Improvements in electric resistance elements

Abstract

Abstract An electric resistance element as claimed in the parent Specification, i.e. one in which an electrically conductive material is added to a compound and exposed to electromagnetic radiation, is provided with a surface coating which prevents variations of resistance value due to moisture. Where the element is a resistance coating on a paper carrier, the paper is also provided with a protective coating on each surface. The waterproof surface coating is a carbon-containing lacquer formed by adding carbon to a solution of a cellulose derivative or a polystyrol solution. Such a lacquer may comprise finely divided carbon beaten into a solution of cellulose acetobutyrate and spermaceti wax in diamyl tartrate and ethylene dichloride. Two separate lacquer layers can be applied to the paper backing of the resistor element, these layers being formed by solutions of two different cellulose derivatives, or one of a cellulose derivative and the other of polystyrol. Such lacquers comprise cellulose nitrate, acetate, or acetobutyrate with benzyl abietate and butyl stearate dissolved in ethyl acetate, acetone or ethylene dichloride.

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