GB579091A - Improvement in electrostatic condenser and dielectric therefor - Google Patents

Abstract

Regenerated cellulose film is immersed in water at a temperature of at least 40 DEG C. for at least one minute in order to remove substantially all soluble impurities and to render it suitable for use as a dielectric in electrical apparatus such as electrostatic condensers. The treated film exhibits a low power factor and a low power factor-temperature coefficient which may even have a negative value between temperatures of 20-50 DEG or 60 DEG C. The sustained hot-water treatment removes entrapped impurities which are not removed by rapid treatment or by cold water treatment. The treated film may have a power factor at 25 DEG C. and at 60 cycles of 0.2 to 0.4 per cent. While the preliminary dialysis may take place in tap water it is preferable to use distilled water for the final stage of the treatment. Preferably, the water is used at 80-100 DEG C. The elimination of impurities is facilitated by applying an electrical potential difference across the film and the dialyzing bath. The film may pass in contact with an anode surface such as an aluminium drum. The cathode may be a carbon rod placed directly in the bath or in a porous cup. As shown in Fig. 9, film 31 passes <PICT:0579091/IV/1> through tank 34 containing running tap water at 95 DEG C. and then through two more similar tanks containing running hot water. The film then passes through tank 46. Distilled water at 95 DEG C. enters section 47 and flows over the partition 48 into section 49. As the film emerges from the bath, excess water is removed by squeeze rollers 36. The film is then fed over a series of smooth-surfaced aluminium rollers 37. High velocity air blowers 38, containing heating elements 39 direct heated air on to both sides of the film. The dried film passes through an electrically heated oven 42. If the film is to be used as a dielectric separator it may be passed through a solution of polystyrene in xylol and ethyl chlorobenzene. The resulting coated film is flexible, and moisture-proof. The film may be cut and placed between plate electrodes or it may be wound as a continuous web between ribbons of foil-like electrodes to form a roll-type electrostatic condenser (see Group XXXVI).