Abstract:
The present invention relates to self-cleaning reversible window assemblies comprising one or more photocatalytic layers deposited on two generally opposed major surfaces of a transparent substrate. When the major surfaces are exposed to ultraviolet radiation, such as that present in sunlight, the photocatalytic layers chemically degrade organic contaminants deposited on the surfaces of the substrate. The self-cleaning reversible window assemblies of the present invention are reversible thereby allowing for either of the opposed major surfaces to be exposed to ultraviolet radiation from sunlight.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to reversible window assemblies which include features that provide self cleaning characteristics. More particularly, the present invention provides a reversible window assembly wherein one or more photocatalytic coatings are applied to opposed surfaces of a transparent substrate.  
         BACKGROUND OF THE INVENTION  
         [0002]    There is an increasing search to functionalize glazings on glass substrates by depositing at the surface thereof thin layers intended to confer a specific property according to the targeted application. One problem a functional coating is intended to remedy is the reduction or prevention of window soiling. Keeping windows and other glass surfaces clean is a relatively expensive and time-consuming process. While cleaning any individual window is not terribly troublesome, keeping a larger number of windows clean can be a significant burden. For example, with modern glass towers, it takes significant time and expense to have window washers regularly clean the exterior and interior surfaces of the windows.  
           [0003]    Windows and other transparent substrates can become “dirty” or “soiled” in a variety of ways. Two of the primary manners in which windows can collect dirt involve the action of water on the glass surface. First, the water itself can deposit dirt on the surface of a window. Obviously, dirty water landing on a window will leave residue on the window upon drying. Even if relatively clean water lands on a window, each water droplet will tend to include and/or collect dust and other airborne particles. These particles, and any other chemicals that become dissolved in the water, will become more concentrated over time. The result is a characteristic spot (i.e. a drying ring) on the glass surface.  
           [0004]    The second way in which water tends to give a window or other glass surface a soiled or less attractive appearance is tied to an attack on the glass surface itself. As a droplet of even relatively clean water sits on a glass surface, it will begin to leach alkaline components from the glass. For typical soda lime glass, the soda and lime will be leached out of the glass, increasing the pH of the droplet. As the pH increases, the attack on the glass surface will become more aggressive. As a result, the glass that underlies a drying water droplet will become somewhat rough by the time the water droplet has completely dried. In addition, the alkaline components that were leached out of the glass will be re-deposited on the glass surface as a drying ring. Not only does this dried alkaline material detract from the appearance of the glass, it also has a tendency to form a solution when the glass surface is wetted again. Thus, water droplets that subsequently coalesce on the glass surface will tend to have a high pH as soon as they are formed.  
           [0005]    Additionally, transparent substrates regularly accumulate foreign matter due simply to use. The touching of the transparent substrate by humans, birds, animals, plants or any other living species can leave marks, such as organic residue on the surface. Therefore, in order to maintain a clear surface and preserve the overall appearance and integrity of the transparent substrate, some action to clean the substrate must be taken.  
           [0006]    It is understood that “self-cleaning” glazings or coatings on transparent substrates, like windows, can maintain over time the appearance and surface properties of the substrate. In particular, such glazings or coatings require less frequent cleaning and/or improve the visibility of the substrate by removing dirt or soiling material which is gradually deposited at the surface of the substrate over time.  
           [0007]    Various products have been developed to enable a self-cleaning substrate. One such product currently being investigated includes the application of self-cleaning photocatalytic coatings to a substrate. Research in this area is founded on the ability of certain coatings, such as metal oxides, to absorb ultraviolet radiation and photocatalytically break down organic materials such as oil, plant matter, fats, greases and other organic matter deposited on the surface of the substrate. The most powerful of these photocatalytic metal oxides appears to be titanium dioxide (titania). However, other metal oxides also appear to possess photocatalytic properties. Examples of photocatalytic coatings include, but are not limited to, oxides of titanium, iron, silver, copper, tungsten, aluminum, zinc, strontium, palladium, gold, platinum, nickel, and cobalt. In addition to being photocatalytic, titanium dioxide is hydrophilic which makes possible complete wetting of the substrate surface when water condensation or rain is deposited on the coating. The hydrophlicity is quickly lost when the ultraviolet radiation stops, but it can be fully recovered after re-exposure to ultraviolet radiation.  
           [0008]    Generally, photocatalytic reactions occur by the irradiation of light on semiconductors. For example, when light contacts the surface of a transparent substrate that is coated with a photocatalytic coating, the photon energy at the surface of the substrate increases. When the photon energy is greater than or equal to the band gap energy of the photocatalytic coating, an electron (e−) is promoted from the valence band into the conduction band, leaving a void. Some of the excited electrons in the conduction band and some of the voids in the valence band recombine and dissipate the input energy as heat. However, a number of voids can diffuse to the surface of the titanium dioxide and react with molecules absorbed on the surface to form radicals, such as —OH radicals, which can decompose organic compounds existing on the surface into CO 2  and H 2 O. Moreover, to the extent that the residue may survive this photocatalysis, such residue may be more easily removed by washing or, for outdoor applications, by run-off water, such as rainwater.  
           [0009]    Various light sources, such as fluorescent lamps or sunlight, are capable of emitting light having a higher energy than the band gap energy of a photocatalyst. The photoexcitation wavelength for a photocatalyst such as titania is in the ultraviolet region. In this instance, when the titania-containing coating is exposed to the sunlight, it can be advantageously photoexcited by ultraviolet light contained in the sunlight.  
           [0010]    The utilization of coatings on transparent substrates for insulation or antireflection purposes has been disclosed in previously issued patents. For example, in U.S. Pat. No. 4,235,048, Gillery discloses the use of coated glass articles in a reversible window unit for insulation purposes. More particularly, the coated glass surfaces are used to reflect or absorb incident solar energy depending upon how the coated surface is oriented.  
           [0011]    Additionally, photocatalytic coatings have been utilized and disclosed in art for preserving and cleaning the outside surface of a substrate in U.S. Pat. No. 6,090,489 (Hayakawa et. al.) and U.S. Pat. No. 6,103,363 (Boire et. al). This provides the benefit of a self-cleaning outside surface, but does nothing to clean the self-clean the inside surface.  
           [0012]    It would be advantageous to provide a reversible window unit with photocatalytic coatings on each side of the glass surface for self-cleaning purposes that can be activated or reactivated, depending on the orientation of the window unit, by exposure to the ultraviolet radiation in the sunlight.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention involves a reversible self-cleaning window assembly comprising a transparent substrate coated with one or more photocatalytic layers and a reversible framing assembly. The photocatalytic coatings chemically degrade organic material deposited on the surface of the substrate to a point wherein the organic material disappears or is readily washed away. The photocatalytic layers may include, but are not limited to, oxides comprised of such metals as titanium, iron, silver, copper, tungsten, aluminum, zinc, strontium, palladium, gold, platinum, nickel, and cobalt. The coated transparent substrate is useful as a window and can be self-cleaned by facing the photocatalytic layer toward the sun. Therefore, the reversible self-cleaning window assembly is most useful as a window unit which is reversible so that the major surfaces of the substrate, coated by the photocatalytic layer, may be alternately self-cleaned depending upon which major surface is exposed to the ultraviolet radiation in the sunlight. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic cross-sectional view of a transparent substrate containing a coating in accordance with the invention;  
         [0015]    [0015]FIG. 2 is a schematic cross-sectional view of a multi-pane insulated transparent substrate unit containing a coating in accordance with the invention;  
         [0016]    [0016]FIG. 3 is a schematic of a reversible window assembly set on a pivot bearing a coating in accordance with the invention;  
         [0017]    [0017]FIG. 4 is a schematic of a reversible window assembly having a vertical swing reversing mechanism without any inward projection of the window during reversal;  
         [0018]    [0018]FIG. 5 is a schematic of a reversible self-cleaning window assembly having a horizontal swing reversing mechanism without any inward projection of the window during reversal;  
         [0019]    [0019]FIG. 6 is a schematic of a reversible window assembly wherein the window may be completely removed from the outer frame for reversal. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    In the present invention, the reversible self-cleaning window assemblies normally comprise a transparent substrate, coated with photocatalytic material, which is retained by a reversible framing assembly. Generally, the transparent material, preferably glass, plexiglass or the like, is usually in the planer form of a film or sheet. FIG. 1 schematically illustrates a transparent substrate bearing a coating in accordance with one useful embodiment of the present invention. In the illustrated embodiment, the transparent substrate  10  comprises glass, such as soda-lime-silica glass, with major constituents including but not limited to, SiO 2 , Na 2 O, CaO, MgO, K 2 O and Al 2 O 3 .  
         [0021]    The transparent substrate  10  depicted in FIG. 1 includes opposing major surfaces  15  and  16 . For ease of discussion, first major surface  15  will be designated exterior face and second major surface  16  will be designated interior face. (The designation of “interior” and “exterior” face in the ensuing discussion is somewhat arbitrary. It is assumed, though, that in most circumstances the exterior face will be exposed to an ambient environment outside a building wherein it may come into contact with dirt, water, and the like. The interior face may also be oriented toward the same kind of ambient environment only inside a building. In the embodiments illustrated in FIGS.  3 - 6 , this interior face is oriented towards a low UV environment). Exterior face  15  is coated with photocatalytic layer  11 . Similarly, interior face  16  is coated with photocatalytic layer  12 . The photocatalytic layers  11  and  12  may be comprised of any photocatalytic material or materials, such as an oxide of a metal selected from the group consisting of titanium, iron, silver, copper, tungsten, aluminum, zinc, strontium, palladium, gold, platinum, nickel, cobalt and any combination thereof. One embodiment of a suitable photocatalytic coating comprises an inorganic titanium compound, such as an oxide of titanium.  
         [0022]    It is noted that the substrate  10  of the present application may also be comprised of a double paned insulated glass unit, wherein the exterior surface  15  is located on a first substrate and exposed to the ambient atmosphere outside a building and the interior face  16  is located on a second substrate and exposed to the ambient atmosphere inside a building. See FIG. 2 for an illustration of one embodiment of an insulated glass unit.  
         [0023]    Generally, an insulated unit is comprised of two or more transparent substrate panels separated by a sealed dry air space, and a means of precisely separating the substrate panels, such as spacers. FIG. 2 is a schematic illustration of a multi-pane insulated unit in accordance with an embodiment of the invention. Such an insulated unit would generally comprise two panes of transparent substrates,  20  and  21 , held in a spaced-apart relationship by a spacer  22  thereby creating an interpane space  23 . In this embodiment, the photocatalytic coating is deposited on the exterior face of transparent substrate  20  oriented away from transparent substrate  21  as well as on the interior face of transparent substrate  21  oriented away from transparent substrate  20 . That is, both coatings, interior and exterior, should be oriented away from the opposing transparent substrate pane. The spacer  22  is bonded on one side to the interior surface  24  of transparent substrate  20  and to the interior surface  25  of transparent substrate  21 . Typically, the spacer  22  will be formed of metal, such as stainless steel or the like and will have a desiccant  26  retained therein. This desiccant will be allowed to communicate with a gas, such as argon, in the interpane space  23  to remove any moisture which may seep between the panes of glass. An exterior seal  28  may be carried around the external periphery of the spacer  22  to form a reliable gas and moisture barrier.  
         [0024]    A variety of photocatalytic coatings can be formed on the transparent substrate using a variety of deposition processes, such as magnetron sputtering, pyrolytic coating and any other coating process known in the art. For example, useful photocatalytic coatings are described in U.S. Pat. No. 5,874,701 (Watanabe et al), U.S. Pat. No. 5,853,866 (Watanabe et al), U.S. Pat. No. 5,961,843 (Hayakawa et al.), U.S. Pat. No. 6,139,803 (Watanabe et al), U.S. Pat. No. 6,191,062 (Hayakawa et al.), U.S. Pat. No. 5,939,194 (Hashimoto et al.), U.S. Pat. No. 6,013,372 (Hayakawa et al.), U.S. Pat. No. 6,090,489 (Hayakawa et al.), U.S. Pat. No. 6,210,779 (Watanabe et al), U.S. Pat. No. 6,165,256 (Hayakawa et al.), U.S. Pat. No. 5,616,532 (Heller et al.), U.S. Pat. Nos. 5,849,200, 5,849,200 (Hayakawa et al.), and U.S. Pat. Nos. 5,845,169, 5,849,200 (Hayakawa et al.), the entire contents of each of which are incorporated herein by reference.  
         [0025]    In a particularly advantageous embodiment, the photocatalytic coating comprises a sputtered film of titanium oxide. The titanium oxide can be sputter deposited in several ways. First, targets formed of metallic titanium can be sputtered in oxidizing atmospheres thereby creating a layer of an oxide of titanium on the substrate&#39;s surface. Second, targets formed of titanium dioxide can be sputtered in inert atmospheres. Examples of useful magnetron sputtering techniques and equipment are also disclosed in United States patents, such as U.S. Pat. No. 4,166,018, issued to Chapin, the entire teachings of which are incorporated herein by reference.  
         [0026]    In one embodiment of the present invention, a titanium dioxide coating may be deposited on a substrate by sputtering substoichiometric titanium oxide targets. These targets are especially preferred since they have high electrical conductivity, allowing them to be sputtered at high rates. Targets of this nature are described in U.S. Pat. No. 6,461,686, the entire contents of which is incorporated herein by reference. Targets of this nature are available from well known commercial suppliers, such as Bekaert VDS nv, which is located in Deinze, Belgium. Thus, in this embodiment, the oxide of titanium film is deposited by positioning a substrate beneath one or more substoichiometric titanium oxide targets. The targets are then sputtered, most preferably in a sputtering atmosphere comprising argon, oxygen, or a mixture of argon and oxygen. Suitable mixtures include, but are not limited to, 70-90% argon by volume and 10-30% oxygen by volume. The use of substoichiometric titanium oxide targets is also described in U.S. Pat. No. 6,461,686.  
         [0027]    The photocatalytic coating may be applied or added to additional coatings or coating stacks that are in turn applied to the transparent substrate in order to provide antireflective, absorptive or insulating properties. For example, the photocatalytic coating may be added to a coating stack including a reflective layer comprising a metal such as silver, and an absorptive layer comprising a semiconducting material such as silicon dioxide. The photocatalytic coating may also be applied to self-clean an insulated glass unit, such as an insulated glass unit designed to conserve energy.  
         [0028]    As previously suggested the application of one or more photocatalytic coatings may be in addition to other coating stacks administered to one or both of the substrates of the insulated glass unit. For example, a photocatalytic coating may be applied to an insulated glass unit in addition to one or more coating stacks having insulative or reflective characteristics such as low emissivity coatings, high transmittance coatings, solar coatings, tinted coatings and the like.  
         [0029]    Additionally, the reversible window assembly of the present invention includes a reversible frame assembly. FIG. 3 depicts one embodiment of a reversible frame assembly of the present invention that comprises a window sash  34  adjoined to an outer frame  35  by one or more pivoting devices  36 . Such an assembly is commercially available from Weatherseal, Weatherseal Holdings Ltd, Weatherseal House, The Phoenix Centre, Road 1, Winsford Industrial Estate, Winsford, Cheshire CW7 3PZ.  
         [0030]    As depicted in FIG. 3, the outer frame  35  includes an upper jamb  32  and a lower sill  33  at the top and bottom thereof and a pair of side jambs  37 ,  38  secured at their ends to upperjamb  32  and lower sill  33 . The outer frame  35  may be made of materials including, but not limited to, wood, vinyl, plastic, metal, fiberglass or any other suitable material which allows the outer frame  35  to be mounted in a building opening (not shown).  
         [0031]    The window sash  34  positions and retains the transparent substrate  10  by extending around and embracing the periphery of the transparent substrate  10 . The window sash  34  generally includes a pair of upper and lower horizontal members  40 ,  41  and a pair of vertical members  42 ,  43  coupled at their ends to the horizontal members  40 ,  41 . The window sash  34  may be made of such materials, as described above for outer frame  35 , and that are suitable to retain the transparent substrate  10 .  
         [0032]    Additionally, the embodiment depicted in FIG. 3 is a reversible self cleaning window assembly wherein the pivoting device  36  is one or more pivot pins that are centrally secured to the outer frame  35 , either between side jambs  37 ,  38  (as shown) or between the upper jamb  32  and lower sill  33 . The pivot pins may be comprised of any suitable means for securing and pivoting the window sash  34  and substrate  10 , such as rivots, screws, bolts or the like. As previously suggested, the pivot device  36  generally adjoins the outer frame  35  to the vertical members  42 ,  43  or the horizontal members  40 ,  41  of the window sash  34 , as described above, to allow the transparent substrate  10  enclosed within window sash  34  to be rotated. As depicted in FIG. 3, pivot pins  36  adjoin the outer frame  35  to the window sash  34  centrally at the vertical members  42 ,  43 .  
         [0033]    In operation, the transparent substrate  10  incorporated within the embodiment of the reversible self-cleaning window assemblies depicted in FIG. 3 may be set with either its interior face or exterior face facing outwards. Upon the accumulation of soil-like material, such as organic matter, on the interior face of the substrate or insulated glass unit, the transparent substrate  10  may be rotated 180 degrees upon the pivot device  36  to reverse the face of the transparent substrate  10 , thereby exposing the dirty surface to the higher concentration of UV light, such as sunlight, outside. The rotation of the window sash  34  can be initiated by unlocking window sash  34  from outer frame  35  and applying a gentle force to the top or bottom of the window sash  34  causing it to swing outwards. Once the transparent substrate  10  is rotated to the desired orientation, window sash  34  is again locked to outer frame  35  to prevent transparent substrate  10  from further rotation. To rotate transparent substrate  10  back to its original orientation, window sash  34  is unlocked from outer frame  35 , a gentle force is applied to the top or bottom of window sash  34  causing it to swing outwards and allowing it to rotate back to its original position. Additionally, as will be obvious to one skilled in the art, other pivot mechanisms for reversing a window may be used. In this as well as other reversible window configurations, the transparent substrate  10  includes photocatalytic coatings on both its interior face and exterior face for self-cleaning purposes.  
         [0034]    The photocatalytic coated transparent substrate may also be rotated in a reversible frame assembly as described in U.S. Pat. No. 4,616,443 (Araki et. al.), which is hereby incorporated by reference herein. This type of reversible frame assembly has a top swing reversing mechanism configured to prevent inward projection of the window during reversal. Top swing reversible frame assemblies are commercially available from Kawneer UK Ltd, Kawneer UK Ltd, Astmoor Road, Astmoor Ind Est, Runcom WA7 1QQ UK. as well as BlindCraft Edinburgh, BlindCraft Edinburgh 2 Peffer Place, Edinburgh EH16 4BB UK.  
         [0035]    As depicted in FIG. 4, an embodiment of the reversible self-cleaning window assemblies includes a reversible frame assembly with a pivoting device  36  in the form of a top swing mechanism. The reversible frame assembly with the top swing mechanism comprises a window sash  34  that embraces and retains the photocatalyticly coated transparent substrate  10 , and is adjoined to an outer frame  35 . The top swing mechanism includes guide rollers  50  attached to opposite sides of a horizontal member  40  of the window sash  34  and are inserted in concave grooves provided in side jambs  37 ,  38  of outer frame  35 . The concave grooves extend the length of side jambs  37 ,  38  to allow guide rollers  50  to move in an up and down direction.  
         [0036]    To each of the side jambs  37 ,  38  of outer frame  35  is attached a link assembly. Generally, the link assemblies utilized in this embodiment of the present invention comprise a fixed linked member  51  attached to side jambs  37 ,  38  through suitable means such as rivets or screws, and first movable link member  52  pivotably connected to the fixed link member  51  by a pivot pin  56 . Next, a second moveable link member  53  is hingedly connected to first moveable link member  52  and to window sash  34  at vertical side members  42 ,  43  by pivot pins  55 ,  56 .  
         [0037]    Upon the determination of a dirty interior face of the transparent substrate  10 , the reversible self cleaning window assembly depicted in FIG. 4, is reversed by pushing outwardly the lower end of window sash  34  toward the outdoor direction. The guide rollers  50  move downwards inside concave grooves (not shown) allowing the window sash  34  and photocatalyticly coated transparent substrate  10  to rotate 180 degrees through pivot pins  55 ,  56 . To rotate transparent substrate  10  back to its original orientation, the upper portion of window sash  34  is pushed outwards in the outdoor direction allowing the guide rollers  50  to move from the bottom towards the top inside the concave grooves, thereby allowing the window sash  34  to rotate inwardly at the pivot pins  55 ,  56 . Again, the transparent substrate  10  generally has photocatalytic coating on both its interior and exterior faces to provide the self cleaning charactistics to both sides of the substrate  10 .  
         [0038]    [0038]FIG. 5. depicts an alternate embodiment of FIG. 4 wherein window sash  34  enclosing transparent substrate  10  is rotated horizontally, instead of vertically. In FIG. 5 the pivoting device  36  includes guide rollers  50  that are placed on the upper and lower members  40  and  41  of window sash  34 . Concave grooves (not shown) are provided in upper jamb  32  and lower sill  33  and extend substantially the entire length thereof. To rotate window sash  34  and transparent substrate  10 , window sash  34  is first disengaged from outer frame  35  and a gentle force is applied to the right side of window sash  34  causing it to swing outwards. Guide rollers  50  then move across the concave grooves towards the side jamb  38  and window sash  34  rotates 180 degrees through pivot pins  55 ,  56  attached to a linkage assembly as described above. The linkage assembly in this embodiment originates from upper jamb  32  and lower sill  33 . To rotate window sash  34  back to the original orientation, force is applied to the left side of window sash  34  causing it to swing outwards and guide rollers  50  to move back across outer frame  35  and to their original position at side jamb  37 .  
         [0039]    FIG. 6  depicts another alternate embodiment of a reversible window assembly containing no attachable pivoting mechanism, for attaching the window sash  34  to the outer frame  35 . However, the pivoting device  36  of the embodiment illustrated in FIG. 6 is a plurality of reversible brackets  65  that position and retain the substrate in place regardless of which surface faces the outside environment. In this type of reversible window assembly, the window sash  34 , which embraces the transparent substrate  10 , is manually placed in outer frame  35  and locked into place with the brackets  65 . The brackets  65  may include any type of hooking and locking mechanisms known in the art. To reverse the window sash  34  and the photocatalyticly coated transparent substrate  10 , brackets  65  are unlocked and the window sash  34  and substrate  10  are pulled from the outer frame  35 . The window sash  34  and substrate  10  are next manually rotated 180 degrees and placed back in outer frame  35 . The brackets  65  are then locked so as to secure the sash  34  and substrate  10  in the rotated position. Similar to the previously described embodiments, photocatalytic coatings can again be applied to both the interior and exterior faces of transparent substrate  10  in order to provide the desired self-cleaning properties.  
         [0040]    While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as encompassed by the scope of the appended claims.