WO1990005931A1

WO1990005931A1 - Prevention of condensation on a mirror

Info

Publication number: WO1990005931A1
Application number: PCT/GB1989/001370
Authority: WO
Inventors: Geoffrey Francis Le Maistre
Original assignee: Geoffrey Francis Le Maistre
Priority date: 1988-11-18
Filing date: 1989-11-17
Publication date: 1990-05-31
Also published as: AU4625189A; GB9109298D0; GB2242831A; GB2242831B; EP0444099A1

Abstract

A bathroom mirror assembly is provided including a mirror and an anti-condensation device. The anti-condensation device includes a laminar heating pad (6) arranged to be disposed in close abutment to the rear surface of the mirror. The heating pad may include a backing (16) of reflective material and is suitably releasably held on the rear surface of the mirror by magnetic attraction between magnetically attractable materials provided on each of the confronting surfaces.

Description

PREVENTION OF CONDENSATION ON A MIRROR

The present invention relates to an anti- condensation device for a mirror and to a mirror, particularly a bathroom mirror, including such a device. Condensation on bathroom mirrors presents a significant problem. The presence of such condensation after a hot bath or shower means that the bather must first wipe the mirror before he can use it for shaving or other purposes. If the atmosphere in the bathroom remains humid, repeated wiping is necessary.

Various prior proposals have been put forward to overcome the problem of condensation but have been directed to vehicle mirrors. U.K. Patent No. 1545770 disclosed a motor vehicle mirror where a covering layer is secured to the rear of the mirror by an adhesive and a heating element is secured to the covering layer by the adhesive so as to form a unitary body in which the adhesive provides support for the mirror in the event of the mirror being broken.

U.K. Patent No. 1246430 discloses a heater unit for a vehicle window, vehicle mirror and the like in which a resistance wire is supported until pressed against the mirror and then the support is removed to leave the wire in position.

U.K. Published Application No. 2041859 and U.K. Patent No. 1244161 disclose similar arrangements for vehicle mirrors.

The devices of the prior art are arranged for low vol age applications and would be unsuitable for domestic application with the higher voltage and damp conditions entailed.

According to the present invention there is provided a bathroom mirror assembly including as separate and discrete components, an anti- condensation device comprising a laminar heating pad including an electrical heating element positioned within an electrically insulating body, and a mirror, the an i-condensation device being dimensioned so that, in use, it may be positioned behind "the mirror and, when actuated, may co- operate with the mirror so as to heat the mirror in order to disperse condensation forming on the front thereof. The invention also includes an anti-condensation device for a bathroom mirror comprising a laminar heating pad including an electric heating element disposed within an electrically insulating body. The electric heating element may either be encapsulated within a plastic insulating body or may be sandwiched between insulating layers in a laminated composite. In either arrangement the heating element must be electrically isolated from the damp conditions prevailing in a bathroom in order to avoid electrical shock due to the higher voltage of mains connections. In addition, the electrical heating element is suitably electrically double insulated.

In a preferred arrangement the device may include a reflective layer placed behind the heating element to reflect heat transmitted away from the mirror back towards the mirror. The fixing between the heating element and the mirror may be by means of any suitable heat and water resistant adhesive since the surface temperature of the heating pad need never rise above a level that would impair the performance of such an adhesive. Alternatively, the heating pad may be provided with a magnetised coating and the surface of the mirror provided with a coating of a medium comprising an adhesive carrier and a distributed ferromagnetic material. A coating of such a medium has the effect of making the previously non-magnetic rear of the mirror attractive to a magnetised coating. The medium preferably also includes a conductive powder such as aluminium or copper powder in suspension in the adhesive carrier to improve heat conduction from the heating pad to the mirror. Some embodiments of a device for providing heating to a bathroom mirror will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows a transverse section through a mirror and a first embodiment of the device;

Figure 2 shows a partial section through a second embodiment of the device;

Figure 3 is a perspective view of a third embodiment of the device;

Figure 4 is a perspective view of an electrical connecting device for a heating device applied to a bathroom mirror;

Figure 5 is a section on X - X in Figure 4; and

Figure 6 is a diagrammatic, partially sectioned, side elevation of a further alternative embodiment.

In the first embodiment disclosed in the drawings, a mirror (2) has a reflective backing or silvered layer (4) in conventional manner. Applied to the rear surface of the mirror is a layer of a medium (5). The medium (5) is a spray adhesive carrier in which there is suspended finely divided ferromagnetic powder and also a conductive powder providing a smooth layer of about one or two microns in thickness. The ferromagnetic powder may be iron powder and the conductive powder is preferably aluminium or copper powder. The use of this conductive powder facilitates heat conduction from the heating pad through to the mirror as will be explained.

The adhesive may be any material which will form a securely attached film on the rear of the mirror surface and may be a lacquer, cellulose or a paint.

Shown separated from the mirror (2) in Figure 1 is the anti-condensation device (6) which comprises a laminar heating pad containing an electric heating element (8) connected to a power supply cable (10). A thermostatic control switch

(11) is provided in circuit with the heating element (8) in order to prevent overheating where it is necessary to provide a relatively high current to the heating element to ensure sufficient heat to deal promptly with potentially heavy condensation. The thermostat (11) is of the type which cuts in and out within a predetermined temperature range.

In view of the high voltage of the mains system into which the anti-condensation device (6) is to be connected, the heating element (8), thermostat (11), and power supply cable (10) are integrally cast into a flexible plastics material

(12) so as that the heating element (8) is encapsulated therein. The overall thickness of the heating pad is typically 100 microns. The heating element (8) may be a laminar carbon film, though other types of element may be employed. The use of a carbon film provides an even distribution of heating avoiding hot spots.

The power supply cable (10) is provided with a plug (14) which allows power to be supplied from the mains. The plug (14) may be adapted to fit into a normal bathroom shaver socket. Alternatively, it will be appreciated that the power cable may be permanently connected to the mains power supply with a switch means interposed in the circuit to control the supply of power to the heating element.

A sheet (16) of heat-reflective material is placed behind the heating pad with its reflective surface facing towards the mirror (2). The sheet (16) may comprise a sheet of aluminium foil for example. The purpose of the sheet is to reflect the heat directed away from the mirror back towards the mirror to increase the efficiency of the heating pad in warming the front surface of the mirror. The space between the sheet (16) and the wall against which the mirror is mounted is preferably filled with a layer of insulating material (18), such as expanded polystyrene, which can be cut to the appropriate size to fill the remaining space.

In order to secure the anti-condensation device (6) to the rear of the mirror (2), a magnetised coating (20) is applied to one major surface of the heating pad. Such magnetised flexible coatings are known in the art and are extensively used with advertising materials to allow them to be fixed to any ferromagnetic surface. Magnetised vinyl plastics and magnetised rubber are examples of suitable materials for this coating. An appropriate materials for the coating is FLEXIBLE FERRITE which is a flexible magnetic material supplied by Magnet Developments Limited, of Swindon, Wiltshire. Flexible magnet sheets are also described in US-A-3 629 756 and GB-A-903 287 and GB-A-950 277. Any other type of coating which provides a magnetised surface may be employed.

The magnetised coating (20) enables the anti- condensation device (6) to be secured to the rear of the mirror (2) by magnetic attraction with the medium (5) incorporating ferromagnetic material applied to the rear surface of the mirror (2).

An alternative to the magnetic fixing of the anti-condensation device disclosed in Figure 1 , the heating pad may be bonded to the back of the mirror (2) directly using a suitable heat and water resistant releasable adhesive. The level of heating necessary to prevent condensation on the surface of the mirror is relatively moderate so that the requirement for heat-resistant adhesive does not impose an undue constraint on the type of releasable adhesive that may be used for this purpose. It is envisaged that the heating pad will never need to rise above a temperature where it can be safely touched by the hand. Heavy duty tape applied around the edges could also be used to fix the pad to the back of the mirror or two- sided releasable adhesive film could be employed for fixing. A further alternative is to provide a resilient layer such as, an expanded foam rubber or similar synthetic substance, which is positioned between the anti-condensation device (6) and the wall when positioning the anti- condensation device behind the mirror (2). The thickness of the layer is chosen so that it is compressed to permit its inherent resilience to push the anti-condensation device (6) against the back of the mirror (2) thereby achieving maximum heating efficiency.

It is also an advantage to cover the front of the anti-condensation device (6), at least along its side edges, with a thin layer of expanded plastic foam which presses against the rear of the mirror (2) trapping air in the expanded bubbles. This reduces heat loss by convection due to heat, absorbed by the glass of the mirror and re- radiated, being carried upwardly in a 'chimney' behind the mirror. With the 'chimney' blocked the heat being re-radiated heats the surrounding materials which, in turn, heat the air trapped in the bubbles .

Also, as an alternative to a spray-on coating (5), the required ferromagnetic layer (5) may be produced by fixing a stainless steel foil to the back of the mirror. The foil may be secured to the mirror by means of an adhesive. A steel foil could also be used provided it is covered with a varnish or similar protection to prevent rusting. It will also be understood that the ferromagnetic layer could also be magnetised and disposed so as to be attracted to the magnetised material on the heating pad.

The thermostat (11) may be omitted if the current is low enough to restrict the possibility of overheating.

An alternative embodiment of the anti- condensation device is illustrated diagrammatically in Figure 2. This drawing shows a partial section through the device. In this arrangement the device is built up on a piece of thin but somewhat flexible plastics sheet (30) capable of being post-formed such that it has an arc of very large radius. A sheet of FORMICA (Registered Trade Mark) may be employed for this purpose. A layer (32) of polystyrene is applied to the convex face of the sheet (30) and supports a heating pad (34) of the type previously described. The assembly is held together by means of a shrink-wrap type of plastics film (36) which is wrapped around the whole assembly and heat sealed to the rear of the sheet (30). On withdrawal of air from the space within the shrink-wrap sheet (36), the layers are held tightly together. Other types of sealing could be employed to hold the layers together. Although the heating pad (34) is shown as an element embedded in a plastics coating, in this embodiment, this additional protective layer may not be necessary.

The device is then fixed to the back of the mirror (not shown) . The back of the mirror is adjacent the convex face of the device. When the device is held between the mirror and a wall space the resultant deformation of the slightly convex device into a plane results in good thermal contact being maintained between the back of the mirror and the heating pad. In order to make large size heating devices, it may be preferable to produce the heating elements in modular form. This is the basis of the embodiment shown in Figure 3. As illustrated the heating pad comprises two panels (40). The right hand side panel is shown exposed but the left hand side panel is shown with a polystyrene insulating layer (42) in position. Each heating panel includes a heating film extending between two copper electrodes (44) and (46) to which electrical contact is made by conductors in the cable (48). The cable (48) also includes the conductors making contact with the corresponding electrodes of the heating panels of other modules. In order to provide space for the cable to pass between the modules, channels are provided in the polystyrene layer. A plastics layer (50) is laminated to the front of the device to provide protection for the heating film. This plastics layer (50) may also be extended around the edges of the device in order to seal it. The plastics layer (50) also provides insulation for the soldered joints between the conductors and the electrodes (44) (46). The cable (48) may be bonded to the laminating film layer (50) using, for example, an epoxy resin adhesive. In order to provide mechanical strength at the outlet of the cable (48) from the device it is proposed to provide a plastics support pad, possibly made up of several layers of plastics film, to which the cable may be fixed by means of a heavy duty staple (54). _

The device may also incorporate a silvered, reflective layer behind the polystyrene in order to increase the transmission of heat towards the mirror,

It will be appreciated that in any of the embodiments described above, the heating pad or element may be of any shape. Since the heated area of the mirror will be free of condensation, the shape of the heating pad will determine the condensation-free area of the mirror surface. Fun effects can be produced by shaping the heating pad or the heating element within it so that a design is produced on the mirror surface. For example, the profile of a cartoon character could readily be produced on the user's mirror surface by shaping the heating pad or heating element appropriately.

In order that the an i-condensation device of the present invention can be fixed behind an existing bathroom mirror, the overall thickness is desirably kept to a minimum. This is readily possible since heating elements of thickness of 100 microns are available and the magnetised vinyl coating or adhesive layer need only be a few microns thick.

Where a heating device is to cover a very large area, several devices of the type described may be employed and wired together in parallel.

In the embodiments disclosed the anti- condensation device it has been proposed either to plug the device into a shaver socket or make direct electrical connection with supply. However, there is very limited space between a mirror and a wall to which it is affixed and therefore Figures 4 and 5 disclose a connection device which enables the anti-condensation unit to be installed with maximum speed and safety and at minimum trouble and cost.

In order to be safely installed the minimum acceptable size of electric supply cable is 3mm wide whereas the design clearance between a mirror and a supporting wall is typically 4mm. Although the cable can be run providing there are no sharp turns, the sheer awkwardness of connection when installing and at the same time ensuring complete electrical safety for the installer (or repair man should the mirror be broken), are considerable. The connection device of Figures 4 and 5

(viewed from the back), which overcomes this i convenience, comprises a plastic plate (140) constructed to fit a standard electric outlet box (not shown) and is provided with screw holes (142) located at the standard centres. It will be understood that by "standard electric outlet" it is intended to embrace electric outlets which meet different standards in different countries. The plate (140) is 68mm square and 4mm thick which enables it to be mounted within the standard outlet box of the United Kingdom such that the surface of the plate finishes up level or slightly below the edge of the mounting box and the surrounding surface. The centre of the plate (140) is provided with a substantially rectangular opening (14 ) .

A second plate (146) includes a rectangular pillar (148) having a passage (150) passing therethrough and opening on opposite sides of the pillar at different longitudinal positions as seen from Figure 5. The rectangular pillar (148) passes through the opening (144) in the first plate (140) which is a sliding fit thereon and, in order to prevent the first plate from being removed from the pillar (148), the pillar (148) has a fixed collar (152) at its free end. The second plate (146) also includes two holes (156) which are aligned with the holes (142) in the first plate in order to allow a screw-driver to be passed through the second plate in order to tighten mounting screws holding the first plate to the outlet box. Positioned on the free end of the rectangular pillar (148) are two springs (158) which, when the first plate (140) is screwed into connection with the outlet box, will force the connection unit forward so that the second plate (146) is pushed forward into contact with the anti-condensation device (160). The second plate (146) is designed to be mounted on the edge of the main anti- condensation device (160) and may be shaped to co- operate therewith. Electrical connection to the electrical supply is made at the electric outlet box by means of an electrical connector block (164) mounted on the back of the first plate (140).

In use the device of Figures 4 and 5 allows simple connection between the anti-condensation device (160) and the electrical supply once the basic spur outlet box has been established in the wall adjacent the mirror position. In particular, the main electrical cable is connected to one side of the connector block (164) and the supply cable from the anti-condensation device is threaded through the passage (150) without appearing in the open and so as to emerge below the collar (152) for connection to the other side of the connection block (164). The plate (140) is then tightened to the outlet box by two screws passing through the aligned holes (156) and (142). Although the connecting device has been particularly described with the plate (146) mounted to the edge of the anti-condensation device (160), he connecting device may be positioned at any convenient location as determined by the wiring of the anti-condensation device (160). Once in position the force of the twc springs (158) help urge the device (160) into firm contact with the back of the mirror. The connection device is suitably used with the cirrangement where the an i-condensation device is secured to the back of a mirror by means of magnetic attraction. Suitably the front of the anti-condensation device is provided with a removable insulating plastics sheet arranged to prevent magnetic connection between the an i- condensation device and the mirror before this is desired. In order to fix the mirror in its final position, the plastic sheet is removed so that the anti-condensation device affixes to the rear surface of the mirror by magnetic attraction. The mirror is affixed to the wall in the normal way by means of fixing screws and the spring mounting of the electrical connection will help support the weight of the anti-condensation unit so that the magnetic effect required to maintain the anti- condensation device in position can be kept to a minimum... In Figure 6 there is disclosed a further alternative arrangement. In this embodiment a laminar heating pad (200) comprises a heating element (202) encapsulated against moisture ingress within a plastics cassette (204) having sufficient rigidity to provide structural coherence to the heating pad. The face of the heating pad (200) which is to abut the rear surface of the mirror (not shown) is covered with a layer of heat conducting soft form plastics (206). Extending rearwardly from a central region of the heating pad (200) is a tubular pillar (208) through which electrical supply wires (210) pass. The pillar (208) has an enlarged collar (212) at its free end and, slidable along the pillar (208), is a first locking member (214) having an annular groove (215) about its external surface.

The pillar (208) and collar (212) are dimensioned to co-operate with an electrical terminal box (216) to mains supply. The terminal box (216) has a central opening (218) substantially complimentary in size and shape to allow the collar (212) to pass through into the terminal box (216). Disposed on the terminal box (216) about the opening (218) is a second locking member (220). The second locking member (220) is tubular and extends away from the terminal box (216). The free end portion of the second locking member (220) comprises a resilient annular wall (222), dimensioned to receive the body of the first locking member (214). The resilient wall (222) terminates in a bulbous portion (224) which may co-operate with the annular groove (215) of the first locking member (214) so that the first and second locking members (214, 220) may form a releasable snap-fit interconnection.

Aligned with the pillar (208) on the rear surface of the terminal box (216) is a spring means (226) for acting against the pillar (208) as will be explained. The terminal box (216) further includes, in conventional manner, suitable electrical connectors (228) and screw means (230) for securing the terminal box to the wall.

In the embodiment of Figure 6, the pillar (206) serves to locate the heating pad (200) in space and helps support the heating pad (200) in space and helps support the heating pad (200) by interconnection with the terminal box (216). In use, the wires (210) are first connected to the appropriate electrical connector (228) and the terminal box (214) screwed into position. Then the pillar (206), of the heating pad (200), with the first locking member (214) thereon is pushed through the opening (218). In this way the body of the first locking member (214) is inserted into the tubular second locking member (220) and they snap-fit together by co-operation between the annular groove (215) and the bulbous portion (224). This locks the heating pad (200) to the terminal box (216) whilst allowing the spring means (226) to move the pillar (206) relative to the terminal box (216). In this way, the layer

(206) of the heating pad (200) is pushed into firm abutment with the rear of the mirror to provide the necessary close thermal contact whilst at the same time retaining physical independence from the mirror. The application of a spring force centrally of the rear of the heating pad (200) provides an even pressure across the front of the pad (200) against the mirror.

The pillar (206) is preferably a moulded part of the heating pad (200). Also, if a releasable magnetic connection is to be provided between the heating pad (200) and the rear of the mirror, the layer (206) may be a magnetically impregnated plastics as discussed above.

If desired, further support for the heating pad (200) could be provided by the provision of plastics arms (not shown) extending radially outwardly of the pillar (206) and each including a hole at its free end. The holes of the arms would be aligned to receive the respective screws at the corners of the mirrors used to support the mirror on the wall so as to be supported thereon. Although the connection has been shown as connection between electrical wires (210) and connectors (228), the electrical wires (210) could terminate in a pin connection at the end of the pillar (206) suitable for countries with 110 volt mains supply.

The anti-condensation device of the present invention may be actuated in any suitable way, for example, it may be manually switched on by an appropriate switch at the electrical socket, or may be connected into the main bathroom light circuit or may even include a passive infra-red detector operable to actuate the device for a pre- determined time period upon detecting a user in front of the mirror.

The preferred heated mirror of the present invention has several advantages over prior arrangements particularly: (i) heat is produced and conveyed to the front of the mirror to demist the surface in an improved manner so as to provide optimum performance; (ii) the mirror and the heating pad are separate elements so that the device may be installed simply whilst maintaining safety requirements and, if required, the mirror may be removed from a supporting wall without interfering with the electricity supply to the heating pad; (iii) the heating pad is laminar to allow installation in the confined space behind a mirror and has wiring arranged to leave the heating pad to an electrical socket in a neat and safe manner; and, (iv) the heating element is electrically isolated for safety to guard against electrical shock due to the relatively higher voltage of a mains system as opposed to the low voltage systems of the prior art.

Claims

CLAIMS 1. A bathroom mirror assembly including as separate and discrete components, an anti- condensation device comprising a laminar heating pad including an electrical heating element positioned within an electrically insulating body, and a mirror, the anti-condensation device being dimensioned so that, in use, it may be positioned behind the mirror and, when actuated, may co¬ operate with the mirror so as to heat the mirror in order to disperse condensation forming on the front thereof.

2. A bathroom mirror assembly according to claim 1 wherein the electric heating element is encapsulated with an insulating body.

3. A bathroom mirror assembly according to claim 1 or 2 wherein the electric heating element is a laminar carbon film.

4. A bathroom mirror assembly according to any one of claims 1 to 3 wherein the an i- condensation device includes means whereby the device firmly abuts the rear of the mirror.

5. A bathroom mirror assembly according to claim 4 wherein said means comprises two magnetically attractable components, one applied to each one of the rear surfaces of the mirror and the front surface of the laminar heating pad.

6. A bathroom mirror assembly according to claim 4 wherein said means comprises a resilient layer between the laminar heating pad and a supporting wall which urges the laminar heating pad against the rear of the mirror.

7. A bathroom mirror assembly comprising a mirror having a front reflective surface and a rear surface, and an anti-condensation device positioned behind the rear surface of the mirror, the anti-condensation device being laminar in shape and including heating means, insulating means for electrically isolating the heating means and means for connecting the heating means to a power supply.

8. A bathroom mirror assembly according to claim 7 wherein the means for securing comprises a heat and water resistant adhesive.

9. A bathroom mirror assembly according to claim 7 wherein the means for securing comprises a magnetised coating applied to one of the rear surfaces of the mirror and the anti-condensation device, and a coating of a medium comprising an adhesive carrier and a distributed ferro magnetic material applied to the other of the rear surface of the mirror and the anti-condensation device.

10. A bathroom mirror assembly according to claim 9 wherein the medium also includes a conductive powder in suspension in the adhesive carrier to improve heat conduction from the anti- condensation device to the mirror surface to be heated.

11. A bathroom mirror assembly according to- any one of the preceding claims, further comprising a reflective backing layer on the other side of the anti-condensation device from the securing means.

12. A bathroom mirror assembly according to any one of the preceding claims, further comprising an insulating layer on the other side of the anti-condensation device from the fixing means.

13. A bathroom mirror assembly comprising a mirror having a front reflective surface and a rear surface, and an anti-condensation device including electrically insulated heating means secured to the rear surface of the mirror by magnetic attraction between, a magnetised material applied to one of the rear surface of the mirror and the electrically insulated heating means, and a magnetically attractable ferro magnetic material applied to the other of the rear surface of the mirror and the electrically insulated heating means.

14. A bathroom mirror assembly according to any one of the preceding claims further including a connecting device for electrically connecting the anti-condensation device to a power supply, said connecting device comprising a first plate dimensioned to fit a standard electric outlet box and means defi ing a passage through which a power cable may pass from the anti-condensation device to the rear of the first plate for electrical connection with the power supply.

15. A bathroom mirror assembly according to claim 14 wherein the passage defining means comprises a pillar fixed to a second plate and movable relative to the first plate through an opening in the first plate.

16. A bathroom mirror assembly according to claim 15 including spring means co-operating with the pillar such that, when the connecting device is positioned behind the mirror, the connecting device is forced forwardly causing the electrically insulated heating means to be forcibly abutted against the rear of the mirror.

17. An anti-condensation device for a bathroom mirror comprising a laminar heating pad including an electric heating element positioned within an electrically insulating body.

18. An anti-condensa ion device according to claim 17 wherein the electric heating element is encapsulated within an insulating body.

19. An anti-condensation device according to claim 17 or 18 wherein the electric heating element is a laminar carbon film.

20. An anti-condensation device according to any one of claims 17 to 20 wherein the laminar heating pad includes a pillar extending outwardly from a central portion of the heating pad through which electrical connection is made.

21. An anti-condensation device according to claim 20 wherein the insulating body is of plastics material of sufficient rigidity to provide structural integrity to the laminar heating pad and the heating pad is at least partially supportable on the pillar.

22. A bathroom mirror assembly including a mirror and an anti-condensation device according to claim 20 further including a terminal box for electrical mains connection, the terminal box including an opening for receiving the pillar and spring means for biassing the pillar and thus the heating pad against the rear of the mirror.

23. A bathroom mirror assembly according to claim 22 wherein the pillar includes a first locking member and the terminal box including a second locking member, the first and second locking members being inter-engageable to form a releasable snap-fit interconnection.

24. A bathroom mirror assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

25. An anti-condensation device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.