GB2251379A

GB2251379A - Mirror assembly

Info

Publication number: GB2251379A
Application number: GB9123681A
Authority: GB
Inventors: Trevor John Johnson
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-11-12
Filing date: 1991-11-07
Publication date: 1992-07-08
Also published as: GB9123681D0; GB9024524D0

Abstract

A mirror assembly comprises a mirror, a heater unit, and mounting means holding the heater unit generally centrally against the rear of the mirror. The heater unit is a relatively thin flat box with a rear plate of structural material (steel) and a cover panel of heat-conducting material (aluminium), and contains a heater element extending over substantially the whole area of the cover panel. The heater element may be of sinuous shape, with a layer of thermally insulating material between it and the rear plate. In the embodiment shown the mounting means 21 comprises a back plate 30 having brackets 42, 43 for securing it to the mirror 20 and 42, 44 for attachment to a wall or the like, and resilient means 40 for urging the heater unit 22 against the mirror, and has a connection box 31, 32 attached to and depending below it. An indicator light 36 is visible through an unsilvered area 37 of the mirror. <IMAGE>

Description

Mirror assembly r- A sBs e m tD1 y The present invention relates to mirror assemblies.

A normal domestic mirror consists of a sheet of glass which is silvered on the back surface. The nature of the surface of glass, in combination with its thermal conductivity and thermal capacity, renders such mirrors liable to misting up, particularly in bathrooms, where the use of hot water, particularly for showers, provides an abundant supply of hot humid air.

Such misting up is irritating to the users. It normally takes a considerable time for the mirror to heat up and so clear itself naturally, and the user rarely has the tirne to wait for this. The user can alternatively try to wipe the mirror, but this easily leads to smearing, and can be frustrated by the mirror misting up again.

Dernisting and mist inhibiting chemicals are available, but are generally not satisfactory for bathroom use; their efficiency is limited and their effect is impermanent.

It has been proposed to provide a source of heat behind the mirror to alleviate this problem. More specifically, mirror assernblies have been proposed (in GB 2 241 435 A) in which a heater is mounted behind the mirror and towards its bottom edge; in one form, the heater is a wire-wound rod spaced away from the mirror, and in another form, the mirror is backed by a foil disc having a heater pad attached thereto. These arrangements are however mechanically not robust and electrically and thermally poor at achieving safe and efficient demisting.

The main object of the present invention is to provide a more efficient arrangement for heating a mirror.

Accordingly the present invention provides a mirror assembly comprising a mirror, a heater unit, and mounting means holding the heater unit generally centrally against the rear of the mirror, the heater unit being a relatively thin flat box with a rear plate of structural material and a cover panel of heat conducting material and containing a heater element extending over substantially the whole area of the cover panel.

Preferably the rear plate is steel and the cover panel is aluminium, and a layer of thermal insulation is preferably provided over the inside of the rear plate. The heater element may be formed integrally with the cover plate, to improve the heat flow characteristics of the heater. The heater element may conveniently be of strip-like or sinuous shape and may be a flexible element, such as a printed resistive material on a sheet of plastics material, plastic sheathed cable or flat heating tape (which latter may conveniently be glued to the front plate), or a flat heating mat. The heater element may have a negative temperature.' coefficient of resistance.

An eiectrical power supply has to be available at or adjacent to the mirror assembly. However, it will be realized that in modern bathrooms, a suitable electrical power supply is normally already available adjacent to a mirror located over a washbasin, in the form of a strip light and/or shaving socket.

It will therefore usually be easy to connect the heater unit to the strip light and shaving socket assembly. A short length of wire will usually be unobtrusive, or the wire can be embedded in the wall when the bathroom is being decorated.

The cover panel may be formed with a slight overall convexity, so that when the unit is attached firmly to the mirror, it is pressed flat to assure good thermal contact between the cover panel and the mirror over most of the cover panel. The cover panel may alternatively be formed with a plurality of local convexities for the same purpose, resulting in a regular pattern of areas of good thermal contact.

Alternatively or additionally, a layer of heat-conducting grease or the like can be used to improve thermal contact between the cover panel and the mirror.

If this is done, then it may also be desirable to provide a sealing ring to be placed between the cover panel and the mirror and to pass around the edge of the cover panel. Instead of grease, glue may be used to ensure permanent thermal contact between the front plate and the mirror.

The cover panel may be covered with an electrically insulating layer such as ceramic, glass, or the like, preferably having good heat conductivity, either alone or in combination with a heat-conducting grease or the like.

The present mirror assembly can be utilized ln three main ways. It can be sunk in the wall, allowing the mirror to be mountea slush on tne wali: it can be mounted on the wall, with the mirror being mounted on it and so standing proud of the wall; or it can be mounted on the back of a free-standing mirror (which may have a pivoted mounting).

The heater unit and the mounting means may together form- a mounting assembly of box-like form having fixing means for fixing the mirror and mounting box together and attachment means of form chosen according to the manner in which the mirror assembly is to be utilized. For wall mounting, the attachment means may include means allowing it to be fixed to the surface of the wall; for recessed wall mounting, the attachment means may also include a flange around the front edge of the mounting assembly which will lie over the adjacent uncut wall surface, so ensuring that the back surface of the mirror, which will be mounted on the mounting assembly generally flush with the wall, will make satisfactory contact with the cover plate of the heater unit.

1 The mirror assembly may be made integrally with a light and/or a shaver socket, particularly if it is intended for wall mounting. (It may be less convenient to provide an integral light and/or shaver socket with a unit which is mounted on a mirror which is not fixed.) The heater unit may include, or have associated with it, a switch (preferably of the pull cord type) for switching the heater on and off, and a pilot light for indicating when it is on. Alternatively, it can be wired permanently in parallel with a room light.

It is possible to have the heater permanently on. However, the power required to keep the mirror mist-free will vary widely, depending on such factors as the ambient temperature and humidity and the particular patterns of usage of the bathroom. Sensor means can be provided for sensing such factors and adjusting the power level accordingly.

In practice, the user will normally expect to turn it on and off manually.

Since the user is likely to want rapid demisting, a fairly high power rating is desirable. However, this is likely to lead to excessive heating if the heater is left on. Thus a compromise is needed between fast heating and restriction of the temperature produced by continuous heating. To minimize the response time, the thermal capacity of the front plate of the heater should be kept small.

One way of achieving fast response without excessive heating is automatic timed switch-off. If the mirror is not demisted by one switching on, the user can switch the heater oh again shortly after its automatic switch-off. If the heater rating is high, then some form of overheating safety cut-out is also desirable. j Another possibility is the use of a heater element with a negative temperature coefficient of resistance.

In a mirror of approximately 200 x 300 mm, a power rating of l0 W has been found to be adequate, though we have found a higher rating (eg 20 W) to be preferable; For a typical mirror, this achieves a temperature rise above ambient of about 3 "C after about 5 minutes, rising to about 13 "C after about 30 minutes.

Two heater units and three assemblies including these units and embodying the invention will now be described, by way of example, with reference to the drawings, in which: Fig. l is a partial perspective drawing of the first heater unit; Fig. 2 is a perspective drawing of a mounting assembly for recessed mounting including the unit; Fig. 3 is a perspective drawing of a mounting assembly for projecting mounting including the unit; Fig. 4 is a perspective exploded drawing of the second heater unit; and Fig. 5 is a perspective exploded drawing of a mirror assernbly including the second unit.

Referring to Fig. 1, the heater unit comprises a sheet aluminium front plate or cover panel 2 and sheet steel back plate 3. The two plates both have their top and bottom edges bent to form double flanges so that the plates can be fixed together by fixings 6, and the back plate also has its sides bent to form flanges which, together with the top and bottom flanges, enclose the interior of the unit. The top and bottom flanges of the back plate also have holes 7 by means of which the unit can be mounted.

A sinuous heater element 1 is mounted in the interior of the unit, and is coupled to an electrical connection block 4. The element 1 may be attached to or formed integrally with the cover panel 2. A layer of thermal insulation 5 is provide5≈over the interior of the back plate 3, between it and the heater element 1.

Fig. 2 shows a mounting assembly suitable for recessed fitting in a wall, such that a mirror can be mounted substantially flush with the wall over it.

The heater unit 8 is contained, with its cover plate facing outwards, in a mount ing box 9 of plastics material having a flange 10. The assembly is intended to be fitted into a recess cut in a wall, with the flange 10 lying over the original wall surface adjacent to the recess. A suitable plane mirror can then be fixed to the wall, over the mounting assembly, with its rear face in contact with the cover plate of the heater unit.

Control of the heather unit can be provided by means of a switch (not shown) such as a pull cord, which may be mounted on the unit or on the ceiling; alternatively, the heater unit can be wired into the lighting circuit.

Fig. 3 shows a mounting assembly suitable for surface (projecting) mounting on a wall. The heater unit 8 is contained, with its cover plate facing outwards, in a mounting rox 11 of plastics material, having mouldings 15 by means of which the assembly can oe screwed to a wall. 1'he mounting box also contains a pull cord on/off switch 12, a pilot light 13, and an electrical connection block 14. Holes 16 in the box 11 permit the fitting of brackets to support a variety of sizes, shapes, and types of mirror (e.g. with our without frames).For the pilot light to be visible, it is desirable for a small hole to be made in the mirror silvering (backing) at the appropriate place. (This can readily be accomplished if the heater unit is manufactured as part of a mirror assembly comprising the heater unit combined with a mirror.) Fig. 5 shows a mirror assembly comprising a mirror 20 with an attached mounting assembly 21 which in turn includes mounting means and a heater unit 22, the mounting means holding the heating unit in close contact with the back of the mirror.

Fig. 4 shows the heater unit 22, which includes a heater element 23 consisting of a sheet of insulating film with carbon ink resistor strips 24 screen printed thereon. The resistor strips may be arranged in any convenient pattern. Connections are made between the heater strips by silver connectors (not shown), printed similarly, and connections are made to the heater element by printed silver pads to which connecting wires (not shown) are riveted.

The heater element 23 is sandwiched between two further insulating film sheets 25. An aluminium front plate 26 and a steel back plate 27 form the outer casing of the heater unit; the front plate 26 has flanges along its top and bottom edges by which it is bolted to the back plate 27, and the back plate 27 has flanges 27A along is sides to complete the encasing of the heater unit. A layer of thermal insulating foam 28 is retained between the back plate 27 and the films 24 and 25, as shown, to press the films towards the front plate 27.

The heater unit 22 forms, together with the mounting means, the mounting assembly 21, which retains the heater unit with the mirror 20. The main component of the mounting means is a back plate 30, of rigid wood (e.g. WPB plywood) or plastics material. The back plate 30 has attached to it four silicone foam pads 40 which urge the heater unit 22 forward against the mirror 20. A pair of angle strips 41 are attached to the top and bottom edges of the back plate. The forward edges of these angle strips engage over the flanges 26A of the front plate 26 of the heater unit 22. and limit its forward movement when the mounting assembly is removed from the mirror 20.

A connection box 31 is attached to the back plate 30 and depends below it.

The box 31 has a cover 32, and contains a connector 33 for live and neutral, an earth point 34, a pull cord switch 35, and a neon indicator light 36. The mirror 20 has an unsilvered area 37 located in front of the light 36.

A pair of steel strips 42 are screwed to the sides of the back plate, carrying mirror brackets 43 at their ends which engage with the mirror 20 to hold the heater unit against the mirror, and mounting brackets 44 along their length for mounting the mirror assembly on a wall.

Claims

Clai ms

1 A mirror assembly comprising a mirror, a heater unit, and mounting means holding the heater unit generally centrally against the rear of the mirror, the heater unit being a relatively thin flat box with a rear plate of structural material and a cover panel of heat-conducting material and containing a heater element extending over substantially the whole area of the cover panel.

2 A mirror assembly according to claim 1 wherein the rear plate is steel and the cover panel is aluminium.

3 A mirror assembly according to any previous claim wherein the heater element is of strip-like or sinuous shape.

4 A mirror assembly according to any previous claim wherein the heater element has a negative temperature coefficient of resistance.

5 A mirror assembly according to any previous claim wherein the heater unit includes a layer of thermally insulating material between the heater element and the rear plate.

6 A mirror assembly according to any previous claim wherein the mounting means comprises a back plate having brackets for securing it to the mirror and for attachment to a wall or the like, and resilient means for urging the heater unit against the mirror.

7 A mirror assembly according to claim 6 wherein the the back plate has a connection box attached to and depending below it.

8 A mirror assembly according to any previous claim including an indicator light visible through an unsilvered area of the mirror.

9 A mirror assembly substantially as herein described and illustrated, 10 Any novel and inventive feature or combination of features specifically disclosed herein within the meaning of Article 4H of the International Convention (Paris Convention).