Radiant heating panels of resistive circuits on polyimide support - where the circuit is immersed in the core panel surface for protection

摘要

The parent patent described radiant heaters comprising a panel of polyimide resin filled with silica fibres and supporting on the panel surface an electrical resistance circuit (like a printed circuit), coated with an insulating (silicone resin) varnish and covered with a metallic or metallised foil to act as a reflector. This addition describes panels having support layers of polyimide resin contg. 40-90, pref. 55-80% wt. of either fibres or of fillers having a platelet form and bearing on both faces heating circuits which are substantially or totally immersed into the support surface before the latter is cured. The surface is sealed with a varnish different from but compatible with the core resin, e.g. a polyesterimide, or polyamide-imide or a different polyimide. Suitable for making pliable (10-10 mu m thick) or self supporting (0.5-3 mm thick) radiant heating panels producing approx. 0.2.0.5 W/cm3, e.g. of 48 x 25 cm size for a 400W heater operating at 150-250 deg rees C. Compared with panels where the heating element is proud of the sub-panel surface, heating circuit is better protected from atmospheric oxidation/corrosion, the panel surface can be smooth and risk of short circuits via the reflective surface layer by local damage is reduced.