GB588949A - Improvements in cellulosic doping systems for aircraft fabrics - Google Patents

Abstract

An aeroplane fabric dope comprises a blend of nitrocellulose, of viscosity not less than 5 seconds, and ethyl cellulose, the inherent plastic viscosity of the blend being in the range of 20.1 to 28.2 centipoises and the proportion of ethyl cellulose to nitrocellulose being within the limits of 4 : 1 and 1 : 1.5, and the dope also including a plasticiser. Fungicides such as copper, mercury, or zinc, naphthenate, or phenyl mercury oleate, or tolyl mercury salicylate, may be incorporated in the dope. Pigments may also be included. The inherent plastic viscosity of the mixed cellulose derivatives is determined with a capillary tube viscometer using a 5 per cent solution of the mixture in ethyl acetate. In an example, the dope comprises nitrocellulose (5-6 seconds viscosity), ethyl cellulose, triphenyl phosphate, butyl acetate, sec.-butyl alcohol, ethyl alcohol, toluene and xylene, and it is used for spraying on to an aircraft fabric. Seven or eight coats are applied if the dope is sprayed cold, but only three or four coats are required if it is sprayed hot. Over the priming coats there may be applied a single lap coat of a similar composition, but containing aluminium powder. A top coat containing pigment such as Medium Chrome Yellow may then be applied. Other plasticisers which may be used are tricresyl phosphate, dibutyl phthalate and polyesters of sebacic acid and polyhydric alcohols chemically combined with castor oil. Copper naphthenate or other metal soap added as a fungicide, also functions as a wetting agent and facilitates the penetration of the dope into the fabric.