Abstract:
A wall-mounted mirror which can be convectively and radiatively heated to prevent fogging by a sheet heater separated from the mirror interior surface by an air gap. The mirror is electrically insulated and grounded to prevent electric shock.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to mirrors such as are installed on bathroom walls, and more particularly to a mirror heated convectively and radiatively to a temperature exceeding ambient temperature to prevent fogging when water vapor is in the air. 
     2. Description of the Related Art 
     Devices for electrically heating and thereby defogging mirrors in warm and humid environments such as bathrooms have been disclosed in many patents. U.S. Pat. No. 4,665,304 to A. G. Spencer provides an extensive survey of the U.S. patent literature up to 1984. More recent U.S. patents disclosing heated mirrors are U.S. Pat. No. 4,940,317 to R. Reuben, U.S. Pat. No. 5,155,334 to J. A. Marstiller et al., U.S. Pat. No. 5,302,809 to A. Ghiassy, U.S. Pat. No. 5,380,981 to B. Feldman et al., U.S. Pat. No. 5,406,049 to C. Reiser et al., U.S. Pat. No. 5,731,569 to G. Crescenzo, U.S. Pat. No. 5,821,501 to H. Zorn, U.S. Pat. No. 5,904,874 to J. Winter, and U.S. Pat. No. 6,198,073 B1 to F. Gonzalez. 
     Electrical heating of a mirror is accomplished in all these references by a device rigidly attached to or otherwise in good thermal contact with the mirror so that heating occurs by conduction. In contrast, my U.S. Pat. No. 6,365,876 B1 discloses a wall-mounted cabinet having a pivotable door with opposed exterior and interior mirrors which are convectively and radiatively heated by a sheet heater disposed between the two mirrors and separated from each mirror by an air gap. The present invention uses the same technique to heat a single wall-mounted mirror. 
     Self-heated rear view mirrors for automotive vehicles such as cars and trucks are also known. GB1414905 to R. G. Gray discloses a mirror assembly having a mirror glass and a cover glass spaced apart by a peripheral seal to form a cavity between the two glasses which is filled with an inert gas. An electrical heating element is mounted in the cavity for demisting the glasses. The heating element is in the form of a coiled filament adjacent to the lower edge of the glasses. U.S. Pat. No. 2,797,287 to P. E. Prutzman discloses mirror assemblies, particularly for trucks, incorporating two resistance-wire coils mounted on a stiff asbestos board. Because the coils are in the major lower portion of the mirror casing, that portion is heated primarily by radiant heat while the casing upper portion is heated primarily by convection and conduction. 
     OBJECTS OF THE INVENTION 
     In view of the limitations of the related art, it is an object of the present invention to provide a wall-mounted mirror which can be defogged by a sheet heater separated from the mirror by an air gap. 
     Another object of the invention is to provide a mirror assembly which is protected against electrical shock. 
     A further object of the invention is to provide a mirror assembly that can be easily manufactured using high quality components. 
     Yet another object of the invention is to provide a mirror which can be reliably defogged in a warm, humid environment. 
     Other objects of the invention will become evident when the following description is considered with the accompanying drawing figures. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and description. 
     SUMMARY OF THE INVENTION 
     These and other objects are achieved by the present invention which provides a wall-mounted mirror assembly including a frame having parallel top and bottom portions and parallel left and right portions orthogonal to the top and bottom portions, the four portions determining a rectangular aperture. The assembly further includes a mirror having parallel exterior and interior surfaces bounded by top, left, bottom and right edges coated with a layer of electrically non-conductive material. The bottom edge is closely received within and attached to a J-shaped metallic sheeting, and the interior surface is circumferentially attached to the four frame portions. The assembly further includes a rectangular sheet heater including a blanket with opposed electrically non-conductive first and second surfaces, and a bottom edge proximate to which are attached two electrical terminals. The blanket first surface is separated by an air gap from the mirror interior surface. 
    
    
     A more complete understanding of the present invention and other objects, aspects and advantages thereof will be gained from a consideration of the following description of the preferred embodiment read in conjunction with the accompanying drawings provided herein. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a wall-mounted mirror assembly according to the invention, including an electrically insulated mirror attached to a frame and separated by an air gap from an electrical sheet heater attached to the frame and backed by a thermally insulating sheet. 
     FIG. 2 is a side elevational view of the FIG. 1 assembly showing the mirror, frame, heater and insulating sheet. 
     FIG. 3 is a cross-sectional view of the FIG. 1 assembly through the lines  3 — 3 . 
     FIG. 4 is a bottom plan view of the FIG. 1 assembly. 
     FIG. 5 is an enlarged detail view of the oval regions “ 5 ” in FIG. 4, showing stannous chloride, silver nitrate, copper sulfate, and protective paint coatings on the interior surface of the mirror, and an electrically non-conductive coating at the mirror edge. 
     FIG. 5A is a further enlarged detailed view of FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While the present invention is open to various modifications and alternative constructions, the preferred embodiment shown in the drawings will be described herein in detail. It is to be understood, however, there is no intention to limit the invention to the particular form disclosed. On the contrary, it is intended that the invention cover all modifications, equivalences and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims. 
     Where used herein, the word “attached” means that the two parts referred to are either fabricated in a single piece, or bonded, screwed, soldered or clamped together. However, other forms of attachment may be suitable, consistent with simplicity of manufacture and reliability of operation. 
     Referring to FIGS. 1,  2 ,  3  and  4 , a mirror assembly  10  according to the invention includes a generally rectangular frame  12  having generally planar, generally parallel top and bottom portions  12 A,  12 B, respectively, and generally planar, generally parallel left and right portions  12 C,  12 D, respectively, generally orthogonal to portions  12 A,  12 B. The four portions determine a generally rectangular aperture  12 E. Assembly  10  further includes a mirror  14  having an exterior surface  14 A, an interior surface  14 B having a lowermost portion  15 , top and bottom edges  14 C,  14 D, respectively, and left and right edges  14 E,  14 F, respectively. Surface  14 B is circumferentially attached to frame portions  12 A,  12 B,  12 C,  12 D. Preferably, the mirror is about 3 to 4 millimeters (mm) in thickness. Assembly  10  further includes a thin, generally rectangular sheet heater  16  including a blanket  18  with opposed electrically non-conductive first and second surfaces  18 A,  18 B, respectively, and a bottom edge  18 E proximate to which are attached first and second electrical terminals  20 A,  20 B. Surface  18 A is circumferentially attached to the frame portions  12 A,  12 B,  12 C,  12 D. Preferably, frame  12  is made from an aluminum alloy, wood or a plastic, and has a thickness such that the air gap between mirror surface  14 B and blanket surface  18 A is about 1.0 to about 4.5 mm. Heater  16  further includes a resistive heating element  22  attached to terminals  20 A,  20 B which preferably is made of NICHROME# wire having a thickness between 0.25 and 0.30 mm. Blanket  18  is made from a silicone rubber material and has a thickness in a range from about 0.35 to about 0.5 mm. A positive (hot) wire  24 A carrying 110-120 volt alternating current is attached to terminal  20 A, a negative (neutral) wire  24 B is attached to terminal  20 B, and a ground wire  24 C is attached to a rear portion  26 A of a “J”-shaped thin metallic sheeting  26 , arcuately extending in a front portion  26 B, which closely receives and is attached to bottom edge  14 D and lowermost portion  15  of mirror interior surface  14 B by a thin layer  27  of electrically conductive adhesive (see FIG.  2 ). Preferably, sheeting  26  is about 10 centimeters (cm) in width, portion  26 A is about 22 to 23 mm in length, and portion  26 B is about 3 mm in length. Preferably, the sheeting is aluminum about 0.4 to 0.6 mm in thickness. Because heater  16  is isolated from mirror  14  by air gap  28 , the mirror is heated convectively and by direct radiation, rather than conductively as in all of the related art devices. Assembly  10  further includes a generally planar, generally rectangular sheet  30  made of a thermally insulating material, which is generally congruent to heater  16 . Sheet  30  has first and second surfaces  30 A,  30 B, respectively. Preferably, sheet  30 , which also is rigid and electrically non-conductive, is made of fiberglass and has a thickness in a range from about 1.6 to about 3.2 mm. Sheet  30 , attached to heater  16  by juxtaposing and bonding surfaces  18 B and  30 A, minimizes heat loss due to rearward radiation. 
     Referring to FIGS. 5 and 5A, a first coating  40  of stannous chloride is attached to interior surface  14 B of mirror  14 , followed by a second coating  42  of silver nitrate, a third coating  44  of copper sulfate, and a fourth coating  46  of protective paint. Mirror edges  14 C,  14 D,  14 E and  14 F are each coated with a layer of electrically non-conductive material  48 . Circumferential layer  48  and ground wire  24 C make it unlikely that a person touching the mirror would receive an electric shock. However, since contiguous metallic coatings  40 ,  42  and  44  are in effect one plate of a capacitor, and heating element  22 , although electrically insulated, could become through leakage an opposed plate, a person touching the mirror conceivably might receive an electrostatic shock. The combination of sheeting  26  which acts as a grounding plate, and adhesive layer  27  prevents this possibility.