Patent GB-1391425-A (GB)
Title: Electrically heated panels
IPC: A47G1/02
Filed: 1971-06-09
Abstract: 1391425 Resistance heating elements GLAVERBEL 7 June 1972 [9 June 1971] 19736/71 Heading H5M An electrically heated mirror comprises a resistance heating element in the form of a coating separated from the light reflecting coating by a solid insulating layer. The heating element may be in the form of a continuous coating or in the form of a plurality of discrete coatings. The heating element may be made from Au, Cu, Ag, Al, Cr, SnO 2 , In 2 O 3  or graphite. The insulating layer may be in the form of a coating of TiO 2 , ZrO 2 , Cr 2 O 3 , CoO, Fe 2 O 3  and Sr 2 O 3 . It may be formed by glass sheets, sheets of organic polymeric material ceramic sheets or vitroceramic sheets. In Fig. 1, a sheet 1 of chemically tempered float glass or sodalime glass of specified composition is coated with a silver reflecting layer 2, a protective copper layer 3 and a protective paint or varnish layer 4. A second chemically or thermally tempered or soda-lime glass sheet 5 is coated with a gold resistive layer 6, preferably coated on one or both sides with a layer of Bi 2 O 3 , or by a 95% Al, 5% Sb alloy by abrasion transfer from a rotating disc of said alloy, or by a coating of SnO 2 . The two coated sheets 1 and 5 are secured together by a polyvinylbutyral foil 7 which is softened by heat and pressure.  In an alternative embodiment (Fig. 3, not shown), the coated glass sheets are separated from each other by a silicone spacer glued to the uncoated margins of the sheets to form a sealed space between the sheets. The heating element may be a coating of In 2 O 3  or Cu strips glued by polyvinylbutyral to the heated sheet. In a modification of this embodiment (Fig. 4, not shown), the heated sheet comprises a heating element sandwiched between two glass sheets. The heating element may be polyvinylbutyral sheet coated with graphite. In Fig. 5 (not shown), a sheet of glass carrying the reflective layer has a further insulating layer of Cr 2 O 3  protecting the reflecting layer and is spaced from a glass layer provided with a heating layer by a pair of metal frame members which act as supply electrode. Further insulated or insulating frame members may be provided on the other margins of the glass sheets. In Fig. 6 (not shown), a glass sheet provided with a resistive layer protected by an insulating SiO 2  coating is secured in spaced relation to a glass sheet coated with a reflecting layer by ceramic frame members and two brass electrodes which seal the space between the sheets. In Fig. 7, not shown, a silvered glass sheet bearing a protective silicone layer and a glass sheet bearing a heating element composed of graphite impregnated polyvinylbutyral protected by a plastics sheet are secured together by adhesive tapes around the sheet margins. In Fig. 8 (not shown), a glass sheet with a reflective coating protected by an insulating P.T.F.E. is clamped to a sheet provided with an aluminium resistor by marginal clamps. In Fig. 9 (not shown), a glass sheet with a reflecting layer is clamped to a glass sheet bearing a heating layer so that the reflecting layer is insulated from the heating layer by the glass sheet. In Fig. 10 (not shown), a tinted mirror comprises a single glass sheet with a transparent gold resistive layer on one surface and a silver reflecting layer on the other surface. The glass sheets may be replaced by wired glass sheets or vitroceramic sheets. The mirror may be used as a space heater. In one embodiment, the sheet carrying the reflecting coating is spaced from that carrying the resistive coating by a sealed space filled with dry gas at reduced pressure, the rise in this gas pressure causing bowing of the sheets.