Patent Publication Number: US-2015075603-A1

Title: Novel hydrophobic coatings and methods and compositions relating thereto

Description:
RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application Ser. No. 61/614,074, which was filed on Mar. 22, 2012, and which is incorporated herein by reference for all purposes. 
    
    
     FIELD 
     The present invention relates generally to novel hydrophobic coatings and methods and compositions relating thereto. More particularly, the present invention relates to metal oxide hydrophobic coatings and methods of making and compositions relating thereto. 
     BACKGROUND 
     Many products, such as display devices, electronic devices, medical devices and pharmaceuticals, are sensitive to liquids, such as water, and exposure to them causes product deterioration and/or product performance degradation. Consequently, plastic coatings or layers are commonly used as a protective measure to safeguard against such undesired exposure. 
     Unfortunately, these coatings and layers suffer from durability, adhesion and performance degradation as they are easily scratched or abraded or removed from the surface entirely. As a result, these coatings are typically reapplied in order to retain surface performance. Moreover, this translates into higher maintenance cost for the current protective coatings. 
     What is therefore needed, are novel coating layer designs that do not suffer from the drawbacks encountered by conventional techniques of protecting underlying structures. 
     SUMMARY 
     In view of the foregoing, in one aspect, the present teachings provide a coating layer. The coating layer includes a metal oxide layer that includes a surface having a water contact angle greater than 90 degrees. 
     In accordance with one exemplar structure of the present coating, the metal oxide layer is substantially free of voids. By way of example, the metal oxide layer is more than about 50% free of voids on a volume basis. Preferably, the metal oxide layer is more than about 85% free of voids on a volume basis, and more preferably, the metal oxide layer is more than about 95% free of voids on a volume basis. 
     The metal oxide layer may include a mixed-metal oxide. By way of example, the metal oxide layer includes a first type of metal oxide and a second type of metal oxide, and the first type of metal oxide is different from said second type of metal oxide. In another exemplar structure, the present coating further includes a third type of metal oxide and/or a fourth type of metal oxide. In this example, the third type of metal oxide and the fourth type of metal oxide are different from each other and are also different from the first and the second types of metal oxide. 
     Regardless of whether the third or the fourth types of metal oxide are present, the first and the second types of metal oxide composition are present in said metal oxide layer to form an amorphous metal oxide layer that is more than about 90% amorphous. In accordance with one embodiment of the present teachings, the first type of metal oxide has a concentration that is between about 5% by weight of the metal oxide layer and about 95% by weight of the metal oxide layer and the second type of metal oxide has a concentration that is between about 5% by weight of the metal oxide layer and about 95% by weight of the metal oxide layer. In a preferred embodiment of the present teachings, the first type of metal oxide has a concentration that is between about 20% by weight of the metal oxide layer and about 80% by weight of the metal oxide layer and the second type of metal oxide has a concentration that is between about 20% by weight of the metal oxide layer and about 80% by weight of the metal oxide layer. In a more preferred embodiment of the present teachings, the first type of metal oxide has a concentration that is between about 20% by weight of the metal oxide layer and about 60% by weight of the metal oxide layer and the second type of metal oxide has a concentration that is between about 20% by weight of the metal oxide layer and about 60% by weight of said metal oxide layer. 
     The first type of metal oxide may include a first type of metal and the second type of metal oxide may include a second type of metal, and oxygen is provided in the metal oxide layer in effective amounts to react with a substantial amount of the first and the second types of metal and produce the first and the second types of metal oxides. By way of example, oxygen is provided in the metal oxide layer in a range that is between about 10% and about 50% by weight of the metal oxide layer. The first type of metal oxide may include at least one metal chosen from a group comprising aluminum, silver, silicon, zinc, tin, titanium, tantalum, niobium, ruthenium, gallium, platinum, vanadium and indium. The second type of metal oxide may include at least one metal chosen from a group comprising aluminum, silver, silicon, zinc, tin, titanium, tantalum, niobium, ruthenium, gallium, platinum, vanadium and indium. 
     In one embodiment of the present teachings, the metal oxide layer is substantially amorphous. By way of example, the metal oxide layer is about 5% crystalline. The thickness of the metal oxide layer may be between about 20 nm and about 1 μm. The metal oxide layer is preferably substantially transparent. By way of example, the metal oxide layer transmits between about 70% and about 99% of the light incident upon it. 
     In another aspect, the present teachings provide a solar module. The solar module includes: (i) a solar cell; (ii) a transparent window; and (ii) a coating disposed adjacent to the transparent window, the coating comprising a metal oxide layer that includes a surface having a water contact angle greater than 90 degrees. The solar cell preferably includes at least one member chosen from a group comprising silicon, cadmium telluride, cigs, cis, organic photovoltaics and dye-sensitized solar cells. 
     In yet another aspect, the present teachings provide a display. The display includes: (i) a front glass; and (ii) a coating disposed adjacent to the front glass, such that the coating includes a metal oxide layer that includes a surface having a water contact angle greater than 90 degrees. The display includes one member chosen from a group comprising, for example, electrophoretic display, organic light emitting diode and liquid crystal display. The display is preferably touch-sensitive. The display may be used in a device chosen from a group comprising smartphone, computer tablet, computer monitor and television. 
     In yet another aspect, the present teachings provide a glass-based body. The glass-based body includes: a glass-based substrate; and a coating disposed adjacent to the glass-based substrate. The coating includes a metal oxide layer, which, in turn, includes a surface having a water contact angle greater than 90 degrees. The glass-based body may include a smart window or an insulated glass unit. The smart window preferably includes at least one member chosen from a group comprising electrochromic window, photochromic window and thermochromic window. The insulated glass unit preferably includes a skylight. 
     In yet another aspect, the present teachings provide a flexible object. The flexible object includes: (i) a flexible substrate; and (ii) a coating disposed adjacent to the flexible substrate. The coating includes a metal oxide layer, which, in turn, includes a surface having a water contact angle greater than 90 degrees. The flexible substrate includes at least one member chosen from a group comprising polyester, polyolefin, polyether-ether ketone, polyimide, polyvinyl chloride, polyvinyl alcohol and fluoropolymer. 
     In yet another aspect, the present teachings provide a cooking utensil. The cooking utensil includes: (i) a cooking surface; and (ii) a coating disposed adjacent to the cooking surface. The coating includes a metal oxide layer that includes a surface having a water contact angle greater than 90 degrees. 
     In yet another aspect, the present teachings provide a process of fabricating a coating. The process includes: (i) placing a metal oxide composition inside a chamber; (ii) introducing oxygen inside the chamber; (iii) striking a metal-oxide plasma inside the chamber to produce inside the chamber a metal oxide layer that includes a surface having a water contact angle greater than 90 degrees. The process further preferably includes providing a substrate inside the chamber and wherein striking includes striking the metal-oxide plasma inside the chamber to fabricate the metal oxide layer adjacent to the substrate. Striking the metal oxide plasma may involve at least one technique chosen from a group comprising sputtering, reactive sputtering, chemical vapor deposition and plasma-enhanced chemical vapor deposition. Striking the metal oxide plasma is preferably carried out at a temperature that is between about 10° C. and about 300° C. In preferred embodiments of the present teachings, striking the metal oxide plasma is carried out at a pressure that is between about 0.001 mTorr and about 30 mTorr. 
     In one embodiment, the present process of fabricating the coating further includes evacuating the chamber to create a substantial vacuum inside the chamber, and such evacuation may be carried out before introducing oxygen inside the chamber. The above-mentioned introducing may include introducing an inert gas inside the chamber. 
     In yet another aspect, the present teachings provide metal-oxide coating compositions. The metal-oxide coating compositions include: (i) an effective amount of a first type of metal; (ii) an effective amount of a second type of metal; (iii) an effective amount of oxygen to react with said first type and said second type of metal to produce a first type and a second type of metal oxides; and (iv) wherein said first type and said second type of metal oxides produce a structure that is greater than about 50% (by volume) amorphous. In preferred embodiments of the present compositions, each of the first type and the second type of metal oxides includes at least one member independently chosen from a group comprising aluminum, silver, silicon, zinc, tin, titanium, tantalum, niobium, ruthenium, gallium, platinum, vanadium and indium. 
     The construction of inventive coatings and methods of manufacturing and compositions relating thereto, however, and their advantages, are facilitated by accompanying figures and descriptions of exemplar embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a perspective view of one exemplar inventive coating that is used for a wide variety of substrates. 
         FIG. 1B  shows a perspective view of the coating shown in  FIG. 1A  having disposed thereon water droplets. 
         FIG. 2  shows a side-sectional view of a substrate having disposed thereon the coating and water droplets shown in  FIG. 1B . 
         FIG. 3  is a top view of an exemplar machine used for manufacturing the coating shown in  FIG. 1A . 
         FIG. 4  is a process flow diagram of an exemplar inventive method for making the coating shown in  FIG. 1A . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without limitation to some or all of these specific details. In other instances, certain well-known process steps have not been described in detail in order to not unnecessarily obscure the invention. 
       FIG. 1A  shows a coating  100  according to one example of the present teachings. According to this exemplar teaching, coating  100  is a metal oxide layer that is substantially hydrophobic. In this aspect, water or water vapor contacting coating  100  do so at a contact angle that is greater than about 90 degrees. In preferred embodiments of the present teachings, coating  100  is dense and substantially void free. By way of example, coating  100  is more than about 50% free of voids on a volume basis, is preferably more than about 85% free of voids on a volume basis and more preferably, more than about 95% free of voids on a volume basis. 
     Coating  100  may be a mixed-metal oxide. By way of example, the mixed-metal oxide is a metal oxide alloy. The metal oxide alloy may include at least two different types of metal oxides, i.e., a first metal oxide and a second metal oxide. In one aspect, the first metal oxide is an oxide of one metal, which is chosen from a group comprising aluminum, silver, silicon, zinc, tin, titanium, tantalum, niobium, ruthenium, gallium, platinum, vanadium and indium. The second metal oxide is an oxide of another metal, which is chosen from a group comprising aluminum, silver, silicon, zinc, tin, titanium, tantalum, niobium, ruthenium, gallium, platinum, vanadium and indium. In other embodiments, coatings according to the present teachings include a third type and/or a fourth type of metal oxide. In this embodiment, the third and the fourth types of metal oxides are different from each other, and also different from the first and the second types of metal oxides. 
     According to one present teaching, the first and the second type of metal oxides are present in the metal oxide layer to form an amorphous metal oxide layer that is more than 90% amorphous. In one present arrangement, the first type of metal oxide, present in metal oxide of coating  100 , has a concentration that is between about 5% by weight of the metal oxide and about 95% by weight of the metal oxide. In this arrangement, the second type of metal oxide, present in the metal oxide coating  100 , has a concentration that is between about 5% by weight of the metal oxide and about 95% by weight of the metal oxide. In one preferred arrangement, however, each of the first type and the second type of metal oxides, present in metal oxide of coating  100 , have a concentration that is between about 20% by weight of the metal oxide and about 80% by weight of the metal oxide. In a more preferred arrangement, each of the first type and the second type of metal oxides, present in metal oxide of coating  100 , have a concentration that is between about 20% by weight of the metal oxide and about 60% by weight of the metal oxide. 
     In one aspect of the present teachings, the first type of metal oxide includes a first type of metal and the second type of metal oxide includes a second type of metal. In this aspect, oxygen is present, in the metal oxide of coating  100 , in sufficient amounts to react with a substantial amount of the first type and the second type of metals to produce the first type of metal oxide and the second type of metal oxide, respectively. By way of example, in the metal oxide of coating  100 , enough oxygen is present to react with between about 90% and about 100% of the first type and the second type of metals to produce the first type of metal oxide and the second type of metal oxide, respectively. In accordance with one embodiment of the present teachings, oxygen is present in the metal oxide layer, such as in coating  100 , in an amount that is between about 10% by weight of the metal oxide layer and about 50% by weight of metal oxide layer. Examples of the different types of the first metal oxide and the second metal oxide so produced are listed above. 
     Metal oxide layer of coating  100  may be substantially amorphous. If coating  100  entirely comprises metal oxide, then the coating may be substantially amorphous. According to one present arrangement, metal oxide composition of coating  100  is about 5% crystalline. 
     If the metal oxide composition is present in coating  100  in layer form, then metal oxide layer has a thickness that is between about 20 nm and about 1 μm. In one preferred embodiment of the present teachings, the metal oxide layer is substantially transparent for effective energy transmission to a structure underlying (e.g., layer  306  of  FIG. 2 ) coating  100 . By way of example, the metal oxide composition in coating  100  transmits between about 70% and about 99% of light incident upon the metal oxide layer to the structure underlying coating  100 . 
     In accordance with a preferred embodiment of the present arrangement, coating  100  includes a metal oxide composition or layer having a surface with a liquid (e.g.,) water contact angle greater than 90 degrees. 
       FIG. 1B  shows a present arrangement  200  comprising a coating  202  having disposed thereon one or more liquid (e.g., water) droplets  204 . According to this figure, liquid droplets have contact angle that is greater than 90 degrees. A contact angle is the angle where the liquid/vapor interface meets a solid surface. The fact that the contact angle of liquid  204  with solid  202  is greater than 90 degrees may also convey that solid  202  is hydrophobic in nature. 
       FIG. 2  shows a side view of another present arrangement  300 . According to this figure, liquid droplets  304  have a contact angle that is greater than 90 degrees when the liquid droplets contacts a (solid) coating  302  disposed above an underlying structure  306 . Liquid droplets  304 , and coating  302  are substantially similar to liquid  204  and coating  202 . Underlying structure  306  may be of any type that requires protection from a liquid, such as water. 
     By way of example, present arrangement  300  of  FIG. 2  includes one arrangement chosen from a group comprising solar module, display, glass-based body, flexible object and cooking utensil. For such arrangements, underlying structure  306  include one structure chosen from a group comprising solar cell, front glass, glass-based substrate, flexible substrate and cooking surface, respectively. Other examples of underlying structure  306  include eyeglasses, door hardware, door hinges, metal protection for bridges, metal used in structural applications, plumbing fixtures and mirrors used in bathrooms and in automotive. 
     In embodiments where underlying structure  306  include a solar cell, the solar cell preferably includes at least one member chosen from a group comprising silicon, cadmium telluride, cigs, cis, organic photovoltaics and dye-sensitized solar cells. In those instances where present arrangement  300  includes a display, the display includes at least one member selected from a group comprising electrophoretic display, organic light emitting diode and liquid crystal display. The display contemplated in one aspect of the present teachings is touch-sensitive. In other implementations of the present teachings, the display may be that is used in a smartphone, computer tablet, computer monitor and television. 
     In those embodiments where underlying structure  306  include a glass body, the glass body includes a smart window or an insulated glass (e.g., skylight). Smart window may include at least one member chosen from a group comprising electrochromic window, photochromic window and thermochromic window. If underlying structure  306  is a flexible substrate, then such flexible substrate includes at least one member chosen from a group comprising polyester, polyolefin, polyether-ether-ketone, polyimide, polyvinyl alcohol and fluoropolymer. 
     Although coatings of the present teachings (e.g., coating  100  of  FIG. 1A , coating  202  of  FIG. 1B  and coating  300  of  FIG. 3 ) may be made using any technique well known to those skilled in the art, using a roll-to-roll technique, which provides a relatively high throughput, represents a preferred embodiment of the present teachings.  FIG. 3  shows a top view of a machine  400 , according to one embodiment of the present teachings. Machine  400  may also be thought of as a “roll coater” as it coats a roll of a flexible material (e.g., underlying structure  306  of  FIG. 2 ), which requires protection from a liquid, with a coating (e.g., coating  100  of FIG.  1 , coating  202  of  FIG. 1B  and coating  302  of  FIG. 2 ). Coating machine  400  includes an unwind roller  402 , an idle roller  404 , a take-up roller  406 , a temperature controlled deposition drum  408 , one or more deposition zones  410 , and a chamber  412 . Each of one or more deposition zones  410  include a target material, which is ultimately deposited on the flexible material, a power supply and shutters, as explained below. 
     A coating process, according to one embodiment of the present teachings, begins when a flexible material  414  is loaded onto unwind roller  402 . Flexible material  414  is preferably wrapped around a spool that is loaded onto unwind roller  402 . Typically a portion of the wrapped flexible material is pulled from the spool and guided around idle rollers  404  and deposition drum  408 , which is capable of rotating, so that it connects to take-up roller  406 . In the operating state of coating machine  400 , unwind roller  402 , take-up roller  406  and deposition drum  408  rotate, causing flexible material  414  to displace along various locations around cooled deposition drum  408 . 
     Once flexible material  414  is loaded inside coating machine  400 , the coating process includes striking plasma inside deposition zone  410 . Shutters in the coating zones direct charged particles in the plasma field to collide with and eject the target material so that it is deposited on the flexible material. During the coating process, a temperature of flexible material  414  is controlled using deposition drum  408  preferably to values such that no damage is done to the material. In those embodiments of the present teachings where flexible substrate  414  includes a polymeric material, deposition drum  408  is cooled such that the temperature of the deposition drum is preferably near or below a glass transition temperature of the polymeric material. The cooling action prevents melting of, among other materials, the polymer-based material during the deposition process, and thereby avoids degradation of the polymer-based material that might occur in the absence of deposition drum  408 . 
     As can be seen from  FIG. 3 , multiple deposition zones are provided, each of which may be dedicated to effect deposition of one particular material on the polymeric material. By way of example, the target material, in one of the deposition zones, includes at least one member chosen from a group comprising metal, metal oxide, metal nitride, metal oxy-nitride, metal carbo-nitride, and metal oxy-carbide to facilitate deposition of a coating (e.g., coating  100  of  FIG. 1A , coating  202  of  FIG. 1B  and coating  300  of  FIG. 3 ). By displacing flexible substrate  414  from one location to another, different types and different thicknesses of target material, at different deposition zones, may be deposited on the substrate. Coating machine  400  may be used to implement at least one technique chosen from a group comprising sputtering, reactive ion sputtering, evaporation, reactive evaporation, chemical vapor deposition and plasma-enhanced chemical vapor deposition. 
     It is noteworthy that instead of displacing the substrate from one position to another to facilitate deposition of one or more coatings, the inventive features of the present invention may be realized by holding the material (which is to be coated) stationary and displacing at least a portion of the coating machine or by displacing both the material and the coating machine. 
     Regardless of the specific process implemented for deposition, it will be appreciated that the roll-to-roll techniques of the present teachings allows for very rapid deposition of different types and thicknesses of layers on a material to deposit a protective coating thereon. The roll-to-roll fabrication processes of the present invention realize a very high throughput, which translates into increased revenue. 
       FIG. 4  shows a coating process  500  in accordance with one embodiment of the present teachings. Coating process  500  includes a step  502 , which involves placing a metal composition inside a chamber (e.g., chamber  412  of  FIG. 3 ). Next, in a step  504 , oxygen is introduced inside the chamber. This is followed by a step  506 , which includes striking metal-oxide plasma inside the chamber to produce a hydrophobic coating. The hydrophobic coating is preferably deposited on a flexible material as explained in connection with  FIG. 3 . The hydrophobic layer may be one that, when in contact with water, has a water contact angle greater than 90 degrees. In those instances where the material, which is to be coated, is not a flexible one, coating process may include at least one technique selected from a group comprising sputtering, reactive ion sputtering, evaporation, reactive evaporation, chemical vapor deposition and plasma-enhanced chemical vapor deposition. 
     The coatings according to the present teachings represent a marked improvement over the current techniques of protecting underlying structures, e.g., electronic devices, medical devices and pharmaceuticals. By way of example, external surfaces of the present coatings (e.g., coating  100  of  FIG. 1A , coating  202  of  FIG. 1B  and coating  302  of  FIG. 2 ) may be fabricated such that they are not susceptible to soiling (e.g., due to fingerprints) or accumulation of foreign contamination. As another example, coatings of the present teachings lend themselves to easy cleaning as they may be applied to an external surface for modifying its free surface energy. As yet another example, present coatings are durable as they have a high contact angle of greater than 90 degrees when they come in contact with liquids, such as water. 
     Although illustrative embodiments of the present teachings have been shown and described, other modifications, changes, and substitutions are intended. By way of example, the present teachings disclose coatings substantially impervious to liquids; however, it is also possible to reduce the transport of organic material using the systems, processes, and compositions of the present teachings. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure, as set forth in the following claims.