Abstract:
A self-cleaning transparent structure is described herein having dust resistant qualities and improved optical qualities. A transparent surface is provided with randomly positioned protrusions attached to a transparent surface. The protrusions act upon particles that settle on the protrusions, by diminishing the particles surface adhesion. Furthermore, the transparent features of the transparent surface are no diminished, since the period between each protrusion is less than the wavelength of visible light.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority to U.S. Provisional Application No. 60/510,371 filed on Oct. 10, 1003 entitled “Self Cleaning Window Structure” which is herein incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     As commonly known maintaining glass or windows can be an arduous and costly undertaking. Although structures (i.e. buildings) with few windows rarely encounter this quandary, it does pose an immense problem for structures (i.e. buildings, greenhouses) with many windows. Moreover, as building heights increase the numbers of windows increase. Consequently, the cost of maintaining these windows increases. Also, adding to the rising cost of maintaining windows are various safety measures and procedures, which must be implemented in order to safeguard the wellbeing of those brave individuals who endeavor to maintain the scores of windows on these vast structures.  
         [0003]     Furthermore, because the sources that soil the windows vary the application of a universal method or cleaning solution does not always achieve the desired result. For instance a cleaning solution or method applicable to dusk may not be applicable to acid rain. Also problematic is the storage of glass in humid environments, which can lead to water droplets forming on the glass during storage, thereby, causing the leaching of alkaline material from the glass.  
         [0004]     Presently many techniques or chemical processes are utilized in order to overcome this predicament and to allow glass to maintain a spotless and pristine appearance. One such process utilizes photocatalytic metal oxides to coat the surface of the structure; however, this process is most proficient in eradicating biological matter. Consequently, its effect on non-biological matter is doubtful and uncertain.  
         [0005]     Another technique coats the glass with a silica-based coating, for example, U.S. Pat. No. 5,424,130 (Nakanishi, et al., the teachings of which are incorporated herein by reference). The silica-based material causes water to bead up once it touches the surface of the coated glass. Although this process would avert the aforementioned difficulty such as alkaline leaching, it is must suitable for environments with an abundant airstream. Accordingly, this process would have limited application and success in environments of little or no airstream.  
         [0006]     Another technique produces the self-cleaning effect via elevations and depressions of the surface of the structure, for example U.S. Ser. No. 10/120,366 (Nun, et al., the teachings of which are incorporated herein by reference). Although, the aforementioned technique produces a self-cleaning effect it however, has limited optical quality. Consequently, the use of this technique is limited to surfaces where transparency is not a concern. The aforementioned technique teaches that its self-cleaning surface can be made transparent to the extent that only sunlight can penetrate the surface. Consequently, the aforementioned invention has limited optical quality and would not be suitable where optical quality is a necessity (i.e. windows, winds shields).  
         [0007]     Presently, all the aforementioned approaches to self-cleaning glass consist of utilizes a coating material to attain the ability of limiting or thwarting soiled glass. Although these approaches achieve various degrees of success there are inherent disadvantage with each. The first is the appearance of coloration in the glass due to light, which is ever present when elevated structures are positioned on a transparent structure. Another disadvantage is the lack of random placement of the elevated structures, which contribute to coloration, because, as ambient light strikes the glass surface the light cannot scatter.  
         [0008]     Although several processes address de-coloration, the processes are accomplished by chemical means, which add addition time and expense to the manufacturing process. Moreover, many of the coating techniques have little resistances to abrasion. Consequently, given certain environments and time the self-cleaning characteristics will cease.  
         [0009]     The solution to this dilemma was found in nature. The Lotus plant or flower is well known as having self-cleaning leaves. 1  Its discovery by Wilhelm Barthlott of the University of Bonn in Germany led to attempts to harness this naturally occurring phenomenon in the fields of paint, and on certain hard surfaces. The lotus plant is unique because the leaves have very small bumps on the surface. Consequently, the surface of the leaves are rough in comparison to other plant leaves. This roughness gives the Lotus Plant hydrophobic characteristics. The hydrophobic characteristic is primarily due to a reduced contact area between the water and leaf. As water droplets settle on the leaves of the Lotus Plant the bumps reduce the contact area to only 2-3%. Moreover, at certain contact angles the droplets roll-off, and wash away any dust particle the droplets encounters, thereby producing a self-cleaning effect. The result is the Lotus Plant will stay clean and dry even during torrential down pours.    1  See, e.g., ScienceWorld, January 2000, Hans Christian Von Baeyer, “The secret of the self-cleaning leaves of the lotus plant, like the subtlest applications of high technology, is simplicity itself”, which is incorporated by reference herein.    
         [0010]     For the foregoing reasons, there is a need for a self-cleaning window structure that is transparent and is not subject to coloration, diminished optical quality and erosion and that can be inexpensively manufactured.  
       SUMMARY  
       [0011]     The present invention is directed to a self-cleaning transparent structure, which satisfies the need for a dust resistant glass surface, which can maintain sufficient optical quality. The transparent structure comprises a glass surface with a plurality of spaced apart protrusions, each protrusion having a distal end and an end protruding from the base level of the glass surface; wherein the protrusions are configured and positioned upon the base level to minimize deviation from transparency. 
     
    
     DESCRIPTION OF THE DRAWING  
       [0012]     These and other features, aspects, and advantages of the present invention will become better understood with regards to the following description, appended claims, and accompanying drawings where:  
         [0013]      FIG. 1  shows an enlarged view of a transparent surface;  
         [0014]      FIG. 2  shows an enlarged view of the protrusions of a transparent surface,  
         [0015]      FIG. 3  shows a transparent structure with randomly placed protrusions,  
         [0016]      FIG. 4  shows a float glass manufacturing facility; and  
         [0017]      FIG. 5  shows a vacuum device used for protruding protrusions.  
     
    
     DESCRIPTION OF THE INVENTION  
       [0018]     The present invention herein provides a dust resistant transparent surface with self-cleaning qualities, wherein protrusions extend therefrom.  
         [0019]     Referring to  FIG. 1 , an enlarged portion of a transparent surface  10  is shown. Extending from the transparent surface  10  are protrusions  12 . The protrusions  12  are connected to the transparent surface  10  via the base level  14 . The protrusions can be integral with the base level  14  or adhered to the base level  14 . The base level  14  is the region of the transparent surface  10  where the protrusions  12  start and the transparent surface  10  terminates. Located at the apex of each protrusion  12  is a distal or a terminal end  16 . In addition in certain embodiments the distal end  16  of each protrusion  12  may have a roll-off angle of about 1 degree to about 10 degrees. Positioned on top of the distal end  16  can be one or more particles  18 . Consequently, during the particle resistance phase, a particle  18  settles on one or more protrusions  12 , the particle  18  is acted upon by the protrusions  12 , thereby limiting particles surface adhesion and precluding particle  18  bonding.  
         [0020]     Furthermore where optical transparency or certain other optical qualities are desired, the positioning and configuration of the protrusions may be altered depending of the optical quality needed. For example in the preferred embodiment where transparency is desired, the protrusions are positioned in a non-pattern or random configuration. In another embodiment where limited transparency is required the protrusions are positioned in a semi-patterned configuration. In yet another embodiment where an image, design or opaqueness is required the protrusions are positioned in such a way that the design, image or opaqueness is produced.  
         [0021]     As compared to the transparent surface  10  the protrusions  12  are elevated, accordingly, the spatial areas  20  between the protrusions  12  can be a planar or a chasm configuration. Furthermore, the distance between each protrusion  12  is such that the optical effect of Bragg&#39;s Law is reduced or eliminated. It is understood that the spatial areas  20  between the protrusions  12  are not limited to a planar or a chasm configuration, and can be any suitable horizontal expression. For purposes of illustration the protrusions  12  appear conical, however, the protrusions  12  are not limited to a conical configuration. Consequently, the protrusions can be circular, ciliated and rod shaped. Furthermore, to enhance the dust resistant qualities of the transparent surface  10 , the protrusions  12  can be made of or finished with a hydrophobic material.  
         [0022]     Accordingly, when the transparent surface  10  is exposed to dust or other particles  18 , the surface area where contact lies is extremely small, as the particles  18  only contact the protrusions  12 . Further, due to the small diameter of the distal ends  16  of the protrusions  12 , the contact angle between the protrusions  12  and the particle  18  is very large. Thus, adhesion of the particles  18  is minimized or eliminated, and miniscule agitations cause any droplets to traverse the transparent surface  10 .  
         [0023]     In a preferred embodiment the transparent surface  10  comprises glass. Producing the protrusions  12  on the surface of glass is simple and cost effective, due to the transparent nature and composition of glass and, its ability to be shaped and molded.  
         [0024]     In another preferred embodiment the transparent surface  10  comprises plastic material. Suitable plastic substrates include synthetic organic polymeric substrates, for example, acrylic polymers, polyesters, polyamides, polyimides, acrylonitrile-styrene copolymers, styrene-acrylonitrile-butadiene tertpolymers, polyvinyl chloride, butarates, polyethylene and the like. A particular substrate that may benefit from the present invention and enjoys widespread use is polycarbonate, such as Lexan® commercially available from General Electric Company. Further, the substrate may be substantially rigid, or in certain embodiments flexible substrates may benefit from the coating layer of the present invention.  
         [0025]     It is understood that the material used to fabricate the transparent surface is not limited to glass, plastic or polycarbonate material and can be any suitable transparent material which does not have limited transparency or diminished optical quality upon implementation of the protrusions  12 .  
         [0026]     Referring to  FIG. 2 , shown is an enlarged view of the protrusions  12 . As previously mentioned the apex of each protrusion  12  has a distal end  16 , where the diameter is shown as D t . Furthermore, the height from the base surface  14  of the transparent surface  10  to the distal end  16  is shown as H nh  and the period between each protrusion  12  is P nh .  
         [0027]     In a preferred embodiment, the diameter of the distal end  16  is substantially less than 0.5 μm, which is the average diameter of a particle of dust. Preferably, the diameter of the distal end D t  is such that the contact area of a particle (e.g., dust) atop plural protrusions is less than 2%, as in the Lotus plant. Consequently, protrusions  12  which are substantially less than 0.5 μm will prevent a particle  18  from bonding to a single protrusion  12 . In addition, the height of the protrusions  12  may be on the order of about 5 μm to 10 μm, which is the height of the bumps located on the cuticle of the lotus plant. In certain embodiments, the ratio of H nh /D t  is at least 20. However, the ratio of H nh /D t  may be any ratio suitable for limiting surface adhesion.  
         [0028]     In another preferred embodiment, the period between each protrusion  12  is sized in order to minimize or eliminate optical deviations caused by well known Bragg&#39;s Law diffraction.  
         [0029]     Referring to  FIG. 3 , shown is a magnified view of a transparent surface  10  of a transparent structure  20 . Further illustrated are protrusions  12 , which are, in preferred embodiments, positioned in a non-pattern or random configuration. The protrusions  12  are arranged in a non-pattern or random configuration in order to preclude coloration and optical distortion.  
         [0030]     As mentioned before the protrusions  12  can be integral to the transparent surface  10  or adhered to the transparent surface  10 . In order to apply the protrusions  12  to the transparent surface  10 , various manufacturing methods can be implemented. In one embodiment the transparent surface  10  is set and maintained at a temperature suitable for processing. Next the protrusions  12  are formed on the transparent surface  10 , where the protrusions  12  will extend from the base level  14 .  
         [0031]     Referring to  FIG. 4 , shown is a float glass manufacturing system. The float glass manufacturing system  22  is another example of a manufacturing method to form protrusions  12  onto the transparent surface  30 . Under this method a raw material dispenser  24 , dispenses raw float glass  26  into a fluid course  28 . The float glass  26  is then floated on the fluid course  28  of molten indium or tin; furthermore do to its properties the glass will not interact with the indium or tin. As the float glass  26  floats down the fluid course  28 , various procedures and apparatus act upon the float glass  26 , thereby given the float glass  26  it&#39;s chosen configuration. Next one or more surfaces  30  of the float glass structure  26  is maintained in a continuous or segmented soft molten state (e.g., about 1000 deg. C.). Subsequently, the protrusions  12  are formed on the glass surface  30  while the glass surface  30  is in a molten state. It is understood that the fluid course  28  is not limited to indium or tin, but can be any substrate capable of maintaining the float glass  26  in a molten state, without reacting with the float glass  26 .  
         [0032]     Another embodiment uses the method of embossing to form the protrusions  12 . During embossing one or more surfaces  30  of a float glass structure  26  is maintained in a continuous or segmented soft molten state. Next, the float glass structure  26  is directed through a pair of rollers  32  in line of the float glass assembly. Embossing features  31  are positioned on one of the aforementioned rollers (or both if dual surfaces  30  are desired). As the float glass structure  26  emerges from the rollers  32 , the protrusions  12  have been embossed onto the surface  30  of the float glass structure  26 .  
         [0033]     In another embodiment the process of stamping forms the protrusions  12 . While the float glass structure is in the continuous or segmented soft molten state, the protrusions are stamped onto the surface  30  of the float glass structure  26 .  
         [0034]     In yet another embodiment the process of brushing forms the protrusions  12 . While the float glass structure is in the continuous or segmented soft molten state, the protrusions  12  are brushed onto the surface  30  of float glass structure  26 , via bristles.  
         [0035]     Referring to  FIG. 5 , shown is a vacuum device, for producing protrusions on the surface of a float glass structure. In this embodiment a vacuum device is used to form the protrusions  12  on the glass surface  34 , while the glass surface is in a continuous or molten state. For example a method of making a suitable vacuum device is describes in U.S. Ser. No. 10/017,186, entitled “Device For Handling Fragile Objects”, which describes a handler for use in semi-conductor processing, herein incorporated by reference. This apparatus includes a suction force or a vacuum  42  and a handler  36 , for a fragile object (i.e. glass surface) that possesses sufficient rigidity and strength to withstand potentially rough mechanical handling, and also capable of serving as a substrate for a transparent structure. The suction force or vacuum  42  is attached to a handler  36 . The handler  36  includes a front surface  38 . The handler  36  is capable of subjecting objects (i.e. glass surface) of extreme fragility to the suction force  42 . The front surface  38  possess a plurality of holes  40 , which break the front surface  38  in a designated pattern. For purposes of illustration the plurality of holes  40  are shown has patterned. However, it is understood that the plurality of holes  40  are not limited to this configurations and can be any configuration suitable to produce protrusions, which have self-cleaning characteristics and optimal transparent capability. These holes form a low air resistance vacuum passage for a well-distributed suction force or vacuum  42  to be applied to the glass surface  34 . Consequently, the suction force  42  pulls on the molten glass surface  34 , thereby producing the protrusions. It is understood that the vacuum is not limited to an oval shape and can be any shape suitable to produce a suction force capable of creating protrusions.  
         [0036]     In all of the above examples, when the glass cools, the protrusions remain on the surface of the float glass structure. Furthermore it is understood that protrusion production can be preformed by all conventional float glass manufacturing process and/or techniques.  
         [0037]     Although self-cleaning structures or processes are well known, they are limited as to optical quality. Accordingly, the above described invention overcomes this defect with a unique approach to protrusion positioning. The present invention positions the protrusions on the surface of the structure in such a way that optical quality is not affected. The present invention randomly, places the protrusions, thereby allowing light to scatter once the light strikes the structure, however, the protrusion can also be positioned to limit optical quality if so desired. Consequently, the present invention achieves the self-cleaning affect without losing optical quality.  
         [0038]     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.