Hydrophobic coating including DLC on substrate

[0002] This is a continuation-in-part (CIP) of U.S. patent application Ser. No. 09/303,548, filed May 3, 1999, now 6,261,693, and a continuation-in-part (CIP) of U.S. patent application Ser. No. 09/442,805, filed Nov. 18, 1999 now abandoned, the disclosures of which are both hereby incorporated herein by reference.

[0003] This invention relates to a hydrophobic coating system including diamond-like carbon (DLC) provided on (directly or indirectly) a substrate of glass, plastic, ceramic, or the like, and a method of making the same. The coating system may include one or more layers and may be deposited on the substrate utilizing plasma ion beam deposition in certain embodiments.

[0004] Conventional soda inclusive glasses are susceptible to environmental corrosion which occurs when, e.g., sodium (Na) diffuses from or leaves the glass interior, as well as to retaining water on their surfaces in many different environments, including when used as automotive windows (e.g. backlites, side windows, and/or windshields). When water is retained or collects on automotive windows, the water may freeze (i.e. forming ice) in certain environments. Additionally, the more water retained on a windshield, the higher power wiper motor(s) and/or wiper blade(s) required.

[0005] In view of the above, it is apparent that there exists a need in the art for (i) a coated article (e.g. coated glass, ceramic or plastic substrate) that can repel water and/or dirt, and a method of making the same, (ii) a coated soda inclusive glass where the coating(s) reduces the likelihood of visible stains/corrosion forming; and/or (iii) a protective hydrophobic coating system that is somewhat resistant to scratching, damage, or the like.

[0006] It is known to provide diamond like carbon (DLC) coatings on glass. U.S. Pat. No. 5,637,353, for example, states that DLC may be applied on glass. Unfortunately, the DLC of the '353 patent would not be an efficient hydrophobic coating and/or would not be an efficient corrosion minimizer on glass in many instances.

[0007] U.S. Pat. No. 5,900,342 to Visser et al. discloses a fluorinated DLC layer on an electrophotographic element. From about 25-65% fluorine content by atomic percentage is provided at an outermost surface, to provide for low surface energy in an attempt to make removal of xerographic toner easier. Unfortunately, this DLC inclusive layer of the '342 patent would be too soft for use on a glass substrate in automotive applications and the like. Its apparent lack of sp³C—C bonds and/or lack of Si—O bonds contribute to its softness. It is also believed that continuous exposure to sun, rain, humidity, dust, windshield wipers, and/or the environment in general would cause the '342 DLC layer to break down or degrade rather quickly over time.

[0008] Thus, there also exists a need in the art for a DLC inclusive coating that has sufficient hardness and durability to withstand the environment while still exhibiting satisfactory hydrophobic qualities.

[0009] It is a purpose of different embodiments of this invention to fulfill any or all of the above described needs in the art, and/or other needs which will become apparent to the skilled artisan once given the following disclosure.

[0010] An object of this invention is to provide a durable coated article that can shed or repel water (e.g. automotive windshield, automotive backlite, automotive side window, architectural window, bathroom shower glass, residential window, bathroom shower door, coated ceramic article/tile, etc.).

[0011] Another object of this invention is to provide a hydrophobic coating system including one or more diamond-like carbon (DLC) inclusive layers.

[0012] Yet another object of this invention, in embodiments where a hydrophobic coating system includes multiple DLC inclusive layers, is to form (e.g., via ion beam deposition techniques) a first underlying DLC inclusive layer using a first precursor or feedstock gas and a second DLC inclusive layer over the first underlying DLC inclusive layer using a second precursor or feedstock gas. In certain embodiments, the first underlying DLC inclusive layer may function as an anchoring and/or barrier layer while the second or overlying DLC inclusive layer may be more scratch resistant (i.e., harder) and more dense so as to improve the coated article's durability and/or scratch resistance characteristics.

[0013] Another object of this invention is to provide a DLC inclusive coating system including (i) an underlying DLC inclusive layer formed using a precursor/feedstock gas such as tetramethylsilane (TMS), and (ii) another DLC inclusive layer formed over the underlying layer (i) using another precursor/feedstock gas such as acetylene (C₂H₂), in a manner such that layer (i) functions as a barrier and/or anchoring layer and the overlying layer (ii) is of a more durable (e.g., scratch resistance and/or hard) nature. In such embodiments, the underlying DLC inclusive layer (i) may include silicon (Si) so as to provide improved bonding of the overlying layer (ii) to the substrate. The overlying layer may or may not include silicon (Si) in different embodiments.

[0014] Another object of this invention is to provide a coated substrate, wherein a coating system includes sp³carbon-carbon bonds and has a wettability W with regard to water of less than or equal to about 23 mN/m, more preferably less than or equal to about 21 mN/m, even more preferably less than or equal to about 20 mN/m, and in most preferred embodiments less than or equal to about 19 mN/meter. This can also be explained or measured in Joules per unit area (mJ/m²)

[0015] Another object of this invention is to provide a coated substrate, wherein a DLC inclusive coating system includes sp³carbon-carbon bonds and has a surface energy γ_C(on the surface of the coated article) of less than or equal to about 20.2 mN/m, more preferably less than or equal to about 19.5 mN/m, and most preferably less than or equal to about 18 mN/m.

[0016] Another object of this invention is to provide a coated substrate, wherein a DLC inclusive coating system has an initial (i.e. prior to being exposed to environmental tests, rubbing tests, acid tests, UV tests, or the like) water contact angle θ of at least about 80 degrees, more preferably of at least about 100 degrees, even more preferably of at least about 110 degrees, and most preferably of at least about 125 degrees.

[0017] Another object of this invention is to provide a coating system for a glass substrate, wherein the coating system includes a greater number of sp³carbon-carbon (C—C) bonds than sp²carbon-carbon (C—C) bonds. In certain of these embodiments, the coating system need not include many sp²carbon-carbon (C—C) bonds.

[0018] Another object of this invention is to provide a coated glass article wherein a DLC inclusive coating system protects the glass from acids such as HF, nitric, and sodium hydroxide (the coating may be substantially chemically inert).

[0019] Another object of this invention is to provide a coated glass article that is abrasion resistant.

[0020] Another object of this invention is to provide a DLC coating system on a substrate, wherein the coating includes different portions or layers with different densities and different sp³carbon-carbon bond percentages. The ratio of sp³to sp²carbon-carbon bonds may be different in different layers or portions of the coating. Such a coating system with varying compositions at different portions thereof may be continuously formed (e.g., by varying feedstock and/or precursor gas(es) used, and/or by varying the ion energy used in the deposition process, using a single ion beam deposition device). Thus, a DLC inclusive coating system may have therein an interfacial layer with a given density and chemical makeup, and another outer or overlying layer portion having a higher density of sp³carbon-carbon (C—C) bonds and greater scratch resistance and/or durability.

[0021] Another object of this invention is to manufacture a coating system having hydrophobic qualities wherein the temperature of an underlying glass substrate may be less than about 200° C., preferably less than about 150° C., most preferably less than about 80° C., during the deposition of a DLC inclusive coating system. This reduces graphitization during the deposition process, as well as reduces detempering and/or damage to low-E and/or IR-reflective coatings already on the substrate in certain embodiments.

[0022] Yet another object of this invention is to fulfill any and/or all of the aforesaid objects and/or needs.

[0023] In certain embodiments, this invention fulfills any and/or all of the above listed objects and/or needs by providing a coated article comprising:

[0024] a substrate;

[0025] a coating system including first and second diamond-like carbon (DLC) inclusive layers provided on said substrate, said first layer further including silicon (Si); and

[0026] wherein said coating system has an initial contact angle θ with a drop of water of at least about 80 degrees, and an average hardness of at least about 10 GPa.

[0027] In other embodiments, this invention fulfills any and/or all of the above-listed needs and/or objects by providing a method of making a coated article, the method comprising the steps of:

[0028] providing a substrate;

[0029] depositing a first DLC inclusive layer on the substrate using a first gas including silicon (Si); and

[0030] depositing a second DLC inclusive layer on the substrate and on the first DLC inclusive layer using a second gas different than the first gas in a manner such that the resulting article has an initial contact angle θ of at least about 80 degrees.

[0031] In yet other embodiments, this invention fulfills any and/or all of the above listed objects and/or needs by providing a method of making a coated article, comprising the steps of:

[0032] providing a substrate;

[0033] depositing a first diamond-like carbon inclusive layer on the substrate by using at least one of the following gases in an ion beam deposition apparatus: a silane compound, an organosilane compound, an organosilazane compound, and an organo-oxysilicon compound; and

[0034] depositing a second diamond-like carbon inclusive layer directly on and over the first diamond-like carbon inclusive layer by using a hydrocarbon gas in an ion beam deposition apparatus. The same or different ion beam deposition apparatus(es) may be used in the different steps. In certain embodiments, the second diamond-like carbon inclusive layer may have greater hardness and greater density than the underlying first diamond-like carbon inclusive layer, to make the coating system more durable.

[0035] In still other embodiments, this invention fulfills any and/or all of the above listed needs and/or objects by providing a coated article comprising:

[0036] a substrate;

[0037] a coating system including at least one diamond-like carbon (DLC) inclusive layer provided on said substrate; and

[0038] wherein said coating system has an initial contact angle θ with a drop of water of at least about 80 degrees, an initial tilt angle β of no greater than about 30 degrees, and an average hardness of at least about 10 GPa.

[0039] This invention will now be described with respect to certain embodiments thereof, along with reference to the accompanying illustrations.

[0040] FIG. 1 is a side cross sectional view of a coated article according to an embodiment of this invention, wherein a substrate is provided with a DLC inclusive coating thereon having hydrophobic qualities and multiple layers or layer portions.

[0041] FIG. 2 is a side cross sectional view of a coated article according to another embodiment of this invention, wherein the DLC inclusive coating or coating system of FIG. 1 is provided over an intermediate layer(s).

[0042] FIG. 3 is a side cross sectional partially schematic view illustrating a low contact angle θ of a drop on a glass substrate.

[0043] FIG. 4 is a side cross sectional partially schematic view illustrating the coated article of the FIG. 1 or FIG. 2 embodiment of this invention and the contact angle θ of a water drop thereon.

[0044] FIG. 5 is a perspective view of a linear ion beam source which may be used in any embodiment of this invention for depositing a DLC inclusive coating system including one or more DLC inclusive layer(s).

[0045] FIG. 6 is a cross sectional view of the linear ion beam source of FIG. 5.

[0046] FIG. 7 is a diagram illustrating tilt angle as discussed herein in accordance with certain embodiments of this invention.

[0047] FIG. 8 is a chart illustrating the atomic amounts of carbon, oxygen, and silicon (relative only to one another) at different thicknesses of a sample coating system in accordance with the FIG. 1 embodiment of this invention.

[0048] FIG. 9 is a thickness vs. atomic concentration graph illustrating the different amounts of the materials of FIG. 8 as a function of depth into the coating system of the FIG. 8 coating system.

[0049] Referring now more particularly to the accompanying drawings in which like reference numerals indicate like elements throughout the accompanying views.

[0050] FIG. 1 is a side cross sectional view of a coated article according to an embodiment of this invention, wherein a diamond-like carbon (DLC) inclusive coating system 5 including at least two layer 2, 3 is provided on substrate 1. Substrate 1 may be of glass, plastic, ceramic, or the like. In preferred embodiments, each of the layer 2 and 3 of the coating system 5 in the FIG. 1 embodiment includes at least some amount of highly tetrahedral amorphous carbon (ta-C). Highly tetrahedral amorphous carbon (ta-C) forms sp³carbon-carbon bonds, and is a special form of diamond-like carbon (DLC). Coating system 5 functions in a hydrophobic manner (i.e., it is characterized by high water contact angles θ and/or low surface energies as described below), and optionally may be characterized by low tilt angle(s) β in certain embodiments.

[0051] According to certain embodiments of this invention, while layer 2 and 3 each include DLC, the two layers are deposited using different precursor or feedstock gases so that the two layers have different characteristics. In an exemplary embodiment, underlying or anchor DLC inclusive layer 2 is deposited using an ion beam deposition technique utilizing a TMS (tetramethylsilane) inclusive precursor or feedstock gas; while overlying DLC inclusive layer 3 is deposited using an ion beam deposition technique utilizing a C₂H₂(acetylene) inclusive precursor or feedstock gas. It is believed that the underlying layer 2 (a silicon doped DLC alloy) deposited using TMS functions as a barrier layer to prevent certain impurities from getting into or out of the substrate. Moreover, when TMS is used in the deposition process of underlying anchor layer 2, the Si (silicon) in layer 2 helps to enable overlying layer 3 to better bond and/or adhere to the glass via anchor layer 2.

[0052] Surprisingly, it has also been found that the use of anchor layer 2 (e.g., deposited via TMS gas) provides a more continuous/contiguous coating on a glass surface at very thin thicknesses as compared to a DLC inclusive layer deposited using C₂H₂(acetylene) gas directly on glass. As a result, anchor layer 2 can be deposited first directly on the glass at a relatively thin thickness, and the overlying layer 3 need not be as thick as would otherwise be required. In general, the thinner layer 3, the higher the transmission of the overall coating system. Moreover, the provision of anchor layer 2 may enable improved yields to be achievable, as the occurrence of pinholes in the coating system is less likely.

[0053] In such embodiments where DLC inclusive layer 3 is formed on the substrate using a C₂H₂(acetylene) inclusive precursor or feedstock gas and underlying DLC inclusive layer 2 is formed on the substrate using at least a TMS (tetramethylsilane) inclusive precursor or feedstock gas, the layer 2 and 3 tend to intermix with one another during the deposition process. Thus, there may not be a clear line delineating or separating the two layer 2 and 3 in the final product, due to this intermixing (i.e., ion mixing) of the material from the two layers. However, for purposes of simplicity, the two layer 2 and 3 are referred to and illustrated herein as separate layers due to the different deposition processes (e.g., gases and/or energies) used in their respective depositions.

[0054] It has been found that the outer DLC inclusive layer 3 formed using a hydrocarbon gas, such as C₂H₂(acetylene), inclusive precursor or feedstock tends to have a greater hardness and density than does underlying DLC inclusive layer 2 formed using a TMS (tetramethylsilane) inclusive precursor or feedstock gas. For example, in certain exemplary embodiments of this invention, overlying layer 3 may have an average hardness (measured via a nano-indentation hardness measuring technique) of from about 45-85 GPa, more preferably from about 50-70 GPa, and most preferably from about 55-60 GPa. Meanwhile, underlying DLC inclusive layer 2 may have an average hardness of from about 10-35 GPa, and more preferably from about 15-30 GPa. Thus, the overlying layer is harder than the underlying layer, so as to make the end product more scratch and/or abrasion resistant. Using the aforesaid nano-indentation hardness measuring technique, the final coating system 5 including both layer 2 and 3 may have a hardness of from about 25-60 GPa, more preferably from about 30-45 GPa, which is at a hardness value between the respective hardnesses of the two DLC inclusive layer 2 and 3.

[0055] Thus, coating system 5 includes silicon (Si) and DLC inclusive layer 2 which functions to improve the bonding characteristics of overlying and harder DLC inclusive layer 3 to the substrate. While the Si in layer 2 improves the bonding of layer 3 to substrate 1, it is preferred that less Si be provided in overlying layer 3 than in layer 2 because the provision of Si in a DLC inclusive layer may result in decreased scratch resistance and/or decreased hardness. Layer may or may not include Si in different embodiments of this invention. While layer 2 allows for improved bonding to the substrate, the provision of DLC and some sp³carbon-carbon bonds therein allows this anchor layer 2 to have rather high hardness values as discussed above so as to render the resulting product more durable and thus resistant to scratching, abrasions, and the like.

[0056] In embodiments where substrate 1 is of or includes glass (e.g., soda-lime-silica glass), anchor or intermediate DLC inclusive layer 2 may be from about 10 to 250 angstroms (A) thick, more preferably from about 10 to 150 angstroms thick, and most preferably about 50 angstroms thick; while outer DLC inclusive layer 3 may be from about 10 to 250 angstroms thick, more preferably from about 10 to 150 angstroms thick, and most preferably about 60-90 angstroms (Å) thick. However, these thicknesses are not limiting and the layers may be of other appropriate thicknesses in certain embodiments of this invention. Moreover, in embodiments where substrate 1 is of or includes plastic, layer 2, 3 may be of greater thickness(es) than those described above.

[0057] In certain embodiments, layer 3 may have an approximately uniform distribution of sp³carbon-carbon bonds throughout a large portion of its thickness, so that much of the layer has approximately the same density. In such embodiments, layer 2 may include a lesser percentage of sp³carbon-carbon bonds near the interface with substrate 1, with the percentage or ratio of sp³carbon-carbon bonds increasing throughout the thickness of the coating system 5 toward the outermost surface. In overlying DLC inclusive layer 3, at least about 40% (more preferably at least about 60%, and most preferably at least about 80%) of the carbon-carbon bonds in layer 3 are of the sp³carbon-carbon type.

[0058] It is believed that the presence of sp³carbon-carbon bonds in layer 3 increases the density and hardness of the coating system, thereby enabling it to satisfactorily function in automotive environments. Layer 3 may or may not include sp³carbon-carbon bonds in different embodiments, although formation of sp²carbon-carbon bonds is likely in both layer 2 and 3.

[0059] In order to improve the hydrophobic nature of coating system 5, atoms in addition to carbon (C) may be provided in at least overlying layer 3 in different amounts in different embodiments. For example, in certain embodiments of this invention layer 3 (taking the entire layer thickness, or only a thin 10 A thick layer portion thereof into consideration) may include in addition to the carbon atoms of the sp³carbon-carbon bonds, by atomic percentage, from about 0-20% Si (more preferably from about 0-10%), from about 0-20% oxygen (O) (more preferably from about 0-15%), and from about 5-60% hydrogen (H) (more preferably from about 5-35% H. Optionally, layer 3 may include and from about 0-10% (atomic percentage) fluorine (F) (more preferably from about 0-5% F) in order to further enhance hydrophobic characteristics of the coating. In general, the provision of H in layer 3 reduces the number of polar bonds at the coating's surface, thereby improving the coating system's hydrophobic properties by reducing the polar component of the surface energy.

[0060] In certain embodiments, the outermost layer portion (e.g., 5-15 angstrom thick outermost or exterior layer portion) of layer 3 may include additional H and/or F atoms for the purpose of increasing the coating system's hydrophobic qualities. In such embodiments, the deposition of additional H atoms near layer 3's surface results in a more passive or non-polar coating surface. It is noted that deposition of the H atoms near the coating's surface may tend to etch away any sp²or graphite C—C bonds in that area. This increase in H near the layer's surface may also decrease the layer's density at this outermost layer portion.

[0061] FIG. 2 is a side cross sectional view of a coated article according to another embodiment of this invention, including substrate 1 (e.g. glass), hydrophobic DLC inclusive coating system 5 including layer 2, 3, as described above with regard to the FIG. 1 embodiment, and intermediate layer(s) 4 provided between layer 2 and substrate 1. Intermediate layer 4 may be of or include, for example, any of silicon nitride, silicon oxide, an infrared (IR) reflecting layer or layer system, an ultraviolet (UV) reflecting layer of layer system, another DLC inclusive layer(s), or any other type of desired layer(s). In this embodiment, it is noted that coating system 5 is still “on” substrate 1. The term “on” herein means that substrate 1 supports DLC coating system 5, regardless of whether or not other layer(s) (e.g. 4) are provided therebetween. Thus, hydrophobic coating system 5 may be provided directly on substrate 1 as shown in FIG. 1, or may be provided on substrate 1 with another coating or layer 4 therebetween as shown in FIG. 4.

[0062] Exemplar coatings/layers that may be used as low-E or other coating(s)/layer(s) 4 are shown and/or described in any of U.S. Pat. Nos. 5,837,108, 5,800,933, 5,770,321, 5,557,462, 5,514,476, 5,425,861, 5,344,718, 5,376,455, 5,298,048, 5,242,560, 5,229,194, 5,188,887 and 4,960,645, which are all hereby incorporated herein by reference.

[0063] In certain embodiments, coating system 5 is at least about 75% transparent to or transmissive of visible light rays, preferably at least about 85%, and most preferably at least about 95%.

[0064] When substrate 1 is of glass, it may be from about 1.0 to 5.0 mm thick, preferably from about 2.3 to 4.8 mm thick, and most preferably from about 3.7 to 4.8 mm thick. In certain embodiments, another advantage of coating system 5 is that the ta-C therein may reduce the amount of soda (e.g., from a soda-lime-silica glass substrate 1) that can reach the surface of the coated article and cause stains/corrosion. In such embodiments, substrate 1 may be soda-lime-silica glass and include, on a weight basis, from about 60-80% SiO₂, from about 10-20% Na₂O, from about 0-16% CaO, from about 0-10% K₂O, from about 0-10% MgO, and from about 0-5% Al₂O₃. Iron and/or other additives may also be provided in the glass composition of the substrate 1. In certain other embodiments, substrate 1 may be soda lime silica glass including, on a weight basis, from about 66-75% SiO₂, from about 10-20% Na₂O, from about 5-15% CaO, from about 0-5% MgO, from about 0-5% Al₂O₃, and from about 0-5% K₂O. Most preferably, substrate 1 is soda lime silica glass including, by weight, from about 70-74% SiO₂, from about 12-16% Na₂O, from about 7-12% CaO, from about 3.5 to 4.5% MgO, from about 0 to 2.0% Al₂O₃, from about 0-5% K₂O, and from about 0.08 to 0.15% iron oxide. Soda lime silica glass according to any of the above embodiments may have a density of from about 150 to 160 pounds per cubic foot (preferably about 156), an average short term bending strength of from about 6,500 to 7,500 psi (preferably about 7,000 psi), a specific heat (0-100 degrees C) of about 0.20 Btu/lbF, a softening point of from about 1330 to 1345 degrees F, a thermal conductivity of from about 0.52 to 0.57 Btu/hrftF, and a coefficient of linear expansion (room temperature to 350 degrees C) of from about 4.7 to 5.0×10⁻⁶degrees F. Also, soda lime silica float glass available from Guardian Industries Corp., Auburn Hills, Mich., may be used as substrate 1. Any such aforesaid glass substrate 1 may be, for example, green, blue or grey in color when appropriate colorant(s) are provided in the glass in certain embodiments.

[0065] In certain other embodiments of this invention, substrate 1 may be of borosilicate glass, or of substantially transparent plastic, or alternatively of ceramic. In certain borosilicate embodiments, the substrate 1 may include from about 75-85% SiO₂, from about 0-5% Na₂O, from about 0 to 4% Al₂O₃, from about 0-5% K₂O, from about 8-15% B₂O₃, and from about 0-5% Li₂O.

[0066] In still further embodiments, an automotive window (e.g. windshield or side window) including any of the above glass substrates laminated to a plastic substrate may combine to make up substrate 1, with the coating system(s) of any of the FIGS. 1-2 embodiments provided on the outside surface of such a window. In other embodiments, substrate 1 may include first and second glass sheets of any of the above mentioned glass materials laminated to one another, for use in window (e.g. automotive windshield, residential window, commercial architectural window, automotive side window, vacuum IG window, automotive backlight or back window, etc.) and other similar environments.

[0067] When substrate 1 of any of the aforesaid materials is coated with at least DLC inclusive coating system 5 according to any of the FIGS. 1-2 embodiments, the resulting coated article has the following characteristics in certain embodiments: visible transmittance (Ill. A) greater than about 60% (preferably greater than about 70%, and most preferably greater than about 80%), UV (ultraviolet) transmittance less than about 38%, total solar transmittance less than about 45%, and IR (infrared) transmittance less than about 35% (preferably less than about 25%, and most preferably less than about 21%). Exemplary visible, “total solar”, UV, and IR transmittance measuring techniques are set forth in U.S. Pat. No. 5,800,933, incorporated herein by reference.

[0068] Hydrophobic performance of coating system 5 in any of the above embodiments is a function of contact angle θ, surface energy γ, tilt angle β, and/or wettability or adhesion energy W.

[0069] The surface energy γ of coating system 5 may be calculated by measuring its contact angle θ (contact angle θ is illustrated in FIGS. 3-4). A sessile drop 31 of a liquid such as water is placed on the coating as shown in FIG. 4. A contact angle θ between the drop 31 and underlying coating system 5 appears, defining an angle depending upon the interface tension between the three phases in the point of contact. Generally, the surface energy γ_Cof coating system 5 can be determined by the addition of a polar and a dispersive component, as follows: γ_C=γ_CP+γ_CD, where γ_CPis the coating's polar component and γ_CDthe coating's dispersive component. The polar component of the surface energy represents the interactions of the surface which is mainly based on dipoles, while the dispersive component represents, for example, van der Waals forces, based upon electronic interactions. Generally speaking, the lower the surface energy γ_Cof coating system 5, the more hydrophobic the coating and the higher the contact angle θ.

[0070] Adhesion energy (or wettability) W can be understood as an interaction between polar with polar, and dispersive with dispersive forces, between coating system 5 and a liquid thereon such as water. γ^Pis the product of the polar aspects of liquid tension and coating/substrate tension; while γ^Dis the product of the dispersive forces of liquid tension and coating/substrate tension. In other words, γ^P=γ_LP*γ_CP; and γ^D=γ_LD*γ_CD; where γ_LPis the polar aspect of the liquid (e.g. water), γ_CPis the polar aspect of coating system 5; γ_LDis the dispersive aspect of liquid (e.g. water), and γ_CDis the dispersive aspect of coating system 5. It is noted that adhesion energy (or effective interactive energy) W, using the extended Fowkes equation, may be determined by:

[0071] W=[γ_LP*γ_CP]^½+[γ_LD*γ_CD]^½=γ_l(1+cosθ),

[0072] where γ_lis liquid tension and θ is the contact angle. W of two materials (e.g. coating system 5, specifically outermost or overlying layer 3 and water thereon) is a measure of wettability indicative of how hydrophobic the coating system is.

[0073] When analyzing the degree of hydrophobicity of outermost layer 3 of the coating system 5 with regard to water, it is noted that for water γ_LPis 51 mN/m and γ_LDis 22 mN/m. In certain embodiments of this invention, the polar aspect γ_CPof surface energy of layer 3 is from about 0 to 0.2 (more preferably variable or tunable between 0 and 0.1) and the dispersive aspect γ_CDof the surface energy of layer 3 is from about 16-22 mN/m (more preferably from about 16-20 mN/m). Using the above-listed numbers, according to certain embodiments of this invention, the surface energy γ_Cof layer 3 (and thus coating system 5) is less than or equal to about 20.2 mN/m, more preferably less than or equal to about 19.5 mN/m, and most preferably less than or equal to about 18.0 mN/m; and the adhesion energy W between water and layer 3 is less than about 25 mN/m, more preferably less than about 23 mN/m, even more preferably less than about 20 mN/m, and most preferably less than about 19 mN/m. These low values of adhesion energy W and layer 3 surface energy γ_C, and the high initial contact angles θ achievable, illustrate the improved hydrophobic nature of the coating system 5 according to different embodiments of this invention. While layer 3 functions to provide much of the hydrophobic nature of the coating system 5, underlying DLC inclusive layer 2 improves the bonding characteristics of the coating system 5 to the substrate 1 (e.g., glass substrate) and yet still provides adequate hardness characteristics regarding the coating system 5 as a whole.

[0074] The initial contact angle θ of a conventional glass substrate 1 with sessile water drop 31 thereon is typically from about 22-24 degrees, although it may dip as low as 17 or so degrees in some circumstances, as illustrated in FIG. 3. Thus, conventional glass substrates are not particularly hydrophobic in nature. The provision of coating system 5 on substrate 1 causes the contact angle θ to increase to the angles discussed herein, as shown in FIG. 4 for example, thereby improving the hydrophobic nature of the article. As discussed in Table 1 of 09/303,548, the contact angle θ of a ta-C DLC layer is typically from about 5 to 50 degrees. However, the makeup of DLC-inclusive coating system 5 described herein enables the initial contact angle θ between overlying layer 3 and a water drop (i.e. sessile drop 31 of water) to be increased in certain embodiments to at least about 80 degrees, more preferably to at least about 100 degrees, even more preferably at least about 110 degrees, and most preferably at least about 125 degrees, thereby improving the hydrophobic characteristics of the DLC-inclusive coating system. An “initial” contact angle θ means prior to exposure to environmental conditions such as sun, rain, abrasions, humidity, etc.

[0075] FIGS. 5-6 illustrate an exemplary linear or direct ion beam source 25 which may be used to deposit layer 2 and 3 of coating system 5, clean a substrate, or surface plasma treat a DLC inclusive coating with H and/or F according to different embodiments of this invention. Ion beam source 25 includes gas/power inlet 26, anode 27, grounded cathode magnet portion 28, magnet poles 29, and insulators 30. A 3 kV DC power supply may be used for source 25 in some embodiments. Linear source ion deposition allows for substantially uniform deposition of layer 2 and 3 as to thickness and stoichiometry.

[0076] Ion beam source 25 is based upon a known gridless ion source design. The linear source is composed of a linear shell (which is the cathode and grounded) inside of which lies a concentric anode (which is at a positive potential). This geometry of cathode-anode and magnetic field 33 gives rise to a close drift condition. The magnetic field configuration further gives rise to an anode layer that allows the linear ion beam source to work absent any electron emitter. The anode layer ion source can also work in a reactive mode (e.g. with oxygen and nitrogen). The source includes a metal housing with a slit in a shape of a race track as shown in FIGS. 5-6. The hollow housing is at ground potential. The anode electrode is situated within the cathode body (though electrically insulated) and is positioned just below the slit. The anode can be connected to a positive potential as high was 3,000 volts. Both electrodes may be water cooled in certain embodiments. Feedstock/precursor gases, described herein, are fed through the cavity between the anode and cathode. The gas(es) used determines the make-up of the resulting layer deposited on an adjacent substrate 1.

[0077] The linear ion source also contains a labyrinth system that distributes the precursor gas (e.g., TMS (i.e., (CH₃)₄Si or tetramethylsilane); acetylene (i.e., C₂H₂); 3MS (i.e., trimethyldisilane); DMS (i.e., dichloro-dimethylsilane); HMDSO (i.e., hexamethyldisiloxane); TEOS (i.e., tetraethoxysilane), etc.) fairly evenly along its length and which allows it to supersonically expand between the anode-cathode space internally. The electrical energy then cracks the gas to produce a plasma within the source. The ions are expelled out at energies in the order of eVc-a/2 when the voltage is Vc-a. The ion beam emanating from the slit is approximately uniform in the longitudinal direction and has a Gaussian profile in the transverse direction. Exemplary ions 34 are shown in FIG. 6. A source as long as one meter may be made, although sources of different lengths are anticipated in different embodiments of this invention. Finally, electron layer 35 is shown in FIG. 6 completes the circuit thereby enabling the ion beam source to function properly.

[0078] In alternative embodiments of this invention, an ion beam source device or apparatus as described and shown in FIGS. 1-3 of U.S. Pat. No. 6,002,208 (hereby incorporated herein by reference in its entirety) may be used to deposit/form DLC inclusive layer 2 and 3 on substrate 1 in accordance with either the FIG. 1 or FIG. 2 embodiment of this invention. One or multiple such ion beam source devices may be used.

[0079] In certain embodiments, the same ion beam source 25 may be used to deposit both of layer 2 and 3; one after the other. In other embodiments of this invention two separate ion beam sources may be provided, a first for depositing layer 2 on substrate 1 and the second for depositing layer 3 over layer 2. In certain embodiments, another ion beam source may be provided for initially cleaning the surface of substrate 1 prior to deposition of layer 2, 3.

[0080] Referring to FIG. 7, tilt angle β characteristics associated with certain embodiments of this invention will be explained. In a hydrophobic coating, it is often desirable in certain embodiments to have both a high contact angle θ (see FIG. 4) in combination with a low tilt angle β. As shown in FIG. 7, tilt angle β is the angle relative to the horizontal 43 that the coated article must be tilted before a 30 μL (volume) drop 41 (e.g., of water) thereon begins to flow down the slant at room temperature without significant trail. A low tilt angle means that water and/or other liquids may be easily removed from the coated article upon tilting the same or even in high wind conditions. In certain embodiments of this invention, coated articles herein (with layer 2, 3) have an initial tilt angle β of no greater than about 30 degrees, more preferably no greater than about 20 degrees, and even more preferably no greater than about 10 degrees. In certain embodiments, the tilt angle does not significantly increase over time upon exposure to the environment and the like, while in other embodiments it may increase to some degree over time.

[0081] Referring to FIGS. 1-2 and 5-6, an exemplary method of depositing a coating system 5 on substrate 1 will now be described. This method is for purposes of example only, and is not intended to be limiting.

[0082] Prior to coating system 5 being formed on glass substrate 1, the top surface of substrate 1 is preferably cleaned by way of a first linear or direct ion beam source. For example, a glow discharge in argon (Ar) gas or mixtures of Ar/O₂(alternatively CF₄plasma) may be used to remove any impurities on the substrate surface. Such interactions are physio-chemical in nature. This cleaning creates free radicals on the substrate surface that subsequently can be reacted with other monomers yielding substrate surfaces with specialized properties. The power used may be from about 100-300 Watts. Substrate 1 may also be cleaned by, for example, sputter cleaning the substrate prior to actual deposition of coating system 5; using oxygen and/or carbon atoms at an ion energy of from about 800 to 1200 eV, most preferably about 1,000 eV.

[0083] After cleaning, the deposition process begins using a linear ion beam deposition technique via second ion beam source as shown in FIGS. 5-6, or in FIGS. 1-3 of the '208 patent; with a conveyor having moved the cleaned substrate 1 from first source to a position under the second source. The second ion beam source functions to deposit a ta-C (or DLC) inclusive layer 2 on substrate 1, with at least TMS being used as the precursor or feedstock gas fed through the source. Because of the Si in the TMS gas used in the source, the resulting layer 2 formed on substrate includes Si as well as DLC. The Si portion of DLC inclusive layer 2 enables good bonding of layer 2 to substrate 1, and thus will also improve the bonding characteristics of layer 3 to the substrate via layer 2.

[0084] After layer 2 has been formed, either the same or another ion beam source is used to deposit layer 3 over (directly on in preferred embodiments) layer 2. To deposit overlying DLC inclusive layer 3, another gas such as at least C₂H₂is fed through the source so that the source expels the ions necessary to form layer 3 overlying layer 2 on substrate 1. The C₂H₂gas may be used alone, or in exemplary alternative embodiments the gas may be produced by bubbling a carrier gas (e.g. C₂H₂) through a precursor monomer (e.g. TMS or 3MS) held at about 70 degrees C (well below the flashing point). Acetylene feedstock gas (C₂H₂) is used in certain embodiments to prevent or minimize/reduce polymerization and to obtain an appropriate energy to allow the ions to penetrate the surface on the substrate and subimplant therein, thereby causing layer 3 to intermix with layer 2 in at-least an interface portion between the layers. The actual gas flow may be controlled by a mass flow controller (MFC) which may be heated to about 70 degrees C. In certain optional embodiments, oxygen (O₂) gas may be independently flowed through an MFC. The temperature of substrate 1 may be room temperature; an arc power of about 1000 W may be used; precursor gas flow may be about 25 sccm; the base pressure may be about 10⁻⁶Torr. The optimal ion energy window for the majority of layer 2, 3 is from about 100-1,000 eV (preferably from about 100-400 eV) per carbon ion. At these energies, the carbon in the resulting layer 2, 3 emulates diamond, and sp³C—C bonds form. However, compressive stresses can develop in ta-C when being deposited at 100-150 eV. Such stress can reach as high as 10 GPa and can potentially cause delamination from many substrates. It has been found that these stresses can be controlled and decreased by increasing the ion energy during the deposition process to a range of from about 200-1,000 eV.

[0085] As stated above, layer 2 and 3 intermix with one another at the interface between the two layers, thereby improving the bonding between the layers. At particle energies (carbon energies) of several hundred eV, a considerable material transport can take place over several atomic distances. This is caused by the penetration of fast ions and neutrals as well as by the recoil displacement of struck atoms. At sufficiently high particle energies and impact rates, there is an enhanced diffusion of the thermally agitated atoms near the film surface that occurs via the continuously produced vacancies. In the formation of ta-C:H, these effects can help improve film adhesion by broadening the interface (i.e., making it thicker, or making an interfacial layer between the two layer 2 and 3 (or between layer 2 and glass 1) due to atom mixing). After layer 2 is deposited, the carbon from layer 3 implants into layer 2 (i.e., subimplantation) so as to make the bond better of layer 3 to the substrate. Thus, layer 2 and 3 are contiguous due to this intermixing, and this “smearing” between the layers enhances the adhesion of layer 3 to both layer 2 and thus the substrate 1.

[0086] High stress is undesirable in the thin interfacing portion of layer 2 that directly contacts the surface of a glass substrate 1 in the FIG. 1 embodiment. Thus, for example, the first 1-40% thickness (preferably the first 1-20% and most preferably the first 5-10% thickness) of layer 2 may optionally be deposited on substrate 1 using high anti-stress energy levels of from about 200-1,000 eV, preferably from about 400-500 eV. Then, after this initial interfacing layer portion of layer 2 has been grown, the ion energy in the ion deposition process may be decreased (either quickly or gradually while deposition continues) to about 100-200 eV, preferably from about 100-150 eV, to grow the remainder of layer(s) 2 and/or layer 3. Thus, in certain embodiments, because of the adjustment in ion energy during the deposition process, DLC inclusive layer 2, 3 may optionally have different densities and different percentages of sp³C—C bonds at different layer portions thereof (the lower the ion energy, the more sp³C—C bonds and the higher the density).

[0087] While direct ion beam deposition techniques are preferred in certain embodiments, other methods of deposition may also be used in different embodiments. For example, filtered cathodic vacuum arc ion beam techniques may be used to deposit layer 2, 3. Also, in certain embodiments, CH₄may be used as a feedstock gas during the deposition process instead of or in combination with the aforesaid C₂H₂gas.

[0088] A third or even fourth ion beam source is optional. In certain embodiments of this invention, the hydrophobicity of coating system 5 can be further enhanced using a plasma treatment by another source or grafting procedure after the main portion of DLC-inclusive coating system 5 has been deposited. This technique using a another ion beam source may remove certain polar functional groups at the outermost surface of layer 3, thereby altering the surface chemical reactivity (i.e. lowering surface energy) while the bulk of coating system 5 remains the same or substantially unaffected. In such optional embodiments, after a conveyor has moved the DLC-coated substrate from the second source station to a position under this source, the plasma treatment by this source may introduce, e.g., hydrogen (H) atoms into the outermost surface of layer 3, thereby making the coating's surface substantially non-polar and less dense than the rest of the coating. These H atoms are introduced, because H₂and/or ArH₂feedstock gas is used by this source in certain embodiments. Thus, third source 63 does not deposit any significant amounts of C atoms or Si atoms; but instead treats the outermost surface of the ta-C:SiO coating by adding H atoms thereto in order to improve its hydrophobic characteristics. This plasma treatment may also function to roughen the otherwise smooth surface. It is noted that H₂feedstock gas is preferred in the ion beam source when it is not desired to roughen the surface of coating system 5, while ArH₂feedstock gas is preferred in surface roughing embodiments. In other optional embodiments, this source may be used to implant F ions/atoms in to the outermost surface of layer 3.

[0089] Coating system 5 according to different embodiments of this invention may have the following characteristics: coefficient of friction of from about 0.02 to 0.15; good abrasion resistance; an average density of from about 2.0 to 3.0 g/cm²; permeability barrier to gases and ions; surface roughness less than about 0.5 nm; inert reactivity to acids, alkalis, solvents, salts and water; corrosion resistance; variable or tunable surface tension; tunable optical bandgap of from about 2.0 to 3.7 eV; IR transmission @ 10 μm of at least about 85%; UV transmission @ 350 nm of no greater than about 30%; tunable refractive index @ 550 nm [n=1.6 to 2.3; k=0.0001 to 0.1], permittivity @ GHz 4.5; an undoped electrical resistivity of at least about 10¹⁰Ω/cm; dielectric constant of about 11 @ 10 kHz and 4 @ 100 MHz; an electrical breakdown strength (V cm⁻¹) of about 10⁶; thermal coefficient of expansion of about 9×10⁻⁶/C; and thermal conductivity of about 0.1 Wcm K.

[0090] Three examples of TMS-formed DLC inclusive anchor layer 2 are as follows. Each such layer 2 was deposited on substrate 1 using tetramethylsilane (TMS) and O₂gas introduced within the linear ion beam source apparatus of FIGS. 5-6. All samples were of approximately the same thickness of about 750 A. A low energy electron flood gun was used to sharpen the spectral analysis conducted by x-ray photo electron spectroscopy (XPS) for chemical analysis. In XPS analysis of a layer 2, high energy x-ray photons (monochromatic) impinge on the surface of the layer. Electrons from the surface are ejected and their energy and number (count) measured. With these measurements, one can deduce the electron binding energy. From the binding energy, one can determine three things: elemental fingerprinting, relative quantity of elements, and the chemical state of the elements (i.e. how they are bonding). Components used in the XPS analysis include the monochromatic x-ray source, an electron energy analyzer, and electron flood gun to prevent samples from charging up, and an ion source used to clean and depth profile. Photoelectrons are collected from the entire XPS field simultaneously, and using a combination of lenses before and after the energy analyzer are energy filtered and brought to a channel plate. The result is parallel imaging in real time images. Sample Nos. 1-3 of DLC inclusive layer 2 were made and analyzed using XPS, which indicated that the samples included the following chemical elements by atomic percentage (H was excluded from the chart below).

[0091] H was excluded from the XPS analysis because of its difficulty to measure. Thus, H atoms present in the coating Sample Nos. 1-3 were not taken into consideration for these results. For example, if Sample No. 1 included 9% H by atomic percentage, then the atomic percentages of each of the above-listed elements C, O, Si and F would be reduced by an amount so that all five atomic percentages totaled 100%. As can be seen, F is optional and need not be provided. Oxygen is also optional.

[0092] While TMS is described above as a primary precursor or feedstock gas utilized in the ion beam deposition source for depositing the underlying DLC inclusive layer 2, other gases may in addition or instead be used. For example, other gases such as the following may be used either alone, or in combination with TMS, to form layer 2: silane compounds such as TMS, diethylsilane, TEOS, dichlorodimethylsilane, trimethyldisilane, hexamethyldisiloxane, organosilane compounds; organosilazane compounds such as hexamethyldisilazane and tetramethyldisilazane; and/or organo-oxysilicon compounds such as tetramethyldisiloxane, ethoxytrimethylsilane, and organo-oxysilicon compounds. Each of these gases includes Si; and each of these gases may be used either alone to form layer 2, or in combination with one or more of the other listed gases. In certain embodiments, the precursor gas may also further include N, F and/or O in optional embodiments, for layer 2 and/or layer 3.

[0093] With regard to layer 3, a hydrocarbon gas such as acetylene is preferred for forming the layer. However, other gases such as ethane, methane, butane, cyclohexane, and/or mixtures thereof may also (or instead) be used in the ion beam source to form layer 3.

[0094] In certain embodiments of this invention, coating system 5 has a contact angle of at least about 70°, more preferably at least about 80°, and even more preferably at least about 100° after a taber abrasion resistance test has been performed pursuant to ANSI Z26.1. The test utilizes 1,000 rubbing cycles of coating system 5, with a load a specified in Z26.1 on the wheel(s). Another purpose of this abrasion resistance test is to determine whether the coated article is resistive to abrasion (e.g. whether hazing is less than 4% afterwards). ANSI Z26.1 is hereby incorporated into this application by reference.

[0095] FIGS. 8-9 illustrate the makeup of a coating system 5 including layer 2 and 3 according to an embodiment of this invention. X-ray Photoelectron Spectroscopy (XPS)/Electron Spectroscopy for Chemical Analysis (ESCA) was used to develop these graphs from the sample product. This is used to characterize inorganic and organic solid materials. In order to perform such measurements on a sample product as was done with regard to FIGS. 8-9, the surface of the coating system was excited with Al monochromatic x-rays (1486.6 eV) and the photoelectrons ejected from the surface were energy analyzed. Low resolution analysis, i.e., a survey scan, can be used to identify elements (note that H, He, and F were not included in the analysis of FIGS. 8-9 even though at least H and/or F were present in the coating system 5) and establish the illustrated concentration table in units of atomic percentage (%). Detection limits were from about 0.1 to 0.05 atom %. High resolution analysis of individual photoelectron signals, i.e., C 1s, can be used to identify chemical bonding and/or oxidation state. Information on the surface is obtained from a lateral dimension as large as 1 mm diameter and from a depth of 0-10 μm. To acquire information from slightly greater depths, angle resolved measurements can be made.

[0096] Referring more particularly to FIG. 8, that figure illustrates the makeup with regard to C, O and Si throughout the thickness of coating system 5 in the FIG. 1 embodiment, including both of layer 2 and 3. Cycle number 1 is at the surface of the coating system 5 where layer 3 meets the surrounding atmosphere, while cycle number 19 is believed to be within the underlying glass substrate 1. Thus, it is believed that the interface between glass substrate 1 and underlying DLC inclusive layer 2 is at about cycle number 15 where the C % begins to significantly decrease. The “time” and “depth” columns refers to depth into coating system 5 from the exterior surface thereof as compared to the depth into a conventional SiO₂that would be achieved over the same time period. Thus, the angstrom depth illustrated in FIG. 8 is not the actual depth into coating system 5, but instead is how deep into a SiO₂layer the sputtering would reach over the corresponding time.

[0097] In FIG. 8, cycle number 1 may be affected from contamination of the outer surface of the coating system 5 and may be disregarded in effect. At least cycle numbers 2-6 refer or correspond to overlying DLC inclusive layer 3 as evidenced by the high carbon amounts (i.e., greater than 94% C in layer 3 according to FIG. 8). Meanwhile, at least cycle numbers 9-13 refer or correspond to underlying DLC inclusive layer 2, as evidence by the lower C amounts shown in FIG. 8. Thus, it can be seen that layer 2 includes less C than layer 3, and is therefor less dense and less hard. Moreover, it can be seen that layer 2 includes more Si than layer 3 (and optionally more oxygen (O)). Cycle numbers 7-8 refer or correspond to the interface or intermixing layer portion between layer 2 and 3; as the coating system 5 at these thickness portions includes C and Si amounts between the amounts in respective layer 2 and 3. Thus, these cycle numbers 7-8 illustrate the intermixing (i.e., subimplantation of atoms from layer 3 in layer 2) or smearing between layer 2, 3 discussed herein. Meanwhile, cycle numbers 14-15 refer or correspond to the interfacial layer between layer 2 and the glass substrate 1, while cycle numbers 16-19 refer or correspond to the glass itself with its high SiO₂content.

[0098] Still referring to FIG. 8, it can be seen that layer 2 (cycles 9-13) includes more Si than layer 3. Moreover, it can be seen that portions of layer 2 (cycles 9-13) generally include at least about twice as much C as Si; while portions of layer 3 (cycles 2-6) generally include at least about ten (10) times as much C as Si, more preferably at least about twenty (20) times as much C as Si (from an atomic perspective). Additionally, it can be seen that select cross sections of layer 2 include at least about five (5) times as much Si as select cross sections of layer 3, more preferably at least about seven (7) times as much, and most preferably at least about eight (8) times as much. Elements such as H and F, one or both of which are in layer 2 and/or 3, are not shown in the FIG. 8 analysis. Finally, it can be seen in FIG. 8 (and in FIG. 9) that throughout a substantial portion of coating system 5 (i.e., at least about half of the thickness of the DLC portion of the coating system) the amount of C progressively increases through the thickness toward the exterior surface of the coating system, while the amount of Si progressively decreases through the thickness toward the exterior surface of the coating system. Optionally, the amount of oxygen (O) may also progressively decrease through the thickness toward the exterior surface of the coating system as shown in FIGS. 8-9.

[0099] FIG. 9 is a depth (relative to SiO₂) versus atomic concentration graph illustrating the respective amounts of C, O and Si atoms in the coating system 5 sample analyzed in FIG. 8. It is noted that these three materials were the only types analyzed in these two Figures so that the atomic concentration percentage is relative to only these three types of atoms. As can be seen in FIG. 9, the C percentage is higher the closer to the exterior surface of layer 3 one gets which is indicative of the greater hardness and density of layer 3 relative to layer 2. Moreover, it can be seen that the Si atom percentage increases the deeper one goes into the coating system 5 illustrating that layer 2 has more Si atoms than layer 3 at certain cross sectional thickness thereof. It can also be seen that the number of O atoms increases the deeper into the coating system one goes.

[0100] While the embodiments described above illustrate only two DLC inclusive layer 2 and 3, it will be understood by those skilled in the art that additional DLC inclusive layers may be provided in other embodiments of this invention. Such additional DLC inclusive layer(s) may be located under layer 2, or between layer 2 and 3. In still further embodiments of this invention, other types of layer(s) may be provided between layer 2 and 3.

[0101] As will be appreciated by those skilled in the art, coated articles according to different embodiments of this invention may be utilized in the context of automotive windshields, automotive side windows, automotive backlites (i.e., rear windows), architectural windows, residential windows, ceramic tiles, shower doors, and the like.

[0102] Once given the above disclosure, many other features, modifications, and improvements will become apparent to the skilled artisan. Such other features, modifications, and improvements are, therefore, considered to be a part of this invention, the scope of which is to be determined by the following claims.