 g/mol may be used, preferably 1000-2000 g/mol. For example, CAPA brand polyester polyols available commercially from Perstorp Corporation, or ARCOL brand polyether based polyols commercially available from Bayer Material Science may be used.

(6) Representative polyester and polyether polyols include polycaprolactone diols or triols, polyethyleneoxide diols or triols, polypropylene diols and triols with weight average molecular weights within the ranges noted above may satisfactorily be employed. Preferably, a polycaprolactone triol with the structure:

(7) ##STR00001##
where m+n+p=7-16 may be used.

(8) Polyamines can alternatively be used in the same manner with reaction of the isocyanate-terminated silane through an urea linkage. The polyurea silane can be produced from a wide range of molecular, oligomeric, or polymeric polyamines possessing at least 2 primary or secondary amine groups, preferably 3 or 4 amines per molecule. Polyamines with molecular weights between 50 and 10,000 g/mol may be used, preferably 100-1000 g/mol. For example, diethylenetriamine or JEFFAMINE amines commercially available from Huntsman Petrochemical Corporation, such as JEFFAMINE T-403 polyether amine may be employed satisfactorily.

(9) By the term, polyamine as used herein, it is meant any aliphatic or aromatic compound containing two or more primary or secondary amine functional groups. The polyamine compound may have any suitable backbone chain structure including saturated or unsaturated, and linear, branched, or cyclic. Representative polyamines include polyetheramines such as diamines with the structure:

(10) ##STR00002##
where x=2-70, preferably x is 2-7.

(11) Alternatively the polyetheramine is a triamine with the structure:

(12) ##STR00003##
where n=0-5, and x+y+z are 3-100. Preferably n=1 and x+y+z=5-6.
B. Inorganic Metal Alkoxide

(13) The inorganic metal alkoxide component of the coating material comprises at least one metal alkoxide, such as those based on Si, Al, Ti, Zr, and the like. Preferred are silicon alkoxides. The silicon alkoxides may also comprise monofunctional organic moieties such as epoxide, alkyl, phenyl, vinyl, mercapto, methacrylate, and the like or be bis-silane terminated, such as bis-trimethoxysilylethane.

(14) The preferred metal alkoxide comprises at least one hydrolyzable compound having at least one silane group, Si(R.sup.1).sub.x(R.sup.2).sub.4-x, per molecule, wherein R.sup.1 represents an alkyl group (for example a C.sub.1-C.sub.8, polymerizable group (e.g. epoxide, vinyl, acrylic), or other alkyls terminated with another organic moiety (hydroxyl, isocyanate, amino, thiol, etc.), R.sup.2 represents a hydrolyzable group (for example an alkoxy or halide group, preferably methoxy, ethoxy or chloro) and x is 0, 1, 2, 3. Preferably, the metal alkoxide is tetraethoxysilane or tetramethoxysilane.

(15) C. Fluorinated Silane

(16) Representative examples of fluorinated silane compounds include those having the formula Rf.sup.1Si(R.sup.1)x(R.sup.2).sub.3-x where Rf.sup.1 represents a fully or partially perfluorinated segment (for example a 3,3,3-trifluoropropyl, (perfluorobutyl)ethyl, (perfluorohexyl)ethyl, (perfluorooctyl)ethyl, perfluorododecyl, perfluorotetradecyl, heptadecafluoro-1,1,2,2-tetrahydrodecyl, nonafluorohexyl or tridecafluoro-1,1,2,2-tetrahydrooctyl), R.sup.1 represents an alkyl group (for example a C.sub.1-C.sub.8, preferably C.sub.1-C.sub.4 primary or secondary alkyl group) and R.sup.2 represents a hydrolyzable group (for example an alkoxy or halide group, preferably methoxy, ethoxy or chloro) and x is 0, 1, or 2.

(17) Preferably, fluorinated silane compounds according to formula Rf.sup.2[Q-C(R).sub.2Si(R.sup.1).sub.x(R.sup.2).sub.3-x].sub.z are used wherein Rf.sup.2 represents a multivalent poly(perfluorooxyalkyl) or poly(perfluoroxyalkylene) segments, Q represents an organic divalent linking group (examples include amide, ether, ester or urethane linking group), R.sup.1 represents an alkyl group (for example a C.sub.1-C.sub.8, preferably C.sub.1-C.sub.4 primary or secondary alkyl group) and R.sup.2 represents a hydrolyzable group and x is 0, 1, or 2; R represents hydrogen or an alkyl group of 1 to 4 carbon atoms and the R groups may be the same or different. Preferably R is hydrogen.

(18) The hydrolyzable groups R.sup.2 may be the same or different and are generally capable of hydrolyzing under appropriate conditions, for example under acidic aqueous conditions, such that the fluorochemical silane compound can then undergo condensation reactions. Preferably, the hydrolyzable groups upon hydrolysis yield groups capable of undergoing condensation reactions, such as silanol groups.

(19) Certain embodiments will employ a fluorinated silane component which comprises either a bis-silane terminated polyfluoropolyether or a fluoro-terminated silane, such as (3,3,3-trifluoropropyl)trimethoxysilane, nonafluorohexyltrimethoxysilane, and the like.

(20) D. Metal Oxide Particles

(21) Metal oxide particles may optionally be used in the coating formulation to impart desired properties, such as abrasion resistance, electrical or optical properties. For example, metal oxide particles of silica, titania, zirconia, and/or alumina may be used. Silica (SiO.sub.2) is preferred. For optical transparency, it is preferred that the particles are less than about 100 nm, e.g. between about 1 nm to about 100 nm. The preferred particle size is 1-10 nm diameter spherical nanoparticles. If present, the particles can be included in the formulation up to about 50 wt. %, preferably between about 20 wt. % to about 30 wt. %, based on total formulation weight.

(22) D. Composition and Properties

(23) The composition of the formulation can vary depending on the desired final properties for flexibility, hardness, abrasion resistance, transparency, or other desired physical properties. Generally the weight ratio of the polymeric silane to the metal alkoxide or organic functional metal alkoxide in the formulation may be between about 1:10 to about 10:1, preferably about 3:1. The weight percentage of the fluorosilane in the formulation could be used in a range of from about 0.0001 to 1 weight %, preferably between about 0.0005 to about 0.001 weight %.

(24) The coating materials may be produced by mixing the inorganic and organic components in a suitable solvent, such as isopropanol, with water and an aqueous acid catalyst. The aqueous acid catalyst is added to initiate the hydrolysis of the hydrolyzable silane groups. Preferred acid catalysts include mineral acid such as hydrochloric acid, sulfuric acid and nitric acid, or an organic acid, such as acetic acid. Sufficient acid catalyst is added to reduce the pH of the reaction mixture to below 5, preferably a pH of between about 2 to about 4.

(25) The fluorinated silane component may then be added directly to the solution of inorganic and organic components. Alternatively, the fluoro component may be prehydrolyzed with acidified water in a suitable solvent with or without the aid of a fluoro-functionalized surfactant prior to addition to the coating solution. The coating formulation is produced by hydrolysis and condensation of the organic, inorganic and fluoro silane components, leading to a fluoro-functionalized organic-inorganic network through SiOSi bonds.

(26) The thus obtained coating formulation may be mixed in a solvent, or alternatively without a solvent. If used, the solvent may be an alcohol (methanol, ethanol, propanol, isopropanol, butanol, or the like) or other water miscible solvents, such as acetone. The concentration of the solids in the formulation will depend on the desired thickness for the end application, or application methods. Typically however, the formulation will have between about 5 wt. % to about 100 wt. % solids, with a preferred solids concentration being between about 15 wt. % to about 25 wt. %.

(27) A solution of the coating material may be applied to the substrate using any convenient coating method including dip, brush, flow coat, spray, and the like. The curing of the coating can be accomplished at a wide range of temperatures depending upon the desired properties, for example abrasion resistance, flexibility, etc., or thermal limitations for the coated substrate. The coating may be cured at temperatures ranging from about 25 C. to about 150 C., preferably about 75 C. The temperature of curing may be modified for compatibility with the substrate.

(28) The thickness of the cured coating may range from about 0.5 micron to about 20 microns, preferably from about 1 micron to about 5 microns.

(29) The cured hydrophobic coatings as described herein will exhibit optical transparency. Specifically, the cured hydrophobic coatings will exhibit a transparency to visible light of at least about 99.5%, preferably at least about 100%. The coatings will also exhibit a change in haze to visible light less than 1% and preferable less than 0.1%.

(30) The hydrophobic coatings described herein are suitable for coating a variety of substrate materials to provide increased chemical resistance, oil repellency, water repellency, liquid/gas barrier, abrasion resistance, corrosion resistance, and watershed capability to the substrate. Suitable substrates include, but are not limited to, glass, metals such as aluminum and steel, plastics such as polycarbonate and acrylic, hardened cement, concrete, or grout, wood and painted surfaces.

(31) The present invention will be further understood by reference to the following non-limiting examples thereof.

Example 1

(32) A coating material comprising the following formulation was applied as a coating of about 1-5 micron thickness onto a 3/16 inch thick polycarbonate substrate. The coating was cured at a temperature of about 90 C. The coated substrate was thereafter tested for contact angle, watershed angle and visual appearance including transparency, haze and clarity characteristics and compared to an uncoated polycarbonate substrate.

(33) Coating Material Formulation:

(34) Synthesis of Silane Functional Polyol:

(35) Polycaprolactone polyol is measured into cleaned and thoroughly dried glassware. In a separate cleaned and thoroughly dried piece of glassware, the correct molar ratio of isocyanate silane is measured (e.g. a polycaprolactone diol would require twice the molar amount of isocyanate to caprolactone). The isocyanate glassware is covered with a nitrogen blanket and sealed with a rubber septum. The catalyst (i.e. dibutyltin dilaurate) is measured into the polycaprolactone polyol. It is to be 0.1%, by weight, in relation to the combined measurements of isocyanate and polycaprolactone polyol. This bottle is then also covered with a nitrogen blanket and sealed with a rubber septum.

(36) The polycaprolactone polyol and catalyst are set to stir in an ice bath. The isocyanate is slowly added dropwise into the stirring caprolactone-catalyst mixture, using a positive nitrogen flow to control the addition rate. The ice bath should be maintained during the addition step; the reaction generates heat and the ice bath decreases the chances of side reactions. Once all of the isocyanate is added, the reaction is allowed to come to room temperature as the ice bath melts. The reaction is stirred for at least six hours at ambient temperature. The reduction of the isocyanate peak (2270 cm.sup.1) can be measured via FTIR. Once the isocyanate is fully reacted and the peak removed, the polyurethane silane should be bottled and covered with nitrogen. The bottle should be amber glass, or other dark glass, to reduce the exposure to light, as this may cause discoloration of the remaining catalyst.

(37) Standard Coating Synthesis:

(38) The silanes are mixed first. A molar ratio of 0.4 moles organic silane and 0.6 moles of inorganic silane is typical. A small amount of a fluorinated silane, not to exceed 0.5% of the total coating formulation, is added. To this mixture, a fluorosurfactant is added in a comparable amount to the fluorosilane. This will allow for better mixing of the fluorosilane in the solvent-based system.

(39) Next, the solvent is added to the silane mixture. The solvent volume should be approximately 50-80% of the total coating solution, but can be up to 90% depending on the desired coating thickness. Typical solvents include isopropanol, ethanol, or 1-propanol.

(40) Following full dispersal of the silanes into the solvent, acidified water is added. The water should be acidified to a molarity of 0.05-0.1M, depending on the rate of hydrolysis desired. Hydrochloric acid or nitric acid can be used to decrease the pH of the water solution. The acidified water is added in the molar ratio sufficient to hydrolyze the alkoxy groups on the silanes.

(41) The coating solution will be mixed for 1-2 hours depending on hydrolysis completion. Once the silanes are hydrolyzed, the coating is filtered through a 1 m filter prior to coating. Coating application can be performed using a flow, brush, spray or dip coat method for best results. Once coated, allow excess coating to roll off the substrate before curing. The coating is tack free in approximately 15 minutes at ambient temperature. The coating may alternatively be cured at 75-90 C. for at least 30-60 minutes for increased hardness and toughness.

(42) TABLE-US-00001 TABLE 1 Specific coating formulation A B 3-Isocyanatopropyl silane 74.211 g 74.211 g Capa 3050 Polyester polyol 54.0 g 54.0 g Dibutyltindilaurate 0.0641 g 0.0641 g Tetraethoxy silane 35.8 g 35.8 g Perfluoropolyether silane 0.349 g 0.349 g Isopropanol 461 g 461 g IPA-ST Colloidal silica 233 g 0.05M HNO.sub.3 57.1 g 57.1 g

(43) Table 2 shows increased water contact angle and decreased watershedding angle for selected coated substrates.

(44) TABLE-US-00002 TABLE 2 Water contact angle and watershedding angle for coated and upcoated substrates Water Watershed Angle Substrate Contact Angle (120 L) Polycarbonate 80 26 Coating A on Polycarbonate 112 3 Glass 50 30 Coating A on Glass 112 3 Acrylic 75 24 Coating A on Acrylic 111 4

(45) Table 3 shows excellent optical properties for coated substrates, with no loss of transparency, haze, or clarity.

(46) TABLE-US-00003 TABLE 3 Optical properties for coated and uncoated substrates Transparency Haze Clarity Substrate (%) (%) (%) Polycarbonate 92.4 1.5 100 Coating A on polycarbonate 92.4 1.3 99.9 Glass 93.9 0.8 100 Coating A on glass 94.1 0.3 100 Acrylic 94.0 0.69 100 Coating A on Acrylic 94.0 0.4 100

(47) Table 4 shows that the coatings provide improved abrasion resistance to the treated substrate as measured by lower haze values.

(48) TABLE-US-00004 TABLE 4 Effect of Taber Abrasion on light transmission properties for coated and upcoated substrates (ASTM D4060 - 500 g/500cycles; CS10F wheels) Transparency Haze Substrate (%) (%) Polycarbonate 89.0 35.0 Coating A on polycarbonate 90.5 4.9 Polyurethane 89.2 18.8 Coating A on Polyurethane 90.6 5.9 Acrylic 93.3 29.4 Coating A on Acrylic 93.8 4.2

(49) The addition of colloidal silica (Nissan Chemical Snowtex IPA-ST) has the ability to improve abrasion resistance as shown in Table 5.

(50) TABLE-US-00005 TABLE 5 Effect of abrasion (Reciprocal steel wool) with addition of colloidal silica: Coating A vs Coating B Substrate Coating A Coating B Water contact angle 111 112 Water shedding angle 4 4 Transparency 93.6% 93.9% Haze 0.33% 0.48% Haze after 50 cycles abrasion 2.93% 1.45% Haze after 100 cycles abrasion 3.59% 1.06%

Example 2

(51) Synthesis of Silane Functional Polyamine:

(52) The polyamine (e.g. diethylenetriamine) was measured into cleaned and thoroughly dried glassware. In a separate cleaned and thoroughly dried piece of glassware, the correct molar ratio of isocyanate silane was measured (e.g. diethylenetriamine requires three times the molar amount of isocyanate). The isocyanate glassware was covered with a nitrogen blanket and sealed with a rubber septum.

(53) The polyamine was set to stir in an ice bath. The isocyanate was slowly added dropwise into the stirring amine mixture, using a positive nitrogen flow to control the addition rate. The ice bath was maintained during the addition step since the reaction generates heat and the ice bath decreases the chances of side reactions. Once all of the isocyanate was added, the reaction was allowed to come to room temperature as the ice bath melts. The reaction was stirred for at least six hours at ambient temperature. The reduction of the isocyanate peak (2270 cm-1) was measured via FTIR. Once the isocyanate was fully reacted and the peak removed, the polyurea silane was bottled and covered with nitrogen.

(54) While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.