Abstract:
A wall-mounted cabinet having a pivotable door with opposed exterior and interior mirrors which can be convectively and radiatively heated to prevent fogging, by a sheet heater between the two mirrors. The exterior mirror is electrically insulated, and the exterior and interior mirrors are grounded to prevent electric shock.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to cabinets with mirrored doors such as are installed in bathrooms, and more particularly to a cabinet having a door with opposed exterior and interior mirrors heated 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, directed to an electrical sheet heater sufficiently thin that it can be mounted behind a sheet of conventional mirror glass without preventing the use of standard mirror mounting hardware or frames, provides an extensive survey of the U.S. patent literature up to 1984. Spencer observed that although numerous proposals had been made to heat bathroom mirrors above the dew point so as to prevent condensation, none of these met with substantial commercial success. 
     More recently, U.S. Pat. No. 4,940,317 to R. Reuben discloses a heating device secured to a rear coated surface of a mirror, which includes two conductive strips attached at opposed edges of the coated surface and a resistive conductor element extending between the two strips. U.S. Pat. No. 5,155,334 to J. A. Marstiller et al. is directed to an electrical sheet heater attached to a sheet of insulating material that can be mounted on a wall or attached to a mirror back before the miror is mounted or hung in place. U.S. Pat. No. 5,302,809 to A. Ghiassy is directed to a planar resistive sheet heater which extends downwardly from and is supported by an elongated frame member disposed along the top of a wall-mounted mirror. U.S. Pat. No. 5,380,981 to B. Feldman et al. discloses an electric heating unit for attachment to a rear surface of a mirror which operates at low voltage and restricts the size of the heated area to conserve power. The unit includes a heat barrier formed of a layer of closed cell plastic foam, an insulated low resistance heater wire mounted on the surface of the foam layer, aluminum foil covering the wire and foam surface, and an adhesive layer with peel-off backing to permit attachment of the unit to a mirror. U.S. Pat. No. 5,821,501 to H. Zorn discloses a heated exterior mirror for motor vehicles which includes a mirror glass with a transparent conductive coating on its front surface divided into two zones by a narrow non-conductive gap, an electrical heater thermally bonded to the glass front surface behind a reflective coating, and an electrical circuit connected between the two zones to sense changes in resistance and/or capacitance of the gap due to deposition of moisture on the front surface. 
     U.S. Pat. No. 5,852,284 to R. S. Teder et al. discloses a sheet of low emissivity glass with a resistive coating connected to a power source. A capacitor coupled to the coating is used to increase the impedance and control the power dissipated by the coated glass. When used in an insulating glass unit for commercial freezer and refrigerator doors, the heated glass prevents condensation from forming on the doors. 
     None of these references addresses the problem of heating two opposed mirrors separated by a small air gap, such as may be installed in bathroom cabinets. Typically, a planar (i.e., non-magnifying) mirror is mounted on or set into the exterior surface of a hinged door, and a smaller, concave magnifying mirror, mounted on or set into the door interior surface, is accessible when shaving or applying cosmetics by opening the door. 
     Each of the devices in the related art for electrically heating a single mirror is rigidly attached to or is otherwise in good thermal contact with a mirror surface so that heating occurs by conduction. For a door-mounted double mirror assembly, the spacing between the mirrors can be no greater than the door frame width, so using two laterally juxtaposed heaters would be infeasible in addition to being wasteful of energy. What is needed is a device which fits within the door frame and simultaneously heats both mirrors. A second problem arises because the parallel configuration of the mirrors and the materials used in their manufacture form a capacitor which can cause an electrical shock even when power is switched off. A mirror is made by first polishing one surface of a glass blank with an abrasive slurry which exposes a virgin surface to which is applied, after polishing and rinsing, a “tinning” solution of stannous chloride (SnCl 2 ). Next, a solution of silver nitrate (AgNO 3 ) is poured or sprayed onto the tinned surface to form a reflective surface which is then rinsed with deionized water. The silver coating is protected by a coating of copper sulfate (CuSO 4 ) followed by one or more layers of protective (“mirror-backing”) paint. Because the stannous chloride, silver nitrate and copper sulfate layers are electrically conductive, a capacitor is formed. The charge stored in a capacitor is the product of its capacitance and the source voltage (here, 110-120 volts). Capacitance equals the product of plate area and dielectric constant (a measure of the ability of a material to hold electric charge without allowing current flow), divided by the distance between the plates. Since the plate areas (i.e., the metallic coating areas) are large and their spacing is small, considerable charge can be stored in a cabinet-sized dual mirror assembly heated by household current even when there is no dielectric other than air between the coatings. Consequently, a manufacturer of such cabinets must incorporate elements which eliminate the possibility of electric shock. 
     OBJECTS OF THE INVENTION 
     In view of the limitations of the related art, it is an object of the present invention to provide a cabinet with exterior and interior mirrors, mounted on a pivotable door, which can be defogged by a single electrical heating device mounted within the frame. 
     Another object of the invention is to provide a cabinet with exterior and interior mirrors which are mounted on a pivotable door protected against electrical shock. 
     A further object of the invention is to provide a cabinet with heatable exterior and interior mirrors in a door-mounted assembly that can be easily manufactured using high quality components. 
     Yet another object of the invention is to provide a cabinet with exterior and interior mirrors 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 in one aspect provides a cabinet including a cabinet body having a rectangular rear wall and a cabinet door pivotally attached to the body. The door includes 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 door further includes: an exterior mirror having parallel exterior and interior surfaces bounded by top, left, bottom and right edges, with the interior surface circumferentially attached to the four frame portions; and an opposed interior mirror having parallel exterior and interior surfaces bounded by top, left, bottom and right edges, with the interior surface circumferentially attached to the four frame portions. The interior surfaces of the exterior and interior mirrors are parallel and separated by an air gap. The door further includes means for convectively and radiatively heating the mirrors. 
     In another aspect the invention provides a wall-mounted cabinet including a cabinet body having a rectangular rear wall and a cabinet door pivotally attached to the body. The door includes 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 door further includes: an exterior mirror having parallel exterior and interior surfaces bounded by top, left, bottom and right edges, with the interior surface circumferentially attached to the four frame portions; and an opposed interior mirror having parallel exterior and interior surfaces bounded by top, left, bottom and right edges, with the interior surface circumferentially attached to the four frame portions. The interior surfaces of the mirrors are parallel and separated by an air gap. The door further includes a rectangular, electrically non-conductive spacer having a circumferential groove determining a rectangular aperture. The spacer is symmetrically disposed within the frame aperture and is interposed between and maintains rigid parallel alignment of the mirrors. The door further includes a rectangular sheet heater having a blanket with opposed electrically non-conductive surfaces, and a bottom edge proximate to which are attached two electrical terminals. The heater is rigidly disposed within the circumferential groove so that the blanket surfaces are equidistant from the mirror interior surfaces. 
     In yet another aspect the invention provides a wall-mounted cabinet including a cabinet body having a rectangular rear wall and a cabinet door pivotally attached to the body. The door includes 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 door further includes an exterior 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 first J-shaped metallic foil. The interior surface is circumferentially attached to the four frame portions. The door further includes an opposed interior mirror having parallel exterior and interior surfaces bounded by top, left, bottom and right edges, with the interior surface circumferentially attached to the four frame portions. The bottom edge is closely received within and attached to a second J-shaped metallic foil. The interior surfaces of the mirrors are parallel and separated by an air gap. The door further includes a rectangular, electrically non-conductive spacer having a circumferential groove determining a rectangular aperture. The spacer is symmetrically disposed within the frame aperture and is interposed between and maintains rigid parallel alignment of the mirrors. The door further includes a rectangular sheet heater having a blanket with opposed electrically non-conductive surfaces, and a bottom edge proximate to which are attached two electrical terminals. The heater is rigidly disposed within the spacer circumferential groove so that the blanket surfaces are equidistant from the mirror interior surfaces. 
     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 a perspective view of a cabinet according to the invention, having a hinged door including opposed exterior and interior mirrors attached to a frame, and an electrical sheet heater mounted within a spacer disposed within the frame and between the two mirrors. 
     FIG. 2 is an exploded perspective view of the FIG. 1 cabinet showing the exterior mirror, heater, spacer, frame, and interior mirror. 
     FIG. 3 is a sectional view taken along line  3 — 3  in FIG. 1, showing the heater mounted within the spacer. 
     FIG. 4 is a sectional view taken along line  4 — 4  in FIG. 1, showing the exterior and interior mirrors and frame, the FIG. 3 spacer, and two electrical terminals. 
     FIG. 5 is an enlarged detail view of the oval regions “ 5 ” in FIG. 4, showing the stannous chloride, silver nitrate, copper sulfate, and protective paint coatings on the interior surface of the exterior mirror, and an electrically non-conductive coating at each mirror edge. 
     FIG. 6 is an enlarged detail view of the oval region “ 6 ” in FIG. 4, showing the stannous chloride, silver nitrate, copper sulfate, and protective paint coatings on the interior surface of the interior mirror. 
    
    
     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 FIG. 1, a cabinet  10  according to the invention includes a cabinet door  12  pivotally attached to a cabinet body  14  by hinges  16 A,  16 B,  16 C. Body  14  includes a generally rectangular rear wall  18 , with a hole  18 H therethrough, which typically is attached to a bathroom wall. Door  12  includes a generally rectangular frame  20  to which are attached a generally rectangular exterior mirror  22  and an opposed generally rectangular interior mirror  24 . 
     Referring to FIGS. 2,  3  and  4 , frame  20  includes planar, parallel top and bottom portions  20 A,  20 B, respectively, and planar, parallel left and right portions  20 C,  20 D, respectively, generally orthogonal to portions  20 A,  20 B. The four portions determine a generally rectangular aperture  20 E. Mirror  22  has an exterior surface  22 A, an interior surface  22 B, top and bottom edges  22 D,  22 E, respectively, and left and right edges  22 F,  22 G, respectively. Mirror  24  has an exterior surface  24 A and an interior surface  24 B. Opposed surfaces  22 B and  24 B are each circumferentially attached to frame portions  20 A,  20 B,  20 C,  20 D. Preferably, the mirrors are each about 3 to 4 millimeters (mm) in thickness. A generally rectangular, electrically non-conductive spacer  26 , symmetrically disposed within aperture  20 E, is interposed between and maintains rigid the parallel alignment of mirrors  22 ,  24 . Spacer  26  has a circumferential groove  28 , determining a generally rectangular aperture  26 A, within which is closely received a thin, generally rectangular sheet heater  30  including a blanket  32  with opposed electrically non-conductive surfaces  32 A,  32 B, and a bottom edge  34  proximate to which are attached electrical terminals  36 A,  36 B. Heater  30  is rigidly disposed within groove  28  so that the separations between surfaces  32 A,  22 B and surfaces  32 B,  24 B are equal. Preferably, heater  30  has a resistive heating element made of NICHROME™ wire having a thickness between 0.25 and 0.30 mm. Blanket  32  is made from a silicone rubber material and has a thickness in a range from about 1.0 to about 1.5 mm. Preferably, the separation between mirror surfaces  22 B and  24 B is 9 to 10 mm, so that the gap between each interior mirror surface and the proximate heater blanket surface is about 3.7 to about 4.5 mm. Preferably, frame  20  is made from an aluminum alloy, wood or a plastic, and spacer  26  is made from a polycarbonate plastic. A non-metallic sheathed electrical cable  40 , connected to 110-120 volt alternating current and fed through hole  18 H, terminates in a positive (hot) wire  40 A attached to terminal  36 A, a negative (neutral) wire  40 B attached to terminal  36 B, and a ground wire  40 C having bifurcated ends  41 A,  41 B. End  41 A is attached to a rear portion  42 A of a first “J”-shaped thin copper foil  42 , arcuately extending in a front portion  42 B, which closely receives and is attached to bottom edge  22 E of mirror  22  (see FIG.  3 ). Similarly, end  41 B is attached to a rear portion  43 A of a second “J”-shaped thin copper foil  43 , extending in a front portion  43 B, which closely receives and is attached to the bottom edge of mirror  24 . Preferably, foils  42 ,  43  are each about 10 centimeters (cm) in width, portions  42 A,  43 A are each about 22 to 23 mm in length, and portions  42 B,  43 B are each about 3 mm in length. Wires  40 A,  40 B are conveniently attached to the heater terminals via an ON/OFF switch controlling the room lighting. Alternatively, the wires may be attached to an ON/OFF switch mounted within the cabinet body  14 . Because heater  30  is isolated from mirrors  22 ,  24  by air gaps  44 A,  44 B, respectively, the mirrors are heated convectively and by direct radiation, rather than conductively as in all of the related art devices. 
     Referring to FIG. 5, a first coating  50  of stannous chloride is attached to interior surface  22 B of exterior mirror  22 , followed by a second coating  52  of silver nitrate, a third coating  54  of copper sulfate, and a fourth coating  56  of protective paint. Edges  22 D,  22 E,  22 F and  22 G are each coated with a layer of electrically non-conductive material  58 . Circumferential layer  58  and ground wire  40 C ensure that a person touching mirror surface  22 A or  24 A cannot receive an electric shock. 
     Referring to FIG. 6, a first coating  60  of stannous chloride is attached to interior surface  24 B of interior mirror  24 , followed by a second coating  62  of silver nitrate, a third coating  64  of copper sulfate, and a fourth coating  66  of protective paint.